KR20180091555A - Compound for a semiconductor layer of a power cable and power cable including the same - Google Patents

Abstract

A compound for a semiconductor layer of a power cable includes 3-10 wt% of carbon nanotubes (CNT), 2-20 wt% of non-carbonated inorganic particles, and the remainder consisting of a polymer resin. Accordingly, the electrical conduction characteristics, the mechanical characteristics, and the heat transfer characteristics are stably improved.

Description

TECHNICAL FIELD [0001] The present invention relates to a compound cable for a power cable, and a power cable including the same. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

TECHNICAL FIELD The present invention relates to a power cable for semiconductors and a power cable using the same. More particularly, the present invention relates to a carbon nanotube (CNT), a semiconducting compound for a power cable, and a non-carbon-based inorganic particle having an average diameter of nanometers or less A compound for a semiconductive layer for a power cable, and a power cable including the compound.

The power cable consists of a conductor, an inner semiconductive layer, an insulating layer, an outer semiconductive layer, a neutral conductor and an outermost sheath from the center. The conductors serve to transfer electrical energy, and the inner semiconductive layer allows the electric field distribution to be formed uniformly in the outward direction. In addition, the insulating layer is electrically insulated, and the outer semiconductive layer serves to form an electric field and to connect with a ground wire.

The power table is usually designed to be used for a long period of time of more than 30 years. In some cases, the design life is not used and the insulation breakdown occurs prematurely. One of the main factors of this early insulation breakdown is that protrusions formed in the inner semiconductive layer and the outer semiconductive layer during the extrusion process cause electric field concentration and cause the dielectric breakdown of the insulating layer in the future.

The inner semiconductive layer or the outer semiconductive layer is generally formed of a polymer resin such as ethylene vinylacetate (EVA), ethylene ethyl acrylate (EEA), or ethylene butylacrylate (EBA) Negative conductive carbon black particles are used as raw materials. The raw materials are mixed in a kneader such as a kneader or a twin screw extruder, and then pelletized and impregnated with a cross-linking agent to prepare a semiconductive layer.

At this time, the conductive carbon black is not completely dispersed with the polymer resin, and forms a protrusion on the surface of the inner and outer semiconductive layers. In fact, conductive carbon black is very difficult to mix with the polymer resin in a completely dispersed state. If the protrusions are present, it is known that an electric field is concentrated on this portion, which ultimately destroys the insulation of the power cable.

Therefore, the thickness of the insulation layer is regulated on the assumption that the size of the projections is maintained to a certain extent when manufacturing the power cable, and that some protrusion exists in the interface between the semiconductor layer and the insulation layer. Therefore, in order to reduce the thickness of the insulating layer, it is necessary to develop a technique capable of significantly reducing surface projections.

In order to overcome these problems, attempts have been recently made to use polymer resin, conductive carbon black, and carbon nanotube (CNT) as a semiconducting material for power cables. Hereinafter, carbon nanotubes are referred to as CNTs regardless of the type.

Since the method of mixing the CNTs and the conductive carbon black is difficult to disperse only CNTs, CNTs and carbon blacks are mixed and used. However, since this method also uses a conductive carbon black, there is a limitation in reducing the projections .

Another method is a method of producing semi-conductive compounds by completely excluding conductive carbon black, that is, using only CNTs.

However, this method also has a problem. When the CNT is mixed with the polymer resin used as the base resin of the semi-conductive compound, the CNTs are not completely dispersed, and the CNTs are present in a state of aggregation. The low dispersibility of the CNT in the polymer resin adversely affects the tensile strength and elongation, especially the elongation, of the semi-conductive compound. In order to prevent this, it is possible to improve the dispersibility by compounding the semi-conducting compound once again several times. However, this method also causes a problem that the manufacturing cost of the compound is greatly increased due to excessive processing, which is likely to cause a commercial disadvantage or a rapid thermal degradation.

In addition, when a semi-conductive compound is formed by mixing only CNT with a polymer resin, a peculiar phenomenon occurs. That is, the electrical conductivity of a specimen produced by compression molding is very high, while the electrical conductivity of the specimen produced through the extrusion process is remarkably reduced. There is a phenomenon that the electric conductivity changes rapidly according to the extrusion rate in the extrusion process. For example, when the extrusion speed is low, the decrease in the electrical conductivity is not severe, whereas when the extrusion speed is relatively high, the electrical conductivity of the specimen is considerably reduced.

This is because, when the semiconducting compound containing CNT is extruded at a relatively high extrusion speed, the CNT is oriented in the extrusion direction. Thus, a process condition of an extrusion process capable of suppressing the orientation of CNT to the maximum is required.

When the conventional semiconducting compound is made only of conductive carbon black, the conductive carbon black has 30 to 40 parts by weight. Thus, the semiconducting compound can maintain a relatively hard physical property. On the other hand, when the conductive carbon black and the CNT are mixed to produce the semiconducting compound, the content of the CNT to be mixed is generally lowered.

However, when the semi-conductive compound is manufactured using only CNT, the content of the CNT becomes very low, so that the overall thermal conductivity of the entire semiconducting compound is low although the thermal conductivity of the CNT is high. Therefore, if an emergency situation occurs and a local overheating occurs, the heat dissipation is not smooth, which may cause the power cable to fail.

Therefore, in order to solve these problems, it is necessary to reduce the number of kneading processes to a minimum, to have an acceptable electrical conductivity, that is, a volume resistivity, to prevent a significant decrease in tensile strength and elongation, The invention of technology is necessary.

It is an object of the present invention to provide a semi-conductive compound for a power cable by using only CNT as a conductive material without using conductive carbon black, The present invention provides a semi-conductive compound for a power cable having improved properties and improved heat radiation capability of the semi-conductive compound itself, and a power cable made therefrom.

In order to achieve the above object, the present invention provides a semi-conductive compound for a power cable comprising carbon nanotubes (CNTs) having 3 to 10 wt%, non-carbonaceous inorganic particles having 2 to 20 wt% .

In one embodiment of the present invention, the non-carbon based inorganic nano-particles may include at least one of silicon nano-particles and non-carbon-based inorganic nano-particles containing titanium or zirconium as a main component.

Here, the silicon nanoparticles may include at least one of magnesium silicate, silicate having a layered structure, and fumed silica.

In one embodiment of the present invention, the polymer resin includes at least one of an ethylene group, a propylene group, a vinyl acetate group, an acrylate group, an acrylate group, a butyl acrylate group, a butyl acrylate group, a diene group, and a butadiene group Polymer, copolymer or blend thereof.

In one embodiment of the present invention, the carbon nanotube (CNT) may include at least one of a single-wall, double wall, and multi-wall carbon nanotubes.

In preparing semi-conductive compounds for power cables by mixing polymeric resin and CNT according to embodiments of the present invention, non-carbon based inorganic particles of nano-sized diameter are mixed together to produce semi-conductive compounds. As a result, compared with the case where the inorganic particles are not used, the semi-conductive compound can remarkably reduce the increase in the volume ratio resistance, thereby achieving a stable electrical conduction characteristic and an improvement in mechanical characteristics such as tensile strength and elongation. In addition, since the semi-conductive compound includes the inorganic filler in an amount more than a certain amount, the inorganic particles contribute to the heat transfer of the semiconductive layer itself, thereby making the heat distribution more uniform in the extrusion process or in actual use.

By using the technique of the present invention, the electrical properties of the semiconductive layer can be stably realized by suppressing the orientation of the CNTs during the power cable extrusion, the mechanical properties such as tensile strength and elongation can be improved, This is advantageous.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is capable of various modifications and various forms, and specific embodiments are illustrated in the drawings and described in detail in the text. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. In the accompanying drawings, the sizes and the quantities of objects are shown enlarged or reduced from the actual size for the sake of clarity of the present invention.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprise", "comprising", and the like are intended to specify that there is a feature, step, function, element, or combination of features disclosed in the specification, Quot; or " an " or < / RTI > combinations thereof.

On the other hand, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

Power cable Semi-conductor compound

Hereinafter, the content of the present invention will be described in detail.

Semi-conductive compounds according to one embodiment of the present invention include polymeric resin, CNT, and non-carbon based inorganic particles.

The semi-conductive compound may further contain additives such as other stabilizers.

The polymer resin may be a resin capable of producing a semi-conductive compound for a power cable. For example, the polymer resin may be a polymer comprising functional groups such as ethylene, propylene, butadiene, vinyl acetate, acrylic acid and acrylate groups and styrene, a polymer having functional groups modified from these functional groups, Or a blend of one or more of the foregoing.

The carbon nanotubes may include at least one of single wall, double wall, and multi wall carbon nanotubes. Particularly, carbon nanotubes in which impurities are removed through removal of metallic and other impurities, or treatment of these carbon nanotubes through acid treatment or water treatment, can be used without limitation. Hereinafter, regardless of the kind of carbon nanotube (CNT), it is referred to as CNT.)

The CNT may have a content ranging from 2 to 10 parts by weight based on the total weight of the compound. As a result, the compound can exhibit a stable volume specific resistance. If the content of CNT is less than 2 parts by weight, the volume specific resistance is too high to perform the semiconductive layer function. On the other hand, if the content of CNT exceeds 10 parts by weight, the mechanical properties of the semiconductive compound may deteriorate. Preferably, the content of CNT may range from 3 to 7 parts by weight.

The non-carbon based inorganic particles include nanoparticles having a diameter of less than 1 micron, that is, a submicron size. The non-carbon based inorganic particles may comprise silica or a silicate component. For example, the non-carbon based inorganic particles may include silicate particles such as talc or a silicate particle having a layered structure (Nano clay), fumed silica, or silica-based inorganic particles, which are magnesium silicate particles .

Alternatively, the non-carbon based inorganic particles may include titanium or zirconium as a main component.

The nano-inorganic particles may have a content ranging from 2 to 20 parts by weight based on the total weight. If the nano-inorganic particles have a content of less than 2 parts by weight, the inorganic particle content may be too low to compensate the mechanical properties and deteriorate the orientation-inhibiting effect of the CNTs. On the other hand, when the nano-inorganic particles have a content of more than 20 parts by weight, the nanoparticles are excessively large and the extrusion characteristics in the extrusion process may be deteriorated.

In an embodiment of the present invention, a coupling agent may be additionally used to improve the kneading property or interfacial bonding force between the non-carbon-based inorganic particles and the polymer resin.

In one embodiment of the present invention, a stabilizer may additionally be included in the semiconductive compound. That is, the semi-conductive compound is manufactured through a kneading process in which a shear force is applied for a predetermined time in a heated state. Therefore, the presence of the stabilizer such as the antioxidant in the kneading process, which is likely to degrade the polymer resin due to the oxidation reaction, can suppress the phenomenon that the polymer resin deteriorates due to the oxidation reaction.

In one embodiment of the present invention, additives may additionally be included in the semiconductive compound. For example, processing aids may be used to assist in the dispersion of the nanomineralized particles. In addition, when one or more polymers are used in combination, a compatibilizer may be added to improve the compatibility of the two polymer resins.

In order to use the semiconducting compound produced by the above technique as a semiconducting compound for an actual power cable, a crosslinking agent is impregnated into the semi-conducting compound in the form of granules produced by the above-described technique.

In the step of impregnating the cross-linking agent, the granules may be prepared and placed in a vibrating vessel for applying vibration, and the cross-linking agent may be added while heating to penetrate the cross-linking agent molecules into the pellets. The crosslinking agent may have a content of less than 2 parts by weight.

Evaluation of compound for power cable semiconducting layer

Various physical properties of the semi-conductive compound prepared in the present invention are as follows.

Measurement of Tensile Properties: Mechanical properties such as tensile strength and elongation were obtained by making semi-conductive compound particles into a sheet of 1 mm thickness in a compression molding machine and then taking a dumbbell-shaped specimen.

Bulk Resistivity: Semi-conductive compound granules were re-extruded into a twin screw extruder and made into tapes with 0.4 mm thickness and 50 mm width and used as specimens. The bulk specific resistances of the tape were measured in the machine direction (MD) and the transverse direction (TD), and the volume resistivity was not significantly different between the MD and TD directions. Therefore, the volume resistivity value in the longitudinal direction was taken as the volume resistivity value of the compound.

Hereinafter, the present invention will be described in more detail with reference to Comparative Examples and Examples. The present Comparative Examples and Examples will be described using fumed silica, which is one of representative non-carbon based inorganic particles.

In the present Comparative Examples and Examples, the thermal conductivity of the semiconductive compound of the present invention was not separately measured. This is because it is a method of using an inorganic filler together with the use of CNT, so it is obvious that the thermal conductivity is improved compared with the case of using only CNT. Generally, mixing and kneading of inorganic particles with a polymer resin can provide sufficient kneading effect even when the inorganic particles assist the heat transfer and the compounding temperature is lowered. Therefore, the effect of the present invention can be sufficiently obtained without separately measuring the thermal conductivity.

≪ Comparative Examples 1-3 and 1-2 >

Comparative Examples 1-3 and 1-2 show the composition ratios of the semi-conductive compounds and the mechanical properties and the volume specific resistances thereof. In this Comparative Example and Example, EEA was Elvaloy ^? AC2116 resin of DuPont USA, CNT NC7000 of CNC Nanocyl, and S5130 of Sigma-Aldrich silica were used as fumed silica.

Comparative Example 1 Comparative Example 2 Comparative Example 3 Example 1 Example 2 Content ratio
(Parts by weight)

EEA 100 90 95 85 80 Fumed silica - 10 - 10 15 CNT - - 5 5 5 Bulk Resistivity (Ω ^. Cm)
- - > 10 ⁷ 10 ⁵ 10 ³ Tensile strength (N / mm ² )
25.0 26.9 15.2 23.5 23.2 Elongation (%)
470 455 184 260 245

The properties of Comparative Examples 1 to 3 and Example 1

Comparing Comparative Examples 1 to 3, it can be seen that, even when 10 parts by weight of fumed silica, which is a typical non-carbon-based inorganic particle, is mixed in EEA as a polymer resin, tensile strength and elongation are almost similar to those of base resin, It means that the blendability of the fumed silica and the EEA is excellent. On the other hand, in Comparative Example 3, it can be seen that when the base resin is mixed with only 5 parts by weight of CNT, the tensile strength and elongation of the compound are significantly lowered.

Comparing Comparative Example 3 and Example 1, when 5 parts by weight of CNT was mixed with EEA as the base resin (Comparative Example 3), the volume resistivity of the specimen was 10 ⁷ Ω ^. cm. On the other hand, when 10 parts by weight of the non-carbon-based inorganic particles, fumed silica, is mixed (Example 1), the volume resistivity is 10 ⁵ Ω ^. cm, and the tensile strength and elongation were improved as compared with Comparative Example 3. [

Further, when the content of the non-carbon-based inorganic particles is increased to 15 parts by weight (Example 2), the volume resistivity is again 10 ³ Ω ^. cm. < / RTI > However, it can be seen that the tensile strength and elongation are somewhat lower than those of Example 1. [

Comparing the results of Comparative Examples 1-3 and 1-2, it can be seen that when the semi-conductive compound is prepared by mixing the base resin and the fumed silica in addition to the base resin and the CNT in the production of the EEA / MWCNT semi-conductive compound, Mechanical properties such as tensile strength and elongation are greatly improved, and the volume resistivity characteristic is greatly improved.

≪ Examples 1 and 3-4 >

Examples 1 and 3-4 compare physical properties when 5, 6, and 7 parts by weight of CNT are used in a state where the fumed silica content is fixed to 10 parts by weight.

Example 1 Example 3 Example 4 Content ratio
(Parts by weight) EEA 85 84 83 Fumed silica 10 10 10 CNT 5 6 7 Bulk Resistivity (Ω ^. Cm)
10 ⁵ 10 ⁴ 10 ³ Tensile strength (N / mm ² )
23.5 20.5 20.1 Elongation (%)
260 166.5 158.7

Properties of Example 1 and Examples 3 and 4

As can be seen from the results in Table 2, when the CNT content is higher than 5 parts by weight, the specific resistivity is further reduced, and the electrical conductivity of the semi-conducting compound is further improved. On the other hand, the tensile strength and elongation decrease, especially the elongation decrease.

In the above comparative examples and examples, when CNT alone is mixed with a polymeric resin to produce a semi-conductive compound for a power cable, addition of nanosize inorganic particles together with melt mixing causes tensile strength and elongation It is understood that the mechanical properties are improved and the volume resistivity is lowered even though 10 parts by weight of the inorganic filler is mixed, so that the electric conduction characteristic is further improved.

The technique of the present invention has a great advantage in that it is possible to produce a semi-conductive compound having such a property that it can be used as a semi-conductive compound for a power cable by a single kneader kneading.

The semiconductive compound according to the present invention is applied not only to the inner semiconductive layer of the power cable but also to the semiconductive compound for the outer semiconductive layer.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims. It can be understood that it is possible.

Claims (6)

Carbon nanotubes (CNT) having 3 to 10% by weight;
A non-carbon-based inorganic particle having 2 to 20% by weight; And
Semi-conductive compound for power cables containing extra polymeric resin. The semi-conductive compound for electric power cable according to claim 1, wherein the non-carbon based inorganic nano-particles include at least one of silicon nano-particles and non-carbon-based inorganic nano-particles containing titanium or zirconium as a main component. The semi-conducting compound of claim 2, wherein the silicon nanoparticles comprise at least one of magnesium silicate, silicate having a layered structure, and fumed silica. The polymeric resin according to claim 1, wherein the polymer resin comprises at least one of an ethylene group, a propylene group, a vinyl acetate group, an acrylic acid group, an acrylate group, a butyl acrylate group, a butyl acrylate group, a diene group and a butadiene group, ≪ RTI ID = 0.0 > a < / RTI > copolymer or a blend. The semi-conducting compound for a power cable according to claim 1, wherein the carbon nanotube (CNT) comprises at least one of a single-wall, double wall and multi-wall carbon nanotubes. A power cable comprising the semiconducting compound of any one of claims 1 to 5.