JPS5822056B2 - Heat resistant rubber composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a silicone rubber composition comprising a composite additive that imparts thermal conductivity and silicone rubber.

More specifically, the present invention relates to a silicone rubber composition consisting of silicone rubber and a composite additive that imparts thermal conductivity consisting of α-alumina powder and boron nitride powder having a certain blending ratio.

In recent years, molded products of "synthetic resin and rubber-like materials" (hereinafter referred to as "polymer materials") have been widely used for insulating substrates, sealants, heat dissipation sheets, etc. of electronic components.

However, these molded products have low thermal conductivity when they are made of a single polymeric substance, and therefore have poor heat dissipation effects, making it easy to damage circuit elements due to heat accumulation.

Based on the above, in order to improve the thermal conductivity of molded bodies of polymeric materials, it is common practice to mix electrically insulating inorganic compounds with high thermal conductivity. As the ratio increases, the mechanical properties of the resulting molded product decrease (not only does the molding processability during the production of the molded product decrease, There is a natural limit to how high thermal conductivity can be achieved in molded materials.

As inorganic fillers with high thermal conductivity and volume resistivity, α-alumina and "boron nitride" (r
BNl) is known.

Among these, when only BN is blended into a polymer material,
If it is possible to incorporate a high proportion of polymeric substances, it is possible to greatly improve the thermal conductivity of the resulting compound while maintaining its electrical insulation properties.

However, since it is generally difficult to blend high amounts of BN into polymeric substances, there is a natural limit to increasing the thermal conductivity of the blend, and even if a high blend of BN can be achieved, the resulting blend is mechanically brittle. This causes problems in practical use.

On the other hand, since α-alumina has lower thermal conductivity than BN, a compound (composition) having high thermal conductivity cannot be obtained unless it is highly blended (highly filled) with a polymeric substance.

However, as the content of α-alumina in the polymeric material is increased, the mechanical properties of the resulting composition decrease.

For these reasons, it has been difficult to obtain a composition of polymeric substances that has both high thermal conductivity and excellent mechanical properties.

Based on the above, we have conducted various searches to obtain additives whose compositions have high thermal conductivity and excellent mechanical properties when blended with polymeric materials. It has been discovered that when a composite additive having a volume ratio of BN powder/α-alumina of 0.2 to 3.5 is blended into silicone rubber, both of these properties are imparted, and the present invention has been achieved.

In producing the composite additive used in the present invention, by using a specific type of α-alumina powder, a silicone rubber composition with good electrical insulation properties can be obtained.

The α-alumina powder used in the present invention includes:
Examples include conventionally produced fused alumina, calcined alumina, and sintered alumina.

Among these, highly pure alumina is preferred from the viewpoint of electrical insulation properties of the composition.

In addition, if the particle size is very fine, it will be difficult to fill the silicone rubber with high density.On the other hand, if the particle size is relatively large, it will be difficult to fill the silicone rubber composition with the mixer used when manufacturing the silicone rubber composition. damage the molding machine used to manufacture molded products from the

For these reasons, it is desirable that the particle size is in the range of 0.5 to 100 microns.

Further, the shape of the particles is preferably close to spherical in order to achieve high filling.

In addition, regarding BN powder, 2 to 20
Although it is possible to use micron fine powder, from the viewpoint of moldability, it is preferable to use a powder obtained by granulating the above-mentioned fine powder.

Therefore, it is preferable that the particle size of the powder is 20 to 500 μm, particularly preferably 30 to 100 μm.

The blending ratio of the above α-alumina powder and BN powder (BN powder/α-alumina powder) is 0.2 to 3.5 in terms of volume ratio, preferably 0.25 to 0.90.

This is because if the ratio of BN powder/ct-alumina powder is outside the range of 0.2 to 3.5, the resulting composition will not have satisfactory mechanical strength such as tear strength, especially when blended into rubber or the like.

When compounding the composite additive used in the present invention into silicone rubber, the compounding amount of the composite additive in the entire composition obtained is 65 to 78% by volume, which improves processability and thermal conductivity of the composition obtained. From the viewpoint of performance, 66 to 76% by volume is preferable.

In the present invention, when blending the composite additive and silicone rubber, depending on the intended use of the composition, stabilizers, processability improvers, vulcanizing agents, vulcanization accelerators, vulcanization accelerators, scotch inhibitors, Additives such as flame retardants and colorants may also be added.

To produce the compound, mixing methods generally used in the synthetic resin and rubber industry may be applied, including uniform melt-kneading using a mixer such as a Banbury mixer, roll mill, or extruder. The method is appropriate.

The compound (composition) obtained in this way can be processed by molding methods used in these industries (e.g. extrusion method,
It is used after being molded into a desired shape by injection molding method, press molding method).

For example, in the case of forming a heat sink, the sheet is processed into a sheet using a calender roll and a press, cut into desired dimensions and shapes, and then used.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

In addition, in the Examples and Comparative Examples, the thermal conductivity was measured using a quick heat conduction needle (manufactured by Showa Denko Co., Ltd., trade name: QT).
M-MD) at room temperature.

The tear strength was also measured according to the method of JISK-6301.

Examples 1 to 7, Comparative Examples 1 to 8 As a composite additive, α-
α-alumina powder (particle size distribution 1-40μ) made by crushing (lightly crushing) alumina and B
N powder (particle size distribution 1 to 50μ) was prepared.

Silicone rubber (average degree of polymerization 7500, linear polyorganosiloxane, 97.5 mol% methyl groups, 2.5 mol% vinyl groups) 100 parts by weight and 0.4 parts by weight of dicumyl peroxide and blending ratio The α-alumina powder and BN powder shown in Table 1 were kneaded using a mixing roll (diameter 8 inches) for 30 minutes at room temperature (25°C) to prepare a sheet (thickness approximately Lmi).

Each sheet obtained was heated to 5 kg/c at a temperature of 170°C.
Pressing (compression molding) was performed for 10 minutes under the pressure of step 4 to create a pressed sheet.

After curing each sheet for 2 hours using a gear open machine set at 200°C, the thermal conductivity and tear strength were measured.

These results are shown in Table 1.

In Table 1, the volume % of the composite additive is the volume % that the blended α-alumina powder and BN powder occupy in the sheet.

Moreover, BN/α-A1203 is the ratio of BN powder to α-alumina powder.

Comparative Example 9 α- used as a component of the composite additive in Example 1
Other than changing the blending amount of alumina to 1300 parts by weight and the blending amount of BN powder used as other components to 100 parts by weight (the blending ratio of the composite additive to the total composition was 78.4% by volume), An attempt was made to create a sheet using a mixing roll under the same conditions as in Example 1.

However, it was not possible to obtain a sheet.

Claims (1)

[Claims] 1(A) A composite additive consisting of α-alumina powder and boron nitride powder, with a volume ratio of boron nitride powder/α-alumina powder of 0.2 to 3.5; ) A silicone rubber composition which is also a silicone rubber composition and in which the blending ratio of a composite additive is 65 to 78% by volume.