Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1998-08-20
2001-02-27
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S281100
Reexamination Certificate
active
06194122
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a waterless planographic printing plate raw plate which makes possible printing without the use of dampening water and, in particular, it relates to a directly imageable waterless planographic printing plate precursor (raw plate) which enables the plate making process to be carried out directly with irradiation from a laser beam, hereinafter called “laser light”.
PRIOR TECHNIQUES
Direct plate making, that is to say, directly producing an offset printing plate from an original without using a plate making film is beginning to become popular not only in short run printing fields but also more generally in the offset printing and gravure printing fields, on account of its special features such as its simplicity and lack of requirement for skill, its speediness in that the printing plate is obtained in a short time, and the possibility of selection from diverse systems according to quality and cost.
In particular, very recently, as a result of rapid advances in output systems such as prepress systems, image setters and laser printers, etc, new types of various planographic printing materials have been developed.
Classifying these planographic printing plates by the plate making method employed, such methods include the method of irradiating with laser light, the method of inscribing with a thermal head, the method of locally applying voltage with a pin electrode, and the method of forming an ink repellent layer or ink receptive layer with an ink jet. Of these, the method employing laser light is more outstanding than the other systems in terms of resolution and the speed of the plate making process, and there are many varieties thereof.
There are two types of planographic printing plate employing laser light, the photon mode type which depends on photo-reaction and the heat mode type in which light-to-heat conversion takes place and a thermal reaction is brought about. With the heat mode type there is the advantage that handling is possible in a light room and, furthermore, due to rapid advances in the output of the semiconductor lasers which serve as the light source, recently a fresh look has been taken at the usefulness thereof.
For example, in U.S. Pat. No. 5,379,698 and U.S. Pat. No. 5,632,204, there are described directly imageable waterless planographic printing plates which employ a thin metal film as a heat sensitive layer, and the heat sensitive layer is melted away by laser light irradiation, but there is the problem that the laser light passes through the thin metal film itself, so that the printing plate sensitivity is poor. Hence, in order to raise the laser light absorption factor, a reflection layer must be provided, which further increases the number of application stages and is costly. Moreover, in order to form a thin metal layer, there needs to be used a dry process technique in a vacuum such as the PVD (physical vapour deposition) method or CVD (chemical vapour deposition) method, which results in further expense.
Again, in U.S. Pat. No. 5,339,737, U.S. Pat. No. 5,353,705 and U.S. Pat. No. 5,551,341, there are described directly imageable waterless planographic printing plate precursor which use laser light as the light source.
The heat sensitive layer in these printing plate precursors uses, for example, carbon black as a laser light absorbing compound, and employs nitrocellulose as a thermally-decomposing compound, on the surface of which there is applied a silicone layer. The carbon black in the heat sensitive layer absorbs the laser light, converting it into heat energy and the heat sensitive layer is broken down by this heat. Moreover, finally, this region is eliminated by developing, as a result of which the silicone rubber layer, which does not accept ink, separates away at the same time, thereby forming the image regions which accept ink.
The nitrocellulose employed as the thermally-decomposing substance is an explosive material, and while it is therefore excellent in terms of plate material sensitivity and development properties, care is needed in its handling. Furthermore, since it is an autoxidizing substance, due to the combustion accompanying the laser light irradiation, harmful nitrogen oxide (NOx) is generated, which is undesirable from the point of view of environmental hygiene. Moreover, due to the magnitude of this combustibility, breakdown tends to extend beyond the laser-irradiated region of the heat sensitive layer, so that the boundary between the image and non-image areas is not distinct and there is the problem that the form of the halftone dots following development is impaired.
Again, when the heat sensitive layer is melted away or broken down, the grooves formed by laser irradiation into which ink is to be accepted, hereinafter called “image ditch cells” are deepened, so that the ink mileage is impaired and the printed matter has a feeling of coarseness. Furthermore, with offset printing, either the oven length is extended to evaporate off the ink solvent or it is necessary to drop the printing speed. Hence, if the image ditch cells are deep, this has numerous disadvantages in the printing process. On the other hand, if the heat sensitive layer remains behind in the image areas, then the image ditch cells become shallower, so the ink acceptability and ink mileage are improved and high quality printed materials are obtained. However, in order for the heat sensitive layer to remain behind, it has been necessary hitherto to suppress the heat induced breakdown of the heat sensitive layer, with the result that development of the silicon rubber layer has tended to be impossible, and it has been difficult to obtain a stable high sensitivity plate material.
In JP-A-09-319074, there is described a directly imageable waterless planographic printing plate precursor in which the heat sensitive layer contains a sulphonylhydrazide derivative, which is a foaming agent. With this type of plate material where the silicon rubber layer is separated by foaming of the heat sensitive layer, there is the disadvantage that the heat sensitive layer is embrittled and it is difficult not to remove also the residual heat sensitive layer.
The present invention seeks to overcome these problems of the prior art by providing a directly imageable waterless planographic printing plate precursor of high sensitivity where the heat sensitive layer is removed without employing nitrocellulose in the heat sensitive layer. Furthermore, the invention seeks to provide a residual heat sensitive layer type directly imageable waterless planographic printing plate precursor, where a stable plate material of high sensitivity is obtained by adjusting the heat sensitive layer composition, the laser light irradiation conditions and/or the developing conditions.
DISCLOSURE OF THE INVENTION
In order to solve the abovementioned problems, the present invention provides a printing element comprising a substrate on which is disposed at least a heat sensitive layer, which heat sensitive layer contains a light-to-heat converting material (A) and a compound containing an N—N group, hereinafter referred to as a “hydrazine compound” (B).
Preferably, the printing element is a directly imageable waterless planographic printing plate precursor formed by laminating, in turn, on a substrate, at least a heat sensitive layer and a silicone rubber layer.
More preferably, it is a directly imageable waterless planographic printing plate precursor where the hydrazine compound contains hydroxyl groups, or where it is an acid hydrazine obtained by reaction with a copolymer of (meth)acrylic acid and (meth)acrylate ester, or where it is an ethylenically unsaturated resin containing carboxylic acid groups having hydrazo bonds within the molecule.
Moreover, the invention also provides a directly imageable waterless planographic printing plate precursor which is characterized in that the laser irradiated regions form the image areas and some heat sensitive layer remains behind in the image areas.
PREFERRED EMBODIMENTS OF THE INVENTION
In this specification, “dire
Fujimaru Koichi
Goto Kazuki
Ichikawa Michihiko
Ikeda Norimasa
Kawamura Ken
Baxter Janet
Gilmore Barbara
Morrison & Foerster / LLP
Toray Industries Inc.
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