Direct-imaging flexible offset printing plate and method of manufacture

摘要

A flexible offset printing plate is formed from a directly imaged electrophotographic member comprising an inorganic coating of a photoconductive material on a polyester substrate. The photoconductive material is an oriented crystalline deposit about 3000 Angstroms thick which has been directly sputtered with radiofrequency energy in a process using a Langmuir sheath to produce a light sensitive, readily imaged abrasion-resistant, transparent coating. It is deposited on a sheet of dimensionally stable, transparent polyester film having a thickness of about 0.005 inch with an intervening sandwiched layer of ohmic material such as indium-tin oxide about 300 Angstroms thick. The transparency of the ohmic layer and the photoconductive coating on a transparent substrate result in a transparent plate. The electrophotographic member is imaged by charging, exposure and toning with a suitable toner. The non-imaged parts of the surface are rendered hydrophilic (having a strong affinity for water and repellant to greasy ink) by suitable chemical and/or mechanical treatment while the imaged and toned parts are rendered hydrophobic (water-repellant and having a strong affinity for greasy ink). This may simply comprise choosing a type of toner which is inherently hydrophobic. The plate is mounted in an offset press and printing effected as though it were a conventional offset plate using the usual grease- or oil-based inks.