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

Abstract

Provided is a titanium oxide powder, wherein the A / BET specific surface area is 2.3×10-5[ms-1 / (m2 / g)] or higher when calculated from the BET specific surface area and the inverse A of the spin-spin relaxation response time T2 measured by performing pulsed NMR on a liquid mixture in which the BET specific surface area measured via the nitrogen adsorption method is at least 80m2 / g and less than 300m2 / g, the anatase content of the crystal phase measured by the powder X-ray diffraction (XRD) method is 90% or more, and the titanium oxide content prepared using ion-exchanged water is 10 mass%.

Description

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

[0001] This disclosure relates to titanium dioxide powder, titanium dioxide slurry, and methods for producing the same.

[0002] Titanium(IV) Oxide (TiO) ２ Titanium dioxide is a chemically stable material and is widely used industrially in various fields as a white pigment, etc. Patent Document 1 discloses a coating composition in which titanium dioxide nanoparticles are used as an ultraviolet shielding agent, and which contains titanium dioxide nanoparticles that have undergone a specific surface treatment. Patent Document 2 discloses organic siloxane oligomer-modified inorganic oxide ultrafine particles containing rutile-type titanium dioxide, 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: the anatase phase, the brookite phase, and the rutile phase. In particular, the anatase type of titanium dioxide has a high hydrophilicity and high dispersibility due to having many hydroxyl groups on its surface compared to other crystalline phases. Because the anatase type of titanium dioxide has many hydroxyl groups on its surface, it is highly reactive with other metal elements. Therefore, there is a high demand for anatase type titanium dioxide as a raw material for dielectric materials and battery materials. Among dielectric and battery material applications, particularly strict composition control is required for electronic device applications. Therefore, it is desirable that titanium dioxide powder used as a raw material for electronic device materials be easily and uniformly dispersible in order to reduce abnormal particles and compositional deviations caused by poor dispersion in the reaction solution and the resulting reaction failures.

[0004] In recent years, there has been a demand for anatase-type fine titanium oxide powder with a high specific surface area to exhibit higher functionality in these applications. Non-patent document 1 discloses that as the particle size of the particles constituting the powder decreases, the specific surface area of ​​the particles increases, thereby increasing the viscosity of the slurry.

[0005] Journal of Colloid and Interface Science Volume 33, Issue 1, May 1970, Pages 150-160 JP 2015-212355 JP 2010-95392

[0006] From the perspective of reaction solution viscosity, when using powders composed of small particles, it becomes difficult to uniformly mix and react the raw materials unless the solid content concentration of the reaction solution is dilute. Therefore, selecting powders composed of small particles as raw materials inevitably reduces the production volume per unit time, significantly lowering the production capacity of the manufacturing process.

[0007] Therefore, there is a need for anatase-type titanium dioxide powder that can be uniformly dispersed in a solvent and form a low-viscosity slurry even at high concentrations, thereby increasing the manufacturing efficiency of the production line.

[0008] This disclosure provides titanium dioxide powder, titanium dioxide slurry, and a method for producing the same, which can form a slurry with a high anatase content and low viscosity.

[0009] This disclosure includes the following embodiments: [Embodiment 1] BET specific surface area measured by nitrogen adsorption method is 80 m² ２ / g or more 300m ２ The mixture, which has an anatase content of 90% or more in the crystalline phase as measured by powder X-ray diffraction (XRD) and a titanium dioxide content of 10% by mass as prepared using deionized water, is measured by pulsed 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 is 2.3 × 10⁻¹⁴. －５ [ms －１ / (m ２Titanium oxide powder having a content of 100 ms or more (1 / g). [Aspect 2] Titanium oxide powder according to Aspect 1, wherein the spin-spin relaxation response time T2 is 100 ms or more and 500 ms or less. [Aspect 3] Titanium oxide powder according to Aspect 1 or 2, wherein the Si content is 0.1 mass% or less and the P content is 0.1 mass% or less. [Aspect 4] Titanium oxide powder according to any one of Aspects 1 to 3, wherein the Na content is 0.1 mass% or less and the Mg content is 0.1 mass% or less. [Aspect 5] Titanium oxide powder according to any one of Aspects 1 to 4, wherein the full width at half maximum of the diffraction peak in measurement by powder X-ray diffraction (XRD) is in the range of 24.5° to 26.0° and the diffraction angle 2θ is in the range of 0.50° to 2.00°. [Aspect 6] Titanium oxide powder according to any one of Aspects 1 to 5, wherein the zeta potential is 25 mV or more and 63 mV or less in absolute value. [Aspect 7] Titanium dioxide powder according to any one of aspects 1 to 6, wherein the viscosity of the slurry prepared using ion-exchanged water, having a titanium dioxide content of 40% by mass, is less than 3000 mPa·s at 25°C. [Aspect 8] Titanium dioxide slurry comprising the titanium dioxide powder according to any one of aspects 1 to 7 and a liquid medium. [Aspect 9] A method for producing titanium dioxide slurry, comprising mixing the titanium dioxide powder according to any one of aspects 1 to 7 and a liquid medium so that the titanium dioxide content is 3 to 40% by mass to produce a slurry.

[10] A method for producing titanium dioxide powder, comprising a synthesis step of reacting titanium tetrachloride and an acid to produce titanium dioxide, a drying step of drying the titanium dioxide powder, and a calcination step of calcining the titanium dioxide powder, wherein 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 moisture before calcination and the calcination temperature in the calcination step satisfy (1). Acidic functional group [mol] / Ti [mol] × 800 + Pre-calcination moisture content [mass%] × 300 / Calcination temperature [K°] ≥ 60.0 ... (1)

[0010] According to this disclosure, it is possible to provide titanium dioxide powder, titanium dioxide slurry, and a method for producing the same, which can form a slurry with a high anatase content and low viscosity.

[0011] The following describes an example of an embodiment of the present invention. The present invention is not limited to the following embodiments.

[0012] In the present disclosure, when "~" is used for a numerical range, the numerical values at both ends are the upper limit value and the lower limit value, respectively, and are included in the numerical range. When there are multiple upper limit values or lower limit values described, a numerical range can be formed from all combinations of the upper limit values and the lower limit values. Similarly, when multiple numerical ranges are described, separate numerical ranges can be formed by individually selecting and combining the upper limit values and the lower limit values from those numerical ranges.

[0013] In the present disclosure, "titanium oxide" refers to titanium(IV) oxide (TiO ２ ), unless otherwise specified. Further, the "Ti concentration" is the concentration (mol / L) obtained by dividing the amount of substance (mol) of Ti atoms considering all components containing all Ti atoms constituting titanium compounds, ions containing Ti, complexes containing Ti, etc. by the volume (L) of the liquid containing Ti.

[0014] <1-1. Titanium Oxide Powder> The titanium oxide powder of one embodiment has a BET specific surface area measured by the nitrogen adsorption method of 80 m ２ / g or more and less than 300 m ２ / g, anatase content of the crystal phase measured by powder X-ray diffraction method (XRD) of 90% or more, and the reciprocal A of the spin-spin relaxation response time T2 measured by pulse NMR of a mixed solution having a titanium oxide content of 10% by mass prepared using ion-exchanged water, and the A / BET specific surface area calculated from 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 the titanium oxide powder is 80 m ２ / g or more. When it is 80 m ２ / g or more, due to the fine particle size, an ultrafine particle material can be obtained when titanium oxide reacts with other substances. Specific examples of the ultrafine particle material include a 0201-sized multilayer ceramic capacitor material. From the same perspective, the BET specific surface area of the titanium oxide powder is preferably 110 m ２ / g or more, and 120 m ２A concentration of 300 m² or more is more preferable. The BET specific surface area of ​​titanium dioxide powder is 300 m². ２ It is less than / g. 300m ２ If the amount is less than 1 / g, abnormal grain growth of titanium dioxide can be suppressed even when reacted with barium carbonate at high temperatures, resulting in a narrower particle size distribution of the resulting barium titanate material. From a similar perspective, the BET specific surface area of ​​titanium dioxide powder is 260 m². ２ Preferably less than / g, and 180m ２ It is more preferable to have less than / g, and 160m ２ A value of less than or equal to / g is even more preferable. In this 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 titanium dioxide powder is 90% or more. When titanium dioxide is reacted with other substances, a high anatase content in the titanium dioxide powder is advantageous because it increases reactivity. From a similar viewpoint, an anatase content of 95% or more is more preferable, 99% or more is even more preferable, and 100% is particularly preferable. There is no particular upper limit to the anatase content, but for example, it can be 100% or less, 99% or less, or 98% or less. In this disclosure, the anatase content means the content of anatase-type crystals in the crystalline phase of titanium dioxide 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 closely related to molecular motion. １ This method allows for rapid measurement of the relaxation response times of H nuclei, specifically the spin-lattice relaxation response time T1 and the spin-spin relaxation response time T2. Pulsed NMR has seen a rapid increase in use in recent years, and known measurement methods in pulsed NMR include the Hahn echo method, solid echo method, 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 the H nucleus, 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. The １ spin-spin relaxation response time T2 of the H nucleus of １ is considered to be a physical property related to the state of water molecules bound to the surface of titanium oxide particles. Specifically, it is considered that the smaller the spin-spin relaxation response time T2, the more water molecules are bound to the surface of titanium oxide particles, that is, the thicker the hydration layer, and thus the easier the dispersibility of titanium oxide particles is improved.

[0019] (Reciprocal A of the spin-spin relaxation response time T2 (A = 1 / T2)) The reciprocal A (= 1 / T2) of the spin-spin relaxation response time T2 described above is an index of the strength of the interaction acting between free water and the surface of titanium oxide particles. Since the stronger the interaction between the surface of titanium oxide particles and free water, the higher the hydrophilicity of titanium oxide in the aqueous solvent, A is used as an alternative index for 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 carboxy groups derived from organic acids on the surface of titanium oxide particles. It is speculated that the hydrophilicity of titanium oxide increases as long as the hydroxyl groups and carboxy groups derived from organic acids on the surface of titanium oxide particles are not in a condensed state and the total number per specific surface area is large. From the above, in order to accurately relatively evaluate the hydrophilicity between titanium oxide powders, it is considered necessary to compare the factors affecting hydrophilicity such as hydroxyl groups per specific surface area of titanium oxide powders. Therefore, the hydrophilicity of each titanium oxide powder can be relatively compared using the value obtained by dividing A, which is an alternative index for hydrophilicity, by the BET specific surface area of titanium oxide.

[0021] The A / BET specific surface area calculated from the reciprocal A of the spin-spin relaxation response time T2 measured by pulsed 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) ] That is more. 2.3 × 10 －５ [ms －１ / (m ２ If the ratio is greater than or equal to [ / g], the hydrophilicity can be increased. From a similar viewpoint, the A / BET specific surface area is 2.4 × 10 －５ [ms －１ / (m ２ Preferably 2.5 × 10 (g) or more. －５ [ms －１ / (m ２ A / BET specific surface area of ​​3.2 × 10 is more preferable. －５ [ms －１ / (m ２ A ratio of [A / BET] or less is preferable because it makes aggregation and precipitation of titanium oxide particles in the slurry less likely. From a similar viewpoint, the A / BET specific surface area is 2.9 × 10⁻⁶. －５ [ms －１ / (m ２ ( / g) 2.8 × 10 －５ [ms －１ / (m ２ ( / g) The following is even more preferable.

[0022] (Full Width at Half Maximum (FWHM) of diffraction peaks measured by powder X-ray diffraction (XRD)) For titanium oxide powder, the full width at half maximum (FWHM) of diffraction peaks with a diffraction angle 2θ in the range of 24.5° to 26.0° measured by powder X-ray diffraction (XRD) is preferably 0.50° or higher. A smaller FWHM of titanium oxide powder is preferable as it indicates higher crystallinity. However, making the FWHM very small requires high temperatures for the reaction, which makes aggregation of titanium oxide particles more likely, thus reducing the BET specific surface area. Therefore, from the viewpoint of suppressing aggregation of titanium oxide particles, it is desirable to keep the FWHM above a certain level, for example, 0.50° or higher is preferred. From the same viewpoint, an FWHM of 0.70° or higher is more preferred, and 0.90° or higher is even more preferred.

[0023] The above FWHM is preferably 2.00° or less. This is because the better the crystallinity of titanium oxide, the more improved the crystallinity of the product manufactured 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 the 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, the titanium oxide concentration during material synthesis can be increased, and it is efficient. 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. When it is 25 mV or more, the dispersibility is increased due to the repulsion of charges 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. When the absolute value of the zeta potential is 63 mV or less, the zeta potential is not too high, so overdispersion in the step of dispersing particles in a solvent, such as when producing barium titanate, can be suppressed. 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 device applications, in order to avoid degrading the properties of the electronic device material, the titanium oxide powder preferably does not contain metalloid elements such as Si (silicon) and P (phosphorus), metallic elements such as Na (sodium) and Mg (magnesium), and polymeric organic acid chains such as polyols. When titanium oxide powder is used as a raw material for dielectric materials, P (phosphorus), Na (sodium), and Mg (magnesium) may cause a decrease in dielectric constant. Therefore, the P content, Na content, Mg content, and S content of the titanium oxide powder are 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 is no particular restriction on the lower limit, but from the viewpoint of manufacturing cost, 0.000001% by mass or more is preferred. The Si content is preferably 0.1% by mass or less, more preferably 0.05% by mass or less. There is no particular restriction on the lower limit, but from the viewpoint of manufacturing cost, 0.001% by mass or more is preferred.

[0027] To suppress the precipitation of carbon-derived by-products, the carbon 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 are no particular restrictions on the lower limit, but from the viewpoint of manufacturing costs, 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 Dioxide Slurry> The titanium dioxide slurry of one embodiment comprises titanium dioxide powder and a liquid medium. Examples of the liquid medium include water; organic solvents such as alcohols; and mixtures thereof. The liquid medium is not particularly limited, but industrially, water, especially deionized water, is preferred.

[0030] Since titanium oxide slurry exhibits significantly low fluidity when its viscosity is 3000 mPa·s or higher, 3000 mPa·s is considered the flow failure point, and it is preferable that the titanium oxide content of the titanium oxide slurry that gives rise to the flow failure point at 25°C is more than 40% by mass. A content of more than 40% by mass allows for a higher and more efficient titanium oxide concentration during material synthesis. From a similar viewpoint, 42% by mass or higher is more preferable, and 44% by mass or higher is even more preferable. The upper limit of the titanium oxide content of the titanium oxide slurry that gives rise to the flow failure point may be, for example, 60% by mass or less, or 50% by mass or less. In this disclosure, the titanium oxide content of the titanium oxide slurry that gives rise to the flow failure point is measured by the method described in the examples.

[0031] <2. Method for Producing Titanium Oxide Powder> The following describes a method for producing titanium oxide powder according to one embodiment. 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 Step> The synthesis step is a step of producing titanium oxide by reacting titanium tetrachloride and an acid. The production of titanium oxide is carried out, 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 to obtain a mixed solution containing titanium tetrachloride, an acid, and an aqueous medium, and a heating step to heat the mixed solution and cause a reaction. Examples of aqueous mediums include water, alcohols such as methanol, and mixed solvents thereof. The aqueous medium is preferably water.

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

[0033] The acid adheres to the generated titanium dioxide particles, stabilizing their surface and acting as a phase transition inhibitor, suppressing the phase transition from the anatase phase to the rutile phase. The acid also has the effect of increasing the hydrophilicity of the generated titanium dioxide particles and suppressing their aggregation. Examples of acids 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 a similar 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 the aggregation suppression effect, the molecular weight of the organic acid is preferably 30 or more, and more preferably 100 or more.

[0035] From the viewpoint of having a high effect in suppressing the phase transition to the rutile phase, carboxylic acids are preferred as the acid, α-hydroxycarboxylic acids are more preferred, and malic acid (molecular weight 134.09), citric acid (molecular weight 192.12), and tartaric acid (molecular weight 150.09) are even more preferred. The acid may be used alone or in combination of two or more types.

[0036] The Ti concentration in the mixture is preferably 0.01 mol / L or higher. This is to favorably promote the hydrolysis reaction. From a similar viewpoint, 0.05 mol / L or higher is more preferable, and 0.30 mol / L or higher is even more preferable. The Ti concentration is preferably 2.00 mol / L or lower. This is to suppress the phase transition to the rutile phase. From a similar viewpoint, 1.50 mol / L or lower is more preferable, and 1.00 mol / L or lower is even more preferable.

[0037] Regarding the content of acidic functional groups in the mixture, the ratio of the amount of acidic functional groups to the amount of Ti in the mixture (acidic functional groups [mol] / Ti [mol]) (molar ratio) is preferably 0.040 or higher. This is to suppress the phase transition from the anatase phase to the rutile phase. It is also to facilitate the imparting of acidic functional groups to the surface of titanium dioxide particles. From a similar viewpoint, 0.050 or higher is more preferable, and 0.055 or higher is even more preferable. From the viewpoint of suppressing reaction inhibition, the above ratio of the amount of substance (acidic functional groups [mol] / Ti [mol]) is preferably 0.100 or lower, and more preferably 0.070 or lower.

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

[0039] When water is used as the aqueous medium, the pH of the mixture is preferably 3 or lower. This is to allow the hydrolysis reaction to proceed more favorably. From a similar viewpoint, a pH of 2 or lower is more preferable, and 1 or lower is even more preferable.

[0040] In the mixing process, it is preferable to maintain the liquid temperature at 40°C or below, and more preferably at 30°C or below, in order to allow the hydrolysis reaction to proceed slowly.

[0041] <<Heating Process>> In the heating process, the mixture is heated to allow the reaction to proceed. By heating the mixture, titanium dioxide can be precipitated. Heating is preferably carried out while stirring to increase the reaction efficiency. From the viewpoint of productivity, it is preferable to heat the mixture at a high heating rate. Therefore, it is preferable to heat the mixture to the synthesis temperature at a heating 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, in order to suppress the precipitation of amorphous titanium dioxide and improve crystallinity, it is preferable to suppress the rapid progress of the reaction and reduce the heating rate to allow sufficient crystal growth. Therefore, it is preferable to heat the mixture to the synthesis temperature at a heating rate of 1.5°C / min or less, and 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. This is to favorably promote the hydrolysis reaction. The synthesis temperature is preferably 100°C or lower. This is to suppress the phase transition of the stable phase to the rutile phase.

[0043] The holding time of the mixture at the synthesis temperature can be set arbitrarily; it may be cooled without holding, or it may be held for a predetermined time. A holding time of 15 minutes or more is preferable from the viewpoint of allowing the reaction to proceed sufficiently. After the reaction is complete, it is preferable to allow it to cool to room temperature.

[0044] <2-2. Neutralization Step> The method for producing titanium dioxide powder preferably includes a neutralization step between the synthesis step and the drying step to neutralize the mixture. 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 out chloride ions derived from titanium tetrachloride, the raw material, and excess acid contained in the slurry in the subsequent purification step.

[0045] The base is preferably free of metallic and metalloid elements, and ammonia is preferred. From the viewpoint of purifying the prepared slurry to a high degree of purity, the pH is preferably 6 or higher, more preferably 7 or higher, and even more preferably 7.5 or higher.

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

[0047] <2-4. Dehydration Step> The method for producing titanium dioxide powder may further include a dehydration step in which the slurry containing titanium dioxide powder is dehydrated. 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. If the method for producing titanium dioxide 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 process involves heating the obtained titanium dioxide powder as needed to dry it until it reaches the desired moisture content. The moisture content of the titanium dioxide powder after the drying process is preferably 15% by mass or less, more preferably 10% by mass or less. The moisture content of the titanium dioxide powder after the drying process is preferably 1.0% by mass or more.

[0049] The dry atmosphere may be either an atmospheric atmosphere or an inert gas atmosphere.

[0050] Titanium dioxide powder may be dried in a slurry form dispersed or dissolved in an aqueous medium, or it may be dried after being dehydrated using a filter press or the like.

[0051] The drying temperature is preferably 100°C or higher and less than 200°C, and more preferably 150°C or higher and less 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 includes a calcination step in which titanium dioxide powder is heated and calcined. Heating the titanium dioxide powder in the calcination process promotes crystallization into the anatase phase and reduces the moisture content. Although not bound by any particular theory, the hydroxyl and carboxyl groups on the particle surface of the titanium dioxide powder obtained in the drying process condense with adjacent functional groups to form an "-O-" structure. When this state of titanium dioxide powder is heated in a moisture-containing environment, the condensed functional groups react with water molecules, and the "-O-" structure returns to the "-OH" state. As a result, the hydrophilicity of the titanium dioxide powder is improved.

[0053] In the firing process, it is preferable to adjust the moisture content of the titanium dioxide powder before firing (also called the moisture content before firing) in order to improve the hydrophilicity of the titanium dioxide powder after firing. The moisture content can be adjusted, for example, by adding deionized water to the titanium dioxide powder. The moisture content of the titanium dioxide powder before firing is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. Since a longer drying time 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 firing is measured by the method described in the examples.

[0054] It is preferable that the ratio of the amount of acidic functional groups to the amount of Ti (acidic functional groups [mol] / Ti [mol]), the amount of moisture before firing, and the firing temperature satisfy the following relationship: Acidic functional groups [mol] / Ti [mol] × 800 + Amount of moisture before firing [mass%] × 300 / Firing temperature [K°] ≥ 60.0 ... (1) Here, the amount of acidic functional groups represents the sum of the amounts of acidic functional groups of the acid contained in the mixture. The amount of acidic functional groups and the amount of Ti are values ​​calculated from the amount of raw materials used to prepare the mixture. When equation (1) is satisfied, the decrease of acidic functional groups due to the effect of moisture during heating in the firing process is suppressed, and it is easy to maintain high hydrophilicity. The upper limit of Acidic functional groups [mol] / Ti [mol] × 800 + Amount of moisture before firing [mass%] × 300 / Firing temperature [K°] may be, for example, 100 or less, or 90 or less.

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

[0056] In the calcination process, the material is calcined until the moisture content reaches, for example, 0.1% to 1.0% by mass, to obtain a solid mass of titanium dioxide. The obtained solid mass is then crushed in a mortar and pestle to obtain titanium dioxide powder.

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

[0058] <3. Method for Producing Titanium Dioxide Slurry> <3-1. Slurry Formation Process> One embodiment of the method for producing titanium dioxide slurry involves mixing titanium dioxide powder with a liquid medium to produce a slurry. Examples of the liquid medium include water; organic solvents such as alcohol; and mixtures thereof. There are no particular restrictions on the liquid medium, but industrially, water, especially deionized water, is preferred. The titanium dioxide content in the titanium dioxide 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 dioxide content in the titanium dioxide 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 lower.

[0059] Examples and comparative examples of the present invention will be described below, but these are not intended to limit the technical scope of the present invention.

[0060] <Example 1> To an aqueous titanium tetrachloride solution with a Ti concentration of 15% by mass, ion-exchanged water adjusted to 30°C and citric acid monohydrate were added to adjust the concentration so that the Ti molar concentration was 0.75 mol / L and the acid / Ti (molar ratio) (amount of substance of citric acid [mol] / amount of substance of Ti [mol]) was 0.020, thereby obtaining a mixed solution. The liquid temperature was kept at 30°C throughout this mixing process.

[0061] Next, the mixture was transferred to a glass reactor. The mixture in the reactor was stirred at 60 rpm using a stirrer, and 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. After that, the mixture was allowed to cool to room temperature (25°C). The cooled slurry was neutralized to pH = 8 with ammonia water, and the slurry was recovered by filtration using an ultrafiltration membrane (Microza UF, Asahi Kasei Corporation), and the recovered material was washed with deionized water. The washed slurry was dewatered 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 to 180°C and dried until the moisture content reached 10% by mass to obtain a solid. This solid was pulverized to obtain titanium dioxide powder. Deionized water was added to the obtained titanium dioxide powder so that the moisture content of the powder was 55% by mass, and then it was baked in an oven adjusted to 250°C for 3 hours to obtain a solid. The obtained solid was pulverized in a mortar to obtain the titanium dioxide powder of Example 1.

[0062] <Example 2> 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% by mass and the firing temperature was 350°C.

[0063] <Example 3> 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% by mass and the firing temperature was 400°C.

[0064] <Example 4> 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% by mass and the firing temperature was 500°C.

[0065] <Example 5> 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% by mass and the firing temperature was 550°C.

[0066] <Example 6> 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% by 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 calcination was changed to 34% by 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% by mass.

[0069] <Comparative Example 1> 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 moisture content before calcination was changed to 46% by mass, and the calcination temperature was changed to 400°C.

[0070] <Comparative Example 2> Titanium oxide powder for Comparative Example 2 was obtained in the same manner as in Example 4, except that the moisture content before calcination was changed to 18% by mass.

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

[0072] <Comparative Example 4> Titanium oxide powder for 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% by mass, and the calcination temperature was changed to 400°C.

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

[0074] <Comparative Example 6> 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% by 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 calcination was changed to 55% by mass, and the calcination temperature was changed to 400°C.

[0076] Table 1 shows the conditions for preparing the titanium dioxide powder in Examples 1 to 8 and Comparative Examples 1 to 7.

[0077]

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

[0079] <BET Specific Surface Area> The specific surface area of ​​titanium dioxide powder was calculated from nitrogen adsorption isotherms using the BET method in accordance with JIS Z 8830:2013. The BET specific surface area (also called BET specific surface area) was measured using a QUADRASORB evo (Quantachrome) on a sample that had been pretreated by heating to 180°C and flowing nitrogen gas through it for 20 minutes. The BET method is applicable to P / P ０ The range was set to 0.00 to 0.95.

[0080] <Spin-Spin Relaxation Response Time T2> Titanium dioxide powder was calcined in an electric furnace until its moisture content was 1% by mass or less. Then, deionized water was added and mixed to prepare a mixture containing 10% by mass of titanium dioxide. This mixture was filled into a disposable NMR sample tube AS1 NMR (AS ONE Corporation), and pulse NMR measurement was immediately performed using an Acorn Area (XiGo Nanotools) to measure the spin-spin relaxation response time T2 of the titanium dioxide powder. The measurement was performed under the following conditions: Measurement frequency: 13.1 MHz, Measurement nucleus: １ After a single pulse irradiation at H and 90°, 180° pulses were irradiated at 0.5 mS intervals, and this scan was repeated four times. Measurement method: CPMG pulse sequencing method, sample volume: 0.5 mL, temperature: 23°C, Specific Surface Relaxivity (Ka): 0.0075 g / m² ２ / ms

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

[0082] <FWHM of Diffraction Peaks in Powder X-ray Diffraction (XRD) Measurements> Powder X-ray diffraction (XRD) measurements were performed on titanium oxide powder using SmartLab SE (Rigaku Corporation). Using the Cu-Kα1 line from a copper target, measurements were performed under the following conditions: tube voltage 45kV, tube current 40mA, measurement range 2θ = 24.5 to 26.0 [deg], sampling width 0.0167 [deg], and scanning speed 0.0192 [deg / s]. The FWHM of the main peak of the anatase phase around 2θ = 25° was analyzed. For the analysis, the background was measured using only the glass cell, and the diffraction pattern of the sample was corrected by subtracting the background diffraction intensity from the diffraction intensity measured with the sample containing titanium oxide and the glass cell.

[0083] <Elemental Analysis> The Si, P, Na, and Mg content of the titanium dioxide powder was measured using an atomic absorption spectrometer Z-2300 (Hitachi, Ltd.) after completely dissolving the titanium dioxide powder in an aqueous solution of hydrogen fluoride using a microwave sample preparation device ETHOS EASY (Milestone General Co., Ltd.). The C and S content of the titanium dioxide powder was measured using a carbon-sulfur analyzer CS744 (LECO Corporation).

[0084] <Slurry Viscosity> 30 mL of deionized water was weighed into a 100 mL glass beaker, and titanium dioxide powder was added at room temperature (25°C) to obtain a slurry. The mixture was stirred with a plastic spatula. The viscosity of the slurry was measured at 25°C using a rotary vibrating viscometer VISCOMATE VM-10A-M (Sansho Co., Ltd.). Furthermore, the amount of titanium dioxide powder added was gradually increased, and the concentration of titanium dioxide powder when the viscosity of the slurry reached 3000 mPa·s was determined as the titanium dioxide content of the titanium dioxide slurry that produced a flow failure point.

[0085] <Zeta Potential> A slurry with a titanium dioxide content of 0.1% by mass was prepared using deionized water at room temperature (25°C). This slurry was packed into a sapphire cell, and the zeta potential was measured at room temperature (25°C) using an ELSZ-2000 (Otsuka Electronics Co., Ltd.).

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

[0087]

[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 number following "<". For example, the P content of Example 1 is less than 10 ppm. The symbol "≧" indicates that the value is greater than or equal to the number following "≧". For example, the slurry viscosity of Comparative Example 1 is 3000 mPa·s or greater. "-" indicates that measurement was not performed.

[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 slurry that gives flow failure points. Therefore, they have good dispersibility even at high concentrations and do not become highly viscous, thus preventing flow failure, making them suitable for the synthesis of 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 slurry that gives flow failure points, and are more prone to flow failure at higher concentrations than the titanium oxide powders of the Examples.

Claims

1. The BET specific surface area measured by the nitrogen adsorption method was 80 m². ２ / g or more 300m ２ The mixture, which has an anatase content of 90% or more in the crystalline phase as measured by powder X-ray diffraction (XRD) and a titanium dioxide content of 10% by mass as prepared using deionized water, is measured by pulsed 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 is 2.3 × 10⁻¹⁴. －５ [ms －１ / (m ２ Titanium dioxide powder in a quantity of 1 / g or more.

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. Titanium oxide powder according to claim 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.

4. Titanium oxide powder according to claim 1 or 2, wherein the Na content is 0.1% by mass or less and the Mg content is 0.1% by mass or less.

5. The titanium oxide powder according to claim 1 or 2, wherein the full width at half maximum of the diffraction peaks, where the diffraction angle 2θ is in the range of 24.5° to 26.0° in measurements by powder X-ray diffraction (XRD), is 0.50° to 2.00°.

6. Titanium oxide powder according to claim 1 or 2, having a zeta potential of 25 mV or more and 63 mV or less in absolute value.

7. The titanium dioxide powder according to claim 1 or 2, wherein the viscosity of the slurry prepared using ion-exchanged water, having a titanium dioxide content of 40% by mass, is less than 3000 mPa·s at 25°C.

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

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

10. A method for producing titanium dioxide powder, comprising a synthesis step of reacting titanium tetrachloride with an acid to produce titanium dioxide, a drying step of drying the titanium dioxide powder, and a calcination step of calcining the titanium dioxide powder, wherein the ratio of the amount of acidic functional groups to the amount of Ti in the synthesis step (acidic functional groups [mol] / Ti [mol]), and the amount of moisture before calcination and the calcination temperature in the calcination step satisfy (1). Acidic functional groups [mol] / Ti [mol] × 800 + Amount of moisture before calcination [mass%] × 300 / Calcination temperature [K°] ≥ 60.0 ... (1)

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