JPH0428009B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a method for producing conductive silicone rubber. Specifically, by using a diluent, conductive filler,
In particular, the present invention relates to a method for producing conductive silicone rubber that can incorporate a large amount of carbon black, has excellent roll workability and moldability, and has low volume resistivity. [Prior art and problems] Conventionally, electrically insulating silicone rubber is blended with electrically conductive fillers such as carbon black, graphite, carbon fiber, and metal powder to produce electrically conductive silicone rubber. It has been used in a wide range of fields, from semiconductive to highly conductive. In particular, with the remarkable development of the electrical and electronic industries, there is an increasing demand for highly conductive silicone rubber.
There is a strong demand for materials with high conductivity of 1Ω-cm or less. Incidentally, carbon black is usually used as the conductive filler because of its ease of availability and its conductive properties. When silicone rubber is blended with carbon black, and as the amount of carbon black blended increases, it becomes highly conductive, but as a result, kneading with rolls becomes difficult and eventually becomes impossible. However, conventional methods had limitations in achieving high conductivity. [Object of the invention] The present invention solves the above-mentioned drawbacks, makes it possible to incorporate a large amount of conductive filler, especially carbon black, into silicone rubber, and has excellent roll workability and molding workability. They discovered a method for easily producing highly conductive silicone rubber, which was not possible using conventional methods. [Structure of the Invention] The above-mentioned object of the present invention is to provide (a) an organopolysiloxane having a viscosity of at least 100 centistokes at 25°C;
When mixing 100 parts by weight (b) of 30 to 300 parts by weight of conductive filler and (c) any amount of crosslinking agent, [however, component (c) is the same as component (a), component (b), and component (d). ) components may be added after mixing. ] (d) Cyclic or linear organopolysiloxane with a degree of polymerization of 10 or less. Mix while diluting with 10 to 300 parts by weight, during or after molding,
(d) This can be achieved by a method for producing conductive silicone rubber characterized by removing the component. The organopolysiloxane used in the present invention, component (a), is a base material for silicone rubber, and has an average unit formula of (In the formula, R is a monovalent hydrocarbon group, and a is 1.95 to
2.05) is a linear or slightly branched linear polymer. R includes an unsubstituted monovalent hydrocarbon group such as a methyl group, an ethyl group, a propyl group, an octyl group, a vinyl group, an allyl group, a phenyl group, a 2-cyanoethyl group, a 3,3,3-trifluoropropyl group, etc. The substituted monovalent hydrocarbon group is exemplified. It is preferred that at least 90 mol% of R is a methyl group. Viscosity is 100 at 25℃
The centistoke is used because if it is less than 100 centistoke, the physical properties after curing become hard and brittle, and the upper limit is the range up to the gum-like state that can be produced. Preferably the viscosity at 25℃ is 1000~
It is in the range of 10,000,000 centistokes. (c)
Organic peroxides are often used as crosslinking agents for components, but when organohydrodiene polysiloxane is used as a crosslinking agent and crosslinking is carried out by addition reaction in the presence of a platinum-based compound as a catalyst,
(a) It is necessary that at least two alkenyl groups exist in one molecule of component. In addition, when using an organosilicon compound having a hydrolyzable group as a crosslinking agent, and when crosslinking is carried out by a condensation reaction in the presence of an organosilicon compound having a hydrolyzable group and its catalyst, (a) It is necessary that the molecular chain end of the component is a hydroxyl group. Therefore, the molecular chain terminal of component (a) is not particularly limited, and may be a triorganosilyl group such as a trimethylsilyl group, dimethylvinylsilyl group, or methylphenylvinylsilyl group, or a silanol group. It may also be a hydrolyzable group. Component (a) is a homopolymer or a copolymer, but a mixture of two or more of these polymers can also be used. The conductive filler as component (b) used in the present invention is:
It is used to impart conductivity to silicone rubber, and examples thereof include carbon black, graphite, carbon fiber, metal fiber, metal powder, etc. Carbon black and graphite are preferred, and particularly preferred. is carbon black. Carbon blacks are conventionally known carbon blacks that are usually used in conductive rubber, such as channel black, furnace black, thermal black, and acetylene black. It is preferable that To give specific examples, furnace blacks include Continex CF (manufactured by Continental Carbon), Vulcan C (manufactured by Cabot), Continex SCF (manufactured by Continental Carbon), Vulcan SC (manufactured by Cabot),
Asahi HS-500 (manufactured by Asahi Carbon Co., Ltd.), Vulcan XC-72
Examples of channel blacks include Kourax L (manufactured by Degutsa), and examples of acetylene blacks include Denka Acetylene Black (manufactured by Denki Kagaku Kogyo Co., Ltd.). chain black
EC (manufactured by Akzo) can also be mentioned. The amount of component (B) used is based on 100 parts by weight of component (B).
Although the amount is set to be in the range of 30 to 300 parts by weight, it is possible to employ the method of the present invention even outside this range.
However, if it is less than 30 parts by weight, the desired high conductivity cannot be obtained, and if it exceeds 300 parts by weight, the silicone rubber becomes brittle and impractical. Therefore, the preferred range is 50 to 200 parts by weight. The crosslinking agent (C) component used in the present invention is for curing component (B) into a rubber-like state in the presence or absence of a catalyst. Curable organic peroxides, addition reaction type organohydrodiene polysiloxanes, condensation reaction curing types, and hydrolyzable organosilicon compounds are used. Examples of this organic peroxide include benzoyl peroxide, 2.4-dichlorobenzoyl peroxide, 2.5-bis(t-butylperoxy)-2.5-
Examples include dimethylhexane, dicumyl peroxide, monochlorobenzoyl peroxide, and t-butyl perbenzoate. Among these, carbon black may inhibit vulcanization, so when using carbon black, it is necessary to take this into consideration when selecting. The organic peroxide is usually used in an amount of 0.3 to 6 parts by weight per 100 parts by weight of component (a). When organohydrodiene polysiloxane is used as a curing agent, a platinum-based compound is required as an addition reaction catalyst, and an alkenyl group must be present in component (a). and,
In order to achieve sufficient curing, there must be at least two alkenyl groups in one molecule of component (a) and at least two SiH groups in one molecule of organohydrodiene polysiloxane, and ( b) Ingredient 1
Conditions are required such that the total number of alkenyl groups in a molecule and the number of SiH groups in one molecule of organohydrodiene polysiloxane is at least five. Typical examples of organohydrodiene polysiloxane include methylhydrodienepolysiloxane, tetramethyltetrahydrodienecyclotetrasiloxane, and a copolymer of methylhydrodienesiloxane and dimethylsiloxane. However, it is not limited to this,
It may contain an alkyl group other than a methyl group or a phenyl group. Further, the degree of polymerization is 2 or more, and a degree of polymerization that can be manufactured is allowed. Platinum-based catalysts include chloroplatinic acid, alcohol-modified chloroplatinic acid, complexes of platinum and olefin or vinyl siloxane, fine particulate platinum adsorbed on carriers such as alumina and silica,
Examples include palladium catalysts and rhodium catalysts, but platinum compounds are preferred. The amount of platinum-based compound to be used may be as long as it is sufficient to cure the present composition, but from an economic standpoint and to obtain a good cured state, the amount of platinum based on the weight of component (A) should be 1. A range of ~1000 ppm is preferred. Furthermore, when an organosilicon compound having a hydrolyzable group is used as a crosslinking agent, it is necessary that component (a) has a hydroxyl group at the end of the molecular chain. This organosilicon compound has an average unit formula (In the formula, R is a monovalent hydrocarbon group, a methyl group,
Ethyl group, propyl group, octyl group, vinyl group,
Examples include phenyl group and 3,3,3-trifluoropropyl group. Examples of Y include hydrolyzable groups such as an acyloxy group, an amino group, an aminoxy group, a ketoxime group, an alkenyloxy group, an alkoxy group, an amide group, an imide group, and an isocyanate group. b is 0≦b≦2, c is 0<c≦4, but b+c is 0<b+c≦4. ),
It is an organosilane or organopolysiloxane having at least two hydrolyzable groups bonded to silicon atoms in one molecule. Preferred is an organosilane having three hydrolyzable groups bonded to silicon atoms in one molecule. The amount of the organic silicon compound having a hydrolyzable group is usually 1 to 20 parts by weight per 100 parts by weight of component (a). When this organosilicon compound having a hydrolyzable group is used as a crosslinking agent, a conventionally known catalyst for condensation reaction may be used. Typical examples include metal salts of organic carboxylic acids and organic titanate esters. Examples of metal salts of organic carboxylic acids include organic carboxylic acids such as acetic acid, octylic acid, lauric acid, stearic acid, oleic acid, linoleic acid, benzoic acid, and naphthoic acid, as well as tin, iron, lead, zirconium, antimony, cadmium, etc. It is a metal salt of an organic carboxylic acid consisting of a metal, and among these, tin compounds are widely used. Specific examples include dibutyltin dioctoate, dibutyltin dilaurate, and dioctyltin dilaurate. Specific examples of organic titanate esters include tetrabutyl titanate, tetraisopropyl titanate, bis(acetylacetonate) titanium diisopropoxide, bis(acetylacetonate) titanium dibutoxide, and bis(acetoacetate ethylate) titanium diisopropoxy. Examples include de. The cyclic or linear organopolysiloxane with a degree of polymerization of 10 or less as component (2) used in the present invention is
It is a diluent for blending a large amount of the conductive filler (B) component, especially carbon black, into the present composition, and by increasing the amount of this component (D),
Theoretically, an unlimited number of component (B) can be blended into silicone rubber. However, even if 300 parts by weight or more of the component (B) is blended with 100 parts by weight of the component (A), most of the physical properties as a rubber will be lost and the rubber will be impractical, so the upper limit was set at 300 parts by weight. Component (2), organopolysiloxane, is often harmful to the physical properties when present in silicone rubber, so it must be removed during or after molding, and for this reason, it is relatively volatile. desirable. For this reason, the degree of polymerization of the organopolysiloxane was set to 10 or less, and was limited to cyclic bodies and linear bodies. Among these, linear ones with a degree of polymerization of 2 to 8 or cyclic ones with a degree of polymerization of 4 to 8 are preferable, and cyclic ones are particularly preferable from the viewpoint of ease of exhibiting appropriate properties. Further, it is preferable that the reactivity with component (a) and component (c) is low or absent.
Component (d) may be used as a mixture of two or more. Examples of the organic group bonded to the silicon atom of component (d) include methyl group, ethyl group, propyl group, octyl group, vinyl group, phenyl group, and 3,3,3-trifluoropropyl group. , methyl group is most preferred from the viewpoint of ease of exertion. When a linear one is used, it is preferable that the molecular chain terminal thereof is capped with a triorganosilyl group, particularly a trimethylsilyl group. Therefore, those represented by the following general formula are preferably used. general formula general formula (d) If the volatility of the component is too high, it will scatter during kneading and the dilution effect will be weakened, and if the volatility is too low, it will be difficult to remove.Octamethylcyclotetrasiloxane with appropriate volatility and decamethylcyclopentasiloxane are preferably used. The amount of component (d) added varies depending on the type and amount of component (b), but usually per 100 parts by weight of component (b).
Use in a range of 10 to 300 parts by weight. This is because if the amount is less than 10 parts by weight, the effect as a diluent will be low, so component (B) cannot be sufficiently blended, and it is uneconomical to use more than 300 parts by weight. In the present invention, the above-mentioned components (a) to (d) may be mixed at the same time, but depending on the type of component (c), the curing reaction starts at the same time as the addition, so component (c) is mixed last. You may also do so. Further, although the components (b) and (d) may be mixed at once, it is preferable to add them in several parts. In the present invention, when mixing components (A) to (C) using roll kneading or a kneader mixer, component (II) is used as a diluent to uniformly mix the components (II) during or after molding.
It removes components. This makes it possible to easily mix a large amount of component (B) into component (A), making it possible to easily obtain highly conductive silicone rubber that has not been possible until now. . (d) The method for removing components is from room temperature to 400 ml.
It may be removed at ℃ under normal pressure or reduced pressure. Although it varies depending on the type of component (2) used and the state of the silicone rubber, it is usually removed by heating to 150 to 300°C under normal pressure. If there is a problem with heating, it may be left at room temperature for a long time, or it may be removed at room temperature under reduced pressure. Furthermore, when component (2) having a high boiling point is used, it may be removed under reduced pressure while heating. (d) There are no particular limitations on the method of removing the component. It is preferable to completely remove component (d), but depending on the use of the silicone rubber, it may remain to an extent that does not pose a problem. Furthermore, when producing in large quantities, it is economically preferable to recover and reuse component (2). In addition to the above-mentioned components (a) to (d), the present invention also includes fuyum silica, wet silica, fine quartz powder, diatomaceous earth, zinc white, basic magnesium carbonate, aluminum silicate, talc, mica, etc. Powder, cerium oxide, cerium hydroxide, asbestos, glass fiber, pigment, addition reaction retarder, antioxidant, etc. can be blended. [Examples of the Invention] Next, the present invention will be explained with reference to Examples. In the examples, parts refer to parts by weight, and the viscosity is
This is a measured value at 25°C. Example 1 100 parts by weight of organopolysiloxane raw rubber (weight degree 3000) consisting of 99.8 mol% dimethylsiloxane units and 0.2 mol% methylvinylsiloxane units,
As carbon black, 100 parts of Denka Black (acetylene black) manufactured by Denki Kagaku Kogyo Co., Ltd., 50 parts of octamethylcyclotetrasiloxane, 2.5-dimethyl-2.5-di(tert-butylperoxy)
1 part of hexane was kneaded using two rolls. At that time, the ease of molding when molded into a sheet with a thickness of 5 mm was observed. In addition, a silicone rubber sheet with a thickness of 2 mm was prepared by uniformly kneading and press-forming at 170°C for 10 minutes, and then heat-treated at 200°C for 4 hours in a hot air circulation oven to produce octamethylcyclotetrasiloxane. was removed.
The physical properties of this sheet were measured and the results are shown in Table 1. Further, a rubber sheet was prepared in the same manner as above except that Denka black in the above composition was changed to 130 parts and 70 parts of octamethylcyclotetrasiloxane, and the physical properties were measured. As a comparative example, rubber sheets were prepared using the same composition and conditions as above, except that octamethylcyclotetrasiloxane was removed from each of the above two compositions, and the physical properties were measured. The results are shown in Table 1. Although the roll workability of the present invention was good, it was extremely difficult in Comparative Example 1 in which octamethylcyclotetrasiloxane was not added, indicating that this condition was the limit. Therefore, in Comparative Example 2, molding was not possible.

[Table] Example 2 100 parts by weight of the organopolysiloxane raw rubber (degree of polymerization 3000) used in Example 1, 65 parts of Denka Black used in Example 1, and 25 parts of Kettien Black EC (Furness Black) manufactured by Lion Akzo.
parts, 5 parts of octamethylcyclotetrasiloxane,
1 part of 2.5-dimethyl-2.5-di(tert-butylperoxy)hexane was kneaded using two rolls. After kneading, the mixture was pressure-molded at 170°C for 10 minutes to produce a silicone rubber sheet with a thickness of 2 mm, and then heated in a hot air circulation oven at 200°C for 4 hours to remove octamethylcyclotetrasiloxane. As a comparative example, the above composition except octamethylcyclotetrasiloxane was kneaded, but the sheet cracked and molding was impossible. The test was also carried out using carbon black that had been previously treated with octamethylcyclotetrasiloxane. That is, 65 parts of Denka Black and 25 parts of Ketsuchen Black E.C were placed in a four-necked flask equipped with a stirrer and a condenser, 50 parts of octamethylcyclotetrasiloxane was added, and the temperature was raised while stirring to 200°C. It was treated for 4 hours. Then, octamethylcyclotetrasiloxane was distilled off.
The entire amount of the treated carbon black was used and kneaded with 100 parts of the above organopolysiloxane raw rubber, but the sheet cracked and could not be molded. Therefore, I tried adding 5 parts of octamethyltetracyclosiloxane, which slightly improved the kneading process, but did not lead to molding.

【table】

[Table] Example 3 100 parts of organopolysiloxane raw rubber used in Example 1, Denka Black used in Example 1
100 parts, octamethylcyclotetrasiloxane 50
The mixture was mixed using two rolls until uniform. To this, 2 parts of methylhydrodiene polysiloxane having a viscosity of 10 centistokes as a crosslinking agent and having both ends of the molecular chain blocked with trimethylsilyl groups, 1 part of an isopropyl alcohol solution containing 1% by weight of chloroplatinic acid as a catalyst, and 0.2 parts of an isopropyl alcohol solution containing 30% by weight benzotriazole as a reaction retarder was added and mixed until homogeneous. This was heated and pressurized at 170° C. for 10 minutes to produce a silicone rubber sheet with a thickness of 2 mm, and then heated in a hot air circulation oven at 200° C. for 4 hours to remove octamethylcyclotetrasiloxane. A silicone rubber sheet was prepared under the same conditions as above, except that 75 parts of Denka Black and 25 parts of Kettien Black E.C were used instead of 100 parts of Denka Black in the above composition. As a comparative example, rubber sheets were produced under the same conditions except that only octamethylcyclotetrasiloxane was removed from both of the above compositions. These physical properties are shown in Table 3.

[Table] Example 4 100 parts of dimethylpolysiloxane having a viscosity of 6000 centistokes and having both ends of the molecular chain blocked with dimethylvinylsilyl groups, 100 parts of Denka Black used in Example 1, and graphite with a surface area of 10 m ² /g.
100 parts of decamethylcyclopentasiloxane were mixed with a two-blade mixer until uniform. This was mixed with 2 parts of methylhydrodiene polysiloxane with a viscosity of 10 centistokes and capped with trimethylsilyl groups at both ends as a crosslinking agent, 1 part of an isopropyl alcohol solution containing 1% by weight of chloroplatinic acid as a catalyst, and 3 parts as an addition reaction retarder. 0.1 part of 5-dimethyl-1-hexyn-3-ol was added and mixed until uniform. This was heated and pressurized at 170° C. for 10 minutes to produce a silicone rubber sheet with a pressure of 2 mm, and then heated in a hot air circulation oven at 230° C. for 4 hours to remove decamethylcyclopentasiloxane. The physical properties are shown in Table 4.
In this example, the kneading operation was carried out well, but it was impossible to knead the product without adding decamethylcyclopentasiloxane.

〔Effect of the invention〕

The present invention allows silicone rubber to be blended with a large amount of conductive filler, and also has excellent roll workability and molding workability, making it possible to create highly conductive silicone rubber that has not been achieved using conventional methods. Because it can be easily manufactured, it is useful in fields such as various electrical and electronic devices, communication devices, and mechanical devices. In particular, keyboards that require highly conductive silicone rubber,
Extremely useful for switches, connectors, rolls, belts, gaskets, shields, electrodes, ignition cables, etc.

Claims (1)

[Claims] 1. (a) An organopolysiloxane having a viscosity of at least 100 centistokes at 25°C.
When mixing 100 parts by weight (b) of 30 to 300 parts by weight of conductive filler and (c) any amount of crosslinking agent, [however, component (c) is the same as component (a), component (b), and component (d). ) components may be added after mixing. ] (d) Cyclic or linear organopolysiloxane with a degree of polymerization of 10 or less: Mix while diluting with 10 to 300 parts by weight, during or after molding,
(d) A method for producing conductive silicone rubber, characterized by removing the component. 2. The method for producing conductive silicone rubber according to claim 1, wherein component (b) is carbon black or graphite. 3. Claim 1, wherein component (c) is an organic peroxide, an organohydrodiene polysiloxane, or an organosilicon compound having a hydrolyzable group.
A method for producing conductive silicone rubber as described in Section 1. 4. The method for producing conductive silicone rubber according to claim 1, wherein component (2) is octamethylcyclotetrasiloxane or decamethylcyclopentasiloxane. 5. The method for producing conductive silicone rubber according to claim 1, wherein the method for removing component (ii) is heating at room temperature to 400°C, preferably 150 to 300°C.