12392Re: Making Negative for Photopolymer Plates
- Feb 25, 2011
> > Sheet photopolymers are more light sensitive and have a such short exposure latitude that using negatives produced on a laser printer don't have enough density. However, we have excellent results with liquid photopolymers using negatives made a laser printer. We imprint wooden tokens on a C&P with dies made with liquid photopolymer.Liquid photopolymer has a much greater exposure latitude. As a trial we left some on a shelf for about 5 years and noticed that exposure times had to be increased from 1 minute to 1 minute 45 seconds through the base on the older material. Our normal exposure time using F20T12BLB fluorscent bulbs is 1 minute base, 2 minutes through the negative with a 5 minute in-water post exposure. Our lights are about 3 inches away from the negative.
> Is this because only some of the exposure is through the negative, and the rest through the back of the liquid? Or does the liquid have a different exposure latitude?
> What is your experience with shelf-life, both raw liquid and processed material? I have a processed sample of Merigraph liquid photopolymer that is still supple and it is over twenty years old (but never exposed to ink or solvent).
> Eric Holub, SF
The finished die tends to yellow with age, but doesn't seem to deteriorate. We've been using both sheet and liquid photopolymers since 1982. Both the total thickness and relief depth are easily controlled with liquid photopolymers.
Since the printing plates we need in my print shop are usually less than 10 square inches, scrub out is done in the sink. Liquid photopolymer scrubs out in less than a minute, compared to about 5 minutes for sheet photopolymer which we seldom use. Hard liquid (95 durometer) works as well for making stamp matrix as metal backed hard sheet.
In no way am I discouraging the use of hard sheet photopolymer, but in our applications the liquid is more practical.
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