Manufacturing method of titanium oxide powder and titanium oxide powder

Abstract

To provide a manufacturing method of titanium oxide powder that can manufacture titanium oxide powder with relatively high purity while easily maintaining particle shape, and to provide titanium oxide powder.SOLUTION: A manufacturing method of titanium oxide powder according to the present invention is a method for manufacturing titanium oxide powder comprising TiO2, and comprises a granulation step of using raw material powder comprising TiO2 having a BET specific surface area of 10 m2 / g to 100 m2 / g and a rutilization rate of less than 10% and performing spray drying on the raw material powder using a slurry comprising the raw material powder and water as a dispersion medium to obtain granulated powder.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing titanium oxide powder and titanium oxide powder. [Background technology]

[0002] Titanium dioxide powder, which contains TiO2 as a functional material, not only has high whiteness and opacity, but also exhibits catalytic activity when irradiated with light, and also has excellent properties such as dispersibility, weather resistance, and chemical stability. For this reason, titanium dioxide powder is widely used not only as a white pigment and UV-shielding filler, which have been its main applications, but also in photocatalysts, electronic devices, and various other applications.

[0003] Depending on the application, titanium dioxide powder with a relatively large particle size may be required. One method for increasing the particle size is granulation, in which the constituent particles of the raw material powder are bonded together using a binder or the like to form larger granules.

[0004] In this regard, for example, Patent Document 1 discloses a "method for producing highly dispersible granulated titanium oxide powder, which comprises adding water, an organic solvent, or a mixture of the two as a dispersion medium to titanium oxide powder, granulating the mixture in an agitation granulator, and then drying the granulated titanium oxide powder." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3394062 Summary of the Invention [Problem to be solved by the invention]

[0006] In the method described in Patent Document 1, an agitation granulator is used for granulation. When an agitation granulator is used, the inner surface of the agitation granulator wears away due to agitation during granulation, and this can lead to the titanium oxide powder being contaminated with metal from the inner surface as an impurity, resulting in a decrease in purity. To address this issue, it is believed that using a spray dryer is effective.

[0007] Here, when raw material powder is granulated using a spray drying apparatus, if a slurry of the raw material powder is prepared using a dispersion medium composed of an organic solvent, the constituent particles of the raw material powder can be effectively bonded. However, in this case, a large amount of carbon (C) in the organic solvent used as the dispersion medium remains in the granulated powder obtained after granulation. Depending on the application, titanium oxide powder containing carbon may not be desirable. On the other hand, when a slurry is prepared using a dispersion medium containing water, the raw material powder particles do not solidify sufficiently during granulation. As a result, when the resulting granulated powder is dried, the granules easily crumble, making it difficult to maintain the desired shape, such as a spherical shape.

[0008] The present invention addresses the above-mentioned problems, and its object is to provide a method for producing titanium oxide powder that is capable of producing titanium oxide powder that is likely to maintain its particle shape and has a relatively high purity, and titanium oxide powder. [Means for solving the problem]

[0009] As a result of extensive research, the inventors have found that by using a raw material powder having a BET specific surface area within a predetermined range and a relatively low rutile content, granulation by spray drying can be effectively carried out even when a slurry containing the raw material powder contains water as a dispersion medium.

[0010] The method for producing titanium oxide powder of the present invention is a method for producing titanium oxide powder containing TiO2, and the BET specific surface area is 10 m 2 / g~100m 2The method includes a granulation step in which a raw material powder containing TiO2 having a rutile content of less than 10% and a particle size of 1 / g is used, and a slurry containing the raw material powder and water as a dispersion medium is used to spray-dry the raw material powder to obtain a granulated powder.

[0011] The slurry used in the granulation step preferably contains only water as a dispersion medium.

[0012] The above manufacturing method preferably includes a heat treatment step of heating the granulated powder after the granulation step to sinter constituent particles of granules in the granulated powder to obtain a sintered powder containing sintered particles.

[0013] In this case, the chlorine (Cl) content of the sintered powder obtained in the heat treatment step is preferably less than 0.001 mass %.

[0014] The above manufacturing method can produce titanium oxide powder used as an optical material.

[0015] The titanium oxide powder of the present invention contains TiO2, has a metal impurity content of 5 mass ppm or less, and a carbon (C) content of 0.01 mass % or less.

[0016] The titanium oxide powder may be a granulated powder containing granules. In this case, the BET specific surface area is 10 m 2 / g~100m 2 / g may occur.

[0017] Alternatively, the titanium oxide powder may be a sintered powder containing sintered particles, in which case the average crushing strength may be 10 MPa to 20 MPa and the chlorine (Cl) content may be less than 0.001 mass %. [Effects of the Invention]

[0018] According to the method for producing titanium oxide powder of the present invention, it is possible to produce titanium oxide powder that is likely to maintain its particle shape and has a relatively high purity.The titanium oxide powder of the present invention is likely to maintain its particle shape and has a relatively high purity. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a photograph of the titanium oxide powder obtained in Example 1. [Figure 2] 1 is a photograph of the titanium oxide powder obtained in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0020] The method for producing titanium oxide powder and embodiments of the titanium oxide powder of the present invention will be described in detail below. A method for producing titanium oxide powder according to one embodiment of the present invention is a method for producing titanium oxide powder containing TiO. This production method includes a granulation step in which a raw material powder is spray-dried using a slurry containing the raw material powder and water as a dispersion medium to obtain a granulated powder.

[0021] In the granulation step, granulated powder is obtained by spray drying, which avoids the inclusion of metal impurities due to wear on the inner surface during agitation when using an agitation granulator, thereby reducing the content of metal impurities in the titanium oxide powder finally produced. In addition, by using a slurry subjected to spray drying that contains water as a dispersion medium, it is possible to prevent the inclusion and residue of organic solvent components in the titanium oxide powder. Therefore, compared to when a slurry containing an organic solvent as a dispersion medium is used, the titanium oxide powder has a lower content of carbon (C) derived from the organic solvent. As a result, titanium oxide powder with high purity can be produced.

[0022] In the granulation process, raw material powder with a BET specific surface area of ​​10 m 2 / g~100m 2A raw powder containing TiO2 with a rutile content of less than 10% and a rutilated content of 1 / g is used. With a raw powder with such a low rutilated content, the raw powder particles are well packed together during granulation, and the shape of the granules in the granulated powder obtained after granulation is easily maintained. This results in a titanium oxide powder that is likely to maintain the desired particle shape, such as a shape close to spherical.

[0023] (Raw material powder) The raw material powder may be any powder containing TiO2, having a predetermined BET specific surface area and a predetermined rutile content. Such raw material powder may be commercially available, but can also be produced, for example, by a gas-phase method in which titanium chloride is reacted with an oxidizing gas in the gas phase to produce TiO2.

[0024] When preparing raw material powder by a gas-phase method, titanium chloride gas such as titanium tetrachloride and an oxidizing gas are preheated and then mixed at a predetermined high temperature in a reactor, and the titanium chloride gas is brought into contact with the oxidizing gas. Examples of the oxidizing gas include oxygen gas and water vapor. Hydrogen gas and / or an inert gas may also be supplied. More specifically, for example, titanium chloride gas can be mixed with an inert gas to dilute it, and then supplied into the reactor together with water vapor and, if necessary, oxygen gas and hydrogen gas.

[0025] In the reactor, titanium chloride gas reacts with oxygen gas and / or water vapor in the flame of a combustion burner to produce a raw material powder containing TiO2. When titanium tetrachloride gas is used as the titanium chloride gas, this reaction is expressed by the reaction formula TiCl4 + O2 → TiO2 + 2Cl2 or TiCl4 + 2H2O → TiO2 + 4HCl. The reaction temperature may be any temperature at which TiO2 is produced, and can be, for example, 600°C to 1100°C. The gas containing the raw material powder is then cooled by contact with a cooling gas such as air, and the raw material powder is collected.

[0026] The raw material powder obtained by the reaction in the reactor may contain chlorine (Cl), and it is preferable to subject it to a dechlorination treatment to reduce this content. This not only prevents corrosion of the equipment used in the granulation and heat treatment steps by chlorine (Cl), but also allows the production of titanium oxide powder with a relatively low chlorine (Cl) content. In the dechlorination treatment, for example, the raw material powder can be brought into contact with a dechlorination gas such as water vapor and / or air that has been preheated to approximately 650°C to 700°C. Note that, because chlorine (Cl) can be released in the heat treatment step described below, it may not always be necessary to subject the raw material powder to a dechlorination treatment.

[0027] The raw powder obtained in this way has a BET specific surface area of ​​10m 2 / g~100m 2 / g, typically a BET specific surface area of ​​20 m 2 / g~40m 2 / g. If the BET specific surface area of ​​the raw material powder is too small, it may cause a decrease in the strength of the granulated powder, and if it is too large, the specific surface area after sintering may be outside the target range. The BET specific surface area is measured by the BET method (gas adsorption method), and a fully automatic specific surface area measuring device (Macsorb (registered trademark)) manufactured by Mountech Co., Ltd. can be used. The BET specific surface area of ​​titanium oxide powder, which will be described later, is measured in the same manner.

[0028] The rutile content of the raw material powder is less than 10%, preferably 4% to 8%. If the rutile content of the raw material powder is high, when the raw material powder is granulated in the subsequent granulation step, the constituent particles of the granules in the granulated powder do not easily solidify together, and the shape is not maintained, making it impossible to obtain titanium oxide powder of the desired shape. If the rutile content of the raw material powder is too low, there is a concern that the chlorine component will not easily escape during the heat treatment step. The rutile content can be measured by X-ray diffraction. The rutile content of titanium oxide powder described below can be measured in the same manner. To produce a raw material powder with a low rutile content by the above-mentioned gas phase method, the preheating temperature of the raw material gas can be set to, for example, 600°C to 700°C.

[0029] The raw material powder preferably has a metal impurity content of 5 mass ppm or less and a carbon (C) content of 0.01 mass % or less. Examples of metal impurities include Fe, Cr, and Al. When multiple types of metal impurities are contained, the content of the metal impurities refers to the total content of those metal impurities. The presence of metal impurities and the content are measured by ion exchange separation-ICP atomic emission spectroscopy. The carbon (C) content is measured by combustion-infrared absorption spectroscopy (in accordance with JIS H1617 and JIS Z2615).

[0030] (granulation process) In the granulation step, the raw material powder is mixed with water as a dispersion medium to form a slurry, and the raw material powder is granulated using this slurry by spray drying. As a result, multiple particles in the raw material powder are aggregated to form granules, and a granulated powder containing the granules is obtained.

[0031] When preparing a slurry to be subjected to spray drying, the dispersion medium with which the raw material powder is mixed is water. If the dispersion medium is water, contamination of the components of an organic solvent can be suppressed. The slurry may contain a dispersion medium other than water, but it is preferable that the dispersion medium contains substantially only water. Furthermore, the slurry may contain substances other than the dispersion medium, but from the viewpoint of further increasing the purity of the titanium oxide powder, it is preferable that the slurry consists of the raw material powder and water. Spray drying can be performed well without adding other substances.

[0032] Examples of water used to prepare the slurry include tap water, industrial water, distilled water, purified water, ion-exchanged water, pure water, and ultrapure water. The mass ratio of water to the raw material powder in the slurry is preferably 100% to 130%, and more preferably 115% to 120%. If the amount of water is too large relative to the amount of raw material powder, the particle size of the constituent particles of the granules after granulation may become small, and if the amount of water is too small, the particle size of the constituent particles of the granules after granulation may become large.

[0033] Various spray drying devices can be used to spray-dry raw powder in a slurry. In one example of a spray drying device, the slurry is supplied to a rotating disk inside the device, and the rotation of the disk causes droplets of the slurry to fly around. During this process, the droplets evaporate as they fly due to contact with hot air blown around the disk separately from the slurry. During this process, the raw powder particles contained in the droplets dry and solidify, forming granules of a size corresponding to the size of the droplets. If necessary, if granules exceeding a predetermined size are formed, the large granules may be classified by allowing them to fall out of the airflow within the spray drying device under their own weight. In this way, the raw powder is granulated to produce a granulated powder containing granules of a predetermined size. Since spray drying simply involves scattering the slurry as droplets and drying, it is unlikely that a significant amount of metals from the spray drying device will be mixed into the granulated powder. The spray drying conditions can be appropriately set taking into account the raw powder, the titanium oxide powder to be produced, and other factors.

[0034] The granulated powder obtained by spray drying has a tap density of 0.80 g / cm 3 ~1.20g / cm 3 , and 0.90 g / cm 3 ~1.10g / cm 3 If the TAP density of the granulated powder is too high, fine powder may be mixed in, which may result in poor flowability, while if it is too low, voids may be formed in the granulated powder, which may result in the formation of air bubbles in the product. The TAP density is measured in accordance with JIS R1628-1997 using a tap density measuring instrument, Tap Denser KYT-4000, manufactured by Seishin Enterprise Co., Ltd.

[0035] The granulated powder obtained in the granulation step can be used as titanium oxide powder. Alternatively, if necessary, the granulated powder may be further subjected to a heat treatment step described below, and the sintered powder obtained in the heat treatment step may be used as titanium oxide powder.

[0036] (Heat treatment process) The granulated powder obtained in the granulation step may be subjected to a heat treatment step, if necessary. In the heat treatment step, the granulated powder is heated to sinter the particles that make up the granules in the granulated powder. This turns the granules into sintered particles, and titanium oxide powder is obtained as a sintered powder containing these sintered particles. Furthermore, heating in the heat treatment step increases the rutilated ratio of TiO2, resulting in titanium oxide powder with a high rutilated ratio.

[0037] In the heat treatment step, the conditions are not particularly limited as long as the constituent particles of the granules in the granulated powder can be sintered. For example, the granulated powder can be heated to a temperature of 800°C to 900°C in a slightly reduced pressure atmosphere in the air. Other atmospheres may result in insufficient desorption of chlorine. Furthermore, if the heating temperature is too high, sintering between the granules of the granulated powder may occur, resulting in reduced fluidity. If the heating temperature is too low, there is a concern that residual chlorine components may not be sufficiently desorbed. Various heating furnaces and other heating devices can be used as long as they are capable of heating the granulated powder in this way.

[0038] (Titanium oxide powder) The titanium oxide powder, such as the granulated powder obtained in the granulation process or the sintered powder obtained in the heat treatment process, contains TiO2 and has a low content of metal impurities and carbon (C). The TiO2 content of the titanium oxide powder can be confirmed by X-ray diffraction (XRD). The TiO2 content can be measured by ammonium iron (III) sulfate titration.

[0039] When the titanium oxide powder is a granulated powder, the BET specific surface area of ​​the titanium oxide powder may be approximately the same as the BET specific surface area of ​​the raw material powder, for example, 10 m 2 / g~100m 2 / g, typically 20m 2 / g~40m 2 / g.

[0040] When the titanium oxide powder is a sintered powder, the BET specific surface area of ​​the titanium oxide powder is 5.0 m 2 / g~10.0m2 / g, and 6.0m 2 / g~9.0m 2 If the BET specific surface area of ​​the titanium oxide powder is too small, the granules of the granulated powder may be connected to each other, and if it is too large, there is a concern that the heat treatment may be insufficient and chlorine may not be sufficiently desorbed.

[0041] The rutile content of titanium oxide powder as granulated powder may be similar to that of the raw material powder (for example, less than 10%, typically 4% to 8%). The rutile content of titanium oxide powder as sintered powder may be 90% or more, typically 99% or more. Such a high rutile content indicates that the material has been sufficiently heat-treated.

[0042] The content of metal impurities in the titanium oxide powder is preferably 5 mass ppm or less, and more preferably 3 mass ppm or less. Examples of metal impurities include Fe, Cr, and Al. When multiple types of metal impurities are contained, the above content refers to the total content of those metal impurities. The presence of metal impurities is confirmed by ion exchange separation-ICP emission spectroscopy, and the content is measured by ion exchange separation-ICP emission spectroscopy.

[0043] The carbon (C) content of the titanium oxide powder is preferably 0.01% by mass or less, more preferably 0.005% by mass or less The carbon (C) content is measured by a combustion-infrared absorption method.

[0044] As mentioned above, when the titanium oxide powder of the sintered powder is obtained by subjecting granulated powder to a heat treatment process, the titanium oxide powder tends to have the same metal impurity content and carbon (C) content as the granulated powder.

[0045] Furthermore, titanium oxide powder as a sintered powder tends to have a low chlorine (Cl) content due to the heat treatment process described above. The chlorine (Cl) content of titanium oxide powder is preferably less than 0.001% by mass, and even less than 0.0005% by mass. Excessive chlorine (Cl) content can corrode and damage manufacturing equipment used in the manufacture of products using titanium oxide powder. The chlorine (Cl) content in titanium oxide powder is measured by silver nitrate titration, in which titanium oxide powder is dispersed in a nitric acid solution and the chlorine (Cl) dissolved in the solution is titrated with a silver nitrate standard solution. Specifically, 10.0 g of sample and 5 mL of nitric acid (1 + 1) are placed in approximately 100 mL of water in a 200 mL polybeaker, and titrated with silver nitrate standard solution (0.02 mol / L) using an automatic titrator (Nitto Seiko Analytech Co., Ltd., Model: GT-200) (inflection point: 150 mV).

[0046] The average circularity of titanium oxide powder as a sintered powder can be, for example, 0.85 to 0.95, typically 0.87 to 0.93. Too low an average circularity can result in poor fluidity and reduced metering capability. To measure the average circularity of titanium oxide powder, particles are photographed using a Keyence microscope to determine the area and perimeter of each particle. The average circularity is calculated by the ratio of the perimeter of a circle equivalent to the particle's area (area S = π × diameter D squared, where D is calculated, and perimeter L = π × D) to the actual perimeter ((perimeter of the circle with the same area) ÷ (perimeter)). As mentioned above, if titanium oxide powder is produced by spray-drying spherical droplets, the sintered particles tend to have a nearly spherical shape, resulting in a high average circularity.

[0047] The titanium oxide powder described above can be suitably used, for example, in prisms and other optical materials that utilize the high refractive index of TiO. For such applications, the titanium oxide powder is required to have a certain degree of high fluidity, to be resistant to scattering, and to be strong enough to withstand damage during supply and transportation, and the titanium oxide powder of the above-described embodiment can meet these requirements. [Example]

[0048] Next, the method for producing titanium oxide powder of the present invention was experimentally carried out, and its effects were confirmed, which will be described below. However, this description is for illustrative purposes only and is not intended to be limiting.

[0049] A slurry containing the raw material powders shown in Table 1 was granulated to obtain titanium oxide powders shown in Table 1 as granulated powders.

[0050] Granulation was performed using a spray dryer in Examples 1 and 2 and Comparative Example 2, and an agitation granulator as described in Patent Document 1 was used in Comparative Example 1. In Examples 1 and 2, the dispersion medium contained in the slurry subjected to spray drying was water. In Comparative Example 2, polyvinyl alcohol (PVA) was used as the dispersion medium contained in the slurry.

[0051] Optical microscope photographs of the titanium oxide powders (granulated powders) of Example 1 and Comparative Example 1 are shown in FIGS. 1 and 2, respectively.

[0052] [Table 1]

[0053] It can be seen from Table 1 that the titanium oxide powders (granulated powders) of Examples 1 and 2 have lower metal impurity or carbon contents and higher purity than those of Comparative Examples 1 and 2.

[0054] The granulated powder of Example 2 was also heat-treated at 800°C under a slightly reduced pressure to obtain a sintered powder. The crushing strength and chlorine (Cl) content of this sintered powder were measured and compared with those of the granulated powder before heat treatment. The results are shown in Table 2.

[0055] [Table 2] The crushing strength (compression load and diameter when the titanium oxide powder breaks) [MPa] of the heated titanium oxide powder was measured using a microcompression testing machine (manufactured by Shimadzu Corporation, product name: MCTM-510) in accordance with JIS R1639-5 (Fine ceramics - Determination of granule characteristics - Part 5: Single granule crushing strength). Ten particles were measured in the same manner as above, and the average crushing strength was calculated by arithmetically averaging the obtained values.

[0056] Table 2 shows that the sintered powder has a higher average crushing strength than the granulated powder and a reduced chlorine (Cl) content. When such a sintered powder is used as titanium oxide powder, it can be said that the particle shape is more easily maintained. The average crushing strength is preferably 10 MPa to 20 MPa.

[0057] From the above, it was found that according to the present invention, it is possible to produce titanium oxide powder that is easy to maintain its particle shape and has a relatively high purity.

Claims

1. TiO 2 A method for producing a titanium oxide powder containing BET specific surface area is 10m 2 / g to 100m 2 / g and the rutile content is less than 10% 2 a granulation step of spray-drying a raw material powder containing the raw material powder and water as a dispersion medium to obtain a granulated powder; A method for producing titanium oxide powder, comprising:

2. 2. The method for producing a titanium oxide powder according to claim 1, wherein the slurry used in the granulation step contains only water as a dispersion medium.

3. 2. The method for producing titanium oxide powder according to claim 1, further comprising a heat treatment step of heating the granulated powder after the granulation step to sinter constituent particles of granules in the granulated powder to obtain a sintered powder containing sintered particles.

4. The method for producing a titanium oxide powder according to claim 3, wherein the chlorine (Cl) content of the sintered powder is less than 0.001 mass%.

5. The method for producing titanium oxide powder according to any one of claims 1 to 4, which produces titanium oxide powder used as an optical material.

6. TiO 2 The titanium oxide powder contains A titanium oxide powder having a metal impurity content of 5 mass ppm or less and a carbon (C) content of 0.01 mass % or less.

7. A granulated powder containing granules, having a BET specific surface area of ​​10 m 2 / g to 100m 2 The titanium oxide powder according to claim 6, wherein the solubility is 1 / g.

8. The titanium oxide powder according to claim 6, which is a sintered powder containing sintered particles, has an average crushing strength of 10 MPa to 20 MPa, and has a chlorine (Cl) content of less than 0.001 mass%.

9. The titanium oxide powder according to any one of claims 6 to 8, which is used as an optical material.

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