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| Posted on 1/30/08 at 10:25 AM | |
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Hello Cameron, Thank you for trying KIWO and for your inquiry. I applaud you detailed explanation and control of your process. That tells me you do pay close attention to your processing variables and take pride in the work you do. Polycol One-Coat in combination with Diazo D has become one of the most popular choices among discharge screen printers. As you may know, discharge inks can be very brutal on emulsions. Diazo D helps to boost the water / discharge resistance, as well as improve the stencils anchoring ability. You have already controled one of the most important variables when printing with water-based or discharge inks, which is dryng and storing your coated emulsion in low humidity right up until the point of exposure. The next most important variable is to achieve optimum exposure. This is what you are currently trying to dial in. Polycol One-Coat is a very fast exposing emulsion, but when Diazo D is added the exposure time quadruples. IF the exposure distance from your 1K point light is approximately 40 inches (the only variable I didn't see in your post), it should take about 4-5 minutes to achieve full complete stencil hardening and water resistance. Please let me know if your exposure distance is different. I base this guestimate on my numbers using a 5K Olec lamp at 40 inches on 156-64 yellow mesh. Using the same coating technique as you, I achieved full water resistance at 1 minute using Diazo D. If you have very good vacuum and film positive density, you will be able to open up your fine details by developing with the pressure washer, as you alluded to in your post as a possible solution. We've tested various washout methods in our applications lab and found that Polycol One-Coat held better resolution when developing with a 1,000 to 1,600 psi pressure washer on fan setting at a distance of approximately 18-20 inches. When using cold tap water with a hose end sprayer we were unable to open up our fine highlight dots and found more scum at the edges of the stencil. Surprisingly we also anchored the shadow dots very well. I have experienced printers trying to resolve dots and lines that are mismatched for the mesh count - too fine for a coarse mesh. I've seen printers trying to resolve 55 lpi dots on a 156 mesh only to find that they loose many dots when developing. The dots can not anchor to air they need at least a couple of threads. I am assuming this is not what you are doing. Also, remember you are now using a water resistant emulsion so developing will not occur as quickly and easily as it would using emulsions without water resistance. Your ragged edges may be emulsion scum left in the screen at the edge of the stencil, or coming from a low res film positive. I hope this is helpful. I apologize for such a long reply. Please give me a call if you would like additional help, or if you run into further difficulties (800) 549-6872, and thank you again for trying KIWO emulsions. Dave | |
  
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