Effect of Plate Material on Solid and Halftone Printing Quality.

Letterpress printing experiments were conducted to evaluate the printing quality of a variety of metal, plastic, and rubber plates. Identical transfer and print quality were found with all smooth hard plates, but roughened metal plates transferred less ink to the paper and required more ink for print coverage. Although rubber plates also transferred less, they provided better coverage and uniformity of solid prints than metal plates. On the other hand, dot fidelity of halftone prints was better with the harder plates. The halftones also required less ink for full coverage than the corresponding solids. The results suggest that the printing quality of hard plates depends on initial smoothness rather than on material, and the effectiveness of soft plates is due to enhancement of lateral ink flow in the deformed nip rather than to improvements in contact area. Since lateral flow is desirable for coverage of solids but not for dot fidelity, rubber plates are recommended for solid printing whereas hard plates are preferable for halftone printing.