JP2731691B2 - Conductive silicone rubber composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a conductive silicone rubber composition having excellent processability and high conductivity.

[0002]

BACKGROUND OF THE INVENTION Silicone compositions that cure to silicone rubber have been well known and have excellent properties such as weather resistance, heat resistance, cold resistance, and electrical insulation. Utilizing potting materials for electrical and electronic components,
Widely used for coating materials, molding materials for molding, etc. In addition, a silicone composition, which is originally an insulating material, is given conductivity and used.
As a method of imparting conductivity to the silicone composition as described above, a method of blending conductive carbon black is generally used in many cases. For example, JP-A-54-139659 discloses a conductive organopolysiloxane elastomer using a combination of furnace black and acetylene black having a specific surface area of 40 to 100 m ² / g. In addition, JP-A-55-120656 discloses a liquid organopolysiloxane composition containing carbon black having a specific surface area of 900 m ² / g or more and containing hollow shell-like particles.
No. 108455 discloses an extrusion-moldable liquid organopolysiloxane composition using a combination of carbon black and conductive fibers,
Further, Japanese Patent Application No. 56-120761 discloses a silicone rubber composition using carbon black having a specific surface area of 80 m ² / g or more. Carbon black used for the purpose of imparting conductivity as described above is classified into thermal black, furnace black, acetylene black, and the like according to the method for producing the carbon black. As a method for imparting high conductivity, a phenyl group-containing organosilicon compound may be used as disclosed in Japanese Patent Publication No. 3-47663, or a cyclic or linear polymer having a polymerization degree of 10 or less as disclosed in Japanese Patent Publication No. 4-28009. A method of diluting a chain organopolysiloxane with a large amount is known. However, the former has a phenyl group, which impairs the inherent cold resistance and physical properties of the silicone, and the physical properties vary depending on the method of kneading, and the latter has a shrinkage of several percent or more during molding. It was hard to say that the technology could endure. In addition, carbon black, which is generally classified as conductive carbon black, is blended into these.However, these have extremely developed structures, and when blended with silicone rubber, calender separation characteristics, sheeting properties, and extrusion operations are not improved. There are many difficulties, conductive silicone rubber with excellent processability, and 10
It has been strongly desired to establish a technology for a highly conductive silicone rubber composition that can provide a volume resistivity up to the ^-1 (Ω · cm) level.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in order to address such problems of the prior art, and has as its object to provide a silicone rubber composition having excellent workability and good conductivity. Things.

[0004]

The present inventors have conducted intensive studies in order to achieve the above object. As a result, in a conductive silicone rubber composition containing carbon black, it is effective to use a carbon black having specific properties. This led to the completion of the present invention. That is, the present invention provides a conductive silicone rubber composition containing carbon black, wherein part or all of the carbon black is produced by an oil furnace method, and has a specific surface area of 25 to 50 m ² /
g, a carbon black having a DBP oil absorption of 100 to 150 ml / 100 g and a toluene coloring transmittance of 90 to 100%. The conductive silicone rubber composition of the present invention basically comprises a polyorganosiloxane composition that becomes a rubber elastic body by being cured at room temperature or by heating or the like, carbon black satisfying the above conditions, and various types of It contains additives and the like.

[0005] The quality characteristics of the above-mentioned reinforced conductive carbon black have the following meanings. That is, the first characteristic of the carbon black used in the present invention resides in that it is produced by an oil furnace method. Generally available carbon blacks for imparting conductivity include furnace black (produced by burning creosote oil or the like in a high-temperature furnace) and acetylene black (produced by exothermic decomposition of acetylene gas). Because of the manufacturing method, graphite crystal parts are formed inside, so that it is not well compatible with the silicone-based polymer, and the processability has been reduced. Furnace black is frequently used for general rubber (natural rubber and various organic synthetic rubbers) other than silicone rubber, mainly for the purpose of reinforcement. These are clearly distinguished and widely used according to ASTM D 1765 by their particle size and properties imparted to rubber. However, no matter how these carbon blacks were used for general organic rubbers other than silicone rubber, the development of conductivity could not be expected. Because it is impossible to knead and compound these carbon blacks alone to the level of the level of expressing conductivity, it is often necessary to use process oils such as naphthene-aroma-based and paraffin-based plasticizers, which are often referred to as plasticizers. This is because a large amount was blended. The present inventors have newly found that only in the case of silicone rubber, a large amount of this furnace black can be compounded alone and high conductivity can be achieved. Next, the carbon black used in the present invention is required to have a specific surface area of 25 to 50 m ² / g. Here, the specific surface area is represented by a surface area (m ² ) per unit weight (g) of carbon black, and a specific surface area of 25 to 50 m ² / g is a value smaller than that of a general furnace black. It is. The DBP oil absorption is defined in JIS K 6221 "Testing methods for carbon black for rubber" and indicates the degree of structure that is a complex aggregation due to chemical and physical bonding between carbon black particles. Means the number of ml of oil contained per 100 g of carbon black. Here, DBP is dibutyl phthalate. In the present invention, the value of the DBP oil absorption is defined as 100 to 150 ml / 100 g. This value is a relatively high value in normal furnace black. In addition, the toluene color transmittance, another quality item, is also specified in JIS K 6221, and is a scale indicating the degree of residual undecomposed organic substances contained in carbon black when pure toluene is 100%. It represents the transmittance of light of a certain wavelength. The present inventor has paid attention to the toluene coloring transmittance, and as a result of various studies, found that 90 to 100% imparts high conductivity to silicone. As a result, by satisfying the specific surface area, the DBP oil absorption, and the toluene permeability under the above conditions, it is possible to highly fill the silicone rubber with high conductivity and good workability. .

As described above, in the present invention, carbon black having the above-mentioned properties is used as at least a part of the blended carbon black in order to improve processability and to give good conductivity. . The usage ratio of the reinforced conductive carbon black in the total carbon black is determined in consideration of the amount of the total carbon black to be filled and the like, but is usually preferably in the range of 40 to 90% by weight. In addition, in order to impart high conductivity, such as high filling of carbon black, the ratio of the reinforcing conductive carbon black in the total carbon black is 90 to 100.
A range of weight% is preferred. The type of the conductive carbon black used in combination is not particularly limited.

On the other hand, the polyorganosiloxane composition which is the main component of the silicone rubber composition of the present invention comprises (a) a polyorganosiloxane base polymer, (b) a curing agent,
As required, various additives and the like are blended and uniformly dispersed. Among the various components used in such a polyorganosiloxane composition, (a) a silicone base polymer and (b) a curing agent are appropriately selected depending on a reaction mechanism for obtaining a rubber-like elastic body. is there. The reaction mechanism includes (1) a crosslinking method using an organic peroxide vulcanizing agent,
(2) A method based on an addition reaction and the like are known, and it is well known that a preferable combination of the component (a) and the component (b), that is, a curing catalyst or a crosslinking agent is determined by the reaction mechanism. That is, when the crosslinking method of the above (1) is applied, the base polymer of the component (a) is usually
Polyorganosiloxane in which at least two of the organic groups bonded to silicon atoms in one molecule are alkenyl groups such as vinyl, propenyl, butenyl, and hexenyl is used. In particular, vinyl-based compounds are frequently used because of their ease of synthesis and availability of raw materials. Further, as the curing agent of the component (b), benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, cumyl-t-butyl peroxide, 2,5-dimethyl-2,5
Various organic peroxide vulcanizing agents such as -di-t-butylperoxyhexane, di-t-butyl peroxide and the like are used, and give particularly low compression set. , 2,5
-Dimethyl-2,5-di-t-butylperoxyhexane, di-t-butyl peroxide are preferred. In addition, these organic peroxide vulcanizing agents are used as one kind or as a mixture of two or more kinds. The compounding amount of the organic peroxide as the curing agent of the component (b) is preferably in the range of 0.05 to 15 parts by weight based on 100 parts by weight of the silicone base polymer of the component (a).
If the compounding amount of the organic peroxide is less than 0.05 part by weight, the vulcanization is not sufficiently performed, and if the compounding amount exceeds 15 parts by weight, not only there is no further special effect, but also the physical properties of the obtained silicone rubber are reduced. This is because it may have an adverse effect. Also,
When the addition reaction of (2) is applied, as the base polymer of the component (a), the same base polymer as in the above (1) is used. As the curing agent of the component (b), a platinum catalyst such as chloroplatinic acid, a platinum olefin complex, a platinum vinyl siloxane complex, platinum black, and a platinum triphenylphosphine complex is used as a curing catalyst. A polydiorganosiloxane having an average of at least two hydrogen atoms bonded to silicon atoms per molecule is used. Among the curing agents of the component (b), the amount of the curing catalyst is preferably in the range of 1 to 1000 ppm in terms of platinum element based on the base polymer of the component (a). If the amount of the curing catalyst is less than 1 ppm as platinum element,
Curing does not proceed sufficiently, and even if it exceeds 1000 ppm, particularly improvement of the curing speed cannot be expected. The compounding amount of the crosslinking agent is preferably such that 0.5 to 4.0 hydrogen atoms bonded to silicon atoms in the crosslinking agent per one alkenyl group in the component (a), more preferably 1.0 to 1.0. It is an amount such that it becomes ~ 3.0 pieces. When 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. The physical properties and heat resistance of the composition are reduced.
The organic group in the polyorganosiloxane as the base polymer of the component (a) used in the various reaction mechanisms as described above is a monovalent substituted or unsubstituted hydrocarbon group, such as a methyl group, an ethyl group, or a propyl group. , Butyl group,
An unsubstituted hydrocarbon group such as an alkyl group such as a hexyl group or a dodecyl group, an aryl group such as a phenyl group, an aralkyl group such as a β-phenylethyl group or a β-phenylpropyl group, a chloromethyl group, And a substituted hydrocarbon group such as a 3,3-trifluoropropyl group. In general, a methyl group is frequently used because of ease of synthesis and the like. In the present invention, from the viewpoint of conductivity, the polysiloxane base polymer preferably has a degree of polymerization of 1,000 or more, that is, a so-called millable type. This is presumed to be because the shearing stress at the time of mixing is appropriate, and the above-mentioned effect is more exhibited by the compounding.

In the present invention, the total amount of carbon black is arbitrarily selected depending on the degree of polymerization of the polysiloxane base polymer and the characteristics of the obtained silicone rubber composition, and is not particularly limited. 1 to 500 per 100 parts by weight of polysiloxane base polymer
It is used in an amount of 5 parts by weight, preferably 5 to 200 parts by weight. The conductive silicone rubber composition of the present invention may optionally further contain a filler, a pigment, a heat resistance improver, a flame retardant, and the like, and other polyolefins may be used as long as the effects of the present invention are not impaired. An organosiloxane may be used in combination. Examples of such materials include fumed silica, precipitated silica, reinforcing fillers such as diatomaceous earth, titanium oxide, aluminum oxide, zinc oxide, iron oxide, cerium oxide, mica, clay, zinc carbonate, and carbonic acid. Examples thereof include manganese, cerium hydroxide, glass beads, polydimethylsiloxane, alkenyl group-containing polysiloxane, and polyorganosilsesquioxane.

[0009]

Hereinafter, embodiments of the present invention will be described.
The present invention is not limited to these. In the following text, all “parts” indicate “parts by weight”. Example 1, Comparative Examples 1 and 2 A terminal surface was capped with a trimethylsilyl group, and 100 parts of a vinyl group-containing polydimethylsiloxane containing 0.50 mol% of a methylvinylsiloxane unit (degree of polymerization: about 6000) was used as a carbon black to obtain a specific surface area of 34 m ² / g, DBP oil absorption 110ml /
100g, furnace black a with toluene color transmittance of 95%
(Mitsubishi Kasei Co., Ltd., product name "DIABLACK E
Y ") 50 parts, hydrochloric acid absorption amount 10ml / 5g, iodine adsorption amount 48mg
/ g of acetylene black (trade name: Denka Black HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.) in a kneader at a ratio of 10 parts and kneading, followed by 2,5-dimethyl-2,5 as a crosslinking agent. 1.5 parts of -di-t-butylperoxyhexane was charged and uniformly mixed to obtain a silicone rubber composition. Next, as a comparison with the present invention, specific surface area 78 m ² / g, DBP oil absorption 105 ml / 100
g, furnace black b with toluene color transmittance of 83%
(Mitsubishi Kasei Co., Ltd., product name "DIABLACK
H ") to obtain a silicone rubber composition for comparison (Comparative Example 1) in the same manner as in the above example. Also, using acetylene black alone (60 parts) without using furnace black a as carbon black, another comparative silicone rubber composition (comparative example 2) was obtained in the same manner as in the above example. . Regarding the processability of each silicone rubber composition thus obtained, as an extrusion property evaluation, φ30 mm L / D
= 16 mm outer diameter, 2 mm inner diameter using screw type extruder
A tube of φ was extruded and the appearance of the extruded skin was compared at a linear speed of m / min at which the defect was observed. In order to evaluate the sheeting characteristics, a thickness of up to a thickness of 8 mm roll was compared and evaluated for uniform sheeting. The conductivity was evaluated by measuring the volume resistivity of a 1 mm thick sample sheet prepared using each silicone rubber composition.
The sample sheet was pressed and vulcanized at 170 ° C for 10 minutes after the sheet was formed.
It was prepared by performing hot air vulcanization at 4 ° C. for 4 hours.
Table 1 shows the measurement results.

[0010]

[Table 1]

Example 2, Comparative Examples 3 to 5 100 parts of a polyorganosiloxane containing 0.15 mol% of a methylvinylsiloxane unit has a specific surface area of 43 m ² / g as carbon black, a DBP oil absorption of 130 ml / 100 g, and toluene coloring transmission. Furnace black c (manufactured by Mitsubishi Kasei Corporation, trade name "DIABLACK F") having a degree of 97% is kneaded in a 90-part kneader, and 2,5-dimethyl- is further used as a crosslinking agent.
2.0 parts of 2,5-di-t-butylperoxyhexane was charged and uniformly mixed to obtain a silicone rubber composition. or,
As a comparison with the present invention, furnace black d having a specific surface area of 50 m ² / g, a DBP oil absorption of 127 ml / 100 g, and a toluene coloring transmittance of 76% (trade name “DIABLACK”, manufactured by Mitsubishi Kasei Co., Ltd.) was used in place of furnace black c. SF "), furnace black e having a specific surface area of 96 m ² / g, a DBP oil absorption of 120 ml / 100 g, and a toluene coloring transmittance of 80% (manufactured by Mitsubishi Kasei Corporation,
Similarly, silicone rubber compositions (comparative examples 3 to 5) were obtained by using trade name "DIABLACK N339") and acetylene black f (trade name "Denka black granular", manufactured by Denki Kagaku Kogyo Co., Ltd.) as conductive carbon black. ) Was prepared, and its physical properties and conductivity were confirmed. Physical properties are JIS K 6301
170 ° C x 2mm sheet according to (Vulcanized Rubber Physical Test Method)
Samples were prepared by 10 'press and hot air vulcanization at 200 ° C for 4 hours. In the case of acetylene black f, 90 parts do not enter,
Since the comps were broken apart, the data for just 80 copies were collected.

[0012]

[Table 2]

Next, an example in which the furnace black a used in Example 1 is blended with another general organic synthetic rubber will be described below. Reference Examples 1-2 The furnace black a was blended with an ethylene / propylene / diene terpolymer (trade name “EPDM3045” manufactured by Mitsui Petrochemical Industries, Ltd.). First, as shown in Table 3,
As in Example 1, 50 parts of Furnace Black a was kneaded in a 3 L pressurized banbury in an attempt to blend 50 parts with 100 parts of ethylene-propylene-diene terpolymer. Has become granular. Therefore, the compounds were put together in a maximum amount of 25 parts of furnace black a in which the compounds could be integrated.
Next, in order to mix 50 parts, paraffin-based oil was added to a cohesive amount and kneaded similarly. Thereafter, each sheet was taken out and pressed at 150 ° C. for 15 minutes to prepare a 1 mm sheet, and the volume resistivity was measured.
It was 10 ¹⁵ Ω · cm, and in Reference Example 2, it was 7.6 × 10 ¹² Ω · cm.

[0014]

[Table 3]

Reference Examples 3 and 4 The above furnace black c was prepared using chloroprene rubber (trade name "DENKA chloroprene M-4", manufactured by Denki Kagaku Kogyo KK).
0 "). First, as shown in Table 4, to mix 90 parts of furnace black c with 100 parts of chloroprene rubber in the same manner as in Example 2, kneading was carried out using a 3 L pressurized banbury. I couldn't do it and the compound became granular. Therefore, the compounds were put together in a maximum amount of 35 parts of furnace black c, in which the compounds were united. Next, to mix 90 parts, dioctyl phthalate was added to a mass and kneaded in the same manner. Thereafter, each sheet was taken out and pressed at 145 ° C. × 15 minutes to form a 1 mm sheet, and the volume resistivity was measured. In Reference Example 3, it was 4.0 × 10 ⁵ Ω · cm.
× 10 ¹⁵ Ω · cm.

[0016]

[Table 4]

Claims (1)

(57) [Claims] 1. A conductive silicone rubber composition containing carbon black, wherein part or all of the carbon black is produced by an oil furnace method, has a specific surface area of 25 to 50 m ² / g, and a DBP oil absorption of 100. ~ 150ml / 100g,
A conductive silicone rubber composition comprising carbon black having a transmittance of 90 to 100% of toluene coloring.