Method for producing water-resistant inorganic oxide hollow particles

Abstract

To provide hollow inorganic oxide particles with excellent water resistance. [Solution] A water-resistant inorganic oxide hollow particle in which the outer shell that partitions the hollow portion is composed of an inorganic oxide that contains Group 2 element oxides, aluminum oxide, boron oxide and silicon oxide, and does not contain Group 1 element oxides, The electrical conductivity measured by the following method is 8.5 mS / m or less. Water-resistant inorganic oxide hollow particles. (Measurement of electrical conductivity) In a glass beaker, inorganic oxide hollow particles and distilled water are mixed in a liquid-to-solid ratio of 33:1 (wt%), and the mixture is boiled for 5 minutes. After the mixture cools to 25°C, its electrical conductivity is measured.

Description

Technical Field

[0001] The present invention relates to a method for producing water - resistant inorganic oxide hollow particles.

Background Art

[0002] Since inorganic oxide hollow particles have cavities inside the particles, they are excellent in heat resistance and light weight and are widely used as heat - insulating materials, heat - shielding materials, catalyst carriers, building materials, electronic materials, etc. Conventionally, for example, minute mullite hollow particles (Patent Document 1) containing Al2O3, SiO2 and mullite in specific ratios and controlling the average circularity, average particle diameter and the thickness of the shell within a specific range, silica - containing hollow particles (Patent Document 2) having a shell (outer shell part) containing silica and comprising metal and / or metal compound nanoparticles encapsulated in the shell, etc., various compositions of inorganic oxide hollow particles have been proposed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, due to the remarkable progress of information network technology and the expansion of services utilizing the information network, further high - speed processing and high - speed transmission of information are desired, and the high - frequency conversion of transmission signals of electronic devices is being promoted. However, due to this high - frequency conversion, the transmission loss of printed wiring boards of electronic devices becomes large. Therefore, for inorganic oxide hollow particles used in printed wiring boards, dielectric properties​ Excellence is required. However, when the inventors immersed a resin molded product containing inorganic oxide hollow particles in water, We discovered that there is a problem of degraded dielectric properties. In order to investigate the cause of this, this The inventors analyzed the immersed water and confirmed an increase in electrical conductivity, thus indicating that inorganic Ionic components leach from the surface of the oxide hollow particles, creating pores on the particle surface and allowing water to penetrate the inside of the cavity. It was inferred that this was the cause. Therefore, applying inorganic oxide hollow particles to electronic materials To achieve this, it is necessary to improve the water resistance of the inorganic oxide hollow particles and suppress the deterioration of their dielectric properties. . The object of the present invention is a method for producing inorganic oxide hollow particles with excellent water resistance, and inorganic oxide hollow particles The objective is to provide a method for improving the water resistance of and water-resistant inorganic oxide hollow particles. [Means for solving the problem]

[0005] The inventors heated inorganic oxide hollow particles to a predetermined temperature, and then cooled them at a constant average rate. By slowly cooling to a predetermined temperature, the particle surface becomes densified and stable, and as a result, when immersed in water... When this occurs, the elution of ionic components from the particle surface is suppressed, resulting in an inorganic oxide with excellent water resistance. We discovered that empty particles can be obtained.

[0006] In other words, the present invention provides the following [1] to [6]. [1] Inorganic oxide hollow particles within a range of -500°C ± 150°C relative to the melting point of the hollow particles A first step involves heating to a certain temperature, The heated inorganic oxide hollow particles are cooled to a temperature of 1 / 2 ± 150°C of the heating temperature at a rate of 1°C / mi. A second step involves slow cooling at an average cooling rate of n or more and 28°C / min or less. A method for producing water-resistant inorganic oxide hollow particles, including [the specified component]. [2] The heating time of the first step is 15 minutes or more, in the water-resistant inorganic oxide described in [1] above. A method for manufacturing empty particles. [3] Inorganic oxide hollow particles are Group 1 elements of the periodic table, Group 2 elements of the periodic table, and Group 4 elements of the periodic table. , elements of group 8 of the periodic table, elements of group 9 of the periodic table, elements of group 10 of the periodic table, elements of group 11 of the periodic table, The elements of Group 12, Group 13, Group 14, and Group 15 of the periodic table. It is composed of an inorganic oxide containing one or more elements selected from [ A method for producing water-resistant inorganic oxide hollow particles according to (1) or (2). [4] The inorganic oxide hollow particles are heated within a range of -500°C ± 150°C relative to the melting point of the hollow particles. A first step involves heating to a certain temperature, The heated inorganic oxide hollow particles are cooled to a temperature of 1 / 2 ± 150°C of the heating temperature at a rate of 1°C / mi. A second step involves slow cooling at an average cooling rate of n or more and 28°C / min or less. A method for improving the water resistance of hollow inorganic oxide particles, including [the specified element]. [5] Water-resistant inorganic material having an electrical conductivity of 8.5 mS / m or less as measured by the following method. Oxide hollow particles. (Measurement of electrical conductivity) In a glass beaker, mix inorganic oxide hollow particles and distilled water in a liquid-to-solid ratio of 33:1 (wt%). Then, boil the mixture for 5 minutes. After the mixture has cooled to 25°C, measure its electrical conductivity. To determine. [6] Hollow particles of water-resistant inorganic oxide as described in [5], wherein the hollowness ratio is 70% or more. [Effects of the Invention]

[0007] According to the present invention, it is possible to produce water-resistant inorganic oxide hollow particles with simple operations. Furthermore, the inorganic oxide hollow particles of the present invention not only have improved water resistance, but also sufficient It has a void ratio and excellent dielectric properties, and is particularly useful as an electronic material.

Mode for Carrying Out the Invention

[0008] 〔Method for Producing Water-Repellent Inorganic Oxide Hollow Particles〕 The method for producing water-repellent inorganic oxide hollow particles is characterized by including a first step and a second step. Hereinafter, each step will be described in detail.

[0009] (Preparation Step) In this step, inorganic oxide hollow particles are prepared prior to the first step. Here, in this specification, "hollow particles" refer to particles having a hollow structure inside, particles having an outer shell portion partitioning the hollow portion, and are different from porous particles having a plurality of pores extending from the surface of the particles to the inside. The hollow particles can be distinguished from porous particles by a transmission electron microscope (TEM) image. Further, "inorganic oxide hollow particles" refer to hollow particles in which the outer shell portion partitioning the hollow portion is composed of an inorganic oxide. The inorganic oxide is not particularly limited as long as it can constitute the outer shell portion. For example, inorganic oxides 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, Group 14 elements, and Group 15 elements of the periodic table can be mentioned. The inorganic oxide can contain one kind or two or more kinds. Examples of Group 1 elements of the periodic table include lithium, sodium, potassium, and cesium.

[0010] As the inorganic oxide, there is no particular limitation as long as it can constitute the outer shell portion. For example, it can include inorganic oxides 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, Group 14 elements, and Group 15 elements of the periodic table. The inorganic oxide can contain one kind or two or more kinds. Examples of Group 1 elements of the periodic table include lithium, sodium, potassium, and cesium. Examples of Group 2 elements of the periodic table include beryllium, magnesium, calcium, strontium, and barium. Examples of Group 4 elements of the periodic table include titanium, zirconium, and hafnium. Examples of Group 8 elements of the periodic table include iron, ruthenium, and osmium. Examples of Group 9 elements of the periodic table include cobalt, rhodium, and iridium.

[0011] Examples of Group 1 elements of the periodic table include lithium, sodium, potassium, and cesium. ​It is possible to do so. Examples of Group 2 elements in the periodic table include magnesium, calcium, and sulfamethasone. Examples include thorontium and barium. Examples of Group 4 elements in the periodic table include titanium and d(x) Ruthenium is one example. Examples of Group 8 elements in the periodic table include iron and ruthenium. It is possible. Examples of Group 9 elements in the periodic table include cobalt, rhodium, and iridium. Examples include nickel, palladium, and platinum, which are elements of Group 10 of the periodic table. It is possible. Examples of Group 11 elements in the periodic table include copper, silver, and gold. Examples of Group 12 elements in the periodic table include zinc and cadmium. (Group 13 elements in the periodic table) Examples include boron, aluminum, gallium, indium, and thallium. Examples of Group 14 elements in the periodic table include silicon, germanium, tin, and lead. Examples of Group 15 elements in the periodic table include phosphorus, arsenic, antimony, and bismuth. It is possible.

[0012] In particular, the periodic table group 1 elements, periodic table group 2 elements, and periodic table elements are particularly well-suited to enjoying the effects of the present invention. Periodic Table Group 4 Elements, Periodic Table Group 8 Elements, Periodic Table Group 11 Elements, Periodic Table Group 12 Elements, Periodic Table Elements One or more inorganic oxides containing elements selected from Group 13 and Group 14 of the periodic table. Preferably, elements from Group 1, Group 2, Group 8, and Group 12 of the periodic table. One or more elements including elements selected from the elements of Group 13 and Group 14 of the periodic table. Inorganic oxides of sodium, potassium, magnesium, calcium, iron, One or more inorganic oxides containing elements selected from zinc, boron, aluminum, and silicon. The material is more preferably an alkali metal oxide, a group 2 element oxide, or aluminum oxide. It is more preferable to include one or more selected from um, boron oxide, and silicon dioxide. stomach.

[0013] Examples of inorganic compounds include sodium oxide, potassium oxide, and magnesium oxide. Um, barium oxide, calcium oxide, zinc oxide, copper oxide, aluminum oxide, iron oxide, Examples include silicon dioxide, aluminosilicate, aluminoborosilicate, and bariumborosilicate. This is possible. Furthermore, composite oxides combining inorganic oxides are also acceptable.

[0014] Inorganic oxide hollow particles can be commercially available or synthesized. It is also possible to use known methods for producing inorganic oxide hollow particles, and there are no particular limitations. It is not fixed. For example, the sol-gel method and the spray pyrolysis method can be cited. Sol-gel method The production of inorganic oxide hollow particles by the method described in, for example, Japanese Patent Publication No. 2015-044987, It is possible to refer to publication no. 2013-193950, and also the spray pyrolysis method. For example, the production of hollow oxide particles is described in Japanese Patent Publication No. 2003-019427 and Japanese Patent Publication No. 2013. You can refer to publication no. 220967.

[0015] (First step) In this process, the inorganic oxide hollow particles are heated to -500°C ± 1°C relative to the melting point of the hollow particles. Heat to a temperature within the range of 50°C. This ensures that sufficient heat is supplied to the particle surface, resulting in a denser texture. This can increase the melting point. The melting point was determined using a thermogravimetric differential thermal analyzer (TG-DTA). It can be measured by differential thermal analysis. For example, when using hollow inorganic oxide particles with a melting point of 1100°C in this process, The heating temperature is set within the temperature range of 450 to 750°C [(1100°C - 500°C) ± 150°C]. The inorganic oxide hollow particles are then heated. If the set temperature is higher than the upper limit mentioned above, the particle surface... Excess heat accumulates on the surface, causing it to contract and reducing the hollow ratio. On the other hand, the set temperature is below the lower limit mentioned above. If the temperature is lower than this, sufficient heat is not supplied to the particle surface, making densification difficult, and thus the water resistance improvement effect is not observed. It is not possible. From this perspective, the heating temperature should be -500°C relative to the melting point of the inorganic oxide hollow particles. It is preferable to keep the temperature within a range of ±100℃.

[0016] A method for heating inorganic oxide hollow particles involves heating the inorganic oxide hollow particles to a predetermined temperature. It is not particularly limited, if possible. For example, inorganic oxide hollow particles are placed in a crucible and then... It should be heated in a heating device that maintains a constant temperature. The heating device is not particularly limited as long as it can withstand the heating temperature, but for example, electric Examples include steam furnaces, gas furnaces, and oil furnaces. Heating can be carried out at normal pressure; pressurization or vacuum is not required. The heating atmosphere can be either an air atmosphere or an inert gas atmosphere, and a mixture of these can be used. It is acceptable to operate under a mixed gas atmosphere. Examples of inert gases include nitrogen, helium, and algonium. One example is n.

[0017] If the heating time is too short, sufficient heat will not be supplied to the particle surface, making densification difficult, thus improving water resistance. The effect is likely to be insufficient. Therefore, the heating time is preferably 15 minutes or more, and 20 minutes or less. The above is more preferable, and 25 minutes or more is even more preferable. Also, if the heating time is too long, the particle surface Excess heat accumulates and causes contraction, leading to a tendency for the hollow ratio to decrease. Therefore, the heating time is Preferably 60 minutes or less, more preferably 50 minutes or less, and even more preferably 40 minutes or less.

[0018] (Second step) In this process, the inorganic oxide hollow particles after heating are heated to the heating temperature set in the first step. To a temperature of 1 / 2 ± 150℃, with an average cooling rate of 1℃ / min to 28℃ / min. Slow cooling is performed. This allows the densified state of the particle surface to be stably maintained. As a result, when inorganic oxide hollow particles come into contact with water, the elution of ionic components from the particle surface is suppressed. This process can be controlled, and water resistance can be imparted to the hollow inorganic oxide particles. For example, if the inorganic oxide hollow particles are heated to 500°C in the first step, in this step It is slowly cooled to a temperature of 100-400°C [(500°C / 2) ± 150°C]. If the target temperature is set lower than 1 / 2 ± 150°C, the accumulated temperature (°C·min) will When there is an excess of heat, excess heat accumulates on the particle surface, causing it to shrink and reducing the hollowness ratio. On the other hand, after slow cooling... If the target temperature is set higher than 1 / 2 ± 150°C of the heating temperature, the accumulated temperature ( Because the temperature (℃·min) is insufficient and sufficient heat is not supplied, densification is difficult, and therefore the water resistance improvement effect cannot be obtained. It is not possible. From this perspective, the temperature of the second step should be within the range of 1 / 2 ± 100°C of the heating temperature. It is preferable to set it.

[0019] In this process, the inorganic oxide hollow particles are slowly cooled at a predetermined average cooling rate, but in this specification "Average cooling rate" refers to the rate at which the temperature is reduced from the set temperature of the first process to the set temperature of the second process. This refers to the average speed over time, and the set temperature of the first process, the set temperature of the second process, and the time required for cooling. Based on the time elapsed, it can be calculated using the following formula.

[0020] Average slow cooling rate (℃ / min)=(AB) / C [In the formula, A represents the set temperature (°C) of the first process, and B represents the set temperature (°C) of the second process.] This indicates that C reaches the set temperature (°C) of the second process from the set temperature (°C) of the first process. This indicates the time (in minutes) required to do it.

[0021] For example, in the first step, the inorganic oxide hollow particles are heated to 500°C, and in this step for 30 minutes. When slowly cooling inorganic oxide hollow particles to 350°C, the average slow cooling rate is 5°C / min. The process is [(500℃-350℃) / 30 minutes].

[0022] If the average rate of cooling is too fast, the accumulated temperature (°C·min) will be insufficient, and not enough heat will be supplied. Because it is difficult to densify, the water resistance improvement effect is insufficient. Therefore, the average cooling rate is 1°C / A temperature of 1°C / min to 20°C / min is preferable, and a temperature of 1°C / min to 20°C / min is more preferable. Preferably, the temperature is 1°C / min or more and more preferably 15°C / min or less.

[0023] The method for slowly cooling the inorganic oxide hollow particles is not particularly limited, but for example, in the first and second steps Using a heating device that allows control of temperature and time, a predetermined time has elapsed since the end of the first process. When this happens, the heating device will reach the set temperature of the second process from the set temperature of the first process. You just need to set the temperature and cooling time. Then, when the set temperature for the second process is reached, the inorganic oxide hollow particles are removed from the heating device. Simply remove it and let it cool to room temperature. For example, the removed inorganic oxide hollow particles can be used as a deterrent. The inorganic oxide hollow particles can be stored in the cicator until their temperature reaches room temperature.

[0024] The water-resistant inorganic oxide hollow particles obtained by the manufacturing method of the present invention are the water-resistant inorganic oxides described below. It can possess the properties described for hollow particles.

[0025] [Water-resistant inorganic oxide hollow particles] The water-resistant inorganic oxide hollow particles of the present invention do not release ionic components from the particle surface even when immersed in water. It possesses the characteristic of being difficult to dissolve. Pure water conducts very little electricity, so its electrical conductivity is extremely low. Furthermore, when inorganic oxide hollow particles are immersed in water, ionic components leach from the surface of the particles and are contained in the water. The amount of ions released increases, and the electrical conductivity rises. Thus, the amount of ions released increases the electrical conductivity. Because it is correlated with the rate, the increase in electrical conductivity when inorganic oxide hollow particles are immersed in water is suppressed. If so, it can be determined that it has excellent water resistance. Specifically, when measuring electrical conductivity using the method described below, the value should be kept below 8.5 mS / m. This is possible. From the viewpoint of improving water resistance, such electrical conductivity is preferably 8.0 mS / m or less. Furthermore, a value of 7.5 mS / m or less is more preferable, and 7.0 mS / m or less is even more preferable. Electrical conductivity can be measured using an electrical conductivity meter.

[0026] (Measurement of electrical conductivity) In a glass beaker, mix inorganic oxide hollow particles and distilled water in a liquid-to-solid ratio of 33:1 (wt%). Then, boil the mixture for 5 minutes. After the mixture has cooled to 25°C, measure its electrical conductivity. To determine.

[0027] Furthermore, the water-resistant inorganic oxide hollow particles of the present invention have a sufficient hollowness ratio. The hollowness ratio of aqueous inorganic oxide hollow particles is usually 70% or more, preferably 75% or more. The hollow ratio can be calculated from the apparent density and true density using the following formula.

[0028] Hollowness = (True density - Apparent density) × 100 / True density

[0029] The water-resistant inorganic oxide hollow particles of the present invention have an average particle diameter of typically 0.5 to 50 μm. Preferably, the particle size is 0.5 to 20 μm, and more preferably 1 to 10 μm. Here, In this document, "average particle size" refers to the particle size distribution of a sample in accordance with JIS R 1629. When created using the product basis, the particle size (d) corresponding to 50% of the integrated distribution curve 50 ) means. Oh, as a particle size distribution analyzer, for example, we use Microtrac (manufactured by Nikkiso Co., Ltd.) It is possible.

[0030] The surface-coated inorganic oxide hollow particles of the present invention have an outer shell thickness of typically 50 nm to 1 μm. The thickness of the outer shell is preferably 50 to 500 nm. Because sufficient thermal insulation is ensured, it is possible to exhibit excellent thermal insulation, heat shielding, and dielectric properties. The thickness of the outer shell can be measured from a transmission electron microscope (TEM) image.

[0031] The water-resistant inorganic oxide hollow particles of the present invention can be used, for example, as thermal insulation materials, heat shielding materials, catalyst carriers, and in construction. It can be applied to materials and electronic materials, and has high water resistance and excellent dielectric properties. It is particularly preferable to apply it to electronic materials.

[0032] The water-resistant inorganic oxide hollow particles of the present invention can be manufactured by any appropriate method if they possess the above-described properties. It can be manufactured, for example, the water-resistant inorganic oxide hollow particles of the present invention as described above. It can be manufactured by the method used for manufacturing this product.

[0033] [Method for improving the water resistance of hollow inorganic oxide particles] The present invention provides a method for improving the water resistance of inorganic oxide hollow particles, and the present invention provides a method for improving the water resistance of inorganic oxide hollow particles. The present invention is characterized by comprising a first step and a second step, similar to the manufacturing method. The method for improving water resistance may include a preparation step, similar to the manufacturing method described above. The specific configuration of the preparation process, the first process, and the second process is as described above. be. [Examples]

[0034] The embodiments of the present invention will be described in more detail below with reference to examples. However, the present invention This is not limited to the following embodiments.

[0035] 1. Measurement of Hollow Ratio An Accupic (manufactured by Shimadzu Corporation) was used as a dry automatic densimeter to measure inorganic oxide hollow particles. The apparent density and true density were measured and calculated using the following formula. Note that the true density excludes the cavity portion. To remove it, it was heated in a box-type electric furnace above its melting point for 6 hours, then cooled and measured with a dry automatic density meter. It was decided.

[0036] Hollowness ratio (%) = (True density - Apparent density) × 100 / True density

[0037] 2. Measurement of the melting point Differential thermal analysis of inorganic oxide hollow particles was performed using a thermogravimetric differential thermal analyzer (TG-DTA). The melting point was determined from the endothermic peak in the obtained DTA curve.

[0038] 3. Measurement of electrical conductivity Inorganic oxide hollow particles and distilled water were mixed in a glass beaker in a liquid-to-solid ratio of 33:1 (wt%). The mixture was heated on a heater and boiled for 5 minutes. Then, the mixture was cooled to 25°C. The electrical conductivity of the mixed liquid was measured using an electrical conductivity meter (manufactured by HORIBA).

[0039] Manufacturing Example 1 The aqueous solution containing the raw inorganic compound was added to the reaction vessel, and the aqueous solution containing the raw inorganic compound was left for 3 hours. The mixture was stirred. At this time, the temperature of the aqueous solution was adjusted to 5°C using a chiller. The aqueous solution containing the compound contains 0.045 mol / L of calcium nitrate (manufactured by Osaki Industries) and aluminum nitrate. 0.091 mol / L of nium (manufactured by Hakuko Chemical Industry), tetraethyl orthosilicate (Tama Chemical) (Manufactured by Gaku Kogyo Co., Ltd.) 0.215 mol / L, boric acid (Yoneyama Chemical Industry Co., Ltd.) 0.270 mol / L It was prepared by dissolving it in tap water. Subsequently, this aqueous solution containing the raw inorganic compound was mixed with three fluids. The liquid is supplied to the nozzle, and the aqueous solution containing the raw material inorganic compound is sprayed from the nozzle into the spray pyrolysis furnace, 11 The inorganic oxide hollow particles were recovered by firing at 50°C. The obtained inorganic oxide hollow particles had a melting point The temperature was 1100℃.

[0040] Comparative Example 1 The hollow fraction and electrical conductivity of the inorganic oxide hollow particles obtained in Production Example 1 were measured. The results are shown in Table 1.

[0041] Example 1 3 g of the inorganic oxide hollow particles obtained in Production Example 1 were placed in a 30 mL alumina crucible, It was heated for 30 minutes in a tabletop high-speed heating electric furnace maintained at 500°C. Then, this electric furnace The inorganic oxide hollow particles, after heating, are slowly cooled to 350°C at an average cooling rate of 1°C / min. Next, when it reached 350°C, it was removed from the electric furnace and left in a desiccator until it reached room temperature. It was cooled. The average cooling rate was such that the temperature of the heating device went from 500°C to 350°C in 150 minutes. The temperature and cooling time of the electric furnace were set and controlled to reach the target. Then, the inorganic oxidation after cooling was performed. The hollowness ratio and electrical conductivity of hollow particles were measured. The results are shown in Table 1.

[0042] Examples 2-17 and Comparative Examples 2-11 The inorganic oxide hollow particles were heated at the temperatures and times shown in Table 1, and the heated inorganic oxide hollow particles were then... The process was the same as in Example 1, except that the temperature was slowly cooled to the temperature shown in Table 1 using the average cooling rate shown in Table 1. This was carried out by the following procedure. Then, the hollowness and electrical conductivity of the inorganic oxide hollow particles after cooling were examined. Conductivity was measured. The results are shown in Table 1.

[0043] [Table 1]

[0044] From Table 1, the following can be seen: In the first step, the inorganic oxide hollow particles are heated to a temperature relative to the melting point of the hollow particles (1100°C). When heated at a temperature lower than -500℃±150℃, such that sufficient heat is not generated on the particle surface. Because it was not supplied and difficult to densify, no improvement in water resistance was observed (Comparative Examples 2-5). On the other hand, when heated at a temperature of 800°C, which is higher than -500°C ± 150°C relative to the melting point, the grains Excessive heat accumulated on the surface, resulting in a decrease in the hollow ratio (Comparative Example 6). Furthermore, in the second step, when slowly cooling the inorganic oxide hollow particles after heating, the target after slow cooling is If the target temperature is set to a temperature higher than 1 / 2 ± 150°C of the heating temperature, the accumulated temperature (°C·min) Because there is insufficient heat supply to the particle surface, densification is difficult, and therefore no water-resistance improvement effect is observed. It was not possible (Comparative Example 7). On the other hand, if the target temperature after slow cooling is lower than 1 / 2 ± 150°C, the accumulated temperature ( The temperature (℃·min) becomes excessive, causing excessive heat to accumulate on the particle surface and reducing the hollowness ratio (comparison). Example 8). Furthermore, in the second step, the heated inorganic oxide hollow particles are cooled at an average temperature of 30°C / min. Rapid cooling results in insufficient accumulated temperature (°C·min), preventing sufficient heat from being supplied to the particle surface. Because it was difficult to densify, no improvement in water resistance was observed (Comparative Examples 9-11). In contrast, the inorganic oxide hollow particles are subjected to a temperature of -50 degrees relative to the melting point of the hollow particles (1100°C). The inorganic oxide hollow particles are heated to a temperature within the range of 0℃ ± 150℃, and then the heated inorganic oxide hollow particles are heated to the temperature An average cooling rate of 1°C / min to 28°C / min down to a temperature of 1 / 2 ± 150°C. By slowly cooling the particles, the surface becomes densified and stable, and ionic components are eluted from the particle surface. This was suppressed, and water resistance was improved (Examples 1-17).

Claims

1. A water-resistant inorganic oxide hollow particle in which the outer shell that partitions the hollow portion is composed of an inorganic oxide containing Group 2 element oxides, aluminum oxide, boron oxide, and silicon oxide, but not Group 1 element oxides, The electrical conductivity measured by the following method is 8.5 mS / m or less. Water-resistant inorganic oxide hollow particles. (Measurement of electrical conductivity) In a glass beaker, inorganic oxide hollow particles and distilled water are mixed in a liquid-to-solid ratio of 33:1 (wt%), and the mixture is boiled for 5 minutes. After the mixture cools to 25°C, the electrical conductivity of the mixture is measured.

2. The water-resistant inorganic oxide hollow particle according to claim 1, wherein the hollowness ratio is 70% or more.

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