Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
2002-07-03
2003-11-04
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
06641980
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel developer for a presensitized plate for use in making a lithographic printing plate (hereinafter possibly referred to as “PS plate”) and a method for preparing a lithographic printing plate. More specifically, the present invention relates to a developer optimum for developing a photopolymerizable presensitized plate for use in making a lithographic printing plate (hereinafter possibly referred to as “photopolymerizable PS plate”), which never shows any reduction of developing characteristics due to the elapse of a long period of time and repeated use, can ensure a good ability to develop the non-image area (non-exposed area) of the lithographic printing plate, does not damage the image area (exposed area) of the plate due to the development, ensures the formation of firm images and allows the achievement of high printing durability as well as a method for preparing a lithographic printing plate.
BACKGROUND OF THE INVENTION
The developers widely used conventionally for developing a photopolymerizable PS plate may roughly be divided into the following three groups: a) non-aqueous developers mainly comprising organic solvents; b) aqueous developers mainly comprising inorganic alkalis; and c) aqueous developers mainly comprising organic bases.
Among these, those presently used include, for instance, aqueous developers b) and c) at the request of the environmental protection.
Characteristic properties of these two developers will be detailed below. The inorganic alkaline developer b) is characterized in that it usually comprises a silicate and has a pH value in the proximity to 12 in order to hydrophilize the surface of a substrate of the printing plate after the development.
This silicate component is essential for the subsequent hydrophilization treatment or for preventing the non-image area from being contaminated by ink during printing, i.e., for the prevention of scumming.
For instance, there have been known a developer having a pH value of not less than 12 such as those disclosed in Japanese Un-Examined Patent Publication (hereunder referred to as “J.P. KOKAI”) No. Hei 8-248643 and a developer having a pH value of not more than 12 such as those disclosed in J.P. KOKAI No. Hei 11-65129. However, the former or the developer having a pH value of not less than 12 is liable to dissolve aluminum currently used as a substrate for the printing plate and, in particular, in case of a dot (small dot) occupying a small image area, it may dissolve the aluminum substrate immediately below the image area due to the so-called side etching phenomenon and this results in a phenomenon in which small dots are removed from the substrate (skipping of small dots) during printing. In other words, this developer suffers from such a problem that it may significantly deteriorate the printing durability of the resulting printing plate.
Moreover, the latter or the developer having a pH value of not more than 12 is excellent in the foregoing printing durability and an ability of preventing any contamination of printed matter, but it is liable to cause reduction of the pH value when continuing the developing treatment over a long period of time due to, for instance, the effect of carbon dioxide present in the air and the developer causes separation of a silicate during the development and this in turn leads to the occurrence of such a novel problem that it never allows any stable development.
In addition to the foregoing, J.P. KOKAI Nos. Sho 61-109052, 2000-81711 and Hei 11-65126 and West German Patent No. 1,984,605 disclose developers free of any silicate, but all of them were not only inferior in the prevention of any contamination of printed matter to those comprising silicates, but also could simultaneously satisfy the requirements for the printing durability and the prevention of any contamination of printed matter, only with great difficulty.
On the other hand, there have been known, as the organic base-containing developer c), for instance, those each comprising an organic amine such as ethanolamine and an alcoholic organic solvent such as benzyl alcohol as an auxiliary developer. In this case, however, such a developer undoubtedly has a low pH value on the order of 10 and therefore, it is not susceptible to the influence of carbon dioxide and is excellent in the processing stability. However, it also suffers from problems in that it is not only disadvantageous in the hydrophilization of the substrate, but also has an extremely high ability of penetration into the image area, that it adversely affects, in particular, small dots and that it is accompanied by the deterioration of the image-forming ability or such a phenomenon that small dots are removed from the substrate during development.
In other words, under the existing circumstances, there is not proposed any developer suitably used for developing the photopolymerizable PS plate, while taking into consideration, for instance, the image-forming ability, prevention of any scumming and printing durability as well as the processing stability.
Regarding the composition of the developer, it has been known that factors such as the presence of a silicate, the level of pH and the presence of an inorganic or organic alkali may exert a great influence on the developing phenomenon, but any combination thereof conventionally proposed has never permitted the solution of the foregoing problems at all.
Moreover, in case of the photopolymerizable PS plate, when continuing the developing treatment over a long period of time, insolubles are accumulated, agglomerated and settled down in the developer to thus form developing sludge and this may make the development treatment unstable.
Components constituting such developing sludge have not yet been clearly elucidated. As a result of the analysis thereof, however, most of them are found to be components included in a light-sensitive layer of a PS plate and insoluble in the developer.
As such developer-insoluble components, there may be listed, for instance, a variety of coloring agents added to the light-sensitive layer for distinguishing the exposed area from the non-exposed area. These coloring agents used in the photopolymerizable PS plate are so-called pigments, which are dispersed in the light-sensitive layer in the form of aggregates in which they maintain their crystalline conditions rather than in a molecularly dispersed state, for the purpose of inhibiting any desensitization due to the capture of radicals or unnecessary interaction (such as energy transfer or electron migration) with an initiator system (for instance, an initiator alone or a combination of a sensitizing dye and an initiator). However, such a pigment is essentially insoluble in a developer. Therefore, it is only temporarily dispersed in the developer in the initial stage of the developing step for removing the non-exposed area, but when continuing the developing treatment over a long period of time, it is accumulated, agglomerated and settled down in the developer to thus form developing sludge.
On the other hand, a variety of photopolymerization initiators (radical generators) have been incorporated into the photopolymerizable PS plate for coping with the recently progressed laser light sources and among them, titanocene type initiators have been known as initiators, which are excellent in stability and sensitivity and which are light-sensitive in the wavelength ranges of laser light sources. However, this titanocene type initiator is an organic metal and thus insoluble in the developer like the foregoing pigments as coloring agents. Therefore, it is temporarily dispersed in the developer, but when continuing the developing treatment over a long period of time, it is also accumulated, agglomerated and settled down in the developer to thus form developing sludge.
Regarding the processing stability, it is quite critical to solve not only the foregoing problem of the silicate-separation associated with the reduction of pH, but also the problem of the developing sludge-formation
Kunita Kazuto
Nagase Hiroyuki
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Le Hoa Van
LandOfFree
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