Glass-coated aluminum nitride powder and method for manufacturing the same, polymer molding

Abstract

To provide glass-coated aluminum nitride powder having high water resistance, in which the surface of the particles is substantially completely coated with glass, and a polymer molding which contains the powder as a filler and has high water resistance.SOLUTION: Glass-coated aluminum nitride powder is composed of glass-coated aluminum nitride particles in which the surface of aluminum nitride particles is coated with glass, wherein D50 of the aluminum nitride particles is 0.5 to 100 μm, glass thickness is 2 to 100 nm, and a glass coating rate of the particle surface is 95% or more. Glass precursor-coated aluminum nitride particles are prepared by drying a mixed liquid containing aluminum nitride particles and a glass precursor in a misty state or a state of being spread on the surface, and glass-coated aluminum nitride particles are prepared by forming the glass precursor into a glass by heating.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a glass-coated aluminum nitride powder and a polymer molded article containing the same. [Background technology]

[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. However, depending on the conditions, not only before but also after mixing, aluminum nitride can be converted into aluminum hydroxide, which has low thermal conductivity, and generate corrosive ammonia when exposed to moisture in the air. Therefore, efforts are being made to improve the water resistance of aluminum nitride powder by coating it with glass or other materials.

[0003] Patent Document 1 discloses a method for producing glass-coated aluminum nitride particles having a d50 of 10 to 200 μm, in which aluminum nitride particles are mixed with glass frit having a d50 of 0.3 to 50 μm, the mixture is placed in a crucible or formed into pellets, and heat-treated at a temperature above the glass transition temperature of the glass frit and below 2000°C to coat the aluminum nitride particles with the glass frit to obtain coated particles, and the coated particles are crushed. In the examples, the glass coating thickness is 10 to 660 nm.

[0004] Patent Document 2 discloses a method for producing glass-coated aluminum nitride particles, in which a mixture of aluminum nitride particles having a d50 of 10 to 200 μm and a composition powder containing a glass component and having a d50 of 0.3 to 50 μm is mixed by a mechanochemical method while applying shearing force, the mixture is placed in a crucible and heat-treated at a temperature equal to or higher than the glass transition temperature of the glass component and equal to or lower than 2000°C, and the heat-treated product is crushed.

[0005] Patent Document 3 discloses a method for producing aluminum nitride particles coated with a silicon-containing oxide (silica or silicon-aluminum composite oxide), in which an organosilicon compound is added to aluminum nitride particles by spraying or the like while stirring the particles, followed by dry mixing to coat the surfaces of the aluminum nitride particles with the organosilicon compound, and the coated aluminum nitride particles are heated at a temperature of 300°C or higher but lower than 1000°C. The silicon-containing oxide coated aluminum nitride particles have a carbon atom content of less than 1000 ppm by mass, a coverage of the silicon-containing oxide coating of 15% or more and 100% or less as determined by LEIS analysis, and the silicon atom content relative to the specific surface area satisfies a specific relationship. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6739669 [Patent Document 2] Patent No. 6606628 [Patent Document 3] Patent No. 7419938 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the manufacturing methods described in Patent Documents 1 and 2, the mixture is placed in a crucible or formed into pellets and then heat-treated, i.e., the particles are in contact with each other. This means that the glass melt penetrates between the aluminum nitride particles due to strong capillary forces, causing the particles to aggregate. The degree of aggregation increases as the aluminum nitride particles become smaller in diameter (e.g., D50 is approximately 0.5 to 5 μm). This requires the subsequent crushing process to require a considerable amount of energy, which results in peeling or destruction of the coated glass layer, reducing the glass coverage and water resistance.

[0008] Furthermore, the low-energy ion scattering (LEIS) analysis in Patent Document 3 provides information on a shallow region of about 0.1 nm from the surface, and therefore detects even the slightest adhesion of silica or silicon-aluminum composite oxide, with the maximum coverage being 88% in Example 6. Regarding coverage, it is stated that "it is more preferably 95% or less... (omitted)...it has been found that if it exceeds 95%, thermal conductivity may decrease," but no specific examples of coverage exceeding 95% are given. Therefore, it can be inferred that nearly complete coverage (95% or more) has not been achieved.

[0009] Therefore, an object of the present invention is to provide a highly water-resistant glass-coated aluminum nitride powder in which the particle surfaces are almost completely coated with glass, and a highly water-resistant polymer molded article containing the powder as a filler. [Means for solving the problem]

[0010] [1] A glass-coated aluminum nitride powder consisting of glass-coated aluminum nitride particles in which the particle surfaces of aluminum nitride particles are coated with glass, wherein the D50 of the aluminum nitride particles is 0.5 to 100 μm, the glass thickness is 2 to 100 nm, and the glass coverage of the particle surface is 95% or more.

[0011] [2] The glass-coated aluminum nitride powder according to [1], wherein the aluminum nitride particles have a D50 of less than 10 μm.

[0012] [3] The glass-coated aluminum nitride powder according to [1] or [2], wherein the glass thickness is less than 10 nm.

[0013] [4] The glass-coated aluminum nitride powder according to any one of [1] to [3], wherein the glass coverage is 100%. The glass coverage is measured by TEM analysis, and regions with a glass thickness of less than 2 nm are considered to be substantially uncoated, since they are insufficiently coated from the viewpoint of water resistance.

[0014] [5] A polymer molded article made of a polymer material containing the glass-coated aluminum nitride powder according to any one of [1] to [4] above as a filler.

[0015] [6] A polymer molded article made of a polymer material containing, as a filler, at least two types of the glass-coated aluminum nitride powder according to any one of [1] to [4] above, each having a different D50.

[0016] [7] The polymer molded article according to [5], which is a heat dissipation member.

[0017] [8] The polymer molded article according to [6], which is a heat dissipation member.

[0018] [9] A glass precursor coating step of producing a glass precursor-coated aluminum nitride powder consisting of glass precursor-coated aluminum nitride particles whose particle surfaces are coated with a glass precursor by drying a mixed liquid containing aluminum nitride particles and a glass precursor in a mist form or in a state where the mixed liquid is spread on a surface; a heat treatment step of heating the glass precursor-coated aluminum nitride particles to a temperature equal to or higher than the melting point of the glass precursor to vitrify the glass precursor, thereby producing glass-coated aluminum nitride powder consisting of glass-coated aluminum nitride particles whose particle surfaces are coated with glass; A method for producing a glass-coated aluminum nitride powder, comprising:

[0019]

[10] The method for producing a glass-coated aluminum nitride powder according to [9], wherein the glass precursor coating step is carried out by spray drying, in which the mixed solution is sprayed into the air.

[0020]

[11] The method for producing glass-coated aluminum nitride powder according to [9], wherein the glass precursor coating step is carried out by spreading the mixed liquid on the surface of the receiving member in a film or dispersed form.

[0021]

[12] The method for producing a glass-coated aluminum nitride powder according to any one of [9] to

[11] , wherein a crushing step of crushing aggregated glass precursor-coated aluminum nitride particles is carried out between the glass precursor coating step and the heat treatment step.

[0022]

[13] The method for producing a glass-coated aluminum nitride powder according to any one of [9] to

[12] , wherein the heat treatment step is carried out by continuously charging the glass precursor-coated aluminum nitride particles in a state of being dispersed in a carrier gas into a tubular furnace.

[0023]

[14] The method for producing a glass-coated aluminum nitride powder according to any one of [9] to

[12] , wherein the heat treatment step is carried out by continuously supplying the glass precursor-coated aluminum nitride particles to a rotary kiln.

[0024]

[15] The method for producing a glass-coated aluminum nitride powder according to any one of [9] to

[12] , wherein the heat treatment step is carried out by placing the glass precursor-coated aluminum nitride particles in a sheath and passing them through a roller hearth kiln.

[0025]

[16] A method for producing glass-coated aluminum nitride powder, which comprises drying a mixed liquid containing aluminum nitride particles and a glass precursor in a mist or spread state on a surface while heating the mixed liquid to a temperature equal to or higher than the temperature at which the glass precursor melts, thereby producing glass-coated aluminum nitride powder consisting of glass-coated aluminum nitride particles whose particle surfaces are coated with glass obtained by vitrifying the glass precursor. [Effects of the Invention]

[0026] According to the present invention, it is possible to provide a highly water-resistant glass-coated aluminum nitride powder in which the particle surfaces are almost completely coated with glass, and a highly water-resistant polymer molded article containing the powder as a filler. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a schematic diagram illustrating the spray drying in Example 1. [Figure 2] FIG. 2 is a schematic diagram illustrating the heat treatment in Example 1. [Figure 3] FIG. 3 is a schematic diagram illustrating the crushing treatment (before the heat treatment) in Example 1. [Figure 4] FIG. 4 is a TEM photograph of the glass-coated aluminum nitride particles of Comparative Example 6 at a magnification of 500,000 times. [Figure 5] FIG. 5 is a TEM photograph of the glass-coated aluminum nitride particles of Example 1 at a magnification of 1,350,000 times. [Figure 6] FIG. 6 is a TEM photograph of the glass-coated aluminum nitride particles of Example 2 at a magnification of 1,350,000 times. [Figure 7] FIG. 7 is a TEM photograph of the glass-coated aluminum nitride particles of Example 5 at a magnification of 500,000 times. DETAILED DESCRIPTION OF THE INVENTION

[0028] <1> Raw aluminum nitride particles The raw material aluminum nitride powder may contain substances other than aluminum nitride, such as rare earth compounds and calcium compounds, derived from the manufacturing process, but the amount should be as small as possible. If the content is high, the composition of the glass will change significantly when incorporated into the glass, which will increase the melting point of the glass, making it difficult to melt, or it may fall outside the vitrification range and not form a glass. To achieve a glass coverage of 95% or more, it is preferable to reduce the content of substances other than aluminum nitride to 0.5% by weight or less, and more preferably 0.2% by weight or less. A known method for reducing the content is leaching treatment using inorganic or organic acids. When the average particle size (median diameter) D50 of the raw material aluminum nitride powder is 0.5 μm or more, it is less likely to aggregate and is therefore easier to use, and when it is 100 μm or less, it is easier to make the polymer molded article thinner. When D50 is less than 10 μm, it is preferable because the glass precursor coating step can be easily performed by the spray drying method and the heat treatment step can be easily performed while the powder is dispersed in the carrier gas.

[0029] <2> Glass The glass is not particularly limited, but examples thereof include silicate glass, borosilicate glass, bismuth-based glass, tin-phosphate-based glass, vanadium-based glass, and lead-based glass. The glass preferably contains two or more components selected from SiO2, Al2O3, and B2O3. The glass may contain a ZnO component to reduce the thermal expansion coefficient. The glass may contain oxides of alkali metals such as Na2O and K2O, but from the viewpoint of moisture resistance, the smaller the content, the better. The glass may contain optional components such as CaO, SrO, MgO, BaO, and SnO.

[0030] If the glass thickness is 2 nm or more, the glass coating is sufficient from the viewpoint of water resistance, and if it is 100 nm or less, the decrease in thermal conductivity due to the presence of glass can be suppressed. If the glass thickness is less than 10 nm, the decrease in thermal conductivity due to the presence of glass can be further suppressed, which is preferable.

[0031] A glass coverage of 95% or more improves water resistance, and a glass coverage of 100% further improves water resistance.

[0032] <3> Glass precursor coating process In the glass precursor coating process of the present invention, a mixed liquid containing aluminum nitride particles and a glass precursor is dried in a mist or spread over a surface, resulting in rapid drying. For glass precursor coating, it is essential to rapidly promote the precipitation of salts of each element of the glass components that occurs during the drying process. The saturation solubilities of the salts of each element of the glass components are different, and they precipitate in order of decreasing saturation solubility during the drying process. However, prolonged drying increases the heterogeneity of the distribution of each element of the glass components after precipitation. Therefore, if heat treatment is performed to obtain molten glass with a homogeneous composition, it becomes necessary to heat the glass at a higher temperature for a longer period of time. According to the present invention, rapid drying as described above reduces the heterogeneity of the distribution of each element of the glass components after precipitation, and molten glass with a homogeneous composition can be obtained even with low-temperature, short-time heat treatment, which is advantageous in terms of energy cost and production efficiency.

[0033] The glass precursor coating step is not particularly limited, but the following can be exemplified. (A) Spray drying, in which the mixture is sprayed into the air. This method is suitable when the raw aluminum nitride powder has a D50 of less than 10 μm, which makes it difficult to settle. (A) The mixture is spread on the surface of a receiving member in a film or dispersed form. This method is suitable when the raw aluminum nitride powder has a D50 of 10 μm or more, which makes it prone to settling. The receiving member is not particularly limited, but examples include PET film, glass plate, and ceramic plate.

[0034] <4> Crushing process (if necessary) In the glass precursor coating process of the present invention, aluminum nitride particles are easily dispersed one by one. Ideally, each droplet sprayed during spray drying contains one aluminum nitride particle. However, as shown in Figure 3(a), depending on the solids concentration of the raw slurry and the spraying conditions, multiple aluminum nitride particles may be contained in one droplet, and after drying, multiple particles may aggregate to form agglomerated particles. In this case, it is preferable to perform a crushing process before the heat treatment process, as necessary. As shown in Figure 3(b), it is expected that the mixed salt of glass component elements that was present at the bond between particles will be largely carried away by one of the particles during the crushing process, and in some cases the surface of the aluminum nitride particles may become exposed. As shown in Figure 3(c), even if the coating layer of the glass precursor-coated powder is uneven, by melting the coating layer through heat treatment, it will wet and spread over the surface of the aluminum nitride particles, and become a homogeneous coating layer again. Although there will be slight differences in the coating thickness for each particle, on average it will be roughly the thickness as designed.

[0035] <5> Heat Treatment Process The heat treatment step is not particularly limited, but the following can be exemplified. (a) Glass precursor-coated aluminum nitride particles are dispersed in a carrier gas and continuously fed into a tubular furnace. This method is preferred because the particles do not come into contact with each other. This method is suitable when the raw aluminum nitride powder has a D50 of less than 10 μm, which makes it easy for the powder to flow in the carrier gas. (a) Continuously supplying glass precursor-coated aluminum nitride particles to a rotary kiln. This method is suitable for raw aluminum nitride powder with a D50 of 10 μm or more, which is difficult to flow in a carrier gas. (c) Glass precursor-coated aluminum nitride particles are placed in a sheath and passed through a roller hearth kiln. This method is suitable when the raw aluminum nitride powder has a D50 of 10 μm or more and is difficult to flow with a carrier gas. These methods allow for rapid heating and cooling. Note that in (b) and (c), unlike (a), particles come into contact with each other, but because the particle size is large and the glass thickness is small, aggregation that accompanies glass melting hardly occurs.

[0036] <6> Applications of glass-coated aluminum nitride powder The applications of the glass-coated aluminum nitride powder are not particularly limited, but examples thereof include fillers to be mixed into materials such as polymer materials, greases, adhesives, and paints.

[0037] <7> Polymer molded body The aluminum nitride powder of the present invention can be used as a filler in a polymer material to produce a polymer molded article having high thermal conductivity. Furthermore, by filling a polymer material with at least two types of glass-coated aluminum nitride powder with different D50 values, the filling rate of the glass-coated aluminum nitride powder increases, making it possible to produce a polymer molded product with even higher thermal conductivity. Examples of polymeric materials include resins, rubbers, elastomers, etc. Applications of polymeric molded articles are not particularly limited, but examples include heat dissipation members for heat generating bodies such as semiconductors. [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. Aluminum nitride powders of Comparative Examples 1 to 4 shown in Table 1 were prepared, and glass-coated aluminum nitride powders of Comparative Examples 5 and 6 and Examples 1 to 9 were produced.

[0039] [Table 1]

[0040] (Comparative Example 1) Comparative Example 1 is an uncoated aluminum nitride powder, "A-01-F" (D50 = 1.15 μm, specific surface area 3.06 m) manufactured by MARUWA Co., Ltd. (the applicant of the present application). 2 / g).

[0041] (Comparative Example 2) Comparative Example 2 is an uncoated aluminum nitride powder, "A-04-F" (D50 = 3.98 μm, specific surface area 0.67 m) manufactured by the same company. 2 / g).

[0042] (Comparative Example 3) Comparative Example 3 is an uncoated aluminum nitride powder, "S-30" (D50 = 37.6 μm, specific surface area 0.06 m) manufactured by the same company. 2 / g).

[0043] Comparative Example 4 Comparative Example 4 is an uncoated aluminum nitride powder, "S-80" (D50 = 82.8 μm, specific surface area 0.03 m) manufactured by the same company. 2 / g).

[0044] (Comparative Example 5) Comparative Example 5 is an aluminum nitride powder obtained by coating the starting material "A-01-F" with glass according to the method of Patent Document 1 as follows. (1) SiO2 was used as the Si source, B2O3 as the B source, Al2O3 as the Al source, lithium carbonate as the Li source, and potassium carbonate as the K source, and these were mixed to be 71.7 mol%, 24.8 mol%, 0.7 mol%, 2.5 mol%, and 0.3 mol%, respectively, calculated as oxides (SiO2, B2O3, Al2O3, Li2O, and K2O). The mixture was melted in a glass melting furnace, cooled, and then dry-pulverized to produce glass frit with a primary particle size of 0.1 μm. (2) The glass frit of (1) was added to the "A-01-F." The amount added was adjusted according to the specific surface area of ​​the AlN powder and the target glass thickness. The target glass thickness in this example was 9 nm. (3) (2) was placed in a sealed polypropylene container, and liquid paraffin and alumina balls with a diameter of 10 mm were added and mixed in a dry ball mill. (4) (3) was filled into a mold with a diameter of 30 mm and molded under a pressure of 10 MPa. (5) The compact from (4) was heated in nitrogen at 1350°C for 30 minutes in a box furnace (Motoyama Co., Ltd., Superburn NLT-2025D). (6) The compact of (5) was crushed in a jet mill to obtain aluminum nitride powder consisting of glass-coated aluminum nitride particles.

[0045] (Comparative Example 6) Comparative Example 6 is an aluminum nitride powder obtained by using the above-mentioned "A-04-F" as a starting raw material powder, which was subjected to a treatment using acid to dissolve impurities other than aluminum nitride, and then coating the powder with glass in accordance with the method described in Patent Document 1 as follows. (1) SiO2 was used as the Si source, B2O3 as the B source, and Al2O3 as the Al source, and these were mixed at 73.4 mol%, 25.4 mol%, and 1.2 mol%, respectively. These were melted in a glass melting furnace, cooled, and then dry-pulverized to produce glass frit with a primary particle size of 0.1 μm. (2) The glass frit of (1) was added to the starting material powder. The amount added was adjusted depending on the specific surface area of ​​the AlN powder and the target glass thickness. In this example, the target glass thickness was 9 nm. Thereafter, the same procedures as in (3) to (6) of Comparative Example 5 were carried out to obtain an aluminum nitride powder consisting of glass-coated aluminum nitride particles.

[0046] Example 1 Example 1 is an aluminum nitride powder obtained by coating the starting material "A-01-F" with glass as follows. (1) Tetraalkoxysilane modified to make it water-soluble was used as the Si source, boric acid as the B source, aluminum nitrate nonahydrate as the Al source, lithium nitrate as the Li source, and potassium nitrate as the K source. These were mixed to give oxide equivalents (SiO, B, O, Al, Li, O, and K), of 71.7 mol%, 24.8 mol%, 0.7 mol%, 2.5 mol%, and 0.3 mol%, respectively (the same composition as in Comparative Example 5), and dissolved in alcohol. (2) A slurry of "A-01-F" was prepared using the same alcohol as used in (1) as the dispersion medium. The solid content was 10 vol%. After adding "A-01-F" to the dispersion medium, it was subjected to ultrasonic dispersion treatment. (3) (1) was added to (2) and stirred. The amount added was adjusted depending on the specific surface area of ​​the AlN powder and the target glass thickness. In this example, the target thickness was 9 nm. (4) (3) was sprayed into a mist using a spray dryer (B-290, manufactured by Buchi) and then heated and dried to obtain glass precursor-coated aluminum nitride particles, as shown in Figure 1. The drying temperature was 220°C, and nitrogen was used as the drying gas. (5) The glass precursor-coated aluminum nitride particles (4) were crushed in a dry jet mill (Nippon Pneumatic Mfg. Co., Ltd., PJM-80) as shown in Figure 3(b). The crushing pressure was 0.1 MPa. (6) Glass-coated aluminum nitride particles were obtained by continuously supplying the glass precursor-coated aluminum nitride particles (6) (5) into a tubular furnace using nitrogen as a carrier gas, as shown in Figure 2. The amount of carrier gas was adjusted so that the residence time in the furnace, calculated from the carrier gas flow rate and the inner diameter of the furnace tube, was approximately 30 seconds to 2 minutes. The maximum temperature in the furnace was set to 1350°C so that the glass precursor-coated aluminum nitride particles supplied into the furnace would be heated above the melting point of the complex oxide that forms the glass. The glass precursor remained molten in the furnace for approximately 5 to 20 seconds, and when the particles emerged from the furnace, the molten liquid was rapidly cooled and vitrified, becoming glass-coated aluminum nitride particles.

[0047] Example 2 Example 2 is an aluminum nitride powder obtained by using the above-mentioned "A-04-F" as a starting raw material powder, which was subjected to a treatment using acid to dissolve impurities other than aluminum nitride, and then coating the powder with glass as follows. (1) Tetraalkoxysilane modified to make it water-soluble was used as the Si source, boric acid as the B source, and aluminum nitrate nonahydrate as the Al source. These were mixed to 73.4 mol%, 25.4 mol%, and 1.2 mol%, respectively, calculated as oxides (SiO, B, O, Al, O) (the same composition as in Comparative Example 6), and dissolved in alcohol. (2) The same alcohol as used in (1) was used as a dispersion medium to prepare a slurry of the starting material powder. The solid content was 10 vol%. After the starting material powder was added to the dispersion medium, it was subjected to an ultrasonic dispersion treatment. (3) (1) was added to (2) and stirred. The target thickness was 3 nm. (4) (3) was powdered using a spray dryer to obtain glass precursor-coated aluminum nitride particles, as shown in Figure 1. The drying temperature was 150°C, and nitrogen was used as the drying gas. (5) The glass precursor-coated aluminum nitride particles of (4) were heated in the same manner as in Example 1 to obtain glass-coated aluminum nitride particles. The maximum temperature in the furnace was set to 1500°C.

[0048] Example 3 Example 3 is an aluminum nitride powder that is glass-coated in the same manner as Example 2, except that the target thickness is changed to 6 nm.

[0049] Example 4 Example 4 is an aluminum nitride powder that is glass-coated in the same manner as Example 2, except that the target thickness is changed to 9 nm.

[0050] Example 5 Example 5 is an aluminum nitride powder that is glass-coated in the same manner as Example 2, except that the target thickness is changed to 15 nm.

[0051] Example 6 Example 6 is an aluminum nitride powder coated with glass in the same manner as Example 2, except that the target thickness was changed to 30 nm and the solid content concentration of the slurry was changed to 5 vol %.

[0052] Example 7 In Example 7, the "S-30" was classified to have a D50 of 20.5 μm and a specific surface area of ​​0.11 m 2 / g powder, which was then treated with acid to dissolve impurities other than aluminum nitride. This was used as the starting powder, and the aluminum nitride powder was then glass-coated as follows. (1) Tetraalkoxysilane modified to make it water-soluble was used as the Si source, boric acid as the B source, aluminum nitrate nonahydrate as the Al source, sodium nitrate as the Na source, and potassium nitrate as the K source. These were mixed to give oxide equivalents of 83.1 mol%, 11.5 mol%, 1.3 mol%, 3.8 mol%, and 0.3 mol%, respectively, (SiO2, B2O3, Al2O3, Na2O, and K2O), and dissolved in alcohol. (2) (1) was added to the starting material powder and prepared into a paste using a planetary mixer. The amount of (1) added was adjusted according to the specific surface area of ​​the aluminum nitride powder and the target glass thickness. In this example, the target thickness was 9 nm. (3) The solution was applied to a 0.05 mm thick polyethylene terephthalate (PET) film using a film applicator to a thickness of 0.5 mm. (4) (3) was placed in a dryer heated to 220°C to remove the solvent and powder the mixture, thereby obtaining glass precursor-coated aluminum nitride particles. (5) The glass-coated aluminum nitride particles from (4) were packed into a sheath and passed through a roller hearth kiln heated to a top temperature of 1350°C in a nitrogen gas flow to obtain glass-coated aluminum nitride particles. The residence time in the kiln was set to 30 minutes, and the temperature profile in the kiln was adjusted so that the time during which the particles were heated above the melting point of the glass-forming composite oxide was 10 minutes or less.

[0053] Example 8 Example 8 is a glass-coated aluminum nitride powder similar to Example 7, except that the starting raw material powder used was the above-mentioned "S-30" which had been treated with acid to dissolve impurities other than aluminum nitride.

[0054] Example 9 Example 9 is a glass-coated aluminum nitride powder similar to Example 7, except that the starting raw material powder used was the above-mentioned "S-80" which had been treated with acid to dissolve impurities other than aluminum nitride.

[0055] [Characteristics of glass-coated aluminum nitride powder] 1. Average particle size (median diameter) D50 0.5 g of the glass-coated aluminum nitride powder of each example (comparative examples 1 to 4 were uncoated) was added to 50 ml of a 0.1 mass % aqueous solution of sodium pyrophosphate, and dispersed for 3 minutes at 80% output using a US-300E model manufactured by Nippon Seiki Seisakusho Co., Ltd. The volumetric particle size distribution was measured using a laser diffraction particle size distribution analyzer, model SALD-2200 manufactured by Shimadzu Corporation. The D50 [μm] is shown in Table 1.

[0056] 2. Glass thickness TEM observations were performed on 30 particles with a D50 [μm] ±40%. For each particle, eight photographs were taken at magnifications of 500,000 to 2,000,000, rotated 45° each time. The glass thickness at the center of each photograph was measured and the average of all measurements was calculated. The glass thickness [μm] is shown in Table 1. If necessary, the samples for observation were embedded in resin and thinned using focused ion beam (FIB) processing, etc. The actual observations were performed using a JEOL Ltd. field emission transmission electron microscope JEM-2100F. The accelerating voltage was 200 kV. The boundary between the glass layer and the AlN particles was determined by the presence or absence of a crystal lattice image (the glass layer is amorphous, so a crystal lattice image is not visible) or by the presence or absence of detection of glass components (mainly Si in this case) by elemental analysis. Figure 4 shows TEM photographs of Comparative Example 6, Figure 5 shows TEM photographs of Example 1, Figure 6 shows TEM photographs of Example 2, and Figure 7 shows TEM photographs of Example 5, in which the added white dashed lines indicate the boundary between the aluminum nitride particle surface and the glass.

[0057] 3.Glass coverage Using the TEM photographs, the glass coverage was calculated by regarding the area where the glass thickness was less than 2 nm as being substantially uncoated, since the coverage was insufficient from the viewpoint of water resistance. The glass coverage is shown in Table 1. In Comparative Examples 5 and 6, the glass coating peeled off or broke due to crushing after the heat treatment, and the glass coating rate was low at 65% or less. In contrast, in Examples 1 to 9, the glass coverage was 95% or more.

[0058] 4.85℃ water resistance time (1) 10 g of distilled water (Hayashi Pure Chemical Industries, Ltd., GR grade, pH 5.5 to 6.0) was weighed into a sealed polypropylene container. (2) 1 g of powder was added to (1) and placed in an ultrasonic bath for 3 minutes to disperse the mixture. (3) The container was placed in an 85°C thermostatic bath (PHP-2J, Espec Corporation), and the time until the pH of the water in the container reached 9 or higher was measured. This was measured for up to 500 hours. The 85°C water resistance time [h] is shown in Table 1. Comparative Examples 1 to 4 have a short 85°C water resistance time of less than 1 hour, and Comparative Examples 5 and 6 do not have a significant improvement in 85°C water resistance time. In contrast, the water resistance was significantly improved in Examples 1 to 9. In particular, Examples 1 and 3 to 9 had a glass coverage of 100%, and therefore the water resistance was further improved.

[0059] [Production of resin molded body (Application Examples 1 to 8)] The resin molded articles of Application Examples 1 to 8 shown in Table 2 were produced as follows.

[0060] [Table 2]

[0061] (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) At least two types of glass-coated aluminum nitride powders (Comparative Examples 1 to 4 were uncoated) with different D50 values ​​were blended in the prescribed proportions shown in Table 2 to the resin composition of (1), and added as fillers to achieve a final volume of 75 or 80 vol% after curing. The mixture was then kneaded for 2 minutes under reduced pressure of 50 Torr while being degassed. (3) The powder-blended 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 powder-blended 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 sheet measuring 5 cm long, 5 cm wide, and 0.7 mm thick.

[0062] [Characteristics of resin composite] 1. Thermal conductivity Three samples measuring 1 cm long x 1 cm wide were cut from the resin molded sheet obtained by the above method, and their thermal diffusivities were measured using the flash method (NETZSCH LFA-467). The measured value was multiplied by the specific heat and density of the sheet to calculate the thermal conductivity, and the average value of the three samples was used. The thermal conductivity [W / (mK)] is shown in Table 2. Application example 6 has a high thermal conductivity because it does not have a glass coating, whereas application examples 1 to 3 have a glass coating but a small glass thickness, so the thermal conductivity is equally high. Application examples 4 and 5 have a slightly larger glass thickness, so the thermal conductivity is slightly lower, but they may be practical depending on the application. Similarly, Application Example 8 has a high thermal conductivity because it does not have a glass coating, whereas Application Example 7 has a glass coating but a small glass thickness, so its thermal conductivity is equally high.

[0063] 2. Water resistance test (95℃ water resistance time) and change in thermal conductivity after the water resistance test (1) 90 g of distilled water (Hayashi Pure Chemical Industries, Ltd., GR grade, pH 5.5 to 6.0) was weighed into a 100 mL polypropylene airtight container. (2) Three samples, each 1 cm long and 1 cm wide, cut out from the resin molded sheet were placed in (1). (3)(2) was placed in a 95°C thermostatic bath (PHP-2J, Espec Corporation), and the time until the pH of the water in the container reached 8 or higher was measured. This was measured for up to 1000 hours. The 95°C water resistance time [h] is shown in Table 2. (4) The thermal conductivity of the samples was measured when the pH was 8 or higher or after 1000 hours had passed, and the percentage change from the measured value before the water resistance test was calculated. The percentage change in thermal conductivity [%] is shown in Table 2. Application examples 6 and 8 do not have a glass coating, so the 95°C water resistance time is short and the rate of change (decrease) in thermal conductivity is large. In contrast, Application Examples 1 to 5 and 7 had glass coating, and therefore showed a significant improvement in both the 95°C water resistance time and the rate of change in thermal conductivity.

[0064] 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 glass-coated aluminum nitride powder is made of glass-coated aluminum nitride particles in which the particle surfaces of aluminum nitride particles are coated with glass, wherein the D50 of the aluminum nitride particles is 0.5 to 100 μm, the glass thickness is 2 to 100 nm, and the glass coverage of the particle surfaces is 95% or more.

2. 2. The glass-coated aluminum nitride powder according to claim 1, wherein the aluminum nitride particles have a D50 of less than 10 μm.

3. 2. The glass-coated aluminum nitride powder according to claim 1, wherein the glass thickness is less than 10 nm.

4. 2. The glass-coated aluminum nitride powder according to claim 1, wherein the glass coverage is 100%.

5. A polymer molded article made of a polymer material containing the glass-coated aluminum nitride powder according to any one of claims 1 to 4 as a filler.

6. 5. A polymer molded article made of a polymer material containing at least two kinds of the glass-coated aluminum nitride powder according to claim 1, each having a different D50, as a filler.

7. 6. The polymer molded article according to claim 5, wherein the polymer molded article is a heat dissipating member.

8. 7. The polymer molded article according to claim 6, wherein the polymer molded article is a heat dissipation member.

9. a glass precursor coating step of producing a glass precursor-coated aluminum nitride powder consisting of glass precursor-coated aluminum nitride particles whose particle surfaces are coated with a glass precursor by drying a mixed liquid containing aluminum nitride particles and a glass precursor in a mist form or in a state where the mixed liquid is spread on a surface; a heat treatment step of heating the glass precursor-coated aluminum nitride particles to a temperature equal to or higher than the melting point of the glass precursor to vitrify the glass precursor, thereby producing glass-coated aluminum nitride powder consisting of glass-coated aluminum nitride particles whose particle surfaces are coated with glass; A method for producing a glass-coated aluminum nitride powder, comprising:

10. 10. The method for producing a glass-coated aluminum nitride powder according to claim 9, wherein the glass precursor coating step is carried out by spray drying, in which the mixed solution is sprayed into the air.

11. 10. The method for producing glass-coated aluminum nitride powder according to claim 9, wherein the glass precursor coating step is carried out by spreading the mixed liquid on the surface of the receiving member in the form of a film or dispersion.

12. 10. The method for producing a glass-coated aluminum nitride powder according to claim 9, wherein a crushing step of crushing aggregated glass precursor-coated aluminum nitride particles is carried out between the glass precursor coating step and the heat treatment step.

13. The method for producing a glass-coated aluminum nitride powder according to any one of claims 9 to 12, wherein the heat treatment step is carried out by continuously charging the glass precursor-coated aluminum nitride particles in a state of being dispersed in a carrier gas into a tubular furnace.

14. The method for producing a glass-coated aluminum nitride powder according to any one of claims 9 to 12, wherein the heat treatment step is carried out by continuously supplying the glass precursor-coated aluminum nitride particles to a rotary kiln.

15. The method for producing a glass-coated aluminum nitride powder according to any one of claims 9 to 12, wherein the heat treatment step is carried out by placing the glass precursor-coated aluminum nitride particles in a sheath and passing the sheath through a roller hearth kiln.

16. A method for producing glass-coated aluminum nitride powder, comprising drying a mixed liquid containing aluminum nitride particles and a glass precursor in a mist form or while spread on a surface, and heating the mixed liquid to a temperature equal to or higher than the temperature at which the glass precursor melts, thereby producing glass-coated aluminum nitride powder consisting of glass-coated aluminum nitride particles whose particle surfaces are coated with glass obtained by vitrifying the glass precursor.

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