Soft polyolefin resin composition for power cable having excellent insulation properties and molded article made therefrom

Abstract

The present invention relates to a soft polyolefin resin composition having excellent insulation properties suitable for power cables and a molded article made thereof. The polyolefin resin composition according to the present invention not only has excellent insulation properties, but also has excellent heat resistance, voltage resistance properties, space charge control ability and mechanical properties. Therefore, the polyolefin resin molded article made thereof can be effectively used as an insulation layer of high voltage power cables and extra high voltage power cables.

Description

TECHNICAL FIELD

[0001] The present invention relates to a soft polyolefin resin composition having excellent insulation properties suitable for power cables and a molded product thereof. More particularly, the present invention relates to a soft polyolefin resin composition suitable for high-voltage and extra-high-voltage power cables and a molded product thereof, which not only has excellent insulation properties but also has excellent heat resistance, voltage resistance, space charge control ability, and mechanical properties. BACKGROUND

[0002] Generally, polypropylene resins are widely used in products requiring both insulation properties and heat resistance under high voltage, such as packaging of important components of electronic products, housings of electrical parts for automobiles, protection of main parts of electrical products, and surfaces of small electric heaters, due to their excellent rigidity and high heat resistance, stability to chemical agents, and high insulation properties.

[0003] In addition, polypropylene has excellent mechanical strength, abrasion resistance, and water resistance, as well as excellent dielectric properties, and thus is effectively used for insulation of extra-high-voltage products.

[0004] However, polypropylene resins are difficult to be applied to curved parts and are not resistant to impact, particularly, are easily broken at low temperature conditions, because of their high rigidity and whitening phenomenon upon bending, and thus are not suitable for use as an insulator of high-voltage or extra-high-voltage electric wires installed in outdoor environments.

[0005] At present, as an insulating material for electric wires, polyethylene, ethylene-propylene rubber (EPR), ethylene-propylene-diene rubber (EPDM), etc. having low dielectric constant and non-polarity are used. In addition, in the case of transmission of a large amount of high-voltage and extra-high-voltage current, cross-linked polyethylene (XLPE) obtained by cross-linking low-density polyethylene is used to improve heat resistance.

[0006] However, the use of cross-linked polyethylene has a problem in that cross-linking residues cause accumulation of space charges, which deteriorates the insulation properties of direct current insulators. When the product life ends or a defect occurs, it cannot be recycled but only incinerated, which is not environmentally friendly, and additional equipment costs are incurred in the recycling process. In addition, there is a high possibility that cross-linking by-products generated in the cross-linking process cause environmental pollution, and a drying process is additionally required for water cross-linked products, and if excessive cross-linking occurs due to heat generated during extrusion, processability is limited.

[0007] To solve these problems, attempts have been made to improve softness or impact properties by mixing EPR, ethylene-a-olefin rubber, EPDM, etc. in a polypropylene resin having excellent heat resistance. In this case, due to phase separation of the polypropylene matrix and the rubber, it can cause a decrease in electrical insulation properties, or when the proportion of the rubber is too high, phase inversion of the matrix and the rubber can occur to decrease heat resistance.

[0008] To solve these problems, research is being conducted to improve softness and impact resistance while ensuring voltage resistance properties and heat resistance for a polyolefin resin composition having polypropylene as a main component.

[0009] For example, in International Patent Application Publication No. 2013 / 0148028, by mixing ethylene-a-olefin rubber or EPDM in polypropylene, the change in AC breakdown voltage strength with cooling rate was observed, but there was no mention of improvement in heat resistance and softness.

[0010] In Korean Patent Application Publication No. 10-2012-0086071, a method of preparing an insulating material having excellent volume resistivity and insulation breakdown strength by mixing nano-inorganic particles with a polypropylene resin was disclosed, but the problem is that it is difficult to uniformly disperse the nano-inorganic particles in the polypropylene.

[0011] In Korean Patent Publication No. 10-1784333, a thermoplastic polymer for ensuring softness by using a copolymer of a-olefin and propylene was disclosed, but the problem is that if the content of the rubber is small, it is difficult to erect and install when used as an insulating material due to a decrease in softness, and if the content of the rubber is high, the advantage of polypropylene, which has a large impact on mechanical properties, disappears.

[0012] In Korean Patent Application Publication No. 10-2014-0102407, an insulating layer for a power cable, which improves insulation properties by adding an insulating fluid to polypropylene and can be recycled, and in Korean Patent Publication No. 10-1810542, a polypropylene resin, which has a crystalline size reduced by adding an organic nucleating agent, was disclosed for use in an insulating layer of a power cable. However, in order to solve the problem of a decrease in windability due to the high rigidity of polypropylene, a large amount of rubber needs to be additionally mixed, and thus it is possible that local physical property deterioration caused by non-uniform mixing occurs, and in addition, the organic nucleating agent added to reduce the crystalline size causes an increase in cost and defects caused thereby, and thus improvement is required to use polypropylene for an insulating layer of a power cable.

[0013] Korean Patent Publication No. 0246138 discloses a polypropylene resin composition consisting of polypropylene and ethylene-propylene copolymer resin or ethylene-α-olefin copolymer rubber, thereby having improved durability, impact resistance and cold impact resistance, but does not disclose actual results on improvement in cold impact resistance at -40℃, and in addition, the content of ethylene-propylene rubber or ethylene-α-olefin rubber mixed to secure softness for application to electric wires is increased, and thus tensile properties and mechanical properties and heat distortion are more severely deteriorated, and thus it is not suitable for use as electric wire materials.

[0014] In addition, high voltage and extra high voltage power cables are usually transported in the form of a reel, and are bent and twisted according to the terrain during installation. The thickness of the insulation layer is increased as the load voltage of the power cable is increased, and thus such a soft characteristic becomes more important.

[0015] Therefore, in order to overcome the drawbacks of the above patent documents, there is a need to develop a soft polypropylene-based polyolefin resin composition having excellent insulation characteristics suitable for high voltage and extra high voltage power cables.

[0016]

Prior Art Documents

[0017]

Patent Documents

[0018] (Patent Document 1) International Patent Application Publication No. 2013 / 0148028;

[0019] (Patent Document 2) Korean Patent Application Publication No. 10-2012-0086071;

[0020] (Patent Document 3) Korean Patent Publication No. 10-1784333;

[0021] (Patent Document 4) Korean Patent Application Publication No. 10-2014-0102407;

[0022] (Patent Document 5) Korean Patent Publication No. 10-1810542;

[0023] (Patent Document 6) Korean Patent Publication No. 0246138. SUMMARY

[0024] TECHNICAL PROBLEM

[0025] The present application aims to provide a soft polyolefin resin composition suitable for high voltage power cables and extra high voltage power cables, which not only has excellent insulation characteristics, but also has excellent heat resistance, voltage resistance, space charge control ability and mechanical properties.

[0026] Another object of the present application is to provide a molded article made of the polyolefin resin composition.

[0027] Technical Solution

[0028] To achieve the above object, according to one embodiment of the present application, the present application provides a polyolefin resin composition comprising: an ethylene-propylene block copolymer (A) accounting for 60 to 100% by weight in the total weight of components (A) and (B), and being produced by the segmented polymerization of a propylene homopolymer or an ethylene-propylene random copolymer with an ethylene-propylene rubber copolymer in a reactor; an ethylene-a-olefin rubber copolymer (B) accounting for 0 to 40% by weight in the total weight of components (A) and (B); and a β nucleating agent (C) for forming β crystals, the content of the β nucleating agent (C) being 0.02 to 0.5 parts by weight with respect to 100 parts by weight of components (A) and (B).

[0029] In a specific embodiment of the present application, when the ethylene-propylene block copolymer (A) is extracted with a xylene solvent at room temperature, the content of the extracted rubber component (solvent extract) can be 1 to 45% by weight, preferably 15 to 40% by weight.

[0030] In a specific embodiment of the present application, the intrinsic viscosity of the above-mentioned solvent extract measured in a decalin solvent at 135°C can be 1.0 to 3.0 dl / g.

[0031] In a specific embodiment of the present application, the melting temperature (Tm) of the ethylene-propylene block copolymer (A) can be 150 to 165°C.

[0032] In a specific embodiment of the present application, the melt index of the ethylene-propylene block copolymer (A) can be 0.5 to 20.0 g / 10 min, preferably 0.5 to 10.0 g / 10 min, when measured according to ASTM D1238 at 230°C under a load of 2.16 kg.

[0033] In a specific embodiment of the present application, the ethylene content in the ethylene-a-olefin rubber copolymer (B) can be 5 to 90% by weight, preferably 10 to 70% by weight.

[0034] In a specific embodiment of the present application, the ethylene-a-olefin rubber copolymer (B) can comprise at least one selected from the group consisting of ethylene-propylene rubber, ethylene-1-butene rubber, ethylene-butene rubber, ethylene-1-pentene rubber, ethylene-1-hexene rubber, ethylene-1-heptene rubber, ethylene-1-octene rubber, and ethylene-4-methyl-1-pentene rubber.

[0035] In a specific embodiment of the present application, the β nucleating agent (C) can comprise at least one selected from the group consisting of γ-quinacridone, δ-quinacridone, quinacridonequinone, indigosol and cibantine organic pigments, calcium carbonate modified with dimer aluminates, a mixture of calcium stearate and pimelic acid, calcium and zinc salts of dibasic acids, diamines of adipic acid or suberic acid, N,N'-dicyclohexylterephthalamide and N',N'-dicyclohexyl-2,6-naphthalene-dicarboxylic amide.

[0036] In a specific embodiment of the present application, the polyolefin resin composition can further comprise at least one additive selected from the group consisting of antioxidants, neutralizing agents, UV stabilizers, long-term heat resistance stabilizers, slip agents, anti-blocking agents, reinforcing agents, fillers, weather resistance stabilizers, antistatic agents, lubricants, nucleating agents, flame retardants, pigments and dyes.

[0037] In a specific embodiment of the present application, the content of the extracted rubber component (solvent extract) can be 25 to 45% by weight, preferably 30 to 40% by weight, when the polyolefin resin composition is extracted with a xylene solvent at room temperature.

[0038] In a specific embodiment of the present application, the intrinsic viscosity of the above-mentioned solvent extract measured in decalin solvent at 135°C can be 1.0 to 3.0 dl / g.

[0039] In a specific embodiment of the present application, the melting temperature (Tm) of the polyolefin resin composition can be 150°C to 165°C.

[0040] In a specific embodiment of the present application, the melt index of the polyolefin resin composition can be 0.5 to 20.0 g / 10 min, preferably 0.5 to 10.0 g / 10 min, when measured at 230°C under a load of 2.16 kg according to ASTM D1238.

[0041] In a specific embodiment of the present application, the glass transition temperature of the rubber component of the polyolefin resin composition can occur in the ranges of -60 to -40°C and -40 to -20°C, respectively, when measured by a dynamic mechanical analysis device.

[0042] According to another embodiment of the present application, the present application provides a polyolefin resin molded article molded from the above-mentioned polyolefin resin composition.

[0043] In a specific embodiment of the present application, the flexural modulus of the polyolefin resin molded article can be less than 400 MPa.

[0044] In a specific embodiment of the present application, the volume resistance of the polyolefin resin molded article measured at room temperature can be 10 16Ωcm or more, the volume resistance of the same test piece after heating (aging) at 140°C for 30 days can be 10 16 Ωcm or more.

[0045] In a specific embodiment of the present application, the elongation of the polyolefin resin molded article can be 400% or more, and the elongation of the same test piece after heating (aging) at 140°C for 30 days can be 75% or more of the initial elongation (elongation before heating).

[0046] In a specific embodiment of the present application, when the polyolefin resin molded article is a film having a thickness of 80 μm, the DC insulation breakdown strength can be 300 kV / mm or more, and the DC insulation breakdown strength of the same test piece after heating (aging) at 140°C for 30 days can be 300 kV / mm or more.

[0047] In a specific embodiment of the present application, the polyolefin resin molded article can have a deformation rate of less than 50% after being subjected to a load of 1.6 kg at 130°C for 6 hours under the condition of having a length of 30 mm, a width of 15 mm, and a thickness of 2 mm.

[0048] In a specific embodiment of the present application, the polyolefin resin molded article can be an insulation layer of a high-voltage power cable or an ultra-high-voltage power cable.

[0049] Advantageous Effects

[0050] The polyolefin resin composition according to the embodiment of the present application not only has excellent insulation properties, but also has excellent heat resistance, voltage resistance properties, space charge control ability, and mechanical properties. Therefore, the polyolefin resin molded article made therefrom can be suitably used for high-voltage power cables and ultra-high-voltage power cables. DETAILED DESCRIPTION

[0051] Hereinafter, the present application will be described in detail.

[0052]

Polyolefin Resin Composition

[0053] According to one embodiment of the present application, the present application provides a polyolefin resin composition, which comprises: an ethylene-propylene block copolymer (A) accounting for 60 to 100% by weight in the total weight of components (A) and (B), and being produced by the segmented polymerization of a propylene homopolymer or an ethylene-propylene random copolymer with an ethylene-propylene rubber copolymer in a reactor; an ethylene-a-olefin rubber copolymer (B) accounting for 0 to 40% by weight in the total weight of components (A) and (B); and a β nucleating agent (C) for forming β crystals, the content of the β nucleating agent (C) being 0.02 to 0.5 parts by weight with respect to 100 parts by weight of components (A) and (B).

[0054] Ethylene-propylene block copolymer (A)

[0055] The polyolefin resin composition according to the embodiment of the present application contains an ethylene-propylene block copolymer (A). At this time, the ethylene-propylene block copolymer (A) is obtained by the segmented polymerization of a propylene homopolymer or an ethylene-propylene random copolymer and an ethylene-propylene rubber copolymer in a reactor.

[0056] In the specific embodiment of the present application, the propylene homopolymer or the ethylene-propylene random copolymer is first polymerized to produce a polypropylene matrix, and then the ethylene-propylene rubber component is block copolymerized in the polypropylene matrix, thereby making it possible to produce the ethylene-propylene block copolymer (A) resin.

[0057] In the specific embodiment of the present application, when the ethylene-propylene block copolymer (A) is extracted with a xylene solvent at room temperature, the content of the extracted rubber component (solvent extract) can be 1 to 45% by weight, preferably 15 to 40% by weight. When the content of the solvent extract in the ethylene-propylene block copolymer (A) exceeds 45% by weight, phase inversion occurs between the polypropylene matrix and the rubber component, resulting in a high heat distortion rate and low tensile strength and elongation, and thus it is not suitable for application to electric wires.

[0058] In the specific embodiment of the present application, the intrinsic viscosity of the above-described solvent extract measured in a decalin solvent at 135°C can be 1.0 to 3.0 dl / g. When the intrinsic viscosity of the solvent extract is less than 1.0 dl / g, the impact strength of a molded product decreases, and when the intrinsic viscosity of the solvent extract exceeds 3.0 dl / g, the rubber component is condensed in the ethylene-propylene block copolymer (A), and space charge accumulation and electric field distortion occur at the interface between the polypropylene matrix and the rubber component.

[0059] In the specific embodiment of the present application, the melting temperature (Tm) of the ethylene-propylene block copolymer (A) can be 150 to 165°C. If the melting temperature of the ethylene-propylene block copolymer (A) is less than 150°C, the heat resistance of a molded product is not sufficient, and the resin can be denatured by heat. Thus, it is not suitable for application to high-voltage power cables in which the working temperature and the instantaneous temperature can rise to 130°C or more.

[0060] In a specific embodiment of the present application, the melt index of the ethylene-propylene block copolymer (A) can be 0.5 to 20.0 g / 10 min, preferably 0.5 to 10.0 g / 10 min, when measured at 230°C under a load of 2.16 kg according to ASTM D1238. If the melt index of the ethylene-propylene block copolymer (A) is less than 0.5 g / 10 min, the extrusion temperature and load will increase, resulting in a decrease in production efficiency and the generation of carbides, and if it exceeds 20 g / 10 min, sagging can occur during the formation of the extrudate, and thus is not preferred.

[0061] The polyolefin resin composition according to the embodiment of the present application contains 60 to 100 wt% of the above-described ethylene-propylene block copolymer (A) based on the total weight of components (A) and (B). If the content of the ethylene-propylene block copolymer (A) is less than 60 wt%, the heat resistance of the molded article becomes poor and the heat distortion characteristics decrease, which can result in a serious change in appearance during high-temperature operation.

[0062] The method for preparing the above-described ethylene-propylene block copolymer (A) is not particularly limited, and a method for preparing an ethylene-propylene block copolymer known in the art to which the present application pertains can be directly used, or can be used after being appropriately modified.

[0063] Preferably, the Hypol process of Mitsui, which is capable of continuous polymerization by connecting two bulk reactors and one gas phase reactor in series, can be utilized, and the ethylene-propylene block copolymer can be prepared according to a polymerization method known to those skilled in the art.

[0064] Specifically, in the first and second stage reactors, a propylene homopolymer can be prepared by separately adding propylene, or an ethylene-propylene random copolymer can be prepared by additionally adding ethylene. When the polymerization of the ethylene-propylene random copolymer is performed, an equal amount of ethylene can be copolymerized in each polymerization reactor. In the subsequent third stage reactor, an ethylene-propylene rubber component can be block copolymerized by adding ethylene and propylene, thereby obtaining the final ethylene-propylene block copolymer. The melt index of the produced copolymer can be controlled by injecting hydrogen in each reactor.

[0065] In the above-described polymerization step, a catalyst known in the art can be used without limitation. For example, a Ziegler-Natta catalyst or a single-site catalyst, etc. can be used, and a catalyst capable of producing a polypropylene resin having high stereoregularity is preferably used.

[0066] In a specific embodiment of the present application, the catalyst can be prepared by reacting a titanium compound and an internal donor on a magnesium chloride or a dialkylmagnesium support. For example, a Ziegler-Natta catalyst can be configured to include a support composed of dialkylmagnesium particles, titanium tetrachloride, and an internal donor, wherein the dialkylmagnesium particles are obtained by reacting metallic magnesium and an alcohol in the presence of a halogen compound or a nitrogen halide compound as a reaction initiator.

[0067] The form of the metallic magnesium particles used to prepare the dialkylmagnesium support is not particularly limited, but it is preferably in the form of a powder having an average particle diameter of 10 to 300 μm, and more preferably in the form of a powder having an average particle diameter of 50 to 200 μm. When the average particle diameter of the metallic magnesium is less than 10 μm, the average particle diameter of the support as a product is too small and is not preferred. When the average particle diameter of the metallic magnesium exceeds 300 μm, the average particle diameter of the support is too large, and the shape of the support is difficult to form a uniform spherical shape, and thus is not preferred.

[0068] Preferably, the above-obtained catalyst is used together with an organic aluminum compound (e.g., triethylaluminum) as a cocatalyst and a dialkyldialkoxysilane compound (e.g., dicyclopentyldimethoxysilane) as an external donor.

[0069] Ethylene-α-olefin rubber copolymer (B)

[0070] The polyolefin resin composition according to the embodiment of the present application can include an ethylene-α-olefin rubber copolymer (B). The ethylene-α-olefin rubber copolymer (B) can function to improve the softness of a molded article.

[0071] In a specific embodiment of the present application, the α-olefin in the ethylene-α-olefin rubber copolymer (B) can have 3 to 8 carbon atoms. Specifically, the ethylene-α-olefin rubber copolymer (B) can include at least one selected from the group consisting of an ethylene-propylene rubber, an ethylene-1-butene rubber, an ethylene-butene rubber, an ethylene-1-pentene rubber, an ethylene-1-hexene rubber, an ethylene-1-heptene rubber, an ethylene-1-octene rubber, and an ethylene-4-methyl-1-pentene rubber. Preferably, the ethylene-α-olefin rubber copolymer (B) can be an ethylene-propylene rubber.

[0072] In a specific embodiment of the present application, the ethylene content in the ethylene-α-olefin rubber copolymer (B) can be 5 to 90 wt%, preferably 10 to 70 wt%. Specifically, the ethylene content in the ethylene-α-olefin rubber copolymer (B) can be 5 to 90 wt%, preferably 10 to 70 wt% when measured with a Fourier transform infrared spectrometer. When the ethylene content is less than 5 wt%, the ethylene-propylene rubber crystallizes, thereby reducing the cold impact strength of the polyolefin resin composition, and when the ethylene content exceeds 90 wt%, it is difficult to obtain a rubber copolymer.

[0073] The polyolefin resin composition according to the embodiment of the present application contains 0 to 40 wt% of the ethylene-α-olefin rubber copolymer (B) based on the total weight of the components (A) to (B). The addition of the ethylene-α-olefin rubber copolymer (B) increases the softness of the molded article, but when it exceeds 40 wt%, the heat resistance of the molded article can sharply decrease.

[0074] The ethylene-α-olefin rubber copolymer (B) can be polymerized by further adding ethylene and α-olefin monomers in the presence of the ethylene-propylene block copolymer (A) in the fourth-stage gas-phase reactor in the Hypol production process described above.

[0075] In another method, the polyolefin resin composition of the present application can also be prepared by blending a commercially available ethylene-α-olefin rubber copolymer (B) to the ethylene-propylene block copolymer (A) obtained in the Hypol production process. The commercially available ethylene-α-olefin rubber copolymer (B) can be selected from Versify (Dow Chemical), Vistamaxx (ExxonMobil), Tafmer (Mitsui), KEP (Kumho Petrochemical), Engage (Dow Chemical), Exact (ExxonMobil), Lucene (LG Chemical), Solumer (SK Chemical), etc., but is not particularly limited thereto.

[0076] Beta nucleating agent (C)

[0077] The polyolefin resin composition according to the embodiment of the present application further contains a β nucleating agent (C). The β nucleating agent (C) can promote the generation of β crystals at the time of molding of the molded article, thereby improving the softness, insulation properties, voltage resistance properties without reducing the heat resistance.

[0078] In a specific embodiment of the present application, the β nucleating agent (C) can include at least one selected from the group consisting of γ-quinacridone, δ-quinacridone, quinacridonequinone, indigosol and cibantine organic pigments, calcium carbonate modified with dimer aluminates, a mixture of calcium stearate and pimelic acid, calcium and zinc salts of dibasic acids, diamines of adipic acid or suberic acid, N,N'-dicyclohexylterephthalamide and N',N'-dicyclohexyl-2,6-naphthalene-dicarboxylic amide.

[0079] The polyolefin resin composition according to the embodiment of the present application can include 0.02 to 0.5 parts by weight of the β nucleating agent (C) with respect to 100 parts by weight of the component (A) and the component (B).

[0080] If the content of the β nucleating agent (C) is less than 0.02 parts by weight, β crystals cannot be sufficiently formed, so that it can be impossible to significantly improve the elongation, impact resistance and voltage resistance characteristics of the molded article. When the content of the β nucleating agent (C) exceeds 0.5 parts by weight, β crystals cannot be sufficiently grown into spherulites, so that the impact resistance, voltage resistance characteristics and space charge control effect of the molded article are reduced.

[0081] Additive (D)

[0082] The polyolefin resin composition according to the embodiment of the present application can further include an additive (D) without departing from the scope of the present application. Specifically, the content of the additive (D) can be 0.3 to 2.0 parts by weight with respect to 100 parts by weight of the component (A) and the component (B) in the polyolefin resin composition according to the embodiment of the present application. If the content of the additive (D) is less than 0.3 parts by weight, it is difficult to expect the effect of the additive, and if it exceeds 2.0 parts by weight, the effect of the additive can not be significantly increased but the economy of the product can be reduced, and the additive can reduce the electrical properties as an impurity.

[0083] For example, the additive (D) can include an antioxidant, a neutralizing agent, a UV stabilizer, a long-term heat resistance stabilizer, a slip agent, an anti-blocking agent, a reinforcing agent, a filler, a weather resistance stabilizer, an antistatic agent, a lubricant, a nucleating agent, a flame retardant, a pigment and a dye, etc., but is not limited thereto.

[0084] As a preferred embodiment, the polyolefin resin composition according to the embodiment of the present application can further include an antioxidant. As the antioxidant, a phenolic antioxidant, a phosphite antioxidant, etc. can be used, and specifically, at least one selected from the group consisting of pentaerythritol tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 1,3,5-trimethyl-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene and tris(2,4-di-tert-butylphenyl)phosphite can be included, but is not limited thereto.

[0085] As a preferred embodiment, the polyolefin resin composition according to the embodiment of the present application can further include a neutralizing agent. The neutralizing agent can include at least one selected from the group consisting of hydrotalcite and calcium stearate, but is not limited thereto.

[0086] Preparation of polyolefin resin composition

[0087] The method for preparing the polyolefin resin composition according to the embodiment of the present application is not particularly limited, and a blending method commonly known in the art to which the present application pertains can be directly used, or can be used after being appropriately modified.

[0088] Specifically, for example, the polyolefin resin composition of the present application can be prepared by adding the required amounts of the above-mentioned respective resins and additives to a kneader, a roll, a Banbury mixer, or the like, and then blending the added raw materials by using these machines.

[0089] In a specific embodiment of the present application, when the polyolefin resin composition is extracted with a xylene solvent at room temperature, the content of the extracted rubber component (solvent extract) can be 25 to 45% by weight, and preferably 30 to 40% by weight. When the content of the solvent extract in the polyolefin resin composition is less than 25% by weight, the strength of the molded product is high but the flexibility is poor. When the content of the solvent extract in the polyolefin resin composition exceeds 45% by weight, phase inversion occurs between the polypropylene matrix and the rubber component, resulting in high heat distortion and low tensile strength and elongation, and thus is not suitable for application to electric wires.

[0090] In a specific embodiment of the present application, the above-mentioned solvent extract has an intrinsic viscosity of 1.0 to 3.0 dl / g, as measured in a decalin solvent at 135°C. When the intrinsic viscosity of the solvent extract is less than 1.0 dl / g, the impact strength of the molded product is reduced, and when the intrinsic viscosity of the solvent extract exceeds 3.0 dl / g, the rubber component is coagulated in the resin composition, and space charge accumulation and electric field distortion occur at the interface between the polypropylene matrix and the rubber component.

[0091] In a specific embodiment of the present application, the polyolefin resin composition has a melting temperature (Tm) of 150 to 165°C. If the melting temperature of the polyolefin resin composition is lower than 150°C, the heat resistance of the molded product is insufficient, and the resin can be denatured by heat. Thus, it is not suitable for application to high-voltage power cables in which the working temperature and the instantaneous temperature can rise to 130°C or higher.

[0092] In a specific embodiment of the present application, the polyolefin resin composition can have a melt index of 0.5 to 20.0 g / 10 min, preferably 0.5 to 10.0 g / 10 min, when measured at 230°C under a load of 2.16 kg according to ASTM D1238. If the melt index of the polyolefin resin composition is less than 0.5 g / 10 min, the extrusion temperature and load are increased, resulting in a decrease in production efficiency and generation of carbides, and if it exceeds 20 g / 10 min, sagging can occur during the formation of an extrudate, and thus is not preferred.

[0093] In a specific embodiment of the present application, the glass transition temperature of the rubber component of the polyolefin resin composition can occur in the ranges of -60 to -40°C and -40 to -20°C, respectively, when measured by a dynamic mechanical analyzer. If the glass transition temperature of the rubber component occurs only in the range of -60 to -40°C, the mixing property of the resin composition is decreased and whitening can occur, and electric field distortion can occur at the interface between the polypropylene matrix and the rubber component. If the glass transition temperature of the rubber component occurs only in the range of -40 to -20°C, the cold impact resistance measured at -40°C is decreased.

[0094]

Molded article

[0095] According to another embodiment of the present application, the present application provides a polyolefin resin molded article molded from the above polyolefin resin composition.

[0096] The method of producing a molded article from the polyolefin resin composition according to the embodiment of the present application is not particularly limited, and a method known in the art to which the present application pertains can be used. For example, the polyolefin resin composition according to the embodiment of the present application can be molded by a conventional method such as injection molding, extrusion molding, casting molding, etc., to thereby produce a polyolefin resin molded article.

[0097] In a specific embodiment of the present application, the polyolefin resin molded article can have a flexural modulus of less than 400 MPa. When the flexural modulus of the molded article is in this range, the softness of the molded article is excellent, and thus when it is applied to an insulation layer of an ultra-high voltage power cable, it has excellent windability even if the thickness of the insulation layer is thick, thereby facilitating the erection of a high voltage or ultra-high voltage power cable.

[0098] In a specific embodiment of the present application, the polyolefin resin molded article can have a volume resistance of 10 16 Ωcm or more, and the volume resistance of the same test piece after heating (aging) at 140°C for 30 days can still be 10 16Ωcm or above. When the volume resistivity of the molded article is within this range, the molded article can function well as an insulator.

[0099] In specific embodiments of the present invention, the elongation of the polyolefin resin molded article can be 400% or more, and the elongation of the same test piece after being heated (aged) at 140°C for 30 days can be 75% or more of the initial elongation (elongation before heating). When the elongation of the molded article is less than 400%, the outermost part of the curved portion of the molded article may break.

[0100] In a specific embodiment of the present invention, when the polyolefin resin molded product is an 80 μm thick film, the DC insulation breakdown strength can be 300 kV / mm or higher. The DC insulation breakdown strength of the same test piece after being heated (aged) at 140°C for 30 days can also be 300 kV / mm or higher. When the DC insulation breakdown strength of the molded product is within this range, the molded product exhibits excellent voltage withstand characteristics, thus effectively fulfilling its role as an insulator.

[0101] In a specific embodiment of the present invention, when the length of the polyolefin resin molded article is 30 mm, the width is 15 mm, and the thickness is 2 mm, the deformation rate after applying a 1.6 kg load at 130°C and holding it for 6 hours can be less than 50%. When the deformation rate of the molded article is within the stated range, the molded article can function well as an insulator. If the deformation rate of the molded article exceeds this range, heat will be generated during power transmission and distribution, which may cause the shape and structure of the molded article to collapse.

[0102] In a specific embodiment of the present invention, the polyolefin resin molded article may be the insulation layer of a high-voltage or ultra-high-voltage power cable.

[0103]

Example

[0104] The present invention will now be described in more detail through embodiments and comparative examples. However, the following embodiments are for illustrative purposes only, and the scope of the invention is not limited thereto.

[0105] Examples 1 to 3 and Comparative Examples 1 to 5

[0106] Preparation of ethylene-propylene block copolymer

[0107] The polymerization of ethylene-propylene block copolymers utilized Mitsui's Hypol process, which enables continuous polymerization by connecting two bulk reactors and one gas-phase reactor in series. The operating temperatures and pressures of the first and second stage bulk reactors were 68°C to 75°C and 25 kg / cm³, respectively. 2 Up to 35kg / cm 2 and 60℃ to 67℃, 20kg / cm 2 Up to 30kg / cm2 The operating temperature and pressure of the third stage reactor as a gas phase reactor were 75 to 82°C and 15 to 20 kg / cm 2 2 In the first and second stage bulk reactors, when polymerizing propylene homopolymer, the melt index was adjusted by further adding hydrogen gas to each reactor in addition to the addition of propylene, and when polymerizing ethylene-propylene random copolymer, the ratio of ethylene and propylene was adjusted so that an equivalent amount of ethylene was copolymerized in each reactor.

[0108] Preparation of polyolefin resin composition

[0109] After the preparation of the ethylene-propylene block copolymer, an ethylene-α-olefin rubber copolymer was continuously copolymerized by further adding ethylene and α-olefin monomers in the presence of the ethylene-propylene block copolymer in the fourth stage gas phase reactor subsequent to the Hypol preparation process described above, or an ethylene-α-olefin copolymer selected from Versify (Dow Chemical), Vistamaxx (ExxonMobil), Tafmer (Mitsui), KEP (Kumho Petrochemical), Engage (Dow Chemical), Exact (ExxonMobil), Lucene (LG Chemical), Solumer (SK Chemical) was blended into the ethylene-propylene block copolymer. The detailed resin components and physical properties are shown in Table 1. NAB-82 (GCH Technology) as a β nucleating agent or Millard 3988 (DMDBS; Milliken) as an α nucleating agent was added to the resin obtained above to obtain a polyolefin resin composition.

[0110] Experimental examples

[0111] The physical properties of the compositions and molded test pieces prepared in Examples 1 to 3 and Comparative Examples 1 to 5 above were measured according to the methods and standards described below. The results are shown in Tables 1 and 2 below.

[0112] 1. Melt index

[0113] Measured according to ASTM D 1238 method at 230°C under a load of 2.16 kg.

[0114] 2. Content of solvent extract (xylene solubles)

[0115] ​The weight of the polypropylene resin or composition after dissolution in xylene at 140℃ for 1 hour at a concentration of 1%, after standing for 2 hours at room temperature and extraction was measured and expressed as a percentage relative to the total weight of the resin or composition.

[0116] 3. Intrinsic viscosity of solvent extract

[0117] The intrinsic viscosity of the solvent extract obtained in the above "2. Content of solvent extract" was measured using a viscometer in decalin solvent at 135℃.

[0118] 4. Melting temperature

[0119] Using a Q2000 differential scanning calorimeter (DSC) of TA Instrument, the sample was held at a constant temperature of 200℃ for 10 minutes to eliminate thermal history, then crystallized by cooling from 200℃ to 30℃ at a rate of 10℃ per minute to have the same thermal history, then held at a constant temperature of 30℃ for 10 minutes, and the temperature was again increased at a rate of 10℃ per minute, and the melting temperature (Tm) was obtained from the peak temperature.

[0120] 5. Glass transition temperature

[0121] Using a dynamic mechanical analyzer (DMA; Q800 of TA instrument), the temperature was increased from -140℃ to 145℃ at a rate of 2℃ / min, and the glass transition temperature (Tg) of the rubber component was obtained from the stress relaxation curve.

[0122] 6. Flexural modulus (FM)

[0123] It was measured according to the method of ASTM D 790. The size of the injection-molded test piece was 100mm x 10mm x 3mm.

[0124] 7. Heat distortion

[0125] A test piece having a width of 15㎜ and a thickness of 2㎜ was molded at an injection molding temperature of 240℃, then the thickness of the distortion was obtained by applying a load of 1.6kg at 130℃ for 6 hours according to the method of KSC IEC 60811-508, and the distortion rate was obtained by dividing the thickness of the distortion by the initial thickness.

[0126] 8. IZOD impact strength

[0127] Determined according to the method of ASTM D 256 at -40°C.

[0128] 9. Elongation at break

[0129] Determined according to IEC 60811-501 at 25 mm / min. In the aging test, the same test piece was aged for 30 days in a convection constant temperature oven at 140°C, and the elongation was determined after the aging, and the value was divided by the initial elongation to obtain the elongation retention rate.

[0130] 10. DC insulation breakdown voltage

[0131] The polypropylene test piece was a sheet having a thickness of 80 μm, which was produced using an experimental extruder (HAAKE extruder), and the DC insulation breakdown voltage was determined at room temperature according to the method of ASTM D 149-92 using sphere electrodes having a diameter of 12.7 mm. In the aging test, the same test piece was aged for 30 days in a convection constant temperature oven at 140°C, and the DC insulation breakdown voltage was determined after the aging.

[0132] 11. Volume resistance

[0133] An injection-molded test piece having a size of 10 cm x 10 cm x 2 mm was prepared at an injection molding temperature of 240°C, and was aged for 2 days at room temperature, and then determined according to ASTM D 257. In the aging test, the same test piece was aged for 30 days in a convection constant temperature oven at 140°C, and the volume resistance was determined after the aging.

[0134]

Table 1

[0135]

[0136]

Table 2

[0137]

[0138]

[0139] As shown in Tables 1 and 2, the molded article made of the resin composition according to the examples within the scope of the present application has a low flexural modulus and excellent softness, and has excellent impact resistance due to the low glass transition temperature of the ethylene-α-olefin rubber copolymer.

[0140] The compositions of Comparative Examples 1 and 2 do not contain a β nucleating agent, and thus the softness of the molded articles is insufficient. The compositions of Comparative Examples 3 and 4 have a high content of solvent extract, and thus the heat resistance and electrical properties of the molded articles are poor. The composition of Comparative Example 5 has an excessively high content of β nucleating agent, and thus the effect of improving the physical properties of the molded article is reduced.

[0141] The polyolefin resin composition according to the embodiments of the present application not only has excellent insulating properties, but also has excellent heat resistance, voltage resistance properties, space charge control ability, and mechanical properties. Thus, the polyolefin resin molded article made therefrom can be effectively used as an insulating layer of a high-voltage power cable and an extra-high-voltage power cable.

Claims

1. A polyolefin resin composition for power cables, comprising: an ethylene-propylene block copolymer (A) in an amount of 60 to 95% by weight in the total weight of components (A) and (B), and produced by the segmented polymerization of a propylene homopolymer or an ethylene-propylene random copolymer with an ethylene-propylene rubber copolymer in a reactor; an ethylene-a-olefin rubber copolymer (B) in an amount of 5 to 40% by weight in the total weight of components (A) and (B); and a β nucleating agent (C) for forming β crystals in an amount of 0.02 to 0.5 parts by weight with respect to 100 parts by weight of components (A) and (B), wherein the content of the extracted rubber component is 25 to 45% by weight when the polyolefin resin composition is extracted with a xylene solvent at room temperature, the content of ethylene in the ethylene-a-olefin rubber copolymer (B) is 5 to 90% by weight.

2. The polyolefin resin composition for power cables according to claim 1, characterized by, the content of the extracted rubber component is 1 to 45% by weight when the ethylene-propylene block copolymer (A) is extracted with a xylene solvent at room temperature.

3. The polyolefin resin composition for power cables according to claim 2, characterized in that, the intrinsic viscosity of the extracted rubber component is 1.0 to 3.0 dL / g when the ethylene-propylene block copolymer (A) is extracted with a xylene solvent at room temperature.

4. The polyolefin resin composition for power cables according to claim 1, characterized in that, the melting temperature of the ethylene-propylene block copolymer (A) is 150 to 165°C.

5. The polyolefin resin composition for power cables according to claim 1, characterized in that, the melt index of the ethylene-propylene block copolymer (A) is 0.5 to 20.0 g / 10 min when measured according to ASTM D1238 at 230°C under a load of 2.16 kg.

6. The polyolefin resin composition for power cables according to claim 1, characterized in that, the ethylene-a-olefin rubber copolymer (B) comprises at least one selected from the group consisting of ethylene-propylene rubber, ethylene-1-butene rubber, ethylene-1-pentene rubber, ethylene-1-hexene rubber, ethylene-1-heptene rubber, ethylene-1-octene rubber, and ethylene-4-methyl-1-pentene rubber.

7. The polyolefin resin composition for power cables according to claim 1, characterized in that, the β nucleating agent (C) comprises at least one selected from the group consisting of γ-quinacridone, δ-quinacridone, quinacridonequinone, indican, and Ciba organic pigments, calcium carbonate modified with dimeric aluminate, a mixture of calcium stearate and pimelic acid, calcium and zinc salts of dibasic acid, diamine of adipic acid or suberic acid, N,N'-dicyclohexylterephthalamide, and N',N'-dicyclohexyl-2,6-naphthalene-dicarboxyamide.

8. The polyolefin resin composition for power cables according to claim 1, characterized in that, at least one additive selected from the group consisting of antioxidants, neutralizing agents, UV stabilizers, long-term heat resistance stabilizers, slip agents, anti-blocking agents, reinforcing agents, fillers, weather resistance stabilizers, antistatic agents, lubricants, nucleating agents, flame retardants, pigments, and dyes is further included.

9. The polyolefin resin composition for power cables according to claim 1, characterized in that, the intrinsic viscosity of the extracted rubber component is 1.0 to 3.0 dL / g when measured in a decahydronaphthalene solvent at 135°C.

10. The polyolefin resin composition for power cables according to claim 1, characterized in that, the melting temperature of the polyolefin resin composition is 150 to 165°C.

11. The polyolefin resin composition for power cables according to claim 1, characterized in that, the melt index of the polyolefin resin composition is 0.5 to 20.0 g / 10 min when measured according to ASTM D1238 at 230°C under a load of 2.16 kg.

12. The polyolefin resin composition for power cables according to claim 1, characterized in that, The glass transition temperature of the rubber component of the polyolefin resin composition appears in the ranges of -60 to -40°C and -40 to -20°C, respectively, when measured by a dynamic mechanical measuring device.

13. A polyolefin resin molded article molded from the polyolefin resin composition according to any one of claims 1 to 12, which is an insulation layer of a high-voltage power cable or an ultra-high-voltage power cable.

14. The polyolefin resin molded article according to claim 13, characterized by, The bending modulus is less than 400 MPa.

15. The polyolefin resin molded article according to claim 13, characterized by, The volume resistance measured at room temperature is 10 16 Ωcm or more, and the volume resistance of the same test piece after heating for 30 days at 140°C is still 10 16 Ωcm or more.

16. The polyolefin resin molded article according to claim 13, characterized by, The elongation is 400% or more, and the elongation after heating of the same test piece at 140°C for 30 days is 75% or more of the initial elongation.

17. The polyolefin resin molded article according to claim 13, characterized by, When the polyolefin resin molded article is a film having a thickness of 80 μm, the direct current insulation breakdown strength is 300 kV / mm or more, and the direct current insulation breakdown strength after heating of the same test piece at 140°C for 30 days is 300 kV / mm or more.

18. The polyolefin resin molded article according to claim 13, characterized by, The polyolefin resin molded article has a deformation rate of less than 50% after application of a load of 1.6 kg at 130°C for 6 hours under conditions of a length of 30 mm, a width of 15 mm, and a thickness of 2 mm.

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