Polyethylene insulating material, preparation method thereof and high-voltage direct-current cable

Abstract

The invention relates to the technical field of cables, in particular to a polyethylene insulating material, a preparation method thereof and a high-voltage direct-current cable. The polyethylene insulation material provided by the invention is prepared from the following preparation raw materials: 70 to 100 parts of polyethylene matrix, 0.1 to 30 parts of grafting master batch, 1 to 2 parts of cross-linking agent and oxidation inhibitor, the grafting master batch is prepared from the following raw materials: polyethylene resin, a grafting monomer and an antioxidant, wherein the grafting monomer comprises one or more of compounds with a structure as shown in a formula (I). The polyethylene insulating material provided by the invention has relatively high breakdown strength and 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 Each independently selected from hydrogen, C1~C 10 alkyl, , or , and R 11and R 14 At least one of , or ; Each time m appears, it is independently any integer from 0 to 10;

[0012] R 12 and R 13 Each independently selected from a single bond or C1~C 10 Alkylene;

[0013] Y is each independently selected from or ;

[0014] L1 and L2 are each independently selected from a single bond, O, or ; and L1 and L2 are not single bonds at the same time.

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

[0016] R 12 Selected from a single bond or C1~C3 alkylene, R 13 Selected from C1~C3 alkylene;

[0017] L1 is selected from a single bond or ; L2 is selected from ;

[0018] R 11 Selected from hydrogen, or ; R 14 Selected from or ; Each time m appears, it is independently any integer from 0 to 10.

[0019] In one embodiment, the grafting monomer comprises , , , , , , and One or more of .

[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 of the embodiments, the mass ratio of the polyethylene resin to the grafting monomer is 100:(0.1~10).

[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:(0.1-0.3);

[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:(0.1-0.3);

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

[0031] In one embodiment, the polyethylene insulation 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-di-tert-butylperoxyisopropylbenzene and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

[0036] In one embodiment, the oxidation inhibitor comprises a hindered phenol oxidation inhibitor having 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 insulation material according to any one of the embodiments of the first aspect of the present application, comprising the following steps:

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

[0039] The intermediate material, the grafting monomer and the initiator are melt-blended and extruded to prepare the grafting masterbatch;

[0040] Mixing the graft masterbatch, the polyethylene matrix and the oxidation inhibitor to prepare an insulation material precursor;

[0041] 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.

[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 of the melt blending include: a temperature of 125°C to 130°C;

[0045] (3) The extrusion process parameters include: 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 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.

[0048] A third aspect of the present application provides a high-voltage DC cable, comprising the polyethylene insulation material described in any one of the embodiments of the first aspect of the present application.

[0049] The polyethylene insulation material provided in this application has at least the following advantages:

[0050] The present application adopts a grafting monomer with an unsaturated hydrocarbon group, which can be bonded to the polyethylene resin through a grafting reaction, and the grafting monomer is a five-membered ring or six-membered ring compound with an ether bond, a carbonyl group or an ester group. The ring structure of the five-membered ring or six-membered ring included in the grafting monomer restricts the free rotation of the grafted masterbatch, and the introduction of the ring structure reduces the internal defects of the material, which helps to improve the heat resistance, creep resistance and cracking resistance of the grafted masterbatch. In addition, the introduction of the above-mentioned polar groups and the bonded grafting monomers can enhance the compatibility of the polyethylene resin with other components, so that it has excellent and stable uniform dispersion and migration and precipitation resistance. At the same time, the presence of polar groups can improve the dielectric properties of polyethylene materials, by promoting the movement of charges or introducing trap energy levels to capture electrons, reducing the accumulation of space charges, and reducing the electrical conductivity of the material; the ring structure efficiently absorbs and consumes high-energy electron energy, and the two work together to improve the breakdown strength of the material, so that it has excellent insulation properties.

[0051] In addition, the above-mentioned graft masterbatch, with the cooperation of components such as the polyethylene matrix and the cross-linking agent, can effectively improve the dispersion performance of the graft masterbatch and enhance its compatibility with other insulating material components. The trap energy levels introduced by the grafted monomer are conducive to capturing electrons and reducing the conductive current of the material, thereby improving the insulating performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

[0056] Figure 5 This is the infrared spectrum of Preparation Example 5 of this application. DETAILED DESCRIPTION

[0057] The following is a further complete and clear description of the polyethylene insulation material and its preparation method and the high-voltage DC cable of the present application in conjunction with specific embodiments. The present 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 disclosure of the present application more thorough and comprehensive.

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

[0059] In the present application, "unsaturated hydrocarbon group" refers to a hydrocarbon group containing double bonds or triple bonds. It can be an alkenyl group with one double bond, or a dienyl group or a trienyl group with two or more double bonds. It can be an alkynyl group with one triple bond, or a dialkynyl group with two or more triple bonds. It can be straight-chain or branched. 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 may be 2, 3, 4, 5, 6, 7, 8, 9 or 10 independently of each other. Among them, as a straight-chain 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" refers to a monovalent residue formed by the loss of a hydrogen atom from a saturated hydrocarbon containing a primary (normal) carbon atom, a secondary carbon atom, a tertiary carbon atom, a quaternary carbon atom, or a combination thereof. Phrases containing this term, such as "C1~C 10 "Alkyl" refers to a straight or branched chain alkyl group containing 1 to 10 carbon atoms, and each occurrence can be independently C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, C9 alkyl or C 10Alkyl. Suitable examples include, but are not limited to, methyl (Me, -CH3), ethyl (Et, -CH2CH3), 1-propyl (n-Pr, n-propyl, -CH2CH2CH3), 2-propyl (i-Pr, i-propyl, -CH(CH3)2), 1-butyl (n-Bu, n-butyl, -CH2CH2CH2CH3), 2-methyl-1-propyl (i-Bu, i-butyl, -CH2CH(CH3)2), 2-butyl (s-Bu, s-butyl, -CH(C H3)CH2CH3), 2-methyl-2-propyl (t-Bu, t-butyl, -C(CH3)3), 1-pentyl (n-pentyl, -CH2CH2CH2CH2CH3), 2-pentyl (-CH(CH3)CH2CH2CH3), 3-pentyl (-CH(CH2CH3)2), 2-methyl-2-butyl (-C(CH3)2CH2CH3), 3-methyl-2-butyl (-CH(CH3)CH(CH3)2), 3-methyl-1-butyl (- CH2CH2CH(CH3)2), 2-methyl-1-butyl (-CH2CH(CH3)CH2CH3), 1-hexyl (-CH2CH2CH2CH2CH2CH3), 2-hexyl (-CH(CH3)CH2CH2CH2CH3), 3-hexyl (-CH(CH2CH3)(CH2CH2CH3)), 2-methyl-2-pentyl (-C(CH3)2CH2CH2CH3), 3-methyl-2-pentyl (-CH(CH3)CH( 2), 2-methyl-3-pentyl (-CH(CH2CH3)CH(CH3)2), 2,3-dimethyl-2-butyl (-C(CH3)2CH(CH3)2), 3,3-dimethyl-2-butyl (-CH(CH3)C(CH3)3 and octyl (-(CH2)7CH3).

[0061] "Alkylene" refers to a hydrocarbon group with two monovalent radical centers derived from an alkyl group by removing a hydrogen atom, which can be a saturated branched alkyl group or a saturated straight chain alkyl group. 10 "Alkylene" means that the alkyl portion contains 1 to 10 carbon atoms, and each occurrence can be independently C1 alkylene, C4 alkylene, C5 alkylene, C6 alkylene, C7 alkylene, C8 alkylene, C9 alkylene, C 10Alkylene. Suitable examples include, but are not limited to, methylene (—CH2—), 1,1-ethyl (—CH(CH3)—), 1,2-ethyl (—CH2CH2—), 1,1-propyl (—CH(CH2CH3)—), 1,2-propyl (—CH2CH(CH3)—), 1,3-propyl (—CH2CH2CH2—), and 1,4-butyl (—CH2CH2CH2CH2—).

[0062] "Cycloalkyl" refers to a non-aromatic hydrocarbon containing ring carbon atoms, which can be a monocyclic alkyl, a spirocyclic alkyl, or a bridged cycloalkyl. Phrases containing this term, such as "C3~C 10 "Cycloalkyl" refers to a cycloalkyl group containing 3 to 10 carbon atoms, and each occurrence can be independently C3 cycloalkyl, C4 cycloalkyl, C5 cycloalkyl, C6 cycloalkyl, C7 cycloalkyl, C8 cycloalkyl, C9 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 containing double bonds include cyclopentenyl, cyclohexenyl, cyclohexadienyl, and cyclobutadienyl.

[0063] "Haloalkyl" refers to an alkyl group substituted with 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 that is "fully halogenated" at a particular carbon atom 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, and the like.

[0064] "Haloalkylene" refers to an alkyl group having two monovalent radical centers derived from a "haloalkyl" group by removing a hydrogen atom. Suitable examples include, but are not limited to, -CH(Cl)-, -C(Cl)(CH3)-, -CH2CH(Cl)-, -C(Cl)(CH2CH3)-, -CH2C(Cl)(CH3)-, -CH2CH2CH(Cl)-, and -CH2CH2CH2CH(Cl)-.

[0065] "Unsaturated hydrocarbon group" refers to a hydrocarbon group having at least one unsaturated site, i.e., an alkenyl group or an alkynyl group. Among them, an alkenyl group refers to a hydrocarbon group containing a carbon-carbon sp 2"Alkynyl" refers to a hydrocarbon containing a positive, secondary, tertiary, or cyclic carbon atom with a carbon-carbon sp triple bond. Phrases containing this term, such as "C2~C 10 The term "unsaturated hydrocarbon group" refers to an alkenyl or alkynyl group comprising 2 to 10 carbon atoms. Each occurrence may be independently C2 alkenyl, C3 alkenyl, C4 alkenyl, C5 alkenyl, C6 alkenyl, C7 alkenyl, C8 alkenyl, C9 alkenyl, C 10 alkenyl, C2 alkynyl, C3 alkynyl, C4 alkynyl, C5 alkynyl, C6 alkynyl, C7 alkynyl, C8 alkynyl, C9 alkynyl, C 10 Suitable examples include, but are not limited to, vinyl (-CH=CH2), allyl (-CH2CH=CH2), cyclopentenyl (-C5H7) and 5-hexenyl (-CH2CH2CH2CH2CH=CH2), ethynyl (-C≡CH) and propargyl (-CH2C≡CH).

[0066] In the present application, "*" indicates a connection site or a fusion site. In the present application, when a connection site is not specified in a group, it indicates that an optional connection site in the group is used as a connection site; in the present application, when a fusion site is not specified in a group, it indicates that an optional fusion site in the group is used as a fusion site, and preferably two or more sites in the ortho position in the group are fusion sites.

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

[0068] In the present application, the single bond to which the substituent is connected runs through the corresponding ring, indicating that the substituent can be connected to any position of the ring, for example R is connected to any substitutable position of the benzene ring.

[0069] As used herein, "halogen" or "halo" refers to -F, -Cl, -Br or -I.

[0070] In this application, , R 13 When selected from single bonds, express .

[0071] The vast majority of extruded insulated plastic cables currently used are cross-linked polyethylene insulated cables, which are widely used in AC power transmission. However, under long-term high-voltage DC operating conditions, space charge accumulation is prone to occur inside the cross-linked polyethylene insulation medium, which leads to electric field distortion in the medium, reduces its insulation performance, and even causes insulation breakdown. Therefore, suppressing space charge accumulation has become a key technical issue that needs to be solved in the development of high-voltage XLPE DC cables to higher voltage levels.

[0072] Based on this, the present application adopts a grafting monomer with a specific structure to undergo a grafting reaction with polyethylene to modify the polyethylene resin. The grafting group formed on the surface of the polyethylene resin can improve the compatibility between the components and reduce internal defects in the material. At the same time, the grafting monomer introduces deep traps, inhibits the injection of space charges, thereby reducing carrier mobility and enabling the material to have higher breakdown strength and lower electrical conductivity.

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

[0074] Polyethylene matrix 70~100 parts,

[0075] Graft masterbatch 0.1~30 parts,

[0076] 1~2 parts of cross-linking agent and oxidation inhibitor.

[0077] 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):

[0078]

[0079] Among them, R 11 and R 14 Each independently selected from hydrogen, C1~C 10 alkyl, , or , and R 11 and R 14 At least one of , or ; m, when it appears each time, is independently any integer from 0 to 10. For example, m is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0080] R 11 and R 14 Non-limiting examples of include, but are not limited to, H, -CH=CH2, -CH2CH=CH2, or -CH2CH2CH=CH2.

[0081] Among them, R 12 and R 13 Each independently selected from a single bond or C1~C 10 Alkylene.

[0082] R 12 and R 13Non-limiting examples include, but are not limited to, a single bond, -CH2-, -CH2CH2-, -CH2CH2CH2-, -C(CH3)2-, -CH2CH2CH2CH2-, -CH2C(CH3)2-, -CH(CH3)CH2CH2-, or -C(CH3)2-.

[0083] Y is each independently selected from or .

[0084] Wherein, L1 and L2 are each independently selected from a single bond, O, or ; and L1 and L2 are not single bonds at the same time.

[0085] The present application adopts a grafting monomer with an unsaturated hydrocarbon group, which can be bonded to the polyethylene resin through a grafting reaction, and the grafting monomer is a five-membered ring or six-membered ring compound with an ether bond, a carbonyl group or an ester group. The ring structure of the five-membered ring or six-membered ring included in the grafting monomer restricts the free rotation of the modified polyethylene material, and the introduction of the ring structure reduces the internal defects of the material, which helps to improve the heat resistance, creep resistance and cracking resistance of the modified polyethylene material. In addition, the introduction of the above-mentioned polar groups and the bonded grafting monomers can enhance the compatibility of the polyethylene resin with other components, so that it has excellent and stable uniform dispersion and migration and precipitation resistance. At the same time, the presence of polar groups can improve the dielectric properties of polyethylene materials, by promoting the movement of charges or introducing trap energy levels to capture electrons, reducing the accumulation of space charges, and reducing the electrical conductivity of the material; the ring structure efficiently absorbs and consumes high-energy electron energy, and the two work together to improve the breakdown strength of the material, so that it has excellent insulation properties.

[0086] In addition, the above-mentioned graft masterbatch, with the cooperation of components such as the polyethylene matrix and the cross-linking agent, can effectively improve the dispersion performance of the graft masterbatch and enhance its compatibility with other insulating material components. The trap energy levels introduced by the grafted monomer are conducive to capturing electrons and reducing the conductive current of the material, thereby improving the insulating performance of the material.

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

[0088] In one example, Y is selected from . R 12 is selected from a single bond or a C1~C3 alkylene group. 13 is selected from C1 to C3 alkylene. L1 is selected from a single bond or . L2 is 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 hydrogen bonds with hydrogen bond donors in other components, thereby improving the dispersibility, helping the grafted masterbatch to form a more stable interface with other components, and helping to ensure that the polyethylene insulation material has both high breakdown strength and low conductivity.

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

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

[0091] Compound 1: R 11 is H; L1 is a single bond; R 12 is a single bond; Y is ; R 13 is -CH2-; L2 is O; R14 for ; m is 0.

[0092] Compound 2: R 11 is H; L1 is a single bond; R 12 is a single bond; Y is ; R 13 is a single bond; L2 is ; R 14 for ; m is 0.

[0093] Compound 3: R 11 is H, L1 is a single bond; R 12 is a single bond; Y is ; R 13 is a single bond; L2 is ; R 14 for ; m is 0.

[0094] Compound 4: R 11 for , m is 0; L1 is a single bond; R 12 is a single bond; Y is ; R 13 is a single bond; L2 is ; R 14 It is methyl.

[0095] Compound 5: R 11 is H; L1 is a single bond; R 12 is a single bond; Y is ; R 13 is -CH2-; L2 is ; R 14 for ; m corresponds to 0.

[0096] For example, 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 120000-150000. The weight average molecular weight of the polyethylene resin includes but is not limited to: 120000, 130000, 140000, or 150000; or a range consisting of any two of the above values ​​as end values.

[0098] In one example, the number average molecular weight of the polyethylene resin is 20000-40000. The number average molecular weight of the polyethylene resin includes but is not limited to: 20000, 25000, 28000, 30000, 31000, 33000, 35000, 36000, 38000, or 40000; or a range formed by any two of the above point values ​​as 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. For example, 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 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. The present application defines the ratio of the weight average molecular weight to the number average molecular weight of the polyethylene resin as 3 to 5, which indicates that the polyethylene resin group has a narrower molecular weight distribution and a higher 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 grafted monomer and the polyethylene main chain.

[0101] Defining the mass ratio of polyethylene resin and grafting monomer plays an important role in ensuring the degree of grafting reaction, the performance of grafting reaction and the cost-effectiveness of the product. In one example, the mass ratio of the polyethylene resin and the grafting monomer is 100: (0.1~10). Specifically, the mass ratio of the polyethylene resin and the grafting 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 end values.

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

[0103] The initiator decomposes to produce free radicals, which can capture the unsaturated bonds in the grafted monomer and initiate a chemical reaction between the grafted monomer and the polyethylene resin. Limiting the mass ratio of the polyethylene resin to the initiator can avoid the failure to fully initiate the reaction due to a slightly low initiator, or unnecessary side reactions such as chain transfer caused by a slightly high initiator. Furthermore, 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 end values.

[0104] In one example, the initiator includes dicumyl peroxide ( )、Benzoyl peroxide( ) and di-tert-butyl peroxide ( )

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

[0106] 100 parts of polyethylene resin,

[0107] Initiator 0.1~0.3 parts,

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

[0109] It is understood that the weight fraction of the initiator can be selected from any value between 0.1 and 0.3. The weight fraction of the initiator includes, but is not limited to, 0.1, 0.13, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28 or 0.3; or any two of the above values ​​as end values. The weight fraction of the grafted monomer includes, but is not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1; or any two of the above values ​​as 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 include the following components in parts by weight:

[0112] 100 parts of polyethylene resin,

[0113] Initiator 0.1~0.3 parts,

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

[0115] Antioxidant 0.1~0.3 parts.

[0116] It is understandable that the weight fraction of the initiator can be selected from any value between 0.1 and 0.3 parts. The weight fraction of the initiator includes but is not limited to 0.1, 0.13, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28 or 0.3 parts; or any two of the above points are used as end values. The weight fraction of the grafted monomer includes but is not limited to 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1 part; or any two of the above points are used as end values. The weight fraction of the antioxidant includes but is not limited to 0.1, 0.13, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28 or 0.3 parts; or any two of the above points are used as end values.

[0117] In one example, the antioxidant includes a hindered phenol antioxidant having a melting point of 10° C. to 100° C. For example, 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] Furthermore, the antioxidant includes 3,5-di-tert-butyl-4-hydroxyphenylpropionate (antioxidant 1135) 、3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and 2,4-di(n-octylthiomethylene)-6-methylphenol One or more of .

[0119] In one example, the weight average molecular weight of the polyethylene matrix is ​​120000-150000. The weight average molecular weight of the polyethylene matrix includes but is not limited to: 120000, 130000, 140000, or 150000; or a range formed by any two of the above point values ​​as end values.

[0120] In one example, the number average molecular weight of the polyethylene matrix is ​​20000-40000. The number average molecular weight of the polyethylene matrix includes but is not limited to: 20000, 25000, 28000, 30000, 31000, 33000, 35000, 36000, 38000, or 40000; or a range formed by any two of the above point values ​​as 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. For example, 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 consisting of any two of the above point values ​​as end values. The polyethylene matrix is ​​selected to be a polyethylene resin with similar properties to the graft masterbatch, which can further enhance the compatibility between the graft masterbatch and the polyethylene matrix.

[0122] In one example, the cross-linking agent includes dicumyl peroxide ( )、1,4-di-tert-butylperoxyisopropylbenzene( ) and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane ( )

[0123] In one example, the oxidation inhibitor includes a hindered phenolic oxidation inhibitor having a melting point of 10° C. to 100° C. For example, the melting point of the hindered phenolic 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 3,5-di-tert-butyl-4-hydroxyphenylpropionate (antioxidant 1135) 、3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and 2,4-di(n-octylthiomethylene)-6-methylphenol One or more of .

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

[0126] Furthermore, the polyethylene insulating material comprises the following raw materials in parts by weight:

[0127] Polyethylene matrix 70~100 parts,

[0128] Graft masterbatch 0.1~30 parts,

[0129] 1~2 parts of cross-linking agent, and

[0130] Oxidation inhibitor 0.1~0.3 parts.

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

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

[0133] S20, melt-blending the intermediate material, the grafting monomer and the initiator, and extruding them to prepare the grafting masterbatch.

[0134] S30, mixing the graft masterbatch, the polyethylene matrix and the oxidation inhibitor to prepare an insulating material precursor.

[0135] S40, subjecting the cross-linking agent and the insulating material precursor to a first mixing treatment at 70°C-75°C, a second mixing treatment at 60°C-70°C, a third heat preservation treatment at 70°C-80°C, and cooling to prepare the polyethylene insulating material.

[0136] In one example, in step S10, 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. For example, 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 of the melt blending include: a temperature of 125°C to 130°C;

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

[0139] The preparation method of the grafting masterbatch provided in the present application can further control the grafting reaction process, prevent excessive cross-linking of free radicals or grafting monomers, reduce the occurrence of micro-cross-linking negative reactions, and avoid gel impurities generated by excessive cross-linking, 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: a mixing temperature of 125°C to 130°C and a rotation speed of 100 r / min to 250 r / min. For example, 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 a first mixing treatment of the crosslinking agent and the insulating material precursor at 70°C to 75°C includes: melting the crosslinking agent at 70°C to 75°C, sieving, and then performing a first mixing treatment with the insulating material precursor at 70°C to 75°C. Further, the preparation method of the polyethylene insulating material includes the following steps:

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

[0143] b2. Melting the cross-linking agent at 70° C. to 75° C., sieving, and mixing the cross-linking agent with the insulating material precursor at 70° C. to 75° C. to prepare a first mixed material;

[0144] b3, subjecting the first mixed material to a second mixing treatment at 60° C. to 70° C. to prepare a second mixed material;

[0145] b4. Subjecting the second mixed material to a third heat preservation treatment at 65° C. to 75° C., and cooling the mixed material to prepare the polyethylene insulating material.

[0146] In step b2, the cross-linking agent is pre-melted and dispersed, which is beneficial to remove impurities and improve the cross-linking effect. In step b2, the temperature for the first mixing treatment can be selected from any value between 70°C and 75°C. Furthermore, the temperature of the first mixing treatment includes but is not limited to 70°C, 71°C, 72°C, 73°C, 74°C or 75°C. In addition, the process parameters of the first mixing treatment also include: a mixing speed of 10rpm~20rpm, and a mixing time of 5min~10min. By way of example, the device for 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 mesh, wherein the filter mesh number is 300-500 meshes.

[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. In addition, the process parameters for the second mixing treatment also include: a mixing speed of 30rpm to 60rpm, and a mixing time of 50min to 60min. For example, the device for 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. In addition, the process parameters of the third heat preservation treatment also include: the heat preservation time is 16h~24h. For example, the device for the third heat preservation treatment in step b4 is a heat preservation tank.

[0150] A third aspect of the present application provides a high-voltage DC cable, comprising the polyethylene insulation material described in any example of the first aspect of the present application.

[0151] In one example, the high voltage DC cable has a voltage level of 500 kV.

[0152] The following further specific examples are provided to explain the present application in detail. It should also be understood that the following examples are only used to further explain the present application and cannot be understood as limiting the scope of protection 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 belong to the scope of protection of the present application. The specific process parameters of the following embodiments are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not necessarily limited to the specific values ​​of the embodiments below.

[0153] [Grafting 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: ; Tetrahydrofuran acrylate; Commercially available, CAS: 2399-48-6, purchased from: Shanghai Jizhi Biochemical Technology Co., Ltd.

[0159] Preparation Example 1 to Preparation Example 7

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

[0161] The preparation method of the graft masterbatch comprises the following steps: (1) adding the polyethylene resin and the antioxidant into a twin-screw extruder, extruding, granulating, 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 drying to obtain an intermediate material. (2) adding the intermediate material, the grafting monomer and the initiator into an internal mixer (mixing temperature is 130°C, mixing time is 3-5 min), extruding, granulating, cooling (extrusion temperature is 120°C, cooling method is water cooling), and drying to obtain a graft masterbatch.

[0162] Among them, the infrared spectra of the graft masterbatch of Preparation Example 1 to Preparation Example 5 are as follows Figure 1~Figure 5 shown. Figure 1 At 1264cm -1 With 1039cm -1 The stretching vibration peak of COC in (vinyloxymethyl)benzene can be observed, but the chain end C=C is not found, indicating that (vinyloxymethyl)benzene has been connected to the polyethylene chain. Figure 2 At 1225cm -1 With 1029cm -1 The stretching vibration peak of COC in phenyl acrylate is 1732 cm -1 The characteristic peak of C=O is shown at , indicating that phenyl acrylate has been connected to the polyethylene chain after initiation by the cross-linking agent. Figure 3 At 1198cm -1 With 1032cm -1 The stretching vibration peak of COC in phenyl methacrylate is 1740 cm -1The characteristic peak of C=O is shown at , indicating that phenyl methacrylate has been successfully connected to the polyethylene chain. Figure 4 Medium 1700cm -1 The characteristic peak of C=O in 1-(4-vinyl-phenyl)-ethanone is 1262cm -1 The peak at the center is the stretching vibration peak of CO in the carbonyl group, indicating that 1-(4-vinyl-phenyl)-ethanone has been successfully connected to the polyethylene chain. Figure 5 Medium 1264cm -1 With 1026cm -1 The stretching vibration peak of the main chain COC of tetrahydrofuran acrylate is 1701 cm -1 The characteristic peak of C=O is 1098cm -1 With 897cm -1 The peak at is the stretching vibration peak of the furan ring COC, indicating that tetrahydrofuran acrylate has been connected to the polyethylene chain.

[0163] Embodiment 1 to Embodiment 7

[0164] The raw materials for preparing polyethylene insulation material include: 90 parts of polyethylene matrix (weight average molecular weight of 120000-150000, number average molecular weight of 20000-40000, ratio of weight average molecular weight to number average molecular weight of 3-7.5), 20 parts of graft masterbatch, 1.5 parts of crosslinking agent (1,4-di-tert-butylperoxyisopropylbenzene (BIPB)), and 0.2 parts of oxidation inhibitor (3,5-di-tert-butyl-4-hydroxyphenylpropionate). The selection of graft masterbatch in Example 1 to Example 7 and the weight proportion of each component are shown in Table 2.

[0165] The preparation method of polyethylene insulation material comprises the following steps: (1) melt-blending the polyethylene matrix, the grafted masterbatch and the oxidation inhibitor to prepare an insulation material precursor; (2) melting the cross-linking agent at 73°C, filtering out impurities through a filter, and then mixing the cross-linking agent with the insulation material precursor in a mixing tank at a temperature of 75°C and a rotation speed of 20 rpm for 10 minutes to prepare a first mixture; (3) subjecting the first mixture to a second mixing treatment in a shaking tank at a temperature of 65°C and a rotation speed of 50 rpm for 60 minutes to prepare a second mixture; and (4) subjecting the second mixture to a third insulation treatment in an insulation tank at 75°C for 24 hours, and cooling the second mixture to prepare the polyethylene insulation material.

[0166] Comparative Example 1

[0167] The raw materials for preparing polyethylene insulation material include: 90 parts of polyethylene matrix (weight average molecular weight of 120000-150000, number average molecular weight of 20000-40000, ratio of weight average molecular weight to number average molecular weight of 3-7.5), 1.5 parts of crosslinking agent (1,4-di-tert-butyl peroxyisopropylbenzene (BIPB)), and 0.2 parts of oxidation inhibitor (3,5-di-tert-butyl-4-hydroxyphenylpropionate). The weight parts of each component in Comparative Example 1 are shown in Table 2.

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

[0169] Performance Testing:

[0170] (1) Determination of electrical conductivity of insulating materials:

[0171] Conductivity current was measured using a picoammeter and a standard two-electrode test system. The sample thickness was (200 ± 10) μm. o C oven for short circuit treatment for more than 24 hours, place the sample between the upper and lower electrodes of the test system, and then short circuit treatment for about 30 minutes at room temperature until the short circuit current on the picoammeter decays to less than 0.02 A. Under certain temperature conditions, the electric field strength starts from 10kV / mm and increases in steps of 10kV / mm until it reaches 30kV / mm, and the ammeter data is read.

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

[0173] The space charge test adopts the electroacoustic pulse method (PEA), the sample thickness is (200±10)μm, and the sample is placed at 50 o C in an oven for short circuit treatment, the treatment time is more than 24h, the test temperature is 70℃, and the electric field strength is 30kV / mm. By analyzing the acoustic wave signal, the charge distribution and electric field strength distortion information in the material are obtained.

[0174] (3) Pressure resistance test of film samples

[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 in a continuous boosting manner, and 12 data points are tested for each formula. The DC breakdown field strength is obtained by the ratio of the breakdown voltage to the sample thickness, 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 embodiments and the comparative examples, it can be seen that embodiments 1 to 5 are basically the same, and the main difference is that the selected grafting masterbatch is different. Among them, the DC conductivity of the insulating materials prepared in embodiments 1 to 5 at 25°C and 70°C is similar, indicating that they all have excellent insulation properties. However, from the perspective of field strength distortion rate and breakdown field strength, the insulating material in embodiment 5 has a lower field strength distortion rate and a higher breakdown field strength, which indicates that the insulating material in embodiment 5 has more excellent electrical properties. Embodiments 5 to 7 are basically the same, and the main difference is that the amount of grafting masterbatch added in embodiments 5 to 7 is different. In embodiment 5, the weight portion of the added grafting masterbatch is 5 parts, and its technical effect is better than that of other embodiments 6 and 7.

[0183] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0184] The above-described embodiments only express several implementation methods of the present application, which is convenient for understanding the technical solution of the present application in detail, but it cannot be understood as limiting the scope of protection of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the scope of protection 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 solutions provided in the present application are all within the scope of protection of the claims attached to the present application. Therefore, the scope of protection of the patent of this application shall be based on the content of the attached claims, and the description can be used to interpret 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 one or more of the compounds having the structure shown in formula (I): ； Among them, R 11 and R 14 Each independently selected from hydrogen, C1~C 10 alkyl, , or , and R 11 and R 14 At least one of , or ; Each time m appears, it is independently any integer from 0 to 10; R 12 and R 13 Each independently selected from a single bond or C1~C 10 Alkylene; Y is each independently selected from or ; L1 and L2 are each independently selected from a single bond, O, or ; and L1 and L2 are not single bonds at the same time.

2. The polyethylene insulation material according to claim 1, characterized in that: Y is selected from ; R 12 Selected from a single bond or C1~C3 alkylene, R 13 Selected from C1~C3 alkylene; L1 is selected from a single bond or ; L2 is 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.

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

4. The polyethylene insulating material according to any one of claims 1 to 3, 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.

5. 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).

6. The polyethylene insulation material according to claim 5, 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.

7. 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.

8. 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.

9. 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.

10. A method for preparing the polyethylene insulation material according to any one of claims 1 to 9, 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.

11. The method for preparing polyethylene insulation material according to claim 10, 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.

12. A high voltage DC cable, characterized in that: The invention comprises the polyethylene insulating material as described in any one of claims 1 to 9.

Images