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2020 Quarter 4 Vol. 6, No. 4

Medical Applications for UV/EB Curing Photopolymerization of Methylene Malonates Monitoring Degree of Cure Effects of Post-Curing in 3D Printing

Official Publication of RadTech International North America


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FEATURES 16

26 30 ON THE COVER

AST Products (Billerica, MA) developed a lubricious and hydrophilic treatment (featuring electron beam technology) to coat the interior of an IOL injector used in ophthalmic surgical products. The cover was finished by Royle Printing Company, Sun Prairie, Wisconsin, using a multi-step UV-curing process called Rough Reticulated Strike-Through. First, the 4-color process was laid down and a UV varnish was applied as a spot application in the areas that did not receive the gloss UV treatment (photograph and copy). The UV varnish was cured with UV lights, and then an LED curing system was used to cure the 4-color process inks. A flood gloss UV was applied over the entire cover, which “reacted” to the UV varnish and created the matte varnish – staying glossy in the areas that were knocked out to receive the gloss UV. The final step was a pass under another UV curing system to cure the coating. This process was performed in one pass on press.

32

President’s Message ............................................ 4 Association News ................................................ 6 Technology Showcase ....................................... 24 Industry ............................................................... 50 New Faces .......................................................... 50 Regulatory News ............................................... 54 Calendar ............................................................. 56 Advertising Index .............................................. 56

2 | UV+EB Technology • Quarter 4, 2020

Medical Market Outlook

With the focus on disinfection, UV and EB curing technologies eye opportunities in other areas of the medical industry. By Dianna Brodine, managing editor, UV+EB Technology

RadTech Fall Meeting Goes Virtual for 2020

With travel curtailed, RadTech hosted its annual fall meeting over three days in November. By Dianna Brodine, managing editor, UV+EB Technology

Real-Time Monitoring and Degree of Cure of UV-Cured Resin

The utility of dielectric cure monitoring allows measurement of the degree of cure and the response of UV-curable resins to irradiance and exposure. By Huan Lee and Stephen Pomeroy, Lambient Technologies

40

Electron-Beam Induced Grafting Enables Ophthalmic Surgical Products

AST Products received recognition for its use of electron beam technology for the surface treatment application of a lubricious hydrophilic layer onto the inner surface of an intraocular lens injector. By Liz Stevens, contributing writer, UV+EB Technology

42

DEPARTMENTS

Photopolymerization of Methylene Malonates

Recent developments in the industrial-scale synthesis of methylene malonates promise to make new monomers and oligomers based on this chemistry widely available, with an impact on photopolymerization. By J. Taylor Goodrich, Alexander Y. Polykarpov and Anushree Deshpande, Sirrus, Inc.

Effect of Post-Curing Process on the Performance of Automotive 3D-Printed Specimens

The effect of the post-curing process on the mechanical properties of three different 3D-printed, non-stabilized UVcurable resins systems was studied. By Forough Zareanshahraki, Eastern Michigan University; Amelia Davenport, Colorado Photopolymer Solutions; and Neil Cramer, Christopher Seubert, Ellen Lee and Matthew Cassoli, Ford Motor Company

52

Economic Update

An economist weighs the impact of the presidential election on the US and the world. By Chris Kuehl, Armada Corporate Intelligence

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TECHNOLOGY 2020 Quarter 4 Vol. 6, No. 4

CHAMPIONS THIS ISSUE

RadTech International North America’s Editorial Board facilitates the technical articles featured in UV+EB Technology. Smaller teams of Issue Champions review and approve articles and provide overall content management for each issue, as needed.

COLUMNS 8

UV Curing Technology UV Process Control: Can We Give it Two Thumbs Up? By Jim Raymont, EIT LLC

10

EB Curing Technology

Syed T. Hasan

Gary Sigel

Editorial Board Co-Chair Key Account Manager, Security Inks BASF Corporation

Editorial Board Co-Chair Senior Principle Scientist Armstrong Flooring

Maria Muro-Small

Sheng “Sunny” Ye

Chen Wang

Rachel Davis

EB in 3D? By Sage Schissel, PCT Ebeam and Integration, LLC

12

Innovations Myerson Emerges as Leader in UV-Cured Dental Technology By Liz Stevens, UV+EB Technology

14

Professor’s Corner Special Topic: Microgels, Part 1 By Byron K. Christmas, Ph.D., Professor of Chemistry, Emeritus

UV+EB TECHNOLOGY EDITORIAL BOARD Syed Hasan, BASF Corporation Co-Chair/Editor-in-Chief Gary Sigel, Armstrong Flooring Co-Chair/Editor-in-Chief Susan Bailey, Michelman, Inc. Darryl Boyd, US Naval Research Laboratory Byron Christmas, Professor of Chemistry, Retired Amelia Davenport, Colorado Photopolymer Solutions Rachel Davis, Azul 3D, Inc. Charlie He, Glidewell Laboratories Mike Higgins, Phoseon Technology

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Molly Hladik, Michelman, Inc. Mike J. Idacavage, Colorado Photopolymer Solutions JianCheng Liu, PPG Industries Sudhakar Madhusoodhanan, Applied Materials Maria Muro-Small, Spectra Group Limited, Inc. Jacob Staples, Wausau Coated Products Chen Wang, National Renewable Energy Lab Huanyu Wei, Chase Corp. Sheng “Sunny” Ye, Facebook Reality Labs

Director of Marketing Spectra Group Limited, Inc.

Researcher National Renewable Energy Lab

Material Scientist Facebook Reality Labs

Senior Chemist, Azul 3D, Inc.

UV+EB Technology • Quarter 4, 2020 | 3


PRESIDENT’S MESSAGE “Cooking, eating and drinking are expected to be common ways to pass time over the next several months.”

I

n a normal year, one would expect this reference is anticipatory of a happy holiday season when we expect to pass time in this way with family and friends. However, this year continues to be far from normal, and this actually is the Eileen Weber conclusion by a leading consumer market President research firm. It reflects the continued uncertainty and unfortunate hardship caused by the coronavirus. Several more months … For those of us fortunate enough to be doing OK, it is difficult to gauge how our future will progress, what “new normal” trends may continue – and how this will impact us in the UV/EB industry. As we approach the end of a year that many of us are eager to put behind us, I thought it may be instructive to review some of the trends impacting our industry. Consumer spending represents the largest part of our economy, translating into the demand for a myriad of UV/EB- made goods. While difficult to project consumer spending habits moving forward, we certainly know that some industries are not doing well. One emerging trend shows the purchase of physical products in place of services where it may be difficult to social distance – vacations, restaurant meals, sporting events and gym memberships – which are taking huge hits. On the product side, however, summer sales were strong in a number of economic categories, including sporting goods, cooking and bakeware, small appliances, hobby kits, books, music items and, of course, storebought food, beverages and personal care items. The furniture and electronics industries also continue to be a bit brighter than the economy as a whole, as many households self-isolate and remake their living spaces to address the new normal. Looking ahead, the market research group NPD forecasts that “many of these ‘needs’ will have been satisfied, and consumers will begin to purchase items they consider to be ‘wants’ or gifts for the holiday season,” such as TVs, electronic entertainment gear, toys – and, in general, products to help people stay productive, educated, connected and entertained at home. “As we get into the colder months and holiday season, consumers will be even more eager to participate in activities that take place in the home, as spending time outdoors won’t be as much of an option. This presents the food and home industries an opportunity

to meet this new set of consumer needs.” While the impact on UV/EB seems to reflect this unevenness, innovation continues in many hard-hit applications preparing for a resumption of activity, and perhaps a new way to look at their operations and product offerings. Zooming out from these micro market trends, a recent Manufacturers Alliance for Productivity and Innovation (MAPI) business economics survey points to several potential macro movements that may have large impacts on our businesses. MAPI members are carefully monitoring the US relationship with China. If “decoupling” accelerates – with companies moving operations – the potential exists for more supply chain and production capacity to move in-country to the US; for the reconfiguration of the factory floor and footprint to reflect the need for safety and the downsizing of some operations; and for the continued investment into smart manufacturing and digitalization. For the industrial micro sales trends, and these MAPI macro areas of interest, there are opportunities and threats to our members. Given the various supply chain positions, markets and technologies of our members, such impacts will be felt quite differently and unevenly by our industry, and so it seems increased instability may be our new normal. As such, we can find solace in that organizations such as RadTech offer a small measure of stability, continuing to press forward with initiatives on behalf of members and the entire UV/ EB industry. And now, as my term for serving you is quickly coming to an end and this my last president’s message, I would like to take a moment to thank all of our members and friends for your kind service and outreach. I also would like to thank several members who are rotating off our board with the end of this year, including: David Biro, Sun Chemical; Chris Seubert, Ford Motor Co.; Hui Yang, P&G; and Sunny Ye, Facebook. At this point, you should have received our election ballot for our 2021-22 term, and I welcome Susan Bailey as our new President; Mike Gould our incoming President; and new board members, including Jennifer Heathcote, GEW; Helen Rallis, Sun Chemical; Neil Cramer, CPS; Jonathan Graunke, INX; Rachel Davis, Azul; Jake Staples, Wausau Coated Products, Inc.; and Dan Theiss, P&G. We have a tremendous group of volunteers, and I am excited to continue to engage with RadTech and our members to advance UV/EB technology. Eileen Weber President, RadTech Board of Directors Global Marketing Manager, PC&I Radcure, allnex USA, Inc.

... innovation continues in many hard-hit applications preparing for a resumption of activity... 4 | UV+EB Technology • Quarter 4, 2020

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ASSOCIATION NEWS

RadLaunch Ready to Recognize More Technology Initiatives in UV/EB RadTech has called for entries in its annual competition to identify and recognize new UV/EB technology initiatives – RadLaunch 2021. RadLaunch invites start-up ideas, concepts and prototypes in new materials, optics, design, printing, packaging, 3D printing, inkjet, building products, plastics, medical, electronics and more. This event is going virtual, presenting winners in early spring 2021. Each winning entry will receive a cash award, webinar opportunity, inclusion in a special RadLaunch image video and article in UV+EB Technology magazine. RadTech also will connect start-ups with mentoring resources to assist in research and market development efforts. A new category for students will offer scholarships for the advancement of research and educational opportunities in UV/EB. In addition, RadLaunch will accept start-up ideas on behalf of the International Ultraviolet Association – UV for public health and the environment. The RadLaunch application deadline is January 15. For details, visit www.radlaunch.org. Registration Open for December Virtual UV Disinfection Conference Registration is open for the International Conference on Ultraviolet Disinfection for Air and Surfaces (ICUDAS) taking place online December 8-9. ICUDAS features two days of conference presentations and live video networking. The vision for this conference is to bring together industry leaders involved in all aspects of air and surface UV disinfection to spur communication and networking. An exciting technological feature of this virtual conference is that the presentations from internationally recognized speakers will move seamlessly into multiple “table” breakout sessions. These breakout tables will include Q&A’s with the presenters, exhibitor displays and many other networking opportunities. To register, visit https://iuva.org/2020-ICUDAS.

Fall Webinar Series Videos Feature Advanced Photopolymer Concepts In October, RadTech presented a series of webinars on advanced photopolymer concepts. The first, presented by Christopher Bowman at the University of Colorado, was “Smart, Responsive Polymers Based on Covalent Adaptable Networks: Photoactivatable Dynamic Covalent Chemistry and Its Applications in Polymer Networks.” Participants explored distinct approaches to covalent adaptable networks based on photochemically triggered responses. Second in the series was “3D Photocuring and Photomechanics in Digital Light Processing Additive Manufacturing for Soft Functional Composites and 4D Printing,” presented by H. Jerry Qi of the Georgia Institute of Technology. The presentation introduced strategies to use light grayscale to create a part with locally controlled properties for soft functional composites and 4D printing. “Dentistry as a Driver of Photo-based 3D Printing” was presented by Jeffrey Stansbury, University of Colorado Anschutz Medical Campus. The presentation highlighted the use of photopolymerization-based 3D printing with SLA/DLP and ink jet processes to demonstrate the widespread use of the technology as well as the challenges and opportunities associated with photoprinted polymer application areas. The final series webinar, “Pushing the Limits of CRP and Post-polymerization Modification to Access New Materials,” was presented by Brent Sumerlin, University of Florida. In the webinar, he discussed a method for preparing “inverted” block copolymers, whereby the traditional order of monomer addition has been reversed through the use of photoiniferter-mediated radical polymerization. For more information, or to review videos of the presentations, visit https://radtech.org/education/advanced-photopolymerconcepts-webinars-new.

RadTech Fall Meeting Virtual Event for 2020 Like many events in this unusual year, the 2020 RadTech Fall Meeting was scheduled virtually as a series of three meetings in November. Participants were asked to register for each week separately, as each required a unique meeting ID and password. RadTech Member Update and RadLaunch was set for Nov. 5, the 3D Printing Committee was scheduled Nov. 12 and the EHS/ Sustainability Committee meetings were planned for Nov. 19. For more information, see page 30 of this issue or visit https://radtech. org/component/k2/item/140-radtech-virtual-fall-meeting-2020.

6 | UV+EB Technology • Quarter 4, 2020

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Rolland Featured Speaker as Industry Thought Leader The first UV+EB Industry Thought Leaders webinar featured Jason Rolland, senior vice president at Carbon. Rolland’s topic was “How Additive Manufacturing Materials are Enabling Breakthroughs in a Quickly Evolving BioMedical Environment.” For more information and to view a video of the presentation, visit https://radtech.org/ education/thought-leader-webinars-new. NAI, RadTech Collaborate on Mentorship Program The RadTech Young Professionals Committee has announced access to a mentorship platform through RadTech’s membership in the National Academy of Inventors (NAI). When RadTech became the first nonprofit trade association to join NAI as a member, it introduced opportunities for RadTech members to sign up as mentors or mentees on the Global Academic Inventors Network. For more information or to become part of the mentorship program, visit https://nai.firsthand.co. RadTech Initiates Young Professionals Committee RadTech International North America has initiated a new committee designed to engage students and professionals under the age of 35 or with less than five years of experience in utilizing UV and EB technologies in industry, government and academia. The mission of the YP Committee is “to help young professionals’ (YPs) growth in the use and development of UV & EB technology. We are a group dedicated to enhancing interactions between YPs and senior experts within RadTech.”

As its first undertaking, with an initial goal of enhancing interactions between young professionals and experienced industry members, the YP Committee is working to develop a mentorship program. All RadTech members are invited to sign up, whether as a mentor or a mentee, through a platform called Firsthand. This platform is available due to RadTech’s membership in the National Academy of Inventors (NAI). RadTech members sign up at nai.firsthand. co, using the email associated with RadTech membership or with their personal LinkedIn account. Once enrolled, the program matches mentors and mentees for career development and networking, helping young professionals better connect and deepen interactions within the UV/EB community.

Ye

Davis

Future projects under discussion for the YP Committee could include interviews with YP members, a webpage on the RadTech.org website and networking events, whether virtual or at industry tradeshows. The RadTech YP Committee is led by Rachel Yang Davis, Azul 3D; Kejia Yang, Ares Materials; and Sunny Ye, Facebook Reality Lab, under the direction of Gary Cohen, executive director of RadTech International North America. For more information or to ask questions, contact the committee via email at yp@radtech.org. 

BOARD OF DIRECTORS

Published by:

President Eileen Weber – allnex USA, Inc.

TECHNOLOGY An official publication of: RADTECH INTERNATIONAL NORTH AMERICA 6935 Wisconsin Ave, Suite 207 Chevy Chase, MD 20815 240-497-1242 radtech.org EXECUTIVE DIRECTOR Gary M. Cohen gary@radtech.org SENIOR DIRECTOR Mickey Fortune

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President-elect Jo Ann Arceneaux – allnex USA, Inc. Secretary Susan Bailey – Michelman Treasurer Paul Elias – Miwon North America Immediate Past-President Lisa Fine – Ink Systems, Inc. Board of Directors Evan Benbow – Wikoff Color Corporation David Biro – Sun Chemical Mike Bonner – Saint Clair Systems, Inc. Todd Fayne – Pepsico Michael Gould – Rahn USA Jeffrey Klang – Sartomer Diane Marret – Red Spot Paint & Varnish Jim Raymont – EIT LLC Chris Seubert – Ford Motor Company P.K. Swain – Heraeus Noblelight America Karl Swanson – PCT Ebeam and Integration Hui Yang – Procter and Gamble Sheng “Sunny” Ye – Facebook Reality Labs

2150 SW Westport Drive, Suite 101 Topeka, Kansas 66614 785-271-5801 petersonpublications.com Publisher Jeff Peterson

National Sales Director Janet Dunnichay janet@petersonpublications.com

Art Director Becky Arensdorf

Managing Editor Dianna Brodine dianna@petersonpublications.com

Contributing Editors Nancy Cates Liz Stevens

Circulation Manager Brenda Schell brenda@petersonpublications.com

ENews Kelly Adams

UV+EB Technology • Quarter 4, 2020 | 7


UV CURING TECHNOLOGY QUESTION & ANSWER

UV Process Control: Can We Give It Two Thumbs Up? B

een watching a little more TV than usual recently? When channel surfing, do you have some favorite movies that you will watch even if you have seen them a dozen or more times before? Do you know some of the lines better than the characters? The column this quarter looks at movie quotes that could be used to start a guidebook on UV measurement and process control. 1. “You gotta ask yourself a question: ‘Do I feel lucky?’ Well, do ya, punk?” Dirty Harry The surest way to guarantee you will attract UV curing problems is to ignore good process measurement practices and roll the dice on your operating conditions. Sooner, rather than later, the “if it ain’t broke don’t fix it” approach is destined to break, particularly when this laissez-faire approach applies to UV source maintenance and the care/calibration of your radiometer. 2. “Life is like a box of chocolates. You never know what you’re gonna get.” Forrest Gump UV curing, like most complex processes, can be characterized by the amount of variability (or in mathematical terms, the dispersion or standard deviation) of many critical variables. Variables that can affect the outcome include UV source (type, wavelength, irradiance, energy density, bulb age), process (speed/ belt uniformity, lamp height, lamp/focus, reflector cleanliness), coating (age, thickness) and/or substrate (dyne levels). Those who run a well-documented process know what results to expect and have established lower and upper process window thresholds. Consistent UV data collection (radiometer and/or or real-time measurements) and control of the other variables minimize unwanted surprises. As pointed out in several previous columns, it’s important to use your radiometer within its design specifications. 3. “How many times do I have to teach you: Just because something works doesn’t mean it can’t be improved.” Black Panther But why stop at establishing a UV cure window that just prescribes what is necessary to get an acceptable result? The best operators are those who perform a series of controlled experiments to establish the best or optimum settings for achieving the best results. Best could be the lowest film build, fastest line speed, lowest energy consumption or other process variable that provides superior performance of the most economical process.

8 | UV+EB Technology • Quarter 4, 2020

4. “Houston, we have a problem.” Apollo 13 Of course, even the most well engineered solutions don’t always go as planned. Operators can make unintentional errors, and equipment sometimes breaks unpredictably. It is at these times knowing when and where to get help becomes important. However, for help to be timely and efficient, having reliable data to share will make it easier to obtain expert advice. 5. “What we have here is failure to communicate.” Cool Hand Luke One of the major benefits of proper measurement technique is that everyone working on your UV process can speak the same language. Suppliers of formulations (ink, coating, adhesive), sources, system/presses and substrates – and your R&D staff, lab technicians and plant personnel – all should be able to communicate with each other. Without data, troubleshooting is hit-or-miss. The better the data, the easier the troubleshooting. If the parameters under which the data were obtained are unknown, it can create a confusing and inefficient tower of babble across the supply chain. Record the conditions in detail, including the location (line number), lamp type, radiometer make and model, irradiance, energy density and operating conditions such as line speed, lamp distance, time and temperature. Avoid poorly specified processes in which process values are not tracked. I often get phone calls when something has gone wrong. Most situations can be categorized into one of three buckets:  Lack of source maintenance or failures that happen naturally as components age  Human-related errors unintentionally caused by operators  Improper collection of data, use or care of the radiometer 6. “She never gets old! Marcee can’t be real; she never gets old!” A Beautiful Mind Process equipment degrades, and UV lamps age. The ends of mercury arc lamps can blacken, and the clarity of the quartz can become cloudy (vitrify), causing a drop in the UV levels. Reflectors get dirty, oxidize and corrode. Power supply transformers and capacitors dry out and fail. Magnetrons in microwave systems fail. Mercury arc lamps, especially those with additives (doped) like iron or gallium can change their spectra over time. LED arrays can degrade if they are not properly cooled. The result of aging can be a gradual deterioration detectable over time or a quick, unpredictable failure of a component.

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7. “What we do is, if we need that extra push over the cliff, you know what we do? Put it up to eleven.” Spinal Tap Human-related errors can involve someone “turning things up.” The power supply is “turned up” to try and compensate for aging bulbs or dirty reflectors. The conveyor speed is “turned up” to try and meet needed production capacity. Human-related errors also can involve “doctoring” the formulation to attempt to get cure/ better cure. These shortcuts usually have consequences like undercured parts and premature equipment failure.

rework by assuring that all production takes place in a well-designed process window. Good measurement helps avoid costly downtime due to equipment failure through early detection of problems. Among the leading producers, good measurement saves money through optimizing the cure process so that energy efficiency and production speeds are optimized. Parting thought paraphrased from A League of Their Own: “There’s no crying in UV.” 

8. “Here’s looking at you kid.” Casablanca Other operator mistakes affect UV curing as well. For instance, even those plants that regularly monitor and inspect their UV lamps and clean their reflectors can accidently fail to leave their UV equipment properly positioned. Since UV curing almost always involves good line-of-sight alignment between the UV source and the curing surface, a mispositioned lamp can fail to provide adequate cure. Similarly, placing a lamp too far from – or too close to – the target can result in problematic changes of irradiance. The same is true of correct radiometer placement. Comparing measurements taken in different locations makes it impossible to observe any trend in UV performance. Good operators establish procedures that reduce this variability by taking their readings in the same spot(s) every time.

Jim Raymont Director of Sales EIT LLC jraymont@eit.com

9. “Only one thing alive with less than four legs can hear this frequency, Superman, and that’s you.” Superman Your process is most efficient when the chemistry is matched to the UV source. All UV sources are not created equal. For broadband sources, be attentive when replacing bulbs to ensure that the same type bulb is installed. If your production process calls for a mercury-gallium bulb in position one, do not install a mercury bulb in this location. Mistakes also can be made in the laboratory, where bulb types may be changed more frequently. Two different brands of LED arrays could have the same center wavelength (CWL) and power classification (12 W/cm2) but could have very different Joule values. Carefully evaluate before making any supplier changes. Be sure that your purchasing team understands the importance of buying on value and not just price. For best performance, match your measurement device (response, dynamic range, sample rate) to the UV source and process. 10. “Oh yes, the past can hurt. But you can either run from it or learn from it.” The Lion King The mistakes we have observed made by others can help us avoid our own costly mistakes. As TV’s Frasier Crane said, “It may be an unwise man who doesn’t learn from his own mistakes, but it’s an absolute idiot that doesn’t learn from other people’s.” 11. “Show me the money.” Jerry McGuire The bottom line is that good measurement practices save money several ways. Good measurement avoids costly scrap and uvebtechnology.com + radtech.org

IST AMERICA U.S. OPERATIONS 121-123 Capista Drive Shorewood, IL 60404-8851 Tel. +1 815 733 5345 info@usa.ist-uv.com www.ist-uv.com

HANDCURE LED Mobile Curing UV+EB Technology • Quarter 4, 2020 | 9


EB CURING TECHNOLOGY QUESTION & ANSWER

EB in 3D? A

ny discussion of 3D processing these days almost immediately turns to additive manufacturing – in which electron beam does indeed have a role1,2 – but outside the scope of 3D printing lie plenty of challenges for UV and EB in this 3D world. In contrast to thermal processing, users of UV/EB must be cognizant of how a curve or an angle or any similar complexity will affect the energy distribution over a 3D surface. This is one of the primary reasons why traditionally low-energy, area-type3 electron beam (≤ a) b) 300 kV) has been a processing technique Figure 1. An example of the dose distribution of electron beam at multiple angles. Data for flat, roll-to-roll web applications, such collected at 200 kV on a Comet EBLab unit using GEX dosimetry. as cross-linking plastic films or curing overprint varnish on printed substrate. Most current industrial electron beam installations are configured the larger distances between the beam and the product than are to process web-based product. However, electron beam does experienced with flat substrates. Radiochromic dosimeters can be not have to be relegated to 2D applications; customer need, used to quantify the energy distribution over complex geometries. advancements in the technology and a bit of ingenuity have Figure 1 shows an example of using dosimetry to determine the caused a movement of EB into the third dimension. dose distribution at multiple angles. These results indicate that, at 200 kV, even a surface orthogonal to the beam (90°) receives 60% Yet, there can be challenges in using EB to process complex of the dose that was seen by a flat surface (0°). While electron geometries. First and foremost is the challenge of shielding. scatter alone will not reach 360° around a product, it can be used Accelerated electrons produce bremsstrahlung x-rays when for non-flat products, such as those with curved surfaces. interacting with matter.4 The electron beam system must be shielded – often with lead – to contain these x-rays and provide a If electron scatter isn’t sufficient, another way to achieve energy safe working environment. Designing shielding to accommodate distribution in 3D is to articulate the product, presenting every the movement of 3D products into and out of the beam requires side to the beam. A classic example of this is the process of more skill and ingenuity than that needed for a thin film. In festooning cables to cross-link the cable insulation.6 The cable addition, the vacuum system that accompanies the beam (the is run back and forth under the beam multiple times, and at each electrons must be produced and accelerated in high vacuum) pass it is turned so that once it has exited the beam, every angle can be cumbersome to creative configurations. This challenge has received an equal dose. Another possibility is to spin the has been greatly alleviated by the advent of sealed EB emitters, product as it is passed once in front of the beam, again exposing in which the required vacuum is achieved during production of every angle equally. An example of this type of configuration is the emitter, the emitter is sealed and no vacuum equipment is shown in Figure 2: The drum rotates the cylindrical parts in front necessary for operation.5 The lack of vacuum equipment makes of the EB emitter, and, simultaneously, the parts are spun for the sealed emitter more compact and nimble than a traditional EB complete exposure. system. Depending on the product, it may be preferable to articulate the Despite these challenges, there are multiple ways that electron beam emitter instead. A sealed emitter makes it feasible to angle beam can be used to process 3D products. The first way is the beam in one direction, then, for example, change that angle to simply be aware and make use of the electron scatter. The before the product is presented to the beam a second time. Attach accelerated electrons the beam produces don’t just interact with a sealed emitter to a robotic arm and just about any angle is the product in an orderly, unidirectional manner. Instead, they are achievable. scattered every which way as they collide with the window foil and then air molecules before reaching the product. Accelerating Finally, 3D electron beam processing also can be accomplished voltage is an important aspect of the electron scatter, and higher with multiple emitters. Two emitters, both facing inward, can voltages (i.e., ~150 to 300 kV) may be required to overcome be used to irradiate both the top and bottom of the product as 10 | UV+EB Technology • Quarter 4, 2020

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®

Transform the economics of UV

Figure 2. A cutaway drawing of an EB designed and built for the 3D treatment of cylinder-shaped product. (Image courtesy of PCT Ebeam and Integration)

it passes between them. This method can be combined with articulation of the product by causing it to freefall as it passes through both beams.7 When choosing EB to process complex geometries, it is good practice to consider the different configuration options. Some options may be more feasible or cost effective than others depending on the handling of the product, complexity of design, amount of shielding necessary, number of emitters, etc. Whatever the case, know that EB in 3D is a possibility!  References: 1. Gonzales-Martinez, I.G., Bachmatiuk, A., Bezugly, V., Kunstmann, J., Gemming, T., Liu, Z., Cuniberti, G., Rummeli, M.H., Electronbeam induced synthesis of nanostrucutures: a review. Nanoscale, 2016, 8, 11340-11362. 2. Kumar, S., Additive Manufacturing Processes. Springer International Publishing, 2020. 3. Mehnert, R., Pincus, A., Janorsky, I., Stowe, R., Berejka, A., UV & EB Curing Technology & Equipment. John Wiley & Sons, Inc.: London, 1998. 4. Chapiro, A., Radiation Chemistry of Polymeric Systems. John Wiley & Sons, Inc.: New York, 1962. 5. Haag, Werner, Sealed electron beam emitter for use in narrow web curing, sterilisation and laboratory applications. RadTech Conference Proceedings 2012. 6. Makuuchi, K., Cheng, S., 2012. Radiation processing of polymer materials and its industrial applications. Wiley. 7. Laatu: Non-thermal, in-plant microbial reduction solution for dry foods. Buhler, 2019. https://www.buhlergroup.com/content/ buhlergroup/global/en/services/Digitalservices/laatu.html

Sage Schissel, Ph.D. Applications Specialist PCT Ebeam and Integration LLC sage.schissel@pctebi.com uvebtechnology.com + radtech.org

UV+EB Technology • Quarter 4, 2020 | 11


INNOVATIONS INDUSTRY ADVANCES WITH RADLAUNCH WINNERS

Myerson Emerges as Leader in UV-Cured Dental Technology By Liz Stevens, contributing writer, UV+EB Technology

H

eadquartered in Chicago, Illinois, Myerson LLC, founded in 1917, is a manufacturer of high-quality, aesthetically appealing denture teeth. The company specializes in the removable prosthetics market: in addition to denture teeth, it offers materials and equipment for fabricating flexible partial dentures and sleep appliances. The company is earning attention for its innovative use of UV curing of a patented plastic resin formula used to create ultra-strong, natural-looking permanent replacement teeth. Jim Swartout, Myerson LLC’s CEO, described the industry’s history and the collaborative journey that led to the company’s 3D-printed, UV-cured dental appliances.

In the early 1900s, ceramic (specifically porcelain) became the material of choice for replacement teeth. Ceramic teeth are affixed by hand into the denture base material, using a tiny gold pin to anchor each tooth. The rising price of gold and the labor-intensive nature of the assembly process made this method increasingly prohibitive and, in the 1960s, the industry embraced the ’60s miracle substance: plastic. Heat-polymerized polymethacrylate – natural-looking and affordable – became the world’s favored tooth material. In the last decades, the baby-boomer population has created a surge in demand for replacement teeth and, simultaneously, the tooth-setting craft has declined dramatically. As with other industries eager to modernize, dentistry began to embrace digitization. The traditional method of making of dental impressions, for example – utilizing a platter of soft silicone – is giving way to digital wands that record the contours of a patient’s gums and teeth. For the manufacture of replacement teeth, CNC milling has become the mainstay, and while it is fast, it also has limitations and is wasteful of materials. Additive manufacturing has looked attractive for dentistry, but it is only since the cost of printers has dropped and CAD software has matured that it has become a feasible avenue to explore. Dental laboratories began buying 3D printers early on but, until just recently, they were used mostly for process material for in-lab use rather than for appliances in a patient’s mouth. Jim Swartout explained that one big reason the industry has not yet fully jumped onboard with 3D printing for dental appliances is “the materials have not met the need. They have tended to be very short-term as opposed to being suitable for permanent use 12 | UV+EB Technology • Quarter 4, 2020

in the mouth – which is a very challenging environment for any material. The first generation of 3D material was not sufficiently tough and didn’t have the right aesthetic qualities for it to be widely accepted.” Twelve years ago – Hybrid Ceramics, a San Francisco, California, company led by a dental bio-materials specialist and a prosthodontist – presented Myerson LLC and Swartout with a new and improved plastic material for making conventional, heatcured denture teeth, and asked if the company would like to use it. “We spent 10 years,” said Swartout, “trying to take this highly advanced formula and put it into a 1960s-based manufacturing process for heat-curing false teeth.” Three years ago, Swartout brought the trend toward digital manufacturing in dental labs and the dental industry to the attention of his business partners. “I said 3D printing is where people ultimately want to go. So instead of buying prefabricated denture teeth, for example, they would want to be able to print them on-site, right away, using 3D resins.” Swartout wondered whether the improved material created by Hybrid Ceramics, which has some remarkable mechanical properties, could be converted to a 3D printing material. He checked with Hybrid Ceramics. “The bio-materials expert said I think it would make an excellent printing material, and that’s what really started us on our journey.” A host of unique mechanical properties is necessary for dental applications since the human mouth is a complicated environment, and teeth must withstand extraordinary pressures. The new printing material created through Myerson’s collaboration with Hybrid Ceramics has extremely high mechanical properties, comparable to engineered polymers like PEEK, which is used for orthopedic implants. With this patented-formula material, said Swartout, “you can achieve incredible toughness that’s retained in the presence of water.” Other materials might be tough, but they may not remain tough in the watery environment of the mouth, or they might not be bio-compatible, or they might not look nice. Swartout explained that replacement teeth must withstand sudden or prolonged biting force without cracking or deforming, which calls for high strength plus some flexibility. They also must have a low rate of absorption to resist picking up stains or odors from food and beverages. “The unique thing about this material that Hybrid Ceramics developed,” said Swartout, “is that it is very uvebtechnology.com + radtech.org


tough, it maintains that toughness in water and you can make dental materials out of it that look very natural and are almost indistinguishable from human teeth. The ability to do all of those things is what is unique.” Swartout described that the biggest challenge during the multi-year project was the team-building angle. “We’ve been in business for over 100 years, but it doesn’t mean that the relationships we built over time were the right relationships to advance this technology. I had to build an entirely new network of advisers and people to help bring this project along at a fast pace.” To develop a resin material with specific properties that was also amenable to 3D printing, Swartout had to build a network of scientific and business advisers to help commercialize a radically new dental application. “We had to find the best people in their fields to help us. It’s still a new area in dentistry, so the experts weren’t falling out of trees.” The team considered DLP printing but realized that – while this method is portable, fast and predictable – it does not easily allow for working with multiple colors. Natural-looking replacement teeth need to have the translucence and variation in color that matches real human teeth. 3D inkjet printing was chosen since it can work with multiple colors. UV stood out as an affordable curing method that delivers the high quality required for medical

devices. Swartout pointed out that the UV wavelength employed for this project is based on standardization and availability. “The first wave of 3D printers tended to be in the 405nm wavelength,” he said, “because it was affordable and fast and accurate. You are seeing more and more 385nm printers because they are able to be even faster and still deliver excellent resolution. Our job is to tune our formula to those two standard platforms – the 385nm and 405nm.” Myerson LLC’s plan, which was delayed somewhat by the pandemic, is for beta testing of the new material and 3D printers during the last quarter of 2020 and commercialization in the first half of 2021 in dental laboratories within the company’s existing network.  RadTech, the nonprofit for UV+EB, celebrated the 2020 Emerging Technology Award winners at the RadTech 2020 Conference, March 8-11, in Orlando, Florida. RadTech’s Emerging Technology Committee selects award winners among end users of the technology, based on new, promising and/or novel use of UV and/or EB. RadTech has recognized applications ranging from 3D printing/additive manufacturing to floor coatings to novel electronics to unique uses for automotive and aerospace. Myerson LLC was one of the 2020 Emerging Technology Award winners.

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TECHNOLOGY

UV+EB Technology • Quarter 4, 2020 | 13


PROFESSOR’S CORNER BACK TO THE BASICS OF UV/EB

Special Topic: Microgels – Part 1

T

he first seven editions of “Professor’s Corner” focused on the fundamentals of polymer chemistry as they apply to the field of UV/EB polymerization. In this eighth edition, a special topic is introduced. It is probably not well known that a typical UV/EB polymerization process produces films that contain vast numbers of particles or domains or phases known as “microgels.” This article introduces this mysterious species that is lurking in most all energy-cured films, particularly those based on (meth)acrylatefunctional monomers and oligomers and produced by free radical addition polymerization processes.

What is a microgel? In photopolymerization, microgels are amorphous cross-linked particles that range from roughly 50 to 100 nm in size.1 They are imbedded in the cross-linked polymer matrix and represent a separate phase from the network, which itself is typically amorphous! Not only are they of varying size and shape, they also possess very different morphologies from each other and from that of the network polymer matrix. Each microgel domain, in principle, will exhibit its own particular glass transition temperature (Tg). Recall that the Tg is a property of amorphous portions of a polymer film only.

H et ero gen eo u s S t ru c t u re

H o m o gen eo u s S t ru c t u re

Uniformly Amorphous

Narrow Thermal Transitions Figure 1. Conceptualizing nanogels. Used with Permission of Heraeus Japan.

One might rightly ask why such photopolymer films are transparent rather than hazy or cloudy, as with other multiphase heterogenous mixtures, such as colloids. The transparency is a strong indication that, in such cases, it is probably inappropriate to label them as “microgels.” Rather, they are “nanogels.” Were they actually of micrometer (mm) size, such a multiphase system would scatter visible light, producing translucent or opaque polymer films. Microgels are well-known entities, often of mm size, that are typically introduced intentionally into various polymer matrices to provide a variety of property enhancements. But these applications are not being considered in this discussion of photopolymer nanogels. Who cares? Tens of thousands of perfectly fine UV/EBpolymerized coatings, inks, adhesives and other end-use products are produced every day that are not negatively impacted by the presence of nanogels. So why do they matter? There are at least three answers to this very valid question: 1) In many, if not in most applications, they don’t matter! 2) There is value in knowledge for its own sake. The more we understand about the fundamental nature of the UV/EB polymerization process and the molecular structure of the products produced by this technology, the more well prepared we are to interpret experimental results and to address problems when they arise. 3) Since the nanogels represent separate phases, the interface between them and the polymer matrix represents locations where stress can build up and cracks can propagate, causing enhanced brittleness. So, in 14 | UV+EB Technology • Quarter 4, 2020

Figure 2. DMA scan of UV-polymerized film

applications where impact resistance is needed, for example, the nanogels might lead to application failure. Grasping the concept. Figure 1 provides a conceptual image of a UV/EB polymer matrix with embedded nanogels.2 The right side of the figure shows a uniformly amorphous structure. Of course, the word “amorphous” literally means “without structure.” We can think of this as being “homogeneously heterogeneous.” In contrast to this image, the left side of the figure shows a polymer matrix with imbedded nanogels of varying sizes and shapes. This represents heterogeneity at the molecular level. This morphology will produce a wide Tg temperature range, since each nanogel and the matrix itself may, in principle, all have different Tgs. In a dynamic mechanical analysis (DMA) scan, this will be indicated uvebtechnology.com + radtech.org


  

    

      

       

     

Still Heterogeneous

Heterogeneous Initially

  

           

Figure 3

Figure 4

    

           Heterogeneity Continues

Heterogeneous Regions in Final Film

Figure 5

Figure 6 Figures 3 through 6. Sequential process of nanogel formation.

by a quite wide half-height width of the tan ď ¤ curve. In Figure 2, the half-height width is roughly 100°C! Also, it has a “shoulder,â€? indicating a tendency, in this particular case, toward a bimodule distribution of nanogels in the film. Recall the discussion of the tan ď ¤ curve in a previous edition of “Professor’s Corner.â€?3 This curve represents a range of different Tgs within the polymer sample. The peak of the curve represents the Tg of the largest cohort of similar amorphous domains and is typically reported as the Tg of the sample. Were there no nanogels present, the tan ď ¤ curve would be much narrower. In the ideal limit of a perfectly uniformly amorphous morphology, it would be a “spike.â€?

same time, producing nanogels. The discussion of the formation of nanogels will be continued in a future edition of “Professor’s Corner.â€? ď ľ

Figures 3 through 6 depict schematically the sequential process of nanogel formation during a UV polymerization process. These are images graciously provided for use in presentations by the late Charles E. Hoyle of the University of Southern Mississippi. In Figure 3, there is very little conversion to polymer, and the nanogels are beginning to form. In Figures 4 and 5, the nanogels continue to increase in concentration. Finally, in Figure 6, the full polymer network has formed, demonstrating a complex amorphous structure with a high concentration of nanogels at the end of the process.

References 1. Hoyle, Charles E., personal communication, 2008. 2. Image produced by Fusion UV Systems Japan KK (now Heraeus Japan) in 2008 and used by permission for presentation at RadTech Conferences, Heraeus Japan UV Seminars, and this column. 3. Christmas, B. K., “Professor’s Corner,� UV+EB Technology, 6, No. 2, 2nd Quarter, 2020, pp. 12-13.

What causes nanogels to form? Nanogels form primarily through a process described as “cyclization.� This process causes entrapment of free radicals, reducing the overall conversion of multifunctional monomers and oligomers to polymer and, at the uvebtechnology.com + radtech.org

Technical Questions? What are your technical questions about polymer science, photopolymerization or other topics concerning the chemistry and technology of UV/EB polymerization? Your questions will help guide future topic decisions for this column. Please submit your questions via email to Dianna Brodine at dianna@ petersonpublications.com.

Byron K. Christmas, Ph.D. Professor of Chemistry, Emeritus University of Houston-Downtown b4christmas@gmail.com UV+EB Technology • Quarter 4, 2020 | 15


PHOTOPOLYMERIZATION By J. Taylor Goodrich, Alexander Y. Polykarpov and Anushree Deshpande, Sirrus, Inc.

Photopolymerization of Methylene Malonates *Editor’s Note: A discussion ensued amongst the authors and the Editorial Board regarding the use of the term “post-cure.” In this publication and in the 3D printing industry as a whole, post-cure often has been used to describe UV exposure of the 3D-printed objects. In this article, the term refers to additional polymerization that takes place after UV has been turned off. Introduction t could be said that the modern era of commercial photopolymerization began in 1964 with the installation of the first electron beam cure unit at Boise Cascade for wood finishing. Fifty-five years later, the field of photopolymerization continues to expand: A simple search on Google Scholar for “photopolymerization” from 2019 returns more than 8,440 entries. Acrylates and methacrylates continue to be the materials of choice for the majority of photopolymerization applications, with relatively less attention being spent on epoxides, oxiranes, vinyl ethers/esters and vinyl compounds for reaction with thiols.1 Methylene malonates have been relatively unexplored. The interest in this class of compounds was low, likely due to the lack of commercially viable synthetic routes. Recent developments in the industrial-scale synthesis of methylene malonates2 promise to make new monomers and oligomers based on this chemistry widely available within a few years. With their unique reactivity,3 methylene malonates are likely to make an impact in many polymer applications, including photopolymerization.

I

Methylene malonates: Unique possibility for dual cure Methylene malonates contain a carbon-carbon double bond that is 1,1-disubstituted with ester groups. Selected examples of methylene malonate structures are shown in Figure 1. The two ester groups in methylene malonates activate the double bond, making it more electron deficient and more suitable for reaction with electron donors. This activation is weaker than that in cyanoacrylates and is stronger than in acrylates that have only one electron withdrawing group connected to the double bond. Because of this, methylene malonates possess an intermediate reactivity: They do not instantly polymerize on contact with water like cyanoacrylates, yet they can react with weak bases and nucleophiles much more readily and under milder conditions than acrylates and methacrylates. Methylene malonates still can undergo rapid anionic polymerization at room temperature when initiated with a base or a nucleophile.3 Additionally, the carboncarbon double bond of methylene malonates readily participates in Michael-addition reactions with amines and in catalyzed Michael-addition reactions with polyols.4 The geminal ester groups also can be transesterified while preserving the double bond to create a variety of new monomer structures or, when a polyol is used, a O O

O

O

n O

O

O

O

BD-PES

O

O

O

O

DHMM

O

O

O

O

DCHMM

Figure 1. Structures of selected methylene malonates. (BD-PES is methylene malonate oligomer based on 1,4-butanediol. DHMM is dihexyl methylene malonate. DCHMM is dicyclohexyl methylene malonate.)

16 | UV+EB Technology • Quarter 4, 2020

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variety of multifunctional methylene malonates. Methylene malonates also can be polymerized via a free-radical mechanism analogous to acrylates and methacrylates. This combination of dual reactivity toward free radicals and nucleophiles coupled with the relative ease of transesterification and low odor of the compounds should allow methylene malonates to become a unique and versatile platform for UV cure applications. Materials and methods Materials Methylene malonate monomers including dihexyl methylene malonate (DHMM), dicyclohexyl methylene malonate (DCHMM) and methylene malonate oligomer based on 1,4-butanediol (BD-PES) were available from Sirrus, Inc. Figure 2. Cure profiles of 1,4-butanediol methylene malonate vs. 1,4-BDDA 1,4-butanediol diacrylate (BDDA), 1,4-butanediol and 1,4-BDDMA dimethacrylate (BDDMA), isobornyl acrylate (IBOA) and isobornyl methacrylate (IBOMA) were obtained from Arkema. Radical photoinitiators and irradiated with a mercury arc lamp spot cure system from 1-hydroxycyclohexyl phenyl ketone and diphenyl(2,4,6Synchron, Inc. The irradiance at the sample was 20 mW/cm2 trimethylbenzoyl)phosphine oxide (TPO) were supplied by UVA. Free- standing films were prepared by casting liquid MilliporeSigma and Rahn AG, respectively. Photolatent base photopolymer resin between glass plates with plastic spacers NVOC-DEA was synthesized from commercial products and clamping them together. They were then passed through a according to Xi, W. et al5. Ethyl 1-methyl-3-piperidinecarboxylate Heraeus Noblelight LC6B UV curing conveyor with a Fusion D (EMPC) and methanesulfonic acid (MSA) were obtained from bulb at a speed of 5 ft/min. Each pass provided 6.7 J/cm2 UVA MilliporeSigma. energy to the sample. Photopolymerization techniques Curing profiles were measured by FT-IR during photopolymerization. These samples were cast between glass microscope slides with an 850-micron-thick rubber spacer

This combination of dual reactivity toward free radicals and nucleophiles coupled with the relative ease of transesterification and low odor of the compounds should allow methylene malonates to become a unique and versatile platform for UV cure applications. uvebtechnology.com + radtech.org

FT-IR A Perkin-Elmer Spectrum One Fourier-transform infrared spectrometer was used to measure the conversion of carboncarbon double bonds. For time-resolved measurements the alkene conversion was calculated as the disappearance of the near-IR peak found at 6190 cm-1 in the transmission spectra of the samples. For cured polymer films, the alkene conversion was measured by attenuated total reflectance (ATR) as the fractional decrease in the area of the mid-IR peak occurring at 804 cm-1. These mid-IR spectra were normalized by the area of the carbonyl peak at 1720 cm-1. DSC Heat-cool-heat experiments were performed on a TA Instruments DSC 250. Heating and cooling cycles were run at 5°C/min with a maximum temperature of 200°C. The glass transition temperature of samples was calculated from the second heating cycle by the half-height midpoint method. DMA Dynamic mechanical analyses were performed to measure tensile properties of prepared polymer films. Tests were performed on a TA instruments Q800 DMA. Multifrequency multistrain tests were run in tensile mode at 1 Hz with 0.1% strain from -60°C to 250°C at a heating rate of 5°C/min. Two heating cycles page 18  UV+EB Technology • Quarter 4, 2020 | 17


PHOTOPOLYMERIZATION  page 17 were recorded for each sample. Glass transition temperatures were recorded as the temperature at which the tan delta peak reached its maximum value. Strain ramp tests were performed at room temperature with a strain rate of 2%/min. Free-radical cure Methylene malonates have been thermally, freeradically copolymerized.6 Thermoplastics can be produced with a wide range of glass transition temperatures and degrees of crystallinity. Multifunctional methylene malonates can be incorporated to produce cross-linked materials with excellent solvent resistance as well as high hardness or desired flexibility. The geminal substitution with two electron Figure 3. Cure profiles of DCHMM and DHMM vs. IBOA and IBOMA withdrawing ester groups leads to resonance stabilization of the radical adducts of methylene malonates and induces steric hindrance in polymerization. phenyl ketone photoinitiator in each compound followed by the Therefore, the propagation of free-radical polymerization of UV exposure as described in the Materials and Methods section. methylene malonates is generally slower than that of acrylates and The specimens were irradiated with 20 mW/cm2 UVA at t = 3 is more similar to that of methacrylates, where the radical adducts minutes. Double bond conversion was calculated from the area of receive additional stabilization from the methyl group, which the near-IR peak found at 6190 cm-1 relative to that peak’s area also increases the steric hindrance.7 Curing speed is important before irradiation. in implementing a photopolymerization chemistry industrially because it saves time, increases productivity and lowers the As shown in Figure 2, the room temperature rate of energy costs of irradiation. It has been recently demonstrated that polymerization of the BD-PES methylene malonate was indeed methylene malonates copolymerize favorably with methacrylates slower than that of BDDA. The initial rate of polymerization of and can enhance the rate of cure of some methacrylates when BD-PES was faster than that for BDDMA, and the final double copolymerized.8 bond conversion was higher. As can be seen from Figure 3, DCHMM cured at a similar rate to IBOMA, while DHMM was Multifunctional methylene malonates are obtained by slower. Interestingly, while the DHMM cured was slower, it transesterification of monomeric methylene malonates with attained a higher double bond conversion than IBOMA and the various di- and polyols. Such processes result in mixtures same conversion as DCHMM and IBOA after 10 minutes of of oligomeric structures, which may enhance the cure due irradiation. to the additional cross-linking from molecules with higher functionality. In this work, a multifunctional methylene Thermal characterization malonate made by transesterification of diethyl malonate and Films of UV cured multifunctional methylene malonate and its 1,4- butanediol (BD-PES) was compared to 1,4-butanediol blends with monofunctional methylene malonates were compared diacrylate and dimethacrylate. Monofunctional dicyclohexyl and against the cured films of 1,4-butanediol diacrylate. Each of these dihexyl methylene malonates were compared in reactivity with films was prepared by dissolving 2 wt% 1-hydroxycyclohexyl monofunctional (meth)acrylates. This is the first comparison of phenyl ketone photoinitiator in the monomer composition. The a multifunctional methylene malonate with a multifunctional compositions were then cast at a thickness of 500 microns and acrylate and methacrylate, and the authors strongly believe passed through the UV conveyor four times. page 20  that more comparisons with different types of Composition, wt% Double Bond Tg by DSC, °C Tg by DMA, °C G’ at 25°C, oligomers will shortly MPa Conversion, % follow. 1410 BD-PES 88.5 56 103 Cure profiles Photopolymer samples were prepared by dissolving 2 wt% 1-hydroxycyclohexyl

80% BD-PES, 20% DCHMM

95.4

82

129

1020

80% BD-PES, 20% DHMM

93.4

45

93

930

BDDA

87.6

87

114

1230

Table 1. Thermal properties of UV cured methylene malonates and BDDA

18 | UV+EB Technology • Quarter 4, 2020

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PHOTOPOLYMERIZATION  page 18 The cured films were O characterized for double bond O O O KȞ + CO2 + conversion, Tg and tensile N O N modulus. The results can be H found in Table 1. The double O NO O NO2 bond conversion for the BDPES sample was similar to Figure 4. Photogeneration of diethylamine from NVOC-DEA the BDDA sample, despite the BD-PES sample having an average functionality more Duration of Post-Cure DB Conversion Tg G’ at 25 °C than 3 compared to an average 10 minutes 38% -15 °C 8.3 MPa functionality of 2 for BDDA. 24 hours 67% 62 °C 440 MPa The Tg was 11°C higher by Table 2. Double bond conversion and thermal properties of BD-PES before and after a 24-hour DMA for BDDA over BDanionic postcure PES. Diluting BD-PES with methylene malonate monomers increased the extent of the Components Base Conversion after UV, % Conversion after 24 hours, % double bond conversion in the BD-PES None 40 40 cured film. Adding 20 wt% of BDDA None 44 45 a high-Tg monomer, DCHMM, increased the film Tg by BD-PES 100 ppm EMPC 43 69 26°C, and adding 20 wt% of BDDA 100 ppm EMPC 36 36 a low Tg monomer, DHMM, Table 3. Double bond conversion by FTIR for methylene malonate and (meth)acrylates before and decreased the film Tg by 10°C. after a 24h postcure period The storage modulus was 15% higher for BD-PES compared to BDDA. Photoinduced anionic polymerization 1,4-butanediol-methylene malonate polyester oligomer was mixed with 2 wt% of NVOC-DEA photolatent base (6-nitroveratryl chloroformate coupled with diethylamine). This mixture was shown to be stable (sample was still liquid with no noticeable increase in viscosity) after 14 days. This mixture was cast between glass plates to obtain a film thickness of 125 microns and then passed through the UV conveyor six times, applying 40 J/cm2 UVA energy to the specimen. The double bond conversion was 38%, and a tacky, free-standing film was produced. The concentration of NVOCDEA, as well as the applied dose of UV energy, were selected so that the cured film would have sufficient structural integrity but to leave as many methylene malonate double bonds unreacted as possible to maximize the potential for anionic post-cure*. Increasing either the photolatent base concentration or the UVA exposure resulted in a higher double bond conversion immediately after UV exposure. After irradiation, the sample remained at room temperature in the dark for 24 hours. The double bond conversion after 24 hours was 67%. These results indicate that the anionic polymerization of methylene malonate continues after the UV exposure in the dark. DMA analysis of the photocured film immediately after irradiation and 24 hours later showed an increase in Tg and storage modulus after this post-curing period. The results can be found in Table 2. 20 | UV+EB Technology • Quarter 4, 2020

EMPC content (ppm)

Gelation Time (min)

110

255

115

180

120

180

125

127

130

113

135

82

Table 4. BD-PES gelation time vs. EMPC level

2K compositions (UV cure + added base) Instead of using a photolatent base, anionic post-cure of methylene malonate also can be achieved through the addition of a relatively weak base prior to UV exposure: as long as sufficient pot life is obtained. This allows for the photoinduced free-radical cure to take place before significant anionic cure has occurred. To illustrate this effect, BD-PES and blends of acrylates were prepared with and without the addition of a weak base, ethyl 1-methyl-3-piperidinecarboxylate (EMPC). EMPC was added 5 minutes before a UV exposure of two passes under the UV conveyor system. TPO photoinitiator was used for the freeradical UV cure. The concentration of TPO was 0.2 wt% in the BD-PES samples and 0.01 wt% in the BDDA samples. These concentrations were chosen so that films with approximately 40% conversion of double bonds would be achieved. Limiting the conversion during UV free-radical cure assured the samples uvebtechnology.com + radtech.org


Stress

a) 8 7 6 5 4 3

b)

t

Strain-to-Break

Strip, UV cured Strip, 24 hrspost-cure

2

Overlay, 24 hrs post-cure

1 0 0

1

2

3

Strain (%)

4

5

6

Figure 5. Increase of the bond strength between two layers of UV cured BD-PES. a) Strain-to-break tests compare a green, UV cured material and that same material after 24 hours of anionic postcure with an overlay of separate strips of the UV cured material which postcured while in contact. b) An illustration of the overlay sample that was stretched to test the bonding between the pieces.

would have sufficient level of unreacted methylene malonate groups available for potential anionic post-cure. The double bond conversion of these films was measured immediately after UV irradiation and then again 24 hours later. These results are compiled in Table 3. The 1,4-butanediol diacrylate was not expected to react with this relatively weak tertiary amine. Therefore, significant postcure was only observed in the methylene malonate formulation, which was mixed with EMPC before UV irradiation. The BD-PES control test without added EMPC did not post-cure. Thus, the post-cure must have proceeded through the anionic polymerization pathway. It is important to add the weak base to the methylene malonate photopolymer resin at an appropriate level such that anionic cure is slow enough for the first-stage photoinduced free-radical polymerization to occur before anionic polymerization has significantly increased the viscosity of the resin. Table 4 shows how the pot life of BD-PES can be controlled by varying the level of the weak base added. For these tests, BD-PES sample was first mixed with 50 ppm methanesulfonic acid (MSA) and 2000 ppm TPO photoinitiator (to mimic the presence of photoinitiator in UV cure, though the samples were not exposed to UV this time). EMPC was then dissolved in the samples. Gelation time was recorded as the point at which the samples would no longer flow under their own weight. Potential for 3D printing An application that can benefit from anionic post-cure is 3D printing, especially the SLA or DLP types. One challenge faced by UV 3D printing methods is creation of objects with isotropic properties while maintaining high conversion and reducing shrinkage.9 Strength in the direction perpendicular to the cured layers (the z-directional strength) composing a 3D printed object uvebtechnology.com + radtech.org

is typically weaker than the strength parallel to the layers. This is due to limited covalent bonding across the printed layers and the tendency of the object to fail adhesively between the layers. As shown in Figure 5, anionic post-cure in a 3D printed methylene malonate system can improve this by creating additional bonds between the printed layers. While UV-initiated radical cure occurs primarily within the layers, anionic cure will occur throughout the entire volume of the object, including between the printed layers. A 500-micron-thick film of BD-PES was UV cured using 0.2 wt% TPO photoinitiator by irradiating with 6 J/cm2 UVA. Before UV curing, 100 ppm of EMPC was added to slowly initiate anionic polymerization. The Young’s Modulus was 0.036 MPa immediately after UV cure, which increased to 2.02 MPa after 24 hours of post-cure time. To show bonding between layers, a strip of this film was cut and overlaid immediately after UV curing. It was then left to post-cure at room temperature in the dark for 24 hours. The overlaid area was 25% of the total area between the DMA clamps. This overlay sample had a modulus of 1.76 MPa and underwent cohesive failure, showing excellent bonding between the two overlay pieces. If the two overlay pieces were not in contact during the post-cure, they would have individually cured tack-free and showed no adhesion when pressed together. Conclusion Methylene malonates were shown to free radically cure at a rate similar to methacrylates. It also was shown that methylene malonates can be UV cured anionically with the use of a photolatent base. UV cure of methylene malonates with a photolatent base led to postcuring of remaining unreacted double bonds in the dark, which was not observed for either methylene malonates or acrylates that were partially polymerized free page 22  UV+EB Technology • Quarter 4, 2020 | 21


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22 | UV+EB Technology • Quarter 4, 2020

References 1. Some recent examples of other than (meth)acrylate functional groups used in UV cure can be found in: T. Robert, S. Eschig, T. Biemans, F. Sheifler, “Bio-based polyester itaconates as binder resins for UV-curing offset printing inks,� J. Coat. Technol. Res. 2019, 16, 3, 689-697. G. Peer, A. Eibel, C. Gorsche, Y. Catel, G. Gescheidt, N. Moszner, R. Liska, “Ester- Activated Vinyl Ethers as Chain Transfer Agents in Radical Photopolymerization of Methacrylates,� Macromolecules, 2019, 52, 7, 2691-2700. 2. A. Malofsky, T. Dey, J. Sullivan, Y. Chen, S. Wojciak, B. Malofsky, “Synthesis of Methylene Malonates Substantially free of Impurities,� US 8,609,885, 2013. 3. B. Malofsky, A. Malofsky, M. Ellison, “Ink Coating Formulations and Polymerizable Systems for Producing the Same,� US 9,234,107, 2016; A. Holzer, A. Deshpande, A. Palsule, J. Sullivan, “Process for UV Curing of Methylene Malonates,� WO 2019014528, 2018. 4. A. Palsule, J. Sullivan, K. Vanderpool, A. Holzer, A. Deshpande, J. Klier, “Coatings Containing Polyester Macromers Containing 1,1-Dicarbonyl-Substituted 1-Alkenes,� US 9,567,475, 2017. 5. W. Xi, H. Peng, A. Aguirre-Soto, C. Kloxin, J. Stansbury, C. Bowman, “Spatial and Temporal Control of Thiol-Michael Addition via Photocaged Superbase in Photopatterning and Two-Stage Polymer Networks Formation,� Macromolecules, 2014, 47, 61596165. 6. G. Bachman, H. Tanner, “Preparation of Methylene Dialkyl Malonates,� US 2,212,506, 1939. 7. K. McCurdy, K. Laidler, “Rates of Polymerization of Acrylates and Methacrylates in Emulsion Systems,� Can. J. Chem. 1964, 42, 825-829. 8. M. Guichard, B. McGrail, W. Wolf, J. Klang, “Curable Compositions and Uses Thereof,� WO 2018219729, 2018. 9. A. Bagheri, J. Jin, “Photopolymerization in 3D Printing,� Appl. Polym. Mater. 2019, 1, 593-611.

Acknowledgments We thank our colleagues Mark Holzer, Aniruddha Palsule and Jeff Sullivan, all of Sirrus, Inc., for helpful discussions and our parent company, Nippon Shokubai, for their support. uvebtechnology.com + radtech.org


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TECHNOLOGY SHOWCASE Sun Chemical Offers Sustainable Inks Sun Chemical Corporation, Parsippany, New Jersey, a producer of printing inks and more, has launched new energy-curable inks that meet low-migration standards and are BPA-free. SunCure® Accuflex UV is an energy-curable ink for primary and secondary food packaging that is not manufactured with Bisphenol A (BPA)-based materials and meets low migration specifications. It is compliant with the strictest global standards in the marketplace, meets the latest photoinitiator safe packaging guidelines and provides low odor and very low residual extractables characteristics. Also introduced by Sun Chemical are SunVisto® AquaGreen water-based inks, which have significantly higher levels of biorenewable naturally derived resin content. These carefully formulated inks are not only resistant to abrasion, water and grease – they also offer superior performance and sustainability. For more information, visit www.sunchemical.com. Innovations in Optics Introduces LED Pattern Projector High-Power LED Driver Innovations in Optics, Inc., Woburn, Massachusetts, a provider of high-power LED light sources, has introduced the Pattern Blazer™, a high-power, LED fixed-pattern projector for structured lighting and stereovision in 3D machine vision. Pattern Blazer™ applications include determination of object shape and orientation, contour mapping of parts, surface defect detection, depth measurements, guidelines, edge detection and alignment. The Pattern Blazer projects patterns with an intensity that is at least 5X to 10X greater at the same distance than other “high power” LED pattern projectors for similar pattern size and wavelength. It can be operated in continuous, PWM or pulsed current modes. The company also has introduced the Model 5000H switched-mode LED driver/controller for powering its high-power LED light engines. It also can be used with thirdparty LED illuminators as a constant current, DC to DC driver/ controller. The 5000H LED Driver provides constant current in continuous or pulsed mode for LED arrays connected in parallel, single large-format LED chips and laser diodes with a compliance voltage up to 7.0 VDC. The compact device can be bench-, panel- or DIN rail-mounted. Two options selected at time of order support either common anode or common cathode LED arrays. For more information, visit www.innovationsinoptics.com. Michelman Has Growing Portfolio of BPI-Certified Compostable Coatings Michelman, Cincinnati, Ohio, a developer and manufacturer of environmentally friendly advanced materials for industry – offering solutions for the coatings, printing & packaging and industrial manufacturing markets – has announced the certification of three products. PFAS-free coatings Michem® Coat 2000, Michem® Coat 525 and Hydraban® 8000 have complied with the specifications established by the American Society for 24 | UV+EB Technology • Quarter 4, 2020

Testing and Materials standards ASTM D6400 and D6868 per the terms and conditions of Biodegradable Products Institute’s (BPI) certification program for compostable products. Michem® Coat 2000 and Michem® Coat 525 are functional coatings that provide maximum oil and grease performance in fiber-based food service applications. Hydraban® 8000 is a water-resistant paper coating with excellent gluability and printability used for food packaging. For more information, visit www.Michelman.com. Gigahertz-Optik Offers UV-C Radiometer The X1-1-UV-3727 handheld radiometer, from Germany-based Gigahertz-Optik Inc., a manufacturer of innovative UV-VIS-NIR optical radiation measurement instrumentation, provides a realtime display of irradiance or dose and includes a peakhold function. The device also may be operated via its USB interface with optional S-X1 software. Each meter is supplied with a traceable calibration certificate from the ISO-17025-accredited Gigahertz-Optik optical radiation calibration laboratory. Far-UVC light, for example 222nm produced by Kr-Cl excimer lamps, has been shown to effectively inactivate bacteria but with less photobiological hazard for humans because far-UVC light cannot penetrate human skin or eyes as deeply as longer wavelength UV radiation. The UV-3727 detector provides the uncommon ability to measure 222nm excimer lamps (Kr-Cl) which are becoming more popular in germicidal applications. For more information, visit www.gigahertz-optik.com. Wikoff Formulates 3D Printing Color Dispersions The specialists at ink and coating manufacturer Wikoff Digital, Fort Mill, South Carolina, have formulated a new set of color dispersions for 3D printing resins. As 3D printing moves from a prototyping mechanism to a viable production method, the expectations of the finished products have shifted. During prototyping color didn’t matter, but it is crucial to full-scale production. Printers now can design and create in full color with the help of these Wikoff Digital colorants. Wikoff Digital has developed color dispersions for 3D printing resins used in SLA, DLP and inkjet technologies. These resins are typically formulated and manufactured by the 3D printer manufacturers, each with their own unique characteristics, making stable dispersion formulations critical to success. For more information, call 803.548.2210 or visit www.wikoff.com. OMET Introduces DigiPack OMET Americas Inc., Elk Grove Village, Illinois, a packaging printing machine manufacturer, has introduced DigiPack, a digital finishing solution that meets today’s demands, and future-proofs investments for tomorrow. The DigiPack features a completely modular platform, allowing it to be designed to meet customers’ needs. It is offered in widths of 17", 20", 26" and 33" for finishing uvebtechnology.com + radtech.org


tags and labels all the way up to flexible packaging and shrink sleeves. The DigiPack is designed to precisely re-register digital jobs to maintain excellent quality with minimal waste. Features include multiple flexo stations for coatings, spot colors, white and adhesives; UV, UV LED, water base and solvent base ink systems; embellishments such as cold foil, hot foil and lamination, along with diecutting, rotary screen and gravure. For more information, visit www.ometamericasinc.com. Phoseon Introduces FireJet™ ONE LED-based solutions provider Phoseon Technology, Hillsboro, Oregon, has introduced the smallest, highest-powered member of its air-cooled product line, the FireJet™ ONE. These 20W/ cm2 UV LED curing lamps are designed primarily for the inkjet, flexographic and screen printing markets where high power in a compact form factor is a key requirement. The FireJet ONE lamps, in widths from 75 to 375mm, scale simply by placing units next to one another, daisy-chaining them together. Phoseon’s unique optics ensure consistent uniformity at the substrate surface. The FireJet ONE is a simple-to-integrate self-contained unit. The lamps can be controlled using PLC signals to provide instant on-off, intensity control and other primary functions. For more information, visit www.phoseon.com. DSM Offers New Digital Light Processing Resin Royal DSM, The Netherlands, announced Somos® QuickGen 500, a fast-printing, general purpose engineered resin for digital light processing (DLP) and liquid crystal display (LCD) 3D printing. Somos® QuickGen 500 is the go-to resin for functional and general prototyping needs. The time and cost savings offered by DLP or LCD printing due to its printing speed compared to other technologies, paired with Somos® QuickGen 500’s competitive print speeds and price point, make the material a game changer. Its performance offers those using DLP and LCD printing increased productivity while cutting time and costs. A colorless resin, Somos® QuickGen 500 has a print speed 2x faster than similar materials. Easy to print, the resin prints with accuracy and is ideal for functional and general prototypes, semi-flexible applications, applications with detailed features and – due to its translucency – fluid flow analysis. Somos® QuickGen 500 offers unique flexibility but is stiffer than elastomers, offering both flexibility and spring back. It performs consistently independent of how quickly force or strain are applied. For more information, visit www.dsm.com/additive-manufacturing/.  uvebtechnology.com + radtech.org

TECHNOLOGY

SHARE YOUR KNOWLEDGE WITH OUR READERS UV+EB Technology, the official magazine of RadTech International North America, promotes the use and benefits of ultraviolet and electron beam curing technologies. SUBMIT AN ARTICLE FOR CONSIDERATION

UV+EB Technology features non-commercial content, including technical articles and case studie. All technical content is reviewed by RadTech’s Editorial Board.

For complete editorial guidelines: uvebtechnology.com dianna@petersonpublications.com UV+EB Technology • Quarter 4, 2020 | 25


MARKETS By Dianna Brodine, managing editor, UV+EB Technology

UV Curing in the Medical Market in the Age of COVID-19 U

V disinfection is in the spotlight as the world continues to grapple with effective mitigation of the spread of COVID-19. A search for the word “disinfection” on Amazon brings up several pages of UV light sanitizers, UVC cleaners, UV disinfection boxes and portable UV lamps… Whether these products are effective or are shipped to consumers with adequate health and safety information would be the subject of another article. However, there’s no doubt that disinfection technologies utilizing ultraviolet lamps have been brought to the attention of the general public. UV curing technologies also have seen increased usage since the onset of the pandemic, although without much fanfare. From 3D printing of swabs used for testing to syringes for eventual vaccine use, UV curing plays an important role behind the scenes.

UV+EB Technology spoke with Chris DeMell, global medical market manager for IDS, a division of ITW; Carlos Alvarez, vice president of global sales – curing, and Pamela Lee, sr. product manager, OmniCure, Excelitas Technologies; and Kevin Joesel, director of sales – UV, and Lonnie Murphy, sales manager – North America West, Heraeus Noblelight America, to learn more about the ways UV curing has influenced the medical market. Q: How has the pandemic accelerated medical market growth? “The medical market has seen tremendous growth with the onset of COVID-19, due to the various products that are required to deal with the pandemic, such as testing kits, catheters and drug delivery components,” said DeMell. “And, keep in mind that almost all of the coronavirus-related uses are in addition to the everyday needs that the medical market serves. People still need all the products that they needed before the pandemic. Production has been increased, and the forecast is that this will continue for the next several years.” Increased demand for disposable products that are needed during the pandemic has spurred demand for UV curing equipment as well. “The traditional advantage of UV curing – speed of cure with 100% immediate property development for many formulations – is valued when used in medical applications,” said Joesel. Murphy added, “The adhesives and bonding subsegment has seen an increase as a lot of the test kits for COVID-19 are plastic-to-plastic bonded. In fact, needle bonding, single-use catheters, tube sets – these all can be bonded with UV. And some of the processes used to make masks involve UV curing, too.” page 28  26 | UV+EB Technology • Quarter 4, 2020

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MARKETS  page 26 Alvarez agreed, saying “What we’re seeing is our product being used to build or facilitate the solution for COVID-19 issues. For instance, our spot curing product is being used with catheters, endoscopy products and needle assembly. In all of these cases, a UV adhesive is used.” The medical market demand driven by the pandemic isn’t likely to subside soon, as DeMell added, “The other major piece of the puzzle has to deal with the pending vaccinations that are planned. The syringe market has a large production capacity, however it needed to be enhanced greatly to meet current needs as well as the upcoming surge of demand. Major medical companies have been acquiring additional equipment to expand production and start stocking up. This growth will push the market for at least the next few years.” Q: What medical applications will see higher rates of growth in the next three to five years? “In addition to the products that are being ramped up for the pandemic, the largest areas of growth have focused on pharmarelated drug delivery,” said DeMell. “Ever since the introduction of auto-inject pen technology, such as the Epi-Pen, pharma companies have embraced the use of patient-delivered drug delivery. These can be single use for emergency use, or multi-use devices.” Patient-delivered applications also are a trend seen by Murphy. “Needle bonding has been big for our customers, and there are coatings that go onto the outside of catheters that are a growth area, too. But I also see transdermal patches and hydrogels, which are all UV technologies now, increasing. Alvarez said, “It’s interesting because if I would have taken you back seven years, catheters were fairly simple devices, but today the amount of complexity added to catheters has increased drastically – and that’s as a result of the public’s demand for noninvasive surgery. We continue to see the areas of catheters and endoscopy expand, as well as personalized diagnostic devices.” Joesel added, “These new applications are driven by the formulators, and we’re here to help and support their explorations with as many options as we can.” Q: What about medical marking applications? “UV has been a growing technology within the medical market for curing pad print inks as compared to traditional solvent inks,” said DeMell. “Much of this has to deal with quality, as well as production rates. Solvent inks can require additional cure times, depending on the formulations, and speed is paramount with any automated production systems. UV offers a full cure immediately, which allows for either bulk production without fears of ink transfer, or turnkey solutions that allow for decoration followed by assembly and packaging. Recently, COVID-19 test kits had to be designed, requiring clear markings and indicators that typically are addressed with pad printing.” 28 | UV+EB Technology • Quarter 4, 2020

In addition to the products that are being ramped up for the pandemic, the largest areas of growth have focused on pharma-related drug delivery. Alvarez said, “In the medical industry, traceability, indexing and the ability to track batches and lots are very important.” In highproduction environments, UV curing during the marking process keeps the manufacturing line moving without worries that the inks will smudge as the product moves to fill or assembly. Q: What is the role of UV equipment manufacturers in medical market advances? “The true driver in all of this is the formulator,” said Joesel. “As an equipment supplier of all the different platforms – UVC, broadband emitters, arc lamps, LEDs, infrared – we provide the means. The UV units that used for testing and evaluation in laboratories are the same equipment used on the production line, so it’s directly scalable, which is a very important attribute in the medical industry.” Murphy added, “Because we have so many types of UV photon emitters, we’re involved in the development of equipment that the end users or formulators can use to develop their process. We’re also working with the chemistry suppliers and the raw material suppliers, and we have our own chemists on staff. We put a lot of resources into trying to understand the chemistry, and our strength is in the application centers we have around the world. We’re positioned to support the formulators.” Excelitas also has a materials science lab, which offers validation of the technology with the formulations. Lee added, “In these types of applications, accuracy, repeatability and a high-quality cure are required. Our products have been popular in medical device manufacturing because we have closed-loop feedback capabilities that allow customers to validate the process and ensure standardization.” Alvarez concluded, “As these devices get more complicated, the materials change and the adhesives changes. We’re trying to put the formulation and a UV curing instrument together in a way that solves the customer’s problems. Because we don’t make any of the formulations, we tend to be a little more objective about the solutions.” 

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EVENTS

RadTech Fall Meeting Goes Virtual in 2020 T

he 2020 RadTech Fall Meeting was held online this year, in the format of three Zoom meetings on consecutive Thursdays in the month of November.

to develop new initiatives to document the sustainable benefits of UV/EB and how the curing technology fits in the circular economy. An overview of federal and AQMD regulatory initiatives impacting UV/EB also were reviewed, with a focus on US EPA in terms of trends in new chemical registrations and the outcomes from those efforts. Also discussed was a continuing concern from Europe’s risk assessment committee regarding a study on TMTPA monomer and its classification as a likely human carcinogen Class 2, which has since been rebutted.

On Thursday, November 5, the focus was on the association, with a RadTech Member Update and the kickoff of RadLaunch 2021. President Eileen Weber led the event with a discussion about the impact of COVID-19 on RadTech membership and the UV/ EB industry as a whole. Attendees also received information on upcoming events for RadTech, including tentative plans for a virtual BIG IDEAS! Conference in the Spring of 2021. Managing RadTech International North America hopes to bring the industry Editor Dianna Brodine provided an overview of UV+EB together again face-to-face in 2022. In the meantime, virtual Technology magazine distribution and an update on the current events will keep members and interested industry parties up to status of the editorial board. RadTech’s new Young Professionals date on new developments and advances in UV/EB technologies (YP) committee was introduced (for more information, see page and applications.  7), and the RadLaunch 2021 contest kickoff was announced, with short presentations from several past winners. Winners of the 2021 RadLaunch Significant impacts of coronavirus to your company contest will be announced with an online ceremony in February 2021. On November 12, the focus was on the 3D Printing Committee. The opening presentation was by Tom McKeag from The Berkeley Center for Green Chemistry. His talk described some of the recent work by the UC Berkeley Center for Green Chemistry to address human and environmental health challenges in the field of additive manufacturing, and how integrating hazard assessment of the materials used into the research, design and development process can lead to innovation and value. The committee also reviewed the webinars that have been done recently and discussed potential activities to promote 3D printing and additive manufacturing virtually in 2021, including a potential multiple-speaker event. In addition, the committee reviewed a new publication from NIST, documenting the photopolymer additive manufacturing workshop late last year, and discussed opportunities for future directions for research and development work through a partnership between NIST and RadTech. On November 19, the RadTech Sustainability and Environmental Health and Safety committees teamed up to present the latest RadTech efforts

Distancing employees Restricting visitors to facilities Canceled large group events Implementing daily office cleanings/sanitizations Applied for government assistance program

90.5% 88.3% 81.0% 61.9% 33.3%

RadTech Member Survey October 2020

5

How do you believe UV+EB demand will be impacted in 2021 in the following market segments as a result of COVID-19? 4

3

Weighted Average 2

1

0 Disinfection equipment

Medical devices

Food/consumer goods packaging

Labels

3D printing/additive manufacturing

Plastics

Wood and building products

Electronics

Automotive

Commercial printing

Aerospace

RadTech Member Survey October 2020

30 | UV+EB Technology • Quarter 4, 2020

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CURE MONITORING By Huan Lee and Stephen Pomeroy, Lambient Technologies

Real-Time Monitoring and Degree of Cure of UV-Cured Resin Abstract igh-speed dielectric cure monitoring has the unique ability to measure cure in real time under actual process conditions, which is valuable for studying materials that polymerize in seconds, such as H.B. Fuller U3345,1 the UV-curable adhesive used for this study. Under UV irradiation, U3345 reacts rapidly and exhibits dynamic behavior that would be difficult or impossible to see with other methods. The utility of dielectric cure monitoring allows measurement of the degree of cure and the response of UV-curable resins to irradiance and exposure.

H

Dielectric cure monitoring Dielectric cure monitoring, also known as dielectric analysis (DEA), measures a polymer’s resistivity (ρ) and permittivity (ε’), which are a material’s dielectric properties. Resistivity itself has a frequency independent (ρDC) component due to the flow of mobile ions and a frequency dependent (ρAC) component due to the rotation of stationary dipoles. Although often called DC resistivity, frequency independent resistivity actually extends across a range of frequencies that includes DC (0 Hz). Because a thermoset’s degree of cure affects both mechanical viscosity and frequency independent resistivity, the term ion viscosity was coined to emphasize the relationship between the two. Ion viscosity (IV) is therefore defined as: Equation 1.

IV = ρDC (ohm-cm)

This paper presents and discusses data for log(ion viscosity), which will be called log(IV) for brevity. At constant or near-constant temperature, the change in log(IV) often has a linear or near-linear relationship with the change in degree of cure, as measured by glass transition temperature and other methods.2,3,4 Because ion viscosity correlates with cure state, it is a useful probe of the material state of epoxies, polyurethanes, polystyrenes and especially UV-cured resins. Dielectric sensors Dielectric cure monitors measure the resistance (R) and capacitance (C) of material between a pair of electrodes, which can be modeled as a resistance in parallel with a capacitance. A common configuration is the comb structure or interdigitated electrode, such as the example of Figure 1, the Quarto-Varicon5 dielectric sensor used in this study. This sensor is constructed as a thin polyimide flex circuit with an electrode width and separation of 100 microns. As a rule of thumb, interdigitated electrodes with the same width and separation measure to a depth approximately equal to the electrode width. Consequently, the sensor used in this study makes a very localized measurement only 100 microns into the sample. 32 | UV+EB Technology • Quarter 4, 2020

Figure 1. Dielectric sensor with interdigitated electrodes uvebtechnology.com + radtech.org


measurement of irradiance, so it was estimated from the rising and falling temperature profile during a test. These data were used to model a hypothetical thermal source for each exposure. The temperature of this hypothetical source was assumed to be proportional to actual irradiance at the sample and was used to derive the relative irradiances of Table 1. Without absolute UV power measurements, irradiance during a test was given a relative value from Table 1 to enable comparisons among results.

Figure 2. Test set-up for UV cure

For UV curing, interdigitated sensors may be placed within a sample and away from the surface to avoid any confounding effects from oxygen inhibition, which prevents cure at the interface with the atmosphere. Ultraviolet light source The SunSpot 2 UV/Visible Light Curing System6 was the UV source for this study. The high-power output from its arc lamp is wide-band and intensity at the end of the light guide is typically >18,000 mW/cm2 in UVA (320 to 390 nm), with adjustable settings from I = 0 to I = 10 for intensity ranging from 60% to 100%, respectively, of full power. This UV source uses both a dichroic filter and mirror to greatly reduce IR transmission through the light guide. Absorption of radiation in the remaining visible/UVA/UVB/UVC wavelengths, nevertheless, can produce considerable heating of samples at high irradiances. Procedure U3345 is a UV-curable, modified acrylate adhesive using a phenyl bis(2,4,6-trimethylbenzoyl)-phosphine oxide photoinitiator. After excitation, this photoinitiator undergoes cleavage to produce initiating radicals that drive cure. Since these photoproducts have reduced absorption in the visible/UV spectrum, the photoinitiator becomes bleached, enabling deeper penetration of UV and curing of thicker coatings. The experimental set-up is shown in Figure 2. At the end of the light guide, a collimator concentrated the light and projected it onto a platform for the sample. For each test, U3345 UVcurable adhesive was applied to a new dielectric sensor, resulting in a sample 7 mm x 20 mm in area and approximately 1 mm thick. The sample was placed on the platform at the estimated center of the irradiance profile. A thermocouple beside the sensor enabled temperature measurements during and after exposure. Each test used a standoff of 15 cm, 20 cm, 38 cm or 48 cm between the collimator and platform. UV source intensity was set to I = 0, 5 or 10, corresponding to 60%, 83% or 100% of full intensity, respectively. Lack of a UV meter prevented direct uvebtechnology.com + radtech.org

An LT-631 High-Speed Dielectric Cure Monitor7 measured ion viscosity with an excitation frequency of 100 Hz at a rate of 60 ms/data point. To ensure capture of the entire cure, the UV source was turned on five seconds after the start of data acquisition.

Standoff

UV Source Intensity Setting I = 0 (61%)

I = 5 (83%)

I = 10 (100%)

15 cm

10.9

14.8

17.8

20 cm

9.3

12.7

15.3

38 cm

2.1

2.9

3.4

48 cm

1.0

1.4

1.6

Table 1. Relative irradiance for tested combinations of standoff and intensity

Cure from a single, low-intensity exposure After a single exposure of U3345 to brief, low intensity UV, the ion viscosity and temperature were measured for 60 seconds. Standoff was 48 cm and the UV source intensity setting was I = 0 with an exposure time of one second. From Table 1 the relative irradiance = 1.0. Ion viscosity data from this test, shown in Figure 3, reveals three events: 1. UV cure during exposure. Before irradiation, the U3345 is at 0% degree of cure and the initial log(IV) = 6.9. During the one-second exposure, ion viscosity suddenly increases to log(IV) = 7.0 due to the curing process. Thermocouple temperature increases about 0.5°C due to absorption of light. Measured as the change in ion viscosity, cure is relatively slight, probably due to a time lag in the presence of activated photoinitiators at sensor level as they diffuse from the surface. 2. Dark cure after exposure. The activated photoinitiators continue to diffuse to the sensor and drive cure, indicated by the increase in ion viscosity, for a considerable time after UV exposure ends. As the photoinitiators are consumed, the cure process slows and ion viscosity asymptotically approaches a constant value. Because the sample is approximately 1 mm thick, cure should be both quicker and more complete near the surface, or quicker and more complete with a thinner coating. 3. End of cure. The asymptotic value of log(IV) = 7.8 at the end of cure, which occurs at approximately 60 seconds after exposure. page 34  UV+EB Technology • Quarter 4, 2020 | 33


CURE MONITORING  page 33 Cure from cumulative exposures To investigate the effect of successive exposures, three samples of U3345 at different standoffs were exposed for one second at

a time with UV source intensity = 0 and at one-minute intervals. The samples, which had standoffs of 48 cm, 38 cm and 20 cm, have relative irradiances of 1.0, 2.1 and 9.3, respectively, with each exposure. The results are shown in Figure 4. The plot of Figure 3 actually is the first minute of the data in Figure 4 for a 48 cm standoff. Although the reaction in Figure 3 essentially ends after about 60 seconds, it is clear from Figure 4 that cure is incomplete at this point. Furthermore, the data show that maximum log(IV) after each incremental cure is proportional to the cumulative exposure. In each case, higher ion viscosity also corresponds to higher degree of cure.

Figure 3. Ion viscosity of U3345, single exposure

Figure 4. Ion viscosity of U3345, multiple exposures of one second each

Standoff

Exposure Number

Relative Irradiance at Sensor

Cumulative Relative Exposure

Max Log(IV)

Degree of Cure

Point

48 cm

1

1.0

1.0

7.75

20%

A

48 cm

2

1.0

2.0

9.04

55%

B

48 cm

3

1.0

3.0

10.37

90%

C

38 cm

1

2.1

2.1

9.18

58%

D

38 cm

2

2.1

4.2

10.87

100%

E

38 cm

3

2.1

6.3

10.87

100%

F

20 cm

1

9.3

9.3

10.79

100%

G

20 cm

2

9.3

18.6

10.79

100%

H

20 cm

3

9.3

27.9

10.79

100%

I

Table 2. Standoff distances, relative irradiances and relative exposures

34 | UV+EB Technology • Quarter 4, 2020

The data show that two exposures at relative irradiance = 2.1 are sufficient to reach a plateau of log(IV) ~10.8, while only one exposure at relative irradiance = 9.3 is necessary. Also, once the plateau is reached, additional exposures do not change the ion viscosity level, indicating the U3345 has reached 100% degree of cure. It is important to note that Figure 4 describes the behavior of cure at the bottom of a 1 mm thick sample, with the cure rate there depending on the concentration of photoinitiators as they diffuse from the top. Coatings of different thicknesses would have different profiles of ion viscosity versus exposure and time, which in turn may yield information about diffusion rates. Table 2 lists the relative irradiances and cumulative relative exposures for each test. Max log(IV) is the value at the end of cure following each exposure and is indicated in Figure 4 as well as listed in Table 2. Figure 5 plots maximum log(IV) versus cumulative relative exposure. Uncured resin with 0% degree of cure has a log(IV) = 6.9 and fully cured resin, presumed to be 100% degree of cure, has a log(IV) page 36  uvebtechnology.com + radtech.org


CURE MONITORING  page 34 ~10.8. For many thermosets and polymers, the change in log(IV) is proportional to the change in degree of cure, therefore by interpolation it is possible to correlate cumulative relative exposure with both an ion viscosity and a degree of cure.

Figure 5. Maximum ion viscosity and degree of cure for U3345 vs. cumulative relative exposure

Figure 6. Ion viscosity of U3345, showing cure inhibition

Figure 5 shows log(IV) and degree of cure increase in proportion to the cumulative exposure, until reaching a maximum value that corresponds to complete cure. This result is expected because the total amount of activated photoinitiator is proportional to the total irradiation, and the amount of activated photoinitiator, in turn, determines the extent of polymerization. If absolute irradiance could be measured at the sample, then it would be possible to relate cumulative exposure with the resulting degree of cure. Cure inhibition from long exposures Curing behavior with long exposures may have significantly different dynamics compared to brief exposures. Figure 6 plots ion viscosity for four tests with increasing exposure times. 1) Relative irradiance = 9.3, exposure time = 1 s. Ion viscosity increases normally and monotonically through UV and dark cure to the plateau of log(IV) ~10.8, indicating a typical approach to 100% degree of cure. 2) Relative irradiance = 15.3, exposure time = 5 s. Ion viscosity shows a very slight knee at about 9 s (4 s after start of exposure) then a typical approach to 100% degree of cure.

Figure 7. Determination of cure inhibition time

36 | UV+EB Technology • Quarter 4, 2020

3) and 4) Relative irradiance = 15.3, exposure time = 10 s and 20 s. Ion viscosity shows a pronounced knee at about 9 s (4 s after start of exposure) while temperature continues to increase significantly due to the intense light. Log(IV) page 38  uvebtechnology.com + radtech.org


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CURE MONITORING  page 36 decreases until the end of exposure at 10 s for curve 3, and 20 s for curve 4. Subsequently, dark cure proceeds to the ion viscosity plateau and 100% degree of cure. This “knee” in ion viscosity has been observed in thermally cured resins (thermosets) if cure stops during an increasing temperature ramp.8 Ion viscosity is determined by both degree of cure and temperature, and has two basic behaviors:  At constant temperature, ion viscosity increases as degree of cure increases.  At constant degree of cure, ion viscosity decreases (increases) as temperature increases (decreases). Normally, log(IV) increases as cure advances, and in most cases this response dominates even as temperature increases. However, if cure stops while the temperature continues to increase, then the degree of cure is constant, and ion viscosity decreases, resulting in the “knee.”

Figure 8. Cure inhibition time as a function of relative irradiance

Figure 9. Ion viscosity of U3345, exposure time = 30 s

38 | UV+EB Technology • Quarter 4, 2020

Similarly, for U3345, the knee in log(IV) – slightly visible for curve 2, prominent in curve 3 and even more prominent in curve 4 – indicates polymerization has stopped. In fact, cure has been temporarily inhibited, because ion viscosity increases again after exposure ends and the U3345 undergoes dark cure. Since ion viscosity in Figure 6 reaches the maximum value of ~10.8 (100% degree of cure) for each of the four curves, the U3345 has experienced only a delayed time to end of cure for the 5-, 10- and 20-second exposures. This cure inhibition may be a general phenomenon because it has been observed in all of four UVcured resins examined to date. It is difficult to determine a precise time for the start of cure inhibition, but it can be estimated by the intersection of asymptotes on either side of the knee, as shown in Figure 7. Cure inhibition time is defined as the difference between the start of exposure and the start of cure inhibition. Figure 8 plots the cure inhibition times for several tests across a range of irradiance. The quantity of activated photoinhibitor increases with irradiance, and the trend line of Figure 8 shows increasing irradiation corresponds with shorter inhibition times. This relationship suggests a connection between the level of activated photoinitiator (or, conversely, photoinitiator depletion) and the onset of cure inhibition. Cure inhibition cannot be due to the depletion of activated photoinitiators because dark cure indicates the continued presence of initiating radicals. It is possible cure inhibition results from high exposures that generate too many initiating radicals, which encounter and cancel one another. High exposures also may create excessive amounts of short polymer chains and no long ones. Perhaps bleaching of all photoinitiators eliminates screening of UV radiation from the monomers, causing them to absorb UV photons and become too energetic to bond. Although the cause of cure inhibition is not yet known, further study may yield interesting information about photoinitiator chemistry. Cure degradation from long exposures Long exposures with high irradiances risk over-cure and degradation of a UV-cured adhesive. Figure 9 shows the progression over three tests of increasing irradiance with an exposure time of 30 seconds. 1) Relative irradiance = 2.1, exposure time = 30 s. Normal uvebtechnology.com + radtech.org


cure but total energy is only sufficient to achieve final log(IV) = 10.2 and degree of cure = 85%. 2) Relative irradiance = 2.9, exposure time = 30 s. Normal cure and total energy sufficient to achieve final log(IV) = 10.7 and degree of cure ~100%. 3) Relative irradiance = 3.4, exposure time = 30 s. Cure shows cure inhibition and over-cure from excessive total energy, resulting in reduced final log(IV) = 10.1 and degradation.

Figure 10. UV damage with increasing exposure

Compared to the value at 100% degree of cure, a reduction in final ion viscosity, despite greater irradiance, indicates the presence of damage. Lower ion viscosity is the result of greater conductivity (lower resistivity) due to degradation byproducts and broken bonds. Figure 10 shows four tests with varying irradiances and exposure times. Lack of absolute UV power measurements necessitates use of relative exposure, given by Equation 2, to allow comparison among tests: Equation 2. Relative exposure = Relative irradiance • time (s) Test 1, with a relative exposure = 87, shows normal cure that achieves log(IV) ~10.7 and ~100% degree of cure. Tests 2, 3 and 4 have higher relative exposures but lower final ion viscosities, with log(IV) ~10 – a clear sign of degradation. Additional evidence of degradation are irregular features such as the dip starting at 30 s in Test 2.

Figure 11. Correctly exposed (a), slightly (b) and significantly overexposed (c) samples

Figure 11 shows the effect on UV-cured resin with different degrees of exposure. Extreme deterioration (Figure 11 b and c) is apparent as voids from overheating. More subtle degradation is visible as yellowing or discoloration, which may be faint or subjective. Dielectric measurements, however, can provide a supplemental, objective measure of damage caused by overexposure. Conclusion Real-time dielectric cure monitoring (DEA) of UV-cured resins can complement traditional laboratory tests to relate degree of cure and exposure energy, measure the effect of formulation on cure and identify degradation from overexposure. The ability of dielectric cure monitoring to capture events in real time allows uvebtechnology.com + radtech.org

observation of transient phenomena such as cure inhibition, which appears to be a response of UV-cured resins in general to very long exposures.  Acknowledgements The authors would like to thank Uvitron International for the SunSpot 2 UV Spot System and H.B. Fuller for the UV-curable materials used in this study. In addition, we would like to thank Martin Thompson of Domino Printing for comment and discussion. References Visit uvebtechnology.com for a complete list of references.

UV+EB Technology • Quarter 4, 2020 | 39


APPLICATION

Electron-Beam Induced Grafting Enables Ophthalmic Surgical Products By Liz Stevens, contributing writer, UV+EB Technology

A

ST Products, Inc., Billerica, Massachusetts, produces a range of ophthalmic surgical products. It was selected for a RadTech 2020 Emerging Technology Award for its novel and innovative use of electron beam technology for the surface treatment of a medical device. The surface treatment applies a lubricious hydrophilic layer onto the inner surface of an intraocular lens (IOL) injector used in cataract surgery.

To work in conjunction with the company’s IOL-folding technology, AST Products developed a lubricious and hydrophilic treatment (featuring electron beam technology) to coat the interior of an IOL injector. The treatment eliminates coefficient of friction in wet environments, protecting the delicate intraocular lens and preventing it from adhering to the injector during insertion into the eye.

William Lee, Ph.D., vice president, R&D and Regulatory Affairs at AST Products, shared information with UV+EB Technology about LubriMATRIXTM, the company’s proprietary treatment for IOL injectors.

William Lee explained that the company’s IOL injectors are treated with “a chemical synthesis initiated by electron beam to graft a layer of polymerized hydrophilic and lubricious monomers onto the inner wall of the IOL injectors, especially those areas where the IOL will pass through and enter into the patient’s eye.”

Cataract is a common problem that develops slowly in aging adults, causing a cloudy area in the lens of one’s eye. When the condition affects vision to a serious degree, out-patient surgery is the usual solution, during which the natural lens in a patient’s eye is removed and replaced with an IOL – an artificial lens made of polymeric or silicone materials. To facilitate performing surgery in the least-invasive way, the designers at AST Products created a patent-pending method for folding the artificial lens prior to it being inserted via an IOL injector, allowing the lens to be inserted through the smallest of incisions. Maneuvering a folded lens into the tiny incision in a patient’s eye calls for a delivery device that is ergonomically superior, that works flawlessly every time, and that operates as smoothly as silk. 40 | UV+EB Technology • Quarter 4, 2020

“The area that needs surface modification is actually the lumen of the tip,” said Lee as he also described how IOL folding and injection takes place. The IOL is placed into a cartridge and then into the injector, ready for folding and insertion. “The plunger will push the IOL towards the taper tip end and enter the patient’s eye. Certainly, the smaller the tip end size (and the incision size), the better to avoid sutures and to have a faster recovery from surgery.” “Typically, an IOL has a diameter of 6 mm,” said Lee. “The tip end [of the injector] is 2.2 mm (current typical size), so the trick is how to push the IOL all the way through the tip end, like sucking a Frisbee through a vacuum cleaner hose.” So smaller lens area is better, and friction of any kind must be eliminated, presenting a uvebtechnology.com + radtech.org


two-fold design challenge. “The only way is to fold the IOL like a taco, and then push it. But by doing so, now a high friction is created between the surface of the IOL and where it touches the interior of the tip/cartridge, because both are plastic material.” What to do to mitigate the problem of plastic-on-plastic? “This is where the hydrophilic/lubricious treatment comes in – to act like a banana skin to let the IOL slide all the way through into the patient’s eye.” (So, to get the Frisbee through the vacuum cleaner hose, one folds it like a taco and then uses a banana skin to help it slide through the hose. And, people say UV/EB technology is all scientific and inaccessible!) Along with causing a potential hang-up of the lens within the injector tip, any friction may also scratch the IOL itself. To avoid this, a treatment needs to provide a slippery surface while simultaneously protecting the IOL. The company’s proprietary treatment, created with the aid of electron beam technology, creates a lubricious-hydrophilic brush on the interior of the IOL injector tip, composed of polymerized lubricious monomers and hydrophilic monomers. When Lee and his associates set out to develop this solution, they were in search of a treatment that was economically feasible, that was capable of producing the thinnest of layers (on the submicron order, around several hundreds of nanometer), and that was able to withstand being sterilized via autoclave and other sterilization methods. Lee laid out the hurdles to be overcome in developing the treatment. “One of the biggest challenges was to screen for various formulations that could function with all of the different types of plastics used to make the cartridges for IOL injectors,” he explained. “While all IOL cartridges are mainly made of medicalgrade PP (polypropylene) material, they don’t all behave the same because there are various types of PPs, and the injection molding process also influences the properties of the molded cartridges.” In addition to variability in cartridge material, there are variables in the lens material itself. The lens material may be hydrophilic or hydrophobic, and its stiffness can vary as well. In addition, as a medical device, an IOL injector must clear all biocompatibility and sterilization tests. And it also must have an adequate shelflife. What was needed was a menu of different formulations. With its menu of formulations developed, AST Products chose electron beam-induced grafting to produce the alternating lubricious- and hydrophilic-monomer brush layer in the tip of the injectors. Lee explained that electron beam was chosen for the polymerization process for three reasons: “It can be scaled up easily. It is a relatively clean process. And functionalized products can be sterilized with all sterilization methods.”

currently applied only to ophthalmic medical devices – to branch out in the medical and biochemistry industries. The technology, he said, “can be applied onto interventional medical devices, such as catheters. It can also be used for the biochemical and molecular biological tools industry that needs hydrophilization or other functionalization.”  To watch a two-minute animated video showcasing AST Product’s pioliTM IOL Delivery System, visit https://www.youtube. com/watch?v=e82ePg3LahY. RadTech, the nonprofit for UV+EB, celebrated the 2020 Emerging Technology Award winners at the RadTech 2020 Conference, March 8-11, in Orlando, Florida. RadTech’s Emerging Technology Committee selects award winners among end users of the technology, based on new, promising and/or novel use of UV and/or EB. RadTech has recognized applications ranging from 3D printing/additive manufacturing to floor coatings to novel electronics to unique uses for automotive and aerospace. Nominations now are open for the 2021 Emerging Technology Awards. Find more information at www.radtech.org.

AST Products now uses its solution on a variety of IOL injector product types, including those that use the company’s pioli, bioli and lioli delivery systems. Lee sees avenues for the technology – uvebtechnology.com + radtech.org

UV+EB Technology • Quarter 4, 2020 | 41


3D PRINTING By Forough Zareanshahraki, Coatings Research Institute, Eastern Michigan University; Amelia Davenport, Colorado Photopolymer Solutions; and Neil Cramer, Christopher Seubert, Ellen Lee and Matthew Cassoli, Research and Innovation Center, Ford Motor Company

Effect of post-curing process on the performance of automotive 3D-printed specimens Abstract he final material properties of 3D-printed parts that utilize UV-curable resins are highly dependent on any post-cure processing used after printing. This post-cure step is needed to crosslink unreacted double bonds remaining after the print process is complete. However, differences in part geometry, pigmentation, stabilization and resin formulation can make it difficult to employ a generic, one-size-fits-all post-cure process.

T

In this study, the effect of the post-curing process on the mechanical properties of three different 3D-printable, non-stabilized UV-curable resin systems was studied. Two of the systems (A and B) used thiol-ene-based chemistries, while the third one (C) used acrylate-based chemistry. To this end, ASTM D638 type IV tensile bars were printed using a DLP printer and post-cured using one of five different processes: no post-cure, UV only, heat only, UV+ heat and electron beam (EB) curing. Bulk tensile properties and nano-hardness values were measured for each of the systems and post-cure conditions. Results indicated that post-cure process had a significant effect on the final performance of the resins and was dependent on the chemistry. Thermal curing was not as effective as UV for System C compared to the two other systems, which could undergo thermal polymerization as well. System B, however, showed the smallest change in mechanical properties before and after post-curing, regardless of the type of post-curing. EB postcuring, even at very low dosages, i.e. from 0.05 Mrad to 1 Mrad, resulted in considerable cross-linking, to the point of embrittlement and a significant drop in percent elongation at break (%E) above 0.5 Mrad of dosage. Overall, provided a suitable post-curing process was employed, all the systems demonstrated promising potential for automotive applications. 1. Introduction 3D printing is an additive manufacturing (AM) process in which layers of material are successively deposited on top of each other to form a 3D object. Advances in 3D printing have opened new horizons to more robust designs with lower costs and reduced lead times in various fields, including the automotive industry1,2. Technological advancements in AM have enabled the fabrication of 3D objects from a wide range of raw materials including metals, ceramics, fibers, as well as polymers, which are the focus of this study3. Thermoplastic polymers are usually processed by melt-type 3D printing methods, such as fused filament fabrication (FFF) and selective laser sintering (SLS). However, these techniques usually result in relatively low resolution, and in the case of FFF, slow processing and weak interlayer adhesion. To address these problems, new 3D printing technologies, which use thermoset resins, have emerged. Vat photopolymerization, one of these techniques, is based on selective photopolymerization of a light-reactive liquid resin in a reservoir.4 Photopolymerization is a widely used polymerization mechanism in many engineering applications such as coatings5â&#x20AC;&#x201C;8 and dental restoration9, thanks to advantages such as rapid curing, low to zero VOC formulations and low capital investment10. Due to chemistry-related innovations, photopolymerization-based 3D printing 42 | UV+EB Technology â&#x20AC;˘ Quarter 4, 2020

uvebtechnology.com + radtech.org


techniques have attracted special attention in the past decades4. In addition to the aforementioned advantages, photopolymerization offers other attractive benefits in 3D printing. Versatility and high spatial/temporal control over photopolymerization reactions can significantly Figure 1. (a) Step-growth mechanism of thiol-ene photopolymerization; (b) chain growth mechanism of enhance the printing acrylates photopolymerization resolution and speed in such technologies. Moreover, higher interactions between the layers lead to improved A post-curing step often is employed after printing to cross-link mechanical properties. Stereolithography (SLA), digital light some of the unreacted species before the parts are put into service. processing (DLP) and continuous liquid interface production However, differences in part geometry, pigmentation, stabilization (CLIP) are examples of photopolymerization-based 3D printing and resin formulation can make it difficult to employ a universal, techniques. The main differences among these techniques are one-size-fits-all post-cure process. For instance, Zguris’ studies the source and pattern of radiation as well as the mechanism of clearly demonstrated that different 3D photopolymerizable separation of the printed layer from the vat. resins require different time and temperature conditions to reach full cure and show good chemical performance14. On the other Materials used in 3D photopolymerization printing are hand, most of the former literature on mechanical properties photosensitive liquid oligomers and monomers that can of 3D-printed parts is concentrated on the effect of various rapidly convert to a solid polymeric network upon exposure to processing parameters15–19, and to the best of our knowledge, radiation. In the most common free-radical photopolymerization a detailed study of the effect of the post-curing process on the process, under irradiation, the photoinitiator decomposes performance of 3D-printed automotive parts is lacking. There is a into active radicals, that attach to monomers to initiate the need to delve deeper into this subject. photopolymerization reaction. The activated monomers then react with carbon double bonds of unsaturated monomers, increasing The purpose of this study was to investigate the effect of the the polymer chain lengths. The propagated polymer chains then post-cure process on the performance of 3D-printed materials start to connect to form a network structure, solidifying the liquid based on acrylate and thiol-ene chemistries. The effect of the polymer. During this process, the material properties of the post-curing process on the mechanical properties of three different cured material change dramatically. Examples of photosensitive 3D-printable, UV-curable resin formulations (Systems A and B chemistries include acrylates and thiol-enes. The latter proceeds with thiol-ene chemistry, and System C with acrylate chemistry) via a step-growth polymerization (Figure 1a) and is reported was studied. ASTM D638 Type IV tensile bars were printed using to offer no inhibition to oxygen, delayed gel times, more a digital light processing (DLP) printer and post-cured using one homogenous networks and lower shrinkage stress compared to the of five different processes: no post-cure, UV-only, heat-only, UV conventional acrylate systems that polymerize through a chainplus heat and electron beam (EB) curing. Bulk tensile properties growth mechanism11 (Figure 1b). These unique features make and nano-hardness values were measured for each of the systems thiol-ene an ideal chemistry for DLP printing 4,12. and post-cure conditions. To ensure an acceptable z-direction resolution during printing, the penetration depth of UV into the resin solution is typically limited by using various UV absorbers, such as pigments or dyes. As a result, complete conversion of the carbon double bonds usually does not occur during the printing process. This postprint conversion state is referred to as the “green state.” In their green state, the printed parts typically contain unreacted species that can undergo additional cross-linking when exposed to UV. If this UV exposure occurs during service, it can change the part’s mechanical properties over time, which is not desirable in the automotive industry13. uvebtechnology.com + radtech.org

2. Experimental 2.1. Materials The three UV-curable resin formulations used in this study were provided by Colorado Photopolymer Solutions (CPS, Boulder, Colorado). As previously mentioned, Systems A and B were based on thiol-ene chemistry, while System C was formulated from conventional acrylates. The alkene source in System B contains a low molecular weight aromatic heterocycle structure, while System A contains high molecular weight aliphatic urethane acrylates. Therefore, System B comprises more functional groups, which makes it more reactive than System A in nature. It should page 44  UV+EB Technology • Quarter 4, 2020 | 43


3D PRINTING ď ´ page 43

Figure 2. Schematic set-up of a DLP 3D printer

H=



(1)



Epox

CPS system

depth

(a)

(b)

Figure 3. Typical shape (a) of indentation by Berkovich tip and (b) microscopic image of indents in this study

be mentioned that these systems did not include any hindered amine light stabilizers (HALS) in their formulations for light stabilization. However, the formulation did contain carbon black as a strong UV-absorber to ensure a good z-resolution. 2.2. Methods 2.2.1. Printing method A series of type IV dumbbell-shape tensile bars, with dimensions as described in ASTM D638, were printed with an Origin One DLP printer, using the printing parameters as described in the CPS technical datasheets, and a 75Îźm layer thickness. The bottom surface of the resin vat in this printer is composed of a transparent polytetrafluoroethylene (PTFE) sheet to facilitate detachment of the printed layer from the vat. The UV source in the printer emits light at a wavelength of 385 nm with an intensity of 5 mW/m2. The area of UV illumination is 144 mm Ă&#x2014; 81 mm. 44 | UV+EB Technology â&#x20AC;˘ Quarter 4, 2020

The 3D-printing process occurred as follows: First, the geometry of the sample was modeled using a computer aided design (CAD) program. Next, this model was converted to an image of slices, i.e., a series of thin layers that together form the whole sample. Afterward, the motor-powered build platform was moved down until the gap between the PTFE sheet and the platform was equal to the intended layer thickness (75Οm in this study). The image of the layer then was projected through the vat bottom onto the build platform, using UV for a specific time period (25 s exposure for the 1st layer, 10 s exposure for layers 2 through 6, and 3 s exposure for all the next layers). Finally, the UV light was turned off, and the platform moved up so that the photopolymer resin could flow back to the projected area. The former steps were repeated until the sample was completely printed20,21. After being printed, the samples were placed in an ultrasonicated IPA bath for 3 minutes to clean off any uncured resin, followed by drying in an oven at 25°C (Figure 2). All the samples were then wrapped in aluminum foil and kept in a dark place to prevent any additional light-induced polymerization before testing. 2.2.2. Post-curing process The printed samples were post-cured using one of the following processes: no post-cure, UV only, heat only or UV plus heat. As a complementary study, the effect of EB curing also was studied for System B only, which demonstrated the most desirable mechanical properties among all the systems. Thermal post-curing was conducted by placing the samples in an oven for 1h at 150°C. An ELC-4001 UV Flood system with a broad-spectrum lamp was used for UV post-curing. UV curing was performed for four minutes and thirty seconds on each side of the samples, i.e., a total curing time of nine minutes. The UV plus heat uses the previously described procedures consecutively using the UV procedure first, then the heat procedure. EB-cured samples were post-cured by EB irradiation film using an EB accelerator equipped with a variable speed fiberglass carrier web (Broad Beam EP Series, PCT Ebeam and Integration, LLC, Davenport, Iowa). 2.2.3. Tensile properties The tensile properties of the specimens were measured by an Instron 3366 tensile machine, using a 30-kN load cell, 65 mm initial distance between the grips and a 25 mm extensometer according to ASTM D638. Five test specimens were tested and averaged for each post-cure condition. The testing was carried out at a constant displacement rate of 5 mm/min in ambient conditions. 2.2.4. Nano-hardness To study the nano-harness profile in various depths, a strip of each uvebtechnology.com + radtech.org


Tensile strength

Young's Modulus (MPa)

sample was cut using a manual cutter, cold-mounted in epoxy the tensile strength, Young’s modulus and percent elongation at resin and polished. Polishing was conducted in an order of 600, break (%E) were studied for Systems A, B and C. 1200 and 2400 grit #, followed by fine polishing using abrasive slurries, in an order of 5 μm, 3 μm, 1 μm and 0.3 μm. An Anton For System A, regardless of the post-curing method, tensile Paar (Graz, Austria) nano-indentation Tester (NHT³) was used to strength and Young’s modulus both improved during post-cure, as measure the nano-hardness of the samples. The major components page 46  of this instrument include a mobile indenter 120 3500 head, an optical microscope attached 3000 100 to a video camera and a sample holder 2500 80 rigidly fixed to an x–y–z motorized table. 2000 60 The Berkovich indenter, mounted on the 1500 indenter head, is a three-sided triangular40 1000 based pyramidal diamond with a well20 500 defined geometry, capable of making well0 0 defined indentation impressions, as shown no post Heat only UV only UV + Heat no post Heat only UV only UV + Heat cure cure in Figure 3a. Post cure method (a) (b) Post cure method

3. 3.1.

Results and Discussion Effect of post-curing process on the tensile properties The effects of the post-curing method on uvebtechnology.com + radtech.org

4

27.3 ±

%

3 2 1 0

no post cure Heat only UV only UV + Heat Post cure method

(c)

Figure 4. Effect of post-curing process on tensile properties of System A: (a) tensile strength, (b) Young’s modulus and (c) %E

120 Young's Modulus (MPa)

6000

100 80 60 40 20 0

(a)

no post cure

5000 4000 3000 2000 1000 0

UV only Heat only UV + Heat (b)

Post Cure Method

no post cure

UV only Heat only UV + Heat Post Cure Method

5

3 2

7.95 ± 1.65

4

%

2.2.5. Fourier-transform infrared (FTIR) spectroscopy Fourier-transform infrared (FTIR) spectra were collected to study the nature of reactions induced by heat and EB curing in the thiol-ene systems. Spectra were measured using KBr standard disks on Bruker Tensor 27 FTIR analyzer at 64 scans and 2 cm−1 of resolution in the frequency range of 400 to 4000 cm−1.

5

Tensile Strength (MPa)

During the nano-indentation process, the Berkovich tip approaches the surface of the sample. The force-displacement data is used to determine the point of contact. After the sample is contacted, the force is linearly increased, and the tip indents into the surface of the sample. A short dwell time occurs at the maximum load, 50 mN in this case, and then the sample is unloaded. At the initial point of unloading, the hardness (H) is measured. In this study, Oliver and Phaar’s method22 was used to calculate the hardness by dividing the maximum load, Pmax, by the contact area of indent (A), as described in Equation 1. The indents were made along a path of 50 μm in the x-direction and 50 μm in the y-direction, to a total length of approximately 350 μm (Figure 3b). Eight different indentations were used to calculate the average hardness as a function of depth.

1 0

(c)

no post cure

UV only Heat only UV + Heat Post Cure Method

Figure 5. Effect of post-curing process on tensile properties of System C: tensile strength, (b) Young’s modulus and (c) %E

UV+EB Technology • Quarter 4, 2020 | 45


3D PRINTING  page 45 demonstrated in Figure 4. Tensile strength increased by ⁓200%, from 11.2 MPa to 33.7 MPa, and Young’s modulus increased by 111%, from 758 MPa to ⁓1600 MPa. However, %E reduced by more than 85%, from 27.3 to ⁓3.5. Both the UV and thermal postcure steps produced similar tensile properties because thiol-ene systems can undergo polymerization via radiation11 or heating23

(a)

3500 Young's Modulus (MPa)

Tensile Strength (MPa)

120

processes. The significant reduction in %E after post-curing might not be ideal in automotive parts that require a high amount of %E retention during their service life. System A might be a good option for parts that need high flexibility, such as decorative parts or badges, but are not exposed to mechanical forces that can induce dimensional changes.

100 80 60 40 20 0 no post cure

3000 2500 2000 1500 1000 0

UV only Heat only UV + Heat

(b)

Post Cure Method

500 no post UV only Heat only UV + Heat cure Post Cure Method

5 4 %

3 2 1 0

(c)

no post cure

UV only

Heat only UV + Heat

Post Cure Method

Figure 6. Effect of post-curing process on tensile properties of System B: (a) tensile strength, (b) Young’s modulus and (c) %E

(b)

(a)

(c)

Figure 7. Effect of one-step versus step-by-step EB post-curing on tensile properties of System B: tensile strength, (b) Young’s modulus and (c) %E

46 | UV+EB Technology • Quarter 4, 2020

For System C, an acrylate-based system, thermal post-curing was not as effective as UV post-curing (Figure 5). According to the results, UV-curing resulted in ~285% increase in tensile strength, from 21 MPa to 104 MPa, and 274% increase in Young’s modulus, from 1174 MPa to 4390 MPa. These values were about 45% (from 27.1 MPa to 39.5 MPa) and 109.6% (from 1174 MPa to 2461 MPa) for heat post-curing, respectively. While it is known that acrylate groups can undergo thermal polymerization24, this system did not contain any thermal initiators, so it is unlikely any significant cross-linking occurred as a result of the 150oC/ 1 hour “heat only” post-cure step. As a result, UV post-curing seems to provide the best tensile properties among all post-curing processes for System C. However, System C exhibited a similar post-cure reduction in %E to that of System A, e.g., UV post-curing decreased %E by 58%, from 7.9 to 3.3. Again, this means System C should not be used in applications that may significantly stress or load the part. Utilization of both UV and thermal postcuring together had a negative effect on mechanical properties of this system for unknown reasons. Some possible reasons could be rapid degradation of the UV-cured sample after being heated at 150°C for one hour. Finally, for System B, post-curing did not have a considerable effect on the tensile properties, as depicted in Figure 6. Postcuring processes improved the tensile strength and Young’s modulus slightly but did not result in significant reduction of %E, as was the case with the two other systems. While systems A and B are both thiol-ene systems, System B includes a heterocyclic core structure with lower molecular weight and, in turn, higher functionalities than System A. These systems show a different behavior upon post-curing. The UV radiation during uvebtechnology.com + radtech.org


the printing process likely resulted in a vitrified network with limited segmental mobility that hindered further conversion of unreacted groups. This vitrification effect was slightly mitigated by heat treatment in case of UV plus heat post-curing. Moreover, higher functionalities can mitigate the oxygen inhibition effect more effectively, which, in turn, can result in higher conversions. According to the results, it seems that ample cross-linking of the free radicals occurs during the printing process. Therefore, postcuring does not seem to be necessary for System B, which could be beneficial in high-volume manufacturing environments. Considering the aforementioned points, System B could be a promising option for the automotive parts that require good retention of tensile properties, including %E. To assess the effectiveness of an electron beam (EB) post-cure process, System B samples were exposed to varying levels of EB radiation. EB curing through free radical polymerization differs from UV curing mainly in the initiation process. No photoinitiator is needed in the EB process because the electron beam energy is high enough to form the initiative species by cleavage of a bond located on the monomer25. Since the initiating radical is formed from the resin itself, rather than from an added initiator, EB curing allows for a small amount of additional cross-linking compared to UV curing26. EB cure systems are known to have the drawback of being inhibited by oxygen, and therefore are usually conducted in an inert atmosphere, like nitrogen.

excess of EB dosage or if the samples were heated during the EB post-curing process. Therefore, two changes were made to the EB post-curing process. First, EB curing was conducted in successive 2.5 Mrad steps for dosages greater than 2.5 Mrad, with a pause between successive exposures to cool the samples in ambient conditions to eliminate the effect of heat-curing as much as possible (Figure 7). Although page 48 

(a)

(b)

(c)

Figure 8. Effect of EB post-curing with low dosages on tensile properties of System B: tensile strength, (b) Young’s modulus and (c) %E

However, this drawback could be overcome by the utilization of thiol-ene chemistry. All these advantages make the EB-curable thiol-ene resin systems an interesting option for DLP 3D printing. As shown in Figure 7, higher dosages of EB post-cure (i.e., one-step 5, 10 and 20 Mrad) resulted in significant embrittlement of samples of System B compared to standard UV post-curing. The %E values were reduced by ⁓ 50%, regardless of the dosage. Moreover, increasing the EB dosage from 5 to 20 Mrad decreased the tensile strength by ⁓38%, from 50.6 to 31.2 MPa, while the Young’s modulus increased by ⁓ 27%, from 2732 to 3480. It was unknown if this was simply due to an uvebtechnology.com + radtech.org

Figure 9. Effect of post-curing process on nano-hardness of System C

UV+EB Technology • Quarter 4, 2020 | 47


3D PRINTING  page 47 step-by-step curing in higher dosages improved tensile strength and Young’s modulus to some extent, %E was still far from the values achieved using the standard UV post-cure method. Second, EB postcuring dosages were reduced to 0.05, 0.1, 0.5, 1 and 2.5 Mrad (Figure 8). Reducing EB dosages resulted in higher %E values. Those less than 2.5 Mrad resulted in Young’s modulus values close to that of standard UV post-cure and tensile strengths more than that of UV post-cure. These results indicate that higher dosages of EB likely induce excessive cross-linking of the system, which will be investigated in our future studies using Raman spectroscopy. 3.2.

Effect of post-curing process on nano-hardness To study the nano-hardness profile, as an approximation of the cure state at various depths, a strip of each sample was coldmounted in epoxy resin to be polished. Depth profiling was conducted to assess whether any possible gradient in cure state exists for different post-curing methods. Figure 9 shows that the surface nanohardness of System C increased by more than 200% after post-curing (from ~50 to >150 MPa) regardless of the process used. Moreover, no gradient in hardness as a function of depth was observed, which is particularly interesting in the case of UV curing. Heat curing showed a similar trend. For System B, nano-hardness results were in good agreement with the tensile properties, i.e., the nano-hardness was slightly improved, regardless of the postcuring process (Figure 10). Similarly, nano-hardness was observed to be independent of depth, showing a uniform conversion as a function of depth.

Figure 10. Effect of post-curing process on nano-hardness of System B

Figure 11. FTIR spectra of (a) System B before and after heat, UV and EB post-curing processes; and (b) System C before and after heat and UV post-curing processes

When cured by UV only, System A showed a gradient in hardness as a function of depth, i.e., the hardness decreased as the depth increased. This might be due to the higher UV absorption of this system, which limits the depth of cure. However, further research, e.g. Raman microscopy and UV-Vis spectroscopy studies, are needed to effectively investigate the possible reasons. 3.3. FTIR studies FTIR spectroscopy was used to track the effect of the post-curing process on the condensation thiol-ene reaction in System B and free radical polymerization of acrylate double bonds in System 48 | UV+EB Technology • Quarter 4, 2020

C. As displayed in Figure 11a, in System B, the absorption peak at 2620 cm−1, which is attributed to S-H stretch, was completely diminished after post-curing, regardless of the post-curing type. Similarly, the absorptions of C=C stretch at 1637 cm−1 and C=C bending at 810 cm−1 were also significantly reduced by postcuring. This shows that polymerization of thiol-ene systems could occur via heating, UV curing, and EB curing. For System C (Figure 11b), UV curing resulted in a significant reduction in absorption of C=C stretch at 1637 cm−1 and C=C bending at 810 cm−1, while heat curing resulted in no such uvebtechnology.com + radtech.org


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significant reduction in absorption of those peaks. Thus, FTIR results are in good alignment with the mechanical property measurements, showing that heat only was not an effective postcure process for cross-linking. 4. Conclusion The goal of this study was to investigate the effects of various post-curing processes on the mechanical performance of DLP 3D-printed parts for automotive applications to provide insight into selecting the proper post-curing method per formulation/ application. Three resin systems with two different chemistries were used to print the bars used for Instron testing. The bars were then post-cured using the five following methods: no postcure, UV only, heat only, UV plus heat and EB curing. Tensile properties, nano-hardness and FTIR results demonstrated that thermal curing was not as effective as UV for acrylate-based resins, such as System C, compared to the two other systems, which could undergo thermal polymerization as well. On the other hand, EB curing, even at very low dosages, was very effective for cross-linking of one of the thiol-ene-based resins, to the point of embrittlement for EB dosages above 0.5 Mrad. Regardless of the type of post-curing, the thiol-ene-based resin of System B showed the smallest change in mechanical properties as a result of post-curing. Therefore, post-curing does not seem to be necessary for System B, which could be a benefit in certain applications. Also, System B could be a promising option for automotive parts that require good retention of tensile properties including %E. Systems A and C did not show a very high %E retention. However, considering their other properties, and provided a suitable post-curing process, they might be suitable options for automotive parts that are not exposed to mechanical forces that could induce dimensional changes. The current studies indicate that the performance of 3D printed parts can be tailored by a combination of resin chemistry and formulation, print process and post-cure process. Continued investigation is needed to extend the performance to meet stringent automotive requirements. ď ľ Acknowledgement The authors would like to thank Sage Schissel, from PCT Ebeam and Integration for conducting the EB curing experiments. References Visit uvebtechnology.com for a complete list of references.

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UV+EB Technology â&#x20AC;˘ Quarter 4, 2020 | 49


INDUSTRY GEW Rolls Out New Website GEW (EC) Limited, Crawley, West Sussex, UK, a manufacturer of Arc and UV LED curing systems for printing, coating and converting applications, has announced the rollout of a new website, with the English language version being the first building block. The company will roll out other language versions, with an aim to offer a better user experience for all customers, whatever their primary language. The new site features a clearer structure to product pages, separating them by curing method; an outline of the key application categories, with each main application category having further sub-applications, which then link to the most suitable product for that sub-application; and much more. For more information, visit www.gewuv.com. LogoJET Opens Office in Minneapolis LogoJET, Lafayette, Louisiana, a supplier of light industrial inkjet printing equipment with printing solutions and accessory configurations that use specialty inks such as UV curable, eco solvent and edible ink, has announced the opening of its newest office in Minneapolis as a regional sales and support office. The office will be the hub for LogoJET sales and service throughout the Midwest and is equipped with printers to demonstrate UV printing. Daniel Shamp will manage the Minneapolis office. For more information, visit www.logojet.com. Wikoff Color Rebrands Technical Service Arm to Wikoff Technical Solutions Fort Mill, South Carolina, ink company Wikoff Color has introduced Wikoff Technical Solutions, formerly known as the Technical Service Group. The name change follows an expansion of services and support offered. The Wikoff Technical Solutions team is built on three key pillars: print/press/ink optimization (PPI), color confidence and value-added pressroom supplies. For print/press/ink optimization, The Wikoff Technical Solutions team offers troubleshooting, best practices, consulting, training, analytical services and inkjet services. For color confidence, the team provides G7® calibration, SGS/GMI fingerprinting, X-Rite equipment and software, Techkon, pressSIGN, ink dispensing units and customer training. Value-added pressroom supplies include Wikoff Graphics photopolymer plates, ESKO pre-press products, lithographic blankets, pressroom chemicals, press supplies and lithographic rollers. For more information, visit www.wikoff.com. Michelman Increases Focus on Growth Markets with Updated Website Michelman, Cincinnati, Ohio, a developer and manufacturer of materials for industry, invites visitors to explore its updated website, highlighting the company’s portfolio of sustainable solutions, strong community involvement and legacy of collaborative innovation. Customers can locate solutions, including Michelman’s portfolio of BPI-certified compostable 50 | UV+EB Technology • Quarter 4, 2020

coatings, water-based primers and overprint coatings, fiber sizings, advanced seed treatments, and performance additives. They also can access technical data, find a distributor and connect with Michelman experts. Industry partners and suppliers will find a dedicated space to learn about Michelman’s approach to its business relationships through its six core values. For more information, visit www.michelman.com. Gigahertz-Optik Updates Instrument Page to Add UV-C Radiometer Selector Guide Germany-based Gigahertz-Optik, a manufacturer of metrological solutions for optical radiation, has updated its UV-C instrument page to include a handy UV-C radiometer selector guide in the form of a flow diagram to assist in choosing the right instrumentation for the job. In response to questions regarding issues such as spectral data requirements, low pressure Hg lamp requirements and spectral irradiance needs, the flow chart leads to one of seven germicidal UV meters offered by the company. For more information, visit www.gigahertz-optik.de/en-us. SPE Announces ANTEC® 2021 Call for Technical Papers SPE, Danbury, Connecticut, has announced its Call for Technical Papers for ANTEC® 2021. ANTEC® attracts over 3,000 plastics professionals from around the world with job functions encompassing managers, engineers, research and development, academia, operations and consulting. Technical papers submitted for consideration for presentation at ANTEC® 2021 will focus on the latest in industrial, national laboratory and academic work. Papers will share findings in polymer research or new and improved products and technologies. The technical paper submission deadline is November 15, 2020. For information about submitting a technical paper to ANTEC® 2021, as well as a full range of paper submission topics, visit www.4spe.org/anteccfp. Phoseon Named Finalist at Label Industry Global Awards Phoseon Technology, Hillsboro, Oregon, a provider of LEDbased solutions, was named a finalist for Environmental and Sustainability at the Label Industry Global Awards for its UV LED curing technology. This award is for a specific sustainable product or process introduced by a converter or supplier company in the label industry. To choose a winner, judges will be looking for a company that has introduced a specific product or process, has maintained the most sustainable and environmentally acceptable working practices in its purchasing and manufacturing operations, and can demonstrate key materials, production and performance or consumer benefits. The Label Industry Global Awards are the label and package printing industry’s highest accolades. For more information, visit www.phoseon.com. Sun Chemical Organizes Committee to Drive Sustainability in Packaging Sun Chemical, Parsippany, New Jersey, a producer of printing inks, coatings and supplies, pigments, polymers, liquid compounds, solid compounds and application materials, has uvebtechnology.com + radtech.org


organized a Corporate Sustainability Committee to further strengthen its approach to addressing the sustainability needs of the packaging industry. Composed of eight executive leaders – Myron Petruch, Carlo Musso, Chris Parrilli, Fernando Tavara, Robert Fitzka, Greg Hayes, Russell Schwartz and Jim Van Horn – the Corporate Sustainability Committee will work to guarantee company-wide engagement in sustainability initiatives and will build and oversee the company’s sustainability strategy, ensuring that proper resources are assigned for timely and effective implementation. Nicolas Bétin will assume the role of sustainability business leader for all of Sun Chemical and Dr. Nikola Juhasz will become the technical director of sustainability. For more information, visit www.sunchemical.com. BASF to Open Distribution Center to Support Colors & Effects® Chemical manufacturer BASF, Ludwigshafen, Germany, has announced that pigment customers worldwide will benefit from an even more flexible warehousing and delivery service from spring 2021 onward. Colors & Effects®, BASF’s brand focused on the global pigment business, will use a new finished goods warehouse and distribution center located in the industrial area in Ladenburg, Baden-Württemberg, Germany. Customers can expect even greater adherence to delivery dates in the future, even with short lead times. The future warehouse will offer sufficient space to cover the expected volume of growth in the coming years, especially for high-performance color and effect pigments. Construction of the new 20,000 square meter building has just

begun. Inauguration is scheduled for the first half of 2021. For more information, visit www.colors-effects.eu and www.basf.com. Arkema Strengthens Partnership with Continuous Composites Arkema, Colombes Cedex – France, a leader in high-performance materials for composites and photocurable liquid resins for additive manufacturing, is strengthening its partnership with Continuous Composites, Coeur d’Alene, Idaho, creator of Continuous Fiber 3D Printing technology (CF3D®). Arkema has invested in the American start-up to rapidly advance the development of 3D composite manufacturing, an innovation for strong, lightweight structures. Continuous Composites has reinvented composite manufacturing techniques using the company’s extensively patented CF3D® technology with a complete solution including software, hardware, materials and motion platforms. The company’s core technology is driving a fundamental shift in composites design and manufacturing capabilities utilizing highperformance thermosets resins. For more information, visit www. arkema.com and www.continuouscomposites.com.

NEW FACES Lloyd Lirio has joined Hampford Research, Inc., Stratford, Connecticut, as director of operations. In this role, Lirio will be responsible for overseeing all aspects of manufacturing, engineering services and maintenance at the 35-year-old specialty chemical manufacturing company. Lirio brings 15 years of experience in the manufacturing industry, working in both laboratory and operations settings. He was most recently plant manager at Laticrete International in Bethany, Connecticut. IGM Resins, Waalwijk, The Netherlands, a supplier of products to the energy curing coatings and inks market, has appointed Andre Berry as vice president, North America. Berry is part of IGM Resins’ Global Executive Leadership team and will report to Edward Frindt, IGM Berry Resins’ CEO. Berry joins IGM from the Bostik division of Arkema. He has held positions of increasing strategic leadership in Arkema, with his most recent position as Asia regional business director, Industrial Adhesives Global Business Unit for Bostik Asia, where Berry was based in Shanghai since 2016. Penn Color, Doylestown, Pennsylvania, a provider of color and additive concentrates, masterbatches, pigment dispersions uvebtechnology.com + radtech.org

and engineered coatings, has announced the appointment of Vicki Irons to the position of key account manager and Simon Clarke to the position of European industry manager, Irons Clarke packaging. Irons has more than 30 years of sales and business experience with global companies, most recently as a key account manager with Clariant’s Masterbatch Division. Clarke has more than 30 years of technical, commercial, marketing and business development experience with global and local brand owners. InkJet, Inc., Willis, Texas, a supplier of industrial fluids and printers, has promoted its director of operations and development, Jeane Schalm, to chief executive officer. For the past five years, Schalm has served as the vice president of operations and development for InkJet, leading Schalm the growth of the company in all aspects of operations including the laboratory, production, logistics, supply, materials management, plant maintenance, environmental health and safety, technical service, new product development and IT.  UV+EB Technology • Quarter 4, 2020 | 51


ECONOMIC OUTLOOK By Chris Kuehl, managing director, Armada Corporate Intelligence

2020 and 2021: No End to Chaos in Sight Editor’s Note: Due to magazine press deadlines, Chris Kuehl submitted this article on the morning after the election. Several states had not yet been called for either President Trump or former Vice President Biden. Opinions expressed by the author do not necessarily reflect those of the association or the publisher.

I

t has been pointed out for years that business hates uncertainty more than anything – even certainty over bad news and crisis is preferable to not knowing what is happening. Planning is the essence of business – setting strategies that can be executed and evaluated in terms of whether they are reaching set goals. How does one set strategy in these times? Not only is there a global pandemic that worsens by the day, but the politics in the US have never been so tense, with real doubt regarding whether half the country will accept the outcome. As of this writing, we still are in doubt as regards both of these issues. It would be nice to assume that we have reached a turning point that allows us to put 2020 in the rear view mirror and look ahead to 2021 with a return of life to some semblance of normal… but that seems highly unlikely.

We have had an election – and one that will rank as the angriest and most contentious in decades. The winner is unknown at this point and may not be known for weeks to come. Trump already has demonstrated a determination to declare himself the winner even before the race is decided and has stated that he will oppose efforts to count all the votes. It appears the Senate has not flipped, but that remains in some doubt as well, as many states still are undecided – and that will mean recounts and several weeks of uncertainty over which party will control Congress. The House of Representatives will remain in the hands of the Democrats. It appears there has not been anything close to a “blue wave” and, once again, the pollsters are revealed as completely out of touch with the voters. The state races are varied as well, and many of these will not be clear for weeks to come. In a normal year, the election would be the focal point for the business community and society in general, but this has been anything but a normal year as the pandemic continues to rage and the reaction to this virus will continue to dominate every political and economic decision well into the coming year. The question that will confront the political leaders will be the same one that confronted them before. To see what lies ahead for the US, one only has to look at Europe right now. The “winter wave” of the pandemic has arrived there (as it has started to in the US). The number of cases, hospitalizations and fatalities have surged, and this has provoked a return to the lockdown strategy. In country after country, there have been decisions to shutter public places, ban gatherings, shift schools to virtual 52 | UV+EB Technology • Quarter 4, 2020

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platforms and, in some cases, prohibit people from leaving their homes. The impact on the economy has been devastating already, with predictions of a return to full-on recession in the fourth quarter. The estimate now is that Europe will be in recession for at least the first half of 2021. Unemployment will be back to doubledigit numbers, tens of thousands of businesses will shut down and governments will break debt and deficit records. This is the fate that awaits the US as the confident assertions begin to fade. The Conference Board was looking at two options for 2021 – an upside and a downside projection. The upside expected growth at the end of this year that carried into the first half of 2021 but then faded a little toward the end of the year. The downside saw anemic growth this year and into next but then expected an improvement as 2021 progressed. The good news was that both of these projections had the economy back to where it started 2020 by the end of 2021. The latest iteration of the analysis now has a third option, and it isn’t good. This is the real downside projection and is based on a renewed national lockdown that sends the economy back into a recession. That double dip means an economy that is worse off at the end of 2021 than it was in the second quarter of this year. Economic Priority #1: Coronovirus What can we expect as far as economic priorities? Obviously, the only thing that will matter in the next year will be dealing with the pandemic, and that will have profound economic implications. It is more likely there will be a national lockdown of some kind under a Democrat-led government, but it is not guaranteed. If Trump retains control, the pandemic response will continue to be in the hands of the 50 states. The best estimate is there will be an extension of the partial shutdown rather than the total approach taken last spring. The primary focus for the coming year will be rolling out the vaccine. Reports suggest that several versions already are in production and are waiting for the conclusion of the phase 3 trials. Thus far, these have been panning out as expected. What happens after this crisis has been addressed? This election has focused very little on issues other than the pandemic, and that creates a certain amount of anxiety as campaigns make a lot of promises that are not intended to be kept. There appear to be three areas a Democratic administration will want to emphasize. The first of these is climate change. This came up repeatedly in the campaign, and it is something that both moderates and progressives seem to be able to agree on. This would likely involve promotion of alternate energy and efforts to reduce use of fossil fuel. The challenge is there is little room in the budget for incentives and promotion of alternatives, and there will be reluctance to return to the days when OPEC controlled the US energy destiny. Fracking is not popular, but it has been key to the US economic rejuvenation over the last several years. If the Republicans continue to hold the Senate, the chances for a shift in energy policy are minimal. Climate change has not been of interest to the GOP thus far, and there is powerful support for the fossil fuel industry in general. uvebtechnology.com + radtech.org

Economic Priority #2: Tax Reform A second priority will be tax reform. There will be a desire to hike taxes on the wealthy on the part of the Democrats, but there also is recognition that the upper 25% of the consuming public spends the majority of its disposable income on services – and this is the very sector of the economy that will need the most help to recover from the recession. The easiest step will be to allow the tax cuts instituted at the start of the Trump years to expire. There has even been some GOP support for this move, given the number of fiscal conservatives in the party that are concerned about the size of the debt and deficit. There also will be talk of cuts in spending, but the reality is that over 65% of the budget is mandatory (social security, Medicare and Medicaid). Another 7% is interest paid to those that bought the government debt, and that leaves 28% as discretionary spending. Spending on defense accounts for over half of that 28%. That leaves about 15% for all other spending, and there is just not much that can be cut these days. Economic Priority #3: Foreign Policy and Trade A third priority is likely to be foreign policy and trade. Alliances with Europe and Latin America are in tatters, and the Biden camp would be far more hostile to Russia than Trump. Neither party is a fan of China, but the business community recognizes the country’s role in global trade. The fact is that foreign policy is the area a President was created to deal with by the founders. The US relies on trade for almost 20% of the GDP, and the last four years have been marked by reductions in export activity. Trump has pursued an isolationist and protectionist approach and Biden favors more traditional diplomacy, but every country in the world now will be favoring policies that benefit their own economies. The election remains in doubt at the time of this writing and might not be settled for weeks. Even when some declaration is made, there will be months of challenges and refusal. The election has revealed an incredibly divided and angry electorate. The Trump support has been overwhelming in the rural areas, and Biden’s support has been in the urban areas. There had been some faint hope of a moderate middle emerging from among centrist Democrats and Republicans, but that has evaporated and what is left is hard right and hard left in Congress. With the Senate in GOP hands and the House in Democratic hands, the next four years will feature the kind of gridlock and animosity the last four years have featured.  Chris Kuehl is managing director of Armada Corporate Intelligence. Founded by Keith Prather and Chris Kuehl in January 2001, Armada began as a competitive intelligence firm, grounded in the discipline of gathering, analyzing and disseminating intelligence. Today, Armada executives function as trusted strategic advisers to business executives, merging fundamental roots in corporate intelligence gathering, economic forecasting and strategy development. Armada focuses on the market forces bearing down on organizations. For more information, www.armada-intel.com UV+EB Technology • Quarter 4, 2020 | 53


REGULATORY NEWS

Doreen M. Monteleone, Ph.D., director of sustainability & EHS initiatives, RadTech International North America doreen@ radtech.org

Increased TSCA New Chemical Fees Update The US Environmental Protection Agency’s (US EPA’s) decision to increase its Toxic Substances Control Act (TSCA) new chemical notification fees by as much as 540% has resulted in a significant drop in applications and has discouraged innovation, according to the Society of Chemical Manufacturers and Affiliates (SOCMA). The group is calling on the agency to halve its fees for submitting premanufacture notices (PMNs) and significant new use notices (SNUNs) to reverse the “chilling effect” the higher rate has had on annual submissions. SOCMA’s request comes as the agency begins work to revise its fee schedule for TSCA, with a proposal expected in December 2020 before a final rule in October 2021, according to the latest regulatory agenda. A 50% reduction in PMN and SNUN fees would help encourage submissions while still factoring in the work the agency staff put into reviewing the case, it argued. US EPA Proposes SNURs for Certain Chemical Substances US EPA proposed significant new use rules (SNURs) under TSCA for chemical substances that are the subject of premanufacture notices (PMNs): 85 Fed. Reg. 52294. This action would require EPA notification at least 90 days before commencing manufacture (defined by statute to include import) or processing of any of these chemical substances for an activity that is designated as a significant new use by this proposed rule. This action would further require that neither manufacture nor processing for the significant new use begin until a Significant New Use Notice (SNUN) has been submitted, and EPA has conducted a review of the notice, made an appropriate determination and taken any risk management actions required as a result of that determination. NSR Plantwide Applicability Limitation Provisions Guidance The US Environmental Protection Agency issued a guidance memorandum on plantwide applicability limitation (PAL) provisions under the New Source Review (NSR) regulation. The agency promulgated the PAL regulations as part of the 2002 NSR Reform. A PAL is an optional flexible permitting mechanism available to major stationary sources that involves the establishment of a plantwide emission limit. Once a PAL is established, changes to facility operations that affect that pollutant can forego NSR, a costly and time-consuming process for industry. The purpose of the memorandum was to provide guidance on the PAL regulations to address specific concerns. Read the memorandum at https://www.epa.gov/sites/production/ files/2020-08/documents/pal_guidance_final_-_signed.pdf eGRID Website Updated Facilities calculating their carbon footprint utilize information found on the US EPA Emissions & Generation Resource Integrated Database (eGRID) website. eGRID is a comprehensive source of data on the environmental characteristics of almost all power generated in the US. The data include emissions, emission rates, generation, heat input, resource mix and many other attributes. eGRID is typically used for greenhouse gas registries and inventories, carbon footprints, consumer information disclosure, emission inventories and standards, power market changes and avoided emission estimates. Learn more at www.epa.gov/egrid. SGP Working Toward Offering Supplier Certification The Sustainable Green Printing Partnership (SGP), the leading authority in sustainable printing certifications for print manufacturers, has announced it is working toward offering a sustainability certification for suppliers to the printing industry. The criteria for SGP Supplier certification are similar to those for SGP Printers in that they specify the requirements for management and production operations that define sustainable practices encompassing the economic, environmental and social areas of sustainability. The draft criteria document, based on SGP’s successful printer certification efforts, defines the core elements of the SGP certification program, including development and adoption of a sustainability management system (SMS) and best practices. Learn more at www.sgppartnership.org or contact Doreen Monteleone at doreen@radtech.org.

News from the West Coast SCAQMD Fails to Meet Federal Standards According to the US Environmental Protection Agency (EPA), the South Coast Air Quality Management District (SCAQMD) has failed to meet National Ambient Air Quality Standards (NAAQS), prompting the issuance of a new rule declaring the failure by the attainment date. The EPA first promulgated the NAAQS for PM2.5 in July 1997. The 24-hour PM2.5 standard was set at a level of 65 micrograms per cubic meter (μg/ m3). The annual PM2.5 standard was set at a level of 15 μg/m3. In 2006, the EPA strengthened the 24-hour 54 | UV+EB Technology • Quarter 4, 2020

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Rita Loof, director of regional environmental affairs, RadTech International North America rita@radtech.org

standard to 35 μg/m3. The annual standard stayed at 15 μg/m3 until December 14, 2012, when it was reduced to 12 μg/m3. Since the Basin did not meet the federal 2006 24-hour PM2.5 standard by the 2019 deadline, the Clean Air Act requires that a revision to the State Implementation Plan (SIP) be submitted to EPA within 12 months after the applicable attainment date to demonstrate attainment of the standard no later than five years from the date of the EPA’s final determination of failure to attain the standard. In addition to the attainment demonstration, the updated SIP also must address several other federal CAA requirements. A minimum of 5% annual reductions in directly emitted PM or PM precursor (such as VOCs, ammonia and sulfur oxides) is required. SCAQMD prefers what it calls a “NOx heavy” strategy, as it is believed that a reduction of NOx is the most efficient approach. According to SCAQMD staff, the South Coast Air Basin is expected to attain the 2006 24-hour PM2.5 standard during or before 2023. Given the plan is due to the EPA by December 31, 2020, the first year to demonstrate the 5% reduction is 2021, and the last year is 2023 – the new attainment date. Staff believe that existing regulations already achieve more than the 5% NOx emissions reductions per year required by EPA. The PM2.5 Plan revisions also include an analysis of Reasonably Available Control Technology/Reasonably Available Control Measures (RACT/RACM). A final draft of the plan was expected to be released in November 2020, and revisions are scheduled to be presented to the SCAQMD board in December 2020. The plan then will move on the California Air Resources Board and, subsequently, to the EPA for approval. California’s EICG/CTR Regulations The California Air Resources Board (CARB) scheduled a public hearing in November 2020 to consider amendments to parallel regulations for (1) Emission Inventory Criteria and Guidelines (EICG) Report for the Air Toxics “Hot Spots” Program and (2) the reporting of criteria air pollutants and toxic air contaminants (CTR). Approximately 60,000 California facilities will be affected by the regulations. EICG. Under this program, stationary sources are required to report the types and quantities of certain toxic substances their facilities routinely release into the air. The program requires collection of emission data, identifying facilities having the potential for localized impacts, ascertaining health risks and requiring that owners of significant-risk facilities reduce their risks below the level of significance. Additionally, CARB is to compile a list of “substances of concern” identified by other agencies and scientific bodies. Since the 2007 EICG update, CARB staff identified more than 1,000 new substances that meet the criteria for reporting under the Hot Spots Act. The compliance requirements and the economic impact of the proposed amendments would begin with the 2023 reporting year, based on emissions data from 2022. CTR. CTR requires the annual reporting of criteria pollutant and toxic air contaminant emissions by facilities subject to the applicability requirements of the regulation. Effective January 1, 2020, the CTR established statewide annual reporting of criteria air pollutant and toxic air contaminant emissions data for three facility categories: (1) subject to Greenhouse Gas Mandatory Reporting Regulation, (2) authorized to emit > 250 tons per year of a nonattainment criteria pollutant (such as volatile organic compounds) and (3) received an “elevated Toxics Hot Spot” prioritization score. Last fall, CARB proposed to add 812 new substances to the AB 2588 Chemical List and unveiled a list of categories under review as follows: Category

Count*

Carcinogens

200

Developmental and Reproductive Toxicants (DART)

134

Pesticides

117

Metals

22

Other Inorganics

20

Pharmaceuticals**

154

Neurotoxins

123

Other

348

CARB plans to implement the program in different phases, with the program only applying to facilities that have been issued a Permit to Operate by a California air district, so low-VOC operations – such as UV/EB processes that are exempt from permitting – would not be subject to the reporting. The agency expects the rulemaking to be finalized in late 2020. 

* The counts by category may overlap (e.g., a substance could be both a pesticide and a DART) ** The majority of pharmaceuticals were added to Table A-III (substances that need not be reported unless manufactured by the facility)

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UV+EB Technology • Quarter 4, 2020 | 55


CALENDAR Due to COVID-19, event calendars can change rapidly. Please check event websites for up-todate information.

JANUARY 2021 15: Application deadline for RadLaunch 2021. For more information, visit www.radlaunch.org.

MAY 2021 17-21: NPE 2021, Orange County Convention Center, Orlando, Florida. For more information, visit www.npe.org.

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56 | UV+EB Technology â&#x20AC;˘ Quarter 4, 2020

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UV+EB Technology - 2020 Quarter 4  

Official Publication of RadTech International North America

UV+EB Technology - 2020 Quarter 4  

Official Publication of RadTech International North America

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