JP7398733B2 - Method for producing composite aluminum nitride particles, and composite aluminum nitride particles - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act (1) Proceedings of the 68th Annual Conference of the Society of Polymer Science and Technology published on May 14, 2019 (2) Proceedings of the 68th Annual Conference of the Society of Polymer Science and Technology published on May 29, 2019 (3) Proceedings of the 68th Polymer Symposium, published on September 11, 2019 (4) Published on October 18, 2019 Proceedings of the 40th Japan Symposium on Thermophysical Properties

The present invention relates to a method for producing composite aluminum nitride particles and composite aluminum nitride particles.

BACKGROUND ART Resin compositions containing thermally conductive fillers and molded products thereof have been known as resin materials with improved thermal conductivity. The resin composition or its molded product can be used as a heat sink or a thermally conductive insulating material placed between a heat sink and a metal heat sink, in addition to supporting and sealing a heat generating element in electronic devices and mechanical devices. It is used. For example, Patent Document 1 discloses a thermally conductive resin in which a thermally conductive filler is added to an electrically insulating resin as a material for a heat dissipating member.
However, in the thermally conductive resin described in Patent Document 1, it is stated that even if a high thermal conductivity filler is used as the filler, sufficient thermal conductivity cannot be obtained unless the filling rate is increased. has been done. In particular, in the case of hard fillers such as aluminum nitride and diamond, it is known that the thermal conductivity does not increase significantly compared to alumina, which has a lower thermal conductivity.
The reason for this is that the contact between the hard fillers tends to be point contact, and even if an attempt is made to form a heat conduction path, contact thermal resistance is likely to occur. Therefore, in order to obtain high thermal conductivity with a hard filler, it is necessary to fill it highly.

Attempts have been made to combine hard fillers and soft fillers as a method of reducing contact thermal resistance during hard filler filling. However, most of them, as in Patent Document 2, simply mix the two, and even if it were possible to mix them uniformly and place the soft filler around the hard filler, the soft filler would not be able to be placed around the hard filler by kneading it with the resin. is destroyed, and a sufficient effect of improving thermal conductivity cannot be achieved.
On the other hand, Patent Document 3 reports a composite filler that exhibits high thermal conductivity by fixing a plurality of magnesium oxide particles to the surface of silicon carbide particles, which have high thermal conductivity and are hard. However, aluminum nitride, which is also a hard filler, has difficulty bonding with and adsorbing the soft filler, making it difficult to hold the soft filler around the aluminum nitride.

Japanese Patent Application Publication No. 2005-281467 JP2017-88696A Japanese Patent Application Publication No. 2017-154937

The present invention relates to aluminum nitride particles, which are hard fillers, which can lower the contact thermal resistance than before when filled in a resin, thereby providing a method for producing composite aluminum nitride with excellent thermal conductivity, and a composite Our objective is to provide aluminum nitride.

As a result of extensive studies to achieve the above object, the present inventors have discovered a precipitation step of precipitating zinc hydroxide on the surface of aluminum nitride particles in an aqueous solvent, and aluminum nitride particles A obtained in the precipitation step. It has been discovered that the above-mentioned problems can be solved by a method for manufacturing composite aluminum nitride particles that includes a firing step of firing at 600° C. or higher, and the present invention has been completed.

The gist of the present invention is the following [1] to [5].
[1] Features include a precipitation step of precipitating zinc hydroxide on the surface of aluminum nitride particles in an aqueous solvent, and a firing step of baking the aluminum nitride particles A obtained in the precipitation step at 600°C or higher. Method for producing composite aluminum nitride particles.
[2] The method for producing composite aluminum nitride particles according to [1] above, wherein the precipitation step is performed by adding a basic substance to an aqueous solvent containing zinc salt and aluminum nitride particles.
[3] Composite aluminum nitride particles, characterized in that zinc oxide is fixed to the surface of at least a portion of the aluminum nitride particles via a composite oxide layer of aluminum and zinc.
[4] A thermally conductive filler comprising the composite aluminum nitride particles described in [3] above.
[5] A resin composition comprising the thermally conductive filler described in [4] above.

According to the present invention, it is possible to provide a method for producing composite aluminum nitride particles and composite aluminum nitride particles that have excellent thermal conductivity when filled in a resin.

1 is a scanning electron micrograph of the thermally conductive filler produced in Production Example 1. 3 is a scanning electron micrograph of the thermally conductive filler produced in Production Example 2.

[Method for producing composite aluminum nitride particles]
The method for producing composite aluminum nitride particles of the present invention includes a precipitation step in which zinc hydroxide is precipitated on the surface of aluminum nitride particles in an aqueous solvent, and aluminum nitride particles A obtained in the precipitation step are fired at 600°C or higher. Includes firing process.

<Precipitation process>
The precipitation step is a step of precipitating zinc hydroxide on the surface of aluminum nitride particles in an aqueous solvent. Through this precipitation step, aluminum nitride particles A having zinc hydroxide attached to their surfaces are generated.
The aqueous solvent used in the precipitation process is a solvent that contains water, and may be a solvent consisting only of water or a mixed solvent of water and a hydrophilic organic solvent such as alcohol. It is preferable that the solvent consists of only Here, it is preferable to use ion-exchanged water, distilled water, or the like as the water.

The precipitation step is a step in which aluminum nitride powder, which will be described later, is mixed with an aqueous solvent, and zinc hydroxide is precipitated on the surface of the aluminum nitride particles in the aqueous solvent.
The means for precipitating zinc hydroxide on the surface of aluminum nitride particles in an aqueous solvent is not particularly limited, but from the viewpoint of making it easier to precipitate zinc hydroxide and making it easier to obtain composite aluminum nitride particles with high thermal conductivity. From this point of view, it is preferable to use a method in which zinc hydroxide is precipitated by adding a basic substance to an aqueous solvent containing aluminum nitride particles and a zinc salt.
The aqueous solvent containing aluminum nitride particles and zinc salt can be obtained by mixing aluminum nitride powder and zinc salt produced by a known method described below in an aqueous solvent.
Specifically, zinc salt and aluminum nitride powder are added to an aqueous solvent and mixed to prepare a suspension. Then, by adding a basic substance to the suspension, the aqueous solution is made basic and zinc hydroxide is generated. Zinc hydroxide may not be dissolved in the basic suspension and may exist in a suspended state. Zinc hydroxide adheres to at least a portion of the surface of the aluminum nitride particles, and becomes zinc oxide fixed to the surfaces of the aluminum nitride particles in the firing step described later. Hereinafter, each raw material used in the precipitation step and precipitation conditions will be explained.

<Aluminum nitride powder>
《Manufacturing method》
Aluminum nitride powder is composed of aluminum nitride particles, and methods for producing it include known methods such as direct nitriding, reductive nitriding, vapor phase synthesis, and sintering.

《Particle size, particle size distribution》
The average particle size of the aluminum nitride powder is not particularly limited, but is preferably 0.7 to 120 μm, more preferably 0.7 to 100 μm. Note that the average particle size means the particle size at 50% cumulative volume (D50) in the particle size distribution measured by a laser diffraction scattering particle size distribution analyzer.
Further, it is preferable that the aluminum nitride powder has one or two maximum values of the volume frequency measured by a laser diffraction scattering particle size distribution analyzer, since this improves the filling property of the powder into the resin. When there are two maximum values, it is desirable that the volume frequency of one is three times or more that of the other.
Aluminum nitride powder with such a particle size distribution can be obtained by various manufacturing methods, but if necessary, it may be crushed using a ball mill, jet mill, etc., or classified using a vibrating sieve or air classifier. Therefore, the filling properties of the resin, which will be described later, can be improved.

《Particle shape》
The aluminum nitride powder includes a plurality of aluminum nitride particles that are primary particles. The shape of the primary particles is not particularly limited, and may be any shape, such as an irregular shape, a spherical shape, a polyhedral shape, a columnar shape, a whisker shape, and a flat plate shape. Among these, a spherical shape is desirable because it has good filling properties into the resin and has high reproducibility of thermal conductivity. Further, it is desirable that the aspect ratio of the particles is small from the viewpoint of resin filling properties and insulation properties. A preferred aspect ratio is 1-3.
The aluminum nitride powder may also include aggregated particles of primary particles. Agglomerated particles may cause a reduction in the filling properties of the resin, so it is desirable that the particles be deagglomerated by kneading with the resin or dispersed in a solvent, or that the particles have a small number of internal voids. Incidentally, aggregated particles may be removed by a classification operation or the like.

"impurities"
The aluminum nitride powder may contain up to about 5% by mass of impurities such as alkaline earth elements and rare earth elements derived from raw materials or intentionally added during the synthesis process. Further, boron nitride may be contained as an impurity derived from an anti-agglomeration agent or a setter, with an upper limit of about 5% by mass. However, from the viewpoint of suppressing a decrease in thermal conductivity, the aluminum nitride content in the aluminum nitride powder is preferably 90% by mass or more, more preferably 95% by mass or more.

《Oxide film》
The aluminum nitride powder used in the present invention may have an aluminum oxide layer on its surface from the viewpoint of suppressing hydrolyzability or increasing the bondability with zinc oxide formed from zinc hydroxide. This aluminum oxide layer may be an oxide film layer formed by natural oxidation during storage of the aluminum nitride powder, or may be an oxide film layer formed by an intentional oxidation treatment process. This oxidation treatment step may be performed during the manufacturing process of the aluminum nitride powder, or may be performed as a separate step after the aluminum nitride powder is manufactured. For example, aluminum nitride powder obtained by a reductive nitriding method undergoes an oxidation treatment step during the manufacturing process for the purpose of removing carbon used in the reaction, so an aluminum oxide layer is present on the surface. The aluminum nitride powder produced by the reductive nitriding method thus obtained may be further subjected to an additional oxidation treatment step. In the direct nitriding method and the sintering method, since there is no oxidation treatment step, an oxidation treatment step may be additionally performed as necessary.

When the oxidation treatment step is performed as a separate step, the conditions are as follows.
The oxidation treatment step is performed by heating aluminum nitride powder obtained by various methods in an oxygen-containing atmosphere. Thereby, an aluminum oxide layer can be formed on the surface of the aluminum nitride particles. At this time, the heating temperature is preferably 400 to 1,000°C, more preferably 600 to 900°C. The heating time is preferably 10 to 600 minutes, more preferably 30 to 300 minutes. As the oxygen-containing atmosphere, for example, oxygen, air, water vapor, carbon dioxide, etc. can be used, but the aluminum oxide layer can also be formed even when the treatment is carried out in air, particularly under atmospheric pressure.

On the other hand, the oxidation treatment is preferably carried out at 900°C or lower. In this case, the formation of a thick aluminum oxide layer on the surface of the aluminum nitride particles is suppressed, thereby reducing the coefficient of thermal expansion between the aluminum nitride and aluminum oxide layers. It is possible to prevent cracking of the oxide film layer due to the difference, and as a result, the surface of the core aluminum nitride particle is no longer exposed. Aluminum nitride particles whose surfaces are not exposed have good binding properties with zinc oxide and good hydrolysis resistance.
Further, the thickness of the aluminum oxide layer of the aluminum nitride particles is preferably 0.005% to 0.2% of the diameter of the particles. When the thickness of the aluminum oxide layer is within this range, the aluminum nitride powder maintains a high thermal conductivity and has good bondability with zinc oxide and good hydrolysis resistance.

The aluminum nitride powder may be surface-treated in advance. By performing the surface treatment in advance, the agglomeration of the aluminum nitride particles is loosened, making it easier to deposit zinc hydroxide on the surface of each aluminum nitride particle, and making it easier to obtain the desired composite aluminum nitride particles. Furthermore, the filling properties of the resin are improved, and as a result, it becomes easier to obtain composite aluminum nitride particles with high thermal conductivity. Agglomerates, which affect the filling properties of resin, are caused by hydrogen bonds between hydroxyl groups on the surface of particles, and particles are strongly tied together to form coarse lumps, but surface treatment can weaken these bonds. It is thought that this makes it difficult to aggregate.

<Zinc salt>
The zinc salt used in the precipitation step is not particularly limited as long as it is a compound that can precipitate zinc hydroxide on the surface of aluminum nitride particles in an aqueous solvent. The zinc salt is preferably a compound that is water-soluble and can form zinc hydroxide in an alkaline aqueous solution, such as zinc acetate, zinc carbonate, zinc nitrate, zinc sulfate, zinc chloride, etc. However, zinc acetate is preferred because of its safety and ease of waste liquid treatment. Further, as zinc acetate, it is preferable to use a dihydrate because of its higher solubility in water.

The amount of zinc salt used in the precipitation step is preferably adjusted so that the molar ratio of aluminum nitride particles to zinc oxide falls within a predetermined range when zinc oxide is formed through the firing step described below. Specifically, zinc salt is prepared such that the molar ratio of aluminum nitride particles to zinc oxide (aluminum nitride/zinc oxide) is preferably 60/40 to 97/3, more preferably 70/30 to 95/5. It is preferable to blend. The molar ratio (aluminum nitride/zinc oxide) is the same as the molar ratio (aluminum atoms/zinc atoms) between aluminum atoms in the aluminum nitride powder used as a raw material and zinc atoms in the zinc salt (for example, zinc acetate).
When the molar ratio (aluminum nitride/zinc oxide) is equal to or higher than these lower limits, formation of a large amount of zinc oxide with low thermal conductivity can be suppressed, and the thermal conductivity improves. When the aluminum atom/zinc atom ratio is below these upper limits, more than a certain amount of zinc oxide is formed, and when composite aluminum nitride particles are filled in a resin, the particles tend to come into surface contact with each other, resulting in a decrease in thermal conductivity. will improve.

(basic substance)
Examples of the basic substance used in the precipitation step include sodium hydroxide, potassium hydroxide, and aqueous ammonia. The basic substance may be added in such an amount that zinc hydroxide is formed, and it may be added so that the pH of the aqueous solvent is preferably 10 to 14.

(Precipitation conditions)
From the viewpoint of suppressing hydrolysis of the aluminum nitride particles in the aqueous solvent, the immersion time of the aluminum nitride particles in the aqueous solvent in the precipitation step is preferably 90 minutes or less, more preferably 60 minutes or less. Further, the temperature of the aqueous solvent is preferably 50°C or lower, more preferably 15°C or lower.

The above-described precipitation process produces aluminum nitride particles A having zinc hydroxide attached to their surfaces. After the precipitation step, it is preferable that the solution containing the aluminum nitride particles A is immediately subjected to a solid-liquid separation operation, and the resulting solid is washed with water or alcohol to remove basic substances, and then dried. . As the solid-liquid separation operation, Nutsche filtration using a filter, centrifugal filtration, filter press, etc. are preferable because the subsequent water washing operation is easy. The atmosphere during drying may be air, inert gas, or vacuum. The drying temperature is preferably 50 to 180°C.

In addition, in this precipitation step, in addition to the aluminum nitride particles A with zinc hydroxide attached to the surface, other components other than the aluminum nitride particles A, such as aluminum nitride particles and zinc hydroxide that are not attached to each other, are also usually used. obtained at the same time. Therefore, in this precipitation step, a filler composition (precursor of a thermally conductive filler to be described later) containing aluminum nitride particles A is obtained.

<Baking process>
The firing step is a step of firing the aluminum nitride particles A obtained in the above precipitation step at 600° C. or higher. By firing, the zinc hydroxide adhering to the aluminum nitride particles becomes zinc oxide, and the composite aluminum nitride particles of the present invention are obtained. In the composite aluminum nitride particles, zinc oxide adheres to at least a portion of the surface of the aluminum nitride, as described later, and thereby a zinc oxide layer is formed on at least a portion of the particle surface. The fixing is done through a composite oxide layer of aluminum and zinc. Here, the composite oxide of aluminum and zinc includes, for example, zinc aluminate (ZnAl ₂ O ₄ ).
The firing temperature is preferably 600 to 900°C, more preferably 600 to 800°C. If the firing temperature is less than 600°C, the crystallinity of the zinc oxide formed will be low, the thermal conductivity of the zinc oxide layer will not increase, and as a result, the thermal conductivity of the composite aluminum nitride particles obtained will decrease. . On the other hand, by setting the firing temperature to 900° C. or lower, the formation of a composite oxide layer of aluminum and zinc with low thermal conductivity is suppressed, and as a result, the thermal conductivity of the resulting composite aluminum nitride particles becomes high.
The firing atmosphere is not particularly limited, but an atmosphere containing oxygen is preferable because zinc oxide is likely to be produced.
Composite aluminum nitride particles are manufactured by the method including the above-described precipitation step and firing step.

[Composite aluminum nitride particles]
The composite aluminum nitride particles of the present invention are composite aluminum nitride particles characterized in that zinc oxide is fixed to at least a portion of the surface of the aluminum nitride particles via a composite oxide layer of aluminum and zinc.

FIG. 1 shows a scanning electron microscope (SEM) photograph of composite aluminum nitride particles of the present invention. FIG. 1 is a SEM observation photograph of a thermally conductive filler obtained in Production Example 1, which will be described later. Composite aluminum nitride particles 13 to which zinc oxide 12 is adhered are observed on at least a portion of the surface of aluminum nitride particles 11 . What is shown by the symbols "11" and "12" in FIG. 1 are aluminum nitride particles and zinc oxide, respectively, can be confirmed by elemental analysis using an energy dispersive X-ray spectrometer (EDX) equipped in a scanning electron microscope (SEM). It is clear from the results.
Further, the adhesion of zinc oxide to the surface of the aluminum nitride particles is achieved through a composite oxide layer of aluminum and zinc. Here, the composite oxide of aluminum and zinc means, for example, zinc aluminate (ZnAl ₂ O ₄ ). The production of zinc aluminate was confirmed from the X-ray diffraction pattern. It is estimated that zinc aluminate is produced by the reaction between aluminum oxide on the surface of aluminum nitride and zinc hydroxide or zinc oxide.

In the composite aluminum nitride particles 13 of the present invention, zinc oxide 12 is fixed to the surface of the aluminum nitride particles 11. Furthermore, as shown in FIG. 1, at least a portion of the zinc oxide 12 exists so as to connect the composite aluminum nitride particles 11.
Therefore, even when composite aluminum nitride particles 13 are highly filled in a resin and pressed under pressure, zinc oxide 12 is difficult to detach from the surface of aluminum nitride particles 13. Zinc oxide has a low Mohs hardness of 4 to 5 and is a soft filler, so it plays a role in intervening between composite aluminum nitride particles in the resin and connecting the particles. It is thought that surface contact becomes easier and thermal conductivity improves.

On the other hand, when aluminum nitride particles and zinc oxide are simply mixed to form a composite as in the past, zinc oxide only adheres to the surface of the aluminum nitride particles, and the composite aluminum nitride particles of the present invention Compared to this, the adhesion between aluminum nitride particles and zinc oxide is weaker. Therefore, when conventional aluminum nitride particles with zinc oxide attached to the surface are filled with resin and pressed, the zinc oxide is easily released, and as a result, the contact between aluminum nitrides becomes point contact, and the thermal conductivity decreases. It is thought that it will be lower.

[Thermal conductive filler]
The thermally conductive filler of the present invention contains the above-described composite aluminum nitride particles. The thermally conductive filler is obtained by firing the thermally conductive filler precursor obtained in the above-described precipitation step. In the precipitation step, as described above, other components may be produced in addition to the aluminum nitride particles A to which zinc hydroxide is attached. Therefore, in addition to the composite aluminum nitride particles, the firing process may produce aggregates of aluminum nitride particles, fine zinc oxide powder, aggregates of fine zinc oxide powder, and the like.
The thermally conductive filler of the present invention may contain, in addition to the above composite aluminum nitride particles, aggregates of aluminum nitride particles, fine powder of zinc oxide, aggregates of fine powder of zinc oxide, and the like.
The amount of zinc oxide in the thermally conductive filler is preferably 3 to 40 mol%, more preferably 5 to 30 mol%, based on 100 mol% of the aluminum nitride particles and zinc oxide.

[Resin composition]
The resin composition of the present invention is a resin composition containing the above-described thermally conductive filler. The resin composition has a thermally conductive filler dispersed in the resin and has high thermal conductivity. The type of resin is not particularly limited, and may be either a thermoplastic resin or a thermosetting resin.
Examples of the thermoplastic resin include polyethylene, polypropylene, ethylene-propylene copolymer, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyvinyl alcohol, polyacetal, and fluororesin. (for example, polyvinylidene fluoride, polytetrafluoroethylene, etc.), polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, polystyrene, polyacrylonitrile, styrene-acrylonitrile copolymer, ABS resin, polyphenylene ether (PPE) resin, Modified PPE resin, aliphatic polyamide, aromatic polyamide, polyimide, polyamideimide, polymethacrylic acid, polymethacrylic acid ester (e.g. polymethyl methacrylate, etc.), polyacrylic acid, polyacrylic acid ester (e.g. polymethyl acrylate, etc.) , polycarbonate, polyphenylene sulfide, polysulfone, polyethersulfone, polyethernitrile, polyetherketone, polyetheretherketone, polyketone, liquid crystal polymer, ionomer, and the like.
Examples of the thermosetting resin include epoxy resin, acrylic resin, urethane resin, silicone resin, phenol resin, imide resin, thermosetting modified PPE, and thermosetting PPE.

As a mixing device for mixing the resin and the thermally conductive filler, for example, a common kneading machine such as a roll, kneader, Banbury mixer, or rotation/revolution mixer is preferably used.

The resin composition of the present invention may be molded into a molded article by a known method. Examples of the molding method include injection molding, transfer molding, extrusion molding, bulk molding compound molding, compression molding, and molding by casting using a solvent, etc. However, from the viewpoint of easily achieving the effects of the present invention, It is preferable to form a molded body by compression molding. Since the resin composition of the present invention contains the composite aluminum nitride particles described above, zinc oxide is difficult to detach from the aluminum nitride particles during compression molding, so the aluminum nitride particles are likely to come into surface contact with each other, and the thermal conductivity of the molded product is improved. Becomes good.
In addition, ordinary aluminum nitride particles without zinc oxide adhering to their surfaces have high hardness and may wear out parts used during molding, such as contact members of molding equipment, and objects to be used for molded bodies. However, since the composite aluminum nitride particles of the present invention have soft zinc oxide adhered to the surface, the above-described wear is suppressed.
The shape of the molded body is not particularly limited, and examples include sheet, film, disk, and rectangular shapes.

The molded body is preferably used as various heat radiating members. For example, it is preferable to use it as a heat radiating member for efficiently radiating heat generated from semiconductor components installed in home appliances, automobiles, notebook personal computers, and the like. Specific examples of the heat dissipation member include heat dissipation grease, heat dissipation gel, heat dissipation sheet, phase change sheet, adhesive, and the like. In addition to these, it can also be used, for example, as an insulating layer used in metal base substrates, printed circuit boards, flexible substrates, etc., semiconductor encapsulants, underfills, casings, heat radiation fins, and the like.

EXAMPLES Hereinafter, examples will be shown to further specifically explain the present invention, but the present invention is not limited to these examples.
In the examples, various physical properties were measured by the following methods.

[Average particle size]
Aluminum nitride powder was added to ethanol at a concentration of 1% by mass, and after 3 minutes of ultrasonic irradiation of about 200 W, the particle size distribution was measured using a laser diffraction scattering particle size distribution meter. In the volume frequency distribution of particle diameters, the value of the particle diameter at which the cumulative value of the volume frequency becomes 50% was defined as D50, and this was defined as the average particle diameter.

[Thermal conductivity]
The thermal conductivity of each molded body at room temperature (25° C.) was calculated from the product of thermal diffusivity, specific heat, and density. The thermal diffusivity was measured by a laser flash method using a thermal constant measuring device (TC7000, manufactured by ULVAC Riko Co., Ltd.). The specific heat was measured using a differential scanning calorimeter (DSC, Seiko Instruments Co., Ltd., DSC6200). Density was measured by the flotation method.

[Scanning electron microscope]
The thermally conductive filler obtained in each production example was observed using a scanning electron microscope (SEM-EDX). The device used was JSM-6610LA manufactured by JEOL.

[Powder X-ray diffraction]
The crystal structure of the thermally conductive filler obtained in each production example was analyzed using a wide-angle X-ray diffraction device. The device used was Rigaku's SmartLab.

[Powder compressibility]
Powder was put into a mold with a depth of 3 mm and a diameter of 30 mm, and the displacement of the thickness with respect to the pressure P was investigated when the powder was compressed at a speed of 1 mm per minute. The amount of space ε in the compacted powder was calculated from the displacement and the specific gravity of the powder components. According to the following formula (1), lnP was plotted on the horizontal axis and ε was plotted on the vertical axis, and the slope, -(1/F), and intercept c of the approximate straight line obtained using the least squares method were obtained. The F value determined from this slope represents the compressibility of the powder, and the smaller the F value, the easier it is to compact the powder, that is, it is an index of the softness of the powder. c is a compression constant specific to the powder and depends on the bulk density and the like.
ε=-(1/F)・lnP+c (1)

[Materials used]
The aluminum nitride powder, zinc salt, and solvent used in Examples and Comparative Examples are as follows.
<Aluminum nitride powder>
The following aluminum nitride powder obtained by a reductive nitriding method or sintered was used.
AlN1... "FAN-15-Al" manufactured by Furukawa Electronics Co., Ltd., average particle size (D50) = 8 μm
AlN2: "HF-01D" manufactured by Tokuyama Co., Ltd., average particle size (D50) = 0.7 μm
AlN3... "FAN-30-Al" manufactured by Furukawa Electronics Co., Ltd., average particle size (D50) = 31.3 μm
AlN4... "FAN-50-Al" manufactured by Furukawa Electronics Co., Ltd., average particle size (D50) = 59.3 μm
<Zinc salt>
Zinc acetate dihydrate (Zn(Ac) _{2.2H 2} O)
<Zinc oxide>
Zinc oxide powder produced by the method shown in Production Example 9 <Solvent>
Distilled water

(Manufacturing example 1)
Zinc acetate dihydrate and aluminum nitride powder (AlN1) were added to distilled water at the molar ratio shown in Table 1 and mixed to prepare a suspension. The molar ratios listed in Table 1 correspond to the molar ratios of aluminum atoms in aluminum nitride and zinc atoms in zinc acetate.
Subsequently, an aqueous sodium hydroxide solution having a concentration of 3.33 mol/L was added dropwise to the suspension over 15 minutes to make a basic suspension, and the mixture was stirred at 23° C. for 1 hour to generate zinc hydroxide. The pH of the basic suspension was 13. The suspension was filtered under reduced pressure to obtain a solid, which was washed with 100 ml of methanol and dried in an air atmosphere in a constant temperature bath at 120°C for 17 hours to form a nitrided substance with zinc hydroxide attached to the surface. A precursor of a thermally conductive filler containing aluminum particles A was obtained.
The thermally conductive filler precursor described above was introduced into an electric furnace and fired at 700° C. for 2 hours to obtain a thermally conductive filler containing composite aluminum nitride particles of the present invention.
The results of observing the obtained thermally conductive filler using a scanning electron microscope are shown in FIG. The explanation of FIG. 1 is as described above, and composite aluminum nitride particles 13 to which zinc oxide 12 was adhered were observed on at least a portion of the surface of aluminum nitride particles 11. Further, as a result of performing X-ray diffraction measurement on the obtained thermally conductive filler, it was confirmed that a very small amount of zinc aluminate (ZnAl ₂ O ₄ ) was generated.
From the above results, it was confirmed that the composite aluminum nitride particles of the present invention were produced in Production Example 1.

(Manufacturing examples 2 to 8)
A thermally conductive filler was obtained in the same manner as in Production Example 1, except that the type of aluminum nitride powder used and the amount of zinc acetate dihydrate (molar ratio of AlN and ZnO) were changed as shown in Table 1.
The thermally conductive filler obtained in Production Example 2 was observed using a scanning electron microscope. As a result, as shown in FIG. 2, composite aluminum nitride particles 13 to which zinc oxide 12 was adhered were observed on at least a portion of the surface of aluminum nitride particles 11. Further, as a result of performing X-ray diffraction measurement on the obtained thermally conductive filler, it was confirmed that a very small amount of zinc aluminate (ZnAl ₂ O ₄ ) was generated.
(Manufacturing example 9)
A powder consisting only of zinc oxide was obtained in the same manner as in Production Example 1 except that aluminum nitride powder was not added.

(Example 1)
6.15 g of thermally conductive filler obtained in Production Example 2, 0.94 g of epoxy resin (bisphenol F type; jER807 manufactured by Mitsubishi Chemical), amine curing agent (dicyanodicyclohexacylethane; jER Cure 113 manufactured by Mitsubishi Chemical). 0.4g was kneaded in an agate mortar, and the filler filling rate shown in Table 2 was 60vol. % resin composition. Next, the resin composition was compression molded using a compression molding machine (F-37 manufactured by Kamito Metal Industry Co., Ltd.). A cylindrical jig made of SUS was used for molding. Compression molding was carried out under the conditions of a press pressure of 2.2 GPa, a temperature of 423 K, and a curing time of 20 minutes to obtain a disc-shaped molded product with a diameter of 10 mm and a thickness of 1 mm. Table 2 shows the evaluation results of the obtained molded bodies.

(Examples 2 to 25)
Example 1 was carried out in the same manner as in Example 1, except that the type of thermally conductive filler, the amount of thermally conductive filler, epoxy resin, and amine curing agent, filler filling rate, and press pressure were changed as shown in Tables 2 and 3. A molded body was obtained. The evaluation results of the obtained molded bodies are shown in Tables 2 and 3. Regarding Examples 16 to 19, Table 3 shows the compressibility evaluation results for each of the thermally conductive filler powders obtained in Production Examples 5 to 8.

(Comparative example 1)
Using AlN1 as the aluminum nitride powder, it was mixed with an epoxy resin and an amine curing agent in the same manner as in Example 1 to obtain a filler filling rate of 60 vol. % resin composition was obtained, and compression molding was performed in the same manner as in Example 1 to obtain a molded article. Table 2 shows the evaluation results of the obtained molded bodies.

(Comparative Examples 2-3)
A molded article was obtained in the same manner as in Comparative Example 1, except that the amounts of the thermally conductive filler, epoxy resin, and amine curing agent, and the filler filling rate were changed as shown in Table 2. Table 2 shows the evaluation results of the obtained molded bodies.

(Comparative example 4)
AlN1, which is an aluminum nitride powder, and the zinc oxide powder obtained in Production Example 9 were mixed at the molar ratio shown in Table 2 to obtain a mixed filler. Using the mixed filler as a thermally conductive filler, it was mixed with an epoxy resin and an amine curing agent in the same manner as in Example 1 to obtain a resin composition with a filler filling rate of 60% by volume. Compression molding was performed in the same manner to obtain a molded product. Table 2 shows the evaluation results of the obtained molded bodies.

(Comparative Examples 5-6)
A molded body was obtained in the same manner as Comparative Example 4 except that the filler filling rate was changed as shown in Table 2. Table 2 shows the evaluation results of the obtained molded bodies.
(Comparative example 7)
A molded body was obtained in the same manner as in Comparative Example 1, except that AlN4 was used as the aluminum nitride powder and the filler filling rate was changed as shown in Table 3. Furthermore, Table 3 shows the results of compressibility evaluation of AlN4 powder.
(Comparative Examples 8 to 10)
A molded body was obtained in the same manner as in Comparative Example 4, except that AlN4 was used as the aluminum nitride powder and the filler filling rate was changed as shown in Table 3. Furthermore, Table 3 shows the results of compressibility evaluation of AlN4 powder.

Comparing the molded bodies of Examples and Comparative Examples with the same amount of filler filling, it was found that the molded bodies of Examples had higher thermal conductivity. Therefore, it was found that the manufacturing method of the present invention provides composite aluminum nitride particles that have improved thermal conductivity when filled in a resin. It was also found that in the composite aluminum nitride particles, zinc oxide was fixed to at least a portion of the surface of the aluminum nitride particles via a composite oxide layer of aluminum and zinc.
The powder compressibility results shown in Table 3 show that aluminum nitride particles coated with zinc oxide have a higher compressibility F value than those without zinc oxide or with only zinc oxide powder mixed. It became smaller. Since the powder containing the composite aluminum nitride particles has soft zinc oxide fixed to the aluminum nitride particles, the compressibility value becomes small due to the deformation of the zinc oxide between the aluminum nitride particles during compression. In other words, it is assumed that the powder becomes softer.

11 Aluminum nitride particles 12 Zinc oxide 13 Composite aluminum nitride particles

Claims (5)

Composite nitriding characterized by comprising a precipitation step of precipitating zinc hydroxide on the surface of aluminum nitride particles in an aqueous solvent, and a firing step of baking the aluminum nitride particles A obtained in the precipitation step at 600 to 900°C. Method for producing aluminum particles. 2. The method for producing composite aluminum nitride particles according to claim 1, wherein the precipitation step is performed by adding a basic substance to an aqueous solvent containing zinc salt and aluminum nitride particles. Composite aluminum nitride particles characterized in that zinc oxide is fixed to at least a portion of the surface of the aluminum nitride particles via a composite oxide layer of aluminum and zinc. A thermally conductive filler comprising the composite aluminum nitride particles according to claim 3. A resin composition comprising the thermally conductive filler according to claim 4.