Negative image-recording material

Radiation imagery chemistry: process – composition – or product th – Diazo reproduction – process – composition – or product – Composition or product which contains radiation sensitive...

Reexamination Certificate

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C430S176000, C430S270100, C430S281100, C430S283100, C430S285100, C430S288100, C430S302000

Reexamination Certificate

active

06733948

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image-recording material usable for lithographic printing plates, color proofs, photoresists and color filters. In particular, the present invention relates to a negative image-recording material which can be directly processed by scanning with an IR laser on the basis of digital signals from a computer or the like, and which is therefore usable for directly-processable recording layers for lithographic printing plates.
2. Description of the Related Art
For a system of directly processing a recording material from digital data of a computer, heretofore proposed have been <1> electrophotography, <2> exposure of photopolymerization materials to blue or green-emitting lasers, <3> silver lamination on photosensitive resin, and <4> silver diffusion transfer photography.
However, these all have some drawbacks. Specifically, the image-forming process of electrophotography <1> is troublesome, in requiring complicated steps of electric charging, exposure to light and development, and this requires a complicated, large apparatus. Photopolymerizable plates for <2> are highly sensitive to blue and green light, and are difficult to handle in light rooms. In the processes of <3> and <4> using silver salts, development is troublesome, and, in addition, the wastes contain silver.
On the other hand, the recent development of laser technology has been remarkable, and high-power, small solid lasers and semiconductor lasers for emitting IR radiation within a wavelength range of from 760 nm to 1200 nm are easily available. For a light source for directly processing a recording material from digital data of a computer or the like, these lasers are extremely useful. However, many practicable photosensitive recording materials are sensitive to visible light falling within a wavelength range of at most 760 nm, to which, therefore, these IR lasers are not applicable for recording images thereon. Accordingly, recording materials capable of being processed with IR lasers are desired.
An image-recording material capable of being processed with an IR laser is described in U.S. Pat. No. 4,708,925, which features an onium salt, a phenolic resin and a color sensitizer. This is a positive image-recording material, in which the onium salt and the phenolic resin express dissolution resistance to developers, and is not a negative image-recording material as in the present invention. On the other hand, a negative image-recording material is disclosed in U.S. Pat. No. 5,340,699, which features an IR absorber, an acid generator, a resol resin and a novolak resin. For image formation thereon, however, this material requires heat treatment after exposure to a laser. Therefore, a negative image-recording material not requiring heat treatment after exposure to light has been desired.
For example, Japanese Patent Application Publication (JP-B) No. 7-103171 discloses a recording material that includes a cyanine dye having a specific structure, an iodonium salt, and an ethylenically unsaturated double bond-having addition-polymerizable compound. This does not require heat treatment after imagewise exposure to light. However, the strength of the image area of this material is low. Therefore, this is unfavorable for lithographic printing plates, as the number of prints from a lithographic printing plate is small. In addition, storage stability of a coating liquid for an image-recording layer of the material is not good. Therefore, if the coating liquid is used in producing lithographic printing plates after having been stored for a long period of time, non-image areas of prints from the printing plate are often stained, and, in addition, the strength of image areas of the printing plates is greatly lowered and the number of prints from the printing plates is further reduced.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a negative image-recording material which can be imagewise exposed to IR radiation from an IR-emitting solid laser or semiconductor laser, which ensures direct image formation from digital data of a computer or the like, and which, when used in a lithographic printing plate, exhibits good printing durability, even if not heated for image formation thereon, and ensures a large number of good prints from the printing plate.
Having specifically noted the constituent components of negative image-recording materials and having assiduously studied them, we, the present inventors have found that the above-mentioned object can be attained when a cyanine dye having a specific partial structure is used as an IR absorber in a negative image-recording material. On the basis of this finding, we have completed the present invention.
The present invention provides a negative image-recording material for heat-mode exposure, which includes (A) an IR absorber, (B) a radical generator having an onium salt structure, (C) a radical-polymerizing compound, and (D) a reducing additive, and which is imagewise exposed to IR radiation for image formation.
Although not clear, the advantages of the negative image-recording material of the present invention may result from the addition of the reducing additive (D) to the material. Specifically, the reducing additive (D) added to the photosensitive layer of the negative image-recording material that includes (A) the IR absorber, (B) the radical generator having an onium salt structure and (C) the radical-polymerizing compound will promote decomposition of the onium salt serving as the radical generator in the layer, and will therefore promote polymerization of the radical-polymerizing compound therein to thereby increase the sensitivity of the layer. As a result, the film strength of the image area of the material processed for image formation may be increased and the printing durability of the material when used in printing plates may be thereby enhanced.
The mechanism by which the reducing additive promotes the decomposition of the onium salt-type radical generator is not clear. One presumed mechanism may be a redox-chain reaction of the reducing additive to decompose the onium salt, as in, for example,
Eur. Polym. J
., p. vol. 23, p. 737 (1987);
J. Heterocycl. Chem
., vol. 27, p. 1903 (1990);
Polymer
, vol. 32, p. 2289 (1991);
Thermchim. Acta
., vol. 197, p. 285 (1992);
J. Org. Chem
., vol. 59, p. 1381 (1994);
Macromol. Chem. Phys
., vol. 198, p. 19 (1997);
Macromol. Symp
., vol. 134, p. 177 (1998); and the like. The presumed decomposition mechanism of the reaction between an iodonium salt, one example of the onium salt-type radical generator, and a cyclic ether compound, one example of the reductive additive, is shown below.
In the above presumed mechanism, the decomposition of the onium salt serving as a radical generator is accompanied by formation of a cationic compound derived from the reductive additive. Accordingly, some hardening reaction caused by the thus-formed cation will occur in the photosensitive layer of the recording material of the present invention. This will also be effective for increasing the film strength of the image area of the processed material and for enhancing the printing durability of the processed material in printing plates.
The recording material of the present invention is for “heat-mode exposure”, and this means that the recording material is subjected to heat-mode exposure for image formation. The specifics of heat-mode exposure are described in detail below. As in Hans-Joachim Timpe, IS & Ts NIP 15:1999
International Conference on Digital Printing Technologies
, page 209, it is known that, with regard to a process comprising photo-excitation of a light-absorbing substance (e.g., dye) in a photographic material followed by chemical or physical change thereof for image formation in a layer of the material, the process of image formation comprising photo-excitation of the light-absorbing substance followed by chemical or physical change thereof includes two major modes. Specifica

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