JPH11279406A - Highly heat conductive silicone rubber composition and heat conduction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition excellent in thermal conductivity and heat radiating properties, good in tackiness and adhesion and useful as a heat radiating sheet for electronic parts generating heat by including carbon fibers having a length within a specific range in a silicone rubber substrate. SOLUTION: This composition is obtained by including (B) carbon fibers which have 10-150 μm length and preferably 300-1,200 W/m.K thermal conductivity and are preferably pitch-based carbon fibers in (A) a silicone rubber substrate. The amount of the contained component B is preferably 50-150 wt.% based on the component A. The component A consists essentially of an organopolysiloxane having preferably 0.5-30 Pa.s viscosity at 25 deg.C before curing and 100-20,000 average degree of polymerization and represented by the average compositional formula; Ra SiO(4-a)/2 [R is a (substituted) 1-10C monovalent hydrocarbon; (a) is 1.85-2.10].

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a highly heat-conductive silicone rubber composition having high thermal conductivity and excellent adhesiveness or adhesion, which is suitable for use as a heat-dissipating sheet for electronic components that generate heat. The present invention relates to a heat conducting device using a silicone rubber composition.

[0002]

2. Description of the Related Art In recent years, the amount of heat generated by a CPU (Central Processing Unit) has increased with the miniaturization and high performance of portable information devices, especially notebook computers, and how this heat is released to the outside for cooling. Is a big problem. Conventionally, as such a radiation measure, for example, a radiation plate made of aluminum or the like to which a heat pipe is connected has been widely used. This radiator plate needs to be fixed on the CPU, and a method of tightening with a screw is generally employed.

However, in this case, inevitably, the CP
Since thermal resistance occurs at the contact interface between U and the heat sink,
The original performance of the heat dissipating component cannot be exhibited, and the heat dissipating property is also reduced. On the other hand, if the thermal resistance is too large, the heat diffusion due to the radiation from the CPU also increases, which may adversely affect peripheral components. Therefore, it is important to efficiently transfer heat to the heat sink by reducing the contact resistance between the CPU and the heat sink.

As means for reducing the contact thermal resistance,
JP-A-6-155517, JP-A-7-26635
No. 6, JP-A-8-238707, etc., in order to enhance thermal conductivity, metal powder or ceramic powder such as aluminum oxide, boron nitride, aluminum nitride or carbon such as natural graphite and carbon black. A heat-dissipating silicone rubber sheet in which a filler such as powder is added to an adhesive silicone rubber substrate has been proposed.

However, since the thermal conductivity of such a silicone rubber sheet is ultimately greatly affected by the frequency of contact between filler particles, the inherent high thermal conductivity of the filler is not sufficiently exhibited. Although the contact thermal resistance is reduced, there is a problem that the heat radiation performance is still insufficient. On the other hand, if the compounding amount of the filler is increased to increase the contact frequency, there is a problem in the manufacturing process that the base material does not cure or the adhesiveness of the finished rubber sheet is reduced.

Japanese Patent Application Laid-Open No. 7-207160 discloses that a silicone polymer base material is kneaded with a fine powder filler called a thickener and a metal or an alloy, and further mixed with a carbon material such as carbon fiber. Discloses a method for producing a silicone composition having excellent heat conductivity and conductivity.

However, the above-mentioned carbon material is a component only for the purpose of improving or stabilizing the conductivity of the silicone composition, and is not disclosed as a component for improving the thermal conductivity. No method is disclosed for imparting high thermal conductivity to the silicone composition using fibers.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art, and to provide a high heat conductive silicone rubber composition having excellent heat conductivity and heat dissipation, and good adhesion and adhesion. Is to provide.

[0009]

That is, the highly heat-conductive silicone rubber composition of the present invention has a length of 1 mm on a silicone rubber substrate.
It is characterized by adding carbon fibers of 0 to 150 μm.
Further, the heat conducting device of the present invention is a device in which a heat generating portion and a heat radiating portion are connected by using the silicone rubber composition.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The silicone rubber substrate used in the present invention is not particularly limited, and known ones can be used. In particular, the viscosity at room temperature (25 ° C.) before curing is usually 0.1. 1 to 300 Pa · s, preferably 0.
3 to 100 Pa · s, more preferably 0.5 to 30 P
a · s is used. The silicone rubber composition can be diluted or dissolved or dispersed with an aromatic or aliphatic solvent so as to have a workable viscosity.

As the silicone rubber substrate, either a one-part curing type or a two-part curing type can be used, but a two-part curing type is preferably used. The silicone rubber substrate may contain an organopolysiloxane represented by an average composition formula of R _a SiO _{(4-a) / 2} as a main component, and may not contain an inorganic filler, or may contain an inorganic filler.

Here, in the above average composition formula, R is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms (for example, methyl group, ethyl group, propyl group, butyl group, 2-ethylbutyl group and Alkyl group such as octyl group, alkenyl group such as vinyl group, allyl group or hexenyl group, cycloalkyl group such as cyclohexyl group and cyclopentyl group, aryl group such as phenyl group and tolyl group, and aralkyl group such as phenylethyl group. In these groups, some or all of the hydrogen atoms may be substituted with a halogen atom or a cyano group.)
And a is preferably a positive number of 1.85 to 2.10. The average degree of polymerization of this organopolysiloxane is
It is preferably from 100 to 20,000, more preferably from 300 to 2,000 for a liquid type, and preferably from 6,000 to 12,000 for a rubber type.

As the inorganic filler which can be blended with the silicone rubber substrate, generally, metal oxide, boron nitride and the like can be mentioned. Specifically, aluminum oxide, magnesium oxide, silicon dioxide, beryllium oxide, cubic Examples thereof include boron nitride, hexagonal boron nitride, silicon carbide, and silicon nitride, and these may be used alone or in combination of two or more. . In this case, the amount varies depending on the heat conductive inorganic filler to be compounded, but the heat conductive inorganic filler is added to 100 parts by weight of the organopolysiloxane.
It is preferable to add 1,000 parts by weight.

The silicone rubber substrate may be vulcanized at room temperature or heat under the temperature conditions at the time of vulcanization. In the vulcanization method, peroxide vulcanization, addition vulcanization, UV vulcanization, electron beam Any of vulcanization and the like can be selected. In addition, known additives such as a reinforcing agent, a dispersant, a heat resistance improver, a flame retardant, a conductivity imparting agent, and a pigment may be added to these silicone rubber substrates.

The carbon fibers used in the present invention are used for the purpose of improving the thermal conductivity. Usually, pitch-based, polyacrylonitrile-based, rayon-based carbon fibers, and whisker-like carbon fibers can be used. Precursor fibers of carbon fibers can also be used. The precursor fiber of the pitch-based carbon fiber is a fiber after spinning, a fiber obtained by infusibilizing the fiber, and a pre-carbonized fiber obtained by pre-carbonizing. Also,
Here, the carbon fiber is a fiber obtained by carbonizing the precursor fiber or a fiber obtained by graphitizing.

Although the treatment temperature varies depending on the individual process, usually, the flame-proofing treatment or the infusibilization treatment is performed at 200 to 450 ° C. in an oxidizing atmosphere, and the pre-carbonizing treatment is performed at 400 to 1000 ° C. in a non-oxidizing atmosphere. Is carried out at 1000 to 1500 ° C. in a non-oxidizing atmosphere, and the graphitization treatment is carried out at 2000 to 3000 ° C. in a non-oxidizing atmosphere.

In the present invention, any of these carbon fibers can be used, but among them, pitch-based carbon fibers which can easily exhibit high thermal conductivity are particularly preferably used.

In the present invention, the carbon fiber may be composed of (A) a carbon fiber as an essential component and (A) a carbon fiber and (B) a carbon fiber as described below. (A) The carbon fiber is a main component of the heat conductive filler and has a fiber length of usually 10 to 1500 μm, preferably 10 to 70 μm.
0 μm, more preferably 30 to 300 μm, and still more preferably 50 to 200 μm.

In the present invention, a carbon fiber having the above-mentioned fiber length can be obtained by spinning the precursor fiber into a short fiber or cutting and pulverizing the continuous carbon fiber after the spinning. Here, if the fiber length is less than the above range, contact between carbon fibers in the silicone rubber base material is difficult to obtain, and the effect of the heat conductive filler cannot be exhibited, which is not preferable. If the ratio exceeds the above range, the dispersibility of the carbon fibers in the silicone rubber substrate is reduced, which is not preferable.

The amount of the carbon fiber (A) added to the silicone rubber substrate is usually 10 to 300% by weight, preferably 30% by weight.
To 200% by weight, more preferably 50 to 150% by weight
It can be. Here, when the addition amount is less than the above range, the contact frequency between the carbon fibers in the silicone rubber base material is reduced, and it is not preferable because a desired thermal conductivity cannot be obtained. If the above range is exceeded, the viscosity of the silicone rubber substrate increases, and at the same time it becomes difficult to sufficiently stir and mix the substrate and carbon fiber,
It is not preferable because the base material hardly hardens, or the uniformity and tackiness of the obtained silicone rubber composition decrease.

The thermal conductivity of the carbon fiber (A) of the present invention is usually 100 to 1200 W / m · K, preferably 150 to 12 W / m · K.
00W / m · K, more preferably 300-1200W /
m · K can be used. In the present invention, as the (A) carbon fiber, a pitch-based carbon fiber capable of easily exhibiting high thermal conductivity is preferably used, and is usually 2000 to 3000 ° C., preferably 2 ° C. in a non-oxidizing atmosphere.
Those graphitized at 300 to 3000 ° C. are preferably used.

The carbon fiber (B) is intricately entangled with the carbon fiber (A) and is used for the purpose of (A) ensuring or further increasing the contact between the carbon fibers, and the fiber length is usually 1 to 20 mm. , Preferably 2 to 10 mm, more preferably 3 to 5 mm.

In the present invention, a carbon fiber having the above-mentioned fiber length can be obtained by spinning the precursor fiber into a short fiber or cutting and pulverizing the continuous carbon fiber after the spinning. When the fiber length is less than the above range, (A)
It is not preferable because the frequency of contact with carbon fibers or the number of contact points decreases. In addition, when it exceeds the above range, the dispersibility in the base rubber decreases, and (B) the carbon fibers become entangled rather than (A) the carbon fibers,
(B) It is not preferable because the original purpose of the carbon fiber cannot be achieved.

The amount of the carbon fiber (B) added to the silicone substrate is usually 0.1 to 10% by weight, preferably 0.5 to 10% by weight.
To 5% by weight, more preferably 1 to 3% by weight. Here, when the amount of (B) carbon fiber added is less than the above range, it is difficult to obtain contact with (A) carbon fiber, and as a result, the high thermal conductivity of (A) carbon fiber is sufficiently exhibited. It is not preferable because a desired thermal conductivity cannot be obtained. If the ratio exceeds the above range, the silicone rubber substrate becomes bulky at the time of stirring and mixing, whereby the fluidity is impaired, and it becomes difficult to pour into a filling container. Further, the shape of the carbon fiber (B) is not particularly limited, but a curled shape is preferably used.

The curled carbon fiber may be any non-linear carbon fiber, and may have any degree of curl, but preferably has a radius of curvature of 1 to 10,000 mm. The curled carbon fiber may be carbonized or graphitized, for example, after pre-carbonized carbon fiber is previously wound around a bobbin having an outer diameter of 0.5 to 100 cm or laminated in a can in a circular or curved line. It can be obtained by adding a curling baking habit.

The thermal conductivity of the carbon fiber (B) of the present invention is usually 5 to 1200 W / m · K, more preferably 10 to 100 W / m · K.
W / m · K can be used. In the present invention, a highly heat-conductive silicone rubber composition can be formed into a sheet to produce a silicone rubber sheet suitable as a heat dissipation sheet, but the final sheet thickness is usually 0.1 to 10 mm, preferably Is 0.5 to 5 mm, more preferably 0.8 to 3 mm. The silicone rubber sheet can be used in a state where it is crushed and thinned without being limited to a thickness at the time of manufacturing in order to minimize contact heat resistance between the heat radiating portion and the heat generating portion.

When the silicone rubber sheet is obtained from the high thermal conductive silicone rubber composition, a predetermined amount of the high thermal conductive silicone rubber composition having a desired thickness is filled in a molding container and cured, and the sheet is cured. Obtainable. Further, the silicone rubber composition can be formed into a block shape, and a sheet having a desired thickness can be cut out therefrom. In this case, when the silicone rubber composition is too soft to cut out, the composition can be cooled to a temperature at which it can be cut out and then cut out. As a cooling means, a refrigerator, a freezer, ice, dry ice, liquid nitrogen, liquid helium and the like can be appropriately selected and used. As described above, the silicone rubber sheet can be obtained by any of the methods, but usually the former method is preferably used.

Using the silicone rubber composition or the silicone rubber sheet obtained in the present invention, a heat conducting device in which a heat generating portion and a heat radiating portion are connected can be obtained. As a specific example, FIG. 1 shows an embodiment in which it is assumed that the highly heat conductive silicone rubber composition of the present invention is used as a heat dissipation sheet. In the figure, 1 is a heat radiating plate, 2 is a CPU, 3 is a personal computer housing, and 4 is a heat radiating silicone rubber sheet.
Although not shown in FIG. 1, a plurality of heat radiating plates and / or a plurality of heat-generating components such as a CPU can be connected to the silicone rubber sheet of the present invention, and the silicone rubber sheet is sandwiched between the heat radiating plates. It is possible to laminate with
The heat radiating section or the heat generating section can be connected to the personal computer housing with a silicone rubber sheet.

In the present invention, the higher the thermal conductivity of the highly heat-conductive silicone rubber composition, the better. The thermal conductivity of the highly heat-conductive silicone sheet of the present invention is generally 0.2 to 10 W / m · K, preferably 0.6 to 10 W / m.
m · K, more preferably 1.0 to 10 W / m · K, still more preferably 1.5 to 10 W / m · K, and most preferably 2 to 5 W / m · K.

[0030]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. [Example 1] To a silicone gel base material (trade name: TSE3070) manufactured by Toshiba Silicone Co., Ltd., as a thermally conductive filler, a (A) pitch type having a thermal conductivity of about 600 W / m · K and a length of about 100 μm was used. Add 150% by weight of carbon fiber to the substrate, 1% by weight of curl-shaped (B) pitch-based carbon fiber having a thermal conductivity of about 20 W / m · K and a length of 3 mm, and add 200 × 200 ×
The silicone rubber composition was obtained by pouring into a 20 mm Teflon resin container up to a height of about 2 mm and performing defoaming and curing treatment. The obtained composition was taken out of the container to obtain a silicone rubber sheet having a thickness of about 2 mm. The thermal conductivity of the sheet was measured and found to be 4.46 W / m as shown in Table 1.
-With K, a highly thermally conductive silicone rubber sheet having excellent thermal conductivity was obtained.

[Example 2] The silicone rubber substrate used in Example 1 was mixed with the pitch-based carbon fiber (A) used in Example 1 as a heat conductive filler in an amount of 80% by weight based on the substrate. After adding 2% by weight of the pitch-based carbon fiber (B) used in Example 1 with respect to the base material and performing sufficient stirring and mixing,
The silicone rubber composition was obtained by pouring into a Teflon resin container of 200 × 200 × 20 mm up to a height of about 2 mm and performing defoaming and curing treatment. The obtained composition was taken out of the container, and a silicone rubber sheet having a thickness of about 2 mm was obtained in the same manner as in Example 1. When the thermal conductivity of the sheet was measured, it was 2.42 W / m · K as shown in Table 1, and a high thermal conductive silicone rubber sheet having excellent thermal conductivity was obtained.

Example 3 The silicone rubber base material used in Example 1 was used as a heat conductive filler, with a heat conductivity of about 600.
W / m · K, (A) pitch-based carbon fiber having a length of about 50 μm and a weight of 150 wt% with respect to the base material and a thermal conductivity of about 20 W /
After adding 1% by weight of curled (B) pitch-based carbon fiber having a length of 1 m and a length of 1 mm to the base material and sufficiently stirring and mixing, a 200 × 200 × 20 mm Teflon resin container is used. To a height of about 2 mm, followed by defoaming and curing to obtain a silicone rubber composition. The obtained composition was taken out of the container, and was about 2 mm thick as in Example 1.
A silicone rubber sheet was obtained. The thermal conductivity of the sheet was measured and found to be 4.00 W / m · K as shown in Table 1.
Thus, a highly heat-conductive silicone rubber sheet having excellent heat conductivity was obtained.

Example 4 The silicone rubber base material used in Example 1 was used as a heat conductive filler, with a heat conductivity of about 800.
50% by weight of (A) pitch-based carbon fiber having a W / m · K length of about 100 μm with respect to the substrate and 1% by weight of (B) pitch-based carbon fiber used in Example 1 with respect to the substrate Was added and thoroughly stirred and mixed, and then 200 × 200 × 2
The mixture was poured into a 0 mm Teflon resin container to a height of about 2 mm, and subjected to defoaming and curing treatment to obtain a silicone rubber composition. The obtained composition was taken out of the container and prepared in Example 1.
In the same manner as in the above, a silicone rubber sheet having a thickness of about 2 mm was obtained.
When the thermal conductivity of the sheet was measured, it was found to be 3.51 W / m · K, as shown in Table 1, and a highly thermally conductive silicone rubber sheet having excellent thermal conductivity was obtained.

Example 5 The silicone rubber substrate used in Example 1 was used as a heat conductive filler, and had a heat conductivity of about 300.
W / m · K, about 100 μm long (A) pitch-based carbon fiber of 150% by weight based on the base material and thermal conductivity of about 50 W
/ M · K, 3 mm in length, 1% by weight of curled (B) pitch-based carbon fiber is added to the substrate, and after sufficient stirring and mixing, 200 × 200 × 20 mm Teflon resin The silicone rubber composition was obtained by pouring into a container to a height of about 2 mm and performing defoaming and curing treatment. The obtained composition was taken out of the container and had a thickness of about 2 m as in Example 1.
m of silicone rubber sheet was obtained. The thermal conductivity of the sheet was measured and found to be 2.61 W / m · K as shown in Table 1.
Thus, a highly heat-conductive silicone rubber sheet having excellent heat conductivity was obtained.

Comparative Example 1 The silicone rubber composition used in Example 1 was poured into a 200 × 200 × 20 mm Teflon resin container up to a height of about 2 mm, and the silicone rubber composition was subjected to defoaming and curing treatment. I got The obtained composition was taken out of the container, and was about 2 mm thick as in Example 1.
A silicone rubber sheet was obtained. When the thermal conductivity of the sheet was measured, it was 0.16 W / m · K as shown in Table 1.

[Example 6] The silicone rubber substrate used in Example 1 was replaced with only one component (A) of the pitch-based carbon fiber used in Example 1 as a thermally conductive filler.
0% by weight, and sufficiently stirred and mixed.
Approx. 2m high in a Teflon resin container of × 200 × 20mm
m, followed by defoaming and curing to obtain a silicone rubber composition. The obtained composition was taken out of the container, and a silicone rubber sheet having a thickness of about 2 mm was obtained in the same manner as in Example 1. Table 1 shows the measured thermal conductivity of the sheet.
As shown in Table 2, at 0.85 W / m · K, a high heat conductive silicone rubber sheet suitable as a heat radiating sheet could not be obtained.

[Comparative Example 2] Only one component of the pitch-based carbon fiber (B) used in Example 1 was used as a heat conductive filler in the silicone rubber base material used in Example 1 with respect to the base material. % By weight, and after sufficient stirring and mixing, 200 × 2
A silicone rubber composition was obtained by pouring into a Teflon resin container of 00 × 20 mm up to a height of about 2 mm and performing defoaming and curing treatment. Remove the resulting composition from the container,
A silicone rubber sheet having a thickness of about 2 mm was obtained in the same manner as in Example 1. When the thermal conductivity of the sheet was measured, it was 0.16 W / m · K as shown in Table 1, and a high heat conductive silicone rubber sheet suitable as a heat radiating sheet could not be obtained.

Example 7 The silicone rubber base material used in Example 1 was used as a heat conductive filler, with a heat conductivity of about 600.
W / m · K, about 100 μm long (A) pitch-based carbon fiber is 5% by weight based on the base material and thermal conductivity is about 20 W / m
K, 3 mm in length, curled (B) pitch-based carbon fiber is added at 1% by weight based on the base material, sufficiently stirred and mixed, and then placed in a 200 × 200 × 20 mm Teflon resin container. Poured to a height of about 2 mm, defoamed and cured to obtain a silicone rubber composition. The obtained composition was taken out of the container, and a silicone rubber sheet having a thickness of about 2 mm was obtained in the same manner as in Example 1. The thermal conductivity of the sheet was measured to be 0.28 W / m · K as shown in Table 1,
A high heat conductive silicone rubber sheet suitable as a heat radiation sheet could not be obtained.

Example 8 The silicone rubber base material used in Example 1 was used as a heat conductive filler, with a heat conductivity of about 600.
W / m · K, about 1 mm length of (A) pitch-based carbon fiber is 150% by weight based on the substrate and thermal conductivity is about 20 W / m
-K, 3 mm in length, curled (B) pitch-based carbon fiber was added in an amount of 1% by weight based on the base material, and stirring and mixing were attempted. Could not do. Then, as it is, 2
A silicone rubber composition was obtained by pouring into a 00 × 200 × 20 mm Teflon resin container up to a height of about 2 mm and performing defoaming and curing treatment. When the obtained composition was taken out of the container, the obtained silicone rubber sheet was a patchy and non-uniform molded product, and the thermal conductivity was 0.47 W / m · K as shown in Table 1, A high heat conductive silicone rubber sheet suitable as a heat radiation sheet could not be obtained.

Example 9 The silicone rubber substrate used in Example 1 was used as a heat conductive filler, and had a heat conductivity of about 600.
W / m · K, (A) pitch-based carbon fiber having a length of about 100 μm and a weight of 150 wt% with respect to the base material and a thermal conductivity of about 20 W
/ M · K, 500 μm length of pitch-based carbon fiber (B) was added at 1% by weight to the base material, and the mixture was sufficiently stirred and mixed, and then placed in a 200 × 200 × 20 mm Teflon resin container. The silicone rubber composition was obtained by pouring to a thickness of about 2 mm and performing defoaming and curing treatment. The obtained composition was taken out of the container, and a silicone rubber sheet having a thickness of about 2 mm was obtained in the same manner as in Example 1. When the thermal conductivity of the sheet was measured, it was 0.86 W / m · K as shown in Table 1, and a high heat conductive silicone rubber sheet suitable as a heat radiating sheet could not be obtained.

[Example 10] The silicone rubber base material used in Example 1 was used as a heat conductive filler, and had a heat conductivity of about 60%.
(A) pitch-based carbon fiber having a length of about 100 μm and a weight of about 100 μm, and having a thermal conductivity of about 20 wt.
W / m · K, a 50 mm length of curled (B) pitch-based carbon fiber was added at 1% by weight to the substrate, and the mixture was stirred and mixed, but (B) the carbon fibers were entangled with each other, It could not be uniformly dispersed in the silicone rubber substrate. Next, a silicone rubber sheet having a thickness of 2 mm was obtained in the same manner as in Example 1. The thermal conductivity of the sheet was 0.87 W / m · K as shown in Table 1, and the high thermal conductivity suitable for a heat dissipation sheet was obtained. A silicone rubber sheet could not be obtained.

[0042]

[Table 1]

[0043]

According to the present invention, it is possible to provide a highly heat-conductive silicone rubber composition having excellent heat conductivity and heat dissipation, good adhesion and adhesion, and high heat conductivity.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment using a highly heat conductive silicone rubber composition of the present invention as a heat dissipation sheet.

[Explanation of symbols]

1: heat radiating plate, 2: CPU, 3: personal computer housing, 4: heat radiating silicone rubber sheet.

Claims (2)

[Claims] 1. A silicone rubber substrate having a length of 10 to 150
A highly heat-conductive silicone rubber composition comprising μm carbon fiber. 2. A heat conduction device in which a heat generating part and a heat radiating part are connected by using the silicone rubber composition according to claim 1.