Inorganic oxide hollow particles

Abstract

To provide inorganic oxide hollow particles having excellent water resistance as well as dielectric properties.SOLUTION: Non-porous inorganic oxide hollow particles each having a cavity inside an outer shell, comprise an inorganic oxide containing 0.5 to 13 mass% of zirconia, 2 mass% or more of a Group 2 element oxide, 10 mass% or more of a Group 13 element oxide, and 70 mass% or less of silicon oxide.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to inorganic oxide hollow particles.

Background Art

[0002] In recent years, with the spread of high-speed communication standards such as 5G and 6G, materials used in high-frequency band devices are required to have excellent dielectric properties such as low relative permittivity and dielectric loss tangent. Since inorganic oxide hollow particles have excellent dielectric properties, the demand for them as filler materials in the field of electronic materials is increasing.

[0003] As such a filler material, for example, inorganic oxide hollow particles are known that include a plurality of independent spaces in which cavities covered with an outer shell are partitioned by one or more partition walls, and contain 10% by mass or more and 40% by mass or less of boron oxide, 5% by mass or less of sodium oxide, 1% by mass or more and 50% by mass or less of calcium oxide, and 14% by mass or more and less than 20% by mass of aluminum oxide (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Since the above-described inorganic oxide hollow particles have excellent dielectric properties, they are useful as filler materials required in the field of electronic materials. However, the inventors have found that when a resin molded product containing the inorganic oxide hollow particles is produced and a water immersion test is performed, the dielectric properties may be insufficient. Therefore, an object of the present invention is to provide inorganic oxide hollow particles that are excellent not only in dielectric properties but also in water resistance.

Means for Solving the Problems

[0006] Since the inorganic oxide hollow particles described above are non-porous without openings in the outer shell, it is generally difficult to imagine that water would penetrate into the cavity during the immersion test. However, since the electrical conductivity increased, it was inferred that water had penetrated into the cavity. Regarding the cause, the inventors analyzed it in detail and found that, in some cases, ions on the particle surface elute to form pores, allowing water to penetrate into the cavity. Therefore, the inventors conducted a detailed study on the chemical composition of the inorganic oxide hollow particles. As a result, they found that by containing a certain amount of an oxide of a specific element as the inorganic oxide constituting the inorganic oxide hollow particles, inorganic oxide hollow particles with excellent water resistance can be obtained while maintaining excellent dielectric properties.

[0007] That is, the present invention provides the following [1] to [3]. [1] Non-porous inorganic oxide hollow particles having a cavity inside the outer shell, The inorganic oxide hollow particles are composed of an inorganic oxide containing 0.5 to 13% by mass of zirconia, 2% by mass or more of a Group 2 element oxide, 10% by mass or more of a Group 13 element oxide, and 70% by mass or less of silicon oxide. [2] The inorganic oxide hollow particles according to [1] above, having an electrical conductivity of 5 mS / m or less as measured by the following Test Method 1. [Test Method 1] Put distilled water and inorganic oxide hollow particles into a beaker at a mass ratio (liquid: solid) of 33:1, mix for 1 minute, and then measure the electrical conductivity of the liquid in the beaker with a conductivity meter. [3] The inorganic oxide hollow particles according to [2] above, having a difference (Δσ) in electrical conductivity calculated by the following formula (1) of 3 mS / m or less based on the electrical conductivity measured by the following Test Method 2 and the electrical conductivity measured by Test Method 1. [Test Method 2] In Test Method 1, a beaker containing distilled water and inorganic oxide hollow particles, in which the electrical conductivity was measured, is heated until it boils and then boiled for 5 minutes. Next, it is left to cool until the temperature of the liquid in the beaker reaches 25°C. After cooling, the electrical conductivity of the liquid in the beaker is measured with a conductivity meter. Difference in electrical conductivity (Δσ) = X - Y (1) [In formula (1), X represents the electrical conductivity measured by Test Method 2, and Y represents the electrical conductivity measured by Test Method 1.] [Advantages of the Invention]

[0008] According to the present invention, it is possible to provide inorganic oxide hollow particles that are excellent not only in dielectric properties but also in water resistance. [Modes for Carrying Out the Invention]

[0009] As used herein, the term "hollow particle" refers to a particle having a cavity inside, and the cavity is covered by an outer shell. The inorganic oxide hollow particles of the present invention have a plurality of independent spaces in which the cavities covered by the outer shell are partitioned by one or more partition walls, and these independent spaces may be formed by air bubbles (hereinafter also referred to as "independent air bubbles") that are not in communication with each other and are separated by the partition walls. By having such independent air bubbles, the particle strength can be further increased. Here, as used herein, the term "outer shell" refers to the wall located on the outermost surface side of the particle, which is in contact with only one independent air bubble inside the particle, and the term "partition wall" refers to the wall that partitions adjacent independent air bubbles inside the particle. The outer shell is composed of an inorganic oxide, and when it has a plurality of independent air bubbles, the exterior and the partition walls are composed of an inorganic oxide. In addition, since the inorganic oxide hollow particles of the present invention are non-porous without openings in the outer shell, the closed cells are completely closed. Having such closed cells and being non-porous not only provides excellent dielectric properties but also enables the manifestation of excellent heat insulation and heat shielding properties. The fact that the outer shell is non-porous can be confirmed by a scanning electron microscope (SEM) image or by floating in water. Therefore, the inorganic oxide hollow particles of the present invention are different from porous particles having a plurality of pores extending from the particle surface to the inside.

[0010] The inorganic oxide hollow particles of the present invention have an outer shell composed of an inorganic oxide containing zirconia (ZrO2), a Group 2 element oxide, a Group 13 element oxide, and silicon oxide. Here, in this specification, the "Group 2 element oxide" refers to an oxide of an element belonging to Group 2 in the periodic table, and the same meaning shall be construed for oxides of elements belonging to other groups. Although the inorganic oxide hollow particles of the present invention essentially contain zirconia, the inventors have confirmed that even if an oxide of titanium (TiO2), which is a Group 4 element like zirconium, is contained, the water resistance becomes insufficient.

[0011] Examples of the Group 2 element oxide include calcium oxide, magnesium oxide, strontium oxide, and barium oxide. Among them, from the viewpoint of improving dielectric properties, calcium oxide and magnesium oxide are preferred. Examples of the Group 13 element oxide include boron oxide, aluminum oxide, gallium oxide, indium oxide, and thallium oxide. Among them, from the viewpoint of improving dielectric properties, boron oxide and aluminum oxide are preferred.

[0012] The inorganic oxide hollow particles of the present invention may contain inorganic oxides other than the above four types. Examples of such inorganic oxides include Group 1 element oxides, Group 8 element oxides, Group 9 element oxides, Group 10 element oxides, Group 11 element oxides, and Group 12 element oxides, but composite oxides such as aluminosilicate, aluminoborosilicate, and barium borosilicate may also be used.

[0013] Examples of Group 1 element oxides include lithium oxide, sodium oxide, potassium oxide, rubidium oxide, and cesium oxide. Examples of Group 8 element oxides include iron oxide and ruthenium oxide. Examples of Group 9 element oxides include cobalt oxide, rhodium oxide, and iridium oxide. Examples of Group 10 element oxides include nickel oxide, palladium oxide, and platinum oxide. Examples of Group 11 element oxides include copper oxide, silver oxide, and gold oxide. Examples of Group 12 element oxides include zinc oxide and cadmium oxide.

[0014] Among them, as inorganic oxides other than the above four types, in terms of being likely to enjoy the effects of the present invention, one or more inorganic oxides selected from Group 1 element oxides, Group 8 element oxides, Group 11 element oxides, and Group 12 element oxides are preferred, one or more inorganic oxides selected from Group 1 element oxides and Group 12 element oxides are more preferred, and Group 1 element oxides are even more preferred.

[0015] Preferable embodiments of the inorganic oxide hollow particles of the present invention can include the following chemical compositions. (i) Inorganic oxide hollow particles composed of an inorganic oxide containing zirconia, a Group 2 element oxide, a Group 13 element oxide, and silicon oxide. (ii) Inorganic oxide hollow particles composed of an inorganic oxide containing zirconia, one or more inorganic oxides selected from Group 1 element oxides, Group 8 element oxides, Group 11 element oxides, and Group 12 element oxides, a Group 2 element oxide, a Group 13 element oxide, and silicon oxide. (iii) Inorganic oxide hollow particles composed of an inorganic oxide containing zirconia, one or more inorganic oxides selected from Group 1 element oxides and Group 12 element oxides, a Group 2 element oxide, a Group 13 element oxide, and silicon oxide. (iv) Inorganic oxide hollow particles composed of an inorganic oxide containing zirconia, a Group 1 element oxide, a Group 2 element oxide, a Group 13 element oxide, and silicon oxide. (v) Inorganic oxide hollow particles composed of an inorganic oxide containing zirconia, calcium oxide, magnesium oxide, boron oxide, aluminum oxide, and silicon oxide. (vi) Inorganic oxide hollow particles composed of an inorganic oxide containing zirconia, one or more Group 1 element oxides selected from lithium oxide, sodium oxide, and potassium oxide, calcium oxide, magnesium oxide, boron oxide, aluminum oxide, and silicon oxide.

[0016] Preferred embodiments of the content of each inorganic oxide are as follows. (1) Zirconia In the above-described embodiments (i) to (vi), the content of zirconia in the inorganic oxide hollow particles is 0.5 to 13% by mass. From the viewpoint of further improving water resistance, 0.6% by mass or more is preferable, 0.8% by mass or more is more preferable, 1% by mass or more is still more preferable. From the viewpoints of further improving water resistance and dielectric properties and suppressing a decrease in particle density and hollow ratio, 12% by mass or less is preferable, 11% by mass or less is more preferable, and 10% by mass or less is still more preferable.

[0017] (2) Group 2 element oxide In the above-described embodiments (i) to (iv), the content of the Group 2 element oxide in the inorganic oxide hollow particles is 2% by mass or more. From the viewpoint of further improving water resistance and dielectric properties, 4% by mass or more is preferable, 6% by mass or more is more preferable, 8% by mass or more is still more preferable, and 50% by mass or less is preferable, 40% by mass or less is more preferable, 30% by mass or less is still more preferable, and 20% by mass or less is even more preferable. In the above-described aspects (v) to (vi), from the viewpoint of further improving water resistance and dielectric properties, the calcium oxide content in the inorganic oxide hollow particles is preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass or less, and even more preferably 15% by mass or less. In the above-described aspects (v) to (vi), from the viewpoint of further improving water resistance and dielectric properties, the magnesium oxide content in the inorganic oxide hollow particles is preferably 1% by mass or more, more preferably 1.5% by mass or more, still more preferably 2% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 8% by mass or less.

[0018] (3) Group 13 element oxide In the above-described aspects (i) to (iv), the content of the Group 13 element oxide in the inorganic oxide hollow particles is 10% by mass or more. However, from the viewpoint of further improving water resistance and dielectric properties, it is preferably 15% by mass or more, more preferably 20% by mass or more, still more preferably 25% by mass or more, and preferably 50% by mass or less, more preferably 45% by mass or less, still more preferably 40% by mass or less. In the above-described aspects (v) to (vi), from the viewpoint of further improving water resistance and dielectric properties, the boron oxide content in the inorganic oxide hollow particles is preferably 3% by mass or more, more preferably 7% by mass or more, still more preferably 10% by mass or more, and preferably 25% by mass or less, more preferably 20% by mass or less, still more preferably 18% by mass or less. In the above-described aspects (v) to (vi), from the viewpoint of further improving water resistance and dielectric properties, the aluminum oxide content in the inorganic oxide hollow particles is preferably 7% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 35% by mass or less, more preferably 30% by mass or less, still more preferably 25% by mass or less.

[0019] (4) Silicon oxide In the above-described aspects (i) to (vi), the content of silicon oxide in the inorganic oxide hollow particles is 70% by mass or less. From the viewpoint of further improving water resistance and dielectric properties, 65% by mass or less is preferable, 60% by mass or less is more preferable, 55% by mass or less is still more preferable, and 30% by mass or more is preferable, 35% by mass or more is more preferable, and 40% by mass or more is still more preferable.

[0020] (5) Inorganic oxides other than the above four types In the above-described aspects (i) to (iv), from the viewpoint of further improving water resistance and dielectric properties, the content of inorganic oxides other than the above four types in the inorganic oxide hollow particles is preferably 20% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less, and even more preferably 2% by mass or less. The lower limit of the content of inorganic oxides other than the above four types in the inorganic oxide hollow particles may be 0% by mass. In the above-described aspects (v) to (vi), from the viewpoint of further improving water resistance and dielectric properties, the content of the Group 1 element oxide in the inorganic oxide hollow particles is preferably 5% by mass or less, more preferably 3% by mass or less, and still more preferably 1% by mass or less. The lower limit of the content of the Group 1 element oxide in the inorganic oxide hollow particles may be 0% by mass.

[0021] In this specification, the content of each inorganic oxide described above is measured in terms of oxide by a fluorescence X-ray analyzer (ZSX primus II, manufactured by Rigaku Corporation) after forming inorganic oxide hollow particles into briquettes using a press machine, and the chemical components are calculated.

[0022] The hollow ratio of the inorganic oxide hollow particles is usually 55% or more. From the perspective of further improving the dielectric properties, 57% or more is preferable, 60% or more is more preferable, and 65% or more is even more preferable. The upper limit value of such a hollow ratio is preferably 95% or less, and more preferably 90% or less, from the perspective of ensuring sufficient strength. Here, in this specification, the "hollow ratio" is a value calculated by the following formula from the true density of the particles measured using a dry automatic densitometer. Since it is difficult to measure each individual particle, it is the cavity ratio of the particle group. Here, in this specification, the "true density" is measured with a dry automatic densitometer after heating in a box-type electric furnace at a temperature equal to or higher than the melting point for 6 hours and then cooling to remove the cavity part. As the dry automatic densitometer, for example, Accupic (Shimadzu Corporation) can be used.

[0023] Hollow ratio = (True density - Particle density) × 100 / True density

[0024] The average particle diameter of the inorganic oxide hollow particles of the present invention is preferably 5 μm or less, more preferably 4.5 μm or less, and even more preferably 4 μm or less, from the perspective of application as an electronic material. The lower limit value of such an average particle diameter is preferably 0.3 μm or more, more preferably 0.4 μm or more, and even more preferably 0.5 μm or more, from the perspective of ensuring sufficient cavities. Here, in this specification, the "average particle diameter" means the particle diameter (D 50 ) corresponding to 50% of the cumulative distribution curve when the particle size distribution of the sample is created on a volume basis in accordance with JIS R 1629. For the measurement of the particle size distribution, for example, a laser diffraction / scattering type particle size distribution measuring device can be used.

[0025] The particle density of the inorganic oxide hollow particles of the present invention is preferably 0.97 g / cm 3 or less, more preferably 0.95 g / cm 3 or less, and even more preferably 0.93 g / cm 3 or less, from the perspective of improving the dielectric properties. The lower limit value of the particle density is preferably usually 0.20 g / cm 3 or more, and more preferably 0.30 g / cm 3The above is more preferable, 0.40 g / cm 3 The above is even more preferable. In this specification, "particle density" refers to a value measured by the gas displacement method in accordance with JIS R 1620. As a particle density measuring device, for example, a dry automatic densitometer "Accupic (manufactured by Shimadzu Corporation)" can be used.

[0026] The inorganic oxide hollow particles of the present invention preferably have a dissipation factor of 0.0045 or less, more preferably 0.0040 or less, and even more preferably 0.0035 or less from the viewpoint of improving dielectric properties. The lower limit value of the dissipation factor is not particularly limited and may be 0. Further, the inorganic oxide hollow particles of the present invention preferably have a relative permittivity of 2.4 or less, more preferably 2.3 or less, and even more preferably 2.2 or less from the viewpoint of improving dielectric properties. The lower limit value of the relative permittivity is not particularly limited and may be 0. Here, in this specification, "dissipation factor" and "relative permittivity" refer to the dissipation factor and relative permittivity at 1 GHz, and are measured at 1 GHz in an environment of a temperature of 25 °C and a humidity of 60%. The dissipation factor and relative permittivity can be measured using, for example, a perturbation type cavity resonator (manufactured by KEYCOM).

[0027] The inorganic oxide hollow particles of the present invention usually have an electrical conductivity of 5 mS / m or less as measured by the following Test Method 1. However, from the viewpoint of improving water resistance, it is preferably 4.5 mS / m or less, more preferably 4 mS / m or less, and even more preferably 3.5 mS / m or less. The lower limit value of such electrical conductivity is not particularly limited and may be 0 mS / m.

[0028] 〔Test Method 1〕 Put distilled water and inorganic oxide hollow particles into a beaker at a mass ratio (liquid: solid) of 33:1, mix for 1 minute, and then measure the electrical conductivity of the liquid in the beaker with an electrical conductivity meter.

[0029] In addition, the inorganic oxide hollow particles of the present invention have a difference in electrical conductivity (Δσ) calculated by the following formula (1) based on the electrical conductivity (X) measured by the following test method 2 and the electrical conductivity (Y) measured by the above-described test method 1. Usually, it is 3 mS / m or less. From the viewpoint of improving water resistance, it is preferably 2.5 mS / m or less, more preferably 2 mS / m or less, and still more preferably 1.5 mS / m or less.

[0030] 〔Test method 2〕 After measuring the electrical conductivity by test method 1, a beaker containing distilled water and inorganic oxide hollow particles is heated and boiled for 5 minutes after boiling. Then, it is left to cool until the temperature of the liquid in the beaker reaches 25°C. After cooling, the electrical conductivity of the liquid in the beaker is measured with a conductivity meter.

[0031] Difference in electrical conductivity (Δσ) = X - Y (1) 〔In formula (1), X represents the electrical conductivity measured by test method 2, and Y represents the electrical conductivity measured by test method 1.〕

[0032] When the electrical conductivity of the inorganic oxide hollow particles after boiling increases significantly, it is presumed that ionic components elute from the particle surface, pores are formed on the particle surface, and water penetrates into the cavity inside. That is, when the difference in electrical conductivity (Δσ) of the inorganic oxide hollow particles before and after boiling exceeds 3, there is concern about the penetration of water into the cavity inside. On the other hand, the smaller the difference in electrical conductivity (Δσ) of the inorganic oxide hollow particles before and after boiling, the more surely the penetration of water into the cavity inside is suppressed, and it can be judged that the water resistance is more excellent. The electrical conductivity can be measured using, for example, a conductivity meter (manufactured by HORIBA).

[0033] The shape of the inorganic oxide hollow particles of the present invention may be any of substantially spherical shapes such as a true sphere, a flat ellipsoid, or an oblong ellipsoid. From the viewpoint of improving the dielectric properties, the average circularity is preferably 0.85 or more, and more preferably 0.90 or more. Here, the "circularity" is measured from a scanning electron microscope photograph to obtain the projected area (A) and the perimeter (PM) of the particle. Assuming that the area of a perfect circle with respect to the perimeter (PM) is (B), the circularity of the particle is expressed as A / B. Therefore, the perimeter and area of a perfect circle having the same perimeter as the perimeter (PM) of the sample particle are PM = 2πr and B = πr 2 respectively. Therefore, B = π × (PM / 2π) 2 and the circularity of this particle is circularity = A / B = A × 4π / (PM) 2 which is calculated as such. The circularity is measured for 100 particles, and the average value is taken as the average circularity.

[0034] 〔Method for producing inorganic oxide hollow particles〕 The method for producing the inorganic oxide hollow particles of the present invention can be produced by a known method. For example, the spray pyrolysis method can be mentioned. For the spray pyrolysis method, reference can be made to, for example, JP-A-2003-019427 and JP-A-2013-220967. It will be briefly described below.

[0035] The method for producing inorganic oxide hollow particles by the spray pyrolysis method includes, for example, a step of spraying a solution of a raw material compound containing the elements constituting the above-described inorganic oxide from a spraying device installed in a spray pyrolysis apparatus and thermally decomposing the sprayed droplets (mist).

[0036] The spray pyrolysis apparatus preferably has a heat decomposition furnace with a rigid cylindrical shape, and the size of the heat decomposition furnace can be appropriately selected according to the production scale. Examples of the spraying device include fluid nozzles such as a two-fluid nozzle, a three-fluid nozzle, and a four-fluid nozzle. The type of the fluid nozzle may be an internal mixing type or an external mixing type. Note that one or two or more spraying devices can be installed.

[0037] The total concentration of the raw material compounds in the raw material compound solution is usually 0.01 to 1.0 mol / L, preferably 0.1 to 0.9 mol / L. Note that each content of the raw material compounds in the raw material compound solution may be an amount that satisfies the stoichiometric composition based on the preset inorganic oxide hollow particles. The raw material compounds are not particularly limited as long as they contain the elements constituting the inorganic oxide and are soluble in water, and examples thereof include inorganic salts, organic salts, alkoxides, and the like. The flow rate of the raw material compound solution is usually 1 to 100 L / h, preferably 3 to 80 L / h, and more preferably 5 to 60 L / h. The ejection rate of the raw material compound solution is usually 1 to 50 m / s, preferably 5 to 35 m / s, and more preferably 10 to 20 m / s.

[0038] Examples of the heating device include a combustion burner, a hot air heater, an electric heater, etc. One or more heating devices can be installed. The temperature of the heating device is usually 800 to 1500 °C, preferably 1000 to 1400 °C, and more preferably 1200 to 1300 °C.

[0039] The non-porous inorganic oxide hollow particles generated by heating are moved to a recovery device by an induction fan from the downstream of the heating furnace and recovered. Examples of the recovery device include a cyclone powder recovery machine and a bag filter.

Examples

[0040] Hereinafter, the embodiments of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[0041] 1. Analysis of Chemical Composition The inorganic oxide hollow particles were molded with a press to produce briquettes, and the briquettes were measured by a fluorescent X-ray analyzer (ZSX primus II, manufactured by Rigaku Corporation) in terms of oxides to calculate the chemical components.

[0042] 2. Analysis of Particle Shape For 100 randomly selected inorganic oxide hollow particles, they were observed using a scanning electron microscope (JSM-7001F, manufactured by JEOL Ltd.). The number of independent air bubbles inside the particles was confirmed. When the particles with two or more independent air bubbles accounted for more than half, they were judged as "multi-bubble type". Also, from the scanning electron micrographs, the projected area (A) and the perimeter (PM) of the particles were measured, and the circularity was calculated by the following formula. Particles with two or more independent air bubbles inside the particles being less than half and circularity ≧ 0.85 were judged as "true spherical".

[0043] Circularity = A×4π / (PM) 2

[0044] 3. Measurement of particle density It was measured by the gas displacement method using a dry automatic densitometer (Accupic 1340, manufactured by Shimadzu Corporation). That is, after putting the sample into the cell, an inert gas was filled into it to measure the volume of the sample, and the particle density was obtained from this volume and the sample mass measured in advance.

[0045] 4. Measurement of hollowness ratio Accupic (manufactured by Shimadzu Corporation) was used as the dry automatic densitometer to measure the particle density and the true density, and it was calculated by the following formula. The true density was measured with a dry automatic densitometer after heating in a box-type electric furnace at a temperature above the melting point for 6 hours and then cooling to remove the hollow part.

[0046] Hollowness ratio = (True density - Particle density)×100 / True density

[0047] 5. Measurement of average particle diameter Using a laser diffraction particle size distribution measuring device (MT3000II, manufactured by Microtrac BEL Corporation), a volume-based particle size distribution was created in accordance with JIS R 1629, and the particle diameter (D 50 ) corresponding to 50% of the cumulative distribution curve was obtained.

[0048] 6. Measurement of dielectric loss tangent and relative permittivity It was measured at 1 GHz in an environment of temperature 25°C and humidity 60% using a perturbation type cavity resonator (manufactured by KEYCOM).

[0049] 7. Measurement of Electrical Conductivity (1) Test Method 1 - Electrical Conductivity Before Boiling - Distilled water and inorganic oxide hollow particles were placed in a beaker at a mass ratio (liquid:solid) of 33:1 and mixed for 1 minute. Then, the electrical conductivity of the liquid in the beaker was measured with an electrical conductivity meter (manufactured by HORIBA). (2) Test Method 2 - Electrical Conductivity After Boiling - After measuring the electrical conductivity by Test Method 1, the beaker containing distilled water and inorganic oxide hollow particles was heated and boiled for 5 minutes after boiling. Then, it was left to cool until the temperature of the liquid in the beaker reached 25°C. After cooling, the electrical conductivity of the liquid in the beaker was measured with an electrical conductivity meter (manufactured by HORIBA). And the difference in electrical conductivity (Δσ) was calculated by the following formula (1).

[0050] Difference in Electrical Conductivity (Δσ) = X - Y (1) 〔In formula (1), X represents the electrical conductivity measured by Test Method 2, and Y represents the electrical conductivity measured by Test Method 1.〕

[0051] Example 1 Raw material compounds (colloidal silica, tetraethyl orthosilicate, aluminum nitrate nonahydrate, zirconium nitrate, magnesium nitrate hexahydrate, boric acid) were dissolved in 250 kg of ion-exchanged water to reach the molar concentrations shown in Table 1, and the raw material mixed aqueous solution was charged into a solution tank. The charged aqueous solution was sent to a two-fluid nozzle by a liquid delivery pump. The spraying conditions of the two-fluid nozzle were a nozzle air volume of 450 L / min and a liquid delivery volume of 350 mL / min, and it was sprayed into a spray pyrolysis furnace and heated at 1250°C. It was rapidly cooled by a cooling mechanism installed at the outlet of the reaction zone, and then the particles were collected using a bag filter to obtain pore-free inorganic acid hollow particles. And the obtained inorganic acid hollow particles were analyzed. The results are shown in Table 2.

[0052]

Table 1

[0053] Examples 2 to 4 and Comparative Examples 2 and 3 Inorganic acid hollow particles were obtained in the same manner as in Example 1, except that the ratio of the raw material compounds in the aqueous solution was changed so as to obtain the chemical composition shown in Table 2, and heating was performed at the temperature shown in Table 2. The obtained inorganic acid hollow particles were then analyzed. The results are shown in Table 2.

[0054] Comparative Example 1 Inorganic acid hollow particles were obtained in the same manner as in Example 1, except that zirconium nitrate was not used as a raw material compound and heating was performed at the temperature shown in Table 2. The obtained inorganic acid hollow particles were then analyzed. The results are shown in Table 2.

[0055] Comparative Example 4 Inorganic acid hollow particles were obtained by the same procedure as in Example 1, except that titanium nitrate was used as the raw material compound instead of zirconium nitrate. The obtained inorganic acid hollow particles were then analyzed. The results are shown in Table 2.

[0056] [Table 2]

[0057] In Comparative Example 1, since zirconia was not contained in the inorganic oxide hollow particles, the electrical conductivity before and after boiling was high, and the difference between the two (Δσ) exceeded 3, resulting in insufficient water resistance. Comparative Examples 2 and 3 contain zirconia in the inorganic oxide hollow particles, but Comparative Example 2 has an excessively high zirconia content, and therefore has excellent water resistance, but the relative dielectric constant increases and the particle density and hollowness decrease. On the other hand, Comparative Example 3 has an excessively low zirconia content, and therefore has insufficient water resistance. Comparative Example 4 contains titanium oxide (TiO2), which is in the same group as zirconium, but fails to exhibit water resistance equivalent to that of zirconia. On the other hand, in Examples 1 to 4, inorganic oxide hollow particles excellent not only in particle characteristics and dielectric characteristics but also in water resistance were obtained. Therefore, it can be said that controlling the content of zirconia in the inorganic oxide hollow particles within a specific range greatly contributed to this result.

Claims

Claim 1 An airless inorganic oxide hollow particle having a cavity inside a shell, composed of an inorganic oxide containing 0.5 to 13% by mass of zirconia, 2% by mass or more of a Group 2 element oxide, 10% by mass or more of a Group 13 element oxide, and 70% by mass or less of silicon oxide. Inorganic oxide hollow particle. Claim 2 The inorganic oxide hollow particle according to Claim 1, wherein the electrical conductivity measured by the following Test Method 1 is 5 mS / m or less. [Test Method 1] Put distilled water and inorganic oxide hollow particles into a beaker at a mass ratio (liquid: solid) of 33:1, mix for 1 minute, and then measure the electrical conductivity of the liquid in the beaker with a conductivity meter. Claim 3 The inorganic oxide hollow particle according to Claim 2, wherein the difference (Δσ) in electrical conductivity calculated by the following formula (1) based on the electrical conductivity measured by the following Test Method 2 and the electrical conductivity measured by Test Method 1 is 3 mS / m or less. [Test Method 2] Heat the beaker containing distilled water and inorganic oxide hollow particles in which the electrical conductivity was measured in Test Method 1, boil for 5 minutes after boiling. Then, leave it to cool until the temperature of the liquid in the beaker reaches 25°C. After cooling, measure the electrical conductivity of the liquid in the beaker with a conductivity meter. Difference in electrical conductivity (Δσ) = X - Y (1) [In formula (1), X represents the electrical conductivity measured by Test Method 2, and Y represents the electrical conductivity measured by Test Method 1.]

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