In theory, exposing screen printing screens is fairly straightforward. It all starts with printing (or even hand-drawing) a crisp, dark positive of the artwork you want to print. It’s important to make sure your positive is dark enough to block incoming light; if you hold the artwork up to a light and it shines through, it’s not dark enough. You can layer multiple copies of your artwork to completely block out light, but make sure you align them precisely. In order to make your artwork into a crisp stencil, you need to block out light as carefully and completely as possible.
Next you need to adjourn to your dark room, where you’ll evenly coat a clean screen with photosensitive (responsive to light) emulsion. It’s important to do this in an area where the emulsion won’t be affected by UV light – this doesn’t necessarily mean totally dark, as long as the lights you’re using are UV safe; yellow bug lights are a cheap solution you can find just about anywhere.
An important tool to help you evenly apply emulsion to your screens is a scoop coater, which most screen printing supply companies should be able to provide. Choose one that fits comfortably inside your screen, leaving an inch or two between your coater and the frame. First, carefully coat the print side (the side that will actually be touching the t-shirt), then repeat on the side you’ll be inking. Work your way from the bottom of the screen to the top – it might be a good idea to have a rack to hold your screen in place, it can be a messy process and being able to control the coater with two hands will help you apply emulsion evenly. Depending on your artwork and mesh count, it may be necessary to apply a second coat of emulsion. Let your screens dry completely before exposing them.
Now that you’ve got your screen coated with emulsion, it’s time to turn the artwork into a stencil by exposing it. This means that the emulsion on the screen is exposed to ultraviolet (UV) light and solidified, making any part of the screen the light touches impermeable to ink. By placing your artwork positive between the light source and the screen, the art should block the light from hardening the emulsion, allowing you to wash it out and press ink through the image area.
Any source of UV light will expose a screen (even the sun), but in order to ensure consistency you should have an exposure unit. You can buy one or build one yourself, but keep in mind that different light sources require different exposure times. Your emulsion manufacturer will probably recommend an ideal exposure time, but an exposure calculator is an important tool to have around your shop to help you figure out exactly how long you need to expose your screens to light. Now if you’ve set up your artwork, emulsion and light source correctly, as you expose the screen to light the emulsion should harden everywhere except where the light is blocked by the artwork positive. Make sure the glass of the exposure unit is clean, place the artwork positive on the glass, then align the screen on top of it and expose it to light.
You’re almost there! The next step is to wash out the screen indoors, away from UV light. Using lukewarm water through a hose with a sprayer or a power washer, spray both sides of the screen to remove the soft emulsion from the stencil. Spray the entire screen carefully and evenly, not just the artwork area. If everything’s gone right so far, the stencil should wash away easily, leaving the rest of the screen coated with hard emulsion. Now ink will only pass through the areas you want, and be blocked by the exposed emulsion everywhere else. Let your screens dry thoroughly in a drying rack in your dark room, laying them flat to avoid any leftover soft emulsion or excess water running down the screen.
Now you’ve got screens ready for printing!
Anatol manufactures reliable, innovative equipment not only for pre-press, but for any step in the t-shirt screen printing process. To learn more about how we can help provide perfectly tailored solutions for your operation, contact us!