Printing – Planographic – Lithographic printing plates
Reexamination Certificate
2001-07-10
2004-01-06
Funk, Stephen R. (Department: 2854)
Printing
Planographic
Lithographic printing plates
C101S456000, C101S462000
Reexamination Certificate
active
06672210
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a lithographic printing plate precursor having a novel hydrophilic layer. More particularly, the present invention relates to a lithographic printing plate precursor having an excellent sensitivity and stain resistance which can be in either positive-working or negative-working form. Even more particularly, the present invention relates to a lithographic printing plate precursor which can be subjected to imagewise scanning exposure to laser beam according to digital signal so that it requires no development and thus can be directly processed for plate making.
BACKGROUND OF THE INVENTION
Lithography is a printing method using a surface having a lipophilic area which can receive an ink and a hydrophilic or lipophobic area which cannot receive an ink. At present, a photosensitive lithographic printing plate precursor (PS plate) has been widely used as a printing plate material.
As PS plate, a printing plate comprising a photosensitive layer provided on a support such as aluminum plate has been put in practical use and widely used. In operation, such a PS plate is subjected to imagewise exposure and development to remove the photosensitive layer from the non-image area. The hydrophilicity of the surface of the substrate and the lipophilicity of the photosensitive layer on the image area are utilized to effect printing.
However, this PS plate is disadvantageous in that when the hydrophilicity of the surface of the substrate is insufficient, the non-image area is stained.
A so-called direct plate making process involving direct making of offset printing plate from an original without using a plate-making film has begun to be used in the art of ordinary offset printing by making the best of its simplicity requiring no skill, reduced labor and quick operation enabling the formation of printing plate in a short period of time. In particular, with the recent rapid progress of output systems such as pre-press system, image setter and laser printer, a new type of various lithographic printing materials have been developed.
These techniques may be applied to a so-called on-press platemaking, i.e., platemaking process which comprises mounting the printing plate material on the plate cylinder of the printing machine where it is imagewise irradiated with laser beam to make a printing plate. However, these techniques are not suitable for direct printing plate requiring development with an alkaline developer.
As a printing plate requiring no development there has been well-known an unprocessed printing plate comprising a crosslinked hydrophilic layer provided on a substrate and a microcapsulated heat-fusible material contained in the hydrophilic layer as disclosed in WO94/23954. In this printing plate, heat generated by irradiation with laser beam causes the microcapsules to be destroyed, causing the lipophilic material to be eluted and hence hydrophobicizing the surface of the hydrophilic layer. The use of this printing plate precursor makes it possible to obtain the desired printing plate requiring no development. However, this printing plate precursor is disadvantageous in that as printing proceeds, the occurrence of stain gradually increases.
As the hydrophilic substrate or hydrophilic layer to be incorporated in lithographic printing plates there has heretofore been used an anodized aluminum substrate or a substrate or hydrophilic layer obtained by treating the anodized aluminum substrate with an undercoating agent such as silicate, polyvinylphosphonic acid (JP-A-7-1853 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”)) and polyvinylbenzoic acid to enhance the hydrophilicity thereof. Extensive studies of hydrophilic substrate or hydrophilic layer comprising such an aluminum support have been made. JP-A-59-101651 discloses a technique involving the use of a polymer having a sulfonic acid group as a subbing layer for photosensitive layer.
On the other hand, referring to hydrophilic layer comprising a flexible support such as PET (polyethylene terephthalate) and cellulose acetate instead of metal support such as aluminum substrate, there are well-known techniques such as swelling hydrophilic layer comprising a hydrophilic polymer and a hydrophobic polymer disclosed in JP-A-8-292558, PET support having a microporous hydrophilic crosslinked silicate surface disclosed in EP0709228 and hydrophilic layer comprising a hydrophilic polymer which is hardened by a hydrolyzed tetraalkylorthosilicate disclosed in JP-A-8-272087 and JP-A-8-507727.
These hydrophilic layers can give a lithographic printing plate which provides printed matters free of stain at the beginning of printing. From the practical standpoint of view, however, a lithographic printing plate precursor has been desired which exhibits a higher hydrophilicity on the hydrophilic layer and thus can prevent the hydrophilic layer from being peeled off the support to provide printed matters of stain even under severe printing conditions.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a lithographic printing plate precursor which can provide printed matters free of stain.
It is another object of the present invention to provide a lithographic printing plate precursor which can be subjected to scanning exposure to laser beam for image formation in a short period of time so that the plate making can be achieved by a simple water development process or the plate making can be achieved by directly mounting the printing plate on the printing machine without development processing, whereby a good press life (i.e., a good printing durability) can be given and printed matters free of stain can thus be obtained even under severe printing conditions.
It is a further object of the present invention to provide a positive-working or negative-working lithographic printing plate precursor which exhibits a high hydrophilicity on the hydrophilic layer and hence an improved printing stain resistance and thus can give printed matters free of stain under severe printing conditions.
These and other objects of the present invention will become apparent from the following detailed description and examples.
The present inventors made extensive studies of accomplishment of the foregoing objects. As a result, it was found that the foregoing problems can be further solved by incorporating a hydrophilic graft chain in the crosslinked hydrophilic layer and forming an image-forming layer on the crosslinked hydrophilic layer. The present invention has thus been achieved.
The present invention lies in the following aspects:
(1) A lithographic printing plate precursor comprising a crosslinked hydrophilic layer having a crosslinked structure and containing a hydrophilic polymer compound having a hydrophilic graft chain, provided on a support.
(2) The lithographic printing plate precursor according to the above item (1), wherein the crosslinked hydrophilic layer contains a compound which renders the surface of the crosslinked hydrophilic layer hydrophobic when acted upon by heat or when irradiated.
(3) A lithographic printing plate precursor comprising a crosslinked hydrophilic layer having a crosslinked structure and containing a hydrophilic polymer compound having a hydrophilic graft chain and an image-forming layer, provided on a support in this order.
(4) The lithographic printing plate precursor according to the above item (3), wherein the image-forming layer contains a polymer compound having a functional group which changes in its hydrophilicity or hydrophobicity when acted upon by heat or acid, or when irradiated.
(5) The lithographic printing plate precursor according to the above item (1), wherein said crosslinked hydrophilic layer is formed by crosslinking a graft copolymerization polymer using a hydrophilic macromonomer.
The present invention is characterized by an arrangement that the polymer chain in the crosslinked structure in the crosslinked hydrophilic layer has a hydrophilic group incorporated therein as a graft chain. Accor
Kawamura Koichi
Takahashi Miki
Burns Doane , Swecker, Mathis LLP
Funk Stephen R.
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