Not all emulsions respond the same when coating screens: some emulsions require adjustments in pressure and speed, depending on the emulsion thickness and the type of mesh on the screen. The end result should give a nice glisten that makes a great stencil for the next screen printing job. Here are everything screen printers need to know about how to coat a screen.
EMULSION DIFFERENCES
There are a couple of different types of emulsions screen printers can use. Presensitized emulsion is highly sensitive, exposes quicker, has a longer shelf-life, and captures fine detail beautifully. Dual-cure emulsion relies on diazo to make it sensitive to light. Adding diazo creates a six-week shelf life for dual-cure emulsions. The emulsion printers chosen depends on their darkroom setups.
Pro Tip: Keep the emulsion in a cool place, like a refrigerator, to extend the shelf life of dual-cure emulsion to eight weeks.
RELATED: WHAT TO KNOW ABOUT PRESENSITIZED EMULSION VS. DUAL CURE EMULSION
DARKROOM CONDITIONS
Every darkroom requires a few things to keep it in the best condition possible. First, the darkroom should be warm, dry, and light-safe. Install yellow or red UV-safe lights, block out all other lights, and invest in a dehumidifier to keep the air in the darkroom dry. Keep the darkroom clean by sweeping and mopping regularly so dust and debris don’t get in the screens as they’re drying. Screens dry best with airflow, so setting up a fan or two to blow across the screens will make a big difference.
A hygrometer is a great tool to help keep track of the temperature and humidity in the darkroom. The best darkroom is around 75°-80°F and under 40% humidity. No UV light shines into the darkroom from doors, windows, or lights. If this sounds like your shop, a sensitive emulsion like Baselayr Complete is a great option. For darkrooms that aren’t as dialed in, a dual-cure Baselayr Long Lasting is much more forgiving and will still create a great stencil.
RELATED: TIPS FOR DRYING SCREENS PROPERLY IN ANY DARKROOM
SCREEN COATING TECHNIQUES
A scoop coater has two sides — a round edge and a sharp edge. The sharp edge is designed to cut the emulsion more, giving the printer more control over the amount of emulsion they coat on the screen.
The round side is more active; it shoves the emulsion and creates a thinner stencil. Due to having less control over the rounded side, printers who feel comfortable in their coating skills will have more luck creating a smooth, glistening coat with the round side.
TWO METHODS TO COAT A SCREEN
There are a couple of different ways screen printers choose to coat screens. One way is to hold the screen in one hand and use the other hand to apply the emulsion via the scoop coater. In this version, use even pressure on the front and back of the scoop coater. Start the screen at an angle and as you bring the scoop coater up the screen, then slowly straighten the screen until it's upright when you finish the emulsion application.
When you flip it over to do the other side, turn it 180°F so the top of your first side of the coating is now on the bottom. On the side that touches the t-shirt, apply two coats of emulsion. On the squeegee side, apply one coat.
Another way to coat a screen is to hold it on the floor and coat it with one hand or use a coating stand and coat the screen with both hands. As long as the action creates an even coat of emulsion, it doesn’t matter which way printers choose to coat screens.
A perfectly coated screen creates a glistening effect. This happens when you hold your screen up to a light and it reflects, no dull areas exist. A glistening screen means the emulsion on top and bottom of the threads has fully encapsulated the threads. It's important that the emulsion is wrapped around the threads because that's how it holds onto the screen.
FINISHING UP
To finish the screen coating process, place the screen in a drying rack. Make sure to lay it with the squeegee side up, and t-shirt side down. The emulsion needs to settle on the t-shirt side to make it a little thicker for the stencil.
Test out coating methods to get the best results. Every darkroom is a little different, and every screen printer has a different preference.