Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
2001-08-23
2003-01-28
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
C430S493000
Reexamination Certificate
active
06511790
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid developer suitable for alkaline development for processing a lithographic printing plate precursor, i.e., a presensitized plate for use in making a lithographic printing plate (hereinafter possibly referred to as “PS plate”) which is directly imageable by scanning an infrared (IR) laser on the basis of digital signals through a computer, etc., i.e., a directly-imageable lithographic printing plate precursor. The present invention further relates to a method for preparing a lithographic printing plate wherein said liquid developer is used.
2. Description of the Prior Art
Recently, progress of technique on a laser has been remarkable, and particularly, a solid state laser or semiconductor laser having an emission range of from near infrared ray to infrared ray is very useful as a light exposure source in a system wherein a printing plate precursor is directly imaged by digital data, since such laser of high powered and compact type has been easily available.
As an image recording material suitable for laser-writing, for example, Japanese Patent Un-examined Publication (hereunder referred to as “J.P. KOKAI” ) No. Hei 7-285275 has suggested a positive-working image recording material comprising (a) a binder such as a cresol resin, (b) a compound which absorbs light so as to generate the heat, and (c) a compound such as quinonediazide which is heat-decomposable, whose pre-decomposition state being capable of substantially decreasing a solubility of said binder. The mechanism of this material is that on IR radiation, the light-exposed area becomes alkaline-soluble (i.e., heat-mode type), since the compound (b) generates the heat in the light-exposed area and then the compound (c) is decomposed. However, the generated heat is absorbed in some degree by a substrate aluminum plate and so the thermal efficiency of this mechanism is poor, and therefore the solubility of the light-exposed area to an alkaline liquid developer is not satisfactory in a development process. Consequently, alkaline strength of liquid developer must be raised to ensure the solubility of the light-exposed area.
On the other hand, in the lithographic printing plate precursor of heat-mode type, the resistance of non-heated areas (i.e., image areas) to dissolution in an alkaline liquid developer is poor under the above highly alkaline concentration, and when the image recording material has slightly scratches on the surface thereof, said scratched areas may be easily dissolved. Accordingly, there is a problem such that the image areas, particularly fine line areas and the like are easily impaired. This tendency is particularly serious in a positive-working lithographic printing plate precursor employing a polymeric compound which is highly soluble to an alkaline aqueous solution.
Consequently, the raise in alkaline strength of liquid developer should be limited, though said raise in alkaline strength is intended not to leave undissolved materials on non-image areas, and it is difficult to form a highly sharp and clear image without impairment to the formed image areas. There is therefore a need for improved sharpness and reproducibility of images, particularly fine images comprising a dot pattern, fine lines and the like.
Incidentally, in association with recent improvement on image recording materials of IR-laser exposure type, it tends to use an IR-absorbing agent in the image recording material, which absorber is more insoluble in an alkaline liquid developer than a conventional IR-absorbing dye such as o-quinonediazide. When such image recording material is processed in an alkaline liquid developer, insoluble matter originated from the IR-absorbing agent is discharged into the developer, and such insoluble matter may further interact with a component of binder polymers in the image recording material or inorganic substances in water to generate insoluble matter. The above insoluble matter may adhere to a plate during development procedure in making a printing plate so as to impair image areas of the plate. In addition, there is a large labor or cost for maintenance of processing tanks, since it is necessary to regularly remove the precipitated insoluble matter in the processing tanks.
DETAILED EXPLANATION OF THE INVENTION
Summary of the Invention
Accordingly, an object of the present invention is to provide an alkaline liquid developer for a lithographic printing plate, which developer can overcome the above conventional drawbacks, and form a highly sharp and clear image in a lithographic printing plate without damages to the formed image areas.
Another object of the present invention is to provide an alkaline liquid developer for a lithographic printing plate, which developer can prevent occurrence of insoluble matter originated from a binder resin and/or an IR-absorbing agent, as well as adherence of the insoluble matter to the surface of a plate during processing, while retaining liquid conditions suitable for an alkaline liquid developer, said developer being capable of providing a stable processing procedure in an extended period.
Another object of the present invention is to provide a method for preparing a lithographic printing plate which does not cause the formation of insoluble matter during development processing even when a large quantity of lithographic printing plate precursor are processed over a long time period and which allows stable treatment of a lithographic printing plate precursor.
Under such circumstances, the inventors of this invention have searched a compound which prevents the occurrence of insoluble matter and enhances the inhibition on dissolution of image areas in an alkaline liquid developer, while retaining liquid conditions suitable for an alkaline liquid developer such as a balance between a suitable alkaline concentration (hydroxide ion concentration) and SiO
2
concentration, and have found that the use of a specific surfactant in a liquid developer can prevent the occurrence of insoluble matter, adherence of said insoluble matter to the surface of a plate and deposit of said insoluble matter in processing tanks, and also can inhibit the dissolution of image areas on a plate to an alkaline aqueous solution. Thus the inventors have completed the present invention.
Consequently, the present invention is directed to an alkaline liquid developer suitable for development of an infrared radiation-presensitized plate for use in making a lithographic printing plate, which developer comprises at least one selected from the group consisting of amphoteric surfactants and cationic surfactants. The present invention is also directed to a method for preparing a lithographic printing plate comprising the steps of imagewise light-exposing to infrared radiation, a presensitized plate for use in making a lithographic printing plate, said presensitized plate having an image-forming layer which comprises an IR-absorbing agent, and then developing the light-exposed plate with an alkaline liquid developer comprising at least one selected from the group consisting of amphoteric surfactants and cationic surfactants.
Description of the Preferred Embodiments The present invention will be described in more detail below.
An alkaline liquid developer and a method for preparing a lithographic printing plate according to the present invention can be applied to a processing procedure of all kinds of a presensitized plate for use in making a lithographic printing plate, said presensitized plate having an image-forming layer which comprises an IR-absorbing agents.
The alkaline liquid developer (hereinafter possibly referred to as simply “developer”) according to the present invention is fundamentally an alkaline aqueous solution, and the composition of said alkaline aqueous solution can be selected from conventional ones.
The alkaline aqueous solution includes an alkaline aqueous solution comprising an alkaline silicate or a nonreducing sugar, and a base, said solution's pH being preferably from 12.5 to 14.0.
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Le Hoa Van
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