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Platemaking Supplies Category

Tell me how to put new adhesive on an old letterpress plate.

If you start to see gunk stuck in the adhesive (cat hair, human hair, your lunch crumbs, etc.), then it’s time to put new adhesive on your polymer plate. This should be a pretty easy process but does require a little muscle.

First, peel up the old adhesive to remove it. You’ll need some good fingernails to get between the adhesive and your plate. Since the adhesive holds onto the plate strongly, you can potentially kink the plastic backing if you’re not careful. We recommend that you lay the plate face down on a flat surface. Hold the plate down with one hand while peeling the adhesive off with the other. Try and keep the plate from flexing inordinately while you carefully tug the adhesive off the back of the plate. The adhesive might tear into pieces, but you can simply pull it up in strips.

Now, put on the new adhesive. If you have purchased a 12” x 18” sheet of adhesive, lay the blue release paper on a flat surface and have the brown silicone paper side face up. You will remove this silicone paper to show the sticky adhesive. If you have a roll of adhesive, pull out or unroll the adhesive so the sticky side is face up. When you first mount the adhesive to the plate, start with one side or corner of the plate and lay down the plate to the adhesive so that it makes as few air gaps or bubbles as possible. If the bubbles happen, work them out with your fingers or pierce them, through the back of the adhesive, with one prick of an Exacto knife or awl. You should be able to get all the bubbles out at this point.

If bubbles form underneath the plate when you mount it to the base, first try working these out to the edges of the plate with your fingers. If that fails, you can puncture the bubbles by sticking an Exacto knife through the BACK of the plastic backing of the plate (the blue side) to release the trapped air.

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When do I replace my kreene in my platemaker? And how do I replace kreene?

Kreene, a flexible and matte transparent plastic, is used in a platemaker’s vacuum frame to hold films securely against photopolymer plates during exposure. But over time, it’s the nature of kreene to get wrinkled and lose flexibility. When you find that your kreene no longer creates a smooth seal, it’s time for a kreene replacement! At Boxcar Press, we replace our kreene every few days, but we process a lot of plates. With lower use, kreene can last for several months.

To replace your kreene: cut out a square of kreene to the size of the previous kreene piece (your kreene will be slightly larger than the grooves in the vacuum table). If your platemaker has one, pull the round bar out the previous sheet of kreene. Affix the new sheet of kreene to the bar with double-stick tape. Lay the kreene in position on the vacuum table and turn the vacuum on. Work out any wrinkles in the kreene so it remains flat. Using double-stick tape, affix the kreene edge opposite the bar to the vacuum table. You can then roll the kreene out over your vacuum table and start exposing your polymer plates. To increase the life of your Kreene, roll it out flat in your platemaker at the end of the day.

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When do I replace my platemaker’s brushes?

A platemaker’s brushes wear out after prolonged use: these brushes should be replaced every 6-36 months. You can tell when a brush is tired out because the bristles are matted down. You can lengthen your brush life by keeping the brushes wet all the time and running your fingers through them to encourage the bristles to stand up. We sell replacement brushes for all of our platemakers: please e-mail or call us to order these.

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How do I maintain the mounting rubber on my platemaker?

Magnetic mounting rubber and rigid mounting rubber come pre-sealed. Over time, this seal breaks down. You can make touch-up repairs with our green die sealer. Remove any old die sealer and apply green die sealer in a thin bead to the edge of the mounting rubber. Let dry overnight.

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Is processing a photopolymer plate toxic?

None of the byproducts of processing photopolymer plates are known to have health risks, except if you’re allergic by contact to plastic. Check out the MSDS’s for more specific health information. You can find each plate’s MSDS on it’s product page: plastic-backed plates; steel-backed plates; intaglio plates.

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How do I process my photopolymer plates?

Because processing your own plates can get complicated – and the results need to be excellent for quality letterpress printing – we recommend using a dedicated photopolymer platemaker. If you don’t already own one of these machines, we can help you source out light boxes, washout and exposure units, whatever your budget. If you’d rather learn how to hand-process your plates, we recommend checking out Letterpress Commons and, if you can, taking a class at one of these great book arts centers: Center for Book Arts (NYC); Minnesota Center for Book Arts; San Francisco Center for Book Arts; Columbia College Center for Book and Paper Arts (Chicago). You’ll find essential exposure information in your plate’s datasheets, though you’ll want to use a Stouffer Gauge to perfect exposure. We can always process your plates professionally for you through our platemaking services.

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If I purchase unexposed photopolymer, do I need to purchase adhesive too?

It depends on the plate. If you’re purchasing unexposed plastic-backed plates, you’ll need adhesive to adhere the plate to your printing base. We sell adhesive in 12×18 sheets and 27 yard rolls. Apply to the back of the plate after processing. If you’re purchasing unexposed steel-backed plates, there’s no need to purchase adhesive. Adhesive is included if we process the plastic-backed plates for you.

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How often must I change the adhesive on my polymer plates?

As long as you’re careful about not getting dust or debris on the adhesive, and you carefully replace the blue protective release paper after use, the adhesive on your letterpress plates should remain sticky for many years. Keep in mind that adhesive can always be inexpensively replaced.

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How do I use a Stouffer Gauge to help process my plates?

Instructions for using the Stouffer Gauge to accurately figure out the exposure time for your photopolymer plates: The Stouffer gauge is a reusable piece of continuous-tone film that you should use to test photopolymer plate exposures. Place the Stouffer Gauge in contact with a 1” x 6” strip of plate material (after you peel off the plate’s protective plastic cover). Then expose the plate.

You’ll have to guess the first exposure time because that varies depending on the equipment that you use. Start with the exposure time listed on your plate’s tech data sheet. For exposure times, please keep in mind that these times are for commercial photopolymer platemaking equipment. Any alternative photopolymer platemaking devices may have very different times and you’ll have to experiment more to find your ideal time.

Also check the plate’s tech data sheet for the Stouffer value you’re trying to hold during exposure. For example, the 94FL has a Stouffer value of 18. Make sure that the exposure used with the Stouffer Gauge hardens the plate for all the numbers up to and including #18. If you goal is #18, and #19 and #20 start to harden during your exposure time, then your exposure time is too long– decrease the exposure time. If your goal is #18, and #17 hardens but #18 washes out on the test plate, then increase the exposure time.

You most likely will have to expose several different test plates at several different exposure times to find the perfect exposure. Since the Stouffer gauge is small, you won’t waste much plate material in the process.

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How should I store my polymer plates?

To preserve your plates, the manufacturers recommend storing polymer plates in a constant humidity between 50% and 60%. At the very least, avoid extreme fluctuations in humidity. If stored properly (and cleaned correctly), your letterpress plates can last for one year or more.

  • For your exposed plates, maintain a constant humidity by storing plates in a ziplock bag. Keep your plates away from ultraviolet light that will crack the surface of your plate (i.e. store in a drawer or cabinet).
  • For your unexposed plates, store in a black light-blocking bag that is taped shut.

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My letterpress plates are starting to curl. How do I flatten them out?

Like our skin, plates can be affected by the room temperature, humidity, and age. When humidity levels are low, the plates can look and feel brittle. With the passage of time, the thinner polymer on the plate edges are pulled towards the denser polymer text and images on the front—this causes curling. With a life expectancy of up to 1 year or more, polymer plates do age, but these simple steps can hydrate your plates and give them extra longevity.

Step 1. Place your plate back in your platemaking washout system for up to ½ a minute (or, if you don’t have a washout unit, simply immerse in water). We suggest room temperature for a quick dunking. A ½ minute may only be necessary if your plates are severely curled.

Step 2. Sponge off the water and place back in the drying oven of the platemaker for 5-10 minutes. If you don’t have a platemaker, use a hair dryer to warm the plate and make it more pliable.  Placing your plate in a box and blowing the hair dryer into the box will keep the warm air more contained and warm the plates more effectively.

Step 3. After the plate warms and starts to become more pliable, place the plate in its bag and set a heavy object on it to keep the flattened shape.

This should help your plates relax so you can adhere them to your base for additional print runs.

Here’s some final advice:

  • if using a hair dryer, take care to avoid putting it too close to the plates.
  • be patient, as warming the plates takes time.
  • watch that you don’t handle your letterpress plates too roughly after the wash and during drying so your relief images don’t chip.
  • remember to store your plates flat out of direct light and in a bag so that fluctuations in humidity don’t affect the polymer.
  • check your adhesive backing, to see if the adhesive needs to be re-applied to the back of your polymer plate for a secure hold on your base.

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