Lesson Two in Screen Printing!
After you’ve degreased your new screens, its time to coat them. Coating simply means to cover your mesh with emulsion. Once the emulsion dries your screen is ready to be exposed! All emulsions are light sensitive and when they are exposed to UV rays there is a chemical reaction which causes the emulsion to become hard. Any area that is not exposed to UV rays (due to blocking light with the black ink of your transparency) will remain soft and can easily be washed out – thus creating your printable stencil!
We use the CCI ProChem Dual Cure Diazo Emulsion which works with both waterbased and plastisol inks. This emulsion is more reliable and won’t break down as fast as other emulsions because it’s resistant to water and cleaning solvents. Some emulsions come pre-sensitized to light, however the CCI ProChem Dual Cure Diazo Emulsion needs to be sensitized by you before it can be used. This is a fairly simple process and allows you to have more control over the product(s) you’re using. A Diazo Sensitizer and some distilled water is all you need!
ALL OF THESE STEPS NEED TO BE DONE UNDER UV SAFE LIGHTS / BUG LIGHTS
Step One: Sensitizing the Emulsion
1) Mix about 3/4 of distilled water into your Diazo Sensitizer and shake until the powder has completely dissolved.
2) Then mix your dissolved liquid into your emulsion, trying to avoid adding too much air as you stir.
3) After most of the streaks have gone and you feel confident its been mixed thoroughly, allow it to stand for 2 hours.
After most of the bubbles have risen and the chemicals have had time to blend into your mixed emulsion, you’re ready to coat!
While I am using the floor of our darkroom to coat our screens, we suggest that you use a screen coating stand. This will provide more consistent and accurate results in your coating. You’re also going to need a Scoop Coater which is the tool that holds your emulsion while you’re coating.
Step Two: Coating your Screen (always use a newly degreased screen!)
1) Fill your Scoop Coater with sensitized emulsion.
2) Starting on the outside or “Print” side of your screen, lay your coater against the mesh, tilt it to a 90º angle and wait for the emulsion to touch your screen (this is called a bead).
3) When the bead reaches your mesh, slowly but firmly apply pressure and pull the coater up towards the top of your screen.
4) Once you reach the top you’ll need to do a sawing motion to separate the emulsion in the coater from the emulsion on the screen (don’t let it drip!).
5) Now you’re going to repeat the same steps for the inside or “Squeegee” side of your screen. Regardless of which side you start on, always ensure that you end on the “Squeegee” side/inside of the screen.
6) Lay the screen flat to dry with the print side down on supports so that nothing is touching the mesh or emulsion. The screen needs to be print side down so the emulsion can dry thicker on your “Print” side.
You’re all done!
Thoroughly clean your scoop coater immediately after you have finished coating. Always check the blade edges of your coater for any nicks or cuts before coating to avoid inconsistencies.
Screens need to be air-dried in a light safe, dust free and humidity controlled room for about 2 or more hours. Screens also need to be stored in a UV free light safe environment until after they are exposed.
Sometimes you’ll want to do two passes (two coatings) on the outside / “Print” side of your screen to create a thicker stencil. White plates or single solid colors (spot color) are a great example of when you’d want to do two passes. The thicker the stencil is, the deeper the well will be where your ink lays. This creates a thicker deposit with just one squeegee pass/swipe during printing.
If I can do it, you can do it!
All of the items we used in this video can be bought from SilkScreeningSupplies.com.