PU Resins for Printing Inks and Coatings

In a printing ink the pigment provides colour and the binder provides everything else: adhesion to the substrate, film formation, gloss, resistance to rub and heat, and the rheology that lets the ink run on press without fisheyes or skipping.

Why a PU binder

Polyurethane binders are chosen when adhesion to a difficult substrate or resistance to heat matters more than the lowest possible raw material cost. They are common in:

• Flexographic and gravure inks on treated PE, PP, PET and metallised film.
• Heat-seal and protective lacquers.
• Coatings where nitrocellulose or acrylic systems have reached their adhesion or heat limit.

What to balance

A harder resin gives gloss and block resistance; a softer one gives flexibility and adhesion. Heat resistance tends to cost flexibility. The right point on that triangle depends on what the pack will do after printing, not on a generic "best" grade.

Trials

Send the ink formulation target, substrate and process temperature. A grade and a sample are proposed, and the trial is run at the ink maker rather than at the resin plant, because the ink is the system that has to work.