I have found that when I use a 1 (shirt side) 1 (ink side) coating technique I get alot of pin holes after wash out. I have tried adding a third coat after the first 2 coats dry....the pin holes aren't showing up. I put the third coat on the ink side, are there any problems with this technique that I may not be seeing?
Ryonet uses your technique but not to cover pin holes so there shouldn't be a problem but if you don't need the extra thickness of the layered emulsion to make a thicker layer of ink, there are better ways to take care of pin holes. By the way, you can aquire a very good set of DVDs pertaining to most parts of screen printing by following the "trail" of clues in the contest put on by Ryonet at the top of this page. I got one and its worth having.
You could probably get a suitable stencil that won't show pinholes if you coat 2/2 wet on wet. Always apply the last wet coat to the squeegie side.
If you're after thickness, then you will have to do a coat-dry-coat stencil. If it's just for pinholes, you probably don't need to.
I think my pinhole issues were from too thin of a coat with dual-cure and not a long enough exposure time.
You can actually do it with more coats as you want... if your process would only be spot color process. If you tend burning your screen with tones - thicker coats will be a problem.
An important thing is to degrease your screens before coating it with PE.
With my experimenting, doing an additional coat after the initial dries is not worth it. Actually, the stencil thickness was higher on the wet on wet coats than on the face coats with the same amount of strokes. Just add an extra stroke or two wet on wet and you'll get a great stencil with no pinholes because of the coating technique, it will be because of something else.
The biggest mistake people use in coating that results in pin holes is coating too fast, this results in air bubbles that pop open during drying, the coarser the mesh the more of a problem this causes, i have to keep reminding my screen guy to slow down his coatings.
the biggest mistake people use in coating that results in pin holes is coating too fast, this results in air bubbles that pop open during drying, the coarser the mesh the more of a problem this causes, i have to keep reminding my screen guy to slow down his coatings.
With my experimenting, doing an additional coat after the initial dries is not worth it. Actually, the stencil thickness was higher on the wet on wet coats than on the face coats with the same amount of strokes. Just add an extra stroke or two wet on wet and you'll get a great stencil with no pinholes because of the coating technique, it will be because of something else.
Alan is correct! use the glisten method (do a search here on the forum) and that will give you the proper coating thickness. It should take you about 3 seconds to coat. I use the dull side for everything. 2+1 on thicker screens and 1+1 on special smartmesh screens.
Pinholes with the SBQ/pure Photopolymer emulsion are often related to the chemicals used to decompose/dissolve/degrade the ink (your first chemical used to remove the ink). If there is any left in the screen or if it splashes on the screen while you are washing another one, you will get fisheyes. Make sure you rinse the screens with a garden hose when done washing it, this will remove any residual sediments without spraying all over the place and introducing the contaminants.
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Too fast or too slow are very subjective and relative terms. According to murakami, automatic coaters coat (a 24-26" long screen???) for 10-12 seconds per coating pass. Slower coating means lesser pinholes. Manual coating is about 6-7 seconds per coat. Coating a low tensioned screen too fast can result in a thicker coat. Apply a constant coating pressure along the length of the emulsion.
For 100-180 mesh screens use the dull side of the coater.
screen coating technique 
