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13699Re: [PPLetterpress] Buying a Platemaker, advice needed.

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  • jpow
    Jan 25, 2014
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      Thanks so much Eric and Tom for the explanations. My understanding of the process has increased tremendously!

      This is what I have learned (please correct if I am wrong):
      Post exposure, the TOP layer of areas that have been exposed, is hardest (since it is closest to the light source). However, because the light has to diffuse through the photopolymer as it travels through it, the lower layers are less "cured" and hence hardness starts to decrease as we get to the bottom layers. The diffusion / scattering of the light (as it travels through the polymer) also results in what we call "shoulders", where a larger volume of photopolymer gets exposed to less intense UV light.

      Because the bottom layers are less "cured", they are more susceptible to being "washed away", which may result in the harder, top layers "detaching" from the backing during a vigorous washout.

      The post exposure, then is required to harden up everything!



      On Sun, Jan 26, 2014 at 1:01 AM, <typetom@...> wrote:

      hi JP,
      Eric Holub's comments, as usual, are excellent and important for understanding the process, what works, what can go differently with different setups.
      No there is not a chemical reaction during washout. (The only chemical change is when UV light hits photopolymer the polymers recombine differently. I don't know the chemistry but the material exposed to UV light hardens and becomes not soluble in water.)
      The timing limits I feel for washout are due in part as Eric describes to the length of time the surface is subject to damage by the brush, but that is also affected by the fact that the material has been exposed from the surface down toward the base - which I think makes the surface more completely exposed and the lower part of the material still susceptible to the effects of water and still not as hardened against the effects of the brush. So there becomes a limit, as you wash away the lower material that surrounds and supports the printing surface, when the brush will separate surface details from the softer material below. Thin lines can begin to move and get wobbly; serifs can come loose and break off; punctuation can vanish. You might find tiny scraps of these surface details in the wash - they have not been worn by brushing, but have been separated from the base material. Longer exposure time also can harden that base material more, but that also can swell the material around the surface lines and result in a bolder image in printing. So the solution to problems requires a compromise between exposure and washout, and those are the critical times to watch. That's my sense of what happens, anyhow, and the easy answer is to watch the second hand of the clock, resist the urge to clean the plate all the way to the metal everywhere, and stop - even the shallower plates are deep enough for printing even if not completely washed to the base.
      Best wishes,
      In a message dated 1/25/2014 9:06:37 A.M. Mountain Standard Time, jp@... writes:

      Dear Tom,

      Thanks for the tips :) Extremely helpful. I'll be sourcing DIY exposure equipment later today. 

      Regarding Vacuum, I saw  a video on youtube (http://www.youtube.com/watch?v=8WJn5YFANxU) of someone using a "spacesaver bag" to sandwich plate + negative. I'll try that to see if it works well.

      Separate question:
      I understand how Exposure time affects the plate curing, but how does washout timing affect things? 
      Does some chemical reaction happen during washout, which makes timing very important?

      Thanks again!

      On Sat, Jan 25, 2014 at 3:39 AM, <typetom@...> wrote:
      Hi JP,
      Exposure time and time in the washout are the two most critical factors. Washout temperature not so critical. I use water comfortably warm to the hands but not hot; I use a hand-held hair dryer, and dry steel-backed plates until they are too hot to hold and then somewhat longer.
      (If they haven't been dried long enough they may still hold moisture that will eventually dry further and curl the plate, not a critical problem except for storing and reusing plates but they can be flattened again in hot water for printing again later).
      I have a homemade lightbox with four 18" bulbs, something like 2" above the plate material in an old NewArc vacuum frame. My lights are placed face-down on top of the glass. I found the vacuum was bending the glass very slightly and allowing irregular contact and exposure between the negative and the plate - matboard pieces to support the glass around the material solved all that. Funky system perhaps but routinely excellent plates can be done by hand.
      Trials and understanding what is happening in the process can get you there - UV exposure and changing of the polymer happen from the surface down toward the base; the UV light spreads as it travels past the negative into the material; unexposed polymer is water-soluble.
      (I do plates easily up to the size of cards and invitations, 4x6, 5x8; larger plates take longer with hand washout because you can't brush the whole surface at once - about 4 minutes in the water by my experience, it's time to stop).
      Best wishes,
      Tom Parson/ Now It's Up To You
      157 S Logan, Denver CO 80209
      (303) 777-8951 - home & letterpress printshop
      (720) 480-5358 - cellphone
      In a message dated 1/24/2014 10:51:33 A.M. Mountain Standard Time, jp@... writes:
      Hi Peter,

      I've done a bit more research and decided that it would be better to DIY a quality UV exposure unit, than to pay for a cheap "All-in-one" platemaker.

      In your experience, are the KF152/KF95 plates very sensitive to factors like drying and washing temperature/time? If not, doing washing / drying by hand seems like a good way for me to start! 

      Some questions on your UV Exposure unit:
      -When you mention 4 sets of 2 T12 Damar bulbs, this gives a total of 8 x 40W = 320 Watts? 
      -How far apart are your bulbs from each other? I've read online that 2 inch (center to center) works well, but ideally I'd like to follow whatever works for you.
      -How far above the bulbs is the glass surface?

      Many thanks in advance :)

      On Wed, Jan 22, 2014 at 3:41 AM, Peter Nevins <nevins.peter@...> wrote:
      Guess it depends on the size of film, but i've sent you here pictures of the system that's been in place at the print collective i have joined.  I just jumped in and started using it and i've had no problems.

      Our setup:
      4 sets of 2 Damar F40 blacklights
      Heavy glass
      Various sized pieces of black foam
      Plywood enclosure
      A heavy weight, like 1/2 a cinder block, or in our case a litho grinding wheel.

      Best exposure time has been 10mins for kf152 and 8 min for the thinner kf 95.

      Don't forget importance of warm or hot water in rinsing

      Shurline 'handipainter' foam handle paint brush works great for gently  washing out.

      Have fun!

      Photos of exposure unit:
      1st picture: unit open with 2 pieces of foam. Plate and film under foam against glass.

      2nd photo: unit closed with weight.  The 2 pieces of foam have been chosen for thickness and even pressure.


      p.s. the unit has mainly been for silkscreen exposure but 3 or 4 more minutes and it's perfect for photopolymer.

      Ok!  ciao!


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      On Jan 21, 2014, at 9:33 AM, "J. Pow" <jp@...> wrote:


      Hi Peter,

      Thanks for the tips :) Starting off with a UV box sounds good.

      Do you have any pics of how you weight down your slides with the dark foam?

      Also, how many lamps does your UV box have? I've read that 6 x 25 watt is a minimum?


      On Wed, Jan 22, 2014 at 12:22 AM, Peter Nevins <nevins.peter@...> wrote:

      Most important for me has been really good opaque film transparencies, a wide, soft, flat brush ($2.99 painting brush on flat styrofoam handle) and using warm/hot water to rinse!  I've just burned 10 in a row 12"x12" kf152 and kf95 photopolymer plates without losing one.  No vacuum, just dark foam weighted down on my uv fluorescent blacklight box.
      Have fun!


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      On Jan 21, 2014, at 12:19 AM, <jp@...> wrote:


      Hi everyone,

      I am just starting out with home processing of plates and am thinking of getting a platemaker. 

      Ideally, I'd get a quality one, but given space and budget constraints,  I am thinking of getting one of the China/India type platemakers (3 in one, exposure, drying, washout).
      These range from USD1k - 2.5k. Alternatively, doing something DIY might cost me a few hundred dollars.

      As far as I know, the china/india machines' exposure units have vacuum sheets and are timer controlled. Washout units are typical (automated brush + water).

      --Is there anything in particular I should be looking out for / asking the equipment sellers?
      --Is exposure typically controlled just by time factor? Or are there are other variables such as lamp intensity etc that I should be considering?
      --Is drying process really important? Apart from time factor is it important to control heat temperature etc as well?

      I was thinking of going a DIY route, but that would probably set me back a few hundred dollars + time required to build everything up. I am not sure if DIY will also give consistency (given lack of vacuum screen, hand washing, hand drying). As such, going for a cheaper machine (USD1k range) might be a more viable option.

      Appreciate any tips / advice :)



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