A radiation sensitive element including a pretreated carrier, two radiation sensitive layers and a top layer, a diazo resin as negative useful for lithographic printing plates

摘要

A radiation sensitive element including (a) an optionally pretreated carrier and (b) a first radiation sensitive layer on the carrier including at least one diazo resin of given formula as negative, and (c) = a second radiation sensitive layer which is applied to the first one is new. A radiation sensitive element including (a) an optionally pretreated carrier and (b) a first radiation sensitive layer on the carrier including as negative at least one diazo resin of formula (I): R1 and R2 = H, alkyl or alkoxy, R3 = H, alkyl, alkoxy, or COOR, R = alkyl or aryl, X = organic or inorganic anion selected so that 1 g of diazo resin can be dissolved in 100 ml of water at 20 degrees C, Y = spacer group, m/n = 0.5-2, (c) a second radiation sensitive layer which is applied to the first one and includes at least one photo-crosslinkable polyvinyl acetal containing the structural units (A), (B), (C), and (D). R4 = 4C alkyl, optionally substituted by an acid group, where the phenyl group has 1 to 2 other substituents selected from halogen, amino-, methoxy-, ethoxy-, methyl- and ethyl, or a group -Z-BR5-CO-Q-COOH, Z = aliphatic, aromatic, or araliphatic spacer group, R5 = H, or aliphatic, aromatic, or araliphatic residue, and Q = optionally saturated chain- or ring shaped spacer group, k = 1-3, R6 and R7 = H or Me, R8 and R9 = H or 4C at maximum alkyl, or R8 together with the two C atoms to which it is bonded form a 5- or 6-membered carbocyclic ring, unit C can contain several independent repeated R4, unit D can contain several repeated R6-R9 residues including k, and at least one photosensitizer for photocycloaddition, where the second radiation sensitive layer does no contain a diazo compound. Independent claims are also included for the following: (1) Process for preparation of the radiation sensitive element including: (i) Preparation of an optionally pretreated carrier; (ii) Application of an aqueous solution including at least one water soluble diazo resin as defined above as negative, and optionally at least one additive, selected from: acids, surfactants, sealing agents, contrast colorants or pigments, exposure indicators, and plasticizers; (iii) Drying; (iv) Application of a water insoluble solution including at least one photo-crosslinkable polyvinyl acetate as defined above, and at least one photosensitizer for photocycloaddition, where the solution is free from diazo compound; (v) Drying; and (vi) Optional application of a waterborne top layer; and (2) Lithographic printing plate obtained by: (i) Preparation of a radiation sensitive element as defined above; (ii) Picture-like exposure of the radiation sensitive element with UV; and (iii) Development of the exposed element with an alkaline aqueous developer.