Titanium oxide powder, titanium oxide slurry, and method for producing the same

Abstract

The BET specific surface area measured by nitrogen adsorption method is 80m 2 / g or more 300m 2 / g or less, and the anatase content of the crystalline phase measured by powder X-ray diffraction (XRD) is 90% or more; The A / BET specific surface area calculated from the reciprocal A of the spin-spin relaxation response time T2 measured by pulse NMR for a mixed solution containing 10 mass% titanium oxide prepared using ion-exchanged water and the BET specific surface area was 2.3 × 10 -5 [ms -1 / (m 2 / g)] or more.

Description

[Technical Field]

[0001] The present disclosure relates to a titanium oxide powder, a titanium oxide slurry, and a method for producing the same. [Background technology]

[0002] Titanium(IV) oxide (TiO2) is a chemically stable material and is used industrially in a wide range of fields, including as a white pigment. Patent Document 1 discloses that titanium oxide fine particles that have been subjected to a specific surface treatment are blended into a coating composition that uses titanium oxide fine particles as an ultraviolet screening agent. Patent Document 2 discloses organosiloxane oligomer-modified inorganic oxide ultrafine particles containing rutile titanium oxide, which have a high refractive index and excellent transparency, dispersibility, light resistance, weather resistance, etc.

[0003] Titanium dioxide is known to have three main crystalline structures: anatase, brookite, and rutile. Anatase titanium dioxide, in particular, has a higher surface hydroxyl group content than other crystalline phases, resulting in high hydrophilicity and dispersibility. Anatase titanium dioxide has a higher surface hydroxyl group content, resulting in high reactivity with other metal elements. Therefore, anatase titanium dioxide is in high demand as a raw material for dielectric materials or battery materials. Among dielectric and battery material applications, strict composition control is particularly required for electronic device applications. Therefore, titanium dioxide powder used as a raw material for electronic device materials is desirable to be easily and uniformly dispersible in order to reduce abnormal particles and compositional deviations caused by poor dispersion in reaction solutions and the resulting reaction failures.

[0004] In recent years, there has been a demand for fine anatase titanium dioxide powder with a high specific surface area to achieve higher functionality in these applications. Non-Patent Document 1 discloses that as the particle diameter of the particles constituting the powder decreases, the specific surface area of ​​the particles increases, resulting in an increase in the viscosity of the slurry. [Prior art documents] [Patent documents]

[0005] [Non-Patent Document 1] Journal of Colloid and Interface Science Volume 33, Issue 1, May 1970, Pages 150-160 [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-212355 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-95392 Summary of the Invention [Problem to be solved by the invention]

[0006] From the viewpoint of viscosity of the reaction solution, when using a powder composed of particles with a small particle size, it is difficult to mix and react the raw materials uniformly unless the solid concentration of the reaction solution is diluted. Therefore, if a powder composed of particles with a small particle size is selected as the raw material, the production volume per unit time must be reduced, which significantly reduces the production capacity of the manufacturing process.

[0007] For these reasons, there is a demand for an anatase type titanium oxide powder that can be uniformly dispersed in a solvent and that can form a low-viscosity slurry even at high concentrations so as to increase the production efficiency of the production line.

[0008] The present disclosure provides a titanium oxide powder that has a high anatase content and can form a low-viscosity slurry, a titanium oxide slurry, and a method for producing the same. [Means for solving the problem]

[0009] The present disclosure encompasses the following aspects. [Aspect 1] The BET specific surface area measured by nitrogen adsorption method is 80m 2 / g or more 300m 2 / g or less, and the anatase content of the crystalline phase measured by powder X-ray diffraction (XRD) is 90% or more; The A / BET specific surface area calculated from the reciprocal A of the spin-spin relaxation response time T2 measured by pulse NMR for a mixed solution prepared using ion-exchanged water and containing 10% by mass of titanium oxide and the BET specific surface area is 2.3 × 10 -5 [ms -1 / (m 2 / g)] or more. [Aspect 2] The titanium oxide powder according to the above-mentioned aspect 1, having a spin-spin relaxation response time T2 of 100 ms or more and 500 ms or less. [Aspect 3] 3. The titanium oxide powder according to aspect 1 or 2, wherein the Si content is 0.1% by mass or less and the P content is 0.1% by mass or less. [Aspect 4] The titanium oxide powder according to any one of the above aspects 1 to 3, having an Na content of 0.1% by mass or less and an Mg content of 0.1% by mass or less. [Aspect 5] 5. The titanium oxide powder according to any one of Aspects 1 to 4, wherein the half-value width of a diffraction peak at a diffraction angle 2θ in the range of 24.5° to 26.0°, as measured by powder X-ray diffractometry (XRD), is 0.50° to 2.00°. [Aspect 6] 6. The titanium oxide powder according to any one of Aspects 1 to 5, having a zeta potential of 25 mV or more and 63 mV or less in absolute value. [Aspect 7] 7. The titanium oxide powder according to any one of Aspects 1 to 6, wherein a slurry prepared using ion-exchanged water and containing 40% by mass of titanium oxide has a viscosity of less than 3000 mPa·s at 25°C. [Aspect 8] A titanium oxide slurry comprising the titanium oxide powder according to any one of the above aspects 1 to 7 and a liquid medium. [Aspect 9] A method for producing a titanium oxide slurry, comprising mixing the titanium oxide powder according to any one of the above aspects 1 to 7 with a liquid medium so that the titanium oxide content is 3 to 40 mass % to produce a slurry.

[10] a synthesis step of reacting titanium tetrachloride and an acid to produce titanium oxide; A drying step of drying the titanium oxide powder; and A firing process to fire titanium oxide powder A method for producing a titanium oxide powder, comprising: A manufacturing method in which the ratio of the amount of substance of acidic functional groups to the amount of substance of Ti in the synthesis step (acidic functional groups [mol] / Ti [mol]), and the amount of water before firing and the firing temperature in the firing step satisfy (1). Acidic functional group [mol] / Ti [mol] × 800 + moisture content before calcination [mass%] × 300 / calcination temperature [K°] ≥ 60.0…(1) [Effects of the Invention]

[0010] According to the present disclosure, it is possible to provide a titanium oxide powder that has a high anatase content and can form a low-viscosity slurry, a titanium oxide slurry, and a method for producing the same. DETAILED DESCRIPTION OF THE INVENTION

[0011] An example of an embodiment of the present invention will be described below, but the present invention is not limited to the following embodiment.

[0012] In this disclosure, when "~" is used to describe a numerical range, the numerical values ​​at both ends are the upper and lower limits, respectively, and are included in the numerical range. When multiple upper or lower limits are listed, numerical ranges can be created using all combinations of the upper and lower limits. Similarly, when multiple numerical ranges are listed, separate numerical ranges can be created by individually selecting and combining the upper and lower limits from those numerical ranges.

[0013] In this disclosure, "titanium oxide" refers to titanium(IV) oxide (TiO2) unless otherwise specified. Furthermore, "Ti concentration" refers to the concentration (mol / L) calculated by dividing the amount of Ti atoms (mol) by the volume (L) of the Ti-containing liquid, taking into account all titanium-atom-containing components that make up titanium compounds, titanium-containing ions, titanium-containing complexes, etc.

[0014] <1-1. Titanium oxide powder> In one embodiment, the titanium oxide powder has a BET specific surface area of ​​80 m as measured by a nitrogen adsorption method. 2 / g or more 300m 2 / g, the anatase content of the crystalline phase measured by powder X-ray diffraction (XRD) is 90% or more, and the A / BET specific surface area calculated from the reciprocal A of the spin-spin relaxation response time T2 measured by pulse NMR for a mixed solution containing 10% by mass of titanium oxide prepared using ion-exchanged water, and the BET specific surface area is 2.3 × 10 -5 [ms -1 / (m 2 / g)] or more.

[0015] (BET specific surface area) The BET specific surface area of ​​titanium oxide powder is 80m 2 / g or more. 80m 2 / g or more, the particle size is so small that when titanium oxide is reacted with other substances, an ultrafine particle material can be obtained. A specific example of an ultrafine particle material is a 0201 size multilayer ceramic capacitor material. From the same perspective, the BET specific surface area of ​​titanium oxide powder is 110 m 2 / g or more is preferable, and 120m 2 / g or more is more preferable. The BET specific surface area of ​​the titanium oxide powder is 300m 2 / g. 2 When the BET specific surface area of ​​the titanium oxide powder is less than 260 m / g, abnormal grain growth of the titanium oxide can be suppressed even when reacted with barium carbonate at high temperatures, and the particle size distribution of the resulting barium titanate material can be narrowed. 2 / g or less is preferable, and 180m 2 / g or less is more preferable, and 160m 2 / g or less is more preferable. In the present disclosure, the BET specific surface area is measured by the method described in the Examples.

[0016] (anatase content) The anatase content of the crystalline phase of the titanium oxide powder is 90% or more. When titanium oxide is reacted with other substances, a high anatase content in the titanium oxide powder is advantageous because it increases reactivity. From the same perspective, the anatase content is more preferably 95% or more, even more preferably 99% or more, and particularly preferably 100%. The upper limit of the anatase content is not particularly limited, but can be, for example, 100% or less, 99% or less, or 98% or less. In the present disclosure, the anatase content refers to the content of anatase-type crystals in the crystalline phase of titanium oxide particles, and is measured by the method described in the Examples.

[0017] (Spin-spin relaxation response time T2) Unlike high-resolution NMR, pulsed NMR does not provide chemical shift information, but instead provides information on molecular dynamics that is closely related to the 1 This is a technique that can rapidly measure the relaxation response time of H nuclei, specifically the spin-lattice relaxation response time T1 and the spin-spin relaxation response time T2. The use of pulsed NMR has rapidly spread in recent years, and known measurement methods in pulsed NMR include the Hahn echo method, the solid echo method, the CPMG method, and 90° pulsed NMR. In this disclosure, the spin-spin relaxation response time T2 is measured by the CPMG (Carr Purcell Meiboom Gill) method. 1 This refers to the spin-spin relaxation response time T2 of H nuclei, and is measured by the method described in the Examples.

[0018] The spin-spin relaxation response time T2 is preferably 100 ms or more, more preferably 110 ms or more, and even more preferably 120 ms or more. The spin-spin relaxation response time T2 is preferably 500 ms or less, more preferably 480 ms or less, and even more preferably 450 ms or less. 1The spin-spin relaxation response time T2 of H nuclei is thought to be a physical property related to the state of water molecules bound to the titanium oxide particle surface. Specifically, the shorter the spin-spin relaxation response time T2, the more water molecules are bound to the titanium oxide particle surface, i.e., the thicker the hydration layer, which is thought to facilitate improved dispersibility of the titanium oxide particles.

[0019] (The reciprocal of the spin-spin relaxation response time T2, A (A=1 / T2)) The reciprocal A (= 1 / T) of the spin-spin relaxation response time T described above is an index of the strength of the interaction between free water and the titanium oxide particle surface. The stronger the interaction between the titanium oxide particle surface and free water, the more hydrophilic the titanium oxide becomes to the aqueous solvent, so A is used as an alternative index of the hydrophilicity of titanium oxide.

[0020] ((A / BET specific surface area))) The spin-spin relaxation response time T2 varies depending on the total number of hydroxyl groups and organic acid-derived carboxyl groups on the titanium oxide particle surface. It is presumed that the greater the total number of hydroxyl groups and organic acid-derived carboxyl groups on the titanium oxide particle surface per specific surface area, rather than in a condensed state, the greater the hydrophilicity of the titanium oxide. Based on the above, to accurately evaluate the hydrophilicity of titanium oxide powders, it is necessary to compare factors that affect hydrophilicity, such as hydroxyl groups, per specific surface area of ​​the titanium oxide powder. Therefore, the hydrophilicity of each titanium oxide powder can be compared using the value obtained by dividing A, an alternative indicator of hydrophilicity, by the BET specific surface area of ​​the titanium oxide.

[0021] The A / BET specific surface area calculated from the reciprocal A of the spin-spin relaxation response time T2 measured by pulse NMR for a mixture containing 10 mass% titanium oxide prepared using ion-exchanged water and the BET specific surface area was 2.3 × 10 -5 [ms -1 / (m 2 / g)] or more. -5 [ms -1 / (m 2 / g)] or more, the hydrophilicity can be increased. From the same viewpoint, the A / BET specific surface area is 2.4 × 10 -5 [ms -1 / (m 2 / g)] or more is preferable, and 2.5 × 10 -5 [ms -1 / (m 2 / g)] or more is more preferable. -5 [ms -1 / (m 2 / g) or less, the titanium oxide particles are less likely to aggregate and precipitate in the slurry, which is preferable. From the same viewpoint, the A / BET specific surface area is 2.9 × 10 -5 [ms -1 / (m 2 / g)] or less is more preferable, and 2.8 × 10 -5 [ms -1 / (m 2 / g)] or less is even more preferable."

[0022] (FWHM of diffraction peak measured by powder X-ray diffraction (XRD)) The full width at half maximum (FWHM) of the diffraction peak of the titanium oxide powder in the diffraction angle 2θ range of 24.5° to 26.0° measured by powder X-ray diffractometry (XRD) is preferably 0.50° or more. The smaller the FWHM of the titanium oxide powder, the higher the crystallinity, which is preferable. However, achieving a very small FWHM is likely to cause aggregation of titanium oxide particles due to the high temperature reaction, which reduces the BET specific surface area. Therefore, from the viewpoint of suppressing aggregation of titanium oxide particles, it is desirable to set the FWHM at a certain level or more, for example, 0.50° or more is preferable. From the same viewpoint, the FWHM is more preferably 0.70° or more, and even more preferably 0.90° or more.

[0023] The FWHM is preferably 2.00° or less. This is because the better the crystallinity of titanium oxide, the better the crystallinity of products produced using titanium oxide. From the same perspective, the FWHM is more preferably 1.50° or less, and even more preferably 1.30° or less. The FWHM is measured by the method described in the Examples.

[0024] (viscosity) The viscosity of a slurry containing 40% by mass of titanium oxide prepared using ion-exchanged water is preferably less than 3000 mPa·s at 25°C. Within this range, a titanium oxide slurry with low viscosity can be obtained, which is efficient in increasing the titanium oxide concentration during material synthesis. In the present disclosure, the viscosity of the slurry is measured by the method described in the Examples.

[0025] (zeta potential) The absolute value of the zeta potential of the titanium oxide powder is preferably 25 mV or more and 63 mV or less. If it is 25 mV or more, dispersibility will be increased due to charge repulsion between particles. From the same perspective, the absolute value of the zeta potential is more preferably 26 mV or more, and even more preferably 28 mV or more. If the absolute value of the zeta potential is 63 mV or less, the zeta potential is not too high, so over-dispersion can be suppressed in the process of dispersing particles in a solvent, such as when producing barium titanate. From the same perspective, the absolute value of the zeta potential is more preferably 37 mV or less, and even more preferably 34 mV or less. The zeta potential is measured by the method described in the Examples.

[0026] (Elemental analysis) When titanium oxide powder is used for electronic devices, it is preferable that it does not contain metalloid elements such as Si (silicon) and P (phosphorus), metal elements such as Na (sodium) and Mg (magnesium), or polymeric organic acid chains such as polyols, so as not to degrade the properties of the electronic device material. When titanium oxide powder is used as a raw material for a dielectric material, P (phosphorus), Na (sodium), and Mg (magnesium) may cause a decrease in the dielectric constant. Therefore, the P content, Na content, Mg content, and S content of the titanium oxide powder are each preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and even more preferably 0.01% by mass or less. There are no particular restrictions on the lower limit, but from the perspective of production costs, 0.000001% by mass or more is preferable. The Si content is preferably 0.1% by mass or less, more preferably 0.05% by mass or less. There are no particular restrictions on the lower limit, but from the perspective of production costs, 0.001% by mass or more is preferable.

[0027] To suppress the deposition of by-products derived from C (carbon), the C content of the titanium oxide powder is preferably 0.50% by mass or less, more preferably 0.30% by mass or less, and even more preferably 0.10% by mass or less. There is no particular restriction on the lower limit, but from the viewpoint of production costs, a C content of 0.00001% by mass or more is preferred.

[0028] The content of each atom is measured by the method described in the Examples.

[0029] <1-2. Titanium oxide slurry> In one embodiment, the titanium oxide slurry contains titanium oxide powder and a liquid medium. Examples of the liquid medium include water, organic solvents such as alcohol, and mixtures thereof. The liquid medium is not particularly limited, but industrially, water, particularly ion-exchanged water, is preferred.

[0030] Since titanium oxide slurries with a viscosity of 3000 mPa·s or higher have significantly low fluidity, the flow point is set to 3000 mPa·s, and the titanium oxide content of a titanium oxide slurry that imparts a flow point at 25°C is preferably greater than 40% by mass. A titanium oxide content of greater than 40% by mass is efficient because it allows for a high titanium oxide concentration during material synthesis. From the same perspective, a titanium oxide content of 42% by mass or greater is more preferable, and 44% by mass or greater is even more preferable. The upper limit of the titanium oxide content of a titanium oxide slurry that imparts a flow point may be, for example, 60% by mass or less, or 50% by mass or less. In the present disclosure, the titanium oxide content of a titanium oxide slurry that imparts a flow point is measured by the method described in the Examples.

[0031] <2. Titanium oxide powder manufacturing method> A method for producing titanium oxide powder according to one embodiment will be described below. The method for producing titanium oxide powder according to one embodiment includes a synthesis step, a drying step, and a calcination step. <2-1. Synthesis process> The synthesis step is a step of reacting titanium tetrachloride with an acid to produce titanium oxide. Titanium oxide is produced, for example, by mixing a liquid containing titanium tetrachloride, an acid, and an aqueous medium and reacting them to precipitate titanium oxide. Preferably, the synthesis step includes a mixing step of obtaining a mixed liquid containing titanium tetrachloride, an acid, and an aqueous medium, and a heating step of heating the mixed liquid to cause the reaction. Examples of aqueous media include water, alcohols such as methanol, and mixed solvents thereof. The aqueous medium is preferably water.

[0032] <<Mixing process>> The mixing step is carried out, for example, by adding an acid to a solution containing titanium tetrachloride, by adding a solution containing an acid to a solution containing titanium tetrachloride, or by adding titanium tetrachloride to a solution containing an acid. From the viewpoint of uniformly mixing titanium tetrachloride and the acid, it is desirable to add the acid to the solution containing titanium tetrachloride.

[0033] The acid adheres to the titanium oxide particles to stabilize their surfaces and acts as a phase transition inhibitor, inhibiting the phase transition from anatase to rutile. The acid also enhances the hydrophilicity of the titanium oxide particles and inhibits their aggregation. Examples of the acid include organic acids such as carboxylic acids and sulfonic acids, and inorganic acids such as hydrochloric acid.

[0034] The molecular weight of the organic acid is preferably 300 or less. When the molecular weight of the organic acid is 300 or less, the organic acid can uniformly modify the surface of the titanium oxide particles, thereby improving the dispersibility of the particles. From the same viewpoint, the molecular weight of the organic acid is more preferably 250 or less, and even more preferably 200 or less. From the viewpoint of enhancing the phase transition suppression effect and aggregation suppression effect, the molecular weight of the organic acid is preferably 30 or more, and more preferably 100 or more.

[0035] The acid is preferably a carboxylic acid from the viewpoint of a high effect of inhibiting the phase transition to the rutile phase, more preferably an α-hydroxycarboxylic acid, and even more preferably malic acid (molecular weight 134.09), citric acid (molecular weight 192.12), or tartaric acid (molecular weight 150.09). The acid may be used alone or in combination of two or more kinds.

[0036] The Ti concentration in the mixed solution is preferably 0.01 mol / L or more. This is to allow the hydrolysis reaction to proceed preferentially. From the same viewpoint, it is more preferably 0.05 mol / L or more, and even more preferably 0.30 mol / L or more. The Ti concentration is preferably 2.00 mol / L or less. This is to suppress the phase transition to the rutile phase. From the same viewpoint, it is more preferably 1.50 mol / L or less, and even more preferably 1.00 mol / L or less.

[0037] Regarding the content of acidic functional groups in the mixed solution, the ratio of the amount of substance of acidic functional groups to the amount of substance of Ti in the mixed solution (acidic functional groups [mol] / Ti [mol]) (molar ratio) is preferably 0.040 or more. This is to suppress the phase transition from anatase phase to rutile phase. It also makes it easier to impart acidic functional groups to the surface of titanium oxide particles. From the same viewpoint, it is more preferably 0.050 or more, and even more preferably 0.055 or more. From the viewpoint of suppressing reaction inhibition, the ratio of the amount of substance (acidic functional groups [mol] / Ti [mol]) is preferably 0.100 or less, and more preferably 0.070 or less.

[0038] The amount of substance of the acidic functional group in the mixture represents the sum of the amounts of substance of the acidic functional groups of the acids contained in the mixture. For example, if the acids contained in the mixture are 1 mol of malic acid and 1 mol of citric acid, the amount of substance of the acidic functional group in the mixture is 5 mol because malic acid has two acidic functional groups and citric acid has three acidic functional groups.

[0039] When water is used as the aqueous medium, the pH of the mixture is preferably 3 or less, in order to allow the hydrolysis reaction to proceed preferentially. From the same viewpoint, the pH is more preferably 2 or less, and even more preferably 1 or less.

[0040] In the mixing step, in order to allow the hydrolysis reaction to proceed slowly, the liquid temperature is preferably maintained at 40°C or lower, more preferably at 30°C or lower.

[0041] <<Heating process>> In the heating step, the mixed solution is heated to promote the reaction. Titanium oxide can be precipitated by heating the mixed solution. Heating is preferably performed while stirring to increase the reaction efficiency. From the viewpoint of productivity, the mixed solution is preferably heated at a high temperature increase rate. Therefore, the mixed solution is preferably heated to the synthesis temperature at a temperature increase rate of 0.1°C / min or more, more preferably 0.3°C / min or more, and even more preferably 0.6°C / min or more. On the other hand, to suppress the precipitation of amorphous titanium oxide and improve crystallinity, it is preferable to suppress the rapid progress of the reaction and to suppress the temperature increase rate so as to ensure sufficient crystal growth. Therefore, the mixed solution is preferably heated to the synthesis temperature at a temperature increase rate of 1.5°C / min or less, more preferably 1.0°C / min or less.

[0042] The synthesis temperature is preferably 50°C or higher, and more preferably 70°C or higher, in order to allow the hydrolysis reaction to proceed predominantly. The synthesis temperature is preferably 100°C or lower, in order to suppress the phase transition from the stable phase to the rutile phase.

[0043] The time for which the mixed solution is held at the synthesis temperature can be set as desired, and the temperature may be lowered without holding, or may be held for a predetermined time. From the viewpoint of allowing the reaction to proceed sufficiently, it is preferable that the mixed solution be held at the synthesis temperature for 15 minutes or more. After the reaction is completed, it is preferable to allow the mixture to cool to room temperature.

[0044] <2-2. Neutralization process> The method for producing titanium oxide powder preferably includes a neutralization step between the synthesis step and the drying step, in which the mixed solution is neutralized. In the neutralization step, a base is added to the slurry obtained in the synthesis step to adjust the pH of the slurry. By adjusting the pH, the zeta potential of the particle surface is adjusted, making it easier to wash away chloride ions derived from the raw material titanium tetrachloride and excess acid contained in the slurry in the subsequent purification step.

[0045] The base is preferably one that does not contain metal elements or metalloid elements, and is preferably ammonia. From the viewpoint of purifying to a high purity, the pH of the slurry after adjustment is preferably 6 or more, more preferably 7 or more, and even more preferably 7.5 or more.

[0046] <2-3. Purification process> The method for producing titanium oxide powder preferably includes a purification step of purifying titanium oxide. The purification step is performed after the synthesis step. Since the purification step is performed in a state where the titanium oxide powder is dispersed in a liquid, it is preferably performed before the drying step. The purification step can be performed using, for example, one or more selected from an ultrafiltration membrane, a reverse osmosis membrane, an ion exchange resin, and an electrodialysis membrane. By performing the purification step, it is possible to remove Cl (chlorine), S (sulfur), Si (silicon), Fe (iron), Al (aluminum), P (phosphorus), Na (sodium), Mg (magnesium), etc. from the slurry containing the titanium oxide powder obtained in the synthesis step.

[0047] <2-4. Dehydration process> The method for producing titanium oxide powder may further include a dehydration step of dehydrating a slurry containing titanium oxide powder. The dehydration can be carried out, for example, by dehydrating the slurry using a filter press or the like to obtain a cake. The dehydration step is carried out after the synthesis step and before the drying step. When the method for producing titanium oxide powder includes a purification step, it is preferable to carry out the dehydration step after the purification step. By carrying out the dehydration step, the drying step can be carried out efficiently.

[0048] <2-5. Drying process> The drying step is a step in which the obtained titanium oxide powder is heated as necessary and dried until it reaches a desired moisture content. The moisture content of the titanium oxide powder after the drying step is preferably 15% by mass or less, more preferably 10% by mass or less. The moisture content of the titanium oxide powder after the drying step is preferably 1.0% by mass or more.

[0049] The drying atmosphere may be either air or an inert gas atmosphere.

[0050] The titanium oxide powder may be dried in the form of a slurry dispersed or dissolved in an aqueous medium, or may be dried after being dehydrated using a filter press or the like.

[0051] The drying temperature is preferably 100° C. or higher and lower than 200° C., and more preferably 150° C. or higher and lower than 190° C. The drying time is preferably 3 to 48 hours, and more preferably 5 to 30 hours. <2-6. Firing process>

[0052] The calcination process involves heating and calcining titanium oxide powder. Heating titanium oxide powder in the calcination process promotes crystallization into the anatase phase and reduces the moisture content. Without being bound by any theory, the hydroxyl and carboxyl groups on the particle surface of the titanium oxide powder obtained in the drying process condense with adjacent functional groups to form an "-O-" structure. By heating titanium oxide powder in this state in a moist environment, the condensed functional groups react with water molecules, and the "-O-" structure returns to an "-OH" state. This improves the hydrophilicity of the titanium oxide powder.

[0053] In the calcination step, it is preferable to adjust the moisture content of the titanium oxide powder before calcination (also referred to as the moisture content before calcination) in order to improve the hydrophilicity of the titanium oxide powder after calcination. The moisture content can be adjusted, for example, by adding ion-exchanged water or the like to the titanium oxide powder. The moisture content of the titanium oxide powder before calcination is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. Because this increases the drying time and is disadvantageous in terms of cost, it is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. The moisture content before calcination is measured by the method described in the Examples.

[0054] It is preferable that the ratio of the amount of substance of acidic functional groups to the amount of substance of Ti (acidic functional groups [mol] / Ti [mol]), the amount of water before firing, and the firing temperature satisfy the following relationship. Acidic functional group [mol] / Ti [mol] × 800 + moisture content before calcination [mass%] × 300 / calcination temperature [K°] ≥ 60.0…(1) Here, the amount of substance of the acidic functional group represents the sum of the amounts of substance of the acidic functional groups of the acids contained in the mixed solution. The amount of substance of the acidic functional group and the amount of substance of Ti are values ​​calculated from the amounts of raw materials used to prepare the mixed solution. When formula (1) is satisfied, the decrease in acidic functional groups due to the influence of moisture during heating in the firing step is suppressed, making it easier to maintain high hydrophilicity. The upper limit of acidic functional group [mol] / Ti [mol] × 800 + moisture content before firing [mass%] × 300 / firing temperature [K°] may be, for example, 100 or less, or 90 or less.

[0055] The firing temperature is preferably 200° C. or higher and 700° C. or lower, more preferably 230° C. or higher and 600° C. or lower. The firing time is preferably 1 to 48 hours, more preferably 2 to 30 hours.

[0056] In the firing step, firing is carried out until the moisture content reaches, for example, 0.1% to 1.0% by mass to obtain a titanium oxide solid. The obtained solid is pulverized in a mortar or the like to obtain titanium oxide powder.

[0057] According to the above embodiment, it is possible to provide an anatase type titanium oxide powder that has high hydrophilicity and dispersibility and can form a low viscosity slurry even at a high concentration.

[0058] <3. Titanium oxide slurry manufacturing method> <3-1. Slurrying process> In one embodiment, a method for producing a titanium oxide slurry involves mixing titanium oxide powder with a liquid medium to produce a slurry. Examples of the liquid medium include water; organic solvents such as alcohol; and mixtures thereof. While the liquid medium is not particularly limited, industrially, water, particularly ion-exchanged water, is preferred. The titanium oxide content in the titanium oxide slurry is preferably 3% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more. The titanium oxide content in the titanium oxide slurry is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. The mixing temperature is preferably 45°C or less. [Example]

[0059] Examples and comparative examples of the present invention will be described below, but they do not limit the technical scope of the present invention.

[0060] Example 1 Ion-exchanged water adjusted to 30°C and citric acid monohydrate were added to an aqueous titanium tetrachloride solution with a Ti concentration of 15% by mass, and the concentration was adjusted to a Ti molar concentration of 0.75 mol / L and an acid / Ti (molar ratio) (amount of citric acid [mol] / amount of Ti [mol]) of 0.020, to obtain a mixed solution. The liquid temperature was always kept at 30°C during this mixing process.

[0061] Next, the mixed solution was transferred to a glass reactor. While stirring the mixed solution in the reactor at 60 rpm using a stirrer, the temperature was raised to 95°C at a rate of 1.0°C / min using an external heater and maintained at 95°C for 30 minutes. The mixed solution was then allowed to cool to room temperature (25°C). After cooling, the slurry was neutralized to pH 8 with aqueous ammonia and recovered by filtration using an ultrafiltration membrane (Microza UF, Asahi Kasei Corporation). The recovered product was washed with ion-exchanged water. The washed slurry was dehydrated using a filter press to obtain a cake with a solid content of 40% by mass. The obtained cake was placed in an oven set at 180°C and dried until the moisture content reached 10% by mass, yielding a solid. This solid was pulverized to obtain a titanium oxide powder. Ion-exchanged water was added to the obtained titanium oxide powder so that the moisture content of the powder was 55% by mass, and then the powder was baked in an oven set at 250°C for 3 hours to obtain a solid. The obtained solid was pulverized in a mortar to obtain the titanium oxide powder of Example 1.

[0062] <Example 2> The titanium oxide powder of Example 2 was obtained in the same manner as in Example 1, except that the moisture content before firing was 82 mass % and the firing temperature was 350°C.

[0063] Example 3 The titanium oxide powder of Example 3 was obtained in the same manner as in Example 1, except that the moisture content before firing was 35 mass % and the firing temperature was 400°C.

[0064] Example 4 The titanium oxide powder of Example 4 was obtained in the same manner as in Example 1, except that the moisture content before firing was 47 mass % and the firing temperature was 500°C.

[0065] <Example 5> The titanium oxide powder of Example 5 was obtained in the same manner as in Example 1, except that the moisture content before firing was 42 mass % and the firing temperature was 550°C.

[0066] Example 6 The titanium oxide powder of Example 6 was obtained in the same manner as in Example 1, except that the moisture content before firing was 42 mass % and the firing temperature was 600°C.

[0067] Example 7 The titanium oxide powder of Example 7 was obtained in the same manner as in Example 4, except that the acid was changed to malic acid, the acid / Ti (molar ratio) was changed to 0.030, and the moisture content before firing was changed to 34 mass %.

[0068] Example 8 The titanium oxide powder of Example 8 was obtained in the same manner as in Example 4, except that the acid was changed to tartaric acid, the acid / Ti (molar ratio) was changed to 0.030, and the moisture content before calcination was changed to 38 mass %.

[0069] <Comparative Example 1> A titanium oxide powder of Comparative Example 1 was obtained in the same manner as in Example 1, except that the acid / Ti (molar ratio) was changed to 0.016, the water content before calcination was changed to 46 mass %, and the calcination temperature was changed to 400°C.

[0070] <Comparative Example 2> A titanium oxide powder of Comparative Example 2 was obtained in the same manner as in Example 4, except that the moisture content before firing was changed to 18 mass %.

[0071] <Comparative Example 3> A titanium oxide powder of Comparative Example 3 was obtained in the same manner as in Example 6, except that the moisture content before firing was changed to 8 mass %.

[0072] <Comparative Example 4> A titanium oxide powder of Comparative Example 4 was obtained in the same manner as in Example 7, except that the acid / Ti (molar ratio) was changed to 0.018, the moisture content before calcination was changed to 48 mass %, and the calcination temperature was changed to 400°C.

[0073] <Comparative Example 5> A titanium oxide powder of Comparative Example 5 was obtained in the same manner as in Example 7, except that the moisture content before firing was changed to 16% by mass.

[0074] <Comparative Example 6> A titanium oxide powder of Comparative Example 6 was obtained in the same manner as in Example 8, except that the moisture content before firing was changed to 18 mass % and the firing temperature was changed to 350°C.

[0075] <Comparative Example 7> Titanium oxide powder of Comparative Example 7 was obtained in the same manner as in Example 8, except that the acid / Ti (molar ratio) was changed to 0.018, the moisture content before firing was changed to 55% by mass, and the firing temperature was changed to 400°C.

[0076] Table 1 shows the production conditions of the titanium oxide powders of Examples 1 to 8 and Comparative Examples 1 to 7.

[0077]

Table 1

[0078] The titanium oxide powders of Examples 1 to 8 and Comparative Examples 1 to 7 were evaluated by the following evaluation methods.

[0079] <BET specific surface area> The specific surface area of the titanium oxide powder was calculated from the nitrogen adsorption isotherm by the BET method in accordance with JIS Z 8830:2013. The measurement of the specific surface area by the BET method (also referred to as the BET specific surface area) was carried out using QUADRASORB evo (Quantachrome) for a sample heated to 180°C and flowed with nitrogen gas for 20 minutes as a pretreatment. The applicable range of the BET method was set to P / P0 = 0.00 to 0.95.

[0080] [[ID=2,7]]<Spin-spin relaxation response time T2> After firing the titanium oxide powder in an electric furnace until the water content became 1% by mass or less, an ion-exchanged water was added and mixed to prepare a mixed solution having a titanium oxide content of 10% by mass. This mixed solution was filled into a Dispo NMR sample tube AS1NMR (As One Corporation), and immediately pulse NMR measurement was carried out using Acorn Area (XiGo Nanotools) to measure the spin-spin relaxation response time T2 of the titanium oxide powder. The measurement was carried out under the following conditions. Measurement frequency: 13.1 MHz, measurement nucleus: 1After a single pulse at 90°, a 180° pulse was applied at 0.5 ms intervals, and this scan was repeated four times. Measurement method: CPMG pulse sequence method, sample volume: 0.5 mL, temperature: 23°C, Specific Surface Relaxivity (Ka):0.0075g / m 2 / ms

[0081] <Anatase content and rutile content> The titanium dioxide powder was measured by powder X-ray diffraction (XRD), and the anatase content and rutile content were calculated from the peak intensity (Ia) corresponding to the anatase crystal phase, the peak intensity (Ib) corresponding to the brookite crystal phase, and the peak intensity (Ir) corresponding to the rutile crystal phase. The anatase content of the titanium dioxide powder crystal phase was calculated using the following formula: Anatase content [%] = {Ia / (Ia+Ib+Ir)} x 100 The rutile content (rutile rate) of the crystalline phase of the titanium oxide powder was calculated using the following formula. Rutile content [%] = {Ir / (Ia+Ib+Ir)} × 100 The measurements were performed using a SmartLab SE (Rigaku) ​​with a copper target and Cu-Kα1 radiation under the following conditions: tube voltage 45 kV, tube current 40 mA, measurement range 2θ = 20 to 35 [deg], sampling width 0.0167 [deg], and scan speed 0.0192 [deg / s]. Ia: Intensity of the peak (2θ = 24.5° to 26.0°) corresponding to the anatase-type crystalline phase Ir: Intensity of the peak (2θ=26.6°~28.1°) corresponding to the rutile crystal phase Ib: Intensity of the peak (2θ = 30.8° to 32.3°) corresponding to the brookite-type crystal phase

[0082] <FWHM of diffraction peak measured by powder X-ray diffraction (XRD)> Powder X-ray diffraction (XRD) measurements were performed on titanium dioxide powder using a SmartLab SE (Rigaku). Using a copper target and Cu-Kα1 radiation, measurements were performed under conditions of 45 kV tube voltage, 40 mA tube current, a measurement range of 2θ = 24.5–26.0°, a sampling width of 0.0167°, and a scan rate of 0.0192° / s. The FWHM of the main peak of the anatase phase near 2θ = 25° was analyzed. The background intensity measured with the glass cell alone was subtracted from the diffraction intensity measured with the titanium dioxide and glass cell sample to correct the sample diffraction pattern.

[0083] <Elemental analysis> The Si, P, Na, and Mg contents of the titanium oxide powder were measured using an atomic absorption spectrometer Z-2300 (Hitachi, Ltd.) after mixing the titanium oxide powder with an aqueous hydrogen fluoride solution and completely dissolving it using a microwave sample pretreatment device ETHOS EASY (Milestone General Co., Ltd.). The C and S contents of the titanium oxide powder were measured using a carbon-sulfur analyzer CS744 (LECO).

[0084] <Slurry viscosity> 30 mL of ion-exchanged water was weighed into a 100 mL glass beaker, and titanium oxide powder was added at room temperature (25°C) to a titanium oxide content of 40 mass%. The mixture was stirred with a plastic spoon to obtain a slurry. The viscosity of the slurry was measured at 25°C using a VISCOMATE VM-10A-M rotational vibration viscometer (Sansho Corporation). The amount of titanium oxide powder added was gradually increased, and the concentration of titanium oxide powder at which the viscosity of the slurry reached 3000 mPa·s was determined to be the titanium oxide content of the titanium oxide slurry that gave the flow failure point.

[0085] <Zeta potential> A slurry containing 0.1% by mass of titanium oxide was prepared using ion-exchanged water at room temperature (25° C.) The slurry was filled into a sapphire cell, and the zeta potential was measured at room temperature (25° C.) using an ELSZ-2000 (Otsuka Electronics Co., Ltd.).

[0086] <Moisture content and moisture content before baking> Using a heat-drying moisture meter MX50 (A&D), 2 g of titanium oxide powder was heated to 200°C, and then infrared heating was performed at 120°C until the weight change was 0.01% by mass or less, and the moisture content and moisture content of the titanium oxide powder before firing were measured.

[0087] [Table 2-1] [Table 2-2]

[0088] Table 2 shows the physical properties of the titanium oxide powders of Examples 1 to 8 and Comparative Examples 1 to 7. In Table 2, the symbol "<" indicates that the value is less than the value following "<". For example, the P content of Example 1 is less than 10 ppm. The symbol "≧" indicates that the value is equal to or greater than the value following "≧". For example, the slurry viscosity of Comparative Example 1 is 3000 mPa s or greater. "-" indicates that the value was not measured.

[0089] As shown in Table 2, the titanium oxide powders of Examples 1 to 8 have a high titanium oxide content of 44.1% by mass or more in the titanium oxide slurries that cause flow defects, and therefore have good dispersibility even at high concentrations, do not become highly viscous, and do not cause flow defects, making them suitable for synthesizing dielectric materials and battery materials. On the other hand, the titanium oxide powders of Comparative Examples 1 to 7 have a titanium oxide content of 39.2% by mass or less in the titanium oxide slurries that cause flow defects, and are more likely to cause flow defects at high concentrations than the titanium oxide powders of the Examples.

Claims

1. The BET specific surface area measured by nitrogen adsorption method is 80 m ２ / g or more 300m ２ / g or less, the anatase content of the crystalline phase measured by powder X-ray diffraction (XRD) is 90% or more, A mixed solution containing 10% by mass of titanium oxide prepared using ion-exchanged water was measured by pulse NMR. The A / BET specific surface area calculated from the reciprocal A of the spin-spin relaxation response time T2 and the BET specific surface area was 2.3 × 10 －５ [ms －１ / (m ２ / g)] or more.

2. 2. The titanium oxide powder according to claim 1, wherein the spin-spin relaxation response time T2 is 100 ms or more and 500 ms or less.

3. 3. The titanium oxide powder according to claim 1, wherein the Si content is 0.1% by mass or less and the P content is 0.1% by mass or less.

4. 3. The titanium oxide powder according to claim 1, wherein the Na content is 0.1% by mass or less and the Mg content is 0.1% by mass or less.

5. 3. The titanium oxide powder according to claim 1, wherein the half-width of a diffraction peak in the diffraction angle 2θ range of 24.5° to 26.0° measured by powder X-ray diffraction (XRD) is 0.50° to 2.00°.

6. 3. The titanium oxide powder according to claim 1, having a zeta potential of 25 mV or more and 63 mV or less in absolute value.

7. 3. The titanium oxide powder according to claim 1, wherein a slurry containing 40% by mass of titanium oxide prepared using ion-exchanged water has a viscosity of less than 3,000 mPa·s at 25°C.

8. A titanium oxide slurry comprising the titanium oxide powder according to claim 1 or 2 and a liquid medium.

9. A method for producing a titanium oxide slurry, comprising mixing the titanium oxide powder according to claim 1 or 2 with a liquid medium to produce a slurry.

10. a synthesis step of reacting titanium tetrachloride and an acid to produce titanium oxide; A drying step of drying the titanium oxide powder; and A firing process to fire titanium oxide powder A method for producing a titanium oxide powder, comprising: A manufacturing method in which the ratio of the amount of substance of acidic functional groups to the amount of substance of Ti (acidic functional groups [mol] / Ti [mol]) in the synthesis step, and the moisture content before firing and firing temperature in the firing step satisfy (1). Acidic functional group [mol] / Ti [mol] × 800 + moisture content before firing [mass%] × 300 / firing temperature [K°] ≧ 60.0 (1)

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