Planographic printing plate precursor

Details Planographic printing plate precursor Planographic printing plate precursor

2002-04-09

2004-05-04

Huff, Mark F. (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, C430S281100, C101S453000

Reexamination Certificate

active

06730456

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel planographic printing plate precursor. More specifically, the present invention relates to a planographic printing plate precursor on which an image can be scan-exposed using a laser and based on digital signals, and which is excellent in sensitivity and blemish-resistant.
2. Description of the Related Art
Planographic printing uses a printing plate which includes a oleophilic region to receive ink and an ink-repellent (i.e., hydrophilic) region to receive moistening water. Photosensitive planographic printing plate precursors (“PS plates”) are now generally used for planographic printing.
A PS plate, which comprises a support made of aluminum, for example, and a photosensitive layer provided on the support has become practical and is widely used. This PS plate is used for printing by: image exposing and developing the PS plate to remove the photosensitive layer at non-image portions, and printing using the hydrophilic property of the support surface and the oleophilic property of the photosensitive layer. Accordingly, the support surface of the PS plate must have a good hydrophilic property to prevent blemishes in non-image portions.
Conventionally, an anodized aluminum support is used as a hydrophilic support or a hydrophilic layer for a planographic printing plate; this support is generally silicate treated to further increase the hydrophilic property thereof. The hydrophilic support and hydrophilic layer using this aluminum support are now being intensively studied. For example, a support undercoated with polyvinyl sulfonic acid is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 7-1853, and use of a polymer which has a sulfonic acid group as an undercoat of a photosensitive layer is disclosed in JP-A No. 59-101651. Use of a polyvinyl benzonic acid as an undercoat has also been proposed.
Instead of metals such as aluminum, flexible supports such as polyethylene terephthalate (PET) and cellulose acetate, may be used as the support. In this case, many techniques have been proposed to form a hydrophilic layer. Examples thereof include the following: a swollen hydrophilic layer, which comprises a hydrophilic polymer and a hydrophobic polymer, disclosed in JP-A No. 8-292558; a PET support which has a microporous hydrophilic cross-linked silicate surface, disclosed in EP 0709228; and a hydrophilic layer which contains a hydrophilic polymer and is cured by using hydrolyzed tetraalkylorthosilicate, disclosed in JP-A Nos. 8-272087 and 8-507727.
These hydrophilic layers provide printing plates that exhibit a hydrophilic property, which is improved over the prior art, and produce unblemished printing matter when printing is initiated. However, these hydrophilic layers have problems such as the hydrophilic layer peeling off from the support after repeated printing, and the hydrophilic property deteriorating over time. Accordingly, there is a demand for a planographic printing plate precursor, which is able to print many sheets with no blemishes and whose hydrophilic layer does not peel off from the support causing the hydrophilic property of the support surface to deteriorate, under even more severe printing conditions. Further, from the viewpoint of utility, there is a demand for an even more improved hydrophilic property.
Moreover, a printing plate for use in a computer-to-plate system, for which recent developments have been remarkable, has been widely studied. To promote even more streamlining of processes and to solve problems involving disposal of waste liquids, a planographic printing plate precursor, which can be mounted on a printing machine for printing directly after exposure, i.e., without undergoing development, has been studied and various methods using the same have been proposed.
One of these methods is known as an on-machine developing, which is carried out in the following manner. An exposed printing plate precursor is mounted on a cylinder of a printing machine. Moistening water and ink are applied to the printing plate precursor while the cylinder is rotated to remove the non-image portion of the printing plate precursor. In this method, since the printing plate precursor is exposed and then printed on a printing machine, the processing is completed during printing.
To be suitable for use in the on-machine developing, the planographic printing plate must have a photosensitive layer that is soluble in moistening water or an ink solvent, and must be able to be handled in daylight so that it can be developed in a printing machine in a bright room.
WO 94/23954 discloses a printing plate which needs no developing. This printing plate includes a support and a cross-linking hydrophilic layer provided on the support. The cross-linking hydrophilic layer has a heat-fusing substance encapsulated in micro-capsules. In this printing plate, due to heat generated in an area exposed by laser, the micro-capsules break and oleophilic substances are eluted from within, whereby the surface of the hydrophilic layer is made hydrophobic. Although this printing plate precursor requires no developing, it has a problem in that blemishes increase in the non-image portion after repeated printing.
SUMMARY OF THE INVENTION
The present invention is intended to overcome the above-described conventional drawbacks and to achieve the following objects. An object of the present invention is to provide a positive- or negative-type planographic printing plate precursor which has an improved blemish-resistance and with which much unblemished printed matter can be printed even under severe printing conditions, by disposing thereon a hydrophilic layer having superior persistence and high hydrophilic property.
Another object of the present invention is to provide a planographic printing plate precursor which can be made, after an image is formed thereon, by scan-exposure based on digital signals, and either a simple developing operation using water, or by remaining mounted to a printing machine and print without being specially developed.
The present inventors, as a result of intensive studies, have found that the conventional problems can be solved by introducing a hydrophilic graft chain into the cross-linking hydrophilic layer and forming a negative- or positive-type image forming layer on the cross-linking hydrophilic layer, and accomplished the present invention.
A planographic printing plate precursor of the present invention comprises a support and a cross-linking hydrophilic layer disposed thereon, which cross-linking hydrophilic layer has a cross-linking structure and includes a hydrophilic high molecular compound having a hydrophilic graft chain. The planographic printing plate precursor of the present invention is characterized in that the cross-linking hydrophilic layer is produced by reacting a hydrophilic high molecular compound having, on the backbone polymer thereof, a group which is able to react with a cross-linking agent, with the cross-linking agent.
It is preferable to provide an image forming layer on the cross-linking hydrophilic layer. A preferable image forming layer includes a high molecular compound having a functional group whose polarity changes between hydrophilic and hydrophobic due to acid, heat or exposure to radiation, and forms an image by using the change between the hydrophobic property and hydrophilic property of the surface thereof. The cross-linking hydrophilic layer preferably further includes a compound which is able to form a hydrophobic area on the surface of the cross-linking hydrophilic layer when exposed to heat or radiation.
Regarding the effects of the present invention, the present inventors have the following assumptions. The cross-linked hydrophilic layer has a cross-linking structure formed by a hydrophilic high molecular compound having, on the backbone thereof, a group which is able to react with a cross-linking agent, which high molecular compound being made to react with a cross-linking agent. The tight cross-linking structure imparts, to the

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