KR100443872B1 - Cable insulation composition with resistance of water tree growth - Google Patents

Abstract

The present invention relates to a cable insulator composition, comprising: 95.0 to 98.9% by weight of a polyolefin resin blend, a base resin, 0.01 to 1.0% by weight of crosslinking agent, 1.0 to 3.0% by weight of crosslinking agent, and 0.1 to 1.0% by weight of antioxidant. When the composition is used as an insulator for power cables, it not only has excellent resistance to water tree growth, but also has excellent dielectric and processing properties.

Description

Cable Insulation Composition Resistant to Water Tree Growth {CABLE INSULATION COMPOSITION WITH RESISTANCE OF WATER TREE GROWTH}

The present invention relates to an insulator composition of a cable. More specifically, the present invention relates to a cable insulator composition having resistance to water tree growth by using a polyolefin resin blend as a base resin and adding a crosslinking aid for the purpose of reducing crosslinking by-products while improving crosslinking efficiency.

During the breakdown of medium and high voltage power cable insulators, the breakdown of the insulator by the tree has a serious effect on the cable life. This tree phenomenon is caused by the periodic partial discharge inside the insulator, which ultimately causes the breakdown of the electric tree. It is classified as a water tree that causes deterioration of insulators in the form of bushes or branches when the electric tree and the insulator are simultaneously exposed to moisture and electric fields.

Double water trees are known to occur mainly in areas where electric fields are concentrated, for example, at rough interfaces or projections between insulators and semiconducting layers, or in areas where water interacts with voids and mixed foreign matter in the insulators. have. Generally, water trees found in power cables are divided into vented tree and bow-tie tree, which grow symmetrically from voids or foreign matter inside the insulator. As it grows from the semiconducting layer to the insulating layer and continues to grow across the insulating layer, it has a fatal effect on the cable life.

In order to solve such a water tree problem, conventionally, steam curing is replaced with gas curing, thereby minimizing water inevitably formed during cable manufacturing, or triple co-extrusion method (triple co). -Extrusion keeps the interface between internal and external semi-conductor and insulator smooth or applies metal barrier film or swelling tape to the outside of the insulator to prevent infiltration of moisture or ions from the outside of the cable. By using a manufacturing method to prevent the voids and moisture generated in the cable insulator to minimize, and to prevent the water and foreign substances that are mixed into the cable to prevent cable breakage by the water tree.

However, the cable manufactured by adopting the conventional method as described above frequently prevents water or ions, which are inevitably generated during the cable manufacturing process, and water or ions introduced from the external environment after installation. There is a problem. Therefore, there is an urgent need for the development of new insulating materials resistant to water tree growth in terms of stable supply of electricity and economical aspects.

As a method of developing an insulating material resistant to water tree growth, a method of adding additives and modifying a polymer structure, which are advantageous in terms of economical and fairness, is used rather than a polymerization method of synthesizing and characterizing new materials. The method of using the dual additive is based on the addition of alcohol in US Pat. No. 4,206,260, including polyethylene glycol, polycarboxylic ester, fatty acid metal salt, organic isocyanate, Inorganic fillers and the like are used as additives. However, among these additives, it is difficult to expect a lasting effect in the long term because it is volatilized at high temperature or transferred from the resin.

As a method of modifying a polymer structure, a blending method that can mix two or more polymers together and achieve physically and chemically improved and stable properties without special polymerization is widely used. Insulation materials that can be used as insulators for medium and high voltage power cables are ethylene homopolymers such as low density polyethylene (LDPE), high density polyethylene (HDPE), ultra low density polyethylene (VLDPE), linear low density polyethylene (LLDPE), and ethylene vinyl. Ethylene copolymers such as acetate, ethylene alkyl acrylate, and ethylene propylene rubber (EPR) and ethylene propylene diene rubber (EPDM) and blends thereof.

Blend forms of dual low density polyethylene / ethylene vinyl acetate (EVA), low density polyethylene / ethylene ethyl acrylate (EEA), low density polyethylene / ethylene methyl acrylate (EMA), low density polyethylene / linear low density polyethylene are preferred, US patents 4,859,810 discloses reducing water tree growth by blending ethylene ethyl acrylate copolymers in low density polyethylene. It is believed that the good toughness properties of the ethylene copolymer can inhibit and retard the growth of the water tree.

However, the ethylene copolymer has a problem in that it can act as a negative factor in terms of long-term stability of the cable by reducing the dielectric properties, which is an important characteristic of the power cable because the polar group is present in the molecular structure.

In addition, U.S. Patent No. 5,246,783 discloses that crosslinked polyethylene crosslinked with polyethylene (hereinafter referred to as metallocene polyethylene) produced by using a metallocene catalyst alone is the same as that of crosslinked polyethylene crosslinked with low density polyethylene prepared by a conventional high pressure process. It is disclosed that it has dielectric properties and excellent water tree resistance, but even though metallocene polyethylene has the same density and melt index as conventional low density polyethylene, its molecular weight distribution is uniformly narrow, so it melts during cable extrusion. The higher the viscosity, the higher the processing load. The increased processing load causes premature decomposition of the crosslinking agent in the extruder, thereby forming an early crosslinking material called "scorch," which may lower the electrical properties. .

The present invention is to solve the above problems, to provide an insulator composition of a power cable having not only excellent resistance to water tree growth, but also excellent dielectric and processing characteristics.

1 shows an apparatus for measuring acceleration water tree deterioration of an insulator composition of the present invention.

FIG. 2 is an enlarged view of the needle inserter of the deterioration measuring apparatus of FIG. 1 shown in FIG. 1. FIG.

Reference numeral 1 is a 10 KV, 60 Hz power supply to the acceleration water deterioration measuring device, 2 is a platinum wire, 3 is a 0.1M AgNO ₃ aqueous solution, 4 is a needle inserter of the degradation measuring device, 5 is a needle used Is the needle angle, 6 is the needle tip, and 7 is the position from the sample tip to the needle in mm.

In order to achieve the above object, the present invention comprises a base resin polyolefin resin combination blend of 95.0 to 98.9 wt%, 0.01 to 1.0 wt% crosslinking aid, 1.0 to 3.0 wt% crosslinking agent and 0.1 to 1.0 wt% antioxidant It provides a cable insulator composition.

Hereinafter, the present invention will be described in detail.

Using the base resin and additives (crosslinking aid, crosslinking agent and antioxidant) of the present invention, a method for producing a cable insulator composition resistant to a water tree can be produced through the following conventional methods.

Crosslinking aids and antioxidant master batches are prepared using a Bambary mixer, a twin screw kneader and a roll mill, in a temperature range of 100 ° C. to 150 ° C. Alternatively, the cross-linking aid and the antioxidant masterbatch were prepared using a biaxial stretching kneader (Roll mill only), and the base resin, the crosslinking aid and the antioxidant masterbatch were extruded into a twin screw extruder at a temperature range of 120 ° C. to 190 ° C. to be extruded. Granulate into a phase. The compound in the pellet is placed in a Henschel mixer maintained at 80 ° C., followed by preheating for several minutes, and then a crosslinking agent is added while stirring at low speed. At this time, the total stirring time is about 30 minutes. The final composition is prepared by keeping the compound containing the crosslinking agent in a circulation oven maintained at 80 ° C. for 20 hours so that the crosslinking agent is evenly dispersed in the pellet.

The base resin may be prepared by using at least one polymer (1) and a metallocene catalyst selected from the group consisting of ethylene homopolymers and ethylene copolymers having a density of 0.87 to 0.965 g / cm 3 and a melt index of 0.1 to 50 g / 10 min. The polymer is prepared and blended with metallocene polyethylene (2) having a density of 0.87 to 0.92 g / cm 3 and a melt index of 0.5 to 50 g / 10 minutes. The ethylene polymer includes ultra low density polyethylene, low density polyethylene, high density polyethylene, and the like. Linear low density polyethylene ethylene copolymers are ethylene and α-olefins having 3 or more carbon atoms (eg propylene, 1-butene, 1-pentene, 1-hexene ( 1-hexene), 1-octene). In particular, the ethylene copolymers are polar ethylene vinyl acetate, ethylene ethyl atryl, ethylene methyl acrylate, ethylene normal butyl It may be an ethylene copolymer such as attrilate, and preferably has a density of 0.90-0.960 g / cm 3 and a melt index of 0.1-30 g / 10 min. In addition, the metallocene polyethylene may be a cyclopentadiene derivative and a periodic table. Metallocene catalyst, an organometallic compound formed by a ligand bond with a transition metal such as titanium, zirconium, hafnium, or vanadium of groups 4b, 5b, and 4b, 5b, and 6b in the phase. By means ethylene or polyethylene made from α-olefins having 3 or more carbon atoms.

The amount of the base resin is preferably 95.0 to 98.9% by weight based on 100% by weight of the total composition content.

Among the additives of the present invention, the crosslinking coagent is added to activate the radicals generated from the crosslinking agent to improve the crosslinking efficiency. In general, the cross-linking by-products, moisture, etc. generated during the decomposition of the cross-linking agent are volatilized or aggregated to form voids in the insulator. Moisture agglomerates or condenses into the voids thus formed and the electric field is concentrated, thereby acting as a place where the water tree can be started and grown.

Therefore, in order to reduce the defects formed by this phenomenon, the content of the crosslinking agent should be reduced. If the content of the crosslinking agent is simply reduced below a certain content, the thermal / mechanical properties of the cable cannot be satisfied. Therefore, crosslinking aids were used to maintain a certain level of crosslinking and to reduce crosslink dispersion.

Materials that can be used as the crosslinking aid include compounds including allyl, acrylate, and vinyl groups having unsaturated double bonds in the molecule. The crosslinking aid of the present invention is a crosslinking aid comprising an acrylate, and includes an ethylene glycol dimethacrylate having at least one unsaturated double bond in a molecule and containing at least one carboxyl group. glycol dimethacrylate), trimethylol propane trimethacrylate, trimethylol propane triacrylate, trimethol propane propoxylate triacrylate, In addition, triallyl isocyanurate, triallyl cyanurate, trially trimelliteate, meta-phenylene-bismaleicimide, and m-phenylene-bismaleicimide And the like can also be used.

The amount of the crosslinking aid to be used is 0.01 to 1.0% by weight, preferably 0.01 to 0.5% by weight.

The crosslinking agent is added to form a crosslinking initiation point in the base resin, and the crosslinking agent is dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, tertiary Tertiary-butyl dicumyl peroxide, alpha-alpha-bis (t-butylperoxy isopropyl) benzene, 2,5-dimethyl -2,5-di (tertary-butylperoxy) hexane (2,5-dimethyl-2,5-di (tertiary-butylperoxy) hexane), di (tertary-butyl) peroxide (di (tertiary-butyl) peroxide) or a similar structure can be used.

The amount of the crosslinking agent used is 1.0 to 3.0% by weight, preferably 1.5 to 2.5% by weight based on the total composition.

As the antioxidant, 2,2'-thio diethyl bis- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate] (2,2'-thiodiethylbis- [ 3- (3,5-di-tertiary-butyl-4-hydroxy phenyl) -propionate]), pentaerythritol-terrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl ) -Propionate] (pentaaerythrityl-tetrakis [3- (3,5-di-tertiary-butyl-4-hydroxy phenyl) -propionate]), octadecyl 3- (3,5-di-tert-butyl- 4-hydroxy phenyl) -propionate (octadecyl 3- (3,5-di-tertiary-butyl-4-hydroxy phenyl) propionate), triethylene glycol-bis-3 (tert-butyl-4- Phenolic antioxidants such as hydroxy-5-methylphenyl) propionate (triethylene glycol-bis-3 (3-tertiary-4-hydroxy-5-methyl phenyl) propionate), disterylthiodiprop Thioester-based antioxidants such as disionaryl thiodipropionate and dilauryl thiodipropionate alone or in combination Acids may be used in more than the combined type or the like.

The amount of the antioxidant used is in the range of 0.1 to 1.0% by weight based on the total composition.

The following presents preferred examples and comparative examples to aid in understanding the invention. However, the following examples are provided only to more easily understand the present invention, and the present invention is not limited to the following examples.

Example 1

97.75 weight% of polymer blend which mixed low density polyethylene: metallocene polyethylene in weight ratio 95: 5 as a base resin, 0.05 weight% of trimehtylol propane triacrylate as a crosslinking adjuvant, 1.80 dicumyl peroxide as a crosslinking agent % By weight 2,2'-thio diethylbis- [3- (3,5-di-tert-butyl-4-hydroxy phenyl) -propionate] and dilauryl thiodipropionate as antioxidants (dilaurylthiodipropionate) to prepare a cable insulator composition by reacting with a composition of 0.2% by weight.

When the composition is prepared, a crosslinking aid and an antioxidant master batch are prepared using a banbury mixer, a twin screw kneader in a temperature range of 100 ° C. to 150 ° C., and a twin screw kneader, a roll mill, and then 120 ° C. to 150 ° C. The base resin, the crosslinking aid and the antioxidant masterbatch were put into a twin screw extruder at 190 ° C. and extruded into pellets. The compound of the prepared pellets was placed in a Henschel mixer maintained at 80 ° C. for several minutes. After preheating, the crosslinking agent was added while stirring at low speed. At this time, the total stirring time was about 30 minutes. The final composition was prepared by holding the compound containing the crosslinker for 20 hours in a circulating oven maintained at 80 ° C. so that the crosslinker was evenly dispersed in the pellet.

Comparative Example 1

A cable insulator composition was prepared in the same manner as in Example 1 except for using a polymer blend in which a normal butyl acrylate copolymer including low density polyethylene: 25% normal butyl acrylate was mixed in a weight ratio of 95: 5.

Comparative Example 2

97.80% by weight of a polymer blend of polyethylene: metallocene polyethylene in a weight ratio of 95: 5 as a base resin, 1.80% by weight of dicumyl peroxide as a crosslinking agent and 2,2'-thio diethylbis- [3- (as an antioxidant 3,5-di-tert-butyl-4-hydroxyphenyl) -propionate] and dilauryl thiodipropionate using 0.2 wt% of each of the cable insulators in the same manner as in Example 1 The composition was prepared.

Comparative Example 3

97.80% by weight of a polymer blend containing a polyethylene: 25% normal butyl acrylate copolymer as a base resin in a weight ratio of 95: 5, 1.80% by weight of dicumyl peroxide as a crosslinking agent and 2, as an antioxidant 0.2% by weight of 2'-thio diethylbis- [3- (3,5-di-tert-butyl-4-hydroxy phenyl) -propionate] and dilaurylthiodi propionate Using the same method as in Example 1 to prepare a cable insulator composition.

Comparative Example 4

A cable insulator composition was prepared in the same manner as in Example 1 except that crosslinked polyethylene prepared by crosslinking LG Chem Low Density Polyethylene (LUTENE CB1700) alone was used as a base resin.

Experimental Example 1: Water tree measurement

The compositions prepared in Examples 1-2 and Comparative Examples 1-3 were prepared by using an automatic press to test the physical properties and the water tree measurement by the following apparatus and method. A sample was prepared by forming an insulator composition into a plate shape, and the prepared sample was inserted into a needle inserter capable of inserting eight conical needles of FIG. 2 and inserted until it reached a position 2 mm from the end of the sample. Pressed at ° C to prepare a cross-sectional specimen for measuring the water tree. The needle angle of the needle used at this time was 60 °, the radius of curvature of the needle tip was 5 ㎛.

The water tree length of the prepared specimen was measured by the following method using an accelerated water tree deterioration apparatus as shown in FIG. 1. 0.1 M of silver nitrate (AgNO ₃ ) solution was poured into the prepared specimen, 50 mm platinum wire was inserted, and a 10 kV alternating voltage was applied for 96 hours. Water tree length measurement was made by cutting the specimen thinly and using an optical microscope to measure the final growth of the water tree length. The measured water tree length is an average value of the measured total specimens, and the results are shown in Table 1 below.

The measurement of the water tree growth rate is the same as the water tree length measurement, but is only disclosed in U.S. Patent No. 4,144,202 as a method of obtaining the water tree growth rate with respect to time by measuring the water tree length for several time zones. Equation was used to calculate the rate constant (k) for each composition. Water tree growth rate was expressed as the rate constant ratio of the composition prepared in Examples 1-2 and Comparative Example 1-2 to the rate constant of Comparative Example 3, the results are shown in Table 1 below.

division Degree of crosslinking (%) ¹⁾ Thermal elongation (%) ²⁾ Speed constant k (mm ³ / V ² mm ² ) Water tree growth rate (%) Example 1 85 50 2.91 × 10 ^-12 0.21 Comparative Example 1 83 70 4.10 × 10 ^-12 0.30 Comparative Example 2 84 65 4.40 × 10 ^-12 0.32 Comparative Example 3 82 80 5.11 × 10 ^-12 0.37 Comparative Example 4 82 80 1.37 × 10 ^-11 1.00

In Table 1 above,

1) The degree of crosslinking was put into 0.2-0.3 g of the thinly cut specimen in boiling xylene (Xylene) solution, measured for 24 hours, the weight of the remaining specimen was measured and calculated by the following equation (1).

[Equation 1]

Degree of crosslinking (%) = (weight of specimen before measurement-weight of specimen after measurement) ÷ (weight of specimen before measurement)

× 100

2) The thermal elongation was calculated by the following Equation 2 as the strain of the specimen measured after applying 20 N / ㎠ load for 15 minutes at 200 ℃.

[Equation 2]

Thermal elongation (%) = (standard length of specimen after measurement minus initial length of specimen) ÷

(Mark length of initial specimen) x 100

As shown in Table 1, the cable insulator composition of the present invention can be seen that the water tree growth rate is small.

The cable insulator composition of the present invention is a composition comprising a polyolefin resin blend, a crosslinking aid, a crosslinking agent, and an antioxidant, which is a base resin, and has excellent resistance to water tree growth when the composition is used as an insulator of a power cable. Excellent processing characteristics

Claims (9)

A cable insulator composition having resistance to water tree growth, a) 95.0 to 98.9 weight percent of base resin; b) 0.01 to 1.0% by weight of crosslinking aid; c) 1.0 to 3.0 weight percent of crosslinking agent; And d) 0.1 to 1.0% by weight of antioxidant, The base resin of a) At least one polymer selected from the group consisting of ethylene homopolymers and ethylene copolymers having a density of 0.87 to 0.965 g / cm 3 and a melt index of 0.1 to 50 g / 10 minutes; Metallocene polyethylene prepared using a metallocene catalyst and having a density of 0.87 to 0.92 g / cm 3 and a melt index of 0.5 to 50 g / 10 min. A cable insulator composition that is a blended polymer. delete The method of claim 1, The ethylene copolymer is polymerized from ethylene and an α-olefin having 3 or more carbon atoms, and the α-olefin having 3 or more carbon atoms is propylene, 1-butene, 1-pentene, 1-pentene, A cable insulator composition selected from the group consisting of 1-hexene and 1-octene. The method of claim 1, A cable insulator composition wherein said ethylene homopolymer is selected from the group consisting of ultra low density polyethylene, low density polyethylene and high density polyethylene. The method of claim 1, The metallocene catalyst is an organic metal compound formed by a ligand bond between a cyclopentadiene derivative and a titanium, zirconium, hafnium, or vanadium. The method according to claim 1 or 3, The ethylene copolymer has one or more selected from the group consisting of ethylene vinyl acetate, ethylene ethyl acrylate, ethylene methyl acrylate or ethylene normal butyl acrylate and has a copolymerized density of 0.90 to 0.960 g / cm 3 and a melt index of 0.1 to 30. A cable insulator composition which is a copolymer having g / 10 min. The method of claim 1, Ethylene glycol dimethacrylate, trimethol propane trimethacrylate, trimethylol propane trimethacrylate comprising a functional group selected from the group consisting of allyl, acrylate, vinyl groups Trimethylol propane triacrylate, trimethylol propane propoxylate triacrylate, triallyl isocyanurate, triallyl cyanurate, A cable insulator composition selected from the group consisting of triallyl trimelliteate and meta-phenylene-bismaleicimide. The method of claim 1, The crosslinking agent of c) is dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, tertary-butyl dicumyl peroxide, alpha Alpha-bis-tert-butylperoxy isopropyl (benzene), 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane (2,5-dimethyl-2,5-di (tertiary-butylperoxy) hexane), and di (tertiary-butyl) peroxide (di (tertiary-butyl) peroxide). The method of claim 1, The antioxidant of d) is 2,2'-thio diethyl bis- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate] (2,2'-thiodiethylbis -[3- (3,5-di-tertiary-butyl-4-hydroxy phenyl) -propionate]), pentaerythritol-terrakis- [3- (3,5-di-tert-butyl-4- Hydroxyphenyl) -propionate] (pentaaerythrityl-tetrakis [3- (3,5-di-tertiary -butyl-4-hydroxy phenyl) -propionate]), octadecyl 3- (3,5-di-tertiary -Butyl-4-hydroxy phenyl) -propionate (octadecyl 3- (3,5-di-tertiary-butyl-4-hydroxy phenyl) -propionate), triethylene glycol-bis-3 Butyl-4-hydroxy-5-methyl phenyl) propionate (triethylene glycol-bis-3 (3-tertiary-4-hydroxy-5-methyl phenyl) propionate), disteraryl thiodipropionate And at least one selected from the group consisting of dilauryl thiodipropionate.