JP7129892B2 - aluminum nitride powder - Google Patents

Description

The present invention provides a novel aluminum nitride powder. Specifically, by including amorphous aggregates in which relatively small-diameter aluminum nitride particles are fused to each other, an aluminum nitride-resin composite obtained by filling and curing a resin, especially a liquid resin, has high thermal conductivity. To provide an aluminum nitride powder capable of imparting

BACKGROUND ART Compositions obtained by filling silicone rubber or silicone grease with a thermally conductive filler are used as heat-dissipating materials that are widely used in various electronic devices as heat-dissipating sheets and heat-dissipating greases. As the thermally conductive filler, aluminum nitride has attracted attention because of its excellent electrical insulation and high thermal conductivity.

In order to improve the thermal conductivity of heat dissipating materials, it has been considered important to highly fill a filler with high thermal conductivity. Therefore, it is preferable that the particles constituting the aluminum nitride powder used as the filler of the heat dissipating material be spherical and have a wide particle size distribution of about several tens to several hundreds of μm to achieve a fine packing structure. (See Patent Document 1).

In order to achieve the above fine packing structure, relatively small-diameter aluminum nitride particles are used together, but it is difficult to maintain the above mixture uniformly, and when the mixture is put into a hopper or the like, There is concern that the small-diameter particles may be unevenly distributed during storage in the hopper, during filling into the resin, and even after filling. In particular, when the resin is a liquid resin, uneven distribution of small-diameter particles tends to occur due to the difference in sedimentation of the particles during or after filling into the resin.

International Application No. WO2011/093488

Therefore, the object of the present invention is to achieve high thermal conductivity in filling a resin, especially a liquid resin, without unevenness even when mixed with particles with a large particle size, despite containing aluminum nitride particles with a small particle size. To provide an aluminum nitride powder capable of imparting

The inventors of the present invention have made intensive studies to solve the above problems, and found that aluminum nitride containing amorphous aggregates formed by mutual fusion of relatively small-diameter aluminum nitride particles by a specific manufacturing method We succeeded in obtaining a powder, and when such agglomerates are filled in a resin, they have moderate strength due to the mutual fusion of aluminum nitride particles, and form a high heat conduction path between the particles. The present inventors have found that high thermal conductivity can be imparted to the molded article, and have completed the present invention.

That is, according to the present invention, it contains amorphous aggregates formed by mutual fusion of aluminum nitride particles having an average particle diameter of 1 to 10 μm, and has a tapped bulk density (ρ _t ) of 0.4 g/cm ³ or less, and the ratio (ρ _t /ρ ₀ ) of the tapped bulk density (ρ _t ) to the initial bulk density (ρ ₀ ) is more than 1 and 1.2 or less. is provided.

Further, in the aluminum nitride powder, the proportion of the aggregates is preferably 40% or more in terms of area proportion in an image taken with a scanning electron microscope.

Furthermore, the aluminum nitride powder of the present invention is suitable as a filler for resins, and in particular, when mixed with a liquid resin that does not require a high shear when mixed with a resin, the fused portion of the small-diameter particles is maintained and high performance is achieved. is suitable for a method of producing an aluminum nitride-resin composite by impregnating aluminum nitride powder with a curable liquid resin and then curing the curable liquid resin.

A preferred method for producing the aluminum nitride powder of the present invention includes alumina powder, carbon powder, and a sulfur component, and the amount of the sulfur component exceeds 20 parts by mass in terms of elemental sulfur with respect to 100 parts by mass of alumina powder. is heated at a temperature of 1500 to 2000° C. in a nitrogen gas atmosphere to reduce and nitride the alumina powder.

The aluminum nitride powder of the present invention contains amorphous agglomerates formed by the relatively small-diameter aluminum nitride particles fused together and strongly bonded to each other, so that it can be mixed with a resin, particularly a liquid resin. , The aluminum nitride-resin composite obtained by impregnating and curing the liquid resin has a heat conduction path formed by fusion of the aluminum nitride particles of the aggregate and a high Adhesion makes it possible to impart high thermal conductivity to composites filled with it.

In addition, even when the aluminum nitride powder of the present invention contains aluminum nitride particles together with the aggregates, the aggregates adhere to the interface with the aluminum nitride particles while maintaining an appropriate aggregate state, and similarly form a composite. High thermal conductivity can be imparted.

Scanning electron microscope (SEM) photograph of a representative aluminum nitride powder of the present invention.

The aluminum nitride powder of the present invention is amorphous aggregates formed by mutual fusion of relatively small aluminum nitride particles having an average particle size of 1 to 10 μm, preferably 1 to 7 μm, particularly 1 to 4 μm. It is characterized by including aggregates.

In addition, in the present invention, the average particle size of the aluminum nitride powder is obtained from an image of a 500-fold SEM photograph.

In the present invention, as shown in the image shown in FIG. 1, it is confirmed that adjacent aluminum nitride particles are partially fused to form an aggregate structure. In addition, the shape of the aggregates is irregular, and according to the image taken by the SEM, there are various sizes of aggregates of about 1000 μm ² or more, and large aggregates are , as high as 90000 μm ² . Many of such large aggregates have a neck portion and are easily broken at that portion during handling or when blended into a resin. can do.

In addition, in the image taken by the SEM, the aggregates are present in an area ratio of 40% or more, preferably 50% or more, particularly 60 to 95%, with respect to the total area of the aluminum nitride powder. is preferred.

The aluminum nitride particles other than the agglomerated particles are not particularly limited, but aluminum nitride particles having an average particle diameter of about 10 to 80 μm may be present in the aluminum nitride powder obtained by the production method described later. many. In addition, it is possible to further mix aluminum nitride powder other than the above aluminum nitride particles. In that case, aluminum nitride powder having an average particle size of about 1 to 80 μm is added in a range that satisfies the abundance ratio of the aggregates. Mixing is preferred.

Furthermore, the aluminum nitride powder of the present invention contains relatively strong agglomerates due to fusion bonding of the particles, so that the tapped bulk density (ρ _t ) has a high void of 0.4 g/cm ³ or less, and The ratio (ρ _t /ρ ₀ ) of the tapped bulk density (ρ _t ) to the initial bulk density (ρ ₀ ) exceeds 1 and is 1.2 or less, and the change is small. These values are presumed to be due to the low fluidity of the particles due to their irregular shape and the property that the aggregation between the particles is difficult to break.

Therefore, even when the aluminum nitride powder of the present invention is mixed with a resin, the particles are less likely to be crushed due to the high bonding strength between the particles, and the heat conduction paths between the particles can be maintained at a high level.

In the present invention, the initial bulk density (ρ ₀ ) and tapped bulk density (ρ _t ) of the aluminum nitride powder are values measured using a tapped bulk density measuring device (manufactured by Seishin Enterprise Co., Ltd.).

Since the aluminum nitride powder of the present invention contains the agglomerate, voids are easily formed in the powder and exhibits a high oil absorption. Specifically, it is possible to achieve an oil absorption of 50 cc/100 g or more, particularly 70 to 200 cc/100 g.

As described above, the aluminum nitride particles of the present invention contain characteristic agglomerates, and when used as a filler, it is important not to apply an excessively strong shear to the agglomerated particles when mixed with a resin. preferred to maintain. Preferably, a liquid resin such as an epoxy resin or a silicone resin is used as the resin, mixed with a small share and molded, or aluminum nitride powder is filled in a mold and molded, and then impregnated with the liquid resin. , a method of obtaining a molded article by curing the above resin is recommended. Of course, it is also possible to mix and knead it with a thermoplastic resin having a high melt flow rate and to mold it.

(Method for producing aluminum nitride particles)
Although the method for producing the aluminum nitride powder of the present invention is not particularly limited, the following method can be mentioned as a representative example of the production method.

That is, the aluminum nitride powder of the present invention contains alumina powder, carbon powder, and a sulfur component, and the sulfur component is present in an amount exceeding 20 parts by mass based on 100 parts by mass of alumina powder in terms of elemental sulfur. can be produced by heating at a temperature of 1500 to 2000° C. in a nitrogen gas atmosphere and reducing and nitriding the above alumina powder.

The above method will be described in detail below.

(starting material)
<Alumina powder>
In the method for producing the aluminum nitride powder of the present invention, known alumina such as α-alumina and γ-alumina can be used without any limitation as alumina, which is one of the raw materials, but usually α-alumina is preferably used. . Its purity is 99.0% by mass or more, preferably 99.5% by mass or more. Also, the average particle diameter is preferably 0.5 to 10 μm. Alumina in the form of granules can also be used without limitation.

<Carbon powder>
In the method for producing the aluminum nitride powder of the present invention, known carbon powders such as furnace black, channel black, thermal black, acetylene black, etc. can be used without any limitation as the carbon powder acting as a reducing agent. It is preferable to use those having an average particle diameter of 100 nm or less, preferably 50 nm or less. In addition, the BET specific surface area is preferably 20 to 200 m ² /g, preferably 40 m ² /g or more by the nitrogen adsorption method. Further, it is preferable that the DBP oil absorption is 50 to 150 cm ³ /100 g, preferably 70 to 130 cm ³ /100 g.

In the method for producing an aluminum nitride powder of the present invention, synthetic resin condensates such as phenol resins, melamine resins and epoxy resins; hydrocarbon compounds such as pitch and tar; , sucrose, starch, polyvinylidene chloride, and organic compounds such as polyphenylene may be used as the carbon source.

<Sulfur component>
In the method for producing the aluminum nitride powder of the present invention, examples of the sulfur component include elemental sulfur and sulfur compounds such as aluminum sulfide, nitrogen sulfide, and thiouric acid. Moreover, the sulfur component may be used singly or in combination. Moreover, the sulfur component may originally be contained in the carbon powder, and such a sulfur component is also used as part of the sulfur component in the present invention.

(Raw material mixing process)
In the method for producing an aluminum nitride powder of the present invention, the amount of carbon powder used is not particularly limited as long as it is an amount that can completely reduce and nitride the alumina powder serving as the base material, but preferably the alumina powder 100 It is preferably in the range of 36 to 250 parts by mass, more preferably 50 to 200 parts by mass.

In the method for producing an aluminum nitride powder of the present invention, the amount of the transition metal component used is 0.05 to 5 parts by mass, preferably 0.1 to 3 parts by mass, in terms of element, with respect to 100 parts by mass of the alumina powder. It is preferable that it is a part.

In the method for producing an aluminum nitride powder of the present invention, the amount of the sulfur component used is an amount exceeding 20 parts by mass, preferably 21 to 25 parts by mass with respect to 100 parts by mass of alumina powder. It is preferred to form particles and to form aggregates in which these particles are partially fused together. That is, in the reductive nitriding reaction of the present invention, the sulfur component used in the above range is presumed to act as a fusing agent and form the aggregates.

The amount of the sulfur component used is determined by taking into consideration the amount of sulfur contained in the carbon powder and the amount of sulfur powder and/or sulfur compound added to the raw material mixture, and adjusting these amounts accordingly. The above range can be satisfied. If the above range is satisfied in consideration of the amount of sulfur contained in the carbon powder, the amount of carbon powder used may be adjusted so that it falls within the above range, or carbon powder with a high sulfur content and sulfur-containing A small amount of carbon powder may be used and the mixing ratio thereof may be adjusted so as to fall within the above range.

In the present invention, the method of mixing the starting materials to obtain the raw material mixture is not particularly limited as long as it is a method capable of uniformly mixing the starting materials. Examples thereof include a method using a general mixer such as a vibration mill, bead mill, ball mill, Henschel mixer, drum mixer, and the like. When the starting materials are put into the mixer and mixed, they may be mixed by a dry method, or may be mixed by adding a solvent to the starting materials and mixing them by a wet method.

(Reduction nitriding step)
In the method for producing an aluminum nitride powder of the present invention, the reductive nitriding step is carried out by drying the raw material mixture as necessary and then heating it in a nitrogen gas atmosphere. In this case, the nitriding temperature and treatment time can be set to the conditions that generally allow aluminum nitride to be obtained, for example, the temperature range is 1500 to 2000° C. for 3 to 20 hours.

The reduction-nitridation process of the present invention can be carried out using a known apparatus capable of controlling the reaction atmosphere. For example, an atmosphere-controlled high-temperature furnace in which heat treatment is performed by high-frequency induction heating or heater heating can be used. In addition to batch furnaces, continuous nitriding reactors such as pusher-type tunnel furnaces and vertical furnaces can also be used.

(Oxidation process)
In the method for producing an aluminum nitride powder of the present invention, since the aluminum nitride particles after the reductive nitriding reaction contain surplus carbon powder, it is preferable to remove the surplus carbon powder by an oxidation treatment, if necessary. As the oxidizing gas for the oxidation treatment, any gas that can remove carbon, such as air, oxygen, and carbon dioxide, can be used without limitation. Also, the treatment temperature is generally preferably 500°C to 900°C.

EXAMPLES Hereinafter, examples will be shown to describe the present invention more specifically, but the present invention is not limited to these examples.

In the examples, various measurements were performed by the following methods.

(1) Tapped Bulk Density and Initial Bulk Density Using a tapped bulk density measuring device (manufactured by Seishin Enterprise Co., Ltd.), the initial bulk density was measured when the weighed aluminum nitride powder was put into a 100 cm ³ cell without compaction with a feeder. confirmed from the value of The tap bulk density was confirmed from the value obtained by setting the tap height to 50 mm and the number of taps to 500 times.

(2) SEM observation A SEM (TM3030, manufactured by Hitachi High-Technologies Co., Ltd.) photograph at a magnification of 100 times was taken, and the ratio of amorphous aggregates formed by mutual fusion of aluminum nitride particles was calculated from the area ratio. confirmed.

(3) Thermal conductivity of molded body The resin composition was molded into a test piece, and thermal diffusivity, density, and specific heat were obtained based on the following formula.

Thermal conductivity=thermal diffusivity×density×specific heat The thermal diffusivity was measured by the laser flash method, the density was measured by the Archimedes method, and the specific heat was measured by the DSC method.

Example 1
Sulfur powder is added to a mixture of 100 parts by mass of alumina powder and 50 parts by mass of carbon powder so that the amount of sulfur component in the mixture is 22 parts by mass with respect to 100 parts by mass of the alumina powder, and these are uniformly mixed. The raw material mixture was obtained by mixing with a vibrating stirrer until the ingredients were mixed.

The obtained raw material mixture was subjected to reductive nitriding treatment in a nitrogen gas atmosphere at 1750° C. for 10 hours using a reactor. Next, heat treatment was performed at 670° C. in the air atmosphere to burn off unreacted carbon powder to obtain aluminum nitride powder.

In addition, it was confirmed that the obtained aluminum nitride powder formed amorphous aggregates formed by mutual fusion of particles. Moreover, the SEM photograph of the obtained aluminum nitride particles is shown in FIG.

As can be confirmed from the photograph, the aluminum nitride aggregates in the obtained aluminum nitride powder were aggregates of particles having an average particle diameter of 2 μm, and the area ratio was 60% in the viewing range. In addition, the tap bulk density is 0.38 g/cm ³ and the tap bulk density ratio (ρ _t /ρ ₀ ) is 1.13. was confirmed.

In addition, the aluminum nitride powder was mixed with 100 parts by mass of the epoxy resin so as to be 408 parts by mass, and the molded body obtained by curing had a thermal conductivity of 6.1 W/m·K. .

Example 2
An aluminum nitride powder was obtained in the same manner as in the manufacturing method of Example 1, except that the mass parts of the carbon powder was changed to 38 mass parts.

The aluminum nitride aggregates in the obtained aluminum nitride powder were aggregates of particles with an average particle diameter of 3 μm, and the area ratio was 67% in the visual field range. The tap bulk density was 0.33 g/cm ³ and the tap bulk density ratio (ρ _t /ρ ₀ ) was 1.06.

In addition, the aluminum nitride powder was mixed with 100 parts by mass of the epoxy resin so as to be 408 parts by mass, and the molded body obtained by curing had a thermal conductivity of 6.5 W/m·K. .

Comparative example 1
Aluminum nitride powder was obtained in the same manner as in Example 1, except that the amount of sulfur added in the raw material mixture of Example 1 was changed to 10 parts by mass.

From the SEM observation of the obtained aluminum nitride powder, the amorphous aggregates formed by mutual fusion of particles existed only 20% in terms of area ratio, and the tapped bulk density ratio (ρ _t /ρ ₀ ) was 1.38. In addition, the aluminum nitride powder was blended in an amount of 408 parts by mass with respect to 100 parts by mass of the epoxy resin, and the molded body obtained by curing had a thermal conductivity of 4.9 W/m·K. .

Claims (3)

It contains amorphous aggregates formed by mutual fusion of aluminum nitride particles with an average particle diameter of 1 to 10 μm, and has a tapped bulk density (ρ _t ) of 0.4 g/cm ³ or less, and an initial An aluminum nitride powder, wherein the ratio (ρ _t /ρ ₀ ) of tapped bulk density (ρ _t ) to bulk density (ρ ₀ ) is greater than 1 and equal to or less than 1.2. 2. The aluminum nitride powder according to claim 1, wherein the proportion of aggregates in said aluminum nitride powder is 40% or more in terms of area proportion in an image taken with a scanning electron microscope. 3. The aluminum nitride powder according to claim 1, which is a filler for resin.

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