Method for producing inorganic particle and method for producing composite material

Abstract

A method for producing inorganic particles according to the present invention comprises a step for treating inorganic particles with at least one hydrophobic agent selected from a group consisting of metal hydride compounds and organometallic compounds. It is thus possible to produce inorganic particles that exhibit good dispersibility when dispersed in an organic material. In addition, a method for producing a composite material according to the present invention comprises a step for mixing the inorganic particles obtained by the method for producing inorganic particles with a resin composition. It is thus possible to produce a composite material in which inorganic particles have good dispersibility.

Description

Method for producing inorganic particles and method for producing composite materials

[0001] This disclosure relates to a method for producing inorganic particles and a method for producing composite materials.

[0002] In the manufacturing of semiconductor devices, functional layers are provided to improve various properties such as physical, thermal, and electrical characteristics. For forming these functional layers, composite materials are widely used, which are made by blending inorganic fillers such as silica and alumina, conductive particles such as nickel, and magnetic particles with organic materials such as resins.

[0003] Generally, the surfaces of inorganic particles are hydrophilic, while organic materials such as resins are hydrophobic, which often leads to insufficient dispersibility when inorganic particles are mixed with organic materials. Therefore, improving the dispersibility of inorganic particles in organic materials by treating their surfaces with surface treatment agents is being investigated (see, for example, Patent Documents 1 and 2).

[0004] JP-A-8-48910 JP-A-10-25427

[0005] In recent years, with the increasing speed, miniaturization, and integration of semiconductor devices, the required properties for composite materials of inorganic particles and organic materials have been steadily rising. As part of this effort, increasing the amount of inorganic particles is being considered to improve the various properties imparted to the composite material. However, even when using surface-treated inorganic particles, increasing the amount of inorganic particles tends to result in insufficient dispersibility, making it difficult to impart properties to the composite material that are commensurate with the amount of inorganic particles included.

[0006] One aspect of this disclosure aims to provide a method for producing inorganic particles that exhibit good dispersibility when dispersed in an organic material. Another aspect of this disclosure aims to provide a method for producing a composite material in which inorganic particles exhibit good dispersibility.

[0007] This disclosure includes the following aspects: [1] A method for producing inorganic particles, comprising the step of treating inorganic particles with at least one hydrophobic agent selected from the group consisting of metal hydride compounds and organometallic compounds. [2] The method for producing inorganic particles according to [1], wherein the hydrophobic agent is at least one selected from lithium aluminum hydride and Grignard reagents. [3] The method for producing inorganic particles according to [1] or [2], wherein the inorganic particles are inorganic particles treated with a surface treatment agent. [4] The method for producing inorganic particles according to [3], wherein the inorganic particles are inorganic oxide particles and the surface treatment agent is a coupling agent. [5] The method for producing inorganic particles according to [3] or [4], wherein the inorganic particles are silica particles or alumina particles and the surface treatment agent is a silane coupling agent. [6] A method for producing a composite material, comprising the step of mixing inorganic particles obtained by the method for producing inorganic particles according to any one of [1] to [5] with a resin composition.

[0008] According to one aspect of this disclosure, it is possible to provide a method for producing inorganic particles that exhibit good dispersibility when dispersed in an organic material. Furthermore, according to another aspect of this disclosure, it is possible to provide a method for producing a composite material in which the inorganic particles exhibit good dispersibility.

[0009] The present disclosure is described in detail below. In this specification, the term "process" includes not only independent processes but also processes that are indistinguishable from other processes as long as the intended function of the process is achieved. In this specification, numerical ranges indicated using "~" indicate a range that includes the numbers written before and after "~" as the minimum and maximum values, respectively. For example, the statement "10 or more" means 10 and numbers greater than 10, and the same applies when the numbers are different. For example, the statement "10 or less" means 10 and numbers less than 10, and the same applies when the numbers are different. Furthermore, in numerical ranges described in stages, the upper or lower limit of a numerical range in one stage may be replaced with the upper or lower limit of a numerical range in another stage, or with the values ​​shown in the examples. In this specification, the content of each component in a composition means the total content of multiple types of substances present in the composition, unless otherwise specified, if there are multiple types of substances corresponding to each component in the composition. The same applies to the content of each component in a composite material. In this specification, the term "layer" includes not only structures that are formed across the entire surface when viewed in a plan view, but also structures that are formed in only a portion of the surface.

[0010] [Method for producing inorganic particles] One embodiment of the present disclosure relates to a method for producing inorganic particles. The method for producing inorganic particles according to this embodiment comprises a step of treating inorganic particles with at least one hydrophobic agent selected from the group consisting of metal hydride compounds and organometallic compounds (hydrophobic step).

[0011] In this specification, "inorganic particles" refer to particles having an inorganic compound on their surface. Inorganic particles include not only particles composed of inorganic compounds, but also particles in which the entire or partial surface of a core particle is coated with an inorganic compound. Examples of particles in which the surface of a core particle is coated with an inorganic compound include insulating coated magnetic particles, in which the surface of magnetic powder is coated with an insulating material such as silica. The core particle may also contain an organic compound.

[0012] The inorganic particles subjected to the hydrophobicization process are not particularly limited as long as they can have hydroxyl groups and / or adsorbed water on their surface. Furthermore, the hydroxyl groups on the surface of the inorganic particles include those that form hydrogen bonds with adjacent hydroxyl groups (hydrogen-bonding hydroxyl groups) and hydroxyl groups that do not participate in the formation of hydrogen bonds (isolated hydroxyl groups). The inorganic compounds constituting the inorganic particles may be, for example, metals or inorganic oxides.

[0013] The metal may include, for example, at least one selected from the group consisting of base metal elements, noble metal elements, transition metal elements, and rare earth elements. Examples of metals include iron (Fe), copper (Cu), titanium (Ti), manganese (Mn), cobalt (Co), nickel (Ni), zinc (Zn), niobium (Nb), aluminum (Al), tin (Sn), chromium (Cr), barium (Ba), strontium (Sr), lead (Pb), silver (Ag), praseodymium (Pr), neodymium (Nd), samarium (Sm), and dysprosium (Dy). The metal may be a single element composed of only one of the above-mentioned metal elements, or it may be an alloy composed of two or more metal elements. The alloy may include at least one selected from the group consisting of solid solutions, eutectic compounds, and intermetallic compounds. The alloy may be, for example, an iron alloy such as Fe-Cr alloys and Fe-Ni-Cr alloys, a copper alloy such as Cu-Sn alloys, Cu-Sn-P alloys, Cu-Ni alloys and Cu-Be alloys, or a solder alloy mainly composed of Sn and containing metals such as Pb, Ag, Cu, and Bi.

[0014] Examples of inorganic oxides include silicon dioxide (silica, etc.), aluminum oxide (alumina, etc.), titanium oxide (titania, etc.), cerium oxide (ceria, etc.), zirconium oxide (zirconia, etc.), magnesium oxide (magnesia, etc.), yttrium oxide (yttria, etc.), zinc oxide, iron oxide, tin oxide, scandium oxide, vanadium oxide, and chromium oxide. Inorganic oxides may also be complex oxides composed of two or more metals. Examples of such complex oxides include lithium titanate, barium titanate, and magnesium aluminum oxide. Inorganic oxides may be prepared by methods such as melting, sol-gel, and liquid-phase methods.

[0015] The inorganic particles to be subjected to the hydrophobization step may be inorganic particles that have been treated with a surface treatment agent. In addition, the method for producing inorganic particles according to the present embodiment may further include a surface treatment step of treating the inorganic particles with a surface treatment agent before the hydrophobization step. Furthermore, when inorganic particles that have not been subjected to treatment with a surface treatment agent are supplied to the hydrophobization step, a surface treatment step of treating the inorganic particles with a surface treatment agent may be further provided after the hydrophobization step. That is, the present embodiment includes the following aspects (a), (b) and (c). However, the surface treatment step is not essential, and a commercially available product can also be used as the inorganic particles treated with the surface treatment agent. In addition, the "surface treatment agent" as referred to herein does not include the hydrophobizing agent used in the hydrophobization step. (a) A method for producing inorganic particles, comprising a hydrophobization step of treating inorganic particles with at least one hydrophobizing agent selected from the group consisting of metal hydride compounds and organometallic compounds. (b) A method for producing inorganic particles, comprising: a surface treatment step of treating inorganic particles with a surface treatment agent; and a hydrophobization step of treating the inorganic particles after the surface treatment step with at least one hydrophobizing agent selected from the group consisting of metal hydride compounds and organometallic compounds. (c) A method for producing inorganic particles, comprising: a hydrophobization step of treating inorganic particles with at least one hydrophobizing agent selected from the group consisting of metal hydride compounds and organometallic compounds; and a surface treatment step of treating the inorganic particles after the hydrophobization step with a surface treatment agent.

[0016] According to the inventors' research, even when inorganic particles are treated with a surface treatment agent, hydroxyl groups and / or adsorbed water may remain on the surface of the treated inorganic particles. For example, among the hydroxyl groups present on the surface of inorganic oxide particles, isolated hydroxyl groups can react with surface treatment agents such as silane coupling agents, but hydrogen-bonding hydroxyl groups tend not to react with surface treatment agents. In conventional composite materials, even when surface-treated inorganic particles are used, the dispersibility tends to become insufficient as the amount of inorganic particles increases. This is thought to be due to hydrogen-bonding hydroxyl groups remaining on the surface of the inorganic particles, resulting in the surface of the inorganic particles not being sufficiently hydrophobized. In contrast, in the method for producing inorganic particles according to this embodiment, both isolated hydroxyl groups and hydrogen-bonding hydroxyl groups, as well as surface adsorbed water, can be sufficiently removed by a hydrophobic agent selected from the group consisting of metal hydride compounds and organometallic compounds. Therefore, it is thought that the dispersibility of inorganic particles in the resin can be sufficiently improved.

[0017] Examples of surface treatment agents include coupling agents such as silane coupling agents and titanium coupling agents; aliphatic carboxylic acids such as palmitic acid, stearic acid, arachidic acid, and oleic acid; aromatic carboxylic acids such as terephthalic acid, pyromellitic acid, and o-phenoxybenzoic acid; aliphatic alcohols such as cetyl alcohol, stearyl alcohol, isobornylcyclohexanol, and tetraethylene glycol; aromatic alcohols such as p-phenylphenol; alkylamines such as octylamine, dodecylamine, and stearylamine; aliphatic nitriles such as stearonitrile and decanonitrile; and polymeric treatment agents such as polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, or silicone oligomers. Surface treatment agents may be used individually or in combination of two or more.

[0018] When the inorganic particles are inorganic oxide particles such as silica particles and alumina particles, the surface treatment agent may be, for example, a silane coupling agent such as a trimethylsilylating agent. Examples of the trimethylsilylating agent include trimethylsilylazane, hexamethyldisilazane, trimethylchlorosilane, trimethylsilylimidazole, N,O-bis(trimethylsilyl)trifluoroacetamide, N-methyl-N-(trimethylsilyl)trifluoroacetamide, dimethyldichlorosilane and the like. The surface treatment with a silane coupling agent can be performed, for example, by dispersing inorganic particles in a dispersion medium, then adding the silane coupling agent and heating the mixture. The dispersion medium is preferably one that hardly reacts with the silane coupling agent, and examples thereof include methyl ethyl ketone, hexane, toluene, ethyl acetate and the like.

[0019] In the hydrophobization step, the metal hydride compound and organometallic compound used as the hydrophobizing agent are not particularly limited as long as they can remove hydroxyl groups and / or adsorbed water present on the surface of the inorganic particles.

[0020] The hydrophobizing agent may be, for example, a metal hydride compound. Examples of the metal hydride compound include lithium aluminum hydride (LiAlH ４ ), lithium hydride, sodium hydride, beryllium hydride, magnesium hydride, potassium hydride, calcium hydride, rubidium hydride, strontium hydride and the like.

[0021] For example, when the inorganic particles are silica particles and the hydrophobizing agent is lithium aluminum hydride, the reaction represented by the following formula (1) proceeds, and the surface of the silica particles is hydrophobized. That is, along with the reaction between the surface hydroxyl group of silica (OH of SiOH in formula (1)) and lithium aluminum hydride (LiAlH ４ ), Si-O-Li and (Si-O-) ３ Al are formed, and H ２ is generated. 4SiOH + LiAlH ４ →Si-O-Li + (Si-O-) ３ Al + 4H ２ (1)

[0022] Further, when the inorganic particles are alumina particles and the hydrophobizing agent is lithium aluminum hydride, the reaction represented by the following formula (2) proceeds, and the surfaces of the alumina particles are hydrophobized. That is, along with the reaction between the surface hydroxyl groups of alumina (the OH of AlOH in formula (2)) and lithium aluminum hydride (LiAlH ４ ), Al-O-Li and (Al-O-) ３ Al are formed, and H ２ is generated. 4AlOH + LiAlH ４ →Al-O-Li + (Al-O-) ３ Al + 4H ２ (2)

[0023] The hydrophobizing agent may be, for example, an organometallic compound. When an organometallic compound is used as the hydrophobizing agent, the surfaces of the inorganic particles can be modified with organic groups along with the hydrophobization of the inorganic particles, so that a surface treatment step does not need to be provided before or after the hydrophobization step. As the organometallic compound, for example, a Grignard reagent (RMgX: R represents an organic group such as an alkyl group or an aryl group, and X represents a halogen such as chlorine, bromine or iodine) can be used. Examples of the Grignard reagent include tert-butylmagnesium chloride, methylmagnesium chloride, methylmagnesium iodide, trimethylsilylmagnesium chloride, ethylmagnesium chloride, ethylmagnesium bromide, vinylmagnesium chloride, isopropylmagnesium chloride and the like. Further, as the organometallic compound, triethylaluminum, diethylaluminum ethoxide, triisobutylaluminum, diisobutylaluminum hydride and the like may be used.

[0024] The hydrophobizing agent can be used in the form of a solution (treatment liquid) obtained by dissolving the hydrophobizing agent in a solvent. Examples of the solvent include ethers such as diethylene glycol dimethyl ether and tetrahydrofuran. The content of the hydrophobizing agent in the treatment liquid may be, for example, 0.1 to 5 mol / L.

[0025] The treatment temperature in the hydrophobication process can be appropriately selected depending on the type and amount of inorganic particles, the type and amount of hydrophobic agent, etc. For example, if the inorganic particles are inorganic oxides such as silica and alumina, and the hydrophobic agent is lithium aluminum hydride, the treatment temperature may be, for example, 0 to 30°C. The hydrophobication process can be carried out, for example, in an inert gas atmosphere such as nitrogen, or in a dry air atmosphere.

[0026] The amount of hydrophobic agent used and the processing time can be appropriately selected depending on the type and amount of inorganic particles, the type of hydrophobic agent, etc. Furthermore, for example, if the inorganic particles are inorganic oxide particles such as silica and alumina, and the hydrophobic agent is lithium aluminum hydride, the H produced as the reaction progresses... ２ Collect the gas, H ２ The point at which gas production ceases can be considered the endpoint of the reaction. Furthermore, according to equations (1) and (2) above, H ２ The amount of gas in moles corresponds to the amount of hydroxyl groups on the surface of inorganic oxide particles, so the collected H ２ The amount of gas can be used to estimate the amount of surface hydroxyl groups on inorganic oxide particles.

[0027] The inorganic particle manufacturing method according to this embodiment allows for sufficient removal of surface hydroxyl groups and / or adsorbed water from the inorganic particles. As a result, inorganic particles can be obtained that have good dispersibility in resins and can impart various properties to composite materials, such as physical properties (mechanical strength, heat resistance, moisture resistance, etc.), thermal properties (thermal conductivity, etc.), electrical properties (insulation, conductivity, low dielectric properties, etc.), and magnetic properties. Therefore, the inorganic particle manufacturing method according to this embodiment is useful in the manufacture of inorganic fillers (inorganic fillers) blended into laminate materials, encapsulants, NCF (Non-Conductive Film), ACF (Anisotropic Conductive Film), DAF (Die Attach Film), etc.; conductive particles blended into conductive adhesives, ACF, etc.; and magnetic particles blended into magnetic materials.

[0028] [Method for Manufacturing Composite Materials] Another embodiment of the present disclosure relates to a method for manufacturing composite materials. The method for manufacturing composite materials according to this embodiment comprises the step of mixing inorganic particles obtained by the above-described method for manufacturing inorganic particles with a resin composition.

[0029] The resin composition may be, for example, a thermosetting resin composition. Examples of resin components included in the thermosetting resin composition include epoxy resins, polyimide resins, phenolic resins, and triazine resins (such as melamine resins). The thermosetting resin composition may also contain additives such as polymerizable monomers (such as (meth)acrylic monomers), curing agents, and curing accelerators.

[0030] The resin composition may be, for example, a photocurable resin composition. Examples of resin components included in the photocurable resin composition include acrylic resin (acrylate resin), epoxy resin, polyurethane resin, and polyester resin. The photocurable resin composition may also contain additives such as polymerizable monomers such as (meth)acrylic monomers, photopolymerization initiators, ultraviolet absorbers, and sensitizers.

[0031] When composite materials are used in the form of a film, the resin composition may include a film-forming agent (for example, thermoplastic resins such as phenoxy resin, polystyrene resin, polyester resin, or polyvinyl butyral resin).

[0032] The mixing of inorganic particles and the resin composition may be carried out without a solvent or with a predetermined solvent. The mixing method is not particularly limited, and for example, a stirring blade, a rotational stirring method, a planetary mixer, a roll mill, a disc mill, or a ball mill can be used. The processing conditions such as temperature and time during mixing can be selected as appropriate.

[0033] According to the method for manufacturing composite materials of this embodiment, the dispersibility of inorganic particles in the resin composition is good, thus improving various properties such as physical properties (mechanical strength, heat resistance, moisture resistance, etc.), thermal properties (thermal conductivity, etc.), electrical properties (insulation, conductivity, low dielectric properties, etc.), and magnetic properties. Therefore, the method for manufacturing composite materials of this embodiment is useful, for example, in the manufacture of laminate materials, encapsulants, NCF, high heat dissipation NCF, ACF, DAF, conductive adhesives, magnetic materials, and the like.

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

[0035] [Example 1] (Inorganic particles) Silica particles were used as inorganic particles (product name: KE-S50, manufactured by Nippon Shokubai Co., Ltd., surface area: 5.5 m²). ２ A sample of silica ( / g) was prepared. Before subjecting the silica particles to the hydrophobicization process, they were pre-dried at 160°C for 5 hours under vacuum, and then stored in an argon atmosphere. For the silica particles, a moisture content analysis was performed to determine the contribution of adsorbed water remaining on the silica particle surface after the pre-drying and vacuum drying in the reaction vessel, as described later. Specifically, the silica particles were vacuum-dried at 160°C for 7 hours (corresponding to the total processing time for pre-drying and vacuum drying in the reaction vessel), and then a moisture content analysis was performed. The moisture content analysis was performed under the following conditions, and the average of two measured values ​​was taken as the moisture content. Measurement method: Karl Fischer method (moisture vaporization method + coulometric titration method) Equipment: Hiranuma Sangyo Co., Ltd. AQ-300 (measurement unit), EV-2000 (vaporizer) Reagents: Kanto Chemical Co., Ltd. Aqualight RS-A 150 mL, Aqualight CN 15 mL Moisture vaporization conditions: 250°C 5 min, Ar 150 ml / min Amount of flow sample (silica particles): 0.1 g.

[0036] (Hydrophobic agent) LiAlH in a glove bag at room temperature ４ The powder (product name: lithium aluminum hydride, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 95% by mass) is added to anhydrous diethylene glycol dimethyl ether (water content by Karl Fischer method: less than 50 ppm) and stirred, and LiAlH ４ Solution (LiAlH ４A concentration of 0.2 mol / L was obtained.

[0037] (Hydrophobicization process) 1 g of the above silica particles was placed in a reaction vessel (two-necked round-bottom flask), and adsorbed water was removed by vacuum drying at 160°C for 2 hours. Next, LiAlH was used with a syringe. ４ 20 mL of the solution was poured into the reaction vessel, and the silica particle surface was hydrophobized at room temperature. During this process, H₂O₃ was generated as the hydrophobization progressed. ２ The gas was collected in a graduated cylinder (capacity 50 mL) by water displacement. After no further increase in the collected gas was observed, ethanol was injected into the reaction vessel, and gas generation was confirmed. The gas generation due to the addition of ethanol was due to the excess LiAlH in the reaction vessel after hydrophobization. ４ This means that a sufficient amount of LiAlH remained, which was enough to react with the hydroxyl groups on the surface of the silica particles. ４ It can be seen that it was injected. Also, as a blank measurement, LiAlH was used with a syringe in the same manner as above, except that silica particles were not placed in the reaction vessel. ４ The solution was poured into the reaction vessel, and the amount of gas generated was checked. This gas contained LiAlH ４ Air pushed out of the reaction vessel by the injection of the solution, and H generated by the reaction with the reaction vessel. ２ It contains volatile components of gas and solvent. Hydrophobicity of the silica particle surface is given by the following formula (1): 4SiOH + LiAlH ４ →Si-O-Li+ (Si-O-) ３ Al + 4H ２ The process proceeds according to (1), and all hydroxyl groups on the surface of the silica particles (isolated hydroxyl groups and hydrogen-bonded hydroxyl groups) are converted to LiAlH ４ Assuming that the surface was hydrophobized by [the following factor], the amount of surface hydroxyl groups was calculated. That is, according to the equation of state PV = nRT, the amount of collected H ２ The volume of the gas at room temperature (a corrected value obtained by subtracting the contribution of adsorbed water remaining after the blank measurement of gas generation and drying at 160°C for 7 hours) was converted to the volume at 0°C. ２ The volume of the gas at 0°C (converted value) is divided by 22.4 L (volume of 1 mol of gas at 0°C), and the amount of H generated per gram of silica particles is calculated. ２ The number of moles of gas was calculated.２ The number of surface hydroxyl groups per unit area can be calculated from the number of moles of gas (corresponding to the number of moles of surface hydroxyl groups per gram of silica particles; see formula (1) above) and the surface area of ​​the silica particles, resulting in 4.6 groups / nm. ２ That was the case.

[0038] (Evaluation of Dispersibility) The dispersibility of the hydrophobized silica particles obtained in the above hydrophobicization process in a solvent (water or methyl isobutyl ketone (MIBK)) was evaluated using the following procedure. Hydrophobized silica particles and each solvent were placed in a screw tube (capacity 10 ml), and the dispersion treatment was performed in an ultrasonic bath for 5 minutes to obtain a dispersion (content of hydrophobized silica particles: 0.1 mass%). The average particle size of the silica particles in the obtained dispersion was measured using a particle size analyzer (product name: nanoSAQLA, manufactured by Otsuka Electronics Co., Ltd.). The results are shown in Table 1. When the solvent is water, a smaller average particle size value indicates higher hydrophilicity. When the solvent is methyl isobutyl ketone, a smaller average particle size value indicates higher hydrophobicity.

[0039] (Evaluation of Dielectric Properties) The dielectric properties of the hydrophobized silica particles obtained in the above hydrophobicization process were evaluated in accordance with JIS C2565:1992 (Test Method for Microwave Ferrite Magnetic Cores). The filler to be measured was packed into a quartz tube and inserted into a 10 GHz resonator (AET, cavity resonator method (TM mode)) connected to a network analyzer "P9377B" (Keysight Technologies), and the dielectric constant and dielectric loss tangent were measured under 10 GHz conditions. The values ​​of dielectric constant and dielectric properties were corrected so that the volume fraction of the filler to be measured was 100%. The obtained results are shown in Table 1.

[0040] [Example 2] The hydrophobicization process and evaluation of dispersibility and dielectric properties were carried out in the same manner as in Example 1, except that a Grignard reagent (1 mol / L solution of tert-butylmagnesium chloride, solvent: tetrahydrofuran) was used as the hydrophobic agent. The results obtained are shown in Table 1.

[0041] [Example 3] The hydrophobicization process was carried out in the same manner as in Example 1, except that the inorganic particles used were silica particles (untreated silica particles) similar to those in Example 1, but with a silane coupling agent (trimethylsilazane) applied to the surface (hereinafter referred to as "surface-treated silica particles"). H collected in the hydrophobicization process ２ Based on the amount of gas, the number of surface hydroxyl groups was calculated in the same manner as in Example 1, resulting in 1.5 groups / nm. ２ In this example, all isolated hydroxyl groups on the silica particle surface react with the silane coupling agent, and all hydrogen-bonding hydroxyl groups on the surface-treated silica particle surface react with LiAlH ４ Assuming hydrophobicity is achieved, the total number of hydroxyl groups on the surface of untreated silica particles is 4.6 groups / nm. ２ (Value calculated in Example 1), the number of hydrogen-bonding hydroxyl groups is 1.5 / nm ２ The number of isolated hydroxyl groups is 4.6 - 1.5 = 3.1 per nm. ２ It was estimated that this was the case. Furthermore, the dispersibility and dielectric properties of the surface-treated silica particles after the hydrophobicization process were evaluated in the same manner as in Example 1. The results obtained are shown in Table 1.

[0042] [Comparative Example 1] Dispersibility and dielectric properties were evaluated in the same manner as in Example 1, except that untreated silica particles similar to those in Example 1 were used as inorganic particles. The results obtained are shown in Table 1.

[0043]

[0044] [Example 4] Alumina particles as inorganic particles (product name: AA-04, manufactured by Sumitomo Chemical Co., Ltd., surface area: 4.6 m²) ２ The hydrophobicization process was carried out in the same manner as in Example 1, except that ( / g) was used. Hydrophobicization of the alumina particle surface was performed using the following formula (2): 4AlOH + LiAlH ４ →Al-O-Li+ (Al-O-) ３ Al + 4H ２ (2) The process proceeds according to (2), and all hydroxyl groups on the surface of the alumina particles (isolated hydroxyl groups and hydrogen-bonded hydroxyl groups) become LiAlH ４ Assuming that the surface was hydrophobized by [the following factor], the amount of surface hydroxyl groups was calculated. That is, according to the equation of state PV = nRT, the amount of collected H２ The volume of the gas at room temperature (a corrected value obtained by subtracting the contribution of adsorbed water remaining after the blank measurement of gas generation and drying at 160°C for 7 hours) was converted to the volume at 0°C. ２ The volume of the gas at 0°C (converted value) is divided by 22.4 L (volume of 1 mol of gas at 0°C), and the amount of H generated per gram of alumina particles is calculated. ２ The number of moles of gas was calculated. This H ２ Using the number of moles of gas (corresponding to the number of moles of surface hydroxyl groups per gram of alumina particles, see formula (2) above) and the surface area of ​​the alumina particles, the number of surface hydroxyl groups per unit area can be calculated to be 7.9 groups / nm. ２ The hydrophobized alumina particles obtained in the hydrophobicization process were evaluated for their dispersibility and dielectric properties in the same manner as in Example 1. The results are shown in Table 2.

[0045] [Example 5] The hydrophobicization process and evaluation of dispersibility and dielectric properties were carried out in the same manner as in Example 1, except that alumina particles similar to those in Example 4 were used as inorganic particles and a Grignard reagent similar to that in Example 2 was used as the hydrophobic agent. The results obtained are shown in Table 2.

[0046] [Example 6] The hydrophobicization process was carried out in the same manner as in Example 1, except that the inorganic particles used were alumina particles (untreated alumina particles) similar to those in Example 4, which were surface-treated with a silane coupling agent (trimethylsilazane) (hereinafter referred to as "surface-treated alumina particles"). H collected in the hydrophobicization process ２ Based on the amount of gas, the number of surface hydroxyl groups was calculated in the same manner as in Example 4, resulting in 5.5 groups / nm. ２ In this example, all isolated hydroxyl groups on the surface of the alumina particles reacted with the silane coupling agent, and all hydrogen-bonding hydroxyl groups on the surface of the surface-treated alumina particles reacted with LiAlH ４ Assuming hydrophobization occurs, the total number of hydroxyl groups on the surface of untreated alumina particles is 7.9 groups / nm. ２ (Value calculated in Example 4), the number of hydrogen-bonding hydroxyl groups is 5.5 / nm ２ The number of isolated hydroxyl groups is 7.9 - 5.5 = 2.4 per nm. ２It was estimated that this was the case. Furthermore, the dispersibility and dielectric properties of the surface-treated alumina particles after the hydrophobicization process were evaluated in the same manner as in Example 1. The results obtained are shown in Table 2.

[0047] [Comparative Example 2] Dispersibility and dielectric properties were evaluated in the same manner as in Example 1, except that untreated alumina particles, similar to those in Example 4, were used as inorganic particles. The results obtained are shown in Table 2.

[0048]

Claims

1. A method for producing inorganic particles, comprising the step of treating inorganic particles with at least one hydrophobic agent selected from the group consisting of metal hydride compounds and organometallic compounds.

2. The method for producing inorganic particles according to claim 1, wherein the hydrophobic agent is at least one selected from lithium aluminum hydride and Grignard reagents.

3. The method for producing inorganic particles according to claim 1, wherein the inorganic particles are inorganic particles treated with a surface treatment agent.

4. The method for producing inorganic particles according to claim 3, wherein the inorganic particles are inorganic oxide particles and the surface treatment agent is a coupling agent.

5. The method for producing inorganic particles according to claim 3, wherein the inorganic particles are silica particles or alumina particles, and the surface treatment agent is a silane coupling agent.

6. A method for producing a composite material, comprising the step of mixing inorganic particles obtained by the method for producing inorganic particles according to any one of claims 1 to 5 with a resin composition.

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