Pad Printing
Pad printing lifts ink out of an etched plate with a silicone pad and transfers it onto a curved or recessed surface.
- Part
- Finishing
- Revised
- 2026-08-11
At a glance
- Family
- Printing
- Typical tolerances
- Image position typically within ±0.005 in (±0.13 mm); the transferred ink film is a few microns and adds nothing dimensionally
- Surface finish
- Adds a very thin ink film that follows the substrate; gloss is set by the ink system
- Typical volumes
- A few hundred to millions of parts; tooling cost is low enough for short runs
- Lead time
- 1–2 weeks including cliché and fixture; 2–5 business days for a repeat order
- Materials
- Plastic, Metal, Glass, Ceramic
What it is
Pad printing transfers ink from an etched plate to a part using a soft silicone pad. The pad picks the image out of the etched recess, the ink's surface chemistry changes during the brief transit, and the pad releases the image onto the part as it deforms against the surface. Because a silicone pad conforms to whatever it touches, pad printing is the standard way to put graphics onto curved, spherical, recessed, stepped and textured surfaces that no flat printing process can reach.
The etched plate — the cliché — is typically cut to 20–30 µm (0.0008–0.0012 in) deep, and the ink film that survives onto the part is a fraction of that: a thin, low-build mark that adds essentially nothing dimensionally. One pad and one cliché produce one color, so multi-color work uses multi-station machines with registration typically held within about ±0.005 in (±0.13 mm). Typical applications are keycaps, medical device graduations, cosmetic closures, automotive switchgear, toys and instrument dials.
How it works
- Etch the cliché. The image is etched into a steel or photopolymer plate to a controlled depth of roughly 20–30 µm (0.0008–0.0012 in). Depth is critical: too shallow and the pad cannot pick up enough ink, too deep and the pad cannot pull all the ink out, leaving a hollow center in solid areas.
- Flood and doctor. Ink floods the plate and a doctor blade or sealed ink cup wipes the surface clean, leaving ink only in the etched image.
- Pick up. The silicone pad presses onto the plate and lifts the ink film. Silicone's very low surface energy is what makes the process work — ink prefers almost any other surface to the pad.
- Transit. As the pad travels, solvent flashes from the exposed outer face of the ink film, making it tackier on the outside than on the pad side. This asymmetry is what drives near-complete release onto the part.
- Transfer. The pad deforms against the part and rolls the image on from the center outward. Pad shape matters: a pointed pad rolls air out ahead of the print, while a flat pad traps it and causes voids.
- Cure. One-component solvent inks air dry or force dry. Two-component catalyzed inks — epoxy and polyurethane — crosslink over hours to days and give the adhesion and chemical resistance needed on hard plastics, glass and metal. UV inks cure in seconds under a lamp.
Surface energy governs adhesion
Ink will not wet a low-energy surface. Roughly 38 dyne/cm is the working threshold, and polypropylene, polyethylene, acetal and fluoropolymers all fall below it as molded. Those materials require flame, corona or plasma treatment immediately before printing, and the treatment decays over hours to days, so it has to be scheduled as part of the print operation rather than done in advance.
Design guidelines
Keep the image inside a printable zone
The pad has to conform to the surface without folding. Compound curves, deep pockets, steps and edges within the image area cause distortion, smearing or voids. Keep artwork on a single continuous surface, stay at least 0.040 in (1 mm) away from an edge or a parting line, and avoid printing across a radius tighter than the pad can follow.
Size features to the process
Minimum line width of roughly 0.004 in (0.1 mm) is achievable with a well-controlled cliché and a fine pad. Fine serifs, small reversed-out text and tight halftones lose definition. Solid areas larger than about 0.5 in (13 mm) across risk a hollow center — designers break large solids into a screened fill or accept a specialized deep-etch cliché.
Budget one setup per color
Each color needs its own cliché, pad, ink and station. A four-color graphic on a curved surface is a four-station machine or four passes, with registration typically ±0.005 in (±0.13 mm). Design registration tolerance into the artwork with trapping rather than assuming perfect alignment.
Specify the ink system and the adhesion test
Ink chemistry, not the printing, determines whether the graphic survives. Specify the ink family (one-component, two-component catalyzed, or UV), any required pretreatment, and an acceptance test — cross-hatch tape adhesion to ASTM D3359 plus whatever solvent, abrasion or sterilization exposure the product will see.
Account for surface energy at the design stage
If the part is polypropylene, polyethylene, acetal or a fluoropolymer, plan for flame, corona or plasma treatment as an in-line step. Mold release, plasticizers and antistatic additives migrate to the surface and destroy adhesion, so the resin formulation matters as much as the base polymer.
Provide a locating feature
The part must sit in a nest that positions it repeatably relative to the pad. A flat, a boss, a pair of holes or a molded-in datum makes fixturing simple; a free-form part without one drives fixture cost and registration scatter.
| Feature | Recommended | Limit | Why |
|---|---|---|---|
| Cliché etch depth | 20–30 µm (0.0008–0.0012 in) | — | Too shallow starves the pad; too deep hollows solids |
| Minimum line width | 0.008 in (0.2 mm) | 0.004 in (0.1 mm) | Fine detail loses definition in transfer |
| Solid area size | Under ~0.5 in (13 mm) across | Screen or deep-etch beyond | Large solids print with a hollow center |
| Distance from edge | 0.040 in (1 mm) minimum | — | Pad folds and smears at an edge |
| Registration (multi-color) | ±0.005 in (±0.13 mm) | Design in trapping | Each color is a separate station |
| Substrate surface energy | ≥ 38 dyne/cm | Pretreat PP, PE, POM, PTFE | Ink cannot wet a low-energy surface |
Cost drivers
Pad printing carries very low tooling cost and moderate per-part cost, which makes it economical from a few hundred pieces upward.
- Number of colors. Each color is a cliché, a pad, an ink station and a setup. Color count is the dominant cost variable.
- Cliché type. Photopolymer plates are cheap and fast but wear; steel clichés cost more and last for long production runs.
- Fixturing. A simple nest is inexpensive; a multi-cavity or indexing fixture for a contoured part is real tooling amortized over the program.
- Pretreatment. Flame, corona or plasma treatment on low-energy plastics is an in-line operation with its own equipment and process control.
- Ink system and testing. Two-component catalyzed inks have a pot life and produce waste; qualification testing for adhesion, chemical and abrasion resistance is a fixed program cost.
Cost-reduction tactics:
- Reduce the color count. A single-color mark on a molded-in contrasting surface is dramatically cheaper than a four-color graphic.
- Design the artwork within one continuous surface so a simple pad and nest will do the job.
- Choose a printable resin — an ABS or PC part avoids the pretreatment line entirely.
- Use molded-in text or texture for content that never changes, and print only what varies.
- Where the surface is flat and the run is long, compare against screen printing, which lays down a heavier, more opaque film per pass at a lower per-piece rate.
Questions
6 questionsWhat can pad printing print on that other processes cannot?
Curved, spherical, recessed, stepped and textured surfaces. The silicone pad deforms to whatever it touches and rolls the image on from the center outward, which is why pad printing is used for keycaps, medical device graduations, cosmetic closures and instrument dials that no flat process can reach.
How fine a detail can pad printing hold?
Roughly 0.004 in (0.1 mm) minimum line width with a well-controlled cliché, though 0.008 in (0.2 mm) is a safer design target. Fine serifs, small reversed-out text and tight halftones lose definition, and solid areas larger than about 0.5 in (13 mm) across risk printing with a hollow center.
Why does ink not stick to my polypropylene part?
Surface energy. Ink cannot wet a surface below roughly 38 dyne/cm, and polypropylene, polyethylene, acetal and fluoropolymers all fall below that as molded. They require flame, corona or plasma treatment immediately before printing, and the treatment decays over hours to days so it must be an in-line step.
How many colors can pad printing do?
As many as the machine has stations, but each color requires its own cliché, pad, ink and setup, so color count is the main cost driver. Registration between colors is typically held within about ±0.005 in (±0.13 mm), so artwork should include trapping rather than assume perfect alignment.
How thick is a pad-printed ink film?
Very thin. The cliché is etched only 20–30 µm (0.0008–0.0012 in) deep and the film that survives onto the part is a fraction of that — a few microns. It adds nothing dimensionally, but it also means pad printing is a poor choice where heavy opacity over a dark substrate is required.
Pad printing or screen printing?
Pad printing for curved, recessed or textured surfaces and small graphics with low tooling cost. Screen printing for flat or gently curved surfaces where a much heavier, more opaque ink film is needed, or where the image area is large — a screen lays down far more ink per pass at a lower per-piece rate on long runs.