Polypropylene resin composition having enhanced flexibility for electric cable insulation layer

Abstract

Disclosed are: a recyclable polypropylene resin composition for an electric cable insulation layer, which has excellent heat resistance stability and flexibility; and a foam and a molded product comprising same. The present invention provides a polypropylene resin composition for an electric cable insulation layer, and a foam and a molded article comprising same, the polypropylene resin composition comprising: 60 to 90 parts by weight of a propylene block copolymer in which ethylene-propylene rubber (EPR) is dispersed in a propylene-ethylene random copolymer; and 10 to 40 parts by weight of a polyolefin elastomer (POE).

Description

Polypropylene resin composition for the insulation layer of wire cables with enhanced flexibility

[0001] The present invention relates to a polypropylene resin composition for an insulation layer of a wire cable, and more specifically, to a polypropylene resin composition for an insulation layer of a wire cable with enhanced flexibility.

[0002] This application claims priority and interest to Korean Patent Application No. 10-2024-0157221 filed on November 7, 2024, the full text of which is incorporated herein by reference.

[0003] Cross-linked materials such as polyethylene (PE), polyvinyl chloride (PVC), and ethylene-propylene rubber (EPR) are mainly used as insulation materials for electric wire cables, and foamed insulators are used to reduce signal transmission loss and increase transmission distance by using gas or foaming agents to lower the dielectric constant to enhance transmission performance.

[0004] The foamed insulation layer of conventional electric wire cables is composed of high-density polyethylene (HDPE) or fluorinated ethylene propylene (FEP) resin. However, cables using HDPE lack heat resistance, and cables using FEP consume a lot of energy during the processing stage due to the high melting temperature of the fluorine resin. Additionally, the resin is expensive, has high density, and has low elasticity, so the insulation structure in a deformed state can affect data transmission. Furthermore, fluorine-containing resins such as FEP use fluorine-based blowing agents such as chlorofluorocarbons (CFCs), which release ozone-depleting substances upon high-temperature decomposition. As regulations banning their use are expected to be implemented by the international community, there is a problem regarding environmentally hazardous substances. In the case of cross-linked polyethylene, since it is a cross-linked polymer, it cannot be recycled and must be incinerated for disposal, which is also an issue of not being environmentally friendly.

[0005] Korean Published Patent No. 10-2021-0066316 discloses a polypropylene resin composition for an insulation layer of a power cable comprising a polypropylene block copolymer in which an ethylene-propylene rubber copolymer is dispersed within a propylene homopolymer, and a polyolefin elastomer of propylene-ethylene rubber and ethylene-1-octene rubber, but it does not mention its application as a foamed insulator, and even if this resin composition is applied as a foamed insulator, there are limitations in satisfying the required heat resistance and flexibility.

[0006] The present invention aims to provide a polypropylene resin composition for an insulation layer of a recyclable wire cable having excellent heat stability and flexibility, as well as a foam and a molded article containing the same.

[0007] To solve the above problem, the present invention provides a polypropylene resin composition for an insulating layer of a wire cable comprising: 60 to 90 parts by weight of a propylene block copolymer in which ethylene-propylene rubber (EPR) is dispersed within a propylene-ethylene random copolymer; and 10 to 40 parts by weight of a polyolefin elastomer (POE).

[0008] In addition, the present invention provides a polypropylene resin composition for an insulation layer of a wire cable, characterized in that the ethylene-derived repeating unit of the propylene block copolymer is included in the propylene-ethylene random copolymer at a weight of 0.1 to 5%, in the ethylene-propylene rubber (EPR) at a weight of 30 to 60%, and in the propylene block copolymer at a weight of 5 to 25%.

[0009] In addition, the present invention provides a polypropylene resin composition for an insulation layer of a wire cable, characterized in that the propylene block copolymer has a melting point of 150 to 170°C and a xylene-soluble content of 10 to 40 weight% in the propylene block copolymer.

[0010] In addition, the present invention provides a polypropylene resin composition for an insulation layer of a wire cable, characterized in that the polyolefin elastomer (POE) is a propylene-ethylene rubber (PER) having an ethylene content of 10 to 30 weight%.

[0011] In addition, a polypropylene resin composition for an insulation layer of a wire cable is provided, characterized by further including 1 to 15 parts by weight of high melt strength polypropylene (HMS-PP) having a branching index of 0.85 or less.

[0012] In addition, the resin composition has a density of 0.87 to 0.91 g / cm³ as measured according to the following method. 3The present invention provides a polypropylene resin composition for an insulation layer of a wire cable, characterized by having a melt tension of 5 to 30 cN, a melting point of 150 to 165℃, and a flexural modulus of 600 MPa or less.

[0013] [Density Measurement Method]

[0014] The density of the resin composition was measured using the underwater displacement method according to ASTM D792 standard;

[0015] [Method for Measuring Melting Tension]

[0016] Molten spring at 200°C using a Rheotens device (Rheotens 97, GOTTFERT)

[0017] The fiber is extruded through a circular die with a diameter of 1 mm, the extruded strand is located 100 mm (spinline length) below the die exit, and the winding acceleration is 120 mm / s 2 When wound by a progressively increasing Leotens wheel, the force (cN) applied to the wheel is recorded as a function of the winding speed (mm / s), and the peak force applied before the strand breaks or at break is defined as the melt tension;

[0018] [Method for Measuring Melting Point]

[0019] Using a differential scanning calorimeter (DSC, Perkin-Elmer Co.), 10 mg of the test specimen was pre-melted at 220°C for 5 minutes under a nitrogen gas atmosphere, the temperature was lowered to 40°C at a cooling rate of 5°C / min, and then the temperature was raised at a heating rate of 5°C / min to measure the peak temperature of the maximum peak of the obtained melt endothermic curve;

[0020] [Method for Measuring Flexural Modulus]

[0021] Measured at 10 mm / min according to ASTM D790 standard.

[0022] To solve the above additional problem, the present invention provides a foam for an insulation layer of an extruded wire cable comprising the resin composition and a foaming agent.

[0023] In addition, the above foam has a density of 0.25 to 0.45 g / cm³ as measured according to the following method. 3 The present invention provides a foam for an insulation layer of a wire cable, characterized by having a flexural modulus of 250 MPa or less, a foam cell size of 200 μm or less, a degree of foaming of 55% or more, and a relative permittivity of 2 or less.

[0024] [Density Measurement Method]

[0025] The density of the foam was measured using the underwater displacement method according to ASTM D792 standards;

[0026] [Method for Measuring Flexural Modulus]

[0027] Measured under 10 mm / min conditions according to ASTM D790 standard;

[0028] [Method for Measuring Foam Cell Size]

[0029] For an image captured by magnifying the cross-section of the foam under a microscope, the cell diameters of 10 random points are measured and the average value is calculated;

[0030] [Method for Measuring Foaming Level]

[0031] Calculated according to the following mathematical formula 1 using the change in density before and after foaming;

[0032] <Mathematical Formula 1>

[0033]

[0034] [Method for Measuring Relative Permittivity]

[0035] A specimen (thickness 2 mm, width 2 cm, length 2 cm) manufactured according to ASTM D150 standards was measured at 60°C conditions by applying an AC voltage of 1 V at a frequency of 1 MHz using an LCR Meter (electrode radius 5 mm, electrode type G10 type).

[0036] To solve the above additional problem, the present invention provides a wire cable comprising the foam as an insulating layer.

[0037] The present invention can provide a polypropylene resin composition for an insulation layer of a recyclable wire cable with excellent heat stability and flexibility, and a foam and a molded article containing the same, by using a propylene block copolymer in which ethylene-propylene rubber (EPR) is dispersed within a propylene-ethylene random copolymer and a polyolefin elastomer (POE).

[0038] FIG. 1 is a schematic diagram showing a cross-section of a wire cable manufactured from a resin composition according to the present invention.

[0039] The present invention will be described in detail below through preferred embodiments. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor may appropriately define the concepts of terms to best describe their invention, they should be interpreted in a meaning and concept consistent with the technical spirit of the present invention. Therefore, the configurations of the embodiments described in this specification are merely the most preferred embodiments of the present invention and do not represent all aspects of the technical spirit of the present invention; thus, it should be understood that various equivalents and modifications capable of replacing them may exist at the time of filing this application.

[0040]

[0041] The present invention discloses a polypropylene resin composition for an insulating layer of a wire cable comprising 60 to 90 parts by weight of a propylene block copolymer in which ethylene-propylene rubber (EPR) is dispersed within a propylene-ethylene random copolymer; and 10 to 40 parts by weight of a polyolefin elastomer (POE).

[0042] The following describes in detail each component of the insulating resin composition for a wire cable according to the present invention.

[0043] Polypropylene can be classified into homopolypropylene (H-PP), propylene random copolymer (R-PP), and propylene block copolymer (B-PP). Among these, propylene random copolymer and propylene block copolymer are more suitable for electrical wire cables because they possess higher flexibility and flexibility compared to homopolypropylene. Furthermore, since propylene block copolymer has the advantage of superior flexibility compared to propylene random copolymer, propylene block copolymer is used in this invention.

[0044] In the present invention, the propylene block copolymer is a type of RTPO (Reactor-made Thermoplastic Polyolefin elastomers) and refers to a polymer containing multiple polymers exhibiting rubbery properties within a polymer comprising units derived from propylene monomers.

[0045] In the present invention, the propylene block copolymer can be obtained, for example, by reacting propylene and ethylene in a bulk reactor to polymerize a propylene-ethylene random copolymer, and then copolymerizing gases of propylene and ethylene in a gas-phase reactor in the presence of the propylene-ethylene random copolymer through continuous polymerization to disperse ethylene-propylene rubber (EPR) within the propylene-ethylene random copolymer. By being manufactured through continuous polymerization as described above, the ethylene-propylene rubber (EPR) can be uniformly dispersed into small-sized domains within a polypropylene matrix. At this time, while the use of a propylene homopolymer as the polypropylene matrix may be considered, in the present invention, the propylene-ethylene random copolymer is used as the matrix to provide advantages in mixing due to its high affinity with the polyolefin elastomer (POE) described later. Accordingly, the high elasticity and chain entanglement characteristics imparted by the polyolefin elastomer (POE) are enhanced, thereby increasing melt strength and improving foaming performance.

[0046] Here, in the present invention, the domain size and degree of dispersion of the ethylene-propylene rubber (EPR) are not limited, but considering the thermal and electrical properties of the final resin composition, the average size of the domain may be 0.1 to 5 μm, preferably 0.5 to 2 μm, and the degree of dispersion of the domain may be 0.1 to 0.7, preferably 0.2 to 0.6. The domain size and degree of dispersion can be measured by cutting a specimen prepared by compression molding (at 220°C for 4 minutes) of the resin composition into a width of 1 mm and a length of 10 cm, immersing it in xylene at 60°C to elute the ethylene-propylene rubber, and analyzing the pores present on the surface of the specimen using a scanning electron microscope (SEM).

[0047] In the present invention, the propylene block copolymer may comprise 30 to 70 weight% of a propylene-ethylene random copolymer and 30 to 70 weight% of ethylene-propylene rubber (EPR), preferably 45 to 65 weight% of a propylene-ethylene random copolymer and 35 to 55 weight% of ethylene-propylene rubber (EPR), and more preferably 50 to 60 weight% of a propylene-ethylene random copolymer and 40 to 50 weight% of ethylene-propylene rubber (EPR). The propylene block copolymer is in the form in which ethylene-propylene rubber (EPR) particles are dispersed in a propylene-ethylene random copolymer matrix. Specifically, the propylene block copolymer may be a block copolymer in which ethylene-propylene rubber (EPR) is polymerized stepwise in a reactor with a propylene-ethylene random copolymer. The above-mentioned propylene block copolymer contains ethylene-propylene rubber (EPR) dispersed within a specific content range, and thus has a lower flexural modulus compared to propylene homopolymers or propylene-ethylene random copolymers. When applied as a foamed insulation layer for electrical cables, it can maximize flexibility and elasticity, as well as improve thermal and electrical properties. Furthermore, when mixed with the polyolefin elastomer (POE) described later, it exhibits excellent miscibility due to uniform dispersion, thereby maximizing thermal properties and flexibility.

[0048] In the present invention, the propylene block copolymer is produced by using a high content of ethylene in a polymerization reactor to generate a large amount of ethylene-propylene rubber (EPR). Compared to conventional propylene block copolymers, it contains a high content of repeating units derived from ethylene-propylene rubber (EPR), which has the advantage of high tensile strength and excellent flexibility.

[0049] Although not limited by theory, the propylene block copolymer generally produced in a reactor may have an ethylene-derived repeating unit content of 5 to 25 weight% in the total block copolymer, preferably 10 to 20 weight%. Additionally, the ethylene-derived repeating unit content may be 0.1 to 5 weight% in the propylene-ethylene random copolymer, preferably 0.1 to 3 weight%, more preferably 0.5 to 2 weight%, and 30 to 60 weight% in the ethylene-propylene rubber (EPR), preferably 35 to 50 weight%. Thermal and electrical properties can be maximized within the above range of ethylene-derived repeating unit content. Furthermore, if the ethylene-derived repeating unit content exceeds 5 weight% in the propylene-ethylene random copolymer, the melting point of the block copolymer may be lowered to below 150°C, thereby reducing heat stability.

[0050] In addition, the propylene block copolymer may have a melting point of 150 to 170°C, and preferably 150 to 160°C. When the melting point of the propylene block copolymer satisfies the above range, the thermal properties and flexibility intended to be achieved in the present invention can be satisfied when applied as a foamed insulation layer for a wire cable.

[0051] In addition, the propylene block copolymer may have a xylene-soluble (XS) content of 10 to 40 weight%, preferably 15 to 35 weight%, and more preferably 20 to 30 weight%. The xylene-soluble content depends on the ethylene-propylene rubber (EPR) content contained in the propylene block copolymer, and flexibility, thermal properties, and electrical properties can be maximized within the above content range.

[0052] In the present invention, the propylene block copolymer may be included in an amount of 60 to 90 parts by weight, preferably 65 to 85 parts by weight, and more preferably 70 to 80 parts by weight. If the propylene block copolymer content is less than 60 parts by weight, electrical properties and heat stability are reduced, and if it exceeds 90 parts by weight, flexibility is reduced.

[0053] The present invention includes a polyolefin elastomer (POE) as a modifier to improve thermal properties, electrical properties, and foaming performance, along with the flexibility of the final resin composition.

[0054] The above polyolefin elastomer comprises repeating units derived from ethylene, repeating units derived from propylene, and (C4-C 12 It comprises two or more types selected from the group consisting of repeating units derived from alpha-olefins, wherein it may include repeating units derived from ethylene or repeating units derived from propylene. For example, it may be a copolymer of ethylene and propylene, or a random or block copolymer elastomer of alpha-olefins with one of ethylene and propylene and 1-butene, 1-pentene, 1-hexene, 1-octene, etc., or a combination of these elastomers. Considering dispersibility, electrical properties, and foaming performance, propylene-ethylene rubber (PER) or ethylene-1-octene rubber (EOR) may be used more preferably, and propylene-ethylene rubber (PER) may be used most preferably. In this regard, when propylene-ethylene rubber (PER) is used as the polyolefin elastomer (POE), the ethylene content is preferably 10 to 30 weight%, and more preferably 15 to 25 weight%.

[0055] The above polyolefin elastomer (POE) may be included in an amount of 10 to 40 parts by weight, preferably 15 to 35 parts by weight, and more preferably 15 to 30 parts by weight. If the polyolefin elastomer (POE) content is less than 10 parts by weight, the flexibility, thermal properties, electrical properties, and foaming performance of the final resin composition are reduced, and if it exceeds 40 parts by weight, it is difficult to further improve electrical properties and heat stability is reduced.

[0056] In order to further improve flexibility, thermal properties, electrical properties, and foaming performance as a resin composition for an insulation layer of a recyclable wire cable in the present invention, a specific amount of high melt strength polypropylene (HMS-PP) may be further included in the propylene block copolymer and polyolefin elastomer (POE) of the composition described above.

[0057] The above HMS-PP is a type of high melt strength polyolefin or long-chain branched polyolefin, which can be added to a thermoplastic elastomer composition to impart excellent heat resistance, elastic recovery, scratch resistance, and mechanical properties. In the present invention, it is used as a modifier in a resin composition for the insulation layer of an electrical wire cable to maximize flexibility, thermal properties, electrical properties, and foaming performance.

[0058] Specifically, the above HMS-PP is designed to compensate for the low melt tension of general polypropylene having a linear structure. This HMS-PP can be manufactured by adding and reacting a composition capable of branching to the polypropylene polymer chains with a linear structure to form an interconnected structure, or by increasing the molecular weight or molecular weight distribution (MWD). For example, a method may be applied in which the polypropylene backbone chain with a linear structure is first cut by a chemical method (using a catalyst) or a physical method (using high-temperature shear force), and then a relatively low-molecular-weight long-chain branch (LCB) is branched or rearranged on the cut polypropylene backbone.

[0059] The HMS-PP used in the present invention has a branching index of 0.85 or less, specifically 0.1 to 0.85, and preferably 0.1 to 0.75. As the branching index becomes less than 1, the number of LCBs increases, allowing tie molecules to be formed. These tie molecules connect the polypropylene crystal lamellae, resulting in a more robust crystal structure. Consequently, the melt tension increases, thereby strengthening heat resistance and improving flexibility and electrical properties. However, if the branching index exceeds 0.85, the degree of improvement in melt tension may not be satisfactory.

[0060] Meanwhile, the above LCB is a branch attached to the main chain of polypropylene formed from carbon-carbon bonds, and generally refers to a branched chain with 6 or more carbon atoms. The above branching index can be calculated according to the following Equation 2 by measuring the viscosity of branched polypropylene and linear polypropylene, respectively.

[0061] <Mathematical Formula 2>

[0062]

[0063] The above HMS-PP may be included in an amount of 1 to 15 parts by weight in relation to the relative content of the components constituting the total polypropylene resin composition, preferably in an amount of 2 to 13 parts by weight, and more preferably in an amount of 3 to 12 parts by weight. If the content of the above HMS-PP is less than 1 part by weight, the degree of improvement in flexibility, thermal properties, electrical properties, and foaming performance may be negligible, and if it exceeds 15 parts by weight, the cell size increases, making it difficult to maintain the shape of the foam cells in a bent structure when bent.

[0064] In addition to the above components, the resin composition according to the present invention may further include one or more additives commonly used when applied as an insulation layer for wire cables, for example, may further include an antioxidant and a water tree inhibitor.

[0065] The polypropylene resin composition for the insulation layer of a wire cable according to the present invention can be manufactured by mixing and extruding the above components according to conventional methods known in the art. For example, the resin composition can be manufactured by feeding the above components into a twin-screw extruder and melt-kneading them.

[0066] The resin composition for an insulation layer of a wire cable according to the present invention comprises a propylene block copolymer and a polyolefin elastomer (POE) within a certain compositional range, thereby exhibiting an appropriate density suitable for use as a foamed insulation layer, and enabling the realization of improved heat stability and flexibility required in the relevant technical field. That is, the resin composition for an insulation layer of a wire cable according to the present invention has a density of 0.87 to 0.91 g / cm³ as measured by the following method. 3 And, the melt tension is 5 to 30 cN, the melting point is 150 to 165°C, and the flexural modulus may be 600 MPa or less, and preferably the density is 0.875 to 0.905 g / cm³ 3And, the melt tension measured according to the following method may be 8 to 25 cN, the melting point may be 151 to 164°C, and the flexural modulus may be 300 to 600 MPa, and more preferably the density may be 0.88 to 0.90 g / cm³ 3 And, according to the following method, the melt tension measured may be 10 to 25 cN, the melting point may be 152 to 163℃, and the flexural modulus may be 350 to 550 MPa.

[0067] [Density Measurement Method]

[0068] The density of the resin composition was measured using the underwater displacement method according to ASTM D792 standard;

[0069] [Method for Measuring Melting Tension]

[0070] Molten spring at 200°C using a Rheotens device (Rheotens 97, GOTTFERT)

[0071] The fiber is extruded through a circular die with a diameter of 1 mm, the extruded strand is located 100 mm (spinline length) below the die exit, and the winding acceleration is 120 mm / s 2 When wound by a progressively increasing Leotens wheel, the force (cN) applied to the wheel is recorded as a function of the winding speed (mm / s), and the peak force applied before the strand breaks or at break is defined as the melt tension;

[0072] [Method for Measuring Melting Point]

[0073] Using a differential scanning calorimeter (DSC, Perkin-Elmer Co.), 10 mg of the test specimen was pre-melted at 220°C for 5 minutes under a nitrogen gas atmosphere, the temperature was lowered to 40°C at a cooling rate of 5°C / min, and then the temperature was raised at a heating rate of 5°C / min to measure the peak temperature of the maximum peak of the obtained melt endothermic curve;

[0074] [Method for Measuring Flexural Modulus]

[0075] Measured at 10 mm / min according to ASTM D790 standard.

[0076] In another aspect, the present invention provides a foam for an insulation layer of an extruded wire cable comprising the above-mentioned polypropylene resin composition and a foaming agent.

[0077] The above-mentioned blowing agent may be fed together with the above-mentioned polypropylene resin composition using, for example, an extruder to be extruded into a foam. In the present invention, fluorine-based blowing agents such as CFCs are excluded as such blowing agents, and inorganic blowing agents such as sodium bicarbonate, sodium carbonate, ammonium bicarbonate, ammonium carbonate, and ammonium nitrite may be used. Considering the foaming performance according to the composition of the above-mentioned polypropylene resin composition, sodium bicarbonate or sodium carbonate may be preferably used, and most preferably, sodium bicarbonate may be used.

[0078] The foam for the insulation layer of a wire cable according to the present invention exhibits an appropriate density suitable for use as a foamed insulation layer, and is capable of exhibiting excellent electrical characteristics along with improved flexibility and foaming performance required in the relevant technical field. That is, the foam for the insulation layer of a wire cable according to the present invention has a density of 0.25 to 0.45 g / cm³ as measured by the following method. 3 The flexural modulus may be 250 MPa, the foam cell size may be 200 μm or less, the degree of foaming may be 55% or more, and the relative dielectric constant may be 2 or less; preferably, the flexural modulus may be 100 to 250 MPa, the foam cell size may be 100 to 200 μm, the degree of foaming may be 55 to 80%, and the relative dielectric constant may be 1.8 or less; more preferably, the flexural modulus may be 150 to 200 MPa, the foam cell size may be 115 to 180 μm, the degree of foaming may be 55 to 70%, and the relative dielectric constant may be 1.6 or less.

[0079] [Density Measurement Method]

[0080] The density of the foam was measured using the underwater displacement method according to ASTM D792 standards;

[0081] [Method for Measuring Flexural Modulus]

[0082] Measured under 10 mm / min conditions according to ASTM D790 standard;

[0083] [Method for Measuring Foam Cell Size]

[0084] For an image captured by magnifying the cross-section of the foam under a microscope, the cell diameters of 10 random points are measured and the average value is calculated;

[0085] [Method for Measuring Foaming Level]

[0086] Calculated according to the following mathematical formula 1 using the change in density before and after foaming;

[0087] <Mathematical Formula 1>

[0088]

[0089] [Method for Measuring Relative Permittivity]

[0090] A specimen (thickness 2 mm, width 2 cm, length 2 cm) manufactured according to ASTM D150 standards was measured at 60°C conditions by applying an AC voltage of 1 V at a frequency of 1 MHz using an LCR Meter (electrode radius 5 mm, electrode type G10 type).

[0091] According to another aspect of the present invention, a wire cable can be manufactured using a foam for the insulation layer of the wire cable. FIG. 1 schematically shows a cross-section of a wire cable manufactured using a foam for the insulation layer of a wire cable according to the present invention.

[0092] Referring to FIG. 1, a wire cable manufactured from a foam for an insulating layer of a wire cable according to the present invention comprises a conductor (1), an inner semiconducting layer (2) surrounding the conductor (1), an insulating layer (3) surrounding the inner semiconducting layer (2), an outer semiconducting layer (4) surrounding the insulating layer (3), and a sheath layer (5) surrounding the outer semiconducting layer (4), wherein the insulating layer (3) may comprise a foam according to the present invention. Since the details of each layer constituting the wire cable, excluding the insulating layer, are commonly known to those skilled in the art, a detailed description is omitted in the present invention.

[0093] Hereinafter, specific manufacturing examples and embodiments according to the present invention will be explained in more detail.

[0094]

[0095] Preparation Example: Preparation of propylene block copolymer

[0096] Propylene and ethylene were reacted in a bulk reactor to obtain a propylene-ethylene random copolymer, and the propylene-ethylene random copolymer polymerized in the bulk reactor, along with ethylene and propylene, were fed into a gas-phase reactor to carry out a copolymerization reaction of ethylene and propylene in a continuous process to produce a propylene block copolymer. The prepared propylene block copolymer had a weight ratio of propylene-ethylene random copolymer to ethylene-propylene rubber (EPR) of 55:45 (xylene-soluble content (XS) = 25 wt%), and ethylene-derived repeating units were 2 wt% in the propylene-ethylene random copolymer, 35 wt% in the ethylene-propylene rubber (EPR), and 15 wt% in the total copolymer, with a melting point of 152°C. The xylene-soluble content and melting point of the propylene block copolymer were measured according to the following methods.

[0097] - Xylene Soluble (XS): According to ASTM D5492, the propylene block copolymer was dissolved in boiling xylene and cooled to room temperature to separate it into xylene-soluble and xylene-insoluble portions. The xylene-soluble portion was collected separately, the xylene was evaporated using a hot plate, and the weight percentage of the remaining portion was measured.

[0098] - Melting point: Using a differential scanning calorimeter (DSC, Perkin-Elmer Co.), 10 mg of the test specimen was pre-melted at 220°C for 5 minutes under a nitrogen gas atmosphere, the temperature was lowered to 40°C at a cooling rate of 5°C / min, and then the temperature was raised at a heating rate of 5°C / min to measure the peak temperature of the maximum peak of the melt endothermic curve obtained.

[0099]

[0100] Examples and Comparative Examples

[0101] A mixture composed of the base resin component composition (unit: parts by weight) of Table 1 below was mixed with a mixer for 5 minutes, and then extruded with a twin-screw extruder at a temperature of 190 to 230°C to produce a resin composition in the form of pellets.

[0102] In addition, 100 parts by weight of the resin composition on the above pellets were fed into an extruder, and 1 part by weight of the foaming agent listed in Table 1 below was fed together to extrude a foamed body.

[0103]

[0104] Test example

[0105] For the resin composition and foam on pellets manufactured above, density, melt tension, melting point, flexural modulus, foam cell size, degree of foaming, and relative dielectric constant were measured according to the following method, and the results are shown together in Table 1 below.

[0106] [measurement method]

[0107] (1) Density

[0108] The density of the resin composition and foam was measured using the underwater displacement method according to ASTM D792 standards;

[0109] (2) Melt Strength

[0110] Molten spring at 200°C using a Rheotens device (Rheotens 97, GOTTFERT)

[0111] The fiber is extruded through a circular die with a diameter of 1 mm, the extruded strand is located 100 mm (spinline length) below the die exit, and the winding acceleration is 120 mm / s 2 When wound by a progressively increasing Leotens wheel, the force (cN) applied to the wheel is recorded as a function of the winding speed (mm / s), and the peak force applied before the strand breaks or at break is defined as the melt tension.

[0112] (3) Melting point (Tm)

[0113] Using a differential scanning calorimeter (DSC, Perkin-Elmer Co.), 10 mg of a test specimen was pre-melted at 220°C for 5 minutes under a nitrogen gas atmosphere, the temperature was lowered to 40°C at a cooling rate of 5°C / min, and then the temperature was raised at a heating rate of 5°C / min to measure the peak temperature of the maximum peak of the melt endothermic curve obtained.

[0114] (4) Flexural modulus

[0115] Measurements were taken at 10 mm / min according to ASTM D790 standards.

[0116] (5) Cell Size

[0117] For the image captured by magnifying the cross-section of the foam with a microscope, the cell diameters of 10 random points were measured and the average value was calculated.

[0118] (6) Foaming

[0119] It was calculated according to the following mathematical formula 1 using the change in density before and after foaming.

[0120] <Mathematical Formula 1>

[0121]

[0122] (7) Relative permittivity

[0123] A specimen (thickness 2 mm, width 2 cm, length 2 cm) manufactured according to ASTM D150 standards was measured at 60°C conditions by applying an AC voltage of 1 V at a frequency of 1 MHz using an LCR Meter (electrode radius 5 mm, electrode type G10 type).

[0124]

[0125] Classification Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Base Resin Composition R base RTPO PP 80 70 80 70 --- 100 50 H base RTPO PP --------- 80 POE 20 30 15 20 ----5 20 HMS PP -- 5 10 100 HDPE ----90 ----- LDPE ----10 ----- FEP ----- 100 Resin Composition Physical Properties Density (g / cm3) 0.88 80.88 70.89 20.89 00.94 52.15 0.90 89 0.87 50.89 Melt Strength (cN) 12 12 15 18 62 45 68 9Tm (°C) 15 2 15 11 6 2 16 3 13 4 2 10 16 2 15 11 5 11 63 Flexural Modulus (MPa) 4 5 0 40 0 ​​50 0 48 0 78 0 63 4 2 10 0 8 5 0 28 0 480 Foam Processing Conditions Blowing Agent: Sodium Bicarbonate, CFC, Sodium Bicarbonate, Sodium Bicarbonate, Sodium Bicarbonate, Sodium Bicarbonate Extrusion Temperature (°C) 18 0 18 0 19 0 19 16 0 30 0 18 0 18 0 18 190 Foam Physical Properties Density (g / cm3) 0.38 5 0.35 7 0.32 5 0.29 8 0.17 10.97 4 0.15 5 0.75 5 0.65 8 0.586 Flexural Modulus (MPa) 195 160 182 154 141 287 361 465 20 22 35 Cell Size (μm) 14 31 20 160 17 53 00 24.2 210 11 116 91 53 Degree of Foaming (%) 56 60 63 66 825 4.6 31 52 534 Dielectric Constant 1.6 1.6 1.4 1.4 1.3 1.4 1.5 2.0 1.9 1.8 * Note - R base RTPO PP: Propylene block copolymer prepared according to the preparation example - H base RTPO PP: Propylene block copolymer prepared by the same method as the preparation example, except that a propylene homopolymer was obtained instead of a propylene-ethylene random copolymer in the bulk reactor - POE: Propylene-ethylene rubber, Vistamaxx™ 6102FL, ethylene content 16 wt%, Exxonmobil Chemical - HMS-PP: High melt strength Polypropylene, Branching Index 0.65, HMS-120, Lotte Chemical - HDPE: High-density polyethylene, MF5000, Lotte Chemical - LDPE: Low-density polyethylene, XL510H, Lotte Chemical - FEP: Fluoroethylene propylene resin, FEP-510-J, DuPont.

[0126]

[0127] Referring to Table 1, according to the present invention, a resin composition for insulating wire cables (Examples 1 to 2) and a foam molded using the same, which use a propylene block copolymer in which ethylene-propylene rubber (EPR) is dispersed within a propylene-ethylene random copolymer and a polyolefin elastomer (POE) in a specific content ratio, have excellent heat resistance compared to a conventional material (see Comparative Example 1) that uses HDPE with a melting point of 150°C or higher and uses a polypropylene material as a base resin. In the rubber region, the composition contains 25% by weight of the RTPO base resin and an additional 20 to 30% by weight of POE at a high concentration, so the flexural modulus is very low, resulting in excellent flexibility. Furthermore, due to the rubber region, the elasticity is high, allowing for excellent maintenance and recovery of the foam cell structure, thereby enabling excellent insulation properties to be maintained after mechanical impact. In addition, due to the entanglement characteristics of the rubber region, it imparts a melt strength favorable for foam molding, allowing it to be utilized as a lightweight material through foaming. It is evaluated as a highly suitable material for foamed insulation layers because the foam cell size is small (less than 150 μm) and it exhibits a high degree of foaming of approximately 60%. Furthermore, with a relative dielectric constant of 1.6, it exhibits an excellent dielectric constant reduction effect due to the air layer after foaming, which is advantageous for high-speed signal propagation. Additionally, since all components constituting the resin composition are made of thermoplastic resin, it is recyclable, and due to the excellent moisture resistance of polypropylene, it can be suitablely used in electrical products requiring moisture protection.

[0128] In addition, when HMS-PP, which can increase melt tension, is included in a specific content range while slightly reducing the POE content in the rubber component (Examples 3 and 4), the melting point and melt tension increase due to the inclusion of HMS-PP. The high melt tension is more favorable for foam formation, resulting in a further increase in the degree of foaming and a further decrease in the relative dielectric constant. This plays a role in increasing the propagation speed, which can predict the realization of improved electrical performance. Furthermore, although the flexural modulus of the resin composition increases slightly due to the inclusion of HMS-PP, the melt tension increases significantly, resulting in rheological properties that are more favorable for foam formation. Consequently, the flexural modulus of the foam is lowered due to the high degree of foaming, thereby further improving flexibility.

[0129] In this regard, when a base resin in which LDPE is blended with HDPE, which is used as a foamed insulation layer for conventional wire cables (Comparative Example 1), has the advantages of good foaming, excellent processability, and low cost as a raw material, the cell size of the foam becomes excessively large, forming a non-uniform cell structure. In addition, although the degree of foaming is very high, the strength is lower and the elasticity is less compared to polypropylene material, making it difficult to maintain the shape of the foam cells in a bent structure on a curved surface, and the heat resistance is reduced due to the low melting point. Furthermore, although the relative dielectric constant is lower due to the high degree of foaming and exhibits a relatively faster propagation speed, there is a problem in that it is difficult to maintain long-term performance due to durability issues.

[0130] In addition, when using fluoroethylene propylene resin, which is used as a foamed insulation layer for conventional wire cables, as a base resin (Comparative Example 2), the fluoropolymer resin used has high temperature resistance, excellent corrosion resistance, and chemical resistance, but the flexibility is reduced, and high temperatures are required in the processing range, resulting in high energy consumption during production, high raw material costs, and high density, making it difficult to lighten the cable after foaming, and there is a risk of generating halogen acids when burned.

[0131] In addition, when only HMS-PP, a material specialized for foaming, is used as the base resin (Comparative Example 3), the foam cell size is large and the flexural modulus is high, making it difficult to provide flexibility as a cable material for electrical wires.

[0132] Meanwhile, when the base of the RTPO resin is a propylene-ethylene random copolymer and it is used alone without mixing POE (Comparative Example 4), the melt strength of the resin composition is lowered, so the foamed cells are not maintained stably and are destroyed, resulting in a low degree of foaming. Consequently, the flexural modulus of the foam is maintained at a high 465 MPa, making it unsuitable for use as a wire, and a whitening phenomenon occurs when bent and the material breaks.

[0133] In addition, when the base of the RTPO resin is a propylene homopolymer (Comparative Example 6), the melt strength of the resin composition is lowered, and the miscibility of the POE and the propylene block copolymer is reduced, resulting in unstable foaming on a non-uniform surface, which leads to a low degree of foaming and a relatively higher flexural modulus compared to when the same mixing ratio is applied (Example 1). Consequently, signal processing becomes disadvantageous because the dielectric constant is relatively high.

[0134] In addition, when the polyolefin elastomer (POE) content is excessive (Comparative Example 5), the melt strength decreases slightly, making it difficult to maintain the cell structure during foaming, resulting in a low degree of foaming. Although a similar level of flexural modulus is exhibited, the dielectric constant is relatively high due to the low degree of foaming, which is disadvantageous for signal processing.

[0135]

[0136] Preferred embodiments of the present invention have been described in detail above. The description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without changing the technical concept or essential features of the present invention.

[0137] Accordingly, the scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning, scope, and equivalent concepts of the claims should be interpreted as being included within the scope of the present invention.

Claims

1. 60 to 90 parts by weight of a propylene block copolymer in which ethylene-propylene rubber (EPR) is dispersed within a propylene-ethylene random copolymer; and 10 to 40 parts by weight of polyolefin elastomer (POE); A polypropylene resin composition for an insulation layer of a wire cable comprising 2. In Paragraph 1, The ethylene-derived repeating unit of the above propylene block copolymer, 0.1 to 5 weight percent is included in the above propylene-ethylene random copolymer, and 30 to 60 weight percent is included in the above ethylene-propylene rubber (EPR), and A polypropylene resin composition for an insulation layer of a wire cable, characterized by containing 5 to 25 weight percent of the above-mentioned propylene block copolymer.

3. In Paragraph 1, A polypropylene resin composition for an insulation layer of a wire cable, characterized in that the above-mentioned propylene block copolymer has a melting point of 150 to 170°C and the xylene-soluble content is 10 to 40 weight% in the above-mentioned propylene block copolymer.

4. In Paragraph 1, A polypropylene resin composition for an insulation layer of a wire cable, characterized in that the above polyolefin elastomer (POE) is a propylene-ethylene rubber (PER) having an ethylene content of 10 to 30 weight%.

5. In Paragraph 1, A polypropylene resin composition for an insulation layer of a wire cable, characterized by further including 1 to 15 parts by weight of high melt strength polypropylene (HMS-PP) having a branching index of 0.85 or less.

6. In Paragraph 1, The above resin composition has a density of 0.87 to 0.91 g / cm³ as measured according to the following method. 3 A polypropylene resin composition for an insulation layer of a wire cable, characterized by having a melt tension of 5 to 30 cN, a melting point of 150 to 165℃, and a flexural modulus of 600 MPa or less: [Density Measurement Method] The density of the resin composition was measured using the underwater displacement method according to ASTM D792 standard; [Method for Measuring Melting Tension] Molten spring at 200°C using a Rheotens device (Rheotens 97, GOTTFERT) The fiber is extruded through a circular die with a diameter of 1 mm, the extruded strand is located 100 mm (spinline length) below the die exit, and the winding acceleration is 120 mm / s 2 When wound by a progressively increasing Leotens wheel, the force (cN) applied to the wheel is recorded as a function of the winding speed (mm / s), and the peak force applied before the strand breaks or at break is defined as the melt tension; [Method for Measuring Melting Point] Using a differential scanning calorimeter (DSC, Perkin-Elmer Co.), 10 mg of the test specimen was pre-melted at 220°C for 5 minutes under a nitrogen gas atmosphere, the temperature was lowered to 40°C at a cooling rate of 5°C / min, and then the temperature was raised at a heating rate of 5°C / min to measure the peak temperature of the maximum peak of the obtained melt endothermic curve; [Method for Measuring Flexural Modulus] Measured at 10 mm / min according to ASTM D790 standard.

7. A foam for an insulation layer of an extruded wire cable comprising a resin composition and a foaming agent according to any one of claims 1 to 6.

8. In Paragraph 7, The above foam has a density of 0.25 to 0.45 g / cm³ as measured according to the following method. 3 A foam for an insulation layer of a wire cable characterized by having a flexural modulus of 250 MPa or less, a foam cell size of 200 μm or less, a degree of foaming of 55% or more, and a relative permittivity of 2 or less: [Density Measurement Method] The density of the foam was measured using the underwater displacement method according to ASTM D792 standards; [Method for Measuring Flexural Modulus] Measured under 10 mm / min conditions according to ASTM D790 standard; [Method for Measuring Foam Cell Size] For an image captured by magnifying the cross-section of the foam under a microscope, the cell diameters of 10 random points are measured and the average value is calculated; [Method for Measuring Foaming Level] Calculated according to the following mathematical formula 1 using the change in density before and after foaming; <Mathematical Formula 1> [Method for Measuring Relative Permittivity] A specimen (thickness 2 mm, width 2 cm, length 2 cm) manufactured according to ASTM D150 standards was measured at 60°C conditions by applying an AC voltage of 1 V at a frequency of 1 MHz using an LCR Meter (electrode radius 5 mm, electrode type G10 type).

9. A wire cable comprising the foam of paragraph 7 as an insulating layer.

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