JP7500337B2 - Composite thermally conductive filler and thermally conductive composition containing same - Google Patents

Description

The present invention relates to a thermally conductive filler that can produce a composite material with excellent thermal conductivity, and a composition containing the same.

In recent years, with the miniaturization and high integration of electronic devices, heat generation from mounted components has become a very important issue. Resins used for adhesives and sealing materials have low thermal conductivity, so resin compositions are used in which resin is blended with a filler that has good thermal conductivity. In particular, for applications requiring insulation, ceramic-based thermally conductive fillers such as aluminum oxide are used, but the thermal conductivity of resin compositions blended with such thermally conductive fillers is limited to around 1 to 3 W/(m·K).

In recent years, however, aluminum nitride has been attracting attention as a material with higher thermal conductivity. Aluminum nitride has no anisotropy and has a very high thermal conductivity of 285 W/(m·K) for single crystals. In addition, since the thermal conductivity of a resin composition containing a filler material is lower than that of the filler material itself, attempts have been made to improve thermal conductivity by combining fillers with different shapes and particle sizes to improve the contact between the fillers and the amount of filling. For example, Patent Document 1 discloses a thermally conductive particle composition in which boron nitride coarse powder with an average particle size of 20 to 150 μm and scale-shaped boron nitride fine powder with an average particle size of 1 to 10 μm and an average thickness of 0.001 to 1 μm are treated with a silane coupling agent and attached to the coarse powder.

Patent No. 6231031

However, since the particles described in Patent Document 1 are scaly, the viscosity increases when the particles are filled into the resin, so pressurization is essential. As a method of not applying pressure, there is a method of reducing the filling amount to lower the viscosity, but there is a risk that sufficient thermal conductivity cannot be obtained.
Therefore, an object of the present invention is to provide a thermally conductive filler and a composition thereof that solves these problems, suppresses an increase in viscosity, and has high thermal conductivity.

As a result of thorough investigation in light of the above circumstances, it was found that a thermally conductive filler in which thermally conductive particles having a small particle size are attached to thermally conductive particles having a large particle size, and a composition using the same, can solve the problems.
That is, the gist of the present invention lies in the following [1] to [4].
[1] A composite thermally conductive filler comprising: first thermally conductive particles having an average particle size of 10 μm or more and 150 μm or less; and second thermally conductive particles having an average particle size of 0.1 μm or more and 5 μm or less adhered to surfaces of the first thermally conductive particles, in which 20% or more and 80% or less of the surface of the first thermally conductive particles is covered by the second thermally conductive particles.
[2] The composite thermally conductive filler according to [1], wherein the first thermally conductive particles and the second thermally conductive particles are each made of aluminum nitride.
[3] The composite thermally conductive filler according to [1], further comprising 2 mass% or less of a binder based on the total amount of the composite thermally conductive filler.
[4] A thermally conductive composition comprising at least one polymer compound selected from the group consisting of rubber, a thermoplastic resin, and a thermosetting resin, and the thermally conductive filler according to any one of [1] to [3], wherein the amount of the thermally conductive filler is 50 parts by volume or more and 1,500 parts by volume or less per 100 parts by volume of the polymer compound.

The composite thermally conductive filler of the present invention has high thermal conductivity. Furthermore, since the increase in viscosity is suppressed even when the filler is filled into a resin, it is possible to fill a sufficient amount, and it is possible to maintain a high thermal conductivity of the resulting thermally conductive composition.

(a) Electron microscope image in Example 1, (b) Electron microscope image in Example 2, (c) Electron microscope image in Example 3 (a) Electron microscope image of Comparative Example 1, (b) Electron microscope image of Comparative Example 2, (c) Electron microscope image of Comparative Example 3, (d) Electron microscope image of Comparative Example 4

Hereinafter, an embodiment of the present invention will be described in detail.
(Composite thermally conductive filler)
The composite thermally conductive filler according to the present invention is a filler comprising first thermally conductive particles having a specific average particle size, and second thermally conductive particles attached to the surfaces of the first thermally conductive particles and having a specific average particle size smaller than that of the first thermally conductive particles.

It is preferable that the second thermally conductive particles cover 20% or more of the surface of the first thermally conductive particles, and more preferably 30% or more. It is also preferable that the second thermally conductive particles cover 80% or less of the surface of the first thermally conductive particles, and more preferably 70% or less. If the proportion of the surface of the first thermally conductive particles covered by the second thermally conductive particles is less than 20% or more than 80%, the increase in viscosity cannot be sufficiently suppressed.

(First thermally conductive particles)
The first thermally conductive particles are thermally conductive particles having an average particle diameter of 10 μm or more, more preferably thermally conductive particles having an average particle diameter of 15 μm or more. If the average particle diameter is less than 10 μm, the thermal conductivity tends to decrease. On the other hand, the first thermally conductive particles are thermally conductive particles having an average particle diameter of 150 μm or less, more preferably thermally conductive particles having an average particle diameter of 80 μm or less. If the diameter exceeds 150 μm, the particles can only be used in places with large clearances, which limits the applications, or when the particles are made into a resin compound, the interface between the resin and the filler is likely to break, resulting in insufficient strength. In addition, when used in adhesives or sealants, clogging may occur, or the filler filling may not be uniform, making it difficult to use as a filler.

As the material of the first thermally conductive particles, known materials generally used as thermally conductive materials can be used without any particular restrictions. For example, metals such as silver, aluminum, copper, and alloys containing them, and ceramic materials such as alumina, aluminum nitride, and boron nitride can be mentioned. Among them, aluminum nitride is preferably used as an insulating thermally conductive material in applications where insulation is required because it has high thermal conductivity.
The shape of the first thermally conductive particles is not particularly limited, but from the viewpoint of suppressing an increase in viscosity, spherical, approximately spherical, or granular shapes are preferred.

(Second Thermally Conductive Particles)
The second thermally conductive particles of the present invention are thermally conductive particles having an average particle size of 0.1 μm or more, more preferably 1 μm or more. If the average particle size is less than 0.1 μm, the surface area tends to be large and the filling ability into the resin tends to be poor. On the other hand, the second thermally conductive particles are thermally conductive particles having an average particle size of 5 μm or less, more preferably 3 μm or less. If the average particle size exceeds 5 μm, it tends to be difficult to adhere to the first thermally conductive particles.

As with the first thermally conductive particles, the second thermally conductive particles may be made of any known material that is generally used as a thermally conductive material, without any particular restrictions. The second thermally conductive particles may be made of the same material as the first thermally conductive particles, or may be made of a different material.

(Second thermally conductive particle attachment step)
The composite thermally conductive filler of the present invention can be obtained by mixing the first thermally conductive particles and the second thermally conductive particles, and adhering the second thermally conductive particles to the first thermally conductive particles. As a mixing method, any known method can be used without particular limitation. For example, mixing using a mortar, mixing using a vibration mixer, mixing using a planetary mixer, and a rotation/revolution type mixer can be mentioned.

A binder may also be used to facilitate adhesion of the second thermally conductive particles. There are no particular limitations on the binder, and any additive that can adhere the second thermally conductive particles to the surface of the first thermally conductive particles can be used. Examples of such binders include high molecular weight additives generally known as dispersants such as wetting dispersants, surface conditioners, rheology agents, adhesion agents, antifoaming agents, defoaming agents, etc. Among these, dispersants are particularly suitable for use from the viewpoint of dispersion.

The amount of this binder is preferably 2% by mass or less, and more preferably 1% by mass or less, based on the total amount of the composite thermally conductive filler. The amount of this binder is preferably 0.01% by mass or more, and more preferably 0.1% by mass or more, based on the total amount of the composite thermally conductive filler. If the amount of the binder is within this range, the second thermally conductive particles can be adhered well.

(Thermal Conductive Composition)
The composite thermally conductive filler of the present invention can be mixed with a polymer compound such as rubber, thermoplastic resin, or thermosetting resin to form a thermally conductive composition. Examples of the rubber include natural rubber, synthetic rubber, butadiene rubber, and silicone rubber. Examples of the thermoplastic resin include acrylic resin, polyethylene, and polyester resin. Examples of the thermosetting resin include epoxy resin, phenol resin, and urea resin.

The amount of the composite thermally conductive filler is preferably 50 parts by volume or more and 1500 parts by volume or less, more preferably 100 parts by volume or more and 1000 parts by volume or less, relative to 100 parts by volume of the polymer compound. If the amount is 50 parts by volume or more and 1500 parts by volume or less, the viscosity can be reduced.
The thermally conductive composition may contain other components such as dispersants other than the dispersant used as the binder, colorants, plasticizers, etc., as long as the effects of the present invention are not impaired.

The present invention will be explained below using examples. First, the test methods and raw materials used in these examples are shown below.

(Test method)
[Particle size measurement]
(Particle size distribution measurement (measurement by laser diffraction/scattering method))
The particle size distribution of the thermally conductive filler of each of the Examples and Comparative Examples was measured by dispersing the filler in water using a laser diffraction particle size distribution measuring device (MT3300EXII, manufactured by Microtrac-Bell, Inc.).

(Photographed using an electron microscope)
The raw material particles to be measured were photographed at a magnification of 1000 times using an electron microscope (JSM-7200F, manufactured by JEOL Ltd.).

(Measurement of Coverage)
The thermally conductive filler to be measured was photographed with an electron microscope, and one first thermally conductive particle was selected using image analysis and measurement software (WinROOF2018 Ver.4.7 manufactured by Mitani Shoji Co., Ltd.), and the second thermally conductive particles attached to the first thermally conductive particle were separated by binarization processing, and the ratio of the image area of the second thermally conductive particle to the total image area of the first thermally conductive particles was calculated. The same processing was carried out for 10 first thermally conductive particles, and the average value was taken as the coverage rate.

[viscosity]
The viscosity of each of the prepared samples was measured using a cone-plate viscometer (DV2T manufactured by BROOKFIELD) at a rotation speed of 2.5 rpm, except for samples with high viscosity, which were measured at 1.0 rpm.

[Thermal conductivity]
Each sample used for viscosity measurement was poured into a disk-shaped silicon mold having a diameter of 25 mm and a thickness of 5 mm, molded, and treated at 150° C. for 60 minutes to obtain a sample for thermal conductivity measurement. The thermal conductivity of each obtained sample for thermal conductivity measurement was measured by a non-steady-state method using a thermal conductivity measuring device (TCi manufactured by C-THERM).

(raw materials)
[Crushed filler]
Aluminum nitride filler (crushed product)...TFZ-S20P (average particle size D50: 20 μm, tap density: 1.62 g/cm ³ ) manufactured by Toyo Aluminum Co., Ltd. (hereinafter referred to as "S20P").
Aluminum nitride filler (crushed product)...TFZ-N01P (average particle size D50: 1 μm, tap density: 1.11 g/cm ³ ) manufactured by Toyo Aluminum Co., Ltd. (hereinafter referred to as "N01P").

[resin]
Epoxy resin: jER825 (density: 1.16 g/cm ³ ) manufactured by Mitsubishi Chemical Corporation (hereinafter simply referred to as "resin")

[Binding Agent]
Dispersant: BYK Japan Co., Ltd., DISPERBYK-142

Example 1
[Preparation of thermally conductive filler]
18 g of S20P, 2 g of N01P, and 0.1 g of dispersant were mixed uniformly in a PTFE (polytetrafluoroethylene) mortar for 5 minutes to prepare a thermally conductive filler. This was photographed using an electron microscope according to the method described above, and the coverage was measured. The results are shown in Table 1. The image taken by the electron microscope is shown in Figure 1 (a).

[Preparation of thermally conductive composition]
18.67 g of the thermally conductive filler obtained above was mixed with 2.72 g of resin, and then the mixture was mixed evenly using a three-roll mill (BR-150V, manufactured by Imex Co., Ltd.) to prepare a thermally conductive composition having a filler amount of 233 volume % relative to the resin. The viscosity and thermal conductivity of the obtained thermally conductive composition were measured according to the methods described above. The results are shown in Table 1.

Example 2
The coverage was measured and a thermally conductive composition was prepared in the same manner as in Example 1, except that the amount of S20P was 17 g and the amount of NO1P was 3 g. Next, the viscosity and thermal conductivity of the obtained thermally conductive composition were measured according to the above-mentioned method. The results are shown in Table 1. Also, an image taken by an electron microscope is shown in FIG. 1(b).

Example 3
The coverage was measured and a thermally conductive composition was prepared in the same manner as in Example 1, except that the amount of S20P in Example 1 was 16 g and the amount of N01P was 4 g. Next, the viscosity and thermal conductivity of the obtained thermally conductive composition were measured according to the above-mentioned method. The results are shown in Table 1. Also, an image taken by an electron microscope is shown in FIG. 1(c).

(Comparative Example 1)
After mixing S20P18g and N01P2g, the mixture was photographed using an electron microscope in the same manner as described above to measure the coverage. The results are shown in Table 1. The electron microscope image is shown in Figure 2(a).
The above mixed filler (18.58 g), dispersant (0.09 g), and resin (2.72 g) were mixed together, and then the mixture was mixed evenly using the triple roll mill to prepare a thermally conductive composition with a filler content of 233% by volume relative to the resin. The thermal conductivity of the obtained thermally conductive composition was measured according to the method described above. The results are shown in Table 1.
The viscosity was too high to measure.

(Comparative Example 2)
The coverage was measured and a thermally conductive composition was prepared in the same manner as in Comparative Example 1, except that the amount of S20P was 17 g and the amount of N01P was 3 g. Next, the viscosity and thermal conductivity of the obtained thermally conductive composition were measured according to the above-mentioned method. The results are shown in Table 1. Also, an image taken by an electron microscope is shown in FIG. 2(b).

(Comparative Example 3)
The coverage was measured and a thermally conductive composition was prepared in the same manner as in Comparative Example 1, except that the amount of S20P was 16 g and the amount of N01P was 4 g. Next, the thermal conductivity was measured using the obtained thermally conductive composition according to the above-mentioned method. The results are shown in Table 1. Also, an image taken by an electron microscope is shown in FIG. 2(c).
The viscosity was too high to measure.

(Comparative Example 4)
The coverage was measured and a thermally conductive composition was prepared in the same manner as in Comparative Example 1, except that the amount of S20P was 14 g and the amount of NO1P was 6 g. Next, the thermal conductivity was measured using the obtained thermally conductive composition according to the above-mentioned method. The results are shown in Table 1. Also, an image taken by an electron microscope is shown in FIG. 2(d).

These results show that the thermally conductive filler of the present invention can suppress the increase in viscosity if the same filler and filling rate are used.

Claims (2)

A thermal conductive particle having a first thermal conductive particle having an average particle diameter of 10 μm or more and 150 μm or less, and a second thermal conductive particle having an average particle diameter of 0.1 μm or more and 5 μm or less and attached to a surface of the first thermal conductive particle,
the first thermally conductive particles and the second thermally conductive particles are each made of aluminum nitride;
A composite thermally conductive filler in which 20% or more and 80% or less of the surface of the first thermally conductive particles is covered with the second thermally conductive particles. The composite thermally conductive filler according to claim 1 further contains a binder in an amount of 2 mass% or less based on the total amount of the composite thermally conductive filler.