Two processes put almost all of the graphics you see on molded plastic products: a silicone pad that lifts ink out of an etched plate and lays it onto a shaped surface, and a mesh screen that a squeegee pushes ink through onto a flat one. They cost about the same per part and use similar inks. Choosing between them is decided by geometry first, image quality second, and cost a distant third.
Get it wrong and the symptom is predictable. Screen printing forced onto a curved bezel gives a logo that thins toward the edges; pad printing forced onto a large flat panel gives visible pad edges and uneven density.
How Each Process Works
Pad printing
Artwork is etched into a steel or photopolymer plate called a cliché, to a depth of roughly 20 to 25 microns. Ink floods the etch, a doctor blade wipes the surface clean, and a silicone pad presses down, lifts the ink film, and rolls it onto the part. Because the pad deforms, it conforms to compound curves, recesses, and textures nothing else can reach. Each color needs its own cliché and station.
Screen printing
A polyester mesh on a frame is coated with photo emulsion and exposed through a film positive, opening the image area. A squeegee forces ink through the mesh onto the part below. The part must be flat or a simple developable surface — a cylinder can be rotated under a stationary squeegee, a doubly curved shape cannot.
Geometry Decides First
- Compound curves, dished faces, textured surfaces: pad printing, with no real competition.
- Flat panels, overlays, lens covers: screen printing.
- Cylinders and cones: screen printing on a rotary jig.
- Recessed logos in a pocket: pad printing, since the pad reaches in.
- Print areas larger than about four inches square: screen printing, because pad size and film thickness limit large solid coverage.
Image Quality and What Each Can Resolve
Screen printing lays a thicker ink film — commonly 8 to 15 microns versus 4 to 8 for a single pad impression. That matters for opacity: white on a dark housing looks solid in screen and often needs a double hit in pad. Screen also holds large solid areas evenly, which pad printing cannot.
Pad printing wins on fine detail, resolving lines down to about 0.1 mm and text to roughly 4 point, which is why regulatory marks and instrument scales are usually padded. Screen printing on plastic bottoms out near 0.15 to 0.2 mm line width.
Registration between colors is tighter in screen printing, generally ±0.1 mm against ±0.15 to 0.25 mm for multicolor pad work. If artwork depends on colors butting perfectly, design in a trap or a keyline — a detail to settle during the CMF stage, not at the decorator.
Tooling, Setup, and Per-Part Cost
Both processes are cheap to tool compared with anything that touches a mold.
- A pad printing cliché runs $60 to $150 per color; silicone pads are $30 to $120 and are consumables.
- A screen with emulsion and film runs $40 to $120 per color and wears out after a few thousand impressions.
- Part-holding fixtures are the real tooling cost on both: $300 to $2,500, one per part geometry.
- Setup and color matching runs one to three hours of shop time, typically $150 to $400 per job.
Per-part pricing for a single color lands around $0.08 to $0.30 for either process, rising with each added color. Below a thousand parts, setup dominates and the two are indistinguishable on cost. Above roughly a hundred thousand a year, the question becomes whether the graphic should be molded in at all — the argument for in-mold labeling or a textured molded-in logo, laid out alongside the other options in how to put a logo on a product.
Ink Adhesion Is the Part That Fails
Print quality problems get caught at the decorator. Adhesion problems get caught by your customer six weeks later, when the logo rubs off under a thumb.
Substrate is the dominant variable. ABS, PC, PC/ABS, PVC, and acrylic accept standard inks well. Polypropylene, polyethylene, POM, and PTFE are low surface energy plastics that reject ink unless treated — flame, corona, or plasma to raise surface energy above roughly 42 dynes per centimeter, checked with dyne pens before printing. If the print requirement is known early, it should influence the resin decision described in how to choose the right plastic.
Mold release is the second killer. Silicone-based release agents migrate to the surface and defeat every ink. Specify a release-free process or a paintable release, and require solvent wiping before decoration.
Qualify adhesion with real tests, not a thumbnail:
- Cross-hatch tape test per ASTM D3359 — cut a lattice, pull specified tape, grade the removal. Require the top classification on a signed sample.
- Solvent rub — isopropyl alcohol under fixed load, typically 50 double rubs, for products that meet cleaning wipes.
- Abrasion — crockmeter or Taber cycles matched to the use case.
- Environmental — humidity soak, thermal cycling, and sunscreen or sanitizer exposure, then repeat the tape test.
Two-component catalyzed inks give the best chemical resistance but have a limited pot life and need a cure cycle, often 24 hours at room temperature. UV-curable inks cure in seconds and suit high volume but adhere to fewer substrates. Printing over a soft-touch coating is its own adhesion problem, and printing on painted metal follows the rules in powder coating versus wet paint.
When Laser Marking Beats Both
Laser marking removes ink from the equation. A fiber or UV laser either ablates a painted top layer to reveal a contrasting base coat — the backlit keypad effect — or foams a laser-additive-loaded resin directly. No tooling per graphic, no color matching, no adhesion test, and serialization becomes free.
The limits are real: one color, set by the resin or base coat, so brand colors need pre-painting; a few seconds of cycle time per part; and contrast that must be validated on the exact resin lot. It is the right answer for variable data, regulatory legends, and the icon sets discussed in product icons and markings.
Decide Decoration Before the Mold Is Cut
Print area flatness, draft on the decorated face, texture in the print zone, and fixturing datums are all mold decisions. Projects House works these into the part design for US clients and manages decoration qualification through a global manufacturing network. Send your part files and artwork through our contact form.