ARC-GRAINED LITHOPLATE AND TWO-STEP METHOD FOR MAKING IT

摘要

ARC-GRAINED LITHOPLATE AND TWO-STEP METHOD FOR MAKING IT An essentially flat "arc-grained" surface of a sheet of aluminum alloy is produced with a coarse and non-uniform microstructure which, after it is coated with a durable phosphate-free coating, provides excellent lithoplate. Though such arc-grained microstructure is much coarser than an electrochemically etched surface typically used on lithoplate, the very coarse surface is peculiarly well-adapted to provide durable lithoplate after it is coated with a phosphate-free protective surface. After the coated surface is coated with a photoresist the excellent resolution of prints is maintained over a large number of repeated uses in an off-set printing press. A method of producing lithoplate comprises, controlledly rastering an A-C, or D-C reverse polarity plasma-generating electric arc on an aluminum sheet less than 30 mils thick, kept distortion-free on a mounted surface such as on a cylindrical drum; then coating the arcgrained surface with a hard and durable, inert phosphatefree coating while maintaining a capillary microstructure in the surface adapted to provide a support for a photoresist for use in lithographic printing of adequate resolution.