Abstract: A method for producing a water developable lithographic printing plate which comprises treating at least one surface of a metal sheet substrate with a layer of a lithographically suitable, light sensitive, water soluble substance and subsequently coating the thus treated base sheet with an upper layer of a water insoluble, ink receptive, lithographically suitable photosensitive composition. Said photosensitive layers must be either both positive working or both negative working. Upon imagewise exposure through a mask by standard methods the exposed areas of said upper photosensitive composition are alternatively characterized as either water permeable or water impermeable and the unexposed areas are alternatively water impermeable or water permeable as opposed to the exposed areas. Upon said imagewise exposure, the exposed lower level areas in a negative system are rendered water insoluble whereas the exposed lower level areas in a positive system are rendered more water soluble than the unexposed areas.

Abstract: A method for preparing aluminum based lithographic printing plates which comprises treating at least one surface of an aluminum base sheet with an interlayer composition, thereafter anodizing the thus treated aluminun surface, optionally retreating the coated, anodized aluminum plate with another stratum of the interlayer composition and then applying to said surface a suitable light sensitive composition to yield the desired photosensitive lithographic printing plate of improved characteristics.

Abstract: Apparatus for applying a coating of photographically sensitive liquid on one side of a moving aluminum web is constructed with a backing or support roller having stepped portions at each end of an unstepped central portion. The latter is engaged with the anterior surface of the web and is narrower than the web so that coating liquid applied to one surface of the web does not migrate to the edges of the web to contaminate the anterior side thereof. The width of the central portion is great enough so that mechanical stress on the web is not excessive and the undercut height is sufficient to exceed deflection of the web at the edges thereof.