Thermochromic laminate

Abstract: A thermochromic laminate was provided which comprises a thermochromic layer, and a coating layer or layers laminated thereon containing a light-intercepting pigment and a light stabilizer; the coating layer or layers containing the light-intercepting pigment and the light stabilizer dispersed and fixed in a first film-forming material, and the thermochromic layer constituted of a homogeneous solid composed of an electron-donating coloring organic compound, an electron-accepting compound, and an organic compound medium for adjusting color reaction temperature dispersed and fixed in a second film forming material; the light-intercepting pigment being one or more pigments selected from metallic luster pigments, transparent titanium dioxide, transparent iron oxide, transparent cesium oxide, and transparent zinc oxide; and the light stabilizer being one or more chemicals selected from ultraviolet absorbers, antioxidants, singlet oxygen quenchers, superoxide anion quenchers, ozone quenchers, visible light absorbers, and infrared absorbers. The thermochromic laminate has remarkably improved light-fastness.

Description: The present invention relates to a thermochromic laminate. More specifically, the present invention relates to a thermochromic laminate having remarkably improved light-fastness. Many attempts have been made to improve the light-fastness of thermochromic materials. For example, JP-B-4-18543 describes lamination of a synthetic resin layer containing an ultraviolet absorber, an antioxidant, and the like on the thermochromic layer. ("JP-B" herein means an "examined Japanese patent publication".) In another attempt, a light reflection layer or a light absorption layer is provided on a thermochromic layer to reflect or absorb ultraviolet light or visible light to protect the underlying thermochromic layer from light. In a still another attempt, a color filter is employed. The above attempts have disadvantages. When the thermochromic material contains an electron-donating coloring organic compound and an electron-accepting compound, deterioration by light of the electron-donating coloring organic material cannot be completely prevented by single use of a UV-intercepting means like the UV absorber. The light reflection layer, which gives satisfactory effect, makes the thermochromic layer whitish owing to the reflectivity of the reflection layer, preventing visual observation of color change of the underlying thermochromic layer. The light absorption layer, which is inevitably dark colored or blackish, also prevents visual observation of the color change of the underlying thermochromic layer. With the color filter, for example, one having a yellow-colored layer, a blue-colored thermochromic layer is observed to be green visually owing to the yellow layer since the electron-donating coloring organic compound absorbs yellow light and reflects blue light; when the thermochromic layer turns colorless, only the yellow light reflected by the yellow color layer is observed visually since the electron-donating coloring organic compound reflects all visible light; thereby the observed color changes reversibly between green and yellow. Thus, use of a color filter visualizes the reversible change between two colored states, but is not capable of visualizing the reversible color change between a colored state and a colorless state. EP-A-0523888 describes a thermochromic laminate capable of reversible change from metallic luster to colorless which comprises a first layer for regulating the wavelength of reflected light and composed of a metal luster pigment and a film-forming material, and a second layer composed of a thermochromic material which consists of an electron donating compound, an electron accepting compound and an organic medium enabling a reversible color forming reaction between those compounds and a film-forming material. In accordance with the present invention, there is now provided a thermochromic laminate comprising a thermochromic layer and a coating layer or layers laminated thereon containing a light-intercepting pigment and a light stabilizer, one of the coating layers being a combined layer which contains both the light-intercepting pigment and the light stabilizer dispersed and fixed in a film-forming material, the light-intercepting pigment being one or more pigments selected from metallic luster pigments, transparent titanium dioxide, transparent iron oxide, transparent cerium oxide and transparent zinc oxide, and the light stabilizer being one or more chemicals selected from ultraviolet absorbers, antioxidants, singlet oxygen quenchers, superoxide anion quenchers, ozone quenchers, visible light absorbers, and infrared absorbers; and the thermochromic layer being a homogeneous solid mixture of an electron-donating coloring organic compound, an electron-accepting organic compound, and an organic compound medium for adjusting the color reaction temperature dispersed and fixed in an amount of 0.5 - 40 % based on the weight of the thermochromic layer, in a film-forming material. The thermochromic laminate of the present invention differs from the thermochromic laminate described in EP-A-0523888 by including a coating layer which contains a light stablizer as well as, inter alia, the metallic luster pigment and the film-forming material. The present invention is described in greater detail below by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional view of an example of a prior art thermochromic laminate; Fig. 2 is a cross-sectional view of another example of a prior art thermochromic laminate; Fig. 3 is a cross-sectional view of an example of a thermochromic laminate of the present invention; Fig. 4 is a cross-sectional view of a further example of a thermochromic laminate of the present invention; and Fig. 5 is a cross-sectional view of a still further example of a thermochromic laminate of the present invention. Referring to the drawings, the thermochromic laminate 1 comprises a thermochromic layer, and a coating layer or layers laminated thereon containing a light-intercepting pigment and a light stabilizer. The light-intercepting pigment is one or more pigments selected from metallic luster pigments, transparent titanium dioxide, transparent iron oxide, transparent cesium oxide, and transparent zinc oxide. The light stabilizer is one or more chemicals selected from ultraviolet absorbers, antioxidants, singlet oxygen quenchers, superoxide anion quenchers, ozone quenchers, visible light absorbers, and infrared absorbers. The combined coating layer 5 is constituted of the light-intercepting pigment and the light stabilizer dispersed and fixed in a film forming material, and the thermochromic layer 2 is constituted of a homogeneous solid composed of an electron-donating coloring organic compound, an electron-accepting compound, and an organic compound medium for adjusting the color reaction temperature dispersed in a film forming material. In the prior art materials, the coating layer is constituted by two layers, a light-intercepting pigment layer 3 and a light stabilizer layer 4, the light-intercepting pigment layer containing a light-intercepting pigment dispersed and fixed in a film-forming material, and the light stabilizer layer containing a light stabilizer dispersed and fixed in a film-forming material. The light stabilizer layer 4 may be laminated on or underneath the light-intercepting layer 3. (Coating layer type (1) shown in Figs. 1 and 2.) According to the invention, the coating layer includes a single combined layer 5 containing both the light-intercepting pigment and a light stabilizer dispersed in a film-forming material (Coating layer type (2), shown in Fig. 3.) The coating layer may also have a light stabilizer layer 4 laminated on the combined layer 5 (Coating layer type (2-1) as shown in Fig. 4) or underneath the combined layer 5 (Coating layer type (2-2) as shown in Fig. 5). Preferably, the light-intercepting pigment is a metallic luster pigment composed of particulate natural mica coated with titanium oxide in a particle size of from 5 to 100 µm, and the light stabilizer is selected from ultraviolet absorbers. Specific examples of the metallic luster pigment include a gold metallic luster pigment composed of natural mica coated with 41 to 44 % by weight of titanium oxide and having a particle size of 5 to 60 µm; a gold metallic luster pigment composed of natural mica coated with 30 to 38 % by weight titanium oxide and further coated thereon with 0.5 to 10 % by weight of non-thermochromic colored pigment and having a particle size of 5 to 60 µm; a silver metallic luster pigment composed of natural mica coated with 16 to 39 % by weight of titanium oxide and having a particle size of 5 to 100 µm; a metallic color luster pigment composed of natural mica coated with 45 to 58 % by weight of titanium oxide; a metallic color luster pigment composed of natural mica coated with 45 to 58 % by weight of titanium oxide, and further coated thereon with 4 to 10 % by weight of iron oxide; and a metallic color luster pigment composed of natural mica coated with 45 to 58 % by weight titanium oxide and further coated thereon with 0.5 to 10 % by weight of a non-thermochromic colored dye or pigment. Light stabilizers useful in the present invention are shown below specifically. The ultraviolet absorber includes: benzophenone type ultraviolet absorbers such as 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2',4,4'-tetrahydrobenzophenone, 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid, 2-hydroxy-4-octyloxybenzophenone, bis(2-methoxy-4-hydroxy-5-benzoylphenyl)methane, 2-(2'-hydroxy-3',5'-di-t-amylphenyl)benzophenone, 2-hydroxy-4-dodecyloxybenzophenone (trade name: Seesorb 103, produced by Shipro Kasei K.K.), 2-hydroxy-4-octadecyloxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-benzyloxybenzophenone, and 2-(2'-hydroxy-3',5'-di-t-amylphenyl)benzophenone; salicylic acid type ultraviolet absorbers such as phenyl salicylate, p-t-butylphenyl salicylate, p-octylphenyl salicylate, 2,4-di-t-butylphenyl-3,5-di-t-butyl-4-hydroxybenzoate, phenyl salicylate, 4-t-butylphenyl salicylate 4-octylphenyl salicylate, and resorcinol monobenzoate; cyanoacrylate type ultraviolet absorbers such as (ethyl)-(2-cyano-3,3'-diphenyl acrylate), 2-ethylhexyl-2-cyano-3,3'-diphenyl acrylate, 2-ethylhexyl-2-cyano-3-phenyl cinnate; benzotriazole type ultraviolet absorbers such as 2-(5-t-butyl-2-hydroxyphenyl)benzotriazole (trade name: Tinuvin-PS, produced by Ciba Geigy Co.), 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, 2-(3,5-di-t-butyl-2-hydroxyphenyl)benzotriazole, 2-(3-t-butyl-5-methyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(3,5-di-t-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(3,5-di-t-amyl-2-hydroxyphenyl)benzotriazole (trade name: Tinuvin 328, produced by Ciba Geigy Co.), condensate of methyl-3-[3-t-butyl-5-(2H-benzotriazole-2-yl)-4-hydroxyphenyl) propionate-polyethylene glycol (molecular weight: 300) (trade name: Tinuvin 213, produced by Ciba Geigy Co.), 2-(3-dodecyl-5-methyl-2-hydroxyphenyl)benzotriazole, condensate of methyl-3-[3-(2H-benzotriazol-2-yl)-5-t-butyl-4-hydroxyphenyl) propionate-polyethylene glycol (molecular weight: 300), (trade name: Tinuvin 213, produced by Ciba Geigy Co.) 2-(3-t-butyl-5-propyloxycarbonylethyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(2-hydroxy-5-t-octylphenyl)-2H-benzotriazole, 2-(3-t-butyl-5-octyloxycarbonylethyl-2-hydroxyphenyl)benzotriazole (trade name: Tinuvin 384, produced by Ciba Geigy Co.), 2-(2-hydroxy-5'-methylphenyl)benzotriazole, 2-(2-hydroxy-4-octyloxyphenyl)benzotriazole, 2-[2'-hydroxy-3'-(3",4",5",6"-tetrahydrophthalimidomethyl)-5'-methylphenyl]benzotriazole, and 2-(2-hydroxy-5-t-butylphenyl)benzotriazole; oxanilide type ultraviolet absorbers such as ethanediamido-N-(2-ethoxyphenyl)-N'-(4-isododecylphenyl), and 2,2,4,4-tetramethyl-20-(β-lauryloxycarbonyl)ethyl-7-oxa-3,20-diazodispiro[5.1.11.2]heneicosanoic acid-21-one. The antioxidant includes: hindered amine type antioxidants such as dimethyl succinate[1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine]polycondensate (trade name: Tinuvin 622LD, produced by Ciba Geigy Co.), poly[{6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-triazin-2,4-diyl}{(2, 2,6, 6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}], 2-(3,5-di-t-butyl-4-hydroxybenzyl)-2-n-butyl-malonate-bis(1,2,2,6,6-pentamethyl-piperidyl), N,N'-bis(3-aminopropyl)ethylenediamine-2,4-bis[N,butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino]-6-chloro-1,3,5-triazine condensate (trade name: Chimassorb 119FL, produced by Ciba Geigy Co.), bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, and bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate; phenol type antioxidants such as 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-4-methoxyphenol, 2,6-di-t-butyl-4-ethylphenol, octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,2-methylenebis(4-methyl-6-t-butylphenol), 4,4-thiobis(2-methyl-6-t-butylphenol), 2,2-thiobis(4-methyl-6-t-butylphenol), 4,4-butylidenebis(3-methyl-6-t-butylphenol), 3,9-bis[1,1-dimethyl-2-[β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydrdoxybenzyl)benzene, tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (trade name: Sumilizer BP-101, produced by Sumitomo Chemical Co.), 2,2-ethylenebis(4,6-di-t-butylphenol), 1,3,5-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)-s-triazine-2,4,6-(1H,3H,5H)-trione, tocopherol, 1,3,5-tris(4-t-butyl-3-hydroxy-,2,6-dimethylbenzyl) isocyanurate, pentaerythritol tetrakis(3-laurylthiopropionate), triethylene glycol bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] (trade name: Irganox 245, produced by Ciba Geigy Co.), 1,6-hexanediol bis[3,5-di-t-butyl-4-hydroxyphenyl)propionate], 2,2-thioethylene-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], N,N'-hexamethylene-bis(3,5-di-t-butyl-4-hydroxy-hydrocinnamide) (trade name: Irganox 1098, produced by Ciba Geigy Co.), tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate (trade name: Irganox 3114, produced by Ciba Geigy Co.), polymerized-2,2,4-trimethyl-1,2-hydroquinone, styrenatedphenol, 2,5-di-t-butylhydroquinone, and bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate; 2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine, and octylated diphenylamine. sulfur type antioxidants such as dilauryl 3,3'-thiodipropionate, dimyristyl 3,3'-thiodipropionate, distearyl 3,3'-thioodipropionate, and stearylthiopropylamide; phosphite type antioxidants such as tris(2,4-di-t-butylphenyl) phosphite, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, 3,5-di-t-butyl-4-hydroxybenzyl phosphanate diethyl ester, triphenyl phosphite, diphenyl isodecyl phosphite, phenyl isodecyl phosphite, 4,4'-butylidenebis(3-methyl-6-t-butylphenylditridecyl) phosphite, octadecyl phosphite, tris(nonylphenyl) phosphite, diisodecyl pentaerythritol diphosphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene, 10-(3,5-di-t-butyl-4-hydroxybenzyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-decyloxy-9,10-dihydro-9-oxa-10-phosphaphenanthrene, cyclic neopentan-tetra bis(2,4-di-t-butylphenyl) phosphite, cyclic neopentan-tetrayl-bis(2,6-di-t-butyl-4-methylphenyl) phosphite, and 2,2-methylenebis(4,6-di-t-butylphenyl)octyl phosphite. The singlet oxygen quencher includes carotenes, dyes, amines, phenols, nickel complexes and sulfides, specifically exemplified by 1,4-diazabicyclo[2.2.2]octane (DABCO), β-carotene, 1,3-cyclohexadiene, 2-diethylaminomethylfuran, 2-phenylaminomethylfuran, 9-diethylaminomethylanthracene, 5-diethylaminomethyl-6-phenyl-3,4-dihydroxypyrane, nickel dimethyldithiocarbamate, nickel 3,5-di-t-butyl-4-hydroxybenzyl-O-ethyl phosphonate, nickel 3,5-di-t-butyl-4-hydroxybenzyl-O-butyl phosphonate, nickel [2,2'-thiobis(4-t-octylphenolate)](n-butylamine), nickel [2,2'-thiobis(4-t-octylphenolate)](2-ethyhexylamine), nickel bis[2,2'-thiobis(4-t-octylphenolate)], nickel bis[2,2'-sulfone-bis(4-t-octylphenolate)], nickel bis[2-hydroxy-5-methoxyphenyl-N-n-butylaldimine), nickel bis(dithiobenzyl), and nickel bis(dithioacetyl). The superoxide anion quencher includes superoxide dismutase complex with nickel or cobalt. The ozone quencher includes 4,4'-thiobis(6-t-butyl-m-cresol), 2,4,6-tri-t-butylphenol, 1,4-diazabicyclo[2.2.2]octane, N-phenyl-β-naphthylamine, α-tocopherol, 4,4'-methylenebis(2,6-di-t-butylphenol), p,p'-diaminodiphenylmethane, 2,2'-methylenebis(6-t-butyl-p-cresol), N,N'-diphenyl-p-phenylenediamine, N,N'-diphenylethylenediamine and N-isopropyl-N'-phenyl-p-phenylenediamine. Visible light absorbers include dyes, pigments, and other colored substances. The dyes are exemplified by C.I. Solvent Yellow 19, 21, and 61; C.I. Solvent Orange 5, and 6; C.I. Solvent Red 8, and 24; C.I. Solvent Violet 14, and 21; C.I. Solvent Blue 11, and 25; and C.I. Solvent Black 5, and 125. The pigments are exemplified by those of Color Index numbers of 10825, 11680, 11725, 11780, 12060, 12120, 12490, 12500, 12710, 21090, 21110, 21165, 21180, 21205, 45170, 50440, 58055, 69800, 69810, 70600, 74160, 74265, and 127755. The infrared absorber is a compound which has absorption maximum at the near-infrared region of from 700 to 2000 nm and does not exhibit large absorption in visible region of from 400 to 700 nm, and is exemplified by the compounds represented by the chemical formulas below: where R 1 , R 2 , R 3 , and R 4 are an alkyl group independently; X is a halogen atom or a hydrogen atom; and Me is nickel, palladium, or platinum, where R 1 , R 2 , R 3 , and R 4 are an alkyl group independently; Me is nickel, palladium, or platinum; and X is a carbon atom, an oxygen atom, or a sulfur atom, where R 1 , R 2 , R 3 , and R 4 are an alkyl group independently; X is a halogen atom or a hydrogen atom; and Me is nickel, palladium, or platinum, where, R is a hydrogen atom, an alkyl group, a phenyl group, an alkyl- or alkoxy-substituted phenyl group, or a thienyl group; and Me is nickel, palladium, or platinum, where R is an alkyl group, and X is an anion group selected from perchlorate (ClO 4 - ), fluoroborate (BF 4 - ), trichloroacetate (CCl 3 COO - ), trifluoroacetate (CF 3 COO - ), picrate [(NO 3 ) 3 C 6 H 2 O - ], hexafluoroarsenate (AsF 6 - ), hexachloroantimonate (SbCl 6 - ), hexafluoroantimonate (SbF 6 - ), benzenesulfonate (C 6 H 5 SO 3 - ), alkylsulfonate (RSO 3 - ), phosphate (PO 4 3- ), sulfate (SO 4 2- ), chloride (Cl - ), and bromide (Br - ). The thermochromic layer is constituted of a thermochromic material containing an electron-donating coloring organic compound, an electron-accepting compound, and an organic compound medium (color change temperature controlling agent) for controlling the temperature of color reaction between the above two compounds. Such thermochromic materials are described for example, in JP-B-51-35414, JP-B-51-44706 and JP-B-1-17154. The thermochromic materials include: (1) Reversible thermochromic materials containing essentially three components of (a) an electron-donating coloring organic compound, (b) a compound having a phenolic hydroxyl group, and (c) a higher aliphatic monohydric alcohol having no polar substituent; (2) Reversible thermochromic materials containing essentially three components of (a) an electron-donating coloring organic compound, (b) a compound having a phenolic hydroxyl group, and (c) an ester derived from an aliphatic monohydric alcohol having no polar substituent and an aliphatic monocarboxylic acid having no polar substituent; (3) Reversible thermochromic materials containing essentially three components of (a) an electron-donating coloring organic compound, (b) a compound having a phenolic hydroxyl group, and (c) a compound selected from higher aliphatic monohydric alcohols having no polar substituent and esters derived from an acyclic aliphatic monohydric alcohol having no polar substituent and an aliphatic monocarboxylic acid having no polar substituent, the three components being enclosed in microcapsules; and (4) Reversible thermochromic materials containing essentially three components of (a) an electron-donating coloring organic compound, (b) a compound having a phenolic hydroxyl group, and (c) a compound selected from higher aliphatic monohydric alcohols having no polar substituent and esters derived from an acyclic aliphatic monohydric alcohol having no polar substituent and an aliphatic monocarboxylic acid having no polar substituent, the three components being dissolved or dispersed in a vehicle. The thermochromic materials also include that described in JP-B-4-17154, which is equivalent to GB-B-2 184 250, containing a thermochromic color memory dye which changes color with high hysteresis characteristics. That is, this material exhibits very different color-temperature dependence for the temperature rise from that for the temperature drop through the color-changing temperature range, and memorizes the changed color state at a temperature between the upper color change temperature and the lower color change temperature. The above-described thermochromic materials are usually applied in an enclosed state in microcapsules, but are effective also in a free state. The thermochromic material may be used in the form of a thermochromic coating layer formed by coating of a coloring material composed of the material dispersed in a binder-containing solvent; in the form of a sheet-shaped thermochromic layer formed by application on a release paper sheet and separation form it; or in the form of a thermochromic film or sheet formed from melt-blend of a microcapsule containing the thermochromic material with a thermoplastic resin. The thermochromic layer is not limited to be in a sheet form, but may be a thermochromic article in any desired shape comprising the thermochromic material enclosed in microcapsules dispersed in a thermoplastic resin or a thermosetting resin. The thermochromic material is contained in a film-forming material, or a thermoplastic or thermosetting resin in an amount of from 0.5 to 40 % by weight, preferably from 1 to 30 % by weight. At the content of lower than 0.5 % by weight, sharp color change is not observed visually, while, at the content of higher than 40 % by weight, the thermochromic material is excessive to cause residual color in a decolored state. The light-intercepting pigment layer 3 may be formed by dispersing a light-intercepting material in a solvent containing a film-forming binder and applying it, or may be formed in a film or a sheet shape from a blend of the light-intercepting material in a thermoplastic resin. The light-intercepting pigment has a particle diameter of from about 5 to about 100 µm and is dispersed uniformly in a film-forming material at a content of from 0.1 to 40 % by weight, preferably from 5 to 30 % by weight to achieve a desired light interception effect. The light stabilizer layer 4 contains one or more of the aforementioned light stabilizers at a content of from 1 to 40 % by weight, preferably from 5 to 30 % by weight, and is formed in a form of a coating layer, a film, or a sheet. The combined layer 5 contains both a light-intercepting pigment layer and a light stabilizer dispersed and fixed in one and the same layer, containing the light-intercepting pigment at a content of from 0.1 to 40 % by weight, preferably from 5 to 30 % by weight, and the light stabilizer at a content of from 1 to 40 % by weight, preferably from 5 to 30 % by weight, in the total amount thereof of from 1.5 to 60 % by weight, preferably from 5 to 40 % by weight. The combined layer may be formed by coating, or by molding in a shape of a film or a sheet as the aforementioned layers. The laminate 1 may be formed, specifically, in a known manner: including printing processes such as screen printing, offset printing, gravure printing, coater printing, tampo printing, and transfer printing; and coating processes such as brush coating, spray coating, electrostatic coating, electrodeposition,flow coating, roller coating, and immersion coating. Otherwise, the layers may be formed into sheets by extrusion molding or other molding process, and stuck together, or the thermochromic layer and the coating layer may be formed integrally by multifilm coextrusion. The base material for the thermochromic layer may be any material on which the thermochromic layer can be formed. The examples thereof includes sheets, films, paper sheets, synthetic paper sheets, knits, textiles, cloths, non-woven, synthetic leather, plastics, glass, porcelain, metal, wood and stone. The laminate may be a molded article in a certain shape, and may have a rough surface, or may be in a fiber form. The aforementioned thermochromic layer 2 may contain additionally a non-thermochromic pigment in an appropriate amount to give a variety of color change. Letters or drawings may be placed underneath the thermochromic layer to hide the images by color change. The film forming material includes: ionomer resins, isobutylene-maleic anhydride copolymer resins, acrylonitrile-acrylic styrene copolymer resins, acrylonitrile-styrene copolymer resins, acrylonitrile-butadiene-styrene copolymer resins, acrylonitrile-chlorinated polyethylene-styrene copolymer resins, ethylene-vinyl chloride copolymer resins, ethylene-vinyl acetate copolymer resins, ethylene-vinyl acetate-vinyl chloride graft copolymer resins, vinylidene chloride resins, vinyl chloride resins, chlorinated vinyl chloride resins, vinyl chloride-vinylidene chloride copolymer resins, chlorinated polyethylene resins, chlorinated polypropylene resins, polyamide resins, high density polyethylene resins, medium density polyethylene resins, linear low density polyethylene resins, polyethylene terephthalate resins, polybutylene terephthalate resins, polycarbonate resins, polystyrene resins, high-impact polystyrene resins, polypropylene resins, polymethylstyrene resins, polyacrylate ester resins, polymethyl methacrylate resins, epoxyacrylate resins, alkylphenol resins, rosin-modified phenol resins, rosin-modified alkyd resins, phenol-resin-modified alkyd resins, epoxy resin-modified alkyd resins, styrene-modified alkyd resins, acryl-modified alkyd resins, aminoalkyd resins, vinyl chloride-vinyl acetate resins, styrene-butadiene resins, epoxy resins, unsaturated polyester resins, polyurethane resins, vinyl acetate type emulsion resins, styrene-butadiene type emulsion resins, acrylate ester type emulsion resins, water-soluble alkyd resins, water-soluble melamine resins, water-soluble urea resins, water-soluble phenol resins, water-soluble epoxy resins, water-soluble polybutadiene resins, cellulose acetate, cellulose nitrate and ethylcellulose. Of the above film forming materials, suitable ones for formation of the coating layer include alkylphenol resins, rosin-modified phenol resins, rosin-modified alkyd resins, styrene-modified alkyd resins, acryl-modified alkyd resins, aminoalkyd resins, vinyl chloride-vinyl acetate resins, styrene-butadiene resins, epoxy resins, acrylate ester resins, unsaturated polyester resins, polyurethane resins, vinyl acetate type emulsion resins, styrene-butadiene type emulsion resins, acrylate ester type emulsion resins, water-soluble alkyd resins, water-soluble melamine resins, water-soluble urea resins, water-soluble phenol resins, water-soluble epoxy resins, water-soluble polybutadiene resins and cellulose derivatives. These resins are applied in a form of a solution or dispersion in water or an organic solvent. For formation of the film or the sheet, suitable film forming materials include ionomer resins, isobutylene-maleic anhydride copolymer resins, acrylonitrile-acrylic styrene copolymer resins, acrylonitrile-styrene copolymer resins, acrylonitrile-butadiene-styrene copolymer resins, acrylonitrile-chlorinated polyethylene-styrene copolymer resins, ethylene-vinyl chloride copolymer resins, ethylene-vinyl acetate copolymer resins, ethylene-vinyl acetate-vinyl chloride graft copolymer resins, vinylidene chloride resins, vinyl chloride resins, chlorinated vinyl chloride resins, vinyl chloride-vinylidene chloride copolymer resins, chlorinated polyethylene resins, chlorinated polypropylene resins, polyamide resins, high density polyethylene resins, medium density polyethylene resins, linear low-density polyethylene resins, polyethylene terephthalate resins, polybutylene terephthalate resins, polycarbonate resins, polystyrene resins, high-impact polystyrene resins, polypropylene resins, polymethylstyrene resins, polyacrylate ester resins, polymethyl methacrylate resins, epoxy resins, epoxyacrylate resins, alkyd resins and polyurethane resins. The laminate of the present invention may be formed on a base material, and may be a laminate of a film composed of a melt blend containing a light-intercepting pigment dispersed therein on a thermochromic film composed of a melt blend containing a thermochromic material dispersed therein. The light-intercepting pigment layer of the present invention performs both functions of light absorption (or light reflection) and light transmittance. Thereby, at least a part of ultraviolet light or visible light which causes deterioration of the function of the thermochromic layer is reflected or absorbed, and visible light is transmitted through the layer in a suitable ratio not to prevent visible observation. The functions of a system comprising a metallic luster pigment are explained below. This system intercepts near-ultraviolet light and visible blue light (having the shortest wavelength and the highest energy of the visible light) which greatly affect photolytic decomposition of a blue light-developing electron-donating organic compound of the thermochromic pigments. The metallic luster pigment itself also intercepts ultraviolet light, and reflects blue light selectively and allows yellow light to penetrate through the layer. In the case where the thermochromic pigment is blue, the electron-donating coloring organic compound absorbs yellow light and reflects blue light, whereby the reflected color is observed to be blue in combination with the blue light reflected by the metallic luster pigment. When the thermochromic pigment has turned colorless, the electron-donating coloring organic compound reflect all the visible light, and the yellow light transmitted through the metallic luster pigment layer is also reflected by the thermochromic pigment layer. Consequently, all the wave lengths of light is reflected, and the reflected light is observed to be colorless. Thereby, color changes between a blue color and non-color. This phenomenon cannot occur in a system of prior art employing a color filter. In this system, a part of the visible light is intercepted, and yet the reflected light in a decolored state is made colorless, thereby light-fastness is improved. The above system containing a metallic luster pigment enables color change from a gold color, a silver color or a metallic color owing to the rainbow effect caused by selective interference of visible light, light transmission effect, and luminosity of the thermochromic layer. In the present invention, formation of a combined layer improves light-fastness as shown in the light-fastness test results in Tables 3 to 6 in comparison with the Comparative Examples of Table 2: the coating layer including the coating layer of type (1) having a light stabilizer layer 4 laminated on or underneath the light-intercepting pigment layer 3 (Figs. 1 and 2) is therefore inferior to that in which the coating layer of type (2) having a combined layer 5 containing a light-intercepting pigment layer and a light stabilizer dispersed in the same film-forming material (Fig. 3); the coating layer of type (2-1) having a light stabilizer layer 4 laminated on the above combined layer 5 (Fig. 4); and the coating layer of type (2-2) having a light stabilizer layer 4 laminated underneath the above combined layer 5 (Fig. 5). It was found that the coating layer of type (2) (Fig. 3) which contains both a light-intercepting pigment and a light absorber dispersed in one and the same layer greatly improves the light-fastness in comparison with the coating layer of type (1) (Figs. 1 and 2) which has a light stabilizer layer 4 laminated on or underneath the light-intercepting pigment layer 3. The thermochromic laminate of the present invention is described below specifically by reference to Examples and Comparative Examples with the results of light-fastness tests. In the description below, "parts" are by weight. (1) Composition and color-changing properties of thermochromic pigment: Table 1 shows the compositions and the color-changing properties of the thermochromic pigments (A to F) applied to thermochromic layer of Examples 11 to 51 and Comparative Examples 1 to 10. The thermochromic pigment was a microcapsular pigment which was prepared by encapsulating, in a microcapsule, a homogeneous mixture of three components of an electron-donating coloring organic compound, an electron-accepting compound and an organic compound medium for controlling color-changing temperature by a known microcapsulation method. The thermochromic pigments for which the lower and higher color change temperatures are shown exhibit color memory thermochromism. (2) Preparation of the laminates of Comparative Examples 1 to 10: A thermochromic layer of about 40 µm thick was formed by mixing with agitation 10 parts of thermochromic pigment, 45 parts of 50% acrylic resin solution in xylene, 20 parts of xylene, and 20 parts of methyl isobutyl ketone, and applying the mixture on a white polyvinyl chloride sheet by spraying. On the thermochromic layer, a light-intercepting pigment layer of about 40 pm thick was formed by mixing with agitation one part of a light-intercepting pigment, 45 parts of 50% acrylic resin solution in xylene, 20 parts of xylene, and 20 parts of methyl isobutyl ketone, and applying the mixture by spraying. Further on the light-intercepting pigment layer, a light stabilizer layer of about 35 µm thick was prepared by agitating and mixing a predetermined amount (see Table 2) of a light stabilizer, 45 parts of 50% acrylic resin solution in xylene, 20 parts of xylene, and 20 parts of methyl isobutyl ketone, and applying the mixture by spraying. (3) Preparation of laminates of Examples 11 to 29 according to the invention: The thermochromic layer,was prepared in the same manner as in the above Comparative Examples 1 to 10. On the thermochromic layer, a combined layer of about 35 µm thick was formed by agitating and mixing one part of the light-intercepting pigment layer, a predetermined amount of a light stabilizer (see Tables 3 and 4), 45 parts of 50% acrylic resin solution in xylene, 20 parts of xylene, and 20 parts of methyl isobutyl ketone, and applying the mixture by spraying. (4) Preparation of laminates of Examples 30 to 51 according to the invention: The thermochromic layer and the combined layer were prepared in the same manner as in the above item (3), and the light stabilizer layer was formed on or beneath the combined layer in the same manner as in formation of the light stabilizer layer of the above item (2). (5) Light-fastness test: A test sample before light irradiation was subjected to measurement of the optical densities for the lightness degrees at a colored state and at a decolored state by a color difference meter. The difference of the lightness degrees is taken as 100 %. After light irradiation by a carbon arc fade meter for 0, 40, 80, 120, 160, and 200 hours respectively, the lightness was measured and the rate of decay of the optical density was calculated relative to the above 100 % value. (6) Conditions of Examples and Comparative Examples, and results of light-fastness test: Table 2 shows the conditions and the results of light-fastness test of the Comparative Examples, and Tables 3 to 6 show those of the Examples of the invention. In Tables, Iriodins (100, 205, 219, 225, and 235) are pearl-luster pigments produced by Merck Japan Co.; MEARLINs (hi-lite colors blue, hi-lite colors violet, hi-lite colors green, pearl white, and super white) are pearl-luster pigment produced by The Mearl Corporation (USA); Tinuvins (328, 384, 1130, and PS) are benzotriazole type UV absorbers produced by Ciba Geigy Co.; Irgastab 2002 is a singlet oxygen quencher produced by Ciba Geigy Co.; Seesorb 103 is a benzophenone type UV absorber produced by Shipro Kasei K.K.; and Antigen NBC is a singlet oxygen quencher produced by Sumitomo Chemical Co., Ltd. The thermochromic laminate of the present invention has greatly improved light-fastness, and has a permanent color change function as shown in the light-fastness test results owing to the effects of the combined layer containing both a light-intercepting pigment and a light stabilizer dispersed and fixed in a film-forming material, on the thermochromic layer. Such a laminate has remarkably improved light-fastness in comparison with the laminate having a combination of the above separate single layers. Additional lamination of a light stabilizer layer on or underneath the above combined layer gives further improvement. This lamination of a light stabilizer layer as the uppermost layer gives appropriate gloss of the laminate which is practically useful. The light-intercepting pigment layer of the present invention allows transmission of visible light appropriately not to prevent visual observation, so that the color change of the thermochromic layer is visualized effectively. In particular, the laminate employing a metallic luster pigment visualizes multicolor change of metallic luster owing to synergism of the rainbow effect caused by selective interference and transmission of visible light and reflection effect of visible light in the thermochromic layer. Thus, the present invention provides a thermochromic laminate which is useful in a variety of application fields such as toys, ornament, teaching materials, fiber materials, household goods, sporting goods, indoor and outdoor articles, clothes and printing articles.

Claims: A thermochromic laminate (1) comprising a thermochromic layer (2) and a coating layer or layers laminated thereon containing a light-intercepting pigment and a light stabilizer, one of the coating layers being a combined layer (5) which contains both the light-intercepting pigment and the light stabilizer dispersed and fixed in a film-forming material, the light-intercepting pigment being one or more pigments selected from metallic luster pigments, transparent titanium dioxide, transparent iron oxide, transparent cerium oxide and transparent zinc oxide, and the light stabilizer being one or more chemicals selected from ultraviolet absorbers, antioxidants, singlet oxygen quenchers, superoxide anion quenchers, ozone quenchers, visible light absorbers, and infrared absorbers; and the thermochromic layer (2) being a homogeneous solid mixture of an electron-donating coloring organic compound, an electron-accepting organic compound, and an organic compound medium for adjusting the color reaction temperature dispersed and fixed in an amount of 0.5 - 40 % based on the weight of the thermochromic layer, in a film forming material. A thermochromic laminate according to claim 1, wherein a light stabilizer layer (4) is laminated on or underneath the combined layer (5). A thermochromic laminate according to claim 1 or claim 2, wherein the light-intercepting pigment is a metallic luster pigment composed of natural mica whose surface is covered with titanium oxide, and having a particle size of from 5 to 100 µm. A thermochromic laminate according to any one of claims 1 to 3, wherein the homogeneous mixture of electron-donating coloring organic compound, electron-accepting organic compound and organic compound medium for adjusting the color reaction temperature, is enclosed in microcapsules.

Inventors: FUJITA KATSUYUKI, SHIBAHASHI YUTAKA, FUJITA, KATSUYUKI, SHIBAHASHI, YUTAKA
Applicants: PILOT INK CO LTD, THE PILOT INK CO., LTD.
Application year: 1995
Main classification: B32B27
IPC codes: B32B27, B44F1, B41M5