Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
2002-07-05
2004-11-02
Gilliam, Barbara (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
C430S281100, C430S309000, C430S434000, C430S435000, C430S494000
Reexamination Certificate
active
06811952
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a photopolymerization process involving the exposure of a photosensitive lithographic printing plate containing a specific dye to laser beam having a wavelength of not greater than 450 nm and a plate-making process involving the development of the photosensitive lithographic printing plate with a specific developer. More particularly, the present invention relates to a process for the production of a lithographic printing plate which gives a high productivity, provides a very contrast image with little printing stain due to optical fog and enables remarkable reduction of development tailings.
BACKGROUND OF THE INVENTION
As a lithographic printing plate there has heretofore been widely used a PS plate comprising an ink-receptive photosensitive resin layer provided on a water-receptive support. An ordinary plate-making process for producing such a PS plate comprises subjecting a photosensitive material to mask exposure (areal exposure) via a lithographic film, and then dissolving the non-image area away to obtain a desired printing plate.
In recent years, a digitization technique involving electronic processing, storage and outputting of image data using computer has been widely spread. Various new image outputting systems corresponding to the digitization technique have been put to practical use. As a result, a computer-to-plate (CTP) has been desired which comprises scanning light beam having a high directionality such as laser beam according to digitized image data to directly produce a printing plate without using lithographic film. It has been an important technical assignment to obtain a printing plate precursor adapted for this CTP technique.
With regard to conventional CTP system involving the use of long wavelength visible light source such as Ar laser (488 nm) and FD-YAG laser (532 nm) as a light source, it has been required to write data at a higher rate for the purpose of enhancing the productivity at the plate-making step. However, this demand has never been met because the output of the light source is not sufficiently high and the sensitivity of the photosensitive material is not sufficiently high.
Examples of such a photosensitive lithographic printing plate include a photosensitive lithographic printing plate comprising an initiation system formed by titanocene and coumarine in combination as disclosed in Japanese Patent (Application) Laid-Open No. 1997-268185, Japanese Patent Laid-Open No. 1994-192309 and Japanese Patent Laid-Open No. 1998-204085. Such a photosensitive material needs to be handled in a very dark room from the stand point of photosensitive properties. Such a photosensitive lithographic printing plate has been desired to have improvements in this respect, too.
In recent years, on the other hand, a semiconductor laser capable of continuously oscillating in a wavelength range of from 350 nm to 450 nm (violet LD) has been put to practical use with an InGaN-based material. A scanning exposure system comprising such a short wavelength light source is advantageous in that such a semiconductor laser can be produced at a reduced cost from the structural standpoint of view, making it possible to build an economical system.
This system also allows the use of a photosensitive material sensitive to short wavelength which can be processed under a brighter safelight as compared with the conventional system involving the use of ED-YAG or Ar laser. When an inner drum type exposing machine, which is most ordinary, is used, the image drawing rate depends on the rotary speed of the inner mirror from the standpoint of the structure of the exposing machine. On the other hand, when the violet LD is used, the image drawing rate can be raised as compared with the conventional system involving the use of Ar laser (488 nm) or FD-YAG laser (532 nm) because the rotary speed of the inner mirror can be raised.
Under these circumstances, it has been keenly desired in the art to provide a lithographic printing plate precursor adapted for CTP system comprising a semiconductor laser having a wavelength as relatively short as from 350 nm to 450 nm.
An initiation system formed by a specific dye and a titanocene compound in combination has been heretofore known as an initiation system having a relatively high sensitivity. Japanese Patent Laid-Open No. 1997-80750 discloses a combination of a styryl-based dye and titanocene. Japanese Patent Laid-Open No. 1998-101719 discloses a combination of a dye having a 5-membered heterocyclic acidic nucleus and titanocene. It is certain that these initiation systems have a high sensitivity. However, the sensitivity of these initiation systems is not sufficiently high. Further, when laser beam having a wavelength of not greater than 450 nm is used, these initiation system cannot exhibit a practically sufficient sensitivity. Thus, these initiation systems are not adapted for short wavelength light source. There are no suggestions on adaptability to safelight.
These high sensitivity printing plates are disadvantageous in that when irradiated with a slight amount of lightbeam coming through the system during handling, storage or exposure the polymerizable components; in the photosensitive layer undergo polymerization to cure, causing so-called optical fog, i.e., print stain on the non-image area caused by the presence of material left unremoved even after development. In particular, when an inner drum type laser exposing machine is used to effect exposure, such a high sensitivity printing plate can easily undergo optical fog by reflected light (flare light). For example, when a negative-working plate, if used as a photosensitive material, is exposed to light through an image such as total solid image on one surface thereof, it undergoes weak fog sort of underdevelopment if the other surface is a non-image area. If the other surface (about 140° to 220° if the other surface is 180° with respect to light source) of the negative-working plate is halftone, dots are expanded, making it difficult to reproduce a minute image or highlighted area to disadvantage. It has thus been desired to overcome these difficulties.
Further, when these printing plates are subjected to development for a long period of time, unnecessary matters are accumulated, agglomerated and precipitated in the developer to produce development tailings that labilize development.
The provision of a photopolymerizable composition having a high sensitivity to light beam having a wavelength of from 350 nm to 450 nm from the aforementioned short wavelength laser is an important technique which has been demanded more and more in a wide industrial field other than CTP, e.g., laser imaging such as optical imaging, holography and color hard copy, production of electronic material such as photoresist and photosetting resin material such as ink, coating compound and adhesive.
SUMMARY OF THE INVENTION
An object of the present invention to provide a process for the photopolymerization of a high sensitivity photosensitive lithographic printing plate which enables the inhibition of optical fog and the reduction of development tailings resulting in the enhancement of development stability and a plate-making process involving the development of the photosensitive lithographic printing plate thus processed with a specific developer.
The foregoing object of the present invention will become apparent from the following detailed description and examples.
The present inventors made extensive studies of solution to these problems. As a result, it was found that the aforementioned object of the present invention is accomplished by the following photopolymerization process and plate-making process.
(1) A photopolymerization process which comprises exposing a photosensitive lithographic printing plate containing at least one of sensitizing dyes represented by the following general formula (I) to laser beam having a wavelength of not greater than 450 nm:
wherein T represents OR, SR, N(R)
2
or SO
2
R and at least one T is present in the ortho or para position
Burns Doane Swecker & Mathis L.L.P.
Gilliam Barbara
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