JPH066715B2 - Thermally conductive silicone grease - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to silicone grease. More specifically, among various electric / electronic elements incorporated in electric / electronic devices, a heat-dissipating grease used for the purpose of radiating heat when an element that generates heat is stored and fixed to the devices,
The present invention relates to a heat conductive silicone grease which has both excellent heat conductivity and electric insulation and has a low oil separation degree.

[Technical Background of the Invention and its Problems] With the recent miniaturization and high density of various electric / electronic devices, electric / electronic elements incorporated in these devices, such as power transistors, thyristors, rectifiers, transformers, etc. Measures against heat generation in Japan have been greatly highlighted.

Conventionally, heat dissipation grease has been used as a heat dissipation measure when fixing such electric / electronic elements that generate heat to a radiator or a metal chassis. Among them, the silicone grease that uses polyorganosiloxane as the base oil has less change in characteristics such as consistency with temperature change and more heat resistance than the grease that uses general hydrocarbon lubricating oil as the base oil. Is used because it is excellent.

As a heat radiation filler for forming such a grease composition, metal oxides such as zinc oxide and aluminum oxide, bentonite, and carbon black are used. However, since the thermal conductivity of these fillers themselves is not very high, if the compounding amount is small, the heat radiation effect is not so good.If the compounding amount is increased to improve the thermal conductivity, the grease becomes too hard. There is a problem that it is difficult to use. Further, when a metal powder having a high thermal conductivity is used as the filler, there is a problem that the electrical insulation is lost in spite of the high thermal conductivity.

That is, there is a problem that the heat dissipation grease currently used does not sufficiently dissipate heat generated by various electric / electronic elements.

[Object of the Invention] The present invention has been made to solve such conventional problems, and an object thereof is to obtain a silicone grease having excellent thermal conductivity and electrical insulation.

[Outline of the Invention] That is, the heat conductive silicone grease of the present invention comprises (A) a general formula [R ¹ _a SiO _{(4-a) / 2} ] n (where R ¹ is an alkyl group having 1 to 12 carbon atoms). A monovalent group selected from the group consisting of a group, an alkenyl group, and a substituted or unsubstituted aryl group, a is a number from 1.9 to 2.7, and n is a positive number) 100 parts by weight of a polyorganosiloxane (B ) Boron nitride (particle size, 0.01-100 μm) 50-
It is characterized by comprising 1000 parts by weight.

The polyorganosiloxane (A) of the present invention, represented by the general formula [R ¹ _a
R ¹ in SiO _{(4-a) / 2} ] n is a monovalent group selected from the group consisting of alkyl groups having 1 to 12 carbon atoms, alkenyl groups, and substituted or unsubstituted aryl groups. When the carbon number exceeds 12, it is not preferable because handling becomes inconvenient and the thermal stability is lowered. R ¹ may be the same or different. R ¹ is a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, an octyl group,
Alkyl group such as decyl group and dodecyl group, vinyl group,
Examples thereof include an alkenyl group such as an allyl group, a phenyl group, and an aryl group such as a chlorinated phenyl group, but a methyl group is most commonly used from the viewpoint of ease of synthesis and heat resistance.

Further, if a in the general formula (A) is smaller than 1.9, it cannot be used because it becomes hard, and if larger than 2.7, an appropriate viscosity range cannot be obtained. Further, n in the general formula (A) is preferably a number that satisfies the viscosity described below.

That is, these (A) polyorganosiloxanes have a temperature of 2
It preferably has a viscosity of 30 to 500000 cSt at 5 ° C, and more preferably 50 to 100000 cSt. When it is less than 30 cSt, the volatility of the polyorganosiloxane becomes large and the grease obtained may easily flow, which is not preferable. On the contrary, its viscosity is 500000
Those exceeding cSt are not preferable because they may be difficult to synthesize and may be difficult to work.

The boron nitrite of (B) is a powder having a crystal structure of a stack of hexagonal mesh planes, and is a ceramic showing extremely high thermal conductivity. Although this boron nitride can be obtained with various particle diameters depending on the production method, in order to obtain a composition having good thermal conductivity in the present invention and maintaining a grease state, the particle diameter is 0.01 It is preferable to use those having a thickness of -100 μm. Boron nitride of less than 0.01 μm may be difficult to produce, and it may be difficult to form a uniform silicone grease by mixing with the polyorganosiloxane (A). On the other hand, when it exceeds 100 μm, it is difficult to keep the resulting composition in a greasy state, and the amount of polyorganosiloxane (A) separated may increase over time, which is not preferable.

It should be noted that, as boron nitride, a better grease-like composition can be obtained by blending several types of boron nitride within a particle size range of 0.01 to 100 μm, rather than using those having the same particle size. To be

The blending amount of the boron nitrite (B) is 50 to 1000 parts by weight, more preferably 66 to 1000 parts by weight, based on 100 parts by weight of the polyorganosiloxane (A). If it is less than 50 parts by weight, good thermal conductivity cannot be obtained, and if it exceeds 1000 parts by weight, not only the effect of improving the thermal conductivity decreases, but also the composition which is difficult to mix with (A) and is obtained. It is too hard to keep the grease state.

The basic composition of the composition of the heat conductive silicone grease of the present invention is as described above, and it is possible to obtain a silicone grease which is excellent in heat conductivity and electric insulation and has small oil separation. When finely separated grease is required, it is preferable to share silica fine powder.
Examples of such fine silica powder include fumed silica and those obtained by surface-treating it with organosilane, polyorganosiloxane, polyorganosilazane and the like.
The amount of the fine silica powder blended is preferably 10 parts by weight or less, more preferably 0.1 to 10 parts by weight, based on 100 parts by weight of the polyorganosiloxane (A). When it exceeds 10 parts by weight, the composition is hardened and the thermal conductivity is lowered.

Further, other heat-dissipating fillers such as zinc oxide and aluminum oxide may be used in combination, or an antioxidant such as an amine-based compound or a selenium-based compound may be added as an additive to be added to an ordinary grease, if necessary, An oiliness improver or the like may be added in an arbitrary amount as long as the object and effect of the present invention are not impaired.

In the production of the heat conductive silicone grease of the present invention, for example, the components (A) and (B) and, if necessary, fillers and additives are blended, charged into a heating pot equipped with a stirrer, and stirred to be uniform. Further, a method of further heating and kneading at about 100 to 160 ° C., returning to room temperature, and homogenizing using a three-roll, a paint roll, etc., or a composition obtained by homogenizing without heating, a three-roll, a paint roll, etc. There is a method for homogenizing with, and it can be selected according to need.

[Advantages of the Invention] According to the present invention, it is possible to obtain a grease having excellent heat conductivity and electrical insulation, which is not present in the conventional silicone grease for heat dissipation. In addition, the obtained grease has advantages such as small oil separation and low specific gravity as compared with conventional silicone grease using a metal oxide.

[Examples of the Invention] Hereinafter, the present invention will be described with reference to Examples. All parts in the examples are parts by weight, and the thermal conductivity, consistency and oil separation were measured by the following devices or methods.

Thermal conductivity: Shower Denko Co., Ltd., Theotherm QT
M-DII Rapid thermal conductivity meter Consistency: Measure mixing consistency according to JIS K 2220 Oil separation degree: Heat at 150 ° C for 24 hours according to JIS K 2220 Example 1 Formula 100 parts of polydimethylsiloxane having a viscosity of 1000 cSt at 25 ° C. and 100 parts of boron nitride (Denka boron nitride-GP, particle size 1 to 5 μm, trade name manufactured by Denki Kagaku Kogyo Co., Ltd.) powder Charge in an additional heating kettle, stir at room temperature to mix evenly, and then add 150
The mixture was heated and mixed at 0 ° C for 2 hours. The mixture was allowed to cool and returned to room temperature, and then homogenized with a bain troll to obtain a silicone grease S-1.

As a comparative example, the polydimethylsiloxane of Example 1 was used.
0 parts and 100 parts of zinc oxide powder were prepared in the same manner as in Example 1 to obtain silicone grease C-1.

Also, as a comparative example, the polydimethylsiloxane of Example 1 was used.
100 parts, 300 parts of zinc oxide powder, and 12 parts of fumed silica treated with hexamethyldisilazane were prepared in the same manner as in Example 1 to obtain silicone grease C-2.

Example 2 Formula And 100 parts of polyorganosiloxane represented by
150 parts of the boron nitride powder used in Example 1 was prepared in the same manner as in Example 1 to obtain silicone grease S-2.

As a comparative example, the polyorganosiloxane 100 of Example 2 was used.
Parts and 400 parts of aluminum oxide powder were prepared in the same manner as in Example 1 to obtain silicone grease C-3.

Example 3 Formula In the same manner as in Example 1, 100 parts by weight of the polyorganosiloxane shown in Example 1, 120 parts of the boron nitride powder used in Example 1 and 5 parts of fumed silica treated with hexamethyldisilazane were prepared, and a silicone grease was prepared. S-
Got 3.

Example 4 Formula And 100 parts of polyorganosiloxane represented by
233 parts of boron nitride used in Example 1 was prepared in the same manner as in Example 1 to obtain silicone grease S-4.

With respect to the greases S-1 to S-4 of the present invention and the greases C-1 to C-3 of the comparative examples obtained above, the thermal conductivity, the specific gravity, the consistency and the oil separation degree were measured. The results are shown in the following table

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Claims (4)

[Claims] 1. (A) General formula [R ¹ _a SiO 2 _{(4-a) / 2} ]
_n (wherein R ¹ is a monovalent group selected from the group consisting of an alkyl group having 1 to 12 carbon atoms, an alkenyl group, and a substituted or unsubstituted aryl group, a is a number of 1.1 to 2.7, and n is Is a positive number) 100 parts by weight of polyorganosiloxane (B) Boron nitride (particle size, 0.01 to 100 μm) 50 to
Thermally conductive silicone grease, which is composed of 1000 parts by weight. 2. The viscosity of (A) at 25 ° C. is 30 to 500000 cS.
The thermally conductive silicone grease according to claim 1, which is t. 3. The viscosity of (A) at 25 ° C. is 50 to 100,000 cS.
The thermally conductive silicone grease according to claim 1, which is t. 4. The compounding amount of boron nitride of (B) is (A) 10.
The heat conductive silicone grease according to claim 1, wherein the amount is 66 to 1000 parts by weight relative to 0 parts by weight.