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Discussion Starter #1
Hello there!

I read through other "halftone problem" posts on here, but I can't fix my problem.

I have tried 5 or 6 times to properly expose a halftone design. I got 1 to come out correctly, but it took be an hour to washout!

Specs: 230 mesh yellow with a halide light.

I know the halide light works because I have exposed 30 normal transparencies in the last few days.

I have tried exposing the halftones for 10 min, 7 min, 5 min, 3 min, and 1.5 min

On the 2 most recent ones they would not washout but if I would "gentyl" rub a section of the screen with my thumb for 5 seconds the emulsion would rub off.

Thanks! CRB

p.s. - If another printer came to your shop and asked to expose a screen for them, approximately how much would you charge per screen :)
 

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Hello there!

I read through other "halftone problem" posts on here, but I can't fix my problem.

I have tried 5 or 6 times to properly expose a halftone design. I got 1 to come out correctly, but it took be an hour to washout!

Specs: 230 mesh yellow with a halide light.

I know the halide light works because I have exposed 30 normal transparencies in the last few days.

I have tried exposing the halftones for 10 min, 7 min, 5 min, 3 min, and 1.5 min

On the 2 most recent ones they would not washout but if I would "gentyl" rub a section of the screen with my thumb for 5 seconds the emulsion would rub off.

Thanks! CRB

p.s. - If another printer came to your shop and asked to expose a screen for them, approximately how much would you charge per screen :)
If your emulsion rubs off by rubbing it with your thumb, it sounds like you have underexposed screens. If are you spending an hour to washout your screens, you are most likely overexposing. You will have to find a happy median. Are you using a vaccum exposure unit? If not, are you applying pressure to your screen and exposure unit for contact?

There are a lot of variables to this situation: Printer, artwork, exposure unit, emulsion, time, etc.
 

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Discussion Starter #3
If your emulsion rubs off by rubbing it with your thumb, it sounds like you have underexposed screens. If are you spending an hour to washout your screens, you are most likely overexposing. You will have to find a happy median. Are you using a vaccum exposure unit? If not, are you applying pressure to your screen and exposure unit for contact?

There are a lot of variables to this situation: Printer, artwork, exposure unit, emulsion, time, etc.
Yes, pressure is being applied for contact.
I tried 10 min, 7, 5, 3, and 1.5

If it's rubbing off shouldnt it washout out incorrectly as well? As in, just completely wash out when I spray?
 

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I was exposing at 10-20 sec. on photopolymer - qtx and chromablue. I swithed to udc-2 dual cure and my exposure times went up to 60-120 sec, depending on how many coats of emulsion I use. At first with the dual cure, I had problems- pin holes, emulsion washing out,...
Make sure you expose long enough, nice even smooth coat of emulsion, good and dry and not too much humidity,clean glass and film, dont wash out too long. Hope you find a cure.
 

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Discussion Starter #7
Yeah, the thing is I am using halide lights because my exposure unit is too small.
Ive been exposing normal transparencies (non-halftone designs) with no problem at all - they completely washout in about 2 minutes. But when I'm exposing the halftones, even if I expose it for just 2 minutes, (down from 13-15 minutes on non-halftone designs) and I just spray in one spot, nothing comes out.

BUT if i rub it with my thumb "gently" it comes off...

I am confused....
 

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Hey CRB,

If It was working fine for your regular seps and now you are having a problem with half-tones. It sounds like the problem might be that your half-tones might not be the right size, frequency, shape or angle. The angle has more to do with avoiding moray patterns. However the other settings directly affect the exposure and washing out of the screen. Standard half-tone settings are way to small and perfectly round which are impossible to achieve with our screens in comparison to offset comercial printers, which is what most software titles output for. Have you checked your settings and adjusted them for your mesh count?
 

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what wattage is your light?

is it made for screen printing? metal halide bulbs off of the shelf rarely contain the correct spectrum for exposing the screens. the emulsion is likely only getting partially exposed.

regardless, 10 minutes is way too long for halftones as most of the dots will close up regardless of how dense your positive is. try lower times and then give the emulsion a rub all-over with your palm when you first get it wet. this will break up the surface tension and just wash it out carefully. be sure to post expose in the sun otherwise this will be a very weak screen.

as for burning screens for other printers, it probably isn't worth your time.

Hello there!

I read through other "halftone problem" posts on here, but I can't fix my problem.

I have tried 5 or 6 times to properly expose a halftone design. I got 1 to come out correctly, but it took be an hour to washout!

Specs: 230 mesh yellow with a halide light.

I know the halide light works because I have exposed 30 normal transparencies in the last few days.

I have tried exposing the halftones for 10 min, 7 min, 5 min, 3 min, and 1.5 min

On the 2 most recent ones they would not washout but if I would "gentyl" rub a section of the screen with my thumb for 5 seconds the emulsion would rub off.

Thanks! CRB

p.s. - If another printer came to your shop and asked to expose a screen for them, approximately how much would you charge per screen :)
 

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Discussion Starter #13
I was wrong, I said I was using halide, but I am actually using Halogen 500Wx2 . I realize this is not ideal light, but it was working for my non-halftone positives.
Do you think this is my problem?

It could also be my halftone settings. I used Adobe Photoshop to generate the halftone. I will check what the output settings were and repost.

Thanks for your help

CRB
 

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general purpose halogen bulbs are tough to get fine detail with.

for 230 yellow mesh i would recommend using the following halftone settings:

50 lpi
61 degree angle

also, if you are doing this in photoshop by changing the mode to bitmap then be sure to bump up your output resolution to something high like 1200 dpi so that you will have smoother edges to your dots.
 

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also, if you are doing this in photoshop by changing the mode to bitmap then be sure to bump up your output resolution to something high like 1200 dpi so that you will have smoother edges to your dots.
Well, that makes two of us (although I usually output them at 600dpi) who think this makes a difference. Almost everyone else seem to think 300 is fine, but for those of us who remember the old 300 dpi laser printers, when the Laserwriter 4m came out with 600 dpi, it was like night and day.
 

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i think it is not with the halftone of the darkness of the layout, or the time element of exposure. maybe u forgot to sensitize your emulsion, or your dried screen was pre-exposed to another source of light (are u darker enough at your processing area?) even a strand of hair will wash out so its not so much on the transparency. when the emulsion rubbed-off, it means that maybe you have not degreased your silkscreen before application. or how many coats u apply to your screens, normally i do it 2 coats (coat/dry/then coat again). i think i can help you.. jst pm me in case
 
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