KR20220068022A - Polypropylene resin composition for power cable - Google Patents

Abstract

Disclosed is a polypropylene composition for a power cable having excellent flexibility, mechanical properties, and electrical properties. Provided is a resin composition for a power cable which comprises: 60 to 90 wt% of an ethylene-propylene random copolymer; 5 to 20 wt% of a linear low-density polyethylene; and 5 to 20% of an ethylene-α-olefin rubber copolymer.

Description

Polypropylene resin composition for power cable

The present invention relates to a polypropylene resin composition for a power cable, and more particularly, to a polypropylene resin composition for a power cable having excellent flexibility and electrical properties.

As the insulation material of the cable, a material obtained by crosslinking polyethylene (PE), polyvinyl chloride (PVC), ethylene/propylene elastic copolymer (EPR), etc. is mainly used. Among them, cross-linked polyethylene (XLPE) converts the linear molecular structure of polyethylene into a three-dimensional network structure through a cross-linking process. It has been used as a cable insulation layer. However, in the case of cross-linked polyethylene, since it is a cross-linked polymer, recycling is impossible, and in order to dispose of it, it has to be incinerated, which is somewhat unfriendly to the environment.

Meanwhile, research on an environmentally friendly insulating layer that can be recycled using non-crosslinked high-density polyethylene (HDPE) or low-density polyethylene (LDPE) has also been conducted, but its use is somewhat limited due to inferior heat resistance compared to cross-linked cross-linked polyethylene. There is a hostile problem.

Accordingly, the development of an insulating layer using a polypropylene (PP) material that is easy to recycle and has high heat resistance is being developed. Compared with cross-linked polyethylene, polypropylene has a simpler manufacturing method and is environmentally friendly in a non-cross-linked form. It does not generate toxic substances such as methane gas and various by-products during the manufacturing process, and it also reduces greenhouse gases such as carbon dioxide (CO ₂ ) generated during the manufacturing process. It is possible to reduce about 30% compared to cross-linked polyethylene. Polypropylene is recyclable, and it is strong against heat, so the power transmission capacity can be increased.

It may be considered to use an environmentally friendly polypropylene resin as a base resin because the polymer itself has excellent heat resistance without crosslinking at a melting point of 160°C or higher. However, due to low flexibility due to high rigidity, etc., polypropylene resin has a problem in that workability is deteriorated during the installation of cables manufactured therefrom and its use is limited.

In order to overcome this limitation, a power cable technology made of polypropylene has been developed. For example, Korean Patent Application Laid-Open No. 10-2019-0079535 discloses a polypropylene resin composition for a power cable including a polypropylene resin and a polyolefin-based elastomer including polypropylene and high-density polyethylene, but polyethylene is limited to high-density polyethylene Therefore, there is a problem in that electrical characteristics are deteriorated due to low compatibility.

Korean Patent No. 1943224 discloses (A) at least one polyolefin resin selected from the group consisting of propylene homopolymer, α-olefin-propylene random copolymer and ethylene-propylene block copolymer, (B) ethylene-propylene rubber copolymer It contains a resin and (C) C4~C8 α-olefin-ethylene rubber copolymer resin, and has a melt index of 0.5~10 g/10min, a flexural strength of 100~800 MPa when measured at 230℃ under a load of 2.16 kg, and a melt strength of 100~800 MPa. Although a polyolefin resin composition having a polyolefin resin composition having a temperature of 140 to 170° C. is described, there is a problem in that mechanical properties and electrical properties are deteriorated unless the size and dispersibility of the rubber phase are adjusted using two rubber phases.

An object of the present invention is to provide a polypropylene composition for a power cable having excellent flexibility, mechanical properties and electrical properties.

The present invention in order to solve the above problems, ethylene- propylene random copolymer 60 to 90% by weight; 5 to 20% by weight of linear low density polyethylene; and 5 to 20 wt% of an ethylene-α-olefin rubber copolymer; provides a resin composition for a power cable comprising.

In addition, the ethylene-propylene random copolymer provides a resin composition for a power cable, characterized in that the ethylene content is 2 to 6% by weight.

In addition, the linear low-density polyethylene provides a resin composition for power cables, characterized in that the melt index (MI, 190 ℃, 2.16 kg load) of 0.2 to 5 g / 10 min.

In addition, the ethylene-α-olefin rubber copolymer provides a resin composition for a power cable, characterized in that it is a copolymer of ethylene and an α-olefin having 2 to 10 carbon atoms.

In addition, the resin composition provides a resin composition for power cables, characterized in that the flexural modulus measured according to the following method is 600 MPa or less, and the AC dielectric breakdown strength is 50 kV/mm or more.

[Method of measuring flexural modulus]

According to ASTM D790 standard, the span of the specimen (127 × 12.7 × 6.4 mm) is fixed at 100 mm and a flexural load is applied at a rate of 28 mm/min. The measured value is the flexural modulus.

[Method for measuring AC dielectric breakdown strength]

After the resin composition was prepared in a sheet shape with a thickness of 1 mm using a press molding machine, 30 kV was initially applied for 5 minutes according to ASTM D149, and then the process was increased by 10 kV and maintained for 5 minutes. Continue until it occurs, and if dielectric breakdown occurs, the value obtained by dividing the breakdown voltage by the thickness of the specimen is referred to as the AC dielectric breakdown strength.

In the polypropylene resin composition for power cables, the present invention presents ethylene-propylene random copolymer, linear low-density polyethylene, and ethylene-α-olefin rubber copolymer in specific content ratios, so compatibility that is difficult to reach with existing polypropylene resin compositions It is possible to provide a polypropylene resin composition for a power cable exhibiting improved flexibility and electrical properties while implementing.

Hereinafter, the present invention will be described in detail through preferred embodiments. Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor should properly understand the concept of the term in order to best describe his invention. Based on the principle that can be defined, it should be interpreted as meaning and concept consistent with the technical idea of the present invention. Accordingly, since the configuration of the embodiments described in the present specification is only the most preferred embodiment of the present invention and does not represent all the technical spirit of the present invention, various equivalents and modifications that can be substituted for them at the time of the present application It should be understood that there may be

The present invention is an ethylene-propylene random copolymer 60 to 90% by weight; 5 to 20% by weight of linear low density polyethylene; and 5 to 20 wt% of an ethylene-α-olefin rubber copolymer; discloses a resin composition for a power cable comprising.

Hereinafter, each component of the polypropylene resin composition for power cables according to the present invention will be described in detail.

Polypropylene can be classified into homo polypropylene (H-PP), propylene random copolymer (R-PP) and propylene block copolymer (B-PP). Among them, propylene random copolymer and propylene block copolymer are more suitable for power cables because they have higher flexibility than homo polypropylene, and in the present invention, compatibility between polypropylene and ethylene-α-olefin rubber copolymer An ethylene-propylene random copolymer in which ethylene is added to polypropylene was used to increase the polypropylene.

The ethylene-propylene random copolymer is not particularly limited in its preparation method, and may be prepared by a conventional method known in the art to which the present invention pertains.

The ethylene content of the ethylene-propylene random copolymer may be 2 to 6% by weight, preferably 2 to 5% by weight, more preferably 3 to 4% by weight. If the ethylene content is less than 2% by weight, the flexibility of the final resin composition may be reduced, and if it exceeds 6% by weight, heat resistance may be insufficient, and an appearance problem may occur due to heat generation during use.

The ethylene-propylene random copolymer may have a melt index (MI, ASTM D 1238, load of 2.16 kg at 230°C) of 0.1 to 5 g/10min, preferably 0.5 to 3 g/10min. If the melt index is less than 0.1 g/10min, cable workability may be reduced due to an increase in the extruder load, and if it exceeds 3 g/10min, eccentricity of the cable is likely to occur, and the mechanical properties of the final resin composition may be reduced. have.

In the present invention, the ethylene-propylene random copolymer may be included in an amount of 60 to 90% by weight, preferably 65 to 80% by weight, more preferably 65 to 75% by weight. When the content of the ethylene-propylene random copolymer is less than 60% by weight, electrical properties are deteriorated, and when it exceeds 90% by weight, flexibility is reduced.

In the ethylene-propylene random copolymer, the interface between the crystal spheroids and the spheroids acts as an electrical insulation weakness, and as the interface develops, the electrical properties deteriorate. In contrast, in the present invention, the linear low-density polyethylene serves to improve the electrical properties by preventing the development of the spheroids and the interface between the spheroids of the ethylene-propylene random copolymer.

The linear low-density polyethylene may have a melt index (MI, ASTM D1238, 190°C, 2.16 kg load) of 0.2 to 5 g/10min in order not to impair compatibility with polypropylene and wire formability, and preferably is 0.3 to 4 g/10min may be used, more preferably 0.4 to 3 g/10min may be used, and still more preferably 0.5 to 2 g/10min may be used. If the melt index is less than 0.2 g/10min, compatibility with polypropylene may decrease, and if it exceeds 5 g/10min, wire formability using the final resin composition may be reduced.

In the present invention, the linear low-density polyethylene may be included in an amount of 5 to 20% by weight, preferably 7 to 15% by weight, and more preferably 8 to 12% by weight. When the amount of the linear low-density polyethylene is less than 5% by weight, electrical properties of the final resin composition are deteriorated, and when it exceeds 20% by weight, flexibility and mechanical properties are deteriorated.

The ethylene-α-olefin rubber copolymer is to improve the flexibility of the resin composition according to the present invention, is dispersed in an ethylene-propylene random copolymer matrix, and is a copolymer of ethylene and an α-olefin having 2 to 10 carbon atoms. can

Preferred examples of the ethylene-α-olefin rubber copolymer include ethylene-propylene copolymer, ethylene-1-butene copolymer, and ethylene-1-octene copolymer, and improved flexibility along with improvement of electrical properties of the final resin composition Each may have a range of comonomer content and flow characteristics to ensure that this is maintained. That is, the ethylene-propylene copolymer may have an ethylene content of 5 to 15% by weight and a melt index (230°C, 2.16 kg load) of 1 to 3 g/10min), and the ethylene-1-butene copolymer has an ethylene content This 70 to 90% by weight and melt index (230°C, 2.16 kg load) may be 1 to 3 g/10min, and the ethylene-1-octene copolymer has an ethylene content of 45 to 60% by weight and a melt index (230°C). , 2.16 kg load) may be 1 to 3 g/10 min.

In the present invention, the ethylene-α-olefin rubber copolymer may be included in an amount of 5 to 35% by weight, preferably 10 to 30% by weight, more preferably 15 to 25% by weight. When the amount of the ethylene-α-olefin rubber copolymer is less than 5% by weight, the flexibility of the final resin composition is reduced, and when it exceeds 30% by weight, the flexibility is increased, but electrical properties are deteriorated.

In addition to the above components, the polypropylene resin composition according to the present invention may include antioxidants and catalyst neutralizers that are generally used when applied for power cables, and if necessary, impact modifiers and heat stabilizers within the range that does not significantly impair their properties. , and may further include other additives such as a nucleating agent.

The polypropylene resin composition for electric power according to the present invention may be prepared by mixing and extruding the above components according to a conventional method known in the art. For example, the components may be introduced into a twin-screw extruder and melt-kneaded to prepare a polypropylene resin composition.

The polypropylene resin composition for a power cable in the present invention has excellent flexibility and electrical properties, and specifically has a flexural modulus of 600 MPa or less, preferably 400 to 600 MPa, more preferably 500 to 580, measured according to the following method. It may be MPa, and the AC breakdown strength may be 50 kV/mm or more, preferably 53 kV/mm or more.

[Method of measuring flexural modulus]

According to ASTM D790 standard, the span of the specimen (127 × 12.7 × 6.4 mm) is fixed at 100 mm and a flexural load is applied at a rate of 28 mm/min. The measured value is the flexural modulus.

[Method for measuring AC dielectric breakdown strength]

After the resin composition was prepared in a sheet shape with a thickness of 1 mm using a press molding machine, 30 kV was initially applied for 5 minutes according to ASTM D149, and then the process was increased by 10 kV and maintained for 5 minutes. Continue until it occurs, and if dielectric breakdown occurs, the value obtained by dividing the breakdown voltage by the thickness of the specimen is referred to as the AC dielectric breakdown strength.

Hereinafter, specific examples and comparative examples according to the present invention will be described.

First, the specifications of the components used in Examples and Comparative Examples of the present invention are as follows.

(A) Ethylene-propylene random copolymer

An ethylene-propylene random copolymer having an ethylene content of 3.5% by weight and a melt index (230° C., 2.16 kg load) of 0.9 g/10min was used.

(B1) Ethylene-α-olefin rubber copolymer (ethylene-1-butene copolymer)

An ethylene-1-butene copolymer having an ethylene content of 80% by weight and a melt index (230° C., 2.16 kg load) of 2 g/10 min was used.

(B2) Ethylene-α-olefin rubber copolymer (ethylene-propylene copolymer)

An ethylene-propylene copolymer having an ethylene content of 11 wt% and a melt index (230°C, 2.16 kg load) of 2 g/10 min was used.

(B3) Ethylene-α-olefin rubber copolymer (ethylene-1-octene copolymer)

An ethylene-propylene copolymer having an ethylene content of 53% by weight and a melt index (230° C., 2.16 kg load) of 2 g/10 min was used.

(C) linear low density polyethylene

Density 0.920 g/cm ³ and a linear low-density polyethylene having a melt index (190° C., 2.16 kg load) of 1 g/10 min.

Example and comparative example

The mixture consisting of the component composition (unit: wt%) of Table 1 below was mixed with a mixer for 5 minutes and then extruded with a twin-screw extruder at 190 to 230° C. to prepare a polypropylene resin composition on pellets.

division Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 A 70 70 70 80 100 70 70 70 B1 20 - - 10 - 30 - - B2 - 20 - - - - 30 - B3 - - 20 - - - - 30 C 10 10 10 10 - - - -

test example

A specimen was prepared using the prepared polypropylene resin composition on the pellets, and physical properties were measured according to the following method, and the results are shown in Table 2 below.

[How to measure]

(1) Tensile strength

The prepared specimen (ASTM D638 Type I standard) was measured under 50 mm/min condition using a universal testing machine according to ASTM D638 standard.

(2) IZOD impact strength

The notch impact strength of the 1/8" specimen was measured at room temperature according to ASTM D256.

(3) Flexural modulus

According to ASTM D790 standard, the support span of the specimen (127×12.7×6.4 mm) was fixed to 100 mm, and a flexural load was applied at a rate of 28 mm/min. The measured value was used as the flexural modulus. When the flexural modulus is 600 MPa or less, it is judged that the flexibility is excellent.

(4) dielectric breakdown strength

After the resin composition is manufactured in a sheet shape with a thickness of 1 mm using a press molding machine, 30 kV is initially applied for 5 minutes according to ASTM D149, and then is increased by 10 kV and maintained for 5 minutes. Continue until the time of failure, the value obtained by dividing the breakdown voltage by the thickness of the specimen was used as the AC dielectric breakdown strength. When the AC breakdown strength is 50 kV/mm or more, the electrical characteristics are judged to be excellent.

division unit Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 The tensile strength kgf/cm2 210 205 190 205 290 200 200 185 IZOD impact strength (23℃) kgf cm/cm NB NB NB NB 8 NB NB NB flexural modulus MPa 570 530 550 580 990 550 430 500 AC dielectric breakdown strength kV/mm 56 53 54 52 43 45 46 48 * NB: Non-Break

Referring to Tables 1 and 2 above, according to the present invention, a polypropylene resin composition for a power cable comprising an ethylene-propylene random copolymer, a linear low-density polyethylene and an ethylene-α-olefin rubber copolymer in a specific composition (Examples 1 to 3) shows a high dielectric breakdown strength while having a low flexural modulus at a certain level, confirming that the balance between flexibility and electrical properties is excellent. However, when the content of the ethylene-α-olefin rubber copolymer is relatively low (Example 4), the flexibility and electrical properties are somewhat lowered, and the improved compatibility that is difficult to reach with the existing polypropylene resin composition is realized. It can be seen that there is a specific content ratio section of the ideal ethylene-propylene random copolymer, linear low-density polyethylene, and ethylene-α-olefin rubber copolymer that can implement flexibility and electrical properties.

On the other hand, when the ethylene-propylene random copolymer is used alone (Comparative Example 1), it shows an excessive flexural modulus, so flexibility and laying properties are not good when manufacturing a cable, and when the linear low-density polyethylene is not included (Comparative Examples 2 to 4) It can be seen that the flexural modulus is low and the flexibility is excellent, but the electrical properties are remarkably deteriorated due to the low AC dielectric breakdown strength.

The preferred embodiment of the present invention has been described in detail above. The description of the present invention is for illustration, and those of ordinary skill in the art to which the present invention pertains will understand that other specific forms can be easily modified without changing the technical spirit or essential features of the present invention.

Accordingly, the scope of the present invention is indicated by the claims described later rather than the detailed description, and all changes or modifications derived from the meaning, scope, and equivalent concept of the claims are included in the scope of the present invention. should be interpreted

Claims (5)

60 to 90% by weight of an ethylene-propylene random copolymer;
5 to 20% by weight of linear low density polyethylene; and
5 to 20% by weight of an ethylene-α-olefin rubber copolymer;
A resin composition for a power cable comprising a. The method of claim 1,
The ethylene-propylene random copolymer is a resin composition for a power cable, characterized in that the ethylene content is 2 to 6% by weight. The method of claim 1,
The linear low-density polyethylene has a melt index (MI, 190°C, load of 2.16 kg) of 0.2 to 5 g/10min. The method of claim 1,
The ethylene-α-olefin rubber copolymer is a resin composition for a power cable, characterized in that it is a copolymer of ethylene and an α-olefin having 2 to 10 carbon atoms. The method of claim 1,
The resin composition has a flexural modulus measured according to the following method of 600 MPa or less, and an AC dielectric breakdown strength of 50 kV/mm or more.
[Method of measuring flexural modulus]
According to ASTM D790 standard, the span of the specimen (127 × 12.7 × 6.4 mm) is fixed at 100 mm and a flexural load is applied at a rate of 28 mm/min. The measured value is used as flexural modulus.
[Method for measuring AC dielectric breakdown strength]
After the resin composition was prepared in a sheet shape with a thickness of 1 mm using a press molding machine, 30 kV was initially applied for 5 minutes according to ASTM D149, and then the process was increased by 10 kV and maintained for 5 minutes. Continue until breakdown occurs, and when dielectric breakdown occurs, the value obtained by dividing the breakdown voltage by the thickness of the specimen is referred to as the AC dielectric breakdown strength.