Direct-current cable insulation material capable of resisting space charge accumulation, preparation method and application

Abstract

The invention belongs to the technical field of cable insulation material application, and particularly discloses a direct-current cable insulation material capable of resisting space charge accumulation. Comprising the following components: blended matrix resin of 85 to 90 parts of low-density polyethylene and 10 to 15 parts of linear low-density polyethylene, 2.0 to 2.8 parts of KH550 silane modified nano Al2O3, 0.3 to 0.5 part of organic montmorillonite, 2.5 to 3.5 parts of maleic anhydride grafted polyethylene, 0.8 to 1.0 part of dicumyl peroxide, 0.2 to 0.4 part of triallyl isocyanurate, 0.15 to 0.25 part of an antioxidant 1010, 0.15 to 0.25 part of an antioxidant 168 and 0.08 to 0.12 part of calcium stearate. The preparation method has the beneficial effects that the low-density polyethylene and the linear low-density polyethylene are blended, so that the crystallinity of the material can be regulated and controlled to be 40-5%, and charge trapping sites of an interface between a crystal region and an amorphous region are reduced. KH550 modified nano Al2O3 is uniformly dispersed in a matrix, and shallow trap sites are introduced, so that migration and recombination of trapped charges are accelerated, and long-term accumulation of the charges is avoided. The polar group of maleic anhydride grafted polyethylene can reduce the potential barrier of an electrode-insulation interface and reduce the charge injection amount.

Description

Technical Field

[0001] This invention belongs to the field of cable insulation material application technology, specifically relating to a DC cable insulation material, preparation method and application that resists space charge accumulation. It is suitable for the preparation of insulation layers for ±110kV-±500kV high voltage / ultra-high voltage DC cables, and can improve the long-term service stability and withstand voltage performance of the cable. Background Technology

[0002] With the rapid development of high-voltage direct current (HVDC) transmission technology, DC cables are widely used in inter-regional power transmission, submarine power transmission, and other scenarios. However, under the long-term action of a DC electric field, the insulation layer of DC cables is prone to space charge accumulation. This space charge is caused by factors such as electrode injection, impurity ionization, and polarization distortion, which can lead to severe distortion of the local electric field inside the insulation (the degree of distortion can reach 2-3 times the rated field strength), accelerate electrical tree growth and insulation breakdown, and greatly shorten the service life of DC cables.

[0003] Currently, the mainstream insulation material for DC cables is cross-linked polyethylene (XLPE). However, conventional XLPE insulation materials have the following defects: First, impurities such as residual catalysts, metal ions, and moisture in the matrix can easily form deep traps, promoting the capture and accumulation of space charges; second, the molecular chain has a high degree of crystallinity (usually >60%), and the interface between crystalline and amorphous regions can easily become charge accumulation sites; third, a single matrix material cannot simultaneously achieve the synergistic effect of "blocking charge injection, accelerating charge dissipation, and inhibiting charge migration".

[0004] Existing improvement technologies mostly focus on single modification methods, such as simple nano-doping or polar group grafting, but they have obvious shortcomings: nanofillers are prone to agglomeration to form deep traps, which in turn aggravates the accumulation of space charge; excessive polar group grafting can lead to a decrease in the mechanical properties of the material; and the lack of impurity control throughout the entire process of insulating material preparation makes it difficult to eliminate trap sources at the root.

[0005] Therefore, based on the above problems, the present invention provides a DC cable insulation material resistant to space charge accumulation, a preparation method, and its application. Summary of the Invention

[0006] Purpose of the invention: The purpose of this invention is to provide a DC cable insulation material, preparation method and application that resists space charge accumulation, to solve the technical problems of poor resistance to space charge accumulation, severe local electric field distortion and short service life of existing DC cable insulation materials in the background art, to achieve efficient suppression of space charge, and at the same time ensure the excellent mechanical properties and insulation stability of the material.

[0007] Technical solution: The first aspect of the present invention provides a DC cable insulation material that resists space charge accumulation, comprising, by weight, the following components: a blend matrix resin of 85-90 parts of low-density polyethylene and 10-15 parts of linear low-density polyethylene, 2.0-2.8 parts of KH550 silane-modified nano-Al2O3, 0.3-0.5 parts of organomontmorillonite, 2.5-3.5 parts of maleic anhydride-grafted polyethylene, 0.8-1.0 parts of dicumyl peroxide, 0.2-0.4 parts of triallyl isocyanurate, 0.15-0.25 parts of antioxidant 1010, 0.15-0.25 parts of antioxidant 168, and 0.08-0.12 parts of calcium stearate.

[0008] In this technical solution, the low-density polyethylene has a melt index (MI) of 1.8-2.2 g / 10 min and an ash content ≤10 ppm; the linear low-density polyethylene is an octene copolymer with a melt index (MI) of 0.8-1.2 g / 10 min and a branch density of 0.6-1.0 branches / 1000C; the KH550 silane-modified nano-Al2O3 has a particle size of 15-25 nm and a specific surface area of ​​80-100 m² / g; the organomontmorillonite has an interlayer spacing ≥3.0 nm; the maleic anhydride-grafted polyethylene has a grafting rate of 1.0%-1.5% and a melt index (MI) of 0.6-1.0 g / 10 min; and the dicumyl peroxide has a purity ≥99% and a half-life of 1 min.

[0009] The second aspect of the present invention provides a method for preparing a DC cable insulation material resistant to space charge accumulation, comprising the following steps: (1) raw material pretreatment, wherein KH550 silane-modified nano-Al2O3 and organomontmorillonite are dried at 110-130℃ and -0.08~-0.10MPa for 3-5 hours, and low-density polyethylene, linear low-density polyethylene and maleic anhydride-grafted polyethylene are dried at 80-90℃ for 2-3 hours; (2) functional masterbatch preparation, wherein 30% KH550 silane-modified nano-Al2O3 / linear low-density polyethylene masterbatch and 20% KH550 silane-modified nano-Al2O3 / linear low-density polyethylene masterbatch are prepared respectively. (3) Premixing of the mixture: Weigh each component according to the formula ratio and mix for 12-18 min at 700-900 r / min and 75-85℃; (4) Ultra-purified melt blending: Feed the premix into a twin-screw extruder at an extrusion temperature of 120-175℃ and a screw speed of 140-160 r / min. After filtration through a 10μm precision filter, the mixture is extruded and granulated; (5) Secondary purification and drying: Dry the primary particles at 90-110℃ and -0.09~-0.10MPa for 2-4 h to obtain the finished product.

[0010] In this technical solution, in step (2), KH550 silane-modified nano-Al2O3 masterbatch is prepared by weighing linear low-density polyethylene and dried KH550 silane-modified nano-Al2O3 at a mass ratio of 7:3, adding them to a high-speed mixer, and mixing them for 10-15 minutes at 800-1000 r / min and 70-80℃. Then, the mixture is fed into a twin-screw extruder for extrusion granulation. The extrusion temperature is set to 110-120℃ in zone 1, 130-140℃ in zone 2, 150-160℃ in zone 3, and 140-150℃ in zone 4. The screw speed is 180-220 r / min to obtain KH550 silane-modified nano-Al2O3 with a content of 30%.

[0011] In this technical solution, in step (2), the organic montmorillonite masterbatch is prepared by weighing low-density polyethylene and dried organic montmorillonite at a mass ratio of 8:2, adding them to a high-speed mixer, mixing them for 10-15 minutes at 800-1000 r / min and 70-80℃, and then feeding them into a twin-screw extruder for extrusion granulation. The extrusion temperature is set to 110-120℃ in zone 1, 130-140℃ in zone 2, 150-160℃ in zone 3, and 140-150℃ in zone 4, with a screw speed of 180-220 r / min, to obtain an organic montmorillonite masterbatch with a content of 20%.

[0012] In step (3) of this technical solution, the blended matrix resin, KH550 silane-modified nano-Al2O3 masterbatch and organomontmorillonite masterbatch, organic modifier, maleic anhydride-grafted polyethylene diisopropylbenzene peroxide, triallyl isocyanurate, antioxidant 1010, antioxidant 168 and calcium stearate are weighed according to the formula ratio, added to a high-speed mixer, and mixed for 12-18 minutes at 700-900 r / min and 75-85℃ to obtain a premix.

[0013] In this technical solution, in step (4), the premixed material is fed into a twin-screw extruder equipped with a static mixer for ultra-clean melt blending. The extrusion temperature is set to 120-130℃ in zone 1, 140-150℃ in zone 2, 160-170℃ in zone 3, and 170-175℃ at the die head. The screw speed is 140-160 r / min, and the shear rate is 300-500 s. －1 The material is filtered through a 10μm precision filter and then extruded and granulated to obtain primary insulating material particles.

[0014] The third aspect of the present invention provides a ±110kV-±500kV DC cable, which uses a DC cable insulation material resistant to space charge accumulation and is prepared by the above-mentioned method; wherein, a three-layer co-extrusion process is used, the insulation layer extrusion temperature is 170-175℃, the pressure is 15-20MPa, the traction speed is 4-6m / min, the crosslinking temperature is 175-185℃, the steam pressure is 0.8-1.0MPa, the crosslinking time is 15-20min, and the cooling adopts segmented cooling with water temperatures of 60-70℃, 40-50℃, and 25-30℃ respectively.

[0015] Compared with existing technologies, the beneficial effects of the present invention on DC cable insulation material, preparation method, and application that resists space charge accumulation are as follows: 1. Matrix blending control: Blending low-density polyethylene with linear low-density polyethylene can control the crystallinity of the material to 40%-5%, reducing charge trapping sites at the interface between crystalline and amorphous regions; the uniform distribution of short branches in linear low-density polyethylene further reduces the density of deep traps and improves charge transport channels. 2. Synergistic doping of functional fillers: KH550-modified nano-Al2O3 is uniformly dispersed in the matrix, introducing shallow trapping sites, accelerating the migration and recombination of trapped charges, and avoiding long-term charge accumulation; the layered structure of organomontmorillonite forms a spatial barrier network, inhibiting long-distance charge migration and reducing local charge accumulation. The two work synergistically to simultaneously accelerate charge dissipation and block charge migration. 3. Molecular Modification and Compatibilization: The polar groups of maleic anhydride-grafted polyethylene can lower the potential barrier at the electrode-insulator interface, reducing charge injection. Simultaneously, the polyethylene backbone of maleic anhydride-grafted polyethylene exhibits excellent compatibility with the matrix resin. The maleic anhydride groups can form hydrogen bonds with the hydroxyl groups on the surface of KH550 silane-modified nano-Al2O and organomontmorillonite, improving the interfacial bonding between the functional filler and the matrix and preventing filler agglomeration that could form deep traps. 4. Ultra-Purified Process: Ultra-purified melt blending involves comprehensive impurity control throughout the entire process, including raw material drying, precision filtration, and vacuum degassing. This keeps the content of impurities such as moisture and metal ions in the insulation material below 10 ppm, eliminating deep traps caused by impurities at their source and reducing the origin of space charge generation. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0017] In the description of this invention, it should be noted that the terms "top," "bottom," "one side," "the other side," "front," "back," "middle part," "inner," "top," and "bottom," etc., indicating orientation or positional relationships, are based on the shown orientation or positional relationships and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention; the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly, for example, they can be fixed connections, detachable connections, or integral connections; they can be mechanical connections or electrical connections; they can be direct connections or indirect connections through an intermediate medium; they can be internal connections between two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0018] The present invention discloses a DC cable insulation material for resisting space charge accumulation, comprising, by weight, the following components: a blended matrix resin of 85-90 parts low-density polyethylene and 10-15 parts linear low-density polyethylene, 2.0-2.8 parts KH550 silane-modified nano-Al2O3, 0.3-0.5 parts organomontmorillonite, 2.5-3.5 parts maleic anhydride-grafted polyethylene, 0.8-1.0 parts dicumyl peroxide, 0.2-0.4 parts triallyl isocyanurate, 0.15-0.25 parts antioxidant 1010, 0.15-0.25 parts antioxidant 168, and 0.08-0.12 parts calcium stearate.

[0019] In addition, preferably, the low-density polyethylene has a melt index (MI) of 1.8-2.2 g / 10 min (190℃ / 2.16 kg) and an ash content of ≤10 ppm; the linear low-density polyethylene is an octene copolymer with a melt index (MI) of 0.8-1.2 g / 10 min and a branch density of 0.6-1.0 branches / 1000℃; the KH550 silane-modified nano-Al2O3 has a particle size of 15-25 nm and a specific surface area of ​​80-100 m² / g; the organomontmorillonite has an interlayer spacing of ≥3.0 nm; the maleic anhydride-grafted polyethylene has a grafting rate of 1.0%-1.5% and a melt index (MI) of 0.6-1.0 g / 10 min; and the dicumyl peroxide has a purity of ≥99% and a half-life of 1 min (171℃).

[0020] The present invention provides a method for preparing a DC cable insulation material resistant to space charge accumulation, comprising the following steps: (1) raw material pretreatment, wherein KH550 silane-modified nano-Al2O3 and organomontmorillonite are dried at 110-130℃ and -0.08~-0.10MPa for 3-5 hours, and low-density polyethylene, linear low-density polyethylene and maleic anhydride-grafted polyethylene are dried at 80-90℃ for 2-3 hours; (2) preparation of functional masterbatch, wherein 30% KH550 silane-modified nano-Al2O3 / linear low-density polyethylene masterbatch and 20% KH550 silane-modified nano-Al2O3 / linear low-density polyethylene masterbatch are prepared respectively. (3) Premixing of the mixture: Weigh each component according to the formula ratio and mix for 12-18 min at 700-900 r / min and 75-85℃; (4) Ultra-purified melt blending: Feed the premixed material into a twin-screw extruder at an extrusion temperature of 120-175℃ and a screw speed of 140-160 r / min. After filtration through a 10μm precision filter, the material is extruded and granulated; (5) Secondary purification and drying: Dry the primary particles at 90-110℃ and -0.09~-0.10MPa for 2-4 h to obtain the finished product.

[0021] In addition, preferably, in step (2), KH550 silane-modified nano-Al2O3 masterbatch is prepared by weighing linear low-density polyethylene and dried KH550 silane-modified nano-Al2O3 at a mass ratio of 7:3, adding them to a high-speed mixer, and mixing them for 10-15 minutes at 800-1000 r / min and 70-80℃. Then, it is fed into a twin-screw extruder for extrusion granulation. The extrusion temperature is set to 110-120℃ in zone 1, 130-140℃ in zone 2, 150-160℃ in zone 3, and 140-150℃ in zone 4, with a screw speed of 180-220 r / min, to obtain KH550 silane-modified nano-Al2O3 with a content of 30%.

[0022] In addition, preferably, in step (2), the organic montmorillonite masterbatch is prepared by weighing low-density polyethylene and dried organic montmorillonite at a mass ratio of 8:2, adding them to a high-speed mixer, mixing them for 10-15 minutes at 800-1000 r / min and 70-80℃, and then feeding them into a twin-screw extruder for extrusion granulation. The extrusion temperature is set to 110-120℃ in zone 1, 130-140℃ in zone 2, 150-160℃ in zone 3, and 140-150℃ in zone 4, with a screw speed of 180-220 r / min, to obtain an organic montmorillonite masterbatch with a content of 20%.

[0023] In addition, preferably, in step (3), the blended matrix resin, KH550 silane-modified nano-Al2O3 masterbatch and organomontmorillonite masterbatch, organic modifier, maleic anhydride-grafted polyethylene diisopropylbenzene peroxide, triallyl isocyanurate, antioxidant 1010, antioxidant 168 and calcium stearate are weighed according to the formula ratio, added to a high-speed mixer, and mixed for 12-18 minutes at 700-900 r / min and 75-85℃ to obtain a premix.

[0024] In addition, preferably, in step (4), the premixed material is fed into a twin-screw extruder equipped with a static mixer for ultra-clean melt blending. The extrusion temperature is set to 120-130℃ in zone 1, 140-150℃ in zone 2, 160-170℃ in zone 3, and 170-175℃ at the die head. The screw speed is 140-160 r / min, and the shear rate is 300-500 s. －1 The material is filtered through a 10μm precision filter and then extruded and granulated to obtain primary insulating material particles.

[0025] The ±110kV-±500kV DC cable of this invention uses DC cable insulation material resistant to space charge accumulation, prepared by the above-mentioned method. Specifically, a three-layer co-extrusion process is used, with the insulation layer extrusion temperature at 170-175℃, pressure at 15-20 MPa, traction speed at 4-6 m / min, cross-linking temperature at 175-185℃, steam pressure at 0.8-1.0 MPa, and cross-linking time at 15-20 min. Cooling is achieved through segmented cooling, with water temperatures successively at 60-70℃, 40-50℃, and 25-30℃.

[0026] The DC cable insulation material of this invention exhibits excellent resistance to space charge accumulation: When pressurized for 3 hours at 80℃ and a 40kV / mm DC electric field, the space charge density is ≤0.8C / m³, with no obvious local charge accumulation peak; after polarity reversal, the charge dissipation rate is ≥80% / 1h, effectively suppressing local electric field distortion; it balances insulation and mechanical properties, with a DC breakdown strength ≥75kV / mm and a volume resistivity ≥5×10⁻⁶. 15 Ω·m (90℃); tensile strength ≥20MPa, elongation at break ≥400%, elongation at break (200℃, 0.2MPa, 15min) ≤10%, permanent deformation ≤2%, meeting the requirements for use of high voltage DC cables.

[0027] The method for preparing DC cable insulation material with anti-space charge accumulation of the present invention has strong controllability. It uses a masterbatch method to prepare functional filler masterbatch, which significantly improves the uniformity of filler dispersion. At the same time, the whole process of ultra-clean process can be upgraded on the basis of existing twin-screw extrusion equipment without the need for new special equipment, making it suitable for large-scale industrial production.

[0028] The ±110kV-±500kV DC cables prepared using the method of this invention, which are made of DC cable insulation material resistant to space charge accumulation, have significantly improved resistance to electrical treeing and aging, extending the expected service life of the DC cables to more than 40 years.

[0029] Example 1 A DC cable insulation material resistant to space charge accumulation, comprising the following components by weight: 85 parts low-density polyethylene, 15 parts linear low-density polyethylene, 2.5 parts KH550 silane-modified nano-Al2O3, 0.5 parts organomontmorillonite, 0.2 parts organic modifier, 3.0 parts maleic anhydride-grafted polyethylene, 0.9 parts dicumyl peroxide, 0.3 parts triallyl isocyanurate, 0.2 parts antioxidant 1010, 0.2 parts antioxidant 168, and 0.1 parts calcium stearate.

[0030] The DC cable insulation material for resisting space charge accumulation in this embodiment is prepared using the following method: (1) Raw material pretreatment: KH550 silane-modified nano-Al2O3 and organomontmorillonite were dried at 120℃ and -0.09MPa for 4h, and low-density polyethylene, linear low-density polyethylene and maleic anhydride-grafted polyethylene were dried at 85℃ for 2.5h.

[0031] (2) Preparation of functional masterbatch: linear low-density polyethylene and dried KH550 silane-modified nano-Al2O3 were weighed at a mass ratio of 7:3 and added to a high-speed mixer. The mixture was mixed for 12 min at 800 r / min and 75℃. Then it was fed into a twin-screw extruder for extrusion granulation. The extrusion temperature was set to 115℃ in zone 1, 135℃ in zone 2, 155℃ in zone 3, and 145℃ in zone 4. The screw speed was 200 r / min to obtain KH550 silane-modified nano-Al2O3 with a content of 30%. Low-density polyethylene and dried organomontmorillonite were weighed at a mass ratio of 8:2 and added to a high-speed mixer. The mixture was mixed for 12 min at 800 r / min and 75℃. Then it was fed into a twin-screw extruder for extrusion granulation. The extrusion temperature was set to 115℃ in zone 1, 135℃ in zone 2, 155℃ in zone 3, and 145℃ in zone 4. The screw speed was 200 r / min to obtain organomontmorillonite masterbatch with a content of 20%.

[0032] (3) Premix the mixture, weigh each component according to the formula ratio, and mix for 15 min at 800 r / min and 80℃.

[0033] (4) Ultra-purified melt blending: The premixed material is fed into a twin-screw extruder. The extrusion temperature is 125℃ in zone 1, 145℃ in zone 2, 165℃ in zone 3, and 172℃ at the die head. The rotation speed is 150r / min and the shear rate is 400s. －1After being filtered through a 10μm filter, the material is extruded and granulated. After being filtered through a 10μm precision filter, the material is extruded and granulated.

[0034] (5) Secondary purification and drying: the primary particles are dried at 100℃ and -0.095MPa for 3 hours to obtain the finished insulation material.

[0035] Performance testing: The insulation material was pressurized at 80℃ and 40kV / mm electric field for 3h, with a space charge density of 0.6C / m³, a DC breakdown strength of 82kV / mm, a tensile strength of 22MPa, an elongation at break of 450%, a thermal elongation of 8%, and a permanent deformation of 1.5%.

[0036] Example 2 A DC cable insulation material resistant to space charge accumulation, comprising the following components by weight: 90 parts low-density polyethylene, 10 parts linear low-density polyethylene, 2.0 parts KH550 silane-modified nano-Al2O3, 0.3 parts organomontmorillonite, 0.3 parts organic modifier, 2.5 parts maleic anhydride-grafted polyethylene, 0.8 parts dicumyl peroxide, 0.2 parts triallyl isocyanurate, 0.15 parts antioxidant 1010, 0.15 parts antioxidant 168, and 0.08 parts calcium stearate.

[0037] The DC cable insulation material for resisting space charge accumulation in this embodiment is prepared using the following method: (1) Raw material pretreatment: KH550 silane modified nano-Al2O3 was dried at 110℃ and -0.09MPa for 5h, organomontmorillonite was dried at 120℃ and -0.09MPa for 4h, and low-density polyethylene, linear low-density polyethylene and maleic anhydride grafted polyethylene were dried at 85℃ for 2.5h.

[0038] (2) Preparation of functional masterbatch: linear low-density polyethylene and dried KH550 silane-modified nano-Al2O3 were weighed at a mass ratio of 7:3 and added to a high-speed mixer. The mixture was mixed for 12 min at 800 r / min and 75℃. Then it was fed into a twin-screw extruder for extrusion granulation. The extrusion temperature was set to 115℃ in zone 1, 135℃ in zone 2, 155℃ in zone 3, and 145℃ in zone 4. The screw speed was 200 r / min to obtain KH550 silane-modified nano-Al2O3 with a content of 30%. Low-density polyethylene and dried organomontmorillonite were weighed at a mass ratio of 8:2 and added to a high-speed mixer. The mixture was mixed for 12 min at 800 r / min and 75℃. Then it was fed into a twin-screw extruder for extrusion granulation. The extrusion temperature was set to 115℃ in zone 1, 135℃ in zone 2, 155℃ in zone 3, and 145℃ in zone 4. The screw speed was 200 r / min to obtain organomontmorillonite masterbatch with a content of 20%.

[0039] (3) Premix the mixture, weigh each component according to the formula ratio, and mix for 15 min at 800 r / min and 80℃.

[0040] (4) Ultra-clean melt blending: The premixed material is fed into a twin-screw extruder. The extrusion temperature is 125℃ in zone 1, 145℃ in zone 2, 165℃ in zone 3, and 172℃ at the die head. The rotation speed is 140r / min and the shear rate is 400s. －1 After being filtered through a 10μm filter, the material is extruded and granulated. After being filtered through a 10μm precision filter, the material is extruded and granulated.

[0041] (5) Secondary purification and drying: the primary particles are dried at 100℃ and -0.095MPa for 3 hours to obtain the finished insulation material.

[0042] Performance testing: The insulation material was pressurized at 80℃ and 40kV / mm electric field for 3h, with a space charge density of 0.7C / m³, a DC breakdown strength of 78kV / mm, a tensile strength of 21MPa, an elongation at break of 420%, a thermal elongation of 9%, and a permanent deformation of 1.8%.

[0043] Comparative Example 1: A conventional XLPE insulation material (without linear low-density polyethylene blending or functional filler doping) was used, with other components identical to those in Example 1. Performance testing: Under an electric field of 40 kV / mm at 80℃ for 3 hours, the space charge density was 3.5 C / m³; the DC breakdown strength was 55 kV / mm; the tensile strength was 18 MPa; and the elongation at break was 350%.

[0044] Comparative Example 2: No PE-g-MAH added; other components were the same as in Example 1. Performance testing: Under pressure of 80℃ and 40kV / mm electric field for 3h, the space charge density was 2.2C / m³; the DC breakdown strength was 62kV / mm; the tensile strength was 16MPa; and the elongation at break was 320% (due to the decrease in mechanical properties caused by filler agglomeration).

[0045] It should be noted that, in this document, terms such as "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0046] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A DC cable insulation material according to claim 1, characterized in that: The low-density polyethylene has a melt index MI=1.8-2.2 g / 10 min and an ash content ≤10 ppm; the linear low-density polyethylene is an octene copolymer type and has a melt index MI=0.8-1.2 g / 10 min and a branch density of 0.6-1.0 branches / 1000C; the KH550 silane-modified nano-Al2O3 has a particle size of 15-25 nm and a specific surface area of 80-100 m² / g; the organic montmorillonite has an interlayer spacing ≥3.0 nm; the maleic anhydride grafted polyethylene has a grafting rate of 1.0%-1.5% and a melt index MI=0.6-1.0 g / 10 min; and the dicumyl peroxide has a purity ≥99% and a half-life of 1 min.

2. A process for the preparation of a DC cable insulation material resistant to space charge accumulation according to claim 1 or 2, characterized in that: The method comprises the following steps, (1) raw material pretreatment, the KH550 silane-modified nano-Al2O3 and the organic montmorillonite are dried at 110-130 ℃ and -0.08~-0.10 MPa for 3-5 h, and the low-density polyethylene, the linear low-density polyethylene and the maleic anhydride grafted polyethylene are dried at 80-90 ℃ for 2-3 h; (2) functional masterbatch preparation, the KH550 silane-modified nano-Al2O3 / linear low-density polyethylene masterbatch with a content of 30% and the organic montmorillonite / low-density polyethylene masterbatch with a content of 20% are prepared respectively; (3) premixing of the mixture, the components are weighed according to the formula proportion, and are mixed at 700-900 r / min and 75-85 ℃ for 12-18 min; (4) ultra-purification melt blending, the premixed material is sent into a double-screw extruder, the extrusion temperature is 120-175 ℃, the screw rotation speed is 140-160 r / min, and the primary particles are extruded and granulated after being filtered through a 10 μm precision filter screen; (5) secondary purification and drying, the primary particles are dried at 90-110 ℃ and -0.09~-0.10 MPa for 2-4 h to obtain the finished product.

3. A process for the preparation of a DC cable insulation compound resistant to space charge accumulation according to claim 3, characterized in that: In the step (2), the KH550 silane-modified nano-Al2O3 masterbatch is prepared, the linear low-density polyethylene and the dried KH550 silane-modified nano-Al2O3 are weighed according to a mass ratio of 7:3, are added into a high-speed mixer, are mixed at 800-1000 r / min and 70-80 ℃ for 10-15 min, and then are sent into a double-screw extruder for extrusion and granulation, the extrusion temperature is set as zone 1 110-120 ℃, zone 2 130-140 ℃, zone 3 150-160 ℃ and zone 4 140-150 ℃, and the screw rotation speed is 180-220 r / min, so as to obtain the KH550 silane-modified nano-Al2O3 with a content of 30%.

4. A process for the preparation of a DC cable insulation compound resistant to space charge accumulation according to claim 3, characterized in that: In the step (2), the organic montmorillonite masterbatch is prepared, the low-density polyethylene and the dried organic montmorillonite are weighed according to a mass ratio of 8:2, are added into a high-speed mixer, are mixed at 800-1000 r / min and 70-80 ℃ for 10-15 min, and then are sent into a double-screw extruder for extrusion and granulation, the extrusion temperature is set as zone 1 110-120 ℃, zone 2 130-140 ℃, zone 3 150-160 ℃ and zone 4 140-150 ℃, and the screw rotation speed is 180-220 r / min, so as to obtain the organic montmorillonite masterbatch with a content of 20%.

5. A process for the preparation of a DC cable insulation compound resistant to space charge accumulation according to claim 3, characterized in that: The step (3) in the formula proportion weighing blending matrix resin, KH550 silane modified nano Al2O3 masterbatch and organic montmorillonite masterbatch, organic modifier, maleic anhydride grafted polyethylene, dicumyl peroxide, triallyl isocyanurate, antioxidant 1010, antioxidant 168 and calcium stearate, into the high speed mixer, 700-900r / min, 75-85℃ conditions mixing 12-18min, get premix.

6. A process for the preparation of a DC cable insulation compound resistant to space charge accumulation according to claim 3, characterized in that: The premix is fed into a double screw extruder with static mixer in step (4) for super purification melt blending, the extrusion temperature is set to 120-130°C in zone 1, 140-150°C in zone 2, 160-170°C in zone 3, and 170-175°C in the die head, the screw rotation speed is 140-160 r / min, and the shear rate is 300-500 s －1 After the material is filtered through a 10 μm precision filter screen, it is extruded and granulated to obtain primary insulating material particles.

7. ±110kV-±500kV DC cable characterized in that: using the DC cable insulation material of anti-space charge accumulation of claims 1-2, prepared by the preparation method of claims 3-7; wherein, using three-layer co-extrusion process, the extrusion temperature of insulation layer is 170-175℃, the pressure is 15-20Mpa, the pulling speed is 4-6m / min, the crosslinking temperature is 175-185℃, the steam pressure is 0.8-1.0MPa, the crosslinking time is 15-20min, the cooling is adopted by subsection cooling, the water temperature is 60-70℃, 40-50℃, 25-30℃ in turn.