具体实施方式：
[0031]The silicone resin composition of the invention contains a silicone derivative and metal oxide fine particles, and a great feature thereof is that specific metal oxide fine particles (referred to also as fine particles B) is dispersed in a silicone resin (referred to also as silica fine particle-containing silicone resin) obtained by reacting a siloxane derivative having an alkoxysilyl group and/or a silanol group at a molecular end thereof and having a weight-average molecular weight (Mw) as determined by the gel permeation method of 300 to 6,000, with silica fine particles having silanol groups on the surface thereof (referred to also as fine particles A).
[0032]Silicone resins are hydrophobic and have high water repellency, and it is therefore difficult to disperse hydrophilic metal oxide fine particles therein. In the invention, silica fine particles having silanol groups on the surface thereof (fine particles A) are hence reacted with a siloxane derivative having a reactive alkoxysilyl group and/or silanol group at a molecular end thereof, whereby the fine particles A become capable of being held and dispersed in silicone resins. As a result, a composition which not only has the heat resistance inherent in silicon resins but also has improved weatherability and excellent mechanical strength is obtainable because the silica fine particles as an inorganic component have been tenaciously bonded through reaction. This silicone resin composition has excellent transparency because the silica fine particles have been satisfactorily dispersed in the silicone resin, and further has better stability than general organic polymers. However, it was found that this resin composition decreases in stability by the action of ultraviolet rays, etc. when exposed to an outdoor environment or the like over a prolonged time period. The stability during storage can be improved by further incorporating metal oxide fine particles (fine particles B) which have high transparency in the visible light region and have high blocking properties in the ultraviolet region. Consequently, it is possible to obtain a silicone resin composition which, besides having those properties, has excellent transparency in the visible light region, blocks ultraviolet rays, and has excellent heat resistance and weatherability.
[0033]The silicone resin composition of the invention includes a siloxane derivatives, silica fine particles having silanol groups on the surface thereof (fine particles A), and metal oxide fine particles (fine particles B).
[0034]The siloxane derivative in the invention has a reactive alkoxysilyl group and/or silanol group at a molecular end thereof. It is preferred that this derivative should be a derivative obtained using a compound represented by the following formula (I):
[0035]
in which R1 and R2 each independently represent an alkyl group or an aromatic group, and R3 and R4 each independently represent a hydrogen atom or an alkyl group, and/or using a compound represented by formula (II):
[0036]
in which R5, R6, and R7 each independently represent a hydrogen atom or an alkyl group, and X represents a monovalent organic group.
[0037]The derivative obtained using a compound represented by formula (I) and/or a compound represented by formula (II) is obtained by hydrolyzing and condensation-polymerizing a compound represented by formula (I) alone, a compound represented by formula (II) alone, or a mixture of a compound represented by formula (I) and a compound represented by formula (II), and the composition thereof is not particularly limited.
[0038]R1 and R2 in formula (I) each independently represent an alkyl group or an aromatic group. The number of carbon atoms of the alkyl group is preferably 1 to 18, more preferably 1 to 12, even more preferably 1 to 6, from the standpoints of controlling the hydrophilicity/hydrophobicity of the surface of the fine particles, efficiency of the polycondensation reaction of the siloxane derivative(s), etc. Examples of the alkyl group include methyl, ethyl, propyl, and isopropyl. Of these, it is especially preferred that R1 and R2 each independently are methyl or an aromatic group.
[0039]R3 and R4 in formula (I) each independently represent a hydrogen atom or an alkyl group. The number of carbon atoms of the alkyl group is preferably 1 to 4, more preferably 1 to 2, from the standpoints of reactivity with the surface of the fine particles and the hydrolysis rate. Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, and butyl. Of these, methyl and ethyl are preferred.
[0040]R5, R6, and R7 in formula (II) each independently represent a hydrogen atom or an alkyl group. The number of carbon atoms of the alkyl group is preferably 1 to 4, more preferably 1 to 2, as in the alkyl groups represented by R3 and R4 in formula (I). Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, and butyl. Of these, methyl and ethyl are preferred.
[0041]X in formula (II) represents a monovalent organic group, and can be any of various functional groups from the standpoint of imparting properties suited for applications of the silicone resin composition to be obtained. Examples thereof include alkyl groups, phenyl, glycidyl, vinyl, epoxycyclohexyl, amino, and a thiol group. These groups (e.g., glycidyl) may contain any other desired atom(s), e.g., oxygen atom, and examples of such groups include methacryloxypropyl, glycidoxypropyl, epoxycyclohexylethyl, and aminopropyl.
[0042]Methods for hydrolyzing and condensation-polymerizing a compound represented by formula (I) alone, a compound represented by formula (II) alone, or a mixture of a compound represented by formula (I) and a compound represented by formula (II) are not particularly limited, and the hydrolysis and polycondensation can be conducted by a known method.
[0043]The siloxane derivative thus obtained has an alkoxysilyl group and/or a silanol group at a molecular end thereof.
[0044]In the invention, a compound represented by the following formula (III):
[0045]
in which R8, R9, and R10 each independently represent a hydrogen atom or an alkyl group, and n represents an integer of 1 or larger,
can be used as the siloxane derivative having an alkoxysilyl group and/or a silanol group at a molecular end thereof.
[0046]R8, R9, and R10 in formula (III) each independently represent a hydrogen atom or an alkyl group. The number of carbon atoms of the alkyl group is preferably 1 to 4, more preferably 1 to 2, as in the alkyl groups represented by R3 and R4 in formula (I). Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, and butyl. Of these, methyl and ethyl are preferred.
[0047]Symbol n in formula (III) represents an integer of 1 or larger, and preferably is an integer of 1 to 10.
[0048]The compound represented by formula (III) can be produced, for example, by mixing a methylhydrogensilicone oil with vinyltrimethoxysilane in toluene, sufficiently conducting replacement with nitrogen, adding a platinum catalyst thereto and reacting the mixture at 80° C. for 5 hours, subsequently cooling the mixture to room temperature, and distilling off the solvent. However, methods for producing the compound should not be limited to the example shown above.
[0049]In this specification, the term “siloxane derivative having a reactive alkoxysilyl group and/or silanol group at a molecular end thereof” means an alkoxysilane derivative having an alkoxysilyl group at a molecular end thereof, a silanol derivative having a silanol group at a molecular end thereof, or a siloxane derivative having an alkoxysilyl group and a silanol group at molecular ends thereof. One of these derivatives can be used alone, or two or more thereof can be used in combination. The silanol derivative preferably is a disilanol derivative having a silanol group at each of both molecular ends thereof.
[0050]The siloxane derivative in the invention has an alkoxy group in an amount of preferably 10 to 45% by weight, more preferably 15 to 45% by weight, per one molecule thereof, from the standpoint of reactivity with the silica fine particles. In the case where a plurality of derivatives are used as the siloxane derivative, it is preferred that the weighted-average value of the amount of alkoxy group of these derivatives should be within that range. The amount of alkoxy group means the molecular-weight proportion of the alkoxy group to one molecule of the derivative. In this specification, the amount of alkoxy group can be determined through 1H-NMR analysis and from a weight loss on heating.
[0051]The silanol functional group equivalent is preferably 50 to 500 mol/g, more preferably 50 to 250 mol/g, from the standpoint of affinity for the fine particles. In the case where a plurality of derivatives are used as the siloxane derivative, it is preferred that the weighted-average value of the silanol functional group equivalents of these derivatives should be within that range. In this specification, the silanol functional group equivalent can be determined through 1H-NMR analysis.
[0052]In this specification, the molecular weights of silicone derivatives are determined by gel permeation chromatography (gel permeation method; GPC). Consequently, the term “molecular weight of a siloxane derivative” in the invention means the weight-average molecular weight (Mw) determined by the gel permeation method, which is determined through a measurement made by the gel permeation method and a calculation. This molecular weight is referred to as “weight-average molecular weight (gel permeation method)” or simply as “weight-average molecular weight” or “molecular weight”. The weight-average molecular weight of the siloxane derivative is 300 to 6,000, preferably 300 to 3,000, from the standpoint of solubility in reaction solvents. In the case where the siloxane derivative contains a disilanol derivative, the weight-average molecular weight thereof is preferably 300 to 3,000. In the case where a plurality of derivatives are used as the siloxane derivative, it is preferred that the weighted-average value of the weight-average molecular weights of these derivatives should be within that range.
[0053]In the invention, the siloxane derivative to be used can be a commercial product. Examples of suitable commercial products include “KC89” (weight-average molecular weight, 400; molecular-weight distribution, 300-500; methoxy content, 46% by weight), “KR500” (weight-average molecular weight, 1,000; molecular-weight distribution, 1,000-2,000; methoxy content, 28% by weight), “X-40-9225” (weight-average molecular weight, 3,000; molecular-weight distribution, 2,000-3,000; methoxy content, 24% by weight), and “X-40-9246” (weight-average molecular weight, 6,000; molecular-weight distribution, 4,000-10,000; methoxy content, 10% by weight), all manufactured by Shin-Etsu Chemical Co., Ltd. Examples thereof further include disilanol derivatives such as “X-21-3153” (weight-average molecular weight, 300; molecular-weight distribution, 200-400), “X-21-5841” (weight-average molecular weight, 1,000; molecular-weight distribution, 600-1,500), and “KF9701” (weight-average molecular weight, 3,000; molecular-weight distribution, 2,000-4,000), all manufactured by Shin-Etsu Chemical Co., Ltd. Furthermore, a siloxane derivative having a weight-average molecular weight within that range may be prepared by hydrolyzing or condensation-polymerizing any of these commercial products and used. Those siloxane derivatives can be used alone or used in combination of two or more thereof so long as the weight-average molecular weight thereof is within that range. Any desired two or more derivatives may be used in combination so long as the weighted-average value of the weight-average molecular weights thereof is within that range. Those compounds each have one or more methyl groups as a silicon-bonded substituent other than the alkoxy group and/or hydroxy group.
[0054]Silicone derivatives other than the siloxane derivatives may be contained in the silicone resin composition of the invention so long as the effects of the invention are not impaired. Such other silicone derivatives are not particularly limited. However, examples thereof include dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, and tetraethoxysilane from the standpoints of reactivity with the silica fine particles and solubility in reaction solvents. When the siloxane derivatives and the other silicone derivatives are inclusively referred to as all silicone derivatives, then the total content of the siloxane derivatives in the silicone resin composition of the invention is preferably 50% by weight or more, more preferably 80% by weight or more, based on all silicone derivatives.
[0055]The silica fine particles (fine particles A) in the invention are not particularly limited so long as the fine particles have silanol groups on the surface thereof. However, the silica fine particles preferably have an average particle diameter in the range of 1 to 100 nm from the standpoint of ensuring transparency and colloidal silica having an average particle diameter in the range of 1 to 100 nm is particularly preferred. In this specification, the term “silica fine particles having silanol groups on the surface thereof” means silica fine particles which have undergone no surface treatment or silica fine particles which have undergone a surface treatment but on which silanol groups capable of reacting with the siloxane derivative are substantially present.
[0056]The colloidal silica preferably is one having a narrow particle size distribution, from the standpoint of ensuring transparency. More preferred is colloidal silica in which the primary particles are in the state of being dispersed without aggregating. The average particle diameter of the primary particles is preferably 1 to 100 nm, more preferably 1 to 50 nm, even more preferably 1 to 30 nm, from the standpoint of the transparency of molded products to be obtained from the composition. In this specification, the average particle diameter of fine particles can be determined through an examination of a dispersion of the particles for particle diameter by the dynamic light-scattering method or through a direct examination with a transmission electron microscope.
[0057]It is preferred that the fine particles in the colloidal silica should have undergone no surface treatment. It is also preferred that the pH of the surface of the fine particles and the pH of the aqueous colloidal silica dispersion should be on the acidic side or on the basic side from the standpoint of controlling the rate of the reaction to inhibit gelation. Specifically, the pH values thereof are preferably 2 to 4, more preferably 2 to 3, when on the acidic side, and are preferably 8 to 10, more preferably 9 to 10, when on the basic side.
[0058]Examples of suitable commercial products of the colloidal silica include the “Snowtex” series manufactured by Nissan Chemical Industries, Ltd.
[0059]The content of the silica fine particles (fine particles A) is preferably 3 to 40 parts by weight, more preferably 3 to 35 parts by weight, even more preferably 5 to 30 parts by weight, per 100 parts by weight of all silicone derivatives. When the content thereof is 3 parts by weight or more, there is no possibility of giving a composition which has too low strength thereby impairing handling ability. When the content thereof is 40 parts by weight or less, the resultant composition is not excessively hard and has satisfactory handling ability.
[0060]The metal oxide fine particles (fine particles B) in the invention have transparency in the visible light region and have the property of blocking ultraviolet rays. The term “metal oxide fine particles which block ultraviolet rays” means metal oxide fine particles which have a maximum-absorption wavelength in the range of preferably 250 to 450 nm, more preferably 250 to 420 nm. It is thought that such metal oxide fine particles hence can absorb ultraviolet rays to inhibit the rays from passing through.
[0061]Examples of the metal oxide fine particles include titanium oxide (maximum-absorption wavelength, 420 nm), zinc oxide (maximum-absorption wavelength, 380 nm), and cerium oxide (maximum-absorption wavelength, 400 nm). Preferred of these are titanium oxide and zinc oxide, which have no absorption in the visible light region. For use in applications where complete transparency in the visible light region is required, zinc oxide is more preferred. Incidentally, metal oxide fine particles can be prepared from a metal-oxide precursor having the constituent metal. Specifically, in the case where the metal oxide to be yielded is, for example, zinc oxide (ZnO), the metal oxide can be prepared by subjecting a metal salt such as zinc acetate, zinc nitrate, or zinc chloride to hydrolysis (hydrothermal synthesis, etc.) or pyrolysis. The kind of salt is not particularly limited, and examples thereof include acetate, nitrate, chloride, bromide, fluoride, cyanide, diethylcarbamate, oxalate, perchlorate, and trifluoroacetate. Of these, acetate and nitrate are preferred because these salts have a relatively low heat decomposition temperature. Such precursors may be anhydrides or may be hydrates.
[0062]The average particle diameter of the fine particles B is preferably 1 to 100 nm, more preferably 1 to 50 nm, even more preferably 1 to 20 nm, from the standpoint of the transparency of molded products to be obtained from the composition. It is preferred that the fine particles B should have a narrower particle size distribution.
[0063]The fine particles B to be used can be ones produced by a known method. However, fine particles B obtained by a process such as, for example, the hydrothermal synthesis method or the sol-gel method are preferred, because when particles in a solid state are added to and dispersed in a solution, aggregates are apt to generate. The fine particles obtained by the process can be mixed with resins while maintaining the dispersed state of the primary particles.
[0064]The fine particles B can be subjected to a surface treatment from the standpoint of imparting satisfactory dispersibility in the silica fine particle-containing silicone resin.
[0065]Preferred as a surface-treating agent for the fine particles B, from the standpoint of dispersibility in the silicone resin, is a silane derivative which has a reactive alkoxysilyl group at a molecular end thereof and has a weight-average molecular weight (Mw) as determined by the gel permeation method of 100 to 1,000. Examples hereof include an alkoxysilane derivative which has a reactive alkoxysilyl group at a molecular end thereof and has a weight-average molecular weight (Mw) as determined by the gel permeation method of 100 to 1,000 (silane coupling agent) and a siloxane derivative which has a reactive alkoxysilyl group at a molecular end thereof and has a weight-average molecular weight (Mw) as determined by the gel permeation method of 300 to 1,000. The alkoxysilane derivative and the siloxane derivative may contain an organic functional group (e.g., a methyl group) as a silicon-bonded substituent other than the alkoxy group.
[0066]The alkoxysilane derivative which has a reactive alkoxysilyl group at a molecular end thereof and has a weight-average molecular weight (Mw) as determined by the gel permeation method of 100 to 1,000 (silane coupling agent) is not particularly limited so long as the derivative is a known silane coupling agent having a molecular weight within that range. However, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, which is represented by formula (IV):
[0067]
is suitable. Compounds having an epoxycyclohexyl group in the molecule thereof have the effects of having relatively excellent heat resistance among silane coupling agents for use as surface-treating agents and of imparting satisfactory dispersibility. Incidentally, “KBM303” (molecular weight, 246.4), manufactured by Shin-Etsu Chemical Co., Ltd., is suitable as 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.
[0068]Suitable examples of the siloxane derivative which has a reactive alkoxysilyl group at a molecular end thereof and has a weight-average molecular weight (Mw) as determined by the gel permeation method of 300 to 1,000 include compounds represented by formula (V):
[0069]
in which m represents an integer of 1 or larger.
[0070]Suitable as such derivatives are “KC89” (weight-average molecular weight, 400; molecular-weight distribution, 300-500; methoxy content, 46% by weight; organic functional group, methyl) and “KR500” (weight-average molecular weight, 1,000; molecular-weight distribution, 1,000-2,000; methoxy content, 28% by weight; organic functional group, methyl), both manufactured by Shin-Etsu Chemical Co., Ltd.
[0071]Also suitable as the siloxane derivative which has a reactive alkoxysilyl group at a molecular end thereof and has a weight-average molecular weight (Mw) as determined by the gel permeation method of 300 to 1,000 are compounds represented by formula (VI):
[0072]
in which p and q each represent an integer of 1 or larger.
[0073]The content of the surface-treating agent is preferably 50 to 1,000 parts by weight, more preferably 80 to 700 parts by weight, per 100 parts by weight of the metal oxide fine particles to be subjected to the surface treatment (or a precursor for the metal oxide).
[0074]Methods for the surface treatment are not particularly limited, and the surface treatment may be conducted by known methods. Examples thereof include a method in which metal oxide fine particles prepared beforehand and a surface-treating agent are stirred in a solvent at −10 to 30° C. for 6 to 24 hours (sol-gel method) and a method in which a precursor for metal oxide fine particles and a surface-treating agent are stirred in a solvent at 200 to 300° C. for 0.1 to 1 hour (wet method). In the case where zinc oxide particles are synthesized by the hydrothermal method, treatment with a surface-treating agent may be conducted simultaneously with particle generation, and the particles can be thereby rendered dispersible in the silicone resin, while being kept in the dispersed state.
[0075]The content of the metal oxide fine particles (fine particles B) is preferably 1 to 12 parts by weight, more preferably 2 to 10 parts by weight, per 100 parts by weight of all silicone derivatives. When the content thereof is 1 part by weight or more, the resin composition obtained can block ultraviolet rays. When the content thereof is 12 parts by weight or less, the resin composition is not excessively hard and has satisfactory handling ability.
[0076]In the invention, the silicone resin composition may contain metal oxide fine particles other than the silica fine particles (fine particles A) and the metal oxide fine particles (fine particles B) unless the effects of the invention are impaired thereby. Examples of the other metal oxide fine particles include known metal oxide fine particles. The total content of the fine particles A and B in all metal oxide fine particles used is preferably 80% by weight or more, more preferably 90% by weight or more, even more preferably substantially 100% by weight.
[0077]The silicone resin composition of the invention may contain additives, such as an aging inhibitor, modifier, surfactant, dye, pigment, discoloration inhibitor, and ultraviolet absorber other than the metal oxide fine particles, besides the siloxane derivative, silica fine particles, and metal oxide fine particles so long as the effects of the invention are not impaired thereby.
[0078]The silicone resin composition of the invention can be prepared, for example, by adding an organic solvent according to need to a dispersion of the silica fine particles, adjusting the pH of the solution to 2-4, subsequently reacting the silica fine particles at 40-80° C. with a resin solution containing the siloxane derivative, and then dispersing metal oxide fine particles in the resultant liquid reaction mixture. From the standpoint of improving the hydrophobicity of the silica fine particles to facilitate reaction with a high-molecular siloxane derivative, the fine particles may be reacted with another silicone derivative, such as dimethyldimethoxysilane or tetraethoxysilane, before being reacted with the siloxane derivative. In the invention, use may be made of a method in which a liquid obtained by dispersing metal oxide fine particles in a siloxane derivative is mixed with a dispersion of silica fine particles and polymerization reaction is thereafter conducted to prepare the silicone resin composition.
[0079]The organic solvent is not particularly limited. However, alcohols are preferred from the standpoint of enhancing compatibility between the siloxane derivative and the silica fine particles. More preferred are 2-propanol and 2-methoxyethanol. The amount of the organic solvent to be present is not particularly limited so long as the reaction proceeds sufficiently.
[0080]The silicone resin composition obtained can be formed into a sheet, for example, by applying the composition in an appropriate thickness on a release sheet (e.g., a polyethylene substrate) or glass substrate, the surface of which has been treated with a releasant, by a technique such as casting, spin coating, or roll coating, and drying the composition at such a temperature that solvent removal is possible. Consequently, the invention provides a sheet-shaped silicone resin molded product (hardcoat material, silicone resin sheet, or silicone resin film) obtained by applying the silicone resin composition of the invention on a substrate and drying the composition. Examples of the sheet-shaped molded product include molded products having a thickness of about 10 to 1,000 μm. The temperature at which the resin solution is dried cannot be unconditionally determined because the temperature varies depending on the kinds of the resin and solvent. However, the drying temperature is preferably 80 to 250° C. The drying may be conducted in two stages. In this case, the temperature in the first stage is preferably 80 to 150° C. and the temperature in the second stage is preferably 100 to 250° C.
[0081]The silicone resin composition of the invention has high light transmittance in the visible light region because the composition contains metal oxide fine particles having transparency in the visible light region. In the case where the silicone resin composition is formed into a sheet having a thickness of, for example, 10 to 500 μm, the transmittance of incident light having wavelengths of 400 to 700 nm is desirably 80% or more, preferably 82% or more, more preferably 85% or more, even more preferably 85 to 100%, especially preferably 90 to 100%. In this specification, light transmittance is measured by the method described in the Examples which will be given later.
[0082]Since the silicone resin composition of the invention contains metal oxide fine particles which block ultraviolet rays, the composition has low light-transmitting properties in the ultraviolet region. For example, in the case where the silicone resin composition is formed into a sheet having a thickness of 10 to 500 μm, the transmittance of incident light having wavelengths shorter than 400 nm is desirably 30% or less, preferably 20% or less, more preferably 15% or less, even more preferably substantially 0%.
EXAMPLES
[0083]The invention will be described below with reference to Examples, but the invention should not be construed as being limited by the Examples, etc.
[Molecular Weight of Silicone Derivative]
[0084]The molecular weight is determined as a value measured by gel permeation chromatography (GPC) in terms of polystyrene.
[Alkoxy Group Content of Silicone Derivative]
[0085]The alkoxy group content is calculated through determination by 1H-NMR analysis using an internal reference and from a value of weight loss on heating in differential thermal analysis/thermogravimetry.
[Average Particle Diameter of Fine Particles]
[0086]The term “average particle diameter of fine particles” in this specification means the average particle diameter of primary particles, and is 50% volume cumulative diameter (D50) determined through an examination of a dispersion of the fine particles by the dynamic light-scattering method and a calculation.
[Maximum-Absorption Wavelength of Metal Oxide Fine Particles]
[0087]A dispersion solution of the metal oxide fine particles is examined as a sample with a spectrophotometer (U-4100, manufactured by Hitachi High-Technologies Corp.) in the wavelength range of 300 to 800 nm to obtain a UV spectrum, and the maximum-absorption wavelength therein is measured.
[Luminance-Maximum Wavelength of Metal Oxide Fine Particles]
[0088]A dispersion solution of the metal oxide fine particles is excited, as a sample, at a wavelength of 365 nm using Hitachi Fluorometer (F4500) to obtain a fluorescence spectrum, and the luminance-maximum wavelength therein is measured.
Production Example 1 for Metal Oxide Fine Particles (Fine Particles B)
[0089]Into a glass vessel for autoclave were introduced 1.54 g (4 mmol) of anhydrous zinc acetate, 8.97 g of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane “KBM303” (manufactured by Shin-Etsu Chemical Co., Ltd.; molecular weight, 246.4) [36 mmol; 582 parts by weight per 100 parts by weight of the metal-oxide precursor (anhydrous zinc acetate)], and 80 mL of tetraethylene glycol. The glass vessel was placed in an autoclave (manufactured by Taiatsu Techno Corp.), and 30 g of tetraethylene glycol was introduced into the gap between the glass vessel and the reaction vessel of the autoclave, which was then closed. The reaction mixture was heated to 300° C. at a rate of 20° C./min with stirring, held at 300° C. for 10 minutes, and then gradually cooled to room temperature (25° C.). Thereafter, the solution obtained was subjected to precipitation from ethyl acetate, and the resultant yellow-white solid (fine particles of fluorescent zinc oxide) was recovered with a centrifugal separator. The fine particles obtained were redispersed in 2-propanol so as to result in a solid concentration of 20% by weight. The fine particles had an average particle diameter of 10 nm, and the solution obtained by redispersing the fine particles had a maximum-absorption wavelength of 370 nm and a luminance-maximum wavelength of 470 nm.
Production Example 2 for Metal Oxide Fine Particles (Fine Particles B)
[0090]Into a glass vessel for autoclave were introduced 1.54 g (4 mmol) of anhydrous zinc acetate, 8.0 g of a siloxane derivative having a reactive alkoxysilyl group at a molecular end (“KC89”, manufactured by Shin-Etsu Chemical Co., Ltd.; weight-average molecular weight, 400; molecular-weight distribution, 300-500; organic functional group, methyl; methoxy group content, 46% by weight) [20 mmol; 519 parts by weight per 100 parts by weight of the metal-oxide precursor (anhydrous zinc acetate)], and 80 mL of tetraethylene glycol. The mixture was reacted in the same manner as in Production Example 1. The solution obtained was subjected to precipitation from diethyl ether, and the resultant yellow-white solid (fine particles of fluorescent zinc oxide) was recovered with a centrifugal separator. The fine particles obtained were redispersed in ethyl acetate so as to result in a solid concentration of 10% by weight. The fine particles had an average particle diameter of 11 nm, and the solution obtained by redispersing the fine particles had a maximum-absorption wavelength of 370 nm and a luminance-maximum wavelength of 470 nm.
Production Example 3 for Metal Oxide Fine Particles (Fine Particles B)
[0091]In 100 mL of anhydrous ethanol was dissolved 1.84 g (4 mmol) of zinc acetate dihydrate. This solution was cooled to 0° C. with stirring. A solution prepared by suspending 0.58 g (4 mmol) of lithium hydroxide monohydrate in 100 mL of anhydrous ethanol was added dropwise to the cooled solution over 30 minutes and mixed therewith. This mixture was reacted with stirring at 0° C. for 5 hours. Thereafter, a solution prepared by dissolving 2.0 g of methylmethoxysilane “KBM13” (manufactured by Shin-Etsu Chemical Co., Ltd.; molecular weight, 136.2) [36 mmol; 83 parts by weight per 100 parts by weight of all metal-oxide precursors (the zinc acetate dihydrate and the lithium hydroxide monohydrate)] in 2.0 g of anhydrous ethanol was added dropwise to the reaction mixture. After completion of the dropwise addition, the mixture was w