Aluminum nitride powder, method for producing the same, and polymer composition

Abstract

To provide an aluminum nitride powder having a small particle diameter and excellent wettability with a polymer material such as a resin.SOLUTION: An oil absorbent having a median size (D50) of less than 1.5 μm and an oil absorption measured in accordance with JISK5101 13-1:2004 (refined linseed oil method) using silicone oil instead of refined linseed oil (hereinafter referred to simply as "oil absorption"). In the aluminum nitride powder of the present invention, 21g / 100g is equal to or less than 10. In the method for producing the aluminum nitride powder, the aluminum nitride powder is crushed by a dry jet mill so that the oil absorption / BET specific surface area after crushing is ≤ 80% of that before crushing.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an aluminum nitride powder.

[0002] Taking advantage of its excellent thermal conductivity, aluminum nitride powder is used as a filler to be mixed into materials such as resins, greases, adhesives, and paints. The material properties required of a filler include packing ability, kneadability, and thermal conductivity, and various efforts are being made to improve the material properties.

[0003] Previously, in Patent Document 1, the applicant of the present application reported that the filling property, kneadability, and thermal conductivity can be improved by using a spherical aluminum nitride powder with high sphericity, in which 70% or more of the particles have an outer periphery that does not include sharp corners or uneven portions.

[0004] Furthermore, the applicant of the present application reported in Patent Document 2 that fluidity and filling properties can be improved by using spherical aluminum nitride powder having a median diameter (D50) of 1.9 to 4.0 μm, 10% or less of particles having a particle diameter of 0.9 μm or less, 10% or less of particles having a particle diameter of 7 μm or more, and a sphericity of 0.8 or more.

[0005] The spherical aluminum nitride powders of Patent Documents 1 and 2 are basically produced by adding and mixing a rare earth compound powder, a calcium compound powder, and a carbon powder to an aluminum nitride raw material powder, heat treating the mixture in a non-oxidizing atmosphere to promote particle spheroidization and growth, and then heat treating the mixture in an oxidizing atmosphere to decarburize the particles.

[0006] Next, Patent Document 3 states the general idea that if coarse particles are contained in the filler, clogging occurs when filling gaps, resulting in uneven filling, voids, molding defects, etc., and that the presence of agglomerated particles can also cause deterioration of fluidity.The document then states that no aluminum nitride powders have been reported in which the amount of coarse particles or agglomerated particles has been controlled, and reports an aluminum nitride powder that has been classified by removing excess coarse particles.

[0007] Regarding classification, Patent Document 3 states that various methods can be used, including dry methods (sieve classification, air classification) and wet methods (wet filter classification, fluid classification), but that air classification and wet classification are more efficient at removing coarse particles, and further states that wet classification leaves fewer coarse particles remaining after classification than air classification, and that wet filter classification has better accuracy and higher productivity than fluid classification, but then employs only wet filter classification in the examples. Wet filter classification is a classification method in which powder is dispersed in a solvent, deagglomerated, and then passed through a filter.

[0008] Patent Document 4 describes an aluminum nitride powder for blending with oils, in which -OR groups (O: oxygen, R: alkyl group) are present on part or all of the particle surface. This powder is produced by pulverizing aluminum nitride powder in the presence of alcohols and heat-treating the resulting powder at 40 to 400°C. This powder is said to have reduced oil absorption and excellent dispersibility in oils or resins. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 6700460 [Patent Document 2] Patent No. 7149379 [Patent Document 3] Patent No. 7017556 [Patent Document 4] Patent No. 4228161 Summary of the Invention [Problem to be solved by the invention]

[0010] However, the aluminum nitride powders of Patent Documents 1 and 2, when produced by the above methods, still have room for improvement in terms of wettability with polymeric materials such as resins.

[0011] The inventors of the present application suspected that wet classification of aluminum nitride powder as in Patent Document 3 might affect its wettability with polymeric materials such as resins, and conducted a follow-up test on the aluminum nitride powder in the examples of Patent Document 3. As a result, it was found that the wettability with polymeric materials such as resins was actually worse after classification than before classification.

[0012] The inventors of the present application also carried out a reproduction experiment (see Comparative Examples 3 to 5 described later) on the aluminum nitride powder of Patent Document 4, and found that although a decrease in oil absorption was expected, the D50 / D50 ratio described later BET Since the particle diameter was large, it is presumed that there were many aggregated particles and that the shape was distorted. When such powder is used as a filler in a resin at a high loading, the viscosity tends to increase or the loading does not become high, and as a result, it is predicted that the filled resin composition will not be able to achieve high thermal conductivity.

[0013] Furthermore, when aluminum nitride powder is to be highly loaded into a resin, by using aluminum nitride powder with a large particle size as the main filler and aluminum nitride powder with a small particle size as the sub-filler (in combination), the sub-filler is placed between the main fillers, enabling a higher loading, which is advantageous for improving the heat dissipation of the filler-loaded resin composition.

[0014] However, aluminum nitride powder with a small particle size is more prone to aggregation than aluminum nitride powder with a large particle size. In particular, aluminum nitride powder with a D50 of less than 1.5 μm could not be obtained with the prior art techniques described in Patent Documents 1 to 4 and other documents that exhibit excellent wettability with resins.

[0015] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an aluminum nitride powder having a small particle size and excellent wettability with polymeric materials such as resins. [Means for solving the problem]

[0016] The inventors further investigated whether it would be possible to improve the wettability of aluminum nitride powder with polymeric materials such as resins by changing the particle surface condition of the aluminum nitride powder. As a result, they found that it was possible to improve the wettability of aluminum nitride powder with polymeric materials such as resins by subjecting the aluminum nitride powder to crushing using a dry jet mill, and after further investigation, they arrived at the present invention.

[0017] [1] Aluminum nitride powder having a D50 of less than 1.5 μm and an oil absorption (hereinafter simply referred to as "oil absorption") of 21 g / 100 g or less, measured in accordance with JIS K5101-13-1:2004 (refined linseed oil method) using silicone oil instead of refined linseed oil.

[0018] [2] D50 / D50 BET The aluminum nitride powder according to [1], wherein the value of [amount of SiO2] is 3 or less. Here, D50 BET is the particle diameter (BET specific surface area equivalent sphere diameter) calculated based on the actually measured BET specific surface area, assuming that the particles are spherical with the same diameter and free of aggregation, and will be described in detail later.

[0019] [3] The aluminum nitride powder according to either [1] or [2], wherein the ratio of oil absorption to BET specific surface area is 7 or less.

[0020] [4] A polymer composition in which the aluminum nitride powder according to any one of the above [1] to [3] is filled as a filler in a polymer material.

[0021] [5] A method for producing aluminum nitride powder, in which aluminum nitride powder is crushed using a dry jet mill so that the BET specific surface area after crushing is 110% or more of the BET specific surface area before crushing.

[0022] [6] A method for producing aluminum nitride powder, comprising crushing the aluminum nitride powder using a dry jet mill so that the oil absorption after crushing is 95% or less of the amount before crushing.

[0023] [7] A method for producing aluminum nitride powder, which comprises crushing aluminum nitride powder using a dry jet mill so that the oil absorption / BET specific surface area after crushing is 80% or less of that before crushing. [Effects of the Invention]

[0024] According to the present invention, it is possible to provide an aluminum nitride powder having a small particle size and excellent wettability with polymeric materials such as resins. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 shows SEM photographs of the aluminum nitride powders of Comparative Example 1 and Example 8. DETAILED DESCRIPTION OF THE INVENTION

[0026] <1> Aluminum nitride powder as starting material The aluminum nitride powder used as the starting material preferably has a D50 of 0.5 to 2 μm. The composition of the aluminum powder is not particularly limited, but may contain, in addition to aluminum nitride, a rare earth compound derived from the manufacturing method, and may further contain a calcium compound. The content of the rare earth compound is not particularly limited, but is preferably 3.0 mass% or less in terms of oxide relative to 100 mass% of aluminum nitride. If the content of the rare earth compound exceeds 3.0 mass%, the purity of aluminum nitride decreases, which may result in a decrease in thermal conductivity. The rare earth compound is not particularly limited, but examples thereof include oxides or halides of Y, Yb, La, Nd, and Sm. The content of the calcium compound is not particularly limited, but is preferably 0.5 mass% or less in terms of oxide relative to 100 mass% of aluminum nitride. If the calcium compound content exceeds 0.5 mass%, the purity of aluminum nitride decreases, which may result in a decrease in thermal conductivity. The aluminum nitride powder may be produced by any method known in the art, including the methods described in Patent Documents 1 and 2.

[0027] <2> Crushing with a dry jet mill In the crushing process using a dry jet mill, gas is ejected from a jet nozzle, the resulting jet stream accelerates the raw material particles, and the particles are crushed by collisions between themselves and between the particles and a collision plate. The dry jet mill used for this purpose is not particularly limited, and any known or commercially available dry jet mill can be used.

[0028] By subjecting aluminum nitride powder with a D50 of 1 to 1.5 μm to dry jet milling, the agglomerated powder is broken down and the oil absorption rate is reduced. By treating under appropriate conditions, the crushing of primary particles is suppressed while only the agglomerated particles are broken down, and the BET specific surface area and D50 / D50 ratio are improved. BET This action results in an aluminum nitride powder with less aggregation, an isotropic shape, reduced oil absorption, and high wettability with polymeric materials such as resins, despite its small particle size.

[0029] The crushing using a dry jet mill can be carried out under the following conditions. (A) Crushing is performed so that the BET specific surface area after crushing is 110% or more (preferably 115% or more, more preferably 118% or more) of that before crushing. However, as the BET specific surface area increases, it generally becomes more difficult to mix with resin (in other words, a larger amount of resin is required to wet the aluminum nitride powder). Therefore, crushing is preferably performed so that the BET specific surface area after crushing is 130% or less of that before crushing. (a) The oil absorption after crushing is 95% or less (preferably 85% or less, more preferably 80% or less) of that before crushing. (c) The treatment is carried out so that the oil absorption / BET specific surface area after crushing is 80% or less (preferably 75% or less, more preferably 70% or less) of that before crushing.

[0030] It should be noted that wet classification can adjust the particle size distribution to the same level as dry jet mill classification, but the oil absorption does not decrease.The reasons for this difference in oil absorption despite the same particle size distribution are currently unknown, but one possible reason is that the state of the particle surfaces newly exposed by the dry jet mill is different from the state of the surfaces that were originally exposed.

[0031] <3> Aluminum nitride powder after crushing (A) D50 The D50 of the aluminum nitride powder after crushing is set to less than 1.5 μm so that it is suitable for use as a sub-filler, etc. The lower limit of D50 is not particularly limited, but is preferably 0.5 μm or more.

[0032] (a) Oil absorption amount The oil absorption of the aluminum nitride powder after crushing is determined in accordance with JIS K5101-13-1:2004 (refined linseed oil method), by adding small amounts of silicone oil (instead of refined linseed oil) to 10 g of powder, kneading the mixture with a spatula, and determining the amount of silicone oil added so that the mixture can be spread without breaking or crumbling and still lightly adhere to a measuring plate, and converting this amount into the amount of silicone oil added per 100 g of powder. The smaller the oil absorption value, the better the wettability of the powder with oil, and the better the wettability with polymeric materials such as resins. This oil absorption is preferably 20.5 g / 100 g or less, more preferably 18.5 g / 100 g or less, and most preferably 17.5 g / 100 g or less.

[0033] (c) BET specific surface area The BET specific surface area of ​​the aluminum nitride powder after crushing is a specific surface area measured by the BET single-point method, which is a nitrogen gas adsorption method.

[0034] (D) D50 / D50 BET The degree of particle aggregation of the aluminum nitride powder after the crushing is expressed as D50 / D50 BET It can be evaluated as follows. The particle diameter calculated based on the measured BET specific surface area A, assuming that the particles are of the same diameter, spherical, and free of agglomeration, is D50. BET (BET specific surface area sphere equivalent diameter). The calculation method is as follows: Particle diameter D, volume V, surface area S, density ρ (ρ for AlN is 3.26 g / cm 3 ), weight M, and from the formula, V=(π×D 3 ) / 6 S=π×D 2 M=V×ρ=(π×D 3 ×ρ) / 6 The measured BET specific surface area A = S / M = 6 / (D50 BET ×ρ) ∴D50 BET =6 / (ρ×A)=6 / (3.26×A)=1.84 / A

[0035] The BET specific surface area measured by gas adsorption is calculated from the amount of gas molecules that are much smaller than the particles being measured and that adhere to the particle surface. This makes it possible to measure powders that contain many agglomerated particles by penetrating into the gaps between the particles. On the other hand, in particle size distribution measurement using a laser diffraction scattering system, powder is dispersed in a liquid and measured, but for particles that do not disaggregate, the size of the aggregated particles is measured as is, so the particle diameter D50 measured by a laser diffraction scattering meter is D50 calculated from the BET specific surface area. BET take a larger value. This effect is quantified as the degree of cohesion, D50 / D50 BET is. D50 is a powder with little agglomeration. BET The difference between the two becomes smaller (D50 becomes smaller, resulting in D50 / D50 BET becomes smaller). That is, D50 / D50 BET The closer to 1, the fewer agglomerated particles there are and the closer the particle shape is to a perfect sphere. This D50 / D50 BET (=D50 / (1.84 / A)) is preferably 3 or less, more preferably 2.5 or less, and most preferably 2.1 or less.

[0036] (E) Oil absorption / BET specific surface area The ratio of oil absorption to BET specific surface area of ​​the aluminum nitride powder after the crushing is preferably 7 or less, more preferably 6 or less, and most preferably 5.5 or less.

[0037] <4> Purpose The applications of the aluminum nitride powder of the present invention are not particularly limited, but examples thereof include fillers to be mixed with materials such as polymeric materials, greases, adhesives, paints, etc. Examples of polymeric materials include resins, rubbers, elastomers, etc. A polymer composition in which the aluminum nitride powder of the present invention is filled as a filler in a polymer material can be highly filled and has high thermal conductivity. The filler-filled polymer composition of the present invention can be used to mold a polymer molded article. Applications of the polymer molded article are not particularly limited, and examples thereof include circuit boards used in semiconductor modules, LED packages, Peltier modules, printers, multifunction peripherals, semiconductor lasers, optical communications, high frequency applications, general-purpose heat dissipation members, heat dissipation members (heat sinks) for power semiconductor modules, insulating plates, etc. [Example]

[0038] Next, examples embodying the present invention will be described with reference to the drawings, while comparing them with comparative examples. Note that 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.

[0039] Aluminum nitride powders of Examples 1 to 8 and Comparative Examples 1 to 5 were obtained or prepared as shown in Table 1. Hereinafter, the term "each example" refers to each of Examples 1 to 8 and Comparative Examples 1 to 5.

[0040] [Table 1]

[0041] In Comparative Example 1, aluminum nitride powder "A-01-F" (average particle size 1 μm) manufactured by MARUWA Co., Ltd. (the applicant of the present application) was used as is, and was not subjected to crushing.

[0042] In Examples 1 to 8, the starting material "A-01-F" was crushed by colliding particles with each other in a dry jet mill (referred to as "JM" in Table 1) using a "PJM-80" manufactured by Nippon Pneumatic Mfg. Co., Ltd. The collection method for the dry jet mill is a cyclone, which has the advantage that particularly fine crushed particles are removed and not included in the crushed powder. The raw material supply rate (processing rate) was set to 150 g / hr. The atmosphere throughout the line was atmospheric. The crushing pressure was 0.1 MPa in Example 1, 0.2 MPa in Example 2, 0.3 MPa in Example 3, and 0.4 MPa in Examples 4-8. The number of disintegration passes was 1 in Examples 1 to 4, and 2, 3, 4, and 5 passes in Examples 5, 6, 7, and 8, respectively.

[0043] In Comparative Example 2, aluminum nitride powder "H1 grade" (average particle size 1.5 μm) manufactured by Tokuyama Corporation was used as is, without being crushed.

[0044] Comparative Example 3 reproduces the aluminum nitride powder of Example 1 of Patent Document 4 exactly as described therein. Specifically, isopropyl alcohol was added to aluminum nitride powder "UM grade" (average particle size 6.5 μm) manufactured by Toyo Aluminum K.K., and the powder was pulverized at room temperature using a vibration mill, and the pulverized powder was heat-treated at 150°C for 1 hour. However, as in Examples 1 to 8 and Comparative Examples 1 and 2, the oil absorption was calculated in units of g / 100g using silicone oil instead of refined linseed oil (the same applies to Comparative Examples 4 and 5 described below).

[0045] Comparative Example 4 is a reproduction of Example 2 of Patent Document 4 exactly as described therein. That is, isopropyl alcohol was added to the "UM grade" and the mixture was pulverized using a vibration mill. Steam was introduced into the water jacket during pulverization to heat the powder, and the pulverized powder was heat-treated at 80°C for 1 hour.

[0046] Comparative Example 5 is a reproduction of Comparative Example 1 of Patent Document 4 exactly as described therein. That is, acetone was added to the "UM grade" and the mixture was pulverized using a vibration mill at room temperature (a large amount of cooling water was supplied to the outer wall of the mill), and the pulverized powder was heat-treated at 150°C for 1 hour.

[0047] The aluminum nitride powder obtained in each example was subjected to the following observations and measurements, and the results are shown in FIG.

[0048] (1) SEM photograph observation SEM photographs of Comparative Example 1 and Example 8 were observed (see FIG. 1).

[0049] (2) BET specific surface area For each example, the BET specific surface area was measured by the BET single-point method as described above using a Monosorb MS-21 model manufactured by Quantachrome.

[0050] (3) Particle size distribution For each example, 0.5 g of aluminum nitride powder from each example was added to 50 ml of a 0.1 mass % aqueous solution of sodium pyrophosphate, and the dispersion was carried out for 3 minutes at 80% output using a US-300E model manufactured by Nippon Seiki Seisakusho Co., Ltd., and the volume-based particle size distribution was measured using a laser diffraction particle size distribution analyzer, SALD-2200 model manufactured by Shimadzu Corporation. Note that for Comparative Examples 3 to 5, only D50 was measured.

[0051] (4) D50 / D50 BET For each example, the value was calculated using the following formula as described above. D50 / D50 BET =D50 / (1.84 / A)

[0052] (5) Oil absorption amount For each example, the oil absorption was measured in accordance with JIS K5101-13-1:2004 as described above, using silicone oil instead of refined linseed oil. The silicone oil used was KF96-300CS (density 0.97 g / mL) manufactured by Shin-Etsu Chemical Co., Ltd. The oil absorption was measured 10 times, and the average value was used.

[0053] (6) Oil absorption / BET specific surface area For each example, the oil absorption / BET specific surface area was calculated.

[0054] (7) Variation rate relative to Comparative Example 1 The rates of variation of the BET specific surface area, oil absorption, and oil absorption / BET specific surface area of ​​Examples 1 to 8 (by dry jet mill crushing under each condition) relative to Comparative Example 1 were calculated.

[0055] [Consideration] (A) As shown in FIG. 1, compared to Comparative Example 1, Example 8 has clearly fewer agglomerates of aluminum nitride powder. (a) "A-01-F" originally mainly contains 1 μm particles, but the D50 of Comparative Example 1 is 1.34 μm because some of the 1 μm particles are agglomerated. The D50 of Examples 1 to 8 is 1.17 μm or less because the agglomerated particles are crushed by the dry jet mill, but the D50 of Examples 1 to 8 is not 1 μm or less because no or little crushing of the 1 μm particles occurs. (c) The oil absorption was smaller in Examples 1 to 8 than in Comparative Example 1. As mentioned above, one reason for this is thought to be that the state of the particle surface newly exposed by crushing using a dry jet mill is different from the state of the surface originally exposed. (d) As shown in Examples 1 to 4, as the crushing pressure was increased from 0.1 MPa to 0.3 MPa, the BET specific surface area clearly increased and the oil absorption clearly decreased, but even when the crushing pressure was increased from 0.3 MPa to 0.4 MPa, the changes in the BET specific surface area and oil absorption were small. (e) As in Examples 4 to 8, even when the number of passes was increased from 1 to 5, the changes in the BET specific surface area and oil absorption were irregular. (f) Comparing Examples 1 to 8 with Comparative Examples 1 and 2, Examples 1 to 8 have smaller particle diameters, larger BET specific surface areas, and lower oil absorptions (the value of oil absorption / BET specific surface area is 7 or less in Examples 1 to 8, while it is greater than 8 in Comparative Examples 1 and 2). Generally, the smaller the particle diameter and the larger the BET specific surface area, the higher the oil absorption. However, it can be said that the present invention makes it possible to produce aluminum nitride powders that have small particles but low oil absorption. (G) When D50 is about 2 μm as in Comparative Examples 3 to 5, the oil absorption is low, but in Examples 1 to 8, the oil absorption can be reduced to the same level despite the smaller particle diameter.

[0056] [Application example] The filled resin compositions of Application Examples 1 to 3 shown in Table 2 were prepared as follows.

[0057] [Table 2]

[0058] (1) A resin composition consisting of bisphenol F epoxy resin (ADEKA Corporation, EP-4901H), imidazole curing agent (ADEKA Corporation, EH-2021), dispersant, and diluent solvent PGMEA (propylene glycol monomethyl ether acetate) was kneaded for 2 minutes in a planetary centrifugal mixer (Thinky Corporation, ARV-200). The rotation speed was 1000 rpm and the revolution speed was 2000 rpm. (2) The resin composition of (1) contains the following four types of aluminum nitride powders with different particle sizes (all manufactured by MARUWA Co., Ltd.) as fillers. ·80μm class: “S-80” (D50=82.8μm, BET specific surface area 0.03m 2 / g) ·30μm class: "S-30" (D50=37.6μm, BET specific surface area 0.06m 2 / g) ·4μm class: “A-04-F” (D50=3.98μm, BET specific surface area 0.67m 2 / g) 1 μm class: Comparative Example 1, Example 4, or Example 8 These were mixed in a ratio (weight ratio) of 80μm class:40μm class:4μm class:1μm class = 4:3:1.5:1.5, and added so that after hardening three levels of charge filling ratio were produced: 82.5vol%, 85vol%, and 87.5vol%, and then kneaded for 2 minutes to fill the filler. After that, the mixture was degassed while kneading for 2 minutes under reduced pressure of 50 Torr. (3) The filler-loaded resin composition of (2) was applied to two 0.05 mm thick PET films using a film applicator to a thickness of 0.8 mm. (4)(3) was dried at 90°C for 30 minutes to remove the diluting solvent. (5) Two sheets of the filler-filled resin composition (4) were stacked together with the surfaces not in contact with the PET substrate facing each other, and then hot-pressed at 120°C, 10 MPa, and 30 minutes to obtain a resin molded body measuring 5 cm long, 5 cm wide, and 0.7 mm thick.

[0059] The porosity of the resin molded articles of Application Examples 1 to 3 was calculated by the following method. 1) The resin molded body is heat treated at 600°C for 2 hours to decompose / remove organic components. 2) Using the decomposition residue rate of the organic components measured in advance, the content of the organic components is calculated from the rate of weight loss and change, and the theoretical filling rate of the filler is calculated assuming that the remainder is all filler. 3) The theoretical density (porosity 0%) is calculated from the calculated theoretical filling rate of the filler, the density of the resin molded body made only from organic components, and the density of the filler. 4) The porosity in the green body is calculated from the ratio of the green body density measured before heating to the theoretical density.

[0060] Compared to Application Example 1 (containing Comparative Example 1 as a sub-filler), Application Examples 2 and 3 (containing Examples 4 and 8 as sub-fillers) have lower porosities at all loading rates, and the higher the loading rate (i.e., the closer to the limit the loading rate), the more clearly the difference in porosity from Application Example 1 becomes. This is thought to be because, in Application Example 1, the greater the loading amount, the less resin is needed to wet the filler, especially the 1 μm class filler, and the filler is unable to be completely wetted, resulting in the formation of pores inside the molded body. In contrast, in Application Examples 2 and 3, the filler, especially the 1 μm class filler, has good wettability with the resin, so it can be wetted with a small amount of resin, and as a result, the resin amount is less likely to be insufficient, and the porosity remains low. Therefore, in Application Examples 2 and 3, higher filling is possible compared to Application Example 1, and therefore higher heat dissipation of the molded body can be expected.

[0061] The present invention is not limited to the above-described embodiments, and can be embodied by making appropriate modifications within the scope of the gist of the invention.

Claims

1. The aluminum nitride powder has a median diameter (D50) of less than 1.5 μm and an oil absorption (hereinafter simply referred to as "oil absorption") of 21 g / 100 g or less, measured in accordance with JIS K5101-13-1:2004 (refined linseed oil method) using silicone oil instead of refined linseed oil.

2. D50 / D50 ＢＥＴ 2. The aluminum nitride powder according to claim 1, wherein the value of σ is 3 or less.

3. 2. The aluminum nitride powder according to claim 1, wherein the ratio of oil absorption to BET specific surface area is 7 or less.

4. A polymer composition comprising a polymer material filled with the aluminum nitride powder according to any one of claims 1 to 3 as a filler.

5. A method for producing aluminum nitride powder, comprising crushing the aluminum nitride powder using a dry jet mill so that the BET specific surface area after crushing is 110% or more of the BET specific surface area before crushing.

6. A method for producing aluminum nitride powder, comprising crushing the aluminum nitride powder using a dry jet mill so that the oil absorption after crushing is 95% or less of that before crushing.

7. A method for producing aluminum nitride powder, comprising crushing the aluminum nitride powder using a dry jet mill so that the oil absorption / BET specific surface area after crushing is 80% or less of that before crushing.

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