Title of Invention	IMPROVED STRIPPABLE CABLE SHIELD COMPOSITIONS
Abstract	An insulation shield material is provided having improved performance without the need for expensive additives, complex polymer formulations, or specially prepared carbon black. The semiconductive composition used to make the strippable semiconductive insulation shield layer in contact with the outer surface of a wire and cable insulation layer has a base polymer having a weight average molecular weight of not more than 200,000, an adhesion modifying additive system having at least two components and a conductive carbon black. Each of the adhesion modifying additive system components is different from the base polymer. The first component of the adhesion modifying additive system contains a hydrocarbon wax or ethylene vinyl acetate wax and ...

Title of Invention

IMPROVED STRIPPABLE CABLE SHIELD COMPOSITIONS

Abstract

An insulation shield material is provided having improved performance without the need for expensive additives, complex polymer formulations, or specially prepared carbon black. The semiconductive composition used to make the strippable semiconductive insulation shield layer in contact with the outer surface of a wire and cable insulation layer has a base polymer having a weight average molecular weight of not more than 200,000, an adhesion modifying additive system having at least two components and a conductive carbon black. Each of the adhesion modifying additive system components is different from the base polymer. The first component of the adhesion modifying additive system contains a hydrocarbon wax or ethylene vinyl acetate wax and ...

Full Text	WO 2006/119067 PCT/US2006/016350 IMPROVED STRIPPABLE CABLE SHIELD COMPOSITIONS FIELD OF THE INVENTION [0001] The invention relates to semiconducting insulation shield compositions for electric power cables having a base polymer and a two-component adhesion modifying additive system. The invention also relates to the use of these semiconducting insulation shield compositions to manufacture semiconductive insulation shields for use in electric cables, electric cables made from these compositions and methods of making electric cables from these semiconducting insulation shield compositions. The semiconducting insulation shield compositions of the invention may be used as strippable insulation shields in power cables, primarily with medium voltage cables having a voltage from about 5 kV up to about 100 kV. BACKGROUND OF THE INVENTION [0002] A typical insulated electric power cable generally comprises one or more conductors in a cable core that is surrounded by several layers of polymeric materials including an inner semiconducting shield layer (conductor or strand shield), an insulating layer, an outer semiconducting shield layer (insulation shield), a metallic wire or tape shield used as the ground phase, and a protective jacket. Additional layers within this construction such as moisture impervious materials, are often incorporated. The invention pertains to the outer semiconducting insulation shield layer, i.e., the insulation shield and cables made with the outer semiconducting insulation shield in accordance with the invention. [0003] In general, semiconducting dielectric insulation shields can be classified into two distinct types, the first type being a type wherein the dielectric shield is securely bonded to the polymeric insulation so that stripping the dielectric shield is only possible by using a cutting tool that removes the dielectric shield alone with some of the cable insulation. This type of dielectric shield is preferred by companies that believe that this adhesion minimizes 1 WO 2006/119067 PCT/US2006/016350 the risk of electric breakdown at the interface of the shield and insulation. The second type of dielectric shield is the "strippable" dielectric shield wherein the dielectric shield has a defined, limited, adhesion to the insulation so that the strippable shield can be peeled cleanly away from the insulation without removing any insulation. Current strippable shield compositions for use over insulation materials selected from polyethylene, cross-linked polyethylenes, or one of the ethylene copolymer rubbers such as ethylene-propylene rubber (EPR) or ethylene-propylene diene terpolymer (EPDM) are usually based on an ethylene- vinyl acetate (EVA) copolymer base resin rendered conductive with an appropriate type and amount of carbon black. [0004] Strippable shield formulations of EVA and nitrile rubbers have been described by Ongchin, U.S. Pat. Nos. 4,286,023 and 4,246,142; Burns et al. EP Application No. 0,420,271B, Kakizaki et al U.S. Pat. No. 4,412,938 and Janssun, U.S. Pat. No. 4,226,823, each reference being herein incorporated by reference into this application. A problem with these strippable shield formulations of EVA and nitrile rubber is that the EVA's needed for this formulation have a relatively high vinyl acetate content to achieve the desired adhesion level with the result that the formulations are more rubbery than is desired for high speed extrusion of a commercial electric cable. [0005] Alternative adhesion-adjusting additives have also been proposed for use with EVA, for example waxy aliphatic hydrocarbons (Watanabe et al. U.S. Pat. No. 4,933,107, herein incorporated by reference); low-molecular weight polyethylene (Burns Jr., U.S. Pat. No. 4,150,193 herein incorporated by reference); silicone oils, rubbers and block copolymers that are liquid at room temperature (Taniguchi et al. U.S. Pat. No. 4,493,787 herein incorporated by reference); chlorosulfonated polyethylene, ethylene-propylene rubbers, polychloroprene, styrene-butadiene rubber, and natural rubber. However, the only adhesion-adjusting additives that appear to have found commercial acceptance have been paraffin waxes. 2 WO 2006/119067 PCT/US2006/016350 [0006] U.S. Patent No. 6,284,374 to Yamazaki, et al discloses a multi-component polymer composition for use in strippable semiconductive shields suitable for a polyolefin-insulated wire and cable crosslinked by silane grafting/water crosslinking. The main polymer component of the composition is mainly composed of an ethylene/vinyl acetate copolymer having a weight average molecular weight not less than 300,000. [0007] Commonly assigned U.S. Patent Nos. 6,274,066 and 6,013,202 disclose a strippable semiconductive shield made from a base polymer and an adhesion modifying additive. [0008] US Published Patent Application 2004/0217329A1 to Easter discloses a two component base polymer together with adhesion adjusting additives [0009] WO 2004/088674 Al to Person discloses a strippable semiconductive shield made from a base polymer which is a soft polymer and a hard polymer. [0010] The use of amide wax additives in a conductor shield has been proposed in commonly assigned U.S. Patent No. 6,491,849 to Easter to improve aging characteristics of the electric cable. [0011] In the manufacture of commercial quantities of electric cable, minor cost improvements to polymeric compositions where the resulting composition and/or cable employing the composition have acceptable physical or electric properties are considered significant advances in the art. This is because the competitive environment places great demands on product pricing as well as performance and longevity. An improvement which not only reduces cost but improves properties is considered extremely significant, as it positively impacts both cost and quality. [0012] It would be desirable to develop lower cost, easier to compound, strippable semiconductive insulation shield compositions. Other proposals require complicated compounding methods or additives that are, on average, twice as expensive as the base polymers when used to achieve lower adhesion and/or strippability. 3 WO 2006/119067 PCT/US2006/016350 [0013] A novel two component adhesion modifying additive system for strippable insulation shields is proposed which provides remarkable adhesion results while also improving cost over earlier systems. SUMMARY OF THE INVENTION [0014] The invention provides an insulation shield material with improved performance without the need for expensive additives, complex polymer formulations, or specially prepared carbon black. [0015] The invention also provides a semiconductive composition for use as a strippable semiconductive insulation shield layer in contact with the outer surface of a wire and cable insulation layer, the composition comprising a base polymer having a weight average molecular weight of not more than 200,000 and an adhesion modifying additive system comprising at least two components, each of said an adhesion modifying additive system components being different from said base polymer, said first component comprising a hydrocarbon wax or ethylene vinyl acetate wax and said second component comprising an amide wax; and a conductive carbon black. [0016] In embodiments of the invention the base polymer is selected from the group consisting of ethylene vinyl acetate copolymers, ethylene alkyl acrylate copolymers wherein the alkyl group is selected from Cl to C6 hydrocarbons, ethylene alkyl methacrylate copolymers wherein the alkyl group is selected from Cl to C6 hydrocarbons and ethylene alkyl acrylate alkyl methacrylate terpolymers wherein the alkyl group is independently selected from Cl to C6 hydrocarbons, and mixtures thereof. Preferably the base polymer comprises ethylene vinyl acetate copolymer having from about 28% to about 40% vinyl acetate. 4 WO 2006/119067 PCT/US2006/016350 [0017] In preferred embodiments of the invention the first component of the adhesion modifying additive system is an ethylene vinyl acetate wax having a vinyl acetate content of from about 10% to about 20% vinyl acetate. [0018] The amide wax may be selected from stearamide, oleamide, erucamide, ethylene bis- stearamide, ethylene bis-oleamide, ethylene bis-erucamide, behenamide, and mixtures thereof. [0019] An electrically conductive cable utilizing the insulation shield in accordance with the invention is also provided. DETAILED DESCRIPTION OF THE INVENTION [0020] Conventional electrical insulators used in medium voltage cables include polyethylenes, cross-linked polyethylenes (XLPE), ethylene-propylene rubbers and ethylene propylene diene rubbers (EPDM rubbers). The term polyethylene is meant to include both polymers and copolymers wherein ethylene is the major component, this would include, for example metallocene or single site catalyzed ethylenes that are copolymerized with higher olefins. [0021] The polymers (other than those described below for use in the semiconductive composition for use as a strippable semiconductive insulation shield layer in accordance with the invention) utilized in the protective jacketing, insulating, conducting or semiconducting layers of the inventive cables may be made by any suitable process which allows for the yield of the desired polymer with the desired physical strength properties, electrical properties, tree retardancy, and melt temperature for processability. [0022] The strippable semiconductive insulation shields of the invention comprise a base polymer, a two-component adhesion modifying additive system and conductive carbon blacks. The conductive carbon blacks are added in an amount sufficient to decrease the 5 WO 2006/119067 PCT/US2006/016350 electrical resistivity to less than 550 ohm-meter. Preferably the resistivity of the semiconductive shield is less than about 250 ohm-meter and even more preferably less than about 100 ohm-meter. SHIELD POLYMERS [0023] The invention provides a semiconductive resin composition for use as a semiconductive layer in contact with a wire and cable insulation layer. The resin composition comprises about 40 to about 85 weight percent, based upon the weight of the semiconductive resin composition, of a base polymer. [0024] The base polymer has a weight average molecular weight of not more than 200,000, preferably not more than 150,000 and more preferably not more than 100,000. [0025] The base polymer may be selected from ethylene vinyl acetate copolymers, ethylene alkyl acrylate copolymers wherein the alkyl group is selected from Cl to C6 hydrocarbons, ethylene alkyl methacrylate copolymers wherein the alkyl group is selected from Cl to C6 hydrocarbons and ethylene alkyl acrylate alkyl methacrylate terpolymers wherein the alkyl group is independently selected from Cl to C6 hydrocarbons. [0026] The ethylene vinyl acetate copolymer used in the base polymer can be any EVA copolymer with the following properties: the ability to accept high loadings of conductive carbon filler, elongation of 150 to 250 percent and sufficient melt strength to maintain its shape after extrusion. EVA copolymers with vinyl acetate levels above about 25 percent and below about 45 percent having these properties are known. Accordingly, the EVA copolymers in accordance with the invention can have a vinyl acetate percentage range of about 25 to 45 percent. A preferred EVA copolymer will have a vinyl acetate percentage range of about 25 to 40 percent and an even more preferred EVA copolymer will have a vinyl acetate percentage of about 28 to 40 percent, most preferably about 28 to about 33 percent. 6 WO 2006/119067 PCT/US2006/016350 [0027] The ethylene alkyl acrylate copolymers used in the base polymer can be any suitable ethylene alkyl acrylate copolymers with the following properties: the ability to accept high loadings of conductive carbon filler, elongation of 150 to 250 percent and sufficient melt strength to maintain its shape after extrusion. The alkyl group can be any alkyl group selected from the Cl to C6 hydrocarbons, preferably the Cl to C4 hydrocarbons and even more preferable methyl. Some ethylene alkyl acrylate copolymers with alkyl acrylate levels above about 25 percent and below about 45 percent have these properties. The ethylene alkyl acrylate copolymers can have an alkyl acrylate percentage range of about 25 to 45 percent. A preferred ethylene alkyl acrylate copolymer will have an alkyl acrylate percentage range of about 28 to 40 percent and an even more preferred ethylene alkyl acrylate copolymer will have an alkyl acrylate percentage of about 28 to 33 percent. The ethylene alkyl acrylate copolymer used in the base polymer has a weight average molecular weight of not more than 200,000, preferably not more than 150,000 and more preferably not more than 100,000. [0028] The ethylene alkyl methacrylate copolymers used in the base polymer can be any suitable ethylene alkyl methacrylate copolymer with the following properties: the ability to accept high loadings of conductive carbon filler, elongation of 150 to 250 percent and sufficient melt strength to maintain its shape after extrusion. The alkyl group can be any alkyl group selected from the Cl to C6 hydrocarbons, preferably the Cl to C4 hydrocarbons and even more preferable methyl. Some ethylene alkyl methacrylate copolymers with alkyl methacrylate levels above about 25 percent and below about 45 percent have these properties. The ethylene alkyl methacrylate copolymers can have an alkyl methacrylate percentage range of about 25 to 45 percent. A preferred ethylene alkyl methacrylate copolymer will have an alkyl methacrylate percentage range of about 28 to 40 percent and an even more preferred ethylene alkyl methacrylate copolymer will have an alkyl methacrylate percentage of about 28 to 33 percent. 7 WO 2006/119067 PCT/US2006/016350 [0029] The ternary copolymers of ethylene with alkyl acrylates and alkyl methacrylates used in the base polymer can be any suitable ternary copolymer with the following properties: the ability to accept high loadings of conductive carbon filler, elongation of 150 to 250 percent and sufficient melt strength to maintain its shape after extrusion. The alkyl group can be any alkyl group independently selected from the Cl to C6 hydrocarbons, preferably the Cl to C4 hydrocarbons and even more preferable methyl. Usually a ternary copolymer will be predominantly either an alkyl acrylate with a small portion of an alkyl methacrylate or an alkyl methacrylate with a small portion of an alkyl acrylate. The proportions of alkyl acrylate and alkyl methacrylate to ethylene will be about the same as the proportions described for ethylene alkyl acrylate copolymers or for ethylene alkyl methacrylate copolymers as well as the molecular weight ranges described for ethylene alkyl acrylate and ethylene alkyl methacrylate. [0030] The adhesion modifying additive system comprises at least two components, each of the adhesion modifying additive system components being different from the base polymer. The first component comprises a hydrocarbon wax or ethylene vinyl acetate wax and the second component comprises an amide wax. [0031] Suitable hydrocarbon waxes and ethylene vinyl acetate waxes for use in the invention are disclosed in commonly assigned U.S. Patent Nos. 6,274,066 and 6,402,993, the disclosures of which are incorporated herein by reference. EPO334992 to Watanabe and U.S. Patent No. 4,150,193 to Burns, the disclosures of which are incorporated herein by reference, also disclose suitable hydrocarbon waxes and ethylene vinyl acetate waxes for use in the invention. In preferred embodiments, the semiconductive composition adhesion modifying additive system has an ethylene vinyl acetate wax having a vinyl acetate content of from about 10% to about 20% vinyl acetate, more preferably about 14%, and most preferably about 11%. One of the advantages of the invention is that the more expensive 14% vinyl 8 WO 2006/119067 PCT/US2006/016350 acetate wax can be replaced with the less expensive 11% vinyl acetate wax (in combination with the amide wax additive component) while still maintaining performance. In other preferred embodiments the first component additive is an ethylene vinyl acetate (EVA) wax and has a molecular weight from about 15,000 Daltons to about 40,000 Daltons and a vinyl acetate content of from about 2% to about 28%, preferably from about 10% to about 20%. In other preferred embodiments, the EVA wax has a molecular weight from about 15,000 Daltons to about 30,000 Daltons and a vinyl acetate content of from about 12% to about 15%. [0032] The ethylene vinyl acetate wax or hydrocarbon wax is about 0.5 to about 5 weight percent, based upon the weight of the semiconductive composition, preferably about 1 to about 3 weight percent, based upon the weight of the semiconductive composition. Mixtures of ethylene vinyl acetate waxes and/or hydrocarbon waxes may be used as well. [0033] The amide wax is about 0.5 to about 5 weight percent, based upon the weight of the semiconductive composition, preferably about 1 to about 3 weight percent, based upon the weight of the semiconductive composition. Mixtures of amide waxes may be used as well. [0034] The present invention is based upon the discovery that certain waxes in combination produce a shield composition having enhanced strippability. The amide waxes of the invention, i.e., the second component of the additive system, are selected from stearamide, oleamide, erucamide, ethylene bis-stearamide, ethylene bis-oleamide, ethylene bis- erucamide, behenamide, oleyl palmitamide, and mixtures thereof. Refined erucamides, refined oleamides, ethylene bis-stearamide and blends of ethylene bis-stearamide and ethylene bis-oleamide are preferred. [0035] In the present invention, commercially available, conventional carbon black is added to the polymer compositions to impart semi-conductive properties to the composition. The carbon black added to the polymer may be one of the various available conventional carbon blacks, including finely divided carbon such as lamp black, furnace black, or acetylene black, 9 WO 2006/119067 PCT/US2006/016350 i.e. carbon black made by pyrolyzing acetylene. Ketjin black may be used in the compositions of the invention as well as many of the commercial carbon black grades described in ASTM D 1765 98b, for example, N351, N293 and N550. Preferably, to avoid problems associated with carbon black dust, the carbon black is pelletized, although non- pelletized carbon black, such as in its fluffy form, may also be used with equal success. The carbon black is generally present in the composition in the amount of from about 0.1% to about 65% by weight of the polymer composition. Preferably the carbon black is present in an amount of from about 10% to about 50% by weight, based on the weight of the total composition. [0036] A tremendous number of compounds have been suggested for use as additives in semiconducting shield compositions. Typically, these compounds fall into the category of antioxidants, curing agents, vulcanizing agents, crosslinking agents, boosters and retardants, processing aids, pigments, dyes, colorants, fillers, coupling agents, ultraviolet absorbers or stabilizers, antistatic agents, nucleating agents, slip agents, plasticizers, lubricants, viscosity control agents, tackifiers, anti-blocking agents, surfactants, extender oils, acid scavengers, and metal deactivators. [0037] All of the components of the compositions utilized in the invention are usually blended or compounded together prior to their introduction into an extrusion device from which they are to be extruded onto an electrical conductor. The polymer and the other additives and fillers may be blended together by any of the techniques used in the art to blend and compound such mixtures into homogeneous masses. For instance, the components may be fluxed on a variety of apparatus including multi-roll mills, screw mills, continuous mixers, compounding extruders and Banbury mixers. [0038] After the various components of the composition are uniformly admixed and blended together, they are further processed to fabricate the cables of the invention. Prior art methods 10 WO 2006/119067 PCT/US2006/016350 for fabricating polymer insulated cable and wire are well known, and fabrication of the cable of the invention may generally be accomplished any of the various extrusion methods. [0039] In a typical production method of, for example, a peroxide cross-linked insulation layer of a cable, an (optionally) heated conducting core to be coated is pulled through a heated extrusion die, generally a cross-head die, in which a layer of melted polymer is applied to the conducting core. Upon exiting the die, the conducting core with the applied polymer layer is passed through a heated vulcanizing section, or continuous vulcanizing section where they are completely cross-linked in a short time, and then a cooling section, generally an elongated cooling bath, to cool. Multiple polymer layers may be applied by consecutive extrusion steps in which an additional layer is added in each step, or with the proper type of die, multiple polymer layers may be applied simultaneously. The semiconductive shield, insulating layer and strippable semiconductive shield are then passed through a heated vulcanizing section, or continuous vulcanizing section where all three layers are cross-linked simultaneously and then a cooling section, generally an elongated cooling bath, to cool. The vulcanizing section is heated as hot as possible without thermally decomposing the polymer layers of the cable. [0040] In other production methods for producing a peroxide cross-linked insulation layer of a cable, the extruded core and polymer layers are passed through a heated salt bath or an electron beam section where all three layers are cross-linked simultaneously. In yet another method, the extruded core and polymer layers are passed through a heated bath of lead or heated lead is extruded over the core and the heat energy in the lead cures the cable in a short time. [0041] In contrast, moisture crosslinked cables are typically extruded directly into a elongated cooling trough and cooled in an uncross-linked state. The process used is the same as that for the production of a thermoplastic cable that is not cross-linked. The moisture 11 WO 2006/119067 PCT/US2006/016350 cross-linkable cable is then placed in a bath of hot water or in a source of steam, sometimes referred to as a "sauna", where it slowly cures over time. The rate of cure is dependent on the thickness and the moisture permeability of the layers of the cable and the type of catalyst used and can range from several hours to several days. While heat slightly increases the rate at which water permeates the cable, the temperature must be kept below the melting point of the outer layer of the cable to prevent it softening and sticking to itself. Because of this moisture cure is undesirable for cables of higher voltage that require thicker layers of insulation. The number of water tanks or saunas required becomes too great. [0042] The conductor of the invention may generally comprise any suitable electrically conducting material, although generally electrically conducting metals are utilized. Preferably, the metals utilized are copper or aluminum. In power transmission, aluminum conductor/steel reinforcement (ACSR) cable, aluminum conductor/aluminum reinforcement (ACAR) cable, or aluminum cable is generally preferred. [0043] The weight average molecular weight may be measured by light scattering or by other conventional means. The number average molecular weight may be measured by osmometry or by other conventional means. The melting point may be measured based on the melting point determined from a crystal melting peak obtained using a differential scanning calorimeter, or by other conventional means. 12 WO 2006/119067 PCT/US2006/016350 EXPERIMENTAL [0044] The compositions described in the examples were made up by the procedure set out below, and made up into molded plaques measuring 150 mm square by 2 mm thick, one face being plaques measuring 150 mm square by 2 mm thick, one face being bonded to an XLPE block of the same dimensions and the two compositions cured together in the press for 20 minutes at 180°C. In each case adhesion was measured by the peel strength tests detailed below. Identification of ingredients also follows. [0045] Batches of about 1350 g (3.31b) of each composition were made up using a Farrell model BR Banbury mixer with a capacity of 1.57 1. All of the ingredients were added to the Banbury mixer and the ram was lowered. They were then mixed for two minutes at the middle speed setting. The mixture was discharged, milled into a flat sheet and promptly molded. [0046] Plaque samples were tested by cutting completely through the thickness of the layer of the experimental shield composition in parallel lines to define a strip 12.5 m (1/2 inch) wide; one end was lifted and turned back 180° to lie along the surface of the portion still adhered, and the force required to peel at a rate of 0.0085 m/s (20 in/min) measured; peel strength was calculated in pounds per 1/2 inch. RESULTS Comparative Examples A through G shown in Table I are the adhesion results on plaques for compositions having either having no adhesion modifying additive (A) or a single type of adhesion modifying additive, such as an EVA wax (B & C), one amide wax (D, E & G), or combination of two amide waxes (F). It can also be seen that 14% EVA wax yields the best results in Table I, however as stated above, 14% EVA wax is an expensive material. 13 WO 2006/119067 PCT/US2006/016350 TABLE I COMPARATIVE EXAMPLES Results on Plaques [0047] Examples 1 through 8 shown in Table II are the adhesion results on plaques for compositions in accordance with the invention. In all instances, the invention is an improvement over both the performance of the single type of prior art adhesion modifying additive and an improvement over the cost of the prior art adhesion modifying additives. WO 2006/119067 PCT/US2006/016350 TABLE II EXAMPLES Results on Plaques [0048] Comparative Examples H through K shown in Table III are the adhesion results on plaques for compositions having EVA wax as a single type of adhesion modifying additive. They clearly demonstrate that increasing the amount of a single type of adhesion modifying additive above 2.5 weight percent has little or no positive effect. Moreover, at levels of 10 weight per cent, performance dramatically decreases. Thus, Comparative Examples H through K also show (when compared to Table II) that the two-part strippable additives in accordance with the invention clearly have a synergistic effect. In particular, the total amount of adhesion modifying additive in accordance with the invention for Examples 1-6 & 8 is approximately 7 weight percent, of which approximately 4 weight percent is 11% EVA wax. The adhesion results for the adhesion modifying additive in accordance with invention are dramatically improved when compared to the similar amounts of 11% EVA wax shown in Table III. 15 WO 2006/119067 PCT/US2006/016350 TABLE HI COMPARATIVE EXAMPLES Results on Plaques [0049] Comparative Example L in Table IV shows the adhesion results on cable for a composition having an expensive 14% EVA wax. Examples 9 and 10 in Table IV show the adhesion results on cables for compositions in accordance with the invention. In all instances, the invention exceeds the performance of the prior art adhesion modifying additives. TABLE IV Results on Cable [0050] These experimental data are by no means exhaustive of the possible formulations or results encompassed by the invention. For this reason, reference should be made solely to the appended claims for the purposes of determining the true scope of this invention. 16 WO 2006/119067 PCT/US2006/016350 What is claimed is: 1. A semiconductive composition for use as a strippable semiconductive insulation shield layer in contact with an outermost surface of a wire and cable insulation layer, said composition comprising, 40 to 85 weight percent, based upon the weight of the semiconductive composition, of a base polymer having a weight average molecular weight of not more than 200,000 and; an adhesion modifying additive system comprising at least two components, each of said an adhesion modifying additive system components being different from said base polymer, said first component comprising a hydrocarbon wax or ethylene vinyl acetate wax and said second component comprising an amide wax; and 15 to 45 weight percent, based upon the weight of the semiconductive resin composition, of a conductive carbon black. 2. The semiconductive composition of claim 1 wherein the base polymer is selected from the group consisting of ethylene vinyl acetate copolymers, ethylene alkyl acrylate copolymers wherein the alkyl group is selected from Cl to C6 hydrocarbons, ethylene alkyl methacrylate copolymers wherein the alkyl group is selected from Cl to C6 hydrocarbons and ethylene alkyl acrylate alkyl methacrylate terpolymers wherein the alkyl group is independently selected from C1 to C6 hydrocarbons, and mixtures thereof. 3. The semiconductive composition of claim 2 wherein the base polymer comprises ethylene vinyl acetate copolymer. 17 WO 2006/119067 PCT/US2006/016350 4. The semiconductive resin composition of claim 3 wherein said ethylene vinyl acetate has from about 28% to about 40% vinyl acetate. 5. The semiconductive composition of claim 1 wherein the first component of the adhesion modifying additive system is an ethylene vinyl acetate wax having a vinyl acetate content of from about 10% to about 20% vinyl acetate. 6. The semiconductive composition of claim 1 wherein said amide wax is selected from stearamide, oleamide, erucamide, ethylene bis-stearamide, ethylene bis-oleamide, ethylene bis-erucamide, behenamide, oleyl palmitamide and mixtures thereof. 7. The semiconductive composition of claim 1 wherein said amide wax is about 0.5 to about 5 weight percent, based upon the weight of the semiconductive composition. 8. The semiconductive composition of claim 1 wherein said amide wax is about 1 to about 3 weight percent, based upon the weight of the semiconductive composition. 9. The semiconductive composition of claim 1 wherein said ethylene vinyl acetate wax is about 0.5 to about 5 weight percent, based upon the weight of the semiconductive composition. 10. The semiconductive composition of claim 1 wherein said ethylene vinyl acetate wax is about 1 to about 3 weight percent, based upon the weight of the semiconductive composition. 11. A conductive cable comprising: a centrally located conductive core, an insulation layer external to said conductive core, and a strippable semiconductive insulation shield layer in contact with an outermost surface of said insulation layer, said insulation shield layer comprising, 40 to 85 weight percent, based upon the weight of the semiconductive composition, of a base polymer having a weight average molecular weight of not more than 200,000 and; 18 WO 2006/119067 PCT/US2006/016350 an adhesion modifying additive system comprising at least two components, each of said an adhesion modifying additive system components being different from said base polymer, said first component comprising a hydrocarbon wax or ethylene vinyl acetate wax and said second component comprising an amide wax; and 15 to 45 weight percent, based upon the weight of the semiconductive resin composition, of a conductive carbon black. 12. The conductive cable of claim 11 wherein the base polymer is selected from the group consisting of ethylene vinyl acetate copolymers, ethylene alkyl acrylate copolymers wherein the alkyl group is selected from C1 to C6 hydrocarbons, ethylene alkyl methacrylate , copolymers wherein the alkyl group is selected from C1 to C6 hydrocarbons and ethylene alkyl acrylate alkyl methacrylate terpolymers wherein the alkyl group is independently selected from C1 to C6 hydrocarbons, and mixtures thereof. 13. The conductive cable of claim 12 wherein the base polymer comprises ethylene vinyl acetate copolymer. 14. The conductive cable composition of claim 13 wherein said ethylene vinyl acetate has from about 28% to about 40% vinyl acetate. 15. The conductive cable of claim 11 wherein the first component of the adhesion modifying additive system is an ethylene vinyl acetate wax having a vinyl acetate content of from about 10% to about 20% vinyl acetate. 16. The conductive cable of claim 11 wherein said amide wax is selected from stearamide, oleamide, erucamide, ethylene bis-stearamide, ethylene bis-oleamide, ethylene bis-erucamide, behenamide, oleyl palmitamide and mixtures thereof. 19 WO 2006/119067 PCT/US2006/016350 17. The conductive cable of claim 11 wherein said amide wax is about 0.5 to about 5 weight percent, based upon the weight of the semiconductive composition. 18. The conductive cable of claim 11 wherein said amide wax is about 1 to about 3 weight percent, based upon the weight of the semiconductive composition. 19. The conductive cable of claim 11 wherein said ethylene vinyl acetate wax is about 0.5 to about 5 weight percent, based upon the weight of the semiconductive composition. 20. The conductive cable of claim 11 wherein said ethylene vinyl acetate wax is about 1 to about 3 weight percent, based upon the weight of the semiconductive composition. 20 An insulation shield material is provided having improved performance without the need for expensive additives, complex polymer formulations, or specially prepared carbon black. The semiconductive composition used to make the strippable semiconductive insulation shield layer in contact with the outer surface of a wire and cable insulation layer has a base polymer having a weight average molecular weight of not more than 200,000, an adhesion modifying additive system having at least two components and a conductive carbon black. Each of the adhesion modifying additive system components is different from the base polymer. The first component of the adhesion modifying additive system contains a hydrocarbon wax or ethylene vinyl acetate wax and the second component of the adhesion modifying additive system contains an amide wax.

Full Text

WO 2006/119067 PCT/US2006/016350
IMPROVED STRIPPABLE CABLE SHIELD COMPOSITIONS
FIELD OF THE INVENTION
[0001] The invention relates to semiconducting insulation shield compositions for electric
power cables having a base polymer and a two-component adhesion modifying additive
system. The invention also relates to the use of these semiconducting insulation shield
compositions to manufacture semiconductive insulation shields for use in electric cables,
electric cables made from these compositions and methods of making electric cables from
these semiconducting insulation shield compositions. The semiconducting insulation shield
compositions of the invention may be used as strippable insulation shields in power cables,
primarily with medium voltage cables having a voltage from about 5 kV up to about 100 kV.
BACKGROUND OF THE INVENTION
[0002] A typical insulated electric power cable generally comprises one or more conductors
in a cable core that is surrounded by several layers of polymeric materials including an inner
semiconducting shield layer (conductor or strand shield), an insulating layer, an outer
semiconducting shield layer (insulation shield), a metallic wire or tape shield used as the
ground phase, and a protective jacket. Additional layers within this construction such as
moisture impervious materials, are often incorporated. The invention pertains to the outer
semiconducting insulation shield layer, i.e., the insulation shield and cables made with the
outer semiconducting insulation shield in accordance with the invention.
[0003] In general, semiconducting dielectric insulation shields can be classified into two
distinct types, the first type being a type wherein the dielectric shield is securely bonded to
the polymeric insulation so that stripping the dielectric shield is only possible by using a
cutting tool that removes the dielectric shield alone with some of the cable insulation. This
type of dielectric shield is preferred by companies that believe that this adhesion minimizes
1

WO 2006/119067 PCT/US2006/016350
the risk of electric breakdown at the interface of the shield and insulation. The second type of
dielectric shield is the "strippable" dielectric shield wherein the dielectric shield has a
defined, limited, adhesion to the insulation so that the strippable shield can be peeled cleanly
away from the insulation without removing any insulation. Current strippable shield
compositions for use over insulation materials selected from polyethylene, cross-linked
polyethylenes, or one of the ethylene copolymer rubbers such as ethylene-propylene rubber
(EPR) or ethylene-propylene diene terpolymer (EPDM) are usually based on an ethylene-
vinyl acetate (EVA) copolymer base resin rendered conductive with an appropriate type and
amount of carbon black.
[0004] Strippable shield formulations of EVA and nitrile rubbers have been described by
Ongchin, U.S. Pat. Nos. 4,286,023 and 4,246,142; Burns et al. EP Application No.
0,420,271B, Kakizaki et al U.S. Pat. No. 4,412,938 and Janssun, U.S. Pat. No. 4,226,823,
each reference being herein incorporated by reference into this application. A problem with
these strippable shield formulations of EVA and nitrile rubber is that the EVA's needed for
this formulation have a relatively high vinyl acetate content to achieve the desired adhesion
level with the result that the formulations are more rubbery than is desired for high speed
extrusion of a commercial electric cable.
[0005] Alternative adhesion-adjusting additives have also been proposed for use with EVA,
for example waxy aliphatic hydrocarbons (Watanabe et al. U.S. Pat. No. 4,933,107, herein
incorporated by reference); low-molecular weight polyethylene (Burns Jr., U.S. Pat. No.
4,150,193 herein incorporated by reference); silicone oils, rubbers and block copolymers that
are liquid at room temperature (Taniguchi et al. U.S. Pat. No. 4,493,787 herein incorporated
by reference); chlorosulfonated polyethylene, ethylene-propylene rubbers, polychloroprene,
styrene-butadiene rubber, and natural rubber. However, the only adhesion-adjusting
additives that appear to have found commercial acceptance have been paraffin waxes.
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[0006] U.S. Patent No. 6,284,374 to Yamazaki, et al discloses a multi-component polymer
composition for use in strippable semiconductive shields suitable for a polyolefin-insulated
wire and cable crosslinked by silane grafting/water crosslinking. The main polymer
component of the composition is mainly composed of an ethylene/vinyl acetate copolymer
having a weight average molecular weight not less than 300,000.
[0007] Commonly assigned U.S. Patent Nos. 6,274,066 and 6,013,202 disclose a strippable
semiconductive shield made from a base polymer and an adhesion modifying additive.
[0008] US Published Patent Application 2004/0217329A1 to Easter discloses a two
component base polymer together with adhesion adjusting additives
[0009] WO 2004/088674 Al to Person discloses a strippable semiconductive shield made
from a base polymer which is a soft polymer and a hard polymer.
[0010] The use of amide wax additives in a conductor shield has been proposed in commonly
assigned U.S. Patent No. 6,491,849 to Easter to improve aging characteristics of the electric
cable.
[0011] In the manufacture of commercial quantities of electric cable, minor cost
improvements to polymeric compositions where the resulting composition and/or cable
employing the composition have acceptable physical or electric properties are considered
significant advances in the art. This is because the competitive environment places great
demands on product pricing as well as performance and longevity. An improvement which
not only reduces cost but improves properties is considered extremely significant, as it
positively impacts both cost and quality.
[0012] It would be desirable to develop lower cost, easier to compound, strippable
semiconductive insulation shield compositions. Other proposals require complicated
compounding methods or additives that are, on average, twice as expensive as the base
polymers when used to achieve lower adhesion and/or strippability.
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[0013] A novel two component adhesion modifying additive system for strippable insulation
shields is proposed which provides remarkable adhesion results while also improving cost
over earlier systems.
SUMMARY OF THE INVENTION
[0014] The invention provides an insulation shield material with improved performance
without the need for expensive additives, complex polymer formulations, or specially
prepared carbon black.
[0015] The invention also provides a semiconductive composition for use as a strippable
semiconductive insulation shield layer in contact with the outer surface of a wire and cable
insulation layer, the composition comprising a base polymer having a weight average
molecular weight of not more than 200,000 and an adhesion modifying additive system
comprising at least two components, each of said an adhesion modifying additive system
components being different from said base polymer, said first component comprising a
hydrocarbon wax or ethylene vinyl acetate wax and said second component comprising an
amide wax; and a conductive carbon black.
[0016] In embodiments of the invention the base polymer is selected from the group
consisting of ethylene vinyl acetate copolymers, ethylene alkyl acrylate copolymers wherein
the alkyl group is selected from Cl to C6 hydrocarbons, ethylene alkyl methacrylate
copolymers wherein the alkyl group is selected from Cl to C6 hydrocarbons and ethylene
alkyl acrylate alkyl methacrylate terpolymers wherein the alkyl group is independently
selected from Cl to C6 hydrocarbons, and mixtures thereof. Preferably the base polymer
comprises ethylene vinyl acetate copolymer having from about 28% to about 40% vinyl
acetate.
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WO 2006/119067 PCT/US2006/016350
[0017] In preferred embodiments of the invention the first component of the adhesion
modifying additive system is an ethylene vinyl acetate wax having a vinyl acetate content of
from about 10% to about 20% vinyl acetate.
[0018] The amide wax may be selected from stearamide, oleamide, erucamide, ethylene bis-
stearamide, ethylene bis-oleamide, ethylene bis-erucamide, behenamide, and mixtures
thereof.
[0019] An electrically conductive cable utilizing the insulation shield in accordance with the
invention is also provided.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Conventional electrical insulators used in medium voltage cables include
polyethylenes, cross-linked polyethylenes (XLPE), ethylene-propylene rubbers and ethylene
propylene diene rubbers (EPDM rubbers). The term polyethylene is meant to include both
polymers and copolymers wherein ethylene is the major component, this would include, for
example metallocene or single site catalyzed ethylenes that are copolymerized with higher
olefins.
[0021] The polymers (other than those described below for use in the semiconductive
composition for use as a strippable semiconductive insulation shield layer in accordance with
the invention) utilized in the protective jacketing, insulating, conducting or semiconducting
layers of the inventive cables may be made by any suitable process which allows for the yield
of the desired polymer with the desired physical strength properties, electrical properties, tree
retardancy, and melt temperature for processability.
[0022] The strippable semiconductive insulation shields of the invention comprise a base
polymer, a two-component adhesion modifying additive system and conductive carbon
blacks. The conductive carbon blacks are added in an amount sufficient to decrease the
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electrical resistivity to less than 550 ohm-meter. Preferably the resistivity of the
semiconductive shield is less than about 250 ohm-meter and even more preferably less than
about 100 ohm-meter.
SHIELD POLYMERS
[0023] The invention provides a semiconductive resin composition for use as a
semiconductive layer in contact with a wire and cable insulation layer. The resin
composition comprises about 40 to about 85 weight percent, based upon the weight of the
semiconductive resin composition, of a base polymer.
[0024] The base polymer has a weight average molecular weight of not more than 200,000,
preferably not more than 150,000 and more preferably not more than 100,000.
[0025] The base polymer may be selected from ethylene vinyl acetate copolymers, ethylene
alkyl acrylate copolymers wherein the alkyl group is selected from Cl to C6 hydrocarbons,
ethylene alkyl methacrylate copolymers wherein the alkyl group is selected from Cl to C6
hydrocarbons and ethylene alkyl acrylate alkyl methacrylate terpolymers wherein the alkyl
group is independently selected from Cl to C6 hydrocarbons.
[0026] The ethylene vinyl acetate copolymer used in the base polymer can be any EVA
copolymer with the following properties: the ability to accept high loadings of conductive
carbon filler, elongation of 150 to 250 percent and sufficient melt strength to maintain its
shape after extrusion. EVA copolymers with vinyl acetate levels above about 25 percent and
below about 45 percent having these properties are known. Accordingly, the EVA
copolymers in accordance with the invention can have a vinyl acetate percentage range of
about 25 to 45 percent. A preferred EVA copolymer will have a vinyl acetate percentage
range of about 25 to 40 percent and an even more preferred EVA copolymer will have a vinyl
acetate percentage of about 28 to 40 percent, most preferably about 28 to about 33 percent.
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[0027] The ethylene alkyl acrylate copolymers used in the base polymer can be any suitable
ethylene alkyl acrylate copolymers with the following properties: the ability to accept high
loadings of conductive carbon filler, elongation of 150 to 250 percent and sufficient melt
strength to maintain its shape after extrusion. The alkyl group can be any alkyl group selected
from the Cl to C6 hydrocarbons, preferably the Cl to C4 hydrocarbons and even more
preferable methyl. Some ethylene alkyl acrylate copolymers with alkyl acrylate levels above
about 25 percent and below about 45 percent have these properties. The ethylene alkyl
acrylate copolymers can have an alkyl acrylate percentage range of about 25 to 45 percent. A
preferred ethylene alkyl acrylate copolymer will have an alkyl acrylate percentage range of
about 28 to 40 percent and an even more preferred ethylene alkyl acrylate copolymer will
have an alkyl acrylate percentage of about 28 to 33 percent. The ethylene alkyl acrylate
copolymer used in the base polymer has a weight average molecular weight of not more than
200,000, preferably not more than 150,000 and more preferably not more than 100,000.
[0028] The ethylene alkyl methacrylate copolymers used in the base polymer can be any
suitable ethylene alkyl methacrylate copolymer with the following properties: the ability to
accept high loadings of conductive carbon filler, elongation of 150 to 250 percent and
sufficient melt strength to maintain its shape after extrusion. The alkyl group can be any alkyl
group selected from the Cl to C6 hydrocarbons, preferably the Cl to C4 hydrocarbons and
even more preferable methyl. Some ethylene alkyl methacrylate copolymers with alkyl
methacrylate levels above about 25 percent and below about 45 percent have these properties.
The ethylene alkyl methacrylate copolymers can have an alkyl methacrylate percentage range
of about 25 to 45 percent. A preferred ethylene alkyl methacrylate copolymer will have an
alkyl methacrylate percentage range of about 28 to 40 percent and an even more preferred
ethylene alkyl methacrylate copolymer will have an alkyl methacrylate percentage of about
28 to 33 percent.
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WO 2006/119067 PCT/US2006/016350
[0029] The ternary copolymers of ethylene with alkyl acrylates and alkyl methacrylates used
in the base polymer can be any suitable ternary copolymer with the following properties: the
ability to accept high loadings of conductive carbon filler, elongation of 150 to 250 percent
and sufficient melt strength to maintain its shape after extrusion. The alkyl group can be any
alkyl group independently selected from the Cl to C6 hydrocarbons, preferably the Cl to C4
hydrocarbons and even more preferable methyl. Usually a ternary copolymer will be
predominantly either an alkyl acrylate with a small portion of an alkyl methacrylate or an
alkyl methacrylate with a small portion of an alkyl acrylate. The proportions of alkyl acrylate
and alkyl methacrylate to ethylene will be about the same as the proportions described for
ethylene alkyl acrylate copolymers or for ethylene alkyl methacrylate copolymers as well as
the molecular weight ranges described for ethylene alkyl acrylate and ethylene alkyl
methacrylate.
[0030] The adhesion modifying additive system comprises at least two components, each of
the adhesion modifying additive system components being different from the base polymer.
The first component comprises a hydrocarbon wax or ethylene vinyl acetate wax and the
second component comprises an amide wax.
[0031] Suitable hydrocarbon waxes and ethylene vinyl acetate waxes for use in the invention
are disclosed in commonly assigned U.S. Patent Nos. 6,274,066 and 6,402,993, the
disclosures of which are incorporated herein by reference. EPO334992 to Watanabe and U.S.
Patent No. 4,150,193 to Burns, the disclosures of which are incorporated herein by reference,
also disclose suitable hydrocarbon waxes and ethylene vinyl acetate waxes for use in the
invention. In preferred embodiments, the semiconductive composition adhesion modifying
additive system has an ethylene vinyl acetate wax having a vinyl acetate content of from
about 10% to about 20% vinyl acetate, more preferably about 14%, and most preferably
about 11%. One of the advantages of the invention is that the more expensive 14% vinyl
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WO 2006/119067 PCT/US2006/016350
acetate wax can be replaced with the less expensive 11% vinyl acetate wax (in combination
with the amide wax additive component) while still maintaining performance. In other
preferred embodiments the first component additive is an ethylene vinyl acetate (EVA) wax
and has a molecular weight from about 15,000 Daltons to about 40,000 Daltons and a vinyl
acetate content of from about 2% to about 28%, preferably from about 10% to about 20%. In
other preferred embodiments, the EVA wax has a molecular weight from about 15,000
Daltons to about 30,000 Daltons and a vinyl acetate content of from about 12% to about 15%.
[0032] The ethylene vinyl acetate wax or hydrocarbon wax is about 0.5 to about 5 weight
percent, based upon the weight of the semiconductive composition, preferably about 1 to
about 3 weight percent, based upon the weight of the semiconductive composition. Mixtures
of ethylene vinyl acetate waxes and/or hydrocarbon waxes may be used as well.
[0033] The amide wax is about 0.5 to about 5 weight percent, based upon the weight of the
semiconductive composition, preferably about 1 to about 3 weight percent, based upon the
weight of the semiconductive composition. Mixtures of amide waxes may be used as well.
[0034] The present invention is based upon the discovery that certain waxes in combination
produce a shield composition having enhanced strippability. The amide waxes of the
invention, i.e., the second component of the additive system, are selected from stearamide,
oleamide, erucamide, ethylene bis-stearamide, ethylene bis-oleamide, ethylene bis-
erucamide, behenamide, oleyl palmitamide, and mixtures thereof. Refined erucamides,
refined oleamides, ethylene bis-stearamide and blends of ethylene bis-stearamide and
ethylene bis-oleamide are preferred.
[0035] In the present invention, commercially available, conventional carbon black is added
to the polymer compositions to impart semi-conductive properties to the composition. The
carbon black added to the polymer may be one of the various available conventional carbon
blacks, including finely divided carbon such as lamp black, furnace black, or acetylene black,
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WO 2006/119067 PCT/US2006/016350
i.e. carbon black made by pyrolyzing acetylene. Ketjin black may be used in the
compositions of the invention as well as many of the commercial carbon black grades
described in ASTM D 1765 98b, for example, N351, N293 and N550. Preferably, to avoid
problems associated with carbon black dust, the carbon black is pelletized, although non-
pelletized carbon black, such as in its fluffy form, may also be used with equal success. The
carbon black is generally present in the composition in the amount of from about 0.1% to
about 65% by weight of the polymer composition. Preferably the carbon black is present in
an amount of from about 10% to about 50% by weight, based on the weight of the total
composition.
[0036] A tremendous number of compounds have been suggested for use as additives in
semiconducting shield compositions. Typically, these compounds fall into the category of
antioxidants, curing agents, vulcanizing agents, crosslinking agents, boosters and retardants,
processing aids, pigments, dyes, colorants, fillers, coupling agents, ultraviolet absorbers or
stabilizers, antistatic agents, nucleating agents, slip agents, plasticizers, lubricants, viscosity
control agents, tackifiers, anti-blocking agents, surfactants, extender oils, acid scavengers,
and metal deactivators.
[0037] All of the components of the compositions utilized in the invention are usually
blended or compounded together prior to their introduction into an extrusion device from
which they are to be extruded onto an electrical conductor. The polymer and the other
additives and fillers may be blended together by any of the techniques used in the art to blend
and compound such mixtures into homogeneous masses. For instance, the components may
be fluxed on a variety of apparatus including multi-roll mills, screw mills, continuous mixers,
compounding extruders and Banbury mixers.
[0038] After the various components of the composition are uniformly admixed and blended
together, they are further processed to fabricate the cables of the invention. Prior art methods
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WO 2006/119067 PCT/US2006/016350
for fabricating polymer insulated cable and wire are well known, and fabrication of the cable
of the invention may generally be accomplished any of the various extrusion methods.
[0039] In a typical production method of, for example, a peroxide cross-linked insulation
layer of a cable, an (optionally) heated conducting core to be coated is pulled through a
heated extrusion die, generally a cross-head die, in which a layer of melted polymer is
applied to the conducting core. Upon exiting the die, the conducting core with the applied
polymer layer is passed through a heated vulcanizing section, or continuous vulcanizing
section where they are completely cross-linked in a short time, and then a cooling section,
generally an elongated cooling bath, to cool. Multiple polymer layers may be applied by
consecutive extrusion steps in which an additional layer is added in each step, or with the
proper type of die, multiple polymer layers may be applied simultaneously. The
semiconductive shield, insulating layer and strippable semiconductive shield are then passed
through a heated vulcanizing section, or continuous vulcanizing section where all three layers
are cross-linked simultaneously and then a cooling section, generally an elongated cooling
bath, to cool. The vulcanizing section is heated as hot as possible without thermally
decomposing the polymer layers of the cable.
[0040] In other production methods for producing a peroxide cross-linked insulation layer of
a cable, the extruded core and polymer layers are passed through a heated salt bath or an
electron beam section where all three layers are cross-linked simultaneously. In yet another
method, the extruded core and polymer layers are passed through a heated bath of lead or
heated lead is extruded over the core and the heat energy in the lead cures the cable in a short
time.
[0041] In contrast, moisture crosslinked cables are typically extruded directly into a
elongated cooling trough and cooled in an uncross-linked state. The process used is the same
as that for the production of a thermoplastic cable that is not cross-linked. The moisture
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WO 2006/119067 PCT/US2006/016350
cross-linkable cable is then placed in a bath of hot water or in a source of steam, sometimes
referred to as a "sauna", where it slowly cures over time. The rate of cure is dependent on the
thickness and the moisture permeability of the layers of the cable and the type of catalyst
used and can range from several hours to several days. While heat slightly increases the rate
at which water permeates the cable, the temperature must be kept below the melting point of
the outer layer of the cable to prevent it softening and sticking to itself. Because of this
moisture cure is undesirable for cables of higher voltage that require thicker layers of
insulation. The number of water tanks or saunas required becomes too great.
[0042] The conductor of the invention may generally comprise any suitable electrically
conducting material, although generally electrically conducting metals are utilized.
Preferably, the metals utilized are copper or aluminum. In power transmission, aluminum
conductor/steel reinforcement (ACSR) cable, aluminum conductor/aluminum reinforcement
(ACAR) cable, or aluminum cable is generally preferred.
[0043] The weight average molecular weight may be measured by light scattering or by other
conventional means. The number average molecular weight may be measured by osmometry
or by other conventional means. The melting point may be measured based on the melting
point determined from a crystal melting peak obtained using a differential scanning
calorimeter, or by other conventional means.
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WO 2006/119067 PCT/US2006/016350
EXPERIMENTAL
[0044] The compositions described in the examples were made up by the procedure set out
below, and made up into molded plaques measuring 150 mm square by 2 mm thick, one face
being plaques measuring 150 mm square by 2 mm thick, one face being bonded to an XLPE
block of the same dimensions and the two compositions cured together in the press for 20
minutes at 180°C. In each case adhesion was measured by the peel strength tests detailed
below. Identification of ingredients also follows.
[0045] Batches of about 1350 g (3.31b) of each composition were made up using a Farrell
model BR Banbury mixer with a capacity of 1.57 1. All of the ingredients were added to the
Banbury mixer and the ram was lowered. They were then mixed for two minutes at the
middle speed setting. The mixture was discharged, milled into a flat sheet and promptly
molded.
[0046] Plaque samples were tested by cutting completely through the thickness of the layer
of the experimental shield composition in parallel lines to define a strip 12.5 m (1/2 inch)
wide; one end was lifted and turned back 180° to lie along the surface of the portion still
adhered, and the force required to peel at a rate of 0.0085 m/s (20 in/min) measured; peel
strength was calculated in pounds per 1/2 inch.
RESULTS
Comparative Examples A through G shown in Table I are the adhesion results on plaques for
compositions having either having no adhesion modifying additive (A) or a single type of
adhesion modifying additive, such as an EVA wax (B & C), one amide wax (D, E & G), or
combination of two amide waxes (F). It can also be seen that 14% EVA wax yields the best
results in Table I, however as stated above, 14% EVA wax is an expensive material.
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WO 2006/119067 PCT/US2006/016350
TABLE I
COMPARATIVE EXAMPLES
Results on Plaques

[0047] Examples 1 through 8 shown in Table II are the adhesion results on plaques for
compositions in accordance with the invention. In all instances, the invention is an
improvement over both the performance of the single type of prior art adhesion modifying
additive and an improvement over the cost of the prior art adhesion modifying additives.

WO 2006/119067 PCT/US2006/016350
TABLE II
EXAMPLES
Results on Plaques

[0048] Comparative Examples H through K shown in Table III are the adhesion results on
plaques for compositions having EVA wax as a single type of adhesion modifying additive.
They clearly demonstrate that increasing the amount of a single type of adhesion modifying
additive above 2.5 weight percent has little or no positive effect. Moreover, at levels of 10
weight per cent, performance dramatically decreases. Thus, Comparative Examples H
through K also show (when compared to Table II) that the two-part strippable additives in
accordance with the invention clearly have a synergistic effect. In particular, the total amount
of adhesion modifying additive in accordance with the invention for Examples 1-6 & 8 is
approximately 7 weight percent, of which approximately 4 weight percent is 11% EVA wax.
The adhesion results for the adhesion modifying additive in accordance with invention are
dramatically improved when compared to the similar amounts of 11% EVA wax shown in
Table III.
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WO 2006/119067 PCT/US2006/016350
TABLE HI
COMPARATIVE EXAMPLES
Results on Plaques

[0049] Comparative Example L in Table IV shows the adhesion results on cable for a
composition having an expensive 14% EVA wax. Examples 9 and 10 in Table IV show the
adhesion results on cables for compositions in accordance with the invention. In all
instances, the invention exceeds the performance of the prior art adhesion modifying
additives.
TABLE IV
Results on Cable

[0050] These experimental data are by no means exhaustive of the possible formulations or
results encompassed by the invention. For this reason, reference should be made solely to the
appended claims for the purposes of determining the true scope of this invention.
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WO 2006/119067 PCT/US2006/016350
What is claimed is:
1. A semiconductive composition for use as a strippable semiconductive insulation
shield layer in contact with an outermost surface of a wire and cable insulation layer, said
composition comprising,
40 to 85 weight percent, based upon the weight of the semiconductive composition, of
a base polymer having a weight average molecular weight of not more than 200,000 and;
an adhesion modifying additive system comprising at least two components, each of
said an adhesion modifying additive system components being different from said base
polymer, said first component comprising a hydrocarbon wax or ethylene vinyl acetate wax
and said second component comprising an amide wax; and
15 to 45 weight percent, based upon the weight of the semiconductive resin
composition, of a conductive carbon black.
2. The semiconductive composition of claim 1 wherein the base polymer is selected
from the group consisting of ethylene vinyl acetate copolymers, ethylene alkyl acrylate
copolymers wherein the alkyl group is selected from Cl to C6 hydrocarbons, ethylene alkyl
methacrylate copolymers wherein the alkyl group is selected from Cl to C6 hydrocarbons
and ethylene alkyl acrylate alkyl methacrylate terpolymers wherein the alkyl group is
independently selected from C1 to C6 hydrocarbons, and mixtures thereof.
3. The semiconductive composition of claim 2 wherein the base polymer comprises
ethylene vinyl acetate copolymer.
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WO 2006/119067 PCT/US2006/016350
4. The semiconductive resin composition of claim 3 wherein said ethylene vinyl acetate
has from about 28% to about 40% vinyl acetate.
5. The semiconductive composition of claim 1 wherein the first component of the
adhesion modifying additive system is an ethylene vinyl acetate wax having a vinyl acetate
content of from about 10% to about 20% vinyl acetate.
6. The semiconductive composition of claim 1 wherein said amide wax is selected from
stearamide, oleamide, erucamide, ethylene bis-stearamide, ethylene bis-oleamide, ethylene
bis-erucamide, behenamide, oleyl palmitamide and mixtures thereof.
7. The semiconductive composition of claim 1 wherein said amide wax is about 0.5 to
about 5 weight percent, based upon the weight of the semiconductive composition.
8. The semiconductive composition of claim 1 wherein said amide wax is about 1 to
about 3 weight percent, based upon the weight of the semiconductive composition.
9. The semiconductive composition of claim 1 wherein said ethylene vinyl acetate wax
is about 0.5 to about 5 weight percent, based upon the weight of the semiconductive
composition.
10. The semiconductive composition of claim 1 wherein said ethylene vinyl acetate wax
is about 1 to about 3 weight percent, based upon the weight of the semiconductive
composition.
11. A conductive cable comprising:
a centrally located conductive core,
an insulation layer external to said conductive core, and
a strippable semiconductive insulation shield layer in contact with an outermost
surface of said insulation layer, said insulation shield layer comprising,
40 to 85 weight percent, based upon the weight of the semiconductive composition, of
a base polymer having a weight average molecular weight of not more than 200,000 and;
18

WO 2006/119067 PCT/US2006/016350
an adhesion modifying additive system comprising at least two components, each of
said an adhesion modifying additive system components being different from said base
polymer, said first component comprising a hydrocarbon wax or ethylene vinyl acetate wax
and said second component comprising an amide wax; and
15 to 45 weight percent, based upon the weight of the semiconductive resin
composition, of a conductive carbon black.
12. The conductive cable of claim 11 wherein the base polymer is selected from the group
consisting of ethylene vinyl acetate copolymers, ethylene alkyl acrylate copolymers wherein
the alkyl group is selected from C1 to C6 hydrocarbons, ethylene alkyl methacrylate ,
copolymers wherein the alkyl group is selected from C1 to C6 hydrocarbons and ethylene
alkyl acrylate alkyl methacrylate terpolymers wherein the alkyl group is independently
selected from C1 to C6 hydrocarbons, and mixtures thereof.
13. The conductive cable of claim 12 wherein the base polymer comprises ethylene vinyl
acetate copolymer.
14. The conductive cable composition of claim 13 wherein said ethylene vinyl acetate has
from about 28% to about 40% vinyl acetate.
15. The conductive cable of claim 11 wherein the first component of the adhesion
modifying additive system is an ethylene vinyl acetate wax having a vinyl acetate content of
from about 10% to about 20% vinyl acetate.
16. The conductive cable of claim 11 wherein said amide wax is selected from
stearamide, oleamide, erucamide, ethylene bis-stearamide, ethylene bis-oleamide, ethylene
bis-erucamide, behenamide, oleyl palmitamide and mixtures thereof.
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WO 2006/119067 PCT/US2006/016350
17. The conductive cable of claim 11 wherein said amide wax is about 0.5 to about 5
weight percent, based upon the weight of the semiconductive composition.
18. The conductive cable of claim 11 wherein said amide wax is about 1 to about
3 weight percent, based upon the weight of the semiconductive composition.
19. The conductive cable of claim 11 wherein said ethylene vinyl acetate wax is about 0.5
to about 5 weight percent, based upon the weight of the semiconductive composition.
20. The conductive cable of claim 11 wherein said ethylene vinyl acetate wax is about 1
to about 3 weight percent, based upon the weight of the semiconductive composition.
20

An insulation shield material is provided having improved performance without the need for expensive additives,
complex polymer formulations, or specially prepared carbon black. The semiconductive composition used to make the strippable
semiconductive insulation shield layer in contact with the outer surface of a wire and cable insulation layer has a base polymer
having a weight average molecular weight of not more than 200,000, an adhesion modifying additive system having at least two
components and a conductive carbon black. Each of the adhesion modifying additive system components is different from the base
polymer. The first component of the adhesion modifying additive system contains a hydrocarbon wax or ethylene vinyl acetate wax
and the second component of the adhesion modifying additive system contains an amide wax.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=rh/PMlYDB1ccnrwb3k0k3Q==&loc=wDBSZCsAt7zoiVrqcFJsRw==

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Patent Number

271462

Indian Patent Application Number

4444/KOLNP/2007

PG Journal Number

09/2016

Publication Date

26-Feb-2016

Grant Date

22-Feb-2016

Date of Filing

19-Nov-2007

Name of Patentee

GENERAL CABLE TECHNOLOGIES CORPORATION

Applicant Address

4 TENNESSER DRIVEGENERAL CABLE CORPORATION, FOUR TESSENEER DRIVE, HIGHLAND HEIGHTS, KY

Inventors:

#	Inventor's Name	Inventor's Address
1	EASTER MARK R	4020 NORTH PENNSYLVANIA STREET, INDIANAPOLIS, IN 46205

PCT International Classification Number

H01B 7/00

PCT International Application Number

PCT/US2006/016350

PCT International Filing date

2006-05-01

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	11/117395	2005-04-29	U.S.A.