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
2000-07-26
2003-04-01
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
C430S950000
Reexamination Certificate
active
06541180
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a photosensitive lithographic printing plate having thereon a microscopic embossment which is termed “mat”.
BACKGROUND
JP-A-58-137469/1983 (the term “JP-A” as used herein means an unexamined published Japanese patent application) deals with a process for providing mats on a recording material. It discloses the distribution (distribution number), the height and the size (diameter) of mats to be formed. JP-A-10-133383/1998 touches on a photosensitive lithographic printing plate provided with microscopic patterns. It describes the average diameter, the average height and the distribution (distribution number) of the macroscopic patterns to be formed.
SUMMARY OF THE DISCLOSURE
However, various problems have been encountered in the course of investigations toward the present invention. Namely, pressure is applied to the mat-attached face of the photosensitive lithographic printing plate provided with mats resulting from the aforementioned prior art after production but before use (e.g., during storage, packaging and delivery etc.) so that the height of the mats will be varied to cause a problem that the effect of shortening vacuum adhesion time, which is the primary function of the mats, will be prominently deteriorated.
Accordingly, an object of the present invention is to provide a photosensitive lithographic printing plate in which prominent deterioration of the vacuum-adhesion-time-shortening effect which is a properly expected function of the mats will be prevented even in case that the matted face of a photosensitive lithographic printing plate having the mats thereon is subjected to pressure after production but before use of the photosensitive lithographic printing plate.
In order to solve the above problem, it would be one idea to attach a large amount of large-diameter mats for overcoming the applied pressure by virtue of their sufficient sum of areas. However, it was difficult to put this idea into practice because the mats of the large-diameter tend to deteriorate the reproducibility of small dots of small dot images upon exposure.
Therefore, the present inventors tried to control the mean volume of the mats and form many of the mats as largely as possible within a range that deterioration of small dot image reproducibility will be avoided. Consequently, it was found that a photosensitive lithographic printing plate provided with a specific ratio of the mats each having particular range of volume to the total mats can ensure good reproducibility of small dots of the small dot images, endure the pressure affecting after production but before use, and maintain the function of the mats. Thus the present invention has been completed on the basis of the above findings.
Namely, according to one aspect of the present invention, the above object can be attained by a photosensitive lithographic printing plate having mats attached thereon wherein a number of the mats, each having volume of not less than 4,500 &mgr;m
3
and less than 18,000 &mgr;m
3
, exceeds 20% relative to a total number of the attached mats. The photosensitive lithographic printing plate of the present invention will be embodied as follows.
It is preferred to control the number of the mats each having volume of not less than 18,000 &mgr;m
3
to be less than 10% relative to the number of all the attached mats. The mats can be formed through atomizing a liquid containing resin dissolved therein with a rotary atomizer. All of the number ranges disclosed in this specification must include the both end values and also all of arbitrary midway values involved therebetween.
PREFERRED EMBODIMENTS OF THE INVENTION
In the photosensitive lithographic printing plate of the present invention, the number of the mats each having volume of not less than 4,500 &mgr;m
3
but less than 18,000 &mgr;m
3
exceeds 20% relative to the total number of the mats attached thereon. Preferably, they are controlled to be not less than 30%, and more preferably, not less than 40%. The mats each having volume of not less than 18,000 &mgr;m
3
are preferably controlled to be less than 10% (more preferably, less than 8%) relative to the number of all the attached mats.
A photosensitive lithographic printing plate includes at least a substrate and a photosensitive layer, and optionally, other layers. Materials of the substrate and the photosensitive layer may be those conventionally used for the usual photosensitive lithographic printing plate. The mats may be provided on places where the vacuum-adhesion-time-shortening effect of their essential function can be taken. Usually, they are provided at least on the surface of the photosensitive layer.
The mats are preferably distributed not less than 25/mm
2
(more preferably, not less than 30/mm
2
, still more preferably, not less than 40/mm
2
). The mats may be made of a material which has been conventionally used for the usual photosensitive lithographic printing plate such as various types of resin and etc.
[The Maximum Volume Value of the Mat]
A film image can be transferred to a photosensitive lithographic printing plate by bringing the film into close contact with the printing plate during exposure. When a thick air gap exists between the film and the photosensitive lithographic printing plate during this procedure, what is called “burn blur” phenomenon will occur, and accordingly, the image cannot be transferred faithfully. In order to avoid this, it is usually practiced that the film and the photosensitive lithographic printing plate are placed in a depressurized place to evacuate the air existed between them. A mat layer is necessary to be formed on the surface of the photosensitive lithographic printing plate for evacuating this air easily.
The mat layer has a function of maintaining a suitable gap between the film and the photosensitive lithographic printing plate which is appropriate for making the air existed between them easily evacuated. However, if the mat is too high, the following phenomenon will occur, i.e., the above gap will be enlarged too wide to make it impossible to transfer the film image to the printing plate with good fidelity.
Further, a large-diameter mat makes it difficult to transfer the image onto a mat-deposited spot. This phenomenon will occur as a result of excessively forming the mats with large volumes. Accordingly, it is important to inhibit the mat from exceeding certain volume. On this account, it is preferable to make the volume of one mat less than 18,000 &mgr;m
3
.
[The Minimum Volume Value of the Mat]
A photosensitive lithographic printing plate can be prepared by forming a photosensitive layer, a mat layer and optionally other layer(s) on a continuous web-formed substrate. In this process, contact with rollers made of various materials, winding up, stacking after cutting, and other operations are performed. The prepared photosensitive lithographic printing plate reaches the user's hand by way of preservation, packaging, delivery and other steps. In the periods of these steps, i.e., after production but before use, forces such as pressure and the like applied, for example, on the surface of the printing plate deform the shape of the mats formed on the surface. To cope with these forces, forming a large number of mats as large as possible is an effective way for decreasing the deformation of the mats. Accordingly, it is preferable to make the volume of one mat not less than 4,500 &mgr;m
3
.
[Production of the Photosensitive Lithographic Printing Plate]
The photosensitive lithographic printing plate of the present invention can be prepared through forming mats, which include those of specific volumes as defined in the present invention which are in particular ratios as determined in the present invention, on a photosensitive lithographic printing plate or a precursor thereof. The finished or unfinished photosensitive lithographic printing plate can be prepared through forming, for example, at least a photosensitive layer on a substrate before forming mats. Materials of
Fuji Photo Film Co. , Ltd.
Hamilton Cynthia
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