Titanium oxide particles and method for producing the same

Abstract

The present invention produces titanium oxide particles which have a sufficiently small average aggregate particle diameter (D50), while containing much less amorphous components.　According to the present invention, a solution containing titanium (oxy)chloride and a carboxylic acid and / or a salt thereof is heated at a temperature that is not less than 95°C but not more than the boiling point of the solution (first hydrolysis step); and a solution, which is obtained by mixing a solution that contains a product of the first hydrolysis step with titanium (oxy)chloride and a carboxylic acid and / or a salt thereof, is heated at a temperature that is not less than 95°C but not more than the boiling point of the solution (second hydrolysis step). In addition, the present invention provides titanium oxide particles which have an average aggregate particle diameter (D50) of 15 nm to 200 nm, while having a content of amorphous components of 7% by mass or less.

Description

[Technical Field]

[0001] This invention relates to titanium dioxide particles and a method for producing the same. [Background technology]

[0002] Barium titanate is used as a dielectric material in electronic components such as multilayer ceramic capacitors (MLCCs). High-purity titanium oxide particles are used in the production of barium titanate. With the miniaturization of electronic devices, there is a growing demand for smaller MLCCs, requiring barium titanate with smaller particle sizes, and consequently, smaller titanium oxide particles, which are the raw material for barium titanate.

[0003] Methods for producing high-purity titanium dioxide particles include the "gas-phase method," which involves oxidizing or hydrolyzing titanium oxychlorides such as titanium tetrachloride in the gas phase, and the "liquid-phase method," which involves hydrolyzing titanium oxychlorides such as titanium tetrachloride in the liquid phase. Generally, titanium dioxide particles obtained by the "liquid-phase method" contain less chlorine from the raw materials compared to those obtained by the "gas-phase method," making them suitable as a raw material for barium titanate. However, in the "liquid-phase method," since titanium dioxide particles are generated in a solution, primary titanium dioxide particles tend to aggregate and form aggregated particles. Therefore, various attempts are being made to suppress the aggregation of primary particles in the "liquid-phase method" and reduce the size of aggregated titanium dioxide particles.

[0004] For example, Patent Document 1 describes a method for producing titanium dioxide particles, which involves heating a solution containing titanium tetrachloride and citric acid at 92°C (first hydrolysis), and then adding titanium tetrachloride to the solution containing the product after the first hydrolysis and heating it again at 92°C (second hydrolysis). Furthermore, Patent Document 1 describes a method for producing titanium dioxide particles, which involves mixing an alkali into an aqueous solvent containing (oxy)titanium chloride so that the pH is in the range of 0 to 9, then heating it to a temperature of 50°C to 110°C (first hydrolysis), and then mixing (oxy)titanium chloride into the aqueous solvent containing the product of the first hydrolysis to adjust the pH to a range of 1 or less, and then heating it to a temperature of 50°C to 110°C (second hydrolysis). (However, no examples corresponding to this production method are described.) It is believed that titanium oxide particles with a small primary particle size and a small aggregate particle size can be obtained through this two-stage hydrolysis process.

[0005] Furthermore, Patent Document 2 describes a method for producing titanium dioxide particles, in which an aqueous solution containing ammonia is added to a solution containing titanium tetrachloride and citric acid to hydrolyze a portion of the titanium tetrachloride (first hydrolysis), and the solution containing the product after the first hydrolysis is heated at 90°C to hydrolyze the remaining titanium tetrachloride (second hydrolysis). Patent Document 2 also states that by going through such a two-stage hydrolysis process, titanium dioxide particles with a low degree of aggregation can be obtained.

[0006] Furthermore, Patent Document 3 describes a method for producing titanium oxide particles, in which an aqueous solution containing 34.5 g / L (in TiO2 equivalent) of titanium tetrachloride and ammonium acetate is heated, ammonia water is added when the temperature reaches 70°C, and then the solution is heated to its boiling point. Patent Document 3 also states that the titanium oxide particles produced in this way have high crystallinity. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2016 / 002755 [Patent Document 2] International Publication No. 2019 / 189307 [Patent Document 3] Japanese Patent Publication No. 2011-63496 [Overview of the project] [Problems that the invention aims to solve]

[0008] Titanium oxide particles produced by the "liquid phase method" described in Patent Documents 1 and 2 have a problem in that, in addition to crystalline components (crystalline titanium oxide components), they contain a relatively large amount of amorphous components (amorphous titanium oxide components) that are stable at high temperatures. When the content of amorphous components is high, differences in properties and functions between them and crystalline components are likely to appear. Furthermore, it is understood that the amorphous components can cause primary titanium dioxide particles to bind together, making it difficult for aggregated titanium dioxide particles to break apart. These issues can lead to, for example, non-uniform reactivity with other raw materials and poor handling when mixing with other raw materials, when synthesizing complex oxides such as barium titanate. Therefore, there is a need for a method to further reduce the content of the amorphous components contained in titanium oxide particles.

[0009] Furthermore, Patent Document 3 states that titanium oxide particles produced by the manufacturing method are highly crystallin (and therefore have a low amount of amorphous components) based on the value expressed as "specific surface area equivalent diameter / crystallite diameter". However, the aforementioned value expressed as "specific surface area equivalent diameter / crystallite diameter" cannot quantify the amount of amorphous components that are stably present in the high-temperature range, and there is a problem in that the amount of amorphous components cannot be specifically identified. In addition, titanium oxide particles obtained by the manufacturing method of Patent Document 3 contain a relatively large amount of amorphous components as specified in this application. For example, there is a need for further reduction of the amount of amorphous components that are stably present in the high-temperature range. [Means for solving the problem]

[0010] The inventors diligently studied methods to reduce the content of amorphous components (amorphous titanium oxide components) generated during the hydrolysis of titanium oxychloride, such as titanium tetrachloride. They discovered that titanium oxide particles with a low content of amorphous components can be obtained by controlling the hydrolysis temperature of titanium oxychloride and the presence of carboxylic acids in the solution during hydrolysis, thus completing the present invention.

[0011] In other words, the present invention is (1) Titanium oxide particles having an average aggregated particle diameter (D50) of 15 nm or more and 200 nm or less, and an amorphous component content of 7% by mass or less. (2) BET specific surface area is 100m 2 / g or more 400m 2 Titanium oxide particles as described in (1), which are less than or equal to / g (3) A first hydrolysis step in which a solution containing (oxy)titanium chloride and a carboxylic acid and / or a salt thereof is heated to a temperature of 95°C or higher and below the boiling point of the solution, A second hydrolysis step involves heating a solution containing the product after the first hydrolysis step, a mixture of (oxy)titanium chloride, and a carboxylic acid and / or its salt, at a temperature of 95°C or higher and below the boiling point of the solution. A method for producing titanium dioxide particles, including (4) A method for producing titanium oxide particles according to (3), wherein in the second hydrolysis step, a solution containing (oxy)titanium chloride and a carboxylic acid and / or a salt thereof is mixed with a solution containing the product after the first hydrolysis step. (5) A method for producing titanium oxide particles according to (3) or (4), wherein in the second hydrolysis step, a solution containing (oxy)titanium chloride and a carboxylic acid and / or a salt thereof is added intermittently or continuously to the solution containing the product after the first hydrolysis step, (6) A first hydrolysis step in which a solution containing titanium (oxy)chloride and a carboxylic acid and / or a salt thereof is mixed with an alkali at a temperature of 20°C to 65°C, A solution containing the product after the first hydrolysis step, titanium (oxy) chloride, and a carboxylic acid and / or its salt is heated at 95°C or higher and below the boiling point of the solution in a second hydrolysis step. A method for producing titanium oxide particles, comprising: (7) Medium Hydrolyze with water. The aforementioned The 1 Canada In the hydrolysis step, a solution containing titanium (oxy) chloride and a carboxylic acid and / or its salt is mixed in an alkali. The method for producing titanium oxide particles according to (6). And so on.

Effects of the Invention

[0012] According to the method for producing titanium oxide particles of the present invention, titanium oxide particles having a sufficiently small average aggregated particle diameter (D50) and further reduced amorphous components that are stably present in a high-temperature region can be produced. It has been found that the amorphous components affect various properties such as D50 and it is important to reduce them.

Brief Description of the Drawings

[0013] [Figure 1] An electron micrograph of the titanium oxide particles of Example 1. X [Figure 2] An electron micrograph of the titanium oxide particles of Example 2. [Figure 3] An electron micrograph of the titanium oxide particles of Example 3. [Figure 4] An electron micrograph of the titanium oxide particles of Comparative Example 1. [Figure 5] An electron micrograph of the titanium oxide particles of Comparative Example 2. [Figure 6] An X-ray diffraction spectrum of the titanium oxide particles of Example 1. [Figure 7] An X-ray diffraction spectrum of the titanium oxide particles of Example 3. [Figure 8] A DSC curve of the titanium oxide particles of Example 1. [Figure 9] A DSC curve of the titanium oxide particles of Example 3. [Figure 10] This is the DSC curve for titanium dioxide particles in Comparative Example 1. [Figure 11] This is the DSC curve for titanium dioxide particles in Comparative Example 2. [Modes for carrying out the invention]

[0014] The titanium oxide particles of the present invention have a small aggregate particle size and a very low amorphous component content. Specifically, the average aggregate particle size (D50) is between 15 nm and 200 nm, and the amorphous component content is 7% by mass or less.

[0015] The titanium dioxide particles of the present invention have high titanium dioxide purity and low impurity content. The titanium dioxide purity is preferably 99.0% by mass or more, more preferably 99.5% by mass or more, and even more preferably 99.9% by mass or more, when converted to TiO2. The impurities can be measured by known methods, such as by X-ray fluorescence analysis or ICP analysis.

[0016] The "titanium oxide" in the titanium oxide particles of this invention includes titanium dioxide, titanium monoxide, as well as hydrated titanium oxide, hydrated titanium oxide, metatitanic acid, orthotitanic acid, and the like. The titanium oxide particles of the present invention may have any of the following crystal forms: anatase, rutile, or brookite, or they may be a mixture of two or more crystal forms, or they may contain some amorphous material. The anatase form is preferred for producing titanium composite oxides, and is also preferred when used in photocatalysts, etc. The crystal form of the titanium oxide particles is determined from the X-ray diffraction spectrum measured using an X-ray diffractometer (Ultima IV, manufactured by Rigaku Corporation).

[0017] In the present invention, when the titanium dioxide particles have an anatase crystal structure, the rutile content is preferably 10% or less, and more preferably 5% or less. The rutile content refers to the percentage of rutile-type titanium dioxide in the total titanium dioxide particles and is calculated based on Formula 2 described later.

[0018] The particle size distribution of titanium dioxide particles is measured using a dynamic light scattering particle size distribution analyzer (NANOTRAC® WAVE II EX150, manufactured by Microtrac-Bel). As described later, a sample prepared by adding a polycarboxylic acid-based dispersant to a titanium dioxide particle slurry, adding a media (such as zircon beads), and processing it in a disperser is measured.

[0019] The 50% cumulative volume particle size distribution diameter in the particle size distribution measured as described above is defined as the average aggregated particle diameter (D50). The average aggregated particle diameter (D50) is preferably small, specifically between 15 nm and 200 nm, preferably between 15 nm and 100 nm, more preferably between 15 nm and 90 nm, and even more preferably between 15 nm and 80 nm.

[0020] The amorphous components contained in the titanium oxide particles of the present invention are quantified according to a known method (specifically, the method described in "Kawase S, Sugimoto K, Fujiwara R, Ono S, Journal of Analytical Chemistry, Vol. 59, No. 10, pp. 921-926 (2010)"). Specifically, using a differential scanning calorimeter (DSC), the thermal history of titanium oxide particles as a sample is measured as a DSC curve when the heating temperature of the sample is changed. The heat of crystallization ΔH (J / g) is calculated from the area of ​​the exothermic peak detected in the DSC curve when the amorphous components contained in the titanium oxide particles transition to the anatase type or the like due to heating. The exothermic peaks mentioned above are known to originate from the crystallization transition of the amorphous component of titanium dioxide and are detected between 300°C and 600°C. The heat of crystallization ΔH (J / g) is calculated from the area of ​​these exothermic peaks.

[0021] When titanium dioxide particles are produced, if organic substances such as carboxylic acids are used as raw materials, the titanium dioxide particles may contain organic substances derived from the raw materials. When titanium dioxide particles containing such organic substances are measured with a differential scanning calorimeter, the exothermic peaks of these organic substances are detected, and multiple exothermic peaks may be observed between measurement temperatures of 300°C and 600°C. In such cases, the exothermic peaks derived from the organic substances are excluded when calculating the heat of crystallization ΔH (J / g). Exothermic peaks derived from organic substances can be identified, for example, by whether or not the mass of the sample decreases while the sample is being heated. If the mass decreases along with the exothermic peaks seen in the DSC curve, it can be determined that these exothermic peaks originate from the decomposition of organic substances. Of course, the method for determining the exothermic peak originating from amorphous components is not limited to the above, and a comprehensive determination can be made by combining various known methods. The X-ray diffraction spectra of samples heated at different temperatures are measured using an X-ray diffractometer, and the amorphous components contained in the heated samples are quantified using a method employing Rietveld analysis. Using this method, the heating temperature at which the amount of amorphous components in the sample becomes less than 1% is identified. The exothermic peak in the DSC observed around that heating temperature (i.e., the temperature at which the amorphous components in the sample transition to crystalline components such as anatase) can be determined to be the exothermic peak originating from the amorphous components. For details on the quantitative method of amorphous components using Rietveld analysis, please refer to the following (specifically, "Kawase S, Sugimoto K, Fujiwara R, Ono S, Journal of Analytical Chemistry, Vol. 59, No. 10, pp. 921-926 (2010)").

[0022] The baseline for calculating the area of ​​the exothermic peak described above is the straight line connecting the measurement temperature at which the exothermic peak originating from the amorphous component rises and the measurement temperature at which the peak disappears. As the measurement temperature at which the peak disappears, the heating temperatures identified by Rietveld analysis or DSC curves for samples heated at different temperatures as described above can be used.

[0023] The crystallization heat ΔH (J / g) of the titanium oxide particles of the present invention calculated as described above, and the crystallization heat ΔH of the reference sample (amorphous titanium oxide) in which 100% by mass is amorphous. std Using the (J / g) value, the amount of amorphous component contained in the titanium oxide particles of the present invention is calculated using the following formula 1. Amount of amorphous components in the sample (mass %) = ΔH / ΔH std ×100...(Formula 1)

[0024] The heat of crystallization ΔH of a reference sample (amorphous titanium oxide) with 100% amorphous content. std For (J / g), we will use the literature value (217 J / g) shown in the reference (specifically, "B. Ohtani, Y. Ogawa, S. Nishimoto: J. Phys. Chem., B, 101, 3746 (1997)").

[0025] As calculated above, the amorphous component content of the titanium oxide particles of the present invention is 7% by mass or less, preferably 0.5% by mass or more and 7% by mass or less, and more preferably 0.5% by mass or more and 5% by mass or less.

[0026] The amorphous component of the titanium oxide particles of the present invention is a stable amorphous component that crystallizes in the high-temperature range (specifically, 300°C to 600°C). It is understood that such amorphous components affect various properties (e.g., disintegrability). To quantify such amorphous components, measurement by DSC, which involves heating the sample to a high temperature range, is necessary. On the other hand, Patent Document 3 describes a value expressed as "specific surface area equivalent diameter / crystallite diameter" as an indicator of the amount of amorphous components. However, this indicator cannot distinguish between amorphous components that exist stably in the high-temperature range and other components. In other words, the amount of amorphous components in the titanium oxide particles of the present invention cannot be quantified using the measurement method (specific surface area equivalent diameter / crystallite diameter) described in Patent Document 3.

[0027] The BET specific surface area of ​​the titanium oxide particles of the present invention is 100 m². 2 / g or more 400m 2 Preferably less than / g, 150m2 400 m or more per g 2 Less than or equal to per g is more preferable. The BET specific surface area can be determined by the nitrogen adsorption method (BET method) using a flow-type specific surface area automatic measuring device (FlowSorb II 2300, manufactured by Shimadzu Corporation).

[0028] The first production method of the titanium oxide particles of the present invention is a method of heating and hydrolyzing (oxy) titanium chloride in a solution, and includes a first hydrolysis step and a second hydrolysis step. The hydrolysis methods in both the first hydrolysis step and the second hydrolysis step are heating hydrolysis.

[0029] Further, the second production method of the titanium oxide particles of the present invention is a method in which (oxy) titanium chloride is neutralized and hydrolyzed with an alkali, and then the product after neutralization hydrolysis is heated and hydrolyzed in a solution together with (oxy) titanium chloride. In this method, the neutralization hydrolysis corresponds to the first hydrolysis step, and the heating hydrolysis corresponds to the second hydrolysis step.

[0030] In both the first production method and the second production method, in the first hydrolysis step, nuclei of titanium oxide particles are generated, and in the second hydrolysis step, the nuclei generated in the first hydrolysis step are grown.

[0031] <The First Production Method of the Titanium Oxide Particles of the Present Invention> Hereinafter, the first production method of the titanium oxide particles of the present invention will be described in detail. In the first hydrolysis step of the first production method, first, a solution containing (oxy) titanium chloride and a carboxylic acid and / or its salt is prepared. "(Oxy) titanium chloride" means titanium chloride or oxytitanium chloride. As "(oxy) titanium chloride", titanium tetrachloride, titanium trichloride, oxytitanium chloride, etc. can be used. Among them, titanium tetrachloride is preferable.

[0032] "Carboxylic acids and / or salts thereof" include monocarboxylic acids, poly(polyvalent)carboxylic acids and their salts, and form complexes with titanium (oxy)chloride in solution to stabilize titanium (oxy)chloride in solution. Examples of "carboxylic acids and / or salts thereof" are those listed in (a) to (g) below. (a) Carboxylic acids: For example, formic acid, acetic acid, propionic acid. (b) Polycarboxylic acids: especially dicarboxylic acids and tricarboxylic acids, such as oxalic acid and fumaric acid. (c) Hydroxypoly(polyvalent)carboxylic acids: especially hydroxydi- or hydroxytri-carboxylic acids, such as malic acid, citrate, or tartronic acid. (d) Polyhydroxy monocarboxylic acids: for example, glucoheptonic acid or gluconic acid. (e) Poly(polyvalent)-hydroxycarboxylic acids: For example, tartaric acid. (f) Dicarboxyl amino acids and their corresponding amides: for example, aspartic acid, asparagine (2-amino-3-carbamoylpropionic acid), or glutamic acid. (g) Hydroxylated or unhydroxylated monocarboxyl amino acids: for example, lysine, serine, or threonine.

[0033] As the carboxylic acid mentioned above, hydroxypoly(polyvalent)carboxylic acids are preferred, and citric acid is more preferred. Furthermore, any salt of the carboxylic acid can be used without restriction; for example, alkali metal salts such as sodium and potassium, and ammonium salts can be used.

[0034] In the first method for producing titanium oxide particles of the present invention, the above-mentioned (oxy)titanium chloride, a carboxylic acid and / or its salt, and an aqueous solvent are mixed to prepare a solution before the first hydrolysis reaction. The aqueous solvent refers to water or a solvent prepared by mixing water with an organic solvent such as alcohol. When an organic solvent is mixed, its content is preferably about 10% by mass or less of the aqueous solvent.

[0035] In this case, there are no particular restrictions on the order in which the titanium (oxy)chloride, carboxylic acid and / or its salt, and aqueous solvent are mixed. For example, a solution may be prepared in advance by mixing the carboxylic acid and / or its salt with an aqueous solvent and then mixing it with titanium (oxy)chloride; or a solution may be prepared in advance by mixing titanium (oxy)chloride and an aqueous solvent and then mixing it with the carboxylic acid and / or its salt; or a solution may be prepared in advance by mixing titanium (oxy)chloride and the carboxylic acid and / or its salt with an aqueous solvent and then mixing it with an aqueous solvent; or the aqueous solvent, carboxylic acid and / or its salt, and titanium (oxy)chloride may be mixed all at once.

[0036] The concentration of (oxy)titanium chloride in the first hydrolysis step is preferably 10 g / L or more and 100 g / L or less when converted to titanium dioxide (TiO2), and more preferably 10 g / L or more and 70 g / L or less. This ensures that the hydrolysis reaction in the first hydrolysis step is completed reliably and more effectively prevents unreacted titanium (oxy)chloride from remaining in the solution. If unreacted titanium (oxy)chloride remains in the solution, it can be hydrolyzed or neutralized under unintended conditions in subsequent steps after the first hydrolysis step, such as the step of adjusting the pH to a range of 6 to 8 when filtering the hydrolysis product, resulting in the formation of amorphous components.

[0037] The amount of carboxylic acid and / or its salt used in the first hydrolysis step is preferably 0.2 mol% to 4.0 mol% relative to titanium (oxy)chloride, and more preferably 0.4 mol% to 2.0 mol%.

[0038] As described above, carboxylic acids have the effect of stabilizing titanium (oxy)chloride in solution. When generating nuclei for titanium oxide particles by heating in the first hydrolysis step, it is preferable to have a mixture of carboxylic acids and / or their salts in the solution within the above range in order to control the hydrolysis reaction of titanium (oxy)chloride until the predetermined temperature is reached and to more effectively suppress the generation of amorphous components due to unintended hydrolysis reactions.

[0039] On the other hand, if the amount of carboxylic acid mixed in the solution is too large, the reaction in the first hydrolysis step will not proceed sufficiently due to its strong stabilizing effect, and it will not be possible to generate a sufficient amount of titanium dioxide particle nuclei. From the viewpoint of more effectively avoiding this problem, it is preferable that the amount of carboxylic acid used in the first hydrolysis step be within the above range.

[0040] Furthermore, by including a carboxylic acid and / or its salt in the solution during the first hydrolysis step, the rutile rate of the final titanium dioxide particles can be reduced.

[0041] In the first hydrolysis step, the temperature of the solution prepared as described above is raised to 95°C or higher and below the boiling point of the solution, thereby hydrolyzing titanium (oxy)chloride. More preferably, the temperature for the first hydrolysis is 97°C or higher and below the boiling point of the solution. By allowing the hydrolysis reaction of titanium (oxy)chloride to proceed sufficiently within the above temperature range, it is possible to prevent unreacted titanium (oxy)chloride from remaining in the solution and further suppress the generation of amorphous components due to unintended hydrolysis or neutralization in subsequent steps. The solution temperature should preferably be maintained within the specified temperature range mentioned above for several tens of minutes to several hours.

[0042] The pH of the solution in the first hydrolysis step is preferably adjusted to 1 or less, and more preferably between -1 and 1. This allows for control of the hydrolysis reaction of (oxy)titanium chloride and more effectively suppresses the formation of amorphous components due to unintended hydrolysis or neutralization. The pH can be adjusted by the amount of (oxy)titanium chloride in the solution and the amount of carboxylic acid and / or its salt mixed in. Since amorphous components are easily formed when (oxy)titanium chloride is neutralized by adding alkali, it is preferable to hydrolyze (oxy)titanium chloride by heating without adding alkali in the first hydrolysis step.

[0043] Following the first hydrolysis step described above, a second hydrolysis step is performed. In the second hydrolysis step, the solution containing the product from the first hydrolysis step (nuclei of titanium oxide particles), a solution mixed with (oxy)titanium chloride and a carboxylic acid, is heated to 95°C or higher and below the boiling point of the solution. The titanium (oxy)chloride and carboxylic acid and / or salt thereof used in the second hydrolysis step can be the same as those used in the first hydrolysis step described above. The amount of titanium (oxy)chloride mixed can be appropriately set according to the desired aggregate particle size and BET specific surface area of ​​titanium oxide. For example, it is preferably 0.4 mol to 20 mol per 1 mol of the product from the first hydrolysis step, more preferably 0.8 mol to 10 mol, and even more preferably 1 mol to 5 mol.

[0044] In the second hydrolysis step, there are no particular restrictions on the mixing order of the solution containing the product after the first hydrolysis step, titanium (oxy)chloride, and the carboxylic acid and / or its salt. For example, titanium (oxy)chloride and the carboxylic acid and / or its salt may be added separately to the solution containing the product after the first hydrolysis step, or a pre-mixed mixture of titanium (oxy)chloride and the carboxylic acid and / or its salt may be added. Alternatively, a pre-mixed mixture of titanium (oxy)chloride and the carboxylic acid and / or its salt may be prepared, and the solution containing the product after the first hydrolysis step may be added to this mixture. However, it is preferable to pre-mix (oxy)titanium chloride with a carboxylic acid and / or its salt, as this facilitates the formation of a complex between (oxy)titanium chloride and the carboxylic acid, makes it easier to control the hydrolysis reaction of (oxy)titanium chloride, and more effectively suppresses the generation of amorphous components due to hydrolysis or neutralization under unintended conditions.

[0045] When adding a solution containing (oxy)titanium chloride and a carboxylic acid and / or its salt to the solution containing the product after the first hydrolysis step in the second hydrolysis step, it is preferable to add it gradually over time (intermittently or continuously) rather than adding it all at once in a short time. In this case, the addition time is preferably 10 minutes or more and 3 hours or less. Adding a solution containing (oxy)titanium chloride and a carboxylic acid and / or its salt intermittently or continuously in this manner makes it easier to control the hydrolysis reaction of (oxy)titanium chloride and suppresses the formation of amorphous components due to hydrolysis or neutralization under unintended conditions, which is therefore preferable. Here, "intermittent" refers to a state in which the addition of the solution continues but is interrupted, and "continuous" refers to a state in which the addition of the solution continues without interruption.

[0046] The amount of carboxylic acid and / or its salt used in the second hydrolysis step is preferably 0.4 mol% to 12.5 mol%, and more preferably 0.6 mol% to 4.0 mol%, relative to the titanium (oxy)chloride added in the second hydrolysis step.

[0047] By doing so, the stabilizing effect of the carboxylic acid controls the hydrolysis reaction of (oxy)titanium chloride during the growth of titanium oxide particle nuclei in the second hydrolysis step, thereby more effectively suppressing the generation of amorphous components due to unintended hydrolysis reactions. In particular, in the second hydrolysis step, the solution temperature has been raised to 95°C or higher in the first hydrolysis step, and since titanium (oxy)chloride is mixed and hydrolysis is carried out under these conditions, the hydrolysis reaction of titanium (oxy)chloride tends to proceed rapidly. For this reason, adding a predetermined amount of carboxylic acid and / or its salt in the second hydrolysis step can more effectively suppress the rapid hydrolysis reaction (and consequently, the formation of amorphous components).

[0048] However, if the amount of carboxylic acid mixed in the solution is too large, the reaction in the second hydrolysis step will not proceed sufficiently due to its stabilizing effect, and unreacted (oxy)titanium chloride will remain in the solution, leading to unintended hydrolysis or neutralization (formation of amorphous components) in subsequent steps. From the viewpoint of more effectively avoiding this problem, it is preferable to keep the amount of carboxylic acid mixed in the second hydrolysis step within the above range.

[0049] In the second hydrolysis step, the solution containing the product from the first hydrolysis step is mixed with (oxy)titanium chloride and a carboxylic acid and / or its salt in the procedure described above, and the temperature of the solution is raised to 95°C or higher and below the boiling point of the solution to hydrolyze the (oxy)titanium chloride. In this way, the nuclei of the titanium oxide particles, which are the product of the first hydrolysis step, act as seed crystals, and nuclear growth is promoted in the second hydrolysis step, generating titanium oxide particles in the solution. The temperature of the solution in the second hydrolysis step is more preferably 97°C or higher and below the boiling point of the solution. It is preferable to maintain the above temperature range because if unreacted (oxy)titanium chloride remains in the solution, it is more effectively possible to suppress the generation of amorphous components due to unintended hydrolysis or neutralization in subsequent steps.

[0050] In the second hydrolysis step, the pH of the solution is preferably adjusted to 1 or less, and more preferably between -1 and 1. This controls the hydrolysis reaction of (oxy)titanium chloride and suppresses the formation of amorphous components due to unintended hydrolysis or neutralization. The pH of the solution can be adjusted by the amount of (oxy)titanium chloride and the amount of carboxylic acid and / or its salt in the solution. Since amorphous components are easily formed when (oxy)titanium chloride is neutralized by adding alkali, it is preferable to hydrolyze (oxy)titanium chloride by heating without adding alkali in the second hydrolysis step.

[0051] In the second hydrolysis step, a solution containing (oxy)titanium chloride and a carboxylic acid and / or its salt may be added to the solution containing the product after the first hydrolysis step, and then the solution may be aged for several tens of minutes to several hours while maintaining its temperature. The aging time is preferably 5 minutes to 3 hours. Aging can be expected to increase the reaction yield, sharpen the particle size distribution of the resulting titanium dioxide particles, or improve the crystallinity of the titanium dioxide particles.

[0052] By adding an alkali or acid to the solution containing the titanium dioxide particles produced by the above method, adjusting the pH to a range of 6 to 8 as needed, and optionally adding a flocculant, then filtering and drying, powdered titanium dioxide particles can be obtained.

[0053] <Second method for producing titanium oxide particles of the present invention> The second method for producing titanium oxide particles of the present invention is described in detail below. In the first hydrolysis step of the second manufacturing method, first, a solution containing (oxy)titanium chloride and a carboxylic acid and / or its salt is prepared. The "(oxy)titanium chloride" and "carboxylic acid and / or its salt" can be the same as those used in the first manufacturing method of titanium oxide particles described above.

[0054] In the second manufacturing method, the above-mentioned titanium (oxy)chloride, carboxylic acid and / or its salt, and an aqueous solvent are mixed to prepare a solution before the first hydrolysis reaction. The aqueous solvent refers to water or a solvent prepared by mixing water with an organic solvent such as alcohol. When an organic solvent is mixed, its content is preferably about 10% by mass or less of the aqueous solvent.

[0055] In this case, there are no particular restrictions on the order in which the titanium (oxy)chloride, carboxylic acid and / or its salt, and aqueous solvent are mixed. For example, a solution may be prepared in advance by mixing the carboxylic acid and / or its salt with an aqueous solvent and then mixing it with titanium (oxy)chloride; or a solution may be prepared in advance by mixing titanium (oxy)chloride and an aqueous solvent and then mixing it with the carboxylic acid and / or its salt; or a solution may be prepared in advance by mixing titanium (oxy)chloride and the carboxylic acid and / or its salt with an aqueous solvent and then mixing it with an aqueous solvent; or the aqueous solvent, carboxylic acid and / or its salt, and titanium (oxy)chloride may be mixed all at once.

[0056] The concentration of (oxy)titanium chloride in the first hydrolysis step is preferably 50 g / L to 200 g / L in terms of titanium dioxide (TiO2), and more preferably 75 g / L to 150 g / L. This ensures that the hydrolysis reaction in the first hydrolysis step is completed reliably. If the concentration of (oxy)titanium chloride in the first hydrolysis step is too high, unreacted (oxy)titanium chloride will remain in the solution, and in a step after the first hydrolysis step, for example, in a step where the pH is adjusted to a range of 6 to 8 when filtering the hydrolysis product, unintended hydrolysis or neutralization may occur, resulting in the formation of amorphous components. From the viewpoint of more effectively avoiding this problem, it is preferable to set the concentration to 200 g / L or less. Also, if the concentration of (oxy)titanium chloride in the first hydrolysis step is too low, the amount of titanium dioxide particle nuclei generated decreases, which reduces the production amount of titanium dioxide particles of the present invention. From the viewpoint of more effectively avoiding this problem, it is preferable to set the concentration to 50 g / L or more. Furthermore, setting the concentration to 50 g / L or more is preferable because it makes it easier to control the hydrolysis rate and more effectively suppresses the formation of amorphous components due to unintended hydrolysis reactions.

[0057] The amount of carboxylic acid and / or its salt used in the first hydrolysis step is preferably 0.2 mol% to 4.0 mol% relative to titanium (oxy)chloride, and more preferably 0.4 mol% to 2.0 mol%.

[0058] As described above, carboxylic acids have the effect of stabilizing titanium (oxy)chloride in solution. In order to control the hydrolysis reaction of titanium (oxy)chloride and more effectively suppress the generation of amorphous components due to unintended hydrolysis reactions when generating nuclei of titanium oxide particles by neutralization with alkali in the first hydrolysis step, it is preferable to have a mixed amount of carboxylic acid and / or its salt within the above range in the solution.

[0059] On the other hand, if the amount of carboxylic acid mixed in the solution is too large, the reaction in the first hydrolysis step will not proceed sufficiently due to its strong stabilizing effect, and it will not be possible to generate a sufficient amount of titanium dioxide particle nuclei. From the viewpoint of more effectively avoiding this problem, it is preferable that the amount of carboxylic acid used in the first hydrolysis step be within the above range.

[0060] Furthermore, by including a carboxylic acid and / or its salt in the solution during the first hydrolysis step, the rutile rate of the final titanium dioxide particles can be reduced.

[0061] In the first hydrolysis step, an alkali is prepared. Any alkaline compound can be used as the alkali, but examples include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, ammonium compounds such as aqueous ammonia and ammonia gas, and amine compounds such as alkylamines and ethanolamines. As the alkali, ammonium compounds and amine compounds that do not remain as impurities in the titanium oxide particles are preferred, and aqueous ammonia is particularly preferred. The alkali may also be diluted with pure water or the like.

[0062] In the first hydrolysis step, the solution containing (oxy)titanium chloride and a carboxylic acid and / or its salt, prepared as described above, is mixed with an alkali. This causes the (oxy)titanium chloride to undergo hydrolysis (neutralization hydrolysis).

[0063] In the above mixing step, the order of mixing is not particularly limited. That is, an alkali may be mixed with a solution containing (oxy)titanium chloride and a carboxylic acid and / or its salt, or an alkali may be mixed with a solution containing (oxy)titanium chloride and a carboxylic acid and / or its salt, or an alkali may be mixed simultaneously with a solution containing (oxy)titanium chloride and a carboxylic acid and / or its salt. Among these, it is preferable to mix a solution containing (oxy)titanium chloride and a carboxylic acid and / or its salt into the alkali. This makes it possible to more effectively suppress the formation of amorphous components in the second hydrolysis.

[0064] Furthermore, the liquid temperature during the mixing process should be between 20°C and 65°C, preferably between 30°C and 63°C, and more preferably between 40°C and 60°C. At this time, each solution may be at the above temperature range before mixing, or it may be reached during the mixing process, or it may be reached after mixing. By maintaining the above temperature range, the formation of amorphous components in the second hydrolysis can be suppressed.

[0065] In the first hydrolysis step, known mixing equipment such as stirrers, mixers, homogenizers, and agitators can be used as needed. The solution may also be aged for several tens of minutes to several hours while maintaining its temperature. The aging time is preferably 5 minutes to 1.5 hours.

[0066] The pH of the solution after the first hydrolysis is preferably between 5 and 10, and more preferably between 6 and 9.5. During the aging process described above, a pH adjusting agent may be added as needed to bring the pH within the aforementioned range. Known pH adjusting agents can be used.

[0067] In the second hydrolysis step, the solution containing the product from the first hydrolysis step is mixed with titanium (oxy)chloride and a carboxylic acid and / or its salt. This mixture is heated to a temperature of 95°C or higher and below the boiling point of the solution to hydrolyze the titanium (oxy)chloride. This promotes nucleation growth in the second hydrolysis step, using the titanium oxide particles, which are the product of the first hydrolysis step, as seed crystals, thereby generating titanium oxide particles in the solution and suppressing the formation of amorphous components in the second hydrolysis. The same titanium (oxy)chloride, carboxylic acid, and / or its salt as described above can be used.

[0068] In the second hydrolysis step, there are no particular restrictions on the mixing order of the solution containing the product after the first hydrolysis step, titanium (oxy)chloride, and the carboxylic acid and / or its salt. For example, titanium (oxy)chloride and the carboxylic acid and / or its salt may be added separately to the solution containing the product after the first hydrolysis step, or a pre-mixed mixture of titanium (oxy)chloride and the carboxylic acid and / or its salt may be added. Alternatively, a pre-mixed mixture of titanium (oxy)chloride and the carboxylic acid and / or its salt may be prepared, and the solution containing the product after the first hydrolysis step may be added to this mixture. However, it is preferable to pre-mix (oxy)titanium chloride with a carboxylic acid and / or its salt, as this facilitates the formation of a complex between (oxy)titanium chloride and the carboxylic acid, makes it easier to control the hydrolysis reaction of (oxy)titanium chloride, and more effectively suppresses the generation of amorphous components due to hydrolysis or neutralization under unintended conditions.

[0069] Next, the solution obtained in the above mixing step is heated to 95°C or higher, but below the boiling point of the solution. More preferably, the heating temperature is 97°C or higher, but below the boiling point of the solution. This temperature range is preferable because if unreacted (oxy)titanium chloride remains in the solution, it can more effectively suppress the formation of amorphous components through unintended hydrolysis.

[0070] In the second hydrolysis step, the pH of the solution is preferably adjusted to 1 or less, and more preferably between -1 and 1. This allows for control of the hydrolysis reaction of (oxy)titanium chloride and more effectively suppresses the formation of amorphous components due to unintended hydrolysis reactions. The pH of the solution can be adjusted by the amount of (oxy)titanium chloride and the amount of carboxylic acid and / or its salt in the solution. Since amorphous components are easily formed when (oxy)titanium chloride is neutralized by adding alkali, it is preferable to hydrolyze (oxy)titanium chloride by heating without adding alkali in the second hydrolysis step.

[0071] In the second hydrolysis step, a solution containing (oxy)titanium chloride and a carboxylic acid and / or its salt may be added to the solution containing the product after the first hydrolysis step, and then the solution may be aged for several tens of minutes to several hours while maintaining its temperature. The aging time is preferably 5 minutes to 3 hours. Aging can be expected to have effects such as increasing the reaction yield, sharpening the particle size distribution of the generated particles, or increasing the crystallinity of the particles.

[0072] By adding an alkali or acid to the solution containing the titanium dioxide particles produced by the above method, adjusting the pH to a range of 6 to 8 as needed, and optionally adding a flocculant, then filtering and drying, powdered titanium dioxide particles can be obtained.

[0073] Furthermore, the obtained titanium oxide particles may be wet-ground and sizing by known methods as needed, and then, if necessary, the particle surface may be coated with a hydrated oxide, hydroxide, or oxide of at least one metal selected from the group consisting of aluminum, silicon, zirconium, tin, titanium, and zinc. The amount of coating is preferably 1% to 50% by mass, and more preferably 5% to 30% by mass, relative to the base titanium oxide particles. It is preferable to keep the coating within the above range from the viewpoint that if the amount of coating is too little, the desired effects such as weather resistance cannot be obtained, and conversely, if the amount of coating is too much, aggregation will occur and it will also be economically disadvantageous. Furthermore, when the obtained titanium oxide particles are used as a catalyst support, catalyst, photocatalyst, or adsorbent, catalyst components, such as metals or compounds like platinum, tungsten, copper, silver, or gold, may be supported on them by conventional methods.

[0074] To coat titanium dioxide particles with an inorganic compound, for example, a wet method can be used in which an inorganic compound is added to a slurry in which titanium dioxide particles are dispersed in water while stirring, the pH is adjusted to precipitate the inorganic compound on the surface of the titanium dioxide particles, and then the slurry is filtered, washed, and dried.

[0075] Furthermore, the surface of the titanium dioxide particles may be coated with organic compounds such as fatty acids and their salts, alcohols, alkoxysilane compounds, and aminoalkoxysilane compounds. The alkoxysilane compounds and aminoalkoxysilane compounds may be coated in a hydrolyzed state. The amount of organic compound coating is preferably 1% to 50% by mass, and more preferably 5% to 30% by mass, relative to the base titanium dioxide particles. The above range is preferred because if the coating amount is too low, the desired effects such as dispersibility cannot be obtained, and conversely, if the coating amount is too high, aggregation will occur and it will also be economically disadvantageous. Two or more types of organic compounds may be used in combination depending on the application and purpose. Examples of alkoxysilane compounds include vinyltrimethoxysilane, methyltrimethoxysilane, propyltrimethoxysilane, isobutyltrimethoxysilane, n-butyltrimethoxysilane, n-hexyltrimethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, n-decyltrimethoxysilane, and phenyltrimethoxysilane. Examples of aminoalkoxysilane compounds include γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and N-β(aminoethyl)γ-aminopropyltrimethoxysilane.

[0076] To coat titanium dioxide particles with an organic compound, one of the following methods can be used: (1) a dry method in which titanium dioxide particles are placed in a high-speed stirrer such as a Henschel mixer and stirred while an organic compound, an aqueous solution or alcohol solution of the organic compound is added dropwise or by spray, and then dried; or (2) a wet method in which a slurry of titanium dioxide particles dispersed in water is stirred while an organic compound, an aqueous solution or alcohol solution of the organic compound is added, and then filtered, washed, and dried. [Examples]

[0077] Examples of the present invention are shown below, but the present invention is not limited to these examples.

[0078] (Example 1) A titanium tetrachloride solution was kept at room temperature, and 3% by mass of anhydrous citric acid (1.25 mol%) was added relative to the titanium tetrachloride (TiO2 equivalent). Further, pure water was added to adjust the concentration of titanium tetrachloride in the solution to 30 g / L (TiO2 equivalent). This solution was stirred at room temperature for 30 minutes, and then the temperature of the solution was raised to 98°C using a heater. After raising the temperature, the solution was maintained at 98°C for 30 minutes to perform the first hydrolysis. The pH of the solution after the first hydrolysis was below 0.

[0079] Next, a solution was prepared by adding 3% by mass of anhydrous citric acid (1.25 mol%) relative to the titanium tetrachloride (TiO2 equivalent) to 70 g of titanium tetrachloride solution. This solution was continuously added to the solution after the first hydrolysis over a period of 30 minutes. During the addition, the solution temperature was maintained at 98°C to carry out the second hydrolysis, obtaining a slurry containing titanium oxide particles. The pH of the solution after the second hydrolysis was also below 0.

[0080] A slurry containing titanium dioxide particles was neutralized with ammonia water until the pH reached 6.5, then filtered, washed, and dried at 120°C for 16 hours to obtain the titanium dioxide particles of Example 1. An electron microscope image of the titanium dioxide particles of Example 1 is shown in Figure 1.

[0081] (Example 2) Except for the modification in the second hydrolysis step of Example 1, in which a mixed solution of titanium tetrachloride and anhydrous citric acid was added to the solution after the first hydrolysis over a period of 60 minutes, the titanium oxide particles of Example 2 were obtained in the same manner as in Example 1. 2 Figure 2 shows an electron microscope image of titanium dioxide particles.

[0082] (Example 3) A titanium tetrachloride solution was kept at room temperature, and 3% by mass of anhydrous citric acid (1.25 mol%) was added relative to the titanium tetrachloride (TiO2 equivalent). Further, pure water was added to adjust the concentration of titanium tetrachloride in the solution to 100 g / L (TiO2 equivalent). After stirring this solution for 30 minutes, the solution was added to ammonia water over 1 to 2 hours, and the first hydrolysis was carried out while maintaining a temperature below 60°C. The pH of the solution after the first hydrolysis was between 7 and 9.

[0083] Next, a solution was prepared by adding 2% by mass of anhydrous citric acid (0.83 mol%) relative to the titanium tetrachloride (TiO2 equivalent) to 76.95 g of aqueous titanium tetrachloride. To this solution, the solution after the first hydrolysis was added, and after the addition was complete, the temperature was raised to 98°C to perform the second hydrolysis, obtaining a slurry containing titanium oxide particles. The pH of the solution after the second hydrolysis was below 0.

[0084] The slurry containing titanium dioxide particles was neutralized with ammonia water until the pH reached 6.5, then filtered, washed, and dried at 120°C for 16 hours to obtain the titanium dioxide particles of Example 3. An electron microscope image of the titanium dioxide particles of Example 3 is shown in Figure 3.

[0085] (Comparative Example 1) 1 liter of titanium tetrachloride aqueous solution containing 30 g / L of TiO2 was kept at room temperature, and 3% by mass of anhydrous citric acid (1.25 mol%) relative to the TiO2 was added and stirred for 30 minutes. The pH was below 0. This was then heated to 92°C and stirred for 30 minutes to perform the first hydrolysis. Next, at a temperature of 92°C, 70g of titanium tetrachloride aqueous solution and ammonia water were simultaneously added over 60 minutes each, and a second hydrolysis was performed when the pH of the solution was in the range of 0.8 to 1.2. The obtained titanium dioxide slurry was neutralized with ammonia water until the pH reached 6.5, then filtered, washed, and dried to obtain titanium dioxide particles of Comparative Example 1. An electron microscope image of the titanium dioxide particles of Comparative Example 1 is shown in Figure 4.

[0086] (Comparative Example 2) A titanium tetrachloride solution was kept at room temperature, and 3% by mass of anhydrous citric acid (1.25 mol%) was added relative to the titanium tetrachloride (TiO2 equivalent). Further, pure water was added to adjust the concentration of titanium tetrachloride in the solution to 100 g / L (TiO2 equivalent). After stirring this solution for 30 minutes, the temperature was raised to 70°C, and ammonia water containing 120 mol% ammonia relative to the titanium tetrachloride was added over 30 minutes. The temperature was then maintained to perform the first hydrolysis. Next, the temperature of the solution containing the product of the first hydrolysis was raised to 98°C and held for 60 minutes to hydrolyze the remaining titanium tetrachloride (second hydrolysis) and precipitate titanium oxide particles.

[0087] The obtained titanium dioxide slurry was neutralized with ammonia water until the pH reached 6.5, then filtered, washed, and dried to obtain titanium dioxide particles of Comparative Example 2. An electron microscope image of the titanium dioxide particles of Comparative Example 2 is shown in Figure 5.

[0088] <Evaluation 1: Crystalline form and rutile content> Using titanium oxide particles from the examples and comparative examples as samples, the X-ray diffraction spectra were measured using an X-ray diffractometer (Ultima IV, Rigaku Corporation) under the following conditions: X-ray tube: CuKα, tube voltage: 40kV, tube current: 40mA, divergence slit: 1 / 2°, scattering slit: 8mm, receiving slit: open, sampling width: 0.020°, scanning speed: 10.00° / min, and the crystal type was determined. The X-ray diffraction spectrum of the titanium oxide particles from Example 1 is shown in Figure 6, and the X-ray diffraction spectrum of the titanium oxide particles from Example 3 is shown in Figure 7. The rutile conversion rate was calculated using Equation 2 below, based on the peak height (Hr) of the maximum peak corresponding to the rutile-type crystal (2θ=27.4°) and the peak height (Ha) of the maximum peak corresponding to the anatase-type crystal (2θ=25.2°) in the X-ray diffraction spectrum. Rutile content (%) = Hr / (Hr+Ha) × 100 ... (Equation 2)

[0089] <Evaluation 2: Particle size> A slurry was prepared by adding 3 g of titanium dioxide powder from the examples and comparative examples to 30 ml of pure water, and then adding 3% by mass of a polycarboxylic acid-based dispersant (Nopcospers 5600, manufactured by Sunnopco) to each sample. This slurry and 60 g of 0.09 mm zircon beads as media were placed in a 70 ml mayonnaise bottle and dispersed for 60 minutes using a paint shaker (paint conditioner, manufactured by RED DEVIL).

[0090] These samples were used for evaluation, and their particle size distribution was measured using a dynamic light scattering particle size distribution analyzer (NANOTRAC® WAVE II EX150, manufactured by Microtrac-Bell). The measurement settings were as follows: (1) Refractive index of solvent (water): 1.333 (2) Refractive index of titanium dioxide particles For the Anatass type: 2.52 For rutile type: 2.72 (3) Density of titanium dioxide particles For the Anatase type: 3.9 g / cm³ 3 For rutile form: 4.2 g / cm³ 3 In the case of mixed crystals of anatase and rutile types, the conditions (particle refractive index, density) were set according to the crystal type with the higher abundance ratio.

[0091] The 50% cumulative volume particle size distribution diameter in the particle size distribution measured in this way was defined as the average aggregated particle size (D50).

[0092] <Rating 3: BET specific surface area> For the titanium dioxide particle powders of the examples and comparative examples, the BET specific surface area (m²) was measured using the nitrogen adsorption method (BET method) with a flow-type automatic specific surface area analyzer (FlowSorbII 2300, manufactured by Shimadzu Corporation). 2 The concentration (per g) was determined. Desorption was performed under nitrogen gas flow conditions at room temperature, and adsorption was performed at a temperature of 77 K.

[0093] <Evaluation 4: Quantitative determination of amorphous components> Using a differential scanning calorimeter ThermoPuls EVO2 DSC Vesta (manufactured by Rigaku Corporation), the thermal history of titanium oxide powder samples from the examples and comparative examples was measured as a DSC curve while the heating temperature of the samples was varied. 5 mg of the sample was packed into a measurement Pt pan (outer diameter 5 mmφ), and an empty Pt pan was used as the control sample. The DSC measurement conditions are as follows. (1) Heating rate: 10℃ / min (2) Measurement temperature range: Room temperature to 600°C (3) Measurement atmosphere: In the air

[0094] Based on the above measurement results, the heat of crystallization ΔH (J / g) was calculated from the area of ​​the exothermic peak when amorphous components detected between 300°C and 600°C crystallize, following the method described in the above reference (specifically, "Kawase S, Sugimoto K, Fujiwara R, Ono S, Journal of Analytical Chemistry, Vol. 59, No. 10, pp. 921-926 (2010)"). Figure 8 shows the DSC curve for the titanium dioxide particles of Example 1. As shown in the figure, two exothermic peaks were observed in the titanium dioxide particles of Example 1 between 300°C and 600°C. Of these, the exothermic peak observed around 350°C is the exothermic peak when the citric acid contained in the titanium dioxide particles decomposes, and the exothermic peak observed between 400°C and 500°C is the exothermic peak when the amorphous components contained in the titanium dioxide particles crystallize. Therefore, in Example 1, the exothermic peak observed around 400°C to 500°C was targeted, and the crystallization heat ΔH (J / g) was calculated from the area enclosed by the solid line (DSC curve) and the dashed line in Figure 8. The endpoint of the dashed line was determined by Rietveld analysis. In Example 2 (not shown), Example 3 (see Figure 9), Comparative Example 1 (see Figure 10), and Comparative Example 2 (see Figure 11), similar to Example 1, two exothermic peaks were observed in the DSC curve between 300°C and 600°C due to the use of citric acid during manufacturing. Therefore, the crystallization heat ΔH (J / g) was calculated for Example 2, Example 3, Comparative Example 1, and Comparative Example 2 in the same manner as in Example 1.

[0095] Furthermore, using the above-mentioned literature value (217 J / g) as the heat of crystallization value for a sample (amorphous titanium oxide) in which the amorphous component is 100% by mass, the amount of amorphous component contained in the titanium oxide particles of the present invention was calculated using the following formula 3. Amount of amorphous components in the sample (mass%) = ΔH / 217 × 100 ... (Equation 3)

[0096] Table 1 shows the average aggregated particle size (D50), BET specific surface area, rutile rate, and amorphous component content measured by the above method.

[0097] [Table 1]

[0098] As shown in Table 1, the titanium oxide particles of Example 1, Example 2, and Example 3 of the present invention have a reduced content of amorphous components compared to the titanium oxide particles of Comparative Example 1 and Comparative Example 2. In the second hydrolysis step of the first manufacturing method of the present invention, the temperature of the reaction solution has already reached a high temperature. In the first manufacturing method of the present invention, in the titanium oxide particles of Example 1 and Example 2, citric acid is added along with titanium tetrachloride not only in the first hydrolysis (nucleation) step but also in the second hydrolysis (nucleation growth) step. As a result, even if the second hydrolysis step is performed at a high temperature, the rapid progress of the reaction is suppressed. Consequently, it is understood that the formation of amorphous components is suppressed. On the other hand, in Comparative Example 1, citric acid was not added in the second hydrolysis (nucleation growth) step of the titanium dioxide particles. Since the reaction solution after the first hydrolysis step has already reached a high temperature, when titanium tetrachloride is mixed in alone, the hydrolysis reaction tends to proceed rapidly. Due to these factors, the formation of amorphous components is likely to occur in Comparative Example 1.

[0099] Furthermore, in the titanium oxide particles of Comparative Example 2, the titanium tetrachloride remaining in the first hydrolysis step is subjected to heat hydrolysis in the second hydrolysis step. In contrast, in the titanium oxide particles of Example 3, which is the second manufacturing method of the present invention, in the second hydrolysis step, a solution containing the product of the first hydrolysis is added to a solution containing titanium tetrachloride and citric acid and mixed, thereby causing the newly added titanium tetrachloride to be subjected to heat hydrolysis. In other words, in the titanium oxide particles of Example 3, unlike the titanium oxide particles of Comparative Example 2, the titanium tetrachloride added in the first hydrolysis step is completely hydrolyzed in the first hydrolysis step, and in the second hydrolysis step, the newly added titanium tetrachloride is hydrolyzed. This suppresses unintended hydrolysis reactions. As a result, it is understood that the formation of amorphous components is suppressed.

[0100] However, when adopting a formulation design that reduces the content of amorphous components, as in the titanium dioxide particles of the present invention, it is possible that the aggregated particle size (D50) may increase or the BET specific surface area may decrease in some cases. In this respect, the titanium dioxide particles of Examples 1, 2, and 3 of the present invention maintain aggregated particle size (D50) and BET specific surface area at a level comparable to the titanium dioxide particles of Comparative Examples 1 and 2, which have a relatively small aggregated particle size and a relatively large BET specific surface area. [Industrial applicability]

[0101] The titanium oxide particles of the present invention have a sufficiently small average aggregated particle size (D50) and a sufficiently reduced amorphous component. Because they become easily broken down by means such as crushing, it is expected that titanium composite oxides using these titanium oxide particles as a raw material will have smaller particle sizes, making them useful as a raw material for producing titanium composite oxides. Furthermore, they are also useful as catalyst supports, catalysts, photocatalysts, adsorbents, and the like.

Claims

1. Titanium oxide particles having an average aggregated particle diameter (D50) of 15 nm or more and 200 nm or less, and containing 7% by mass or less of amorphous titanium oxide components.

2. BET specific surface area is 100 m ２ / g or more 400m ２ Titanium oxide particles according to claim 1, wherein the amount is less than or equal to / g.

3. A first hydrolysis step involves heating a solution containing (oxy)titanium chloride and a carboxylic acid and / or its salt at a temperature of 95°C or higher and below the boiling point of the solution. A second hydrolysis step involves heating a solution containing the product after the first hydrolysis step, a mixture of (oxy)titanium chloride, and a carboxylic acid and / or its salt, at a temperature of 95°C or higher and below the boiling point of the solution. Includes, A method for producing titanium oxide particles, comprising the second hydrolysis step of intermittently or continuously adding a solution containing (oxy)titanium chloride and a carboxylic acid and / or a salt thereof to a solution containing the product after the first hydrolysis step over a period of 10 minutes to 3 hours.

4. A method for producing titanium oxide particles according to claim 3, wherein in the second hydrolysis step, a solution containing (oxy)titanium chloride and a carboxylic acid and / or a salt thereof is mixed with a solution containing the product after the first hydrolysis step.

5. A first hydrolysis step of mixing a solution containing (oxy)titanium chloride and a carboxylic acid and / or a salt thereof with an alkali at a temperature of 20°C to 65°C, A second hydrolysis step involves heating a solution containing the product after the first hydrolysis step, a mixture of (oxy)titanium chloride, and a carboxylic acid and / or its salt, at a temperature of 95°C or higher and below the boiling point of the solution. A method for producing titanium dioxide particles, including

6. The method for producing titanium oxide particles according to claim 5, wherein in the first hydrolysis step of neutralization hydrolysis, a solution containing (oxy)titanium chloride and a carboxylic acid and / or a salt thereof is mixed in an alkali.

Images