Method for selecting inorganic filler, method for manufacturing surface-modified inorganic filler, and method for manufacturing composite material

Abstract

The present invention provides a method for selecting an inorganic filler, which can select an inorganic filler suitable for use in combination with a silane coupling agent using a functional group present on the filler surface as an index, and a method for producing a surface-treated inorganic filler and a method for producing a composite material using the selected inorganic filler. [Solution] The method for selecting an inorganic filler is a method for selecting an inorganic filler having a hydroxyl group, and includes the steps of: reacting the inorganic filler having a hydroxyl group with a trimethylsilylating agent to obtain an inorganic filler having a trimethylsilyl group; measuring the carbon concentration in the inorganic filler having a trimethylsilyl group by elemental analysis and calculating the concentration A of trimethylsilylated hydroxyl groups in the inorganic filler having a trimethylsilyl group based on the carbon concentration; and selecting an inorganic filler having a hydroxyl group based on the hydroxyl group concentration A.

Description

[Technical Field]

[0001] The present invention relates to a method for selecting an inorganic filler, a method for producing a surface-modified inorganic filler, and a method for producing a composite material. [Background technology]

[0002] Silane coupling agents have a structure in which both functional groups that react with organic materials and functional groups that react with inorganic materials are present within the molecule, and are widely used for purposes such as surface modification of inorganic materials and improving adhesion between organic and inorganic materials in composites. Silane coupling agents are used in a wide range of product fields, including electronic materials, mobility, and infrastructure facilities. For example, it is known that silane coupling agents are added to organic materials such as epoxy resins and inorganic fillers, which are inorganic materials, when manufacturing epoxy molding compounds (EMCs), which are a type of sealing material (see Patent Documents 1 and 2 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-96205 [Patent Document 2] Japanese Patent Publication No. 2023-48215 Summary of the Invention [Problem to be solved by the invention]

[0004] The inorganic fillers used in the above methods contain functional groups that form chemical bonds when surface modifiers such as silane coupling agents react with them, and the concentration of these functional groups can vary depending on the manufacturing process. For example, the concentration of hydroxyl groups present on the surface of fused silica fillers varies depending on the processing temperature during the manufacturing process. Higher processing temperatures tend to result in a lower concentration of hydroxyl groups on the surface than lower-temperature processed silica fillers, as more dehydration condensation reactions between hydroxyl groups occur. Thus, the surface functional group concentration of inorganic fillers varies depending on the manufacturing method, and this affects the properties of the composite (e.g., fluidity, thermal expansion coefficient, etc.).

[0005] Therefore, the present invention aims to provide a method for selecting an inorganic filler that can select an inorganic filler suitable for use in combination with a silane coupling agent using functional groups present on the filler surface as an indicator, as well as a method for producing a surface-treated inorganic filler and a method for producing a composite material using the selected inorganic filler. [Means for solving the problem]

[0006] In some aspects, the present invention provides the following [1] to [5].

[0007] [1] A method for selecting an inorganic filler having a hydroxyl group, comprising the steps of: reacting the inorganic filler having a hydroxyl group with a trimethylsilylating agent to obtain an inorganic filler having a trimethylsilyl group; measuring the carbon concentration in the inorganic filler having a trimethylsilyl group by elemental analysis and calculating a concentration A of trimethylsilylated hydroxyl groups in the inorganic filler having a trimethylsilyl group based on the carbon concentration; and selecting an inorganic filler having a hydroxyl group based on the hydroxyl group concentration A. [2] A method for selecting an inorganic filler having hydroxyl groups, comprising the steps of: reacting the inorganic filler having hydroxyl groups with a trimethylsilylating agent to obtain an inorganic filler having trimethylsilyl groups; measuring the carbon concentration in the inorganic filler having trimethylsilyl groups by elemental analysis and calculating the concentration A of trimethylsilylated hydroxyl groups in the inorganic filler having trimethylsilyl groups based on the carbon concentration; calculating the hydroxyl group concentration T in the inorganic filler having hydroxyl groups by a lithium aluminum hydride method; and selecting an inorganic filler having hydroxyl groups based on the hydroxyl group concentration A and the ratio X of the hydroxyl group concentration A to the hydroxyl group concentration T. [3] A method for selecting an inorganic filler having a hydroxyl group, comprising the steps of: reacting the inorganic filler having a hydroxyl group with a trimethylsilylating agent to obtain an inorganic filler having a trimethylsilyl group; measuring the carbon concentration in the inorganic filler having a trimethylsilyl group by elemental analysis and calculating a concentration A of trimethylsilylated hydroxyl groups in the inorganic filler having a trimethylsilyl group based on the carbon concentration; calculating a hydroxyl group concentration B in the inorganic filler having a trimethylsilyl group by a lithium aluminum hydride method; and selecting an inorganic filler having a hydroxyl group based on the hydroxyl group concentration A, the hydroxyl group concentration B, and / or a ratio Y of the hydroxyl group concentration A to the total concentration of the hydroxyl group concentration A and the hydroxyl group concentration B. [4] The method for selecting an inorganic filler according to any one of [1] to [3], wherein the trimethylsilylating agent is hexamethyldisilazane. [5] A method for producing a surface-modified inorganic filler, comprising a step of reacting an inorganic filler having a hydroxyl group concentration A within a predetermined range, selected by the selection method according to any one of [1] to [4], with a silane coupling agent capable of reacting with and bonding to hydroxyl groups. [6] A method for producing a composite material, comprising the steps of: preparing a composite material precursor containing an inorganic filler having a hydroxyl group concentration A and a ratio X each within a predetermined range, selected by the selection method described in [2]; a silane coupling agent capable of reacting with and bonding to the hydroxyl groups; and a resin. [7] A method for producing a composite material, comprising the steps of: preparing a composite material precursor containing an inorganic filler having a hydroxyl group concentration A, a hydroxyl group concentration B, and / or a ratio Y, each of which is within a predetermined range, selected by the selection method described in [3]; a silane coupling agent capable of reacting with and bonding to the hydroxyl groups; and a resin. [8] The method for producing a composite material according to [6] or [7], wherein the composite material is a dielectric material. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for selecting an inorganic filler that can select an inorganic filler suitable for use in combination with a silane coupling agent using functional groups present on the filler surface as an indicator, as well as a method for producing a surface-treated inorganic filler and a method for producing a composite material using the selected inorganic filler. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes in detail an embodiment of the present invention (hereinafter referred to as the "present embodiment"). The present invention is not limited to the following embodiment.

[0010] <How to select inorganic fillers> (First selection method) The first selection method for an inorganic filler of the present embodiment is a method for selecting an inorganic filler having a hydroxyl group, and includes step A1 of reacting an inorganic filler having a hydroxyl group with a trimethylsilylating agent to obtain an inorganic filler having a trimethylsilyl group; step A2 of measuring the carbon concentration in the inorganic filler having a trimethylsilyl group by elemental analysis and calculating the concentration A of trimethylsilylated hydroxyl groups in the inorganic filler having a trimethylsilyl group based on the carbon concentration; and step D1 of selecting an inorganic filler having a hydroxyl group based on the hydroxyl group concentration A.

[0011] [Process A1] Examples of inorganic fillers having hydroxyl groups include silica particles, boron nitride, zeolite, aluminum oxide (alumina), titanium oxide (titania), and other metal oxides.

[0012] The inorganic filler having a hydroxyl group can be obtained by a known method. For example, silica particles may be synthesized by a melting method or a sol-gel method.

[0013] The average primary particle size of the inorganic filler may be 0.005 to 100 μm, 0.05 to 50 μm, or 0.3 to 30 μm. In this specification, the average primary particle size of particles means the d50 value (median diameter) in the particle size distribution obtained using a particle size distribution measuring device.

[0014] Examples of trimethylsilylating agents that can be used include hexamethyldisilazane, trimethylchlorosilane, trimethylsilylimidazole, N,O-bis(trimethylsilyl)trifluoroacetamide, N-methyl-N-(trimethylsilyl)trifluoroacetamide, dimethyldichlorosilane, etc. Among these, hexamethyldisilazane can be used from the viewpoints of high reactivity, being halogen-free, and cost.

[0015] The reaction between the inorganic filler having a hydroxyl group and the trimethylsilylating agent can be carried out, for example, by dispersing the inorganic filler in a dispersion medium, adding the trimethylsilylating agent, and heating.

[0016] As the dispersion medium, a solvent that does not react with the trimethylsilylating agent, such as methyl ethyl ketone, hexane, toluene, or ethyl acetate, can be used.

[0017] The amount of the trimethylsilylating agent added can be set based on the mass of 1 equivalent defined by the following formula, and may be 1 to 10 equivalents, or 3 to 7 equivalents. Mass of 1 equivalent of trimethylsilylating agent (g) = [Mass of inorganic filler (g)] × [Specific surface area of ​​inorganic filler (m 2 / g)] / [minimum coverage area of ​​trimethylsilylating agent (m 2 / g)] The minimum coverage area of ​​the trimethylsilylating agent can be calculated using the Stuart-Briegleb molecular model. Specifically, the area occupied by one molecule of the trimethylsilylating agent when it is bonded to the surface of an inorganic filler having a hydroxyl group is calculated as 13 × 10, which corresponds to the area of ​​a circle with a radius equal to the distance between the Si-O bonds. -20 (m 2 ) and convert it into the exclusive area per unit mass shown in the following formula, the minimum coverage area can be calculated. Minimum coverage area=[NA×(13×10 -20 )] / [M / n] [In the formula, NA represents Avogadro's constant, M represents the molecular weight of the trimethylsilylating agent, and n represents the number of Si atoms present in one molecule of the trimethylsilylating agent that can react with hydroxyl groups.]

[0018] The heating temperature may be 20 to 120° C., or may be 55 to 65° C. The heating time may be 1 to 10 hours, or may be 3 to 5 hours.

[0019] In step A1, the reaction product (inorganic filler having trimethylsilyl groups) may be purified after the reaction. For example, the purification may be performed by filtering, washing with a solvent, and drying under reduced pressure, in this order. Specifically, the reaction product can be purified by filtering the reaction solution to obtain a filter cake, washing it with the dispersion medium used in the reaction, and then drying it under reduced pressure at room temperature to 40°C.

[0020] [Process A2] The carbon concentration in the inorganic filler having a trimethylsilyl group can be measured by elemental analysis according to the following procedure. (1) 200 mg of sample is weighed into a ceramic crucible and a combustion improver is added. (2) Using a carbon-sulfur analyzer, the amount of carbon (g) in 1 g of sample is determined by the high-frequency heating infrared absorption method.

[0021] As the combustion improver, for example, W powder, Sn powder, etc. can be used.

[0022] As the carbon / sulfur analyzer, "EMIA-920V" (product name, manufactured by HORIBA Corporation), "CS844" (product name, manufactured by LECO Corporation), or the like can be used.

[0023] The concentration A of trimethylsilylated hydroxyl groups in an inorganic filler having trimethylsilyl groups is calculated from the amount of carbon (g) in 1 g of the sample obtained above according to the following formula. Hydroxyl group concentration A (mol / g) = [amount of carbon (g) in 1 g of sample] / [3 x 12.011]

[0024] [Process D1] The hydroxyl group concentration A calculated in step A2 can be used as an index showing the concentration of hydroxyl groups (hereinafter sometimes referred to as "isolated hydroxyl groups") that can react with a coupling agent and bond in an inorganic filler having hydroxyl groups. Therefore, by using the hydroxyl group concentration A as an index, it is possible to select an inorganic filler that can bond with a desired amount of silane coupling agent depending on the type of silane coupling agent.

[0025] Furthermore, the selection method according to this embodiment allows for the formation of a trimethylsilyl group with a relatively small size, making it possible to adequately estimate the amount of a silane coupling agent that is commonly used as a surface treatment agent.

[0026] (Second selection method) The second selection method for an inorganic filler of the present embodiment is a method for selecting an inorganic filler having a hydroxyl group, and includes: a step A1 of reacting an inorganic filler having a hydroxyl group with a trimethylsilylating agent to obtain an inorganic filler having a trimethylsilyl group; a step A2 of measuring the carbon concentration in the inorganic filler having a trimethylsilyl group by elemental analysis and calculating the concentration A of trimethylsilylated hydroxyl groups in the inorganic filler having a trimethylsilyl group based on the carbon concentration; a step T1 of calculating the hydroxyl group concentration T in the inorganic filler having a hydroxyl group by a lithium aluminum hydride method; and a step D2 of selecting an inorganic filler having a hydroxyl group based on the hydroxyl group concentration A and the ratio X of the hydroxyl group concentration A to the hydroxyl group concentration T.

[0027] [Process A1 and Process A2] Steps A1 and A2 can be performed in the same manner as steps A1 and A2 in the first selection method.

[0028] [Process T1] The lithium aluminum hydride method involves reacting hydroxyl groups with lithium aluminum hydride in a solvent and measuring the amount of hydrogen generated. The amount of hydrogen generated can be measured using the following procedure. (1) Place 6 g of sample in a two-necked recovery flask and vacuum dry at 160°C for 2 hours. (2) A tetrahydrofuran solution containing lithium aluminum hydride at a concentration of 0.2 mol / L is added to a two-necked recovery flask. (3) The gas generated by the reaction is collected in a measuring cylinder using the water displacement method, and the volume (L) of the gas generated is measured.

[0029] The hydroxyl group concentration T in the inorganic filler having hydroxyl groups is calculated from the volume of gas generated per 1 g of sample (L / g, @0° C.) according to the following formula: Hydroxyl group concentration T (mol / g) = [Volume of gas generated per 1 g of sample (L / g, @0°C)] / 22.4

[0030] [Process D2] As described above, the hydroxyl group concentration A calculated in step A2 can be used as an index showing the concentration of isolated hydroxyl groups in an inorganic filler having hydroxyl groups. Therefore, by using the hydroxyl group concentration A as an index, it is possible to select an inorganic filler to which a desired amount of silane coupling agent can be bonded depending on the type of silane coupling agent.

[0031] Incidentally, two methods are known for synthesizing composite materials by mixing inorganic materials such as fillers with organic materials such as resins: one method involves reacting the filler with a silane coupling agent in advance and then mixing it with the resin, and the other method involves simultaneously mixing the filler, silane coupling agent, and resin (the integral blend method). The latter, the integral blend method, is widely used because of its ease of use when performing large-scale synthesis in factories, but with this method it is difficult to confirm the extent to which the filler and silane coupling agent have reacted.

[0032] Furthermore, the properties of composites containing inorganic fillers can be affected not only by the surface modification of the inorganic filler by the silane coupling agent, but also by the polar groups present on the surface. For example, dielectric properties, one of the physical properties, are known to be affected by the amount of polar groups such as hydroxyl groups. The higher the polarizability per unit volume, the greater the dielectric properties (Clausius-Mossotti relation). Therefore, when a composite material is dielectric, obtained using an inorganic filler with hydroxyl groups and a coupling agent, the greater the hydroxyl groups present in the inorganic filler, the worse its dielectric properties (e.g., the higher the dielectric constant and dielectric loss tangent).

[0033] The hydroxyl group concentration T obtained in step T1 indicates the concentration of all hydroxyl groups in the hydroxyl group-containing inorganic filler, and therefore the ratio X of the hydroxyl group concentration A to the hydroxyl group concentration T can be used as an index indicating the proportion of hydroxyl groups in the hydroxyl group-containing inorganic filler that can be reacted with a silane coupling agent to bond (hereinafter also referred to as the "hydroxyl group reaction rate"). In addition, the amount of hydroxyl groups remaining unreacted on the surface of the inorganic filler can also be calculated from the hydroxyl group reaction rate.

[0034] Therefore, by using the hydroxyl group concentration A and the ratio X as indicators, it is possible to estimate the amount of silane coupling agent that can bond with an inorganic filler depending on the type of silane coupling agent, and to select an inorganic filler that will have a desired range of hydroxyl groups remaining after reaction with the coupling agent (hereinafter also referred to as "residual hydroxyl groups"). Furthermore, the hydroxyl group concentration A and the ratio X can be used to confirm or modify the reaction conditions between the inorganic filler and the coupling agent in the integral blend method.

[0035] The above selection method can also be used when selecting an inorganic filler to be used in the integral blend method, and is particularly useful in the production of dielectrics.

[0036] (Third selection method) The third selection method for an inorganic filler of the present embodiment is a method for selecting an inorganic filler having a hydroxyl group, and includes: a step A1 of reacting an inorganic filler having a hydroxyl group with a trimethylsilylating agent to obtain an inorganic filler having a trimethylsilyl group; a step A2 of measuring the carbon concentration in the inorganic filler having a trimethylsilyl group by elemental analysis and calculating the concentration A of trimethylsilylated hydroxyl groups in the inorganic filler having a trimethylsilyl group based on the carbon concentration; a step B1 of calculating the hydroxyl group concentration B in the inorganic filler having a trimethylsilyl group by a lithium aluminum hydride method; and a step D3 of selecting an inorganic filler having a hydroxyl group based on the hydroxyl group concentration A, the hydroxyl group concentration B, and / or the ratio Y of the hydroxyl group concentration A to the total concentration of the hydroxyl group concentration A and the hydroxyl group concentration B.

[0037] [Process A1 and Process A2] Steps A1 and A2 can be performed in the same manner as steps A1 and A2 in the first selection method.

[0038] [Process B1] In step B1, the hydroxyl group concentration B in the inorganic filler having trimethylsilyl groups obtained in step A1 is calculated by the following procedure. (1) Place 6 g of sample in a two-necked recovery flask and vacuum dry at 160°C for 2 hours. (2) A tetrahydrofuran solution containing lithium aluminum hydride at a concentration of 0.2 mol / L is added to a two-necked recovery flask. (3) The gas generated by the reaction is collected in a measuring cylinder using the water displacement method, and the volume (L) of the gas generated is measured. (4) Calculate the hydroxyl group concentration T from the volume of gas generated per 1 g of sample (L / g, @0°C) according to the following formula. Hydroxyl group concentration B (mol / g) = [Volume of gas generated per 1 g of sample (L / g, at 0°C)] / 22.4

[0039] [Process D3] As described above, the hydroxyl group concentration A calculated in step A2 can be used as an index showing the concentration of isolated hydroxyl groups in an inorganic filler having hydroxyl groups. Therefore, by using the hydroxyl group concentration A as an index, it is possible to select an inorganic filler to which a desired amount of silane coupling agent can be bonded depending on the type of silane coupling agent.

[0040] The hydroxyl group concentration B calculated in step B1 can be used as an index showing the concentration of unreacted hydroxyl groups in the inorganic filler having trimethylsilyl groups. Therefore, by using the hydroxyl group concentration A and the hydroxyl group concentration B as indices, it is possible to estimate the amount of silane coupling agent that can bond with the inorganic filler depending on the type of silane coupling agent, and to select an inorganic filler that has a desired range of residual hydroxyl groups. Furthermore, the hydroxyl group concentrations A and B can be used to confirm or modify the reaction conditions between the inorganic filler and the coupling agent in the integral blend method.

[0041] Furthermore, the ratio Y of the hydroxyl group concentration A to the total concentration of the hydroxyl group concentration A and the hydroxyl group concentration B can be used as an index showing the reaction rate of the hydroxyl groups in the inorganic filler having hydroxyl groups.

[0042] Furthermore, according to the third selection method described above, it is possible to obtain an index for determining the amount of adsorbed water in an inorganic filler having hydroxyl groups or an inorganic filler whose surface has been modified with a silane coupling agent. If an inorganic filler has a large number of hydroxyl groups, the amount of adsorbed water in the inorganic filler is likely to increase, leading to deterioration of the dielectric properties. Therefore, information on the hydroxyl group concentration obtained by the third selection method is useful when producing a dielectric using an inorganic filler having hydroxyl groups and a silane coupling agent.

[0043] <Method for manufacturing surface-modified inorganic filler> The method for producing the surface-modified inorganic filler of this embodiment includes a step of reacting an inorganic filler having a hydroxyl group concentration A within a predetermined range, selected by any of the first to third selection methods described above, with a silane coupling agent that can react with and bond to the hydroxyl groups.

[0044] According to the method for producing a surface-modified inorganic filler of this embodiment, a surface-modified inorganic filler having desired properties can be stably obtained.

[0045] <Manufacturing method for composite materials> (First manufacturing method) The first method for producing a composite material of this embodiment includes a step of preparing a composite material precursor containing an inorganic filler having a hydroxyl group concentration A and a hydroxyl group ratio X each within a predetermined range, selected by the second selection method described above, a silane coupling agent capable of reacting with and bonding to the hydroxyl groups, and a resin.

[0046] (Second manufacturing method) The second manufacturing method of the composite material of this embodiment includes a step of preparing a composite material precursor containing an inorganic filler having a hydroxyl group concentration A, a hydroxyl group concentration B and / or a ratio Y each within a predetermined range selected by the third selection method described above, a silane coupling agent capable of reacting with and bonding to the hydroxyl groups, and a resin.

[0047] In the first and second production methods, the composite precursor can be converted into a composite material by optionally undergoing treatments such as heating, molding, and curing.

[0048] According to the first and second manufacturing methods described above, composite materials having desired properties can be stably obtained.

[0049] In the first and second manufacturing methods, the composite material may be a dielectric material, in which case a composite material having desired dielectric properties can be stably obtained. [Example]

[0050] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples.

[0051] Example 1 (Process A1 and Process A2) 1 g of silica filler "KE-S50" (trade name, manufactured by Nippon Shokubai Co., Ltd.) and 5 g of methyl ethyl ketone were placed in a vial that had been stored in a desiccator at 0% RH and subjected to ultrasonic treatment in an ultrasonic cleaner for 10 minutes. Five equivalents of hexamethyldisilazane were then added and the mixture was heated at 60°C for 4 hours. After air-cooling to room temperature, the mixture was suction filtered, washed with a solvent, and dried under reduced pressure to obtain a silica filler trimethylsilylated with hexamethyldisilazane.

[0052] The carbon concentration in the trimethylsilylated silica filler obtained above was measured by the following procedure. (1) 200 mg of sample is weighed into a ceramic crucible and combustion improver (W powder, Sn powder) is added. (2) Using a carbon-sulfur analyzer "EMIA-920V" (manufactured by HORIBA Corporation, product name), the amount of carbon (g) in 1 g of sample is determined by the high-frequency heating infrared absorption method. (3) From the amount of carbon (g) in 1 g of sample obtained above, calculate the hydroxyl group concentration A in the trimethylsilylated silica filler according to the following formula. Hydroxyl group concentration A (mol / g) = [amount of carbon (g) in 1 g of sample] / [3 x 12.011]

[0053] (Process T1) The hydroxyl group concentration T of silica filler "KE-S50" (product name, manufactured by Nippon Shokubai Co., Ltd.) was calculated by the following procedure. (1) Place 6 g of sample in a two-necked recovery flask and vacuum dry at 160°C for 2 hours. (2) A tetrahydrofuran solution containing lithium aluminum hydride at a concentration of 0.2 mol / L is added to a two-necked recovery flask. (3) The gas generated by the reaction is collected in a measuring cylinder using the water displacement method, and the volume (L) of the gas generated is measured. (4) Calculate the hydroxyl group concentration T from the volume of gas generated per 1 g of sample (L / g, @0°C) according to the following formula. Hydroxyl group concentration T (mol / g) = [Volume of gas generated per 1 g of sample (L / g, @0°C)] / 22.4

[0054] (Process B1) For the trimethylsilylated silica fillers obtained in steps A1 and A2, the hydroxyl group concentration B was calculated by the following procedure. (1) Place 6 g of sample in a two-necked recovery flask and vacuum dry at 160°C for 2 hours. (2) A tetrahydrofuran solution containing lithium aluminum hydride at a concentration of 0.2 mol / L is added to a two-necked recovery flask. (3) The gas generated by the reaction is collected in a measuring cylinder using the water displacement method, and the volume (L) of the gas generated is measured. (4) Calculate the hydroxyl group concentration T from the volume of gas generated per 1 g of sample (L / g, @0°C) according to the following formula. Hydroxyl group concentration B (mol / g) = [Volume of gas generated per 1 g of sample (L / g, at 0°C)] / 22.4

[0055] Example 2 The hydroxyl group concentration A and the hydroxyl group concentration T were calculated in the same manner as in the example, except that the silica filler was changed to silica filler "SFP-130MC" (trade name, manufactured by Denka Co., Ltd.).

[0056] [Table 1]

[0057] [Evaluation of inorganic fillers and surface-modified inorganic fillers] The dielectric properties of the untreated silica filler and the trimethylsilylated silica filler were evaluated by the following method.

[0058] (Measurement of dielectric constant and dielectric loss tangent) The filler to be measured was filled 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 at 10 GHz. The values ​​of the dielectric constant and dielectric properties were corrected so that the volume fraction of the target filler was 100%.

[0059] [Table 2]

[0060] As shown in Table 2, it can be seen that the dielectric properties tend to deteriorate (for example, the dielectric constant and dielectric dissipation factor increase) when the inorganic filler contains a large number of hydroxyl groups. The hydroxyl group concentration A and ratio X determined in Example 2 are useful for determining the tendency of the dielectric properties of inorganic fillers that have been surface-treated with a silane coupling agent.

Claims

1. A method for selecting an inorganic filler having a hydroxyl group, comprising the steps of: a step of reacting the inorganic filler having a hydroxyl group with a trimethylsilylating agent to obtain an inorganic filler having a trimethylsilyl group; measuring a carbon concentration in the inorganic filler having a trimethylsilyl group by elemental analysis, and calculating a concentration A of trimethylsilylated hydroxyl groups in the inorganic filler having a trimethylsilyl group based on the carbon concentration; selecting an inorganic filler having a hydroxyl group based on the hydroxyl group concentration A; The method for selecting an inorganic filler comprises:

2. A method for selecting an inorganic filler having a hydroxyl group, comprising the steps of: a step of reacting the inorganic filler having a hydroxyl group with a trimethylsilylating agent to obtain an inorganic filler having a trimethylsilyl group; measuring a carbon concentration in the inorganic filler having a trimethylsilyl group by elemental analysis, and calculating a concentration A of trimethylsilylated hydroxyl groups in the inorganic filler having a trimethylsilyl group based on the carbon concentration; calculating a hydroxyl group concentration T in the inorganic filler having a hydroxyl group by a lithium aluminum hydride method; selecting an inorganic filler having a hydroxyl group based on the hydroxyl group concentration A and a ratio X of the hydroxyl group concentration A to the hydroxyl group concentration T; The method for selecting an inorganic filler comprises:

3. A method for selecting an inorganic filler having a hydroxyl group, comprising the steps of: a step of reacting the inorganic filler having a hydroxyl group with a trimethylsilylating agent to obtain an inorganic filler having a trimethylsilyl group; measuring a carbon concentration in the inorganic filler having a trimethylsilyl group by elemental analysis, and calculating a concentration A of trimethylsilylated hydroxyl groups in the inorganic filler having a trimethylsilyl group based on the carbon concentration; calculating a hydroxyl group concentration B in the inorganic filler having a trimethylsilyl group by a lithium aluminum hydride method; selecting an inorganic filler having a hydroxyl group based on the hydroxyl group concentration A, the hydroxyl group concentration B, and / or a ratio Y of the hydroxyl group concentration A to the total concentration of the hydroxyl group concentration A and the hydroxyl group concentration B; The method for selecting an inorganic filler comprises:

4. The method for selecting an inorganic filler according to any one of claims 1 to 3, wherein the trimethylsilylating agent is hexamethyldisilazane.

5. A method for producing a surface-modified inorganic filler, comprising a step of reacting an inorganic filler having a hydroxyl group concentration A within a predetermined range selected by the selection method according to any one of claims 1 to 3 with a silane coupling agent capable of reacting with and bonding to hydroxyl groups.

6. 3. A method for producing a composite material, comprising: preparing a composite material precursor containing an inorganic filler having a hydroxyl group concentration A and a ratio X each within a predetermined range, selected by the selection method according to claim 2; a silane coupling agent capable of reacting with and bonding to the hydroxyl groups; and a resin.

7. A method for manufacturing a composite material, comprising the steps of: preparing a composite material precursor containing an inorganic filler having a hydroxyl group concentration A, a hydroxyl group concentration B and / or a ratio Y each within a predetermined range, selected by the selection method of claim 3; a silane coupling agent capable of reacting with and bonding to the hydroxyl groups; and a resin.

8. The method for producing a composite material according to claim 6 or 7, wherein the composite material is a dielectric material.

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