2026-11-08 · Technical note
What a Polyurethane Resin Actually Does in a Printing Ink
The binder decides adhesion, flexibility, gloss and heat resistance. A short guide to reading a PU resin requirement.
Ink is pigment, binder, solvent and additives. The pigment is what you see. The binder is what makes the print survive.
Four jobs
Adhesion. The binder wets the substrate and forms a film that sticks to it. On treated PE or PP the surface energy is marginal, and the resin is the difference between a print that stays and one that rubs off in the reel.
Film formation. After the solvent leaves, the resin has to form a continuous film around the pigment. Poor film formation shows as low gloss and poor rub resistance.
Flexibility. A pouch is folded, formed and filled. A rigid print cracks at the fold. Soft resins flex; hard resins resist blocking and give gloss. This is the main trade-off in grade selection.
Heat resistance. Heat sealing, hot fill and retort all put the print through temperature. Standard PU binders soften; high-temperature grades such as HY-PU30C are specified where that matters.
Reading a requirement
| If the problem is | The resin property to change |
|---|---|
| Print rubs off | Adhesion, or substrate treatment |
| Print cracks on the former | Flexibility / elongation |
| Low gloss | Film formation, resin molecular weight |
| Blocking in the reel | Hardness, blocking resistance |
| Fails at heat seal | Heat resistance grade |
What to send a resin supplier
Substrate, solvent system, pigment and loading, the process temperature and the defect you are trying to fix. That is a specification. "We need a PU resin" is not, and it usually results in three samples and three trials that answer nothing.