Hello - I was hoping somebody could suggest some solutions to a recent printing problem I am having. I am pretty new to letterpressing, so this could be a beginner mistake, however.. I recently had some polymer plates made and I mounted them onto a boxcar base. Everything seems fine, but when I print the stock is picking up ink from the edge of the polymer as well as the impression?! I’ve tried making sure there is as little ink as possible, everything is clean, so i don’t understand how this is making an impression too? Is there a setting I could tweak or try?
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Roller settings are critical with photopolymer. It sounds like your rollers are hitting the plate a little too much and inking the edges of the plate. Are you using the deep relief or standard polymer? Which base? You should check the roller diameter versus the truck diameter — they need to be very close to the same, the rollers 1 or 2 thousandths larger if any. Also check your rail heights — they should be .918. You may need to tape roller trucks or rails to get the rollers just kissing the image area.
Thanks for getting back to me! I’m using the deep relief. I haven’t touched the rollers as I’m a little concerned I’ll through out all the settings, but I think that could be a good place to start. I assume I need something to measure the depth with to check this?
oh and the base i have is cast aluminium and fits my Adana 8″ x 5″, Base dimensions: 3.5″ x 6.5″ / 88.9mm x 165.1mm x 21.79mm.
Sarah, you might just try a quick fix — get some vinyl electrician’s tape and put one layer, with the ends butted, not overlapping, on each truck, and check your inking again. Keep adding layers one at a time, with the ends of each offset from the previous layer, until you’re no longer inking the edges of the plate. Also, check the plate edges to be sure they aren’t slightly raised, either because there is a thickness of polymer or because the edges got distorted in cutting. If you’re going to use photopolymer a lot, it would be worthwhile investing in a roller gauge, the “lollypop” type. You hold the gauge on the bed and run the inked rollers over it carefully, then read the stripe of ink. It should be within spec, probably about 1/8 inch wide, for the best roller setting.
If you have a good metal straightedge, place it on edge across your roller rails and measure under it with a type-high gauge or a piece of type. Measure in several places — they should all be type-high.
Thanks so much Bob, I’m going to have a go again hopefully this week so I’ll try all the things your suggesting first! Fingers crossed - thanks for the advice!
if your rollers are old and swollen at the ends-check are parallel, higher shore for photopolymer roller inking too, not soft rollers