Aluminum nitride filler and resin composition

Abstract

This invention provides an aluminum nitride-based filler with excellent water resistance and thermal conductivity, and a resin composition with excellent water resistance and thermal conductivity. The aluminum nitride-based filler of this invention comprises fibrous aluminum nitride particles forming an oxide film on their surface. The oxide film of the aluminum nitride particles is surface-treated with a phosphorus-based compound, and the surface oxygen content, as detected by NDIR, is between 1.98% and 9.40%. The specific surface area of ​​the aluminum nitride particles, as detected by BET, is denoted as X[m]. When [2 / g], it is characterized by surface treatment with a phosphorus content of 0.11 parts by mass to 11.0 parts by mass relative to 100 parts by mass of the aluminum nitride filler.

Description

Aluminum nitride filler and resin composition The present invention relates to an aluminum nitride-based filler and a resin composition. Aluminum nitride is widely known as a material with excellent thermal conductivity and electrical insulation properties. Leveraging these properties, aluminum nitride is used in a variety of applications. In particular, it has attracted attention as a thermally conductive filler used to enhance the thermal conductivity of resin compositions. For example, resin-made electronic components (resin products), starting with semiconductor substrates, have seen an increase in demand for heat dissipation measures (heat dissipation methods) due to the miniaturization and increased integration of electronic devices. Consequently, various proposals have been made for technologies that incorporate aluminum nitride as a filler in resins. However, aluminum nitride is inherently reactive with water. In other words, it is known that aluminum nitride reacts with water to produce ammonia through the following hydrolysis reaction. 2O→Al(OH) 3+NH 3↑ Even aluminum nitride contained in the resin may react with moisture in the atmosphere or in the resin, thereby deteriorating the quality of the resin product. Therefore, attempts are currently being made to solve the various problems mentioned above by surface treating the surface of aluminum nitride particles. For example, a powder composed of composite particles having a covering layer formed on the surface of aluminum nitride particles has been proposed, wherein (1) the covering layer contains Si (sulfur), O (oxygen), H (hydrogen) and an alkyl group, and (2) the organic carbon content of the powder is 0.02 to 1.0 wt% (Patent Document 1). For example, a filler is proposed that forms an oxide film on the surface of aluminum nitride particles. The filler uses the measured value of the specific surface area through BET detection as A (m 2 / g), and the calculated value of the specific surface area when the shape is spherical is taken as B (m 2 / g), and an aluminum nitride-based filler with an [A / B] value of 1 to 29.9 (Patent Document 2). However, in these technologies, fibrous aluminum nitride-based fillers intended to further improve thermal conductivity have not yet been able to provide aluminum nitride-based fillers that satisfy water resistance and other requirements, and there is room for further improvement in this regard. [Prior Art Literature] [Patent Literature] [Patent Document 1] Japanese Patent Application Publication No. 2006-290667 [Patent Document 2] Japanese Patent Application Publication No. 2021-127288 [Problems to be Solved by the Invention] The present invention aims to provide an aluminum nitride-based filler having excellent water resistance and thermal conductivity, and also to provide a resin composition having excellent water resistance and thermal conductivity. [Means for Solving the Problems] Such an object can be achieved by the present invention as described in the following (1) to (6). (1) An aluminum nitride filler comprising fibrous aluminum nitride particles having an oxide film formed on the surface, wherein the oxide film of the aluminum nitride particles is surface-treated with a phosphorus compound, and the surface oxygen content measured by NDIR is 1.98% or more and 9.40% or less, and the specific surface area of ​​the aluminum nitride particles measured by BET is X [m 2 / g], the surface treatment is performed with phosphorus in an amount of 0.11X parts by mass to 11.0X parts by mass relative to 100 parts by mass of the aluminum nitride-based filler. (2) The aluminum nitride-based filler as described in (1) above, wherein the phosphorus-based compound is an inorganic phosphoric acid compound or an organic phosphoric acid compound. (3) Aluminum nitride filler as described in (1) or (2) above, wherein the specific surface area measured by the BET method is 1.0 m 2 / g above 4.0m 2 / g or less. (4) The aluminum nitride filler as described in any one of (1) to (3) above, wherein the aspect ratio of the aluminum nitride particles is greater than or equal to 2 and less than or equal to 200. (5) A resin composition comprising the aluminum nitride-based filler as described in any one of (1) to (4) above; and a resin. (6) The resin composition as described in (5) above, wherein the content of the aluminum nitride filler is not less than 5% by volume and not more than 60% by volume. [Effects of the Invention] The present invention can provide an aluminum nitride-based filler having excellent water resistance and thermal conductivity, and can also provide a resin composition having excellent water resistance and thermal conductivity. [1] Aluminum nitride filler First, the aluminum nitride filler of the present invention will be described in detail. The aluminum nitride filler of the present invention comprises fibrous aluminum nitride particles having an oxide film formed on the surface. The oxide film of the aluminum nitride particles is surface-treated with a phosphorus compound. The surface oxygen content of the aluminum nitride filler of the present invention is determined to be between 1.98% and 9.40% as measured by NDIR (Non-Dispersive Infrared) method. The specific surface area of ​​the aluminum nitride particles as measured by BET method is X[m 2 / g], the surface treatment is characterized in that phosphorus is applied in an amount of 0.11X parts by mass to 11.0X parts by mass relative to 100 parts by mass of the aluminum nitride-based filler. By satisfying these conditions, an aluminum nitride-based filler having excellent water resistance and thermal conductivity can be provided. More specifically, the aluminum nitride filler comprises fibrous aluminum nitride particles with an oxide film formed on the surface. By surface treating the oxide film of the aluminum nitride particles with a phosphorus-based compound, excellent water repellency can be imparted to the aluminum nitride filler. In particular, by ensuring that the surface oxygen content of the aluminum nitride filler (surface oxygen content detected by the NDIR method) is within the aforementioned range, an appropriate amount of phosphorus can be stably attached to the surface of the aluminum nitride particles constituting the aluminum nitride filler, thereby allowing the aluminum nitride filler to have both excellent water resistance and thermal conductivity. Furthermore, by setting the phosphorus content (phosphorus surface-treated content) relative to the aluminum nitride particles in the aluminum nitride filler to be within the aforementioned range, the aluminum nitride filler can have excellent water repellency and thermal conductivity. Furthermore, by making the aluminum nitride particles fibrous and the aluminum nitride filler fibrous, the contact points between the aluminum nitride fillers can at least ensure a suitable heat conduction path. Furthermore, by reducing the number of contact points between the aluminum nitride fillers, thermal resistance can be reduced. This allows the aluminum nitride filler to have excellent thermal conductivity. In contrast, when the above conditions are not met, the excellent effects described above cannot be obtained. For example, if the surface oxygen content of the aluminum nitride filler is less than the lower limit, it becomes difficult to attach a sufficient amount of phosphorus to the surface of the aluminum nitride particles, and the water repellency of the aluminum nitride filler cannot be sufficiently excellent. Furthermore, if the surface oxygen content of the aluminum nitride filler exceeds the upper limit, the thermal conductivity of the aluminum nitride filler decreases. Furthermore, for example, if the amount of phosphorus relative to the aluminum nitride particles in the aluminum nitride filler (the amount of phosphorus surface-treated particles) is less than the aforementioned lower limit, the aluminum nitride filler will not be sufficiently water-resistant. Furthermore, if the amount of phosphorus relative to the aluminum nitride particles in the aluminum nitride filler (the amount of phosphorus surface-treated particles) exceeds the aforementioned upper limit, the thermal conductivity of the aluminum nitride filler will decrease. In the present invention, the surface oxygen content of the aluminum nitride-based filler refers to the oxygen content on the surface of the aluminum nitride-based filler, including the oxygen content in the oxide film and the oxygen content in the surface treated portion by the phosphorus-based compound. Furthermore, the oxygen content of the oxide film can generally be calculated by subtracting the oxygen content of the phosphorus-based compound used for surface treatment from the surface oxygen content (the surface oxygen content of the aluminum nitride-based filler). The oxygen content of the phosphorus-based compound can also be calculated by subtracting the oxygen content of the oxide film of the aluminum nitride particles from the surface oxygen content. In the following description, the aluminum nitride-based filler of the present invention may be simply referred to as a "filler". [1-1] Aluminum Nitride Particles Aluminum nitride particles are particles that serve as the core of the aluminum nitride-based filler of the present invention, and an oxide thin film is formed on the surface of the particles. Typically, the proportion of the surface treated portion of the aluminum nitride filler with the phosphorus compound is very small compared to the proportion of the aluminum nitride particles. The aluminum nitride particles have the same shape and size as the corresponding aluminum nitride filler. In other words, the aluminum nitride particles are also fibrous. The aspect ratio of the aluminum nitride particles, that is, the value of L1 / L2 when the length of the long axis direction of the aluminum nitride particles is L1 [μm] and the length of the short axis direction perpendicular to the long axis direction is L2 [μm], is preferably greater than 2 and less than 200, more preferably greater than 3 and less than 180, and even more preferably greater than 5 and less than 150. This can further enhance the aforementioned effects and can also improve the fluidity and formability of the resin composition when the aluminum nitride-based filler is used as the resin composition. In this specification, the "aspect ratio" refers to the arithmetic average of the aspect ratios of 30 randomly selected target particles. Regarding the aluminum nitride filler, it is also preferred that the aspect ratio of the aluminum nitride particles be the same as that of the aluminum nitride particles, thereby achieving the same effects as above. The average particle size of the aluminum nitride particles is not particularly limited, but D50, as measured by volume distribution using a laser scattering particle size analyzer, is preferably 0.1 μm to 500 μm, more preferably 1 μm to 100 μm, and even more preferably 1 μm to 50 μm. This can further improve the water resistance of the aluminum nitride-based filler and further improve the non-catalytic toxicity and filling properties of the resin composition when the aluminum nitride-based filler is dispersed in the resin. Regarding the aluminum nitride filler, it is also preferred that the average particle size of the aluminum nitride particles satisfy the same conditions as those mentioned above, thereby achieving the same effects as above. [1-1-1] Oxide Thin Film An oxide thin film is formed on the surface of the aluminum nitride particles. By forming an oxide thin film, excellent water repellency, non-catalytic toxicity, filling properties, etc. can be imparted to aluminum nitride particles. The oxide thin film may be a surface layer that covers at least a portion of the surface of the aluminum nitride particles, and preferably substantially covers the entire surface of the aluminum nitride particles. As oxides, various metal or non-metal oxides can be used. For example, aluminum nitride, silicon oxide, titanium oxide, zirconium oxide, cerium oxide, etc. can be mentioned. One or more of these oxides may be included. Furthermore, among the above oxides, oxides obtained by the sol-gel method can also be appropriately used. The amount of the oxide thin film formed (coverage) is preferably 0.1 parts by mass or more and 50 parts by mass or less relative to 100 parts by mass of the aluminum nitride particles. This can improve the waterproofness and thermal conductivity of the aluminum nitride-based filler. The thickness of the surface layer is not particularly limited and may be between 1 nm and 200 nm. This can improve the waterproofness and thermal conductivity of the aluminum nitride-based filler. The surface oxygen content of the aluminum nitride particles is preferably not less than 0.5% and not more than 3.0%. Thus, when the surface is treated with the phosphorus-based compound, the phosphorus-based compound can be more appropriately adhered to the oxide film, and the waterproofness and thermal conductivity of the aluminum nitride-based filler can be improved. The surface oxygen content of the aluminum nitride particles can be determined, for example, by measuring the surface oxygen content of the aluminum nitride particles used as a raw material of the aluminum nitride-based filler using the NDIR method described above. The BET specific surface area of ​​aluminum nitride particles is 0.5 m 2 / g above 4.0m 2 / g or less is preferred. Thus, when the surface is treated with a phosphorus-based compound, a sufficient amount of phosphorus can be attached to the surface, thereby improving the waterproofness and thermal conductivity of the aluminum nitride-based filler. [1-2] Surface Treatment with Phosphorus-Based Compound In the aluminum nitride-based filler of the present invention, the oxide thin film of the aluminum nitride particles is surface-treated with a phosphorus-based compound. The phosphorus compound is not particularly limited, but an inorganic phosphoric acid compound or an organic phosphoric acid compound is preferably used. Thereby, the OH groups present in the oxide film of the aluminum nitride particles react with phosphoric acid to form a chemical bond, and the phosphorus compound can be closely attached to the aluminum nitride particles, which can give the aluminum nitride particles better water repellency. Examples of the inorganic phosphoric acid compound include phosphoric acid, orthophosphoric acid, pyrophosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, ammonium phosphate, ammonium hydrogenphosphate, ammonium dihydrogenphosphate, aluminum phosphate, and sodium phosphate. As an organic phosphoric acid compound, for example, the general formula (RO) 2P(O)OH or ROP(O)(OH) Examples of the acidic phosphate esters represented by 2 (wherein R is an alkyl, alkenyl or aryl group having 1 to 18 carbon atoms) include methyl acid phosphate, ethyl acid phosphate, butyl acid phosphate, 2-ethylhexyl acid phosphate, lauryl acid phosphate, palmitoyl acid phosphate, stearoyl acid phosphate, oleyl acid phosphate, phenyl acid phosphate and nonylphenyl acid phosphate. Other examples of the organic phosphoric acid compound include monoalkyl, dialkyl, alkenyl or aryl esters of pyrophosphoric acid or polyphosphoric acid, such as di-2-ethylhexyl pyrophosphate; phosphonic acids and esters thereof, such as methylene phosphonic acid, aminomethylene phosphonic acid, t-butyl nitrilobis (methylene phosphonic acid), n-butyl nitrilobis (methylene phosphonic acid), nitrilotris (methylene phosphonic acid), ethylenediaminetetramethylene phosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, butyl hydro-diene phosphonate, and the like. phosphate), 2-ethylhexyl hydro-diene phosphite, lauryl hydro-diene phosphite, dibutyl hydroxymethyl phosphonate, etc.; organic phosphoric acid compounds such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, tricresyl phosphate, and triphenyl phosphate. Among these, it is preferred to use at least one selected from the group consisting of phosphoric acid, orthophosphoric acid, polyphosphoric acid, phosphorous acid, ammonium phosphate, ammonium dihydrogen phosphate, acidic phosphate esters, and salts thereof. [1-3] Other conditions: The BET specific surface area of ​​the aluminum nitride filler of the present invention is 1.0 m 2 / g above 4.0m 2 / g or less is preferred. Thus, when the aluminum nitride-based filler of the present invention is used as a resin composition, the adhesion between the filler and the resin is improved, so that the strength and thermal conductivity of the molded body manufactured using the resin composition can be improved. [2] Method for producing aluminum nitride-based filler Next, a method for producing aluminum nitride-based filler will be described. The aluminum nitride-based filler of the present invention can be suitably produced, for example, through a preparation step comprising preparing fibrous aluminum nitride particles having an oxide thin film formed on their surfaces and a surface treatment step comprising surface-treating the aluminum nitride particles with a phosphorus-based compound. [2-1] Preparation Step In the preparation step, fibrous aluminum nitride particles with an oxide thin film formed on the surface are prepared. The aluminum nitride particles may contain other components (e.g., Al 2O 3, etc.) are also acceptable. Aluminum nitride particles can be produced by any method, for example, aluminum nitride particles obtained by direct nitridation or reduction. Furthermore, a sol-gel method as described below is preferably used to form an oxide thin film on the surface of the aluminum nitride particles. In other words, fibrous aluminum nitride particles having an oxide thin film formed on their surfaces can be suitably produced by a method comprising: (a) a first step of preparing a mixed solution by adding an alkoxide compound to a dispersion of aluminum nitride powder in a solvent; (b) a second step of hydrolyzing the alkoxide compound by adding an acidic catalyst to the mixed solution; (c) a third step of adding a basic catalyst to the mixed solution after the hydrolysis; and (d) a fourth step of drying the obtained reaction product. Specifically, for example, aluminum nitride particles having an oxide thin film formed on the surface can be produced by the method described in Japanese Patent Application Laid-Open No. 2021-127288. Furthermore, commercially available aluminum nitride particles may be used. For example, "Tharmalnite" manufactured by U-MAP Corporation can be used as commercially available aluminum nitride particles. [2-2] Surface Treatment Step In the surface treatment step, the aluminum nitride particles are surface-treated with a phosphorus-based compound. Specifically, for example, by mixing a dispersion in which aluminum nitride particles are dispersed in a solvent and a phosphorus-based compound, the phosphorus-based compound can be attached to the surface of the aluminum nitride particles. The solvent used in the dispersion is not particularly limited, but an aqueous solvent is preferred. As the aqueous solvent, at least one of water, a water-soluble organic solvent, and a mixed solvent thereof can be appropriately used. Specific examples of the water-soluble organic solvent include alcohols such as methyl alcohol, ethanol, isopropyl alcohol, n-propyl alcohol, t-butyl alcohol, n-butyl alcohol, and isobutyl alcohol; celluloid solvents such as ethyl cellosolve and butyl cellosolve; ethers such as propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, and propylene glycol monopropyl ether; and ketones such as acetone. The content of the aluminum nitride particles in the dispersion is not particularly limited, but is preferably 10% by mass or more and 60% by mass or less. The phosphorus compound may be mixed directly with a dispersion of aluminum nitride particles in a solvent, or may be mixed in the form of an aqueous solution. When an aqueous solution of the phosphorus compound is used, the concentration of the phosphorus compound in the aqueous solution may be, for example, from 0.05 g / L to 100 g / L. When adding the phosphorus compound to a dispersion of aluminum nitride particles in a solvent, the method for adding the phosphorus compound is not particularly limited and may be a method of adding the entire compound all at once, a method of adding the compound in two or more portions, or a method of adding the compound dropwise. Furthermore, it is preferred that the phosphorus compound be added while stirring the dispersion. The amount of the phosphorus compound used is appropriately set according to the type of the phosphorus compound, and the specific surface area of ​​the aluminum nitride particles measured by the BET method is X [m 2 / g], the phosphorus content is determined to be in a ratio of 0.11X parts by mass to 11.0X parts by mass relative to 100 parts by mass of the aluminum nitride-based filler. The dispersion can be prepared and stirred using conventional mixing devices, stirring devices, and the like. Examples of the mixing devices and stirring devices include kneaders, mixers, rotary container mixers, stirring reaction tanks, V-type mixers, double cone mixers, spiral mixers, sigma mixers, flash mixers, air flow mixers, ball mills, and wheel mills. The treatment temperature is usually set to be below the boiling point of the solvent used, but this is not limiting. The stirring time is not particularly limited and can be from 30 minutes to 4 hours. [2-3] Drying Step The method for producing the aluminum nitride-based filler may further include a drying step of drying the obtained reaction product in addition to the above steps. In the surface treatment step, the reaction product in the dispersion is generated as a solid component. If necessary, solid-liquid separation is performed to separate and recover the solid component, and then the reaction product can be dried. The solid-liquid separation method can be a conventional method, for example, filtration, centrifugation, etc. The drying temperature is not particularly limited, but is preferably 50°C to 150°C. The drying time also depends on the drying temperature, but is preferably 5 minutes or longer. In addition to the above-mentioned thermal drying, the solvent can also be removed by vacuum decompression. After drying, heat treatment may be performed as needed. The heat treatment temperature is not particularly limited, but is preferably between 200°C and 800°C, and more preferably between 300°C and 500°C. The treatment environment is not particularly limited, and may be, for example, in the air. [3] Application of aluminum nitride-based fillers Next, the application of the aluminum nitride-based fillers of the present invention will be described. The aluminum nitride-based filler of the present invention can be used as various fillers (filling materials), and can be particularly suitably used as a filler to be dispersed in a resin. The aluminum nitride-based filler of the present invention has particularly excellent thermal conductivity due to the use of aluminum nitride as core particles. Therefore, it can be suitably used as a filler for imparting high thermal conductivity (heat dissipation) to a resin composition. Furthermore, the aluminum nitride-based filler of the present invention comprises aluminum nitride particles with an oxide film formed on their surface. Due to the surface oxygen and phosphorus content meeting predetermined conditions, it exhibits excellent water repellency. Therefore, even when the aluminum nitride-based filler of the present invention is dispersed in a resin, degradation of the resin quality caused by the reaction between the aluminum nitride and moisture can be effectively suppressed. As described above, the aluminum nitride-based filler of the present invention can be particularly suitably used as a filler in a resin composition. [4] Resin Composition Next, the resin composition of the present invention will be described. The resin composition of the present invention includes the aluminum nitride-based filler and a resin. This can provide a resin composition with excellent waterproofness and thermal conductivity. In addition, the reaction between the aluminum nitride filler and moisture in the air or in the resin can be appropriately suppressed, thereby maintaining high quality for a long time. Dispersing the fibrous aluminum nitride filler in the resin with its length direction oriented in a random direction can increase the contact density per unit volume of the aluminum nitride fillers, thereby imparting high thermal conductivity to the resin composition even in a small amount. The above-mentioned effects are exhibited not only in the resin composition but also in the molded article produced using the resin composition. As the resin, various thermoplastic resins, thermosetting resins, etc. can be used. More specifically, as the resin, for example, silicone resin, acrylic resin, epoxy resin, polyester resin, polyurethane resin, polyvinyl acetate resin, nitrocellulose resin, fluororesin, etc. can be mentioned. In particular, the effects of the present invention can be more significantly exerted when a resin (e.g., silicone resin) is polymerized and cured using a catalyst in which nitrogen in aluminum nitride serves as a catalyst poisoning source. The method for mixing the aluminum nitride-based filler and the resin is not particularly limited. For example, various methods can be used, such as (a) kneading the filler with molten resin and (b) adding the filler to resin powder and then melt-kneading. The content (volume ratio) of the resin in the resin composition is preferably 5% by volume or more and 60% by volume or less, and more preferably 10% by volume or more and 50% by volume or less. This improves the fluidity of the resin composition, improves the waterproofness and thermal conductivity of the molded article produced using the resin composition, and further improves the mechanical properties of the molded article, such as strength and flexibility. The content of the aluminum nitride-based filler in the resin composition can be 5 parts by mass or more and 900 parts by mass or less based on 100 parts by mass of the resin. The content (volume ratio) of the aluminum nitride-based filler in the resin composition is preferably 5% by volume to 60% by volume, and more preferably 10% by volume to 50% by volume. This improves the fluidity of the resin composition, improves the waterproofness and thermal conductivity of the molded article produced using the resin composition, and further improves the mechanical properties of the molded article, such as strength and flexibility. Furthermore, the resin composition of the present invention may contain other components in addition to the aluminum nitride-based filler and resin described above. Hereinafter, such components are referred to as "other components." Examples of other components include fillers other than the aluminum nitride-based filler of the present invention, surfactants, hardeners, bridging agents, ultraviolet absorbers, static electricity removers, thickeners, colorants, corrosion inhibitors, and the like. The content of other components in the resin composition of the present invention is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less. [5] Molded Article Next, the molded article according to the present invention will be described. The molded article of the present invention is preferably one containing the aluminum nitride-based filler of the present invention. In particular, the molded article of the present invention is preferably one produced using the resin composition of the present invention. When the molded article of the present invention is produced using the resin composition of the present invention, it is preferred that the molded article have the same composition as the resin composition, thereby achieving the same effects as described above. The molded article of the present invention may be any object, and can be suitably used in electronic parts, vehicle parts, and the like that require high heat dissipation and waterproofness. The method for forming the molded body using the resin composition is not particularly limited, and depending on the type of resin used, for example, conventional methods such as press molding and injection molding can be used. The bending stress of the molded body is preferably 0.2 MPa or more, more preferably 0.4 MPa or more. This allows the molded body to be suitably used as various parts. In this specification, the bending stress of a molded article is a value measured by a three-point bending test using a three-point bending test jig in accordance with the method described in JIS K7171:2016. Furthermore, the thermal conductivity of the molded article at 25° C. is preferably 1.0 W / (m·K) or higher, and more preferably 4.0 W / (m·K) or higher. This makes it possible to suitably apply to molded bodies requiring high thermal conductivity (heat dissipation). Preferred embodiments of the present invention have been described above, but the present invention is not limited thereto. For example, the aluminum nitride filler of the present invention is not limited to that produced by the above-mentioned production method. More specifically, the aluminum nitride filler of the present invention can be produced by a method having other steps in addition to the above-mentioned steps. [Example] The following specific examples further illustrate the present invention, but the present invention is not limited to these examples. In the following description, all treatments performed at room temperature, specifically 25°C, are performed unless otherwise specified. Furthermore, all numerical values ​​for various measurement conditions, unless otherwise specified, represent data at room temperature, specifically 25°C. [6] Production of Aluminum Nitride Filler (Example 1) First, Tharmalnite manufactured by U-MAP was prepared as fibrous aluminum nitride particles having an oxide film formed on the surface. The BET specific surface area of ​​the aluminum nitride particles is 2.10 g / m 2 , with an aspect ratio of 7.0. 1500 g of isopropyl alcohol was placed in a 3 L container with a lid. While stirring the isopropyl alcohol, 20.0 g of the aluminum nitride particles were added and fully dispersed. To this dispersion, 1.2 g of a 10% by mass aqueous phosphoric acid solution was slowly added. After stirring for 30 minutes, the mixture was filtered to remove fine powder and separate the solid and liquid. The resulting solid was dried in a vacuum at 70°C to obtain an aluminum nitride filler surface-treated with phosphoric acid. (Examples 2 to 6) Aluminum nitride-based fillers surface-treated with phosphoric acid were produced in the same manner as in Example 1, except that the amount of phosphoric acid used was changed as the conditions for the fibrous aluminum nitride particles used as the raw material. (Comparative Example 1) The aluminum nitride particles were used directly as the aluminum nitride filler in Comparative Example 1 without undergoing surface treatment with a phosphorus compound. (Comparative Examples 2-4) Aluminum nitride fillers surface-treated with phosphoric acid were prepared in the same manner as in Example 1, except that the amount of phosphoric acid used was changed, using fibrous aluminum nitride particles as the raw material. [7] Evaluation The following evaluations were performed on the aluminum nitride-based fillers of the above-mentioned embodiments and comparative examples. [7-1] Surface oxygen content The surface oxygen content was measured by thermal decomposition in an inert gas and infrared absorption detection. The measurement was performed using an oxygen / nitrogen analyzer (EMGA-2800) manufactured by Horiba, Ltd. [7-2] BET specific surface area The BET specific surface area was measured using a fully automatic specific surface area measuring device (Macsorb (registered trademark) HM Model-1201) manufactured by MOUNTECH. [7-3] Evaluation of Waterproofness The aluminum nitride-based fillers of the above-mentioned Examples and Comparative Examples were exposed to a high-temperature and high-humidity environment of 85° C. and 85% RH for 16 hours using an environmental testing machine (ESPEC SH242) manufactured by ESPEC. The surface oxygen content before and after exposure to a high temperature and high humidity environment was measured, and the rate of change was calculated using the following formula: Rate of change (%) = {(surface oxygen content after exposure - surface oxygen content before exposure) / surface oxygen content before exposure} × 100 The smaller the value of the change rate is, the better the waterproofness is. [7-4] Evaluation of Thermal Conductivity: The aluminum nitride-based fillers of the aforementioned Examples and Comparative Examples were dispersed in silicone resin to produce resin compositions. The aluminum nitride-based filler content in the resin composition was 5% by volume, and the resin content in the resin composition was 95% by volume. The thermal conductivity of the silicone resin at 25°C was 0.2 W / (m·K). The obtained resin composition was injection-molded into a disk-shaped silicon mold with a diameter of 25 mm and a thickness of 5 mm, and then treated at 150° C. for 60 minutes to obtain a molded body as a sample for thermal conductivity detection. The thermal conductivity of each of the obtained thermal conductivity test samples was measured using a thermal conductivity tester (TCi) manufactured by C-THERM Corporation using a non-steady method. These evaluation results are shown in FIG1 together with the composition of the aluminum nitride filler of each embodiment and each comparative example. In FIG1, the value of "phosphorus amount [mass parts]" represents the ratio of phosphorus to 100 parts by mass of aluminum nitride, and the column of "phosphorus amount (relationship with specific surface area) [mass parts]" represents the ratio of phosphorus to 100 parts by mass of aluminum nitride. 2 / g], the amount of phosphorus used for surface treatment of 100 parts by mass of the aluminum nitride-based filler is expressed as including x. As is clear from Figure 1 , the present invention can achieve excellent waterproofness and thermal conductivity. In contrast, the comparative examples cannot achieve satisfactory results. Furthermore, except for various changes in the content of the aluminum nitride-based filler within the range of 5% by mass to 60% by mass, the aluminum nitride-based fillers of the above-mentioned embodiments were used to produce molded articles in the same manner as in [7-4] above. In any of these embodiments, excellent results were obtained when measuring bending stress. [Industrial Applicability] The present invention can provide an aluminum nitride-based filler having excellent water resistance and thermal conductivity, and can also provide a resin composition having excellent water resistance and thermal conductivity. Therefore, the present invention has industrial applicability. none FIG. 1 is a table showing the composition and evaluation results of the aluminum nitride-based fillers of each Example and each Comparative Example.

Claims

1. An aluminum nitride-based filler comprising fibrous aluminum nitride particles having an oxide film formed on their surface, wherein the oxide film of the aluminum nitride particles is surface-treated with a phosphorus compound, and the surface oxygen content, as determined by NDIR, is 1.98% to 9.40%, and the specific surface area of ​​the aluminum nitride particles, as determined by BET, is X [m² / g], and the surface treatment is performed with a phosphorus content at a ratio of 0.11 X parts by mass to 11.0 X parts by mass relative to 100 parts by mass of the aluminum nitride-based filler.

2. The aluminum nitride-based filler as described in claim 1, wherein the phosphorus compound is an inorganic phosphoric acid compound or an organic phosphoric acid compound.

3. The aluminum nitride-based filler as described in claim 1 or 2, wherein the specific surface area as determined by the BET method is 1.0 m² / g or more and 4.0 m² / g or less.

4. The aluminum nitride-based filler as described in claim 1 or 2, wherein the aspect ratio of the aluminum nitride particles is more than 2 and less than 200.

5. A resin composition comprising an aluminum nitride filler as described in claim 1 or 2; and a resin.

6. The resin composition as described in claim 5, wherein the content of the aluminum nitride filler is more than 5% by volume and less than 60% by volume.

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