WO1996034767A1

WO1996034767A1 - Composite ablation-transfer imaging medium for printing plate production

Info

Publication number: WO1996034767A1
Application number: PCT/US1996/005966
Authority: WO
Inventors: Ganghui Teng; Ernest W. Ellis
Original assignee: Polaroid Corporation
Priority date: 1995-05-01
Filing date: 1996-04-30
Publication date: 1996-11-07

Abstract

Disclosed is a composite ablation-transfer imaging medium for (and method of) preparing a lithographic printing plate by irradiating the composite imaging medium imagewise while in contiguous relation with a lithographic printing plate receptor. The imaging medium includes a layer of visually observable colorant material (or colorant precursor convertible subsequently to a colored species) for ready visualization of the image transferred to the lithographic plate receptor.

Description

COMPOSITE ABLATION-TRANSFER IMAGING MEDIUM FOR PRINTING PLATE PRODUCTION

BACKGROUND OF THE INVENTION This invention relates to a composite ablation-transfer imaging medium and to a method of preparing an image on an image receptor placed in contiguous relation with the imaging medium. More particularly, it relates to a composite ablation-transfer imaging medium for the production therefrom, by radiation-induced ablative transfer, of an image which can be recognized readily and visually or which by simple further treatment can be converted to a visible image.

The production of images by the radiation-induced displacement and transfer of imaging substance from a donor medium to an adjacent receptor element has been well known in the imaging arts. Typically, a laser will be used to effect the simultaneous imagewise displacement of an imaging substance from a donor element and the adherent transfer of the imaging substance to a receptor element positioned in contiguous or spaced-apart relation to the donor element. Examples of the production of images by methods of the aforesaid type can be found, for example, in U.S. Pat. No. 3,962,513 (issued Jun. 8, 1976 to A.C. Eames); U.S. Pat. No. 3,964,389 (issued Jun. 22, 1976 to J.O.H. Peterson); U.S.

Pat. No. 4,245,003 (issued Jan. 13, 1981 to R.L. Oranslcy, et al.); U.S. Pat. 5, 156,938 (issued Oct. 20, 1992 to D.M. Foley, et al.); and in U.S. Pat. No. 5,171,650 (issued Dec. 15, 1992 to E.W. Ellis, et al.).

In the last-mentioned U.S. Pat. No. 5,171,650, there is described an ablation-transfer imaging medium which includes a dynamic release layer which interacts with imaging (e.g., laser) radiation and effects/enhances the imagewise transfer of an overlying (topcoat) layer onto a receptor element which is placed in contiguous registration therewith. The composite imaging medium, useful for a wide variety of applications, can include in the transferable topcoat layer any of a variety of contrast imaging materials which serve to delineate a pattern of intelligence on the receptor element. Among contrast imaging materials disclosed in the aforementioned U.S. Pat. No. 5,171,650 are such contrast imaging materials as magnetic substances, hydrophobic ink-accepting resins, pigments, and colorless UV-readable substances.

It will be appreciated that, depending upon a particular application or requirement and the field in which a composite imaging medium of the type described in the aforementioned U.S. Pat. No. 5,171,650 is to be utilized, the nature of the contrast imaging material thereof will vary widely. In certain applications, such as in the production of a lithographic printing plate, it will be advantageous to employ a contrast imaging material which includes at least one component which comprises or which can be converted to a hydrophobic ink- accepting resin. Typically, a hydrophobic ink-accepting resin suited for the production of a printing surface will be a colorless or substantially colorless material. As a consequence, the image pattern transferred, for example, onto the aluminum surface of a plate receptor may be invisible or nearly so. This detracts materially from practical utilization of a printing plate and it will be beneficial if the platemaker is able to observe and distinguish readily the transferred hydrophobic (printing) surfaces from the hydrophilic (background) areas of the plate, in advance of placing the printing plate onto a printing press for the conduct of a printing run.

The incorporation of a colorant into a layer to impart its characteristic and predetermined coloration remains a practical expedient for many applications. In a composite ablation-transfer imaging medium of the type described in the aforementioned U.S. Pat. No. 5,171,650, and which is dependent for proper functioning upon the occurrence of certain mechanisms therein described, the simple addition of colorant to a radiation-ablative layer may be attended by practical considerations which dictate an alternative to such an expedient. For example, a colorant of desired hue and intensity may be physically incompatible with the principal components of the radiation-ablative layer, such that, the colorant material cannot be dissolved adequately in a solvent compatible with such principal components or cannot be distributed uniformly throughout the layer. Incorporation of a colorant or colorant precursor into the radiation-ablative layer can result in reduced sensitivity, higher energy demand and reduced adhesivity of the layer for the receptor element. Further, the colorant or colorant precursor may be chemically incompatible with a component of the radiation- ablative layer or may interfere with a subsequent photohardening (e.g., UV curing) of the transferred image.

It will be appreciated that a means of providing a visually observable transferred image pattern by resort to ablation-transfer methodology, in a facile and efficient manner with minimal adverse affect on the ablation transfer, will find application in the graphic arts field.

SUMMARY OF THE INVENTION

It has been found that a lithographic printing plate having a visually observable image pattern (or an image pattern which can be made so by simple further treatment) can be provided in an efficient and kinetically rapid manner by resort to an ablation transfer imaging/recording technique. This is accomplished by utilizing a composite ablation-transfer imaging medium for the transfer of contrast imaging material to a lithographic printing plate receptor, the composite ablation-transfer imaging medium comprising, in order: a support substrate transparent to imagewise radiation; a dynamic release layer; a layer of material for delineating an image pattern on said lithographic printing plate receptor, said material comprising a visually observable colorant material or precursor thereof; and a radiation-ablative layer including as a contrast imaging material an oleophilic ink-receptive polymer or precursor thereof; said dynamic release layer being capable of absorbing said radiation at a rate sufficient to effect imagewise ablation to a contiguous printing plate receptor of the volume of at least said radiation-ablative layer and said colorant (or colorant precursor) material in areas subjected to said radiation.

According to a method aspect of the present invention, there is provided a method of making a lithographic printing plate which comprises: placing a lithographic printing plate receptor into contiguous registration with a composite ablation-transfer imaging medium; said composite ablation-transfer imaging medium comprising, in order, a support substrate transparent to imagewise radiation; a dynamic release layer; a layer of material for delineating an image pattern on said printing plate receptor, comprising a visually observable colorant or precursor thereof; and a radiation-ablative layer including a contrast image-providing oleophilic ink-receptive polymer or precursor thereof; said dynamic release layer being capable of absorbing said radiation at a rate sufficient to effect imagewise ablation to said contiguous printing plate receptor of the volume of at least said radiation-ablative layer and said colorant or precursor thereof in areas subjected to said radiation; irradiating said ablation-transfer imaging medium imagewise according to a pattern of intelligence, with an intensity sufficient to effect the imagewise ablation mass transfer of the volume of the image-wise exposed areas of at least said radiation-ablative layer and said layer of colorant or precursor thereof; and simultaneously transferring said areas adherently onto said lithographic printing plate receptor substrate, thereby to delineate thereon said pattern of intelligence. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic cross-sectional view of a composite ablation-transfer imaging medium of the invention.

FIG. 2A is a diagrammatic cross-sectional view of the composite ablation-transfer imaging medium of FIG. 1 in face-to-face (contiguous) registration with a lithographic printing plate substrate, the composite medium being subjected to imagewise irradiation through the support substrate thereof.

FIG. 2B is a diagrammatic cross-sectional view of the composite medium and printing plate substrate of FIG. 2A in separated relation after imagewise photoirradiation, for production of a lithographic printing plate.

DETAILED DESCRIPTION OF THE INVENTION

As mentioned previously, the present invention makes possible the production (in rapid and efficient manner via radiation-induced ablation transfer) of a lithographic printing plate bearing a pattern of intelligence which can be readily observed by the platemaker upon production thereof, or which can by simple treatment, be made readily visible for inspection.

As used herein, "radiation-induced ablation transfer" imaging/recording refers to an imaging (recording) mechanism which entails photoradiation-induced complex non-equilibrium physical and chemical mechanisms; the rapid and transient accumulation of pressure beneath and/or within the radiation-ablative imaging layer of the composite imaging medium of the present invention, as a consequence of such photoirradiation; and the concommitant transfer adherently to an adjacent receptor element, by the force produced upon release of such pressure, of substantially the entire volume of both the colorant (or colorant precursor) and radiation-ablative imaging layers.

The term "dynamic release layer" refers to a layer, intermediate the support of the composite imaging medium and the overlying colorant (or colorant precursor) and imaging layers, which interacts with imagewise irradiation to effect the transfer imagewise to a lithographic substrate material of such overlying layers, at an energy/fluence less that would be required in the absence thereof.

According to the present invention, there is provided a composite imaging medium, the utilization of which, in a method of producing a lithographic printing plate, is dependent upon complex interactions between imagewise irradiation, the dynamic release layer of the imaging medium and the overlying colorant/imaging layers. While the precise mechanisms in explanation of such interactions are not entirely understood, such interactions make possible the production of receptor plates having practical application in lithographic printing. The facile and direct radiation-induced transfer of an image pattern to a printing plate substrate permits, according to a preferred embodiment, the production of a "computer-to-plate" printing plate. Such production involves the utilization of digital image signals (representative of desired image values) which are acquired by known scanning methods and stored in computer form. These signals can then be used to actuate a source of irradiation, as a function of such image values, to induce the transfer directly to a lithographic plate substrate of portions of the imaging and colorant (or colorant precursor) layers of the irradiated composite imaging medium. Referring to FIG. 1, there is shown a preferred composite laser- ablative imaging medium 10 which includes dynamic release layer 16 and overlying colorant (or colorant precursor) layer 18 and laser-ablative imaging layer 19. In FIG. 2A, composite imaging medium 10 is shown in face-to-face contiguous relationship with a printing plate receptor element 20 which comprises a suitable lithographic printing plate substrate material 22 carrying or surface- treated with one or more layers or coatings (not shown). Composite imaging medium 10 and printing plate receptor 20 are shown in contiguous interfacial contact along imaginary line 15-15'. Irradiation of imaging medium 10 (for example, by laser irradiation in the area between arrows 17 and 17', as shown in FIG. 2A) induces complex interactions of the type mentioned previously. The dynamic release layer 16 is believed by absorption of the irradiation, and upon rapid accumulation of pressure and release of force, to eliminate effectively the adhesive/bonding forces which serve to secure the colorant/colorant precursor and imaging layers 18 and 19, respectively, via dynamic release layer 16, to support layer 12. As a consequence of propulsive forces generated in and/or beneath layers 18 and 19, there is effected an expulsive transfer adherently to the surface 26 of lithographic plate substrate 22 of substantially the entire volume of layers 18 and 19 in imagewise irradiated areas. Shown in FIG. 2B is a transferred image area 24 which includes transferred portions 18t and 19t, respectively, of colorant/colorant precursor layer 18 and imaging layer 19. The resulting lithographic printing plate 20a carrying oleophilic printing areas such as printing area 24 on a hydrophilic surface 26 of the plate is shown in FIG. 2B separated from imaging medium 10a. Image medium 10a carries retained non-irradiated portions 18r and 19r, respectively, of layers 18 and 19.

Dynamic release layer 16 can comprise one or more layers and can be of organic or inorganic composition, or a combination thereof. The dynamic release layer must have a capacity to absorb at least a portion of the imaging irradiation sufficient to diminish the adhesion of layers 18 and 19 thereto and to effect the transfer of portions of layers 18 and 19 to the lithographic printing plate substrate 22. Dynamic release layer 16 can comprise material which is intrinsically absorptive of imaging radiation or can comprise a material which is sensitized to absorption of such radiation by the addition of a radiation-absorbing sensitizer compound. Suitable dynamic release layer materials include black body and non-black body absorbing materials. It will be preferred that dynamic release layer 16 comprise a material which intrinsically absorbs imaging radiation such that a thin layer can be employed for the rapid and efficient transfer of overlying layers to the printing plate substrate material 22.

Suitable materials for dynamic release layer 16 include thin films (layers) of metals, metal oxides and metal sulfides which melt, vaporize or otherwise change in physical property upon subjection to imaging radiation.

Preferred will be materials which exhibit little or no toxicity and which reflect a minimal portion of incident imaging radiation and effect the transfer of overlying layers with minimal energy requirement. Examples of suitable metals include the metallic elements of Groups lb, lib, Ilia, IVa, IVb, Va, Vb, Via, VIb, VLIb and Vπi of the Periodic Table. Alloys of such metals and alloys thereof with elements of Groups la, Ila, and iπb of the Periodic Table, and mixtures thereof, can also be employed.

Preferred metallic materials for dynamic release layer 16 include aluminum, bismuth, tin, indium and zinc, and alloys thereof. Alloys of such metals with elements from Groups la, Ila and Illb of the Period Table, and mixtures thereof, can also be employed.

Among the metallic oxides and sulfides that can be used as or in a dynamic release layer 16 are the oxides and sulfides of aluminum, bismuth, tin, indium, zinc, titanium, chromium, molybdenum, tungsten, cobalt, iridium, nickel, palladium, platinum, copper, silver, gold, zirconium, tellurium and mixtures thereof

Dynamic release layer 16 can comprise organic materials which absorb imaging radiation intrinsically or which can be sensitized for absorption by incorporation of an absorber. Among organic materials that can be employed are monomeric and polymeric substances. Representative monomeric compounds include the metal phthalocyanines, metal dithiolenes and anthraquinones. These can, for example, be formed into a thin layer by vacuum deposition methods. Representative polymeric compounds include the polythiophenes, polyanilines, polyacetylenes, polyphenylenes, polyphenylene sulfides, polypyrroles, and derivatives or mixtures thereof.

A suitable polymeric dynamic release layer 16 comprises a combination of polymeric binder and an ablation sensitizer/absorber for rendering the layer absoφtive of imaging irradiation. Absorbers/sensitizers which absorb radiation in the near infrared region of the electromagnetic spectrum can be employed, as can compounds which absorb in the visible range. The polymeric binder will preferably comprise a binder which undergoes a rapid partial decomposition, such as an acid catalyzed decomposition. Suitable binders of this type are known and are described in U.S. Pat. No. 5,156,938 (issued Oct. 20, 1992 to D.M. Foley, et al.).

Other dynamic release layer materials suitable for the provision of dynamic release layer 16 can be found in the aforementioned U.S. Pat. No. 5,171,650. Dynamic release layer 16 can be applied to substrate material 12 by resort to any of a variety of coating and deposition methods which will vary with the nature of the particular material employed as the dynamic release layer. Organic materials can be suitably coated from an aqueous and/or organic solvent appropriate for the particular material. Vapor deposition, vacuum coating and sputtering operations can be employed for the deposition onto support substrate 12 of a metallic dynamic release layer.

The thickness of dynamic release layer 16 can vary depending upon the particular material employed. Typically, the layer will be a thin layer so as to make possible a rapid accumulation of pressure and release of force sufficient to effect the desired transfer of overlying imagewise irradiated portions of layers 18 and 19. In the case of a metallic dynamic release layer 16, a thickness in the range of about one monolayer of the metal to about 500 Angstroms will be preferred. Good results are obtained in the case of a preferred aluminum layer at a thickness of about 40 to 120 Angstroms.

Colorant (or colorant precursor) layer 18 serves important functions in the ablative-transfer imaging medium of the invention. A principal function of layer 18 is to provide a means for ready visualization of color in image areas 24 of printing plate 20a. This can be accomplished by including in layer 18 a material which is colored intrinsically and which provides its coloration to the transferred printing areas 24. Alternatively, layer 18 can comprise materials which are substantially colorless but which, upon transfer by ablation to printing plate substrate 22, can by simple treatment be converted to colored material. Such materials, referred to herein as "colorant precursor" materials can be converted to visually observable colored species by exposure to ultraviolet radiation, by thermal exposure, by change in pH, or by other simple treatment. In either case, it will be beneficial that the coloration imparted to the plate be substantially stable to the conditions of a lithographic printing operation and, in particular, that the coloration not be affected adversely by the influences of the lithographic fountain and ink compositions typically used in a printing operation.

Depending upon the nature of the materials employed in colorant (or colorant precursor) layer 18, and particularly upon any intrinsic absoφtion capacity of the layer or components thereof for imagewise irradiation, layer 18 can function as a dynamic release layer in concert with dynamic release layer 16 for the ablation transfer of irradiated areas of both layers 19 and 18, as shown in FIG. 2B.

Oftentimes, layer 18 will comprise a dye or pigment of predetermined color (hue and saturation) distributed uniformly in a binder therefor. Suitable binders include polymeric acrylic binders (e.g., polymethylenethacrylates), polyvinylchloride, polyvinylacetates, polystyrene, polyamides, polyesters, polyurethanes, polyvinylalcohol, cellulosic binders such as hydroxyethyl cellulose, carboxymethyl cellulose and nitrocellulose, and phenoxy resins and epoxy-phenolic copolymers. Colorants for incoφoration into layer 18 include any of a variety of organic dyes and organic or inorganic pigments that can be incoφorated into a binder and deposited as a thin film. Examples include such inorganic pigments as copper sulfate, barium sulfate, yellow lead, bismuth oxychloride, chromium vermilion, titanium dioxide, cadmium red, navy blue, carbon black, calcium carbonate, ultramarine, iron oxide and mixtures thereof. Examples of organic dyes and pigments include dyes and pigments of the azo class, the vat series of dyes and pigments, the phthalocyanines, dyes of the triphenylmethane class, quinacrydone pigments, perylene dyes and the like.

A preferred class of organic pigments for incoφoration into layer 18 comprises the phthalocyanines. Such materials can be used in any suitable crystalline form and can be substituted or unsubstituted in either ring or straight- chain portions thereof. Reference is made to the book "Phthalocyanine Compounds", by F.H. Moser and A.L. Thomas, published by Reinhold Publishing

Company, 1963 Edition, for a detailed description of the nature and synthesis of phthalocyanine compounds. In general, phthalocyanines useful in the present invention include four isoindole groups linked by four nitrogen atoms in such a manner as to form a conjugated chain. Such compounds have the general formula

(CnH.N^Rn

wherein R is hydrogen or a metal such as lithium, sodium, copper, silver, calcium, zinc, aluminum, chromium, nickel, palladium or the like; and n is a value greater than zero and equal to or less than two. Ring- or aliphatically-substituted metallic and/or non-metallic phthalocyanines can be used.

A preferred class of metallic phthalocyanines for use in layer 18 comprises the copper phthalocyanines which can be deposited onto dynamic release layer 16 as a dispersion of colorant particles. The phthalocyanine particles are insoluble in lithographic printing press fluids, and are not washed away by such fluids. As a result they provide a durable surface layer 18t and a measure of wear resistance for image areas 24. In addition, they are color stable and contribute materially to the ability of the printing press operator, by monitoring the observed coloration of the image areas, to gauge the useful life of the printing plate and the press run. While applicants do not wish to be bound by any particular theory or mechanism in explanation of advantageous durability and press-run length observed in a printing plate having stable and observable coloration imparted by a phthalocyanine pigment, it is believed that such advantages are the result, at least in part, of the aforementioned insolubility of the pigment material and the ability of the phthalocyanine pigment material to provide a surface 18t in image areas 24 which serves to protect underlying areas 19t during the course of a press run. In addition, the utilization of phthalocyanine particles in layer 18 is believed to permit firm attachment thereto of layer 19, as the result of inteφenetration of binder and other components of layer 19 into layer 18. Upon transfer of image portions 24 of layers 18 and 19 onto plate 22, the firm anchorage of particulate-containing layer 18t to underlying image layer 19t is believed to provide durability by preventing wear and undercutting of image areas 19t during the conduct of a press run. The expulsive force needed to attach portions of layers 18 and 19 adherently to the lithographic plate receptor 22 may also be augmented by any intrinsic absoφtion of the phthalocyanine pigment for imagewise irradiation and consequent ablation-promoting influences.

Phthalocyanine compounds that can be used in layer 18 are well known and described in the aforementioned publication "Phthalocyanine Compounds". Examples of such compounds can also be found in U.S. Pat. No. 3,816,118 (issued Jun. 11, 1974 to J.F. Byrne). Layer 18 can include a colorant precursor material convertible to a colored species by subsequent treatment. Suitable treatments include exposure to ultraviolet (UV) radiation, heating, or combined UV and infrared (IR) irradiations. For example, the colorless compound, leuco crystal violet, can be used. Upon transfer to lithographic plate 22, the resulting plate can then be subjected to the irradiation of a conventional fluorescent lamp or to the irradiation from any of a number of lamps which emit UV irradiation. Alternatively, the plate can be heated or can be subjected to the combined (e.g., simultaneous or sequenced) effects of UV and IR exposures. Conversion by such treatments to a desired coloration enables the platemaker and press operator to distinguish readily the image areas from non-image areas of the plate. It will be appreciated that when a color precursor material is used, it will be preferred that the color- generating step and the particular color precursor compound utilized be selected with a view to providing a coloration which will be substantially stable to the influences of printing press fluids.

Colorant-precursor compounds suitable for the production of a colored species can be found among compounds known to undergo colorless-to- colored shifts. Suitable examples include bis 4-diethylamino o-tolyl(4- diethylamino-phenyl) methane and tris(2-methyl-4-diethylaminophenyl) methane. If desired, a layer containing a colorant precursor can additionally contain an image radiation absorber/sensitizer or a UV- or heat-activatable compound capable on activation of generating a proton and a desired color-forming reaction.

Radiation-ablative layer 19 provides important functionality in composite ablation-transfer imaging medium 10 and in a printing plate which is prepared therefrom. Layer 19 includes a contrast imaging material which is a polymeric oleophilic (ink-receptive) material or a precursor of such a material, i.e., one or more compounds which under the conditions of an ablative-transfer method form such a substance, or which, can be converted to such a substance by treatment of plate 20a after the ablative transfer. In any case, layer 19 comprises a polymeric oleophilic substance, or a precursor thereof, which can be transferred by the method of the present invention so as to provide image areas such as image area 24 shown in FIG. 2B. Suitable polymeric oleophilic substances useful as the contrast imaging-providing material which delineates the image pattern transferred to printing plate substrate 22 include a variety of ink-receptive materials known to be useful in the printing arts. These include a variety of vinylic polymers such as vinylidene chloride copolymers (e.g., vinylidene chloride/acrylonitrile copolymers, vinylidene chloride/methylmethacrylate copolymers and vinylidene chloride/vinyl acetate copolymers); ethylene/vinyl acetate copolymers; polyvinyl alcohol resins; synthetic rubbers (e.g., butadiene/acrylonitrile copolymers; chlorinated isoprene and chloro-2-butadiene-l, 3-polymers); polyvinyl esters (e.g., polyvinyl acetate/acrylate copolymers, polyvinyl acetate and polyvinyl acetate/methylmethacrylate copolymers); polyacrylate and polyalkylacrylate esters

(e.g., polymethymethacrylate); and polyvinyl chloride copolymers (e.g., vinyl chloride/vinylacetate copolymers). Also suitable are cellulosic esters and ethers (e.g., cellulose acetate butyrate, cellulose acetate propionate, and methyl, ethyl benzyl cellulose). Polymers of the condensation type, such as the polycarbonates, polyesters, polyamides, polyesteramides, polyurethanes and phenol-formaldehyde resins can also be employed. Epoxy resins such as the resins prepared by the reaction of a fatty acid amide with the reaction product of an epoxy compound (e.g., epichlorohydrin) and a bisphenolic compound (e.g., 2,2,-bis(4- hydroxyphenyl)-propane) can also be used.

Layer 19 will typically include an ablation sensitizer/absorber which includes any of a variety of compounds capable of absorbing imaging radiation and initiating and promoting the desired ablation process. Such compounds absorb imaging radiation and transfer absorbed energy into an expulsive force. Compounds suited to this puφose include known compounds which absorb in the near infrared region and include compounds such as Cyasorb- IR 165, 126 and 99. Other IR-absorbing compounds (dyes) that can be utilized include the alkylpyrylium-squarylium dyes, disclosed in U.S. Pat. No. 4,508,811

(issued Apr. 2, 1985 to D. J. Gravesteijn, et al.), and including l,3-bis[2,6-di-t- butyl-4H-thiopyran-4-ylidene)methyl]-2,4dihydroxy-dihydroxidecyclobutene diylium-bis{innersalt}. Other suitable IR-absorbing dyes include 4-[7-(4H-pyran- 4-ylide)heptal,3,5-trienyl]pyrylium tetraphenylborate and 4-[[3-[7-diethylamino-2- (1,1 -diemethylethyl — benz[b]-4H-pyran-4-ylidene)methyl]-2-hydroxy-4-oxo-2- cyclobuten- 1 -ylidene]methyl]-7-diethylamino-2-( 1 , 1 -dimethyl ethyl)- benz[b]pyrylium hydroxide inner salt. Other IR-absorbing compounds can be found in U.S. Pat. No. 5,227,499 (issued Jul. 13, 1993, to D.A. McGowan, et al.); U.S. Pat. No. 5,354,873 (issued Oct. 11, 1994 to R.M. Allen, et al.); and U.S. Pat. No. 5,405,976 (issued Apr. 11 , 1995 to S. J. Telfer, et al.).

Layer 19 can include preformed resinous materials as the image contrast-providing substance thereof. It will be preferred, however, from the standpoint of reducing the amount of energy required to effect ablation transfer, that the image contrast-providing material comprise the precursor component(s) of the ink-receptive polymer which is to be embodied in the image areas (24) of plate 20a. It is believed that the utilization of precursor compounds which, in general, will have lower molecular weights than preformed polymers will be transferred in a more facile manner and/or with lower energy requirement. Completion of polymer formation can be accomplished in a subsequent treating step, for example, by subjecting plate 20a to photohardening (e.g., UV) irradiation.

Among precursor compounds useful in layer 19 for providing the ink-receptive polymer of image areas 24 are various monomeric, oligomeric and polymeric compounds which can be converted to such ink-receptive polymer. These include cross-linkable compounds, cross-linking agents, polymerizable monomers, oligomers and other reactive compounds. Conversion of precursor compounds to an ink-receptive polymer can be accomplished according to mechanisms (reactions) that vary with the nature of the particular precursor compounds employed. In general, such conversion will be the result of an insolubilization, curing or hardening reaction occurring after radiation-induced ablation transfer of layer 19 to printing plate substrate 22. Such conversion can be effected by heat treatment of printing plate 20b, exposure of the plate to UV radiation, or such other treatment(s) as may be required to initiate and/or bring to suitable degree of completion the desired hardening, curing or insolubilization reaction.

Suitable precursor materials for incoφoration into layer 19 include the reaction components for production of an epoxy-based, cross-linked, ink- receptive polymer. A reaction system for such puφose can include, for ex-ample, a multifunctional (cross-linkable) resin, such as epichlorohydrin/tetraphenylol ethane epoxy resin, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate or bis-(3,4- epoxycyclohexylmethyl)adipate); and a cationic photoinitiator such as the mixed triarylsulfonium hexafluorophosphate salts or mixed triarylsulfonium hexafluoroantimonate salts. The reactive components of such a system can be combined with a suitable binder (from among binders mentioned hereinbefore) and can be coated over colorant (or colorant precursor) layer 18. In general, the layer 19 is bonded adhesively and by inteφenetration into layer 18 to provide a composite imaging medium 10 of the invention. Upon irradiation-induced ablative transfer of composite layers 18t and 19t to plate substrate 22, hardening of image areas 24 can be photoinitiated and brought to desired cure by UV exposure of plate 20a. If desired, layer 19 can comprise an unreacted mixture of copolyester precursor reactants and an acidic photogeneratable catalyst. For example, a layer 19 including a mixture of dicarboxylic and diol compounds (i.e., precursor compounds to a condensation polymer) and an acidic photogeneratable catalyst can be transferred by the method of the present invention along with layer

18, to form image areas 24 which can be photohardened by UV irradiation or a combined photoirradiation and heat treatment. In like manner, urethane-based ink receptive polymers can be formed by photoactivation of a urethane reaction- promoting catalyst after an ablation transfer according to the method of the present invention.

Preformed polymers which can be incoφorated into layer 19 but which require post-irradiation treatment to provide photohardened image areas 24 include preformed polymers having pendant cross-linked groups. Preformed polymers having pendant crosslinkable groups include, for example, the reaction product of a hydroxyl-containing polymer (e.g., a polyester of a dicarboxylic acid and a polyhydric alcohol) and a vinyl monomer containing isocyanate groups (e.g., isocyanatoethyl acrylate or methacrylate). Cross-linking agents and photoinitiators can be used in layer 19 to permit the production, by post-ablation transfer photoirradiation of plate 20a, of image areas having photohardened areas 19t of polymer having urethane linkages. Other preformed polymers having pendant reactive groups such as cinnamate groups can be used in layer 19. For example, polyvinyl alcohol (PVA) cinnamate formed by the esterification of hydroxy groups of PVA using cinnamic acid, can be used. Cross-linking can be effected by treatment of plate 20a for photodimerization of cinnamoyl groups. Preformed polymers having pendant pyridinium ylide groups which groups, upon photoexposure, undergo ring expansion (photorearrangement) to a diazepine group with accompanying insolubilization can also be employed as a precursor material to an ink-receptive polymer in layer 19. Examples of polymers having such groups are described in U.S. Pat. No. 4,670,528 (issued Jun. 2, 1987 to L.D. Taylor, et al.).

A preferred precursor system for producing polymeric ink-receptive areas on plate 20a comprises a polymerizable monomer which by photoexposure, after ablation transfer of layers 18 and 19 to receptor plate 22, can be polymerized to desired ink-receptive areas. Suitable monomers are the photopolymerizable ethylenically unsaturated monomers having at least one terminal ethylenic group capable of forming a high polymer by free-radical initiated, chain-propagated addition polymerization. Polymerization can be effected using a photoinitiator, i.e., a free-radical generating, addition polymerization-initiating system activatable by actinic radiation. Such addition polymerization-initiating systems are known and examples thereof are described hereinafter.

Suitable photopolymerizable ethylenically unsaturated monomers for use in layer 19 include polyfunctional acrylate monomers such as are represented by the acrylate and methacrylate esters of ethylene glycol, trimethylolpropane and pentaerythritol. Examples of such monomers include difunctional and trifunctional acrylates and methacrylates such as pentaerythritol triacrylate and trimethylolpropane triacrylate. Other suitable monomers include ethylene glycol diacrylate (or dimethacrylate) and mixtures thereof; glycerol diacrylate; glycerol triacrylate; and the ethoxylates of such monomers.

Photoinitiators useful in layer 19 for the initiation of monomer polymerization in image areas 24 of plate 20a, using actinic radiation, include photoinitiators known in the polymer arts. Suitable photoinitiators include the acetophenone derivatives (such as 2,2-dimethoxy-2-phenylacetophenone), benzoin or an alkyl-substituted anthraquinone, azobisisobutyro-nitrile and azo-bis-4-cyano-pentanoic acid, although others can be employed.

A preferred composition for the production of layer 19 includes a water-soluble macromolecular binder, the polymerizable monomer and a photoinitiator. Preferably, the composition will also include an ablation sensitizer/absorber of the type aforesaid. The composition can be suitably coated into a layer which can be ablated and transferred onto receptor plate 22. The resulting plate 20a can then be exposed to UV radiation and, if desired, heated for cure. The insolubilization and hardening of image areas 24 as the result of homopolymerization of the polymerizable monomer and grafting of the monomer onto the macromolecular binder adapts the plate to lithographic printing operations. If desired, cross-linking agents such as those of the difunctional type (e.g., divinylbenzene) can be included in layer 19 to promote cross-linking via the unsaturated moieties thereof to polymerizable monomer and/or binder components of image areas 19t and/or to binder or other components of image areas 18t.

In the production of a composite ablation-transfer medium 10 of the invention, respective layers 16, 18 and 19 can be applied by resort to known coating and deposition methodologies appropriate to the nature and composition of each of the layers. Radiation-ablative layer 19 can include materials or adjuvants to adapt the layer 19 to particular requirements, including polymeric materials for promoting adhesion to the image receptor, particulate filler materials and surface active agents. Dyes or pigment colorants can also be included. Such adjuvants should, however, be of a character as not to interfere by spectral absoφtion or otherwise, with desired ablation-transfer mechanisms. Such adjuvants should be employed in minor amounts so as to minimize interference with such mechanisms.

It will be understood that inteφenetration of layers may result from the coating of a layer such as radiation-ablative layer 19 onto colorant (or colorant precursor) layer 18, particularly where the respective layers are deposited from the same solvent or from solvents of like organic or aqueous character. Thickness of the respective layers can vary with the nature of the layer but, in general, it will be desired to utilize thin layers toward minimizing the amount of energy required to effect radiation-induced ablation transfer. The thickness of layers shown in FIGS. 1, 2 A and 2B are not to scale. Lines of demarcation between layers 16 and 18, and between layers 18 and 19, may be influenced by the effects of coating solvents utilized in the deposition of the layers. Interdiffusivity of components between the layers, and polymer inteφenetration between the layers, may also result, depending upon the coating formulations and methodologies employed.

Support substrate 12 will comprise a film which is transparent to the imaging radiation. Examples of suitable materials include glass, polyesters (such as polyethylene terephthalate), polystyrenes, polycarbonates, polyurethanes, cellulosic supports such as cellulose acetate, cellulose triacetate and cellulose acetate butyrate. The thickness of support substrate 12 can vary with the nature of the particular layers of medium 10 and especially the nature of any apparatus used for handling the medium and for placement of medium 10 into registration with plate receptor 22.

As shown in FIG. 1, support substrate 12 is shown with an anti- reflection layer 14. Such a layer, while optional, will be preferred from the standpoint of minimizing reflection of incident image-forming radiation and allowing efficient utilization of the incident irradiation for the desired laser- ablation transfer. Suitable anti-reflection materials for layer 14 are known and include commercially available fluoropolymers which have an index of refraction of about 1.3 to 1.4, such as the Fluorad FC-721 fluoropolymer of 3M Company. Other suitable anti-reflection materials are known and can be utilized, including anti-reflection materials and layers described in U.S. Pat. No. 3,793,022 (issued Feb. 19, 1974 to E.H. Land, et al.).

Printing plate 20a can be prepared by the ablative transfer of layers 18t and 19t to a printing plate substrate 22 placed in face-to-face relation to imaging medium 10, as is shown in FIG. 2A. Printing plate substrate 22 can comprise any of a variety of sheet-like materials of suitable durability for use in a printing operation, including plates comprising metals and metal alloys. Paper or paper laminates can be employed, as can polymeric sheets or foils such as polyethylene, polyethylene terephthalate, cellulose triacetate, polystyrene, polycarbonate and the like.

Preferred substrates 22 are the metallic substrates of aluminum, zinc, steel or copper. These include the known bi-metal and tri-metal plates such as aluminum plates having a chromium layer; steel plates having copper and chromium layers; and aluminum alloy plates having a cladding of pure aluminum. Especially preferred are the grained aluminum plates, where the surface of the plate is roughened mechanically or chemically (e.g., electrochemically) or by a combination of roughening treatments. Anodized plates can be used to provide an oxide surface. Anodization can be performed in an aqueous alkaline electrolytic solution, including, for example, alkali metal hydroxides, phosphates, aluminates, carbonates and silicates, as is known in the art. An aluminum plate, grained and/or anodized, which, for example, has been treated with an aqueous alkali metal silicate, such as with sodium silicate, or which has been treated with polyvinyl phosphonic acid or otherwise provided with a resinous or polymeric hydrophilic layer, can be suitably employed as substrate 22.

Examples of printing plate substrate materials 22 which can be used in the production of printing plates of the invention, and methods of graining, anodizing and hydrophilizing such substrates are described, for example, in U.S. Pat. No. 4,153,461 (issued May 8, 1979 to G. Berghauser, et al.); U.S. Pat. No. 4,492,616 (issued Jan. 8, 1985 to E. Pliefke, et al.); U.S. Pat.

No. 4,618,405 (issued Oct. 21, 1986 to D. Mohr, et al.); U.S. Pat. No. 4,619,742 (issued Oct. 28, 1986 to E. Pliefke); and U.S. Pat. No. 4,661,219 (issued Apr. 28, 1987 to E. Pliefke). In FIGS. 2A and 2B, printing plate receptor 22 is shown by a diagrammatic cross-sectional representation. It will be appreciated that, depending upon the particular nature of substrate 22, and especially in the case of grained metallic substrates, that the surface 26 of printing plate receptor 22 may exhibit a surface microstructure (not shown). The nature of surface 26, and particularly any inherent topographical microstructure thereof, can influence, the adhesion to plate 22 of the image areas 24 imparted to the plate as the result of the propulsive transfer to the plate of layers of the composite imaging medium 10. Good printing results and good durability of plate 20a can be obtained using a grained aluminum receptor plate 22. Other printing plate receptor substrates 22 can, however, be used. Surface treatments of the substrates can vary with the particular substrate and can be utilized to improve adhesion to the substrate.

Exposure of imaging medium 10 to imagewise irradiation can be accomplished using irradiation in the visible and near infrared spectral ranges. Examples of radiation-emitting devices which can be used include solid state lasers, semiconductor diode lasers, gas lasers, dye lasers, xenon lamps, mercury arc lamps and other visible and near infrared radiation sources which are capable of providing sufficient energy to equal, or exceed, the threshold energy for ablation transfer and of providing this energy at such a rate as to institute that phenomenon of transient pressure accumulation discussed earlier and believed responsible for the ablative transfer process.

The actual value of threshold energy is intensity dependent as well as materials dependent. Typically, when employing imaging media constructions comprising a dynamic release layer composed of high thermal conductivity thin metal films such as aluminum, at least 50 mJ/cm² at 10⁶ watts/cm² is required, while at least 100 mJ/cm² at 10⁴ watts/cm² is more typical for organic constructions. When these conditions are not satisfied, undesirable processes rather than, or in addition to, ablation-transfer may occur, e.g., melting, sublimation or charring. Incomplete transfer and/or image quality degradation may result. Other constraints on the exposure device include the ability to focus the imaging radiation to a desirable spot size and depth and to modulate the radiation at dwell times suitable for the desired imaging application. Particularly representative devices for providing the imaging radiation include the Nd:YAG laser emitting at 1064 nm, for example, the laser incoφorated in the imaging hardware of the Crosfield Datrax 765 laser facsimile writer, laser diode systems emitting at 780-840 nm, or other radiation sources designed to provide a power density of 10⁴ watts/cm² or greater. The radiation source is preferably focused to provide the most efficient utilization of energy when it is impinged upon the imaging medium.

The composite ablation-transfer imaging medium and lithographic printing plate receptor can be brought into face-to-face relation in an imaging apparatus for exposure through the support of the imaging medium. If desired, the imaging medium and printing plate receptor can be packaged for handling as a unitary structure and the unitary structure can be imaged in a suitable imager apparatus. An assemblage of the imaging medium and receptor, can include vacuum means for maintaining the imaging medium and receptor in face-to-face relation. An air-tight enclosure can be utilized for enclosing the imaging medium and plate receptor and for maintaining the assemblage under conditions free of dust and debris. A packaged assemblage of this character is disclosed in the application of Ernest W. Ellis, for MASS TRANSFER IMAGING MEDIA AND METHODS OF MAKING AND USING THE SAME, U.S. Ser. No. 08/421,757, filed April 14, 1995. The following are examples representative of the present invention and are intended as being illustrative and not limitative. Except where otherwise indicated, all proportions are by weight. EXAMPLE 1

This example describes the production of a composite ablation- transfer imaging medium for the production therefrom of a lithographic printing plate having an image (printing) pattern in cross-linked epoxy resin. A composite ablation-transfer imaging medium was prepared in the following manner. Onto a polyester substrate (a sheet of polyethylene terephthalate having a thickness of 0.076 mm.), there was applied by vacuum deposition an aluminum/aluminum oxide layer having a thickness of about 80 Angstroms. There was then applied onto the metallized surface of the polyester sheet (using a #4 Meyer coating rod) a cyan pigment layer having a thickness of about 0.06 micron, applied from a coating having the following ingredients in the stated parts by weight:

Ingredients Parts bv Weight

Pigment Blue (copper phthalocyanine) 0.442

Nitrocellulose (dispersant) 0.33

Epoxy vegetable fatty acid ester

(Vikoflex 4050 dispersant/plasticizer;

Elf atochem, Bloomington, Minnesota) 0.086

Dibutyl phthalate 0.046

Ethyl acetate 0.719

Ethanol 58.00

Isopropanol 30.68

Butanol 9.70

Onto the cyan pigment layer obtained by drying the above- described coating in an oven at 80°C for about two minutes, there was applied a radiation-ablative layer of approximately 0.6 micron thickness. The radiation- ablative layer was applied by coating the following composition and allowing the coating to dry for about two minutes in an oven at 80°C:

Ingredients Parts by Weight

3 ,4-Epoxycyclohexylmethyl-3 ,4- epoxycyclohexane carboxylate (UVR- 6110, Union Carbide Chemicals and

Plastics Company, Inc. 1.23

Epichlorohydrin/tetraphenylol ethane epoxy resin (EPON Resin 1031, Shell

Chemical Company 4.02

Mixed triarylsufonium hexafluoroantimonate salts (cationic photoinitiator, UVI-6974 from Union Carbide Chemicals and Plastics

Company, Inc.) 1.05

IR-absorbing dye (Cyasorb IR165, Glendale Protective Technologies, Inc.,

Lakeland, Florida) 0.70

Methyl ethyl ketone 23.25

Cyclohexanone 23.26

Ethylacetate 46.50

The ablation-transfer imaging medium obtained in the aforedescribed manner was utilized in the production of a lithographic printing plate. The composite imaging medium was placed in face-to-face registration with the hydrophilic surface of a surface-grained and anodized aluminum printing plate substrate. The resulting imaging medium/aluminum plate combination was placed onto the internal surface of the drum of a laser imaging apparatus, the polyester side of the imaging medium being outermost for exposure therethrough with a YAG laser emitting at a wavelength of about 1060 nanometers. Vacuum was applied to the imaging medium and aluminum plate combination to achieve good face-to-face contact and to hold the combination securedly to the drum surface. The YAG laser irradiation was directed by a rotating polygonal mirror onto the imaging medium for imagewise exposure through the polyester side of the imaging medium. The YAG laser was activated using digitized signals representative of the desired image information. The imaging medium was scanned by the laser at a speed of 140 meters/second (1333 dots/cm., 200 lines/inch). The laser power was about 4.5 watts (about 10 micron diameter beam; full width half maximum).

After imagewise irradiation, the imaging medium and aluminum plate were separated. The aluminum plate carried an imagewise recordation in image contrast providing material. The image pattern was readily visible and of color and hue characteristic of the cyan (phthalocyanine) pigment. The thus- recorded printing plate was then subjected to a curing step comprising infrared radiation from an IR tube and ultraviolet radiation from an array of UV lamps. The cured printing plate was then finished in conventional manner (using Kleergum) and placed onto the cylinder of a printing press for the conduct of lithographic printing .

The printing plate showed blue imaging (printing) areas characteristic of the cyan pigment utilized in the composite ablation-transfer imaging medium. The printing plate was used on a duplicator (business forms) press for printing (using conventional lithographic fountain solution and printing ink) onto paper. The plate was utilized for a run length of 80,000 impressions. The characteristic color of the cyan pigment remained substantially stable, i.e., unaffected, as evident from the still clearly visible color of the plate at completion of the print run.

A printing plate having the same order and arrangement of layers as described in EXAMPLE 1 was prepared by utilizing a composite imaging medium incoφorating, in place of the solvent dispersion coated Pigment Blue layer thereof, a layer of Pigment Blue (50 Angstrom thickness) deposited by vacuum vapor deposition. The plate showed the coloration characteristic of the Pigment Blue (phthalocyanine) pigment.

EXAMPLE 2

A composite ablation-transfer imaging medium was prepared in the manner described in EXAMPLE 1, except that, in lieu of the image contrast- providing (radiation-ablative) layer thereof, there was provided the radiation- ablative image contrast-providing layer obtained by coating onto the cyan layer (using a #6 Meyer coating rod) the following composition:

Ingredients Parts by Weight

3,4-Epoxycyclohexylmethyl-3,4- epoxycyclohexane carboxylate (UVR- 6110, Union Carbide Chemicals and

Plastics Company, Inc. 1.06

Epichlorohydrin/tetraphenylol ethane epoxy resin (EPON Resin 1031, Shell

Chemical Company 3.45

Mixed triarylsufonium hexafluoroantimonate salts (cationic photoinitiator, UVI-694 from Union

Carbide Chemicals and Plastics

Company, Inc.) 1.06

Poly(methylmethacrylate); NeoCryl B-

728 from ICI Resins US, Wilmington,

Massachusetts; 15% solution in methyl ethyl ketone 8.40

IR-absorbing dye (Cyasorb IR165) 0.70

Cyclohexanone 13.87

Diethyl ketone 32.37

Methyl ethyl ketone 39.10

The printing plate obtained after laser induced ablation transfer and curing (all in the manner described in EXAMPLE 1) was utilized for printing onto paper. The characteristic cyan color was evident immediately upon production of the plate and endured throughout the printing run. The printing run length was 25,000 impressions, at which time major printing defects became evident.

EXAMPLE 3

This example illustrates the production of a composite ablation- transfer imaging medium incoφorating a blue organic dye colorant material.

A polyester film material carrying a layer of aluminum/aluminum oxide was prepared in the manner of EXAMPLE 1. A layer of organic dye material was deposited onto the metallized surface, by coating the following composition, using a #4 Meyer coating rod: Ingredients Parts bv Weight Luxol Fast Blue ARN 1.00

Ethanol 19.80

Isopropanol 39.60

2-Butanol 39.60

Using a #6 Meyer coating rod, a radiation-ablative contrast image providing layer was deposited onto the Luxol Fast Blue ARN layer, by coating and spreading a composition having the ingredients and parts by weight specified in EXAMPLE 1. Upon drying of the layer, the imaging medium was laser irradiated in the manner described in EXAMPLE 1 for the production of a plate which upon curing in the manner therein described was used on a printing plate for the printing of paper. A printing run length of less than 5,000 printing impressions was obtained. The characteristic blue of the dye employed in the imaging medium was immediately visible in the image (printing) areas of the printing plate. Upon completion of the printing run, the blue color was diminished in intensity relative to the initial coloring of the image areas.

EXAMPLE 4

A composite ablation -transfer imaging medium was prepared in the manner described in EXAMPLE 3, except that, the radiation-ablative layer was a layer obtained by coating (using a #6 Meyer rod) the composition described in EXAMPLE 2. The imaging medium was exposed to laser irradiation for transfer by ablation to an aluminum plate and the resulting plate was cured for the production of a lithographic printing plate, all in the manner described in EXAMPLE 1.

Inspection of the plate after ablation transfer showed image quality to be Good (less than 20 small visible spots of less than 0.25 cm. diameter, resulting from non-transfer). Observed coloration of image areas was characteristic of the Luxol Fast Blue ARN dye material.

EXAMPLE 5

This example illustrates the production of a composite ablation- transfer imaging medium useful for the production therefrom of a lithographic printing plate having image (printing) areas in photopolymerized ethylenically unsaturated monomer (trimethylolpropane triacrylate).

Polyester carrying layers, respectively, of aluminum/aluminum oxide and Pigment Blue were prepared in the manner described in EXAMPLE 1. Onto the cyan pigment layer, there was deposited (using a #6 Meyer coating rod) a photopolymerizable monomer-containing layer having the following composition:

Ingredients Parts bv Weight

NeoCryl B-728 poly(methyl- 4.2515 methacrylate) p-Methoxyphenol 0.0018

UV Photoinitiator (2,2-dimethoxy-2- phenylacetophenone, Irgacure 651 ,

Ciba Geigy Co.) 0.5226

Antioxidant (Tetrakis{methylene(3,5- di-tert-2 butyl-4- hydroxhyrocinnamate) } methane,

Irganox 1010, Ciba Geigy Co.) 0.0170

Irganox 1035 (Thiodiethylene bis-(3-5 di-tert-butyl-4 hydroxy) hydrocinnamate, Ciba Geigy Co.) 0.0170

Trimethylolpropane triacrylate 1.4901

Cyasorb IR-165 0.7000

Cyclohexanone 13.9500

Diethyl ketone 32.5500

Methyl ethyl ketone 46.5000

The resulting composite imaging medium was brought into face-to- face relation with an aluminum printing plate substrate material and was imaged, all in the manner described in EXAMPLE 1. An image in blue color was readily observable on the printing plate substrate. The image areas (in polymerizable material) were polymerized/cross-linked by exposure of the plate to ultraviolet irradiation from an array of UV lamps. The plate was then heat cured using an IR tube. The resulting printing plate was inspected for the image quality of the printing areas on the plate and judged to be between Good and Poor, where Good indicates the formation of some (less than 20) small (less than 0.25 cm.) visible spots due to non-transfer; and Poor indicates the presence of more than 20 spots of less than 0.25 cm. or large areas (> one cm.) of non-transfer.

EXAMPLE 6

This example illustrates the production of a composite ablation- transfer imaging medium including a colorant precursor convertible after ablation transfer to a colored species.

Onto a polyester carrying an aluminum/aluminum oxide dynamic release layer (prepared in the manner of EXAMPLE 1) there was applied a layer of leuco crystal violet, having a thickness of about 0.15 microns and coated from a 2% solution in methyl ethyl ketone. Upon drying of the layer, there was coated thereon an epoxy-based contrast image-providing layer having the composition of the contrast image-providing layer specified in EXAMPLE 1. The resulting composite imaging medium was placed into face-to-face contact with a lithographic aluminum substrate receptor and exposed to laser irradiation in the manner described in EXAMPLE 1, to provide image areas on the plate. Inspection of the imaged plate showed image quality to be Excellent (no visual defects). Image areas were of a light brown coloration. Replicate samples of the plate were subjected to various treatments for conversion of the light-brown colored image areas to a more readily observable coloration. Samples subjected to the irradiation from conventional ambient office fluorescent lighting (for two hours) showed image areas in blue. Samples subjected to the irradiation of an array of ultraviolet lamps showed the blue coloration indicative of the conversion of the leuco crystal violet material to a colored species. Samples which had been subjected to ambient office fluorescent lightening, and then either (1) exposure to an infrared-irradiating tube or (2) a combination of simultaneous ultraviolet lamp and infrared tube treatments, showed conversion to a deeper blue color.

What is claimed is:

Claims

1. A composite ablation-transfer imaging medium for providing a visually observable transfer image in contrast imaging material on an image receptor which comprises, in order: a support substrate transparent to imagewise radiation; a thin-film metal or metal oxide dynamic release layer; a layer for delineating an image pattern on said image receptor, said layer comprising a uniform dispersion of visually observable pigment colorant particles in a binder; and a radiation-ablative layer attached firmly to said layer containing said colorant pigment particles, said radiation-ablative layer including a contrast image-providing oleophilic ink-receptive polymer or precursor thereof; said dynamic release layer being capable of absorbing said radiation at a rate sufficient to effect imagewise ablation transfer to a contiguous image receptor of the volume of at least said radiation-ablative layer and said pigment colorant particles and binder in areas subjected to said radiation; said pigment colorant particles delineating said image pattern in said areas on said image receptor.

2. The composite ablation-transfer imaging medium of Claim 1 wherein said pigment colorant particles comprise phthalocyanine pigment particles.

3. The composite ablation-transfer imaging medium of Claim 1 wherein said radiation-ablative layer includes at least one material convertible to said oleophilic polymer during said imagewise ablation transfer to said contiguous image receptor or by treatment of said image receptor including said image pattern subsequent to said imagewise ablation transfer.

4. The composite ablation-transfer imaging medium of Claim 3 wherein said at least one material comprises reactive components for photoirradiation-induced formation in said image pattern subsequent to said imagewise ablation transfer of an oleophilic ink-receptive polyepoxide.

5. The composite ablation-transfer imaging medium of Claim 3 wherein said at least one material comprises reactive components for photoirradiation-induced formation in said image pattern subsequent to said imagewise ablation transfer of an oleophilic ink-receptive polymer having polymerized units of an ethylenically unsaturated monomer.

6. The composite ablation-transfer imaging medium of Claim 5 wherein said reactive components comprise a macromolecular organic binder, a photopolymerizable ethylenically unsaturated monomer having at least one terminal ethylenic group capable of forming a high polymer by free-radical initiated, chain-propagated addition polymerization, and a free-radical generating, addition polymerization-initiating system activatable by actinic radiation.

7. The composite ablation-transfer imaging medium of Claim 1 wherein said radiation-ablative layer includes at least one laser absorber/sensitizer which absorbs in the near infrared spectrum region of the electromagnetic spectrum.

8. A method of making a lithographic printing plate which comprises: placing a lithographic printing plate receptor into contiguous registration with a composite ablation-transfer imaging medium; said composite ablation-transfer imaging medium comprising, in order: a support substrate transparent to imagewise radiation; a thin-film metal or metal oxide dynamic release layer; a layer for delineating an image pattern on said printing plate receptor, said layer comprising a uniform dispersion of visually observable pigment colorant particles in a binder; and a radiation-ablative layer attached firmly to said layer containing said colorant pigment particles, said radiation- ablative layer including a contrast image-providing oleophilic ink-receptive polymer or precursor thereof; said dynamic release layer being capable of absorbing radiation at a rate sufficient to effect imagewise ablation to a contiguous printing plate receptor of the volume of at least said radiation-ablative layer and said pigment colorant particles and binder in areas subjected to said radiation; irradiating said ablation-transfer imaging medium imagewise according to a pattern of intelligence, with an intensity sufficient to effect the imagewise ablation mass transfer of the volume of the image-wise exposed areas of at least said radiation-ablative layer with said pigment colorant particles and binder anchored firmly thereto onto said lithographic printing plate receptor.

9. The method of Claim 8 including the step of holding printing plate receptor substrate and said composite ablation-transfer imaging medium in said contiguous registration by a vacuum.

10. The method of Claim 8 wherein said step of irradiating is performed by exposure through said transparent support substrate with laser irradiation in the near infrared region of the electromagnetic spectrum.

11. The method of Claim 8 wherein in said radiation-ablative layer of said composite ablation-transfer imaging medium there is included at least one laser absorber/sensitizer which absorbs in the near infrared region of the electromagnetic spectrum.

12. The method of Claim 8 wherein said lithographic printing plate receptor substrate comprises a grained hydrophilic aluminum substrate.

13. The method of Claim 8 wherein said pigment colorant particles comprise phthalocyanine pigment particles.

14. The method of Claim 8 wherein said radiation-ablative layer includes at least one material convertible to said oleophilic polymer during said step of irradiating or by treatment of said printing plate receptor substrate including said image pattern subsequent to said step of transferring said areas.

15. The method of Claim 14 wherein said at least one material comprises reactive components for photoirradiation-induced formation in said image pattern, subsequent to said step of transferring said areas, of an oleophilic ink-receptive polyepoxide.

16. The method of Claim 14 wherein said at least one material comprises reactive components for photoirradiation-induced formation in said image pattern subsequent to said imagewise ablation transfer of an oleophilic ink- receptive polymer.