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| Posted on 12/3/07 at 08:05 AM | |
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I don't think changing your emulsion will help with this situation until you double check how you actually coat. With all direct emulsions, they are more water than solids. When the water evaporates, the film that remains takes on the bumpy shape of the mesh. Sometimes there isn't enough coating to survive the drying process and you might get holes in the openings of the mesh. 315 mesh and 86 mesh must be coated differently to completly fill the thickness of the mesh. Because the mesh has holes in it, emulsion ends up on the other side of the mesh, so we aren't even actually 'coating' mesh until the first application dries and we make a face coat. Start by coating on the stencil side of the screen until you create a glossy film on the inside of the screen. This means you have completely filled all the holes in the mesh. This is almost impossible with a sharp coater on 86 mesh. See pictures at: http://www.ulano.com/FAQ/FAQcoating.htm The picture of the EOM measurements after drying shows that even 6 coats didn't add any emulsion thickness to the mesh. When you turn a screen around with incomplete penetration, you may get pinholes because air is usually caught in the holes. If you need a smooth capillary film like coating on the stencil, especially for graphic printing, you have to make 'face coats' with the sharp edge of the coater. Duplicate the test I have shown on the coating page of the Ulano web site and see what multiple coats delivers. ==== Color is a pigment dispersion added to the emulsion and has nothing to do with durability, but many printers like dark colors like blue, because they look more "solid". Many screen makers like dark colors because they are easier to block out pinholes because of the contrast. I like light colored stencils because they expose faster and are easier to register. If you use the method I describe above you won't have any pinholes in your stencils unless you have dirty positives or exposure glass. [Edited on 12/3/07 by richardgreaves] ____________________ Richard Greaves, ASPT Ulano Corp. New York Technical Services 718-943-1338 direct | |
  
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