ZA200107761B - Stabilized telecommunication cable insulation composition. - Google Patents

Description

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Stabilized Telecommunication Cable Insulation Composition

The present invention pertains to a polyolefin composition for use as insulation for wire and cable that has improved resistance to the deleterious effects of heat, oxygen and moisture. The stabilized compositions are suitable for use as telecommunications (telecom) cable.

A typical telecom cable is constructed of twisted pairs of polyolefin-insulated copper wire which are bundled together and protected by a cable sheath. The cable sheath is composed of a metal foil and/or armor in combination with a polymeric jacketing material. The entire system is referred to as “telecom cable”.

To reduce the risk of water penetration into the cable system and to minimize the : deleterious effects of moisture on the polyolefin insulation, the system is made water-tight by filling the voids in the cable with a hydrophobic grease. Cable systems of this type are described for example in U.S. Patent Nos. 3,888,709, 4,044,200, 4,218,577, 5,502,288 and

European patent application 565,868 A2, and the references therein. The cable filler grease is known to extract stabilizers incorporated into the wire insulation. This is discussed for example in "Plastics Additives Handbook", 3" Edition, R. Gachter, H. Muller, Eds., Hanser

Publishers, pages 116-119 (1990)].

Junctions of two or more telecom cables are often required and this is accomplished in an outdoor enclosure known as a pedestal or an interconnection box. Inside the pedestal, the cable sheathing is removed, the cable filler grease is wiped off, and the transmission wires are joined as necessary. The exposed insulated wires are now subject to the adverse conditions of heat, oxygen and moisture. The polyolefin insulation, having lost a portion of its stabilizer additives to extraction by the filler grease, is especially vuinerable to these environmental conditions and may exhibit premature oxidative failure. This failure exhibits itself in the loss of physical properties of the insulation which ultimately results in a loss of electrical transmission performance.

The stabilization of polyolefin wire insulation in telecom applications with hindered phenolic antioxidants is known. A state of the art stabilizer system includes the use of a hindered phenol together with a metal deactivator such as Irganox® MD 1024, 1,2 -bis(3,5-di-

-2. N tert-butyl-4-hydroxyhydrocinnamoyl)hydrazine or Naugard® XL-1, 2,2’-oxalyldiamido-bis- [ethyl 3-(3,5-di-tert-butyl-4-hydroxylphenyl)propionate]. A typical stabilizer package includes, as the primary antioxidant, Irganox® 1010, pentaerythritol tetrakis [3-(3,5-di-tert-buty!-4- hydroxyphenyl) propionate), and as the metal deactivator, irganox® MD 1024. This system is disclosed in European patent application 565,868 A2 and U.S. Patent Nos. 4,044,200, 5,380,591 and 5,575,952. Irganox®is a protected trade name of Ciba Specialty Chemicals

Corp., Naugard® is a protected trade name of Uniroyal.

U.S. Patent No. 4,044,200 discloses the stabilization of polyethylene wire insulation in the presence of a moisture barrier filler with a combination of an alkylhydroxyphenylalkanoyl hydrazide and/or a substituted amido triazole together with a high molecular weight hindered phenolic antioxidant. Specifically disclosed is the combination of irganox® MD 1024 and

Irganox® 1010.

U.S. Patent No. 4,812,500 discloses a polyolefin composition having improved resistance to deterioration when exposed to hot oxygenated water, chlorinated water, and :

UV radiation. The composition comprises a hindered amine UV stabilizer, a hindered phenolic thermal stabilizer and a chelating (metal deactivating) agent. The hindered phenolic is selected from a specific group including Irganox® 1010, pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate), and Irganox® 3114, tris(3,5-di-tert-butyl-4- hydroxybenzyl) isocyanurate. The chelating agent is selected from a group including

Irganox® MD 1024, 1,2 -bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazine. Irganox® is a trademark of Ciba Specialty Chemicals Corp. Itis contemplated that the invention may be used for various systems where water or moisture are present, including wire and cable coatings. There is no mention of grease filled cable systems where the potential for extraction of the additives exists.

U.S. Patent Nos. 5,380,591, 5,453,322, 5,575,952, 5,766,761 and 5,807,635 disclose the stabilization of hydrocarbon grease filled telephone cables with the combination of a mixture of an alkylhydroxyphenylalkanoyl hydrazine with a functionalized hindered amine. irganox® MD 1024 is specifically disclosed as the hydrazine in each case.

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U.S. Patent No. 5,474,847 teaches the stabilization of polyolefin wire insulation in grease filled telephone cables with the reaction products of hydrazide derivatives of hindered phenols or hindered amines or amino derivatives of hindered amines with a quinone.

U.S. Patent No. 5,502,288 discloses the stabilization of polyolefin wire insulation in telephone cables with the use of Irganox® MD 1024 or Naugard® XL-1 or mixtures thereof with selected antioxidants.

European patent application 565,868 A2 teaches the stabilization of polyolefin wire insulation compositions exposed to water-blocking cable fillers with a combination of divalent metal salts of phenolic carboxylic or phosphonic acids together with a metal deactivator.

Specifically named metal deactivators are irganox® MD 1024 and Naugard® XL-1. A preferred composition also includes the use of irganox® 1010.

WO 93/24935 teaches the use of the reaction products of an anhydride of an unsaturated aliphatic diacid with one or more functionalized hindered amines and/or functionalized hindered phenols for the stabilization of polyolefin wire insulation in grease filled telephone cables.

WO 93/24938 discloses a grease filled cable construction in which the polyolefin wire insulation which has bonded to it, through an anhydride of an aliphatic diacid, one or more functionalized hindered amines and/or functionalized hindered phenols.

In order to protect the polyolefin wire insulation that is exposed to environmental conditions in the interconnection box, and to counteract the extraction of stabilizers by the cable filler grease, it has been suggested that high loadings of the stabilizer system be employed. There is a need to find more efficient primary antioxidant/metal deactivator combinations than those that are the state of the art in order to reduce the high cost associated with the use of these levels of stabilizers. Stabilizer efficiency in this context is the combined ability of the stabilizer system to resist extraction from the polyolefin wire insulation into the cable filler grease and to provide the polyolefin with resistance to the deleterious effects of heat, oxygen and moisture.

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Surprisingly, it has been found that the combination of one or more primary phenolic antioxidants selected from Irganox® 1098, N,N'-hexane-1 ,6-diylbis-(3-(3,5-di-tert-butyl-4- hydroxyphenylpropionamide)), rganox® 3114, tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, and Irganox® 3125, tris(2-(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyloxy)ethyl) isocyanurate, together with one or more alkythydroxyphenylalkanoyl hydrazine metal deactivators is especially effective towards providing oxidative stability for polyolefin wire insulation in grease filled telecom cables. Irganox® is a trademark of Ciba Specialty

Chemicals Corp.

The present invention pertains to a novel hydrocarbon grease filled cable construction wherein the polyolefin wire insulation has improved oxidative stability.

More particularly, the novel cable construction of this invention comprises ' (i) a plurality of insulated electrical conductors having interstices therebetween, : said insulation comprising (a) one or more polyolefins, and (b) one or more primary antioxidants selected from the group of N,N’-hexane-1,6- diylbis-(3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide)), tris(3,5-di-tert-butyl-4- hydroxybenzyl) isocyanurate and tris(2-(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyloxy)ethy!) isocyanurate, and (c) one or more metal deactivators selected from the alkylhydroxyphenylalkanoy! hydrazines, and (it) hydrocarbon cable filler grease within the interstices, and (iii) a sheath surrounding components (i) and (ii).

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The polyolefins of component (a) are generally thermoplastic resins, which are crosslinkable. They can be homopolymers or copolymers produced from two or more comonomers, or a blend of two or more of these polymers, conventionally used in film, sheet, and tubing, and as jacketing and/or insulating materials in wire and cable applications.

The monomers useful in the production of these homopolymers and copolymers can have 2 to 20 carbon atoms, and preferably have 2 to 12 carbon atoms. Examples of these monomers are alpha-olefins such as ethylene, propylene, 1-butene, 1-hexene, 4-methyl-1- pentene, and 1-octene; unsaturated esters such as vinyl acetate, ethyl acrylate, methyl acrylate, methyl methacrylate, t-butyl acrylate, n-butyl acrylate, n-butyl methacrylate, 2- ethylhexyl acrylate, and other alkyl acrylates; diolefins such as 1,4-pentadiene, 1,3- hexadiene, 1,5-hexadiene, 1,4-octadiene, and ethylidene norbornene, commonly the third monomer in a terpolymer; other monomers such as styrene, p-methyl styrene, alpha-methy! styrene, p-chlorostyrene, vinyl naphthalene, and similar aryl olefins; nitriles such as } acrylonitrile, methacrylonitrile, and alpha-chloroacrylonitrile; vinyl methyl ketone, vinyl methyl ether, vinylidene chloride, maleic anhydride, vinyl chioride, vinylidene chloride, vinyl alcohol, tetrafluoroethylene, and chorotrifiuoroethylene; and acrylic acid, methacrylic acid, and other similar unsaturated acids.

The homopolymers and copolymers referred to can be non-halogenated, or halogenated in a conventional manner, generally with chorine or bromine. Examples of halogenated polymers are polyvinyl chloride, polyvinylidene chloride, and polytetrafluoroethylene. The homopolymers and copolymers of ethylene and propylene are preferred, both in the non-halogenated and halogenated form. Included in this preferred group are terpolymers such as ethylene/propylene/diene monomer rubbers.

Other examples of ethylene polymers are as follows: a high pressure homopolymer of ethylene; a copolymer of ethylene and one or more alpha-olefins having 3 to 12 carbon atoms; a homopolymer or copolymer of ethylene having a hydrolyzable silane grafted to their backbones; a copolymer of ethylene and alkenyl trialkyloxy silane such as trimethoxy vinyl silane; or a copolymer of an alpha-olefin having 2 to 12 carbon atoms and an unsaturated ester having 4 to 20 carbon atoms, e.g., an ethylene/ethyl acrylate or vinyl acetate copolymer; an ethylene/ethyl acrylate or vinyl acetate/hydrolyzable silane terpolymer; and ethylene/ethyl acrylate or vinyl acetate copolymers having a hydrolyzable silane grafted to their backbones.

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With respect to polypropylene: Homopolymers and copolymers of propylene and one or more other alpha-olefins wherein the portion of the copolymer based on propylene is at least about 60 percent by weight based on the weight of the copolymer can be used to provide the polyolefin of the invention. Preferred polypropylene alpha-olefin comonomers are those having 2 or 4 to 12 carbon atoms.

Polyolefins, i.e. the polymers of monoolefins exemplified above, for example polyethylene and polypropylene, can be prepared by different, and especially by the following, methods: 1) radical polymerization (normally under high pressure and at elevated temperature). 2) catalytic polymerization using a catalyst that normally contains one or more than one ’ metal of groups IVb, Vb, Vib or VIII of the Periodic Table. These metals usually have one or more than one ligand, typically oxides, halides, alcoholates, esters, ethers, amines, alkyls, alkenyls and/or aryls that may be either p- or s-coordinated. These metal complexes may be in the free form or fixed on substrates, typically on activated magnesium chloride, titanium(l) chloride, alumina or silicon oxide. These catalysts may be soluble or insoluble in the polymerization medium. The catalysts can be used by themselves in the polymerization or further activators may be used, typically metal alkyls, metal hydrides, metal alkyl halides, metal alkyl oxides or metal alkyloxanes, said metals being elements of groups la, lla and/or lla of the Periodic Table. The activators may be modified conveniently with further ester, ether, amine or silyl ether groups. These catalyst systems are usually termed Phillips,

Standard Oil Indiana, Ziegler (-Natta), TNZ (DuPont), metallocene or single site catalysts (SSC).

The homopolymer or copolymers can be crosslinked or cured with an organic peroxide, or to make them hydrolyzable, they can be grafted with alkeny! trialkoxy silane in the presence of an organic peroxide which acts as a free radical generator or catalyst. Useful alkenyl! trialkoxy silanes include the vinyl trialkoxy silanes such as vinyl trimethoxy silane, vinyl triethoxy silane, and vinyl triisopropoxy silane. The alkenyl and alkoxy radicals can have 1 to 30 carbon atoms and preferably have 1 to 12 carbon atoms. The hydrolyzable polymers can be moisture cured in the presence of a silanol condensation catalyst such as

~ 7. dibutyl tin dilaurate, dioctyl tin maleate, stannous acetate, stannous octoate, lead naphthenate, zinc octoate, iron 2-ethyl hexoate, and other metal carboxylates.

The homopolymers or copolymers of ethylene wherein ethylene is the primary comonomer and the homopolymers and copolymers of propylene wherein propylene is the primary comonomer may be referred to herein as polyethylene and polypropylene, respectively.

The polyolefins of component a) are preferably polyethylene or polypropylene or mixtures thereof.

The alkylhydroxyphenylatkanoy! hydrazines of component (c) are described in U.S.

Patent Nos. 3,660,438 and 3,773,722. Preferably the compounds of component (c) are of . the following structure:

H

: \

R, 0 NTR, be \

Ly (CH), H

R, wherein n is 0 or an integer from t to 5;

R; is a straight or branched chain alkyl having 1 to 6 carbon atoms:

R. is hydrogen or Ry; and

Rs is hydrogen, an alkanoyl having 2 to 18 carbon atoms, or a group of the formula hb. N

R, 0]

LL - (CH,),

R, wherein n, R; and R; independently have the same definitions as above.

The radical R; is preferably in the ortho-position to the OH group.

Preferably, the metal deactivator of component (c) is Irganox® MD 1024, 1,2 -bis(3,5-di- tert-butyl-4-hydroxyhydrocinnamoyl)hydrazine, Ciba Specialty Chemicals Corp.

The hydrocarbon cable filler grease of component (ii) is a mixture of hydrocarbon compounds, which is semisolid at use temperatures. It is known industrially as “cable filling compound.” A typical requirement of cable filling compounds is that the grease has minimal leakage from the cut end of a cable at a 60° C or higher temperature rating. Another typical requirement is that the grease resist water leakage through a short length of cut cable when water pressure is applied at one end. Among other typical requirements are cost competitiveness; minimal detrimental effect on signal transmission: minimal detrimental effect on the physical characteristics of the polymeric insulation and cable sheathing materials; thermal and oxidative stability; and cable fabrication processability.

Cable fabrication can be accomplished by heating the cable filling compound to a temperature of approximately 100° C. This liquefies the filling compound so that it can be pumped into the multiconductor cable core to fully impregnate the interstices and eliminate all air space. Alternatively, thixotropic cable filling compounds using shear induced flow can be processed at reduced temperatures in the same manner. A cross section of a typical finished grease filled cable transmission core is made up of about 52 percent insulated wire and about 48 percent interstices in terms of the areas of the total cross section. Since the interstices are completely filled with cable filling compound, a filled cable core typically contains about 48 percent by volume of cable filling compound.

Claims (8)

What is claimed is:

1. A stabilized cable construction, which comprises (i) a plurality of insulated electrical conductors having interstices therebetween, said insulation comprising (a) one or more polyolefins, and (b) one or more primary antioxidants selected from the group of N,N'-hexane-1,6- diylbis-(3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide)), tris(3,5-di-tert-butyl-4- hydroxybenzyl) isocyanurate and tris(2-(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyloxy)ethyl) isocyanurate, and (c) one or more metal deactivators selected from the alkylhydroxyphenylalkanoyl hydrazines, and (ii) hydrocarbon cable filler grease within the interstices, and (iii) a sheath surrounding components (i) and (ii).

2. A cable construction according to claim 1 wherein said polyolefins of component (a) are polyethylene or polypropylene or mixtures thereof.

3. A cable construction according to claim 1 in which the metal deactivators of component (c) are of the formula

H \ R, 0 NTR, N no—¢ \ (CH), H R, wherein n is 0 or an integer from 1 to 5;

R. is a straight or branched chain alkyl having 1 to 6 carbon atoms:

R. is hydrogen or Ry; and Ra is hydrogen, an alkanoyl having 2 to 18 carbon atoms, or a group of the formula R, O Ly (CH,), R, wherein n, R, and R; independently have the same definitions as above.

4. A cable construction according to claim 1 in which the metal deactivator of component (c) is 1,2 -bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazine.

5. A cable construction according to claim 1 in which said antioxidants of component (b), in total, are present in the range from about 0.05 weight percent to about 1.0 weight percent based on the weight of the polyolefin of component (a).

6. A cable construction according to claim 1 in which said metal deactivators of component (c), in total, are present in the range from about 0.1 weight percent to about 2.0 weight percent based on the weight of the polyolefin of component (a).

7. A cable construction according to claim 1 in which the hydrocarbon cable filler grease of component (ii) or one or more of the hydrocarbon constituents thereof is present in the polyolefin of component (a).

8. A cable construction according to claim 1 in which the hydrocarbon cable filier grease of component (ii) or one or more of the hydrocarbon constituents thereof, in total, is present in the polyolefin of component (a) in the range of about 3 to about 30 weight percent based on the weight of component (a).