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13581RE: Re: [PPLetterpress] RE: I'm a newbie and I can't find the exposure time.

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  • parallel_imp
    Oct 22, 2013
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      For various letterpress photopolymer plates, I find 250-430, 360, 300-400, 366 and 350 specified.

      Screen printing uses a much thinner photopolymer emulsion than does any letterpress plate, so intensity may be a bigger issue than wavelength. Exposure units for relief photopolymer typically use a close bank of UV tubes, where screen and litho exposure units often use point-light exposure further from the film plane.




      ---In PPLetterpress@yahoogroups.com, <ppletterpress@yahoogroups.com> wrote:

      What is the correct wavelength needed for plate exposure?

      Shab

      On 10/18/2013 8:46 PM, Justin Miller wrote:
      ����
      It is also possible that the wavelength your screenprint exposure unit produces is not correct for the plate you are exposing.����
      I print my negatives on translucent UV paper on my laser printer. I double up the prints to get enough density to stop out the light.����
      There are ways to get around using professional image setting equipment, but you may have to do some trial and error.����

      Justin Miller

      Sent from my iPod

      On Oct 18, 2013, at 7:34 PM, <Bieler@...> wrote:

      ����

      Fabio


      Just a further note: the type of plate you mentioned is not actually formulated for letterpress. The hardness rating is not up to spec.


      Gerald



      ---In ppletterpress@yahoogroups.com, <Bieler@...> wrote:

      Hi Fabio

      I suspect you have already pinpointed the problem; wrong method of exposure, not up to spec film, old plate material. Sort of a perfect storm.

      The industry spent a good half century perfecting this technology, things tend to work quite smoothly when following normative practices.

      Fix the vacuum problems and check the lamps and ballasts on your machine. Buy some new plate material and have your film supplier ship the film to you. You will see some dramatic improvement.

      Gerald

      On 10/10/13 12:45 PM, NeroInferno wrote:
      ����
      Dear photopolymer friends,
      I'm a screenprinter and about 3 years ago I bought a Windmill 10x15. I changed the engine to run at 220V instead 380v and cleaned generally the press, changing the air tubes and so on. In all these years I haven't never printed with it cause my screenprinting job is really hard. On July I've bought a photopolymer exposure machine, and changed some parts. I still must recover the vacuum and the transparent film for the vacuum, but the washout brushes works perfectly, and the heating system too.

      Today I wanted to try an exposure but I failed. I have used the Tolorelief "WF175MY3" photopolymer, but I've made the exposure on my large screenprinting exposure frame (100x140cm). The film I used was printed on an Epson Stylus Pro 7880 plotter, using the MATTE BLACK ink.

      I know the best way to print film is with the imagesetter but here the most near imagesetter service is an hour and half from me..so I was using the film I commonly use for the screenprinting. I also know the density isn't the same, but I wanted to try.

      I must say you the Tolorelief "WF175MY3" photopolymer I've is not a new batch, but an old one, bought with the photopolymer exposure machine.

      I tried 200, 250, 300 and 450 seconds. All the time the photopolymer washed completly from the plates...what I cannot understand is why? If the exposure time is too high or the black density of the film isn't so high the UV rays should have passed between the film and hardened the photopolymer..but it completly washes away.

      Any help is really appreciated!

      Thanks,
      Fabio


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