A three-layer co-extruded power bushing and its preparation method

Abstract

This invention relates to the field of power bushing technology, specifically to a three-layer co-extruded power bushing and its manufacturing method. The power bushing comprises a flame-retardant layer, a high-molecular-weight polyethylene-modified polypropylene layer, and a wear-resistant layer, stacked sequentially from the inside out. The flame-retardant and wear-resistant layers have flat-wall structures, while the high-molecular-weight polyethylene-modified polypropylene layer has a corrugated structure. This power bushing achieves the effect of an inner flame-retardant layer, a high-strength middle layer, and an outer wear-resistant layer through the sequential arrangement of the flame-retardant, high-molecular-weight polyethylene-modified polypropylene, and wear-resistant layers. The flat-wall structure of the flame-retardant and wear-resistant layers and the corrugated structure of the high-molecular-weight polyethylene-modified polypropylene layer, along with the gaps between the three layers after co-extrusion, improves the impact resistance of the three-layer co-extruded power bushing.

Description

Technical Field

[0001] This invention relates to the field of power bushing technology, specifically to a three-layer co-extruded power bushing and its preparation method. Background Technology

[0002] Electrical conduits are used to protect cables and need to possess characteristics such as high tensile strength, resistance to deformation, and weldability. The materials for electrical conduits are mostly plastic-coated steel pipes or polyvinyl chloride (PVC) pipes. Chinese utility model patent application number 201720794212.0 discloses a double-layer plastic-coated steel pipe, comprising a steel pipe with an outer coating on its outer surface and a first inner coating on its inner surface. A grid is provided inside the first inner coating, which is fitted onto the outside of a frame. A second inner coating is sprayed and connected to the inside of the frame. This plastic-coated steel pipe has high compressive strength and is not prone to static electricity, but it has the disadvantage of being difficult to bend. PVC pipes have good deformation performance, but their adhesive connection strength is low, making joints prone to breakage during pipe pulling, and their heat resistance is poor. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a three-layer co-extruded power bushing with good heat resistance and excellent mechanical properties, and a method for preparing the same.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a three-layer co-extruded electrical bushing, comprising a flame-retardant layer, an ultra-high molecular weight polyethylene modified polypropylene layer and a wear-resistant layer stacked sequentially from the inside to the outside, wherein the flame-retardant layer and the wear-resistant layer have a flat wall structure and the ultra-high molecular weight polyethylene modified polypropylene layer has a corrugated structure.

[0005] Another technical solution adopted in this invention is: the preparation method of the above-mentioned three-layer co-extruded power bushing, wherein the preparation method of the wear-resistant layer is as follows: polypropylene and additives are mixed at 170-185°C for 5-10 minutes, then the temperature is raised to 195-210°C and polypropylene carbon microspheres are added and mixed for 2-4 minutes to obtain a mixture, and the mixture is extruded to obtain the wear-resistant layer.

[0006] The beneficial effects of this invention are as follows: The three-layer co-extruded power bushing of this invention achieves the effects of flame retardancy in the inner layer, high strength in the middle layer, and wear resistance in the outer layer through the flame-retardant layer, ultra-high molecular weight polyethylene modified polypropylene layer, and wear-resistant layer arranged sequentially from the inside to the outside; placing the ultra-high molecular weight polyethylene modified polypropylene layer in the middle layer can avoid the appearance problem of weld lines caused by its poor fluidity; the flame-retardant layer and the wear-resistant layer have a flat wall structure, and the ultra-high molecular weight polyethylene modified polypropylene layer has a corrugated structure. After the three layers are co-extruded together, there are gaps, which can improve the impact resistance of the three-layer co-extruded power bushing. Detailed Implementation

[0007] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments.

[0008] A three-layer co-extruded electrical bushing includes a flame-retardant layer, an ultra-high molecular weight polyethylene modified polypropylene layer, and a wear-resistant layer stacked sequentially from the inside out. The flame-retardant layer and the wear-resistant layer have a flat-wall structure, while the ultra-high molecular weight polyethylene modified polypropylene layer has a corrugated structure.

[0009] The corrugated structure includes crests and troughs, which are alternately connected and integrally formed.

[0010] As can be seen from the above description, the beneficial effects of the present invention are as follows: the inner layer of the three-layer co-extruded power bushing of the present invention is a flame-retardant layer, possessing flame retardancy and heat resistance; the outer layer is a wear-resistant layer, possessing excellent wear resistance; the middle layer is a layer of ultra-high molecular weight polyethylene modified polypropylene. Ultra-high molecular weight polyethylene has high strength, impact resistance, wear resistance, and corrosion resistance, but its flowability is poor and it can produce weld line defects. The present invention places the ultra-high molecular weight polyethylene modified polypropylene layer in the middle layer, which can avoid the appearance problems caused by weld lines. Among them, the flame-retardant layer and the wear-resistant layer have a flat wall structure, and the ultra-high molecular weight polyethylene modified polypropylene layer has a corrugated structure, which creates gaps between the three layers of co-extrusion, thereby improving the impact resistance of the three-layer co-extruded power bushing.

[0011] Furthermore, the flame-retardant layer comprises the following raw materials: polyvinyl chloride, mica sheets, and nano-titanium dioxide.

[0012] Furthermore, the mass ratio of polyvinyl chloride, mica sheets, and nano-titanium dioxide is 10–13:1:1.

[0013] As described above, during combustion, nano-titanium dioxide migrates to the polymer surface, forming a dense titanium layer that isolates the polymer from flame retardancy. Therefore, nano-titanium dioxide exhibits excellent flame retardant properties and heat resistance. Adding mica sheets can give the flame-retardant layer high electrical insulation properties.

[0014] Furthermore, the ultra-high molecular weight polyethylene modified polypropylene layer includes the following raw materials: polypropylene mixed granules, stiffening nucleating agent and ultra-high molecular weight polyethylene compatibilizer and toughening agent.

[0015] As described above, stiffening nucleating agents facilitate the crystallization of polypropylene granules in high-temperature environments, thereby increasing the hardness of polypropylene. Ultra-high molecular weight polyethylene compatibilizers and toughening agents can improve the material's strength, toughness, impact resistance, abrasion resistance, and corrosion resistance.

[0016] Furthermore, ultra-high molecular weight polyethylene compatibilizers and toughening agents include ultra-high molecular weight polyethylene, linear low-density polyethylene, POE, and maleic anhydride graft polymers.

[0017] POE is a thermoplastic elastomer produced by in-situ polymerization of ethylene and octene using a metallocene catalyst.

[0018] Furthermore, the mass ratio of ultra-high molecular weight polyethylene, linear low-density polyethylene, POE and maleic anhydride grafted polymer is 2.5–3.7:1:1:1.

[0019] As can be seen from the above description, maleic anhydride grafted polymers are used as compatibilizers; POE is an elastic material that can enhance the toughness of polypropylene; ultra-high molecular weight polyethylene has high strength, wear resistance, and corrosion resistance; linear low-density polyethylene can improve the heat and cold resistance and toughness of polypropylene; blending ultra-high molecular weight polyethylene with linear low-density polyethylene can increase the crystallization rate of linear low-density polyethylene, increase the modulus, and thus improve the impact resistance of the material.

[0020] Furthermore, the grafting rate of the maleic anhydride-grafted polymer is ≥0.5%.

[0021] Preferably, the grafting rate of the maleic anhydride-grafted polymer is ≥2%.

[0022] As described above, the anhydride groups in maleic anhydride-grafted polymers can react with polar groups under high temperature and screw shearing, enabling chemical coupling between incompatible polar and non-polar substances and achieving effective modification. The higher the grafting rate of the maleic anhydride-grafted polymer, the better the coupling effect and the better the modification effect.

[0023] Furthermore, the maleic anhydride-grafted polymer includes at least one of PP-g-MAH (maleic anhydride-grafted polypropylene), EPDM-g-MAH (maleic anhydride-grafted ethylene propylene diene monomer rubber), and POE-g-MAH (maleic anhydride-grafted POE).

[0024] Furthermore, the polypropylene blended granules include block copolymer polypropylene granules, homopolymer polypropylene granules, and random copolymer polypropylene granules.

[0025] Furthermore, the weight ratio of block copolymer polypropylene granules, homopolymer polypropylene granules, and random copolymer polypropylene granules is 1:2:3 to 5.

[0026] As can be seen from the above description, when block copolymer polypropylene granules, homopolymer polypropylene granules and random copolymer polypropylene granules are blended in a fixed ratio, the crystallinity can be increased, the impact performance and toughness can be improved, and the strength of the polypropylene blend granules can be made to be at the same level as that of pure random copolymer polypropylene granules.

[0027] Furthermore, the wear-resistant layer comprises the following raw materials: polypropylene, polypropylene carbon microspheres, and additives.

[0028] Furthermore, the mass ratio of polypropylene to polypropylene carbon microspheres is 100:1 to 5.

[0029] As can be seen from the above description, carbon microspheres have stable chemical properties and are heat-resistant, which can improve the heat resistance, corrosion resistance and wear resistance of polypropylene; and because carbon microspheres contain a large number of hydrogen bonds, they have a good bonding effect with polypropylene, which can reduce the brittleness problem caused by the incompatibility of inorganic and organic materials.

[0030] Furthermore, the pore volume of the polypropylene carbon microspheres is 0.5–1.0 cm³. 3 / g, with a pore size of 50–100 nm.

[0031] As can be seen from the above description, polypropylene carbon microspheres with excessively large pore volume and pore size are prone to breakage, while polypropylene carbon microspheres with excessively small pore volume and pore size have fewer hydrogen bonds. It is necessary to strictly control their pore volume and pore size to achieve a balance between density and the number of hydrogen bonds, while simultaneously achieving the goal of high hydrogen bond density and high mechanical strength.

[0032] Another technical solution adopted in this invention is: the preparation method of the above-mentioned three-layer co-extruded power bushing, the preparation method of the wear-resistant layer is as follows: polypropylene and additives are mixed at 170-185℃ for 5-10 minutes, then the temperature is raised to 195-210℃ and polypropylene carbon microspheres are added and mixed for 2-4 minutes to obtain a mixture, and the mixture is extruded to obtain the wear-resistant layer.

[0033] As can be seen from the above description, polypropylene carbon microspheres are easily broken. After polypropylene is mixed with additives, the melt temperature is increased to improve the melt fluidity. Then, polypropylene carbon microspheres are added for mixing, which can reduce the mixing time of polypropylene carbon microspheres and reduce their breakage.

[0034] Furthermore, the flame-retardant layer is prepared by blending polyvinyl chloride, mica sheets and nano-titanium dioxide and then extruding to obtain the flame-retardant layer.

[0035] Furthermore, the preparation method of the ultra-high molecular weight polyethylene modified polypropylene layer is as follows: ultra-high molecular weight polyethylene compatibilizer, toughening agent, stiffening nucleating agent and polypropylene mixed granules are blended and then extruded to obtain a tubular ultra-high molecular weight polyethylene modified polypropylene layer.

[0036] Furthermore, the preparation method of the ultra-high molecular weight polyethylene compatibilizer and toughening agent is as follows: ultra-high molecular weight polyethylene, linear low density polyethylene, POE and maleic anhydride graft polymer are dried and then blended to obtain a blend. The blend is then extruded and granulated to obtain the ultra-high molecular weight polyethylene compatibilizer and toughening agent.

[0037] The raw material types / grades used in the following examples are as follows:

[0038] UHMWPE: Mitsui Chemicals L1000 (Japan); Block copolymer polypropylene granules: Daqing Petrochemical H2464; Homopolymer polypropylene granules: Dushan Petrochemical T30S; Random copolymer polypropylene granules: Yangzi Petrochemical K8003; Stiffening nucleating agent: Guangdong Weilinna New Material Technology Co., Ltd. WNA108; Linear low-density polyethylene: Dushan Petrochemical 7042; POE: Dow Chemical POE8150 (USA); PP-g-MAH: Shanghai Rizhisheng New Technology Development Co., Ltd. CMG9801; EPDM-g-MAH: Shanghai Rizhisheng New Technology Development Co., Ltd. CMG9802; POE-g-MAH: Shanghai Rizhisheng New Technology Development Co., Ltd. CMG9805.

[0039] Embodiment 1 of the present invention is a method for preparing a three-layer co-extruded power bushing, comprising the following steps:

[0040] S1: Add 60kg of polyvinyl chloride, 5kg of mica sheets and 5kg of nano titanium dioxide to a high-speed mixer and mix at 2000rpm for 15min to obtain a blend, which will be used as the raw material for the flame retardant layer; the flame retardant layer has a flat wall structure.

[0041] S2: 3 kg of ultra-high molecular weight polyethylene, 1 kg of linear low-density polyethylene, 1 kg of POE and 1 kg of PP-g-MAH were dried at 90℃ for 4 h, and then added to a high-speed mixer and mixed at 2000 rpm for 10 min to obtain a blend; the blend was placed in a screw extruder and extruded and granulated at 200℃ to obtain an ultra-high molecular weight polyethylene compatibilizer and toughening agent; the grafting rate of PP-g-MAH was 2.7%.

[0042] S3: Add 6 kg of ultra-high molecular weight polyethylene compatibilizer and toughening agent, 0.1 kg of stiffening nucleating agent and 100 kg of polypropylene mixed granules into a high-speed mixer and mix at 2000 rpm for 10 min to obtain a blend, which is used as raw material for ultra-high molecular weight polyethylene modified polypropylene layer; the ultra-high molecular weight polyethylene modified polypropylene layer has a corrugated structure.

[0043] The polypropylene mixed granules consist of 16.7 kg of block copolymer polypropylene granules, 33.3 kg of homopolymer polypropylene granules, and 50 kg of random copolymer polypropylene granules.

[0044] S4: Mix 100kg of polypropylene and 3kg of silica at 180℃ for 8 minutes, then heat to 200℃ and add 3kg of polypropylene carbon microspheres and mix for 3 minutes to obtain a mixture, which is used as the raw material for the wear-resistant layer; the wear-resistant layer has a flat wall structure.

[0045] The pore volume of the polypropylene carbon microspheres is 0.5708 cm³. 3 / g, pore size is 80nm;

[0046] S5: The flame-retardant layer material, the ultra-high molecular weight polyethylene modified polypropylene layer material, and the wear-resistant layer material are simultaneously extruded to the module by a single-screw extruder, a twin-screw extruder A, and a twin-screw extruder B, respectively. Under the action of high temperature at the die orifice, after vacuum adsorption and cooling and shaping, a three-layer co-extruded power sleeve is formed by equiaxial thermal fusion welding from the inside to the outside.

[0047] The barrel temperature of the single-screw extruder is 173℃ in zone 1, 168℃ in zone 2, 154℃ in zone 3, 155℃ in zone 4, 150℃ in zone 5, and 160℃ in zone 6. The main engine speed of the single-screw extruder is 200 rpm.

[0048] The barrel temperatures of twin-screw extruder A are 210℃ in zone 1, 190℃ in zone 2, 175℃ in zone 3, 180℃ in zone 4, 170℃ in zone 5, and 200℃ in zone 6. The main motor speed of the twin-screw extruder is 300 rpm.

[0049] The barrel temperature of the twin-screw extruder is 200℃ in zone 1, 180℃ in zone 2, 170℃ in zone 3, 175℃ in zone 4, 165℃ in zone 5, and 190℃ in zone 6. The main motor speed of the twin-screw extruder is 200 rpm.

[0050] Embodiment 2 of the present invention is: a method for preparing a three-layer co-extruded power bushing, the steps of which are as follows:

[0051] S1: Add 60kg of polyvinyl chloride, 5kg of mica sheets and 5kg of nano titanium dioxide to a high-speed mixer and mix at 2000rpm for 15min to obtain a blend, which will be used as the raw material for the flame retardant layer; the flame retardant layer has a flat wall structure.

[0052] S2: 3 kg of ultra-high molecular weight polyethylene, 1 kg of linear low-density polyethylene, 1 kg of POE and 1 kg of EPDM-g-MAH were dried at 90℃ for 4 h, and then added to a high-speed mixer and mixed at 2000 rpm for 10 min to obtain a blend. The blend was placed in a screw extruder and extruded and granulated at 200℃ to obtain an ultra-high molecular weight polyethylene compatibilizer and toughening agent. The grafting rate of EPDM-g-MAH was 2.4%.

[0053] S3: Add 6 kg of ultra-high molecular weight polyethylene compatibilizer and toughening agent, 0.1 kg of stiffening and nucleating agent and 100 kg of polypropylene mixed granules into a high-speed mixer and mix at 2000 rpm for 10 min to obtain a blend; use it as raw material for ultra-high molecular weight polyethylene modified polypropylene layer; ultra-high molecular weight polyethylene modified polypropylene layer has a corrugated structure;

[0054] The polypropylene mixed granules consist of 14.3 kg of block copolymer polypropylene granules, 28.6 kg of homopolymer polypropylene granules, and 57.1 kg of random copolymer polypropylene granules.

[0055] S4: Mix 100kg of polypropylene and 3kg of silica at 170℃ for 10min, then heat to 195℃ and add 3kg of polypropylene carbon microspheres and mix for 2min to obtain a mixture, which is used as raw material for the wear-resistant layer; the wear-resistant layer has a flat wall structure.

[0056] The pore volume of the polypropylene carbon microspheres is 0.5 cm³. 3 / g, pore size is 50nm;

[0057] S5: The flame-retardant layer material, the ultra-high molecular weight polyethylene modified polypropylene layer material, and the wear-resistant layer material are simultaneously extruded to the module by a single-screw extruder, a twin-screw extruder A, and a twin-screw extruder B, respectively. Under the action of high temperature at the die orifice, after vacuum adsorption and cooling and shaping, a three-layer co-extruded power sleeve is formed by equiaxial thermal fusion welding from the inside to the outside.

[0058] The barrel temperature of the single-screw extruder is 173℃ in zone 1, 168℃ in zone 2, 154℃ in zone 3, 155℃ in zone 4, 150℃ in zone 5, and 160℃ in zone 6. The main engine speed of the single-screw extruder is 200 rpm.

[0059] The barrel temperatures of twin-screw extruder A are 210℃ in zone 1, 190℃ in zone 2, 175℃ in zone 3, 180℃ in zone 4, 170℃ in zone 5, and 200℃ in zone 6. The main motor speed of the twin-screw extruder is 300 rpm.

[0060] The barrel temperature of the twin-screw extruder is 200℃ in zone 1, 180℃ in zone 2, 170℃ in zone 3, 175℃ in zone 4, 165℃ in zone 5, and 190℃ in zone 6. The main motor speed of the twin-screw extruder is 200 rpm.

[0061] Embodiment 3 of the present invention is a method for preparing a three-layer co-extruded power bushing, comprising the following steps:

[0062] S1: Add 60kg of polyvinyl chloride, 5kg of mica sheets and 5kg of nano titanium dioxide to a high-speed mixer and mix at 2000rpm for 15min to obtain a blend, which is used as the raw material for the flame retardant layer; the flame retardant layer has a flat wall structure.

[0063] S2: 3 kg of ultra-high molecular weight polyethylene, 1 kg of linear low-density polyethylene, 1 kg of POE, and 1 kg of POE-g-MAH were dried at 90°C for 4 hours, and then added to a high-speed mixer and mixed at 2000 rpm for 10 minutes to obtain a blend. The blend was placed in a screw extruder and extruded and granulated at 200°C to obtain an ultra-high molecular weight polyethylene compatibilizer and toughening agent. The grafting rate of POE-g-MAH was 3.1%.

[0064] S3: Add 6 kg of ultra-high molecular weight polyethylene compatibilizer and toughening agent, 0.1 kg of stiffening and nucleating agent and 100 kg of polypropylene mixed granules into a high-speed mixer and mix at 2000 rpm for 10 min to obtain a blend; use it as raw material for ultra-high molecular weight polyethylene modified polypropylene layer; ultra-high molecular weight polyethylene modified polypropylene layer has a corrugated structure;

[0065] The polypropylene mixed granules consist of 12.5 kg of block copolymer polypropylene granules, 25 kg of homopolymer polypropylene granules, and 62.5 kg of random copolymer polypropylene granules.

[0066] S4: Mix 100kg of polypropylene and 3kg of silica at 185℃ for 5 minutes, then heat to 210℃ and add 3kg of polypropylene carbon microspheres and mix for 4 minutes to obtain a mixture, which is used as the raw material for the wear-resistant layer; the wear-resistant layer has a flat wall structure.

[0067] The pore volume of the polypropylene carbon microspheres is 1.0 cm³. 3 / g, with a pore size of 100nm;

[0068] S5: The flame-retardant layer material, the ultra-high molecular weight polyethylene modified polypropylene layer material, and the wear-resistant layer material are simultaneously extruded to the module by a single-screw extruder, a twin-screw extruder A, and a twin-screw extruder B, respectively. Under the action of high temperature at the die orifice, after vacuum adsorption and cooling and shaping, a three-layer co-extruded power sleeve is formed by equiaxial thermal fusion welding from the inside to the outside.

[0069] The barrel temperature of the single-screw extruder is 173℃ in zone 1, 168℃ in zone 2, 154℃ in zone 3, 155℃ in zone 4, 150℃ in zone 5, and 160℃ in zone 6. The main engine speed of the single-screw extruder is 200 rpm.

[0070] The barrel temperatures of twin-screw extruder A are 210℃ in zone 1, 190℃ in zone 2, 175℃ in zone 3, 180℃ in zone 4, 170℃ in zone 5, and 200℃ in zone 6. The main motor speed of the twin-screw extruder is 300 rpm.

[0071] The barrel temperature of the twin-screw extruder is 200℃ in zone 1, 180℃ in zone 2, 170℃ in zone 3, 175℃ in zone 4, 165℃ in zone 5, and 190℃ in zone 6. The main motor speed of the twin-screw extruder is 200 rpm.

[0072] Embodiment 4 of the present invention is a power bushing prepared using the preparation method of Embodiment 1.

[0073] Comparative Example 1 of the present invention is:

[0074] The only difference between Comparative Example 1 and Example 1 is that: S4: 100 kg of polypropylene and 3 kg of silica are mixed at 170°C for 10 min to obtain a mixture, which is used as a raw material for the wear-resistant layer.

[0075] Comparative Example 2 of the present invention is as follows:

[0076] The only difference between Comparative Example 2 and Example 1 is: S4: 100 kg of polypropylene, 3 kg of silica and 3 kg of polypropylene carbon microspheres are mixed at 170°C for 10 min to obtain a mixture, which is used as the raw material for the wear-resistant layer.

[0077] Comparative Example 3 of the present invention is as follows:

[0078] The difference between Comparative Example 3 and Example 1 is that the polypropylene mixed granules are only random copolymer polypropylene granules.

[0079] Comparative Example 4 of the present invention is as follows:

[0080] The difference between Comparative Example 4 and Example 1 is that the ultra-high molecular weight polyethylene modified polypropylene layer has a flat wall structure.

[0081] The performance of the power bushings prepared in Example 1 and Comparative Examples 1 to 4 were tested respectively, and the test results are shown in Table 1.

[0082] Table 1

[0083]

[0084]

[0085] Comparing Comparative Example 1, Comparative Example 2, and Example 1, it can be seen that by controlling the pore volume and pore size of the polypropylene carbon microspheres, as well as the addition time and temperature, the wear resistance can be improved while significantly reducing the impact of the polypropylene carbon microspheres on the toughness and brittleness of polypropylene. Comparing Comparative Example 3 and Example 1, it can be seen that by blending block copolymer polypropylene granules, homopolymer polypropylene granules, and random copolymer polypropylene granules in a fixed ratio, the impact resistance and toughness can be improved while maintaining the material's strength at the same level as pure random copolymer polypropylene granules. Comparing Comparative Example 4 and Example 1, it can be seen that setting the middle layer as a corrugated structure in this invention can effectively improve the toughness and impact resistance of polypropylene.

[0086] In summary, the three-layer co-extruded power bushing provided by this invention has the following advantages:

[0087] 1. Achieve the technical effect of an inner layer that is flame-retardant and heat-resistant, an outer layer that is wear-resistant, a middle layer that is impact-resistant, and has excellent toughness.

[0088] 2. The middle layer has a corrugated structure, while the inner and outer layers have flat wall structures, which creates gaps between the three co-extruded layers, thus improving the impact resistance of the three-layer co-extruded power bushing.

[0089] 3. Nano-titanium dioxide is added to the inner layer to improve the flame retardancy of the material, and the addition of mica sheets can give the flame retardant layer high electrical insulation function.

[0090] 4. The use of ultra-high molecular weight polyethylene compatibilizer and toughening agent in the intermediate layer can improve the material's strength, toughness, impact resistance, wear resistance, and corrosion resistance. When block copolymer polypropylene granules, homopolymer polypropylene granules, and random copolymer polypropylene granules are blended in a fixed ratio in the intermediate layer, crystallinity is increased, impact performance and toughness are improved, and the strength of the polypropylene blend granules is made to be equivalent to that of pure random copolymer polypropylene granules.

[0091] 5. Adding carbon microspheres to the outer layer provides stable chemical properties and heat resistance, improving the heat and corrosion resistance and wear resistance of polypropylene. Furthermore, due to the large number of hydrogen bonds in the carbon microspheres, they bond well with polypropylene, reducing brittleness issues caused by incompatibility between inorganic and organic materials. However, carbon microspheres are easily broken. Therefore, by strictly controlling their pore volume and diameter, as well as the addition time and temperature, a balance between density and the number of hydrogen bonds is achieved, simultaneously achieving high hydrogen bonding and high mechanical strength.

[0092] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made using the present invention specification, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A three-layer co-extruded power bushing, characterized in that, It includes a flame-retardant layer, an ultra-high molecular weight polyethylene modified polypropylene layer, and a wear-resistant layer that are stacked and connected sequentially from the inside to the outside. The flame-retardant layer and the wear-resistant layer have a flat wall structure, and the ultra-high molecular weight polyethylene modified polypropylene layer has a corrugated structure. The flame-retardant layer comprises the following raw materials: Polyvinyl chloride, mica sheets and nano titanium dioxide; The ultra-high molecular weight polyethylene modified polypropylene layer comprises the following raw materials: polypropylene mixed granules, stiffening nucleating agent and ultra-high molecular weight polyethylene compatibilizer and toughening agent; the ultra-high molecular weight polyethylene compatibilizer and toughening agent comprises ultra-high molecular weight polyethylene, linear low density polyethylene, POE and maleic anhydride graft polymer. The wear-resistant layer is prepared as follows: polypropylene and additives are mixed at 170-185℃ for 5-10 minutes, then the temperature is raised to 195-210℃, polypropylene carbon microspheres are added, and the mixture is mixed for 2-4 minutes to obtain a mixture. The mixture is then extruded to form the wear-resistant layer; the pore volume of the polypropylene carbon microspheres is 0.5-1.0 cm³. 3 / g, with a pore size of 50~100 nm.

2. The three-layer co-extruded power bushing according to claim 1, characterized in that, The grafting rate of the maleic anhydride-grafted polymer is ≥0.5%.

3. The three-layer co-extruded power bushing according to claim 1, characterized in that, The polypropylene mixed granules include block copolymer polypropylene granules, homopolymer polypropylene granules, and random copolymer polypropylene granules.

4. The three-layer co-extruded power bushing according to claim 3, characterized in that, The weight ratio of the block copolymer polypropylene granules, homopolymer polypropylene granules, and random copolymer polypropylene granules is 1:2:3~5.

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