COMPOSITION FOR INSULATING ELECTRICAL WIRE AND CABLE

Abstract: Disclosed are a composition for insulating electrical wire and cable comprising an ethylene-vinyl acetate copolymer, at least one hindered phenolic compound, and a polyphosphite; a process for producing wire and cable insulated with the com­ position; and a cable insulated with the composition. Cables insulated with the composition, which composition has been irradiated after extrusion about a wire conductor, show good heat resistance and improved water resistance.

Description: Composition for Insulating Electrical Wire and Cable This invention relates to a composition useful as insulation for electrical wire and cable having good heat resistance and improved water resistance, and to a method for preparing wire and cable insulated with the composition. Conventionally, for use as electrical insulation, a nonconductive polymeric material, or a blend of two or more polymeric materials, is modified by the addition of specific additives to enhance or tone down the various physical characteristics of the polymeric material or blend so that the resulting composition will meet the needs of the specific environment in which wire and cable insulated with the composition is to be used. U.S. Patents, Nos. 3,419,524 and 3,375,304, to Larrison disclose polyphosphites of a group in which the polyphosphite of this invention appears to fall, and their use as stabilizers for polymers and to improve the fire resistance of, inter alia, polyolefins. However, these patents do not disclose a composition having good heat resistance and low water absorption characteristics suitable for use as insulation for electrical wire and cable. According to the invention a composition comprising a polymer and a polyphosphite stabilizer is characterized in that the polymer is an ethylene-vinyl acetate copolymer material which is capable of being cross-linked by ionizing radiation, the polyphosphite has the formula: EMI1.1 and is present in an amount from about 0.5% to about 5%, by weight of the copolymer, and the composition contains from about 0.5% to about 5%, by weight of the copolymer, of at least one hindered phenolic compound. This invention also comprises a method for producing the electrical wire and cable insulated with the composition by admixing a polymer and a polyphosphite stabilizer to form a composition, extruding the composition about a wire conductor, and subjecting the composition on the wire conductor to electron beam radiation or ionizing radiation to cause the desired amount of cross-linking which is characterized in that the polymer is an ethylene-vinyl acetate copolymer material capable of being cross-linked by radiation, the polyphosphite has the formula set forth above and is present in an amount from about 0.5% to about 5%, by weight of the copolymer, and the composition is admixed with from about 0.5% to about 5%, by weight of the copolymer, of at least one hindered phenolic compound. The composition exhibits good heat resistance and low water absorption and is useful as insulation for electrical wire and cable. All parts and percentages in this disclosure are by weight of the total composition unless otherwise indicated. Preferably the hindered phenolic compound and the polyphosphite are each present in an amount from about 0.5% to about 3%. The ethylene-vinyl acetate copolymer material comprises one or more ethylene-vinyl acetate copolymers. Preferably each copolymer has a polymerized vinyl acetate content of from about 8% to about 20% by weight of the copolymer, and most preferably from about 8% to about 12%. Suitable hindered phenols include tetrakis[methylene (3,5-di-t-butyl-4-hydroxy-hydrocinnamate)3methane and tris (3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate. The polyphosphite of this invention can be prepared by any of the methods set forth in the U.S. Patent, No. 3,419,524, to Larrison. Typically, the composition will contain conventional compounding ingredients, such as stabilizers, flame retardants, fillers, hydroperoxide decomposers, coupling agents, crosslinking agents, lubricants and other process aids, and mixtures thereof. Suitable stabilizers include zinc oxide and zinc sulfide. Typical flame retardant materials include halogenated aromatic compounds, such as decabromodiphenyl oxide and N, N'-ethylene-bis(tetrabromophthalimide), and inorganic compounds, such as antimony oxides. Antimony oxides, carbon black and the like can be used as fillers. Typical hydroperoxide decomposers include distearylthiodipropionate. Vinyl tris(2-methoxyethoxy) silane is a suitable coupling agent. Trimethylol propane trimethacrylate can be employed as the crosslinking agent. Suitable lubricants include zinc stearate. Ethylenepropylene-diene monomer elastomeric resins are typical process aids which can be added to the composition of this invention. The composition is used by extruding it as a coating about a wire conductor, such as copper, and irradiating it on the wire with a sufficient amount of ionizing radiation to achieve the degree of cross-linking desired. Two or more of these extrusion coated wire conductors can be used to form a cable by gathering the insulated wire conductors, optionally twisting them together, to form a bundle of suitable size, and extruding an outer layer of the same or different polymeric material about the bundled coated conductors. Suitable materials for a different polymeric outer layer are polyethylene, ethylene-propylene copolymer rubbers, and chlorosulfonated polyethylene. Optionally, the polymeric outer layer material can contain a filler. Suitable sources of ionizing radiation include high energy election accelerators, gamma rays and X-rays. Typically, a dose of from about 1 megarad to about 50 megarads for about 0.1 second to about 30 seconds is sufficient to cause the desired amount of cross-linking. The following examples illustrate aspects of the present invention. They are not intended to limit the invention. Modifications of the specific compositions, insulated conductors, cables and procedures of these examples can be made without departing from the spirit and scope of this invention. Examples 1-3 This example illustrates three specific embodiments of the composition of this invention, and how to prepare them. The specific components and the proportions of each component used for each composition are set forth below in Table I. Table I Examples 1 2 3 Concentration in parts Components by weight Ethylene-vinyl acetate 100 100 100 copolymer Tris(3,5-di-t-butyl-4- 2 2 hydroxybenzyl)isocyanurate Tetrakis[methylene(3,5-di-t- 2 - 2 butyl-4-hydroxy hydrocinnamate)] methane Polyphosphite 2 2 2 Decabromodiphenyl oxide 60 60 60 Antimony trioxide 30 30 30 Zinc oxide 4 4 4 Vinyl-tris(2-methoxy- I 1 1 ethoxysilane Trimethylol propane 6 6 6 trimethacrylate The embodiments of Table 1 are made by placing the components in a mixer and stirring until a homogeneous mixture is obtained. Wire specimens are insulated by extrusion coating the compositions about a copper wire conductor and radiating until the desired extent of cross-linking of the composition is achieved. In actual work with wire insulated with the compositions of this invention, which compositions have been subsequently cross-linked by ionizing radiation, the typical results set forth below were obtained. The water absorption of each of the wire specimens insulated with the compositions of Examples 1, 2, and 3 as set forth in Table I, and of each of the three control specimens insulated with the compositions as set forth in Table I for Examples 1, 2, and 3, respectively, except that in each of the control specimens distearyl pentaerythritol diphosphite is used instead of the polyphosphite of this invention was tested. Three sections, approximately 15 ft. in length, of each of the insulated wire specimens are used to conduct the water absorption test, 10 ft. of which is submerged in a water bath maintained at 750C. throughout the test. The three sections of each of the specimens are tested according to the procedures of the IPCEA accelerated water absorption test, a standard test for water absorption. Basically this test is an electrical measure of the water absorption of the insulation material. The IPCEA test requires that the 1 to 14 day change in capacitance be no greater than 3%, and that the 7 to 14 day change in capacitance be no greater the 1.5%. The results are shown in Table II. Table II IPCEA water absorption, % change Ex. C.S.* Ex. C.S. Ex. C.S. 1 1 2 2 3 3 Test I 1-14 days zero 13.81 zero 5.03 2.03 7.92 7-14 days zero 2.99 0.16 1.39 0.55 2.14 Test II 1-14 days zero 13.15 3.92 6.52 2.24 6.64 7-14 days zero 3.84 0.63 0.88 0.36 2.18 Test III 1-14 days 0.17 9.51 0.63 4.75 3.20 6.59 7-14 days 1.22 3.11 zero 1.96 1.48 2.17 *C.S. = control specimen Typical heat resistance of wire specimens, except that six sections, approximately 5" in length, of each of the wire specimens are used, is shown in Table III below. The tensile strength and elongation of each section of each wire specimen was measured by an Instron tensile tester. Each of the 5 sect ions was placed in an oven maintained at the temperature indicated in the data set forth in Table III throughout the period of time indicated in Table III. At the end of each test period, each of the wire specimen sections was removed from the oven, and the tensile strength and elongation measured by an Instron tensile tester. The wire specimens sections gave the results set forth below in Table III. Table III Heat Resistance Ex. C.S.* Ex. C.S. Ex. C.S. 1 1 2 2 3 3 Initial Tensile Strength, psi 2251 2513 2176 2281 2518 2467 Initial % Elongation 437 420 407 403 470 433 Air Aging, 3 days at 1800C Tensile 1978 2357 - - 2233 2307 % Elongation 377 387 - - 407 443 Air Aging, 5 days at 1800C Tensile, psi 816 971 - - 925 % Elongation 10 33 - - 10 Air Aging, 7 days at 1580C. Tensile, psi 2053 2331 1761 1910 2339 2387 % Elongation 467 490 337 387 463 473 Air Aging, 14 days at 1580C Tensile, psi 2078 2422 777 796 2287 2334 % Elongation 373 400 - 7 387 417 Air Aging, 21 days at 1580C Tensile, psi 1855 2383 - - 1953 % Elongation 297 367 0 - 323 Air Aging, 25 days at 1580C Tensile, psi 1187 2331 - - 1388 % Elongation 12 353 - - 17 *C.S.=control specimen Thus, it can be seen from the water absorption test data set forth in Table II that the control specimens insulated with compositions containing the distearyl pentaerythritol diphosphite and at least one hindered phenolic compound evidenced very poor water resistance, whereas the wire specimens insulated with compositions containing the polyphosphite instead of the distearyl pentaerythritol diphosphite together with at least one hindered phenolic compound evidenced good water resistance. The heat resistance test data set forth in Table III show that the control specimens insulated with compositions containing the distearyl pentaerythritol diphosphite and at least one hindered phenolic compound generally had good heat aging, whereas the wire specimens insulated with compositions containing the polyphosphite in place of the distearyl pentaerythritol diphosphite in combination with at least one hindered phenolic compound usually evidenced somewhat less, but still good, thermal stability. It should be noted, however, that the wire specimen insulated with the composition of Example 3 evidenced better long range heat resistance than control specimen 3. Example 4 This example illustrates another embodiment of the composition of this invention. The composition is prepared according to the procedure set forth in Examples 1-3 using the components set forth below. Concentration in parts Components by weight Ethylene-vinyl acetate 90 copolymer Tris(3,5-di-t-butyl-4- 2 hydroxybenzyl)isocyanurate Tetrakis[methylene(3,5-di-t- 2 butyl- 4-hydroxy- hydrocinnamate) j methane Polyphosphite 2 N, N'-ethylenebis(tetra- 60 bromophthalimide) Antimony trioxide 30 Zinc sulfide 4 Vinyl-tris(2-methoxy- 1 ethoxy)silane Tr imethylol propane 6 trimethacrylate Distearylthiodipropionate 1 Zinc stearate 1 Ethylene-propylene-diene 10 monomer elastomeric resin* *Marketed under the trademark Nordel 2722 by E. I. duPont de Nemours & Co. The water absorption and heat resistance of wire specimens insulated with the composition of Example 4, which composition was subsequently cross-linked by ionizing radiation, were also tested in the manner indicated above for the other wire specimens. Typical results of these tests are set forth in Table IV. Table IV IPCEA water absorption, % change Test I 1-14 days 1.12 7-14 days zero Test II 1-14 days 2.07 7-14 days 0.18 Test III 1-14 days 1.50 7-14 days 0.37 Heat Resistance Initial Tensile Strength, psi 2777 Initial % Elongation 410 Air Aging, 3 days at 1800C Tensile 2323 % Elongation 307 Air Aging, 5 days at 1800C Tensile, psi 2036 % Elongation 313 Air Aging, 7 days at 1580C. Tensile, psi 2445 % Elongation 365 Air Aging, 14 days at 1580C Tensile, psi 2539 % Elongation 372 Air Aging, 21 days at 1580C Tensile, psi 1932 % Elongation 277 Air Aging, 25 days at 1580C Tensile, psi 1451 % Elongation 180 As the test data set forth in Table IV show, the wire specimen insulated with the composition of Example 4 of this invention evidenced good water resistance and good thermal resistance. Thus, this invention provides useful compositions having good heat resistance and improved water resistance. Other features, advantages and specific embodiments of this invention will become readily apparent to those exercising ordinary skill in the art after reading the foregoing disclosures. In this regard, while specific embodiments of this invention have been dscribed in considerable detail, variations and modifications of these embodiments can be effected without departing from the spirit and scope of the invention as disclosed and claimed.

Claims: 1. A composition for insulating electrical wire and cable which comprises a polymer and a polyphosphite stabilizer is characterized in that the polymer is an ethylenevinyl acetate copolymer capable of being cross-linked by radiation, the polyphosphite has the formula: EMI11.1 and is present in an amount and from about 0.5% to about 5%, by weight of the copolymer, and the composition contains from about 0.5% to about 5%, by weight of the copolymer, of at least one hindered phenolic compound. 2. The composition of claim 1 wherein the ethylenevinyl acetate copolymer has a polymerized vinyl acetate content from about 8% to about 20% by weight of the copolymer. 3. The composition of claim 2 wherein the ethylenevinyl acetate copolymer has a polymerized vinyl acetate content from about 8% to about 12% by weight of the copolymer. 4. A cable which comprises at least two wire conductors and an outer layer of an extruded polymeric material is characterized in that the wire conductors are insulated with the composition of claim 1. 5. A cable which comprises at least two wire conductors and an outer layer of an extruded polymeric material is characterized in that the wire conductors are insulated with the composition of claim 2. 6. A process for making an insulated electrical cable by admixing a polymer and a polyphosphite stabilizer to form a composition; extruding the composition about a wire conductor; and irradiating the composition on the wire conductor until the desired amount of cross-linking has been achieved is characterized in that the polymer is an ethylene-vinyl acetate copolymer capable of being cross-linked by radiation, the polyphosphite has the formula: EMI12.1 and is present in an amount from about 0.5% to about 5%, by weight of the copolymer, and the composition is further mixed with from about 0.5* to about 5%, by weight of the copolymer, of at least one hindered phenolic compound. 7. The process of claim 6 wherein the ethylene-vinyl acetate copolymer has a polymerized vinyl acetate content from about 8% to about 20% by weight of the copolymer.

Inventors: MCRAE, HOWARD FRANCIS
Applicants: CHAMPLAIN CABLE CORPORATION
Application year: 1984
Main classification: H01B3
IPC codes: C08K5, C08L101, C08L23, C08L31, H01B3