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| Posted on 3/9/06 at 07:23 AM | |
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I can suggest two ideas. 1. Perhaps your positive is not opaque enough to stop all the UV light, and some of the image area is hardening. Test this by taping something totally opaque to an unused section of the screen, like a dime. If that area washes out differently, it may point to a solution. 2. It sounds like unexposed "tears of emulsion" are drying in the open area. The sticky, partially exposed areas on the inside of the screen (during washout, the sticky slime on the inside is called scum), may be the source of those tears because they take a much longer time to wash away, compared to the unexposed stencil that dissolves easily and goes right down the drain. I don't know why QTX would not wash away as well as the Autotype product, but only an expose test can answer that question. 5 to 10 different progressive exposures on the same screen with an positive taped in place, will show you how much light it will take from your lamp to fully expose the stencil, and how much light from your lamp will begin to under-cut fine lines and close them so much that ink won't transfer through the mesh. If you only have large open area, over exposure is usually not a problem. After washout, use a window squeegee and a rag to get rid of any pesky emulsion loaded drops of water on the inside of the screen. Then blot the open areas with newsprint or old newpapers to absorb the "tears of emulsion". Sometimes when the stencil is undersexposed and the inside is sticky, the newprint sticks to the stencil. Don't worry about it this time, but you should washout or expose longer next time! I have had 'some' success in emergency situations where I have masked the open area with tape, then sprayed the open area with a high pressure plastisol spot remover gun, or scrubbed the masked area stencil remover. Like dents in wood from a hammer, it is better to prevent the problem by blotting the tears. Richard Greaves, ASPT Ulano Corp. Technical Product manager 800-221-0616 x330 | |
  
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