KR101408924B1 - Insulation Material Composition For DC Power Cable And The DC Power Cable Using The Same - Google Patents

Abstract

The present invention is a polypropylene for the base resin of 100 parts by weight of silicon oxide (SiO _2), titanium dioxide (TiO _2), carbon black, graphite powder and a surface-modified cube-type nano inorganic least one selected from the group consisting of magnesium oxide And 0.5 to 5 parts by weight of particles. A direct current power cable having an insulator formed from the insulating material composition according to the present invention has a superior space charge reducing effect and improved extrudability.

Description

Technical Field [0001] The present invention relates to an insulation material composition for a DC power cable, and a DC power cable using the same.

The present invention relates to an insulation material composition for a direct current power cable. When the insulation material composition of the present invention is used, a direct current power cable with improved extrudability can be provided since the cross-linking step is not required.

As shown in FIGS. 1A and 1B, the power cable used in the domestic market includes an inner semiconductive layer 2, an insulating layer 3, an outer semiconductive layer 4, A sheath layer 5 and a polyethylene (PE) sheath layer 6. Conventionally, the insulating layer 3 constituting the power cable was manufactured using a composition containing crosslinked polyethylene (XLPE) and a dicumylperoxide crosslinking agent.

However, since it is difficult to recycle the crosslinked polyethylene resin as described above, it is not preferable to use a crosslinked polyethylene resin in view of the international environment where the environmental regulations are getting worse, and if the crosslinking or scorch occurs early, It is not preferable because it causes deterioration of long-term extrudability such that it can not be exerted.

Further, when the cross-linking agent is used for cross-linking, crosslinked by-products such as alpha-methylstyrene or acetophenone are generated. The biggest problem is that a space charge is easily formed due to the injection of charges from the electrodes and the influence of crosslinked byproducts on the insulator when a direct current high voltage is applied to the power cable. If such a space charge is accumulated in the insulator by the DC voltage applied to the power cable, the electric field strength in the vicinity of the conductor of the power cable rises, and the breakdown voltage of the cable is lowered. Conventionally, in order to solve the above problems, degassing for removing crosslinked byproducts has been added, or spherical magnesium oxide has been used. Examples of power cables using spherical magnesium oxide for suppressing crosslinking by-product furnace are Japanese Patent Nos. 2541034 and 3430875. However, when inorganic particles such as spherical magnesium oxide are added, there is a problem that the extrudability is further lowered.

Therefore, there is a continuing need for a research for suppressing crosslinked byproducts while improving the extrudability in a power cable comprising an insulator produced by crosslinked polyethylene or the like.

The technical problem of the present invention is to improve the extrudability of an insulation material composition for a power cable for direct current while suppressing crosslinking by-products generated in the manufacturing process.

In order to achieve the above object, the insulating material composition for DC power cable according to the present invention comprises silicon oxide (SiO ₂ ), titanium dioxide (TiO ₂ ), carbon black, graphite powder and And 0.5 to 5 parts by weight of at least one nano-inorganic particle selected from the group consisting of surface-modified cube-type magnesium oxide.

A direct current power cable having an insulator manufactured by using the insulating material composition of the present invention has excellent space charge reducing effect and improved extrudability.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. No.
1A is a longitudinal sectional view of a DC power cable.
1B shows a cross-sectional view of a DC power cable.
2A shows a SEM photograph of a cubic magnesium oxide.
2B shows an SEM photograph of a layered (terrace) magnesium oxide.
2C shows a SEM photograph of a rod magnesium oxide.
Figure 2D shows a TEM photograph of a porous porosity magnesium oxide.
Figure 2E shows a SEM photograph of spherical magnesium oxide.
3A shows an SEM photograph of the nano-sized cubic magnesium oxide of the present invention.
3B is a TEM photograph of the nano-sized cubic magnesium oxide of the present invention.
4 is a TEM photograph of an insulator including a nano-sized cube-type magnesium oxide of the present invention.

Hereinafter, the present invention will be described in detail.

The insulating material composition according to the present invention is characterized by comprising, per 100 parts by weight of the polypropylene base resin, 1 part selected from the group consisting of silicon oxide (SiO ₂ ), titanium dioxide (TiO ₂ ), carbon black, graphite powder and surface- 0.5 to 5 parts by weight of at least nano-inorganic particles.

It is preferred that the polypropylene base resin of the present invention is copolymerized with at least one monomer selected from the group consisting of i) C4 to C8 alpha olefins and ii) ethylene. The polypropylene resin is a polypropylene random copolymer obtained by polymerizing alpha-olefin and / or ethylene without regularity.

The nano-inorganic particle of the present invention means a nano-sized inorganic particle having an average particle diameter of 10 to 1000 nm. The nano-inorganic particles preferably include 0.5 to 5 parts by weight. With respect to the above numerical range, if it is contained in an amount of less than 0.5 parts by weight, the effect of reducing space charge is exhibited, but the DC insulation breakdown strength is relatively lowered. When the amount exceeds 5 parts by weight, mechanical performance and continuous extrudability .

In addition, although magnesium oxide has a crystal structure of a face centered cubic structure (FCC) basically, it may have various shapes, purity, crystallinity, and physical properties depending on a synthesis method. The shape of the magnesium oxide produced according to the synthesis method can be classified into a cubic shape, a terrace shape, a rod shape, a porous shape, and a spherical shape as shown in FIGS. 2A to 2E In the present invention, a cubic magnesium oxide is used. SEM and TEM photographs of the nano-sized cubic magnesium oxide of the present invention are shown in FIGS. 3A and 3B, respectively.

Preferably, the magnesium oxide is surface-modified with vinylsilane, stearic acid, oleic acid, aminopolysiloxane, or the like. Generally, magnesium oxide is hydrophilic with high surface energy, whereas polypropylene base resin is hydrophobic with low surface energy. Therefore, there is a problem that magnesium oxide has poor dispersibility to polypropylene base resin and adversely affects electrical properties have. Therefore, it is preferable to modify the surface of magnesium oxide to solve such a problem.

If the magnesium oxide particles are not surface-modified, a gap is formed between the magnesium oxide and the polypropylene resin, thereby deteriorating the mechanical properties and lowering the electrical insulation properties such as the dielectric breakdown strength.

On the other hand, the magnesium oxide of the present invention exhibits improved electrical properties by showing a better dispersibility to the polypropylene base resin by surface modification with vinyl silane or the like. A hydrolyzate such as vinylsilane is chemically bonded to the surface of the magnesium oxide by a condensation reaction to form a surface-modified magnesium oxide. Thereafter, a silane group or the like of magnesium oxide surface-modified with vinylsilane or the like reacts with the polypropylene base resin, thereby ensuring excellent dispersibility.

The magnesium oxide preferably has a purity of 99.9% to 100% and an average particle size of 500 nm or less, and may have a single crystal or polycrystal form.

Further, in the present invention, 0.1 to 2 parts by weight of an antioxidant may further be added to the insulating material composition according to other purposes. As the antioxidant of the present invention, any one or more selected from the group consisting of amine type, dialkyl ester type, thioester type and phenol type antioxidant may be used.

The insulator manufactured using the insulating material composition of the power cable according to the present invention can be used in the manufacture of a power cable for direct current.

[Example]

Hereinafter, the present invention will be described in more detail by way of examples. The average skilled person in the field of the present invention can modify the present invention in various other forms besides the embodiment described in the following examples. The following examples illustrate the present invention, but the technical idea of the present invention is not limited thereto It should not be construed as an intention to limit the scope to example.

In order to examine the performance of the insulating material composition for DC power cable of the present invention, the insulating material compositions of Examples and Comparative Examples were prepared with the composition shown in Table 1 below. The unit of the content of each component in Table 1 is parts by weight.

ingredient Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Base resin content 100 100 100 100 100 100
Oxidation
magnesium
content 2.0 2.0 2.0

No additives 2.0 2.0 shape Cube type Cube type Cube type Laminated type rectangle D50 (nm) 70 100 240 100 100 D99 (nm) 110 150 270 150 150 water(%) 99.95 99.95 99.95 99.95 99.95 Antioxidant content 0.4 0.4 0.4 0.4 0.4 0.4

[Description of components used in the table]

* Base resin: Polypropylene resin

* Magnesium oxide: magnesium oxide surface-modified with vinylsilane. D99 (D99 represents the maximum size of the particles) is D50 (note that D50 is the average size of the particles, ) Is used so as not to exceed three times

* Antioxidant: tetrakis- (methylene- (3,5-di- (tert-butyl-4-hydrosinamate)) methane (tetrakis- 4-hydrocinnamate)) methane)

Measurement and evaluation of physical properties

A master batch compound was prepared using the insulating material compositions according to Examples (1 to 3) and Comparative Examples (1 to 3), and a twin-screw extruder having a screw diameter of 25 mm (L / D = 60) Was used for the extrusion process. As a result, the cubic magnesium oxide contained in the insulator of the present invention can be confirmed through the TEM photograph of FIG.

The insulators prepared according to Examples (1 to 3) and Comparative Examples (1 to 3) were hot-pressed to prepare specimens having a thickness of 0.1 mm for measuring the dielectric breakdown strength of DC and sheets having a thickness of 1 mm for measuring impulse strength (ASTM D149) and impulse strength were measured. The results are summarized in Table 2 below. The brief experimental conditions are as follows.

㉠ DC insulation breakdown strength

The DC breakdown strength (kV) is measured at 90 ° C.

Impulse Strength

The electrodes are connected to the specimen of 1 mm in thickness, and the impulse strength is measured by increasing the voltage by 5 kV at 50 kV until destruction.

Item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 DC insulation breakdown strength
(kV / mm) 117 108 110 53 80 95 Impulse strength (kV / mm) 110 105 100 120 90 90

As a result of measuring the physical properties as listed in Table 2, the specimens of Examples 1 to 3 of the present invention were compared with Comparative Example 1 (magnesium oxide was not used), Comparative Example 2 (using stacked magnesium oxide), Comparative Example 3 The dielectric breakdown strength of DC was somewhat higher than that of specimen of magnesium. That is, it can be seen that the specimens of Examples 1 to 3 of the present invention using the cubic magnesium oxide exhibit excellent electrical insulation properties.

It can also be seen that the specimens of Examples 1 to 3 of the present invention in the impulse strength hardly deteriorate in impulse strength as compared with the specimens of Comparative Example 1 (magnesium oxide is not used). That is, although the specimens of the present invention use surface-modified magnesium oxide as an inorganic additive in order to exhibit excellent electrical insulation properties, the degree of impulse strength is comparable to that of Comparative Example 1 in which no inorganic additive such as magnesium oxide is used at all .

Particularly, in the case of Example 1 having the smallest average particle diameter among the specimens of Examples 1 to 3 of the present invention, the DC insulation breakdown strength and the impulse strength were excellent.

From the above results, it can be seen that the insulator produced by the insulation material composition for electric power cable for direct current according to the present invention and the electric power cable having the insulator produced excellent effects in DC insulation breakdown strength and impulse strength for the following reasons. That is, i) the magnesium oxide of the cube, which is the nano-inorganic particle, functions as a space charge reducing agent, ii) the surface energy of the magnesium oxide of the cube becomes similar to the surface energy of the polypropylene base resin, Polypropylene base resin to induce chemical bonding to ensure optimal dispersibility, and iii) each component constituting the insulating material composition was mixed at an appropriate ratio.

As described above, optimal embodiments of the present invention have been disclosed. Although specific terms have been employed in the specification to include the present embodiment, it should be understood that they have been used only for those of ordinary skill in the art for the purpose of illustrating the invention in detail and have been used to limit the scope of the invention as defined in the claims Or not.

The symbols shown in Figs. 1A and 1B mean the following.
One … Conductor
2 … Inner semiconductive layer
3 ... Insulating layer
4 … Outer semiconductive layer
5 ... Lead sheath layer
6 ... Polyethylene (PE) sheath layer

Claims (6)

Based on 100 parts by weight of a polypropylene base resin in which at least one monomer selected from the group consisting of alpha-olefins of C4 to C8 and ethylene is copolymerized,
And 0.5 to 5 parts by weight of a surface-modified cubic magnesium oxide. The method according to claim 1,
With respect to 100 parts by weight of the polypropylene base resin,
And 0.1 to 2 parts by weight of an antioxidant. delete The method according to claim 1,
Wherein the magnesium oxide has a purity of 99.9% or more and an average particle size of 500 nm or less. 5. The method of claim 4,
Wherein the magnesium oxide is single crystal or polycrystalline. A direct current power cable comprising an insulator produced by using the insulation material composition of the direct current power cable of claim 1.

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