Lithographic printing plate precursor

Details Lithographic printing plate precursor Lithographic printing plate precursor

2000-08-22

2001-05-29

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

C430S275100, C430S525000, C430S166000, C430S160000, C430S944000, C430S945000, C101S457000, C101S458000, C101S459000

Reexamination Certificate

active

06238839

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a lithographic printing plate precursor, in particular, relates to a lithographic printing plate precursor capable of plate-making by scanning exposure based on digital signals, having high sensitivity, high press life and high strength, and capable of providing printed matters with no staining.
BACKGROUND OF THE INVENTION
A lithographic printing plate precursor capable of forming an image by a heat source such as a heat-sensitive head, etc., and a lithographic printing plate precursor capable of forming an image by heat which is converted from irradiated light, are known in the lithographic printing technique. In particular, the latter lithographic printing plate precursor is promising as the lithographic printing plate precursor for computer to plate (CTP) technique capable of directly making a printing plate without necessitating a film by scanning highly directional active radiant rays such as laser rays in accordance with digitized image data.
As the support of a lithographic printing plate precursor capable of forming an image by the work of heat (called heat-sensitive type image recording), metals such as aluminum and polyethylene terephthalate (PET) are widely used.
When metals are used as the support of a lithographic printing plate precursor, since metals do not absorb water and a solvent, moreover, are excellent in strength, even if water and a solvent is used after that in a developing step, dimensional accuracy of the support does not deteriorate and the recorded image is correctly reproduced. Further, since metals are fundamentally excellent in strength, the obtained lithographic printing plate precursors have excellent press life in many cases.
However, since metals have a high heat-conductivity, even if it is tried to form an image by irradiation of light for image-recording, e.g., laser rays, and converting the light to heat, the heat is liable to be dissipated to a metal support and a satisfactory image is difficult to be formed. That is, the sensitivity of the lithographic printing plate precursor becomes very low, and staining due to ink is generated on the non-image area of a printed matter. Therefore, sufficient energy becomes necessary to form an image, for instance, by raising light output and delaying writing time, but if light output is increased, the manufacturing cost of a writing unit increases, as a result, the advantage of the manufacturers of the unit is lowered, and if writing time is delayed, plate-making takes longer time, as a result, the advantage of the printing press is lowered.
On the other hand, when PET is used as the support of a lithographic printing plate precursor, it has been known that since PET is comparatively low in heat conductivity as compared with metals, PET is very advantageous in the point of the minimum energy necessary for writing an image, i.e., sensitivity.
However, since PET absorbs water, although as small as 0.4% or so, when water and a solvent are used at printing, a support absorbs water and the dimension of a printing plate extends in some cases. Accordingly, in particular in four color printing, images are not be correctly reproduced (image disorder occurs) and in many cases unmarketable. There is another drawback that PET is lower in strength as compared with metals, hence the press life is inferior.
For the purpose of aiming at solving the above problem, a technique of providing a heat-insulating layer on the metal surface of the support of a lithographic printing plate precursor, and a hydrophilic hardening layer thereon is disclosed in WO 96/507727. However, the compatibility of sensitivity with press life could not be solved even by this technique.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a lithographic printing plate precursor having high sensitivity and capable of obtaining printed matters of clear images having no staining in heat-sensitive type image-recording.
As a result of earnest investigation, the present inventors have found that an image can be formed by newly providing a heat-insulating layer of a specific material having low heat conductivity between metal layers and an image-recording layer as the uppermost layer on a lithographic printing plate precursor, and irradiating the printing plate precursor with light of low output from the uppermost layer side. That is, the lithographic printing plate precursor according to the present invention comprises a metal support having provided thereon a heat-insulating layer, a metal layer having a hydrophilic surface, and a lipophilic layer which is abraded (i.e., fused and removed) by heating or whose solubility to alkali is transformed by heating, in this order from the support. By this constitution of the lithographic printing plate precursor of the present invention, the heat given in the lipophilic layer for forming an image is difficult to be dissipated to the outside of the lipophilic layer due to the insulating effect of the heat-insulating layer, as a result, the heat can be used effectively for forming an image and sensitivity is improved. Further, the recorded image can be correctly reproduced due to high dimensional stability of the metal support even if water or a solvent is used in a developing step, and press life can be improved due to the high strength of the metal support as well. In addition, as a metal layer having a hydrophilic surface is provided on the lithographic printing plate precursor of the present invention, surface roughness, surface shape, and adsorption surface area can be freely controlled by conventionally well-known surface treating techniques such as mechanical abrasion, anodic oxidation and electrochemical etching, thus the above object of the present invention has been accomplished without selecting specific material of the image-recording layer.


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Tabata et al, Pub-No. JP411291654A, English abstract of JP 11-291654 A, Japanese patent abstracts, JPO, 1999, one page obtained from online West database in USPTO.

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