CS252395B1 - Polymer material especially for cable products - Google Patents

Abstract

The solution concerns cable products, in which the chemically crosslinked isolation polyethylene should exhibit electrical power stress increased resistance to vandalism as well as the electric tree. The essence of the solution is that it chemically crosslinkable polyethylene is added a three-component additive containing alkxysilane formula / R2 R: Si-R, \ R. L the alkyl derivative of thiodipropionate in general of formula S (CHžCHzCOO) 2 R and a phenolic antioxidant.

Description

The invention relates to polymeric materials suitable for cable products with increased resistance to the formation of water and electric trees, in particular for high voltage high voltage cables insulated from chemically crosslinked polyethylene.

The purpose of the solution is to obtain cable products in which the insulator made of chemically cross-linked polyethylene exhibits significantly increased resistance to water and electric tree under operating conditions under electrical stress.

When using power cables insulated with cross-linked polyethylene, it can be observed that even after a relatively short period of electrical stress and relatively low electrical gradient, electrical insulation breakdown often results in a significant reduction in their reliability and durability. Analyzing the causes of this phenomenon, it was found that defects in polyethylene insulation, the so-called " water trees, which are formed in the polymer under the conditions of electrical stress and the simultaneous presence of water and also the so-called water trees. electric trees which are formed in the polymer under conditions of electrical stress in the presence of inhomogeneity in the insulation, which may be foreign impurities with higher permittivity, oxidized polymer particles and also formed water trees. Both water and electric trees significantly impair the electrical properties of the insulation and ultimately lead to electrical breakdown of the cable insulation. Moisture conducive to the formation of water trees penetrates the insulation either by production technology, i. j. in steam and cold crosslinking! water, or penetration of water from the environment in which the cables are stored during operation. A more substantial limitation of such water ingress is very costly and technically difficult.

Several methods have been proposed to prevent the formation of water trees, such as mechanical protection of the cable insulation from the ingress of water from the environment or treatment of the insulating material with additives designed to prevent water penetration into polyethylene by chemical water binding. Such additives are, for example, some organic silanes, selected aliphatic alcohols, metal salts such as MgCl 2 and calcium stearate, siloxane oligomers, substituted quinoline, allyl derivatives of aromatic and aliphatic hydrocarbons, and the like. In principle, the inhibition of the formation of electric trees is addressed by a different approach. In this field, increasing resistance is achieved by low ionizing energy additives capable of binding a portion of electrons accelerated by the electric field, such as alkylbenzenes, condensed aromatic hydrocarbons, halogenated polycyclic and aromatic hydrocarbons, derivatives of aniline and substituted aromatic diamines, and the like. or additives with higher electrical conductivity, such as, for example, metal selidimidazoline, alkylaminethylene oxide derivatives and the like, which reduce the electric pole gradient in some of the inhomogeneities occurring in the insulation as an immediate cause of electric tree formation. The fact that water trees are the seed of electric trees under certain circumstances justifies the need for a simultaneous stabilization of the polymer against the formation of both water and electric trees, which the prior art solutions do not consider.

These residuals are solved by the invention, which consists in the fact that in the simultaneous inhibition of the formation of water and electric silicon, the chemically cross-linked polyethylene contains a three-component additive composed of: the alkoxysilane or a mixture of alkoxysilanes of the general formula R 2 -R 1 -Si-R 5,

R 1 is a vinyl, meta, cover, mercaptyl, amine or epoxy radical,

R 1, R 1, R 1 are alkoxy radicals having a carbon number of C 1 to C 8 and the silicon content in the molecule is 10 to 23% by weight. The species component is an alkyl derivative of thiodipropionate

5 (CI-LC / IRCOO) zR where

R is an alkyl radical and the sulfur content of the molecule is 4 to 8% by weight. The third component is a phenolic antioxidant containing 6 to 12% by weight of sulfur.

The ratio of the individual components is in the range of 1: 1: 1 to 1: 10: 10, irrespective of their order, the total concentration of the three-component additive in the polymer being 0.3 to 3% by weight.

This combination of active ingredients achieves both the binding of water in the polyethylene cable insulation by chemical reaction with the alkoxy group of the present silane, thereby reducing the likelihood of formation of water trees, and the other two inhibit the radical degradation processes of polyethylene which interact and promote both water and electric trees.

When applying the solution according to the invention, the additives are homogenized with the polyethylene melt at a temperature of 110 to 200 ° C, either in the preliminary preparation of the mixture or only during the extrusion extrusion. The cable insulation is extruded in the usual manner at a temperature of 110 to 200 ° C and subsequent crosslinking is carried out at a temperature of 200 to 400 degrees Celsius.

The following examples of the composition of polyethylene simultaneously inhibited against the formation of both water and electric trees explain the possible combinations of the additives used.

Example 1

In a screw mixer at 100 degrees Celsius, 100 wt. polyethylene with a melt flow index of 2 g / 10 min. 0.3 wt. vinyl-tri (2-methoxyethoxy) silane, 0.5% by weight, dilauryl thiodipropionate -a 0.3% by weight 4,4'-thiobis / 3-methyl-6-tert-butylphenol. , 5 wt.% of dicumyl peroxide, and the mixture was further homogenized for 3 minutes. the blend is compressed into 4 mm thick plate while crosslinking, i.e. for 20 minutes compression at ^180? C

The plates were subjected to a water-tree resistance test in the electrode tip-surface arrangement. The tip to which a 3 kV / / 50 Hz voltage was applied was formed by a needle extruded into a prism-shaped sample. The opposing surface was immersed in water, which formed a kind of electrode. The distance of the needle tip from this area was 2 mm. After 5 days of such stressing of 10 samples, the length of the water tree formed at the tip of the needle was measured and calculated, the mean value being, in this case, 5 µπι. The average length of the water trees of polyethylene crosslinked by the same procedure without the mentioned stabilizing additives was 24 μΐη. For further evaluation of the polyethylene resistance to water stress under electrical stress, samples were prepared with a cylindrical depression with a thickness of 0.1 mm and a 0.5 mm edge. 40 mm diameter glass beads filled with distilled water were pressed on both sides of the sample. A voltage was applied to the thus formed water electrodes so that the measured portion of the sample was subjected to a 25 kV / mm field. The time to cross-section of 10 samples was monitored, with a mean value of 80 hours compared to 15 hours found in a crosslinked sample without stabilizers.

To assess the resistance of polyethylene to the formation of electric trees, samples of the same cylindrical shape were used as in the previous test, aluminum electrodes were applied to both samples on both sides and applied to a voltage so that the electric pole intensity in the measured part was 30 kV millimeter. The time to breakthrough of 10 samples was monitored with a mean value of 80 h. For crosslinked polyethylene without stabilizing additives, the mean value is up to 60 h.

Example 2

By the same procedure as in Example 1, a crosslinkable mixture was prepared having the following composition: 100 wt. % polyethylene with a melt index of 7 g / 10 min, 1.85 wt. % dicumyl peroxide, 0.5 wt. vinylsilane containing 19% silicon, 0.6% wt. % dilauryl thiodipropionate and 0.4 wt. 4,4'-thiobis (3-methyl-6-tert-butylphenol) 4 mm thick plates and cylindrical samples were pressed from the mixture similar to Example 1 and the resistance to formation of both water and electric trees was evaluated. The time to break through in case of stress in the presence of water was 90 h and the time to break through in case of electrical stress without water was 180 µm.

Example 3

0.3 wt. % vinyltriethoxysilane, 0.3 wt. % distearyitiodipropionate and 0.3 wt. 2,2'-thiobis (4-methyl-6-tert-butylphenol) which were mixed into molten polyethylene with a melt index of 2 g / 10 min by mixing the ingredients for 5 minutes followed by 1.5% mixing for 3 minutes peroxide-bis (tert-butylperoxiisopropyl) benzene at 150-C in a screw mixer. After pressing the test samples as in Example 1, the resistance to formation of water and electric trees was evaluated. The length of the formed water tree was 6 μηι. water was 45 h and the time to break through the electric field stressed samples without water was 75 h.

Example 4

The same procedure was used to prepare the mixture as in Example 1, wherein the mixture consisted of 100 wt. % polyethylene having a melt index of 20 g / 10 min., 3.8 wt. % dicumyl peroxide, 1 wt. % of methacryloxypropylmethoxysilane, 0.5 wt. % dioctyltiodipropionate and 0.5 wt. 4,4'-thiobis (3-methyl-6-tert-butylphenol). After preparing and evaluating the test samples as in Example 1, the average water tree length was 4 µm, the time to break through the samples stressed in the presence of water 50 h and the time to break through the electric furnace stressed samples without water 92 h.

Example 5

100 wt. of crosslinkable polyethylene with a relative elongation at thermal and mechanical stress of 50 to 120%, which was melted at 130 ° C in a screw mixer and homogenized with 2% by weight for 5 minutes. % γ-aminopropyltrimethoxysilane, 0.4 wt. % dioctyltiodipropionate and 0.6 wt. 2,2'-Thiodiethylbis- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate] Test samples as in Example 1 were prepared from the mixture, followed by testing as described in Example 1. Water Length time in the samples tested was 2 μΐη, the time to break through the samples stressed in water was 70 h and the time to break through the samples stressed in the electric field without water was 75 h. For this commercial crosslinkable polyethylene without additives when water is applied for 20 h and the time to break through the electric field without water is 65 h.

Example 6

Up to 100 wt. of molten commercial crosslinkable polyethylene was added at 150 ° C to 1.5 wt. χ-mercaptopropyltrimethoxysilane, 1 wt. % dioctyltiodipropionate and 0.3 wt. 4,4'-thiobis (3-methyl-6-tert-butylphenol). As in Example 1, test samples were prepared to evaluate the resistance to formation of water and electric trees. The length of the formed water tree was 5 gm, the time to break through in the presence of water 65 h and the time to break through after electrical stress without water 95 h.

Example 7

The same procedure was used to prepare the mixture as in Example 1, wherein the mixture consisted of 100 wt. % polyethylene having a melt flow index of 2 g / 10 min., 0.7 wt. peroxide-bis (tert-butylperoxy-isopropyl) benzene,

0.6 wt. % of a mixture of γ-glycidoxypropyitrimethoxysilane and vinyltrimethoxysilane in a 1: 1 ratio to each other, 0.7 wt. % dilauryl thiodipropionate and 0.4 wt. 2,2'-thiobis (4-methyl-6-tert-butylphenol). The preparation of the test samples and their evaluation was as in Example 1. The water tree length was 8 μΐη, the time to break through after water stress was 45 h and the time to break through after the electric field without water was 100 h.

After the modifications according to Examples 1 to 7, the important electrical and electrical insulation properties of the material remain unchanged compared to the unmodified types, i. j.

tg S maximum 4.10 ⁴ permittivity maximum 2,75 electrical strength minimum 35 kV / min. · Internal resistance at least 10 ~ ^{14 14} . m.

The solution according to the invention enables efficient production of cable articles with the required higher technical parameters. Compared to the existing solutions, the reliability and service life of the products are prolonged. Increased effect of resistance to two serious destructive phenomena - water and electric trees - is achieved simultaneously.

The implementation of the invention does not require changes in technology, and the production of cable products is customary as in the prior art application of similar crosslinkable polyethylene materials in the cable industry. The marked changes in composition also have a positive effect on some electrical, physical and mechanical properties of the end products.

Claims (2)

Polymeric material especially for cable products with increased resistance to formation of water and electric trees, cross-linked or cross-linked with peroxides, characterized in that it consists of branched polyethylene with a melt flow index of 0.2 to 20 g / / min, containing a three-component stabilizing additive in an amount of 0.3 to 3 wt. a base polymer consisting of alkoxylanes or a mixture of alkoxylanes of the general formula / R2 R1-Si-R5, R4 wherein: R 1 is vinyl, methacrylic, mercapto, amino or epoxy radical, R 2 to R 4 are alkoxy radicals having a carbon number of C 1 to C 6 and a silicon content in the range of 10 to 25% by weight, followed by an alkyl derivative of the thiodipropionate of the general formula S (CH 2 CH 2 COO) 2 R, R is an alkyl radical and the sulfur content of the molecule is 4 to 8% by weight, and the phenolic type antioxidant is 6 to 12% by weight. Sulfur, which are in a ratio of 1: 1: 1 to 1:10: 10 in any order, wherein in the case of uncrosslinked polyethylene it contains 0.2 to 4.9 wt. dialkyl peroxide as crosslinking agent.