JP6936442B2 - Method for manufacturing thermally conductive filler, thermally conductive composite material, and thermally conductive filler - Google Patents

Description

The present invention relates to a thermally conductive filler, a thermally conductive composite material using the same, and a method for producing the thermally conductive filler.

Boron nitride is known as a highly insulating material having high thermal conductivity, and various thermally conductive composite materials in which boron nitride particles are dispersed in a matrix as a thermally conductive filler have been developed. Further, a thermally conductive composite material in which such boron nitride particles are used in combination with particles of other thermally conductive materials such as aluminum oxide, aluminum nitride, silicon oxide, silicon nitride, silicon carbide, zinc oxide, and graphite. Has also been developed.

For example, in Japanese Patent Application Laid-Open No. 2001-158610 (Patent Document 1), aluminum nitride powder composed of a pulverized product of an aluminum nitride sintered body and having an average particle size of more than 50 μm and aluminum nitride having an average particle size of 3 μm or less are used. , A mixed powder made by mixing one or more kinds of good thermal conductive ultrafine powders selected from silicon nitride, boron nitride, silicon carbide, graphite, aluminum, silicon, copper, silver and gold, and A resin composition containing the mixed powder is disclosed.

Further, in Japanese Patent Application Laid-Open No. 2014-162679 (Patent Document 2), the (002) diffraction line and the (100) diffraction line of the X-ray diffraction of the surface measured from the direction parallel to the height direction of the molded body are described. Degree of orientation obtained by a predetermined formula from the intensity ratio and the intensity ratio of the (002) diffraction line and the (100) diffraction line of the X-ray diffraction of the surface measured from the direction perpendicular to the height direction of the molded body. To a boron nitride molded body (sintered body) having a calcium content of 500 to 5000 ppm and a graphitization index of 0.8 to 4.0 by powder X-ray diffraction. A boron nitride resin molded body impregnated with a resin dispersion containing one or more ceramic powders selected from the group of aluminum oxide, silicon oxide, zinc oxide, silicon nitride, aluminum nitride and aluminum hydroxide. It is disclosed.

Further, in Japanese Patent Application Laid-Open No. 2014-172768 (Patent Document 3), boron nitride powder, which is an aggregate of boron nitride particles to which primary particles of hexagonal boron nitride are bonded, has an average particle size of 0.1 to 10 μm. A composite powder obtained by spray-granulating a slurry containing one or more ceramic powders selected from the group consisting of aluminum oxide, zinc oxide, silicon nitride, and aluminum nitride and then firing the powder, and having a void ratio of 5. The peak intensity ratio I (002) / I (100) of the (002) plane to the (100) plane of boron nitride in the powder X-ray diffractometry is 9.0 or less, with an average particle size of about 55% and an average particle size of 20 to 100 μm. A boron nitride composite powder and a resin composition containing the composite powder are disclosed.

Further, in Japanese Patent Application Laid-Open No. 2015-214339 (Patent Document 4), boron nitride plate-like particles having an average particle size of 10 to 100 μm, alumina, magnesium oxide, zinc oxide, beryllium, silica, boron nitride, aluminum nitride, and the like. Mechanochemical treatment is performed in which at least one inorganic particle selected from the group consisting of cordierite, forsterite, zircon, mulite, silicon carbide, boron carbide and titanium carbide is mixed and mixed while applying a high shearing force. The composite powder thus obtained and the resin composition containing the composite powder are disclosed.

However, even with such a conventional heat conductive composite material, there is a limit to the improvement of the heat conductivity, and it is not always possible to achieve sufficient heat conductivity.

Japanese Unexamined Patent Publication No. 2001-158610 Japanese Unexamined Patent Publication No. 2014-162679 Japanese Unexamined Patent Publication No. 2014-172768 Japanese Unexamined Patent Publication No. 2015-214339

The present invention has been made in view of the above-mentioned problems of the prior art, and is a heat conductive filler capable of efficiently improving heat conductivity, a method for producing the same, and heat conduction having excellent heat conductivity. It is an object of the present invention to provide a sex composite material.

As a result of diligent research to achieve the above object, the present inventors have adopted a combination of boron nitride and aluminum nitride as a heat conductive material, and compressed and calcined a mixture of boron nitride powder and aluminum nitride powder. By crushing the aluminum nitride particles after the above, a thermally conductive filler in which more than half of the aluminum nitride particles are contained in the boron nitride particles can be obtained. We have found that it is possible to efficiently improve the thermal conductivity and obtain a thermally conductive composite material having excellent thermal conductivity, and have completed the present invention.

In the present specification, the "state in which the aluminum nitride particles are encapsulated in the boron nitride particles" means that "50% or more of the outer surface of the aluminum nitride particles is contained inside the boron nitride particles and the boron nitride particles are included." It refers to a "contacted state", and the aluminum nitride particles forming a composite particle with the boron nitride particles in such a state are counted as "aluminum nitride particles contained in the boron nitride particles".

That is, the thermally conductive filler of the present invention is a thermally conductive filler containing boron nitride particles and aluminum nitride particles.
The average particle size of the boron nitride particles is 1 to 100 μm.
The average particle size of the aluminum nitride particles is in the range of 1/30 to 1 / 0.5 of the average particle size of the boron nitride particles.
50% or more of the total particles of the aluminum nitride particles were included in the inside of the boron nitride particles and 50% or more of the outer surface of the aluminum nitride particles was in contact with the boron nitride particles. In this state, composite particles of the aluminum nitride particles and the boron nitride particles are formed .
It contains at least one sintering aid component selected from the group consisting of calcium compounds and yttrium compounds as sintering aids, and compounds derived from these sintering aids.
It is characterized by that.

Further, the heat conductive composite material of the present invention is characterized by comprising a matrix and the heat conductive filler of the present invention dispersed in the matrix.

In such a heat conductive filler and a heat conductive composite material of the present invention, the content of the aluminum nitride particles is 5 to 95% by volume with respect to the total amount of the boron nitride particles and the aluminum nitride particles. It is preferable to have.

Further, in the heat conductive filler and the heat conductive composite material of the present invention, it is preferable that the heat conductive filler is a pulverized product of a compression-fired product of a mixture of boron nitride powder and aluminum nitride powder.

The method for producing a thermally conductive filler of the present invention is
A step of obtaining a compressed fired body by pressurizing a mixture of boron nitride powder , aluminum nitride powder, and at least one sintering aid selected from the group consisting of a calcium compound and an yttrium compound and firing the mixture while compressing the mixture. ,
After pre-grinding the compression-fired body, the pre-crushed fluid containing the compression-fired body is jetted from a nozzle at a high pressure of 30 to 250 MPa at a flow velocity of 200 to 800 m / s to perform wet collision crushing, thereby nitriding. A thermally conductive filler containing boron particles and aluminum nitride particles, the average particle size of the boron nitride particles is 1 to 100 μm, and the average particle size of the aluminum nitride particles is the average particle size of the boron nitride particles. 50% or more of the total particles of the aluminum nitride particles are in the range of 1/30 to 1 / 0.5, and 50% or more of the outer surface of the aluminum nitride particles is the nitrided particles. A step of obtaining a thermally conductive filler forming a composite particle of the aluminum nitride particles and the boron nitride particles while being contained inside the boron particles and in contact with the boron nitride particles.
It is a method characterized by including.

In such a method for producing a thermally conductive filler of the present invention, it is preferable to bake a mixture of the boron nitride powder and the aluminum nitride powder while compressing it under a pressure condition of 10 to 500 MPa.

Although it is not always clear why the thermally conductive filler of the present invention makes it possible to obtain a thermally conductive composite material having excellent thermal conductivity, the present inventors presume as follows.

That is, first, in order to improve the thermal conductivity of the thermally conductive composite material in which the thermally conductive filler is dispersed in the matrix, it is important to use particles made of a material having high thermal conductivity as the filler particles. However, since heat conduction in such a heat conductive composite material is achieved by transferring heat through a portion where the filler particles (heat conductive particles) are in contact with each other, heat at the contact interface between the filler particles is achieved. Reducing resistance is also an important factor. Here, in view of boron nitride (BN) and aluminum nitride (AlN) used as the thermally conductive materials in the present invention, both are materials having excellent thermal conductivity, but AlN has a higher thermal conductivity than BN. Has conductivity. On the other hand, since AlN is a material that is much harder than BN, AlN particles are less likely to be deformed at the contact interface than BN particles, and when AlN particles are involved, they basically form point contact, so the contact area becomes smaller. The thermal resistance at the contact interface increases. Therefore, conventionally, even if AlN particles are used in combination with BN particles, the effect of improving the thermal conductivity due to the use of AlN particles having high thermal conductivity is not sufficiently exhibited, and the desired excellent thermal conductivity is achieved. It was not possible to obtain the composite material to have.

On the other hand, in the present invention, BN particles having a specific average particle size and AlN particles having a specific average particle size smaller than the BN particles are used in combination as the heat conductive filler, and half of the AlN particles are used. The above particles are contained in the BN particles, that is, 50% or more of the outer surface of the AlN particles is contained inside the BN particles and is in contact with the BN particles. Therefore, the contact interface between the contained AlN particles and the BN particles containing the AlN particles is not a point contact but a surface contact, and the thermal resistance is small. Further, in the thermally conductive composite material of the present invention obtained by using such a thermally conductive filler, AlN at the contact interface between the particles is compared with the state where the AlN particles and the BN particles are simply dispersed. The proportion of contact interfaces involving particles is low, and the proportion of contact interfaces involving BN particles is relatively high. BN is a material having a Morse hardness of about 2, and is a relatively soft material among thermally conductive materials. The BN particles are slightly deformed during interparticle contact to secure a larger contact area than in the case of point contact. Therefore, in the heat conductive composite material of the present invention, the thermal resistance at the contact interface between particles is also small. Therefore, if the heat conductive filler of the present invention is used, the total interfacial thermal resistance in the heat conduction path in the obtained composite material is reduced, and the heat conductive composite material having excellent heat conductivity can be obtained. The inventors speculate.

Further, in the method for producing a heat conductive filler of the present invention, a mixture of BN powder and AlN powder is pressed and fired while being compressed to form a compressed fired body, and then pulverized to obtain a heat conductive filler. ing. Therefore, in the production method of the present invention, since the AlN particles and the BN particles are closely bonded to each other in the compression sintered body, the BN having a hardness smaller than that of the AlN and easily cracking due to opening when pulverized. Phases are selectively disrupted (opened or peeled off), and as a result, composite particles in which AlN particles are encapsulated in BN particles can be efficiently obtained. Further, in the production method of the present invention, since the BN powder as a raw material is sintered into BN particles in the composite material, high heat conduction in the BN is performed as in the mechanochemical treatment of mixing while applying a high shearing force. The high thermal conductivity crystal structure in the BN remains sufficiently retained without destroying the sex crystal structure. Therefore, the present inventors presume that according to the production method of the present invention, a heat conductive filler effective for obtaining a heat conductive composite material having excellent heat conductivity can be obtained.

According to the present invention, it is possible to provide a heat conductive filler capable of efficiently improving heat conductivity, a method for producing the same, and a heat conductive composite material having excellent heat conductivity.

It is a schematic diagram which shows the columnar thermal conductivity composite material produced in Example and Comparative Example, and the thermal conductivity (x-axis direction) measurement sample cut out from it. It is a scanning electron micrograph which shows the SEM image of the cross section of the heat conductive composite material obtained in Example 1. FIG. It is a scanning electron micrograph which shows an example of the SEM image of the cross section of the heat conductive filler obtained in Example 1. FIG. It is a scanning electron micrograph which shows another example of the SEM image of the cross section of the heat conductive filler obtained in Example 1. FIG. It is a scanning electron micrograph which shows the SEM image of the cross section of the heat conductive composite material obtained in Example 2. FIG. It is a scanning electron micrograph which shows the SEM image of the cross section of the heat conductive composite material obtained in the comparative example 1. FIG. It is a scanning electron micrograph which shows the SEM image of the cross section of the heat conductive composite material obtained in the comparative example 2. FIG. It is a scanning electron micrograph which shows the SEM image of the cross section of the heat conductive composite material obtained in the comparative example 3. FIG. It is a scanning electron micrograph which shows the SEM image of the cross section of the heat conductive composite material obtained in the comparative example 4. FIG.

Hereinafter, the present invention will be described in detail according to the preferred embodiment thereof.

(Thermal conductive filler)
First, the thermally conductive filler of the present invention will be described. The thermally conductive filler of the present invention is a thermally conductive filler containing boron nitride particles and aluminum nitride particles.
The average particle size of the boron nitride particles is 1 to 100 μm.
The average particle size of the aluminum nitride particles is in the range of 1/100 to 1 / 0.2 of the average particle size of the boron nitride particles.
50% or more of the total particles of the aluminum nitride particles were included in the inside of the boron nitride particles and 50% or more of the outer surface of the aluminum nitride particles was in contact with the boron nitride particles. In this state, composite particles of the aluminum nitride particles and the boron nitride particles are formed.
It is characterized by that.

In the present invention, boron nitride (BN) particles and aluminum nitride (AlN) particles are used in combination as the heat conductive filler. The boron nitride that constitutes the boron nitride particles used in the present invention includes a hexagonal normal pressure phase and a cubic high pressure phase, but from the viewpoint of ease of opening and thermal conductivity, a hexagonal plate shape is used. It is preferably boron nitride particles. Further, since aluminum nitride can form an interface in close contact with boron nitride by sintering as compared with other hard high thermal conductive materials such as diamond and alumina, the boron nitride and the above-mentioned By forming composite particles, excellent thermal conductivity can be obtained.

The average particle size of the boron nitride particles in the thermally conductive filler of the present invention needs to be 1 to 100 μm. When the average particle size of the boron nitride particles is less than 1 μm, the sheet-like structure of boron nitride that contributes to the development of thermal conductivity is cut off, and the number of interfaces between the particles increases in the obtained composite material, so that the overall thermal resistance increases. do. On the other hand, if the average particle size of the boron nitride particles exceeds 100 μm, the dispersion uniformity and filling rate of the thermally conductive filler in the obtained composite material are lowered, and sufficient thermal conductivity cannot be obtained. From the same viewpoint, it is more preferable that the lower and upper limits of the average particle size of the boron nitride particles are 3 μm and 50 μm, respectively. The average particle size of the boron nitride particles is such that all the boron nitride particles contained in the thermally conductive filler, that is, the boron nitride particles forming the composite material and the boron nitride not forming the composite material. It is the average particle size of the whole with the particles. Further, even if the boron nitride particles are partially cleaved and have cleavage planes inside or at the ends of the particles, the particles that are partially continuous are regarded as one boron nitride particle.

Further, the average particle size of the aluminum nitride particles in the thermally conductive filler of the present invention needs to be 1/100 to 1 / 0.2 of the average particle size of the boron nitride particles used in combination. When the average particle size of the aluminum nitride particles is less than 1/100 of the average particle size of the boron nitride particles used in combination, the number of grain boundaries between the boron nitride particles and the aluminum nitride particles and between the aluminum nitride particles in the obtained composite material. Increases the overall thermal resistance. On the other hand, if the average particle size of the aluminum nitride particles exceeds 1 / 0.2 of the average particle size of the boron nitride particles used in combination, the aluminum nitride particles are less likely to be included in the boron nitride particles, resulting in the formation of the composite particles. The effect of improving the thermal conductivity cannot be sufficiently obtained, and in the obtained composite material, when the boron nitride particles come into contact with the aluminum nitride particles, it becomes difficult to follow them due to deformation, so that the overall thermal resistance increases. From the same viewpoint, it is more preferable that the lower and upper limits of the average particle size of the aluminum nitride particles are 1/30 and 1 / 0.5 of the average particle size of the boron nitride particles used in combination, respectively. It is even more preferably 1/20 and 1/1, and particularly preferably 1/10 and 1/2. The average particle size of the aluminum nitride particles is such that all the aluminum nitride particles contained in the heat conductive filler, that is, the aluminum nitride particles forming the composite material and the aluminum nitride not forming the composite material. It is the average particle size of the whole with the particles. Further, even if the aluminum nitride particles have cracks inside, those recognized as one particle are regarded as one aluminum nitride particle.

The "average particle size" of the boron nitride particles and the aluminum nitride particles in such a thermally conductive filler can be measured by scanning electron microscope (SEM) observation. Specifically, for example, the thermally conductive filler is dispersed in a matrix such as an epoxy resin so that the content of the thermally conductive filler in the obtained composite material is about 5% by volume (diluted condition) and then cured. Let it be a composite material. Then, with respect to the cross section of the obtained composite material, for example, 10 or more measurement regions having a width of 60 μm or more and a length of 40 μm or more are arbitrarily extracted, and the particle diameters of the boron nitride particles and the aluminum nitride particles in the SEM image of each measurement region. , And further, by calculating the average value of all the measurement regions, the "average particle size" of the boron nitride particles and the aluminum nitride particles in the thermally conductive filler can be obtained. The particle size means the diameter of the minimum circumscribed circle when the cross section is not circular.

In the heat conductive filler of the present invention, the boron nitride particles and the aluminum nitride particles are included as the heat conductive particles, and 50% or more of the total particles of the aluminum nitride particles are 50% or more. However, a composite particle of the aluminum nitride particles and the boron nitride particles is formed in a state where 50% or more of the outer surface of the aluminum nitride particles is contained inside the boron nitride particles and is in contact with the boron nitride particles. doing. As described above, more than half of the aluminum nitride particles in the thermally conductive filler of the present invention are contained in the boron nitride particles, so that the included aluminum nitride particles and their nitrides are encapsulated. The contact interface with the boron nitride particles containing the aluminum particles is not a point contact but a surface contact, and the thermal resistance is small. If the ratio of the aluminum nitride particles forming the composite particles in the state of being encapsulated in the boron nitride particles is less than 50%, the thermal resistance at the contact interface is not sufficiently reduced, and the thermal conductivity of the obtained composite material is sufficient. Does not improve. From the same viewpoint, the ratio of the aluminum nitride particles forming the composite particles in the state of being encapsulated in the boron nitride particles is more preferably 60% or more, and particularly preferably 70% or more. ..

The ratio of the aluminum nitride particles forming the composite particles in such a thermally conductive filler in a state of being encapsulated in the boron nitride particles can be measured by scanning electron microscope (SEM) observation. Specifically, for example, the thermally conductive filler is dispersed in a matrix such as an epoxy resin so that the content of the thermally conductive filler in the obtained composite material is about 5% by volume (diluted condition) and then cured. Let it be a composite material. Then, with respect to the cross section of the obtained composite material, for example, 10 or more measurement regions having a width of 60 μm or more and a length of 40 μm or more are arbitrarily extracted, and in the SEM image of each measurement region, 50% or more of the outer surface is boron nitride. By obtaining the ratio (number basis) of the aluminum nitride particles that are contained inside the particles and are recognized to be in contact with the boron nitride particles, and by calculating the average value of all the measurement regions, the heat is generated. The ratio of the aluminum nitride particles contained in the boron nitride particles in the conductive filler can be obtained.

The state in which 50% or more of the outer surface of the aluminum nitride particles is contained inside the boron nitride particles means that 50% or more of the outer surface of the aluminum nitride particles is continuously or intermittently nitrided in the SEM image. A state in which it is recognized that the boron particles are wrapped inside or fitted at the edges. Further, the state in which 50% or more of the outer surface of the aluminum nitride particles is in contact with the boron nitride particles means that 50% or more of the outer surface of the aluminum nitride particles is continuously or intermittently in contact with the boron nitride particles in the SEM image. A state in which it is recognized that the particles are in close contact with the surface of the particle.

In such a heat conductive filler and a heat conductive composite material of the present invention, the content of the aluminum nitride particles is 5 to 95% by volume with respect to the total amount of the boron nitride particles and the aluminum nitride particles. It is preferably 20 to 70% by volume, and more preferably 20 to 70% by volume. If the content of the aluminum nitride particles is less than the lower limit, the effect of improving the thermal conductivity by combining the aluminum nitride particles having a higher thermal conductivity in combination with the boron nitride particles cannot be sufficiently obtained, and the effect can be obtained. The thermal conductivity of the composite material tends not to improve sufficiently. On the other hand, when the content of the aluminum nitride particles exceeds the upper limit, the contact interface having a large thermal resistance in which the aluminum nitride particles are involved relatively increases in the obtained composite material, so that the composite material has an expected excellent thermal conductivity. There is a tendency that composite materials cannot be obtained.

Further, in the thermally conductive filler of the present invention, at least one sintering aid component selected from the group consisting of calcium compounds and yttrium compounds as sintering aids and compounds derived from these sintering aids. Is more preferably contained. Since the aluminum nitride used in the present invention is a relatively difficult-sintering substance, the aluminum nitride particles and nitride are nitrided by adding a sintering aid and firing in the method for producing a heat conductive filler of the present invention, which will be described later. Since the sintering aid intervenes and sinters at the bonding interface with the boron nitride, the adhesion (bonding strength) is increased, and the aluminum nitride particles described above are encapsulated in the boron nitride particles by subsequent pulverization. The composite particles that are present can be obtained more efficiently. The calcium compound as a sintering aid is not particularly limited, and examples thereof include calcium oxide, calcium-aluminum compound, calcium carbide, calcium fluoride, and calcium hydroxide. The yttrium compound as the sintering aid is not particularly limited, and examples thereof include yttrium oxide and yttrium fluoride. Further, the compound derived from the sintering aid is not particularly limited, and examples thereof include decomposition products obtained by firing the sintering aid. When the sintering aid component is contained in the heat conductive filler of the present invention, the content thereof is preferably 0.2 to 10% by mass in the heat conductive filler.

Further, in the boron nitride particles and the aluminum nitride particles used as the thermally conductive filler in the present invention, hydroxyl groups, carboxyl groups, ester groups and amides are formed on their surfaces from the viewpoint of further improving dispersibility in the matrix described later. A functional group such as a group or an amino group may be bonded.

The above-mentioned heat conductive filler of the present invention has been obtained by the method for producing the heat conductive filler of the present invention described below. Therefore, the heat conductive filler of the present invention includes boron nitride. It is preferably a pulverized product of a compression fired product of a mixture of the powder and the aluminum nitride powder.

(Manufacturing method of thermally conductive filler)
The method for producing a thermally conductive filler of the present invention is
A process of obtaining a compressed fired body by pressurizing a mixture of boron nitride powder and aluminum nitride powder and firing it while compressing it.
By crushing the compression fired body, boron nitride particles and aluminum nitride particles are contained, and 50% or more of the outer surface of the aluminum nitride particles is contained inside the boron nitride particles and the boron nitride particles. The process of obtaining a thermally conductive filler containing composite particles formed in contact with the
It is a method characterized by including.

The boron nitride powder used here is a raw material powder that becomes boron nitride particles in the above-mentioned thermally conductive filler of the present invention, and the average particle size thereof is preferably 1 to 100 μm, and preferably 3 to 50 μm. More preferred. If the average particle size of the boron nitride powder is less than the lower limit, the thermal conductivity tends to decrease due to an increase in thermal resistance due to an increase in the number of particle interfaces, while if it exceeds the upper limit, uniform dispersion of particles becomes difficult. It tends to be.

The aluminum nitride powder used here is a raw material powder that becomes aluminum nitride particles in the above-mentioned heat conductive filler of the present invention, and its average particle size is 1 / of the average particle size of the boron nitride powder used in combination. It is preferably 100 to 1 / 0.2, more preferably 1/30 to 1 / 0.5, even more preferably 1 / 20-1 / 1, and 1/10 to 1/1. 2 is particularly preferable. If the average particle size of the aluminum nitride powder is less than the lower limit of the average particle size of the boron nitride powder used in combination, the thermal conductivity tends to decrease due to the increase in thermal resistance due to the increase in the number of particle interfaces, while the upper limit tends to decrease. If it exceeds, it tends to be difficult to uniformly disperse the particles.

The "average particle size" of the boron nitride powder and aluminum nitride powder used as the raw material powder is the cumulative 50% particle size (median size) in the particle size distribution obtained by the laser diffraction / scattering method (or particle size measurement with an electron microscope), respectively. : D50).

In the method for producing a thermally conductive filler of the present invention, first, a mixture (mixed powder) of the boron nitride powder and the aluminum nitride powder is obtained. The mixing method in this mixing step is not particularly limited, and for example, a wet ball mill crushing and mixing method, a dry ball mill crushing and mixing method, a mechanical mixing method, a stirring mixing method, a mixing method using a mortar and the like are adopted, and if necessary. , Filtering, washing, drying, pulverization and the like to obtain the mixture. The treatments such as filtration, washing, drying, and granulation are not particularly limited, and known methods can be appropriately adopted.

The ratio of the boron nitride powder and the aluminum nitride powder to be mixed in this mixing step is not particularly limited, but is appropriately determined according to the ratio of the boron nitride particles to the aluminum nitride particles in the target heat conductive filler. The content of the aluminum nitride powder is preferably 5 to 95% by mass, more preferably 20 to 70% by mass, based on the total amount of the selected boron nitride powder and the aluminum nitride powder. If the content of the aluminum nitride particles is less than the lower limit, the effect of improving the thermal conductivity by combining the aluminum nitride particles having a higher thermal conductivity in combination with the boron nitride particles cannot be sufficiently obtained, and the effect can be obtained. The thermal conductivity of the composite material tends not to improve sufficiently. On the other hand, when the content of the aluminum nitride particles exceeds the upper limit, the contact interface having a large thermal resistance in which the aluminum nitride particles are involved relatively increases in the obtained composite material, so that the composite material has an expected excellent thermal conductivity. There is a tendency that composite materials cannot be obtained.

Further, in the method for producing a thermally conductive filler of the present invention, it is preferable that at least one sintering aid selected from the group consisting of the calcium compound and the yttrium compound described above is further added to the mixture. Since the aluminum nitride used in the present invention is a relatively difficult-to-sinter substance, by adding a sintering aid and firing, the sintering aid intervenes at the bonding interface between the aluminum nitride particles and the boron nitride particles. Then, the adhesion (bonding strength) is increased due to sintering, and the composite particles in which the above-mentioned aluminum nitride particles are encapsulated in the boron nitride particles can be obtained more efficiently by the subsequent pulverization. When such a sintering aid is added, the amount of the sintering aid added is preferably 0.2 to 10% by mass in the mixture.

Next, in the method for producing a thermally conductive filler of the present invention, a compressed fired product is obtained by pressurizing the mixture (mixed powder) and firing it while compressing it. In this firing step, it is necessary to fire (hot press) the mixture under pressurized conditions in which the mixture is placed in a mold and compressed, and the pressure at that time is preferably 10 to 500 MPa, preferably 50 to 300 MPa. Is more preferable. If the pressure is less than the lower limit, the particles will not be sufficiently adhered even after firing, and the interface between the aluminum nitride particles and the boron nitride particles will be destroyed by the subsequent pulverization, making it difficult to obtain the above-mentioned composite particles. There is a tendency. On the other hand, when the pressure exceeds the upper limit, the particles tend to be excessively cracked and the thermal conductivity tends to decrease. The compression method is not particularly limited, and may be uniaxial compression or biaxial compression. It may also be isotropically compressed with hydrostatic pressure.

The temperature and time in this firing step may be any condition as long as the mixture is sufficiently sintered, and is not particularly limited, but is preferably 1 to 5 hours at 1000 to 2500 ° C. Further, the atmosphere of the firing step is not particularly limited, but is preferably an atmosphere of an inert gas such as nitrogen or argon.

Next, in the method for producing a thermally conductive filler of the present invention, the thermally conductive filler can be obtained by crushing the compressed fired body. That is, in the above-mentioned compression sintered body, since the aluminum nitride particles and the boron nitride particles are sufficiently adhered to each other, the hardness is smaller than that of aluminum nitride when pulverized, and the nitride is liable to crack due to opening. A thermally conductive filler containing composite particles in which the boron nitride phase is selectively destroyed (opened or peeled off) and the aluminum nitride particles are encapsulated in the boron nitride particles can be efficiently obtained.

The crushing method in this crushing step is not particularly limited, and a crushing method using various crushers (mills) or dairy pots, wet ball mill crushing, dry ball mill crushing, etc. may be used, but the compression fired body is prepared as necessary. After pulverization, a method (wet pulverization method) in which a fluid containing the pre-pulverized compressed fired body particles is injected from a nozzle at a high pressure to perform wet collision pulverization is preferably adopted. According to such a wet pulverization method, the boron nitride phase tends to be more selectively destroyed (opened or peeled off) from the aluminum nitride phase or the interface between the aluminum nitride particles and the boron nitride particles. The surface of the boron nitride particles to be formed is partially opened, and the partially opened boron nitride particles tend to be easily obtained. When the surface of the boron nitride particles is partially opened in this way, the portion of the boron nitride that is opened at the time of contact between the particles is easily deformed in a form that reduces the voids generated by the opening. In the composite material, the particles can be brought into contact with each other in a state of higher adhesion, the area of the contact interface between the particles is increased, the thermal resistance is reduced, and the thermal conductivity tends to be further improved.

In such a wet pulverization method, by injecting a fluid containing the compressed calcined body particles as raw material particles from a nozzle at a high pressure, the particles collide with each other or become finer due to shear flow, thereby destroying the crystal structure. While wet pulverization is performed while suppressing excessive fineness, the pressure applied to the particles suddenly disappears by rapidly reducing the pressure from the state in which the particles are sheared, flowed and compressed at high pressure in the fluid. As a result, a force that expands from the inside of the particle to the outside acts, and the particle is pulled outward accordingly, causing partial opening inside and at the end of the particle, and the above-mentioned composite material and partially opened boron nitride particle. Will be obtained efficiently.

The apparatus used in such a wet pulverization method is not particularly limited, and is a commercially available wet pulverizer (wet pulverization) based on the principle of injecting a fluid containing raw material particles from a nozzle at a high pressure to perform wet collision pulverization to make the particles finer. A device) can be used. Further, from the viewpoint of wet pulverization while suppressing destruction of the crystal structure and excessive miniaturization, it is preferable to use a wet pulverizer provided with a straight nozzle.

The average particle size of the pre-crushed compressed calcined body particles used as the raw material particles is not particularly limited, and depends on the average particle size of the boron nitride particles and the aluminum nitride particles in the target heat conductive filler. It is preferably 2 to 200 μm, more preferably 10 to 60 μm.

Further, the dispersion medium of the fluid jetted from the nozzle together with the compressed calcined body particles is not particularly limited, and for example, N-methyl-2-pyrrolidone, chloroform, dichloromethane, carbon tetrachloride, acetone, methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone. , Methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, isopentyl acetate, amyl acetate, tetrahydrofuran, dimethyl formaldehyde, dimethylacetamide, dimethylsulfoxide, acetonitrile, methanol, ethanol, propanol, isopropanol, butanol , Hexanol, octanol, hexafluoroisopropanol, ethylene glycol, propylene glycol, tetramethylene glycol, tetraethylene glycol, hexamethylene glycol, diethylene glycol, benzene, toluene, xylene, chlorobenzene, dichlorobenzene, trichlorobenzene, chlorophenol, phenol, tetrahydrofuran, Examples thereof include organic solvents such as sulfolane, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, N-dimethylpyrrolidone, pentane, hexane, neopentane, cyclohexane, heptane, octane, isooctane, nonane, decane and diethyl ether. ..

Further, the concentration of the fluid (dispersion liquid) containing the compressed calcined particles is not particularly limited, but the content of the compressed calcined particles is preferably 0.1 to 20% by volume, preferably 0.5 to 10% by volume. More preferred.

The conditions for the wet pulverization method are not particularly limited, but the following conditions are preferable from the viewpoint of efficiently obtaining the above-mentioned composite material and partially cleaved boron nitride particles.
Pre-injection pressure: 30-250 MPa (more preferably 50-200 MPa)
Post-injection pressure: Normal pressure Nozzle diameter: 0.1 to 0.5 mm
Flow rate: 0.1 to 7.0 L / min (more preferably 0.5 to 1.1 L / min)
Nozzle injection flow rate: 200 to 800 m / s (more preferably 300 to 700 m / s).

If the pre-injection pressure, the flow rate, or the nozzle injection flow velocity in the wet pulverization method is less than the lower limit, it becomes difficult for the boron nitride particles to proceed, and the composite material and the partially opened boron nitride particles tend to be insufficiently obtained. be. On the other hand, when the pre-injection pressure, the flow rate, or the nozzle injection flow velocity in the wet pulverization method exceeds the upper limit, in addition to the opening of the boron nitride particles, the opening of the aluminum nitride particles and the opening of the interface between the aluminum nitride particles and the boron nitride particles Tends to proceed easily, and the above-mentioned composite material tends not to be sufficiently obtained.

Further, the wet pulverization method may be applied once to the compressed fired body particles, but the wet pulverization method may be repeatedly applied to obtain a thermally conductive filler containing the desired amount of the above-mentioned composite material and partially opened boron nitride particles. You may try to get it. When the wet pulverization method is repeatedly applied in this way, the number of repetitions (number of passes) is preferably about 2 to 20 times (more preferably 2 to 10 times).

In the wet pulverization method, after the treatment by the wet pulverization method, if necessary, treatments such as filtration, centrifugation, washing, drying, and granulation are performed to obtain the heat conductive filler. The treatments such as washing, drying, and granulation are not particularly limited, and known methods can be appropriately adopted.

(Thermal conductive composite material)
Next, the heat conductive composite material of the present invention will be described. The thermally conductive composite material of the present invention is characterized by comprising a matrix and the thermally conductive filler of the present invention dispersed in the matrix.

As the matrix in such a thermally conductive composite material of the present invention, an insulating resin or an insulating oil is preferably used, and there is no particular limitation, but the resin is, for example, an epoxy resin or a phenol resin. , Thermocurable resins such as silicone resin, polystyrene, polymethylmethacrylate, polycarbonate, polyolefin (eg polyethylene, polypropylene), polyolefin elastomer, polyethylene terephthalate, nylon, ABS resin, polyamide, polyimide, polyamideimide, ethylene-propylene- Examples thereof include thermoplastic resins such as diene rubber (EPDM), butyl rubber, natural rubber, polyisoprene, and polyetherimide. Examples of the oil include silicone oil, fluoroether oil, mineral oil, animal and vegetable natural oil, paraffin and the like. These resins and oils may be used alone or in combination of two or more.

Further, in the thermally conductive composite material of the present invention, the content of the thermally conductive filler is not particularly limited, but is preferably 10 to 90% by volume, preferably 15 to 70% by volume, based on the total amount of the composite material. It is more preferably%, and particularly preferably 20 to 60% by volume. If the content of the heat conductive filler is less than the lower limit, a network structure of heat conductive paths in which heat is diffused through the contact portion between the heat conductive fillers in the composite material is not sufficiently formed, and the resulting composite material Thermal conductivity tends not to improve sufficiently. On the other hand, when the content of the thermally conductive filler exceeds the upper limit, the obtained composite material tends to be brittle and it tends to be difficult to obtain a self-supporting composite material.

Further, in the thermally conductive composite material of the present invention, the porosity is not particularly limited, but is preferably 30% by volume or less, and more preferably 10% by volume or less. When the void ratio exceeds the upper limit, the thermally conductive fillers do not sufficiently contact each other in the matrix in the obtained composite material, and as a result, it tends to be difficult to sufficiently obtain the effect of improving the thermal conductivity. , The effect of bonding by the matrix between the fillers is not sufficiently obtained, and the material tends to be brittle.

The "porosity" is calculated by the following formula (1):
Porosity [volume%] = {1- (ρ _meas / ρ _calc )} × 100 (1)
{In the formula (1), ρ _meas indicates the measured value of the density of the composite material measured by the Archimedes method, and ρ _calc is the following formula (2):
ρ _calc = {ρ _BN × x + ρ _AlN × (1-x)} y + ρ _matrix × (1-y) (2)
(In formula (2), ρ _BN is the density of BN (ρ _BN = 2.27 in Examples and Comparative Examples), and ρ _AlN is the density of AlN (ρ _AlN = 3.26 in Examples and Comparative Examples). , Ρ _matrix is the density of the matrix (ρ _matrix = 1.16 in Examples and Comparative Examples), x is the volume of BN in the filler, and y is the volume of the filler in the composite material.)
The calculated value of the density of the composite material obtained by (theoretical value of the density of the composite material assuming that there is no void) is shown. }
Means the value obtained by.

(Manufacturing method of thermally conductive composite material)
The method for producing the above-mentioned thermally conductive composite material of the present invention is not particularly limited, and can be obtained, for example, by dispersing the thermally conductive filler of the present invention in the matrix as follows.

That is, first, the heat conductive filler and the matrix are mixed. At that time, the mixing ratio of the heat conductive filler and the matrix is determined so that the content of the heat conductive filler in the obtained composite material becomes the desired content. Further, the method of mixing the thermally conductive filler and the matrix is not particularly limited, and a known mixing method is appropriately used.

When the resin is used as such a matrix, the heat conductive filler and the resin are mixed to form a homogeneous mixture, and the obtained mixture is molded to obtain the heat conductive composite material. When the thermally conductive filler and the resin are mixed in this way to form a homogeneous mixture, a dispersion medium may be further added to form a homogeneous slurry. In that case, the dispersion medium is removed by a known method such as vacuum drying. It is preferable to mold after the above. The dispersion medium is not particularly limited, and an organic solvent similar to the organic solvent mentioned as the dispersion medium of the fluid jetted from the nozzle together with the compressed calcined body particles may be appropriately used.

When the oil is used as such a matrix, the thermally conductive composite material can be obtained by mixing the thermally conductive filler and the oil to form a uniform slurry.

Further, it is preferable to pressurize and compress the mixture when molding it. Such a compression method is not particularly limited, and may be uniaxial compression or biaxial compression. It may also be isotropically compressed with hydrostatic pressure. The pressure during compression is also not particularly limited, but is preferably 5 to 20 MPa. When the pressure at the time of compression is less than the lower limit, voids tend to remain in the obtained composite material, while when the pressure exceeds the upper limit, the fracture deformation of the filler in the obtained composite material becomes remarkable and the residual strain. Tends to occur.

Further, the method for solidifying the resin when molding the mixture is not particularly limited, and a known method, for example, when a thermoplastic resin is used as the resin, a cooling method such as allowing to cool, various methods (heat, When a curable resin (light, water) is used, an appropriate curing method can be adopted for each. Moreover, such solidification may be carried out either at the time of molding or after molding.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

(Example 1)
<Preparation of thermally conductive filler>
37.3 g of "Dencaboron nitride powder GP" (average particle size: 8 μm) manufactured by Denka Co., Ltd. as boron nitride particles, and "High-purity aluminum nitride powder / granules E grade" (average particle size) manufactured by Tokuyama Co., Ltd. as aluminum nitride particles. 12.4 g of 1 μm) and 0.25 g of calcium nitride (average particle size: about 10 μm) previously crushed in a ball mill as a sintering aid are placed in a 500 ml plastic container, and synthetic zeolite (Wako Pure Chemical Industries, Ltd.) is placed therein. After adding 150 ml of ethanol dried with "Molecular Sieves 3A"), wet ball mill pulverization using zirconia balls (diameter: 5 mm) was carried out for 20 hours to obtain a slurry. Next, the solid content in the obtained slurry is filtered through a sieve (opening: 500 μm), washed with ethanol, the ethanol is distilled off under reduced pressure with an evaporator, and the mixture is further vacuum dried and then sieved (opening: 500 μm). A mixture (mixed powder) was obtained through 200 μm).

Next, 38.4 g of the obtained mixture (mixed powder) was placed in a carbon mold (inner dimensions: length 30 mm x width 40 mm), and under a nitrogen atmosphere at 1800 ° C. for 2 hours under uniaxial pressurization conditions of 40 MPa. A firing treatment (hot press) was performed underneath, and after cooling, the mixture was taken out to obtain a compressed fired body having a length of 30 mm, a width of 40 mm, and a thickness of 10 mm.

Next, the obtained compression-fired body was cut into small pieces having a diameter of 5 to 10 mm with a hammer, further crushed in an alumina mortar, and then pre-crushed through a stainless sieve (opening: 53 μm) (average particle size: about). 40 μm) was obtained.

Subsequently, 3.3 g of the pre-crushed compressed fired body was dispersed in 60 ml of ethanol to prepare a dispersion liquid, and a commercially available wet pulverizer equipped with a straight nozzle was used to set the pressure in the chamber before injection to 100 MPa, and the dispersion liquid was prepared. Is injected from a nozzle (nozzle diameter: 0.2 mm) at a flow rate of 1.1 L / min and a flow rate of about 600 m / s, and wet pulverization is performed by rapidly reducing the pressure from a state of shear flow compression at high pressure to normal pressure. A treated dispersion was obtained. Then, the pulverized product was filtered from the obtained dispersion liquid, washed with ethanol, and then vacuum dried to obtain a thermally conductive filler as the pulverized product obtained by wet pulverizing the compression fired product.

<Preparation of thermally conductive composite material>
Using the obtained thermally conductive filler and a one-component thermosetting epoxy resin (“epoxy resin EP160” manufactured by Cemedine Co., Ltd.) as a matrix, the thermally conductive filler content was 40% by volume as follows. A thermosetting composite material was obtained. That is, first, 2.95 g of the thermally conductive filler and 2.09 g of the epoxy resin are mixed in 10 ml of dichloromethane, and the obtained slurry is volatilized while stirring, and then vacuum dried for about 15 minutes to dichloromethane. Was completely removed to obtain a mixture in which the thermally conductive filler was dispersed in the epoxy resin. Next, the obtained mixture was filled in a cylindrical container (inner diameter: 14 mmφ) preheated to 120 ° C., and the epoxy was maintained at 120 ° C. for 30 minutes in a state of being compressed at a pressure of 7.5 MPa in the longitudinal direction of the cylindrical container. The resin was cured to obtain a columnar heat conductive composite material.

<Measurement of thermal conductivity of thermally conductive composite materials>
As shown in FIG. 1, a sample 2 for measuring thermal conductivity (length in the x-axis direction: 2 mm, length in the y-axis direction: 10 mm, length in the z-axis direction: 10 mm) was cut out from the columnar composite material 1 and described above. The heat diffusion rate in the direction perpendicular to the compression direction (x-axis direction) was measured using a xenon flash analyzer (“LFA 447 NanoFlash” manufactured by NETZSCH) with the thickness direction (x-axis direction) of the sample as the heat flow direction. Similarly, a sample for measuring thermal conductivity (thickness in the z-axis direction: 2 mm, diameter: 14 mmφ, not shown) is cut out from the columnar composite material 1, and the thickness direction (z-axis direction) of the sample is determined. The heat diffusion rate in the direction parallel to the compression direction (z-axis direction) was measured using a xenon flash analyzer (“LFA 447 NanoFlash” manufactured by NETZSCH) as the heat flow direction.

Further, the specific heat of the sample was measured by the DSC method using a thermal vibration type differential scanning calorimetry device (manufactured by TA Instruments). Further, the density of the sample was determined by the underwater substitution method (Archimedes method). From these results, the following equation:
Thermal conductivity (W / (m · K)) = specific heat (J / (kg · K)) x density (kg / m ³ ) x thermal diffusivity (m ² / sec)
The thermal conductivity in the direction perpendicular to the compression direction (x-axis direction) and the direction parallel to the compression direction (z-axis direction) was determined. The results obtained are shown in Table 1.

<Measurement of porosity of thermally conductive composite material>
_{In the thermal conductivity measurement, the measured value (ρ meas} ) of the density of the composite material obtained by the underwater substitution method (Archimedes method) and the calculated value of the density of the composite material obtained by the above formula (2) (assuming that there are no voids). From the theoretical value of the density of the composite material: ρ _calc ), the void ratio of the composite material was determined by the above formula (1). The results obtained are shown in Table 1.

<Electron microscope observation of thermally conductive composite material>
A sample for electron microscope observation of the cross section is cut out from the columnar composite material, and a polishing machine (Buehler's "Minimet ^TM 1000") is used as a polishing agent for an arbitrary region of 60 μm in length and 40 μm in width using diamond paste and alumina paste. After mechanical polishing using, perform oxygen plasma etching ("Plasma Reactor PR300" manufactured by Yamato Scientific Co., Ltd.) at 120 W for 3 minutes, apply osmium coating with an osmium coater, and scan electron microscope (manufactured by Hitachi High Technologies Co., Ltd.). The cross section was observed with an electron microscope using "NB-5000"). The obtained scanning electron micrograph (SEM image) is shown in FIG. In FIG. 2, light gray corresponds to the aluminum nitride phase, gray corresponds to the boron nitride phase, and dark gray corresponds to the matrix resin phase (the same applies to the SEM image below).

<Electron microscope observation and structural analysis of thermally conductive filler>
The above-mentioned <Preparation of thermally conductive composite material> except that the content of the thermally conductive filler in the obtained composite material was set to 5% by volume and the pressure at which the epoxy resin was cured was set to atmospheric pressure. Similarly, a composite material for observing the heat conductive filler under an electron microscope was obtained.

Next, a sample for electron microscope observation of the cross section was cut out from the obtained composite material, and the above-mentioned <electron microscope observation of the heat conductive composite material was performed for arbitrary 10 cross section measurement regions (regions of 60 μm in length and 40 μm in width). >, The cross section was observed with an electron microscope. An example (enlarged SEM image) of the obtained scanning electron micrograph (SEM image) is shown in FIGS. 3A and 3B.

Then, in the SEM image of each measurement area, based on the brightness and shape,
(I) Total number of aluminum nitride particles (ii) Aluminum nitride particles recognized that 50% or more of the outer surface is contained inside the boron nitride particles and is in contact with the boron nitride particles (FIG. 3A and FIG. 3A). The number (indicated by the arrow in FIG. 3B) is obtained, the values of (ii) / (i) in each measurement region are calculated, and the average value of all the measurement regions is calculated. The ratio of the aluminum nitride particles contained in the boron nitride particles was determined in. The results obtained are shown in Table 1.

Also, in the SEM image of each measurement area, based on the brightness and shape,
(Iii) Particle size of boron nitride particles (iv) Particle size of aluminum nitride particles is obtained, and the average value of all measurement regions is calculated to obtain boron nitride particles and aluminum nitride particles in the thermally conductive filler to be measured. The average particle size of each was determined. The results obtained are shown in Table 1.

(Example 2)
A thermally conductive filler was obtained in the same manner as in Example 1 except that the pressure inside the chamber before injection in the wet pulverization treatment was set to 200 MPa, and the thermally conductive filler was used in the same manner as in Example 1 to obtain a thermally conductive composite. Obtained the material.

The thermal conductivity and porosity of the obtained thermally conductive composite material were measured in the same manner as in Example 1, and the obtained results are shown in Table 1. Further, the obtained thermally conductive composite material was observed with an electron microscope in the same manner as in Example 1, and the obtained scanning electron micrograph (SEM image) is shown in FIG. Further, the thermally conductive filler used was observed by an electron microscope and structural analysis in the same manner as in Example 1, and the obtained results are shown in Table 1.

(Comparative Example 1)
37.3 g of "Dencaboron nitride powder GP" (average particle size: 8 μm) manufactured by Denka Co., Ltd. as boron nitride particles, and "High-purity aluminum nitride powder / granules E grade" (average particle size) manufactured by Tokuyama Co., Ltd. as aluminum nitride particles. 1 μm) 12.4 g is placed in a 500 ml plastic container, and 150 ml of ethanol dried with synthetic zeolite (“Molecular Sieves 3A” manufactured by Wako Pure Chemical Industries, Ltd.) is added thereto, and then zirconia balls (diameter: 5 mm). ) Was carried out for 20 hours to obtain a slurry. Next, the solid content in the obtained slurry is filtered through a sieve (opening: 500 μm), washed with ethanol, the ethanol is distilled off under reduced pressure with an evaporator, and the mixture is further vacuum dried and then sieved (opening: 500 μm). A mixture (mixed powder) was obtained through 200 μm).

Heat conduction in the same manner as in Example 1 except that the mixture (mixed powder) thus obtained is used as a heat conductive filler without being subjected to subsequent compression firing treatment and wet pulverization treatment. A sex composite material was obtained.

The thermal conductivity and porosity of the obtained thermally conductive composite material were measured in the same manner as in Example 1, and the obtained results are shown in Table 1. Further, the obtained thermally conductive composite material was observed with an electron microscope in the same manner as in Example 1, and the obtained scanning electron micrograph (SEM image) is shown in FIG. Further, the thermally conductive filler used was observed by an electron microscope and structural analysis in the same manner as in Example 1, and the obtained results are shown in Table 1.

(Comparative Example 2)
The mixture (mixed powder) obtained in Example 1, that is, the mixture (mixed powder) obtained by mixing boron nitride particles, aluminum nitride particles, and calcium carbide in the same manner as in Example 1 (wet ball mill pulverization). Premolding using 47.4 g under pressurized conditions of 5 MPa at room temperature, firing treatment at 1800 ° C. for 2 hours under atmospheric pressure conditions (no pressurization) in a nitrogen atmosphere, and taking out after cooling. A fired body having a length of 30 mm, a width of 40 mm, and a thickness of about 15 mm was obtained. Next, the obtained fired body was pulverized with a mill (“Mini Blender MB-2” manufactured by AS ONE Co., Ltd.) for 10 seconds to obtain a thermally conductive filler, and the thermally conductive filler was used in the same manner as in Example 1. A thermally conductive composite material was obtained.

The thermal conductivity and porosity of the obtained thermally conductive composite material were measured in the same manner as in Example 1, and the obtained results are shown in Table 1. Further, the obtained thermally conductive composite material was observed with an electron microscope in the same manner as in Example 1, and the obtained scanning electron micrograph (SEM image) is shown in FIG. Further, the thermally conductive filler used was observed by an electron microscope and structural analysis in the same manner as in Example 1, and the obtained results are shown in Table 1.

(Comparative Example 3)
The fired body obtained in the same manner as in Comparative Example 2 was pulverized in an alumina dairy pot for 1 minute to obtain a thermally conductive filler, and the thermally conductive filler was used to obtain a thermally conductive composite material in the same manner as in Example 1. rice field.

The thermal conductivity and porosity of the obtained thermally conductive composite material were measured in the same manner as in Example 1, and the obtained results are shown in Table 1. Further, the obtained thermally conductive composite material was observed with an electron microscope in the same manner as in Example 1, and the obtained scanning electron micrograph (SEM image) is shown in FIG. Further, the thermally conductive filler used was observed by an electron microscope and structural analysis in the same manner as in Example 1, and the obtained results are shown in Table 1.

(Comparative Example 4)
The fired body obtained in the same manner as in Comparative Example 2 was pulverized in an alumina dairy pot for 1 minute, and then passed through a stainless steel sieve (opening: 53 μm) to obtain a thermally conductive filler, and the thermally conductive filler was used in the same manner as in Example 1. A thermally conductive composite material was obtained.

The thermal conductivity and porosity of the obtained thermally conductive composite material were measured in the same manner as in Example 1, and the obtained results are shown in Table 1. Further, the obtained thermally conductive composite material was observed with an electron microscope in the same manner as in Example 1, and the obtained scanning electron micrograph (SEM image) is shown in FIG. Further, the thermally conductive filler used was observed by an electron microscope and structural analysis in the same manner as in Example 1, and the obtained results are shown in Table 1.

As is clear from the results shown in Table 1 and FIGS. It was confirmed that the thermally conductive fillers of Examples 1 and 2 contained a high proportion of composite particles in which the aluminum nitride particles were encapsulated in the boron nitride particles. Then, in the heat conductive composite material of Examples 1 and 2 obtained by using such a heat conductive filler of the present invention, the heat conduction obtained by simply mixing the boron nitride powder and the aluminum nitride powder. Compared with the thermally conductive composite material of Comparative Example 1 obtained by using the sex filler, the contact interface between the aluminum nitride particles and the boron nitride particles has a high proportion of close surface contact rather than point contact. It was confirmed that the ratio of the contact interface involving the boron nitride particles was relatively higher than the contact interface involving the aluminum nitride particles at the contact interface between the particles, and the thermal conductivity was improved.

Further, in the thermally conductive fillers obtained in Examples 1 and 2, since the compression fired body is pulverized by a wet pulverization method, the surface of the boron nitride particles is partially opened to partially open the boron nitride particles. It was confirmed that the ratio of Therefore, in the thermally conductive composite materials of Examples 1 and 2 obtained by using such a thermally conductive filler of the present invention, a portion of boron nitride that is opened during particle-particle contact is generated by the opening. It was confirmed that the particles are easily deformed in a form that reduces the voids, and the area of the contact interface between the particles is large.

On the other hand, as is clear from the results shown in Table 1 and FIGS. 6 to 8, the comparison obtained by pulverizing the calcined product obtained by calcining the mixture of the boron nitride powder and the aluminum nitride powder without pressurization. In the heat conductive fillers of Examples 2 to 4, the interface between the aluminum nitride particles and the boron nitride particles in the fired body is easily broken, and the aluminum nitride particles are nitrided, even though they are pulverized for a short time in a mill or a dairy pot. It was confirmed that the composite particles contained in the boron particles were hardly contained. Then, in the heat conductive composite materials of Comparative Examples 2 to 4 obtained by using such a heat conductive filler, not only the heat conductive composite materials of Examples 1 and 2 but also the heat conductivity of Comparative Example 1 It was confirmed that the thermal conductivity was inferior to that of the composite material.

As described above, according to the present invention, it is possible to provide a thermally conductive filler capable of efficiently improving thermal conductivity, a method for producing the same, and a thermally conductive composite material having excellent thermal conductivity. Is possible. Therefore, since the composite material of the present invention is excellent in thermal conductivity, it is useful as, for example, a heat radiating material or a heater material for automobiles, electronic devices, electronic devices, and various electric products.

1: Composite material 2: Sample for measuring thermal conductivity (x-axis direction).

Claims (7)

A thermally conductive filler containing boron nitride particles and aluminum nitride particles.
The average particle size of the boron nitride particles is 1 to 100 μm.
The average particle size of the aluminum nitride particles is in the range of 1/30 to 1 / 0.5 of the average particle size of the boron nitride particles.
50% or more of the total particles of the aluminum nitride particles were included in the inside of the boron nitride particles and 50% or more of the outer surface of the aluminum nitride particles was in contact with the boron nitride particles. In this state, composite particles of the aluminum nitride particles and the boron nitride particles are formed .
It contains at least one sintering aid component selected from the group consisting of calcium compounds and yttrium compounds as sintering aids, and compounds derived from these sintering aids.
A thermally conductive filler characterized by that. The thermally conductive filler according to claim 1, wherein the content of the aluminum nitride particles is 5 to 95% by volume with respect to the total amount of the boron nitride particles and the aluminum nitride particles. The thermally conductive filler according to claim 1 or 2, wherein it is a pulverized product of a compression-fired body of a mixture of boron nitride powder and aluminum nitride powder. A thermally conductive composite material comprising a matrix and the thermally conductive filler according to any one of claims 1 to 3 dispersed in the matrix. A step of obtaining a compressed fired body by pressurizing a mixture of boron nitride powder , aluminum nitride powder, and at least one sintering aid selected from the group consisting of a calcium compound and an yttrium compound and firing the mixture while compressing the mixture. ,
After pre-grinding the compression-fired body, the pre-crushed fluid containing the compression-fired body is jetted from a nozzle at a high pressure of 30 to 250 MPa at a flow velocity of 200 to 800 m / s to perform wet collision crushing, thereby nitriding. A thermally conductive filler containing boron particles and aluminum nitride particles, the average particle size of the boron nitride particles is 1 to 100 μm, and the average particle size of the aluminum nitride particles is the average particle size of the boron nitride particles. 50% or more of the total particles of the aluminum nitride particles are in the range of 1/30 to 1 / 0.5, and 50% or more of the outer surface of the aluminum nitride particles is the nitrided particles. A step of obtaining a thermally conductive filler forming a composite particle of the aluminum nitride particles and the boron nitride particles while being contained inside the boron particles and in contact with the boron nitride particles.
A method for producing a thermally conductive filler, which comprises. The method for producing a thermally conductive filler according to claim 5 , wherein a mixture of the boron nitride powder and the aluminum nitride powder is fired while being compressed under a pressure condition of 10 to 500 MPa. The method for producing a thermally conductive filler according to claim 5 or 6 , wherein the thermally conductive filler is the thermally conductive filler according to any one of claims 1 to 3.

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