Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B21/00—Nitrogen; Compounds thereof
  • C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
  • C01B21/072—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with aluminium
  • C01B21/0726—Preparation by carboreductive nitridation
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B21/00—Nitrogen; Compounds thereof
  • C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
  • C01B21/072—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with aluminium
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
  • C09K5/08—Materials not undergoing a change of physical state when used
  • C09K5/14—Solid materials, e.g. powdery or granular
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/12—Surface area

Definitions

• the present invention relates to a new aluminum nitride powder. More specifically, it provides submicron-sized aluminum nitride powder suitable for filler applications.
• heat-dissipating materials such as heat-dissipating sheets and heat-dissipating grease are generally used between the heat-generating part and the cooling member.
• these heat-dissipating materials are required to have high thermal conductivity.
• the filler When filling the above fillers, if the filler has a single particle size, it will thicken and will not be possible to fill it at a high density, so it is common to design the mixture to contain multiple fillers with different particle sizes between submicrons and several hundred microns, with the small particles filling the gaps between the larger particles.
• the role of fine fillers with particle sizes in the submicron range is extremely important for filling the fine gaps between the fillers and increasing the thermal conductivity of the heat dissipation material.
• aluminum nitride which is a material with particularly excellent thermal conductivity among the above fillers, the development of aluminum nitride powder with a particle size in the submicron range is particularly important.
• Patent Document 1 discloses a method in which organic aluminum is heated in an ammonia gas and nitrogen atmosphere.
• Patent Document 2 discloses an aluminum nitride powder produced by wet pulverizing aluminum nitride coarse powder of about several ⁇ m.
• Patent Document 3 discloses an aluminum nitride powder having a submicron-sized particle size and not containing coarse particles.
• Patent Document 1 Although the method described in Patent Document 1 produces fine aluminum nitride powder, this powder has an aggregated structure, and therefore has the problem that when mixed as a filler with a resin, the resin thickens and it is difficult to achieve high loading.
• the primary particle size of the particles is 0.06 ⁇ m or less, the surfaces of the aluminum nitride particles may be oxidized and hydrolyzed in air, which may reduce the thermal conductivity of the particles.
• Patent Document 2 aluminum nitride having a particle size of about 1 ⁇ m can be produced as a raw material coarse powder, and it is believed that further pulverization can produce aluminum nitride powder of submicron size.
• the powder whose particle size has been adjusted by the above-mentioned pulverization has an indefinite particle shape, and moreover, the pulverization also produces a large amount of fine powder of 0.2 ⁇ m or less, so there is a concern that if it is kneaded into a resin as a filler, the viscosity will increase, making it difficult to achieve high loading.
• the aluminum nitride powder described in Patent Document 3 is obtained by simply classifying and removing coarse aggregated particles, and particles having an aggregated structure remain.
• the object of the present invention is therefore to provide an aluminum nitride powder suitable for use as a filler, which is submicron in size, contains almost no agglomerated particles or fine powder that would prevent the powder from being filled into a resin material, and has a rounded particle shape.
• Means for solving the above problems include the following aspects.
• An aluminum nitride powder having a cumulative volume 50% particle size (D50) of 0.3 to 1.0 ⁇ m in a particle size distribution measured with a laser diffraction/scattering type particle size distribution analyzer, a ratio of particles having a size of 0.20 ⁇ m or less being 10% or less in terms of volume frequency, a ratio of an average primary particle size (Dp: ⁇ m) of 500 particles observed at a magnification of 20,000 times with a scanning electron microscope to the D50, D50/Dp, being 1.0 to 1.4, and an average circularity of 0.7 or more.
• D50 cumulative volume 50% particle size
• Dp average primary particle size
• ⁇ 2> The aluminum nitride powder according to ⁇ 1>, having an oxygen content of 3.0% or less.
• the aluminum nitride powder of the present invention has a fine particle size in the submicron range, but there is almost no aggregation between particles, and it is possible to provide aluminum nitride powder with a rounded particle shape.
• a filler with a larger particle size and kneaded with resin it is less likely to thicken and can be highly filled, making it possible to impart high thermal conductivity to the resin material filled with it.
• a range of values expressed using "to” means a range that includes the values before and after "to” as the lower and upper limits.
• the term "to” indicating a range of numerical values means that the units written before or after it indicate the same units, unless otherwise specified.
• a combination of two or more preferred aspects is a more preferred aspect.
• the aluminum nitride powder of the present invention has a cumulative volume 50% particle size (D50) of 0.3 to 1.0 ⁇ m in the particle size distribution measured with a laser diffraction scattering type particle size distribution analyzer. Since the aluminum nitride powder has the above-mentioned submicron-sized particle size, when used in combination with particles of a larger particle size, it is possible to highly fill the resin with the aluminum nitride powder, due to the small amount of fine powder, the absence of aggregation, and the high circularity (average circularity of 0.7 or more, as described below). The measurement with a laser diffraction scattering type particle size distribution analyzer will be specifically shown in the Examples.
• the aluminum nitride powder of the present invention has a volumetric frequency of 10% or less, preferably 5% or less, and more preferably 3% or less, of particles with a size of 0.20 ⁇ m or less. If the volumetric frequency of particles with a size of 0.20 ⁇ m or less is more than 10%, the viscosity of the resin increases drastically when filled with the aluminum nitride powder, and kneadability decreases, making high filling difficult. There is no particular lower limit for the ratio of particles with a size of 0.20 ⁇ m or less, but it is preferable that the ratio be 0% or more.
• the volume frequency of the proportion of particles of 0.20 ⁇ m or less can be determined by calculating the proportion of particles of 0.20 ⁇ m or less from the particle size distribution curve obtained by measurement with the laser diffraction scattering type particle size distribution meter.
• the aluminum nitride powder of the present invention has a ratio of the average primary particle diameter (Dp: ⁇ m) of 500 particles observed at 20,000 times magnification with a scanning electron microscope to D50, D50/Dp, of 1.0 to 1.4, preferably 1.0 to 1.3, and more preferably 1.0 to 1.2.
• the D50/Dp indicates the ratio of D50 measured with a laser diffraction scattering type particle size distribution meter to the average primary particle diameter, and is an index indicating the proportion of agglomerated particles in the aluminum nitride powder. The closer this value is to 1, the fewer the agglomerated particles are.
• the aluminum nitride powder of the present invention has such a value of 1.0 to 1.4, it has very few agglomerated particles and is composed of a high proportion of single particles having the average primary particle diameter. Therefore, the increase in viscosity caused by the agglomerated particles when the aluminum nitride powder is filled into a resin is very small, and the aluminum nitride powder of the present invention can contribute to high filling into the resin.
• the aluminum nitride powder of the present invention has an average circularity of 0.7 or more, preferably 0.8 or more. That is, the particles constituting the aluminum nitride powder of the present invention are nearly spherical in shape and can exhibit high fluidity, so that when the aluminum nitride powder is filled into a resin together with other particles having a larger particle size, the particles can easily move through the gaps between the other particles and the resin, thereby improving the fillability of the aluminum nitride powder into the resin.
• aluminum nitride powders whose particle size has been adjusted by crushing in the prior art are irregular particles, and their average circularity is less than 0.6.
• the circularity which will be described in detail in the Examples below, was calculated from the projected particle area and perimeter by observing the aluminum nitride powder using a scanning electron microscope (SEM), and the circularity at 50% of the cumulative distribution on a volume frequency basis was taken as the average circularity.
• the cumulative distribution on a volume frequency basis was calculated by approximating the volume of the primary particles to a sphere whose diameter is the longest diameter of the primary particles. There is no particular upper limit to the average circularity, but it is preferably 1 or less.
• the specific surface area (S: m2 /g) is in the range of 3.5/(D50) or less with respect to D50 ( ⁇ m). Since the range of the above-mentioned optimum specific surface area varies depending on the particle size, the range is corrected by (D50: ⁇ m).
• the range of the specific surface area calculated from the formula using the (D50) indicates the presence of fine particles and the complexity of the particles. In addition, it is assumed that particles within the range are unlikely to be composed of aggregates of fine particles, are likely to be rounded, have few particles with complex shapes, and are suppressed from producing fine powder due to crushing, etc.
• the specific surface area may be 2.0/(D50) or more, particularly 2.2/(D50) or more.
• the oxygen content is preferably 3.0 mass% or less, and more preferably 2.5 mass% or less.
• oxygen content is less likely to dissolve in the aluminum nitride crystals, a thick oxide film is less likely to form on the particle surface, and the thermal conductivity of the particles tends to improve.
• the aluminum nitride powder of the present invention having the above-mentioned properties, enables filling of resin at a high filling rate when used in combination with other fillers having larger particle sizes.
• the aluminum nitride powder of the present invention is useful in combination with a large-particle-size filler having a particle size of, for example, 2 to 20 ⁇ m.
• a powder having a particle size even larger than the large-particle-size filler can be appropriately determined and used.
• any known resin may be used without any particular limitation.
• the method for producing the aluminum nitride powder of the present invention is not particularly limited, but representative production methods include a reduction-nitridation step of heating a raw material mixture containing alumina powder and carbon powder under a nitrogen atmosphere to reduce and nitride alumina to obtain aluminum nitride powder, a crushing step of crushing the aluminum nitride powder containing carbon powder obtained in the reduction-nitridation step, a re-firing step of heating the carbon-containing aluminum nitride powder obtained in the crushing step at a temperature of 1400 to 1800°C for 1 to 10 hours in the presence of nitrogen, and a decarburization step of decomposing and removing carbon from the powder obtained in the heat treatment step.
• examples of the raw material alumina include alumina having a crystal structure such as ⁇ , ⁇ , ⁇ , ⁇ , ⁇ , and ⁇ .
• Alumina may be used alone or in a mixture of different types.
• ⁇ -alumina and ⁇ -alumina are preferably used because they are particularly highly reactive and easy to control the reaction.
• the average particle size of the alumina can be appropriately set according to the particle size of the aluminum nitride powder to be obtained, and is preferably 0.2 to 1.0 ⁇ m, and more preferably 0.3 to 0.9 ⁇ m.
• alumina having an average particle size of 0.2 ⁇ m or more is used, aluminum nitride powder having a particle size of the desired submicron size is easily obtained, and since the alumina particles are strongly fused together during the heating process and are difficult to be reduced and nitrided, the increase of agglomerated particles that are not disintegrated by the disintegration described below is suppressed.
• alumina having an average particle size of 1.0 ⁇ m or less aluminum nitride powder having a desired submicron size is more easily obtained.
• the alumina used has an average circularity of preferably 0.6 or more, more preferably 0.8 or more. If fibrous alumina with low circularity or alumina in an aggregated form with large irregularities is used as the raw material, the shape of the alumina is maintained even after the reduction-nitridation reaction, and the circularity of the aluminum nitride powder decreases.
• the raw carbon powder may be any known one without any particular restrictions.
• Carbon black, graphite, and carbon precursors that can be carbon sources at high temperatures in a reaction gas atmosphere may be used without any restrictions.
• carbon black is suitable as the carbon powder from the viewpoint of the amount of carbon per weight and the stability of physical properties.
• the particle diameter of these carbon blacks is arbitrary, but is preferably 5 to 250 nm, more preferably 10 to 100 nm. When the particle diameter of the carbon black is 5 nm or more, the powder is less likely to become bulky, improving productivity.
• the carbon particles can be uniformly attached to the surface of the alumina particles, so that the generation of agglomerated particles is suppressed.
• a liquid carbon source such as liquid paraffin may be used in combination to prevent the raw material from scattering.
• the method for mixing the alumina powder and the carbon powder may be any method that disperses the alumina particles and uniformly adheres the carbon powder to the particle surfaces, but the preferred mixing means is usually a blender, a mixer, or a ball mill.
• the alumina powder and the carbon powder may be mixed in a dry state or in a wet state using an organic solvent or the like.
• the carbon powder is preferably blended in an amount of 45 parts by mass or more, more preferably 60 parts by mass or more, and even more preferably 70 parts by mass or more, converted into carbon, per 100 parts by mass of the alumina powder.
• amount of carbon is 45 parts by mass or more converted into carbon, unreacted alumina is less likely to remain, and separation between the alumina and aluminum nitride particles is sufficient, suppressing the occurrence of aggregation during firing.
• the upper limit of the carbon amount is preferably 1000 parts by mass, more preferably 700 parts by mass, and even more preferably 500 parts by mass.
• the aluminum nitride powder of the present invention can be produced by a known reduction-nitridation method in which a mixture of alumina powder and carbon powder is heated under nitrogen flow to promote the reduction-nitridation reaction.
• the heating temperature is not particularly limited, but is preferably 1400 to 1800°C, and more preferably 1500°C to 1750°C. If the temperature is 1400°C or higher, the nitridation reaction proceeds sufficiently, so that unreacted alumina can be reduced. If the firing temperature is 1800°C or lower, sintering between particles is difficult to occur, so that the generation of agglomerated powder is suppressed.
• the time for the reduction-nitridation is not particularly limited, but is preferably 1 to 10 hours, and more preferably 3 to 8 hours.
• the flow rate of nitrogen gas is not particularly limited as long as the alumina is sufficiently reduced and nitrided, and may be appropriately determined taking into consideration the type of alumina used, the capacity of the reaction device, the structure of the device, and the like.
• the powder after the reduction nitridation step is preferably crushed under conditions that crush the aggregated aluminum nitride particles into single particles and do not cause crushing of primary particles. Such conditions can be determined by carrying out experiments in advance depending on the crusher to be used, and the optimum conditions can be determined.
• any known device can be used without any particular restrictions, and representative examples include a ball mill, a jet mill, a bead mill, etc.
• the crushing step the aggregated particles obtained after reduction nitridation are crushed, and the portions bonded by aggregation may exist as crushed surfaces (flat surfaces). In such cases, it is preferable to perform a process to make the crushed surfaces round in order to further improve the circularity of the particles.
• the crushed powder is heated at a temperature of 1400 to 1800°C under a nitrogen flow, which makes it possible to round the crushed surfaces of the particles that may occur in the crushing step. Furthermore, the oxide film formed on the particle surface during crushing can be removed by a reduction-nitridation reaction.
• the time for the re-firing is preferably 1 to 10 hours, more preferably 3 to 5 hours.
• the re-firing is preferably carried out in the presence of carbon. Therefore, if the mixed state of aluminum nitride and carbon after crushing is not uniform, it is preferable to re-mix them using the same device as used in the mixing step before the re-firing step. In addition, additional carbon powder may be added to make up for the carbon powder lost in the reduction-nitridation step.
• the powder after the re-firing process contains excess carbon, it is heated in an oxidizing gas to decarburize it.
• the oxidizing gas any gas that can oxidize and remove carbon, such as air or oxygen, can be used without any restrictions, but air is preferred in consideration of economic efficiency and the oxygen content of the resulting aluminum nitride.
• the heating temperature is generally preferably 500 to 900°C, more preferably 600 to 750°C. If the heating temperature is 900°C or less, the surface of the aluminum nitride powder is not excessively oxidized, improving the thermal conductivity of the particles, making it difficult for sintering to occur between particles, and suppressing the generation of agglomerated powder. If the heating temperature is 500°C or more, carbon can be sufficiently removed.
• the powder after the decarbonization step contains coarse particles, they may be removed by classification.
• the classification method is not particularly limited, and examples thereof include air classification using inertial force or centrifugal force, and wet filter classification in which coarse particles are removed by passing the powder through a filter.
• Particle size “D50” A 100 mL glass beaker was charged with 0.01 g of aluminum nitride powder and 100 mL of ion-exchanged water, and the beaker was dispersed by irradiating ultrasonic waves at 200 W for 3 minutes with the probe immersed at a depth of 4 cm. The dispersion was analyzed by laser diffraction. The measurement was performed using a scattering type particle size distribution meter (Microtrac Bell: particle size distribution measuring device MT3300EXII). In the particle size distribution, the volume frequency was accumulated from the smallest particle size, and the particle size at which the cumulative value reached 50% was determined. The value was set to D50.
• Dp volume average primary particle diameter
• Proportion of particles smaller than 0.20 ⁇ m As in the case of D50, the dispersion in which the aluminum nitride powder was dispersed was measured using a laser diffraction scattering type particle size distribution analyzer, and the volume frequency of particles detected in the range of 0.02 to 0.20 ⁇ m was added up to determine the proportion of particles having a size of 0.20 ⁇ m or less. The ratio of particles having a size of 0.20 ⁇ m or less was judged as ⁇ when it was more than 10%, as ⁇ when it was more than 5% but not more than 10%, and as ⁇ when it was 5% or less.
• the BET specific surface area of the aluminum nitride powder was measured by the BET method (single-point nitrogen adsorption method) using a specific surface area measuring device (Shimadzu Corporation: Flowsorb 2-2300). 2 g of aluminum nitride powder was used for the measurement, which had been previously dried at 100° C. for 1 hour in a nitrogen gas flow.
• the oxygen concentration was determined by burning aluminum nitride powder in an oxygen stream using an "EMGA-620W” manufactured by Horiba, Ltd., and measuring the amount of CO gas generated.
• Viscosity In order to evaluate the properties of the aluminum nitride powder as a filler, the viscosity of a resin composition obtained by kneading it with a thermosetting silicone resin (TSE3070(A) manufactured by Momentive Performance Materials Japan, LLC) was measured. A powder with good filling properties is expected to have the effect of reducing the viscosity.
• the paste for measurement was prepared by kneading the resin and filler with an automatic kneading machine for 3 minutes and scraping it off three times.
• a rheometer (Discovery HR-2 manufactured by TA Instrument Co., Ltd.) was used to measure the viscosity.
• a 40 mm flat plate was used, and measurements were performed under conditions of a gap of 1000 ⁇ m and a temperature of 25° C., and the viscosity at a shear rate of 1.0 s ⁇ 1 was compared.
• Example 1 100 parts by mass of ⁇ -alumina having an average particle size of 0.4 ⁇ m and 100 parts by mass of carbon black having an average particle size of 20 nm were mixed using a rotary ball mill. The resulting mixed powder was placed in a graphite container and fired at a firing temperature of 1650° C. for 7 hours while flowing nitrogen gas at 1 L/min. The fired powder was treated with an opposed jet mill to break down the aluminum nitride agglomerated particles contained in a portion of the powder. The broken powder was placed in a graphite container again and fired again at a firing temperature of 1650° C. for 4 hours while flowing nitrogen gas at 1 L/min.
• the powder was fired in an air atmosphere at a firing temperature of 700° C. for 8 hours to obtain an aluminum nitride powder.
• the particle size, specific surface area, oxygen concentration, average circularity, and viscosity of the obtained powder were measured by the above-mentioned methods, and the results are shown in Table 1.
• the viscosity was reduced compared to a resin composition (paste) prepared without blending the aluminum nitride of the present invention, and improvement in filling property was confirmed.
• Example 2 Except for changing the average particle size of the raw alumina to 0.65 ⁇ m, an aluminum nitride powder was obtained in the same manner as in Example 1. The particle size, specific surface area, oxygen concentration, average circularity and viscosity of the obtained powder were measured, and the results are shown in Table 1.
• Example 3 An aluminum nitride powder was obtained in the same manner as in Example 1, except that the firing temperature in the reduction-nitridation step was 1550° C. and the firing time was 10 hours. The particle size, specific surface area, oxygen concentration, average circularity and viscosity of the obtained powder were measured, and the results are shown in Table 1.
• Example 4 An aluminum nitride powder was obtained in the same manner as in Example 1, except that the firing temperature in the reduction-nitridation step was 1750° C. and the firing time was 5 hours. The particle size, specific surface area, oxygen concentration, average circularity and viscosity of the obtained powder were measured, and the results are shown in Table 1.
• Comparative Example 1 An aluminum nitride powder was obtained in the same manner as in Example 1, except that the firing temperature in the reduction-nitridation step was 1,850° C. and the firing time was 5 hours. The particle size, specific surface area, oxygen concentration, average circularity and viscosity of the obtained powder were measured, and the results are shown in Table 1.
• Comparative Example 2 An aluminum nitride powder was obtained in the same manner as in Example 1, except that the amount of carbon powder added in the mixing step was 40 parts by mass per 100 parts by mass of alumina powder. The particle size, specific surface area, oxygen concentration, average circularity and viscosity of the obtained powder were measured, and the results are shown in Table 1.
• Comparative Example 3 100 parts by mass of aluminum powder having an average particle size of 20 ⁇ m and 200 parts by mass of aluminum nitride powder having an average particle size of 1.0 ⁇ m were mixed using a rotary ball mill. The resulting mixed powder was placed in a graphite container and set in a reaction vessel. After the reaction vessel was degassed to a predetermined pressure, nitrogen was introduced to the reaction vessel to a pressure of 40 atmospheres, and the powder was ignited by applying electricity to cause a direct nitriding reaction. The resulting lump-shaped aluminum nitride was pulverized for 30 minutes at 350 rpm using a planetary ball mill using an alumina pot and alumina balls to obtain aluminum nitride powder. The particle size, specific surface area, oxygen concentration, average circularity, and viscosity of the resulting powder were measured and the results are shown in Table 1.

Landscapes

• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Combustion & Propulsion (AREA)
• Thermal Sciences (AREA)
• Materials Engineering (AREA)
• Ceramic Products (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=92971801

Family Applications (1)

Country Status (6)

Citations (7)

• 2024
  • 2024-03-29 JP JP2025512535A patent/JPWO2024210054A1/ja active Pending
  • 2024-03-29 KR KR1020257031439A patent/KR20250170589A/ko active Pending
  • 2024-03-29 WO PCT/JP2024/013056 patent/WO2024210054A1/ja not_active Ceased
  • 2024-03-29 EP EP24784840.1A patent/EP4691974A1/en active Pending
  • 2024-03-29 CN CN202480021452.XA patent/CN120936569A/zh active Pending
  • 2024-04-02 TW TW113112567A patent/TW202506543A/zh unknown

Patent Citations (7)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events