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
2000-07-20
2002-07-23
Ashton, Rosemary (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
Reexamination Certificate
active
06423471
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a photosensitive composition having excellent stability and handling characteristics as well as high sensitivity, and to an image formation method using such a composition. In particular, the invention relates to a photosensitive composition and an image formation method suitably applicable to a lithographic printing plate precursor material which enables platemaking with scanning exposure based on digital signals.
BACKGROUND OF THE INVENTION
Hitherto the presensitized plate (abbreviated as “PS plate” hereinafter) comprising a hydrophilic support and an ink-receptive photopolymer layer provided thereon has been widely used as a lithographic printing plate. In a conventional method for making such a printing plate, mask exposure (area exposure) is generally carried out via a lith film, and then the non-imaging area is dissolved and removed with a developer.
In recent years has been widely spread the technology to digitize image information by electronically processing, storing and outputting the image information by the use of a computer. And a variety of new image-output systems which can keep up with such digitization technology have become practical. Under these circumstances, it has been anxiously awaited to develop the computer-to-plate (CTP) technology which enables the direct platemaking to be performed by scanning highly directional light, such as laser beams, corresponding to the digitized image information, but not using a lith film. And the development of printing plate precursors suitable for such technology has been an important technical problem.
As a method of enabling the utilization of scanning exposure in case of making a lithographic printing plate, the structure that a photopolymerizable composition having a high photosensitization speed (hereinafter also referred to as a photosensitive composition) is incorporated in an ink-receptive photopolymer layer (hereinafter also referred to as a photosensitive layer) provided on a hydrophilic support was proposed, and the lithographic plate precursors having such a structure have already been on the market. Those plate precursors are simple in development processing, and provide desirable plate-making and printing performances, including high resolution, excellent inking properties, a long press life and high scum resistance.
The photosensitive composition having ink receptivity is basically constituted of an ethylenically unsaturated compound and a photopolymirization initiator. Further, a binder resin can be contained therein, if needed. Such a composition forms images by a mechanism that the photopolymerization initiator absorbs light to produce active radicals, and these radicals set off the addition polymerization of the ethylenically unsaturated compound to render the photosensitive layer insoluble.
As to the light source which is used at the time when the lithographic printing plate precursor of photopolymerization type is exposed for platemaking, visible light sources of long wavelengths, such as Ar laser (488 nm) and FD-YAG laser (532 nm), have been employed, but there has been a desire to increase the productivity by writing at a higher speed. In the photopolymer-CTP system of conventional type, however, the writing at a higher speed is not yet realized because the output of light sources usable therefor is not sufficiently high and the usable plate precursors also don't have sufficiently high sensitivity. Further, the conventional systems are disadvantageous in that, as they are designed so as to respond to Ar laser (488 nm) or FD-YAG laser (532 nm), the photosensitive materials used therefor is required to have high sensitivity in the vicinity of 500 nm. As a result, it is necessary to carry out all the operations, including those for taking out a plate from a cardboard package, loading a plate setter in a cassette and inserting a plate in a plate setter, under a red safelight, so that the workability is considerably low. Therefore, it has been desired to make it possible to handle plates under daylight.
In recent years, on the other hand, semiconductor laser devices possible to continuously oscillate in the wavelength region of 350 to 450 nm, wherein InGaN or ZnSe materials are used, have been in a practical-use stage. The scanning exposure system using such a light source of short wavelengths carries an advantage that it can have satisfactory output, and besides, can be constructed economically because the production of semiconductor laser devices is inexpensive from the structural point of view. Further, such exposure systems make it possible to use the photosensitive materials having their sensitivities in short wavelength region to enable operations to be performed under a bright safelight, compared with conventional systems using FD-YAG or Ar laser devices.
However, there have not yet been known any photopolymerization initiators having sensitivity high enough for scanning exposure in the short wavelength region of 350 nm to 450 nm.
Furthermore, the techniques to obtain a photosensitive composition suitable for laser scanning and having high productivity and excellent handling properties under daylight have been extensively longed for in the imaging field. And it is expected to apply such techniques to the image formation by, e.g., photo-molding, holography or color hard copy, and to the field for the production of electronic materials, such as photoresist.
SUMMARY OF THE INVENTION
Therefore, a main object of the invention is to construct a CTP system that can achieve excellent productivity, operation suitability and economical efficiency. More specifically, what the invention is mainly aiming at is providing a photosensitive composition having high sensitivity at the oscillation wavelengths of inexpensive short-wavelength semiconductor laser devices and capable of being handled also under bright safelight, and a method for image formation using the composition.
Other objects and effects of the present invention will become apparent from the following description.
As a result of extensive studies made by the present inventors to achieve the aforementioned objects, it has been found that the sensitivity high enough to enable high-speed scanning exposure and the suitability for operations under bright safelight can be both attained with a photosensitive composition comprising (i) at least one titanocene compound, (ii) an addition polymerizable compound containing at least one ethylenically unsaturated double bond and (iii) at least one pigment having an optical characteristic such that the transmittance at 500 nm is relatively smaller than the transmittance at 400 nm. Thus, the present invention is based on this finding.
DETAILED DESCRIPTION OF THE INVENTION
A first problem for completion of the invention consists in acquisition of sensitivity high enough to enable high-speed scanning exposure in the wavelength region of 350 nm to 450 nm. For solution of such a problem, it is necessary to search for an appropriate photo-initiation system. We have now found that the sensitivity sufficient in a practical sense can be achieved when a titanocene compound is employed and, if necessary, in combination with a sensitizing dye. The usefulness of a titanocene compound-containing photo-initiation system as a photopolymerizable composition suitable for scanning exposure is disclosed, e.g., in JP-B-4-47680 (the term “JP-B” as used herein means an “examined Japanese patent publication”). In addition, the photo-initiation system comprising the combinations of carbomerocyanine dyes with titanocene are disclosed in JP-A-9-328505, JP-A-8-272096 and JP-A-8-262715 (the term “JP-A” as used herein means an “unexamined published Japanese patent application), the photopolymerizing composition comprising a photoreducing dye and a titanocene in combination with a specified polymerizing monomer is disclosed in JP-A-4-221958, the photo-initiation systems comprising the combinations of titanocene with particular aminobenzilideneketone dyes are disclosed in JP-A-4-1948
Murota Yasufumi
Sorori Tadahiro
Ashton Rosemary
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
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