Inorganic oxide hollow particles

Abstract

To provide hollow inorganic oxide particles that can suppress the deterioration of dielectric properties. [Solution] The outer shell that partitions the hollow chamber is composed of an inorganic oxide containing boron oxide, silicon oxide, and oxides of elements other than boron and silicon, and is an inorganic oxide hollow particle. The boron oxide content is 3% by mass or more. The silicon dioxide content is 30% by mass or more. After being left to cool for 100 hours in an environment of 50°C and 95% RH relative humidity, the weight loss rate when heated to 300°C at a heating rate of 10°C / min is 1% by mass or less. Inorganic oxide hollow particles.

Description

[Technical Field]

[0001] This invention relates to inorganic oxide hollow particles. [Background technology]

[0002] In recent years, data communication in information and communications has seen a rapid increase in both capacity and processing speed. High-frequency devices used in such communication equipment exhibit high dielectric loss if the relative permittivity is high, and high dielectric loss tangent not only increases dielectric loss but can also increase heat generation. Therefore, when applying inorganic oxide hollow particles to electronic materials such as high-frequency devices, low relative permittivity and dielectric loss tangent, along with excellent dielectric properties, are required.

[0003] Conventionally, when spherical silica particles are heated from 50°C to 1000°C at a heating rate of 5°C / min, the number of water molecules detached from the spherical silica particles is 0.001 to 0.010 mmol / g, and the specific surface area is 0.1 to 2.0 m². 2 It has been reported that a lower dielectric loss tangent can be achieved by filling a resin with spherical silica particles at a density of / g (Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-61872 [Overview of the project] [Problems that the invention aims to solve]

[0005] Patent Document 1 found that the presence of numerous silanol groups and adsorbed water on the surface of spherical silica particles is a factor that worsens the dielectric loss tangent. Focusing on the number of water molecules that detach from the particles when the spherical silica particles are heated under predetermined conditions, the document proposes a technique for selecting silica particles with a low dielectric loss tangent by using the number of water molecules as an indicator. The inventors investigated the application of inorganic oxide hollow particles, composed of inorganic oxides including silicon oxide and other inorganic oxides different from those described in Patent Document 1, such as boron oxide, to electronic materials. They discovered that when these inorganic oxide hollow particles are stored in the atmosphere for a long period, the dielectric loss tangent increases (deterioration of dielectric loss tangent), and the dielectric properties deteriorate. To investigate the cause, the inventors conducted a detailed investigation and found that the boron oxide contained in the inorganic oxide hollow particles reacts with moisture in the atmosphere during storage to precipitate boric acid, which is the cause of the deterioration of dielectric properties. Furthermore, since this problem of deterioration of dielectric properties due to boric acid precipitation does not exist in borosilicate glass, which has a skeleton formed of boron oxide and silicon oxide, it was found to be a problem specific to inorganic oxide hollow particles composed of inorganic oxides including silicon oxide and boron oxide, as well as oxides of elements different from these. The object of the present invention is to provide inorganic oxide hollow particles that can suppress the deterioration of dielectric properties. [Means for solving the problem]

[0006] In view of the above problems, the present inventors conducted research and found that the dielectric loss tangent of inorganic oxide hollow particles is closely related to the weight loss rate when heated under predetermined conditions, and that if the weight loss rate is below a predetermined value, the dielectric loss tangent is low, and inorganic oxide hollow particles with suppressed deterioration of dielectric properties can be obtained.

[0007] In other words, the present invention provides the following [1] to [7]. [1] An inorganic oxide hollow particle in which the outer shell partitioning the hollow chamber is composed of an inorganic oxide containing boron oxide, silicon oxide, and oxides of elements other than boron and silicon, The boron oxide content is 3% by mass or more. The silicon dioxide content is 30% by mass or more. After being left to cool for 100 hours in an environment of 50°C and 95% RH relative humidity, the weight loss rate when heated to 300°C at a heating rate of 10°C / min is 1% by mass or less. Inorganic oxide hollow particles. [2] The inorganic oxide hollow particles described in [1] above, wherein the oxides of elements other than boron and silicon include magnesium oxide, calcium oxide, and aluminum oxide. [3] The magnesium oxide content is 0.05 to 7% by mass, The calcium oxide content is 1-20% by mass. The aluminum oxide content is 5-35% by mass. The inorganic oxide hollow particles described in [2] above. [4] Hollow inorganic oxide particles according to any one of [1] to [3] above, wherein the precipitation of boric acid is suppressed. [5] An inorganic oxide hollow particle according to any one of [1] to [4] above, wherein the electrostatic loss tangent is less than 0.0020. [6] An inorganic oxide hollow particle in which the outer shell partitioning the hollow chamber is composed of an inorganic oxide containing boron oxide, silicon oxide, and oxides of elements other than boron and silicon, Inorganic oxide hollow particles, having a boron oxide content of 3% by mass or more and a silicon oxide content of 30% by mass or more, are left to cool for 100 hours in an environment of 50°C and 95% RH relative humidity, and then heated to 300°C at a heating rate of 10°C / min. The weight loss rate during this heating process is controlled to be 1% by mass or less. A method for suppressing the deterioration of dielectric properties of hollow inorganic oxide particles. [7] An inorganic oxide hollow particle in which the outer shell partitioning the hollow chamber is composed of an inorganic oxide containing boron oxide, silicon oxide, and oxides of elements other than boron and silicon, Inorganic oxide hollow particles, having a boron oxide content of 3% by mass or more and a silicon oxide content of 30% by mass or more, are left to cool for 100 hours in an environment of 50°C and 95% RH relative humidity, and then heated to 300°C at a heating rate of 10°C / min. The weight loss rate during this heating process is controlled to be 1% by mass or less. A method for suppressing boric acid precipitation from hollow inorganic oxide particles. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide inorganic oxide hollow particles capable of suppressing a decrease in dielectric properties. Therefore, the inorganic oxide hollow particles of the present invention are useful for electronic materials, particularly materials for high-frequency devices and the like.

Brief Description of the Drawings

[0009] [Figure 1] It is a figure showing an X-ray diffraction pattern of inorganic oxide hollow particles obtained in Examples and Comparative Examples.

Embodiments for Carrying Out the Invention

[0010] <Inorganic Oxide Hollow Particles> The inorganic oxide hollow particles of the present invention are characterized in that an outer shell partitioning a hollow chamber is composed of an inorganic oxide containing boron oxide, silicon oxide, and an oxide of an element other than boron and silicon, and the weight loss rate when heated under predetermined conditions is 1% by mass or less.

[0011] (Hollow Particles) As used herein, the "hollow particles" refer to particles having a cavity (hollow structure) inside and 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 the porous particles by a transmission electron microscope (TEM) image.

[0012] The inorganic oxide hollow particles of the present invention may be multi-vesicular. As used herein, "multi-vesicular" means having a plurality of independent bubbles (hereinafter also referred to as "independent bubbles") in which the cavities covered by the outer shell are separated by one or more partition walls. Since the independent bubbles are separated by partition walls, they do not communicate with each other. The "partition wall" referred to here means a wall partitioning two adjacent independent bubbles inside the particles.

[0013] The inorganic oxide hollow particles of the present invention preferably have no openings in their outer shell and are non-porous. This allows for the complete containment of closed bubbles within the outer shell, thereby further improving dielectric properties. The non-porous nature of the outer shell can be confirmed by scanning electron microscope (SEM) images or by observing whether the particles float on water.

[0014] (Inorganic oxides) The inorganic oxide hollow particles of the present invention have an outer shell composed of inorganic oxide. Furthermore, if the inorganic oxide hollow particles are polycellular, the outer shell and partitions are composed of inorganic oxide.

[0015] Inorganic oxides include boron oxide, silicon oxide, and oxides of elements other than boron and silicon. The oxides of elements other than boron and silicon are not particularly limited as long as they contain elements that constitute inorganic oxides. For example, oxides containing one or more elements selected from Group 1 to Group 16 (excluding boron and silicon) can be listed. A single inorganic oxide may contain one or more elements. Hereinafter, "Group 1 elements" refers to elements belonging to Group 1 of the periodic table, and the same meaning shall apply to elements belonging to other groups.

[0016] Examples of Group 1 element oxides include lithium oxide, sodium oxide, potassium oxide, rubidium oxide, and cesium oxide. Examples of Group 2 element oxides include magnesium oxide, calcium oxide, strontium oxide, and barium oxide. Examples of Group 3 element oxides include yttrium oxide. Examples of Group 4 element oxides include titanium oxide and zirconium oxide. Examples of Group 5 element oxides include niobium oxide and tantalum oxide. Examples of Group 6 element oxides include chromium oxide, molybdenum oxide, and tungsten oxide. Examples of Group 7 element oxides include manganese 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. Examples of Group 13 element oxides include any oxide other than boron oxide, such as aluminum oxide, gallium oxide, indium oxide, and thallium oxide. Examples of Group 14 element oxides include any oxide other than silicon oxide, such as germanium oxide, tin oxide, and lead oxide. Examples of Group 15 element oxides include phosphorus oxide, arsenic oxide, antimony oxide, and bismuth oxide. Examples of Group 16 element oxides include sulfur oxides and selenium oxide. Hereinafter, "Group 1 element oxide" refers to an oxide of an element belonging to Group 1 of the periodic table, and the same meaning applies to oxides of elements belonging to other groups. In addition, composite oxides combining these oxides can also be cited. Examples of composite oxides include aluminosilicate, calcium silicate, aluminoborosilicate, and bariumborosilicate.

[0017] In particular, as oxides of elements other than boron and silicon, it is preferable to include one or more inorganic oxides selected from Group 2 element oxides and Group 13 element oxides (excluding boron) from the viewpoint of suppressing a decrease in dielectric properties while ensuring a hollow structure, more preferably to include one or more inorganic oxides selected from calcium oxide, magnesium oxide and aluminum oxide, and even more preferably inorganic oxides containing calcium oxide, magnesium oxide and aluminum oxide.

[0018] A preferred embodiment of the inorganic oxide constituting the hollow inorganic oxide particles of the present invention is any of the following embodiments (i) to (iii), with embodiment (iii) being more preferred, from the viewpoint of ensuring a hollow structure while suppressing a decrease in dielectric properties. Optionally, one or more Group 1 element oxides, such as sodium oxide and potassium oxide, may be included. (i) A mixture comprising boron oxide, silicon oxide, and one or more inorganic oxides selected from Group 2 element oxides and Group 13 element oxides (excluding boron). (ii) comprising boron oxide, silicon oxide, and one or more inorganic oxides selected from calcium oxide, magnesium oxide, and aluminum oxide. (iii) Inorganic oxides including boron oxide, silicon oxide, calcium oxide, magnesium oxide and aluminum oxide

[0019] The inorganic oxide hollow particles of the present invention may have an appropriate chemical composition, but the respective contents of boron oxide and silicon oxide are as follows. The boron oxide content is 3% by mass or more, but from the viewpoint of ensuring a hollow structure while suppressing a decrease in dielectric properties, 5% by mass or more is preferred, and 7% by mass or more is even more preferred. Furthermore, from the viewpoint of ensuring a hollow structure while suppressing a decrease in dielectric properties, the boron oxide content is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 33% by mass or less. The silicon dioxide content is 30% by mass or more, but from the viewpoint of ensuring a hollow structure while suppressing a decrease in dielectric properties, 33% by mass or more is preferred, 35% by mass or more is more preferred, and 38% by mass or more is even more preferred. Furthermore, from the viewpoint of ensuring a hollow structure while suppressing a decrease in dielectric properties, the silicon dioxide content is preferably 70% by mass or less, more preferably 65% ​​by mass or less, even more preferably 60% by mass or less, and even more preferably 55% by mass or less.

[0020] The content of oxides of elements other than boron and silicon can be set as appropriate, but for example, a preferred embodiment in (i) is as follows: The content of Group 2 element oxides is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more, from the viewpoint of ensuring a hollow structure while suppressing a decrease in dielectric properties. Furthermore, the content of Group 2 element oxides is preferably 27% by mass or less, more preferably 23% by mass or less, and even more preferably 20% by mass or less, from the viewpoint of ensuring a hollow structure while suppressing a decrease in dielectric properties. The content of Group 13 element oxides (excluding boron) is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, from the viewpoint of ensuring a hollow structure while suppressing a decrease in dielectric properties. Furthermore, the content of Group 13 element oxides (excluding boron) is preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less, and even more preferably 25% by mass or less, from the viewpoint of ensuring a hollow structure while suppressing a decrease in dielectric properties. When a group 1 element oxide is included, the content of the group 1 element oxide is preferably 3% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less. The lower limit of the content of the group 1 element oxide is not particularly limited and may be 0% by mass.

[0021] Furthermore, preferred embodiments in (ii) or (iii) are as follows: From the viewpoint of ensuring a hollow structure while suppressing a decrease in dielectric properties, the calcium oxide content is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more. Furthermore, from the viewpoint of ensuring a hollow structure while suppressing a decrease in dielectric properties, the calcium oxide content is preferably 20% by mass or less, more preferably 18% by mass or less, and even more preferably 15% by mass or less. From the viewpoint of ensuring a hollow structure while suppressing a decrease in dielectric properties, the magnesium oxide content is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more. Furthermore, from the viewpoint of ensuring a hollow structure while suppressing a decrease in dielectric properties, the magnesium oxide content is preferably 7% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less. From the viewpoint of ensuring a hollow structure while suppressing a decrease in dielectric properties, the aluminum oxide content is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. Furthermore, from the viewpoint of ensuring a hollow structure while suppressing a decrease in dielectric properties, the aluminum oxide content is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less. When one or more selected from sodium oxide and potassium oxide are included, the total content of sodium oxide and potassium oxide is preferably 3% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less. The lower limit of the total content of sodium oxide and potassium oxide is not particularly limited and may be 0% by mass.

[0022] In this specification, the content of each inorganic oxide described above is the value obtained by measuring the oxide equivalent using X-ray fluorescence analysis and calculating the chemical composition. The individual chemical composition is calculated by correcting the total value of the oxides of the element to be analyzed using the following formula so that it equals 100% by mass.

[0023] Chemical composition (after correction) (mass%) =Chemical composition (before correction) × 100 / [100 - Impurities (mass%)]

[0024] In the formula, the impurity (mass%) is calculated by subtracting the total chemical composition of the oxides mentioned above from 100.

[0025] (Weight reduction rate) The inorganic oxide hollow particles of the present invention have a weight loss rate of 1% by mass or less when heated to 300°C at a heating rate of 10°C / min. However, from the viewpoint of further suppressing the deterioration of dielectric properties, a weight loss rate of 0.9% by mass or less is preferred, 0.8% by mass or less is more preferred, and 0.7% by mass or less is even more preferred. The lower limit of this weight loss rate is not particularly limited and may be 0% by mass. The weight loss rate can be used as an indicator when determining whether or not boric acid precipitates from the inorganic oxide hollow particles. That is, the smaller the weight loss rate, the more the precipitation of boric acid from the inorganic oxide hollow particles is suppressed, and the more the deterioration of dielectric properties is suppressed. The presence or absence of boric acid precipitation can be determined by performing X-ray diffraction analysis on the inorganic oxide hollow particles using the method described in the examples below. If no peak derived from boric acid is confirmed at the X-ray diffraction angle (2θ) = 28° in the obtained X-ray diffraction pattern, it can be determined that there is no precipitation of boric acid from the inorganic oxide hollow particles (Figure 1).

[0026] In this specification, the "weight loss rate" shall be measured by the following method. Inorganic oxide hollow particles are left to stand for 100 hours in an environment with a temperature of 50°C and a relative humidity of 95% RH. These inorganic oxide hollow particles are then cooled to room temperature (25°C). Next, the cooled inorganic oxide hollow particles are heated from room temperature (25°C) to 300°C in a nitrogen atmosphere at a heating rate of 10°C / min using a thermogravimetric differential thermal analyzer. The weight loss rate (mass%) is then calculated from the weights of the inorganic oxide hollow particles before and after heating. For example, a high-sensitivity differential thermal balance (STA 2500 Regulus, Bruker AXS) can be used as the thermogravimetric differential thermal analyzer.

[0027] (Other physical properties) Since the inorganic oxide hollow particles of the present invention are minute particles, they 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 10 μm or less, more preferably 8 μm or less, and still more preferably 5 μm or less. The lower limit of the average particle diameter is preferably 0.1 μm or more, more preferably 0.3 μm or more, and still more preferably 0.5 μm or more from the viewpoint of ensuring the hollow structure. 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 measurement of the particle size distribution, for example, a laser diffraction / scattering type particle size distribution measuring device can be used.

[0028] The inorganic oxide hollow particles of the present invention usually have a particle density of 1.00 g / cm 3 or less, but from the viewpoint of further reducing the dielectric loss tangent, it is preferably 0.80 g / cm 3 or less, more preferably 0.70 g / cm 3 or less, and still more preferably 0.60 g / cm 3 or less. The lower limit of the particle density is preferably 0.20 g / cm 3 or more, more preferably 0.30 g / cm 3 or more, and still more preferably 0.40 g / cm 3 or more from the viewpoint of ensuring sufficient strength. Here, in this specification, the "particle density" means a value measured by the gas displacement method in accordance with JIS R 1620. As a particle density measuring device, for example, a dry type automatic densitometer "Accupic (manufactured by Shimadzu Corporation)" can be used.

[0029] The inorganic oxide hollow particles of the present invention typically have a void ratio of 55% or more, but are preferably 60% or more, more preferably 65% ​​or more, even more preferably 70% or more, and even more preferably 75% or more. The upper limit of this void ratio is preferably 95% or less, and even more preferably 90% or less, from the viewpoint of ensuring sufficient strength. Hereinafter, "void ratio" refers to a value calculated from the bulk density and true density of particles measured using a dry automatic densimeter, using the following formula. Note that since it is difficult to measure for individual particles, this represents the void ratio of the particle group as a whole. Hereinafter, "bulk density" refers to a value measured by the gas displacement method in accordance with JIS R 1620. For example, an Accupic (manufactured by Shimadzu Corporation) can be used as the dry automatic densimeter.

[0030] Cavity = (True density - Bulk density) × 100 / True density

[0031] The inorganic oxide hollow particles of the present invention preferably have an electrostatic loss tangent of less than 0.0020, more preferably 0.0019 or less, and even more preferably 0.0018 or less, from the viewpoint of suppressing a decrease in dielectric properties. The lower limit of the electrostatic loss tangent is not particularly limited and may be 0. Hereinafter, "dielectric loss tangent" refers to the dielectric loss tangent at 1 GHz, and shall be measured at 1 GHz in an environment of 25°C and 60% humidity. The dielectric loss tangent can be measured, for example, using a perturbation type cavity resonator (manufactured by KEYCOM).

[0032] The inorganic oxide hollow particles of the present invention can be applied to thermal insulation materials, heat shielding materials, catalyst supports, building materials, electronic materials, etc. However, due to their small particle size and low dielectric loss tangent, they are particularly useful for electronic materials, especially for high-frequency devices, such as wiring circuit boards and semiconductor encapsulants.

[0033] <Method for producing hollow inorganic oxide particles> The inorganic oxide hollow particles of the present invention can be manufactured by any method as long as the weight loss rate described above is 1% by mass or less. For example, they can be manufactured by obtaining inorganic oxide hollow particles by spray pyrolysis and then treating these inorganic oxide hollow particles with a silane coupling agent. More specifically, they can be subjected to a process including the first and second steps described below.

[0034] (First step) The first step involves spraying the liquid to be sprayed from a spraying device installed inside the spray pyrolysis apparatus, and then thermally decomposing the sprayed droplets of the liquid to be sprayed to generate hollow inorganic oxide particles. The spray pyrolysis apparatus preferably has a vertical cylindrical pyrolysis furnace, and the size of the pyrolysis furnace can be appropriately selected depending on the production scale.

[0035] The sprayed liquid contains a raw material compound having elements that constitute an inorganic oxide, and a solvent. As raw material compounds, a compound containing boron, a compound containing silicon, and a compound containing one or more elements selected from Group 1 to Group 16 elements (excluding boron and silicon) may be appropriately selected. The raw material compounds are preferably soluble in water, and are preferably in the form of a salt or an alkoxide. 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, propions, oxalates, and citrates.

[0036] For example, in the embodiment of (i) described above, one or more compounds selected from compounds containing boron, compounds containing silicon, compounds containing group 2 elements, and compounds containing group 13 elements (excluding boron) may be used as raw material compounds, and if desired, compounds containing group 1 elements may also be included.

[0037] Examples of compounds containing boron include boric acid and borates. 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 silicon-containing compounds include silicates and silicate alkoxides. Examples of silicates include sodium silicate, potassium silicate, and tetramethylammonium silicate, while examples of silicate alkoxides include tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), tetrapropyl orthosilicate (TPOS), and tetrabutoxysilane. Examples of compounds containing Group 2 elements include magnesium salts and calcium salts. Examples of magnesium salts include magnesium nitrate, magnesium sulfate, magnesium chloride, magnesium phosphate, and magnesium hydroxide, while examples of calcium salts include calcium nitrate, calcium chloride, calcium hydroxide, calcium formate, calcium acetate, and calcium propionate. Examples of compounds containing Group 13 elements (excluding boron) include aluminum salts and aluminum alkoxides. 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. Furthermore, complex compounds containing structures in which two or more elements are chemically bonded can also be used, such as aluminosilicates. Examples of aluminosilicates include sodium aluminosilicate, potassium aluminosilicate, and calcium aluminosilicate.

[0038] Water is preferred as the solvent for the sprayed liquid, considering its environmental impact and manufacturing costs.

[0039] The amount of raw material compound and solvent used is such that the total concentration of the raw material compound in the sprayed liquid is typically 0.01 to 1.0 mol / L, preferably 0.1 to 0.9 mol / L. The individual amounts of the raw material compound in the sprayed liquid should be such that they satisfy the stoichiometric composition based on pre-defined hollow particles.

[0040] Examples of spraying devices include fluid nozzles such as two-fluid nozzles, three-fluid nozzles, and four-fluid nozzles. There are two types of fluid nozzles: an internal mixing method where the gas and raw material solution are mixed inside the nozzle, and an external mixing method where the gas and raw material solution are mixed outside the nozzle; both can be used. The gas supplied to the nozzle can be, for example, air, nitrogen, argon, or other inert gases. Of these, air is preferred from an economic standpoint. The spraying device can be installed as one or more units.

[0041] The flow rate of the sprayed liquid is typically 1 to 100 L / h, preferably 3 to 80 L / h, and more preferably 5 to 60 L / h. The ejection velocity of the sprayed liquid is typically 1 to 50 m / s, preferably 5 to 35 m / s, and more preferably 10 to 20 m / s.

[0042] Examples of heating devices include combustion burners, hot air heaters, and electric heaters. One or more heating devices can be installed. Any commercially available combustion burner, hot air heater, or electric heater can be used. The temperature of the heating device is usually 400 to 1800°C, but 600 to 1500°C is preferred, 700 to 1400°C is more preferred, and 800 to 1300°C is even more preferred.

[0043] The hollow inorganic oxide particles produced by the pyrolysis reaction are recovered from the downstream side of the pyrolysis furnace. High-performance cyclone powder recovery machines or powder recovery systems using bag filters can be used to recover the hollow inorganic oxide particles.

[0044] (Second step) The second step is to treat the surface of the inorganic oxide hollow particles with a silane coupling agent. As a silane coupling agent, from the viewpoint of suppressing the decrease in dielectric properties, the following formula (1); R 1 n Si(OR 2 ) 4-n (1) (In the formula, R 1 R indicates a nitrogen-containing organic group. 2 (where n represents a methyl group or an ethyl group, and n represents 1 or 2.) It is preferable to use a silane coupling agent represented by [formula]. Note that one or more silane coupling agents may be used, and they may be manufactured by known methods or commercially available.

[0045] R 1 The organic group involved is not particularly limited, but an alkanediyl group is preferred. The number of carbon atoms in the alkanediyl group is preferably 2 to 10, more preferably 3 to 8, and even more preferably 3 to 6. Examples of nitrogen-containing groups in organic groups include amino groups, alkylamino groups, isocyanurate groups, ureido groups, and isocyanate groups. The number of carbon atoms in the alkyl group of an aminoalkyl group is preferably 1 to 4. The amino group and alkylamino group may also be in the form of a salt.

[0046] Among them, R 1 From the viewpoint of further suppressing the deterioration of dielectric properties, examples include aminoalkanediyl groups, isocyanatealkanediyl groups, and ureidoalkanediyl groups, which may be substituted with aminoalkyl groups.

[0047] R 2 From the viewpoint of further suppressing the deterioration of dielectric properties, an ethyl group is preferred. From the viewpoint of further suppressing the deterioration of dielectric properties, n is preferably 1.

[0048] Preferred silane coupling agents include trifunctional amino group-containing silane coupling agents, trifunctional isocyanate group-containing silane coupling agents, trifunctional isocyanurate group-containing silane coupling agents, and trifunctional ureido group-containing silane coupling agents. Specific examples of such silane coupling agents include, for example, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-2-(aminoethyl)-8-aminooctyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane, isocyanatetopropyltriethoxysilane, isocyanatetopropyltriethoxysilane, tris(trimethoxysilylpropyl)isocyanurate, and ureidopropyltrialkoxysilane.

[0049] The processing method is not particularly limited, and any known method can be used; it can be either wet or dry. Among these, dry processing is preferred because it allows for easier enjoyment of the effects of the present invention. Dry treatment can be performed, for example, by dropping or spraying a silane coupling agent or a silane coupling agent diluted in a suitable solvent onto inorganic oxide hollow particles being stirred in a tank, thereby coating the surface of the inorganic oxide hollow particles with the silane coupling agent. Examples of solvents used to dilute the silane coupling agent include alcohols, ethers, ketones, and hydrocarbons. One or more solvents can be used in combination. The concentration of the silane coupling agent in the diluent can be set as appropriate, but is usually between 10 and 50% by mass.

[0050] The amount of silane coupling agent used is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.7% by mass or more, and preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less, relative to the inorganic oxide hollow particles, from the viewpoint of preventing destruction of the hollow structure and suppressing the deterioration of dielectric properties. Note that the amount used here is the effective amount of silane coupling agent.

[0051] The second step yields hollow inorganic oxide particles whose surfaces are coated with a silane coupling agent. Optionally, the surface-coated hollow inorganic oxide particles may be dried after the second step. Examples of drying methods include a box dryer, a band dryer, and a spray dryer. The drying temperature and drying time can be appropriately set depending on the type of solvent used.

[0052] In this way, the precipitation of boric acid from the inorganic oxide hollow particles is suppressed, and inorganic oxide hollow particles with suppressed dielectric degradation can be obtained. [Examples]

[0053] The embodiments of the present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following embodiments.

[0054] 1. Analysis of chemical composition Inorganic oxide hollow particles were molded into briquettes using a press machine. These briquettes were then measured in terms of oxide equivalent using an X-ray fluorescence analyzer (ZSX primus II, Rigaku Corporation). The chemical composition of each briquette was calculated by correcting the total value of the oxides of the target elements (SiO2, B2O3, Al2O3, MgO, CaO) using the following formula so that the total value would be 100%.

[0055] Chemical composition (after correction) (mass%) =Chemical composition (before correction) × 100 / [100 - Impurities (mass%)] [In the formula, impurities (mass%) are calculated by subtracting the total chemical composition of the oxides mentioned above from 100.]

[0056] 2. Measurement of average particle size Using a laser diffraction particle size distribution analyzer (MT3000II, manufactured by Microtrac Bell), a volume-based particle size distribution was created in accordance with JIS R 1629, and the particle size (d) corresponding to 50% of the integrated distribution curve was determined. 50 ) was sought.

[0057] 3. Measurement of particle density and void ratio Using a dry automatic densimeter (AccuPic, manufactured by Shimadzu Corporation), the particle density and true density of hollow inorganic oxide particles were measured, and the void ratio was calculated using the following formula. The true density in the formula was measured using a dry automatic densimeter before and after treatment with a silane coupling agent to remove the void portion.

[0058] Cavity ratio = (True density - Bulk density) × 100 / True density (1)

[0059] 4. Measurement of weight loss rate The samples were cured for 100 hours at a temperature of 50°C and a humidity of 95% RH, and then cooled to room temperature (25°C). Using a high-sensitivity differential thermobalance (STA 2500 Regulus, Bruker AXS), the samples were heated from room temperature (25°C) to 300°C at a heating rate of 10°C / min under a nitrogen atmosphere. The weight loss rate (mass%) was calculated from the weights of the inorganic oxide hollow particles before and after heating.

[0060] 5. Measurement of Dielectric Loss Tangent Measurements were taken using a perturbation-type cavity resonator (manufactured by KEYCOM) at a frequency of 1 GHz under conditions of 25°C and 60% humidity.

[0061] 6. Confirmation of the presence or absence of boric acid precipitation. After curing for 100 hours in an environment of 50°C and 95% RH, X-ray diffraction analysis (CuKα, current 40mA, voltage 40kV) was performed using an X-ray diffraction analyzer (D8advance, Bruker) to check for the presence or absence of a peak at the X-ray diffraction angle (2θ) of 28°.

[0062] Example 1 The raw material compounds (colloidal silica, tetraethyl orthosilicate, aluminum nitrate nonahydrate, magnesium nitrate hexahydrate, and boric acid) were dissolved in 250 kg of deionized water to the molar concentrations shown in Table 1, and the raw material mixture aqueous solution was introduced into a solution tank. The introduced aqueous solution was delivered to a two-fluid nozzle by a liquid transfer pump. The spraying conditions for the two-fluid nozzle were set to a nozzle air volume of 50 L / min and a liquid transfer volume of 470 mL / min, and the solution was sprayed into a spray pyrolysis furnace and heated at 1100°C. The solution was rapidly cooled using a cooling mechanism installed at the outlet of the reaction zone, and then the foamy inorganic acid hollow particles were recovered using a bag filter. The foamy nature of the hollow particles was confirmed by scanning electron microscopy (SEM) imaging. Next, the recovered foamy inorganic acid hollow particles were subjected to surface treatment using a dry treatment method. Specifically, 1 g (1.0 wt%) of silane coupling agent (KBE-903: manufactured by Shin-Etsu Chemical Co., Ltd.) was added to 100 g of foamy inorganic acid hollow particles, stirred in a planetary mixer for 10 minutes, and then dried at 120°C for 3 hours. Analysis was performed on the surface-coated, multi-foamed, inorganic acid hollow particles obtained after drying. The results are shown in Table 4.

[0063] [Table 1]

[0064] Examples 2 and 3 Except for changing the type of silane coupling agent as shown in Table 4, surface-coated, multi-foamed inorganic salt oxide hollow particles were manufactured and analyzed using the same procedure as in Example 1. The results are shown in Table 4.

[0065] Example 4 Except for the change in the raw material solution shown in Table 2, surface-coated, multi-foamed inorganic salt oxide hollow particles were manufactured and analyzed using the same procedure as in Example 1. The results are shown in Table 4.

[0066] [Table 2]

[0067] Example 5 Except for the change in the raw material solution shown in Table 3, surface-coated, multi-foamed inorganic salt oxide hollow particles were manufactured and analyzed using the same procedure as in Example 1. The results are shown in Table 4.

[0068] [Table 3]

[0069] Comparative Examples 1-4 Surface-coated, multi-foamed inorganic salt oxide hollow particles were produced and analyzed using the same procedure as in Example 1, except that they were treated with the silane coupling agent shown in Table 5. The results are shown in Table 5.

[0070] Comparative Example 5 Hollow particles of polyfoaming inorganic salt oxide were prepared and analyzed using the same procedure as in Example 1, except that they were not treated with a silane coupling agent. The results are shown in Table 5.

[0071] Comparative Example 6 Hollow particles of polyfoaming inorganic salt oxide were produced and analyzed using the same procedure as in Example 4, except that they were not treated with a silane coupling agent. The results are shown in Table 5.

[0072] Comparative Example 7 Hollow particles of polyfoaming inorganic salt oxide were produced and analyzed using the same procedure as in Example 5, except that they were not treated with a silane coupling agent. The results are shown in Table 5.

[0073] [Table 4]

[0074] [Table 5]

[0075] In Comparative Examples 1-7, the inorganic oxide hollow particles had a weight loss rate of 1.5-3.6% by mass and a dielectric loss tangent of 0.0020 or higher. In the X-ray diffraction pattern shown in Figure 1, a peak originating from boric acid was observed at the X-ray diffraction angle (2θ) = 28°. As the intensity of this peak increased, the weight loss rate increased and the dielectric loss tangent became higher. On the other hand, in all of the inorganic oxide hollow particles of Examples 1 to 5, the weight loss rate was 1% by mass or less. In the X-ray diffraction pattern shown in Figure 1, almost no peak originating from boric acid was observed at the X-ray diffraction angle (2θ) = 28°, and the dielectric loss tangent was less than 0.0020. From the above, it can be seen that if the weight loss rate when heated under specified conditions is 1% by mass or less, the dielectric loss tangent can be kept low, and the deterioration of dielectric properties can be suppressed.

Claims

1. The outer shell that partitions the hollow chamber is composed of an inorganic oxide hollow particle containing an inorganic oxide including boron oxide, silicon oxide, and oxides of elements other than boron and silicon, The boron oxide content is 3% by mass or more. The silicon dioxide content is 30% by mass or more. After being left to cool for 100 hours in an environment of 50°C and 95% relative humidity RH, the weight loss rate when heated to 300°C at a heating rate of 10°C / min is 1% by mass or less. Inorganic oxide hollow particles.

2. The inorganic oxide hollow particles according to claim 1, wherein the oxides of elements other than boron and silicon include magnesium oxide, calcium oxide, and aluminum oxide.

3. The magnesium oxide content is 0.05 to 7% by mass. The calcium oxide content is 1 to 20% by mass. The aluminum oxide content is 5 to 35% by mass. The inorganic oxide hollow particles according to claim 2.

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