Crosslinked copolymer microspheres and their preparation methods, crosslinkable polyethylene compositions, crosslinked polyethylene and its applications

Abstract

This invention relates to the field of vinyl copolymers, and discloses a crosslinked copolymer microsphere and its preparation method, a crosslinkable polyethylene composition, crosslinked polyethylene, and its applications. The crosslinked copolymer microsphere comprises structural unit A and structural unit B; wherein structural unit A has the structure shown in formula (1), and structural unit B is derived from a crosslinking agent; based on the total mass of the crosslinked copolymer microsphere, the content of structural unit A is 80-95 wt%, and the content of structural unit B is 5-20 wt%; formula (1). This copolymer microsphere contains polar structural units and crosslinked structural units, and has high electron affinity and surface double bond content.

Description

Technical Field

[0001] This invention relates to the field of vinyl copolymers, and more specifically to a crosslinked copolymer microsphere and its preparation method, a crosslinkable polyethylene composition, crosslinked polyethylene and its applications. Background Technology

[0002] Cross-linked polyethylene (XLPE) is currently the mainstream material for high-voltage cable insulation due to its excellent mechanical strength, processing performance, and dielectric stability. However, problems such as space charge accumulation, resistivity temperature sensitivity, and electric field distortion caused by cross-linking byproducts under high temperature and high field conditions limit its application in ultra-high voltage scenarios. The performance of insulation materials directly determines the transmission capacity, service life, and operational safety of cables. Therefore, developing high-performance XLPE insulation modification technology is key to breaking through the bottleneck of domestic production of high-voltage cables.

[0003] To obtain high-voltage XLPE materials, performance optimization can be achieved through three pathways: chemical grafting, inorganic nanofilling, and blending modification. Chemical grafting modification involves introducing polar molecules (such as maleic anhydride and aniline compounds) onto the XLPE molecular chain to construct a deep trap network that suppresses carrier transport. However, this typically involves using a crosslinking agent during vulcanization to simultaneously initiate crosslinking and grafting reactions, thereby grafting functional molecules onto the polyethylene molecular chain to improve the material's electrical properties. Crosslinking and grafting reactions are competitive; to ensure a certain degree of crosslinking, the amount of crosslinking agent in the reaction system needs to be increased. This leads to an increase in crosslinking byproducts, which in turn affects the material's electrical properties and is detrimental to high-voltage cable manufacturing. Inorganic nanofilling technology adds fillers such as nano-MgO and SiO2, utilizing the interfacial charge trapping effect to suppress space charge accumulation. However, nanoparticles are prone to agglomeration, clogging extrusion equipment filters, and have poor compatibility with the non-polar XLPE matrix. Blending modification often improves electrical dendrite resistance by adding benzophenone-based voltage stabilizers, but small molecule additives are prone to migration and loss, resulting in significant performance degradation after long-term operation. The phase separation problem in the blend system also leads to unstable dielectric properties.

[0004] While the aforementioned methods have achieved some success in specific scenarios, their common bottlenecks significantly restrict the application of XLPE in the ultra-high voltage field. First, byproducts such as acetic acid and aldehydes generated by traditional peroxide crosslinking processes form shallow traps, inducing space charge distortion and exacerbating carrier transport runaway. Second, organic small molecules or nanofillers lack chemical anchoring and migrate under long-term electric fields and temperatures, leading to performance degradation; the interfacial bonding between polar fillers and the non-polar XLPE matrix is ​​weak, making it difficult to control dispersion uniformity. These problems collectively make it difficult for existing modification methods to meet the stringent insulation reliability requirements of ultra-high voltage cables. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems existing in the prior art and provide a crosslinked copolymer microsphere and its preparation method, a crosslinkable polyethylene composition, crosslinked polyethylene and its application. The copolymer microsphere contains polar structural units and crosslinked structural units, and has high electron affinity and surface double bond content.

[0006] To achieve the above objectives, a first aspect of the present invention provides a cross-linked copolymer microsphere, the cross-linked copolymer microsphere comprising structural unit A and structural unit B;

[0007] Wherein, structural unit A has the structure shown in formula (1), and structural unit B comes from a crosslinking agent;

[0008] Equation (1);

[0009] Wherein, R1 is a substituted or unsubstituted phenyl group, a substituted or unsubstituted aromatic heterocyclic group, or a group represented by formula (2);

[0010] Equation (2);

[0011] Among them, R2, R3 and R4 are each independently H, a straight-chain alkyl group of C1-C5 or a branched alkyl group of C3-C5;

[0012] The crosslinking agent is a compound containing at least two vinyl groups, wherein at least one vinyl group is derived from the group shown in formula (3);

[0013] Equation (3);

[0014] Wherein, R5 is H, a straight-chain alkyl group of C1-C5 or a branched alkyl group of C3-C5;

[0015] R6 is a C1-C5 straight-chain alkylene or a C3-C5 branched alkylene;

[0016] Based on the total mass of the cross-linked copolymer microspheres, the content of structural unit A is 80-95 wt%, and the content of structural unit B is 5-20 wt%.

[0017] A second aspect of the present invention provides a method for preparing cross-linked copolymer microspheres, the method comprising:

[0018] S1. Mix the emulsifier, initiator and solvent;

[0019] S2. Add monomers and crosslinking agents to the above mixture to react;

[0020] S3. The product after the reaction is subjected to solid-liquid separation to obtain cross-linked copolymer microspheres;

[0021] Wherein, the monomer is at least one of the compounds represented by formula (4);

[0022] Equation (4);

[0023] Wherein, R1' is a substituted or unsubstituted phenyl group, a substituted or unsubstituted aromatic heterocyclic group, or a group represented by formula (5);

[0024] Equation (5);

[0025] Among them, R2', R3' and R4' are each independently H, a straight-chain alkyl group of C1-C5 or a branched alkyl group of C3-C5;

[0026] The crosslinking agent is a compound containing at least two vinyl groups, wherein at least one vinyl group is derived from the group shown in formula (6);

[0027] Equation (6);

[0028] Wherein, R5' is H, a straight-chain alkyl group of C1-C5 or a branched alkyl group of C3-C5;

[0029] R6' is a C1-C5 straight-chain alkylene or a C3-C5 branched alkylene;

[0030] Based on the total mass of monomer and crosslinking agent, the amount of monomer is 80-95 wt% and the amount of crosslinking agent is 5-20 wt%.

[0031] A third aspect of the present invention provides cross-linked copolymer microspheres prepared by the preparation method described above.

[0032] A fourth aspect of the present invention provides a crosslinkable polyethylene composition comprising a polyethylene base material, a crosslinking agent, and crosslinked copolymer microspheres as described above;

[0033] Based on 100 parts by weight of polyethylene matrix, the amount of crosslinking agent is 1.5-3 parts by weight, and the amount of crosslinked copolymer microspheres is 0.5-5 parts by weight.

[0034] A fifth aspect of the present invention provides a cross-linked polyethylene, which is prepared from the cross-linkable polyethylene composition as described above.

[0035] The sixth aspect of the present invention provides the use of the crosslinked copolymer microspheres as described above, or the crosslinkable polyethylene composition as described above, or the crosslinked polyethylene as described above, in high-voltage cables.

[0036] Through the above technical solution, the present invention can achieve at least the following beneficial effects:

[0037] The cross-linked copolymer microspheres provided by this invention contain polar structural units and cross-linked structural units, and the polar structural units and cross-linked structural units satisfy a certain ratio. The cross-linked copolymer microspheres have high electron affinity, high surface double bond content, and high degree of cross-linking.

[0038] When the cross-linked copolymer microspheres provided by this invention are added to a cross-linkable polyethylene composition as a cross-linkable polyethylene modifier, the cross-linked polyethylene prepared from this composition has excellent electrical properties. At the same time, the cross-linked polymer microspheres have better migration resistance in the cross-linked polyethylene, ensuring the long-term stable use of the insulating material. Attached Figure Description

[0039] Figure 1 This is a scanning electron microscope image of the cross-linked copolymer microspheres A3 prepared in Example 3. Detailed Implementation

[0040] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0041] The first aspect of the present invention provides a cross-linked copolymer microsphere, the cross-linked copolymer microsphere comprising structural unit A and structural unit B;

[0042] Wherein, structural unit A has the structure shown in formula (1), and structural unit B comes from a crosslinking agent;

[0043] Equation (1);

[0044] Wherein, R1 is a substituted or unsubstituted phenyl group, a substituted or unsubstituted aromatic heterocyclic group, or a group represented by formula (2);

[0045] Equation (2);

[0046] Among them, R2, R3 and R4 are each independently H, a straight-chain alkyl group of C1-C5 or a branched alkyl group of C3-C5;

[0047] The crosslinking agent is a compound containing at least two vinyl groups, wherein at least one vinyl group is derived from the group shown in formula (3);

[0048] Equation (3);

[0049] Wherein, R5 is H, a straight-chain alkyl group of C1-C5 or a branched alkyl group of C3-C5;

[0050] R6 is a C1-C5 straight-chain alkylene or a C3-C5 branched alkylene;

[0051] Based on the total mass of the cross-linked copolymer microspheres, the content of structural unit A is 80-95 wt%, and the content of structural unit B is 5-20 wt%.

[0052] In this invention, structural unit A in the crosslinked copolymer microspheres is a polar structural unit with high electron affinity; structural unit B provided by the crosslinking agent provides more double bonds on the surface of the microspheres, which can be used as a crosslinking agent for crosslinked polyethylene. When used to prepare crosslinked polyethylene, the amount of small molecule crosslinking agent can be reduced.

[0053] In this invention, the content of structural unit A and structural unit B in the crosslinked copolymer microspheres is within the above-mentioned range. This can increase the content of double bonds on the surface of the microspheres while ensuring the content of polar groups in the microspheres, which is beneficial for capturing charge carriers and further improving the electrical properties of crosslinked polyethylene.

[0054] More preferably, based on the total mass of the cross-linked copolymer microspheres, the content of structural unit A is 85-90 wt%, and the content of structural unit B is 10-15 wt%.

[0055] In this invention, the structural formula in This represents the connection position between the stated group and the copolymer or compound.

[0056] According to the present invention, preferably, R1 is an unsubstituted phenyl group, an unsubstituted aromatic heterocyclic group, or a group represented by formula (2);

[0057] R2, R3, and R4 are each independently a straight-chain alkyl group consisting of H or C1-C3 atoms.

[0058] In some specific embodiments of the present invention, R1 is an unremoved phenyl group; R2 and R3 are each independently H, methyl or ethyl.

[0059] In some specific embodiments of the present invention, R1 is an imidazole group; R2 and R3 are each independently H, methyl or ethyl.

[0060] In some specific embodiments of the present invention, R1 is the group shown in formula (2), R4 is methyl or ethyl; R2, R3 and R4 are each independently H, methyl or ethyl.

[0061] According to the present invention, preferably, the crosslinking agent is a compound containing at least two vinyl groups, wherein the at least two vinyl groups are derived from the group represented by formula (3);

[0062] Wherein, R5 is H, methyl, or ethyl;

[0063] R6 is methylene, ethylene, or propylene.

[0064] In this invention, preferably, the crosslinking agent is selected from at least one of allyl cinnamate, diallyl phthalate, allyl oxalate, diallyl isophthalate, diallyl malate, triallyl trimellitate, allyl acrylate, allyl methacrylate, diallyl maleate, and triallyl citrate.

[0065] In some specific embodiments of the present invention, the crosslinking agent is allyl acrylate. That is, the crosslinking agent contains two vinyl groups, one of which comes from the group shown in formula (3), where R5 is H and R6 is methylene.

[0066] More preferably, the crosslinking agent is a compound containing at least three vinyl groups, and at least two of the vinyl groups are derived from the group shown in formula (3).

[0067] In this invention, when the crosslinking agent is a compound containing at least three vinyl groups, the surface double bond content of the crosslinked copolymer microspheres can be further increased.

[0068] In some specific embodiments of the present invention, the crosslinking agent is diallyl maleate. That is, the crosslinking agent contains three vinyl groups, two of which are derived from the group shown in formula (3), R5 is H and R6 is methylene.

[0069] According to the present invention, preferably, the surface double bond content of the crosslinked copolymer microspheres is 0.15-0.3 mmol / g.

[0070] In this invention, the surface double bond content of the cross-linked copolymer microspheres refers to the content of C=C double bonds. Specifically, the test method is as follows: a certain mass of copolymer microspheres is mixed with CHCl3 solvent, and Widmanstätten reagent (I to Cl molar ratio of 1:1) is added and allowed to stand to allow ICl to fully react with the C=C bonds in the microspheres. After the reaction is complete, KI solution is added, and the generated I2 is titrated with Na2S2O3 standard solution. Double bond content = M(V0-V1) / W, where M is the concentration of Na2S2O3 standard solution (mmol / L); V0 and V1 are the volumes (L) of Na2S2O3 standard solution consumed by the blank sample and the sample sample, respectively, where the blank sample is a mixed solution of CHCl3 and Widmanstätten reagent without copolymer microspheres; W is the weight (g) of copolymer microspheres.

[0071] In this invention, the surface double bond content of the cross-linked copolymer microspheres within the above-mentioned range is more conducive to the full reaction between the cross-linked copolymer microspheres and the double bonds in polyethylene.

[0072] More preferably, the surface double bond content of the crosslinked copolymer microspheres is 0.25-0.28 mmol / g.

[0073] According to the present invention, the number-average particle size of the cross-linked copolymer microspheres is 50-100 nm, and the particle size polydispersity index is 1.01-1.2.

[0074] In this invention, the test method for the number-average particle size and particle size polydispersity index of the cross-linked copolymer microspheres is as follows: the particle size of 100 microspheres is measured using a scanning electron microscope (SEM) and calculated, and the calculation formula is as follows:

[0075]

[0076]

[0077]

[0078] In the formula, Dn is the number-average diameter; Dw is the weight-average diameter; and PDI is the particle size polydispersity index.

[0079] In this invention, the number-average particle size of the cross-linked copolymer microspheres is within the above-mentioned range, which can provide more cross-linking sites during the preparation of cross-linked polyethylene; the particle size polydispersity index within the above-mentioned range is more conducive to its uniform dispersion in the polyethylene matrix.

[0080] More preferably, the number-average particle size of the cross-linked copolymer microspheres is 55-80 nm, and the particle size polydispersity index is 1.06-1.18.

[0081] According to the present invention, preferably, the gel content of the cross-linked copolymer microspheres is 80-90%.

[0082] In this invention, the degree of crosslinking of the crosslinked copolymer microspheres is characterized by gel content. The gel content is tested as follows: microspheres are weighed and placed in a filter paper bag of known mass. Extraction is performed using tetrahydrofuran. After drying, the weight of the filter paper bag is weighed. The gel content (wt%) is calculated as (m2-m0) / (m1-m0)×100%, where m0 is the mass of the filter paper bag (g), m1 is the total mass before extraction (g), and m2 is the total mass after drying (g).

[0083] In this invention, the gel content of the crosslinked copolymer within the above-mentioned range is more conducive to crosslinking with the polyethylene matrix to form a network structure.

[0084] More preferably, the gel content of the cross-linked copolymer microspheres is 85-90 wt%.

[0085] A second aspect of the present invention provides a method for preparing cross-linked copolymer microspheres, the method comprising:

[0086] S1. Mix the emulsifier, initiator and solvent;

[0087] S2. Add monomers and crosslinking agents to the above mixture to react;

[0088] S3. The product after the reaction is subjected to solid-liquid separation to obtain cross-linked copolymer microspheres;

[0089] Wherein, the monomer is at least one of the compounds represented by formula (4);

[0090] Equation (4);

[0091] Wherein, R1' is a substituted or unsubstituted phenyl group, a substituted or unsubstituted aromatic heterocyclic group, or a group represented by formula (5);

[0092] Equation (5);

[0093] Among them, R2', R3' and R4' are each independently H, a straight-chain alkyl group of C1-C5 or a branched alkyl group of C3-C5;

[0094] The crosslinking agent is a compound containing at least two vinyl groups, wherein at least one vinyl group is derived from the group shown in formula (6);

[0095] Equation (6);

[0096] Wherein, R5' is H, a straight-chain alkyl group of C1-C5 or a branched alkyl group of C3-C5;

[0097] R6' is a C1-C5 straight-chain alkylene or a C3-C5 branched alkylene;

[0098] Based on the total mass of monomer and crosslinking agent, the amount of monomer is 80-95 wt% and the amount of crosslinking agent is 5-20 wt%.

[0099] In this invention, preferably, the amount of monomer is 85-90 wt% and the amount of crosslinking agent is 10-15 wt%, based on the total mass of monomer and crosslinking agent.

[0100] In this invention, the emulsifier can be any conventional choice in the art, as long as it can achieve the purpose of this invention.

[0101] Preferably, the emulsifier is selected from at least one of sodium dodecylbenzenesulfonate, octylphenol polyoxyethylene ether, and polyvinylpyrrolidone. The weight-average molecular weights of the octylphenol polyoxyethylene ether and polyvinylpyrrolidone can be arbitrarily selected according to requirements; for example, the weight-average molecular weight of the octylphenol polyoxyethylene ether can be 500-1000 g / mol, and the weight-average molecular weight of the polyvinylpyrrolidone can be 10000-50000 g / mol.

[0102] In this invention, the initiator can be any conventional choice in the art, as long as it can achieve the purpose of this invention.

[0103] Preferably, the initiator is selected from at least one of ammonium persulfate, sodium persulfate, and potassium persulfate.

[0104] In this invention, the solvent can be any conventional choice in the art, as long as it can achieve the purpose of this invention.

[0105] Preferably, the solvent is water.

[0106] In this invention, the amount of solvent added is not particularly limited, as long as a stable reaction environment can be provided.

[0107] In this invention, preferably, R1' is an unsubstituted phenyl group, an unsubstituted aromatic heterocyclic group, or a group represented by formula (5).

[0108] Preferably, R2', R3' and R4' are each independently a straight-chain alkyl group of H or C1-C3.

[0109] In some specific embodiments of the present invention, the monomer is styrene (R1' is phenyl, R2' and R3' are H).

[0110] In some specific embodiments of the present invention, the monomer is methacrylate (R1' is the group shown in formula (5), R2' is H, and R3' and R4' are methyl).

[0111] In some specific embodiments of the present invention, the monomer is N-vinylimidazole (R1' is an imidazole group, and R2' and R3' are H).

[0112] In this invention, preferably, the crosslinking agent is a compound containing at least two vinyl groups, and the at least two vinyl groups are derived from the groups shown in formula (6);

[0113] Wherein, R5' is H, methyl, or ethyl;

[0114] R6' is methylene, ethylene, or propylene.

[0115] In this invention, preferably, the crosslinking agent is selected from at least one of allyl cinnamate, diallyl phthalate, allyl oxalate, diallyl isophthalate, diallyl malate, triallyl trimellitate, allyl acrylate, allyl methacrylate, diallyl maleate, and triallyl citrate.

[0116] In some specific embodiments of the present invention, the crosslinking agent is allyl acrylate. It contains two vinyl groups, one of which comes from the group shown in formula (6), where R5' is H and R6' is methylene.

[0117] In some specific embodiments of the present invention, the crosslinking agent is diallyl maleate. It contains three vinyl groups, two of which are derived from the group shown in formula (6), where R5' is H and R6' is methylene.

[0118] According to the present invention, preferably, the total mass ratio of the monomer and crosslinking agent, the initiator and the emulsifier is 100:1-5:5-20.

[0119] In this invention, the proportions of each raw material meet the above ratio, which is more conducive to the stability of the polymerization reaction and to obtaining cross-linked copolymer microspheres with uniform particle size.

[0120] More preferably, the total mass ratio of the monomer and crosslinking agent, and the mass ratio of the initiator and emulsifier is 100:1-3:7-11.

[0121] According to the present invention, preferably, the reaction conditions include: a reaction temperature of 60-90°C and a reaction time of 3.5-15 h.

[0122] More preferably, the reaction conditions include: a reaction temperature of 60-85°C and a reaction time of 4-13 hours.

[0123] In this invention, the method of adding the monomer and crosslinking agent to the mixture in step S2 is not particularly limited and can be a conventional operation in the art. To improve the stability of the reaction, the monomer and crosslinking agent can be added dropwise to the above system at a stirring rate of 200-500 r / min, with a dropping rate of 0.5-2 mL / min.

[0124] According to the present invention, preferably, in step S2, the crosslinking agent is added in two steps.

[0125] In this invention, adding the crosslinking agent in two steps is more conducive to increasing the double bond content on the surface of the microspheres. The residual double bonds on the surface of the microspheres can undergo a crosslinking reaction with polyethylene during the vulcanization process, acting as part of the crosslinking agent. This increases the degree of crosslinking of the matrix while reducing the amount of crosslinking agent, reducing the concentration of by-products, and improving the electrical properties of the crosslinked polyethylene.

[0126] According to the present invention, preferably, in step S2, based on the total mass (100wt%) of the crosslinking agent, monomers and 30-50wt% of crosslinking agent are added to the above mixture and reacted for 0.5-5 hours, followed by the addition of the remaining crosslinking agent to continue the reaction. Wherein, the total mass of the crosslinking agent is 100wt%.

[0127] In this invention, the crosslinking agent is added in two steps, and the total reaction time is the same as the above-mentioned reaction time, which is 3.5-15h, preferably 4-13h.

[0128] In this invention, the reactions described in steps S2 and S3 are carried out under a protective atmosphere, preferably provided by nitrogen.

[0129] In this invention, preferably, step S2 is carried out under stirring.

[0130] More preferably, the stirring rate is 350-450 r / min.

[0131] In this invention, the method of solid-liquid separation is not particularly limited and can be any conventional operation in the art. For example, centrifugation can be used.

[0132] In this invention, the preparation method may further include washing and / or drying the prepared crosslinked copolymer microspheres. The washing and drying methods are conventional operations in the art.

[0133] A third aspect of the present invention provides cross-linked copolymer microspheres prepared by the preparation method described above.

[0134] A fourth aspect of the present invention provides a crosslinkable polyethylene composition comprising a polyethylene base material, a crosslinking agent, and crosslinked copolymer microspheres as described above;

[0135] Based on 100 parts by weight of polyethylene matrix, the amount of crosslinking agent is 1.5-3 parts by weight, and the amount of crosslinked copolymer microspheres is 0.5-5 parts by weight.

[0136] In this invention, the composition includes specific components, particularly the addition of cross-linked copolymer microspheres as described above, and each component is used in specific amounts, so that the cross-linked polyethylene prepared from the composition has exceptionally superior electrical properties.

[0137] More preferably, based on 100 parts by weight of polyethylene matrix, the amount of crosslinking agent is 1.5-2 parts by weight, and the amount of crosslinked copolymer microspheres is 1.5-2 parts by weight.

[0138] In this invention, the polyethylene base material can be a commercially available product or prepared by conventional methods in the art. Preferably, the polyethylene base material is low-density polyethylene.

[0139] More preferably, the low-density polyethylene has a weight-average molecular weight of 66,000-80,000 g / mol and a density of 0.915-0.922 g / cm³. 3 .

[0140] In this invention, the composition may further include an antioxidant.

[0141] More preferably, the amount of antioxidant used is 0.1-0.3 parts by weight.

[0142] In this invention, the crosslinking agent can be any conventional choice in the art, as long as it can crosslink polyethylene. Preferably, the crosslinking agent is an organic peroxide.

[0143] More preferably, the crosslinking agent is selected from at least one of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, dicumyl peroxide, benzoyl peroxide, and di-tert-butyl peroxide.

[0144] In this invention, the antioxidant can be any conventional choice in the art. Preferably, the antioxidant is a hindered phenolic antioxidant.

[0145] More preferably, the antioxidant is selected from at least one of 2,6-di-tert-butyl-4-methylphenol, 4,6-bis(octylthiomethyl)o-cresol, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,2'-thionyl glycol bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 3,5-di-tert-butyl-4-hydroxyphenylpropionate, and 4,4'-thiobis(6-tert-butyl-3-methylphenol).

[0146] A fifth aspect of the present invention provides a cross-linked polyethylene, which is prepared from the cross-linkable polyethylene composition as described above.

[0147] In this invention, the preparation method includes:

[0148] S1. Mix 100 parts by weight of polyethylene base material, 0.5-5 parts by weight of crosslinked copolymer microspheres, and 1.5-3 parts by weight of crosslinking agent;

[0149] S2. The mixed materials are subjected to open milling at 120-130℃;

[0150] S3. The thin sheets after open milling are vulcanized and compressed at 170-185℃.

[0151] In this invention, the cross-linked polyethylene, due to the addition of cross-linked copolymer microspheres and the appropriate amount of each raw material within a certain range, exhibits high cross-linking degree, high resistivity, and high breakdown strength.

[0152] In this invention, the mixing method in step S1 is not particularly limited, as long as the raw materials can be mixed evenly.

[0153] In this invention, if the composition also includes an antioxidant, the antioxidant is added in step S1.

[0154] According to the present invention, preferably, in step S2, the temperature of the reaction is 124-127°C.

[0155] According to the present invention, preferably, in step S3, the reaction temperature is 175-180°C and the time is 10-15 min.

[0156] According to the present invention, preferably, the gel content of the cross-linked polyethylene is 85-90 wt%.

[0157] In this invention, the test method for the content of cross-linked polyethylene gel is the same as the test method for the content of cross-linked copolymer microsphere gel described above.

[0158] More preferably, the gel content of the cross-linked polyethylene is 88-90 wt%.

[0159] According to the present invention, preferably, the cross-linked polyethylene has a volume resistivity of 20 × 10⁻⁶ at 30°C. 12 -35×10 12 Ω·m.

[0160] According to the present invention, preferably, the cross-linked polyethylene has a volume resistivity of 3 × 10⁻⁶ at 70°C. 12 -10×10 12 Ω·m.

[0161] According to the present invention, preferably, the cross-linked polyethylene has a volume resistivity of 2 × 10⁻⁶ at 90°C. 12 -5×10 12 Ω·m.

[0162] In this invention, the test method for volume resistivity is based on standard GB / T 31838.3-2019, and the test voltage is 30kV / mm.

[0163] In this invention, the volume resistivity of the cross-linked polyethylene meets the above-mentioned range, which can better match the application requirements of high-voltage cables.

[0164] More preferably, the cross-linked polyethylene has a volume resistivity of 28 × 10⁻⁶ at 30°C. 12 -35×10 12 Ω·m.

[0165] More preferably, the cross-linked polyethylene has a volume resistivity of 5 × 10⁻⁶ at 70°C. 12 -10×10 12 Ω·m.

[0166] More preferably, the cross-linked polyethylene has a volume resistivity of 3.5 × 10⁻⁶ at 90°C. 12 -5×10 12 Ω·m.

[0167] According to the present invention, preferably, the cross-linked polyethylene has an AC breakdown field strength of 100-115 kV / mm at 30°C.

[0168] According to the present invention, preferably, the cross-linked polyethylene has an AC breakdown field strength of 85-100 kV / mm at 70°C.

[0169] According to the present invention, preferably, the cross-linked polyethylene has an AC breakdown field strength of 75-90 kV / mm at 90°C.

[0170] In this invention, the test method for AC breakdown field strength refers to standard GB / T 1408.2-2016, with a pressure application rate of 2kV / s and a sample thickness of 0.2mm.

[0171] In this invention, the AC breakdown field strength of the cross-linked polyethylene meets the above-mentioned range, which can better match the application requirements of high-voltage cables.

[0172] More preferably, the cross-linked polyethylene has an AC breakdown field strength of 105-115 kV / mm at 30°C.

[0173] More preferably, the cross-linked polyethylene has an AC breakdown field strength of 94-100 kV / mm at 70°C;

[0174] More preferably, the cross-linked polyethylene has an AC breakdown field strength of 84-90 kV / mm at 90°C.

[0175] The sixth aspect of the present invention provides the use of the crosslinked copolymer microspheres as described above, or the crosslinkable polyethylene composition as described above, or the crosslinked polyethylene as described above, in high-voltage cables.

[0176] The cross-linked polyethylene provided by this invention has excellent electrical properties and can meet the requirements of high-voltage cables.

[0177] The present invention will be described in detail below through embodiments. It should be understood that the following embodiments are only used to further explain and illustrate the content of the present invention, and are not intended to limit the present invention.

[0178] Unless otherwise specified, all reagents and materials used in the following examples were purchased from reputable chemical reagent suppliers and were of analytical purity.

[0179] In the following examples, the low-density polyethylene was obtained from a commercially available product with a weight-average molecular weight of 78,000 g / mol and a density of 0.916 g / cm³. 3 .

[0180] Polyvinylpyrrolidone is a commercially available product with a weight-average molecular weight of 40,000 g / mol.

[0181] In the following embodiments, the content of structural units of the cross-linked copolymer microspheres was determined by infrared spectroscopy. Standard spectra of characteristic group types and contents were established, and the contents of structural unit A and structural unit B were determined by the ratio of the characteristic peak areas of the characteristic groups.

[0182] Example 1

[0183] S1. Mix the emulsifier (polyvinylpyrrolidone), initiator (sodium persulfate), and 100 mL of deionized water;

[0184] S2. Add 18g of styrene and 45wt% crosslinking agent (diallyl maleate) dropwise to the above mixed solution at 450r / min;

[0185] S3. Under a nitrogen atmosphere, the mixture was stirred at high speed at 75°C for 1 hour at a stirring speed of 450 r / min.

[0186] S4. Add the remaining 55wt% crosslinking agent and react for 7 hours under the same conditions;

[0187] S5. The reacted emulsion is centrifuged, washed, and dried to obtain cross-linked copolymer microspheres A1.

[0188] The styrene content in the styrene and crosslinking agent is 90 wt%, and the crosslinking agent content is 10 wt%. The mass ratio of styrene to crosslinking agent, initiator, and emulsifier is 100:1.2:7. The content of structural units, gel content, surface double bond content, number-average particle size, and particle size polydispersity index in A1 are shown in Table 1.

[0189] Example 2

[0190] Crosslinked copolymer microspheres A2 were prepared according to the method of Example 1, except that styrene was replaced with N-vinylimidazole;

[0191] The content of N-vinylimidazole in the N-vinylimidazole and crosslinking agent is 88 wt%, and the content of crosslinking agent is 12 wt%.

[0192] Example 3

[0193] Crosslinked copolymer microspheres A3 were prepared according to the method of Example 1, except that the content of styrene in styrene and crosslinking agent was 87 wt% and the content of crosslinking agent was 13 wt%. Figure 1 The scanning electron microscope image (A3) shows that the cross-linked copolymer microspheres of the present invention have smooth surfaces and uniform sizes.

[0194] Example 4

[0195] Crosslinked copolymer microspheres A4 were prepared according to the method of Example 1, except that 75 wt% of crosslinking agent was added in step S2 and 25 wt% of crosslinking agent was added in step S3.

[0196] Example 5

[0197] Crosslinked copolymer microspheres A5 were prepared according to the method of Example 1, except that all the crosslinking agent was added in step S1.

[0198] Example 6

[0199] Crosslinked copolymer microspheres A6 were prepared according to the method of Example 1, except that diallyl maleate was replaced with allyl acrylate.

[0200] Comparative Example 1

[0201] Crosslinked copolymer microspheres D1 were prepared according to the method of Example 1, except that the content of styrene in styrene and crosslinking agent was 99 wt% and the content of crosslinking agent was 1 wt%.

[0202] Comparative Example 2

[0203] Crosslinked copolymer microspheres D2 were prepared according to the method of Example 1, except that the crosslinking agent was replaced with divinylbenzene.

[0204] Table 1

[0205]

[0206] Preparation Example

[0207] 100 parts by weight of low-density polyethylene, 0.2 parts by weight of 4,4'-thiobis(6-tert-butyl-3-methylphenol), 1 part by weight of crosslinked copolymer microspheres prepared in the examples and comparative examples, and 1.7 parts by weight of dicumyl peroxide were added to a two-roll mill and mixed. After the two-roll mill temperature was 125°C, the mixture was pressed into sheets at 180°C to obtain crosslinked polyethylene B1-B6 and DB1, DB2.

[0208] Cross-linked polyethylene prepared according to the above method without the addition of cross-linked polymer microspheres was used as the control sample DB3.

[0209] Cross-linked polyethylene prepared according to the above method without adding cross-linked polymer microspheres, and with the amount of dicumyl peroxide increased to 2.7 parts by weight, was used as the control sample DB4.

[0210] Test Example 1

[0211] The electrical properties of the cross-linked polyethylene prepared by the test example are shown in Table 2.

[0212] Volume resistivity was tested according to standard GB / T 31838.3-2019, and AC breakdown strength was tested according to standard GB / T1408.2-2016.

[0213] Table 2

[0214]

[0215] Test Example 2

[0216] The gel content and migration rate of the cross-linked polyethylene microspheres prepared in the test preparation example are shown in Table 3.

[0217] The test method for gel content is as described above.

[0218] The migration rate test method is as follows: the sample obtained by mixing in an open mill is pressed into a thin sheet at 120℃, and 5g of the sample to be tested is soaked in n-hexane for 24h. The sample is then taken out and dried in a vacuum oven at 60℃ for 48h, and the mass of the sample is weighed.

[0219] Migration rate (%) = (m3-m4) / 5×100%, where m3 is the mass of the blank cross-linked polyethylene sample (without cross-linked copolymer microspheres, composition the same as DB3), and m4 is the mass of the test sample after drying.

[0220] No cross-linked copolymer microspheres migrated from cross-linked polyethylene B1-B6 and DB1, DB2.

[0221] Table 3

[0222]

[0223] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A cross-linked copolymer microsphere, characterized in that, The cross-linked copolymer microspheres comprise structural unit A and structural unit B; Wherein, structural unit A has the structure shown in formula (1), and structural unit B comes from a crosslinking agent; Equation (1); Wherein, R1 is a substituted or unsubstituted phenyl group, a substituted or unsubstituted aromatic heterocyclic group, or a group represented by formula (2); Equation (2); Among them, R2, R3 and R4 are each independently H, a straight-chain alkyl group of C1-C5 or a branched alkyl group of C3-C5; The crosslinking agent is a compound containing at least two vinyl groups, wherein at least one vinyl group is derived from the group shown in formula (3); Equation (3); Wherein, R5 is H, a straight-chain alkyl group of C1-C5 or a branched alkyl group of C3-C5; R6 is a C1-C5 straight-chain alkylene or a C3-C5 branched alkylene; Based on the total mass of the cross-linked copolymer microspheres, the content of structural unit A is 85-90 wt%, and the content of structural unit B is 10-15 wt%. The cross-linked copolymer microspheres have a surface double bond content of 0.2-0.3 mmol / g and a particle size polydispersity index of 1.01-1.

2. The number-average particle size of the cross-linked copolymer microspheres is 50-100 nm.

2. The crosslinked copolymer microspheres according to claim 1, wherein, R1 is an unsubstituted phenyl group, an unsubstituted aromatic heterocyclic group, or a group represented by formula (2); Equation (2); R2, R3, and R4 are each independently H or C1-C3 straight-chain alkyl groups; And / or, the crosslinking agent is a compound containing at least two vinyl groups, wherein at least two vinyl groups are derived from the groups shown in formula (3); Equation (3); Wherein, R5 is H, methyl, or ethyl; R6 is methylene, ethylene, or propylene.

3. The crosslinked copolymer microspheres according to claim 1 or 2, wherein, The gel content of the cross-linked copolymer microspheres is 80-90 wt%.

4. A method for preparing cross-linked copolymer microspheres, characterized in that, The preparation method includes: S1. Mix the emulsifier, initiator and solvent; S2. Add monomers and crosslinking agents to the above mixture to react; S3. The product after the reaction is subjected to solid-liquid separation to obtain cross-linked copolymer microspheres; Wherein, the monomer is at least one of the compounds represented by formula (4); Equation (4); Wherein, R1' is a substituted or unsubstituted phenyl group, a substituted or unsubstituted aromatic heterocyclic group, or a group represented by formula (5); Equation (5); Among them, R2', R3' and R4' are each independently H, a straight-chain alkyl group of C1-C5 or a branched alkyl group of C3-C5; The crosslinking agent is a compound containing at least two vinyl groups, wherein at least one vinyl group is derived from the group shown in formula (6); Equation (6); Wherein, R5' is H, a straight-chain alkyl group of C1-C5 or a branched alkyl group of C3-C5; R6' is a C1-C5 straight-chain alkylene or a C3-C5 branched alkylene; Based on the total mass of monomers and crosslinking agents, the amount of monomers is 85-90 wt%, and the amount of crosslinking agents is 10-15 wt%. The preparation method further includes: in step S2, the crosslinking agent is added in two steps; In step S2, based on the total mass of the crosslinking agent, monomers and 30-50 wt% crosslinking agent are added to the above mixture and reacted for 0.5-5 hours, and then the remaining crosslinking agent is added to continue the reaction. The total mass ratio of the monomer and crosslinking agent, and the mass ratio of the initiator and emulsifier are 100:1-5:5-20; The surface double bond content of the cross-linked copolymer microspheres is 0.2-0.3 mmol / g.

5. The preparation method according to claim 4, wherein, The reaction conditions include: a reaction temperature of 60-90℃ and a reaction time of 3.5-15h.

6. Crosslinked copolymer microspheres prepared by the preparation method according to claim 4 or 5.

7. A crosslinkable polyethylene composition, characterized in that, The composition comprises a polyethylene base material, a crosslinking agent, and crosslinked copolymer microspheres according to any one of claims 1-3 and 6; Based on 100 parts by weight of polyethylene matrix, the amount of crosslinking agent is 1.5-3 parts by weight, and the amount of crosslinked copolymer microspheres is 0.5-5 parts by weight.

8. A cross-linked polyethylene, characterized in that, The cross-linked polyethylene is prepared from the cross-linkable polyethylene composition of claim 7.

9. The cross-linked polyethylene according to claim 8, wherein, The gel content of the cross-linked polyethylene is 85-90 wt%.

10. The cross-linked polyethylene according to claim 8, wherein, The crosslinked polyethylene has a volume resistivity at 30°C of 20 x 10 12 -35 x 10 12 Ω-m; And / or, the cross-linked polyethylene has a volume resistivity of 3 × 10⁻⁶ at 70°C. 12 -10×10 12 Ω·m; And / or, the cross-linked polyethylene has a volume resistivity of 2 × 10⁻⁶ at 90°C. 12 -5×10 12 Ω·m.

11. The cross-linked polyethylene according to claim 8, wherein, The cross-linked polyethylene has an AC breakdown field strength of 100-115 kV / mm at 30°C. And / or, the cross-linked polyethylene has an AC breakdown field strength of 85-100 kV / mm at 70°C; And / or, the cross-linked polyethylene has an AC breakdown field strength of 75-90 kV / mm at 90°C.

12. The use of the crosslinked copolymer microspheres according to any one of claims 1-3 and 6, or the crosslinkable polyethylene composition according to claim 7, or the crosslinked polyethylene according to any one of claims 8-11, in high-voltage cables.

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