TW201431825A - Method for producing sintered aluminum nitride granules - Google Patents

Abstract

This invention provides a method for producing sintered aluminum nitride granules, which have high heat conductivity and an excellent property of being filled in a resin, have an average grain diameter of 10 to 200 micron, and are useful as a filler for heat-dissipating materials such as a heat-dissipating resin, grease, adhesive or coating agent, in a simple manner. The method for producing sintered aluminum nitride granules according to the present invention is characterized by comprising: a reduction nitridation step of carrying out the reduction nitridation of porous alumina granules at a temperature of 1400 to 1700 DEC C to produce porous aluminum nitride granules; and a sintering step of sintering the porous aluminum nitride granules produced in the reduction nitridation step at a temperature of 1580 to 1900 DEG C.

Description

Method for producing aluminum nitride sintered particles

The present invention relates to an aluminum nitride sintered pellet and a method for producing the same, and, in particular, to a resin or a heat-dissipating paste which is excellent in heat conductivity and excellent in filling property to a resin, and has an average particle diameter of 10 to 200 μm and which can be used for heat dissipation. A method of filling a heat dissipating material such as a coating agent or a coating material.

Aluminum nitride has high thermal conductivity and excellent electrical insulation, and is used for a highly thermally conductive substrate, a heat dissipating member, a filler for insulating heat dissipation, and the like. In recent years, semiconductor electronic components such as integrated circuits (ICs) and central processing units (CPUs), which are used in high-performance electronic devices such as notebook computers and information terminals, have been continuously miniaturized. As a result of the accumulation of high-products, it is necessary to reduce the size of the heat dissipating member. The heat dissipating member used for the above-mentioned components is, for example, a heat sink, a film-like spacer filled with a highly thermally conductive filler in a matrix such as a resin or a rubber (Patent Document 1); and filled with a silicone oil The highly thermally conductive filler makes a fluid thermal grease (Patent Document 2); a heat-dissipating adhesive which fills a highly thermally conductive filler with an epoxy resin (Patent Document 3). Further, aluminum nitride, boron nitride, aluminum oxide, magnesium oxide, cerium oxide, graphite, various metal powders or the like can be used as the high thermal conductive filler.

In order to improve the thermal conductivity of the heat dissipating material, it is an important part to fill the filler with high thermal conductivity. Therefore, it is preferably a few micrometers to several spheres. Aluminum nitride powder composed of ten micron aluminum nitride particles. However, aluminum nitride powders produced by a general method are mostly submicron-sized particles, and it is difficult to obtain aluminum nitride particles having a large particle diameter of several tens of micrometers.

As a method of spheroidizing aluminum nitride powder, the following methods have been disclosed.

For example, disclosed in Patent Document 4 is a method of producing spherical aluminum nitride particles by reduction nitridation of spherical alumina particles; and the method disclosed in Patent Document 5 is to add a sintering aid to an aluminum nitride powder. Spraying and drying with a binder and a solvent, and sintering the obtained spherical granulated powder; the following method is also disclosed, in which alkaline earth elements, oxides or nitrides of rare earth elements are decomposed by heating Further, in the co-solvent comprising a precursor of a salt, a hydroxide, a halide or an alkoxide of the above substance, a heat treatment or an aluminum nitride-based composition synthesized by adding a co-solvent in advance is directly used. After heat treatment and spheroidizing, the co-solvent is dissolved to separate the aluminum nitride powder (Non-Patent Document 1).

However, in the method of Patent Document 4, as the conversion rate of aluminum nitride is increased, voids are generated in the particles, and it is difficult to obtain a true spherical product. Further, even if a product having a substantially true spherical shape is obtained, there is a problem that the crushing strength of the particles is small due to the above-mentioned voids, and foaming is likely to occur when filling the resin. On the other hand, in the method disclosed in Patent Document 5, since the spherical granules in which the sintering aid is added to the aluminum nitride are sintered, particles having no voids and high crushing strength can be obtained. However, by using aluminum nitride powder as a raw material, not only the raw material price is high, but also the problem that particles are easily bonded to each other by sintering. Further, the method disclosed in Non-Patent Document 1 has a high raw material price and a complicated procedure, which is disadvantageous in industrial implementation.

Advanced technical literature Patent literature

Patent Document 1: JP-A-2005-146214

Patent Document 2: Japanese Laid-Open Patent Publication No. Hei 6-209057

Patent Document 3: Japanese Patent Publication No. 6-17024

Patent Document 4: Japanese Patent Publication No. 4-74705

Patent Document 5: Japanese Patent Laid-Open No. Hei 3-295853

Non-patent literature

Non-Patent Document 1: CERAMICS, 39, September 2004, pp. 692-695

Accordingly, an object of the present invention is to provide a method for producing aluminum nitride sintered particles which are excellent in thermal conductivity and filling property, and having an average particle diameter of 10 to 200 μm and which can be used for a filler for a heat dissipating material, which is inexpensive and simple.

The inventors of the present invention conducted intensive studies in order to achieve the aforementioned object of the spherical aluminum nitride powder for the filler. As a result, porous alumina particles or alumina hydrate particles (collectively referred to as "porous alumina particles" in the present specification) are used as raw materials to be reduced and nitrided to form porous aluminum nitride particles. After that, the porous aluminum nitride particles are fired and sintered, whereby the fine pores from the alumina particles are eliminated, and the hollow aluminum nitride sintered particles are not hollow inside, and the finished particles are completed. invention.

That is, the present invention is a method for producing aluminum nitride sintered particles, characterized by comprising: a reduction nitridation step of reducing and nitriding porous alumina particles at a temperature of 1400 ° C or higher and 1700 ° C or lower to become porous And a sintering step of sintering the porous aluminum nitride particles obtained in the reduction nitridation step at 1580 ° C or higher and 1900 ° C or lower.

In the present invention, the porous alumina particles preferably have an average particle diameter of 10 to 200 μm and a BET specific surface area of 2 to 250 m ² /g.

Further, it is preferred that the reduction nitridation step and the sintering step be carried out in a state in which the porous alumina particles and the porous aluminum nitride particles are mixed with the carbonaceous powder.

Further, the reduction nitridation step and the sintering step are continuously carried out in the same furnace, and it is not necessary to reduce the temperature and reheat after the reduction nitridation, which is economical.

According to the production method of the present invention, dense aluminum nitride sintered particles having an average particle diameter of 10 to 200 μm and a BET specific surface area of 0.05 to 0.5 m ² /g can be obtained.

Further, the aluminum nitride sintered particles of the present invention can be used for a filler for a heat dissipating material.

According to the production method of the present invention, for example, porous alumina particles composed of aggregates obtained by molding alumina or alumina hydrate powder are subjected to reduction nitridation and sintering as a raw material, and therefore, with respect to aluminum nitride powder A conventional method of raw materials can obtain aluminum nitride sintered pellets at relatively low cost.

Further, a conventional method of reducing and nitriding by using alumina particles having a large particle diameter as a raw material is likely to occur in a hollow body; whereas, in the production method of the present invention, porous alumina particles are used as a raw material, and once Become porous After the aluminum nitride particles are sintered, aluminum nitride sintered particles having high solidity, high thermal conductivity, and high filling property with respect to a resin or the like can be obtained.

Further, as will be described in detail later, when the above-described reduction nitriding and sintering are carried out in a state in which a specific amount of carbonaceous powder is mixed, it is possible to prevent the particles from being bonded to each other, and it is possible to produce a stable and satisfactory aluminum nitride sintered pellet.

Fig. 1 is a scanning electron microscope photograph showing the particle structure of the aluminum nitride sintered particles obtained in Example 2.

Fig. 2 is a scanning electron microscope photograph showing an enlarged particle structure of the aluminum nitride sintered particles obtained in Example 2.

Hereinafter, a method for producing the aluminum nitride sintered particles of the present invention will be described in detail.

[Starting materials]

In the method for producing aluminum nitride sintered particles of the present invention, porous alumina particles are used as a starting material. Specifically, porous alumina particles or alumina hydrate particles are exemplified. More specifically, alumina, boehmite, diaspore, gibbsite having a crystal structure of α, γ, θ, δ, η, κ, χ, or the like. , α- gibbsite (bayerite), towdite (tohdite) and the like by heating for dehydration conversion and finally converted into α-alumina material, all of which can be used. The porous alumina particles may be used alone or in a mixture of different materials, among which α-alumina, γ-alumina, and boehmite are highly reactive and easy to control. It is especially suitable for use.

In the present invention, the porous alumina particles are not particularly limited in specific surface area as long as they have a porous structure, but preferably have a specific surface area of 2 to 250 m ² /g. When the above specific surface area less than 2m ² / g, easy to change the shape of the particles; sphericity aluminum nitride sintered particles if the specific surface area of 250m ² / g is exceeded, the obtained tends to become low. Further, the average particle diameter of the porous alumina particles is preferably from 10 to 200 μm, more preferably from 15 to 150 μm, particularly preferably from 20 to 100 μm. When the average particle diameter is less than 10 μm, the effect of high filling by the large particle size of the filler may be reduced. If the particle diameter exceeds 200 μm, the reduction nitridation reaction may not proceed to the inside of the pellet. There is a tendency to remain unreacted alumina inside the particles.

The porous alumina particles are generally in the form of aggregates in which alumina powder or alumina hydrate powder (hereinafter collectively referred to as "alumina powder") is aggregated and aggregated, and can be known by The granulation method was obtained. Specifically, granulation, tumbling granulation, and the like of the alumina powder by spray drying are exemplified, but in order to obtain a porous body, granulation by spray drying is applied. In addition, at the time of granulation, a dispersant or a binder resin, a lubricant, or an alkaline earth metal compound, a rare earth metal compound, an alkali earth metal fluoride, an alkaline earth element may be used as a reduction nitridation reaction. A composite compound of a promoter and a sintering aid is mixed and formulated with an alumina powder. The amount of these additives to be used can be appropriately determined within the range of conventional addition.

In the present invention, in order to obtain an aluminum nitride sintered particle having a high degree of sphericity and a spherical shape as a target as described later, the above-mentioned granulation by spray drying can efficiently obtain a spherical shape. Porous alumina particles in the industry It is particularly advantageous.

In the present invention, by the voids between the particles of the alumina powder constituting the porous alumina particles, in the reduction nitridation using the porous alumina particles, and the use of the melt-free method In the case where the porous alumina is used as a raw material, the effect is that no void is formed inside the obtained aluminum nitride particles.

[Reduction nitridation step]

In the present invention, the reduction nitridation step is a step of nitriding the porous alumina particles in the presence of a reducing agent to produce porous aluminum nitride particles.

The above-mentioned reducing agent is known, and it is not particularly limited in use, but a carbonaceous material, a reducing gas or the like is generally used. The above carbonaceous material, carbon black, graphite, and a carbonaceous precursor which can be a carbon source in a high-temperature, reaction gas atmosphere can be used without any limitation. Among them, carbon black is suitable because of its carbon content per unit weight and stability of physical properties. The particle size of the carbonaceous material is not limited, but it is preferably 0.01 to 20 μm. Further, a liquid carbon source such as liquid paraffin may be used in combination to prevent scattering of the raw material.

Further, when a reducing gas is used, it can be used without any limitation as long as it exhibits a reducing gas. Specifically, hydrogen, carbon monoxide, ammonia, a hydrocarbon gas, etc. are mentioned. These gases may be used singly or in combination with the above-described carbonaceous materials, carbon precursors, and the like.

In the present invention, when a carbonaceous material is used as the reducing agent, the porous alumina particles and the carbonaceous material are mixed and used in a state in which the carbonaceous material is present between the porous alumina particles, and the particles are prevented from each other in the reduction nitridation. Aggregation is preferred.

Further, the above mixing method may be any method as long as it can uniformly mix the porous alumina particles and the carbonaceous material, but generally, the mixing method is applied by a blender or a mixer. ), a mix of ball mills.

In the present invention, the ratio of the porous alumina particles to the carbonaceous material may be adjusted in any compounding ratio as long as it is equal to or higher than the equivalent ratio. However, in order to prevent agglomeration of the particles and improve reactivity, the porous oxide is oxidized. The aluminum particles can be blended in an amount of 1 to 3 times, preferably 1.2 to 2 times, equivalent to carbon equivalents in terms of carbonaceous materials.

Further, when a reducing gas is used as the reducing agent, in the reaction described later, a method in which a gas of a theoretical amount or more is brought into contact with the porous alumina particles is generally used.

The reaction in the reduction nitridation step of the present invention is preferably carried out by firing porous alumina particles in the presence of a carbonaceous material and/or a reducing gas under nitrogen flow.

The firing is carried out at a temperature of 1400 ° C or higher and 1700 ° C or lower. That is, when the firing temperature is less than 1400 ° C, the nitriding reaction is not sufficiently performed, and when the firing temperature exceeds 1700 ° C, oxynitride (AlON) having a low thermal conductivity is formed. Further, when reduction nitridation is performed at an excessive temperature, the crystal growth of the produced aluminum nitride is easily progressed, and it is difficult to sufficiently densify in the subsequent sintering step.

In the reduction nitridation step of the present invention, the reaction time may vary depending on the conditions employed, and cannot be generalized, but is generally applicable for 1 to 10 hours, preferably 3 to 8 hours.

The above reduction nitridation reaction can be carried out by a conventional reaction apparatus. Specific examples thereof include a static reaction apparatus such as a muffle furnace, a flow type reaction apparatus such as a fluidized bed, and a rotary reaction apparatus such as a rotary kiln.

In the above-described reduction nitridation step, by using the porous alumina particles, porous aluminum nitride particles which are sufficiently nitrided in a porous state to the inside can be obtained. Here, the nitridation ratio showing the degree of nitridation described above is preferably as high as possible from the viewpoint of thermal conductivity, and the conversion of aluminum nitride defined in the examples is preferably 50% or more, particularly preferably 60%. The above is more preferably 80% or more. In the method of the present invention, 100% conversion can be obtained for the above reasons, and more preferably. Further, the specific surface area of the porous aluminum nitride particles may vary depending on the firing conditions, but generally it is preferably 0.5 to 50 m ² /g, particularly preferably 0.7 to 10 m ² /g, More preferably, it has a specific surface area of 0.9 to 5 m ² /g.

[Sintering step]

In the present invention, the sintering step is to form the nitrogen constituting the porous aluminum nitride particles by firing the porous aluminum nitride particles obtained in the above-described reduction nitridation step under a reducing atmosphere or a neutral atmosphere. The aluminum particles are further densified by sintering to obtain a step of sintering the aluminum nitride particles.

The firing temperature for the above sintering is 1880 ° C or higher and 1900 ° C or lower, preferably 1600 ° C or higher and 1800 ° C or lower. That is, when the firing temperature is lower than 1,580 ° C, sintering is not sufficiently performed. When the firing temperature is higher than 1900 ° C, carbon is dissolved in aluminum nitride, which causes a problem that the thermal conductivity is lowered.

Further, in the atmosphere during firing, any of the conditions under a reducing atmosphere or a neutral atmosphere may be used, but the reduction nitridation step and the burning are continuously performed as described later. The step of the step is preferably carried out under the same reducing atmosphere as the reduction nitridation step.

Therefore, the formation of the reducing atmosphere can be re-supplied if the reducing agent used in the reduction nitridation step of the previous step still exists. In particular, the carbonaceous material powder previously used as a reducing agent is fired, and it is preferable to effectively prevent sintering of particles which are likely to occur at the time of sintering.

In the sintering step of the present invention, the firing time may vary depending on the conditions employed, and cannot be generalized, but is generally applicable for 1 to 12 hours, preferably 3 to 10 hours.

Further, the above-described sintering step can be carried out using the same apparatus as that used in the above-described reduction nitridation step.

By the sintering step of the present invention, aluminum nitride sintered particles having a dense structure can be obtained. That is, the aluminum nitride sintered particles obtained by the method of the present invention have an average particle diameter of 10 to 200 μm and a BET specific surface area of 0.05 to 0.5 m ² /g, and pores are scarcely present. For example, in the aluminum nitride sintered particles of the present invention, the pore volume measured for pores having a pore diameter of 2 μm or less is 0.2 cm ² /g or less, preferably 0.1 cm ² /g or less.

[Continuous implementation of reduction nitridation step and sintering step]

In the present invention, the reduction nitridation step and the sintering step can be carried out separately, but if it is continuously carried out without lowering the temperature, an effect of reducing the energy source for reheating or the like can be obtained, which is preferable.

Specifically, in the reaction apparatus used in the re-reduction nitridation step, the porous aluminum nitride particles are not taken out, and the fired state in the sintering step or the like is continuously performed in the same reaction apparatus. At this point, the step switch The firing temperature used in the reduction nitridation step is adjusted to the temperature used in the sintering step, and only the nitrogen supply amount can be adjusted as needed, which is extremely simple in operation.

Further, the reduction nitridation step and the sintering step may be carried out at the same temperature because the firing temperature range is repeated, and at this time, the flow rate of the supplied nitrogen gas may be adjusted only as needed, and the above steps may be continuously performed.

In the above successive steps of the present invention, the firing time may be determined by the total time of the firing time in each of the above steps, and is generally 2 to 34 hours, preferably 6 to 18 hours.

[Oxidation treatment]

In the present invention, when a carbonaceous material is used in the reduction nitridation step or the like, since the carbonaceous material remains in the obtained aluminum nitride sintered particles, it is preferred to carry out an oxidation treatment to finally remove the carbonaceous material. The oxidizing gas at the time of the above oxidation treatment can be used without any limitation as long as it is a gas capable of removing carbon such as air or oxygen. However, considering the economy and the oxygen content of the obtained aluminum nitride, the air is suitable. . In addition, the treatment temperature is generally from 500 ° C to 900 ° C, and is considered to be 600 ° C to 750 ° C in consideration of the efficiency of decarburization and excessive oxidation of the surface of the aluminum nitride. Further, the time of the oxidation treatment can be appropriately determined depending on the amount of the remaining carbonaceous material.

[use]

The aluminum nitride sintered particles of the present invention can be widely used for various applications in which the properties of aluminum nitride are utilized, and in particular, fillers for heat dissipating materials such as a heat sink, a heat dissipating paste, a heat dissipating agent, a coating material, and a thermal conductive resin.

Here, examples of the resin or paste which is a matrix of the heat dissipating material include thermosetting properties such as an epoxy resin and a phenolic resin. Resin; thermoplastic resin such as polyethylene, polypropylene, polyamide, polycarbonate, polyimide, polyphenylene sulfide; Rubber such as silicone rubber, EPR, SBR, etc.; silicone oil. 150 to 1000 parts by weight per 100 parts by weight of the resin or paste may be added as a heat dissipating material. In such a heat dissipating material, in addition to the aluminum nitride sintered particles of the present invention, one or several kinds of fillers of alumina, boron nitride, zinc oxide, tantalum carbide, graphite, or the like may be filled. These fillers may also be used as a surface treatment with a decane coupling agent. The shape and particle diameter of the aluminum nitride sintered particles of the present invention and other fillers thereof may be selected depending on the characteristics, use, and the like of the heat dissipating material. Further, the mixing ratio of the aluminum nitride sintered particles in the heat dissipating material to the filler other than the filler may be appropriately adjusted in the range of 1:99 to 99:1. Further, an additive such as a plasticizer, a vulcanizing agent, a hardening accelerator, and a releasing agent may be further added to the heat dissipating material.

The average particle diameter of the aluminum nitride sintered particles of the present invention may be in the range of 10 to 200 μm, but it is preferably 15 to 150 μm, more preferably 20 to 100 μm, for the filler. The aluminum nitride sintered particles falling within this range are easily filled with a high matrix and are also easily used in combination with other fillers.

On the other hand, the true sphericity of the aluminum nitride sintered particles of the present invention is preferably 0.80 or more, particularly preferably 0.85 or more, more preferably 0.90 or more. Here, the true sphericity is obtained by dividing the short diameter of the particle by the long diameter of the particle, and the closer to 1, the closer to the true ball, and the fluidity is improved. In addition, close to the true ball will follow the pattern of the most dense filling, and it is easy to fill the resin, paste and the like.

When a granule having the above particle diameter, which is the object of the present invention, is obtained by a conventional method, it may occur along with an increase in the conversion ratio of aluminum nitride. The combination, deformation, and the like of the particles may have a tendency to be insufficient in sphericity; however, the aluminum nitride sintered particles obtained by the method of the present invention are characterized in that: by forming the porous alumina particles of the raw material into a spherical shape, Even when the aluminum nitride conversion rate is 100%, the obtained aluminum nitride sintered particles maintain a high degree of true sphericity.

Example

Hereinafter, the present invention will be specifically described, but the present invention is not limited to these examples. The various physical properties in the examples and comparative examples were measured by the following methods.

(1) specific surface area

The specific surface area is measured by the BET one-point method.

(2) Average particle size

The sample was dispersed in an aqueous solution of sodium pyrophosphate by a homogenizer, and the average particle diameter (D50) was measured by a laser diffraction particle size distribution apparatus (MICROTRAC HRA, manufactured by Nikkiso Co., Ltd.).

(3) Aluminum nitride conversion rate

X-ray diffraction (CuKα, 10~70°), by the main peak of aluminum nitride (AlN) (peak from the (100) plane) and each alumina component (α-alumina, θ-alumina, The ratio of the total peak intensity of the main peaks of γ-alumina, δ-alumina, or the like is determined by a calibration curve method (formula (1)).

Example of the main peak of each alumina component

Α-alumina: peak from (113) plane

Γ-alumina: peak from (400) plane

Θ-alumina: peak from (403) plane

Δ-alumina: the peak from the (046) plane.

(4) True sphericity

From the photo image of the electron microscope, 100 arbitrary particles were selected, and the long diameter (DL) and the short diameter (DS) of the particle image were measured with a scale, and the average value of the ratio (DS/DL) was the true sphericity.

(5) pore size distribution

The pore diameter distribution of the aluminum nitride powder was determined by a mercury intrusion method using a pore distribution measuring apparatus (manufactured by Micromeritics Co., Ltd., AutoPore IV 9510 (trade name)).

(6) Thermal conductivity of polyoxyethylene rubber sheet

The thermally conductive polyoxyethylene rubber composition was molded into a size of 10 cm × 6 cm and a thickness of 3 mm, and was heated in a hot air circulating oven at 150 ° C for 1 hour to be cured, and a thermal conductivity measuring device (QTM manufactured by Kyoto Electronics Co., Ltd.) was used. -500) Determine the thermal conductivity. Further, in order to prevent electric leakage from the detecting portion, a polyvinylidene chloride film having a thickness of 10 μm was used for measurement.

Example 1

The particulate aluminate (boehmite) having an average particle diameter of 63 μm and a specific surface area of 164 m ² /g was heat-treated at 1200 ° C for 5 hours, and the α-alumina was a porous alumina pellet. 280 g of the spherical porous alumina particles and 140 g of carbon black were mixed, and then filled in a carbon container, and fired at a firing temperature of 1600 ° C for 5 hours in a resistance heating atmosphere furnace apparatus under a nitrogen flow. (Reduction nitridation step).

After that, in the same device, the firing temperature is raised to 1750 ° C. For 5 hours of firing (sintering step). Next, oxidation treatment was performed at 680 ° C for 8 hours under air flow to obtain aluminum nitride sintered pellets.

The average particle diameter and specific surface area, aluminum nitride conversion ratio, true sphericity, and pore diameter distribution of the obtained aluminum nitride sintered pellets were measured by the above methods, and the results are shown in Table 1.

Further, 450 parts by weight of the obtained aluminum nitride sintered particles, 100 parts by weight of a polymer type polyoxynoxide (TSE201 manufactured by Momentive Performance Materials Japan LLC), and 0.5 part by weight of the release mold were twisted by a press kneader. Agent. Next, after the composition was cooled, the mixture was mixed with 0.5 part by weight of a crosslinking agent, and then press-pressed at 180 ° C for 15 minutes to obtain a sheet having a length of 10 cm, a width of 6 cm, and a thickness of 3 mm. The obtained sheet was measured for thermal conductivity by the above method, and the results are shown in Table 1.

In addition, in order to confirm the particle state of the porous aluminum nitride particles after the reduction nitridation step, the firing was stopped at the time when the reduction nitridation step was completed under the same conditions as in the above examples, and the obtained porous nitrogen was obtained. The aluminum oxide particles were measured for specific surface area and aluminum nitride conversion, and the results are shown in Table 1.

Further, the above measurement is carried out after the oxidation treatment for removing the coexisting carbonaceous material powder.

Example 2

Aluminum nitride sintered particles were obtained in the same manner as in Example 1 except that the firing temperature in the reduction nitridation step was 1,450 ° C and the firing temperature in the sintering step was 1,750 ° C. The measurement results of the average particle diameter and specific surface area, the aluminum nitride conversion ratio, the true sphericity, and the pore diameter distribution of the obtained aluminum nitride sintered particles are shown in Table 1.

The obtained aluminum nitride powder was formed into a sheet in the same manner as in Example 1. The thermal conductivity and hardness were measured, and the results are shown in Table 1.

The aluminum nitride sintered pellets obtained under the conditions of Example 2 were observed under a scanning electron microscope, and the photographs observed are shown in Fig. 1 and Fig. 2 . According to the understanding of Fig. 1, spherical aluminum nitride sintered particles are obtained. Further, as can be understood from Fig. 2, the densification of the aluminum nitride crystal particles constituting the particles proceeds to obtain fine-pores-free and dense aluminum nitride particles.

In addition, in order to confirm the particle state of the porous aluminum nitride particles after the reduction nitridation step, the firing was stopped at the time when the reduction nitridation step was completed under the same conditions as in the above examples, and the obtained porous nitrogen was obtained. The aluminum oxide particles were measured for specific surface area and aluminum nitride conversion, and the results are shown in Table 1.

Further, the above measurement is carried out after the oxidation treatment for removing the coexisting carbonaceous material powder.

Example 3

As the porous alumina particles, particulate hydrated boehmite having an average particle diameter of 40 μm and a specific surface area of 135 m ² /g was used, and 280 g of the above porous alumina particles and 140 g of carbon black were mixed. Next, the mixed powder was filled in a carbon container, and the calcination temperature was 1,450 ° C for 5 hours in a resistance-heating atmosphere furnace apparatus, and the reduction nitridation step was carried out, followed by raising and burning. The firing temperature was changed to 1750 ° C for 5 hours, and a sintering step was carried out. Thereafter, oxidation treatment was performed at 680 ° C for 8 hours under air flow to obtain aluminum nitride sintered pellets. The average particle diameter and specific surface area, aluminum nitride conversion ratio, true sphericity, and pore diameter distribution of the obtained aluminum nitride sintered pellets were measured by the above methods, and the results are shown in Table 1.

Further, the obtained aluminum nitride sintered pellets were the same as in the first embodiment. The sheet was formed into a sheet, and the thermal conductivity was measured. The results are shown in Table 1.

In addition, in order to confirm the particle state of the porous aluminum nitride particles after the reduction nitridation step, the firing was stopped at the time when the reduction nitridation step was completed under the same conditions as in the above examples, and the obtained porous nitrogen was obtained. The aluminum oxide particles were measured for specific surface area and aluminum nitride conversion, and the results are shown in Table 1.

Further, the above measurement is carried out after the oxidation treatment for removing the coexisting carbonaceous material powder.

Comparative example 1

Aluminum nitride sintered pellets were obtained in the same manner as in Example 1 except that the reduction nitridation step and the sintering step were carried out at a firing temperature of 1,450 ° C for 5 hours. The measurement results of the average particle diameter and specific surface area, the aluminum nitride conversion ratio, the true sphericity, and the pore diameter distribution of the obtained aluminum nitride sintered particles are shown in Table 2.

The obtained aluminum nitride sintered pellets were formed into a sheet in the same manner as in Example 1, and the thermal conductivity was measured. The results are shown in Table 1.

Comparative example 2

Aluminum nitride sintered particles were obtained in the same manner as in Example 1 except that the firing temperature in the reduction nitridation step was 1,450 ° C and the firing temperature in the sintering step was 1,550 ° C. The measurement results of the average particle diameter and specific surface area, the aluminum nitride conversion ratio, the true sphericity, and the pore diameter distribution of the obtained aluminum nitride sintered particles are shown in Table 2.

The obtained aluminum nitride sintered pellets were formed into a sheet in the same manner as in Example 1, and the thermal conductivity was measured. The results are shown in Table 2.

Comparative example 3

Aluminum nitride sintered pellets were obtained in the same manner as in Example 1 except that the reduction nitridation step and the sintering step were carried out at a firing temperature of 1800 ° C for 10 hours. The measurement results of the average particle diameter and specific surface area, the aluminum nitride conversion ratio, the true sphericity, and the pore diameter distribution of the obtained aluminum nitride sintered particles are shown in Table 2.

The obtained aluminum nitride sintered pellets were formed into a sheet in the same manner as in Example 1, and the thermal conductivity was measured. The results are shown in Table 2.

Example 4

Adding 5 parts by weight of oxygen to 100 parts by weight of boehmite powder Hydrazine, 100 parts by weight of toluene solvent, 5 parts by weight of butyl methacrylate, 2 parts by weight of hexaglycerin monooleate, mixed in a ball mill for 5 hours, by spray drying ( The obtained slurry was spray-dried by a spray-dry method to obtain particles having an average particle diameter of 50 μm. The obtained pellets were subjected to heat treatment at 1200 ° C for 5 hours under air flow to be α-alumina, to obtain porous alumina pellets.

After mixing 280 g of the obtained porous alumina particles and 140 g of carbon black, the reduction nitridation step and the sintering step were simultaneously fired at 1600 ° C for 10 hours under nitrogen flow, followed by air. The oxidation treatment was carried out at 680 ° C for 8 hours under circulation to obtain aluminum nitride sintered pellets. The average particle diameter and specific surface area, aluminum nitride conversion ratio, true sphericity, and pore diameter distribution of the obtained aluminum nitride sintered pellets were measured by the above methods, and the results are shown in Table 3.

Further, the obtained aluminum nitride sintered pellets were formed into a sheet in the same manner as in Example 1, and the thermal conductivity was measured. The results are shown in Table 3.

Example 5

Aluminum nitride sintered pellets were obtained in the same manner as in Example 4 except that 5 parts by weight of calcium carbonate was added in place of cerium oxide. The measurement results of the average particle diameter and specific surface area, the aluminum nitride conversion ratio, the true sphericity, and the pore diameter distribution of the obtained aluminum nitride sintered particles are shown in Table 3. The obtained aluminum nitride sintered pellets were formed into a sheet in the same manner as in Example 1, and the thermal conductivity was measured. The results are shown in Table 3.

Industrial availability

The spherical aluminum nitride sintered particles obtained by the present invention have a shape and a particle diameter suitable for the filler, and can be highly filled with a resin, a paste, etc., and can obtain a heat sink having a high thermal conductivity, a heat dissipation paste, and heat dissipation. Followers and so on.

Claims (6)

A method for producing aluminum nitride sintered particles, comprising: a reduction nitridation step of reducing and nitriding porous alumina particles at a temperature of 1400 ° C or higher and 1700 ° C or lower to form porous aluminum nitride particles; And a sintering step of sintering the porous aluminum nitride particles obtained in the reduction nitridation step at 1580 ° C or higher and 1900 ° C or lower. The method for producing aluminum nitride sintered particles according to claim 1, wherein the porous alumina particles have an average particle diameter of 10 to 200 μm and a BET specific surface area of 2 to 250 m ² /g. The method for producing aluminum nitride sintered particles according to claim 1 or 2, wherein the reduction nitridation step is carried out in a state in which the porous alumina particles and the porous aluminum nitride particles are mixed with the carbonaceous powder. And the above sintering step. The method for producing aluminum nitride sintered particles according to claim 1, wherein the reduction nitridation step and the sintering step are continuously performed. The method for producing aluminum nitride sintered particles according to claim 1, wherein the obtained aluminum nitride sintered particles have an average particle diameter of 10 to 200 μm and a BET specific surface area of 0.05 to 0.5 m ² /g. A filler for a heat dissipating material, which is characterized by being sintered aluminum nitride particles obtained by the method described in claim 1 of the patent application.