Glass-coated aluminum nitride powder, method for manufacturing same, and polymer molded body

Abstract

[Problem] To provide: a glass-coated aluminum nitride powder in which particle surfaces are almost completely covered with glass and which has high water resistance; and a polymer molded body which contains the powder as a filler and which has high water resistance. [Solution] This glass-coated aluminum nitride powder comprises glass-coated aluminum nitride particles in which particle surfaces of aluminum nitride particles are coated with glass. The D50 of the aluminum nitride particles is 0.5-100 μm. The thickness of the glass is 2-100 nm. The glass coverage of the particle surfaces is 95% or more. The glass-coated aluminum nitride particles are produced by: drying a liquid mixture containing the aluminum nitride particles and a glass precursor in a mist state or in a state of being spread on a surface to produce glass precursor-coated aluminum nitride particles; and heating the same to vitrify the glass precursor.

Description

Glass-coated aluminum nitride powder, its manufacturing method, and polymer molded product

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

[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 equal to or higher than the glass transition temperature of the glass frit and equal to or lower than 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) by adding an organosilicon compound by spraying or the like to aluminum nitride particles while stirring them and dry-mixing them to coat the surfaces of the aluminum nitride particles with the organosilicon compound, and then heating the coated aluminum nitride particles at a temperature of 300° C. or higher but lower than 1000° C. The aluminum nitride particles coated with a silicon-containing oxide have a carbon atom content of less than 1000 ppm by mass, a coverage of the silicon-containing oxide coating of 15% or higher but 100% or lower as determined by LEIS analysis, and the silicon atom content relative to the specific surface area is said to satisfy a specific relationship.

[0006] Patent No. 6739669 Patent No. 6606628 Patent No. 7419938

[0007] However, in the manufacturing methods of 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. Therefore, 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). Therefore, a considerable amount of energy must be input for subsequent crushing, 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, and the maximum coverage is 88% in Example 6. Furthermore, 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 is presumed 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.

[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 surfaces 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 where the glass thickness is less than 2 nm are considered to be substantially uncoated because they are insufficiently coated from the viewpoint of water resistance.

[0014] [5] A polymer molded article molded from 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 molded from a polymer material containing at least two kinds of glass-coated aluminum nitride powders according to any one of [1] to [4] above, each having a different D50, as a filler.

[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 method for producing a glass-coated aluminum nitride powder, comprising: 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 the form of a mist or in a state where the mixed liquid is spread on a surface; and 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 a glass-coated aluminum nitride powder consisting of glass-coated aluminum nitride particles whose particle surfaces are coated with glass.

[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 a 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-like 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, comprising drying a mixed liquid containing aluminum nitride particles and a glass precursor in the form of a mist or in a state where the mixed liquid is 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.

[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.

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

[0028] <1> Raw Aluminum Nitride Particles The raw 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. A high content significantly changes the composition of the glass when incorporated into the glass, thereby increasing the melting point of the glass and making it difficult to melt, or causing it to fall outside the vitrification range and fail to 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 wt. % or less. More preferably, it is 0.2 wt. % or less. Known methods for reducing the content include leaching treatment using inorganic or organic acids. An average particle size (median diameter) D50 of the raw aluminum nitride powder is 0.5 μm or more, making it less likely to aggregate and easier to use, while a D50 of 100 μm or less facilitates thinning of the polymer molded body. A D50 of less than 10 μm is preferable because it facilitates the glass precursor coating process by spray drying and the heat treatment process in a state 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. ２ , Al ２ O ３ and B ２ O ３ The glass may contain ZnO to reduce the thermal expansion coefficient. ２ O.K. ２ The glass may contain oxides of alkali metals such as O, but from the viewpoint of moisture resistance, the content is preferably small. The glass may contain optional components such as CaO, SrO, MgO, BaO, and SnO.

[0030] When the glass thickness is 2 nm or more, the glass coating is sufficient from the viewpoint of water resistance, and when it is 100 nm or less, the decrease in thermal conductivity due to the presence of glass can be suppressed.When 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] When the glass coverage is 95% or more, water resistance is improved, and when the glass coverage is 100%, water resistance is further improved.

[0032] <3> Glass Precursor Coating Step In the glass precursor coating step of the present invention, a mixed liquid containing aluminum nitride particles and a glass precursor is dried in a mist or in a spread state on a surface, so drying is rapid. It is essential for the coating of the glass precursor 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 and hold the molten 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 process is not particularly limited, but examples thereof include: (a) a spray-drying process in which the mixed solution 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 less likely to settle; (b) a process in which the mixed solution is spread in a film or dispersed form on the surface of a receiving member. This method is suitable when the raw aluminum nitride powder has a D50 of 10 μm or more, which makes it more likely to settle. The receiving member is not particularly limited, but examples thereof include a PET film, a glass plate, a ceramic plate, etc.

[0034] <4> Crushing Process (Optional) The glass precursor coating process in the present invention facilitates the dispersion of individual aluminum nitride particles. 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 a single droplet, resulting in agglomerated particles after drying. In this case, it is preferable to perform a crushing process before the heat treatment process as needed. As shown in Figure 3(b), it is expected that the mixed salt of glass component elements present at the bonded portions between particles will be largely transferred to one of the particles by the crushing process, potentially exposing the surface of the aluminum nitride particles. As shown in Figure 3(c), even if the coating layer in the glass precursor coating powder has an uneven surface, the coating layer is melted by heat treatment, spreading over the aluminum nitride particle surface and forming a homogeneous coating layer again. Although slight variations in coating thickness occur between particles, the average thickness is approximately the designed thickness.

[0035] <5> Heat Treatment Step The heat treatment step is not particularly limited, but the following can be exemplified: (a) A method in which glass precursor-coated aluminum nitride particles dispersed in a carrier gas are 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 to flow in the carrier gas. (b) A method in which glass precursor-coated aluminum nitride particles are continuously fed into a rotary kiln. This method is suitable when the raw aluminum nitride powder has a D50 of 10 μm or more, which makes it difficult to flow in the carrier gas. (c) A method in which 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, which makes it difficult to flow in the carrier gas. These methods enable rapid heating and cooling. In (b) and (c), unlike (a), the particles come into contact with each other, but because the particle size is large and the glass thickness is small, aggregation due to glass melting hardly occurs.

[0036] <6> Uses of Glass-Coated Aluminum Nitride Powder The uses of the glass-coated aluminum nitride powder are not particularly limited, but examples include fillers to be mixed into materials such as polymer materials, greases, adhesives, and paints.

[0037] <7> Polymer Molded Articles By filling a polymer material with the aluminum nitride powder of the present invention as a filler, a polymer molded article with high thermal conductivity can be produced and used. 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 article with even higher thermal conductivity. Examples of polymer materials include resins, rubbers, elastomers, and the like. Applications of the polymer molded article are not particularly limited, but examples include heat dissipation components for heat-generating devices such as semiconductors.

[0038] Next, examples embodying the present invention will be described with reference to the drawings, while being compared with comparative examples. Note that the materials, quantities, and conditions of each part in the examples are merely examples and can be changed as appropriate without departing from the spirit 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]

[0040] Comparative Example 1 Comparative Example 1 was 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 was 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 was 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 was 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) SiO as a Si source ２ , B as a source ２ O ３ , Al as an Al source ２ O ３ , lithium carbonate as a Li source, potassium carbonate as a K source, and an oxide (SiO ２ , B ２ O ３ , Al ２ O ３ , Li ２ O.K. ２ The components were blended to yield 71.7 mol%, 24.8 mol%, 0.7 mol%, 2.5 mol%, and 0.3 mol% AlN powder, respectively, calculated as AlN (O). The blend was melted in a glass melting furnace, cooled, and then dry-pulverized to produce glass frit with a primary particle diameter of 0.1 μm. (2) The glass frit of (1) was added to the "A-01-F." The amount added was adjusted depending on 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 10 mm diameter alumina balls were added and mixed in a dry ball mill. (4) (3) was filled into a 30 mm diameter mold and molded at a pressure of 10 MPa. (5) The molded body of (4) was heated in nitrogen at 1350°C for 30 minutes in a box furnace (Motoyama Corporation, 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 is an aluminum nitride powder obtained by using the starting raw material powder "A-04-F" after acid treatment to remove impurities other than aluminum nitride, and then coating the powder with glass in accordance with the method of Patent Document 1 as follows: (1) SiO as a Si source２ , B as a source ２ O ３ , Al as an Al source ２ O ３ , and were blended to 73.4 mol%, 25.4 mol%, and 1.2 mol%, respectively, and melted in a glass melting furnace. After cooling, the mixture was 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 raw material powder. The amount added was adjusted depending on the specific surface area of ​​the AlN powder and the target glass thickness. The target glass thickness in this example was 9 nm. Thereafter, an aluminum nitride powder consisting of glass-coated aluminum nitride particles was obtained in the same manner as in (3) to (6) of Comparative Example 5.

[0046] Example 1 In Example 1, the starting material "A-01-F" was coated with glass as follows: (1) Using tetraalkoxysilane modified to make it water-soluble 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, an oxide (SiO ２ , B ２ O ３ , Al ２ O ３ , Li ２ O.K. ２The components were blended to yield 71.7 mol%, 24.8 mol%, 0.7 mol%, 2.5 mol%, and 0.3 mol% (calculated as 0), 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 concentration was set to 10 vol%. After "A-01-F" was added to the dispersion medium, an ultrasonic dispersion treatment was performed. (3) (1) was added to (2) and stirred. The amount added was adjusted according to 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 (Buchi, B-290) as shown in Figure 1, and then heated and dried to powder, yielding glass precursor-coated aluminum nitride particles. The drying temperature was set to 220°C, and nitrogen was used as the drying gas. (5) The glass precursor-coated aluminum nitride particles of (4) were crushed using a dry jet mill (PJM-80, manufactured by Nippon Pneumatic Mfg. Co., Ltd.) as shown in Figure 3(b). The crushing pressure was 0.1 MPa. (6) The glass precursor-coated aluminum nitride particles of (5) were continuously supplied into a tubular furnace using nitrogen as a carrier gas as shown in Figure 2 to obtain glass-coated aluminum nitride particles. 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 to above the melting point of the composite oxide that forms the glass. The glass precursor remained molten in the furnace for approximately 5 to 20 seconds, and when the particles exited the furnace, the melt was rapidly cooled and vitrified to form glass-coated aluminum nitride particles.

[0047] Example 2 In Example 2, the starting raw material powder "A-04-F" was treated with acid to dissolve impurities other than aluminum nitride, and the resulting aluminum nitride powder was glass-coated as follows: (1) Using tetraalkoxysilane modified to make it water-soluble as the Si source, boric acid as the B source, and aluminum nitrate nonahydrate as the Al source, an oxide (SiO ２ , B ２ O ３ , Al ２ O３ The starting material powders were blended to 73.4 mol%, 25.4 mol%, and 1.2 mol%, respectively, calculated as % by weight of the starting material powder (the same composition as in Comparative Example 6), and dissolved in alcohol. (2) A slurry of the starting material powder was prepared using the same alcohol as in (1) as the dispersion medium. The solid content was 10 vol%. After the starting material powder was added to the dispersion medium, it was dispersed using ultrasonic waves. (3) (1) was added to (2) and stirred. The target thickness was 3 nm. (4) (3) was powdered using a spray dryer as shown in Figure 1 to obtain glass precursor-coated aluminum nitride particles. 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 1500°C.

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

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

[0050] Example 5 Example 5 is an aluminum nitride powder coated with glass in the same manner as Example 2, except that the target thickness was 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 obtain a powder with a D50 of 20.5 μm and a specific surface area of ​​0.11 m ２ / g powder, which was then subjected to a treatment using acid to dissolve impurities other than aluminum nitride, and the resulting powder was then glass-coated as follows: (1) A tetraalkoxysilane was modified to be water-soluble as a Si source, boric acid was used as a B source, aluminum nitrate nonahydrate was used as an Al source, sodium nitrate was used as a Na source, and potassium nitrate was used as a K source to produce an oxide (SiO ２ , B ２ O ３ , Al ２ O ３ , Na ２ O.K. ２ The aluminum nitride particles were blended to yield concentrations of 83.1 mol%, 11.5 mol%, 1.3 mol%, 3.8 mol%, and 0.3 mol%, calculated as 0.001% by weight of aluminum nitride powder, respectively, and dissolved in alcohol. (2) (1) was added to the starting raw material powder and prepared into a paste using a planetary mixer. The amount of (1) added was adjusted depending on 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 mixture 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, yielding 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 stream to obtain glass-coated aluminum nitride particles. The residence time in the furnace was set to 30 minutes, and the temperature profile in the furnace was adjusted so that the time during which the mixture was heated to the melting point or higher of the composite oxide that forms the glass was 10 minutes or less.

[0053] Example 8 is a glass-coated aluminum nitride powder similar to that of Example 7, except that the starting raw material powder used was the "S-30" obtained by dissolving impurities other than aluminum nitride using an acid.

[0054] Example 9 Example 9 is a glass-coated aluminum nitride powder similar to that of Example 7, except that the starting raw material powder used was the "S-80" obtained by dissolving impurities other than aluminum nitride using an acid.

[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 the powder was dispersed for 3 minutes at 80% output using a US-300E model manufactured by Nippon Seiki Seisakusho Co., Ltd. The volume-based particle size distribution was measured using a SALD-2200 laser diffraction particle size distribution analyzer manufactured by Shimadzu Corporation. The D50 [μm] is shown in Table 1.

[0056] 2. TEM observations were performed on 30 particles with a glass thickness D50 [μm] ±40%. For each particle, photographs were taken at eight locations, rotating the particle by 45°, at magnifications ranging from 500,000 to 2,000,000. 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. Observation samples were embedded in resin and thinned using focused ion beam (FIB) processing or other techniques, as necessary. Actual observations were performed using a JEOL Ltd. JEM-2100F field emission transmission electron microscope. The accelerating voltage was 200 kV. The boundary between the glass layer and the AlN particles was identified by the presence or absence of a crystal lattice image (since the glass layer was amorphous, no crystal lattice image was visible) or by the presence or absence of glass components (mainly Si in this case) detected by elemental analysis. FIG. 4 is a TEM photograph of Comparative Example 6, FIG. 5 is a TEM photograph of Example 1, FIG. 6 is a TEM photograph of Example 2, and FIG. 7 is a TEM photograph of Example 5. The white broken lines indicate the boundaries between the surfaces of the aluminum nitride particles and the glass.

[0057] 3. Glass Coverage Using the above-mentioned TEM photographs, regions where the glass thickness was less than 2 nm were considered to be substantially uncoated, since they were insufficiently coated from the viewpoint of water resistance, and the glass coverage was calculated. The glass coverage is shown in Table 1. In Comparative Examples 5 and 6, the glass coverage was low at 65% or less because peeling and destruction of the glass coating occurred due to crushing after heat treatment. In contrast, in Examples 1 to 9, the glass coverage was 95% or more.

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

[0059] [Preparation of Resin Molded Articles (Application Examples 1 to 8)] The resin molded articles of Application Examples 1 to 8 shown in Table 2 were prepared as follows.

[0060]

[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) To the resin composition of (1), at least two types of glass-coated aluminum nitride powders (Comparative Examples 1 to 4 are uncoated) with different D50 values ​​were blended in the proportions shown in Table 2. These powders were added as fillers to achieve a final volume of 75 vol% 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 diluent solvent. (5) Two sheets of the powder-blended resin composition of (4) were stacked with the surfaces not in contact with the PET substrate facing each other, and hot-pressed at 120°C x 10 MPa x 30 minutes to obtain a resin molded product sheet measuring 5 cm long x 5 cm wide x 0.7 mm thick.

[0062] [Resin Composite Properties] 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 the thermal diffusivity was measured using the flash method (using a 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 due to the absence of a glass coating, while Application Examples 1 to 3 have similarly high thermal conductivities due to the small glass thickness despite the glass coating. Application Examples 4 and 5 have slightly lower thermal conductivities due to the slightly larger glass thickness, but are still practical for some applications. Similarly, Application Example 8 has a high thermal conductivity due to the absence of a glass coating, while Application Example 7 has similarly high thermal conductivities due to the small glass thickness despite the glass coating.

[0063] 2. Water Resistance Test (95°C Water Resistance Time) and Change in Thermal Conductivity After Water Resistance Test (1) 90 g of distilled water (Hayashi Pure Chemical Industries, Ltd., GR grade, pH 5.5-6.0) was weighed into a 100 mL polypropylene sealed container. (2) Three 1 cm x 1 cm samples cut from the resin molded sheet were placed into (1). (3) (2) was placed in a 95°C thermostatic bath (Espec Corporation, PHP-2J), and the time until the pH of the water in the container reached 8 or higher was measured. This test was continued for up to 1,000 hours. The 95°C water resistance time [h] is shown in Table 2. (4) The thermal conductivity of the samples whose pH reached 8 or higher or after 1,000 hours had elapsed was measured, and the rate of change from the measured value before the water resistance test was calculated. The rate of change in thermal conductivity [%] is shown in Table 2. Because Application Examples 6 and 8 did not have a glass coating, the 95°C water resistance time was short and the rate of change (decrease) in thermal conductivity was large. In contrast, in Application Examples 1 to 5 and 7, because of the presence of glass coating, both the 95°C water resistance time and the rate of change in thermal conductivity were significantly improved.

[0064] The present invention is not limited to the above-described embodiments, and can be embodied by making appropriate modifications without departing from the spirit of the invention.

Claims

1. 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.

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

4. 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. A polymer molding formed from a polymer material containing at least two types of glass-coated aluminum nitride powder according to any one of claims 1 to 4, each having a different D50, as a filler.

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

8. The polymer molded article according to claim 6, wherein said polymer molded article is a heat dissipating member.

9. A method for producing glass-coated aluminum nitride powder, comprising: a glass precursor coating step of producing 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 the form of a mist or in a state where the mixed liquid is spread over a surface; and 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.

10. The method for producing 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. 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 in a film or dispersed form on the surface of the receiving member.

12. 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. A method for producing 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 dispersed in a carrier gas into a tubular furnace.

14. A method for producing 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. A method for producing 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, in which a mixed liquid containing aluminum nitride particles and a glass precursor is dried in a mist or spread over a surface, and heated to a temperature above the melting point of the glass precursor, thereby producing glass-coated aluminum nitride powder consisting of glass-coated aluminum nitride particles whose particle surfaces are coated with glass formed by vitrifying the glass precursor.

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