JP6016494B2 - Composite oxide powder, aqueous dispersion and oil dispersion - Google Patents

Description

  The present invention relates to a composite oxide powder containing two or more metal elements or metalloid elements selected from the group consisting of Groups 14 and 15 of the periodic table, and an aqueous dispersion and an oil dispersion thereof. This composite oxide is suitably used as a raw material for forming a thin film useful for various optical materials.

As conventional techniques related to composite oxides containing two or more elements selected from Group 14 and Group 15 of the periodic table, those described in, for example, Patent Document 1 and Patent Document 2 are known. Patent Document 1, pigment represented by Bi _x M _y O _z is described. In the formula, examples of M include Sn, Sb, and Si. This pigment is used for laser marking.

  Patent Document 2 describes BiMO fine particles used for a photoconductive layer constituting a radiation imaging panel. Some examples of M include Sn and Si.

  Apart from the techniques described in Patent Documents 1 and 2, Patent Document 3 describes a dispersion liquid in which fine particles of various metal oxides or composite metal oxides are dispersed in an organic dispersion medium. The thin film obtained by using this dispersion liquid has a high plasma erosion resistance film, a mercury shielding film, an infrared reflection film, a transparent conductive film, a display, and the like by utilizing the denseness of the film and the high visible light transmittance. It is described in the same document as being used for high refractive index films, fluorescent films, magnetic films, photocatalysts, gas sensors, and protective films for various devices for improving the light extraction efficiency of LEDs.

JP 2002-206062 A JP 2010-150118 A JP 2007-197296 A

Incidentally, in the technical field of optical materials, materials having high transparency and high refractive index are required. The composite oxides described in Patent Documents 1 and 2 described above belong to the technical field of optical materials in a broad sense, but in these documents, examinations from high transparency and high refractive index are not made. . On the other hand, Patent Document 3 describes forming a high refractive index film using a dispersion liquid containing fine particles of a composite metal oxide, but there is no mention of a specific composite oxide. In fact, the dispersions produced in the examples of this document only contain Y ₂ O ₃ , Al ₂ O ₃ , Ce ₂ O ₃ and TiO ₂ . Among these, since TiO ₂ has a photocatalytic ability, when a dispersion containing TiO ₂ is applied to the surface of a substrate made of plastic, for example, to form a thin film, the plastic that is the substrate is formed by the photocatalytic ability of TiO _2. May break down.

  An object of the present invention is to provide a composite oxide powder, an aqueous dispersion and an oil dispersion suitable as an optical material.

The present invention relates to a composite oxide powder containing Sn and Bi, wherein the value of brightness L * indicated in the CIE 1976 (L * a * b *) color space is 70 or more. The powder is provided.
The present invention is also a composite oxide powder containing Sb and Bi, wherein the value of brightness L * indicated in the CIE 1976 (L * a * b *) color space is 70 or more. A powder is provided.

The present invention provides an aqueous dispersion containing the composite oxide powder, the composite oxide powder, the refractive index of the aqueous dispersion when prepared as its concentration of 5 wt% It provides an aqueous dispersion which is N _DS + 1 × 10 ^{−5 to} N _DS + 1 × 10 ⁻¹ (where N _DS represents the refractive index of the dispersion medium).

Furthermore, the present invention is an oily dispersion containing the above composite oxide powder, wherein the composite oxide particles are subjected to lipophilic treatment on the surface thereof, and the composite is subjected to lipophilic treatment. When the oxide powder is prepared so that its concentration is 5% by mass, the refractive index of the oily dispersion is N _DS + 1 × 10 ^{−5 to} N _DS + 1 × 10 ⁻¹ (where N _DS is the dispersion) It represents an oily dispersion that represents the refractive index of the medium.

  ADVANTAGE OF THE INVENTION According to this invention, the powder of complex oxide which has high transparency and a high refractive index, an aqueous dispersion, and an oil-based dispersion liquid are provided.

Hereinafter, the present invention will be described based on preferred embodiments thereof. The composite oxide according to the present invention is an oxide containing two or more elements selected from metal elements and metalloid elements. That is, the composite oxide according to the present invention is represented by the general formula M ¹ _X M ² _Y O _Z. M ¹ and M ² represent metal elements or metalloid elements, and these metal elements and metalloid elements are selected from Groups 14 and 15 of the periodic table. Examples of metal elements and metalloid elements selected from Group 14 include Si, Ge, Sn, and Pb. On the other hand, As, Sb, and Bi are mentioned as a metal element and metalloid element selected from 15th group. The composite oxide according to the present invention preferably contains two or more elements selected from Si, Ge, Sn, Pb, As, Sb and Bi. The subscripts X and Y in the general formula are the number of moles of the elements M ¹ and M ² contained in the composite oxide, and Z is 2Z = Xn ¹ + Yn ² (n ¹ and n ² are the elements M ¹ and Represents the valence of M ² ).

  The composite oxide according to the present invention may be in the form of a powder that is an aggregate of particles. Alternatively, the powder may be in the form of an aqueous dispersion in a state of being dispersed in water as a medium or in the form of an oily dispersion in a state of being dispersed in an organic dispersion medium.

  When the composite oxide according to the present invention is in the form of a powder, the powder is characterized by its color. Specifically, the composite oxide powder of the present invention exhibits a white color. Conventionally known composite oxide powders of this type, for example, the composite oxide powders described in Patent Documents 1 and 2 described above, are brown or yellow. On the other hand, since the complex oxide powder of the present invention exhibits a white color as described above, the complex oxide powder is suitable as an optical material. Conventional complex oxides exhibiting brown or yellow color have low transparency due to their colors, and are not suitable for optical materials.

  In general, the color of a substance varies depending on the chemical structure of the substance, the composition of elements, and the like. Therefore, the complex oxide powder of the present invention is white, whereas the complex oxide powder described in Patent Documents 1 and 2 is brown, which means It means that the chemical structure of the composite oxide, the composition of elements, and the like are different between the powder and the composite oxide powder described in Patent Documents 1 and 2. The details of the difference between the two have not yet been clarified, but as a result of the inventor's investigation, the composite oxide powder of the present invention exhibiting a white color is disclosed in Patent Document 1 and Unlike the composite oxide powder described in 2, it was found to have a high refractive index. Therefore, the composite oxide powder of the present invention is suitable as an optical material.

  In order to have a sufficient refractive index as an optical material, the composite oxide powder of the present invention needs to have a brightness L * value of 70 or more shown in the CIE 1976 (L * a * b *) color space. As a result of the study by the present inventor, it has become clear. In particular, when the value of the brightness L * is preferably 80 or more, more preferably 85 or more, the composite oxide powder of the present invention has a satisfactory refractive index. In the present invention, the value of the lightness L * of the composite oxide powder is measured, for example, according to the method described in Examples described later.

  In order to set the lightness L * of the composite oxide powder of the present invention to the above value or more, for example, the composite oxide may be produced by a method described later.

  As described above, the metal element and / or metalloid element constituting the composite oxide powder of the present invention is selected from Group 14 and Group 15 of the periodic table. Among these elements, when an element selected from the group consisting of the fifth period and the sixth period of the periodic table is used, the value of the lightness L * of the composite oxide powder can be easily set to the above value or more. It is preferable because it is possible. Examples of elements belonging to the fifth period and the sixth period in the Group 14 elements include Sn and Pb. On the other hand, Sb and Bi are mentioned as an element which belongs to the 5th period and the 6th period in the group 15 element.

  In particular, the composite oxide powder of the present invention includes one or more metal elements selected from Group 14 of the periodic table and one or more metal elements or metalloid elements selected from Group 15. It is preferable. By selecting such an element, the value of the lightness L * of the composite oxide powder can be more easily set to the above value or more. For example, the composite oxide powder of the present invention preferably contains Sn and Bi. In this case, when the molar ratio Bi / Sn of Bi and Sn in the composite oxide is preferably 0.5 to 2, and more preferably 0.5 to 1.5, the lightness L of the composite oxide powder. The value of * can be made even more easily above the above value.

  The composite oxide powder of the present invention preferably contains one metal element and one metalloid element selected from Group 15 of the periodic table. In this case, the complex oxide does not include an element selected from Group 14. By selecting such an element, the value of the lightness L * of the composite oxide powder can be made more easily than the above value. For example, the composite oxide powder of the present invention preferably contains Sb and Bi, which are Group 15 elements, and does not contain any Group 14 element. In this case, when the molar ratio Bi / Sb between Bi and Sb in the composite oxide is preferably 0.5 to 2, more preferably 0.5 to 1.5, the lightness L of the composite oxide powder. The value of * can be made even more easily above the above value.

  The composite oxide powder of the present invention may contain only a metal element or a metalloid element selected from Group 14 and Group 15, and may contain substantially no other metal element or metalloid element. preferable. Furthermore, it is preferable that elements other than oxygen are not substantially contained among the elements of the first period to the third period. “Substantially not containing” means that the intentional inclusion of these elements is excluded, and the presence of trace amounts of elements inevitably mixed is allowed.

  In the composite oxide according to the present invention, the number of moles of oxygen atoms contained in the composite oxide is 1.0 to 10 based on the total number of moles of metal atoms and metalloid atoms contained in the composite oxide. It is preferable that it is 2 times, especially 1.2 to 5 times.

  The composite oxide according to the present invention may be crystalline or amorphous. As a result of the study by the present inventors, it was found that when the composite oxide is amorphous, the value of the lightness L * of the composite oxide powder of the present invention can be easily increased to the above value or more. Whether the composite oxide according to the present invention is crystalline or amorphous can be controlled by the manufacturing conditions of the composite oxide described later.

  As described above, the composite oxide according to the present invention may be in the form of an aqueous dispersion or an oil dispersion. Since the composite oxide has a high refractive index and a low Abbe number, an aqueous dispersion and an oil dispersion containing the composite oxide are suitable as raw materials for producing optical materials such as optical lenses. It will be a thing. This aqueous dispersion or oil dispersion is prepared by dispersing the above-described composite oxide powder in water or an organic dispersion medium. In the following description, the aqueous dispersion and the oil dispersion are collectively referred to simply as “dispersion”.

The composite oxide powder used for the preparation of the dispersion preferably has a BET specific surface area of 15 to 150 m ² / g. As a result of the study by the present inventors, by using composite oxide particles having a BET specific surface area within this range, even when the particles are fine particles, the particles can be stably and highly dispersed at a high concentration. found. In particular, when the composite oxide powder has a BET specific surface area of more preferably 15 to 120 m ² / g, more preferably 35 to 120 m ² / g, and still more preferably 70 to 120 m ² / g, Highly stable dispersion can be achieved at a higher concentration. The BET specific surface area as referred to here is a composite oxide powder before being dispersed in water or an organic dispersion medium.

  When the BET specific surface area of the composite oxide powder is in the above range, the concentration of the dispersion can be easily increased. As will be described later, since the composite oxide particles contained in the dispersion are fine particles, it is not easy to disperse such fine particles at a high concentration. It was surprisingly found that fine composite oxide particles can be easily and highly dispersed at a high concentration by using one having a specific BET specific surface area. In the present invention, the concentration of the composite oxide particles is preferably as high as 5 to 50% by mass. A more preferable concentration is 5 to 40% by mass, a more preferable concentration is 5 to 30% by mass, and an even more preferable concentration is 5 to 20% by mass. Such a high-concentration dispersion is advantageous in that a thin film having a desired thickness can be formed even if the number of times of application is reduced, for example, when an optical lens is produced by application of the dispersion.

The complex oxide particles in the form of a dispersion are also characterized by being fine particles. In detail, the volume equivalent maximum particle diameter D _max of the composite oxide particles is preferably 100 nm or less, more preferably 90 nm or less, and still more preferably 85 nm or less. By setting the volume-converted maximum particle diameter D _max to 100 nm or less, it is possible to effectively prevent a decrease in the transparency of the dispersion due to the scattering of visible light. There is no particular limitation on the lower limit value of the volume converted maximum particle diameter _Dmax , and it is preferably as small as possible. However, if the volume converted maximum particle diameter _Dmax is reduced to about 20 nm, the transparency of the dispersion becomes sufficiently high. The volume equivalent maximum particle diameter D _max of the composite oxide particles is measured by a dynamic light scattering method using a photon correlation method. For example, it is measured using a nanotrack particle size distribution measuring device manufactured by Nikkiso Co., Ltd. or a Zetasizer manufactured by Spectris.

The volume-converted maximum particle diameter _Dmax of the composite oxide particles contained in the dispersion is as described above, and the volume-converted average particle diameter D50 of the particles is preferably 1 to ₅₀ nm, preferably 1 to 40 nm. More preferably, it is more preferably 5 to 40 nm. In addition to the volume-converted maximum particle diameter D _max being in the above range, the volume-converted average particle diameter D ₅₀ is in this range, whereby the transparency of the dispersion is further improved. In terms of volume average particle diameter D ₅₀ is measured by the reduced volume maximum particle diameter D _max the same method.

  As the shape of the composite oxide particles, for example, a spherical shape, a polyhedral shape, a needle shape, or the like can be adopted. In particular, when the composite oxide particles are spherical, it is preferable from the viewpoint that birefringence hardly occurs in the optical lens when the optical lens is produced from the dispersion liquid of the present invention containing the particles.

  The dispersion may further contain metal oxide particles having a high refractive index in addition to the composite oxide particles. Examples of such metal oxides include Mg, Ca, Ti, Zn, Zr, Ta, Nb, Ga, Ge, Sn, In, Hf, Y, and lanthanoids (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) and other metal oxides. These metal oxides can be used alone or in combination of two or more. These metal oxides can be used in an amount of about 0.1 to 50% by mass with respect to the entire particles as solids contained in the dispersion.

  The dispersion of the present invention is also characterized by high stability when stored for a long period of time. In order to increase the stability of the dispersion, in the present invention, when the dispersion is an aqueous dispersion, the pH of the aqueous dispersion is 2.0 to 7.0, particularly 2.5 to 5 in the acidic region. .5, especially 2.5 to 5.0 is preferable. In place of this pH region, it is also preferable to set the alkaline region to 8.0 to 13.0, particularly 9.0 to 13.0, and particularly 9.5 to 13.0. When the pH of the aqueous dispersion is less than 2.0, the composite oxide may react with the acid, and the target dispersion may not be obtained. On the other hand, when the pH of the aqueous dispersion exceeds 13.0, it is difficult to maintain the dispersion state and precipitation may occur. Further, when the pH is more than 7.0 and less than 8.0, the dispersion state may be difficult to maintain because of the vicinity of the isoelectric point of the composite oxide particles. These pH values are values at temperatures during storage or use of the aqueous dispersion.

  In order to adjust the pH of the aqueous dispersion within the above range and increase the dispersion stability of the composite oxide particles, various dispersants exhibiting acidity or basicity may be added to the aqueous dispersion. Examples of such a dispersant include mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid, and carboxylic acids such as acetic acid and phthalic acid, tetramethylammonium hydroxide, aqueous ammonia, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and the like. Tetraalkylammonium hydroxide, isopropylamine, isopropanolamine, isobutylamine, ethylenediamine, diisopropylamine, diisobutylamine, diisopropylethylamine, diethanolamine, diethylamine, diethylenetriamine, diphenylamine, dimethylamine, triethanolamine, triethylamine, trioctylamine, tri-n -Butylamine, tripropylamine, trimethylamine, t-butylamine, propylene di Min, monoethanolamine, monoethylamine, include phosphates, such as nitrogen-containing compounds as well as sodium hexametaphosphate, such as monomethylamine. These dispersing agents can be used individually by 1 type or in combination of 2 or more types. The amount of the dispersant added to the aqueous dispersion may be an amount such that the pH of the aqueous dispersion is in the above range.

  The aqueous dispersion may contain water as a medium, only complex oxide particles as a medium, and may contain other particle components such as other metal oxide particles as much as possible except containing a dispersant as necessary. desirable.

  On the other hand, when the dispersion is an oily dispersion using an organic compound as a dispersion medium, the surface of the composite oxide particles as a dispersoid is subjected to a lipophilic treatment, whereby the oily dispersion is stored for a long period of time. Stability can be increased. Examples of the lipophilic treatment include lipophilic treatment using an organometallic compound. By this lipophilic treatment, the surface of the composite oxide particles is coated with the organometallic compound. Examples of organometallic compounds include various coupling agents. As the coupling agent, for example, a silane coupling agent, a zirconium coupling agent, a titanium coupling agent, an aluminum coupling agent, or the like can be used. The surface treatment method of the composite oxide particles using these coupling agents will be described later.

  As silane coupling agents, vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxy Propylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, N-2 (aminoethyl) 3-aminopropylmethyldimethoxysilane, N-2 (aminoethyl) 3-amino Propyltrimethoxysilane, N-2 (aminoethyl) 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N- (1,3-dimethyl -Butylidene) propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N- (vinylbenzyl) -2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride, 3-ureidopropyltriethoxysilane, 3- Chloropropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis (triethoxysilylpropyl) tetrasulfide, 3-isocyanatopropyltriethoxysilane, tetramethoxysilane, Tiger silane, methyl trimethoxy silane, methyl triethoxy silane, dimethyl silane, phenyltriethoxysilane, hexamethyldisilazane, hexyltrimethoxysilane, and decyl trimethoxysilane. Among these, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2 (aminoethyl) 3-amino have good affinity with the organic dispersion medium and high alkali resistance. Preference is given to using propyltrimethoxysilane and N-phenyl-3-aminopropyltrimethoxysilane.

  Titanium coupling agents include tetraisopropyl titanate, tetranormal butyl titanate, butyl titanate dimer, tetra (2-ethylhexyl) titanate, tetramethyl titanate, titanium acetylacetonate, titanium tetraacetylacetonate, titanium ethylacetoacetate, titanium octane Examples include diolate, titanium lactate, titanium triethanolamate, and polyhydroxytitanium stearate.

  Zirconium coupling agents include zirconium normal propyrate, zirconium normal butyrate, zirconium tetraacetylacetonate, zirconium monoacetylacetonate, zirconium bisacetylacetonate, zirconium monoethylacetoacetate, zirconium acetylacetonate bisethylacetoacetate, Examples thereof include zirconium acetate and zirconium monostearate.

  Aluminum coupling agents include aluminum isopropylate, mono sec-butoxyaluminum diisopropylate, aluminum sec-butylate, aluminum ethylate, ethyl acetoacetate aluminum diisopropylate, aluminum tris (ethyl acetoacetate), alkyl acetoacetate aluminum di Isopropylate, aluminum monoacetylacetonate bis (ethylacetoacetate), aluminum tris (acetylacetonate), aluminum monoisopropoxymonooleoxyethylacetoacetate, cyclic aluminum oxide isopropylate, cyclic aluminum oxide octylate, cyclic aluminum oxide stearate Rate and so on.

  The above various coupling agents can be used alone or in combination of two or more. When a silane coupling agent is used as the coupling agent, the surface of the composite oxide is coated with a silane compound. The silane compound preferably has a lipophilic group such as an alkyl group or a substituted alkyl group. The alkyl group may be linear or branched. In any case, the alkyl group preferably has 1 to 20 carbon atoms, particularly 1 to 10 carbon atoms, from the viewpoint of good affinity with the organic dispersion medium. When the alkyl group is substituted, an amino group, vinyl group, epoxy group, styryl group, methacryl group, acrylic group, ureido group, mercapto group, sulfide group, isocyanate group and the like can be used as the substituent. The amount of the silane compound that covers the surface of the composite oxide is 0.01 to 100% by weight, particularly 0.1 to 50% by weight, based on the weight of the composite oxide. It is preferable from the point which becomes favorable.

  When the dispersion is an oily dispersion, the organic compound used as the dispersion medium is not particularly limited as long as it does not dissolve the composite oxide. For example, aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, ketones, acetones, esters, amines, thiols and the like can be used. A combination of two or more of these can also be used. In particular, it is preferable to use a polyhydric alcohol derivative and a monoalcohol derivative as the dispersion medium because the aggregation of the composite oxide particles can be effectively suppressed.

  Examples of the monoalcohol derivative include dimethyl ether, diethyl ether, methyl phenyl ether, ethyl phenyl ether, and tetrahydrofuran. Examples of the polyhydric alcohol derivatives include monoethers, diethers, monoesters and diesters of polyhydric alcohols. Specifically, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-butoxy-2-propanol, diethylene glycol ethyl methyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether, Diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether, ethylene glycol diacetate, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, ethylene glycol dimethyl ether, ethylene glycol monoacetate, ethylene Recall monoisopropyl ether, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, ethylene glycol monohexyl ether, ethylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene Derivatives of dihydric alcohols such as glycol monomethoxymethyl ether; glycerin monoacetate, glycerin diacetate, glycerin triacetate, glycerin dialkyl ether (eg, 1,2-dimethylglycerin, 1,3-dimethylglycerin, 1, And trihydric or higher polyhydric alcohol derivatives such as 3-diethylglycerin). Of these, 1-methoxy-2-propanol, 1-ethoxy-2-propanol and 1-butoxy-2-propanol are particularly preferable. These compounds can be used individually by 1 type or in combination of 2 or more types.

  When the composite oxide dispersion is an oily dispersion, the surface of the particles is treated with the above-mentioned coupling agent for the purpose of further improving the dispersibility and long-term storage stability of the particles, and the lipophilicity is obtained. In addition to making the oil dispersion, various surfactants (cationic surfactant, anionic surfactant, nonionic surfactant, amphoteric surfactant), titanium chelate, zirconium chelate Or various dispersing agents, such as aluminum chelate, can also be mix | blended. These dispersants can be used alone or in combination of two or more. Examples of titanium chelates include titanium diisopropoxy bis (acetylacetonate), titanium tetraacetylacetonate, titanium di-2-ethylhexoxy-bis (2-ethyl-3-hydroxyhexoxide), and titanium diisopropoxy-bis. (Ethyl acetoacetate), titanium diisopropoxy-bis (triethanolaminate), titanium lactate ammonium salt, titanium lactate, titanium lactate and the like can be used. Examples of the zirconium chelate include zirconium tetraacetylacetonate, zirconium tributoxy monoacetylacetonate, zirconium dibutoxybis (ethylacetoacetate), zirconium tetraacetylacetonate and the like.

  The oil-based dispersion of the present invention uses an organic compound as a medium, and only the composite oxide particles that have been subjected to lipophilic treatment as a medium. It is desirable to contain as little metal oxide particles as possible.

  Regardless of whether it is aqueous or oily, the dispersion of the present invention is also characterized by being highly transparent in the wavelength region of visible light (400 to 800 nm). Specifically, the transmittance at a wavelength of 588 nm, which is a part of the wavelength region of visible light, is preferably 65% or more, more preferably 70% or more, and even more preferably 75% when measured using a cell having an optical path length of 1 cm. It is highly transparent. Thus, when a coating film is formed using a highly transparent dispersion liquid, the transparency of the coating film after drying becomes extremely high. Therefore, the dispersion liquid of the present invention is very useful for the production of a transparent film having a high refractive index and a low Abbe number in the visible light wavelength region. A transparent film having a high refractive index and a low Abbe number in the wavelength region of visible light contributes to a reduction in the thickness of an optical lens such as a sheet lens. The transparency of the aqueous dispersion can be measured, for example, by the method described in Examples described later.

  In addition to having high transparency, the dispersion of the present invention has high stability even after long-term storage. For example, it has a stability that does not cause precipitation even when stored for 1 month at room temperature.

Furthermore, the dispersion liquid of the present invention contains a complex oxide powder having a high refractive index, and thus the dispersion liquid itself has a high refractive index. Specifically, when the refractive index of the dispersion medium of the dispersion is N _DS , the refractive index of the dispersion when the concentration of the composite oxide powder is adjusted to 5% by mass is N _DS + 1 × 10 ^{−5 to} N _DS + 1 × 10 ⁻¹ , and N _DS + 1 × 10 ^{−4 to} N _DS + 2 × 10 ⁻² is preferable. The refractive index referred to here is that when light having a wavelength of 588 nm is used. The refractive index of the dispersion can be measured using, for example, KPR-2000 manufactured by Shimadzu Device Manufacturing Co., Ltd.

In order to prepare a 5% by mass dispersion from a certain concentration of dispersion, for example, the dispersion medium is removed to obtain a dried composite oxide powder, and the dried composite oxide powder is removed from the dispersion medium. When the dispersion is again dispersed in the same type of dispersion medium, the concentration may be adjusted to obtain a 5% by mass dispersion. In order to remove the dispersion medium, for example, an operation of heating the dispersion liquid at atmospheric pressure at a temperature of M _p −50 ° C. to M _p + 100 ° C. with respect to the boiling point M _P (° C.) of the dispersion medium may be performed.

  Next, a preferred method for producing the composite oxide powder of the present invention and a dispersion containing the powder will be described. First, a method for producing a composite oxide powder will be described. The composite oxide powder is obtained by adding a compound of a metal element and / or a metalloid element as a raw material to a basic aqueous solution to form a coprecipitate containing these elements in the aqueous solution. The coprecipitate is separated by filtration, dried, and then fired in an oxygen-containing atmosphere.

  As said basic aqueous solution, aqueous solution of alkali metal hydroxides, such as sodium hydroxide, ammonia water, carbonate aqueous solution, etc. can be used, for example. The pH of the basic aqueous solution is preferably set to 5.0 or higher, particularly 10.0 or higher at the reaction temperature.

Examples of the metal element and / or metalloid compound added to the basic aqueous solution include oxides, halides, hydroxides, and water-soluble salts of these elements. When the element is bismuth, for example, Bi ₂ O ₃ , Bi (OH) ₃ , BiOCl, (BiO) ₂ CO ₃ , 4BiNO ₃ (OH) ₂ .BiO (OH), Bi (NO ₃ ) _3. 5H ₂ O, Bi ₂ (SO ₄ ) ₃ , Bi (OOCCH ₃ ) ₃ , BiCl ₃ , BiBr _3, or the like can be used. When the element is, for example, Sn, SnO ₂ , Sn (II) Cl ₂ , Sn (II) Cl ₂ .2H ₂ O, Sn (IV) Cl ₄ , Sn (IV) Cl ₄ .5H ₂ O, Sn (OOCCH ₃ ) ₂ , SnBr ₃ , SnF ₂ , SnSO _{4 and the} like can be used. For example, when the element is Sb, Sb ₂ O ₃ , Sb (III) Cl ₃ , Sb (OOCCH ₃ ) ₃ , SbBr _3, or the like can be used.

  The metal element and / or metalloid compound added to the basic aqueous solution can be added in a solid state or dissolved in a solvent such as water. When adding in the state melt | dissolved in water, when melt | dissolution in water is not easy, melt | dissolution may be accelerated | stimulated by adding acids, such as hydrochloric acid, and a base.

  In this production method, it is important to add a compound of a metal element and / or a metalloid element to a basic aqueous solution. On the contrary, when a basic aqueous solution is added to an aqueous solution containing a compound of a metal element and / or a metalloid element, it is not easy to obtain a target white complex oxide powder.

  The addition of the compound of the metal element and / or the metalloid element to the basic aqueous solution may be performed at once, or may be added continuously or intermittently over a predetermined time. In any case, the temperature of the basic aqueous solution during the reaction can be room temperature (20 to 25 ° C.). In some cases, the reaction can be carried out with heating using an autoclave. The heating temperature is preferably 50 to 130 ° C, more preferably 60 to 120 ° C. When the reaction is carried out under heating, the reaction system is preferably a closed system. When the reaction is carried out under heating in an enclosed system using an autoclave, the intended composite oxide is thereby obtained. According to this method, an amorphous composite oxide is easily obtained.

  The addition amount of the metal element and / or metalloid element compound to the basic aqueous solution may be 0.2 to 5 times the molar amount.

  When producing a complex oxide containing Bi and Sn as the complex oxide, 0.5 to 2.0 mol, particularly 0.5 to 1.5 mol, of Bi is used with respect to 1 mol of Sn. It is preferable. When producing a complex oxide containing Bi and Sb as the complex oxide, 0.5 to 2.0 mol, particularly 0.5 to 1.5 mol, of Bi is used with respect to 1 mol of Sb. It is preferable.

  When the desired coprecipitate is formed by adding a metal element and / or metalloid compound to the basic aqueous solution, the coprecipitate is filtered, washed with water and dried, and then subjected to a firing step. . In addition, when it reacts under a heating using the autoclave mentioned above, since the target complex oxide will produce | generate by it, it is unnecessary to perform this baking process. The firing step can be generally performed in an oxygen-containing atmosphere such as air. The firing temperature affects the crystal state, particle size, and BET specific surface area of the composite oxide to be produced. Specifically, an amorphous composite oxide can be obtained by setting the firing temperature to a relatively low temperature of 200 ° C. to 550 ° C., more preferably 200 ° C. to 450 ° C. On the other hand, by setting the firing temperature to a relatively high temperature of more than 550 ° C. and not more than 1000 ° C., more preferably not less than 550 ° C. and not more than 800 ° C., a crystalline composite oxide can be obtained. In addition, when the baking is performed at a high temperature, the BET specific surface area can be reduced as compared with the case of baking at a low temperature. Therefore, by controlling the calcination temperature, a composite oxide powder having a desired BET specific surface area, high dispersibility in water and high dispersion stability, and capable of preparing an aqueous dispersion having high transparency. Can be obtained. In the case of firing at a low temperature, the firing time is preferably 0.5 to 12 hours, particularly 1 to 6 hours. Also in the case of baking at a high temperature, it is preferably 0.5 to 12 hours, particularly 1 to 6 hours.

  The composite oxide powder obtained in this way is white, and the lightness L * is higher than the value described above. The composite oxide powder and water are mixed to form a slurry, and wet pulverization is performed by a media mill such as a paint shaker. Examples of the beads to be used include zirconia beads and alumina beads having a diameter of about 0.1 mm. In this case, it becomes easy to bring the composite oxide particles close to a monodispersed state by performing the pulverization operation by adding the above-described various dispersants to the slurry and adjusting the pH.

  After the wet pulverization, the liquid and beads are separated, and the coarse particles are removed by a membrane filter to obtain the intended aqueous dispersion. The aqueous dispersion thus obtained is colorless and transparent and has a high visible light transmittance. Moreover, it is stable and does not cause precipitation even when stored for a long time.

An aqueous dispersion is thus obtained. On the other hand, the oil dispersion can be produced from an aqueous dispersion. For example, the solvent replacement operation is performed by adding an organic compound as a dispersion medium of the oil dispersion to the aqueous dispersion. By repeating this operation, an oily dispersion can be obtained. Prior to solvent replacement, various coupling agents are added to the aqueous dispersion, whereby the surface of the composite oxide particles can be subjected to lipophilic treatment. Incidentally, in terms of volume average particle diameter D ₅₀ and in terms of volume maximum particle diameter D _max of the particles of the composite oxide, that there is no substantial change before and after the lipophilic treatment using a coupling agent, the present inventors I have confirmed.

  The dispersion obtained in this way is made of various optical materials and electronic materials using the high refractive index and low Abbe number of the composite oxide contained therein and the transparency to visible light of the aqueous dispersion. Can be used. For example, it can be used for optical system parts such as lenses, antireflection films, infrared transmission films and the like. Specifically, the dispersion is applied to the surface of various substrates, such as transparent substrates and lenses, to form a coating film, and the coating film is dried to provide high transparency, high refractive index, and low wavelength dispersion. A thin film having properties can be formed. The dried thin film may be fired as necessary under an inert atmosphere, an oxidizing atmosphere such as air, or a weakly reducing atmosphere (for example, a hydrogen-containing atmosphere having an explosion limit concentration or less). This thin film is useful for further increasing the refractive index of the lens or as a thin lens itself. Furthermore, the dispersion liquid of the present invention is also suitably used as a raw material for a resin lens in which a composite oxide contained therein is dispersed in a resin.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” means “mass%”.

[Example 1]
1) Production of bismuth-tin composite oxide powder (BiO) _{2 A 3 having} the composition shown in Table 1 below using ₂ CO ₃ , SnCl ₄ .5H ₂ O, 35% hydrochloric acid, sodium hydroxide and pure water And solution B were prepared.

  Next, the B liquid (pH = 13.5) was stirred at room temperature, and the A liquid was fed into the B liquid at 10 ml / min with a feed pump, and both liquids were reacted to form the bismuth-tin coprecipitate. A precursor compound was obtained. The obtained precursor compound was repulped with pure water, and the cake after filtration was dried at 120 ° C. for 6 hours to obtain a bismuth-tin precursor compound powder.

  10 g of this bismuth-tin precursor compound powder was fired at 400 ° C. for 4 hours in the air to obtain a bismuth-tin composite oxide powder. When the composition was confirmed by XRD, it was an amorphous bismuth-tin composite oxide. Table 4 below shows the results of measuring the BET specific surface area, the lightness L * indicated in the CIE 1976 (L *, a *, b *) color space, and the composition ratio by fluorescent X-ray analysis (XRF).

2) Production of aqueous dispersion In a 50 ml resin container, 2.0 g of the amorphous bismuth-tin composite oxide powder obtained in 1) and 1% tetramethylammonium hydroxide (hereinafter “TMAH”) A slurry was obtained by adding 23 g of an aqueous solution. Further, 100 g of zirconia beads having a diameter of 0.1 mmΦ was added, the container was sealed, and wet pulverized with a paint shaker (manufactured by Asada Tekko) for 3 hours. Finally, the pulverized slurry was passed through a 0.2 μm membrane filter to remove coarse particles, thereby obtaining a target aqueous dispersion of bismuth-tin composite oxide. This aqueous dispersion was slightly white but transparent. The aqueous dispersion had a pH (25 ° C.) of 11.7 and a refractive index of 1.347083. The refractive index of the aqueous dispersion prepared so that the concentration of the composite oxide powder was 5% was 1.338804. The refractive index N _{DS of} water as a dispersion medium is 1.333362. The refractive index of the composite oxide was 2.56. Furthermore, the volume conversion average particle diameter D ₅₀ and the volume conversion maximum particle diameter D _max were measured using a Zetasizer manufactured by Spectris. The results are shown in Table 5. When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, the formation of precipitate was not confirmed, and it was confirmed that the highly dispersed state was maintained.

In the above measurement, the BET specific surface area was measured by using a nitrogen-helium mixed gas containing 30% by volume of nitrogen as an adsorbing gas and 70% by volume of helium as a carrier gas. It was measured according to (3.5) one-point method of 6.2 flow method of JIS R 1626 “Method for measuring specific surface area of fine ceramic powder by gas adsorption BET method” using Micromerix Flowsorb II2300 manufactured by Seisakusho.
The composition ratio was calculated by fluorescent X-ray analysis (manufactured by Rigaku Corporation, ZSX Primus II).
For the lightness L *, the lightness of the powder was directly measured using a spectrocolorimeter (manufactured by Konica Minolta, CM-2600d) according to JIS Z 8729 “Method of displaying object color by U * V * W * system”.
In terms of volume average particle diameter D ₅₀ and in terms of volume maximum particle diameter D _max is a small amount of metal oxide powder, stirred in pure water 10 ml, and was dispersed by ultrasonic. Thereafter, a part of the obtained dispersion was taken out, and the particle size distribution was measured with a particle size distribution measuring device (Spectras Co., Ltd., Zetasizer), and the volume converted average particle size D ₅₀ and the volume converted maximum particle size D _max were determined. Asked.
The transparency of the aqueous dispersion was measured at a wavelength of 588 nm using a spectrophotometer U-4000 manufactured by Hitachi High-Technologies Corporation and a quartz cell having an optical path length of 1 cm.
The refractive index was measured using the method described in [0073] of JP-A-2007-17892. The measurement wavelength was 588 nm.

[Example 2]
1) Manufacture of bismuth-antimony composite oxide powder (BiO) ₂ liquids A and B having the composition shown in Table 2 below using ₂ CO ₃ , SbCl ₃ , 35% hydrochloric acid, sodium hydroxide and pure water. Prepared.

  Next, liquid B (pH = 14.0) was stirred at room temperature, liquid A was fed into liquid B at 10 ml / min with a feed pump, and both liquids were reacted to form a bismuth-antimony coprecipitate. A precursor compound was obtained. The obtained precursor compound was repulped with pure water, and the cake after filtration was dried at 120 ° C. for 6 hours to obtain a bismuth-antimony precursor compound powder.

  3 g of this bismuth-antimony precursor compound powder was fired at 500 ° C. for 4 hours in the air to obtain a bismuth-antimony composite oxide powder. When the composition was confirmed by XRD, it was an amorphous bismuth-antimony composite oxide. Table 4 shows the measurement results of the BET specific surface area, the lightness L * indicated in the CIE 1976 (L *, a *, b *) color space, and the composition ratio by X-ray fluorescence analysis (XRF).

2) Production of aqueous dispersion In a 50 ml resin container, 2.0 g of the amorphous bismuth-antimony composite oxide powder obtained in 1) and 23 g of 1% TMAH aqueous solution were added to obtain a slurry. Further, 100 g of zirconia beads having a diameter of 0.1 mmΦ was added, the container was sealed, and wet pulverized with a paint shaker (manufactured by Asada Tekko) for 3 hours. Finally, the pulverized slurry was passed through a 0.2 μm membrane filter to remove coarse particles, thereby obtaining a target aqueous dispersion of bismuth-antimony composite oxide. This aqueous dispersion was slightly white but transparent. Further, this aqueous dispersion had a pH of 12.4 and a refractive index of 1.344611. The refractive index of the aqueous dispersion prepared so that the concentration of the composite oxide powder was 5% was 1.339209. The refractive index of the composite oxide was 2.61. Furthermore, the volume conversion average particle diameter D ₅₀ and the volume conversion maximum particle diameter D _max were measured using a Zetasizer manufactured by Spectris. The results are shown in Table 5. When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, the formation of precipitate was not confirmed, and it was confirmed that the highly dispersed state was maintained.

Example 3
A bismuth-tin composite oxide powder was obtained in the same manner as in Example 1 except that the firing conditions of the bismuth-tin precursor compound powder were changed to 600 ° C. for 4 hours. When the composition was confirmed by XRD, it was a crystalline bismuth-tin composite oxide. Table 4 shows the measurement results of the BET specific surface area, the lightness L * indicated in the CIE 1976 (L *, a *, b *) color space, and the composition ratio by X-ray fluorescence analysis (XRF). Using this bismuth-tin composite oxide, an aqueous dispersion was prepared in the same manner as in Example 1. This aqueous dispersion was slightly brownish and transparent. Further, this aqueous dispersion had a pH of 11.1 and a refractive index of 1.345920. The refractive index of the aqueous dispersion prepared so that the concentration of the composite oxide powder was 5% was 1.338682. The refractive index of the composite oxide was 2.52. Further, the volume-converted average particle diameter D ₅₀ and the volume-converted maximum particle diameter D _max were measured in the same manner as in Example 1. The results are shown in Table 5. When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, the formation of precipitate was not confirmed, and it was confirmed that the highly dispersed state was maintained.

Example 4
An aqueous dispersion was prepared in the same manner as in Example 1 except that 23 g of 1% diisopropylamine (hereinafter referred to as “DIPA”) aqueous solution was used instead of 23 g of 1% TMAH aqueous solution. This aqueous dispersion was slightly white but transparent. The aqueous dispersion had a pH of 10.5 and a refractive index of 1.348029. The refractive index of the aqueous dispersion prepared so that the concentration of the composite oxide powder was 5% was 1.338624. The refractive index of the composite oxide was 2.51. Further, the volume-converted average particle diameter D ₅₀ and the volume-converted maximum particle diameter D _max were measured in the same manner as in Example 1. The results are shown in Table 5. When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, the formation of precipitate was not confirmed, and it was confirmed that the highly dispersed state was maintained.

Example 5
In Example 1, an aqueous dispersion was prepared in the same manner as in Example 1 except that 23 g of 1% triethylamine (hereinafter referred to as “TEA”) aqueous solution was used instead of 23 g of 1% TMAH aqueous solution. This aqueous dispersion was slightly white but transparent. The aqueous dispersion had a pH of 10.4 and a refractive index of 1.352461. The refractive index of the aqueous dispersion prepared so that the concentration of the composite oxide powder was 5% was 1.338423. The refractive index of the composite oxide was 2.45. Further, the volume-converted average particle diameter D ₅₀ and the volume-converted maximum particle diameter D _max were measured in the same manner as in Example 1. The results are shown in Table 5. When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, the formation of precipitate was not confirmed, and it was confirmed that the highly dispersed state was maintained.

Example 6
In Example 1, an aqueous dispersion was prepared in the same manner as in Example 1 except that 23 g of 1% acetic acid aqueous solution was used instead of 23 g of 1% TMAH aqueous solution. This aqueous dispersion was slightly white but transparent. The aqueous dispersion had a pH of 3.3 and a refractive index of 1.346470. The refractive index of the aqueous dispersion prepared so that the concentration of the composite oxide powder was 5% was 1.338680. The refractive index of the composite oxide was 2.52. Further, the volume-converted average particle diameter D ₅₀ and the volume-converted maximum particle diameter D _max were measured in the same manner as in Example 1. The results are shown in Table 5. When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, the formation of precipitate was not confirmed, and it was confirmed that the highly dispersed state was maintained.

Example 7
1) Production of Bismuth-Tin Composite Oxide Slurry After preparing a bismuth-tin precursor compound in the same manner as in Example 1, this was repulp washed and a 10% slurry was prepared without drying the resulting cake. did. This slurry was put into an autoclave and reacted by heating at 80 ° C. for 4 hours in a closed system. In this way, particles of bismuth-tin composite oxide were generated in the liquid. When the obtained bismuth-tin composite oxide slurry was dried at 120 ° C. and the composition was confirmed by XRD, it was an amorphous bismuth-tin composite oxide. Table 4 shows the measurement results of the BET specific surface area, the lightness L * indicated in the CIE 1976 (L *, a *, b *) color space, and the composition ratio by X-ray fluorescence analysis (XRF).

2) Production of aqueous dispersion 20 g of 10% bismuth-tin composite oxide slurry obtained in 1) and 1.3 g of 15% TMAH aqueous solution were put into a 50 ml resin container to obtain a slurry. Thereafter, an aqueous dispersion was obtained in the same manner as in Example 1. This aqueous dispersion was slightly whitish but transparent, had a pH of 11.1 and a refractive index of 1.346876. The refractive index of the aqueous dispersion prepared so that the concentration of the composite oxide powder was 5% was 1.338785. The refractive index of the composite oxide was 2.55. Moreover, the volume conversion average particle diameter D ₅₀ and the volume conversion maximum particle diameter D _max were measured using a Zetasizer manufactured by Spectris. The results are shown in Table 5. When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, the formation of precipitate was not confirmed, and it was confirmed that the highly dispersed state was maintained.

Example 8
Liquids A and B (pH = 13.5) having the composition shown in Table 3 below were prepared using (BiO) ₂ CO ₃ , SnCl ₄ .5H ₂ O, 35% hydrochloric acid, sodium hydroxide and pure water. did. Using these liquids, a bismuth-tin composite oxide powder was obtained in the same manner as in Example 1. When the composition was confirmed by XRD, it was an amorphous bismuth-tin composite oxide. Table 4 below shows the results of measuring the BET specific surface area, the lightness L * indicated in the CIE 1976 (L *, a *, b *) color space, and the composition ratio by fluorescent X-ray analysis (XRF).

An aqueous dispersion was prepared in the same manner as in Example 7 using the obtained bismuth-tin composite oxide. This aqueous dispersion was slightly whitish but transparent and had a pH of 10.9 and a refractive index of 1.346572. Further, the refractive index of the aqueous dispersion prepared so that the concentration of the composite oxide powder was 5% was 1.338781. The refractive index of the composite oxide was 2.55. It was also measured in terms of volume average particle size D ₅₀ and in terms of volume maximum particle diameter D _max using Malvern Co. Zetasizer. The results are shown in Table 5. When this aqueous dispersion was stored at room temperature (25 ° C.) for 1 month and the storage stability was examined, the formation of precipitate was not confirmed, and it was confirmed that the highly dispersed state was maintained.

[Comparative Example 1]
This comparative example corresponds to the example described in [0041] of Patent Document 1. 50.8 g Bi ₂ O ₃ powder and 49.2 g SnO ₂ powder were ground together in water for 1.5 hours to thoroughly mix and then dried at 105 ° C. The dried powder was fired at 1070 ° C. for 7 hours. When the obtained product was pulverized, it was light brown. X-ray diffraction confirmed the presence of Bi ₂ Sn ₂ O ₇ and SnO ₂ phases in the product. Moreover, the volume conversion average particle diameter was 7 micrometers. Using this product, an aqueous dispersion was prepared in the same manner as in Example 1. However, a transparent dispersion was not obtained due to the large particle size. In addition, regarding the storage stability, precipitation was confirmed immediately because the particle size was also large. The refractive index could not be measured.

[Comparative Example 2]
This comparative example corresponds to Example 8 of Patent Document 2. 3.30 g of tin (IV) -t-butoxide was mixed with 2.38 g of triethanolamine. To this was added 76 ml of water and heated at 100 ° C. for 24 hours. 38.2 g of bismuth citrate (purity 99.99%) and 38.6 g of triethanolamine were dissolved in 280 ml of water, and the total amount of the tin (IV) -t-butoxide solution and 80 ml of 4N-KOH solution were added thereto. The reaction solution was heated to 40 ° C. Furthermore, after heating to 90 degreeC and continuing stirring for 5 hours, it cooled to normal temperature. The resulting yellow precipitate was filtered and purified. When the XRD of the particles obtained by drying the precipitate was measured, a crystal structure of Bi ₁₂ SnO ₂₀ was obtained. Further, SEM observation of the particles confirmed that the volume-converted average particle size was about 4 μm. Using the obtained particles, an aqueous dispersion was prepared in the same manner as in Example 1. However, because of the large particle size, a transparent dispersion could not be obtained. Further, regarding the storage stability, the particle size was similarly large, and precipitation was immediately confirmed. The refractive index could not be measured.

Example 9
In this example, an oily dispersion was produced. 15.0 g of the aqueous dispersion obtained in 2) of Example 7 and 0.15 g of silane coupling agent KBM-903 (manufactured by Shin-Etsu Chemical Co., Ltd.) were placed in a 30 ml resin container, and the container was sealed. The container was placed on a paint shaker (manufactured by Asada Tekko), and the contents were mixed for 10 minutes to perform lipophilic treatment to coat the surface of the particles with a silane compound. The amount of the silane compound covering the surface of the composite oxide was 10.0% based on the weight of the composite oxide. The aqueous dispersion was solvent-substituted with 1-methoxy-2-propanol as an organic dispersion medium. 15 g (solid content concentration 10%) of the oily dispersion obtained by solvent substitution and 50 g of 0.3 mmφ zirconia beads were placed in a 30 ml resin container, and the container was sealed. This container was placed in a paint shaker (manufactured by Asada Tekko) and the contents were mixed for 2 hours. Next, the dispersion was subjected to solid-liquid separation, and then replaced with 50 g of 0.1 mmφ zirconia beads, and further wet pulverized with a paint shaker (manufactured by Asada Tekko) for 2 hours. Finally, the pulverized slurry was passed through a 0.2 μm membrane filter to remove coarse particles, thereby obtaining an oily dispersion of the desired bismuth-tin oxide. This oily dispersion was transparent and the refractive index was 1.412856. Further, the refractive index of the oily dispersion prepared so that the concentration of the composite oxide powder was 5% was 1.406305. The refractive index N _DS of 1-methoxy-2-propanol as a dispersion medium is 1.401114. The volume-converted average particle diameter D ₅₀ and maximum particle diameter D _max were measured using a Zetasizer manufactured by Spectris Co., Ltd. The results are shown in Table 6. When this oily dispersion was stored at room temperature (25 ° C.) for 1 month and storage stability was examined, the formation of precipitate was not confirmed, and it was confirmed that the highly dispersed state was maintained.

Claims (16)

  A composite oxide powder comprising Sn and Bi, wherein the value of brightness L * indicated in the CIE 1976 (L * a * b *) color space is 70 or more.   2. The composite oxide powder according to claim 1, wherein a molar ratio Bi / Sn of Bi and Sn in the composite oxide is 0.5 to 2. 3.   A composite oxide powder comprising Sb and Bi, wherein the value of brightness L * indicated in the CIE 1976 (L * a * b *) color space is 70 or more. Composite oxide powder according to any one of from BET specific surface area of 15~150m ² / g 請 Motomeko 1 to Ru der 3.   The composite oxide powder according to any one of claims 1 to 4, wherein the composite oxide is amorphous. An aqueous dispersion containing the composite oxide powder according to any one of claims 1 to 5, wherein the composite oxide powder is aqueous when the concentration is adjusted to 5% by mass. An aqueous dispersion in which the refractive index of the dispersion is N _DS + 1 × 10 ^{−5 to} N _DS + 1 × 10 ⁻¹ (where N _DS represents the refractive index of the dispersion medium). The aqueous dispersion according to claim 6, wherein the composite oxide particles have a volume-converted average particle diameter D ₅₀ of 1 to ₅₀ nm and a volume-converted maximum particle diameter D _max of 100 nm or less.   The aqueous dispersion according to claim 6 or 7, which has a pH of 2.0 to 6.5 or 8.0 to 13.0.   The aqueous dispersion according to any one of claims 6 to 8, wherein the concentration of the composite oxide powder is 5 to 50% by mass.   The aqueous dispersion according to any one of claims 6 to 9, wherein the transmittance at a wavelength of 588 nm is 65% or more. An oily dispersion comprising the composite oxide powder according to any one of claims 1 to 5, wherein the composite oxide particles are subjected to lipophilic treatment on a surface thereof, and the lipophilic treatment is performed. The refractive index of the oil-based dispersion liquid when the concentration of the applied composite oxide powder is adjusted to 5% by mass is N _DS + 1 × 10 ^{−5 to} N _DS + 1 × 10 ⁻¹ (formula among, oil dispersions which are N _DS represents the refractive index of the dispersion medium). The oil-based dispersion according to claim 11, wherein the composite oxide particles have a volume-converted average particle diameter D50 of 1 to ₅₀ nm and a volume-converted maximum particle diameter _Dmax of 100 nm or less.   The oily dispersion according to claim 11 or 12, wherein the concentration of the composite oxide powder is 5 to 50% by mass.   The oil-based dispersion liquid according to any one of claims 11 to 13, wherein the transmittance at a wavelength of 588 nm is 65% or more.   The oily dispersion according to any one of claims 11 to 14, wherein a surface of the composite oxide particles is coated with an organometallic compound to perform lipophilic treatment.   The oil-based dispersion liquid according to any one of claims 11 to 15, wherein the oil-based dispersion medium is a polyhydric alcohol derivative or a monoalcohol derivative.