A cross-linked polyethylene insulated power cable

Abstract

This invention relates to the field of cable technology and proposes a cross-linked polyethylene (XLPE) insulated power cable, comprising, from the inside out, a conductor, a conductor shielding layer, a XLPE insulation layer, an insulating shielding layer, a metal shielding layer, and a sheath layer. The raw materials for the XLPE insulation layer include the following components: polyethylene, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, isocyanate-based alkoxysilane-modified silica, vinylalkoxysilane-modified silica, and a cross-linking agent. This technical solution solves the problem in related technologies where the incompatibility between silane coupling agent-modified silica and XLPE insulation material is insufficient, leading to poor mechanical strength of the XLPE insulation material.

Description

Technical Field

[0001] This invention relates to the field of cable technology, and more specifically, to a cross-linked polyethylene insulated power cable. Background Technology

[0002] Cross-linked polyethylene (XLPE), including radiation-crosslinked polyethylene, peroxide-crosslinked polyethylene, and silane-crosslinked polyethylene, is a polymer material made by chemically or physically transforming polyethylene from a linear chain structure into a three-dimensional network structure with cross-linked molecular chains. Compared to polyethylene, XLPE has better heat resistance and aging resistance, and is widely used as insulation material for power cables.

[0003] During production, transportation, and installation, power cables are subjected to various external forces, thus requiring their insulation materials to possess a certain level of mechanical strength. Currently, to improve the mechanical strength of cross-linked polyethylene (XLPE) insulation materials, silica is typically added to the raw materials. However, silica contains a large number of hydroxyl groups on its surface, which easily form aggregates, affecting the uniform dispersion of silica in XLPE insulation materials. Therefore, surface modification treatment of silica is necessary. Commonly used modifiers include silane coupling agents. However, the compatibility between modified silica and XLPE insulation materials is insufficient, leading to inadequate mechanical strength in XLPE insulation materials. Summary of the Invention

[0004] This invention proposes a cross-linked polyethylene insulated power cable, which solves the problem in related technologies where the incompatibility between silane coupling agent-modified silica and cross-linked polyethylene insulation material is insufficient, resulting in poor mechanical strength of the cross-linked polyethylene insulation material.

[0005] The technical solution of the present invention is as follows: A cross-linked polyethylene insulated power cable comprises, from the inside out, a conductor, a conductor shielding layer, a cross-linked polyethylene insulation layer, an insulation shielding layer, a metal shielding layer, and a sheath layer. The raw materials of the cross-linked polyethylene insulation layer include the following components: polyethylene, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, isocyanate-based alkoxysilane modified silica, vinylalkoxysilane modified silica, and a cross-linking agent.

[0006] The conductor is the conductive part of a power cable used to transmit electrical energy, and can be made of copper or aluminum. Compared to aluminum, copper has better electrical conductivity and mechanical properties, but copper is more expensive. Therefore, to reduce production costs, aluminum is preferred as the conductor in this invention.

[0007] The conductor shielding layer eliminates the increase in electric field intensity on the conductor surface caused by surface roughness, ensuring better contact between the cross-linked polyethylene insulation layer and the conductor. Simultaneously, an insulating shielding layer is placed between the cross-linked polyethylene insulation layer and the metallic shielding layer to ensure good contact. The outermost sheath layer protects the power cable from external damage.

[0008] As a further technical solution, the mass content of vinyl acetate in the ethylene-vinyl acetate copolymer is 12%~15%.

[0009] Ethylene-vinyl acetate copolymers with a vinyl acetate (VA) content of 12%–15% exhibit good compatibility not only with polyethylene but also with ethylene-vinyl alcohol copolymers. Adding VA as a raw material improves the compatibility between polyethylene and ethylene-vinyl alcohol copolymers, ensuring good overall compatibility of the cross-linked polyethylene insulation layer and further enhancing its mechanical strength. Conversely, low VA content leads to decreased compatibility with ethylene-vinyl alcohol copolymers, while high VA content decreases compatibility with polyethylene, resulting in a decline in the mechanical strength of the cross-linked polyethylene insulation layer.

[0010] As a further technical solution, the mass ratio of the isocyanate-based alkoxysilane-modified silica to the vinyl alkoxysilane-modified silica is 2~3:1.

[0011] During the experiment, the inventors unexpectedly discovered that when the mass ratio of isocyanate-based alkoxysilane-modified silica to vinyl alkoxysilane-modified silica was 2 to 3:1, the mechanical strength of the cross-linked polyethylene insulation material was further improved.

[0012] As a further technical solution, the raw materials for the isocyanate-based alkoxysilane modified silica include isocyanate-based alkoxysilane and silica in a mass ratio of 0.1~0.5:100; the raw materials for the vinylalkoxysilane modified silica include vinylalkoxysilane and silica in a mass ratio of 0.1~0.5:100.

[0013] When the amount of alkoxysilane is too low, the coating rate of the modifier is too low, and a good modification effect cannot be achieved. Conversely, when the amount of alkoxysilane is too high, the modifier molecules will entangle and polymerize, hindering the dispersion of silica. Therefore, during the modification process, when the mass ratio of isocyanate-based alkoxysilane to silica is 0.1~0.5:100, and the mass ratio of vinylalkoxysilane to silica is 0.1~0.5:100, the modification effect is better, and the dispersion of silica is improved.

[0014] As a further technical solution, the isocyanate-based alkoxysilane includes one or more of 3-isocyanate-based propyltriethoxysilane, 3-isocyanate-based propyltrimethoxysilane, and 3-isocyanate-based propylmethyldimethoxysilane.

[0015] As a further technical solution, the vinylalkoxysilane includes one or more of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltri(2-methoxyethoxy)silane, and vinyltriisopropoxysilane.

[0016] As a further technical solution, the preparation method of the isocyanate-based alkoxysilane modified silica includes the following steps: mixing silica and ethanol solution, then adding isocyanate-based alkoxysilane for modification to obtain the isocyanate-based alkoxysilane modified silica; the preparation method of the vinylalkoxysilane modified silica includes the following steps: mixing silica and ethanol solution, then adding vinylalkoxysilane for modification to obtain the vinylalkoxysilane modified silica.

[0017] In the preparation of isocyanate-based alkoxysilane-modified silica, silica and an ethanol solution are first initially mixed, followed by the addition of isocyanate-based alkoxysilane for modification. The preferred modification temperature is 45-55℃, and the preferred modification time is 2.5-3.5 h. After modification, the mixture is centrifuged, washed, and dried to obtain isocyanate-based alkoxysilane-modified silica. Similarly, in the preparation of vinylalkoxysilane-modified silica, silica and an ethanol solution are first initially mixed, followed by the addition of vinylalkoxysilane for modification. The preferred modification temperature is 45-55℃, and the preferred modification time is 2.5-3.5 h. After modification, the mixture is centrifuged, washed, and dried to obtain vinylalkoxysilane-modified silica.

[0018] As a further technical solution, the mass ratio of the isocyanate-based alkoxysilane-modified silica and the vinyl alkoxysilane-modified silica to the mass ratio of the polyethylene, ethylene-vinyl acetate copolymer, and ethylene-vinyl alcohol copolymer is 3~6:100:5~7:2~5.

[0019] As a further technical solution, the raw materials also include additives, which include one or more of flame retardants, voltage stabilizers, lubricants, antioxidants, softeners, and pigments.

[0020] As a further technical solution, the additives are antioxidants and voltage stabilizers in a mass ratio of 1.5:1~3.

[0021] The addition of antioxidants can inhibit or delay the oxidation of polymer materials during processing, while the addition of voltage stabilizers can reduce the generation of macromolecular free radicals and deep traps during aging, thereby improving the dendrite initiation voltage of polyethylene and the breakdown strength of aged samples. The antioxidants include one or more of antioxidants 1010, 1076, 330, 4010, and 168, preferably antioxidant 168. The voltage stabilizers include one or more of aminoquinoline, N,N'-diphenyl-p-phenylenediamine, and dibenzoyl-p-benzoquinone dioxime, preferably dibenzoyl-p-benzoquinone dioxime.

[0022] As a further technical solution, the mass ratio of the polyethylene to the crosslinking agent is 100:1.5~2.5.

[0023] As a further technical solution, the crosslinking agent includes one or both of dicumyl peroxide and benzoyl peroxide.

[0024] As a further technical solution, the mass ratio of the polyethylene to the additive is 100:2.5~4.5.

[0025] As a further technical solution, the preparation method of the cross-linked polyethylene insulation layer includes the following steps: after mixing polyethylene, ethylene-vinyl acetate copolymer and ethylene-vinyl alcohol copolymer, first add isocyanate-based alkoxysilane modified silica and continue mixing, then add vinyl alkoxysilane modified silica and mix evenly, finally add cross-linking agent and mix, extrude and coat the outside of the conductor shielding layer, cross-link, and obtain the cross-linked polyethylene insulation layer.

[0026] In the process of preparing cross-linked polyethylene insulation layer, isocyanate-based alkoxysilane-modified silica and vinyl alkoxysilane-modified silica are added stepwise. The isocyanate-based alkoxysilane-modified silica is added first and mixed evenly before vinyl alkoxysilane-modified silica is added, which further improves the mechanical strength of cross-linked polyethylene insulation material.

[0027] As a further technical solution, the preparation method of the cross-linked polyethylene insulation layer includes the following steps: after mixing polyethylene, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer and additives, first add isocyanate-based alkoxysilane modified silica and continue mixing, then add vinyl alkoxysilane modified silica and mix evenly, finally add cross-linking agent and mix, extrude and coat the outside of the conductor shielding layer, cross-link, and obtain the cross-linked polyethylene insulation layer.

[0028] The working principle and beneficial effects of this invention are as follows: This invention simultaneously incorporates ethylene-vinyl acetate copolymer and ethylene-vinyl alcohol copolymer into a cross-linked polyethylene insulation layer. Furthermore, a portion of the silica is modified with isocyanate-based alkoxysilane, and the other portion with vinyl alkoxysilane. This improves the compatibility between silica and the cross-linked polyethylene insulation material, thereby enhancing the mechanical strength of the cross-linked polyethylene insulation material. On one hand, the addition of ethylene-vinyl acetate copolymer ensures good compatibility between the ethylene-vinyl alcohol copolymer and polyethylene. Simultaneously, the hydroxyl groups in the ethylene-vinyl alcohol copolymer molecular structure can interact with the isocyanate groups in the isocyanate-based alkoxysilane-modified silica. On the other hand, polyethylene contains a small amount of carbon-carbon double bonds, which can interact with the vinyl groups in the vinyl alkoxysilane-modified silica during insulation layer processing. These two aspects improve the compatibility between silica and the cross-linked polyethylene insulation material, thereby increasing the mechanical strength of the cross-linked polyethylene insulation material. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] In the following embodiments and comparative examples: The polyethylene is low-density polyethylene (LDPE), INEOS BPD2142; The ethylene-vinyl acetate copolymer is DuPont EVA 670. The ethylene-vinyl alcohol copolymer is Kuraray EVOH G176B from Japan; The silica is Degussa A200 fumed silica; A method for preparing a cross-linked polyethylene (XLPE) insulated power cable includes the following steps: extruding a conductor shielding layer, a XLPE insulation layer, and an insulation shielding layer sequentially around an aluminum conductor; then wrapping a metal shielding layer around it; and finally extruding a sheath layer to obtain the XLPE insulated power cable. The method for preparing the XLPE insulation layer is as follows: Example 1 By weight, 100 parts of silica and 700 parts of 75% ethanol aqueous solution were mixed and stirred at 350 rpm for 20 min. Then, 0.5 parts of 3-isocyanate-propyltriethoxysilane were added, the temperature was raised to 45℃ and stirring was continued for 3.5 h. The mixture was then centrifuged, the product was washed with water and dried to obtain isocyanate-alkoxysilane modified silica. Mix 100 parts of silica and 700 parts of 75% ethanol aqueous solution, stir at 350 rpm for 20 min, add 0.5 parts of vinyltriethoxysilane, heat to 45℃ and continue stirring for 3.5 h, centrifuge, wash the product with water and dry to obtain vinylalkoxysilane modified silica. 100 parts of polyethylene, 7 parts of ethylene-vinyl acetate copolymer, 5 parts of ethylene-vinyl alcohol copolymer, 1.5 parts of antioxidant 168, and 1 part of dibenzoyl-p-benzoquinone dioxime were mixed evenly. Then, 3 parts of isocyanate-based alkoxysilane-modified silica and 3 parts of vinylalkoxysilane-modified silica were added and mixed for another 10 minutes until uniform. Finally, 1.5 parts of dicumyl peroxide were added and mixed. The mixture was then extruded and coated onto the outside of the conductor shielding layer and crosslinked to obtain a crosslinked polyethylene insulation layer.

[0031] Example 2 By weight, 100 parts of silica and 800 parts of 75% ethanol aqueous solution were mixed and stirred at 300 rpm for 15 min. Then, 0.1 parts of 3-isocyanate-propyltrimethoxysilane were added, the temperature was raised to 55℃ and stirring was continued for 2.5 h. The mixture was then centrifuged, the product was washed with water and dried to obtain isocyanate-alkoxysilane modified silica. Mix 100 parts of silica and 900 parts of 75% ethanol aqueous solution, stir at 350 rpm for 25 min, add 0.1 parts of vinyltrimethoxysilane, heat to 55℃ and continue stirring for 2.5 h, centrifuge, wash the product with water and dry to obtain vinylalkoxysilane modified silica. 100 parts of polyethylene, 5 parts of ethylene-vinyl acetate copolymer, 2 parts of ethylene-vinyl alcohol copolymer, 1.5 parts of antioxidant 168, and 3 parts of dibenzoyl-p-benzoquinone dioxime were mixed evenly. Then, 1.5 parts of isocyanate-based alkoxysilane-modified silica and 1.5 parts of vinylalkoxysilane-modified silica were added and mixed for another 5 minutes until uniform. Finally, 2.5 parts of dicumyl peroxide were added and mixed. The mixture was then extruded and coated onto the outside of the conductor shielding layer and crosslinked to obtain a crosslinked polyethylene insulation layer.

[0032] Example 3 The only difference from Example 1 is that 4 parts of isocyanate-based alkoxysilane-modified silica and 2 parts of vinylalkoxysilane-modified silica are added and mixed further.

[0033] Example 4 The only difference from Example 1 is that 4.5 parts of isocyanate-based alkoxysilane-modified silica and 1.5 parts of vinylalkoxysilane-modified silica are added and mixed further.

[0034] Example 5 The only difference from Example 1 is that 5.5 parts of isocyanate-based alkoxysilane-modified silica and 0.5 parts of vinylalkoxysilane-modified silica are added and mixed further.

[0035] Example 6 The only difference from Example 4 is that: after mixing 100 parts of polyethylene, 7 parts of ethylene-vinyl acetate copolymer, 5 parts of ethylene-vinyl alcohol copolymer, 1.5 parts of antioxidant 168, and 1 part of dibenzoyl-p-benzoquinone dioxime evenly, 4.5 parts of isocyanate-based alkoxysilane modified silica are added and mixed for 5 minutes, then 1.5 parts of vinylalkoxysilane modified silica are added and mixed for 5 minutes until uniform. Finally, 1.5 parts of dicumyl peroxide are added and mixed, extruded and coated on the outside of the conductor shielding layer, and crosslinked to obtain a crosslinked polyethylene insulation layer.

[0036] Example 7 The only difference from Example 4 is that: after mixing 100 parts of polyethylene, 7 parts of ethylene-vinyl acetate copolymer, 5 parts of ethylene-vinyl alcohol copolymer, 1.5 parts of antioxidant 168, and 1 part of dibenzoyl-p-benzoquinone dioxime evenly, 1.5 parts of vinylalkoxysilane modified silica are added and mixed for 5 minutes, then 4.5 parts of isocyanate-based alkoxysilane modified silica are added and mixed for 5 minutes until uniform. Finally, 1.5 parts of dicumyl peroxide are added and mixed. The mixture is then extruded and coated onto the outside of the conductor shielding layer and crosslinked to obtain a crosslinked polyethylene insulation layer.

[0037] Comparative Example 1 The only difference from Example 1 is that the isocyanate-based alkoxysilane modified silica is replaced with an equal amount of vinylalkoxysilane modified silica.

[0038] Comparative Example 2 The only difference from Example 1 is that the vinylalkoxysilane modified silica is replaced with an equal amount of isocyanate-based alkoxysilane modified silica.

[0039] Comparative Example 3 The only difference from Example 1 is that ethylene-vinyl acetate copolymer and ethylene-vinyl alcohol copolymer are not added.

[0040] Referring to the test method in GB / T 2951.11-2008, the tensile strength of the cross-linked polyethylene insulation layer obtained in the above examples and comparative examples was tested. The test specimen was a dumbbell specimen with a thickness of 1.5 mm and a tensile speed of 25 mm / min. The average value of the test results of the 5 test specimens was recorded as the final result, which is shown in Table 1.

[0041] Table 1. Tensile strength test results of cross-linked polyethylene insulation layer

[0042] As shown in Table 1, the cross-linked polyethylene insulation layer provided by this invention has a tensile strength of over 21.2 MPa, exhibiting high mechanical strength. The tensile strength of the cross-linked polyethylene insulation layers obtained in Examples 1-7 is higher than that in Comparative Examples 1-3, indicating that the combined use of ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, isocyanate-based alkoxysilane-modified silica, and vinylalkoxysilane-modified silica improves the mechanical strength of the cross-linked polyethylene insulation layer.

[0043] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cross-linked polyethylene insulated power cable, comprising, from the inside out, a conductor, a conductor shielding layer, a cross-linked polyethylene insulation layer, an insulation shielding layer, a metallic shielding layer, and a sheath layer, characterized in that, The raw materials for the cross-linked polyethylene insulation layer include the following components: polyethylene, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, isocyanate-based alkoxysilane-modified silica, vinylalkoxysilane-modified silica, and cross-linking agent.

2. The cross-linked polyethylene insulated power cable according to claim 1, characterized in that, The mass ratio of the isocyanate-based alkoxysilane-modified silica to the vinyl alkoxysilane-modified silica is 2~3:

1.

3. The cross-linked polyethylene insulated power cable according to claim 1, characterized in that, The raw materials for the isocyanate-based alkoxysilane-modified silica include isocyanate-based alkoxysilane and silica in a mass ratio of 0.1~0.5:100; the raw materials for the vinylalkoxysilane-modified silica include vinylalkoxysilane and silica in a mass ratio of 0.1~0.5:

100.

4. A cross-linked polyethylene insulated power cable according to claim 1, characterized in that, The preparation method of the isocyanate-based alkoxysilane-modified silica includes the following steps: mixing silica and ethanol solution, then adding isocyanate-based alkoxysilane for modification to obtain the isocyanate-based alkoxysilane-modified silica; the preparation method of the vinylalkoxysilane-modified silica includes the following steps: mixing silica and ethanol solution, then adding vinylalkoxysilane for modification to obtain the vinylalkoxysilane-modified silica.

5. A cross-linked polyethylene insulated power cable according to claim 1, characterized in that, The mass ratio of the isocyanate-based alkoxysilane-modified silica and the vinyl alkoxysilane-modified silica to the mass ratio of the polyethylene, ethylene-vinyl acetate copolymer, and ethylene-vinyl alcohol copolymer is 3~6:100:5~7:2~5.

6. A cross-linked polyethylene insulated power cable according to claim 1, characterized in that, The raw materials also include additives, which include one or more of flame retardants, voltage stabilizers, lubricants, antioxidants, softeners, and pigments.

7. A cross-linked polyethylene insulated power cable according to claim 6, characterized in that, The additives are antioxidants and voltage stabilizers in a mass ratio of 1.5:1~3.

8. A cross-linked polyethylene insulated power cable according to claim 1, characterized in that, The mass ratio of the polyethylene to the crosslinking agent is 100:1.5~2.

5.

9. A cross-linked polyethylene insulated power cable according to claim 7, characterized in that, The mass ratio of the polyethylene to the additive is 100:2.5~4.

5.

10. A cross-linked polyethylene insulated power cable according to claim 1, characterized in that, The method for preparing the cross-linked polyethylene insulation layer includes the following steps: after mixing polyethylene, ethylene-vinyl acetate copolymer and ethylene-vinyl alcohol copolymer, isocyanate-based alkoxysilane modified silica is added and mixed further, then vinyl alkoxysilane modified silica is added and mixed evenly, and finally a cross-linking agent is added and mixed, extruded and coated on the outside of the conductor shielding layer, and cross-linked to obtain the cross-linked polyethylene insulation layer.

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