Melt blending preparation process of semiconductive shielding material for ultrahigh-pressure crosslinked polyethylene cable

Abstract

The invention discloses a melt blending preparation process of a semiconductive shielding material for an ultrahigh-pressure crosslinked polyethylene cable, which comprises the following steps: S1, premixing low-density polyethylene and an ethylene-vinyl alcohol copolymer in proportion, the vinyl alcohol chain segment content of the ethylene-vinyl alcohol copolymer being 25%-45%; s2, performing plasma surface treatment on carbon black, and compounding the carbon black with carbon nanotubes to form a conductive filler system; s3, under the protection of inert gas, adding the matrix resin in the step S1 and the conductive filler in the step S2 into a double-screw extruder in stages, and synchronously adding a hindered phenol and phosphite compound antioxidant; and S4, carrying out segmented mixing under the temperature gradient of 160-210 DEG C. Through synergistic compounding of the plasma surface modified carbon black and the carbon nanotubes and in combination with a staged feeding process, directional dispersion of the conductive filler is realized, a three-dimensional interpenetrating conductive network is formed, and the local electric field homogenization capability of the ultrahigh-voltage cable is remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of cable shielding materials, and in particular to a melt blending preparation process of a semi-conductive shielding material for an ultra-high voltage cross-linked polyethylene cable. Background Art

[0002] Semi-conductive shielding material for high-voltage cross-linked polyethylene cables is a key transition material between the cable conductor and the insulation layer. Its core function is to even out the electric field distribution on the conductor surface and suppress local discharge. At the same time, it needs to form a defect-free interface with the insulation layer to ensure long-term operational stability.

[0003] At present, the preparation of semi-conductive shielding materials generally adopts the melt blending process, but it is difficult to balance the dispersion uniformity and interface bonding strength of the conductive filler in the traditional process. Carbon black and carbon nanotubes are prone to agglomeration due to the difference in surface energy, resulting in discontinuous conductive network, which is easy to cause resistivity fluctuation and electric field distortion under ultra-high voltage conditions. Secondly, the compatibility between the matrix resin and the filler is not well regulated. Especially when a high content of vinyl alcohol segmented copolymer is introduced, the difference in melt index can easily cause phase separation, resulting in micropores or cracks at the interface between the shielding layer and the insulating layer. Finally, the temperature field and shear force field have poor coordination during the mixing process, and the carbon nanotube structure is easily damaged by high temperature and high shear. At the same time, the uneven dispersion of antioxidants leads to insufficient thermal oxidation stability of the material, and after long-term operation, problems such as conductivity attenuation and increased thermal extension deformation occur.

[0004] In response to the above problems, we have introduced a melt blending preparation process for semi-conductive shielding materials for ultra-high voltage cross-linked polyethylene cables. Summary of the invention

[0005] The invention discloses a melt blending preparation process of a semi-conductive shielding material for an ultra-high voltage cross-linked polyethylene cable, aiming to solve the technical problems in the background technology.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A melt blending preparation process for a semi-conductive shielding material for an ultra-high voltage cross-linked polyethylene cable comprises the following steps: S1. Premixing low-density polyethylene and ethylene-vinyl alcohol copolymer in proportion, wherein the vinyl alcohol segment content of the ethylene-vinyl alcohol copolymer is 25%-45%; S2, performing plasma surface treatment on carbon black, and compounding with carbon nanotubes to form a conductive filler system; S3, under the protection of inert gas, adding the base resin of step S1 and the conductive filler of step S2 into a twin-screw extruder in stages, and simultaneously adding hindered phenol and phosphite compound antioxidants; S4. Perform staged mixing under a temperature gradient of 160 - 210 °C, and the rotational speed ratio of the main feeding section to the side feeding section is 1:1.2 - 1.8; S5. Granulate the melt by water-cooled strand pelletizing, and control the aspect ratio of the pellets to be 1.5 - 2.0.

[0007] In a preferred embodiment, the mass proportion of the ethylene-vinyl alcohol copolymer in the matrix resin composite system is 8% - 15%, and the difference in melt index between it and the low-density polyethylene does not exceed 2 g / 10 min.

[0008] In a preferred embodiment, the plasma surface treatment of the carbon black in step S2 is refined into the following steps: S11. Place the carbon black in the reaction chamber; S12. Introduce a mixed gas containing amino silane and vinyltrimethoxysilane for treatment for 10 - 30 minutes, and maintain the treatment pressure at 0.1 - 0.5 MPa.

[0009] In a preferred embodiment, the screw combination of the twin-screw extruder includes at least three mixing sections, where the temperature of the first mixing section is 160 - 175 °C, the temperature of the second mixing section is 180 - 195 °C, and the temperature of the third mixing section is 200 - 210 °C.

[0010] In a preferred embodiment, the addition method of the antioxidant in step S3 is the melt impregnation method, and the addition timing is the starting stage of the second mixing section.

[0011] In a preferred embodiment, the addition of the conductive filler in step S3 is divided into two stages, which are respectively: In the first stage, 60 - 70% of the total mass of carbon black is added; In the second stage, the remaining carbon black and all carbon nanotubes are added.

[0012] In a preferred embodiment, in step S3, an organophilic montmorillonite with a mass fraction not exceeding 5% is added as an auxiliary dispersant, and the addition timing is synchronized with the first-stage conductive filler.

[0013] In a preferred embodiment, the water temperature for underwater pelletizing in step S5 is controlled at 25 - 40 °C, the wind speed for hot air drying is 3 - 5 m / s, and the air temperature is 50 - 70 °C.

[0014] In a preferred embodiment, its volume resistivity ≤ 1.0×10² Ω·cm (23 °C), and it is applicable to the conductor shielding layer of cross-linked polyethylene cables with a rated voltage of 220 kV and above.

[0015] The melt blending preparation process of the semiconductive shielding material for extra-high voltage cross-linked polyethylene cables provided by the present invention has the following advantages: 1. Through the synergistic compounding of plasma surface-modified carbon black and carbon nanotubes, combined with the staged feeding process, the directional dispersion of conductive fillers is achieved, forming a three-dimensional interpenetrating conductive network, which significantly improves the local electric field equalization capability of the ultra-high voltage cable.

[0016] 2. The melt index matching design of ethylene-vinyl alcohol copolymer and low-density polyethylene, combined with the auxiliary dispersion effect of organic montmorillonite, effectively enhances the interface compatibility between the resin matrix and the conductive filler, and the interface transition between the shielding layer and the insulating layer is smooth after the cable is extruded.

[0017] 3. The segmented mixing process with gradient temperature control and rotation speed coordination is adopted to accurately control the melt shear force field within the range of 160-210℃, which not only ensures the integrity of the carbon nanotube structure, but also avoids thermal degradation of the resin in the high temperature zone. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The present invention is a schematic diagram of the overall steps of a melt blending preparation process for a semi-conductive shielding material for ultra-high voltage cross-linked polyethylene cable.

[0019] Figure 2 This is a schematic diagram of the S1 refinement step of the melt blending preparation process of a semi-conductive shielding material for ultra-high voltage cross-linked polyethylene cable proposed by the present invention. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application usually described and marked in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0021] The invention discloses a melt blending preparation process of a semi-conductive shielding material for an ultra-high voltage cross-linked polyethylene cable.

[0022] Reference Figure 1 and Figure 2As shown, a melt blending preparation process for a semiconductive shielding compound for ultra-high voltage cross-linked polyethylene cables premixes a matrix resin with low-density polyethylene and an ethylene-vinyl alcohol copolymer with a specific proportion of ethylene alcohol segments. The proportion of this copolymer in the composite system is controlled within the range of 8% - 15%, and the difference in melt index between the two resins does not exceed 2 g / 10 min. When implementing plasma surface treatment on carbon black, the material is placed in a closed reaction chamber, and a mixed gas containing amino silane and vinyltrimethoxysilane is introduced. It is treated at a pressure of 0.1 - 0.5 MPa for 10 - 30 minutes. The treated carbon black and carbon nanotubes are compounded in a predetermined proportion to form a conductive system.

[0023] In the twin-screw extrusion process, the matrix resin and the conductive filler are fed in two stages: 60 - 70% of the carbon black is added during the first feeding and simultaneously mixed with no more than 5% of the organic montmorillonite. The remaining carbon black and all the carbon nanotubes are added during the second feeding. The entire extrusion process is protected by inert gas. The temperatures of each mixing section are set in a gradient of 160 - 175°C, 180 - 195°C, and 200 - 210°C, and the rotational speed ratio of the main and side feeding sections is maintained at 1:1.2 - 1.8. The compound antioxidant system of hindered phenols and phosphite esters is injected through melt impregnation at the starting position of the second mixing section.

[0024] In the molding stage, the extruded melt is introduced into a water cooling system at 25 - 40°C, and the aspect ratio of the pellets is adjusted to 1.5 - 2.0 by adjusting the traction speed. Subsequently, it is treated with a hot air drying system with a wind speed of 3 - 5 m / s and a wind temperature of 50 - 70°C. The prepared material is detected to show a volume resistivity lower than 1.0×10² Ω·cm. Microstructural observation confirms that the conductive filler forms a continuous network, and the hot elongation deformation rate ≤ 5%. When actually applied to the conductor shielding layer of cables with 220 kV and above, the interface between the material and the insulation layer is tightly combined, and the withstand field strength exceeds 68 kV / mm, meeting the long-term operation requirements of ultra-high voltage cables.

[0025] As described above, it is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. The substitution may be the substitution of some structures, devices, and method steps, or a complete technical solution. Any equivalent substitution or change made according to the technical solution and inventive concept of the present invention should be covered within the protection scope of the present invention.

Claims

1. A melt blending preparation process for a semiconductive shielding material used in extra-high voltage cross-linked polyethylene cables, characterized in that, It includes the following steps: S1. Premix low-density polyethylene and ethylene-vinyl alcohol copolymer in proportion, wherein the ethylene alcohol segment content of the ethylene-vinyl alcohol copolymer is 25%-45%; S2. Perform plasma surface treatment on carbon black and compound it with carbon nanotubes to form a conductive filler system; S3. Under the protection of inert gas, add the matrix resin in step S1 and the conductive filler in step S2 to a twin-screw extruder in stages, and synchronously add a compound antioxidant of hindered phenol and phosphite; S4. Carry out staged mixing at a temperature gradient of 160-210 °C, and the rotation speed ratio of the main feeding section to the side feeding section is 1:1.2-1.8; S5. Granulate the melt by water-cooled strand pelletizing, and control the length-diameter ratio of the pellets at 1.5-2.

0.

2. The melt blending preparation process of the semiconductive shielding material for extra-high voltage cross-linked polyethylene cables according to claim 1, characterized in that, The mass ratio of the ethylene-vinyl alcohol copolymer in the matrix resin composite system is 8%-15%, and the difference in melt index between it and the melt index of low-density polyethylene does not exceed 2 g / 10 min.

3. The melt blending preparation process of the semiconductive shielding material for extra-high voltage cross-linked polyethylene cables according to claim 1, characterized in that, The plasma surface treatment of the carbon black in step S2 is refined into the following steps: S11. Place the carbon black in the reaction chamber; S12. Pass a mixed gas containing amino silane and vinyltrimethoxysilane to treat for 10-30 minutes, and maintain the treatment pressure at 0.1-0.5 MPa.

4. The melt blending preparation process of the semiconductive shielding material for extra-high voltage cross-linked polyethylene cables according to claim 2, characterized in that, The screw combination of the twin-screw extruder includes at least three mixing sections, wherein the temperature of the first mixing section is 160-175 °C, the temperature of the second mixing section is 180-195 °C, and the temperature of the third mixing section is 200-210 °C.

5. The melt blending preparation process of the semiconductive shielding material for extra-high voltage cross-linked polyethylene cables according to claim 1, characterized in that, The addition method of the antioxidant in step S3 is the melt impregnation method, and the addition time is the starting stage of the second mixing section.

6. The melt blending preparation process of the semiconductive shielding material for extra-high voltage cross-linked polyethylene cables according to claim 2, characterized in that, The addition of the conductive filler in step S3 is divided into two stages, which are respectively: In the first stage, add 60-70% of the total mass of carbon black; In the second stage, add the remaining carbon black and all carbon nanotubes.

7. The melt blending preparation process of the semiconductive shielding material for extra-high voltage cross-linked polyethylene cables according to claim 2, characterized in that, Add an organophilic montmorillonite with a mass fraction not exceeding 5% as an auxiliary dispersant in step S3, and the addition time is synchronous with the first-stage conductive filler.

8. The melt blending preparation process of the semiconductive shielding material for extra-high voltage cross-linked polyethylene cables according to claim 1, characterized in that, In step S5, the water temperature of underwater pelletizing is controlled at 25-40 °C, the wind speed of hot air drying is 3-5 m / s, and the air temperature is 50-70 °C.

9. The melt blending preparation process of the semiconductive shielding material for extra-high voltage cross-linked polyethylene cables according to any one of claims 1-8, characterized in that, Its volume resistivity ≤ 1.0×10² Ω·cm (23 °C), and it is applicable to the conductor shielding layer of cross-linked polyethylene cables with a rated voltage of 220 kV and above.

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