JP7435294B2 - High thermal conductivity grease composition - Google Patents

Description

The present invention relates to a highly thermally conductive grease composition, and more particularly to a highly thermally conductive grease composition containing a thermally conductive filler.

Grease compositions in which thermally conductive particles are dispersed in matrix oil have excellent thermal conductivity, and can be used as heat conductive materials to conduct heat from electronic components that generate heat to cooling components, and as heat dissipation materials to remove heat. Useful.

As such a grease composition, for example, Japanese Patent Laid-Open No. 2000-169873 (Patent Document 1) discloses aluminum nitride powder α having an average particle size of 0.5 to 5 μm and aluminum nitride powder having an average particle size of 6 to 20 μm. An aluminum nitride powder mixture in which two types of aluminum nitride powder (powder β) have an average particle size of 1 to 10 μm after mixing, an organopolysiloxane, and an oxidized mixture having an average particle size of 0.5 to 100 μm A silicone grease composition containing at least one inorganic compound powder selected from the group consisting of zinc, alumina, boron nitride, and silicon carbide is disclosed.

Furthermore, Japanese Patent Application Publication No. 2009-185212 (Patent Document 2) describes a thermally conductive material (A) with an average particle size of 15 to 30 μm, and a thermally conductive material (A) with an average particle size of 1.0 to 5 μm. (B), a thermally conductive material (C) having an average particle diameter of 0.1 to 0.9 μm, and a silicone oil modified with an alkyl group, the thermally conductive material (A), ( A thermally conductive grease is disclosed in which B) and (C) are at least one selected from the group consisting of metallic aluminum, aluminum nitride, and zinc oxide.

Furthermore, JP 2010-242022A (Patent Document 3) discloses that (A) organopolysiloxane, and (B) at least one of alumina powder and aluminum nitride powder having an average particle size of 5 to 20 μm. , (C) a thermally conductive silicone grease composition containing at least one of zinc oxide powder and aluminum hydroxide powder having an average particle size of 0.5 to 5 μm.

Furthermore, JP 2019-43804 A (Patent Document 4) discloses that a mixture of boron nitride powder and aluminum nitride powder is fired while being compressed to produce a compressed fired body, and this compressed fired body is pulverized. containing boron nitride particles and aluminum nitride particles obtained by the above method, in which 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. A thermally conductive composite material (grease composition) is disclosed in which a thermally conductive filler including formed composite particles is dispersed in a matrix oil.

However, the greases described in Patent Documents 1 to 4 do not necessarily have sufficiently high thermal conductivity, and there is still room for improvement.

Japanese Patent Application Publication No. 2000-169873 Japanese Patent Application Publication No. 2009-185212 JP2010-242022A JP 2019-43804 Publication

The present invention has been made in view of the problems of the prior art described above, and an object of the present invention is to provide a grease composition with excellent thermal conductivity.

As a result of intensive research to achieve the above object, the present inventors found that after compression molding a mixture of a highly thermally conductive powder, a non-porous hexagonal boron nitride powder, and a boric acid complex at a specific pressure, Composite particles in which hexagonal boron nitride particles are bonded to at least part of the surface of highly thermally conductive particles via porous boron nitride, which are obtained by firing and pulverizing the obtained compacted sintered body. It has been discovered that a grease composition with excellent thermal conductivity can be obtained by further dispersing zinc oxide particles in a grease composition in which a thermally conductive filler containing 40% or more is dispersed in a matrix oil, The present invention has now been completed.

That is, the high thermal conductive grease composition of the present invention comprises isotropic high thermal conductive particles having an average particle diameter of 0.2 to 100 μm and a thermal conductivity of 20 W/mK or more, and the high thermal conductive particles. contains non-porous hexagonal boron nitride particles having an average particle diameter of 0.01 to 5 times the average particle diameter of Consisting of a pulverized sintered body in which the porosity of the boron nitride phase formed is 10 to 50 vol%, 40% or more of the highly thermally conductive particles in the pulverized material are: Contains a thermally conductive filler, zinc oxide particles, and matrix oil forming composite particles in which the hexagonal boron nitride particles are bonded to at least a portion of the surface of the highly thermally conductive particles via the porous boron nitride. The thermally conductive filler and zinc oxide particles are dispersed in the matrix oil.

In the highly thermally conductive grease composition of the present invention, the highly thermally conductive particles are at least one selected from the group consisting of aluminum nitride particles, silicon nitride particles, cubic boron nitride particles, silicon carbide particles, and diamond particles. It is preferable that the filler is a particle, and it is preferable that the thermally conductive filler has a bimodal or more particle size distribution.

Further, in the highly thermally conductive grease composition of the present invention, the average particle diameter of the zinc oxide particles is preferably 0.1 to 1 μm, and the matrix oil is silicone oil, modified silicone oil, fluoroether oil. The oil is preferably at least one selected from the group consisting of , mineral oil, natural animal and vegetable oil, paraffin and synthetic oil.

Furthermore, the highly thermally conductive grease composition of the present invention preferably further contains true spherical nanoparticles.

The reason why the grease composition of the present invention has excellent thermal conductivity is not necessarily clear, but the inventors of the present invention speculate as follows. In other words, in a grease composition in which a thermally conductive filler is dispersed in a matrix oil, heat is transferred through the areas in contact with the filler particles, but highly thermally conductive particles such as aluminum nitride particles have a small internal thermal resistance. However, since they are generally hard particles, the particles do not deform when they come into contact with each other, resulting in a point contact with a small contact area, resulting in a large interparticle thermal resistance (interfacial thermal resistance).

Therefore, among highly thermally conductive particles, boron nitride particles are relatively soft particles, and the contact area is larger than that of point contacts, resulting in lower interparticle thermal resistance (interfacial thermal resistance). By using the high thermal conductivity particles and boron nitride particles together, the contact area was increased and the interparticle thermal resistance was reduced. However, the reduction in interparticle thermal resistance was not necessarily sufficient.

In addition, since zinc oxide particles have excellent thermal conductivity, in conventional grease compositions, by using the high thermal conductivity particles and zinc oxide particles together, many heat conduction paths are formed and heat is generated. It improved conductivity. However, since the interparticle thermal resistance (interfacial thermal resistance) between the highly thermally conductive particles and the zinc oxide particles is large, the thermal conductivity was not necessarily sufficient.

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

Furthermore, since the grease composition of the present invention contains zinc oxide particles having excellent thermal conductivity, many thermally conductive paths are formed by the zinc oxide particles. Furthermore, since the contact thermal resistance (interfacial thermal resistance) between boron nitride and zinc oxide is small, in the grease composition of the present invention, the interparticle heat between the zinc oxide particles and the hexagonal boron nitride particles is low. It is presumed that the resistance will also be reduced.

As described above, in the grease composition of the present invention, the interparticle thermal resistance between the high thermal conductive particles and the hexagonal boron nitride particles is further reduced, and the zinc oxide particles provide a large amount of heat conduction. It is presumed that the thermal conductivity is improved by the formation of a magnetic path and by the reduction in interparticle thermal resistance between the zinc oxide particles and the hexagonal boron nitride particles.

According to the present invention, it is possible to obtain a grease composition with excellent thermal conductivity.

Hereinafter, the present invention will be explained in detail based on its preferred embodiments.

The highly thermally conductive grease composition of the present invention contains a thermally conductive filler, zinc oxide particles, and matrix oil, and the thermally conductive filler and zinc oxide particles are dispersed in the matrix oil.

(thermal conductive filler)
The thermally conductive filler used in the present invention includes isotropic highly thermally conductive particles having an average particle diameter of 0.2 to 100 μm and a thermal conductivity of 20 W/mK or more, and an average of the highly thermally conductive particles. It contains non-porous hexagonal boron nitride particles having an average particle diameter of 0.01 to 5 times the particle diameter and porous boron nitride, and is formed by the hexagonal boron nitride particles and the porous boron nitride. It is made of a pulverized sintered body in which the porosity of the boron nitride phase is 10 to 50 vol%. Further, in this thermally conductive filler, 40% or more of all the highly thermally conductive particles in the pulverized material have the porous structure on at least a part of the surface of the highly thermally conductive particles. The hexagonal boron nitride particles are bonded together via 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 with a thermal conductivity of 20 W/mK or more, such as aluminum nitride particles, silicon nitride particles, cubic nitride particles, etc. Examples include boron particles, aluminum oxide particles, zinc oxide particles, silicon carbide particles, and diamond particles. These highly thermally conductive particles may be used alone or in combination of two or more. Furthermore, among these highly thermally conductive particles, sintering can form an interface in close contact with the hexagonal boron nitride particles, and 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. Note that the thermal conductivity in this specification is the thermal conductivity at room temperature (20° C.).

The average particle diameter of the highly thermally conductive particles is 0.2 to 100 μm. When the average particle diameter of the highly thermally conductive 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 highly thermally conductive particles increases in the resulting grease composition. Therefore, the overall thermal resistance increases. On the other hand, if the average particle diameter of the highly thermally conductive particles exceeds the upper limit, the dispersion uniformity and filling rate of the thermally conductive filler in the resulting grease composition will decrease, resulting in a decrease in thermal conductivity. Further, from the same viewpoint, the average particle diameter of the highly thermally conductive particles is preferably 0.3 to 95 μm, more preferably 0.5 to 90 μm, even more preferably 0.5 to 50 μm, and particularly 1 to 20 μm. preferable. In the present invention, the average particle diameter of the highly thermally conductive particles is determined by the average particle diameter of all the highly thermally conductive particles contained in the thermally conductive filler, that is, the particles that form a composite particle with the hexagonal boron nitride particles. This is the average particle diameter of all the high thermal conductive particles including the high thermal conductive particles and the high thermal conductive particles that do not form composite particles with the hexagonal boron nitride particles.

In addition, in this specification, "average particle diameter" refers to the average value of the particle diameter of 300 or more particles randomly selected by scanning electron microscopy (SEM) observation, etc., excluding catalog values related to raw material powder etc. means. Furthermore, if the particle is not spherical (having a circular cross section), a circumcircle of the particle (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 have excellent thermal conductivity. The average particle diameter of such hexagonal boron nitride particles is 0.01 to 5 times the average particle diameter of the high thermal conductivity particles used in combination. When the average particle diameter of the hexagonal boron nitride particles is less than the lower limit, in the resulting grease composition, there is a space between the hexagonal boron nitride particles and the high thermal conductivity particles, and between the hexagonal boron nitride particles and the zinc oxide described below. Since the number of grain boundaries between grains and between the hexagonal boron nitride grains increases, the overall thermal resistance increases. On the other hand, if the average particle diameter of the hexagonal boron nitride particles exceeds the upper limit, the dispersion uniformity and filling rate of the thermally conductive filler in the resulting grease composition will decrease, resulting in a decrease in thermal conductivity. Further, from the same viewpoint, the average particle diameter of the hexagonal boron nitride particles is preferably 0.03 to 3 times, and 0.05 to 1 times, the average particle diameter of the highly thermally conductive particles used in combination. More preferred. In addition, in the present invention, the average particle diameter of the hexagonal boron nitride particles is such that they form composite particles with all the hexagonal boron nitride particles contained in the thermally conductive filler, that is, the highly thermally conductive particles. This is the average particle diameter of all the hexagonal boron nitride particles, including the hexagonal boron nitride particles, the high thermal conductivity particles, and the hexagonal boron nitride particles that do not form composite particles.

Further, it is preferable that the hexagonal boron nitride particles have a graphitization index of 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 decreases, resulting in a decrease in the thermal conductivity of the resulting grease composition.

Furthermore, the high thermal conductivity particles and the hexagonal boron nitride particles have hydroxyl groups, carboxyl groups, ester groups, amide groups, amino groups, etc. on their surfaces in order to further improve their dispersibility in matrix oil. A functional group may be bonded.

The porous boron nitride according to the present invention binds the high thermal conductive particles and the hexagonal boron nitride particles with high bonding force in the sintered body according to the present invention and the thermally conductive filler used in the present invention. It is. In addition, if such porous boron nitride has too high orientation, it may be placed in a position that impedes heat conduction between the high thermal conductivity 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 that the particles have a turbostratic structure.

Further, in the porous boron nitride, the half width of the X-ray diffraction peak derived from the 002 plane is preferably 0.5 to 10°, more preferably 0.5 to 5°, and 0.5 to 10°. Particularly preferred is 5° to 2°. When the half-width of the X-ray diffraction peak derived from the 002 plane of porous boron nitride becomes less than the lower limit, the proportion of the turbostratic structure decreases, and the bond between the high thermal conductivity particles and the hexagonal boron nitride particles decreases. The strength and bonding force tend to decrease, and on the other hand, when the above upper limit is exceeded, the crystals are disordered due to the turbostratic structure, so that the thermal conductivity tends to decrease.

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

The thermally conductive filler used in 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 increases, and the thermal resistance between the particles is reduced. Further, it is possible to simultaneously improve the adhesion between the high thermal conductivity particles and the hexagonal boron nitride particles and improve 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, although the thermal conductivity of the boron nitride phase improves, the porous boron nitride is not preferentially ruptured when the sintered body is crushed. Composite particles in which the hexagonal boron nitride particles are bonded to at least a portion of the surface of the highly thermally conductive particles via the porous boron nitride are difficult to form, and the content of the composite particles in the resulting thermally conductive filler is It becomes less. On the other hand, if the porosity of the boron nitride phase exceeds the upper limit, the thermal conductivity of the boron nitride phase decreases, and therefore the thermal conductivity of the resulting grease composition also decreases. In addition, since the adhesion between the high thermal conductive particles and the hexagonal boron nitride particles decreases, the hexagonal boron nitride particles are likely to be detached from the surface of the high thermal conductive particles during the pulverization of the sintered body. In the thermally conductive filler, the content of composite particles in which the hexagonal boron nitride particles are bonded to at least a portion of the surface of the highly thermally conductive particles via the porous boron nitride is reduced. Further, from the same viewpoint, the porosity of the boron nitride phase is preferably 15 to 40 vol%.

Furthermore, in the thermally conductive filler used in the present invention, 40% or more of all the highly thermally conductive particles in the pulverized material are present on at least a portion of the surface of the highly thermally conductive particles. The hexagonal boron nitride particles are bonded to each other via the porous boron nitride to form composite particles. A thermally conductive filler in which 40% or more of all the highly thermally conductive particles form the composite particles has a small thermal resistance between particles, and the thermal conductivity of the resulting grease composition 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 particles, and the thermal conductivity of the resulting grease composition is reduced. From the viewpoint of further reducing the thermal resistance between particles in the thermally conductive filler and further improving the thermal conductivity of the obtained grease composition, particles that account for 50% or more of all the high thermally conductive particles on a number basis It is preferable that the particles form the composite particles, and it is more preferable that 55% or more of the particles form the composite particles. Note that the number of all high thermal conductive particles is determined by the number of high thermal conductive particles having the hexagonal boron nitride particles bonded to at least a portion of their surfaces, and the high thermal conductive particles having no hexagonal boron nitride particles bonding to at least a portion of their surfaces. It means the number of all the above-mentioned high thermal conductive particles including.

Furthermore, in the thermally conductive filler used in the present invention, the entire surface of the high thermally conductive particles in the composite particles does not necessarily have to be covered with the hexagonal boron nitride particles; Preferably, 40% or more of the surface is coated, more preferably 55% or more, and particularly preferably the entire surface is coated.

In the thermally conductive filler used in the present invention, the volume ratio of the high thermally conductive particles to the boron nitride phase (the phase formed by the hexagonal boron nitride particles and the porous boron nitride) : boron nitride phase) is not particularly limited, but is preferably 30:70 to 98:2, more preferably 40:60 to 90:10. If the volume ratio of the highly thermally conductive particles to the boron nitride phase is less than the lower limit, the effect of improving thermal conductivity by the highly thermally conductive particles will not be sufficiently obtained, and the thermal conductivity of the resulting grease composition will decrease. On the other hand, if the upper limit is exceeded, the number of contact interfaces with high thermal resistance involving the highly thermally conductive particles increases relatively, resulting in excellent thermal conductivity. There is a tendency that a grease composition having the following properties cannot be obtained.

Further, in the thermally conductive filler used in 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; :90 to 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 with low thermal resistance involving the hexagonal boron nitride particles is relatively reduced, resulting in excellent thermal conduction. On the other hand, if the upper limit is exceeded, the adhesion between the highly thermally conductive particles and the hexagonal boron nitride particles decreases. The hexagonal boron nitride particles are easily detached from the surface of the highly thermally conductive particles, and the content of the composite particles is reduced in the resulting thermally conductive filler, resulting in a grease composition having excellent thermal conductivity. There tends to be no.

Furthermore, the surface of the thermally conductive filler used in the present invention is preferably alkylated. This makes it possible to suppress the agglomeration of the thermally conductive filler in the matrix oil and improve the fluidity of the grease composition, resulting in a grease composition with even better thermal conductivity and even lower thermal resistance. It becomes possible to obtain things.

(Method for manufacturing thermally conductive filler)
Such a thermally conductive filler can be manufactured by the following method. That is, 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 0.01 to 5 times the average particle size of the high thermal conductive powder. A mixture of a non-porous hexagonal boron nitride powder having an average particle size of The body is fired at a temperature of 1800 to 2200°C in an inert gas atmosphere [second step], and the compressed sintered body obtained in the second step is pulverized [third step]. A thermally conductive filler containing composite particles in which hexagonal boron nitride particles are bonded to at least a portion of the surface of the conductive particles via porous boron nitride can be obtained.

Further, it is preferable that the surface of the thermally conductive filler thus obtained is reacted with a silazane coupling agent or a titanate coupling agent to alkylate the surface of the thermally conductive filler [fourth step] .

(First step)
In the first step, first, a mixture of high thermal conductivity powder, hexagonal boron nitride powder, and boric acid complex is prepared. The highly thermally conductive powder used here is a raw material powder that becomes the highly thermally conductive particles in the thermally conductive filler, and its average particle size is 0.2 to 100 μm, preferably 0.3 to 95 μm. It is more preferably 0.5 to 90 μm, even 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 the hexagonal boron nitride particles in the thermally conductive filler, and its average particle size is 0% of the average particle size of the highly thermally conductive powder used in combination. It is .01 to 5 times, preferably 0.03 to 3 times, and more preferably 0.05 to 1 times.

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

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

There is no particular restriction on the mixing ratio of the high thermal conductivity powder, the hexagonal boron nitride powder, and the boric acid complex, but in the resulting thermal conductive filler, the volume of the high thermal conductivity particles and the boron nitride phase It is preferable that the ratio and the volume ratio of the hexagonal boron nitride particles to the porous boron nitride fall within the above range.

Next, the mixture thus obtained is compression molded at a predetermined pressure. Thereby, it is possible to obtain a compression molded body in which the high thermal conductivity 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. If the pressure during compression molding is less than the lower limit, the high thermal conductivity particles and the hexagonal boron nitride particles will not be in close contact with each other through the boric acid complex, and the high thermal conductivity particles and the hexagonal boron nitride particles will It is difficult to form composite particles in which the particles are bonded with high bonding force through the porous boron nitride, and the thermal conductivity of the resulting thermally conductive filler and grease composition tends to be difficult to improve.

There are no particular limitations on the method of compression molding the mixture, but compression molding under hydrostatic pressure is preferred. As a result, pressure is uniformly applied to the mixture, and a compression molded article in an effective and tightly adhered state can be obtained. Moreover, by compression molding under hydrostatic pressure, 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 molding history, and is therefore undesirable in some cases.

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

Examples of the inert gas include nitrogen, rare gases (eg, 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. Further, the firing time is not particularly limited as long as the mixture is sufficiently sintered, but 0.5 to 6 hours is preferable, and 1 to 4 hours is more preferable.

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

There are no particular limitations on the method of pulverizing the compressed sintered body, and for example, pulverizing methods using various types of pulverizers (mills) or mortars, pulverizing methods using wet ball mills, dry ball mills, etc. can be adopted.

(Fourth step)
In the fourth step, the thermally conductive filler obtained in the third step is reacted with a silazane coupling agent or a titanate coupling agent. At this time, the hexagonal boron nitride particles in the thermally conductive filler react with the silazane coupling agent or the titanate coupling agent, so that the surface of the thermally conductive filler is alkylated and the matrix oil is Since agglomeration of the thermally conductive filler can be suppressed and the fluidity of the grease composition is improved, it is possible to obtain a grease composition with further reduced thermal resistance and even better thermal conductivity. becomes.

On the other hand, when the surface of the thermally conductive filler obtained in the third step is treated with a silane coupling agent or an aluminate coupling agent, hydrolysis of the silane coupling agent or aluminate coupling agent As the reaction progresses, the coupling agent gels, and the reaction between the hexagonal boron nitride particles in the thermally conductive filler and the silane coupling agent or aluminate coupling agent does not proceed, so the heat The surface of the conductive filler is not alkylated, and aggregation of the thermally conductive filler in the matrix oil cannot be suppressed, resulting in a decrease in fluidity of the grease composition. In addition, the presence of the gel increases the contact thermal resistance between the thermally conductive fillers. As a result, the grease composition does not have reduced thermal resistance or improved thermal conductivity.

Among the silazane coupling agent and the titanate coupling agent, the aggregation of the thermally conductive filler can be sufficiently suppressed, the fluidity of the grease composition is improved, and the thermal conductivity is improved due to the presence of gel. A silazane-based coupling agent is preferable from the viewpoint that the thermal resistance of the obtained grease composition is further reduced and the thermal conductivity thereof is further increased because the contact thermal resistance between the fillers does not increase.

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

The mixing ratio of the thermally conductive filler and the silazane coupling agent or titanate coupling agent is such that the amount of the silazane coupling agent or titanate coupling agent is 100 parts by mass of the thermally conductive filler. The amount is preferably 1 to 20 parts by weight, more preferably 5 to 10 parts by weight.

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

(zinc oxide particles)
The zinc oxide particles used in the present invention are particles with excellent thermal conductivity, and form many heat conduction paths in the grease composition of the present invention. Furthermore, since the zinc oxide particles have a small interparticle thermal resistance (interfacial thermal resistance) with the hexagonal boron nitride particles in the thermally conductive filler, the thermal conductivity of the resulting grease composition is improved. . On the other hand, when silver particles or alumina particles are used instead of zinc oxide particles, many thermal conductive paths are formed in the resulting grease composition, but these particles and the hexagonal paths in the thermally conductive filler are Since the interparticle thermal resistance (interfacial thermal resistance) between crystalline boron nitride particles is large, the thermal conductivity of the resulting grease composition is not sufficiently improved.

The average particle diameter of such zinc oxide particles is not particularly limited, but is preferably 0.1 to 1 μm, more preferably 0.2 to 1 μm, even more preferably 0.5 to 1 μm, and even more preferably 0.7 to 0. 9 μm is particularly preferred. When the average particle diameter of the zinc oxide particles is less than the lower limit, the number of grain boundaries between the hexagonal boron nitride particles and the zinc oxide particles and between the zinc oxide particles increases in the resulting grease composition, so that the overall Thermal resistance tends to increase, and on the other hand, when the upper limit is exceeded, the dispersion uniformity and filling rate of the zinc oxide particles in the resulting grease composition tend to decrease, leading to a decrease in thermal conductivity.

(matrix oil)
The matrix oil used in the present invention is not particularly limited as long as it can uniformly disperse the thermally conductive filler and the zinc oxide particles, but insulating oils are preferred, such as silicone oil and modified silicone oil. , fluoroether oil, mineral oil, animal and vegetable natural oil, paraffin, synthetic oil, etc., and silicone oil, modified silicone oil, paraffin, and synthetic oil having a boiling point of 200° C. or higher are preferred. These oils may be used alone or in combination of two or more.

(True spherical nanoparticles)
The grease composition of the present invention may contain true spherical nanoparticles from the viewpoint of promoting rolling between particles and reducing the viscosity of the grease composition. Moreover, such true spherical nanoparticles may be subjected to surface treatment. Note that even if the grease composition contains true spherical nanoparticles, the effect of reducing thermal resistance is maintained, and a grease composition with excellent thermal conductivity can be obtained.

As such true spherical nanoparticles, true spherical silica nanoparticles, surface-treated Preferably, spherical silica nanoparticles are coated with silica nanoparticles. Moreover, it is preferable that such true spherical nanoparticles are adsorbed on the surface of the thermally conductive filler. This improves dispersibility in the matrix oil and reduces interparticle friction, thereby reducing the viscosity of the grease composition.

In addition, the average particle diameter of such true spherical nanoparticles is determined from the viewpoint of uniformity of adsorption to the surface of the thermally conductive filler and avoidance of interfacial heat conduction inhibition by the true spherical nanoparticles. The particle diameter is preferably 1/2 or less times, more preferably 1/4 times or less, particularly preferably 1/5 times or less.

[Grease composition]
In the grease composition of the present invention, the thermally conductive filler, the zinc oxide particles, and, if necessary, true spherical nanoparticles are dispersed in the matrix oil.

In the grease composition of the present invention, the content of the thermally conductive filler is not particularly limited, but is preferably from 10 to 90 vol%, more preferably from 15 to 70 vol%, and more preferably from 15 to 70 vol%, based on the total amount of the grease composition. ~60 vol% is particularly preferred. When the content of the thermally conductive filler is less than the lower limit, a network structure of thermally conductive paths in which heat diffuses through the contact areas between the thermally conductive fillers in the grease composition is not sufficiently formed, and the resulting grease Thermal conductivity of the composition tends not to improve sufficiently, and on the other hand, if the content of the thermally conductive filler exceeds the upper limit, the frictional force between particles becomes too large and the fluidity of the grease composition decreases. Therefore, the thickness of the grease composition film cannot be reduced, and it tends to be difficult to reduce the thermal resistance.

Further, in the grease composition of the present invention, the content of the zinc oxide particles is not particularly limited, but is preferably 1 to 50 vol%, more preferably 5 to 40 vol%, based on the total amount of the grease composition. Particularly preferred is 5 to 30 vol%. When the content of the zinc oxide particles is less than the lower limit, a network structure of heat conduction paths in which heat diffuses through contact sites between the zinc oxide particles in the grease composition is not sufficiently formed, and the resulting grease composition On the other hand, if the content of the zinc oxide particles exceeds the upper limit, there is a tendency for the thermal conductivity of the zinc oxide particles to increase between the thermally conductive filler or between the thermally conductive filler and the zinc oxide particles in the grease composition. A network structure of heat conduction paths through which heat diffuses through contact sites with particles is not sufficiently formed, and the thermal conductivity of the resulting grease composition tends not to be sufficiently improved.

Further, in the grease composition of the present invention, the content of the matrix oil is not particularly limited, but it is preferably 10 to 90 vol%, more preferably 20 to 70 vol%, and 40 to 90 vol% based on the total amount of the grease composition. Particularly preferred is ~70 vol%. If the content of the matrix oil is less than the lower limit, the matrix oil will not be able to fill the voids between the particles, making it difficult for the particles to flow in the matrix oil, and the fluidity of the grease composition will decrease. On the other hand, if the content of the zinc oxide particles exceeds the upper limit, the grease composition tends to be thin and difficult to spread, and has a high thermal resistance. During this time, a network structure of heat conduction paths through which heat diffuses through the contact area between the thermally conductive filler and the zinc oxide particles is not sufficiently formed, and the thermal conductivity of the resulting grease composition is not sufficiently improved. There is a tendency.

Further, when the grease composition of the present invention contains the true spherical nanoparticles, the content thereof is preferably 0.1 to 20% by mass, and 0.5 to 10% by mass, based on the total amount of the grease composition. % is more preferable, and 0.5 to 5% by mass is particularly preferable. If the blending amount of the true spherical nanoparticles is less than the lower limit, the effect of blending the true spherical nanoparticles tends to be insufficient, while if it exceeds the upper limit, contact between the thermally conductive fillers may be inhibited. This tends to impede interfacial heat conduction and reduce the thermal conductivity of the grease composition.

Furthermore, in the grease composition of the present invention, it is preferable that the thermally conductive filler has a bimodal or more particle size distribution. This reduces the viscosity of the grease composition, improves the fluidity of the grease composition, and reduces the thickness of the grease composition, further reducing the thermal resistance of the grease composition and further improving its thermal conductivity. improves. Such thermally conductive fillers having a bimodal or more particle size distribution include, for example, a mixture of two or more types of thermally conductive fillers having different particle size distributions. The thermally conductive filler having a particle size distribution that is more than peak-like is not limited to this. In addition, in the thermally conductive filler having a bimodal or more particle size distribution, the viscosity of the resulting grease composition is reduced, and the fluidity of the grease composition is improved, thereby reducing the thickness of the grease composition. Therefore, from the viewpoint of further reducing the thermal resistance of the grease composition and further improving the thermal conductivity, the ratio of the thermally conductive filler that forms the peak with the largest particle size among the peaks in the particle size distribution is 70 to 70. It is preferably 95% by mass, more preferably 75 to 90% by mass.

Such a grease composition of the present invention can be produced, for example, as follows. That is, the grease composition of the present invention can be obtained by mixing the thermally conductive filler, the zinc oxide particles, and the matrix oil to form a uniform slurry. At this time, the mixing ratio of the thermally conductive filler, zinc oxide particles, and matrix oil is determined so that the content of the thermally conductive filler and zinc oxide particles in the resulting grease composition becomes the desired content. Further, the method of mixing the thermally conductive filler, zinc oxide particles, and matrix oil is not particularly limited, and any known mixing method may be used as appropriate.

Further, when the grease composition of the present invention includes the true spherical nanoparticles, the true spherical nanoparticles are mixed together with the thermally conductive filler, the zinc oxide particles, and the matrix oil when these are mixed. However, before mixing the thermally conductive filler, the zinc oxide particles, and the matrix oil, the spherical nanoparticles may be adsorbed to the thermally conductive filler by mixing with the thermally conductive filler in advance. It is preferable. Thereby, the true spherical nanoparticles are easily dispersed in the matrix oil, and the viscosity of the grease composition is reduced by reducing interparticle friction.

EXAMPLES 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 boric acid melamine complex and the method for preparing the thermally conductive filler used in Examples and Comparative Examples are shown below.

(Synthesis example 1)
24 g of boric acid was added to 800 ml of water heated to 95° C. and dissolved by stirring, and then 16 g of melamine was added and dissolved by stirring. The boric acid and melamine were allowed to react with each other by continuing heating and stirring for 10 minutes, and the resulting reaction solution was cooled with water and left at room temperature for 12 hours. Thereafter, the precipitated crystals were collected by filtration and vacuum dried at 40°C to obtain 31.5 g of a boric acid melamine complex.

(Preparation example 1)
First, the composition ratio of the obtained compressed sintered body was adjusted so that the composition ratio was aluminum nitride particles (AlN particles) / boron nitride particles (BN particles) / porous boron nitride (porous BN) = 70 vol% / 15 vol% / 15 vol%. In a polyethylene pot, 22.8 g of 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), which is isotropic high thermal conductivity particles, was placed in a polyethylene pot. 3.40 g of non-porous hexagonal BN powder (3M ^TM boron nitride cooling filler Platelets001, average particle size 1 μm) and 17.01 g of the boric acid melamine complex obtained in Synthesis Example 1 were added, and then , 500 g of zirconia balls (3 mm diameter) and 165 g of acetone were added and mixed in a ball mill at 400 rpm for 12 hours. Thereafter, the zirconia balls were removed by filtration, and the acetone was completely removed by evaporation and vacuum drying. The obtained mixture was compressed under a 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 compressed sintered body to room temperature, the porosity of the boron nitride phase was determined according to the following method. The results are shown in Table 1.

Next, the obtained compressed sintered body was milled for 60 seconds and passed through a sieve with an opening of 53 μm to obtain coarse particles. The coarse particles are classified to collect particles 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 porous BN. Ta. The proportion of AlN/BN composite particles in the thermally conductive filler was determined according to the following method. Further, the volume-based particle size distribution of the thermally conductive filler was measured according to the method described below, and the maximum particle size and average particle size were determined. These results are shown in Table 1.

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

<Porosity of boron nitride phase>
A cross section for electron microscopy observation was cut from the obtained compressed sintered body, and 20 measurement areas (60 μm in length and 40 μm in width) randomly extracted from this cross section were coated with diamond suspension and colloidal silica as abrasives. After mechanical polishing was performed using a polishing machine ("Minimet ^TM 1000" manufactured by Buehler), oxygen plasma etching was performed for 3 minutes at 120 W using a small plasma device ("PR300" manufactured by Yamato Scientific Co., Ltd.), and further, osmium Osmium coating was applied using a coater. The obtained measurement cross section was observed using a scanning electron microscope ("NB-5000" manufactured by Hitachi High-Technologies Corporation).

In the obtained SEM image, the total area of the region corresponding to the BN phase and the total area of the region corresponding to the voids in the BN phase are determined and calculated using the following formula:
Porosity of BN phase [vol%] = Total area of regions corresponding to voids in BN phase / {Total area of regions corresponding to voids in BN phase + Total area of regions corresponding to 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 determined.

<Ratio of AlN/BN composite particles>
The obtained thermally conductive filler was observed using a scanning electron microscope (“NB-5000” manufactured by Hitachi High-Technologies Corporation). In the obtained SEM image, based on the brightness and shape,
(i) AlN particles (ii) AlN particles whose surfaces are at least partially covered with BN particles (AlN/BN composite particles)
Extract (i) the number of AlN particles and (ii) the number of AlN/BN composite particles in the field of view, and calculate the proportion of AlN particles covered with BN particles among all AlN particles in the field of view. {(ii)/[(i)+(ii)]} was calculated. This ratio was determined for 10 visual fields, and the average value was determined.

<Particle size distribution of thermally conductive filler>
The obtained thermally conductive filler was dispersed in ethanol, and the thermally conductive filler was measured using a laser diffraction/scattering method using a laser diffraction/scattering particle size distribution measuring device ("MT3300EX" manufactured by Microtrac Bell Co., Ltd.). The particle size distribution on a volume basis was measured.

(Preparation example 2)
Instead of the AlN powder with an average particle size of 5 μm (“High Thermal Conductive AlN Filler FAN-f05” manufactured by Furukawa Electronics Co., Ltd.), we used AlN powder with an average particle size of 1 μm (Tokuyama Co., Ltd.), which is isotropic and highly thermally conductive particles. "High Purity Aluminum Nitride Powder/Granules E Grade" (thermal conductivity: 180 W/mK) manufactured by Manufacturer Co., Ltd. The composition ratio of the compressed sintered body obtained was AlN particles/BN particles/porous BN = 80 vol%/10 vol%/10 vol. A compression molded body was prepared in the same manner as in Preparation Example 1 except that 22.8 g of the AlN powder, 1.98 g of the BN powder, and 9.98 g of the boric acid melamine complex were mixed so that the A thermally conductive filler containing composite particles (AlN/BN composite particles) in which AlN particles and the BN particles were bonded via porous BN was prepared. In the same manner as in Preparation Example 1, the porosity of the boron nitride phase, the proportion of AlN/BN composite particles in the thermally conductive filler, and the maximum particle size and average particle size of the thermally conductive filler were determined. These results are shown in Table 1. Further, in the same manner as in Preparation Example 1, thermally conductive filler B whose surface was methylated with HMDS was obtained.

(Example 1)
362 mg of the thermally conductive filler A whose surface was methylated with HMDS obtained in Preparation Example 1, true spherical silica nanoparticles ("Shin-Etsu Silicone QSB-170" manufactured by Shin-Etsu Chemical Co., Ltd., average particle diameter: 170 nm)3. 6 mg, zinc oxide grease (Shin-Etsu Silicone G-776 manufactured by Shin-Etsu Chemical Co., Ltd., zinc oxide particle content: 40 vol%, average particle diameter of zinc oxide particles: 0.8 μm), 359 mg, and silicone oil (Toray Dow Corning) 177 mg of "SRX310" manufactured by Co., Ltd.) were mixed, and the resulting mixture was mixed at 1200 rpm for 2 minutes and then at 2000 rpm for 2 minutes using an autorotation/revolution mixer ("Awatori Rentaro ARV-310" manufactured by Thinky Co., Ltd.). A grease composition (thermally conductive filler A: 28 vol%, zinc oxide particles: 12 vol%) was obtained by stirring.

(Example 2)
289 mg of the thermally conductive filler A whose surface was methylated with HMDS obtained in Preparation Example 1, 72 mg of the thermally conductive filler B whose surface was methylated with HMDS obtained in Preparation Example 2, true spherical silica nanoparticles (Shin-Etsu Silicone QSB-170, manufactured by Shin-Etsu Chemical Co., Ltd., average particle diameter: 170 nm) was dry mixed to adsorb true spherical silica nanoparticles on the surfaces of the two types of thermally conductive fillers. The above two types of thermally conductive fillers with spherical silica nanoparticles adsorbed on the surface and zinc oxide grease ("Shin-Etsu Silicone G-776" manufactured by Shin-Etsu Chemical Co., Ltd., zinc oxide particle content: 40 vol%, average of zinc oxide particles) Particle size: 0.8 μm) and 177 mg of silicone oil (SRX310 manufactured by Dow Corning Toray Industries, Inc.) were mixed, and the resulting mixture was stirred in the same manner as in Example 1 to form a grease composition (thermally conductive filler). A: 22.4 vol%, thermally conductive filler B: 5.6 vol%, zinc oxide particles: 12 vol%) were obtained.

(Example 3)
The amount of the thermally conductive filler A is 350 mg, the amount of the thermally conductive filler B is 39 mg, the amount of the true spherical silica nanoparticles is 3.9 mg, the amount of the zinc oxide grease is 386 mg, and the silicone oil is A grease composition (thermal conductive filler A: 27.1 vol%, thermal conductive filler B: 3 vol%, zinc oxide particles: 12.9 vol%) was prepared by stirring in the same manner as in Example 2, except that the amount of was changed to 159 mg. ) was obtained.

(Comparative example 1)
As the grease composition, zinc oxide grease ("Shin-Etsu Silicone G-776" manufactured by Shin-Etsu Chemical Co., Ltd., zinc oxide particle content: 40 vol%, average particle diameter of zinc oxide particles: 0.8 μm) was used as it was.

(Comparative example 2)
500 mg of the thermally conductive filler A whose surface was methylated with HMDS obtained in Preparation Example 1, and 5 mg of true spherical silica nanoparticles ("Shin-Etsu Silicone QSB-170" manufactured by Shin-Etsu Chemical Co., Ltd., average particle diameter: 170 nm). The spherical silica nanoparticles were adsorbed onto the surface of the thermally conductive filler A by dry mixing. The thermally conductive filler A having spherical silica nanoparticles adsorbed on its surface and 253 mg of silicone oil ("SRX310" manufactured by Dow Corning Toray Industries, Inc.) were mixed, and the resulting mixture was stirred in the same manner as in Example 1 to prepare grease. A composition (thermally conductive filler A: 40 vol%) was obtained.

(Comparative example 3)
High thermal conductivity grease (Silver Ice 710NS manufactured by TIMTRONICS) was centrifuged (4800 rpm, 1 minute) and washed with toluene to separate and collect the filler, and the obtained filler was vacuum dried. When the X-ray diffraction pattern of this filler was measured, it was confirmed that the filler was a silver filler. Moreover, the average particle diameter of the silver filler was 2.5 μm. Furthermore, the volume fraction of the silver filler in the grease was determined from the mass fraction of the silver filler, the density of silver, and the density of the oil (1 g/cm ³ ), and was found to be 23 vol %. The grease containing this silver filler was used as it is as a grease composition.

(Comparative example 4)
245 mg of the thermally conductive filler A whose surface was methylated with HMDS obtained in Preparation Example 1, 63 mg of the thermally conductive filler B whose surface was methylated with HMDS obtained in Preparation Example 2, true spherical silica nanoparticles (Shin-Etsu Silicone QSB-170, manufactured by Shin-Etsu Chemical Co., Ltd., average particle diameter: 170 nm) was dry mixed to adsorb true spherical silica nanoparticles on the surfaces of the two types of thermally conductive fillers. The two types of thermally conductive fillers with true spherical silica nanoparticles adsorbed on the surface and the silver filler-containing grease (Silver Ice 710NS manufactured by TIMTRONICS, average particle diameter of silver filler: 2.5 μm, silver filler content: 23 vol) %) and 126 mg of silicone oil ("SRX310" manufactured by Dow Corning Toray Co., Ltd.) were mixed, and the resulting mixture was stirred in the same manner as in Example 1 to form a grease composition (thermally conductive filler A: 22.4 vol). %, thermally conductive filler B: 5.6 vol%, silver filler: 12 vol%).

(Comparative example 5)
Grease ("SilCool TIG400BX" manufactured by MOMENTIVE) was subjected to centrifugation (4800 rpm, 1 minute) and toluene washing to separate and recover the filler, and the obtained filler was vacuum-dried. When the X-ray diffraction pattern of this filler was measured, it was confirmed that the filler was an alumina filler. Moreover, the average particle diameter of the alumina filler was 7.3 μm. Further, the volume fraction of the alumina filler in the grease was determined from the mass fraction of the alumina filler, the density of the alumina, and the density of the oil (assumed to be 1 g/cm ³ ), and was found to be 87.8 vol %. The grease containing this alumina filler was used as it is as a grease composition.

(Comparative example 6)
245 mg of the thermally conductive filler A whose surface was methylated with HMDS obtained in Preparation Example 1, 63 mg of the thermally conductive filler B whose surface was methylated with HMDS obtained in Preparation Example 2, true spherical silica nanoparticles (Shin-Etsu Silicone QSB-170, manufactured by Shin-Etsu Chemical Co., Ltd., average particle diameter: 170 nm) was dry mixed to adsorb true spherical silica nanoparticles on the surfaces of the two types of thermally conductive fillers. The two types of thermally conductive fillers with true spherical silica nanoparticles adsorbed on their surfaces and the alumina-containing grease ("SilCool TIG400BX" manufactured by MOMENTIVE), average particle diameter of alumina filler: 7.3 μm, alumina filler content: 87.8 vol %) and 253 mg of silicone oil ("SRX310" manufactured by Dow Corning Toray Co., Ltd.) were mixed, and the resulting mixture was stirred in the same manner as in Example 1 to form a grease composition (thermally conductive filler A: 22.4 vol). %, thermally conductive filler B: 5.6 vol%, silver filler: 12 vol%).

<Thermal resistance of grease composition>
The grease compositions (approximately 4 μl) obtained in Examples and Comparative Examples were sandwiched between ceramic plates with a diameter of 14 mm and a thickness of 1 mm to produce a laminate, and a pressure of 3 MPa was applied to the laminate to prepare a laminate. The thermal diffusivity of the laminate was measured using a flash analyzer ("LFA447 NanoFlash" manufactured by NETZSCH). Further, the thickness of the laminate was measured using a micrometer. The thermal resistivity of the grease composition was calculated using the thermal diffusivity and thickness of the obtained laminate, the thermal diffusivity, density, specific heat, and thickness of the ceramic plate, and the density and specific heat of the grease composition. . In addition, the thermal resistance ratio of each grease composition to the grease compositions containing only additive particles (zinc oxide particles, silver filler, or alumina filler) (Comparative Examples 1, 3, and 5) was determined. These results are shown in Table 2.

As shown in Table 2, a grease composition containing a thermally conductive filler containing composite particles (AlN/BN composite particles) in which AlN particles and BN particles are bonded via porous BN, and zinc oxide particles. (Examples 1 to 3) have lower thermal resistance and superior thermal conductivity than grease compositions containing only zinc oxide particles (Comparative Example 1) or only the thermally conductive filler (Comparative Example 2). I found out that

On the other hand, the grease composition containing the thermally conductive filler and the silver filler (Comparative Example 4) is different from the grease composition containing only the silver filler (Comparative Example 3) or only the thermally conductive filler (Comparative Example 2). It was found that the thermal resistance was higher and the thermal conductivity was lower than that of the

Furthermore, the grease composition containing the thermally conductive filler and the alumina filler (Comparative Example 6) is different from the grease composition containing the alumina filler (Comparative Example 5) or only the thermally conductive filler (Comparative Example 2). In comparison, it was found that the thermal resistance was extremely large and the thermal conductivity was even worse.

From the above results, thermal conductivity can be improved in a grease composition containing a thermally conductive filler containing composite particles (AlN/BN composite particles) in which AlN particles and BN particles are bonded via porous BN. It has been found that blending zinc oxide particles is effective for this purpose.

As explained above, according to the present invention, it is possible to obtain a grease composition with excellent thermal conductivity. Therefore, since the grease composition of the present invention has excellent thermal conductivity, it is useful as a thermally conductive grease composition used, for example, in automobiles, electronic devices, various electrical appliances, and the like.

Claims (6)

Isotropic high thermal conductive 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. The boron nitride phase formed by the hexagonal boron nitride particles and the porous boron nitride has a porosity of 10 to 50 vol. % of the sintered body, and 40% or more of all the highly thermally conductive particles in the pulverized material have the particles on at least a portion of the surface of the highly thermally conductive particles. a thermally conductive filler forming composite particles in which the hexagonal boron nitride particles are bonded via porous boron nitride;
Contains zinc oxide particles and matrix oil,
A highly thermally conductive grease composition characterized in that the thermally conductive filler and zinc oxide particles are dispersed in the matrix oil. 2. The highly thermally conductive particles are at least one particle selected from the group consisting of aluminum nitride particles, silicon nitride particles, cubic boron nitride particles, silicon carbide particles, and diamond particles. High thermal conductivity grease composition as described. 3. The highly thermally conductive grease composition according to claim 1, wherein the thermally conductive filler has a bimodal or more particle size distribution. The highly thermally conductive grease composition according to any one of claims 1 to 3, wherein the zinc oxide particles have an average particle diameter of 0.1 to 1 μm. Claims 1 to 4, wherein the matrix oil is at least one selected from the group consisting of silicone oil, modified silicone oil, fluoroether oil, mineral oil, natural oil of animal and vegetable origin, paraffin, and synthetic oil. A highly thermally conductive grease composition according to any one of the above. The highly thermally conductive grease composition according to any one of claims 1 to 5, further comprising true spherical nanoparticles.