ONE-COMPONENT ELECTRICALLY CONDUCTIVE ORGANOPOLYSILOXANE COMPOSITIONS

Abstract: A one-component electrically conductive composition containing (1) an organopolysiloxane having aliphatically un­ saturated groups, (2) an organosilicon compound having sili­ con-bonded hydrogen atoms, (3) from 40 to 65 percent, based on the weight of the organopolysiloxane (1) of an electrically conductive carbon black consisting of a mixture of (a) from 20 to 50 percent by weight of furnace black having a surface area of from 40 to 1500 m²/g and (b) from 80 to 50 percent by weight of acetylene black based on the weight of the mixture of car­ bon black, and (4) a catalyst capable of promoting the addition of the silicon-bonded hydrogen to the aliphatically unsaturated groups. The electrically conductive composition is prepared by (A) heating a mixture containing (1) the organopolysiloxane having aliphatic unsaturation and/or (3) an electrically conduc­ tive carbon black, and (4) catalyst to an elevated temperature, and thereafter (B) adding (2) an organosilicon compound hav­ ing silicon-bonded hydrogen to the mixture after it has cooled to ambient temperature. The resultant composition, which can be stored at room temperature can be crosslinked by heating to a temperature of about 100°C or above.

Description: ONE-COMPONENT ELECTRICALLY CONDUCTIVE ORGANOPOLYSILOXANE COMPOSITIONS The present invention relates to an electrically conductive composition, more particularly to one-component electrically conductive organopolysiloxane compositions and to a method for preparing the same. Background of the Invention Electrically conductive organopolysiloxane compositions are described in s. S. Patent No. 4,273,697 to Sumimura et al in which the composition contains (A) 100 parts of a curable liquid organopolysiloxane, (B) from 0.1 to 70 parts by weight of carbon black having a specific surface area of at least 900 mê/g, (C) from 0 to 50 parts by weight of a hydroxyl endblocked polydiorganosiloxane whose degree of polymerization is 50 or less, and (D) a crosslinking agent for the curable organopolysiloxane. Also, U. S. Patent No. 4,250,075 to Monroe et al discloses electrically conductive compositions containing (A) vinyldiorganosiloxy endblocked polydiorgaaosiloxanes, (B) carbonaceous particles having an average diameter of less than 20 micrometers, (C) a polyorganohydrogensiloxane having an average of at least 2.1 silicon-bonded hydrogen atoms per mole -cule, (D) a platinum containing catalyst, and (E) a platinum catalyst inhibitor, in which at least 2 percent by weight of phenyl radicals are present based on the weight of the cured composition, In contrast to the compositions described in these patents, the compositions of this invention exhibit improved electrical conductivity, i.e., the compositions of this invention have an electrical resistivity of less than 2 ohm-cm, whereas the electrical resistivity of the compositions described in U. S. Patent No. 4,273,697 have an electrical resistivity of from 6 to 55 ohm-cm. Although one-component organopolysiloxane compositions containing (1) organopolysiloxanes having silicon-bonded aliphatic unsaturation, (2) organopolysiloxanes having siliconbonded hydrogen atoms and (3) platinum group metals are nown in the art, these compositions contain an inhibitor which retards cr inhibits the addition of the silicon-bonded hydrogen atoms to the silicon-bonded aliphatically unsaturated groups at room temperature. Various types of inhibitors which may be incorporated in platinum catalyzed organopolysiloxane compositions to inhibit the addition of the silicon-bonded hydrogen atoms to the siliconbonded aliphatically unsaturated groups are described in, for example, U. S. Patent No. 3,192,181 to Moore; U. S. Patent No. 3,344,111 to Chalk; U. S. Patent No. 3,445,420 to Kookootsedes et al;.U. S. Patent No. 3,383,356 to Nielsen; U. S. Patent No. 3,882,083 to Berger et al and U. S. Patent No. 3,992,355 to Itoh et al. One of the disadvantages of incorporating inhibitor in an organopolysiloxane composition in order to obtain shelf stability is that often times the inhibitors will evaporate from the composition. The composition will then begin to cure unpredictably while in storage. Also, some of the inhibitors may change -over a period of time and are not effective in inhibiting the addition of the silicon-bonded hydrogen atoms to the siliconbonded aliphatically unsaturated groups. Thus, it is preferred that the electrically conductive organopolysiloxane composition be free of inhibitors, but still have an indefinite shelf-life. Therefore, it is an object of the present invention to provide a one-component electrically conductive organopolysiloxane composition. Another object of the present invention is to provide a one-component electrically conductive organopolysiloxane composition having an indefinite shelf-life. Still another object of the present invention is to provide a onecomponent electrically conductive composition which is free of inhibitors. A further object of the present invention is to provide an electrically conductive elastomer. A still further object of the present invention is to provide an electrically conductive organopolysiloxane elastomer which has an electrical resistance of less than 2 ohm-cm. Still a further object of the present invention is to provide a process for preparing onecomponent electrically conductive organopolysiloxane compositions which have an indefinite shelf-life. Summary of the Invention The foregoing objects and others which will become apparent from the following description are accomplished in accordance with this invention, generally speaking, by providing a one-component electrically conductive organopolysiloxane composition containing (1) an organopolysiloxane having siliconbonded aliphatic unsaturation, (2) an organosilicon compound having silicon-bonded hydrogen atoms, (3) from 40 to 65 percent by weight, based on the weight of the organopolysiloxane (1) of an electrically conductive carbon black consisting of a mixture of (a) furnace black having a surface area of from 40 to 1500 m2/g in an amount of from 20 to 50 percent by weight and (b) acetylene black in an amount of from 80 to 50 percent by weight based on the weight of the carbon black, and (4) a catalyst capable of promoting the addition of silicon-bonded hydrogen to silicon-bonded aliphatically unsaturated groups. The one-component electrically conductive composition is prepared by (A) heating a mixture containing (1) an organopolysiloxane having aliphatic unsaturation, and/or (3) from 40 to 65 percent by weight based on the weight of the organopolysiloxane (1) of an electrically conductive carbon black consisting of a mixture of (a) from 20 to 50 percent by weight of furnace black having a surface area of from 40 to 1500 m2/g and (b) from 80 to 50 percent by weight of acetylene black, based on the weight of the mixture of carbon black, and (4) a catalyst capable of promoting the addition of silicon-bonded hydrogen atoms to silicon-bonded aliphatically unsaturated groups, to an elevated temperature and thereafter (B) adding (2) an organosilicon compound having silicon-bonded hydrogen atoms to the mixture after it has cooled to ambient temperature The resultant composition which can be stored at room temperature without crosslinking, can be crosslinked by heating to an elevated temperature to form an elastomer having an electrical resistivity of less than 2 ohm-cm. Detailed Description of the Invention The organopolysiloxanes (1) used in the electrically conductive compositions of this invention may be any diorganopolysiloxane which could have been used heretofore in diorganopolysiloxane-based compositions containing electrically conductive carbon black which could be cross-linked to form electrically conductive organopolysiloxane elastomers by the addition of silicon-bonded hydrogen to silicon-bonded aliphatic multiple bonds or through ionization radiation. Diorganopolysiloxanes which may be used are especially those of the general formula: R3Sio(SiR2O)nSiR3 wherein R represents the same or different monovalent or substituted monovalent hydrocarbon radicals having up to 18 carbon atoms, in which an average of at least two aliphatically unsaturated groups are present per molecule and n is an integer having a value of at least 10. Although this is generally not shown in the formula illustrated above, the siloxane chain of the aforementioned diorganopolysiloxanes may contain siloxane units in addition to the diorganosiloxane units (SiR20). Examples of such other siloxane units, which are generally present only as impurities, are those corresponding to the formulas RSio3/2, R3SiO1/2 and Six4/2, where R is the same as above. It is, however, preferred that such other siloxane units be present in an amount less than 1 mole percent. Still other siloxane units, for example, those of the formula -SiR2RISiR2O-, where R is the same as above and R' is a bivalent hydrocarbon radical, for example, a phenyl radical, may be present in larger amounts. It is preferred that the substituted hydrocarbon radicals represented by R contain from 1 to 8 carbon atoms. Examples of hydrocarbon radicals represented by R are alkyl radicals, for example, the methyl and ethyl radical, as well as propyl, butyl, hexyl and octadecyl radicals; alkenyl radicals such as the vinyl, allyl, ethylallyl and butadienyl radicals; aryl radicals such as the phenyl radical; alkaryl radicals such as the tolyl radicals; and aralkyl radicals such as the beta-phenylethyl radical. Examples of substituted monovalent hydrocarbon radicals represented by R are halogenated hydrocarbon radicals, such as the 3,3,3-trifluoropropyl radical, chlorophenyl and bromotolyl radicals; and cyanoalkyl radicals, such as the beta-cyanoethyl radical. Because of their availability, it is preferred that at least 80 percent of the R radicals be methyl radicals. Preferred diorganopolysiloxanes are those having trimethylsiloxy or vinyldimethylsiloxy groups as terminal units and contain from 0.01 to 5 mole percent of methylvinylsiloxane units. More preferably the diorganopolysiloxanes are those containing from 0.1 to 2 mole percent of methylvinylsiloxane units and the remaining diorganosiloxane units are dimethylsiloxane units. When the compositions are to be cross-linked by the addition of silicon-bonded hydrogen to a silicon-bonded aliphatic multiple bond, it is essential that the diorganopolysiloxane which constitutes the base of the composition have at least two alkenyl radicals for each molecule of diorganopolysiloxane. The viscosity of the diorganopolysiloxane used in the preparation of the compositions of this invention is preferably 100 mPa.s at 250C and more preferably at least 105.mPa.s at 250C. When the compositions are to be cross-linked by the addition of silicon-bonded hydrogen to a silicon-bonded aliphatic multiple bond, then the composition must contain in addition to the electrically conductive carbon black and the diorganopolysiloxane containing alkenyl radicals, at least one organosilicon compound having at least 3 silicon-bonded hydrogen atoms per molecule and a catalyst which promotes the addition of siliconbonded hydrogen to the silicon-bonded aliphatic multiple bonds. The organosilicon compounds containing at least 3 silicon-bonded hydrogen atoms per molecule are-generally organopolysiloxanes, especially methylhydrogenpolysiloxanes. The organosilicon compounds may contain units repre- sented by the formula EMI5.1 where R1 represents hydrogen or is the same as R, in which at least 2 and preferably 3 silicon-bonded hydrogen atoms are present per molecule and a is 1, 2 or 3. Preferred compounds are those having RHSiO-units, R2Sio- and R3 SlO - units in 1/2 which a silicon-bonded hydrogen atom is present for each 3 to 100 silicon atoms in the compounds and have a viscosity of from 10 to 50,000 mPa.s at 250C. The organosilicon ccmpounds having at least 3 siliconbonded hydrogen atoms per molecule are preferably used in an amount of from 0.5 to 20 percent by weight, based on the weight of the diorganopolysiloxane containing alkenyl radicals. Examples of catalysts which promote the addition of silicon-bonded hydrogen to aliphatic multiple bonds are metallic and finely dispersed platinum, ruthenium, rhodium, palladium and iridium. These metals may be dispersed on- carriers, such as the carbon black used in accordance with this invention, silicon dioxide, ainminum oxide or activated carbon. Furthermore, it is possible to use compounds or complexes of these metals1 such as PtCl4, H2PtCl6.6H20, Na2PtCl4.4H20, platinum-olefin complexes, platinum-alcohol complexes, platinum-alcoholate complexes, platinum-ether complexes, platinum-aldehyde complexes, platinumketone complexes, ammonium platinum complexes, platinum-vinyl S iloxane complexes, especially platinum-divinyltetranethyldi- siloxane complexes with or without any detectable, inorganically bonded halogen, trimethylenedipyridine platinum dichloride; as well as iron, nickel and cobalt carbonyls. When one of the above metals, compounds and/or complexes of said metals is used as a catalyst to promote the addition of silicon-bonded hydrogen to aliphatic multiple bonds, then such catalysts are preferably used in an amount of from 0.5 to 500 ppm (parts per million by weight), calculated as the metallic elements and based on the weight of the diorganopolysiloxane containing alkenyl radicals. It is preferred that the electrically conductive compositions of this invention contain a total of from 40 to 65 percent by weight of carbon black and more preferably from about 44 to about 61 percent by weight of carbon black based on the weight of the organopolysiloxane (1). Preferably the carbon black consists of two types; one type consisting of a- furnace type carbon black which is present in an amount of from 20 to 50 percent based on the weight of the carbon black and having a surface area of from about 40 to about 1500 m2/g and the other being an acetylene black which is present in an amount of from 80 to 50 percent by weight based on the weight of the carbon black and having a surface area of, for example, from 40 to 1000 m2jg. Preferably, the amount of furnace black will range from about 20 to 45 percent by weight, based on the weight of the carbon black, and will have a surface area of from about 500 to 1200 mê/g. The amount of acetylene black present in the composition will preferably range from about 80 to about 55 percent by weight based on the weight of the carbon black and will preferably have a surface area of from 50 to 800 m2/g. The surface areas described herein are determined by means of nitrogen absorption according to the ASTM Special Technical Bulletin Nd. 51, 1941, page 95. (Generally described as the "Bet" Method.) The term "furnace black" is also described in the German Chemical Literature (cf. "Ullmanns Encyklopadie der technischen Chemie", Volume 14, Munich-Berlin, 1963, page 799). When the surface area of the furnace black is less than 40 m2/g, then the compositions produce elastomers whose electrical resistivity is greater than 2 ohm-cm. On the other hand, if the surface area of the furnace black is in excess of 1500 m2/g, then the resultant compositions become difficult to process. A commercial form of a furnace type carbon black is TM Ketjenblack EC. The surface area of the acetylene black is not critical and may range from about 40 to 1000 mê/g, and more preferably from about 45 to 800ê/g. A commercial form of this type of carbon black is Shawinigan # acetyne black. It is, however, essential that the mixture of carbon black used in the compositions of this invention have a broad range of surface area, i.e., when a furnace black having a surface area of from 1000 to 1500 m2/g is used, then it is preferred that the surface area of the acetylene black be less than 1000 m2/g. When the compositions, which are to be cross-linked, contain less than about 40 percent by weight, based on the weight of the organopolysiloxane, of carbon black, then the omposiions form elastomers having an electrical resistance above 2 ohm-cm. On the other hand, if the compositions, which are to ba cross-linked, contain more than of about 65 percent by weight of carbon black, based on the weight of the organopolysiloxane (1), then the resultant compositions are difficult to process and form materials having unsatisfactory elastomeric properties. Likewise, it has been found that when furnace black or acetylene black is used alone in the compositions of this invention, that elastomers having desirable physical properties and an electrical resistivity of less than 2 ohm-cm cannot be obtained. However, surprisingly it was found that when a mixture of carbon black is incorporated in the organopolysiloxane compositions of this invention, the compositions can be easily processed and form elastomers which have an electrical resistivity of less than 2 ohm-cm and also have desirable physical properties. In addition to the diorganopolysiloxanes which constitutes the base of these compositions, the electrically conductive carbon black, the organosilicon compound containing at least 3 silicon-bonded hydrogen atoms per molecule, and a catalyst which promotes the addition of silicon-bonded hydrogen to silicon-bonded aliphatically unsaturated groups, the compositions of this invention may contain additional substances such as could have been used heretofore in the preparation of diorganopolysiloxane-based compositions containing electrically conductive carbon black, for the preparation of electrically conductive organopolysiloxane elastcmers by the addition of silicon-bonded hydrogen to aliphatic multiple bonds or by ionization radiation. Additional substances which may be added to these compositions are reinforcing and non-reinforcing fillers other than furnace black and acetylene black, stabilizers, antioxidants, processing aids such as organopolysiloxanes containing silicon-bonded hydroxyl groups and having a maximum of 100 silicon atoms per molecule, and plasticizers, as well as substances which may improve other properties of the elastomers other than electrical conductivity. Examples of plasticizers are especially trimethylsiloxy end-blocked dimethylpolysiloxanes having a maximum of 1000 silicon atoms per molecule. Examples of fillers other than furnace black and acetylene black which may be incorporated in the compositions of this invention are pyrogenically produced silicon dioxide, silicic acid hydrogel which has been dehydrated while maintaining its structure, silicic acid xerogels, pyrogenically produced aluminum oxide and pyrogenically produced titanium dioxide. Examples of non-reinforcing fillers which may be used are quartz meal and diatomaceous earth. The compositidns of this invention may also contain fibrous fillers, such as glass fibers having an average length up to about 0.5 mm, and/or asbestos fibers. All of the previously cited fillers, including the various types of carbon black, or a portion of said fillers may have organopolysiloxane groups on their surfaces. This can, for example, be achieved by treating a portion of the fillers with hexamethyldisilazane either before or after they have been mixed with the diorganopolysiloxanes which form the base of these compositions. Adhesive promoters, such as glycidyloxypropyltrialkoxysilane, may be used to improve the adhesion of the elastomers to the surfaces. The electrically conductive organopolysiloxane compo- sitions may be prepared by heating a mixture containing (1) an organopolysiloxane having silicon-bpnded aliphatic unsaturation and/or (3) from 40 to 65 percent by weight based on the weight of the organopolysiloxane (1) of an electrically conductive carbon black containing (a) from 20 to 50 percent by weight of furnace black, having a surface area of from 40 to 1500 m2 /g and (b) from 80 to 50 percent by weight of acetylene black based on the weight of the organopolysiloxane (1) and (4) a catalyst which is capable of promoting the addition of silicon-bonded hydrogen to silicon-bonded aliphatically unsaturated groups, to an elevated temperature and thereafter adding (3) an organosilicon compound containing silicon-bonded hydrogen atoms to the resultant mixture after it has cooled to form a one-component composition capable of being crosslinked at an elevated tonper- ature to form an electrically conductive elastomer. In addition, the electrically conductive organopolysiloxane compositions may be prepared by heating a mixture con taining (1) an organopolysiloxane having silicon-bonded aliphatic unsaturation and (4) a catalyst which is capable of promoting the addition of silicon-bonded hydrogen to siliconbonded aliphatically unsaturated groups to an elevated temperature and thereafter adding (2) an organosilicon compound containing silicon-bonded hydrogen atoms and (3) from 40 to 65 percent by weight based on the weight of the organopolysiloxane (1) of an electrically conductive carbon black containing (a) from 20 to 50 percent by weight of furnace black, having a surface area of from 40 to 1500 mê/g and (b) from 80 to 50 percent by weight of acetylene black based on the weight of the organopolysiloxane (1) to the resultant mixture after it has cooled to form a one-component composition capable of being crosslinked at an elevated temperature to form an electrically conductive elastomer. Also, the electrically conductive organopolysiloxane compositions may be prepared by heating a mixture containing carbon black (3) and catalyst (4) to an elevated temperature and thereafter adding organopolysiloxane (1) and organosilicon compound (2) to the resultant mixture after it has cooled to form a one-component composition capable of being crosslinked at an elevated temperature. In preparing the one-component compositions of this invention, it is preferred that the mixture containing the organopolysiloxane (1) and/or carbon black (3) and catalyst (4) be heated to a temperature of from about 1000 up to about 300"C and more preferably from about 1500 to about 2500C for at least 5 minutes and more preferably from about 30 minutes up to about 2 hours. Obviously, the higher the temperature, the shorter the heating time. It is preferred that the compositions be heated in the presence of an inert atmosphere such as nitrogen at atmospheric pressure. Higher or lower pressures may be employed if desired. The resultant compositions are cooled and then mixed with the organosilicon compound (2). The compositions may be stored at ambient temperature until they are ready to use. One advantage of the compositions of this invention over those known heretofore is that the compositions containing the organopolysiloxane (1), and/or carbon black (3), and catalyst (4) may be cooled and mixed immediately with tne organosilicon compound (2) and stored without any apparent evidence of crosslinking. In preparing these compositions, it is not essential that all the organopolysiloxane (1) and/or carbon black (3) be mixed with the catalyst (4) and heated. It is, however, preferred that at least one-half of the carbon black (3) and/or the organopolysiloxane (1) be mixed with catalyst (4) and heated and then the remainder of the organopolysiloxane (1) and/or carbon black (3) may be added to the heated mixture along with the organosilicon compound (2). Likewise, a portion of the catalyst (4) may be added to the organopolysiloxane (1) and the remainder may be admixed with the organosilicon compound (2) or added prior to, simultaneously with, or after the addition of the organosilicon compound (2). These compositions may be crosslinked by heating them to a temperature of from about 100"C to about 4000C, and more preferably to a temperature of from about 175 to 250"C, Crosslinking may also be achieved by other sources. Examples of other sources are ultraviolet, X-ray, microwave energy, alpha, beta and/or gamma radiation. When the compositions are to be cross-linked exclusively by radiation, a dose of from 5 to 8 megarad is preferred. Since the cross-linked electrically conductive elastomers of this invention have an electrical resistance of less than about 2 ohm-cm, they are especially useful in the preparation of electrically conductive applications, such as plates, coatings, bands, films, etc. Also, they may be used as cores for ignition cables, as gaskets for microwave ovens and in computer devices. The following examples are for purposes of illustration and are not to be construed as being limited to the following embodiments. In these examples all parts are by weight unless otherwise specified. Preparation of Platinum Catalyst The platinum catalyst used in the following examples was prepared in the following manner: An aminofunctional silicon composition is prepared by heating a mixture containing about 266.4 parts of octalncthyl- cyclotetrasiloxane1 22.4 parts of ss-(aminoethyl)- 7¯-aminopropyl- trimethoxysilane and 0.29 part of potassium hydroxide to a temperature of 1450C for three hours. After cooling the liquid product to room temperature, 0.29 part of acetic acid is added to neutralize the potassium hydroxide. The product is filtered and a liquid product having a viscosity of about 40 mpa.s at 25"C is recovered. About 28.8 parts of the aminofunctional silicon composition prepared above is added to a reactor under an atmosphere of nitrogen. About 100 parts of isopropanol, 1.04 parts of chloroplatinic acid hexahydrate, and 45 parts of toluene are added to the reactor and the reaction mixture is stirred for 30 minutes at 270C. The resultant transparent orange colored product which contains 0.16 weight-percent of platinum is identified as being an ammonium platinum complex. Example 1 About 100 parts of a trimethylsiloxy endblocked diorganopolysiloxane which consists of 99.86 mole percent of dimethylsiloxane units and 0.14 mole percent of methylvinylsiloxane units and having a plasticity value of about 105 are mixed with 45 parts of acetylene black having a surface area of about 65 m2/g, an average particle size of 420 + 25 millimicrons and a nigrometer value of 93 (available as qhawinìganX from Shawinigan Product Corporation), 12 parts of furnace black having a surface area of 1000 mê/g, a particle size of about 30 millimicrons (available from Armak Company as RetjenblackTM EC), and 2.5 parts of the platinum catalyst prepared above and heated for I hour at 183aC in the presence of nitrogen and then cooled to room temperature. To the resultant mixture are added 2.4 parts of WetjenblackTM EC, 0.8 parts of the platinum, catalyst and 1.6 parts of methylhydrogenpolysiloxane having a silicon to hydrogen ratio of 1:1 and a viscosity of 5.0 mpa.s at 25"C. The mixture is then stored at room temperature for 2 months. The plasticity values are shown in Table I After 3 months storage a sample of the mixture is extruded to form a film, which is press-cured at about 175OC for 10 minutes and then post-cured at 200C for about 4 hours. The electrical resistivity is shown in Table II. TABLE I Storage Time Plasticity 1 hour 1075 1 day 1164 5 days 1226 7 days 1238 14 days '1225 21 days 1236 1 month 1248 2 months 1348 TABLE II Cure Conditions Electrical Resistivity 10 min/1750C 1.5 ohm-cm 4 hrj2040C 1.4 ohm-cm Example 2 The procedure of Example 1 is repeated except that 13 parts of furnace black (KetjenDiackTM EC) are added to the compo- sition. The electrical resistivity is shown below. Cure Conditions Electrical Resistivity 10 min/1750C 1.6 ohm-cm 4 hr/2040C 1.4 ohm-cm Example 3 The procedure of Example 1 is repeated except that 43 parts of acetylene black (available as Shawinigan # black) and 12 parts parts of furnace black (available as Ketjenblack EC) are substituted for 45 parts of acetylene black and 14.4 parts of furnace black. The electrical resistance is shown below: Cure Conditions Electrical Resistivity 10 min/1750C 1.9 ohm-cm 4 hr/2040C 1.7'ohm-cm Example 4 The procedure of Example 3 is repeated except that 12.6 parts of furnace black (available as KetjenblackTM EC) are substituted for the 12 parts of furnace black. The electrical resistance is shown below: Cure Conditions Electrical Resistivity 10 mi/1750C 1.8 ohm-cm 4 hr/204 C 1.5 ohm-cm Example 5 The procedure of Example 1 is repeated except a solution of chloroplatinic acid in isopropanol in an amount such that 15 ppm of platinum are substituted for the platinum catalyst whose preparation is described above. The resultant composition shows no apparent crosslinking after being stored for 3 months. It is then extruded and press-cured for 10 minutes at 1750C and then post-cured at 204"C. The resultant elastomer has an electrical resistance of less than 2 ohm-cm. Example 6 The procedure of Example 5 is repeated except that 15 ppm of a platinum-ketone complex solution are substituted for the chloroplatinic acid. The platinum-ketone complex is prepared by adding one part of chloroplatinic acid (H2PtCl6.6H20) to 200 parts of cyclohexanone which has been heated to 800C. The solution is maintained at 800C for 45 minutes and then dried over anhydrous sodium sulfate. The resultant composition is stored for 2 months, then extruded, press-cured and post-cured It forms an elastomer having an electrical resistivity of less than 2 ohm-cm. Example 7 The procedure of Example 1 is repeated except that 45 parts of acetylene black having a surface area of about 65 mê/g, 12 parts of furnace black having a surface area of 1000 m2/g are combined with 2.5 parts of the ammonium platinum complex and heated for I hour at 183or in the presence of nitrogen and then cooled to room temperature. To the resultant mixture are added 100 parts of a trimethylsiloxy endblocked diorganopolysiloxane having 99.86 mole percent of dimethylsiloxane units and 0.14 mole percent of methylvinylsiloxane units and a Williams plasti TM city value of about 1û5, 2.4 parts of Ketjenblack EC, 0.8 parts of the ammonium platinum complex and 1.6.parts of methylhydrogen polysiloxane having a silicon to hydrogen ratio of 1:1 and a viscosity of 5.0 mPa.s at 250C. The plasticity value of the resultant composition is substantially unchanged after storing for 2 months at room temperature. Example 8 About 100 parts of a trimethylsiloxy endblocked diorganopolysiloxane which consists of 99.86 mole percent of dimethylsiloxane units and 0.14 mole percent of methylvinylsiloxane units and having a Williams plasticity value of about 105 are mixed with a solution of chloroplatinic acid in isopropanol in an amount such that 15 ppm of platinum is present and heated for 1 hour at 1830C in the presence of nitrogen and then cooled to room temperature. To the resultant mixture are added 45 parts of acetylene black having a surface area of about 65 mê/g, an average particle size of 420 + 25 millimicrons and a nigrometer value of 93 (available as Shawinigan black from Shawinigan Product Corporation), 15 parts of furnace black having a surface area of 1000 m2/g, a particle size of about 30 millimicrons TM (available from Armak Company as Ketjenblack EC), and 1.6 parts of methylhydrogenpolysiloxane having a silicon to hydrogen ratio of 1:1 and a viscosity of .5.0 mPa.s at 250C. The mixture is then stored at roan temperature for 2 months. The plasticity value of the resultant composition is substantially unchanged after storing for 2 months at room temperature. Comparison Example V1 About 100 parts of a trimethylsiloxy'endblocked diorganopolysiloxane which consists of 99.86 mole percent of dimethylsiloxane units and 0.14 mole percent of methylvinylsiloxane units and having a plasticity value of about 105 are mixed with 2.5 parts of the ammonium platinum complex prepared above and 31 parts of pyrogenically prepared silicon dioxide having a surface area of 200 m2/g and heated for 1 hour at 1830C in the presence of nitrogen. The mixture is cooled to room temperature and mixed with 0.5 parts of the ammonium platinum complex and 1 part of methylhydrogen polysiloxane having a silicon to hydrogen ratio of 1:1 and a viscosity of 5 mpa.s at 250C. A sample of the mixture is immediately extruded to form a film which is first heated for 10 minutes at 1750C and then at 2040C for about 4 hours. The electrical resistivity is shown in the following table. Cure Conditions Electrical Resistivity 10 min/1750C 1.4 X 1015 ohm-cm 4 hr/2050C 5.2 X 1015 ohm-cm Comparison Example V2 The procedure of Example V1 is repeated except that 25 parts parts of furnace black (available as Ketjenblack EC) are sub- stituted for the silicon dioxide. The electrical resistivity is shown below: Cure Conditions Electrical Resistivity 10 min/175 C 11.7 ohm-cm 4 hr/204 C 3.7 ohm-cm Comparison Example V3 The procedure of Example V1 is repeated except that 55 parts of acetylene black having a surface area of about 65 m2 Ig (available from Shawinigan Products Corporation) are substituted fai: the silicon dioxide., The electrical resistivity is shown below: : Cure Conditions Electrical Resistivity 10 min/1750C 7.8 ohm-cm 4 hr/2040C 3.9 ohm-cm Comparison Example V4 About 100 parts of a trimethylsiloxy endblocked diorganopolysiloxane which consists of 99.86 mole percent of dimethylsiloxane units and having a plasticity value of about 105 are mixed with 45 parts of acetylene black having a surface 2 area of about 65 m /g, an average particle size of 420 + 25 millimicrons and a nigrometer value of 93 (available as Shawini ga black from Shawinigan Product Corporation), 105 parts of 2 furnace black having a surface area of 1000 m /g, a particle size of about 30 millimicrons (available from Armak Company as Ketjenblack TM EC), 2.5 parts of the ammonium platinum complex prepared above, and 1.6 parts of methylhydrogenpolysiloxane having a silicon to hydrogen ratio of 1:1 and a viscosity of 5.0 mPa.s at 250C. The mixture cures within 10 minutes to a solid mass.

Claims: Claims: 1. A one-component composition which is curable to an elasto niter having an electrical conductivity of less than 2 ohm-cm based on organopolysiloxanes, crosslinking agents, carbon black and catalysts, characterized in that said composition comprises (1) an organopolysiloxane having silicon-bonded aliphatic unsaturation, (2) an organosilicon compound having silicon-bonded hydrogen atoms, (3) from 40 to 65 percent by weight of carbon black based on the weight of the organopolysiloxane (1) in which the carbon black consists of a mixture containing (a) from 20 to 50 percent by weight of furnace black and (b) from 80 to 50 percent by weight of acetylene black based on the total weight of the carbon black and (4) a catalyst capable of promoting the addition of the silicon-bonded hydrogen to the silicon-bonded aliphatically unsaturated groups. 2. The composition of claim 1, characterized in that the acetylene black has a surface area of from 40 to 1000 mê/g and the furnace black has a surface area of from 40 to 1500 mê/g. 3. The composition of claim 1, characterized in that the organopolysiloxane (1) is represented by the formula SiR R3SiO(SiR2O)nSiR3 where R is selected from the group consisting of monovalent hydrocarbon radicals and substituted monovalent hydrocarbon radicals having up to 18 carbon atoms in which an average of at least two R groups per molecule contain aliphatically unsaturated groups and n has a value of at least 10. 4. A method for preparing the one-component composition of claim 1 characterized -in (A)' heating- a mixture containing -(1) an organopolysiloxane having silicon-bonded aliphatically unsaturated groups, and (4) a catalyst which is capable of promoting the addition of silicon-bonded hydrogen to siliconbonded aliphatically unsaturated groups, to an elevated temperature, (B) cooling the resultant mixture and thereafter (C) adding (3) from 40 to 65 percent by weight of a mixture of carbon black based on the weight of the organopolysiloxane (t), in which the carbon black mixture contains from 20 to 50 percent by weight of furnace black and from 80 to 50 percent by weight acetylene black based on the weight of the carbon black mixture, and (2) an organosilicon compound having at least 3 silicon-bonded hydrogen atoms per molecule. 5. The method of claim 4, characterized in that a mixture containing organopolysiloxane (1), carbon black (3) and catalyst (4) is heated to an elevated temperature, cooled and then mixed with organosilicon compound (2). 6. The method of claim 4, characterized in that a mixture containing carbon black (3) and catalyst (4) is heated to an elevated temperature, cooled and then mixed with organopolysiloxane (1) and organosilicon compound (2). 7. The method of claim 4, characterized in that a portion of the organopolysiloxane (1) is heated with the catalyst (4) and thereafter the remainder of the organopolysiloxane (1), organosilicon compound (2) and carbon black (3) are added to the heated mixture after cooling. 8. The method of claim 4, characterized in that the organopolysiloxane (1) contains at least two silicon-bonded aliphatically unsaturated groups per molecule. 9. The method of claim 4, characterized in that the organopolysiloxane (1), carbon black (3) and catalyst (4) are heats ed to a temperature of at least 100"C. 10. Employment of the one-component composition which has been prepared to any of the proceeding methods for curing to an elastomer having an electrical conductivity of less than 2 ohmcm by heating said composition to a temperature of at least 100 C to promote cross-linking.

Inventors: SHEN, MING
Applicants: SWS SILICONES CORPORATION
Application year: 1983
Main classification: C08L83
IPC codes: C08L83, H01B1, C08K3