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144Re: [PPLetterpress] Re: Exposure/washout units

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  • Frank Cabral
    Oct 2, 2001
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      Dear Gerald

      The exposure for the KM 152, depending on image, the more solid the
      shorter, is for about 2.5 minutes and wash out about 3 minutes. I have
      found that this material is easier to wash away. After about two and half
      minutes I will check with a loupe every 15 to 30 seconds until the bevel on
      the edge is correct and that the periods, dots over 'i' and end of lines
      are not undercut. The arrangement of positive and negative space on the
      negative will affect this.

      I will use the KM 152 for solids, when the general image is large
      (backgrounds, large block type etc.) While this material is capable of
      holding fine lines I find when printing that it is a softer, more generous
      and will spread more than the MLD. The 152 is great for printing on plastic
      and responds best to soft packing.

      MLD after the final exposure is quite hard, but brittle, and holds up to
      the letterpress look (deep impression) that is so popular today. I have
      found it holds fine lines and dots with a longer washout than the 152. The
      longer washout is important, it reveals the edges of the typeface, washes
      away the shoulder and makes the printing more accurate as to its design.
      Especially on the different surfaces and thickness of paper. Printing is
      primarily on 10x15 Heildelbergs' and 21x28 Heidelberg cylinder presses.

      I don't remember how I got to this choice but it has worked so well I
      haven't found a reason to look further. Most problems are operator error
      either in how I made the plates, my make ready or some mystery that is
      plainly obvious to everyone but me.

      I think the spec sheet I have for MLD recommends it for all the
      processes you mention but I thought it also included letterpress. I will be
      at the shop tomorrow if it is any different I will send you a note.

      What material do you use?

      With regards

      Gerald Lange wrote:

      > Dear Frank
      > Since we are using the same machine I have some questions I hope you
      > will address. I also keep the temperature down a bit. 90 to 100 max
      > for KM 95s (.038).
      > But I would like to know your exposure times for KM 152 (.060). You
      > wash these out for four minutes right? What are your exposure settings
      > here for say reverses,/solids, then type, then fine lines/halftones?
      > And a curious question, why MLD 145s for text? These aren't even on my
      > spec sheet for letterpress!!!! Aren't the MLDs for molds, hot
      > stamping, flexography, rubber stamps, etc.? How did you get to this
      > choice?
      > Gerald

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