Lithographic printing plate precursor

Details Lithographic printing plate precursor Lithographic printing plate precursor

2002-02-04

2003-11-04

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

C430S138000, C430S270100, C430S271100, C430S302000

Reexamination Certificate

active

06641977

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a lithographic printing plate precursor and, more particularly, to a lithographic printing plate precursor which exhibits high sensitivity and is fit for scanning exposure based on digital signals, which can be mounted on a printing press after development with water or without development to carry out printing. A printing plate prepared therefrom has a long press life and provides stain-free printed matter.
BACKGROUND OF THE INVENTION
Computer-to-plate (CTP) technology has recently seen marked development, and a number of studies have been given to printing plate precursors for CTP. In particular, processless plate precursors that can be mounted on a printing press after imagewise exposure without requiring chemical development have been researched in the art, and various techniques have been proposed to data.
A so-called onpress development system is one of the methods realizing processless platemaking, in which an exposed printing plate precursor is fixed onto the plate cylinder of a printing press, and a fountain solution and ink are fed thereto while revolving the cylinder to remove non-image areas. This technique allows an exposed printing plate precursor to be mounted on a press and be made into a printing plate on an ordinary printing line.
A lithographic printing plate precursor fit for the onpress development system is required to have a photosensitive layer soluble in a fountain solution or an ink solvent and to have daylight handling properties for onpress development.
For example, Japanese Patent 2938397 discloses a lithographic printing plate precursor having, on a water-wettable support, a photosensitive layer made of thermoplastic hydrophobic polymer fine particles dispersed in a hydrophilic binder resin. According to the teachings, the precursor is exposed to an infrared laser beam to thermally bind the thermoplastic hydrophobic polymer particles to form an image, fixed to the cylinder of a printing press, and onpress developed with a fountain solution and/or ink.
Although this imaging method simply relying on thermal binding of hydrophobic particles achieves satisfactory onpress developability, the resulting printing plate has an insufficient press life because of the small image film strength. Where a heat-sensitive layer (image-forming layer) is provided directly on an aluminum support, the heat generated is dissipated through the aluminum support so that the particles are not bound in the support/heat-sensitive layer interface, which results in an insufficient press life.
JP-A-9-127683 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-9-123387, JP-A-9-123388, JP-A-9-131850, and WO99/10186 also propose onpress platemaking after thermally binding thermoplastic fine particles. These methods cannot get rid of the problem of insufficient press life on account of weak image strength, either.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a lithographic printing plate precursor which, after imaging, is fitted to a printing press and used to carry out printing without requiring development, which has high sensitivity and a satisfactory press life and is capable of producing printed matter free from residual colors and stains.
Another object of the invention is to provide a lithographic printing plate precursor which is capable of direct imaging of digital image data particularly by use of a solid state laser, a semiconductor laser, etc. which irradiate infrared rays.
As a result of extensive investigations, the present inventors have found that the above objects are accomplished by a lithographic printing plate precursor comprising a support having a water-wettable surface and a heat-sensitive layer provided thereon, wherein the heat-sensitive layer comprises a resin having a hydrogen-donating group and a resin having a hydrogen-accepting group, at least one of, preferably both of, the resins being finely particulate.
The hydrogen-donating group is preferably selected from a hydroxyl group, a carboxyl group, and a nitrogen atom having a hydrogen atom, and the hydrogen-accepting group is preferably selected from a carbonyl group, an ether group, and a nitrogen atom that does not have a hydrogen atom.
The heat-sensitive layer containing a resin having a hydrogen-donating group and a resin having a hydrogen-accepting group at least one which is finely particulate is easily removable from the support with water and/or ink. That is, unexposed, i.e., intact areas of the precursor is removed from the support with water and/or ink. On the other hand, the particles in exposed areas are melted by the photothermally generated heat. It follows that the resin having a hydrogen-donating group and the resin having a hydrogen-accepting group are brought into contact to form a hydrogen bond between the hydrogen-donating group and the hydrogen-accepting group thereby forming a firm film of hydrogen-bonding polymer complex. Therefore, the exposed areas remain on the plate to form image areas with a satisfactory press life.
The lithographic printing plate precursor of the invention is capable of imaging with reduced exposure energy. It enables direct platemaking from digital data from a computer, etc. by the use of a solid state laser or a semiconductor laser emitting infrared rays to provide a lithographic printing plate having a satisfactory press life and causing no stains.
DETAILED DESCRIPTION OF THE INVENTION
The lithographic printing plate precursor of the present invention comprises a support having a water-wettable surface and a heat-sensitive layer provided thereon, wherein the heat-sensitive layer (also called an image-forming layer) comprises a resin having a hydrogen-donating group (hereinafter referred to as a resin A) and a resin having a hydrogen-accepting group (hereinafter referred to as a resin B), at least one of the resins A and B being finely particulate.
The resin A is a resin having a functional group capable of donating hydrogen to form hydrogen bonds. While any resins having such a functional group are usable, those having a hydrogen-donating group selected from a hydroxyl group, a carboxyl group and a nitrogen atom having a hydrogen atom are preferred.
Resins A can be prepared either by starting with a monomer having the functional group or by introducing the functional group into a polymer through a polymer reaction. In using a resin A in the form of fine particles, a particulate resin A is prepared by emulsion polymerization or suspension polymerization of a monomer having the functional group. It can also be prepared by dissolving a polymer having the functional group in an organic solvent, emulsifying or dispersing the polymer solution in the presence of an emulsifier or a dispersant, and removing the organic solvent by evaporation.
Monomers having a hydrogen-donating group or a functional group that can be led to a hydrogen-donating group, which can be used to synthesize the resin A, include, but are not limited to, acetoxystyrene, butyloxystyrene, methoxymethyloxystyrene, phenol, cresol, vinyl acetate, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, vinylbenzoic acid, allylamine, allylaniline, N-vinylaniline, acetylaminostyrene, t-butyloxycarbonylaminomethylstyrene, N-vinylacetamide, acrylamide, methacrylamide, vinylbenzoic acid amide, N-methylacrylamide, and N-ethylmethacrylamide.
The resin A may be either a homopolymer of the above-recited monomer having a hydrogen-donating group or a functional group that can be led to a hydrogen-donating group or a copolymer comprising two or more of these monomers. In order to control the melting temperature, film-forming properties and the like of the resin A, a component having no hydrogen-donating group may be incorporated as a comonomer. Examples of such a comonomer include, but are not limited to, styrene, methylstyrene, t-butylstyrene, dimethylstyrene, trimethylstyrene, stilbene, vinylnaphthalene, vinylanthracene, fluorostyrene, chlorostyrene,

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