In gravure, the image is engraved as millions of tiny cells into a chrome-plated copper cylinder. The cylinder runs in an ink bath, a doctor blade wipes the non-image surface clean, and the ink remaining in the cells transfers to the substrate under pressure.
It gives exceptional consistency over very long runs, excellent image quality and heavy, uniform ink lay-down. The cylinder cost is high, which is why gravure suits long runs and flexo suits short ones.
Gravure inks are low in viscosity — typically 15-25 seconds on a Zahn cup — because the ink must flow into and release cleanly from the cells. Solvent-based polyurethane systems dominate the packaging segment for their adhesion and flexibility on film.
The practical formulation concerns are cell release, drying rate matched to press speed, and viscosity stability as solvent evaporates from the ink pan during a long run.