Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
2000-01-10
2002-06-25
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
C430S191000, C430S192000, C430S193000, C430S905000, C430S926000, C430S944000
Reexamination Certificate
active
06410207
ABSTRACT:
The present invention relates to a novel positive photosensitive composition sensitive to a light ray in a wavelength region of from 650 to 1300 nm. More particularly, it relates to a positive photosensitive composition suitable for direct plate making by means of a semiconductor laser or a YAG laser, a positive photosensitive lithographic printing plate employing the composition and a method for making a positive photosensitive lithographic printing plate.
Along with the progress in the image treating technology by computers, an attention has been drawn to a photosensitive or heat sensitive direct plate making system wherein a resist image is formed directly from digital image information by a laser beam or a thermal head without using a silver salt masking film. Especially, it has been strongly desired to realize a high resolution laser photosensitive direct plate making system employing a high power semiconductor laser or YAG laser, from the viewpoint of downsizing, the environmental light during the plate making operation and plate making costs.
On the other hand, as image-forming methods wherein laser photosensitivity or heat sensitivity is utilized, there have heretofore been known a method of forming a color image by means of a sublimable transfer dye and a method of preparing a lithographic printing plate. Known as the latter is, for example., a method of preparing a lithographic printing plate by means of the curing reaction of a diazo compound (e.g. JP-A-52-151024, JP-B-2-51732, JP-A-50-15603, JP-B-3-34051, JP-B-61-21831, JP-B-60-12939 and U.S. Pat. No. 3,664,737), or a method of preparing a lithographic printing plate by means of the decomposition reaction of nitrocellulose (e.g. JP-A-50-102403 and JP-A-50-102401).
In recent years, a technique in which a chemical amplification type photoresist is combined with a long wavelength light ray absorbing dye, has been proposed. For example, JP-A-6-43633 discloses a photosensitive material wherein a certain specific squarilium dye is combined with a photo-acid-generator and a binder.
Further, as a technique of this type, a technique for preparing a lithographic printing plate by exposing a photosensitive layer containing an infrared ray absorbing dye latent Bronsted acid, a resol resin and a novolak resin, in an image pattern by e.g. a semiconductor laser has been proposed (JP-A-7-20629). Further, the same technique wherein a s-triazine compound is used instead of the above latent Bronsted acid, has also been proposed (JP-A-7-271029).
However, these conventional techniques were not necessarily adequate in their performance from a practical viewpoint. As a more serious problem, in the case of such a chemical amplification type photosensitive plate, it was usually essential to have a heat treatment step after exposure, and due to variation of heat treatment conditions or the like, the stability in the quality of the image thereby obtainable was not necessarily adequate, and a technique containing no such a step has been desired. In the above-mentioned JP-A-7-20629 and JP-A-7-271029, a method for obtaining a positive image without requiring the above-mentioned post heat treatment, is proposed, but no specific Examples are given, and no specific method or no fact of obtaining such a positive image is disclosed. Further, in such a technique, the photosensitive material is sensitive also to ultraviolet light, and it is necessary to carry out the operation under yellow light containing no ultraviolet light, such being problematic from the viewpoint of the operation efficiency.
Further, in U.S. Pat. No. 5,491,046, a plate-making method particularly an exposure method, using such a composition is disclosed, but no Example is given for a positive image.
Further, JP-A-60-175046 discloses a radiation sensitive composition comprising an alkali-soluble phenol resin and a radiation sensitive onium salt, which is photo-dissolvable. It is disclosed that in the composition, photo-decomposable decomposition of the onium salt induces the resin to regain the solubility, to satisfy the basic requirement for a photo-dissolvable system, and that the onium salt can be sensitized by an electromagnetic spectrum of a wide range ranging from ultraviolet light to visible light or even to infrared light.
Such an image is formed essentially by a difference in the solubility in a developer as between an exposed portion and a non-exposed portion. For such a difference to be caused, it is common that one of the components in the composition undergoes a chemical change, and to induce such a chemical change, an additive such as a photo-acid-generator, a radical initiator, a crosslinking agent or a sensitizer, is frequently required, whereby there has been a problem that a system will be complicated.
The present invention has been made in view of the above-described various problems.
Namely, it is an object of the present invention to provide a positive photosensitive composition and a positive photosensitive lithographic printing plate, which are simple in their construction, which are suitable for direct recording by e.g. a semiconductor laser or a YAG laser and which have high sensitivity and excellent storage stability.
Another object of the present invention is to provide a novel positive photosensitive material and a positive photosensitive lithographic printing plate, which are highly sensitive to an infrared ray and which require no post exposure heat treatment.
A further object of the present invention is to provide a photosensitive material and a positive photosensitive lithographic printing plate, which do not require an operation under yellow light and whereby the operation can be carried out under usual white light containing ultraviolet light.
A still further object of the present invention is to provide a positive photosensitive lithographic printing plate which is excellent in a burning property as a lithographic printing plate.
Still another object of the present invention is to provide a plate-making method, whereby a positive photosensitive lithographic printing plate can be exposed at high sensitivity.
Such objects of the present invention can be accomplished by the following constructions of the present invention:
A positive photosensitive composition showing a difference in solubility in an alkali developer as between an exposed portion and a non-exposed portion, which comprises, as components inducing the difference in solubility,
(a) a photo-thermal conversion material, and
(b) a high molecular compound, of which the solubility in an alkali developer is changeable mainly by a change other than a chemical change.
A positive photosensitive composition comprising a photo-thermal conversion material and an alkali-soluble resin and having a characteristic represented by B<A where A is the solubility, in an alkali developer, at an exposed portion of the composition, and B is the alkali solubility after heating of the exposed portion.
A positive photosensitive lithographic printing plate having such a positive photosensitive composition formed on a support.
A method for making a positive photosensitive lithographic printing plate, which comprises a step of scanning and exposing such a positive photosensitive lithographic printing plate by means of a light ray belonging to a wavelength region of from 650 to 1100 nm and having a light intensity sufficient to let the high molecular compound form an image.
Now, the present invention will be described in detail with reference to the preferred embodiments.
Heretofore, as a positive photosensitive composition, a system has been known which comprises an alkali-soluble resin and an o-quinone diazide group-containing compound as a photosensitivity-imparting component. It is believed that with this system, upon irradiation of ultraviolet light which can be absorbed by the o-quinone diazide group-containing compound, the diazo moiety will decompose to finally form carboxylic acid, whereby the alkali-solubility of the resin increases, so that only the exposed portion will dissolve in an alkali developer
Murata Akihisa
Nagasaka Hideki
Chu John S.
Mitsubishi Chemical Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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