Method for producing inorganic oxide hollow particles

Abstract

To provide a method for producing inorganic oxide hollow particles capable of efficiently producing fine particles while suppressing generation of coarse particles.SOLUTION: A method for producing inorganic oxide hollow particles comprises sending a raw material compound-containing solution to a spray apparatus, spraying droplets of the raw material compound-containing solution from the spray apparatus, and thermally decomposing the same, the method further comprising adjusting a surface tension of the raw material compound-containing solution to 25 to 55 mN / m.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing inorganic oxide hollow particles. [Background technology]

[0002] Hollow inorganic oxide particles have cavities surrounded by an outer shell, and are lighter in weight, have lower thermal conductivity, and are superior in thermal stability compared to solid particles, and are therefore widely used as heat insulating materials, heat shielding materials, catalyst supports, building materials, electronic materials, etc. Hollow inorganic oxide particles can be produced, for example, by a spray pyrolysis method in which a solution containing raw material compounds is sprayed from a spraying device into a heating furnace, but this method tends to produce not only fine particles but also coarse particles.

[0003] It has been reported that, for example, a spray device having a rotating hollow cylinder with many internal holes is used to evenly distribute liquid inside the cylinder to the inner wall and internal holes, and the volumetric flow rate of the liquid per internal hole is controlled within a specific range, thereby spraying droplets with a narrow size distribution and enabling the production of fine particles (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 8-507469 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, electronic devices have rapidly become more compact and have improved in performance, and coatings, resin products, and film products used in electronic devices are required to be thinner. Therefore, the inorganic oxide hollow particles used in these products are required to be fine. An object of the present invention is to provide a method for producing inorganic oxide hollow particles that can efficiently produce fine particles while suppressing the generation of coarse particles. [Means for solving the problem]

[0006] The present inventors have noted a correlation between the size of droplets formed by a spraying device and the size of inorganic oxide particles formed from the droplets, and have hypothesized the following: A raw compound-containing solution sprayed from a spraying device is sheared by compressed air to form droplets. If the surface tension of the raw compound-containing solution is low, the cohesive energy between molecules in the solution decreases, making it easier to shear, allowing for the formation of finer droplets. This leads to smaller inorganic oxide particles, which in turn reduces the diameter of the inorganic oxide particles, thereby suppressing the generation of coarse particles. Based on this hypothesis, the present inventors have conducted various studies and found that by spraying a raw compound-containing solution with a surface tension controlled within a specific range from a spraying device, it is possible to efficiently produce fine inorganic oxide hollow particles while suppressing the generation of coarse particles.

[0007] The present invention provides the following [1] to [4]. [1] A method for producing inorganic oxide hollow particles, comprising the steps of: sending a solution containing a raw material compound to a spraying device; and spraying droplets of the solution containing the raw material compound from the spraying device to thermally decompose the solution, adjusting the surface tension of the raw material compound-containing solution to 25 to 55 mN / m; A method for producing hollow inorganic oxide particles. [2] The method for producing inorganic oxide hollow particles according to [1] above, wherein a surfactant is added to adjust the surface tension of the solution containing the raw material compound. [3] The method for producing inorganic oxide hollow particles according to [2], wherein the surfactant is at least one selected from the group consisting of an ionic surfactant having a Krafft point of 18°C ​​or less and a nonionic surfactant having a cloud point of 20°C or more. [4] The method for producing inorganic oxide hollow particles according to any one of [1] to [3] above, wherein the raw material compound-containing solution contains one or more raw material compounds selected from lithium salts, sodium salts, potassium salts, cesium salts, magnesium salts, calcium salts, barium salts, titanium salts, zirconium salts, boric acid, borates, aluminum salts, zinc salts, silicates, aluminosilicates, silicate alkoxides, and aluminum alkoxides. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for producing inorganic oxide hollow particles that can efficiently produce fine particles while suppressing the generation of coarse particles. DETAILED DESCRIPTION OF THE INVENTION

[0009] As used herein, "hollow particles" refer to particles having a cavity inside the outer shell. The inorganic oxide hollow particles of the present invention may have a plurality of independent spaces in which the cavity covered by the outer shell is further separated by one or more partition walls. In this case, these independent spaces are each formed by bubbles that are not connected to each other and are separated by partition walls (hereinafter also referred to as "closed bubbles"). Here, as used herein, "outer shell" refers to the wall located on the outermost surface of the particle and that contacts only one closed bubble inside the particle. "Clutter wall" refers to the wall that separates two adjacent closed bubbles inside the particle. Furthermore, the inorganic oxide hollow particles of the present invention have no openings in the outer shell and are non-porous. Therefore, the inorganic oxide hollow particles of the present invention have completely closed closed cells, and are therefore different from porous particles having multiple pores extending from the particle surface to the interior. The non-porous nature of the outer shell can be confirmed by scanning electron microscope (SEM) images or by floating on water.

[0010] The production method of the present invention produces inorganic oxide hollow particles by a spray pyrolysis method, which includes a step of spraying droplets of a solution containing a raw material compound into a pyrolysis furnace and pyrolyzing the droplets, and is characterized in that the surface tension of the raw material compound-containing solution is adjusted to 25 to 55 mN / m. By adjusting the surface tension of the raw material compound-containing solution within this range, the generation of coarse particles can be suppressed, and fine inorganic oxide hollow particles can be produced efficiently.

[0011] The surface tension of the solution containing the raw material compound is 25 to 55 mN / m. From the viewpoint of forming fine particles while maintaining a sufficient hollowness, the surface tension is preferably 31 mN / m or more, more preferably 33 mN / m or more, and even more preferably 35 mN / m or more. From the viewpoint of forming fine particles while suppressing the generation of coarse particles, the surface tension is preferably 50 mN / m or less, more preferably 47 mN / m or less, and even more preferably 43 mN / m or less. In this specification, the "surface tension of the solution containing the raw material compound" is measured by the pendant drop method at a liquid temperature of 25°C. The surface tension can be measured using, for example, a Drop Master 500 (manufactured by Kyowa Interface Science Co., Ltd.) contact angle meter.

[0012] The method for adjusting the surface tension of the raw material compound-containing solution is not particularly limited as long as the surface tension of the raw material compound-containing solution is within the above range, and any appropriate method can be used. Examples include increasing the liquid temperature of the raw material compound-containing solution and adding a surfactant to the raw material compound-containing solution. Among these, adding a surfactant is preferred because it makes it easier to adjust the surface tension of the raw material compound-containing solution to a desired value. It is anticipated that adjusting the surface tension by adding a surfactant would result in porous particles with through-holes in the outer shell, since the surfactant volatilizes when forming an inorganic oxide from the raw material compound by spray pyrolysis. However, the present inventors have surprisingly found that non-porous inorganic oxide hollow particles can be obtained.

[0013] The surfactant is not particularly limited and may be either ionic or nonionic, as long as it can adjust the surface tension of the solution containing the raw material compound within the above range. The ionic surfactant may be any of anionic surfactants, cationic surfactants, and amphoteric surfactants. Examples of anionic surfactants include fatty acid soaps, carboxylates such as alkyl ether carboxylates, sulfonates such as alkyl benzene sulfonates, alkyl naphthalene sulfonates, and α-olefin sulfonates, sulfates such as higher alcohol sulfates and alkyl ether sulfates, and phosphates such as alkyl phosphates. Examples of cationic surfactants include aliphatic amine salts and aliphatic ammonium salts. Examples of amphoteric surfactants include carboxylates and betaines. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene distyrenated phenyl ethers, polyglycerin fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene ethers of glycerin esters, polyethylene glycol fatty acid esters, glycerin esters, and sorbitan esters.

[0014] Among these, surfactants that are soluble in water at 20°C are preferred from the viewpoint of forming fine particles while generating coarse particles. Surfactants with such properties can be selected, for example, by using the Krafft point as an indicator in the case of ionic surfactants, or by using the cloud point as an indicator in the case of nonionic surfactants. Here, the Krafft point can be measured according to the method described in Kaoru Tsujii, Naoyuki Sato, and Takashi Takeuchi, Journal of Physical Chemistry, 84, 2287 (1980). The cloud point can be determined by gradually changing the temperature of a sample, similar to the cloud point test method for petroleum products described in JIS K 2269, and the temperature at which the sample becomes cloudy is identified as the cloud point. That is, in the case of surfactants, a test tube containing 45 mL of a 1 wt % aqueous surfactant solution is placed in a thermostatic bath, the solution is heated or cooled, and the test tube is removed every time the temperature of the solution increases or decreases by 1°C. The temperature at which clouding occurs can be determined as the cloud point.

[0015] The Krafft point of an ionic surfactant is usually 18° C. or lower, preferably 15° C. or lower, and more preferably 12° C. or lower. The lower limit of the Krafft point is 1° C. or higher, from the viewpoint of availability, although ionic surfactants with a Krafft point of 0° C. or lower are also applicable, since the lower the Krafft point, the more practical the water solubility of the ionic surfactant. An example of an ionic surfactant having such a Krafft point is sodium dodecyl sulfate, a higher alcohol sulfate ester salt, which has a Krafft point of 9° C.

[0016] The cloud point of a nonionic surfactant is usually 20° C. or higher, preferably 30° C. or higher, more preferably 50° C. or higher, and even more preferably above 80° C. The higher the cloud point, the more practical the water solubility of the nonionic surfactant. Therefore, although there are nonionic surfactants with an upper limit of 100° C. or higher that can be used, from the viewpoint of availability, the upper limit is preferably 100° C. or lower, more preferably 95° C. or lower, and even more preferably 90° C. or lower. Specific examples of polyoxyethylene alkylphenyl ethers as nonionic surfactants having such a cloud point are as follows: For example, polyoxyethylene (8) nonylphenyl ether has a cloud point of 33°C, polyoxyethylene (8) octylphenyl ether has a cloud point of 44°C, polyoxyethylene (9.5) nonylphenyl ether has a cloud point of 53°C, polyoxyethylene (10) nonylphenyl ether has a cloud point of 61°C, polyoxyethylene (10) octylphenyl ether has a cloud point of 74°C, and polyoxyethylene (24) octylphenyl ether, polyoxyethylene (12) nonylphenyl ether, polyoxyethylene (15) nonylphenyl ether, and polyoxyethylene (20) nonylphenyl ether all have cloud points of 80°C or less.

[0017] The surfactant may be present in the solution containing the raw material compound when the solution containing the raw material compound is sprayed from the spraying device. For example, the surfactant may be added during or after the preparation of the solution containing the raw material compound. The order of adding the raw material compound and the surfactant is not particularly limited.

[0018] The amount of surfactant used is not particularly limited as long as the surface tension of the raw material compound-containing solution falls within the above range. However, from the viewpoint of forming fine particles while suppressing the generation of coarse particles, the amount of surfactant used in the raw material compound-containing solution is preferably 0.05% by mass or more, more preferably 0.15% by mass or more, and even more preferably 0.2% by mass or more. From the viewpoint of forming fine particles while ensuring a hollow ratio, the amount of surfactant used in the raw material compound-containing solution is preferably 1.5% by mass or less, more preferably 1.2% by mass or less, and even more preferably 1% by mass or less.

[0019] The raw material compound is not particularly limited as long as it contains an element that constitutes an inorganic oxide. For example, it can be a compound containing one or more elements selected from Group 1 elements, Group 2 elements, Group 4 elements, Group 8 elements, Group 9 elements, Group 10 elements, Group 11 elements, Group 12 elements, Group 13 elements, and Group 15 elements. Here, in this specification, "Group 1 element" refers to an element belonging to Group 1 in the periodic table, and the same meaning is understood for elements belonging to other groups. The raw material compound can contain one or more elements.

[0020] Examples of Group 1 elements include lithium, sodium, potassium, and cesium. Examples of Group 2 elements include magnesium, calcium, strontium, and barium. Examples of Group 4 elements include titanium and zirconium. Examples of Group 8 elements include iron and ruthenium. Examples of Group 9 elements include cobalt, rhodium, and iridium. Examples of Group 10 elements include nickel, palladium, and platinum. Examples of Group 11 elements include copper, silver, and gold. Examples of Group 12 elements include zinc and cadmium. Examples of Group 13 elements include boron, aluminum, gallium, indium, and thallium. Examples of Group 14 elements include silicon, germanium, tin, and lead. Examples of Group 15 elements include phosphorus, arsenic, antimony, and bismuth. Among these, as the raw material compound, one or more compounds selected from the group consisting of a compound containing a Group 1 element, a compound containing a Group 2 element, a compound containing a Group 4 element, a compound containing a Group 12 element, a compound containing a Group 13 element, and a compound containing a Group 14 element are preferably used.

[0021] The raw material compound is preferably one that dissolves in water, and is preferably in the form of a salt or an alkoxide, for example. The salt may be an inorganic salt or an organic salt. Examples of inorganic salts include nitrates, sulfates, carbonates, hydroxides, and halides. Examples of organic salts include formates, acetates, propionates, oxalates, and citrates.

[0022] Examples of compounds containing Group 1 elements include lithium salts, sodium salts, potassium salts, and cesium salts. Examples of lithium salts include lithium nitrate, lithium chloride, lithium hydroxide, and lithium sulfate. Examples of sodium salts include sodium nitrate, sodium chloride, sodium hydroxide, and sodium sulfate. Examples of potassium salts include potassium nitrate, potassium chloride, potassium hydroxide, and potassium sulfate. Examples of cesium salts include cesium nitrate, cesium sulfate, and cesium chloride.

[0023] Examples of compounds containing Group 2 elements include magnesium salts, calcium salts, and barium salts. Examples of magnesium salts include magnesium nitrate, magnesium sulfate, magnesium chloride, magnesium phosphate, and magnesium hydroxide. Examples of calcium salts include calcium nitrate, calcium chloride, calcium hydroxide, and calcium propionate. Examples of barium salts include barium nitrate, barium chloride, and barium hydroxide.

[0024] Examples of compounds containing Group 4 elements include titanium salts and zirconium salts. Examples of titanium salts include titanium nitrate, titanium sulfate, and titanium chloride. Examples of zirconium salts include zirconium oxynitrate and zirconium oxychloride. Examples of compounds containing a Group 12 element include zinc salts, such as zinc nitrate, zinc sulfate, and zinc chloride.

[0025] Examples of compounds containing Group 13 elements include boric acid, borate salts, aluminum salts, and aluminum alkoxides. Examples of borates include metaborates such as sodium borate and potassium borate, tetraborates such as sodium tetraborate and potassium tetraborate, and pentaborates such as sodium pentaborate and potassium pentaborate. Examples of aluminum salts include aluminum nitrate, aluminum sulfate, aluminum chloride, aluminum phosphate, aluminum hydroxide, aluminum acetate, and aluminum oxalate. Examples of aluminum alkoxides include aluminum methoxide, aluminum ethoxide, and aluminum isopropoxide.

[0026] Examples of compounds containing a Group 14 element include silicates and silicate alkoxides. Examples of silicates include sodium silicate, potassium silicate, and tetramethylammonium silicate. Examples of silicate alkoxides include tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), tetrapropyl orthosilicate (TPOS), and tetrabutoxysilane. Alternatively, the compound may be a composite compound having a structure in which two or more elements are chemically bonded, such as an aluminosilicate, such as sodium aluminosilicate, potassium aluminosilicate, or calcium aluminosilicate.

[0027] Among these, the raw material compound is preferably one or more selected from lithium salts, sodium salts, potassium salts, cesium salts, magnesium salts, calcium salts, barium salts, titanium salts, zirconium salts, boric acid, borates, aluminum salts, zinc salts, silicates, aluminosilicates, silicate alkoxides, and aluminum alkoxides; more preferably one or more selected from lithium salts, sodium salts, potassium salts, magnesium salts, calcium salts, titanium salts, boric acid, borates, aluminum salts, zinc salts, silicates, aluminosilicates, silicate alkoxides, and aluminum alkoxides; and even more preferably one or more selected from sodium salts, potassium salts, magnesium salts, calcium salts, boric acid, borates, aluminum salts, silicates, aluminosilicates, silicate alkoxides, and aluminum alkoxides.

[0028] Examples of inorganic oxides formed from these raw material compounds include lithium oxide, potassium oxide, sodium oxide, magnesium oxide, calcium oxide, titanium oxide, boron oxide, alumina, zinc oxide, and silica, as well as composite oxides formed by combining these oxides.

[0029] Suitable inorganic oxide hollow particles include inorganic oxide hollow particles composed of an inorganic oxide containing preferably 10% by mass or less, more preferably 5% by mass or less, a Group 1 element oxide, preferably 35% by mass or less, more preferably 1-35% by mass, a Group 2 element oxide, preferably 60% by mass or less, more preferably 4-50% by mass, a Group 13 element oxide, and preferably 30% by mass or more, more preferably 35-60% by mass, of silicon oxide. Herein, "Group 1 element oxide" refers to an oxide of an element belonging to Group 1 of the periodic table, and the same applies to oxides of elements belonging to other groups. The content of the Group 1 element oxide may be 0% by mass.

[0030] The solution containing the raw material compound is usually prepared by mixing the raw material compound with water and / or an organic solvent such as ethanol.

[0031] The total concentration of the raw material compounds in the raw material compound-containing solution is usually 0.01 to 1.0 mol / L, and preferably 0.1 to 1.0 mol / L. The content of each raw material compound in the raw material compound-containing solution may be an amount that satisfies the stoichiometric composition based on the predetermined inorganic oxide hollow particles.

[0032] The pyrolysis furnace is preferably a vertical cylindrical furnace, and the size of the pyrolysis furnace can be appropriately selected depending on the production scale.

[0033] Examples of spraying devices include fluid nozzles such as two-fluid nozzles, three-fluid nozzles, and four-fluid nozzles. Fluid nozzles include an internal mixing system in which a gas and a raw material solution are mixed inside the nozzle, and an external mixing system in which a gas and a raw material solution are mixed outside the nozzle; either system can be employed. Examples of gases that can be supplied to the nozzle include air and inert gases such as nitrogen and argon. Among these, air is preferred from the viewpoint of economy. One or more spraying devices can be installed.

[0034] The flow rate of the solution containing the raw material compound is usually 1 to 100 L / h, preferably 3 to 80 L / h, and more preferably 5 to 60 L / h. The spray speed of the solution containing the raw material compound is usually 1 to 50 m / s, preferably 5 to 35 m / s, and more preferably 10 to 20 m / s.

[0035] The volume ratio of the gas flow rate per unit time to the amount of the solution containing the raw material compound sprayed per unit time can be set as appropriate, but from the viewpoint of forming fine particles while producing coarse particles, it is preferably 0.20 to 2.00, more preferably 0.23 to 1.00, and even more preferably 0.25 to 0.70.

[0036] The droplets sprayed from the spraying device are heated by a heating device in the pyrolysis furnace to form a film containing an inorganic compound, and hollow inorganic oxide particles are formed from this as starting points.

[0037] Examples of the heating device include a combustion burner, a hot air heater, and an electric heater. One or more heating devices can be installed. Any combustion burner, hot air heater, or electric heater that is commercially available can be used. The temperature of the heating device is preferably 400 to 1800° C., more preferably 600 to 1500° C., and even more preferably 800 to 1200° C. At such a temperature, pyrolysis is sufficient and the particles are less likely to aggregate when discharged out of the pyrolysis furnace.

[0038] The inorganic oxide hollow particles produced by the thermal decomposition reaction are recovered from the downstream side of the pyrolysis furnace using a powder recovery device such as a high-performance cyclone powder recovery machine or a bag filter.

[0039] The hollowness of the inorganic oxide hollow particles produced by the method of the present invention is preferably 40% or more, more preferably 50% or more, even more preferably 60% or more, even more preferably 70% or more, and even more preferably 80% or more. The upper limit of the hollowness is preferably 95% or less, more preferably 90% or less, from the viewpoint of ensuring sufficient strength. Herein, the "hollowness" is a value calculated from the bulk density and true density of the particles measured using a dry automatic densimeter using the following formula. Since it is difficult to measure the hollowness of individual particles, the hollowness refers to the percentage of voids in the particle group. Herein, the "bulk density" is measured by the gas displacement method in accordance with JIS R 1620. The "true density" is measured by heating the particles in a box-type electric furnace at or above the melting point for 6 hours to remove voids, followed by cooling and measurement using a dry automatic densimeter. As the density measuring device, for example, an Accupyc dry automatic density meter (manufactured by Shimadzu Corporation) can be used, and as the dry automatic density meter, for example, an Accupyc dry automatic density meter (manufactured by Shimadzu Corporation) can be used.

[0040] Void ratio = (true density - bulk density) x 100 / true density

[0041] The inorganic oxide hollow particles produced by the method of the present invention are minute particles, and therefore can be easily applied to electronic device components that require miniaturization and thinning. More specifically, the average particle diameter of the inorganic oxide hollow particles is preferably 5 μm or less, more preferably 3 μm or less, and even more preferably 2 μm or less. From the viewpoint of ensuring sufficient voids, the lower limit of the average particle diameter is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more. Here, in this specification, the "average particle diameter" refers to the particle diameter (D) corresponding to 50% of the cumulative distribution curve when the particle size distribution of a sample is prepared on a volume basis in accordance with JIS R 1629. 50 ) For measuring the particle size distribution, for example, a laser diffraction / scattering particle size distribution measuring device can be used.

[0042] The inorganic oxide hollow particles produced by the method of the present invention can be used in heat insulating materials, heat shielding materials, catalyst supports, building materials, electronic materials, etc., and because they are small particles, they have excellent dispersibility in media, making them useful for electronic materials, particularly wiring circuit boards and semiconductor encapsulants. [Example]

[0043] The following examples will explain the present invention in more detail, but the present invention is not limited to the examples below.

[0044] 1. Measurement of the surface tension of the solution containing the raw compound A Drop Master 500 (Kyowa Interface Science Co., Ltd.) was used as a contact angle meter, and measurements were taken at a liquid temperature of 25°C using the pendant drop method.

[0045] 2. Chemical composition analysis The inorganic oxide hollow particles were molded in a press to prepare briquettes, and the briquettes were measured in terms of oxides using an X-ray fluorescence analyzer (ZSX primus II, manufactured by Rigaku Corporation) to calculate the chemical components.

[0046] 3. Hollowness analysis The bulk density and true density of the particles were measured using an Accupyc (Shimadzu Corporation) as a dry automatic density meter, and calculated using the following formula: "Bulk density" was measured by the gas displacement method in accordance with JIS R 1620. "True density" was measured by heating the particles at or above the melting point in a box-type electric furnace for 6 hours to remove voids, and then cooling them and measuring them with the dry automatic density meter.

[0047] Hollow ratio = (true density - bulk density) x 100 / true density

[0048] 4. Average particle size analysis Using a particle size distribution analyzer (MT3000II, manufactured by Microtrackbell Co., Ltd.), a volume-based particle size distribution was created in accordance with JIS R 1629, and the particle diameter (D 50 ) was sought.

[0049] 5. Ratio of coarse particles Based on the volume-based particle size distribution created above, the proportion of inorganic oxide hollow particles having a particle size of 10 μm or more was calculated.

[0050] Example 1 The raw material compound-containing aqueous solution was added to a reaction vessel and stirred for 3 hours. The raw material compound-containing aqueous solution was prepared by dissolving sodium nitrate (manufactured by Toko Shoji) at 0.056 mol / L, calcium nitrate (manufactured by Osaki Kogyo) at 0.025 mol / L, magnesium nitrate (manufactured by Ako Kasei) at 0.019 mol / L, aluminum nitrate (manufactured by Hakuko Chemical Industry) at 0.048 mol / L, tetraethyl orthosilicate (manufactured by Tama Chemical Industry) at 0.138 mol / L, and boric acid (manufactured by Yoneyama Chemical Industry) at 0.097 mol / L in tap water. Then, 0.5 wt% of polyoxyethylene (20) nonylphenyl ether was added and dissolved. Next, this aqueous solution containing the raw material compound was sent to a two-fluid nozzle, and the aqueous solution containing the raw material compound and nozzle air were sprayed from the nozzle into a spray pyrolysis furnace so that the volume ratio of the nozzle air volume to the liquid volume per hour was 0.28. The resulting particles were fired at 1000°C to produce porous inorganic oxide hollow particles. The recovered inorganic oxide hollow particles were then analyzed. The chemical composition of the inorganic oxide hollow particles is shown in Table 1, and the analysis results are shown in Table 2.

[0051] [Table 1]

[0052] Examples 2 to 7 Poreless inorganic oxide hollow particles were produced in the same manner as in Example 1, except that the type and / or amount of surfactant was changed as shown in Table 1. The collected inorganic oxide hollow particles were then analyzed. The analytical results are shown in Table 2.

[0053] Comparative Example 1 Pore-free inorganic oxide hollow particles were produced in the same manner as in Example 1, except that no surfactant was used. The collected inorganic oxide hollow particles were analyzed. The analytical results are shown in Table 2.

[0054] [Table 2]

[0055] Table 1 shows that by adjusting the surface tension of the raw material compound-containing solution to 25 to 55 mN / m, sending it to a spraying device, and spraying droplets of the raw material compound-containing solution from the spraying device for thermal decomposition, it is possible to efficiently produce fine inorganic oxide hollow particles while suppressing the generation of coarse particles.

Claims

1. A method for producing inorganic oxide hollow particles, comprising the steps of: sending a solution containing a raw material compound to a spraying device; and spraying droplets of the solution containing the raw material compound from the spraying device to thermally decompose the solution, adjusting the surface tension of the raw material compound-containing solution to 25 to 55 mN / m; A method for producing hollow inorganic oxide particles.

2. 2. The method for producing inorganic oxide hollow particles according to claim 1, wherein the surface tension of the solution containing the raw material compound is adjusted by adding a surfactant.

3. 3. The method for producing inorganic oxide hollow particles according to claim 2, wherein the surfactant used is at least one selected from the group consisting of an ionic surfactant having a Krafft point of 18°C ​​or less and a nonionic surfactant having a cloud point of 20°C or more.

4. The method for producing inorganic oxide hollow particles according to any one of claims 1 to 3, wherein the raw material compound-containing solution contains one or more raw material compounds selected from lithium salts, sodium salts, potassium salts, cesium salts, magnesium salts, calcium salts, barium salts, titanium salts, zirconium salts, boric acid, borates, aluminum salts, zinc salts, silicates, aluminosilicates, silicate alkoxides, and aluminum alkoxides.

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