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
2001-05-15
2004-10-19
Gilliam, Barbara (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, C101S454000, C101S456000
Reexamination Certificate
active
06806031
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a support for a lithographic printing plate and a presensitized plate, particularly to a positive working presensitized plate having a photosensitive layer that can become alkali-soluble by photothermal conversion with laser beams and a support for a lithographic printing plate used for the positive working presensitized plate.
2. Description of the Related Arts
Lithographic printing is a printing method using the property that water and oil are immiscible. On the printing surface of the lithographic printing plate used for the method, areas (hereunder referred to as non-image areas) that accept water and repel oil ink and areas (hereunder referred to as image areas) that repel water and accept oil ink are formed.
The support for a lithographic printing plate, which is used so as to carry the non-image areas of the surface, requires various properties such as water wettability and water receptivity, and further good adhesion to a photosensitive layer provided thereon, which are incompatible.
When the water wettability of the support is too low, ink attaches on the non-image areas during printing and a stain is generated on a blanket cylinder, then a so-called scum develops on a print. When the water receptivity of the support is too low, a significant amount of fountain solution is needed to prevent clogging on shadow areas during printing. Therefore, a so-called water range becomes narrow.
Recent years, accompanied with development of image formation technology, it has come to be possible to make a printing plate directly by scanning narrow focused laser beams on the printing plate and by forming a manuscript of letters, images and the like directly on the plate without using a film manuscript.
For example, in the case of a so-called thermal positive working type presensitized plate in which a positive image is formed by making a photosensitive layer alkali-soluble by photothermal conversion in the photo sensitive layer, heat generated from photothermal conversion materials in the photosensitive layer by applying laser beams induces image forming reaction.
Here, when a deep pit generated by graining treatment exists on the surface of support treated for graining, thickness of the portion of the photosensitive layer becomes thicker, and image forming reaction on the bottom of the pit becomes inadequate. As a result, local residual layers (hereunder referred to also as dot residual layers) are generated on the non-image areas, causing a problem of scum developing on the non-image areas during printing.
Moreover, the amount of the fountain solution is decided based on a water gloss on the plate in the event of controlling fine adjustment of water scale during printing operation. Accordingly, in the case where the pit is shallow after graining treatment, a gloss of the non-image areas increases, thus resulting in difficulty in fine adjustment of the amount of the fountain solution during printing.
In order to solve the problems described above, specifying of a surface shape of the support has been proposed before.
For example, a rough surface shape having a pit, in which the slope of a straight line by the first order regression analysis of a pit diameter and the maximum depth in a direction perpendicular to the diameter is 0.300 or less under 1.5 &mgr;m or less of the pit diameter, has been proposed in JP-A-9-86068 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”). Here, it is described that the rough surface shape prevents scum developing on the non-image areas during printing and provides excellent ballpoint pen characteristics. However, though the method shown in the above gazette could solve the problem with dot residual layers, the method was not sufficient for fine control of water volume and a water range during printing.
The brush graining process in which at least two kinds of brushes are used for graining to prevent scum and clogging on the shadow areas has been proposed in JP-A-6-135175. However, though the method shown in the foregoing gazette was sufficient for fine control of water volume and water width during printing, the method could not solve the problem with the dot residual layers sufficiently.
Moreover, a support comprising a double structure of small and large pits, in which an average opening diameter of a larger pit with uniformity is 3 m or more and 6 m or less, an average opening diameter of a small pit is 0.2 &mgr;m or more and 0.8 &mgr;m or less, and a ratio of depth to the opening diameter of the small pit is not more than 0.2 &mgr;m, has been proposed in JP-A-11-184074. Here, it is described that the support could improve dot gain with high definition, resistance to stain developing on a blanket, scum resistance under small water volume and printability on YUPO paper. Although the method described in the foregoing gazette could provide better fine control of water volume, further improvements in restraining the dot residual layers are desired.
In the presensitized plate using an aluminum support which has been treated for graining and having an anodized layer formed thereon, since thermal conductivity of the support is much higher than that of the photosensitive layer, heat generated around an interface of the photosensitive layer and the support moves into the support before image forming reaction (alkali-soluble reaction) occurs sufficiently. As a result, solubility of the photosensitive layer to plate developer becomes inadequate around the interface of the photosensitive layer and the support, and the residual layers are easily generated on the areas which must be non-image areas originally. Therefore, high sensitive developer must be used, but by using it, non-image portions are easily generated on the area to be the image area. That is, slight variation of sensitivity of the developer indicated by electronic conductivity during developing easily causes development failure, and the intrinsic problem remains, in which development latitude is much narrower than the conventional PS plate system that has been used before. In order to solve the problem, various methods for improving development performance of the photosensitive layer around the interface of the photosensitive layer and the support in the presensitized plate of a thermal positive working type have been studied, but the result has not reached a satisfactory level.
When the photosensitive layer that can become alkali-soluble by heating sustains damage by some causes, the area to be an image area also becomes easily soluble in developer. That is, the printing plate sustains damage easily in practical use. For this reason, scratch-like non-image portions is generated by tiny contact to the plate surface such as bumping in handling the printing plate, tiny abrasion in interleaving sheets and contact to the plate surface by fingers. Accordingly, handling of the printing plate is very difficult under the present circumstance.
In particular, in the presensitized plate of a thermal positive working type, when the alkali-soluble level of the photosensitive layer by exposure of laser is not that high, sometimes a slightly soluble layer is formed as the top layer of the photosensitive layer to obtain clear discrimination of an image on development. In this case, since other parts than the slightly soluble layer are soluble in alkali, the foregoing narrowness of development latitude and the generating of the scratch-like non-image portion are especially problematic.
It is also indispensable for a recording layer of such a thermal type to contain infrared absorbent having a photothermal conversion function. Since solubility of the absorbent is low due to high-molecular weight of the absorbent and further the absorbent adsorbed in micro openings on the anodized layer of the support can not be removed easily, there has been the problem that the residual layers are easily generated on a development process with alkali developer.
In order to solve this problem, various un
Endo Tadashi
Hotta Hisashi
Masuda Yoshitaka
Nishino Atsuo
Teraoka Katsuyuki
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