Infra-red switchable mixture for producing lithographic printing plate
Water-based mixtures that can be applied to substrates to produce infra-red sensitive layers with hydrophilic surfaces, which may be switched by image-wise exposure in an infrared imaging plate-setter to give oleophilic printing areas, for producing processless offset lithographic printing plates.
1 . A mixture for producing infra-red sensitive layers with hydrophilic surfaces, which may be switched by image-wise exposure to give oleophilic printing areas, comprising:
polyacrylic acid;
polyvinyl alcohol;
aminoplast cross-linking agent;
infrared sensitive dye or pigment; and
acidic hydrophobic polymeric emulsion,
wherein said mixture is deposited from an aqueous carrier liquid.
2 . The mixture of claim 1 , additionally comprising at least one of wetting agents, fillers and exotherms.
3 . The mixture of claim 1 , wherein the polyacrylic acid and the polyvinyl alcohol comprise together between 20% and 58% of the total solids of the mixture.
4 . The mixture of claim 1 , wherein the polyvinyl alcohol comprises less than 15% of the total solids of the polyacrylic acid.
5 . The mixture of claim 1 , wherein the aminoplast resin is water-soluble.
6 . The mixture of claim 1 , wherein the aminoplast resin provides crosslinking of the polyacrylic and polyvinyl alcohol resins to help insolublize them.
7 . The mixture of claim 1 , wherein the mixture does not contain catalysts for the cross-linking process involving the aminoplast.
8 . The mixture of claim 1 , wherein the aminoplast does not exceed 40% of the polyvinyl alcohol/polyacrylic acid mixture.
9 . The mixture of claim 1 , wherein the aminoplast is methyl methylol urea.
10 . The mixture of claim 1 , wherein the dye is water-soluble.
11 . The mixture of claim 1 , wherein the infrared absorbing pigment comprises water-dispersed carbon black and wherein the dyes dissolve in water miscible solvents.
12 . A method of producing a processless offset lithographic printing plate, comprising the steps of
providing a mixture comprising
polyacrylic acid;
polyvinyl alcohol;
aminoplast cross-linking agent;
infrared sensitive dye or pigment; and
acidic hydrophobic polymeric emulsion, said mixture deposited from an aqueous carrier;
applying a layer of the mixture onto a substrate to produce an infra-red sensitive layer with a hydrophilic surface;
drying the applied layer; and
switching the hydrophilic surface by image-wise exposure to infrared imaging to give oleophilic printing areas.
13 . The method of claim 12 , wherein said substrate comprises an offset lithographic printing plate precursor.
14 . The method of claim 12 , wherein said substrate comprises the surface of a printing press cylinder.
15 . The method of claim 12 , wherein said mixture additionally comprises at least one of wetting agents, fillers and exotherms.
16 . The method of claim 12 , wherein the polyacrylic acid and the polyvinyl alcohol comprise together between 20% and 58% of the total solids of the mixture.
17 . The method of claim 12 , wherein the polyvinyl alcohol comprises less than 15% of the total solids of the polyacrylic acid.
18 . The method of claim 12 , wherein the aminoplast resin is water-soluble.
19 . The method of claim 12 , wherein the aminoplast resin provides crosslinking of the polyacrylic and polyvinyl alcohol resins to help insolublize them.
20 . The method of claim 12 , wherein the mixture does not contain catalysts for the cross-linking process involving the aminoplast.
21 . The method of claim 12 , wherein the aminoplast does not exceed 40% of the polyvinyl alcohol/polyacrylic acid mixture.
22 . The method of claim 12 , wherein the aminoplast is methyl methylol urea.
23 . The method of claim 12 , wherein the dye is water-soluble.
24 . The method of claim 12 , wherein the infrared absorbing pigment comprises water dispersed carbon black.