Titanium Oxide Particles and Method for Producing the Same

Abstract

A reaction step of introducing a raw material gas (G1) containing titanium tetrachloride and an inert gas, and an oxidizing gas (G2) containing at least one of oxygen gas and water vapor and an inert gas into a reaction tube to generate a reaction gas; a cooling step of introducing a cooling medium to cool the reaction gas to obtain raw material titanium oxide particles; a first dechlorination step of heating at 300 °C or higher and 600 °C or lower while bringing the raw material titanium oxide particles into contact with water vapor, wherein the mass ratio of water to the raw material titanium oxide particles (mass of water / mass of raw material titanium oxide particles) is 0.01 or more; and a second dechlorination step of heating at 30 °C or higher and less than 100 °C while bringing the raw material titanium oxide particles that have undergone the first dechlorination step into contact with water vapor, wherein the mass ratio of water to the raw material titanium oxide particles (mass of water / mass of raw material titanium oxide particles) is 0.01 or more. A method for producing titanium oxide particles including these steps.

Description

Technical Field

[0001] The present disclosure relates to titanium oxide particles and a method for producing the same.

Background Art

[0002] The industrial application fields of titanium oxide are extremely wide, represented by cosmetics, ultraviolet shielding materials, additives to silicone rubber, etc. In recent years, applications such as photocatalysts, solar cells, dielectric raw materials, electrode material raw materials for Li-ion batteries, etc. cover a wide range. Note that although "titanium oxide" is described as titanium dioxide in Japanese Industrial Standards (JIS), since titanium oxide is widely used as a common name, titanium dioxide (TiO2) is abbreviated as titanium oxide in the present disclosure.

[0003] Recently, titanium oxide has attracted particular attention as a raw material for high-performance dielectric materials, for example, a raw material for BaTiO3. BaTiO3 is obtained by the following reaction under heating. BaCO3 + TiO2 → BaTiO3 + CO2

[0004] The above reaction is a solid-phase reaction. It is said that first, BaCO3 decomposes at a high temperature to form BaO, and BaO diffuses and solid-solves into TiO2 particles to become BaTiO3. Therefore, the size of BaTiO3 particles is governed by the size of TiO2 particles. In recent years, with the miniaturization of multilayer ceramic capacitors, thinning of the dielectric layer has become a problem, and for this purpose, micronization and size uniformity of BaTiO3 particles are essential. Also, if BaTiO3 particles larger than the dielectric layer thickness exist, a short circuit occurs in the multilayer ceramic capacitor, leading to device failure. Therefore, it is necessary to micronize and uniformize the size of TiO2 particles, which are the raw materials for BaTiO3 particles, and it is preferable that no coarse TiO2 particles are contained. Similarly, in other applications, titanium oxide particles are required to be micronized and size-uniform, and it is better that no coarse particles are contained.

[0005] Patent Document 1 describes a method for producing titanium oxide particles with less mass variation caused by adsorbed moisture by oxidizing a gas containing titanium tetrachloride with an oxidizing gas by a vapor phase method to produce titanium oxide particles having a lower-order layer of physically adsorbed water. Patent Document 2 describes a method for producing titanium oxide particles characterized by reacting a gas containing titanium tetrachloride and an oxidizing gas under specific conditions for the purpose of obtaining titanium oxide particles with excellent size uniformity by a vapor phase method.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] The uniformity of the size of BaTiO3 particles is greatly affected not only by the uniformity of the size of TiO2 particles as the raw material but also by the uniformity of the reaction. In particular, when coexisting Cl reacts with BaCO3, a flux of BaCl2 is generated. This flux tends to localize and causes non-uniformity and aggregation in the solid-phase reaction, so the generation of the flux is not desirable. Therefore, in order to improve the uniformity of the size of BaTiO3 particles, it is required that the chlorine content of the raw materials be low. In order to synthesize high-performance dielectrics, it is also important to strictly control the BaO / TiO2 ratio. Specifically, it is necessary to manage the compounding components up to the ppm order. Of course, impurities such as the aforementioned Cl are problematic, but the adsorbed water on the surface of titanium oxide particles is a more serious problem. The adsorbed water on the surface of titanium oxide particles repeats moisture absorption and desorption according to changes in environmental humidity, so it is susceptible to the influence of seasons and weather. Therefore, in order to strictly control the BaO / TiO2 ratio, it is necessary to perform absolute drying and weighing immediately before synthesis, and there are some incalculable equipment and economic burdens. In particular, the smaller the particle size, the larger the specific surface area, so the amount of adsorbed water per unit mass of TiO2 is large, and it is difficult to control the BaO / TiO2 ratio. Furthermore, in the case of industrial use, since the raw materials are usually handled in an atmosphere where water coexists, it is extremely difficult to control the moisture content on the particle surface.

[0008] Although Patent Document 1 proposes a method for producing titanium oxide particles with a small mass change rate in a high-humidity atmosphere, it has been difficult to improve the particle refinement, reduction of the mass change rate, and reduction of the chlorine content in a well-balanced manner.

[0009] According to Patent Document 2, titanium oxide particles with few coarse particles can be produced, but titanium oxide fine particles with a small mass change rate in a high-humidity atmosphere have not been disclosed.

[0010] The present disclosure provides titanium oxide particles having a high anatase content, a low chlorine content, and a small mass change rate in a high-humidity atmosphere, and a method for producing the same.

Means for Solving the Problems

[0011] The present disclosure includes the following aspects. [Aspect 1] A reaction step of introducing a raw material gas (G1) containing titanium tetrachloride and an inert gas and an oxidizing gas (G2) containing at least one of oxygen gas and water vapor and an inert gas into a reaction tube to generate a reaction gas; A cooling step of introducing a cooling medium to cool the reaction gas to obtain raw material titanium oxide particles; A first dechlorination step of heating the raw material titanium oxide particles at 300 °C or higher and 600 °C or lower while bringing them into contact with water vapor, wherein the mass ratio of water to the raw material titanium oxide particles (mass of water / mass of raw material titanium oxide particles) is 0.01 or more; A second dechlorination step of heating the raw material titanium oxide particles that have undergone the first dechlorination step at 30 °C or higher and less than 100 °C while bringing them into contact with water vapor, wherein the mass ratio of water to the raw material titanium oxide particles (mass of water / mass of raw material titanium oxide particles) is 0.01 or more; A method for producing titanium oxide particles including the above steps. [Aspect 2] The method for producing titanium oxide particles according to Aspect 1 above, wherein the mass ratio of water to the raw material titanium oxide particles (mass of water / mass of raw material titanium oxide particles) in the first dechlorination step and the second dechlorination step is 0.04 or more. [Aspect 3] The method for producing titanium oxide particles according to Aspect 1 or 2 above, wherein the heating temperature in the first dechlorination step is 410 °C or higher and 550 °C or lower. [Aspect 4] A blowing outlet for a purge medium is provided on the inner wall or upper part of the reaction tube. In the cross-section of the reaction tube perpendicular to the central axis of the reaction tube, the blowing angle α of the purge medium with respect to the line connecting the blowing outlet of the purge medium and the central axis of the reaction tube is 50° or more, and the blowing flow rate of the purge medium is 35 m / s or more. The method for producing titanium oxide particles according to any one of Aspects 1 to 3 above. [Aspect 5] The method for producing titanium oxide particles according to any one of the above aspects 1 to 4, wherein the ratio (S1 / S2) of the cross-sectional area (S1) of the inlet of the reaction tube to the total cross-sectional area (S2) of the outlets of the introduction pipes of the raw material gas (G1) and the oxidizing gas (G2) is 1.0 or more and 10.0 or less. [Aspect 6] The BET specific surface area is 15 to 100 m 2 / g, the anatase content is 70% or more, the Cl content is 2000 mass ppm or less, and When the BET specific surface area is α (m 2 / g) and the mass loss rate when calcined in an electric furnace maintained at 900 °C for 1 hour is defined as the calcination loss X (mass %), the calcination loss X of the titanium oxide particles satisfies the formula (1). 2.1×{[α×1.3 / (6×10 4 )]×18+[(α×1.3-β) / (6×10 4 )]×9}×100≧X≧0.60×{[α×1.3 / (6×10 4 )]×18+[(α×1.3-β) / (6×10 4 )]×9}×100 ···(1) In the formula (1), β represents the BET specific surface area (m 2 / g) of the powder after calcination in an electric furnace maintained at 900 °C for 1 hour. [Aspect 7] The titanium oxide particles according to the above aspect 6, wherein D90(LD) / D50(LD) measured by the laser diffraction / scattering analysis method is more than 1.0 and 2.0 or less, and the particle concentration (number basis) of coarse particles having a primary particle diameter exceeding 16 times D50(SEM) of the primary particles observed by a field emission scanning electron microscope is 20 ppm or less. [Aspect 8] The titanium oxide particles according to the above aspect 6 or 7, wherein D90(LD) is 3000 nm or less and D50(LD) is 1000 nm or less. [Aspect 9] The titanium oxide particles according to any one of the above aspects 6 to 8, wherein the contents of Na, Al, S, Fe, Ni, Cr, Nb, and Zr are each 50 mass ppm or less, and the contents of Si and C are each 500 mass ppm or less. [Aspect 10] A slurry containing titanium oxide particles according to any one of the above aspects 6 to 9. [Aspect 11] A dispersion containing titanium oxide particles according to any one of the above aspects 6 to 9. [Aspect 12] A composition containing titanium oxide particles according to any one of the above aspects 6 to 9. [Aspect 13] A dielectric raw material containing titanium oxide particles according to any one of the above aspects 6 to 9. [Advantages of the Invention]

[0012] According to the present disclosure, it is possible to provide titanium oxide particles having a high anatase content, a low chlorine content, and a small mass change rate in a high-humidity atmosphere, and a method for producing the same. The titanium oxide particles of the present disclosure can be suitably used as a slurry, a dispersion, a composition, and a dielectric raw material. [Brief Description of the Drawings]

[0013]

Figure 1

Figure 2

Figure 3

[0014] Hereinafter, embodiments of the present invention will be described, but it should be understood that the present invention is not limited only to these embodiments, and various applications are possible within the spirit and scope of implementation thereof.

[0015] In the present disclosure, when using "~" for a numerical range, the numerical values at both ends are the upper limit value and the lower limit value respectively, and are included in the numerical range. When multiple upper limit values or lower limit values are described, a numerical range can be formed from all combinations of the upper limit value and the lower limit value. Similarly, when multiple numerical ranges are described, separate numerical ranges can be formed by individually selecting and combining the upper limit value and the lower limit value from those numerical ranges.

[0016] In the present disclosure, for the numerical values of various measured values, unless otherwise specified and unless it is suggested from the context before and after that they have different meanings, the defined numerical values are determined considering significant figures. For example, 0 ppm means less than 0.5 ppm.

[0017] [Titanium Oxide Particles] The titanium oxide particles in one embodiment have a BET specific surface area of 15 to 100 m 2 / g, anatase content of 70% or more, Cl content of 2000 mass ppm or less, and when the BET specific surface area is α (m 2 / g) and the mass loss rate when calcined in an electric furnace maintained at 900 °C for 1 hour is defined as the calcination loss X (mass %), the titanium oxide particles satisfy the formula (1). 2.1 × {[(α × 1.3 / (6 × 10 4 ))] × 18 + [(α × 1.3 - β) / (6 × 10 4 ))] × 9} × 100 ≥ X ≥ 0.60 × {[(α × 1.3 / (6 × 10 4 ))] × 18 + [(α × 1.3 - β) / (6 × 10 4 ))] × 9} × 100 ··· (1) In formula (1), β represents the BET specific surface area (m 2 / g) of the powder after calcination in an electric furnace maintained at 900 °C for 1 hour.

[0018] (BET Specific Surface Area) The BET specific surface area of the titanium oxide particles in one embodiment is 15 to 100 m 2 / g. When the BET specific surface area is 15 m 2If it is / g or more, the surface area is high and the reactivity is high, so it is suitable as a raw material for electronic materials. From the same viewpoint, the BET specific surface area is 20 m 2 / g or more is preferable, and 25 m 2 / g or more is more preferable. If the BET specific surface area is 100 m 2 / g or less, the dispersibility is excellent. The BET specific surface area is preferably 95 m 2 / g or less, and more preferably 90 m 2 / g or less. In the present disclosure, the BET specific surface area is measured by the method described in the examples.

[0019] (Anatase content) In one embodiment, the anatase content (molar basis) of the titanium oxide particles is 70% or more, preferably 75% or more. If the anatase content is 70% or more, high reaction activity is exhibited. The upper limit of the anatase content is not particularly limited, but can be, for example, 100% or less, 99% or less, or 98% or less. In the present disclosure, the anatase content means the content of anatase-type crystals in the titanium oxide particles and is measured by the method described in the examples.

[0020] (Loss on ignition and theoretical value of loss on ignition) In one embodiment, the mass loss rate (% by mass) (also referred to as loss on ignition X) when the titanium oxide particles are calcined in an electric furnace maintained at 900 °C for 1 hour satisfies the formula (1) when the BET specific surface area is α (m 2 / g) and the BET specific surface area of the powder after calcination in an electric furnace maintained at 900 °C for 1 hour (m 2 / g) is β. 2.1 × {[(α × 1.3 / (6 × 10 4 ))] × 18 + [(α × 1.3 - β) / (6 × 10 4 ))] × 9} × 100 ≧ X ≧ 0.60 × {[(α × 1.3 / (6 × 10 4 ))] × 18 + [(α × 1.3 - β) / (6 × 10 4 ))] × 9} × 100 ···(1) The titanium oxide particles that satisfy the formula (1) have a small mass change rate even in a high-humidity atmosphere and are suitable for raw materials that require a highly accurate charged amount. From the same viewpoint, 1.5×{[α×1.3 / (6×10 4 )]×18+[(α×1.3-β) / (6×10 4 )]×9}×100≧X≧0.8×{[α×1.3 / (6×10 4 )]×18+[(α×1.3-β) / (6×10 4 )]×9}×100 It is preferable that 1.3×{[α×1.3 / (6×10 4 )]×18+[(α×1.3-β) / (6×10 4 )]×9}×100≧X≧0.9×{[α×1.3 / (6×10 4 )]×18+[(α×1.3-β) / (6×10 4 )]×9}×100 In the present disclosure, β and the ignition loss X are measured by the method described in the Examples.

[0021] Next, the meaning of the above formula will be described. The formula on which these formulas are based is the following formula (2). Note that α and β have the same meanings as in formula (1). [(α×1.3×10 19 ) / (6×10 23 )]×18+{[(α×1.3-β)×1.0×10 19 ] / (6×10 23 )}×0.5×18 ····(2) Equation (3) is a rearrangement of equation (2). [α×1.3 / (6×10 4 )]×18+[(α×1.3-β) / (6×10 4 )] × 9 (3) Equation (2) can be decomposed into the following two equations. [(α〔m 2 / g]×1.3×10 19 [pcs / m 2 〕) / (6×10 23 [pieces / mol])]×18[g / mol] ····(4) {(α〔m 2 / g]×1.3×10 19 [pcs / m 2 〕-β〔m 2 / g) × 1.0 × 10 19 〔pieces / m 2 〕) / (6 × 10 23 〔pieces / mol〕)} × 0.5 × 18 〔g / mol〕 ····(5)

[0022] As a factor of the mass reduction during heating, the water molecules adsorbed on the particle surface are desorbed due to heating. On the surface of titanium oxide particles, there are about 1.0 × 10 19 〔pieces / m 2 〕 of OH in the case of rutile-type crystals and about 1.3 × 10 19 〔pieces / m 2 〕 of OH in the case of anatase-type crystals (written by Manabu Kiyono, "Titanium Oxide", published by Gijutsu-Houdou Publishing Co., Ltd., issued in 1991, p. 54). Since the anatase content of the titanium oxide particles of the present disclosure is 70% or more, for simplicity, it is assumed that all are anatase-type. Assuming that the OH on the surface of this number of anatase-type crystals is each combined with 1 molecule of H2O and that it is desorbed as water due to heating during calcination, the mass ratio of the adsorbed water desorbed from the particles is represented by Equation (4).

[0023] As a factor of the mass reduction during heating, the detachment of OH groups due to the decrease in specific surface area by heating is also mentioned. Due to heating during calcination, the titanium oxide particles undergo grain growth and the specific surface area decreases. At this time, since the anatase-type crystal transfers to the rutile-type crystal, the decrease amount of OH groups is represented by (α × 1.3 - β) × 10 19 〔pieces / g〕. At this time, since 1 molecule of water is generated from 2 OH groups on the surface of the titanium oxide particles, 0.5 is multiplied in Equation (5). That is, the mass ratio of the water desorbed due to the decrease in specific surface area is represented by Equation (5).

[0024] The theoretical value of the mass ratio of the water desorbed during heating is the sum of Equation (4) and Equation (5), that is, Equation (2) and Equation (3). Equation (2) and Equation (3) are the theoretical values of the loss on ignition. Equation (1) is Equation (2) as a percentage and further with a certain range.

[0025] When the loss on ignition X / the theoretical value of the loss on ignition is less than 1, the moisture content is less than the theoretical value, and it is in a state where it is easy to absorb moisture. When it is greater than 1, the moisture content is more than the theoretical value, and it is in a state where it is easy to release moisture. Therefore, titanium oxide particles in which the measured value of the loss on ignition, that is, the loss on ignition X, is close to the theoretical value of the loss on ignition determined from the BET specific surface area and its change amount have a small mass change rate in a high-humidity atmosphere and are suitable for raw materials that require a high-precision charging amount. It is preferable that the loss on ignition / the theoretical value of the loss on ignition is 0.60 or more and 2.1 or less because the moisture amount stability is high. From the same viewpoint, 0.8 or more and 1.5 or less is more preferable, and 0.9 or more and 1.3 or less is even more preferable.

[0026] (Mass change rate in a high-humidity atmosphere) The mass change rate of the titanium oxide particles in a high-humidity atmosphere is preferably 2.5% by mass or less, more preferably 2.0% by mass or less, still more preferably 1.8% by mass or less, and may be 0% by mass or more, or 0.1% by mass or more. In the present disclosure, the mass change rate in a high-humidity atmosphere is measured by the method described in the examples.

[0027] (Chlorine (Cl) content) In one embodiment, the Cl (chlorine atom) content of the titanium oxide particles is 2000 mass ppm or less. If the Cl content is 2000 mass ppm or less, problems are less likely to occur in subsequent processes when the titanium oxide particles are used as a raw material. For example, when titanium oxide particles with a Cl content of 2000 mass ppm or less are used as a raw material such as BaTiO3, the generation of flux during firing can be suppressed. When flux is generated, the following problems may occur. The molten flux tends to localize, and in the localized part, aggregation increases, and quality variations may occur between other parts. When the particles aggregate, the crystals of the BaTiO3 particles grow into abnormal particles, which may also reduce the dielectric properties of BaTiO3. From this perspective, the Cl content of the titanium oxide particles is preferably 1500 mass ppm or less, more preferably 1300 mass ppm or less, and even more preferably 950 mass ppm or less. The lower limit of the Cl content of the titanium oxide particles is not particularly limited, but can be 100 mass ppm or more, 200 mass ppm or more, or 500 mass ppm or more. In the present disclosure, the Cl content is measured by the method described in the examples using the silver nitrate potentiometric titration method.

[0028] (Content of other impurities) The contents of Na, Al, S, Fe, Ni, Cr, Nb and Zr in the titanium oxide particles are preferably 50 mass ppm or less, more preferably 10 mass ppm or less, respectively. The contents of Si and C in the titanium oxide particles are preferably 500 mass ppm or less, more preferably 100 mass ppm or less, respectively. If the content of impurities is within the above range, problems are less likely to occur in the subsequent process when the titanium oxide particles are used as a raw material. For example, when a dielectric is obtained using the titanium oxide particles as a raw material, a decrease in dielectric properties due to the presence of impurities is suppressed. When the titanium oxide particles are used for photocatalyst or solar cell applications, a decrease in transparency due to coloring by Fe is prevented or suppressed, and a decrease in the function as a photocatalyst or solar cell due to lattice defects caused by Al, S, etc. is also prevented or suppressed. The contents of Na, Al, S, Fe, Ni, Cr, Nb and Zr in the titanium oxide particles may each be 0.01 mass ppm or more. The contents of Si and C in the titanium oxide particles may each be 1 mass ppm or more. In the present disclosure, the content of other impurities is measured by the method described in the examples.

[0029] (D50(LD) and D90(LD) by laser diffraction / scattering analysis method) Titanium oxide particles generally often form secondary particles in which their primary particles are aggregated. The aggregation state of titanium oxide particles, that is, the particle sizes D50 and D90 of the aggregates of primary particles and secondary particles, are measured by a laser diffraction particle size distribution apparatus. In the present disclosure, D50 (LD) and D90 (LD) are the 50% particle size and 90% particle size, respectively, in the volume-based cumulative particle size distribution measured by the laser diffraction / scattering analysis method. According to the "Ultra-Fine Particle Handbook" supervised by Shinsuke Saito, Fuji Techno System, p93, (1990), the measurement methods for the particle size distribution of particles include the sedimentation method, the microscopic method, the laser diffraction / scattering analysis method (light scattering method), the direct counting method, etc. Among these, the sedimentation method is applicable when the measurable particle size is several hundred nm or more, and it is not suitable for measuring the particle size distribution of fine particles with a particle size of 100 nm or less. On the other hand, the laser diffraction / scattering analysis method (light scattering method) can measure the particle size in the range of several nm to several μm and is suitable for measuring fine particles. In the present disclosure, D50 (LD) and D90 (LD) are measured by the method described in the examples.

[0030] The D50 (LD) of titanium oxide particles is preferably 1000 nm or less, more preferably 500 nm or less. D50 (LD) corresponds to the effective diameter (aggregation diameter) when dispersed in a solvent, and the finer the value, the better the dispersibility. The D50 (LD) of titanium oxide particles may be 50 nm or more or 100 nm or more.

[0031] The D90 (LD) of titanium oxide particles is preferably 3000 nm or less, more preferably 2000 nm or less, still more preferably 1000 nm or less, and even more preferably 900 nm or less. If the value of D90 (LD) is small, it is judged that the aggregation force of titanium oxide particles is weak and they show good dispersibility in the solvent. The D90 (LD) of titanium oxide particles may be 100 nm or more or 200 nm or more.

[0032] The D90(LD) / D50(LD) of the titanium oxide particles is preferably greater than 1.0. The D90(LD) / D50(LD) of the titanium oxide particles may be 1.2 or more, or 1.3 or more. The D90(LD) / D50(LD) of the titanium oxide particles is preferably 2.0 or less, more preferably 1.9 or less, and still more preferably 1.8 or less. If it is within the above range, the slurry is excellent in uniformity.

[0033] (D50(SEM) of the primary particles of titanium oxide particles observed with a field emission scanning electron microscope) The D50 of the primary particles of the titanium oxide particles observed with a field emission scanning electron microscope (also referred to as D50(SEM)) is preferably 10 to 100 nm, more preferably 15 to 50 nm, and still more preferably 12 to 45 nm. Such titanium oxide particles are suitable for applications such as dielectric raw materials that require a submicron particle size. In the present disclosure, D50(SEM) is the 50% particle size in the number-based cumulative particle size distribution of the primary particles of titanium oxide measured by a field emission scanning electron microscope. In the present disclosure, D50(SEM) is measured by the method described in the examples.

[0034] (Particle concentration of coarse titanium oxide particles) The coarse particles in the titanium oxide particles are defined by the size of the primary particles measured by a field emission scanning electron microscope (SEM), and the particle concentration of the coarse titanium oxide particles is also measured by a field emission scanning electron microscope. In the present disclosure, the particle concentration of the coarse titanium oxide particles is measured by the method described in the examples.

[0035] Coarse primary particles and aggregated particles (also referred to as secondary particles) should be distinguished by appearance. For example, the coarse particles have an appearance as shown in the central part of Fig. 1(a). The particles composed of fine primary particles as shown in Fig. 1(b) are regarded as aggregated particles and are not counted as coarse particles. When it is difficult to distinguish between coarse particles and aggregated particles, it is desirable to increase the observation magnification to an extent that is easy to distinguish.

[0036] In the present disclosure, the coarse particles of titanium oxide refer to particles having a primary particle diameter of a specific size or more as measured by the above measurement method, or particles exceeding 16 times the D50(SEM). The particle concentration (number basis) of the coarse particles having a primary particle diameter exceeding 16 times the D50(SEM) is preferably 20 ppm or less, more preferably 10 ppm or less, still more preferably 5 ppm or less, and even more preferably 0 ppm. It is particularly preferable that the titanium oxide particles do not contain coarse particles having a primary particle diameter exceeding 16 times the D50(SEM).

[0037] When the coarse particles contain chlorine inside, chlorine is difficult to escape even through the dechlorination step, and the Cl content of the obtained titanium oxide particles tends to be high. Therefore, when the particle concentration (number basis) of the coarse particles having a primary particle diameter exceeding 16 times the D50(SEM) is 20 ppm or less, it is easy to reduce the Cl content.

[0038] [Slurry, Dispersion, Composition and Dielectric Raw Material] The slurry, dispersion, composition and dielectric raw material in one embodiment contain the aforementioned titanium oxide particles. A slurry is a mixture in which particles are mixed in a liquid, but often refers to a highly viscous fluid. A dispersion generally widely refers to a mixture in which solid particles are dispersed in a liquid, including those with a low concentration. A composition refers to a composition composed of a plurality of components. A dielectric raw material refers to a raw material for manufacturing a dielectric. The slurry, dispersion, composition and dielectric raw material of one embodiment are suitable for photocatalytic applications, solar cell applications, dielectric applications, etc. Other uses of the slurry, dispersion and composition containing titanium oxide particles are known. As a method for manufacturing a slurry, dispersion, composition and dielectric raw material using the titanium oxide particles of the present disclosure, a known method can be used. The slurry, dispersion, composition and dielectric raw material containing the titanium oxide particles of one embodiment have a low Cl content and a small mass change rate in a high-humidity atmosphere, so the uniformity and quality of the final product can be improved.

[0039] [Method for Producing Titanium Oxide Particles] A method for manufacturing titanium oxide particles in one embodiment includes a reaction step of introducing a raw material gas (G1) containing titanium tetrachloride and an inert gas, and an oxidizing gas (G2) containing at least one of oxygen gas and water vapor and an inert gas into a reaction tube to generate a reaction gas, a cooling step of introducing a cooling medium to cool the reaction gas to obtain raw material titanium oxide particles, and a first dechlorination step of heating the raw material titanium oxide particles while bringing them into contact with water vapor at a temperature of 300°C or higher and 600°C or lower, wherein the mass ratio of water to the raw material titanium oxide particles (mass of water / mass of raw material titanium oxide particles) is 0.01 or more, and a second dechlorination step of heating the raw material titanium oxide particles that have undergone the first dechlorination step while bringing them into contact with water vapor at a temperature of 30°C or higher and less than 100°C, wherein the mass ratio of water to the raw material titanium oxide particles (mass of water / mass of raw material titanium oxide particles) is 0.01 or more. The reaction step and the cooling step may be collectively referred to as a synthesis step. In the present disclosure, the titanium oxide particles before the dechlorination step are referred to as "raw material titanium oxide particles".

[0040] <Synthesis step> (Reaction tube) The reaction tube may be a horizontal reaction tube, but a vertical reaction tube is preferred because it is easy to make the flow of various gases uniform, and a reaction tube with a circular cross-section is preferred. In the case of a circular vertical reaction tube, the preheated raw material gas (G1) and the oxidizing gas (G2) are introduced downward into the reaction tube through their respective introduction pipes from the upper end of the heated reaction tube to generate a reaction gas. This step is called the reaction step. A blowout port for the cooling medium is provided on the inner wall of the reaction tube, and the cooling medium is blown out from there and mixed with the reaction gas to cool the reaction gas. This step is called the cooling step.

[0041] The section from the raw material gas inlet to the cooling medium blowout port in the reaction tube is called the reaction region, and the section from the cooling medium blowout port to the discharge port side is called the cooling region. When there are multiple cooling medium blowout ports, the section from the raw material gas inlet to the first cooling medium blowout port in the reaction tube is called the reaction region, and the section from the first cooling medium blowout port to the discharge port side is called the cooling region.

[0042] The cooled raw material titanium oxide particles and the remaining gas are discharged to the outside at the lower part of the reaction tube. Note that the reaction gas may contain titanium oxide as a reaction product.

[0043] <<Reaction process>> The raw material gas (G1) and the oxidizing gas (G2) are introduced in the axial direction of the reaction tube from the inlet (end face side) of the reaction tube. The ratio (S1 / S2) of the cross-sectional area (S1) of the reaction tube inlet (end face or cross-section of the reaction tube) to the total cross-sectional area (S2) of the outlets of the introduction pipes of the raw material gas (G1) and the oxidizing gas (G2) is preferably 1.0 or more and 10.0 or less. By setting it within this range, the temperature in the reaction region or the residence time in the high-temperature region can be made closer to uniform. In the present disclosure, the cross-sectional area (S1) of the reaction tube inlet is the cross-sectional area including the cross-sectional areas (S2) of the outlets of the introduction pipes of the raw material gas (G1) and the oxidizing gas (G2). The ratio (S1 / S2) is preferably 1.0 or more, more preferably 1.5 or more, still more preferably 3.0 or more, and particularly preferably 6.0 or more. The ratio (S1 / S2) is preferably 10.0 or less, more preferably 7.0 or less. The raw material gas (G1) and the oxidizing gas (G2) are preferably introduced in the gas flow direction in the reaction tube respectively.

[0044] The temperature of the reaction region where the raw material gas (G1) and the oxidizing gas (G2) are introduced is preferably 800°C or more and less than 1,200°C, more preferably 850°C or more and less than 1,100°C. If the temperature of the reaction region is 800°C or more, the reaction proceeds sufficiently, and the particle size distribution of the raw material titanium oxide particles becomes uniform and the crystallinity can be enhanced. By increasing the temperature of the reaction region, the reaction can be completed simultaneously with mixing, homogeneous nucleation can be promoted, and the reaction zone can be reduced. On the other hand, if the temperature of the reaction region is less than 1,200°C, since particle growth proceeds moderately while aggregation hardly occurs, coarse particles are hardly generated. Further, by setting the temperature of the reaction region to less than 1,200°C, the anatase content can be increased.

[0045] (Raw material gas (G1)) The raw material gas (G1) contains titanium tetrachloride (G1T) and an inert gas (G1I). The titanium tetrachloride in the raw material gas is in a gaseous state.

[0046] The flow rate (F G1 ) of the raw material gas is preferably 1000 mol / hr or more. By being 1000 mol / hr or more, the residence time of the raw material gas (G1) in the reaction region becomes short, and over-sintering and coarsening of titanium oxide are less likely to occur. From the same viewpoint, F G1 is more preferably 1200 mol / hr or more, and even more preferably 1500 mol / hr or more. The upper limit of F G1 can be appropriately set according to production conditions such as the size of the reaction tube and the temperature of the reaction region and is not particularly limited. For example, it can be 10000 mol / hr or less, 5000 mol / hr or less, or 2000 mol / hr or less.

[0047] The flow rate (F G1T ) of titanium tetrachloride is preferably 100 mol / hr or more, more preferably 150 mol / hr or more, and even more preferably 200 mol / hr or more from the viewpoint of increasing the yield per unit time. From the viewpoint of suppressing the growth of sintered particles due to reaction heat, F G1T is preferably 5000 mol / hr or less, more preferably 3000 mol / hr or less, and even more preferably 2000 mol / hr or less.

[0048] Examples of the inert gas include nitrogen gas, helium gas, argon gas, etc. Nitrogen gas is preferred from an economic viewpoint.

[0049] The raw material gas (G1) is preferably introduced into the reaction tube at 600°C or higher and less than 1200°C, more preferably at 700°C or higher and less than 1150°C, and even more preferably at 800°C or higher and less than 1120°C.

[0050] (Oxidizing gas (G2)) The oxidizing gas (G2) contains at least one of oxygen gas (G2O) and water vapor (G2W) and an inert gas (G2I).

[0051] The flow rate (F G2 ) of the oxidizing gas is preferably 1000 mol / hr or more. By being 1000 mol / hr or more, the residence time of the oxidizing gas (G2) in the reaction region becomes short, and over-sintering and coarsening of titanium oxide are less likely to occur. From the same viewpoint, F G2 is more preferably 1500 mol / hr or more, and even more preferably 2000 mol / hr or more. The upper limit of F G2 can be appropriately set according to production conditions such as the size of the reaction tube and the temperature of the reaction region and is not particularly limited. For example, it can be 4000 mol / hr or less, 3500 mol / hr or less, or 3200 mol / hr or less.

[0052] The total flow rate (F G2W+G2O ) of water vapor (G2W) and oxygen gas (G2O) is preferably 800 mol / hr or more, more preferably 1200 mol / hr or more, and even more preferably 1500 mol / hr or more. From the viewpoint of suppressing sintered particle growth due to reaction heat, F G2W+G2O is preferably 3800 mol / hr or less, more preferably 3500 mol / hr or less, and even more preferably 3200 mol / hr or less.

[0053] The oxidizing gas (G2) is preferably introduced into the reaction tube at 600°C or more and less than 1200°C.

[0054] The residence time (also referred to as the high-temperature region residence time) of both the raw material gas (G1) and the oxidizing gas (G2) in the reaction region in the high-temperature region of 800°C or more and less than 1200°C is preferably 0.1 second or less, more preferably 0.03 second or less, and even more preferably 0.02 second or less. If it is 0.1 second or less, excessive grain growth does not occur, which is preferable.

[0055] Examples of the inert gas include nitrogen gas, helium gas, argon gas, etc. From an economic viewpoint, nitrogen gas is preferable. It is preferable that the inert gas in the oxidizing gas (G2) is the same chemical species as the inert gas in the raw material gas (G1).

[0056] (Flow rate of reaction gas) The flow rates of the raw material gas (G1) and the oxidizing gas (G2) are calculated from the introduction rate (flow rate) from the inlet of the reaction tube and the cross-sectional area of the reaction tube. The flow rate (m 3 / s) of the reaction gas flow after the reaction of the raw material gas (G1) and the oxidizing gas (G2) is calculated from the flow rates of the raw material gas (G1) and the oxidizing gas (G2) and the reaction formula. In the present disclosure, the flow velocity (A) (m / s) of the reaction gas flow in the reaction tube is, under the assumption that the raw material gas and the oxidizing gas react immediately, the total flow rate (m 3 / s) of the reaction gas flow after the reaction of the raw material gas (G1) and the oxidizing gas (G2) divided by the cross-sectional area (m 2 ) of the reaction tube (m / s).

[0057] The flow velocity (A) (m / s) of the reaction gas flow is preferably 1 m / s or more, more preferably 10 m / s or more, and even more preferably 20 m / s or more. When the flow velocity is 1 m / s or more, the residence time of the reaction gas flow is shortened, and over-sintering and coarsening of titanium oxide are suppressed.

[0058] (Purge medium) A blowout port for the purge medium may be provided on the inner wall or the upper part of the reaction tube, and the purge medium may be introduced. By flowing the purge medium while swirling along the inner wall of the reaction tube, adhesion of titanium oxide particles to the inner wall of the reaction tube can be prevented. Examples of the shape of the blowout port of the purge medium include a single hole and a slit.

[0059] When the generated raw material titanium oxide particles adhere to and stay on the inner wall of the reaction tube, they coarsen due to sintered particle growth. If the coarsened particles detach from the inner wall and mix into the obtained raw material titanium oxide particles, it may cause non-uniformity of the particle size distribution. By introducing the purge medium, adhesion and retention of raw material titanium oxide particles on the inner wall of the reaction tube can be suppressed. The purge medium can be introduced continuously or intermittently.

[0060] As the purge medium, a gas or a liquid can be used. Examples of the purge medium include gases such as air, nitrogen gas, carbon monoxide, and liquids such as sprayed water. The gas may be a mixed gas, or a gas and a liquid may be used in combination.

[0061] The blowing angle α of the purge medium P (see Figure 2) is defined as the angle at which the purge medium P is blown out (the angle with respect to the central axis 4 of the outlet 5 of the purge medium P in the direction of the central axis 4 of the reaction tube 1) when the line connecting the outlet 5 of the purge medium P and the central axis 4 of the reaction tube 1 is set to 0° in a cross-sectional plane perpendicular to the central axis 4 (the flow direction of the reaction gas) of the reaction tube 1, and is preferably 50° or more. By setting the angle α to 50° or more, the purge medium can be swirled near the inner wall of the reaction tube, and the adhesion of titanium oxide to the inner wall of the reaction tube can be effectively suppressed. The angle α is less than 90°.

[0062] The blowing angle β of the purge medium P (see Figure 3) is preferably 60° or more, more preferably 70° or more, and even more preferably 80° or more when the flow direction of the reaction gas in the direction of the central axis of the reaction tube 1 is set to 0° in a longitudinal cross-sectional plane including the central axis (the flow direction of the reaction gas) of the reaction tube 1. The blowing direction of the purge medium P is preferably from a direction perpendicular to the flow direction of the reaction gas to the same direction, that is, the blowing angle β of the purge medium P is preferably 90° or less. By setting the blowing angle β of the purge medium P to such an angle, the adhesion of titanium oxide to the inner wall of the reaction tube can be effectively suppressed.

[0063] From the viewpoint of suppressing the adhesion of raw material titanium oxide particles to the inner wall of the reaction tube, it is preferable that there be one or more purge medium outlets, and more preferably two or more. From the same viewpoint, in the same cross-section of the reaction tube, it is preferable that there be one or more purge medium outlets, and more preferably two or more. Generally, the larger the angle α or the higher the flow rate of the purge medium, the smaller the number of purge medium outlets per circumference of the outer periphery of the cross-section of the reaction tube can be. The purge medium outlet may be located at one position along the central axis direction of the reaction tube in the same longitudinal section of the reaction tube, or may be at two or more positions. The purge medium outlets may be arranged spirally on the inner wall of the reaction tube. The purge medium outlets are preferably installed in the reaction region, and more preferably installed in both the reaction region and the cooling region. It is preferable that a swirling flow of the purge medium along the inner wall of the reaction tube be formed in both the reaction region and the cooling region.

[0064] From the viewpoint of effectively suppressing the adhesion of the generated raw material titanium oxide particles to the inner wall of the reaction tube, the blowing flow rate of the purge medium is preferably 35 m / s or more, more preferably 50 m / s or more, and still more preferably 55 m / s or more. The upper limit of the blowing flow rate of the purge medium is not particularly limited, but for example, it can be 100 m / s or less, 75 m / s or less, or 65 m / s or less. In the present disclosure, the blowing flow rate of the purge medium is defined as the flow rate of the purge medium (m 3 / s) divided by the cross-sectional area (m 2 ) of the purge medium outlet (m / s).

[0065] The temperature of the purge medium is preferably 0°C to 100°C, and more preferably 10°C to 90°C. The temperature of the purge medium is preferably higher than the temperature of the cooling medium. Thereby, the cooling effect by the cooling medium can be enhanced.

[0066] <<Cooling Step>> (Cooling Medium) In one embodiment, a blowing outlet for the cooling medium is provided on the inner wall of the reaction tube, and the reaction gas is cooled by blowing out the cooling medium and mixing it with the reaction gas to stop the reaction and obtain raw material titanium oxide particles.

[0067] As the cooling medium, a gas or a liquid can be used. Examples of the cooling medium include gases such as air, nitrogen gas, carbon monoxide, and liquids such as spray water. The gas may be a mixed gas, or a gas and a liquid may be used in combination. From the viewpoint of enhancing the cooling effect, the temperature of the cooling medium is preferably from 0°C to 100°C, more preferably from 10°C to 90°C.

[0068] The blowing angle γ of the cooling medium Q (see Figure 2) is defined as the angle at which the cooling medium Q is blown out (the angle with respect to the central axis 4 of the reaction tube 1 in the direction of the central axis of the blowing outlet 3 of the cooling medium Q) when the line connecting the blowing outlet 3 of the cooling medium Q and the central axis 4 of the reaction tube 1 is set to 0° in a cross-sectional plane perpendicular to the central axis 4 of the reaction tube 1 (the flow direction of the reaction gas). The blowing angle γ is 0° or more, preferably less than 50°. When the angle γ is 0° or more and less than 50°, the cooling medium can flow near the center of the reaction tube, and can be sufficiently mixed with the reaction gas to obtain a high cooling effect. From the same viewpoint, the angle γ is more preferably 0° or more and 30° or less.

[0069] The blowing angle δ of the cooling medium Q (see Figure 3) is preferably 60° or more, more preferably 70° or more, and still more preferably 80° or more when the flowing direction of the reaction gas in the direction of the central axis of the reaction tube 1 is set to 0° in a longitudinal cross-sectional plane including the central axis of the reaction tube 1 (the flow direction of the reaction gas). The blowing direction of the cooling medium Q is preferably from the direction perpendicular to the flow direction of the reaction gas to the same direction, that is, the blowing angle δ of the cooling medium Q is preferably 90° or less. By setting the blowing angle δ of the cooling medium Q to such an angle, a high cooling effect can be obtained.

[0070] From the viewpoint of promoting the mixing of the cooling medium and the reaction gas, there is one or more blowing outlets of the cooling medium, and two or more are preferred. From the same viewpoint, the blowing outlet of the cooling medium may be one in the same cross-sectional plane of the reaction tube, or two or more. The blowing outlet of the cooling medium may be one along the central axis direction of the reaction tube in the same longitudinal cross-sectional plane of the reaction tube, or two or more.

[0071] In the cooling region following the reaction region of the reaction tube, if there is a temperature range exceeding 500°C, sintering between particles can occur. Therefore, the residence time in the region of 500°C or higher is preferably 1 second or less, more preferably 0.5 second or less, and even more preferably 0.3 second or less. If it is 1 second or less, excessive grain growth does not occur, which is preferable.

[0072] <Dechlorination process> The produced raw material titanium oxide particles are subjected to dechlorination treatment in the dechlorination process. When synthesizing raw material titanium oxide particles with a high rutile content, a higher temperature can be applied compared to the case of synthesizing raw material titanium oxide particles with a high anatase content. Therefore, raw material titanium oxide particles with a low Cl content can be easily produced. On the other hand, for raw material titanium oxide particles with a high anatase content, it is difficult to produce raw material titanium oxide particles with a low Cl content, and it is even more difficult to achieve both a low Cl content and an appropriate amount of adsorbed moisture on the particle surface. In the method for producing titanium oxide particles according to one embodiment, the dechlorination process is carried out in two stages. Although not wishing to be bound by theory, by performing the dechlorination process in two stages, performing an efficient dechlorination treatment in the first stage, and performing the dechlorination treatment under milder conditions in the second stage compared to the first stage, titanium oxide particles with an appropriate amount of adsorbed moisture on the surface and a low Cl content can be produced. That is, the first dechlorination process is a process of promoting dechlorination by heating under relatively high temperature and high humidity while suppressing aggregation by sufficient heating, and the second dechlorination process is a process of dechlorination while retaining the adsorbed moisture on the surface hydroxyl groups by heating under relatively low temperature and high humidity. By using this dechlorination process, sufficient dechlorination can be promoted, and titanium oxide particles with an appropriate amount of moisture retained on the surface can be obtained. The two-stage dechlorination process may be a continuous process or a discontinuous process.

[0073] The first dechlorination step is a step of heating the raw material titanium oxide particles at 300°C or higher and 600°C or lower while bringing them into contact with water vapor. The mass ratio of water to the raw material titanium oxide particles (= mass of water / mass of raw material titanium oxide particles; the same applies hereinafter) in the first dechlorination step is 0.01 or higher. If the mass ratio of water to the raw material titanium oxide particles is 0.01 or higher, an effect of suppressing grain growth is recognized. The mass ratio of water to the raw material titanium oxide particles is preferably 0.03 or higher, more preferably 0.04 or higher, and even more preferably 0.05 or higher. From the perspective of economy, the upper limit is preferably 2 or lower, more preferably 1 or lower, even more preferably 0.5 or lower, and particularly preferably 0.1 or lower.

[0074] When the heating temperature is 600°C or lower, it is difficult for sintering of the raw material titanium oxide particles to proceed, and the primary particle size is likely to be uniform. For the same reason, the heating temperature is more preferably 550°C or lower, and even more preferably 500°C or lower. When the heating temperature is 300°C or higher, the dechlorination efficiency is high. For the same reason, the heating temperature is preferably 410°C or higher, and more preferably 430°C or higher. The treatment time is preferably 10 minutes to 150 minutes, and more preferably 15 minutes to 130 minutes.

[0075] The second dechlorination step is a step of heating the raw material titanium oxide particles that have undergone the first dechlorination step at 30°C or higher and lower than 100°C while bringing them into contact with water vapor. The mass ratio of water to the raw material titanium oxide particles is the same as in the first dechlorination step. The mass ratio of water to the raw material titanium oxide particles in the first dechlorination step and the second dechlorination step may be the same or different.

[0076] When the heating temperature is 30°C or higher, aggregation between particles is less likely to occur and dechlorination proceeds gently. From the same perspective, 50°C or higher is preferable, and 60°C or higher is more preferable. When the heating temperature is lower than 100°C, the surface hydroxyl groups of the particles are more likely to combine with moisture in the air, and moisture is more likely to be retained. For the same reason, the heating temperature is preferably 90°C or lower, and more preferably 75°C or lower. The treatment time is preferably 10 minutes to 150 minutes, more preferably 15 minutes to 130 minutes, and even more preferably 15 minutes to 80 minutes.

Examples

[0077] Hereinafter, examples and comparative examples will be specifically described, but the present invention is not limited thereto in any way.

[0078] The method for measuring the physical properties of titanium oxide particles is as follows.

[0079] (1) BET specific surface area In accordance with JIS R 1626:1996, a fully automatic BET specific surface area measuring device (“Macsorb HM model-1208”, manufactured by Mountech Co., Ltd.) was used. As a pretreatment, the sample heated to 180°C and with nitrogen gas flowing for 20 minutes was measured using nitrogen gas as the adsorbate by the BET three-point method. The applicable range of the BET method was P / P0 = 0.00 to 0.95.

[0080] (2) Anatase content The content of anatase-type crystals (anatase content) in titanium oxide particles was measured by the powder X-ray diffraction method. Specifically, for the dried titanium oxide particles, “X’pertPRO” (manufactured by PANalytical) was used as the measuring device, a copper target was used, Cu-Kα1 rays were used, and X-ray diffraction measurement was performed under the conditions of tube voltage 45 kV, tube current 40 mA, measurement range 2θ = 10 to 80 deg, sampling width 0.0167 deg, and scanning speed 0.0192 deg / s. The peak height (Ha) of the maximum peak corresponding to the anatase-type crystal, the peak height (Hb) of the maximum peak corresponding to the brookite-type crystal, and the peak height (Hr) of the maximum peak corresponding to the rutile-type crystal were obtained, and the content of anatase-type crystals (anatase content) in titanium oxide particles was obtained by the following calculation formula. Anatase content (%) = [Ha / (Ha + Hb + Hr)] × 100

[0081] (3) Chlorine (Cl) content The Cl content in titanium oxide particles was measured by potentiometric titration with silver nitrate. Specifically, 0.5 g of titanium oxide particles was weighed to prepare a solution. Then, a silver nitrate solution (concentration 0.02 mol / L) was added dropwise to this solution, and the potential difference was measured to determine the mass of chlorine atoms in the solution, and the chlorine content (mass ppm) was calculated.

[0082] (4) Content of other impurities The measurement methods for each impurity are as follows. Fe: Atomic absorption spectrometry (Z-2300 type atomic absorption spectrophotometer, Hitachi High-Tech Corporation) Al, Si: X-ray fluorescence analysis (XRF) (Simaltrex 10, Rigaku Corporation) C, S: High-frequency induction furnace combustion - infrared absorption method Na, Ni, Cr, Nb, Zr: Inductively coupled plasma - mass spectrometry

[0083] (Loss on ignition X) 10 g of titanium oxide particles were heated in an electric furnace under an air atmosphere maintained at 900 °C for 1 hour and then cooled to room temperature. The mass of the titanium oxide particles before and after the treatment was measured, and the loss on ignition X (mass %) was calculated from the following formula. Loss on ignition X = [(mass of titanium oxide particles before treatment - mass of titanium oxide particles after treatment) / mass of titanium oxide particles before treatment] × 100

[0084] (BET specific surface area (β) after treatment at 900 °C) 10 g of titanium oxide particles were heated in an electric furnace under an air atmosphere maintained at 900 °C for 1 hour and then cooled to room temperature. The BET specific surface area of the titanium oxide particles after treatment was measured according to (1) the BET specific surface area and determined as the BET specific surface area (β) (m 2 / g) after treatment at 900 °C.

[0085] (Mass change rate in a high-humidity atmosphere (20 °C 80% RH 5 hr)) 2 g of titanium oxide particles were placed in a 10-cm-diameter glass petri dish so that the thickness was uniform, and left standing in an air environment at 20 °C and a relative humidity of 80% for 5 hours. The mass change rate (mass %) based on the mass before standing was determined. Mass change rate in a high-humidity atmosphere = [(Mass change amount of titanium oxide particles before and after standing) / Mass of titanium oxide particles before standing] × 100

[0086] (D50 (SEM) of primary particles of titanium oxide particles by field emission scanning electron microscope) 1 g of the sample was put into 100 mL of ethanol and irradiated with ultrasonic waves (30 W, 5 min) to obtain a dispersion. The obtained dispersion was separated with a Pasteur pipette and about 0.05 g was dropped onto an aluminum foil. It was naturally dried in the laboratory atmosphere, the aluminum foil was fixed to the SEM sample stage, and measurement was carried out using a field emission scanning electron microscope (S-5500, Hitachi High-Technologies Corporation). The measurement condition of the SEM was an acceleration voltage of 2.0 kV. An image was taken such that the number of primary particles per field of view was 200 to 300, and the primary particle diameter (equivalent circle diameter, specifically Heywood diameter) of each of about 200 to 300 particles on the image was determined using image analysis software. As the image analysis software, Particle Analysis Ver3 (Sumitomo Metal Technology Corporation) and Mac-View Ver3 (Mountech Co., Ltd.) were used. The same operation was performed for another field of view of the same sample, and the same operation was repeated until the total number of particles used for calculating the primary particle diameter exceeded at least 1000. The D50 (SEM) of the particle size when the cumulative total value of the reference amount from the smaller particle size in the cumulative particle size distribution based on the obtained number was 50% of the total cumulative value was calculated.

[0087] (D50 (LD) and D90 (LD) by laser diffraction / scattering analysis method) In a 100 mL tall beaker, 0.05 g of titanium oxide particles, 50 mL of pure water, and 100 μL of a 10 mass% sodium hexametaphosphate aqueous solution were added to prepare a slurry. While stirring the slurry in the tall beaker using a φ8 mm polytetrafluoroethylene rod, ultrasonic waves were irradiated for 3 minutes (50 KHz, 100 W). Stirring was performed only for 1 minute from the start of ultrasonic irradiation. The ultrasonic bath was box-shaped with inner dimensions of 230 mm × 200 mm × 152 mm, and the amount of water was 450 mL. The position of the tall beaker during ultrasonic irradiation was near the center of the ultrasonic bath. The particle size distribution (volume integrated particle size distribution) of this slurry was measured using a laser diffraction particle size distribution measuring device (Microtrac MT3300EXII, Microtrac). D50 (LD) and D90 (LD) were calculated from the obtained particle size distribution.

[0088] (Particle concentration of coarse particles) Using a field emission scanning electron microscope (S-5500, Hitachi High-Technologies Corporation), an image was taken such that the number of primary particles per field of view was 8000 - 12000, and the presence or absence of particles with a specific dimension or more (200 nm or more, 300 nm or more, etc.) considering D50 (SEM) was confirmed using the particle measurement tool of the image analysis software. When there were particles corresponding to a specific dimension or more, the primary particle diameter (equivalent circle diameter, specifically the Heywood diameter) of those particles was determined using the image analysis software. The same operation was performed for another field of view of the same sample, and observations were made for fields of view corresponding to the observation of at least 1 million or more particles. The number of particles with a specific dimension or more described in Table 2 divided by the total number of all observed particles was determined as the particle concentration of coarse particles. The number of particles having a primary particle diameter exceeding 16 times D50 (SEM) divided by the total number of all observed particles was determined as the particle concentration of coarse particles having a primary particle diameter exceeding 16 times D50 (SEM).

[0089] Example 1 <Synthesis process> A vertical reaction tube with a circular cross-section was used as the reaction tube. Titanium tetrachloride diluted gas (G1) obtained by diluting 1053 mol / hr of gaseous titanium tetrachloride (purity of titanium tetrachloride ≥ 99.99 mass%) with 223 mol / hr of nitrogen gas was preheated to 950 °C, and an oxidizing gas (G2) obtained by mixing 22 mol / hr of nitrogen gas with 982 mol / hr of oxygen and 1786 mol / hr of steam was preheated to 900 °C, and these gases (G1 and G2) were introduced into the top of the reactor. In the reactor, the ratio (S1 / S2) of the cross-sectional area (S1) of the reaction tube to the total cross-sectional area (S2) of the outlets of the introduction pipes of the titanium tetrachloride diluted gas (G1) and the oxidizing gas (G2) was 6.7. A purge medium was introduced into the reaction tube from the side surface of the reaction tube so that the residence time in the high-temperature region of 800 °C or higher and less than 1200 °C was 0.05 seconds, and a cooling medium was introduced into the cooling region so that the residence time in the region of 500 °C or higher was 0.6 seconds, and the passed raw material titanium oxide particles were collected at the lower part of the reaction tube by a polytetrafluoroethylene bag filter. Air was used as the purge medium and the cooling medium. The conditions of the synthesis step and the dechlorination step are shown in Table 1. The flow velocity (A) (m / s) of the reaction gas stream was calculated from the cross-sectional area (m 2 ) of the reaction tube and the calculated value of the flow rate (m 3 / s) of the reaction gas stream after the raw material gas and the oxidizing gas reacted.

[0090] <Dechlorination step> The obtained raw material titanium oxide particles were passed through a cylindrical rotary heating furnace for dechlorination treatment. Specifically, using steam mixed with air, dechlorination treatment was carried out for 120 minutes under the conditions that the mass ratio of steam to raw material titanium oxide particles (mass of steam / mass of raw material titanium oxide particles) was 0.06 and the temperature was 450 °C (the first dechlorination step), and then, using steam mixed with air, dechlorination treatment was carried out for 20 minutes under the conditions that the mass ratio of steam to raw material titanium oxide particles (mass of steam / mass of raw material titanium oxide particles) was 0.04 and the temperature was 70 °C (the second dechlorination step), and titanium oxide particles were obtained. Various physical properties of the obtained titanium oxide particles were measured. The results of the physical property evaluation are shown in Table 2.

[0091] Examples 2 to 3 Titanium oxide particles were obtained in the same manner as in Example 1 except that the conditions described in Table 1 were used. The physical property evaluation results are shown in Table 2.

[0092] Comparative Examples 1 to 6 Titanium oxide particles were obtained in the same manner as in Example 1 except that the conditions described in Table 1 were used. The physical property evaluation results are shown in Table 2. In Comparative Examples 1 to 3, there was no introduction of a purge medium in the reaction step and no second dechlorination step was carried out. In Comparative Examples 4 to 9, no second dechlorination step was carried out.

[0093]

Table 1-1

Table 1-2

[0094]

Table 2-1

Table 2-2

Table 2-3

[0095] In the titanium oxide particles of Comparative Examples 1 to 3, since there was no introduction of a purge medium in the reaction step, there were many coarse particles, and further, since there was no second dechlorination step, the Cl content was high. In Comparative Examples 4 to 6, since a purge medium was introduced in the reaction step, the generation of coarse particles was suppressed and the Cl content could be reduced to a certain extent, but it was not sufficient. In Comparative Examples 7 to 9, by introducing a purge medium in the reaction step and further doubling the treatment time of the first dechlorination step compared to Comparative Examples 4 to 6, the Cl content could be sufficiently reduced, but the loss on ignition X decreased significantly, and as a result, the mass change rate in a high-humidity atmosphere increased. In Examples 1 to 3, following the first dechlorination step, a second dechlorination step was carried out, and it was possible to reduce the Cl content and reduce the mass change rate in a high-humidity atmosphere.

Explanation of Symbols

[0096] 1 Reaction tube 3 Cooling medium outlet 4 Reaction tube center 5 Purge medium outlet G1 Feed gas G2 Oxidizing gas P Purge medium Q Cooling medium α Blowing angle of the purge medium (in the plane perpendicular to the flow direction of the reaction gas) β Blowing angle of the purge medium (in the plane including the flow direction of the reaction gas) γ Blowing angle of the cooling medium (in the plane perpendicular to the flow direction of the reaction gas) δ Blowing angle of the cooling medium (in the plane including the flow direction of the reaction gas)

Claims

1. A reaction step of introducing a raw material gas (G1) containing titanium tetrachloride and an inert gas and an oxidizing gas (G2) containing at least one of oxygen gas and water vapor and an inert gas into a reaction tube to generate a reaction gas, A cooling step of introducing a cooling medium to cool the reaction gas to obtain raw material titanium oxide particles, A first dechlorination step of heating at 300 ° C or higher and 600 ° C or lower while bringing the raw material titanium oxide particles into contact with water vapor, wherein the mass ratio of water to the raw material titanium oxide particles (mass of water / mass of raw material titanium oxide particles) is 0.01 or more, the first dechlorination step, A second dechlorination step of heating at 30 ° C or higher and less than 100 ° C while bringing the raw material titanium oxide particles that have undergone the first dechlorination step into contact with water vapor, wherein the mass ratio of water to the raw material titanium oxide particles (mass of water / mass of raw material titanium oxide particles) is 0.01 or more, the second dechlorination step, A method for producing titanium oxide particles including

2. The method for producing titanium oxide particles according to claim 1, wherein the mass ratio of water to the raw material titanium oxide particles (mass of water / mass of raw material titanium oxide particles) in the first dechlorination step and the second dechlorination step is 0.04 or more.

3. The method for producing titanium oxide particles according to claim 1 or 2, wherein the heating temperature in the first dechlorination step is 410 ° C or higher and 550 ° C or lower.

4. A purge medium outlet is provided on the inner wall or upper part of the reaction tube. In the cross section of the reaction tube perpendicular to the central axis of the reaction tube, with respect to the line connecting the purge medium outlet and the central axis of the reaction tube, the blowing angle α of the purge medium is 50 ° or more, and the blowing flow rate of the purge medium is 35 m / s or more. The method for producing titanium oxide particles according to claim 1 or 2.

5. The method for producing titanium oxide particles according to claim 1 or 2, wherein the ratio (S1 / S2) of the cross-sectional area (S1) of the inlet of the reaction tube to the total cross-sectional area (S2) of the outlets of the introduction pipes of the raw material gas (G1) and the oxidizing gas (G2) is 1.0 or more and 10.0 or less.

6. The BET specific surface area is 15 to 100 m ２ / g, the anatase content is 70% or more, and the Cl content is 2000 mass ppm or less, and When the BET specific surface area is α (m ２ / g), and the mass reduction rate when calcined in an electric furnace maintained at 900 °C for 1 hour is defined as the loss on ignition X (mass %), titanium oxide particles in which the loss on ignition X satisfies the formula (1). 2.1 × {[(α × 1.3 / (6 × 10 ４ ))] × 18 + [((α × 1.3 - β) / (6 × 10 ４ ))] × 9} × 100 ≥ X ≥ 0.60 × {[(α × 1.3 / (6 × 10 ４ ))] × 18 + [((α × 1.3 - β) / (6 × 10 ４ ))] × 9} × 100... (1) In formula (1), β represents the BET specific surface area (m ２ / g) of the powder after calcination in an electric furnace maintained at 900 °C for 1 hour.

7. The titanium oxide particles according to claim 6, wherein D90 (LD) / D50 (LD) measured by the laser diffraction / scattering analysis method is more than 1.0 and 2.0 or less, and the particle concentration (number basis) of coarse particles having a primary particle diameter exceeding 16 times D50 (SEM) of the primary particles observed by a field emission scanning electron microscope is 20 ppm or less.

8. The titanium oxide particles according to claim 6, wherein D90 (LD) is 3000 nm or less and D50 (LD) is 1000 nm or less.

9. The titanium oxide particles according to claim 6, wherein the contents of Na, Al, S, Fe, Ni, Cr, Nb and Zr are each 50 mass ppm or less, and the contents of Si and C are each 500 mass ppm or less.

10. A slurry containing the titanium oxide particles according to any one of claims 6 to 9.

11. A dispersion containing the titanium oxide particles according to any one of claims 6 to 9.

12. A composition containing the titanium oxide particles according to any one of claims 6 to 9.

13. A dielectric raw material containing the titanium oxide particles according to any one of claims 6 to 9.

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