WO2010047469A1 - Thermoplastic polyurethane elastomer-based composition for insulation layers and electric cable equipped therewith - Google Patents

Thermoplastic polyurethane elastomer-based composition for insulation layers and electric cable equipped therewith Download PDF

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Publication number
WO2010047469A1
WO2010047469A1 PCT/KR2009/004822 KR2009004822W WO2010047469A1 WO 2010047469 A1 WO2010047469 A1 WO 2010047469A1 KR 2009004822 W KR2009004822 W KR 2009004822W WO 2010047469 A1 WO2010047469 A1 WO 2010047469A1
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Prior art keywords
weight
insulation layer
thermoplastic polyurethane
composition
polyurethane elastomer
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Ceased
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PCT/KR2009/004822
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French (fr)
Inventor
Whan-Ki Kim
Gun-Joo Lee
Gi-Joon Nam
Won-Jung Kim
Ju-Ha Lee
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LS Cable and Systems Ltd
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LS Cable Ltd
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Priority to EP09822145A priority Critical patent/EP2346943A1/en
Publication of WO2010047469A1 publication Critical patent/WO2010047469A1/en
Anticipated expiration legal-status Critical
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L75/00—Compositions of polyureas or polyurethanes; Compositions of derivatives of such polymers
    • C08L75/04—Polyurethanes
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/01—Use of inorganic substances as compounding ingredients characterized by their specific function
    • C08K3/016—Flame-proofing or flame-retarding additives
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L51/00—Compositions of graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers
    • C08L51/06—Compositions of graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers grafted on to homopolymers or copolymers of aliphatic hydrocarbons containing only one carbon-to-carbon double bond
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
    • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
    • H01B3/302—Polyurethanes or polythiourethanes; Polyurea or polythiourea
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L2203/00—Applications
    • C08L2203/20—Applications use in electrical or conductive gadgets
    • C08L2203/202—Applications use in electrical or conductive gadgets use in electrical wires or wirecoating

Definitions

  • the present invention relates to a thermoplastic polyurethane elastomer (TPU or
  • TPE-U TPE-U-based composition for insulation and sheath layers and an electric cable equipped therewith.
  • the present invention relates to a composition for insulation and sheath layers, in which an inorganic component such as a metal hydroxide flame-retardant or the like is uniformly dispersed in a thermoplastic elastomer structure to ensure harmony of the mechanical properties, and an electric cable equipped therewith.
  • the electric cable industries have widely used polyvinyl chloride (PVC) or a polyethylene-based resin added with a halogen-based flame-retardant to form an insulation or sheath layer of an insulating cable having flame retardancy of a certain level or higher.
  • PVC polyvinyl chloride
  • a polyethylene-based resin added with a halogen-based flame-retardant to form an insulation or sheath layer of an insulating cable having flame retardancy of a certain level or higher.
  • These resins have excellent properties and high flame retardancy and economical efficiency, but are hazardous to the environment. For this reason, they will become more difficult to use in forming insulation and sheath layers of flame-retardant cables.
  • the developed countries are strongly forcing to use plastic materials in forming insulation and sheath layers of electric cables since the plastic materials are recyclable. With this current trend, use of materials that are not recyclable will be prohibited in the end.
  • the European Union adopted the Restriction of Hazardous Substances Directive (RoHS) that restricts the use of certain hazardous substances in electrical and electronic equipments and sets collection, recycling and recovery targets for electrical goods.
  • the RoHS directive took effect on July 1, 2006.
  • the EU also adopted the End-of-Life Vehicle (ELV) directive that has an impact on the automotive industries.
  • the aim of this directive is to increase the rate of re-use and recovery to 95% in terms of average weight per vehicle/year by 2015.
  • the length of cables used in a car is generally about 2 km, it is important to recycle a greater amount of plastic material of electric cables so as to attain the target recycling rate.
  • a halogen-free polyethylene resin is widely used in place of PVC.
  • the halogen-free polyethylene resin When the halogen-free polyethylene resin is crosslinked, the halogen-free polyethylene resin has good mechanical properties such as strength and so on, and excellent flame retardancy and economical efficiency.
  • the crosslinked polyethylene resin cannot be recycled. This is a drawback as a material for an insulation layer of an insulating cable.
  • polypropylene Compared with the polyethylene resin, polypropylene has low flame retardancy. To make up for low flame retardancy of the polypropylene-based resin, a large amount of an inorganic flame-retardant such as metal hydroxide or the like is added. However, the resultant end-products have deterioration in moldability and mechanical properties such as tensile strength and so on.
  • thermoplastic elastomer TPE
  • the thermoplastic elastomer has both of elasticity of rubbers and moldability of thermoplastic plastics such as polyethylene or the like.
  • the thermoplastic elastomer is a copolymer of a soft monomer and a hard monomer, or a blend of a soft polymer and a hard polymer.
  • a thermoplastic polyurethane TPU represents the thermoplastic elastomer.
  • the thermoplastic elastomer satisfies the specific level of mechanical properties without crosslinking, and has excellent recyclability, heat resistance and abrasion resistance.
  • thermoplastic elastomer does not reach the specific level of flame retardancy.
  • the thermoplastic elastomer is inevitably added with a large amount of a halogen-free inorganic flame- retardant (generally metal hydroxide).
  • the metal hydroxide has a low compatibility with the thermoplastic elastomer. Unless the metal hydroxide is specially treated, the metal hydroxide is not uniformly dispersed in the thermoplastic elastomer, but agglomerates with each other. The uneven dispersion of the metal hydroxide causes reduction in tensile strength, elongation and flexibility, resulting in deterioration in mechanical properties. Disclosure of Invention Technical Problem
  • thermoplastic polyurethane elastomer-based composition in which an inorganic flame-retardant such as metal hydroxide or the like is uniformly dispersed in a thermoplastic polyurethane elastomer to ensure harmony of mechanical properties.
  • the present invention provides a thermoplastic polyurethane elastomer-based composition for an insulation layer or sheath layer of an electric cable.
  • the composition comprises a base resin consisting of 50 to 98 weight% of a ther- moplastic polyurethane elastomer, and 2 to 50 weight% of a polyolefin grafted with a polar functional group; and 50 to 200 parts by weight of an inorganic flame-re tardant based on 100 parts by weight of the base resin.
  • the standard deviation for the weight loss of a unit section from a thermogravimetric analysis is within 5% of an average weight of unit sections before said thermogravimetric analysis, said unit section being a unit section of the insulation layer or sheath layer manufactured from said composition, and the inorganic particles of the residue obtained from dissolving said insulation layer or sheath layer with an organic solvent have an average maximum diameter of 0.5 to 100 ⁇ m, 30% or more of said inorganic particles falling within a diameter range of 1.0 to 50 ⁇ m.
  • the thermoplastic polyurethane elastomer is a polymer alloy of thermoplastic polyurethane elastomers.
  • the thermoplastic polyurethane elastomer has a molecular weight of 20,000 to 700,000 and a hardness of 2OD to 80D using the Shore D scale.
  • the polyolefin grafted with a polar functional group may be polyethylene, ethylene-vinyl acetate (EVA) copolymer or ethylene-ethyl acrylate copolymer, grafted with maleic anhydride or glycidyl methacrylate.
  • the insulation layer or sheath layer formed using the thermoplastic polyurethane elastomer-based composition is very flexible and maintains its mechanical strength to a specific level.
  • the insulation or sheath layer is also excellent in oil resistance, heat resistance and abrasion resistance.
  • an electric cable equipped with the insulation or sheath layer is environmentally friendly and excellent in properties, flexibility, elasticity, heat resistance, abrasion resistance and so on.
  • FIGs. 1 and 2 are cross-sectional views of electric cables equipped with an insulation layer and a sheath layer formed using a thermoplastic polyurethane elastomer according to an embodiment of the present invention, respectively. Best Mode for Carrying out the Invention
  • the present invention provides a thermoplastic polyurethane elastomer-based composition for an insulation layer or sheath layer of an electric cable and an electric cable equipped with the insulation layer or sheath layer.
  • the present invention provides a thermoplastic polyurethane elastomer-based composition for an insulation layer or sheath layer of an electric cable.
  • the composition comprises a base resin including a thermoplastic elastomer and a polyolefin grafted with a polar functional group, an inorganic flame-retardant and a secondary flame-retardant, and selectively an additive.
  • the base resin of the composition according to the present invention includes 50 to 98 weight% of a thermoplastic polyurethane resin and 2 to 50 weight% of a polyolefin grafted with a polar functional group.
  • the present invention uses a thermoplastic polyurethane elastomer
  • thermoplastic polyurethane elastomer As the thermoplastic elastomer, the thermoplastic polyurethane elastomer is excellent in mechanical properties, abrasion resistance, flexural properties, oil resistance and so on, and thus is proper for an insulation layer or sheath layer of an electric cable. Generally, the thermoplastic elastomer has properties varying depending on a composition ratio of soft and hard segments, and its purpose of use is determined according to the properties.
  • the thermoplastic polyurethane elastomer usable in the present invention comprises a hard segment of diisocyanate and a soft segment of polyol, and preferably has a molecular mass of 20,000 to 700,000.
  • the thermoplastic polyurethane elastomer does not exhibit its peculiar abrasion resistance and strength. If the molecular mass is more than 700,000, the thermoplastic polyurethane elastomer has an excessive viscosity, causing a processing problem and unfavorable flexibility and flexural properties. Meanwhile, because the composition of the present invention is used for an insulation layer or sheath layer of an electric cable, the thermoplastic polyurethane elastomer has preferably a hardness of 2OD to 80D using the Shore D scale. If hardness is less than 2OD, the thermoplastic polyurethane elastomer does not satisfy the hardness or strength standards required for an insulation layer or sheath layer of an electric cable. And, if hardness is more than 80D, the thermoplastic polyurethane elastomer excessively increases the hardness of an electric cable and causes deterioration in flexural properties.
  • thermoplastic polyurethane elastomer satisfying the property conditions is, for example, polycarbonate-based polyol type TPU, ether-based polyol type TPU, caprolactone-based polyester type TPU and adipate-based polyester type TPU according to the component of a soft segment.
  • the thermoplastic polyurethane elastomer encompasses polymer alloys of the exemplary TPUs.
  • thermoplastic polyurethane elastomer may include a polyolefin containing a polar functional group, specifically, polyethylene, ethylene- vinyl acetate copolymer and ethylene-ethyl acrylate that are grafted with maleic anhydride or glycidyl methacrylate.
  • a polyolefin containing a polar functional group specifically, polyethylene, ethylene- vinyl acetate copolymer and ethylene-ethyl acrylate that are grafted with maleic anhydride or glycidyl methacrylate.
  • the thermoplastic polyurethane elastomer is included in the base resin at an amount of 50 to 98 weight%.
  • the content of the thermoplastic polyurethane elastomer is in the range, the thermoplastic polyurethane elastomer has improvement in its mechanical strength, abrasion resistance, oil resistance and heat resistance. If the content of the thermoplastic polyurethane elastomer is less than 50 weight%, the thermoplastic polyure thane elastomer has reduction in mechanical properties, oil resistance and abrasion resistance.
  • thermoplastic polyurethane elastomer If the content of the thermoplastic polyurethane elastomer is more than 98 weight%, dispersion of an inorganic filler such as an inorganic flame- retardant or the like reduces, and consequently the thermoplastic polyurethane elastomer has a reduction in mechanical properties.
  • an inorganic filler such as an inorganic flame- retardant or the like
  • thermoplastic polyurethane elastomer-based composition of the present invention comprises 50 to 200 parts by weight of an inorganic flame-retardant based on 100 parts by weight of the base resin.
  • the content of the inorganic flame- retardant is in the range, the composition stably satisfies the following flame-retardant test standards.
  • the inorganic flame-retardant may be magnesium hydroxide, aluminium hydroxide, calcium hydroxide, huntite (Mg 3 Ca(CO 3 ) 4 ), hydromagnesite (Mg 5 (CO 3 ) 4 (OH) 2 ) or mixtures thereof.
  • magnesium hydroxide is used as the inorganic flame-retardant since magnesium hydroxide has a minimum change in tensile strength and elongation at room temperature and a desired level of flame retardancy.
  • the inorganic flame-retardant is magnesium hydroxide, aluminium hydroxide or mixtures thereof.
  • the inorganic flame-retardant may be used without surface coating or be surface-coated with a coating material selected from the group consisting of an organic silane, an organic acid and an organic polymer.
  • the organic silane as the coating material includes vinyl silane, amino silane, methacrylate silane and so on.
  • the organic acid may include fatty acid, stearic acid, oleic acid and so on.
  • the organic acid may include a phosphoric acid that is an inorganic acid.
  • thermoplastic polyurethane elastomer-based composition of the present invention may comprise a secondary flame-retardant to reduce an amount of the inorganic flame-retardant and improve flame retardancy.
  • a secondary flame-retardant may be included based on 100 parts by weight of the base resin.
  • the secondary flame-retardant may be a zinc borate-based flame-retardant, an organic phosphorous acid-based flame-retardant, a melamine derivative and so on.
  • the present invention is characterized in that the inorganic flame-retardant based on metal hydroxide having a low compatibility with plastics is uniformly dispersed in the thermoplastic polyurethane elastomer to ensure harmony of the mechanical properties such as tensile strength, elongation, flexibility and so on.
  • the present invention uses a polyolefin, in which a polymer is grafted with a polar functional group. Said poly olefin is hereinafter referred to as poly olefin grafted with a polar functional group.
  • the polyolefin grafted with a polar functional group increases compatibility between the inorganic flame-retardant and the thermoplastic polyurethane elastomer.
  • the present invention uses a mixed resin of TPU and thermoplastic polyurethane elastomer as the base resin.
  • the polyolefin grafted with a polar functional group is included at an amount of 2 to 50 weight% of the base resin.
  • the content of the polyolefin with a polar functional group is in this range, compatibility increases between a polymer resin and a polar inorganic filler such as the inorganic flame-retardant.
  • a source of the polar functional group may be, for example, maleic anhydride, glycidyl methacrylate or mixtures thereof.
  • the polyolefin to be grafted with the polar functional group may be, for example, polyethylene, an ethylene- vinyl acetate (EVA) copolymer and/or an ethylene-ethyl acrylate copolymer.
  • EVA ethylene- vinyl acetate
  • the polyolefin is grafted with 0.1 to 10 weight% of monomers containing the polar functional group based on weight of the polyolefin.
  • the content of the polar functional group is in this range, it is preferable in aspects of compatibility between the thermoplastic polyurethane elastomer and the inorganic flame-retardant as well as thermal stability of the thermoplastic polyurethane elastomer-based composition. If the content of the polar functional group is less than 0.1 weight%, the improvement in compatibility between the thermoplastic polyurethane elastomer and the inorganic flame-retardant is negligible. If the content of the polar functional group is more than 10 weight%, there is a reduction in thermal stability of the thermoplastic polyurethane elastomer-based composition.
  • composition for the inventive insulating material is carefully controlled so as to achieve uniform dispersion of a certain level or higher.
  • an insulation layer or sheath layer formed using the composition of the present invention should satisfy the following levels of dispersion characterized by thermogravimetric analysis and of particle size distribution characterized by an organic solvent extraction.
  • the dispersion is measured by thermogravimetric analysis in such a way that an insulation layer or sheath layer of an electric cable is cut into a plurality of unit sections, this unit sections are then thermally decomposed using a thermogravimetric analyzer, and the deviation for the residual weight is determined.
  • thermogravimetric analysis when an insulation layer formed using a composition comprising a base resin and a magnesium hydroxide flame-retardant is thermally decomposed in a thermogravimetric analysis, the polymer resin disappears as vapor, volatile components and so on, and magnesium oxide remains as shown in chemistry figure 1.
  • thermogravimetric analysis an insulation layer or sheath layer is cut into unit sections having a size of about 10 mg and these sections are put in a thermogravimetric analyzer under a nitrogen atmosphere while raising the temperature from room temperature to up to 800 0 C at a temperature ramp rate of 10 °C/min, and the change in weight is measured. Subsequently, the unit sections are thermally decomposed at 800 to 900 0 C under an oxygen atmosphere, and the residue is weighed out. If the thermogravimetric analysis is carried out under an oxygen atmosphere from the beginning, additives and the mixture would react to interfere with an accurate analysis. Also, the unit sections may pop in the case of a severe reaction with oxygen.
  • the resultant weight loss for each unit section i.e., a difference between the residual weight of a unit section and the weight of the unit section before the thermogravimetric analysis (hereinafter referred to as an initial weight of the unit section) is calculated. Then, the standard deviation for this weight loss is calculated and compared to the average initial weight of the unit sections in weight percents. This converted value of weight loss in weight percents is defined as the residual deviation. If an insulation layer or sheath layer of an electric cable has a high dispersion, the average residual deviation is very small because each unit section has a uniform composition with the same elements and contents.
  • An insulation layer or sheath layer of an electric cable formed using the composition of the present invention has an average residual deviation of 5 weight% or less by thermogravimetric analysis, that is, the standard deviation for weight loss falls within 5% of the average initial weight of unit sections. If the average residual deviation is more than 5%, the inorganic flame-retardant is not uniformly dispersed in the thermoplastic polyurethane resin within each unit section.
  • the particle size distribution is measured by organic solvent extraction in such a way that an insulation layer or sheath layer of an electric cable is dissolved in an organic solvent to remove a polymer and an organic substance, and the particle size of the inorganic residue is measured.
  • an insulation layer or sheath layer is cut into unit sections having a size of about 300 mg, put in an organic solvent of 12O 0 C and dissolved with reflux for 24 hours or longer. Then, this organic solvent mixture is filtered with a filter paper to obtain the precipitate or suspension of the inorganic particles. After the precipitate or suspension is dried, the particle size distribution of the inorganic residue is measured using a particle size analyzer.
  • the inorganic particles extracted within an organic solvent is outside the range of 0.5 to 100 ⁇ m, the inorganic particles are not uniformly dispersed in the thermoplastic polyurethane elastomer. If a ratio of inorganic particles with a diameter of 1.0 to 50 ⁇ m to the whole inorganic particles is less than 30%, the inorganic particles are not uniformly dispersed in the thermoplastic polyurethane elastomer.
  • thermoplastic polyurethane elastomer-based composition of the present invention may further comprise an additive generally used in the art, such as an antioxidant, a UV stabilizer, a hydrolysis inhibitor, a lubricant, a processing aid and so on.
  • an additive generally used in the art such as an antioxidant, a UV stabilizer, a hydrolysis inhibitor, a lubricant, a processing aid and so on.
  • antioxidant UV stabilizer
  • hydrolysis inhibitor hydrolysis inhibitor
  • lubricant processing aid
  • the antioxidant and UV stabilizer may be each included at an amount of 1 to 10 parts by weight based on 100 parts by weight of the base resin, and the hydrolysis inhibitor, lubricant and processing aid may be each included at an amount of 0.5 to 15 parts by weight based on 100 parts by weight of the base resin.
  • a twin-screw extruder is advantageous for uniform dispersion of an inorganic flame-retardant in a polymer compound comprising the base resin and the inorganic flame-retardant.
  • the twin-screw extruder has a length-to-diameter (L/D) ratio of 24 or more and at least two kneading blocks for uniform dispersion of the inorganic flame-retardant through improved mixing.
  • the present invention also provides an electric cable equipped with an insulation layer or sheath layer formed using the thermoplastic polyurethane elastomer-based composition, and the electric cable of the present invention is described with reference to FIGs. 1 and 2.
  • FIG. 1 is a cross-sectional view of an electric cable equipped with an insulation layer formed using the thermoplastic polyurethane elastomer-based composition according to an embodiment of the present invention.
  • FIG. 2 is a cross-sectional view of an electric cable equipped with a sheath layer formed using the thermoplastic polyurethane elastomer-based composition according to a embodiment of the present invention.
  • the electric cable 10 equipped with an insulation layer formed using the thermoplastic polyurethane elastomer-based composition according to an embodiment of the present invention is formed of a conductive wire having a circular cross section.
  • the electric cable 10 comprises a conductor 11 and an insulator 12 surrounding the conductor 11.
  • the conductor 11 may be copper, a tin-plated copper and so on, and its thickness may be controlled according to necessity.
  • the insulator 12 is made from the thermoplastic polyurethane elastomer-based composition of the present invention.
  • the insulator 12 is formed on the surface of the conductor 11 by mix- milling the thermoplastic polyurethane elastomer-based composition into a pellet form and extruding the pellets by an extruder.
  • the electric cable 15 equipped with a sheath layer formed using the thermoplastic polyurethane elastomer-based composition according to an embodiment of the present invention is a fiber to the home (FTTH) leading-edge optical cable used in the FTTH network, in which a single mode optical fiber for the long wavelength is used as a coated fiber.
  • a core and a cladding 16 of the optical fiber are mainly made from quartz -based glass, and an inner coating 17 of the optical fiber is made from a resin such as PVC, PE, PBT and so on.
  • An outer coating 18 is arranged around the optical fiber uniformly and concentrically with a strength member of aramid yarn or the like.
  • a sheath layer 19 is made from the thermoplastic polyurethane elastomer-based composition of the present invention.
  • the sheath layer 19 is formed on the surface of the inner structure (16, 17, 18) having a circular cross section by mix- milling the thermoplastic polyurethane elastomer-based composition into a pellet form and extruding the pellets by an extruder.
  • thermoplastic polyurethane elastomer-based composition for an insulation layer or sheath layer
  • compositions of examples and comparative examples were prepared according to the elements and contents of Table 1.
  • TPU Skythane R185A (Specific gravity: 1.21, Shore hardness: 36D, Softening point: 90 0 C) from SK Chemical
  • Inorganic flame-retardant Magnesium hydroxide
  • Additives Antioxidant: 0.5 to 2 parts by weight of IrganoxlOlO phenol-based antioxidant from Ciba, UV stabilizer: 0.5 to 2 parts by weight of Tinuvin from Ciba, Hydrolysis inhibitor: 0.5 to 2 parts by weight of Stabilizer7000 from RASCHIG, Lubricant and Processing aid: 0.5 to 2 parts by weight of PE wax from Lionchem
  • An insulation layer specimen for an electric cable was formed using the compositions of examples and comparative examples prepared according to Table 1.
  • a twin-screw extruder was used to induce uniform dispersion of an inorganic material.
  • the twin-screw extruder had an L/D ratio of 28 and two kneading blocks for uniform dispersion of the inorganic material through improved mixing, and a compound temperature was in the range of 170 to 220 0C.
  • comparative example 2 mill-mixed the composition at 18O 0 C for 20 minutes by a two roll mill, instead of a twin-screw extruder.
  • thermogravimetric analysis an insulation layer or sheath layer for an electric cable was cut into 10 unit sections having a size of about 10 mg and put in a thermogravimetric analyzer under a nitrogen atmosphere while raising the temperature from room temperature up to 800 0 C at a temperature ramp rate of 10 °C/min, and a change in weight was measured.
  • the unit sections were thermally decomposed at 800 to 900 0 C under an oxygen atmosphere, and the standard residual deviation from thermogravimetric analysis was relatively compared to an average initial weight of the unit sections that is converted in weight percents (an average residual deviation).
  • an insulation layer or sheath layer or an electric cable was cut into unit sections having a size of about 300 mg, these sections were put in a tetrahydrofuran (THF) solvent of room temperature and dissolved with reflux for 6 hours or longer. Then, this organic solvent mixture was filtered with a filter paper to obtain the precipitate or suspension. After the precipitate or suspension was dried, the particle size distribution of the inorganic residue was measured using a particle size analyzer.
  • THF tetrahydrofuran
  • thermogravimetric analysis results and dispersion of inorganic particles are shown in Table 2. [55] Table 2 [Table 2] [Table ]
  • the tensile strength and elongation of the insulation layer specimen were measured at a test rate of 200 mm/min according to the ASTM D 638 standards.
  • the limited oxygen index (LOI) of the insulation layer specimen was measured according to the ISO 4589-3 standards, and determined as flame retardancy.
  • the abrasion resistance was evaluated by moving back and forth repeatedly up to 300 times in the plane of the surface of the insulation layer specimen, a needle having a thickness of 3 mm under a load of 700 g applied against said surface, and measuring wear of the specimen.
  • a jacket material for an electric cable should have a tensile strength of 1.0 kgf/mm 2 or more, an elongation of 100% or more, LOI of at least 28 as flame retardancy, and a degree of wear of 10% or less.
  • the comparative examples 1 and 2 have lower tensile strength and elongation due to the reduced dispersion.
  • the comparative example 3 shows a great degree of wear.
  • the comparative example 4 has a significant reduction in LOI, and thus is not suitable for a jacket material of an electric cable.

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Abstract

Disclosed are a halogen-free insulating composition comprising a thermoplastic polyurethane elastomer and an insulating cable equipped with an insulation layer or sheath layer formed using the composition. The composition comprises a base resin consisting of a thermoplastic polyurethane elastomer and polyolefin grafted with a polar functional group, and a halogen-free inorganic flame-retardant. The standard deviation for the weight loss of a unit section from a thermogravimetric analysis is within 5% of an average weight of unit sections before said ther- mogravimetric analysis, said unit section being a unit section of the insulation layer or sheath layer manufactured from said composition, and the inorganic particles of the residue obtained from dissolving said insulation layer or sheath layer with an organic solvent have an average maximum diameter of 0.5 to 100 μm, 30% or more of said inorganic particles falling within a diameter range of 1.0 to 50 μm.

Description

THERMOPLASTIC POLYURETHANE ELASTOMER-BASED COMPOSITION FOR INSULATION LAYERS AND ELECTRIC CABLE EQUIPPED THEREWITH
The present invention relates to a thermoplastic polyurethane elastomer (TPU or TPE-U)-based composition for insulation and sheath layers and an electric cable equipped therewith. In particular, the present invention relates to a composition for insulation and sheath layers, in which an inorganic component such as a metal hydroxide flame-retardant or the like is uniformly dispersed in a thermoplastic elastomer structure to ensure harmony of the mechanical properties, and an electric cable equipped therewith.
The electric cable industries have widely used polyvinyl chloride (PVC) or a polyethylene-based resin added with a halogen-based flame-retardant to form an insulation or sheath layer of an insulating cable having flame retardancy of a certain level or higher. These resins have excellent properties and high flame retardancy and economical efficiency, but are hazardous to the environment. For this reason, they will become more difficult to use in forming insulation and sheath layers of flame-retardant cables. Furthermore, the developed countries are strongly forcing to use plastic materials in forming insulation and sheath layers of electric cables since the plastic materials are recyclable. With this current trend, use of materials that are not recyclable will be prohibited in the end. The European Union (EU) adopted the Restriction of Hazardous Substances Directive (RoHS) that restricts the use of certain hazardous substances in electrical and electronic equipments and sets collection, recycling and recovery targets for electrical goods. The RoHS directive took effect on July 1, 2006. The EU also adopted the End-of-Life Vehicle (ELV) directive that has an impact on the automotive industries. The aim of this directive is to increase the rate of re-use and recovery to 95% in terms of average weight per vehicle/year by 2015. However, taking into consideration that the length of cables used in a car is generally about 2 km, it is important to recycle a greater amount of plastic material of electric cables so as to attain the target recycling rate.
A halogen-free polyethylene resin is widely used in place of PVC. When the halogen-free polyethylene resin is crosslinked, the halogen-free polyethylene resin has good mechanical properties such as strength and so on, and excellent flame retardancy and economical efficiency. However, the crosslinked polyethylene resin cannot be recycled. This is a drawback as a material for an insulation layer of an insulating cable. Compared with the polyethylene resin, polypropylene has low flame retardancy. To make up for low flame retardancy of the polypropylene-based resin, a large amount of an inorganic flame-retardant such as metal hydroxide or the like is added. However, the resultant end-products have deterioration in moldability and mechanical properties such as tensile strength and so on.
Accordingly, the electric cable manufacturers have readily studied to develop an environmentally friendly insulating material that is free of halogen and has excellent flame retardancy, mechanical and chemical properties such as flexibility, oil resistance and so on. Under this circumstance, thermoplastic elastomer (TPE) meeting the conditions becomes the center of attention. The thermoplastic elastomer has both of elasticity of rubbers and moldability of thermoplastic plastics such as polyethylene or the like. The thermoplastic elastomer is a copolymer of a soft monomer and a hard monomer, or a blend of a soft polymer and a hard polymer. Typically, a thermoplastic polyurethane (TPU) represents the thermoplastic elastomer. The thermoplastic elastomer satisfies the specific level of mechanical properties without crosslinking, and has excellent recyclability, heat resistance and abrasion resistance.
However, the thermoplastic elastomer does not reach the specific level of flame retardancy. To achieve the specific level of flame retardancy, the thermoplastic elastomer is inevitably added with a large amount of a halogen-free inorganic flame-retardant (generally metal hydroxide). The metal hydroxide has a low compatibility with the thermoplastic elastomer. Unless the metal hydroxide is specially treated, the metal hydroxide is not uniformly dispersed in the thermoplastic elastomer, but agglomerates with each other. The uneven dispersion of the metal hydroxide causes reduction in tensile strength, elongation and flexibility, resulting in deterioration in mechanical properties.
Therefore, it is an object of the present invention to provide an electric cable equipped with an insulation layer or sheath layer formed using a thermoplastic polyurethane elastomer-based composition, in which an inorganic flame-retardant such as metal hydroxide or the like is uniformly dispersed in a thermoplastic polyurethane elastomer to ensure harmony of mechanical properties.
To achieve the object, the present invention provides a thermoplastic polyurethane elastomer-based composition for an insulation layer or sheath layer of an electric cable. The composition comprises a base resin consisting of 50 to 98 weight% of a thermoplastic polyurethane elastomer, and 2 to 50 weight% of a polyolefin grafted with a polar functional group; and 50 to 200 parts by weight of an inorganic flame-retardant based on 100 parts by weight of the base resin. The standard deviation for the weight loss of a unit section from a thermogravimetric analysis is within 5% of an average weight of unit sections before said thermogravimetric analysis, said unit section being a unit section of the insulation layer or sheath layer manufactured from said composition, and the inorganic particles of the residue obtained from dissolving said insulation layer or sheath layer with an organic solvent have an average maximum diameter of 0.5 to 100 μm, 30% or more of said inorganic particles falling within a diameter range of 1.0 to 50 μm.
In the present invention, the thermoplastic polyurethane elastomer is a polymer alloy of thermoplastic polyurethane elastomers. Preferably, the thermoplastic polyurethane elastomer has a molecular weight of 20,000 to 700,000 and a hardness of 20D to 80D using the Shore D scale. The polyolefin grafted with a polar functional group may be polyethylene, ethylene-vinyl acetate (EVA) copolymer or ethylene-ethyl acrylate copolymer, grafted with maleic anhydride or glycidyl methacrylate.
According to the present invention, the insulation layer or sheath layer formed using the thermoplastic polyurethane elastomer-based composition is very flexible and maintains its mechanical strength to a specific level. The insulation or sheath layer is also excellent in oil resistance, heat resistance and abrasion resistance. Thus, an electric cable equipped with the insulation or sheath layer is environmentally friendly and excellent in properties, flexibility, elasticity, heat resistance, abrasion resistance and so on.
FIGs. 1 and 2 are cross-sectional views of electric cables equipped with an insulation layer and a sheath layer formed using a thermoplastic polyurethane elastomer according to an embodiment of the present invention, respectively.
Hereinafter, the present invention will be described in detail. The present invention provides a thermoplastic polyurethane elastomer-based composition for an insulation layer or sheath layer of an electric cable and an electric cable equipped with the insulation layer or sheath layer.
According to an aspect, the present invention provides a thermoplastic polyurethane elastomer-based composition for an insulation layer or sheath layer of an electric cable. The composition comprises a base resin including a thermoplastic elastomer and a polyolefin grafted with a polar functional group, an inorganic flame-retardant and a secondary flame-retardant, and selectively an additive. The base resin of the composition according to the present invention includes 50 to 98 weight% of a thermoplastic polyurethane resin and 2 to 50 weight% of a polyolefin grafted with a polar functional group.
In the base resin, the present invention uses a thermoplastic polyurethane elastomer (TPU) as the thermoplastic elastomer. Of the thermoplastic elastomer, the thermoplastic polyurethane elastomer is excellent in mechanical properties, abrasion resistance, flexural properties, oil resistance and so on, and thus is proper for an insulation layer or sheath layer of an electric cable. Generally, the thermoplastic elastomer has properties varying depending on a composition ratio of soft and hard segments, and its purpose of use is determined according to the properties. The thermoplastic polyurethane elastomer usable in the present invention comprises a hard segment of diisocyanate and a soft segment of polyol, and preferably has a molecular mass of 20,000 to 700,000. If the molecular mass is less than 20,000, the thermoplastic polyurethane elastomer does not exhibit its peculiar abrasion resistance and strength. If the molecular mass is more than 700,000, the thermoplastic polyurethane elastomer has an excessive viscosity, causing a processing problem and unfavorable flexibility and flexural properties. Meanwhile, because the composition of the present invention is used for an insulation layer or sheath layer of an electric cable, the thermoplastic polyurethane elastomer has preferably a hardness of 20D to 80D using the Shore D scale. If hardness is less than 20D, the thermoplastic polyurethane elastomer does not satisfy the hardness or strength standards required for an insulation layer or sheath layer of an electric cable. And, if hardness is more than 80D, the thermoplastic polyurethane elastomer excessively increases the hardness of an electric cable and causes deterioration in flexural properties.
The thermoplastic polyurethane elastomer satisfying the property conditions is, for example, polycarbonate-based polyol type TPU, ether-based polyol type TPU, caprolactone-based polyester type TPU and adipate-based polyester type TPU according to the component of a soft segment. In the present invention, the thermoplastic polyurethane elastomer encompasses polymer alloys of the exemplary TPUs. For example, the thermoplastic polyurethane elastomer may include a polyolefin containing a polar functional group, specifically, polyethylene, ethylene-vinyl acetate copolymer and ethylene-ethyl acrylate that are grafted with maleic anhydride or glycidyl methacrylate.
Preferably, the thermoplastic polyurethane elastomer is included in the base resin at an amount of 50 to 98 weight%. When the content of the thermoplastic polyurethane elastomer is in the range, the thermoplastic polyurethane elastomer has improvement in its mechanical strength, abrasion resistance, oil resistance and heat resistance. If the content of the thermoplastic polyurethane elastomer is less than 50 weight%, the thermoplastic polyurethane elastomer has reduction in mechanical properties, oil resistance and abrasion resistance. If the content of the thermoplastic polyurethane elastomer is more than 98 weight%, dispersion of an inorganic filler such as an inorganic flame-retardant or the like reduces, and consequently the thermoplastic polyurethane elastomer has a reduction in mechanical properties.
The thermoplastic polyurethane elastomer-based composition of the present invention comprises 50 to 200 parts by weight of an inorganic flame-retardant based on 100 parts by weight of the base resin. When the content of the inorganic flame-retardant is in the range, the composition stably satisfies the following flame-retardant test standards.
In the present invention, the inorganic flame-retardant may be magnesium hydroxide, aluminium hydroxide, calcium hydroxide, huntite (Mg3Ca(CO3)4), hydromagnesite (Mg5(CO3)4(OH)2) or mixtures thereof. According to an embodiment of the present invention, magnesium hydroxide is used as the inorganic flame-retardant since magnesium hydroxide has a minimum change in tensile strength and elongation at room temperature and a desired level of flame retardancy.
In an embodiment of the present invention, the inorganic flame-retardant is magnesium hydroxide, aluminium hydroxide or mixtures thereof. In the present invention, the inorganic flame-retardant may be used without surface coating or be surface-coated with a coating material selected from the group consisting of an organic silane, an organic acid and an organic polymer.
The organic silane as the coating material includes vinyl silane, amino silane, methacrylate silane and so on. And, the organic acid may include fatty acid, stearic acid, oleic acid and so on. Furthermore, the organic acid may include a phosphoric acid that is an inorganic acid.
Meanwhile, the thermoplastic polyurethane elastomer-based composition of the present invention may comprise a secondary flame-retardant to reduce an amount of the inorganic flame-retardant and improve flame retardancy. For example, 5 to 70 parts by weight of the secondary flame-retardant may be included based on 100 parts by weight of the base resin. The secondary flame-retardant may be a zinc borate-based flame-retardant, an organic phosphorous acid-based flame-retardant, a melamine derivative and so on.
The present invention is characterized in that the inorganic flame-retardant based on metal hydroxide having a low compatibility with plastics is uniformly dispersed in the thermoplastic polyurethane elastomer to ensure harmony of the mechanical properties such as tensile strength, elongation, flexibility and so on. For uniform dispersion, the present invention uses a polyolefin, in which a polymer is grafted with a polar functional group. Said polyolefin is hereinafter referred to as polyolefin grafted with a polar functional group. The polyolefin grafted with a polar functional group increases compatibility between the inorganic flame-retardant and the thermoplastic polyurethane elastomer. Thus, for uniform dispersion of the inorganic flame-retardant, the present invention uses a mixed resin of TPU and thermoplastic polyurethane elastomer as the base resin.
Preferably, the polyolefin grafted with a polar functional group is included at an amount of 2 to 50 weight% of the base resin. When the content of the polyolefin with a polar functional group is in this range, compatibility increases between a polymer resin and a polar inorganic filler such as the inorganic flame-retardant.
In the present invention, a source of the polar functional group (polar functionality monomer) may be, for example, maleic anhydride, glycidyl methacrylate or mixtures thereof. The polyolefin to be grafted with the polar functional group may be, for example, polyethylene, an ethylene-vinyl acetate (EVA) copolymer and/or an ethylene-ethyl acrylate copolymer. Preferably, the polyolefin is grafted with 0.1 to 10 weight% of monomers containing the polar functional group based on weight of the polyolefin. When the content of the polar functional group is in this range, it is preferable in aspects of compatibility between the thermoplastic polyurethane elastomer and the inorganic flame-retardant as well as thermal stability of the thermoplastic polyurethane elastomer-based composition. If the content of the polar functional group is less than 0.1 weight%, the improvement in compatibility between the thermoplastic polyurethane elastomer and the inorganic flame-retardant is negligible. If the content of the polar functional group is more than 10 weight%, there is a reduction in thermal stability of the thermoplastic polyurethane elastomer-based composition.
The composition for the inventive insulating material is carefully controlled so as to achieve uniform dispersion of a certain level or higher. Specifically, an insulation layer or sheath layer formed using the composition of the present invention should satisfy the following levels of dispersion characterized by thermogravimetric analysis and of particle size distribution characterized by an organic solvent extraction.
The dispersion is measured by thermogravimetric analysis in such a way that an insulation layer or sheath layer of an electric cable is cut into a plurality of unit sections, this unit sections are then thermally decomposed using a thermogravimetric analyzer, and the deviation for the residual weight is determined. For example, when an insulation layer formed using a composition comprising a base resin and a magnesium hydroxide flame-retardant is thermally decomposed in a thermogravimetric analysis, the polymer resin disappears as vapor, volatile components and so on, and magnesium oxide remains as shown in chemistry figure 1.
ChemistryFigure 1
Figure PCTKR2009004822-appb-C000001
In a typical thermogravimetric analysis, an insulation layer or sheath layer is cut into unit sections having a size of about 10 mg and these sections are put in a thermogravimetric analyzer under a nitrogen atmosphere while raising the temperature from room temperature to up to 800 OC at a temperature ramp rate of 10 OC/min, and the change in weight is measured. Subsequently, the unit sections are thermally decomposed at 800 to 900 OC under an oxygen atmosphere, and the residue is weighed out. If the thermogravimetric analysis is carried out under an oxygen atmosphere from the beginning, additives and the mixture would react to interfere with an accurate analysis. Also, the unit sections may pop in the case of a severe reaction with oxygen. The resultant weight loss for each unit section, i.e., a difference between the residual weight of a unit section and the weight of the unit section before the thermogravimetric analysis (hereinafter referred to as an initial weight of the unit section) is calculated. Then, the standard deviation for this weight loss is calculated and compared to the average initial weight of the unit sections in weight percents. This converted value of weight loss in weight percents is defined as the residual deviation. If an insulation layer or sheath layer of an electric cable has a high dispersion, the average residual deviation is very small because each unit section has a uniform composition with the same elements and contents.
An insulation layer or sheath layer of an electric cable formed using the composition of the present invention has an average residual deviation of 5 weight% or less by thermogravimetric analysis, that is, the standard deviation for weight loss falls within 5% of the average initial weight of unit sections. If the average residual deviation is more than 5%, the inorganic flame-retardant is not uniformly dispersed in the thermoplastic polyurethane resin within each unit section.
The particle size distribution is measured by organic solvent extraction in such a way that an insulation layer or sheath layer of an electric cable is dissolved in an organic solvent to remove a polymer and an organic substance, and the particle size of the inorganic residue is measured. For example, an insulation layer or sheath layer is cut into unit sections having a size of about 300 mg, put in an organic solvent of 120 OC and dissolved with reflux for 24 hours or longer. Then, this organic solvent mixture is filtered with a filter paper to obtain the precipitate or suspension of the inorganic particles. After the precipitate or suspension is dried, the particle size distribution of the inorganic residue is measured using a particle size analyzer.
If the maximum diameter of inorganic particles extracted within an organic solvent is outside the range of 0.5 to 100 μm, the inorganic particles are not uniformly dispersed in the thermoplastic polyurethane elastomer. If a ratio of inorganic particles with a diameter of 1.0 to 50 μm to the whole inorganic particles is less than 30%, the inorganic particles are not uniformly dispersed in the thermoplastic polyurethane elastomer.
The thermoplastic polyurethane elastomer-based composition of the present invention may further comprise an additive generally used in the art, such as an antioxidant, a UV stabilizer, a hydrolysis inhibitor, a lubricant, a processing aid and so on.
The antioxidant, UV stabilizer, hydrolysis inhibitor, lubricant and processing aid are typical ones used in the art.
The antioxidant and UV stabilizer may be each included at an amount of 1 to 10 parts by weight based on 100 parts by weight of the base resin, and the hydrolysis inhibitor, lubricant and processing aid may be each included at an amount of 0.5 to 15 parts by weight based on 100 parts by weight of the base resin.
A twin-screw extruder (TSE) is advantageous for uniform dispersion of an inorganic flame-retardant in a polymer compound comprising the base resin and the inorganic flame-retardant. Preferably, the twin-screw extruder has a length-to-diameter (L/D) ratio of 24 or more and at least two kneading blocks for uniform dispersion of the inorganic flame-retardant through improved mixing.
The present invention also provides an electric cable equipped with an insulation layer or sheath layer formed using the thermoplastic polyurethane elastomer-based composition, and the electric cable of the present invention is described with reference to FIGs. 1 and 2.
FIG. 1 is a cross-sectional view of an electric cable equipped with an insulation layer formed using the thermoplastic polyurethane elastomer-based composition according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of an electric cable equipped with a sheath layer formed using the thermoplastic polyurethane elastomer-based composition according to a embodiment of the present invention.
As shown in FIG. 1, the electric cable 10 equipped with an insulation layer formed using the thermoplastic polyurethane elastomer-based composition according to an embodiment of the present invention is formed of a conductive wire having a circular cross section. The electric cable 10 comprises a conductor 11 and an insulator 12 surrounding the conductor 11. The conductor 11 may be copper, a tin-plated copper and so on, and its thickness may be controlled according to necessity. The insulator 12 is made from the thermoplastic polyurethane elastomer-based composition of the present invention. The insulator 12 is formed on the surface of the conductor 11 by mix-milling the thermoplastic polyurethane elastomer-based composition into a pellet form and extruding the pellets by an extruder.
As shown in FIG. 2, the electric cable 15 equipped with a sheath layer formed using the thermoplastic polyurethane elastomer-based composition according to an embodiment of the present invention is a fiber to the home (FTTH) leading-edge optical cable used in the FTTH network, in which a single mode optical fiber for the long wavelength is used as a coated fiber. A core and a cladding 16 of the optical fiber are mainly made from quartz-based glass, and an inner coating 17 of the optical fiber is made from a resin such as PVC, PE, PBT and so on. An outer coating 18 is arranged around the optical fiber uniformly and concentrically with a strength member of aramid yarn or the like. A sheath layer 19 is made from the thermoplastic polyurethane elastomer-based composition of the present invention. The sheath layer 19 is formed on the surface of the inner structure (16, 17, 18) having a circular cross section by mix-milling the thermoplastic polyurethane elastomer-based composition into a pellet form and extruding the pellets by an extruder.
Hereinafter, the present invention will be described in detail through examples and exemplary production method. Prior to the description, it should be understood that the terms used in the specification and appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present invention on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation.
<Example 1> Preparation of a thermoplastic polyurethane elastomer-based composition for an insulation layer or sheath layer
To evaluate the performance of an electric cable equipped with an insulation layer or sheath layer formed using the thermoplastic polyurethane elastomer-based composition of the present invention, compositions of examples and comparative examples were prepared according to the elements and contents of Table 1.
Table 1
Element(parts by weight) Examples Comparative examples
1 2 3 4 5 1 2 3 4
TPU 50 70 90 90 95 100 100 45 90
Polyolefin grafted with polar functional group 50 30 10 10 5 - - 55 10
Partial sum of weight 100 parts by weight(base resin)
Inorganic flame-retardant 150 150 150 180 150 150 150 150 40
Additives 5 5 5 5 5 5 5 5 5
[Particulars of Table 1]
TPU: Skythane R185A (Specific gravity: 1.21, Shore hardness: 36D, Softening point: 90 OC) from SK Chemical
Polyolefin grafted with a polar functional group: ethylene-vinyl acetate copolymer resin grafted with maleic anhydride monomer (Content of vinyl acetate monomer: 28%, Melt flow index: 1.5)
Inorganic flame-retardant: Magnesium hydroxide
Additives: Antioxidant: 0.5 to 2 parts by weight of Irganox1010 phenol-based antioxidant from Ciba, UV stabilizer: 0.5 to 2 parts by weight of Tinuvin from Ciba, Hydrolysis inhibitor: 0.5 to 2 parts by weight of Stabilizer7000 from RASCHIG, Lubricant and Processing aid: 0.5 to 2 parts by weight of PE wax from Lionchem
An insulation layer specimen for an electric cable was formed using the compositions of examples and comparative examples prepared according to Table 1. In the manufacture of an electric cable specimen, a twin-screw extruder was used to induce uniform dispersion of an inorganic material. The twin-screw extruder had an L/D ratio of 28 and two kneading blocks for uniform dispersion of the inorganic material through improved mixing, and a compound temperature was in the range of 170 to 220 OC. Meanwhile, comparative example 2 mill-mixed the composition at 180 OC for 20 minutes by a two roll mill, instead of a twin-screw extruder.
<Example 2> Evaluation of dispersion of an insulation layer specimen
The dispersion of inorganic particles in the insulation layer specimen formed as mentioned above was evaluated by thermogravimetric analysis and organic solvent extraction.
According to thermogravimetric analysis, an insulation layer or sheath layer for an electric cable was cut into 10 unit sections having a size of about 10 mg and put in a thermogravimetric analyzer under a nitrogen atmosphere while raising the temperature from room temperature up to 800 OC at a temperature ramp rate of 10 OC/min, and a change in weight was measured. Subsequently, the unit sections were thermally decomposed at 800 to 900 OC under an oxygen atmosphere, and the standard residual deviation from thermogravimetric analysis was relatively compared to an average initial weight of the unit sections that is converted in weight percents (an average residual deviation).
According to organic solvent extraction, an insulation layer or sheath layer or an electric cable was cut into unit sections having a size of about 300 mg, these sections were put in a tetrahydrofuran (THF) solvent of room temperature and dissolved with reflux for 6 hours or longer. Then, this organic solvent mixture was filtered with a filter paper to obtain the precipitate or suspension. After the precipitate or suspension was dried, the particle size distribution of the inorganic residue was measured using a particle size analyzer.
The thermogravimetric analysis results and dispersion of inorganic particles are shown in Table 2.
Table 2
Examples Comparative examples
1 2 3 4 5 1 2 3 4
Average residual deviation(%) 0.5 1 1 0.5 0.7 6 8 0.5 1
Average particle size of inorganic particles(μm) 22.0 13.5 31.0 10.0 25 50.0 65.0 12 5
Percentage of inorganic particles of 1 to 50 μm diameter(%) 50 5 60 35 50 28 15 50 60
It is found from Table 2 that the insulation layer specimens according to examples meet the standards of the present invention in aspects of average residual deviation, average particle size and particle size distribution of inorganic particles. The comparative examples 1 and 2 have problems about dispersion of inorganic particles. The comparative examples 3 and 4 have problems about ball wear rate or flame retardancy, not about dispersion of inorganic particles.
<Example 3> Evaluation of properties of an insulation layer specimen
The insulation layer specimens of examples and comparative examples were evaluated in aspects of properties such as tensile strength, elongation and flame retardancy. The properties were tested as follows.
The tensile strength and elongation of the insulation layer specimen were measured at a test rate of 200 mm/min according to the ASTM D 638 standards.
The limited oxygen index (LOI) of the insulation layer specimen was measured according to the ISO 4589-3 standards, and determined as flame retardancy.
The abrasion resistance was evaluated by moving back and forth repeatedly up to 300 times in the plane of the surface of the insulation layer specimen, a needle having a thickness of 3 mm under a load of 700 g applied against said surface, and measuring wear of the specimen.
Typically, a jacket material for an electric cable should have a tensile strength of 1.0 kgf/mm2 or more, an elongation of 100% or more, LOI of at least 28 as flame retardancy, and a degree of wear of 10% or less.
The test results are shown in Table 3.
Table 3
Examples Comparative examples
1 2 3 4 5 1 2 3 4
Tensile strength (kgf/mm2) 1.5 1.4 1.6 1.1 1.7 0.9 0.8 1.4 2.0
Elongation (%) 240 220 200 150 190 90 50 300 500
Degree of wear(%) 3 2.5 2 2.2 1.5 0.5 0.5 50 1.0
Limiting oxygen index(%) 32 34 34 37 34 33 32 31 26
It is found from Table 3 that the specimens of examples manufactured according to the present invention have better tensile strength, elongation, flame retardancy and abrasion resistance due to the improved dispersion, than the specimens of comparative examples manufactured according to the prior art.
However, the comparative examples 1 and 2 have lower tensile strength and elongation due to the reduced dispersion. The comparative example 3 shows a great degree of wear. The comparative example 4 has a significant reduction in LOI, and thus is not suitable for a jacket material of an electric cable.
The present invention has been described in detail. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

Claims (6)

  1. A composition for an insulation layer or sheath layer of an electric cable, comprising:
    a base resin consisting of:
    50 to 98 weight% of a thermoplastic polyurethane elastomer, and
    2 to 50 weight% of a polyolefin grafted with a polar functional group; and
    50 to 200 parts by weight of an inorganic flame-retardant based on 100 parts by weight of the base resin,
    wherein the standard deviation for the weight loss of a unit section from a thermogravimetric analysis is within 5% of an average weight of unit sections before said thermogravimetric analysis, said unit section being a unit section of the insulation layer or sheath layer manufactured from said composition, and
    wherein the inorganic particles of the residue obtained from dissolving said insulation layer or sheath layer with an organic solvent have an average maximum diameter of 0.5 to 100 μm,
    30% or more of said inorganic particles falling within a diameter range of 1.0 to 50 μm.
  2. The composition for an insulation layer or sheath layer of an electric cable according to claim 1,
    wherein the thermoplastic polyurethane elastomer is a polymer alloy of thermoplastic polyurethane elastomers.
  3. The composition for an insulation layer or sheath layer of an electric cable according to claim 1,
    wherein the thermoplastic polyurethane elastomer has a molecular weight of 20,000 to 700,000 and a hardness of 20D to 80D using the Shore D scale.
  4. The composition for an insulation layer or sheath layer of an electric cable according to claim 1,
    wherein the polyolefin grafted with a polar functional group is polyethylene, ethylene-vinyl acetate (EVA) copolymer or ethylene-ethyl acrylate copolymer, grafted with maleic anhydride or glycidyl methacrylate.
  5. The composition for an insulation layer or sheath layer of an electric cable according to claim 1,
    wherein the inorganic flame-retardant is at least one selected from the group consisting of magnesium hydroxide, aluminium hydroxide, calcium hydroxide, huntite (Mg3Ca(CO3)4) and hydromagnesite (Mg5(CO3)4(OH)2).
  6. An insulating cable, comprising a metal conductor bundle of a single or multiple mode fiber or a single or multiple mode optical fiber; and an insulation layer or sheath layer surrounding the metal conductor bundle or optical fiber,
    wherein the insulation layer or sheath layer is formed from a composition comprising:
    a base resin consisting of:
    50 to 98 weight% of a thermoplastic polyurethane elastomer, and
    2 to 50 weight% of a polyolefin grafted with a polar functional group; and
    50 to 200 parts by weight of an inorganic flame-retardant based on 100 parts by weight of the base resin,
    wherein the standard deviation for the weight loss of a unit section from a thermogravimetric analysis is within 5% of an average weight of unit section before said thermogravimetric analysis, said unit section being a unit section of the insulation layer or sheath layer manufactured from said composition, and
    wherein the inorganic particles of the residue obtained from dissolving said insulation layer or sheath layer with an organic solvent have an average maximum diameter of 0.5 to 100 μm,
    30% or more of said inorganic particles falling within a diameter range of 1.0 to 50 μm.
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