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2019 Quarter 2 Vol. 5, No. 2

Driving Innovation in the Transportation Industry Studying Clearcoat Durability Measuring Radiation Yields Eliminating Red Rust

Official Publication of RadTech International North America


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With a worldwide installation base unequaled in the industry that spans multiple markets and applications, our UV experience is OLWHUDOO\VHFRQGWRQRQH:HRIIHUWKHะบQHVWLQSURYHQ89WHFKQRORgy including LED, Traditional and Hybrid combinations of the two. When considering the addition of UV curing to your operation, let ,67SURYLGHWKHXOWLPDWH89VROXWLRQIRU\RXUFRPSDQ\7KHUHDUH lots of choices out there, as true UV professionals we can help you make an educated and informed decision on the right UV path to pursue to meet and exceed the needs of your company. 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


FEATURES 14

The RadTech UV Clearcoat Durability Study: How Paint Performance is Assessed by Ford Motor Company RadTech is collaborating with Ford Motor Company on a followup to a 2003 study of UV-curable clearcoats to determine how well current products meet automotive durability requirements. By Christopher M. Seubert, Ph.D., Ford Motor Company

20

A dual-cure system using pyrylium salt as photoinitiator and a hydroperoxide or vinyl ether as coinitiator releases a proton that could initiate polymerization at room temperature as well as under UV or LED, offering options to speed formation of fiber-reinforced polymer. By M. Lecompère and X. Allonas, Laboratory of Macromolecular Photochemistry and Engineering, University of Haute Alsace; and D. Maréchal and A. Criqui, Mäder Research

ON THE COVER

UV Curing of Weatherable, Scratch-Resistant Clear Coat on Polycarbonate Headlamp Lens. Photo courtesy of Red Spot Paint and Varnish. 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.

DEPARTMENTS

President’s Message ............................................ 4 Association News ................................................ 6 Technology Showcase ....................................... 30 Industry ............................................................... 56 New Faces .......................................................... 57 Regulatory News ............................................... 58 Calendar ............................................................. 60 Advertisers’ Index .............................................. 60

2 | UV+EB Technology • Issue 2, 2019

New UV LED Technologies for Carbon-Fiber Reinforced Polymers

26

3D-Printed Clothing Emphasizes Innovation, Sustainability A Miami-based clothing design company’s innovation is stirring up interest in reducing environmental impact while creating new production methods in the $804 billion global textile industry. Edited by Nancy Cates, UV+EB Technology

COLUMNS 8

UV Curing Technology UV LED Lessons Learned from Others By Jim Raymont, EIT LLC

10

Innovations: A Look at Industry Advances Virginia Tech Team Develops Model to 3D-Print Piezoelectric Materials

12

Professor’s Corner The Science of UV/EB Polymerization By Byron K. Christmas, Ph.D., Professor of Chemistry, Emeritus

uvebtechnology.com + radtech.org


TECHNOLOGY 2019 Quarter 2 Vol. 5, No. 2

32

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.

Counting Radicals: Methods to Measure Radiation Yields of Monomers in EB Polymerization To provide insight into the kinetics of electron beam polymerization, two new methods to determine initiation rate and radiation yield are presented. By Nicole L. K. Thiher and Julie L. P. Jessop, University of Iowa, and Sage M. Schissel, PCT Ebeam and Integration, LLC

42

BIG IDEAS Conference Review RadTech’s BIG IDEAS for UV+EB Technology event was held in Redondo Beach, California, on March 19 and 20. In addition to 49 session topics, the RadLaunch class of 2019 presented their winning innovation ideas. By Dianna Brodine, UV+EB Technology

44

Eliminating Red Rust and Improving Customer Satisfaction

Susan Bailey

Editorial Board Co-Chair Business Development Manager, Digital & Specialty Printing Michelman, Inc.

Syed T. Hasan

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

UV coating technology can offer line pipe producers a costeffective means of reducing end customer issues with red rust and corrosion. By Michael Kelly, Allied PhotoChemical, Inc.

49

Viscosity Control of Spray Applied Coatings – Balancing Environmental Compliance and Performance Options exist to minimize cost, optimize output and balance regulatory issues when choosing UV-curable coatings. By Kristy Wagner, Red Spot Paint and Varnish

Byron Christmas

Professor of Chemistry Retired

Molly Hladik

Technical Project Leader, Print & Packaging Technology Michelman, Inc.

UV+EB TECHNOLOGY EDITORIAL BOARD Susan Bailey, Michelman, Inc. Co-Chair/Editor-in-Chief Syed Hasan, BASF Corporation Co-Chair/Editor-in-Chief Darryl Boyd, US Naval Research Laboratory Byron Christmas, Professor of Chemistry, Retired Amelia Davenport, Colorado Photopolymer Solutions Charlie He, Glidewell Laboratories Mike Higgins, Phoseon Technology Molly Hladik, Michelman, Inc. Mike J. Idacavage, Colorado Photopolymer Solutions

uvebtechnology.com + radtech.org

JianCheng Liu, PPG Industries Sudhakar Madhusoodhanan, Applied Materials Gary Sigel, Armstrong Flooring Maria Muro-Small, Spectra Group Limited, Inc. Jacob Staples, Ashland, Inc. R.W. Stowe, Heraeus Noblelight America LLC Chen Wang, Formlabs, Inc. Huanyu Wei, ITW Sports Branding Division Jinping Wu, PolyOne Corporation Sheng “Sunny” Ye, Facebook Reality Labs

Chen Wang

Materials Scientist Formlabs, Inc.

UV+EB Technology • Issue 2, 2019 | 3


PRESIDENT’S MESSAGE

H

ard to believe, but 2019 is flying by! It never fails that when a new year starts it seems that the road ahead is long, but it always unfolds to fly by quickly.

It is no different for RadTech. We’ve already had a lot of activity, completing the BIG IDEAS Conference in March. It was officially a success, and officially a record event! With more than 300 participants Eileen Weber and nearly 70% of them new registrants, it President reflects how RadTech continues to grow and evolve in serving the interests of the UV/EB industry and community. Before we close the book on the BIG IDEAS event, I want to give a few shout-outs. First, as always, a big thanks to Gary Cohen and Mickey Fortune for coordinating the event and the subsequent annual meeting. Most of us do not realize all the time and energy – much of it behind the scenes – that goes into coordinating and successfully executing these events, but it is always amazing to me how effortless Gary and Mickey can make it all seem for the outsider looking in. Secondly, during the annual winter meeting, we recognized a couple of outstanding volunteers that I want to spotlight again to our larger community of readers and give another round of congratulations and nod of appreciation. This year, Michael Gould of Rahn USA was the recipient of RadTech President’s Award for outstanding leadership and volunteerism, and Doug DeLong of Doctor UV was recognized for his work on the West Coast. Both Doug and Michael have done phenomenal work on behalf of the RadTech organization. They are passionate people who continually go above and beyond the call of duty. It is members like Doug and Michael that make RadTech such a great organization! We again thank you both for all that you do in representing and serving the RadTech community.

Now, as we look at this edition of UV+EB Technology, we note the focus on the transportation market. RadTech, of course, serves the entire energy cure market, but the transportation sector is always interesting to me because of the multitude of ways the technology can offer solutions to this particular market. From coatings to inks to adhesives to 3D printing, practically every aspect of what RadTech represents can be part of a solution and offer an advantage to the transportation market. And, as this market continues to evolve, I believe that UV/EB technology will be instrumental in moving the needle of progress. Specific to the transportation sector, it also is exciting to see the growing number of events that RadTech is taking part in this year to showcase these points – starting with the SAE World Congress event that took place in April in downtown Detroit. RadTech is on its fourth year of participation in in the SAE event, and each year the interest continues to grow regarding ways UV/EB technology can benefit the automotive market. New for RadTech this year was participation in the Detroit Society of Coating Technology’s FOCUS Conference in Plymouth, Michigan, in early May, and RadTech will be at the SPE TOPCON Plastics Decorating Symposium in Franklin, Tennessee, June 2 through 4. Finally, I would like to look ahead a bit to the 2020 RadTech UV+EB Expo and Conference. The conference will be earlier than in previous years, so be sure to mark your calendars for March 9 through 11, 2020, and come join us in Orlando! More importantly right now though, please submit your abstracts for papers! (For more information, see Association News, page 6 of this issue.) We want to post another record RadTech event with yet another high-quality technical conference at the 2020 show, but that can only happen with the assistance of our innovative community of members, so please consider participating and help spread the word! 

BOARD OF DIRECTORS

Published by:

President Eileen Weber – Red Spot Paint & Varnish Co., 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

4 | UV+EB Technology • Issue 2, 2019

President-elect Jo Ann Arceneaux – allnex USA Inc. Secretary Jennifer Heathcote – Eminence UV Treasurer Paul Elias – Miwon North America Immediate Past-President Lisa Fine – Joules Angstrom UV Printing Inks Board of Directors Susan Bailey – Michelman David Biro – Sun Chemical Mike Bonner – Saint Clair Systems, Inc. Todd Fayne – Pepsico Mark Gordon – INX International Ink Company Michael Gould – Rahn USA Jeffrey Klang – Sartomer George McGill – Precision Ink Jim Raymont – EIT LLC Chris Seubert – Ford Motor Company P.K. Swain – Heraeus Noblelight America 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 Lara Copeland Nancy Cates

Circulation Manager Brenda Schell brenda@petersonpublications.com

ENews & Website Developer Mikell Burr

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ASSOCIATION NEWS 11 in Detroit, Michigan. With a theme of UV/EB Leading the Way for the Future of Automotive, the RadTech conference session – organized by Mary Ellen Rosenberger of BaySpring Solutions and Chris Seubert of Ford Motor Co., Ltd. – featured six presentations, including topics on additive manufacturing/3D printing and advanced coatings technologies.

RadTech Plans 2020 UV+EB Technology Expo and Conference Call for Abstracts, Exhibit Sales Open RadTech’s biennial conference is heading to Orlando, Florida, in 2020: March 9 through 11 at the Disney Coronado Springs Resort. This is the foremost event for the UV/EB industry. As the industry has evolved, so has UV/EB technology grown to meet the new challenges. RadTech’s conference program will feature key areas of interest to the industry. Abstracts are invited and will be due September 20. Exhibit and sponsorship sales now are open and typically sell out. Email Mickey Fortune at mickey@radtech.org for exhibit and sponsorship details. For more information, visit https://radtech2020.com.

IUVA Americas Conference Co-Locates with RadTech 2020 An IUVA Pavilion will be included on the RadTech 2020 exhibition floor. The 2020 IUVA Americas Conference deadline for abstracts is October 11. Visit http://www.iuva.org/AC20Call-For-Abstracts. For answers to questions about abstracts or exhibits for RadTech or IUVA, please email Mickey Fortune at mickey@radtech.org or call 240.643.0517.

RadTech members staffed the booth, featuring UV/EB curable parts and RadTech literature. The event showcased ways UV/ EB technology advancements are helping the automotive industry work toward lowering energy consumption, vehicle lightweighting, reduced greenhouse gas emissions, faster manufacturing cycle times, small-footprint manufacturing, speedy prototype development and additive manufacturing – all creating a revolution in manufacturing.

Eighth-Grader’s Air/Water Purification System Earns RADLAUNCH’s Future Scientist Award RadTech chose 8th-grader Mealy Cronin for its prestigious RADLAUNCH “Future Scientist” award for her invention: an “Air/Water Purification Ion-Exchange Resin & UVC Filtration System.” The commercial name for the invention is “Detect and Clear,” and Mealy has nicknamed it “Zephyr.” “Through a series of resin membrane matrix ion-exchange filtration technologies,” Mealy explained, “this system detects toxins in the air or water and draws the toxins in, purifies the air or water and then releases the purified air or water back into the atmosphere or back to its water source.” Once Mealy came up with the idea for her invention, she had to construct a prototype to meet one of the requirements of her patent application, so she solicited funding and component parts

RadTech at SAE WCX ’19 The RadTech Transportation Committee, chaired by Mike Dvorchak, offered a strong technical program and hosted a busy exhibition booth at the SAE WCX ’19, April 9 through

Darryl Boyd (left), a research chemist from the United States Naval Research Laboratory and member of the UV+EB Technology Editorial Board, presents RadTech’s “Future Scientist” award to Mealy Cronin (center). At right is Ellis Glover, headmaster of Westminster School, Annandale, Virginia, where Mealy is in 8th grade.

6 | UV+EB Technology • Issue 2, 2019

uvebtechnology.com + radtech.org


from different companies. In doing so, she came across several companies that sponsored competitions for new inventions. RadTech, sponsor of the RADLAUNCH competition, was one of the groups with which she shared her proposal. The RadTech judging team was quite impressed with her invention, but even more so by the fact that its creator is in the 8th grade. She is the youngest person ever to receive the “Future Scientist” award from RadTech.

Thomas Griesser, University of Leoben; Céline CroutxéBarghorn and Xavier Allonas, Université de Haute Alsace; Jason Burdick, University of Pennsylvania; Sandra Schloegl, Polymer Competence Center Leoben GmbH; Tim Scott, University of Michigan; Chris Kloxin, University of Delaware; Rong Tong, Virginia Polytechnic Institute; and Alan Aguire, Tecnológico de Monterrey. Early registration deadline is June 30. The conference is presented by RadTech – The Association for UV & EB Technology and Colorado Photopolymer Solutions (CPS). For more information, contact Neil Cramer at neil.cramer@colorado.edu.

Staples Joins UV+EB Editorial Board

Register Now for Upcoming Photopolymerization Conference Photopolymerization Fundamentals 2019, the premier scientific conference for the photopolymerization industry, is scheduled for September 15 through 18 at the Monterey Plaza Hotel & Spa, Monterey, California. Highlights of the meeting include:  Scientific presentations on a wide range of photopolymerization topics  An open atmosphere where interaction and technical networking are encouraged  A poster session and vendor exhibit  Student poster competition/award sponsored by the Polymer Chemistry journal  Reduced rates for students to promote interaction between industrial scientists and students The meeting includes a short course with a series of presentations from leaders in the photopolymerization field, as well as a tabletop vendor exhibit concurrent with the poster sessions. Vendors committed to attend include Allnex, Colorado Photopolymer Solutions, Daicel, FlackTek, Heraeus Noblelight, Honle UV, IGM Resins, National Polymer and Sartomer. Invited speakers who plan to present include Conference Chair Christopher Bowman and Stephanie Bryant, University of Colorado; Christopher Ellison, University of Minnesota; Allan Guymon, University of Iowa; Jeffrey Stansbury, University of Colorado Denver; Marco Sangermano, Politecnico di Torino; uvebtechnology.com + radtech.org

Jacob Staples, technical team leader in radiation cure for Ashland, Inc., Oak Creek, Wisconsin, has been named to the editorial board of UV+EB Technology. Staples has more than 20 years of experience at Ashland in technical service, product management, research and development. He is responsible for leading and mentoring chemists and technicians working on projects in the lab, supporting sales by developing new products to meet customer requirements, attending field trials, meeting with customers to discuss technical projects, troubleshooting issues with existing products and serving as a technical expert in the UV/ EB product line of coatings, adhesives and food packaging. He has an undergraduate degree in physics and an MS in mechanical engineering from the University of Wisconsin-Milwaukee.

RadTech to Present at SPE Decorating & Assembly Division and IMDA Joint Conference RadTech will sponsor presentations and distribute copies of UV+EB Technology magazine at the SPE Decorating and Assembly Division TopCon and IMDA Symposium, June 3 and 4 in Nashville, Tennessee. For more information, visit https:// plasticsdecorating.com/topcon-2019/. Other Upcoming RadTech events: RadTech Europe 2019 October 15–16, 2019 Munich, Germany www.radtech-europe.com RadTech Asia 2019 Conference and Exhibition Hangzhou, China, October 17–20, 2019 http://radtechasia2019.csp.escience.cn 

UV+EB Technology • Issue 2, 2019 | 7


UV CURING TECHNOLOGY QUESTION & ANSWER

UV LED Lessons Learned from Others O

ne of my favorite quotes on learning is from the television show Frasier. Kelsey Grammer, as the title character, best summed it up: “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.”

Parameter

August 2017 (Initial readings)

January 2018 (Readings when project resumed)

February 2018 Readings at customer location after instrument check at manufacturer

Irradiance

7.7 W/cm2

4.6 W/cm2

4.6 W/cm2

420 mJ/cm2

250 mJ/cm2

250 mJ/cm2

Energy Density

Figure 1. Comparison of initial readings, when project resumed and after instrument check

How can we apply this valuable lesson to monitoring UV and establishing/maintaining a process window? Consider the realworld experiences below:

Trust but verify … A manufacturer with multiple products utilizes UV LEDs on some assembly lines and broadband (arc) sources on others. On products manufactured with the UV LEDs, the LED is extremely close to the product, and the process is optimized for a high-intensity, narrow-bandwidth (monochromatic) UV source. On products manufactured with a broadband (arc) lamp, the source is set up for far-field distant curing with low intensity levels. The UV sources on all assembly lines are well shielded, and the light source is not visible.

Left LED Source

Right LED Source

W/cm2

J/cm2

W/cm2

J/cm2

1.336

1.382

2.014

1.873

1.672

1.650

2.039

1.962

Figure 2. Nonoptimized radiometer comparison of LED units

LED that was specified. Once the correct wavelength LEDs were in place, production moved along smoothly. Lesson #2: The purchasing team may be tasked with buying products that require special knowledge. Be clear: Specify part numbers, manufacturers, etc. Ask to review the purchase order or supplier’s sales order acknowledgment before delivery.

Don’t handcuff the transition team …

One production team was extremely frustrated with the readings from their radiometer. What they failed to consider was that an instrument optimized to measure 395 nm LED sources up to 40 W/cm2 of power was being used to measure their mercurybased source with an output of less than 50 mW/cm2.

A medical product supplier assembled a team to transition from its current broadband UV source to an LED source. The formulation was being cured with a broadband source (H+ bulb), which is rich in UVC output, and the current process window called for an extremely tight UVC specification.

When the production team switched to an instrument with the right response and proper dynamic range for the source, they quickly got back on track.

The transition team was told that, due to the regulatory process, no modifications could be made to the current formulation. Is it realistic to expect that a 365 nm LED will have the same ability to cure the product, given the requirement for UV energy in the shorter UVC wavelengths? To be certain, the transition team is testing a 365 nm LED.

Lesson #1: Verify the type of source being used and match the instrument to it.

Clearly communicate your needs … An industrial parts manufacturer partnered with a coating and LED supplier to develop a new product. Lab work established the key process parameters for the application, and a large number of LED sources were ordered based on laboratory trials. When the LED sources arrived, the cure results could not be replicated. Further investigation and radiometer testing revealed that a 395 nm LED source was mistakenly ordered instead of the 365 nm 8 | UV+EB Technology • Issue 2, 2019

Lesson #3: Have realistic expectations when transitioning to an LED source.

Look in the mirror … A company working to develop a new UV LED process measured its LED laboratory system in August 2017. The project was put on hold, and when work resumed in January 2018, the team noticed a sharp decrease in radiometer readings. Following a conference call to discuss process variables and instrument care, the customer uvebtechnology.com + radtech.org


took additional readings and was convinced that the instrument had changed. When evaluated, it was found the instrument was reading correctly and was returned to the customer.

Normal +/- 5 nm from a CWL of 365 nm

A new set of readings was obtained in February 2018, when the instrument was returned (Figure 1). The first instinct of many companies when things are not curing is to “question” (blame) the Variation in the reading based on CWL formulator. However, in this case, the company with instrument response not optimized was doing its own formulation. UV source for the LED measured suppliers are usually the next to be questioned. The company dismissed the idea that the UV source was a possible culprit in the drastic change because Figure 3. Variation in readings with nonoptimized instrument of the inherent stability of LEDs. After further testing confirmed the radiometer’s performance, the company refocused its attention on the LED source. Careful inspection revealed that the optical glass on the LED array had been coated with a thin film of ink. After cleaning the ink from the face of the LED window, the instrument readings jumped back to the August 2017 levels. Lesson #4: When things change, work through the process variables to understand what happened.

radiometer. An instrument designed for high-intensity sources may not provide accurate readings of low-irradiance sources and can lead to variations in the readings, run to run. Using an instrument designed for low- to medium-intensity sources to measure a powerful LED source can “peg” or exceed the range of the instrument, making it appear to be a very consistent source. Check to make sure the instrument has a dynamic range that will support the type of source being measured. Follow the suggested (dynamic) operating range provided by the manufacturer.

Trust but verify … Part 2

Instrument Responsivity

A customer with side-by-side LED units mounted across a curing conveyor obtained the readings in Figure 2 and wanted to understand the differences. After some digging, it was discovered that the readings were taken with a radiometer not optimized for source type. The LED sources were 365 nm, and the instrument was optimized for a 395 nm source. One UV LED array had a center wave length (CWL) closer to 360 nm and the other was closer to 370 nm. When a radiometer with a proper response was used, the two different LED systems compared very closely. Lesson #5: LED sources with similar specifications can vary slightly in their spectral output. These spectral differences were only noticed when an instrument with a response not matched to the source was used.

The Takeaways: Select the right instrument Match your instrument to the source. Use an instrument with the correct:  Dynamic range to the irradiance of the light source to be used  Responsivity to the proper wavelengths used in your process

Instrument Dynamic Range Using a truck scale to weigh an infant does not provide good results. The same is true with the “scale” or dynamic range on a uvebtechnology.com + radtech.org

Radiometers designed for mercury sources have responses (and dynamic ranges) matched to the broadband output and the irradiance levels of a mercury-based source. You will get a “number” if you use a broadband radiometer to measure an LED, but the number most likely will not report the true value of the source. Work with the manufacturer to determine whether a particular instrument response and bandwidth range is matched to the type of source being measured. UV LEDs are commonly sold with a +/- 5 nm CWL variation. A 395 nm LED can be expected to have its CWL output from 390 to 400 nm, and a 365 nm LED can be expected to have its CWL between 360 and 370 nm. An instrument with the correct responsivity and dynamic range will take the normal CWL variations into account when multiple sources are measured.

This column’s parting thought Q: Does light have mass? A: Of course not. It’s not even Catholic! 

Jim Raymont Director of Sales EIT LLC jraymont@eit.com UV+EB Technology • Issue 2, 2019 | 9


INNOVATIONS A LOOK AT INDUSTRY ADVANCES

Virginia Tech Team Develops Model to 3D-Print Piezoelectric Materials A

team from the Virginia Polytechnic Institute and State University College of Engineering has developed methods to 3D-print piezoelectric materials that can be custom-designed to convert movement, impact and stress from any direction into electrical energy. “Piezoelectric materials convert strain and stress into electric charges,” explained group leader Xiaoyu “Rayne” Zheng, assistant professor of mechanical engineering and member of Virginia Tech’s Macromolecules Innovation Institute, in Blacksburg. “We have developed a design method and printing platform to freely design the sensitivity and operational modes of piezoelectric materials.”

While most piezoelectric materials, which require a clean room for manufacture, are made of brittle ceramics or crystal films or blocks – limiting their shape – Zheng’s team developed a model that permits manipulation of the design. The new 3D-printed materials are not restricted by shape or size and can be activated to provide the next generation of intelligent infrastructures and smart materials for tactile sensing, impact and vibration monitoring, energy harvesting and other applications. “By programming the 3D active topology,” Zheng continued, “you can achieve pretty much any combination of piezoelectric coefficients within a material and use them as transducers and sensors that are not only flexible and strong, but also respond to pressure, vibrations and impacts via electric signals that tell the location, magnitude and direction of the impacts within any location of these materials.” A factor in current piezoelectric fabrication is the natural crystal used: The orientation of atoms is fixed. Zheng’s team has produced a substitute that mimics the crystal but allows for the lattice orientation to be altered by design. “We have synthesized a class of highly sensitive piezoelectric inks that can be sculpted into complex three-dimensional features with ultraviolet light,” Zheng said. “The inks contain highly concentrated piezoelectric nanocrystals bonded with UV-sensitive gels, which form a solution – a milky mixture, like melted crystal – that we print with a high-resolution digital light 3D printer.” 10 | UV+EB Technology • Issue 2, 2019

The technology is currently used in everything from cell phones to musical greeting cards. The Virginia Tech team has printed and demonstrated smart materials worn on hands and fingers to convert motion and harvest the mechanical energy, but the applications go well beyond wearables and consumer electronics. Zheng sees the technology as a leap into robotics, energy harvesting, tactile sensing and intelligent infrastructure, where a structure is made entirely with piezoelectric material, sensing impacts, vibrations and motions, and allowing for those to be monitored and located. The team has printed a small smart bridge to demonstrate its applicability to sensing the locations and magnitude of dropping impacts while absorbing the impact energy. The team also demonstrated the application of a smart transducer that converts underwater vibration signals to electric voltages. The team demonstrated the 3D-printed materials at a scale measuring fractions of the diameter of a human hair. “We can tailor the architecture to make them more flexible and use them, for instance, as energy-harvesting devices, wrapping them around any arbitrary curvature,” Zheng said. “We can make them thick and light, stiff or energy-absorbing.” uvebtechnology.com + radtech.org


The material has sensitivities five-fold higher than flexible piezoelectric polymers. The stiffness and shape of the material can be tuned and produced as a thin sheet resembling a strip of gauze, or as a stiff block, Zheng explained. “We have a team making them into wearable devices, like rings, insoles and fitting them into a boxing glove, where we will be able to record impact forces and monitor the health of the user.� “The ability to achieve the desired mechanical, electrical and thermal properties will significantly reduce the time and effort needed to develop practical materials,� said Shashank Priya, associate vice president for research at Pennsylvania State University and former professor of mechanical engineering at Virginia Tech. The team’s work is supported, in part, by the National Science Foundation, Air Force Office of Scientific Research, the Office of Naval Research and the Virginia Tech Institute of Critical Technology Junior Faculty Award.

The research team included, from left, Huachen Cui, Desheng Yao, Xiaoyu “Rayne� Zheng and Ryan Hensleigh. Photo courtesy of Virginia Tech.

Researchers shared their work in a recent article in Nature Materials, which features the following authors from Virginia Tech’s Department of Mechanical Engineering, except as listed:

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Phone: 703-478-0700

Web: eit.com

UV+EB Technology • Issue 2, 2019 | 11


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

The Science of UV/EB Polymerization T

he first edition of this column included a brief “Introduction to Polymer Science.”1 Polymeric materials were defined as those containing molecules of very large size and molecular mass. These “macromolecules” then were classified into three different categories: linear polymers, branched polymers and crosslinked polymers. Any given sample may contain mixtures of two or more of these, as well as low molecular mass materials. In this second edition, some of the key differences between the properties of polymers and those of other materials will be discussed. Polymers vs. low molecular mass materials What are the key properties that would differentiate polymers from other types of materials? How can these property differences be used to identify a polymer? What are some of the reasons for these differences? Most people who studied chemistry at the university level spent the majority of their time studying the chemical and physical properties of relatively low molecular mass materials. They may or may not have gained insights into the unique properties of polymers. Clearly, one can see that items such as plastics, rubber-based materials, fibers, coatings, adhesives and other types of polymer-based materials behave very differently from low molecular mass compounds, elements and mixtures thereof. One would not likely mistake a polymeric material – such as polycarbonate (PC), polyvinyl chloride (PVC), a rubber band or a strand of nylon fiber – for a piece of steel, a sample of sulfur, a block of ice, a sample of liquid acetone or a powdered form of a transition metal complex. These low molecular mass or “monomolecular” materials are very different in their physical properties from those of polymer-based materials, and these differences are rather obvious. In what follows, we will discuss several key physical properties that demonstrate the differences one observes between macromolecular polymeric materials and monomolecular materials. Melting temperature and Tg In organic chemistry lab, one of the ways for testing the purity of low molecular mass organic compounds is to measure the melting temperature. Pure solids will have a sharp and distinct melting temperature, while a broad temperature range for melting would indicate that a mixture is present. Polymer-based materials, on the other hand – even if free of impurities – will normally have a broad temperature transition from the solid to the liquid state. This is a strong indication that polymers are almost always “mixtures” of macromolecules. Even if the polymer consists of a single chemical 12 | UV+EB Technology • Issue 2, 2019

species, such as polyethylene (PE), it will most likely contain macromolecules with widely different molecular masses. It also may contain mixtures of linear and branched macromolecules. Note that crosslinked polymers, including all practical energycured polymers, cannot be melted. To do so would involve breaking covalent chemical bonds, thus constituting decomposition – a chemical, rather than physical, change. The process of melting is a quite endothermic primary phase transition involving solid components changing to liquid. Many polymers also go through a much smaller endothermic secondary phase transition at a lower temperature. This is called the “glass transition,” or Tg, and involves “softening,” not liquification. It is the temperature range over which a “glassy” brittle material softens to a “rubbery” flexible material – a transition described by Stevens2 as occurring at the onset of segmental motions within the macromolecules. Most monomolecular materials are crystalline in the solid state and, therefore, do not exhibit a glass transition. The Tg is a property of amorphous solids; solids that have a disordered, noncrystalline structure at the molecular level. The presence of a measurable Tg, then, is another indication that a material is most likely polymeric. Flexibility and compressibility Low molecular mass materials in the solid state tend to be inflexible and brittle. Even in the liquid state, monomeric materials, such as water, are not easily compressed, indicating that the molecules sit very close to each other in the liquid state. This is illustrated by automotive brake fluid, which would not function effectively if the liquid could be compressed. By contrast, many polymers are quite flexible. This flexibility arises from the noncrystalline nature of amorphous polymers and the presence of significant “free volume.” This is volume within the sample that is between and among the molecules, constituting “empty space.” Imagine a container filled with several layers of small spheres closely spaced in an organized fashion. This can represent a crystalline monomolecular material. It has a relatively small amount of free volume and, in this case, that volume is not accessible to the spheres because of their size and the fact that they are in direct contact with one another. Now imagine a bowl of spaghetti with a very random arrangement of the individual strands. This is a simplistic but useful model of a linear polymer. Because of the long chains, polymers are typically inhibited from fully organizing into highly ordered crystalline arrays. Segments of the chains are quite mobile and can move rather easily when uvebtechnology.com + radtech.org


a stress is applied. But even so, they must have “room to move,” and this is provided by the free volume present. Molecular chain length and the presence of free volume contribute to the flexibility observed in many polymers. Temperature dependence of physical properties In addition to flexibility, some of the physical properties of low molecular mass materials, such as surface hardness and brittleness, are relatively independent of temperature, while those of polymers may change significantly with a change in temperature. As temperature increases, the average kinetic energy of the molecules of a material increases. This increased energy of motion mostly is exhibited in rotations, vibrations and translations of the molecules. Lower molecular mass solids often are locked in tight crystalline structures, effectively restricting certain of these motions. On the other hand, the free volume within amorphous polymer solids allows for more molecular motions, producing a larger temperature dependence of the physical properties. The nature of solutions An important property of the liquid state, including that of liquid solutions, is the viscosity – the resistance of the material to flow. A higher resistance to flow corresponds to a higher viscosity. Therefore, a convenient way to measure viscosity involves using a rotating spindle within the solution. As the spindle is rotated, frictional forces shear the liquid and resist the spinning. The higher the viscosity, the stronger the resistance for a given rotational speed. Solutions of materials – such as sucrose table sugar or table salt – typically have the same viscosity, regardless of how fast or slow the spindle is moving. They are said to be “Newtonian fluids,” named for Sir Isaac Newton, an early investigator of viscosity. Polymer solutions often are non-Newtonian, wherein the measured viscosity depends heavily on the speed of the spindle’s rotation. This dependency is due to the very large size of the molecules and their tendency toward molecular entanglement. Shearing such solutions may cause increased chain entanglements, increasing viscosity with shear rate. Or it may cause disentanglements, reducing the viscosity with increasing rate of the rotation. Note that for a polymer to be soluble, even in principle, it must be linear or branched. Just as with melting, crosslinked polymers cannot be dissolved. To do so would involve breaking covalent chemical bonds – a chemical change. This means energy-cured polymers cannot actually be dissolved. However, low molecular mass, or other noncrosslinked components of the polymer, may be soluble and extractable from the polymer sample. Many linear or branched polymers also are insoluble because of large amounts of chain entanglement or strong intermolecular forces of attraction, such as hydrogen bonding. What’s next? Having contrasted some of the key properties of low molecular uvebtechnology.com + radtech.org

mass materials from those of polymers, in the next edition of the “Professor’s Corner,” we will look further at structure/property relationships for polymers. We will also begin terminology clarification, seeking to improve communications within the field of energy curing.  Technical questions? What are your technical questions about polymer science, photopolymerization or other topics concerning the chemistry and technology of UV/EB polymerization? Please submit your questions via email directly to Dianna Brodine, managing editor, UV+EB Technology at dianna@petersonpublications.com. References 1. “Professor’s Corner,” UV+EB Technology, 2019 Quarter 1, Vol 5, No. 1, p 5. 2. Malcolm P. Stevens, Polymer Chemistry: An Introduction, 3rd ed., 1999, p. 70.

Byron K. Christmas, Ph.D. Professor of Chemistry, Emeritus University of Houston-Downtown b4christmas@gmail.com

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UV+EB Technology • Issue 2, 2019 | 13


PAINT PERFORMANCE STUDY By Christopher M. Seubert, PhD, Ford Motor Company

The RadTech UV Clearcoat Durability Study: How Paint Performance is Assessed by Ford Motor Company R

adTech and Ford Motor Company have teamed up to conduct an extensive study to evaluate the longterm performance of UV-curable clearcoats designed for exterior and interior automotive applications. This study is intended to follow up on a 2003 study that included in-depth chemical and physical analyses on what was, at the time, state-of-the-art UV-curable clearcoats to determine if they performed well enough for exterior automotive applications.1,2 Cracking/embrittlement during service proved to be a significant issue and demonstrated the limitation of the tested materials. In this new study, coatings from a range of suppliers will be tested to determine if, over the last 15 years, these cracking issues were resolved, if the coatings otherwise degrade in a similar manner and for what type of automotive application (exterior or interior) these coatings are most suited. To assess the weathering performance of these coatings, some specialized analytical techniques and metrics will be used to quantify the degradation and compare the performance of clearcoat systems. This article will discuss these techniques in detail and review why such techniques are needed to evaluate the performance of not only these, but all exterior and interior clearcoat systems evaluated by Ford Motor Company.

Background and methodology In order to achieve >90% customer satisfaction at 10 years in service, an automotive coating must be durable for at least eight years of Florida exposure for vehicles sold in the US and at least five years of Florida exposure for vehicles sold in Europe. This is true for both exterior and interior coatings. Types of coating failures that automotive OEMs are trying to avoid include coating delamination, cracking, blistering, significant color change or loss of gloss. Examples of these types of failures are shown in Figure 1. Photooxidation Weathering failures occur for a variety of reasons, including photooxidation, hydrolysis, additive ineffectiveness, erosion, fracture and adhesion loss. Exposure to sunlight, be it inside or outside the vehicle, can cause chemical composition changes to the coating. When chemical changes become so large that a paint system can no longer cope with mechanical stresses, the paint system fails. To monitor how much a coating changes during weathering, photooxidation is measured using Fourier-transform IR (FTIR) spectroscopy. Transmission FTIR can be used to measure photooxidation within an isolated clearcoat applied to a silicon disc, or photoacoustic FTIR (PAS-FTIR) can be used to measure photooxidation on a sample taken from a coated paint panel.3,4 The mechanism of photooxidation is shown in Figure 2, and ideally would be monitored in all layers of the paint system. Photooxidation is quantified by examining the generic portion of an IR spectrum of the paint layer and measuring the ratio of the (-OH, -NH) area to the (-CH) area, as shown in Figure 3.3 As weathering occurs, the change in this ratio, as shown in Figure 4, gives an indication of how slowly or quickly the coating is chemically degrading. A large change in this ratio could signal that the coating has degraded so significantly 14 | UV+EB Technology â&#x20AC;˘ Issue 2, 2019

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A

B

C

Figure 1: Examples of paint failures including (A) gloss loss, (B) yellowing and (C) delamination.

that mechanical stresses may lead to a catastrophic failure. How much photooxidation a coating can tolerate before a mechanical failure occurs is dependent on the specific coating and use case (exterior, interior, etc.). Fracture energy While chemical degradation is not the direct cause of mechanical failures within a coating system, it does increase the chances that a mechanical failure will occur. However, once the stress in the coating or at an interface becomes larger than the failure stress, a mechanical failure will result. These stresses arise from mismatches in thermal and moisture expansion coefficients, continued crosslinking of the coatings, and physical aging of the coating below the glass transition temperature (Tg). Often it is useful to quantify how susceptible a coating is to mechanical failure, specifically, cracking. One method that can

Figure 2: Schematic of the chemical mechanism of photooxidation in a polymer/coating. Free radicals are formed by light absorption. This is followed by a propagation step where the radical reacts with oxygen. Chain branching then forms PO° and °OH radicals through light/heat reaction. uvebtechnology.com + radtech.org

be used to quantify this material property is the fracture energy measurement.5 By measuring the strain needed to generate cracks within a clearcoated paint panel, and utilizing Equation 1, one can quantify the fracture energy (Gc) of the clearcoat at different stages of the weathering process. The necessary equation and needed material properties are shown below:

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2 In the equation, vf is Poisson’s ratio of the clearcoat, Ef is the modulus of the clearcoat, ɛo is the strain to cracking, h is the clearcoat thickness and g(αβ) is a factor related to the modulus mismatch between the clearcoat and the substrate.6

(1)

While the absolute value of a coating’s fracture energy is important, where anything below 40 J/m2 would likely crack during typical environmental cycling, the rate at which the fracture energy drops during weathering and/or if the rate of decay starts to slow, or even cease, also is important. This behavior, over time, can be used to predict if the coating will crack in the nearterm or if the chemical changes within the coating have slowed enough to keep the fracture energy above the 40 J/m2 threshold and resist future cracking. These types of tests are of particular importance to UV-curable clearcoats, which have a tendency to embrittle and crack in service due to their high crosslink densities.1 Light stabilizers In addition to measuring chemical and physical changes within the coating system, the presence and loss rate of stabilizers, specifically ultraviolet light absorbers (UVAs) and hindered amine light stabilizers (HALS), are of great importance. The effect of these stabilizers on photooxidation rate and degradation varies among coating systems, so it is important to know how long these additives will provide protection for the base resin. UVA loss rate can be measured using isolated clearcoats and a standard transmission UV/VIS spectrometer3 or through use of a UV microscope.7 HALS are a bit harder to monitor and require the use of an electron spin resonance (ESR) spectrometer, as well as a microtome if depth profiles are desired.8,9 page 16  UV+EB Technology • Issue 2, 2019 | 15


PAINT PERFORMANCE STUDY  page 15 exposure dosage that is dependent on where, within the vehicle, the material or coating will be used in-service.

Figure 3: Typical IR absorption spectrum of a paint system (new and old). The generic portion of the spectrum that contains –OH, -NH and –CH information is used to quantify the chemical degradation state of the coating.

Accelerated weathering To monitor the photooxidation, changes in fracture energy and stabilizer loss rate during weathering, a standardized method to weather samples is needed. Natural, outdoor exposure of materials is the most accurate form of weathering. However, to ensure 10year durability is achieved, one needs to expose the same system that will be used in production for eight to 10 years. Any change to the formulation/material requires the weathering “clock” to be reset. To reduce the time needed to obtain the necessary exterior durability data, accelerated weathering machines are used. These devices attempt to accurately recreate outdoor weathering conditions. They utilize a high intensity xenon light source and frequent wet/dry cycles to accelerate the weathering process. If the accelerated exposure does not produce the same chemical changes and mechanical stresses that occur during natural weathering, the test’s usefulness is severely limited. Thankfully, significant work has been done to find light filters and environmental cycles that produce accurate degradation and failure modes,10,11,12,13 all of which were used to create the ASTM D7869 exterior test method. Materials and coatings designed for use on the interior of a vehicle also are tested using accelerated weathering machines using the Ford Laboratory Test Method BO 116-01 protocol. This test employs cycles similar to those described in the SAE J2412 test protocol, but utilizes a glass lantern that surrounds the entire lamp unit to filter out shorter wavelengths of light, similar to the wavelengths filtered out by automotive glazing. This method does employ light and dark cycles, but no water is directly sprayed onto the samples. Materials and coatings must perform over a specified 16 | UV+EB Technology • Issue 2, 2019

Materials and samples For the first part of this study, we talked to a number of material suppliers and requested UV-curable clearcoat formulations that could potentially meet the stringent automotive material specifications for either exterior or interior applications. Eight clearcoat systems were submitted for exterior testing while seven clearcoat systems were submitted for interior testing. Two of the interior formulations were dual-cure systems, while one was a waterborne system. The rest of the submitted systems were monocure. A standard thermoset clearcoat that is commonly used for OEM exterior applications also was obtained and tested. While specific resin chemistry information was not made available, the UV materials are presumed to contain acrylate functional resins and oligomers.

In order to evaluate the rate of photooxidation in each system, a thin layer of clearcoat was applied and cured on an IR transparent silicon disc. Samples for four formulations of each clearcoat system (fully formulated [containing UVA and HALS], UVA only, HALS only and no stabilizers) were made for each submitted system. This is done to determine how each individual stabilizer affects the photooxidation rate of the clearcoat. These samples will be measured using transmission FTIR and will continue to be evaluated as they weather in their respective exterior/interior environments. Photooxidation also will be measured on samples punched from steel (0.5" in diameter) primed panels that were coated with each clearcoat system. Again, samples of each of the four formulations were created and measured using PAS-FTIR. This measurement technique allows quantification of the photooxidation state of the top 8 to 12 mm of the clearcoat layer. Again, these samples will continue to be measured to assess the change in photooxidation state as the materials weather. Primed panels coated with each clearcoat system also were used to assess the fracture energy of each system and formulation. To measure the fracture energy at each exposure time, a full 3x5-inch panel must be destructively measured and analyzed. Due to the large number of panels needed to measure fracture energy of each system and stabilized formulation, only the fully stabilized formulations were measured for each clearcoat system. This allows for a comparison of photooxidation state to brittleness state for the most durable version of each clearcoat system. To assess the UVA loss rate for each coating system, isolated clearcoats of fully formulated and UVA only formulations were applied to quartz slides and weathered. These samples will be measured using a UV/VIS spectrometer to monitor the absorbance page 18  uvebtechnology.com + radtech.org


PAINT PERFORMANCE STUDY  page 16 at 340nm over time. If needed, samples taken from the PAS-FTIR punches may be used to track UVA retention using a UV microscope. This study will not include samples to monitor HALS loss rate due to the complexity of the measurement. Exterior samples will be measured after 750, 1,500, 3,000 and 4,500 hours in the accelerated weathering chamber, which correlates to one, two, four and six years of natural Florida weathering, respectively. Interior samples will be measured after 226 kJ/m2, 601 kJ/m2, 977 kJ/m2, 2406 kJ/m2 and 3609 kJ/m2, each of which represents threshold exposure values for different locations on the vehicle interior. Outlook The analytical techniques discussed here will be Figure 4: Regions of IR absorption spectrum measured and ratioed to used to determine how well current, state-of-the-art quantify photooxidation state of the coating. Notice that, as the polymer UV curable clearcoats perform against automotive photooxidizes, the –OH,-NH region of the IR spectrum grows. OEM coating durability requirements. The results will provide material suppliers much needed data to fine-tune their formulations to create products that can meet Polymer degradation and stability, 72(1), 89-97. 8. Kucherov, A. V., Gerlock, J. L., & Matheson Jr, R. R. (2000). the stringent automotive requirements that exist today for both Determination of active HALS in weathered automotive paint exterior and interior coatings. While some interior UV clearcoats systems: I. Development of ESR based analytical techniques. already meet these standards, those that meet the exterior Polymer degradation and stability, 69(1), 1-9. standards are lacking. Preliminary data are being collected on 9. Gerlock, J. L., Kucherov, A. V., & Smith, C. A. (2001). weathered samples, and the results of this work will be presented Determination of active HALS in automotive paint systems II: at a future RadTech conference (likely RadTech 2020) and/or HALS distribution in weathered clearcoat/basecoat paint systems. published in a peer-reviewed scientific journal.  Polymer degradation and stability, 73(2), 201-210. References 1. Seubert, C. M., Nichols, M. E., Cooper, V. A., & Gerlock, J. L. (2003). The long-term weathering behavior of UV curable clearcoats: I. Bulk chemical and physical analysis. Polymer degradation and stability, 81(1), 103-115. 2. Seubert, C. M., Nichols, M. E., & Kucherov, A. V. (2005). Longterm weathering behavior of UV-curable clearcoats: Depth profiling of photooxidation, UVA, and HALS distributions. JCT research, 2(7), 529-538. 3. Gerlock, J. L., Smith, C. A., Cooper, V. A., Dusbiber, T. G., & Weber, W. H. (1998). On the use of Fourier transform infrared spectroscopy and ultraviolet spectroscopy to assess the weathering performance of isolated clearcoats from different chemical families. Polymer Degradation and Stability, 62(2), 225-234. 4. Gerlock, J.L., Smith, C.A., Nichols, M.E., Tardiff, J.L., Kaberline, S.L., Prater, T.J., Carter, R.O. III, Dusbiber, T.G., Cooper, V.A., and Misovski, T., Proc. 2nd Conference on Service Life Prediction of Organic Coatings, Monterey, CA, ACS, Washington, D.C., November 1999. 5. Nichols, M. E., Darr, C. A., Smith, C. A., Thouless, M. D., & Fischer, E. R. (1998). Fracture energy of automotive clearcoats—I. Experimental methods and mechanics. Polymer degradation and stability, 60(2-3), 291-299. 6. J.L. Beuth, Int. J. Solids Struct. 29 (1992) 1657. 7. Smith, C. A., Gerlock, J. L., & Carter III, R. O. (2001). Determination of ultraviolet light absorber longevity and distribution in automotive paint systems using ultraviolet micro-spectroscopy.

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10. Misovski, T., Nichols, M. E., & Hardcastle, H. K. (2009). The influence of water on the weathering of automotive paint systems. In Service Life Prediction of Polymeric Materials (pp. 295-308). Springer, Boston, MA. 11. Nichols, M., Misovski, T., Henderson, K., Smith, D., Boisseau, J., Pattison, L., & Quill, J. (2009). Understanding, Optimizing, and Measuring Water in Xenon-Arc Accelerated Weathering for Automotive Exterior Coatings. In 4th European Weathering Symposium: Natural and Artificial Ageing of Polymers,” Publication (No. 11, pp. 189-210). 12. Gerlock, J. L., Peters, C. A., Kucherov, A. V., Misovski, T., Seubert, C. M., Carter, R. O., & Nichols, M. E. (2003). Testing accelerated weathering tests for appropriate weathering chemistry: ozone filtered xenon arc. Journal of Coatings Technology, 75(936), 35-45. 13. Nichols, M., Boisseau, J., Pattison, L., Campbell, D., Quill, J., Zhang, J., ... & Misovski, T. (2013). An improved accelerated weathering protocol to anticipate Florida exposure behavior of coatings. Journal of Coatings Technology and Research, 10(2), 153173.

For nearly 20 years, Christopher M. Seubert has been a research engineer with Ford Motor Company in Dearborn, Michigan. He currently leads research efforts to improve LIDAR reflectivity of automotive coatings and materials to support autonomous vehicle development as well as research to reassess the durability and performance of UV/EB materials used in coatings and 3D-printed parts. uvebtechnology.com + radtech.org


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DUAL-CURE INITIATING SYSTEMS By M. Lecompère and X. Allonas, Laboratory of Macromolecular Photochemistry and Engineering, University of Haute Alsace; and D. Maréchal and A. Criqui, Mäder Research

New UV LED Technologies for Carbon-Fiber Reinforced Polymers D

ual-cure initiating systems have emerged as promising alternatives to perform fast and on-demand curing of thick polymers. In this paper, a system based on pyrylium salt as photoinitiator and a hydroperoxide or a vinyl ether as coinitiator is reported to be efficient in the polymerization of epoxide resins. The chemical mechanisms involved are studied by spectroscopic methods. It is found that the interaction between pyrylium salts and coinitiator releases a proton that could initiate the polymerization reaction at room temperature as well as under UV or LED. The combination of both methods allows the polymerization of a thick sample by photoinduced thermal polymerization. With this new, dual initiating system, the photocuring of carbon-fiber reinforced polymers was demonstrated to be possible using a robotized LED at 395 nm. This work opens new opportunities to speed the formation of fiber-reinforced polymer. Introduction Epoxy resins represent an important family of monomers and oligomers widely used in industry. They are particularly interesting for materials exhibiting good mechanical and thermal properties. Fiber-reinforced polymers represent one of the most important current developments using epoxy resin for the manufacture of carbon composites. However, conventional systems based on epoxy resins in this field require long processing times (up to 16 hours) and quite often high temperature for cure (up to 160°C). This represents a severe drawback for productivity, leading to increased lead time, high cost and high energy waste. Photocuring of epoxy resins is quite fast and requires relatively little energy. However, photocuring is highly efficient as far as light can penetrate the medium. Obviously, in the case of carbon-fiber composite, the light does not penetrate the substrate, and only a surface cure is expected to occur. Although it is quite easy to find a cationic photoinitiator to cure the epoxy resin under UV-blue light,1 the situation becomes trickier in the depth of an opaque sample. To overcome this limitation, we tried to develop a new initiating system that can be effective both photochemically and thermally. The surface photopolymerization would release an exotherm, which could

Figure 1. Absorption spectrum of TPP+ (left) and photopolymerization under LED at 395 nm and 365 nm band of a mercury lamp (right).

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thermally decompose the initiator in depth.2-4 This so-called photoinduced thermal frontal polymerization would ultimately be able to cure the carbon composite at room temperature – and within a couple of minutes. For this purpose, the photochemical and thermal initiating ability of pyrylium salts was investigated. We irradiated 2,4,6-triphenylpyrylium tetrafluoroborate (TPP+) in a dicycloaliphatic epoxy resin, and the conversion curve was monitored by Real-Time FTIR. The thermal reactivity at room temperature also was studied in the resin and in the presence of hydroperoxides or vinyl ethers as coinitiators. Finally, the dualcure behavior is demonstrated, allowing the fabrication of a 5 mm-thick carbon-fiber composite by irradiation with a robotized LED at 395 nm. Results and Discussion a) Photopolymerization ability of TPP+ Triphenylpyrylium tetrafluoroborate (TPP+, see structure in Figure 1) is known to be a good photosensitizer. It exhibits an absorption band (lowest transition at 405 nm in acetonitrile) that matches quite well both the 365 nm emission of a mercury lamp and the 395 nm emission band of an LED.5 When using 3 wt% of TPP+ as photoinitiator, the photopolymerization of (3,4-epoxycyclohexane)-methyl-3,4-epoxycyclohexylcarboxylate (EPOX) was found to be quite effective under both LED at 395 nm and filtered Hg lamp at 365 nm (70 mW/cm2). This demonstrates that TPP+ can act as cationic photoinitiator, leading to about 60% of conversion under these experimental conditions. b) Thermal initiation at room temperature A 3 wt% of TPP+ in EPOX leads to the formation of a gel in the dark within three to four hours and a glassy polymer in about one day. To speed the thermal curing, two different coinitiators were employed: hydrogen peroxide (HP) and isobutylvinylether (IBVE).6

Scheme 1 Hydrogen peroxide is able to react with TPP+ according to Scheme 1, leading to the release of a proton. As expected, the proton acts as a reactive species toward EPOX, speeding the curing process. Indeed, a gel time of 15 minutes is observed.7

Scheme 2 In the case of IBVE, a nucleophilic attack of the 2- and 4uvebtechnology.com + radtech.org

As both photopolymerization and thermal polymerization can take place using TPP+, this system is potentially usable to cure fiber-reinforced polymer through a photoinduced thermal frontal polymerization.9 positions of TPP+ occurs, leading to an additional reaction. A reactive carbocation is formed, which could initiate the polymerization of EPOX (Scheme 2). A gel time of 20 minutes is observed in the case of Scheme 2.8 Therefore, when using HP or IBVE, a reactive initiating system is formed, allowing the curing of EPOX within 15 to 20 minutes. As can be seen, TPP+ is an effective thermal initiator, provided that a coinitiator is added to speed the reaction. c) Dual-cure process As both photopolymerization and thermal polymerization can take place using TPP+, this system is potentially usable to cure fiber-reinforced polymer through a photoinduced thermal frontal polymerization.9 A mixture of 3 wt% of TPP+ and EPOX was placed in a silicone mold 12 mm in diameter and 20 mm deep and irradiated with UV (700 mW/cm−2) for one minute. The temperature jump due to polymerization reaction was measured simultaneously by thermocouples at the surface and at different depths in the bulk. Then the light is switched on for 60 seconds, and the temperature profiles are monitored. Figure 2 shows the change in temperature for both systems based on TPP+ (3 wt%), EPOX and coinitiator (either HP at 1 mol% or IVBE at 1.5 wt%). First it can be seen that the surface temperature rises rapidly by virtue of the exotherm of photopolymerization. Secondly, this temperature increase induces a thermal decomposition in depth, and a nice thermal front propagates within the medium. From these curves, a front velocity can be determined to be 21 mm/min for HP and 9 mm/min for IBVE, demonstrating the photoinduced thermal frontal polymerization of EPOX under light. Dual-curing of carbon-fiber composite To avoid a premature gelation of the resin through thermal polymerization during the composite preparation process and page 22  UV+EB Technology • Issue 2, 2019 | 21


DUAL-CURE INITIATING SYSTEMS  page 21

Figure 2. Top: Photoinduced thermal frontal polymerization using TPP+ in EPOX in the presence of a reactive resin for HP as coinitiator (left) and IBVE (right). Bottom: Corresponding velocities of the frontal polymerization.

was operated under vacuum. The total amount of resin was 34 wt%. After infusion, the preparation was irradiated by an LED emitting at 395 nm (FireJet FJ200, 12 W, from Phoseon) with a maximum irradiance peak at 395 nm (FWHM = 15 nm) and mounted on the arm of a robot (Kuka, Figure 3). Irradiation time was two minutes at full intensity. During the irradiation, the surface temperature increased to 105°C as a consequence of the curing process. After 20 minutes of cooling at room temperature, the composite was removed from the mold and analyzed.

Flexural modulus was measured using three-point bending test (ISO 14125). A mean value of 52.4 GPa was found for the carbon-fiber composite, demonstrating the validity of the process. This new initiating system can be used for either opaque fibers or transparent ones. Figure 4 shows the carbon-fiber composite discussed above and a glass-fiber sample made of 20 plies. In our lab, the maximum thickness obtained using this process for carbon-fiber was 20 mm.

Figure 3. Experimental robotized set-up for the irradiation of the composite with an LED.

before irradiation, we used inhibitors. A pot-life of more than one hour can be ensured, leaving enough time for the process. Six plies of carbon fiber (200g/m2) were used for the fabrication of a composite. Infusion of the formulation (3 wt% TPP+, 1.5 wt% IBVE, 1 wt% inhibitor, 94.5 wt% of a modified epoxy resin) 22 | UV+EB Technology • Issue 2, 2019

Conclusion As demonstrated, the dual-cure concept could be considered today as a smart technology for the curing of thick epoxy media. This “cure-ondemand” process opens up new opportunities to improve the manufacturing of carbon-fiber composites within a few minutes. Such systems appear to be promising alternatives to conventional high-temperature processes. 

References 1. S. Shi, C. Croutxé-Barghorn, X. Allonas, Prog. Polym. Sci. (2016) 65, 1-41 2. J. A. Pojman, Polym. Sci.; Compr. Ref. (2012), 4, 957. 3. J. V. Crivello, U. Bulut, J. Polym. Sci., Polym. Chem. (2006) 44, 6750. page 24  uvebtechnology.com + radtech.org


0LZRQ«WKHGHULYDWLRQÁRZV from “Original Beauty” As the leading-edge supplier of the highest market quality materials, Miwon now offers unique Monomers and Oligomers as compliant alternatives (HAP/Toluene - Free materials) to meet increasingly stringent downstream enduse ink, coating & adhesive market formulation requirements. *HW LQ WKH ´ÁRZµ DQG H[SHULHQFH WKH Beauty of Market Compliance with Miwon Products and Technology! Contact toll-free – 1-877-44 MIWON www.Miramer.com


DUAL-CURE INITIATING SYSTEMS  page 22 4. 5. 6. 7. 8. 9.

M. Retailleau, A. Ibrahim, X. Allonas, Polym. Chem. (2014) 5, 6503. M. Lecompère, X. Allonas, D. Maréchal, A. Criqui, J. Photopolym. Sci. Techn., (2017) 4, 399-404. D. Maréchal, X. Allonas, M. Lecompère, A. Criqui, Macromol. Chem. Phys., (2016) 217, 1169-1173. M. Lecompère, X. Allonas, D. Maréchal, Adrien Criqui, Polym. Chem., (2017) 8, 388-395. M. Lecompère, X. Allonas, D. Maréchal, Adrien Criqui, Macromol. Rapid Com., (2017) 38, 1600660. D. Maréchal, A. Criqui, X. Allonas, M. Lecompère, WO2015136180

Figure 4. Example of carbon-fiber and glass-fiber samples obtained using the dual-

cure technology. Xavier Allonas earned a PhD in 1995 and has led the Laboratory of Macromolecular Photochemistry and Engineering at University of Haute Alsace, Mulhouse, France, since 2006. His research interests include photochemistry, polymers and material characterization. Maxime Lecompère, PhD, also at the Laboratory of Macromolecular Photochemistry and Engineering at University of Haute Alsace, researches polymeric materials, 3D printing and dual-cure

24 | UV+EB Technology • Issue 2, 2019

polymerization. D. Maréchal and A. Criqui, both of Mäder Research, Mulhouse, France, also study cationic polymerization, expoxide and pyrylium salt.

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Bringing it all Together. With nearly 6,000 employees in 20 countries, NAGASE supplies innovative, quality materials to the chemicals market globally. We oďŹ&#x20AC;er a wide portfolio of UV/EB raw materials, including cationic and free radical solutions, hybrid grades, acrylamides, thiols, long wavelength and UV-LED active photoinitiators, photosensitizers and more to enhance formulations from coatings to additive manufacturing.

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APPLICATION

3D-Printed Clothing Emphasizes Innovation, Sustainability Edited by Nancy Cates, contributing editor, UV+EB Technology

I

magine a sustainable, low-waste, highly personalized method of designing, fitting and producing clothing and accessories. How? How about with a 3D printer? That’s the concept and goal being pursued by Julia Daviy in her Miami, Florida, 3D Printed Clothing Lab. Daviy, who presented a 3D-printed collection at New York Fashion Week last fall, is committed to reducing environmental impact and sparking creativity with her revolutionary approach to fashion design. This spring, she shared her ideas and designs with attendees at the RadTech BIG IDEAS for UV+EB Technology conference in Redondo Beach, California.

discovered that this method of production is a dead end. We need technology and new approaches to react adequately to challenges in traditional clothing manufacturing. Changing fabrics and dyeing techniques is just not enough.” 3D-printed fashion Daviy explained that the first experiments in 3D-printed shapes and hard materials developed from 2010 to 2014. “I found that

The beginning Daviy said she began out of the desire to create a sustainable method of clothing production and to implement her vision of clothing with new levels of functionality. “I had a lot of curiosity and was continuously asking myself ‘what if’ questions,” she said. “I permitted myself to experiment, make mistakes and not have any specific business in mind.” Daviy, whose educational background includes degrees in environmental science and international economics, previously operated a successful international business and had experience working as a corporate executive in the clean technology industry. That work led to invitations to judge innovation contests and increased curiosity about modern approaches to invention. “I took an online course from the University of Maryland on the creation of innovations,” she said. “My journey in fashion started from launching an activewear line made from organic fabrics and innovative ‘eco-friendly’ dyeing techniques. At that stage, my main idea was to create clothing that followed the highest standards of environmental impact that – at the same time – did not sacrifice design. From a business point of view, I probably should have kept that project and continued to develop it. But, after investigating the situation in each stage of the clothing-making chain, I 26 | UV+EB Technology • Issue 2, 2019

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3D printing in the clothing industry is developing slowly because it needs a combination of knowledge – in traditional clothing design, in 3D modeling and in 3D printing,” she explained. “At that time, we did not have any specialists – probably in the entire world –who had technical knowledge in all three areas. Three years ago, I decided to learn all of these and dove into learning and experimentation.” Design has taken on a new dimension for Daviy. “Current day design in the clothing industry has an absolutely different meaning than it did in the past. It is about the creation of new products – the clothing that will be able to solve problems. It’s also about designing a new, smart and ethical method of production.” Daviy said the traditional methods of fashion industry production involve hard work for little pay. In addition, she said, the methods include unethical treatment of animals, wasted time and resources (about one-third of all fabric made is discarded after patterns are cut) and result in clothing that doesn’t meet current needs. Daviy said feedback from other designers, potential clients and others has run the gamut. “Many fashion designers around the world are writing me,” she said. “Some want to obtain knowledge, some like my approach of using 3D printing for achieving sustainable clothing production, some mention that my works inspired them with their own experimentation, design and work in fashion technology. Others are very far away from 3D printing and cannot even realize what it means to ‘3D-print’ clothing. Recently, when I visited a textile expo, I realized that even people from the clothing industry rarely understand that what we do is actually possible.” Daviy’s process of creating and designing an article of clothing is interactive and, at this stage of development, is considered a luxury segment. “We created a software platform that permits the consumer to feel like a designer. Now we are at the stage of testing it. For example, you may customize your one-of-a-kind 3D-printed skirt and get it made to order. At this first test stage, you can customize length, style, pattern, add pockets and regulate the height of a waist wrap. Launching sales of 3D-printed, madeto-order and digitally customizable garments is an important step for me and my team.” Her work has attracted potential customers who are interested in specific 3D-printed clothes – so many that the lab can’t satisfy all the requests. The lab is involved with research and development projects and also is exploring possibilities with business-tobusiness clients. Meeting future needs During her presentation, Daviy noted that the current global leather market is worth $43 billion (US), with 3.7 billion animals killed for leather, according to Common Objective data. “The page 28  uvebtechnology.com + radtech.org

Top: Models show Julia Daviy’s 3D clothing designs at RadTech’s recent BIG IDEAS conference. Bottom: Sleeve detail of the 3D-printed dress. Photos by Becky Arensdorf.

UV+EB Technology • Issue 2, 2019 | 27


APPLICATION  page 27 leather goods industry is a potential market that can be completely rethought and used for 3D printing companies’ expansion,” she asserted. “We can see that 3D printing can bring a much better experience,” she continued. “Moreover, it is on time. Some 75% of consumers representing Generation Z will choose a product to support an ethical mission that does not create harm. So, to be profitable in the future, you will need to start empathizing with your new generation of consumers. I would say that we underestimate the marketing potential of sustainability itself. It is the fastest growing trend in fashion. It also affects consumption and the way we buy clothing and accessories.” Daviy said ethics and eliminating fur and leather for clothing and accessories is another strong trend. “3D printing is able to bring an absolutely new level of design work – shapes, patterns, colors and textures that are impossible to make in the leather industry. Traditional leather, in comparison, is a boring material. 3D-printed accessories and clothing also means customization, which is impossible in the traditional way of production.” In looking at the global textile industry – worth $804 billion, with 5% growth anticipated this year – Daviy cited other advantages of 3D-printed clothing and accessories:  Smart production, with a transparent and short production chain  Ease of management  Opportunities to create smart clothing and accessories by incorporating wearable electronics  High potential for recycling How does the cost of production compare? “If we will calculate all the prices correctly during the long production and supply chain in the traditional industry,” Daviy said, “then I would not say it will differ today, and I believe the cost will decrease in future.”

We need technology and new approaches to react adequately to challenges in traditional clothing manufacturing. She explained further: “Let’s say a Gucci jacket costs about $3,500. I 3D-modeled and printed a jacket, inspired by this product, with my unique 3D patterns, and the lining and finishing was made by a high-level seamstress who works for luxury brands such as Balenciaga and Chanel. With 3D printing, we got a jacket that is far more unique, of the highest quality of finishing, and at the same time has a trendy, high-fashion look. Is that possible to do for about $3,500 retail? I think, yes.” Obstacles remain in creating 3D clothing, and Daviy and a partner are patenting some potential solutions. “Everyone wants faster 3D printing,” she said, “and I’m not an exception. I dream about 3D printers that are able to create highelastic durable clothes 3D-printed as one single piece without the need for long post-processing and trimming. A much bigger 3D printing volume is essential. I would change the internal design of the STL 3D printer completely.” Her description of the perfect 3D SLA printer? A low 3D printer with a print area of 1 square meter, with a transparent light bath, on the bottom of which the structure is formed using technology similar to the continuous liquid interface production (CLIP). Considering the challenges that continue to slow progress in the 3D-printed fashion industry, Daviy noted issues with decisionmaking, implementation and acceptance of change as factors. “Innovation and 3D-printing challenges need absolutely new kinds of people or artificial intelligence,” she said. “I am afraid that a decade or even longer will be needed in order for the fashion industry to gain understanding, knowledge and desire for the wide use of 3D printing.” Challenges don’t stop progress, though. In her presentation, Daviy noted that files for 3D-printed shoes, among other items, are available online at thingiverse.com. And, on the mass production scale, the technology has developed enough to have 3D-printed wearable products successfully marketed: “For example,” Daviy said, “Adidas did not focus on negatives. It simply produced 100,000 sneakers with 3D-printed midsoles last year.”  For more information about Daviy’s 3D Printed Clothing Lab, visit www.juliadaviy.com.

28 | UV+EB Technology • Issue 2, 2019

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TECHNOLOGY SHOWCASE Phoseon Technology Introduces FireEdge™ FE410 LED Curing Systems Phoseon Technology, Hillsboro, Oregon, announced the FireEdge™ FE410 LED curing product solution with features that deliver up to 50% higher irradiance, power and dose than the original FireEdge FE400. With builtin intensity control options, the FireEdge FE410 can be used for both full cure and pinning applications, such as inkjet pinning, 3D print and adhesives curing. With the segment control feature, FE410 can help users save energy and achieve more precise UV coverage when needed. The air-cooled product offers process stability with Phoseon’s patented TargetCure™ technology to provide users with precise and predictable UV output. Phoseon’s scaling feature allows units to be stacked end-to-end with contiguous, uniform UV output to fit any application size. FireEdge FE410 accessories include cables, power supply, hub unit, window frame options, protective cover glass and extended warranty. For more information, visit www.phoseon.com.

DuraCure “freezes” all colors across the image and maintains a uniform, optimal color brilliance and gloss. For more information, visit www.xeikon.com.

Heraeus Introduces New Generation of Semray® UV LED Series Heraeus Noblelight, Hanau, Germany, introduced the new generation of its Semray® UV4103. It stands out with more power and lighter weight resulting from innovative material combinations. It now is easier to integrate into complex setups, portable machines or onto movable machine parts. The combination of higher power and lighter weight enables higher production speed, saves energy in the process and enhances productivity. In addition, the curing process is faster due to a more powerful UV LED solution, increasing overall production efficiency. The new generation is based on the Semray® UV LED system that offers the flexibility to combine 75 mm segments to cover different curing widths – from single lamps on moveable set-ups to wide curing widths exceeding 250 cm. For more information, visit www.heraeus.com.

ACTEGA North America Launches Dual Care Flexo Inks

Xeikon Introduces Panther DuraCure Xeikon, Eede, Netherlands, has applied to patent its Panther DuraCure UV curing technology for use with Xeikon PantherCure UV inks. The Panther DuraCure curing technology is a unique technique achieving optimal gloss effects in all colors, as well as durability for multiple applications across multiple sectors. Key benefits are consistent curing performance, long-term durability and the lowest possible energy consumption. Working with the Panther UV-Inkjet series of digital presses, the Panther DuraCure curing process operates in a number of ways. UV “pinning” of white keeps the ink from spreading and bleeding into the CMYK inks. UV “pinning” after black following CMYK transfer means 30 | UV+EB Technology • Issue 2, 2019

ACTEGA North America, Delran, New Jersey, has added a dual cure UV and LED flexo ink system to its ACTExact® family. It is designed specifically to meet the requirements of both LED and UV curing systems on press. Printers can reduce the number of ink systems on the floor without sacrificing high performance. This system has shown improved press speeds due to the balanced cure speeds of all of the colors. ACTExact® UV LED Flexo Ink system is formulated to reduce ink spitting and the resulting challenges. Designed for expanded color gamut printing, the system is G7 First 5.0 focused. For more information, visit www.actega.com/press.

SONGWON Presents Expanded Range of Specialty Chemicals SONGWON Industrial Co., Ltd., Ulsan, South Korea, expanded its range of specialty chemicals. Its new water-based (WB) product range is a group of water-miscible products that have been developed to meet the increased demand for environmentally acceptable additives. The company also launched functional monomers. The first two ranges of functional monomers now are available, and a third line is under development. ERM-6100 is uvebtechnology.com + radtech.org


the latest addition to SONGWON’s range of dicyclopentadiene (DCPD) phenol resins. These monomers are mainly used during the manufacture of epoxy composites as epoxy resin modifiers (ERMs) in epoxy chain-extending reactions and as hardeners. The new monomer, which combines high functionality with low viscosity, has been developed especially for electronic applications and high-performance resins such as polybenzoxazine (PBO). SONGWON also has added two bisphenol (BP) monomers to its portfolio. BP-TMC is used to modify epoxy resins as well as nonoptical polycarbonate and polyester polymers. For more information, visit www.songwon.com.

Flexo Technologies Enters UV Flexo Ink Market Flexo Technologies, South El Monte, California, has released UVW91 Radiant White. This UV/LED curable Opaque White is Nestle, REACH and TSCA compliant. While low in viscosity, it exhibits very high opacity, brightness and good cure speed. It has outstanding adhesion to films and paper, and its flexibility allows it to be used for shrink applications. This product complies with CONEG, RoHS and Prop 65 as well. For more information, visit www.flexotechnologies.com.

aperture (NA). Model 2400B-505 light engine can produce over 10 W of radiant flux from a 5 mm-diameter clear aperture with 0.60 NA. LumiBright UV-LED Light Engines are available with wavelengths centered near 365 nm, 385 nm, 395 nm and 405 nm. For photolithography, 435 nm LEDs also are available. For spot curing applications, LumiBright UV LED Light Engines easily couple to liquid light guides for the ultraviolet. For more information, visit www.innovationsinoptics.com.

Wikoff to Offer New Inkjet Primers Wikoff Color Corporation, Fort Mill, South Carolina, launched a new set of five market-proven inkjet primers at InPrint USA in April. Three of the new products are UV primers appropriate for UV inkjet applications like standard adhesion and high adhesion for nonabsorbent substrates, plus a paper-specific primer. The two other products are aqueous primers, formulated for UV inkjet applications on both paper and film, respectively, plus one aqueous primer appropriate for water-based inkjet. Wikoff Digital primers seal absorbent substrates and smooth otherwise rough or uneven substrates. For more information, visit www.wikoff.com. 

Sartomer Invests in In-House EB Labs Sartomer, a business line of Arkema, has launched in-house electron beam (EB) labs with equipment to enable customers to develop and test innovative EB curing formulations on a small scale using Sartomer’s advanced liquid resin solutions. The company has recently installed EB lab units – standalone, compact, simple-to-use electron accelerators – in its France and USA R&D centers. A third installation is planned for its Asia operations. For more information, visit www.sartomer.com.

Innovations in Optics Introduces LumiBright™ UV-LED Light Engines Innovations in Optics, Inc., Woburn, Massachusetts, introduced LumiBright™ UV LED Light Engines, powerful solid-state sources that are being used within OEM equipment applied to photocuring of adhesives and coatings, as well as photomask exposure systems for photolithography. LumiBright™ UV LED Light Engines feature UV die arrays bonded on MCPCB substrates that enhance thermal performance for high current density operation. The specialized primary optic is a nonimaging concentrator made from fused silica, ideal for high power UV flux. With active cooling, the 2400B-405 model can emit greater than 20 W from a 7.5 mm-diameter clear aperture with a 0.66 numerical uvebtechnology.com + radtech.org

Clean Air The SCAQMD is the air pollution control agency in Southern California for all of Orange County and the urban portions of Los Angeles, Riverside and San Bernardino counties. Our mission is to clean the air and protect the health of all residents in the South Coast Air District through practical and innovative strategies.

South Coast Air Quality Management District @SouthCoastAQMD

UV+EB Technology • Issue 2, 2019 | 31


RADIATION YIELD MEASUREMENT By Nicole L. K. Thiher and Julie L. P. Jessop, University of Iowa, and Sage M. Schissel, PCT Ebeam and Integration, LLC

Counting Radicals: Methods to Measure Radiation Yields of Monomers in EB Polymerization Introduction or photopolymerization, many methods exist to determine kinetic parameters, such as quantum yield of photoinitiators and rate of photoinitiation. However, due to the harsh conditions of the electron beam, relatively few studies have examined the kinetics of EB polymerization. Here, two new methods for determining rate of initiation and radiation yield (the number of radicals per 100 electron volts [eV] delivered) are presented, which will enable more detailed kinetic studies of EB polymerization.

F

The major difference in ultraviolet (UV) and electron beam (EB) polymerization lies within the initiation mechanism.1 In a generalized mechanistic description of free-radical UV initiation, a photoinitiator molecule (I) absorbs energy, which causes the photoinitiator to decompose into two primary radical species (R•). One or both radical species can then react with a monomer molecule (M) to form an activated monomer (M•) (Scheme 1)

Scheme 1. The UV-initiation mechanism for free-radical polymerization. Adapted from Reference 1. The resulting rate of initiation (Ri) is described by the following equation:

(1)

where Ia is the intensity of absorbed light (moles of light quanta per liter second) and ϕ is the quantum yield (number of propagating chains initiated per light photon absorbed).1 During EB initiation, ionizing radiation provides sufficient energy to generate primary radicals directly from the monomer molecules: (2) The resulting rate of radical formation (RR) is described by the following equation: (3) where G(R•) is the primary radical radiation yield (number of primary radicals created by 100 eV of energy absorbed by the system), is the density of the system (g/mL), and is the dose rate (kilogray, or kGy).2 Different monomer chemistries are expected to have different radiation yields, or G-values, when exposed to EB, just as photoinitiators have unique quantum yields. Unlike photoinitiated systems, the primary radicals generated by EB often undergo further reactions,3 including: recombination (reaction of two primary radicals to form a small molecule), initiation (reaction of a primary radical and a monomer molecule to form a growing polymer chain), crosslinking (reaction of two 32 | UV+EB Technology • Issue 2, 2019

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primary radicals on the backbone of a growing polymer chain P – R• to form a network connection X), or termination (reaction of a primary radical and a growing polymer chain to form a dead polymer Pn). Other primary radicals will be inherently inert or trapped by the forming network and will not undergo further reactions (Scheme 2).

Table 1. G-values (radiation yields) of possible reactions of primary radicals formed during EB initiation.

G-value

Species

G(R•)

Primary radical

G(M•)

Propagating radical

G(X)

Crosslinking radical

G(t)

Terminating radical

G(n)

Non-reacting and/or recombination radical

radicals, and the yield that is measured is the apparent primary radical radiation yield G(R•)': (6)

Scheme 2. Possible reactions of primary radicals formed during EB initiation. Adapted from Reference 3. Similar to the primary radical radiation yield, each of these possible reactions can be defined in terms of a radiation yield. In general, G(A) is the number of species A created or destroyed per 100 eV of energy absorbed by the system (Table 1).4 In literature, the G-value has been used to define and quantify a wide variety of radiation-induced events from scission and grafting to ionization and gas evolution.5-8 Because the primary radicals can react in many ways, simply calculating the total number of primary radicals does not completely describe the complex system. Thus, the primary radical radiation yield can be described as the sum of the radiation yields of all possible primary radical reactions, as shown in Equation 4. (4) If all the primary radicals further react with monomer molecules to initiate polymerization [i.e., G(R•)=G(M•)], then the rate of initiation (Ri ) can be expressed as (5) The assumption G(R•) = G(M•) is often made, and Equation 5 is used to describe the rate of initiation of EB polymerization.2,3 However, during a typical EB polymerization, all the reactions portrayed in Scheme 2 take place, and Equation 5 may not be valid. To further complicate the matter, measuring the concentration of radicals directly is very difficult. The number of radicals is often determined by adding a compound that will react with any radicals in the system, and that is easily measured via spectroscopy or another analytical technique.2 This method for determining radical concentration will only count the reactive uvebtechnology.com + radtech.org

The apparent primary radical radiation yield only accounts for the radicals that are important to polymerization and network formation. The fraction of propagating radicals [ f(M•)], crosslinking radicals [ f(X)] and terminating radicals [ f(t)] can be determined from the ratio of the G-value of the desired fraction over the apparent radiation yield. For example, see Equation 7. (7) As these three f-values account for all the measurable radicals formed by the EB, their sum is one (Equation 8). (8) These f-values provide insight into network formation and can be used to relate the apparent radiation yield to the rate of initiation as follows in Equation 9: (9) Despite the ability to derive what radiation yield values are important in understanding EB initiation, determining these G-values for EB-initiated polymer systems has proven difficult. After an extensive literature search, the G(R•)' values of only a handful of continuous EB-initiated monomer chemistries have been found.2,9-11 One method used to determine G(R•)' relies on building a kinetic profile (conversion vs. time), calculating the resulting gel fraction and determining of the number-averaged degree of polymerization (Xn).9 Not only does this method require multiple experiments, it is also necessary to make numerous assumptions about network formation, rate of polymerization and termination that may not be appropriate for all systems. As a result, it is desirable to develop a new method to determine G(R•)' and/or G(M•) for EB reactions that is easier to implement and can page 34  UV+EB Technology • Issue 2, 2019 | 33


RADIATION YIELD MEASUREMENT  page 33

(A)

(B)

(C)

Figure 1. Chemical structures of (A) monomer PA, (B) photoinitiator DMP and (C) inhibitor DPPH.

Aldrich). THF was filtered through 0.2 μm nylon filter disks (Cole Parmer) and degassed before use. All other materials were used as received and stored at room temperature.

be used for any monomer that polymerizes via the free-radical mechanism. Other methods for determining G-values have been developed for gamma-initiated systems, but these methods have not been implemented for EB-initiated systems.2 Because gamma-initiated polymerizations typically take place at dose rates that are orders of magnitude lower than those used for EB polymerization, not all methods used for gamma-initiated systems can easily be adapted to EB initiation. Furthermore, in the gamma-initiated polymerization literature, G(M•), G(R•), and G(R•)' are not carefully defined, and the different G-values are often used interchangeably.2 Modification to select methods will allow distinct G-values to be determined for EB-initiation. Determination of the radiation yields and investigation of the kinetics of EB polymerization will help develop formulation chemistry/processing conditions/polymer properties relationships that are lacking in EB-initiated systems. Here, two methods are developed, one to determine G(R•)' and a second to determine G(M•). Comparing the G-values resulting from these methods provides insight into the number and types of radicals that are formed during EB exposure. Experimental Materials The monomer phenyl acrylate (PA, TCI America) was chosen to investigate the radiation yield during EB initiation. Experiments carried out under UV irradiation were photoinitiated by 2,2-dimethoxy-2-phenylacetophenone (DMPA, Sartomer). If an inhibitor was required for the experiment, 2,2-diphenyl-1picrylhydrazyl (DPPH, TCI America) was used. Finally, the solvent used in the experiments was tetrahydrofuran (THF,

Methods Protocol 1 – Measuring G(R•)' Sample Preparation. Formulations of PA with 2% DPPH by weight were prepared and sonicated for 60 minutes. This concentration of DPPH was larger than the concentration of radicals created by the EB to ensure that all of the radicals could react with the inhibitor. After sonication, 100 μL of the formulation was pipetted into aluminum weigh dishes with an 11 mm diameter. The aluminum weigh dishes were secured to Q-panels for easy transport and EB exposure. Electron-Beam Exposure. EB exposure was performed on two different EB units to check for differences in the equipment. An EBLab unit (Comet Technologies, Inc.) and an EB Pilot Line (BroadBeam EP Series, PCT Ebeam and Integration, LLC) were used. The voltage was set at 200 kV, and nitrogen flow was used to reduce the oxygen concentration to less than 200 ppm to minimize the effects of oxygen inhibition. Up to 10 exposure conditions were used for these experiments, all at a consistent dose rate of 197±4 kGy/s. Each Q-panel held three aluminum weigh dishes and was exposed to a unique dose of radiation, while the dose rate was held constant by controlling the line speed. The dose and line speed combinations used for both EB units in this experiment are shown in Table 2.

UV-Vis Analysis. After polymerization, 10 μL of sample from each aluminum weigh dish and 1,000 μL of acetone were pipetted into a cuvette with a path length of 1 cm. The absorbance of each sample was measured at 525 nm using a DU62 Spectrophotometer Table 2. Dose and line speed combinations used to create the kinetic profiles for the inhibition (Beckman). experiments.

Lab Unit Dose (kGy)

200

100

67

50

40

33

29

25

22

20

3

6

9

12

15

18

21

24

27

30

Line speed (m/min)

Pilot Line Dose (kGy) Line speed (m/min)

400

280

240

200

100

80

8

11

13

15

30

38

34 | UV+EB Technology • Issue 2, 2019

Protocol 2 – Measuring G(M•) Raman Spectroscopy of EB samples. Pure PA was prepared for EB exposure using the sample preparation described in Protocol

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1. After polymerization on the EBLab unit, using the dose and line-speed combinations listed in Table 2, the EB samples were transferred to quartz capillary tubes, and Raman spectroscopy was used to determine the conversion. To eliminate error from instrumental variations, a reference peak was used. Previous work has established the reaction peak at 1,636 cm-1 (indicative of the -C=C- bond in the acrylate moiety) and the reference peak at 1,613 cm-1 (indicative of the -C=C- bonds in the phenyl ring).12 Conversion was calculated using the following equation: (10) where Irxn (P) and Iref (P) are the peak intensities of the reaction and reference peak of the polymer, respectively; Irxn (M) and Iref (M) are the peak intensities of the reaction and reference peak of the monomer.13 Raman spectra of the samples were collected using a holographic probe head (Mark II, Kaiser Optical Systems, Inc.) connected to a modular research Raman spectrograph (HoloLab 5000R, Kaiser Optical Systems, Inc.) via a 100-μm collection fiber. A single-mode excitation fiber carried an incident beam of 785 nm near-infrared laser to the quartz capillary tube. Laser power at the sample was approximately 180 mW. Spectra were collected with

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an exposure time of 250 ms and 5 accumulations. Ten monomer and sample spectra were collected and averaged to provide accurate values for Equation 10, and conversions were reported. Real-Time Raman Spectroscopy of UV Samples. Formulations of PA containing five different concentrations of the initiator DMPA (0.1%, 0.2%, 0.3%, 0.4%, and 0.5% by weight) were created and pipetted into capillary tubes. Real-time Raman spectroscopy was used to monitor conversion during illumination with a mercury arc lamp fitted with a 250 to 450 nm filter (Omnicure Ultraviolet/ Visible Spot Cure system, EXFO Photonic Solutions, Inc.) for 30 seconds at an effective irradiance of 1.74 W/cm2 as measured with a radiometer (R2000, Omnicure, wavelength range 250 nm to 1 μm). Spectra were acquired using the same set-up as described for the EB samples. The spectra were collected with 0.5 second exposure time and one accumulation during illumination. Ten monomer spectra were collected before illumination and averaged to provide accurate values for Equation 10. After illumination, conversion was calculated using Equation 10. The conversion data were used to calculate the rate of polymerization (Rp), which is equal to the rate of disappearance of monomer . The instantaneous concentration of monomer ([M]) was determined using the following equation: page 36 

UV+EB Technology • Issue 2, 2019 | 35


RADIATION YIELD MEASUREMENT  page 35

(11) where [M]0 is the initial monomer concentration. A linear best-fit line was drawn through the data points. The absolute value of the slope of the best fit line is equal to Rp. Gel Permeation Chromatography (GPC) of UV Samples. The same formulations of PA and initiator used for real-time Raman analysis were used for GPC analysis. Glass slides were coated with two layers of Rain-X®, glass cover slips were placed on each side of one glass slide to act as a spacer, a second glass slide was placed on top of the cover slips such that the Rain-X coated sides were both facing inward, and the mold was clamped together with binder clips on each end. Each mold was injected with one of the five formulations of PA containing DMPA. The samples were illuminated with a UV belt lamp system (Fusion UV Systems, Inc.) equipped with a mercury arc lamp with an effective irradiance of 1.7 W/cm2. After illumination, the films were removed from the molds and transferred to vials that were filled with tetrahydrofuran (THF) and allowed to dissolve for 48 hours. Finally, the samples were filtered through No. 1 filter paper (Whitman). The filtrate was injected through a 20-μL loop, and THF pushed the sample through the GPC system at a flow rate of 1.0 mL/ minute. The sample was fractionated by a PL-gel 5μm mixed-D column (Agilent, Inc.) before multi-angle light scattering analysis (DAWN HELEOS-II, Wayatt Technology) and refractive index measurements (Optilab T-Rex, Wayatt Technology) were performed. Data analysis gave the number-averaged molecular weight Mn, which was used to determine Xn via the following equation: (12)

(13) Calibration Curve Mixtures of PA containing between 0.015 and 0.03 mol/L DPPH were formulated to build a calibration curve. The absorbance of each formulation with known concentration was measured at 525 nm, the wavelength at which DPPH exhibits maximum absorption. Absorbance (A) was plotted as a function of DPPH concentration ([DPPH]), and the resulting best fit line, from the average of three trials, was determined to be A=81.084 [DPPH] + 0.1513 (Figure 2). Apparent Rate of Primary Radical Formation After calculating the concentration of DPPH for all samples using the UV-Vis calibration curve, the rate of disappearance of DPPH was determined. The concentration of DPPH was graphed as a function of EB exposure time, which is calculated from the line speed and EB window width using the following equation: (14) The slope of the resulting best fit line is equal to the rate of disappearance of DPPH (Figure 3). This procedure was repeated three times, and the resulting rate of disappearance of DPPH was 0.0080±0.0005 mol/L⋅s. Because each molecule of DPPH reacts with one radical, the rate of disappearance of DPPH is equal to the apparent rate of primary radical formation. Apparent Primary Radical Radiation Yield G(R•)' Equation 13 was used to calculate G(R•)' from the apparent rate of radical formation. Because numerous unit conversions are necessary, a sample calculation is provided and explained here:

where Mr is the molecular weight of the repeat unit.1 Results and Discussion Protocol 1 – Measuring G(R•)' Protocol 1 was adapted from a method to determine what was referred to as the G(R•) of monomers initiated with gamma radiation.2 However, the protocol actually measures what has been defined in this paper as G(R•)'. In Protocol 1, inhibitor DPPH was added to the formulations to react with primary radicals. When DPPH reacts with a primary radical, a color change occurs that can be measured using UV-Vis spectroscopy. According to Beer’s Law, this color change is proportional to the change in concentration of DPPH. A calibration curve was built to determine the concentration of DPPH in a sample from the measured absorbance. Because each molecule of DPPH reacts with one radical, the rate of disappearance of DPPH is equivalent to the apparent rate of radical formation (RR'). The apparent radiation yield G(R•)' was then calculated according to the following equation. 36 | UV+EB Technology • Issue 2, 2019

First, the dose was converted from kGy to the SI units J/g. A second conversion was used to transform the energy from J to eV. The volume units in the density term were converted from mL to L. Next, Avogadro’s number was used to convert from a molar basis to a radical basis. Finally, the answer was multiplied by 100 eV so that the reported value would be consistent with the definition of radiation yield. Three trials were conducted on each EB unit, and the resulting G(R•)' values and standard deviation of PA are reported in Table 3. The average G(R•)' values resulting from the three trials was 0.37±0.02 using the EBLab unit and 0.38±0.01 for the Pilot Line. There is no statistical difference between the G(R•)' values of PA gathered using the EBLab unit vs. the EB Pilot Line. Furthermore, page 38  uvebtechnology.com + radtech.org


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RADIATION YIELD MEASUREMENT  page 36 Kinetic Constants in Photopolymerization The typical method to determine the kinetic constants of a photopolymerization requires samples to be polymerized using different concentrations of photoinitiator, which result in different values of Rp and Xn. Because there is no initiator used for EB polymerizations, it is difficult to alter Rp and Xn without changing the formulation or processing conditions. For this reason, the kinetic constants of termination and propagation for this experiment were determined using photopolymerization. Because the propagation and termination steps of EB and UV polymerizations are thought to be the same, the kinetic constants of propagation and termination are also assumed to be the same for both initiation mechanisms. The ratio of the kinetic constants can be related to Rp, Xn, and a constant for chain transfer to the monomer (CM) as follows: Figure 2. Representative plot shows the calibration curve used to calculate concentration of DPPH from absorbance measured using UVVis. The goodness of fit, reported as the R2 value, for the calibration curve was ≥0.9765 for all three trials.

(15) Rp was calculated from real-time Raman data, and Xn was calculated from GPC data. A graph of is shown in Figure 4. A linear best fit line was drawn though the data points, resulting in a slope of 0.031 mol⋅s/L, which is equal to . Thus, the ratio of the kinetic constants needed to calculate the rate of EB polymerization was determined to be 0.062 mol⋅s/L.

Rate of EB Polymerization Because real-time Raman measurements are not possible during EB polymerization, the kinetic profile could not be constructed in the same manner as described for the photopolymerization experiments. Instead, the conversion was determined for individual samples that received increasing doses of radiation. The kinetic profile was then pieced together from the conversion measurements of successive experiments. Once the Figure 3. Representative plot shows the consumption of DPPH with kinetic profile was constructed, the method to determine increasing EB exposure time. The slope of the resulting trend line is R p was followed from the photopolymerization the change in inhibitor concentration with respect to time, which is experiments. The instantaneous concentration of proportional to the apparent rate of radical formation. The goodness of fit, monomer was determined using Equation 11, and Rp was reported as the R2 value, was ≥0.9523 for all three trials. calculated as the absolute value of the slope of the best the error on both EB units is similar. These results indicate that fit line. The disappearance of monomer as a function of time for G-values are not dependent on the EB unit or total dose used to the EB polymerization reaction is shown in Figure 5. A linear best perform the polymerization as long as the dose rate is consistent. fit line was drawn through the data points with greater than 5% conversion and averaged from three trials. Thus, Rp for the EB Protocol 2 – Measuring G(M•) polymerization of neat PA was determined to be 2.5 mol/L⋅s. Protocol 2 was adapted from a method to determine quantum yield of initiators during photopolymerizations.1 In Protocol 2, Propagating Radical Radiation Yield G(M•) • the propagating radical radiation yield, G(M ), was calculated Assuming radical formation reaches steady state, Equation 16 can from Equation 5. To determine the Ri value necessary for this be used to determine the rate of EB initiation as follows:1 calculation, a ratio of the kinetic constants of propagation (kp) and termination (kt), as well as the rate of EB propagation (RP), are (16) needed. 38 | UV+EB Technology • Issue 2, 2019

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Equation 16 was used to calculate Ri, and from that, G(M•) was calculated using Equation 5. Three trials were conducted, and the resulting G(M•) values are reported in Table 4.

Table 3. The apparent radiation yield values resulting from three trials of Protocol 1 for both EB units.

Apparent Radiation Yield, G(R•)' Trial 1

Trial 2

Trial 3

Average

EBLab 0.37 0.39 0.34 0.37±0.02 The average G(M•) value resulting from EB Pilot Line 0.38 0.39 0.37 0.38±0.01 the three trials was 0.33 ±0.05. Using Equation 7, the fraction of propagating Table 4. The propagating radical radiation yields resulting from three trials of Protocol 2. radicals [ f(M•)] is 0.89. EB reactions often result in highly crosslinked Trial 1 Trial 2 Trial 3 Average polymer, so not all of the primary radicals Propagating Radical 0.28 0.38 0.33 0.33±0.05 are expected to initiate polymerization. • Radiation Yield, G(M ) However, Equation 5 is used to calculate G(M•) and is only valid if all the Conclusions primary radicals react with monomer to become propagating Protocols have been developed to determine the apparent primary radicals, which is not the case for EB-initiated polymerizations. radical radiation yield G(R•)' and the propagating radical radiation Furthermore, it was assumed that the kinetic constants of EB yield G(M•) for EB-initiated polymerizations. For the monomer in polymerization were the same as those for photopolymerization. this study, results show that 89% of the primary radicals further Because EB initiation typically results in more highly crosslinked react to initiate polymerization. Using these protocols, G-values of polymers, this assumption may not be accurate. Despite these different monomers can be calculated to determine how monomer assumptions, as expected, the resulting G(M•) value is lower chemistry impacts radical formation. Determining the G-values than the value of G(R•). In future work, it would be ideal to find a method to calculate G(M•) without the assumptions needed in Protocol 2, but these protocols provide a good starting point. page 40 

Hybrid LED+UV

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UV+EB Technology • Issue 2, 2019 | 39


RADIATION YIELD MEASUREMENT  page 39 of different monomers and calculating the fraction of radicals that go on to initiate polymerization will provide insight into the kinetics of EB polymerization. These G-values can be used to help develop the structure/ processing conditions/properties relationships that are currently lacking for EB polymerization.  Acknowledgements This material is based upon work supported by the National Science Foundation under Grant No. 1264622 and The University of Iowa Mathematical & Physical Sciences Funding Program. The authors would also like to acknowledge Kyle McCarthy and Renae Kurpius for their contributions to data collection. Figure 4. A plot of Equation 15 for the photopolymerization of neat PA. References The slope of the linear best fit line was used to determine the ratio of the 1. Odian, G., Principles of Polymerization, fourth ed. John kinetic constants of propagation and termination . The goodness of fit, Wiley & Sons, Inc.: New Jersey, 2004. reported as the R2 value, was equal to 0.93. 2. Chapiro, A., Radiation Chemistry of Polymeric Systems. John Wiley & Sons, Inc.: New York, 1962. 3. Richter, K.B., Pulsed Electron Beam Curing of Polymer Coatings. Proquest: Michigan, 2007. 4. ICRU Report 33, 1980. Radiation Quantities and Units, International Commission on Radiation Units and Measurement: Washington D.C., pp. 25 5. Abraham, R. J., Whiffen, D. H., 1957. Electron Spin Resonance Spectra of Some γ-irradiated Polymers, Trans. Raraday Soc. 54, 1291-1299 6. Ohnishi, S. I., Ikeda, Y., Kashiwagi, M., Nitta, I., 1961. Electron spin resonance studies of irradiated polymers I. Factors affecting the electron spin resonance spectra of irradiated polymers, Polym. 2, 119-141 7. Fessenden, R. H., 1964, Measurement of Short Radical Lifetimes by Electron Spin Resonance Methods. J. Phys. Chem., 68(6), 1508-1515 8. Wilson, J. E., 1974. Radiation Chemistry of Monomers, Polymers, and Plastics. Marcel Dekker, Inc.: New York 9. Labana, S.S., Kinetics of high‐intensity electron‐beam Figure 5. The disappearance of neat PA during EB polymerization. The polymerization of a divinyl urethane. J. Polym. Sci. Part slope of the best fit line through the data points with greater than 5% A-1: Polym. Chem. 6(12), 1986, pp. 3283–3293. conversion was equal to the negative rate of EB polymerization. The 10. Squire, D. R., Cleaveland, J. A., Hossain, T. M. A., goodness of fit, reported as the R2 value, was ≥0.9809 for all three trials. Oraby, W., Stahel, E. P., and Stannett, V. T., Studies in Radiation-Induced Polymerization of Vinyl Monomers at High Dose Rates. I. Styrene. J. Appl. Polym. Sci. Vol 16, 1972, pp. 645-661. 11. Allen, C. C., Oraby, W., Hossain, T. M. A., Stahel, E. P., Squire, D. Nicole L. K. Thiher is working to understand and expand the use R., and Stannett, V. T., Studies in Radiation-Induced Polymerization of electron-beam polymerization as she pursues a doctorate in of Vinyl Monomers at High Dose Rates. II. Methyl Methacrylate. J. chemical engineering at the University of Iowa. Julie L. P. Jessop, Appl. Polym. Sci. Vol 18, 1974, pp.709-725. previously a fauclty member at the University of Iowa, is now a 12. Schissel, S.M., Lapin, S.C., Jessop, J.L.P., Internal reference professor, associate director and Hunter Henry Chair at the Dave validation for EB-cured polymer conversions measured via Raman C. Swalm School of Chemical Engineering at Mississippi State spectroscopy. RadTech Rep. 28(4), 2014, pp. 46–50. University. Sage M. Schissel, previously a graduate research and 13. Cai, Y., Jessop, J.L.P., Decreased oxygen inhibition in teaching assistant at the University of Iowa, is an applications photopolymerized acrylate/epoxide hybrid polymer coatings as specialist at PCT Ebeam and Integration, LLC, Davenport, Iowa. demonstrated by Raman spectroscopy. Polym. 47(19), 2006, pp. 6560–6566.

40 | UV+EB Technology • Issue 2, 2019

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EVENT

BIG IDEAS Bring 300 Attendees to Redondo Beach R

adTech International North America hosted more than 300 participants for the BIG IDEAS for UV+EB Technology Conference, held March 19 and 20 at the Crowne Plaza, Redondo Beach, California. Nearly 70% of event attendees were new registrants – indicating growing interest in the use of curing technologies for 3D printing, food and beverage, automotive and more. Program sets the stage for further innovation Over the course of a day and a half, 49 topics were presented to an eager audience. Tracks divided the sessions by topics that included additive manufacturing, UV in horticulture, data-driven materials, UV for food and beverage safety, and emerging technologies. Presenters included Jason Roland from Carbon, Tim Luong from Ceredrop, Dr. Ellen Lee from Ford Motor Company, Dr. Darryl Boyd from the US Naval Research Lab and Callie Higgins from NIST, among many others. With an emphasis on innovation, sessions focused on new material development for 3D printing; faster and production-capable additive manufacturing; UV disinfection technologies; photoinitiator choices; and equipment advances in electron beam curing. The regulatory environment for curing technologies also was addressed by RadTech’s Rita Loof.

Attendees now can download the event proceedings at www. bigideasconference.com. 2019 RadLaunch class featured in special session RadLaunch is a unique idea accelerator where students, innovators and UV/EB startups are connected to industry leaders through funding, guidance and speaking/exhibiting opportunities. Members of the 2019 RadLaunch class presented during a special session at the BIG IDEAS Conference, bringing their innovative concepts to a larger audience. Presenters included the following: SUNY Albany, SUNY Polytechnic Institute: UV-/EB-curable Sulfluor, a fluorinated hypervalent sulfur containing polymer cured thin film, is extremely hard, thermally robust and patterns well. It may find utility protecting sensor windows, displays, optical fibers, composite material surfaces, electronic devices and other surfaces where scratch resistance, chemical stability and hydrophobicity are important. Laval University (Quebec City, Quebec, Canada) within the Forestry Geomatic and Geography Faculty in the Wood and Forest Science Department: Enhances hardness of Canadian hardwood through impregnation of acrylate monomers and electron beam polymerization. Origin: Building an open material partner network to power innovation in materials for end use and made through additive mass production. Origin’s 42 | UV+EB Technology • Issue 2, 2019

Top: 30 industry suppliers exhibited at the event, sharing their latest technology and service offerings. Middle: Dr. Ellen Lee of Ford Motor Company discussed additive manufacturing opportunities in automotive. Bottom: Michael Gould receives the RadTech President’s Award from Eileen Weber. uvebtechnology.com + radtech.org


Ares Materials: Pylux Polysulfide thermosets â&#x20AC;&#x201C; a class of transparent, optically-clear polymeric materials that allow for tuning physical properties to produce materials which tackle multiple applications â&#x20AC;&#x201C; are specifically engineered for the fastgrowing flexible display markets, such as smartphone makers, displays and display-related fabrication equipment. Daetec, LLC: Protective encapsulant and sealing on substrate, rapid cure for automotive assembly. Polymer compositing with reactive diluents makes it possible to use CAD-fed delivery tools that offer cure on contact, with robotic-operated equipment on vertical, overhead or irregular surface contours.

Jason Roland, Carbon, presents at the BIG IDEAS Conference.

production system uses programmable photopolymerization (P3) to turn materials into isotropic parts and products ready for end use. MicroMaker3D: A new 3D printer for making the unimaginably small, enabling microfabrication-level rapid prototyping for microsensors, wearable technology, IoT devices, micro-robotics, aerospace applications and more.

Volunteers recognized for dedication to industry RadTechâ&#x20AC;&#x2122;s winter meeting was held immediately following the final session of the BIG IDEAS Conference. In addition to the regularly scheduled committee meetings, two volunteers were honored for their years of service and dedication to the UV and EB curing industries. The RadTech Presidentâ&#x20AC;&#x2122;s Award for outstanding leadership and volunteerism was presented Michael Gould of Rahn USA; with Doug DeLong of Doctor UV receiving an appreciation award for his leadership in RadTech efforts on the West Coast. ď ľ

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UV+EB Technology â&#x20AC;˘ Issue 2, 2019 | 43


RUST ELIMINATION By Michael Kelly, Allied PhotoChemical, Inc.

Eliminating Red Rust and Improving Customer Satisfaction I

n today’s manufacturing environment, it is critical to utilize proven technology to eliminate problematic red rust and continue to drive overall customer satisfaction. This can be accomplished with UV coatings technology that delivers improved return on investment for overall business. Over the years, pipe producers have been utilizing liquid coatings to offer short-term red rust protection for their product during storage and shipment to their end-user customers. Too many times, end-user customers of OCTG (oil country tubular goods)/line pipe are dissatisfied with the delivered product – red rust and overall poor coating appearance. Serious quality costs and overall lost opportunity costs are experienced and are very costly to the OCTG/line pipe producer. These costs can be reduced or minimized with the right coating solution. Pipe producer problems: Red rust – Endcustomer returns  VOC (volatile organic compounds) exposure  Flammable coatings in production environment  Overall appearance/performance of coating  Damage to downstream equipment caused by non-dry coatings  Overall, poor ASTM B117 salt fog resistance testing results Some examples of line pipe producerincurred costs:  Actual problem engagement with end customer  Time-to-resolve issue; impact to other business activities  “Charge-backs” for return of product/transportation  Relationship impact  Opportunity costs: lost future orders These problems were very similar in the mechanical tube marketplace. For the past 10 years, mechanical tube producers have evolved their coating processes to eliminate white rust through embracing UV coatings technology. Now it is time for the line pipe producers to make similar upgrades and enhancements to optimize the supply chain to their end-customers.

44 | UV+EB Technology • Issue 2, 2019

Figure 1. Example of red rust on pipe

Figure 2. Another example of red rust on pipe uvebtechnology.com + radtech.org


Current landscape Pipe producers’ legacy systems are typically water-based liquid coatings, with a few solvent-based systems remaining. While water-based coating technology had some advantages in the past, these have been surpassed by the evolution and adoption of UV coatings into this market vertical. Water-based coating technology limitations include:  Legacy coatings have high VOC content  Co-solvents added for improved rheology; flammability issue  Ongoing equipment maintenance: induction heaters, coating buildup on rollers, damage to equipment downstream, etc.  Temperature and humidity impacting quality and performance  Coatings can freeze; must be transported and stored carefully

Figure 5. Pipe coating samples: After 24 hours – ASTM B117 salt fog testing cabinet

UV-based coating technology has the following advantages:  Improved corrosion performance – (see Figures 5 and 6)  No volatile organic compounds / No hazardous air pollutants  Coating cost per linear foot is competitive  Nonflammable  Coatings will not freeze: No winter shipment restrictions Figure 3. Truckload of red-rusted pipe

Figure 4. Pipe coating samples: Coated (before any testing / 0.4 – 0.5 mils dry film thickness / ASTM D 4138) uvebtechnology.com + radtech.org

This article details the following:  Testing - ASTM B117 Salt Fog Testing – Water-based vs. UV Coating o Salt spray test used to produce relative corrosion resistance information for specimens of metals and coated metals exposed in a standardized corrosive environment. o Typically measured intervals – 8 hour / 24 hour / 72 hour / 144 hour / 300 hour / 600 hour  Financial model – Water-based and UV coatings cost per linear foot  UV coating process overview  Looking forward Testing – ASTM B117 Salt Fog Testing Observations: After 24 hours ASTM B117 Salt Fog Testing (Figure 5)  Water-based No. 1 Coating o Coating is offering NO red-rust protection and is merely cosmetic in appearance page 46  UV+EB Technology • Issue 2, 2019 | 45


RUST ELIMINATION  page 45 Table 1. Coating cost per linear foot review:

Figure 6. Pipe coating samples – After 600 hours – ASTM B117 Salt Fog Testing Cabinet

Note: Coating actually started failing at roughly six hours o Coating is flaking  Water-based No. 2 Coating o Some red-rust protection, but limited o Coating is beginning to flake  UV Coating o No presence of red-rust o Good overall gloss level o No coating softening, blistering or flaking Observations: After 600 hours ASTM B117 Salt Fog Testing (Figure 6)  Water-based No. 1 Coating o Total failure of coating  Water-based No. 2 Coating o Total failure of coating  UV Coating o Less than 3% impact o Good overall gloss level o Very minor coating blistering or flaking o Good adhesion (ASTM 3359-17)/ mpact resistance (ASTM 14-88) Financial model: water-based and UV coatings cost per linear foot – 9.625" diameter pipe Outlined at right, Table 1 compares Water-based 1 and Waterbased 2 coatings to UV coating in terms of cost per linear foot. Note: Pricing per gallon is typically determined by coat specification requirements, volumes and contractual commitments. 46 | UV+EB Technology • Issue 2, 2019

Overall, for 9.625" OD Pipe/0.5 mils dry film thickness, UV coating offers savings of $0.0031 and $0.0089 per linear foot. UV coatings/per linear foot, will offer cost savings on a daily, weekly, monthly and yearly production operation – not to mention less incoming freight costs, less material handling, reduced customer complaints, etc. Note:  Water-based 1 coating is 27% coating and 73% water; coverage per gallon is 434.2 square feet at 1 mil thick o 27% of 1,608 square feet = 434.2 square feet @ 1 mil thick page 48  uvebtechnology.com + radtech.org


Go Bomar Ahead. Flex. Oligomers Can Take It. ยฎ

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RUST ELIMINATION  page 46  Water-based 2 coating is 18% coating and 82% water; coverage per gallon is 289.4 square feet at 1 mil thick  UV coating is 100% coating (no water, solvent or fillers); coverage per gallon is 1,608 square feet at 1 mil thick o 100% of 1,608 square feet = 1,608 square feet @ 1 mil thick  Prices are based on customer feedback/competitive marketplace. Water-based coatings have a low price per gallon, but users are paying for 73% and 82% water, respectively, in the case outlined in Table 1. In addition, other factors have significant impact/cost on the bottom line:  Transportation costs  Possible flammability; use coFigure 7. Typical large pipe UV coating line. (Courtesy of Terrell Manufacturing Services, Muskegon, Michigan) Line speed capabilities: 50 to 300 or more feet per minute solvents to assist in rheology (depending on line pipe producer needs/system design). water-based coating faster  Winter shipment rules; cannot ship water-based coatings in extreme cold conditions  Cleaner:  Storage rules; cannot store water-based coatings in near/ o No VOCs or HAPs below 32°F conditions o No co-solvents UV coatings have a higher cost per gallon, since users receive 100% coating, no water, solvent or fillers. In addition, these other factors benefit the bottom line:  Nonflammable  No winter restrictions on shipments  UV can be stored in unheated areas  Shipping costs are greatly reduced – more than 65% less overall  Overall applied coating cost per linear foot price is lower: applied cost of $0.0329 vs. $0.0360 per linear foot In addition to the above-listed benefits, the overall UV coating process offers significant process advantages over other technologies:  Smaller: o Small physical footprint of equipment – (See Figure 7) o No drying tables or temperature/humidity issues  Faster: o Speed: ability to run faster/produce more pipe feet per minute Due to instant cure of coating o Coating is fully dry: no more sticky, un-cured coating that will damage downstream equipment Safety is not compromised when handling pipe: slippage, lubrication effect, etc. Fewer quality rejects 48 | UV+EB Technology • Issue 2, 2019

UV coating process overview The complete UV coating system can be installed with less than 20 feet of in-line space. This includes pre-heat (less than 55°F), reclaim spray booth and UV curing system. Upon exit of UV curing system, pipe can be processed, stacked, band coated, etc., immediately. Looking forward Over the past year, several large line pipe producers have implemented UV coating systems as part of their quality improvement effort, significantly reducing their exposure to red rust/corrosion issues with end customers. It cannot be emphasized enough that UV coatings technology offers significant process advantages, per-part cost savings and improved end-part quality. The line pipe producer community will need to continue to improve its overall end-product quality, and UV coatings technology offers a cost-effective and improved corrosion protection solution, rewarding customers with an improved overall product and greatly enhanced customer satisfaction.  Michael Kelly has years of executive and sales/marketing experience. He is vice president of global sales for Allied PhotoChemical, Inc. and can be reached at mkelly@ alliedphotochemical.com.

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VISCOSITY CONTROL By Kristy Wagner, Red Spot Paint and Varnish

Viscosity Control of Spray Applied Coatings – Balancing Environmental Compliance and Performance Abstract olvent-free, UV-curable coatings can be the first choice for many finishers looking to simplify their regulation processes. However, other options may be available for UV-curable, spray-applied coatings that can maximize process windows and still keep costs and regulatory issues manageable.

S

Introduction To avoid complicated and expensive air permitting, many finishers turn to UV-curable coating technology. A 100% solids formulation will not emit environmentally damaging solvents into the atmosphere. This technology can be successfully employed in many market segments. However, when lower viscosity formulations are needed, there can be added costs due to higher priced/specialty raw materials, narrowed processing windows and /or specialty application equipment. Formulation Typical UV-curable coatings can contain oligomer(s), reactive diluent(s), photoiniator(s), additives and sometimes pigments. Oligomers For free radically cured formulas, a variety of acrylated oligomers exist to provide the proper coating properties. Lower functional aliphatic urethane acrylates provide the best exterior durable properties. With the proper oligomer selection, the coating will not yellow, crack or lose adhesion when exposed to the exterior environment. Polyester acrylates make excellent pigment wetters. Epoxy acrylates can make some of the most abrasion- and heat-resistant coatings. Oligomers will provide the bulk of the coating properties; however, this also is the component that can have the largest effect on viscosity. Some urethane and epoxy acrylates’ viscosities are so high that they must be cut in reactive diluents just to get them page 50  uvebtechnology.com + radtech.org

UV hard coat is applied to polycarbonate headlamp lens via flow coating. Photo courtesy of Red Spot Paint and Varnish. Table 1. Acrylated Oligomer Viscosities Chemistry

Viscosity (20C)

Di-functional Urethane Acrylate

43,930 cPs

1

Hexafunctional Urethane Acrylate

2

35,000 cPs

Epoxy Acrylate3

25,000 cPs (cut 20% in reactive diluent

Polyester Acrylate4

40,000 cPs

1. Rahn, Genomer 4230 2. Rahn, Genomer 4622 3. Rahn, Genomer 2259 4.Allnex, Ebecryl 1871

UV+EB Technology • Issue 2, 2019 | 49


VISCOSITY CONTROL  page 49 Table 2. Irritation of Reactive Diluents – Draize1 Reactive Diluent

Skin Irritation (8 max)

Eye Irritation (110 max)

IBOA (Isobornyl Acrylate)

2-5 (minimal)

15 - 25 (minimal)

TPGDA (Tripropylene Glycol Diacrylate)

2.5 (minimal)

57 (moderate)

PETA (Pentaerythritol Triacrylate)

4.6 (moderate)

109.2 (severe)

TMPTA (Trimetholpropane Triacrylate)

5 (moderate)

46 (moderate)

HDDA (Hexane Diol Diacrylate)

6.2(severe)

16 (mild)

Allnex, A Guide to Safety and Handling of Acrylate Oligomers and Monomers, 2014

1

out of the reactor. Even then, they may require the addition of heat to allow for handling. Some typical oligomer viscosities are listed in Table 1.

orientation and/or prevention of pigment settlement. For some additives, compatibility can be an issue. Polarity of the system may come into play. To help control polarity, choice of reactive diluents is once more key. Also, some additives, such as UV Absorbers (UVAs) and Hindered Amine Light Stabilizers (HALs) can be solids, again relying on solvency of the reactive diluents. Pigments Pigments are used to provide color or special effects to a coating. For an opaque white, high levels of titanium dioxide are typically used. As a rule, the higher concentration of pigment, the higher the viscosity. In addition, matting additives – typically, but not always silica – can be used to lower the gloss of a coating. This can be problematic in solvent-free coatings in two ways: viscosity increase and flat orientation. The majority of fillers used to lower gloss tend to cause a dramatic increase in viscosity. Also, in order for the particles to be effective, they must orient at the surface of the coating. If the viscosity is too high, these particles will be trapped in the interior of the coating and will not have the intended effect of lowering the gloss.

Processing Reactive Diluents UV-curable coatings have the advantage of much shorter Reactive diluents will vary by structure (linear or cyclic) and processing and more compact line designs than conventional functionality (one to six acrylate groups being the most common). coatings. A typical process would be five to 10 minutes in Reactive diluents can greatly enhance the coating’s properties. duration and include: spray, flash, cure. (See Figure 1 for a line They also are the best means to control viscosity. Unfortunately, schematic.) some also can be strong skin and/or eye irritants. Irritancy can be rated on the Draize scale: The higher the number, the more 100% Solids irritating the material. Common reactive diluents and their ratings Without any solvent in the formulation, finishers do not have to are listed in Table 2. Hexane diol diacrylate (HDDA) is one of be concerned with air permitting for volatile organic compounds. the most efficient viscosity reducers; however, it also has one In addition, since there is no solvent to evacuate, flash time of the highest Draize ratings for skin irritancy. Pentaerythritol and temperatures can be shorter and lower. This is extremely Triacrylate (PETA) is excellent for abrasion resistance, but is important when dealing with heat-sensitive substrates, such as categorized as a severe eye irritant. Formulators can be challenged PVC. The purpose of a flash zone in solvent-free coatings would to find the right balance of properties and minimize irritancy concerns for solvent-free Table 3. Spray Equipment Comparison coating systems. Gun Type

Viscosity Range

Cost (Relative)

Photoinitiators Conventional and HVLP 22 seconds (Zahn 1) – 25 seconds $ Photoinitiators are the chemicals necessary (Zahn 2) to start the curing mechanism. They can be Air Assisted Airless Up to 28 seconds (Zahn 3) $$ liquid or solid. When the photoinitiator is Rotary Atomization Up to 45 seconds (Zahn 3) $$$$$$ a solid, solvency in a 100% solids coating formulation needs to be addressed. Again, reactive Table 4. Oligomer Viscosity with Reactive Diluent Reductions diluents are called upon to achieve this task. Oligomer Viscosity 25% HDDA 25% TPGDA 25% IBOA 25% TMPTA Additives Typically, additives can be used for flow and leveling, slip and mar, enhanced adhesion, protection from exterior degradation, pigment

Di-functional Urethane Acrylate (Genomer 4230)

43,930 cPs1

Brookfield DV 1 Viscometer, 60 rpm, 21.5°C 1 spindle RV-7 2 spindle RV-5 3 spindle RV-6

50 | UV+EB Technology • Issue 2, 2019

4,720 cPs2

8,233 cPs3

8,133 cPs3

18,200 cPs1

page 52  uvebtechnology.com + radtech.org


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VISCOSITY CONTROL  page 50 apparent which diluent has the biggest effect on viscosity. As previously mentioned, the use of certain diluents can increase the chance of skin and/or eye irritancy. In addition, some diluents are considered “swelling monomers.” This means that they can attack and etch certain substrates. HDDA, one of the best diluents but higher in skin irritancy, is such an example. Polycarbonate and certain grades of ABS are examples of polymers that can be etched by too aggressive use of diluents/solvents. A blend of diluents is usually employed to balance viscosity, irritancy, cost and performance.

Figure 1. UV line diagram

be for flow and leveling rather than solvent evacuation. However, depending on the properties desired, sprayable viscosities can be difficult or costly to achieve. Table 3 lists various type of spray guns and optimum viscosity ranges. In general, as the ability to spray higher viscosities increases, so does the cost of the equipment. This is important information to consider when applying 100% solids formulations. As previously mentioned, viscosities of acrylated oligomers can be on the high side. To control application viscosity as a formulator, some oligomers with optimum properties may be eliminated due to inability/expense of processing.

Even lower viscosity coatings are critical when spraying low (5 to 7 microns) dry film thickness. If the viscosity is too high, the coating will not have acceptable leveling, leading to orange peel and other surface defects. An extended or higher temperature flash may be required to achieve acceptable appearance, thus adding to process time. Of course, there are mechanical ways to lower the viscosity. Coatings can be heated prior to spraying to lower the viscosity and improve flow and leveling. Some care is required to make sure that excessive heat is not used, nor that the coating be exposed to extended time at elevated temperatures. Doing so can cause degradation of stabilizers and lead to premature polymerization. These options will add cost to the line design. Basic heated coating systems can run $5,000 to $7,000 to install.

Conventional Solvents Conventional solvents can solve a lot of the previously mentioned issues. Much lower viscosities can be obtained with the same amount of organic solvent. Expanding on Table 4, Table 5 compares the same oligomer reduced with either acrylate monomers or organic solvents, all at the same 3:1 reduction rate. Organic Table 5. Oligomer Viscosity with Reactive Diluent and Organic Solvents Reductions solvents also are much more efficient Viscosity 25% 25% 25% 25% Butyl at lowering viscosities. To go one Oligomer 25% IPA (cPs) HDDA TMPTA Acetone Acetate step further, Table 6 shows the ability of certain solvents to achieve similar Di-functional 18,200 1,333 Urethane Acrylate 43,9301 4,7202 460 cPs3 1,193 cPs2 viscosity reductions at much lower 1 2 cPs cPs (Genomer 4230) additions. So, even if solvent-free formulations are not an option, higher Brookfield DV 1 Viscometer, 60 rpm, 21.5°C 1 spindle RV-7 solid versions may be. To bring the coating viscosity down, more reactive diluents may be required. Table 4 lists the viscosity effects of various monomers on one oligomer, Genomer 4230 (Rahn). Each diluent was added to the oligomer at a 3:1 mix ratio. It quickly becomes

2 spindle RV-5 3 spindle RV-4

Table 6. Oligomer Viscosity Varying Amount of Organic Solvent Oligomer

Viscosity (cPs)

25% HDDA

10% Acetone

25% TMPTA

5% Acetone

Di-functional Urethane Acrylate (Genomer 4230)

43,9301

4,7202

5,3402

18,2001

15,7003

Brookfield DV 1 Viscometer, 60 rpm, 21.5°C 1 spindle RV-7 2 spindle RV-5 3 spindle RV-6

52 | UV+EB Technology • Issue 2, 2019

Although the cost of solvents will vary, the majority of solvents used in the coating industry are lower in cost than most reactive diluents. This will, in turn, reduce the cost of the coating. In addition, organic solvents tend to have lower surface tensions than reactive diluents (Table 7). Having a lower coating surface tension can help wet out less than perfectly molded parts, consequently widening the process window and decreasing uvebtechnology.com + radtech.org


Table 7. Surface Tensions of Organic Solvents and Reactive Diluents Solvent / Reactive Diluent

Surface Tension (dynes / cm2)

Isopropyl Alcohol1

21.3

t-Butyl acetate

22.4

1

Butyl Acetate1 Methyl Amyl Ketone

25.1 1

Dimethyl Carbonate

26.1 22.3

Acetone1 1

28.5 29.5

IBOA

2

TPGDA2

32

HDDA

34.5

2

TMPTA2

35

PETA2

38

Eastman Chemical Company Solvent Selector Chart, 2016 2 Eternal Chemical UV Curable Materials Monomers and Oligomers, 2013 1

Table 8. HAP Listed Solvents Benzene

Methyl Ethyl Ketone

Diethanolamine

Methyl Isobutyl Ketone

Ethylene Glycol

Toluene

Hexane

Xylene

Methanol Clean Air Act Amendment of 1990

scrap rates. In addition, for low-gloss coatings, as the solvent evaporates, it carries the silica matting additives to the surface and improves the appearance of matte finishes. As the name suggests, organic solvents also are beneficial when needing to dissolve solid raw materials, such as photoiniators and UVA/HALs. Although organic solvents offer multiple benefits, they are considered destructive to the environment and may require cumbersome permitting and regulations. In addition, there are some solvents that are considered Hazardous Air Pollutants (HAPs). These are solvents that are known to cause cancer and other serious health impacts. Even stricter regulations are required for these materials. A list of some common HAP solvents is in Table 8. Like aggressive reactive diluents, certain solvents can attack sensitive substrates. This likelihood increases as flash time/ temperature increases. Slower evaporating solvents will greatly improve flow and leveling; however, the slower the evaporation, the longer the dwell time in the flash oven – which, consequently, lengthens processing time and can potentially lead to substrate attack. uvebtechnology.com + radtech.org

Weatherable, scratch-resistant clear coat on polycarbonate headlamp lens is UV cured. Photo courtesy of Red Spot Paint and Varnish.

Safety Considerations In general, UV-curable materials have low volatility; however, during spray applications, aerosols are generated that may cause issues if not properly addressed. When at all possible, engineering controls, such as mechanized spraying, should be utilized to minimize human exposure to aerosol mists. Always wear personal protective equipment, as listed in the safety data sheet of each coating. Spray booth equipment must be properly bonded and grounded. If solvents are used to reduce coating viscosity, the area must be explosion-proof as well. Local exhaust/ventilation is imperative to minimize worker exposure to generated vapors. Since UV-curable materials will not cure unless exposed to UV, coating overspray also will need to be addressed. The spray booth can contain either filter media or water. Either system must follow state and local disposal regulations. Another option is to collect overspray to re-use in subsequent applications. If it has been reduced with solvent, solids of the collected overspray will need to be measured and adjusted accordingly prior to re-spraying. Because all coating compositions vary, it always is advised to contact the coating manufacturer for its recommendations on proper engineering controls and to follow state and local regulations. Water Water-reducible UV coatings also can address several of these issues. Water is not under regulation by the Environmental Protection Agency and is not a skin or eye irritant. Many finishers are finding success with aqueous UV-curable coatings. As with all options, there are drawbacks. If the substrate is nonporous, flash times can be longer to ensure evacuation of all the water. Additionally, some co-solvents, which can be subject to regulations, still may be necessary to assist in water evacuation. Although improving, water-reducible oligomer choices are limited, especially if exterior durability is needed. In addition, a limited number of photoiniators and additives are compatible page 54  UV+EB Technology • Issue 2, 2019 | 53


VISCOSITY CONTROL  page 53 Table 9. Flash Points of Organic Solvents and Reactive Diluents Solvent / Reactive Diluent

Flash Point (°C)

Acetone1

-20

t-Butyl acetate

4

1

Isopropyl Alcohol

13

1

27

Butyl Acetate1 Methyl Amyl Ketone HDDA

1

2

39 93

TMPTA2

>100

TPGDA2

>100

IBOA2

>100

PETA

>100

2

Eastman Chemical, Tag Closed Cup Allnex SDS, Cleveland Open Cup

in raw material selections, and finishers must process properly to avoid this problem. Volatile Organic Compound (VOC)-Exempt Solvents By definition, a solvent is considered VOC-exempt if it has reactivity levels lower than or equal to ethane. Such solvents are not considered to increase ground-level ozone concentrations. These materials do not require permitting for emissions. Acetone is the most common VOC-exempt solvent. By using VOC-exempt solvents, finishers can get the benefits of adding solvent to a coating (lower viscosity, lower cost, improved silica orientation, solvency-to-solid formula components, polarity control and lower surface tension) without the burden of the regulations.

1 2

in an aqueous UV coating. As a result, the materials that are available tend to be higher in cost. Since the coatings contain water, storage and shipping conditions are critical in the winter months. If stored or shipped at belowfreezing temperatures, the coating can freeze and must be thawed prior to using. In some instances, this can negatively affect the formulation’s stability. Finally, some aqueous UV coatings can be susceptible to moisture after curing. Formulators must be diligent

But, nothing is a panacea. Since they still are solvents, they will require a heated flash zone. Duration and temperature will vary, based on solvent selection. Most VOC-exempt solvents, like traditional solvents, still will be classified as flammable (flash point below 38°C). Table 9 lists flash points of several solvents and reactive diluents. All flammable materials require proper safety precautions to prevent sparking, fires and/or explosions. There are fewer choices of VOC-exempt solvents as compared with other organic solvents. Acetone has a very high evaporation rate, which can lead to issues during application. Other VOCexempt solvents may be considered to have an offensive odor. Conclusion There is no perfect solution for lowviscosity spray-applied coatings, but there are multiple options. By balancing performance needs, capital investment and regulatory issues, a choice can be made that will optimize output and minimize costs. When one’s priorities are addressed, a UVcurable coating and process can be realized that is profitable to the finisher while minimizing negative impacts on the environment.  Kristy Wagner, who holds a degree in biochemistry from Indiana University, Bloomington, is a UV commercial products senior chemist with Red Spot Paint and Varnish. For more information, visit www.redspot.com.

UV protective clear coat is flow coated onto polycarbonate headlamp lens. Photo courtesy of Red Spot Paint and Varnish.

54 | UV+EB Technology • Issue 2, 2019

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INDUSTRY Sun Chemical Announces Three Employees Honored with NAPIM Awards

Phoseon Donates UV LED Curing System to Sonoco Institute

Three employees from Sun Chemical, Parsippany, New Jersey, were honored with awards during the National Association of Printing Ink Manufacturers’ (NAPIM) annual convention. Patrick Carlisle, the founder of Joules Angstrom U.V. Printing Inks Corp., which was acquired by Sun Chemical in 2017, received the Ault Award, a recognition that honors “outstanding individuals who have played major roles in the progress of the printing ink industry.” Sun Chemical’s Juanita Parris, Ph.D., and Brian Chwierut each were presented with a Pioneer Award, which honors those who have given more than 20 years of service to the printing ink industry through their work with one or several printing ink companies or suppliers, in addition to service work with ink associations, production clubs and other committees. For more information, visit www.sunchemical.com.

Phoseon Technology, a Hillsboro, Oregonbased provider of UV LED industrial curing solutions, will donate LED curing systems to Clemson University’s Sonoco Institute of Packaging Design and Graphics in Clemson, South Carolina. In partnership with OMET Americas, Phoseon is donating FireJet™ FJ605 light sources with Flex Tower and mounting brackets, installed in OMET’s Varyflex narrow-web press. This press is housed in the Sonoco Institute’s Advanced Print Lab. For more information, visit www.phoseon.com.

Arkema Starts a 30% Photocure Resin Production Capacity Increase in China

IST Metz and Heidelberg further expanded their cooperation in the sheetfed offset printing sector. UV unit manufacturer IST Metz will cover the LED retrofit business for various Heidelberg Speedmaster series and manage the handling and installation of the systems directly. IST Metz also will supply LED curing systems for various new machines in the Speedmaster series for small- and medium-size formats. Heidelberg and IST Metz have been working together successfully in the UV printing sector for more than 20 years. For more information, visit www.ist-uv.com or www.heidelberg.com.

Arkema has successfully started up the 30% capacity extension of its photocure advanced liquid resin production plant in Nansha, located south of Canton, China. This new production line will help to meet the strong demand in Asia in the electronics, 3D printing, adhesives and inkjet printing market. The line will produce UV, LED and EB (electron beam) liquid resins, which provide high efficiency and performance benefits to photocuring systems dedicated to high-end applications. The line also will manufacture Sartomer’s ever-expanding portfolio of unique N3xtDimension® resins for 3D-printed products. For more information, visit www.arkema.com.

Henkel Opens New OEM Application Center Henkel Adhesive Technologies announced the opening of its new OEM Application Center in Rocky Hill, Connecticut. The lab expands Henkel’s capabilities to deliver innovative solutions and design customized applications, technologies and production processes. The lab also incorporates audiovisual and interactive telepresence systems, which enable more rapid collaboration and virtual demonstrations with OEM customers, distributors and process operators. The OEM Application Center in Rocky Hill is the third lab of its kind for Henkel, with two other labs located in Western Europe and Asia-Pacific. The new lab was modified to meet the diverse customer needs of the region. For more information, visit www.henkel-northamerica.com. 56 | UV+EB Technology • Issue 2, 2019

IST Metz and Heidelberg to Intensify LED Curing Cooperation

Graphco and GEW Join Forces United Kingdom-based manufacturer of arc and LED UV curing systems GEW (EC) Limited and Graphco of Cleveland, Ohio, a provider of offset, digital and print finishing solutions, signed a distribution agreement covering the Midwestern US, allowing customers in the region access to LED-UV technology to upgrade the capabilities, run-ability and productivity of Left to right: Peter Marszalek (Polpress), their existing sheet-fed Roman Majewski (Polpress), and Chris offset presses. GEW Manley (President of Graphco) has a fully staffed US sales and technical support facility in Ohio. GEW makes heavy use of IoT (Internet of Things) technology, which allows seamless real time technical support from GEW’s technical headquarters. GEW LED UV lamps feature patented lamp cooling technology, maintaining consistent cooling across even the longest VLF lamps. For more information, visit www.graphco.com.

Kopp Glass Releases UV LED Product Database Kopp Glass, Inc., a Pittsburgh, Pennsylvania-based technical glass manufacturer, announced the release of a UV LED product uvebtechnology.com + radtech.org


database that enables users to easily evaluate and select the optimal UV LED for specific applications. With hundreds of UV LEDs available, researching and comparing the various options is a tedious, time-consuming process. This database streamlines the selection process. The comprehensive resource contains more than 700 UV LEDs from 29 different manufacturers – including products from industry leaders such as Seoul Viosys, LG Innotek and Rayvio. The sortable database provides specification data on peak wavelength, product type (chip, COB, SMD, T-Type), product code, radiant flux, forward current, forward voltage and emission angle. For more information, visit www.koppglass.com.

Harris Williams Advises Whitford Worldwide on its Sale to PPG Harris Williams, Richmond, Virginia, a global investment bank specializing in M&A advisory services, announced that it exclusively advised Whitford Worldwide Company (Whitford) on its sale to PPG Industries, Inc. Whitford is a global manufacturer that specializes in low-friction and nonstick coatings for industrial applications and consumer products. Whitford, a privately held company headquartered in Elverson, Pennsylvania, was founded in 1969. Whitford employs more than 700 people and operates

10 manufacturing facilities. For more information, visit www. harriswilliams.com or www.whitfordww.com.

In Memoriam: Dr. Marshall Cleland Dr. Marshall Cleland of Hauppauge, New York, passed away on April 24, 2019. Born in 1926, Cleland obtained his degree in physics from the University of South Dakota and earned his doctorate in nuclear physics at Washington University. Following a year at the National Bureau of Standards, Cleland devoted his efforts to developing high power accelerators. This led to his co-founding of Radiation Dynamics, Inc., and to the development and commercialization of his innovative accelerator, the Dynamitron™. Cleland was awarded 18 US patents and corresponding foreign issuances. He published more than 200 papers and chaired numerous sessions at radiation and accelerator conferences. He also was a member of the American Nuclear Society, the New York Academy of Sciences, ASTM International and the Council on Ionizing Radiation Measurements and Standards (CIRMS), of which he was a co-founder and first president. Among many other honors, the Rad Journal honored Cleland with its Gunderson Award in 2011 for his lifetime contributions to Radiation Safety and Technology. 

NEW FACES IST America Corporation Announces Team Additions IST America Corporation, headquartered in the US in Shorewood, Illinois, announced two new members to its team. Hank Baird returns to IST America after having the opportunity to be Baird Jones the lead operator and lead trainer at Johns Byrne Company in Chicago. Baird’s new role will have him focused on sheeted system sales for new presses and retrofit projects. Matthew Jones, with more than 30 years in sales, will assume the position of national web sales specialist. Jones will focus on the narrow web and wide web markets direct with end users as well as associated OEMs. For more information, visit www.ist-uv.com.

BASF 3D Printing Solutions Appoints Minec as CCO François Minec was appointed chief commercial officer at BASF 3D Printing Solutions GmbH (B3DPS), a wholly owned subsidiary of BASF New Business GmbH (BNB), located in Heidelberg, Germany. He has more than 15 years’ experience in business development in specialty plastics and chemicals. He previously founded the company Advanc3D Materials, which specialized in material solutions for powder bed fusion. For more information, visit www.basf.com. uvebtechnology.com + radtech.org

Harris Joins Allied Allied PhotoChemical, Inc., Macomb, Michigan, created the Sales Operations Group internally to lead its “Customer First” activities. Colin Harris has joined Allied to proactively engage and drive customer satisfaction by focusing on specific customer needs and requirements, then delivering on these. For more information, visit www.alliedphotochemical.com.

Harris

SONGWON Announces Appointments SONGWON Industrial Co., Ltd., Ulsan, South Korea, announced leadership changes. Elena Scaltritti assumes the position as division leader of Industrial Chemicals for SONGWON, which includes the Scaltritti polymer stabilizers and fuel and lubes businesses. Gerard Mulqueen will take on the role of leader, fuel and lubes. Olivier Keiser has been appointed the organization’s first chief sustainability officer. Keiser, who has been with SONGWON since 2011, will continue to head the global procurement and international supply and logistics teams. For more information, visit www.songwon.com. 

Mulqueen

Keiser

UV+EB Technology • Issue 2, 2019 | 57


REGULATORY NEWS

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

PFAS Regulation Update There has been a proliferation of state legislative and regulatory activity involving per- and polyfluoroalkyl substances (PFAS), a class of man-made chemicals used for more than 70 years in a variety of products, such as nonstick cookware, firefighting foam, waterproofing and stain-resistant coatings, and in industrial manufacturing. PFAS in groundwater and drinking water sources have been associated as possible links to negative impacts on human health, including decreased fertility rates, increased risk of certain cancers and impaired immune system function. PFAS used in food packaging have been linked to cancer and organ damage due to migration of the chemicals in the packaging from the wrappers into the food. Although use of PFAS chemicals in manufacturing has decreased with heightened public awareness of their potential harm and expanding state regulation, PFAS continue to persist in the environment. The US Environmental Protection Agency (EPA) has released a broad and fairly detailed PFAS Management Plan. Potentially affected companies must stay abreast of both pending federal action and rapidly evolving state regulatory and legislative initiatives that follow differing approaches to address risks from a variety of PFAS contaminants. Download the PFAS Management Plan at http://src.bna.com/FBy. Pre-Notification Deadline for Chemical Substances in South Korea On Jan. 1, 2019, South Korea’s amendment to Registration and Evaluation of Chemical Substances (K-REACH) came into effect. It requires the registration of all existing chemical substances listed on South Korea’s chemical inventory that are manufactured in or imported into South Korea at greater than or equal to one ton per year. Korea has implemented a phase-in period whereby existing substances that have been “pre-notified” prior to June 30, 2019, will benefit from registration grace periods, similar to the REACH regulation within the European Union (EC 1907/2006). The subsequent registration deadlines are listed in the table below. All new substances must be registered prior to exceeding manufacture or import volumes of 100 kg/year. In addition, any substances designated as Priority Existing Chemicals must be registered prior to manufacture/import. Substance Type

Registration Deadline

>1000 t/y existing substances >1 t/y CMR substances

Dec. 31, 2021

100-1000 t/y existing substances

Dec. 31, 2024

10-100 t/y existing substances

Dec. 31, 2027

1-10 t/y existing substances

Dec. 31, 2030

Foreign manufacturers that export chemical substances to Korea may appoint a Korea-based-only representative to submit pre-notification or registrations. Downstream users and foreign traders cannot submit pre-notifications. Learn more at http://ncis.nier.go.kr/en/main.do. Nestlé Publishes Negative List of Packaging Materials Nestlé published a “negative list” of packaging materials “for which recycling schemes are unlikely to be established.” The company stated that “[t]hese materials will no longer be used in new product packaging and we will also immediately begin phasing them out from existing packaging.” The identified materials and applications include: (a) polyvinyl chloride (PVC) used, for example, in “sleeves, labels, films, trays, printing inks, sealing layers;” (b) polyvinylidene chloride (PVDC) used, for example, as coating on bi-oriented polypropylene (PP) films; (c) polystyrene (PS) used, for example, in “trays, yogurt pots, lids for ice cream cones and coffee cups;” (d) expanded PS (ePS) used, for example, in “trays, pots, tubs, transport protections and sleeves;” (e) regenerated cellulose used, for example, in twist wraps and pack windows; and (f) “non-recyclable plastics/paper combinations,” such as paper/plastic laminates or laminated paper cups. Read more at https://www.nestle.com/asset-library/documents/media/press-release/2019-january/ nestle-action-tackle-plastic-waste-negative-list.pdf.

58 | UV+EB Technology • Issue 2, 2019

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Working Group to Improve Chemical Facility Security and Safety The Occupational Safety and Health Administration (OSHA), US Department of Homeland Security and US EPA created and signed the Chemical Facility Security and Safety Working Group Charter. The working group, which includes other federal agency representatives, was established by an executive order in response to several chemical facility catastrophes. The charter reaffirms the group’s commitment to work with stakeholders to address safety and security at chemical facilities and reduce risks associated with hazardous chemicals to workers and communities. For more information, visit https://www.osha.gov/ chemicalexecutiveorder/.

News from the West Coast

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

UV/EB/LED in Spotlight at SCAQMD The South Coast Air Quality Management District (SCAQMD) once again is proposing changes to its Marine Coatings Rule (R1106). In 2015, staff proposed a similar rule, which the board scrapped in an 8-2 vote in favor of RadTech’s proposal. While only a sector of our membership is involved in marine coatings, RadTech has followed this regulation closely, as some of the issues raised in this proposal – such as test method – may set a dangerous precedent that can have a negative impact on many other UV/EB/LED market sectors. In response to requests from RadTech and many members who submitted letters in support of the Association, the current proposal eliminates most of the burdensome record-keeping requirements, raises the exemption threshold from 10 grams per liter to 50 grams per liter and includes an allowance for the RadTech test method ASTM D7767-11. The issue of using the currently approved American Society for Testing and Materials (ASTM) method for UV/EB thin films is a reoccurring one at the SCAQMD, even according to some of its board members. During the rulemaking for Rule 1106 – Marine Coatings, agency staff stated that ASTM D7767-11 would not be an adequate method for compliance purposes, leaving our association to ask the question: If not ASTM D7767-11, then which method would be used by facilities that are applying thin films to prove they are in compliance with the district rules? Staff recently proposed new language for the exemption language, which now reads as follows: “Exemptions: The provisions of this rule shall not apply to: (1) Marine or pleasure craft coatings that have a VOC content of 50 g/L or less, or its equivalent, less water and exempt compounds, as applied, provided that for energycurable coatings, product formulation data and test results, determined by ASTM D7767-11, shall first be submitted to the Executive Officer by the manufacturer.” At a recent meeting of the SCAQMD, board members expressed support for the UV/EB/LED industry. One board member even told the staff that our business should be welcomed with “open arms.” Here are some highlights of the committee meeting:  Joe Lyou: “We all know that the technology can get us emission reductions, so let’s figure out how to work with them instead of against them and embrace it. … I think we should be welcoming businesses like this with open arms.”  Judy Mitchell: “We think these kinds of coatings are very good, and we want to encourage them. We don’t want to discourage the development of these or the use of these.”  Mayor Ben Benoit: “If we can show a product is this much better than everything else, then why are we putting that kind of a requirement on a business?” The committee hearing (first item on agenda until about 25:33 on the video time ribbon) can be found at: http://www.aqmd.gov/home/news-events/webcast/live-webcast?ms=Ael1jzWesdk. The staff presentation at the last working group meeting can be found at http://www.aqmd.gov/docs/defaultsource/rule-book/Proposed-Rules/1106/par1106_wgm_02_presentation_03-12-19.pdf. The rule adoption hearing was scheduled for early May. Contact rita@radtech.org for additional information. 

uvebtechnology.com + radtech.org

UV+EB Technology • Issue 2, 2019 | 59


CALENDAR MAY

OCTOBER

22-23: The Inkjet Conference USA, Chicago O’Hare, Chicago, Illinois. For more information, visit usa.theijc.com.

3-5: PRINT 19, McCormick Place North, Chicago, Illinois. For more information, visit www.printtechnologies.org.

JUNE

15-16: RadTech Europe Conference & Exhibition 19, Westin Grand Munich, Munich, Germany. For more infomation, visit www.radtech2019.com

2-4: SPE Decorating & Assembly Division TopCon and IMDA Symposium, Franklin, Tennessee. For more information, visit www.plasticsdecorating.com.

SEPTEMBER 15-18: PHOTOPOLYMERIZATION FUNDAMENTALS 2019, Monterey Plaza Hotel & Spa, Monterey, California. For more information, visit www.radtechintl.org/ Photopolymer2019

23-25: Printing United, Kay Bailey Hutchison Convention Center, Dallas, Texas. For more information, visit www.printingunited.com.

NOVEMBER 8-11: Pack Expo International, McCormick Place, Chicago, Illinois. For more information, visit www.packexpointernational.com.

ADVERTISING INDEX Alberdingk Boley ...................................................................... alberdingkusa.com ............................................................................................... 43 American Ultraviolet ................................................................. americanultraviolet.com ...................................................................................... 37 BCH North America Inc............................................................ bch-bruehl.com .................................................................................................... 41 Dymax ........................................................................................ dymax-oc.com/flex............................................................................................... 47 EIT Instrument Markets ............................................................ eit.com .................................................................................................................. 11 Excelitas Technologies ............................................................. excelitas.com .........................................................................................Back Cover GEW........................................................................................... gewuv.com ............................................................................................................ 39 Heraeus ..................................................................................... heraeus-noblelight.com/uvamericas .................................................................. 35 Honle UV America Inc. ............................................................. honleuv.com ........................................................................................................... 5 IGM Resins ................................................................................ igmresins.com/contact ..............................................................Inside Back Cover IST America ............................................................................... ist-uv.com ...................................................................................Inside Front Cover Kao Collins ................................................................................ kaocollins.com ...................................................................................................... 24 Miltec UV ................................................................................... miltec.com ............................................................................................................ 51 Miwon Specialty Chemical Co., Ltd. ....................................... miramer.com ......................................................................................................... 23 Nagase ...................................................................................... nagaseamerica.com/uveb ................................................................................... 25 Phoseon Technology ................................................................ retrofit.phoseon.com ........................................................................................... 19 PRINT 19 .................................................................................... printevent.com ..................................................................................................... 55 RadTech Europe........................................................................ radtech2019.com .................................................................................................. 29 RAHN ......................................................................................... rahn-group.com...................................................................................................... 1 Siltech Corporation .................................................................. siltech.com ............................................................................................................ 13 South Coast AQMD.................................................................. aqmd.gov .............................................................................................................. 31 Ushio .......................................................................................... ushio.com/uv ........................................................................................................ 17

60 | UV+EB Technology • Issue 2, 2019

uvebtechnology.com + radtech.org


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UV + ED Technology Issue 2 2019  

UV + ED Technology Issue 2 2019  

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