Radiation imagery chemistry: process – composition – or product th – Microcapsule – process – composition – or product
Reexamination Certificate
2001-12-13
2003-05-20
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Microcapsule, process, composition, or product
C430S270100, C430S271100, C430S302000, C430S348000, C101S453000, C101S467000
Reexamination Certificate
active
06566029
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a negative-working lithographic printing plate precursor. More particularly, it relates to a lithographic printing plate precursor which enables plate making by scan exposure based on digital signals, which shows a high sensitivity and a high printing durability, which can produce stain-free prints, and which can be mounted on a printing press without conducting a special development processing after image formation.
BACKGROUND OF THE INVENTION
A number of studies have been made on printing plates for use in the computer-to-plate system having a remarkable development. In the course of the studies, lithographic printing plate precursors which can be mounted on a printing press without being subjected to development processing after imagewise exposure have been studied, and various methods have so far been proposed.
As one method which does not require the development processing, there is a method, called an on press developing method, which comprises mounting an exposed printing plate precursor on a cylinder of a printing press and removing non-image areas of the printing plate precursor by feeding a dampening water and an ink while rotating the cylinder. That is, it is a method of mounting an exposed printing plate precursor on a printing press and completing development processing during the common printing procedures.
A lithographic printing plate precursor adapted for such on press development is required to have a light-sensitive layer soluble in the dampening water or an ink solvent and such bright room handling properties that it can be developed on a printing press placed in a bright room.
For example, Japanese Patent No. 2938397 discloses a lithographic printing plate precursor comprising on a hydrophilic support a heat-sensitive layer wherein fine particles of a thermoplastic hydrophobic polymer are dispersed in a hydrophilic binder polymer. In this patent, it is described that, in the lithographic printing plate precursor, the fine particles of the thermoplastic hydrophobic polymer are fused to each other by heat generated by an infrared laser exposure to thereby form an image, and that the resulting printing plate can be mounted on a cylinder of a printing press and on press developed with a dampening water and/or an ink.
However, in the method of forming an image merely by thermally fusing the thermoplastic polymer, the plate has such a weak strength in image areas of the recording layer that there results insufficient printing durability, though non-image areas show a good on press developability. In the case of providing a heat-sensitive layer directly on an aluminum substrate conventionally used as a substrate in the lithographic printing plate precursor, the heat generated by exposure predominantly conducts to the aluminum substrate having a high heat conductivity, and hence the heat energy is not well utilized for image formation, i.e., for thermally fusing the fine particles, in the vicinity of the interface between the substrate and the heat-sensitive layer, resulting in insufficient printing durability.
SUMMARY OF THE INVENTION
The present invention provides a lithographic printing plate precursor which solves the above-described problems in the prior art. That is, it provides a lithographic printing plate precursor having a good on press developability, high sensitivity and excellent printing durability.
As a result of various investigations to solve the above-described problems, the inventors have found that, in order to enhance the sensitivity and printing durability, it is most important to prevent the generated heat from predominantly conducting to the aluminum substrate and, as a result of examining various heat-insulating and hydrophilic supports, have found that a support having a hydrophilic surface comprising a graft polymer has a high hydrophilicity and an excellent heat-insulating effect, to complete the invention. Specifically, the invention includes:
(1) A lithographic printing plate precursor which comprises a support having a hydrophilic surface containing hydrophilic graft polymer chains and a heat-sensitive layer containing at least either of fine particulate polymer and microcapsules.
(2) The lithographic printing plate precursor as described in (1), wherein the fine particulate polymer is a thermoplastic fine particulate polymer.
(3) The lithographic printing plate precursor as described in (1), wherein the fine particulate polymer is a fine particulate polymer having a heat-reactive functional group.
(4) The lithographic printing plate precursor as described in (1), wherein the microcapsules retain a compound having a heat-reactive functional group.
(5) The lithographic printing plate precursor as described in (1), wherein the fine particulate polymer is a thermoplastic fine particulate polymer having a functional group capable of mutually acting with the hydrophilic graft polymer.
(6) The lithographic printing plate precursor as described in (1), wherein the microcapsules are microcapsules retaining a compound having a functional group capable of mutually acting with the hydrophilic graft polymer.
The present invention is described in more detail below.
The lithographic printing plate precursor of the invention comprises a support having a specific hydrophilic surface and a heat-sensitive layer containing fine particulate polymer or microcapsules.
In the invention, the support is provided with a hydrophilic surface wherein hydrophilic graft polymer chains exist. This surface has a high hydrophilicity and exhibits an excellent heat-insulating effect owing to the polymer layer and, therefore, the heat generated in the heat-sensitive layer does not diffuse into the aluminum substrate but is effectively used for image formation, thus sensitivity is more enhanced. In the heat-sensitive layer of the lithographic printing plate precursor of the invention, the fine particulate compound or the compound contained in the inside of the microcapsules is fused in exposed areas to form image areas. By introducing into the compound a functional group capable of mutually acting with the hydrophilic graft polymer component on the support, strong bonds are formed with the hydrophilic graft polymer, thus a lithographic printing plate precursor having high printing durability is obtained. In addition, in the non-image areas, the support surface is highly hydrophilic, and the high molecular compound participating image formation, which is neither fused nor make mutual action with the hydrophilic graft polymer chains, can easily be dispersed and removed with a small amount of water or a hydrophilic component, thus excellent on press developability is obtained as well.
(A) Support Having a Hydrophilic Surface Wherein Hydrophilic Graft Polymer Chains Exist
First, the hydrophilic surface of support is described.
The hydrophilic surface of the support of the invention means a surface wherein hydrophilic graft polymer chains exist. In the surface, the hydrophilic graft polymer chains may directly be bound to the surface of the support or, alternatively, a polymer compound wherein the hydrophilic graft polymer chains are bound to the main chain of the polymer compound may be bound to the surface of the support or may be provided by coating or by coating followed by crosslinking. In the invention, the hydrophilic graft polymer chains directly bound to the surface of the support is referred to as “surface graft”, and the layer in which the hydrophilic graft polymer chains are introduced into a crosslinked polymer film structure is referred to as “hydrophilic graft chain-introduced crosslinked hydrophilic layer”.
Surface Graft Method
The surface formed by the surface graft method means a surface formed by grafting a monomer by a conventionally known graft polymerization method using, for example, light, an electron beam or heat. The monomer used may be a monomer having a positive charge such as ammonium or phosphonium or a monomer having a negative charge or an acid group capable of being dissociated to form a negati
Kawamura Koichi
Maemoto Kazuo
Oohashi Hidekazu
Takahashi Miki
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