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Screen Printing: Production
Optimizing White InkThese five factors play a major role in successfully printing with this ink color.
I visit many screen-printing shops around the country — both small and large facilities — and one of the biggest, and costliest, issues that challenges screen printers is working with white ink. Sure, everyone prints with it, but are they doing so correctly?
Following are five factors to consider to ensure you are printing the best-possible designs using this ink color.
1. Proper Mesh Selection: Coverage and image detail are the main factors in mesh selection. Nearly every shop I visit uses 110 mesh for its underbases, which I always question. In response, I’m often told that it results in better coverage or the ink is too thick to pass through a higher mesh count.
While sometimes true, this is not the real issue when printing using a premium white ink. Such inks have undergone hours of testing and development on press in laboratories, as well as beta tests at screen-printing shops, before being released to market.
2. Screen Coating: Minimal stencil thickness, or complete lack thereof, is the primary cause of failure for most printers using white ink. If you cannot feel the image area on the screen’s substrate side, you will never get a proper ink laydown. “Emulsion Over Mesh” (EOM) is the commonly used term for having the proper amount of emulsion thickness on the screen. It’s ideal to have an ink well on the substrate side, as this is a major factor in the amount of ink being laid down.
One topic that always is up for debate is whether to use the sharp or rounded side of the scoop coater. I prefer the latter because it gives you a proper emulsion coating starting on the screen’s substrate side.
Also, remember to dry emulsion with the substrate side down. Coating with the sharp edge basically scrapes off the emulsion. If you ever have seen or used an automatic screen coater, the troughs always have a rounded edge for this reason.
3. Press Setup: Even if the mesh is correct and you have a perfect screen and stencil, incorrect press setup will lead to problems.
Many printers use too much squeegee pressure because they mistakenly think more is better. It’s ideal to print with enough pressure (25-40 psi) to shear off the ink and clear the screen, leaving the ink on top of, rather than pushed through, the garment.
Other contributing factors are squeegee angle and speed. With proper pressure, 15-20 degrees is ideal for shearing the ink.
Today’s inks are formulated to run at high production speeds, disproving the theory that a slower print stroke equals better ink deposit. Squeegee selection is determined by the mesh count, image detail and the viscosity of the ink with which you are printing. A triple-durometer squeegee, such as a 60-90-60, typically works well for white or gray underbases and a 70/90/70 durometer is good for any top colors. But it still remains a personal choice.
4. Flash Temperatures and Time: Mesh selection and screen/print setup are the main contributing factors in flash time and temperature. If these two things are done correctly, you should have the proper ink-film thickness and, as a result, attain a quick flash time. This can increase production.
If you have a thick ink deposit, you will need a longer flash time, which can lead to scorched garments. It also can negate a true ink-film flash cure or even possibly cure the ink, which will lead to the top colors washing off during laundering.
If printed properly, most of today’s white inks will flash at 265˚F in about 1.5-3 seconds, which leads to faster production times and more jobs completed in a day.
5. Cure Time and Temperature: This is where you should reference the ink manufacturer’s recommendations since there are so many different types of white ink available for printing on cotton, 50/50 blends and polyester. White-ink manufacturers have developed different formulas designed to meet specific needs, incuding all-purpose plastisol, fast-flashing, low-bleed and low-cure options. Most will have different settings for their products.
White-ink printing does not have to be the battle that most print shops face on a daily basis. With a little knowledge and practice, you can better perform this technique in no time.
Mark Suhadolnik, who has more than 30 years of experience in screen printing, is the print applications specialist with Graphic Solutions Group (GSG) where he does research and development, product development and product testing. For information or to comment on this article, email Mark at email@example.com.
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