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| Posted on 9/18/08 at 05:17 PM | |
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Pinholes usually means not enough emulsion in the mesh or not enough exposure - or both. QX-1 is half the speed of QTX. Do you coat with a 2mm rounded lip or a sharp lip coater?  Sharp lips are barely able to fill the mesh holes, no matter how many coats. http://www.ulano.com/FAQ/FAQcoating.htm In the multiple coating pictures near the bottom the page, I've coated up to six times with a rounded and sharp edge. You will notice, the sharp edge never pushes enough emulsion through the mesh to link up on the other side.  This means the holes were never actually filled with emulsion. When you turn the screen and make your final coat from the inside, (that pushes all that emulsion to the bottom where it belongs), the tidal wave of emulsion will usually trap air as it covers the inside. When the water in the emulsion evaporates, it will leave 37% solids behind (QX-1), or 46% solids (QTX) - less the amount off air caught in the holes of the mesh. This is another reason to make face coats with a sharp edge after the first coat has dried. Make your own experiments by coating from the stencil side first, until a glossy film is created on the inside. Then turn the screen and make 6 strokes of different lengths and make a test exposure to see what works best to eliminate pinholes. You should coat until the holes are filled.  Then coat as many times as you want for thickeness, keeping in mind, too much emulsion will drip. [Edited on 9/18/08 by richardgreaves] ____________________ Richard Greaves, ASPT Ulano Corp. New York Technical Services 718-943-1338 direct | |
  
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