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
2000-11-14
2003-01-07
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
C430S273100, C430S005000, C430S302000, C430S306000, C430S325000, C430S326000
Reexamination Certificate
active
06503685
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lithographic printing plate used in the field of offset printing, and more particularly to a positive- or negative-type original plate for a lithographic printing plate which is used as a so-called computer-to-plate (CTP) plate that is applicable to direct plate making based on digital signals from a computer or the like.
This application is based on Patent Application No. Hei 10-71825 filed in Japan, the content of which is incorporated herein by reference.
2. Description of Related Art
As systems for direct plate making based on digital signals from a computer, there have hitherto been known (1) a system which uses electrophotography, (2) a system which uses Ar laser exposure and post-heating, (3) a system which uses high power laser exposure and post-heating, (4) a system which uses diffusion transfer of a silver salt, (5) a system which ablates a silicone rubber layer by electric discharge or irradiation with a laser beam, (6) a system which forms a mask layer on a conventional lithographic presensitized plate (PS plate) having a light-sensitive image forming layer, forms an image on the mask layer, performs flood exposure, develops, and performs post-treatment to obtain a printing plate, and the like. At present, these have their own merits and demerits, and further investigation is currently under way. Of the above-described systems, particularly the plate material obtained by the technology described in (6) above provides a high resolution image, is adaptable to a large size plate, and provides a printing plate, which is a final product, which is similar to conventional ones, so that printing operators are accustomed thereto through their experience. For this reason or for other reasons, the system has been regarded as a technology replacement system which can be easily accepted by operators at actual operating sites when replacing a conventional plate making system using a film and a PS plate by a computer-to-plate (CTP) plate making system.
As methods for forming a mask image on a conventional PS plate, there have been known i) an inscribing method performed by an ink jet, ii) a thermal transfer method, iii) a method which includes coating a silver salt layer on a PS plate, image-wise exposing the silver salt layer, and developing by a wet method to obtain a mask image, iv) a method which includes ablation of the mask layer provided on a PS plate with a high power laser beam to form an image, and the like.
Of these, the methods i) and ii) have problems that they do not provide high resolution, or the inscribing speed is low, while the method iii) gives high resolution but involves complicated post-treatment or other problems.
The method using ablation with laser beam is a known technology as described in Japanese Patent Unexamined Publications Nos. 50-113307, 50-102401, 50-158405, 53-23705, 53-33702, 58-18290, 60-83893, 61-36750, etc. It has various practical problems. That is, high resolution is difficult to obtain because of non-uniform ablation traces, there is the concern of contamination of appliances due to scattering or evaporation at the time of inscribing, inscribing on a large plate takes a long time because it requires a high energy of usually 800 to 1,200 mJ/cm
2
, which makes the inscribing speed very slow, and the like. Also, when images are formed using high energy density light, usually a problem called banding occurs. Banding is a phenomenon which is observed as a band-like pattern, caused by a fluctuation in the output power of a laser device used as an optical source or by a difference in light intensity distribution in an incident plane appearing near the boundary between scanning lines when linear scanning is operated. This phenomenon is observed frequently in the case of directly inscribing on a printing material using a high energy density laser.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made with a view to obviating the above-described problems and a first object of the present invention is to provide positive- and negative-type original plates for lithographic printing plates which are amenable to high speed image inscription at a very low optical energy exposure, as low as 150 to 200 mJ/cm
2
, which enables clean treatment and which enables direct inscription thereon with high energy density light.
A second object of the present invention is to provide an original plate for a lithographic printing plate which is free of problems such as banding and the like and provides a high quality printing plate image by relaxation and rendering uniform homogenization over the flood exposure step after the formation of a mask.
A third object of the present invention is to provide an original plate for a lithographic printing plate which can give a final printing plate which is equivalent to a conventional printing plate (PS plate) so that when printing, skilled printing operators can give full play to their experience in working in actual printing sites and which they can handle without a feeling of unfamiliarity.
A fourth object of the present invention is to provide an original plate for a lithographic printing plate, which is a high energy density light inscribable computer-to-plate printing plate which is applied to direct plate making based on digital signals from a computer or the like and which allows the use of a conventional treating apparatus upon development treatment and a conventional printer as it is upon printing.
A fifth object of the present invention is to provide an original plate for a lithographic printing plate having an improved workability which can be operated under ordinary room light or the like without requiring a special safety light, but with which prepares a good printing plate can be prepared.
A sixth object of the present invention is to provide a heat-sensitive composition comprising as an essential component an anionic self water-dispersible resin particle, the composition efficiently absorbing high energy density light and converting it to thermal energy and as a result giving rise to a sharp high resolution latent image.
A seventh object of the present invention is to provide an easy, inexpensive treating method which treats a latent image formed in a heat-sensitive composition layer with an alkaline aqueous solution to form a sharp mask image and such that upon the development treatment of light-sensitive image forming layer as a post-treatment, the mask image layer as well as a non-image portion of the light-sensitive image forming layer can be removed.
An eighth object of the present invention is to provide a process for preparing a printing plate which uses the positive- or negative-type original plate for a lithographic printing plate of the present invention which has attained the above-described objects and with which a good printing plate having the high resolution required for printing can be prepared.
The present invention has been completed based on the finding of a novel process which uses, as a mechanism for forming an inscribed image on a light-sensitive composition layer with high energy density light, formation of a latent image by mutual melting and fusion of resin particles in the image portion due to the heat generated by absorption of light energy and subsequent development of the latent image by removal of the non-modified, non-image portion by a wet method using a treatment liquor, as opposed to a mechanism utilizing chemical reaction such as polymerization reaction on a so-called negative PS plate or the like involving light energy and a monomer or modification accompanying partial decomposition reaction of a polymer with light energy (positive type PS plate). The image forming step for the mask layer according to the present invention is of a mechanism which utilizes physical changes of a substance but is based on a principle quite different from the conventional technology.
That is, in order to achieve the above-described objects, a first aspect of the present invention is a heat-sensit
Kojima Yasuhiko
Oe Koji
Shimizu Shinji
Tasiro Nansei
Watanabe Yasuyuki
Baxter Janet
Dianippon Ink and Chemicals, Inc.
Lee Sin J.
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