Silicone rubber curing, and silicone rubber compositions therefor

Abstract: A silicone rubber composition comprising (A) an organopolysiloxane, (B) an organic peroxide and (C) carbon black cures under anaerobic conditions into silicone rubber. A composition further comprising (D) an organopolysiloxane copolymer consisting essentially of R¹₃SiO 1/2 (M) and SiO₂ (Q) units in a molar M/Q ratio of 6/10 to 9/10 forms an anaerobic adhesive composition which is a useful sealant.

Description: This invention relates to silicone rubber compositions and the curing thereof. In particular, it relates to silicone rubber compositions which can cure under anaerobic conditions. Particular embodiments relate to anaerobic cure at room temperature into silicone rubber suitable for bonding or sealing e.g. of parts such as screws, bolts, joints and flanges. Recently silicone rubber has found a spreading use in a new mode of application where molded silicone rubber is bonded to various substrates. As compared with synthetic rubber building gaskets, silicone rubber gaskets are improved in weatherability and flame retardancy and have low compression set, meeting the requirements as waterproof seals for buildings which require long-lasting reliability. Therefore, silicone rubber gaskets now encounter a rapidly increasing demand as waterproof seals in the building industry. These silicone rubber gaskets are used as waterproof seals by attaching them to metal curtain walls, concrete curtain walls, aluminum sashes, aerated lightweight concrete (ALC) panels and other members used as building exterior walls. The silicone rubber gaskets are bonded to exterior walls, typically using silicone sealants as adhesives. The silicone sealants, however, are adhesive compositions which cure in the presence of moisture and thus require a substantial time until curing is complete. For instance, where silicone gaskets are attached to exterior walls with silicone sealants, the assembly must be allowed to stand for at least one day before a firm bond can be established between the silicone gaskets and the exterior walls. This means that exterior wall panels cannot be conveyed immediately after their manufacture, leading to low factory production and assembly efficiency. Also, silicone rubber is used by applying it to screws, bolts, joints and flanges for fixedly securing or sealing them. For such use, a composition comprising a compound having at least one acryloyl or methacryloyl radical in a molecule and an anaerobic initiator is known from Japanese Patent Application Kokai (JP-A) No. 287115/1989. This composition, however, has the drawbacks of increased resin hardness, brittleness and slow curing due to the use of a compound having an acryloyl or methacryloyl radical. The aim herein is to provide novel anaerobically-curable silicone rubber compositions, and methods of making silicone rubber by anaerobically curing such compositions. In a first aspect we provide a method for producing a silicone rubber by curing, under anaerobic conditions, a silicone rubber composition comprising (A) organopolysiloxane of the general formula: R 1 a SiO (4 -a)/2 wherein groups R 1 are independently selected from substituted and unsubstituted monovalent hydrocarbon radicals, and a is a number in the range from 1.90 to 2.05; (B) organic peroxide of the general formula: wherein X is a radical of the formula: -(C 2 H 4 O) m -C 2 H 4 - where m is an integer of 1 to 4, R 2 and R 3 are selected from monovalent hydrocarbon radicals having from 3 to 10 carbon atoms, and radicals of the formula: -SiR 4 3 where R 4 is an alkyl or aryl radical, and (C) carbon black. In the second aspect we provide a method for producing a silicone rubber by curing, under anaerobic conditions, a silicone rubber composition comprising (A) organopolysiloxane of the general formula R 1 a SiO (4 -a)/2 wherein groups R 1 are independently selected from substituted and unsubstituted monovalent hydrocarbon radicals, and a is a number in the range from 1.90 to 2.05; (B) organic peroxide of the general formula (2): wherein X is a radical selected from the following formulae -(CH 2 ) n - -(C 2 H 4 O) m -C 2 H 4 - wherein n is an integer of 2 to 8 and m is an integer of 1 to 4, R 2 and R 3 are selected from monovalent hydrocarbon radicals having from 3 to 10 carbon atoms, and radicals of the formula: -SiR 4 3 wherein R 4 is an alkyl or aryl radical; (C) carbon black, and (D) organopolysiloxane copolymer consisting essentially of R 1 3 SiO 1/2 units (M units) and SiO 2 units (Q units), R 1 being as defined for (A) above and the molar ratio M/Q being in the range from 0.6 to 0.9. In a third aspect we provide an anaerobically-curable silicone rubber composition comprising (A) organopolysiloxane of the general formula: R 1 a SiO (4 -a)/2 wherein groups R 1 are independently selected from substituted and unsubstituted monovalent hydrocarbon radicals, and a is a number in the range from 1.90 to 2.05; (B) organic peroxide of the general formula: wherein X is a radical of the formula: -(C 2 H 4 O) m -C 2 H 4 - where m is an integer of 1 to 4, R 2 and R 3 are selected from monovalent hydrocarbon radicals having from 3 to 10 carbon atoms, and radicals of the formula: -SiR 4 3 where R 4 is an alkyl or aryl radical, and (C) carbon black. In a fourth aspect we provide an anaerobically-curable silicone rubber composition comprising (A) organopolysiloxane of the general formula R 1 a SiO (4 -a)/2 wherein groups R 1 are independently selected from substituted and unsubstituted monovalent hydrocarbon radicals, and a is a number in the range from 1.90 to 2.05; (B) organic peroxide of the general formula (2): wherein X is a radical selected from the following formulae -(CH 2 ) n - -(C 2 H 4 O) m -C 2 H 4 - wherein n is an integer of 2 to 8 and m is an integer of 1 to 4, R 2 and R 3 are selected from monovalent hydrocarbon radicals having from 3 to 10 carbon atoms, and radicals of the formula: -SiR 4 3 wherein R 4 is an alkyl or aryl radical; (C) carbon black, and (D) organopolysiloxane copolymer consisting essentially of R 1 3 SiO 1/2 units (M units) and SiO 2 units (Q units), R 1 being as defined for (A) above and the molar ratio M/Q being in the range from 0.6 to 0.9. In general, silicone rubber vulcanization techniques involve vulcanization with organic peroxides and vulcanization utilizing platinum catalyzed addition reaction and thus mostly require heat curing during molding. In this regard, we previously proposed the organic peroxides of formula (2) as defined above for use in hot atmospheric vulcanization in JP-A 130663/1988, US-A-5,051,465. Through continuing research we have found that surprisingly a silicone rubber composition containing this organic peroxide and carbon black exhibits an unexpected anaerobic curing phenomenon, that is, can quickly cure under anaerobic conditions even at room temperature. We have first succeeded in providing a silicone rubber composition with anaerobic curing ability in a manner completely distinct from the prior art. The anaerobically cured silicone rubber has physical properties comparable to heat cured ones. Possible curing in a sealed enclosure or under air shielded conditions eliminates a need for heat source. Eliminated use of press machines or vulcanisation towers for providing high temperature results with a substantial reduction of installation cost. Our EP-A-493112, filed before but published after the filing of the present disclosure, describes silicone rubber compositions comprising organopolysiloxane (A) as proposed above, organic peroxide of the formula (2) with formula Options (3) and (4) for the divalent radical X, and conductive carbon black. The composition is cured by hot air vulcanisation. Our EP-A-524026, filed before but published after the filing of the present disclosure, also disclosed conductive silicone rubber compositions comprising organopolysiloxane (A) as disclosed above, organic peroxides of the formula (2) as described above with the formula options (3) and (4) for the divalent radical X, and conductive carbon black. The compositions are proposed for curing by hot air vulcanisation, although a shelf stability test involving gradual cure under covered conditions is described. When the silicone rubber composition further includes the organopolysiloxane copolymer (D) it cures quickly under anaerobic conditions and exhibits good adhesion at an initial curing stage, and is a very useful anaerobic silicone adhesive. DETAILED DESCRIPTION Component (A) of the anaerobic silicone rubber composition is an organopolysiloxane of the following formula (1). R 1 / aSiO (4-a)/2 In formula (1), R 1 is independently selected from substituted or unsubstituted monovalent hydrocarbon radicals, preferably having 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, for example, alkyl radicals such as methyl, ethyl, propyl, and butyl, alkenyl radicals such as vinyl, allyl, and butenyl, aryl radicals such as phenyl and tolyl, and substituted ones of the foregoing radicals in which some or all of the hydrogen atoms attached to the carbon atoms of the radicals are replaced by halogen atoms, cyano and other groups, for example, chloromethyl, chloropropyl, 3,3,3-trifluoropropyl, and 2-cyanoethyl radicals. The radicals represented by R 1 may be the same or different. Letter a is a positive number having a value of from 1.90 to 2.05. The organopolysiloxane preferably has a straight-chain molecular structure although partial inclusion of branched-chain structure in the molecule is acceptable. It is desired that the organopolysiloxane be end-blocked with a triorganosilyl or hydroxyl radical. Examples of the triorganosilyl radical include trimethylsilyl, dimethylvinylsilyl, methylphenylvinylsilyl, methyldiphenylsilyl, methyldivinylsilyl, and trivinylsilyl radicals. The organopolysiloxane is not limited in degree of polymerization although it preferably has a degree of polymerization such that its viscosity is at least 3 x 10 -4 m 2 s -1 (300 centistokes) at 25°C. For better curing properties, the organopolysiloxane may contain 0 to 10 mol%, especially 0.05 to 5 mol% of an alkenyl radical based on the total moles of R 1 radicals. In order that the silicone rubber composition function as an anaerobic adhesive, each organopolysiloxane molecule should preferably contain 0.0001 to 0.5 mol% of an alkenyl radical based on the total moles of R 1 radicals. Also the organopolysiloxane preferably has a degree of polymerization of at least 3,000 because initial adhesion would be sometimes low with a degree of polymerization of less than 3,000. Component (B) is an organic peroxide of the general formula (2). In formula (2), X is a radical selected from the following formulae (3), (4) and (5): -(CH 2 ) n - -(C 2 H 4 O) m -C 2 H 4 - wherein n is an integer of 2 to 8 and m is an integer of 1 to 4. R 2 and R 3 , which may be identical or different, are independently selected from monovalent hydrocarbon radicals having 3 to 10 carbon atoms, for example, n-propyl, isopropyl, t-butyl, n-butyl, n-amyl, t-amyl, hexyl, heptyl, octyl, 2-ethylpropyl, 2-ethylbutyl, 2-ethylhexyl, cumyl or the like. Alternatively, R 2 and R 3 are independently selected from radicals of the following formula (6): -SiR 4 / 3 wherein R 4 is an alkyl radical having 1 to 8 carbon atoms such as methyl and ethyl or an aryl radical having 6 to 10 carbon atoms such as phenyl. Component (B), the organic peroxide, serves as a vulcanizing agent and is preferably used in amounts of 0.1 to 5 parts, especially 0.5 to 3 parts, by weight per 100 parts by weight of organopolysiloxane component (A), or 100 parts by weight of components (A) and (D) combined if (D) is blended. Less than 0.1 parts on this basis of organic peroxide is usually too little to provide for vulcanization, failing to obtain desired or practically acceptable properties. More than 5 parts of organic peroxide tends to leave excess decomposition residue which is deleterious to the cured silicone rubber, and invites a superfluous cost increase. Component (C) is carbon black which is blended for the purpose of improving the curing properties of and/or imparting electrical conductivity to the anaerobic silicone rubber composition. Any carbon black species commonly used in conventional rubber compositions may be used. Examples include acetylene black, conducting furnace black (CF), super conducting furnace black (SCF), extra conducting furnace black (XCF), conducting channel black (CC), and furnace black and channel black heat treated at elevated temperatures of about 1500°C. More particularly, acetylene blacks include Denka Acetylene Black manufactured by Denki Kagaku K.K. and Shawinigan Acetylene Black manufactured by Shawinigan Chemical Co., conducting furnace blacks include Continex® CF manufactured by Continental Carbon Co. and Vulcan® C manufactured by Cabot Corp., super conducting furnace blacks include Continex® SCF manufactured by Continental Carbon Co. and Vulcan® SC manufactured by Cabot Corp., the extra conducting furnace blacks include Asahi HS-500 manufactured by Asahi Carbon K.K. and Vulcan® XC-72 manufactured by Cabot Corp., and the conducting channel blacks include Corax® L manufactured by Degussa Co. Also useful are modified furnace blacks commercially available as Ketjen® Black EC and Ketjen® Black EC-600JD from Ketjen Black International. Carbon black is selected from conductive carbon black species where conductivity is required. For improved curing, furnace black, Ketjen Black, channel black and acetylene black are preferred although others may be used. The amount of carbon black added is not critical although it is preferably added in amounts of 0.1 to 100 parts, more preferably 1 to 70 parts by weight per 100 parts by weight of component (A) or 100 parts by weight of components (A) and (D) combined if (D) is blended. Less than 0.1 parts on this basis of carbon black would be too small to provide for anaerobic curing, failing to obtain desirable cured properties whereas more than 100 parts of carbon black would adversely affect mechanical strength. Where the silicone rubber composition of the invention is to be used as an anaerobic adhesive, desirably it contains the additional component (D) in the form of an organopolysiloxane copolymer, in addition to components (A) to (C). The organopolysiloxane copolymer consists essentially of R 1 / 3SiO 1/2 units referred to as M units and SiO 2 units referred to as Q units. R 1 is as defined above. For the organopolysiloxane copolymer to perform, it is important that the molar ratio of M/Q range from 0.6 to 0.9. Inclusion of more M units beyond this range results in losses of initial adhesion and other properties. Shortage of M units below the range makes it difficult to produce a copolymer in a consistent manner. The organopolysiloxane copolymer (D) may contain up to 50 mol% of units other than M and Q units, for example, R 1 SiO 3/2 and R 1 / 2SiO 2/2 units wherein R 1 is as defined above insofar as the benefit of the composition (that it exhibits high adhesion from an early stage of curing) is not lost. The organopolysiloxane copolymer may be readily prepared by a per se known method, for example, by blending R 1 / 3SiCl and SiCl 4 in amounts such that the molar ratio of M/Q units falls within the above-defined range, followed by co-hydrolysis condensation. Preferably, component (D) is blended with component (A) such that the weight ratio (A)/(D) may range from 30/70 to 70/30, especially from 40/60 to 60/40. If the amount of component (D) is outside the range, there may occur some defects like a loss of initial adhesion. If desired, the silicone rubber composition may contain dispersant, such as low molecular weight siloxane having a degree of polymerization of up to 100, silanol group-containing silane and alkoxy group-containing silanes, heat resistance modifier such as iron oxide, cerium oxide and iron octylate, and pigments. Further, fillers may be blended for reinforcement or extending purposes. Any of well-known fillers may be used, for example, finely divided silica, fumed silica, precipitated silica, diatomaceous earth, metal oxides such as iron oxide, zinc oxide and titanium oxide, which may be surface treated with silanes to have hydrophobic properties, metal carbonates such as calcium carbonate, magnesium carbonate and zinc carbonate, asbestos, glass fibers, powder mica, and fused silica powder. Also optionally included in the composition are thixotropic agents such as polyethylene glycol and derivatives thereof, pigments, dyes, anti-oxidants, antistatic agents, flame retardants such as antimony oxide and chlorinated paraffin, and heat transfer modifiers such as boron nitride and aluminium oxide. There may also be blended tackifiers such as organic silicon compounds having reactive organic radicals such as amino, epoxy and mercapto radicals, and silane coupling agents. Other additives which can be blended herein include plasticizers, anti-sagging agents, anti-staining agents, preservatives, bactericidal agents and fungicidal agents. The silicone rubber composition may be obtained by uniformly blending the components, that is, components (A), (B) and (C) and optional components including component (D). The order of blending these components is not critical although the composition is generally prepared by first blending component (A) or organopolysiloxane with the carbon black and then blending the mixture with the organic peroxide component (B) e.g. by kneading in a Banbury mixer or roll mill. The silicone rubber composition is cured into silicone rubber under anaerobic conditions, for example, in closed conditions or in the absence of air or oxygen. For example, a silicone rubber sheet may be manufactured by interposing the composition between a pair of plastic or metallic plates, and allowing the assembly to stand in air-shielded conditions while pressing the composition therebetween at room temperature. Then the composition will fully cure at room temperature within 1 to 3 days, resulting in a cured sheet having physical properties comparable to those of a heat cured sheet. Alternatively, the composition may be cured by filling narrow spaces such as grooves, holes and gaps with the composition and allowing the fill to stand thereat or by placing the composition within a mold cavity in a sealed manner. It is to be noted that since the silicone rubber composition is of anaerobic curing type, those surface portions thereof in contact with air would be vulcanized to a lesser extent. In this event, if desired, the surface can be fully vulcanized by combining heat vulcanization using hot air. Voluminous moldings such as industrial rolls may be manufactured by wrapping the composition around a mandrel, covering the composition surface with plastic film and allowing the composition to cure at room temperature. Also in this case, heat vulcanization may be additionally effected on the surface side. Since the anaerobic silicone rubber composition cures under anaerobic conditions to silicone rubber having good physical properties, silicone rubber curing methods as described herein are particularly adapted in applying the composition to joints, fittings and flanges of screws, bolts and similar members for adhesion and bonding. The method is also suitable in using the composition as gap sealants, building gaskets, EMI shielding agents or the like. In the embodiment wherein the composition has component (D) blended and serves as an anaerobic adhesive, the composition which readily cures at room temperature under anaerobic conditions is applied to any desired substrate or support such as a building wall. A part to be attached, typically a silicone gasket, is placed on the coated substrate under pressure. Then the composition cures between the substrate and the gasket while exhibiting good adhesion from an early stage of curing. In applying the adhesive to the substrate, the adhesive may be diluted with suitable solvent , for example, hydrocarbon solvents such as toluene, xylene and petroleum ether, and ketone and ester solvents. EXAMPLE Examples of the present invention are given below together with comparative examples by way of illustration and not by way of limitation. All parts are by weight. Me is methyl and Vi is vinyl. EXAMPLE 1 A silicone rubber composition was prepared by kneading 100 parts of an organopolysiloxane consisting of 98.975 mol% of dimethylsiloxane units and 1.0 mol% of methylvinylsiloxane units, blocked with 0.025 mol% of a dimethylvinylsilyl group at each end and having a viscosity of 10 m 2 s -1 (1 x 10 7 cSt) and 45 parts of acetylene black in a pressure kneader, and adding the following peroxide B to the base compound in the amounts shown in Table 1. Peroxide B Next, the silicone rubber composition was sheeted to a thickness of 2 mm through a twin roll mill. The sheet was sandwiched between a pair of PET film covers to shield it from air and allowed to stand at room temperature. With the lapse of time, the sheet was measured at intervals for hardness, tensile strength (TS) and elongation in accordance with JIS K-6301. The results are shown in Table 1. Example 1 Peroxide B (pbw) 0.75 Vulcanizing conditions PET covered, room temperature 1 day Hardness (JIS-A) 51 TS (kgf/cm 2 ) 40 Elongation (%) 320 3 days Hardness (JIS-A) 70 TS (kgf/cm 2 ) 67 Elongation (%) 230 7 days Hardness (JIS-A) 72 TS (kgf/cm 2 ) 67 Elongation (%) 190 As seen from Table 1, an anaerobic silicone rubber composition loaded with peroxide B which is moulded into sheet form begins to cure quickly when its surface is covered with film covers, and has fully cured within about 3 days into a silicone rubber sheet. The sheet's physical properties are comparable to those of a heat-cured sample. Example 2 & Comparative Examples 1,2 In 50 parts of toluene was dissolved 100 parts of an organopolysiloxane consisting of 98.975 mol% of dimethylsiloxane units and 1.0 mol% of methylvinylsiloxane units, blocked with 0.025 mol% of a dimethylvinylsilyl group at each end and having a viscosity of 10 m 2 s -1 (1 × 10 7 cs) at 25°C. To this solution was added 150 parts of a silicone resin I solution which was separately prepared by dissolving a silicone copolymer consisting of Me 2 SiO 1/2 units (M units) and SiO 2 units (Q units) in a molar ratio M/Q of 0.75 and having a viscosity of 0.85 Pa.s (850 centipoise) at 25°C in toluene and a non-volatile content of 70.5% by weight. The mixture was heated at 150°C for 2 hours, obtaining a liquid composition (I) having a viscosity of 3 x 10 -3 m 2 s -1 (3,000 cs) at 25°C and a non-volatile content of 68.7% by weight. To 100 parts of liquid composition (I) was added 2 parts of acetylene black (Denki Kagaku K.K.). The mixture was uniformly milled in a three roll mill. An adhesive composition was prepared by adding 1 part of glycidoxypropyltrimethoxysilane and 1 part of peroxide A, the result being Example 2. Peroxide A For comparison purposes, an adhesive composition was similarly prepared except that peroxide A was omitted (Comparative Example 1). Each of the adhesive compositions was coated onto an aluminium panel to a thickness of 0.5 mm and aged at room temperature for 15 minutes. Then a silicone rubber sheet 2 mm thick, moulded and vulcanized in situ, was compression bonded to the coated panel under a pressure of about 1 kgf/cm 2 . The test piece was measured at intervals for the bonding force between the aluminium panel and the silicone rubber sheet. The results are shown in Table 2. For comparison purposes, a test piece was prepared using Silicone Sealant 45 which was a silicone adhesive commercially available from Shin-Etsu Chemical Co., Ltd. (Comparative Example 2). The results for this test piece are also shown in Table 2. Bonding force (kgf/cm 2 ) Example Comparative Example 2 1 2 30 minutes 1.5 1.5 0.1 10 hours 1.6 1.5 0.3 15 hours 1.8 1.5 1.0 24 hours 2.0 1.6 1.8 48 hours 2.3 1.6 3.0 72 hours 3.0 1.6 3.5 Example 3 & Comparative Example 3 A liquid composition ( ) was prepared in the same manner as in Example 2 except that the silicone resin solution was replaced by a silicone resin solution which was prepared by dissolving a silicone copolymer consisting of ViMe 2 SiO 1/2 units (M units) and SiO 2 units (Q units) in a molar ratio M/Q of 0.75 and having a viscosity of 0.85 Pa.s (850 centipoise) at 25°C in toluene and a non-volatile content of 69.5% by weight. Liquid composition ( ) had a viscosity of 3 x 10 -3 m 2 s -1 (3,000 cs) at 25°C and a non-volatile content of 68.7% by weight. As in Example 2, an adhesive composition was prepared using liquid composition ( ) and a test piece was assembled using the adhesive, to determine the change of bonding force with time. For comparison purposes, an adhesive composition was similarly prepared except that peroxide A was omitted (Comparative Example 3). Using the adhesive, a test piece was similarly assembled for determining a change of bonding force with time. The results are shown in Table 3. Bonding force (kgf/cm 2 ) Example 3 Comparative Example 3 30 minutes 1.5 1.5 10 hours 1.7 1.5 15 hours 1.9 1.5 24 hours 2.0 1.6 48 hours 3.0 1.6 72 hours 5.0 1.6 Example 4 To 100 parts of liquid composition ( ) used in Example 2 was added 2 parts of acetylene black (Denki Kagaku K.K.). The mixture was uniformly milled in a three roll mill. An adhesive composition was prepared by adding 1 part of glycidoxypropyltrimethoxysilane and 1 part of peroxide B (as used in Example 1) to the mixture. The adhesive composition was coated onto an aluminium panel to a thickness of 0.5 mm and aged at room temperature for 15 minutes. Then a silicone rubber sheet 2 mm thick, moulded and vulcanized in situ, was compression-bonded to the coated panel under a pressure of about 1 kgf/cm 2 . The test piece was measured at intervals for the bonding force between the aluminium panel and the silicone rubber sheet. The results are shown in Table 4. Bonding force (kgf/cm 2 ) Example 4 30 minutes 1.6 10 hours 1.8 15 hours 1.9 24 hours 2.1 48 hours 2.4 72 hours 3.3 There has been described a silicone rubber curing method which uses an anaerobic silicone rubber composition comprising components (A), (B) and (C) and having anaerobic curing capability in that it can cure at room temperature in closed conditions or in the absence of air or oxygen whereby the composition cures into silicone rubber having physical properties comparable to those of conventional heat cured silicone rubber. The application of silicone rubber is thus expanded to screw attachment, joint bonding and sealing. An anaerobic adhesive composition having additional component (D) blended can quickly cure under anaerobic conditions while exhibiting good adhesion from an early stage of curing. The composition is thus a very useful silicone sealant which may be used in bonding silicone gaskets for providing waterproof seals. It provides for efficient manufacture of waterproof sealed wall panels, for example.

Claims: A method for producing a silicone rubber by curing, under anaerobic conditions, a silicone rubber composition comprising (A) organopolysiloxane of the general formula: R 1 a SiO (4 -a)/2 wherein groups R 1 are independently selected from substituted and unsubstituted monovalent hydrocarbon radicals, and a is a number in the range from 1.90 to 2.05; (B) organic peroxide of the general formula: wherein X is a radical of the formula: -(C 2 H 4 O) m -C 2 H 4 - where m is an integer of 1 to 4, R 2 and R 3 are selected from monovalent hydrocarbon radicals having from 3 to 10 carbon atoms, and radicals of the formula: -SiR 4 3 where R 4 is an alkyl or aryl radical, and (C) carbon black. A method according to claim 1 in which the organic peroxide (B) is used in an amount of from 0.1 to 5 parts by weight per 100 parts by weight of the organopolysiloxane (A). A method according to claim 1 or claim 2 in which the carbon black (C) is used in an amount of from 1 to 70 parts by weight per 100 parts by weight of the organopolysiloxane (A). A method for producing a silicone rubber by curing, under anaerobic conditions, a silicone rubber composition comprising (A) organopolysiloxane of the general formula R 1 a SiO (4 -a)/2 wherein groups R 1 are independently selected from substituted and unsubstituted monovalent hydrocarbon radicals, and a is a number in the range from 1.90 to 2.05; (B) organic peroxide of the general formula (2): wherein X is a radical selected from the following formulae -(CH 2 ) n - -(C 2 H 4 O) m -C 2 H 4 - wherein n is an integer of 2 to 8 and m is an integer of 1 to 4, R 2 and R 3 are selected from monovalent hydrocarbon radicals having from 3 to 10 carbon atoms, and radicals of the formula: -SiR 4 3 wherein R 4 is an alkyl or aryl radical; (C) carbon black, and (D) organopolysiloxane copolymer consisting essentially of R 1 3 SiO 1/2 units (M units) and SiO 2 units (Q units), R 1 being as defined for (A) above and the molar ratio M/Q being in the range from 0.6 to 0.9. A method according to claim 4 in which the organic peroxide (B) is used in an amount of from 0.1 to 5 parts by weight per 100 parts by weight of the organopolysiloxanes (A) and (D) combined. A method according to claim 4 or claim 5 in which the carbon black (C) is included in an amount of from 1 to 70 parts by weight per 100 parts by weight of the organopolysiloxanes (A) and (D) combined. A method according to any one of claims 4 to 6 in which the organopolysiloxane (D) is blended with the organopolysiloxane (A) such that the weight ratio (A)/(D) is in the range from 30/70 to 70/30. A method according to any one of the preceding claims in which from 0.0001 to 0.5 mol % of the groups R 1 in the organopolysiloxane (A) are alkenyl radicals. A method according to any one of the preceding claims in which the organopolysiloxane (A) has a degree of polymerisation of at least 3000. An anaerobically-curable silicone rubber composition comprising (A) organopolysiloxane of the general formula: R 1 a SiO (4 -a)/2 wherein groups R 1 are independently selected from substituted and unsubstituted monovalent hydrocarbon radicals, and a is a number in the range from 1.90 to 2.05; (B) organic peroxide of the general formula: wherein X is a radical of the formula: -(C 2 H 4 O) m -C 2 H 4 - where m is an integer of 1 to 4, R 2 and R 3 are selected from monovalent hydrocarbon radicals having from 3 to 10 carbon atoms, and radicals of the formula: -SiR 4 3 where R 4 is an alkyl or aryl radical, and (C) carbon black. A composition according to claim 10 in which the organic peroxide (B) is present in an amount of from 0.1 to 5 parts by weight per 100 parts by weight of the organopolysiloxane (A). A composition according to claim 10 or claim 11 in which the carbon black (C) is used in an amount of from 1 to 70 parts by weight per 100 parts by weight of the organopolysiloxane (A). An anaerobically-curable silicone rubber composition comprising (A) organopolysiloxane of the general formula R 1 a SiO (4 -a)/2 wherein groups R 1 are independently selected from substituted and unsubstituted monovalent hydrocarbon radicals, and a is a number in the range from 1.90 to 2.05; (B) organic peroxide of the general formula (2): wherein X is a radical selected from the following formulae -(CH 2 ) n - -(C 2 H 4 O) m -C 2 H 4 - wherein n is an integer of 2 to 8 and m is an integer of 1 to 4, R 2 and R 3 are selected from monovalent hydrocarbon radicals having from 3 to 10 carbon atoms, and radicals of the formula: -SiR 4 3 wherein R 4 is an alkyl or aryl radical; (C) carbon black, and (D) organopolysiloxane copolymer consisting essentially of R 1 3 SiO 1/2 units (M units) and SiO 2 units (Q units), R 1 being as defined for (A) above and the molar ratio M/Q being in the range from 0.6 to 0.9. A composition according to claim 13 in which the organic peroxide (B) is used in an amount of from 0.1 to 5 parts by weight per 100 parts by weight of the organopolysiloxanes (A) and (D) combined. A composition according to claim 13 or claim 14 in which the carbon black (C) is included in an amount of from 1 to 70 parts by weight per 100 parts by weight of the organopolysiloxanes (A) and (D) combined. A composition according to any one of claims 13 to 15 in which the organopolysiloxane (D) is blended with the organopolysiloxane (A) such that the weight ratio (A)/(D) is in the range from 30/70 to 70/30. A composition according to any one of claims 10 to 16 in which from 0.0001 to 0.5 mol % of the groups R 1 in the organopolysiloxane (A) are alkenyl radicals. A composition according to any one of claims 10 to 17 in which the organopolysiloxane (A) has a degree of polymerisation of at least 3000.

Inventors: INOUE YOSHIO, TAKAHASHI MASAHARU, TSUCHIDA TOMIYOSHI, INOUE, YOSHIO, TAKAHASHI, MASAHARU, TSUCHIDA, TOMIYOSHI
Applicants: SHINETSU CHEMICAL CO, SHIN-ETSU CHEMICAL CO., LTD.
Application year: 1993
Main classification: B29C35
IPC codes: C08K3, C08L83, C08K5