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

Abstract

This invention provides an aluminum nitride powder that exhibits excellent wettability with polymer materials such as resins and is suitable as a subfiller for filling polymer materials. [Solution] The aluminum nitride powder has a D50 of less than 1.0 μm and an oil absorption / BET specific surface area of ​​7.0 or less. The aluminum nitride powder can be produced by reducing and nitriding the aluminum oxide powder by mixing a mixed raw material of aluminum oxide powder with calcium compound powder and carbon powder, and then raising the temperature in a nitrogen atmosphere so that the time spent in the temperature range from 1250°C to 1370°C is 1.5 hours or more and the maximum temperature is 1580°C or less, thereby synthesizing aluminum nitride powder, after which the carbon remaining in the aluminum nitride powder is oxidized and removed, and the aluminum nitride powder is crushed.

Description

[Technical Field]

[0001] This invention relates to aluminum nitride powder, a method for producing the same, and a polymer composition.

[0002] Aluminum nitride powder, with its excellent thermal conductivity, is used as a filler mixed into materials such as resins, greases, adhesives, and paints. The material properties required for fillers include filling ability, kneadability, and thermal conductivity, and various efforts are being made to improve these properties.

[0003] Previously, the applicant reported in Patent Document 1 that fluidity and packing properties can be improved by spherical aluminum nitride powder having a median diameter (D50) of 1.9 to 4.0 μm, with less than 10% of particles having a particle size of 0.9 μm or less, less than 10% of particles having a particle size of 7 μm or more, and a sphericity of 0.8 or higher. This spherical aluminum nitride powder is basically manufactured by adding and mixing rare earth compound powder, calcium compound powder, and carbon powder to aluminum nitride raw material powder, heat treating it in a non-oxidizing atmosphere to promote the sphericization and growth of particles, and then heat treating it in an oxidizing atmosphere to decarburize it.

[0004] Incidentally, when densely filling a resin with aluminum nitride powder, using aluminum nitride powder with a large particle size as the main filler and aluminum nitride powder with a small particle size as a subfiller (in combination) allows for denser filling by having the subfiller between the main fillers, which is advantageous for increasing the thermal conductivity of the filler-filled resin composition. However, the method described in Patent Document 1 could not obtain aluminum nitride powder that could be used as a subfiller, having a D50 of less than 1.0 μm and excellent wettability with the resin.

[0005] Patent Document 2 describes, as an example of Example 4, a mixed powder (starting material) made by combining aluminum oxide powder with an average particle size of 0.2 μm, carbon black with an average particle size of 0.02 μm, and calcium carbonate powder is placed in a carbon container and fired in a non-oxidizing nitrogen gas atmosphere at a heating rate of 500°C / hr from room temperature to 1000°C, 250°C / hr from 1000°C to 1400°C, and held at a maximum temperature of 1400°C for 2 hours to synthesize aluminum nitride powder through an Al2O3-C-N2 reduction-nitridation reaction. Furthermore, this is heat-treated in an oxidizing air atmosphere at 700°C for 4 hours to oxidize and remove the remaining carbon, thereby obtaining aluminum nitride powder with a particle size of 0.9 μm.

[0006] However, the method described in Patent Document 2 (low-temperature synthesis technique) aims to synthesize easily sinterable aluminum nitride powder, and therefore the synthesized aluminum nitride powder has a high oil absorption rate and is unsuitable as a filler (see Comparative Example 4 of this application, which reproduces Example 4 of Patent Document 2). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 7149379 [Patent Document 2] Japanese Patent Application Publication No. 5-221618 [Overview of the project] [Problems that the invention aims to solve]

[0008] Therefore, the object of the present invention is to provide an aluminum nitride powder that has a small particle size and a large specific surface area, yet has low oil absorption, and thus excellent wettability with polymer materials such as resins, making it suitable as a subfiller for filling polymer materials. [Means for solving the problem]

[0009] The inventors have devised a method for synthesizing aluminum nitride powder by a reduction nitridation reaction from aluminum oxide powder, and have found that aluminum nitride powder with a small particle size and a low oil absorption amount can be obtained. Through further studies, the present invention has been achieved.

[0010] [1] Aluminum nitride powder having a D50 of less than 1.0 μm and an oil absorption amount / BET specific surface area (the oil absorption amount is the oil absorption amount measured using silicone oil instead of refined linseed oil in accordance with JIS K5101-13-1:2004 (refined linseed oil method)).) of 7.0 or less.

[0011] [2] The aluminum nitride powder according to [1], wherein the D50 is 0.4 μm or more and 0.9 μm or less.

[0012] [3] The aluminum nitride powder according to [1] or [2], wherein the oil absorption amount / BET specific surface area is 4.0 or more and 6.0 or less.

[0013] [4] A polymer composition obtained by filling the above-mentioned [1], [2] or [3] aluminum nitride powder as a filler into a polymer material.

[0014] [5] A polymer composition obtained by filling a polymer material with aluminum nitride powder having a D50 of 1.5 μm or more as a main filler and the above-mentioned [1], [2] or [3] aluminum nitride powder as a sub-filler.

[0015] [6] A mixing step of mixing calcium compound powder and carbon powder with aluminum oxide powder to obtain a mixed raw material, A reduction nitridation step of reducing and nitriding the aluminum oxide powder to synthesize aluminum nitride powder by heating the mixed raw material in a nitrogen atmosphere so that the passing time in the temperature range from 1250 ° C to 1370 ° C is 1.5 hr or more and the maximum temperature is 1580 ° C or less. A decarburization step of heating the aluminum nitride powder after the reduction nitridation step in an oxidizing atmosphere to oxidize and remove the carbon remaining in the aluminum nitride powder. A crushing step of crushing the aluminum nitride powder after the decarbonization step, A method for producing aluminum nitride powder containing

[0016] <Effect> In the reduction nitridation step, in the temperature range from 1250 °C to 1370 °C, aluminum oxide powder and calcium compound powder (auxiliary agent) react to form calcium aluminate on the surface of aluminum oxide particles, which is more easily reduced and nitrided than aluminum oxide. The calcium aluminate on the outermost surface of the particles undergoes a reduction nitridation reaction with carbon powder and nitrogen to become aluminum nitride. Aluminum nitride has a higher sintering start temperature than aluminum oxide, and sintering is difficult to proceed in this temperature range. On the other hand, aluminum oxide also undergoes sintering in this temperature range, and the particles are connected and coarsened. By setting the passing time in the temperature range from 1250 °C to 1370 °C to 1.5 hours or more, the formation of calcium aluminate on the surface of aluminum oxide particles and the reduction nitridation reaction of calcium aluminate proceed sufficiently. Therefore, the formation of the aluminum nitride layer on the outermost surface of the particles also proceeds sufficiently, and the progress of sintering due to the contact of aluminum oxides can be suppressed. In addition, in the temperature range of ≥1370 °C, it is considered that surface smoothing and spheroidization progress due to the synthesis of aluminum nitride via calcium aluminate. By setting the maximum temperature to 1580 °C or lower, the coarsening of the synthesized aluminum nitride powder is suppressed, and those with a small particle size can be obtained. By the crushing step, the aggregation of the aluminum nitride powder is reduced, and the oil absorption amount is decreased. Although sintering between aluminum nitride particles has proceeded slightly, only a slight neck is formed, and it can be easily crushed by this crushing step. Due to the above effects, aluminum nitride powder with a D50 of less than 1.0 μm and an oil absorption amount / BET specific surface area of 7.0 or less can be obtained. That is, although the particle size is small and the BET specific surface area is large, those with a low oil absorption amount can be obtained.

Effect of the Invention

[0017] According to the present invention, it is possible to provide aluminum nitride powder that exhibits excellent wettability with polymer materials such as resins and is suitable as a subfiller for filling polymer materials. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1 is a graph showing the firing patterns of Examples 1-8 and Comparative Example 2. [Figure 2] Figure 2 is a graph showing the firing patterns of Comparative Examples 1, 3 to 5. [Figure 3] Figure 3 shows SEM images of aluminum nitride powder from Examples 1-4 and Comparative Examples 1-4. [Modes for carrying out the invention]

[0019] <1> Starting materials (a) Aluminum oxide powder The particle size of the aluminum oxide powder is not particularly limited, but it is preferable that the D50 is 1.0 μm or less, as this allows for easy formation of the calcium aluminate at low temperatures.

[0020] (i) Calcium compound powder The particle size of the calcium compound powder is not particularly limited, but it is preferable that the D50 is 10.0 μm or less, and more preferably 2.0 μm or less, in that the calcium aluminate can be easily formed at low temperatures. The amount of calcium compound powder added is not particularly limited, but is preferably 0.8 to 15 parts by mass per 100 parts by mass of aluminum nitride produced. While not particularly limited, calcium compounds such as CaCO3, CaO, and CaF2 can be cited. Among these, CaCO3 is preferred in terms of chemical stability and cost.

[0021] (c) Carbon powder The particle size of the carbon powder is not particularly limited, but it is preferable that it be smaller than that of the aluminum oxide in order to increase the contact area with the aluminum oxide or the calcium aluminate. The mixing ratio of aluminum oxide powder to carbon powder is not particularly limited, but a mass ratio of aluminum oxide powder:carbon powder = 1:1 to 2.65:1 is preferred. If there is too little carbon powder, the low-temperature synthesis of aluminum nitride cannot be sufficiently promoted, and the amount of aggregated particles increases. On the other hand, if there is too much carbon powder, the time required for decarburization increases, leading to a decrease in production efficiency, and the amount of aluminum nitride powder obtained decreases, increasing manufacturing costs.

[0022] <2> Raw material mixing process A raw material mixture powder can be obtained by mixing the prepared raw material powders until homogeneous using common methods such as planetary mills, vibratory mills, ball mills, or V-blenders.

[0023] <3> Reduction Nitriding Process In the reduction nitriding process, the time spent in the temperature range from 1250°C to 1370°C is 1.5 hours or more, as described above, but preferably 2 hours or more. There is no particular upper limit to this time, but for efficiency reasons, it is preferably 20 hours or less. In the reduction nitriding process, the maximum temperature is 1580°C or lower, as described above, but preferably 1550°C or lower.

[0024] <4> Decarburization process The oxidizing atmosphere in the decarburization process is not particularly limited, but examples include an air atmosphere and an oxygen atmosphere. In the decarburization process, the heating temperature is not particularly limited, but 500 to 700°C is preferred, and the heating time is not particularly limited, but 4 to 8 hours is preferred.

[0025] <5> Crushing process While there are no particular limitations on the specific crushing methods, examples include jet mills (hereinafter referred to as "JM") and ball mills. Crushing using a dry JM involves ejecting gas from a nozzle, accelerating the raw material particles with the resulting jet stream, and crushing them through collisions between particles and between particles and a collision plate. Since the collection method is a cyclone, it has the advantage of removing particularly fine crushed particles. Through the above process, the aggregated particles are broken down and the amount of oil absorbed decreases. At this time, by processing under appropriate conditions, only the aggregated particles are broken down while suppressing the crushing of primary particles, and the BET specific surface area and D50 / D50 BET It can also suppress the rise.

[0026] <6> Aluminum nitride powder after crushing treatment (a) D50 To make it suitable for use as a subfiller, the D50 of the crushed aluminum nitride powder is less than 1.0 μm, preferably 0.4 μm or more and 0.9 μm or less, and more preferably 0.5 μm or more and 0.9 μm or less.

[0027] (a) Oil absorption amount The amount of oil absorbed by the crushed aluminum nitride powder is determined in accordance with JIS K5101-13-1:2004 (refined linseed oil method). For every 10g of powder, a small amount of silicone oil (instead of refined linseed oil) is dropped and mixed with a spatula. The amount dropped is such that it does not crack or crumble, can be spread into a single putty-like mass, and lightly adheres to the measuring plate. This amount is then converted to the amount dropped per 100g of powder. This value decreases as the wettability of the powder with oil improves, the BET specific surface area of ​​the particles decreases, and the degree of aggregation decreases. Furthermore, if the wettability of the powder with oil improves, the wettability with polymer materials such as resins also improves. The amount of oil absorbed is preferably 35.0 g / 100 g or less, and more preferably 29.4 g / 100 g or less.

[0028] (c) BET specific surface area The BET specific surface area of ​​the crushed aluminum nitride powder is the specific surface area measured by the BET single-point method, which is a nitrogen gas adsorption method. The specific surface area of ​​this BET is 6.5m². 2 It is preferable that the amount be less than or equal to 5.6m 2 It is more preferable that it be less than or equal to / g, and 4.0m 2 / g or more, 5.5m 2 It is most preferable that the value be less than or equal to / g.

[0029] (E) D50 / D50 BET The degree of aggregation of the particles of the aluminum nitride powder after crushing can be evaluated by D50 / D50 BET . For the actually measured BET specific surface area A, the particle diameter calculated assuming that the particles are of the same diameter, spherical, and have no aggregation is D50 BET (BET specific surface area equivalent spherical diameter). The calculation method is as follows. Taking the particle diameter D, volume V, surface area S, density ρ (the ρ of AlN is 3.26 g / cm 3 ), and weight M, from the formula, V = (π × D 3 ) / 6 S = π × D 2 M = V × ρ = (π × D 3 × ρ) / 6 The actually measured BET specific surface area A = S / M = 6 / (D50 BET × ρ) ∴ D50 BET = 6 / (ρ × A) = 6 / (3.26 × A) = 1.8^4 / A

[0030] The BET specific surface area measured by the gas adsorption method is calculated from the amount of gas molecules, which are sufficiently smaller than the particles to be measured, adsorbed on the particle surface. Therefore, even in a powder with many aggregated particles, it is possible to measure by entering the gaps between the particles. On the other hand, in the measurement of the particle size distribution by the laser diffraction scattering system, the powder is dispersed in a liquid for measurement. However, for particles whose aggregation is not eliminated, the size of the aggregated particles is measured as it is. Therefore, the particle diameter D50 measured by the laser diffraction scattering meter is larger than the D50 BET calculated from the BET specific surface area. The numerical value obtained by quantifying this influence as the degree of aggregation is D50 / D50 BET . For a powder with less aggregation, the difference between D50 and D50 BET becomes smaller (D50 becomes smaller, and as a result, D50 / D50 BET becomes smaller). That is, D50 / D50BET The closer the value is to 1, the fewer aggregated particles there are, and the closer the shape is to a perfect sphere. This D50 / D50 BET (=D50 / (1.84 / A)) is preferably 2.4 or less, and more preferably 2.0 or less.

[0031] (O) Oil absorption capacity / BET specific surface area This index normalizes oil absorption capacity by BET specific surface area, taking into account the size of the filler. The smaller this value, the more suitable it is for filler applications. The oil absorption / BET specific surface area of ​​the crushed aluminum nitride powder is 7.0 or less as described above, but more preferably 6.5 or less, and most preferably 4.0 or more and 6.0 or less.

[0032] <7> Purpose The applications of the aluminum nitride powder of the present invention are not particularly limited, but examples include use as a filler to be mixed into materials such as polymer materials, greases, adhesives, and paints. Examples of polymer materials include resins, rubbers, and elastomers. A polymer composition in which the aluminum nitride powder of the present invention is filled into a polymer material allows for high filling capacity and has high thermal conductivity. Polymer molded articles can be manufactured using the filler-filled polymer composition of the present invention. The applications of the polymer molded articles are not particularly limited, but examples include circuit boards used in semiconductor modules, LED packages, Peltier modules, printers, multifunction devices, semiconductor lasers, optical communications, and high-frequency devices, as well as general-purpose heat dissipation members (heat sinks, thermal interface materials (TIMs), etc.), heat dissipation members for power semiconductor modules (same as above), and insulating boards.

[0033] <8> polymer composition In the above polymer composition, when the polymer material is filled with aluminum nitride powder as the main filler and the aluminum nitride powder of the present invention as a subfiller, the D50 of the aluminum nitride powder as the main filler is 1.5 μm or more as described above, but it is preferable that it is 1.8 μm or more and 5 μm or less. [Examples]

[0034] Next, embodiments of the present invention will be described in comparison with comparative examples. Note that the materials, quantities, and conditions in the embodiments are illustrative and can be modified as appropriate without departing from the spirit of the invention.

[0035] Table 1 shows the raw material formulations and manufacturing conditions for Examples 1-8 and Comparative Examples 1-5. Hereafter, "each example" refers to each of Examples 1-8 and Comparative Examples 1-5.

[0036] [Table 1]

[0037] (1) Starting materials For aluminum oxide (Al2O3), the D50 is 0.8 μm and the BET specific surface area is 8.0 m². 2 Powder was used in units of / g. As carbon (C), D50 is 0.04 μm, and the BET specific surface area is 70 m². 2 Powder was used in units of / g. As calcium carbonate (CaCO3), the D50 is 1.9 μm and the BET specific surface area is 7.2 m². 2 Powder in a quantity of / g was used. However, in Example 4, D50 was 5.9 μm and BET specific surface area was 1.45 m². 2 Powder was used in units of / g.

[0038] (2) Mixture Except for Comparative Example 4, the Al2O3 powder and C powder were blended in a mass ratio of 2:1, and in Comparative Example 4, the ratio was 2.65:1. CaCO3 powder was then added in the amounts shown in Table 1 for each example, per 100 parts by mass of the resulting aluminum nitride. However, no CaCO3 powder was added to Comparative Example 1. The starting materials after the above formulation were placed in a fluororesin container along with alumina balls, and mixed using a planetary mill until homogeneous to obtain a raw material mixed powder.

[0039] (3) Reduction Nitriding Process Aluminum nitride powder was synthesized by heating the raw material mixtures shown in Table 1 in a nitrogen atmosphere using a "High Multi 5000" furnace manufactured by Fuji Denpa Kogyo Co., Ltd., as shown in Table 1, Figures 1 and 2, and as described below.

[0040] Examples 1-5 and Comparative Example 2 were heated from room temperature (20°C) to 1250°C at a rate of 300°C / hr, then heated from 1250°C to the maximum temperature of 1500°C at a rate of 30°C / hr, held at the maximum temperature for 5 hours, and then cooled down at a rate of 200°C / hr. Example 6 involved raising the temperature from room temperature to 1250°C at a rate of 300°C / hr, then raising the temperature from 1250°C to the maximum temperature of 1500°C at a rate of 10°C / hr (without holding at the maximum temperature), and finally cooling down at a rate of 200°C / hr. Example 7 involved raising the temperature from room temperature to 1250°C at a rate of 300°C / hr, then raising the temperature from 1250°C to the maximum temperature of 1500°C at a rate of 50°C / hr, holding at the maximum temperature for 5 hours, and then cooling down at a rate of 200°C / hr. Example 8 involved heating from room temperature to 1250°C at a rate of 300°C / hr, then heating from 1250°C to 1300°C at a rate of 60°C / hr, holding at 1300°C for 5 hours, then heating from 1300°C to the maximum temperature of 1500°C at a rate of 60°C / hr, holding at the maximum temperature for 2 hours, and finally cooling at a rate of 200°C / hr.

[0041] Comparative Example 1 involved raising the temperature from room temperature to 1250°C at a rate of 300°C / hr, then raising the temperature from 1250°C to the maximum temperature of 1600°C at a rate of 60°C / hr, holding at the maximum temperature for 5 hours, and then cooling down at a rate of 200°C / hr. Comparative Example 3 involved raising the temperature from room temperature to 1250°C at a rate of 300°C / hr, then raising the temperature from 1250°C to the maximum temperature of 1600°C at a rate of 30°C / hr, holding at the maximum temperature for 5 hours, and then cooling down at a rate of 200°C / hr. Comparative Example 4 involved raising the temperature from room temperature to 1000°C at a rate of 500°C / hr, then raising the temperature from 1000°C to the maximum temperature of 1400°C at a rate of 250°C / hr, holding at the maximum temperature for 2 hours, and then cooling at a rate of 200°C / hr. Comparative Example 4 is a reproduction of Example 4 in Patent Document 2. Comparative Example 5 involved raising the temperature from room temperature to 1250°C at a rate of 300°C / hr, then raising the temperature from 1250°C to the maximum temperature of 1500°C at a rate of 100°C / hr, holding at the maximum temperature for 5 hours, and then cooling down at a rate of 200°C / hr.

[0042] Table 1 shows the time taken to pass through the temperature range from 1250°C to 1370°C during the heating process for each example. Examples 1-8 and Comparative Examples 1-3 had long passage times of 1.5 hours or more. Comparative Examples 4 and 5 had short passage times of less than 1.5 hours.

[0043] (4) Decarburization process A Yamato Scientific "Electric Furnace (FO710)" was used as the decarburization furnace. Each example after the reduction-nitriding process described above was heated at 600°C for 6 hours in an air atmosphere to oxidize and remove any remaining carbon.

[0044] (5) Crushing process The samples from each example other than Comparative Examples 2 and 4 after the reduction nitriding process described above were crushed. Crushing was performed using a bead mill only for Example 5, and using a JM for the other examples. The JM (jet-mixing) procedure was performed using the "PJM-80" dry-type JM machine manufactured by Nippon Pneumatic Mfg. Co., Ltd., with a gas pressure of 0.6 MPa and a supply rate of 100 g / hr. The bead milling was performed using the "Drystar SDA1" continuous dry bead mill manufactured by Ashizawa Finetech Co., Ltd., with alumina beads (3.0 mm in diameter), a filling rate of 70%, a mill peripheral speed of 5.0 m / s, and a feed rate of 500 g / hr.

[0045] The following observations and measurements were performed on each of the obtained aluminum nitride powder samples. The results are shown in Figure 3 and Table 2.

[0046] [Table 2]

[0047] 1. SEM observation Each example was observed using a JEOL Ltd. "JSM IT700HR" SEM. Figure 3 shows SEM images of Examples 1-4 and Comparative Examples 1-4.

[0048] 2. Amount of oxygen, amount of oxygen in AlN only The total oxygen content of the aluminum nitride powder in each example was measured using HORIBA's "EMGA-920" by inert gas fusion-nondispersive infrared absorption spectroscopy (NDIR). The oxygen content of the aluminum nitride alone, after subtracting the oxygen content of calcium compounds from the total oxygen content of the powder, is also shown. A smaller value indicates less oxygen in the aluminum nitride itself.

[0049] 3.BET specific surface area Using a "Monosorb, model MS-21" manufactured by Quantachrome, the BET specific surface area of ​​each example was measured using the BET single-point method as described above.

[0050] 4.Particle size distribution As a pretreatment, 0.5 g of aluminum nitride powder from each example was added to 50 ml of a 2% by mass aqueous solution of sodium pyrophosphate, and dispersed for 3 minutes at 80% power using a "US-300E" manufactured by Nippon Seiki Seisakusho Co., Ltd. After this pretreatment, the volume-based particle size distribution of each sample was measured using the Malvern Mastersizer-3000 by laser diffraction and scattering. The refractive index during measurement was set to 1.95-0.05i (real part 1.95, imaginary part 0.05), and the scattering intensity was set to 5%. Dmax = D99.99.

[0051] 5. (D90-D10) / D50 (D90-D10) / D50 was calculated. This is an indicator of the sharpness of the particle size distribution; the smaller this value, the sharper the particle size distribution.

[0052] 6. D50 / D50 BET D50 / D50 BET This was calculated using the following formula, as mentioned above. As mentioned above, it is an indicator of the aggregated state of the powder, and the smaller this value, the less aggregation there is. D50 / D50 BET =D50 / (1.84 / A)

[0053] 7.Oil absorption amount As described above, in accordance with JIS K5101-13-1:2004, silicone oil was used instead of refined linseed oil, and the oil absorption amount was measured for each example. The silicone oil used was "KF96-300CS" (density 0.97 g / mL) manufactured by Shin-Etsu Chemical Co., Ltd. Ten measurements were taken, and the average value was adopted.

[0054] 8.Oil absorption / BET specific surface area The oil absorption amount / BET specific surface area was calculated.

[0055] [Consideration] (a) Examples 1 to 8 have a D50 of less than 1.0 μm, and more preferably within the range of 0.4 μm or more and 0.9 μm or less, and more preferably within the range of 0.5 μm or more and 0.9 μm or less. In addition, the oil absorption / BET specific surface area is 7.0 or less, and more preferably within the range of 4.0 or more and 6.0 or less. Furthermore, the SEM images confirm the progression of spheroidization of primary particles and the small number of aggregated particles. The more spheroidization progresses, the lower the viscosity when filled into polymers such as resins.

[0056] (i) Comparative Example 1 (an example without CaCO3) shows a slightly larger D50. Also, no spheroidization of primary particles is observed in the SEM image (magnification: 50,000x). Comparative Example 2 (without crushing treatment) shows a considerably large D50 and a large oil absorption / BET specific surface area. The SEM image (magnification: 500x) shows many aggregated particles of around 10 μm, which is considered to be one of the reasons for the large D50 and oil absorption / BET specific surface area. Comparative Example 3 (an example with a maximum temperature of 1600 degrees Celsius) shows a low oil absorption / BET specific surface area ratio, but a slightly larger D50. The SEM image (magnification: 5000x) shows many particles that are linked together as primary particles, which is thought to be one of the reasons for the large D50. Comparative Example 4 (a reproduction of Example 4 in Patent Document 2, an example where the heating rate is high and no crushing occurs) yields particles with a small D50, but the oil absorption / BET specific surface area ratio is considerably large. Numerous aggregated particles of around 10 μm are observed in the SEM image (magnification: 500x), which is considered to be one of the reasons for the large oil absorption / BET specific surface area ratio. Comparative Example 5 (an example with a high heating rate) has a large D50 value.

[0057] <Application Examples> Next, the filler-filled resin compositions for application examples 1 to 6 shown in Table 3 were prepared as follows.

[0058] [Table 3]

[0059] (1) A resin composition consisting of bisphenol F type epoxy resin (ADEKA Corporation, EP-4901HF), imidazole type curing agent (ADEKA Corporation, EH-2021), dispersant, and diluent PGMEA (propylene glycol monomethyl ether acetate) was kneaded for 2 minutes in a rotary-orbit mixer (Sinky Corporation, ARV-200). The rotation speed was 1000 rpm and the orbital speed was 2000 rpm.

[0060] (2) The resin composition of (1) was mixed with the main filler and subfiller shown in Table 3 in a mass ratio of main filler:subfiller = 80:20, and was added to produce three levels of filling rates of 70 vol%, 75 vol%, and 80 vol% after curing. The mixture was then kneaded for 2 minutes to fill the resin. Subsequently, the mixture was degassed while kneading under reduced pressure of 50 Torr for 2 minutes. The main filler used was "A-04-F" from MARUWA Corporation, a 4μm class (D50=3.98μm, BET specific surface area 0.67m²). 2 It is aluminum nitride powder ( / g). Also, "A-02-F" is a 2μm class (D50=2.27μm, BET specific surface area 1.03m²) manufactured by MARUWA Corporation. 2 It is aluminum nitride powder in a quantity of / g. As the subfiller, Example 1, Comparative Example 1, or Comparative Example 4 described above were used.

[0061] (3) The filler-filled resin composition from (2) was applied to a 0.05 mm thick PET film using a film applicator to a thickness of 0.8 mm. Two such films were prepared. (4)(3) was dried at 90°C for 30 minutes to remove the diluting solvent. Two sheets made of the filler-filled resin composition of (5) and (4) were stacked so that the sides not in contact with the PET substrate faced each other, and a resin molded body measuring 5 cm in length, 5 cm in width, and 0.7 mm in thickness was obtained by heat pressing at 120°C × 10 MPa × 30 minutes.

[0062] The porosity of the resin molded articles for application examples 1 to 6 was calculated using 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 previously measured organic component decomposition residue rate, calculate the organic component content from the weight reduction rate, and then calculate the theoretical filler filling rate assuming that the remainder is all filler. 3) Calculate the theoretical density (porosity 0%) from the calculated theoretical filler filling rate, the density of the resin molded product made only from organic components, and the density of the filler. 4) The porosity of the molded body is calculated from the ratio of the molded body density measured before heating to the theoretical density.

[0063] [Consideration] (C) Main filler "A-04-F" Application Example 1 showed low porosity at all filling rates. This is likely because the D50 of Example 1 used as a subfiller was less than 1 μm, and the oil absorption / BET specific surface area was 7.0 or less. In contrast, in application examples 2 and 3, the porosity was high even at filling rates of 70% and 75%, and at a filling rate of 80%, the porosity exceeded 10%, making molding practically impossible. This is thought to be because the D50 of Comparative Example 1, used as a subfiller, exceeded 1 μm in application example 2. Similarly, this is thought to be because the oil absorption rate / BET specific surface area of ​​Comparative Example 4, used as a subfiller, was high in application example 3.

[0064] (Ki) Main filler "A-02-F" In application example 4, the porosity was low at all packing rates. This is thought to be due to the same reasons as described in (k) above. In contrast, in Application Example 5, the porosity was high even at a filling rate of 70% and 75%, and at a filling rate of 80%, the porosity exceeded 10%, making it practically impossible to mold. Similarly, in Application Example 6, the porosity was high even at a filling rate of 70%, and at a filling rate of 75% and 80%, the porosity exceeded 10%, making it practically impossible to mold. This is thought to be due to the same reasons as described in (k) above.

[0065] (c) Therefore, by using the filler of the example as a subfiller in combination with the main filler, it is possible to produce a sheet with low porosity and high filling rate, and it is expected that the thermal conductivity of the molded article will be increased.

[0066] It should be noted that the present invention is not limited to the embodiments described above, and can be appropriately modified and implemented without departing from the spirit of the invention.

Claims

1. Aluminum nitride powder having a D50 of less than 1.0 μm and an oil absorption / BET specific surface area ratio (oil absorption is measured in accordance with JIS K5101-13-1:2004 (refined linseed oil method), using silicone oil instead of refined linseed oil) of 7.0 or less.

2. The aluminum nitride powder according to claim 1, wherein D50 is 0.4 μm or more and 0.9 μm or less.

3. The aluminum nitride powder according to claim 1, wherein the oil absorption rate / BET specific surface area is 4.0 or more and 6.0 or less.

4. A polymer composition comprising a polymer material filled with aluminum nitride powder according to claim 1, 2, or 3 as a filler.

5. A polymer composition comprising a polymer material filled with aluminum nitride powder having a D50 of 1.5 μm or more as a main filler, and aluminum nitride powder according to claim 1, 2, or 3 as a subfiller.

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