Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1999-02-04
2001-07-17
Baxter, Janet (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
C430S272100, C430S278100, C430S281100, C430S302000
Reexamination Certificate
active
06261740
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to negative-working, thermally imageable, lithographic printing plates and their process of use. More particularly, this invention relates to lithographic printing plates which can be digitally imaged by infrared laser light.
2. Description of Related Art
Conventional lithographic printing plates typically have a radiation sensitive, oleophilic image layer coated over a hydrophilic underlayer. The plates are imaged by imagewise exposure to actinic radiation to produce exposed areas which are either soluble (positive working) or insoluble (negative working) in a developer liquid. During development of the imaged plate, the soluble areas are removed by the developer liquid from underlying hydrophilic surface areas to produce a finished plate with ink receptive oleophilic image areas separated by complimentary, fountain solution receptive hydrophilic areas. During printing, a fountain solution and ink are applied to the imaged plate. The fountain solution is applied to the imaged plate to wet the hydrophilic areas, so as to insure that only the oleophilic image areas will pick up ink for deposition on the paper stock as a printed image. Conventional lithographic printing plates typically have been imaged using ultraviolet radiation transmitted imagewise through a suitable litho film in contact with the surface of the printing plate.
With the advent of digitally controlled imaging systems using infrared lasers, printing plates which can be imaged thermally have been developed to address the emerging industry need. In such thermally imaged systems the radiation sensitive layer typically contains a dye or pigment which absorbs the incident infrared radiation and the absorbed energy initiates the thermal reaction to produce the image. However, each of these thermal imaging systems requires either a pre- or post-baking step to complete image formation , or blanket pre exposure to ultraviolet radiation to activate the layer.
Examples of radiation sensitive compositions and their use in making lithographic printing plates are disclosed in U.S. Pat. No. 4,708,925; 5,085,972; 5,286,612; 5,372,915; 5,441,850; 5,491,046; 5,340,699; and 5,466,557; and European Patent Application 0 672 954 A2.
Each of the disclosed radiation sensitive lithographic printing plates requires a development step typically with a highly alkaline developer which is prone to reaction with atmospheric carbon dioxide. After non printing areas are removed the developed plate typically requires rinsing and drying prior to mounting on the printing press. In order to take full advantage of current digitally controlled imaging systems there is a need to reduce or eliminate the time required for plate development so that an imaged plate could be directly used on a printing press.
SUMMARY OF THE INVENTION
These needs are met by the processless lithographic printing plate of this invention which is a negative-working, thermally imageable, lithographic printing plate comprising:
(a) a sheet substrate;
(b) a hydrophilic layer applied to the sheet substrate, wherein the hydrophilic layer comprises about 30 weight % or more of an aluminosilicate or a clay based on the weight of the hydrophilic layer, and wherein the hydrophilic layer has a coating weight of about 5 g/m
2
or more; and
(c) an imaging layer applied to the hydrophilic layer, wherein the imaging layer comprises a thermally sensitive composition.
A further embodiment of this invention is a method for preparing a lithographic printing surface consisting essentially of the steps:
A. providing a negative-working, thermally imageable, lithographic printing plate comprising:
(a) a sheet substrate;
(b) a hydrophilic layer applied to the sheet substrate, wherein the hydrophilic layer comprises about 30 weight % or more of an aluminosilicate or a clay based on the weight of the hydrophilic layer, and wherein the hydrophilic layer has a coating weight of about 5 g/m
2
or more; and,
(c) an imaging layer applied to the hydrophilic layer, wherein the imaging layer comprises a thermally sensitive composition;
B. imagewise exposing the imaging layer to infrared radiation to produce an imaged layer; and
C. treating the imaged layer with a conditioner liquid to produce a lithographic printing surface.
In a preferred embodiment of this invention, the hydrophilic layer has an outer micro-porous surface, and the imaging layer is micro-porous.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to processless thermal lithographic printing plates which can be digitally imaged by infrared laser radiation having a wavelength between 700 and 1300 nm. The thermal lithographic printing plates described herein do not require a chemical development process to remove areas of the imaged plate. Rather, upon exposure to infrared laser radiation, the exposed imaged areas become ink receptive and the non-exposed, non-image areas repel ink after simple treatment with a conditioner such as a fountain solution.
The processless thermal lithographic printing plates of this invention are comprised of a sheet substrate; a hydrophilic layer applied to the sheet substrate; and a thermally sensitive imaging layer applied to the hydrophilic layer. The surface of the hydrophilic layer preferably is micro-porous and the imaging layer preferably is micro-porous. The following detailed description of the invention will describe the preferred embodiment wherein the hydrophilic layer surface and the imaging layer are micro-porous, but is not intended to be limited thereby.
In one embodiment of this invention the hydrophilic layer, which is applied to the sheet substrate, comprises about 30 weight % or more of an aluminosilicate or a clay based on the weight of the hydrophilic layer, and has a coating weight of about 5 g/m
2
or more; and the imaging layer, which is applied to the hydrophilic layer, comprises a thermally sensitive composition and preferably is micro-porous.
In a specific embodiment of this invention the lithographic printing plate comprises: (a) a sheet substrate; (b) a hydrophilic layer applied to the sheet substrate, wherein the hydrophilic layer has an outer surface which is micro-porous and wherein the hydrophilic layer consists essentially of aluminosilicate; and (c) a micro-porous imaging layer applied to the hydrophilic layer, wherein the imaging layer consists essentially of (1) an acid catalyzed, crosslinking resin system; (2) a thermally-activated acid generator; (3) an infrared absorbing compound; and optionally, (4) an indicator dye.
As used herein the term “micro-porous” is intended to include layer surfaces which contain open pores which are a fraction of a micrometer or more in diameter. Such micro-porous surfaces are readily observed in electron micrographs of the surface, such as by use of 5 KV electron and 2000 magnification. Larger pores in hydrophilic surfaces may also be detected using conventional acoustic studies to measure the rate of penetration of water (or ink) into the hydrophilic surface.
Sheet Substrate
Any dimensionally stable sheet material may be used to support the lithographic plate structure of this invention. Thus the substrate may be polymeric films such as polyester films; metal sheets such as aluminum; paper product sheets; and the like. Each of these substrate types may be coated with ancillary layers to improve interlayer adhesion; thermal isolation, particularly for metal substrates; and the like.
A preferred polymeric substrate is a sheet of polyester film such as polyethylene terephthalate, although other polymeric films and composites may also be used such as polycarbonate sheets; and the like. A preferred substrate of this type is a polyethylene terephthalate substrate such as that employed in Myriad and Omega Plus II offset substrates. The Myriad substrate is available from Xante Corporation, Mobile, Ala.; and the Omega Plus II substrate is available from Autotype Americas, Inc., Schaumburg, Ill. Myriad and Omega Plus II polyester offset substrates consist of a polyest
Hallman Robert
Natu Omkar J.
Nguyen My T.
Pappas S. Peter
Patel Jayanti
Baxter Janet
Gilmore Barbara
Kodak Polychrome Graphics LLC
Ratner & Prestia
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