A FLAME-RETARDANT SILICONE FLUID COMPOSITION

Abstract: Silicone fluid-based electric insulating oils can be imparted with greatly enhanced flame retardancy when the base organopolysiloxane contains 0.1 to 30% by moles of vinyl groups relative to the monovalent hydrocarbon groups bonded to the silicon atoms and is admixed with a platinum compound soluble therein, such as chloroplatinic acid, dissolved therein in a specified amount. The flame retardancy of the organopolysiloxane/platinum compound composition can be further improved by the addition of a low-viscosity fluorinated hydrocarbon oil such as an oligomeric polymer of chlorotrifluoroethylene.

Description: The present invention relates to a flame retardant silicone fluid composition or, more particularly, to a flame retardant silicone fluid composition which can be used as an insulating oil in electric equipment. Various kinds of oily materials have hitherto been used as an insulating oil in electric equipment such as electric power cables, capacitors and transformers, for example, including mineral oils, phosphate ester oils, aromatic hydrocarbon oils, chlorinated synthetic oils, silicone fluids and fluorocarbon oils, for example. These conventional insulating oils have their respective problems and disadvantages from the standpoint of practical use. For example, mineral oils, aromatic hydrocarbon oils and low-viscosity silicone fluids are inflammable and chlorinated synthetic oils are notoriously toxic, while fluorocarbon oils have the problem of unduly increasing the weight of the electric equipment filled therewith due to the outstandingly high specific gravity thereof in addition to impractical expensiveness. Silicone fluids having a high viscosity of, for example, about 50 x 10⁻⁶ m²/s (50 centistokes) or higher at 25°C are self-extinguishable and have a relatively high flash point so that they can be more flame retardant than the above named insulating oils of other types. The high-viscosity silicone fluids, however, are not always fully flame retardant and are not usable as a highly reliable flame retardant insulating oil because different methods for the evaluation of the flame retardancy thereof may give different results. Flame retardancy of insulating oil is evaluated by several different methods including the flash point method, ignition point method, oxygen index method, glass tape method and the like, of which the horizontal glass tape method specified in JIS C 2101 may be the most reliable method although a program sponsored by IEC is now under progress to establish a reliable testing method for the evaluation of the flame retardancy of various electric insulating oils. It can be that high-viscosity silicone fluids tested by the horizontal glass tape method (in which a tape of woven glass fibres is soaked with the silicone fluid and held horizontaly to be ignited) and classified as flame retardant are not flame retardant when tested by the vertical glass tape method, in which the silicone fluid-soaked glass tape is held vertically to be ignited. Flame retardancy of a silicone fluid can be enhanced by admixing the fluid with a flame retardant agent and several compounds are proposed as flame retardant agent in, for example, Japanese Patent Kokai 57-28157 and Japanese Patent Publications 49-39173, 51-20720 and 59-226408. However, flame retardant agents in the prior art each have disadvantages. The flame retardant silicone fluid composition provided by the present invention consists essentially of, in admixture: (a) 100 parts by weight of an organopolysiloxane represented by the average unit formula R a Si0 (4-a) /2 , (I) in which R is a substituted or unsubstituted monovalent hydrocarbon group, from 0.1 to 30% by moles of the groups denoted by R in a molecule being vinyl groups, and a is a positive number in the range from 1.8 to 2.3 and having a viscosity in the range from 5 to 1000 x 10⁻⁶ m²/s (5 to 1000 centistokes) at 25°C; and (b) a platinum compound soluble in the organopolysiloxane and in an amount in the range from 0.0001 to, preferably, 0.1 part by weight calculated as platinum. The flame retardancy of the above described silicone fluid composition can be further enhanced when the composition is admixed with (c) from 10 to, preferably, 50 parts by weight of a fluorinated hydrocarbon oil. As is described in the above given summary, the essential ingredients of the inventive flame retardant silicone fluid composition are the specified organopolysiloxane as the base ingredient and the platinum compound in admixture as an additive. The organopolysiloxane as the base material is represented by the above given average unit formula (I), in which the symbol R denotes a substituted or unsubstituted monovalent hydrocarbon group exemplified by alkyl groups, e.g., methyl, ethyl, propyl and butyl groups, cycloalkyl groups, e.g., cyclohexyl group, alkenyl groups, e.g., vinyl and allyl groups, and aryl groups, e.g., phenyl and tolyl groups, as well as those substituted groups obtained by replacing a part or all of the hydrogen atoms in the above named hydrocarbon groups with substituent atoms and/or groups such as halogen atoms and cyano groups, e.g., haloalkyl, for example chloromethyl and 3,3,3-trifluoropropyl groups, and the subscript a is a positive number in the range from 1.8 to 2.3. Although the organopolysiloxane molecules may contain two kinds or more of the hydrocarbon groups denoted by R, from 0.1% to 30% by mole of the groups denoted by R in a molecule should be vinyl groups, the remainder being preferably methyl groups. It is a quite unexpected discovery that no useful flame retardancy can be imparted to the organopolysiloxane fluid when the proportion of vinyl groups in the monovalent hydrocarbon groups bonded to the silicon atoms is smaller than about 0.1 mole %. When the content of vinyl groups in the organopolysiloxane is too large, on the other hand, the heat resistance of the silicone fluid composition may be somewhat decreased with possible increase in the viscosity of the composition during use at an elevated temperature. The viscosity of the organopolysiloxane or the average degree of polymerization thereof is not particularly limited and depends on the intended application of the flame-retardant silicone fluid composition, but the viscosity should at least generally be in the range from 5 to 1000 x 10⁻⁶ m²/s (5 to 1000 centistokes) at 25°C when the composition is used as an insulating oil in electric equipment. The component (b) in the inventive fluid composition is a platinum compound soluble in the organopolysiloxane, so that the quantity of the compound used may dissolve in the organopolysiloxane. As a general guide, platinum compounds with suitable solubility are also soluble in an organic solvent and are exemplified by those compounds used as a catalyst in the hydrosilation reaction, including chloroplatinic acid as such, chloroplatinic acid modified with an alcohol or forming a complex with a vinylsiloxane, and platinum-triphenyl phosphine complex of the formula Pt.P(C₆H₅)₃ disclosed in U.S. Patents No. 3,159,601, No. 3,159,662 and No. 3,775,452 and elsewhere. These platinum compounds should be admixed with and dissolved in the organopolysiloxane as the component (a). The amount of the platinum compound added to the organopolysiloxane should be in the range from 0.0001 to, usually, 0.1 part by weight or, preferably, from 0.001 to 0.01 part by weight calculated as platinum per 100 parts by weight of the organopolysiloxane. When the amount of the platinum compound is too small, the desired effect of flame retardancy can hardly be obtained as a matter of course. On the other hand, no further additional improvement in the flame retardancy can apparently be obtained by increasing the amount of the platinum compound over the above mentioned upper limit there being an economic disadvantage in exceeding the limit because of cost of the platinum compound. In any event the platinum compound will be present as an additive (in a small amount). Further, it has also been discovered unexpectedly that the flame retardancy of the above described flame-retardant silicone fluid composition can be further increased by including in the composition a fluorinated hydrocarbon oil, for example an oligomer of chlorotrifluoroethylene. The oligomer should have a viscosity preferably in the range from 5 to 50 x 10⁻⁶ m²/s (5 to 50 centistokes) at 25°C corresponding to a degree of polymerization of 3 to 5 since a fluorinated hydrocarbon oil having too high a viscosity is poorly miscible with the organopolysiloxane. The amount of the fluorinated hydrocarbon oil in the inventive fluid composition should be in the range from 10 to, preferably, 50 parts by weight per 100 parts by weight of the organopolysiloxane. When the amount is smaller than the above mentioned lower limit, no substantial improvement in the flame retardancy can be obtained thereby. On the other hand, no further additional improvement can be expected by increasing the amount of the fluorinated hydrocarbon oil in excess of the above mentioned upper limit. In the following, the flame retardant silicone fluid composition of the present invention is described in more detail by way of examples, in which the term "parts" always refers to "parts by weight" and each of the values of viscosity was obtained by the measurement at 25°C. The flame retardancy of the silicone fluids prepared in the examples was evaluated by one or more of the following combustion testing methods. (1) Horizontal method Measurement was performed according to the procedure specified in JIS C 2101. (2) Vertical method The same glass fibre tape as used in the above mentioned horizontal method was soaked with a specified amount of the fluid composition and vertically hung to be ignited at the lower end by a flame and to examine the combustibility. (3) Oxygen index method The oxygen index of the fluid composition was measured in an apparatus therefor specified in JIS K 7201 using a metal combustion cell and a glass fibre wick having a diameter of 2.5 mm and a length of 25 mm protruding to a length of 3 mm. (4) Asbestos method An asbestos mat of 20 mm by 40 mm wide having a thickness of 1 to 2 mm and soaked with the fluid composition was put on two horizontal wire bars in parallel and ignited by using a propane gas burner to examine the combustibility. Examples 1 to 9 and Comparative Examples 1 to 8. Nine methyl vinyl polysiloxane fluids having different viscosities and different contents of vinyl groups as indicated in Table 1 below were each admixed with chloroplatinic acid in an amount indicated in Table 1 and the flame retardancy thereof was evaluated by the horizontal method and vertical method to find that each of the fluid compositions was satisfactorily self-extinguishable (Examples 1 to 9). For comparison, the same methyl vinyl polysiloxane fluids as used in the above described Examples 1 to 3 and 7 to 9 were each subjected to the combustion tests without admixture of chloroplatinic acid (Comparative Examples 1 to 6) For further comparison, two dimethyl polysiloxane fluids having a viscosity of 1000 x 10⁻⁶ m²/s and 350 x 10⁻⁶ m²/s (1000 and 350 centistokes) were each admixed with 100 ppm as platinum of chloroplatinic acid and the flame retardancy thereof was evaluated in the same manner as in Examples 1 to 9 (Comparative Examples 7 and 8). The results in these comparative tests were that each of the fluids was self-extinguishable by the horizontal method but combustible by the vertical method. Example No. Organopolysiloxane Chloroplatinic acid added, ppm as Pt Viscosity, (centistokes) 10⁻⁶ m²/s Content of vinyl groups, % by moles 1 775 1 50 2 679 5 100 3 661 10 10 4 500 3 150 5 362 5 150 6 140 5 150 7 350 1 50 8 200 5 50 9 150 10 100 Examples 10 to 13 and Comparative Examples 9 to 11. Methyl vinyl polysiloxane fluids having a viscosity of 20 x 10⁻⁶ m²/s and 50 x 10⁻⁶ m²/s (20 to 50 centistokes) and a content of vinyl groups of 10% or 20% by mole were admixed with chloroplatinic acid in an amount of 50 or 100 ppm as platinum as indicated in Table 2 and each subjected to the evaluation of the flame retardancy by the horizontal method, vertical method and oxygen index method (Examples 10 to 13). The results were that the fluid compositions in Examples 10 to 12 were each self-extinguishable by the horizontal method but combustible by the vertical method while the fluid composition in Example 13 was combustible in both of the horizontal and vertical methods. The oxygen indices are shown in Table 2. For comparison, the same organopolysiloxane fluids as used in Examples 10 and 12 were subjected to the same tests as above without addition of chloroplatinic acid (Comparative Examples 9 and 10, respectively). For further comparison, a dimethyl polysiloxane fluid having a viscosity of 50 x 10⁻⁶ m²/s (50 centistokes) was admixed with chloroplatinic acid in an amount of 100 ppm as platinum and subjected to the same tests (Comparative Example 11). The results were that these comparative fluids were combustible in both of the horizontal method and vertical method. The oxygen indices of these comparative fluids are shown in Table 2. Organopolysiloxane Chloroplatinic acid added, ppm as Pt Oxygen index Viscosity, (centistokes) 10⁻⁶ m²/s Content of vinyl groups, % by moles Example 10 50 20 50 43-45 11 30 10 50 42-44 12 25 20 50 42-44 13 20 20 100 40-42 Comparative Example 9 50 20 0 38-40 10 25 20 0 36-38 11 50 0 100 36-38 Examples 14 to 17. Methyl vinyl polysiloxane fluids, in each of which the content of vinyl groups relative to the hydrocarbon groups was 20% by mole having a viscosity of 16 to 26 x 10⁻⁶ m²/s (16 to 26 centistokes) were each admixed with chloroplatinic acid in an amount indicated in Table 3 below together with an oligomeric chlorotrifluoro ethylene polymer having a viscosity of 20 x 10⁻⁶ m²/s (20 centistokes) referred to as the fluorine polymer herein-below, in an amount also indicated in Table 3 per 100 parts of the methyl vinyl polysiloxane fluid. The thus prepared silicone fluid compositions were each subjected to the evaluation of the flame retardancy by the horizontal method and asbestos method to find that the fluids in Examples 14 and 15 were self-extinguishable in both of the testing methods while the fluids in Examples 16 and 17 were self-extinguishable by the horizontal method but combustible by the asbestos method. Example No. Viscosity of organopolysiloxane, (centistokes) 10⁻⁶ m²/s Chloroplatinic acid added, ppm as Pt Fluorine polymer added, parts 14 16 50 50 15 20 70 30 16 24 90 10 17 26 100 0

Claims: A flame retardant silicone fluid composition which consists essentially of: (a) 100 parts by weight of an organopolysiloxane represented by the average unit formula R a SiO (4-a)/2 , in which R is a substituted or unsubstituted monovalent hydrocarbon group, from 0.1 to 30% by mole of the groups denoted by R in a molecule being vinyl groups, and a is a positive number in the range from 1.8 to 2.3 and having a viscosity in the range from 5 to 1000 x 10⁻⁶ m²/s (5 to 1000 centistokes) at 25°C; and (b) a platinum compound dissolved in the organopolysiloxane in an amount of at least 0.0001 part by weight calculated as platinum. A composition as claimed in claim 1 wherein the groups denoted by R other than vinyl groups are methyl groups. A composition as claimed in claim 1 or claim 2 wherein the platinum compound is chloroplatinic acid. A composition as claimed in any one of the preceding claims which contains not more than 0.1 part by weight calculated as platinum of the platinum compound. A composition as claimed in any one of the preceding claims which further comprises: (c) at least 10 parts and optionally no more than 50 parts by weight of a fluorinated hydrocarbon oil. A composition as claimed in claim 5 wherein the fluorinated hydrocarbon oil is an oligomeric polymer of chlorotrifluoroethylene. A composition as claimed in claim 6 wherein the oligomeric polymer of chlorotrifluoroethylene has a viscosity in the range from 5 to 50 x 10⁻⁶ m²/s (5 to 50 centistokes) at 25°C. The use of a composition as claimed in any one of the preceding claims as an electric insulating oil. An electric power cable, capacitor, transformer or other electric equipment containing a composition as defined in any one of claims 1 to 7.

Inventors: HIRAI, MOTOHIKO, MORI, SHIGERU
Applicants: SHIN-ETSU CHEMICAL CO., LTD.
Application year: 1987
Main classification: C08L83
IPC codes: H01B3, C08K3, C08K5, C08L83