JP2012121793A - Alumina mixed powder and alumina mixed powder-containing resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alumina mixed powder which can be filled in a resin with extremely excellent filling property.SOLUTION: The mixed powder includes alumina powder (I) having an average secondary particle size of 15 μm or more and 50 μm or less; and alumina powder (II) having an average secondary particle size of 2 μm or less. In a pore distribution curve with pore diameter as the horizontal axis and Log differential pore capacity as the vertical axis which is measured by mercury porosimetry, the cumulative pore capacity in a pore radius of 0.002 μm or more and 100 μm or less is 0.10 ml/g or more and 0.23 ml/g or less.

Description

  The present invention relates to an alumina mixed powder having a specific pore structure and a resin composition containing the alumina mixed powder.

  In recent years, the amount of generated heat has been increasing as electronic devices have become smaller and more sophisticated. Therefore, the request | requirement of the thermal radiation characteristic is increasing also with respect to the epoxy resin composition used for a sealing material, a laminated board, etc., and the silicone resin composition used for a thermal radiation sheet. In order to improve the thermal conductivity of the resin composition, it is common to fill with an inorganic filler such as aluminum nitride, boron nitride, alumina, or crystalline silica. Among these, alumina, which is excellent in balance between thermal conductivity, chemical stability, and cost, is most often used as a heat radiation filler.

  However, when the filling amount of the alumina powder blended in the resin is increased, the viscosity of the resin composition increases to cause a problem that moldability is deteriorated and productivity is lowered. Furthermore, since alumina has a high Mohs hardness, there is a problem that the apparatus is easily worn by contact with the metal part of the mold in a state of high viscosity. In order to solve these problems, it is necessary to reduce the viscosity of the resin composition filled with alumina powder, and there are several types of methods using alumina that is close to a spherical shape, not an irregular shape with no crushing shape or cutting edge. A method of combining alumina particles having an average particle diameter with a resin has been proposed.

  In particular, the viscosity of the resin composition is reduced by finding an optimum mixing ratio by combining particles having various average particle diameters. Especially, the viscosity reduction of the resin composition is seen by mixing the fine particle whose average particle diameter is 2 micrometers or less, and the coarse particle of 10 micrometers or more.

  For example, Japanese Patent Application Laid-Open No. 2003-137627 discloses a spherical inorganic powder having a roundness of 0.80 or more as a constituent particle having a particle size range of 3 to 40 μm and a configuration having a particle size range of 0.1 to 1.5 μm. A highly thermally conductive inorganic powder is disclosed in which a spherical or non-spherical inorganic powder having a roundness of 0.30 or more and less than 0.80 is mixed. In the examples, an alumina mixed powder of a non-spherical aluminum oxide powder having an average particle diameter of 0.5 μm or 0.3 μm and a spherical aluminum oxide powder having an average particle diameter of 15 μm or 8 μm is disclosed.

  However, not only alumina but generally inorganic powder has a particle size distribution. Further, even when particles having the same particle diameter are compared, there are cases where the particles are single particles, and some particles are aggregated to form secondary particles. However, the particle diameter measured by a particle diameter measuring method such as a laser diffraction scattering method cannot determine these differences. For this reason, it is difficult to obtain a mixed powder with the best resin filling property by simply mixing the average particle diameter and shape in the optimum region.

JP 2003-137627 A

  The present invention has been made in view of the above, and an object of the present invention is to provide an alumina mixed powder that is extremely excellent in filling properties when filled into a resin, and a resin composition filled with the resin. .

The present invention provides the following [1] to [11].
[1] A mixed powder containing alumina powder (I) having an average secondary particle diameter of 15 μm or more and 50 μm or less and alumina powder (II) having an average secondary particle diameter of 2 μm or less, the horizontal axis being the pore radius, In the pore distribution curve measured by the mercury intrusion method with the vertical axis representing Log differential pore volume, the cumulative pore volume in the region having a pore radius of 0.002 μm to 100 μm is 0.10 ml / g to 0.23 ml / g. An alumina mixed powder characterized by:
[2] The alumina mixed powder according to the above [1], wherein the cumulative pore volume in the region of pore radius of 0.002 μm or more and 0.1 μm or less is 0.015 ml / g or less.
[3] The alumina mixture as described in [1] or [2] above, wherein the Log differential pore volume distribution in a region having a pore radius of 0.1 μm or more and 10 μm or less has a single maximum peak. Powder.
[4] Alumina powder (I) has a pore radius of 0. 0 in a pore distribution curve in which the horizontal axis is the pore radius (μm) of the alumina powder and the vertical axis is Log differential pore volume (ml / g). The cumulative pore volume in the region of 002 μm to 100 μm is 0.1 ml / g to 0.3 ml / g, and the Log differential pore volume is a single maximum in the region of the pore radius of 2 μm to 10 μm. Pore distribution curve with spherical alumina powder having a peak, 60 wt% or more and 95 wt% or less, the horizontal axis is the pore radius (μm) of the alumina powder, and the vertical axis is Log differential pore volume (ml / g) In the region having a pore radius of 0.002 μm or more and 100 μm or less, the cumulative pore volume is 0.2 ml / g or more and 0.4 ml / g or less, and the region having a pore radius of 1 μm or more and less than 2 μm is Log differential fine. Single pore volume Spherical alumina powder having a large peak, characterized in that it is a mixed powder containing a 40 wt% 5 wt% or more or less, the [1] Alumina powder mixture according to [3].
[5] The above-mentioned [1], wherein the cumulative pore volume of the alumina powder (II) in the region having a pore radius of 0.002 μm to 100 μm is 0.2 ml / g to 0.5 ml / g. ] The alumina mixed powder in any one of [4].
[6] The alumina mixed powder according to any one of [1] to [5], wherein the α phase content of the alumina powder (II) is 95% or more.
[7] The alumina mixed powder according to any one of [1] to [6], wherein the alumina powder (I) is an alumina powder produced by a flame melting method.
[8] A resin composition comprising the alumina mixed powder according to any one of [1] to [7].
[9] The resin composition according to [8], wherein the resin is a silicone resin.
[10] The resin composition according to [8], wherein the resin is an epoxy resin.
[11] A molded resin containing the resin composition according to any one of [8] to [10], wherein a molding pressure is 6 MPa or less.

  According to the present invention, it is possible to provide an alumina mixed powder that is extremely excellent in filling properties when filled into a resin.

  Hereinafter, the present invention will be described in detail.

  The alumina mixed powder of the present invention comprises alumina powder (I) having an average secondary particle diameter of 15 μm or more and 50 μm or less measured by a laser diffraction scattering method, and alumina powder (II) having an average secondary particle diameter of 2 μm or less. In the pore distribution curve measured by the mercury intrusion method, the horizontal axis is the pore radius (μm) and the vertical axis is the Log differential pore volume (ml / g). The cumulative pore volume in the region of 002 μm or more and 100 μm or less is 0.10 ml / g or more and 0.23 ml / g or less. The alumina mixed powder of the present invention includes an alumina powder having a relatively large particle size compared to a conventional alumina mixed powder in which alumina particles having several types of particle sizes are combined by reducing the cumulative pore volume. In this case, the filling property can be improved.

The pore structure of the alumina (mixed) powder in the present invention is determined by measurement by a mercury intrusion method. Mercury intrusion is based on the physical principle that it does not penetrate the pores until a sufficient pressure is applied to force the non-wetting liquid to penetrate. That is, the higher the pressure required for the liquid to permeate, the smaller the pore radius. Note that mercury is used as the liquid in this measurement. Mercury is a liquid at room temperature, does not react with alumina powder, and does not have wettability.
The measurement range of the pore radius is 0.002 μm or more and 100 μm or less. The pore radius measured by this method is calculated from the following equation.
P × R = −2 × σ × cos θ
[Wherein P is pressure, σ is the surface tension of mercury, R is the pore radius, and θ is the contact angle between mercury and the sample. ]
In this measurement, σ is set to 480 dynes / cm, and θ is set to 140 °.
In addition, the cumulative pore volume is determined from the volume of mercury that is reduced as mercury penetrates into the pores.

  The alumina mixed powder of the present invention has pores in the pore distribution curve (horizontal axis: pore radius (μm) of alumina mixed powder, vertical axis: Log differential pore volume (ml / g)) measured by the above method. In the region having a radius of 0.002 μm or more and 100 μm or less, it has a cumulative pore volume of 0.10 ml / g or more and 0.23 ml / g or less, preferably 0.15 ml / g or more and 0.23 ml / g or less. When the cumulative pore volume is smaller than 0.10 ml / g, the particles are very densely packed, do not exhibit properties as a powder, and lose the function as a resin filler. On the other hand, when it is greater than 0.23 ml / g, the gap between the powders increases, and the apparent amount of resin in the resin composition decreases when the resin penetrates into the gap during mixing with the resin. As a result, the viscosity of the resin composition increases rapidly.

  Furthermore, the alumina mixed powder of the present invention has a pore distribution curve (horizontal axis: pore radius (μm) of alumina mixed powder, vertical axis: Log differential pore volume (ml / g)) measured by the above method. In a region having a pore radius of 0.002 μm or more and 0.1 μm or less, it has a cumulative pore volume of 0.015 ml / g or less, more preferably 0.010 ml / g or less. Regions with a pore radius of 0.1 μm or less measured by the mercury intrusion method are regions where mercury cannot penetrate unless pressure of about 7 MPa or more is applied. Resins such as silicone resins, epoxy resins, and polyolefin resins In general, since the surface tension is several tens of dynes / cm, even if the resin is compatible with the alumina powder, it is difficult to penetrate when mixed with the resin unless a high pressure is applied. is there. For this reason, the pores generated in this region exist as voids when the resin and the alumina mixed powder are mixed, and the particles having the voids are present as agglomerated particles, which deteriorates the filling property. Furthermore, even though the alumina mixed powder is filled in the resin composition for the purpose of improving the thermal conductivity, there are voids where the resin cannot enter. There is a risk of hindering improvement in conductivity. The lower limit value of the cumulative pore volume in the region having a pore radius of 0.002 μm or more and 0.1 μm or less is not particularly limited, but is usually 0.001 ml / g.

  The alumina mixed powder of the present invention preferably has a pore radius of 0 in the pore distribution curve in which the horizontal axis is the pore radius (μm) of the alumina mixed powder and the vertical axis is the Log differential pore volume (ml / g). The log differential pore volume has a single maximum peak in the region of 1 μm to 10 μm, more preferably 1 μm to 10 μm.

  The average secondary particle diameter of the alumina mixed powder of the present invention measured by the laser diffraction scattering method is preferably 5 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, and further preferably 5 μm or more and 30 μm or less. When the average secondary particle diameter is smaller than 5 μm, it is not preferable because the pore structure of the alumina mixed powder is difficult to satisfy the scope of the present invention. On the other hand, if the average secondary particle diameter is larger than 50 μm, the pore radius becomes relatively large, and the interparticle distance becomes long, which may make it difficult to achieve high filling during resin filling. Further, since a large amount of alumina powder having a large particle size is contained, the mixer used for mixing with the resin and the mold during molding are significantly worn.

The alumina mixed powder of the present invention is a mixture containing alumina powder (I) having an average secondary particle diameter of 15 μm or more and 50 μm or less and alumina powder (II) of 2 μm or less measured by a laser diffraction scattering method. The mixing ratio of the alumina powder (I) and the alumina powder (II) in the alumina mixed powder of the present invention is preferably in the following range based on the total weight of the alumina mixed powder.
Alumina powder (I): 60 to 98% by weight (more preferably 70 to 95% by weight)
Alumina powder (II): 2 to 40% by weight (more preferably 5 to 30% by weight)
When the mixing ratio of the alumina powder (I) and the alumina powder (II) is in the above range, an alumina mixed powder having good resin filling property tends to be obtained, which is preferable.

  The alumina powder (I) used for the alumina mixed powder of the present invention is an alumina powder having an average secondary particle diameter of 15 μm to 50 μm, preferably 15 μm to 40 μm. When the average secondary particle diameter is smaller than 15 μm, when mixed with alumina powder (II), the cumulative pore volume of the alumina mixed powder in the region having a pore radius of 0.002 μm to 100 μm is 0.23 ml / g. It will not be below.

  The alumina powder (I) used for the alumina mixed powder of the present invention is preferably 0.1 ml / g or more and 0.3 ml / g or less, more preferably 0.15 ml in a region having a pore radius of 0.002 μm or more and 100 μm or less. The cumulative pore volume is not less than / g and not more than 0.25 ml / g. When the alumina powder (I) has a cumulative pore volume in the above range, when the alumina powder (I) is mixed with the alumina powder (II), the cumulative pore volume of the alumina mixed powder in the region having a pore radius of 0.002 μm to 100 μm. Can be 0.23 ml / g or less.

  The alumina powder (I) used in the alumina mixed powder of the present invention has pores measured by mercury porosimetry with the horizontal axis representing the pore radius (μm) and the vertical axis representing the Log differential pore volume (ml / g). In the distribution curve, the Log differential pore volume has a single maximum peak, preferably in a region having a pore radius of 1 μm or more and 10 μm or less, more preferably in a region of 1 μm or more and 8 μm or less.

  The alumina powder (I) used in the alumina mixed powder of the present invention is preferably a mixture of two or more kinds of spherical alumina powders having different cumulative pore volumes in a region having a pore radius of 0.002 μm to 100 μm. Specifically, in a pore distribution curve in which the horizontal axis is the pore radius (μm) of the alumina powder and the vertical axis is Log differential pore volume (ml / g), the pore radius is 0.002 μm or more and 100 μm or less. The cumulative pore volume in the region is preferably 0.1 ml / g or more and 0.3 ml / g or less, more preferably 0.15 ml / g or more and 0.3 ml / g or less, and the pore radius is 2 μm or more and 10 μm or less. In the region of the spherical alumina powder (II) whose Log differential pore volume has a single maximum peak, the horizontal axis is the pore radius (μm) of the alumina powder, and the vertical axis is the Log differential pore volume (ml / ml). In the pore distribution curve defined as g), the cumulative pore volume in the region having a pore radius of 0.002 to 100 μm is preferably 0.2 to 0.4 ml / g, more preferably 0.25 ml / g. g or more 0 It is a mixture containing spherical alumina powder (I-II) having a single maximum peak of Log differential pore volume in a region of 4 ml / g or less and a pore radius of 1 μm or more and less than 2 μm. preferable.

  The spherical alumina powder (II) has a pore radius of 2 μm to 10 μm in a pore distribution curve in which the horizontal axis is the pore radius (μm) of the alumina powder and the vertical axis is Log differential pore volume (ml / g). It is a spherical alumina powder in which the Log differential pore volume has a single maximum peak in the following region. The spherical alumina powder (I-II) has a pore distribution curve in which the horizontal axis is the pore radius (μm) of the alumina powder and the vertical axis is Log differential pore volume (ml / g). A spherical alumina powder having a single maximum peak of Log differential pore volume in a region having a radius of 1 μm or more and less than 2 μm.

When the alumina powder (I) is a mixture of the two types of spherical alumina powders, the mixing ratio is preferably in the following range based on the total weight of the alumina powder (I).
Spherical alumina powder (II): 60 wt% or more and 95 wt% or less
(More preferably, 70 wt% or more and 90 wt% or less)
Spherical alumina powder (I-II): 5% to 40% by weight
(More preferably, 10 wt% to 30 wt%)
When the mixing ratio of the spherical alumina powder (II) and the spherical alumina powder (I-II) is in the above range, the cumulative pore volume of the alumina mixed powder tends to decrease when mixed with the alumina powder (II). It is preferable.

  The alumina powders (I), (I-I) and (I-II) used for the alumina mixed powder of the present invention preferably have a spherical shape. Alumina powders (I), (II), and (I-II) having a spherical shape are obtained by flame melting using alumina powder, aluminum hydroxide powder, or metal aluminum powder obtained by Bayer method as raw material powder. be able to. As the raw material powder, it is particularly preferable to use aluminum hydroxide powder. The flame melting method is a method in which such raw material powder is sprayed and formed into droplets in a flame and then cooled and solidified. After cooling and solidifying, an alumina powder can be obtained by collecting it with a cyclone or a bag filter. Alumina powders (II) and (I-II) having a spherical shape are precursor powders obtained by granulating raw material slurry or an aqueous solution in which aluminum ions are dissolved using a spray dryer such as a spray dryer. Can be obtained by charging in a firing furnace such as an electric furnace or a gas furnace and firing at 1300 ° C. or higher for 2 to 12 hours. As the alumina powder (I), (II) and (I-II) used for the alumina mixed powder of the present invention, the particle size distribution can be adjusted, enlargement due to sintering of particles can be reduced, etc. For this reason, it is preferable to use one produced by a flame melting method.

For example, in the case of producing spherical alumina by the flame melting method, when using aluminum hydroxide powder as a raw material powder, for example, a pore distribution curve (horizontal axis: pore radius (μm), vertical axis measured by a mercury intrusion method) : Log differential pore volume (ml / g)), using aluminum hydroxide powder having a log differential pore volume having a maximum peak in a region having a pore radius of 0.2 μm or more and 15 μm or less as a raw material powder. Alumina powders (I), (II) and (I-II) used in the invention can be obtained. In this case, since the cumulative pore volume tends to be reduced as a result of spheroidization, the cumulative pore volume in the region having a pore radius of 0.002 μm or more and 100 μm or less is usually 0.3 ml / g or more and 0.00. What is 7 ml / g or less may be used.
On the other hand, when alumina powder or metal aluminum powder is used as the raw material powder, the powder having a log differential pore volume having a maximum peak in the pore radius region of 0.1 μm or more and 10 μm or less is used as the raw material powder. Alumina powders (I), (II) and (I-II) used in the above can be obtained.

  The alumina powder (II) used for the alumina mixed powder of the present invention is an alumina having an average secondary particle diameter of 2 μm or less, more preferably 0.5 μm or more and 2 μm or less, preferably 0.7 μm or more and 1.5 μm or less. It is a powder. When the average secondary particle diameter is larger than 2 μm, it becomes difficult to enter the pore portion of the alumina powder (I), and as a result, a large amount of small pores are formed in the mixed powder. There is a possibility that the filling property to the will deteriorate. On the other hand, the alumina powder (II) smaller than 0.5 μm always has an average pore radius of 0 even if it exists in an extremely excellent dispersion state in which the secondary particle size corresponds to the primary particle size. Since it is smaller than 1 μm, it contains a large amount of small pores, which may deteriorate the filling property into the resin.

  The alumina powder (II) used in the alumina mixed powder of the present invention has a pore distribution curve (horizontal axis: pore radius (μm), vertical axis: Log differential pore volume (ml / g) measured by mercury porosimetry. ) In the region having a pore radius of 0.002 μm or more and 100 μm or less, preferably 0.2 ml / g or more and 0.5 ml / g or less, more preferably 0.3 ml / g or more and 0.5 ml / g or less. Has a pore volume. When the alumina powder (II) has a cumulative pore volume in the above range, when the alumina powder (I) is mixed with the alumina powder (I), the cumulative pore volume of the alumina mixed powder in the region having a pore radius of 0.002 μm to 100 μm. Is preferably 0.23 ml / g or less.

  The alumina powder (II) used in the alumina mixed powder of the present invention has a pore distribution curve (horizontal axis: pore radius (μm), vertical axis: Log differential pore volume (ml / g) measured by mercury porosimetry. ), Preferably having a maximum peak in a region having a pore radius of 0.1 μm or more and 0.5 μm. When having a maximum peak in a region smaller than 0.1 μm, there will be a large amount of pores that cannot be penetrated by the resin when mixed with the resin, which not only deteriorates the filling property into the resin, There is a risk of lowering the thermal conductivity.

  The alumina powder (II) used in the present invention is obtained by calcining alumina powder obtained by firing aluminum hydroxide powder obtained by the Bayer method or high-purity aluminum hydroxide produced by alkoxide method. Alumina powder, neutralized gel obtained by mixing acidic and alkaline aqueous solutions containing aluminum ions, alumina powder obtained by baking powder such as ammonium alum and dosonite, and the like can be used. From the viewpoint of easily obtaining the alumina powder (II) of the present invention, an alumina powder obtained by the Bayer method or the alkoxide method is preferable.

  Further, as the alumina powder (II), a powder obtained by pulverizing the baked alumina powder using a pulverizer such as a ball mill, a vibration mill, a jet mill, an attritor mill, or a medium stirring mill can be used.

  The mixing of the alumina powders (I) and (II) is not particularly limited as long as the fine powder and the coarse powder can be uniformly mixed, and may be performed either dry or wet. Examples of the dry mixing method include a method of stirring and mixing using an air blender, a V-type blender, a rocking blender, a Henschel mixer, a Nauter mixer, and the like. Examples of the wet mixing method include a method in which a slurry prepared in a solvent such as water is stirred and mixed using a stirrer and then dried.

  In the alumina mixed powder of the present invention, the amount of soluble sodium is preferably 300 ppm or less, more preferably 100 ppm in terms of Na, from the viewpoint of preventing the curing of the resin composition and preventing the moisture resistance reliability of the resin molded product from decreasing. Hereinafter, it is particularly preferably 20 ppm or less.

  In order to reduce the amount of soluble sodium to 300 ppm or less, washing with water or an acidic aqueous solution such as hydrochloric acid or sulfuric acid may be performed. Washing can be performed, for example, by repeating the operations of re-slurrying the alumina powder, then dehydrating using a dehydrator such as a filter press, a centle filter, or a screw decanter, and then reslurry. . The washing of the powder may be performed after mixing the alumina powder, or may be performed individually on the powder before mixing.

  Alumina mixed powder can be obtained by drying the obtained dehydrated cake with a shelf dryer or paddle dryer or by drying the slurry after washing with a spray dryer or vibratory fluid dryer. It is done. The drying temperature is not particularly limited, but is usually 120 ° C. or higher and 300 ° C. or lower.

  The crystal structure of the alumina mixed powder is generally α-phase, but may include intermediate phases such as θ-phase, γ-phase, and δ-phase. However, from the viewpoint of heat dissipation characteristics, the α phase content is preferably 30% by weight or more. The content of the α phase can be calculated by X-ray diffraction measurement. Specifically, a powder obtained by mixing a predetermined amount of alumina powder of each crystal phase is measured, and a calibration curve is created for the ratio of the peak area of the α phase to the peak area of the mixed powder. The content of the α phase in the powder can be calculated. In particular, the alumina powder (II) preferably has an α phase content of 95% or more, more preferably 100%, from the viewpoint of imparting high thermal conductivity.

  The resin composition of the present invention can be obtained by mixing the alumina mixed powder of the present invention and a resin. The filling amount of the alumina mixed powder of the resin composition of the present invention is preferably 40% by volume or more and 90% by volume or less, more preferably 50% by volume based on the total volume of the resin composition, although it depends on the use. It is 80 volume% or less, More preferably, it is 55 volume% or more and 80 volume% or less.

  The resin used in the resin composition of the present invention is not particularly limited, and a resin usually used in this field can be used. For example, a thermoplastic resin or a thermosetting resin can be used. Good. Also, rubber may be used. Examples of the thermoplastic resin include olefin resin, polylactic acid, aromatic polyester resin, aliphatic polyester resin, aromatic polyamide resin, and methacrylic resin. Examples of the thermosetting resin include epoxy resins, silicone resins, vinyl ester resins, phenol resins, unsaturated polyester resins, polyimide resins, polyurethane resins, and melamine resins. Among these, a thermosetting resin is preferable, and an epoxy resin and a silicone resin are more preferable.

The resin composition of the present invention can be produced by a commonly used known method. For example, when a thermoplastic resin is used, the alumina mixed powder and the thermoplastic resin may be melt-kneaded together. Examples of the apparatus used for melt kneading include a Banbury mixer, a plast mill, a Brabender plastograph, a single screw extruder, a twin screw extruder, and the like. The resin molded body of the present invention can be produced by molding the resin composition obtained by melt kneading by a method such as injection molding, press molding, or extrusion molding. Moreover, when using a thermosetting resin, after knead | mixing the alumina mixed powder, the resin before hardening, and a hardening | curing agent, a resin composition can be obtained by performing heat processing. Examples of the kneading method include a method of stirring and mixing in a container, a method of kneading with a vacuum defoaming kneader and a screw type kneader. Examples of a method for obtaining a resin molded body from the resin composition obtained by kneading include press molding, mold molding, transfer molding, and the like. The curing method may be appropriately selected depending on the type of resin, and examples thereof include a method of pouring into a mold and then leaving it at room temperature, a method of heating, and the like.
The molding pressure when producing the resin molded body of the present invention is preferably 6 MPa or less, and more preferably 5 MPa or less. The lower limit of the molding pressure is not particularly limited, but is usually at least atmospheric pressure.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

1) Measurement of pore distribution by mercury porosimetry The alumina powder was dried at 120 ° C. for 4 hours to remove adsorbed moisture. Thereafter, about 0.5 to 0.6 g was weighed with a precision balance and filled into a measurement cell having a diameter of 15 mm and a height of 24 mm. This measurement cell was set in an automatic porosimeter Autopore III9420 (manufactured by Micromeritics) and measured separately on the low pressure side (1 to 10,000 psi) and the high pressure side (10000 to 60000 psi). Summing up these measurement data, the cumulative pore volume, average pore radius, Log differential pore volume distribution in the pore radius range of 0.002 μm to 100 μm, and cumulative fine volume in the range of 0.002 μm to 0.1 μm. The pore volume was calculated.

2) Average secondary particle size measurement The average secondary particle size was measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac HRA X-100; manufactured by Nikkiso Co., Ltd.). A 0.2 wt% sodium hexametaphosphate aqueous solution was used as a dispersion medium, and the average of the values measured twice after 5 minutes of dispersion treatment with ultrasonic waves of 40 W output was taken as the measurement value. In addition, the refractive index of aluminum hydroxide powder used 1.57, the refractive index of alumina powder used 1.76, and the refractive index of aqueous solution used 1.33.

3) Dioctyl phthalate oil absorption (ml / 100 g: hereinafter referred to as “DOP oil absorption”)
The DOP oil absorption was determined according to the method specified in JIS-K-6221. The lower the DOP oil absorption amount of the alumina mixed powder, the better the filling property into the resin, and the more alumina mixed powder can be filled into the resin per unit weight.

4) Viscosity measurement The viscosity of the resin composition was measured using a B-type rotational viscometer (manufactured by Toki Sangyo Co., Ltd.) at a temperature of 25 ° C., a rotational speed of 6 rpm, and a rotor No. 4 (measurement upper limit 100 Pa · s). The resin composition is prepared by mixing a predetermined amount of alumina mixed powder and silicone resin (SE1981H-B solution manufactured by Toray Dow Corning Co., Ltd.) so that the content of the alumina mixed powder is 60% by volume, and vacuum defoaming It was prepared by vacuum defoaming kneading for 30 minutes using a kneader.

  The alumina powder used in the examples or comparative examples is as follows.

[Alumina powder A]
Gibbsite-type aluminum hydroxide powder having an average secondary particle size of 46 μm and a cumulative pore volume of 0.35 ml / g in a region having a pore radius of 0.002 μm to 100 μm, measured by a mercury intrusion method, It was manufactured by supplying into a high-temperature flame of 1500 ° C. or higher formed from soot and spheroidizing.

[Alumina powder B]
Gibbsite-type aluminum hydroxide powder having an average secondary particle size of 9.5 μm and a cumulative pore volume of 0.49 ml / g in the region of pore radius of 0.002 μm to 100 μm measured by mercury porosimetry is combustible It was manufactured by supplying into a high-temperature flame of 1500 ° C. or higher formed from a gas and a combustion-supporting gas and spheroidizing.

[Alumina powder C]
Gibbsite-type aluminum hydroxide powder having an average secondary particle diameter of 59 μm and a cumulative pore volume of 0.38 ml / g in a region having a pore radius of 0.002 μm or more and 100 μm or less, measured by a mercury intrusion method, It was manufactured by supplying into a high-temperature flame of 1500 ° C. or higher formed from a combustion-supporting gas and spheroidizing.

[Alumina powder D]
A gibbsite type aluminum hydroxide powder having an average secondary particle diameter of 4.5 μm and a cumulative pore volume of 0.62 ml / g in a region having a pore radius of 0.002 μm to 100 μm, measured by a mercury intrusion method, is combustible It was manufactured by supplying into a high-temperature flame of 1500 ° C. or higher formed from a gas and a combustion-supporting gas and spheroidizing.

[Alumina powder E]
AL-41-DBM01 (α phase content 100%) manufactured by Sumitomo Chemical Co., Ltd. was used.

[Alumina powder F]
AES-12 (α phase content 100%) manufactured by Sumitomo Chemical Co., Ltd. was used.

  Table 1 shows the physical properties of alumina powders A to D and commercially available alumina powders E and F produced by the above method.

(Preparation of alumina mixed powder)
Said alumina powder AF was mixed in the ratio shown in Table 2, and the alumina mixed powder was obtained. Table 3 shows the physical properties of the obtained alumina mixed powder. In addition, the alumina powders (1) and (2) in Examples 1 to 3 are alumina powders corresponding to the alumina powders (I) and (II) used in the present invention, respectively.

Average secondary particle diameter (D50) after mixing of alumina powder (1) of Example 1, Example 2 and Comparative Example 1 obtained by mixing two kinds of alumina powder, cumulative pores of 0.002 to 100 μm The volume (Vtotal) and the pore radius (R1) showing the maximum peak were as follows.
Alumina powder of Example 1 (1)
D50: 24 μm, Vtotal: 0.18 ml / g, R1: 1.73 μm
Alumina powder of Example 2 (1)
D50: 27 μm, Vtotal: 0.18 ml / g, R1: 2.09 μm
Alumina powder of Comparative Example 1 (1)
D50: 24 μm, Vtotal: 0.18 ml / g, R1: 1.73 μm

  From the results shown in Table 3, it was confirmed that the alumina mixed powder of the present invention had a low DOP oil absorption and excellent filling properties.

  From the results shown in Table 3, it was confirmed that the viscosity of the resin composition can be lowered by using the alumina mixed powder of the present invention.

Claims (11)

  A mixed powder containing alumina powder (I) having an average secondary particle diameter of 15 μm or more and 50 μm or less and alumina powder (II) having an average secondary particle diameter of 2 μm or less. In the pore distribution curve measured by mercury porosimetry with Log differential pore volume, the cumulative pore volume in the region of pore radius of 0.002 μm to 100 μm is 0.10 ml / g to 0.23 ml / g. An alumina mixed powder characterized by that.   2. The alumina mixed powder according to claim 1, wherein the cumulative pore volume in a pore radius region of 0.002 μm or more and 0.1 μm or less is 0.015 ml / g or less.   3. The alumina mixed powder according to claim 1, which has a single maximum peak in a Log differential pore volume distribution in a region of a pore radius of 0.1 μm or more and 10 μm or less.   Alumina powder (I) has a pore radius of 0.002 μm to 100 μm in a pore distribution curve in which the horizontal axis is the pore radius (μm) of the alumina powder and the vertical axis is Log differential pore volume (ml / g). The accumulated pore volume in the following region is 0.1 ml / g or more and 0.3 ml / g or less, and the Log differential pore volume has a single maximum peak in the region having a pore radius of 2 μm or more and 10 μm or less. In a fine pore distribution curve with spherical alumina powder, 60 wt% to 95 wt%, the horizontal axis is the pore radius (μm) of the alumina powder, and the vertical axis is Log differential pore volume (ml / g). In the region where the pore radius is 0.002 μm or more and 100 μm or less, the cumulative pore volume is 0.2 ml / g or more and 0.4 ml / g or less, and in the region where the pore radius is 1 μm or more and less than 2 μm, the Log differential pore volume is Single maximal pin Spherical alumina powder having a click, characterized in that it is a mixed powder containing a 40 wt% 5 wt% or more or less, the alumina mixed powder according to claim 1.   The accumulated pore volume of the alumina powder (II) in a region having a pore radius of 0.002 μm to 100 μm is 0.2 ml / g to 0.5 ml / g, The alumina mixed powder according to any one of the above.   The alumina mixed powder according to claim 1, wherein the α phase content of the alumina powder (II) is 95% or more.   The alumina mixed powder according to any one of claims 1 to 6, wherein the alumina powder (I) is an alumina powder produced by a flame melting method.   The resin composition containing the alumina mixed powder in any one of Claims 1-7.   The resin composition according to claim 8, wherein the resin is a silicone resin.   The resin composition according to claim 8, wherein the resin is an epoxy resin.   The resin molding containing the resin composition according to any one of claims 8 to 10, wherein a molding pressure is 6 MPa or less.