JPH08151522A - Electrically conductive silicone rubber composition - Google Patents

Abstract

PURPOSE: To provide an electrically conductive silicone rubber composition effective for suppressing the variation of electrical conductivity caused by the strain in molding, etc., and enabling the production of an electrically conductive silicone rubber having uniform conductivity in high reproducibility by increasing the affinity of a polyorganosiloxane for a carbon black used as an electrically conductive material. CONSTITUTION: This electrically conductive silicone rubber composition contains (A) 100 pts.wt. of a polyorganosiloxane expressed by the formula, Ra SiO(4-a)/2 (R is an unsubstituted or substituted univalent hydrocarbon group; (a) is a positive number of 1.90-2.05), (B) 3-150 pts.wt. of an electrically conductive carbon black, (C) 0.03-5 pts.wt. of a >=1 fatty acid metal salt and (D) a necessary amount of a curing agent.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a conductive silicone rubber composition for obtaining a conductive silicone rubber having improved stability (uniformity) of conductivity.

[0002]

2. Description of the Related Art Various conductive rubbers in which a conductive material is blended with a rubber-like substance exhibiting electrical insulation have been known in the art. For example, by blending carbon black or the like as the conductive material, the electrical resistance ¹⁰⁵ to conductive rubbers in the range of ⁰ Omega · cm is applied in various fields.

On the other hand, silicone rubber, which is one of the electrically insulating rubber-like substances, is excellent in heat resistance, cold resistance and weather resistance and is widely used as an electrically insulating rubber, but like other rubber-like substances. It has been put to practical use as a conductive silicone rubber by adding a conductive material such as carbon black. Furthermore, a conductive silicone rubber foam obtained by adding a foaming agent and foaming and curing is also known.

In this case, as the conductive material added to the silicone rubber composition, for example, various metal powders such as carbon black, graphite, silver, nickel and copper, non-conductive powder and short fiber surfaces such as silver. Examples include those treated with metal, those mixed with carbon fibers, metal fibers and the like. These are frequently used because the volume resistivity of silicone rubber can be reduced to about 10 ¹⁰ to 10 ^-3 Ωcm depending on the type and filling amount of conductive material without impairing the properties of silicone rubber. Has been done. In particular, in the case of obtaining a highly conductive silicone rubber of 10 ⁵ Ω · cm or less, among these, metal powders such as carbon black, silver and nickel are used, and carbon black is often used from the viewpoint of cost and the like. There is.

However, since polyorganosiloxane, which is the base polymer of silicone rubber, and carbon black have no inherent affinity, when a rubber-like elastic body is obtained from a conductive silicone rubber composition containing carbon black, the rubber composition is not easily molded. There is a problem that strain is generated in the rubber-like elastic body due to the pressure, flow, etc., and the conductivity is varied in the rubber-like elastic body (molded product). If there is a variation in conductivity within the molded product, the current may concentrate in a highly conductive portion, resulting in partial heat generation or partial deterioration.

[0006]

As described above, since the polyorganosiloxane and carbon black have no inherent affinity with each other, the conductive silicone rubber composition containing conventional carbon black is used to obtain a rubber-like elastic body. There was a problem when the conductivity was varied. Since the variation in conductivity in the rubber-like elastic body may cause partial heat generation or partial deterioration, a conductive silicone rubber composition capable of increasing the affinity between polyorganosiloxane and carbon black. Is required.

The present invention has been made in order to solve such a problem, and by increasing the affinity between polyorganosiloxane and carbon black as a conductive material, the conductivity of the conductive material due to strain during molding can be improved. It is an object of the present invention to provide a conductive silicone rubber composition that suppresses the occurrence of variations and enables to obtain a conductive silicone rubber having uniform conductivity with good reproducibility.

[0008]

Means and Actions for Solving the Problems As a result of intensive studies conducted by the present inventors in order to achieve the above object, it was found that the addition of a specific fatty acid metal salt has an affinity for polyorganosiloxane and carbon black. The inventors have found that it is effective in improving the properties and completed the present invention.

That is, the conductive silicone rubber composition of the present invention has the following general formula (a): R _a SiO _{(4-a) / 2} (1) (wherein R is unsubstituted or substituted monovalent Represents a hydrocarbon group, and a is a positive number of 1.90 to 2.05), 100 parts by weight of polyorganosiloxane represented by (b) 3 to 150 parts by weight of conductive carbon black, (c) having 10 or more carbon atoms. It is characterized by containing 0.03 to 5 parts by weight of a fatty acid metal salt and (d) a necessary amount of a curing agent.

The component (a) constituting the conductive silicone rubber composition of the present invention is a polyorganosiloxane represented by the above formula (1) and serves as a base polymer. The R group in the above formula (1) is an alkyl group such as a methyl group, an ethyl group, a propyl group or a butyl group, an alkenyl group such as a vinyl group, an allyl group or a Butaniel group, an aryl group such as a phenyl group or a tolyl group, And a chloromethyl group or a chloropropyl group in which a part or all of hydrogen atoms bonded to carbon atoms of these groups are substituted with a halogen atom, a cyano group, or the like,
It is an unsubstituted or substituted monovalent hydrocarbon group such as a 3,3,3-trifluoropropyl group or a 2-cyanoethyl group. The R groups may be the same or different, and the hydrocarbon group as the R group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 monovalent hydrocarbon groups. The value of a in the formula (1) is a positive number selected from the range of 1.90 to 2.05 for obtaining a rubber-like elastic body. As a part of the R group, an alkenyl group such as a vinyl group is used depending on the curing reaction of the rubber-like elastic material, as described later in detail.

As the polyorganosiloxane, those having a linear molecular structure are preferable, but there is no problem even if a part of the polyorganosiloxane contains a branched molecular structure. Also,
The end of the molecular chain of the polyorganosiloxane may have a structure blocked with a triorganosilyl group or a hydroxyl group, and the triorganosilyl group may be a trimethylsilyl group, a dimethylvinylsilyl group, a methylphenylvinylsilyl group or a methyldiphenylsilyl group. , Methyldivinylsilyl group, trivinylsilyl group and the like. In this case, in order to further reduce surface tack, both ends of the molecular chain should be
It is desirable to use a polyfunctional group such as (CH ₂ = CH) ₂ RSi- and (CH ₂ = CH) ₃ Si-.

The degree of polymerization of the polyorganosiloxane used in the present invention is not particularly limited, but the degree of polymerization is 100.
The above is sufficient. Further, in consideration of workability and processability, those having a polymerization degree of 2,000 to 30,000 are preferable, and further 30
The thing of 00-10000 is more preferable.

The component (b) in the composition of the present invention is a component that imparts conductivity to the obtained rubber-like elastic body. As the conductive carbon black as the component (b), one that is commonly used in conductive rubber compositions can be used. For example, acetylene black, conductive furnace black (CF), super conductive furnace black (SCF), extra conductive furnace black (XCF), conductive channel black (CC), and furnace black and channel black heat-treated at a high temperature of about 1773K. Can be mentioned.

Specific examples of the above acetylene black include electrified acetylene black (manufactured by Denki Kagaku Co., Ltd.),
Shawnigan acetylene black (manufactured by Shawnigan Chemical Co., Ltd.), and as specific examples of conductive furnace black, Continex CF (manufactured by Continental Carbon Co., Ltd.), Vulcan C (manufactured by Cabot Co., Ltd.), etc. As a concrete example of Conductive Furnace Black, there is Continex SCF.
(Manufactured by Continental Carbon Co., Ltd.), Balkan SC
As a specific example of Extra Conductive Furnace Black (manufactured by Cabot Corporation), Asahi HS-5
00 (manufactured by Asahi Carbon Co., Ltd.), Vulcan XC-72
As a specific example of the conductive channel black, COULAX L (manufactured by Degussa Co., Ltd.) is exemplified. Further, Ketjen Black EC or Ketjen Black EC-600JD (manufactured by Ketjen Black International Co., Ltd.), which is a type of furnace black, can also be used.

Among the conductive carbon blacks described above, acetylene black is particularly excellent in imparting conductivity because it has a small amount of impurities and has a developed secondary structure structure, and is suitable for the present invention. Used.

The blending amount of the conductive carbon black as the component (b) is in the range of 3 to 150 parts by weight with respect to 100 parts by weight of the polyorganosiloxane as the component (a). If the amount of conductive carbon black is less than 3 parts by weight, the desired conductivity may not be obtained, and if it exceeds 150 parts by weight, the mechanical strength of the rubber-like elastic body obtained may deteriorate. There is. Conductive carbon black is 5-100
It is particularly preferable to blend in the range of parts by weight in view of the balance between conductivity and mechanical properties.

The component (c) in the composition of the present invention is a fatty acid metal salt having 10 or more carbon atoms, which is a so-called metal soap. By blending such a fatty acid metal salt having 10 or more carbon atoms, the affinity between the polyorganosiloxane of component (a) and the carbon black of component (b), which originally have a low affinity, is increased, and (B) It is possible to make the ingredients easier to blend in. This makes it possible to reduce variations in conductivity in the obtained rubber-like elastic body, that is, to obtain uniform conductivity. That is, the component (c) is a component having a function of reducing the variation in conductivity in the rubber-like elastic body.

The fatty acid metal salt of component (c), which is a normal fatty acid moiety, may be an isomer or one having a substituent, but if the fatty acid moiety has less than 10 carbon atoms, it has a lipophilicity. Since it is low, it is difficult to be compatible with carbon black, and the affinity between the component (a) and the component (b) cannot be sufficiently enhanced. Therefore, as the component (c) of the present invention, a fatty acid metal salt having 10 or more carbon atoms is used. Also,
The fatty acid metal salt used as the component (c) preferably has 30 or less carbon atoms from the viewpoint of ease of synthesis and the like.
Examples of the metal portion of the fatty acid metal salt of component (c) include magnesium, calcium, aluminum, lithium, barium, strontium, zinc, cadmium, and lead, but are not particularly limited. In particular, the carbon number is 12 ~
A fatty acid metal salt having a fatty acid moiety in the range of 20 and having a metal moiety of magnesium, calcium, zinc, aluminum or the like is suitable as the component (c) in the present invention.

Specific examples of the above-mentioned fatty acid metal salt having 10 or more carbon atoms (metal soap) include magnesium stearate, aluminum stearate, calcium stearate, lithium stearate, zinc stearate, strontium stearate, lead stearate, Barium stearate, cadmium stearate, calcium chlorostearate, barium chlorostearate, cadmium chlorostearate, zinc laurate, barium laurate, cadmium laurate, magnesium laurate, zinc myristate, aluminum myristate, barium ricinoleate, Examples thereof include zinc ricinoleate and cadmium ricinoleate, but lead, cadmium, and barium fatty acid salts are toxic and should be avoided if possible. Further, as the component (c) in the present invention,
For example, basic salts such as Al (OH) (C ₁₇ H ₃₅ COO) ₂ and Al (OH) ₂ (C ₁₇ H ₃₅ COO) can be used, and two or more metal soaps can be mixed and used. You may. Specific examples of the fatty acid metal salt suitable as the component (C) are zinc stearate, magnesium stearate, calcium stearate, magnesium laurate, zinc myristate, aluminum myristate, and the like.

If the compounding amount of the above-mentioned component (c) is too small, the polyorganosiloxane of the component (a) and (b)
It is not possible to increase the affinity of the component with carbon black, and if the blending amount is too large, the compression set, heat resistance, mechanical strength, etc. of the rubber-like elastic material obtained will decrease, so the component (a) 0.03 to 5 parts by weight per 100 parts by weight. The component (c) is particularly preferably added in the range of 0.05 to 3 parts by weight.

The curing agent of the component (d) is appropriately selected according to the reaction mechanism for obtaining the rubber-like elastic body.
As the reaction mechanism, (1) crosslinking reaction with an organic peroxide vulcanizing agent, (2) addition reaction and the like are known. Below, (a) in each reaction mechanism of (1) and (2) above
The polyorganosiloxane as the component and the curing agent as the component (d) will be described.

First, in the case of applying the crosslinking reaction of (1) above, as the polyorganosiloxane of the component (a), at least two of the organic groups R bonded to silicon atoms in one molecule are usually used. A polyorganosiloxane which is an alkenyl group such as a vinyl group, a propenyl group, a butenyl group and a hexenyl group is used. Particularly, vinyl group is preferable among the above groups because of easy synthesis and easy availability of raw materials. Further, as the curing agent of the component (d), dicumyl peroxide, cumyl-t-butyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, di-t-
Since various organic peroxides such as butyl peroxide are used as vulcanizing agents and give a particularly low compression set, dicumyl peroxide, cumyl-t-butyl peroxide, 2,5-dimethyl-2,5-dioxide. Preferred is -t-butylperoxyhexane, di-t-butylperoxide. These organic peroxide vulcanizing agents may be used alone or as a mixture of two or more.

The blending amount of the organic peroxide as the curing agent of the component (d) is 100 g of the polyorganosiloxane of the component (a).
It is preferably in the range of 0.05 to 15 parts by weight with respect to parts by weight. If the compounding amount of the organic peroxide is less than 0.05 parts by weight, vulcanization is not sufficiently performed, while if it is more than 15 parts by weight, there is no further particular effect, and the obtained rubber-like elastic body ( The characteristics of the conductive silicone rubber) may be adversely affected.

When the addition reaction (2) is applied, the same polyorganosiloxane as the component (a) is used as in the above (1), and the curing agent for the component (d) is used. A catalyst for addition reaction and a cross-linking agent are used. For example, as the addition reaction (curing) catalyst, chloroplatinic acid, platinum olefin complex, platinum vinyl siloxane complex,
Platinum-based catalysts such as platinum black and platinum triphenylphosphine complex are used, and the cross-linking agent is a polyorganosiloxane having an average of more than 2 hydrogen atoms bonded to silicon atoms in one molecule. .

In the above-mentioned curing agent of component (d), the compounding amount of the curing catalyst is the polyorganosiloxane of component (a).
The amount of the elemental platinum is preferably in the range of 1 to 1000 ppm with respect to 100 parts by weight. If the compounding amount of the curing catalyst is less than 1 ppm as the amount of platinum element, curing does not proceed sufficiently, and 1000
Even if it is blended in excess of ppm, no particular improvement in the curing speed can be expected. The amount of the cross-linking agent is preferably such that the hydrogen atom bonded to the silicon group atom in the cross-linking agent is 0.5 to 4.0 with respect to one alkenyl group in the component (a),
The amount is more preferably 1.0 to 3.0.
If the amount of hydrogen atoms is less than 0.5, curing of the composition does not proceed sufficiently and the hardness of the composition after curing becomes low, and if the amount of hydrogen atoms exceeds 4.0, the composition will not cure. Physical properties and heat resistance are reduced.

In the conductive silicone rubber composition of the present invention, if necessary, a filler other than the above-mentioned components (a) to (d), for example, a reinforcing filler such as fumed silica or precipitated silica, or a normal silicone is used. Quartz powder, fused silica powder, diatomaceous earth, talc, calcium carbonate, titanium oxide, iron oxide, aluminum oxide, clay, etc., which are compounded in the rubber composition, may be added, and further, a low molecular siloxane as a dispersant. Ester, silanol group-containing siloxane, etc.
If cerium oxide or the like is used as the heat resistance improver, a platinum compound or the like is used as the flame retarding agent, and if an organic foaming agent such as azodicarbonamide or azobisisobutyronitrile is used to obtain a sponge-like rubber. Good.

The conductive silicone rubber composition of the present invention is
It can be obtained by kneading the above-mentioned components (a) to (d) with a roll, a kneader, a Banbury mixer, etc. in the same manner as a usual silicone rubber composition. The composition thus prepared is subjected to heat molding under normal pressure or pressure by compression molding, transfer molding, injection molding, extrusion molding, calender molding, dip molding or the like to obtain a conductive silicone rubber. .

[0028]

Embodiments of the present invention will be described below. In addition, all "parts" in the following Examples and Comparative Examples represent "parts by weight".

Example 1 100 parts of vinyl group-containing polydimethylsiloxane (average degree of polymerization = 7000) containing 0.2 mol% of methylvinylsiloxane units at the terminal was blocked with trimethylsilyl group, and acetylene black (electric Chemical Industry) 50 parts, 0.1 parts zinc stearate as a fatty acid metal salt having 10 or more carbon atoms, and 2,5-dimethyl-2,5-di (t-butylperoxy) as a vulcanizing agent (curing agent). ) Hexane was charged into an open kneader at a ratio of 1.5 parts and sufficiently kneaded to obtain a conductive silicone rubber composition.

Next, the above conductive silicone rubber composition is added.
Press vulcanized under conditions of 443K x 10 minutes, thickness 1mm x 200mm
A square rubber sheet was prepared, and thereafter, attic vulcanization was performed in an oven at 473K for 4 hours to obtain a conductive silicone rubber sheet. In order to evaluate the electroconductivity of the electroconductive silicone rubber sheet thus produced, the volume resistivity at 10 points was measured by Loresta AP manufactured by Mitsubishi Petrochemical, and the maximum value, the minimum value and the average value were recorded. . Also, the degree of conductivity variation was calculated from (maximum value-minimum value) / minimum value x 100. The results of these measurements are shown in Table 1 together with the compounding ratio of the conductive silicone rubber composition.

Example 2 In the conductive silicone rubber composition of Example 1 above,
Ketjen Black EC-6 instead of carbon black
A conductive silicone rubber composition was prepared in the same manner as in Example 1 except that 15 parts of 00JD (manufactured by Ketjen Black International Co., Ltd.) was used. Further, using this conductive silicone rubber composition, a conductive silicone rubber sheet was prepared under the same conditions as in Example 1, and the conductivity of the conductive silicone rubber was evaluated in the same manner. The results of these measurements are shown in Table 1 together with the compounding ratio of the conductive silicone rubber composition.

Examples 3 to 5 In the conductive silicone rubber composition of Example 1 above,
Conductive silicone rubber composition as in Example 1 except that magnesium stearate (Example 3), aluminum myristate (Example 4) and zinc laurate (Example 5) were used instead of zinc stearate. Was produced. Further, using these conductive silicone rubber compositions, conductive silicone rubber sheets were prepared under the same conditions as in Example 1, and the conductivity of the conductive silicone rubber was evaluated in the same manner. The results of these measurements are shown in Table 1 together with the compounding ratio of the conductive silicone rubber composition.

Comparative Example 1 In the conductive silicone rubber composition of Example 1 above,
A conductive silicone rubber composition was prepared in the same manner as in Example 1 except that zinc stearate was not added. Further, using this conductive silicone rubber composition, a conductive silicone rubber sheet was prepared under the same conditions as in Example 1, and
Similarly, the conductivity of the conductive silicone rubber was evaluated.
The results of these measurements are shown in Table 1 together with the compounding ratio of the conductive silicone rubber composition.

Comparative Example 2 In the conductive silicone rubber composition of Example 1 above,
A conductive silicone rubber composition was produced in the same manner as in Example 1 except that calcium acetate was used instead of zinc stearate. Further, using this conductive silicone rubber composition, a conductive silicone rubber sheet was prepared under the same conditions as in Example 1, and the conductivity of the conductive silicone rubber was evaluated in the same manner. The results of these measurements are shown in Table 1 together with the compounding ratio of the conductive silicone rubber composition.

[0035]

[Table 1] As is clear from Table 1, all of the conductive silicone rubbers produced using the conductive silicone rubber composition of the present invention have small variations in conductivity and have uniform conductivity.

Example 6 100 parts of vinyl group-containing polydimethylsiloxane (average degree of polymerization = 8000) of which the ends were blocked with dimethylvinylsilyl groups and which contained 0.2 mol% of methylvinylsiloxane units was added to acetylene black as a conductive carbon black. HS-
30 parts of 100 (made by Denki Kagaku Kogyo), 0.05 part of calcium stearate as a fatty acid metal salt having 10 or more carbon atoms, and 1 part of dicumyl peroxide as a vulcanizing agent were charged in an open kneader, which was sufficiently charged. Was kneaded to obtain a conductive silicone rubber composition.

Next, the conductive silicone rubber composition is added.
By press vulcanizing at a pressure of 4 MPa and 10 MPa under the condition of 443 K × 10 minutes to produce rubber sheets with a thickness of 1 mm × 200 mm square, and then performing at-vulcanization for 4 hours in an oven of 473 K, A conductive silicone rubber sheet was obtained for each. The conductivity of these conductive silicone rubber sheets was evaluated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 3 In the conductive silicone rubber composition of Example 6 above,
A conductive silicone rubber composition was produced in the same manner as in Example 6 except that zinc stearate was not added. Further, using this conductive silicone rubber composition, a conductive silicone rubber sheet was prepared under the same conditions as in Example 1, and the conductivity of each conductive silicone rubber was evaluated in the same manner. The results of these measurements are shown in Table 2.

[0039]

[Table 2]

[0040]

As described above, according to the conductive silicone rubber composition of the present invention, a conductive silicone rubber having a small variation in conductivity can be obtained. Therefore,
When used as a contact point of a keyboard, a sheet heating element, an office machine roll, an electromagnetic wave shielding material, or the like, a good conductive silicone rubber which prevents occurrence of partial heat generation, partial deterioration, or the like is provided. By using the conductive silicone rubber composition, it is possible to stably provide the composition.

[0041]

Claims (2)

[Claims] (A) General formula: R _a SiO _{(4-a) / 2} (wherein R represents an unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number from 1.90 to 2.05). 100 parts by weight of a polyorganosiloxane represented by (1), (b) 3 to 150 parts by weight of conductive carbon black, (c) 0.03 to 5 parts by weight of a fatty acid metal salt having 10 or more carbon atoms, and (d) a required amount of A conductive silicone rubber composition comprising a curing agent. 2. The conductive silicone rubber composition according to claim 1, wherein at least a part of the conductive carbon black of the component (b) is acetylene black.