CURABLE COMPOSITIONS

Abstract: Curable compositions essentially comprise a selected class of starting compounds and a selected class of particulate metallic oxides as electrically conductive components, the oxides being coated with a selected class of hydrolyzed silicon compounds of the formula R 1 / mR 2 / nSi(OR³) 4-(m+n) where R¹ and R² each are a hydrocarbon moiety of 1 to 20 carbon atoms or an organic group containing a halogen atom or an epoxy, acrylonitrile, methacrylonitrile, mercapto or amino group, each of the hydrocarbon moiety and organic group forming a Si-C bond, R³ is a hydrocarbon moiety of 1 to 6 carbon atoms or an oxygen-containing hydrocarbon moiety, m and n each are 0, 1 or 2, and the sum of m and n is 1 or 2. The resulting cured coating excels in transparency, abrasion resistance, adhesive strength and electrical conductivity.

Description: This invention relates to curable compositions suitable for use as transparent, electrically conductive coatings. Destaticization is generally required of semiconducting wafer vessels and electronic and electrical appliances. To this end, antistatic coatings are known which contain particulate carbon or metal. Alternatively, carbon particle- or metallic fiber-filled resins have been proposed for use as integrally destaticizable materials. These prior materials are not wholly satisfactory as the resulting coats and moldings are opaquely colorable. Japanese Patent Laid-Open Publication No. 57-85866 discloses a coating composition in which particulate tin oxide is combined as an electrically conductive component with a binder. This coat, though transparent and antistatic, is susceptible to abrasive wear and also to solvent attack because the binder is thermoplastic in nature. In Japanese Patent Laid-Open Publication No. 60-99176, a certain compound is used as a coating binder, which compound is derived by combining electrically conductive tin oxide-based particles with an acryloyl or methacryloyl group-containing oligomer and a maleic anhydride-added isoprene polymer, followed by partial esterification. A further coating composition involves the use of binders made up of tin oxide comminuted and an oligomeric or monomeric material having in the molecule one or more radical-reactive unsaturated groups and one or more hydroxyl groups as taught in Japanese Patent Laid-Open Publication No. 60-219270. Such known coatings excel in ultraviolet curing, electrical conductivity, hardness and solvent resistance, but fail to give sufficient transparency and adequate abrasion resistance. Tin oxide comminuted, because of its greater specific gravity than organic binders, is difficult to homogenize, and if not impossible, is liable to precipitate. It is therefore the primary object of the present invention to provide an improved curable composition which is satisfactorily transparent, has good abrasion-resistance, is sufficiently adhesive and is highly electrically-conductive. The composition according to the invention is particularly suitable for areas of application which require immunity from scarring, dusting and static electricity and which include such articles as vessels for semiconducting wafers, screens for television receivers, organic window panes and covers for lighting fittings. The curable composition in accordance with the invention comprises (a) a base compound having at least two acryloyl or methacryloyl groups, and (b) a particulate electrically-conductive component selected from the group consisting of tin oxide, indium oxide and compounds composed predominantly of at least one of said oxides, the component carrying thereon a hydrolyzed silicon compound of the formula: R 1 / mR 2 / nSi(OR³) 4-(m+n) where R¹ and R² each are a hydrocarbon moiety of 1 to 20 carbon atoms or an organic group containing a halogen atom or an epoxy, acrylonitrile, methacrylonitrile, mercapto or amino group, each of the hydrocarbon moiety and organic group forming a Si-C bond, R³ is a hydrocarbon moiety of 1 to 6 carbon atoms or an oxygen-containing hydrocarbon moiety, m and n each are 0, 1 or 2, and the sum of m and n is 1 or 2. Base compounds (a) useful for the purpose of the present invention are compounds having two or more acryloyl or methacryloyl groups chemically bonded and having a carbon number of 8 to 30. Specific examples include bifunctional acrylates and methacrylates such as ethyleneglycol diacrylate, propyleneglycol diacrylate, propyleneglycol dimethacrylate and tetraethyleneglycol dimethacrylate, and trifunctional and multifunctional acrylates and methacrylates such as trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, glycerol triacrylate, glycerol trimethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, tris(2-hydroxyethyl)-isocyanurate acrylate and tris(2-hydroxyethyl)isocyanurate methacrylate. Compounds of relatively high molecular weights, say about 300 to 10,000, may also be used as compounds (a), examples of which include polyester acrylate, epoxy acrylate and polyurethane acrylate. Compounds (a) may be combined with a monofunctional reactive compound so as to depress viscosity. Useful monofunctional compounds include for example 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate and 2-hydroxypropyl acrylate. Useful electrically-conductive components (b) include particles of tin oxide and indium oxide commonly known in the art, and also of compounds composed predominantly of either one or both of these two oxides. The oxides may be used in the form of metallic dopes such as antimony-doped tin oxide and tinnate-doped indium oxide. Component (b) preferably should in each case have a particle size not exceeding 0.2 micrometer. Larger particle sizes tend to render the resulting coat susceptible to scattered visible rays, and hence of reduced transparency. The amount of component (b) to be added preferably should be in the range of 40 to 80%, more preferably 55 to 70% by weight of the total composition. The component if used in amounts smaller than 40% tends to lead to increased surface resistance, resulting in reduced destaticization, and if larger amounts than 80% are used can adversely affect transparency, abrasion resistance and adhesive strength. According to an important aspect of the invention, the particles of component (b) should carry a hydrolyzed silicon compound of an organic type of the formula: R 1 / mR 2 / nSi(OR³) 4-(m+n) where R¹ and R² each are a hydrocarbon moiety of 1 to 20 carbon atoms or an organic group containing a halogen atom or an epoxy, acrylonitrile, methacrylonitrile, mercapto or amino group, each of the hydrocarbon moiety and organic group forming a Si-C bond, R³ is a hydrocarbon moiety of 1 to 6 carbon atoms or an oxygen-containing hydrocarbon moiety, m and n each are 0, 1 or 2, and the sum of m and n is 1 or 2. Suitable silicon compounds include for example trialkoxy and triacyloxy silanes such as methyltrimethoxy-silane, methytriethoxysilane, methyltrimethoxyethoxysilane, methyltriacetoxysilane, methyltributoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltriacetoxysilane, gamma-chloropropyltrimethoxysilane, gamma-chloropropyltriethoxysilane, gamma-chloropropyl-triacetoxysilane, 3,3,3-trichloropropyltrimethoxysilane, gamma-glycidoxypropyltrimethoxysilane, gamma-glycidoxy-propyltriethoxysilane, gamma-(beta-glycidoxyethoxy)propyl-trimethoxysilane, beta-(3,4-epoxycyclohexyl)ethyltrimethoxy-silane, beta-(3,4-epoxycyclohexyl)ethyltriethoxysilane, gamma-methacryloxypropyltrimethoxysilane, gamma-aminopropyltrimethoxysilane, gamma-aminopropyl-triethoxysilane, gamma-mercaptopropyltrimethoxysilane, N-beta-(aminoethyl)-gamma-aminopropyltriethoxysilane, and beta-cyanoethyltriethoxysilane; and alkoxy and diacyloxy silanes such as methyldimethoxysilane, phenylmethyldimethoxysilane, dimethyldiethoxysilane, gamma-glycidoxypropylmethyldiethoxysilane, gamma-glycidoxypropylmethyldiethoxysilane, gamma-chloropropylmethyldimethoxysilane, gamma-chloropropylmethyldiethoxysilane, gamma-methacyloxypropylmethyldimethoxysilane, gamma-methacryloxypropylmethyldiethoxysilane, gamma-mercaptopropylmethyldimethoxysilane, gamma-mercaptopropylmethyldiethoxysilane, gamma-aminopropylmethyldimethoxysilane, gamma-aminopropylmethyldiethoxysilane, and methylvinyldiethoxysilane. These compounds may be used alone or in combination. Particularly preferred among the above silicon compounds are compounds having C-C double bonds at either one of the R¹ and R² substituents. Components (b) used herein may be obtained by dispersing and hydrolyzing a given silicon compound in water to thereby give a hydrolyzate containing a -Si-OH- or -Si-O-Si- linkage, and then by adding a predetermined comminuted metallic oxide to the hydrolyzate, followed by dispersion with stirring and by subsequent evaporation of water, providing metallic oxide particles having such silicon compound carried thereon as a coating. Hydrolysis allows the silicon compound to be partly chemically attached onto the metallic oxide. The amount of the silicon compound to be used preferably should be in the range of 5 to 40 parts, more preferably 10 to 35 parts by weight based on 100 parts by weight of component (b). Amounts smaller than 5 parts generally are ineffective for improving transparency, abrasion resistance and adhesiveness, whereas amounts larger than 40 parts tend to make the coating objectionably electrically surface-resistant and hence insufficiently antistatic. Photosensitizers may also be employed to improve ultraviolet curing. Suitable photosensitizers include for example ketals such as benzyldimethyl ketal, benzoins such as benzyldimethyl ether, benzoinethyl ether, benzoin-1-propyl ether, benzoin and alpha-methylbenzoin, anthraquinones such as 9,10-anthraquinone, 1-chloroanthraquinone, 2-chloroanthraquinone and 2-ethylanthraquinone, benzophenones such as benzophenone, p-chlorobenzophenone, and p-dimethylamino-benzophenone, propiophenones such as 2-hydroxy-2-methylpropiophenone and 1-(4-isopropylphenone)-2-hydroxy-2-methylpropiophenone, suberones such as dibenzosuberone, sulfur-containing compounds such as diphenyl disulfide, tetramethylthiuram disulfide and thioxanthone, and dyes such as methylene blue, eosine and fluorescene, and combinations thereof. Suitably, the photosensitizer ranges in amount from 0.1 to 10% by weight of the total composition. The composition of the invention may be produced for example by combining a base compound with component (b) and if necessary with an organic solvent, and subsequently by kneading the admixture on a three-roll mill, a sand mill or a ball mill. Such composition may be applied onto a substrate as by spraying, dipping, roll coating or spinnering. Examples of the substrate include sheets and films of polycarbonate, acrylic resin, polyethylene terephthalate and polyvinyl chloride. The coating on removal of the solvent at room temperature or with heat is curable by irradiation of ultraviolet light or electron beam. The following examples are given to further illustrate the present invention, but should not be construed as limiting the invention. Synthesis of Electrically Conductive Components: (a) γ-Acryloxypropyltrimethoxysilane 200 g was dispersed with stirring in 4 liters of water of pH 4.2 for one hour. Particulate antimony trioxide-doped tin oxide 800 g (Mitsubishi Metal Corp., Japan) was then added with stirring for 20 minutes on a homogenizer equipped with a high-speed stirrer (Ntro Atomizer, Denmark). The resulting dispersion was dried at a feed of about one liter per hour with use of a spray drier (Tokushu Kakoki Kogyo K. K., Japan). There was obtained a particulate conductive component (I). b) The procedure of synthesis a) above was followed except that vinyltrimethylsilane 100 g and tinnate-doped indium oxide 900 g were used, thereby giving a conductive component (II). Example 1 A mixture of 1,6-hexanediol diacrylate 34 g, epoxy acrylate 66 g (Ripoxy SP-1509, Showa Highpolymer Co., Ltd., Japan), component (I) 200 g and benzyldimethyl ketal 6 g was kneaded on a three-roll mill. The resulting admixture 100 g was combined with stirring with a solvent 100 g consisting of ethyl acetate 30 phr and n-butyl alcohol 70 phr to thereby provide a curable composition according to the invention. The composition was spinner-coated onto a polycarbonate plate (Mitsubishi Gas Chemical Co., Inc., Japan) and dried at 50°C for 10 minutes. The plate was irradiated at from a distance of 10 cm for 10 seconds with use of a 120 W/cm high-pressure mercury lamp, after which a 5 µm thick coat was formed. Example 2 Pentaerythritol triacrylate 50 g, urethane acrylate oligomer 50 g (Ebecryl Eb-220, UCB, France), component (II) 150 g and benzyldimethyl ketal 6 g were kneaded on a three-roll mill. The mixture 100 g was added with stirring with a solvent 100 g consisting of ethyl acetate 30 phr, ethyl alcohol 25 phr and t-butyl alcohol 45 phr, providing a curable composition. The composition was treated in a manner similar to Example 1 to form a 5 µm thick coat. Comparative Example 1 The procedure of Example 1 was followed except for the use of tin oxide not treated as in synthesis a), giving a 5 µm thick coat. Comparative Example 2 The procedure of Example 2 was followed except that tin oxide free from treatment of synthesis b) was used. There was obtained a 5 µm thick coat. All the coats provided in the above examples were examined for surface electrical resistance, haze, haze after Taber abrasion and adhesiveness, and the results are shown in the Table which follows. It should be noted that the coats according to the invention are highly satisfactory in respect of all the physical characteristics tested, whereas those of the comparative examples were not.

Claims: A curable composition comprising: (a) a base compound having at least two acryloyl or methacryloyl groups; and (b) a particulate electrically-conductive component selected from the group consisting of tin oxide, indium oxide and compounds composed predominantly of at least one of said oxides, said component carrying thereon a hydrolyzed silicon compound of the formula: R 1 / mR 2 / nSi(OR³) 4-(m+n) where R¹ and R² each are a hydrocarbon moiety of 1 to 20 carbon atoms or an organic group containing a halogen atom or an epoxy, acrylonitrile, methacrylonitrile, mercapto or amino group, each of the hydrocarbon moiety and organic group forming a Si-C bond, R³ is a hydrocarbon moiety of 1 to 6 carbon atoms or an oxygen-containing hydrocarbon moiety, m and n each are 0, 1 or 2, and the sum of m and n is 1 or 2. The composition of claim 1, wherein said base compound is ethyleneglycol diacrylate, propyleneglycol diacrylate, propyleneglycol dimethacrylate, tetraethyleneglycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, glycerol triacrylate, glycerol trimethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, tris(2-hydroxyethyl)isocyanurate acrylate, tris(2-hydroxyethyl)isocyanurate methacrylate, polyester acrylate, epoxy acrylate or polyurethane acrylate. The composition of claim 1 or claim 2, wherein said base compound further includes 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate or 2-hydroxypropyl acrylate. The composition of any preceding claim, wherein said component (b) is in the form of antimony-doped tin oxide or tinnate-doped indium oxide. The composition of any preceding claim, wherein said silicon compound is methyltrimethoxysilane, methytriethoxysilane, methyltrimethoxyethoxysilane, methyltriacetoxysilane, methyltributoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltriacetoxysilane, gamma-chloropropyltrimethoxysilane, gamma-chloropropyltriethoxysilane, gamma-chloropropyltriacetoxysilane, 3,3,3-trichloropropyltrimethoxysilane, gamma-glycidoxypropyltrimethoxysilane, gamma-glycidoxypropyltriethoxysilane, gamma-(beta-glycidoxyethoxy)propyltrimethoxysilane, beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, beta-(3,4-epoxycyclohexyl)ethyltriethoxysilane, gamma-methacryloxypropyltrimethoxysilane, gamma-aminopropyltrimethoxysilane, gamma-aminopropyltriethoxysilane, gamma-mercaptopropyltrimethoxysilane, N-beta-(aminoethyl)-gamma-aminopropyltriethoxysilane, beta-cyanoethyltriethoxysilane, methyldimethoxysilane, phenylmethyldimethoxysilane, dimethyldiethoxysilane, gamma-glycidoxypropylmethyldiethoxysilane, gamma-glycidoxypropylmethyldiethoxysilane, gamma-chloropropylmethyldimethoxysilane, gamma-chloropropylmethyldiethoxysilane, gamma-methacyloxypropylmethyldimethoxysilane, gamma-methacryloxypropylmethyldiethoxysilane, gamma-mercaptopropylmethyldimethoxysilane, gamma-mercaptopropylmethyldiethoxysilane, gamma-aminopropylmethyldimethoxysilane, gamma-aminopropylmethyldiethoxysilane or methylvinyldiethoxysilane, or a combination thereof. The composition of any preceding claim, wherein said component (b) has a particle size of smaller than 0.2 micrometer. The composition of any preceding claim, wherein said component (b) is present in an amount of 40 to 80 percent by weight of the total composition. The composition of any preceding claim, further including a photosensitizer. The composition of claim 8, wherein said photosensitizer is benzyldimethyl ketal, benzyldimethyl ether, benzoinethyl ether, benzoin-1-propyl ether, benzoin, alpha-methylbenzoin, 9,10-anthraquinone, 1-chloroanthraquinone, 2-chloroanthraquinone, 2-ethylanthraquinone, benzophenone, p-chlorobenzophenone, p-dimethylaminobenzophenone, 2-hydroxy-2-methylpropiophenone, 1-(4-isopropylphenone)-2-hydroxy-2-methylpropiophenone, dibenzosuberone, diphenyl disulfide, tetramethyl thiuram disulfide, thioxanthone, methylne blue, eosine or fluorescene, or a combination thereof. A substrate having thereon a cured coating of a composition of any preceding claim.

Inventors: SATO, HISATAKE, SUZUKI, AKINORI
Applicants: NIPPON OIL CO. LTD.
Application year: 1988
Main classification: C09D5
IPC codes: C08F290, C08F299, C08F20, C09C1, C09D5, C09D4, H01B1, C08F2, H01B13