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
2001-03-20
2004-01-20
Hamilton, Cynthia (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
C430S138000, C430S296000, C430S967000, C430S271100, C430S302000, C430S964000, C101S457000, C101S450100, C101S451000, C101S453000, C101S467000
Reexamination Certificate
active
06680161
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a lithographic printing plate precursor, more specifically a lithographic printing plate precursor capable of plate-making by scanning exposure based on digital signals and developable with water, or loadable on a printing machine without development and printable.
BACKGROUND OF THE INVENTION
A lithographic printing plate generally comprises a lipophilic image area which receives an ink in a printing process and a hydrophilic non-image area which receives fountain solution. As such a lithographic printing plate precursor, a PS plate comprising a hydrophilic support having provided thereon a lipophilic photosensitive resin layer (an image-recording layer) has so far been widely used. A plate-making method of a lithographic printing plate precursor generally comprises the steps of performing mask exposure through a lith film and then dissolving and removing a non-image area with a developing solution to thereby obtain a desired printing plate.
Digitized techniques of electronically processing, accumulating and outputting image data using a computer have prevailed in recent years, and various image output systems corresponding to these digitized techniques have been put to practical use. With such a tendency, a computer-to-plate technique of directly making a printing plate without using a lith film by scanning exposing digitized image data with highly directional active radiant rays such as laser beams is earnestly desired, and it has become an important technical problem to obtain a printing plate precursor adaptable to this purpose.
On the other hand, the plate-making process of a PS plate hitherto in use is accompanied by the processes of dissolution and removal of a non-image area after exposure, and another problem of the conventional technique which has been desired to be improved is the point that such an additional wet process is indispensable in the plate-making process of a PS plate. In particular in recent years, global environmental protection has been a matter of concern in the industry at large. There are hence increased demands for simplification of processing, switching over to a dry process, and no processing from the environmental aspect and rationalization of the process with digitization.
As one plate-making method which meets the above demands, there is a development on machine system of using a photosensitive layer capable of removing the non-image area of a printing plate precursor in usual printing process, and effecting development after exposure on a printing machine to thereby obtain a final printing plate. However, when a PS plate so far been used is applied to the development on machine system, a printing plate precursor must be stored under a completely light-shielded state and/or under a constant temperature condition after exposure, e.g., during the period of time until the printing plate is loaded on a printing machine, because the photosensitive layer is not fixed.
With respect to the above problems, various types of development which are different from photo-reactions utilized in conventional photosensitive materials for low to middle power density exposure, specifically developments utilizing a chemical change, or a structural change such as a change of phase or form, can be performed in high power density exposure systems using high output solid state lasers, e.g., a semiconductor laser and a YAG laser. A recording system making use of such high power density exposure is called heat mode recording.
Further, conventionally used heat mode positive type printing plate precursors are accompanied by a big drawback such as residual films. That is, the improvement has been required in the point that the change in solubility by exposure is smaller in the vicinity of the support in an ink-receptive layer than in the vicinity of the surface of an ink-receptive layer. Since in a heat mode positive type printing plate precursor, the heat generation by heat mode exposure is based on the light absorption of a light absorbing agent in an ink-receptive layer, the generated quantity of heat is large on the surface of an ink-receptive layer and small in the vicinity of a support. Therefore, the degree of hydrophilization becomes relatively small in the vicinity of a support. As a result, a hydrophobic film is often not removed completely and remains as it is on an exposed area which is substantially to provide a hydrophilic surface. Such a residual film on a non-image area causes smearing on prints. In particular, when a metal support having high heat conductivity such as aluminum which has a preferred printing aptitude is used, since the temperature increase in the vicinity of a support is further inhibited due to heat diffusion, the problem of a residual film is conspicuous. For sufficiently hydrophilizing the vicinity of a support, an extremely large quantity of exposure energy is required or post treatment such as heating after exposure is necessary.
As a method for improving the maleficent influence by heat diffusion to a support at exposure in the foregoing heat mode printing plate, a method to reduce heat diffusion by providing an aluminum oxide layer having a certain thickness or more on the surface of a support is disclosed, e.g., in JP-A-52-37104 and JP-A-52-118417 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”). This method is certainly effective but insufficient, and residual films on a heat mode positive printing plate cannot be got rid of up to the present.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to solve the above-described conventional problems, and to provide a lithographic printing plate precursor developable with water or an aqueous solution, loadable on a printing machine without development after imaging and printable, which is improved in sensitivity and press life, and capable of providing clear printed matters having no residual colors and stains.
Another object of the present invention is to provide a lithographic printing plate precursor capable of plate-making directly from digital data by recording with a solid state laser or a semiconductor laser which radiates infrared rays.
As a result of eager investigation of the present inventors for achieving the above objects, the problems can be solved by the following lithographic printing plate precursor, thus the present invention has been completed.
That is, the present invention is as follows.
(1) A lithographic printing plate precursor which comprises a support having a hydrophilic surface having provided thereon in order of a layer containing a latex (layer A) and an ink-receptive layer (layer B) whose solubility at least either in water or in an aqueous solution is converted by heat, wherein at least one layer of either layer A or layer B contains a light/heat converting agent.
(2) The lithographic printing plate precursor as described in the above item (1), wherein the latex is crosslinked organic resin particles.
(2) The lithographic printing plate precursor as described in the above item (1), wherein the coating amount of the layer containing a latex (layer A) is from 0.05 to 2.0 g/m
2
and the absorbance of layer A at the wavelength of laser beams for imaging is from 0.3 to 2.
“Water or an aqueous solution” in the above lithographic printing plate precursor according to the present invention will be described. When an ink-receptive layer in the lithographic printing plate precursor of the present invention contains the later-described polarity converting high molecular weight compound (irrespective of a positive type or a negative type), “water” may be pure water or water containing other components so long as it can dissolve a non-image area, or may be a fountain solution charged with ink at printing.
When the foregoing ink-receptive layer contains a resin soluble in an alkali aqueous solution (no matter whether it is positive type or negative type), “an aqueous solution” includes conventionally well-known alkali developing solutions besides
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Hamilton Cynthia
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