Semi-conductive flame-retardant PVC high-voltage cable outer sheath material and preparation method thereof

Abstract

The invention discloses a semi-conductive flame-retardant PVC (polyvinyl chloride) high-voltage cable outer sheath material and a preparation method thereof, and the outer sheath material comprises the following components in parts by mass: 60-75 parts of polyvinyl chloride resin, 8-15 parts of a flame retardant, 20-30 parts of calcium carbonate powder, 60-75 parts of a plasticizer, 4-8 parts of a heat stabilizer, 0.5-1 part of an antioxidant, 10-20 parts of a conductive filler, 8-12 parts of polyether block amide resin, 1-2 parts of a lubricant, 1-2 parts of a dispersant and 1-2 parts of a processing aid. And the polyether block amide resin is Pebax MV2080. The surface of the semi-conductive flame-retardant PVC high-voltage cable outer sheath material is smooth and round, and the semi-conductive flame-retardant PVC high-voltage cable outer sheath material has good semi-conductivity and excellent flame-retardant performance and is especially suitable for high-voltage cables.

Description

Technical Field

[0001] The invention belongs to the technical field of high-voltage cable and wire materials, and in particular relates to a semiconductor flame-retardant PVC high-voltage cable outer sheath material and a preparation method thereof. Background Art

[0002] In modern power transmission systems, ultra-high voltage cables of 110KV and above play a vital role. These cables not only need to have excellent electrical performance to ensure efficient and stable power transmission, but also need to have reliable mechanical protection and safety measures to ensure safety during operation. In particular, for ultra-high voltage cables, the design and manufacture of their outer sheaths are particularly important.

[0003] Traditionally, in order to prevent the formation of dangerous voltages at locations far from the site, materials with high insulation resistance are usually used as the outer sheath of the cable, and a layer of semi-conductive material, such as a graphite conductive layer, is further introduced to achieve effective charge release. However, the currently widely used powdered graphite coating method has significant technical defects: first, this process will cause a large amount of graphite dust to be suspended in the air, which not only causes serious pollution to the working environment, but also directly threatens the health of workers and the normal operation of machinery and equipment; second, due to technical and equipment limitations in the coating process, it is difficult to ensure the uniform distribution of the graphite layer, resulting in some areas being too thick or too thin, affecting the overall performance of the cable; Therefore, there is an urgent need for a semiconductor flame-retardant PVC high-voltage cable outer sheath material and a preparation method thereof to solve the deficiencies of the prior art problems. Summary of the invention

[0004] In view of the above problems, the purpose of the present invention is to provide a semi-conductive fire-retardant PVC high-voltage cable outer sheath material and a preparation method thereof. The surface of the semi-conductive fire-retardant PVC high-voltage cable outer sheath material is smooth and round and has good semi-conductivity, environmental protection and flame retardant properties, and is particularly suitable for high-voltage cables.

[0005] To achieve the above objectives, the first aspect of the present invention provides a semiconductor flame-retardant PVC high-voltage cable outer sheath material, which comprises, by mass, 60 to 75 parts of polyvinyl chloride resin, 8 to 15 parts of flame retardant, 20 to 30 parts of calcium carbonate powder, 60 to 75 parts of plasticizer, 4 to 8 parts of heat stabilizer, 0.5 to 1 part of antioxidant, 10 to 20 parts of conductive filler, 8 to 12 parts of polyether block amide resin, 1 to 2 parts of lubricant, 1 to 2 parts of dispersant, and 1 to 2 parts of processing aid; the polyether block amide resin is Pebax MV2080.

[0006] In order to solve the problem that the traditional powdered graphite coating method generates a large amount of dust during the production process and is difficult to ensure the uniform distribution of the graphite layer, the inventors of the present invention find that when the conductive filler is added to the PVC matrix and its filling amount reaches a certain proportion, these fillers will form a continuous conductive network in the matrix, thereby establishing a conductive path in the material, and significantly improving the conductive properties of the material. However, the conductive filler usually has a higher hardness and irregular shape, and it is difficult to disperse evenly during processing, especially when the filling amount is high, the dispersion difficulty is further increased, which easily leads to uneven distribution of the filler in the matrix, thereby forming a convexity or depression on the surface of the material, increasing the surface roughness, and affecting the appearance and practical application performance of the material. Based on this, the inventors of the present application first proposed to use polyether block amide resin as a solution, which is a thermoplastic elastomer copolymerized by a flexible polyether segment and a hard polyamide segment, and the ether oxygen group in the polyether segment can be combined with free ions, and the molecular motion of the low molecular weight polyether and the transfer of charge along the ion network can move the charge in the form of a combination, so that the polymer has good conductive properties. However, polyether block amide resins usually have a high melting point (generally above 200°C), so they are widely used in engineering plastics with high processing temperatures, such as PP, PS, HIPS, ABS, TPU, PMMA, PA, POM, PET, PETG, etc.; while the normal processing temperature of soft PVC is usually below 180°C, which makes it difficult for traditional polyether block amide resins to be directly applied to PVC materials. The inventors have discovered a polyether block amide resin Pebax MV2080 through many experiments. This resin is not only suitable for the PVC processing temperature range but also has good compatibility with the PVC matrix; therefore, by combining the polyether block amide resin Pebax MV2080 with a conductive filler, not only a connected conductive network can be formed, but also the amount of conductive filler added can be greatly reduced, improving the processing performance and appearance of the material. Therefore, the surface of the outer sheath material of the present invention is smooth and round and has good semi-conductivity and environmental protection. At the same time, by adding a flame retardant, the outer sheath material also has excellent flame retardant properties, which is particularly suitable for high-voltage cables.

[0007] Furthermore, the flame retardant of the present invention is a mixture of zinc borate and antimony trioxide. Specifically, the zinc borate is 5 to 10 parts; the antimony trioxide is 3 to 5 parts.

[0008] Furthermore, the plasticizer of the present invention is at least one selected from dioctyl terephthalate, dioctyl phthalate, and trioctyl trimellitate.

[0009] Furthermore, the heat stabilizer of the present invention is a calcium-zinc composite stabilizer.

[0010] Furthermore, the antioxidant of the present invention is selected from at least one of antioxidant 1010, antioxidant 1076, and antioxidant 168.

[0011] Furthermore, the lubricant of the present invention is selected from at least one of polyethylene wax, calcium stearate, zinc stearate, stearic acid amide and paraffin.

[0012] Furthermore, the processing aid of the present invention is an acrylic copolymer (ACR).

[0013] Furthermore, the conductive filler of the present invention is at least one of conductive carbon black and carbon nanotubes. Highly structured conductive carbon black, due to its unique chain branch structure (fibrous structure), can be more effectively interwoven and connected to form more conductive paths, thereby significantly improving the conductive properties of the material. However, carbon nanotubes, with their larger aspect ratio and higher strength, provide a more continuous and efficient conductive path when constructing a conductive network, further enhancing the conductivity and mechanical properties of the material; at the same time, the dispersibility of carbon nanotubes in PVC matrix materials is better than that of conductive carbon black, further ensuring the uniformity and stability of the conductive network. Therefore, the conductive filler is preferably carbon nanotubes.

[0014] Furthermore, the dispersant of the present invention is sodium dodecylbenzene sulfonate; sodium dodecylbenzene sulfonate belongs to the surfactant dispersant, which improves the wettability and dispersibility of the conductive filler in PVC by reducing the surface tension of the conductive filler. At the same time, as an anionic antistatic agent, it can also reduce the resistance of the material and increase the conductivity. Therefore, adding a dispersant can improve the dispersibility of the conductive filler in the rubber material without destroying the structure of the conductive filler, thereby improving the conductive effect.

[0015] Accordingly, the second aspect of the present invention provides a method for preparing a semiconductor flame-retardant PVC high-voltage cable outer sheath material, the steps comprising: S1, adding the formulated amount of polyvinyl chloride resin, plasticizer, flame retardant, calcium carbonate powder, heat stabilizer and lubricant into a mixer and mixing; S2, when the temperature in the mixer reaches 110-120°C, add the formulated amount of antioxidant, conductive filler, polyether block amide resin, dispersant, and processing aid and mix. When the temperature in the mixer reaches 145-155°C, stop mixing to obtain a first mixed material; S3. A double-stage granulating unit is used to extrude and granulate the first mixed material, and then air-cooling, screening, metering and packaging are performed to obtain a semiconductor and flame-retardant PVC high-voltage cable outer sheath material.

[0016] The preparation method of the present invention obtains a semi-conductive flame-retardant PVC high-voltage cable outer sheath material by adopting high-speed mixing, extrusion granulation using a two-stage extruder, and air-cooling screening steps. The preparation method is easy to control and has high production efficiency. The product quality of the prepared semi-conductive flame-retardant PVC high-voltage cable outer sheath material is stable and conducive to industrial production. At the same time, the use of a two-stage extruder can further improve the dispersibility of the conductive filler and further increase the processing speed. In addition, the application of the thin-wall double-layer co-extrusion technology further makes the surface of the outer sheath smooth and round, and tightly adheres to the PVC-based insulation layer, ensuring the long-term stability and reliability of the electrical performance.

[0017] Furthermore, the two-stage granulation unit of the present invention comprises an upper-stage twin-screw extruder and a lower-stage single-screw extruder, the upper-stage twin-screw extruder has a length-to-diameter ratio of 28-48:1 and a diameter of 50-100 mm; the lower-stage single-screw extruder has a length-to-diameter ratio of 7-11:1 and a diameter of 120-240 mm.

[0018] Furthermore, in step S1 of the present invention, the mixing time is 5 to 8 minutes and the mixing speed is 600 to 1000 rpm; and in step S2, the mixing speed is 600 to 1000 rpm.

[0019] Furthermore, the discharge port of the double-stage granulating unit of the present invention is connected to the cyclone separator, the air cooler and the vibrating screen.

[0020] Furthermore, the air-cooling screening of the present invention includes using a cyclone separator and an air cooler to air-cool the outer sheath material pellets coming out of the discharge port.

[0021] Further, the screening of the present invention includes removing powder and strips using a vibrating screen.

[0022] Furthermore, the metering packaging of the present invention comprises: after metering according to specifications, the mixture is packed in a PE inner bag and a kraft paper outer bag and stored in a dry, dark and cool place. DETAILED DESCRIPTION

[0023] In order to better illustrate the purpose, technical scheme and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following implementation method is a further explanation of the present invention and should not be used as a limitation of the present invention.

[0024] The raw materials used in the embodiments and comparative examples are all commercially available; specifically, polyvinyl chloride resin was purchased from Beiyuan Chemical SG-3; heat stabilizer was purchased from Shuize Chemical A-380; calcium carbonate powder was purchased from Meilin Chemical ML-2800; plasticizer was purchased from Dongguan Lingchuang DOTP; lubricant was purchased from Honeywell AC-6A; conductive carbon black was purchased from Cabot XC72A185; processing aid was purchased from Zhongyuan PA-40; PEBAX MV 2080 and Pebax MH 2030 were both purchased from Arkema, France; carbon nanotubes were purchased from Shandong Dazhan Nanomaterials GC-21; antioxidant was purchased from BASF antioxidant 1010; dispersant was purchased from Shandong Longhui Chemical Sodium Dodecylbenzene Sulfonate.

[0025] Example 1 The present embodiment provides a semiconductor flame-retardant PVC high-voltage cable outer sheath material, which includes, by mass, 75 parts of polyvinyl chloride resin, 6 parts of zinc borate, 5 parts of antimony trioxide, 20 parts of calcium carbonate powder, 60 parts of plasticizer, 4 parts of heat stabilizer, 0.5 parts of antioxidant, 20 parts of conductive carbon black, 12 parts of polyether block amide resin, 1 part of lubricant, 1 part of dispersant, and 2 parts of processing aid; the polyether block amide resin is Pebax MV2080.

[0026] This embodiment provides a method for preparing a semiconductor flame-retardant PVC high-voltage cable outer sheath material, the steps comprising: S1. Add the formulated amount of polyvinyl chloride resin, plasticizer, zinc borate, antimony trioxide, calcium carbonate powder, heat stabilizer and lubricant into a high-speed mixer and mix for 8 minutes at a mixing speed of 800 rpm; S2, when the temperature in the high-speed mixer reaches 120° C., add the formulated amount of antioxidant, conductive carbon black, polyether block amide resin, dispersant, and processing aid, and mix at a speed of 1000 rpm. When the temperature in the high-speed mixer reaches 150° C., stop mixing to obtain a first mixture; S3, using a two-stage granulation unit to extrude and granulate the first mixed material, and then using a cyclone separator and an air cooler to air-cool the outer sheath material pellets coming out of the discharge port, using a vibrating screen to remove powder and strips, and after measuring according to specifications, packing them in PE inner bags and kraft paper outer bags and storing them in a dry, dark and cool place to obtain a semiconductor, flame retardant PVC high-voltage cable outer sheath material; The discharge port of the two-stage granulation unit is connected to the cyclone separator, the air cooler and the vibrating screen; the two-stage granulation unit includes an upper-stage twin-screw extruder and a lower-stage single-screw extruder, the upper-stage twin-screw extruder has a length-to-diameter ratio of 42:1 and a diameter of 80 mm; the lower-stage single-screw extruder has a length-to-diameter ratio of 8:1 and a diameter of 200 mm.

[0027] Example 2 The present embodiment provides a semi-conductive flame-retardant PVC high-voltage cable outer sheath material, which includes, by mass, 72 parts of polyvinyl chloride resin, 8 parts of zinc borate, 3 parts of antimony trioxide, 25 parts of calcium carbonate powder, 64 parts of plasticizer, 6 parts of heat stabilizer, 0.8 parts of antioxidant, 17 parts of conductive carbon black, 10 parts of polyether block amide resin, 1.2 parts of lubricant, 1.2 parts of dispersant, and 1.4 parts of processing aid; the polyether block amide resin is Pebax MV2080.

[0028] This embodiment provides a method for preparing a semiconductor flame-retardant PVC high-voltage cable outer sheath material, the steps comprising: S1. Add the formulated amount of polyvinyl chloride resin, plasticizer, zinc borate, antimony trioxide, calcium carbonate powder, heat stabilizer and lubricant into a high-speed mixer and mix for 5 minutes at a mixing speed of 900 rpm; S2, when the temperature in the high-speed mixer reaches 115° C., add the formulated amount of antioxidant, conductive carbon black, polyether block amide resin, dispersant, and processing aid, and mix at a speed of 800 rpm. When the temperature in the high-speed mixer reaches 146° C., stop mixing to obtain a first mixture; S3, using a two-stage granulation unit to extrude and granulate the first mixed material, and then using a cyclone separator and an air cooler to air-cool the outer sheath material pellets coming out of the discharge port, using a vibrating screen to remove powder and strips, and after measuring according to specifications, packing them in PE inner bags and kraft paper outer bags and storing them in a dry, dark and cool place to obtain a semiconductor, flame retardant PVC high-voltage cable outer sheath material; The discharge port of the two-stage granulation unit is connected to the cyclone separator, the air cooler and the vibrating screen; the two-stage granulation unit includes an upper-stage twin-screw extruder and a lower-stage single-screw extruder, the upper-stage twin-screw extruder has a length-to-diameter ratio of 42:1 and a diameter of 80 mm; the lower-stage single-screw extruder has a length-to-diameter ratio of 8:1 and a diameter of 200 mm.

[0029] Example 3 The present embodiment provides a semi-conductive flame-retardant PVC high-voltage cable outer sheath material, which includes, by mass, 69 parts of polyvinyl chloride resin, 7 parts of zinc borate, 4 parts of antimony trioxide, 28 parts of calcium carbonate powder, 70 parts of plasticizer, 8 parts of heat stabilizer, 0.9 parts of antioxidant, 15 parts of conductive carbon black, 8 parts of polyether block amide resin, 1.5 parts of lubricant, 1.4 parts of dispersant, and 1.6 parts of processing aid; the polyether block amide resin is Pebax MV2080.

[0030] This embodiment provides a method for preparing a semiconductor flame-retardant PVC high-voltage cable outer sheath material, the steps comprising: S1. Add the formulated amount of polyvinyl chloride resin, plasticizer, zinc borate, antimony trioxide, calcium carbonate powder, heat stabilizer and lubricant into a high-speed mixer and mix for 7 minutes at a mixing speed of 600 rpm; S2, when the temperature in the high-speed mixer reaches 115° C., add the formulated amount of antioxidant, conductive carbon black, polyether block amide resin, dispersant, and processing aid, and mix at a speed of 700 rpm. When the temperature in the high-speed mixer reaches 152° C., stop mixing to obtain a first mixture; S3, using a two-stage granulation unit to extrude and granulate the first mixed material, and then using a cyclone separator and an air cooler to air-cool the outer sheath material pellets coming out of the discharge port, using a vibrating screen to remove powder and strips, and after measuring according to specifications, packing them in PE inner bags and kraft paper outer bags and storing them in a dry, dark and cool place to obtain a semiconductor, flame retardant PVC high-voltage cable outer sheath material; The discharge port of the two-stage granulation unit is connected to the cyclone separator, the air cooler and the vibrating screen; the two-stage granulation unit includes an upper-stage twin-screw extruder and a lower-stage single-screw extruder, the upper-stage twin-screw extruder has a length-to-diameter ratio of 42:1 and a diameter of 100 mm; the lower-stage single-screw extruder has a length-to-diameter ratio of 8:1 and a diameter of 240 mm.

[0031] Example 4 The only difference between Example 4 and Example 1 is that the conductive carbon black is replaced by carbon nanotubes, and the rest is the same as Example 1.

[0032] Comparative Example 1 This comparative example provides a semi-conductive flame-retardant PVC high-voltage cable outer sheath material, which includes, by mass, 75 parts of polyvinyl chloride resin, 6 parts of zinc borate, 5 parts of antimony trioxide, 20 parts of calcium carbonate powder, 60 parts of plasticizer, 4 parts of heat stabilizer, 0.5 parts of antioxidant, 40 parts of conductive carbon black, 1 part of lubricant, 1 part of dispersant, and 2 parts of processing aid.

[0033] This comparative example provides a method for preparing a semi-conductive flame-retardant PVC high-voltage cable outer sheath material, the steps comprising: S1. Add the formulated amount of polyvinyl chloride resin, plasticizer, zinc borate, antimony trioxide, calcium carbonate powder, heat stabilizer and lubricant into a high-speed mixer and mix for 8 minutes at a mixing speed of 800 rpm; S2, when the temperature in the high-speed mixer reaches 120° C., add the formulated amount of antioxidant, conductive carbon black, dispersant, and processing aid, and mix at a speed of 1000 rpm. When the temperature in the high-speed mixer reaches 150° C., stop mixing to obtain a first mixed material; S3, using a two-stage granulation unit to extrude and granulate the first mixed material, and then using a cyclone separator and an air cooler to air-cool the outer sheath material pellets coming out of the discharge port, using a vibrating screen to remove powder and strips, and after measuring according to specifications, packing them in PE inner bags and kraft paper outer bags and storing them in a dry, dark and cool place to obtain a semiconductor, flame retardant PVC high-voltage cable outer sheath material; The discharge port of the two-stage granulation unit is connected to the cyclone separator, the air cooler and the vibrating screen; the two-stage granulation unit includes an upper-stage twin-screw extruder and a lower-stage single-screw extruder, the upper-stage twin-screw extruder has a length-to-diameter ratio of 42:1 and a diameter of 80 mm; the lower-stage single-screw extruder has a length-to-diameter ratio of 8:1 and a diameter of 200 mm.

[0034] Comparative Example 2 The only difference between this comparative example and Example 1 is that the polyether block amide resin is Pebax MH 2030, and the rest is the same as Example 1.

[0035] Comparative Example 3 The only difference between this comparative example and Example 1 is that the content of the polyether block amide resin is 20 parts, and the rest is the same as Example 1.

[0036] The semiconductor flame-retardant PVC high-voltage cable outer sheath materials of Examples 1 to 4 and Comparative Examples 1 to 3 were plasticized on a plasticizer at a temperature of (165±5)°C for 10 minutes, and then pressed in a hydraulic press at a temperature of (165±5)°C in the order of preheating without pressure, constant temperature pressurization, and pressurized cooling for 10 minutes to make corresponding 1.0 mm dumbbell sheets, resistor sheets, and 3.0 mm oxygen index sheets; and the above seven samples were respectively made into wires using a wire extruder, and the wires were tested with reference to the following standards. The test results are shown in Table 1.

[0037] Refer to GB / T 2411 standard to test the hardness of materials.

[0038] The tensile strength and elongation at break of dumbbell plates were tested with reference to GB / T1040.2 standard.

[0039] The wires were placed in an environment of 100±2℃ for 240 hours for aging treatment, and then the change rate of tensile strength and elongation of the dumbbell plates after aging were tested according to GB / T2951.12 standard to evaluate the aging performance.

[0040] Refer to GB / T2406 standard to test the oxygen index of materials.

[0041] Refer to GB / T3048.3 standard to test the volume resistivity of the material.

[0042] Use visual inspection to inspect the appearance of the wires.

[0043] Table 1

[0044] Comparing Example 1 with Example 4, it can be seen that after replacing the conductive carbon black with carbon nanotubes, the mechanical strength of the semiconductive flame-retardant PVC high-voltage cable outer sheath material is slightly better than that of Example 1. At the same time, its appearance quality, conductivity, and oxygen index are basically the same as those of Example 1, so the conductive filler of the present application is preferably carbon nanotubes.

[0045] Comparing Example 1 with Comparative Example 1, it can be seen that Example 1 reduces the amount of conductive carbon black added, and adds the stronger polyether block amide resin ARKEMA PEBAX MV 2080, and its mechanical strength and appearance are significantly better than those of Comparative Example 1, and its conductive performance is quite close to that of Comparative Example 1. This shows that by combining the polyether block amide resin Pebax MV2080 with a low content of conductive filler, not only can a connected conductive network be formed, but also the amount of conductive filler added can be greatly reduced, thereby improving the processing performance and appearance of the material.

[0046] Polyether block amide resins include Pebax MV1074SA01 (density 1.07g / cm 3 , melting point is 158℃, surface resistance is 3×10 9 Ω / sq, volume resistance is 2.5×10 9 Ω / cm), Pebax MH 1657 (density 1.14g / cm 3 , melting point is 204℃, surface resistance is 1×10 9 Ω / sq, volume resistance is 2.5×10 9 Ω / cm), Pebax MH 2030 (density 1.14g / cm 3 , melting point is 200℃, surface resistance is 1×10 7 Ω / sq, volume resistance is 1×10 7 Ω / cm), volume resistance is 2.5×10 9 Ω / cm), Pebax MV 2080 (density 1.07g / cm 3 , melting point is 160℃, surface resistance is 1×10 7 Ω / sq, volume resistance is 1×10 7 Ω / cm), by comparing different types of Pebax resin, it can be seen that there are large differences in melting point and resistance, which directly affects its processing type and semi-conductive performance in PVC. As shown by comparing Example 1 with Comparative Example 2, although PebaxMH 2030 has lower surface resistance and volume resistance, it cannot be evenly dispersed at the conventional processing temperature of PVC and cannot be well compatible with PVC, resulting in its conductive performance and appearance being significantly inferior to those of Example 1.

[0047] Comparing Comparative Example 3 with Example 1, it can be seen that although ARKEMA Pebax MV 2080 has good compatibility with PVC, its addition amount must be controlled within a certain range, that is, when the addition amount exceeds the maximum compatibility limit with PVC, the material cannot be evenly dispersed, thereby affecting the appearance quality of the product. Therefore, the content of the polyether block amide resin is preferably 8 to 12 parts.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A semiconductor flame-retardant PVC high-voltage cable outer sheath material, characterized in that: The invention comprises, by weight, 60 to 75 parts of polyvinyl chloride resin, 8 to 15 parts of flame retardant, 20 to 30 parts of calcium carbonate powder, 60 to 75 parts of plasticizer, 4 to 8 parts of heat stabilizer, 0.5 to 1 part of antioxidant, 10 to 20 parts of conductive filler, 8 to 12 parts of polyether block amide resin, 1 to 2 parts of lubricant, 1 to 2 parts of dispersant and 1 to 2 parts of processing aid; the polyether block amide resin is Pebax MV2080.

2. The semiconductor flame retardant PVC high voltage cable outer sheath material according to claim 1, characterized in that: The flame retardant is a mixture of zinc borate and antimony trioxide.

3. The semiconductor flame retardant PVC high voltage cable outer sheath material according to claim 1, characterized in that: The plasticizer is selected from at least one of dioctyl terephthalate, dioctyl phthalate and trioctyl trimellitate.

4. The semiconductor flame retardant PVC high voltage cable outer sheath material according to claim 1, characterized in that: The heat stabilizer is a calcium-zinc composite stabilizer.

5. The semiconductor flame retardant PVC high voltage cable outer sheath material according to claim 1, characterized in that: The antioxidant is selected from at least one of antioxidant 1010, antioxidant 1076, and antioxidant 168.

6. The semiconductor flame retardant PVC high voltage cable outer sheath material according to claim 1, characterized in that: The lubricant is selected from at least one of polyethylene wax, calcium stearate, zinc stearate, stearic acid amide and paraffin.

7. The semiconductor flame retardant PVC high voltage cable outer sheath material according to claim 1, characterized in that: The processing aid is an acrylic acid ester copolymer.

8. The semiconductor flame retardant PVC high voltage cable outer sheath material according to claim 1, characterized in that: The conductive filler is at least one of conductive carbon black and carbon nanotubes.

9. A method for preparing the outer sheath material of a semiconductor flame-retardant PVC high-voltage cable according to any one of claims 1 to 8, characterized in that the steps include: S1, adding the formulated amount of polyvinyl chloride resin, plasticizer, flame retardant, calcium carbonate powder, heat stabilizer and lubricant into a mixer and mixing; S2, when the temperature in the mixer reaches 110-120° C., adding a formulated amount of an antioxidant, a conductive filler, a polyether block amide resin, a dispersant, and a processing aid, and when the temperature in the mixer reaches 145-155° C., stopping mixing to obtain a first mixed material; S3, using a two-stage granulation unit to extrude and granulate the first mixed material, and then air-cool, screen, meter and package to obtain a semiconductor flame-retardant PVC high-voltage cable outer sheath material.

10. The method for preparing the outer sheath material of the semiconductor flame retardant PVC high-voltage cable according to claim 9, characterized in that: The two-stage granulation unit comprises an upper-stage twin-screw extruder and a lower-stage single-screw extruder, wherein the upper-stage twin-screw extruder has an aspect ratio of 28-48:1 and a diameter of 50-100 mm; the lower-stage single-screw extruder has an aspect ratio of 7-11:1 and a diameter of 120-240 mm.

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