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
2000-05-26
2002-11-12
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
C430S271100, C430S306000, C101S456000, C101S457000, C101S462000
Reexamination Certificate
active
06479215
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a photosensitive resin plate for letterpress printing, which has a unique protective layer, which offers easy production of a printing plate, good handleability, and is water-developable.
BACKGROUND ART
The “photosensitive resin plate for letterpress printing” referred to in the present invention (hereinafter referred to also as “photosensitive resin plate”) is a photosensitive resin composition molded into a thickness of ordinarily 0.5 to 10 mm, sandwiched between two film layers. In such a photosensitive resin plate, one film is peeled; the film-peeled side of the plate is photosensitized via a negative film; the non-photosensitized portion is removed; thereby, a relief is formed.
Formation of the relief (hereinafter referred to also as production of printing plate) is generally conducted by adhering a negative film to a photosensitive resin composition, applying an actinic ray via the negative film to selectively expose the composition to the actinic ray, and then removing the unexposed portion to form a relief.
In the relief formation, the surface of the photosensitive resin composition is sticky in many cases and usually invites various problems. For example, when a negative film is adhered onto the photosensitive resin composition and is later peeled, the peeling is insufficient due to the stickiness of the composition, damaging both the formed relief (printing plate) and the negative film; bubbles form at the time of adhesion of the negative film, making it impossible to achieve uniform adhesion; thus, the reproducibility of the image is low.
The methods adopted most widely for alleviating the above problems include a method which comprises covering the surface of a photosensitive resin composition with a thin protective layer removable with a developing solution. This method is specifically described in, for example, JP-A-51-49803 (a polyvinyl alcohol having a saponification value of 90% or more), JP-A-54-68224 (a water-soluble polymer) and JP-A-56-110941 (a soluble polyamide).
When there is used a photosensitive resin composition developable with an aqueous treating solution, generally a protective layer is used containing a water-soluble polymer (e.g. a polyvinyl alcohol or a water-soluble cellulose) so that the protective layer also is made developable with the aqueous treating solution.
When such a water-soluble polymer is used; however, the following occurs: the resulting photosensitive resin becomes substantially hydrophilic and therefore contains absorbed water; the photosensitive resin is covered with an ultraviolet-transmitting film and used in a vacuum state in order to enable, for light exposure, uniform adhesion of a negative film to the plate; the absorbed water in the photosensitive resin becomes a water vapor owing to the heat of light exposure and vaporizes from the photosensitive resin layer. As a result, there arises a problem that the water vapor softens the protective layer containing a water-soluble polymer, inducing excessive adhesion of the protective layer to the negative film. Further there arises a problem that the excessive adhesion makes it impossible to remove the water vapor, resulting in the formation of bubbles between the negative film and the plate. These problems arise particularly when a large printing plate is produced or after there has been a long exposure time in order to obtain a precise image. If part of the image to be reproduced happens to be at the site(s) where bubbles have been formed, the reproducibility of that part of the image is extremely low.
When the above-mentioned water-soluble polymer is used, there also takes place the following problem. During production of the printing plate, a cover film (ordinarily, PET film) used for protection of a protective layer is peeled, and the protective layer absorbs water and generates small wrinkles (hereinafter referred to also as wrinkles formed by water absorption) at the surface. When the resulting plate material having these small wrinkles is subjected to light exposure, the small wrinkles are reproduced in the relief. These wrinkles formed by water absorption are different in size depending upon the composition of the protective layer and have heights ranging from about 3 &mgr;m to 20 &mgr;m. This problem is a big obstacle to the spread of a water-developable photosensitive resin plate.
To suppress such excessive adhesion and wrinkles formed by water absorption, it was proposed to apply a matting treatment to a cover film to make matte the side of a protective layer which comes in contact with a negative film. This attempt, however, has a problem in that the matting treatment makes the total operational time long and incurs a higher cost and the control of the surface roughness in the matting treatment is very difficult; and also there is a problem in that the matting treatment causes light scattering and the reproduced image has a low resolution. There is a further problem that the matting treatment strengthens the adhesivity of protective film with cover film, reducing the peelability of cover film.
DISCLOSURE OF THE INVENTION
The present invention aims at providing a photosensitive resin plate for letterpress printing, which is developable with an aqueous treating solution, which can suppress excessive adhesion, wrinkles formed by water absorption and excessive adhesion, generated during production of printing plate, which enables excellent peelability, and which is superior in resolution.
The present inventor made an intensive study in order to solve the above problems. As a result, the present inventor found that when the photosensitive layer is protected by a protective layer having a multilayer structure comprising an intermediate layer and a surface layer, wherein the intermediate layer is in contact with the photosensitive layer and contains a water-soluble resin, and wherein the surface layer contains a resin having a water absorption of 5% by weight or less and having substantially no water-developability, that the surface layer surprisingly exhibits water-developability. The present invention has been completed based on the above finding.
The present invention is as follows.
(1) A water-developable photosensitive resin plate for letterpress printing which comprises a hydrophilic photosensitive resin layer and a protective film contacting therewith, wherein the protective film consists of at least two layers, of which one is a surface layer containing a resin having a water absorption of 5% by weight or less and the other is an intermediate layer containing a water-soluble resin which is in contact with the photosensitive resin layer.
(2) A photosensitive resin plate according to item 1, wherein the intermediate layer further contains fine particles of a hydrophobic resin having a water absorption of 5% by weight or less and the weight ratio of the hydrophobic resin fine particles and the water-soluble resin is 95/5 or less.
(3) A photosensitive resin plate according to item 1 or 2, wherein the intermediate layer and/or the surface layer contains an ultraviolet absorber.
BEST MODE FOR CARRYING OUT THE INVENTION
The photosensitive resin plate for letterpress printing used in the present invention generally has a laminated structure consisting of a base film (ordinarily, a polyethylene terephthalate (PET) film) used as a substrate for maintaining dimensional stability, an adhesive layer, a photosensitive resin (composition) layer, a protective layer and a cover film (ordinarily, a PET film) in this order.
The protective layer is ordinarily formed on the back side of the cover film, and the side of the protective layer not in contact with the cover film is adhered to the photosensitive resin layer.
In the present invention, the protective layer consists of at least two layers and has a surface layer and an intermediate layer. The surface layer is in contact with the cover film, and the intermediate layer is in contact with the photosensitive resin layer.
The water-soluble resin used in the intermediate layer accordin
Haraguchi Keiichi
Nakano Katsuya
Asahi Kasei Kabushiki Kaisha
Baxter Janet
Lee Sin J.
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