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
2000-12-05
2003-06-10
Le, Hoa Van (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, C430S281100, C430S286100, C430S287100, C430S302000, C101S453000, C101S463100
Reexamination Certificate
active
06576397
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a heat-sensitive lithographic printing plate precursor having suitability for computer-to-plate system. More specifically, the present invention relates to a heat-sensitive lithographic printing plate precursor for making a lithographic printing plate, wherein images are recorded by infrared laser scanning exposure based on digital signals and then subjected to development-processing.
BACKGROUND OF THE INVENTION
A large number of studies have been made on lithographic plates for computer-to-plate (CTP) system that has achieved brilliant progress in recent years, and various methods applicable to such lithographic printing plates have been proposed. As one of the methods already in the actual use, there is a method of making a printing plate for CTP system due to utilization of photo-polymerization. More specifically, the printing plate making therein comprises performing laser energy irradiation to cause polymerization in the irradiated areas and render the areas insoluble, thereby forming image areas, and dissolving and removing the unirradiated areas by development.
In JP-A-4-221958, JP-A-5-281728, JP-A-8-146605 and JP-A-8-220758 (the term “JP-A” as used herein means an “unexamined published Japanese patent application) are disclosed the photo-polymerization-utilized lithographic printing plate precursors for CTP system which each comprise (1) a support having a hydrophilic surface, (2) a photo-polymerizable composition layer containing a sensitizing dye, a photo-polymerization initiator, a polymerizable unsaturated monomer and a binder polymer, and (3) an oxygen-blocking overcoat layer which is impervious to oxygen.
Because of utilization of photo-polymerization, those lithographic printing plate precursors for CTP system have a sensitive property in a visible region corresponding to visible laser beams used as a light source, e.g., argon ion laser and FD-YAG laser. As a result, the printing plate precursors cause the inconvenience of having to be handled in a darkroom.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to provide a lithographic printing plate precursor for computer-to-plate (CTP) system, which can eliminate the inconvenience of being used in a darkroom and enables handling in a bright room.
The present inventors have found that the aforementioned object can be attained with a lithographic printing plate precursor in which the thermal polymerization caused by infrared laser irradiation is utilized for image formation, thereby achieving the present invention.
The Embodiments and preferred embodiments of the present invention are shown below:
(1) A heat-sensitive lithographic printing plate precursor, comprising a support having a hydrophilic surface on which (1) a thermal polymerization layer comprising an aqueous alkali-soluble polymer having addition polymerizable unsaturated bonds at its side chains and a thermal polymerization initiator and (2) a water-soluble overcoat layer comprising a water-soluble polymer and a compound capable of converting light into heat are provided in this order.
(2) The heat-sensitive lithographic printing plate precursor as described in Embodiment (1), wherein the addition polymerizable unsaturated bonds are constituted by functional groups in at least one group selected from the group consisting of allyl, acryl and methacryl groups.
(3) The heat-sensitive lithographic printing plate precursor as described in Embodiment (1) or (2), wherein the thermal polymerization initiator is a peroxide or a hexaarylbiimidazole compound.
(4) The heat-sensitive lithographic printing plate precursor as described in any of Embodiments (1) to (3), wherein the water-soluble polymer is a polymer containing vinyl alcohol units in a proportion of at least 65 mole %.
Making additional remark, European Patent 889,363 discloses a near infrared-sensitive composition comprising a near infrared absorbing dye, hexaarylbiimidazole compound (HABI), a photo-polymerization substance and a chain transfer agent. Although this publication has a description such that the exposure is performed via a film having negative or positive images, the present inventor have found that the printing plate made from the light-sensitive composition disclosed therein cannot form images by the laser scanning exposure based on a film-free CTP system. In other words, the publication described above neither discloses nor suggests on a printing plate for CTP system as aimed at by the present invention.
DETAILED DESCRIPTION OF THE INVENTION
As an example of the support having a hydrophilic surface which can be suitably used in the present invention, an aluminum plate is exemplified. Such an aluminum plate (or sheet) includes a pure aluminum plate and alloy plates containing aluminum as a main component and very small amounts of foreign elements. Further, plastic-laminated pure aluminum and aluminum alloy plates may be included therein.
Examples of foreign elements contained in the aluminum alloys include silicon, iron, manganese, copper, magnesium, chromium, zinc, bismuth, nickel, and titanium. The proportion of foreign elements in the alloys is 10% by weight or less. However, the aluminum plate applied to the present invention can be selected properly from aluminum plates made of hitherto well-known conventional materials.
The suitable thickness of such a substrate as described is from about 0.05 mm to about 0.6 mm, preferably from 0.1 mm to 0.4 mm, particularly preferably from 0.15 mm to 0.3 mm.
Prior to using an aluminum plate, it is desirable that surface treatment, such as graining or anodic oxidation treatment, be given to the aluminum plate. This surface treatment can easily secure for the aluminum plate both hydrophilic property and adhesive property to a thermal polymerization layer to be provided thereon.
The graining treatment of an aluminum plate can be effected using various methods, e.g., a method of mechanically graining the surface, a method of electrochemically graining the surface by electrochemical dissolution and a method of chemically graining the surface to cause selective dissolution of the surface. As the mechanical graining method can be used a well known method, e.g., a ball abrasion method, a brush abrasion method, a blast abrasion method and a buff abrasion method. As the chemical graining method, the method as disclosed in JP-A-54-31187 is suitable, wherein the aluminum plate is immersed in a saturated water solution of aluminum salt of mineral acid. As the electrochemical graining method, the method of graining in an electrolytic solution containing an acid, such as hydrochloric acid or nitric acid, by applying thereto alternating or direct current can be exemplified. In addition, an electrolytic graining method using a mixed acid, as described in JP-A-54-63902 may be adopted.
In the above graining method, it is desirable to carry out the graining treatment so that the aluminum plate surface has a center line average surface roughness (Ra) of 0.3 to 1.0 &mgr;m.
The thus grained aluminum plate is subjected to etching treatment with an alkali, such as an aqueous solution of potassium hydroxide or sodium hydroxide, and then is subjected to neutralization treatment, and further anodic oxidation treatment for enhancing abrasion resistance, if desired.
Examples of the electrolytes usable for anodic oxidation of aluminum plates include various electrolytes capable of forming porous oxide film (i.e., oxidation film). In general, sulfuric acid, hydrochloric acid, oxalic acid, chromic acid or a mixture of two or more thereof is employed as such an electrolyte. The electrolyte concentration is properly determined depending on the kind of the electrolyte used.
The treatment conditions for anodic oxidation vary according to the electrolyte used, so they cannot be generalized. However, it is practically favorable to choose the electrolyte concentration from the range of 1 to 80% by weight, the solution temperature from the range of 5 to 70° C., the current density from the range of 5 to 60
Kita Nobuyuki
Maemoto Kazuo
Burns Doane , Swecker, Mathis LLP
Gilliam Barbara
Le Hoa Van
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