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
2000-03-23
2002-03-12
Hamilton, Cynthia (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
C430S270100, C430S944000, C430S945000
Reexamination Certificate
active
06355396
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photosensitive composition suitable as a positive-type image forming material and also to a planographic printing plate precursor using the composition. More specifically, the present invention relates to a positive-type image forming composition that is designed for use with an infrared laser and is characterized by writability with heat, particularly with an infrared laser, thermal head or the like, and by suitability for use in a planographic printing plate precursor that can be prepared by a so-called direct plate production process in which the plate is prepared directly according to digital signals, particularly from a computer or the like. Further, the present invention relates to a planographic printing plate precursor using the foregoing composition.
2. Description of the Related Art
In recent years, owing to progress in technologies related to solid-state lasers and semiconductor lasers emitting rays in regions ranging from a near-infrared region to an infrared region, a system that uses these infrared lasers in a printing plate production process so that a printing plate is prepared directly according to digital data from a computer, has been drawing attention.
Japanese Patent Application Laid-Open (JP-A) No. 7-285,275 discloses a material for a positive-type planographic printing plate precursor for use with an infrared laser in direct plate production. This invention relates to an image forming material comprising a resin soluble in an aqueous alkaline solution, a substance capable of generating heat by absorbing light, and a positive-type photosensitive compound such as a quinone diazide, wherein in image portions, the positive-type photosensitive compound acts as a dissolution inhibiting agent which substantially reduces the solubility of the resin soluble in the aqueous alkaline solution, whereas in non-image portions, the positive-type compound is thermally decomposed to thereby lose its dissolution inhibiting capability and can be removed through developing.
As a result of their investigations, the present inventors have found that a positive image can be obtained without using a quinone diazide in an image recording material. However, mere elimination of the quinone diazide from the image recording material presents a drawback in which the stability of sensitivity with respect to the concentration of a developer, i.e., latitude in development, becomes poor.
On the other hand, an onium salt or a compound capable of forming alkali-insoluble hydrogen bonds is known to act as an agent that inhibits an alkali-soluble polymer from becoming dissolved in an alkali. As to an image forming material for use with an infrared laser, WO 97/39,894 describes that a composition that uses a cationic, infrared-ray absorbing dye as an agent that inhibits an alkali-soluble polymer from being dissolved in an alkali exhibits a positive-type operation. This positive-type operation is an operation in which the infrared-ray absorbing dye absorbs the laser light and generates heat which causes the polymeric film to lose a dissolution-inhibiting effect in an irradiated region, to thereby form an image.
However, this invention is associated with a problem that, although the image-forming performance of the photosensitive composition at a surface thereof irradiated with a laser is satisfactory, a satisfactory effect cannot be obtained in depths of the composition because a sufficient amount of heat is not diffused to the depths, and, as a result, an on-off distinction between exposed areas and unexposed areas is insufficient in a developing process with alkali. Consequently, a good image is not obtained (i.e., low sensitivity and narrow latitude in development occurs). The term “latitude in development” as used herein means the broadness of the allowable range of the alkali concentrations of an alkaline developer for the creation of a good image.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a photosensitive composition characterized by high sensitivity and good latitude in development, and to provide a positive-type planographic printing plate precursor that uses the foregoing composition in a direct plate production process and enables an image to be formed with high sensitivity with an infrared laser.
After a series of studies for the purpose of upgrading image-forming performance, i.e., increasing sensitivity and latitude in development, the present inventors found that latitude in development was improved by use of specific infrared-ray absorbing agents.
Namely, a photosensitive composition of the present invention comprises the following components (a) and (b) and becomes soluble in an aqueous alkaline solution when irradiated with an infrared laser:
(a) infrared-ray absorbing agent represented by the following general formula (I); and
(b) a polymeric compound insoluble in water but soluble in an aqueous alkaline solution (hereinafter referred to at times as polymeric compound soluble in aqueous alkaline solution):
wherein R
1
through R
4
each independently represents a hydrogen atom, alkyl group or aryl group; R
5
and R
6
each independently represents an alkyl group, substituted oxy group or halogen atom; n and m each independently represents an integer from 0 through 4; R
1
and R
2
, or R
3
and R
4
may combine with each other to form a ring, and R
1
and/or R
2
may combine with R
5
, or R
3
and/or R
4
may combine with R
6
, to form a ring; a plurality of R
5
or a plurality of R
6
may combine together to form a ring; Z
1
and Z
2
each independently represents a hydrogen atom, alkyl group or aryl group, at least one of Z
1
and Z
2
representing a hydrogen atom or an alkyl group; Q represents a trimethyne group or pentamethyne group, each of which may have a substituent group, and is able to form a cyclic structure together with a divalent organic group; and X
−
represents a counter anion.
An infrared-ray absorbing agent of the present invention for use in a photosensitive composition for image formation by irradiation with electromagnetic energy is substantially free from quinone diazide and is represented by the above-described formula (I).
Although the working mechanism of the photosensitive composition of the present invention is not clear, the mechanism is presumably as follows. The use of (a) the infrared-ray absorbing agent represented by the general formula (I) causes the photosensitive composition of the present invention to act as a dissolution inhibitor of (b) the polymeric compound soluble in an aqueous alkaline solution. The dissolution-inhibiting effect can be eliminated by heat, which is generated when the infrared-ray absorbing agent absorbs the laser light, in portions irradiated with the laser. Presumably because the infrared-ray absorbing agent of the present invention represented by the general formula (I) has a high dissolution-inhibiting property and allows absorbing and heating of the above-described laser light to be carried out efficiently, a high level of sensitivity and improved latitude in development can be achieved. Further, the infrared-ray absorbing agent of the present invention represented by the general formula (I) has an excellent solubility in a solvent.
Further, a planographic printing plate precursor of the present invention comprises a substrate and a photosensitive layer formed thereon, the photosensitive layer comprising the above-described photosensitive composition.
With the use of the above-described specific infrared-ray absorbing agent of the present invention, the photosensitive composition characterized by high sensitivity, stability of the sensitivity when developers having different densities are used, i.e. good latitude in development, and good storage stability can be provided. Further, the infrared-ray absorbing agent of the present invention has an excellent solubility in a solvent, and demonstrates a satisfactory image forming property even when the amount of the infrared-ray a
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Hamilton Cynthia
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