JPH0370754A - Highly thermally conductive rubber composition - Google Patents

Abstract

PURPOSE:To obtain the title composition good in processability, suitable for preventing the temperature rise of junctions through the releasing the heat generated from exothermic electronic parts by incorporating a rubber with specific graphite surface-treated with a titanate coupling agent. CONSTITUTION:The objective composition can be obtained by incorporating (A) a rubber with (B) pref. 10-50vol.% of specific graphite prepared by flaking expanded graphite. surface-treated with a titanate coupling agent.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a rubber composition with excellent thermal conductivity, and is particularly suitable for dissipating heat generated from heat-generating electronic components and preventing temperature rises at junctions. The present invention relates to a highly thermally conductive rubber composition.

(Prior Art) Electronic components such as thyristors, power transistors, and diodes may gradually deteriorate in characteristics due to heat generation during operation, and sometimes even damage the components themselves. Therefore, the following methods are known as means for quickly removing heat generated from these electronic components while ensuring insulation.

A device in which an insulating material such as mica or polyester sheet is interposed between an electronic component and a heat radiating body, and heat radiating grease is applied to both sides of the insulating material (hereinafter referred to as prior art ■) JP-A-62-25440 An invention related to "a thermally conductive sheet for electrical components comprising a graphite sheet alone or one or both sides of which is coated with silicone rubber" disclosed in Japanese Patent Application Laid-open No. 1983-1989 (hereinafter referred to as prior art ■) 163623, ``A high heat conductive material with a thickness of 0.05 mm or more made of an elastomer or plastic filled with 50% by volume or more of a powder, short fiber, or granular material whose surface is made of a conductive material. An invention relating to a flexible sheet and a method for manufacturing the sheet by a doctor blade method (hereinafter referred to as prior art 2) was disclosed in Japanese Patent Publication No. 16978/1982, and was disclosed in Japanese Patent Publication No. 16978/1983, which is a method for producing a polyalkyl siloxane, which is the main component of silicone rubber. By adding a different type of polyorganosiloxane oil with poor solubility or small size, this oil can be released on the surface of the molded product under normal conditions or when subjected to moderate tightening, creating fine voids at the boundary. Invention related to "Rubber-like molded product for heat dissipation that prevents reduction in heat transfer efficiency due to the presence of air" (hereinafter referred to as prior art ■) JP-A-1988-1
88441, "a.

Thermal material containing chlorinated polyethylene, b, ethylene-vinyl acetate copolymer, thermoplastic elastomer or one of high-density polyethylene, 0.50 to 8% filler, d, and other additives. Inventions related to conductive materials. (hereinafter referred to as Prior Art V) disclosed in Japanese Patent Publication No. 57-52376, "A sheet-like shaped body mainly composed of an inorganic filler and synthetic rubber, the amount of the inorganic filler added to the molded body. is 35 to 70% by volume, and the inorganic filler contains (a)(
b) Consists of two components, (a) component is boron nitride, 0))
The component is one or more of aluminum, silica, magnesia, zinc oxide, and mica, and the ratio is (a) component is Cbut
An invention relating to a heat dissipating sheet having a volume ratio of 0.3 to 3 per minute. (Hereinafter, referred to as prior art ■) (Problems to be solved by the invention) However, prior art I had the following problems.

``■ Mica has poor processability and is difficult to handle. ■ Polyester sheets have poor heat dissipation properties. ■ When heat dissipation grease is used for a long time, oil flows out and the heat dissipation effect decreases.''

Conventional technology ■ uses ordinary graphite, so its thermal conductivity is not so high, and it is coated with silicone rubber to make it easier to attach to electronic components (Example 2.3)
As described in Table 1 of the third report of the publication, the thermal resistance is further increased and the thermal conductivity is lower than that of the graphite sheet alone (Example 1).

The substances with conductive surfaces referred to in Prior Art (■) refer to metal powders, short metal fibers, etc., but as stated in the upper right column of page 2 of the publication, these substances are coated with elastomers etc.
When filled in a large amount of more than % by volume, there is a problem in that mechanical strength and mechanical properties are significantly reduced. Moreover, even if an attempt is made to manufacture the rubber sheet using a calendar, which is a typical method for manufacturing rubber sheets, the calender rolls will be severely scratched and worn, making calendering impossible. Such sheets can be manufactured only by the doctor blade method, resulting in a complicated equipment configuration requiring additional equipment such as a drying device.

Prior art (2) involves adding silicone oil that has no or little compatibility with the base polymer of the silicone rubber, and thus deteriorates the physical properties of the rubber molded product.

The filler of Prior Art V refers to aluminum oxide or aluminum hydroxide, and since it contains a large amount of metal filler of 50 to 80% by weight, the moldability is extremely poor.

Conventional technology (2) uses expensive boron nitride, which increases manufacturing costs.

The present invention has been made in view of the problems of the prior art, and its purpose is to provide a highly thermally conductive rubber composition that has high thermal conductivity, good processability and rubber physical properties, and is inexpensive. There is a particular thing.

(Means for Solving the Problems) In order to achieve the above object, the gist of the present invention is to provide a highly thermally conductive rubber in which graphite obtained by exfoliating expanded graphite and surface-treated with a titanate coupling agent is added to rubber. In the composition.

The exfoliated expanded graphite of the present invention is obtained by heat-treating acid-treated graphite at a high temperature to rapidly vaporize the interlayer components of graphite crystals, and crushing the expanded graphite between the eyebrows. .

The amount of this exfoliated expanded graphite added is 10 to 50
Volume % is preferred. This is because if it is less than 10% by volume, sufficient thermal conductivity cannot be obtained, and if it exceeds 50% by volume, the rubber strength will be greatly reduced.

The titanate coupling agent of the present invention is an agent that performs molecular crosslinking at the interface between an inorganic filler and an organic polymer matrix to improve physical properties, and contains titanium as a central element.

(Function) Typical graphite crystals belong to the macrogonal system, and have a structure in which huge hexagonal mesh planes are piled up in layers, and the anisotropy is extremely large, parallel to the layer planes (a-axis). The thermal conductivity in the direction perpendicular to the layer plane (C axis) is considerably larger than that in the direction perpendicular to the layer plane (C axis).

Expanded graphite is expanded hundreds of times in the C-axis direction while maintaining its original layered structure, so the graphite obtained by crushing this expanded graphite into flakes is highly oriented in the A-axis direction, and is more oriented than normal graphite. The titanate coupling agent combined with the expanded graphite flakes forms a film that is easily compatible with organic substances, significantly improving dispersibility and improving uniform thermal conductivity. can.

Furthermore, since it is an organic filler, there is no risk of damage to the roll even if it is added in large amounts, and it has good flexibility and can be easily processed according to normal processing methods.

In addition, since it has sufficient rubber elasticity, it has good adhesion to electronic components and the like.

(Example) Examples of the present invention will be described below.

(1) Production of filler As the titanate coupling agent, BlenAct KR238S, BlenAct KR134S, BlenAct KR34S, BlenAct KRTTS, and BlenAct KR46B manufactured by Ajinomoto ■ were used. Chemical names corresponding to these trade names will be described later.

Graphite obtained by crushing expanded graphite into flakes (72.6 g of EXP-P L manufactured by Nippon Graphite Industries ■) was added to 300 cc of MEK solution containing 1% by weight of any of the titanate coupling agents mentioned above, and the mixture was stirred for 3 minutes. After being left at room temperature for 2 days, it was dried at about 80° C. for 1 day to obtain a filler according to this example.

Comparison fillers include graphite obtained by crushing the same expanded graphite into flakes (not treated with a titanate coupling agent), natural graphite (HOP manufactured by Nippon Graphite Industries), aluminum, alumina, and conductive carbon black. (Toka Black 5500) was used.

(2) Production of sheet 4 parts by weight of magnesium oxide, 5 parts by weight of zinc oxide and 1 part by weight of stearic acid were added to 100 parts by weight of commercially available chloroprene rubber (Neobrene CRT manufactured by Showa Denko - Tesbon), and the above A predetermined amount of filler (described later) is added and kneaded with a roll to prepare a sheet, approximately 1 mm thick.
A vulcanized sheet with + thickness was obtained at 150° C. for 20 minutes.

(3) Measurement of physical properties of sheet Next, the physical properties of the vulcanized rubber sheet produced by the method described above were measured.

■ As a filler, the filling amount of exfoliated expanded graphite (both the example treated with a titanate coupling agent and the untreated comparative example) was 10.20.40% by volume, natural graphite, aluminum, Thermal conductivity, modulus (M+...), strength at break, elongation at break, and hardness were measured with each filling amount of conductive carbon black being 20% by volume. The results are shown in Table 1 on page 11.

(2) As a filler, the thermal conductivity and modulus (M,

. , M,), breaking strength, breaking elongation, and hardness were measured. The results are shown in Table 2 on page 12.

The thermal conductivity was measured using a Kadochik precision rapid thermophysical property measuring device Thermolab ■.

The chemical names corresponding to each trade name of titanate coupling agents are as follows.

BrenAct KR23BS-Bis(dioctylpyrophosphate) ethylene titanate BrenAct KR13
4S-Dicumylphenyloxyacetate titanate Bren-Act K R, 34S-Isopropyl tricumylphenyl titanate Bren-Act KRTTS = Isopropyl triisostearoyl titanate Bren-Act KR46B = Tetraoctyl bis(ditridecyl phosphite) titanate From Tables 1 and 2 above , ■ The thermal conductivity of the exfoliated expanded graphite treated with a titanate coupling agent and filled with the filler according to this example is the highest, indicating that the present invention can provide a rubber composition with extremely good thermal conductivity. I understand.

(2) Even in Example 3 in which the filling amount was increased to 40% by volume, the increase in hardness was not so large and it seems that the rubber elasticity was sufficient.

■The strength tends to decrease rapidly as the filling amount increases from 10% by volume (Example 1) to 40% by volume (Example 3).
Filling more than % by volume is not preferable.

(2) If the filling amount is less than IO volume %, sufficient thermal conductivity cannot be obtained.

Note that the rubber is not limited to chloroprene rubber, and various synthetic rubbers can be used, and the compounding agents may be changed as appropriate depending on the type of rubber used.

The sheet processing method is not particularly limited,
For example, it can be processed using a commonly used mixing machine such as a Banbury mixer, a roll machine, a calender, etc.

(Effects of the Invention) According to the present invention, a highly thermally conductive rubber composition having high thermal conductivity, good processability, and good rubber physical properties can be provided.

Claims (1)

[Claims] A highly thermally conductive rubber composition in which graphite obtained by exfoliating expanded graphite and surface-treated with a titanate coupling agent is added to rubber.