JP2007161806A - Thermally conductive silicone rubber composition - Google Patents

Abstract

The present invention provides a thermally conductive silicone rubber composition that provides a cured product having high thermal conductivity and low specific gravity even though the thermally conductive particles are not highly filled. (A) One molecule An organopolysiloxane having at least two alkenyl groups bonded to silicon atoms therein,
(B) A thermally conductive silicone rubber composition comprising a fibrous thermally conductive filler and (C) a curing agent.
[Selection figure] None

Description

  The present invention relates to a thermally conductive silicone rubber composition that provides a cured product having high thermal conductivity and a low specific gravity despite being not highly filled with thermally conductive particles.

  In recent years, in the field of electrical equipment such as electronics equipment, generators, motors, etc., high performance and compactness have been remarkably advanced, and various heat conductive silicone rubber compositions have been developed to efficiently dissipate heat generated from the inside. Is used.

Since the thermal conductivity of silicone rubber itself is not high, a method of adding a filler having high thermal conductivity to silicone rubber is generally performed. As such silicone rubbers, those proposed in Patent Documents 1 to 3 have been used. In these, silica, alumina, magnesium oxide or the like is blended as a thermally conductive filler in conventionally used silicone rubber. However, unless these fillers are highly filled, high thermal conductivity cannot be obtained.
JP 58-219259 A JP-A-3-221982 JP-A-10-39666

  Accordingly, an object of the present invention is to provide a thermally conductive silicone rubber composition that gives a cured product having high thermal conductivity and low specific gravity even though the thermally conductive particles are not highly filled.

  As a result of intensive studies to achieve the above object, the present inventor has found that it is effective to use a fibrous heat conductive filler, and has completed the present invention.

Therefore, the present invention
(A) an organopolysiloxane having at least two alkenyl groups bonded to silicon atoms in one molecule;
A thermal conductive silicone rubber composition comprising (B) a fibrous thermal conductive filler, and (C) a curing agent is provided.

  According to the thermally conductive silicone rubber composition of the present invention, a thermally conductive silicone rubber having high thermal conductivity and low specific gravity can be obtained even though the thermally conductive particles are not highly filled.

  Hereinafter, the present invention will be described in detail. In this specification, room temperature means 25 ° C.

[(A) Organopolysiloxane]
As the component (A), for example, the following average composition formula (I):
R _a SiO _{(4-a) / 2} (I)
(In the formula, R is the same or different unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, and a is a positive number of 1.8 to 2.3.)
Can be used.

  R is the same or different monovalent or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, and specific examples thereof include methyl, ethyl, propyl, isopropyl Group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, cyclohexyl group, octyl group, nonyl group, decyl group, etc. alkyl group having 1 to 10 carbon atoms; phenyl group, tolyl group Aryl groups having 6 to 10 carbon atoms such as benzyl group, phenylethyl group and phenylpropyl group; vinyl group, allyl group, propenyl group, isopropenyl group, butenyl group, hexenyl Groups, cyclohexenyl groups, octenyl groups, etc., C 2-10 alkenyl groups; part of the hydrogen atoms of these hydrocarbon groups Fluorine whole, bromine, halogen atom such as chlorine, have been substituted with a cyano group or the like, such as chloromethyl group, chloropropyl group, bromoethyl group, trifluoropropyl group, and cyanoethyl group. Among these, a methyl group, a vinyl group, a phenyl group, and a trifluoropropyl group are preferable, and it is preferable that at least 50 mol%, particularly 80 mol% or more of R is a methyl group. In this case, at least two of R must be alkenyl groups (preferably having 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms). The content of the alkenyl group is preferably 0.0001 to 20 mol%, particularly preferably 0.001 to 10 mol% in the total R. The alkenyl group may be bonded to the silicon atom at the end of the molecular chain, may be bonded to the silicon atom at the non-terminal end of the molecular chain (that is, in the middle of the molecular chain), or may be bonded to both.

  a is a positive number of 1.8 to 2.3, preferably 1.9 to 2.1.

  The (A) component organopolysiloxane is basically linear, but may be partially branched as long as it does not impair the rubber elasticity of the cured product obtained from the composition of the present invention.

  The degree of polymerization of the component (A) is not particularly limited, and components ranging from a liquid organopolysiloxane having a low degree of polymerization and a low viscosity to a raw rubber-like organopolysiloxane having a high degree of polymerization and a high viscosity can be used as the component (A). However, in order for the resulting composition to be cured to become a rubbery elastic body, the degree of polymerization is preferably 100 to 100,000, particularly 150 to 20,000.

  The organopolysiloxane of component (A) may be used alone or in combination of two or more having different molecular structures and polymerization degrees.

  Such an organopolysiloxane undergoes ring-opening polymerization by a known method, for example, by (co) hydrolytic condensation of one or more of organohalogenosilanes, or by using a cyclic polysiloxane with an alkaline or acidic catalyst. Can be obtained.

[(B) Fibrous thermally conductive filler]
The component (B) is a fibrous heat conductive filler. (B) A component may be used individually by 1 type, or may use 2 or more types together.

  When considering applying a thermally conductive filler as a thermal conductivity improver, for example, in a conventional method in which carbon black is mixed into a silicone rubber composition as a thermally conductive filler, carbon powders are connected to each other. As a result, the thermal conductivity of the silicone rubber is improved. Therefore, paying attention to the shape of the heat conductive filler, the heat conductive filler is more likely to be connected to each other when the shape is elongated than the fine powder, and the heat conductivity of the silicone rubber is likely to be improved. That is, by using a fibrous heat conductive filler, the heat conductivity of the silicone rubber is easily improved. Here, the fibrous form means a shape extending in one axial direction. More specifically, the length of the longest axis / the length of the shortest axis (aspect ratio) is usually It means that the shape is 2 or more (for example, 2 to 1000), preferably 40 or more (for example, 40 to 1000).

  The material of the component (B) is not particularly limited, but carbon is particularly preferable. That is, the component (B) is preferably carbon fiber.

  The component (B) is more preferably a carbon fiber obtained by a gas phase method. For example, the component is obtained by a gas phase method, the center is a cavity, and a graphite hexagonal mesh plane is laminated in an annual ring shape. And carbon fiber. Here, the gas phase method refers to a method of growing carbon fibers by thermally decomposing an organic compound (for example, hydrocarbon) in a heating furnace. In addition, the annual ring shape means that a plurality of tube-shaped graphite hexagonal mesh surfaces are concentrically stacked around the longest axis of the carbon fiber. Numerous methods for producing carbon fibers by a gas phase method by thermal decomposition of hydrocarbons are known (Japanese Patent Application Laid-Open No. 2004-339676, Japanese Patent Application Laid-Open No. 7-150419, Japanese Patent Application Laid-Open No. 5-321039, Japanese Patent Application Laid-Open No. -179514, JP-A-60-215816, JP-A-61-70014, JP-B-5-36521, JP-B-3-61768, etc.).

  (B) The average fiber diameter of a component becomes like this. Preferably it is 10-300 nm, More preferably, it is 50-250 nm. Moreover, the average fiber length of (B) component becomes like this. Preferably it is 1-100 micrometers, More preferably, it is 5-90 micrometers. When the average fiber diameter and the average fiber length are within these ranges, the obtained composition is a cured product having high thermal conductivity and low specific gravity even when the component (B) is not highly filled. It becomes easy to give. Here, the average fiber diameter and the average fiber length can be obtained, for example, by measuring the outer diameter and length of about 100 (B) components from a TEM (transmission electron microscope) photograph.

  (B) The addition amount of a component becomes like this. Preferably it is 20-100 mass parts with respect to 100 mass parts of (A) component, More preferably, it is 30-80 mass parts. When the addition amount is within this range, the resulting composition tends to maintain processability, and a cured product of the composition tends to have high thermal conductivity and a low specific gravity.

[(C) Curing agent]
(C) A component is a hardening | curing agent, and if it can harden the heat conductive silicone rubber composition of this invention, it will not specifically limit. (C) A component may be used individually by 1 type, or may use 2 or more types together. Examples of the component (C) include a curing agent capable of curing the silicone rubber composition by heating. Preferred examples include (C-1) addition reaction type curing agent and (C-2) organic peroxidation. Examples of the curing agent include a combination of the component (C-1) and the component (C-2).

((C-1) addition reaction type curing agent)
As the component (C-1), a combination of an organohydrogenpolysiloxane and a hydrosilylation catalyst is used.

Hydrosilylation catalyst The hydrosilylation catalyst is composed of an alkenyl group in the component (A) and a silicon atom-bonded hydrogen atom (hereinafter sometimes referred to as SiH group) of the organohydrogenpolysiloxane in the component (C-1). Is a catalyst for the addition reaction.

  Examples of the hydrosilylation catalyst include a platinum group metal catalyst, and more specifically, for example, a platinum group metal simple substance and a compound thereof. As the platinum group metal catalyst, conventionally known catalysts can be used as the catalyst for the addition reaction curable silicone rubber composition. Examples of the platinum group metal catalyst include fine particle platinum metal adsorbed on a carrier such as silica, alumina or silica gel, platinous chloride, chloroplatinic acid, chloroplatinic acid hexahydrate alcohol solution, palladium catalyst. , Rhodium catalyst and the like, platinum or platinum compounds are preferable.

  The addition amount of the hydrosilylation catalyst may be an amount that can promote the above addition reaction, and is preferably in the range of 1 ppm to 1% by mass with respect to the organopolysiloxane of component (A) on a mass basis in terms of platinum metal. However, it is more preferably in the range of 10 to 500 ppm. When the addition amount is within this range, the addition reaction is likely to be sufficiently promoted, the curing is likely to be sufficient, and the economy is advantageous.

Organohydrogen polysiloxane The organohydrogen polysiloxane may be either linear or cyclic as long as it contains 2 or more, preferably 3 or more SiH groups in one molecule, and is branched. It may be. As such an organohydrogenpolysiloxane, a known organohydrogenpolysiloxane can be used as a crosslinking agent for an addition reaction curable silicone rubber composition. For example, the following average composition formula (II):
R ¹ _p H _q SiO _{(4-pq) / 2} (II)
(Wherein R ¹ represents an identical or different unsubstituted or substituted monovalent hydrocarbon group other than an aliphatic unsaturated group, and p and q are 0 ≦ p <3, 0 <q ≦ 3, and 0 <p + q ≦ 3, preferably 1 ≦ p ≦ 2.2, 0.002 ≦ q ≦ 1, and 1.002 ≦ p + q ≦ 3.
An organohydrogenpolysiloxane represented by the formula can be suitably used.

In the above average composition formula (II), R ¹ is the same or different unsubstituted or substituted other than aliphatic unsaturated group, preferably 1 to 12 carbon atoms, particularly preferably monovalent 1 to 8 carbon atoms. A hydrocarbon group is shown. Specific examples of R ¹ include alkyl groups such as methyl group, ethyl group, and propyl group; cycloalkyl groups such as cyclohexyl group; aryl groups such as phenyl group and tolyl group; benzyl group, 2-phenylethyl group, 2- An aralkyl group such as a phenylpropyl group; and a group in which some or all of the hydrogen atoms of these hydrocarbon groups are substituted with a halogen atom such as a fluorine atom, such as a 3,3,3-trifluoropropyl group. .

When the organohydrogenpolysiloxane is linear, SiH groups are present only at either the molecular chain end or the molecular chain non-terminal (that is, in the middle of the molecular chain) or both. May be. It is preferable that the viscosity at 25 ° C. of the organohydrogenpolysiloxane is 0.5~10,000mm ² / s, particularly preferably 1 to 300 mm ² / s.

  Specific examples of such organohydrogenpolysiloxanes include compounds having the following structural formula.

（式中、ｋは２〜１０の整数であり、ｓ及びｔは０〜１０の整数である。）

(In the formula, k is an integer of 2 to 10, and s and t are integers of 0 to 10.)

  The amount of the organohydrogenpolysiloxane is preferably the number of SiH groups in the organohydrogenpolysiloxane with respect to one aliphatic unsaturated group (alkenyl group, diene group, etc.) in the component (A). The amount is 0.5 to 10, more preferably 0.7 to 5. When the addition amount is within this range, crosslinking is easily formed when the resulting composition is cured, and after curing, sufficient mechanical strength is easily obtained, and other physical properties, particularly heat resistance and low resistance. Easy to maintain compression set. Such an addition amount can be realized, for example, by adding 0.1 to 40 parts by mass of the organohydrogenpolysiloxane with respect to 100 parts by mass of the component (A).

((C-2) organic peroxide)
Examples of the organic peroxide include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, o-methylbenzoyl peroxide, 2,4-dicumyl peroxide, and 2,5-dimethyl. -Bis (2,5-t-butylperoxy) hexane, di-t-butylperoxide, t-butylperbenzoate, 1,6-hexanediol-bis-t-butylperoxycarbonate and the like. These may be used alone or in combination of two or more.

  The addition amount of the organic peroxide is preferably 0.1 to 10 parts by mass, particularly preferably 0.2 to 5 parts by mass with respect to 100 parts by mass of the component (A).

[Reinforcing silica]
In order to give mechanical strength etc. to the hardened | cured material, you may mix | blend reinforcing silica as an arbitrary component with the heat conductive silicone rubber composition of this invention. When the reinforcing silica is blended in the composition, for example, it may be blended in the composition as a mixture of the organopolysiloxane (A) and the reinforcing silica. Examples of reinforcing silica include fumed silica and precipitated (wet) silica. Preferably these silicas BET specific surface area is ^{50 m} 2 / g or more, it is preferable in particular 100 to 400 m ² / g.

  As such silica, silica whose surface is treated with a surface treatment agent such as organopolysiloxane, silazane, chlorosilane, or alkoxysilane may be used as necessary. When the reinforcing silica is blended with the composition as a mixture of the organopolysiloxane of component (A) and the reinforcing silica, the surface treatment is performed when the reinforcing silica is blended with component (A). An agent may be blended.

  When reinforcing silica is added to the composition of the present invention, the amount added is preferably 100 parts by mass or less (for example, 0.1 to 100 parts by mass) with respect to 100 parts by mass of the organopolysiloxane of component (A). More preferably, it is 1-80 mass parts, Most preferably, it is 5-50 mass parts. When the added amount is within this range, reinforcing silica can be easily blended with the composition of the present invention, and rubber physical properties such as rubber strength can be easily maintained. Furthermore, in the case of millable rubber made from raw rubber, it is easy to maintain processability.

[Other ingredients]
In addition to the above components, the composition of the present invention includes, as necessary, fillers such as pulverized quartz, crystalline silica, diatomaceous earth, and calcium carbonate within a range that does not impair the purpose of the present application, a colorant, a tear strength improver, Heat resistance improvers such as iron oxide and cerium oxide, flame retardant improvers such as titanium oxide and platinum compounds, acid acceptors, thermal conductivity improvers such as alumina and boron nitride, mold release agents, dispersants for fillers As various types of alkoxysilanes, particularly phenyl group-containing alkoxysilanes and hydrolysates thereof, diphenylsilanediols, carbon functional silanes, silanol group-containing low molecular siloxanes, and other known fillers in thermosetting silicone rubber compositions Additives may be added.

  Furthermore, when using the addition reaction type curing agent of the component (C-1), a reaction control agent may be used for the purpose of adjusting the curing rate in addition to the hydrosilylation catalyst. Specific examples thereof include acetylene alcohol-based control agents such as ethynylcyclohexanol and tetracyclomethylvinylpolysiloxane.

[Use of composition]
The form of the composition of the present invention may be a millable type or a liquid type.

  The heat conductive silicone rubber composition of the present invention becomes a cured product (silicone rubber) having excellent heat conductivity even when the specific gravity is small, by heating and curing. As the molding method, a known molding method may be selected according to the shape and size of the target molded product. For example, methods such as injection molding, compression molding, injection molding, calendar molding, extrusion molding, coating, and screen printing can be used. The curing conditions may be known conditions in the molding method, and are generally about several seconds to one day at a temperature of 60 ° C. to 450 ° C. Moreover, the compression set of the obtained cured product is reduced, the low molecular siloxane component remaining in the obtained silicone rubber is reduced, or the decomposition product of the organic peroxide in the silicone rubber is removed. For purposes such as post-curing (secondary curing) of 200 ° C. or higher, preferably in an oven at 200 ° C. to 250 ° C. for 1 hour or longer, preferably 1 hour to 70 hours, preferably 1 hour to 10 hours. You may go.

  The silicone rubber can be used as a member for efficiently radiating heat generated from the inside of an electric device such as an electronic device, a generator, or an electric motor. For example, by interposing the silicone rubber between heat-generating electronic components inside these electronic devices and heat dissipating members such as heat sinks and circuit boards, heat generated from the inside of the electric devices can be efficiently dissipated. Can do.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, these Examples do not restrict | limit this invention at all. “Part” means “part by mass”.

[Example 1]
Carbon fiber (trade name: VGCF-H, Showa Denko, the same shall apply hereinafter) 100 parts of dimethylpolysiloxane (degree of polymerization 500) capped with dimethylvinylsiloxy groups at both ends of the molecular chain, average fiber diameter 150 nm, average fiber length 10 μm ) 60 parts, 1.0 part of a methylhydrogenpolysiloxane having a SiH group at both ends of the molecular chain and at the non-end of the molecular chain (polymerization degree 17, amount of SiH group 0.0060 mol / g), ethynylcyclohexanol as a reaction control agent 0.05 part and 0.1 part of a complex of chloroplatinic acid and divinyltetramethyldisiloxane (platinum atom concentration 1 mass%) as a hydrosilylation catalyst were mixed to prepare Composition A.

[Example 2]
80 parts of dimethylpolysiloxane having both ends of the molecular chain blocked with trimethylsiloxy groups and vinyl groups at the non-terminal ends of the molecular chain (polymerization degree 300, vinyl group content 0.000072 mol / g), both ends of the molecular chain are dimethylvinylsiloxy Methyl hydrogen polysiloxane having 20 parts of dimethylpolysiloxane blocked with a group (polymerization degree 500), 55 parts of carbon fiber having an average fiber diameter of 150 nm and an average fiber length of 10 μm, and SiH groups at both molecular chain terminals and molecular chain non-terminals (Polymerization degree 15, amount of SiH group 0.0035 mol / g) 2.8 parts, dimethylpolysiloxane having molecular chain both ends blocked with trimethylsiloxy group and vinyl group at the non-terminal chain (polymerization degree 20, vinyl Group content 0.018 mol / g) 1.2 parts, chloroplatinic acid and divinyltetramethyl as hydrosilylation catalyst It was mixed with 0.1 parts of complex (platinum atom concentration of 1% by mass) of the siloxane was prepared composition portion B.

[Example 3]
100 parts of dimethylpolysiloxane having both ends of the molecular chain blocked with trimethylsiloxy groups and vinyl groups at the non-terminal end of the molecular chain (polymerization degree 300, vinyl group content 0.000072 mol / g), average fiber diameter 150 nm, average fiber length 60 parts of carbon fiber of 10 μm, 2.9 parts of methyl hydrogen polysiloxane having a SiH group at both ends of the molecular chain and at the non-end of the molecular chain (polymerization degree 15, amount of SiH group 0.0035 mol / g), reaction control agent As a mixture, 0.05 part of ethynylcyclohexanol was mixed with 0.1 part of a complex of chloroplatinic acid and divinyltetramethyldisiloxane (platinum atom concentration: 1% by mass) as a hydrosilylation catalyst to prepare a composition C.

[Comparative Example 1]
A composition D was prepared in the same manner as in Example 1 except that 350 parts of pulverized quartz having an average particle diameter of 5 μm was used instead of carbon fibers in Example 1. In the present specification, the average particle diameter is a volume-based cumulative average diameter measured by Microtrac MT3300EX, which is a particle size analyzer manufactured by Nikkiso Co., Ltd.

[Comparative Example 2]
A composition E was prepared in the same manner as in Example 1 except that 400 parts of alumina having an average particle diameter of 12 μm was used instead of carbon fibers in Example 1.

[Measurement]
Each composition A to E was press-cured at 120 ° C. for 10 minutes, and further oven-cured at 200 ° C. for 4 hours, and then the mechanical properties were measured by a method according to JIS K 6249, and the thermal conductivity was measured as thermal conductivity. It measured with the total (QTM-3, Kyoto Electronics Industry Co., Ltd. product). The results are shown in Table 1.

Claims (5)

(A) an organopolysiloxane having at least two alkenyl groups bonded to silicon atoms in one molecule;
(B) A thermally conductive silicone rubber composition comprising a fibrous thermally conductive filler, and (C) a curing agent.   The composition according to claim 1, wherein the component (B) is carbon fiber.   The composition according to claim 1 or 2, wherein the component (B) is a carbon fiber obtained by a vapor phase method.   The composition according to any one of claims 1 to 3, wherein the component (B) has an average fiber diameter of 10 to 300 nm and an average fiber length of 1 to 100 µm. (B) Content of a component is 20-100 mass parts with respect to 100 mass parts of (A) component, The composition which concerns on any one of Claims 1-4.