Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
2002-05-16
2004-03-16
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
C430S272100, C430S273100, C430S280100, C430S281100, C430S348000, C430S413000, C430S434000, C430S494000, C430S944000, C430S945000, C101S463100
Reexamination Certificate
active
06706463
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for making a lithographic printing plate, which comprises the steps of imagewise exposing, to a laser beam, a presensitized plate useful for making a lithographic printing plate (hereinafter, referred to as a PS plate), which permits the heat mode-recording with a laser beam, and then developing the imagewise exposed plate within a short period of time after the imagewise exposure.
The lithographic printing plate in general comprises a lipophilic image area, which receives ink during the printing process, and a hydrophilic non-image area, which receives dampening water. As a plate useful for making such a lithographic printing plate, there has widely been used a PS plate, which comprises a hydrophilic substrate provided thereon with a lipophilic light-sensitive resin layer. The plate-making process for such a PS plate currently comprises exposing the PS plate to light rays through images such as an image-carrying lithfilm and then removing the non-image area through dissolution thereof with a developer to thus give a desired printing plate.
The plate-making process for the conventional PS plates requires the removal of non-image areas through dissolution after the imagewise exposure thereof to light rays. Therefore, it is one of important problems, to be solved, associated with the conventional technique to eliminate or simplify such an additional wet process. In addition, it has recently been a matter of primary concern in the entire industrial fields to dispose or deal with waste liquor exhausted through such wet treatments of imagewise exposed lithographic printing plate from the viewpoint of the environmental protection and it has increasingly and strongly been required to improve the conventional plate-making process in this respect.
As a simple plate-making process proposed in response to such a demand, there has been known a method, which makes use of such a PS plate provided thereon with an image-recording layer whose non-image areas can be removed during the usual printing process and the method comprises the steps of exposing the PS plate to light rays and developing the same on a printing machine to thus give a final printing plate. Such a plate-making process has been referred to as the on-machine developing method. More specifically, this method comprises, for instance, the use of an image-recording layer or non-image areas soluble in the dampening water or a solvent for ink, or the step of mechanically removing the non-image areas through the contact thereof with the impression cylinder or the blanket cylinder in a printing machine. In this respect, however, the imagewise exposed layer is not yet fixed even after the exposure of a PS plate and therefore, the on-machine developing method suffers from an important problem in that it is necessary to adopt a troublesome method for the protection of the imagewise exposed area till the imagewise exposed printing plate is fitted to the printing machine. For instance, the imagewise exposed plate should be stored under completely light-shielded conditions or constant temperature conditions.
On the other hand, there has been another recent tendency in this field. More specifically, there has widely been used digitizing techniques in which image information is electronically processed, accumulated and outputted using a computer and a variety of new image-outputting techniques have been practically used in response to the development of such digitizing techniques. In response to this, the computer-to-plate technique has attracted special interest recently, which comprises the steps of incorporation of digitized image information into highly coherent radiant rays such as laser beams and scanning-exposure of a PS plate to the radiant rays to thus directly prepare a printing plate without using any lithfilm. For this reason, it has recently been an important technical subject to develop a PS plate suitably used for this purpose. Under such circumstances, there has increasingly and still more strongly been desired for the development of a simplified plate-making technique, a dry plate-making method or a treatment free technique, from the viewpoint of both the environmental protection discussed above and the applicability to the digitalization.
Among solid lasers, those having a high power or output such as semiconductor lasers and YAG lasers have been commercially available at a low price and therefore, a plate-making process using these lasers as image-recording means has, in particular, been considered to be a promising technique as the method for preparing printing plates, which makes use of scanning light-exposing step capable of being easily incorporated into the digitized technique. In the conventional plate-making process, an image is recorded by imagewise exposing a light-sensitive plate to light at a low to intermediate illuminance to induce a photochemical reaction and to thus cause imagewise changes of physical properties, while in the method using high power density-exposure with a high output laser, a light-exposed area is convergently exposed to a large quantity of light energy within an instantaneous exposure time to cause a chemical change and/or a thermal change such as a phase change or a change in shape or structure through the effective conversion of the optical energy into thermal energy. In other words, the latter method makes use of the foregoing changes in order to record images on the PS plate or image information is inputted through the optical energy of, for instance, a laser beam, but the image is recorded through a reaction induced by the thermal energy originated from the optical energy. In general, a recording method, which makes use of heat generation due to such high power density light-exposure has been called “heat mode recording” and the conversion of optical energy into heat energy is referred to as “light-heat conversion”.
An important advantage of the plate-making method, which makes use of such a heat mode recording means, is that the PS plate used is not sensitive to light rays having an illuminance of the usual level such as the room illumination and that the fixation of images recorded through light-exposure at a high illuminance is not essential. In other words, if a heat mode recordable light-sensitive material is used in recording images, it is safe against the room illumination prior to the light-exposure thereof and any fixation of images is not essential even after the imagewise exposure of the material. For instance, if using an image-recording layer capable of being solubilized or insolubilized through the heat mode light-exposure and conducting the plate-making process for imagewise removing the exposed image-recording layer to give a printing plate according to the on-machine developing method, a novel printing system can be realized, in which the development (removal of non-image areas) is not adversely affected or the images thus formed are not likewise adversely affected even when the light-sensitive material is exposed to, for instance, the room illumination for a certain time after the imagewise exposure thereof. Therefore, it would be expected that the use of the heat mode recording technique permits the preparation of, in particular, a PS plate desirably used in the on-machine developing method.
As a preferred example of such a method for preparing a lithographic printing plate based on such heat mode recording technique, there has been proposed one comprising the steps of forming a hydrophilic or lipophobic layer on a heat mode recording layer, subjecting the resulting layers to imagewise heat mode exposure, subjecting the recorded layer to abrasion and optionally removing the hydrophilic layer or the lipophobic layer on the exposed area by the wet process.
Examples of such PS plates include those each comprising a heat-sensitive layer containing, for instance, a laser beam-absorbing agent such as carbon black and a self-oxidizable binder such as nitrocellulose, provided thereon with a hydrophilic o
Hirano Tsumoru
Inno Toshifumi
Baxter Janet
Gilliam Barbara
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