Photosensitive lithographic printing plate

Details Photosensitive lithographic printing plate Photosensitive lithographic printing plate

1999-06-16

2001-08-21

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

C430S302000, C430S306000, C430S326000, C430S270100, C430S905000, C430S906000, C430S907000, C430S910000

Reexamination Certificate

active

06277541

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a photosensitive lithographic printing plate, and particularly to a positive working photosensitive lithographic printing plate.
BACKGROUND OF THE INVENTION
In positive working photosensitive lithographic printing plates which have hitherto been widely used, only exposed portions of photosensitive layers are mainly removed by dissolution with developing solutions. In this case, non-image areas are generally developed with alkaline developing solutions mainly containing silicates having hydrophilization action.
This is for preventing the non-image areas from being stained with ink during printing by hydrophilization of the non-image areas with the silicate-containing alkaline developing solutions.
However, when the developing ability is somewhat decreased by exhaustion of developing solutions and developing replenishers, variation with the elapse of time of the positive working photosensitive lithographic printing plates, or insufficient exposure, the photosensitive layers of portions to form the non-image areas are not sufficiently removed by dissolution with the developing solutions, which causes residues of photosensitive layer components to remain on the plates in some cases.
When the photosensitive layer components remain on the non-image areas in the developing process as described above, the non-image areas can not be sufficiently hydrophilized only by the use of the silicates, resulting in the phenomenon of allowing ink to adhere to the non-image areas in the course of printing, namely the problem of developing scum.
Then, the present inventors have developed intermediate layers containing the polymers described in JP-A-10-69092 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) as a method for retaining the adhesion between aluminum supports to which sufficient hydrophilicity is given and photosensitive layers during printing, and sufficiently removing the photosensitive layers and the intermediate layers by dissolving them with alkaline developing solutions in the non-image areas, thereby realizing the compatibility of press life with scumming prevention. This improves the adhesion of image areas, and in the non-image areas, the photosensitive layers and the intermediate layers can be sufficiently removed with the alkaline developing solutions. Accordingly, surfaces of the hydrophilized supports are exposed, and scumming prevention performance can also be maintained.
According to this method, however, deletion performance (image removability in removing unnecessary images using chemical agents generally called deletion fluids) is not sufficient, and particularly, significantly deteriorates with an increase in the area of images to be deleted. Further, there is the problem that binders contained in the photosensitive layers remain on the non-image areas of the supports, which causes the scum during printing (hereinafter referred to as photosensitive layer removability). It has been therefore desired to improve it.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a photosensitive lithographic printing plate in which press life, deletion performance, photosensitive layer removability and image reproducibility are compatible with one another, using a hydrophilized support having scumming prevention performance. Further, another object of the present invention is to provide a photosensitive lithographic printing plate having good scumming prevention performance, press life, deletion performance, photosensitive layer removability and image reproducibility, even when it is developed using a developing solution containing no silicate.
As a result of intensive studies, the present inventors have discovered that the above-mentioned objects can be attained by adding a specific polymer adjusted in number-average molecular weight to a specified range, thus completing the present invention.
That is to say, the present invention provides a photosensitive lithographic printing plate comprising an aluminum support hydrophilized after anodic oxidization, an intermediate layer provided thereon containing an alkali-soluble polymer adjusted in a number-average molecular weight (Mn) to the range of 300 to 5,000 by using an initiator in combination with a chain transfer agent in radical polymerization, and a photosensitive layer provided on the intermediate layer.
Previously, for retaining the adhesion between the hydrophilized aluminum supports and the photosensitive layers during printing, and sufficiently removing the photosensitive layers and the intermediate layers by dissolving them with the alkaline developing solutions in the non-image areas, the intermediate layers containing the water-insoluble, alkali-soluble polymers have been developed, thereby realizing the compatibility of press life with scumming prevention. According to this method, however, deletion performance significantly deteriorates particularly with an increase in the area of images to be deleted. Further, an increase in hydrophilization action results in deterioration of photosensitive layer removability.
In contrast, it has become clear that, surprisingly, the polymer discovered according to the present invention, which is polymerized by using the initiator in combination with the chain transfer agent, and has a number-average molecular weight (Mn) ranging from 300 to 5,000, improves deletion performance, photosensitive layer removability and image reproducibility, as well as press life. This is presumedly because it becomes possible to control the adhesion of the polymer to the support and the solubility thereof in a solvent by adjusting the molecular weight of the polymer with an effective chain transfer agent effectively functions.
In addition, it has been known that chain transfer agent-derived functional groups introduced into ends of the polymer have a great influence on the adhesion and solubility of the polymer. It is therefore presumed that one of the important factors is that it has become possible to adjust the adhesion and solubility by the selection of the structure of the chain transfer agent.
DETAILED DESCRIPTION OF THE INVENTION
The polymers used for formation of the intermediate layers in the photosensitive lithographic printing plates of the present invention are described in detail below.
The polymers used in the present invention are compounds obtained by polymerizing constituents having at least acid groups. Further, compounds obtained by copolymerizing constituents having at least acid groups and constituents having at least onium groups are more preferred. The acid groups are preferably acid groups having an acid dissociation constant (pKa) of 7 or less, and more preferably —COOH, —SO
3
H, —OSO
3
H, —PO
3
H
2
, —OPO
3
H
2
, —CONHSO
2
and —SO
2
NHSO
2
—. —COOH is particularly preferred. The onium groups are preferably onium groups comprising the group V or IV atoms in the periodic table, and more preferably onium groups comprising nitrogen, phosphorus or sulfur atoms. Onium groups comprising nitrogen atoms are particularly preferred.
Of these polymers, polymers having vinyl polymers such as acrylic resins, methacrylic resins or polystyrene, urethane resins, polyesters or polyamides as main chains are preferred.
More preferably, the polymers are polymers having vinyl polymers such as acrylic resins, methacrylic resins or polystyrene as main chains.
Polymers are particularly preferred in which the constituents having acid groups are polymerizable compounds represented by the following general formula (1) or (2), and the constituents having onium groups are compounds represented by the following general formula (3), (4) or (5).
wherein A represents a divalent connecting group; B represents an aromatic group or a substituted aromatic group; D and E each independently represents a divalent connecting group; G represents a trivalent connecting group; X and X′ each independently represents an acid group having a pKa of 7 or less, or an alkali metal salt or a

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