KR20010049164A - Composition for electric cables - Google Patents

Abstract

The present invention relates to a composition for an electric cable. The composition of the present invention comprises an ethylene copolymer comprising (poly) alkylene glycol mono (meth) acrylate of the formula (I). The composition of the present invention can be used as an insulating layer or semiconductive layer of an electric cable.

Where

R ₁ is H or CH ₃ ,

R ₂ is H or CH ₃ ,

n is 1 to 20.

Description

Composition for electric cable {COMPOSITION FOR ELECTRIC CABLES}

The present invention relates to a composition for an electric cable. More particularly, the present invention relates to (meth) acrylate-ester containing ethylene polymers usable in compositions for electrical cables, in particular for inner and outer semiconducting layers for electrical cables as well as for insulating layers.

Electrical cables for medium and high voltages, in particular power cables, consist of a plurality of polymer layers extruded around an electrical conductor. Electrical conductors are usually first covered with an inner semiconductor layer and then with an insulating layer, then with an outer semiconductor layer, then if necessary, with a waterproofing layer, and with a protective layer on the outside.

The insulating layer and the semiconductor layer generally consist of crosslinked ethylene homopolymers and / or copolymers. In connection with the extrusion of cables, peroxides, for example LDPE (low density polyethylene, ie polyethylene produced by radical polymerization at high pressure) crosslinked by the addition of dicumyl peroxide, are currently the main cable insulation material. A limitation of conventional LDPE is that, under the presence of moisture and the action of a strong electric field, it is exposed to the formation of dendrite cracking defects called water trees, which can lead to breakdown and possible electrical disturbances. Is in the tendency of This tendency is strongly influenced by the heterogeneity, microcavity and the presence of impurities in the material. Water trituration has been carefully studied since the 1970s, when polymeric materials, especially crosslinked polyethylene, were the main insulating material for electrical cables for medium and high voltages. Over the past few years, these studies have improved the quality and cleanliness of cable construction, manufacturing methods and materials used. These improvements have increased the life of cables produced. However, there is a need for more improved materials with regard to resistance to water trituration. Such improved resistance to water triaging is desirable for semiconductor layer materials as well as for insulating layer materials of electrical cables. Another important characteristic of the semiconducting material of electrical cables is their high resistance to cracking formation.

European Patent Application EP-A-0 057 604 discloses 0.1 to 20 weights of polyethylene glycol having a molecular weight of about 1000 to 20,000 in a semiconducting composition consisting mainly of 5 to 50 weights of carbon black based on the weight of the polyolefin and the total composition. It is known to suppress water trituration by addition. This composition is used for the semiconductive layer of an electric cable, and it is thought that by adding polyethylene glycol, the water tree which grows to an insulating layer from the interface between an insulating layer and a semiconductive layer can be removed.

Moreover, US patent application US-A-4,812,505 describes a composition that can be used as an insulating layer in electrical cables and is resistant to water trituration. The composition comprises 0.1 to 20 weights of polyethylene glycol having a molecular weight of about 1000 to 20000, in addition to a copolymer of ethylene and one or more α-olefins having 4 to 8 carbon atoms, for example 1-butene, 1-hexane or 1-octane. do.

A disadvantage associated with the use of water tree inhibitory additives, such as polyethylene glycol, is due to the insufficient compatibility of polyethylene glycol with the base polymer (polyethylene), especially when the molecular weight of polyethylene glycol is small, There is a danger of sweating out. On the other hand, when the molecular weight is large, the possibility of efficient mixing is adversely affected.

European Patent Application EP-A-0 538 033 discloses, in addition to ethylene, an agent selected from the group consisting of vinyl ethers, allyl esters and acrylic or methacrylic acid esters containing from 7 to 30 weight percent hydroxy acetate, and free of hydroxyl groups. Extruded ethylene hydroxy acrylate copolymers or terpolymers are described which comprise from 0 to 40 weight of 3 monomers. Hydroxy acrylate may consist of any ester of glycol or polyglycol with acrylic acid or methacrylic acid, but hydroxyethyl methacrylate, hydroxymethyl methacrylate, hydroxypropyl acrylate or hydroxypropyl methacrylate It is preferable that it is a rate. According to the patent application, hydroxy acrylates are already known in connection with hot melts and the extruded products according to the patent application, for example films, are hydrophilic, absorb and transfer moisture, and ethylene hydroxy acrylate Copolymers, for example, improve adhesion to polar plastics and other materials, and improve strength properties due to hydrogen bonding. The patent application does not describe the use of polymers in compositions for electrical cables.

From Derwent Abstract 77-85827Y / 48 of Japanese Patent Application JP 7644050, 25 to 99.9 weights of ethylene, 75 to 0.1 weight of polyalkylene glycol monoacrylate and 0 to 65 weight of other ethylenically unsaturated monomers Including ethylene copolymers are known. It is known that this polymer can be used as a coating agent for metals, paper, wool, etc. in paints, inks, and the like, as an adhesive. The use of polymers in electrical cables is not described.

According to the present invention, it has surprisingly been found that the use of (poly) alkylene glycol mono (meth) acrylates as comonomers in ethylene polymers can provide compositions for electrical cables with improved resistance to water trituration.

According to the present invention there is provided a composition for an electrical cable comprising an ethylene copolymer comprising (poly) alkylene glycol mono (meth) acrylate having the formula (I) as comonomer:

Where

R ₁ is H or CH ₃ ,

R ₂ is H or CH ₃ ,

n is 1-20.

More particularly, the use of the compositions according to the invention in insulating and semiconducting layers for electrical cables is contemplated.

Other features and advantages of the invention will be apparent from the following detailed description and the appended claims.

As used herein, the term "ethylene copolymer" means an ethylene based polymer obtained by the polymerization of ethylene with at least one other monomer, one of these other monomers being a (poly) alkylene glycol having formula (I) It consists of mono (meth) acrylate. Preferably, the ethylene copolymer consists of a polymer of ethylene and a monomer of formula (I) or a polymer of ethylene, a monomer of formula (I) and a further monomer, in the latter case being termed terpolymer.

As used herein, the terms "(meth) acrylic acid" and "(meth) acrylate" refer to acrylic acid and acrylate as well as methacrylic acid and methacrylate.

As can be seen from the above formula (I), the (poly) alkylene glycol mono (meth) acrylate of the formula (I) is an ester of acrylic acid or methacrylic acid with (poly) alkylene glycol, and the alkylene glycol is ethylene Is selected from glycol or propylene glycol, and the number of alkylene oxide units is 1 to 20, i.e. in formula (I), n is 1 to 20, preferably 1 to 10. Preferably, R ₁ in formula (I) is CH ₃ , ie esterified acid is methacrylic acid, and R ₂ in formula (I) is H, ie esterified (poly) alkylene glycol is (poly) ethylene Glycol. When n is 1, the monomer of formula (I) is hydroxyethyl methacrylate (HEMA) in which R ₁ and R ₂ have the defined preferred meanings. When n is 6, the monomer of formula (I) is hexaethylene glycol methacrylate, in which R ₁ and R ₂ have the defined preferred meanings.

The amount of comonomer of formula (I) in the ethylene copolymer can have a wide range, but constitutes about 0.1 to 15 weight, more preferably about 2 to 14 weight of the copolymer.

As mentioned above, the ethylene copolymer may optionally comprise further comonomers in addition to the comonomer of formula (I), and it is preferred that the comonomer contains such additional monomers, ie the copolymer is a terpolymer. Such additional comonomers may be selected from ethylene and monomers capable of copolymerizing with (poly) alkylene glycol mono (meth) acrylates of formula (I). Such monomers are well known to those skilled in the art and need not be enumerated extensively, but include, for example, vinylic unsaturated monomers such as C ₃ -C ₈ alpha olefins such as propene, butene and the like; Mention may be made of vinylically unsaturated monomers containing functional groups such as hydroxyl groups, alkoxy groups, carbonyl groups, carboxyl groups and ester groups. Such monomers include, for example, (meth) acrylic acid and alkyl esters thereof, such as methyl-, ethyl- and butyl (meth) acrylates; Vinyl unsaturated hydrolyzable silane monomers such as vinyl trimethoxysilane; Vinyl acetate and the like.

The amount of additional comonomer (s) other than the (poly) alkylene glycol mono (meth) acrylates of formula (I) is 0 to about 40 weight, preferably about 1 to 30 weight of the ethylene copolymer.

For the aforementioned monomers, the sum of all monomer contents is 100 weights.

Ethylene copolymers of the present invention can be prepared by graft copolymerization or free radical initiated high pressure polymerization.

Since graft copolymerization is a polymerization method well known in the art, it will not need to be described in detail. Generally, graft copolymerization involves copolymerization of vinyl unsaturated monomers with ethylene polymers such as ethylene homopolymers or ethylene copolymers under the influence of free radical initiators such as dicumyl peroxide (DCP), a peroxide. Is performed. The temperature of the graft copolymerization should be sufficient for free radicals to be formed to decompose the free radical initiator, which means about 150 to 200 ° C. using dicumyl peroxide as an initiator, wherein the polymerization, for example, It can actually be achieved by mixing in the extruder.

Free radical initiated high pressure polymerizations, which are also well known in the art, allow monomers to be reacted under the influence of radical initiators such as peroxides, hydroperoxides, oxygen or azo compounds, in reactors such as autoclaves or tube reactors, It is usually carried out by reacting at a high pressure of about 100 to 300 MPa and an elevated temperature of about 80 to 300 ° C. Once the reaction is complete, the temperature and pressure are lowered and the resulting unsaturated polymer is recovered. For further details on the preparation of ethylene polymers by high pressure polymerization during free radical initiation, see Encyclopedia of Polymer Science and Engineering, Volume 6 (1986), pp 383-410, in particular pp 404-407. Can be.

As described above, according to the present invention, when (poly) alkylene glycol mono (meth) acrylate of formula (I) is used in an ethylene copolymer, the water tree resistance (WTR) is improved, whereby such an ethylene copolymer It has been found to be usable as a material for electrical cables, for example as an insulating layer material or a semiconducting layer material. The (poly) alkylene glycol mono (meth) acrylate of formula (I), which produces water tree resistance, is polymerized into a polymer, which is firmly anchored in the polymer molecule, moving or swapping, unlike when using conventional WTR additives. Cannot be wetted out. This is a particular advantage of the polymers of the present invention. In addition to advantageous water tree resistance, it has been found that other advantageous and desirable properties are also derived when the ethylene copolymer of the present invention is used as a material in electrical cables. Thus, it has been found that the ethylene copolymer according to the invention results in an improvement in dielectric strength, useful for both the insulating and semiconducting layers of electrical cables. In addition, the ethylene copolymer of the present invention has good environmental stress cracking resistance (ESCR), useful for semiconducting layers of electrical cables.

The invention is further illustrated by, but not limited to, the following examples and comparative examples.

Example 1

The water tree resistance (WTR) for the three polymer compositions, namely Polymer 1, Polymer 2 and Polymer 3, was measured by the so-called Ashcraft test.

The Ashcraft test, a test method for determining the WTR properties of polymers, is described in Ashcraft, A. Ashcraft, A. C., "Water Treeing in Polymeric Dielectrics", World Electrotechnical Congress in Moscow, USSR, 22 June 1977. By ashcraft testing, a well characterized effect, i.e. a pronounced moisture filled indentation, was provided by the needles in the press-molded cup. A voltage of 5 kV / 6 kHZ was applied across the water, while the bottom of the cup was connected to ground. The temperature was kept constant at 65 ° C. The average length of the water tree after aging for 72 hours was considered as a measure of the growth rate of the water tree in the particular insulating material.

For testing, pressure molded test pieces were prepared from various polymers, of which polymer 1 consisted of low density polyethylene (LDPE) with a melt flow rate (MFR) of 2 g / 10 min, used as reference, and polymer 2 0.56 parts by weight of polyethylene glycol (PEG) having a molecular weight of about 20000 consisted of 99.1 parts by weight of the same type of LDPE, added as a conventional formulation that inhibits water tritization, and Polymer 3 is a composition according to the invention, ethylene, methylacrylic Consisting of 79.8 parts by weight of the same type of LDPE, 20.0 parts by weight of a terpolymer of late (13 weights) and hexaethylene glycol monomethacrylate (3 weights) of formula (I), wherein in formula (I), R ₁ Is CH ₃ , R ₂ is H and n is 6. The polymer composition also contained about 2 parts by weight of dicumyl peroxide as well as a stabilizer (about 0.2 parts by weight). The results from the ashcraft test are listed in the table below.

Composition Water tree Average length (μm Average length () Polymer 1 (standard) 374 100 Polymer 2 (Comparative) 149 40 Polymer 3 (invention) 126 34

As a result of the tests, it was clearly shown that the WTR properties of the compositions according to the invention were improved.

Example 2

In this example, the water tree resistance of the two compositions according to the invention was compared by Ashcraft test. The composition is formula (I) wherein low density polyethylene (LDPE) with a MFR of 2 g / 10 min is 20 weights of ethylene, vinyl acetate and hydroxyethyl methacrylate (R ₁ is CH ₃ , R ₂ is H and n is 1). HEMA), a comonomer of HEMA), was formulated in combination with various amounts of water tree inhibitory polymer, consisting of a 9 weight terpolymer. One composition contained 6.5 weight of water tree inhibitory polymer, while the other composition contained 14 weights. By ashcraft testing, the average length of the water tree was calculated as as of the average length of the water tree relative to the reference polymer in Example 1, and was 46 for the composition having EVA-HEMA 6.5 weight and was applied to the composition having EVA-HEMA 14 weight. About 21. Therefore, it is evident that the water tree resistance increases with increasing content of the water tree inhibitory polymer containing the monomer of formula (I).

Example 3

In this example, the dielectric strengths of three semiconducting polymer compositions, i.e., polymers A, B, and C, which constitute the internal semiconductor of the electrical cable, were measured.

The first composition (Polymer A) was composed of ethylene vinyl acetate copolymer (EVA) having 18 weights of vinyl acetate, containing about 40 weights of carbon black to be semiconductive. This composition was used as a reference.

The second composition (polymer B) was composed of the same EVA polymer as the first composition, except that 0.6 weight of polyethylene glycol (PEG) having a molecular weight of about 20000 was added. The second composition also contained about 40 weights of carbon black. This composition was used as an example of a conventional composition.

The third composition (polymer C) consisted of a terpolymer of ethylene, 18 weights of vinyl acetate and 3 weights of monomers of formula (I). The monomer of formula (I) consisted of hexaethylene glycol monomethacrylate, that is, in formula (I), R ₁ is CH ₃ , R ₂ is H and n is 6. This composition was a composition according to the present invention.

The three compositions, when viewed from the inside outwards, consist of a 1.4 mm copper conductor, an inner semiconducting layer with an outer diameter of 2.8 mm, an insulating layer with an outer diameter of 5.8 mm and an outer semiconducting layer with an outer diameter of 6.1 mm. It was integrated as an internal semiconducting layer. The insulating layer consisted of low density polyethylene with an MFR of 2g / 10min, and the outer semiconducting layer consisted of ethylene butyl acrylate copolymer added with about 40 weight of carbon black.

The dielectric strength test was developed by Alcatel AG & Co. Hannover, Germany, and described by Land HG, Schadlich Hans, "Model Cable Test for Evaluating the Ageing Behavior Under Water. Influence of Compounds for Medium Voltage Cables ", Conference Proceedings of Jlcable 91, 24-28 June 1991, Versaille, France. As a dielectric strength value, it was found to be 63 of E _max from a Weibull diagram (kV / mm). Dielectric strength was measured on the one hand after aging for 16 hours at 90 ° C. in air, and on the other hand, after aging for 1000 hours at 9 kV / mm in 85/70 ° C. water. . The test results are shown in the table below.

Composition Dielectric strength A (kv / mm) B (kV / mm) Polymer A (standard) 77.9 39.6 Polymer B (Prior Art) 95.6 40.6 Polymer C (Invention) 93.6 45.4

As can be seen from the test results and the gating, the composition according to the present invention showed good properties as an internal semiconducting layer, and especially had excellent electrical dielectric strength after aging for 1000 hours at 9 kV / mm in 85/70 ° C water. .

Example 4

In this example, the dielectric strength is about 15 weights of ethylene, methylacrylate and hexaethylene glycol monomethacrylate as the inner semiconducting layer, ie about 2 weights of the same monomer of formula (I) in Example 3, and An electrical cable having about 40 weights of carbon black was tested in a similar manner to Example 3. In the test, a dielectric strength (63 of E _max ) of 59.4 kV / mm was obtained after aging for 1000 hours at 9 kV / mm in 85/70 ° C. water.

Example 5

In this example, stress cracking resistance (ESCR) was tested, which is an important characteristic, in particular for the outer semiconducting layer of electrical cables. The test was carried out in 10 Igepal at 50 ° C. on the one hand and in air at 50 ° C. on the other hand according to ASTM D 1693.

Three semiconductive polymer compositions (polymers 1, 2 and 3) were tested and these compositions were as follows.

Polymer 1 (comparative composition): Ethylene vinyl acetate copolymer having 9 weights of vinyl acetate and having an MFR of 9.5dg / 10 min. Moreover, the composition contained about 36 weight of carbon black.

Polymer 2 (comparative composition): Ethylene vinyl acetate copolymer having 18 weights of vinyl acetate and having an MFR of 9 dg / 10 min. Moreover, the composition contained about 40 weight of carbon black.

Polymer 3 (composition of the invention): Ethylene vinyl acetate hydroxyethyl methacrylate terpolymer having 9 weights of vinyl acetate, 10 weights of hydroxyethyl methacrylate and MFR 6dg / 10 min. Moreover, the composition contained about 36 weight of carbon black.

The test results of the ESCR are shown in the table below and expressed as the number of test fragments in all 10 test fragments, measured in units of time and broken down in the test after a certain time.

Composition Number of test fragments destroyed / hour ESCR (air 50 ℃) ESCR (10Igepal) Polymer 1 10/0 9/0 Polymer 2 3/4 9 / 1.5 Polymer 3 1/6 7/24

As can be seen from the test results, the composition according to the invention had a markedly improved ESCR, which makes it very suitable as a material for the outer semiconducting layer of electrical cables.

Claims (10)

A composition for an electrical cable, comprising an ethylene copolymer comprising (poly) alkylene glycol mono (meth) acrylate of formula (I) as comonomer: Where R ₁ is H or CH ₃ , R ₂ is H or CH ₃ , n is 1-20. The composition of claim 1, wherein R ₁ is CH ₃ , R ₂ is H, and n is 1-10. The composition of claim 1 or 2, wherein n is one. 3. A composition according to claim 1 or 2, wherein n is 6. 3. The composition of claim 1, wherein the (poly) alkylene glycol mono (meth) acrylate of formula (I) constitutes 0.1 to 15 weight of the ethylene copolymer. 3. The method of claim 1, wherein the ethylene copolymer comprises further vinylic unsaturated comonomers in addition to the (poly) alkylene glycol mono (meth) acrylates of formula (I). 4. Composition. The method of claim 6 wherein the further vinylic unsaturated monomer is selected from the group consisting of C ₃ -C ₈ alpha olefins, (meth) acrylic acid and esters thereof, vinyl acetate, and vinylic unsaturated hydrolyzable silane monomers. Composition. 8. A composition according to claim 6 or 7, wherein the further vinylic unsaturated comonomer comprises 1 to 40 weight of the ethylene copolymer. The composition of claim 1 or 2, wherein the insulation layer of the electrical cable is formed. The composition of claim 1, wherein the composition comprises an amount of carbon black sufficient to form a semiconducting layer of the electrical cable and to make the composition semiconductive.