Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
2002-11-20
2004-03-09
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
Reexamination Certificate
active
06703185
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for on-press developing a lithographic printing plate precursor having an image-forming layer containing a hydrophobizing precursor. More specifically, the present invention relates to an on-press developing method of performing the on-press development by using fountain solution-clarifying means of removing the hydrophobizing precursor mingled into the fountain solution from the image-forming layer.
BACKGROUND OF THE INVENTION
Generally, the lithographic printing plate comprises a hydrophobic (ink-receptive) image area of repelling a fountain solution and receiving an ink in the printing process and a hydrophilic non-image area of receiving a fountain solution. Such a lithographic plate has been heretofore manufactured by subjecting a PS plate comprising a hydrophilic support having provided thereon an ink-receptive photosensitive resin layer to mask exposure through a lith. film and then dissolving and thereby removing the photosensitive resin layer in the non-image area using a developer.
In recent years, digitization technology of electronically processing, storing and outputting image information using a computer has been widespread and in turn, demands are increasing for computer-to-plate (CTP) techniques where an image is directly formed on a lithographic printing plate precursor without intervention of a lith. film by scanning light having high directivity, such as laser light, according to the digitized image information.
In conventional manufacturing methods of a printing plate using a PS plate, the step of dissolving and thereby removing the non-image area after exposure is indispensable. Furthermore, an after-processing step of water-washing the developed printing plate or treating the plate with a rinsing solution containing a surfactant or with a desensitizing solution containing gum arabic, a starch derivative or the like is also necessary. These additional wet processing steps are cumbersome and particularly in view of care on the global environment, which is recently growing as a matter of great concern, raise another problem to be solved in conventional techniques.
Accordingly, simple processing, dry processing and no processing are more keenly demanded from both the environmental aspect and the aspect of more streamlining the steps accompanying the above-described digitization. More specifically, a printing plate precursor for CTP systems, which can be used as it is for printing without passing through any wet processing after image recording, is demanded.
As one of the methods for dispensing with the processing step, a method called on-press development is known, where an exposed printing plate precursor is fixed on a cylinder of a press, and a fountain solution and/or an ink are supplied while rotating the cylinder, thereby removing the non-image area of the image-forming layer of the printing plate precursor. Namely, this is a system of fixing a printing plate precursor as it is on a press after exposure and completing the processing in the course of normal printing.
As the CTP-use lithographic printing plate precursor suitable for such on-press development, for example, Japanese Patent 2,938,397 describes a lithographic printing plate precursor where a photosensitive layer comprising a hydrophilic binder polymer having dispersed therein thermoplastic hydrophobic polymer fine particles is provided on a hydrophilic support. In this patent publication, it is stated that the on-press development can be performed by exposing the lithographic printing plate with an infrared laser to cause combination (fusion) of thermoplastic hydrophobic polymer fine particles due to heat and thereby form an image, then fixing the plate on a plate cylinder of a press, and supplying a fountain solution and/or an ink.
Also, JP-A-2001-253180 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) describes a technique where a heat-sensitive lithographic printing plate precursor comprising an aluminum support having an anodic oxide film and having on the support a hydrophilic layer which contains a hydrophilic binder and a microcapsule enclosing a hydrophobic component and converts into an image area by heat can be on-press developed.
SUMMARY OF THE INVENTION
However, these lithographic printing plate precursors have a problem in that when many plates are continuously on-press developed, printing staining occurs. The object of the present invention is to solve this problem. That is, the object of the present invention is to provide an on-press developing method where even if the on-press development is continued, printing staining does not occur.
The present invention is as follows.
1. A method for on-press developing a lithographic printing plate precursor having an image-forming layer containing a hydrophobizing precursor, the method having fountain solution-clarifying means of aggregating a hydrophobizing precursor mingled in the fountain solution and removing it by filtration.
2. A method for on-press developing a lithographic printing plate precursor having an image-forming layer containing a hydrophobizing precursor, the method having fountain solution-clarifying means of adding a coagulant (flocculant) to the fountain solution and filtering said fountain solution.
The present inventors have presumed that the above-described printing staining occurred on continuously on-press developing many plates is generated because the components in the removed image-forming layer increase in the fountain solution as the on-press development continues and these deteriorate the on-press developability or adhere to the non-image area of the printing plate. Therefore, studies have been made to clarify the fountain solution by removing, out of image-forming layer components mingled in the fountain solution, a hydrophobizing precursor which becomes ink-receptive. The hydrophobizing precursor is a fine particle having a particle size of 0.01 to 20 &mgr;m and therefore, can be hardly removed only by normal filtration. The present inventors have found that the object of the present invention can be achieved by aggregating the fine particles using the surface electric charge thereof and removing the hydrophobizing component as an agglomerate easy to filter.
DETAILED DESCRIPTION OF THE INVENTION
The practical embodiment of the present invention is described in detail below. In the following, unless otherwise indicated, “%” is “mass % (% by weight)”.
The lithographic printing plate precursor for use in the present invention is a lithographic printing plate precursor having an image-forming layer containing a hydrophobizing precursor.
The hydrophobizing precursor for use in the present invention is a fine particle capable of changing the hydrophilic image-forming layer to be hydrophobic upon application of heat and examples thereof include a thermoplastic polymer fine particle, a thermosetting polymer fine particle, a polymer fine particle having a heat-reactive functional group, and a microcapsule enclosing a hydrophobic substance, which are dispersed in the hydrophilic image-forming layer. When heat is applied, the polymer fine particles are fused or reacted with each other and combined or the capsule wall of the microcapsule is ruptured to cause bleeding of the hydrophobic substance out of the capsule, whereby the hydrophilic image-forming layer is changed to be hydrophobic. These fine particles can be used individually or in combination of two or more in the image-forming layer.
Suitable examples of the thermoplastic polymer fine particle for use in the present invention include thermoplastic polymer fine particles described in
Research Disclosure,
No. 33303 (January, 1992), JP-A-9-123387, JP-A-9-131850, JP-A-9-171249, JP-A-9-171250 and EP931647. Specific examples of the thermoplastic polymer include monomers and homopolymers of ethylene, styrene, vinyl chloride, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, vinylidene chloride, acrylonitrile and vinyl carbazole, a
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Le Hoa Van
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