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screen printing => Screen Making => Topic started by: StuJohnston on May 17, 2012, 10:09:04 AM
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I know that this has been asked before, but I think mine might be related to my exposure unit and I was wondering if anyone had any ideas. I am using an OLEC AL-53 with a bulb of unknown age. The bulb type is the standard one, the one that isn't really suited for diazo and that is what I am using. I know that the exposure time will generally go up as the bulb ages, but I was wondering if it would decrease the quality in such a way that it wouldn't expose properly no matter what.
The recommended time for my emulsion on a 5k light is ~130 seconds, which will expose it well enough that it won't be slimy or anything, but I am getting sawtoothing still. I have tried running it over and under that time and still, sawtoothing. The odd thing though, I don't get sawtoothing on lower mesh screens, like 110s, the ones that are sawtoothing are my 305 and 355 mesh screens. Could this be an EOM issue?
The reason that I think that it might be related to the exposure unit is that I was getting good screens when I was just using a grow light. I am going to try to set that up again to see if it would give me better screens, but it is a pain to use in comparison to the olec.
I know that I should be using a calculator, but I seem to have lost mine. I plan to get another soon. I just had thought thatI had it dialed in so I didn't need it anymore and forgot about looking for it. Also, the filter that went on top of it got messed up from sticking to the screen a few times.
I should mention that I am washing the ink out properly, reclaiming fully and degreasing like I should, so I don't think that is it. I also dry them in a box, so I shouldn't be getting any contamination there either.
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vacuum blanket suction maybe?
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Are you lower mesh screens white? The difference between yellow and white mesh on a dual cure exposure time could be the culprit. Try increasing the yellow mesh exposure time by 75% and see if it helps.
On my AL53 with the photopolymer bulb I have to push times up into the 200+ ltu range to get a decent exposure on a 305 yellow frame. I'm shopping for the L1250 bulb to lower those times on my unit.
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It certainly can be EOM.
The article by Douglas Grigar on our home page has photographs, a couple I put here, that show how stencil edges can be affected by the mesh itself when there is insufficient EOM as in the top example
(http://www.thegrendel.com/Shop/osc/images/PWjune05fig10.gif)
(http://www.thegrendel.com/Shop/osc/images/PWjune05fig11.gif)