Polyolefin resin composition for insulation with improved interfacial stability, method for producing the same, and article containing the same.

Abstract

This invention provides a polyolefin resin composition, a method for producing the same, and an article containing the same. [Solution] (A) Ethylene-propylene block copolymer; (B) Propylene-α-olefin rubber copolymer with a propylene content exceeding 60% by weight; and (C) Polyethylene glycol having a number-average molecular weight of less than 20,000 g / mol; A polyolefin resin composition containing the following is provided. [Effects] The polyolefin resin of the present invention has excellent flexibility, low-temperature impact resistance, heat resistance, etc., and good dielectric breakdown characteristics. In particular, it has excellent interfacial stability for improved long-term lifespan, and is therefore suitable for use as an environmentally friendly material for the insulating layer of power cables for low-voltage, high-voltage, or ultra-high-voltage direct current (DC) or alternating current (AC) power transmission or distribution (especially the insulating layer of high-voltage or ultra-high-voltage power cables).

Description

Technical Field

[0001] The present invention relates to an insulating polyolefin resin composition having improved interfacial stability, a method for producing the same, and an article containing the same. More specifically, the present invention relates to an ethylene-propylene block copolymer, a propylene-α-olefin rubber copolymer having a propylene content within a specific range, and a polyethylene glycol having a number average molecular weight within a specific range. The polyolefin resin composition has excellent flexibility, low-temperature impact resistance, heat resistance, etc., good dielectric breakdown characteristics, and particularly excellent interfacial stability for improving long-term life. Therefore, the polyolefin resin composition is preferably used as an environmentally friendly material for an insulating layer of a low-voltage, high-voltage, or ultra-high-voltage direct current (DC) or alternating current (AC) power transmission or distribution cable (particularly, an insulating layer of a high-voltage or ultra-high-voltage power cable), a method for producing the same, and an article (particularly, a power cable) containing the same.

Background Art

[0002] The insulating material in a power cable is located between the conductor that transmits electricity and the external environment and plays a role in preventing the current from flowing out to the outside. In particular, as the voltage increases, the long-term reliability of the cable is required, and excellent electrical insulation performance compared to low voltage, thermal stability that can be stably maintained even at high temperatures, and mechanical flexibility to prevent damage caused by external tension during cable packaging and laying are required. In particular, high-voltage and ultra-high-voltage power cables used in power infrastructure generally have a long service life of 30 to 40 years after laying, and even a single accident can lead to excessive social and industrial losses. Therefore, an insulating material with excellent performance is required.

[0003] Cross-linked polyethylene (XLPE) is used as an insulating layer material for high-voltage and ultra-high-voltage power cables. XLPE has a three-dimensional network structure formed by radical reactions caused by external heat and initiators (such as peroxides), creating chemical bonds between polyethylene polymers. This process provides excellent heat resistance. The cross-linked structure has the advantage of higher thermal stability compared to non-cross-linked polyethylene, as it does not melt even at high temperatures. It can withstand the heat generated when current flows through the conductor, improving power transmission efficiency. However, scorch and cross-linking by-products affect insulation performance, requiring technologies to reduce them. Furthermore, unlike thermoplastics, used XLPE power cables and scrap generated during the manufacturing process are difficult to remelt or reprocess, often resulting in landfill or incineration, which is not environmentally friendly.

[0004] Since polypropylene-based polyolefin compositions are thermoplastic polymers, they do not require a crosslinking process, making them easy to reprocess and recyclable. They also possess excellent electrical insulation properties, making them suitable for use as insulating materials in environmentally friendly power cables. In particular, polypropylene compositions mixed with polyolefin-based elastomers exhibit flexibility comparable to conventional XLPE and can be adjusted to a level applicable to high-voltage and ultra-high-voltage power cables. However, for such multi-component compositions to guarantee long-term insulation performance, phase separation or interfacial separation must not occur.

[0005] Generally, the insulation layer of a power cable thickens as the operating voltage increases, and the insulating intermediate layer cools very slowly during the process from extrusion molding into the cable shape to cooling to room temperature. At this time, because the crystallization rates of each component constituting the multi-component composition are different, localized stress is generated, increasing the likelihood of interfacial separation. This interfacial separation can lead to non-uniformity of the insulating material and pore formation between different phases, causing partial discharge and potentially degrading the insulation performance over time. To solve these problems, it is important to improve the interfacial stability of the polypropylene composition so that a uniform mixing state is maintained even with temperature changes that occur within the insulator during cable processing and throughout the cable's operational life after installation.

[0006] In this regard, Patent Document 1 discloses polyolefin resin compositions containing a propylene homopolymer or an ethylene-propylene block copolymer, an ethylene-α-olefin rubber copolymer, and a copolymer of ethylene and a polar monomer, and evaluates their volume resistivity and DC dielectric breakdown hardness.

[0007] Patent Document 2 discloses an insulating composition for medium-voltage and high-voltage cables comprising a polypropylene copolymer polymerized with a Ziegra-Natta catalyst and an ethylene copolymer or insulating oil, and Patent Document 3 evaluates the properties and copolymer particle size of a polyolefin resin composition for power cable insulation comprising a heterophase propylene copolymer and low-density polyethylene. However, despite the generally known interfacial separation phenomenon between polyethylene and polypropylene, slow cooling conditions are not considered in the processing of high-voltage cables, as is evident from the fact that the evaluation was conducted using injection-molded / hot-press molded test pieces under rapid cooling conditions.

[0008] Patent Document 4 discloses insulating compositions for medium and high voltage cables, comprising a composition of polypropylene, a propylene-based elastomer polymer, and an unsaturated polymer having units that can be chemically crosslinked with these. However, although such compositions have high long-term reliability due to their structure, they are costly and unenvironmentally unfriendly because they cannot be recycled unless the chemical bonds are broken in a post-processing step.

[0009] Patent Document 5 discloses a mixed composition for insulating DC or AC cables, comprising an ethylene-propylene copolymer and a butylene-propylene copolymer, which does not cause interfacial separation at cooling rates of less than 10°C / min. However, while it suppresses void formation that degrades insulation properties, it does not consider stability against interfacial separation under the operating conditions of power transmission cables. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Korean Patent No. 10-2209153 [Patent Document 2] United States Patent No. 10,755,832 [Patent Document 3] United States Patent No. 7,619,165 [Patent Document 4] European Patent No. 2072576 [Patent Document 5] Korean Patent No. 10-1710873 [Overview of the project] [Problems that the invention aims to solve]

[0011] The object of the present invention is to provide a polyolefin resin composition, a method for producing the same, and an article containing the same, which has excellent flexibility and excellent interfacial stability, improves long-term lifespan, and can be suitably used as an environmentally friendly material for insulating layers of high-voltage or ultra-high-voltage power cables. [Means for solving the problem]

[0012] One aspect of the present invention provides a polyolefin resin composition comprising (A) ethylene-propylene block copolymer; (B) propylene-α-olefin rubber copolymer having a propylene content of more than 60% by weight; and (C) polyethylene glycol having a number average molecular weight of less than 20,000 g / mol.

[0013] In one embodiment, the ethylene-propylene block copolymer may be a propylene homopolymer or a polymerization product of an ethylene-propylene random copolymer and an ethylene-propylene rubber copolymer. In one embodiment, the amount of rubber component in 100% by weight of the ethylene-propylene block copolymer may be 1 to 45% by weight when extracted with xylene solvent at 135°C.

[0014] In one embodiment, the intrinsic viscosity of the rubber component in the ethylene-propylene block copolymer may be 1.0 to 4.0 dl / g when measured in decalin solvent at 135°C.

[0015] In one embodiment, the melting temperature (Tm) of the ethylene-propylene block copolymer may be 145 to 165°C.

[0016] In one embodiment, the melt index of the ethylene-propylene block copolymer may be 0.5 to 20.0 g / 10 min when measured at 230°C with a load of 2.16 kg according to ASTM D1238.

[0017] In one embodiment, the propylene-α-olefin rubber copolymer may be at least one selected from the group consisting of propylene-ethylene rubber, propylene-1-butene rubber, propylene-butylene rubber, propylene-ethylene-butylene rubber, propylene-1-pentene rubber, propylene-1-hexene rubber, propylene-1-heptene rubber, propylene-1-octen rubber, and propylene-4-methyl-1-pentene rubber.

[0018] In one embodiment, the polyolefin resin composition may further contain at least one additive selected from the group consisting of antioxidants, neutralizing agents, UV stabilizers, long-term heat-resistant stabilizers, slip agents, antiblocking agents, reinforcing agents, fillers, weather-resistant stabilizers, antistatic agents, lubricants, nucleating agents, flame retardants, pigments, and dyes.

[0019] In one embodiment, the amount of the rubber component in 100% by weight of the polyolefin resin composition may be 25 to 45% by weight when extracted with a xylene solvent at 135°C.

[0020] In one embodiment, the glass transition temperature of the rubber component in the polyolefin resin composition may be -60 to -35°C.

[0021] In one embodiment, the melting temperature (Tm) of the polyolefin resin composition may be 145 to 165°C.

[0022] In one embodiment, the melt index of the polyolefin resin composition may be 0.5 to 20.0 g / 10 min when measured at 230°C under a load of 2.16 kg in accordance with ASTM D1238.

[0023] In one embodiment, the flexural modulus of the polyolefin resin composition may be less than 450 MPa when measured by applying a bending load at a rate of 5 mm / min in accordance with ASTM D790.

[0024] In one embodiment, a 1-mm thick sheet produced by molding the polyolefin resin composition at a cooling rate of 1°C / min or less may not show interfacial separation.

[0025] In one embodiment, a 20-mm thick sheet produced by molding the polyolefin resin composition at a cooling rate of 1°C / min or less may not show interfacial separation when aged at eighty degrees Celsius for 30 days.

[0026] Another aspect of the present invention provides a method for producing a polyolefin resin composition, comprising the steps of (1) copolymerizing propylene and α-olefin in the presence of an ethylene-propylene block copolymer to produce a propylene-α-olefin rubber copolymer having a propylene content of more than 60% by weight, or mixing an ethylene-propylene block copolymer with a propylene-α-olefin rubber copolymer having a propylene content of more than 60% by weight; and (2) adding polyethylene glycol having a number average molecular weight of less than 20,000 g / mol to the product of step (1).

[0027] Yet another aspect of the present invention provides an article comprising the polyolefin resin composition of the present invention.

[0028] In one embodiment, the polyolefin resin composition of the present invention contained in the article may be molded at a cooling rate of 1°C / min or less.

[0029] In one embodiment, the article may be a power cable containing the polyolefin resin composition of the present invention as an insulating layer. [Effects of the Invention]

[0030] The polyolefin resin composition according to the present invention is excellent in flexibility, low-temperature impact resistance, and heat resistance, and has good dielectric breakdown characteristics. In particular, it has excellent interfacial stability for improved long-term lifespan, and can therefore be suitably used as an environmentally friendly material for the insulating layer of power cables for low-voltage, high-voltage, and ultra-high-voltage direct current (DC) or alternating current (AC) power transmission or distribution (especially for the insulating layer of high-voltage and ultra-high-voltage power cables). [Modes for carrying out the invention]

[0031] The present invention will be described in more detail below.

[0032] The polyolefin resin composition of the present invention comprises (A) ethylene-propylene block copolymer; (B) propylene-α-olefin rubber copolymer having a propylene content of more than 60% by weight; and (C) polyethylene glycol having a number average molecular weight of less than 20,000 g / mol.

[0033] (A) Ethylene-propylene block copolymer The polyolefin resin composition of the present invention contains an ethylene-propylene block copolymer.

[0034] In one embodiment, the ethylene-propylene block copolymer may be a polymerization product (e.g., a multi-stage polymerization product) of a propylene homopolymer or ethylene-propylene random copolymer and an ethylene-propylene rubber copolymer. For example, first, a polypropylene matrix of a propylene homopolymer or ethylene-propylene random copolymer can be polymerized, and then an ethylene-propylene rubber component can be block copolymerized into this polypropylene matrix to produce an ethylene-propylene block copolymer.

[0035] In one embodiment, the amount of rubber component in 100% by weight of the ethylene-propylene block copolymer is 1 to 45% by weight when extracted with xylene solvent at 135°C, and this may be the amount of solvent extract obtained from the ethylene-propylene block copolymer using xylene solvent at 135°C. If the amount of rubber component in the ethylene-propylene block copolymer is excessively high above the above level, a phase transition will occur between the polypropylene matrix and the rubber component, increasing the thermal deformation rate and reducing tensile strength and elongation, which may make it unsuitable for application to power cables. More specifically, the amount of rubber component in 100% by weight of the ethylene-propylene block copolymer may be 1% by weight or more, 10% by weight or more, 20% by weight or more, or 30% by weight or more, and may also be 45% by weight or less, or 40% by weight or less, but is not limited to these.

[0036] In one embodiment, the intrinsic viscosity of the rubber component in the ethylene-propylene block copolymer (i.e., a solvent extract obtained from the ethylene-propylene block copolymer using a xylene solvent at 135°C) may be 1.0 to 4.0 dl / g when measured in a decalin solvent at 135°C. If the intrinsic viscosity of the rubber component in the ethylene-propylene block copolymer is too low compared to the above level, the impact strength of the molded article may decrease. Conversely, if it is too high compared to the above level, aggregation of the rubber component may occur within the ethylene-propylene block copolymer, potentially leading to space charge accumulation and electric field strain at the interface between the polypropylene matrix and the rubber component. More specifically, the intrinsic viscosity of the rubber component in the ethylene-propylene block copolymer may be 1.0 dl / g or more, 1.1 dl / g or more, 1.2 dl / g or more, 1.3 dl / g or more, 1.4 dl / g or more, or 1.2 dl / g or more, and may also be 4.0 dl / g or less, 3.5 dl / g or less, 3.0 dl / g or less, 2.7 dl / g or less, 2.6 dl / g or less, or 2.5 dl / g or less, but is not limited to these values.

[0037] In one embodiment, the melting temperature (Tm) of the ethylene-propylene block copolymer may be 145 to 165°C. If the melting temperature of the ethylene-propylene block copolymer is too low compared to the above level, the heat resistance of the molded product will be insufficient, and thermal resin deformation may occur, making it unsuitable for application to high-voltage power cables where the operating temperature and instantaneous temperature rise to 130°C or higher. More specifically, the melting temperature of the ethylene-propylene block copolymer may be 145°C or higher, 146°C or higher, 147°C or higher, 148°C or higher, 149°C or higher, or 150°C or higher, and may also be 165°C or lower, 163°C or lower, 160°C or lower, 158°C or lower, 155°C or lower, or 153°C or lower, but is not limited to these.

[0038] In one embodiment, the melt index of the ethylene-propylene block copolymer may be 0.5 to 20.0 g / 10 min when measured at a load of 2.16 kg and 230°C according to ASTM D1238. If the melt index of the ethylene-propylene block copolymer is too low, the extrusion temperature and extrusion load will increase, reducing productivity and potentially causing carbonization. Conversely, if it is too high, sagging may occur during the molding of the extruded product. More specifically, the melt index of the ethylene-propylene block copolymer may be 0.5 g / 10 min or more, 0.7 g / 10 min or more, 1.0 g / 10 min or more, 1.3 g / 10 min or more, or 1.5 g / 10 min or more, and may also be 20.0 g / 10 min or less, 15.0 g / 10 min or less, 10.0 g / 10 min or less, 5.0 g / 10 min or less, or 3.0 g / 10 min or less, but is not limited to these values.

[0039] In one embodiment, the ethylene content as polymerization units in the ethylene-propylene block copolymer may be 5 to 30% by weight based on 100% by weight of the ethylene-propylene block copolymer, but is not limited to these values. More specifically, the ethylene content in 100% by weight of the ethylene-propylene block copolymer may be 5% or more by weight, 7% or more by weight, 10% or more by weight, 12% or more by weight, or 15% or more by weight, and may also be 30% or less by weight, 28% or less by weight, 25% or less by weight, 23% or less by weight, or 20% or less by weight, but is not limited to these values.

[0040] In one embodiment, the propylene content as polymerization units in the ethylene-propylene block copolymer may be 70 to 95% by weight based on 100% by weight of the ethylene-propylene block copolymer, but is not limited to these values. More specifically, the propylene content in 100% by weight of the ethylene-propylene block copolymer may be 70% or more by weight, 72% or more by weight, 75% or more by weight, 77% or more by weight, or 80% or more by weight, and may also be 95% or less by weight, 93% or less by weight, 90% or less by weight, 88% or less by weight, or 85% or less by weight, but is not limited to these values.

[0041] In one embodiment, the polyolefin resin composition of the present invention may contain ethylene-propylene block copolymer in an amount of 60 to 98% by weight relative to 100% by weight of the total of components (A), (B), and (C). If the content of ethylene-propylene block copolymer in the polyolefin resin composition is too low compared to the above level, the heat resistance of the molded article will decrease, the heat deformation characteristics will worsen, and the appearance may change drastically during high-temperature work. Conversely, if the content is too high compared to the above level, the content of other components will decrease relatively, which may lead to problems such as insufficient effectiveness (for example, poor flexibility). More specifically, the content of ethylene-propylene block copolymer in 100% by weight of the total of components (A), (B), and (C) may be 60% by weight or more, 65% by weight or more, 70% by weight or more, 75% by weight or more, or 80% by weight or more, and may also be 98% by weight or less, 95% by weight or less, 93% by weight or less, 90% by weight or less, 88% by weight or less, or 85% by weight or less, but is not limited to these.

[0042] The method for producing the ethylene-propylene block copolymer is not particularly limited, and the present invention can use known methods for producing ethylene-propylene block copolymers in the art, either as is or with appropriate modifications. For example, bulk polymerization, solution polymerization, slurry polymerization, gas-phase polymerization, etc., can be used, and the process may be carried out in either a batch or continuous manner.

[0043] In one embodiment, the ethylene-propylene block copolymer can be produced by a conventional polymerization method using a process (for example, Mitsui's HYPOL process) in which one or more bulk reactors and one or more gas-phase reactors are connected in series to enable continuous polymerization.

[0044] Specifically, two bulk reactors and one gas-phase reactor are connected in series. In the bulk reactors, propylene can be injected alone to produce a propylene homopolymer, or ethylene can be injected further to produce an ethylene-propylene random copolymer. In the subsequent third-stage reactor, ethylene and propylene are added to block copolymerize the ethylene-propylene rubber component, yielding the final ethylene-propylene block copolymer. The melt index of the resulting copolymer can be controlled by injecting hydrogen into each reactor. When polymerizing a propylene homopolymer, the ratio of ethylene to propylene can be adjusted so that equal amounts of ethylene are copolymerized in each reactor.

[0045] In one embodiment, the ethylene-propylene copolymer may be polymerized in the presence of a Ziegra-Natta catalyst. This catalyst can be produced by reacting a titanium compound with an internal electron donor on a magnesium compound support. Specifically, the internal electron donor may be composed of a combination of a non-aromatic alkoxyester compound and a phthalate ester compound, as in Korean Patent No. 10-1988156, but is not particularly limited thereto. In this catalyst, although not particularly limited, it is preferable to use an organoaluminum compound (e.g., triethylaluminum) as a co-catalyst and an organosilicon compound (e.g., trialkoxysilane) as an external electron donor.

[0046] (B) Propylene-α-olefin rubber copolymer with a propylene content exceeding 60% by weight The polyolefin resin composition of the present invention also includes a propylene-α-olefin rubber copolymer having a propylene content exceeding 60% by weight. This component can play a role in improving the flexibility of molded articles.

[0047] If the propylene content as polymerization units in the propylene-α-olefin rubber copolymer is 60% by weight or less per 100% by weight of the propylene-α-olefin rubber copolymer, the interfacial stability with the ethylene-propylene block copolymer (component A) deteriorates. The upper limit of the propylene content in the propylene-α-olefin rubber copolymer is not particularly limited; for example, it may be 98% by weight or less per 100% by weight of the propylene-α-olefin rubber copolymer, but is not limited to these limits. If the propylene content in the propylene-α-olefin rubber copolymer is too high compared to the above level, the crystallinity may increase, and the cold impact strength of the resin composition may decrease. The propylene content can be measured using known measuring means, such as a Fourier transform infrared spectrometer.

[0048] More specifically, the propylene content in 100% by weight of the propylene-α-olefin rubber copolymer may be more than 60% by weight, 61% or more by weight, 63% or more by weight, 65% or more by weight, 67% or more by weight, 69% or more by weight, 70% or more by weight, 71% or more by weight, 73% or more by weight, 75% or more by weight, 77% or more by weight, 79% or more by weight, or 80% or more by weight, and may also be 98% or less by weight, 95% or less by weight, 93% or less by weight, 90% or less by weight, or 88% or less by weight, but is not limited to these.

[0049] In one embodiment, the α-olefin in the propylene-α-olefin rubber copolymer has 2 to 8 carbon atoms, and there may be one or more copolymer monomers. However, here, the α-olefin is something other than propylene.

[0050] In one embodiment, the propylene-α-olefin rubber copolymer may be at least one selected from the group consisting of propylene-ethylene rubber, propylene-1-butene rubber, propylene-butylene rubber, propylene-ethylene-butylene rubber, propylene-1-pentene rubber, propylene-1-hexene rubber, propylene-1-heptene rubber, propylene-1-octen rubber, and propylene-4-methyl-1-pentene rubber.

[0051] In one embodiment, the melt index of the propylene-α-olefin rubber copolymer may be 0.5 to 30.0 g / 10 min when measured at a load of 2.16 kg and 230°C according to ASTM D1238. If the melt index of the propylene-α-olefin rubber copolymer is too low, the extrusion temperature and load will increase, reducing productivity and potentially causing carbonization. Conversely, if it is too high, the melt behavior will differ from that of the ethylene-propylene block copolymer, potentially leading to poor interfacial stability. More specifically, the melt index of the propylene-α-olefin rubber copolymer may be 0.5 g / 10 min or more, 0.7 g / 10 min or more, or 1.0 g / 10 min or more, and may also be 30.0 g / 10 min or less, 25.0 g / 10 min or less, 20.0 g / 10 min or less, 15.0 g / 10 min or less, or 10.0 g / 10 min or less, but is not limited to these values.

[0052] In one embodiment, the polyolefin resin composition of the present invention may contain propylene-α-olefin rubber copolymer in an amount of 1 to 39% by weight relative to 100% by weight of the total of components (A), (B), and (C). If the content of propylene-α-olefin rubber copolymer in the polyolefin resin composition is too low compared to the above level, problems such as insufficient performance (for example, poor flexibility) may occur, and conversely, if it is too high compared to the above level, the heat resistance of the molded article may rapidly decrease. More specifically, the content of propylene-α-olefin rubber copolymer in 100% by weight of the total of components (A), (B), and (C) may be 1% by weight or more, 3% by weight or more, 5% by weight or more, 7% by weight or more, 10% by weight or more, or 13% by weight or more, and may also be 39% by weight or less, 35% by weight or less, 30% by weight or less, 28% by weight or less, 25% by weight or less, or 20% by weight or less, but is not limited to these.

[0053] In one embodiment, the propylene-α-olefin rubber copolymer can be polymerized in a fourth gas-phase reactor following the HYPOL manufacturing process by further supplying propylene and α-olefin monomers in the presence of an ethylene-propylene block copolymer.

[0054] In another embodiment, the polyolefin resin composition of the present invention can be produced by mixing a commercially available propylene-α-olefin rubber copolymer with an ethylene-propylene block copolymer obtained in the HYPOL manufacturing process. Examples of commercially available propylene-α-olefin rubber copolymers include, but are not limited to, Versify (manufactured by DOW), Vistamaxx (manufactured by ExxonMobil), and Tafmer (manufactured by Mitsui).

[0055] (C) Polyethylene glycol having a number-average molecular weight of less than 20,000 g / mol The polyolefin resin composition of the present invention further comprises polyethylene glycol having a number-average molecular weight of less than 20,000 g / mol. This component can be used to improve the interfacial safety of the resin composition.

[0056] If the number-average molecular weight of the polyethylene glycol is 20,000 g / mol or higher, the effect of enhancing interfacial safety between the ethylene-propylene block copolymer (component A) and the propylene-α-olefin rubber copolymer (component B) decreases. The lower limit of the number-average molecular weight of polyethylene glycol is not particularly limited and may be, for example, 500 g / mol or higher, but is not limited thereto. If the number-average molecular weight of polyethylene glycol is too low compared to the above level, the polyethylene glycol may become liquid at room temperature, exhibit different behavior from polyolefins, and its dispersibility may deteriorate. The number-average molecular weight of polyethylene glycol can be measured using known measuring methods, such as gel permeation chromatography (GPC).

[0057] More specifically, the number-average molecular weight of polyethylene glycol may be less than 20,000 g / mol, 19,000 g / mol or less, 17,000 g / mol or less, 15,000 g / mol or less, 13,000 g / mol or less, 11,000 g / mol or less, 10,000 g / mol or less, or 9,000 g / mol or less, and may also be 500 g / mol or more, 1,000 g / mol or more, 2,000 g / mol or more, 3,000 g / mol or more, 4,000 g / mol or more, 5,000 g / mol or more, 6,000 g / mol or more, or 7,000 g / mol or more, but is not limited to these.

[0058] In one embodiment, the polyolefin resin composition of the present invention may contain polyethylene glycol in an amount of 0.01 to 2% by weight relative to 100% by weight of the total of components (A), (B), and (C). If the polyethylene glycol content in the polyolefin resin composition is too low compared to the above level, a problem may arise in that its effectiveness is insufficient. Conversely, if it is too high compared to the above level, a problem may arise in that the dielectric constant of the resin composition increases, ultimately reducing the insulation performance of the cable. More specifically, the polyethylene glycol content in 100% by weight of the total of components (A), (B), and (C) may be 0.01% by weight or more, 0.05% by weight or more, 0.1% by weight or more, 0.15% by weight or more, 0.2% by weight or more, 0.25% by weight or more, or 0.3% by weight or more, and may also be 2% by weight or less, 1.8% by weight or less, 1.5% by weight or less, 1.3% by weight or less, 1% by weight or less, 0.8% by weight or less, or 0.5% by weight or less, but is not limited to these.

[0059] In addition to the components described above, the polyolefin resin composition of the present invention may further contain one or more additives commonly used in polypropylene resin compositions. In one embodiment, the polyolefin resin composition of the present invention may further contain, but is not limited to, at least one additive selected from the group consisting of antioxidants, neutralizing agents, UV stabilizers, long-term heat-resistant stabilizers, slip agents, antiblocking agents, reinforcing agents, fillers, weather-resistant stabilizers, antistatic agents, lubricants, nucleating agents, flame retardants, pigments, and dyes.

[0060] In one embodiment, the antioxidant is a phenolic antioxidant, a phosphite antioxidant, and more specifically, one or more selected from the group consisting of tetrakis(methylene(3,5-di-t-butyl-4-hydroxy)hydrosilylnate), 1,3,5-trimethyl-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene and tris(2,4-di-t-butylphenyl)phosphite, but is not limited to these.

[0061] In one embodiment, the neutralizing agent may be one or more selected from the group consisting of hydrotalcite and inorganic salts (e.g., calcium salts) stearate, but is not limited to these.

[0062] The content of such additional additives is not particularly limited, and depending on the intended use and application, each additive can be used in a range of, for example, 0.01 to 2 parts by weight, or more specifically, 0.05 to 1 part by weight, per 100 parts by weight of the total amount of the composition of the present invention, but is not limited thereto.

[0063] In one embodiment, the amount of rubber component in 100% by weight of the polyolefin resin composition of the present invention may be 25 to 45% by weight when extracted with xylene solvent at 135°C, and this may be the amount of solvent extract obtained by extracting from the polyolefin resin composition using xylene solvent at 135°C.

[0064] If the amount of rubber component in the polyolefin resin composition is too low compared to the aforementioned level, the strength of the molded article may increase and its flexibility may decrease. Conversely, if the amount is too high compared to the aforementioned level, a phase transition may occur between the polypropylene matrix and the rubber component, forming a gap between the interfaces and causing electric field strain. More specifically, the amount of rubber component in 100% by weight of the polyolefin resin composition may be 25% by weight or more, 30% by weight or more, 35% by weight or more, or 40% by weight or more, and may also be 45% by weight or less, 44% by weight or less, or 43% by weight or less, but is not limited to these.

[0065] In one embodiment, the glass transition temperature of the rubber component in the polyolefin resin composition of the present invention (i.e., a solvent extract obtained by extracting from the polyolefin resin composition using xylene solvent at 135°C) may be -60 to -35°C. The glass transition temperature of the rubber component in the polyolefin resin composition can be measured by known measuring means, for example, a dynamic mechanical analyzer (DMA), and DMA measurement can show a glass transition temperature in the range of -60 to -35°C. If the glass transition temperature of the rubber component is always -35°C or higher, the low-temperature (-20°C) impact resistance of the resin composition may decrease.

[0066] In one embodiment, the melting temperature (Tm) of the polyolefin resin composition of the present invention may be 145 to 165°C. If the melting temperature of the polyolefin resin composition is too low compared to the above level, the heat resistance of the molded product will be insufficient and thermal deformation of the resin may occur, making it unsuitable for application to high-voltage power cables where the operating temperature and instantaneous temperature rise to 130°C or higher. More specifically, the melting temperature of the polyolefin resin composition may be 145°C or higher, 146°C or higher, 147°C or higher, 148°C or higher, 149°C or higher, or 150°C or higher, and may also be 165°C or lower, 163°C or lower, 160°C or lower, 158°C or lower, 155°C or lower, or 153°C or lower, but is not limited to these.

[0067] In one embodiment, the melt index of the polyolefin resin composition of the present invention may be 0.5 to 20.0 g / 10 min when measured at a load of 2.16 kg and 230°C according to ASTM D1238. If the melt index of the polyolefin resin composition is too low, the extrusion temperature and load will increase, reducing productivity and potentially causing carbonization. Conversely, if it is too high, sagging may occur during molding of the extruded product. More specifically, the melt index of the polyolefin resin composition may be 0.5 g / 10 min or more, 0.7 g / 10 min or more, 1.0 g / 10 min or more, 1.3 g / 10 min or more, or 1.5 g / 10 min or more, and may also be 20.0 g / 10 min or less, 15.0 g / 10 min or less, 10.0 g / 10 min or less, 5.0 g / 10 min or less, or 3.0 g / 10 min or less, but is not limited to these values.

[0068] In one embodiment, the flexural modulus of the polyolefin resin composition of the present invention may be less than 450 MPa when measured by applying a bending load at a rate of 5 mm / min according to ASTM D790. When the flexural modulus of a molded article processed according to ASTM D790 using the polyolefin resin composition of the present invention falls within the above range, the molded article exhibits excellent flexibility, and when applied to the insulating layer of an ultra-high voltage power cable, the insulating layer remains highly flexible even if thick, thus facilitating the laying of high-voltage or ultra-high-voltage power cables. More specifically, the flexural modulus of the polyolefin resin composition may be less than 450 MPa, 440 MPa or less, 430 MPa or less, 420 MPa or less, 410 MPa or less, 400 MPa or less, 390 MPa or less, 380 MPa or less, or 370 MPa or less, but is not limited to these. There is no particular limit to the lower limit of the flexural modulus of the polyolefin resin composition; for example, it may be 250 MPa or more, 300 MPa or more, or 320 MPa or more, but is not limited to these.

[0069] In one embodiment, a 1 mm thick sheet obtained by molding the polyolefin resin composition at a cooling rate of 1°C / min or less may not exhibit interfacial separation. More specifically, the cooling rate may be 0.8°C / min or less or 0.5°C / min or less, but is not limited thereto.

[0070] In one embodiment, a 20 mm thick sheet obtained by molding the polyolefin resin composition at a cooling rate of 1°C / min or less may not exhibit interfacial separation when aged at 80°C for 30 days (accelerated aging test). More specifically, the cooling rate may be 0.8°C / min or less or 0.5°C / min or less, but is not limited thereto.

[0071] In one embodiment, the occurrence of interfacial separation can be determined by visual inspection, polarizing microscope, scanning microscope (SEM), or a combination of one or more of these techniques. For example, if the molded article (sheet) of the polyolefin resin composition shows no spots when observed with the naked eye, and if no pores of 5 μm or more (in the case of a sheet with a thickness of 1 mm) or 10 μm or more (in the case of a sheet with a thickness of 20 mm) are formed inside when observed with a scanning microscope at a microscale (preferably 500 nm to 50 μm scale), it is determined that interfacial separation has not occurred.

[0072] Another aspect of the present invention provides a method for producing a polyolefin resin composition, comprising the steps of (1) copolymerizing propylene and α-olefin in the presence of an ethylene-propylene block copolymer to produce a propylene-α-olefin rubber copolymer having a propylene content of more than 60% by weight, or mixing an ethylene-propylene block copolymer with a propylene-α-olefin rubber copolymer having a propylene content of more than 60% by weight; and (2) adding polyethylene glycol having a number average molecular weight of less than 20,000 g / mol to the product of step (1).

[0073] In the method for producing the polyolefin resin composition of the present invention, the ethylene-propylene block copolymer, the propylene-α-olefin rubber copolymer having a propylene content of more than 60% by weight, and the polyethylene glycol having a number average molecular weight of less than 20,000 g / mol are the same as described above.

[0074] In one embodiment, the step of "copolymerizing propylene and α-olefin in the presence of ethylene-propylene block copolymer to produce a propylene-α-olefin rubber copolymer having a propylene content exceeding 60% by weight" can be carried out using known methods in the art of the present invention, either as is or with appropriate modifications. For example, after producing an ethylene-propylene block copolymer using the HYPOL process, which connects the two bulk reactors and one gas-phase reactor in series, copolymerization can be continuously carried out by further supplying propylene and α-olefin monomers to a subsequent fourth-stage gas-phase reactor in the presence of the ethylene-propylene block copolymer, while controlling the amount of propylene added.

[0075] Furthermore, in one embodiment, the step of "mixing an ethylene-propylene block copolymer with a propylene-α-olefin rubber copolymer having a propylene content exceeding 60% by weight" can be carried out using known methods in the art of the present invention, either as is or with appropriate modifications. Specifically, for example, a method is used in which predetermined amounts of the ethylene-propylene block copolymer and the propylene-α-olefin rubber copolymer having a propylene content exceeding 60% by weight, together with other additives, are put into a mixer such as a kneader, roll, or Benbury mixer, or a single-screw / twin-screw extruder, and the put-in raw materials are mixed in the said apparatus.

[0076] In one embodiment, the step of "adding polyethylene glycol having a number average molecular weight of less than 20,000 g / mol to the product of step (1)" can also be carried out using known methods in the art of the present invention, either as is or with appropriate modifications. Specifically, for example, after adding polyethylene glycol having a number average molecular weight of less than 20,000 g / mol to the product of step (1), it can be mixed using a kneader, roll mixer, Benbury mixer or other kneading machine, or a single-screw / twin-screw extruder or the like.

[0077] The polyolefin resin composition according to the present invention is excellent in flexibility, low-temperature impact resistance, heat resistance, and other properties, and also has good dielectric breakdown characteristics. In particular, it is excellent in interfacial stability for improving long-term lifespan, and therefore can be suitably used as an environmentally friendly material for insulating layers of power cables for low-voltage, high-voltage, and ultra-high-voltage direct current (DC) or alternating current (AC) power transmission or distribution (especially for insulating layers of high-voltage and ultra-high-voltage power cables).

[0078] Therefore, yet another aspect of the present invention provides an article comprising the polyolefin resin composition of the present invention.

[0079] In one embodiment, the polyolefin resin composition of the present invention contained in the article may be molded at a cooling rate of 1°C / min or less. More specifically, the cooling rate may be 0.8°C / min or less or 0.5°C / min or less, but is not limited to these.

[0080] In one embodiment, the article may be a power cable containing the polyolefin resin composition of the present invention as an insulating layer. More specifically, the power cable may be, but is not limited to, a high-voltage or ultra-high-voltage power cable.

[0081] There are no particular limitations on the method for producing an article from the polyolefin resin composition of the present invention, and known methods in the art of the present invention (e.g., injection molding, extrusion molding, etc.) can be used.

[0082] The present invention will be described in more detail below through examples and comparative examples. However, the scope of the present invention is not limited in any way by these examples.

[0083] Examples Example 1 (1) Production of ethylene-propylene block copolymer The production of polyolefin resin compositions, including the polymerization of ethylene-propylene block copolymers, was carried out using Mitsui's HYPOL process, which enables continuous polymerization by connecting two bulk slurry reactors and two gas-phase reactors in series. The operating temperatures and pressures of the bulk reactors, the first and second stage reactors, were 68-75°C and 25-35 kg / cm², respectively. 2 60-67°C, 20-30 kg / cm³ 2 The operating temperature and pressure of the third-stage reactor, which is a gas-phase reactor, were 75-82°C and 15-20 kg / cm². 2 In the first and second stage bulk reactors, the ethylene-propylene random copolymer was polymerized (at this time, the ratio of ethylene to propylene was adjusted so that the same amount of ethylene was copolymerized in each reactor). Then, in the third stage reactor, ethylene and propylene were added to block copolymerize the ethylene-propylene rubber component to obtain an ethylene-propylene block copolymer.

[0084] (2) Production of polyolefin resin composition The ethylene-propylene block copolymer prepared as described above was mixed with commercially available propylene-α-olefin rubber copolymers [Versify (DOW), Vistamaxx (DOW), Tafmer (Mitsui)]. Mixing was carried out according to the monomer composition of component (B) shown in Table 1 below. Subsequently, polyethylene glycol #8000 (number average molecular weight: 8,000 g / mol, BASF) was added to the obtained product and mixed to produce a polyolefin resin composition.

[0085] Example 2 (1) Production of ethylene-propylene block copolymer An ethylene-propylene block copolymer was produced in the same manner as in step (1) of Example 1.

[0086] (2) Production of polyolefin resin composition After the production of the ethylene-propylene block copolymer, the propylene-α-olefin rubber copolymer was continuously copolymerized in a four-stage gas-phase reactor following the HYPOL production process described above, by further supplying propylene and α-olefin monomers (ethylene) in the presence of the ethylene-propylene block copolymer. The operating temperature and pressure of the fourth-stage reactor were 68-75°C and 10-17 kg / cm². 2 Subsequently, polyethylene glycol #8000 (number average molecular weight: 8,000 g / mol, manufactured by BASF) was added to the obtained product and mixed to produce a polyolefin resin composition.

[0087] Comparative Example 1 An ethylene-propylene block copolymer was prepared in the same manner as in step (1) of Example 1, and this copolymer was used as is for the following physical property tests.

[0088] Comparative Example 2 (1) Production of ethylene-propylene block copolymer An ethylene-propylene block copolymer was produced in the same manner as in step (1) of Example 1.

[0089] (2) Production of polyolefin resin composition After the production of the ethylene-propylene block copolymer, a polyolefin resin composition was prepared in the same manner as in step (2) of Example 1. Mixing was carried out according to the monomer composition of component (B) shown in Table 1 below.

[0090] Comparative Example 3 (1) Production of ethylene-propylene block copolymer An ethylene-propylene block copolymer was produced in the same manner as in step (1) of Example 1.

[0091] (2) Production of polyolefin resin composition After the production of the ethylene-propylene block copolymer, a polyolefin resin composition was prepared in the same manner as in step (2) of Example 1. Mixing was carried out according to the monomer composition of component (B) shown in Table 1 below.

[0092] Comparative Example 4 (1) Production of ethylene-propylene block copolymer An ethylene-propylene block copolymer was produced in the same manner as in step (1) of Example 2.

[0093] (2) Production of polyolefin resin composition After the production of the ethylene-propylene block copolymer, a polyolefin resin composition was prepared in the same manner as in step (2) of Example 1. Mixing was carried out according to the monomer composition of component (B) shown in Table 1 below.

[0094] Comparative Example 5 (1) Production of ethylene-propylene block copolymer An ethylene-propylene block copolymer was produced in the same manner as in step (1) of Example 1.

[0095] (2) Production of polyolefin resin composition After the production of the ethylene-propylene block copolymer, a polyolefin resin composition was produced in the same manner as in step (2) of Example 1. However, polyethylene glycol #20000 (number average molecular weight: 20,000 g / mol, manufactured by Samchun Pure Chemical) was used.

[0096] Physical property testing The physical properties of the resins or compositions produced in Examples 1-2 and Comparative Examples 1-5, and their molded articles, were measured according to the following methods and standards, and the results are shown in Table 1 below.

[0097] (1) Melt Index (g / 10 min) Measurements were taken according to ASTM D1238, under a load of 2.16 kg at 230°C.

[0098] (2) Amount of rubber component (weight %): Analysis of xylene solvent extract (xylene soluble, XS) The resin or composition was dissolved in xylene at a concentration of 1% at 135°C for 1 hour, then cooled to room temperature after 2 hours for extraction. The weight was then measured and expressed as a percentage of the total weight of the resin or composition.

[0099] (3) Intrinsic viscosity (dl / g) of the rubber component (xylene solvent extract, XS) The intrinsic viscosity of the xylene solvent extract obtained in (2) above was measured using a viscometer in decalin solvent at 135°C.

[0100] (4) Melting temperature (°C) Using a TA Instrument Q2000 differential scanning calorimeter (DSC), the sample was isothermally held at 200°C for 10 minutes to remove its thermal history. Then, it was cooled from 200°C to 30°C at a rate of 10°C per minute to induce crystallization, maintaining the same thermal history. Subsequently, the sample was isothermally held at 30°C for 10 minutes, and then reheated at a rate of 10°C per minute. The melting temperature (Tm) was measured from the peak temperature.

[0101] (5) Glass transition temperature (°C) Using a dynamic mechanical analyzer (DMA; TA instrument Q800), the temperature was increased from -140°C to 145°C at a rate of 2°C / min to obtain a stress relaxation curve, from which the glass transition temperature (Tg) was measured.

[0102] (6) Flexural modulus (FM) (MPa) The flexural modulus was measured for injection-molded specimens measuring 100 mm × 10 mm × 3 mm, according to ASTM D790.

[0103] (7) Observation of interface separation using the naked eye / electron microscope (SEM) Using a hot press device and molds with controllable cooling rates, we fabricated plate-like sheets measuring 80mm x 80mm or larger with thicknesses of 1mm and 20mm.

[0104] The fabricated 1 mm thick sheet was cooled at 0.3°C / min, and the structure and interface separation of the test specimen were observed visually and with an electron microscope (SEM). If there were no spots visible to the naked eye and no pores larger than 5 μm were found to be formed inside the specimen when observed with an SEM, it was determined that no interface separation had occurred.

[0105] Furthermore, the fabricated 20mm thick sheet was cooled at 0.3°C / min and aged in an oven at 80°C for 30 days. After that, the structure of the test specimen and the interfacial separation phenomenon were observed by macroscopic inspection and scanning electron microscope (SEM). If there were no spots when observed with the naked eye and no pores larger than 10 μm were formed inside when observed with SEM, it was determined that interfacial separation had not occurred.

[0106] [Table 1]

[0107] As can be seen from Table 1 above, the molded articles produced from the resin compositions of the examples according to the present invention exhibited excellent flexibility due to a low flexural modulus, a low glass transition temperature advantageous for impact resistance, and excellent interfacial stability.

[0108] On the other hand, the composition of Comparative Example 1 exhibited insufficient flexibility in the molded article and under slow cooling conditions, the composition of Comparative Example 2 exhibited interfacial separation under slow cooling conditions, and the compositions of Comparative Examples 3 to 5 exhibited interfacial separation in the aging test after the slow cooling process.

Claims

1. (A) Ethylene-propylene block copolymer; (B) Propylene-α-olefin rubber copolymer having a propylene content exceeding 60% by weight; and (C) Polyethylene glycol having a number-average molecular weight of less than 20,000 g / mol; A polyolefin resin composition containing the following:

2. The polyolefin resin composition according to claim 1, wherein the ethylene-propylene block copolymer is a polymerization product of a propylene homopolymer or an ethylene-propylene random copolymer and an ethylene-propylene rubber copolymer.

3. The polyolefin resin composition according to claim 1, wherein the amount of rubber component in 100% by weight of the ethylene-propylene block copolymer is 1 to 45% by weight when extracted with a xylene solvent at 135°C.

4. The polyolefin resin composition according to claim 1, wherein the intrinsic viscosity of the rubber component in the ethylene-propylene block copolymer is 1.0 to 4.0 dl / g when measured in a decalin solvent at 135°C.

5. The polyolefin resin composition according to claim 1, wherein the melting temperature (Tm) of the ethylene-propylene block copolymer is 145 to 165°C.

6. The polyolefin resin composition according to claim 1, wherein the melt index of the ethylene-propylene block copolymer is 0.5 to 20.0 g / 10 min when measured at 230°C with a load of 2.16 kg according to ASTM D1238.

7. The polyolefin resin composition according to claim 1, wherein the propylene-α-olefin rubber copolymer is selected from the group consisting of propylene-ethylene rubber, propylene-1-butene rubber, propylene-butylene rubber, propylene-ethylene-butylene rubber, propylene-1-pentene rubber, propylene-1-hexene rubber, propylene-1-heptene rubber, propylene-1-octen rubber, and propylene-4-methyl-1-pentene rubber.

8. The polyolefin resin composition according to claim 1, further comprising at least one additive selected from the group consisting of antioxidants, neutralizing agents, UV stabilizers, long-term heat-resistant stabilizers, slip agents, antiblocking agents, reinforcing agents, fillers, weather-resistant stabilizers, antistatic agents, lubricants, nucleating agents, flame retardants, pigments, and dyes.

9. The polyolefin resin composition according to claim 1, wherein the amount of rubber component in 100% by weight of the polyolefin resin composition is 25 to 45% by weight when extracted with xylene solvent at 135°C.

10. The polyolefin resin composition according to claim 1, wherein the glass transition temperature of the rubber component in the polyolefin resin composition is -60 to -35°C.

11. The polyolefin resin composition according to claim 1, wherein the melting temperature (Tm) of the polyolefin resin composition is 145 to 165°C.

12. The polyolefin resin composition according to claim 1, wherein the melt index of the polyolefin resin composition is 0.5 to 20.0 g / 10 min when measured at 230°C with a load of 2.16 kg according to ASTM D1238.

13. The polyolefin resin composition according to claim 1, wherein the flexural modulus of the polyolefin resin composition is less than 450 MPa when measured by applying a bending load at a speed of 5 mm / min according to ASTM D790.

14. The polyolefin resin composition according to claim 1, wherein a 1 mm thick sheet produced by molding the polyolefin resin composition at a cooling rate of 1°C / min or less does not exhibit interfacial separation.

15. The polyolefin resin composition according to claim 1, wherein a 20 mm thick sheet produced by molding the polyolefin resin composition at a cooling rate of 1°C / min or less does not exhibit interfacial separation when aged at 80°C for 30 days.

16. (1) A step of copolymerizing propylene and α-olefin in the presence of ethylene-propylene block copolymer to produce a propylene-α-olefin rubber copolymer having a propylene content of more than 60% by weight, or a step of mixing ethylene-propylene block copolymer and a propylene-α-olefin rubber copolymer having a propylene content of more than 60% by weight; and (2) Adding polyethylene glycol having a number average molecular weight of less than 20,000 g / mol to the product of step (1); A method for producing a polyolefin resin composition containing [the specified component].

17. An article comprising the polyolefin resin composition according to any one of claims 1 to 15.

18. The article according to claim 17, wherein the polyolefin resin composition is molded at a cooling rate of 1°C / min or less.

19. The article according to claim 17, which is a power cable containing the polyolefin resin composition as an insulating layer.

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