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13312Re: Photopolymer with 'moving' parts

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  • letterpress_man
    Dec 3, 2012
      Lola

      I use the same plates as you are using, I buy them from Boxcar Press and they recomend 25 sec back exposure. They sell and process probibly more plates than anyone one here so there advice should hold some weight. I also agree with the other comments Gerald made.

      Rick

      --- In PPLetterpress@yahoogroups.com, Mª Dolores Jiménez Mondragón <doloresj3@...> wrote:
      >
      > Thank you Gerald for you advices. I will try to improve those parts of the
      > process and I will be back with the results.
      >
      > Regards,
      >
      > Lola
      >
      >
      > 2012/12/3 Gerald Lange <Bieler@...>
      >
      > > Lola
      > >
      > > 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
      > > time.
      > >
      > > 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
      > > surface imaging.
      > >
      > > 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.
      > >
      > > Gerald
      > > http://BielerPress.blogspot.com
      > >
      > >
      > >
      > > 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 ºC, dry out: 10 min at 80 ºC 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,
      > > >
      > >
      > >
      > >
      > >
      > > ------------------------------------
      > >
      > > Yahoo! Groups Links
      > >
      > >
      > >
      > >
      >
      >
      > --
      > María Dolores Jiménez
      >
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