WO2010090438A2 - Thermoplastic ester elastomer-based composition for insulation layers and electric cable equipped therewith - Google Patents

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

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Publication number
WO2010090438A2
WO2010090438A2 PCT/KR2010/000655 KR2010000655W WO2010090438A2 WO 2010090438 A2 WO2010090438 A2 WO 2010090438A2 KR 2010000655 W KR2010000655 W KR 2010000655W WO 2010090438 A2 WO2010090438 A2 WO 2010090438A2
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WO
WIPO (PCT)
Prior art keywords
weight
insulation layer
ester elastomer
composition
retardant
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PCT/KR2010/000655
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French (fr)
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WO2010090438A3 (en
Inventor
Whan-Ki Kim
Gi-Joon Nam
Won-Jung Kim
Ju-Ha Lee
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Ls Cable Ltd.
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Publication of WO2010090438A2 publication Critical patent/WO2010090438A2/en
Publication of WO2010090438A3 publication Critical patent/WO2010090438A3/en

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    • 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
    • H01B3/28—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances natural or synthetic rubbers
    • 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
    • H01B3/42—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 polyesters; polyethers; polyacetals
    • H01B3/421—Polyesters
    • 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
    • H01B3/44—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 vinyl resins; acrylic resins
    • H01B3/441—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 vinyl resins; acrylic resins from alkenes

Definitions

  • the present invention relates to a thermoplastic ester elastomer (TPE-E)-based composition for insulation and sheath layers and an electric cable equipped therewith. More specifically, 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 mechanical property balance, and an electric cable equipped therewith.
  • TPE-E thermoplastic ester elastomer
  • the electric cable industries have widely used polyvinyl chloride (PVC) or a polyethylene-based resin added with a halogen-based flame-retardant to manufacture an insulation or sheath layer of an insulating cable having flame retardancy of a certain level or higher.
  • PVC polyvinyl chloride
  • These resins have high flame retardancy, excellent properties and high economical efficiency, but are hazardous to the environment. For this reason, they will become more difficult to use in manufacturing insulation and sheath layers of flame-retardant cables. Even materials free of environmental hazard are faced with another challenge.
  • the developed countries are strongly forcing to use plastic materials in manufacturing 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 it is crosslinked, the halogen-free polyethylene resin has good mechanical properties such as strength and so on, excellent flame retardancy and high economical efficiency.
  • the crosslinked polyethylene resin cannot be recycled. This is not preferable as a material for an insulation layer of an insulating cable.
  • a polypropylene-based resin has low flame retardancy. To make up for low flame retardancy, the polypropylene-based resin is added with a large amount of an inorganic flame-retardant such as metal hydroxide or the like.
  • the resultant end-products have deterioration in processability and mechanical properties such as tensile strength and so on.
  • thermoplastic elastomer TPE
  • the thermoplastic elastomer has both elasticity of rubbers and processability 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 ester elastomer TPE-E is a representive thermoplastic elastomer.
  • thermoplastic elastomer When it is in a non-crosslinked state, the thermoplastic elastomer satisfies the specific level of mechanical properties and has good oil resistance and heat resistance. If the thermoplastic elastomer is crosslinked, its oil resistance and heat resistance are improved to excellent levels.
  • thermoplastic elastomer also has low flame retardancy.
  • the thermoplastic elastomer is inevitably added with a large amount of a halogen-free inorganic flame-retardant (generally metal hydroxide).
  • metal hydroxide has a very low compatibility with the thermoplastic elastomer. Unless it is specially treated, the metal hydroxide is not uniformly dispersed in the thermoplastic elastomer structure, but agglomerates with each other. The ununiform dispersion of the metal hydroxide causes reduction in tensile strength, elongation and flexibility, resulting in deterioration in mechanical properties.
  • thermoplastic ester elastomer-based insulation layer or sheath layer by uniformly dispersing an inorganic flame-retardant such as metal hydroxide or the like in a thermoplastic ester elastomer structure to ensure mechanical property balance.
  • the present invention provides a thermoplastic ester elastomer-based composition for an insulation layer or sheath layer of an electric cable.
  • the composition comprises a base resin consisting of 60 to 95 weight% of a thermoplastic ester elastomer and 5 to 40 weight% of a polyolefin grafted with a polar functional group; and 50 to 250 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.
  • 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 30 ⁇ m.
  • 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.
  • EVA ethylene-vinyl acetate
  • the present invention also provides an electric cable equipped with an insulation layer or sheath layer manufactured using said composition.
  • the insulation layer or sheath layer manufactured using the thermoplastic ester 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 resistant characteristics and heat resistance.
  • an electric cable equipped with the insulation or sheath layer is environmentally friendly and excellent in properties, flexibility, elasticity, heat resistance and oil resistance.
  • FIGs. 1 and 2 are cross-sectional views of electric cables equipped with an insulation layer (12 of FIG. 1) and a sheath layer (19 of FIG. 2) manufactured using a thermoplastic ester elastomer according to an embodiment of the present invention, respectively.
  • the present invention provides a thermoplastic ester 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 ester 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 optionally an additive.
  • the base resin of the composition according to the present invention includes 60 to 95 weight% of a thermoplastic ester elastomer (TPE-E) and 5 to 40 weight% of a polyolefin grafted with a polar functional group.
  • TPE-E thermoplastic ester elastomer
  • the present invention uses a thermoplastic ester elastomer (TPE-E) as the thermoplastic elastomer.
  • TPE-E thermoplastic ester elastomer
  • the thermoplastic ester elastomer is excellent in mechanical properties, oil resistance and heat resistance, and thus is proper for a sheath layer of an electric cable.
  • the thermoplastic ester elastomer has preferably a molecular mass of 10,000 to 2,000,000. The preferred molecular mass range ensures suitable polymer properties for an insulation or sheath layer of an electric cable. If the molecular mass is less than 10,000, the thermoplastic ester elastomer does not exhibit its peculiar elasticity and mechanical strength. If the molecular mass is more than 2,000,000, the thermoplastic ester elastomer has an excessive viscosity, causing a processing problem and unfavorable flexibility and flexural properties.
  • thermoplastic elastomer vary according to a composition ratio of a soft segment and a hard segment, and the purpose of application of thermoplastic elastomer is determined according to the properties.
  • a soft segment and a hard segment of the thermoplastic ester elastomer usable in the present invention.
  • the hard segment is polybutylene terephthalate
  • the soft segment is polyester, polyether, polycaprolactone or polycarbonate.
  • the soft segment may be a combination of the exemplary polymers.
  • the thermoplastic ester elastomer encompasses polymer alloys of said thermoplastic ester elastomers.
  • the present invention is not limited to a specific relative ratio of a soft segment and a hard segment, and an ordinary person skilled in the art will be able to select a thermoplastic ester elastomer having an appropriate ratio of a soft segment and a hard segment according to the purpose of use. Generally, it is preferable to use a typical thermoplastic ester elastomer having about 50 to 90 weight% of a hard segment. Thermoplastic ester elastomer having said ratio range has balance of mechanical strength and heat resistance requirements, elasticity, flexibility and flexural properties.
  • the thermoplastic ester elastomer is included in the base resin at an amount of 60 to 95 weight%.
  • the thermoplastic ester elastomer has improvement in its mechanical strength, abrasion resistance, oil resistant characteristics and heat resistance. If the content of the thermoplastic ester elastomer is less than 60 weight%, the thermoplastic ester elastomer has reduction in mechanical properties, oil resistant characteristics and abrasion resistance.
  • thermoplastic polyurethane elastomer If the content of the thermoplastic polyurethane elastomer is more than 95 weight%, dispersion of an inorganic filler such as an inorganic flame-retardant or the like reduces, and consequently the thermoplastic ester elastomer has a reduction in mechanical properties.
  • an inorganic filler such as an inorganic flame-retardant or the like
  • the base resin of the present invention includes a residual amount of polyolefin resin with a polar functional group as well as the thermoplastic ester elastomer.
  • a polar polyolefin resin constituting the base resin refers to "a polyolefin grafted with a polar functional group" throughout the specification of the present invention.
  • the polyolefin with a polar functional group has a polar functional group and a non-polar polyolefin, and increases compatibility between the polar inorganic flame-retardant and the thermoplastic ester elastomer to achieve uniform dispersion.
  • a suitable polyolefin grafted with a polar functional group in the present invention may be polyethylene, ethylene-vinyl acetate (EVA) copolymer and/or ethylene-ethyl acrylate copolymer, grafted with maleic anhydride or glycidyl methacrylate.
  • EVA ethylene-vinyl acetate
  • a method for grafting polyolefin with maleic anhydride or glycidyl methacrylate is a well-known technique in the art, and its description is omitted.
  • the polyolefin grafted with a polar functional group is included at an amount of 5 to 40 weight% based on the weight of the base resin.
  • the content of the polyolefin with a polar functional group is in this range, an inorganic flame-retardant is uniformly dispersed in the resin and bonding between the resin and the flame-retardant is improved.
  • the content of the polyolefin grafted with a polar function group is less than 5 weight%, dispersion of inorganic particles reduces, and consequently the composition has a reduction in mechanical properties.
  • the content of the polyolefin grafted with a polar function group is more than 40 weight%, the composition has deterioration in heat resistance and abrasion resistance.
  • thermoplastic ester elastomer-based composition of the present invention comprises 50 to 250 parts by weight of an inorganic flame-retardant based on 100 parts by weight of the base resin.
  • an inorganic flame-retardant based on 100 parts by weight of the base resin.
  • the composition stably satisfies the following flame-retardant test standards while not deteriorating the mechanical properties such as tensile strength, elongation and so on.
  • the inorganic flame-retardant is preferably magnesium hydroxide, aluminium hydroxide 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 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 a 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 coating material may include a phosphoric acid that is an inorganic acid.
  • thermoplastic ester elastomer-based composition of the present invention may comprise a secondary flame-retardant to reduce a usage amount of the inorganic flame-retardant and improve flame retardancy.
  • the secondary flame-retardant may be, for example, calcium hydroxide, huntite (Mg 3 Ca(CO 3 ) 4 ), hydromagnesite (Mg 5 (CO 3 ) 4 (OH) 2 ), red phosphorus, zinc borate, melamine derivative such as melamine cyanurate, and so on.
  • the secondary flame-retardant may be included at an amount of 10 to 100 parts by weight based on 100 parts by weight of the base resin.
  • 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 ester elastomer to ensure balance of the mechanical properties such as tensile strength, elongation, flexibility and so on.
  • the present invention uses a polyolefin grafted with a polar functional group and an inorganic flame-retardant surface-coated with an organic silane and so on. And, it is effective to use a twin-screw extruder (TSE) in processing a polymer compound including the base resin and the inorganic flame-retardant as mentioned below.
  • TSE twin-screw extruder
  • the present invention is characterized in that the composition for an insulation or sheath layer of an electric cable has a controlled component ratio to achieve uniform dispersion of a certain level or higher.
  • an insulation layer or sheath layer manufactured 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 manufactured 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 O C at a temperature increase rate of 10 O C/min, and the change in weight is measured. Subsequently, the unit sections are thermally decomposed at 800 to 900 O 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. Thus, the change in weight is measured using an inert gas at the initial stage.
  • the resultant weight loss for each unit section i.e., the 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 component ratio.
  • An insulation layer or sheath layer of an electric cable manufactured 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%, it is not preferable because the inorganic particles are not uniformly dispersed in the thermoplastic ester elastomer 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 residual inorganic particles 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 100 to 120 O 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 particles is measured using a particle size analyzer.
  • the inorganic particles are not uniformly dispersed in the thermoplastic ester elastomer resin. If a ratio of inorganic particles with a diameter of 1.0 to 30 ⁇ m to the whole inorganic particles is less than 30%, the inorganic particles are not uniformly dispersed in the thermoplastic ester elastomer resin.
  • thermoplastic ester 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.
  • the antioxidant may be a thioester-based antioxidant, a phenol-based antioxidant or mixtures thereof, and be included at an amount of 0.5 to 10 parts by weight based on 100 parts by weight of the base resin.
  • the UV stabilizer may be included at an amount of 1 to 10 parts by weight based on 100 parts by weight of the base resin.
  • the hydrolysis inhibitor may be included at an amount of 0.5 to 15 parts by weight based on 100 parts by weight of the base resin.
  • the lubricant and processing aid may be each included at an amount of 0.5 to 10 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 processing 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 manufactured by using the thermoplastic ester 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 manufactured by using the thermoplastic ester 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 manufactured by using the thermoplastic ester elastomer-based composition according to an embodiment of the present invention.
  • the electric cable 10 equipped with an insulation layer manufactured using the thermoplastic ester 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 ester elastomer-based composition of the present invention.
  • the insulator 12 is formed on the surface of the conductor 11 by mix-milling the thermoplastic ester elastomer-based composition into a pellet form and extruding the pellets using an extruder.
  • the electric cable 15 equipped with a sheath layer manufactured using the thermoplastic ester elastomer-based composition according to an embodiment of the present invention is applied as a signal transmission cable used to weapons (tanks, warships and so on) in the defense industry.
  • the electric cable 15 comprises a unit of seven wires, a shield 18 surrounding the unit of seven wires, and a sheath layer 19 surrounding the shield 18.
  • Each conductor 16 of the unit of seven wires may be made from copper, tin-plated copper and so on, and an insulation layer 17 may be made from a resin such as PVC, PE, PVDF, PBT, TPE and so on and a composition containing the resin.
  • the shield 18 surrounding the unit of seven wires is made from a tin-plated copper, and the sheath layer 19 is made by using the thermoplastic ester elastomer-based composition of the present invention.
  • the sheath layer 19 is formed on the surface of the round inner structure (16, 17, 18) by mix-milling the thermoplastic ester elastomer-based composition into a pellet form and extruding the pellets using an extruder.
  • thermoplastic ester elastomer-based composition for an insulation layer or sheath layer
  • compositions of examples and comparative examples were prepared according to a component ratio of Table 1.
  • An insulation layer specimen for an electric cable was manufactured using the compositions of examples and comparative examples according to Table 1.
  • a twin-screw extruder TSE 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 temperature of a compound was in the range of 150 to 250 O C.
  • comparative example 2 mill-mixed the composition at 160 O C for 20 minutes using a Two Roll Mill, instead of a twin-screw extruder.
  • the comparative example 2 had the same component ratio as the example 2 for investigating the effect of a manufacturing method on the performance.
  • the dispersion of inorganic particles in the insulation layer specimen manufactured as mentioned above was evaluated by thermogravimetric analysis and organic solvent extraction.
  • thermogravimetric analysis an insulation layer or sheath layer for an electric cable manufactured at the composition of Table 1 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 O C at a temperature increase rate of 10 O C/min, and a change in weight was measured. Subsequently, the unit sections were thermally decomposed at 800 to 900 O 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 for an electric cable manufactured from the composition of Table 1 was cut into unit sections having a size of about 300 mg, these sections were put in a trifluoroacetic acid (TFA) solvent of 100 O C and dissolved with reflux for 12 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 particles was measured using a particle size analyzer.
  • TFA trifluoroacetic acid
  • thermogravimetric analysis results and dispersion of inorganic particles are shown in Table 2.
  • 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 example 1 exhibits excellent dispersion of inorganic particles. This means that a large amount of an inorganic flame-retardant and a secondary flame-retardant were uniformly dispersed due to a polyolefin grafted with a polar functional group.
  • the above data shows that as the content of the polar polyolefin decreases, dispersion tends to reduce, however dispersion of the compositions according to the examples is within the range meeting the standards of the present invention.
  • the comparative example 1 was prepared using the same equipment as the examples, but did not include a polyolefin grafted with a polar functional group. Thus, dispersion of inorganic particles did not reach a level required by the present invention.
  • the comparative example 2 had the same component ratio as the example 2, but did not use a two-screw extruder that is employed for the purpose of uniform dispersion. Thus, the comparative example 2 showed different particle size distribution and dispersion of inorganic particles from the example 2.
  • the comparative example 2 included a polyolefin grafted with a polar functional group as the comparative example 1 did not so, but did not fall short of the standard of the present invention in terms of average residual deviation and percentage of inorganic particles with 1 to 30 ⁇ m diameter.
  • the insulation layer specimens of examples and comparative examples were evaluated in aspects of properties such as tensile strength, elongation, oil resistance and heat resistance.
  • the specimen was manufactured by compression molding the composition in a press of 200 O C for 20 minutes at a thickness of 1 mm, and forming in the shape of a dumbbell having a width of 4 mm. The properties were tested as follows.
  • the tensile strength and elongation of the insulation layer specimen were measured at a test rate of 50 mm/min according to the ASTM D 638 standards.
  • the heat resistance of the insulation layer specimen was measured by thermally treating the insulation layer specimen in an oven of 136 O C for 168 hours, putting at room temperature for 24 hours, measuring tensile strength and elongation and comparing the measured values with values measured at room temperature.
  • the oil resistance of the insulation layer specimen was measured by dipping the insulation layer specimen in a diesel for 72 hours while maintaining the temperature of the diesel at 50 O C, measuring tensile strength and elongation at a test rate of 50 mm/min, and comparing the measured values with values measured at room temperature.
  • an insulation or sheath layer for an electric cable should meet the standards, a tensile strength at room temperature of 1.05 kgf/mm 2 or more, an elongation at room temperature of 150% or more, and oil resistance and heat resistance based on tensile strength and elongation (residual tensile strength and residual elongation) of 60% or more relative to tensile strength and elongation at room temperature.
  • the specimens of examples manufactured according to the present invention have balance of tensile strength, elongation, oil resistance and heat resistance due to the improved dispersion, than the specimens of comparative examples manufactured according to the prior art.
  • the mechanical properties are influenced by dispersion of inorganic particles as well as the use of a thermoplastic ester elastomer.
  • the comparative example 1 did not include a polar polyolefin resin that serves to uniformly disperse inorganic particles in a polymer structure. Consequently, the comparative example 1 has good heat resistance and oil resistance, but does not satisfy the tensile strength and elongation standards.
  • the comparative example 1 is not suitable as a coating material.
  • the comparative example 2 had the same component ratio as the example 2, but did not intentionally meet the requirements of particle size distribution and dispersion of inorganic particles. As a result, the comparative example 2 exhibited poorer mechanical properties than comparative example 1 in spite of presence of a polar polyolefin.
  • thermoplastic ester elastomer and a polyolefin grafted with a polar functional group and control particle size distribution and dispersion of inorganic particles so as to achieve the object of the present invention.

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Abstract

Provided is a halogen-free insulating composition comprising a thermoplastic ester elastomer and an insulating cable equipped with an insulation layer or sheath layer manufactured using the composition. The composition comprises a base resin consisting of a thermoplastic ester elastomer and poly olefin grafted with a polar functional group; and a halogen-free inorganic flame-retardant. The insulation or sheath layer manufactured from said composition is cut into a unit section, and a thermogravimetric analysis is conducted, said unit section from the thermo- gravimetric analysis has no greater than ±5% of the standard deviation for the weight loss compared to the unit section before the thermogravimetric analysis, 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 weight% or more of said inorganic particles falling within a diameter range of 1.0 to 30 μm.

Description

THERMOPLASTIC ESTER ELASTOMER-BASED COMPOSITION FOR INSULATION LAYERS AND ELECTRIC CABLE EQUIPPED THEREWITH
The present invention relates to a thermoplastic ester elastomer (TPE-E)-based composition for insulation and sheath layers and an electric cable equipped therewith. More specifically, 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 mechanical property balance, and an electric cable equipped therewith.
<Cross-Reference to Related Application>
This application claims priority to Korean Patent Application No. 10-2009-0009315 filed in Republic of Korea on February 5, 2009, the entire contents of which are incorporated herein by reference.
The electric cable industries have widely used polyvinyl chloride (PVC) or a polyethylene-based resin added with a halogen-based flame-retardant to manufacture an insulation or sheath layer of an insulating cable having flame retardancy of a certain level or higher. These resins have high flame retardancy, excellent properties and high economical efficiency, but are hazardous to the environment. For this reason, they will become more difficult to use in manufacturing insulation and sheath layers of flame-retardant cables. Even materials free of environmental hazard are faced with another challenge. The developed countries are strongly forcing to use plastic materials in manufacturing 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 it is crosslinked, the halogen-free polyethylene resin has good mechanical properties such as strength and so on, excellent flame retardancy and high economical efficiency. However, the crosslinked polyethylene resin cannot be recycled. This is not preferable as a material for an insulation layer of an insulating cable. A polypropylene-based resin has low flame retardancy. To make up for low flame retardancy, the polypropylene-based resin is added with a large amount of an inorganic flame-retardant such as metal hydroxide or the like. However, the resultant end-products have deterioration in processability and mechanical properties such as tensile strength and so on.
Accordingly, the electric cable industries have readily studied to develop an environmentally friendly insulating material that is free of halogen and has advantages of excellent flame retardancy, mechanical properties such as flexibility, chemical properties such as oil resistance, and so on. Under this circumstance, thermoplastic elastomer (TPE) meeting the conditions becomes the center of attention. The thermoplastic elastomer has both elasticity of rubbers and processability 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 ester elastomer (TPE-E) is a representive thermoplastic elastomer. When it is in a non-crosslinked state, the thermoplastic elastomer satisfies the specific level of mechanical properties and has good oil resistance and heat resistance. If the thermoplastic elastomer is crosslinked, its oil resistance and heat resistance are improved to excellent levels.
However, the thermoplastic elastomer also has low 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 very low compatibility with the thermoplastic elastomer. Unless it is specially treated, the metal hydroxide is not uniformly dispersed in the thermoplastic elastomer structure, but agglomerates with each other. The ununiform 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 a thermoplastic ester elastomer-based insulation layer or sheath layer, by uniformly dispersing an inorganic flame-retardant such as metal hydroxide or the like in a thermoplastic ester elastomer structure to ensure mechanical property balance.
To achieve the object, the present invention provides a thermoplastic ester elastomer-based composition for an insulation layer or sheath layer of an electric cable. The composition comprises a base resin consisting of 60 to 95 weight% of a thermoplastic ester elastomer and 5 to 40 weight% of a polyolefin grafted with a polar functional group; and 50 to 250 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. 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 ㎛, 30% or more of said inorganic particles falling within a diameter range of 1.0 to 30 ㎛.
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 present invention also provides an electric cable equipped with an insulation layer or sheath layer manufactured using said composition.
According to the present invention, the insulation layer or sheath layer manufactured using the thermoplastic ester 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 resistant characteristics and heat resistance. Thus, an electric cable equipped with the insulation or sheath layer is environmentally friendly and excellent in properties, flexibility, elasticity, heat resistance and oil resistance.
FIGs. 1 and 2 are cross-sectional views of electric cables equipped with an insulation layer (12 of FIG. 1) and a sheath layer (19 of FIG. 2) manufactured using a thermoplastic ester 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 ester 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 ester 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 optionally an additive. The base resin of the composition according to the present invention includes 60 to 95 weight% of a thermoplastic ester elastomer (TPE-E) and 5 to 40 weight% of a polyolefin grafted with a polar functional group.
In the base resin, the present invention uses a thermoplastic ester elastomer (TPE-E) as the thermoplastic elastomer. The thermoplastic ester elastomer is excellent in mechanical properties, oil resistance and heat resistance, and thus is proper for a sheath layer of an electric cable. There is no special limitation on a thermoplastic ester elastomer usable in the present invention. However, the thermoplastic ester elastomer has preferably a molecular mass of 10,000 to 2,000,000. The preferred molecular mass range ensures suitable polymer properties for an insulation or sheath layer of an electric cable. If the molecular mass is less than 10,000, the thermoplastic ester elastomer does not exhibit its peculiar elasticity and mechanical strength. If the molecular mass is more than 2,000,000, the thermoplastic ester elastomer has an excessive viscosity, causing a processing problem and unfavorable flexibility and flexural properties.
Meanwhile, the properties of the thermoplastic elastomer vary according to a composition ratio of a soft segment and a hard segment, and the purpose of application of thermoplastic elastomer is determined according to the properties. There is no special limitation on a soft segment and a hard segment of the thermoplastic ester elastomer usable in the present invention. For example, preferably the hard segment is polybutylene terephthalate, and the soft segment is polyester, polyether, polycaprolactone or polycarbonate. And, the soft segment may be a combination of the exemplary polymers. Furthermore, in the present invention, the thermoplastic ester elastomer encompasses polymer alloys of said thermoplastic ester elastomers.
The present invention is not limited to a specific relative ratio of a soft segment and a hard segment, and an ordinary person skilled in the art will be able to select a thermoplastic ester elastomer having an appropriate ratio of a soft segment and a hard segment according to the purpose of use. Generally, it is preferable to use a typical thermoplastic ester elastomer having about 50 to 90 weight% of a hard segment. Thermoplastic ester elastomer having said ratio range has balance of mechanical strength and heat resistance requirements, elasticity, flexibility and flexural properties.
Preferably, the thermoplastic ester elastomer is included in the base resin at an amount of 60 to 95 weight%. When the content of the thermoplastic ester elastomer is in this range, the thermoplastic ester elastomer has improvement in its mechanical strength, abrasion resistance, oil resistant characteristics and heat resistance. If the content of the thermoplastic ester elastomer is less than 60 weight%, the thermoplastic ester elastomer has reduction in mechanical properties, oil resistant characteristics and abrasion resistance. If the content of the thermoplastic polyurethane elastomer is more than 95 weight%, dispersion of an inorganic filler such as an inorganic flame-retardant or the like reduces, and consequently the thermoplastic ester elastomer has a reduction in mechanical properties.
The base resin of the present invention includes a residual amount of polyolefin resin with a polar functional group as well as the thermoplastic ester elastomer. Hereinafter, a polar polyolefin resin constituting the base resin refers to "a polyolefin grafted with a polar functional group" throughout the specification of the present invention. In the present invention, the polyolefin with a polar functional group has a polar functional group and a non-polar polyolefin, and increases compatibility between the polar inorganic flame-retardant and the thermoplastic ester elastomer to achieve uniform dispersion. For example, a suitable polyolefin grafted with a polar functional group in the present invention may be polyethylene, ethylene-vinyl acetate (EVA) copolymer and/or ethylene-ethyl acrylate copolymer, grafted with maleic anhydride or glycidyl methacrylate. A method for grafting polyolefin with maleic anhydride or glycidyl methacrylate is a well-known technique in the art, and its description is omitted. For example, it is preferable to use 0.1 to 10 weight% of maleic anhydride based on weight of a polyolefin to be grafted.
Preferably, the polyolefin grafted with a polar functional group is included at an amount of 5 to 40 weight% based on the weight of the base resin. When the content of the polyolefin with a polar functional group is in this range, an inorganic flame-retardant is uniformly dispersed in the resin and bonding between the resin and the flame-retardant is improved. If the content of the polyolefin grafted with a polar function group is less than 5 weight%, dispersion of inorganic particles reduces, and consequently the composition has a reduction in mechanical properties. If the content of the polyolefin grafted with a polar function group is more than 40 weight%, the composition has deterioration in heat resistance and abrasion resistance.
The thermoplastic ester elastomer-based composition of the present invention comprises 50 to 250 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 this range, the composition stably satisfies the following flame-retardant test standards while not deteriorating the mechanical properties such as tensile strength, elongation and so on.
In the present invention, the inorganic flame-retardant is preferably magnesium hydroxide, aluminium hydroxide 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 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.
For example, the organic silane as a 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 coating material may include a phosphoric acid that is an inorganic acid.
Meanwhile, the thermoplastic ester elastomer-based composition of the present invention may comprise a secondary flame-retardant to reduce a usage amount of the inorganic flame-retardant and improve flame retardancy. The secondary flame-retardant may be, for example, calcium hydroxide, huntite (Mg3Ca(CO3)4), hydromagnesite (Mg5(CO3)4(OH)2), red phosphorus, zinc borate, melamine derivative such as melamine cyanurate, and so on. The secondary flame-retardant may be included at an amount of 10 to 100 parts by weight based on 100 parts by weight of the base resin.
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 ester elastomer to ensure balance of the mechanical properties such as tensile strength, elongation, flexibility and so on. For uniform dispersion, the present invention uses a polyolefin grafted with a polar functional group and an inorganic flame-retardant surface-coated with an organic silane and so on. And, it is effective to use a twin-screw extruder (TSE) in processing a polymer compound including the base resin and the inorganic flame-retardant as mentioned below.
And, the present invention is characterized in that the composition for an insulation or sheath layer of an electric cable has a controlled component ratio to achieve uniform dispersion of a certain level or higher. Specifically, an insulation layer or sheath layer manufactured 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 manufactured 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 PCTKR2010000655-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 increase 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. Thus, the change in weight is measured using an inert gas at the initial stage. The resultant weight loss for each unit section, i.e., the 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 component ratio.
An insulation layer or sheath layer of an electric cable manufactured 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%, it is not preferable because the inorganic particles are not uniformly dispersed in the thermoplastic ester elastomer 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 residual inorganic particles 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 100 to 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 particles is measured using a particle size analyzer.
If the maximum diameter of residual inorganic particles obtained by extracting the insulation layer of the electric cable within the organic solvent is outside the range of 0.5 to 100 ㎛, the inorganic particles are not uniformly dispersed in the thermoplastic ester elastomer resin. If a ratio of inorganic particles with a diameter of 1.0 to 30 ㎛ to the whole inorganic particles is less than 30%, the inorganic particles are not uniformly dispersed in the thermoplastic ester elastomer resin.
The thermoplastic ester 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. For example, the antioxidant may be a thioester-based antioxidant, a phenol-based antioxidant or mixtures thereof, and be included at an amount of 0.5 to 10 parts by weight based on 100 parts by weight of the base resin. The UV stabilizer may be included at an amount of 1 to 10 parts by weight based on 100 parts by weight of the base resin. The hydrolysis inhibitor may be included at an amount of 0.5 to 15 parts by weight based on 100 parts by weight of the base resin. The lubricant and processing aid may be each included at an amount of 0.5 to 10 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 processing 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 manufactured by using the thermoplastic ester 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 manufactured by using the thermoplastic ester 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 manufactured by using the thermoplastic ester elastomer-based composition according to an embodiment of the present invention.
As shown in FIG. 1, the electric cable 10 equipped with an insulation layer manufactured using the thermoplastic ester 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 ester elastomer-based composition of the present invention. The insulator 12 is formed on the surface of the conductor 11 by mix-milling the thermoplastic ester elastomer-based composition into a pellet form and extruding the pellets using an extruder.
As shown in FIG. 2, the electric cable 15 equipped with a sheath layer manufactured using the thermoplastic ester elastomer-based composition according to an embodiment of the present invention is applied as a signal transmission cable used to weapons (tanks, warships and so on) in the defense industry. The electric cable 15 comprises a unit of seven wires, a shield 18 surrounding the unit of seven wires, and a sheath layer 19 surrounding the shield 18. Each conductor 16 of the unit of seven wires may be made from copper, tin-plated copper and so on, and an insulation layer 17 may be made from a resin such as PVC, PE, PVDF, PBT, TPE and so on and a composition containing the resin. The shield 18 surrounding the unit of seven wires is made from a tin-plated copper, and the sheath layer 19 is made by using the thermoplastic ester elastomer-based composition of the present invention. The sheath layer 19 is formed on the surface of the round inner structure (16, 17, 18) by mix-milling the thermoplastic ester elastomer-based composition into a pellet form and extruding the pellets using an extruder.
Hereinafter, the present invention will be described in detail through examples. 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.
Preparation of a thermoplastic ester 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 manufactured using the thermoplastic ester elastomer-based composition of the present invention, compositions of examples and comparative examples were prepared according to a component ratio of Table 1.
Table 1
Element(parts by weight) Examples Comparative examples
1 2 3 4 1 2
TPE-E* 60 80 95 95 100 80
Polyolefin grafted with polar functional group** 40 20 5 5 0 20
Mg(OH)2 inorganic flame-retardant 100 100 100 50 100 100
Secondary flame-retardant+ 50 50 50 100 50 50
Additives++ 15
*: Polyester-based TPE, Hytrel 4056 by Dupont in U.S.A. (Melt flow index: 5.6 g/10 min, Density: 1.15 g/cm2, Melting point: 150 OC, under conditions of 190 OC and 2.16 kg load)
**: Ethylene-vinyl acetate copolymer resin grafted with maleic anhydride monomer (Content of vinyl acetate monomer: 28%, Melt flow index: 1.5 g/10 min)
+: Melamine cyanurate and zinc borate at a weight ratio of 50:50
++: Antioxidant- 0.5 to 2 parts by weight of Irganox1010 which is a phenol-based antioxidant from Ciba, UV stabilizer- 0.5 to 2 parts by weight of Tinuvin from Ciba, Hydrolysis inhibitor- 0.5 to 10 parts by weight of Stabilizer 100 from RASCHIG, lubricant and processing aid- 0.5 to 2 parts by weight of PE wax from Lionchemtech
An insulation layer specimen for an electric cable was manufactured using the compositions of examples and comparative examples according to Table 1. In the manufacture of an electric cable specimen, a twin-screw extruder (TSE) 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 temperature of a compound was in the range of 150 to 250 OC. Meanwhile, comparative example 2 mill-mixed the composition at 160 OC for 20 minutes using a Two Roll Mill, instead of a twin-screw extruder. The comparative example 2 had the same component ratio as the example 2 for investigating the effect of a manufacturing method on the performance.
Evaluation of dispersion of an insulation layer specimen
The dispersion of inorganic particles in the insulation layer specimen manufactured 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 manufactured at the composition of Table 1 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 increase 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 for an electric cable manufactured from the composition of Table 1 was cut into unit sections having a size of about 300 mg, these sections were put in a trifluoroacetic acid (TFA) solvent of 100 OC and dissolved with reflux for 12 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 particles 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 1 2
Average residual deviation(%) 0.5 0.8 1.0 1.0 6.0 9.0
Average particle size of inorganic particles(㎛) 17 25 35 36 75 80
Percentage of inorganic particles of 1 to 30㎛ diameter(%) 60 45 35 35 20 15
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. In particular, the example 1 exhibits excellent dispersion of inorganic particles. This means that a large amount of an inorganic flame-retardant and a secondary flame-retardant were uniformly dispersed due to a polyolefin grafted with a polar functional group. The above data shows that as the content of the polar polyolefin decreases, dispersion tends to reduce, however dispersion of the compositions according to the examples is within the range meeting the standards of the present invention.
On the contrary, the comparative example 1 was prepared using the same equipment as the examples, but did not include a polyolefin grafted with a polar functional group. Thus, dispersion of inorganic particles did not reach a level required by the present invention. The comparative example 2 had the same component ratio as the example 2, but did not use a two-screw extruder that is employed for the purpose of uniform dispersion. Thus, the comparative example 2 showed different particle size distribution and dispersion of inorganic particles from the example 2. The comparative example 2 included a polyolefin grafted with a polar functional group as the comparative example 1 did not so, but did not fall short of the standard of the present invention in terms of average residual deviation and percentage of inorganic particles with 1 to 30 ㎛ diameter.
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, oil resistance and heat resistance. The specimen was manufactured by compression molding the composition in a press of 200 OC for 20 minutes at a thickness of 1 mm, and forming in the shape of a dumbbell having a width of 4 mm. The properties were tested as follows.
The tensile strength and elongation of the insulation layer specimen were measured at a test rate of 50 mm/min according to the ASTM D 638 standards.
The heat resistance of the insulation layer specimen was measured by thermally treating the insulation layer specimen in an oven of 136 OC for 168 hours, putting at room temperature for 24 hours, measuring tensile strength and elongation and comparing the measured values with values measured at room temperature.
The oil resistance of the insulation layer specimen was measured by dipping the insulation layer specimen in a diesel for 72 hours while maintaining the temperature of the diesel at 50 OC, measuring tensile strength and elongation at a test rate of 50 mm/min, and comparing the measured values with values measured at room temperature.
Typically, an insulation or sheath layer for an electric cable should meet the standards, a tensile strength at room temperature of 1.05 kgf/mm2 or more, an elongation at room temperature of 150% or more, and oil resistance and heat resistance based on tensile strength and elongation (residual tensile strength and residual elongation) of 60% or more relative to tensile strength and elongation at room temperature.
The test results are shown in Table 3.
Table 3
Standard value Examples Comparative examples
1 2 3 4 1 2
Tensile strength(kgf/mm2) 1.05 1.14 1.23 1.40 1.37 1.07 0.95
Elongation(%) 150 187 168 159 155 136 107
Heat resistance Residual tensile strength (%) 60 83 88 96 97 103 87
Residual elongation (%) 60 63 67 73 72 83 68
Oil resistance Residual tensile strength (%) 60 71 85 95 91 100 86
Residual elongation (%) 60 62 82 92 92 95 81
It is found from Table 3 that the specimens of examples manufactured according to the present invention have balance of tensile strength, elongation, oil resistance and heat resistance due to the improved dispersion, than the specimens of comparative examples manufactured according to the prior art. In particular, it is found through comparison with the comparative examples 1 and 2 that the mechanical properties are influenced by dispersion of inorganic particles as well as the use of a thermoplastic ester elastomer. The comparative example 1 did not include a polar polyolefin resin that serves to uniformly disperse inorganic particles in a polymer structure. Consequently, the comparative example 1 has good heat resistance and oil resistance, but does not satisfy the tensile strength and elongation standards. Thus, the comparative example 1 is not suitable as a coating material. The comparative example 2 had the same component ratio as the example 2, but did not intentionally meet the requirements of particle size distribution and dispersion of inorganic particles. As a result, the comparative example 2 exhibited poorer mechanical properties than comparative example 1 in spite of presence of a polar polyolefin.
The above data shows that it is important to include a thermoplastic ester elastomer and a polyolefin grafted with a polar functional group and control particle size distribution and dispersion of inorganic particles so as to achieve the object of the present invention.
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 (9)

  1. A composition for an insulation layer or sheath layer of an electric cable, comprising:
    a base resin consisting of:
    60 to 95 weight% of a thermoplastic ester elastomer, and
    5 to 40 weight% of a polyolefin grafted with a polar functional group; and
    50 to 250 parts by weight of an inorganic flame-retardant based on 100 parts by weight of the base resin,
    wherein the insulation layer or sheath layer manufactured from said composition is cut into a unit section, and a thermogravimetric analysis is conducted,
    said unit section from the thermogravimetric analysis has no greater than ±5% of the standard deviation for weight loss compared to the unit section before the thermogravimetric analysis, 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 ㎛,
    30 weight% or more of said inorganic particles falling within a diameter range of 1.0 to 30 ㎛.
  2. The composition according to claim 1,
    wherein the thermoplastic ester elastomer has a hard segment of polybutylene terephthalate, and a soft segment selected from the group consisting of polyester, polyether, polycaprolactone and polycarbonate, and mixtures thereof.
  3. The composition according to claim 1,
    wherein the thermoplastic ester elastomer has a molecular weight of 10,000 to 2,000,000.
  4. The composition 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 according to claim 1,
    wherein the inorganic flame-retardant is selected from the group consisting of magnesium hydroxide and aluminium hydroxide, and mixtures thereof.
  6. The composition according to claim 5,
    wherein the inorganic flame-retardant is surface-coated with any one selected from the group consisting of organic silane, organic acid and organic polymer.
  7. The composition according to claim 6,
    wherein the organic silane is selected from the group consisting of vinyl silane, amino silane and methacrylate silane, and
    wherein the organic acid is selected from the group consisting of phosphorous acid, fatty acid, stearic acid and oleic acid.
  8. The composition according to claim 1, further comprising:
    10 to 100 parts by weight of a secondary flame-retardant based on 100 parts by weight of the base resin,
    wherein the secondary flame-retardant is selected from the group consisting of huntite (Mg3Ca(CO3)4), hydromagnesite (Mg5(CO3)4(OH)2) and melamine cyanurate, and mixtures thereof.
  9. An insulating cable, comprising a metal conductor bundle of a single or multiple mode fiber or an optical fiber of a single or multiple mode; and an insulation layer or sheath layer surrounding the metal conductor bundle or the optical fiber,
    wherein the insulation layer or sheath layer is manufactured from a composition comprising:
    a base resin consisting of:
    60 to 95 weight% of a thermoplastic ester elastomer, and
    5 to 40 weight% of a polyolefin grafted with a polar functional group; and
    50 to 250 parts by weight of an inorganic flame-retardant based on 100 parts by weight of the base resin,
    wherein the insulation layer or sheath layer manufactured from said composition is cut into a unit section, and a thermogravimetric analysis is conducted,
    said unit section from the thermogravimetric analysis has no greater than ±5% of the standard deviation for weight loss compared to the unit section before the thermogravimetric analysis, 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 ㎛,
    30 weight% or more of said inorganic particles falling within a diameter range of 1.0 to 30 ㎛.
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104599776A (en) * 2014-12-31 2015-05-06 东莞市高能磁电技术有限公司 Halogen-free flame-retardant insulated electric cable using polybutylene terephthalate composite material
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