JPH07242825A - Electrically conductive silicone rubber composition and its production - Google Patents

Abstract

PURPOSE:To obtain the subject composition, capable of blending a large amount of electrically conductive carbon black, excellent in roll processability and moldability, having a low volume resistivity and useful as a keyboard electrically conductive contact, etc., for electronic calculators by presupporting a low-molecular weight organosiloxane on the carbon black. CONSTITUTION:This composition is obtained by mixing (A) carbon black prepared by presupporting (ii) 5-100 pts.wt. organosiloxane having 3-500 polymerization degree on (i) 100 pts.wt. carbon black with (B) a polyorganosiloxane having >=2000 polymerization degree. Furthermore, e.g. acetylene black is preferably used as the component (i) and, e.g. a polyorganosiloxane expressed by the average composition formula [(a) is 1.98-2.02; R is an (un)substituted monovalent hydrocarbon] is preferably used as the component (B).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a conductive silicone rubber composition and a method for producing the same, more specifically, it is possible to add a large amount of conductive carbon black, and it is excellent in roll processability and moldability. The present invention relates to a technique for providing a conductive silicone rubber having a low volume resistivity.

[0002]

TECHNICAL BACKGROUND OF THE INVENTION AND ITS PROBLEMS It has been generally well known that a conductive silicone rubber composition is obtained by blending silicone rubber with carbon black as a conductive material. Usually, the incorporation of carbon black, but 10 ¹³ ~10 ⁰ Ω · cm approximately conductive silicone rubber with a volume resistivity is obtained, recently more even stronger demand for highly conductive silicone rubber is, 10 ^{0 -} 10 ^-1 Ω · cm is also required. In order to obtain such a highly conductive silicone rubber, it has been dealt with by filling carbon black into the silicone rubber at a high level. There is a problem that the viscosity of the subsequent silicone rubber composition becomes too high, roll processability and moldability are deteriorated, the structure of carbon black is broken, and the conductivity does not become higher than a certain level. Methods for solving such problems are disclosed in JP-A-61-62528 and JP-A-2.
It is proposed in Japanese Patent Laid-Open No. 242855, Japanese Patent Laid-Open No. 5-140327, and the like. The methods proposed in these publications are all obtained by adding a volatile siloxane or a volatile saturated aliphatic hydrocarbon to the composition, lowering the viscosity of the composition, and then rolling and forming the composition. This is a method of heating the formed article to remove volatile components. Although it is possible to obtain a conductive silicone rubber having a volume resistivity of about 10 ⁰ to 10 ^-1 Ω · cm by these methods, on the other hand, since it is necessary to blend a large amount of volatile components, the composition Although the viscosity will decrease to some extent, roll adhesion will increase and molding will not be possible, or the linear shrinkage of the molded product will increase, for example when the molded product bends when integrally molded with the insulating part. However, there is a problem that the workability of the above is deteriorated, and there is a risk of ignition at the time of removing volatile components. Such a problem is caused by the fact that the oil absorption capacity of carbon black adsorbs not only volatile components (low molecular weight compounds) but also polysiloxane which is a main polymer, and the techniques of the above publications are essentially In the coexistence of the volatile component (low molecular weight compound) and the main polymer, it is necessary to add a large amount of the volatile component (low molecular weight compound) in order to prevent the main polymer from being adsorbed on the carbon black, resulting in problems. Is.

[0003]

DISCLOSURE OF THE INVENTION The present invention has been devised in view of the above problems of the prior art, and an object of the present invention is to provide a conductive silicone rubber composition having excellent conductivity and moldability. The present invention further provides a conductive silicone rubber composition in which the content of volatile components is reduced as much as possible.

[0004]

That is, the present invention provides a conductive silicone rubber composition containing carbon black, wherein the carbon black is a carbon black carrying a polyorganosiloxane having a degree of polymerization of 3 to 500, and is a base polymer. A conductive silicone rubber composition in which a certain polyorganosiloxane is a polyorganosiloxane having a degree of polymerization of 2000 or more, and 5 to 100 parts by weight of a polyorganosiloxane having a degree of polymerization of 3 to 500 per 100 parts by weight of carbon black in advance. A method for producing a conductive silicone rubber composition, which comprises mixing carbon black supporting styrene with a polyorganosiloxane having a degree of polymerization of 2000 or more.

The present invention will be described in detail below. The conductive carbon black used in the present invention is usually
Acetylene black, furnace black, channel black, ketjen black and the like which are 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 (XC)
F), Conductive Channel Black (CC) and
Furnace black or channel black heat-treated at a high temperature of about 15,000 ° C. may be mentioned. Specific examples of acetylene black include electrified acetylene black (manufactured by Denki Kagaku Co., Ltd.) and Shawnigan acetylene black (manufactured by Shawnigan Chemical Co., Ltd.), and specific examples of conductive channel blacks include Continex CF (Continental). Carbon Co., Ltd., Vulcan C (made by Cabot Co., Ltd.), and the like, and specific examples of Super Conductive Furnace Black are Continex SCF (made by Continental Carbon Co., Ltd.), Vulcan SC (made by Cabot Co., Ltd.), etc. However, as a specific example of Extra Conductive Furnace Black, Asahi HS-50
0 (manufactured by Asahi Carbon Co., Ltd.), Vulcan XC-72 (manufactured by Cabot Co., Ltd.), etc., and Kolux L (manufactured by Degussa Co., Ltd.), etc. as the conductive channel black are also exemplified. Ketjen Black EC and Ketjen Black EC-600 JD
(Ketjen Black International Co., Ltd.) can also be used. Among these, acetylene black is particularly preferable in the present invention because it has excellent conductivity because it has a small impurity content and has a developed secondary structure structure. In addition, Ketjen Black EC and Ketjen Black EC-600 JD, which have excellent specific surface area and exhibit excellent conductivity even with a low filling amount, can be preferably used. These conductive carbon blacks may be used alone or in combination of two or more.

In the polyorganosiloxane having a degree of polymerization of 3 to 500 (hereinafter referred to as low molecular weight organopolysiloxane) used in the present invention, the organic group bonded to the silicon atom is a methyl group, an ethyl group, a propyl group or a vinyl group. ,
Examples thereof include a phenyl group and a 3,3,3-trifluoropropyl group, which may be cyclic, linear, or branched, but to be supported on carbon black, liquid at a temperature of 150 ° C or lower. It is necessary to be. Examples of the molecular chain end include a triorgansilyl group, a hydrogen atom, a hydroxyl group, and a hydrolyzable group. Further, even if it is a liquid, if the viscosity is too high, it becomes difficult to disperse it in carbon black, and therefore it is necessary that the degree of polymerization is less than 500. Further, if the degree of polymerization is less than 3, that is, the degree of polymerization is 1 or 2, the volatility becomes high and there is a problem in storage stability.

The method of supporting the low molecular weight polyorganosiloxane on the carbon black is not particularly limited, but for example, after charging the carbon black in an apparatus such as a Henschel mixer, the low molecular weight polyorganosiloxane is sprayed while stirring. It can be obtained by dispersing by a method such as dropping. The conditions at this time may be room temperature and normal pressure, and pressurization, depressurization, heating, etc. may be performed as necessary. The amount of the low molecular weight polyorganosiloxane supported can be selected within the range of 5 to 100 parts by weight, preferably 100 parts by weight of carbon black, and preferably
10 to 50 parts by weight. If less than 5 parts by weight, the effect is small,
If the amount exceeds 100 parts by weight, the effect will not change, and problems such as sticking during roll processing will occur.

Next, the polyorganosiloxane having a degree of polymerization of 2000 or more, which is used as the base polymer in the present invention, has the following average composition formula (1) R _a SiO _{(4-a) / 2} (1) (wherein , A is an integer of 1.98 to 2.02, and R is a substituted or unsubstituted monovalent hydrocarbon group.). Specific examples of R include alkyl groups such as methyl group, ethyl group and propyl group, cycloalkyl groups such as cyclopentyl group and cyclohexyl group, alkenyl groups such as vinyl group and allyl group, cycloalkenyl group, phenyl group and tolyl group. And the like, or halogenated hydrocarbon groups and cyanated hydrocarbon groups in which the hydrogen atoms of these groups are partially substituted with chlorine atoms, organic groups such as cyano groups, and the like. The polyorganosiloxane represented by the average composition formula (1), the main chain of the polyorganosiloxane is composed of dimethylsiloxane units, or the main chain of the dimethylpolysiloxane has a phenyl group, a vinyl group, 3,3,3 -The thing which introduce | transduced a trifluoro propyl group etc. can be used conveniently. In addition, this polyorganosiloxane must contain at least one alkenyl group in at least one molecule. In the present invention, the polyorganosiloxane should have a degree of polymerization of 2000 or more. Degree of polymerization
If it is less than 2000, satisfactory workability and moldability may not be obtained, and the mechanical strength of the molded product may be insufficient. The upper limit of the degree of polymerization does not have to be specified, but generally less than 1500 is preferable. If it is 1500 or more, it becomes difficult to mix the conductive carbon black. In the present invention, this degree of polymerization 20
The blending amount of carbon black supporting the low molecular weight polyorganosiloxane with respect to 00 or more polyorganosiloxane (base polymer) is not particularly limited, but is about 5 to 300 parts by weight with respect to 100 parts by weight of the base polymer. Can be appropriately selected within the range.

Further, in the present invention, a curing agent is appropriately added to obtain a molded product. The curing agent is appropriately selected from various conventionally known curing agents that can be vulcanized and cured by utilizing radical reaction, addition reaction, etc. which are usually used for vulcanization of conductive silicone rubber. The curing mechanism is not limited. Examples of such a curing agent include di-t-butylperoxide and 2,5-dimethyl-2,5.
In addition to organic peroxides such as alkyl peroxides such as di (t-butylperoxy) hexene, addition reaction curing agents include at least two hydrogen atoms bonded to silicon atoms in one molecule. A combination of the above-mentioned organohydrogenpolysiloxane and a platinum-based catalyst can be used. The amount of the curing agent added may be the same as in the case of ordinary conductive silicone rubber. The composition of the present invention includes silica hydrogel (hydrous silicic acid), reinforcing silica filler such as silica aerogel (silicic anhydride-fumed silica), clay, calcium carbonate, diatomaceous earth, titanium dioxide, etc., if necessary. Fillers, dispersants such as hexamethyldisilazane, heat resistance improvers such as iron oxide, cerium oxide and iron octylate, various carbon functional silanes to improve adhesion and molding processability, flame retardancy The platinum compound or the like may be added and mixed. The composition of the present invention can be obtained by kneading the above components using a mixer such as a roll, a kneader or a Banbury mixer. Generally, a polyorganosiloxane (base polymer) and a low molecular weight polyorganosiloxane are supported in advance. It is preferable to uniformly knead with the carbon black, and then add a curing agent and other components to this and knead.

[0010]

In the conductive silicone rubber composition of the present invention, carbon black supporting low molecular weight polyorganosiloxane is used as a conductive material. Therefore, a large amount of carbon black is added to obtain high conductivity. However, only the low molecular weight polyorganosiloxane is adsorbed by the oil absorption capacity of carbon black, and the base polymer is hardly adsorbed. Therefore, according to the composition of the present invention,
It is possible to reduce the content of low molecular weight polyorganosiloxane, and as a result, the composition of the present invention is excellent in roll processability and can be molded by a calendar roll or the like. Since the product is excellent in conductivity, it can be applied to a very wide range as a conductive contact of a keyboard for a calculator and a conductive part of a precision part such as a conductive part of a zebra connector or a gasket material for EMI shield.

[0011]

The present invention will be described in detail below with reference to Examples.
The present invention is not limited to this. [Preparation of Conductive Material] 20 parts by weight of octamethylcyclotetrasiloxane was supported on 100 parts by weight of acetylene black to obtain a filler A-1. Ketjen black 10
Octamethylcyclotetrasiloxane based on 0 parts by weight
40 parts by weight was carried to obtain a filler A-2. Dimethyl siloxane unit per 100 parts by weight of acetylene black
A filler A-3 was obtained by supporting 80 parts by weight of diphenylsiloxane unit and 20 parts by weight of diphenylsiloxane unit, and 10 parts by weight of a low molecular weight siloxane having a polymerization degree of 10 and having a terminal blocked with a dimethylmethoxysilyl group. Examples 1 to 3 100 parts by weight of methylvinylpolysiloxane having an average degree of polymerization of 7000 and containing 99.8 mol% of dimethylsiloxane units and 0.3 mol% of methylvinylsiloxane units were added to the filler A-1.
To A-3, and then 1.5 parts by weight of 2,5-dimethyl-2,5-di (t-butylperoxo) hexane were mixed to obtain a composition, 1 mm
Sheeting was performed to evaluate the presence or absence of ear cracks and roll adhesion. Also, the plasticity was measured according to JIS K 6300. Furthermore, this composition was press-vulcanized at 170 ° C for 10 minutes,
Perform hot air vulcanization at 0 ° C for 4 hours, and use 1 for volume resistance measurement.
mm sheet and 2 mm sheet for measuring general physical properties were prepared. The physical properties (JIS K 6301) and volume resistivity (JIS C 2123) of the vulcanized sheet obtained here were measured.

Comparative Examples 1 to 5 When 100 parts by weight of the same methyl vinyl polysiloxane as in the Examples are blended with acetylene black and Ketjen black alone, respectively, octamethyl cyclotetrasiloxane and saturated aliphatic hydrocarbon are obtained at the same time. Boiling point 17
Isoparaffinic solvent (Nisseki Isosol 30
When 0) was blended, a composition was prepared and evaluated in the same manner as in the examples.

[0013]

[Table 1]

As is clear from the results shown in Table 1, the conductive silicone rubber composition containing carbon black supporting a low molecular weight siloxane has a low plasticity, a good roll processability, and a carbon black structure is destroyed. It can be seen that high conductivity is obtained because it is hard to be conducted. On the other hand, Comparative Example 1 in which low molecular weight siloxane does not exist
The compositions of ~ 2 were not kneadable. Further, as shown in Comparative Example 3, when the carbon black and the low molecular weight siloxane are simply blended, the volume resistivity and the like are inferior to those in Example 1. In order to improve the volume resistivity, as shown in Comparative Example 4, a large amount of low-molecular-weight siloxane is required, which deteriorates roll processability and increases linear shrinkage.
The deformation during molding becomes large. Further, as shown in Comparative Example 5, when the isoparaffin solvent is blended, roll processability, volume resistivity and the like are poor.

Claims (2)

[Claims] 1. A conductive silicone rubber composition containing carbon black, wherein the carbon black is a carbon black supporting a polyorganosiloxane having a degree of polymerization of 3 to 500, and the polyorganosiloxane as a base polymer has a degree of polymerization of 2000 or more. 1. A conductive silicone rubber composition, characterized by being a polyorganosiloxane of 2. A carbon black in which 5 to 100 parts by weight of a polyorganosiloxane having a degree of polymerization of 3 to 500 is previously supported with respect to 100 parts by weight of carbon black, and a polyorganosiloxane having a degree of polymerization of 2000 or more are mixed. And a method for producing a conductive silicone rubber composition.