JP2010006629A - Titanium dioxide fine particle and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide titanium dioxide fine particles of which the catalytic activity is controlled while retaining excellent transparency and ultraviolet screening ability, and a production method which prevents difficulty in handling work and lowering of production efficiency due to the thixotropic viscosity of a cake and powdering of a dry substance. <P>SOLUTION: Coatings of high density silica and porous silica are formed on the surfaces of titanium dioxide fine particles having an average particle diameter of ≤100 nm. Specifically, aqueous slurry of titanium dioxide fine particles having an average particle diameter of ≤100 nm is adjusted to pH ≥8 at 70°C, a silicate is added and the aqueous slurry is neutralized with an acid to form high density silica. A silicate and an acid are then added while keeping the aqueous slurry at pH 1-4 to form porous silica. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to titanium dioxide fine particles and a method for producing the same.

Titanium dioxide fine particles use the fine particle shape to surface functional materials such as UV shielding agents, fillers, additives, underlayer materials for magnetic recording media, catalyst carriers, conductive materials, and antibacterial materials. It is also useful as substrate particles that adhere to the surface. In particular, titanium dioxide fine particles are highly transparent and have an excellent ultraviolet shielding ability, particularly an ultraviolet shielding ability (UVB) in the B region (wavelength of 290 to 320 nm), which is said to have the greatest effect on the skin. It is used as an agent in sunscreen cosmetics, paint films, plastic moldings and the like. However, titanium dioxide fine particles have high catalytic activity, photoactivity / oxidation activity, and are easy to alter oils, resins, plastics, etc., which are components of cosmetics, etc., so the surface of titanium dioxide fine particles is coated with silica. The activity is suppressed (see Patent Documents 1 and 2). The silica-coated titanium dioxide fine particles do not react with the dibenzoylmethane-based UVA ultraviolet absorber, so that it can be used in combination with the dibenzoylmethane-based UVA ultraviolet absorber. UV-ultraviolet shielding effect of UVB can be remarkably enhanced.
To coat silica, a method of dispersing titanium dioxide fine particles in ethanol together with tetraethoxysilane and hydrolyzing tetraethoxysilane (Patent Document 1, paragraph 0009), an aqueous slurry of titanium dioxide fine particles, sodium silicate or the like A method of adding a water-soluble alkali metal silicate and neutralizing with an acid (Patent Document 2) is known.

  On the other hand, silica coating is also applied to a titanium dioxide pigment having a large particle diameter of about 0.1 μm (100 nm) to 1.0 μm with respect to the titanium dioxide fine particles. For example, in Patent Document 3, in order to obtain an excellent high pigment concentration titanium dioxide pigment aqueous dispersion in an emulsion paint system and a coating performance having excellent gloss, a treatment that is easily caused in a silica coating treatment step is further disclosed. In order to substantially avoid the difficulty in handling due to the thixotropic viscosity of the slurry or cake and the reduction in production efficiency, the first coating layer of high-density silica and the second coating of porous silica are applied to the titanium dioxide pigment particle surface. And forming a coating layer. Specifically, the aqueous slurry of titanium dioxide pigment is adjusted to pH 9 or higher at 80 ° C. or higher, silicate is then added, and then neutralized slowly with acid. While maintaining the pH of the aqueous slurry of titanium dioxide pigment having 1 to 4, a silicate solution and an acid or alkali are added to cover the porous silica.

Japanese Patent Laid-Open No. 11-217322 Japanese Patent Publication No. 61-49250 JP-A-10-130527

  In Patent Documents 1 and 2, silica is coated on the surface of the titanium dioxide fine particles to suppress the catalytic activity of the titanium dioxide fine particles, but further improvement of the catalytic activity suppression is desired. In addition, when a large amount of silica is coated to suppress the catalyst activity, the content ratio of titanium dioxide is lowered, and the ultraviolet shielding ability is lowered. Furthermore, when silica coating is performed by the methods of Patent Documents 1 and 2, difficulty in handling work due to thixotropic viscosity of the treated slurry and cake, and reduction in production efficiency occur. On the other hand, Patent Document 3 is an improvement in silica coating for obtaining a high concentration and high gloss on a titanium dioxide pigment, and an improvement in handling workability of the titanium dioxide pigment, which has a very high catalytic activity, No mention is made of fine titanium dioxide fine particles whose thixotropic viscosity becomes extremely high with silica coating.

  The inventors of the present invention have studied an industrially advantageous silica coating method capable of sufficiently suppressing the catalytic activity while maintaining the excellent transparency and ultraviolet shielding ability of the titanium dioxide fine particles. Although the high-density silica coating performed is effective in suppressing the catalytic activity of the titanium dioxide fine particles, there are difficulties in handling work due to the thixotropic viscosity of the cake and powdering of the dried product, and a reduction in production efficiency. In the case of porous silica coating performed with a titanium dioxide pigment, the catalyst activity is not sufficiently suppressed, the dispersibility in a solvent or the like is lowered, and the ultraviolet shielding ability is not sufficient. The formation of the coating and porous silica coating found that the desired one was obtained and the present invention was completed.

  That is, the present invention is titanium dioxide fine particles characterized by having a coating of high-density silica and porous silica on the surface of titanium dioxide fine particles having an average particle size of 100 nm or less, and the average particle size is 100 nm or less. The titanium dioxide fine particle aqueous slurry was adjusted to pH 8 or higher at 70 ° C. or higher, then silicate was added, and then neutralized with acid to form high density silica, and then the pH of the aqueous slurry was adjusted to 1. A method for producing fine titanium dioxide particles, characterized in that porous silica is formed by adding silicate and acid while maintaining at ˜4.

The titanium dioxide fine particles of the present invention can improve dispersibility in a solvent or the like, which has been a drawback of porous silica coating, and have excellent transparency and ultraviolet shielding ability. In addition, the catalytic activity of the titanium dioxide fine particles can be sufficiently suppressed. For this reason, it is useful for ultraviolet screening agents, and for various uses such as dispersions, cosmetics, sunscreen cosmetics, pharmaceuticals, external products, ultraviolet screening materials, optical members, transparent members, paints, plastic compositions, etc. Can be used.
In addition, the titanium dioxide fine particle production method of the present invention substantially avoids the difficulty of handling due to the thixotropic viscosity of the processing slurry and cake that are likely to occur in the silica coating process of the titanium dioxide fine particles and the reduction in production efficiency. This is industrially advantageous.

The titanium dioxide fine particles of the present invention are fine titanium dioxide having an average particle diameter of 100 nm or less, and more preferable from the viewpoint of transparency and ultraviolet shielding ability, preferably in the range of 1 to 70 nm, and 5 to 50 nm. A range is more preferred. This average particle diameter is obtained by the following formula using the specific surface area a (m ² / g) of the titanium dioxide fine particles themselves by the nitrogen adsorption method (BET method).
Formula: d = 6 / (ρ · a)
However, d is an average particle diameter (micrometer) and (rho) is specific gravity of titanium dioxide.
Therefore, more preferably in a range of specific surface area 80~160m ² / g of titanium dioxide fine particles per se, and more preferably in the range of 80 to 120 ² / g. The particle shape of the titanium dioxide fine particles may be any shape, but what is called a needle shape, a spindle shape, a rod shape, or the like is preferable. The titanium dioxide fine particles may partially include amorphous particles within a range not impairing the object of the present invention, but preferably have a substantially crystalline structure. Although there is no restriction on the crystal structure, those obtained by hydrolyzing titanyl sulfate are mainly anatase type, and those obtained by hydrolyzing titanium tetrachloride and then subjected to alkali treatment / hydrochloric acid treatment are mainly rutile type.

The surface of the titanium dioxide fine particles has a coating of high-density silica and porous silica. Depending on the pH range during the silica coating treatment, the silica to be coated becomes porous or non-porous (high density). The order of the coating of the high-density silica and the porous silica may be any, but since it is easy to form a dense coating if the high-density silica, the first coating layer of high-density silica is present on the surface of the titanium dioxide fine particles, It is preferred to have a second coating layer of porous silica thereon. The silica coating amount can be appropriately set, and is preferably 30 to 100% by weight as SiO _{2 with} respect to the weight of titanium dioxide expressed by the total amount of high-density silica and porous silica. % Is more preferable. Further, the first coating layer of high-density silica is preferably 5 to 50% by weight, more preferably 10 to 50% by weight, and still more preferably 15 to 40% by weight as SiO _{2 with} respect to the weight of titanium dioxide. On the other hand, the second coating layer of porous silica is preferably 5 to 50% by weight, more preferably 10 to 50% by weight, and still more preferably 15 to 40% by weight as SiO _{2 with} respect to the weight of titanium dioxide. If the silica coating amount is less than the above range, a desired effect such as suppression of the catalyst activity cannot be obtained, and if it is too much, not only is not economically advantageous, but also the ultraviolet shielding ability is impaired. The silica coating can be observed with an electron microscope, and the amount can be measured by a usual method such as fluorescent X-ray analysis or ICP emission analysis.

  When the titanium dioxide fine particles of the present invention are used for various applications such as cosmetics and paints, various inorganic treatment agents used in those fields, for example, inorganic substances such as zinc oxide, zirconium oxide, and aluminum hydroxide are used. The surface of the titanium dioxide fine particles may be coated, may be coated between high-density silica and porous silica, or may be further coated after coating with high-density silica and porous silica. Further, after coating with high-density silica or porous silica, an organic treatment agent such as carboxylic acid, polyol, amine, siloxane, or silane coupling agent may be further coated. In these cases, the dispersibility in cosmetics and paints and the durability of the coating film may be further improved. The amount of the inorganic treatment agent and the organic treatment agent can be appropriately set.

  Next, in order to perform silica coating on titanium dioxide fine particles, an aqueous slurry of titanium dioxide fine particles having an average particle diameter of 100 nm or less is adjusted to a pH of 8 or more at 70 ° C. or more, and then silicate is added. Neutralize to form high density silica, then add silicate and acid to form porous silica while maintaining aqueous slurry pH at 1-4. If the silica coating amount covers the surface of the titanium dioxide fine particles, it becomes a coating layer. In the above method, the high-density silica becomes the first coating layer as viewed from the surface of the titanium dioxide fine particles, and the porous silica becomes the second coating layer. Become.

First, after adjusting pH to 8 or more, preferably 8 to 10 with an alkali compound such as sodium hydroxide, potassium hydroxide, ammonia or the like, in an aqueous slurry of titanium dioxide fine particles, it is heated to 70 ° C. or more, preferably 70 to Set to 105 ° C. Next, silicate is added to the aqueous slurry of titanium dioxide fine particles. As the silicate, various silicates such as sodium silicate and potassium silicate can be used. The coating amount of the high-density silica is preferably 5 to 50% by weight as SiO _{2 with} respect to the weight of titanium dioxide, more preferably 10 to 50% by weight, and still more preferably 15 to 40% by weight. The addition of silicate is usually preferably performed over 15 minutes or more, more preferably 30 minutes or more. Next, after the addition of silicate is completed, the mixture is further sufficiently stirred and mixed as necessary, and then neutralized with an acid while maintaining the temperature of the slurry preferably at 80 ° C. or higher, more preferably 90 ° C. or higher. Examples of the acid used here include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, and acetic acid. The pH of the slurry is preferably adjusted to 7.5 or less, more preferably 7 or less.

Next, an acid such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid or acetic acid is added to the aqueous slurry to adjust the pH to 1 to 4, preferably 1.5 to 3. The slurry temperature is preferably adjusted to 50 to 70 ° C. Next, while maintaining the slurry pH within the above range, a silicate and an acid are added to form a porous silica coating. As the silicate, various silicates such as sodium silicate and potassium silicate can be used. The coating amount of the porous silica is preferably 5 to 50% by weight as SiO _{2 with} respect to the weight of titanium dioxide, more preferably 10 to 50% by weight, and still more preferably 15 to 40% by weight. The addition of silicate is usually preferably performed over 15 minutes or more, more preferably 30 minutes or more. After completion of the addition of silicate, an alkali compound is added as necessary, and the pH of the slurry is adjusted to about 6 to 9, followed by filtration, washing, drying, and pulverization. This pulverization can usually be performed by an airflow pulverizer such as a jet mill or a micronizer, a roller mill, a pulverizer, or the like. The dried or pulverized product may be fired as necessary, and the firing temperature is suitably about 300 to 900 ° C.

  The silica-coated titanium dioxide fine particles can be further surface-treated with various inorganic substances and organic substances as necessary. For example, aluminum hydroxide can be suitably used as the inorganic substance, and stearic acid or a salt thereof can be suitably used as the organic substance. Specifically, the slurry after the porous silica treatment is neutralized with sodium hydroxide and then heated to a temperature of 70 ° C. or higher, and then an aluminum compound is added and coated. Next, stearic acid and / or a salt thereof is added, and then the pH of the slurry is adjusted to 7 to 9, followed by filtration, washing and drying. The coating amount of aluminum hydroxide can be appropriately set, but is preferably about 1 to 10% by weight. As the salt of stearic acid, a salt of sodium, potassium, ammonium or the like is preferably used. The addition amount of stearic acid and / or a salt thereof can be appropriately set, but is preferably 1 to 30% by weight.

  Since the titanium dioxide fine particles of the present invention have an excellent ultraviolet shielding ability, they can be used as an ultraviolet shielding agent. Specifically, it is blended in dispersions, cosmetics, sunscreen cosmetics, pharmaceuticals, external products, paints, plastic compositions, etc., and titanium dioxide fine particles are applied to the surface of articles such as glass, ceramics, plastics, sheets and films. Or used as an ultraviolet shielding material. Moreover, since the titanium dioxide fine particles of the present invention have excellent transparency, they can be used in combination with optical members and transparent members. Specifically, titanium dioxide fine particles are blended into paints, plastic compositions, etc., or titanium dioxide fine particles are arranged on the surface of articles such as glass, ceramics, plastics, sheets, films, etc. as optical members and transparent members Used.

  The dispersion containing the titanium dioxide fine particles of the present invention is dispersed in a solvent such as water, alcohols or oils, and can be used for various applications. It is preferable to use an oily agent that is optically transparent in the region of 300 to 600 nm as the solvent because a highly transparent dispersion can be obtained. The content of the titanium dioxide fine particles can be appropriately set. In addition, cosmetics, sunscreen cosmetics, pharmaceuticals, and external products containing the titanium dioxide fine particles of the present invention are oily components, moisturizers, surfactants, pigments, fragrances, preservatives that are usually used in cosmetics, etc. It can be blended with water, alcohols, thickeners, etc. and used in various forms such as lotion, cream, paste, stick, and emulsion. The compounding quantity of titanium dioxide microparticles | fine-particles, such as cosmetics, can be set suitably. Since these are very transparent, the influence of ultraviolet rays can be effectively prevented without impairing the original appearance of the bare skin.

  The paint containing the titanium dioxide fine particles of the present invention is, for example, polyvinyl alcohol resin, vinyl chloride-vinyl acetate resin, acrylic resin, epoxy resin, urethane resin, alkyd resin, polyester resin, ethylene vinyl acetate copolymer, acrylic-styrene. It is blended in a copolymer, a fiber resin, a phenol resin, an amino resin, etc., and dispersed in water or a solvent. For dispersion, a known method such as a disper or a sand mill can be used, and additives such as a dispersant, a leveling agent, and a curing agent can be appropriately blended. The compounding quantity of the titanium dioxide fine particle of a coating material can be set suitably. Since these are very transparent, the influence of ultraviolet rays can be effectively prevented without impairing the original appearance of organic base materials such as plastic and wood.

  When used as a plastic composition, for example, vinyl chloride resin, ABS resin, polyethylene, polypropylene, vinylidene chloride, polystyrene, polycarbonate, nylon, EVA resin, polyacetal resin, polyamide resin, phenol resin, melamine resin, acrylic resin, polyester It can mix | blend with synthetic resins, such as resin, a urea resin, a silicone resin, and a fluororesin, and can be used for an ultraviolet-ray shielding etc. The compounding quantity of the titanium dioxide fine particles of a plastic composition can be set suitably. Also, for example, if blended in a transparent plastic film and affixed to a substrate, the same effect as a paint can be obtained.

  The paint and dispersant containing the titanium dioxide fine particles of the present invention are applied to the surface of an article such as glass, ceramic, plastic, sheet, film, etc., and the titanium dioxide fine particles are arranged to be used as an ultraviolet shielding material, an optical member, or a transparent member. be able to. Further, when molding a substrate such as plastic, compression board, paper, etc., it may be blended directly as a filler. Further, it can be used as an additive such as toner and silicone rubber, a lower layer material of a magnetic recording material, a catalyst carrier, and a base particle of a conductive material.

  EXAMPLES The present invention will be described in more detail with reference to examples and comparative examples below, but these do not limit the present invention.

Example 1
After hydrolyzing titanium tetrachloride, titanium dioxide fine particles (average particle diameter 15 nm, specific surface area 100 m ² / g) obtained by alkali treatment / hydrochloric acid treatment were used as an aqueous slurry, and an aqueous sodium hydroxide solution was added. After the slurry pH was adjusted to 8-9, the temperature was raised to 75 ° C. and a 300 g / L sodium silicate aqueous solution was added while maintaining the temperature, and then the mixture was stirred for 30 minutes and mixed. Subsequently, after heating up to 90 degreeC, the sulfuric acid aqueous solution was added for 20 minutes, and it neutralized until pH became seven.
Next, after the aqueous slurry was cooled to 70 ° C., sulfuric acid was added to adjust the pH to 2. Subsequently, 300 g / L aqueous sodium silicate solution was added together with sulfuric acid while stirring, while maintaining the pH of the aqueous slurry at 2. Next, an aqueous sodium hydroxide solution was added to neutralize the pH to 7, and then the mixture was stirred and mixed for 30 minutes.
Next, the aqueous slurry was filtered, washed with water, dried and pulverized to obtain titanium dioxide fine particles of the present invention (sample A) having a first coating layer of high-density silica and a second coating layer of porous silica.
The coating amount of the high-density silica of Sample A was 25% by weight with respect to titanium dioxide, and the coating amount of porous silica was 25% by weight with respect to titanium dioxide (silica coating total amount 50% by weight).

Example 2
The same operation as in Example 1 was performed to obtain titanium dioxide fine particles (sample B) of the present invention having a high-density silica coating amount of 20% by weight and a porous silica coating amount of 20% by weight (silica). Covering amount 40% by weight).

Example 3
The same operation as in Example 1 was performed to obtain titanium dioxide fine particles (sample C) of the present invention having a high-density silica coating amount of 25% by weight and a porous silica coating amount of 35% by weight (silica). (Coating total amount 60% by weight).

Comparative Example 1
After hydrolyzing titanium tetrachloride, titanium dioxide fine particles (average particle diameter 15 nm, specific surface area 100 m ² / g) obtained by alkali treatment / hydrochloric acid treatment were used as an aqueous slurry, and an aqueous sodium hydroxide solution was added. After the slurry pH was adjusted to 8-9, the temperature was raised to 75 ° C. and a 300 g / L sodium silicate aqueous solution was added while maintaining the temperature, and then the mixture was stirred for 30 minutes and mixed. Subsequently, after heating up to 90 degreeC, the sulfuric acid aqueous solution was added for 60 minutes, and it neutralized until pH became seven.
Next, the aqueous slurry was filtered, washed with water, dried and pulverized to obtain titanium dioxide fine particles (sample D) having a coating layer of high-density silica.
The coating amount of the high-density silica of Sample D is 50% by weight with respect to titanium dioxide, and the porous silica is not coated (silica coating amount 50% by weight).

Comparative Example 2
After hydrolyzing titanium tetrachloride, titanium dioxide fine particles (average particle diameter 15 nm, specific surface area 100 m ² / g) obtained by alkali treatment / hydrochloric acid treatment were used as an aqueous slurry, heated to 70 ° C., and then sulfuric acid. Was added to adjust the pH to 2. Subsequently, 300 g / L aqueous sodium silicate solution was added together with sulfuric acid while stirring, while maintaining the pH of the aqueous slurry at 2. Next, an aqueous sodium hydroxide solution was added to neutralize the pH to 7.
Next, the aqueous slurry was filtered, washed with water, dried and pulverized to obtain titanium dioxide fine particles (sample E) having a porous silica coating layer.
Sample E was not coated with high-density silica, and the coating amount of porous silica was 50% by weight with respect to titanium dioxide (silica coating amount of 50% by weight).

1. Evaluation of thixotropic viscosity of filter cake and evaluation of properties of dried product In Examples and Comparative Examples, the thixotropic viscosity of filter cake after silica coating and the properties of the dried product were relatively evaluated as follows.
<Thixotropic evaluation>
A small amount of cake was taken in the palm of the hand, and the palm was shaken or the cake was rubbed for evaluation.
“O”: Maintains a solid state even when shaken or swallowed.
“△”: The solid state is maintained as long as it is shaken.
“×”: liquefies only by shaking.
<Evaluation of properties of dried product>
The dried product was picked up and grasped for evaluation.
“○”: keeps a lump when lifted by hand, but collapses when gripped.
“△”: Keeps a lump when lifted by hand, and does not collapse unless gripped with a strong force.
“X”: When trying to lift by hand, it does not powder and keeps a lump.

  The results of this evaluation are shown in Table 1. All of the samples of Examples had low thixotropic viscosity and good handleability of the dried product. On the other hand, Sample D coated with high-density silica showed thixotropic viscosity, and the handleability of the dried product was poor. Sample E coated with porous silica had a low thixotropic viscosity, and the handleability of the dried product was slightly good.

2. Evaluation of transparency and ultraviolet shielding ability Titanium dioxide fine particles (samples A to E) obtained in Examples and Comparative Examples were prepared as pastes assuming cosmetics by the method described below. This paste was applied on a transparent triacetate film with a doctor blade so that the film thickness was about 25 μm, and then air-dried for 30 minutes. The light transmittance T _{300 at} a wavelength of 300 nm and the light transmittance T ₅₅₀ at ₅₅₀ nm were measured using a spectrophotometer (manufactured by Shimadzu Corporation, UV-VIS UV-2200A type) equipped with an integrating sphere. Then, the absorbance ratio A ₃₀₀ / A ₅₅₀ was calculated according to the following formula.
Formula: A ₃₀₀ / A ₅₅₀ = log (100 / T ₃₀₀ ) / log (100 / T ₅₅₀ )

(Paste formulation)
Sample 1.2g
Binder (liquid paraffin / petroleum / stearic acid = 40 / 26.7 / 1 (weight ratio)) 40.0 g
Glass beads 50.0g

(Paste preparation method)
The prescription was charged in a 140 cc glass bottle with a lid, sealed, and then dispersed using a paint conditioner (manufactured by Red Devil (USA), Quick Mill).

Table 2 shows the measurement results of the transmittance with the paste. It was found that the titanium dioxide fine particles of the present invention have good dispersibility even in cosmetics, and also have a high A ₃₀₀ / A ₅₅₀ value, that is, high transparency and excellent ultraviolet shielding ability.

Next, the oxidation activity and photoactivity of the samples A to E of Examples and Comparative Examples were evaluated by the following methods.
<Oxidation activity / photoactivity evaluation method>
Titanium dioxide fine particles (samples A to E) obtained in Examples and Comparative Examples were prepared as pastes with and without vitamin C in the composition shown in Table 3. This paste was applied on a glass plate with a doctor blade so that the film thickness was about 125 μm, and then set for 120 minutes. The color L, a, b of each paste was measured from the lower surface of the glass plate, and the color difference ΔE of the paste with vitamin C and without vitamin C (blank) was calculated by the following formula (oxidation activity). On the other hand, the color L, a, and b after irradiation of black light on the lower surface for 2 hours was measured for the blank-side paste applied, and the color difference ΔE before and after the black light irradiation was calculated (photoactivity).
Formula: ΔE = ((ΔL) ² + (Δa) ² + (Δb) ² ) ^1/2

  The results are shown in Table 4. The samples A to C of the example were as active as the sample D of the comparative example 1, and it was found that the oxidation activity and photoactivity were suppressed by the high-density silica coating. Moreover, it turned out that the suppression of oxidation activity and photoactivity is not enough in the sample E of the comparative example 2 of porous silica coating.

  From the above results, the titanium dioxide fine particles of the present invention have excellent transparency and ultraviolet shielding ability, can sufficiently suppress the catalytic activity, and are caused by the silica coating treatment process in the titanium dioxide fine particles. It has been found that it is possible to substantially avoid the difficulty in handling due to the thixotropic viscosity of the processing slurry and cake that are easy to handle and the reduction in production efficiency.

  Since the titanium dioxide fine particles of the present invention have excellent transparency and UVB shielding ability, they are useful as ultraviolet shielding agents, and are also useful as dispersions, cosmetics, sunscreen cosmetics, pharmaceuticals, external products, ultraviolet shielding materials. , Optical members, transparent members, paints, plastic compositions and the like.

Claims (5)

A titanium dioxide fine particle characterized by having a coating of high-density silica and porous silica on the surface of a titanium dioxide fine particle having an average particle diameter of 100 nm or less. _{2. The} titanium dioxide fine particles according to claim 1, wherein the total amount of the high-density silica and the porous silica is 30 to 100% by weight as SiO _{2 with} respect to the weight of the titanium dioxide. 2. The titanium dioxide fine particles according to claim 1, comprising a first coating layer of high-density silica and a second coating layer of porous silica on the surface of the titanium dioxide fine particles. The first coating layer of high-density silica is 10 to 50% by weight as SiO _{2 with} respect to the weight of titanium dioxide, and the second coating layer of porous silica is 10 to 50% as SiO _{2 with} respect to the weight of titanium dioxide. The titanium dioxide fine particles according to claim 3, wherein the fine titanium dioxide particles are%. An aqueous slurry of titanium dioxide fine particles having an average particle size of 100 nm or less is adjusted to a pH of 8 or higher at 70 ° C. or higher, then silicate is added, and then neutralized with an acid to form high-density silica; A method for producing fine titanium dioxide particles, wherein porous silica is formed by adding silicate and acid while maintaining the pH of the aqueous slurry at 1 to 4.