Pad Printing Plates
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Reference · Pad Printing
Polymer Plate Development Procedures
How EPS makes polymer clichés — the two exposures, the wash, and the exposure times for every plate material we supply.
Download the manual (PDF)
The full ten-page illustrated procedure.
A polymer plate — the cliché — is the tooling that carries your image in pad printing. It is a sheet of photosensitive material that changes chemically when ultraviolet light hits it, a reaction called polymerization. Where light reaches the plate, the surface hardens. Where a film positive blocks the light, it stays soft and washes away, leaving the image etched below the surface for ink to sit in.
This is EPS’s own plate-making procedure, the one our applications lab runs. Follow it in order and you will get repeatable plates; skip the test plates at the start and you will chase problems all week.
Before anything else: control the light. The room you make plates in must be out of direct sun — daylight carries enough UV to fog a plate before you ever expose it. Yellow safe lights, or UV-filtering sleeves inside your existing fixtures, solve it cheaply.
How the two exposures work
Most plates are exposed twice, and the two exposures do completely different jobs.
- The first exposure puts the image on the plate. The film positive sits emulsion-side down; its black areas block UV, so everything around the image hardens and the image itself stays washable.
- The second exposure sets how deep the image etches. A line screen — 90%/120 or 90%/80 lines per cm — is laid over the image and lets a controlled amount of light through, hardening the base of the image area. More light means a shallower etch; less light means a deeper one.
Single-exposure plate material skips the second step and always etches to the same depth, usually around 30 microns. Everything else should be screened. Screening yields higher ink transfer and a wider tonal range, and the finer the ruling, the better fine lines and small type hold up. Which of the two you should be running is a separate question, and Julian Joffe works through it in Selecting the Correct Cliché for Your Pad Printing Job.
Preparing the film positive
Almost every plate problem starts here.
- Place the positive on a light table emulsion-side down, right reading. To check: scratch the right-reading side with a razor. If the emulsion comes off, it is on the wrong side and the image needs to be output mirrored.
- Test the density. Print a solid black square outside the image area and hold the film up to a fluorescent tube. If you can see the bulb through the square, the film is too light — UV will pass through it and polymerize areas that should have washed out.
- Touch up pinholes inside the artwork with a permanent marker or opaque paint and a fine brush.
- Turn the film emulsion-side up and pick off dust and specks with a needle or razor. Anything black that you do not want printed will be etched.
Making the plate
First exposure
- Remove the protective cover from the plate.
- Red polymer only: dust the surface with a make-up brush carrying a little talc. It stops air being trapped and the surface texturing.
- Lay the plate on the base of the exposure unit, position the film positive emulsion-side down against the plate edges, and close the glass. If the unit has a vacuum, wait until it has fully sealed before starting.
- Set the timer and expose.
Second exposure
- Lift the glass and remove the film positive — but leave the plate where it is.
- Lay the line screen over the part of the image to be etched, emulsion-side down, shiny side up. Anything the screen does not cover will not etch.
- Close the glass, wait for vacuum, expose, then remove plate and screen.
Developing
Alcohol wash plates: lay the plate in the developer tray and rub lightly with the developer brush for 35 seconds, changing direction every 10 seconds.
Water wash plates: wash under lukewarm running water for 90 seconds.
Either way, dry immediately — pressurized air gun or a lint-free blot. Drying is what stops the etching; leave it wet and it keeps going. Then bake at 180 °F for 15 minutes to cure, and post-expose in the unit for 15 minutes with no vacuum. Post-exposure is what makes the polymer insoluble and scratch-resistant, and skipping it is a common cause of plates that wear out early.
A finished plate has a slightly recessed image, and on dual-exposure material you will see the screen pattern inside the etch. Drag a fingernail gently across it — it should catch.
Finding your exposure times
The times below are starting points, not settings. Bulb power, bulb age, lamp spacing, distance to the glass, vacuum blanket condition and film type all move the numbers, which is why you make test plates on scrap material first — and re-test with every new batch of plate.
| Code | Material | Wash | 1st exposure | 2nd exposure | Develop | Oven bake | UV post-expose |
|---|---|---|---|---|---|---|---|
| GY1 | Grey Polymer | Alcohol | 60 sec | 150 sec | 35 sec | 15 min | 15 min |
| GY2 | Green Polymer | Alcohol | 45 sec | 30–40 sec | 65 sec | 15 min | 15 min |
| GY3 | NY20 Single Exp | Alcohol | 150 sec | single exposure | 1 min | 15 min | 15 min |
| GY4 | Green Polymer | Alcohol | 60 sec | 140 sec | 50 sec | 15 min | 15 min |
| RD | Red Polymer | Alcohol | 100 sec | 125 sec | 50 sec | 15 min | 15 min |
| OR | Orange Polymer | Water | 35 sec | 30 sec | 75 sec | 15 min | 30 min |
| AQ | Aqua Nylon | Water | 45 sec | 4–5 min | 90 sec | 15 min | 15 min |
| GN1 | Green Polymer | Water | 35 sec | 35 sec | 75 sec | 15 min | 15 min |
| GN2 | Green Polymer | Water | 60 sec | 80 sec | 90 sec | 15 min | 15 min |
| RDW | Red Polymer | Water | 100 sec | 215 sec | 50 sec | 15 min | 15 min |
Read the results like this:
- Area outside the image is washing away or looks pitted → first exposure too low. Increase in 5-second steps.
- Losing fine detail and thin lines → first exposure too high. Decrease in 5-second steps.
- Etch too shallow → second exposure too high. A long second exposure lets the light spread and undercut each dot, broadening the cell so less polymer washes out.
- Etch too deep → second exposure too low. The dot pattern nearly disappears, and a large etched area will then scoop.
Once you have times that work, hold them. But understand why they work — when something changes, that understanding is what lets you correct it.
Troubleshooting
| Symptom | Likely cause |
|---|---|
| Image fuzzy, or will not wash out | Film density too low · emulsion on the wrong side · air trapped between film and plate · over-exposure |
| No image at all | Incorrect light source · under-exposure |
| Etch depth too shallow | Second exposure too long · not enough wash time · developer solution incorrect or expired |
| Surface residue, or plate looks damaged | Not rinsed thoroughly · first exposure too low |
| Blisters | Dryer too hot — above 200 °F |
| Premature wear | Not dried enough · post-exposure too short · improper ink cup tension, or running an open inkwell |
Shelf life and storage
Unexposed plate material keeps about a year in a black bag, somewhere with low humidity. Heat and daylight both shorten that considerably, and a plate that has partially fogged in storage will never expose predictably no matter what you do with the timer.
Related
What you need to run this process.
Common questions about polymer plate making
What is a polymer plate in pad printing?
The cliché — the tooling that carries your image. It is a photosensitive sheet in which the image is etched by UV exposure through a film positive. Ink floods the plate, the doctor blade or ceramic ring wipes it clean, and ink remains only in the etch for the pad to pick up.
Why does a polymer plate need two exposures?
They do different jobs. The first exposure places the image; the second, made through a line screen, controls how deep it etches. Without the second exposure you get whatever depth the material gives you — normally around 30 microns — and no ability to tune it to the substrate.
How deep should a pad printing plate be etched?
Deep enough for the substrate. Porous materials such as wood or leather want a deeper etch than plastics or glass, because they absorb more ink. As a shop check, a fingernail dragged gently across the etched area should catch. If you need more depth, shorten the second exposure; for less, lengthen it.
What is scooping and how do I stop it?
Scooping is the doctor blade or ring flexing down into a large open etched area and dragging ink back out, which prints as a faded center. The fix is half-tone: exposing through a screen leaves tiny evenly spaced peaks inside the etch that support the blade, break the ink surface tension and stop ink migrating during doctoring. Solid areas over about an inch across are where it shows up.
How long do polymer plates last?
Depends on the chemistry — roughly 3,000 to 50,000 cycles across the polymer range. Above about 100,000 cycles a thin steel plate is the better economics, and those run past a million. Unexposed plate material keeps about a year in a black bag in low humidity.
Why is my plate wearing out early?
Three usual causes: it was not dried thoroughly before baking, the post-exposure was too short to make the polymer fully insoluble, or the ink cup tension is wrong. Running an open inkwell system chews through polymer far faster than a sealed cup with a ceramic ring.
Would you rather we made the plate?
Send us the artwork and our applications lab will etch the cliché — 24-hour turnaround, and the same plates we run on our own machines. Or we will supply the exposure equipment and the material and show your team how to do it in house.