screen printing > Screen Making

Speaking of Underexposure

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Frog:
I have one for you that constantly springs up. I have always learned that correct exposure time is correct exposure time regardless of bold shapes, fine detail, or halftone dots.
Could you address this?
Also, does the ability of photopolymer emulsions to benefit from re-exposure enter into this picture?

alan802:
Yes Frog, I've always had issues with getting halftones to wash out when exposing fully.  We usually have to back off of the exposure time by a light unit or 2 with really fine halftones.  I'm sure our film density has a lot to do with this, our emulsion being PP and not dual cure, and maybe other factors I'm not aware of. 

squeezee:
If you over-expose you will get more under-cutting, burn-through and light scatter.  These affect small elements disproportionately (because two are edge effects) which means halftones & fine lines.  Whatever you do you will get scatter from the film, from the mesh, from the exposure booth etc. 
So you expose enough to wash the  details out, then you can post-expose to fully cure the screen that's left.
From the emulsion's point of view, when it's exposed, it isn't going to get more exposed no matter how much light you give it.

DouglasGrigar:

--- Quote from: alan802 on May 20, 2011, 05:53:14 PM ---Yes Frog, I've always had issues with getting halftones to wash out when exposing fully.  We usually have to back off of the exposure time by a light unit or 2 with really fine halftones.  I'm sure our film density has a lot to do with this, our emulsion being PP and not dual cure, and maybe other factors I'm not aware of. 

--- End quote ---

Choosing a good match of dot to mesh helps, as does pressure washer, and art/positive adjustment when needed.

I would rather have a strong, fully exposed screen capable of long runs and quick easy reclaim than to underexpose.

Underexposure is the MAIN problem for new people in this industry, I find many of the suppliers promoting underexposure and it directly harms many of the new people in their early quest for efficient procedures an quality printing.

Have you noticed how many out there selling, hawking, and pushing products are ignorant of correct procedures, exposure, coating, positives, and art production? (Or lying for whatever reason?)

Dottonedan:

--- Quote ---Have you noticed how many out there selling, hawking, and pushing products are ignorant of correct procedures, exposure, coating, positives, and art production? (Or lying for whatever reason?)
--- End quote ---


Phfft.  Yea,  Thats why I dropped using one of he MAJOR suppliers in our area/actually nationwide I guess...and went with using Chris Colton and family. They were all intelligent and honest people. They knew what they were selling and also would tell you what was best after you've chosen to stick with the cheapest. They would lay the truth out for you and let you make the division.  Many just tell you what they sell and push that product....and they don't know for sure if it's good or they lie to you. They just push it because it's what the company is selling that they rep.  14 years ago, one company tried to push an oyo on us  (VERY hard) when it was clear we were looking for a true wet film image setter. It's just what they sold. They pushed so hard and lied to me that I decided not to use them at all for all of the other products that we were getting from them. We had to stick with them for some things and used them on emergency's of course, since they were in town.

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