Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
2000-05-30
2002-02-12
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
C430S270100, C430S281100
Reexamination Certificate
active
06346365
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming material which can be used as an offset printing master, and in particular to a positive photosensitive composition for use with an infrared laser which is used in so-called computer-to-plate printing in which an offset printing plate is formed directly on the basis of digital signals from a computer or the like.
2. Description of the Related Art
Conventionally, computer-to-plate methods have been known which directly form an offset printing plate on the basis of digital data from a computer. Examples of such methods include (1) an electrophotographic method, (2) a photopolymerization method based on the combination of exposure by an Ar laser and post-heating, (3) a method in which a silver salt sensitive material is deposited on a photosensitive resin, (4) a method using a silver master and (5) a method in which a silicone rubber layer is decomposed by discharge breakdown or a laser beam.
However, in the electrophotographic method (1), processings such as charging, exposure and development are complicated, and the device used for the processings is also complicated and large-scale. In the method (2), the post-heating step is required. Further, a highly sensitive plate material is also required, and handling thereof in a light room is difficult. In methods (3) and (4), silver salts are used and thus the processing in the methods is complicated and the cost is high. Method (5) is a relatively complete method, but there remains a problem in that silicone dust remaining on the surface of the offset printing plate must be removed.
Recently, lasers have been remarkably developed. In particular, solid state lasers and semiconductor lasers, which have a luminous band from near infrared ray wavelengths to infrared ray wavelengths and which are small-sized and have a high energy output, can be easily obtained. These lasers are very useful as a light source for exposure when an offset printing plate is directly formed on the basis of digital data from a computer or the like.
In conventional positive lithographic printing plates for an infrared laser which are used in the computer-to-plate system, a resin which is soluble in an alkali aqueous solution and has a phenolic hydroxide group, such as novalak resin, is used as a polymer compound which is soluble in an alkali aqueous solution (hereinafter, alkali aqueous solution soluble polymer compound) As such a recording material, for example, Japanese Patent Application Laid-Open (JP-A) No. 7-285275 discloses image recording materials in which a material absorbing light to generate heat, and various onium salts, quinonediazide compounds or the like are added to an alkali aqueous solution soluble resin having a phenolic hydroxide group, such as novalak resin. In these image recording materials, onium salts, quinonediazide compounds or the like function as a dissolution-inhibiting agent for substantially lowering the solubility of the alkali aqueous solution soluble resin in image portions. On the contrary, the onium salts, quinonediazide compounds or the like are decomposed by heat in non-image portions and their dissolution-inhibiting ability is not exhibited, so that they can be removed altogether with the alkali aqueous solution soluble resin by development, thus allowing formation of images.
In such image recording materials, onium salts, quinonediazide compounds or the like have a light absorbing band (350-500 nm) within the visible ray range. Thus, inconveniently, they can only be handled under yellow lights. The onium salts or the like are decomposed by heat, so as to form non-image portions. Therefore, it is necessary to provide them with energy sufficient for their decomposition, and the decomposed onium salts inevitably react and recombine with the novalak resin. Thus, there are limits to the improvement in sensitivity.
The onium salts, the quinonediazide compounds or the like are not necessarily highly compatible with the alkali aqueous solution soluble polymer compound or the material absorbing light to generate heat. Thus, it is difficult to prepare a uniform coating solution and to obtain a uniform and stable material for lithographic printing plates.
Among conventional materials for positive lithographic printing plates for infrared lasers, there are materials which comprises as essential components an alkali aqueous solution soluble binder resin (without using onium salts, quinonediazide compounds, or the like), an IR dye which absorbs light and generates heat, and the like. The IR dye or the like functions a dissolution-inhibiting agent which, in non-exposed portions (image portions), interacts with the binder resin to lower the solubility of the binder resin substantially. In exposed portions (non-image portions), the interaction of the IR dye or the like with the binder resin is weakened by the generated heat, so that the binder resin is dissolved in an alkali developing solution, thus allowing formation of a lithographic printing plate.
However, the IR dye or the like functions only as a dissolution-inhibiting agent in the non-exposed portions (the image portions), and does not promote the dissolution of the binder resin in the exposed portions (the non-image portions) Although the onium salts, the quinonediazide compounds or the like interact with the binder resin in non-exposed portions (image portions) to function as the dissolution-inhibiting agent, they are decomposed by light in the exposed portions (non-image portions) and generate an acid so as to function as a dissolution-promoting agent.) Accordingly, in the case of the IR dyes or the like, in order to obtain a difference between the non-exposed portions and the exposed portions, there is no choice but to use a resin having high solubility in an alkali developing solution as the binder resin thereby resulting in the problem that the state before development is not stable.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to provide a positive photosensitive composition for use with an infrared laser which is used in a “computer-to-plate” system and has advantages in that the image forming capability of a recording layer comprising an alkali aqueous solution soluble polymer compound is improved, places in which the composition can be handled are not restricted, handling of the composition is easy because of the stability of the state before development, and the stability of sensitivity against changes in the concentration of a developing solution, that is, the development latitude, is good.
The inventors have studied such compositions, and found that a specific combination of an alkali aqueous solution soluble polymer compound and a compound for controlling the solubility of the polymer compound in an alkali aqueous solution improves the solvent-resistance and development latitude to a large extent, and thus arrived at the present invention.
According to the first aspect of the present invention, a positive photosensitive composition for use with an infrared laser comprises one or more alkali aqueous solution soluble polymer compounds (A) having at least one group selected from a phenolic hydroxide group (a-1), a sulfonamide group (a-2), and an active imide group (a-3); a compound (B) which has an I/O value (Y) satisfying the relationship 0.05≦|X−Y|≦0.5 (inequality (1)), in which X is the I/O value of the alkali aqueous solution soluble polymer compound (A), and which is compatible with the polymer compound (A) thereby lowering the solubility of the polymer compound (A) into an alkali aqueous solution, the effect of lowering the solubility being reduced by heating; and a compound (C) which generates heat upon absorbing light. The photosensitive composition dose not contain any compound having a thermal decomposition temperature of 150° C. or less.
Compound (B) has an I/O value (Y), whose relationship with the I/O value (X) of the alkali aqueous solution soluble polymer compound satisfies the above inequality (
Kawauchi Ikuo
Kimura Takeshi
Baxter Janet
Burns Doane , Swecker, Mathis LLP
Gilmore Barbara
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