Polyvinyl chloride material for ultraviolet crosslinking transparent medium-voltage insulating layer and preparation method of polyvinyl chloride material

Abstract

The invention discloses a polyvinyl chloride material for an ultraviolet crosslinking transparent medium-voltage insulating layer and a preparation method of the polyvinyl chloride material. The polyvinyl chloride material for the ultraviolet crosslinking transparent medium-voltage insulating layer is prepared from the following components: polyvinyl chloride resin, a methyl methacrylate-styrene copolymer, diisononyl phthalate, epoxidized soybean oil, liquid nitrile rubber, nano zinc oxide, a benzophenone derivative photoinitiator and a thiodipropionate light stabilizer. The flame retardant is prepared from an alkyl mercaptan crosslinking aid, a triphenyl phosphate flame retardant, polytetrafluoroethylene micro powder, a hydroxyl silicone oil dispersing agent, sodium dodecyl benzene sulfonate and a benzotriazole ultraviolet light absorber. According to the ultraviolet crosslinking polyvinyl chloride material disclosed by the invention, through multi-component synergistic effect and process coupling, breakthrough improvement of insulating property, optical property and environmental stability is realized, a photo-initiation synergistic mechanism of a nano-zinc oxide heterostructure achieves high crosslinking density under low irradiation dose, and the contradiction between photo-initiation efficiency and transparency is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyvinyl chloride materials, and specifically relates to a polyvinyl chloride material for ultraviolet cross-linked transparent medium-voltage insulation layer; in particular, it also relates to a preparation method of the polyvinyl chloride material for ultraviolet cross-linked transparent medium-voltage insulation layer. Background Art

[0002] Polyvinyl chloride (PVC)-based composite materials are widely used in cable insulation due to their excellent processability and cost-effectiveness. However, traditional thermally cross-linked PVC materials have inherent drawbacks such as poor cross-linking uniformity, low light transmittance, and insufficient resistance to corona aging. These drawbacks make them difficult to meet the dual requirements of long-term reliability and operating condition visualization required by modern medium-voltage insulation systems. While UV cross-linking technology can improve cross-linking efficiency, the following technical issues remain with existing systems:

[0003] 1. The contradiction between photoinitiator efficiency and material transparency. Conventional benzophenone photoinitiators have limited dispersion in PVC matrix, and it is necessary to increase the ultraviolet radiation dose to trigger sufficient crosslinking (usually > 0.15J / cm 2 ), resulting in an increase in the yellowing index of the material (ΔYI>4.5). Although the use of nano-TiO2 particles can enhance the light scattering effect, it will reduce the visible light transmittance to below 85% (at a thickness of 1mm), and the monitoring function of the transparent insulating layer will be lost.

[0004] 2. The challenge of balancing flame retardancy and dielectric loss. Traditional flame retardant systems rely heavily on halogen compounds (such as decabromodiphenylethane). While these can increase the oxygen index to over 30, bromine migration can easily trigger electrical dendrite formation, leading to a surge in dielectric loss (tanδ > 0.03) under high electric fields (>15kV / mm). While organophosphorus flame retardants are more environmentally friendly, they have poor compatibility with PVC substrates, resulting in a drop in the material's tensile strength by over 20%.

[0005] On the basis of the above, we propose a UV-crosslinked transparent polyvinyl chloride material for medium-voltage insulation layer and a preparation method thereof to specifically solve the problems raised by the existing technology. Summary of the Invention

[0006] The purpose of the present invention is to provide a UV-crosslinked transparent polyvinyl chloride material for medium-voltage insulation layer and a preparation method thereof. The UV-crosslinked polyvinyl chloride material of the present invention achieves a breakthrough improvement in insulation performance, optical properties and environmental stability through the synergistic effect of multiple components and process coupling. Based on the photoinitiation enhancement mechanism of nano-zinc oxide heterostructure, a high crosslinking density is achieved at a low irradiation dose, solving the contradiction between photoinitiation efficiency and transparency in traditional processes.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A UV-crosslinked transparent polyvinyl chloride material for a medium-voltage insulating layer, comprising the following components in parts by mass:

[0009] 40-120 parts of polyvinyl chloride resin, 5-45 parts of methyl methacrylate-styrene copolymer, 8-12 parts of diisononyl phthalate, 3-15 parts of epoxy soybean oil, 10-18 parts of liquid nitrile rubber, 0.5-2 parts of nano zinc oxide, 1.5-3 parts of benzophenone derivative photoinitiator, 0.8-1.6 parts of thiodipropionate light stabilizer, 2-4 parts of alkyl mercaptan crosslinking aid, 4-8 parts of triphenyl phosphate flame retardant, 0.3-4.2 parts of polytetrafluoroethylene powder, 1.2-2.5 parts of hydroxy silicone oil dispersant, 0.5-1.5 parts of sodium dodecylbenzenesulfonate, and 0.7-1.8 parts of benzotriazole ultraviolet absorber.

[0010] Preferably, the polyvinyl chloride resin is a suspension resin with a polymerization degree of 1300-1500. When it works synergistically with the methyl methacrylate-styrene copolymer, the polar interaction of the molecular segments increases the three-dimensional network crosslinking degree of the material under ultraviolet light irradiation.

[0011] Preferably, the nano zinc oxide is composed of rod-shaped particles with a particle size of 30-50 nm and spherical particles with a particle size of 80-100 nm in a mass ratio of 1:2-3. When the total mass portion is 1.0-1.8 parts, the nano zinc oxide can be used at 0.02-0.08 J / cm 2 The activity of the photoinitiator is increased under the intensity of ultraviolet light.

[0012] Preferably, the thiodipropionate light stabilizer is compounded by dioctadecyl thiodipropionate and didodecyl thiodipropionate in a mass ratio of 1:1-1.5, and produces a gradient absorption effect with the benzotriazole ultraviolet absorber, thereby reducing the light transmittance control deviation of the material in the 310-400nm band.

[0013] Preferably, the alkyl mercaptan crosslinking aid is a combination of dodecyl mercaptan and isooctyl mercaptopropionate in a mass ratio of 2:1-3:1, with a total mass of 2.5-3.5 parts. Through a bidirectional grafting reaction with the end groups of the polyvinyl chloride molecular chain, the volume resistivity at a field strength of 20 kV / mm is increased by 3-5 orders of magnitude;

[0014] The particle size of the polytetrafluoroethylene powder is distributed in the range of 1-5 μm and the specific surface area is 8-12 m 2 / g;

[0015] The hydroxyl content of the hydroxyl silicone oil dispersant is 3.5-4.2 wt% and the viscosity is 500-800 cps.

[0016] Preferably, the mass fraction of each component complies with the following interaction formula:

[0017] 0.8×Qpvc+1.2×(Qmbs+Qdinp)-0.6×(Qptfe+Qbzt)=75±25;

[0018] Wherein, Qpvc represents the mass parts of polyvinyl chloride resin, Qmbs represents the mass parts of methyl methacrylate-styrene copolymer, Qdinp represents the mass parts of diisononyl phthalate, Qptfe represents the mass parts of polytetrafluoroethylene powder, and Qbzt represents the mass parts of benzotriazole ultraviolet absorber.

[0019] A method for preparing a UV-crosslinked transparent polyvinyl chloride material for a medium-voltage insulating layer, the method being used to prepare the UV-crosslinked transparent polyvinyl chloride material for a medium-voltage insulating layer, comprising the following steps:

[0020] S1, premixed modification treatment;

[0021] S2, nano-functional dispersion;

[0022] S3, hot melt dynamic mixing;

[0023] S4, gradient UV cross-linking;

[0024] S5. Functional post-processing.

[0025] Preferably, step S1 is specifically as follows:

[0026] Put 60-80 parts of polyvinyl chloride resin and 15-25 parts of methyl methacrylate-styrene copolymer into a high-speed mixer, and add 8-12 parts of diisononyl phthalate, 3-7 parts of epoxy soybean oil and 10-18 parts of liquid nitrile rubber in sequence. Control the mixing temperature to 80-95°C and the speed to 400-600 rpm. Continue stirring for 15-25 minutes to allow the resin segments to fully swell.

[0027] Step S2 is specifically as follows:

[0028] Add 0.5-2 parts of nano zinc oxide, 1.2-2.5 parts of hydroxy silicone oil dispersant and 0.5-1.5 parts of sodium dodecylbenzene sulfonate into an ultrasonic disperser, and process for 30-50 minutes at a power of 200-300W and a frequency of 40kHz to obtain a uniformly dispersed nano slurry.

[0029] Preferably, step S3 is specifically as follows:

[0030] The S1 premix, S2 nano-slurry, 2-4 parts of alkyl mercaptan crosslinking agent, 4-8 parts of triphenyl phosphate flame retardant, and 0.3-1.2 parts of polytetrafluoroethylene powder were added to a twin-screw extruder. The melt temperature was controlled at 165-175°C and the screw speed was 120-160 rpm. After melt blending, the substrate was extruded into a strip with a thickness of 0.5-1.2 mm.

[0031] Step S4 is specifically as follows:

[0032] The strip substrate was passed through a UV irradiation device and cross-linked in two stages in a nitrogen atmosphere:

[0033] The first stage uses a main wavelength of 365nm and an irradiation intensity of 0.05-0.12J / cm 2 LED light source, action time 30-60s;

[0034] The second stage switches to the main wavelength of 285nm and the irradiation intensity of 0.15-0.25J / cm 2 Excimer light source, action time 15-30s;

[0035] Step S5 is specifically as follows:

[0036] The cross-linked material is immersed in an ethanol solution containing 0.8-1.6 parts of a thiodipropionate light stabilizer and 0.7-1.8 parts of a benzotriazole ultraviolet absorber, ultrasonically immersed at 50-60° C. for 10-20 minutes, and then hot-air dried at 50-70° C. to a moisture content of ≤0.3%.

[0037] Technical effects and advantages of the present invention:

[0038] The nano zinc oxide introduced in this material is composed of rod-shaped particles with a particle size of 30-50nm and spherical particles with a mass ratio of 1:2-3. Its unique geometric heterogeneity forms a multiple scattering effect in the ultraviolet light field. The rod-shaped particles enhance the reflection path length of ultraviolet light in the 365nm band through longitudinal arrangement, while the spherical particles produce a local field enhancement effect in the 285nm band through surface plasmon resonance, which prolongs the excited state lifetime of the benzophenone derivative photoinitiator. At the same time, the hydroxyl groups on the surface of the nano zinc oxide coordinate with the siloxane bonds in the hydroxy silicone oil dispersant to form a stable core-shell structure, which effectively inhibits particle agglomeration. This synergistic effect makes the photoinitiator at 0.05-0.12J / cm 2 Achieve ideal cross-linking conversion rate at low irradiation intensity and avoid yellowing of materials caused by high-dose irradiation;

[0039] Epoxidized soybean oil and liquid nitrile rubber form a dynamic reversible plasticizing system through polar interactions. The epoxy groups in the epoxidized soybean oil form a dipole-dipole interaction with the Cl atoms in the PVC molecular chain, while the cyano groups in the nitrile rubber and the ester groups in the methyl methacrylate-styrene copolymer produce π-π stacking, constructing a temporary physical network of three-dimensional crosslinking points. During the thermal aging process, this network releases internal stress through bond reconstruction, thereby improving the material's elongation at break retention rate.

[0040] Dioctadecyl / dodecylthiodipropionate and benzotriazole UV absorbers form a gradient light stabilization system. The outer layer of thiodipropionate preferentially captures high-energy UV photons by breaking the thioether bond to generate stable thiol free radical intermediates; the inner layer of benzotriazole dissipates the 350-400nm light energy through the intramolecular proton transfer mechanism and forms a charge transfer complex with the PVC molecular chain through the conjugation effect.

[0041] Triphenyl phosphate and polytetrafluoroethylene powder are melt-blended to form a "physical-chemical" dual-mode flame retardant system. The polytetrafluoroethylene powder expands into a flaky barrier layer under high shear, synergistically inhibiting the combustion chain reaction with the PO free radicals generated by the decomposition of triphenyl phosphate. At the same time, the strong hydrophobicity of the fluorocarbon chain reduces the material's moisture absorption rate, and the interfacial polarization inhibition effect of the hydroxyl silicone oil dispersant stabilizes the dielectric loss tangent. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the embodiments described are only a part of the embodiments of the present invention, not all of the embodiments. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0043] This invention proposes a UV-crosslinked transparent polyvinyl chloride material for medium-voltage insulation layers and its preparation method. Through the synergistic effect of multiple components and process coupling, it achieves a breakthrough improvement in insulation performance, optical properties, and environmental stability. Based on the photoinitiation synergistic mechanism of the nano-zinc oxide heterostructure, it achieves a high crosslinking density at a low radiation dose, resolving the contradiction between photoinitiation efficiency and transparency in traditional processes.

[0044] The design of a dynamic plasticizing network of epoxy soybean oil and nitrile rubber gives the material excellent heat aging resistance and stable dielectric response. The construction of a gradient light stabilization system extends the UV aging life and meets the requirements of harsh outdoor working conditions.

[0045] The composite flame retardant system innovatively integrates gas phase and condensed phase flame retardant pathways, solving the industry problem of flame retardant addition and dielectric property degradation. The coordinated optimization of various performance indicators enables the comprehensive performance of this material to far exceed the current medium-voltage insulation material standards. It is particularly suitable for cutting-edge fields such as high-voltage cable insulation layers that require light transmission monitoring in smart grids and insulation modules for new energy charging piles, promoting the upgrade of power equipment towards efficiency and visualization.

[0046] The UV-crosslinked transparent polyvinyl chloride material for medium-voltage insulation layer is composed of the following components:

[0047] Polyvinyl chloride resin, methyl methacrylate-styrene copolymer, diisononyl phthalate, epoxy soybean oil, liquid nitrile rubber, nano zinc oxide, benzophenone derivative photoinitiator, thiodipropionate light stabilizer, alkyl mercaptan crosslinking aid, triphenyl phosphate flame retardant, polytetrafluoroethylene powder, hydroxy silicone oil dispersant, sodium dodecylbenzenesulfonate, benzotriazole UV absorber.

[0048] Among them, the polyvinyl chloride resin uses a suspension resin with a polymerization degree of 1300-1500. When it works synergistically with methyl methacrylate-styrene copolymer, the polar interaction of the molecular chain segments makes the three-dimensional network crosslinking degree of the material improved under ultraviolet light irradiation; nano zinc oxide is composed of rod-shaped particles with a particle size of 30-50nm and spherical particles with a particle size of 80-100nm in a mass ratio of 1:2-3. When the total mass portion is 1.0-1.8 parts, it can reach 0.02-0.08J / cm 2 The activity of the photoinitiator is increased under the intensity of ultraviolet light;

[0049] It should be noted that the thiodipropionate light stabilizer is a compound of dioctadecyl thiodipropionate and didodecyl thiodipropionate in a mass ratio of 1:1-1.5, which produces a gradient absorption effect with the benzotriazole ultraviolet absorber, thereby reducing the deviation of the light transmittance control of the material in the 310-400nm band. The alkyl mercaptan crosslinking aid is a combination of dodecyl mercaptan and isooctyl mercaptopropionate in a mass ratio of 2:1-3:1, with a total mass ratio of 2.5-3.5 parts. Through a bidirectional grafting reaction with the end groups of the polyvinyl chloride molecular chain, the volume resistivity at a field strength of 20kV / mm is increased by 3-5 orders of magnitude.

[0050] The particle size of the polytetrafluoroethylene powder is distributed in the range of 1-5 μm and the specific surface area is 8-12 m 2 / g;

[0051] The hydroxyl content of the hydroxyl silicone oil dispersant is 3.5-4.2 wt% and the viscosity is 500-800 cps.

[0052] In addition, the mass fraction of each component complies with the following interaction formula:

[0053] 0.8×Qpvc+1.2×(Qmbs+Qdinp)-0.6×(Qptfe+Qbzt)=75±25;

[0054] Wherein, Qpvc represents the mass parts of polyvinyl chloride resin, Qmbs represents the mass parts of methyl methacrylate-styrene copolymer, Qdinp represents the mass parts of diisononyl phthalate, Qptfe represents the mass parts of polytetrafluoroethylene powder, and Qbzt represents the mass parts of benzotriazole ultraviolet absorber.

[0055] Based on the above, the preparation method of the UV-crosslinked transparent polyvinyl chloride material for medium voltage insulation layer includes the following steps:

[0056] S1, premixing modification treatment; Step S1 is specifically:

[0057] Put 60-80 parts of polyvinyl chloride resin and 15-25 parts of methyl methacrylate-styrene copolymer into a high-speed mixer, and add 8-12 parts of diisononyl phthalate, 3-7 parts of epoxy soybean oil and 10-18 parts of liquid nitrile rubber in sequence. Control the mixing temperature to 80-95°C and the rotation speed to 400-600 rpm. Continue stirring for 15-25 minutes to allow the resin segments to fully swell.

[0058] S2, nano-functional dispersion; Step S2 is specifically as follows:

[0059] Add 0.5-2 parts of nano zinc oxide, 1.2-2.5 parts of hydroxy silicone oil dispersant and 0.5-1.5 parts of sodium dodecylbenzene sulfonate into an ultrasonic disperser, and process for 30-50 minutes at a power of 200-300W and a frequency of 40kHz to obtain a uniformly dispersed nano slurry.

[0060] S3, hot melt dynamic mixing; step S3 is specifically:

[0061] The S1 premix, S2 nano-slurry, 2-4 parts of alkyl mercaptan crosslinking aid, 4-8 parts of triphenyl phosphate flame retardant, and 0.3-1.2 parts of polytetrafluoroethylene powder are added to a twin-screw extruder. The melt temperature is controlled at 165-175°C and the screw speed is 120-160 rpm. After melt blending, the substrate is extruded into a strip with a thickness of 0.5-1.2 mm.

[0062] S4, gradient UV cross-linking; step S4 is specifically:

[0063] The strip substrate was passed through a UV irradiation device and cross-linked in two stages in a nitrogen atmosphere:

[0064] The first stage uses a main wavelength of 365nm and an irradiation intensity of 0.05-0.12J / cm 2 LED light source, action time 30-60s;

[0065] The second stage switches to the main wavelength of 285nm and the irradiation intensity of 0.15-0.25J / cm 2 Excimer light source, action time 15-30s.

[0066] S5, functional post-processing, step S5 is specifically as follows:

[0067] The cross-linked material is immersed in an ethanol solution containing 0.8-1.6 parts of a thiodipropionate light stabilizer and 0.7-1.8 parts of a benzotriazole ultraviolet absorber, ultrasonically immersed at 50-60° C. for 10-20 minutes, and then hot-air dried at 50-70° C. to a moisture content of ≤0.3%.

[0068] Based on the above, this embodiment provides the following specific examples:

[0069] Example 1

[0070] Component ratio: 58 parts of polyvinyl chloride resin, 32 parts of methyl methacrylate-styrene copolymer, 9 parts of diisononyl phthalate, 9 parts of epoxy soybean oil, 14 parts of liquid butyronitrile, 1.2 parts of nano zinc oxide (rod: sphere = 1:2.5), 2.3 parts of benzophenone derivatives, 1.1 parts of thiodipropionate, 3.0 parts of alkyl mercaptan (dodecyl mercaptan: isooctyl mercaptopropionate = 2.3:1), 6 parts of triphenyl phosphate, 0.8 part of polytetrafluoroethylene powder (D50 = 3μm), 1.8 parts of hydroxy silicone oil (4.0wt%), 0.9 part of sodium dodecylbenzenesulfonate, and 1.3 parts of benzotriazole.

[0071] Preparation parameters: S1 premixing temperature 88℃ / 450rpm×20min; S2 ultrasonic dispersion 260W×40min; S3 extrusion temperature 170℃ / 140rpm; S4 first stage 0.08J / cm 2 ×50s, second stage 0.20J / cm 2 ×25s.

[0072] Example 2

[0073] Component ratio: 105 parts of polyvinyl chloride resin, 18 parts of methyl methacrylate-styrene copolymer, 11 parts of diisononyl phthalate, 12 parts of epoxy soybean oil, 16 parts of liquid butyronitrile, 1.7 parts of nano zinc oxide (rod: sphere = 1:3), 2.8 parts of benzophenone derivatives, 1.4 parts of thiodipropionate (dioctadecyl: didodecyl = 1:1.2), 3.4 parts of alkyl mercaptan (ratio 3:1), 7 parts of triphenyl phosphate, 3.5 parts of polytetrafluoroethylene powder (D50 = 5μm), 2.2 parts of hydroxy silicone oil (3.8wt%), 1.3 parts of sodium dodecylbenzenesulfonate, and 1.1 parts of benzotriazole.

[0074] Preparation parameters: S1 premixing temperature 92℃ / 550rpm×18min; S2 ultrasonic power 300W×35min; S3 extrusion temperature 172℃ / 150rpm; S4 first stage 0.12J / cm 2 ×35s, second stage 0.22J / cm 2 ×28s.

[0075] Example 3

[0076] Component ratio: 82 parts of polyvinyl chloride resin, 39 parts of methyl methacrylate-styrene copolymer, 10 parts of diisononyl phthalate, 7 parts of epoxy soybean oil, 11 parts of liquid butyronitrile, 1.5 parts of nano zinc oxide (rod: sphere = 1:2), 1.8 parts of benzophenone derivative, 1.6 parts of thiodipropionate (ratio 1:1.4), 2.7 parts of alkyl mercaptan (ratio 2.5:1), 5 parts of triphenyl phosphate, 1.2 parts of polytetrafluoroethylene powder (D50 = 2μm), 2.0 parts of hydroxy silicone oil (4.1wt%), 0.7 parts of sodium dodecylbenzenesulfonate, and 1.6 parts of benzotriazole.

[0077] Preparation parameters: S1 premixing temperature 85℃ / 500rpm×22min; S2 processing parameters 250W / 45kHz×45min; S3 melt temperature 168℃ / 130rpm; S4 two-stage irradiation parameters are 0.07J / cm 2 ×55s and 0.18J / cm 2 ×30s.

[0078] The specific performance data of the three groups of embodiments of the present invention are as follows:

[0079] Performance indicators Example 1 Example 2 Example 3 Crosslinking degree (%) 94.5 (UV method) 88.7 92.1 Volume resistivity (Ω·m) <![CDATA[6.5×10 14 ]]> <![CDATA[1.2×10 13 ]]> <![CDATA[3.8×10 14 ]]> Transmittance (380nm,%) 89.7 82.3 91.5 Flame retardant grade V-1 V-0 V-1 Tensile strength (MPa) 38.6 45.2 41.8 Yellowing index (ΔYI) 0.8(QUV 500h) 1.5 0.6

[0080] According to the above table, Example 1 improves the photoinitiation efficiency in the 365nm band while maintaining high transmittance by precisely controlling the nano-zinc oxide compounding ratio (1:2.5) and the UV cross-linking gradient parameters;

[0081] Example 2 uses a higher polytetrafluoroethylene addition amount (3.5 parts) and a specific screw speed combination to improve the flame retardancy of the material to V-0 level, but leads to a relative decrease in the effective concentration of the UV absorber;

[0082] In Example 3, a wide-spectrum UV protection network was constructed in the thiodipropionate composite system (1:1.4), so that the main UV absorption wavelength and the crosslinking wavelength formed a band interval of 12 nm, and the yellowing index was improved.

[0083] In addition, when the Qpvc / Qmbs ratio is greater than 2.5 (as in Example 2), the material exhibits significantly enhanced mechanical properties but sacrifices flexibility; the optimal overall performance is achieved when the ratio is between 1.6 and 2.0 (Example 3);

[0084] When the thiodipropionate compound ratio is 1:1.2-1.5 (Examples 1 and 3), a synergistic protective effect with the ultraviolet absorber can be produced, reducing the transmittance fluctuation of the material in the 380-420nm wavelength range to ±1.3%;

[0085] When the interaction formula parameters deviate from the optimal value by about +20% (such as the calculated value of 96.4 in Example 2), the probability of interfacial phase separation increases, which is manifested as a decrease in volume resistivity by about one order of magnitude.

[0086] In summary, the nano-zinc oxide introduced in this material is composed of rod-shaped particles with a particle size of 30-50nm and spherical particles with a particle size of 80-100nm in a mass ratio of 1:2-3. Its unique geometric heterogeneity forms a multiple scattering effect in the ultraviolet light field. The rod-shaped particles enhance the reflection path length of ultraviolet light in the 365nm band through longitudinal arrangement, while the spherical particles produce a local field enhancement effect in the 285nm band through surface plasmon resonance, thereby extending the excited state lifetime of the benzophenone derivative photoinitiator. At the same time, the hydroxyl groups on the surface of the nano-zinc oxide coordinate with the siloxane bonds in the hydroxy silicone oil dispersant to form a stable core-shell structure, which effectively inhibits particle agglomeration. This synergistic effect enables the photoinitiator to achieve a high optical density of 0.05-0.12J / cm 2 Achieve ideal cross-linking conversion rate at low irradiation intensity and avoid yellowing of materials caused by high-dose irradiation;

[0087] Epoxidized soybean oil and liquid nitrile rubber form a dynamic reversible plasticizing system through polar interactions. The epoxy groups in the epoxidized soybean oil form a dipole-dipole interaction with the Cl atoms in the PVC molecular chain, while the cyano groups in the nitrile rubber and the ester groups in the methyl methacrylate-styrene copolymer produce π-π stacking, constructing a temporary physical network of three-dimensional crosslinking points. During the thermal aging process, this network releases internal stress through bond reconstruction, thereby improving the material's elongation at break retention rate.

[0088] Dioctadecyl / dodecylthiodipropionate and benzotriazole UV absorbers form a gradient light stabilization system. The outer layer of thiodipropionate preferentially captures high-energy UV photons by breaking the thioether bond to generate stable thiol free radical intermediates; the inner layer of benzotriazole dissipates the 350-400nm light energy through the intramolecular proton transfer mechanism and forms a charge transfer complex with the PVC molecular chain through the conjugation effect.

[0089] Triphenyl phosphate and polytetrafluoroethylene powder are melt-blended to form a "physical-chemical" dual-mode flame retardant system. The polytetrafluoroethylene powder expands into a flaky barrier layer under high shear, synergistically inhibiting the combustion chain reaction with the PO free radicals generated by the decomposition of triphenyl phosphate. At the same time, the strong hydrophobicity of the fluorocarbon chain reduces the material's moisture absorption rate, and the interfacial polarization inhibition effect of the hydroxyl silicone oil dispersant stabilizes the dielectric loss tangent.

[0090] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A UV-crosslinked transparent polyvinyl chloride material for medium-voltage insulation layer, characterized by: The UV-crosslinked transparent polyvinyl chloride material for medium-voltage insulation layer is composed of the following components in parts by mass: 40-120 parts of polyvinyl chloride resin, 5-45 parts of methyl methacrylate-styrene copolymer, 8-12 parts of diisononyl phthalate, 3-15 parts of epoxy soybean oil, 10-18 parts of liquid nitrile rubber, 0.5-2 parts of nano zinc oxide, 1.5-3 parts of benzophenone derivative photoinitiator, 0.8-1.6 parts of thiodipropionate light stabilizer, 2-4 parts of alkyl mercaptan crosslinking aid, 4-8 parts of triphenyl phosphate flame retardant, 0.3-4.2 parts of polytetrafluoroethylene powder, 1.2-2.5 parts of hydroxy silicone oil dispersant, 0.5-1.5 parts of sodium dodecylbenzenesulfonate, and 0.7-1.8 parts of benzotriazole ultraviolet absorber.

2. The UV-crosslinked transparent polyvinyl chloride material for medium voltage insulation layer according to claim 1, characterized in that: The polyvinyl chloride resin is a suspension resin with a polymerization degree of 1300-1500. When it works synergistically with the methyl methacrylate-styrene copolymer, the polar interaction of the molecular chain segments increases the three-dimensional network crosslinking degree of the material under ultraviolet light irradiation.

3. The UV-crosslinked transparent polyvinyl chloride material for medium voltage insulation layer according to claim 1, characterized in that: The nano zinc oxide is composed of rod-shaped particles with a particle size of 30-50 nm and spherical particles with a particle size of 80-100 nm in a mass ratio of 1:2-3. When the total mass portion is 1.0-1.8 parts, the nano zinc oxide can be used at 0.02-0.08 J / cm 2 The activity of the photoinitiator is increased under the intensity of ultraviolet light.

4. The UV-crosslinked transparent polyvinyl chloride material for medium voltage insulation layer according to claim 1, characterized in that: The thiodipropionate light stabilizer is compounded by dioctadecyl thiodipropionate and didodecyl thiodipropionate in a mass ratio of 1:1-1.5, and produces a gradient absorption effect with the benzotriazole ultraviolet absorber, thereby reducing the light transmittance control deviation of the material in the 310-400nm band.

5. The UV-crosslinked transparent polyvinyl chloride material for medium voltage insulation layer according to claim 1, characterized in that: The alkyl mercaptan crosslinking agent is a combination of dodecyl mercaptan and isooctyl mercaptopropionate in a mass ratio of 2:1-3:1, with a total mass of 2.5-3.5 parts. Through a bidirectional grafting reaction with the end groups of the polyvinyl chloride molecular chain, the volume resistivity at a field strength of 20 kV / mm is increased by 3-5 orders of magnitude; The particle size of the polytetrafluoroethylene powder is distributed in the range of 1-5 μm and the specific surface area is 8-12 m 2 / g; The hydroxyl content of the hydroxyl silicone oil dispersant is 3.5-4.2 wt% and the viscosity is 500-800 cps.

6. The UV-crosslinked transparent polyvinyl chloride material for medium voltage insulation layer according to claim 1, characterized in that: The mass fraction of each component complies with the following interaction formula: 0.8×Qpvc+1.2×(Qmbs+Qdinp)-0.6×(Qptfe+Qbzt)=75±25; Wherein, Qpvc represents the mass parts of polyvinyl chloride resin, Qmbs represents the mass parts of methyl methacrylate-styrene copolymer, Qdinp represents the mass parts of diisononyl phthalate, Qptfe represents the mass parts of polytetrafluoroethylene powder, and Qbzt represents the mass parts of benzotriazole ultraviolet absorber.

7. A method for preparing the UV-crosslinked transparent polyvinyl chloride material for medium voltage insulation layer according to claim 1, characterized in that: The following steps are involved: S1, premix modification treatment; S2, nano-functional dispersion; S3, hot melt dynamic mixing; S4, gradient UV cross-linking; S5. Functional post-processing.

8. The method for preparing a UV-crosslinked transparent polyvinyl chloride material for medium voltage insulation layer according to claim 7, characterized in that: Step S1 is specifically as follows: Put 60-80 parts of polyvinyl chloride resin and 15-25 parts of methyl methacrylate-styrene copolymer into a high-speed mixer, and add 8-12 parts of diisononyl phthalate, 3-7 parts of epoxy soybean oil and 10-18 parts of liquid nitrile rubber in sequence. Control the mixing temperature to 80-95°C and the speed to 400-600 rpm. Continue stirring for 15-25 minutes to allow the resin segments to fully swell. Step S2 is specifically as follows: Add 0.5-2 parts of nano zinc oxide, 1.2-2.5 parts of hydroxy silicone oil dispersant and 0.5-1.5 parts of sodium dodecylbenzene sulfonate into an ultrasonic disperser, and process for 30-50 minutes at a power of 200-300W and a frequency of 40kHz to obtain a uniformly dispersed nano slurry.

9. The method for preparing a UV-crosslinked transparent polyvinyl chloride material for medium voltage insulation layer according to claim 7, characterized in that: Step S3 is specifically as follows: The S1 premix, S2 nano-slurry, 2-4 parts of alkyl mercaptan crosslinking agent, 4-8 parts of triphenyl phosphate flame retardant, and 0.3-1.2 parts of polytetrafluoroethylene powder were added to a twin-screw extruder. The melt temperature was controlled at 165-175°C and the screw speed was 120-160 rpm. After melt blending, the substrate was extruded into a strip with a thickness of 0.5-1.2 mm. Step S4 is specifically as follows: The strip substrate was passed through a UV irradiation device and cross-linked in two stages in a nitrogen atmosphere: The first stage uses a main wavelength of 365nm and an irradiation intensity of 0.05-0.12J / cm 2 LED light source, action time 30-60s; The second stage switches to the main wavelength of 285nm and the irradiation intensity of 0.15-0.25J / cm 2 Excimer light source, action time 15-30s; Step S5 is specifically as follows: The cross-linked material is immersed in an ethanol solution containing 0.8-1.6 parts of a thiodipropionate light stabilizer and 0.7-1.8 parts of a benzotriazole ultraviolet absorber, ultrasonically immersed at 50-60° C. for 10-20 minutes, and then hot-air dried at 50-70° C. to a moisture content of ≤0.3%.