Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
2001-07-11
2004-02-03
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
Reexamination Certificate
active
06686126
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel developing solution for a photosensitive lithographic printing plate, a plate-making method of a lithographic printing plate, and a photosensitive lithographic printing plate. More specifically, the present invention relates to a developing solution optimal for a photopolymerizable lithographic printing plate which does not cause the reduction of developing properties with the lapse of time and repeated use, has good developing properties to a non-image domain (an unexposed domain) of a lithographic printing plate, prevents staining due to printing, gives less damage due to development to an image domain (an exposed domain), forms a stable image, does not cause printing troubles during printing such as blinding, and realizing high printing durability. The present invention further relates to a plate-making method of a lithographic printing plate and a photosensitive lithographic printing plate.
BACKGROUND OF THE INVENTION
The developing solutions for photopolymerizable lithographic printing plates conventionally widely used are divided broadly into the following a) to c), i.e., a) a non-aqueous developing solution mainly comprising an organic solvent, b) an aqueous developing solution mainly comprising an inorganic alkali, and c) an aqueous developing solution mainly comprising an organic base.
Of the above three developing solutions, developing solutions b) and c) are used these days from the environmental demands.
Describing these two developing solutions in detail, a silicate is contained in the inorganic alkali developing solution b) near pH 12 for carrying out hydrophilizing treatment on a support generally after development.
A silicate is an essential component for performing hydrophilizing treatment, i.e., for preventing staining of a non-image domain at printing.
For example, the developing solution having pH of 12 or higher as disclosed in JP-A-8-248643 (the term “JP-A ”as used herein means an “unexamined published Japanese patent application”) and the developing solution having pH of 12 or lower as disclosed in JP-A-11-65129 are known as developing solution b). However, the former developing solution having pH of 12 or higher is liable to dissolve the aluminum used generally as a support, in particular when an image domain comprises minute dots, the aluminum support just under the image domain is dissolved by a side-etching phenomenon to cause the separation of minute dots from the support (dot-skipping) at printing, which extremely deteriorates a press life (i.e., a printing durability).
Further, a developing solution having pH of 12 or lower is preferred in the point of the above-described press life and the prevention of printing staining, but as a result of continuing development processing for a long period of time, pH is liable to lower due to the effect of, e.g., the carbon dioxide gas in the air, and the silicate precipitates in a developing solution at this time and development processing becomes unstable.
As an example of a developing solution, developing solutions not containing a silicate are disclosed in JP-A-61-109052, West German Patent 1,984,605, JP-A-2000-81711 and JP-A-11-65126, but all of these developing solutions are not only more disadvantageous than those containing a silicate in the point of the printing staining but the press life is also deteriorated.
On the other hand, as the organic base developing solution c), those containing an organic amine such as an ethanolamine and an alcohol-based organic solvent such as a benzyl alcohol as an auxiliary developing agent are known. The pH value of these developing solutions is certainly low, such as about 10, and so they are difficult to be affected by carbon dioxide gas and processing stability is good, but they are not only disadvantageous in the point of hydrophilization to a support, but also their osmotic power to an image domain is too high, thus there arises a problem that minute dots are separated from the support at development, i.e., an image-forming property is deteriorated.
That is, with respect to a photopolymerizable lithographic printing plate, a suitable developing solution is not found yet from the points of image-forming property, resistance to printing staining, printing durability and processing stability.
With respect to the composition of a developing solution, it is known that whether silicate is contained or not, whether pH is high or low, and the difference between an inorganic alkali and an organic alkali greatly influence a development phenomenon but conventional combinations cannot solve the above problems.
Further, when development processing of a photopolymerizable lithographic printing plate is continued for a long period of time, insoluble substance is accumulated, agglomerated, precipitated and becomes development scum, which becomes a main cause of making development processing unstable.
The components of such development scum have not been clearly known until now but it was found from the analysis that much of the scum was insoluble components of a developing solution contained in a photosensitive layer.
As the insoluble components, e.g., various kinds of colorants which are added to a photosensitive layer for the purpose of discriminating an exposed domain from an unexposed domain can be exemplified. In the case of photopolymerizable lithographic printing plates, for the purpose of avoiding desensitization due to radical supplement and desensitization due to unnecessary interaction (energy transfer and electron transfer) with an initiator system (an initiator alone, or combination of an initiator with a sensitizing dye), a pigment is used as the colorant which is not molecularly dispersed in a photosensitive layer but is dispersed as an aggregate with maintaining a crystalline state. However, these pigment are substantially insoluble in a developing solution, therefore they are at first temporarily dispersed in a developing solution in a development step for removing an unexposed area but when development processing is continued for a long period of time, they are accumulated, agglomerated, precipitated and come to development scum.
On the other hand, various photopolymerization initiators (radical generating agents) are used in a photopolymerizable lithographic printing plate to cope with laser light sources which are making progress in recent years. Of these initiators, titanocene-based initiators are known as the initiators which have photosensitivity in the wavelength of laser light source and excellent in stability and sensitivity. However, titanocene-based initiators are organic metals and insoluble in a developing solution similar to the above pigments, and temporarily dispersed in a developing solution but when development processing is continued for a long period of time, they are accumulated, agglomerated, precipitated and also come to development scum.
With respect to the processing stability, it is very important to solve not only the problem of the precipitation of silicate with the reduction of pH but also the problem of development scum.
That is, as the developing solution for a photopolymerizable lithographic printing plate, a developing solution which satisfies the above-described image-forming property, the compatibility of printing staining resistance with printing durability, and processing stability is desired.
Further, since conventionally broadly used negative type photosensitive lithographic printing plates are comprising a hydrophilized aluminum plate having provided thereon a diazo resin, the use of an organic solvent in a developing solution cannot be helped, hence there are fears of the disposal of developing waste solution and the influence to the environment.
Further, an orthoquinonediazide compound is used in combination with a novolak resin in a photosensitive layer of a positive type photosensitive lithographic printing plate, and an alkaline aqueous solution of silicate which can dissolve a novolak resin is used in a developing solution. However, the pH value capable
Kondo Shun-ichi
Kunita Kazuto
Nagase Hiroyuki
Tsuchiya Mitsumasa
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