CN1355445A - Single-base photosensitive imaging system - Google Patents

Abstract

The invention provides a self-contained photosensitive material, comprising: a carrier; an imaging layer on the carrier, the imaging layer comprising a developer material and a plurality of photosensitive microcapsules encapsulated with a photosensitive composition and a colorant precursor; and a protective coating on the imaging layer, said protective coating comprising a cured film of a water-soluble or water-dispersible resin, wherein, by image-wise exposing the imaging layer to actinic radiation and rupturing the microcapsules, the colorant The bodies are released from the microcapsules and react with the developer material to form a color image.

Description

Single base photosensitive imaging system

This invention relates to improvements in photosensitive imaging systems of the type described in US Patent Nos. 4,399,209 and 4,440,846, wherein the photosensitive imaging system includes a protective coating.

Imaging systems employing microencapsulation of radiation-sensitive compositions are the subject of commonly assigned US Patents 4,399,209, 4,416,966, 4,440,846, 4,766,050, 5,783,353, 6,030,740, 6,037,094, and 6,080,520. These imaging systems are characterized by imagewise exposure of an imaging sheet comprising a layer of microcapsules comprising a photohardenable composition in an inner phase to actinic radiation. In the most typical embodiment, the photohardenable composition is a photopolymerizable composition comprising a polyethylenically unsaturated compound and a photoinitiator and the coupler is encapsulated by the photopolymerizable composition. Exposure to actinic radiation can harden the inner phase of the microcapsules. After exposure, the imaged sheeting is developed by subjecting it to a uniform breaking force in the presence of a developer. Image transfer systems in which the developer material is coated on a separate substrate as a separate developer or replica sheet are disclosed in commonly assigned US Patent 4,399,209. Self-contained imaging systems in which encapsulated coupler and developer materials are present in one or two interacting layers are disclosed in commonly assigned US Patent 4,440,846. A self-contained imaging system with an opaque support is disclosed in commonly assigned US Patent 6,080,520. Dual-sided imaging materials are disclosed in commonly assigned US Patent 6,030,740.

Commonly assigned US Patent 5,783,353 discloses a self-contained imaging system in which the imaging layer is sealed between two supports to form an integral unit. The advantage of this form of sealing is that it reduces oxygen transmission and increases media stability. Although this form of sealing improves media stability, some adhesives used between the imaging layer and support can cause discoloration of the imaging layer.

According to the present invention, there is provided a self-contained photosensitive material comprising photosensitive microcapsules and an imaging layer of developer on a support and a protective coating on the imaging layer. A protective coating comprising a water-soluble or water-dispersible resin imparts scratch and water resistance to the imaging media. The protective coating may also include a crosslinking agent.

In another embodiment of the present invention, a self-contained photosensitive material includes a carrier, an imaging layer on the carrier, and a protective coating on the imaging layer, wherein the imaging layer includes a layer of photosensitive microcapsules, and the same layer as the microcapsules. or developer in a different layer.

In a more particular embodiment of the invention, the protective coating comprises an acrylic latex and a polyaldehyde crosslinker.

In another embodiment of the invention, an insolubilizer is present in at least one of the imaging layer and the protective coating. The insolvents used in the present invention improve the stability of photosensitive materials under various storage conditions. In particular, insolvents can improve the humidity stability of imaging media.

Figure 1 is a cross-sectional view of the imaging system of the present invention.

Figure 2 is a cross-sectional view of Figure 1 after exposure and microcapsule rupture.

US Patents 4,399,209, 4,440,846, 5,783,353, 6,030,740, 6,037,094, and 6,080,520 are hereby incorporated by reference to the extent not inconsistent with the teachings herein.

The improved imaging system of the present invention may be embodied as a self-contained replicating sheet in which photosensitive microcapsules and developer material are co-deposited in one or two interacting layers, as described, for example, in US Patent No. 5,783,353. The imaging system of the invention is also specifically a two-sided self-contained system in which the microcapsules and developer are in one or a separate layer as just described on both sides of the opaque support. Each system can be operated by photographically controlling the contact between the chromogenic material and the developer as described above. In self-contained imaging systems, after capsule rupture, the chromogenic material and developer are able to react in the unexposed areas to form a visible image The visible image follows exposure and capsule rupture as the chromogenic material oozes out of the microcapsules And gradually developed. In the most typical embodiment, capsule rupture is performed by applying pressure to the imaging sheet using pressure rollers or roller balls. To record an image the imaging material can be scanned with an LED print head or LCD device and developed by applying pressure to the unit. The media can be imaged using a printer equipped with an LED/developer head as described in US Patent 5,550,627.

According to the invention, the photosensitive element includes a protective coating on the imaging layer. The coating is applied directly to the imaging layer as a solution or dispersion and then dried or cured to form a protective coating. This protective coating serves many of the same functions as the secondary support disclosed in US Pat. No. 5,783,353 in the sealed self-contained imaging media. In particular, the protective coating imparts water and scratch resistance to the imaging media. Additionally, avoiding the use of adhesives for the secondary support in the imaging medium sealed on both sides can improve the humidity stability of the image. The protective coating of one embodiment of the present invention generally comprises a water-soluble or water-dispersible resin and a crosslinking agent. In a particular embodiment of the invention, the protective coating comprises an acrylic latex and a polyaldehyde crosslinker such as glyoxal.

According to another embodiment of the invention, the insolvent is in at least one of the imaging and protective coatings. The insolvent further improves the humidity stability of the imaging media. While not wishing to be bound, applicants believe that insolvents enhance humidity stability by reacting with reactive groups in the binder systems used in the imaging layers and protective coatings.

Resins useful in the protective coating of the present invention include those having film-forming properties. Preferably, the resin is a water-soluble resin or latex dispersed in water. If dried or cured to form a film, the resin should be substantially clear and remain clear over a wide temperature range without clouding or yellowing. The resin film should also impart scratch resistance, water resistance, gloss and durability to the protective coating. Examples of water-soluble resins that can be used in the present invention include natural polymers (e.g., alginic acid compounds, cellulose derivatives, casein, gelatin, etc.), polyvinyl compounds (e.g., polyvinyl alcohol, Sexual polyvinyl alcohol, polyvinyl alcohol modified by carboxylic acid, etc.), polyacrylamide, polyacrylic acid, vinylpyrrolidone-maleic acid copolymer, etc. Examples of water-dispersible resins include acrylic latexes (e.g., acrylates, modified acrylates, acrylate copolymers, modified acrylate copolymers) and other polymer latexes (e.g., styrene-butadiene copolymer , styrene-maleic anhydride copolymer, butadiene-methacrylate copolymer, vinyl acetate-vinyl chloride-ethylene copolymer, vinylidene chloride-acrylonitrile copolymer, etc.).

In one embodiment, the binder used in the protective coating is an acrylic latex. Examples of acrylic latexes include, but are not limited to, acrylates, modified acrylates, acrylate copolymers, and modified acrylate copolymers. A particularly preferred acrylic latex is SA-532 from Nippon Shokubai. The binder is usually used in an amount of about 50-90% by weight, preferably about 60-80% by weight, based on the total solids content of the protective coating.

A crosslinking agent may be added to the protective coating composition according to the kind of polymer used to ensure that the protective coating has desired properties, namely, water resistance, scratch resistance and gloss. Examples of crosslinking agents preferred for use in protective coatings include, but are not limited to, polyvalent aldehyde compounds such as glyoxal, glutaraldehyde, and derivatives of those compounds that retain free aldehyde groups. Glyoxal is the preferred polyaldehyde. Other crosslinking agents useful in the present invention include diisocyanate compounds, epoxy compounds, diethyleneimine compounds, divinyl compounds (e.g., divinylbenzene), methacrylate (or acrylate) esters of polyols (eg, TMPTA), allyl glycidyl ether, diepoxides of polyols, methacrylic anhydride, N-methylolacrylamide, organic peroxides, diamine compounds, bis-2-oxazolines Compounds, polymers with -2 oxazoline groups and compounds with carbodiimide groups. The crosslinking agent is generally present in an amount of about 2-20%, preferably about 4-10%, based on the total solids content of the protective coating.

The protective coating may also include other additional components such as surfactants, UV absorbing compounds, light stabilizers, pigments, matting agents, fillers, and the like. Surfactants, including wetting agents, enable the aqueous coating solution to spread evenly over the surface of the photosensitive layer and give a smooth coating. Generally, the amount of wetting agent in the coating solution should be about 1-10% by weight of the coating solution, more preferably about 4-8%. Examples of wetting agents include sodium dialkylsulfosuccinates and anionic fluoroalkyl-type surfactants. These surfactants are available from Kao Corporation (PELEX OTP) and Dainippon Ink Chemicals, Inc (Megafac F140NK), respectively.

Pigments can be added to protective coatings to improve handling and prevent blocking. Pigments are not particularly limited, and examples of pigments may include inorganic pigments such as calcium carbonate, zinc oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, zinc sulfate, talc, kaolin, clay, and colloidal silica, and organic pigments Such as styrene microspheres, nylon powder, polyethylene powder, urea-formaldehyde resin filler and native starch granules. Colloidal silica is a preferred pigment and is commercially available from Nissan Chemicals under the tradename SNOWTEX.

The protective coating can also include UV absorbing compounds that can improve the lightfastness and stability of the image media. Examples of UV absorbing compounds useful in the present invention include, but are not limited to, salicylic acid-type UV absorbers, benzophenone-type UV absorbers, hindered amine-type UV absorbers, and benzotriazole-type UV absorbers . Preferably, the UV absorber is a benzotriazole compound, especially a high molecular weight benzotriazole emulsion. A particular such material is ULS-1383MG available from Ipposha Oil. The amount of the ultraviolet absorbing compound is not particularly limited, and it is preferable to adjust the amount preferably to 5-30% based on the total solid content of the protective coating.

It has been found that by adding insolvents to photosensitive image media, the deleterious effects of storage under extreme humidity conditions can be avoided. Therefore, the imaging media of the present invention stored under high humidity conditions are less prone to decline in _Dmax and photosensitivity, which can occur with conventional media in many cases. In addition, the photosensitive imaging media of the present invention have good low humidity stability under humidity conditions that would cause discoloration of conventional media.

Insolvents useful in the present invention include those represented by the general structures (I), (II) and (III):

wherein ^R1 and ^R2 are the same or different and represent H, OH, alkyl (C1-C10), hydroxyalkyl, polyhydroxy substituted alkyl, alkylcarbonyloxyalkyl, alkenyl (C2-C10) Carbonyloxyalkyl, or a carbonyloxyalkyl having a carboxyl, carboxyl salt or carboxyl ester group as a terminal group;

wherein ^R is H, OH, alkyl (C1-C10), hydroxyalkyl, polyhydroxy substituted alkyl, alkylcarbonyloxyalkyl, or alkenyl (C2-C10)carbonyloxyalkyl, n ₁ =2-4 and Z ¹ is:

If a dioxane is formed, and if no dioxane is formed, ^Z represents an H atom to form a diol; and

Wherein ^R is H, OH, alkyl (C1-C10), hydroxyalkyl, polyhydroxy substituted alkyl, alkylcarbonyloxyalkyl, or alkenyl (C2-C10)carbonyloxyalkyl; R ⁵ is -CH ₂ - or -CH(OH)-; n ₂ , n ₃ n ₄ are each 1 or 2 and Z ² is the same as Z ¹ above.

Specific examples of insolvents that can be used in the present invention include the following compounds:

A particularly preferred insolvent is Sequarez 755 available from Omnova. Sequarez 755 reacts with the functional groups of the binder, which renders the coating highly insoluble.

The insolvent can be present in the image layer, the protective coating, or both. The imaging layer and/or protective coating then comprise an insolubilizer, which is typically present in an amount of 0.01-15%, more preferably 0.5-10%, based on the total solids content of the imaging layer and protective coating.

A photosensitive material according to one embodiment of the present invention is illustrated in Figure 1 in detail. Self-contained imaging system 10 includes: transparent support 12 , sublayer 11 , imaging composition 14 comprising photohardenable microcapsules 16 and developer material 18 , and protective coating 20 . In another embodiment (not shown), the photohardenable microcapsules and developer material are provided as separate adjacent layers in the imaging layer. Imaging layer 12 typically comprises about 20-80% by weight (dry weight) developer, about 80-20% by weight (dry weight) microcapsules, and 0-20% binder. Imaging layers are typically applied at a dry coat weight of about 8-20 g/ ^cm2 .

Images are formed in the present invention in the same manner as described in US Patent No. 4,440,846. By imagewise exposing the unit to actinic radiation, the microcapsules undergo differential hardening in the exposed regions. The exposure unit is pressurized to rupture the microcapsules. FIG. 2 shows the self-contained imaging system of FIG. 1 after microcapsules 16 have been exposed and ruptured. The ruptured microcapsules 22 release the coupler so that the developer material 18 reacts with the coupler to form the image 24 . The formed image is visible against the carrier 12 through the clear protective coating. The support 12 is preferably an opaque support comprising an opacifying agent such as polyethylene terephthalate (PET), paper or paper lined with a film (polyethylene, polypropylene, polyester, etc.). Most preferably, the opaque support is a polyethylene terephthalate support comprising about 10% titanium dioxide to give a bright white support. This vector is commercially available from ICI Corporation under the tradename Melinex. Typically, PET supports have a thickness of about 2-4 mils, but the present invention can use supports having a thickness of about 4-10 mils for more rigid imaging media.

In general, opaque supports are commercially available. Certain other products that may be used include paper, paperboard, polyethylene, polyethylene coated paper, and the like. Opaque films are composites or mixtures of polymers and pigments in a single layer, films or coated papers. Alternatively, the opacifying agent may be provided in a separate layer under or overlying a polymer film such as PET. The opacifier used for these materials is an inert reflective material with a white opaque background. Materials that can be used as opacifying agents include inert light scattering white pigments such as titanium dioxide, magnesium carbonate or barium sulfate. In a preferred embodiment, the opacifying agent is titanium dioxide.

The center of operation of the imaging system of the present invention is the encapsulated or microcapsule internal phase. According to the invention, the internal phase comprises a photosensitive composition and a chromogenic material. Generally, a photosensitive composition includes a photoinitiator and a substance capable of producing a change in viscosity by light exposure in the presence of the photoinitiator. The material is most commonly a monomer, dimer, or oligomer polymerized into higher molecular weight compounds or it may be a cross-linked polymer. If a negative working imaging material is desired, it may be a compound that depolymerizes or decomposes upon exposure.

Typically, the photosensitive composition is a free radical addition polymerizable or crosslinkable composition. The most common examples of free radical addition polymerizable or crosslinkable compositions useful in the present invention include an ethylenically unsaturated compound, more specifically, a polyethylenically unsaturated compound. These compounds include monomers with one or more ethylenically unsaturated groups, such as vinyl or allyl, and polymers with terminal or pendant ethylenic unsaturation. These compounds are well known in the art and include acrylic and methacrylate esters of polyols such as trimethylolpropane, pentaerythritol, and the like; acrylate or methacrylate terminated epoxies, acrylate or methacrylate End-capped polyester, etc. Representative examples include ethylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, dipentaerythritol hydroxypentaacrylate ( DPHPA), hexanediol-1,6-dimethacrylate, and diethylene glycol dimethacrylate. Other radiation curable materials and radiation depolymerizable materials are described in US Patent 4,399,209.

Color-developing materials used in the present invention include those commonly used in carbonless paper. Generally, these materials are colorless electron-donating dye precursor compounds capable of reacting with developer compounds to form dyes. Representative examples of these dye precursors include substantially colorless compounds having a lactone, lactam, sultone, spiropyran, ester or amido structure in part of their skeleton. Specifically, there are triarylmethane compounds, diphenylmethane compounds, xanthene compounds, thiazine compounds, spiropyran compounds and the like. Typical examples include crystal violet lactone, benzoyl leuco methylene blue, malachite green lactone, p-nitrobenzoyl leuco methylene blue, 3-dialkylamino-7-dialkylamino-fluoran (fluoran ), 3-methyl-2,2'-spirobis(benzo-f-chromium), 3,3-bis(p-dimethylaminophenyl)-2-benzo-[c]furanone, 3-(p-dimethylaminophenyl)-3-(1,2-dimethylindol-3-yl)-2-benzo-[c]furanone, 3-(p-dimethyl Aminophenyl)-3-(2-methylindol-3-yl)-2-benzo-[c]furanone, 3-(p-dimethylaminophenyl)-3-(2-benzene Indol-3-yl)-2-benzo-[c]furanone, 3,3-bis(1,2-dimethylindol-3-yl)-5-dimethylamino-2- Benzo-[c]furanone, 3,3-bis(1,2-dimethylindol-3-yl)-6-dimethylamino-2-benzo-[c]furanone, 3, 3-bis(9-ethylcarbazol-3-yl)-5-dimethylamino-2-benzo-[c]furanone, 3,3-bis(2-phenylindol-3-yl )-5-Dimethylamino-2-benzo-[c]furanone, 3-p-dimethylaminophenyl-3-(1-methylpyrrol-2-yl)-6-dimethyl Amino-2-benzo-[c]furanone, 4,4'-di-dimethylaminobenzoyl benzyl ether, N-halophenyl colorless basic bright yellow, N-2,4,5 -Trichlorophenyl colorless basic bright yellow, rhodamine B-anilinolactam, rhodamine (Thodamine) (p-nitroanilino) lactam, rhodamine-B-(p-chloroanilino ) lactam, 3-dimethylamino-6-methoxyfluoran (fluororan), 3-diethylamino-7-methoxyfluoran (fluororan), 3-diethylamino-7-chloro -6-methylfluoran (fluororan), 3-diethylamino-6-methyl-7-anilinofluoran (fluororan), 3-diethylamino-7-(acetylmethylamino)fluorine Alkane (fluororan), 3-diethylamino-7-(dibenzylamino) fluoran (fluororan), 3-diethylamino-7-(methylbenzylamino) fluoran (fluororan), 3- Diethylamino-7-(chloroethylmethylamino)fluoran (fluororan), 3-diethylamino-7-(diethylamino)fluoran (fluororan), 3-methyl-spiro-di Naphthopyran, 3,3'-dichloro-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho-(3-methoxybenzo )-spiropyran, 3-propyl-spirodibenzodipyran, etc. Mixtures of these dye precursors can also be used as desired. Also useful in the present invention are the fluoran couplers disclosed in US Patent 3,920,510, which is incorporated herein by reference.

In accordance with the present invention, the chromogenic material is added to the internal phase in an amount sufficient to react with the developer to produce a visible image of the desired density. Generally, these amounts will range based on the internal phase solution containing the chromophores (e.g., monomers, oils and other additives) about 0.5-20.0% by weight. A preferred range is about 2-8%. The amount of chromogenic material required to obtain a suitable image depends on the nature of the color body, the nature of the internal phase, and the type of imaging system. Less chromogenic material can be used in the internal phase of a self-contained imaging system where the developer material is co-deposited with the microcapsules on a common substrate. In order to prevent undesired coloration on the self-contained sheet, color inhibitors can be added to the color developing material.

In addition to chromogenic and photosensitive materials, the microcapsule internal phase may also include carrier oils to affect and control the tonal quality of the resulting image. Tonal quality (halftone sequence) is an important factor in faithfully reproducing an image. Initial studies have shown that 20% of a carrier oil such as brominated paraffin improves tint quality if trimethylolpropane triacrylate is used in radiation curable materials. The preferred carrier oil is a weakly polar solvent with a boiling point higher than 170°C, preferably 180-300°C. The carrier oils used in the present invention are generally those commonly used in carbonless paper manufacture. These oils are generally characterized by their ability to dissolve crystal violet lactone at concentrations of 0.5% by weight or greater. But a carrier oil isn't always necessary. Whether a carrier oil should be used depends on the solubility of the chromogenic material in the photosensitive composition prior to exposure, the nature of the chromogenic material and the intrinsic viscosity of the internal phase. Examples of carrier oils, if present, are alkylated biphenyls (e.g., monoisopropylbiphenyl), polychlorinated biphenyls, castor oil, mineral oil, deodorized kerosene, naphthalene mineral oil, diphthalate Butyl esters, dibutyl fumarate, brominated paraffins and mixtures thereof. Alkylated biphenyls are generally less toxic and therefore preferred.

A variety of photoinitiators can be selected for use in the present invention. These compounds absorb exposure radiation and generate free radicals alone or in combination with photosensitizers, usually homolytic photoinitiators that split to form two free radicals, and initiators that convert radiation into active abstraction of hydrogen to generate free radicals. There are also initiators capable of complexing with photosensitizers to generate species capable of forming free radicals, and initiators which otherwise generate free radicals in the presence of photosensitizers. Both can be used. If UV photosensitivity is desired, such as when using UV light for direct image transfer, suitable photoinitiators include α-alkoxyphenyl ketones, O-acrylated-α-oximinyl ketones, polycyclic quinones, benzophenones, and Substituted benzophenones, xanthones, thioxanthones, halogenated compounds such as chlorosulfonyl and chloromethyl polynuclear aromatic compounds, chlorosulfonyl and chloromethyl heterocyclic compounds, chlorosulfonyl and chloromethyl benzophenones and fluorenones, halogenated alkanes, α-halo-α-phenylacetophenones; photoreducible dye-reducing redox couples, halogenated paraffins (e.g., brominated or chlorinated paraffins), and benzoinalkyls ether. Specific photoinitiators useful in the present invention include: α-alkoxyketones, α,α-dialkoxyketones, benzophenones, xanthenes, chloroxanthones, chloromethylxanthones, chlorosulfonyl (sulfoxyl)xanthone, thioxanthone, chloroxanthone, chloromethylthioxanthone, chlorosulfonyl (sulforyl) thioxanthone, chloromethylnaphthalene, chlorosulfonylnaphthalene, chloromethylanthracene, chlorosulfonyl Acyl anthracene, chloromethylbenzoxazole, chloromethylbenzothiazole, chloromethylbenzimidazole, chlorosulfonylbenzoxazole, chlorosulfonylbenzothiazole, chlorosulfonylbenzimidazole, chloromethyl Quinoline, chlorosulfonylquinoline, chloromethylbenzophenone, chlorosulfonylbenzophenone, chloromethylfluorenone, chlorosulfonylfluorenone, carbon tribromide, benzoin methyl ether, benzoin Ethyl ether, benzophenone chloride, benzophenone amine, methylene blue/ascorbic acid, chlorinated aliphatic hydrocarbons and mixtures thereof. The photosensitivity of these compounds can be altered by adding substituents that cause the compounds to generate free radicals when exposed to the desired wavelength of radiation.

Particularly suitable photoinitiators for use in the present invention are cationic dye-borate anion complexes such as those disclosed in U.S. Patent Nos. 5,112,752, 5,100,755, 5,057,393, 4,865,9422, 4,842,980, 4,800,149, 4,772,530, and 4,772,541, which are incorporated herein by reference . If used as a photoinitiator in the present invention, the cationic dye-borate anion complex is generally used in an amount of up to about 1% by weight based on the weight of the photopolymerizable or crosslinkable material in the photohardenable composition. More generally, cationic dye-borate anion complexes are typically used in amounts of about 0.22-0.5% by weight. Although cationic dye-borate anion complexes can be used alone as initiators, it is preferred to use the complexes in combination with an autoxidant. An autooxidant is a compound capable of consuming oxygen in a free radical chain process. Examples of useful autooxidants are N,N-dialkylanilines.

Examples of N,N-dialkylanilines are dialkylanilines substituted at one or more o-, meta- or para positions by: methyl, ethyl, isopropyl, tert-butyl , 3,4-tetramethylene, phenyl, trifluoromethyl, acetyl, ethoxycarbonyl, carboxyl, carboxylate, trimethylsilylmethyl, trimethylsilyl, triethyl Silyl, trimethylgermanyl, triethylgermanyl, trimethylstannyl, triethylstannyl, n-butoxy, n-pentyloxy, phenoxy, Hydroxy, acetyloxy, methylthio, ethylthio, isopropylthio, thio (mercapto), acetyl, fluorine, chlorine, bromine and iodine. Examples of N,N-dialkylanilines useful in the present invention are 4-cyano-N,N-dimethylaniline, 4-acetyl-N,N-dimethylaniline, 4-bromo-N, N-dimethylaniline, 4-(N,N-dimethylamino)ethyl 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,N-dimethylaniline, N,N-dimethylthioanicidine, 4-amino-N,N-dimethylaniline, 3-hydroxy-N,N-dimethylaniline Aniline, N, N, N', N'-tetramethyl-1,4-benzidine, 4-acetylamino-N, N-dimethylaniline, 2,6-diisopropyl-N, N-dimethylaniline, 2,6-diethyl-N,N-dimethylaniline, N,N,2,4,6-pentamethylaniline (PMA) and p-tert-butyl-N, N-Dimethylaniline.

According to one embodiment of the present invention, the photohardenable composition for the microcapsules comprises a dye borate photoinitiator and a disulfide coinitiator. Examples of useful disulfides are described in US Patent 5,230,982.

According to one embodiment of the present invention there is provided a full color imaging system wherein the microcapsules are in three groups comprising cyan, magenta and yellow couplers respectively sensitive to red, green and blue light. For good color balance, the visible light-sensitive microcapsules are sensitive ( _λmax ) at about 450 nm, 540 nm, and 650 nm, respectively. This system can be used with visible light sources in direct transmission or reflection imaging. This material can be used to make contact prints, projection prints of color photographic slides, or digital prints. They can also be used for electronic imaging using laser or light beam sources of appropriate wavelengths. Because digital imaging systems do not require the use of visible light, photosensitivity can be extended to UV and IR. Therefore, photosensitivity can be extended to IR and/or UV to broaden the absorption spectrum of photoinitiators and avoid crosstalk.

Developer materials used in carbonless paper technology can be used in the present invention. Illustrative examples are clays such as acid clay, activated clay, diatomaceous earth, etc.; organic acids such as tannic acid, gallic acid, propyl gallate, etc.; acid polymers such as phenolic resins, phenol acetylene condensation resins, resins having at least one hydroxyl group Condensates of organic carboxylic acids and formaldehyde, etc.; metal salts of aromatic carboxylic acids or their derivatives such as zinc salicylate, tin salicylate, zinc 2-hydroxynaphthoate, 3,5-di-tert-butyl salicylate Zinc acid, zinc 3,5-bis-(α-methylbenzyl) salicylate, oil-soluble metal salts or novolac resins (see, for example, US Patents 3,672,935 and 3,732,120) zinc-modified oils such as those disclosed in US Patent 3,732,120 Soluble phenolic resin, zinc carbonate, etc.; and mixtures thereof. The particle size of the developer material is important to obtain high-quality images. The developer particles should be about 0.2-3 microns, preferably about 0.5-1.5 microns.

Suitable binders such as polyethylene oxide, polyvinyl alcohol, polyacrylamide, acrylic latex, neoprene latex, polystyrene emulsion, and nitrile emulsion, etc. can be combined with the developer and The microcapsules are mixed to form a coating composition. Preferably, the adhesive is also stable under changes in humidity. A preferred binder is NIPOL LX852, a modified acrylate type latex available from Nippon Zeon.

If the microcapsules and developer are mixed and used in one layer or wet coated in adjacent layers to form a self-contained system, the developer material preferably has excellent compatibility with the microcapsule slurry solution. Many materials including zinc salicylate and certain phenolic resin formulations have minimal or poor compatibility with MF microcapsule formulations and thus cause aggregation, believed to be due to the emulsifiers used to prepare the microcapsules and developer incompatible. The problem manifests itself as an increase in solution viscosity or instability of the microcapsule wall or both. Microcapsules can be completely ruptured with complete collapse or fragmentation of the walls. This problem is believed to be caused by the presence of water soluble acid salts in the developer solution. The developer material can be made compatible with the MF microcapsules by modifying the acid salts so that they are water soluble. A preferred developer with good stability is a solution of Schenetady International phenolic resin HRJ-4250.

Microencapsulation is achieved by various known methods including coacervation, interfacial polymerization, polymerization of one or more monomers in oil, and various melting, dispersing and cooling methods. In one embodiment of the invention, the internal phase is encapsulated in a urea-formaldehyde wall former, more particularly a urea-resorcinol-formaldehyde wall former to which resorcinol has been added to enhance its lipophilicity in the dose. Other hydrophilic wall-forming materials that may also be used in the present invention include gelatin (see U.S. Patents 2,730,456 and 2,800,457 to Green et al.), gum arabic, polyvinyl alcohol, carboxymethylcellulose; resorcinol-formaldehyde resins (see issued U.S. Patent 3,755,190 to Hart et al.), isocyanates (see U.S. Patent 3,914,511 to Vassiliades), polyurethanes (see U.S. Patent 3,796,669 to Kiritani et al.), melamine-formaldehyde resins and hydroxypropyl cellulose, urea-formaldehyde wall forming agents, especially urea-resorcinol-formaldehyde wall formers in which lipophilicity is enhanced by the addition of resorcinol (see U.S. Patents 4,001,140, 4,087,376, and 4,089,802 to Foris et al.), melamine-formaldehyde resins, and Hydroxypropylcellulose (see commonly assigned US Patent 4,025,455 to Shackle). To the extent sufficient to fully disclose those wall-forming materials, the above patents are hereby incorporated by reference. Melamine-formaldehyde resin capsules are particularly useful. The present invention intends to provide a pre-wall in the preparation of microcapsules. See US Pat. No. 4,962,010 for particularly preferred encapsulation using pectin and sulfonated polystyrene as system modifiers. The formation of pre-walls is known, but it is better to use larger amounts of polyisocyanate precursors. Capsule size should be chosen to minimize light attenuation.

The average size of the capsules used in the present invention can vary widely, but is generally about 1-25 microns. In principle, image resolution increases with decreasing capsule size, but if the capsule size is too small, the capsule will not fit properly in the carrier, and the carrier may shadow the capsule during exposure. The very small capsules also cannot burst when pressure is applied. In view of the foregoing, it has been found that the preferred average capsule size range is about 1-15 microns, especially about 1-10 microns.

To ensure effective adhesion of the imaging system to the support, an additional layer may be provided between the support and the imaging layer. (The term "imaging layer" refers to a mixed layer of microcapsules and developer or a combination of a layer of microcapsules and a developer layer). According to a preferred embodiment of the present invention, the sublayer is formed from a compound having a chemical moiety such as a hydroxyl group, which is combined with microcapsules such as partially hydrolyzed polyesters of aromatic acids and aliphatic or cycloaliphatic alcohols and Sulfonated polyesters and salts thereof, such as AQ polymers such as AQ38 and AQ55 available from Eastman Chemical, were reacted and bonded. Useful polymers also include polyethylene oxide, more especially AQUAZOL. The secondary layer may be applied at a coat weight of about 1-4 g/ ^cm2 (dry weight).

One technique that can be used to increase media stability consists in conditioning the developer and microcapsule layers at a relative humidity of about 45-80%, preferably about 60%. Most preferably, the layer is conditioned at ambient temperature at about 60% relative humidity for about 2-12 hours or longer. This is beneficial for image retention and actinic speed.

The protective coating is usually applied to the photosensitive layer in the form of an aqueous coating solution. The coating can be applied by any conventional method known in the art, including solvent casting, knife coating, extrusion coating, gravure printing, and reverse roll coating. The preferred viscosity and total solids content of the coating solution depend on the coating method used. The coating should be substantially transparent and should have minimal light spread to minimize image distortion. The coating should maintain these properties over a broad temperature range without appreciable changes in transparency or light scattering properties. The coating is typically applied at a coating thickness of about 4-15 microns, with a preferred coating thickness of about 9 microns.

The invention is described in more detail by the following non-limiting examples.

Simulation laboratory capsule preparation

1. Into a 200 ml stainless steel beaker, weigh 110 grams of water and 4.6 grams of the anhydrous sodium salt of polyvinylbenzenesulfonic acid (VERSA).

2. Clamp the beaker in place on the hot plate under the overhead mixer. A six-bladed, 45° pitch, turbine impeller was used on the mixer.

3. After mixing well, slowly sieve 4.0 grams of pectin (methyl polygalacturonate) into the beaker. The mixture was stirred at room temperature for 2 hours (800-1200 rpm).

4. Adjust the pH to 6.0 with 2% sodium hydroxide.

5. Turn the mixer to 3000 rpm and add the internal phase within 10-15 seconds. Continue to emulsify for 10 minutes. The magenta and yellow precursor phases are emulsified at 25-30°C, and the cyan phase is emulsified at 45-50°C (oil), 25-30°C (water).

6. After starting the emulsification, turn the hot plate up to continue heating during the emulsification process.

7. After 20 minutes, reduce the mixing speed to 2000 rpm and slowly add the solution of melamine-formaldehyde prepolymer. The prepolymer was prepared by adding 6.5 grams of formaldehyde solution (37%) to a dispersion of 3.9 grams of melamine in 44 grams of water. After stirring at room temperature for 1 hour, the pH was adjusted to 8.5 with 5% sodium carbonate and heated to 62° C. until the solution became clear (30 minutes).

8. Adjust the pH to 6.0 with 5% phosphoric acid. The beaker was then covered with foil and placed in a water bath to bring the temperature of the formulation to 75°C. When 75°C was reached, the hot plate was adjusted to maintain this temperature during the 2 hour curing time, during which time the capsule walls formed.

9. After curing, the mixing speed was reduced to 1800 rpm, the formaldehyde trap solution (7.7 grams urea and 7.0 grams water) was added and the solution was cured for an additional 40 minutes.

10. After the 40 minute hold time, reduce the mixing speed to 1100 rpm and adjust the pH to 9.5 using 20% sodium hydroxide solution, then stir overnight at room temperature at 500 rpm.

Three batches of microcapsules were prepared as above using the three internal phase compositions given below for full color imaging sheeting.

Inner phase of yellow capsules (420 nm)

TMPTA 163.6g

Photoinitiator 0.80g

2-Mercaptobenzothiazole (MBT) 0.55g

2,6-Diisopropyldimethylaniline (DIDMA) 0.82g

CP 269 (yellow dye precursor from Hilton Davis) 16.0g

Desmodur N-100 (Bayer Biuret, polyisocyanate resin) 13.09g

Magenta Capsule Inner Phase (550nm)

TMPTA 147.3g

DPHPA 16.3g

Photoinitiator 0.47g

2-Mercaptobenzothiazole (MBT) 0.55g

2,6-Diisopropyldimethylaniline 1.09g

CP 164 (magenta dye precursor from Hilton Davis) 25.3g

Desmodur N-100 (Bayer Biuret, polyisocyanate resin) 13.09g

Cyan capsule inner phase (650 nm)

TMPTA 114.50g

DPHPA 49.10g

Photoinitiator 0.85g

2-Mercaptobenzothiazole (MBT) 0.55g

2,6-Diisopropyldimethylaniline 1.09g

CP 270 (cyan precursor from Yamada Chemical Co.Jpn) 16.0g

Desmodur N-100 (Bayer Biuret, polyisocyanate resin) 13.09g

A photosensitive coating composition was prepared by mixing the microcapsules prepared above in different percentage ratios. This ratio can be varied to obtain the desired photographic characteristics.

A typical coating composition can be applied to a PET support (Melinex) at various dry coat weights. A typical photosensitive microcapsule composition is:

Cyan Capsules 38%

Pinse Capsules 32%

Yellow capsule 30%

The following coating compositions were prepared and the imaging layer composition was coated onto a white PET support. A protective coating is overcoated onto the imaging layer. A comparative imaging medium was prepared in the same manner except that the imaging layer was formulated without the insolubilizer.

1) Imaging layer coating composition components % solid content wet weight (g) dry weight (g) photosensitive microcapsules 22.7 418.5 96 LX852 (Binder) 45.0 44.8 20.16 Sequarez 755 (non-solvent) 50.0 20 10 HRJ 4250 (developer) 33.0 439.4 145 H ₂ O 77.3 total 1000 270.16

2) Protective coating composition components % solid content wet weight (g) dry weight (g) SA 532 (Binder) 23.43 487.5 114.2 ULS-1383MG (UV absorber) 30.0 116 34.8 Glyoxal (crosslinking agent) 40.0 28.6 11.44 Snowtex C (pigment) 20.0 28.6 5.72 PELEX-OTP (surfactant) 5.0 28.6 1.43 F140NK (surfactant) 1.0 40 0.40 H ₂ O 270.7 total 1030 168

Inventive imaging media (I) and comparative imaging media (II) were imagewise exposed and developed using pressure and heat. Humidity stability was determined by measuring _Dmax and D50 before and after storage under high humidity conditions.

Humidity stability results under test conditions of 21°C/80%RH and 21°C/45%RH sample _Dmax D50 C m Y C m Y I (invention) start 1.75 1.72 1.61 1.15 1.16 1.60 I (invention) after 2 weeks at 21°C/80%RH 1.70 1.68 1.59 1.17 1.16 1.62 II (contrast) start 1.79 1.78 1.60 1.17 1.20 1.63 II (comparative) after 2 weeks at 21°C/80%RH 1.48 1.45 1.25 1.40 1.43 1.85

D50 = relative value

Compared to the comparative medium (II), the inventive medium (I) has good humidity stability, maintaining _Dmax , D50 even after storage at 21° C./80% RH.

After the invention has been described in detail according to a preferred embodiment, it will be apparent that modifications and changes can be made without departing from the scope of the invention as defined by the following claims.

Claims (29)

1. A self-contained photosensitive material comprising: carrier; an imaging layer on a support, said imaging layer comprising a developer material and a plurality of photosensitive microcapsules encapsulating a photosensitive composition and a colorant precursor; and a protective coating on the imaging layer, said protective coating comprising a cured film of a water-soluble or water-dispersible resin, Therein, by image-wise exposing the imaging layer to actinic radiation and rupturing the microcapsules, the colorant precursors are released from the microcapsules and react with the developer material to form a color image. 2. The photosensitive material according to claim 1, wherein the water-soluble or water-dispersible resin is an acrylic latex. 3. The photosensitive material according to claim 1, wherein said protective coating further comprises a crosslinking agent. 4. The photosensitive material according to claim 3, wherein the crosslinking agent is a polyvalent aldehyde. 5. The photosensitive material according to claim 4, wherein said polyvalent aldehyde is selected from the group consisting of glyoxal, glutaraldehyde and derivatives thereof. 6. The photosensitive material according to claim 5, wherein said water-soluble resin is acrylic latex and said crosslinking agent is glyoxal. 7. The photosensitive material according to claim 1, wherein said photosensitive material further comprises an accessory layer between said support and said imaging layer. 8. The photosensitive material according to claim 1, wherein said photosensitive material further comprises an insolubilizer. 9. The photosensitive material according to claim 8, wherein said insolubilizer is a compound represented by general formula (I), (II) or (III): wherein ^R1 and ^R2 are the same or different and represent H, OH, alkyl (C1-C10), hydroxyalkyl, polyhydroxy substituted alkyl, alkylcarbonyloxyalkyl, alkenyl (C2-C10) Carbonyloxyalkyl, or a carbonyloxyalkyl having a carboxyl, carboxyl salt or carboxyl ester group as a terminal group;

wherein ^R is H, OH, alkyl (C1-C10), hydroxyalkyl, polyhydroxy substituted alkyl, alkylcarbonyloxyalkyl, or alkenyl (C2-C10)carbonyloxyalkyl, n ₁ =2-4 and Z ¹ is:

If dioxane is formed, ^Z represents an H atom to form a diol if no dioxane is formed; or

Wherein ^R is H, OH, alkyl (C1-C10), hydroxyalkyl, polyhydroxy substituted alkyl, alkylcarbonyloxyalkyl, or alkenyl (C2-C10)carbonyloxyalkyl; R ⁵ is -CH ₂ - or -CH(OH)-; n ₂ , n ₃ , n ₄ are each 1 or 2 and Z ² is the same as Z ¹ above. 10. A photosensitive material according to claim 8, wherein said insolubilizer is present in said imaging layer. 11. The photosensitive material according to claim 8, wherein said insolubilizer is present in said protective coating. 12. The photosensitive material according to claim 9, wherein said insolubilizer is selected from the following compounds:

13. The photosensitive material according to claim 12, wherein said insolubilizer is:

14. The photosensitive element according to claim 8, wherein the insolubilizer is present in an amount of about 0.5-10% based on the combined dry weight of the protective coating and imaging layer. 15. The photosensitive material according to claim 1, wherein said support is an opaque polyethylene terephthalate film comprising a white pigment. 16. The photosensitive material according to claim 1, wherein said imaging layer further comprises a binder. 17. The photosensitive material according to claim 16, wherein said binder is a modified acrylate latex. 18. The photosensitive material according to claim 1, wherein the protective coating comprises about 60-80% by dry weight of the water-soluble or water-dispersible resin and about 4-10% of the cross-linking agent. 19. The photosensitive material according to claim 1, wherein said protective coating further comprises a UV absorber. 20. The photosensitive material of claim 1, wherein the protective coating has a thickness of about 4-15 microns. 21. A photosensitive material according to claim 1, wherein said imaging layer comprises a layer of microcapsules and a separate layer of developer material. 22. A photosensitive material comprising a carrier having a layer of microcapsules thereon, said photosensitive microcapsule comprising an internal phase containing a photosensitive composition and a colorant precursor, wherein said photosensitive material is image-wise exposed Upon rupture of the microcapsules by actinic radiation and in the presence of a developer material, said colorant precursor reacts imagewise with said developer to form a color image, wherein the improvement is that said photosensitive material further comprises A protective coating on the microcapsule layer, said protective coating comprising about 60-80% acrylic latex and about 4-10% polyvalent aldehyde. 23. The photosensitive material according to claim 22, further comprising an insolubilizer. 24. A method for producing a self-contained photosensitive material comprising: (a) coating a photosensitive imaging composition on a support to form an imaging layer, the photosensitive imaging composition comprising a developer material and a plurality of photosensitive microcapsules encapsulated with a photosensitive composition and a colorant precursor; (b) overcoating said imaging layer with a overcoat composition comprising a water soluble or water dispersible resin; and (c) drying and/or curing the protective coating. 25. The method according to claim 24, wherein said water soluble or water dispersible resin is an acrylic latex. 26. The method of claim 24, wherein the protective coating further comprises a crosslinking agent. 27. The method according to claim 26, wherein said water soluble resin is an acrylic latex and said crosslinking agent is glyoxal. 28. The method of claim 24, wherein the protective coating composition further comprises an insolubilizer. 29. The method of claim 24, wherein said imaging composition further comprises an insolubilizer.

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