JP2752901B2 - Conductive silicone rubber composition and method for producing conductive silicone rubber sponge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive silicone rubber composition for obtaining a conductive silicone rubber sponge having fine cells and a method for producing a silicone rubber sponge. In particular, the present invention provides a silicone rubber sponge useful as a conductive sponge roll for office equipment or a sponge gasket for an electromagnetic wave shielding material.

[0002]

Technical Background of the Invention and Problems There have been known various conductive rubbers in which a conductive material is blended with a rubber-like substance having electrical insulation properties. For example, carbon black or the like is blended as a conductive material. Conductive rubber with an electric resistance in the range of 10 ⁵ to 10 Ω · cm has been applied in a wide range of fields. On the other hand, silicone rubber, one of the electrically insulating rubber-like substances, has excellent heat resistance, cold resistance, and weather resistance, and is widely used as an electrically insulating rubber. By adding a conductive material such as the above, it has been put to practical use as a conductive silicone rubber, and a conductive silicone rubber foam which is further foamed and cured by adding a foaming agent is also known. In this case, as the conductive material to be added to the conductive silicone rubber, for example, various metal powders such as carbon black, graphite, silver, nickel, and copper, various non-conductive powders, and the surface of short fibers are treated with a metal such as silver. which was, carbon fibers, those such as a mixture of metal fibers, ¹⁰ 10 volume resistivity of the silicone rubber depending on the type and loading of the conductive material without impairing the peculiar characteristics with silicone rubber
It is frequently used because it can be reduced to about 10 ^-3 Ωcm, and especially when a highly conductive silicone rubber of 10 ⁵ Ωcm or less is obtained, carbon black, silver, nickel, etc. Metal powder, especially carbon black is frequently used from the viewpoint of cost. However, when a conductive silicone rubber composition using carbon black such as acetylene black as a conductive material is to be molded (vulcanized) into a sponge such as a sealing material, a gasket material, or a roll material by extrusion molding or the like. There were very limited vulcanization systems. That is, for example, when performing an organic peroxide vulcanization, a normal pressure hot air vulcanization (HA) of a silicone rubber composition is usually performed.
When an acyl peroxide such as benzoyl peroxide or 2,4-dichlorobenzoyl peroxide used in V) is used in a system containing carbon black, vulcanization is not sufficiently performed due to the influence of carbon black, and satisfactory results are obtained. A molded product cannot be obtained. In addition, dicumyl peroxide, dialkyl peroxide, and 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane conventionally used in conductive silicone rubbers have a high temperature exceeding 170 ° C. Although it shows good vulcanization properties, on the other hand, in the production of conductive sponge, the balance between vulcanization and foaming is poor and a good sponge cannot be obtained. As a method for solving these problems, a method using peroxyketal in Japanese Patent Publication No. 62-49895 and a method using percarbonate in Japanese Patent Application Laid-Open Nos. 5-25393 and 5-43802 are proposed. Have been. However, since these also use one kind of organic peroxide, the balance between foaming and vulcanization is difficult to obtain, and it has been difficult to obtain a sponge having fine cells. These non-cell sponges are charged rolls,
It is unsuitable as a conductive roll for office use such as a transfer roll, a developing roll, a paper feed roll, and a fixing roll, and a conductive silicone rubber sponge having fine cells has been desired.

In order to overcome such difficulties, a method of vulcanizing a silicone rubber composition containing carbon black by addition vulcanization has been considered. In this method, an alkenyl group-containing organopolysiloxane and an organohydrogenpolysiloxane having a silicon-bonded hydrogen atom that undergoes an addition reaction with the alkenyl group are cured by adding a platinum-based addition reaction catalyst. However, this addition reaction method has a problem that shelf life (storage time) is limited in order to partially vulcanize at the time of foaming, and that if the reaction is delayed, good sponge properties cannot be obtained. In addition, when obtaining a conductive silicone rubber foam, in order to obtain a good foam, the vulcanization proceeds to a certain extent by additional vulcanization in order to confine the foaming gas due to the decomposition of the foaming agent in the system (scorch). It is necessary to search for the optimal control agent for controlling the addition reaction,
Also, even if an appropriate control agent is used, the optimum pot life for obtaining a good foam is limited to a very narrow time zone,
It is practically difficult to continuously produce a conductive silicone rubber foam by normal pressure hot air vulcanization by an addition reaction method.
For this reason, there has been a demand for the development of a conductive silicone rubber foam composition having excellent storage stability that can be used by a person engaged in sponge molding and that can be quickly vulcanized.

[0004]

An object of the present invention is to solve the above-mentioned problems, and has excellent storage stability, and can be vulcanized by hot air vulcanization at normal pressure by extrusion or calendering molding. SUMMARY OF THE INVENTION It is an object of the present invention to provide a conductive silicone rubber composition that gives a foamed silicone rubber having the same, and a method for producing the conductive silicone rubber sponge by foaming and curing the composition.

[0005]

The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that it is effective to use a specific alkyl perester in combination with a specific curing agent.
The present invention has been completed.

That is, the present invention relates to (a) an organopolysiloxane represented by the following general formula (1):

[0007]

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(Wherein R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number from 1.90 to 2.05.) (B) Conductive carbon black (c) 1 minute Alkyl perester having a half-life temperature of 110 to 150 ° C (d) Organic peroxide having a one-minute half-life temperature of 150 to 200 ° C, or a curing agent comprising an addition reaction catalyst and a crosslinking agent (e) Organic foaming agent And a conductive silicone rubber characterized in that the conductive silicone rubber composition is heated to a temperature equal to or higher than the decomposition temperature of the organic foaming agent and foamed and hardened. Things.

Hereinafter, the present invention will be described in more detail. The component (A) constituting the composition of the present invention is represented by the above general formula (1)
Wherein R ¹ is an alkyl group such as a methyl group, an ethyl group, a propyl group, or a butyl group, a vinyl group, an allyl group, an alkenyl group such as a butaniel group, a phenyl group, a tolyl group, or the like. A chloromethyl group, a chloropropyl group, a chloropropyl group, a 3,3,3-trifluoropropyl group, in which a part or all of hydrogen atoms bonded to carbon atoms of an aryl group or these groups are substituted with a halogen atom, a cyano group, or the like; Same or different unsubstituted or substituted monovalent hydrocarbon groups selected from cyanoethyl groups and the like, preferably having 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms.
A is a positive number between 1.90 and 2.05. It is preferable that the compound has a linear molecular structure, but there is no problem even if the molecule contains a partially branched compound. Also,
This may be one in which the molecular chain end is blocked with a triorganosilyl group or a hydroxyl group.Examples of the triorganosilyl group include a trimethylsilyl group, a dimethylvinylsilyl group, a methylphenylvinylsilyl group, a methyldiphenylsilyl group, Examples thereof include a methyldivinylsilyl group and a trivinylsilyl group. In this case, in order to further reduce the surface tack, both ends of the molecular chain are (CH ₂ = CH) ₂ RSi-,
It is desirable to use a polyfunctional group such as (CH ₂ = CH) ₃ Si- (R has the same meaning as R ¹ ). The degree of polymerization is not particularly limited, the viscosity at 25 ° C. is 300 cSt
The above are preferred.

As the conductive carbon black constituting the component (b) of the present invention, those commonly used in conductive rubber compositions can be used. For example, acetylene black, conductive furnace black (CF), superconductive 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 1500 ° C. can be used. Specific examples of acetylene black include electrified acetylene black (manufactured by Denki Kagaku) and Shaunigan acetylene black (manufactured by Shaunigan Chemical Co., Ltd.). Specific examples of conductive furnace black include Continex CF (Continental Carbon Stocks). And Vulcan C (Cabot Co., Ltd.). Specific examples of Superconductive Furnace Black include Continex SCF (Continental Carbon Co., Ltd.) and Vulcan SC (Cabot Co., Ltd.). Extra conductive furnace black. As specific examples of Asahi HS-500 (manufactured by Asahi Carbon Co., Ltd.) and Vulcan XC-72 (manufactured by Cabot Co., Ltd.), Kolux L is used as the conductive channel black.
(Made by Degussa Co., Ltd.), and Ketjen Black EC and Ketjen Black EC-600JD (Ketjen Black International Co., Ltd.), which are a kind of furnace black, can also be used. Among these, acetylene black is particularly excellent in conductivity because it has a low impurity content and has a developed secondary structure, and is particularly preferably used in the present invention. Furthermore, Ketjen Black EC and Ketjen Black EC-600J exhibit excellent conductivity even at a low filling amount due to their excellent specific surface area.
D etc. can also be used preferably. The amount of the conductive carbon black to be added is preferably 5 to 100 parts with respect to 100 parts (parts by weight, hereinafter the same) of the organopolysiloxane component.
In particular, it is preferably 10 to 70 parts. If the amount is less than 5 parts, the desired conductivity may not be obtained.
If the amount exceeds 00 parts, the cured product may have poor mechanical strength in some cases.

[0011] The component (c) of the composition of the present invention includes 1
Alkyl peresters having a half-life temperature of 110-150 ° C per minute are used. This alkyl perester, when foaming and curing the conductive silicone rubber composition of the present invention, partially cross-links the rubber and reliably captures gas generated from the organic foaming agent, thereby forming a sponge of fine cells. It is a necessary component to obtain. (C) The decomposition temperature of the component is 1
The half-life temperature per minute must be 110-150 ° C,
If the temperature is lower than 110 ° C, handling at room temperature is dangerous. If the temperature is higher than 150 ° C, the effect of capturing the generated gas is reduced due to the balance with the decomposition temperature of the organic blowing agent. Alkyl peresters in this half-life temperature range include 2,4,4-trimethylpentylperoxy 2-ethylhexanoate, t-amylperoxy-2-ethylhexanoate, and t-butylperoxy-2-. Ethyl hexanoate, t-butyl peroxy-isobutyrate, di-t-butyl peroxy-hexahydroterephthalate and the like are exemplified. Preferred is t-butylperoxy-2-ethylhexanoate. The amount of component (c) added is 0.
It is sufficient to add from 01 to 5 parts. If the amount is less than this, the desired effect cannot be obtained, and if it is more, it is uneconomical.

As the component (d), an organic peroxide having a one-minute half-life temperature of 150 to 200 ° C. or a curing agent comprising an addition reaction catalyst and a crosslinking agent is used. The curing agent is a component necessary for reliably crosslinking the rubber when the conductive silicone rubber composition of the present invention is foamed and cured.
(D) The decomposition temperature when the organic peroxide of the component is used is as follows:
The one-minute half-life temperature must be 150 to 200 ° C. If the temperature is lower than 150 ° C, the rate of vulcanization of the rubber is high, and the rubber is hardened before sufficient foaming is performed. Can not be obtained. On the other hand, when the temperature exceeds 200 ° C., there is a problem that not only energy loss but also long-time vulcanization at a high temperature is required, and thermal deterioration of rubber occurs. Organic peroxides in this half-life temperature range include di-t-butyl peroxide, 2,5-dimethyl-2,5-di- (t-
Butylperoxy) hexane, 2,5-dimethyl-2,5-
Dialkyl peroxides such as di- (t-butylperoxy) hexene, dicumyl peroxide, 1,3-bis- (t-butylperoxy-isopropyl) -benzene, and 1,1-di (t-butylperoxy) ) Peroxyketals such as -3,3,5-trimethylcyclohexane, 1,1-di (t-butylperoxy) cyclohexane, 2,2-di (t-butylperoxy) butane, t-butylperoxy- Alkyl peresters such as 3,5,5-trimethylhexoate, t-butylperoxybenzoate,
1,6-bis (t-butylperoxycarbonyloxy)
Examples include percarbonate such as hexane. Preferred are dialkyl peroxides or peroxyketals, most preferred are dialkyl peroxides. The amount of the organic peroxide added as the component (d) may be 0.01 to 5 parts per 100 parts of the component (a). If the amount is less than this, the desired effect cannot be obtained. Economy. Further, as the curing agent of the component (d),
Instead of the organic peroxide, a catalyst comprising an addition reaction catalyst and a crosslinking agent may be used. As a curing catalyst, a platinum catalyst such as chloroplatinic acid, a platinum olefin complex, a platinum vinyl siloxane complex, platinum black, or a platinum triphenylphosphine complex is used.As a crosslinking agent, a hydrogen atom bonded to a silicon atom is used. It is preferable to use a polyorganosiloxane having an average number of more than two per molecule. In the curing agent of the component (d), the amount of the curing catalyst is from 1 to 10 in terms of the amount of platinum element with respect to the polymer of the component (a).
An amount in the range of 00 ppm is preferred. If the amount of the curing catalyst is less than 1 ppm in terms of platinum element, the curing will not proceed sufficiently, and if it exceeds 1000 ppm, no particular improvement in the curing speed can be expected. The amount of the cross-linking agent is preferably such that the number of hydrogen atoms bonded to silicon atoms in the cross-linking agent is 0.5 to 4.0 with respect to one alkenyl group in the component (a), and more preferably 1.0 to 4.0. It is an amount such that it becomes ~ 3.0 pieces. If the amount of hydrogen atoms is less than 0.5, curing of the composition will not proceed sufficiently, and the hardness of the composition after curing will be low. The physical properties and heat resistance of the composition are reduced.

As the organic foaming agent as the component (e), there can be used various ones which are usually used as foaming agents for silicone rubber sponges, such as azobisisobutyronitrile, dinitropentamethylenetetramine. , P, p'-oxybis (benzenesulfonylhydrazide), N, N'-dinitroso-N, N'-dimethylterephthalamide, azodicarbonamide and the like are used. The foaming agent is not particularly limited, but has a decomposition temperature of 100 to 300.
° C is preferred. If the decomposition temperature is lower than 100 ° C, the product lacks stability. A foaming agent having a relatively high decomposition temperature, such as azobisisobutyronitrile, may be reduced in decomposition temperature by using a decomposition aid such as urea, stearic acid, and zinc oxide. The amount of the foaming agent used is in the range of 0.5 to 30 parts based on 100 parts of the component (A). If the used amount is less than 0.5 part, a sufficiently foamed sponge cannot be obtained, and if it exceeds 30 parts, the obtained sponge becomes brittle, and the heat resistance decreases due to the remaining foaming agent and decomposition residue. .

The conductive silicone rubber composition used in the present invention may optionally contain a filler other than the above-mentioned component (b), for example, a reinforcing filler such as fumed silica or precipitated silica.
Quartz powder, which is usually compounded in a silicone rubber composition,
Fused quartz powder, diatomaceous earth, talc, calcium carbonate,
Titanium oxide, iron oxide, aluminum oxide, clay, etc. may be added. Further, a low molecular weight siloxane ester or a silanol group-containing siloxane as a dispersant, cerium oxide or the like as a heat resistance improver, a flame retardant imparting agent May be blended with a platinum compound or the like.

The conductive silicone rubber composition can be obtained by kneading the above-mentioned components (a) to (e) with a roll, kneader, Banbury mixer or the like in the same manner as a usual silicone rubber composition. The composition thus prepared may be subjected to compression molding, transfer molding, injection molding, extrusion molding, calender molding, dip molding, or the like at normal pressure or under pressure at a temperature not lower than the decomposition temperature of the organic foaming agent (130 to 400 ° C.). By heating for 20 seconds to 1 hour, it becomes a conductive silicone rubber sponge. Further, if necessary, secondary vulcanization at 150 to 250 ° C. for 1 to 24 hours makes full use of the properties of conductive carbon black. A sponge is obtained.

[0016]

According to the present invention, a conductive sponge having a fine cell structure can be easily obtained by hot air vulcanization, and the conductive silicone rubber sponge can be used as a conductive sponge roll for office equipment or a sponge gasket for an electromagnetic wave shielding material. It is effective for such as.

[0017]

Next, the present invention will be described specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples. Example 1 An average degree of polymerization of 7000 and methylvinylsiloxane unit of 0.2
100 parts of dimethylvinylpolysiloxane containing 50 mol% of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) and 50 parts of t-butylperoxy-2- having a half-life temperature of 133 ° C. for 1 minute.
Ethyl hexanoate 0.5 parts, half-life temperature of 1 minute 1
0.5 parts of 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane at 81 ° C. and 5 parts of azobisisobutyronitrile as a foaming agent were added and mixed with a two-roll mill, and the mixture was sized at 10 ° C.
The resulting product was divided into cm × 10 cm × 1 cm and foamed and cured in a hot air drier at 200 ° C. for 1 hour. The foaming ratio and sponge hardness (Asker C) of this product were measured. This sponge was cut, and sponge cells per 1 cm ^{2 of} the cut surface were observed, and the number of cells having a diameter of 1 mm or more was measured. The results are shown in Table 1. Comparative Example 1 In Example 1, 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane was increased to 1.0 part without adding t-butylperoxy-2-ethylhexanoate. Except for the above, a sample was prepared and evaluated in the same manner. The results are shown in Table 1. Comparative Example 2 The same procedure as in Example 1 was repeated except that t-butylperoxy-2-ethylhexanoate and 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane were not added. Di (ter
A sample was prepared and evaluated in the same manner except that 1.0 part of (t-butylperoxy) -3,3,5-trimethylcyclosiloxane was added. The results are shown in Table 1. Comparative Example 3 In Example 1, without adding t-butylperoxy-2-ethylhexanoate and 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane,

[0018]

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A sample was prepared and evaluated in the same manner, except that 1 part of was added. The results are shown in Table 1. Comparative Example 4 In Example 1, 2,5-dimethyl-2,5-di (tert-
A sample was prepared and evaluated in the same manner except that t-butylperoxy-2-ethylhexanoate was increased to 1.0 part without adding butylperoxy) hexane. The results are shown in Table 1. Comparative Example 5 The same procedure as in Example 1 was carried out except that t-butylperoxy-2-ethylhexanoate was added and the half-life temperature for one minute was 1
A sample was prepared and evaluated in the same manner except that 0.5 part of benzoyl peroxide at 30 ° C. was added. The results are shown in Table 1. Example 2 In Example 1, 2,5-dimethyl-2,5-di (tert-
A sample was prepared and evaluated in the same manner except that 0.5 part of 1,1-di-t-butylperoxycyclohexane having a half-life temperature of 156 ° C. for 1 minute was added without adding butylperoxy) hexane. The results are shown in Table 1. Example 3 The average degree of polymerization was 7000 and methylvinylsiloxane unit was 0.13.
100 parts of dimethylvinylpolysiloxane containing mol%, 30 parts of acetylene black (manufactured by Denki Kagaku Kogyo), 5 parts of Ketjen Black EC (manufactured by Ketjen Black International), t-butyl peroxy-2-ethylhexanoate 0.7 parts, azodialbonic acid amide 5 parts as a foaming agent, 0.01 parts of a 2% platinum chloroplatinate 2-ethylhexanol solution as a platinum-based curing agent, 50 parts of a methylhydrogensiloxane unit, and 1.0 part of an organopolysiloxane having a degree of polymerization of 100 Was added and mixed with two rolls, and a sample was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1. Comparative Example 6 A sample was prepared and evaluated in the same manner as in Example 3, except that t-butylperoxy-2-ethylhexanoate was not added. The results are shown in Table 1.

[0020]

[Table 1]

Continuation of front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C08J 9/00-9/42

Claims (3)

(57) [Claims] 1. An organopolysiloxane represented by the following general formula (1): ## STR1 ## (Wherein R ¹ is the same or different unsubstituted or substituted 1
A is a positive number from 1.90 to 2.05. (B) Conductive carbon black (c) Alkyl perester with a one-minute half-life temperature of 110 to 150 ° C (d) Organic peroxide with a one-minute half-life temperature of 150 to 200 ° C, or for addition reaction A conductive silicone rubber composition comprising a curing agent comprising a catalyst and a crosslinking agent (e) an organic foaming agent. 2. The conductive silicone rubber composition according to claim 1, wherein the alkyl perester is t-butylperoxy-2-ethylhexanoate. 3. A method for producing a conductive silicone rubber sponge, wherein the conductive silicone rubber composition according to claim 1 or 2 is heated to a temperature not lower than the decomposition temperature of the organic foaming agent and foamed and cured.