SEMICONDUCTIVE COMPOSITION AND POWER CABLE HAVING SEMICONDUCTIVE LAYER FORMED THEREFROM

Abstract

A semiconductive composition and a power cable having a semiconductive layer formed therefrom may be provided. More particularly, a semiconductive composition may be provided that is environmentally friendly, excellent in mechanical properties, heat resistance, etc., and excellent in extrudability having a trade-off relationship therewith and a power cable having a semiconductive layer formed therefrom.

Claims

1. A semiconductive composition comprising: a polypropylene resin and a polyolefin elastomer as a base resin; and a conductive additive, wherein crystallinity of the semiconductive composition defined by Equation 1 below is 20% to 70%, $\begin{array}{cc}\mathrm{Crystallinity}\left(\%\right)=\mathrm{semiconducting}\mathrm{integral}\mathrm{value}/\mathrm{insulating}\mathrm{integral}\mathrm{value}?100& \left[\mathrm{Equation}1\right]\end{array}$ wherein the semiconducting integral value means a value of integral of an endothermic peak in a temperature section of 100 to 170 degrees Celsius of a first heating curve measured under conditions of a temperature range of 30 to 200 degrees Celsius and a temperature increase rate of 10 degrees Celsius per minute using a differential scanning calorimetry (DSC) for a specimen formed from the semiconductive composition, and the insulating integral value means a value of integral of an endothermic peak in a temperature section of 100 to 170 degrees Celsius of a first heating curve measured under conditions of a temperature range of 30 to 200 degrees Celsius and a temperature increase rate of 10 degrees Celsius per minute using the differential scanning calorimetry (DSC) for a specimen formed from an insulating composition comprising only a non-crosslinked polypropylene resin as a base resin.

2. The semiconductive composition according to claim 1, wherein a content of the non-crosslinked polypropylene resin and a content of the polyolefin elastomer are each independently 25 to 75 parts by weight based on 100 parts by weight of the base resin.

3. The semiconductive composition according to claim 1, wherein the conductive additive comprises carbon black.

4. The semiconductive composition according to claim 3, wherein a content of the carbon black is 30 to 60 parts by weight based on 100 parts by weight of the base resin.

5. The semiconductive composition according to claim 1, further comprising 0.5 to 3 parts by weight of an antioxidant based on 100 parts by weight of the base resin.

6. A power cable comprising: at least one conductor; an inner semiconductive layer configured to enclose the conductor; an insulating layer configured to enclose the inner semiconductive layer; an outer semiconductive layer configured to enclose the insulating layer; and a sheath layer configured to enclose the outer semiconductive layer, wherein at least one of the inner semiconductive layer and the outer semiconductive layer is formed from a semiconductive composition comprising: a polypropylene resin and a polyolefin elastomer as a base resin; and a conductive additive, wherein crystallinity of the semiconductive composition defined by Equation 1 below is 20% to 70%, $\begin{array}{cc}\mathrm{Crystallinity}\left(\%\right)=\mathrm{semiconducting}\mathrm{integral}\mathrm{value}/\mathrm{insulating}\mathrm{integral}\mathrm{value}?100& \left[\mathrm{Equation}1\right]\end{array}$ wherein the semiconducting integral value means a value of integral of an endothermic peak in a temperature section of 100 to 170 degrees Celsius of a first heating curve measured under conditions of a temperature range of 30 to 200 degrees Celsius and a temperature increase rate of 10 degrees Celsius per minute using a differential scanning calorimetry (DSC) for a specimen formed from the semiconductive composition, and the insulating integral value means a value of integral of an endothermic peak in a temperature section of 100 to 170 degrees Celsius of a first heating curve measured under conditions of a temperature range of 30 to 200 degrees Celsius and a temperature increase rate of 10 degrees Celsius per minute using the differential scanning calorimetry (DSC) for a specimen formed from an insulating composition comprising only a non-crosslinked polypropylene resin as a base resin.

7. The power cable according to claim 6, wherein the insulating layer is formed from an insulating composition comprising a non-crosslinked polypropylene resin as a base resin.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 schematically shows a cross-sectional structure of an embodiment of a power cable according to the present disclosure.

[0026] FIG. 2 schematically shows a stepped cross-sectional structure of the power cable shown in FIG. 1.

[0027] FIG. 3 is a graph showing first heating curves of semiconductive press specimens derived from examples using a differential scanning calorimetry (DSC).

DETAILED DESCRIPTION

[0028] Hereinafter, preferred embodiments of the present disclosure will be described in detail. However, the present disclosure is not limited to the embodiments described herein, and may be embodied in various different forms. Rather, these embodiments are provided such that the present disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art. The same reference numbers denote the same elements throughout the specification.

[0029] The present disclosure relates to a semiconductive composition capable of forming a semiconductive layer of a power cable.

[0030] The semiconductive composition according to the disclosure may include a non-crosslinked polypropylene resin and a polyolefin elastomer as a base resin, wherein the polypropylene resin may include a propylene homopolymer and/or a propylene copolymer, preferably a propylene homopolymer, and the propylene homopolymer means polypropylene formed by polymerization of at least 99 wt %, preferably 99.5 wt %, of propylene based on the total weight of a monomer.

[0031] The propylene copolymer may include a copolymer of propylene with ethylene or an ?-olefin of carbon number 4 to 12, for example, a comonomer selected from 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, and a combination thereof, preferably with ethylene. The reason for this is that copolymerization of propylene with ethylene results in rigid yet flexible properties.

[0032] The non-crosslinked polypropylene resin may have a weight average molecular weight (Mw) of 200,000 to 450,000. Furthermore, the non-crosslinked polypropylene resin may have a melting point (Tm) of 140 to 175? C. (as measured by differential scanning calorimetry (DSC)), a melting enthalpy of 50 to 100 J/g (as measured by DSC), and a flexural strength at room temperature of 30 to 1,000 MPa, preferably 60 to 1,000 MPa (as measured according to ASTM D790).

[0033] The non-crosslinked polypropylene resin may be polymerized under a general stereospecific Ziegler-Natta catalyst, a metallocene catalyst, a constrained geometry catalyst, other organometallic or coordination catalysts, preferably under the Ziegler-Natta catalyst or the metallocene catalyst. Here, metallocene is a generic term for bis(cyclopentadienyl) metals, which are novel organometallic compounds in which cyclopentadiene and a transition metal are combined in a sandwich structure, and the general formula of the simplest structure is M (C.sub.5H.sub.5).sub.2 (where M is Ti, V, Cr, Fe, Co, Ni, Ru, Zr, Hf, etc.). Since polypropylene polymerized under the metallocene catalyst has a low catalyst residual of about 200 to 700 ppm, degradation of the electrical properties of an insulating composition including polypropylene by the catalyst residual may be inhibited or minimized.

[0034] The above non-crosslinked polypropylene resin, despite being non-crosslinked, has a high melting point, which enables the non-crosslinked polypropylene resin to exhibit sufficient heat resistance, whereby it is possible to provide a power cable with an improved continuous use temperature, and also exhibits excellent eco-friendliness, such as being recyclable, due to the non-crosslinked form thereof. On the other hand, a conventional crosslinked resin is not only environmentally unfriendly because the crosslinked resin is difficult to recycle, but premature crosslinking or scorching during formation of the semiconductive layer of the cable may cause long-term extrudability degradation, such as inability to achieve uniform production capacity.

[0035] Meanwhile, the polyolefin elastomer may include a copolymer of an ethylene monomer and an ?-olefin other than the ethylene monomer, for example, propylene, butene, propene, hexene, heptene, or octene, preferably an ethylene-butene copolymer, and may have a melting flow rate (MFR) (190? C., 2.16 kg) of 1 to 8 g/10 min and a melting point of 40 to 105? ? C.

[0036] The inventors of the present application have completed the present disclosure by experimentally confirming that, when the crystallinity defined by Equation 1 below is adjusted to 20 to 70% on the premise that the semiconductive composition according to the present disclosure includes the base resin and a conductive additive described below, the mechanical properties, heat resistance, etc. of the semiconductive layer of the cable formed from the semiconductive composition and the extrudability having a trade-off relationship therewith are simultaneously improved.

[00002]$\begin{array}{cc}\mathrm{Crystallinity}\left(\%\right)=\mathrm{semiconducting}\mathrm{integral}\mathrm{value}/\mathrm{insulating}\mathrm{integral}\mathrm{value}?100& \left[\mathrm{Equation}1\right]\end{array}$

[0037] In Equation 1 above, [0038] the semiconducting integral value means the value of the integral of an endothermic peak in a temperature section of 100 to 170? C. of a first heating curve measured under conditions of a temperature range of 30 to 200? ? C. and a temperature increase rate of 10? C./min using a differential scanning calorimetry (DSC) for a pressed specimen formed from a semiconductive composition including a non-crosslinked polypropylene resin and a polyolefin elastomer as a base resin and further including a conductive additive, and [0039] the insulating integral value means the value of the integral of an endothermic peak in a temperature section of 100 to 170? C. of a first heating curve measured under conditions of a temperature range of 30 to 200? C. and a temperature increase rate of 10? C./min using the differential scanning calorimetry (DSC) for a pressed specimen formed from an insulating composition including only a non-crosslinked polypropylene resin as a base resin.

[0040] For example, the content of the non-crosslinked polypropylene resin and the content of the polyolefin elastomer may each independently be 25 to 75 parts by weight based on 100 parts by weight of the base resin.

[0041] If the content of the non-crosslinked polypropylene resin exceeds 75 parts by weight and thus the content of the polyolefin elastomer is less than 25 parts by weight, the crystallinity of the semiconductive composition may be excessive, resulting in insufficient room temperature elongation among the mechanical properties of the semiconductive composition, and in particular, a significant decrease in extrudability, resulting in a significant decrease in surface roughness of the semiconductive layer formed.

[0042] On the other hand, if the content of the polyolefin elastomer exceeds 75 parts by weight and thus the content of the non-crosslinked polypropylene resin is less than 25 parts by weight, the crystallinity of the semiconductive composition may be significantly reduced, resulting in insufficient tensile strength among the mechanical properties of the semiconductive composition, in particular a significant decrease in heat resistance.

[0043] Meanwhile, the semiconductive composition may further include 30 to 60 parts by weight of a conductive additive, such as carbon black, and 0.5 to 3 parts by weight of an antioxidant based on 100 parts by weight of the base resin.

[0044] If the content of the conductive additive, such as carbon black, is less than 30 parts by weight, the semiconductive composition may not exhibit semiconductive properties due to a sharp increase in resistance. On the other hand, if the content of the conductive additive exceeds 60 parts by weight, screw load may increase during extrusion due to an increase in viscosity of the semiconductive composition, which may further significantly reduce workability and extrudability.

[0045] If the content of the antioxidant is less than 0.5 parts by weight, securing long-term heat resistance of the formed semiconductive layer in a high-temperature environment may be difficult. On the other hand, if the content of the antioxidant exceeds 3 parts by weight, a blooming phenomenon in which the antioxidant elutes white onto the surface of the semiconductive layer may occur, resulting in deterioration of semiconductive properties.

[0046] Furthermore, the semiconductive composition may further include other additives, such as processing oil, a stabilizer, and an active agent, in addition to the conductive additives and the antioxidant.

[0047] The present disclosure relates to a power cable having the semiconductive layer formed from the semiconductive composition described above, particularly an inner semiconductive layer, and FIGS. 1 and 2 schematically show the structure of an embodiment of a power cable according to the present disclosure.

[0048] As shown in FIGS. 1 and 2, the power cable according to the present disclosure may include a conductor 10 made of a conductive material such as copper or aluminum, an insulating layer 30 made of an insulative polymer, etc., an inner semiconductive layer 20 configured to enclose the conductor 10, to eliminate an air layer between the conductor 10 and the insulating layer 30, and to relieve localized electric field concentration, the inner semiconductive layer being formed from the semiconductive composition according to the present disclosure described above, an outer semiconductive layer 40 configured to shield the cable and to ensure that an even electric field is applied to the insulating layer 30, the outer semiconductive layer being formed from the semiconductive composition according to the present disclosure described above, and a sheath layer 50 configured to protect the cable.

[0049] The standards of the conductor 10, the insulation layer 30, the semiconductive layers 20 and 40, and the sheath layer 50 may vary depending on the use, transmission voltage, etc. of the cable.

[0050] The conductor 10 may be made of a stranded wire constituted by a plurality of wires in terms of improving cold resistance, flexibility, bendability, laying ability, workability, etc. of the power cable, and in particular may include a plurality of conductor layers formed by arranging a plurality of wires in a circumferential direction of the conductor 10.

[0051] The insulating layer 30 may be formed from an insulating composition including the non-crosslinkable polypropylene resin, which is one of the base resins of the semiconductive composition described above, as a base resin. Consequently, each of the insulating composition and the semi-conductive composition includes the non-crosslinkable polypropylene resin as the base resin. When the insulating layer 30 and the semiconductive layers 20 and 40 are extruded, therefore, extrusion workability may be improved, such as easy control of the extrusion process, and interlayer adhesion may be improved.

Examples

1. Manufacturing Example

[0052] Semiconductive compositions were prepared using a kneader mixer with components and contents listed in Table 1 below, press specimens were manufactured, and crystallinity was measured by calculating the peak integral value from a first heating curve obtained by a DSC, as shown in FIG. 3. In Table 1 below, the unit of the contents is parts by weight.

TABLE-US-00001 TABLE 1 Compar- Compar- Example Example Example ative ative 1 2 3 Example 1 Example 2 Resin 1 75 50 25 80 20 Resin 2 25 50 75 20 80 Additive 1 55 55 55 55 55 Additive 2 1 1 1 1 1 Crystal- 68.7 47.9 21.3 73.4 18.6 linity (%) Resin 1: Polypropylene resin Resin 2: Polyolefin elastomer Additive 1: Carbon Black Additive 2: Antioxidant

2. Evaluation of Physical Properties

1) Evaluation of Room Temperature Elongation

[0053] Elongation at break was measured at a tensile rate of 200 mm/min for the dumbbell specimen according to each of examples and comparative examples in accordance with ASTM D638.

2) Evaluation of Heat Resistance

[0054] In accordance with ASTM D638, the dumbbell specimen according to each of examples and comparative examples was placed in an oven at 136? C. for 240 hours and was then placed in an oven at 150? C. for 240 hours, and the residual elongation, which is the ratio of decreased elongation to elongation before heating, of the dumbbell specimen was measured.

3) Evaluation of Surface Properties

[0055] The number of protrusions by diameter per unit area (90 cm.sup.2) was measured on the surface of the press specimen according to each of examples and comparative examples.

[0056] The results of measurements are shown in Table 2 below.

TABLE-US-00002 TABLE 2 Comparative Comparative Example 1 Example 2 Example 3 Example 1 Example 2 Room temperature elongation (%) 420 587 741 403 764 Residual elongation 136? C. ? 240 h 95.7 93.4 78.1 85.3 62.5 after heating (%) 150? C. ? 240 h 95.3 94.1 75.9 84.6 56.9 Surface properties 201 ?m.sub.? (ea) 101~200 ?m 3 51~100 ?m 2 1 20.sub.?

[0057] As shown in Table 2 above, the semiconductive compositions of Examples 1 to 3 with crystallinity adjusted to 20 to 70% according to the present disclosure were found to have improved mechanical properties such as room temperature elongation, heat resistance such as residual elongation after heating, and extrudability such as surface properties. In contrast, the semiconductive composition of Comparative Example 1 with a crystallinity of more than 70% was found to have lower heat resistance despite having higher crystallinity than the semiconductive composition of Example 1, as well as significantly reduced extrudability, such as formation of a plurality of protrusions on the surface of the pressed specimen. In addition, the semiconductive composition of Comparative Example 2 with a crystallinity of less than 20% was found to have significantly reduced heat resistance.

[0058] Although preferred embodiments of the present disclosure have been described in this specification, those skilled in the art will appreciate that various changes and modifications are possible without departing from the idea and scope of the present disclosure recited in the appended claims. Therefore, it should be understood that such changes and modifications fall within the technical category of the present disclosure as long as the changes and modifications include elements described in the claims of the present disclosure.