Handy Tips for Coating Screens
After learning how to create the best environment for drying screens, now it's time to learn the best practices for coating screens. Screen printing expert Colin Huggins shows what to look for when coating screens to get the best emulsion coverage. 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 you're working with on your screen. You want the end result to a nice glisten that makes a great stencil for your next screen printing job.
DIFFERENCES IN EMULSIONS
All emulsions vary in their consistency. Some emulsions are like honey. The honey-like emulsion is thick and sticky, so if a printer coats the emulsion on quickly, they'll end up hydroplaning across the screen, leaving a thick layer. For this kind of emulsion, a printer would need to coat slowly, it would cut easily and lay down a thinner deposit. Other emulsions don't have this issue: they're able to maintain more body and shape as a printer coats a screen. All in all, it's best to always test the emulsion you are using with the different edges of the scoop coater.
SIDES OF THE SCOOP COATER
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 emulsion like a bull nosing around for food. Due to having less control on the rounded side, printers who feel comfortable in their coating skills will have more luck creating a smooth, glistening coat with the round side.
ANGLE AND PRESSURE WHEN USING THE SCOOP COATER
When applying the scoop coater to the screen, you can either put more pressure on the back of the scoop coater or on the front. If you put more pressure on the back, it permits the coater to cut more. If you put more pressure on the front, it will influence how much emulsion is pushed through the mesh and how much is cut.
You can coat a screen in two ways. 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. You will start the screen at an angle and as you bring the scoop coater up the screen, you will 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° so what was the top of your first side of 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.
You'll know if you coated a screen beautifully if the glisten effect happens. The glisten effect is when you hold your screen up to a light and it reflects, no dull areas exist. The glisten means the emulsion on top and bottom of the threads have fully encapsulated the threads. It's important that the emulsion is wrapped around the threads because that's how it holds onto the screen.
When you're done, put the screen in your drying rack. Make sure to lay it with the squeegee side up, t-shirt side down. The emulsion needs to settle on the t-shirt side to make it a little thicker for the stencil. When you're on press, you'll be able to lay down a good layer of ink.
COATING THIN THREAD VS. STANDARD THREAD
Thin thread has thinner thread compared to standard mesh (shocking, I know). Due to the thinner thread, the open areas between threads are wider. The wider gaps means it's easier to push inks and emulsion through it. Since the spaces are bigger, it's easier to put too much emulsion on the screen. Thicker emulsions will affect your exposure time. To avoid putting too much emulsion on the screen, apply one coat to each side of the screen.
The holes in standard thread are smaller since the threads are thicker. To ensure you have the perfect EOM, apply two coats on the t-shirt side and one coat on the squeegee side.
Overall, there are a ton of ways you can coat a screen with emulsion. In the end, you want to ensure that the screen has enough emulsion on it where the printer will see the glisten effect. Join us next week where Colin will address film and exposing. Make sure you subscribe to Ryonet's YouTube channel and set up notifications so you don't miss the next video.