Processless lithographic printing plate precursor

Abstract

A radiation-sensitive medium comprises hydrophilic polymer particles, the particles comprising a thermally softenable hydrophobic polymer, a hydrophilic polymer and a bonding compound capable of chemically bonding to the hydrophobic polymer and to the hydrophilic polymer. The radiation-sensitive medium further may comprise a substance capable of converting radiation into heat. The radiation-sensitive medium is aqueous-ineluable when coated and dried, and becomes hydrophobic under the action of heat. The polymer particles are made by polymerization of at least one hydrophobic monomer and at least one bonding compound in the presence of the hydrophilic polymer. The radiation-sensitive medium may be provided as a coatable composition to be applied to substrates to form a processless radiation-imageable lithographic printing precursor, which may further be provided with an aqueous eluable hydrophilic overcoat. The processless radiation-imageable lithographic printing precursor so created may be imaged using absorbed radiation that is imagewise converted to heat, resulting in areas of hydrophobic property, while unimaged areas retain their hydrophilic property. This allows the latent image so formed to be employed in creating a negative-working lithographic printing master. The negative-working lithographic printing master so created is irreversible, does not require a substrate of controlled hydrophilicity and provides great toughness in the exposed areas. The radiation-sensitive medium may be coated on-platesetter or on-press onto a suitable substrate, including the drum of the press. It may also be coated off-press on a suitable substrate to create a precoated processless radiation-imageable lithographic printing precursor.

1 . A method for making a negative-working lithographic printing master, the method consisting essentially of, in the order stated: 
 imagewise thermally irradiating a processless radiation-imageable lithographic printing precursor comprising a substrate, a dried and aqueous-ineluable coating of a radiation-sensitive medium on the substrate and, optionally, an aqueous eluable hydrophilic overcoat over the coating of a radiation-sensitive medium, the radiation-sensitive medium comprising: 
 a. a substance capable of converting radiation into heat,  
 b. hydrophilic polymer comprising an amine group, and  
 c. at least one thermally softenable or heat-fusible copolymer of a hydrophobic monomer and a monomer that has a carboxylic acid group,  
 wherein the dried and aqueous-ineluable coating becomes hydrophobic under the action of heat, and  
   treating the precursor with an aqueous medium to remove only said aqueous eluable hydrophilic overcoat, when present.    
     
     
         2 . The method of  claim 1  wherein the aqueous eluable hydrophilic overcoat comprises a water-soluble organic polymer.  
     
     
         3 . The method of  claim 2  wherein the water-soluble organic polymer is at least one of poly(vinyl alcohol), poly(vinyl acetate), poly(acrylic acid), poly(meth)acrylic acid, an alkali metal salt of poly(meth)acrylic acid, an amine salt of poly(meth)acrylic acid, poly 2-hydroxyethyl(meth)acrylate, poly(meth)acrylamide, polyvinyl methyl ether, polyvinyl methyl ether/maleic anhydride copolymer, poly(vinyl pyrrolidone), poly-2-acrylamide-2-methylpropane sulfonic acid, an alkali metal salt of poly-2-acrylamide-2-methylpropane sulfonic acid, an amine salt of poly-2-acrylamide-2-methylpropane sulfonic acid, alginic acid, a salt of alginic acid, protan jelly, carageenin, tragacanth, laminarin sulfate, starch, animal glues, vegetable mucilages, gum arabic, cellulose, a modification product of cellulose and a polysaccharide.  
     
     
         4 . The method of  claim 1 , wherein the substance capable of converting radiation into heat is hydrophobic.  
     
     
         5 . The method of  claim 1  wherein the irradiating is carried out using infrared radiation.  
     
     
         6 . The method of  claim 1  wherein the at least one hydrophilic polymer is at least one of a saccharide, a chitosan polymer, a polyethyleneimine polymer, a polyamine polymer, a polyvinylamine polymer, a polyallylamine polymer, a polydiallylamine polymer, an amino(meth)acrylate polymer, a polyamide polymer, a polyamide-epichlorohydrin polymer, a polyamine-epichlorohydrin polymer, a polyamidepolyamine-epichlorohydrin polymer, a dicyandiamide-polycondensation product polymer and a copolymer thereof.  
     
     
         7 . The method of  claim 6  wherein the at least one hydrophilic polymer is a chitosan polymer.  
     
     
         8 . The method of  claim 1  wherein said optional hydrophilic overcoat further comprises a water-soluble dye, colorant, or surfactant.  
     
     
         9 . The method of  claim 1  that is carried out without any wash-off development.  
     
     
         10 . The method of  claim 1  wherein said aqueous medium is water or a fountain solution.  
     
     
         11 . The method of  claim 1  wherein said coated and dried aqueous-ineluable coating is not removable in said aqueous medium either before or after said imagewise irradiating.  
     
     
         12 . The method of  claim 1  wherein said hydrophilic polymer and said copolymer are bonded in thermally softenable or heat-fusible particles.  
     
     
         13 . The method of  claim 12  wherein said thermally softenable or heat-fusible particles comprise a core predominantly of said copolymer predominantly and a shell of said hydrophilic polymer.  
     
     
         14 . A method for making a negative-working lithographic printing master, the method comprising the steps of: 
 providing a precursor comprising a dried and aqueous-ineluable coating of a radiation-sensitive medium on a substrate and, optionally, an aqueous eluable hydrophilic overcoat over the coating of a radiation-sensitive medium, the radiation-sensitive medium comprising particles of chitosan and at least one thermally softenable or heat-fusible hydrophobic polymer, the coating being hydrophilic and capable of becoming hydrophobic under the action of heat,    imagewise irradiating the precursor with infrared imaging radiation of wavelength between 700 nm and 1200 nm, and    treating the precursor with an aqueous medium to remove said optional hydrophilic overcoat.    
     
     
         15 . The method of  claim 14  wherein the aqueous eluable hydrophilic overcoat comprises a water-soluble organic polymer.  
     
     
         16 . The method of  claim 15  wherein the water-soluble organic polymer is at least one of poly(vinyl alcohol), poly(vinyl acetate), poly(acrylic acid), poly(meth)acrylic acid, an alkali metal salt of poly(meth)acrylic acid, an amine salt of poly(meth)acrylic acid, poly 2-hydroxyethyl(meth)acrylate, poly(meth)acrylamide, polyvinyl methyl ether, polyvinyl methyl ether/maleic anhydride copolymer, poly(vinyl pyrrolidone), poly-2-acrylamide-2-methylpropane sulfonic acid, an alkali metal salt of poly-2-acrylamide-2-methylpropane sulfonic acid, an amine salt of poly-2-acrylamide-2-methylpropane sulfonic acid, alginic acid, a salt of alginic acid, protan jelly, carageenin, tragacanth, laminarin sulfate, starch, animal glues, vegetable mucilages, gum arabic, cellulose, a modification product of cellulose and a polysaccharide.  
     
     
         17 . The method of  claim 14  wherein the overcoat further comprises at least one of a light-to-heat converting agent, a water-soluble dye, a colorant and a surfactant.  
     
     
         18 . The method of  claim 14  that is carried out without any wash-off development.  
     
     
         19 . The method of  claim 14  wherein said particles comprise a core predominantly of said hydrophobic polymer and a shell of chitosan.  
     
     
         20 . The method of  claim 14  wherein said hydrophobic polymer is derived from at least an acrylic acid, methacrylic acid, sulfonated styrene, or phosphonated styrene, and optionally from one or more of substituted or unsubstituted styrene, esters of (meth)acrylic acid, vinyl halide, (meth)acrylonitrile, vinyl ester, silicon-containing polymerizable monomer, and polyether.