JP2021050132A - Thermally conductive filler, thermally conductive composite using the same, and method of producing thermally conductive filler - Google Patents

Abstract

To provide a thermally conductive filler capable of imparting high heat conductivity to a matrix.SOLUTION: A thermally conductive filler is formed of pulverized material of a sintered body comprising: isotropic highly thermally conductive particles having an average particle size of 0.2-100 μm and a thermal conductivity of 20 W/mK or more; non-porous hexagonal boron nitride particles having an average particle size of 0.01-5 times the average particle size of the highly thermally conductive particles; and porous boron nitride. The porosity of the boron nitride phase formed by the hexagonal boron nitride particles and the porous boron nitride is 10-50 vol.%, and 40% or more, on a count basis, of all the highly thermally conductive particles in the pulverized material are in the form of composite particles with the hexagonal boron nitride particles which are bound via the porous boron nitride to at least a part of the surface of the highly thermally conductive particles.SELECTED DRAWING: None

Description

The present invention relates to a thermally conductive filler, a thermally conductive composite material using the same, and a method for producing the thermally conductive filler.

Boron nitride is known as a highly insulating material having high thermal conductivity, and various thermally conductive composite materials in which boron nitride particles are dispersed in a matrix as a thermally conductive filler have been developed. Also, a thermally conductive composite material using such boron nitride particles in combination with particles of other thermally conductive materials such as aluminum oxide, aluminum nitride, silicon oxide, silicon nitride, silicon carbide, zinc oxide, and graphite. It is being developed.

For example, Japanese Patent Application Laid-Open No. 2005-29421 (Patent Document 1) describes _{a raw material powder prepared by mixing a boron nitride compound and a compound having two} NH groups with an aluminum nitride powder by subjecting the raw material powder to low temperature heat treatment. A boron nitride precursor composed of an amorphous BNO binding substance is formed by thermal decomposition, and then the boron nitride precursor is subjected to reduction heat treatment in a hydrogen or nitrogen atmosphere to form a boron nitride having a multi-layer structure. The surface of the aluminum nitride powder is oxidized to form an Al ₂ O ₃ layer, and then the Al ₂ O ₃ layer is heat-treated at a high temperature in the presence of carbon in a nitrogen atmosphere to form the Al 2 O 3 layer. ₂ O ₃ layer a deoxygenated, by forming an aluminum nitride layer was re nitride, a method of manufacturing the aluminum nitride / boron complex nitride powder containing boron nitride 3-40% by volume have been described, such It is also described that the aluminum nitride / boron nitride composite powder obtained in the above is a composite powder in which the surface of the aluminum nitride powder is coated with boron nitride having a disordered layer structure.

Further, in Japanese Patent Application Laid-Open No. 2008-1536 (Patent Document 2), a mixed powder in which the surface of alumina is coated with a boron compound is subjected to low-temperature heat treatment to generate aluminum borate, and then this aluminum borate is used. A method for producing an aluminum nitride / boron nitride composite powder by performing a high-temperature heat treatment in the presence of carbon in a nitrogen atmosphere has been described, and the aluminum nitride / boron nitride composite powder thus obtained is nitrided. It is also described that the boron nitride particles are present in the gaps between the aluminum particles and that the boron nitride particles are attached to the surface of the aluminum nitride particles.

Further, Japanese Patent Application Laid-Open No. 2018-162335 (Patent Document 3) describes boron nitride particles having an average particle diameter of 10 to 100 μm and 1/100 to 1/2 of the average particle diameter of the boron nitride particles. Described is a heat conductive filler which is a mixture of the aluminum nitride particles of the above and has a content of the boron nitride particles of 60 to 90% by volume based on the total amount of the boron nitride particles and the aluminum nitride particles. ..

Further, in Japanese Patent Application Laid-Open No. 2019-43804 (Patent Document 4), a compression-fired body is produced by firing a mixture of boron nitride powder and aluminum nitride powder while compressing, and the compression-fired body is crushed. It contains boron nitride particles and aluminum nitride particles, and is formed in a state where 50% or more of the outer surface of the aluminum nitride particles is contained inside the boron nitride particles and is in contact with the boron nitride particles. It is described that a thermally conductive filler containing the composite particles is obtained.

However, the conventional thermal conductivity filler obtained by forming boron nitride on the surface of the aluminum nitride particles using a boron compound, or the conventional thermal conductivity obtained by mixing the aluminum nitride particles and the boron nitride particles. The filler has a limit in improving the thermal conductivity, and cannot always achieve sufficient thermal conductivity.

Further, Japanese Patent Application Laid-Open No. 2012-171842 (Patent Document 5) provides excellent thermal conductivity by firing composite particles composed of melamine borate and specific scaly boron nitride powder in a non-oxidizing atmosphere. It is described that the boron nitride particles can be obtained. However, since the boron nitride particles thus obtained cannot exceed the thermal conductivity inherent in boron nitride, it has not always been possible to achieve sufficient thermal conductivity.

Japanese Unexamined Patent Publication No. 2005-29421 Japanese Unexamined Patent Publication No. 2008-1536 JP-A-2018-162335 JP-A-2019-43804 Japanese Unexamined Patent Publication No. 2012-171842

The present invention has been made in view of the above-mentioned problems of the prior art, and has a thermally conductive filler capable of imparting high thermal conductivity to the matrix, a method for producing the same, and excellent thermal conductivity. It is an object of the present invention to provide a composite material.

As a result of diligent research to achieve the above object, the present inventors compression-molded a mixture of a highly thermally conductive powder, a non-porous hexagonal boron nitride powder, and a borate complex at a specific pressure, and then, By firing and crushing the obtained compression sintered body, 40% of composite particles in which hexagonal boron nitride particles are bonded to at least a part of the surface of the highly thermally conductive particles via porous boron nitride are 40% on a number basis. It has been found that a thermally conductive filler containing the above can be obtained, and further, it has been found that high thermal conductivity can be imparted to the matrix by using this thermally conductive filler, and the present invention has been completed.

That is, the heat conductive filler of the present invention has an average particle size of 0.2 to 100 μm, an isotropic high heat conductive particle having a heat conductivity of 20 W / mK or more, and an average of the high heat conductive particles. It contains non-porous hexagonal boron nitride particles having an average particle size of 0.01 to 5 times the particle size and porous boron nitride, and is formed of the hexagonal boron nitride particles and the porous boron nitride. It is composed of a pulverized product of a sintered body having a porosity of 10 to 50 vol% in the boron nitride phase.
Of all the high thermal conductive particles in the ground product, 40% or more of the particles are made of the hexagonal boron nitride via the porous boron nitride on at least a part of the surface of the high thermal conductive particles. It is characterized in that the particles form a composite particle in which the particles are bonded.

In the thermally conductive filler of the present invention, the highly thermally conductive particles are selected from the group consisting of aluminum nitride particles, silicon nitride particles, cubic boron nitride particles, aluminum oxide particles, zinc oxide particles, silicon carbide particles, and diamond particles. It is preferable that the particles are at least one kind of particles, and it is preferable that the porous boron nitride has a multi-layer structure. Further, in the thermally conductive filler of the present invention, it is preferable that the surface is alkylated.

Further, the thermally conductive composite material of the present invention is characterized by containing a matrix and the thermally conductive filler of the present invention dispersed in the matrix.

In the thermally conductive composite material of the present invention, the thermally conductive filler preferably has a bimodal or higher particle size distribution.

Further, as the heat conductive composite material of the present invention, a grease composition in which the matrix is oil can be mentioned. As the oil, at least one selected from the group consisting of silicone oil, modified silicone oil, fluoroether oil, mineral oil, animal and vegetable natural oil, paraffin and synthetic oil is preferable.

Further, the method for producing a thermally conductive filler of the present invention comprises an isotropic high thermal conductive powder having an average particle size of 0.2 to 100 μm and a thermal conductivity of 20 W / mK or more, and the high thermal conductivity. The first step of compression molding a mixture of a non-porous hexagonal boron nitride powder having an average particle size of 0.01 to 5 times the average particle size of the powder and a boric acid complex at a pressure of 20 MPa or more and the above. The second step of firing the compression molded product obtained in the first step in an inert gas atmosphere and the compression sintered body obtained in the second step are crushed to form the surface of the highly thermally conductive particles. The method is characterized by including a third step of obtaining a thermally conductive filler containing composite particles in which hexagonal boron nitride particles are bonded via porous boron nitride at least in part.

In the first step, it is preferable to perform compression molding under hydrostatic pressure. Further, in the method for producing a thermally conductive filler of the present invention, it is preferable that the boric acid complex is at least one selected from the group consisting of a borate melamine complex and a borate urea complex.

Further, in the method for producing a thermally conductive filler of the present invention, a fourth method of alkylating the surface of the thermally conductive filler by reacting the thermally conductive filler with a silazane-based coupling agent or a titanate-based coupling agent. It is preferable to further include the above steps.

According to the method for producing a thermally conductive filler of the present invention, thermal conductivity containing composite particles in which the hexagonal boron nitride particles are bonded to at least a part of the surface of the highly thermally conductive particles via the porous boron nitride. The reason why the sex filler is obtained is not always clear, but the present inventors speculate as follows. That is, in the method for producing a thermally conductive filler of the present invention, a mixture of the highly thermally conductive powder, the hexagonal boron nitride powder and a borate complex is compression-molded at a predetermined pressure, and the obtained compression-molded product is obtained. A compression sintered body is formed by firing in an inert gas atmosphere, and the compression sintered body is pulverized to obtain a thermally conductive filler. By compression-molding a mixture of the high thermal conductive powder, the hexagonal boron nitride powder, and the boric acid complex at a predetermined pressure, the high thermal conductive particles and the hexagonal boron nitride particles form the boric acid complex. By firing the compression molded product in such a state in an inert gas atmosphere, the boric acid complex is converted to boron nitride and oxygen and carbon compounds are desorbed. Voids are formed in the boron nitride. As a result, a compression sintered body is obtained in which the highly thermally conductive particles and the hexagonal boron nitride particles are bonded via the porous boron nitride. When such a compression molded body is crushed, the highly thermally conductive particles and the hexagonal boron nitride particles are very hard materials, so that the porous boron nitride is selectively destroyed and the highly thermally conductive particles are destroyed. It is presumed that composite particles in which the hexagonal boron nitride particles are bonded via the porous boron nitride are formed on at least a part of the surface of the sex particles.

Further, the reason why a composite material having excellent thermal conductivity can be obtained by using such a thermally conductive filler of the present invention is not necessarily clear, but the present inventors presume as follows. That is, in a composite material in which a heat conductive filler is dispersed in a matrix, heat is transferred through a portion where the filler particles are in contact, but high heat conductive particles such as aluminum nitride particles have an advantage that the intraparticle thermal resistance is small. However, since the particles are generally hard, the particles do not deform when they come into contact with each other, and the contact area becomes a small point contact, and the interparticle thermal resistance (interfacial thermal resistance) increases. Further, the boron nitride particles are relatively soft particles among the high thermal conductive particles, and the contact area is larger than that of the point contacts, and the interfacial thermal resistance (interfacial thermal resistance) is reduced. Therefore, in the conventional heat conductive filler, although high heat conductive particles such as aluminum nitride particles and boron nitride particles are used in combination to increase the contact area and reduce the thermal resistance between the particles, it is not always sufficient. It wasn't a thing.

On the other hand, the thermally conductive filler of the present invention contains composite particles in which the hexagonal boron nitride particles are bonded to at least a part of the surface of the highly thermally conductive particles via the porous boron nitride. is there. Here, the porous boron nitride not only binds the highly thermally conductive particles and the hexagonal boron nitride particles with a high bonding force, but also has a role of increasing the contact area of these particles. Therefore, in the heat conductive filler of the present invention, it is presumed that the thermal resistance between particles is further reduced and the heat conductivity of the obtained composite material is improved.

According to the present invention, it is possible to obtain a thermally conductive filler capable of imparting high thermal conductivity to a matrix and a composite material having excellent thermal conductivity.

It is a scanning electron micrograph which shows the cross section of the compression sintered body produced in Example A5. It is a scanning electron micrograph (secondary electron image) which shows the heat conductive filler obtained in Example A3. 6 is a scanning electron micrograph (reflected electron image) showing the heat conductive filler obtained in Example A3. 9 is a scanning electron micrograph (randomly sampled 25 μm × 20 μm field of view) showing the thermally conductive filler obtained in Example A4. 6 is a graph showing an X-ray diffraction pattern of particles in which at least a part of the surface of aluminum nitride particles is coated with porous boron nitride. It is a graph which shows the particle size distribution of the heat conductive filler obtained in Examples A7 to A8 and Comparative Example A8. It is a graph which shows the particle size distribution of the heat conductive filler obtained in Example A6, A9 and Comparative Example A9. It is a scanning electron micrograph which shows the compression sintered body produced in Example A4. It is a scanning electron micrograph which shows the heat conductive filler obtained in Example A4. It is a scanning electron micrograph which shows the heat conductive filler obtained in the comparative example A6. It is a schematic diagram which shows the columnar composite material produced in Example and Comparative Example, and the sample for thermal conductivity measurement cut out from it. It is a graph which shows the relationship between the hydrostatic pressure at the time of compression molding, and the thermal conductivity of a composite material.

Hereinafter, the present invention will be described in detail according to the preferred embodiment thereof.

(Thermal conductive filler)
First, the thermally conductive filler of the present invention will be described. The heat conductive filler of the present invention has an isotropic high heat conductive particle having an average particle diameter of 0.2 to 100 μm and a heat conductivity of 20 W / mK or more, and an average particle diameter of the high heat conductive particles. It contains non-porous hexagonal boron nitride particles having an average particle size of 0.01 to 5 times that of the above, and porous boron nitride, and is formed by the hexagonal boron nitride particles and the porous boron nitride. It is composed of a pulverized product of a sintered body having a porosity of 10 to 50 vol% in the boron phase. Further, in the heat conductive filler of the present invention, 40% or more of the high heat conductive particles in the pulverized product are formed on at least a part of the surface of the high heat conductive particles. The hexagonal boron nitride particles are bonded to each other via the porous boron nitride to form composite particles.

The highly thermally conductive particles used in the present invention are not particularly limited as long as they are isotropic thermally conductive particles having a thermal conductivity of 20 W / mK or more, and are, for example, aluminum nitride particles, silicon carbide particles, and cubic crystal nitride. Examples thereof include boron particles, aluminum oxide particles, zinc oxide particles, silicon carbide particles, and diamond particles. These high thermal conductive particles may be used alone or in combination of two or more. Further, among these highly thermally conductive particles, an interface in close contact with the hexagonal boron nitride particles can be formed by sintering, and the composite particles with the hexagonal boron nitride particles have excellent thermal conductivity. From the viewpoint of showing, aluminum nitride particles, silicon nitride particles, cubic boron nitride particles, silicon carbide particles, and diamond particles are preferable, and aluminum nitride particles are particularly preferable. The thermal conductivity in the present specification is a thermal conductivity at room temperature (20 ° C.).

The average particle size of the highly thermally conductive particles is 0.2 to 100 μm. When the average particle size of the high thermal conductive particles is less than the lower limit, the number of grain boundaries between the hexagonal boron nitride particles and the high thermal conductive particles and between the high thermal conductive particles increases in the obtained composite material. Therefore, the overall thermal resistance increases. On the other hand, when the average particle size of the high thermal conductive particles exceeds the upper limit, the dispersion uniformity and filling rate of the thermally conductive filler in the obtained composite material are lowered, and the thermal conductivity is lowered. From the same viewpoint, the average particle size of the highly thermally conductive particles is preferably 0.3 to 95 μm, more preferably 0.5 to 90 μm, further preferably 0.5 to 50 μm, and particularly preferably 1 to 20 μm. preferable. In the present invention, the average particle size of the high thermal conductive particles is such that all the high thermal conductive particles contained in the thermally conductive filler, that is, composite particles with the hexagonal boron nitride particles are formed. It is the average particle diameter of all the high thermal conductive particles including the high thermal conductive particles, the hexagonal boron nitride particles and the high thermal conductive particles that do not form a composite particle.

In the present specification, the "mean particle size" is the average value of the particle size of 300 or more particles randomly selected by scanning electron microscope (SEM) observation or the like, excluding the catalog value for raw material powder and the like. means. When the particles are not spherical (circular cross section), the circumscribed circle of the particles (cross section) is assumed, and the diameter of the circumscribed circle is defined as the particle diameter.

The boron nitride particles used in the present invention are non-porous hexagonal boron nitride particles and are excellent in thermal conductivity. The average particle size of such hexagonal boron nitride particles is 0.01 to 5 times the average particle size of the high thermal conductive particles used in combination. When the average particle size of the hexagonal boron nitride particles is less than the lower limit, the number of grain boundaries between the hexagonal boron nitride particles and the highly thermally conductive particles and between the hexagonal boron nitride particles in the obtained composite material is increased. As it increases, the overall thermal resistance increases. On the other hand, when the average particle size of the hexagonal boron nitride particles exceeds the upper limit, the dispersion uniformity and filling rate of the heat conductive filler in the obtained composite material are lowered, and the heat conductivity is lowered. From the same viewpoint, the average particle size of the hexagonal boron nitride particles is preferably 0.03 to 0.3 times the average particle size of the highly thermally conductive particles used in combination, preferably 0.05 to 1. Double is more preferable. In the present invention, the average particle size of the hexagonal boron nitride particles forms composite particles with all the hexagonal boron nitride particles contained in the thermally conductive filler, that is, the highly thermally conductive particles. It is the average particle diameter of all the hexagonal boron nitride particles including the hexagonal boron nitride particles and the hexagonal boron nitride particles that do not form composite particles with the high thermal conductive particles.

Further, in the hexagonal boron nitride particles, the graphitization index is preferably 2.0 or less. When the graphitization index of the hexagonal boron nitride particles exceeds the upper limit, the thermal conductivity of the hexagonal boron nitride particles itself becomes small, so that the thermal conductivity of the obtained composite material decreases.

Further, in the highly thermally conductive particles and the hexagonal boron nitride particles, functional groups such as a hydroxyl group, a carboxyl group, an ester group, an amide group, and an amino group are functional on the surface thereof from the viewpoint of further improving the dispersibility in the matrix. The groups may be bonded.

The porous boron nitride according to the present invention binds the highly thermally conductive particles and the hexagonal boron nitride particles with a high bonding force in the sintered body according to the present invention and the thermally conductive filler of the present invention. .. Further, if the orientation of such porous boron nitride is too high, it may be arranged at a position that hinders heat conduction between the highly thermally conductive particles and the hexagonal boron nitride particles. From the viewpoint of efficient heat conduction between the highly thermally conductive particles and the hexagonal boron nitride particles, it is preferable to have a multi-layer structure.

Further, in the porous boron nitride, the half width of the X-ray diffraction peak derived from the 002 surface is preferably 0.5 to 10 °, more preferably 0.5 to 5 °, and 0. It is particularly preferably 5 to 2 °. When the half-value width of the X-ray diffraction peak derived from the 002 surface of the porous boron nitride is less than the lower limit, the proportion of the disordered layer structure is reduced, and the bond between the highly thermally conductive particles and the hexagonal boron nitride particles is reduced. The force and bonding force tend to decrease, while when the upper limit is exceeded, the crystal is disturbed due to the disordered layer structure, so that the thermal conductivity tends to decrease.

Such porous boron nitride can be formed, for example, by calcining the boric acid complex in an inert gas atmosphere, as will be described later. The boric acid complex is converted to boron nitride by calcination in an inert gas atmosphere. At this time, since oxygen and carbon compounds are desorbed, voids are formed in the boron nitride, and porous boron nitride can be obtained.

The thermally conductive filler of the present invention is a pulverized product of a sintered body containing the highly thermally conductive particles, the hexagonal boron nitride particles, and the porous boron nitride. In the sintered body, the porosity of the boron nitride phase formed by the hexagonal boron nitride particles and the porous boron nitride is 10 to 50 vol%. When the porosity of the boron nitride phase is within the above range, the contact area between the highly thermally conductive particles and the hexagonal boron nitride particles is increased, and the thermal resistance between the particles is reduced. Further, it is possible to achieve both the improvement of the adhesion between the highly thermally conductive particles and the hexagonal boron nitride particles and the improvement of the thermal conductivity of the boron nitride phase. On the other hand, when the porosity of the boron nitride phase is less than the lower limit, the thermal conductivity of the boron nitride phase is improved, but the porous boron nitride is not preferentially broken during pulverization of the sintered body. It is difficult to form composite particles in which the hexagonal boron nitride particles are bonded to at least a part of the surface of the highly thermally conductive particles via the porous boron nitride, and the content of the composite particles in the obtained thermally conductive filler is high. Less. On the other hand, when the porosity of the boron nitride phase exceeds the upper limit, the thermal conductivity of the boron nitride phase decreases, so that the thermal conductivity of the obtained composite material also decreases. Further, since the adhesion between the high thermal conductive particles and the hexagonal boron nitride particles is lowered, the hexagonal boron nitride particles can be easily desorbed from the surface of the high thermal conductive particles when the sintered body is pulverized. In the thermally conductive filler, the content of the composite particles in which the hexagonal boron nitride particles are bonded to at least a part of the surface of the highly thermally conductive particles via the porous boron nitride is reduced. From the same viewpoint, the porosity of the boron nitride phase is preferably 15 to 40 vol%.

Further, in the heat conductive filler of the present invention, 40% or more of the high heat conductive particles in the pulverized product are formed on at least a part of the surface of the high heat conductive particles. The hexagonal boron nitride particles are bonded to each other via the porous boron nitride to form composite particles. The thermally conductive filler in which 40% or more of the highly thermally conductive particles form the composite particles has a small thermal resistance between the particles, and the thermal conductivity of the obtained composite material is improved. On the other hand, a thermally conductive filler in which the proportion of particles forming the composite particles is less than the lower limit has a high thermal resistance between the particles, and the thermal conductivity of the obtained composite material is lowered. From the viewpoint that the thermal resistance between the particles in the thermally conductive filler is further reduced and the thermal conductivity of the obtained composite material is further improved, 50% or more of the particles among all the highly thermally conductive particles are based on the number of particles. It is preferable that the composite particles are formed, and it is more preferable that 55% or more of the particles form the composite particles. The number of all the high thermal conductive particles is the high thermal conductive particles in which the hexagonal boron nitride particles are bonded to at least a part of the surface and the high thermal conductive particles in which the hexagonal boron nitride particles are not bonded. It means the number of all the highly thermally conductive particles including.

Further, in the thermally conductive filler of the present invention, the composite particles do not necessarily have to have the entire surface of the highly thermally conductive particles coated with the hexagonal boron nitride particles, but the surface of the highly thermally conductive particles It is preferable that 40% or more is coated, 55% or more is more preferably coated, and it is particularly preferable that the entire surface is coated.

In the thermally conductive filler of the present invention, the volume ratio of the highly thermally conductive particles and the boron nitride phase (the phase formed by the hexagonal boron nitride particles and the porous boron nitride) (highly thermally conductive particles: nitride). The boron phase) is not particularly limited, but is preferably 30:70 to 98: 2, and more preferably 40:60 to 90:10. When the volume ratio of the high thermal conductive particles to the boron nitride phase is less than the lower limit, the effect of improving the thermal conductivity of the high thermal conductive particles cannot be sufficiently obtained, and the obtained composite material has sufficient thermal conductivity. On the other hand, when the upper limit is exceeded, the contact interface having a large thermal resistance in which the high thermal conductive particles are involved relatively increases in the obtained composite material, so that the composite material has excellent thermal conductivity. There is a tendency that composite materials cannot be obtained.

Further, in the thermally conductive filler of the present invention, the volume ratio of the hexagonal boron nitride particles to the porous boron nitride (hexagonal boron nitride particles: porous boron nitride) is not particularly limited, but is 10:90. ~ 90:10 is preferable, and 20:80 to 80:20 is more preferable. When the volume ratio of the hexagonal boron nitride particles to the porous boron nitride is less than the lower limit, the contact interface having a small thermal resistance in which the hexagonal boron nitride particles are involved is relatively reduced, resulting in excellent thermal conductivity. On the other hand, if the upper limit is exceeded, the adhesion between the highly thermally conductive particles and the hexagonal boron nitride particles is lowered, so that when the sintered body is pulverized, the above-mentioned The hexagonal boron nitride particles are easily desorbed from the surface of the highly thermally conductive particles, and the content of the composite particles is reduced in the obtained thermally conductive filler, so that a composite material having excellent thermal conductivity cannot be obtained. It is in.

Further, in the thermally conductive filler of the present invention, it is preferable that the surface is alkylated. As a result, when the heat conductive filler is added to the matrix described later, the aggregation of the heat conductive filler can be suppressed and the fluidity of the composite material is improved, so that the thermal resistance is further reduced. It becomes possible to obtain a composite material having further excellent conductivity.

(Manufacturing method of thermally conductive filler)
Next, the method for producing the thermally conductive filler of the present invention will be described. The method for producing a thermally conductive filler of the present invention comprises an isotropic high thermal conductive powder having an average particle size of 0.2 to 100 μm and a thermal conductivity of 20 W / mK or more, and the high thermal conductive powder. The first step of compression-molding a mixture of a non-porous hexagonal boron nitride powder having an average particle size of 0.01 to 5 times the average particle size and a boric acid complex at a pressure of 20 MPa or more and the first step. The second step of firing the compression molded product obtained in the above step at a temperature of 1800 to 2200 ° C. in an inert gas atmosphere and the compression sintered body obtained in the second step are crushed to achieve high thermal conductivity. This method includes a third step of obtaining a thermally conductive filler containing composite particles in which hexagonal boron nitride particles are bonded to at least a part of the surface of the sex particles via porous boron nitride.

Further, in the method for producing a thermally conductive filler of the present invention, a fourth method of alkylating the surface of the thermally conductive filler by reacting the thermally conductive filler with a silazane-based coupling agent or a titanate-based coupling agent. It is preferable to further include the above steps.

(First step)
In the first step, first, a mixture of a highly thermally conductive powder, a hexagonal boron nitride powder, and a boric acid complex is prepared. The high thermal conductive powder used here is a raw material powder that becomes high thermal conductive particles in the thermally conductive filler of the present invention, and the average particle diameter thereof is 0.2 to 100 μm and 0.3 to 95 μm. It is preferably 0.5 to 90 μm, more preferably 0.5 to 50 μm, and particularly preferably 1 to 20 μm. The hexagonal boron nitride powder used here is a raw material powder that becomes hexagonal boron nitride particles in the thermally conductive filler of the present invention, and the average particle size thereof is the average particle of the highly thermally conductive powder used in combination. The diameter is 0.01 to 5 times, preferably 0.03 to 3 times, and more preferably 0.05 to 1 times the diameter.

The boric acid complex is not particularly limited as long as it can form a porous boron nitride by firing in an inert gas atmosphere, and examples thereof include a borate melamine complex and a borate urea complex.

The mixing method when preparing the mixture is not particularly limited, and for example, a wet ball mill crushing mixing method, a dry ball mill crushing mixing method, a mechanical mixing method, a stirring mixing method, a mixing method using a mortar or the like can be adopted. If necessary, treatments such as filtration, washing, drying, and pulverization may be performed. The treatments such as filtration, washing, drying, and granulation are not particularly limited, and known methods can be appropriately adopted.

The mixing ratio of the high thermal conductive powder, the hexagonal boron nitride powder, and the boric acid complex is not particularly limited, but the volume of the high thermal conductive particles and the boron nitride phase in the obtained thermally conductive filler. A mixing ratio in which the ratio and the volume ratio of the hexagonal boron nitride particles and the porous boron nitride are within the above range is preferable.

Next, the mixture thus obtained is compression-molded at a predetermined pressure. As a result, it is possible to obtain a compression molded body in which the highly thermally conductive particles and the hexagonal boron nitride particles are in close contact with each other via the boric acid complex.

The pressure during compression molding is 20 MPa or more, preferably 60 MPa or more, and more preferably 80 MPa or more. When the pressure during compression molding becomes less than the lower limit, the high thermal conductive particles and the hexagonal boron nitride particles do not sufficiently adhere to each other via the boric acid complex, and the high thermal conductive particles and the hexagonal boron nitride particles do not adhere sufficiently to each other. It is difficult to form a composite material in which particles are bonded to each other through the porous boron nitride with a high bonding force, and it tends to be difficult to improve the thermal conductivity of the obtained thermally conductive filler and composite material.

The method for compression molding the mixture is not particularly limited, but compression molding under hydrostatic pressure is preferable. As a result, pressure is uniformly applied to the mixture, and a compression molded product in an effective close contact state can be obtained. Further, by compression molding under hydrostatic pressure, the thermal conductivity anisotropy of the thermally conductive filler due to the orientation of boron nitride can be suppressed. Such thermal conductivity anisotropy of the thermally conductive filler causes thermal conductivity anisotropy due to the molding history, which is not preferable in some cases.

(Second step)
In the second step, the compression molded product obtained in the first step is fired in an inert gas atmosphere. As a result, the boric acid complex in the compression molded product is converted to boron nitride, and oxygen and carbon compounds are desorbed, so that voids are formed in the boron nitride and porous boron nitride can be obtained. ..

Examples of the inert gas include nitrogen, a rare gas (for example, argon, helium, neon) and the like. The firing temperature is not particularly limited as long as the mixture is sufficiently sintered, but is preferably 1600 to 2200 ° C, more preferably 1650 to 1900 ° C. The firing time is not particularly limited as long as the mixture is sufficiently sintered, but is preferably 0.5 to 6 hours, more preferably 1 to 4 hours.

(Third step)
In the third step, the compressed sintered body obtained in the second step is pulverized. At this time, since the porous boron nitride of the compression molded product is selectively broken, the hexagonal boron nitride particles are bonded to at least a part of the surface of the highly thermally conductive particles via the porous boron nitride. Composite particles are formed, and a thermally conductive filler containing a large amount of these composite particles can be obtained.

The crushing method of the compression sintered body is not particularly limited, and for example, a crushing method using various crushers (mills) or mortars, a crushing method using a wet ball mill or a dry ball mill, or the like can be adopted.

(Fourth step)
In the fourth step, the thermally conductive filler obtained in the third step is reacted with a silazane-based coupling agent or a titanate-based coupling agent. At this time, the surface of the thermally conductive filler is alkylated by the reaction between the BN particles in the thermally conductive filler and the silazane-based coupling agent or the titanate-based coupling agent, and heat is generated in the matrix described later. When a conductive filler is added, aggregation of the thermally conductive filler can be suppressed and the fluidity of the composite material is improved. Therefore, a composite material having further reduced thermal resistance and excellent thermal conductivity can be obtained. It becomes possible to obtain.

On the other hand, when the surface of the thermally conductive filler obtained in the third step is treated with a silane-based coupling agent or an aluminate-based coupling agent, the silane-based coupling agent or the aluminate-based coupling agent is hydrolyzed. Since the reaction proceeds and gelation of the coupling agent occurs and the reaction between the BN particles in the thermally conductive filler and the silane coupling agent or the aluminate coupling agent does not proceed, the thermally conductive filler When the surface of the heat conductive filler is not alkylated and the heat conductive filler is added to the matrix described later, the aggregation of the heat conductive filler cannot be suppressed and the fluidity of the composite material is lowered. In addition, the interposition of the generated gel increases the contact thermal resistance between the thermally conductive fillers. As a result, the composite material does not have reduced thermal resistance and does not improve thermal conductivity.

Of the silazane-based coupling agent and the titanate-based coupling agent, the aggregation of the thermally conductive filler can be sufficiently suppressed, the fluidity of the composite material is improved, and the thermally conductive filler due to the presence of the gel. Since the contact thermal resistance between them does not increase, the silazane-based coupling agent is preferable from the viewpoint of further reducing the thermal resistance of the obtained composite material and increasing the thermal conductivity.

As a method of reacting the thermally conductive filler with the silazane-based coupling agent or the titanate-based coupling agent, for example, the thermally conductive filler is dispersed in an organic solvent such as toluene, and silazane is dispersed in the obtained dispersion. A method of heating after adding a system-based coupling agent or a titanate-based coupling agent can be mentioned.

As a mixing ratio of the thermally conductive filler and the silazane-based coupling agent or the titanate-based coupling agent, the amount of the silazane-based coupling agent or the titanate-based coupling agent is 100 parts by mass of the thermally conductive filler. It is preferably 1 to 20 parts by mass, and more preferably 5 to 10 parts by mass.

The reaction temperature is preferably room temperature to 100 ° C, more preferably 40 to 60 ° C. The reaction time is preferably 0.5 to 20 hours, more preferably 1 to 5 hours.

(Thermal conductive composite material)
Next, the heat conductive composite material of the present invention will be described. The thermally conductive composite material of the present invention contains a matrix and the thermally conductive filler of the present invention dispersed in the matrix.

In such a thermally conductive composite material of the present invention, an insulating resin or an insulating oil is preferable as the matrix, and for example, the resin is a thermosetting resin such as an epoxy resin, a phenol resin, or a silicone resin. , Polystyrene, polymethylmethacrylate, polycarbonate, polyolefin (eg polyethylene, polypropylene), polyolefin elastomer, polyethylene terephthalate, nylon, ABS resin, polyamide, polyimide, polyamideimide, ethylene-propylene-diene rubber (EPDM), butyl rubber, natural rubber , Polyisoprene, polyetherimide and the like. Examples of the oil include silicone oil, modified silicone oil, fluoroether oil, mineral oil, animal and vegetable natural oil, paraffin, synthetic oil, etc., and have a boiling point of 200 ° C. or higher, such as silicone oil, modified silicone oil, paraffin, Synthetic oils are preferred. These resins and oils may be used alone or in combination of two or more.

Further, in the thermally conductive composite material of the present invention, it is preferable that the surface of the thermally conductive filler is alkylated. As a result, the aggregation of the thermally conductive filler in the matrix can be suppressed and the fluidity of the composite material is improved, so that the thermal resistance of the composite material is further reduced and the thermal conductivity is further improved.

In the heat conductive composite material of the present invention, the content of the heat conductive filler is not particularly limited, but is preferably 10 to 90 vol% and 15 to 70 vol% with respect to the total amount of the heat conductive composite material. More preferably, 20 to 60 vol% is particularly preferable. When the content of the heat conductive filler is less than the lower limit, a network structure of heat conductive paths in which heat is diffused through the contact portion between the heat conductive fillers in the composite material is not sufficiently formed, and the obtained composite material is obtained. On the other hand, when the content of the thermally conductive filler exceeds the upper limit, the obtained composite material tends to be brittle and it tends to be difficult to obtain a self-supporting composite material. ..

Further, in the thermally conductive composite material of the present invention, it is preferable that the thermally conductive filler has a bimodal or higher particle size distribution. As a result, the viscosity of the composite material is reduced and the fluidity of the composite material is improved, so that the thickness of the composite material is reduced, so that the thermal resistance of the composite material is further reduced and the thermal conductivity is further improved. Examples of the thermally conductive filler having such a bimodal or higher particle size distribution include a mixture of two or more kinds of thermally conductive fillers having different particle size distributions, which are included in the thermally conductive composite material of the present invention. The thermally conductive filler having a bimodal or higher particle size distribution is not limited thereto. Further, in the thermally conductive filler having a particle size distribution of two peaks or more, the viscosity of the obtained composite material is reduced and the fluidity of the composite material is improved, so that the thickness of the composite material is reduced. From the viewpoint of further reducing the thermal resistance of the material and further improving the thermal conductivity, the proportion of the thermally conductive filler forming the peak having the largest particle size among the peaks in the particle size distribution is 70 to 95% by mass. It is preferably 75 to 90% by mass, and more preferably 75 to 90% by mass.

Further, the thermally conductive composite material of the present invention may contain spherical nanoparticles from the viewpoint of promoting rolling between particles and reducing the viscosity of the composite material. Further, such spherical nanoparticles may be surface-treated. Even if the composite material contains spherical nanoparticles, the effect of reducing thermal resistance is maintained, and a composite material having excellent thermal conductivity can be obtained.

As such spherical nanoparticles, spherical silica nanoparticles and surface treatment are applied from the viewpoint of improving the fluidity of the composite material by improving the adsorptivity to the surface of the thermally conductive filler and the dispersibility in the matrix. Spherical silica nanoparticles are preferred. Further, such spherical nanoparticles are preferably adsorbed on the surface of the thermally conductive filler. This improves dispersibility in the matrix and reduces interparticle friction, thus reducing the viscosity of the composite.

The average particle size of such spherical nanoparticles is the average of the thermally conductive fillers from the viewpoint of uniformity of adsorption on the surface of the thermally conductive filler and avoidance of interfacial thermal conduction inhibition by the spherical nanoparticles. The particle size is preferably 1/2 times or less, more preferably 1/4 times or less, and particularly preferably 1/5 times or less.

When the thermally conductive composite material of the present invention contains the spherical nanoparticles, the content thereof is preferably 0.1 to 20% by mass, preferably 0.5 to 20% by mass, based on the total amount of the thermally conductive composite material. 10% by mass is more preferable, and 0.5 to 5% by mass is particularly preferable. When the blending amount of the spherical nanoparticles is less than the lower limit, the effect of blending the spherical nanoparticles tends not to be sufficiently obtained, while when the blending amount exceeds the upper limit, contact between the thermally conductive fillers is caused. It tends to hinder, inhibit interfacial thermal conductivity, and reduce the thermal conductivity of thermally conductive composites.

Such a thermally conductive composite material can be produced, for example, as follows. That is, first, the heat conductive filler and the matrix are mixed. At that time, the mixing ratio of the heat conductive filler and the matrix is determined so that the content of the heat conductive filler in the obtained composite material becomes the desired content. Further, the method of mixing the thermally conductive filler and the matrix is not particularly limited, and a known mixing method is appropriately used.

When the resin is used as such a matrix, the thermally conductive filler and the resin are mixed to form a homogeneous mixture, and the obtained mixture is molded to obtain the thermally conductive composite material. When the thermally conductive filler and the resin are mixed in this way to form a homogeneous mixture, a dispersion medium may be further added to form a homogeneous slurry. In that case, the dispersion medium is removed by a known method such as vacuum drying. It is preferable to mold after the above. The dispersion medium is not particularly limited, and for example, N-methyl-2-pyrrolidone, chloroform, dichloromethane, carbon tetrachloride, acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, methyl acetate, ethyl acetate, propyl acetate, etc. Isopropyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, isopentyl acetate, amyl acetate, tetrahydrofuran, dimethylformaldehyde, dimethylacetamide, dimethylsulfoxide, acetonitrile, methanol, ethanol, propanol, isopropanol, butanol, hexanol, octanol, hexafluoroisopropanol, ethylene Glycol, propylene glycol, tetramethylene glycol, tetraethylene glycol, hexamethylene glycol, diethylene glycol, benzene, toluene, xylene, chlorobenzene, dichlorobenzene, trichlorobenzene, chlorophenol, phenol, tetrahydrofuran, sulfolane, 1,3-dimethyl-2- Examples thereof include organic solvents such as imidazolidinone, γ-butyrolactone, N-dimethylpyrrolidone, pentane, hexane, neopentane, cyclohexane, heptane, octane, isooctane, nonane, decane and diethyl ether.

When molding the mixture, it is preferable to pressurize and compress it. Such a compression method is not particularly limited, and may be uniaxial compression or biaxial compression. It may also be isotropically compressed with hydrostatic pressure. The pressure during compression is also not particularly limited, but is preferably 5 to 20 MPa. When the compression pressure is less than the lower limit, voids tend to remain in the obtained composite material, while when the pressure exceeds the upper limit, fracture deformation of the filler in the obtained composite material becomes remarkable and residual strain is generated. Tends to occur.

The method for solidifying the resin when molding the mixture is not particularly limited, and a known method, for example, when a thermoplastic resin is used as the resin, a cooling method such as allowing to cool, various methods (heat, light, etc.) Water) When a curable resin is used, an appropriate curing method can be adopted for each. Moreover, such solidification may be carried out either at the time of molding or after molding.

When the oil is used as the matrix, the thermally conductive composite material (that is, a grease composition) can be obtained by mixing the thermally conductive filler and the oil to form a uniform slurry.

Further, when the heat conductive composite material of the present invention contains the spherical nanoparticles, the spherical nanoparticles may be mixed together with the heat conductive filler when the matrix is mixed. Before mixing the heat conductive filler and the matrix, it is preferable to mix the heat conductive filler with the heat conductive filler in advance to adsorb spherical nanoparticles on the heat conductive filler. As a result, the spherical nanoparticles are easily dispersed in the matrix, and the friction between the particles is reduced, so that the viscosity of the composite material is reduced.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited to the following Examples. The method for synthesizing the borate melamine complex and the method for preparing the boron nitride pulverized particles used in Examples and Comparative Examples are shown below.

(Synthesis Example 1)
To 800 ml of water heated to 95 ° C., 24 g of boric acid was added and dissolved by stirring, and then 16 g of melamine was further added and dissolved by stirring. The heating and stirring were continued for 10 minutes to react boric acid and melamine, and the obtained reaction solution was water-cooled and then left at room temperature for 12 hours. Then, the precipitated crystals were collected by filtration and vacuum dried at 40 ° C. to obtain 31.5 g of a melamine borate complex.

(Preparation Example 1)
As the raw material boron nitride powder, a non-porous hexagonal boron nitride powder (“3M ^TM Boron Nitride Cooling Filler Platelets003” manufactured by 3M Ltd., average particle size 3 μm) was dispersed in ethanol so as to have a concentration of 5% by mass. The obtained dispersion was injected from a nozzle (nozzle diameter 0.15 mm) at a pressure of 100 MPa using a wet pulverizer, and a wet pulverization treatment was performed in which the pressure was rapidly released from a compressed state to normal pressure. Then, the dispersion liquid subjected to the first wet pulverization treatment is subjected to the second and third wet pulverization treatments under the same conditions, and then the crushed boron nitride powder is recovered by filtration and vacuum dried to pulverize the boron nitride. Particles (BN pulverized particles) were obtained. The average particle size of the BN pulverized particles was 1 μm.

(Example A1)
First, the composition ratio of the obtained compression sintered body is such that aluminum nitride particles (AlN particles) / boron nitride particles (BN particles) / porous boron nitride (porous BN) = 80 vol% / 15 vol% / 5 vol%. , AlN powder (“High-purity aluminum nitride powder / granules E grade” manufactured by Tokuyama Co., Ltd., average particle diameter 1 μm, thermal conductivity 180 W / mK) 22.8 g in a polyethylene pot. , 2.97 g of non-porous hexagonal BN powder (“3M ^TM Boron Nitride Cooling Filler Platelets001” manufactured by 3M, average particle size 1 μm) and 4.95 g of the melamine borate complex obtained in Synthesis Example 1 were added. Further, 500 g of zirconia balls (3 mm diameter) and 165 g of acetone were added and mixed by a ball mill under the condition of 400 rpm for 12 hours. Then, the zirconia balls were removed by filtration, and the acetone was completely removed by evaporation and vacuum drying. The obtained mixture was compressed under hydrostatic pressure of 294 MPa, heated at 380 ° C. for 1 hour in a nitrogen atmosphere, and further fired at 1800 ° C. for 1 hour to obtain a compressed sintered body. After cooling this compression sintered body to room temperature, it is milled for 60 seconds to conduct heat conduction containing composite particles (AlN / BN composite particles) in which the AlN particles and the BN particles are bonded via a porous BN. A sex filler was obtained.

Next, this thermally conductive filler and a one-component thermosetting epoxy resin (“EP160” manufactured by Cemedyne Co., Ltd.) are mixed so that the volume fraction of the filler is 60%, and then dichloromethane is added to the slurry. Was prepared. The obtained slurry was stirred in the air to evaporate dichloromethane, and further vacuum dried for 15 minutes to completely remove dichloromethane. The epoxy resin composition thus obtained is quickly filled in a cylindrical container (inner diameter 14 mm) preheated at 110 ° C. for 30 minutes so that the thickness after molding is within the range of 30 to 40 mm, and then a plunger. The epoxy resin is cured by heating at 110 ° C. for 30 minutes while holding this compressed state with a clamp at a pressure in the range of 5 to 10 MPa in the longitudinal direction of the cylindrical container. A columnar composite material in which the filler was dispersed in the cured epoxy resin was obtained.

(Example A2)
22.8 g of the AlN powder and 3.3 g of the BN powder so that the composition ratio of the obtained compression sintered body is AlN particles / BN particles / porous BN = 80 vol% / 16.7 vol% / 3.3 vol%. And the composite particles (AlN / BN composite particles) in which the AlN particles and the BN particles are bonded via a porous BN in the same manner as in Example A1 except that 3.3 g of the melamine borate complex is mixed. A thermally conductive filler was prepared, and a columnar composite material in which the thermally conductive filler was dispersed in the cured epoxy resin was prepared.

(Example A3)
Except for using 2.97 g of BN pulverized particles (average particle size 1 μm) obtained in Preparation Example 1 in place of the BN powder having an average particle size of 1 μm (“3M ^{TM Boron Nitride Cooling Filler Platelets 001” manufactured by 3M Co., Ltd.).} In the same manner as in Example A1, a heat conductive filler containing composite particles (AlN / BN composite particles) in which the AlN particles and the BN crushed particles are bonded via a porous BN is prepared, and further, the heat conduction A columnar composite material in which the sex filler was dispersed in the cured epoxy resin was prepared.

(Example A4)
AlN powder with an average particle size of 5 μm (Furukawa Denshi) is an isotropic high thermal conductive particle instead of the AlN powder with an average particle size of 1 μm (“High-purity aluminum nitride powder / granule E grade” manufactured by Tokuyama Co., Ltd.). ^{Prepared in place of the BN powder (“3M TM} Aluminum Nitride Cooling Filler Platelets001” manufactured by 3M) with an average particle size of 1 μm using “High Thermal Conductivity AlN Filler FAN-f05” manufactured by Co., Ltd., with a thermal conductivity of 170 W / mK). Using the BN pulverized particles (average particle diameter 1 μm) obtained in Example 1, the composition ratio of the obtained compression sintered body is such that AlN particles / BN particles / porous BN = 80 vol% / 10 vol% / 10 vol%. , The AlN powder and the BN crushed particles formed a porous BN in the same manner as in Example A1 except that 22.8 g of the AlN powder, 1.98 g of the BN crushed particles and 9.98 g of the borate melamine complex were mixed. A thermally conductive filler containing the composite particles (AlN / BN composite particles) bonded via the mixture was prepared, and further, a columnar composite material in which the thermally conductive filler was dispersed in the cured epoxy resin was prepared.

(Example A5)
The AlN powder 22.8 g, the BN crushed particles 2.97 g, and the hoe so that the composition ratio of the obtained compression sintered body is AlN particles / BN particles / porous BN = 80 vol% / 15 vol% / 5 vol%. Heat conduction containing composite particles (AlN / BN composite particles) in which the AlN particles and the BN pulverized particles are bonded via a porous BN in the same manner as in Example A4 except that 4.95 g of the acid melamine complex is mixed. A sex filler was prepared, and a columnar composite material in which the thermally conductive filler was dispersed in the cured epoxy resin was prepared.

(Example A6)
The AlN powder 22.8 g, the BN crushed particles 3.40 g, and the hoe so that the composition ratio of the obtained compression sintered body is AlN particles / BN particles / porous BN = 70 vol% / 15 vol% / 15 vol%. Heat conduction containing composite particles (AlN / BN composite particles) in which the AlN particles and the BN pulverized particles are bonded via a porous BN in the same manner as in Example A4 except that 17.01 g of the acid melamine complex is mixed. A sex filler was prepared, and a columnar composite material in which the thermally conductive filler was dispersed in the cured epoxy resin was prepared.

(Example A7)
22.8 g of the AlN powder, 5.29 g of the BN crushed particles, and the hoe so that the composition ratio of the obtained compression sintered body is AlN particles / BN particles / porous BN = 60 vol% / 20 vol% / 20 vol%. Heat conduction containing composite particles (AlN / BN composite particles) in which the AlN particles and the BN pulverized particles are bonded via a porous BN in the same manner as in Example A4 except that 26.46 g of the acid melamine complex is mixed. A sex filler was prepared, and a columnar composite material in which the thermally conductive filler was dispersed in the cured epoxy resin was prepared.

(Example A8)
The AlN powder 22.8 g, the BN crushed particles 7.94 g, and the hoe so that the composition ratio of the obtained compression sintered body is AlN particles / BN particles / porous BN = 60 vol% / 30 vol% / 10 vol%. Heat conduction containing composite particles (AlN / BN composite particles) in which the AlN particles and the BN pulverized particles are bonded via a porous BN in the same manner as in Example A4 except that 13.2 g of the acid melamine complex is mixed. A sex filler was prepared, and a columnar composite material in which the thermally conductive filler was dispersed in the cured epoxy resin was prepared.

(Example A9)
2. The AlN powder 22.8 g and the BN crushed particles so that the composition ratio of the obtained compression sintered body is AlN particles / BN particles / porous BN = 70 vol% / 22.5 vol% / 7.5 vol%. Composite particles (AlN / BN composite particles) in which the AlN particles and the BN pulverized particles are bonded via a porous BN in the same manner as in Example A4 except that 10 g and 8.51 g of the melamine borate complex are mixed. A thermally conductive filler to be contained was prepared, and a columnar composite material in which the thermally conductive filler was dispersed in the cured epoxy resin was prepared.

(Example A10)
The AlN particles and the above in the same manner as in Example A4 except that 1.98 g of the ^{BN powder (“3M TM} Boron Nitride Cooling Filler Platelets001” manufactured by 3M Co., Ltd.) having an average particle diameter of 1 μm was used instead of the BN pulverized particles. A thermally conductive filler containing composite particles (AlN / BN composite particles) in which BN particles are bonded via a porous BN is prepared, and further, the thermally conductive filler is a columnar shape dispersed in an epoxy resin cured product. The composite material of was prepared.

(Example A11)
The AlN powder 22.8 g, the BN powder 2.97 g, and the boric acid so that the composition ratio of the obtained compression sintered body is AlN particles / BN particles / porous BN = 80 vol% / 15 vol% / 5 vol%. A thermally conductive filler containing composite particles (AlN / BN composite particles) in which the AlN particles and the BN particles are bonded via a porous BN in the same manner as in Example A10 except that 4.95 g of the melamine complex is mixed. Was prepared, and further, a columnar composite material in which the heat conductive filler was dispersed in the cured epoxy resin was prepared.

(Example A12)
Heat conduction containing composite particles (AlN / BN composite particles) in which the AlN particles and the BN particles are bonded via a porous BN in the same manner as in Example A10 except that the hydrostatic pressure is changed to 98.1 MPa. A sex filler was prepared, and a columnar composite material in which the thermally conductive filler was dispersed in the cured epoxy resin was prepared.

(Example A13)
Heat conduction containing composite particles (AlN / BN composite particles) in which the AlN particles and the BN particles are bonded via a porous BN in the same manner as in Example A10 except that the hydrostatic pressure is changed to 29.4 MPa. A sex filler was prepared, and a columnar composite material in which the thermally conductive filler was dispersed in the cured epoxy resin was prepared.

(Comparative Example A1)
The same as in Example A1 except that only 22.8 g of the AlN powder was used without using the BN powder and the melamine borate complex, and compression at hydrostatic pressure and heating at 1800 ° C. were not performed. A thermally conductive filler composed of only AlN particles was prepared, and further, a columnar composite material in which the thermally conductive filler was dispersed in the cured epoxy resin was prepared.

(Comparative Example A2)
22.8 g of the AlN powder and the boric acid so that the composition ratio of the obtained compression sintered body is AlN particles / BN particles / porous BN = 80 vol% / 0 vol% / 20 vol% without using the BN powder. A heat conductive filler containing particles in which at least a part of the surface of the AlN particles is coated with porous BN (porous BN-coated AlN particles) is prepared in the same manner as in Example A1 except that 20 g of the melamine complex is mixed. Further, a columnar composite material in which the heat conductive filler was dispersed in the cured epoxy resin was prepared.

(Comparative Example A3)
It is composed of only the AlN particles in the same manner as in Example A4 except that only 22.8 g of the AlN powder is used without using the BN pulverized particles and the melamine borate complex, and compression is not performed under hydrostatic pressure. A thermally conductive filler was prepared, and a columnar composite material in which the thermally conductive filler was dispersed in an epoxy resin cured product was prepared.

(Comparative Example A4)
22.8 g of the AlN powder and the hoe without using the BN pulverized particles so that the composition ratio of the obtained compressed sintered body is AlN particles / BN particles / porous BN = 80 vol% / 0 vol% / 20 vol%. A heat conductive filler containing particles in which at least a part of the surface of the AlN particles is coated with porous BN (porous BN-coated AlN particles) is provided in the same manner as in Example A4 except that 20 g of the acid melamine complex is mixed. After preparation, a columnar composite material in which the heat conductive filler was dispersed in the cured epoxy resin was prepared.

(Comparative Example A5)
2. 2.8 g of the AlN powder and the BN pulverized particles without using the melamine borate complex so that the composition ratio of the mixture is AlN particles / BN particles / porous BN = 80 vol% / 20 vol% / 0 vol%. Mixed particles of the AlN particles and the BN pulverized particles (AlN / BN mixed particles) in the same manner as in Example A4 except that 96 g was mixed and compression at hydrostatic pressure and heating at 1800 ° C. were not performed. A thermally conductive filler containing the above was prepared, and further, a columnar composite material in which the thermally conductive filler was dispersed in the cured epoxy resin was prepared.

(Comparative Example A6)
Heat containing composite particles (AlN / BN composite particles) in which the AlN particles and the BN crushed particles are bonded via a porous BN in the same manner as in Example A4 except that compression is not performed under hydrostatic pressure. A conductive filler was prepared, and a columnar composite material in which the thermally conductive filler was dispersed in an epoxy resin cured product was prepared.

(Comparative Example A7)
The same as in Example A4 except that only 22.8 g of the AlN powder was used without using the BN pulverized particles and the melamine borate complex, and compression at hydrostatic pressure and heating at 1800 ° C. were not performed. A thermally conductive filler composed of only the AlN particles was prepared, and a columnar composite material in which the thermally conductive filler was dispersed in the cured epoxy resin was prepared.

(Comparative Example A8)
22.8 g of the AlN powder and the hoe without using the BN pulverized particles so that the composition ratio of the obtained compressed sintered body is AlN particles / BN particles / porous BN = 60 vol% / 0 vol% / 40 vol%. Thermal conductivity containing particles in which at least a part of the surface of the AlN particles is coated with porous BN (porous BN-coated AlN particles) in the same manner as in Example A4 except that 52.9 g of the acid melamine complex is mixed. A filler was prepared, and a columnar composite material in which the heat conductive filler was dispersed in the cured epoxy resin was prepared.

(Comparative Example A9)
22.8 g of the AlN powder and the hoe without using the BN pulverized particles so that the composition ratio of the obtained compressed sintered body is AlN particles / BN particles / porous BN = 70 vol% / 0 vol% / 30 vol%. Thermal conductivity containing particles in which at least a part of the surface of the AlN particles is coated with porous BN (porous BN-coated AlN particles) in the same manner as in Example A4 except that 34.0 g of the acid melamine complex is mixed. A filler was prepared, and a columnar composite material in which the heat conductive filler was dispersed in the cured epoxy resin was prepared.

(Comparative Example A10)
Thermal conductivity containing composite particles (AlN / BN composite particles) in which the AlN particles and the BN crushed particles are bonded via a porous BN in the same manner as in Example A4 except that the hydrostatic pressure is changed to 15 MPa. A filler was prepared, and a columnar composite material in which the thermally conductive filler was dispersed in an epoxy resin cured product was prepared.

(Comparative Example A11)
Heat conduction containing composite particles (AlN / BN composite particles) in which the AlN particles and the BN particles are bonded via a porous BN in the same manner as in Example A10 except that the hydrostatic pressure is changed to 2.9 MPa. A sex filler was prepared, and a columnar composite material in which the thermally conductive filler was dispersed in the cured epoxy resin was prepared.

<Electron microscope observation of compression sintered body>
A cross section for electron microscope observation was cut out from the compression sintered body produced in Example A5, and the cross section was mechanically polished by ^{a polishing machine (“Minimet TM 1000” manufactured by Buehler) using a diamond suspension and colloidal silica as abrasives.} After that, oxygen plasma etching was performed at 120 W for 3 minutes using a small plasma device (“PR300” manufactured by Yamato Scientific Co., Ltd.), and further, osmium coating was performed using an osmium coater. The obtained cross section for observation was observed using a scanning electron microscope (“NB-5000” manufactured by Hitachi High-Technologies Corporation). The result is shown in FIG. In FIG. 1, the light gray part 1 is an AlN particle, the gray part 2 is a BN particle, the dark gray part 3 is a porous BN, and the black part 4 is a region corresponding to a void of the porous BN phase. From the results shown in FIG. 1, it was found that in the compressed sintered body, the BN particles were bonded to at least a part of the surface of the AlN particles via the porous BN.

<Electron microscope observation of thermally conductive filler>
The thermally conductive filler obtained in Example A3 was observed using a scanning electron microscope (“NB-5000” manufactured by Hitachi High-Technologies Corporation). FIG. 2A shows a secondary electron image of the heat conductive filler, and FIG. 2B shows a backscattered electron image of the heat conductive filler. The bright part of FIG. 2A is BN, and the bright part of FIG. 2B is AlN. From the results shown in FIGS. 2A and 2B, it was found that the inside of the particles was formed of AlN, the surface was formed of BN, and the surface of the AlN particles was coated with BN particles.

<Elemental distribution of thermally conductive filler>
The thermally conductive filler obtained in Example A4 was observed using a scanning electron microscope (“NB-5000” manufactured by Hitachi High-Technologies Corporation) equipped with an energy dispersive X-ray analyzer. A 25 μm × 20 μm field of view (FIG. 3) was randomly extracted from the obtained SEM image, and boron (B), carbon (C), nitrogen (N), oxygen (O), and aluminum (Al) in this field of view were extracted. The distribution of each element of was observed. As a result, it was confirmed that B was also present in the region where Al was present, and it was found that the surface of the AlN particles was covered with the BN particles. In addition, one measurement point (point A in FIG. 3) was randomly extracted from the region where Al was present, and the elemental composition was analyzed. The results are shown in Table 1.

From the results shown in Table 1, it was confirmed that the surface of the AlN particles was coated with the BN particles.

<Structural analysis of porous boron nitride>
Average particles which are isotropic high thermal conductive particles are placed in a polyethylene pot so that the composition ratio of the obtained compression sintered body is AlN particles / BN particles / porous BN = 50 vol% / 0 vol% / 50 vol%. The AlN powder having a diameter of 5 μm (“High thermal conductivity AlN filler FAN-f05” manufactured by Furukawa Denshi Co., Ltd.) and 4.95 g of the melamine borate complex obtained in Synthesis Example 1 were added, and further, zirconia balls (3 mm diameter) were added. 500 g and 165 g of acetone were added and mixed by a ball mill at 400 rpm for 12 hours. Then, the zirconia balls were removed by filtration, and the acetone was completely removed by evaporation and vacuum drying. The obtained mixture was compressed under hydrostatic pressure of 294 MPa, heated at 380 ° C. for 1 hour in a nitrogen atmosphere, and further fired at 1800 ° C. for 1 hour to obtain a compressed sintered body. After cooling the compression sintered body to room temperature, it is milled for 60 seconds to conduct heat conduction containing particles in which at least a part of the surface of the AlN particles is coated with porous BN (porous BN-coated AlN particles). A sex filler was obtained.

The X-ray diffraction pattern of this thermally conductive filler was measured. The result is shown in FIG. As shown in FIG. 4, in the obtained X-ray diffraction pattern, there were a diffraction peak derived from AlN particles and a diffraction peak derived from porous BN. The diffraction peak derived from the porous BN is the diffraction peak (half width 1.2 °) on the 002 surface of the wide BN, and the porous BN formed by using the borate melamine complex has a disordered layer structure. It turned out to have.

<Diameter distribution of thermally conductive filler>
The thermally conductive fillers obtained in Examples A6 to A9 and Comparative Examples A8 to A9 are dispersed in ethanol, and a laser diffraction / scattering particle size distribution measuring device (“MT3300EX” manufactured by Microtrac Bell Co., Ltd.) is used. , The volume-based particle size distribution of the thermally conductive filler was measured by the laser diffraction / scattering method. The results are shown in FIGS. 5 and 6. As shown in FIGS. 5 and 6, when the BN phase consists only of porous BN (Comparative Example A8, Comparative Example A9), the thermally conductive filler is pulverized to the same size as the raw material AlN powder. On the other hand, when the BN phase is composed of BN particles and porous BN (Examples A7 to A8, Examples A6 and A9), the particle size of the thermally conductive filler is the same as that of the raw material AlN powder. It turned out to be larger than that. This is because when the BN phase consists of BN particles and porous BN (Examples A7 to A8, Examples A6 and A9), the BN particles are bonded to the AlN particles via the porous BN, whereby the machine It is considered that the heat conductive filler contains a large amount of composite particles of AlN particles and BN particles, which have improved target strength and high resistance to the impact force of pulverization.

<Porosity of boron nitride phase>
A cross section for electron microscope observation was cut out from the compression sintered bodies prepared in Examples and Comparative Examples, and 20 measurement regions (60 μm in length and 40 μm in width) randomly selected in this cross section were covered with a diamond suspension as an abrasive. After mechanical polishing with a polishing machine ("Minimet ^TM 1000" manufactured by Buehler) using colloidal silica, oxygen plasma etching at 120 W for 3 minutes using a small plasma device ("PR300" manufactured by Yamato Scientific Co., Ltd.) is performed. Then, an osmium coating was applied using an osmium coater. The obtained cross section for measurement was observed using a scanning electron microscope (“NB-5000” manufactured by Hitachi High-Technologies Corporation). FIG. 7 shows a scanning electron micrograph (SEM image) of the compression sintered body produced in Example A4. In FIG. 7, the light gray portion 5 is an AlN particle, the gray portion 6 is a BN phase, the black portion 7 is a void in the BN phase, and the black portion 8 is a region corresponding to a void outside the BN phase.

In the obtained SEM image, the total area of the region corresponding to the BN phase (gray portion 6) and the total area of the region corresponding to the void in the BN phase (black portion 7) were obtained, and the following formula:
Porosity of the BN phase [vol%] = total area of the region corresponding to the void in the BN phase / {total area of the region corresponding to the void in the BN phase + total area of the region corresponding to the BN phase} × 100
The porosity of the BN phase in each measurement region was calculated, and the average value of the porosity of the BN phase in the 20 measurement regions was obtained. The results are shown in Table 2.

<Ratio of AlN / BN composite particles>
The thermally conductive fillers obtained in Examples and Comparative Examples were observed using a scanning electron microscope (“NB-5000” manufactured by Hitachi High-Technologies Corporation). 8 and 9 show scanning electron micrographs (SEM images) of the thermally conductive fillers obtained in Example A4 and Comparative Example A6, respectively.

In the obtained SEM image, based on the brightness and shape
(I) AlN particles (ii) AlN particles (AlN / BN composite particles) in which at least a part of the surface is coated with BN particles.
, The number of (i) AlN particles and the number of (ii) AlN / BN composite particles in the visual field are determined, respectively, and the ratio of the AlN particles coated with the BN particles among all the AlN particles in the visual field. {(Ii) / [(i) + (ii)]} was calculated. This ratio was calculated for 10 fields of view, and the average value was calculated. The results are shown in Table 2.

<Thermal conductivity of composite materials>
As shown in FIG. 10, a sample 12 for measuring thermal conductivity (thickness in the z-axis direction: 3 mm, diameter: 14 mmφ) was cut out from the columnar composite material 11 obtained in Examples and Comparative Examples, and the obtained sample was obtained. The surface of the was blackened with a black spray. The heat diffusion rate in the direction parallel to the compression direction (z-axis direction) was measured using a xenon flash analyzer (“LFA 447 NanoFlash” manufactured by NETZSCH) with the thickness direction (z-axis direction) of this sample as the heat flow direction.

Further, the specific heat of the sample was measured by the DSC method using a thermal vibration type differential scanning calorimetry device (manufactured by TA Instruments). Further, the density of the sample was determined by an underwater substitution method (Archimedes method). From these results, the following formula:
Thermal conductivity (W / (m · K)) = specific heat (J / (kg · K)) x density (kg / m ³ ) x thermal diffusivity (m ² / sec)
The thermal conductivity in the direction parallel to the compression direction (z-axis direction) was obtained. The results are shown in Table 2.

As is clear from the results shown in Table 2, when a mixture of AlN powder, BN powder and melamine borate complex is compression-molded under hydrostatic pressure of 20 MPa or more and then fired (Examples A1 to A13). , It was found that a compression sintered body having a porosity of 10 to 50 vol% in the BN phase composed of BN particles and porous BN can be obtained. Further, it was found that by pulverizing this compression sintered body, a thermally conductive filler containing 40% or more of AlN / BN composite particles on a number basis can be obtained.

On the other hand, when the AlN powder and the BN powder were simply mixed without using the melamine borate complex (Comparative Example A5), the content of the AlN / BN composite particles in the obtained thermally conductive filler was 0 vol%. It was found that AlN / BN composite particles were not formed.

Further, in the case of firing without compression molding (Comparative Example A6) or in the case of compression molding under hydrostatic pressure of less than 20 MPa and then firing (Comparative Examples A10 to A11), the BN in the obtained sintered body. The porosity of the BN phase consisting of particles and porous BN was 31 vol%, but the content of AlN / BN composite particles in the thermally conductive filler obtained by crushing this compression sintered body was less than 40 vol%. Met. This is because when the hydrostatic pressure is less than 20 MPa, the BN particles are not bonded to the surface of the AlN particles with a high bonding force via the porous BN, so that the BN particles are transferred to the surface of the AlN particles due to the impact force of pulverization. It is probable that it was peeled off from.

Further, as is clear from the results shown in Table 2, the composite material (Examples A1 to A13) containing a heat conductive filler containing 40% or more of AlN / BN composite particles on a number basis is used as the heat conductive filler. Composite materials containing only AlN particles (Comparative Examples A1, A3, A7), composite materials containing only AN particles whose surface is at least partially coated with porous BN as a heat conductive filler (Comparative Examples A2, A4, It was found that A8, A9) are superior in thermal conductivity as compared with the composite material (Comparative Example A5) containing only mixed particles of AlN particles and BN particles as the thermally conductive filler.

Further, the composite material (Examples A1 to A13) containing a heat conductive filler containing 40% or more of AlN / BN composite particles on a number basis is a heat conductive filler having an AlN / BN composite particle content of less than 40 vol%. It was found that the thermal conductivity was excellent as compared with the composite material containing (Comparative Examples A6, A10 to A11).

Further, when the thermal conductivity of the composite materials obtained in Examples A10, A12 to A13 and Comparative Example A11 was plotted against the hydrostatic pressure, as shown in FIG. 11, it was 20 MPa or more (preferably 80 MPa or more). It was found that a composite material having excellent thermal conductivity can be obtained by using a thermally conductive filler obtained by pulverizing a compression sintered body produced by compression molding under hydrostatic pressure.

(Example B1)
First, the composition ratio of the obtained compression sintered body is such that aluminum nitride particles (AlN particles) / boron nitride particles (BN particles) / porous boron nitride (porous BN) = 70 vol% / 15 vol% / 15 vol%. , AlN powder (“High thermal conductivity AlN filler FAN-f05” manufactured by Furukawa Electronics Co., Ltd., average particle diameter 5 μm, thermal conductivity 170 W / mK), 22.8 g, in a polyethylene pot. 3.40 g of non-porous hexagonal BN powder (“3M ^TM Boron Nitride Cooling Filler Platelets001” manufactured by 3M, average particle size 1 μm) and 17.01 g of the melamine borate complex obtained in Synthesis Example 1 were added, and further. , 500 g of zirconia balls (3 mm diameter) and 165 g of acetone were added and mixed by a ball mill under the condition of 400 rpm for 12 hours. Then, the zirconia balls were removed by filtration, and the acetone was completely removed by evaporation and vacuum drying. The obtained mixture was compressed under hydrostatic pressure of 294 MPa and then fired at 1800 ° C. for 1 hour in a nitrogen atmosphere to obtain a compressed sintered body. After cooling this compression sintered body to room temperature, the porosity of the boron nitride phase was determined according to the above method. The results are shown in Table 3.

Next, the obtained compression sintered body was milled for 60 seconds, and coarse particles were obtained through a sieve having a mesh size of 53 μm. The coarse particles are classified to recover particles having a size of 8 μm or less to obtain a thermally conductive filler containing composite particles (AlN / BN composite particles) in which the AlN particles and the BN particles are bonded via a porous BN. It was. According to the above method, the ratio of AlN / BN composite particles in the thermally conductive filler was determined. Further, according to the above method, the volume-based particle size distribution of the thermally conductive filler was measured, and the maximum particle size and the average particle size were determined. These results are shown in Table 3.

Next, 10 g of the thermally conductive filler was dispersed in 100 ml of toluene, and 1 ml of hexamethyldisilazane (HMDS) was further added, and then the container was sealed and heated at 50 ° C. for 5 hours with occasional shaking. Then, centrifugation and toluene washing were repeated twice, and freeze-drying was performed using benzene to obtain a thermally conductive filler whose surface was methylated with HMDS.

Next, 500 mg of the thermally conductive filler whose surface was methylated with HMDS and 253 mg of silicone oil (“SRX310” manufactured by Toray Dow Corning Co., Ltd.) were mixed, and the obtained mixture was used as a rotation / revolution mixer (stock). A grease composition was obtained by stirring at 1200 rpm for 2 minutes and further at 2000 rpm for 2 minutes using "Awatori Rentaro ARV-310" manufactured by Shinky Co., Ltd.

(Example B2)
A thermally conductive filler whose surface was methylated with HMDS was prepared in the same manner as in Example B1. The heat conductive filler 500 mg whose surface is methylated with HMDS and 5 mg of spherical silica nanoparticles (“Shin-Etsu Silicone QSB-170” manufactured by Shin-Etsu Chemical Co., Ltd., average particle size: 170 nm) are dry-mixed to obtain the heat conduction. Spherical silica nanoparticles were adsorbed on the surface of the sex filler. The thermally conductive filler in which spherical silica nanoparticles are adsorbed on the surface is mixed with 253 mg of silicone oil (“SRX310” manufactured by Toray Dow Corning Co., Ltd.), and the obtained mixture is stirred and greased in the same manner as in Example B1. The composition was obtained.

(Example B3)
The AlN powder 22.8 g, the BN powder 1.98 g, and the boric acid so that the composition ratio of the obtained compression sintered body is AlN particles / BN particles / porous BN = 80 vol% / 10 vol% / 10 vol%. A compression molded product was prepared in the same manner as in Example B1 except that 9.98 g of the melamine complex was mixed, and further, composite particles (AlN / BN composite) in which the AlN particles and the BN particles were bonded via a porous BN. A thermally conductive filler containing particles) was prepared. In the same manner as in Example B1, the porosity of the boron nitride phase, the ratio of AlN / BN composite particles in the thermally conductive filler, the maximum particle diameter and the average particle diameter of the thermally conductive filler were determined. These results are shown in Table 3. Further, in the same manner as in Example B1, the surface of the obtained thermally conductive filler was methylated with HMDS.

Further, instead of the AlN powder having an average particle diameter of 5 μm (“High thermal conductivity AlN filler FAN-f05” manufactured by Furukawa Electronics Co., Ltd.), AlN powder having an average particle diameter of 1 μm, which is isotropic high thermal conductive particles (stock). Using "High Purity Aluminum Nitride Powder / Granule E Grade" manufactured by Tokuyama Co., Ltd., thermal conductivity 180 W / mK), the composition ratio of the obtained compression sintered body is AlN particles / BN particles / porous BN = 80 vol% / 10 vol%. A compression molded product was prepared in the same manner as in Example B1 except that 22.8 g of the AlN powder, 1.98 g of the BN powder, and 9.98 g of the melamine borate complex were mixed so as to be / 10 vol%. , A thermally conductive filler containing composite particles (AlN / BN composite particles) in which the AlN particles and the BN particles are bonded via a porous BN was prepared. In the same manner as in Example B1, the porosity of the boron nitride phase, the ratio of AlN / BN composite particles in the thermally conductive filler, the maximum particle diameter and the average particle diameter of the thermally conductive filler were determined. These results are shown in Table 3. Further, in the same manner as in Example B1, the surface of the obtained thermally conductive filler was methylated with HMDS.

Next, 450 mg of the thermally conductive filler having an average particle diameter of 2.6 μm methylated with HMDS on the surface, 50 mg of the thermally conductive filler having an average particle diameter of 0.9 μm methylated with HMDS on the surface, and true. 5 mg of spherical silica nanoparticles (“Shinetsu Silicone QSB-170” manufactured by Shinetsu Chemical Industry Co., Ltd., average particle diameter: 170 nm) were dry-mixed, and spherical silica nanoparticles were adsorbed on the surfaces of the two types of thermally conductive fillers. .. The above two types of thermally conductive fillers in which spherical silica nanoparticles are adsorbed on the surface are mixed with 245 mg of silicone oil (“SRX310” manufactured by Toray Dow Corning Co., Ltd.), and the obtained mixture is stirred in the same manner as in Example B1. To obtain a grease composition.

(Example B4)
The amount of the thermally conductive filler having an average particle diameter of 2.6 μm methylated with HMDS on the surface was 400 mg, and the amount of the thermally conductive filler having an average particle diameter of 0.9 μm methylated with HMDS on the surface was adjusted to 400 mg. A grease composition was obtained in the same manner as in Example B3 except that the blending amount was changed to 100 mg.

(Example B5)
Similar to Example B3, except that 1 ml of a titanate-based coupling agent (“Plenact TTS” manufactured by Ajinomoto Fine-Techno Co., Ltd.) was used instead of hexamethyldisilazane (HMDS), the above-mentioned product having an average particle size of 2.6 μm. The surfaces of the thermally conductive filler and the thermally conductive filler having an average particle size of 0.9 μm were alkylated, respectively.

Next, 400 mg of the thermally conductive filler having an average particle size of 2.6 μm alkylated with a titanate-based coupling agent on the surface and 0.9 μm having an average particle size alkylated with a titanate-based coupling agent on the surface. 100 mg of the heat conductive filler and 5 mg of true spherical silica nanoparticles (“Shinetsu Silicone QSB-170” manufactured by Shinetsu Chemical Industry Co., Ltd., average particle size: 170 nm) are dry-mixed on the surface of the two types of heat conductive fillers. Spherical silica nanoparticles were adsorbed. The above two types of thermally conductive fillers in which spherical silica nanoparticles are adsorbed on the surface are mixed with 245 mg of silicone oil (“SRX310” manufactured by Toray Dow Corning Co., Ltd.), and the obtained mixture is stirred in the same manner as in Example B1. To obtain a grease composition.

(Example B6)
In the same manner as in Example B1, a thermally conductive filler containing composite particles (AlN / BN composite particles) in which the AlN particles and the BN particles were bonded via a porous BN was prepared. 500 mg of this thermally conductive filler and 253 mg of silicone oil (“SRX310” manufactured by Toray Dow Corning Co., Ltd.) were mixed, and the obtained mixture was stirred in the same manner as in Example B1 to obtain a grease composition.

(Comparative Example B1)
Similar to Example B3, the average particle size was 2. except that 1 ml of an aluminate-based coupling agent (“Plenact AL-M” manufactured by Ajinomoto Fine-Techno Co., Ltd.) was used instead of hexamethyldisilazane (HMDS). When the surfaces of the heat conductive filler of 6 μm and the heat conductive filler having an average particle diameter of 0.9 μm were treated, the particles of any of the heat conductive fillers aggregated and could not be isolated. Therefore, the heat conductive filler having an average particle diameter of 2.6 μm whose surface is treated with an aluminate-based coupling agent is 450 mg, and the surface is treated with an aluminate-based coupling agent and has an average particle diameter of 0.9 μm. The two types of dispersion after the second toluene cleaning are mixed so that the heat conductive filler is 50 mg, and further, spherical silica nanoparticles (“Shin-Etsu Silicone QSB-170” manufactured by Shin-Etsu Chemical Co., Ltd., average particles). After mixing 5 mg (diameter: 170 nm) and 245 mg of silicone oil (“SRX310” manufactured by Toray Dow Corning Co., Ltd.), toluene was removed by vacuum drying to prepare a grease composition.

<Thermal resistance of grease composition>
The grease composition (about 4 μl) obtained in Examples and Comparative Examples was sandwiched between ceramic plates having a diameter of 14 mm and a thickness of 1 mm to prepare a laminated plate, and xenon was applied to the laminated plate at a pressure of 3 MPa. The thermal diffusivity of the laminated board was measured using a flash analyzer (“LFA447 NanoFlush” manufactured by NETZSCH). Moreover, the thickness of the laminated board was measured using a micrometer. The thermal diffusivity and thickness of the obtained laminated plate, the thermal diffusivity, density, specific heat and thickness of the ceramic plate, and the density and specific heat of the grease composition were used to calculate the thermal resistance of the grease composition. .. The results are shown in Table 4.

As shown in Table 4, the surface of the thermally conductive filler containing the composite particles (AlN / BN composite particles) in which the AlN particles and the BN particles are bonded via a porous BN is coated with a silazane-based coupling agent (AlN / BN composite particles). When alkylated with HMDS (Examples B1 to B4) or titanate-based coupling agent (Example B5), the thermal resistance of the grease composition is higher than that when no surface treatment is applied (Example B6). Was found to be lower (ie, higher thermal conductivity). This is done by treating the surface of the thermally conductive filler with a silazane-based coupling agent or a titanate-based coupling agent to treat the BN particles in the thermally conductive filler with the silazane-based coupling agent or the titanate-based coupling agent. B-OC bond or B-O-Ti bond is formed by an appropriate reaction with and, and the surface of the thermally conductive filler is alkylated, so that the aggregation of the thermally conductive filler is suppressed. It is considered that this is because the fluidity of the grease composition has improved.

On the other hand, when the surface of the heat conductive filler is treated with an aluminate-based coupling agent (Comparative Example B1), the thermal resistance of the grease composition is higher than that when the surface treatment is not performed (Example B6). Was found to be higher (ie, lower thermal conductivity). This is because when the surface of the thermally conductive filler is treated with an aluminate-based coupling agent, the aluminum-based coupling is compared with the reaction between the BN particles in the thermally conductive filler and the aluminate-based coupling agent. The hydrolysis reaction of the agent was rapid, the BO-Al bond was not sufficiently formed, and the surface of the thermally conductive filler was not alkylated, so that the aggregation of the thermally conductive filler was not sufficiently suppressed. It is considered that this is because the fluidity of the grease composition has decreased.

Further, as shown in Table 4, the grease composition containing the thermally conductive filler whose surface is alkylated and the spherical nanoparticles (Example B2) is a grease composition containing no spherical nanoparticles. It showed the same thermal resistance as (Example B1). From this result, it was confirmed that the effect of reducing the thermal resistance was maintained even when the spherical nanoparticles were added.

Further, the grease compositions (Examples B3 to B4) containing the two types of the thermally conductive filler having an alkylated surface and different average particle diameters are one type of the thermally conductive filler having an alkylated surface. It was found that the thermal resistance was reduced (that is, the thermal conductivity was increased) as compared with the grease composition containing (Example B2).

Further, the grease composition (Example B4) containing the heat conductive filler whose surface is alkylated with a silazane-based coupling agent (HMDS) has the heat conductivity whose surface is alkylated with a titanate-based coupling agent. It was found that the thermal resistance was reduced (that is, the thermal conductivity was increased) as compared with the grease composition containing the sex filler (Example B5).

From the above results, a compression sintered body in which the porosity of the BN phase is within a predetermined range by compression-molding a mixture of AlN powder, BN powder, and borate complex under a predetermined hydrostatic pressure and then firing. By crushing this compression sintered body, a thermally conductive filler containing a large amount of a composite material in which the BN particles are bonded to the surface of the AlN particles with a high bonding force via the porous BN can be obtained. I understood it. Further, it was found that a composite material having excellent thermal conductivity can be obtained by using such a thermally conductive filler. Further, by alkylating the surface of the thermally conductive filler, aggregation of the thermally conductive filler in the matrix is suppressed and the fluidity of the composite material is improved, so that the composite material having further excellent thermal conductivity is further improved. Was found to be obtained.

As described above, according to the present invention, it is possible to obtain a thermally conductive filler capable of imparting high thermal conductivity to the matrix and a composite material containing the same. Therefore, since the composite material of the present invention has excellent thermal conductivity, it is useful as, for example, a heat radiating material, a heater material, a grease composition, etc. for automobiles, electronic elements, and various electric products.

1: Aluminum nitride particles 2: Boron nitride particles 3: Porous boron nitride 4: Voids in the porous boron nitride phase 5: Aluminum nitride particles 6: Porous boron nitride phase 7: Voids in the boron nitride phase 8: Boron nitride phase Outer void 10: Composite material 11: Sample for thermal conductivity measurement

Claims (12)

Isotropic high thermal conductivity particles having an average particle size of 0.2 to 100 μm and a thermal conductivity of 20 W / mK or more, and an average of 0.01 to 5 times the average particle size of the high thermal conductive particles. It contains non-porous hexagonal boron nitride particles having a particle size and porous boron nitride, and the porosity of the hexagonal boron nitride particles and the boron nitride phase formed by the porous boron nitride is 10 to 50 vol. Consists of crushed sintered body, which is%
Of all the high thermal conductive particles in the ground product, 40% or more of the particles are made of the hexagonal boron nitride via the porous boron nitride on at least a part of the surface of the high thermal conductive particles. A thermally conductive filler characterized by forming composite particles in which particles are bonded. That the high thermal conductive particles are at least one kind of particles selected from the group consisting of aluminum nitride particles, silicon nitride particles, cubic boron nitride particles, aluminum oxide particles, zinc oxide particles, silicon carbide particles, and diamond particles. The thermally conductive filler according to claim 1. The thermally conductive filler according to claim 1 or 2, wherein the porous boron nitride has a disordered layer structure. The thermally conductive filler according to any one of claims 1 to 3, wherein the surface is alkylated. A thermally conductive composite material comprising a matrix and the thermally conductive filler according to any one of claims 1 to 4 dispersed in the matrix. The heat conductive composite material according to claim 5, wherein the heat conductive filler has a bimodal or higher particle size distribution. The heat conductive composite material according to claim 5 or 6, wherein the matrix is an oil and the heat conductive composite material is a grease composition. The seventh aspect of claim 7, wherein the oil is at least one selected from the group consisting of silicone oils, modified silicone oils, fluoroether oils, mineral oils, animal and vegetable natural oils, paraffins and synthetic oils. Thermally conductive composite material. An isotropic high thermal conductive powder having an average particle size of 0.2 to 100 μm and a thermal conductivity of 20 W / mK or more, and an average of 0.01 to 5 times the average particle size of the high thermal conductive powder. The first step of compression-molding a mixture of a non-porous hexagonal boron nitride powder having a particle size and a boric acid complex at a pressure of 20 MPa or more, and the compression-molded body obtained in the first step are inert. The second step of firing in a gas atmosphere and the compression sintered body obtained in the second step are crushed and hexagonal nitrided via porous boron nitride on at least a part of the surface of the highly thermally conductive particles. A method for producing a thermally conductive filler, which comprises a third step of obtaining a thermally conductive filler containing composite particles to which boron particles are bonded. The ninth aspect of claim 9, further comprising a fourth step of reacting the thermally conductive filler with a silazane-based coupling agent or a titanate-based coupling agent to alkylate the surface of the thermally conductive filler. How to make a thermally conductive filler. The method for producing a thermally conductive filler according to claim 9 or 10, wherein in the first step, compression molding is performed under hydrostatic pressure. The thermally conductive filler according to any one of claims 9 to 11, wherein the boric acid complex is at least one selected from the group consisting of a borate melamine complex and a borate urea complex. Manufacturing method.

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