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Reaching for the Next Level in Simulated Process

(March 2007) posted on Wed Mar 07, 2007

Explore how a change in mentality, practice, and process can ease the transition into simulated-process-color screen printing on garments.


By Tom Trimingham

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The big difference in changing up from regular spot-color printing into simulated process is that you'll be printing finer lines and halftone dots. A good way to practice is to simply print a variety of halftone dots in solid blocks from 0-100% and in graduated blends to make sure you're selecting screens that can hold the dots. I always advise companies that are just starting out to avoid really fine dots. Newcomers will find it was easier to hold and print a 42-line/in. halftone than a 55-line/in. one. Remember that you'll want to have at least four threads of mesh per dot, so a, 42-line halftone would require an 180-thread/in. mesh. Check the tension of each screen with a tension meter. It's more important for the screens to be similar in tension than all high tension, but having a tension above 18 N/cm really helps control variables such as screen stretch and color peel-up onto the back of the next screen.

Other things to consider and watch are the exposure system and the washout to make sure you're getting a really good, clean border on the dots in your stencil. Look at the dots through a loupe and check for nice clean edges. If your emulsion looks ripped at the edges or distorted, you will have to adjust the exposure time and possibly the pressure of the washout system. The shirt will never be any better than the films—and subsequently the screens—so it's essential that all of your hard-earned work in the art department is properly reproduced on screen.

The final print

Carefully managing all of the other areas in the workflow really takes the pressure off of the printers. The main difference between simulated printing and conventional spot-color printing is what I call skim-rather-than-smash printing. Using tight screens with fine details requires some practice with the press. Start by going through this checklist and make adjustments where necessary:

1. Make sure everything is level (platens, screens in down position, and squeegees if you're using an automatic press).

2. Check your squeegee blades and sharpen them if necessary. I recommend a 70-durometer squeegee or a triple-durometer 60/90/60 for most simulated-process printing.

3. If you're running a manual press, make sure you practice printing some halftone gradations so that you can be sure you're not crushing out your tonal range. Make your body move like a machine, and try to keep even pressure and speed from side to side and through the length of the stroke.

4. Test your inks. Inks commonly need viscosity reduction for halftone printing. Just be careful you don't adjust the opacity by breaking them down too much. A couple of percentage points in viscosity change go a long way.

5. Find the brightest, low-tack (won't stick in the screen) white available to create a good underbase.

6. Test your flash, and flash just enough to gel the ink and avoid pick up on the next screens.

7. Watch for registration shifts that may indicate the press isn't aligned properly or that a poorly stretched screen is causing excessive screen stretch.

8. Control the pressure! This is often the biggest problem. Remember that detailed printing is more about the careful release of the ink from the screen than smashing it through the mesh. Pressure control will help control dot gain. I've seen manual press operators who can print as good a shirt as an automatic press when they carefully control their squeegee pressure.

The final result

Take time to evaluate your simulated-process results and document the problems, as well as the things that are working. Recording the process is a good final step for ensuring that you'll be able to repeat it for the orders that follow. Don't be discouraged if the first print on the press doesn't look right. Try to determine right away whether a color change or art change is the problem. Often a small color change will give good results when the artwork is prepped and separated on target. Switching from spot-color printing to simulated-process printing can seem like a really big hurdle, but with right mindset, careful preparation, and diligent execution, it can lead to garment prints that will make your company proud and your customers ecstatic.


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