Preparing Your Screens the Right Way: Screen Printing Emulsion Techniques and Timing
Once you’ve selected the right emulsion for your print job, it’s time to get your screens ready for stencils!
There are several steps involved in preparing your printing screens, but if you take the time to do it properly and avoid some common mistakes, your screens will have the sharp lines and detail you need to create quality prints.
Step 1: Mixing Your Emulsion
If you’re using the ever popular diazo or dual-cure emulsions, you’ll need to prep your emulsions before you can coat your screens. Preparing your emulsion involves mixing the photosensitizer into the emulsion, either by hand or with a mixer. When doing so, make sure you thoroughly mix the emulsion. Many emulsions come with a sensitizer in a different color, so you’ll be able to see that all streaks have been eliminated and the mixture has been fully combined.
It’s important that you make mixing your emulsion the first step in creating your screens, and leave yourself with a few hours between your mixing time and your actual screen preparation. The vigorous mixing of the emulsion creates air bubbles that can cause pinholes on your screens. Allowing the emulsion to sit in the pot for at least two hours can help to ensure that all of the air bubbles have been released before you apply the emulsion to your screens.
Remember that once the photosensitizer has been added to your emulsion, you’ll have to keep the emulsion away from any UV light.
Step 2: Cleaning Your Screens
Something as small as a piece of dust or an errant string, or grease from your shop worker’s hands can ruin your screen printing run. The best way to avoid odd marks on your screens is to make sure they have been thoroughly cleaned with a degreaser before you apply your emulsion. Once they’ve been washed, it’s best to leave them to dry in a place free from contaminants, like a dedicated drying cabinet.
Step 3: Applying Your Emulsion
Once your emulsion has mixed and settled and your screens are clean and dry, it’s time to apply the emulsion to the screen. Keep in mind that your stencil should sit on the print side of your screen, so as you apply the emulsion, you want to create a solid, even coat on the outside of the screen. With that in mind, you’ll want to apply the emulsion first to the outside of the screen, and then to the inside; the pressure used to apply the emulsion to the inside of the screen will drive the emulsion outward.
The easiest way to apply an even coating of emulsion is to use a scoop coater. You’ll fill the scoop coater with the emulsion and place the screen upright, with a slight tilt away from you — a screen holder can be helpful to hold your screen steady at the right angle. Place the scoop coater at the bottom of the screen, with the blade edge against the screen. Tip the coater so the emulsion builds up against the screen. Applying firm pressure, pull the scoop coater steadily up the screen. Stop about one inch from the top of the screen, rotate the scoop coater back so the emulsion flows back into the coater, then use the blade to sheer the emulsion to the top edge of the screen.
In most cases, one coat of emulsion is adequate. If you need a thicker stencil, such as when printing with white ink or creating a block letter for a jersey, you can apply a second coat of emulsion to the outside of the screen.
Step 4: Drying Your Screens
Once the emulsion has been applied to the screens, it will need to be fully dried before the screens can be exposed. You’ll want to dry the screens in a dark, warm room. Fans can be used to keep the air flowing, but you want to be careful not to introduce dust and debris to your screens. You may also want to use a dehumidifier to keep the air in the room dry. Store the screens lying down, with the outside of the screen down; gravity will help pull the emulsion onto the outside of the screen where you want your stencil. A screen rack is helpful for storing drying screens.
Step 5: Exposing Your Screens
At this point, you should have your artwork positive ready. Make sure that you’re using a high-quality printer and high-quality ink. The ink on the positives must be completely opaque, or it won’t fully block out the light, and the image on your screen will partially cure.
Anatol’s Aurora UV LED exposure unit
exposes screens quickly and efficiently.
Place your screen facedown where you intend to expose it, either within an exposure unit or under a 500-watt utility lamp. Tape your positive into place, and then place a clear piece of glass, Lucite or Plexiglas on top of the positive to hold it firmly against the screen. If the positive isn’t weighted down to the screen to achieve full contact with the screen, light will leak around the positive and expose the area below.
Finally, expose the screen. Exposure times will vary from less than a minute to more than 6 minutes, depending on the type of emulsion and light source you use. Always begin with the emulsion manufacturer’s recommended exposure times. If you feel that your screens aren’t curing fully, gradually increase exposure time. Keep in mind that as the bulbs in your exposure unit or utility lamp age, they’ll become less powerful and you may need to increase your exposure times.
Step 6: Rinse Your Screen
Finally, rinse off your exposed screen to reveal your finished stencil. To do this properly, coat both sides of the stenciled area with water and allow it to sit for just under a minute. Then, spray the screen from the inside to release the unexposed emulsion from the stencil area. With a garden hose attachment or a power sprayer on a low setting, the stencil should release quickly and easily from the screen. If you have difficulty getting the stenciled area cleared, that’s an indication that light made its way through your positive. If the emulsion becomes slimy or runny, that’s a sign that your screen was under-exposed.
Step 7: Check Your Screen
Once your screens have rinsed and dried, hold them up to the light to check the stencil. You should not see pinholes of light coming through portions of the screen that are meant to be solid; you’ll need to fill any holes either with a filler made for that purpose or with tape. Make sure the lines of the stencil are crisp and clear and that all of the fine details are distinct.
If your screen looks good, you’re ready to move on to the printing stage!
Interested in how Anatol equipment can help you prepare crisp screens with more speed and efficiency? Let’s talk about giving your screenmaking department an edge!