Titanium oxide particles and method for producing the same

Abstract

To provide titanium oxide particles with few coarse particles and excellent homogeneity and dispersibility, a method for their production, and a slurry, a dispersion, a composition and a dielectric starting material that comprise the titanium oxide particles.SOLUTION: The titanium oxide particles are such that D90 (LD) / D50 (LD) of the titanium oxide particles as measured by laser diffraction / scattering analysis is greater than 1.0 and less than or equal to 2.0, and the concentration of coarse particles whose primary particle size exceeds 16 times D50 (SEM) of primary particles as observed under a field emission scanning electron microscope is 20 ppm or less (based on the number of particles). For their production, a source gas and oxidizing gas are introduced into a reaction tube and reacted, where a blowing outlet of a purge medium is provided on the inner wall of the reaction tube, and where the blowout angle of the purge medium and the blowout flow velocity (B) of the purge medium from the inner wall of the reaction tube are introduced such that the purge medium swirls along the inner wall of the reaction tube.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to titanium oxide particles, a method for producing the same, and a slurry, a dispersion, a composition, and a dielectric raw material containing the titanium oxide particles.

Background Art

[0002] The industrial application fields of titanium oxide are extremely wide, represented by cosmetics, ultraviolet ray shielding materials, additives to silicone rubber, and in recent years, applications cover a wide range, such as photocatalysts, solar cells, dielectric raw materials, electrode material raw materials for Li-ion batteries, etc. 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 this specification.

[0003] Recently, titanium oxide has attracted particular attention as a raw material for high-performance dielectrics, for example, as a raw material for BaTiO3. BaTiO3 can be obtained by the following reaction under heating. BaCO3 + TiO2 → BaTiO3 + CO2 The above reaction is a solid-phase reaction. At that time, first, BaCO3 decomposes at a high temperature to generate BaO, and it is said that BaO diffuses and solid-solves in TiO2 particles to become BaTiO3. Therefore, the size of BaTiO3 particles is controlled by the size of TiO2 particles. In recent years, with the miniaturization of multilayer ceramic capacitors, the thinning of the dielectric layer has become a problem, and for this purpose, the micronization and uniformization of BaTiO3 particles are essential. Also, if there are BaTiO3 particles larger than the dielectric layer thickness, a short circuit occurs in the multilayer ceramic capacitor, leading to equipment failure. Therefore, it is necessary to micronize and uniformize TiO2, which is a raw material for BaTiO3, and it is preferable that no coarse TiO2 particles are contained. Similarly, in other applications, titanium oxide particles are required to be micronized and uniformized, and it is better that no coarse particles are contained.

[0004] The manufacturing methods of titanium oxide can be roughly classified into a liquid-phase method in which titanium tetrachloride or titanium sulfate is hydrolyzed, and a gas-phase method in which titanium tetrachloride is reacted with oxygen or water vapor at a high temperature.

[0005] The liquid-phase method has the advantage that titanium oxide can be produced under relatively mild conditions and fine primary particles are easily obtained. However, since titanium oxide is obtained in the form of a sol or slurry, there is a problem that its applications are limited when used in this state. In order to use the sol or slurry as titanium oxide particles, it is necessary to dry them, and after drying, aggregation generally becomes intense. Titanium oxide particles with such intense aggregation have a problem that the particle size distribution becomes non-uniform. There is also a problem that the dispersibility is poor when the titanium oxide particles obtained by drying are dispersed in a solvent. If the dispersibility is poor, when mixing raw materials for the production of the above-mentioned BaTiO3, the titanium oxide particles and other raw materials are not sufficiently mixed, resulting in uneven distribution of the raw material components, causing non-uniform growth during the reaction, and variations in quality and the like.

[0006] On the other hand, according to the gas-phase method, the primary particle diameter of the produced titanium oxide can be adjusted by adjusting manufacturing conditions such as temperature. Also, since no solvent is used in the gas-phase method, titanium oxide is obtained as a powder, and the problems mentioned in the liquid-phase method rarely occur. Furthermore, in the gas-phase method, since the reaction is carried out at a relatively higher temperature than in the liquid-phase method, the resulting titanium oxide has a characteristic of high crystallinity.

[0007] However, in the gas-phase method, since the reaction is carried out at a higher temperature than in the liquid-phase method, in the reaction tube or in the cooling tube after introducing the cooling medium, if the heat quantity received by the titanium oxide particles is large, such as the temperature being too high or the residence time of the titanium oxide particles being too long, sintering between the titanium oxide particles proceeds excessively, making it difficult to obtain fine particles of titanium oxide and resulting in a non-uniform particle size distribution. If the temperature of the reaction zone is lowered too much to avoid sintering between titanium oxide particles, nucleation of titanium oxide is not sufficiently carried out, and it is difficult to obtain fine particles or only titanium oxide with low crystallinity can be obtained. On the other hand, by immediately cooling the reaction gas with a cooling medium, sintering between titanium oxide particles can be suppressed, and fine particles of titanium oxide can be obtained. If cooling is not carried out immediately or if there is unevenness in cooling, sintering between particles occurs unevenly, and it is difficult to obtain uniform titanium oxide fine particles.

[0008] Patent Document 1 describes a method for producing titanium oxide particles, which comprises reacting a titanium halide gas and an oxidizing gas under specific conditions for the purpose of obtaining uniform titanium oxide particles by the gas-phase method.

[0009] Further, Patent Document 2 describes a method for producing titanium oxide particles, which comprises reacting TiCl4 vapor and an oxidizing agent for the purpose of obtaining uniform titanium oxide particles without coarse particles by the gas-phase method, introducing the oxidizing agent into the reaction tube in a laminar flow to suppress scale formation in the reaction tube, and having few metal oxide particles with a diameter larger than 100 nm.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0011] As described above, titanium oxide particles with excellent uniformity and dispersibility are desired. However, compared with titanium oxide particles obtained by the liquid phase method, the gas phase method has the advantage of being superior in uniformity and dispersibility. Therefore, the present inventors have been studying to produce titanium oxide particles based on the gas phase method and to produce titanium oxide particles with even better uniformity and dispersibility. However, it has been found that even when producing titanium oxide fine particles with excellent uniformity and dispersibility by the gas phase method, the titanium oxide particles may become significantly coarsened, and there is a problem that the mixing of coarse particles into the titanium oxide fine particles cannot be avoided.

[0012] The present invention has been made to solve the above problems, and an object of the present invention is to provide titanium oxide fine particles having excellent uniformity and dispersibility and few coarse particles in the gas phase method and a method for producing the same, and to provide a slurry, a dispersion, a composition, and a dielectric raw material containing the titanium oxide particles.

Means for Solving the Problems

[0013] As a result of intensive studies in view of the above problems, the present inventors have found that in Patent Document 1, no measures have been taken regarding the adhesion of titanium oxide to the reaction tube wall, and the adhesion of titanium oxide to the reaction tube wall has occurred, and coarse particles in which sintering has progressed due to the adhesion and retention of titanium oxide powder to the reaction tube wall are included. In Patent Document 2, since the Reynolds number of the oxidizing gas must be reduced, problems in productivity and quality such as poor raw material mixability, low conversion rate, and easy non-uniformity of particle size occur. And in the step of producing titanium oxide particles by reacting a gas containing titanium tetrachloride and an inert gas and a gas containing an oxidizing gas in a reaction tube, after introducing the gas containing titanium tetrachloride and the gas containing an oxidizing gas into the reaction tube and reacting them, by introducing a purge medium along the tube wall under specific conditions, it is possible to suppress the adhesion of powder to the tube wall and produce titanium oxide particles having excellent uniformity and preferably dispersibility and few coarse particles, thus completing the present invention.

[0014] According to the present invention, at least the following aspects are provided, but are not limited thereto. (Aspect 1) Titanium oxide particles in which D90(LD) / D50(LD) in titanium oxide particles measured by laser diffraction / scattering analysis is more than 1.0 and 2.0 or less, and the coarse particle concentration (number basis) exceeding 16 times of D50(SEM) of primary particles observed by a field emission scanning electron microscope is 20 ppm or less. (Aspect 2) The titanium oxide particles according to Aspect 1, wherein D90(SEM) / D50(SEM) in the primary particles of the titanium oxide particles observed by a field emission scanning electron microscope is more than 1.0 and 2.0 or less. (Aspect 3) The titanium oxide particles according to Aspect 1 or 2, wherein [D90(SEM) - D10(SEM)] / D50(SEM) in the primary particles of the titanium oxide particles observed by a field emission scanning electron microscope is 0.82 or less. (Aspect 4) The titanium oxide particles according to any one of Aspects 1 to 3, wherein D99(SEM) / D50(SEM) in the primary particles of the titanium oxide particles observed by a field emission scanning electron microscope is more than 1.0 and 2.0 or less. (Aspect 5) The titanium oxide particles according to any one of Aspects 1 to 4, wherein D90(DLS) / D50(DLS) in titanium oxide particles measured by dynamic light scattering method is more than 1.0 and 2.0 or less. (Aspect 6) The titanium oxide particles according to any one of Aspects 1 to 5, wherein D90(DLS) / D90(SEM), which is the ratio of D90(DLS) in the primary particles of titanium oxide particles measured by dynamic light scattering method to D90(SEM) in titanium oxide particles observed by a field emission scanning electron microscope, is 2.2 or less. (Aspect 7) The titanium oxide particles according to any one of Aspects 1 to 6, wherein D90(LD) in titanium oxide particles measured by laser diffraction / scattering analysis is 3000 nm or less. (Aspect 8) The titanium oxide particles according to any one of Aspects 1 to 7, wherein D90 (DLS) of the titanium oxide particles measured by the dynamic light scattering method and D90 (SEM) of the primary particles of the titanium oxide particles observed by a field emission scanning electron microscope are 200 nm or less, and D50 (SEM) is 10 to 150 nm. (Aspect 9) The titanium oxide particles according to any one of Aspects 1 to 8, wherein the anatase content is 70% or more. (Aspect 10) The BET specific surface area is 5 to 200 m 2 / g, and the titanium oxide particles according to any one of Aspects 1 to 9. (Aspect 11) The titanium oxide particles according to any one of Aspects 1 to 10, wherein the Cl content of the titanium oxide particles measured by the silver nitrate potentiometric titration method is 0.2% or less. (Aspect 12) The titanium oxide particles according to any one of Aspects 1 to 11, wherein the contents of Na, Al, S, Fe, Ni, Cr, Nb, and Zr are each 10 mass ppm or less, and the contents of Si and C are each 500 mass ppm or less. (Aspect 13) In the step of producing titanium oxide particles by introducing a raw material gas containing titanium tetrachloride and an inert gas, an oxidizing gas containing at least one of oxygen gas and water vapor and an inert gas into a reaction tube, reacting them, and then cooling, a purge medium outlet is provided on the inner wall of the reaction tube, the purge medium is introduced so as to swirl along the inner wall of the reaction tube, and in a plane projected onto a cross section of the reaction tube perpendicular to the axis of the reaction tube, with respect to a line connecting the purge medium outlet and the central axis of the reaction tube, the blowout angle α of the purge medium from the inner wall of the reaction tube is 50° or more, and the blowout flow rate (B) of the purge medium is 35 m / s or more. A method for producing titanium oxide particles. (Aspect 14) In a plane projected onto a longitudinal section of the reaction tube including the axis of the reaction tube, with respect to the axial direction of the reaction tube, the blowout angle β of the purge medium from the inner wall of the reaction tube is 60° or more with the forward side of the reaction gas flow as 0°, and the method for producing titanium oxide particles according to Aspect 13. (Aspect 15) The method for producing titanium oxide particles according to aspect 13 or 14, wherein when the flow rate of the reaction gas formed from the raw material gas and the oxidizing gas in the reaction tube is A and the blowing flow rate of the purge medium is B, the purge medium is introduced so that B / A is 0.5 or more. (Aspect 16) A slurry containing titanium oxide particles according to any one of aspects 1 to 12. (Aspect 17) A dispersion containing titanium oxide particles according to any one of aspects 1 to 12. (Aspect 18) A composition containing titanium oxide particles according to any one of aspects 1 to 12. (Aspect 19) A dielectric raw material containing titanium oxide particles according to any one of aspects 1 to 12. [Advantages of the Invention]

[0015] According to the present invention, it is possible to provide titanium oxide particles having excellent uniformity, more preferably excellent dispersibility, and few coarse particles, a method for producing the same, and a slurry, a dispersion, a composition, and a dielectric raw material containing the titanium oxide. [Brief Description of the Drawings]

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

[0017] Unless otherwise specified or unless it is suggested from the context that the numerical values of various measurements in this specification have different meanings, the defined numerical values are determined considering significant figures. For example, 0 ppm means less than 0.5 ppm.

[0018] In this specification, D10, D50, D90, and D99 in D10(SEM), D50(SEM), D90(SEM), D99(SEM), D50(LD), D90(LD), D50(DLS), and D90(DLS) mean the particle size (particle diameter) when the cumulative total value of the reference amount from the smaller particle size in each cumulative particle size distribution is 10%, 50%, 90%, and 99% of the total cumulative value, respectively, based on numbers, volumes, masses, mole numbers, etc. SEM represents measurement by a field emission scanning electron microscope, LD represents measurement by a laser diffraction / scattering analysis method, and DLS represents measurement by a dynamic light scattering method.

[0019] In the field of fine particles such as in the present invention, as described later, it is desirable to perform SEM observation, laser diffraction / scattering analysis method measurement, and dynamic light scattering method measurement respectively, and comprehensively judge the uniformity and dispersibility of titanium oxide particles.

[0020] [Titanium Oxide Particles] The titanium oxide particles in one embodiment of the present invention are titanium oxide particles characterized in that D90(LD) / D50(LD) of the titanium oxide particles measured by the laser diffraction / scattering analysis method is more than 1.0 and 2.0 or less, and the coarse particle concentration (number basis) exceeding 16 times of D50(SEM) is 20 ppm or less. Such titanium oxide particles are excellent in uniformity and dispersibility and can be preferably produced by the method for producing titanium oxide particles described later.

[0021] If D90(LD) / D50(LD) of the titanium oxide particles measured by the laser diffraction / scattering analysis method is more than 1.0 and 2.0 or less, the particle size of the titanium oxide particles is excellent in uniformity, preferably 1.8 or less, more preferably 1.6 or less, and most preferably 1.5 or less. If it is 2.0 or less, it is preferable because the particle size distribution is uniform. Also, it can be 1.1 or more. When the coarse particle concentration exceeding 16 times of D50(SEM) is 20 ppm or less, there are few coarse particles of titanium oxide particles. Titanium oxide particles with uniform particle size and few coarse particles are more excellent in the quality and uniformity required for titanium oxide particles, and thus are excellent and useful in a wide range of applications such as cosmetics, ultraviolet ray shielding materials, additives for silicone rubber, photocatalysts, solar cells, dielectric raw materials, electrode material raw materials for Li ion batteries, etc.

[0022] · D50 (LD), D90 (LD) by laser diffraction / scattering method Titanium oxide particles generally often form secondary particles in which their primary particles are aggregated. The particle sizes D50 and D90 in the aggregated state (aggregate of primary particles and secondary particles) of titanium oxide particles are measured by a laser diffraction particle size distribution analyzer (in this specification, the above D50 and D90 are referred to as D50(LD) and D90(LD), respectively). In addition, according to the "Ultra-fine Particle Handbook" supervised by Shinsuke Saito, Fuji Techno System, p93, (1990), the measurement methods of the particle size distribution of particles include sedimentation method, microscopy method, laser diffraction / scattering analysis method (light scattering method), direct counting method, etc. Among these, the sedimentation method and the direct counting method are applicable to particles with a measurable particle size of several hundred nm or more, and are not suitable for measuring the particle size distribution of fine particles with a particle size of 100 nm or less. Also, the measurement value of the microscopy method may vary depending on the sampling of the target sample and the pretreatment of the sample, and it cannot be said to be a preferable measurement method. 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. The details of the measurement procedure of the particle size distribution by the laser diffraction / scattering analysis method (light scattering method) will be described in the examples.

[0023] The D50(LD) of the titanium oxide particles in one embodiment of the present invention is preferably 1000 nm or less, more preferably 500 nm or less. D50(LD) corresponds to the effective diameter (aggregation diameter) when dissolved in a solvent, and the finer the numerical value, the better the dispersibility.

[0024] Also, if the value of D90(LD) is small, it is determined that the cohesive force of the titanium oxide particles is weak and they exhibit good dispersibility in the solvent. The D90(LD) of the titanium oxide particles in one embodiment of the present invention is preferably 3000 nm or less, more preferably 2000 nm or less, still more preferably 1000 nm or less, and even more preferably 600 nm or less.

[0025] · D10 (SEM), D50 (SEM), D90 (SEM), D99 (SEM) of primary particles of titanium oxide particles by field emission scanning electron microscope In one embodiment of the present invention, it is preferable that D90(SEM) / D50(SEM) of the primary particles of the titanium oxide particles observed by a field emission scanning electron microscope is more than 1.0 and 2.0 or less. When it is more than 1.0 and 2.0 or less, the particle size uniformity can be excellent even in the slurried and dispersed titanium oxide particles. From the same viewpoint, D90(SEM) / D50(SEM) is preferably more than 1.2, more preferably 1.3 or more, 1.4 or more, and even more preferably 1.5 or more. Details of the measurement procedure will be described in the examples.

[0026] In one embodiment of the present invention, if the value of D99(SEM) / D50(SEM) of the primary particles of the titanium oxide particles observed by a field emission scanning electron microscope is small, it is determined that they have a uniform particle size distribution of the primary particles. The value of D99(SEM) / D50(SEM) of the titanium oxide particles may be more than 1.0 and 2.0 or less, preferably 1.9 or less, more preferably 1.8 or less, and most preferably 1.7 or less. If it is 2.0 or less, it is preferable because the particle size distribution is uniform. Also, it may be 1.1 or more.

[0027] As described above, D90(SEM) / D50(SEM) is used as an index of the uniformity of the particle size distribution for particles larger than D50(SEM). However, as an index for evaluating the uniformity of the entire particle size distribution including particles finer than D50(SEM) to larger particles, [D90(SEM) - D10(SEM)] / D50(SEM) may be used, which is also applicable in the present disclosure. The smaller the value, the more it is judged to have a uniform particle size distribution. [D90(SEM) - D10(SEM)] / D50(SEM) in one embodiment of the present invention is preferably 0.82 or less, more preferably 0.80 or less. Further, [D90(SEM) - D10(SEM)] / D50(SEM) may be 0.75 or less, 0.71 or less.

[0028] D50(SEM) of the titanium oxide particles in one embodiment of the present invention is preferably 10 to 100 nm, more preferably 10 to 50 nm, still more preferably 10 to 30 nm. Such titanium oxide particles are suitable for applications such as photocatalysts, solar cells, and dielectrics that require a submicron particle size.

[0029] Also, when the value of D90(SEM) is small, the number of particles larger than D90(SEM) is limited. Therefore, D90(SEM) of the titanium oxide particles in one embodiment of the present invention is preferably 200 nm or less, more preferably 100 nm or less, still more preferably 50 nm or less.

[0030] · D50 (DLS), D90 (DLS) by dynamic light scattering method The titanium oxide particles to be measured are disintegrated, and D50 and D90 of the titanium oxide particles are measured by the dynamic light scattering method (in this specification, the above D50 and D90 are referred to as D50(DLS) and D90(DLS), respectively). D50(DLS) and D90(DLS) are measured by a dynamic light scattering particle size distribution apparatus. Here, disintegration refers to a process of separating secondary particles without destroying primary particles, which is different from a pulverization process in which primary particles are destroyed. The particle size distribution of these disintegrated particles is an index indicating the disintegratability and dispersibility of secondary particles, but reflects the bonding state between primary particles and the ease of dissociation of aggregated particles.

[0031] The disintegration treatment may be performed by a method similar to the grinding treatment (especially ball mill treatment), but in order to separate the secondary particles without destroying the primary particles, the size and weight of the balls and the treatment time are adjusted. For D50 (DLS) and D90 (DLS) by the dynamic light scattering method, 300 ml of pure water is added to 100 g of titanium oxide particles, and 5% of a polycarboxylic acid type polymer dispersant (100% ammonium salt of acrylic acid polymer) per weight of titanium oxide is added as a dispersant to make a slurry. This slurry is charged into a 1 L ball mill container (made of polypropylene, dimensions φ92 mm × 198 mm), 1.2 kg of zirconia balls with a diameter of 0.5 mm (YTZ balls made by Nikkato) are added, placed on the base of the ball mill, and rotated at 7 rpm for 72 hours to obtain a titanium oxide slurry after disintegration. The titanium oxide slurry thus obtained is measured for the particle size distribution (volume integrated particle size distribution) by a dynamic light scattering method particle size distribution measuring device. As the particle size distribution measuring device, for example, ELS-Z made by Otsuka Electronics Co., Ltd. may be used. In addition, when grinding occurs during the disintegration treatment, since the primary particle diameter of titanium oxide in the slurry becomes smaller and the BET specific surface area (m 2 / g) increases, it can be confirmed that there is no significant difference between the BET specific surface area obtained by measuring the titanium oxide powder obtained by drying the slurry after disintegration treatment at 100 °C or lower with a BET specific surface area measuring device and the BET specific surface area of the titanium oxide powder before the disintegration treatment. Here, the significant difference means a difference in the BET specific surface area of the titanium oxide powder before and after the disintegration treatment that exceeds the range of the variation deviation during measurement. As the BET specific surface area measuring device, for example, a specific surface area measuring device (Macsorb) made by Mountech Co., Ltd. may be used. The details of the measurement procedure will be described in the examples.

[0032] If the value of D90(DLS) / D50(DLS) is small, it is determined that the titanium oxide particles have a uniform particle size distribution. Therefore, in one embodiment of the present invention, D90(DLS) / D50(DLS) of the titanium oxide particles is preferably more than 1.0 and 2.0 or less, more preferably 1.8 or less, still more preferably 1.7 or less, and most preferably 1.6 or less. If it is 2.0 or less, it is preferable because the particle size distribution is uniform. Also, it may be 1.1 or more.

[0033] If the value of D90(DLS) is small, it can be determined that the cohesive force of the titanium oxide particles is weak and the dispersibility is good. Therefore, in one embodiment of the present invention, D90(DLS) of the titanium oxide particles is preferably 500 nm or less, more preferably 300 nm or less, still more preferably 200 nm or less, and most preferably 100 nm.

[0034] In one embodiment of the present invention, it is preferable that both the values of D90(DLS) and D90(SEM) are 200 nm or less, more preferably 100 nm or less. In one embodiment of the present invention, the value of D90(DLS) / D90(SEM) is preferably 2.2 or less, and may be 1.1 or more and 2.0 or less. If it is 2.2 or less, it indicates that the proportion of secondary particles that are easily dispersed is large, and short - circuit is less likely to occur when used as the dielectric of a multilayer ceramic capacitor. The value of D90(DLS) / D90(SEM) is more preferably 2.1 or less, and even more preferably 2.0 or less.

[0035] In one embodiment of the present invention, D50(DLS) of the titanium oxide particles is preferably 10 - 150 nm, more preferably 10 - 100 nm, still more preferably 10 - 65 nm. The smaller D50(DLS) is, the more likely it is to be well - dispersed in the affinity solvent.

[0036] · Particle concentration of titanium oxide coarse particles Coarse particles in titanium oxide particles are defined by the size of the primary particles measured by a field emission scanning electron microscope (SEM), and the content of titanium oxide coarse particles is also measured by a field emission scanning electron microscope. Details of the measurement procedure are described in the examples.

[0037] Coarse primary particles and aggregated particles (secondary particles) should be distinguished by appearance. For example, coarse particles have an appearance as shown in the central part of Fig. 1(a). Particles composed of fine primary particles gathered as shown in Fig. 1(b) are regarded as aggregated particles and are not counted as coarse particles. When it is difficult to determine whether it is a coarse particle or an aggregated particle, it is desirable to increase the observation magnification to an extent that is easy to distinguish.

[0038] In this specification, coarse particles of titanium oxide refer to particles whose primary particle diameter measured by the above measurement method exceeds 16 times D50(SEM). The titanium oxide particles in one embodiment of the present invention are titanium oxide particles in which the particle concentration (number basis) exceeding 16 times D50(SEM) is 20 ppm or less, more preferably 10 ppm or less, and even more preferably 5 ppm or less.

[0039] The dielectric thickness of multilayer ceramic capacitors is said to be less than 1 μm for the most advanced ones. In one embodiment, it is desirable that titanium oxide contains as few particles of a specific size or more as possible. Generally, in the dielectric layer inside a multilayer ceramic capacitor, in a dielectric layer containing coarse particles, the insulation resistance tends to be lower than that in a dielectric layer not containing coarse particles, and a failure (short circuit) due to poor insulation is likely to occur. Thus, a low content concentration of coarse particles of a specific size or more can be a preferable characteristic in various applications of titanium oxide.

[0040] · Anatase content As described in Patent Document 1, in terms of photoelectrochemical activity, anatase-type titanium oxide is preferred. The anatase content (molar basis) of titanium oxide in one embodiment of the present invention is preferably 70% or more, more preferably 75% or more, and even more preferably 95% or more. If it is 70% or more, it is preferable because the photoelectrochemical activity is sufficiently exhibited. Here, the anatase content refers to the content of anatase-type crystals in titanium oxide.

[0041] · BET specific surface area The BET specific surface area (m 2 / g) of titanium oxide particles in one embodiment of the present invention is preferably 5 to 200 m 2 / g, more preferably 10 to 150 m 2 / g, and even more preferably 20 to 100 m 2 / g from the viewpoint of obtaining titanium oxide particles with excellent uniformity and dispersibility. If the BET specific surface area is larger than 5 m 2 / g, it is preferable because fine particles can be obtained. If the BET specific surface area is smaller than 200 m 2 / g, it is preferable because those with a suitable BET specific surface area can be obtained.

[0042] · Chlorine (Cl) content If the Cl (chlorine atom) concentration of titanium oxide particles in one embodiment of the present invention is 0.20 mass% or less, it is preferable because there are few problems in the subsequent process when using the titanium oxide particles as a raw material. For example, when titanium oxide particles with a Cl concentration exceeding 0.20 mass% are used as a raw material for BaTiO3 or the like, it causes flux during firing. The molten flux tends to localize, and there is more aggregation in the localized part, resulting in quality variations between other parts. Also, when the particles aggregate, the crystals of BaTiO3 particles grow into abnormal particles, which also reduces the dielectric properties of BaTiO3. From this viewpoint, the Cl content in titanium oxide particles is more preferably 0.15 mass% or less, and even more preferably 0.10 mass% or less.

[0043] · Content of other impurities In one embodiment of the present invention, the contents of Na, Al, S, Fe, Ni, Cr, Nb and Zr in the titanium oxide particles are preferably 50 ppm by mass or less, more preferably 10 ppm by mass or less. Also, the contents of Si and C in the titanium oxide particles are preferably 500 ppm by mass or less, more preferably 100 ppm by mass or less. When there are few impurities in this way, there are few problems in the subsequent processes when using the titanium oxide as a raw material. For example, when a dielectric is obtained using the titanium oxide particles as a raw material, it is suppressed that the dielectric properties deteriorate due to the presence of impurities. Further, when the titanium oxide particles are used for applications such as photocatalysts or solar cells, 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 prevented or suppressed.

[0044] The titanium oxide particles of the present disclosure preferably have a titanium oxide content of 99.0% by mass or more, more preferably 99.9% by mass or more. As a result, the purity is increased and the influence of the above impurities is small.

[0045] [Slurry, dispersion, composition and dielectric raw material] The slurry, dispersion, composition, and dielectric raw material in one embodiment of the present invention contain the aforementioned titanium oxide particles. A slurry is a mixture in which particles are mixed in a liquid, and often refers to a highly viscous (gooey) fluid. A dispersion generally refers to a mixture in which solid particles are dispersed in a liquid, including those with low concentrations. A composition refers to a composition composed of multiple 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. Note that other uses of the slurry, dispersion, and composition containing titanium oxide particles are known. For the method of manufacturing a slurry, dispersion, composition, and dielectric raw material using the titanium oxide particles of the present disclosure, known methods can be used. The slurry, dispersion, composition, and dielectric raw material containing titanium oxide particles of one embodiment in one embodiment of the present invention do not contain coarse particles, so the uniformity and quality of the final product can be excellent. In particular, in the thinning of the dielectric film of a multilayer ceramic capacitor, the absence of coarse particles prevents short circuits and contributes to quality improvement. In one example of a multilayer ceramic capacitor, it is desirable to minimize the number of coarse particles of 0.7 μm or more, and further 0.5 μm or more.

[0046] [Method for Producing Titanium Oxide Particles] A method for producing titanium oxide particles according to one embodiment of the present invention is shown. In the production method of one embodiment of the present invention, in the step of producing titanium oxide particles by 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, reacting them, and then cooling, a purge medium outlet is provided on the inner wall of the reaction tube, and the purge medium is introduced so as to swirl along the inner wall of the reaction tube. In a plane projected onto a cross-section of the reaction tube perpendicular to the axis of the reaction tube, the blowing angle α of the purge medium from the inner wall of the reaction tube with respect to the line connecting the purge medium outlet and the central axis of the reaction tube is 50° or more, and the blowing flow rate (B) of the purge medium is 35 m / s or more.

[0047] By setting the blowing angle α of the purge medium from the inner wall of the reaction tube to 50° or more and the blowing flow rate (B) of the purge medium to 35 m / s or more, the purge medium can be introduced while swirling along the reaction tube wall in the reaction tube, promoting the formation of a purge medium layer near the reaction tube wall, preventing titanium oxide powder from adhering and staying on the tube wall surface, and suppressing the sintering of titanium oxide.

[0048] The method for producing titanium oxide particles according to an embodiment of the present invention will be described in more detail below. (Raw material gas G1) The raw material gas G1 contains titanium tetrachloride and an inert gas. From the viewpoint of economy, the supply rate of titanium tetrachloride is preferably 100 mol / hr or more, more preferably 200 mol / hr or more. From the viewpoint of suppressing the growth of sintered particles due to reaction heat, it is preferably 5000 mol / hr or less, more preferably 3000 mol / hr or less, and even more preferably 2000 mol / hr or less. In the raw material gas G1, the content of the inert gas relative to 1 mol of titanium tetrachloride is preferably 0.01 mol or more, more preferably 0.1 mol or more, and even more preferably 1 mol or more from the viewpoint of keeping the particle size of the obtained titanium oxide particles small. Also, from the viewpoint of promoting the reaction, it is preferably 50 mol or less, more preferably 10 mol or less, and even more preferably 5 mol or less. Examples of this inert gas include nitrogen gas, helium gas, argon gas, etc., but nitrogen gas is preferred from an economic viewpoint. G1 is preferably heated (preheated) to 600°C or more and less than 1200°C and then introduced into the reaction tube, more preferably 700°C or more and less than 1200°C, and even more preferably 800°C or more and less than 1200°C.

[0049] (Oxidizing gas G2) The oxidizing gas G2 contains at least one of oxygen gas and water vapor and an inert gas. The total amount of the oxidizing gas and water vapor in the oxidizing gas G2 is preferably 2 to 150 moles, more preferably 2 to 50 moles, and still more preferably 2 to 15 moles per mole of titanium tetrachloride in the raw material gas G1. Increasing the amount of the oxidizing gas G2 not only increases the number of nuclei generated and makes it easier to obtain ultrafine particles, but also shortens the high-temperature residence time, thereby improving the uniformity of the primary particle size. When it exceeds 150 moles, the productivity deteriorates. On the other hand, when at least one of the oxidizing gas and water vapor is less than 2 moles per mole of titanium tetrachloride, titanium oxide with many oxygen defects is formed and it becomes colored. The proportion of at least one of oxygen gas and water vapor in the oxidizing gas G2 containing an inert gas is preferably 80 to 99.5 mol%, and more preferably 90 to 99.5 mol%. It is preferable to heat (preheat) G2 to 600 °C or higher and lower than 1,200 °C and then introduce it into the reaction tube. The inert gas is preferably the same as that described in the section of the raw material gas G1. More preferably, it is the same inert gas as in the raw material gas G1.

[0050] (Reaction tube) In order to make the flows of the raw material gas, the oxidizing gas, the purge medium, and the reaction gas uniform, the reaction tube may be a horizontal reaction tube, but a vertical reaction tube with a circular cross-section is preferred. The preheated raw material gas and the oxidizing gas are introduced from their respective supply pipes downward into the reaction tube from the upper end of the heated reaction tube, and the purge medium is introduced from the side surface of the reaction tube in a direction along the reaction tube wall. It is more preferable that the purge medium can be swirled along the reaction tube wall. Regarding the introduction direction of the purge medium with respect to the reaction tube, it is preferable that the above-mentioned angle α is 50° or more, and the angle β described later is 60° or more. The raw material gas and the oxidizing gas introduced into the reaction tube, and the reaction gas which is a mixed gas thereof, flow downward through the reaction tube. However, by introducing a cooling medium or the like, the reaction gas is cooled to stop the reaction. The introduction angle of the cooling gas may be perpendicular to the flow of the reaction gas and directed toward the center of the circular cross-section of the reaction tube, but it is not necessarily this angle. The titanium oxide particles after cooling 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 which is a reaction product.

[0051] 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 (the end face or cross section of the reaction tube) to the sum of the cross-sectional areas of the outlets of the introduction pipes of the raw material gas G1 and the oxidizing gas G2 (S2) is preferably 1 or more and 7.0 or less. By setting it within this range, the temperature in the reaction region and the high-temperature zone time can be made closer to uniform. Here, 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 more preferably 1 or more and 2.5 or less, 1 or more and 2.0 or less, 1 or more and 1.5 or less. The raw material gas G1 and the oxidizing gas G2 supplied from the introduction pipes are mixed and react in the reaction tube. To make the growth of titanium oxide particles uniform, it is preferable to make the temperature in the reaction region and the high-temperature zone time closer to uniform. When the raw material gas G1 and the oxidizing gas G2 are introduced from the end face side of the reaction tube, the case where the cross-sectional area (S1) of the reaction tube is smaller than the total cross-sectional area (S2) of the raw material introduction pipes (S1 / S2 < 1) is not considered. When S1 / S2 exceeds 2.5, the influence of diffusion in the vertical direction with respect to the gas flow becomes large, so the primary particle size may become non-uniform. Although it is preferable that the raw material gas G1 and the oxidizing gas G2 are introduced into the reaction tube in the gas flow direction in the reaction tube respectively, it is not limited. Conventionally, when S1 / S2 exceeds 2.5, it has been considered difficult to make the primary particle size uniform. However, according to the present embodiment, even under conditions exceeding 2.5, titanium oxide particles with few coarse particles can be produced by adjusting the angle of the purge medium and the like.

[0052] (Reaction temperature and reaction time) The temperature in the reaction zone where the raw material gas G1 and the oxidizing gas G2 are introduced is preferably 800°C or higher and less than 1,200°C, more preferably 800°C or higher and less than 1,100°C. If the temperature of the reaction zone is 800°C or higher, the reaction proceeds sufficiently, the particle size distribution of the titanium oxide particles becomes uniform, and the crystallinity becomes high, which is preferable. By increasing the temperature of the reaction zone, the reaction is completed simultaneously with the mixing, homogeneous nucleation is promoted, and the reaction zone can be reduced. On the other hand, if the temperature inside the reaction tube is less than 1,200°C, particle growth proceeds moderately, and fine particles are obtained, which is preferable.

[0053] The residence time of both the raw material gas G1 and the oxidizing gas G2 in the reaction zone at a high temperature of 800°C or higher and less than 1,200°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. If the reaction gas is not cooled and the residence time in the high-temperature region becomes long, the titanium oxide particles may grow in size, and sintering of the particles may proceed.

[0054] The raw material gas G1 and the oxidizing gas G2 introduced into the reaction tube are preferably preheated to 600°C or higher and less than 1,200°C, more preferably 800°C or higher and less than 1,200°C, and even more preferably 800°C or higher and less than 1,100°C before being introduced into the reaction tube. This can more precisely control the temperature and reaction time of the raw material gas G1 and the oxidizing gas G2 during the reaction, and the particle size distribution of the titanium oxide particles to be produced.

[0055] Also, in the cooling zone following the reaction zone of the reaction tube, if there is a temperature range exceeding 500°C, sintering between the 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.

[0056] (Flow rate and flow velocity of raw material gas, oxidizing gas and reaction gas) The flow rates of the raw material gas and the oxidizing gas can be 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 in the reaction tube after the reaction of the raw material gas G1 and the oxidizing gas G2 can be calculated from the flow rates of the raw material gas G1 and the oxidizing gas G2 and the reaction formula. The flow velocity (A) (m / s) of the reaction gas flow in the reaction tube can be simply calculated, under the assumption that the raw material gas and the oxidizing gas react immediately, from the total flow rate (m 3 / s) of the reaction gas flow after the reaction of the raw material gas and the oxidizing gas and the cross-sectional area (m 2 ) of the reaction tube.

[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. If the flow velocity is less than 1 m / s, the residence time of the reaction gas flow becomes long, and there is a risk of promoting over-sintering and coarsening of titanium oxide.

[0058] ( Purge medium) As the purge medium, methods such as introducing a gas such as air, nitrogen gas, carbon monoxide, or spraying water are also preferably adopted. The purge medium is preferably at 0°C to 100°C, and more preferably at 10°C to 90°C. It is also preferable not to exceed the temperature of the cooling medium described later. Being in this temperature range does not adversely affect the cooling effect by the cooling medium.

[0059] (Purge method) When the generated titanium oxide particles adhere and accumulate on the inner wall of the reaction tube, they coarsen due to the growth of sintered particles, and if they desorb and mix in, it can cause non-uniformity in the particle size distribution. Therefore, a purge medium outlet is provided on the inner wall of the reaction tube or at the upper part of the reaction tube, and the purge medium is introduced while swirling along the reaction tube wall, thereby promoting the formation of a purge medium layer in the vicinity of the reaction tube wall and preventing the titanium oxide particles from adhering and accumulating on the tube wall surface, thus suppressing the sintering of the titanium oxide particles. By introducing the purge medium continuously or intermittently, an effect of preventing the adhesion of titanium oxide can be expected. Also, it is preferable to provide the purge holes at a plurality of locations. Further, the shape of the purge medium outlet can be a single hole or a slit shape.

[0060] ( Purge conditions of the purge medium (direction and flow rate, etc.)) In the present invention, it is characterized in that a purge medium outlet is provided on the inner wall of the reaction tube, and the purge medium is introduced so as to swirl along the inner wall of the reaction tube. In the reaction tube, it can be expected that the purge medium swirling in the vicinity of the inner wall of the reaction tube will prevent the adhesion of titanium oxide particles to the reaction tube wall surface.

[0061] If the direction in which the purge medium is blown out is not close to the inner wall of the reaction tube with respect to the reaction gas flow, the swirling flow cannot be maintained, and an effective effect of preventing the adhesion of titanium oxide to the reaction tube wall surface cannot be expected.

[0062] In the present invention, the blowing direction of the purge medium is such that, on the projection plane onto the cross-section of the reaction tube perpendicular to the flow direction of the reaction gas (axial direction of the reaction tube), the angle α (see FIG. 3) between the line connecting the blowing outlet of the purge medium and the central axis of the reaction tube and the direction of blowing out the purge medium (axial direction of the blowing outlet of the purge medium) is 50° or more. Here, the angle α is the angle at which the blowing outlet is set with respect to the reaction tube on the projection plane onto the cross-section of the reaction tube, and is assumed to be the same as the angle at which the purge medium is blown out from the blowing outlet. After the purge medium is blown out from the blowing outlet and merges with the reaction gas flow, the flow direction within the cross-section of the reaction tube can change, but the angle α is the angle determined by the set direction of the blowing outlet of the purge medium. By the angle α being 50° or more, the purge medium can be swirled close to the inner wall of the reaction tube, and the effect of preventing the adhesion of titanium oxide to the reaction tube wall surface is preferably obtained. The angle α is preferably 60° or more. Generally, the angle α is less than 90°.

[0063] Also, on the projection plane onto the longitudinal section of the reaction tube including the axial direction of the reaction tube (flow direction of the reaction gas), the direction of blowing the purge medium into the reaction tube may be a direction perpendicular to the axis of the reaction tube (axial direction of the reaction gas) (horizontal direction in the case of a vertical reaction tube). This blowing direction perpendicular to the axis of the reaction tube (horizontal direction in a vertical reaction tube) is preferable, but it may be inclined from the blowing direction perpendicular to the axis of the reaction tube toward the flow direction of the reaction gas. Although it is not impossible to blow in the direction opposite to the flow direction of the reaction gas, backflow of the reaction gas may occur. On the projection plane onto the longitudinal section of the reaction tube, the blowing angle β of the purge medium (see FIG. 4) with respect to the axial direction of the reaction tube is preferably 60° or more (inclination angle of 30° or less with respect to the cross-section of the reaction tube), more preferably 70° or more, and even more preferably 80° or more, with the flow direction side of the reaction gas in the axial direction of the reaction tube being 0°. Also, the above-mentioned blowing angle β is particularly preferably 90° or less. Such an angle is preferable because it can be excellent in the effect of preventing the adhesion of titanium oxide to the reaction tube wall surface.

[0064] The installation location of the purge medium blowing outlet for the reaction tube only needs to allow the purge medium to swirl along the inner wall of the reaction tube. In the projection plane onto the cross-section of the reaction tube, it may be at one location, but two or more locations are preferred, three or more locations are more preferred, and four or more locations may also be acceptable. Generally, the number of blowing outlets per outer circumference of the cross-section of the reaction tube can be smaller as the angle α is larger and as the flow rate of the purge medium is larger. Also, the installation location of the purge medium blowing outlet may be in one stage in the axial direction of the reaction tube in the projection onto the longitudinal section of the reaction tube, but it is preferably in two or more stages, and may also be in three or more stages. Further, it is preferable that there are a plurality of purge medium blowing outlets in one or more identical cross-sections in the axial direction in the projection onto the longitudinal section of the reaction tube, but they may be arranged spirally on the inner wall of the reaction tube and do not necessarily have to be in a plurality of locations in the same cross-section.

[0065] The purge medium blowing outlet may be installed from near the raw material gas introduction part in the reaction region to before the cooling region, and preferably is also installed in the cooling region, so that a swirling flow of the purge medium along the inner wall of the reaction tube is preferably formed in these regions.

[0066] The blowing flow rate (B) of the purge medium is 35 m / s or more in order to prevent the generated titanium oxide particles from adhering to the reaction tube wall, preferably 50 m / s or more, and more preferably 60 m / s or more. If it is 35 m / s or more, sufficient swirling occurs on the tube wall surface, and a better effect of preventing titanium oxide adhesion to the tube wall surface can be expected. Here, the blowing flow rate (B) of the purge medium is obtained by dividing the purge gas flow rate (m 3 / s) by the cross-sectional area of the blowing outlet (the unit is m / s).

[0067] When the flow rate (A) of the reaction gas formed from the raw material gas and the oxidizing gas in the reaction tube is A and the blowing flow rate (B) of the purge medium is B, it is preferable that B / A is 0.5 or more, more preferably 1.0 or more, still more preferably 3.0 or more, and most preferably 5.0 or more. When the blowing flow rate (B) of the purge medium blown in the swirling direction is less than 0.5 with respect to the flow rate (A) of the reaction gas flowing in the vertical direction, a sufficient vector in the swirling direction cannot be obtained, and it is difficult for the purge medium to swirl and difficult to obtain uniform particles.

[0068] ( Cooling medium) As the cooling medium, a method of introducing a gas such as air, nitrogen gas, carbon monoxide, or a method of spraying water is also preferably employed. The cooling medium is preferably at 0°C to 100°C, and more preferably at 10°C to 90°C. Having the cooling medium within this temperature range provides a high cooling effect.

[0069] Cooling conditions of the cooling medium (direction and flow rate, etc.) In the present invention, 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.

[0070] If the direction in which the cooling medium is blown out with respect to the reaction gas flow is not close to the center of the reaction tube, the cooling medium will not mix well and a sufficient cooling effect cannot be expected.

[0071] In the present invention, the blowing direction of the cooling medium is such that, on the projection plane onto the cross-section of the reaction tube perpendicular to the flow direction of the reaction gas (axial direction of the reaction tube), the angle γ (see Figure 3) between the line connecting the blowing outlet of the cooling medium and the central axis of the reaction tube and the direction of blowing out the cooling medium (axial direction of the blowing outlet of the cooling medium) is set to be not less than 0° and less than 50°. Here, the angle γ is the angle at which the blowing outlet is set with respect to the reaction tube on the projection plane onto the cross-section of the reaction tube, and is assumed to be the same as the angle at which the cooling medium is blown out from the blowing outlet. After the cooling medium is blown out from the blowing outlet, it merges with the reaction gas flow, so the flowing direction within the cross-section of the reaction tube can change, but the angle γ is determined by the set direction of the blowing outlet of the cooling medium. By the angle γ being not less than 0° and less than 50°, the cooling medium can flow near the center of the reaction tube, and it can be preferably mixed well with the reaction gas to obtain a cooling effect. The angle γ is preferably less than 30°.

[0072] Also, on the projection plane onto the longitudinal section of the reaction tube including the axial direction of the reaction tube (flow direction of the reaction gas), the direction of blowing the cooling medium into the reaction tube may be a direction perpendicular to the axis of the reaction tube (horizontal direction in the case of a vertical reaction tube). This blowing direction perpendicular to the axis of the reaction tube (horizontal direction in a vertical reaction tube) is preferred, but it may be inclined from the blowing direction perpendicular to the axis of the reaction tube toward the flow direction of the reaction gas. Blowing in the direction opposite to the flow direction of the reaction gas is not impossible, but it is not desirable because backflow of the reaction gas may occur. On the projection plane onto the longitudinal section of the reaction tube, the angle δ (see Figure 4) at which the purge medium is blown out with respect to the axial direction of the reaction tube is preferably, for example, not less than 60° (inclination angle not more than 30° with respect to the cross-section of the reaction tube), more preferably not less than 70°, and even more preferably not less than 80°, with the flow direction side of the reaction gas in the axial direction of the reaction tube being 0°. Also, the above-mentioned blowing angle δ is particularly preferably not more than 90°. With such an angle, a preferable cooling effect is obtained.

[0073] The section from the raw material gas inlet to the cooling medium outlet in the reaction tube is called the reaction zone, and the section from the cooling medium outlet to the discharge port side is called the cooling zone. When there are multiple cooling medium outlets, the section from the raw material gas inlet to the first cooling medium outlet in the reaction tube is called the reaction zone, and the section from the first cooling medium outlet to the discharge port side is called the cooling zone.

[0074] The installation position of the cooling medium outlet with respect to the reaction tube only needs to allow the cooling medium to mix with the reaction gas. In the projection plane on the cross-section of the reaction tube, it may be at one location, but it may also be at two or more locations. Also, in the projection plane on the longitudinal section of the reaction tube, the installation position of the cooling medium outlet may be in one stage in the axial direction of the reaction tube, but it is preferably in two or more stages, and may also be in three or more stages. Further, it is preferable that there are a plurality of cooling medium outlets in one or more identical cross-sections in the axial direction in the projection plane on the longitudinal section of the reaction tube.

[0075] Schematic diagram showing the purge method Figs. 2 to 4 are schematic diagrams showing preferred embodiments of the first step (reaction step). Fig. 2 is a longitudinal sectional view (longitudinal sectional view including the axis of the reaction tube) of the reaction tube 1 as viewed from the side. First, the raw material gas G1 and the oxidizing gas G2 are introduced into the reaction tube 1. At this time, it is preferable to preheat the reaction zone 1' so that the temperature in the reaction zone 1' after the introduction of the raw material gas G1 and the oxidizing gas G2 into the reaction tube 1 is within a predetermined temperature range. The reaction gas (based on the raw material gas G1 and the oxidizing gas G2) is retained in the reaction tube 1 for a predetermined time. Also, a purge medium outlet 5 is provided on the tube wall of the reaction tube 1, and the purge medium is introduced continuously or intermittently. Further, the cooling medium is blown out from the cooling medium outlet 3 to rapidly cool the reaction gas containing the raw material gas and the oxidizing gas, and the crude titanium oxide particles as the reaction product are allowed to flow out from the cooling zone 2 together with the cooling medium. Thereby, the crude titanium oxide particles can be suitably produced. The obtained crude titanium oxide particles are sent to the second step (dechlorination step).

[0076] FIG. 3 is a cross-sectional view (a cross-sectional view perpendicular to the axis of the reaction tube) of the reaction tube 1 as seen from above (the introduction side of the raw material gas G1 and the oxidizing gas G2), and shows the purge medium P introduced from the purge medium outlet 5 of the reaction tube 1 and the cooling medium Q introduced from the cooling medium outlet 3 by arrows. The blowing angle of the purge medium is designated as α, and the blowing angle of the cooling medium is designated as γ.

[0077] FIG. 4 is a longitudinal sectional view (a longitudinal sectional view including the axis of the reaction tube) of the reaction tube 1 as seen from the side, and shows the purge medium P introduced from the purge medium outlet 5 of the reaction tube 1 and the cooling medium Q introduced from the cooling medium outlet 3 by arrows. The blowing angle of the purge medium is designated as β, and the blowing angle of the cooling medium is designated as δ.

[0078] The swirling flow of the purge medium can effectively prevent the oxidation titanium particles from adhering to, staying on, and growing on the tube wall by swirling near the tube wall of the reaction tube under specific conditions. Also, it is preferable to form the swirling flow of the purge medium not only in the reaction region but also in the cooling region.

[0079] As described above, the representative form of the reaction apparatus is a vertical type in which the raw material gas G1, the oxidizing gas G2, and the reaction gas R flow from top to bottom. However, when the type of the reaction apparatus is different from this, the method for obtaining the above-mentioned swirling angle is modified accordingly. Also, the introduction direction of the purge medium P does not necessarily have to be the same as the above, but the swirling angle β of the purge medium P with respect to the flow of the reaction gas R is preferably the same as the above.

[0080] (Dechlorination treatment) The crude titanium oxide produced as described above is preferably subjected to dechlorination treatment. Dechlorination of titanium oxide by heating is preferably carried out by heating at a temperature of 200 °C or higher and 550 °C or lower while bringing titanium oxide particles into contact with water vapor so that the mass ratio of water to titanium oxide (= mass of water vapor / mass of titanium oxide; the same applies hereinafter) is 0.01 or more. More preferably, the mass ratio of water to titanium oxide is 0.04 or more, and the heating temperature is 250 °C or higher and 450 °C or lower. When the heating temperature exceeds 550 °C, sintering of titanium oxide particles progresses, and the primary particle diameter becomes non-uniform. When the heating temperature is lower than 200 °C, the efficiency of dechlorination extremely decreases. In order to achieve dechlorination while suppressing grain growth, it is preferable to control the mass ratio of water to titanium oxide. When the mass ratio of water to titanium oxide is 0.01 or more, an effect of suppressing grain growth is recognized, preferably 0.01 or more and 1 or less, more preferably 0.05 or more and 2 or less, and still more preferably 0.2 or more and 1.8 or less.

[0081] The water vapor brought into contact with titanium oxide preferably has a role of efficiently moving chlorine separated from titanium oxide outside the system, and for example, it is preferably used after being mixed with air. When using air, it is preferable that water vapor is contained in air at 0.1% by volume or more, more preferably 5% by volume or more, and particularly preferably 10% by volume or more and 80% by volume or less. The air containing water vapor is preferably heated to 200 °C or higher and 1,000 °C or lower, and more preferably 450 °C or higher and 850 °C or lower.

[0082] In the dechlorination of titanium oxide, as a method of moving chlorine removed from titanium oxide outside the system, a method of reducing the pressure inside the container used for dechlorination is also effective. The degree of vacuum inside the container is preferably 0.5 kPa or more. More preferably, it is 0.5 kPa or more and 3.5 kPa or less. The degree of vacuum here indicates the differential pressure between the pressure inside the depressurized container and the atmospheric pressure.

[0083] The titanium oxide particles according to this embodiment contain almost no chlorine inside the particles, and most of the chlorine on the particle surface can be removed by washing with water or the like. Therefore, it is also possible to reduce the chlorine content in a wet process. Examples of the wet dechlorination method include a method in which titanium oxide particles are suspended in pure water, and chlorine transferred to the liquid phase is separated outside the system by an ultrafiltration membrane, a reverse osmosis membrane, a filter press, or the like.

[0084] · Anatase content In the reaction of titanium oxide, the higher the temperature in the reaction process, the lower the anatase content and the easier rutile transition occurs. However, by adjusting the amount of heat received by titanium oxide by introducing a cooling medium after the reaction, the anatase content can be adjusted. Also, if the temperature in the reaction process is too low, the reaction will not be completed, leading to a decrease in the crystallinity of the obtained titanium oxide.

[0085] · Impurity concentration The less impurities contained in titanium tetrachloride as a raw material, the less impurities in titanium oxide. Therefore, it is preferable to use high-purity titanium tetrachloride with few impurities.

[0086] · BET specific surface area In the reaction of titanium oxide, the higher the temperature in the reaction process, the easier the sintering of titanium oxide particles progresses and the lower the BET specific surface area. As a means to improve the BET specific surface area, suppressing sintering by introducing a dilution gas into the reaction field or by cooling can be mentioned.

Examples

[0087] Hereinafter, examples and comparative examples will be specifically described, but the present invention is not limited thereto in any way.

[0088] The measurement methods for the physical properties of titanium oxide particles are as follows. (1) Anatase content The content of anatase-type crystals (anatase content) in titanium oxide particles was measured by the powder X-ray diffraction method. That is, for the dried titanium oxide particles, using "X'pertPRO" manufactured by PANalytical as the measuring device, with a copper target, using Cu-Kα1 line, X-ray diffraction measurement was carried out under the conditions of tube voltage 45 kV, tube current 40 mA, measurement range 2θ = 10~80 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 the titanium oxide particles was determined by the following calculation formula. Anatase content (%) = {Ha / (Ha + Hb + Hr)} × 100

[0089] (2) BET specific surface area The BET specific surface area (m 2 / g) of the titanium oxide particles was measured with a specific surface area measuring device (Macsorb) manufactured by Mountech. Nitrogen was used as the measuring gas.

[0090] (3) Chlorine (Cl) content The Cl content in the titanium oxide particles was measured by the silver nitrate potentiometric titration method. That is, the titanium oxide particles were weighed. Then, a silver nitrate solution was dropped into the solution of this titanium oxide particle, and the potential difference was measured to obtain the mass of chlorine atoms in the solution, and the chlorine content (mass%) was calculated.

[0091] (4) D10 (SEM), D50 (SEM), D90 (SEM), D99 (SEM) of primary particles of titanium oxide particles by scanning electron microscope 1 g of the sample was put into 100 ml of ethanol. After ultrasonic irradiation (30 W, 5 min), the dispersion was separated with a Pasteur pipette, and about 0.05 g was dropped onto the 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 manufactured by Hitachi High-Technologies Fielding). 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 manufactured by Sumitomo Metal Technology Co., Ltd. or Mac-View Ver3 manufactured by Mounttech Co., Ltd. was 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 the calculation of the primary particles exceeded at least 1000. The particle sizes D10(SEM), D50(SEM), D90(SEM), and D99(SEM) were calculated 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 10%, 50%, 90%, and 99% of the total cumulative value, respectively.

[0092] (5) D50 (LD) of titanium oxide particles by laser diffraction / scattering method 、 D90 (LD) 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 a 100 ml tall beaker to form a slurry, and ultrasonic waves were irradiated for 3 minutes (50 kHz, 100 W) while stirring the slurry in the tall beaker using a φ8 mm Teflon (registered trademark) rod. 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. This slurry was applied to a laser diffraction particle size distribution measuring device (Microtrac MT3300EXII manufactured by Microtrac), and the particle size distribution (volume cumulative particle size distribution) was measured. D50(LD) and D90(LD) were calculated.

[0093] (6) D50 (DLS) of crushed titanium oxide particles by dynamic light scattering method、 D90 (DLS) 300 ml of pure water was added to 100 g of titanium oxide particles, and a slurry was prepared by adding 5% polycarboxylic acid per weight of titanium oxide as a dispersant. This slurry was charged into a ball mill container, 1.2 kg of 0.5 mmφ zirconia balls were added, placed on the stand of the ball mill, and rotated at 7 rpm for 72 hours. The pulverized titanium oxide slurry obtained was subjected to a dynamic light scattering method particle size distribution measuring device (ELS-Z manufactured by Otsuka Electronics Co., Ltd.) to measure the volume-based particle size distribution.

[0094] (7) Particle concentration of coarse particles Using a field emission scanning electron microscope, an image was taken such that the number of primary particles per field of view was, for example, 8000 to 12000. The presence or absence of large particles larger than a specific dimension (for example, 0.20 μm or more, 0.30 μm 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, Heywood diameter) of the particles was obtained 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. Among the coarse particles whose primary particle diameters were measured, the number of coarse particles larger than the specific dimension described in Table 2 was divided by the total number of observed particles, and the resulting value was defined as the content (particle concentration) of the coarse particles. The total number of observed particles was calculated from the number of primary particles per field of view and the number of observed fields of view.

[0095] (8) Content of other impurities The impurity measurement method is as shown below. Fe: Atomic absorption method (Z-2300 type atomic absorption photometer manufactured by Hitachi High-Technologies Corporation) Al, Si: Fluorescent X-ray analysis method (XRF) (Rigaku Denki Kogyo Co., Ltd. Simultix 10) C, S: High-frequency induction furnace combustion - infrared absorption method Na, Ni, Cr, Nb, Zr: Inductively coupled plasma - mass spectrometry

[0096] Example 1 <First step> Using a vertical reaction tube with a circular cross-section, titanium tetrachloride diluted gas (G1) obtained by diluting 1053 mol / hr of gaseous titanium tetrachloride (purity of titanium tetrachloride ≥ 99.99% by mass) with 223 mol / hr of nitrogen gas was preheated to 950 °C, and oxygen of 982 mol / hr and 1786 mol Nm 3 / hr of steam were mixed with 22 mol / hr of nitrogen gas to obtain an oxidizing gas (G2), which was preheated to 870 °C. These gases (G1 and G2) were introduced into the top of a reactor where the ratio (S1 / S2) of the cross-sectional area (S1) of the reaction tube to the total cross-sectional area (S2) of the introduction tubes of the gas (G1) containing titanium tetrachloride and the oxidizing gas (G2) was 6.7. Purge air and cooling air were introduced into the reaction tube from the side surface of the reaction tube so that the high-temperature residence time at 800 °C or higher and less than 1200 °C was 0.05 seconds, and the crude titanium oxide particles were collected at the lower part of the reaction tube using a polytetrafluoroethylene bag filter. Other conditions are shown in Table 1. The flow velocity (m / s) of the reaction gas stream was calculated from the cross-sectional area (m 2 ) of the reaction tube and the flow rate (m 3 / s) of the reaction gas stream after the reaction of the raw material gas and the oxidizing gas.

[0097] <Second Step> The obtained crude titanium oxide particles were passed through a cylindrical rotary heating furnace and dechlorinated at a mass ratio of steam to crude titanium oxide (mass of steam / mass of crude titanium oxide particles) of 0.06 and a heating temperature of 450 °C to obtain titanium oxide particles, and various physical properties were measured. The measurement results are shown in Table 2.

[0098] Examples 2 to 5 The first step was carried out by changing various conditions. The conditions are shown in Table 1. The second step was carried out in the same manner as in Example 1. The measurement results are shown in Table 2.

[0099] Comparative Example 1 The first step and the second step were carried out in the same manner as in Example 1 except for the blowing angle α of the purge medium. The measurement results are shown in Table 2.

[0100] Comparative Example 2 The first and second steps were carried out in the same manner as in Example 2, except for the blowing flow rate (B) of the purge medium. The measurement results are shown in Table 2.

[0101] Comparative Example 3 The first and second steps were carried out in the same manner as in Example 4, except for the preheating temperature of the raw material gas G1, the flow rate of the oxidizing gas G2, and the blowing flow rate (B) of the purge medium. The measurement results are shown in Table 2.

[0102] Comparative Example 4 (liquid phase method) An aqueous solution with a titanium tetrachloride concentration of 0.5 mol / L was heated under reflux at 100 °C for 3 hours for hydrolysis to obtain an ultrafine titanium oxide sol. The obtained titanium oxide sol was repeatedly washed with pure water and then dried at 120 °C for 12 hours using a hot air circulation dryer. Various physical properties of the obtained titanium oxide particles were measured. The measurement results are shown in Table 2.

[0103]

Table 1

[0104]

Table 2

[0105]

Table 3

[0106] Referring to Tables 1 to 3, for the gas-phase titanium oxide particles in Examples 1 to 5 and Comparative Examples 1 to 3, although no clear difference is seen in the particle size distribution shown in Table 2, in Examples 1 to 5, the particle concentration exceeding 16 times D50 (SEM) has decreased, and it is considered that the effect of reducing coarse particles is obtained by introducing the purge medium to the reaction tube wall at a specific angle or more. Also, for the liquid-phase titanium oxide particles in Comparative Example 4, although no coarse particles larger than a specific size were observed, since D50 (LD) and D90 (LD) are large, it is considered that the dispersibility in the dispersion medium is low.

[0107] Thus, according to the present invention, there are provided gas-phase titanium oxide particles having fewer coarse particles and excellent uniformity and dispersibility as compared with conventional titanium oxide particles having an equivalent BET specific surface area, and methods for producing the same. The titanium oxide particles of the present invention are suitable for use in photocatalysts, solar cells, dielectrics, etc. As a powder, a crushing process or the like is unnecessary or only extremely simple equipment is required, and it has extremely great industrial practical value.

Industrial Applicability

[0108] The titanium oxide particles of the present invention are suitable for use in photocatalysts, solar cells, dielectrics, etc. As a powder, a crushing process or the like is unnecessary or only extremely simple equipment is required, and it has extremely great industrial practical value.

Explanation of Signs

[0109] 1 Reaction tube 1’ Reaction region 2 Cooling region 3 Cooling medium outlet 4 Center of reaction tube 5 Purge medium outlet G1 Source gas G2 Oxidizing gas P Purge medium Q Cooling medium R Reaction gas flow direction α Blowing angle of purge medium (in a plane perpendicular to the flow direction of the reaction gas) β Blowing angle of purge medium (in a plane including the flow direction of the reaction gas) γ Blowing angle of cooling medium (in a plane perpendicular to the flow direction of the reaction gas) δ Blowing angle of cooling medium (in a plane including the flow direction of the reaction gas)

Claims

1. Titanium oxide particles in which D90(LD) / D50(LD) measured by laser diffraction / scattering analysis is more than 1.0 and 2.0 or less, and the coarse particle concentration (number basis) exceeding 16 times D50(SEM) of primary particles observed by a field emission scanning electron microscope is 20 ppm or less.

2. The titanium oxide particles according to Claim 1, wherein D90(SEM) / D50(SEM) of primary particles of the titanium oxide particles observed by a field emission scanning electron microscope is more than 1.0 and 2.0 or less.

3. The titanium oxide particles according to Claim 1 or 2, wherein [D90(SEM) - D10(SEM)] / D50(SEM) of primary particles of the titanium oxide particles observed by a field emission scanning electron microscope is 0.82 or less.

4. The titanium oxide particles according to Claim 1 or 2, wherein D99(SEM) / D50(SEM) of primary particles of the titanium oxide particles observed by a field emission scanning electron microscope is more than 1.0 and 2.0 or less.

5. The titanium oxide particles according to Claim 1 or 2, wherein D90(DLS) / D50(DLS) of the titanium oxide particles measured by dynamic light scattering method is more than 1.0 and 2.0 or less.

6. The titanium oxide particles according to Claim 1 or 2, wherein D90(DLS) / D90(SEM), which is the ratio of D90(DLS) of the titanium oxide particles measured by dynamic light scattering method to D90(SEM) of primary particles of the titanium oxide particles observed by a field emission scanning electron microscope, is 2.2 or less.

7. The titanium oxide particles according to Claim 1 or 2, wherein D90(LD) of the titanium oxide particles measured by laser diffraction / scattering analysis is 3000 nm or less.

8. The titanium oxide particles according to Claim 1 or 2, wherein D90(SEM) of primary particles of the titanium oxide particles measured by dynamic light scattering method and observed by a field emission scanning electron microscope is 200 nm or less, and D50(SEM) is 10 to 150 nm.

9. The titanium oxide particles according to Claim 1 or 2, wherein the anatase content is 70% or more.

10. The BET specific surface area is 5 to 200 m ２ / g, and the titanium oxide particles according to claim 1 or 2.

11. The titanium oxide particles according to Claim 1 or 2, wherein the Cl content of the titanium oxide particles measured by silver nitrate potentiometric titration method is 0.2 mass% or less.

12. The titanium oxide particles according to claim 1 or 2, wherein the contents of Na, Al, S, Fe, Ni, Cr, Nb and Zr are each 10 mass ppm or less, and the contents of Si and C are each 500 mass ppm or less.

13. In the process of producing titanium oxide particles by introducing a raw material gas containing titanium tetrachloride and an inert gas and an oxidizing gas containing at least one of oxygen gas and steam and an inert gas into a reaction tube, reacting them, and then cooling, a purge medium outlet is provided on the inner wall of the reaction tube, and the purge medium is introduced so as to swirl along the inner wall of the reaction tube. In a plane projected onto a cross section of the reaction tube perpendicular to the axis of the reaction tube, the blowing angle α of the purge medium from the inner wall of the reaction tube with respect to the line connecting the purge medium outlet and the central axis of the reaction tube is 50° or more, and the blowing flow rate (B) of the purge medium is 35 m / s or more. A method for producing titanium oxide particles.

14. In a plane projected onto a longitudinal section of the reaction tube including the axis of the reaction tube, with respect to the axial direction of the reaction tube, the blowing angle β of the purge medium from the inner wall of the reaction tube is 60° or more with the forward side of the reaction gas flow being 0°. The method for producing titanium oxide particles according to claim 13.

15. When the flow rate of the reaction gas formed from the raw material gas and the oxidizing gas in the reaction tube is A and the blowing flow rate of the purge medium is B, the purge medium is introduced so that B / A is 0.5 or more. The method for producing titanium oxide particles according to claim 13 or 14.

16. A slurry containing the titanium oxide particles according to claim 1 or 2.

17. A dispersion containing the titanium oxide particles according to claim 1 or 2.

18. A composition containing the titanium oxide particles according to claim 1 or 2.

19. A dielectric raw material containing the titanium oxide particles according to claim 1 or 2.

Images