01 Jun Coating Technique
There is a lot of confusion about how to coat a screen. About half of all the shops I visit (anywhere from 500 to over 1,000 a year) and almost every person who attends one of my seminars at the trade shows or at the School of Screenprinting is coating incorrectly. Most often they are upside down with the majority of the stencil on the top side of the screen, or they are so thin on either side that they have to make multiple strokes to get a decent deposit of ink. Some revert to a print-flash-print-flash-print technique to get a salable product. I teach a method that will allow a single pass to get the required amount of ink down on the substrate each and every time. Another side of the problem is in the myriad forums, where anyone spending enough time on the forum to become the “resident expert”, you have to question just how successful they can be and still have time to sit in front of a computer all day and answer questions for free.
Your emulsion coating technique has to be correct. As the attention span today is reached an all-time low, here are the bullet points for those without the budget for the proper screenmaking tools.
1. Fill the scoop coater 3/4 full of emulsion. It should be refilled after each screen to maintain uniformity from screen to screen. If you coat five screens and the last one is coated with a scoop coater that is almost empty, it will take much longer to coat the screen.
2. Sit the screen on its edge and at an 80˚ degree angle. Place the scoop coater with the rounded edge against the print side of the screen, roll the coater toward the mesh. Gravity will make the emulsion flow against the mesh.
3. As the emulsion flows against the mesh, slowly move the coater up the screen using medium pressure. The correct speed is about 1-inch per second.
4. Repeat this until the squeegee side of the screen shines with wet emulsion. This means that the emulsion has sufficiently filled the mesh openings and gone completely through the mesh. No one can tell you how many coats this will take, as it is dependent on the mesh opening, the thread diameter, the tension level, the temperature of the emulsion, and other factors. It will vary from day to day with the difference in the materials used, so don’t get lulled into using two coats on 156-64 and 3 coats on 110-80, as it will not produce consistently coated screens.
Remember that the wet ink deposit is always equal to the thickness of the stencil.
5. When the squeegee side is shiny with emulsion turn the screen around and make a similar pass on the squeegee side to push the emulsion back through the mesh to the substrate side where it will form a proper stencil. Remember that the wet ink deposit is always equal to the thickness of the stencil. An additional coat or two can produce a slightly thicker stencil, which will produce a slightly thicker ink deposit.
6. Using a vinyl applicator or a piece of cardboard, you can scrape any excess residue at the sides of the coated area. If the image area is not smooth, you can always repeat the process until you have a uniform coat of emulsion. You can do this a few times (or until the emulsion begins to dry) as you will only be pushing emulsion from one side to the other.
7. Dry the screen with the print side down. Gravity will allow the emulsion to settle into a smooth stencil as it dries.
8. After the screen is dry you can make optional face coatings on the print side to build up the emulsion over mesh ratio, which will ensure higher edge resolution and more opacity to the ink. Next, if you have an automatic or if you are experience chatter as you glide the squeegee across the mesh, you can make anti-friction coatings on the top side as needed.
9. After making the face coats, the screen is dried with the wet emulsion on the top so that it flows into the dried emulsion to produce a smooth stencil.
If you follow these instructions you should have the proper stencil thickness for the given mesh count, thread diameter, and tension level.