13310Re: [PPLetterpress] Photopolymer with 'moving' parts
- Dec 3, 2012Lola
Your exposure time seems about right to me. But you really do need to
test the exposure time with a 21 steps grey scale. With a hardness
rating of 67 you should get a reading of 14-15 as solid—that means the
14-15 boxes are not washed out or corroded (13 or below should be washed
out). Exposure times can vary dependent upon the condition of your
bulbs/ballasts. Fine lines or dots might need a slightly longer exposure
Basically, you are not giving enough time to build a decent structural
relief if your exposure/washout are out of sync and imaging is drifting.
You do not have to back-exposure this plate, the manufacturer has
already done that.
You washout can vary quite a bit dependent upon bath temp, machine,
brushes, etc. Mainly you want a clean floor with no undercutting of the
Post exposure should be the same or longer than the main exposure. I
usually do about 1.5x.
It is difficult to "read" the validity of a plate immediately after
washout because clinging moisture can cause optical distortion. Your
drying temp seems high. Specs sheet recommends 60-70 C. I'm not sure if
that is the problem but lower the temp and see if that helps.
On 12/3/12 1:58 PM, tinglado_letterpress wrote:
> Dear list members,
> I am using KF95 PP, processing the plate as follows: exposure: 200 s, wash out: 240 s / 21 ÂºC, dry out: 10 min at 80 ÂºC and post exposure 300 s.
> The main problem is that some letters (body size 6 pt) are pushed out of its possition in the PP. Please, check this picture to see what I mean (http://flic.kr/p/dyigw8). I checked it after wash out and they seem to be at the correct position. Do you think that it could be something related to the dry out process? Do you think that a bit of back exposure could fix the exposed photopolymer to the plastic base?
> The problem only happens with the '1' and the 'l' characters.
> I am in trouble, because it happens every time I try to process this work.
> Please, help!!!! :-)
> Thank you in advance and regards,
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