A modified polypropylene composite material for medium voltage cable insulation and a method for its production and use

Abstract

The present application relates to a kind of modified polypropylene composite material for medium voltage cable insulation and its preparation method and application, belong to wire and cable material technical field.The composite material is with polypropylene as matrix, by adding multiphase synergistic toughening agent and functionalized nano filler, and cooperate with composite voltage stabilizer, antioxidant and processing aid composition.The multiphase synergistic toughening agent is the complex system of hydrogenated styrene-butadiene-styrene block copolymer and polyolefin elastomer;The functionalized nano filler is the nano silicon dioxide modified by vinyl silane coupling agent.The present application is through the synergistic effect of multiphase synergistic toughening agent and functionalized nano filler, while significantly improving the toughness of polypropylene, scratch resistance and interface adhesion with shielding layer, maintain excellent electrical insulation and long-term electrical-thermal aging resistance, solve the contradiction of traditional toughening leading to electrical performance degradation, and material can be completely recycled, suitable for manufacturing environment-friendly medium voltage power cable insulation layer.

Description

Technical Field

[0001] This invention relates to the field of wire and cable materials technology, and in particular to a modified polypropylene composite material for medium-voltage cable insulation, its preparation method, and its application. Background Technology

[0002] Cross-linked polyethylene (XLPE) has long dominated the medium-voltage cable insulation market due to its balanced electrical, mechanical, and heat resistance properties. However, as a thermosetting material, it forms an irreversible three-dimensional network structure during cable manufacturing through chemical or irradiation methods. This makes it difficult to recycle after the cable's lifespan, typically requiring landfill or incineration, resulting in increasingly serious resource waste and environmental pollution problems. Polypropylene (PP), as a high thermoplastic, has a high melting point (>160℃), low dielectric loss, and is fully recyclable, making it a potential material for next-generation environmentally friendly cable insulation. However, the direct use of virgin PP resin for medium-voltage insulation faces three major technical bottlenecks: First, it has high low-temperature brittleness and poor flexibility, making the insulation layer prone to micro-cracks or even cracking when bending is required during cable installation, posing a safety hazard; second, it has insufficient scratch resistance, making the insulation surface susceptible to mechanical scratch damage during cable production or laying; and third, it has weak interfacial adhesion with non-polar polyolefin shielding materials, easily creating air gaps at the interface, which can become partial discharge initiation points, seriously threatening the long-term operational reliability of the cable.

[0003] In existing technologies, there are solutions to toughen PP by simply blending elastomers (such as POE). However, while this significantly improves toughness, it inevitably leads to a sharp decline in the material's elastic modulus, tensile strength, hardness, and key electrical properties (such as volume resistivity and dielectric strength), making it unable to meet the stringent requirements for medium-voltage insulation. There have also been attempts to add inorganic fillers for reinforcement, but poor dispersibility and the resulting defects also compromise electrical properties.

[0004] Therefore, developing a modified PP composite material that can synergistically resolve the contradictions between toughness, scratch resistance, interfacial adhesion, and electrical insulation performance is a core prerequisite for realizing the industrial application of PP insulated medium-voltage cables. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a modified polypropylene composite material for medium-voltage cable insulation, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of this application provides a modified polypropylene composite material for medium-voltage cable insulation, comprising, by weight, the following components: 100 parts of polypropylene matrix resin, 8-25 parts of multiphase synergistic toughening agent, 3-12 parts of functionalized nanofiller, 1.5-4.0 parts of composite voltage stabilizer, 0.5-1.5 parts of antioxidant, and 0.2-0.8 parts of processing aid.

[0007] Preferably, the polypropylene is high-purity electrical grade isotactic polypropylene with an ash content of less than 0.02% and a melt flow rate (MFR) of 0.5-3.0 g / 10 min (230℃, 2.16 kg).

[0008] Preferably, the multiphase synergistic toughening agent is a compound system of hydrogenated styrene-butadiene-styrene block copolymer (SEBS) and polyolefin elastomer (POE) in a weight ratio of 1-3:1-3; the hydrogenated styrene-butadiene-styrene block copolymer has a weight-average molecular weight of 70,000-150,000 g / mol, a styrene structural unit mass content of 20-30%, and a degree of hydrogenation greater than 98%; the polyolefin elastomer is an ethylene-octene copolymer with a density of 0.860-0.880 g / cm³. 3 The melt flow rate (MFR) (190℃, 2.16kg) is 0.5-5.0g / 10min, and the octene monomer mass fraction is 15-25%.

[0009] Preferably, the functionalized nanofiller is nano-silica grafted onto the surface of a vinyl silane coupling agent; the vinyl silane coupling agent is vinyltrimethoxysilane or vinyltriethoxysilane, with the vinyl functional group located at the end of the molecule; the particle size of the nano-silica is 20-50 nm.

[0010] Preferably, the composite voltage stabilizer is a mixture of a sterically hindered amine and an aromatic ketone voltage stabilizer in a weight ratio of 1:1; the sterically hindered amine voltage stabilizer is 4-amino-2,2,6,6-tetramethylpiperidine or tetramethylpiperidine alcohol; and the aromatic ketone voltage stabilizer is benzophenone or 4-hydroxybenzophenone.

[0011] Preferably, the antioxidant is a compound of a phenolic primary antioxidant and a phosphite secondary antioxidant in a weight ratio of 1:1-2; the phenolic primary antioxidant is at least one of antioxidant 1010, antioxidant 1076, and antioxidant 3114; and the phosphite secondary antioxidant is at least one of antioxidant 168, antioxidant 126, and antioxidant 626.

[0012] Preferably, the processing aid is at least one of calcium stearate, zinc stearate, or polyethylene wax.

[0013] The second aspect of this application provides a method for preparing a modified polypropylene composite material for medium-voltage cable insulation, comprising the following steps: S1. Premix: Add polypropylene matrix resin, multiphase synergistic toughening agent, functionalized nanofiller, composite voltage stabilizer, antioxidant and processing aid to a high-speed mixer according to the ratio, and mix at 60-80℃ for 5-10 min to obtain premix; S2. Melt blending and granulation: The premixed material is added to a twin-screw extruder and processed through melt extrusion, water cooling, and pelletizing to obtain modified polypropylene composite material granules. The temperature of each section of the extruder is set at 180-220℃, and the screw speed is 200-400rpm.

[0014] A third aspect of this application provides a medium-voltage cable, comprising, from the inside out, a conductor, a conductor shielding layer, an insulation layer, an insulation shielding layer, a copper tape shielding layer, a filler, a wrapping layer, an inner lining layer, an armor layer, and a polyvinyl chloride outer sheath.

[0015] Preferably, the conductor shielding layer and / or insulating shielding layer are made of polar functionalized polyolefin semiconducting material.

[0016] Preferably, the insulating layer is made by extrusion of the modified polypropylene composite material described above.

[0017] Preferably, the conductor shielding layer, the insulation layer, and the insulation shielding layer are formed by simultaneous extrusion of three layers in one step using a three-layer co-extrusion process.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. Breakthrough performance balance: Through the synergistic design of "multiphase synergistic toughening agent" and "functionalized nanofiller", the notched impact strength of PP at room temperature is increased to more than 5 times that of virgin PP, and scratch resistance is significantly improved, while ensuring that the volume resistivity of the composite material (90℃) is maintained at >1×10⁻⁶. 15 With a dielectric strength of ≥40kV / mm and Ω·cm, it fully meets the requirements for medium-voltage insulation and solves the industry problem of electrical performance degradation caused by traditional toughening methods.

[0019] 2. Improved interfacial adhesion: The functionalized nanofillers and polar components in the composite material form a microscopic "anchoring" structure with the non-polar PP matrix. During melt extrusion, they can interact more effectively with the special polar shielding material, increasing the peel strength of the shielding / insulation layer by more than 50% and greatly suppressing interfacial discharge.

[0020] 3. Excellent long-term reliability: The composite voltage stabilizer uses nanofillers as a "carrier" to achieve efficient dispersion and slow release, which significantly improves the material's anti-aging and anti-electrical and anti-water treeing ability under combined electro-thermal stress, and has a long expected service life.

[0021] 4. Maintaining core environmental protection and high temperature resistance advantages: The main material is thermoplastic polyolefin, which can be 100% melt-recycled and has a long-term allowable working temperature of up to 105℃ (90℃ for XLPE). Furthermore, no cross-linking step is required during cable production, avoiding high temperature and high pressure energy consumption, significantly saving energy and reducing carbon emissions. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the medium-voltage cable proposed in this invention; The components are: 1. Conductor; 2. Conductor shielding layer; 3. Insulation layer; 4. Insulation shielding layer; 5. Copper tape shielding layer; 6. Filler; 7. Wrapping layer; 8. Inner lining layer; 9. Armoring layer; and 10. Polyvinyl chloride outer sheath. Detailed Implementation

[0023] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0024] Example 1: A method for preparing a modified polypropylene composite material for medium-voltage cable insulation, comprising the following steps: S1. Premix: Mix 100 parts of polypropylene matrix resin (electrical grade isotactic polypropylene, ash content 0.015%, MFR=1.2g / 10min), 10 parts of multiphase synergistic toughening agent (5 parts SEBS, Mw=120000, styrene content 25%, hydrogenation degree >99%; 5 parts POE, density 0.870g / cm³). 3 5 parts of functionalized nanofiller (vinyltrimethoxysilane grafted nano-SiO2, SiO2 particle size 30nm), 2.0 parts of composite voltage stabilizer (1.0 part of 4-amino-2,2,6,6-tetramethylpiperidine, 1.0 part of benzophenone), 0.8 parts of antioxidant (0.32 parts of antioxidant 1010, 0.48 parts of antioxidant 168) and 0.5 parts of processing aid (calcium stearate) were added to a high-speed mixer and mixed at 70°C for 8 min to obtain a premix. S2. Melt blending and granulation: The premixed material is added to a twin-screw extruder, and the temperature is set sequentially to 180℃, 195℃, 205℃, 210℃ and 210℃, and the screw speed is 300 rpm. After melt extrusion, water cooling and pelletizing, modified polypropylene composite particles are obtained.

[0025] Example 2: A method for preparing a modified polypropylene composite material for medium-voltage cable insulation, comprising the following steps: S1. Premix: Mix 100 parts of polypropylene matrix resin (electrical grade isotactic polypropylene, ash content 0.015%, MFR=1.2g / 10min), 15 parts of multiphase synergistic toughening agent (8 parts SEBS, Mw=120000, styrene content 25%, hydrogenation degree >99%; 7 parts POE, density 0.870g / cm³). 3 The following ingredients were added to a high-speed mixer and mixed at 70°C for 8 minutes: MFR=1.5g / 10min, octene content 20%), 8 parts of functionalized nanofiller (vinyltriethoxysilane grafted nano-SiO2, SiO2 particle size 30nm), 2.5 parts of composite voltage stabilizer (1.25 parts tetramethylpiperidinol, 1.25 parts 4-hydroxybenzophenone), 0.8 parts of antioxidant (0.32 parts antioxidant 1010, 0.48 parts antioxidant 168) and 0.5 parts of processing aid (polyethylene wax). S2. Melt Blending and Granulation: The premixed material is added to a twin-screw extruder, and the temperature is set sequentially to 180℃, 195℃, 205℃, 210℃ and 210℃, and the screw speed is 350 rpm. After melt extrusion, water cooling and pelletizing, modified polypropylene composite particles are obtained.

[0026] Example 3: A method for preparing a modified polypropylene composite material for medium-voltage cable insulation, comprising the following steps: S1. Premix: Mix 100 parts of polypropylene matrix resin (electrical grade isotactic polypropylene, ash content 0.015%, MFR=1.2g / 10min), 20 parts of multiphase synergistic toughening agent (8 parts SEBS, Mw=120000, styrene content 25%, hydrogenation degree >99%; 12 parts POE, density 0.870g / cm³). 3 The following ingredients were added to a high-speed mixer and mixed at 70°C for 8 minutes: MFR=1.5g / 10min, octene content 20%); 12 parts of functionalized nanofiller (vinyltriethoxysilane grafted nano-SiO2, SiO2 particle size 30nm); 3 parts of composite voltage stabilizer (1.5 parts of 4-amino-2,2,6,6-tetramethylpiperidine, 1.5 parts of benzophenone); 0.8 parts of antioxidant (0.32 parts of antioxidant 1076, 0.48 parts of antioxidant 168); and 0.5 parts of processing aid (zinc stearate). S2. Melt blending and granulation: The premixed material is added to a twin-screw extruder, and the temperature is set sequentially to 180℃, 195℃, 205℃, 210℃ and 210℃, and the screw speed is 300 rpm. After melt extrusion, water cooling and pelletizing, modified polypropylene composite particles are obtained.

[0027] Comparative Example 1: A method for preparing a modified polypropylene composite material for medium-voltage cable insulation, comprising the following steps: S1. Premix: Add 100 parts of polypropylene matrix resin (electrical grade isotactic polypropylene, ash content 0.015%, MFR=1.2g / 10min), 0.5 parts of antioxidant (0.2 parts of antioxidant 1010, 0.3 parts of antioxidant 168) and 0.2 parts of processing aid (polyethylene wax) to a high-speed mixer and mix at 70℃ for 8 minutes to obtain a premix. S2. Melt blending and granulation: The premixed material is added to a twin-screw extruder, and the temperature is set sequentially to 180℃, 195℃, 205℃, 210℃ and 210℃, and the screw speed is 300 rpm. After melt extrusion, water cooling and pelletizing, modified polypropylene composite particles are obtained.

[0028] Comparative Example 2: A method for preparing a modified polypropylene composite material for medium-voltage cable insulation, comprising the following steps: S1. Premixing: Mix 100 parts of polypropylene matrix resin (electrical grade isotactic polypropylene, ash content 0.015%, MFR=1.2g / 10min) and 20 parts of POE (density 0.870g / cm³). 3 MFR=1.5g / 10min, octene content 20%), 0.5 parts antioxidant (0.2 parts antioxidant 1010, 0.3 parts antioxidant 168) and 0.2 parts processing aid (polyethylene wax) are added to a high-speed mixer and mixed at 70℃ for 8 minutes to obtain a premix. S2. Melt blending and granulation: The premixed material is added to a twin-screw extruder, and the temperature is set sequentially to 180℃, 195℃, 205℃, 210℃ and 210℃, and the screw speed is 300 rpm. After melt extrusion, water cooling and pelletizing, modified polypropylene composite particles are obtained.

[0029] Performance testing: 1. Notched impact strength: Determined using a V-notch specimen at 23°C using a simply supported beam impact testing machine, in accordance with ISO 179-1:2023 standard.

[0030] 2. Volume resistivity: Referring to GB / T 31838.2-2019 standard, a DC voltage is applied to a 1.0±0.1 mm sample at room temperature, and its volume resistance is measured and resistivity is calculated.

[0031] 3. Dielectric strength: In accordance with GB / T 1408.1-2016 standard, the electrical breakdown strength of insulating oil is determined using spherical electrodes at a voltage ramp rate of 2kV / s.

[0032] 4. Peel strength from shielding material: The "shielding layer / insulation layer / shielding layer" laminated sample was prepared by three-layer co-extrusion. According to IEC 60811-506:2012 standard, a 180° peel test was performed using a universal testing machine at a speed of 50 mm / min. The result is expressed as force per unit width (N / cm).

[0033] 5. Thermal aging: In accordance with GB / T 2951.12-2008, the specimens were placed in an air-circulating aging chamber at 135°C for 168 hours. The elongation at break of the specimens was determined using a universal testing machine at a tensile speed of 50 mm / min. The result was expressed as the percentage of the elongation at break after aging relative to the initial elongation at break (retention rate %).

[0034] 6. Resistance to water treeing: In accordance with GB / T 21224-2007, the sample was immersed in 1.0 mol / L NaCl solution, and an accelerated water treeing initiation test (1000 h) was carried out by applying a 5 kV, 1 kHz AC voltage to the water needle electrode. The morphology of the water tree was observed using an optical microscope.

[0035] 7. Resistance to electrical treeing: A metal needle electrode with a tip curvature radius of (3±1μm) is embedded in the sample. A constant power frequency AC voltage (the initial voltage is 40% of the breakdown voltage) is applied to the sample in an insulating oil medium. The growth of electrical treeing is observed through an optical observation system or by microscopic examination of the section after the test.

[0036] Table: Performance tests were conducted on a modified polypropylene composite material for medium-voltage cable insulation from Examples 1-3 and Comparative Examples 1-2.

[0037] Table 1. Performance Test Results

[0038] Table 2. Performance Test Results

[0039] Data Analysis: 1. Mechanical property analysis: The notched impact strength of Examples 1-3 is 12.5 kJ / m. 2 15.8 kJ / m 2 and 18.2 kJ / m 2 Compared to 2.5 kJ / m² in Comparative Example 1 2 The impact strength of the composite material (pure polypropylene matrix) increased by more than five times, indicating that the addition of multiphase synergistic toughening agents (SEBS and POE compound) and functionalized nanofillers significantly improved the toughness of the composite material, increasing its impact strength to more than five times that of virgin polypropylene. This solved the problem of low-temperature brittleness in polypropylene. In Comparative Example 2, when only POE toughening agent was added, the impact strength reached as high as 25.0 kJ / m. 2However, subsequent electrical performance data showed that simple toughening would lead to a deterioration in electrical insulation performance. In contrast, Examples 1-3 maintained high toughness while exhibiting better electrical performance, demonstrating the balance of the synergistic toughening system.

[0040] The peel strengths of Examples 1-3 were 15.2 N / cm, 16.5 N / cm and 17.8 N / cm, respectively, which were more than 50% higher than those of Comparative Example 1 (4.1 N / cm) and Comparative Example 2 (9.5 N / cm). This is attributed to the interaction between the polar groups of the functionalized nanofiller and the shielding layer material, which enhanced the interfacial adhesion and reduced the risk of air gaps and partial discharge.

[0041] 2. Electrical performance analysis: The volume resistivity of Examples 1-3 is 5.6 × 10⁻⁶. 15 Ω·cm, 3.2×10 15 Ω·cm and 1.8×10 15 Ω·cm, although slightly lower than 8.9×10 in Comparative Example 1. 15 Ω·cm (pure polypropylene), but still far above the threshold required for medium-voltage insulation (greater than 1×10⁻⁶). 15 The volume resistivity (Ω·cm) indicates that the electrical insulation of the composite material was not significantly compromised after the toughness was improved; the volume resistivity of Comparative Example 2 was only 6.3 × 10⁻⁶. 12 The Ω·cm value was three orders of magnitude lower than that of Examples 1-3, confirming that simply adding an elastomer would lead to a sharp decline in electrical performance. The synergistic design of this invention, through the "anchoring" effect of functionalized nanofillers, suppressed the degradation of electrical performance.

[0042] The dielectric strengths of Examples 1-3 were 42kV / mm, 45kV / mm, and 41kV / mm, respectively, which were close to 48kV / mm of Comparative Example 1 and all higher than the industry standard of 40kV / mm, meeting the insulation requirements of medium-voltage cables. The dielectric strength of Comparative Example 2 was only 28kV / mm, which was obviously unqualified. This shows that the composite voltage stabilizer (a combination of sterically hindered amine and aromatic ketone) of the present invention works synergistically with the nanofiller to effectively maintain high dielectric strength.

[0043] 3. Long-term reliability analysis: The elongation at break retention rates of Examples 1-3 were all greater than 70%, while those of Comparative Examples 1 and 2 were greater than 50% (Comparative Example 2 was only 40%). This is attributed to the synergistic protection of the "composite voltage stabilizer" (a combination of sterically hindered amines and aromatic ketones). The amines capture free radicals, the ketones absorb high-energy electrons, delaying polymer chain degradation, and the nanofillers act as a carrier to promote stabilizer dispersion and enhance resistance to thermo-oxidative aging.

[0044] The average length of the water tree in Examples 1-3 is less than 80 μm (Example 3 is even less than 60 μm), while Comparative Example 1 is greater than 300 μm and Comparative Example 2 is greater than 200 μm. The growth of the water tree is related to interface defects and water penetration. In Examples 1-3, the nanofiller hinders the water tree path through the physical barrier effect, while the high peel strength eliminates the interfacial air gap.

[0045] The average length of the electrical tree in Examples 1-3 was less than 1.5 mm (less than 1.0 mm in Example 3), while that in Comparative Example 1 was greater than 3.0 mm and that in Comparative Example 2 was greater than 2.5 mm. The electrical tree started from partial discharge. The strong interfacial adhesion and voltage stabilizer in Examples 1-3 synergistically suppressed the discharge initiation point. Example 3 had the highest amount of nanofiller (12 parts) and the best electrical tree suppression effect, which confirms the electric field distortion dispersion effect of the nanofiller.

[0046] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A modified polypropylene composite material for medium-voltage cable insulation, characterized in that, The product, by weight, comprises the following components: 100 parts polypropylene matrix resin, 8-25 parts multiphase synergistic toughening agent, 3-12 parts functionalized nanofiller, 1.5-4.0 parts composite voltage stabilizer, 0.5-1.5 parts antioxidant, and 0.2-0.8 parts processing aid; the multiphase synergistic toughening agent is a compound of hydrogenated styrene-butadiene-styrene block copolymer and polyolefin elastomer; the functionalized nanofiller is nano-silica that has been surface-grafted and modified with vinylsilane coupling agent.

2. The modified polypropylene composite material for medium-voltage cable insulation according to claim 1, characterized in that, The hydrogenated styrene-butadiene-styrene block copolymer and the polyolefin elastomer have a weight ratio of 1-3:1-3; the hydrogenated styrene-butadiene-styrene block copolymer has a weight-average molecular weight of 70,000-150,000 g / mol, a styrene structural unit mass content of 20-30%, and a degree of hydrogenation greater than 98%; the polyolefin elastomer is an ethylene-octene copolymer with a density of 0.860-0.880 g / cm³. 3 The melt flow rate (190℃, 2.16kg) is 0.5-5.0g / 10min, and the octene monomer mass fraction is 15-25%.

3. The modified polypropylene composite material for medium-voltage cable insulation according to claim 1, characterized in that, The vinyl silane coupling agent is vinyltrimethoxysilane or vinyltriethoxysilane; the particle size of the nano-silica is 20-50 nm.

4. The modified polypropylene composite material for medium-voltage cable insulation according to claim 1, characterized in that, The composite voltage stabilizer is a mixture of sterically hindered amines and aromatic ketones in a weight ratio of 1:1; the sterically hindered amine voltage stabilizer is 4-amino-2,2,6,6-tetramethylpiperidine or tetramethylpiperidine alcohol; the aromatic ketone voltage stabilizer is benzophenone or 4-hydroxybenzophenone.

5. A modified polypropylene composite material for medium-voltage cable insulation according to claim 1, characterized in that, The antioxidant is a compound of a phenolic primary antioxidant and a phosphite secondary antioxidant in a weight ratio of 1:1-2; the phenolic primary antioxidant is at least one of antioxidant 1010, antioxidant 1076, and antioxidant 3114; the phosphite secondary antioxidant is at least one of antioxidant 168, antioxidant 126, and antioxidant 626.

6. The modified polypropylene composite material for medium-voltage cable insulation according to claim 1, characterized in that, The processing aid is at least one of calcium stearate, zinc stearate, or polyethylene wax.

7. A method for preparing a modified polypropylene composite material for medium-voltage cable insulation as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Premix: Add each component to a high-speed mixer according to the proportion, and mix at 60-80℃ for 5-10 minutes to obtain a premix; S2. Melt blending and granulation: The premixed material is added to a twin-screw extruder and melt-extruded at a temperature of 180-220℃ and a screw speed of 200-400rpm, followed by water cooling and pelletizing to obtain the modified polypropylene composite material particles.

8. A medium-voltage cable, comprising, from the inside out, a conductor, a conductor shielding layer, an insulation layer, an insulation shielding layer, a copper tape shielding layer, a filler, a wrapping layer, an inner lining layer, an armor layer, and a polyvinyl chloride outer sheath, characterized in that, The insulation layer is a modified polypropylene composite material for medium-voltage cable insulation as described in any one of claims 1-6, or a modified polypropylene composite material prepared by the preparation method described in claim 8, which is formed by extrusion.

9. A medium-voltage cable according to claim 8, characterized in that, The conductor shielding layer and / or insulating shielding layer are made of polar functionalized polyolefin semiconducting material; the conductor shielding layer, insulating layer and insulating shielding layer are formed by three-layer co-extrusion process in one step.

10. The application of a modified polypropylene composite material for medium-voltage cable insulation according to any one of claims 1-6 in the insulation of power cables with a rated voltage of 6-35kV.

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