Printing the graduation scale looks like a final marking step, but it decides whether dose readings stay legible, whether ink survives sterilisation, and whether the station can run in-line with assembly. A wrong process choice usually surfaces only at trial production or regulatory testing.
Why graduation printing is a critical station
The scale is the only reference a clinician has for reading a dose. Uneven line width, broken lines, faint ink or ink that lifts after sterilisation all create ambiguity and are rejected outright in type testing and final QC. The machine therefore has to deliver three things at once: clean edges on fine lines, durable adhesion on the barrel polymer, and a cycle time that matches the stations before and after it.
Pad printing vs screen printing: side by side
| Criterion | Pad printing | Screen printing |
|---|---|---|
| Surface geometry | A silicone pad conforms to small-diameter curved barrels and slight tapers, giving even coverage around the circumference | Better suited to flat parts or large radii; small barrels need dedicated fixtures |
| Graduation precision | Etched cliché holds 0.2–0.4 mm lines and small characters with clean edges | Heavier ink deposit tends to spread; fine line-width control is harder |
| Ink layer | Thin film, ideal for fine scales on transparent barrels | Thick, opaque layer, better for solid blocks and large marks |
| Changeover | Swap cliché and pad; recipe-based settings cover several specifications | New screens must be made, with longer lead time and cost |
| Line integration | Easily added as an in-line station running at the assembly takt time | Usually off-line or semi-automatic, with more buffering and manual hand-over |
Four parameters to confirm before choosing
- Barrel material and surface energy: PP, PE or copolymer, and whether plasma or flame pre-treatment is needed for adhesion.
- Diameter, taper and print arc length: these set pad hardness, cliché size and fixture location.
- Line width, character height and ink colour: fine lines favour pad printing; dark ink on a transparent barrel needs a contrast check.
- Sterilisation method and acceptance criteria: EO, moist heat or irradiation, with adhesion, rub-resistance and post-sterilisation colour-difference tests on the chosen ink.
In-line inspection, changeover and takt matching
A production-ready printing station does more than deposit ink: vision inspection judges every barrel for missing print, offset, smearing and out-of-tolerance line width, rejecting defects before the next station; tooling and settings are stored as recipes; and the cycle time is configured around the target output of the assembly machine, with bottlenecks handled by parallel stations or buffering. Graduation printing then becomes a verifiable, traceable step instead of an island.
Conclusion and how to get a proposal
For most disposable syringes, small-diameter curves, fine graduations and continuous production point to pad printing. Screen printing remains a sound choice for flat parts, heavy ink deposits or low-speed runs. Send us your barrel drawing, line width, target rate and sterilisation method: we provide free sample printing and a line proposal, verifying adhesion and legibility before any equipment is specified.
