JP7257866B2 - Composite filler - Google Patents

Description

The present invention relates to novel composite fillers containing aluminum nitride powder and inorganic powder. More specifically, the present invention provides a composite filler capable of stably adjusting the thermal conductivity of a resin composition filled with an inorganic powder over a wide range.

In recent years, with the increase in power density of semiconductor devices, materials used in devices are required to have higher heat dissipation properties. Such materials include a group of materials called thermal interface materials, and their use is expanding rapidly. A thermal interface material is a material for reducing the thermal resistance of a path through which heat generated from a semiconductor element is released to a heat sink or a housing, and various forms such as sheet, gel, and grease are used. Generally, a thermal interface material is a resin composition in which a resin such as epoxy or silicone is filled with a thermally conductive filler, and metal oxides are often used as the thermally conductive filler. However, the sheet-shaped molded body formed from the composite material using the metal oxide has a thermal conductivity in the thickness direction of about several W/m·K, and a sheet-shaped molded body having a higher thermal conductivity is available. was requested.

In response to the above requirements, attempts have been made to increase the thermal conductivity of the resulting resin composition by using a plurality of thermally conductive fillers having different particle sizes in combination to enable high loading of thermally conductive fillers. (see Patent Document 1).

On the other hand, in the thermal interface material, there is a demand to adjust the thermal conductivity to, for example, about 10 W/m·K depending on the application. There is also demand for composite fillers that use For example, Patent Literature 2 discloses a composite filler composed of aluminum nitride powder having a large particle size and high thermal conductivity and alumina powder having low thermal conductivity.

However, when a composite filler of aluminum nitride powder and an inorganic powder for adjusting thermal conductivity is made into a resin composition, the thermal conductivity of the resin composition obtained by filling it with the inorganic powder is abnormally lowered. However, there may be a problem that it is difficult to achieve the required thermal conductivity, and there is also a problem that the thermal conductivity of the obtained resin composition varies at the same compounding ratio. There is

JP 2013-189625 A JP 2007-153969 A

Accordingly, an object of the present invention is to provide a composite filler containing an aluminum nitride powder and an inorganic powder, in which the thermal conductivity of the resin composition can be stably adjusted over a wide range by the inorganic powder. to do.

The inventors of the present invention have made intensive studies to solve the above problems. It is possible to easily adjust the thermal conductivity at the time of filling the composite filler resin, and at that time, by using the aluminum nitride powder containing particles having a polyhedral structure, the adjustment of the thermal conductivity can be reproduced. The present inventors have found that the method can be easily performed and the above object can be achieved, and have completed the present invention.

That is, according to the present invention, 50% or more of the surfaces satisfy S/L≧1.0 in terms of the area (S) of planes existing on the particle surface with respect to the major axis (L) observed by scanning electron micrographs. A composite filler containing 10 to 100 parts by volume of inorganic powder (B) containing alumina particles with respect to 100 parts by volume of aluminum nitride powder (A) containing aluminum nitride particles having a polyhedral structure at a rate of 50% by volume or more. and the aluminum nitride powder (A) has a cumulative 50% value (D50) in its particle size distribution curve in the range of 50 to 200 μm, and the inorganic powder (B) has a cumulative 50% value (D50) in its particle size distribution curve. is in the range of 0.005 to 0.1 with respect to the cumulative 50% value (D50) in the particle size distribution curve of the aluminum nitride powder (A).

According to the present invention, when the aluminum nitride powder and the inorganic powder are blended, there is no unstable change in the thermal conductivity of the resin composition obtained by filling the inorganic powder with a change in the blending amount of the inorganic powder, and the blending ratio is It is possible to exhibit stable thermal conductivity according to.

Moreover, it has an excellent property that the adjusted thermal conductivity does not vary among lots.

Although the mechanism of the above effect is not clear, the present inventors found that by including aluminum nitride particles having a polyhedral structure as the aluminum nitride powder having a large particle size, the particles constituting the inorganic powder and the aluminum nitride particles are separated from each other. It is presumed that the opportunities for reliable contact have increased, and it has become possible to adjust the thermal conductivity of the resin composition by adjusting the filling amount of the inorganic powder in a wide range with good reproducibility.

Scanning electron micrograph of one embodiment of aluminum nitride powder containing aluminum nitride particles having a polyhedral structure used in the present invention Scanning electron micrograph of another embodiment of aluminum nitride powder containing aluminum nitride particles having a polyhedral structure used in the present invention

[Aluminum nitride powder (A)]
In the present invention, the aluminum nitride powder used contains particles having a polyhedral structure and has a cumulative 50% value (D50) in the particle size distribution curve of 50 μm to 200 μm, preferably 60 μm to 190 μm. If the D50 is less than 50 μm, the effect of thermal conductivity is not exhibited, and if it is greater than 200 μm, the dispersion in the resin becomes unstable, and a resin composition having stable thermal conductivity cannot be obtained. becomes difficult.

In addition, in the above aluminum nitride powder (A), one that satisfies the above particle size distribution and contains 50% by volume or more, preferably 70% by volume of particles having a polyhedral structure is preferably used.

Examples of the polyhedral structure include forms of particles having at least two flat faces, specifically plate-like, hexagonal prism-like, and moreover, a plurality of planes forming ridges or valleys are randomly present. shape and the like. Among them, those having a polyhedral surface structure of tetrahedron or more are preferable because they may provide more opportunities for contact between the later-described inorganic powder and the surface. Another aspect of the above polyhedral particles includes particles having a structure in which one end or both ends of a polygonal prism does not form a flat surface. Specifically, a shape in which one end of a polygonal column is bowl-shaped is exemplified. Such particles can also be suitably used as long as they have two or more flat surfaces in the polygonal prism portion.

In the present invention, the characteristics of the polyhedral particles can be confirmed by observation with SEM photographs. For example, FIG. 1 is an SEM photograph of a representative aluminum nitride powder used in the present invention. In FIG. 1 above, a particle in which the plurality of planes exist at random is confirmed. It is observed as a polyhedral shape in which the angles of the ridges or troughs form obtuse angles. In the above aluminum nitride particles, at least one of the planes preferably satisfies S/L≧1.0 in the area (S) of planes present on the particle surface with respect to the major axis (L).
In addition, as the aluminum nitride powder of the present invention, any known aluminum nitride powder containing polyhedral particles can be used without limitation. For example, as shown in FIG. 2 of International Publication No. 2017/131239, a body having a hexagonal column is also preferably used. The particles shown in FIG. 2 are aluminum nitride particles in the shape of hexagonal prisms having bowl-shaped protrusions at the ends.

In the aluminum nitride powder used in the present invention, the planes of the polyhedral particles are considered to be derived from the crystal planes of the aluminum nitride, and the crystal planes are 50 % or more, particularly preferably 80% or more, in order to increase the chance of contact with particles of the inorganic powder described later. The above area ratio is a value obtained by image analysis of the state observed in the SEM photograph.

The aluminum nitride powder shown in FIG. 1 is novel, and a typical production method thereof is as follows. In the method of reducing and nitriding the powder, the reduction nitriding is performed with the nitrogen gas atmosphere being a mixed gas of 55 to 30% by volume of nitrogen gas and 45 to 70% by volume of diluent gas, at least in the range of 5 to 50% of the nitriding rate. After the reduction nitriding is completed, the produced aluminum nitride powder is maintained in an atmosphere in which the aluminum nitride powder is not oxidized, while maintaining the heating temperature of the reduction nitriding within ±30° C., for one hour or more. . Moreover, the amount of the sulfur component used is preferably in the range of 1.0 to 20 parts by weight with respect to 100 parts by weight of the alumina powder.

In the method for producing the aluminum nitride powder, α-alumina is particularly preferably used as the alumina powder, which is one component of the raw material, and its purity is particularly preferably 99.5% by weight or more. Also, the average particle diameter is preferably 1 μm to 30 μm. In the method for producing the aluminum nitride powder, known carbon powders such as furnace black can be used as the reducing agent. is more suitable.

In the method for producing the aluminum nitride powder, the sulfur component is a component necessary for producing the desired aluminum nitride particles by acting during the operation for adjusting the atmosphere in the reduction nitriding reaction, which will be described in detail later. The type of compound is not particularly limited as long as it can co-melt with the powder. Examples thereof include sulfur alone and sulfur compounds such as aluminum sulfide, nitrogen sulfide, and thiouric acid. The sulfur component may originally be contained in the carbon powder, and such sulfur component also acts as part of the sulfur component.

In the production method, the amount of the sulfur component present in the raw material mixture containing the alumina powder and the carbon powder is 0.8 to 20 parts by weight, particularly preferably 5 to 20 parts by weight as elemental sulfur, relative to 100 parts by weight of the alumina powder. 10 parts by weight is suitable. The amount of carbon powder used is preferably 36 to 200 parts by weight, more preferably 40 to 100 parts by weight, with respect to 100 parts by weight of alumina powder.

In the method for producing the aluminum nitride powder, the raw material mixture containing the alumina powder, carbon powder, and sulfur component is heated in a reactor under nitrogen gas flow, preferably at a temperature range of 1500 to 2000 ° C., After reducing and nitriding the alumina powder, a suitable method is to keep the aluminum nitride powder produced for 1 hour or longer, preferably 2 hours or longer, and more preferably 5 hours or longer in an atmosphere where the aluminum nitride powder is not oxidized while maintaining the above heating temperature. is. At that time, the nitrogen gas supplied to the reactor is 45% by volume or more, preferably 50% by volume or more, of carbon monoxide alone or part of the carbon monoxide in an inert gas such as argon. Nitrogen gas is used with a diluent gas consisting of the displaced gas mixture. The upper limit of the ratio of the diluent gas contained in the supplied nitrogen gas is preferably 70% by volume or less. On the other hand, if the ratio of the diluent gas in the supplied nitrogen gas is less than 45% by volume, the reductive nitriding reaction will be accelerated and sufficient grain growth will not be possible. It becomes difficult to obtain aluminum nitride particles. Also, the upper limit of the heating and holding time after completion of reduction nitridation is not particularly limited, but is about 10 hours.

In the manufacturing method, after the nitridation ratio of the alumina powder exceeds 50%, the supply of the diluent gas is stopped or reduced, so that the ratio of the diluent gas is less than 45% by volume, Nitriding may be completed under the same conditions.

The reduction nitriding step includes, for example, an atmosphere-controlled high-temperature furnace in which heat treatment is performed by high-frequency induction heating or heater heating. It can be used as appropriate depending on the method.

Moreover, since the obtained aluminum nitride powder contains surplus carbon powder, it is preferable to remove the surplus carbon powder by an oxidation treatment, if necessary. As the oxidizing gas for the oxidation treatment, any gas that can remove carbon, such as air, oxygen, and carbon dioxide, can be used without limitation. Also, the treatment temperature is generally preferably 500°C to 900°C.

[Inorganic powder (B)]
The inorganic powder (B) constituting the composite filler of the present invention is used in combination with the aluminum nitride powder to adjust the thermal conductivity of the resin composition obtained by filling the filler. , containing inorganic powder having lower thermal conductivity than aluminum nitride powder is used without particular limitation. Examples of the inorganic powder having low thermal conductivity include alumina, boron nitride, zinc oxide, silicon carbide, and silicon nitride, with alumina being particularly preferred. Alumina powders having various particle size distributions are commercially available, and it is possible to appropriately prepare alumina powders having an appropriate particle size distribution.

In the present invention, an inorganic powder ( B) can be used as part of Although the shape of the inorganic powder (B) is not particularly limited, it is preferably spherical.

In the present invention, the inorganic powder (B) has a cumulative 50% value (D50) in its particle size distribution curve that is 0.5% higher than the cumulative 50% value (D50) in the particle size distribution curve of the aluminum nitride powder (A). 005 to 0.1, preferably 0.007 to 0.08, the above function is exhibited by contact with the plane surface of the aluminum nitride particles having a polyhedral structure contained in the aluminum nitride powder (A). above.

Moreover, the inorganic powder (B) can be used by mixing two or more kinds of powders having different particle size distributions within the above particle size distribution range. For example, 100 parts by volume of alumina powder with a cumulative 50% value (D50) in the particle size distribution curve in the range of 5 to 20 μm, and a cumulative 50% value (D50) in the particle size distribution curve in the range of 0.5 to 3 μm The inorganic powder (B) is preferably composed of 10 to 100 parts by volume of alumina powder. Furthermore, as the inorganic powder (B), as described above, together with the alumina powder, an inorganic powder ( It is also possible to configure B). In this case, the ratio of the aluminum nitride powder to the inorganic powder (B) is desirably 10% by volume or less.

[Composite filler]
The composite filler of the invention is 100 parts by volume of the aluminum nitride powder (A) having a polyhedral structure and the inorganic powder (B) containing alumina particles described above, and the aluminum nitride powder (A) containing aluminum nitride particles having a polyhedral structure. 10 to 100 parts by volume, preferably 15 to 95 parts by volume, of inorganic powder (B) containing alumina particles.

By changing the ratio of the inorganic powder (B) to the aluminum nitride powder (A) having a polyhedral structure within the above range, it is difficult to adjust the conventional composite filler even when it is filled into a resin to form a resin composition. In addition, it is possible to stably obtain a resin composition having an arbitrary thermal conductivity in a relatively high range, specifically 8 to 11 W/m·K.

In the present invention, the method of mixing the aluminum nitride powder (A) having a polyhedral structure and the inorganic powder (B) containing the alumina particles described above to form a composite filler is a method in which the composite filler is mixed with the above composition when filled in a resin. The above powders may be mixed in a dry manner, or may be mixed together with the resin in the later-described filling into the resin.

[Resin composition]
The resin that fills the composite filler of the present invention is not particularly limited, but examples include polyethylene, polypropylene, ethylene-propylene copolymer, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymer. Combined, polyvinyl alcohol, polyacetal, fluororesin (polyvinylidene fluoride, polytetrafluoroethylene, etc.), polyethylene terephthalate, polybutylene terephthalate, polyethylene 2,6 naphthalate, polystyrene, polyacrylonitrile, styrene-acrylonitrile copolymer, ABS resin, polyphenylene Ether (PPE) resins, modified PPE resins, aliphatic polyamides, aromatic polyamides, polyimides, polyamideimides, polymethacrylic acids (polymethacrylic acid esters such as polymethyl methacrylate), polyacrylic acids, polycarbonates, polyphenylene sulfides, polysulfone, polyethersulfone,
Thermoplastic resins such as polyethernitrile, polyetherketone, polyetheretherketone, polyketone, liquid crystal polymer, ionomer; epoxy resin, curable acrylic resin, curable urethane resin, curable silicone resin, phenolic resin, curable polyimide resin , curable modified PPE, and curable resins such as curable PPE. Among these resins, curable resins are preferable, and liquid curable resins are particularly preferable, in order to produce molded bodies such as plate-shaped molded bodies and thin-film molded bodies.

The resin composition composed of the resin filled with the composite filler preferably contains the composite filler in an amount of 60% to 85% by volume, more preferably 70% to 80% by volume. If the content of the composite filler is less than the above range, the resulting resin composition will have a low thermal conductivity and, for example, when used as a heat-dissipating sheet, it may not be possible to obtain sufficient properties. On the other hand, if the content of the composite filler is more than the above range, when the composite filler and the resin are mixed, the resulting resin composition has a significantly increased viscosity, resulting in extremely poor workability. Defects may occur, and problems such as a decrease in thermal conductivity may occur.

Additives such as a curing agent and a coupling agent may be further added to the above resin composition, if necessary. The resin composition can be obtained by mixing the composite filler, the resin, and other optional components such as the additives with a conventional kneader such as a roll, a kneader, a Banbury mixer, and a rotation/revolution mixer. can be manufactured by By molding the resin composition of the present invention as described above by a conventionally known suitable method, a molded article having high thermal conductivity can be obtained.

Various physical properties in Examples and Comparative Examples were measured by the following methods.

(1) Particle size A sample was dispersed in a 5% sodium pyrophosphate aqueous solution with a homogenizer, and the particle size was measured with a laser diffraction particle size distribution device (MICROTRACHRA manufactured by Nikkiso Co., Ltd.).

(2) Thermal conductivity of the resin composition The thermal conductivity of the molded product obtained by molding the resin composition is measured using a temperature wave thermal analyzer (ai-PhaseMobile1u manufactured by iPhase Co., Ltd.). bottom.

(3) Raw material powder [Method for producing aluminum nitride powder (A)]
Sulfur powder is added to a mixture of 100 parts by weight of alumina powder and 50 parts by weight of carbon powder so that the amount of sulfur component in the mixture is 5 parts by weight with respect to 100 parts by weight of the above alumina powder, and these are uniformly mixed. The raw material mixture was obtained by mixing with a vibrating stirrer until the ingredients were mixed.

The above raw material mixture was stored in a carbon setter to a thickness of 20 mm, set in a reaction vessel in which nitrogen gas can be circulated, and reductive nitridation was performed at a heating temperature of 1775° C. while circulating nitrogen gas. At that time, the ratio of carbon monoxide gas supplied to the reaction vessel was adjusted to 53% by volume, and the reductive nitriding reaction was performed. After the reductive nitriding reaction was completed, the heating temperature was maintained for 5 hours. Then, the reaction product was taken out from the reaction vessel.

After that, the reaction product was heated at 700° C. for 5 hours in an air atmosphere to burn off the unreacted carbon powder and obtain aluminum nitride powder. Table 1 shows the raw material composition and the composition of carbon monoxide gas in the nitrogen gas.

A SEM photograph of the aluminum nitride particles of the present invention contained in the aluminum nitride powder obtained by the above method is shown in FIG. 1(a). The proportion of aluminum nitride particles having a polyhedral structure contained in the aluminum nitride powder was about 70%. In addition, 10 aluminum nitride particles having the above polyhedral structure were arbitrarily selected from the obtained aluminum nitride powder, and the area of each surface was confirmed. S) satisfies S/L≧1.0 in 70% of the cases.

[Inorganic powder (B)]
Commercially available alumina particles Spherical alumina powder with a cumulative 50% value (D50) in the particle size distribution curve of 2, 4, 8, 16, 28, 50, 75 μm, respectively Commercially available aluminum nitride powder Cumulative 50% value (D50) in the particle size distribution curve Spherical aluminum nitride powder with a diameter of 1 μm Examples 1 to 9, Comparative Examples 1 to 21
Aluminum nitride powder (A) and inorganic powder (B) shown in Table 1 were mixed in a mortar in a two-liquid condensation type silicone resin (KE-1013A/B by Shin-Etsu Chemical Co., Ltd.) at the ratios shown in Table 1 to form a liquid. A mixture was obtained. Table 2 shows the filling rate of the powder at this time. In addition, a part of the obtained liquid mixture was cast into a mold body and cured to prepare a test piece made of a resin composition having a diameter of 1 mm and a thickness of 500 μm. Thermal conductivity was measured using ai-PhaseMobile1u). Ten test pieces were prepared for each resin composition, and Table 2 shows the average value of the measured thermal conductivity and the value obtained by subtracting the lowest value from the highest value.

Claims (2)

Aluminum nitride particles having a polyhedral structure in which 50% or more of the faces satisfy S/L≧1.0 in the area (S) of planes present on the particle surface with respect to the major diameter (L) observed by scanning electron micrograph. A composite filler containing 10 to 100 parts by volume of inorganic powder (B) containing alumina particles with respect to 100 parts by volume of aluminum nitride powder (A) containing 50% by volume or more of aluminum nitride powder (A ) has a cumulative 50% value (D50) in the particle size distribution curve in the range of 50 to 200 μm, and the inorganic powder (B) has a cumulative 50% value (D50) in the particle size distribution curve that is the aluminum nitride powder (A ) in the range of 0.005 to 0.1 with respect to the cumulative 50% value (D50) in the particle size distribution curve. 2. The composite filler according to claim 1, wherein the inorganic powder (B) contains alumina particles in a proportion of 50% by volume or more.

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