JP7149379B1 - Spherical aluminum nitride powder and its production method - Google Patents

Abstract

A spherical aluminum nitride powder is provided which has a small median diameter, a sharp particle size distribution with little variation, few agglomerates, high fluidity of the powder, and high fillability in polymeric materials and the like. The particles contain aluminum nitride and a rare earth compound, have a median diameter (D50) of 1.9 to 4.0 μm, contain 10% or less of particles with a particle diameter of 0.9 μm or less, and have a particle diameter of 7 μm or more. is 10% or less and the sphericity is 0.8 or more. [Selection drawing] Fig. 1

Description

The present invention relates to spherical aluminum nitride powder.

Aluminum nitride powder is used as a filler mixed with materials such as resins, greases, adhesives, and paints, taking advantage of its excellent thermal conductivity. Material properties required for fillers include filling properties, kneadability and thermal conductivity, and various efforts have been made to improve the material properties.

For example, Patent Literature 1 discloses a spherical aluminum nitride powder that is spheroidized for the purpose of enhancing fluidity and filling properties when blended with a resin, and a method for producing the same by a flux method. However, in the process of removing the flux with a strong acid, the surface area of each particle is roughened and the surface area of each particle increases, and because the particle size distribution of the particles cannot be controlled, the kneadability and filling properties are reduced. There was a problem of

On the other hand, Patent Literature 2 discloses an aluminum nitride powder for filler containing less fine particles of 1 μm or less and a method for producing the same, in order to improve the filling property and the kneading property without adopting the flux method. However, most of the particles have an uneven surface and an angular outer surface, which reduces filling and kneading properties.

Therefore, the inventors of the present application have previously proposed that 70% or more of the particles of the powder have an outer peripheral shape that does not include angular corners and uneven portions in order to further improve the filling property, kneading property and thermal conductivity. (Patent Document 3).

Japanese Patent Application Laid-Open No. 2002-179413 JP 2017-114706 A Japanese Patent Application Laid-Open No. 2020-23435 (Patent No. 6700460)

The aluminum nitride powder of Patent Document 3 has a high sphericity and a small median diameter (D50) (Examples 2 and 3 of the same document), but more than 10% of the particles have a particle size of 7 μm or more. Since the particle size variation is large, there is a problem that the smaller the particle size is controlled, the worse the fluidity becomes.

Therefore, the present invention has a small median diameter (D50) (for example, compared to Patent Document 3), a sharp particle size distribution, small variations, few agglomerates, and high fluidity of the powder. An object of the present invention is to provide a spherical aluminum nitride powder having a high fillability.

[1] Contains aluminum nitride and a rare earth compound, has a median diameter (D50) of 1.9 to 4.0 μm, contains 10% or less (by volume) of particles having a particle diameter of 0.9 μm or less, and has a particle diameter of 7 μm A spherical aluminum nitride powder containing 10% or less (by volume) of the above particles and having a sphericity of 0.8 or more.

[2] Spherical aluminum nitride powder containing aluminum nitride and a rare earth compound, having a median diameter (D50) of 1.9 to 4.0 μm, a sphericity of 0.8 or more, and a degree of compaction of 40% or less. .

[3] The spherical aluminum nitride powder of [1] or [2] above, containing 0.01 to 0.5% by mass of calcium in terms of oxide.

[4] A spherical aluminum nitride powder whose D50/D50 _BET is 2 or less in the above [1] to [3].

[5] The spherical aluminum nitride powder of [1] to [4], wherein the viscosity of the mixture of 150 g of the spherical aluminum nitride powder and 100 g of silicone oil is 10,000 cps or less.

[6] A polymer molded body in which the spherical aluminum nitride powder of [1] to [5] is filled in a polymer material.

[7] With respect to 100% by mass of aluminum nitride powder, 0.5 to 3.0% by mass of rare earth compounds in terms of oxides, and 0.3 to 1.0% by mass of calcium compounds in terms of oxides; A raw material mixing step of obtaining a mixed powder by mixing ~50% by mass of carbon powder;
A first heat treatment step of heat-treating the mixed powder at 1450 to 1700 ° C. in a non-oxidizing atmosphere;
a second heat treatment step of further heat-treating at 500 to 800° C. in an oxidizing atmosphere after the heat treatment;
A method for producing a spherical aluminum nitride powder, comprising:

[8] In the above [7], the rare earth compound is at least one selected from the group consisting of oxides, halides, carbonates, nitrates, oxalates, hydroxides and alkoxides of Y, Yb, La, Nd and Sm. selected from seeds,
A method for producing a spherical aluminum nitride powder, wherein the calcium compound is selected from at least one selected from the group consisting of oxides, halides, sulfides, carbonates, nitrates, oxalates, hydroxides and alkoxides of calcium.

According to the present invention, the median diameter (D50) is small (for example, compared to Patent Document 3), the particle size distribution is sharp and the variation is small, there are few agglomerates, and the powder has high fluidity. It is possible to provide a spherical aluminum nitride powder with high filling properties.
Therefore, when this spherical aluminum nitride powder is kneaded alone with a polymer material, the variation in particle size is small, so high filling is possible, the median size (D50) is small, and there is little powder with a large particle size. , it is possible to use the polymer molded body thinner than before.
In addition, when this spherical aluminum nitride powder is kneaded with a polymer material together with particles having a larger particle size, there is little variation in particle size and there is little agglomeration, so high filling is possible and the dispersibility of the particles is improved. Since it is good, the viscosity of the kneaded product is low, and a resin molded product with high thermal conductivity can be obtained. Furthermore, when mixed with a soft polymer material, the original flexibility of the polymer material is not impaired, and when mixed with a hard polymer material, the three-point bending strength increases.

1 is a SEM photograph of the spherical aluminum nitride powder of Example 1. FIG. 2 is a SEM photograph of the spherical aluminum nitride powder of Example 7. FIG. 3 is a SEM photograph of the spherical aluminum nitride powder of Example 14. FIG. 4 is an SEM photograph of the spherical aluminum nitride powder of Comparative Example 1. FIG.

<1> Spherical aluminum nitride powder (a) Regarding AlN and rare earth compound The ratio of aluminum nitride to rare earth compound in the spherical aluminum nitride powder is not particularly limited, but is 0.1 to 0.1 in terms of oxide with respect to 100% by mass of aluminum nitride. It preferably contains 3.0% by mass of a rare earth compound, and more preferably 0.5 to 3.0% by mass. If the content of the rare earth compound is less than 0.1% by mass, the effect of reducing dissolved oxygen in the spherical aluminum nitride powder is not sufficiently obtained, resulting in a spherical aluminum nitride powder with low thermal conductivity. If the content of the rare earth compound exceeds 3.0% by mass, the purity of aluminum nitride is lowered, and there is a concern that the thermal conductivity may be lowered.
The rare earth compounds are not particularly limited, but oxides or halides of Y, Yb, La, Nd, and Sm, or precursors (carbonates, nitrates, oxalates, water oxides, alkoxides, etc.).

(b) Containing 0.01 to 0.5% by Mass of Calcium in Calculation of Calcium Including calcium in the spherical aluminum nitride powder itself is not advantageous. However, calcium contributes to spheroidization and grain growth of aluminum nitride while being consumed during heat treatment, and if it is exhausted during heat treatment, this contribution ceases. preferably. On the other hand, when calcium exceeds 0.5% by mass, the purity of aluminum nitride is lowered, and there is a concern that thermal conductivity may be lowered.

(c) Regarding the median diameter (D50) being 1.9 to 4.0 μm When the median diameter is less than 1.9 μm, the degree of compression, which will be detailed below, increases, and the viscosity, which will be detailed below, increases. do.
When the median diameter is more than 4.0 μm, the viscosity and hardness of the polymer compact produced by mixing the spherical aluminum nitride powder with particles having a larger particle diameter increase.

(d) About 10% or less of particles with a particle diameter of 0.9 μm or less When the particles with a particle diameter of 0.9 μm or less exceed 10%, the degree of compression increases and the viscosity increases, which will be described in detail below. The D50/D50 _BET will rise.

(e) About 10% or Less of Particles with a Particle Diameter of 7 μm or More When particles with a particle diameter of 7 μm or more account for more than 10%, the D50/D50 _BET increases.

(f) Regarding sphericity of 0.8 or more The sphericity is an index that indicates how closely the plane projection shape of a particle approximates a perfect circle. The sphericity is determined by the following formula.
4πS/L ²
Here, S is the area of the grain projected on the plane, and L is the perimeter of the grain projected on the plane.
The sphericity value can be calculated by image analysis of the SEM photograph for each particle.
As the number of particles having a particle shape close to a true sphere increases, a powder for filler with high filling properties and kneading properties can be obtained.
If the sphericity is less than 0.8, the compressibility increases, the viscosity increases, and the D50/D50 _BET increases.

(g) Compression degree of 40% or less A method for evaluating fluidity is the degree of compression. Compressibility is calculated as follows from bulk density (density when a container is filled without applying external force) and tap density (density when a predetermined external force is applied after filling a container without applying external force). It is a parameter that can be calculated by a formula, and bulk density and tap density were each measured according to JIS R1628.
Compression degree = (tapped density - bulk density) / (tapped density)
Powders with poor flowability are difficult to be filled into a container unless an external force is applied, resulting in a low bulk density and a high degree of compaction (Comparative Examples 1 to 3).
However, even if the powder has poor fluidity, if the particle size is large (10% or more has a particle size of 7 μm or more), the bulk density increases even if the fluidity is somewhat poor (Comparative Examples 4 to 6). The density when this powder is tapped is larger than the density when the powder with small variation in particle size (particle size of 7 μm or more is less than 10%) is tapped, so the difference between the bulk density and the tap density The degree of compression calculated from is increased.

(h) About D50/D50 _BET Evaluation was performed using D50/D50 _BET as a parameter capable of evaluating the degree of aggregation of particles.
D50 _BET (specific surface area equivalent sphere diameter) is a particle diameter calculated on the assumption that the particles are spherical and not aggregated with respect to the actually measured specific surface area SSA. The calculation method is as follows.
Aggregation degree D50/D50 _BET , particle diameter D, volume V, surface area S, density ρ (ρ of AlN is 3.26), weight M, and from the formula,
V=(π×D ³ )/6
S=π×D ²
M=V×ρ=(π×D ³ ×ρ)/6
Measured specific surface area SSA = S / M = 6 / (D50 _BET × ρ)
→ Specific surface area sphere equivalent diameter D50 _BET = 6/(ρ x SSA)
= 6/(3.26 x SSA)
The specific surface area measured by the gas adsorption method is calculated from the amount of gas molecules sufficiently smaller than the particle to be measured attached to the particle surface. Therefore, it is possible to enter the gaps between the particles and perform measurement even in powders with many agglomerated particles.
On the other hand, in particle size distribution measurement using a laser diffraction scattering system, powder is dispersed in a liquid for measurement, but for particles that do not resolve aggregation, the size of the aggregated particles is measured as it is. The particle diameter D50 takes a larger value than the D50 _BET calculated from the specific surface area.
D50/D50 _BET quantifies this effect as the degree of agglomeration, and D50 of powder with less agglomeration has a smaller difference from D50 _BET (D50 becomes smaller, resulting in smaller D50/D50 _BET ). .

(i) Viscosity of 10,000 cps or less As a method for evaluating the fillability of a polymer material, there is a method of evaluating the viscosity when a predetermined amount of raw material powder and silicone oil are mixed.
In Comparative Examples 4 to 6 (Examples 1 to 3 of Patent Document 3) described later, although there is variation in the particle size distribution, the median diameter (D50) is 3.0 μm or more, so the wettability with the polymer material is good. Therefore, even conventional spherical aluminum nitride powder has a low viscosity and can be easily filled into polymeric materials.
In the present invention, even if the particle size is further reduced (3.0 μm or less), the viscosity is low when mixed with silicone oil, so it was shown that the fillability into polymeric materials was improved.

<2> Polymer Molded Body By filling a polymeric material with the spherical aluminum nitride powder of the present invention, a polymeric molded body having high thermal conductivity can be produced and used. Examples of polymer materials include resins, rubbers, elastomers, and the like.
Here, it is preferable to fill the powder at a high concentration because the thermal conductivity increases, and there are several known examples of filling a large amount of aluminum nitride powder in the resin (eg, Japanese Patent Laid-Open No. 2020-125228).
However, when a large amount of aluminum nitride powder is filled, there is a problem that the polymer molded body becomes hard and the flexibility of the polymer material is impaired, resulting in deterioration of adhesion to the irregularities. Therefore, there is a need for a polymer molded article that maintains flexibility while being highly filled.
In order to achieve high powder filling, it is necessary for small particles to enter the gaps between large particles. becomes possible. However, in reality, there is a distribution of particle sizes (for example, even if the center diameter is 30 μm, there are particles with a diameter of 7 to 50 μm, and even if the center diameter is 2 μm, there are particles with a diameter of 0.5 to 10 μm. Particles containing particles) Particles that cannot enter the gaps between large particles and particles that are small relative to the gaps do not improve the packing rate. When the two are compared at the same filling rate, the former has a lower viscosity of the kneaded material and a lower hardness of the compact after curing. Since the spherical aluminum nitride powder of the present invention suppresses the variation in particle size, the number of particles that can enter the gaps between the large particles increases, and as a result, the hardness of the molded body does not increase, and a flexible polymer molded body can be obtained. Obtainable.

<3> Method for Producing Spherical Aluminum Nitride Powder (a) Aluminum Nitride Raw Material Powder The aluminum nitride raw material powder used as the base material is preferably a high-purity fine powder containing few metal impurities and a low oxygen content. The aluminum nitride raw material powder can be synthesized by any method such as a reduction nitriding method or a direct nitriding method.
Aluminum nitride raw material powder having a median diameter (D50) of 0.01 to 2.0 μm can be used. The median diameter of the raw aluminum nitride powder as the starting material determines the median diameter of the spherical aluminum nitride powder as the final product. In the present embodiment, by setting the median diameter of the aluminum nitride raw material powder to 1.9 μm or less, the median diameter of the spherical aluminum nitride powder can be controlled to 1.9 to 4.0 μm. More preferably, the median diameter of the spherical aluminum nitride powder can be controlled to 1.94-3.98 μm.

(B) Rare earth compound The rare earth compound, which is the first auxiliary agent, is an oxide or halide of Y, Yb, La, Nd, or Sm, or a precursor (carbonate, nitrate) that produces the above by decomposition during heating. , oxalates, hydroxides, alkoxides, etc.). The first auxiliary agent powder is preferably a high-purity fine powder containing few metal impurities.
When the amount of the rare earth compound added is less than 0.5% by mass in terms of oxide, the proportion of small particles having a particle diameter of 0.9 μm or less increases, the sphericity decreases, and the D50/D50 _BET increases.
If the amount of the rare earth compound added exceeds 3.0% by mass in terms of oxide, the proportion of large particles having a particle diameter of 7 μm or more increases, the sphericity decreases, and the D50/D50 _BET increases.
Here, the oxide conversion means a value calculated by converting a compound containing a metal element into an oxide of the metal element.

(c) Calcium compound The calcium compound, which is the second auxiliary agent, is an oxide or halide of calcium, or a precursor (sulfide, carbonate, nitrate, oxalate, hydroxides, alkoxides, etc.), but preferably _CaF2 is used. Addition of CaF ₂ produces CaF ₂ --CaO--Al ₂ O ₃ with a low melting point, which has the effect of further promoting the nitriding reaction and grain growth.
The particle diameter of the calcium compound is desirably smaller than the median diameter (D50) of the target spherical aluminum nitride powder, preferably 0.5 to 2 μm. The use of powder with a median diameter of more than 2 μm may cause non-uniform formation of coarse particles.
When the amount of the calcium compound added is less than 0.3% by mass, the proportion of small particles having a particle size of 0.9 μm or less increases, the sphericity decreases, the D50/D50 _BET increases, and the produced spherical nitrided particles The calcium content of aluminum powder is reduced.
If the amount of the calcium compound added is more than 1.0% by mass, the proportion of large particles with a particle size of 7 μm or more increases, the sphericity decreases, the D50/D50 _BET increases, and the produced spherical aluminum nitride powder. increases the calcium content of
By reducing the amount of CaF ₂ added (0.3 to 1.0%) compared to Patent Document 3 (CaF ₂ 2 to 8%), excessive grain growth of the raw material powder can be suppressed. However, if it is less than 0.3%, fine particles of 0.9 μm or less will be difficult to grow, and a large amount of fine particles of 0.9 μm or less will remain. . Since the calcium component volatilizes during firing, approximately 0.01 to 0.5% remains in the finished product.

(d) Carbon powder Carbon powder is added to prevent fusion between aluminum nitrides in the first heat treatment step.
Furthermore, the carbon powder reacts with oxygen in the raw material mixed powder at high temperature to reduce the oxygen content, thereby contributing to the improvement of the thermal conductivity of the aluminum nitride particles.
Fine particles mainly composed of carbon such as furnace black and acetylene black can be used as the carbon powder. It is preferable to use carbon powder having a median diameter (D50) of 10 to 50 nm and an ash content of 0.1% or less.
If the amount of carbon powder added is less than 8% by mass, the proportion of large particles having a particle diameter of 7 μm or more increases, the sphericity decreases, and the D50/D50 _BET increases.
When the amount of carbon powder added exceeds 50% by mass, grain growth is suppressed, the median diameter decreases, and the ratio of small particles having a particle diameter of 0.9 μm or less increases. In addition, it takes a long time for decarburization in the second heat treatment step, resulting in a decrease in production efficiency.

(E) Raw material mixing step A raw material mixed powder can be obtained by mixing the prepared raw material powders until they are uniformly mixed by a general method such as a vibration mill, a ball mill, or a V-blender.

(f) First heat treatment step (spheroidization and grain growth)
Examples of the non-oxidizing atmosphere in the first heat treatment step include a nitrogen atmosphere and an argon atmosphere.
In the first heat treatment step, when the temperature rises to 1450 to 1700° C. (hereinafter referred to as the “first temperature range”), the added calcium compound generates a liquid phase at a relatively low temperature of about 1230° C., aluminum nitride particles. Wetting the surface of the particles promotes initial spheronization and grain growth. Since this calcium compound is easily decomposed in a non-oxidizing atmosphere and easily volatilized at high temperatures (for example, about 1350° C. or higher), it hardly remains in high temperature ranges such as the first temperature range where aluminum nitride particles grow more. .
After reaching the first temperature range and most of the calcium compound disappears, in the high temperature range, rare earth compounds and the like subsequently act to promote spheroidization and grain growth of the aluminum nitride grains. It is believed that this results in effective spheroidization and grain growth throughout the first heat treatment step.
In other words, by using a rare earth compound together with a calcium compound as an auxiliary agent, it is possible to perform effective spheroidization and grain growth in two stages, a low temperature range and a high temperature range, and make aluminum nitride particles more spherical than before. It is possible to

Here, since the first temperature range is near or below the lower limit of the first temperature range (1450 to 1700° C.) in Patent Document 3, grain growth can be suppressed.
When the first temperature range is less than 1450 ° C., the median diameter (D50) decreases, the proportion of small particles with a particle size of 0.9 μm or less increases, the sphericity decreases, and the D50/D50 _BET increases, The calcium content of the produced spherical aluminum nitride powder is increased.
When the first temperature range is higher than 1700 ° C., the median size increases, the proportion of large particles with a particle size of 7 μm or more increases, the sphericity decreases, the D50/D50 _BET increases, and the produced spherical nitriding The calcium content of aluminum powder is reduced.
Also, the holding time in the first temperature range is preferably 1 to 20 hours. If the holding time is less than 1 hour, grain growth can be suppressed, but the particle size tends to be non-uniform, and if the holding time exceeds 20 hours, the production efficiency decreases.

(g) Second heat treatment step (decarburization)
As an oxidizing atmosphere in the second heat treatment step, the atmosphere or the like can be exemplified.
In the second heat treatment step, the spherical particles are heat treated at 500 to 800° C. (hereinafter referred to as “second temperature range”) for several hours to burn carbon and decarburize. This removes the carbon component from the spherical particle powder.
If the second temperature range is lower than 500° C., the carbon cannot be completely removed, and thus the viscosity increases when mixed with a polymer material.
If the second temperature range is higher than 800°C, the amount of oxygen increases and the thermal conductivity of the filler decreases.

Ideally, the amount of carbon after decarburization is the same as that before mixing the carbon powder (that is, approximately 0), but if it is 0.15% by mass or less of the entire powder, the characteristics are not affected. is known. Therefore, the decarburization treatment was performed until the residual carbon reached 0.15% by mass of the total. Conditions such as temperature and treatment time are arbitrarily determined according to the amount of carbon powder to be added. The residual carbon can be measured by a known method such as combustion in an oxygen stream-infrared absorption method, in which a sample is heated in an oxygen stream to cause an oxidation reaction, and the generated CO2 and CO are detected with an infrared detector.

<4> Uses of Spherical Aluminum Nitride Powder and Polymer Molded Body Applications of the spherical aluminum nitride powder are not particularly limited, but examples thereof include fillers mixed with materials such as polymer materials, greases, adhesives, and paints.
Applications of the polymer molded body obtained by filling a polymer material with the spherical aluminum nitride powder of the present invention as a filler are not particularly limited. Examples include circuit boards used in communication, high frequency, etc., general-purpose heat dissipation members, power semiconductor module heat dissipation members (heat sinks), insulating plates, and the like.

Next, examples embodying the present invention will be described with reference to the drawings while comparing them with comparative examples. The materials, quantities, and conditions of each part in the examples are examples, and can be changed as appropriate without departing from the scope of the invention.

Spherical aluminum nitride powders of Examples 1 to 14 and Comparative Examples 1 to 6 shown in Table 1 were prepared.
Comparative Examples 4, 5 and 6 correspond to Examples 1, 2 and 3 of Patent Document 3, respectively.
Hereinafter, "each example" refers to each of Examples 1 to 14 and Comparative Examples 1 to 6.

[1] Raw material As aluminum nitride raw material powder, which is the main raw material, a median diameter (D50) of 1.9 μm was used in Examples and Comparative Examples 1 to 3, and a median diameter of 2.3 μm was used in Comparative Examples 4 to 6. Using.
A powder of Y ₂ O ₃ was used as the rare earth compound as the first auxiliary agent in each case.
CaF ₂ powder was used in each case as the second auxiliary calcium compound.
Carbon powder having a median diameter of 10 to 50 nm, a specific surface area of 80 m ² /g, and an ash content of 0.1% or less was used in each example.

[2] Production method (i) Material mixing step With respect to 100% by mass of aluminum nitride raw material powder, different mass% of rare earth compound powder, calcium compound powder and carbon powder were blended according to each example as shown in Table 1. . Then, the prepared raw material powders were charged into a ball mill and sufficiently mixed to obtain a raw material mixed powder.

(ii) First heat treatment step Next, the raw material mixed powder is spread in a graphite sagger and put into a heating furnace, and in a nitrogen atmosphere, the temperature varies from 1450 to 1700 ° C. in each case as shown in Table 1. After the temperature was raised to 100°C, a first heat treatment was carried out for a different holding time depending on each case to obtain a spherical particle powder.

(iii) Second heat treatment step Subsequently, the spherical particle powder was subjected to a second heat treatment (decarburization treatment) by heating in an oxidizing atmosphere (air atmosphere) at 750°C for 3 hours in each case. . Then, residual carbon in each sample was measured by combustion in an oxygen stream-infrared absorption method using EMIA-221V manufactured by Horiba, Ltd., and it was confirmed that the carbon content was less than 0.15% by mass.

Spherical aluminum nitride powders of Examples 1 to 14 and Comparative Examples 1 to 6 were obtained through the above steps.

[3] Properties Properties of the obtained spherical aluminum nitride powders of Examples 1 to 14 and Comparative Examples 1 to 6 were measured by the following methods (measurement results are shown in Tables 2 and 3).

(i) SEM photograph observation FIG. 1 is a SEM photograph of the spherical aluminum nitride powder of Example 1, FIG. 2 is Example 7, FIG. 3 is Example 14, and FIG.
The spherical aluminum nitride powders of Examples 1, 7, and 14 had a spherical shape with almost no corners or irregularities on the surface, had a small variation in particle size, and had few agglomerates.
On the other hand, the spherical aluminum nitride powder of Comparative Example 1 has a spherical shape with almost no corners or irregularities on the surface, but the particle size varies greatly and agglomerates are observed.

(ii) Amount of Y and Ca A fluorescent X-ray analyzer (model: ZSX Primus IV) manufactured by Rigaku Corporation was used to measure the amount of Y (in terms of oxide) and the amount of Ca (in terms of oxide).

(iii) Ratio of particles with median diameter (D50) and specific particle diameter 0.5 g of spherical aluminum nitride powder was added to 50 ml of an aqueous solution of 0.1% by mass of sodium pyrophosphate, and a model US- manufactured by Nippon Seiki Seisakusho Co., Ltd. was added. Dispersed for 3 minutes at an output of 80% using 300E, using a laser diffraction particle size distribution analyzer, model SALD-2200 manufactured by Shimadzu Corporation, median diameter (D50) and particle diameter 0 The percentage of particles with a diameter of 9 μm or less (based on volume) and the percentage of particles with a diameter of 7 μm or more (based on volume) were measured.

(iv) Sphericality A mixture of spherical aluminum nitride powder, epoxy resin (Epotato YH-300 manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.), and curing agent (HN-2200 manufactured by Hitachi Chemical Co., Ltd.) was placed in a silicon mold. A molding was obtained by thermal curing. Next, the compact was polished, and the polished surface was photographed with a scanning electron microscope (S-3400N manufactured by Hitachi High-Technologies Corporation) at a magnification of 2000. For the acquired SEM image, image analysis of arbitrary 100 or more particles is performed using the image processing software "ImageJ", the sphericity of all the particles is obtained, and the average value is obtained. , the sphericity (average sphericity) was calculated.

(v) Specific Surface Area The specific surface area was measured by the BET one-point method, which is a nitrogen gas adsorption method. As a measurement device, Monosorb manufactured by Quantachrome, model MS-21 was used.

(vi) D50/D50 _BET
As described above, it was obtained by the following formula.
D50/D50 _BET = D50/(6/(3.26*SSA))

(vii) Bulk Density, Tap Density, and Degree of Compression As described above, the bulk density and tap density were each measured according to JIS R1628, and the degree of compression was determined by the following equation.
Compression degree = (tapped density - bulk density) / (tapped density)

(viii) Slurry viscosity obtained by mixing spherical aluminum nitride powder of each example with silicone oil , Brookfield DV1MHBTJ0 at 100 rpm.

(ix) Characteristics of a molded product formed by mixing the spherical aluminum nitride powder (single filler) of each example with a silicone resin. Momentive silicone resins TSE3033A and TSE3033B were weighed at a weight ratio of 1:1 and mixed in a rotation-revolution mixer. .
16.6% by mass (40% by volume) of the mixed silicone resin and 83.4% by mass (60% by volume) of the spherical aluminum nitride powder of each example as a filler were weighed and mixed in a rotation-revolution mixer. After that, it was kneaded in a three-roll mill. The kneaded material was poured into a mold of φ40 mm and hardened at 150° C. for 2 hours to form a compact of φ40 mm×thickness 10 mm.
Using TECLOCK GS-721G TYPE E, the hardness of the molded body was measured five times, and the average value was calculated.
Moreover, the molded body was cut into a thickness of 1.5 mm×10 mm×10 mm, and the heat conductivity was measured using LFA467 manufactured by Netch.

(x) Characteristics of a molded product obtained by mixing a combination of the spherical aluminum nitride powder of each example and a spherical aluminum nitride powder having a larger particle size (combination filler) into the silicone resin. As in ix), 16.6% by mass: 83.4% by mass, except that the fillers are 30% by mass of spherical aluminum nitride powder of each example, 40% by mass of AlN powder with a center diameter of 80 μm, and A kneaded material was produced in the same manner as in (ix) above, except that a combination filler with 30% by mass of AlN powder was used, and a compact was formed.
Then, hardness and thermal conductivity were measured in the same manner as in (ix) above.
Further, the same kneaded material was molded into a sheet with a thickness of about 1 mm, cured at 150° C. for 2 hours, and then using a mold, the total length was 120 mm, the parallel part length was 40 mm, the parallel part width was 10 mm, and the grip part width was 25 mm. A dumbbell-shaped test piece was produced. The tensile strength of the test piece was measured five times at a test speed of 15 mm/min using Model AG-IS manufactured by Shimadzu Corporation, and the average value was calculated.

(xi) Characteristics of a molded product obtained by mixing epoxy resin with a combination of spherical aluminum nitride powder of each example and spherical aluminum nitride powder with a larger particle size (combination filler) The resin used was Nippon Steel Chemical Co., Ltd. In the same manner as in (x) above, except that the epoxy resins YH-300 and HN-2200 manufactured by Epson Co., Ltd. were used, a kneaded product of the resin and the combined filler was prepared, and the kneaded product was poured into a mold and cured at 150 ° C. for 2 hours. and processed into a length of 40 mm, a width of 10 mm and a thickness of 1 mm. Using a model AG-IS manufactured by Shimadzu Corporation, the three-point bending strength was measured five times at a crosshead speed of 0.5 mm/min and a distance between fulcrums of 20 mm, and the average value was calculated.

[evaluation]
In contrast to Comparative Examples 1 to 6, Examples 1 to 14 are
[1] The median diameter (D50) is in the range of 1.9 to 4.0 μm, the particles having a particle diameter of 0.9 μm or less account for 10% or less, and the particles having a particle diameter of 7 μm or more account for 10% or less, By having a sphericity of 0.8 or more, or
[2] The median diameter (D50) is in the range of 1.9 to 4.0 μm, the sphericity is 0.8 or more, and the compressibility is 40% or less,
The D50/D50 _BET is 2 or less, so there is little aggregation, and the viscosity is 10,000 cps or less, so that the resin is highly packed.
When the spherical aluminum nitride powders of Examples 1 to 14 were kneaded alone with a silicone resin, they did not form resin moldings with very low hardness and high thermal conductivity. Since there is little powder with a large , it is possible to use a thinner resin compact than before.
When the spherical aluminum nitride powders of Examples 1 to 14 are combined with particles having a larger particle diameter and mixed with a silicone resin, a low hardness (the original flexibility of the silicone resin is not impaired) and a high thermal conductivity resin molded body can be obtained. Obtainable. Moreover, when it is combined in the same manner and mixed with an epoxy resin, the three-point bending strength increases.

It should be noted that the present invention is not limited to the above-described embodiments, and can be embodied with appropriate modifications within the scope of the invention.

Claims (8)

It contains aluminum nitride and a rare earth compound, has a median diameter (D50) of 1.9 to 4.0 μm, contains 10% or less particles with a particle diameter of 0.9 μm or less, and contains 10% or less particles with a particle diameter of 7 μm or more. and a spherical aluminum nitride powder having a sphericity of 0.8 or more. A spherical aluminum nitride powder containing aluminum nitride and a rare earth compound, having a median diameter (D50) of 1.9 to 4.0 μm, a sphericity of 0.8 or more, and a compaction of 40% or less. 3. The spherical aluminum nitride powder according to claim 1, containing 0.01 to 0.5% by mass of calcium in terms of oxide. The spherical aluminum nitride powder according to any one of claims 1 to 3, wherein D50/D50 _BET is 2 or less. 5. The spherical aluminum nitride powder according to any one of claims 1 to 4, wherein 150 g of said spherical aluminum nitride powder and 100 g of silicone oil have a viscosity of 10,000 cps or less when mixed. A polymer molded body in which a polymer material is filled with the spherical aluminum nitride powder according to any one of claims 1 to 5. With respect to 100% by mass of aluminum nitride powder, 0.5 to 3.0% by mass of rare earth compounds in terms of oxides, 0.3 to 1.0% by mass of calcium compounds in terms of oxides, and 8 to 50% by mass % of carbon powder to obtain a mixed powder;
A first heat treatment step of heat-treating the mixed powder at 1450 to 1700 ° C. in a non-oxidizing atmosphere;
a second heat treatment step of further heat-treating at 500 to 800° C. in an oxidizing atmosphere after the heat treatment;
A method for producing a spherical aluminum nitride powder, comprising: The rare earth compound is selected from at least one selected from the group consisting of oxides, halides, carbonates, nitrates, oxalates, hydroxides, and alkoxides of Y, Yb, La, Nd, and Sm,
8. The method according to claim 7, wherein the calcium compound is selected from at least one of the group consisting of oxides, halides, sulfides, carbonates, nitrates, oxalates, hydroxides and alkoxides of calcium. A method for producing the described spherical aluminum nitride powder.

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