Printing Tack Development and Coated Paper Structure

We define Printing Tack to be the ink tack in contact with paper in the printing nip. Time-dependent changes in printing tack depend on coating structure and composition. For very absorbent coatings, the printing tack starts from a maximum value, and decreases rapidly. For very non-absorbent coatings, the printing tack increases to a maximum and then slowly decreases. Penetration of the polymer solution phase causes the printing tack to decrease, since printing tack decreases as the effective ink film thickness decreases. Diffusion of the solvent into the coating binder may also cause tack to increase, since the concentration of polymers within the ink would increase. However, a quantitative explanation of these phenomena requires further study of ink-coating-press interactions, including the solution of the equations governing fluid flow through the coating pore structure and solvent diffusion through the coating binder.