KR102003568B1 - Power cable - Google Patents

Abstract

The present invention relates to power cables. Specifically, the present invention relates to a power cable including an insulating layer made from an insulating composition that is environmentally friendly, such as being recyclable, and excellent in heat resistance, flexibility, workability, insulation performance and the like.

Description

Power cable {Power cable}

The present invention relates to power cables. Specifically, the present invention relates to a power cable including an insulating layer made from an insulating composition that is environmentally friendly, such as being recyclable, and excellent in heat resistance, flexibility, workability, insulation performance and the like.

A typical power cable includes a conductor and an insulating layer surrounding the conductor. In the case of a high-voltage or ultra-high voltage cable, an inner semiconductive layer between the conductor and the insulating layer, an outer semiconductive layer surrounding the insulating layer, a sheath layer surrounding the outer semiconductive layer May be further included.

In recent years, development of a high-capacity cable has been required in accordance with an increasing demand for electric power, and it has become necessary to provide an insulating material for manufacturing the insulating layer 3 having excellent mechanical and electrical characteristics. Conventionally, a polyolefin-based polymer such as polyethylene, an ethylene / propylene elastic copolymer (EPR), or an ethylene / propylene / diene copolymer (EPDM) has been used as a base resin constituting the insulating material. Such conventional crosslinked resins maintain excellent flexibility and satisfactory electrical and mechanical properties even at high temperatures.

However, since the crosslinked polyethylene (XLPE) or the like which has been used as the base resin constituting the insulating material is in a crosslinked form, when the life of a cable or the like including an insulating layer made of a resin such as the crosslinked polyethylene is shortened, It is impossible to recycle the resin to be disposed of by incineration and is not environmentally friendly. Further, when polyvinyl chloride (PVC) is used as the material of the sheath layer 5, it is difficult to separate it from the crosslinked polyethylene (XLPE) or the like constituting the insulating material, thereby generating toxic chlorinated materials Which is not friendly.

Further, non-crosslinked high-density polyethylene (HDPE) or low-density polyethylene (LDPE) is environmentally friendly because it can recycle the resin constituting the insulating layer when a cable or the like including the insulating layer produced therefrom reaches its end of life, Type polyethylene (XLPE), which is inferior in heat resistance, and its application is very limited due to its low operating temperature. Further, there is known a technique of adding inorganic particles such as carbon black to improve the heat resistance and the like of the non-crosslinked polyethylene. However, since the production cost is increased by the addition of the carbon black and the compatibility of the carbon black with the resin, That is, the dispersibility of the carbon black to the resin must be solved, and the manufacturing process of the insulating material may be complicated.

On the other hand, it can be considered to use an environmentally friendly polypropylene resin as a base resin because the melting point of the polymer itself is excellent in heat resistance without crosslinking at 160 ° C or higher. However, due to insufficient flexibility and flexibility due to the high rigidity of the polypropylene resin, the workability of the cable including the insulating layer manufactured therefrom is low and the use thereof is limited .

In addition, the polypropylene resin is usually synthesized under a complex of a Ziegler-Natta catalyst with low stereospecificity, typically titanium trichloride and diethyl aluminum chloride, and specific synthetic methods are described in Albizzati et al. in "Polypropylene Handbook ", Chapter 2, page 11 on wards (Hanser Publisher, 1996). When the polypropylene resin is synthesized under the above-mentioned Ziegler-Natta catalyst, the molecular weight distribution of the synthesized resin is somewhat wide, and the processability is excellent. However, the residual amount of the catalyst in the polypropylene resin is rather high, and electrical characteristics such as insulation performance are deteriorated.

Therefore, a power cable including an insulating material excellent in flexibility, bending property and the like, excellent in workability, electrical characteristics and the like and an insulating layer made therefrom is required .

An object of the present invention is to provide a power cable including an insulating layer made of an environmentally friendly insulating material, which is excellent in heat resistance and can be used as an insulating layer without crosslinking and can be recycled.

It is also an object of the present invention to provide a power cable including an insulating layer made from an insulating material having flexibility and bending properties despite its high rigidity.

It is another object of the present invention to provide a power cable including an insulating layer made of an insulating material excellent in workability despite the narrow molecular weight distribution of the base resin.

Further, it is an object of the present invention to provide a power cable including an insulating layer made of an insulating material having a low residual amount of catalyst in the base resin and excellent in electrical characteristics.

In order to solve the above problems,

A power cable comprising at least one conductor, an insulating layer surrounding each conductor, and an outermost sheath layer, wherein the insulating layer comprises a base resin comprising a non-crosslinked polypropylene resin that is polymerized under a metallocene catalyst, From 2.5 to 10 parts by weight of an insulating oil based on 100 parts by weight of the resin.

Wherein the non-crosslinked polypropylene resin polymerized under the metallocene catalyst has a molecular weight of 250,000 to 350,000 and a melting index of 3 to 10.

The present invention also provides a power cable characterized in that the amount of catalyst remaining in the non-crosslinked polypropylene resin polymerized under the metallocene catalyst is 200 to 700 ppm.

Wherein the non-crosslinked polypropylene resin comprises a propylene homopolymer and a propylene-ethylene copolymer, and the blending ratio of the propylene homopolymer and the propylene-ethylene copolymer is 80:20 to 50:50. Cable.

Wherein the content of the ethylene monomer in the propylene-ethylene copolymer is 6 to 7% by weight based on the total weight of the propylene-ethylene copolymer.

On the other hand, the dielectric oil includes monocyclic naphthenic hydrocarbons.

And further comprising 0.2 to 5 parts by weight of an amine-based, dialkyl ester-based, thioester-based or phenol-based antioxidant based on 100 parts by weight of the base resin.

Further, the sheath layer is made from a composition comprising the same base resin as the base resin of the insulating composition.

The power cable further includes an inner semiconductive layer disposed between the conductor and the insulating layer, and an outer semiconductive layer surrounding the insulating layer.

Wherein the inner semiconductive layer, the outer semiconductive layer, or both are fabricated from a semiconductive composition comprising the same base resin as the base resin of the insulating composition.

The power cable according to the present invention is a base resin of the insulating layer constituting the power cable, and it has excellent heat resistance and can be recycled by including non-crosslinked polypropylene which can be used as an insulating layer without crosslinking. .

Further, the electric power cable according to the present invention exhibits an excellent electrical characteristic by minimizing the residual amount of the catalyst in the base resin, including polypropylene polymerized under a metallocene catalyst as a non-crosslinked polypropylene which is a base resin of the insulating layer constituting the electric cable .

In addition, the insulation layer constituting the electric power cable according to the present invention further includes insulating oil in addition to the base resin, thereby exhibiting excellent flexibility, flexibility and workability in spite of high rigidity.

1 is a cross-sectional view schematically showing a cross-sectional structure of a power cable according to the present invention.
2 is a longitudinal sectional view schematically showing a cross-sectional structure of a power cable according to the present invention.

1 and 2 show an embodiment of a power cable according to the present invention.

1 and 2, a power cable according to the present invention includes a conductor 1 made of a conductive material such as copper or aluminum, an insulating layer 3 made of an insulating polymer, (3), thereby suppressing partial discharge at the interface with the conductor (1), eliminating the air layer between the conductor (1) and the insulating layer (3) An outer semiconductive layer 4 serving as a shielding function of the cable and an electric field equivalent to the insulator, a sheath layer 5 for protecting the cable, and the like have.

The dimensions of the conductor 1, the insulating layer 3, the semiconductive layer 2 and 4, and the sheath layer 5 may vary depending on the use of the cable, the transmission voltage, etc. The insulating layer 3, The materials constituting the entire layers (2, 4) and the sheath layer (5) may be the same or different.

The insulating composition forming the insulating layer 3 of the power cable according to the present invention may comprise an uncrosslinked polypropylene resin as the base resin.

The polymer constituting the non-crosslinked polypropylene resin (hereinafter referred to as "polypropylene" or "polypropylene resin") may be a copolymer of propylene homopolymer and / or propylene and ethylene or an α-olefin having 4 to 12 carbon atoms, A comonomer selected from 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene and combinations thereof, Copolymers. This is because copolymerization of propylene and ethylene shows a hard and flexible property. Here, the blending ratio of the propylene homopolymer to the propylene copolymer may be, for example, 80:20 to 50:50.

In the propylene copolymer, the content of the comonomer may be preferably from 6 to 7% by weight, based on the total weight of the monomers constituting the propylene copolymer. Further, the propylene copolymer may be a random copolymer or a block copolymer in which propylene and ethylene and / or? -Olefin are polymerized without regularity. The polypropylene may further comprise a polyolefin such as low-density polyethylene or linear low-density polyethylene.

The polypropylene, that is, the propylene homopolymer and / or copolymer is characterized in that it is synthesized under metallocene catalyst. The metallocene is a generic name of a bis (cyclopentadienyl) metal which is a novel organometallic compound in which cyclopentadiene and a transition metal are bonded in a sandwich structure. The general formula of the simplest structure is M (C ₅ H ₅ ) ₂ Ti, V, Cr, Fe, Co, Ni, Ru, Zr, Hf, etc.).

The metallocene can be prepared by reacting a cyclopentadiene metal compound with a halide of a transition metal such as titanium, zirconium, or hafnium. Methods for making the metallocenes are described in U.S. Patent Nos. 4,752,579, 5,017,714, and European patents 320,762, 416,815, 537,686, 669,340, and in H. Brintzinger et al .; Andrew. cam. (Andrew, Chem.), 107 (1995), 1255; H. Brinz Jinger et al .; J. ORGANOMET. cam. (Organomet. Chem., 232 (1982), 233).

The metallocene catalysts can be systematically controlled by the specific substitution pattern of the ligand sphere, so that the polymerization activity, stereoselectivity, regioselectivity, melting point The Ziegler-Natta catalyst, which has been conventionally used as a polypropylene polymerization catalyst, can synthesize only polypropylene having an isotactic structure in which methyl groups are arranged in the same direction in the same direction .

In addition, the metallocene catalyst exhibits an excellent effect of preventing or minimizing degradation of the electrical properties of the polypropylene due to the low residual amount of the catalyst of the polypropylene synthesized. Specifically, in the case of the polypropylene synthesized by the metallocene catalyst, the residual amount of the catalyst is only 200 to 700 ppm, so that the electrical properties such as the insulation performance of the synthesized polypropylene are not lowered or minimized, while the conventional Ziegler- , The residual amount of the catalyst is in the range of 1,000 to 3,000 ppm, so that the residual amount of the catalyst greatly deteriorates the electrical characteristics such as the insulation performance of the synthesized polypropylene.

The polypropylene synthesized by the metallocene catalyst may have a maximum crystallization temperature of preferably 110 to 125 DEG C (as measured by differential scanning calorimetry (DSC)). If the maximum crystallization temperature is less than 110 캜, the polypropylene melts at aging test conditions (135 or 150 캜) required by the IEC international standard, so that the continuous use temperature of the cable can not satisfy the condition of 110 캜. If the crystallization temperature exceeds 125 ° C, the crystallization rate during cooling tends to be accelerated, and the tensile elongation at room temperature may decrease.

The propylene homopolymer and the copolymer constituting the polypropylene resin may have a weight average molecular weight (Mw) of 200,000 to 450,000 and a melt index (MI) of 3 to 10 dg / min (ASTM D- 1238). ≪ / RTI > Further, the polypropylene resin has a melting point (Tm) of 140 to 175 ° C (as measured by differential scanning calorimetry (DSC)), a melting enthalpy of 30 to 85 J / g (as measured by DSC) The flexural modulus may be from 30 to 1400 MPa, more preferably from 60 to 1000 MPa (measured in accordance with ASTM D790-00).

The method of polymerizing the polypropylene resin under the metallocene catalyst is not particularly limited. For example, the polymerization of the polypropylene resin can be carried out in a bulk, suspension or gas phase, continuously or batchwise, at a temperature of from -60 to 300 캜, at a pressure of from 0.5 to 2,000 bar, , One or more steps.

As described above, in the power cable according to the present invention, the non-crosslinked polypropylene resin which is the base resin of the insulating layer 3 has a high self-melting point despite its non-crosslinked form and exhibits sufficient heat resistance, Not only can provide an improved power cable, but also exhibits excellent environment-friendly effects such as non-crosslinking and recycling.

On the other hand, conventional cross-linked resin is not environmentally friendly because it is difficult to recycle, and when cross-linking or scorch occurs early in forming insulating layer 3, uniform production ability can not be exhibited, . ≪ / RTI >

In addition, the non-crosslinked polypropylene resin is synthesized under a metallocene catalyst, which is not a conventional Ziegler-Natta catalyst, so that the residual amount of the catalyst is low and the damage of the electrical characteristics such as the insulation performance of the insulating layer 3 produced therefrom can be avoided or minimized Exhibit excellent effect.

The insulating composition forming the insulating layer 3 of the power cable according to the present invention may further include an insulating oil in addition to the non-crosslinked polypropylene resin which is a base resin.

The insulating oil may be mineral oil, synthetic oil, or the like. In particular, the insulating oil may be selected from aromatic oils consisting of aromatic hydrocarbon compounds such as dibenzyltoluene, alkylbenzene and alkyldiphenylethane, paraffinic oils composed of paraffinic hydrocarbon compounds, naphthenic oils composed of naphthenic hydrocarbon compounds, Can be used.

Preferably, the insulating oil may be a naphthenic oil composed of mono-cyclic naphthenic hydrocarbons whose general molecular formula is C _n H _2n (where n is an integer of 20 to 60). When n is less than 20, the molecular weight of the monocyclic naphthenic hydrocarbon is too small to decompose and decompose upon extrusion of the insulating layer 3. When n is more than 60, the monocyclic naphthenic hydrocarbon Since the molecular weight of the hydrocarbon is too large, the insulating layer 3 containing the hydrocarbon can be eluted outside the insulating layer 3 during the extrusion process.

Also, the insulating oil has a viscosity of 2 mm 2 / s or more at 20 to 30 ° C, and the insulating oil satisfying the viscosity can avoid or minimize the phenomenon of elution from the insulating layer formed from the insulating composition containing the insulating oil.

On the other hand, the content of the insulating oil may be 2.5 to 10 parts by weight based on 100 parts by weight of the base resin, and when the content of the insulating oil is less than 2.5 parts by weight, the flexibility of the insulating layer 3 , The flexibility of the insulation layer 3 is insufficient, so that the cable including the insulation layer 3 can not easily be installed. When the amount of the insulation layer 3 exceeds 10 parts by weight, The insulating oil may be eluted during the extrusion process for forming the insulating layer 3, which may make it difficult to process the cable.

As described above, the dielectric oil is improved in flexibility, bendability, etc. of the insulation layer 3 made of an insulation composition using a base resin of a polypropylene resin having a high rigidity and a somewhat low flexibility as described above, The polypropylene resin exhibits an excellent effect of maintaining or improving the excellent heat resistance, mechanical and electrical properties inherent in the polypropylene resin. Particularly, the insulating oil shows excellent effect of supplementing the somewhat reduced workability by the somewhat narrow molecular weight distribution of the polypropylene resin which is polymerized under the metallocene catalyst.

The insulating composition forming the insulating layer 3 of the power cable according to the present invention may further include other additives such as an antioxidant in addition to the base resin and the insulating oil. Examples of the antioxidant include amine-based, dialkyl ester-based, thioester-based, and phenol-based antioxidants. Examples thereof include [3- [3- (3,5- (3,5-di-t-butyl-4-hydroxyphenyl) propanoyloxymethyl] propyl] Di-tert-butyl-4-hydroxyphenyl) propanoate, thiodiethylene bis (3,5-di- tert -butyl-4-hydroxyhydrocinnamate), 3,5- Dimethylethyl) -4-hydroxybenzene propionic acid octadecyl ester, propionic acid, 3,3 'thiobis-1,1' dioctadecyl ester, and the like. Here, the content of each of the other additives such as the antioxidant may be 0.2 to 5 parts by weight based on 100 parts by weight of the base resin.

[Example]

Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Rather, the embodiments disclosed herein are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art.

1. Manufacturing Example

In order to evaluate the physical properties of the insulating layer 3 included in the power cable according to the present invention, an insulating composition was prepared with the components and contents shown in Table 1 below, and the insulating composition melted on a copper conductor of a predetermined standard was extruded To prepare the cable specimens of Examples 1 and 2 and Comparative Examples 1 to 4, respectively. Here, the unit of the component content is parts by weight.

Constituent Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Base resin 1 50 50 50 50 Base resin 2 50 50 Base resin 3 50 50 50 50 50 50 Insulating oil 2.5 5 One 15 2.5 5

Base resin 1: Polypropylene resin polymerized under a metallocene catalyst (manufacturer: POLYMER, product name: RM5100; melting index (MI): 3)

Base resin 2: Polypropylene resin polymerized under a Ziegler-Natta catalyst (manufacturer: SK General Chemicals; product name: H920Y; melting index (MI): 3)

- Base resin 3: Propylene-ethylene copolymer (manufacturer: SK General Chemicals; product name: R520Y)

- Insulating oil: Monocyclic naphthenic oil (Manufacturer: Dongnam Petrochemical; Insulating oil No. 4)

2. Measurement and evaluation of physical properties

The tensile strength and tensile elongation at room temperature, the tensile strength retention after heating, the tensile elongation percentage, and the electrical properties of each of the cable specimens prepared in Examples 1 and 2 and Comparative Examples 1 to 4 prepared in the above- The AC breakdown strength (ACBD), which is the physical property, was measured according to the following standard, and the results are shown in Table 2 below.

end. Mechanical properties at room temperature

Measured for each of the cable specimens according to Examples 1 and 2 and Comparative Examples 1 to 4 at a tensile rate of 250 mm / min in accordance with IEC 60811-1-1, the tensile strength measured was 1.27 kgf / mm 2 or more, Should be more than 200%.

I. Mechanical properties after heating

Each of the cable specimens according to Examples 1 and 2 and Comparative Examples 1 to 4 was aged at 150 ° C for 168 hours, and mechanical properties were measured. The measured tensile strength and tensile elongation percentage were 75% or more.

All. Flexural strength

Flexural strength was measured for each of the cable specimens according to Examples 1 and 2 and Comparative Examples 1 to 4 according to the IEC 60811-1-1 standard. The lower the value, the better the flexibility, the bendability, and the durability.

la. Electrical property

The dielectric breakdown strength of each of the cable specimens according to Examples 1 and 2 and Comparative Examples 1 to 4 was measured according to the ASTM D149 standard. The higher the value, the better the electrical properties of the insulation performance.

Properties Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Tensile strength at room temperature (kgf / ㎟) 2.0 1.9 2.4

side
tablet
fire
end 2.1 2.0 Tensile elongation at room temperature (%) 698 712 650 670 680 Residual tensile strength after heating (%) 81 85 88 100 90 Tensile elongation after heating (%) 79 80 76 75 80 Flexural Strength (MPa) 35 32 42 33 34 Dielectric breakdown strength
(kV / mm) 65 65 55 42 45

As shown in Table 2, in Comparative Example 1, when a small amount of insulating oil, that is, 1 part by weight based on 100 parts by weight of the base resin was used, it was confirmed that flexibility, bending property, .

In addition, in the case of Comparative Example 2, since the insulating oil was used in an excess amount, that is, 15 parts by weight based on 100 parts by weight of the base resin, the dielectric oil was eluted during the extrusion process in the production of the cable specimen, causing slippage in the extruder, .

In the case of Comparative Examples 3 and 4, the polypropylene produced under the conventional Ziegler-Natta catalyst was used as the base resin of the insulating layer, so that the dielectric breakdown strength was 65 kV / mm, which is the dielectric breakdown strength of Examples 1 and 2 Which was significantly lower than that of the polypropylene prepared under the Ziegler-Natta catalyst, which was 42 kV / mm and 45 kV / mm, which was significantly lower than that of the polypropylene prepared under the metallocene catalyst used as the base resin of the insulating layer in Examples 1 and 2 It is confirmed that the electrical property such as the insulation performance of the insulating layer is reduced by including a relatively large amount of the catalyst residual amount.

On the other hand, it was confirmed that the cable specimens of Examples 1 and 2 according to the present invention were excellent in mechanical properties after being heated at room temperature, excellent in electrical properties, and also had an appropriate amount of insulating oil to ensure flexibility of the cable.

While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims. . It is therefore to be understood that the modified embodiments are included in the technical scope of the present invention if they basically include elements of the claims of the present invention.

1: conductor 2: inner semiconductive layer
3: insulating layer 4: outer semiconductive layer
5: Sheath layer

Claims (10)

A power cable comprising at least one conductor, an insulating layer surrounding each conductor, and an outermost sheath layer,
Wherein the insulating layer is made from an insulating composition comprising a base resin comprising an uncrosslinked polypropylene resin that is polymerized under a metallocene catalyst and 2.5 to 10 parts by weight of an insulating oil based on 100 parts by weight of the base resin,
Wherein the amount of catalyst remaining in the non-crosslinked polypropylene resin polymerized under the metallocene catalyst is 200 to 700 ppm. The method according to claim 1,
Wherein the non-crosslinked polypropylene resin polymerized under the metallocene catalyst has a molecular weight of 250,000 to 350,000 and a melting index of 3 to 10. delete 3. The method according to claim 1 or 2,
Wherein the non-crosslinked polypropylene resin comprises a propylene homopolymer and a propylene-ethylene copolymer, and the blending ratio of the propylene homopolymer and the propylene-ethylene copolymer is 80:20 to 50:50. 5. The method of claim 4,
Wherein the propylene-ethylene copolymer has an ethylene monomer content of 6 to 7 wt% based on the total weight of the propylene-ethylene copolymer. 3. The method according to claim 1 or 2,
Characterized in that the insulating oil comprises monocyclic naphthenic hydrocarbons. 3. The method according to claim 1 or 2,
Further comprising 0.2 to 5 parts by weight of an amine-based, dialkyl ester-based, thioester-based or phenol-based antioxidant based on 100 parts by weight of the base resin. 3. The method according to claim 1 or 2,
Wherein the sheath layer is made from a composition comprising the same base resin as the base resin of the insulating composition. 3. The method according to claim 1 or 2,
An inner semiconductive layer disposed between the conductor and the insulating layer, and an outer semiconductive layer surrounding the insulating layer. 10. The method of claim 9,
Wherein the inner semiconductive layer, the outer semiconductive layer, or both are fabricated from a semiconductive composition comprising the same base resin as the base resin of the insulating composition.

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