Ok. So, I just bought a new exposure unit. It says its power is 160 watts. I'm trying to expose some screens and, after a 24 minute exposure, the image barely shows up in the emulsion and when I rinse it, the emulsion starts to run slightly. Also, the image will not wash out. Is it possible that it is underexposed even after burning it for 24 minutes? I am using Ryonet's HIFI photopolymer emulsion. Thanks guys, Melissa.
emulsion running, not washing out, image too light
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CANADA-ASC365 Screen Printing
This is the link to the exposure unit that I am using. I am using the one with the lid and the 8 bulbs.
This is the link to the exposure unit that I am using. I am using the one with the lid and the 8 bulbs.
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i use 2 500w shop lights.. and i burn in 5 minutes.
i've seen guys with uv florescent bulb setups like you have (you have the bottom one correct, with lid and 8 bulbs) burn in like 30 seconds.
i have not used an exposure unit yet with actual uv bulbs.. but, i would say you need to do a step test.
i could be wrong.. but i think you are over exposing.. to the tune of maybe like 23 minutes too long.
that's why you arent washing out. because you've burned through your positive.
do a step test, and try a much much much shorter time.
even when i was using 1 500 watt shop light, 14" from my screen, i burned in 10 minutes or less.
your bulbs should be putting out much more uv than my bulbs do.
i've seen guys with uv florescent bulb setups like you have (you have the bottom one correct, with lid and 8 bulbs) burn in like 30 seconds.
i have not used an exposure unit yet with actual uv bulbs.. but, i would say you need to do a step test.
i could be wrong.. but i think you are over exposing.. to the tune of maybe like 23 minutes too long.
that's why you arent washing out. because you've burned through your positive.
do a step test, and try a much much much shorter time.
even when i was using 1 500 watt shop light, 14" from my screen, i burned in 10 minutes or less.
your bulbs should be putting out much more uv than my bulbs do.
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here is how I just did a step test about an hour ago and discovered I had been over exposing my screens. I'm using a 500watt halogen shop light about 18 inches above the screen.
I printed film positive with 14 copies of my logo,( it has thick and thin lines, large and small text) I covered all but one logo with pieces of cardboard turned on the shop light and started my timer counting down from fifteen minutes. At fourteen minutes I uncovered the the next logo, at 13 minutes uncovered the next logo and so on until the last logo was exposed for two minutes.
on my test the 3 minute logo held the most detail when washed out but the surrounding emulsion was still just a little gooey. the 4 minute logo lost a little detail in the thinnest lines but the surrounding emolsion was solid.
here is the link to the file I used as a sample, everyone is welcome to download it (it has my logo plastered all over it!) the square blocks are just to have a solid area to wash out for the test
it's not as accurate as a professional test strip but it will get you close enough for most jobs
BR Design Screen Print Test Strip
I printed film positive with 14 copies of my logo,( it has thick and thin lines, large and small text) I covered all but one logo with pieces of cardboard turned on the shop light and started my timer counting down from fifteen minutes. At fourteen minutes I uncovered the the next logo, at 13 minutes uncovered the next logo and so on until the last logo was exposed for two minutes.
on my test the 3 minute logo held the most detail when washed out but the surrounding emulsion was still just a little gooey. the 4 minute logo lost a little detail in the thinnest lines but the surrounding emolsion was solid.
here is the link to the file I used as a sample, everyone is welcome to download it (it has my logo plastered all over it!) the square blocks are just to have a solid area to wash out for the test
it's not as accurate as a professional test strip but it will get you close enough for most jobs
BR Design Screen Print Test Strip
I bought it new but from an individual that bought it and never used it. The numbers on the bulbs are in some sort of asian writing so I can't read them. What would happen if I bought new bulbs and they were a higher wattage than the ones that are in there?
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847 Posts
Type of bulb matters more than wattage, they have to be unfiltered UV black light bulbs, cool white tubes won't cut it
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