CN111393785B

CN111393785B - Antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material and preparation method thereof

Info

Publication number: CN111393785B
Application number: CN202010080837.7A
Authority: CN
Inventors: 赵洪; 张城城; 李春阳; 孙伟峰
Original assignee: Harbin University of Science and Technology
Current assignee: Harbin University of Science and Technology
Priority date: 2020-02-05
Filing date: 2020-02-05
Publication date: 2022-06-21
Anticipated expiration: 2040-02-05
Also published as: CN111393785A

Abstract

The invention discloses an antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material and a preparation method thereof, and belongs to the technical field of high-voltage direct-current cable preparation. The invention solves the problems that the antioxidant added in the existing crosslinked polyethylene insulating material is easy to migrate and separate out loss in the production, storage and use processes of cables, and meanwhile, the antioxidant has poor compatibility with resin and low effective concentration, thereby reducing the antioxidant effect of the antioxidant. The invention adopts dicumyl peroxide as a cross-linking agent and an initiator, and adopts a reactive antioxidant to prepare the antioxidant graft cross-linked polyethylene insulating material. Because the reactive antioxidant contains polar groups, the polar groups in the antioxidant can be uniformly and densely distributed in the material and introduced into a deep trap state through a grafting reaction, initial carriers in the material can be trapped to form a charge layer and a coulomb force field, and the injection of electrode charges is retarded, so that the accumulation of space charges is inhibited, and the reactive antioxidant has higher withstand electric field strength.

Description

Antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material and preparation method thereof

Technical Field

The invention relates to an antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material and a preparation method thereof, belonging to the technical field of high-voltage direct-current cable preparation.

Background

The direct current cable line has the advantages of small loss, unlimited transmission distance, high operation stability, capability of being connected with an asynchronous power grid and the like, is increasingly emphasized in application, and is suitable for long-distance cross-sea transmission, urban load center capacity increase, wind power grid connection and the like. The extruded polyethylene insulated direct current cable is widely applied to power transmission and distribution engineering due to low price, large transmission capacity, light weight, simple structure of the cable and accessories, convenient installation and maintenance, no oil leakage risk, better mechanical property, dielectric property and chemical stability. However, the polyethylene insulating material has a low melting point, a working temperature of generally below 70 ℃, limited electrical and mechanical properties, and poor environmental stress cracking resistance, and in order to further increase the working temperature and working voltage of the insulating material, the polyethylene may be crosslinked to produce crosslinked polyethylene. The crosslinked polyethylene has good heat resistance and mechanical property, and can endure high working temperature and electric field intensity.

The crosslinked polyethylene is used as a main insulating material of the cable, and is easy to age under the action of heat and oxygen in the production, storage and use processes, so that the change of the microscopic molecular structure of the crosslinked polyethylene and the degradation of the material are caused, the crosslinking degree, the dielectric property, the mechanical property and the thermal stability of the insulating material of the cable are influenced, and the running stability and the service life of the cable are reduced. The antioxidant can delay the oxidative aging of the polymer and is an essential component of the crosslinked polyethylene cable insulation material. The antioxidants used in the crosslinked polyethylene cable insulation material mainly comprise antioxidants 300, 1076, 1035, 1010 and the like, but the antioxidants belong to additive antioxidants, are easy to migrate, precipitate and lose in the production, storage and use processes of cables, and have poor compatibility with resin and low effective concentration, so that the antioxidant effect of the antioxidants is reduced. Therefore, it is necessary to provide an antioxidant graft type high voltage direct current cable crosslinked polyethylene insulation material and a preparation method thereof.

Disclosure of Invention

The invention provides an antioxidant graft type high-voltage direct-current cable crosslinked polyethylene insulating material and a preparation method thereof, aiming at solving the problems that an antioxidant added in the existing crosslinked polyethylene insulating material is easy to migrate, precipitate and lose in the production, storage and use processes of a cable, and meanwhile, the antioxidant has poor compatibility with resin and low effective concentration, so that the antioxidant effect of the antioxidant is reduced.

The technical scheme of the invention is as follows:

an antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material is prepared from 100 parts by weight of low-density polyethylene, 0.02-5 parts by weight of dicumyl peroxide and 0.01-10 parts by weight of a reactive antioxidant; the reactive antioxidant has a grafting group, an aging-resistant group and a polar group.

Further limiting, the grafting group of the reactive antioxidant is a double bond group, and the double bond group is vinyl, maleimide group or acryloyl group.

Further limited, the aging resistant group of the reactive antioxidant is a hindered phenol group or a hindered amine group.

Further limited, the polar group of the reactive antioxidant is hydroxyl, amino, carbonyl, benzene ring, ester group or amide group with the function of inhibiting space charge.

Further defined, the reactive antioxidant is 2- (2-hydroxy-3-tert-butyl-5-methylbenzyl) -4-methyl-6-tert-butylphenyl acrylate, N- (4-anilinophenyl) methacrylamide, N- (4-anilinophenyl) maleimide, N- (3-methacryloyloxy-2-hydroxymethyl) -N' -phenyl-p-phenylenediamine, 2,4, 6-triallylphenol or 3, 5-di-tert-butyl-4-hydroxybenzyl acrylate.

Further limited, dicumyl peroxide is 1.2-3 parts.

A preparation method of an antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material comprises the following steps:

mixing and granulating low-density polyethylene, dicumyl peroxide and a reactive antioxidant to obtain granules;

and step two, carrying out crosslinking and grafting treatment on the granules obtained in the step one to obtain the antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material.

Further limiting, the specific operation process of the step one is as follows: mixing low-density polyethylene, dicumyl peroxide and a reactive antioxidant uniformly at the temperature of 100-120 ℃, and then granulating to obtain granules.

Further limiting, the specific operation process of the step one is as follows: uniformly mixing low-density polyethylene and a reactive antioxidant at the temperature of 130-200 ℃, soaking the mixed material in 60-90 ℃ liquid-phase dicumyl peroxide for 2-18 h, and granulating to obtain granules.

Further, in a laboratory, the specific operation process of the second step is as follows: and (3) putting the granules into a flat vulcanizing machine, carrying out hot press molding under the conditions that the temperature is 90-130 ℃ and the pressure is 10-20 MPa, then carrying out cross-linking and grafting for 20-50 min by using the flat vulcanizing machine under the conditions that the temperature is 140-200 ℃ and the pressure is 10-20 MPa, and carrying out cooling molding to obtain the antioxidant grafted high-voltage direct-current cable cross-linked polyethylene insulating material.

Further, in the cable production, the specific operation process of the second step is as follows: and extruding the granules into cable insulation through an extruder, feeding the cable insulation into a high-temperature high-pressure crosslinking pipeline, and crosslinking and grafting for 10-60 min under the conditions that the temperature is 150-270 ℃ and the pressure is 0.6-1.2 MPa to obtain the antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulation material.

The invention has the following beneficial effects: the invention adopts dicumyl peroxide as a cross-linking agent and an initiator, and adopts a reactive antioxidant to prepare the antioxidant graft cross-linked polyethylene insulating material. Because the reactive antioxidant contains polar groups, the polar groups in the antioxidant can be uniformly and densely distributed in the material and introduced into a deep trap state through a grafting reaction, initial carriers in the material can be trapped to form a charge layer and a coulomb force field, and the injection of electrode charges is retarded, so that the accumulation of space charges is inhibited, the reactive antioxidant has high withstand field strength, and can be used for manufacturing high-voltage direct-current cables. The preparation method of the invention grafts the reactive antioxidant to the polyethylene molecular chain while the polyethylene is subjected to crosslinking reaction through one-step crosslinking and melt grafting processes, so that the small molecular antioxidant is fixed on the crosslinked polyethylene molecular chain, the antioxidant is not easy to migrate and precipitate to cause loss in the cable production, storage and use processes, and has good compatibility with resin, so that the effective concentration can be increased, and the insulating material has good thermo-oxidative aging resistance, and the crosslinking process of the polyethylene is promoted without influencing the grafting process of the polyethylene, so that the antioxidant grafted crosslinked polyethylene has high crosslinking degree, and good mechanical properties are ensured.

Drawings

FIG. 1 is a space charge distribution diagram of a pure crosslinked polyethylene insulation material prepared in comparative example 1;

FIG. 2 is a space charge distribution diagram of the antioxidant 1010/crosslinked polyethylene insulation material prepared in comparative example 2;

FIG. 3 is a space charge distribution diagram of the antioxidant-grafted crosslinked polyethylene insulation material prepared in example 1;

FIG. 4 is a plot of the density-of-state of the pure cross-linked polyethylene of comparative example 1 calculated on a first principle;

FIG. 5 is a first order theory calculated density-of-state curve for the antioxidant-grafted cross-linked polyethylene of example 1;

FIG. 6 is a space charge distribution diagram of the antioxidant-grafted crosslinked polyethylene insulation material prepared in example 2;

FIG. 7 is a first order theory calculated density-of-state curve for the antioxidant-grafted cross-linked polyethylene of example 2;

FIG. 8 is a first order theory calculated density-of-state curve for the antioxidant graft cross-linked polyethylene of example 3;

FIG. 9 is a first order theory calculated density-of-state curve for the antioxidant graft crosslinked polyethylene of example 4;

FIG. 10 is a first order theory calculated density-of-state curve for the antioxidant graft crosslinked polyethylene of example 5;

FIG. 11 is a first order theory calculation of density-of-states curve for the antioxidant-grafted cross-linked polyethylene of example 6.

Detailed Description

The experimental procedures used in the following examples are conventional unless otherwise specified. The materials, reagents, methods and apparatus used, unless otherwise specified, are conventional in the art and are commercially available to those skilled in the art.

Example 1:

uniformly mixing 40g of low-density polyethylene and 0.12g of reactive antioxidant N-4 (anilinophenyl) methacrylamide by using a high-speed mixer, introducing the mixture into a co-rotating parallel double-screw mixer by using a metering and feeding system for mixing, wherein the mixing temperature is 180 ℃, the mixed material is subjected to liquid phase impregnation for 10 hours at 80 ℃ by using 0.8g of dicumyl peroxide, and then the mixed material enters a single-screw granulator for granulation to obtain granules mixed with a crosslinking agent, the granules are placed into a flat vulcanizing machine for hot press molding at 110 ℃ and 15MPa, then the granules are placed into a flat vulcanizing machine at 175 ℃ and 15MPa for crosslinking and grafting for 30 minutes, and cooling and molding are carried out to obtain the antioxidant N-4 (anilinophenyl) methacrylamide grafted high-voltage direct-current cable crosslinked polyethylene insulating material film sample. Then, a DC field of-40 kV/mm was applied to a film sample of 300 μm in thickness of the insulating material, and the space charge density distribution of the sample was measured at intervals of 5s within 40min of pressurization as shown in a in FIG. 3, and then, after the short-circuiting was released, the space charge density distribution of the sample was measured at intervals of 3s within 30min of short-circuiting as shown in b in FIG. 3. And performing other performance tests on the insulating material film sample, wherein the gel content is 88.36%, the breaking elongation is 482.90 tB%, the tensile strength is 25.56MPa, and the breakdown strength is 395.6 kV/mm. The density-of-state curve of antioxidant N-4 (anilinophenyl) methacrylamide grafted crosslinked polyethylene calculated by the first principle is shown in FIG. 5.

Example 2:

uniformly mixing 40g of low-density polyethylene and 0.8g of reactive antioxidant N- (4-anilinophenyl) maleimide by using a high-speed mixer, introducing the mixture into a co-rotating parallel double-screw mixer by using a metering feeding system for mixing, wherein the mixing temperature is 200 ℃, the mixed material is subjected to liquid phase impregnation for 6 hours at 85 ℃ by using 0.8g of dicumyl peroxide, and then the obtained mixture enters a single-screw granulator for granulation to obtain granules mixed with a cross-linking agent, the granules are placed into a flat vulcanizing machine for hot press molding at 90 ℃ and 20MPa, then the obtained product is placed into a flat vulcanizing machine at 160 ℃ and 20MPa for cross-linking and grafting for 40 minutes, and the obtained product is cooled and molded to obtain the antioxidant N- (4-anilinophenyl) maleimide grafted high-voltage direct-current cable cross-linked polyethylene insulating material film sample. Then, a DC field of-40 kV/mm was applied to a film sample of 300 μm in thickness of the insulating material, and the space charge density distribution of the sample was measured at intervals of 5s within 40min of pressurization as shown in a in FIG. 6, and then, after the short-circuiting was released, the space charge density distribution of the sample was measured at intervals of 3s within 30min of short-circuiting as shown in b in FIG. 6. And carrying out other performance tests on the insulating material film sample, wherein the gel content is 87.70%, the elongation at break is 489.20tB, the tensile strength is 25.42MPa, and the breakdown strength is 358.5 kV/mm. The density of states curve of the antioxidant N- (4-anilinophenyl) maleimide grafted crosslinked polyethylene calculated by the first principle is shown in FIG. 7.

Example 3:

respectively feeding 40g of low-density polyethylene and 0.4g of reactive antioxidant 2- (2-hydroxy-3-tert-butyl-5-methylbenzyl) -4-methyl-6-tert-butylphenyl acrylate into a co-rotating parallel double-screw mixing mill for mixing by using a weight-loss material metering scale, wherein the mixing temperature is 160 ℃, the mixed material is subjected to liquid phase impregnation for 4 hours at 90 ℃ by 0.72g of dicumyl peroxide, then the mixed material enters a single-screw granulator for granulation to obtain granules mixed with a crosslinking agent, the granules are placed into a flat vulcanizing machine for hot press molding at 100 ℃ and 12MPa, then the granules are placed into a flat vulcanizing machine at 160 ℃ and 12MPa for crosslinking and grafting for 30 minutes, and the granules are cooled and molded to obtain the antioxidant 2- (2-hydroxy-3-tert-butyl-5-methylbenzyl) -4-methyl-6-tert-butylphenyl acrylate grafted high-voltage direct current cable crosslinked polyethylene of the antioxidant 2- (2-hydroxy-3-tert-butyl-5-methylbenzyl) -4-methyl-6-tert-butylphenyl acrylate An insulating material. The calculated density-of-state curve of the antioxidant 2- (2-hydroxy-3-tert-butyl-5-methylbenzyl) -4-methyl-6-tert-butylphenyl acrylate grafted crosslinked polyethylene according to the first principle is shown in FIG. 8. As can be seen from fig. 8, in the antioxidant grafted high voltage direct current cable crosslinked polyethylene insulation material obtained in the present embodiment, a deep trap state can be introduced due to the grafting of the antioxidant, so that the accumulation of space charge is suppressed.

Example 4:

40g of low-density polyethylene, 2g of a reactive antioxidant N- (3-methacryloyloxy-2-hydroxymethyl) -N' -phenyl-p-phenylenediamine and 0.48g of dicumyl peroxide are uniformly mixed by a high-speed mixer, introducing into a co-rotating parallel double-screw mixing mill by using a metering and feeding system for mixing at 110 deg.C, granulating in a single-screw granulator to obtain granules mixed with a crosslinking agent, hot-pressing the granules in a flat vulcanizing machine at 110 deg.C under 15MPa, and then placing the mixture in a flat vulcanizing machine at 175 ℃ and 15MPa for crosslinking and grafting for 30min, and cooling and forming to obtain the antioxidant N- (3-methacryloyloxy-2-hydroxymethyl) -N' -phenyl p-phenylenediamine grafted high-voltage direct-current cable crosslinked polyethylene insulating material. The density of states curve of antioxidant N- (3-methacryloyloxy-2-hydroxymethyl) -N' -phenyl-p-phenylenediamine grafted crosslinked polyethylene calculated by the first principle is shown in FIG. 9. As can be seen from fig. 9, in the antioxidant grafted high voltage direct current cable crosslinked polyethylene insulation material obtained in the present embodiment, a deep trap state can be introduced due to the grafting of the antioxidant, so that the accumulation of space charge is suppressed.

Example 5:

respectively feeding 40g of low-density polyethylene, 3g of

reactive antioxidant

2,4, 6-triallyl phenol and 1g of dicumyl peroxide into a co-rotating parallel double-screw mixing mill by using a weight-loss material metering scale for mixing, wherein the mixing temperature is 115 ℃, the mixed material enters a single-screw granulator for granulation to obtain granules mixed with a crosslinking agent, the granules are placed into a flat vulcanizing machine for hot press molding at 120 ℃ and 18MPa, then the flat vulcanizing machine is placed at 180 ℃ and 18MPa for crosslinking and grafting for 40min, and the granules are cooled and molded to obtain the

antioxidant

2,4, 6-triallyl phenol grafted high-voltage direct current cable crosslinked polyethylene insulating material. The density of states curve of the

antioxidant

2,4, 6-triallyl phenol graft-crosslinked polyethylene calculated by the first principle is shown in FIG. 10. As can be seen from fig. 10, in the antioxidant grafted high voltage direct current cable crosslinked polyethylene insulation material obtained in the present embodiment, a deep trap state can be introduced due to the grafting of the antioxidant, so that the accumulation of space charge is suppressed.

Example 6:

uniformly mixing 40g of low-density polyethylene and 0.02g of reactive antioxidant 3, 5-di-tert-butyl-4-hydroxybenzyl acrylate by using a high-speed mixer, introducing the mixture into a co-rotating parallel double-screw mixing mill by using a metering feeding system for mixing, wherein the mixing temperature is 150 ℃, the mixed material is subjected to liquid phase impregnation for 16h at 70 ℃ by using 1.2g of dicumyl peroxide, then the impregnated material enters a single-screw granulator for granulation to obtain granules mixed with a crosslinking agent, the granules are placed into a flat vulcanizing machine for hot press molding at 120 ℃ and 16MPa, then the granules are placed into a flat vulcanizing machine at 170 ℃ and 16MPa for crosslinking and grafting for 35min, and cooling and molding are carried out to obtain the antioxidant 3, 5-di-tert-butyl-4-hydroxybenzyl acrylate grafted high-voltage direct-current cable crosslinked polyethylene insulating material. The state density curve of the antioxidant 3, 5-di-tert-butyl-4-hydroxybenzyl acrylate grafted crosslinked polyethylene calculated by the first principle is shown in FIG. 11. As can be seen from fig. 11, in the antioxidant grafted high voltage direct current cable crosslinked polyethylene insulation material obtained in the present embodiment, a deep trap state can be introduced due to the grafting of the antioxidant, so that the accumulation of space charge is suppressed.

Comparative example 1:

40g of low-density polyethylene is subjected to liquid phase impregnation for 10h at 80 ℃ by 0.8g of dicumyl peroxide, and then enters a single-screw granulator for granulation to obtain granules mixed with a cross-linking agent, the granules are placed in a flat vulcanizing machine for hot press molding at 110 ℃ and 15MPa, then the granules are placed in a flat vulcanizing machine at 175 ℃ and 15MPa for cross-linking for 30min, and the pure cross-linked polyethylene insulating material film sample is obtained after cooling molding. Then, a DC field of-40 kV/mm was applied to a film sample of 300 μm in thickness of the insulating material, and the space charge density distribution of the sample was measured at intervals of 5s within 40min of pressurization as shown in a in FIG. 1, and then, after the short-circuiting was released, the space charge density distribution of the sample was measured at intervals of 3s within 30min of short-circuiting as shown in b in FIG. 1. And carrying out other performance tests on the insulating material film sample, wherein the gel content is 85.19%, the breaking elongation is 538.20 tB%, the tensile strength is 26.44MPa, and the breakdown strength is 364.4 kV/mm. The density of state curves of the pure crosslinked polyethylene calculated by the first principle of principle is shown in FIG. 4.

Comparative example 2:

uniformly mixing 40g of low-density polyethylene and 0.12g of antioxidant 1010 by using a high-speed mixer, introducing the mixture into a co-rotating parallel double-screw mixing mill by using a metering feeding system for mixing, wherein the mixing temperature is 180 ℃, the mixed material is subjected to liquid phase impregnation for 10 hours at 80 ℃ by 0.8g of dicumyl peroxide, and then the mixture enters a single-screw granulator for granulation to obtain granules mixed with a crosslinking agent, the granules are placed into a flat vulcanizing machine for hot press molding at 110 ℃ and 15MPa, then the granules are placed into a flat vulcanizing machine at 175 ℃ and 15MPa for crosslinking for 30min, and the granules are cooled and molded to obtain the antioxidant 1010/crosslinked polyethylene insulating material film sample. Then, a DC field of-40 kV/mm was applied to a film sample of 300 μm in thickness of the insulating material, and the space charge density distribution of the sample was measured at intervals of 5s within 40min of pressurization as shown in a in FIG. 2, and then, after the short-circuiting was released, the space charge density distribution of the sample was measured at intervals of 3s within 30min of short-circuiting as shown in b in FIG. 2.

And (3) analyzing the data:

as can be seen from the graph a in FIG. 6 and the graph b in FIG. 6, the space charge accumulation in the antioxidant-grafted high-voltage direct current cable crosslinked polyethylene insulation material prepared in example 2 is very small. As can be seen from fig. 7, in the antioxidant grafted high voltage dc cable crosslinked polyethylene insulation material obtained in this example 2, a deep trap state can be introduced due to the grafting of the antioxidant, so as to inhibit the accumulation of space charge. And the gel content of the antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material prepared in the embodiment 2 is slightly increased compared with that of pure crosslinked polyethylene, which shows that the crosslinking degree is increased, the tensile strength is slightly reduced but is not obvious, and the antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material still maintains excellent mechanical properties.

After the antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material prepared in example 2 is subjected to air heat aging at 135 ℃ for 7 days, although the tensile strength of the insulating material is reduced, the elongation at break is increased, and the change rates of the tensile strength and the elongation at break are respectively 2.2% and 2.9%, which are both far less than 20%, so that the requirements of the insulating material on an air heat aging experiment are met.

And the oxidation induction period of the antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material prepared in the example 2 is obviously prolonged and is far higher than that of the comparative example 2, which shows that the antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material prepared in the example 2 has the advantages of enhanced oxidation and decomposition resistance, improved thermal stability and prolonged service life.

The performance parameters of the insulation materials prepared in example 1, example 2 and comparative example 1 were compared as follows:

from the above table, it can be seen that the gel content of the antioxidant grafted high voltage direct current cable crosslinked polyethylene insulating material obtained in example 1 of the present invention is slightly increased compared with that of pure crosslinked polyethylene, which indicates that the crosslinking degree is increased, and the tensile strength is slightly reduced but not obvious, which indicates that the antioxidant grafted high voltage direct current cable crosslinked polyethylene insulating material still maintains excellent mechanical properties, and the direct current breakdown strength is slightly increased.

The mechanical properties of the materials before and after aging and the oxidation induction period parameters of the materials after the thermal aging of the insulation materials prepared in example 1, example 2, comparative example 1 and comparative example 2 in air at 135 ℃ for 7 days are compared as follows:

from the above table, after being subjected to air heat aging at 135 ℃ for 7 days, the pure crosslinked polyethylene and the antioxidant 1010/crosslinked polyethylene have no regular shape, and the mechanical properties cannot be tested, although the tensile strength of the antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material obtained in example 1 of the invention is reduced, the elongation at break is increased, the change rates of the tensile strength and the elongation at break are respectively 3.6% and 3.9%, which are both far less than 20%, and the requirements of the insulating material on the air heat aging experiment are met. The oxidation induction period of the antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material in the embodiment 1 is obviously prolonged, and is higher than that of the insulating material prepared in the comparative example 2, so that the oxidation decomposition resistance of the antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material is enhanced, the thermal stability is improved, and the service life is prolonged.

Meanwhile, as can be seen from the diagrams a and b in fig. 3 and 3, the internal space charge accumulation of the antioxidant-grafted high-voltage direct current cable crosslinked polyethylene insulating material prepared in example 1 is very small, and the antioxidant-grafted high-voltage direct current cable crosslinked polyethylene insulating material has better space charge inhibition capability than the pure crosslinked polyethylene represented by the diagrams a and b in fig. 1, and the internal space charge accumulation of the antioxidant 1010/crosslinked polyethylene added with the antioxidant 1010 commonly used in cable crosslinked polyethylene insulating materials is obviously increased compared with the pure crosslinked polyethylene as can be seen from the diagrams a and b in fig. 2.

As can be seen from a comparison between fig. 4 and fig. 5, in the antioxidant-grafted crosslinked polyethylene insulating material of example 1, since the grafting of the antioxidant can introduce electron and hole deep trap states into the crosslinked polyethylene, initial carriers in the material can enter and sink to form a charge layer, and the injection of electrode charges is retarded, thereby inhibiting the accumulation of space charges.

From the comprehensive properties, the insulating material prepared in example 1 meets the requirements of the wire and cable insulating material on electrical properties, mechanical properties and thermal aging resistance, and is an excellent direct current cable insulating material.

The detailed information of the raw materials mentioned in the examples and comparative examples of the present invention is as follows:

the low density polyethylene is LD200GH type low density polyethylene of Beijing Yanshan division of petrochemical company, Inc., and has a density of 0.922g/cm³Melt index 2.0g/10 min;

dicumyl peroxide is produced by China petrochemical Shanghai Gaoqiao petrochemical company Limited;

the reaction type antioxidant 2- (2-hydroxy-3-tert-butyl-5-methylbenzyl) -4-methyl-6-tert-butylphenyl acrylate is produced by Qingdajie Geidejia new material science and technology limited, white solid, melting point 130-;

the reactive antioxidant N- (4-anilinophenyl) methacrylamide is produced by Baoyi rubber and plastic auxiliary agents Limited company in Qishan county, Shanxi, the melting point of gray powder is more than or equal to 100-;

the reactive antioxidant N- (4-anilinophenyl) maleimide is produced by Suiyang Sanjing science and technology Limited, the melting point of red powder is more than or equal to 140 ℃, the heating decrement is less than or equal to 0.5 percent, and the ash content is less than or equal to 0.5 percent.

The reaction type antioxidant N- (3-methacryloyloxy-2-hydroxymethyl) -N' -phenyl-p-phenylenediamine is produced by new chemical industry Co., Ltd in Japan, and is a red purple gray powder, the melting point is more than or equal to 115 ℃, the heating loss is less than or equal to 0.5 percent, and the ash content is less than or equal to 0.5 percent;

the

reactive antioxidants

2,4, 6-triallyl phenol and 3, 5-di-tert-butyl-4-hydroxybenzyl acrylate are produced by Bailingwei science and technology Limited and are analytically pure.

The operation procedures of the space charge distribution characteristic test and the oxidation induction period test on the insulating materials obtained in the examples and comparative examples are as follows:

space charge distribution characteristic test:

testing the space charge distribution characteristic of a sample by adopting an electroacoustic pulse method, wherein an acoustic coupling agent adopted in the testing process is silicone oil;

the specific method comprises the following steps: firstly, putting the granules into a flat vulcanizing machine for hot press molding, and then crosslinking and grafting the granules by using the flat vulcanizing machine to prepare a film sample with the thickness of 300 microns; then, a DC electric field of-40 kV/mm is applied to each sample, the space charge density distribution of the sample is measured at intervals of 5s within 40min of pressurization, then the short circuit is removed, and the space charge density distribution of the sample is measured at intervals of 3s within 30min of short circuit.

Oxidative induction period test:

the samples were tested for oxidative induction period (OIT) using Differential Scanning Calorimetry (DSC) according to ASTM-D3895-02.

The specific method comprises the following steps: firstly, placing granules into a flat vulcanizing machine for hot press molding, and then crosslinking and grafting the granules by using the flat vulcanizing machine to obtain a film sample; and then weighing about 5mg of sample under the condition of nitrogen protection, wherein the nitrogen flow rate is 50mL/min, the heating rate is 20 ℃/min, heating to 200 ℃, keeping the temperature for 5min, replacing nitrogen with oxygen, the oxygen flow rate is 50mL/min, replacing oxygen with nitrogen after the rising gradient of heat flow appears for at least 5min, and starting cooling, wherein the cooling rate is 20 ℃/min.

Claims

1. An antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material is characterized by being prepared from 100 parts by weight of low-density polyethylene, 0.02-5 parts by weight of dicumyl peroxide and 0.01-10 parts by weight of a reactive antioxidant; the reactive antioxidant has a grafting group, an aging-resistant group and a polar group;

the reactive antioxidant is 2- (2-hydroxy-3-tert-butyl-5-methylbenzyl) -4-methyl-6-tert-butylphenyl acrylate, N- (4-anilinophenyl) methacrylamide, N- (4-anilinophenyl) maleimide, N- (3-methacryloyloxy-2-hydroxymethyl) -N' -phenyl-p-phenylenediamine, 2,4, 6-triallylphenol or 3, 5-di-tert-butyl-4-hydroxybenzyl acrylate.

2. The antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulating material as claimed in claim 1, wherein the low-density polyethylene is 100 parts, dicumyl peroxide is 1.2-3 parts, and the reactive antioxidant is 0.01-10 parts.

3. The preparation method of the antioxidant grafted high-voltage direct current cable crosslinked polyethylene insulation material of claim 1, characterized by comprising the following steps:

4. The preparation method of the antioxidant grafted high-voltage direct current cable crosslinked polyethylene insulation material according to claim 3, characterized in that the specific operation process of the first step is as follows: mixing low-density polyethylene, dicumyl peroxide and a reactive antioxidant uniformly at the temperature of 100-120 ℃, and then granulating to obtain granules.

5. The preparation method of the antioxidant grafted high-voltage direct current cable crosslinked polyethylene insulation material according to claim 3, characterized in that the specific operation process of the first step is as follows: uniformly mixing low-density polyethylene and a reactive antioxidant at the temperature of 130-200 ℃, then dipping the mixed material in liquid-phase dicumyl peroxide at the temperature of 60-90 ℃ for 2-18 h, and granulating to obtain granules.

6. The preparation method of the antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulation material according to any one of claims 3 to 5, wherein in a laboratory, the specific operation process of the second step is as follows: putting the granules into a flat vulcanizing machine, carrying out hot press molding under the conditions that the temperature is 90-130 ℃ and the pressure is 10-20 MPa, then carrying out cross-linking and grafting for 20-50 min by utilizing the flat vulcanizing machine under the conditions that the temperature is 140-200 ℃ and the pressure is 10-20 MPa, and carrying out cooling molding to obtain the antioxidant grafted high-voltage direct-current cable cross-linked polyethylene insulating material;

in the production of the cable, the specific operation process of the second step is as follows: and extruding the granules into cable insulation through an extruder, feeding the cable insulation into a high-temperature high-pressure crosslinking pipeline, and crosslinking and grafting for 10-60 min under the conditions that the temperature is 150-270 ℃ and the pressure is 0.6-1.2 MPa to obtain the antioxidant grafted high-voltage direct-current cable crosslinked polyethylene insulation material.