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
2001-11-15
2004-04-20
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
C430S273100, C430S275100, C430S278100, C430S281100, C430S286100, C430S287100, C430S288100, C430S302000, C430S306000, C430S348000, C430S434000, C430S494000, C430S944000, C430S945000, C101S453000, C101S463100, C101S465000
Reexamination Certificate
active
06723490
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to lithographic printing. More particularly, this invention relates to multi-layer thermally imageable elements, useful as lithographic printing plate precursors, that can be thermally imaged and processed with aqueous alkaline developers.
BACKGROUND OF THE INVENTION
In lithographic printing, ink receptive regions, known as image areas, are generated on a hydrophilic surface. When the surface is moistened with water and ink is applied, the hydrophilic regions retain the water and repel the ink, and the ink receptive regions accept the ink and repel the water. The ink is transferred to the surface of a material upon which the image is to be reproduced. Typically, the ink is first transferred to an intermediate blanket, which in turn transfers the ink to the surface of the material upon which the image is to be reproduced.
Imageable elements useful as lithographic printing plates, also called printing plate precursors, typically comprise an imageable layer applied over the hydrophilic surface of a substrate. The imageable layer includes one or more radiation-sensitive components, which may be dispersed in a suitable binder. Alternatively, the radiation-sensitive component can also be the binder.
Thermally imageable elements useful as lithographic printing plate precursors, which obviate the need for exposure through a mask, are becoming increasingly important in the printing industry. After imagewise thermal exposure, the rate of removal of the exposed regions by a developer in positive-working elements is greater than the rate of removal of the unexposed regions so that the exposed regions are removed by the developer to form an image. Such systems are disclosed in, for example, Parsons, WO 97/39894 and U.S. Pat. No. 6,280,899; Nagasaka, EP 0 823 327; Miyake, EP 0 909 627; West, WO 98/42507; and Nguyen, WO 99/1145.
One difficulty with the use of lithographic printing plates is ablation of the imageable layer during imaging. The material ablated from these plates during imaging collect on the lenses, optics and focusing devices of the imaging device, known as a platesetter. After a period of reasonable use, the platesetter can have a thin film of ablated material covering the main focusing lens. Imaging errors then occur. Consequently, the platesetter must be cleaned frequently to prevent these errors.
Platesetters using plates designed to ablate on exposure have powerful “vacuum cleaners” and filtration systems. Users do not prefer these machines because of their cost, noise, and size. As the sensitivity of the thermally imageable elements increases, the potential for ablation increases.
Thus, a need exists for imageable elements that have reduced ablation to reduce the cleaning of platesetters and to reduce their cost, noise, and size.
SUMMARY OF THE INVENTION
The invention is a positive-working thermally imageable element, useful as a printing plate precursor, having reduced ablation when thermally imaged. The element comprises:
(a) a hydrophilic substrate;
(b) an underlayer,
(c) a barrier layer; and,
(d) a top layer;
in which:
the top layer comprises a first polymeric material;
the underlayer comprises a second polymeric material;
the barrier comprises a third polymeric material;
the top layer is ink receptive and insoluble in an alkaline developer;
the top layer, the barrier layer, and the underlayer are each removable by the alkaline developer following thermal exposure of the element;
the underlayer comprises a photothermal conversion material; and
the barrier layer and the top layer are substantially free of photothermal conversion material.
DETAILED DESCRIPTION OF THE INVENTION
Unless the context indicates otherwise, in the specification and claims, the terms “first polymeric material,” “second polymeric material,” “third polymeric material,” “photothermal conversion material,” “dissolution inhibitor,” “infrared absorber,” and similar terms also refer to mixtures of such materials.
This invention is a thermally imageable element. The element comprises a hydrophilic substrate, an underlayer, a barrier layer, and a top layer. The underlayer comprises a photothermal conversion material.
Hydrophilic Substrate
The hydrophilic substrate, i.e., the substrate that comprises at least one hydrophilic surface, comprises a support, which may be any material conventionally used to prepare imageable elements useful as lithographic printing plates. The support is preferably strong, stable and flexible. It should resist dimensional change under conditions of use so that color records will register in a full-color image. Typically, it can be any self-supporting material, including, for example, polymeric films such as polyethylene terephthalate film, ceramics, metals, or stiff papers, or a lamination of any of these materials. Metal supports include aluminum, zinc, titanium, and alloys thereof.
The surface of the aluminum support may be treated by techniques known in the art, including physical graining, electrochemical graining, chemical graining, and anodizing. The substrate should be of sufficient thickness to sustain the wear from printing and be thin enough to wrap around a printing form, typically from about 100 to about 600 &mgr;m.
Typically, the substrate comprises an interayer between the aluminum support and the imageable layer. The interlayer may be formed by treatment of the support with, for example, silicate, dextrine, hexafluorosilicic acid, phosphate/fluoride, polyvinyl phosphonic acid (PVPA) or polyvinyl phosphonic acid copolymers.
Underlayer
The underlayer is between the hydrophilic surface of the hydrophilic substrate and the absorber layer. After imaging, it is removed in the imaged regions along with the absorber layer and the top layer by the developer to expose the underlying hydrophilic surface of the substrate. It is preferably soluble in the developer to prevent sludging of the developer.
The underlayer comprises a second polymeric material. The second polymeric material preferably is soluble in an aqueous alkaline developer. In addition, when the second polymeric material and third polymeric material are not the same, the second polymeric material is preferably insoluble in the solvent used to coat the barrier layer so that the barrier layer can be coated over the underlayer without dissolving the underlayer. The second polymeric material is also preferably insoluble in the solvent used to coat the top layer so that the top layer can be coated over the underlayer without dissolving the underlayer.
Polymeric materials useful as the second polymeric material include those that contain an acid and/or phenolic functionality, and mixtures of such materials. Useful polymeric materials include carboxy functional acrylics, vinyl acetate/crotonate/vinyl neodecanoate copolymers, styrene maleic anhydride copolymers, phenolic resins, maleated wood rosin, and combinations thereof.
Solvent resistant underlayers are disclosed in Shimazu, WO 01/46318. Particularly useful polymeric materials are copolymers that comprise, in polymerized form, N-substituted maleimides, especially N-phenylmaleimide; methacrylamides, especially methacylamide; and acrylic and/or methacrylic acid, especially methacrylic acid. More preferably two functional groups are present in the polymeric material, and most preferably all three functional groups are present in the polymeric material. The preferred polymeric materials of this type are copolymers of N-phenylmaleimide, methacrylamide, and methacrylic acid, more preferably those that contain, in polymerized form, about 25 to about 75 mol %, preferably about 35 to about 60 mol % of N-phenylmaleimide; about 10 to about 50 mol %, preferably about 15 to about 40 mol % of methacrylamide; and about 5 to about 30 mol %, preferably about 10 to about 30 mol %, of methacrylic acid. Other hydrophilic monomers, such as hydroxyethyl methacrylate, may be used in place of some or all of the methacrylamide. Other aqueous alkaline soluble monomers, such as acrylic acid, may be used in place of some or all of the methacry
Patel Jayanti
Ray Kevin
West Paul
Williams Kevin
Gilliam Barbara
Huff Mark F.
Kodak Polychrome Graphics LLC
RatnerPrestia
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