Semiconductive rubber foam

Abstract: A semiconductive rubber foam having a volume resistivity that can be controlled to a practical level and retaining an initial softness even after the lapse of time, is obtained by foaming and curing a rubber composition comprising 100 parts by weight of a chlorinated ethylene/α-olefin copolymer rubber and 10 to 50 parts by weight of carbon black. The volume resistivity of this semiconductive rubber foam is in the range of from 10⁵ to 10¹¹ Ω-cm.

Description: The present invention relates to a semiconductive rubber foam. More particularly, the present invention relates to a semiconductive rubber foam in the form of a moulded body which has excellent heat aging resistance and ozone resistance and which retains the initial softness even over time without breakdown by ozone deterioration. The electrophotographic printing process is generally adopted in, for example, a copying machine or a laser printer. Since electric charging is utilized for the mechanism in these machines, electric characteristics are often limited even in a delivery roll. A chloroprene rubber has heretofore been used for such rolls. However, a chloroprene foamed body is defective in that thermal deterioration is caused at the atmospheric temperature used or deterioration is caused by ozone present in the atmosphere used, the foamed body becomes rigid over time and the paper-feeding performance is degraded. Accordingly, use of a foamed rubber roll prepared from an ethylene/propylene rubber EPDM has been tried. However, in this case, it is difficult to control the volume resistivity though the initial softness can be retained even over time. It has been found that this foamed rubber roll, therefore, cannot be put into practical use. It is therefore a primary object of the present invention to overcome the foregoing disadvantages and provide a semiconductive rubber foam in which the volume resistivity can be practically controlled and the initial softness can be retained even over time. JP-A-57/155,240 discloses a process for producing a chlorinated polyethylene foamed body which comprises heating a composition comprising chlorinated polyethylene, carbon black, a foaming agent and a vulcanizing agent or an organic peroxide. The chlorinated polyethylene may contain at most 10% by weight of an α-olefin. The present invention therefore provides a rubber foam having a volume resistivity of 10 5 to 10 11 Ω-cm in the form of a moulded body obtainable by moulding a rubber composition comprising: 100 parts by weight of a chlorinated ethylene/1-butene copolymer rubber (A) having a chlorine content of 20 to 40% by weight, a Mooney viscosity [ML 1+4 (121 °C)] of 30 to 120 and a molar ratio of ethylene units to 1-butene units, before chlorination, of from 50:50 to 90:10; and 15 to 45 parts by weight of carbon black (B), a curing agent and a foaming agent. The present invention also provides a process for producing a rubber foam moulded body having a volume resistivity of 10 5 to 10 11 Ω-cm comprising foaming, moulding and curing a rubber composition comprising 100 parts by weight of a chlorinated ethylene/1-butene copolymer rubber, having a chlorine content of 20 to 40% by weight, a Mooney viscosity [ML 1+4 (121°C)] of 30 to 120 and a molar ratio of ethylene units to 1-butene units, before chlorination, of from 50:50 to 90:10, and 15 to 45 parts of carbon black. The chlorinated ethylene/1-butene copolymer rubber can be obtained by chlorinating an ethylene/1-butene copolymer rubber. The ethylene 1-butene copolymer rubber can further comprise another polymerizable component, and it is especially preferred that up to 30 millimoles of 5-vinyl-2-norbornene be further copolymerized per 100 g of the whole ethylene/1-butene units. The ethylene/1-butene copolymer rubber is a rubbery polymer obtained by random polymerization of the foregoing components. The chlorination of the copolymer rubber is accomplished, for example, by a process in which the copolymer rubber is pulverized, the fine particles are formed into an aqueous suspension and the aqueous suspension is contacted with molecular chlorine at 70 to 90°C, a process in which the copolymer rubber is dissolved in a solvent stable against chlorine, such as carbon tetrachloride or tetrachloroethylene, and the resulting homogeneous solution is contacted with molecular chlorine, and a process in which a chlorine compound such as N-chloroacetamide, N-dichlorosuccinimide or 1,3-dichloro-5,5-dimethylhydatoin is uniformly kneaded into the copolymer rubber by a roll or Banbury mixer and the kneaded mixture is heated to a temperature causing release of chlorine. A process comprising blowing chlorine in a halogenated solvent such as carbon tetrachloride in the presence of a radical initiator is especially preferably adopted. The following post treatments are conducted after the chlorination reaction. In the case where the chlorination is conducted in the state of an aqueous suspension, the chlorinated ethylene/1-butene copolymer rubber is washed with water to remove molecular chlorine and hydrogen chloride formed as a by-product, and then, the copolymer rubber is dried. In the case where the chlorination is conducted in solution, the reaction liquid is thrown into an excess amount of a poor solvent for the chlorinated ethylene/1-butene copolymer rubber, such as methanol, the precipitate is recovered by filtration and the recovered precipitate is washed with the above solvent and dried. The chlorine content of the chlorinated ethylene/1-butene copolymer rubber used in the present invention is 20 to 40% by weight, preferably 25 to 35% by weight, and the chlorination is carried out so that the chlorine content is within this range. From the viewpoint of the moldability and operation adaptability, the Mooney viscosity [ML 1+4 (121°C)] of the copolymer rubber is 30 to 120. In order to obtain desired electric characteristic values in the present invention, it is indispensable that carbon black (B) should be incorporated in an amount of 15 to 45 parts by weight per 100 parts by weight of the chlorinated ethylene/1-butene copolymer rubber (A). If the amount of carbon black (B) is smaller than 10% by weight based on the copolymer rubber (A), the electroconductivity is reduced and the volume resistivity is increased, and it is difficult to obtain a desired volume resistivity. If the amount of carbon black (B) is larger than 50% by weight based on the copolymer rubber (A), the electroconductivity is increased and the volume resistivity is reduced, and it is difficult to obtain a desired volume resistivity. As the carbon black used in the present invention, there can be mentioned channel black such as EPC or MPC, furnace black such as SRF or FEF, thermal black such as FT or MT, and acetylene black. These carbon blacks can be appropriately selected and used. In the foam of the present invention, in addition to the chlorinated ethylene/1-butene copolymer rubber (A) and carbon black (B) as the indispensable components, known additives such as a curing agent, a curing assistant, a foaming agent, a foaming assistant, a rubber filler, a softener, a metal activating agent, a compound having an oxyethylene structure, a scorch-preventing agent an aging-preventing agent and a processing assistant can be incorporated according to the processability and required performances. In the foam of the present invention, a rubber other than the chlorinated ethylene/1-butene copolymer rubber can be used in combination with the chlorinated ethylene/1-butene copolymer rubber, so long as attainment of the intended object of the present invention is not hindered. Triazine curing and organic peroxide curing are effectively adopted for curing the foam of the present invention. In case of triazine curing, a triazine compound of formula (I) is preferably used as the curing agent: wherein R 1 is -NR 2 R 3 , -OR 2 or -SR 2 , in which R 2 and R 3 are the same or different and each is hydrogen, unsubstituted or substituted alkyl or unsubstituted or substituted aryl. As specific examples of the triazine thiol of formula (1), there can be mentioned triazine-2,4,6-trithiol, 2-dibutylaminotriazine-4,6-dithiol, 2-phenylaminotriazine-4,6-dithiol, 2-hexylamine-triazine-4,6-dithiol, 2-diethylaminotriazine-4,6-dithiol and 2-butoxytriazine-4,6-dithiol. The curing agent is generally incorporated in an amount of 1 x 10 -3 to 2.5 x 10 -2 mole, preferably 1.5 x 10 -3 to 2 x 10 -2 mole, especially preferably 3 x 10 -3 to 1.3 x 10 -2 mole, per 100 g of the chlorinated ethylene/1-butene copolymer rubber. If the amount incorporated of the curing agent is too small and below the above-mentioned range, a cured product having a good rubbery elasticity cannot be obtained, and if the amount of the curing agent is too large and exceeds the above-mentioned range, the elongation is reduced and the cured product can hardly be put into practical use. When a triazine compound is used as the curing agent, a curing assistant is added so as to attain a curing speed necessary for practical molding. An organic base having an acid dissociation constant (pKa) of at least 7 or a compound capable of forming such an organic base is incorporated in an amount of 5 x 10 -4 to 2 x 10 -2 mole, preferably 1 x 10 -3 to 1 x 10 -2 mole, per 100 g of the chlorinated ethylene/1-butene copolymer rubber. Such curing assistants can be used singly or in the form of a mixture of two or more of them. As the curing assistant, there can be used 1,8-diazabicyclo(5,4,0)-undecene-7, laurylamine, benzylamine, dibenzylamine, N-methylmorpholine, dicyclohexylamine, zinc dibutyldithiocarbamate, piperizine pentamethylene-dithiocarbamate, piperizine salt pentamethylenedithiocarbamate, N-cyclohexyl-2-benzothiazolylsulfenmide, dicyclohexylamine benzoate, piperidine benzoate, dipentamethylene-thiuram tetrasulfide, tetramethylthiuram disulfide, and onium salts such as tetramethylphosphonium iodide, tetramethylammonium chloride, tetrabutylphosphonium bromide, tetrabutylammonium bromide and distearyldimethylammonium chloride. When organic peroxide curing is carried out, as the curing agent, there can be used dicumyl peroxide, 2,5-dimethyl-2,5-di(tertiary butylperoxy)hexane, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 2,5-dimethyl-2,5-di(tertiary butylperoxy)hexyne-3, di-tertiary-butyl peroxide, di-tertiary-butylperoxy-3,3,5-trimethylcyclohexane and tertiary-butyl hydroperoxide. Among them, dicumyl peroxide, di-tertiary-butyl peroxide and di-tertiary-butylperoxy-3,3,5-trimethylcyclohexane are preferably used. The amount used of the organic peroxide is generally 3 x 10 -4 to 5 x 10 -2 mole, preferably 1 x 10 -3 to 3 x 10 -2 mole, per 100 g of the chlorinated ethylene/1-butene copolymer rubber. When the organic peroxide is used as the curing agent, a curing assistant is preferably used in combination with the curing agent. As the curing assistant, there can be mentioned sulfur, a quinone dioxime type curing assistant such as p-quinonedioxime, a methacrylate type curing assistant such as polyethylene glycol dimethacrylate, an allyl type curing assistant such as diaryl phthalate or triallyl cyanurate, a maleimide type curing assistant and divinylbenzene. The curing assistant is used in an amount of 1/2 to 2 moles, preferably about 1 mole, per mole of the used organic peroxide. As the foaming agent, there can be mentioned, for example, inorganic foaming agents such as sodium hydrogencarbonate, sodium carbonate, ammonium hydrogencarbonate, ammonium carbonate and ammonium nitrite, nitroso compounds such as N,N'-dimethyl-N,N'-dinitrosoterephthalamide and N,N'-dinitropentamethylenetetraamine, azo compounds such as azodicarbonamide, azobisisobutyronitrile, azocyclohexylnitrile, azodiaminobenzene and barium azodicarboxylate, sulfonylhydrazide compounds such as benzene-sulfonylhydrazide, toluenesulfonylhydrazide, p,p'-oxybis(benzene-sulfonylhydrazide) and diphenylsulfone-3,3'-disulfonylhydrazide, and azide compounds such as calcium azide, 4,4'-diphenyldisulfonylazide and p-toluene-sulfonylazide. A nitroso compound, an azo compound and an azide compound are preferably used. The foaming agent is generally incorporated in an amount of 1.0 x 10 -3 to 3.0 x 10 -1 mole, preferably 2.0 x 10 -3 to 2.0 x 10 -1 mole, per 100 g of the chlorinated ethylene/1-butene copolymer rubber, and in general, a foamed body having an apparent specific gravity of about 0.03 to about 0.7 is formed. As the foaming assistant to be used in combination with the foaming agent, there are used organic acids such as salicylic acid, phthalic acid and stearic acid, and urea and derivatives thereof. The foaming assistant exert functions of lowering the decomposition temperature of the foaming agent, promoting the decomposition and uniformalizing cells. A rubber filler can be used so long as the electric characteristics are not adversely influenced. For example, finely divided silicic acid, light calcium carbonate, talc and clay can be used as the rubber filler. The rubber filler is generally used in an amount of up to 150 parts by weight, preferably up to 100 parts by weight, per 100 parts by weight of chlorinated ethylene/1-butene copolymer rubber. As the softener, there can be mentioned, for example, petroleum substances such as process oil, lubricating oil paraffin, liquid paraffin, petroleum asphalt and liquid petrolatum, coal tars such as coal tar and coal tar pitch, fatty oils such as castor oil, linseed oil, rape oil, soybean oil and coconut oil, waxes such as tall oil, bees wax, carnauba wax and hydrous lanoline, fatty acids and salts thereof such as ricinoleic acid, palmitic acid, stearic acid, barium sterate and calcium stearate, synthetic polymeric substances such as a petroleum resin, a coumarone-indene resin and atactic polypropylene, ester type plasticizers such as dioctyl phthalate, dioctyl adipate and dioctyl sebacate, and microcrytalline wax, rubber substitute (factice), liquid polybutadiene, modified liquid polybutadiene and liquid thiocol. The softener is generally incorporated in an amount of up to 100 parts by weight, preferably 70 parts by weight, per 100 parts by weight of the chlorinated ethylene/1-butene copolymer rubber. As the metal activating agent, there can be used magnesium oxide, a zinc salt of a fatty acid, red lead, litharge and calcium oxide. The metal activating agent is used in an amount of 3 to 15 parts by weight, preferably 5 to 10 parts by weight, per 100 parts by weight of the chlorinated ethylene/α-olefin copolymer rubber. In order to cope with various rubber-processing steps, addition of a compound having an oxyethylene structure and a scorch-preventing agent is recommended. As the compound having an oxyethylene structure, there can be mentioned, for example, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol and polypropylene glycol. In general, the compound is incorporated in an amount of 0.1 to 10 parts by weight, preferably 1 to 5 parts by weight, per 100 parts by weight of the chlorinated ethylene/1-butene copolymer rubber. Known scorch retarders can be used as the scorch-preventing agent. For example, there can be mentioned maleic anhydride, a thioimide compound, a sulfenamide compound and a sulfonamide compound. The scorch-preventing agent is used in an amount of 0.2 to 5 parts by weight, preferably 0.3 to 3 parts by weight, per 100 parts by weight of the chlorinated ethylene/1-butene copolymer rubber. When an aging-preventing agent is used, the material life of the foam of the present invention can be prolonged, as in case of ordinary rubbers. As the aging-preventing agent to be used for this purpose, there can be mentioned aromatic secondary amines such as phenylnaphthylamine and N,N'-di-2-naphthyl-p-phenylenediamine, phenolic stabilizers such as dibutylhydroxytoluene and tetrakis [methylene(3,5-di-t-butyl-4-hydroxy)hydroxycinnamato]methane, thioether stabilizers such as bis[2-methyl-4-(3-n-alkylthiopropionyloxy)-5-t-butylphenyl]sulfide, and dithiocarbamate stabilizers such as nickel dibutyldithiocarbamate. These aging-preventing agents can be used singly or in the form of a mixture of two or more of them. The aging-preventing agent is incorporated in an amount of 0.1 to 5 parts by weight, preferably 0.5 to 3 parts by weight, per 100 parts by weight of the chlorinated ethylene/1-butene copolymer rubber. Processing assistants customarily used for rubbers can be used. For example, there can be mentioned higher fatty acids and salts and esters thereof, such as ricinoleic acid, stearic acid, palmitic acid, lauric acid, barium stearate, calcium stearate, zinc stearate, and esters thereof. The processing assistant is generally incorporated in an amount of up to about 10 parts by weight, preferably 1 to 5 parts by weight, per 100 parts by weight of the chlorinated ethylene/1-butene copolymer rubber. The rubber composition is prepared, for example, according to the following method. The chlorinated ethylene/1-butene copolymer rubber, carbon black and additives such as the filler and softener are charged in a mixture such as a Banbury mixer and kneaded at a temperature of about 80 to about 170°C for about 3 to about 10 minutes, and the curing agent, curing assistant, foaming agent and foaming assistant are additionally mixed into the kneaded mixture by using a roll such as an open roll and the mixture is kneaded at a roll temperature of about 40 to about 80°C for about 5 to about 30 minutes. The kneaded mixture is taken out little by little to form a ribbon- or sheet-shaped rubber composition. Alternatively, the chlorinated ethylene/1-butene copolymer rubber and additives are directly fed into an extruder heated at about 80 to about 100°C and pelletized while taking a residence time of about 0.5 to about 5 minutes to obtain a pelletized rubber composition. The so-prepared rubber composition is molded, cured and foamed in a mold by a press molding machine, a transfer molding machine or an injection molding machine. The mold temperature is ordinarily 150 to 220°C, and the time required for curing and foaming is 1 to 30 minutes. Furthermore, when molding is carried out by using an extruder, curing and foaming can be effected by heating the extrudate under a pressureless condition by a hot air heating tank, a glass bead fluidized bed or a microwave heating device. Moreover, curing and foaming can be effected by heating under pressure by a curing pot. In this case, the heating temperature is 150 to 270°C and the time required for curing and foaming is 1 to 30 minutes. The thus-obtained foam has a desired volume resistivity of 10 5 to 10 11 Ω-cm and retains an initial softness even over time. Accordingly, the foam is very valuable as a roll material for apparatus for office automation. The reason why the desired volume resistivity within the above-mentioned range can be easily obtained according to the present invention has not been completely elucidated, but it is presumed that by the chlorination of the ethylene/1-butene copolymer rubber, the affinity of the rubber component with carbon black is increased, and therefore the dispersion of carbon black in the rubber is stabilized. As pointed out hereinbefore, the semiconductive rubber foam of the present invention is composed of a molded body formed by curing and foaming a rubber composition comprising (A) 100 parts by weight of a chlorinated ethylene/1-butene copolymer rubber and (B) 15 to 45 parts by weight of carbon black as indispensable components, and the volume resistivity of this foam is 10 5 to 10 11 Ω-cm. Since the chlorinated ethylene/1-butene copolymer rubber is contained as the indispensable component, the ozone resistance, heat aging resistance and weatherability can be maintained at high levels, and the affinity with carbon black is improved and carbon black is uniformly and stably dispersed. Namely, the dispersion state of the carbon black is good, and adhesiveness and affinity of the carbon black with the rubber component are good. By incorporating carbon black as the other indispensable component in an amount of 15 to 45 parts by weight into 100 parts by weight of the chlorinated ethylene/1-butene copolymer rubber, a desired volume resistivity of 10 5 to 10 11 Ω-cm is attained. If the amount of carbon black is less than 10 parts by weight per 100 parts by weight of the chlorinated ethylene/1-butene copolymer rubber, the volume resistivity increases and exceeds the above range, and if the amount of carbon black is greater than 50 parts by weight per 100 parts by weight of the chlorinated ethylene/1-butene copolymer rubber, the volume resistivity decreases and is often below the above-mentioned range. The volume resistivity can be changed according to, for example, the intended use and hardness even if the composition is the same. If the amount of carbon black is within the above-mentioned range, the volume resistivity can be stably controlled within the above-mentioned range. Thus, according to the present invention, a foam having a desired volume resistivity and retaining an initial softness (hardness)even over time can be obtained. The foam of the present invention is very valuably used as a roll for apparatus, for example, office automation. Furthermore, the foam of the present invention can be applied to fields where a rubber or rubbery elastomer foam having semiconductivity should be used. The present invention will now be described in detail with reference to the following Examples. Example 1 According to procedures described below, a foam of the present invention was prepared and tested. At first, 4.3 ℓ of a composition shown in Table 1 was kneaded for 5 minutes by a Banbury mixer (supplied by Kobe Seiko). The kneaded composition was wound on a 14-inch open roll (supplied by Nippon Roll). The surface temperatures of front roll/back roll were 60°C/70°C. Additives shown in Table 2 were added to the kneaded composition on this open roll. Component Amount (parts by weight) chlorinated ethylene/1-butene copolymer rubber 100.0 FEF carbon 45.0 stearic acid 3.0 magnesia 5.0 DOS 45.0 Additive Amount (parts by weight) curing agent 2.6 curing assistant A 2.6 curing assistant B 1.3 foaming agent 10.0 foaming assistant 3.0 After 2 minutes' kneading, the kneaded composition was cut out in the form of a ribbon. The compound rubber was supplied into a rubber extruder having a screw diameter of 60 mm (supplied by Nakata Zoki; L/D = 16; set temperatures of die/front cylinder/back cylinder = 80°C/70°C/60°C) and extrusion-molded into a tubular molded article, and the molded article was cured and foamed under a pressure of 6 kg/cm 2 (about 160°C) for 30 minutes by steam pot curing. The obtained foam was machined into a hollow foamed rubber roll having an inner diameter of 5 mm and an outer diameter of 15 mm. The foamed rubber roll was subjected to the following tests. (1) Apparent Specific Gravity The measurement was conducted according to the substitution method by using an automatic specific gravity meter supplied by Toyo Seiki (2) Hardness C of JIS The measurement was conducted by the spring type hardness test (C form) of the cured rubber test method of JIS K-6301. (3) Volume Resistivity The measurement was conducted by using VE-40 supplied by Kawaguchi Denki Then, the foam was subjected to the accelerated weatherability test using a sunshine weather-meter. The black panel temperature was 63°C and the test time was 1000 hours. After the accelerated weatherability test, the hardness C of JIS was measured again. The test results are shown in Table 12. Example 2 The procedures of Example 1 were repeated in the same manner except that a chlorinated ethylene/1-butene copolymer having an ethylene/1-butene molar ratio of 90/10, a chlorine content of 35% by weight and ML 1+4 (121°C) of 120 was used instead of the chlorinated ethylene/1-butene copolymer rubber used in Example 1. The obtained results are shown in Table 12. Example 3 The procedures of Example 1 were repeated in the same manner except that the components shown in Table 1 were changed as shown in Table 3. The obtained results are shown in Table 12. Component Amount (parts by weight) chlorinated ethylene/1-butene copolymer rubber 100.0 acetylene black 15.0 stearic acid 3.0 magnesia 5.0 talc 50.0 DOS 30.0 Example 4 The procedures of Example 1 were repeated in the same manner except that the components shown in Table 1 were changed as shown in Table 4 and the components shown in Table 2 were changed as shown in Table 5. The obtained results are shown in Table 12. Component Amount (parts by weight) chlorinated ethylene/1-butene copolymer rubber 100.0 acetylene black 30.0 stearic acid 3.0 magnesia 5.0 clay 25.0 DOS 70.0 Component Amount (parts by weight) curing agent, ZISNET-DB 2.0 curing assistant A 3.0 curing assistant C 0.5 foaming agent 8.0 Example 5 The procedures of Example 1 were repeated in the same manner except that the composition shown in Table 2 was changed as shown in Table 6. The obtained results are shown in Table 12. Comparative Example 1 The procedures of Example 1 were repeated in the same manner except that the composition shown in Table 1 was changed as shown in Table 7. Component Amount (parts by weight) chlorinated ethylene/1-butene copolymer rubber 100.0 talc 60.0 stearic acid 3.0 magnesia 5.0 DOS 30.0 The obtained results are shown in Table 12. Comparative Example 2 The procedures of Example 1 were repeated in the same manner except that the composition shown in Table 1 was changed as shown in Table 8 and the composition shown in Table 2 was changed as shown in Table 9. Component Amount (parts by weight) EPDM 100.0 FEF carbon 45.0 stearic acid 3.0 zinc oxide 5.0 paraffinic process oil 45.0 Component Amount (parts by weight) curing assistant F 0.5 curing assistant G 1.5 curing assistant H 0.5 sulfur 1.5 foaming agent 10.0 foaming assistant 3.0 The obtained results are shown in Table 12. Comparative Example 3 The procedures of Example 1 were repeated in the same manner except that the composition shown in Table 1 was changed as shown in Table 10 and the composition shown in Table 2 was changed as shown in Table 11. Component Amount (parts by weight) chloroprene rubber 100.0 FEF carbon 45.0 stearic acid 1.0 magnesia 4.0 DOS 45.0 Component Amount (parts by weight) zinc oxide 5.0 curing assistant 0.35 foaming agent 10.0 foaming assistant 3.0 The obtained results are shown in Table 12.

Claims: A rubber foam having a volume resistivity of 10 5 to 10 11 Ω-cm in the form of a moulded body obtainable by moulding a rubber composition comprising: 100 parts by weight of a chlorinated ethylene/1-butene copolymer rubber (A) having a chlorine content of 20 to 40% by weight, a Mooney viscosity [ML 1+4 (121°C)] of 30 to 120 and a molar ratio of ethylene units to 1-butene units, before chlorination, of from 50:50 to 90:10; and 15 to 45 parts by weight of carbon black (B), a curing agent and a foaming agent. A rubber foam according to claim 1 wherein the carbon black is channel black, furnace black, thermal black or acetylene black or a mixture of any two or more thereof. A rubber foam according to claim 1 or 2 wherein the curing agent is a triazine compound or an organic peroxide. A rubber foam according to claim 3 wherein the curing agent is a triazine compound of formula (I): wherein R 1 is -NR 2 R 3 , -OR 2 or -SR 2 in which R 2 and R 3 are the same or different and each is hydrogen, unsubstituted or substituted alkyl or unsubstituted or substituted aryl. A rubber foam according to claim 3 or 4 wherein the curing agent contains from 1 x 10 -3 to 2.5 x 10 -2 mole, per 100 g of the chlorinated ethylene/1-butene copolymer rubber, of a triazine compound. A rubber foam according to claim 3 wherein the curing agent is an organic peroxide selected from dicumyl peroxide, di-tertiary-butyl peroxide and di-tertiary-butylperoxy-1,3,5-trimethylcyclohexane. A rubber foam according to claim 3 or claim 6 wherein the curing agent contains from 3 x 10 -4 to 5 x 10 -2 mole, per 100 g of the chlorinated ethylene/1-butene copolymer rubber, of an organic peroxide. A rubber foam according to any one of claims 1 to 7 wherein the foaming agent is a nitroso compound, an azo compound or an azide compound or a mixture of any two or more thereof. A rubber foam according to any one of claims 1 to 8 comprising 1.0 x 10 -3 to 3.0 x 10 -1 mole per 100 g of the chlorinated ethylene/1-butene copolymer, of foaming agent. A process for producing a rubber foam moulded body having a volume resistivity of 10 5 to 10 11 Ω-cm comprising foaming, moulding and curing a rubber composition comprising 100 parts by weight of a chlorinated ethylene/1-butene copolymer rubber, having a chlorine content of 20 to 40% by weight, a Mooney viscosity [ML 1+4 (121°C)] of 30 to 120 and a molar ratio of ethylene units to 1-butene units, before chlorination, of from 50:50 to 90:10, and 15 to 45 parts of carbon black.

Inventors: KEIJI OKADA, TETSUO TOJO, YOSHIHARU KIKUCHI, KEIJI, OKADA, TETSUO, TOJO, YOSHIHARU, KIKUCHI
Applicants: MITSUI PETROCHEMICAL IND, MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Application year: 1991
Main classification: C08J9
IPC codes: C08J9, G03G15, C08K3, H01B1