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Curing screens

949 Views 6 Replies 5 Participants Last post by  PatWibble, 
T
I am using green galaxy emulsion and have done tests using various exposure times to find the ideal time. It seems that it doesn't matter if I expose for 12 minutes or 35 minutes, the back of the screen is slimy after rinsing and seems to be plugging the openings in the screen slightly enough that you can't see it, but you have to use a pressure washer to get it out so the ink will print through the screen. I'm exposing using a 150 watt bulb in a bowl shaped heat lamp light fixture.

Any suggestions??
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J
I think your bulb is to small and probably isn't putting out enough UV. It's not how bright the bulb is or how hot it is, the important part is how much UV it puts out and most bulbs try to minimize UV output.

Have you tried using the sun?
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NoXid
First, that is a weak UV light source. Some 30 years ago I exposed my first screens that way, so it can work, but you have less frustration with a stronger source of UV light. A 500 watt halogen worklight, with the glass removed (it is there to filter out the UV), is the best of the low budget, easy to DIY solutions. This will be faster and better, but still far from fastest or bestest ;-)
EDIT: Yes, the sun is a great UV light source. Google or search on here for details.

Second, you are putting the emulsion on too thick, and/or you are not getting it dry enough before exposing. Get a humidistat (~$10 at Home Depot). If you don't have a place with under 50% humidity, you need to add moderate heat and/or dehumidification.

Third, is your emulsion the type you add Diazo powder to? Polymer type emulsions are typically faster than Diazo, so will expose better with weak light sources. I use Saati PHU (the original, NOT the PHU-2; #2 is for more exposure latitude with ultra-fast LED units, so it is twice as slow).

See my sig for a thread on testing to determine proper exposure time.
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sben763
He is using Green Galaxy which is a green dyed Saati PHU. Go get a 500w halogen, remove glass cover, hang 16-24” expose 3-8 min using a step test. A 150w incandescent in a spot will take hours to expose a screen and it may never stop the back from being slimy.
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T
Thank You all. I tried the step test a few times over the past year but never thought about the uv source. I will try the 500 W halogen. Thanks again.
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sben763
tyhoppy said:
Thank You all. I tried the step test a few times over the past year but never thought about the uv source. I will try the 500 W halogen. Thanks again.
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Just FYI I should have added use a small fan to cool light and screen. The extreme heat can cause issues. A small fan will take care of those issues.
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PatWibble
Check the halogen has a 3200k bulb. A lot of the units around now only come with a 2700k bulb which is still very slow.
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