Photographic printing plate and method of exposing a coated sheet using

Abstract

A method and apparatus for exposing a layer of photoresist on a sheet includes positioning the sheet in a vacuum printing frame comprising a glass photographic printing plate carrying an opaque master pattern of metal or metal oxide on a central area of the printing plate. A light transmissive rubbery material is patterned in such a fashion as to overlie the opaque portions of the master pattern and provide a continuous path between the islands overlying the opaque master pattern. The rubbery material also extends in the peripheral area of the photographic printing plate and a plurality of mesas separated by channels are formed in this peripheral area. The channels have a width substantially greater than the path width formed between adjacent islands of rubbery material overlying the opaque portions of the pattern. The peripheral channels facilitate the evacuation of the plate and reduce evacuation time. The mesas of rubbery material in the peripheral area of the plate through which the channels are formed act as supports to space the printing plate from the resist coating on the metal sheet so that evacuation of the space between the printing plate and the sheet can be achieved without having the printing plate either be sealed-off by the metal sheet or by a second printing plate which is located on the opposite side of the metal sheet.