GB1278293A - Preparation of presensitized printing plates - Google Patents

Abstract

1278293 Photo-sensitive materials and printing plates therefrom WISCONSIN ALUMNI RESEARCH FOUNDATION 2 June 1969 27819/69 Headings G2C and G2M [Also in Divisions C4 and C7] A presensitized printing plate comprising a support of Cu, Zn, Al, Fe, Ag, Sn, Pb, Mg, Cr, Mn, Ni, alloys thereof, brass or steel is produced either by (i) abrading the surface of the support while it is wetted with a diazo resin or (ii) abrading the support while wet and then rubbing the wet abraded support with diazo resin solution. In the first method, the support is preferably cleaned to remove dirt and then either wetted with diazo resin solution before abrasion or diazo resin solution is added to the abrasive paste e.g. rose tripoli, silica glass powder or pumice. An anti-oxidant such as thiourea or hydroquinone may be added to the diazo resin solution or the process carried out in an inert atmosphere to prevent oxidation. The plate produced may be used as a photo-lithographic plate or be further coated with a solution of diazo resin which may be water-soluble (A-stage) preferably coated in an inert atmosphere or in the presence of an anti-oxidant or partially cross-linked (B- stage) if coated in the presence of oxygen. The further coated plate may be imagewise exposedand electrolytically etched which etches the metal in the areas underlying the unexposed areas with the A-stage resin and the metal underlying the exposed areas with the B-stage resin. However, rapid etching of a magnesium support occurs under the unexposed areas irrespective of resin used. The plate may now be developed to remove all the diazo resin and used as a gravure printing plate or etching may be continued until areas of A-stage resin above etch is removed and then the remaining unexposed areas exposed to produce an oleophilic surface and thus produce a lithographic plate. The wells of the gravure plate may be strengthened and made more oleophilic by plating with copper. In the second method, the metal support is scoured with a rose tripoli or white tripoli paste, washed with acid and then water and whilst still wet coated by rubbing with diazo resin solution. This rubbing may be produced by (a) vigorous scrubbing with a squeegee or (b) repeatedly passing the plate between compressed rotating rubber rollers. A- or B- stage diazo resins may be used; the B-stage resin may be produced by heating, after coating. Alternatively, after imagewise exposure, the resin may be hardened by heating or treatment with cupric bromide and a ferrocyanide before electrolytic etching as above to produce a gravure plate.