Polyethylene insulating material, its preparation method, and high-voltage DC cable

Abstract

This application relates to the technical field of cables, specifically to polyethylene insulating materials and their preparation methods, and high-voltage DC cables. The polyethylene insulating material provided in this application comprises the following raw materials for preparation: 70 parts to 100 parts of a polyethylene matrix, 0.1 part to 30 parts of a graft masterbatch, 1 part to 2 parts of a crosslinking agent, and an oxidation inhibitor; the raw materials for preparing the graft masterbatch include a polyethylene resin, a graft monomer, and an antioxidant, and the graft monomer comprises one or more of the compounds having the structure shown in formula (I). The polyethylene insulating material provided in this application has both a relatively high breakdown strength and a relatively low conductivity.

Description

Technical Field

[0001] The present application relates to the field of cable technology, and in particular to polyethylene insulating materials and preparation methods thereof, and high-voltage direct current cables. Background Art

[0002] High-voltage direct current transmission has the advantages of low loss and long transmission distance, and has become the main mode of large-scale, long-distance, and cross-regional power transmission. In recent years, extruded insulated cables have become key equipment for high-voltage direct current transmission. Among them, cross-linked polyethylene (XLPE) is widely used as the main insulation material of extruded cables due to its excellent electrical insulation properties, thermomechanical properties, and extrusion processing properties.

[0003] However, under the long-term operation conditions of high-voltage DC cables, space charge injection will occur in the cross-linked polyethylene, resulting in serious local electric field distortion in the insulation, which shortens the service life of the cable. At present, in order to suppress electric field distortion and improve insulation performance, related technologies add inorganic nanoparticles to the cross-linked polyethylene insulation to suppress space charge injection. However, since most inorganic nanoparticles are incompatible with the resin matrix, they are very likely to agglomerate in the resin matrix, causing the breakdown strength of the insulation material to be greatly reduced, thereby limiting the application of polyethylene insulation materials in high-voltage DC cables. Summary of the invention

[0004] Based on this, the present application provides a polyethylene insulation material and a preparation method thereof, and a high-voltage DC cable. The polyethylene insulation material provided in the present application has both high breakdown strength and low electrical conductivity.

[0005] In a first aspect of the present application, a polyethylene insulating material is provided, which comprises the following raw materials, measured by weight:

[0006] Polyethylene matrix 70~100 parts,

[0007] Graft masterbatch 0.1~30 parts,

[0008] 1~2 parts of cross-linking agent and oxidation inhibitor;

[0009] The raw materials for preparing the graft masterbatch include polyethylene resin, graft monomer and antioxidant, and the graft monomer includes one or more of the compounds having the structure shown in formula (I):

[0010] ;

[0011] Among them, R 11 and R 14 are each independently selected from hydrogen, C 1 ~C 10 alkyl, , or , and R11 and R 14 at least one of which is , or ; each occurrence of m is independently any integer from 0 to 10;

[0012] R 12 and R 13 are each independently selected from a single bond or C 1 ~C 10 alkylene;

[0013] Y is each independently selected from or ;

[0014] L 1 and L 2 are each independently selected from a single bond, O, or ; and L 1 and L 2 are not both single bonds at the same time.

[0015] In one embodiment, Y is selected from ;

[0016] R 12 is selected from a single bond or C 1 ~C 3 alkylene, R 13 is selected from C 1 ~C 3 alkylene;

[0017] L 1 is selected from a single bond or ; L 2 is selected from ;

[0018] R 11 is selected from hydrogen, or ; R 14 is selected from or ; each occurrence of m is independently any integer from 0 to 10.

[0019] In one embodiment, the graft monomer includes , , , , , , and one or more of them.

[0020] In one embodiment, the polyethylene resin has one or more of the following characteristics:

[0021] (1) The weight-average molecular weight of the polyethylene resin is 120,000 to 150,000;

[0022] (2) The number-average molecular weight of the polyethylene resin is 20,000 to 40,000;

[0023] (3) The ratio of the weight-average molecular weight to the number-average molecular weight of the polyethylene resin is 3 to 7.5.

[0024] In one embodiment, the mass ratio of the polyethylene resin to the graft monomer is 100:(0.1 to 10).

[0025] In one embodiment, the raw materials for preparing the graft masterbatch further include an initiator, and the initiator has one or more of the following characteristics:

[0026] (1) The mass ratio of the polyethylene resin to the initiator is 100:(0.1 to 0.3);

[0027] (2) The initiator includes one or more of dicumyl peroxide, benzoyl peroxide, and di-tert-butyl peroxide.

[0028] In one embodiment, the antioxidant has one or more of the following characteristics:

[0029] (1) The mass ratio of the polyethylene resin to the antioxidant is 100:(0.1 to 0.3);

[0030] (2) The antioxidant includes hindered phenol antioxidants with a melting point of 10°C to 100°C.

[0031] In one embodiment, the polyethylene insulating material has one or more of the following characteristics:

[0032] (1) The weight-average molecular weight of the polyethylene matrix is 120,000 to 150,000;

[0033] (2) The number-average molecular weight of the polyethylene matrix is 20,000 to 40,000;

[0034] (3) The ratio of the weight-average molecular weight to the number-average molecular weight of the polyethylene matrix is 3 to 7.5;

[0035] (4) The crosslinking agent includes one or more of dicumyl peroxide, 1,4-bis(tert-butylperoxyisopropyl)benzene, and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane.

[0036] In one embodiment, the oxidation inhibitor includes a hindered phenol oxidation inhibitor with a melting point of 10°C to 100°C.

[0037] In a second aspect of the present application, there is provided a method for preparing the polyethylene insulating material according to any one of the embodiments of the first aspect of the present application, including the following steps:

[0038] Mix the polyethylene resin and the antioxidant to prepare an intermediate material;

[0039] Melt-blend the intermediate material, the graft monomer and the initiator, and after extrusion, prepare the graft masterbatch;

[0040] Mix the graft masterbatch, the polyethylene matrix and the oxidation inhibitor to prepare a precursor of the insulating material;

[0041] Perform a first mixing treatment on the crosslinking agent and the precursor of the insulating material at 70°C to 75°C, perform a second mixing treatment at 60°C to 70°C, perform a third heat preservation treatment at 70°C to 80°C, and after cooling, prepare the polyethylene insulating material.

[0042] In one embodiment, the preparation method has one or more of the following characteristics:

[0043] (1) The process parameters for mixing the polyethylene resin and the antioxidant include: a mixing temperature of 125°C to 130°C and a rotation speed of 100 r / min to 250 r / min;

[0044] (2) The process parameters for the melt-blending include: a temperature of 125°C to 130°C;

[0045] (3) The process parameters for the extrusion include: an extrusion temperature of 110°C to 120°C;

[0046] (4) The process parameters for mixing the graft masterbatch, the polyethylene matrix and the oxidation inhibitor include: a mixing temperature of 125°C to 130°C and a rotation speed of 100 r / min to 250 r / min;

[0047] (5) The step of performing a first mixing treatment on the crosslinking agent and the precursor of the insulating material at 70°C to 75°C includes: melting the crosslinking agent at 70°C to 75°C, passing it through a sieve, and then performing a first mixing treatment with the precursor of the insulating material at 70°C to 75°C.

[0048] In a third aspect of the present application, there is provided a high-voltage DC cable including the polyethylene insulating material according to any one of the embodiments of the first aspect of the present application.

[0049] The polyethylene insulating material provided by the present application has at least the following advantages:

[0050] This application uses a graft monomer with an unsaturated hydrocarbon group, which can be bonded to the polyethylene resin through a graft reaction. The graft monomer is a five - or six - membered ring compound with an ether bond, a carbonyl group or an ester group. The cyclic structure of the five - or six - membered ring included in the graft monomer restricts the free rotation of the graft masterbatch, and the introduction of the cyclic structure reduces the internal defects of the material, which helps to improve the heat resistance, creep resistance and crack resistance of the graft masterbatch. In addition, the introduction of the above - mentioned polar groups and the bonded graft monomers can enhance the compatibility between the polyethylene resin and other components, making it have excellent and stable uniform dispersion and migration - resistance properties. At the same time, the presence of polar groups can improve the dielectric properties of the polyethylene material. By promoting the movement of charges or introducing trap energy levels to capture electrons, the accumulation of space charges is reduced, and the conduction current of the material is lowered; the cyclic structure efficiently absorbs and consumes the energy of high - energy electrons, and the two cooperate with each other to improve the breakdown strength of the material, making it have excellent insulation properties.

[0051] In addition, the above - mentioned graft masterbatch, in cooperation with components such as the polyethylene matrix and cross - linking agent, can effectively improve the dispersion performance of the graft masterbatch, enhance its compatibility with other insulating material components, and the trap energy levels introduced by the graft monomer are beneficial to capturing electrons, reducing the conduction current of the material, and thus improving the insulation properties of the material. Description of the Drawings

[0052] Figure 1 It is the infrared spectrum diagram of Preparation Example 1 of this application;

[0053] Figure 2 It is the infrared spectrum diagram of Preparation Example 2 of this application;

[0054] Figure 3 It is the infrared spectrum diagram of Preparation Example 3 of this application;

[0055] Figure 4 It is the infrared spectrum diagram of Preparation Example 4 of this application;

[0056] Figure 5 It is the infrared spectrum diagram of Preparation Example 5 of this application. Detailed Embodiments

[0057] The following further describes the polyethylene insulating material of this application, its preparation method and the high - voltage DC cable in a more complete and clear manner with specific embodiments. This application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosed content of this application more thorough and comprehensive.

[0058] In this application, "substituted" means that the hydrogen atom in the substituent is replaced by the substituent.

[0059] In the present application, an "unsaturated hydrocarbon group" refers to a hydrocarbon group containing a double bond or a triple bond. It can be an alkenyl group having one double bond, or it can be a group such as a diene group or a triene group having two or more double bonds. It can be an alkynyl group having one triple bond, or it can be a group such as a diynyl group having two or more triple bonds. It can be linear or branched. The "C 2 ~C 10 unsaturated hydrocarbon group" means that the number of carbon atoms constituting the unsaturated hydrocarbon group is 2 to 10, and each time it appears, the number of carbon atoms can independently be 2, 3, 4, 5, 6, 7, 8, 9, or 10. Among them, as a linear unsaturated hydrocarbon group having one double bond in the hydrocarbon group, suitable examples include, but are not limited to: vinyl, propenyl, butenyl, pentenyl, etc. As a branched unsaturated hydrocarbon group having one double bond in the hydrocarbon group, suitable examples include, but are not limited to: propenyl, etc.

[0060] The term "alkyl group" refers to a monovalent residue formed by removing one hydrogen atom from a saturated hydrocarbon containing primary (normal) carbon atoms, or secondary carbon atoms, or tertiary carbon atoms, or quaternary carbon atoms, or a combination thereof. A phrase containing this term, for example, "C 1 ~C 10 alkyl group" means a linear or branched alkyl group containing 1 to 10 carbon atoms, and each time it appears, it can independently be C 1 alkyl group, C 2 alkyl group, C 3 alkyl group, C 4 alkyl group, C 5 alkyl group, C 6 alkyl group, C 7 alkyl group, C 8 alkyl group, C 9 alkyl group or C 10 alkyl group. Suitable examples include, but are not limited to: methyl (Me, -CH 3 ), ethyl (Et, -CH 2 CH 3 ), 1-propyl (n-Pr, n-propyl, -CH 2 CH 2 CH 3 ), 2-propyl (i-Pr, i-propyl, -CH(CH 3 ) 2 ), 1-butyl (n-Bu, n-butyl, -CH 2 CH 2 CH 2 CH 3 ), 2-methyl-1-propyl (i-Bu, i-butyl, -CH 2 CH(CH 3 ) 2 ), 2-butyl (s-Bu, s-butyl, -CH(CH3 ) CH 2 CH 3 )、2-methyl-2-propyl (t-Bu, t-butyl, -C(CH 3 )) 3 )、1-pentyl (n-pentyl, -CH 2 CH 2 CH 2 CH 2 CH 3 )、2-pentyl (-CH(CH 3 ))CH 2 CH 2 CH 3 )、3-pentyl (-CH(CH 2 CH 3 )) 2 )、2-methyl-2-butyl (-C(CH 3 )) 2 CH 2 CH 3 )、3-methyl-2-butyl (-CH(CH 3 ))CH(CH 3 )) 2 )、3-methyl-1-butyl (-CH 2 CH 2 CH(CH 3 )) 2 )、2-methyl-1-butyl (-CH 2 CH(CH 3 ))CH 2 CH 3 )、1-hexyl (-CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 ))、2-hexyl (-CH(CH 3 ))CH 2 CH 2 CH 2 CH 3 ))、3-hexyl (-CH(CH 2 CH 3 )(CH 2 CH 2 CH 3 ))、2-methyl-2-pentyl (-C(CH 3 )) 2 CH 2 CH 2 CH 3 )、3-methyl-2-pentyl (-CH(CH 3 ))CH(CH3 ) CH 2 CH 3 )、4-Methyl-2-pentyl (-CH(CH 3 ) CH 2 CH(CH 3 ) 2 )、3-Methyl-3-pentyl (-C(CH 3 )(CH 2 CH 3 ) 2 )、2-Methyl-3-pentyl (-CH(CH 2 CH 3 ) CH(CH 3 ) 2 )、2,3-Dimethyl-2-butyl (-C(CH 3 ) 2 CH(CH 3 ) 2 )、3,3-Dimethyl-2-butyl (-CH(CH 3 ) C(CH 3 ) 3 and octyl (-(CH 2 ) 7 CH 3 ).

[0061] "Alkylene" refers to a hydrocarbon group derived by removing one hydrogen atom from an alkyl group, having two monovalent group centers, which can be a saturated branched-chain alkyl group or a saturated straight-chain alkyl group. For example, "C 1 ~C 10 alkylene" means that the alkyl part contains 1 to 10 carbon atoms, and each occurrence can independently be C 1 alkylene, C 4 alkylene, C 5 alkylene, C 6 alkylene, C 7 alkylene, C 8 alkylene, C 9 alkylene, C 10 alkylene. Suitable examples include but are not limited to: methylene (-CH 2 -), 1,1-ethyl (-CH(CH 3 ))-, 1,2-ethyl (-CH 2 CH 2 -), 1,1-propyl (-CH(CH 2 CH 3 ))-, 1,2-propyl (-CH 2 CH(CH 3 ))-, 1,3-propyl (-CH 2 CH2 CH 2 -), and 1,4-butylene (-CH 2 CH 2 CH 2 CH 2 -).

[0062] "Cycloalkyl" refers to a non-aromatic hydrocarbon containing ring carbon atoms, which can be a monocyclic alkyl group, a spirocyclic alkyl group, or a bridged cyclic alkyl group. A phrase containing this term, for example, "C 3 ~C 10 cycloalkyl" refers to a cycloalkyl group containing 3 to 10 carbon atoms, and each occurrence can independently be a C 3 cycloalkyl, C 4 cycloalkyl, C 5 cycloalkyl, C 6 cycloalkyl, C 7 cycloalkyl, C 8 cycloalkyl, C 9 cycloalkyl or C 10 cycloalkyl. Suitable examples include, but are not limited to: cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cycloheptyl. In addition, "cycloalkyl" may also contain one or more double bonds, and representative examples of cycloalkyl groups containing double bonds include cyclopentenyl, cyclohexenyl, cyclohexadienyl, and cyclobutadienyl.

[0063] "Haloalkyl" refers to an alkyl group substituted by one or more halogen (chlorine, fluorine, bromine, or iodine) atoms. Polyhaloalkyl groups have the same or mixed types of halogen atoms. "Perhaloalkyl" refers to an alkyl group in which each hydrogen atom is replaced by a halogen atom. A haloalkyl group in which a particular carbon atom is "fully halogenated" means that all hydrogen atoms attached to that carbon are replaced by halogen atoms. Representative mono-, di-, and trihaloalkyl groups include: chloromethyl, chloroethyl, bromomethyl, bromoethyl, iodomethyl, iodoethyl, chloropropyl, bromopropyl, iodopropyl, 1,1-dichloromethyl, 1,1-dibromomethyl, 1,1-dichloropropyl, 1,2-dibromopropyl, 2,3-dibromopropyl, 1-chloro-2-bromoethyl, 2-chloro-3-bromopropyl, trifluoromethyl, trichloromethyl, etc.

[0064] "Subhaloalkyl" refers to an alkyl group formed by removing one hydrogen atom from "haloalkyl" to form an alkyl group with two monovalent group centers. Suitable examples include, but are not limited to: -CH(Cl)-, -C(Cl)(CH 3 ), -, -CH 2 CH(Cl)-, -C(Cl)(CH 2 CH 3 ), -, -CH 2 C(Cl)(CH 3 ), -, -CH 2 CH2 CH(Cl)- and -CH 2 CH 2 CH 2 CH(Cl)-。

[0065] "Unsaturated hydrocarbon group" means a group containing at least one unsaturated moiety, i.e., "alkenyl" or "alkynyl". Among them, "alkenyl" means a hydrocarbon containing a primary, secondary or tertiary carbon atom with a carbon-carbon sp 2 double bond. "Alkynyl" means a hydrocarbon containing a primary, secondary, tertiary or ring carbon atom with a carbon-carbon sp triple bond. Phrases containing this term, for example, "C 2 ~C 10 unsaturated hydrocarbon group" means an alkenyl or alkynyl group containing 2 to 10 carbon atoms. Each occurrence can be independently an alkenyl group of C 2 alkenyl, C 3 alkenyl, C 4 alkenyl, C 5 alkenyl, C 6 alkenyl, C 7 alkenyl, C 8 alkenyl, C 9 alkenyl, C 10 alkenyl, C 2 alkynyl, C 3 alkynyl, C 4 alkynyl, C 5 alkynyl, C 6 alkynyl, C 7 alkynyl, C 8 alkynyl, C 9 alkynyl, C 10 alkynyl. Suitable examples include, but are not limited to: vinyl (-CH=CH 2 ), allyl (-CH 2 CH=CH 2 ), cyclopentenyl (-C 5 H 7 ), and 5-hexenyl (-CH 2 CH 2 CH 2 CH 2 CH=CH 2 ), ethynyl (-C≡CH) and propargyl (-CH 2 C≡CH).

[0066] In this application, "*" represents the connection site or the fusion site. In this application, when the connection site is not specified in the group, it means that any optional connection site in the group can be used as the connection site; in this application, when the fusion site is not specified in the group, it means that any optional fusion site in the group can be used as the fusion site, and preferably two or more sites adjacent to each other in the group are the fusion sites.

[0067] In the present application, when the connection site is not specified in a group, it means that any optional connection site in the group can be used as the connection site.

[0068] In the present application, the single bond to which a substituent is attached passes through the corresponding ring, indicating that the substituent can be attached to any optional position of the ring. For example in which R is attached to any substitutable site of the benzene ring.

[0069] In the present application, "halogen" or "halo group" means -F, -Cl, -Br or -I.

[0070] In the present application, , when R 13 is selected from a single bond, it means .

[0071] Most of the currently used extruded insulated plastic cables are cross-linked polyethylene insulated cables, which are widely used in AC power transmission. However, under long-term operation conditions of high-voltage DC, space charge accumulation is likely to occur inside the cross-linked polyethylene insulating medium, resulting in electric field distortion in the medium, reducing its insulation performance, and even causing insulation breakdown. Therefore, suppressing space charge accumulation has become a key technical problem to be solved urgently for the development of high-voltage XLPE DC cables to higher voltage levels.

[0072] Based on this, the present application uses a graft monomer with a specific structure to carry out a graft reaction with polyethylene to modify the polyethylene resin. The graft groups formed on the surface of the polyethylene resin can improve the compatibility between components and reduce internal defects of the material. At the same time, the graft monomer introduces deep traps to inhibit the injection of space charges, so as to reduce the carrier mobility, making the material have a high breakdown strength and a low conductivity.

[0073] In the first aspect of the present application, there is provided a polyethylene insulating material, which, by weight, comprises the following preparation raw materials:

[0074] 70 parts to 100 parts of a polyethylene matrix,

[0075] 0.1 part to 30 parts of a graft masterbatch,

[0076] 1 part to 2 parts of a cross-linking agent, and an oxidation inhibitor.

[0077] The preparation raw materials of the graft masterbatch include a polyethylene resin, a graft monomer and an antioxidant, and the graft monomer includes one or more of the compounds having the structure shown in formula (I):

[0078]

[0079] wherein, R 11 and R 14Each independently selected from hydrogen, C 1 ~C 10 alkyl, , or , and at least one of R 11 and R 14 is , or ; Each time m appears, it is independently any integer from 0 to 10. By way of example, m is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0080] R 11 and R 14 Non-limiting examples include but are not limited to: H, -CH=CH 2 , -CH 2 CH=CH 2 or -CH 2 CH 2 CH=CH 2 .

[0081] Wherein, R 12 and R 13 Each independently selected from a single bond or C 1 ~C 10 alkylene.

[0082] R 12 and R 13 Non-limiting examples include but are not limited to: single bond, -CH 2 -, -CH 2 CH 2 -, -CH 2 CH 2 CH 2 -, -C(CH 3 ) 2 -, -CH 2 CH 2 CH 2 CH 2 -, -CH 2 C(CH 3 ) 2 -, -CH(CH 3 )CH 2 CH 2 - or -C(CH 3 ) 2 -.

[0083] Y is each independently selected from or .

[0084] Wherein, L 1 and L2 Each independently selected from a single bond, O, or ; and L 1 and L 2 are not simultaneously a single bond.

[0085] This application uses a graft monomer with an unsaturated hydrocarbon group, which can be bonded to the polyethylene resin through a graft reaction. The graft monomer is a five-membered or six-membered ring compound with an ether bond, a carbonyl group, or an ester group. The cyclic structure of the five-membered or six-membered ring included in the graft monomer restricts the free rotation of the modified polyethylene material, and the introduction of the cyclic structure reduces internal defects in the material, which helps to improve the heat resistance, creep resistance, and anti-cracking ability of the modified polyethylene material. In addition, the introduction of the above polar groups and the bonded graft monomers can enhance the compatibility of the polyethylene resin with other components, making it have excellent and stable uniform dispersion and migration resistance properties. At the same time, the presence of polar groups can improve the dielectric properties of the polyethylene material. By promoting the movement of charges or introducing trap energy levels to capture electrons, the accumulation of space charges is reduced, and the conduction current of the material is lowered; the cyclic structure efficiently absorbs and consumes the energy of high-energy electrons, and the two work together synergistically to improve the breakdown strength of the material, making it have excellent insulation properties.

[0086] In addition, the above graft masterbatch, synergistically with components such as the polyethylene matrix and the crosslinking agent, can effectively improve the dispersion performance of the graft masterbatch, enhance its compatibility with other insulating material components, and the trap energy levels introduced by the graft monomer are beneficial for capturing electrons and reducing the conduction current of the material, thereby improving the insulation properties of the material.

[0087] It can be understood that the weight fraction of the polyethylene matrix can be selected from any value between 70 parts and 100 parts. Further, the weight fraction of the polyethylene matrix includes but is not limited to 70 parts, 75 parts, 80 parts, 85 parts, 90 parts, 95 parts, or 100 parts. The weight fraction of the graft masterbatch can be selected from any value between 0.1 part and 30 parts. Further, the weight fraction of the graft masterbatch includes but is not limited to 0.1 part, 0.5 part, 0.8 part, 1 part, 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, or 30 parts. The weight fraction of the crosslinking agent can be selected from any value between 1 part and 2 parts. Further, the weight fraction of the crosslinking agent includes but is not limited to 1 part, 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts, or 2 parts.

[0088] In one example, Y is selected from . R 12 is selected from a single bond or C 1 ~C 3 alkylene. R 13 is selected from C 1 ~C 3 alkylene. L1 Selected from a single bond or . L 2 Selected from . R 11 Selected from hydrogen, or . R 14 Selected from or . Each time m appears, it is independently any integer from 0 to 10. The oxygen atom in the tetrahydrofuran group can form a hydrogen bond with a hydrogen bond donor in other components, thereby improving the dispersibility, helping the graft masterbatch to form a more stable interface with other components, and being beneficial to ensuring that the polyethylene insulating material has both a high breakdown strength and a low conductivity.

[0089] In one example, the graft monomer includes , , , , , , and one or more of them. The above graft monomers containing aromatic groups and tetrahydrofuran groups and containing ether bonds, carbonyl groups and ester groups have high polarity, and the polar groups can reduce the interfacial tension and help the grafted polyethylene to form a more stable interface with other polar materials.

[0090] In one example, the graft monomer includes one or more of the following compounds:

[0091] Compound 1: R 11 is H; L 1 is a single bond; R 12 is a single bond; Y is ; R 13 is -CH 2 -; L 2 is O; R 14 is ; m is 0.

[0092] Compound 2: R 11 is H; L 1 is a single bond; R 12 is a single bond; Y is ; R 13 is a single bond; L 2 is ; R 14 is ; m is 0.

[0093] Compound 3: R 11 is H, L 1 is a single bond; R 12 is a single bond; Y is ; R 13 is a single bond; L 2 is ; R 14 is ; m is 0.

[0094] Compound 4: R 11 is , m is 0; L 1 is a single bond; R 12 is a single bond; Y is ; R 13 is a single bond; L 2 is ; R 14 is methyl.

[0095] Compound 5: R 11 is H; L 1 is a single bond; R 12 is a single bond; Y is ; R 13 is -CH 2 -; L 2 is ; R 14 is ; m correspondingly is 0.

[0096] Exemplarily, Compound 1 is . Compound 2 is . Compound 3 is . Compound 4 is . Compound 5 is .

[0097] In one example, the weight-average molecular weight of the polyethylene resin is 120,000 - 150,000. The weight-average molecular weight of the polyethylene resin includes but is not limited to: 120,000, 130,000, 140,000, or 150,000; or within the range formed by any two of the above point values as the end values.

[0098] In one example, the number-average molecular weight of the polyethylene resin is 20,000 - 40,000. The number-average molecular weight of the polyethylene resin includes but is not limited to: 20,000, 25,000, 28,000, 30,000, 31,000, 33,000, 35,000, 36,000, 38,000, or 40,000; or within the range formed by any two of the above point values as the end values.

[0099] In one example, the ratio of the weight-average molecular weight to the number-average molecular weight of the polyethylene resin is 3 to 7.5. Exemplarily, the ratio of the weight-average molecular weight to the number-average molecular weight of the polyethylene resin includes, but is not limited to, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, or 7.5; or within the range formed by any two of the above point values as the end values.

[0100] The ratio of the weight-average molecular weight to the number-average molecular weight represents the molecular weight distribution (PDI) of the polyethylene resin. It can be understood that PDI = the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of the polyethylene resin. In this application, the ratio of the weight-average molecular weight to the number-average molecular weight of the polyethylene resin is limited to 3 to 5, which indicates that the polyethylene resin group has a relatively narrow molecular weight distribution, as well as a relatively high weight-average molecular weight and number-average molecular weight. The polyethylene resin that meets the above conditions can provide more reaction sites, which helps to improve the reaction efficiency between the graft monomer and the polyethylene main chain.

[0101] Limiting the mass ratio of the polyethylene resin to the graft monomer plays an important role in ensuring the degree of the graft reaction, the performance of the graft reaction, and the cost-effectiveness of the product. In one example, the mass ratio of the polyethylene resin to the graft monomer is 100:(0.1 to 10). Specifically, the mass ratio of the polyethylene resin to the graft monomer includes, but is not limited to, 100:0.1, 100:0.5, 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, or 100:10; or within the range formed by any two of the above point values as the end values.

[0102] In one example, the raw materials for preparing the graft masterbatch further include an initiator, and the mass ratio of the polyethylene resin to the initiator is 100:(0.1 to 0.3).

[0103] The initiator decomposes to generate free radicals, which can capture the unsaturated bonds in the graft monomer and initiate the chemical reaction between the graft monomer and the polyethylene resin. Limiting the mass ratio of the polyethylene resin to the initiator can avoid insufficient initiation of the reaction caused by a slightly lower amount of the initiator, or side reactions such as unnecessary chain transfer that may be caused by a slightly higher amount of the initiator. Further, the mass ratio of the polyethylene resin to the initiator includes, but is not limited to, 100:0.1, 100:0.15, 100:0.2, 100:0.25, or 100:0.3; or within the range formed by any two of the above point values as the end values.

[0104] In one example, the initiator includes diisopropylbenzene peroxide ( ), benzoyl peroxide ( ), and di-tert-butyl peroxide ( one or more of the following.

[0105] In one example, the raw materials for preparing the graft masterbatch, by weight parts, include the following components:

[0106] 100 parts of polyethylene resin,

[0107] 0.1 part to 0.3 part of initiator,

[0108] 0.1 part to 1 part of graft monomer, and antioxidant.

[0109] It can be understood that the weight parts of the initiator can be selected from any value between 0.1 part and 0.3 part. The weight parts of the initiator include but are not limited to 0.1 part, 0.13 part, 0.15 part, 0.18 part, 0.2 part, 0.23 part, 0.25 part, 0.28 part or 0.3 part; or within the range formed by any two of the above point values as the end values. The weight parts of the graft monomer include but are not limited to 0.1 part, 0.2 part, 0.3 part, 0.4 part, 0.5 part, 0.6 part, 0.7 part, 0.8 part, 0.9 part or 1 part; or within the range formed by any two of the above point values as the end values.

[0110] In one example, the mass ratio of the polyethylene resin to the antioxidant is 100:(0.1 - 0.3).

[0111] In one example, the raw materials for preparing the graft masterbatch, by weight parts, include the following components:

[0112] 100 parts of polyethylene resin,

[0113] 0.1 part to 0.3 part of initiator,

[0114] 0.1 part to 1 part of graft monomer, and

[0115] 0.1 part to 0.3 part of antioxidant.

[0116] Understandably, the weight parts of the initiator can be selected from any value between 0.1 part and 0.3 part. The weight parts of the initiator include but are not limited to 0.1 part, 0.13 part, 0.15 part, 0.18 part, 0.2 part, 0.23 part, 0.25 part, 0.28 part, or 0.3 part; or within the range formed by any two of the above point values as the end values. The weight parts of the graft monomer include but are not limited to 0.1 part, 0.2 part, 0.3 part, 0.4 part, 0.5 part, 0.6 part, 0.7 part, 0.8 part, 0.9 part, or 1 part; or within the range formed by any two of the above point values as the end values. The weight parts of the antioxidant include but are not limited to 0.1 part, 0.13 part, 0.15 part, 0.18 part, 0.2 part, 0.23 part, 0.25 part, 0.28 part, or 0.3 part; or within the range formed by any two of the above point values as the end values.

[0117] In one example, the antioxidant includes a hindered phenol antioxidant with a melting point of 10°C to 100°C. Exemplarily, the melting point of the hindered phenol antioxidant included in the antioxidant includes but is not limited to 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C.

[0118] Further, the antioxidant includes isooctyl 3,5-di-tert-butyl-4-hydroxyphenylpropionate (antioxidant 1135) , n-octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and 2,4-bis(n-octylthiomethyl)-6-methylphenol and one or more of them.

[0119] In one example, the weight-average molecular weight of the polyethylene matrix is 120,000 to 150,000. The weight-average molecular weight of the polyethylene matrix includes but is not limited to: 120,000, 130,000, 140,000, or 150,000; or within the range formed by any two of the above point values as the end values.

[0120] In one example, the number-average molecular weight of the polyethylene matrix is 20,000 to 40,000. The number-average molecular weight of the polyethylene matrix includes but is not limited to: 20,000, 25,000, 28,000, 30,000, 31,000, 33,000, 35,000, 36,000, 38,000, or 40,000; or within the range formed by any two of the above point values as the end values.

[0121] In one example, the ratio of the weight-average molecular weight to the number-average molecular weight of the polyethylene matrix is 3 to 7.5. Exemplarily, the ratio of the weight-average molecular weight to the number-average molecular weight of the polyethylene matrix includes, but is not limited to, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, or 7.5; or within the range formed by any two of the above point values as the end values. Selecting a polyethylene resin with properties similar to those in the graft masterbatch for the polyethylene matrix can further enhance the compatibility between the graft masterbatch and the polyethylene matrix.

[0122] In one example, the crosslinking agent includes dicumyl peroxide ( ), 1,4-bis(tert-butylperoxyisopropyl)benzene ( ), and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane ( ), or one or more of them.

[0123] In one example, the oxidation inhibitor includes a hindered phenol oxidation inhibitor with a melting point of 10°C to 100°C. Exemplarily, the melting point of the hindered phenol antioxidant included in the oxidation inhibitor includes, but is not limited to, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C.

[0124] The oxidation inhibitor includes isooctyl 3,5-di-tert-butyl-4-hydroxybenzenepropionate (antioxidant 1135) , n-octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate , and 2,4-bis(n-octylthiomethylene)-6-methylphenol , or one or more of them.

[0125] In one example, based on parts by weight, the oxidation inhibitor is 0.1 part to 0.3 part. The parts by weight of the oxidation inhibitor include, but are not limited to, 0.1 part, 0.13 part, 0.15 part, 0.18 part, 0.2 part, 0.23 part, 0.25 part, 0.28 part, or 0.3 part.

[0126] Furthermore, the polyethylene insulating material, based on parts by weight, includes the following preparation raw materials:

[0127] 70 parts to 100 parts of polyethylene matrix,

[0128] 0.1 part to 30 parts of graft masterbatch,

[0129] 1 part to 2 parts of crosslinking agent, and

[0130] 0.1 part to 0.3 part of oxidation inhibitor.

[0131] In the second aspect of the present application, a method for preparing a polyethylene insulating material is provided, comprising the following steps:

[0132] S10. Mix the polyethylene resin and the antioxidant to prepare an intermediate material.

[0133] S20. Melt-blend the intermediate material, the graft monomer and the initiator, and after extrusion, prepare the graft masterbatch.

[0134] S30. Mix the graft masterbatch, the polyethylene matrix and the oxidation inhibitor to prepare a precursor of the insulating material.

[0135] S40. Perform a first mixing treatment on the crosslinking agent and the precursor of the insulating material at 70°C to 75°C, a second mixing treatment at 60°C to 70°C, and a third heat preservation treatment at 70°C to 80°C. After cooling, prepare the polyethylene insulating material.

[0136] In one example, in step S10, the process parameters for mixing the polyethylene resin and the antioxidant include: the mixing temperature is 125°C to 130°C, and the rotation speed is 100 r / min to 250 r / min. Exemplarily, the mixing temperature includes but is not limited to 125°C, 126°C, 127°C, 128°C, 129°C or 130°C. The rotation speed includes but is not limited to 100 r / min, 120 r / min, 140 r / min, 160 r / min, 180 r / min, 200 r / min, 220 r / min, 240 r / min or 250 r / min.

[0137] In one example, in step S20, the process parameters for the melt-blending include: the temperature is 125°C to 130°C;

[0138] In one example, in step S20, the process parameters for the extrusion include: the extrusion temperature is 110°C to 120°C.

[0139] The method for preparing the graft masterbatch provided by the present application can further control the graft reaction process, prevent excessive crosslinking of free radicals or graft monomers, reduce the occurrence of micro-crosslinking side reactions, and avoid gel impurities generated by excessive crosslinking, so as to improve the performance of the modified polyethylene material.

[0140] In one example, in step S30, the process parameters for mixing the graft masterbatch, the polyethylene matrix, and the oxidation inhibitor include: the mixing temperature is 125°C to 130°C, and the rotation speed is 100 r / min to 250 r / min. Exemplarily, the mixing temperature includes but is not limited to 125°C, 126°C, 127°C, 128°C, 129°C, or 130°C. The rotation speed includes but is not limited to 100 r / min, 120 r / min, 140 r / min, 160 r / min, 180 r / min, 200 r / min, 220 r / min, 240 r / min, or 250 r / min.

[0141] In one example, in step S40, the step of performing the first mixing treatment on the crosslinking agent and the insulation material precursor at 70°C to 75°C includes: melting the crosslinking agent at 70°C to 75°C, and after sieving, performing the first mixing treatment with the insulation material precursor at 70°C to 75°C. Further, the method for preparing the polyethylene insulation material includes the following steps:

[0142] b1. Mix the polyethylene matrix, the graft masterbatch, and the oxidation inhibitor to prepare an insulation material precursor;

[0143] b2. Melt the crosslinking agent at 70°C to 75°C, and after sieving, perform the first mixing treatment with the insulation material precursor at 70°C to 75°C to prepare a first mixture;

[0144] b3. Perform a second mixing treatment on the first mixture at 60°C to 70°C to prepare a second mixture;

[0145] b4. Perform a third heat preservation treatment on the second mixture at 65°C to 75°C, and after cooling, prepare the polyethylene insulation material.

[0146] In step b2, pre-melting and dispersing the crosslinking agent is beneficial to removing impurities and improving the crosslinking effect. In step b2, the temperature for performing the first mixing treatment can be selected from any value between 70°C and 75°C. Further, the temperature for the first mixing treatment includes but is not limited to 70°C, 71°C, 72°C, 73°C, 74°C, or 75°C. Additionally, the process parameters for the first mixing treatment further include: the mixing rotation speed is 10 rpm to 20 rpm, and the mixing time is 5 min to 10 min. Exemplarily, the device for performing the first mixing treatment in step b2 is a mixing tank.

[0147] In step b2, the sieving step includes: sieving out impurities through a filter screen. Among them, the mesh number of the filter screen is 300 mesh to 500 mesh.

[0148] In step b3, the temperature for the second mixing treatment can be selected from any value between 60°C and 70°C. Further, the temperature for the second mixing treatment includes but is not limited to 60°C, 62°C, 64°C, 66°C, 68°C, or 70°C. Additionally, the process parameters for the second mixing treatment further include: the mixing rotation speed is 30 rpm to 60 rpm, and the mixing time is 50 min to 60 min. By way of example, the device for performing the second mixing treatment in step b3 is a shaking tank.

[0149] In step b4, the temperature for the third heat preservation treatment can be selected from any value between 65°C and 75°C. Further, the temperature for the third heat preservation treatment includes but is not limited to 65°C, 67°C, 69°C, 70°C, 72°C, or 75°C. Additionally, the process parameters for the third heat preservation treatment further include: the heat preservation time is 16 h to 24 h. By way of example, the device for performing the third heat preservation treatment in step b4 is a heat preservation tank.

[0150] In the third aspect of the present application, a high-voltage DC cable is provided, including the polyethylene insulating material described in any of the examples of the first aspect of the present application.

[0151] In one example, the high-voltage DC cable is of the 500 kV voltage class.

[0152] The following further specific embodiments are used to illustrate the present application in detail. It should be understood that the following embodiments are only used to further illustrate the present application and cannot be construed as limiting the protection scope of the present application. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present application fall within the protection scope of the present application. The specific process parameters and the like in the following embodiments are also only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, and do not necessarily have to be limited to the specific values in the following embodiments.

[0153] [Graft monomer]

[0154] A1: ; (Vinyloxymethyl)benzene; commercially available, CAS: 935-04-6, purchased from: Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0155] A2: ; Phenyl acrylate; commercially available, CAS: 937-41-7, purchased from: Beijing Huanling Technology Co., Ltd.;

[0156] A3: ; Phenyl methacrylate; commercially available, CAS: 2177-70-0, purchased from: Beijing Huanling Technology Co., Ltd.;

[0157] A4: ; 1-(4-vinyl-phenyl)-ethanone; commercially available, CAS: 10537-63-0, purchased from: Shanghai Huayuan Century Trading Co., Ltd.;

[0158] A5: ; tetrahydrofurfuryl acrylate; commercially available, CAS: 2399-48-6, purchased from: Shanghai Jiji Biochemical Technology Co., Ltd.

[0159] Preparation Examples 1 to 7

[0160] The raw materials for preparing the graft masterbatch include: 100 parts of polyethylene resin (weight average molecular weight of 120,000 to 150,000, number average molecular weight of 20,000 to 40,000, ratio of weight average molecular weight to number average molecular weight of 3 to 7.5), 0.2 parts of initiator (dicumyl peroxide), 0.5 parts of graft monomer, and 0.2 parts of antioxidant (isooctyl 3,5-di-tert-butyl-4-hydroxybenzenepropionate); among them, the structures and component contents of the graft monomers used in Preparation Examples 1 to 7 are shown in Table 1.

[0161] The preparation method of the graft masterbatch includes the following steps: (1) Add the polyethylene resin and the antioxidant to a twin-screw extruder, and after extrusion, granulation, and cooling (wherein, the extrusion temperature in the melting zone is 130 °C, the screw speed is 200 r / min, and the cooling method is water cooling), and obtain an intermediate material after drying. (2) Add the intermediate material, graft monomer, and initiator to a kneader (kneading temperature is 130 °C, kneading time is 3 to 5 min), and after single-screw extrusion, granulation, cooling (extrusion temperature is 120 °C, cooling method is water cooling), and drying, obtain the graft masterbatch.

[0162] Among them, the infrared spectra of the graft masterbatches of Preparation Examples 1 to 5 are as Figures 1 to 5 shown. Figure 1 At 1264 cm -1 and 1039 cm -1 The stretching vibration peak of C-O-C in (vinyloxymethyl)benzene can be observed, but the presence of chain-end C=C is not found, indicating that (vinyloxymethyl)benzene has been grafted onto the polyethylene chain. Figure 2 At 1225 cm -1 and 1029 cm -1 are the stretching vibration peaks of C-O-C in phenyl acrylate, and 1732 cm -1 is the characteristic peak of C=O, indicating that after being initiated by the crosslinking agent, phenyl acrylate has been grafted onto the polyethylene chain. Figure 3 At 1198 cm -1 and 1032 cm -1 are the stretching vibration peaks of C-O-C in phenyl methacrylate, and 1740 cm -1The characteristic peak at C=O indicates that phenyl methacrylate has been successfully grafted onto the polyethylene chain. Figure 4 At 1700 cm -1 The characteristic peak at C=O in 1-(4-vinyl-phenyl)-ethanone is at 1262 cm -1 The stretching vibration peak of C-O in the carbonyl group indicates that 1-(4-vinyl-phenyl)-ethanone has been successfully grafted onto the polyethylene chain. Figure 5 At 1264 cm in -1 And 1026 cm -1 The stretching vibration peak of C-O-C in the main chain of tetrahydrofuran acrylate is at 1701 cm -1 The characteristic peak at C=O is at 1098 cm -1 And 897 cm -1 The stretching vibration peak of C-O-C in the furan ring indicates that tetrahydrofuran acrylate has been grafted onto the polyethylene chain.

[0163] Examples 1 to 7

[0164] The raw materials for preparing the polyethylene insulating material include: 90 parts of a polyethylene matrix (weight average molecular weight of 120,000 to 150,000, number average molecular weight of 20,000 to 40,000, and the ratio of weight average molecular weight to number average molecular weight is 3 to 7.5), 20 parts of a graft masterbatch, 1.5 parts of a crosslinking agent (1,4-bis(tert-butylperoxyisopropyl)benzene (BIPB)), and 0.2 parts of an oxidation inhibitor (isooctyl 3,5-di-tert-butyl-4-hydroxybenzenepropionate); among them, the selection of the graft masterbatch and the weight parts of each component in Examples 1 to 7 are shown in Table 2.

[0165] The preparation method of the polyethylene insulating material includes the following steps: (1) melt-blending the polyethylene matrix, the graft masterbatch, and the oxidation inhibitor to prepare a precursor of the insulating material; (2) melting the crosslinking agent at 73 °C, filtering out impurities through a filter screen, and then performing a first mixing treatment with the precursor of the insulating material in a mixing tank at a temperature of 75 °C and a rotation speed of 20 rpm for 10 min to prepare a first mixture; (3) performing a second mixing treatment on the first mixture in a shaking tank at a temperature of 65 °C and a rotation speed of 50 rpm for 60 min to prepare a second mixture; (4) performing a third heat preservation treatment on the second mixture in a heat preservation tank at 75 °C for 24 h, and after cooling, preparing the polyethylene insulating material.

[0166] Comparative Example 1

[0167] The raw materials for preparing the polyethylene insulating material include: 90 parts of a polyethylene matrix (weight-average molecular weight of 120,000 - 150,000, number-average molecular weight of 20,000 - 40,000, and the ratio of weight-average molecular weight to number-average molecular weight is 3 - 7.5), 1.5 parts of a cross-linking agent (1,4-bis(tert-butylperoxyisopropyl)benzene (BIPB)), and 0.2 parts of an oxidation inhibitor (isooctyl 3,5-di-tert-butyl-4-hydroxybenzenepropionate). The weight parts of each component in Comparative Example 1 are shown in Table 2.

[0168] The preparation method of the polyethylene insulating material comprises the following steps: (1) melt-blending the polyethylene matrix and the oxidation inhibitor to prepare a precursor of the insulating material; (2) melting the cross-linking agent at 73°C, filtering out impurities through a filter screen, and then performing a first mixing treatment for 10 min in a mixing tank with the precursor of the insulating material at a temperature of 75°C and a rotation speed of 20 rpm to prepare a first mixture; (3) performing a second mixing treatment for 60 min in a shaking tank with the first mixture at a temperature of 65°C and a rotation speed of 50 rpm to prepare a second mixture; (4) performing a third heat preservation treatment for 24 h on the second mixture in a heat preservation tank at 75°C, and after cooling, preparing the polyethylene insulating material.

[0169] Performance testing:

[0170] (1) Measurement of the conductivity of the insulating material:

[0171] The measurement of the conduction current is carried out by using a picoammeter and a standard two-electrode test system. The sample thickness is (200 ± 10) µm. Before testing, the sample is short-circuited in an oven at 50 o °C for more than 24 h. The sample is placed between the upper and lower electrodes of the test system, and then short-circuited at room temperature for about 30 min until the short-circuit current on the picoammeter decays to less than 0.02 A. Under a certain temperature condition, the electric field strength starts from 10 kV / mm, increases in steps of 10 kV / mm until it reaches 30 kV / mm, and the ammeter data is read.

[0172] (2) Space charge test (electric field distortion rate) of the insulating material:

[0173] The space charge test is carried out by the electroacoustic pulse method (PEA). The sample thickness is (200 ± 10) µm. Before testing, the sample is short-circuited in an oven at 50 o °C for more than 24 h. The test temperature is 70°C and the electric field strength is 30 kV / mm. By analyzing the acoustic wave signal, the charge distribution and the information of the electric field strength distortion in the material are obtained.

[0174] (3) Dielectric withstand performance test of the film sample

[0175] The withstand voltage test uses a high-voltage DC generator. The electrode system is a spherical electrode with a diameter of 15 mm, and the electrode material is stainless steel. The thickness of the test piece is (0.2 ± 0.01) mm. The test is carried out in an oven, and silicone oil is used as the environmental medium to prevent flashover breakdown. The breakdown is carried out by continuously increasing the voltage, and 12 data points are tested for each formulation. The DC breakdown field strength is obtained by the ratio of the breakdown voltage to the thickness of the specimen, and its statistical data is analyzed using the Weibull distribution. The test results of the above performance tests are shown in Table 3.

[0176] Table 1

[0177]

[0178] Table 2

[0179]

[0180] Table 3

[0181]

[0182] From the comparison between the above-mentioned examples and comparative examples, it can be seen that Examples 1 to 5 are basically the same, and the main difference is that different graft masterbatches are selected. Among them, the DC conductivities of the insulating materials prepared in Examples 1 to 5 are similar at 25 °C and 70 °C, indicating that they all have excellent insulation performance. However, from the perspective of the field strength distortion rate and the breakdown field strength, the insulating material in Example 5 has a lower field strength distortion rate and a higher breakdown field strength, which indicates that the insulating material in Example 5 has more excellent electrical properties. Examples 5 to 7 are basically the same, and the main difference is that: the addition amounts of the graft masterbatch in Examples 5 to 7 are different. In Example 5, the weight fraction of the added graft masterbatch is 5 parts, and its technical effect is more excellent than that of other Examples 6 and 7.

[0183] The technical features of the above-mentioned embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as the combinations of these technical features do not conflict, they should all be considered as the scope recorded in this specification.

[0184] The above-described embodiments merely represent several implementation manners of the present application, which are convenient for understanding the technical solution of the present application specifically and in detail. However, it should not be construed as a limitation on the protection scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several deformations and improvements can be made, and these all belong to the protection scope of the present application. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solution provided by the present application are all within the protection scope of the appended claims of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the content of the appended claims, and the specification can be used to explain the content of the claims.

Claims

1. A polyethylene insulating material, characterized in that: The preparation includes the following raw materials in parts by weight: Polyethylene matrix 70~100 parts, Graft masterbatch 0.1~30 parts, 1~2 parts of cross-linking agent and oxidation inhibitor; The raw materials for preparing the graft masterbatch include polyethylene resin, graft monomer and antioxidant, and the graft monomer includes at least , , , and One or more of .

2. The polyethylene insulation material according to claim 1, characterized in that: The grafted monomer also includes , ,and One or more of .

3. The polyethylene insulation material according to claim 1, characterized in that: The polyethylene resin has one or more of the following characteristics: (1) The weight average molecular weight of the polyethylene resin is 120,000 to 150,000; (2) The number average molecular weight of the polyethylene resin is 20,000 to 40,000; (3) The ratio of the weight average molecular weight to the number average molecular weight of the polyethylene resin is 3 to 7.

5.

4. The polyethylene insulating material according to any one of claims 1 to 3, characterized in that: The mass ratio of the polyethylene resin to the grafting monomer is 100:(0.1-10).

5. The polyethylene insulation material according to claim 4, characterized in that: The raw materials for preparing the graft masterbatch also include an initiator, and the initiator has one or more of the following characteristics: (1) The mass ratio of the polyethylene resin to the initiator is 100:(0.1-0.3); (2) The initiator includes one or more of dicumyl peroxide, benzoyl peroxide and di-tert-butyl peroxide.

6. The polyethylene insulating material according to any one of claims 1 to 3, characterized in that: The antioxidant has one or more of the following characteristics: (1) The mass ratio of the polyethylene resin to the antioxidant is 100:(0.1-0.3); (2) The antioxidant includes a hindered phenol antioxidant having a melting point of 10°C to 100°C.

7. The polyethylene insulating material according to any one of claims 1 to 3, characterized in that: The polyethylene insulation material has one or more of the following characteristics: (1) The weight average molecular weight of the polyethylene matrix is ​​120,000 to 150,000; (2) The number average molecular weight of the polyethylene matrix is ​​20,000 to 40,000; (3) The ratio of the weight average molecular weight to the number average molecular weight of the polyethylene matrix is ​​3 to 7.5; (4) The crosslinking agent includes one or more of dicumyl peroxide, 1,4-di-tert-butylperoxyisopropylbenzene and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

8. The polyethylene insulating material according to any one of claims 1 to 3, characterized in that: The oxidation inhibitor includes a hindered phenol oxidation inhibitor having a melting point of 10° C. to 100° C.

9. A method for preparing the polyethylene insulating material according to any one of claims 1 to 8, characterized in that: The following steps are involved: Mixing the polyethylene resin and the antioxidant to prepare an intermediate material; The intermediate material, the grafting monomer and the initiator are melt-blended and extruded to prepare the grafting masterbatch; Mixing the graft masterbatch, the polyethylene matrix and the oxidation inhibitor to prepare an insulation material precursor; The cross-linking agent and the insulating material precursor are subjected to a first mixing treatment at 70° C. to 75° C., a second mixing treatment at 60° C. to 70° C., a third heat preservation treatment at 70° C. to 80° C., and after cooling, the polyethylene insulating material is prepared.

10. The method for preparing polyethylene insulation material according to claim 9, characterized in that: The preparation method has one or more of the following characteristics: (1) The process parameters for mixing the polyethylene resin and the antioxidant include: a mixing temperature of 125° C. to 130° C. and a rotation speed of 100 r / min to 250 r / min; (2) The process parameters of the melt blending include: a temperature of 125°C to 130°C; (3) The extrusion process parameters include: extrusion temperature of 110°C to 120°C; (4) The process parameters for mixing the graft masterbatch, the polyethylene matrix and the oxidation inhibitor include: a mixing temperature of 125° C. to 130° C. and a rotation speed of 100 r / min to 250 r / min; (5) The step of subjecting the cross-linking agent and the insulating material precursor to a first mixing treatment at 70° C. to 75° C. comprises: melting the cross-linking agent at 70° C. to 75° C., sieving the cross-linking agent, and subjecting the cross-linking agent to a first mixing treatment with the insulating material precursor at 70° C. to 75° C.

11. A high voltage DC cable, characterized in that: The invention comprises the polyethylene insulating material as described in any one of claims 1 to 8.

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