Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2000-12-22
2004-03-02
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S270100, C430S300000, C430S302000, C430S944000, C430S945000, C101S453000, C101S457000, C101S467000
Reexamination Certificate
active
06699638
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a heat-sensitive lithographic printing plate precursor. More particularly, the present invention relates to a negative-working lithographic printing plate precursor wherein images can be recorded by exposure to infrared laser beams based on digital signals and the images recorded can be developed with an alkaline developer.
BACKGROUND OF THE INVENTION
Hitherto have been well-known negative-working heat-sensitive lithographic printing plate precursors having a structure that a thermal cross-linking layer is provided on a support. More specifically, negative images can be produced in those printing plate precursors by the following mechanism: The printing plate precursors evolve heat upon exposure to infrared laser beams, generate acids from acid generators contained therein by the action of the heat evolved, cause thermo cross-linking reaction in their thermal cross-linking layers by undergoing post-baking and utilizing the generated acids as catalyst, thereby rendering the cross-linking layers insoluble, and then dissolving and removing the areas unexposed to laser beams by development.
For instance, in JP-A-7-20629 and JP-A-7-271029 (the term “JP-A” as used herein means an “examined published Japanese patent application) are disclosed negative-working lithographic printing plate precursors having thermal cross-linking layers. These layers contain as main components an infrared absorbing dye capable of evolving heat by absorbing infrared radiation (compound capable of converting light into heat), a latent Brønsted acid or an s-triazine compound as acid generator, a resol resin as cross-linking agent and a novolak resin as both binder and polymer to be cross-linked.
Further, improvements in the sensitivity, the developability, the printing stain resistance and the post-baking stability of negative-working heat-sensitive lithographic printing plate precursors having the thermal cross-linking layers as mentioned above are disclosed in JP-A-10-111564, JP-A-11-84649, JP-A-11-95419, JP-A-11-119428 and JP-A-11-231509, WO 98/51544 and WO 98/31545.
However, the negative-working heat-sensitive lithographic printing plate precursors disclosed in the publications described above, which each have a thermal cross-linking layer on a support, produce a new problem that when the plate surface is touched with fingers the touched areas give an image formation failure in the shape of fingerprints. Accordingly, a special care is needed in handling those printing plate precursors. For instance, workers are required to handle the printing plate precursors with gloves on during the plate-making operations.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to solve the aforementioned problem and, more specifically, to provide a negative-working heat-sensitive lithographic printing plate precursor which is easy to handle and causes no defects in images even when the plate surface is touched with fingers.
The present inventors have found that the foregoing problem can be solved by providing on a thermal cross-linking layer a water-soluble overcoat layer wherein at least one layer of the thermal cross-linking layer and a water-soluble overcoat layer contains a compound capable of converting light into heat, thereby achieving the present invention.
That is, the present invention comprises the following Embodiment (1):
(1) A negative-working heat-sensitive lithographic printing plate precursor comprising a substrate having a water-receptive surface: with the substrate having provided thereon sequentially 1) a thermal cross-linking layer comprising an aqueous alkali-soluble resin having aromatic hydroxyl groups, a cross-linking agent capable of cross-linking the resin by heating in the presence of an acid catalyst and an acid generator, and 2) a water-soluble overcoat layer; wherein the overcoat layer or both the overcoat layer and the thermal cross-linking layer comprise a compound capable of converting light into heat.
DETAILED DESCRIPTION OF THE INVENTION
Practical embodiments of the present invention are described below in detail.
The water-soluble overcoat layer used in the present invention can be removed easily under development, and comprises at least one resin selected from water-soluble organic or inorganic high molecular compounds. The water-soluble organic or inorganic high molecular compounds usable therein are compounds capable of forming films when coated and dried. Examples of such compounds include polyvinyl acetate (having a hydrolysis factor of at least 65%), polyacrylic acid and alkali metal or amine salts thereof polyacrylic acid copolymers and alkali metal or amine salts thereof, polymethacrylic acid and alkali metal or amine salts thereof, polymethacrylic acid copolymers and alkali metal or amine salts thereof, polyacrylamide and polyacrylamide copolymers, polyhydroxyethyl acrylate, polyvinyl pyrrolidone and polyvinyl pyrrolidone copolymers, polyvinyl methyl ether, polyvinyl methyl ether/maleic anhydride copolymer, poly-2-acrylamide-2-methyl-1-propanesulfonic acid and alkali metal or amine salts thereof, poly-2-acrylamide-2-methyl-1-propanesulfonic acid copolymers and alkali metal or amine salts thereof, gum arabic, cellulose derivatives (such as carboxymethyl cellulose, carboxyethyl cellulose and methyl cellulose) and modified products thereof, white dextrin, pullulan and enzyme-decomposed etherified dextrin. These resins may be used as a mixture of two or more thereof, if desired.
When the overcoat layer of the present invention is formed by coating an aqueous solution, nonionic surfactants can be added to the aqueous solution for the purpose of securing uniformity for the layer coated. Examples of nonionic surfactants usable for such a purpose include sorbitan tristearate, sorbitan monopalmitate, sorbitan trioleate, stearic acid monoglyceride, polyoxyethylene nonyl phenyl ether, and polyoxyethylene dodecyl ether.
The suitable proportion of such a nonionic surfactant to the total solid components in the overcoat layer is from 0.05 to 5 weight %, preferably from 1 to 3 weight %.
The suitable thickness of the overcoat layer provided in the present invention is from 0.05 to 4.0 g/m
2
, preferably from 0.1 to 1.0 g/m
2
. When the thickness is too thick, the developing capacity of a developer is lowered, and the overcoat layer remains after development to produce an adverse effect, e.g., no inking on image areas. When the thickness is too thin, on the other hand, the strength of the coating film becomes insufficient.
The aqueous alkali-soluble resin having aromatic hydroxyl groups which can be used in the present invention is at least one resin selected from novolak resins or polyvinyl phenol resins.
The novolak resins usable in the present invention include resins produced by polycondensation between at least one phenolic compound and at least one aldehyde or ketone in the presence of an acid catalyst. Examples of a phenolic compound which can participate in the polycondensation include phenol, o-cresol, m-cresol, p-cresol, 2,5-xylenol, 3,5-xylenol, o-ethylphenol, m-ethylphenol, p-ethylphenol, propylphenol, n-butylphenol, tert-butylphenol, 1-naphthol, 2-naphthol, resorcinol, 4,4 biphenyldiol, bisphenol-A and pyrogallol. Examples of an aldehyde which can participate in the polycondensation include formaldehyde, acetoaldehyde, propionaldehyde, benzaldehyde and furfural. Additionally, paraformaldehyde may be used instead of formaldehyde, and para-acetaldehyde may be used instead of acetaldehyde. Examples of a ketone which can participate in the polycondensation include acetone, methyl ethyl ketone and methyl isobutyl ketone. Of those novolak resins, products of polycondensation between phenols, including phenol, o-cresol, m-cresol, p-cresol, 2,5-xylenol, 3,5-xylenol and resorcinol, and aldehydes, including formaldehyde, acetaldehyde and propionaldehyde, are preferred. In particular, polycondensation products prepared from formaldehyde and mixed phenols, including m-cresol/p-cresol/2,5-xylenol/3,5-xylenol/resorc
Baxter Janet
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Walke Amanda C.
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