Screen Printing with Conductive ink Methodology Report

Screen Printing with Conductive Paint Materials Lab Workshop

Objective The Materials Lab hosted a workshop on screen printing, a simple method of applying printed designs to a paper substrate. Participants learned how to screen print a sensor utilizing conductive paint which was then incorporated into a folded paper lamp. The overall objective for the workshop was the introduction of a new technique, screen printing, and the demonstration of some of the capabilities of a new material, conductive paint, facilitating future student led research and independent prototyping.

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Researchers Advisors Course Semester

Inna Pevzner and Alex St. Angelo Jen Wong and Annie May Johnston Materials Lab Spring 2019

Materials

Tools

Screen Printing:

Screen Printing:

Cardstock Paper - 65 pound, Smooth Finish Conductive Paint - 50ml Jars Silk Screen Frame - Murakami Smartmesh 20’’x24’’ Aluminum Frame

Squeegees Masking tape Scissors

Conductive Circuitry:

Conductive Circuitry:

Conductive Paint - 10ml Pens Light Up Boards Micro USB/USB Power Cable USB Wall Plug

Clear Tape Cutting Mats Utility Knife/Box Cutter Straight Edge Pencil

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Material Notes Silk Screen: The silk screen is a wooden or aluminum frame with a fine mesh of polyethylene fibers. It serves as an extremely fine and precise stencil for ink to be transferred through onto the paper/ designated printable surface.

UV Bed: The UV bed is used to expose the emulsion on the silk screen to ultraviolet rays- causing the emulsion to harden on exposed areas while leaving the areas of the design itself open to allow later transfer of ink.

Bare Conductive Paint: Bare Conductive black paint uses carbon to conduct electricity. It is essentially just like any other water-based paint, except that it conducts electricity. This means that you can paint wires or sensors directly onto almost any material around you, including paper, wood, plastic and glass. The paint is also very importantly nontoxic and easily removed with water.

Bare Conductive Light Up Board: The Bare Conductive Light Up Board is a thin and circular printed circuit board, with six integrated white LEDs and six gold-plated sensor electrodes. It is pre programmed and has several different modes which can be activated by connecting different combinations of electrodes. These modes include touch, dimmer, proximity, candle, spin and dice modes among others.

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Step 1 Creating the Design • • • •

The design for the silk screen can be made both using a hand drawing or a computer generated drawing.

Most importantly, the finalized design lines must appear with a completely solid black color on a Mylar sheet (printed or hand drawn directly on Mylar).

Line thickness should be no less than 0.3 mm (#03 micron pen).

Pens you can draw with include Micron Pens, sharpie markers/pens.

Note: This is a finalized design based on a series of prototypes developed prior to the workshop. To read more about these prototypes and further explorations with different lamp mode configurations and sensor designs see the methodology report appendix.

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Step 2 Preparing the Silk Screen • •

Silk screens vary in size. The rule of thumb for deciding on the correct size is to measure the perimeter of the design and add at least 4’’ on each edge.

Coat screen with photo sensitive emulsion. This should be done in an area not well lit and while emulsion is drying keep screen out of UV light. Let dry for at least 1 hour.

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Step 3 Using the UV Bed • • • • • • • • •

Place Mylar with printed design on the center of the UV bed. Note: UV bed is located in art department ART 2.316.

Place screen on top of the Mylar.

Place rope into frame (indicator for the vacuum action of the light table).

Close and secure cover of UV bed.

Turn on the compressor and suction dials located on the right corner of the table.

Once the indication rope is clearly seen on top of the frame- set timer to 4 minutes, switch dial from LUZ to UV. (The dials located on the left corner of light table).

The UV light will automatically be turned off. Open lid and take out the frame.

Gently rinse the frame using water hose until design appears on screen as smooth lines.

Let the screen dry completely.

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Step 4 Screen Printing •

Place masking tape in the perimeter of the screen so that it masks the area between emulsion and metal edges of the frame. Place screen on wooden board and secure screws on both sides. Place paper/ surface intended to be printed on underneath the screen. Prepare conductive ink paste (consistency should be similar to that of a tacky-glue)

Note: The conductive ink may dry if not used for more than a 6 months from purchase. It is possible to reactivate by dilution with water. The dilution ratio is 1 part of ink to ½ part of water. Mix thoroughly to a consistency resembling one of a Tacky glue.

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Apply ink on the top part of frame. Using a squeegee, press down and sweep ink from top to bottom of frame, repeat at least twice, thicker materials require multiple sweeps.

Carefully lift to separate frame from printed surface. It is possible to repeat the process on additional surfaces up to 5-7 minutes from the moment the ink was applied to the screen.

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Step 5 Cutting Printed Design • •

Cut out printed design for lamp. Completely cut the thin and solid ink lines. Do not cut the thick ink lines. Cut lines are shown in red above in the image above.

Score the back side of the dashed lines for crisp folds. Score lines are shown in red above in the image above.

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Step 6 Positioning the Light Board •

Place light up board on printed cardstock paper. Align electrodes with the corresponding ink lines and mark center point of each electrode with a pencil. This lamp is configured with a sensor, and an on/off switch. The proximity sensor is connected to the E9 electrode. The on/off switch is connected the E1 electrode. Electrodes E2 and E8 are connected with an ink line. Remove the light board from the printed cardstock paper.

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Step 7 Drawing Connections to the Light Board •

Using the conductive paint pen, connect the screen printed lines to the corresponding centerpoint of each electrode as previously marked my pencil. Push the paint with the tip of the pen to ensure an even, well distributed line of paint.

Allow the paint to dry.

Note: The previous two steps are only necessary because we were not able to measure the precise location of each electrode before prototyping the design. The design should have included screen printed paint lines which connected directly to each electrode.

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Step 8 Affixing the Light Board •

Affix the light up board to the printed cardstock paper. Lift the cut paper tabs upwards away from the printed cardstock paper and twist the light up board into place. The light up boards can also be affixed using clear tape.

Note: The cut template for the light up board interfered with the functionality of the electrodes as it was screen printed using conductive paint. “A short circuit happens when the paint bridges paths where it shouldn’t. This can be a connection between your painted switches on the paper template, or across the electrodes on the Light Up Board. If your paint wasn’t dry when you attached the Light Up Board, the twist may have smudged paint across” (Bare Conductive).

This portion of the print could have been done separately with a different screen and non conductive ink. We could have also created a stencil of the cut template, and marked the cut lines with a pencil.

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Step 9 Connecting the Light Board • •

Using the conductive paint pen, connect each electrode to the painted line below using a small dab of paint through the hole at the center of each electrode. Allow the paint to dry.

Carefully insert the micro USB cable into the light board making sure to not break the conductive paint connection between the light up board and the printed paper substrate.

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Step 10 Folding the Lamp •

Fold printed cardstock paper with the three tabs at the left side of the paper inserted into the three corresponding slots at the adjacent piece of paper.

Note: To read more about these prototypes, see the methodology report appendix.

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Step 11 Final Connections •

Plug the USB cable into the wall adapter.

Note: It is important to not touch the ink or light up board when plugging the assembly into a power source. “When the Light Up Board is powered up, it quickly calibrates the sensors depending on its environment. If you are touching the sensors while it calibrates, then the board reads you touching the sensors as its base level and isn’t able to register any actual touches. To avoid this, it’s best practice to first plug in the cable into the Light Up Board, and then power it up” (Bare Conductive).

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Turn on your lamp! When you touch and hold the conductive paint lines connected to electrode E1 you can change the brightness by approaching the conductive paint grid connected to electrode E9. (Image)

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Unresolved Issues Short Circuits: The cut template for the light up board interfered with the functionality of the electrodes. The conductive paint lines were creating a short circuit by bridging certain electrodes that were not supposed to be connected. One solution to this problem was to cut away the portion of the lamp that was interfering with the light up board functionality. The lamp was then assembled by attaching a piece of scrap paper to the back of the opening, affixing the light board and connecting the electrodes to the their respective printed paint lines. The lamp functions successfully as a proximity sensor when modified.

For future iterations of the design, this portion of the print could have been done separately with a different screen and non conductive ink. We could have also created a stencil of the cut template, and marked the cut lines with a pencil. For more information about troubleshooting Bare Conductive products see the attached link: https://www.bareconductive. com/make/light-up-board-troubleshooting/ Dimming Configuration as Designed: The initial intent of the workshop was to have two different types of lamp prototypes: one configured with the sensor mode and a second configured with a dimming mode. The light up board dimming mode configuration like the sensor mode discussed above is calibrated depending on its environment. In the case of the dimming mode, conductive paint is connected to all of the electrodes. Off is controlled by electrode E8, while the lowest level of light is controlled by electrode E9, increasing in order (E10, E0, E1) to the brightest level of light controlled by electrode E2. While the lamp prototype was designed in such a way so the ink lines could be printed in a sequential order from dimmest to brightest, the finalized design involved the power cord crossing three of the drawn ink lines. This might have caused the a short circuit as described above and the lamp never functioned properly. A second successful prototype was created where the power cord did not cross the ink lines. This design however, was painted by hand and was never tested with screen printed ink.

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Next Steps Silk screen printing using conductive ink opens a vast field for experimenting. The layered nature of the silk screen printing process enables the following possibilities to be explored: • • •

Conductive ink can be diluted to achieve the desired conductivity level. It is possible to create surfaces with printed areas of different conductivity. This can be done by using an ink with a different conductivity level to print each (separate) layer on the surface.

Combine non-conductive inks such as Acrylic screen printing inks with conductive ink to create a multi functional surface that will include conductive and non conductive printed areas. This also will allow a wide range of colors to be added to the design.

Vary the color range of the conductive ink itself by mixing it with a white colored acrylic printing ink. Conductivity tests must be performed.

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Images of Conductive Ink on Different Substrates Above (From Top Left - Clockwise) - Card Stock, Wood Veneer, Tyvek, Printer Paper

Appendix Screen Printing on Different Substrates: The printed result of conductive ink differs according to the surface it is printed on.

Technically speaking, the thickness of the substrate material affects the number of sweeps required to achieve a solid, high quality print. In our research we discovered that a minimum of 1 sweep is required for a thin printer paper, whereas no less than 3 sweeps for a wooden veneer sheet. However, It is hard to predict the exact amount of sweeps based only on the material type, therefore, multiple printing tests on the desired substrate material are required to determine the amount of sweeps for an optimal result, especially when the graphical outcome of the print is visible and important to the finalized design.

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Images of Design Prototypes

Appendix Folded Design Prototypes: The lamp design arose from a desire to create a shade utilizing simple cuts and folds. The final design directed the majority of the light from the LED’s out one side while allowing a smaller amount to escape through a smaller aperture at the back. Particular attention was focused on creating smooth folds. Test with a heavier weight cardstock produced a rippling effect on the paper surface when the folds were at too tight of a radius. Scoring the paper surface produced an undesirable overall shape. By using a lighter weight paper, a fold was achieved with the desired radius but without a marred surface texture.

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Images of Sensor Prototypes

Appendix Sensor Design Prototypes: The sensor design was influenced by the Bare Conductive tutorial on sensor design. A selection of the most relevant parameters are listed below. For further information see the attached link: https://www.bareconductive.com/make/sensordesign-basic-rules-of-thumb/. Hatching sensors particularly improves the performance and potential range of proximity detection. When designing a sensor, the ratio of the conductive surface area (sensor) to the size of the object which is meant to trigger (hand) needs to be considered. If you are aiming to create a sensor that detects the presence of a hand, then the outer limit of the sensor should be larger than a hand. In order to make it more sensitive you can reduce the area of the conductive surface.

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