Insulating waterproof cable material and preparation method thereof

Abstract

The invention provides an insulating waterproof cable material and a preparation method thereof. The insulating waterproof cable material is prepared from the following raw materials in parts by weight: 40 to 70 parts of low-density polyethylene, 20 to 35 parts of high-density polyethylene, 15 to 30 parts of cyclotriphosphazene cross-linking agent, 10 to 22 parts of acrylate compound, 8 to 20 parts of ethylene-vinyl acetate copolymer, 3 to 10 parts of nucleating agent, 1.5 to 5 parts of hydrogenated castor oil and 1 to 4 parts of antioxidant. The raw materials are polymerized through irradiation initiation to form a cross-linked network. By adopting the combination of various functional materials, the cable material has excellent mechanical properties, insulating properties, physical properties and chemical stability, can adapt to high-pressure and high-humidity use environments, is resistant to long-term corrosion, and can protect long-term stable work of subway cables. The preparation method is simple in process, simple and convenient in operation steps, low in technical requirement, controllable in process and suitable for large-scale production and application.

Description

Technical Field

[0001] The present invention relates to the technical field of cable materials, and particularly to an insulating and waterproof cable material and a preparation method thereof. Background Art

[0002] As a carrier for electric energy and information transmission, wire and cable are widely used in various fields such as transportation, industrial mines, and electrical communication. During the use of cables, a layer of insulating and flame-retardant coating material needs to be wrapped on the surface, and the quality of the coating material has a great impact on the performance of the cable. Especially in the contemporary era of the rapid development of the subway, the huge differences in climate in different regions also pose higher requirements for cables.

[0003] When the cable coating material is in a humid environment, external moisture is easily penetrated into the internal of the insulating medium, and dendritic discharge channels are formed under the influence of water and electric field at the defect sites, which will cause more water to penetrate into the insulating layer. The water tree grows continuously and eventually leads to breakdown. This problem is prone to occur in polyethylene cables. Therefore, the coating material of polyethylene cables for subways not only needs excellent physical properties but also needs to have waterproof characteristics. The waterproof property of existing polyethylene cables still needs to be improved. Summary of the Invention

[0004] The present invention aims to solve at least one of the above technical problems, and provides a cross-linked polyethylene cable material with good insulating and waterproof performance, which can be effectively applied to cables for subways.

[0005] In the first aspect of the present invention, there is provided an insulating and waterproof cable material, comprising the following raw materials in parts by weight: 40-70 parts of low-density polyethylene, 20-35 parts of high-density polyethylene, 15-30 parts of cyclotriphosphazene cross-linking agent, 10-22 parts of acrylate compound, 8-20 parts of ethylene-vinyl acetate copolymer, 3-10 parts of nucleating agent, 1.5-5 parts of cyclotriphosphazene cross-linking agent, 1.5-5 parts of hydrogenated castor oil, and 1-4 parts of antioxidant; the raw materials form a cross-linked network through radiation-induced polymerization;

[0006] The chemical structural formula of the cyclotriphosphazene cross-linking agent is as follows:

[0007]

[0008] The cyclotriphosphazene crosslinking agent has a cyclic structure with three phosphorus atoms and three nitrogen atoms arranged alternately. The synergistic effect between phosphorus and nitrogen in its structure endows it with excellent flame retardancy. The ends of its structure are acrylate groups, which have excellent hydrophobicity. Acrylate compounds can be used as crosslinking agents to improve the compatibility and crosslinking between raw material components, making the surface of the cable material shiny and smooth, and not easily damaged. The acrylate groups in its structure also have excellent hydrophobicity. Based on this, the present invention is prepared by introducing a cyclotriphosphazene structure into the crosslinked polyethylene polymer backbone through a chemical reaction, which can effectively improve the flame retardant properties of the crosslinked polyethylene cable material. The cyclotriphosphazene structure can also act as a radiation sensitizer to promote the formation of a three-dimensional crosslinked network, and at the same time, in synergy with acrylate compounds, endow the crosslinked polyethylene cable material with excellent waterproof performance. The acrylate groups in the cyclotriphosphazene crosslinking agent and acrylate compounds react with low-density polyethylene, high-density polyethylene, and ethylene-vinyl acetate copolymer through radiation-induced polymerization to form a crosslinked network, making the crosslinked network in the backbone evenly distributed, reducing the grain boundary defects of the crosslinked polyethylene cable material, and forming a dense structure, which can not only ensure the mechanical properties of the crosslinked polyethylene cable material, but also effectively prevent water vapor from penetrating into the interior of the crosslinked polyethylene cable material, greatly improving the waterproof performance. Ethylene-vinyl acetate copolymer can effectively inhibit the accumulation of space charge during the radiation crosslinking process and improve the insulation of the cable material. The nucleating agent can promote the crystallization of low-density polyethylene and high-density polyethylene, make the crystal grains evenly distributed and smaller in size, and can also improve the waterproofness of the cable material. Hydrogenated castor oil can be used as a crosslinking agent, participating in the crosslinking reaction through the hydroxyl group -OH, helping to form a denser and more stable network structure, and can also improve the flexibility, processability, and durability of the cable material, thereby improving the performance of the cable material. The present invention uses a combination of multiple functional materials, has excellent mechanical properties, insulation properties, physical properties, and chemical stability, can adapt to the use environment of high pressure and high humidity, is resistant to long-term corrosion, and can protect the subway cable to work stably for a long time.

[0009] Preferably, the acrylate compound includes at least one of methyl acrylate, ethyl acrylate, methyl 2-methylacrylate, ethyl 2-methylacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, dipropylene glycol diacrylate.

[0010] Preferably, the content of vinyl acetate in the ethylene-vinyl acetate copolymer is 10-20 wt%.

[0011] Preferably, the raw materials of the nucleating agent include white mineral oil, low-density maleic anhydride grafted polyethylene, nano boron nitride, silicone nanospheres, and nano silica aerosol. The nano silica aerogel in the nucleating agent has micropores and forms a composite nucleating agent by compounding and carrying with low-density maleic anhydride grafted polyethylene, nano boron nitride, and silicone nanospheres. The composite nucleating agent is uniformly dispersed in the raw materials of the cross-linked polyethylene cable material. During the irradiation cross-linking process, uniform fine crystal nuclei are first formed, which further promotes the reduction of the crystal grain size of cross-linked low-density polyethylene, forms a dense crystal structure, and reduces grain boundary defects. Nano silica aerosol is beneficial for promoting heterogeneous nucleation, making the crystal grain growth size of low-density polyethylene small and evenly distributed; low-density maleic anhydride grafted polyethylene can enhance the adhesion and compatibility between raw materials and the coupling between inorganic materials and polyolefin materials, and can be used as a re-reaction modifier to improve the coupling effect between polyolefins; low-density maleic anhydride grafted polyethylene, as the matrix, acts together with nano silica aerosol to disperse nano boron nitride and silicone nanospheres, promoting the uniform formation of crystal nuclei; nano boron nitride has excellent thermal stability and chemical stability, high electrical insulation performance, and low polarity, and can be used as a good nucleating agent; silicone nanospheres have a small particle size, good dispersion performance, and hydrophobicity, which can enhance the waterproof property of the cable material. The main components of white mineral oil are alkanes, cycloalkanes, and a small amount of aromatic hydrocarbons; the addition of white mineral oil can improve the melt fluidity and play a role in promoting melting, preventing adhesion, anti-static, and anti-impact effects. The nucleating agent can promote the crystallization of polyethylene, make the crystal grains evenly distributed and smaller in size, and also improve the waterproof property of the cable material. The various raw materials in the nucleating agent act synergistically to jointly improve the mechanical properties, chemical stability, flame retardancy, and waterproof property of the obtained cable material.

[0012] Preferably, the mass ratio of white mineral oil, low-density maleic anhydride grafted polyethylene, nano boron nitride, silicone nanospheres, and nano silica aerosol is 1-2:10-50:3-15:3-15:50-150.

[0013] Preferably, the antioxidant includes a hindered phenol antioxidant and / or a phosphite antioxidant. The hindered phenol antioxidant can be selected from any one or more of antioxidant 1010, antioxidant 1076, antioxidant 264, antioxidant 2246, antioxidant 330, and the phosphite antioxidant can be selected from any one or more of antioxidant 3032, antioxidant 3010, antioxidant 2012, phenol-free environmentally friendly phosphite antioxidant PEP-8T, BASF antioxidant 168, BASF antioxidant 626, antioxidant V75-P, antioxidant Antioxidant24, antioxidant IRGAFOSP-EPQ.

[0014] In the first aspect of the present invention, a method for preparing an insulating and waterproof cable material is provided, comprising the following steps:

[0015] S1. Grind and mix low-density polyethylene, high-density polyethylene, acrylate compounds, nucleating agent, hydrogenated castor oil, and a partial amount of cyclotriphosphazene crosslinking agent evenly by weight, and perform melt blending at 110 - 150 °C to obtain a blend;

[0016] S2. Add ethylene-vinyl acetate copolymer, antioxidant, and the remaining cyclotriphosphazene crosslinking agent to the obtained blend by weight, and continue to knead;

[0017] S3. Put the melt-blended material into a mold and perform hot pressing molding using a flat vulcanizing machine to obtain a molded material;

[0018] S4. Perform irradiation crosslinking on the molded material to finally obtain the cable material.

[0019] The present invention adopts step-by-step melt kneading, first grinds and mixes the main crosslinked skeleton raw materials evenly, and adds the crosslinking agent in two steps, which can better promote the uniformity of the crosslinking process and improve the structural compactness of the cable material. Irradiation crosslinking has the advantages of fast processing speed, low energy consumption, easy control, and separation of the extrusion and crosslinking processes, greatly improving the crosslinking efficiency and effectively improving the material properties. The cable material obtained by the present invention has improved insulation, flame retardancy, withstand voltage ability, temperature and pressure resistance, mechanical properties, and waterproofness. The nucleating agent can promote the crystallization of polyethylene, make the crystal grain distribution uniform and the size smaller, and also improve the waterproofness of the cable material. The addition of ethylene-vinyl acetate copolymer can effectively inhibit the accumulation of space charge during irradiation crosslinking and improve the insulation of the cable material. The preparation method of the present invention has a simple process, convenient operation steps, low technical requirements, process controllability, and is suitable for large-scale production applications.

[0020] Preferably, in step S1:

[0021] The preparation method of the nucleating agent is as follows: Mix white mineral oil and low-density maleic anhydride grafted polyethylene evenly, then add nano boron nitride, organosilica nanospheres, and nano silica aerosol, mix them, and send them into a screw extruder for melt mixing and granulation. Then grind to a D50 particle size ≤ 15 microns and a D90 particle size ≤ 30 microns to obtain the nucleating agent. The addition of white mineral oil can improve the melt fluidity, playing a role in promoting melting, preventing adhesion, antistatic, and impact resistance. Nano silica aerosol is conducive to promoting heterogeneous nucleation, making the crystal grain growth size of low-density polyethylene small and evenly distributed; low-density maleic anhydride grafted polyethylene can enhance the adhesion and compatibility between raw materials, and the coupling between inorganic materials and polyolefin materials, and can be used as a re-reaction modifier to improve the coupling effect between polyolefins. During the preparation process of the nucleating agent, the combined action of white mineral oil, low-density maleic anhydride grafted polyethylene matrix, nano silica aerosol, and extruder is used to ensure the dispersion of nano boron nitride and organosilica nanospheres, promote the uniform formation of crystal nuclei, and thus improve the compactness of the cross-linked structure.

[0022] Preferably, in the step S1: In the nucleating agent, the mass ratio of white mineral oil, low-density maleic anhydride grafted polyethylene, nano boron nitride, organosilica nanospheres, and nano silica aerosol is 1 - 2: 10 - 50: 3 - 15: 3 - 15: 50 - 150.

[0023] Preferably, in the step S1: The addition amount of part of the cyclotriphosphazene cross-linking agent is 1 / 3 - 4 / 5 of the total weight of the cyclotriphosphazene cross-linking agent.

[0024] Preferably, in the step S1: The time of melt blending is 0.5 - 2 h.

[0025] Preferably, in the step S2: The temperature of continuous mixing is 110 - 150 °C, and the time is 0.5 - 2 h.

[0026] Preferably, in the step S3: The temperature of hot pressing is 110 - 150 °C, and the pressure is 2 - 4 MPa.

[0027] Preferably, in the step S4: The irradiation dose of radiation cross-linking is 90 - 200 kGy.

[0028] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0029] 1. The present invention is prepared by introducing a cyclotriphosphazene structure with acrylate groups at the ends into the cross-linked polyethylene polymer backbone through chemical reactions, which can promote the formation of a three-dimensional cross-linked network and effectively improve the flame retardancy and waterproofness of the cross-linked polyethylene cable material. Acrylate compounds can also improve waterproofness and can be used as cross-linking agents to enhance the compatibility and cross-linkability between raw material components, making the surface of the cable material shiny and smooth, and not easily damaged. Ethylene-vinyl acetate copolymer can effectively inhibit the accumulation of space charges during the irradiation cross-linking process and improve the insulation of the cable material. Nucleating agents can promote the crystallization of polyethylene, making the crystal grains evenly distributed and smaller in size, and can also improve the waterproofness of the cable material. Hydrogenated castor oil can be used as a cross-linking agent to help form a denser and more stable network structure, and can also improve the flexibility, processability and durability of the cable material, thereby improving the performance of the cable material. The cyclotriphosphazene cross-linking agent, acrylate compounds, low-density polyethylene, high-density polyethylene, and ethylene-vinyl acetate copolymer form a cross-linked network through irradiation-induced polymerization, making the cross-linked network in the backbone evenly distributed, reducing the grain boundary defects of the cross-linked polyethylene cable material, and forming a dense structure, which can not only ensure the mechanical properties of the cross-linked polyethylene cable material, but also effectively prevent water vapor from penetrating into the interior of the cross-linked polyethylene cable material, greatly improving the waterproof performance.

[0030] 2. The present invention combines a variety of functional materials, has excellent mechanical properties, physical properties and chemical stability, can adapt to the use environment of high voltage and high humidity, is resistant to long-term corrosion, and can protect subway cables to work stably for a long time.

[0031] 3. The present invention adopts step-by-step melt mixing, first grinding and mixing the main cross-linked backbone raw materials evenly, and adding the cross-linking agent in two steps, which can better promote the uniformity of the cross-linking process and improve the structural density of the cable material. Irradiation cross-linking has the advantages of fast processing speed, low energy consumption, easy control, and separation of the extrusion and cross-linking processes, greatly improving the cross-linking efficiency and effectively improving the material properties.

[0032] 4. The preparation method of the present invention has a simple process, simple operation steps, low technical requirements, controllable process, and is suitable for large-scale production applications. Detailed Embodiments

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0034] The chemical reagents and instrument equipment used in the present invention are all commercially available.

[0035] Among them, the density of low-density polyethylene is 0.910 - 0.925 g / cm 3 , and the density of high-density polyethylene is 0.94 - 0.965 g / cm 3 .

[0036] The chemical structural formula of the cyclotriphosphazene cross-linking agent is as follows:

[0037]

[0038] The acrylate compound includes at least one of methyl acrylate, ethyl acrylate, methyl 2-methylacrylate, ethyl 2-methylacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, dipropylene glycol diacrylate.

[0039] The organosilica nanospheres are thiol-functionalized organosilica nanospheres, prepared by referring to the method of Example 1 in Patent CN202010986519.7.

[0040] Example 1

[0041] An insulating and waterproof cable material in this example comprises the following raw materials in parts by weight: 40 parts of low-density polyethylene, 35 parts of high-density polyethylene, 15 parts of cyclotriphosphazene cross-linking agent, 12 parts of methyl acrylate, 8 parts of ethylene-vinyl acetate copolymer, 3 parts of nucleating agent, 1.5 parts of hydrogenated castor oil, 1 part of antioxidant 1010; all the raw materials form a crosslinked network through radiation-induced polymerization. Among them, the content of vinyl acetate in the ethylene-vinyl acetate copolymer is 10 wt%, and the raw materials of the nucleating agent include white mineral oil, low-density maleic anhydride grafted polyethylene, nano boron nitride, organosilica nanospheres, nano silica aerosol, and the mass ratio is 1:50:15:3:150.

[0042] A preparation method of the insulating and waterproof cable material in this example comprises the following steps:

[0043] S1. Grind and mix low-density polyethylene, high-density polyethylene, methyl acrylate, nucleating agent, hydrogenated castor oil, and 1 / 3 part by weight of cyclotriphosphazene cross-linking agent evenly according to parts by weight, and melt-blend at 110°C for 2 h to obtain a blend; among them, the preparation method of the nucleating agent is: mix white mineral oil and low-density maleic anhydride grafted polyethylene evenly, then add nano boron nitride, organosilica nanospheres, and nano silica aerosol and mix them, feed them into a screw extruder for melt mixing and granulation, and then grind to D50 particle size ≤ 15 microns and D90 particle size ≤ 30 microns to obtain the nucleating agent;

[0044] S2. Add ethylene-vinyl acetate copolymer, antioxidant, and the remaining cyclotriphosphazene cross-linking agent to the obtained blend according to parts by weight, and continue to mix at 110°C for 2 h;

[0045] S3. Put the well-melted and blended materials into a mold and perform hot pressing and forming using a flat vulcanizing machine. The temperature for hot pressing and forming is 110 °C and the pressure is 4 MPa to obtain the formed material.

[0046] S4. Use an electron accelerator to emit high-energy electron beams to irradiate and crosslink the formed material. The irradiation dose is 100 kGy, and finally, the cable material is obtained.

[0047] Example 2

[0048] An insulating and waterproof cable material in this example comprises the following raw materials in parts by weight: 70 parts of low-density polyethylene, 20 parts of high-density polyethylene, 30 parts of cyclotriphosphazene crosslinking agent, 22 parts of 1,6-hexanediol diacrylate, 20 parts of ethylene-vinyl acetate copolymer, 10 parts of nucleating agent, 5 parts of hydrogenated castor oil, 2 parts of antioxidant 264, and 2 parts of antioxidant PEP-8T; all raw materials form a crosslinked network through irradiation-induced polymerization. Among them, the content of vinyl acetate in the ethylene-vinyl acetate copolymer is 20 wt%, and the raw materials of the nucleating agent include white mineral oil, low-density maleic anhydride grafted polyethylene, nano boron nitride, organosilica nanospheres, and nano silica aerosol, with a mass ratio of 2:10:3:15:50.

[0049] A preparation method of an insulating and waterproof cable material in this example comprises the following steps:

[0050] S1. Grind and mix evenly low-density polyethylene, high-density polyethylene, 1,6-hexanediol diacrylate, nucleating agent, hydrogenated castor oil, and 4 / 5 parts by weight of cyclotriphosphazene crosslinking agent according to parts by weight, and perform melt blending at 150 °C for 0.5 h to obtain a blended material; the preparation method of the nucleating agent is: mix white mineral oil and low-density maleic anhydride grafted polyethylene evenly, then add nano boron nitride, organosilica nanospheres, and nano silica aerosol and mix them, feed them into a screw extruder for melt mixing and granulation, and then grind to a D50 particle size ≤ 10 microns and a D90 particle size ≤ 20 microns to obtain the nucleating agent;

[0051] S2. Add ethylene-vinyl acetate copolymer, antioxidant, and the remaining cyclotriphosphazene crosslinking agent to the obtained blended material according to parts by weight, and continue to knead at 150 °C for 0.5 h;

[0052] S3. Put the well-melted and blended materials into a mold and perform hot pressing and forming using a flat vulcanizing machine. The temperature for hot pressing and forming is 150 °C and the pressure is 2 MPa to obtain the formed material;

[0053] S4. Use an electron accelerator to emit high-energy electron beams to irradiate and crosslink the formed material. The irradiation dose is 200 kGy, and finally, the cable material is obtained.

[0054] Example 3

[0055] An insulating and waterproof cable material according to this embodiment comprises raw materials in the following parts by weight: 56 parts of low-density polyethylene, 28 parts of high-density polyethylene, 23 parts of cyclotriphosphazene crosslinking agent, 8 parts of trimethylolpropane triacrylate, 10 parts of pentaerythritol tetraacrylate, 15 parts of ethylene-vinyl acetate copolymer, 6.5 parts of nucleating agent, 3.5 parts of hydrogenated castor oil, 1.8 parts of 2246 antioxidant, and 0.7 part of PEP-8T antioxidant; all the raw materials form a crosslinked network through radiation-induced polymerization. Among them, the content of vinyl acetate in the ethylene-vinyl acetate copolymer is 15 wt%, and the raw materials of the nucleating agent include white mineral oil, low-density maleic anhydride grafted polyethylene, nano boron nitride, silicone nanospheres, and nano silica aerosol, with a mass ratio of 1.2:30:10:9:100.

[0056] A preparation method of an insulating and waterproof cable material according to this embodiment comprises the following steps:

[0057] S1. Grind and mix evenly low-density polyethylene, high-density polyethylene, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, nucleating agent, hydrogenated castor oil, and 3 / 5 parts by weight of cyclotriphosphazene crosslinking agent according to parts by weight, and conduct melt blending at 130°C for 1 h to obtain a blend; the preparation method of the nucleating agent is: mix white mineral oil and low-density maleic anhydride grafted polyethylene evenly, then add nano boron nitride, silicone nanospheres, and nano silica aerosol and mix, feed them into a screw extruder for melt mixing and granulation, and then grind to a D50 particle size ≤ 15 μm and a D90 particle size ≤ 25 μm to obtain the nucleating agent;

[0058] S2. Add ethylene-vinyl acetate copolymer, antioxidant, and the remaining cyclotriphosphazene crosslinking agent to the obtained blend according to parts by weight, and continue mixing at 130°C for 1 h;

[0059] S3. Put the melt-blended material into a mold, and use a flat vulcanizing machine for hot pressing and forming. The temperature for hot pressing and forming is 130°C and the pressure is 3 MPa to obtain a formed material;

[0060] S4. Use an electron accelerator to emit high-energy electron beams to irradiate and crosslink the formed material. The irradiation dose is 150 kGy, and finally the cable material is obtained.

[0061] Example 4

[0062] An insulating and waterproof cable material of this embodiment comprises raw materials in the following parts by weight: 48 parts of low-density polyethylene, 25 parts of high-density polyethylene, 25 parts of cyclotriphosphazene crosslinking agent, 10 parts of ethyl 2-methylacrylate, 10 parts of dipropylene glycol diacrylate, 12 parts of ethylene-vinyl acetate copolymer, 5 parts of nucleating agent, 2.5 parts of hydrogenated castor oil, 0.8 part of antioxidant 330, and 1.2 parts of antioxidant 24; all the raw materials form a crosslinked network through radiation-induced polymerization. Among them, the content of vinyl acetate in the ethylene-vinyl acetate copolymer is 12.5 wt%, and the raw materials of the nucleating agent include white mineral oil, low-density maleic anhydride grafted polyethylene, nano boron nitride, organosilica nanospheres, and nano silicon dioxide aerosol, with a mass ratio of 1.5:20:12:7:100.

[0063] A preparation method of an insulating and waterproof cable material of this embodiment comprises the following steps:

[0064] S1. Grind and mix evenly low-density polyethylene, high-density polyethylene, ethyl 2-methylacrylate, dipropylene glycol diacrylate, nucleating agent, hydrogenated castor oil, and 1 / 2 of the parts by weight of the cyclotriphosphazene crosslinking agent according to the parts by weight, and carry out melt blending at 120 °C for 1.5 h to obtain a blend; the preparation method of the nucleating agent is: mix white mineral oil and low-density maleic anhydride grafted polyethylene evenly, then add nano boron nitride, organosilica nanospheres, and nano silicon dioxide aerosol and mix them, feed them into a screw extruder for melt mixing and granulation, and then grind to a D50 particle size ≤ 10 microns and a D90 particle size ≤ 30 microns to obtain the nucleating agent;

[0065] S2. Add ethylene-vinyl acetate copolymer, antioxidant, and the remaining cyclotriphosphazene crosslinking agent to the obtained blend according to the parts by weight, and continue to knead at 120 °C for 1.5 h;

[0066] S3. Put the melt-blended material into a mold, and carry out hot pressing and forming with a flat vulcanizer. The temperature of hot pressing and forming is 120 °C and the pressure is 3.5 MPa to obtain a formed material;

[0067] S4. Use an electron accelerator to emit high-energy electron beams to irradiate and crosslink the formed material. The irradiation dose is 180 kGy, and finally the cable material is obtained.

[0068] Example 5

[0069] An insulating and waterproof cable material of this embodiment comprises raw materials in the following parts by weight: 63 parts of low-density polyethylene, 32 parts of high-density polyethylene, 18 parts of cyclotriphosphazene crosslinking agent, 7 parts of ethyl methacrylate, 8 parts of pentaerythritol tetraacrylate, 17.5 parts of ethylene-vinyl acetate copolymer, 8 parts of nucleating agent, 4.2 parts of hydrogenated castor oil, 2.2 parts of antioxidant 1076, 0.8 part of antioxidant IRGAFOS P-EPQ; all the raw materials form a crosslinked network through radiation-induced polymerization. Among them, the content of vinyl acetate in the ethylene-vinyl acetate copolymer is 16.8 wt%. The raw materials of the nucleating agent include low-density maleic anhydride grafted polyethylene, nano boron nitride, organosilica nanospheres, and nano silica aerosol, and the mass ratio is 1.7:38:7:12:110.

[0070] A preparation method of an insulating and waterproof cable material of this embodiment comprises the following steps:

[0071] S1. Grind and mix evenly low-density polyethylene, high-density polyethylene, ethyl methacrylate, pentaerythritol tetraacrylate, nucleating agent, hydrogenated castor oil, and 7 / 10 parts by weight of cyclotriphosphazene crosslinking agent according to parts by weight, and carry out melt blending at 140 °C for 1 h to obtain a blend; the preparation method of the nucleating agent is: mix white mineral oil and low-density maleic anhydride grafted polyethylene evenly, then add nano boron nitride, organosilica nanospheres, and nano silica aerosol and mix, send them into a screw extruder for melt mixing and granulation, and then grind to a D50 particle size ≤ 15 microns and a D90 particle size ≤ 25 microns to obtain the nucleating agent;

[0072] S2. Add ethylene-vinyl acetate copolymer, antioxidant, and the remaining cyclotriphosphazene crosslinking agent to the obtained blend according to parts by weight, and continue mixing at 140 °C for 1 h;

[0073] S3. Put the melt-blended material into a mold, and carry out hot pressing and forming with a flat vulcanizer. The temperature of hot pressing and forming is 140 °C and the pressure is 3.2 MPa to obtain a formed material;

[0074] S4. Use an electron accelerator to emit high-energy electron beams to irradiate and crosslink the formed material, and the irradiation dose is 125 kGy to finally obtain the cable material.

[0075] Comparative Example 1

[0076] Replace the cyclotriphosphazene crosslinking agent with hexaphenoxy cyclotriphosphazene, and the rest is the same as in Example 3.

[0077] Comparative Example 2

[0078] Remove trimethylolpropane triacrylate and pentaerythritol tetraacrylate, and the rest is the same as in Example 3.

[0079] Comparative Example 3

[0080] Remove ethylene-vinyl acetate copolymer, and the rest is the same as in Example 3.

[0081] Comparative Example 4

[0082] Remove low-density maleic anhydride grafted polyethylene in the nucleating agent, and the rest is the same as in Example 3.

[0083] Comparative Example 5

[0084] Remove nano boron nitride in the nucleating agent, and the rest is the same as in Example 3.

[0085] Comparative Example 6

[0086] Remove silicone nanospheres in the nucleating agent, and the rest is the same as in Example 3.

[0087] Comparative Example 7

[0088] Remove nano silica aerosol in the nucleating agent, and the rest is the same as in Example 3.

[0089] Comparative Example 8

[0090] In the preparation method of the nucleating agent: do not perform grinding, melt and knead with a screw extruder, and directly use after extrusion granulation, and the rest is the same as in Example 3.

[0091] Performance test:

[0092] Conduct an evaluation test and volume resistivity test on the breakdown strength resistance of the cable materials obtained in Examples 1-5 and Comparative Examples 1-8.

[0093] Cut the above cable material samples into rectangular cross-linked plate specimens of the same size (thickness 0.5 mm) for breakdown strength and surface resistance tests.

[0094] I. Breakdown strength test:

[0095] Before the breakdown strength test, treat the specimens in a vacuum oven at 80 °C for 48 h. Simulate the cable operating environment and conduct electrothermal aging in a high humidity environment. Compare the change in breakdown field strength before and after electrothermal aging in a wet environment to evaluate the ability of the cable material to resist the generation of water trees during operation in a wet environment. The specific test is as follows:

[0096] Apply an electrothermal aging electrode with a frequency of 50 Hz and a field strength of 7 kv / mm to the specimens, and age them in an environment with a relative humidity of 80% and a temperature of 70 °C for 25 days to obtain specimens aged in a humid and hot environment.

[0097] Refer to IEC 60243-1:2013 "Test Methods for Electrical Strength of Insulating Materials - Part 1" to test the breakdown field strength of each group of specimens before and after electrothermal aging in a wet environment. The test results are shown in Table 1.

[0098] II. Surface Resistance Test:

[0099] The surface resistance of each group of specimens was tested in accordance with GB / T 31838.3-2019 / IEC 62631-3-2:2015 Dielectric and resistive properties of solid insulating materials - Part 3: Resistive properties (DC methods) - Surface resistance and surface resistivity. The test results are shown in Table 1.

[0100] Table 1

[0101]

[0102]

[0103] As can be seen from the data in Table 1, compared with Comparative Examples 1-8: For the cable materials of Examples 1-5, the reduction rate of the breakdown field strength after electrothermal aging in a high-humidity environment is small, indicating fewer internal defects and a dense structure in the cable materials, and excellent waterproof performance; the cyclotriphosphazene crosslinking agent has a greater impact on the waterproof property of the cable materials, followed by acrylate compounds and nano boron nitride. Compared with Comparative Examples 1-8: For the cable materials of Examples 1-5, the surface resistance reaches 6.42×10 12 Above, the insulation performance is excellent; ethylene-vinyl acetate copolymer has a greater impact on the insulation property of the cable materials, followed by cyclotriphosphazene crosslinking agent and nano silica aerosol. The present invention uses a combination of various functional materials, and the components act synergistically to jointly promote the performance improvement of the cable materials, can adapt to the use environment of high voltage and high humidity, resist long-term corrosion, and can protect the subway cable to work stably for a long time.

[0104] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An insulating and waterproof cable material, characterized in that, It comprises the following raw materials in parts by weight: 40 - 70 parts of low-density polyethylene, 20 - 35 parts of high-density polyethylene, 15 - 30 parts of cyclotriphosphazene crosslinking agent, 10 - 22 parts of acrylate compound, 8 - 20 parts of ethylene-vinyl acetate copolymer, 3 - 10 parts of nucleating agent, 1.5 - 5 parts of hydrogenated castor oil, 1 - 4 parts of antioxidant; the raw materials form a crosslinked network through radiation-induced polymerization; The chemical structural formula of the cyclotriphosphazene crosslinking agent is as follows:

2. An insulating and waterproof cable material according to claim 1, characterized in that, The acrylate compound includes at least one of methyl acrylate, ethyl acrylate, methyl 2-methylacrylate, ethyl 2-methylacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, dipropylene glycol diacrylate.

3. An insulating and waterproof cable material according to claim 1, characterized in that, The content of vinyl acetate in the ethylene-vinyl acetate copolymer is 10 - 20 wt%.

4. An insulating and waterproof cable material according to claim 1, characterized in that, The raw materials of the nucleating agent include white mineral oil, low-density maleic anhydride grafted polyethylene, nano boron nitride, organosilica nanospheres, nano silica aerosol.

5. An insulating and waterproof cable material according to claim 1, characterized in that, The antioxidant includes hindered phenol antioxidants and / or phosphite antioxidants.

6. The preparation method of an insulating and waterproof cable material according to any one of claims 1 to 5, characterized in that, It includes the following steps: S1. Grind and mix evenly low-density polyethylene, high-density polyethylene, acrylate compound, nucleating agent, hydrogenated castor oil, and part of the cyclotriphosphazene crosslinking agent according to parts by weight, and conduct melt blending at 110 - 150 °C to obtain a blend; S2. Add ethylene-vinyl acetate copolymer, antioxidant, and the remaining cyclotriphosphazene crosslinking agent to the obtained blend according to parts by weight, and continue to knead; S3. Put the melt-blended material into a mold, and use a flat vulcanizer for hot pressing to obtain a molded material; S4. Conduct radiation crosslinking on the molded material to finally obtain a cable material.

7. The preparation method of an insulating and waterproof cable material according to claim 6, characterized in that, In the step S1: The preparation method of the nucleating agent is: mix white mineral oil and low-density maleic anhydride grafted polyethylene evenly, then add nano boron nitride, organosilica nanospheres, nano silica aerosol and mix, send it into a screw extruder for melt mixing, extrude and pelletize, and then grind to a D50 particle size ≤ 15 microns and a D90 particle size ≤ 30 microns to obtain the nucleating agent; and / or In the nucleating agent, the mass ratio of white mineral oil, low-density maleic anhydride grafted polyethylene, nano boron nitride, organosilica nanospheres, nano silica aerosol is 1 - 2:10 - 50:3 - 15:3 - 15:50 - 150; and / or The addition amount of part of the cyclotriphosphazene crosslinking agent is 1 / 3 - 4 / 5 of the total weight parts of the cyclotriphosphazene crosslinking agent; and / or The time of melt blending is 0.5 - 2 h.

8. The preparation method of an insulating and waterproof cable material according to claim 6, characterized in that, In the step S2: The temperature for continuous kneading is 110 - 150 °C, and the time is 0.5 - 2 h.

9. The preparation method of an insulating and waterproof cable material according to claim 6, characterized in that, In the step S3: The temperature for hot pressing is 110 - 150 °C, and the pressure is 2 - 4 MPa.

10. The preparation method of an insulating and waterproof cable material according to claim 6, characterized in that, In the step S4: The radiation dose for radiation crosslinking is 90 - 200 kGy.

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