Ultra-smooth semi-conductive shielding layer preparation method based on double-layer co-extrusion technology

Abstract

The invention discloses a preparation method of an ultra-smooth semi-conductive shielding layer based on a double-layer co-extrusion technology. The preparation method comprises the following steps: S1, carrying out surface energy modification on carbon black and carrying out topological structure regulation and control on carbon nanotubes; s2, realizing multi-scale dispersion of the filler under the synergistic effect of the ultrasonic field and the supercritical fluid; s3, controlling the rheological property difference of the melt of the inner layer and the melt of the outer layer for co-extrusion, wherein the viscosity of the melt of the inner layer is 20-50% higher than that of the melt of the outer layer And S4, co-processing of irradiation crosslinking and gradient annealing is carried out on the co-extruded product. Compared with a traditional semi-conductive shielding layer, the surface roughness of the semi-conductive shielding layer prepared through the technology can be greatly reduced, meanwhile, the volume resistivity meets the standard requirement, the semi-conductive shielding layer prepared through the method does not need a subsequent mechanical polishing procedure, and the production speed can be greatly increased.

Description

Technical Field

[0001] The present invention relates to the technical field of cable shielding layer materials, and in particular to a method for preparing an ultra-smooth semi-conductive shielding layer based on a double-layer co-extrusion technology. Background Art

[0002] The semi-conductive shielding layer plays an important role in the uniform electric field and preventing partial discharge in power cables. Its performance directly affects the long-term stability of the insulation system.

[0003] The current preparation process usually adopts single-layer extrusion technology of carbon black-filled polymer, but it is limited by material properties and processing methods. In order to meet the conductive performance requirements, a higher proportion of carbon black filler needs to be added to the formula. However, during the production process, it is easy to cause uneven dispersion of the filler in the matrix and form agglomerates, resulting in obvious bumps on the surface of the extruded layer.

[0004] These surface defects can cause abnormal electric field distribution in high-voltage applications, accelerating the degradation of the insulation material. Traditionally, mechanical polishing has been used to address this issue. However, this process not only reduces the effective thickness of the shielding layer but also significantly increases production costs due to the added processing steps, creating a technical bottleneck that makes it difficult to balance material performance and surface quality.

[0005] To address the above problems, we have introduced a method for preparing an ultra-smooth semi-conductive shielding layer based on double-layer co-extrusion technology. Summary of the Invention

[0006] The invention discloses a method for preparing an ultra-smooth semi-conductive shielding layer based on a double-layer co-extrusion technology, aiming to solve the technical problems in the background technology.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A method for preparing an ultra-smooth semi-conductive shielding layer based on double-layer co-extrusion technology comprises the following steps: S1. Surface energy modification of carbon black and topological structure regulation of carbon nanotubes; S2. Realize multi-scale dispersion of fillers under the synergistic effect of ultrasonic field and supercritical fluid; S3, control the difference in rheological properties of the inner and outer layers for co-extrusion, where the viscosity of the inner layer melt is 20%-50% higher than that of the outer layer; S4. Implementing synergistic treatment of radiation cross-linking and gradient annealing on the co-extruded product.

[0008] In a preferred embodiment, step S1 can be subdivided into: S11. Place carbon black in a plasma reactor, introduce an argon mixed gas containing 1%-3% silane coupling agent, and treat it at a power of 300-500 W for 10-30 min to obtain modified carbon black with siloxane groups grafted on the surface; S12. Immerse carbon nanotubes in an ethanol solution containing 0.5%-1.5% fluorocarbon surfactant, perform ultrasonic treatment at 60-80 °C for 30-60 min, and then dry it under vacuum.

[0009] In a preferred embodiment, the silane coupling agent in step S1 is a mixture of γ-aminopropyltriethoxysilane and γ-methacryloxypropyltrimethoxysilane in a mass ratio of 1:0.5-1.5, and the gas pressure during the plasma treatment is maintained at 10-50 Pa.

[0010] In a preferred embodiment, step S2 includes: The ultrasonic field treatment parameters are set as follows: frequency 28±2 kHz, power density 0.8-1.2 W / cm³, treatment time 20-40 min; The supercritical fluid is a mixed fluid composed of CO2 and ethanol in a mass ratio of 95-99:1-5, the treatment pressure is 10-12 MPa, the temperature is 38-45 °C, and the treatment time is 1.5-2.5 h.

[0011] In a preferred embodiment, during the ultrasonic field treatment stage, control the material temperature not to exceed the glass transition temperature Tg of the matrix resin +15 °C, and immediately perform supercritical fluid treatment after the ultrasonic treatment ends, and the interval time between the two stages is less than 5 min.

[0012] In a preferred embodiment, step S3 includes: The inner layer material is composed of ethylene-vinyl acetate copolymer, modified carbon black and nano-montmorillonite, where: Ethylene-vinyl acetate copolymer 60-70 wt%, modified carbon black 28-35 wt%, nano-montmorillonite 0.5-1.5 wt%; The outer layer material is composed of fluorinated ethylene propylene copolymer, carbon nanotubes and organic vermiculite, where: Fluorinated ethylene propylene copolymer 78-83 wt%, carbon nanotubes 15-20 wt%, organic vermiculite 0.5-1.2 wt%; During the co-extrusion operation, the inner layer melt temperature is 15-25 °C higher than that of the outer layer, and the die head pressure fluctuation is controlled within ±0.3 MPa.

[0013] In a preferred embodiment, both the nano-montmorillonite and the organic vermiculite have been intercalated, their layer spacing has been expanded to 2.5-3.5 nm, and the addition ratio in the inner layer and the outer layer is 1.2-1.8:1.

[0014] In a preferred embodiment, step S4 can be refined as follows: S41. First, perform irradiation crosslinking. Use an electron beam to perform dynamic scanning irradiation under the conditions of a beam current energy of 1.8 - 2.2 MeV and a dose rate of 8 - 12 kGy / min, with a total absorbed dose of 12 - 18 kG; S42. Then, perform gradient annealing. Heat at a rate of 2 - 5 °C / min to 85 - 95 °C and hold for 20 - 40 min, and then slowly cool to room temperature at a rate of 0.5 - 1 °C / min.

[0015] In a preferred embodiment, an axial tensile stress is simultaneously applied during the irradiation crosslinking process. The tensile strength is controlled at 10% - 15% of the material yield strength, and the temperature of the irradiated area is maintained at 40 - 60 °C.

[0016] In a preferred embodiment, a melt rheological property matching process is further included between step S2 and step S3: a. Measure the apparent viscosity of the inner layer melt at a shear rate of 100 s⁻¹ to be 1500 - 2500 Pa·s; b. Adjust the temperature of the outer layer melt so that the apparent viscosity reaches 800 - 1500 Pa·s at the same shear rate; c. Control the viscosity ratio of the inner and outer layer melts within the range of 1.5 - 3.0.

[0017] The method for preparing a super-smooth semi-conductive shielding layer based on a double-layer co-extrusion technology provided by the present invention has the following advantages: For the semi-conductive shielding layer prepared by the above process, compared with the surface roughness of the traditional semi-conductive shielding layer, it can be significantly reduced. At the same time, the volume resistivity also meets the standard requirements, and the semi-conductive shielding layer prepared by this method does not require subsequent mechanical polishing processes, which can greatly improve the production speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the overall steps of a method for preparing a super-smooth semi-conductive shielding layer based on a double-layer co-extrusion technology proposed by the present invention.

[0019] Figure 2 It is a schematic diagram of the refined steps of step S1 of a method for preparing a super-smooth semi-conductive shielding layer based on a double-layer co-extrusion technology proposed by the present invention.

[0020] Figure 3 It is a schematic diagram of the refined steps of step S4 of a method for preparing a super-smooth semi-conductive shielding layer based on a double-layer co-extrusion technology proposed by the present invention.

[0021] Figure 4Schematic diagram of the melt rheological property matching process step for a method of preparing a super-smooth semi-conductive shielding layer based on a double-layer co-extrusion technique proposed by the present invention. Specific embodiments

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying 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. Components of the embodiments of the present application described and marked in the drawings here can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the present application provided in the following drawings is not intended to limit the scope of the present application to be protected, but only represents the selected embodiments of the present application. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative efforts belong to the scope of protection of the present application.

[0023] A method for preparing a super-smooth semi-conductive shielding layer based on a double-layer co-extrusion technique disclosed by the present invention.

[0024] Reference Figures 1 to 4 , a method for preparing a super-smooth semi-conductive shielding layer based on a double-layer co-extrusion technique, comprising the following steps: S1. Modify the surface energy of carbon black and regulate the topological structure of carbon nanotubes; The step S1 can be further divided into: S11. Place carbon black in a plasma reactor, introduce an argon mixed gas containing 1%-3% silane coupling agent, and treat it at a power of 300-500W for 10-30min to obtain modified carbon black with surface-grafted siloxane groups; S12. Immerse carbon nanotubes in an ethanol solution containing 0.5%-1.5% fluorocarbon surfactant, perform ultrasonic treatment at 60-80°C for 30-60min, and then dry it under vacuum.

[0025] In the step S1, the silane coupling agent is a mixture of γ-aminopropyltriethoxysilane and γ-methacryloxypropyltrimethoxysilane in a mass ratio of 1:0.5-1.5, and the gas pressure during the plasma treatment is maintained at 10-50Pa.

[0026] S2. Achieve multi-scale dispersion of fillers under the synergistic action of an ultrasonic field and a supercritical fluid; The step S2 includes: The ultrasonic field treatment parameters are set as: frequency 28±2kHz, power density 0.8-1.2W / cm³, treatment time 20-40min; The supercritical fluid is a mixed fluid composed of CO2 and ethanol with a mass ratio of 95 - 99:1 - 5, the treatment pressure is 10 - 12 MPa, the temperature is 38 - 45 °C, and the treatment time is 1.5 - 2.5 h.

[0027] In the ultrasonic field treatment stage, control the material temperature not to exceed the glass transition temperature Tg of the matrix resin + 15 °C, and immediately perform supercritical fluid treatment after the ultrasonic treatment ends, and the interval time between the two stages is less than 5 min.

[0028] S3. Control the difference in melt rheological properties between the inner and outer layers for co - extrusion, where the melt viscosity of the inner layer is 20% - 50% higher than that of the outer layer; The step S3 includes: The inner layer material is composed of ethylene - vinyl acetate copolymer, modified carbon black and nano - montmorillonite, where: Ethylene - vinyl acetate copolymer 60 - 70 wt%, modified carbon black 28 - 35 wt%, nano - montmorillonite 0.5 - 1.5 wt%; The outer layer material is composed of fluorinated ethylene propylene copolymer, carbon nanotubes and organic vermiculite, where: Fluorinated ethylene propylene copolymer 78 - 83 wt%, carbon nanotubes 15 - 20 wt%, organic vermiculite 0.5 - 1.2 wt%; During the co - extrusion operation, the temperature of the inner layer melt is 15 - 25 °C higher than that of the outer layer, and the die head pressure fluctuation is controlled within ±0.3 MPa.

[0029] Both the nano - montmorillonite and the organic vermiculite have been intercalated, and their layer spacing has been expanded to 2.5 - 3.5 nm, and the ratio of the addition amounts in the inner layer and the outer layer is 1.2 - 1.8:1.

[0030] Between the step S2 and the step S3, there is also a melt rheological property matching process: a. Measure the apparent viscosity of the inner layer melt at a shear rate of 100 s⁻¹ to be 1500 - 2500 Pa·s; b. Adjust the temperature of the outer layer melt to make the apparent viscosity reach 800 - 1500 Pa·s at the same shear rate; c. Control the viscosity ratio of the inner and outer layer melts within the range of 1.5 - 3.0 S4. Perform a coordinated treatment of irradiation cross - linking and gradient annealing on the co - extruded product.

[0031] The step S4 can be refined as: S41. First, perform irradiation cross - linking, and perform dynamic scanning irradiation with an electron beam under the conditions of a beam current energy of 1.8 - 2.2 MeV and a dose rate of 8 - 12 kGy / min, and the total absorbed dose is 12 - 18 kG; S42. Then perform gradient annealing, heating at a rate of 2 - 5 °C / min to 85 - 95 °C and holding for 20 - 40 min, and then slowly cooling to room temperature at a rate of 0.5 - 1 °C / min.

[0032] During the irradiation cross - linking process, an axial tensile stress is applied synchronously, and the tensile strength is controlled at 10% - 15% of the material yield strength, and the temperature in the irradiation area is maintained at 40 - 60 °C.

[0033] In this embodiment, first, a gradient pretreatment of the conductive filler is carried out. Take 500 g of acetylene black with a particle size of 30 - 50 nm and place it in a radio - frequency plasma reactor. Mix argon with γ - aminopropyltriethoxysilane and γ - methacryloxypropyltrimethoxysilane in a volume ratio of 97:2:1 and introduce it into the reaction chamber at a flow rate of 5 L / min. Maintain the chamber pressure at 30 Pa and apply 400 W of plasma for 20 min to obtain modified carbon black with surface - grafted siloxane groups. At the same time, prepare an ethanol solution containing 1.2% ammonium perfluorooctanoate, immerse multi - walled carbon nanotubes in it, and perform ultrasonic treatment at 70 °C for 40 min. After the treatment, dehydrate in a vacuum drying oven at 80 °C until the water content is < 0.3%.

[0034] Put the treated modified carbon black and EVA (VA content 28%) into a mixer at a mass ratio of 32:68, and at the same time add 0.8% of organically modified montmorillonite with an interlayer spacing of 3.2 nm. Start the two - stage mixing process. In the first stage, turn on a 28 kHz ultrasonic generator at 60 °C, set the power density to 1.0 W / cm³, and continuously treat for 25 min. During this period, monitor the material temperature with an infrared thermometer not exceeding 75 °C. In the second stage, immediately transfer it to a supercritical treatment autoclave, inject a mixed fluid of CO2 and ethanol in a ratio of 98:2, maintain the pressure at 11 MPa and the temperature at 42 °C, and perform dynamic stirring treatment for 2 hours. When preparing the outer layer material, mix fluorinated ethylene - propylene copolymer and surface - treated carbon nanotubes in a ratio of 82:17.5, add 0.5% of organic vermiculite and adopt the same dispersion process, but shorten the supercritical treatment time to 1.8 hours.

[0035] After the mixing is completed, a twin-screw extrusion unit is used to match the melt rheological properties. The apparent viscosity of the inner layer material at a shear rate of 100 s⁻¹ measured at 165 °C is 1950 Pa·s. By adjusting the three temperature zones of the outer extruder to 142 °C, 145 °C, and 148 °C, the viscosity at the same shear rate reaches 1050 Pa·s, and the viscosity ratio is 1.86 at this time. During co-extrusion molding, the four temperature settings of the inner extruder are 155 °C, 160 °C, 165 °C, and 168 °C, and the temperature zones of the outer extruder are 138 °C, 142 °C, 145 °C, and 147 °C. The pressure at the die connection is stabilized at 10.5 ± 0.2 MPa, and the traction speed is controlled at 3.2 m / min. Online monitoring shows that the temperature difference at the interface between the inner and outer layer melts remains within the range of 19 - 22 °C.

[0036] The formed composite shielding layer immediately enters the post-treatment process. First, dynamic irradiation is carried out using an electron accelerator. The beam energy is set to 2.0 MeV, and reciprocating scanning is performed at a dose rate of 10 kGy / min until the cumulative absorbed dose reaches 15 kGy. During irradiation, an axial stress of 12 MPa is applied using a servo stretching device, which is equivalent to 13% of the material's yield strength, and the temperature of the irradiation area is controlled at 55 ± 3 °C through a circulating water cooling system. After the irradiation is completed, the product is placed in a programmable temperature control box, heated to 90 °C at a rate of 3 °C / min and kept at a constant temperature for 35 min, and then cooled to room temperature in stages at a rate of 0.8 °C / min, with each cooling step maintained for 10 min to ensure stress release.

[0037] 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 a substitution of part of the structure, device, or 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 method for preparing a super-smooth semi-conductive shielding layer based on a double-layer co-extrusion technique, characterized in that, It includes the following steps: S1. Modify the surface energy of carbon black and regulate the topological structure of carbon nanotubes; S2. Achieve multi-scale dispersion of fillers under the synergistic action of an ultrasonic field and a supercritical fluid; S3. Conduct co-extrusion by controlling the difference in melt rheological properties between the inner and outer layers, where the viscosity of the inner layer melt is 20%-50% higher than that of the outer layer; S4. Perform a synergistic treatment of irradiation cross-linking and gradient annealing on the co-extruded product.

2. The method for preparing a super-smooth semi-conductive shielding layer based on a double-layer co-extrusion technique according to claim 1, wherein The step S1 can be further divided into: S11. Place carbon black in a plasma reactor, introduce an argon mixed gas containing 1%-3% silane coupling agent, and treat it at a power of 300-500W for 10-30min to obtain modified carbon black with surface-grafted siloxane groups; S12. Immerse carbon nanotubes in an ethanol solution containing 0.5%-1.5% fluorocarbon surfactant, ultrasonically treat them at 60-80°C for 30-60min, and then dry them under vacuum.

3. The method for preparing a super-smooth semi-conductive shielding layer based on a double-layer co-extrusion technique according to claim 2, wherein In the step S1, the silane coupling agent is a mixture of γ-aminopropyltriethoxysilane and γ-methacryloxypropyltrimethoxysilane in a mass ratio of 1:0.5-1.5, and the gas pressure during the plasma treatment is maintained at 10-50Pa.

4. The method for preparing a super-smooth semi-conductive shielding layer based on a double-layer co-extrusion technique according to claim 1, characterized in that, The step S2 includes: The ultrasonic field treatment parameters are set as follows: frequency 28±2kHz, power density 0.8-1.2W / cm³, treatment time 20-40min; The supercritical fluid is a mixed fluid composed of CO2 and ethanol in a mass ratio of 95-99:1-5, with a treatment pressure of 10-12MPa, a temperature of 38-45°C, and a treatment time of 1.5-2.5h.

5. The method for preparing a super-smooth semi-conductive shielding layer based on a double-layer co-extrusion technique according to claim 4, wherein During the ultrasonic field treatment stage, control the material temperature not to exceed the glass transition temperature Tg+15°C of the matrix resin, and immediately perform supercritical fluid treatment after the ultrasonic treatment ends, with the interval time between the two stages less than 5min.

6. The method for preparing a super-smooth semi-conductive shielding layer based on a double-layer co-extrusion technique according to claim 1, wherein The step S3 includes: The inner layer material is composed of ethylene-vinyl acetate copolymer, modified carbon black, and nano-montmorillonite, where: Ethylene-vinyl acetate copolymer 60-70wt%, modified carbon black 28-35wt%, nano-montmorillonite 0.5-1.5wt%; The outer layer material is composed of fluorinated ethylene propylene copolymer, carbon nanotubes, and organic vermiculite, where: Fluorinated ethylene propylene copolymer 78-83wt%, carbon nanotubes 15-20wt%, organic vermiculite 0.5-1.2wt%; During the co-extrusion operation, the temperature of the inner layer melt is 15-25°C higher than that of the outer layer, and the die head pressure fluctuation is controlled within ±0.3MPa.

7. The method for preparing a super-smooth semiconductive shielding layer based on a double-layer co-extrusion technique according to claim 6, wherein, Both the nano-montmorillonite and the organic vermiculite have been intercalated, and their layer spacing has been expanded to 2.5-3.5nm, and the addition amount ratio in the inner layer and the outer layer is 1.2-1.8:

1.

8. The method for preparing a super-smooth semi-conductive shielding layer based on a double-layer co-extrusion technique according to claim 1, wherein The step S4 can be refined as: S41. First, perform irradiation cross-linking, and conduct dynamic scanning irradiation using an electron beam under the conditions of beam energy 1.8-2.2MeV and dose rate 8-12kGy / min, with a total absorbed dose of 12-18kG; S42. Then, perform gradient annealing, heat it at a rate of 2-5°C / min to 85-95°C and hold for 20-40min, and then slowly cool it to room temperature at a rate of 0.5-1°C / min.

9. The preparation method of the super-smooth semi-conductive shielding layer based on the double-layer co-extrusion technology according to claim 8, characterized in that, During the irradiation cross-linking process, an axial tensile stress is applied synchronously, and the tensile strength is controlled at 10%-15% of the material's yield strength, and the temperature of the irradiation area is maintained at 40-60°C.

10. The method according to any one of claims 1-9, characterized in that, Between the step S2 and the step S3, there is also a melt rheological property matching process: a. Measure the apparent viscosity of the inner layer melt at a shear rate of 100 s⁻¹ to be 1500-2500 Pa·s; b. Adjust the temperature of the outer layer melt so that the apparent viscosity reaches 800-1500 Pa·s at the same shear rate; c. Control the viscosity ratio of the inner and outer layer melts within the range of 1.5-3.0.

Images