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11944Re: [PPLetterpress] Re: Photopolymer separating from polyester backer

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  • mike day
    Aug 1, 2010
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      Regarding the separation issue, I have observed that washing out for too long will make lines, letters and especially periods lift off the backing of KF152 & 95. Five minutes is usually the maximum wash out time. If all the unexposed area are not clear, it usually can be blamed on old plates or slightly exposed plates. We are starting a new procedure to date our plates with marker so this does not happen. I have seen lines of type go squiggly in an up and down line. Whether it is too long a washout and old plates, I can't be sure.

      As for negatives in Photoshop, we try to never make a film neg from a file lower than 1200dpi. More pixels equal a smother line. We usually convert to greyscale so the files are not huge.

      Hope this helps.

      Mike  Day

      On Sun, Aug 1, 2010 at 8:34 PM, Bill Jones <billjones@...> wrote:

      I am in nearly the same situation as you--10 minute exposure times using an old screen printing exposure unit. I wash out by hand and am new to the whole process.

      Additionally I make my negatives using an inkjet printer (Epson 2880 and polyester film). My major problems come from lines that are too thin on the film. 

      I normally rasterize into photoshop at 600 lpi and at times the lines end up being "hairlines" which by definition are 1 pixel wide. If I am using the 1400 dpi print setting these lines are just too thing to stay on the plate.

      If I am imaging an Illustrator file, I need to look closely at the file to see if there are hairlines. If there are (script types and bodoni like serifs) I stroke those objects with a 1/4 point line to beef them up a bit and then run the plate.

      If the plate survives washout, I have also found that the post processing hardening is also very important. On a good strong sunshine day, putting the washed-out plate in the sun for a few minutes seems to be more effective than running it back through the platemaker to harden it.

      Others with "real platemakers" can probably achieve better results, but beefing up any fine line is the answer in my current situation. I don't have a problem with fine "white" lines in solid printing areas, just fine "black" lines that need to stand on their own.

      Anything that really needs 1/4 point lines and very fine detail should probably be sent out and would cost the long buck.

      Bill Jones

      On Aug 1, 2010, at 11:09 PM, idgradstudent wrote:


      More info:

      Fresh KF95 plates.

      I have a lot of "variables" like oldish brushes, and older bulbs that require a long exposure time (9 minutes according to my stouefer scale). So it would certainly be easy to dismiss my issues by saying "Hey, go do some basic maintenance to your platemaker" and you would be right. Aside from this relatively recent issue the plates have been good so I have opted to spend funds on other more pressing issues as a longer exposure time does not cost me much since I only make plates for myself and the cost for new bulbs and ballasts is not insignificant.

      My washout is probably too long (5 minutes), I will back it off and see if that works. When I first acquired the machine I established my exposure times with a scale and my washout times through trial and error but I may have just gone too far. Generally if I lose anything to this problem it is a crop mark on the edge of a plate, but recently I started losing thin script text and fine lines in graphics if they were also near the edge of the plate.

      My question included limited info as I wanted to know what the root cause of photopolymer/polyester separation was rather than have folks just tell me to do maintenance that is not really an option right now.

      Glenwood Morris

      Oslo Press Inc.

      --- In PPLetterpress@yahoogroups.com, "idgradstudent" <glenwoodemorris@...> wrote:
      > I did some searching and found several discussions about plates that have separated; i.e. the photopolymer has detached from the polyester backer.
      > What I did not find in the discussion was any agreed upon conclusions about why exactly this happens (or I simply missed it).
      > Does anyone know what causes this to occur? I am currently having problems with this with some of my plates and was wondering if there was a "known cause" before I just start changing things and hoping for the best.
      > Thanks,
      > Glenwood Morris
      > Oslo Press Inc.

      Mike Day
      Long Day Press
      Sunnyvale CA

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