Heat-sensitive imaging material for making lithographic...

Details Heat-sensitive imaging material for making lithographic... Heat-sensitive imaging material for making lithographic...

2001-09-18

2003-11-18

Schilling, Richard L. (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Making printing plates

C430S204000, C430S273100, C430S275100, C430S276100, C430S278100, C430S330000, C430S616000, C430S964000

Reissue Patent

active

RE038322

ABSTRACT:

This application claims benefit of Provisional Application Ser. No. 60/079,871 filed Mar. 30, 1998.
FIELD OF THE INVENTION
The present invention relates to a heat-sensitive imaging element for making lithographic printing plates. More specifically the invention relates to a heat-sensitive imaging element which requires no processing.
BACKGROUND OF THE INVENTION
Lithographic printing is the process of printing from specifically prepared surfaces, some areas of which are capable of accepting ink, whereas other areas will not accept ink.
In the art of photolithography, a photographic material is made imagewise receptive to oily or greasy ink in the photo-exposed (negative working) or in the non-exposed areas (positive working) on a ink-repelling background.
In the production of common lithographic plates, also called surface litho plates or planographic printing plates, a support that has affinity to water or obtains such affinity by chemical treatment is coated with a thin layer of a photosensitive composition. Coatings for that purpose include light-sensitive polymer layers containing diazo compounds, dichromate-sensitized hydrophilic colloids and a large variety of synthetic photopolymers. Particularly diazo-sensitized systems are widely used.
Upon imagewise exposure of such light-sensitive layer the exposed image areas become insoluble and the unexposed areas remain soluble. The plate is then developed with a suitable liquid to remove the diazonium salt or diazo resin in the unexposed areas.
On the other hand, methods are known for making printing plates involving the use of imaging elements that are heat-sensitive rather than photosensitive. A particular disadvantage of photosensitive imaging elements such as described above for making a printing plate is that they have to be shielded from the light. Furthermore they have a problem of stability of sensitivity in view of the storage time and they show a lower resolution. The trend towards heat-sensitive printing plate precursors is clearly seen on the market.
EP-A-444 786, JP-63-208036, and JP-63-274592 disclose photopolymer resists that are sensitized to the near IR. So far, none has proved commercially viable and all require wet development to wash off the unexposed regions. EP-A-514 145 describes a laser addressed plate in which heat generated by the laser exposure causes particles in the plate coating to melt and coalescence and hence change their solubility characteristics. Once again, wet development is required.
EP-A-652 483 discloses a lithographic printing plate requiring no dissolution processing which comprises a substrate bearing a heat-sensitive coating, which coating becomes relatively more hydrophilic under the action of hat. Said system yields a positive working printing plate. EP-A-609 941 describes a heat-mode recording material comprising on a substrate a metallic layer and a thin hydrophobic layer which becomes hydrophilic upon exposure. However the lithographic performance of the obtained printing plate is poor.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a heat-sensitive imaging element for preparing lithographic printing plates requiring no dissolution processing and having a high lithographic performance (ink acceptance, scratch resistance, durability)
SUMMARY OF THE INVENTION
According to the present invention there is provided a heat-sensitive imaging element for making lithographic printing plates comprising on a lithographic base, having a hydrophilic surface, a metallic layer or metal oxide layer and on top thereof an
oleophobic

oleophilic
polymer layer having a thickness of less than 5 &mgr;m characterised in that said polymer layer comprises a polymer containing phenolic groups.
DETAILED DESCRIPTION OF THE INVENTION
It has been found that according to the present invention, using an imaging element as described above, lithographic printing plates requiring no processing and having an excellent lithographic performance can be obtained.
Metallic layers or metal oxide layers suitable for use in accordance with the invention comprise metals or metal oxides converting the actinic radiation to heat so that the
oleophobicity

oleophilicity
of the
oleophobic

oleophilic
top-layer is destroyed. The thickness of the metallic layer or metal oxide layer is preferably from 0.01 &mgr;m to 2 &mgr;m, and most preferably from 0.05 &mgr;m to 1.5 &mgr;m. Specific examples of metal layers or metal oxide layers are aluminum, titanium oxide, bismuth and silver of which the three latter are preferred.
A silver layer for use in this invention as the metallic layer can be made according to the principles of the silver complex diffusion transfer reversal process, hereinafter called DTR-process, having been described, e.g. in U.S. Pat. No. 2,352,014 and in the book “Photographic Silver Halide Diffusion Processes” by André Rott and Edith Weyde—The Focal Press—London and New York, (1972).
In the DTR-process non-developed silver halide of an information-wise exposed photographic silver halide emulsion layer material is transformed with a so-called silver halide solvent into soluble silver complex compounds which are allowed to diffuse into an image-receiving element and are reduced therein with a developing agent, generally in the presence of physical development nuclei, to form a silver image having reversed image density values (‘DTR-image’) with respect to the black silver image obtained in the exposed areas of the photographic material.
In another method for providing a metal layer on the lithographic base having a hydrophilic surface a silver halide emulsion disposed on a lithographic base having a hydrophilic surface is strongly exposed to actinic radiation and then developed, or otherwise processed to maximum blackness. The black opaque emulsion is converted to a reflective recording material by heating at least to 270° C. in an oxygen containing environment until the emulsion coating assumes a shiny reflective appearance. Such method is disclosed in U.S. Pat. No. 4,314,260.
According to an alternative method for providing a metal layer on the lithographic base the metal is provided using vapour or vacuum deposition.
According to another embodiment of the invention the metallic layer can be a bismuth layer that can be provided by vacuum deposition.
A drawback of the method of preparation of a thin bismuth recording layer by vacuum deposition is the fact that this is a complicated, cumbersome and expensive process.
Therefore, in EP-A-97201282 the vacuum deposition is replaced by coating from an aqueous medium. According to this disclosure a thin metal layer is formed by the following steps:
(1) preparing an aqueous medium containing ions of a metal,
(2) reducing said metal ions by a reducing agent thus forming metal particles,
(3) coating said aqueous medium containing said metal particles on a transparent support.
As a metal oxide layer preferably a titanium oxide layer is used. This layer can be applied to the substrate by vacuum deposition, electron-beam evaporation or sputtering.
The
oleophobic

oleophilic
layer provided on top of the metallic layer or metal oxide layer comprises a polymer containing phenolic groups. Preferred polymers containing phenolic groups are phenolic resins (e.g. novolac) or hydroxyphenyl substituted polymers (e.g. polyhydroxystyrenes). The
oleophobic

oleophilic
layer has a thickness of less than 5 &mgr;m. As a consequence a highly sensitive heat-sensitive imaging element is obtained. The use of a polymer containing phenolic groups furthermore improves the lithographic performance (ink acceptance, scratch resistance, durability) of the lithographic printing plates obtained according to the present invention.
According to one embodiment of the present invention, the lithographic base having a hydrophilic surface can be an anodised aluminum. A particularly preferred lithographic base having a hydrophilic surface is an electrochemically grained and anodised aluminum support. Most preferably said aluminum support is grained in nitric acid, yiel

Affiliated with

Also associated with

Rating

Heat-sensitive imaging material for making lithographic... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Heat-sensitive imaging material for making lithographic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Heat-sensitive imaging material for making lithographic... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3122040