JP6438701B2 - Heat dissipation rubber composition - Google Patents

Description

  The present invention relates to a heat-dissipating rubber composition used in electronic equipment such as automobile electrical components, personal computers, mobile phones, and home appliances.

An electronic device such as an automobile electrical component includes an electronic circuit board on which a heat generating component such as a CPU and a capacitor is mounted, and a housing that surrounds the outside. The heat-dissipating rubber composition is provided so as to be sandwiched between the electronic circuit board and the housing, and transfers heat generated from the heat-generating component to the housing to escape from the housing, thereby preventing the temperature rise of the electronic device. is there.
Conventional heat-dissipating rubber compositions have come to be used in which heat conductive fillers such as aluminum oxide, magnesium oxide, talc and silica are blended at a high ratio with respect to the base rubber.
For example, Patent Document 1 below discloses a configuration in which water-resistant aluminum nitride is added to silicone rubber. Patent Document 2 discloses a configuration in which silicon carbide is added to silicone rubber and a configuration in which graphitized carbon fiber is further added.

JP 2001-106912 A JP 2003-183498 A

  The heat-dissipating rubber composition has a high thermal conductivity for efficiently transferring heat to the housing and a high elasticity so as not to damage the electronic circuit board and the heat-generating component when incorporated in an electronic device. In addition, it is required to have a high dielectric breakdown voltage to withstand dielectric breakdown due to static electricity.

  The heat dissipation rubber composition in Patent Document 1 achieves a thermal conductivity of 2.78 W / m · K by blending 150 parts by weight of water-resistant aluminum nitride and 250 parts by weight of magnesium oxide with 100 parts by weight of silicone rubber. (See Example 1). However, aluminum nitride is an expensive material as a thermally conductive filler, which may cause an increase in cost.

  The heat-dissipating rubber composition in Patent Document 2 is 10.7 W / m · K by blending 23 parts by weight of aluminum oxide, 24 parts by weight of silicon carbide and 17 parts by weight of graphitized carbon fiber with 36 parts by weight of silicone rubber. (See Example 5 in Table 2). However, silicon carbide, like aluminum nitride, is an expensive thermally conductive filler, which may increase costs, and the electrical conductivity of graphitized carbon fiber is extremely high, leading to energization. At the same time, the dielectric breakdown voltage may be significantly reduced.

  An object of the present invention is to provide a heat radiation rubber having high thermal conductivity, high elasticity, and high breakdown voltage at low cost.

  In order to solve the above problems, the present inventor used a small amount of a highly conductive inorganic filler and a semiconductive tetrapod-like zinc oxide whisker in combination with a silicone rubber containing an insulating inorganic filler. The present inventors have found that high thermal conductivity can be realized without lowering volume resistance and dielectric breakdown voltage, and completed the present invention.

First characterizing feature of the heat dissipation rubber composition of the present invention, the inorganic filler 400 having the polymer component 100 parts by weight, the thermal conductivity of 5~80W / m · K, the more volume resistivity ¹⁰ 10 Ω · cm 600 parts by weight, thermal conductivity of 100 to 300 W / m · K, volume resistivity of 10 ⁻³ to 10 ⁻⁶ Ω · cm, ³ to 30 parts by weight of thermally conductive and conductive filler, and tetrapod-like zinc oxide whisker see contains 20-40 parts by weight, the polymer component lies in a silicone rubber, or acrylic rubber.

[Action and effect]
Since the heat-dissipating rubber composition of this configuration has high thermal conductivity, the heat generated from the heat generating components of the electronic circuit board can be efficiently transferred to the housing and escaped from the housing to reliably prevent the temperature rise of the electronic device. .
In addition, since the heat dissipating rubber composition of this configuration is highly elastic, it does not damage the electronic circuit board and the heat generating component when incorporated in an electronic device, and high adhesion to the heat generating component and the housing is ensured. .
Furthermore, since the heat-dissipating rubber composition having this configuration has a high dielectric breakdown voltage, it can sufficiently withstand dielectric breakdown due to static electricity of electronic equipment.

  The second characteristic configuration is that the aspect ratio of the thermal conductive / conductive filler is 2 to 100.

[Action and effect]
When the aspect ratio of the thermal conductive / conductive filler is 2 to 100, the thermal conductivity can be improved efficiently by providing a contact point with a plurality of inorganic fillers with a small addition amount, and the thermal conductivity. -The amount of conductive filler added can be reduced.

  A third characteristic configuration is that the average fiber length of the needle-like portion in the tetrapod-like zinc oxide whisker is 10 to 20 μm.

[Action and effect]
When the average fiber length of the needle-like portion of the tetrapod-like zinc oxide whisker is 10 to 20 μm, it becomes easy to come into contact with the heat conductive / conductive filler, and the breakdown voltage can be improved.

It is a figure which shows the material composition etc. of a comparative example. It is a figure which shows the material composition etc. of an Example.

Hereinafter, embodiments of the heat dissipating rubber composition of the present invention will be described.
The heat-dissipating rubber composition of the present invention comprises a polymer component, an inorganic filler, a heat conductive / conductive filler, and a tetrapod-like oxidized whisker described below.

(Polymer component)
The polymer component in the present invention means an elastic material having heat resistance and rubber-like elasticity. The polymer component used preferably has a thermal conductivity of 0.1 to 0.3 W / m · K and a volume resistivity of 10 ⁸ to 10 ¹⁵ Ω · cm. Examples of such polymer components include silicone rubber, acrylic rubber, natural rubber, styrene butadiene rubber, butadiene rubber, acrylonitrile butadiene rubber, ethylene propylene rubber, chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, and thermoplastic elastomer. Can be mentioned.

  The thermal conductivity indicates an amount representing the degree of thermal conduction, and means a value obtained by dividing the amount of heat flowing per second in a unit area perpendicular to the heat flow by the temperature difference of the unit length. The volume resistivity means a value indicating an electrical resistance, which is a measure of the conductivity (ease of electricity) of a substance, per unit volume (1 cm × 1 cm × 1 cm).

(Inorganic filler)
The inorganic filler in the present invention means an inorganic material powder having a thermal conductivity of 5 to 80 W / m · K and a volume resistivity of 10 ¹⁰ Ω · cm or more. Moreover, as an inorganic filler to be used, what has an average particle diameter of 1-50 micrometers is desirable. Examples of such an inorganic filler include magnesium oxide (MgO), aluminum oxide (Al ₂ O ₃ ), and silica.

(Thermal conductivity / conductive filler)
The heat conductive / conductive filler in the present invention means a powder having a heat conductivity of 100 to 300 W / m · K and a volume resistivity of 10 ⁻³ to 10 ⁻⁶ Ω · cm. Further, as the heat conductive / conductive filler to be used, those having an average particle diameter of 5 to 100 μm are desirable, and those having an aspect ratio of 2 to 100 are more desirable. Examples of such a heat conductive / conductive filler include metal flakes such as aluminum, copper, silver, and silicon, and scaly graphite.

(Tetrapod-like zinc oxide whisker)
The tetrapod-like zinc oxide whisker in the present invention means a single crystal of zinc oxide (ZnO) grown in a needle shape (tetrapod shape) from the crystal surface toward the outside. The tetrapod-like zinc oxide whisker used has a thermal conductivity of 20 to 60 W / m · K, a volume resistivity of 10 ⁻¹ to 10 ² Ω · cm, and a bulk specific gravity of 0.2 g / cm ³ or less. Those having an average fiber length of 10 to 20 μm are more preferable.

(Production method)
The heat-dissipating rubber composition of the present invention comprises 400 to 600 parts by weight of inorganic filler, 3 to 30 parts by weight of thermally conductive / conductive filler, and tetrapod-like zinc oxide whisker with respect to 100 parts by weight of the polymer component described above. Can be produced by, for example, kneading with an open roll, a kneader mixer or the like, and press vulcanizing at a predetermined temperature condition (for example, at 175 ° C. for 15 minutes). In addition, when manufacturing the heat radiating rubber composition of this invention, you may manufacture by adding other components, such as a plasticizer and a vulcanizing agent, as needed.

  Since the heat-radiating rubber composition of the present invention thus produced has a high thermal conductivity of 1.7 W / m · K or more, the heat generated from the heat-generating component of the electronic circuit board is efficiently transmitted to the housing. As a result, the temperature rise of the electronic device can be surely prevented.

  Moreover, since the heat-radiating rubber composition of the present invention has a high dielectric breakdown voltage of 7 kV / mm or more, it can sufficiently withstand dielectric breakdown due to static electricity of electronic equipment. The dielectric breakdown voltage is a voltage that is applied to an insulator and gradually raised to cause electrical breakdown (part of the insulator melts and holes or carbonizes). This is the voltage when the power is turned on. The dielectric breakdown voltage is expressed as a voltage value with respect to an insulator having a thickness of 1 mm.

  Furthermore, since the hardness of the heat dissipating rubber composition of the present invention is A90 or less, it has high resilience to prevent damage to the electronic circuit board and the heat-generating component when incorporated in an electronic device, and high heat-generating component and housing. Adhesion is ensured.

  According to the material composition shown in FIG.1 and FIG.2, each heat dissipation rubber composition of Examples 1-10 and Comparative Examples 1-4 was produced. As each material, silicone rubber (William plasticity: 120), acrylic rubber (ethylene acrylic elastomer Mooney viscosity: 17.5), heavy burned magnesium oxide A (average particle size: 50 μm silane coupling treatment), heavy burned oxidation Magnesium B (average particle size: 10 μm silane coupling treatment), heavy calcined magnesium oxide C (average particle size: 2 μm silane coupling treatment), tetrapod-like zinc oxide whisker (average fiber length: 10 μm), scaly graphite (average particles) Diameter: 10 μm, aspect ratio: 10), aluminum flake (average particle diameter: 17 μm, aspect ratio: 75), plasticizer (polyether ester type), vulcanizing agent a (hexamethylenediamine carbamate), vulcanizing agent b ( 2,5-dimethyl-2,5-bis (tertiary butyl peroxy ) Hexane 50% dilution product) was used vulcanization accelerator (diphenylguanidine). The numerical value of each material in FIG.1 and FIG.2 is shown by the weight part.

  According to the material composition shown in FIG. 1 and FIG. 2, the materials are weighed for each of Examples 1 to 10 and Comparative Examples 1 to 4, and kneaded until they are uniformly dispersed with an open roll. It was created. Next, the obtained dispensing sheet was charged into a mold, and press vulcanized at 175 ° C. for 10 minutes to prepare a press sheet.

For each of Examples 1 to 10 and Comparative Examples 1 to 4, thermal conductivity, dielectric breakdown voltage, hardness, tensile strength, and elongation at break were measured. The results are shown in FIGS.
About heat conductivity (W / m * K), it measured by the hot-wire method using the rapid thermal conductivity meter QTM-500 by Kyoto Electronics Industry Co., Ltd.
With respect to the dielectric breakdown voltage (kV / mm), the voltage was gradually raised until the sheet sample with a thickness of 1 mm or less was sandwiched between electrodes having a diameter of 40 mm, and the voltage / thickness at the time of dielectric breakdown was confirmed.
The hardness was measured based on JIS K6253-3.
The tensile strength (MPa) and elongation at break (%) were measured based on JIS K6251.

  As shown in FIG. 1, the thermal conductivity of Comparative Examples 1, 2, and 4 containing no tetrapod-like zinc oxide whisker is 1.83 to 2.17 W / m · K, the hardness is A68 to A74, and high heat Although it had conductivity and high elasticity, the dielectric breakdown voltage was as low as 2.68 to 6.48 kV / mm. In Comparative Example 3 including tetrapod-like zinc oxide whisker but not including heat conductive / conductive filler, the dielectric breakdown voltage was 10.2 kV / mm, the hardness was A64, and high thermal conductivity and high Although it had elasticity, the thermal conductivity was as low as 1.61 W / m · K.

  On the other hand, as shown in FIG. 2, the thermal conductivity of Examples 1 to 10 including the tetrapod-like zinc oxide whisker is 1.74 to 2.09 W / m · K, the hardness is A62 to A89, and the insulation. The breakdown voltage was 7.1 to 14.42 kV / mm, and all had high thermal conductivity, high elasticity, and high breakdown voltage.

  The heat-dissipating rubber composition according to the present invention can be applied to electronic devices such as automobile electrical components, personal computers, mobile phones, and home appliances.

Claims (3)

For 100 parts by weight of the polymer component,
400 to 600 parts by weight of an inorganic filler having a thermal conductivity of 5 to 80 W / m · K and a volume resistivity of 10 ¹⁰ Ω · cm or more,
³ to 30 parts by weight of heat conductive and conductive filler having a thermal conductivity of 100 to 300 W / m · K, a volume resistivity of 10 ⁻³ to 10 ⁻⁶ Ω · cm, and a tetrapod-like zinc oxide whisker 20 to 40 weights part only contains,
A heat dissipation rubber composition , wherein the polymer component is silicone rubber or acrylic rubber .   The heat radiation rubber composition according to claim 1, wherein the heat conductive / conductive filler has an aspect ratio of 2 to 100.   The heat dissipation rubber composition according to claim 1 or 2, wherein an average fiber length of the needle-like portion in the tetrapod-like zinc oxide whisker is 10 to 20 µm.

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