Pinholes: They’re a plague for screen printers everywhere. While you can deal with correcting pinholes in post-production, that’s far from ideal. Fixing pinholes takes time and money, and if a print is riddled with pinholes, it might end up in the scrap pile, costing you money. That’s why the best way to deal with pinholes is to prevent them. Here are our 7 best tips for preventing pinholes in your screen printing screens.
1.Start with a clean, degreased screen.
Dust, debris and chemicals on your screens are bound to interfere with your emulsion and result in pinholes. Always clean screens, even brand new screens, or screens that have been left unused for a long period of time. Apply a degreaser with a soft nylon brush, and pressure wash it away. After the pressure wash, rinse with a gentler spray to ensure that a backsplash of chemicals or debris are not clinging to the screen.
2. Avoid exposing screens to dust during drying.
After you’ve washed your screens, you’re not out of the woods when it comes to pinhole-generating dust. Wet screens are dust magnets. The best way to prevent contamination during drying is to dry your screens in a dedicated drying unit. At the very least, dry your screens in a clean, humidity-controlled room. Avoid drying screens with fans, as this can kick dust up into the air, and never dry your screens outside. There are even special vacuums created just for screens that can help suction away the majority of the water that clings to the screen, decreasing drying time and decreasing the chance that dust will cling to the screen.
3. Use quality film and ink when creating positives.
If you don’t start with a good film positive, it’s hard to create a quality stencil that’s free from pinholes. Use a quality printing film, and make sure that it is free from dust, smudges or finger prints that could interfere with ink adhesion. Use an ink that will fully block out the light during exposure.
It’s tempting to buy one emulsion and use it for every project in your shop, but unless you’re always printing on the same substrates with the same ink, you’re putting your screens at risk for pinholes. The emulsion you choose should be suited to your inks and your substrates, or it will break down during press runs, potentially developing pinholes.
5. Apply your emulsion slowly and give it time to dry.
Applying emulsion seems straightforward, and it can be tempting to rush that part of the job, especially if you’re coating a lot of screens at once. Take care when applying emulsion. Applying too quickly can create air bubbles in the emulsion, which will result in pinholes. After mixing your emulsion, allow it to sit for about 15 minutes to allow any trapped air to settle. Apply the emulsion slowly and steadily with a scoop coater, and make sure you’re allowing the emulsion time to fully dry before you expose and washout the stencil.
Incomplete screen exposure creates a weak stencil. A weak stencil can develop pinholes during the washout phase or during the stress of printing. Know the proper exposure time for all of the emulsions you use, and test your exposure periodically. Remember, the bulbs in your exposure unit can weaken over time, which means you’ll need to lengthen your exposure times as your unit ages.
7. Keep your shop clean.
When it comes to pinholes, dirt, dust and chemical cross contamination are the enemy. Keeping a clean shop is crucial for avoiding pinholes. Not sweeping floors, cleaning your press and your other equipment regularly can allow dust to accumulate in the air and land on wet screens or wet emulsion. Dust on the glass of your exposure unit can block UV light during screen exposure, creating pinholes. Have a process in place for keeping the shop clean on a day-to-day basis, and make the time to deep clean your shop on a fairly regular basis.
Pinholes are more than an inconvenience; they can cost your screen printing shop money, either due to prints that have to be scrapped because of pinholes, or in lost productivity due to the time it takes to clean up pinholes on finished prints or tape up stencils that have developed pinholes during press runs. The good news is that pinholes are almost always preventable. You can save your shop the headache and cost of pinholes by practicing proper screen care and proper stencil prep, and by making sure your shop’s environment is free from dirt, debris and potential chemical cross contamination.