Radiation imagery chemistry: process – composition – or product th – Diazo reproduction – process – composition – or product – Composition or product which contains radiation sensitive...
Reexamination Certificate
1999-11-12
2001-08-14
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Diazo reproduction, process, composition, or product
Composition or product which contains radiation sensitive...
C430S175000, C430S176000, C430S303000
Reexamination Certificate
active
06274285
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a recording material having, in sequence, a support, a radiation-sensitive layer and a silicone layer. It furthermore relates to a process for the production of a printing plate for driographic offset printing from the recording material.
2. Description of the Related Art
Recording materials from which driographic (i.e., water free) offset printing plates can be produced are already known. Thus, Great Britain Patent GB 1,399,949 discloses a positive-working material having a support, a radiation-sensitive layer which takes up printing ink, a silicone layer which repels printing ink and preferably also a transparent protective film. The radiation-sensitive layer comprises, as essential constituents, a photopolymerizable, ethylenically unsaturated monomer or oligomer having a boiling point of above 100° C., a photoinitiator and generally also a binder. The binder is preferably a vinyl polymer or copolymer (such as polyvinyl acetate, polyvinyl alcohol, polyvinylbutyral, polyvinyl butyl ether, polyvinyl chloride or polyethylene), a polyether (such as polyethylene oxide or polypropylene oxide), a polyamide, a polyester, a cellulose derivative, a urea-formaldehyde resin, an alkyd resin, a melamine-formaldehyde resin or a phenol-formaldehyde resin. In the exposed areas of the radiation-sensitive layer, the monomer or oligomer is polymerized, causing it to adhere to the silicone layer. The recording material is then treated with a developer solution. During this treatment, the silicone layer swells to a greater extent in the unexposed areas and can be removed by brushing or similar measures. In the exposed areas, by contrast, the silicone layer remains adhering to the photosensitive layer. The adhesion between the photosensitive layer and the silicone layer can be further increased by heating or by full-area exposure. At the same time, the photosensitive layer is cured in the originally unexposed areas, which reduces the scratch sensitivity of the driographic printing plates and allows a longer print run.
The recording material according to European Published Application No. EP-A 0 394 923 likewise comprises a support, a photosensitive layer and a silicone layer. The photosensitive component here is a diazonium salt polycondensation product. The photosensitive layer contains, as a further essential component, a polymeric binder containing units of an ester containing aliphatic hydroxyl groups, or of an amide of acrylic or methacrylic acid. It is in general a polymer containing units of a hydroxyalky 1 (meth)acrylate or (meth)acrylamide. In addition, it may also contain units of other monomers. Examples thereof are monomers containing aromatic hydroxyl groups (such as N-(4-hydroxyphenyl)acrylamide or -methacrylamide, 2-, 3- or 4-hydroxystyrene, (2-, 3-or 4-hydroxyphenyl)acrylate or -methacrylate). Furthermore, the monomers may also be a,b-unsaturated carboxylic acids, substituted alkyl acrylates or -methacrylates, vinyl ethers (such as ethyl vinyl ether, butyl vinyl ether or phenyl vinyl ether), styrenes, vinyl ketones, olefins, N-vinylpyrrolidone, N-vinylcarbazole, 4-vinylpyridine, acrylonitrile or methacrylonitrile. The proportion of hydroxyl groups in the binder (this is apparently taken to mean the proportion of units containing aliphatic hydroxyl groups) is said to be from 5 to 100% by weight, preferably from 20 to 100% by weight, since otherwise the adhesion between the radiation-sensitive layer and the silicone layer is inadequate. After imagewise exposure, the recording material is developed using an aqueous solution containing polar solvents (such as alcohols, ethylene glycol monoalkyl ethers, ketones or esters), alkaline compounds, surfactants and aliphatic, aromatic or halogenated hydrocarbons (such as hexane, heptane, toluene or xylene). This removes the unexposed areas of the radiation-sensitive layer together with the overlying areas of the silicone layer. In addition, a primer layer is arranged between the aluminum support and the radiation-sensitive layer. This is not removed during development. During printing, the ink is transferred from the primer layer, while the areas of the silicone layer which remain repel the printing ink.
The known recording materials for the production of driographic printing plates require organic solvents during development. However, this is disadvantageous for reasons of occupational safety and environmental protection. Disposal of the spent developer solutions is complex and costly. The present invention is directed to overcoming or at least reducing the above problem.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, there is provided a recording material comprising a support, a radiation sensitive layer and a silicone layer, wherein the radiation-sensitive layer contains a radiation-sensitive component comprising a diazonium salt polycondensation product and a binder comprising at least one of a homopolymer of (C
1
-C
12
) alkyl vinyl ether units and a copolymer including at least 5 mol percent of such units, wherein the binder is at least substantially free of aliphatic hydroxyl groups. In accordance with another aspect of the invention, there is provided a process for producing a printing plate for driographic offset printing.
Further objects, features and advantages of the invention will become apparent from the detailed description of preferred embodiments that follows.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The recording material of the present invention has a simple structure. It comprises few layers, and preferably lacks a primer layer. After imagewise exposure, the recording material is capable of development with aqueous solutions, preferably with pure water, to give a printing plate which does not require any damping solution during printing (i.e., a driographic printing plate(s)). In addition, preferably only the silicone layer, but not the radiation-sensitive layer, is removed in the unexposed areas during development. During printing, the ink is transferred from the radiation-sensitve layer areas that are not covered by the silicone layer. Furthermore, the loading of the developer with constituents of the radiation-sensitive layer should be avoided, which leads to a longer service life of the developer.
In a preferred embodiment of the present invention, the binder contains polymers consisting of or comprising methyl vinyl ether units. For example, the binder may be a homopolymer of methyl vinyl ether units or a copolymer containing methyl vinyl ether units. The homopolymers preferably have a K value of from 10 to 80. The copolymers preferably generally have a random or alternating structure, i.e., they are not block copolymers. The preferred units in the copolymers are units of maleic anhydride or monoalkyl maleates, in particular, units of mono (C
1
-C
6
) alkyl maleates, such as monoethyl, monoisopropyl or monobutyl maleate. Methyl vinyl ether-maleic anhydride copolymers are available, for example, under the name
7
Gantrez AN (CAS No. 108-88-3) from GAF Chemicals Corp., USA.
The support may comprise a metal plate or foil. The preferred support materials are plates or foils of aluminum or its alloys. The support is preferably pretreated. Support materials based on aluminum may be mechanically and/or electrochemically roughened and may also be anodically oxidized. Chemical pre-treatment, for example with polyvinylphosphonic acid, silicates, phosphates, hexafluorozirconates or hydrolyzed tetraethyl orthosilicate, is also possible thereafter. Since, in contrast to conventional planographic printing plates, a hydrophilic support surface is not necessary, it is also possible to use support materials such as copper, brass or other oleophilic metals or metal alloys, and also plastics, such as polyester, polycarbonate, polyimide or cellulose acetate.
The polymers used as binders in the radiation-sensitive layer generally have a molecular weight, M
W
, in the range from 40,000 to 2,000,000, preferably from 50,0
Gries Willi-Kurt
Schlosser Hans-Joachim
Agfa-Gevaert NV
Chu John S.
Foley & Lardner
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