阅读说明：本技术 二氧化钛水分散体及其制备方法 (Aqueous titanium dioxide dispersion and process for producing the same ) 是由 友成雅则 永森智 龟田优人 于 2019-01-28 设计创作，主要内容包括：提供了具有高分散性且几乎没有聚集或粗粒子的二氧化钛水分散体及其制备方法。二氧化钛水分散体含有在表面上具有疏水性化合物如高级脂肪酸或其盐的二氧化钛粒子、水分散介质、具有10以上的HLB值的非离子表面活性剂和碱性化合物如烷醇胺,并且pH在8.5至13的范围内。用于制备二氧化钛水分散体的方法具有以下步骤：将在表面上具有疏水性化合物的二氧化钛粒子、水分散介质、具有10以上的HLB值的非离子表面活性剂和碱性化合物混合以使水分散体的pH在8.5至13的范围内。(An aqueous titanium dioxide dispersion having high dispersibility and having few aggregated or coarse particles and a process for producing the same are provided. The aqueous titanium dioxide dispersion contains titanium dioxide particles having a hydrophobic compound such as a higher fatty acid or a salt thereof on the surface, an aqueous dispersion medium, a nonionic surfactant having an HLB value of 10 or more, and a basic compound such as an alkanolamine, and has a pH in the range of 8.5 to 13. The process for preparing the aqueous titanium dioxide dispersion has the following steps: titanium dioxide particles having a hydrophobic compound on the surface, an aqueous dispersion medium, a nonionic surfactant having an HLB value of 10 or more, and a basic compound are mixed so that the pH of the aqueous dispersion is in the range of 8.5 to 13.)

1. An aqueous titanium dioxide dispersion comprising titanium dioxide particles having a hydrophobic compound on the surface, an aqueous dispersion medium, a nonionic surfactant having an HLB value of 10 or more, and a basic compound, wherein the pH of the aqueous titanium dioxide dispersion is in the range of 8.5 to 13.

2. The aqueous titanium dioxide dispersion of claim 1, wherein the basic compound is an alkanolamine.

3. The aqueous titanium dioxide dispersion according to claim 1 or 2, wherein the hydrophobic compound is a higher fatty acid or a salt of said higher fatty acid.

4. The aqueous titanium dioxide dispersion according to any one of claims 1 to 3, wherein the titanium dioxide particles contain lead as an impurity, and the content of the lead is 3ppm or less.

5. The aqueous titanium dioxide dispersion according to any one of claims 1 to 4, wherein the titanium dioxide particles are spherical particles having an aspect ratio of 3 or less.

6. The aqueous titanium dioxide dispersion according to any one of claims 1 to 5, wherein the titanium dioxide particles have the hydrophobic compound on the surface of the titanium dioxide particles coated with an oxide or hydroxide of at least one of zinc, titanium, cerium, iron, silicon and aluminum.

7. A process for producing an aqueous titanium dioxide dispersion, which comprises mixing titanium dioxide particles having a hydrophobic compound on the surface, an aqueous dispersion medium, a nonionic surfactant having an HLB value of 10 or more, and a basic compound so that the pH of the aqueous dispersion is in the range of 8.5 to 13.

8. The process for producing an aqueous titanium dioxide dispersion according to claim 7, wherein said basic compound is an alkanolamine.

Technical Field

The present invention relates to an aqueous dispersion of titanium dioxide particles and a process for preparing the same.

Background

Titanium dioxide particles having a particle diameter of about 3 to 200nm have excellent visible light transparency and ultraviolet shielding properties as well as high safety, and thus are used in cosmetics, paints, inks, chemical fibers, polishing compositions, and the like.

Such fine titanium dioxide has a property that primary particles are easily agglomerated, and when the primary particles are agglomerated, the above-described characteristics (e.g., visible light transparency and ultraviolet shielding property) are lowered. Therefore, a material (i.e., a dispersion) in which titanium dioxide particles are dispersed in a dispersion medium is prepared in advance, and such a dispersion is used to apply the titanium dioxide particles to various uses.

For example, patent document 1 describes an aqueous dispersion containing ultrafine particles of titanium dioxide hydrophobically treated with stearic acid or the like and a nonionic surfactant. Patent document 1 describes that such an aqueous dispersion can suppress agglomeration of ultrafine particles of titanium dioxide and achieve sufficient visible light transparency and ultraviolet shielding properties even in the case of applying the aqueous dispersion to a composition (e.g., a cosmetic) containing an electrolyte component.

Further, patent document 2 describes an aqueous dispersion containing spindle-shaped ultrafine titanium dioxide particles subjected to water repellent treatment with silicone or the like and a dispersant having an HLB value of 10 to 17, wherein the content of the ultrafine titanium dioxide particles, the dispersant and water is 80 mass% or more with respect to the total amount of the dispersion. Patent document 2 describes that such an aqueous dispersion enables the titanium dioxide ultrafine particles subjected to the water repellent treatment to be uniformly dispersed in an aqueous dispersion medium, and thus a moist feeling and a good cosmetic feeling (makeup feeling) can be achieved in an O/W type emulsified cosmetic in which such an aqueous dispersion is blended.

Reference list

Patent document

Patent document 1: JPH 07-247119A

Patent document 2: WO 2013/018827A 1

Disclosure of Invention

Technical problem

In recent years, there has been a demand in the field of cosmetics for further improving the visible light transparency and ultraviolet-shielding property of a titanium dioxide aqueous dispersion. To achieve this demand, a highly dispersed aqueous dispersion of titanium dioxide particles in which agglomeration of primary titanium dioxide particles is further suppressed is required. There is a demand for highly dispersed aqueous dispersions not only in the cosmetic field but also in various fields employing aqueous dispersions of ultrafine particles of titanium dioxide. It is difficult to satisfy such a demand by the above-mentioned aqueous dispersion of conventional ultrafine titanium dioxide particles.

Solution to the problem

As a result of intensive studies to satisfy the above-mentioned demands, the inventors of the present invention have found that, in an aqueous dispersion containing titanium dioxide particles having a hydrophobic compound on the surface thereof and a predetermined dispersant, a highly dispersed aqueous titanium dioxide dispersion in which agglomeration and coarse particles are hardly generated can be obtained by setting the pH of the aqueous dispersion to a specific range, and thus have completed the present invention.

That is, the present invention includes the following inventions:

(1) an aqueous titanium dioxide dispersion comprising titanium dioxide particles having a hydrophobic compound on the surface of the titanium dioxide particles, an aqueous dispersion medium, a nonionic surfactant having an HLB value of 10 or more, and a basic compound, wherein the pH of the aqueous titanium dioxide dispersion is in the range of 8.5 to 13.

(2) The aqueous titanium dioxide dispersion according to (1), wherein the basic compound is an alkanolamine.

(3) The aqueous titanium dioxide dispersion according to (1) or (2), wherein the hydrophobic compound is a higher fatty acid or a salt of a higher fatty acid.

(4) The aqueous titanium dioxide dispersion according to any one of (1) to (3), wherein the titanium dioxide particles contain lead as an impurity, and the content of lead is 3ppm or less.

(5) The aqueous titanium dioxide dispersion according to any one of (1) to (4), wherein the titanium dioxide particles are spherical particles having an aspect ratio of 3 or less.

(6) The aqueous titanium dioxide dispersion according to any one of (1) to (5), wherein the titanium dioxide particles have a hydrophobic compound on the surface of the titanium dioxide particles coated with an oxide or hydroxide of at least one of zinc, titanium, cerium, iron, silicon and aluminum.

(7) A process for producing an aqueous titanium dioxide dispersion, which comprises mixing titanium dioxide particles having a hydrophobic compound on the surface, an aqueous dispersion medium, a nonionic surfactant having an HLB value of 10 or more, and a basic compound so that the pH of the aqueous dispersion is in the range of 8.5 to 13.

(8) The process for producing an aqueous titanium dioxide dispersion as described in (7), wherein the basic compound is an alkanolamine.

Advantageous effects of the invention

The present invention can provide an aqueous titanium dioxide dispersion having high dispersibility and hardly causing agglomeration and coarse particles, which has properties such as excellent visible light transparency and ultraviolet shielding property. Further, such an aqueous dispersion of the present invention can easily maintain the dispersed state of titanium dioxide particles even when an electrolyte component, a coating component or an ink component is added or the pH of the aqueous dispersion is changed depending on the use case. Therefore, the aqueous dispersion of the present invention can be used for preparing various compositions for cosmetics and the like.

Detailed Description

The aqueous dispersion of the present invention contains titanium dioxide particles. The average primary particle diameter of the titanium dioxide particles is preferably 3 to 200nm, more preferably 5 to 100nm, and even more preferably 10 to 100 nm. Titanium dioxide particles having such a particle diameter have high visible light transparency and a favorable ultraviolet ray shielding range. The average primary particle diameter of the titanium dioxide particles is determined by: the particle diameters of 200 particles randomly selected under an electron microscope were measured, and the average value of the particle diameters was calculated (this is also referred to as "electron micrograph method" in the present application).

The shape of the titanium dioxide particles is not particularly limited, and particles having any shape, such as spherical particles, rod-shaped particles, needle-shaped particles, spindle-shaped particles, and plate-shaped particles, can be used. As for the average primary particle diameter of particles having a shape other than a sphere, in the case of rod-shaped particles, needle-shaped particles, and spindle-shaped particles, the average primary particle diameter is defined by the average of the lengths of the short axis sides, and in the case of plate-shaped particles, the average primary particle diameter is defined by the average of the lengths of the diagonal lines on the surface. The ratio of the major axis diameter to the minor axis diameter of the titanium dioxide particles is referred to as the aspect ratio. The aspect ratio is preferably 3 or less, and more preferably 1 to 2. The aspect ratio of the titanium dioxide particles was calculated as the average of the major axis diameter and the minor axis diameter of 200 particles randomly selected under an electron microscope.

The crystal structure of the titanium dioxide particles is not particularly limited, and for example, an anatase type, a rutile type, or a brookite type may be used. From the viewpoint of suppressing photocatalytic activity, the rutile type is preferably used. Except for titanium dioxide (TiO)₂) In addition, the titanium dioxide particles may be composed of metatitanate (TiO)₂·nH₂O) and orthotitanates (Ti (OH)₄) The compound shown in the specification.

The titanium dioxide particles can be produced by various known methods. As a method for producing the above titanium dioxide particles having a smaller average primary particle diameter, for example, the following method can be employed: a method in which an aqueous titanium tetrachloride solution is hydrolyzed by neutralization with a base and the resulting hydrous titanium dioxide is calcined (this is also referred to as "calcination method" in the present application), and a method in which an aqueous titanium tetrachloride solution is hydrolyzed by neutralization with a base, the resulting hydrous titanium dioxide is heat-treated with sodium hydroxide, and the resulting reaction product is heated and aged with an acid (this is also referred to as "wet method" in the present application). In general, spherical titanium dioxide particles can be obtained by the above calcination method, and spindle-shaped titanium dioxide particles can be obtained by the above wet method. Further, the rutile type titanium dioxide particles can be obtained by a calcination method and a wet method. Further, the titanium dioxide particles obtained by the calcination method have an aspect ratio of about 3 or less. Preferably, spherical particles having an aspect ratio of 1 to 2 can be obtained.

In the spherical titanium dioxide particles obtained by the calcination method, the crystallinity is increased by the calcination, and therefore the photocatalytic activity is highly suppressed. Therefore, in applications (for example, cosmetics) where photocatalytic activity is required to be suppressed, it is preferable to use spherical titanium dioxide particles obtained by a calcination method.

The titanium dioxide particles may contain various impurities which are unavoidable for the preparation thereof. Examples of the impurity elements include Al, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Zn, Zr, Ag, Pb, Cl and Nb. Here, among the impurity elements, based on TiO₂The lead (Pb) content is preferably 3ppm or less. The content of impurity elements such as lead (Pb) was measured using an atomic absorption spectrophotometer.

In the case where the aqueous titanium dioxide dispersion of the present invention is used for cosmetics, the influence on the human body can be minimized by reducing the lead content to a very low level (specifically, 3ppm or less). Further, in the case where the aqueous titanium dioxide dispersion of the present invention is used for uses other than cosmetics and is released to the natural environment (for example, the case where the aqueous titanium dioxide dispersion is used for a disposable substance such as a composition for polishing), the load on the environment can be reduced.

As a method that can effectively provide titanium dioxide particles having a lead (Pb) content in the above range, a calcination method or a wet method using the above titanium tetrachloride as a starting material is exemplified.

The titanium dioxide particles may also be such that: the surface of which is coated with other inorganic compounds than the titanium dioxide particles. The material may be coated with a known inorganic surface treatment material. For example, one of zinc, titanium, cerium, iron, silicon and aluminum may be usedAt least one oxide or hydroxide. Based on TiO₂The coating amount is preferably 1% to 30% by mass. The titanium dioxide particles have photocatalytic activity, but when the titanium dioxide particles are coated with the inorganic compound, the photocatalytic activity can be suppressed. In such uses (e.g., cosmetics), titanium dioxide particles coated with an inorganic compound are preferable.

The titanium dioxide particles in the aqueous dispersion of the invention have a hydrophobic compound on their surface. The hydrophobic compound is present on the surface of the titanium dioxide particles and reduces the affinity of the titanium dioxide particles for water. The compound having a hydrocarbon group in the molecule is one representative example of the hydrophobic compound. Examples of hydrophobic compounds that may be used include: silicones such as dimethylpolysiloxane, methylhydrogenpolysiloxane and organic modified silicone oil; coupling agents such as silane-based coupling agents, titanate-based coupling agents, aluminum-based coupling agents, and fluorine-based coupling agents; higher fatty acids or salts thereof; a higher alcohol; and amines having higher alkyl groups.

As the hydrophobic compound, a higher fatty acid (specifically, a monovalent carboxylic acid having 12 or more carbon atoms) or a salt thereof is preferable. By using a higher fatty acid, the dispersibility of the titanium dioxide particles in the aqueous dispersion can be further improved. Examples of the higher fatty acid include saturated fatty acids (e.g., lauric acid, myristic acid, palmitic acid, and stearic acid) and unsaturated fatty acids (e.g., oleic acid), and among them, stearic acid is preferable. As the salt of the higher fatty acid, sodium, potassium, ammonium, and the like are preferable.

The coating amount of the hydrophobic compound is preferably an amount that can uniformly coat the titanium dioxide particles. In particular based on TiO₂The coating amount is preferably 0.5% to 12%, and more preferably 0.5% to 8%, and even more preferably 2% to 5%. The coating amount within such a range enables the titanium dioxide particles to be uniformly coated and ensures sufficient dispersibility and stability in the aqueous dispersion over time. Furthermore, by controlling the coating amount not to be excessive, the generation of foam in the aqueous dispersion caused by the release of the additional hydrophobic compound can be avoided. Can be exemplified bySuch as mixing a hydrophobic compound with the titanium dioxide particles to coat the surface of the titanium dioxide particles with the hydrophobic compound.

It is preferable that the titanium dioxide particles coated with the above hydrophobic compound be contained in the aqueous dispersion at a ratio of 10 to 70 mass%. The titanium dioxide particles in a proportion of 10% by mass or more enable the amount of the aqueous dispersion of the present invention blended in various aqueous compositions to be suppressed. The titanium dioxide particles in a proportion of 70 mass% or less ensure the fluidity of the aqueous dispersion and facilitate the blending of the aqueous dispersion into various aqueous compositions. The upper limit is more preferably 60 mass%, and even more preferably 55 mass% or less. Further, the lower limit is more preferably 15% by mass, and even more preferably 20% by mass. Further, the lower limit is even more preferably 25% by mass from the viewpoint of production efficiency of the aqueous dispersion.

The titanium dioxide particles coated with the hydrophobic compound in the aqueous dispersion of the present invention are dispersed in an aqueous dispersion medium. The aqueous dispersion medium in the present invention contains water as a main component, i.e., the water content is 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass. From the viewpoint of improving the dispersibility of the titanium dioxide particles, the water is preferably pure water. Examples of components other than water include organic solvents dissolved in water, such as methanol, ethanol, isopropanol, butanol, acetone, methyl ethyl ketone, and tetrahydrofuran.

The aqueous titanium dioxide dispersion of the present invention contains a nonionic surfactant having an HLB value of 10 or more. The hydrophilic-lipophilic balance (HLB) value refers to a value indicating the level of affinity of a surfactant with water and oil (i.e., a water-insoluble organic compound), and an HLB value of 10 or more indicates high hydrophilicity.

Examples of the nonionic surfactant include polyoxyalkylene alkyl ethers, polyoxyalkylene fatty acid esters, polyoxyalkylene sorbitan fatty acid esters, polyoxyalkylene castor oils, polyoxyalkylene cured castor oils, polyoxyalkylene sorbitol tetra fatty acid esters, glycerin fatty acid esters, sorbitan fatty acid esters, polyglycerin fatty acid esters, polyoxyalkylene derivatives, sucrose fatty acid estersAn organopolysiloxane having a polyoxyalkylene group, an organopolysiloxane having a polyglyceryl group, and an organopolysiloxane having a sugar chain. Among the various nonionic surfactants exemplified above, the nonionic surfactant of the present invention is a nonionic surfactant having an HLB value of 10 or more, that is, a nonionic surfactant having an HLB range of 10 to 20. Such nonionic surfactant causes interaction such as binding of the hydrophobic group of the nonionic surfactant contained in the aqueous titanium dioxide dispersion of the present invention with the hydrophobic compound of titanium dioxide particles and the hydrophilic group of the nonionic surfactant with OH of the water molecules of the aqueous dispersion medium^-The combined interaction, whereby the titanium dioxide particles can be uniformly and smoothly dispersed in the aqueous dispersion. As the nonionic surfactant, an organopolysiloxane having a polyoxyalkylene group, a polyoxyalkylene derivative, or a polyoxyalkylene fatty acid ester is preferably used. Examples of the organopolysiloxane having a polyoxyalkylene group include methoxypolyethylene glycol polydimethylsiloxane and methoxypolyethylene glycol polydimethylsiloxane. Examples of the polyoxyalkylene derivative include polyoxyalkylene alkyl ether, polyoxyethylene styrenated phenyl ether, polyoxyethylene tribenzylphenyl ether, polyoxyalkylene decyl ether and polyoxyethylene tridecyl ether. Examples of the polyoxyalkylene fatty acid ester include polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, polyethylene glycol monooleate, and polyoxyethylene sorbitan monooleate.

The HLB value of the nonionic surfactant is preferably in the range of 13 to 19, and more preferably in the range of 13 to 16. By using a nonionic surfactant having such an HLB value, an aqueous dispersion having higher dispersibility can be achieved.

The HLB value in the present invention can be calculated by the following equation (1).

HLB value 20X sum of formula weights of hydrophilic moieties/molecular weight of nonionic surfactant (1)

Here, in the case of a nonionic surfactant containing only polyoxyethylene groups as hydrophilic moieties, the following equation (2) may also be used in place of equation (1).

HLB value ═ mass% of polyoxyethylene group/5. cndot. (2)

The above nonionic surfactant is preferably contained in the aqueous dispersion at a ratio of 1 to 10% by mass. By controlling the ratio within such a range, the titanium dioxide particles can be sufficiently dispersed in water (aqueous dispersion medium) while suppressing the cost.

The aqueous dispersion of the invention also contains a basic compound. The basic compound in the present invention has a function in which at least a part of the basic compound is ionized in the aqueous dispersion and thus the pH of the aqueous dispersion is shifted to the alkali side. That is, the basic compound of the present invention is present not only as the basic compound itself in the aqueous dispersion, but also in the form of an ion in which the basic compound has been ionized or in the form of a reaction product.

As such a basic compound, a basic inorganic compound or a basic organic compound can be used. Examples of the basic inorganic compound include hydroxides or various salts (carbonates, bicarbonates, sulfates, acetates or chlorides), ammonia and ammonium salts of alkali metals or alkaline earth metals. Specific examples of the basic inorganic compound include calcium hydroxide, potassium carbonate, potassium hydrogencarbonate, potassium sulfate, potassium acetate, potassium chloride, sodium hydroxide, ammonium carbonate, sodium hydrogencarbonate, sodium carbonate, ammonium carbonate and ammonium hydrogencarbonate.

Examples of the basic organic compound include alkylamines, alkanolamines, and quaternary ammonium compounds. Examples of alkylamines include propylamine. Examples of alkanolamines include monoethanolamine, diethanolamine, and triethanolamine. Examples of quaternary ammonium compounds include hydroxides or salts such as chlorides, carbonates, sulfates, and phosphates of tetramethylammonium, tetraethylammonium, tetrabutylammonium, and the like. Specific examples thereof include tetraalkylammonium hydroxides such as tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetrabutylammonium hydroxide; and tetraalkylammonium salts such as tetramethylammonium carbonate and tetramethylammonium chloride.

The aqueous titanium dioxide dispersions of the invention have a pH in the range from 8.5 to 13. An aqueous dispersion containing titanium dioxide particles coated with a hydrophobic compound, an aqueous dispersion medium, and a nonionic surfactant generally has a pH near neutral (specifically, a pH of about 6 to 8). The pH is adjusted to be within a predetermined range (i.e., 8.5 to 13) by including an alkaline compound. That is, it can be confirmed that the alkali compound is contained in the aqueous dispersion by the fact that the pH of the aqueous dispersion is in the range of 8.5 to 13. The pH of the aqueous dispersion was measured under temperature conditions of 20 ℃ by using a pH meter D-51 available from HORIBA, ltd. The concentration and the addition amount of the basic compound are not particularly limited, and need only be such that the pH of the aqueous dispersion can be adjusted to the above-mentioned range. The pH of the aqueous titanium dioxide dispersion is preferably in the range of 8.5 to 11, and such a range of pH can achieve high dispersibility of titanium dioxide particles.

The aqueous titanium dioxide dispersion of the present invention having a pH in the above range achieves higher dispersibility as compared with the conventional aqueous dispersion having a pH in the vicinity of neutrality. The dispersibility of the aqueous dispersion of the present invention was evaluated by using, as an index, the cumulative 50% size (D50) of the titanium dioxide particles (secondary particles) in the aqueous dispersion or the cumulative frequency of particles having a particle diameter of 1 μm or more (this is also referred to as "coarse particle cumulative frequency" in the present application). The D50 and the coarse particle cumulative frequency can be calculated from the particle size distribution of titanium dioxide particles in the aqueous dispersion measured by using a laser scattering particle size distribution analyzer (LA-950a2, available from HORIBA, ltd.).

In the aqueous titanium dioxide dispersion of the present invention, the cumulative 50% size (D50) of the secondary particles is preferably 75nm or less, and more preferably 70nm or less. Further, the cumulative frequency of secondary particles having a particle diameter of 1 μm or more (coarse particle cumulative frequency) is preferably 10% or less, more preferably 7% or less, and even more preferably 4.5% or less.

Specifically, in the aqueous titanium dioxide dispersion of the present invention, it is preferable that the cumulative 50% size (D50) of the secondary particles is 75nm or less and the cumulative frequency of the coarse particles is 4.5% or less; and more preferably, D50 is 70nm or less, and the coarse particle cumulative frequency is 3% or less.

Further, in the aqueous titanium dioxide dispersion of the present invention, the cumulative frequency of secondary particles having a particle diameter of 1 μm or more (coarse particle cumulative frequency) when an electrolyte (specifically, a salt) is added is preferably 8% or less.

In general, as the concentration of titanium dioxide particles contained in the aqueous dispersion becomes higher, it becomes difficult to reduce the cumulative 50% size (D50) and the cumulative frequency of coarse particles. In contrast, in the aqueous titanium dioxide dispersion of the present invention, the effect of combining the following makes it possible to keep D50 and the coarse particle cumulative frequency within the above-described preferred numerical range even in the case where titanium dioxide particles are contained at a relatively high concentration (specifically, about 25 to 55 mass%): treating the surface of titanium dioxide particles with a hydrophobic compound; using a nonionic surfactant having an HLB value of 10 or more as a dispersant; and the pH of the dispersion is adjusted to 8.5 to 13 by using an alkaline compound. Thus, highly dispersed aqueous titanium dioxide dispersions can be produced efficiently.

Further, in the aqueous titanium dioxide dispersion of the present invention, the value of the ratio (D50/Da) of the cumulative 50% size of the secondary particles to the average primary particle diameter (Da) according to the electron micrograph method is preferably 5 or less, more preferably 3.5 or less, and even more preferably 2 or less.

As the basic compound for adjusting the pH of the aqueous titanium dioxide dispersion to the above range, alkanolamine is preferably used. Alkanolamines are compounds having hydroxyl and amino groups in the alkane backbone. In the case of using an alkanolamine, particularly high dispersibility can be achieved in an aqueous dispersion containing titanium dioxide particles coated with a hydrophobic compound and a specific nonionic surfactant. Specifically, the coarse particle accumulation frequency may be 1% or less. It was confirmed by gas chromatography (GC/MS) that the aqueous dispersion contained alkanolamine as the basic compound.

The aqueous dispersion of the present invention may contain various additives such as a defoaming agent and a preservative in addition to the titanium dioxide particles coated with the hydrophobic compound, the above-mentioned nonionic surfactant and the basic compound. Examples of defoaming agents include: a sorbitan fatty acid ester SOLGEN (registered trademark) 30 (available from DKS co.ltd.); emulsion defoamers KM-73, KM-73A, KM-73E, KM-70, KM-72F, KM-72S and KM-72FS (all available from Shin-Etsu Chemical Co., Ltd.); and silicone type defoamer BYK-044 (available from BYK). Of these, SOLGEN (registered trademark) 30 is preferable.

The aqueous titanium dioxide dispersions of the invention can be prepared by: mixing titanium dioxide particles coated with a hydrophobic compound, an aqueous dispersion medium, a nonionic surfactant having an HLB value of 10 or more, and a basic compound, and controlling the pH of the aqueous dispersion to a range of 8.5 to 13.

The above-mentioned substances can be used as titanium dioxide particles used in such a production method, a hydrophobic compound present on the particle surfaces of the titanium dioxide particles, an aqueous dispersion medium, and a nonionic surfactant having an HLB value of 10 or more. Further, the above-mentioned substances may be used as the basic compound. In particular, in the case of using an alkanolamine as the basic compound, particularly high dispersibility can be achieved in an aqueous dispersion containing titanium dioxide particles coated with a hydrophobic compound and a specific nonionic surfactant. Therefore, in such a production method, it is desirable to use an alkanolamine as the basic compound.

The concentration and the addition amount of the basic compound are not particularly limited, and may be such that the above pH range can be achieved. In the preparation of the aqueous dispersion, the mixing order of the above components is not particularly limited, and as the mixing method, a well-known method and apparatus can be employed.

The aqueous dispersion of the present invention may be subjected to wet-milling treatment for the purpose of improving dispersibility of the titanium dioxide particles. The wet milling can be performed by using various well-known wet mills such as a bead mill and a sand mill. As the grinding medium, for example, glass beads and zircon beads can be used.

In the aqueous titanium dioxide dispersion in which the pH range has been adjusted as described above, the pH may be appropriately readjusted depending on the use of the composition to which the aqueous dispersion is applied. For example, in the case of applying the aqueous dispersion of the present invention to cosmetics, the pH may be adjusted to a range from weak acidity to weak alkalinity (specifically, a range from pH 4.5 to 8.5) by using an acidic compound (for example, sulfuric acid, hydrochloric acid, nitric acid, acetic acid, carbonic acid, oxalic acid, and phosphoric acid). In the aqueous titanium dioxide dispersion of the present invention, even in the case of readjustment of pH, the dispersion state before readjustment can be highly maintained.

The aqueous titanium dioxide dispersion of the present invention has very high dispersibility and maintains its highly dispersed state even with the addition of an electrolyte (specifically, a salt) or a change in pH. Therefore, the aqueous titanium dioxide dispersion of the present invention can be preferably used as an aqueous dispersion to be blended into various compositions requiring high dispersibility (for example, compositions for cosmetics, paints, inks, fibers, pharmaceuticals, and polishing).

The cosmetic prepared by using the aqueous titanium dioxide dispersion of the present invention can be prepared by mixing the aqueous dispersion and optionally raw materials for cosmetics. As an optional raw material for cosmetics, components such as: oils, surfactants, moisturizers, higher alcohols, metal ion chelating agents, natural and synthetic polymers, water-soluble and oil-soluble polymers, ultraviolet screening agents, various extracts, colorants including pigments and organic dyes, preservatives, antioxidants, dyes, thickeners, pH adjusters, perfumes, cooling agents, antiperspirants, fungicides, skin activators, and various powders. Mixtures of these components can be prepared as various forms, such as lotions, creams, pastes, sticks, emulsions.

Coatings prepared by using the aqueous dispersions of the invention can be prepared by: the aqueous dispersion of titanium dioxide is mixed with various resins (e.g., polyvinyl alcohol resin, vinyl chloride-vinyl acetate copolymer resin, acrylic resin, epoxy resin, urethane resin, alkyd resin, polyester resin, ethylene-vinyl acetate copolymer, acrylic-styrene copolymer, cellulose resin, phenol resin, and amino resin), solvent, water, and the like.

The polishing composition prepared by using the aqueous dispersion of the present invention can be prepared by: for example, an aqueous titanium dioxide dispersion, an aqueous dispersion medium, an additive (an acid or a salt thereof, or an alkali or a salt thereof) for adjusting the pH of the polishing composition, an oxidizing agent for oxidizing the surface of the object of polishing, a water-soluble polymer acting on the surface of the object of polishing or the surface of the abrasive particles, a corrosion inhibitor for inhibiting corrosion of the object of polishing, a chelating agent, an antiseptic agent having other functions, and an antifungal agent are mixed.