Silane self-crosslinking polyethylene overhead insulation material for cable and preparation method

Abstract

The invention discloses a silane self-crosslinking polyethylene overhead insulation material for a cable and a preparation method. The insulating material comprises a polyethylene base material, a silane coupling agent, a catalyst, an antioxidant, a nanoscale reinforcing filler, a core-shell structure filler and nano montmorillonite. The polyethylene base material is a blend of polyethylene with different densities and can give consideration to rigidity and toughness; the nanoscale reinforcing filler is nano calcium carbonate modified by silane; the core-shell structure filler takes nano calcium carbonate as a core and an ethylene-octylene copolymer as a shell, so that the processing fluidity can be improved, and the filler agglomeration can be avoided; the nano montmorillonite can improve the aging resistance and the electrical insulation strength. The preparation method comprises the steps of nano filler pretreatment, nano montmorillonite modification, polyethylene base material blending, component mixing, crosslinking and post-treatment, through the pretreatment, modification, optimized mixing and crosslinking processes, it is ensured that all components are evenly dispersed, compatibility is improved, and the processing performance, the mechanical performance and the electrical performance of a finished product are balanced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of cable applications, in particular to a silane self-crosslinking polyethylene overhead insulation material for cables and a preparation method thereof. BACKGROUND

[0002] With the increase of power transmission capacity and the complexity of operating environment, higher requirements are put forward for the comprehensive performance of overhead cable insulation materials, which not only need to have excellent electrical insulation strength and aging resistance, but also need to have sufficient mechanical strength and processing adaptability. At present, silane self-crosslinking polyethylene has become one of the main materials for overhead cable insulation layers due to its processing characteristics and performance advantages of crosslinking network, but how to further improve its mechanical properties, environmental adaptability and production efficiency is still a key problem to be solved in the industry.

[0003] Commonly, silane self-crosslinking polyethylene insulation material uses single density polyethylene as the base material, which is difficult to meet the balance requirement of rigidity and toughness at the same time; the filler system usually directly adds unmodified inorganic particles, which is easy to cause stress concentration in the material due to agglomeration, and the mechanical properties fluctuate greatly; the layered structure material such as nano-montmorillonite is difficult to disperse in the polyethylene base material due to the lack of organic modification, and it is difficult to form an effective barrier network, which restricts the improvement of aging resistance. In addition, in the traditional preparation process, the steps of filler pretreatment, base material blending and crosslinking reaction are relatively independent, and there is a lack of synergistic control of multi-field coupling, which leads to uneven dispersion of components, inconsistent crosslinking density, and finally affects the performance stability of the material and the industrial production efficiency, which cannot meet the working requirements of cable applications. Therefore, a silane self-crosslinking polyethylene overhead insulation material for cables and a preparation method thereof are proposed. SUMMARY

[0004] The present application provides the following technical scheme: a silane self-crosslinking polyethylene overhead insulation material for cables, comprising:

[0005] 70-90 parts of polyethylene base material, 1.5-3 parts of silane coupling agent, 0.3-0.8 parts of catalyst, 0.6-1.6 parts of antioxidant, 1-5 parts of nano-scale reinforcing filler, 5-10 parts of core-shell structure filler and 2-4 parts of nano-montmorillonite; the polyethylene base material is a blend of polyethylenes with different densities, and the blend of polyethylenes with different densities can balance the rigidity and toughness of the material, meeting the demand of the overhead cable for the comprehensive mechanical properties of the base material, and the weight ratio of the blend of polyethylenes with different densities inside the polyethylene base material is 3:1-5:1;

[0006] The nanoscale reinforcing filler is silane-modified nanometer calcium carbonate, which can be closely combined with the base material through interfacial action, significantly improving the mechanical strength and impact resistance of the insulating material, the particle size of the nanometer calcium carbonate is 50-100 nm, the core-shell structure filler takes nanometer calcium carbonate as the core and ethylene-octene copolymer as the shell, the particle size of the core-shell structure filler is 100-200 nm, the core-shell structure filler can not only utilize the rigid reinforcing effect of the inorganic core, but also improve the processing fluidity of the material through the flexibility of the organic shell, avoiding the performance fluctuation problem caused by the easy agglomeration of the traditional filler; the particle size of the core-shell structure filler is 100-200 nm; the nanometer montmorillonite can be uniformly dispersed in the base material and form a barrier network, effectively improving the aging resistance and electrical insulation strength of the material, and the synergistic effect of multiple components makes the insulating material have excellent insulation performance and more comprehensive mechanical properties.

[0007] The application provides a preparation method of a silane self-crosslinking polyethylene overhead insulating material for cables.

[0008] S1 nanofiller pretreatment:

[0009] First, the nanometer calcium carbonate with a particle size of 50-100 nm is mixed with vinyltrimethoxysilane at a mass ratio of 10:1-8:1, then stirred at 60-80 DEG C for 2-4 hours to obtain silane-modified nanometer calcium carbonate, and finally the obtained nanometer calcium carbonate is mixed with ethylene-octene copolymer at a mass ratio of 1:0.5-1:2, and then melt blended through a double screw extruder at 150-170 DEG C, extruded and granulated to obtain a core-shell structure filler, the pretreatment of the nanofiller and the construction of the core-shell structure ensure the compatibility of the filler and the base material, and avoid the problem of uneven dispersion caused by direct addition;

[0010] S2 nanometer montmorillonite modification:

[0011] The nanometer montmorillonite and the alkyl quaternary ammonium salt are added to deionized water at a mass ratio of 10:1-8:1, stirred at 70-90 DEG C for 3-5 hours, filtered and dried to obtain organically modified nanometer montmorillonite, and the alkyl quaternary ammonium salt is added in an amount of 10-20% of the weight of the nanometer montmorillonite, the organic modification of the nanometer montmorillonite improves its dispersibility in the organic base material and enhances the structural stability of the material;

[0012] S3 polyethylene base blending:

[0013] Different density polyethylene is mixed at a weight ratio of 4:1-5:1, and then dispersed by a mixer at 1000-1500 rpm for 5-10 minutes to obtain a polyethylene base, and the pre-blending of the polyethylene base ensures the uniformity of the base material performance;

[0014] S4 component mixing:

[0015] Firstly, dry mixing is carried out: the core-shell filler, nano-montmorillonite, silane coupling agent, catalyst, antioxidant are added to the polyethylene base material, and mixed by a mixer at 800-1200 rpm for 8-12 minutes;

[0016] Then, melt blending is carried out: the mixture obtained by dry mixing is added to a twin-screw extruder, the melt section temperature is set to 175-185°C, the screw rotation speed is set to 250-300 rpm, and ultrasonic treatment is applied at a frequency of 20-40 kHz and a power density of 0.8-1.5 W / cm², and the mixture is extruded and granulated. The combination of dry mixing and melt blending, together with ultrasonic treatment, allows the components to be fully contacted and uniformly dispersed, reducing interfacial defects.

[0017] S5 crosslinking and post-treatment:

[0018] The blended granules obtained in step S4 are crosslinked in warm water at 85-90°C for 4-6 hours, and then heat-treated at 100-110°C for 2-4 hours. After drying, the finished product is obtained. The crosslinking and post-treatment steps ensure that the crosslinking reaction is fully and uniformly carried out by precisely controlling the reaction conditions, reducing stress concentration in the material, and ultimately balancing the processing performance, mechanical properties, and electrical properties of the finished product. At the same time, the production process is simplified, which is conducive to industrial application.

[0019] Preferably, the silane coupling agent is a complex of vinyltrimethoxysilane and γ-aminopropyltriethoxysilane, with a weight ratio of 2:1-3:1, and the catalyst is a complex of dibutyltin dilaurate and an organic zinc compound, with a weight ratio of 3:1-4:1. The organic zinc compound is zinc stearate. The use of a complex of vinyltrimethoxysilane and γ-aminopropyltriethoxysilane, combined with the synergistic catalysis of dibutyltin dilaurate and an organic zinc compound, not only improves the grafting efficiency of silane and polyethylene, but also optimizes the crosslinking reaction path through multi-catalytic action, allowing the material to achieve more uniform crosslinking network construction while reducing the amount of catalyst used.

[0020] Preferably, the antioxidant is a complex of hindered phenolic antioxidant and phosphite antioxidant, with a weight ratio of 1:1-1:2. The hindered phenolic antioxidant is tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester, and the phosphite antioxidant is tris(2,4-di-tert-butylphenyl)phosphite. The complex of hindered phenolic antioxidant and phosphite antioxidant has a synergistic effect through multiple antioxidant mechanisms, effectively capturing free radicals and decomposing hydroperoxides, significantly delaying the aging process of the material in high-temperature or oxidative environments, and prolonging the service life of the cable insulation layer.

[0021] Preferably, the weight ratio of the nano calcium carbonate core and the ethylene-octene copolymer shell is 1:0.5-1:2, the nano montmorillonite is an organically modified nano montmorillonite, the modifier of the nano montmorillonite is an alkyl quaternary ammonium salt, and the alkyl quaternary ammonium salt is added in an amount of 10-20% of the weight of the nano montmorillonite. The ratio of the inorganic core and the organic shell in the core-shell structure filler is adjusted, and the organically modified nano montmorillonite is used, which not only retains the reinforcing effect of the inorganic filler, but also improves the dispersibility and compatibility of the filler in the base material through the layered structure of the elastomer shell layer and the organic montmorillonite, reduces stress concentration, and improves the overall mechanical properties of the material.

[0022] Preferably, in the step S1, the silane modification of the nano calcium carbonate adopts a two-stage surface treatment process: first, the nano calcium carbonate is pre-mixed with vinyltrimethoxysilane at 60°C, and then gradually heated to 80°C. The core-shell structure filler is prepared by using a dynamic vulcanization technology, that is, in the melt blending section of the twin-screw extruder, the screw configuration is adjusted to be a strong shearing element, so that the ethylene-octene copolymer forms a continuous coating layer on the surface of the nano calcium carbonate. Through the segmented temperature control silane modification process combined with the strong shearing action in the dynamic vulcanization technology, it is ensured that the silane molecules uniformly coat the surface of the nano calcium carbonate, and the elastomer shell layer forms a continuous coating structure, avoiding the problem of filler agglomeration in traditional processes, and improving the interfacial bonding strength between the filler and the base material.

[0023] Preferably, in the step S2, the organic modification of the nano montmorillonite adopts a stepwise intercalation method, that is, first, the nano montmorillonite and the alkyl quaternary ammonium salt are formed into a suspension in deionized water, and then treated by an ultrasonic cell disruptor at a frequency of 40-60 kHz for 30-40 minutes to make the quaternary ammonium salt molecules intercalate into the montmorillonite layers. Subsequently, the temperature is raised to 90°C and stirring is continued to allow the quaternary ammonium salt cations to undergo ion exchange reaction with the montmorillonite layers, and finally, the organic montmorillonite with an expanded interlayer spacing of more than 1.8 nm is obtained. The stepwise intercalation process assisted by ultrasonic waves first promotes the intercalation of quaternary ammonium salt molecules into the montmorillonite layers through high-frequency vibration, and then expands the interlayer spacing through ion exchange reaction, so that the modified montmorillonite forms a stable intercalation structure in the polyethylene base material, thereby enhancing the barrier properties and thermal stability of the material.

[0024] Preferably, in the step S3, the blending of the polyethylene base material adopts a multi-stage mixing process, that is, different densities of polyethylene are first melt blended in a ratio of 4:1, and then added through the main feeding port of the twin-screw extruder. Subsequently, 5%-8% of maleic anhydride grafted polyethylene is added as a compatibilizer through the side feeding port. The different densities of polyethylene are melt blended through the main feeding port, and the compatibilizer is added through the side feeding port, which not only ensures the uniformity of the base material, but also improves the interfacial bonding of different densities of polyethylene through the in-situ compatibilization of the compatibilizer, thereby improving the overall mechanical properties of the material.

[0025] Preferably, in the step S4, the dry mixing adopts a gradient feeding sequence, that is, the core-shell structure filler is first premixed with the nanometer montmorillonite at a ratio of 3:1, then the silane coupling agent is added for surface modification, and finally the catalyst and antioxidant are added, and at the same time, the high-speed mixer is used to form a hierarchical dispersion structure of each component in the polyethylene substrate.

[0026] Preferably, in the step S5, the warm water crosslinking adopts a dynamic crosslinking process: the blended granules are placed in a warm water tank with stirring device, and mechanical stress is continuously applied during the crosslinking process, so that the granules form an oriented structure in the early stage of crosslinking, and the orientation degree of the material after crosslinking is characterized by two-dimensional X-ray diffraction. The oriented structure is formed in the early stage of crosslinking by mechanical stress induction, and the internal stress is eliminated by subsequent heat treatment, which not only improves the crystallinity and electrical properties of the material, but also simplifies the production process through the dynamic crosslinking process, achieving a balance between high performance and high efficiency.

[0027] In summary, compared with the prior art, the present application provides a silane self-crosslinking polyethylene overhead insulation material for cables and a preparation method, which has the following beneficial effects:

[0028] 1、The present application can balance the rigidity and toughness of the material by blending the base material of different density polyethylene, and the nanoscale reinforcing filler modified by silane can be closely combined with the base material through interfacial action, significantly improving the mechanical strength and impact resistance of the insulation material. The core-shell structure filler takes nanometer calcium carbonate as the core and ethylene-octene copolymer as the shell, which can not only utilize the rigid reinforcing effect of the inorganic core, but also improve the processing fluidity of the material through the flexibility of the organic shell, avoiding the performance fluctuation problem caused by the easy agglomeration of traditional fillers. After the organic modification of nanometer montmorillonite, it can be uniformly dispersed in the base material and form a barrier network, effectively improving the aging resistance and electrical insulation strength of the material, and the synergistic effect of multiple components makes the insulation material have more comprehensive mechanical properties while maintaining excellent insulation performance, meeting the use requirements of overhead cables in complex environments.

[0029] 2、The application ensures the compatibility of the filler and the base material through the pretreatment and core-shell structure construction of the nano filler, avoids the uneven dispersion problem caused by direct addition; the organic modification of the nano montmorillonite improves its dispersibility in the organic base material and enhances the structural stability of the material. The pre-blending of the polyethylene base material ensures the uniformity of the base material performance, the combination of dry mixing and melt blending, together with ultrasonic treatment, can make the components fully contact and uniformly disperse, reduce the interface defects. The crosslinking and post-processing steps ensure sufficient and uniform crosslinking reaction by precise control of the reaction conditions, reduce the stress concentration in the material, finally make the finished product reach balance in processing performance, mechanical property and electrical property, at the same time, simplify the production process, which is beneficial to industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is the preparation method flow chart of the application. DETAILED DESCRIPTION

[0031] Example 1

[0032] Insulating material composition (parts by weight): polyethylene base material 80 parts (high density polyethylene and linear low density polyethylene weight ratio 3:1), silane coupling agent 2 parts (vinyl trimethoxysilane and gamma-aminopropyl triethoxysilane weight ratio 3:1), catalyst 0.5 parts (dibutyltin dilaurate and zinc stearate weight ratio 3:1), antioxidant 1 part (tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester and tris(2,4-di-tert-butylphenyl) phosphite weight ratio 1:1), nano-scale reinforcing filler 3 parts (nano calcium carbonate modified by silane, particle size 70 nm), core-shell structure filler 7 parts (nano calcium carbonate core and ethylene-octene copolymer shell weight ratio 1:1, particle size 150 nm), nano montmorillonite 3 parts (modified by alkyl quaternary ammonium salt, modifier addition amount is 15% of the weight of nano montmorillonite);

[0033] Preparation method:

[0034] S1: Mix 70 nm nano calcium carbonate and vinyl trimethoxysilane at a mass ratio of 9:1, pre-mix at 60℃, then heat to 80℃ and stir for 3 hours to obtain silane modified nano calcium carbonate; then mix with ethylene-octene copolymer at a ratio of 1:1, melt blend in a twin screw extruder at 160℃ (strong shear type screw configuration) to obtain a core-shell structure filler.

[0035] S2: Add nano montmorillonite and alkyl quaternary ammonium salt to deionized water at a ratio of 9:1, treat with ultrasonic wave at 40 kHz for 30 minutes, heat to 90℃ and stir for 4 hours, filter and dry to obtain modified nano montmorillonite.

[0036] S3: High density polyethylene and linear low density polyethylene were mixed at 4:1, 5% maleic anhydride grafted polyethylene was added, and the mixture was dispersed at 1200 rpm for 8 minutes.

[0037] S4: The core-shell structured filler and nano-montmorillonite were premixed at 3:1, and then mixed with the polyethylene base material after adding silane coupling agent, dry mixing at 800 rpm for 10 minutes; the mixture was added into a twin-screw extruder, the temperature of the melting section was 180°C, the screw rotation speed was 280 rpm, and 30 kHz ultrasonic treatment was performed, and then extrusion granulation was performed.

[0038] S5: The blended granules were crosslinked in warm water (with stirring) at 85°C for 5 hours, and then heat treated at 105°C for 3 hours, and then dried to obtain the finished product;

[0039] Example 2

[0040] The composition of the insulating material (by weight): polyethylene base material 70 parts (high density polyethylene and linear low density polyethylene at a weight ratio of 3:1), silane coupling agent 1.5 parts (vinyl trimethoxysilane and γ-aminopropyl triethoxysilane at a weight ratio of 3:1), catalyst 0.3 parts (dibutyltin dilaurate and zinc stearate at a weight ratio of 3:1), antioxidant 0.6 parts (tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester and tris(2,4-di-tert-butylphenyl) phosphite at a weight ratio of 1:1), nano-sized reinforcing filler 1 part (nano calcium carbonate modified by silane, particle size 50 nm), core-shell structured filler 5 parts (nano calcium carbonate core and ethylene-octene copolymer shell at a weight ratio of 1:1, particle size 100 nm), nano-montmorillonite 2 parts (modified by alkyl quaternary ammonium salt, the amount of modifier added is 15% of the weight of nano-montmorillonite);

[0041] Preparation method:

[0042] S1: 50 nm nano calcium carbonate and vinyl trimethoxysilane were mixed at 10:1, pre-mixed at 60°C, then heated to 75°C and stirred for 2 hours; mixed with ethylene-octene copolymer at 1:0.5, melt blended in a twin-screw extruder at 150°C, to obtain the core-shell structured filler.

[0043] S2: Nano-montmorillonite and alkyl quaternary ammonium salt were added to deionized water at 10:1, treated with 50 kHz ultrasonic wave for 35 minutes, stirred at 80°C for 3 hours, filtered and dried.

[0044] S3: Two kinds of polyethylene were mixed at 3:1, 6% maleic anhydride grafted polyethylene was added, and the mixture was dispersed at 1000 rpm for 5 minutes.

[0045] S4: The core-shell structured filler and nano-montmorillonite were premixed at 3:1, and then mixed with the base material after adding silane coupling agent, dry mixing at 1000 rpm for 8 minutes; the temperature of the melting section of the twin-screw extruder was 175°C, the rotation speed was 250 rpm, 20 kHz ultrasonic treatment was performed, and then extrusion granulation was performed.

[0046] S5:85℃ warm water stirring crosslinking 4 hours, 100℃ heat treatment 2 hours, drying the finished product;

[0047] Example 3

[0048] Insulation material composition (weight parts): polyethylene base material 90 parts (high density polyethylene and linear low density polyethylene weight ratio 3:1), silane coupling agent 3 parts (vinyl trimethoxysilane and gamma-aminopropyl triethoxysilane weight ratio 3:1), catalyst 0.8 parts (dibutyltin dilaurate and zinc stearate weight ratio 3:1), antioxidant 1.6 parts (weight ratio of hindered phenolic and phosphite antioxidant 1:2), nanoscale reinforcing filler 5 parts (100 nm silane modified nano calcium carbonate), core-shell structure filler 10 parts (core-shell weight ratio 1:1, particle size 150 nm), nanometer montmorillonite 4 parts (modifier addition amount 15%);

[0049] Preparation method:

[0050] S1: 100 nm nano calcium carbonate and vinyl trimethoxysilane were mixed at 9:1, pre-mixed at 60℃ and then heated to 80℃ for stirring for 4 hours; mixed with ethylene-octene copolymer at 1:1, and melted and blended at 170℃ to prepare core-shell filler.

[0051] S2: nanometer montmorillonite and alkyl quaternary ammonium salt were treated at 9:1, ultrasonic wave at 60 kHz for 40 minutes, and stirred at 90℃ for 5 hours.

[0052] S3: two kinds of polyethylene were mixed at 4:1, 8% maleic anhydride grafted polyethylene was added, and dispersed at 1500 rpm for 10 minutes.

[0053] S4: the core-shell filler was pre-mixed with montmorillonite, and dry mixed at 1200 rpm for 12 minutes; treated by double screw extruder at 185℃, 300 rpm, and 40 kHz ultrasonic wave.

[0054] S5: 90℃ warm water crosslinking 6 hours, 110℃ heat treatment 4 hours;

[0055] Example 4

[0056] Insulation material composition (weight parts): polyethylene base material 75 parts (high density polyethylene and linear low density polyethylene weight ratio 3:1), silane coupling agent 2.5 parts (complex ratio 3:1), catalyst 0.6 parts (complex ratio 3:1), antioxidant 1.2 parts (complex ratio 1:1), nanoscale reinforcing filler 2 parts (50 nm silane modified nano calcium carbonate), core-shell structure filler 6 parts (core-shell ratio 1:1, 120 nm), nanometer montmorillonite 2.5 parts (modifier 15%);

[0057] Preparation method:

[0058] S1: 50 nm nano calcium carbonate mixed with vinyl trimethoxysilane at 9:1, stirred at 70°C for 3.5 hours; mixed with ethylene-octene copolymer at 1:1, melt blended at 155°C.

[0059] S2: nano montmorillonite treated with alkyl quaternary ammonium salt at 9:1, ultrasonic at 55 kHz for 35 minutes, stirred at 85°C for 3.5 hours.

[0060] S3: two kinds of polyethylene mixed at 3:1, 7% maleic anhydride grafted polyethylene added, dispersed at 1300 rpm for 7 minutes.

[0061] S4: dry mixing at 1000 rpm for 10 minutes; twin-screw extruder at 180°C, 270 rpm, ultrasonic treatment at 35 kHz.

[0062] S5: crosslinked in warm water at 88°C for 5 hours, heat treated at 105°C for 3 hours;

[0063] Comparative Example

[0064] Insulating material composition (parts by weight): polyethylene base material (LLDPE: HDPE = 4:1) 80 parts, silane coupling agent (vinyl trimethoxysilane: γ-aminopropyl triethoxysilane = 2:1) 2 parts, catalyst (dibutyltin dilaurate: zinc stearate = 3:1) 0.5 parts, antioxidant (hindered phenol: phosphite = 1:1) 1 part, nano-sized reinforcing filler (silane-modified nano calcium carbonate, particle size 50 nm) 3 parts, nano montmorillonite (modified with alkyl quaternary ammonium salt, added amount 15%) 3 parts;

[0065] Preparation method:

[0066] S1 nano filler pretreatment: only silane-modified nano calcium carbonate is prepared (same as Example 1);

[0067] S2 nano montmorillonite modification: same as Example 1;

[0068] S3 polyethylene base material blending: same as Example 1;

[0069] S4 component mixing: dry mixing (nano calcium carbonate and montmorillonite pre-mixed at 3:1, then coupling agent, catalyst, antioxidant added) mixed at 800 rpm for 8 minutes; melt blending (175°C, screw 250 rpm, no ultrasonic treatment) extruded and granulated;

[0070] S5 crosslinking and post-treatment: same as Example 1;

[0071] As above, the present application provides a technical solution, a silane self-crosslinking polyethylene overhead insulating material for cables, comprising, in terms of mass percentage of the silane self-crosslinking polyethylene overhead insulating material:

[0072] Polyethylene base material 70-90 parts, silane coupling agent 1.5-3 parts, catalyst 0.3-0.8 parts, antioxidant 0.6-1.6 parts, nano-scale reinforcing filler 1-5 parts, core-shell structure filler 5-10 parts and nano-montmorillonite 2-4 parts; the polyethylene base material is a blend of polyethylenes with different densities, and the weight ratio of the blend of polyethylenes with different densities inside the polyethylene base material is 3:1-5:1;

[0073] The nano-scale reinforcing filler is nano calcium carbonate modified by silane, the particle size of the nano calcium carbonate is 50-100 nm, and the core-shell structure filler has nano calcium carbonate as the core and ethylene-octene copolymer as the shell, and the particle size of the core-shell structure filler is 100-200 nm;

[0074] The silane coupling agent is a compound of vinyltrimethoxysilane and γ-aminopropyltriethoxysilane, and the weight ratio of the two is 2:1-3:1; the catalyst is a compound of dibutyltin dilaurate and an organic zinc compound, and the weight ratio of dibutyltin dilaurate to the organic zinc compound is 3:1-4:1; the organic zinc compound is zinc stearate;

[0075] The antioxidant is a compound of hindered phenolic antioxidant and phosphite antioxidant, and the weight ratio of the hindered phenolic antioxidant to the phosphite antioxidant is 1:1-1:2; the hindered phenolic antioxidant is tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester, and the phosphite antioxidant is tris(2,4-di-tert-butylphenyl)phosphite;

[0076] The weight ratio of the nano calcium carbonate core to the ethylene-octene copolymer shell is 1:0.5-1:2; the nano-montmorillonite is an organically modified nano-montmorillonite, and the modifier of the nano-montmorillonite is an alkyl quaternary ammonium salt; the addition amount of the alkyl quaternary ammonium salt is 10-20% of the weight of the nano-montmorillonite.

[0077] The present application provides a preparation method of a silane self-crosslinking polyethylene overhead insulation material for cables, based on the above-mentioned silane self-crosslinking polyethylene overhead insulation material for cables, comprising the following steps:

[0078] S1 Nano filler pretreatment:

[0079] First, mix nano calcium carbonate with a particle size of 50-100 nm and vinyltrimethoxysilane at a mass ratio of 10:1-8:1, then stir at 60-80°C for 2-4 hours to obtain nano calcium carbonate modified by silane, and finally mix the obtained nano calcium carbonate with ethylene-octene copolymer at a mass ratio of 1:0.5-1:2, and melt blend through a double-screw extruder at 150-170°C, extrude and granulate to obtain a core-shell structure filler;

[0080] The silane modification of the nano calcium carbonate adopts a two-stage surface treatment process: first, the nano calcium carbonate is pre-mixed with vinyl trimethoxysilane at 60°C, then gradually heated to 80°C, and the preparation of the core-shell structure filler adopts a dynamic vulcanization technology, that is, in the melt blending section of the twin-screw extruder, by adjusting the screw configuration to a strong shearing element, the ethylene-octene copolymer forms a continuous coating layer on the surface of the nano calcium carbonate;

[0081] S2 nano montmorillonite modification:

[0082] The nano montmorillonite and the alkyl quaternary ammonium salt are added to deionized water at a mass ratio of 10:1-8:1, stirred at 70-90°C for 3-5 hours, filtered and dried to obtain organically modified nano montmorillonite, and the amount of alkyl quaternary ammonium salt added is 10-20% of the weight of the nano montmorillonite;

[0083] The organic modification of nano montmorillonite adopts a stepwise intercalation method, that is, first, the nano montmorillonite and the alkyl quaternary ammonium salt are formed into a suspension in deionized water, treated by an ultrasonic cell disruptor at a frequency of 40-60 kHz for 30-40 minutes, so that the quaternary ammonium salt molecules are inserted into the interlayer of the montmorillonite, then heated to 90°C and continuously stirred, so that the quaternary ammonium cations and the montmorillonite layers produce an ion exchange reaction, and finally organically modified montmorillonite with an expanded interlayer spacing of more than 1.8 nm is obtained;

[0084] S3 polyethylene substrate blending:

[0085] Different density polyethylene is mixed at a weight ratio of 4:1-5:1, and dispersed by a mixer at 1000-1500 rpm for 5-10 minutes to obtain a polyethylene substrate;

[0086] The blending of the polyethylene substrate adopts a multi-stage mixing process, that is, different density polyethylene is first melt blended at a ratio of 4:1, added through the main feeding port of the twin-screw extruder, and then 5%-8% of maleic anhydride grafted polyethylene is added as a compatibilizer through the side feeding port;

[0087] S4 component mixing:

[0088] First, dry mixing: the core-shell structure filler, nano montmorillonite, silane coupling agent, catalyst, antioxidant are added to the polyethylene substrate, and mixed by a mixer at 800-1200 rpm for 8-12 minutes;

[0089] Then melt blending: the mixture obtained by dry mixing is added to a twin-screw extruder, the melt section temperature is set to 175-185°C, the screw rotation speed is 250-300 rpm, and ultrasonic treatment is applied with a frequency of 20-40 kHz and a power density of 0.8-1.5 W / cm², and then extruded and granulated;

[0090] The dry mixing adopts a gradient feeding sequence, i.e. first, the core-shell filler and the nano-montmorillonite are premixed at a ratio of 3:1, then the silane coupling agent is added for surface modification, and finally the catalyst and the antioxidant are added, and at the same time, the components form a hierarchical dispersion structure in the polyethylene substrate through the turbulent action of the high-speed mixer;

[0091] S5 crosslinking and post-treatment:

[0092] The blended granules obtained in step S4 are crosslinked in warm water at 85-90°C for 4-6 hours, and then heat-treated at 100-110°C for 2-4 hours, and the finished product is obtained after drying;

[0093] The warm water crosslinking adopts a dynamic crosslinking process: the blended granules are placed in a warm water tank with a stirring device, and mechanical stress is continuously applied during the crosslinking process, so that the granules form an oriented structure in the early stage of crosslinking, and the orientation degree of the material after crosslinking is characterized by two-dimensional X-ray diffraction.

[0094] Comparison of experimental data:

[0095] 1. Comparison table of basic properties

[0096] Performance index Unit Example 1 Example 2 Example 3 Example 4 Comparative example Industry standard requirement Tensile strength (23°C) MPa 22.5 20.8 24.1 21.9 18.3 ≥12.5 Elongation at break (23°C) % 485 452 510 473 402 ≥300 Heat shrinkage (135°C, 1 h) % 1.2 1.5 1.0 1.3 2.8 ≤4.0 Volume resistivity (23°C) Ω·m 3.2 x 10 4 ]] 2.8 x 10 4 ]] 3.5 x 10 4 ]] 3.0 x 10 4 ]] 1.5 x 10 4 ]] ≥1.0×10¹³ Dielectric loss tangent (1 MHz) — 0.0015 0.0018 0.0013 0.0016 0.0028 ≤0.005

[0097] 2. Comparison table of aging resistance

[0098] Performance index Unit Example 1 Example 2 Example 3 Example 4 Comparative example Industry standard requirement (change rate) Tensile strength change rate % -3.2 -4.5 -2.8 -3.8 -8.5 ≤±15% Elongation at break change rate % -5.1 -6.3 -4.7 -5.5 -12.8 ≤±20% Dielectric loss tangent change rate % +12.5 +15.3 +10.8 +13.2 +28.6 ≤+30%

[0099] 3. Comparison table of processing properties

[0100] Performance index Unit Example 1 Example 2 Example 3 Example 4 Comparative example Melt flow rate (190°C, 2.16 kg) g / 10 min 2.8 2.5 3.1 2.7 2.0 Extrusion molding temperature ℃ 175-185 175-185 180-190 175-185 180-195 Granulation qualification rate % 98.5 97.8 99.2 98.1 92.3

[0101] This scheme realizes a breakthrough in mechanical properties through the synergistic design of "different density polyethylene blended substrate + silane modified nano calcium carbonate + core-shell filler". As can be seen from the data, the tensile strength of Examples 1-4 is more than 20 MPa, which is increased by 14.2%-31.7% compared with the comparative example, the elongation at break is more than 450%, which is increased by 12.4%-26.9% compared with the comparative example, and the thermal shrinkage rate is less than 1.5%, which is much better than the industry standard of ≤4.0%;

[0102] The core reason is that: high-density polyethylene (HDPE) provides rigid support, linear low-density polyethylene (LLDPE) gives toughness, and a blending ratio of 3:1-5:1 ensures the mechanical balance of the substrate; silane-modified nano calcium carbonate (50-100 nm) is closely combined with the substrate through interfacial action to enhance mechanical strength; the core-shell structure filler (100-200 nm) retains rigidity with nano calcium carbonate as the core and improves interfacial compatibility with ethylene-octene copolymer as the shell, avoiding stress concentration caused by filler aggregation, and finally achieving the synergistic effect of "high strength-high toughness-low thermal shrinkage" to meet the needs of overhead cables in complex stress scenarios such as outdoor stretching and bending;

[0103] The electrical performance data shows that the volume resistivity of Examples 1-4 is all higher than 2.8 x 10 4 Ω·m, which is improved by 86.7%-133.3% compared with the comparative examples, the dielectric loss tangent (1 MHz) is lower than 0.0018, and the dielectric loss tangent change rate after heat aging is lower than 15.3%, which is better than the industry standard and the comparative examples;

[0104] Key technology support includes: organically modified nano-montmorillonite (interlayer spacing ≥1.8 nm) forms a barrier network in the substrate to inhibit charge migration and improve insulation strength; silane coupling agent (vinyl trimethoxysilane and γ-aminopropyl triethoxysilane) improves the interfacial bonding between inorganic fillers and organic substrates, reducing the leakage channel caused by interfacial defects; dynamic crosslinking process (warm water stirring + mechanical stress induction) forms a uniform crosslinking network, avoiding electrical performance fluctuations caused by uneven local crosslinking density, and ensuring the insulation reliability of the cable in high-voltage power transmission environment;

[0105] The heat aging experiment shows that the tensile strength and elongation at break change rate of Examples 1-4 are all controlled within-6.3%, and the dielectric loss tangent change rate is lower than 15.3%, while the performance decay of the comparative examples is significantly higher (tensile strength change rate-8.5%, elongation at break change rate-12.8%);

[0106] Thanks to the synergistic effect of the antioxidant system and nano-montmorillonite: hindered phenolic antioxidants (tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester) capture free radicals, and phosphite antioxidants (tris(2,4-di-tert-butylphenyl) phosphite) decompose hydroperoxides, and a complex ratio of 1:1-1:2 realizes multiple antioxidant mechanisms; the layered structure of organically modified nano-montmorillonite hinders the penetration of oxygen and heat, delaying the aging process, so that the material can withstand harsh outdoor environments such as high temperature and ultraviolet light for a long time, extending the service life of the cable to more than 20 years (traditional materials about 15 years);

[0107] The processing performance data shows that the melt flow rate of examples 1-4 (2.5-3.1 g / 10 min) is increased by 25%-55% compared with the comparative example (2.0 g / 10 min), the extrusion molding temperature is reduced by 5-10℃, the qualified rate of granulation is more than 97.8%, which is increased by 5.9%-7.5% compared with the comparative example;

[0108] Process innovation is the core driving force: the ethylene-octene copolymer shell layer of the core-shell structure filler reduces the melt viscosity and improves the processing flowability; the stepwise intercalation method modifies the nano-montmorillonite (ultrasonic assisted + ion exchange) to improve the dispersibility and avoid the extrusion blockage caused by agglomeration; the gradient feeding sequence (filler premixing to coupling agent modification and then to catalyst / antioxidant addition) cooperates with ultrasonic melt blending (20-40 kHz) to realize the uniform dispersion of each component, reduce impurities and waste products in the granulation process, reduce production cost, and meet the needs of industrial large-scale production.

Claims

1. A silane self-crosslinking polyethylene aerial insulating compound for cables, characterized in that it comprises: comprises, by mass percentage of the silane self-crosslinking polyethylene overhead insulation material: polyethylene base material 70-90 parts, silane coupling agent 1.5-3 parts, catalyst 0.3-0.8 parts, antioxidant 0.6-1.6 parts, nanoscale reinforcing filler 1-5 parts, core-shell structure filler 5-10 parts and nanometer montmorillonite 2-4 parts; the polyethylene base material is a blend of polyethylenes with different densities, and the weight ratio of the blend of polyethylenes with different densities inside the polyethylene base material is 3:1-5:1; The nanoscale reinforcing filler is nanometer calcium carbonate modified by silane, the particle size of the nanometer calcium carbonate is 50-100 nm, and the core-shell structure filler has nanometer calcium carbonate as core and ethylene-octene copolymer as shell, and the particle size of the core-shell structure filler is 100-200 nm.

2. The self-crosslinking silane cable polyethylene insulation material according to claim 1, characterized in that: The silane coupling agent is a compound of vinyltrimethoxysilane and γ-aminopropyltriethoxysilane, and the weight ratio of the two is 2:1-3:1, the catalyst is a compound of dibutyltin dilaurate and organic zinc compound, and the weight ratio of dibutyltin dilaurate and organic zinc compound is 3:1-4:1, and the organic zinc compound is zinc stearate.

3. The self-crosslinking silane cable polyethylene insulation material according to claim 1, characterized in that: The antioxidant is a compound of hindered phenolic antioxidant and phosphite antioxidant, and the weight ratio of the hindered phenolic antioxidant and phosphite antioxidant is 1:1-1:2, the hindered phenolic antioxidant is tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester, and the phosphite antioxidant is tris(2,4-di-tert-butylphenyl)phosphite.

4. The self-crosslinking silane cable polyethylene insulation material according to claim 1, characterized in that: The weight ratio of the nanometer calcium carbonate core and the ethylene-octene copolymer shell is 1:0.5-1:2, the nanometer montmorillonite is organically modified nanometer montmorillonite, the modifier of the nanometer montmorillonite is alkyl quaternary ammonium salt, and the addition amount of the alkyl quaternary ammonium salt is 10-20% of the weight of the nanometer montmorillonite.

5. A process for the preparation of a silane self-crosslinking polyethylene aerial cable insulation compound based on a silane self-crosslinking polyethylene aerial cable insulation compound according to any one of claims 1 to 4, characterized in that, It comprises the following steps: S1 nanofiller pretreatment: First, nanometer calcium carbonate with a particle size of 50-100 nm is mixed with vinyltrimethoxysilane by stirring to obtain nanometer calcium carbonate modified by silane, and then the obtained nanometer calcium carbonate is mixed with ethylene-octene copolymer and melt blended by a double screw extruder to obtain core-shell structure filler; S2 modification of nanometer montmorillonite: Add nanometer montmorillonite and alkyl quaternary ammonium salt to deionized water at a mass ratio of 10:1-8:1, stir at 70-90℃ for 3-5 hours, filter and dry to obtain organically modified nanometer montmorillonite; S3 polyethylene base material blending: Mix polyethylenes with different densities at a weight ratio of 4:1-5:1, and disperse by a mixer to obtain a polyethylene base material; S4 component mixing: First, dry mixing: mix core-shell structure filler, nanometer montmorillonite, silane coupling agent, catalyst, antioxidant into the polyethylene base material; Then melt blend: add the mixture obtained by dry mixing into a double screw extruder and apply ultrasonic treatment, and extrude and granulate; S5 crosslinking and post-treatment: Crosslink the blended granules obtained in step S4 in warm water, then heat treat, and dry to obtain the finished product.

6. A process for the preparation of a silane self-crosslinking polyethylene aerial insulating compound for cables according to claim 5, characterized in that: In the step S1, the silane modification of the nano calcium carbonate adopts a two-stage surface treatment process: first, the nano calcium carbonate is premixed with vinyl trimethoxysilane at 60°C, then gradually heated to 80°C, and the preparation of the core-shell structured filler adopts a dynamic vulcanization technology, i.e. in the melt blending section of the twin-screw extruder, by adjusting the screw configuration to strong shear type elements, the ethylene-octene copolymer forms a continuous coating layer on the surface of the nano calcium carbonate.

7. The process for the preparation of a silane self-crosslinking polyethylene aerial insulating compound for cables according to claim 5, characterized in that: In the step S2, the organic modification of the nano montmorillonite adopts a stepwise intercalation method, i.e. first, the nano montmorillonite and alkyl quaternary ammonium salt are formed into a suspension in deionized water, treated by an ultrasonic cell disruptor at a frequency of 40-60 kHz for 30-40 minutes, so that the quaternary ammonium salt molecules are inserted into the interlayer of the montmorillonite, then heated to 90°C and continuously stirred, so that the quaternary ammonium salt cations and the montmorillonite layers produce an ion exchange reaction, and finally the organic montmorillonite with an expanded interlayer spacing of more than 1.8 nm is obtained.

8. A process for the preparation of a silane self-crosslinking polyethylene aerial insulating compound for cables according to claim 5, characterized in that: In the step S3, the blending of the polyethylene substrate adopts a multi-stage mixing process, i.e. first, different densities of polyethylene are melt blended in a ratio of 4:1, added through the main feeding port of the twin-screw extruder, then 5%-8% of maleic anhydride grafted polyethylene is added as a compatibilizer through the side feeding port.

9. The process for the preparation of a silane self-crosslinking polyethylene aerial insulating compound for cables according to claim 5, characterized in that: In the step S4, the dry mixing adopts a gradient feeding sequence, i.e. first, the core-shell structured filler and the nano montmorillonite are premixed in a ratio of 3:1, then the surface modification is carried out with a silane coupling agent, and finally the catalyst and antioxidant are added, and at the same time, through the turbulent action of the high-speed mixer, the components form a hierarchical dispersion structure in the polyethylene substrate.

10. A process for the preparation of a silane self-crosslinking polyethylene aerial insulating compound for cables according to claim 5, characterized in that: In the step S5, the warm water crosslinking adopts a dynamic crosslinking process: the blended granules are placed in a warm water tank with a stirring device, and mechanical stress is continuously applied during the crosslinking process, so that the granules form an oriented structure in the early stage of crosslinking, and the orientation degree of the material after crosslinking is characterized by two-dimensional X-ray diffraction.

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