HK1050878A - Imaging media containing heat developable photosensitive microcapsules - Google Patents

Description

Imaging media containing thermally developable photosensitive microcapsules

BackgroundInformation of related applications

This application claims priority from provisional patent application No. 60/208,517 filed on 6/1/2001, which is incorporated herein by reference.

The present invention relates to a thermally printable imaging material comprising a chromogenic precursor encapsulated in a photosensitive microcapsule.

Related Art

Photohardenable imaging systems employing microencapsulated radiation-sensitive components are the subject of U.S. Pat. Nos. 4,399,209, 4,416,906, and 4,440,846. These imaging systems are characterized by imagewise exposure of an imaging sheet comprising a layer of microcapsules containing a photohardenable component in the internal phase to actinic radiation. In the most typical embodiment, the photohardenable component is a photopolymerizable component that includes a polyethylenically unsaturated compound and a photoinitiator, and is encapsulated with a chromogenic material. Exposure to actinic radiation may harden the internal phase of the microcapsules. After exposure, the imaging sheet is pressed by a pair of nip rollers to apply a uniform destructive force treatment.

U.S. patent No. 4,440,846 discloses a self-contained imaging sheet in which encapsulated color-developing and developer materials are co-attached as a single layer or adjacent two layers to one surface of a single substrate. After imagewise exposing the imaged sheet and passing the sheet through a pressure roller to apply pressure, the microcapsules rupture and release the internal phase in the form of an image, whereupon the chromogenic material migrates into the developer material, reacts with the developer material and forms a color image.

Variations of the above-described methods for making full color images are also described, as described in U.S. Pat. Nos. 4,772,530 and 4,772,541. In a color system, photosensitive microcapsules containing multiple dyes that form cyan, magenta, and yellow are layered on a support and exposed to red, green, and blue light. The capsule containing the blue-green precursor is subjected to light hardening through red light exposure; the capsules containing the magenta precursor are photohardened by green light exposure and the capsules containing the yellow precursor are photohardened by blue light exposure. Selectively exposing the capsule layer to light of different wavelengths and then rupturing the unexposed capsules can cause the dye in the capsules to produce a full color image on the support sheet after contact with an appropriate developer.

U.S. patent No. 5,783,353 also discloses a self-contained imaging assembly capable of producing full color images as described above wherein a composition comprising photohardened microcapsules and a developer material is disposed between a first transparent support and a second support which may be opaque or transparent, thus forming a sealed assembly. Exposing said assembly to actinic radiation and applying a uniform rupturing force to obtain an image in said assembly, wherein the image is visible on the second opaque support when viewed through the first transparent support and a transparent image if the second support is transparent.

One major drawback associated with the above system is that no mechanism is available to fix the image after the capsules are ruptured (opened) and the dye precursors contact the developer. The image contrast thus becomes stronger after printing resulting in poor preservation of mid-tone (mid-tone) images. In addition, the process has a relatively low printing rate, poor environmental stability and reproducibility, and relatively low resolution due to the large microcapsule size (up to 15 microns) required for destruction and the need for larger capsule rupturing equipment, as described, for example, in U.S. patent No. 5,550,627.

Thermal techniques have been used to generate images using microencapsulated color precursors. U.S. patent No. 4,598,035 discloses a heat-sensitive recording material comprising a support having on one surface thereof an image-forming layer comprising a plurality of microcapsules containing a precursor of a colorant in a binder containing a color developer or color former. The imaging layer is selectively imagewise heated by contact with a thermal recording head such that the colorant precursor and/or developer selectively penetrates the microcapsule wall only in the heated areas to produce a color image.

For color applications, a support comprising three separate imaging layers comprising a microencapsulated diazonium salt or leuco dye and an unencapsulated coupler or developer dispersion capable of forming yellow, magenta, and blue-green images upon contact of the coupler or developer with the diazonium salt or leuco dye has been proposed. The encapsulating material in each layer is designed to be sensitive to different levels of thermal energy so that the topmost yellow layer is selectively activated by thermal head contact at low thermal energy, the middle magenta layer is selectively activated by thermal head contact at medium thermal energy in the form of an image, and the bottom cyan layer is finally activated by higher thermal energy contact. After the respective thermal contacts in the first two steps, the structure is exposed to uv light to decompose the diazonium salt, thereby fixing the yellow and magenta images. This type of multicolor image is disclosed in U.S. patent No. 5,168,029.

Thermal processes of the type described above require complex imaging materials and can suffer from printing/temperature variations, resulting in poor image quality and image reproducibility. In addition, the need to precisely vary and adjust the temperature and thermal energy in the print head to imagewise thermally treat the heat exposed layer necessarily slows the process.

Brief description of the invention

According to the present invention, there is provided a heat-sensitive recording sheet comprising a support layer comprising a transparent sheet, and a heat-sensitive imaging layer disposed on one surface of the first support layer, said imaging layer comprising a mixture of:

i) multiple photosensitive microcapsules comprising a polymeric base or wall material, and a photosensitive polymer

A co-or photo-crosslinking compound, a photoinitiator and a color dye precursor;

ii) a finely divided particulate developer or colour former material which has a melting point or melt flow

The temperature is higher than 70 ℃, and the reaction is carried out to form color when the precursor is contacted with the color precursor; the microcapsules are characterized by being sufficiently high above the glass transition temperature of the polymeric substrate or wall material to form an image during imaging when the recording sheet is heated to a temperature above the melting point or melt flow temperature of the developer or color former, and by being impermeable to the developer or color former material after the microcapsules have been photohardened by exposure to imagewise actinic radiation and the recording sheet has been heated to a temperature above the melting point or melt flow temperature of the developer or color former during imaging. The present invention also provides a thermal imaging process for forming a monochromatic or polychromatic image, comprising:

a) provided is a heat-sensitive recording sheet comprising:

i) a first support layer composed of a transparent sheet;

ii) a thermal slip layer disposed on a surface of the first support layer;

iii) a thermally sensitive imaging layer disposed on an opposite surface of the first support layer; and

iv) a second opaque or transparent sheet adhered to the heat sensitive imaging layer;

the imaging layer comprises a mixture of: (1) a plurality of photosensitive microcapsules comprising a polymeric wall material or substrate, a photosensitive polymeric or photocrosslinkable component, a photoinitiator as an internal phase and a color dye precursor, and (2) a finely divided particulate developer or color former material having a melting point or melt flow temperature in excess of 70 ℃ that reacts to form color upon contact with the color precursor;

b) imagewise exposing the recording sheet to a pattern of actinic radiation, wherein microcapsules sensitive to said radiation are selectively photohardened; and

c) heating the recording sheet to a temperature above the melting point or melt flow temperature of the developer to cause the developer to flow into contact with said microcapsules, wherein the photohardened microcapsules are impermeable to the developer material and the non-photohardened microcapsules are permeable to the developer material sufficient to form a colored image.

The heat-sensitive recording sheet of the present invention features a self-contained imaging assembly capable of producing a color image in two simple steps: 1) imagewise exposing the heat-sensitive recording sheet to actinic radiation, followed by 2) uniformly and rapidly heating the exposed heat-sensitive recording sheet at low pressure to a temperature above the melting point or melt flow temperature of the developer or coupler, for example by contact with a thermal print head, sufficient to develop an image. The method is significantly simpler and faster than the prior imaging methods described above, and does not require the use of high pressure rollers or other types of microcapsule rupturing equipment, registration mechanisms for multiple pass thermal printing, narrow band uv light sources, or multiple image layers. The images produced by the system of the present invention have high density, excellent resolution, and good mid-tone image preservation.

The imaging assemblies of the present invention can be exposed to form an image in any suitable exposure apparatus. The imaging assembly of the present invention is particularly suited for exposure using liquid crystal arrays or light emitting diodes driven with computer generated signals or with video signals to reproduce images from video recorders, cameras, or the like.

Brief description of the drawings

Fig. 1 is a schematic cross-sectional view of a recording sheet according to the present invention;

FIG. 2 is a schematic cross-sectional view of another different specific embodiment of a recording sheet according to the present invention; and

fig. 3 is a schematic cross-sectional view of an imaging layer present in a recording sheet according to the present invention.

Detailed Description

Referring to FIG. 1, the illustrated recording sheet 10 includes a first transparent support sheet 12 having a thermal slip layer 14 disposed on one surface and a color-developing imaging layer 16 disposed on an opposite surface. On the imaging layer 16, a second opaque or transparent sheet material 20 is adhered.

Referring to FIG. 2, another embodiment is shown, a recording sheet 11 comprising the structures 14, 12, 16, and 20 described above, except that an adhesive layer 18 is interposed between the imaging layer 16 and the second sheet 20. Adhesive layer 18 may also contain heat sensitive color chemicals, as described below. Immediately adjacent the outer surface of the sheet layer 20 is an optional pressure sensitive adhesive layer 22 with or without a releasable backing layer.

The transparent sheet that can be used to make the heat-sensitive recording sheet is selected from plastic films or transparent papers having a thickness of about 0.5 to 50 micrometers, preferably about 2 to 20 micrometers, preferably about 3 to 8 micrometers. There is no limitation on the plastic film used. Particularly suitable are synthetic resin transparent films including polyethylene terephthalate (pet), polybutylene terephthalate (pbt), polyethylene naphthalate (pet) and other polyester films, polycycloolefin films, polycarbonate films, polyamide films, polysulfone films, polyethersulfone films, polyetherketone films, polyetherimide films, polyphenylene sulfide films, polyester ether films, polyamide-imide films, fluorocarbon resin films, polyurethane films, acrylic films, and others. These films may be used alone or in a form of being stuck to each other. The preferred film material is a polyethylene terephthalate (PET) film that is biaxially oriented during the film manufacturing process.

Particularly useful membranes are pretreated on one or both sides thereof by the membrane manufacturer with a clear primer (thickness of 0.05 to 0.15 microns) to impart hydrophilic properties to the membrane surface. These primers include acrylic, or methacrylic, and/or ester copolymers, amorphous polyesters, polyurethanes, polyvinyl acetates, polyvinyl alcohols, and similar hydrophilic materials. These primers can enhance the adhesion of certain coatings subsequently applied to the film surface. Another effective technique to enhance adhesion prior to application of subsequent coatings is to treat the film surface with corona or plasma discharge.

In a preferred embodiment of the present invention, a transparent heat slip layer 14 is coated on one surface of the transparent sheet 12. The purpose of this layer is to reduce friction or drag on the film surface when the film is in close proximity or in contact with the thermal print head during the imaging procedure. Suitable materials are relatively stable and do not become sticky at printhead temperatures of about 200-400 c and can be used to reduce the dynamic coefficient of friction between the recording sheet and the printhead to below 0.35, preferably below 0.25. Suitable lubricating materials include waxes, polysiloxanes (silicone oils), phosphates, fatty acid salts, long chain fatty acid esters or amides, fluorinated polymers such as polytetrafluoroethylene (Teflon @), silicone containing polymers such as acrylate silicone graft copolymers, graphite powder and the like. These substances can be applied directly to the membrane surface in the form of a solution or dispersion in water or an organic solvent and dried.

In many cases, it is desirable to use these lubricants in combination with a binder resin component to form a slip layer that can improve the thermal stability of the surface of the recording sheet. Suitable thermally stable binders are crosslinkable polymers formulated with suitable crosslinkers, the components are coated onto a transparent sheet and dried at elevated temperatures to form a thermoset slip layer. Suitable polymers are those containing free hydroxyl groups and which can be crosslinked with polyisocyanates such as toluene diisocyanate; or polymers containing free acid groups which can be crosslinked using polyfunctional amines such as melamine or urea. Suitable such polymers include cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polyester urethane, polyvinyl butyral, urethane, or epoxy prepolymer and the like. Polymers curable by ultraviolet or electron beam radiation, as well as polymers obtained by the photopolymerization of monomers such as epoxy acrylates, can also be used. The binder-containing slip layer may contain from about 1 to about 35 weight percent, preferably from about 5 to 30 weight percent, of a lubricant on a dry weight basis. The remainder of the layer contains the binder polymer, crosslinking agent (if any), and 0-20% of other conventional additives such as antistatic agents, fillers, antioxidants, and the like. The slip layer must also be optically transparent.

These binder-containing slip layers, which comprise a mixture of a polymer that is soluble or dispersible in a suitable organic solvent or water, one or more of the foregoing lubricants, and a suitable crosslinking agent and other conventional additives, can be applied to the surface of a transparent sheet in solution and dried at a temperature sufficient to form a thermoset coating on the surface of the film, ranging from about 50 ℃ to 150 ℃. Such adhesive-containing slip layers may be applied at a dry coating thickness of about 0.1 to 5 microns, or a dry coating weight of 0.1 to 5 grams solids per square meter. It is advantageous to apply the slip layer to the surface of the first support layer and to cure it before applying the color-developing development layer described below, since this eliminates the possibility of thermally induced color-developing reactions occurring.

Slip layers of substrate coatings for thermal transfer printing materials are more fully described in U.S. patent nos. 4,950,641, 5,130,293, 5,277,992, and 5,372,988, the contents of which are incorporated herein by reference.

A color-developing layer 16, hereinafter referred to as an imaging layer, is coated on the surface of the transparent sheet material 12 opposite the slip layer 14. This imaging layer may consist of a single layer or may comprise two layers placed adjacent to each other. The layer contains chemicals that enable the formation of a black or color image within the layer by selective image exposure of the recording sheet to actinic radiation through the slip layer 14 and the support sheet 12, followed by heating of the recording sheet.

As shown in fig. 3, imaging layer 16 comprises a combination of photosensitive microcapsules 31 and finely divided particulate developer material 32 having a melting point or melt flow temperature in excess of 70 c, preferably between 80 c and 250 c, preferably between 90 c and 200 c, optionally dispersed in or associated with a thermoplastic polymer binder 33.

The photosensitive microcapsules 31 comprise a polymeric wall material or substrate, and a photo-polymerization or photo-crosslinking component, a suitable photoinitiator and a color dye precursor as an internal phase. Optionally a crystalline plasticizer, or a thermal solvent, or a heat sensitive agent is added to the internal phase to improve heat sensitivity.

Photopolymerizable or photocrosslinkable components useful in the present invention include multivalent monomeric or oligomeric materials containing vinyl unsaturation that are capable of undergoing a crosslinking reaction via free radical addition polymerization, ionic polymerization, thiol-ene reaction, intercalation, or [2+2] addition reaction. In one embodiment of the invention, the ethylenically unsaturated groups are grafted onto the polymeric wall material or substrate of the microcapsule.

Typical examples of free radical addition polymerizable or crosslinkable compounds for use in the present invention are ethylenically unsaturated compounds, and more particularly, polyethylenically unsaturated compounds. These compounds include monomers having one or more ethylenically unsaturated groups (e.g., vinyl or allyl groups), as well as polymers having terminal or pendant ethylenically unsaturated groups. These compounds are well known in the art and include the acrylate and methacrylate esters of polyhydric alcohols (e.g., trimethylolpropane, pentaerythritol, and the like); and acrylate or methacrylate terminated epoxy resins, acrylate or methacrylate terminated polyesters or polyurethanes, vinyl benzene, vinyl ether, or maleimide terminated oligomers, or polymers and the like. Representative examples include trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, dipentaerythritol hydroxypentaacrylate (DPHPA), tris- (2-hydroxyethyl) isocyanurate triacrylate, 1, 2, 4-butanetriol trimethacrylate, 1, 4-cyclohexanediol diacrylate, 1, 4-benzenediol dimethacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, dipentaerythritol hydroxypentaacrylate (DPHPA), diethylenetriamine tri-methacrylamide; vinyl esters such as divinyl succinate, divinyl adipate, di-vinyl phthalate, di-vinyl terephthalate, and divinylbenzene. Acrylate or methacrylate end-position oligomers, such as epoxies, urethanes, polyethers, and polyesters are also known in the art and may be described in "Radiation Curing of polymeric materials," edited by c.e. hoyle and j.f. kintle, syacs mposium series, vol.417 (1990). A variety of commercially available acrylate or methacrylate terminal oligomers suitable for use herein are available from Sartomer, Radcure, Henkel, or UCB Chemicals.

In addition, monofunctional monomers can also be used to improve the physical properties of the photopolymerizable compounds. Preferred monofunctional monomers suitable for this application are high boiling, water immiscible monomers such as stearyl acrylate, lauryl acrylate, and polypropylene glycol monoacrylate.

It is important that the photopolymerizable or photocrosslinkable monomer or oligomer should not penetrate or soften the microcapsule wall during storage. Particularly preferred monomers are monovinyl unsaturated monomers which also contain functional groups capable of reacting with the wall components during microcapsule manufacture, such as isocyanate, thiol, hydroxyl, epoxy, carboxyl, or amino functional groups. Such monomers include 2-isocyanatoethyl acrylate and methacrylate, TMI (from CynamideCo., USA), hydroxyalkyl acrylates and methacrylates, glycidyl acrylate, and methacrylates, acrylamido methyl glycolate, acetoacetoxyethyl-methacrylate, and the like. In a preferred embodiment, the functionalized monomer is pre-reacted with the wall material (e.g., polyfunctional isocyanate) prior to the emulsification step of microencapsulation. The monomer is grafted to the wall of the microcapsule, whereby bleeding from the inside of the microcapsule during storage can be prevented.

Typical examples include polyhalogenated compounds such as bis- (trichloromethyl) triazine and its derivatives, 1-dimethyl-3, 5-diketocyclohexane, and organosulfur alcohols such as 2-mercaptobenzoxazole, 2-mercaptobenzimidazole, and disulfide derivatives thereof, pentaerythritol tetra- (mercaptoacetate). other useful compounds that can be used as chain transfer agents in photopolymerizable or photocrosslinkable components include α -dimers of methylstyrene, compounds containing allyl and benzylic hydrogens such as cumene, (e) acetals, (f) aldehydes, (g) amides as described in Maclachlan, U.S. Pat. No. 3,390,996, column 12, lines 18 to 58.

To reduce the viscosity of the internal phase and to aid the rate of color development in the emulsification step of microencapsulation, high boiling organic solvents or plasticizers can be used. Examples include tricresyl phosphate, trioctyl phosphate, octyldiphenyl phosphate, tricyclohexyl phosphate, dibutyl phthalate, dioctyl phthalate, dilauryl phthalate, dicyclohexyl phthalate, butyl oleate, diethylene glycol benzoate, dioctyl sebacate, dibutyl sebacate, dioctyl adipate, trioctyl benzenetricarboxylate, octyl maleate, dibutyl maleate, isoamyl biphenyl, or other alkylated biphenyls, alkylated terphenyls, chlorinated paraffins, diisopropylnaphthalenes, 1' dirrollylethane, polypropylene glycol, and polybutylene glycols. Particularly preferred plasticizers are crystalline compounds having a melting point between 70 ℃ and 200 ℃, preferably between 90 ℃ and 150 ℃. Examples of crystalline plasticizers include 1, 2-bis (3, 4-dimethylphenyl) ethane, stearamide, beeswax, terphenyl, diphenyl phthalate, dicyclohexyl phthalate, and glycerol tribenzoate.

Preferred photoinitiators for use in the present invention are ionic dye-reactive counter ion photosensitizers which are selectively photosensitive in the spectral range of about 400 up to 700 nm.

Preferred photoinitiators are cationic dye-borate anion compounds, as shown in formula (I):

wherein D⁺Represents a cationic dye; r₁，R₂，R₃，R₄May be the same or different and each represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstitutedSubstituted alkenyl, substituted or unsubstituted alkynyl, or substituted or unsubstituted heterocyclyl, and R₁，R₂，R₃，R₄Two or more of which may be joined to each other to form a ring structure.

R₁To R₄The alkyl group represented includes a linear, branched, or cyclic alkyl group, and preferably has 1 to 18 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, octyl, stearyl, cyclobutyl, cyclopentyl, cyclohexyl, and the like. R₁To R₄The substituted alkyl group represented includes the above-mentioned alkyl groups having a substituent such as a halogen atom, e.g., a chlorine atom, a bromine atom, etc.; a cyano group; a nitro group; a hydroxyl group; an alkoxy group; aryl, preferably phenyl; a hydroxyl group; -N ═ R₅R₆Wherein R is₅And R₆Each represents a hydrogen atom, an alkyl group having 1 to 14 carbon atoms, or an aryl group; -COOR₇Wherein R is₇Represents a hydrogen atom, an alkyl group having 1 to 14 carbon atoms, or an aryl group; -OCOR₈Radical, OR-OR₈Wherein R is₈Represents an alkyl group having 1 to 14 carbon atoms, or an aryl group.

R₁To R₄The aryl group represented includes aryl groups having 1 to 3 rings, such as phenyl, naphthyl and the like, and R₁To R₄The substituted aryl group represented includes the above-mentioned aryl groups having the same substituent as the above-mentioned alkyl group or alkyl group having 1 to 14 carbon atoms.

R₁To R₄The alkenyl group represented includes a straight chain, branched chain, or cycloalkenyl group having 2 to 18 carbon atoms, and the substituent of the alkenyl group includes the same substituents as the above-mentioned alkyl group.

R₁To R₄The alkynyl group represented includes a straight-chain or branched alkynyl group having 2 to 18 carbon atoms, and the substituent of the alkynyl group includes the same substituents as the above-mentioned alkyl group.

R₁To R₄The heterocyclic group represented includes a 5-or more-membered ring, preferably a 5-to 7-membered ring, containing at least one atom selected from the group consisting of N, S, and OAnd the heterocyclic ring may contain a condensed ring. The substituent of the heterocyclic group includes the same substituents as those of the above-mentioned aryl group.

The borate anion in formula (I) is designed to generate a borate radical upon exposure to light and to dissociate smoothly upon electron transfer to the dye to form a radical, as shown below:

wherein R may be R as defined above₁、R₂、R₃Or R₄。

By way of example, particularly preferred anions are triphenylbutyl borate and trianilino butyl borate anions, since they can readily dissociate into triphenylborane or trianilino borane, and a butyl radical. On the other hand, tetraphenylborate anion is undesirable because it does not readily form phenyl radicals.

Preferably, R of the formula (I)₁、R₂、R₃And R₄At least one but not more than three of which are alkyl groups. Each R₁、R₂、R₃And R₄May contain up to 20 carbon atoms, and they typically contain from 1 to 7 carbon atoms. Preferably, R₁、R₂、R₃And R₄Is a combination of an alkyl group and an aryl group, or an aralkyl group, and a combination of three aryl groups and one alkyl group is preferable. Examples of preferred borate anions represented by formula (I) include triphenylbutylboronAcid radicals, tri-anisylbutyl borate, and tris (2, 3, 4,5, 6-pentafluorophenyl) butyl borate, tetrakis (2, 3, 4,5, 6-pentafluorophenyl) borate, tris- (3-fluorophenyl) -butyl borate, and tris- (3-fluorophenyl) -hexyl borate.

R₁-R₄Representative examples of alkyl groups represented are methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, and stearyl. The alkyl group may be substituted, for example, with one or more halogen, cyano, acyloxy, acyl, alkoxy, or hydroxyl groups.

R₁-R₄Representative of the aryl radicalsIllustrative examples include phenyl, naphthyl, and substituted aryl groups such as anisyl. Alkylaryl groups include tolyl and dimethylphenyl. Representative examples of aralkyl groups include benzyl. Representative alicyclic groups include cyclobutyl, cyclopentyl, and cyclohexyl. Examples of alkynyl groups are propynyl and ethynyl, and examples of alkenyl groups include ethenyl.

Useful dyes will form photoreducible, but light-resistant complexes with borate anions, and can be cationic methine dyes, polymethine dyes, triarylmethane dyes, indoline dyes, thiazine dyes, xanthene dyes, oxazine dyes, and acridine dyes. More particularly, the dyes include cationic cyanine dyes, carbocyanine dyes, hemicyanine dyes, rhodamine dyes, and azomethine dyes, quinonimine oxazine dyes, and thiazine dyes, and quinoline dyes. Cyanine dyes, azine dyes, and dibenzopyran dyes are particularly useful for the present invention. These dyes may be used alone or in combination. Specific examples of such Dyes are described in the literature, for example, in "Dye Handbook, Basic Dyes", ed by the Society of Organic Chemistry ("Enki Sei Senryo (Basic Dyes)" of Senryo Binran (Dye Handbook), edited by the Society of Organic Chemistry) "; "Theory of Photographic processes", pp.194-290, authors t.h. james, published 1977 by Macmillan Publishing company (The Theory of The Photographic Process, pp.194-290, published by Macmillan Publishing co., ltd.1977); functional Coloring matter Chemistry, pages 1-32, 189-206 and 401-413, published by CMC Shuppan Sha (Kinosei Shikisno Kagaku (Chemistry of Functional Coloring Matters), pages 1-32, 189-206, and 401-413, published by CMC Shuppan Sha), and Japanese patent application (OPI) No. 189340/84.

In addition to being cationic, the dyes should not contain groups which would neutralize or desensitize (desensize) the complex or render the complex poorly stable against light. Examples of groups which should not normally be present in the dye are acid groups, for example free carboxylic or sulfonic acid groups.

Practical examples of cyanine dyes useful in the present invention are of the formula(II) a dye represented by:wherein Z₁And Z₂Each represents the atomic group required to form a heterocyclic nucleus, which is commonly used for cyanine dyes, such as, in particular, a thiazole nucleus, a thiazoline nucleus, a benzothiazole nucleus, a naphthylthiazole nucleus, an oxazole nucleus, an oxazoline nucleus, a benzoxazole nucleus, a naphthyloxazole nucleus, a tetrazole nucleus, a pyridine nucleus, a quinoline nucleus, an imidazoline nucleus, an imidazole nucleus, a benzimidazole nucleus, a naphthoimidazole nucleus, a selenazoline nucleus, a selenazole nucleus, a benzoselenazole nucleus, a naphthoselenazole nucleus, and an indolenine nucleus. These nuclei may be substituted with the following groups: lower alkyl (e.g., methyl), halogen atom, phenyl, hydroxy, alkoxy having 1 to 4 carbon atoms, carboxy, alkoxycarbonyl, alkylaminesulfonyl, alkylcarbonyl, acetyl, acetoxy, cyano, trichloromethyl, trifluoromethyl, and nitro.

In the above-listed formula (II), L₁、L₂And L₃Each represents a methine group or a substituted methine group. Examples of the substituent for the substituted methine group are lower alkyl groups(e.g., methyl, ethyl, etc.), phenyl, substituted phenyl, methoxy, ethoxy, and aralkyl (e.g., phenethyl). In the case where m is 3, L₁And R₁、L₃And R₂Or L₂And L₂May be cross-linked via an alkylene group to form a 5-to 6-membered ring.

In the formula (II), R₁And R₂Each represents a lower alkyl group (for example, an alkyl group having preferably 1 to 8 carbon atoms), or an alkyl group substituted with a carboxyl group, a sulfonic acid group, a hydroxyl group, a halogen atom, an alkoxy group having 1 to 4 carbon atoms, a phenyl group, a substituted phenyl group (preferably, an alkylene moiety having 1 to 5 carbon atoms), for example, β -sulfoethyl, γ -sulfopropyl, γ -sulfobutyl, δ -sulfobutyl, 2- [2- (3-sulfopropoxy) ethoxy ] ethoxy]Ethyl, 2-hydroxysulfopropyl, 2-chlorosulfonyl propyl, 2-methoxyethyl, 2-hydroxyethyl, carboxymethyl, 2-carboxyethyl, 2, 3, 3' -tetrafluoropropyl, and 3,3, 3-trifluoroethyl, allyl, or other substituted alkyl groups commonly used in the N-substituent of cyanine dyes.

In the general formula (II), m represents 1, 2 or 3, and X₁ ^-1Represents the same boron compound anion as in formula (I).

Specific examples of xanthene dyes that may be used in the present invention are those represented by formula (III):wherein R is₁To R₇Each represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an aryl group; x represents a boron compound anion as in the general formula (I); and Y represents an alkyl group, an aryl group, a hydrogen atom, or an alkali metal.

Examples of the anionic salts of organoboron compounds which can be used in the preferred organic cationic dye compounds of the present invention are described below, but the present invention is not limited to these compounds. Photoinitiator Structure numberingNo. Ar R' 7A phenyl n-butyl 7B phenyl n-hexyl 7C anisyl n-butylNumbering Ar R' 8A phenyl n-butylmethyl 8B phenyl n-hexylmethyl 8C phenyl n-butyl 8D phenyl n-hexyl n-butyl 8E phenyl n-butyl n-heptyl 8 FphenylN-hexyl-n-heptyl 8G phenyl n-butylethylNumber R R' Ar11A methyl n-butylphenyl 11B methyl-n-hexylphenyl 11C n-butyl-n-butylphenyl 11D n-butyl-n-hexylphenyl 11E n-pentyl-n-butylphenyl 11F n-pentyl-n-hexylphenyl 11G n-heptyl-n-butylphenyl 11H n-heptyl-n-hexylphenylNumber R R' 16A methyl n-butyl 16B methyl n-hexyl 16C n-butyl 16D n-butyl n-hexyl 16E n-pentyl n-butyl 16F n-pentyl n-hexyl 16G n-heptyl n-butyl 16H n-hexylCode No. R R' 21A methyl n-butyl 21B methyl n-hexyl 21C n-butyl 21D n-butyl n-hexyl 21E n-pentyl n-butyl 21F n-pentyl n-hexyl 21G n-heptyl n-butyl 21H n-hexylNumber R R' 22A methyl n-butyl 22B methyl n-hexyl 22C n-butyl 22D n-butyl n-hexyl 22E n-pentyl n-butyl 22F n-pentyl n-hexyl 22G n-heptyl n-butyl 22H n-hexyl

For a more detailed description of these photoinitiator species, see U.S. Pat. Nos. 4,772,530 and 4,772,541, the entire disclosures of which are incorporated herein by reference.

The ionic dye compound is used in an amount of about 2% by weight based on the weight of the photopolymerizable or crosslinkable compound contained in the photohardenable composition. More typically, the photoinitiator is used in an amount of about 0.1 to 1 weight percent. Preferably, the compound is used in combination with a self-oxide. Autoxidizes are compounds that react with oxygen in a free radical chain reaction.

Examples of useful autoxidisable compounds are N, N-dialkylanilines. Examples of preferred N, N-dialkylanilines are dialkylanilines which are substituted in one or more o-, m-or p-positions by: methyl, ethyl, isopropyl, t-butyl, 3, 4-tetramethylene, phenyl, trifluoromethyl, acetyl, ethoxycarbonyl, carboxyl, carboxylate, trimethylsilylmethyl, triethylsilyl, trimethylgermyl, triethylgermyl, trimethylstannyl, triethylstannyl, n-butoxy, n-pentyloxy, phenoxy, hydroxyl, acetyloxy, methylthio, ethylthio, isopropylthio, thio- (methylthio-), acetylthio, fluorine, chlorine, bromine, and iodine.

Representative examples of N, N-dialkylanilines which can be used in the present invention are 4-cyano-N, N-dimethylaniline, 4-acetyl-N, N-dimethylaniline, 4-bromo-N, N-dimethylaniline, ethyl 4- (N, N-dimethylamino) benzoate, 3-chloro-N, N-dimethylaniline, 4-chloro-N, N-dimethylaniline, 3-ethoxy-N, N-dimethylaniline, 4-fluoro-N, N-dimethylaniline, 4-methyl-N, N-dimethylaniline, 4-ethoxy-N, N-dimethylaniline, N-dimethylthioaniline (N, N-dimethylthioaniline), 4-amino-N, N-dimethylaniline, 3-hydroxy-N, N-dimethylaniline, N, N, N ', N' -tetramethyl-1, 4-diphenylamine, 4-acetylamino-N, N-dimethylaniline and the like.

Preferred N, N-dialkylanilines are those having an alkyl substituent in the ortho-position and include 2, 6-diisopropyl-N, N-dimethylaniline, 2, 6-diethyl-N, N-dimethylaniline, N, 2, 4, 6-Pentamethylaniline (PMA), and p-t-butyl-N, N-dimethylaniline.

The amount of autooxide used in the present invention is preferably about 0.5 to 5% by weight, preferably 1 to 2% by weight.

Optionally, disulfide compounds as described in U.S. patent No. 5,230,982 can be used to improve the photothermographic development speed of the present photographic material. The disulfide compounds are sensitive to actinic radiation in the photoinitiator systemParticularly effective co-initiators and are particularly sensitive to actinic radiation in the visible wavelength range. In such systems, each disulfide has at least a portion of its function as an autoxide. Particular such disulfides are compounds having structure (IV), wherein X is selected from S and O, except in particular instances wherein the disulfide is derived from one or more tetrazolyl groups; n represents 0 or 1; a represents a residue of a 5-or 6-membered ring containing N, C, and X atoms, and further, the ring may be fused to an aromatic ring; r in the second sulfide group₂Derived from aromatic groups selected from (1) phenyl (2) benzothiazole plug (3) tetrazolyl (4) benzoxazolyl (5) pyridyl (6) pyrimidinyl (7) thiazolyl (8) oxazolyl (9) quinazolinyl (10) thiadiazolyl, each of which may have a substituent on one or more of the C or N atoms of the ring.

Disulfides of the formula (IV) act as particularly good autoxidizing compounds when used in combination with cationic dye-anionic borate absorbers and with N, N-dimethylanilines, and in particular N, N-dimethylanilines substituted in the ortho-position by one or two alkyl groups. The disulfides which may be used represent from 1 to 12% by weight of the polymerized monomers.

The dye precursors contained within the microcapsules of the imaging layer may be of the type well known in the art, which may be activated by contact with a hot melt proton donating (acidic) or electron accepting developer. Preferred leuco dyes are: fluorane (fluoran), lactone, triarylmethane dibenzofuranone, leuco triarylmethane, thiazine, oxazine, or phenazine leuco dyes such as crystal violet lactone, 3-N-cyclohexyl, N-methyl-amino-6-methyl-7-anilinofluorane, 3-pyrrolidyl-6-methyl-7-anilinofluorane, 3-bis (4-dimethylaminophenyl) dibenzofuranone, 6 '- (dipentylamino) -3' -methyl-2 '- (phenylamino) -spiro [ isobenzofuran-1 (3H), 9' -9[9H ] dibenzopyran ] -3-one, 3-bis (butyl-2-methyl-1H-indol-3-yl) -1- [3H ] -isobenzofuranone 2-phenylamino-3 '-methyl-6' - (dibutylamino) -spiro [ isobenzofuran-1 (3H) -xanthene ] -3-one, 3- [ butyl-2-methylindol-3-yl ] -3- (1-octyl-2-methylindol-3-yl) -1(3H) isobenzofuranone, 3, 6-dimethoxyfluorane, 3, 7-bis (dimethylamino) -10-benzoylphenothiazine, 3-diethylamino-7, 8-benzofluorane, 3-bis- (1-n-butyl-2-methyl-indol-3-yl) dibenzofuranone, 3, 3-bis (1-ethyl-2-methyl-indol-3-yl) dibenzofuranone. More preferred leuco dyes include lactone, fluorane, phenothiazine, and triarylpyridine leuco dyes such as BK400 and BK 350 from Sofix, S206, and Copikem 4 Black N102-T, Copichem 20 Magenta, Copikem 39 cyan, Copikem 34 Black, Copikem 1 Blue CVL-1, ODB-1 and ODB-2 Black leuco dyes from Yamada Chemical, and Pergascript I-3R yellow leuco dyes from Ciba Specialty Chemicals.

Suitable such dyes are more fully described in U.S. Pat. Nos. 4,772,530 and 4,772,541, which are incorporated herein by reference in their entirety.

The dye is present in the microcapsules in the form of a fine submicron-sized dispersion and may constitute about 5 to 40% by weight, preferably 10 to 30% by weight, of the internal phase of the microcapsules.

Microcapsules for use in accordance with the present invention may be formed by methods known in the art, such as those described in U.S. patent No. 5,168,029, which is incorporated herein by reference in its entirety. Capsule wall-forming substances such as polyurea(s), polyimide, polyester, polycarbonate, melamine, etc. can be used. In order to impart the capsule wall with heat-responsive properties, the capsule wall should have a glass transition temperature of from room temperature to 200 ℃, preferably from 70 ℃ to 150 ℃.

In order to control the glass transition temperature (Tg) of the polymeric capsule wall, the capsule wall-forming material is suitably selected. Exemplary preferred embodiments of the wall-forming material are polyurethanes, polyureas, polyamides, polyesters, and polycarbonates, and particularly preferred are polyurethanes, and polyureas. The glass transition temperature of the capsule wall can be further adjusted by pre-reacting the wall material precursor (e.g., polyisocyanate) with the polyol.

The microcapsule used in the present invention is formed by emulsifying a composition containing a wall forming material and an image forming substance (such as a leuco dye, a photoinitiator, and a photopolymerizable compound) and forming a high polymer substance around the emulsified oil droplets. A second wall forming substance may be added to the exterior of the oil droplets to improve barrier properties. Methods of forming the second wall include complex coacervation, liquid-liquid phase separation, and interfacial polymerization.

As a process for forming the microcapsule wall of the present invention, a microencapsulation method by polymerizing reactants from the inside of oil droplets can be used to obtain microcapsules for recording materials having a uniform size and a long shelf life in a short time.

Specific examples of microencapsulation techniques, materials and compounds used are described in U.S. patent nos. 3,276,804 and 3,796,696, the disclosures of which are incorporated herein by reference. For example, in the case of using polyurethane or polyurea as the capsule wall forming material, a polyvalent isocyanate and a second substance (e.g., a polyol and a polyamine) capable of reacting with the polyvalent isocyanate to form a capsule wall are mixed in an aqueous phase or an oily liquid to be encapsulated, and the resulting solution is emulsified and dispersed in water, followed by raising the temperature to cause a high polymer-forming reaction at the interface of oil droplets, thereby forming a microcapsule wall.

The glass transition point of the capsule wall is varied to a large extent by appropriate selection of the first wall-forming substance, polyisocyanate, and the second wall-forming substance, polyol, or polyamine.

As the organic solvent constituting the core of the capsule, a high boiling point oil is used. Specific examples thereof include phosphate esters, phthalate esters, acrylate esters, and methacrylate esters, other carboxylic acids, fatty acid amides, alkylated biphenyls, alkylated terphenyls, alkylated naphthalenes, diarylethanes, chlorinated paraffins, and the like. Preferred organic solvents are crystalline plasticizers having a melting point between 70 ℃ and 200 ℃, preferably between 90 ℃ and 150 ℃. Examples of crystalline plasticizers include 1, 2-bis (3, 4-dimethylphenyl) ethane, stearamide, beeswax, m-terphenyl, o-terphenyl, p-terphenyl, diphenyl phthalate, dicyclohexyl phthalate, glycerol tribenzoate, benzyl-2-naphthyl ether, dimethyl terephthalate, 2-chloropropionylaniline, 4-dibenzyldiphenyl, 1, 2-bis- (3-methylphenoxy) ethane, and dibenzyl oxalate.

The above organic solvents may be used in combination with a low boiling point co-solvent to improve the microencapsulation process. Specific examples of the auxiliary solvent include acetone, ethyl acetate, isopropyl acetate, butyl acetate, methylene chloride, cyclohexanone, and the like.

In order to form stable emulsified oil droplets and to control their particle size, protective colloids or surfactants may be added to the aqueous phase. Generally, water-soluble high polymers can be used as protective colloids. Examples of protective colloids include poly (vinyl alcohol), poly (vinyl pyrrolidone), poly (N-ethyl-2-oxazoline), poly (N-methyl-2-oxazoline), polyacrylic acid, polyacrylamide, poly (styrene-co-maleic anhydride), salts of poly (styrene-co-maleic anhydride), esters of poly (styrene-co-maleic anhydride), poly (ethylene oxide-co-propylene oxide-co-ethylene oxide), and gels, and the like.

In the present invention, the microcapsules have a size of about 0.3 to 20 microns, preferably about 0.5 to 4 microns, and preferably about 0.8 to 2 microns on a volume average to improve image resolution and ease of handling. The use of microcapsules having a size of less than 4 microns provides good image resolution.

The thickness of the microcapsule wall is preferably 0.05 to 1 micron, preferably 0.1 to 0.5 micron in general, although the thickness of the microcapsule wall depends on the nature of the microcapsule wall-forming material and the size of the microcapsule. If the wall thickness is less than 0.05 μm, the barrier effect of the wall between the core material and the outside of the microcapsule becomes insufficient, and therefore, the core material penetrates into the outside of the microcapsule or the outside material penetrates into the inside of the microcapsule, and thus, the desired microcapsule performance cannot be obtained. This will result in a high minimum density (Dmin) or haze. In addition, if the wall thickness exceeds 1 μm, the penetration rate of the developer to the wall during heating may be insufficient and the maximum density (Dmax) of the image will be low.

Generally, the microcapsules are designed to contain about 10 to 30 weight percent of the colored dye precursor, about 0.1 to 2 weight percent of the photoinitiator, and about 10 to 60 weight percent of the photopolymerizable capsule hardener. The total polymer content of the capsule wall material is about 10 to 60% by weight of the microcapsules.

The acidic developer materials useful in the present invention include finely divided particulate materials having an average particle size in the range of 0.2 to 3 microns and a melting point or melt flow temperature of not less than about 70 ℃. It is important that the developer be immovable and in solid form at temperatures that may be encountered during transport or storage of the recording medium, while readily melting and flowing during thermal development when exposed to temperatures of the thermal imaging head in the range of about 180-350 c. Preferred developers have crystalline materials with melting points above about 70 c (e.g., in the range of 70 c to 200 c, preferably in the range of 90 c to 160 c). Any leuco dye developer known in the art and meeting these criteria can be used.

Developer materials conventionally used for carbonless or thermal transfer papers may be used in the present invention. Suitable developers include organic acidic materials, optionally treated with a metal such as zinc or magnesium. Examples of materials that can be used in the present invention include bisphenol a, 4 ' -dihydroxydiphenyl sulfone, phenol-based condensates, salicylic acid derivatives and zinc salts thereof, salicylsalicylic acid esters, p-benzylhydroxybenzoates, sulfonylurea derivatives such as N-p-toluenesulfonyl-N ' -phenylurea, 4 ' -bis (p-toluenesulfonylamino-carbonylamino) diphenylmethane, zinc 2-hydroxynaphthoate, zinc 5-methyl-3-octylsalicylate, zinc 3, 5-bis (methylbenzyl) salicylate; organic acids and acid esters such as gallic acid, and propyl gallate; phenol-formaldehyde novolac resins, such as modified oil-soluble phenol formaldehyde zinc resins and the like, are disclosed in U.S. patent No. 3,732,120. When phenolic condensates such as phenol/formaldehyde novolak resins, or zinc derivatives thereof, are used, they should have relatively low molecular weights, but have glass transition temperatures or melt flow temperatures in excess of 70 ℃. Developers of the sulfonylurea type are particularly useful, including: N-methanesulfonyl-N ' -phenylurea, N-methanesulfonyl-N ' -1-naphthylurea, N-trifluoromethanesulfonyl-N ' -naphthylurea, N-ethanesulfonyl-N ' -1-naphthylurea, N-cyclohexanesulfonyl-N ' -phenylurea, N-allylsulfonyl-N ' -1-naphthylurea, N- (2-methoxyethanesulfonyl) -N ' -biphenylurea, N- (2-tetrahydropyranesulfonyl) -N ' -1-naphthylurea, N- (2-allyloxyethanesulfonyl) -N ' -1-naphthylurea, N-isopropanesulfonyl-N ' -phenylurea, N-isopropylidenesulfonyl-N ' -naphthylurea, N-ethylsulfonylurea, N-ethyl, N-isopropanesulfonyl-N '- (4-methylbenzyl) urea, N-methanesulfonyl-N' - (2-phenoxyethyl) urea, N-methanesulfonyl-N '- (4-chloro-1-naphthyl) urea, N-methanesulfonyl-N' - (4-methoxy-1-naphthyl) urea, N-isopropanesulfonyl-N '- (4-chloro-1-naphthyl) urea, and N-methanesulfonyl-N' -1-naphthyl-thiourea, N-benzylsulfonyl-N '-phenylurea, N- (2-phenoxyethane) sulfonyl-N' -phenylurea, N- (4-methoxybenzyl) -sulfonyl-N '-phenylurea, N-methanesulfonyl-N' - (4-chloro-1-naphthyl) urea, N-methanesulfonyl-N '-phenylurea, N- (2-phenoxyethane) sulfonyl-N' -phenylurea, N- (4-methoxybenzyl) -sulfonyl, N- (2- (p-chlorophenyl) ethane) sulfonyl-N ' -phenylurea, N- (p-biphenyl) sulfonyl-N ' -butylurea, N-benzylsulfonyl-N ' -benzylurea, N-benzylsulfonyl-N ' - (2-phenoxyethyl) urea, N-benzylsulfonyl-N ' - (p-methoxyphenyl) urea, N- (p-methoxyphenyl) sulfonyl-N ' - (2- (p-chlorophenyloxy) ethyl) urea, and N-benzylsulfonyl-N ' -phenyl-thiourea.

The mixture of photosensitive microcapsules and developer is applied to the surface of support layer 12 opposite slip layer 14 to form imaging layer 16. The microcapsules and developer are preferably mixed with a suitable thermoplastic polymer binder to facilitate coating of the imaging layer and adhesion to the support. Suitable binder polymers include amorphous polyesters, polyacrylates, styrene copolymers, and the like. For processing purposes, the preferred polymeric binder of the imaging layer is at least partially water soluble or water dispersible. Which comprises a resinous material or mixture of resinous materials that functions to bind the other components of the layer together. A preferred binder material is polyvinyl alcohol. Other known useful binders include polyvinylpyrrolidone, polyacrylamide, modified cellulose, and starch. Latex polymers such as acrylic latex and polystyrene-butadiene latex, polyvinyl acetate copolymer latex and polyvinylidene chloride copolymer latex may also be used, particularly with water soluble polymers.

The imaging layer may also contain a developer neutralizer, which comprises a neutral, colored, water-insoluble finely divided particulate material, such as magnesium carbonate, or calcium carbonate. In addition to the foregoing, the layer may also include inert fillers, dispersants, antistatic agents, surfactants, wetting agents, preservatives, and defoamers, which are present in the desired small amounts.

The imaging layer may comprise a single layer containing one microcapsule or a mixture of different chromogenic microcapsules or 2 or 3 adjacent layers, each layer containing a mixture of one or more different chromogenic microcapsules. The imaging layer may also comprise three layers next to each other, a first layer comprising only the microcapsules producing cyan color, a second layer comprising only the microcapsules producing magenta color, and a third layer comprising only the microcapsules producing yellow color.

The weight ratio of the photosensitive microcapsules and the developer material contained in the image-forming layer may generally be in the range of about 2/8 to 8/2, preferably 4/6 to 6/4, by weight of solids.

The adhesive layer 18 is prepared using an aqueous latex of a pressure sensitive adhesive polymer, such as rubber based (SBR), or acrylic based polymeric materials, polyvinyl acetate copolymers, ethylene/vinyl acetate copolymers, and similar adhesive materials. These adhesives are commercially available, for example, as NACOR from National Starch^®Brand marketed adhesives. The component may also include surfactants, humectants, thickeners, fillers, and one or more water soluble polymers, such as polyvinyl alcohol, to aid in the adhesion of this layer to other layers. As noted above, the latex binder included in adhesive layer 18 may also be included in imaging layer 16.

The adhesive layer 18 may also be formulated to contain up to about 30% by weight of the above-described particulate developer material. The purpose of the presence of the additional developer in the adhesive layer is to promote the reaction of color formation when the recording sheet is thermally developed.

In another embodiment of the present invention, it has been found that additionally including a hot-melt crystalline compound, or mixtures thereof (a hot solvent and a hot non-solvent that melt at different temperatures) in imaging layer 16 and optionally in adhesive layer 18 can improve the thermal responsiveness and image density of these layers while maintaining good storage stability against image blur. The thermal solvent is a crystalline substance which, after being melted by heating, is a good solvent for the developer. Typically, its melting point is lower than that of the dye or developer. In the present invention, a non-solvent is a substance, which generally has a melting point lower than that of a thermal solvent and is neither a dye nor a solvent for a developer in a liquid form, except at temperatures exceeding 70 ℃. The non-solvent, like a heat transfer fluid, transfers heat from the printer thermal head efficiently and uniformly to the imaging layer and adhesive coating applied adjacent to the support layer.

Typical hot solvents that melt at temperatures of at least about 70 ℃ include bisphenol a diacetate (BDADA), diphenyl phthalate, dicyclohexyl phthalate, diphenyl oxalate, benzylnaphthol (benzyl oxo naphthalene), 1-hydroxy-2-naphthoate, rosin and m-terphenyl derivatives, bis-dialkylaryl ethanes, such as 1, 2-bis (3, 4-dimethylphenyl) ethane, and many of the hot melt crystalline compounds disclosed in column 8 of U.S. patent 4,885,271.

Typical thermal non-solvents which can be melted at a temperature below the melting point of the thermal solvent used include 1, 12-dihydroxydodecane, paraffin wax, beeswax, fatty acids, fatty acid amides, stearic acid, stearamides, zinc stearate, preferably hindered phenols such as 2, 6-di-t-butyl-4-methylphenol (BHT), thiodiethylene hydrocinnamate (IRGANOX from Ciba-Gergy)^TM1035) Tetramethane (IRGANOX from Ciba-Gergy, Inc.)^TM1010) Etc., as described, for example, in U.S. patent 4,885,271 at columns 9, 10, and 11. Waxy materials are somewhat less desirable because they can cause bonding problems when overlaying the base layer 20 to the adhesive layer 18 or imaging layer 16.

If thermal solvents and non-solvents are used, they may be present in an amount in the range of about 5-200 weight percent based on the weight of the acidic developer, and one or both may be about 1 to 30 weight percent of the weight of their incorporated layer on a dry weight basis.

The photothermographic recording sheet of the present invention also includes a second opaque or transparent sheet 20, which may be bonded directly to the heat-sensitive color-developing layer, or may be bonded using a binder layer 18. The sheet material may be composed of a cellulose-based material such as paper, cardboard, light-blocking plastic, or other opaque material, or a transparent plastic sheet as described above for the support layer 12. The thickness of the sheet is typically about 1 to 7 mils, or about 25-180 micrometers. Transparent sheets are particularly useful in color proofing applications, while opaque sheets are suitable for making photographs, labels, stickers, and computer printing paper.

On the back of the sheet layer 20 there may be a coating 22 comprising an adhesive, preferably a pressure sensitive adhesive. The adhesive layer may comprise one or more conventional polymers selected from the group consisting of: the SBR or SBS rubber-based adhesive, the acrylic-based adhesive, the polyvinyl acetate-based adhesive, and the like may be used as the adhesive of the same type contained in the adhesive layer 18. A releasable disposable liner comprising a substrate and a non-tacky silicone, or wax layer on the substrate to assist in the release of the backing sheet from the adhesive layer, may be adhered to the adhesive layer to make the finished recording sheet easy to use. In the case where the heat-sensitive recording sheet is used as printing paper, the adhesive layer 22 and the releasable backing sheet are not required, but are used in the case where the recording sheet is used as a label material or for color proofing applications.

The layers described above may be applied to the respective substrates using known coating techniques. For example, the aqueous dispersion coating composition may be applied by knife coating, VARI-BAR coating, slot die coating, metering BAR coating, pure blade coating, BAR blade coating, short nip coating, curtain coating, gravure coating, and microgravure coating, and after coating, each layer is preferably air-dried.

In a preferred embodiment of the present invention, the photothermographic recording sheet comprises the embodiment shown in FIG. 2 wherein the thermo-slip layer 14 has a dry thickness of about 0.1 to about 2 microns, the transparent support layer 12 is a biaxially oriented PET sheet having a thickness of about 3 to 8 microns, the imaging layer 16 has a thickness of about 2 to 15 microns, and the adhesive layer 18 has a thickness of about 1 to 4 microns.

The recording sheets of the present invention are designed for high speed printing such as computer printer paper, battery-driven printers for digital cameras or personal digital processors, labels, medical imaging and color proofing films. The sheet is sensitive to any form of ultraviolet, infrared, X-ray, ion beam, and visible radiation. They may be used in systems containing modulated exposure elements, such as Light Emitting Diodes (LEDs), liquid crystal display devices (LCDs), lasers, optical fibers, etc. Full color images can be produced optically or with exposure to modulated, well-separated wavelength light sources, such as red, green, and blue LED devices.

After exposure, an image is developed by heating the recording sheet. The preferred heat source is a thermal imaging head of the type commonly used in thermal printing. A thermal head having "n" dots per inch (dpi) may be used, where n is an integer including 0. The thermal head may be segmented or not. Which may be a thin film or thick film thermal head. The advantage of using a thermal head is that its efficiency can be heated to 200 and 400 c in the one millisecond time frame and cooled down in about 10 milliseconds. This unique property allows for very good control of the thermal development process.

The slip layer 14 of the recording sheet is in sliding contact with a thermal head uniformly heated to about 200 and 400 c for a period of time sufficient for development, which is typically about 0.1 to 100 milliseconds, preferably 0.2 to 20 milliseconds, and even more preferably 1 to 12 milliseconds. The recording sheet has a slip layer 14 on its surface, which prevents the surface from dragging on the thermal head and contributes to efficient high-speed printing.

For full color printing, exposure of the recording sheet to red light (650nm) hardens the microcapsules in the imaging layer containing the photoinitiator selectively sensitive to red light and the cyan leuco dye; thermal development causes the capsules containing the magenta and yellow dyes to be penetrated by the developer and mix to form a red image. Similarly, exposure to green light (550nm) and blue light (430nm) selectively photohardens magenta dye-containing capsules and yellow dye-containing capsules, respectively, and develops complementary colors to produce green and blue images, respectively. All microcapsules are exposed to a broad spectrum of radiation (white) to form a colorless (white) image, while none of the microcapsules form a black image when exposed.

The following examples illustrate the invention. The materials used in the following examples are as follows: cellulose from METHOCELTMK 15 Dow Chemiol

Thickening agent of raw materials. AEROSOL (TM) OT bis (2-ethylhexyl) sulfo succinic acid

Sodium salt surfactant TRITONTMX-100 t-octylphenoxy polyethoxyethanol

Pressure sensitive type of ionic surfactant NACORTM8685 National Starch

Latex adhesive AIRVOLTM Air Products and Chemical company

Polyvinyl alcohol SURFYNOL 104 Air Products and Chemical Co

2, 4,7, 9-tetramethyl-5-decyne-4, 7-

Glycol surface tension reducer BHT 2, 6-di-t-butyl-4-methylphenol (thermal non-aqueous)

Solvent) BPA bisphenol A (acid developer) BPADA bisphenol A diacetate (hot solvent)Example 1Preparation of Black leuco dye Capsule B-1 (Table 1)

	Composition (I)	Weight (gram)
			1A	Black leuco dye BK-400	7
1B	Black leuco dye S-205	7
			1C	2-isopropyl naphthalene	10.5
1D	SR-351(TMPTA)	24.5
			1E	Polyisocyanate, DESMODURCB75N (75%)	14
1F	Polyisocyanate, DESMODUR N3300	10.5
			1G	Ethyl acetate	6

Compounds 1A to 1C were mixed with 25 grams of Methyl Ethyl Ketone (MEK) and heated to complete dissolution with a hot plate. The solution was cooled to room temperature. Compounds 1D to 1F were added and stirred until the solution was homogeneous. MEK was removed with a rotary evaporator and the viscous liquid was diluted with ethyl acetate (G). 60 grams of oil were poured at 40 deg.C containing 30 grams of Airvol 540 (9.8%), 30 grams of Airvol 203 (10%), 100 grams of deionized water, and 8 grams of 20% sodium carbonateIn solution. The mixture was emulsified for 20 minutes with a Silverson LR4 mixer at 6000 rpm. A mixture of 0.24 g of dibutyltin dilaurate (DBTDL) and 2.4 g of Diethylenetriamine (DETA) dissolved in 6g of water was added. The resulting emulsion was heated to 60 ℃ and emulsified for an additional 30 minutes, stirred with an overhead stirrer at 700 rpm for an additional 2 hours at 60 ℃ and overnight at room temperature to complete the formation of the capsules. The average size was determined to be about 2.5 microns using a Coulter counter.Example 2Preparation of Black leuco dye Capsule B-2 (Table 2)

	Composition (I)	Weight (gram)
			2A	Black leuco dye BK-400	9.6
2B	Black leuco dye S-205	9.6
			2C	2-isopropyl naphthalene	10.3
2D	SR-351(TMPTA)	28.1
			2E	MEHQ	0.1
2F	Polyisocyanate, DESMODUR N3300	9
			2F	Polyisocyanate, DESMODUR CB75N (75%)	36
2G	Ethyl acetate	10

Compounds 2A to 2E were mixed in a beaker and heated to 100 ℃ until 2A and 2B were completely dissolved. The solution was cooled to room temperature and 2F and 2G were added. The resulting solution was poured into a 30 ℃ solution containing 58 grams of Airvol 540 (9.8%), 58 grams of Airvol 203 (10%), and 100 grams of deionized water. The mixture was emulsified for 30 minutes with a Silverson LR4 mixer at 4000 rpm. The Ph of the resulting dispersion was controlled at 8.0 by the continuous addition of 20% aqueous sodium carbonate. 6 grams of 15% SMA-1440H (Elf Atochem Corp.) and 1.8 grams of DETA were added and stirred at 700 rpm for 3 hours at 60 ℃ using an overhead stirrer to complete capsule formation. The resulting capsules had an average size of 2 microns.Example 3Preparation of photosensitive Black leuco dye Capsule B-3 (Table 3)

	Composition (I)	Weight (gram)
			3A	Black leuco dye BK-400	9.6
3B	Black leuco dye S-205	9.6
			3C	2-isopropyl naphthalene	4.8
3D	SR-351(TMPTA)	28.6
			3E	MEHQ	0.1
3F	Polyisocyanate, DESMODUR CB75N (75%)	36
			3G	Polyisocyanate, DESMODUR N3300	9
3H	Photosensitizer, 3, 3' -carbonylbis (7-diethylaminocoumarin) (CBDC)	0.29
			3I	N' N-Dimethylbenzoic acid ethyl Ester (EPD)	1.14
3J	Ethyl acetate	10

Compounds a to E were mixed in a beaker and heated to 100 ℃ until a and B were completely dissolved. The solution was cooled to room temperature and compounds F to J were added under safe light. The resulting solution was poured into a solution containing 58 grams of Airvol 540 (9.8%), 58 grams of Airvol 203 (10%), and 100 grams of deionized water and emulsified at 4000 rpm for 30 minutes at 30 ℃ using a Silverson LR4 mixer. The pH of the dispersion was controlled at 8.0 using 20% sodium carbonate in deionized water. 1.8 grams DETA and 2.4 grams 15% SMA-1440H were added and the temperature was raised to 60 ℃. The capsules were stirred at 700 rpm for an additional 2.5 hours to complete capsule formation. The resulting capsules had an average size of about 2 microns.Example 4Preparation of photosensitive Black leuco dye Capsule B-4 (Table 4)

	Composition (I)	Weight (gram)
			4A	Black leuco dye BK-400	9.6
4B	Black leuco dye S-205	9.6
			4C	2-isopropyl naphthalene	4.8
4D	SR-351(TMPTA)	28.6
			4E	MEHQ	0.1
4F	PPO (polypropylene oxide, Mn 425)	4.8
			4G	DESMODUR CB75N(75％)	36
4H	DESMODUR N3300	9
			4I	Photosensitizers, CBDCs	0.29
4J	EPD	1.14
			4K	Ethyl acetate	10

The same as example 3 was repeated except that the capsule formulation was changed as shown in Table 4. The capsules had an average size of about 2 microns.Example 5Preparation of photosensitive Black leuco dye Capsule B-5 (Table 5)

	Composition (I)	Weight (gram)
			5A	Black leuco dye BK-400	9.6
5B	Black leuco dye S-205	9.6
			5C	2-isopropyl group	4.8
5D	SR-351(TMPTA)	28.6
			5E	MEHQ	0.1
5F	Hydroquinone bis (2-hydroxyethyl) ether	5.06
			5G	Aerosol OT	0.19
5H	DESMODUR CB75N (75％)	36
			5I	DESMODUR N3300	9
5J	Photosensitizers, CBDCs	0.29
			5K	EPD	1.14
5L	Ethyl acetate	10

The same as example 3 was repeated except that the capsule formulation was changed as shown in Table 5. The capsules had an average size of about 2 microns.Example 6Preparation of photosensitive Black leuco dye Capsule B-6 (Table 6)

	Composition (I)	Weight (gram)
			6A	Black leuco dye BK-400	5.25
6B	Black leuco dye S-205	5.25
			6C	2-isopropyl naphthalene	7
6D	SR-351(TMPTA)	21
			6E	SR399	3.5
6F	PPO (polypropylene oxide, Mn 425)	3.5
			6G	MEHQ	0.02
6H	Aerosol OT	0.35
			6I	Photoinitiator 8C (Cyanine Borate, 550nm)	0.12
6J	Heat stabilizer, Q-1301(Wako Chemicals)，USA， Richmond，VA)	0.02
			6K	DESMODUR CB75N(75％)	24.5
6L	DESMODUR N3300	6.13
			6M	Ethyl acetate	7

The average capsule size was about 2 microns as in example 3, except that the capsule formulation was changed as shown in table 6.Example 7Preparation of developer dispersions

50 grams of BPS-24(2, 4' -dihydroxydiphenylsulfone), 20 grams of 9.8% Airvol 540 in water, 20 grams of 10% Airvol 203 in water, 0.67 grams of AOT, 1.34 grams of SMA1440H, and 73 grams of deionized water were mixed in a stainless steel vessel along with 1000 grams of zirconium ceramic beads. The mixture was stirred with a laboratory mixer overnight until the particle size was less than 1.5 microns.

Other developers and co-developer dispersions prepared in a similar manner include bisphenol-A (BPA), benzyl Hydroxybenzoate (HBB), N-p-toluenesulfonyl-N '-phenylurea (TUPH), 4' -bis (p-toluenesulfonamido-carbonylamino) diphenylmethane (BTUM), bis (3-allyl-4-hydroxyphenyl) sulfone (TGSA), 3 '-diethylenedioxybiphenyl (EDP), 4' -Ethylenebisphenol (EBP), N-bis (2-tolylsulfonyloxyethyl) -p-methylsulfonamide, N- (4-hydroxyphenyl) stearamide, and 4- (benzyloxy) phenol.Example 8Preparation of thermal solvent dispersions

50 grams of m-terphenyl, 20 grams of 9.8% Airvol 540, 20 grams of 10% Airvol 203, 0.67 grams of AOT, 0.67 grams of Surfynol CT-131, and 75 grams of deionized water were mixed in a stainless steel crusher along with 1000 grams of ceramic beads. The mixture was stirred with a laboratory mixer overnight until the particle size was less than 1.5 microns.

Other thermal solvent dispersions prepared in the same way include: diphenyl oxalate (HS-2046), di-methylphenyl oxalate (HS-3051), dicyclohexyl naphthoate (DCP), diphenyl naphthoate (DPP), bisphenol A diacetate, and benzylnaphthol (benzyloxynaphthalene). Other materials that can be used to modify other properties can also be prepared in the same way. These additives include paraffin wax, 2, 6-di-t-butyl-4-methylphenol (BHT), Irganox1035, Irganox 1010, 1, 12-dihydroxydodecane, stearamide, stearic acid, zinc stearate. The average particle size of all dispersions was controlled to be about 1.5-2 microns.Example 9Preparation of imaging coatings

11.95 grams of B-1 black capsules (29.3% solids), 6.68 grams of HBB developer dispersion (34.5% solids, prepared as in example 7), 5.49 grams of m-terphenyl (28% solids, prepared as in example 8), 1.73 grams of 10% Airvol 540, 0.075 grams of Surfynol440, and 4.08 grams of water were thoroughly mixed to give a 25% solids mixture. The pH was adjusted to 8.0 with 20% aqueous sodium carbonate solution. The mixture was coated on a 2mil rod using a #10Myrad bar(thousandths of an inch) on a white PET film and dried at 50 ℃ for 5 minutes. The dry cover layer was measured to be about 5 microns thick with a Mitatoyo thickness gauge.Example 10ImagingPreparation of the coating

7.68 grams of B-1 black capsules (29.3% solids, example 1), 6.0 grams of BPS-24 developer dispersion (27.05% solids, prepared as in example 7), 3.34 grams of HS-2046 (32.42% solids, prepared as in example 8), 0.43 grams of 10% Airvol 540, 0.05 grams of Surfynol440, and 2.48 grams of water were thoroughly mixed. The pH was adjusted to 8.0 with 20% sodium carbonate. The mixture was coated onto 2mil (thousandths of an inch) white PET film with a #10 mylad rod and dried at 50 ℃ for 5 minutes. The dry cover layer was about 5 microns thick as measured by the Mitutoyo thickness gauge.Example 11Preparation of imaging coatings

6.27 grams of B-2 black capsules (34.2% solids, prepared as in example 2), 4.52 grams of TGSA developer dispersion (31.21% solids, prepared as in example 7), 2.9 grams of HS-2046 (32.42% solids), 1.57 grams of 4-benzyloxyphenol (24.77% prepared as in example 7), 0.13 grams of Coatosil 1301 (silicone surfactant, 20% solids in water, OSi, Friendly, Inc., West Virginia), 1.02 grams of 10% Air540, and 3.28 grams of deionized water were mixed thoroughly. The pH was adjusted to 8.0 with 20% sodium carbonate. The mixture was coated onto 2mil (thousandths of an inch) white PET film with a #10 mylad rod and dried at 50 ℃ for 5 minutes. The dry cover layer was measured to be about 5 microns thick using a Mitutoyo thickness gauge.Example 12Preparation of imaging coatings

7.68 grams of B-5 black capsules (28.6% solids, example 5), 4.19 grams of HBB developer dispersion (34.5% solids), 3.44 grams of m-terphenyl (28% solids, prepared as in example 8), 0.83 grams of Ludox AM-30 (30% solids, Grace Davision corporation), 1.73 grams of 10% Airvol 540, 0.05 grams of Surfynol440, and 2.23 grams of water were charged with waterMix to give a 25% solids mixture. The pH was adjusted to 8.0 with 20% sodium carbonate. The resulting mixture was coated on 2mil (thousandths of an inch) white PET film with a #10 mylad rod and dried at 50 ℃ for 5 minutes. The dry cover layer was measured to be about 5 microns thick using a Mitutoyo thickness gauge.Example 13Preparation of imaging coatings

6.28 grams of B-3 black capsules (35% solids, example 3), 4.19 grams of HBB developer dispersion (34.5% solids), 3.44 grams of m-terphenyl (28% solids), 0.83 gramsGrams of Ludox AM-30 (30% solids), 1.57 grams of 10% Airvol 540, 0.05 grams of Surfynol440, and 3.63 grams of water were thoroughly mixed to give a 25% solids mixture. The pH was adjusted to 8.0 with 20% sodium carbonate. The mixture was coated on 2mil (thousandths of an inch) white PET film with a #10 mylad rod and dried at 50 ℃ for 5 minutes. The dry cover layer was measured to be about 5 microns thick with a Mitutoyo thickness gauge.Example 14Preparation of imaging coatings

5.7 grams of B-4 black capsules (38.54% solids, example 4), 4.19 grams of HBB developer dispersion (34.5% solids), 3.44 grams of m-terphenyl (28% solids), 0.83 grams of Ludox AM-30 (30% solids), 1.57 grams of 10% Airvol 540, 0.05 grams of Surfynol440, and 4.21 grams of water were mixed thoroughly to give a 25% solids mixture. The pH was adjusted to 8.0 with 20% sodium carbonate. The mixture was coated onto 2mil (thousandths of an inch) white PET film with a #10 mylad rod and dried at 50 ℃ for 5 minutes. The dry cover layer was measured to be about 5 microns thick with a Mitutoyo thickness gauge.Example 15Production of photothermographic recording sheet

A binder coating comprising 20% (dry weight) Rovent 4823 latex (SBR latex, Mallard Creek Polymers, Inc., Akron, OH), 1% (dry weight) Airvol 540, and 0.5% (dry weight) Coatosil 1301 in water was coated with a #2.5 Myrad bar onto the untreated side of Toray PET tape 4.5F531 (about 4.5 microns thick, one side of which was treated with a thermal slip layer) and dried at 50 ℃ for 5 minutes. The adhesive coated tape was then laminated with an image-forming coating (examples 9-15) at 40 ℃ under pressure to give an optical heat-sensitive recording sheet.

The laminated samples were then printed from the belt side with an Atlantek Model 200 thermal test printer equipped with a Kyocera 200 dpi thermal head, t_cycle4 ms and t_on0-1.2 milliseconds. This gives a high quality, durable glossy black image. Table 7 lists the maximum densities (Dmax) and (Dmin) of the photothermographic recording sheet. Good heat sensitivity was observed for all samples with acceptable minimum density stability. Examples 12-13 were exposed to 100W halogen-tungsten lamp 6 inches from the side of the ribbon for 30 seconds and printed again using the thermal testAnd printing by a printing machine. A significant decrease in maximum density after exposure was observed in all samples. The optical density of the thermally developed sample decreases with increasing exposure time. (Table 7)

Examples	Photosensitivity	Developing agent	Thermal solvent	Additive agent	Dmax	Dmin
							9	Is free of	HBB	M-terphenyl	Is free of	0.88	0.1
10	Is free of	BPS-24	HS-2046	Is free of	0.88	0.12
							11	Is free of	TGSA	M-terphenyl	4- (Benzyloxyphenol)	0.94	0.12
12	UV-blue	HBB	M-terphenyl	Ludox AM	0.95	0.13
							13	UV-blue	HBB	M-terphenyl	Ludox AM	0.96	0.12
14	UV-blue	HBB	M-terphenyl	Ludox AM	0.92	0.15

Example 16(comparative example) thermal development with an infrared heater or a conventional oven

The thermal imaging experiments were repeated except that the thermal head was replaced with an infrared heater or a conventional oven at 60-150 ℃. Very poor Dmin and Dmax were observed in all cases. Example 17 (comparative example) thermal development Using untreated ribbon

The experiment of example 15 was repeated except that a 4.5 micron color band without a hot slip coating was used. The developed image showed significant defects and very poor uniformity.

Attached: reference number 10 recording sheet 11 recording sheet 12 support sheet 14 thermal slip layer 16 imaging layer 18 binder layer 20 opaque or clear sheet material 22 binder layer 31 photosensitive microcapsules 32 particulate developer material 33 thermoplastic polymer binder

Claims (34)

1. A photothermographic recording sheet comprising a first support layer comprising a transparent sheet and a thermally sensitive imaging layer adhered to one surface of said first support layer, said imaging layer comprising a mixture of:

i) a plurality of photosensitive fine particles including a polymer wall material or a base material, and a photopolymerizable or photocrosslinkable compound as an internal phase, a photoinitiator, and a color dye precursor;

ii) finely divided particulate developer material having a melting point or melt flow temperature above 70 ℃, preferably between 70 ℃ and 200 ℃, preferably between 90 ℃ and 180 ℃, which reacts to form colour on contact with said colour precursor;

the particles are characterized in that: the microparticles are permeable to the developer material when the recording sheet is heated above the melting point of the developer sufficiently to form an image during imaging, and are impermeable to the developer material after the microparticles are photohardened by exposure to a pattern of actinic radiation and the recording sheet is heated above the melting point of the developer during imaging.

2. The recording sheet according to claim 1, wherein the transparent support layer further comprises a thermal slip layer attached to the opposite surface of the imaging layer.

3. The recording sheet of claim 2 further comprising a second opaque or transparent sheet affixed to the heat sensitive imaging layer.

4. The recording sheet of claim 3 further comprising an adhesive layer attached between the heat sensitive imaging layer and the second sheet.

5. The recording sheet according to claim 1, wherein the fine particles are microcapsules.

6. The recording sheet of claim 5 wherein at least a portion of the microcapsules comprise a blue-green dye precursor and a photoinitiator having selective sensitivity when exposed to red light.

7. The recording sheet of claim 5 wherein the at least a portion of microcapsules comprise a magenta dye precursor and a photoinitiator having selective sensitivity when exposed to green light.

8. The recording sheet of claim 5 wherein the at least a portion of microcapsules comprise a yellow dye precursor and a photoinitiator having selective sensitivity when exposed to blue light.

9. The recording sheet of claim 5 wherein the microcapsules each comprise one of a blue-green, violet-red, and yellow dye precursor and comprise a photoinitiator having selective sensitivity when exposed to red, green, or blue light, respectively.

10. The recording sheet of claim 2, wherein the thermal slip layer comprises a lubricious release agent dispersed in a thermoset polymeric binder.

11. The recording sheet according to claim 2, wherein the transparent support layer comprises a polyethylene terephthalate film having a thickness of 3-25 microns, preferably 3-8 microns.

12. The recording sheet of claim 1 wherein the microparticles have an average particle size of less than 4 microns.

13. The recording sheet according to claim 3, wherein the second sheet is opaque.

14. The recording sheet of claim 1, wherein the melting point of the developer is in the range of about 70 ℃ to 200 ℃.

15. The recording sheet of claim 1 wherein the imaging layer further comprises a thermoplastic polymer binder.

16. A method of thermal imaging comprising:

a) provided is a heat-sensitive recording sheet comprising:

i) a first support layer composed of a transparent sheet;

ii) a thermal slip layer disposed on a surface of the first support layer;

iii) a heat-sensitive imaging layer disposed on the opposite side of said first support layer; and

iv) a second opaque or transparent sheet bonded to the heat sensitive imaging layer,

the imaging layer comprises a mixture of: (1) a plurality of photosensitive fine particles comprising a polymer wall material or a base material, and as an internal phase, a photopolymerizable or photocrosslinkable compound, a photoinitiator, and a color dye precursor, and

(2) finely divided particulate developer material having a melting point or melt flow temperature greater than 70 ℃ that reacts to form color upon contact with said color precursor;

b) imagewise exposing said recording sheet to a pattern of actinic radiation, wherein microcapsules sensitive to said radiation are selectively photohardened; and

c) heating the recording sheet to a temperature above the melting point or melt flow temperature of the developer to cause the developer to flow into contact with the microparticles, wherein the photohardened microparticles are impermeable to the developer material and the non-photohardened microparticles are permeable to the developer material sufficient to form a colored image.

17. The method of claim 16, wherein said recording sheet further comprises an adhesive layer between said heat sensitive imaging layer and said second sheet material.

18. The method of claim 16, wherein the microparticles are microcapsules.

19. The method of claim 18, wherein at least a portion of the microcapsules comprise a blue-green dye precursor, and a photoinitiator that is selectively sensitive to exposure to red light.

20. The method of claim 18, wherein at least a portion of the microcapsules comprise a magenta dye precursor, and a photoinitiator that is selectively sensitive upon exposure to green light.

21. The method of claim 18, wherein at least a portion of the microcapsules comprise a yellow dye precursor, and a photoinitiator that is selectively sensitive to exposure to blue light.

22. The process of claim 18, wherein at least a portion of said microcapsules contain a dye precursor and a photoinitiator sensitive to ultraviolet light.

23. The process of claim 18, wherein at least a portion of said microcapsules contain a dye precursor and an infrared-sensitive photoinitiator.

24. The method of claim 18, wherein said microcapsules each comprise one of a blue-green, magenta, and yellow dye precursor, and a photoinitiator that is selectively sensitive when exposed to red, green, or blue light, respectively.

25. The method of claim 18, wherein the melting point of the developer is between about 70 ℃ and 200 ℃.

26. The method of claim 18, wherein the heating is performed by moving the slip layer contained in the recording sheet in contact with a thermal print head maintained in a range of about 180 ℃ to 400 ℃.

27. The method of claim 26, wherein the contacting occurs for a time of about 0.1 to 50 milliseconds, preferably about 0.2 to 20 milliseconds.

28. The method of claim 22 wherein the recording sheet is exposed to red, green, and blue light to form a full color image.

29. The method of claim 22, wherein the recording sheet is exposed with red, green, and blue Light Emitting Diodes (LEDs) to form a full color image.

30. The method of claim 16, wherein the microcapsules have an average particle size of less than about 4 microns.

31. The method of claim 26, wherein the thermal head is non-segmented.

32. The method of claim 31, wherein the contacting occurs for a time of about 0.1 to 50 milliseconds, preferably about 0.2 to 20 milliseconds.

33. The method of claim 26, wherein the thermal head is a thin film type thermal head.

34. The method of claim 26, wherein the thermal head is a thick film type thermal head.