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
1999-05-20
2001-07-10
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, C430S287100, C430S281100, C430S286100, C430S914000, C430S920000
Reexamination Certificate
active
06258510
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photosensitive planographic printing plate precursor that can be loaded immediately after exposure into a printing machine so that printing is started without any special processing such as development.
2. Description of the Related Art
According to prior art, in order to obtain prints by using a photosensitive planographic printing plate precursor (hereinafter referred to as a printing plate precursor on occasion), it is necessary to carry out a procedure that comprises exposing the printing plate precursor image-wise and developing the exposed plate with an appropriate developer so that a planographic printing plate precursor having a lipophilic image portion and a hydrophilic non-image portion is produced. After that, agum coating is applied in order to protect the planographic printing plate precursor. Following such wet processing, the planographic printing plate precursor is loaded into a printing machine and printing is started.
For developing processing as a processing step after exposure, a developer, which is an alkaline liquid or an alkaline liquid containing an organic solvent, is generally used. In this regard, because of environmental problems due to waste liquids of the developer or maintenance problems of automated developing machines, there is a demand for a system that requires no developing step.
In order to solve these problems, Japanese Patent Application National Publication (Laid-Open) No. 6-502,931 proposes a photosensitive planographic printing plate precursor having a double-layered photosensitive layer comprising a photosensitive hydrophilic layer and a photosensitive hydrophobic layer provided thereon. This photosensitive planographic printing plate precursor can be loaded immediately after exposure into a printing machine so that printing is started without any processing after exposure. This photosensitive planographic printing plate precursor, however, has a durability problem in printing because the adhesion between the upper layer and the lower layer is insufficient.
WO 96/34316 discloses a photosensitive planographic printing plate precursor having a single-layered photosensitive layer composed of a polymer comprising a photo-hardenable group and an acid group or an acid salt group and a photopolymerization initiator. This photosensitive planographic printing plate precursor can also be loaded immediately after exposure into a printing machine so that printing is started without any processing after exposure. This photosensitive planographic printing plate precursor, however, has insufficient durability in printing. Therefore, the durability in printing becomes very poor if the pH value of dampening water in printing is shifted so as to become alkaline.
Further, Japanese Patent Application Laid-Open (JP-A) No. 47-8,657 discloses that a photosensitive planographic printing plate precursor that can be loaded immediately after exposure into a printing machine so that printing is started without any processing after exposure can be obtained by a photosensitive composition comprising polyvinylpyrrolidone, a polymeric polycarboxylic acid, an olefinically unsaturated monomer, a photopolymerization initiator, and the like. However, the use of the photopolymerization initiator disclosed therein presented problems in terms of sensitivity and fogging after exposure.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a photosensitive planographic printing plate precursor which can be loaded immediately into a printing machine so that printing is started without any post-processing after exposure, which exhibits good durability in printing even in low-exposure areas, and which is less liable to fog in the period between exposure and printing.
After intense studies, the present inventors have achieved the present invention based on a discovery that a combination of a specific photosensitive layer and a specific substrate provides a photosensitive planographic printing plate precursor which can be loaded immediately into a printing machine so that printing is started without any processing after exposure and which always exhibits good durability in printing.
That is, the photosensitive planographic printing plate precursor of the present invention comprises an aluminum substrate surface-treated such that the center line surface roughness thereof (Ra) is in a range of from 0.30 &mgr;m or more to 0.55 &mgr;m or less and a photosensitive layer provided on the substrate and comprised of a photosensitive composition containing (a) a water-soluble or water-dispersible polymer, (b) a monomer or oligomer having at least one ethylenically unsaturated double bond capable of photopolymerization, and (c) a photopolymerization initiation system having &lgr;
max
in a range of from 330 nm or more to 375 nm or less such that the light absorbance A at &lgr;
max
and the absorbance B at 400 nm fulfill a relationship of B/A<0.1.
The above-mentioned (c) photopolymerization initiation system maybe a system containing a photopolymerization initiator having &lgr;
max
in a range of from 330 nm or more to 375 nm or less such that the light absorbance A at &lgr;
max
and the absorbance B at 400 nm fulfill the relationship of B/A<0.1, or may be a system containing a photopolymerization initiator and a sensitizer wherein the system as a whole has &lgr;
max
in a range of from 330 nm or more to 375 nm or less such that the light absorbance A at &lgr;
max
and the absorbance B at 400 nm fulfill the relationship of B/A<0.1.
Generally, although the use of a photopolymerization initiation system like the above-mentioned system whose &lgr;
max
is towards shorter wavelengths produces little fogging in the period between exposure and printing, a problem with such a system is that the sensitivity is so reduced that the durability in printing in low-exposure areas is impaired. However, the present inventors found that the use of an aluminum substrate surface-treated such that the center line surface roughness thereof (Ra) is 0.55 &mgr;m or less increases the durability in printing in low-exposure areas and therefore two requirements, i.e., prevention of fogging and durability in printing in low-exposure areas, can be fulfilled at the same time. In a planographic printing plate precursor comprising a substrate and an ordinary photosensitive layer provided thereon, a substrate having a coarser surface is known to provide better durability in printing due to better adhesion between the photosensitive layer and the substrate. In contrast, a photosensitive layer according to the present invention provides better durability in printing if the photosensitive layer is used in a combination with a substrate having a smooth surface. Although not fully elucidated, the mechanism is presumably as follows. In a photosensitive layer which comprises a water-soluble or water-dispersible polymer and a photopolymerization initiation system having &lgr;
max
towards shorter wavelengths, has excellent hydrophilicity, and requires no developing processing, the image areas become thinner and finally the hydrophilic substrate is exposed after a large number of prints are produced. In this case, if the surface of the substrate is smooth, the substrate is unlikely to be exposed and therefore an image omission due to exposure of the hydrophilic substrate hardly occurs even after a required large number of prints are produced, thus providing excellent durability in printing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Details of the present invention are given below.
In the present invention, (a) a water-soluble or water-dispersible polymer (hereinafter referred to as water-soluble/water-dispersible polymer on occasion) is not particularly limited. Examples of the polymer include water-soluble polymers such as polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, water-soluble nylon, water-soluble urethane, a polymer containing sulfonic acid or a sulfonic
Baxter Janet
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Lee Sin J.
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