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
2000-03-24
2003-01-21
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
C430S281100, C430S286100, C430S287100, C430S288100, C430S302000, C430S348000, C430S944000, C430S945000, C430S964000
Reexamination Certificate
active
06509133
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lithographic printing plate useful 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, as a lithographic printing plate used in the field of offset printing, and more particularly to a lithographic printing plate having a photosensitive layer wherein a latent image is obtained by irradiation of a high power laser having the maximum strength in a near infrared or infrared region, and the latent image is wet developed to thereby form an image.
2. Description of Related Art
With the development of the computer image processing technology, there has been recently developed a method for inscribing an image directly on a photosensitive layer by means of photoirradiation corresponding to digital signals. A computer-to-plate (CTP) system which utilizes the method for a lithographic printing plate and forms an image directly on the printing plate without outputting the image to a silver salt mask film has attracted much attention.
The CTP system having the maximum strength in a near infrared or infrared region and using high power lasers has attracted attention because of the availability of compact and high power lasers, and because it provides a high resolution image with a short period of exposure and the printing plate used for the method may be handled in a lighted room.
As a lithographic printing plate used for the CTP system that uses such a light source, there is disclosed a lithographic printing plate having a photosensitive layer containing a substance which generates acid due to heat (acid generating agent), an infrared absorption agent, a crosslinking agent which crosslinks due to heat, and a resin having a fimctional group capable of crosslinking reactions with the crosslinking agent, in Japanese Patent Unexamined Publications No, 10-228109. The lithographic printing plate, however, has a problem in the preservation stability of the acid generating agent, and a practical problem in that it requires heat processing prior to development after the laser irradiation, in order to accomplish a cation polymerization reaction accompanying the acid generation, hence causing a problem in the reproducibility of halftone dots.
On the other hand, as a lithographic printing plate which does not require heat processing prior to development, after the laser irradiation, in Japanese Patent Unexamined Publication No. 9-171249, there is disclosed a lithographic printing plate in which hydrophobic thermoplastic polymer particles dispersed in a hydrophilic resin are formed on a hydrophilic substrate. With this lithographic printing plate, an image is formed by utilizing a difference in the solubility with respect to the developer between resin fine particles fuision-bonded due to heat and resin fine particles not fusion-bonded. However, this system has problems in that since hydrophobic fine particles that are insoluble in the developer have to be developed together with the hydrophilic resin, the sensitivity, preservation stability and printing resistance are low, and in order to actually utilize it as a printing plate, heat processing is essential after the development. Moreover, in Japanese Patent Unexamined Publication No. 9-171250, there is disclosed a lithographic printing plate in which a hydrophilic resin is crosslinked by means of heat in order to improve the printing resistance, however, since the resin fine particles are not involved in the crosslink, sufficient printing resistance cannot be exerted, and there is also a problem in the preservation stability.
Furthermore, in Japanese Patent Unexamined Publication No. 9-127683, there is disclosed a lithographic printing plate in which a selfwater-dispersible thermoplastic resin particle layer which can be made lipophilic by means of heat is formed on the surface of a hydrophilic substrate. Since this lithographic printing plate does not contain an infrared absorption agent, the sensitivity is low, and in some cases, it is necessary to form a film for prevention of drying out that can be peeled off, such as PET or the like on the resin particle layer, in order to increase the preservation stability. Moreover, when a polyvalent metal ion is used as a crosslinking agent in order to improve the printing resistance, there is a tendency that the development property decreases with the lapse of time.
BRIEF SUMMARY OF THE INVENTION
For obviating the above-described problems, it is an object of the present invention to provide a computer-to-plate (CTP) plate in which an image can be inscribed by a laser beam having the maximum strength in a near infrared or infrared region, and heat processing is not necessary prior to developing a latent image, and which allows the use of a conventional printing apparatus as it is upon printing.
The present inventors made investigations with a view to attaining the above objectives. As a result, the present invention has been completed based on the finding of a novel process of obtaining a printing plate which uses, as a mechanism for forming an inscribed image on a photosensitive layer with high density energy light, formation of a latent image comprising a portion where resin fine particles in the image portion are mutually melted and/or fused due to the heat generated by absorption of light energy and subjected to a polycondensation reaction or polyaddition reaction with the crosslinking agent by means of heat, and subsequent development of the latent image by dissolution and removal of a non-image portion by dipping the lithographic printing plate in a processing solvent, as opposed to a conventional mechanism utilizing only a chemical reaction such as polymerization reaction on a so-called PS plate or the like involving light energy and a monomer that uses a photoinitiator or an acid generating agent (negative type PS plate), or modification accompanying partial decomposition reaction of a polymer with light energy (positive type PS plate).
That is to say, to attain the above described object, the present invention provides (I) a lithographic printing plate having on a substrate, a photosensitive layer comprising a photosensitive composition containing a crosslinking agent, a water dispersion of resin fine particles having a functional group capable of performing cross-linking reactions with the crosslinking agent, and an infrared absorption agent.
Moreover, to attain the above described object, the present invention provides (II) an image forming method characterized in that after an image has been formed on a photosensitive layer of the lithographic printing plate set forth in the above (I) by using a laser beam, the image lis subjected to wet development.
With the lithographic printing plate of the present invention, a plate can be made up without preheating, after the laser inscription. Moreover, the resin fine particles are soluble in an alkaline developer, and are mutually capable of performing cross-linking reactions by means of heat. Hence, the results of sensitivity and preservation stability tests (at 60° C., for 15 hours) are excellent, and show a printing resistance such that the plates can be used sufficiently even just after development. Moreover, it is possible to provide a practical printing plate having an excellent printing resistance by means of burning.
DETAILED DESCRIPTION OF THE INVENTION
The crosslinking agent used in the present invention refers to a crosslinking agent that crosslinks particles with each other by means of heat. For example, there can be used one having a carbodiimide group as a functional group, one having an oxazoline group, one having an amino group or a methylol or alkoxymethyl group, or one generally and widely used as a crosslinking agent. The particles of the present invention are used as water dispersion bodies. Therefore, an aqueous-type crosslinking agent is preferably used.
As the crosslinking agent having an amino group, a methylol group or an alkoxymethyl group, it is prefera
Kojima Yasuhiko
Oe Koji
Saito Naohito
Shimizu Shinji
Takahashi Katsuji
Armstrong Westerman & Hattori, LLP
Baxter Janet
Dainippon Ink and Chemicals Inc.
Gilliam Barbara
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