Semiconductive shielding material and method of making same

Abstract

This invention provides a semiconductive shielding material and its preparation method. Highly branched modified graphene oxide is prepared by in-situ polymerization intercalation of polymeric monomers and branched monomers with graphene oxide, and an ultra-smooth semiconductive shielding material is prepared based on the highly branched modified graphene oxide. After highly branched polybutyl acrylate modifies the surface of graphene oxide (GO), it not only establishes a long-range conductive network in the material, but the modified graphene oxide also improves the dispersibility of carbon black in the matrix resin, reduces the agglomeration of conductive carbon black, and improves the surface smoothness of the high-voltage cable semiconductive shielding material. Simultaneously, the stable presence of aromatic branched structures in the branched molecules improves the thermal stability of the cable operation.

Description

Technical Field

[0001] This invention relates to the field of power cable materials technology, specifically to a high-voltage cable semi-conductive shielding material based on graphene oxide-dispersed conductive carbon black and its preparation method. Background Technology

[0002] In ultra-high voltage cables, one of the functions of the shielding layer is to make the electric field distribution more uniform, thereby reducing the possibility of partial discharge. If the surface of the shielding material is not smooth enough, the electric field may concentrate at irregular surfaces, increasing the risk of partial discharge and thus affecting the safe operation of the cable. A good shielding layer can effectively improve the cable's resistance to external electromagnetic interference and prevent internal current from leaking into the external environment. The smoother the surface, the higher the shielding efficiency, because small protrusions or depressions on a rough surface may become charge accumulation points, weakening the shielding effectiveness.

[0003] Semiconducting shielding materials for cables are mainly prepared by melt blending, extrusion granulation, and compounding of polar matrix resin, conductive carbon black, and additives. During the extrusion granulation process, conductive carbon black is prone to agglomeration in the matrix resin, resulting in noticeable protrusions on the surface of the high-voltage cable shielding material, affecting surface smoothness. Furthermore, stress concentration can occur in the matrix resin, damaging the conductive network and impacting the stability of the mechanical and electrical properties of the high-voltage cable semiconducting shielding layer. Therefore, improving the dispersibility of carbon black in the matrix resin and reducing carbon black agglomeration are key issues that need to be addressed in developing ultra-smooth high-voltage shielding materials for higher voltage ratings.

[0004] For composite modification of acrylates and graphene, mainly applied to interface modification, CN106497301B discloses a graphene-modified acrylamide or N-hydroxymethylacrylamide waterborne coating for use as an antistatic or electromagnetic shielding film. CN113122087A adds graphene oxide to waterborne coatings to enhance the anti-corrosion performance of the coating film. Meanwhile, CN115010121A improves the conductivity of materials by constructing "micro-bag" few-layer graphene structures. Graphene oxide, as a carbon material with high specific surface area and high conductivity, has broad application prospects in the field of electrical conductivity, but its tendency to aggregate is a significant drawback.

[0005] The reaction conditions for existing graphene oxide surface grafting modification technology are relatively complex and difficult to control. Parameters such as temperature, reaction time, and pH need to be precisely controlled, making the operation difficult. Different grafting modification methods correspond to different suitable conditions, which increases the overall complexity. At the same time, the grafting efficiency of graphene oxide grafting groups is limited, and the number of active functional groups available for grafting on the graphene oxide surface is relatively fixed, making it difficult to significantly increase the grafting amount and limiting the degree of further modification. Summary of the Invention

[0006] The purpose of this invention is to provide an ultra-smooth semi-conductive shielding material based on highly branched graphene oxide surface modification and its preparation method. The method utilizes a simple and easy-to-operate free radical "in-situ polymerization intercalation" method to modify the surface of graphene oxide, introducing highly branched polyacrylate molecular chains into the edges or surface of graphene oxide.

[0007] The branched graphene oxide has better compatibility with the polar matrix resin of the shielding material, while solving the agglomeration problem of carbon black and reducing the generation of cable shielding layer protrusions, thereby developing cable shielding materials with higher voltage levels. At the same time, the aromatic branched structure can improve the electrical stability of the material.

[0008] The modified graphene oxide prepared in this invention contains branched structures that provide greater steric hindrance, more effectively preventing particle aggregation. Simultaneously, the introduction of polar polyacrylate branches alters the surface properties of graphene oxide, increasing its compatibility with the polar polymer matrix and thus promoting the uniform distribution of carbon black within the matrix. To achieve the above-mentioned objectives, the technical solution of this invention is as follows:

[0009] This invention provides a semiconductive composition based on acrylate-grafted graphene oxide (GO) dispersed conductive carbon black. After the highly branched polyacrylate polymer modifies the surface of the graphene oxide, a long-range conductive network is established in the material, which also makes the graphene oxide more dispersible in the matrix resin. At the same time, the aromatic compound divinylbenzene is used as a branching monomer, which not only effectively improves the mechanical and electrical properties of the cable material, but also reduces the agglomeration of conductive carbon black and improves the surface smoothness of the high-voltage cable semiconductive shielding material.

[0010] A semiconductive shielding material, comprising the following components:

[0011] 55 to 68 parts by weight of the matrix resin;

[0012] 30 to 35 parts by weight of conductive carbon black;

[0013] 0.4 parts by weight to 1 part by weight of antioxidant;

[0014] 0.5 to 1.5 parts by weight of lubricant;

[0015] 0.8 to 1.3 parts by weight of crosslinking agent;

[0016] 1.5 to 4 parts by weight of modified graphene oxide.

[0017] The matrix resin of the present invention comprises one or more of ethylene-vinyl acetate copolymer (EVA), ethylene-butyl acrylate copolymer (EBA), ethylene-methyl acrylate copolymer (EMA), and ethylene-ethyl acrylate copolymer (EEA), preferably EBA and / or EMA, and more preferably EBA.

[0018] As a preferred embodiment, the mass fraction of vinyl acetate monomer units in the ethylene-vinyl acetate copolymer of the present invention is 15-30%, preferably 16-20%, and more preferably 16-19%.

[0019] As a preferred embodiment, the mass fraction of butyl acrylate monomer units in the ethylene-butyl acrylate copolymer of the present invention is 15-25%, preferably 16-20%, and more preferably 16-19%.

[0020] As a preferred embodiment, the mass fraction of methyl acrylate monomer units in the ethylene-methyl acrylate copolymer of the present invention is 15-25%, preferably 16-20%, and more preferably 16-19%.

[0021] As a preferred embodiment, the conductive carbon black of the present invention is a commercially available conductive carbon black, comprising furnace black and / or acetylene black.

[0022] As a preferred embodiment, the lubricant of the present invention is one or more of zinc stearate, paraffin wax, and polyethylene wax.

[0023] As a preferred embodiment, the antioxidant of the present invention is one or more of antioxidant 1010, antioxidant 168, antioxidant 300, and antioxidant poly-2,2,4-trimethyl-1,2-dihydroquinoline (TMQ).

[0024] As a preferred embodiment, the crosslinking agent of the present invention is one or more of dicumyl peroxide and bis-tert-butyldicumyl peroxide.

[0025] As a preferred embodiment, the method for preparing the modified graphene oxide of the present invention includes the following steps:

[0026] (1) Graphene oxide was ultrasonically dispersed in a solvent to obtain dispersion 1;

[0027] (2) Add the polymerizing monomer and the branching monomer to the dispersion 1 and perform ultrasonic dispersion to obtain dispersion 2;

[0028] (3) Under a nitrogen atmosphere, the dispersion 2 is reacted with the initiator and chain transfer agent;

[0029] (4) Separate the product from step (3), freeze it, and dry it.

[0030] As a preferred embodiment, the graphene oxide of the present invention has a thickness of 0.8–1.2 nm and a sheet diameter of 0.5–5 μm; a carbon content of no more than 44% and an oxygen content of no less than 50%.

[0031] As a preferred embodiment, the initiator of the present invention is one or more of azobisisobutyronitrile and azobisisoheptanenitrile, preferably azobisisobutyronitrile.

[0032] As a preferred embodiment, the chain transfer agent of the present invention is n-dodecyl mercaptan.

[0033] As a preferred embodiment, the polymeric monomer of the present invention comprises (meth)acrylic acid and its esters, suitable examples including but not limited to one or more of acrylic acid, methyl acrylate, ethyl acrylate, isooctyl acrylate, butyl acrylate, methyl methacrylate, butyl acrylate, and vinyl acetate, preferably butyl acrylate (BA).

[0034] As a preferred embodiment, the branched monomer of the present invention is an aromatic compound with two or more carbon-carbon double bond functional groups, preferably divinylbenzene (DVB).

[0035] As a preferred embodiment, the solvent of the present invention is N,N-dimethylformamide (DMF) and / or ethyl acetate, preferably N,N-dimethylformamide (DMF).

[0036] As a preferred embodiment, in the method for preparing modified graphene oxide according to the present invention, the mass concentration of each raw material is: based on the mass of the raw materials for preparing modified graphene oxide including the solvent,

[0037] The graphene oxide content is 0.2-0.7%, preferably 0.3-0.4%.

[0038] The monomer content is 20-30%, preferably 25-29%;

[0039] Branched monomers 3-15%, preferably 5-10%;

[0040] The initiator is 0.15-0.3%, preferably 0.18-0.22%;

[0041] Chain transfer agent 3-7%, preferably 4-6%.

[0042] As a preferred embodiment, the ultrasonic dispersion time of the present invention is 0-1.5h, performed at room temperature, preferably 1-1.5h.

[0043] As a preferred embodiment, in step (3) of the present invention, the reaction time is not less than 8 hours, and preferably 10-14 hours.

[0044] As a preferred embodiment, in step (3) of the present invention, the reaction temperature is 65-85℃, preferably 80℃.

[0045] As a preferred method, BPBA-GO is prepared by free radical in-situ polymerization intercalation, using butyl acrylate (BA) and divinylbenzene (DVB) as the polymerization and branching monomers, respectively, and the two undergo branching copolymerization reaction in a homogeneous graphene oxide solution.

[0046] The preparation method of the semiconductive shielding material of the present invention includes the following steps: adding matrix resin, conductive carbon black, lubricant, antioxidant and modified graphene oxide into a reciprocating mixer for mixing, filtering, extrusion, granulation by an underwater pelletizing system, and drying to obtain a resin composite material.

[0047] Preferably, the mixing section of the reciprocating mixer is a reciprocating single-screw extruder, and filtration is carried out through a filtration system in the molten state.

[0048] The resin composite material is then subjected to a post-absorption process with a crosslinking agent to obtain the semiconductor shielding material.

[0049] The post-absorption process of the present invention includes a post-absorption process of atomizing the crosslinking agent and then reacting it with the resin composite material:

[0050] Preferably, the temperature of the post-absorption process is 60–80°C;

[0051] Preferably, the post-absorption process takes 0.5 to 3 hours.

[0052] The ultra-smooth semi-conductive shielding material of the present invention can be used as a shielding layer for power cables.

[0053] Compared with the prior art, the present invention has the following advantages: by introducing highly branched modified graphene oxide material, carbon black has better dispersibility in the matrix resin, and the aromatic branched structure contained in the branched structure can improve the electrical stability of the material. While effectively improving the mechanical properties and space charge suppression ability of the cable material, it reduces the agglomeration of conductive carbon black and improves the surface smoothness of the semi-conductive shielding material of high voltage cable. Detailed Implementation

[0054] The present invention will be further described below with reference to the embodiments, but the scope of protection of the present invention is not limited to the embodiments, but should also include any other known modifications within the scope of the claims of the present invention.

[0055] Main raw material sources:

[0056] Ethylene-butyl acrylate copolymer: DOW, with a butyl acrylate monomer unit mass fraction of 17%;

[0057] Conductive carbon black: DENKA, acetylene black;

[0058] Antioxidant: TMQ antioxidant from Lanxess Chemical;

[0059] Crosslinking agent: bis(tert-butylperoxyisopropylbenzene), BIPB, Arkema, 99.0% purity;

[0060] Unless otherwise specified, all other raw materials are ordinary raw materials purchased from the market.

[0061] Main testing methods

[0062] To determine whether branched structures were formed in the examples and to characterize the degree of polymer branching, modified graphene oxide was prepared into a 2.5% tetrahydrofuran solution, which was then filtered through a microporous membrane to remove the graphene oxide. The soluble polybutyl acrylate in the filtrate was then tested as follows;

[0063] Multi-detector gel permeation chromatography (GPC / SEC) was used to determine the absolute molecular weight, intrinsic viscosity [η], hydrodynamic volume Rh(η), and Mark-Houwink equation constant α of the polymer. Tetrahydrofuran was used as the mobile phase solvent, the sample concentration was 5–8 mg / mL, the flow rate was 1 mL / min, and the polymer dn / dc value in light scattering was 0.065. The OMNISEC advanced multi-detector GPC / SEC system from Malvern Instruments, UK, was employed.

[0064] The following tests were conducted on the semiconductive shielding materials prepared in the examples and comparative examples.

[0065] Volume resistivity: The volume resistivity at 23℃ shall be determined in accordance with GB / T 3048.3, and the sample shall be acclimated in an environment with a temperature of 23±3℃ and a relative humidity of 50±5% for no less than 24 hours. The volume resistivity at 90℃ shall be determined in accordance with Appendix A of GB / T 3048.3. The volume resistivity at 90℃ after 7 days of heat aging at 135℃ shall be determined in accordance with Appendix A of GB / T 3048.3, and the heat aging shall be performed in accordance with GB / T 2951.12.

[0066] Surface protrusion test: Performed in accordance with Appendix A of Q / GDW 11883.2—2018 standard. The tester is the SSA test equipment of OCS Company, and the resolution of protrusion height should be better than 25μm.

[0067] Example 1

[0068] Preparation of highly branched modified graphene oxide

[0069] The raw material composition is referenced in Table 1. The specific operation steps are as follows: First, add graphene oxide to the solvent and disperse it ultrasonically for 0.5 h. Then, add BA monomer and DVB branched monomer and disperse for another 0.5 h. Then, add the initiator azobisisobutyronitrile (AIBN) and the chain transfer agent n-dodecyl mercaptan (DDT). Let it react in a nitrogen atmosphere and at 80°C in a water bath for 12 h. Then, cool it to room temperature to obtain the reaction solution.

[0070] The reaction solution was centrifuged at 4000 rpm for 10 min to remove the supernatant. After ultrasonic oscillation, the solution was poured into a Buchner funnel for filtration to remove the remaining solvent and unreacted monomers. The solution was then repeatedly ultrasonically dispersed and washed with ethanol and water, followed by filtration. The final sample was ultrasonically dispersed in a 100 mL beaker containing 10 mL of deionized water, sealed with aluminum foil, and frozen solid in a freezer. The solid was then dried in a freeze dryer for 48 h to obtain highly branched modified graphene oxide (BPBA-g-GO-1).

[0071] Example 2

[0072] Preparation of branched modified graphene oxide

[0073] The preparation method is the same as in Example 1, and the raw material ratio is the same as in Table 1, to obtain branched grafted modified graphene oxide (BPBA-g-GO-2).

[0074] Comparative Example 1

[0075] Preparation of modified graphene oxide

[0076] The preparation method is as described in Example 1, and the raw material ratio is as described in Table 1, to obtain modified graphene oxide (PBA-g-GO).

[0077] Table 1. Preparation and testing results of modified graphene oxide materials.

[0078]

[0079] Example 3

[0080] Preparation of ultra-smooth semiconductive shielding material

[0081] According to the composition in Table 2, EBA resin, conductive carbon black, lubricant, antioxidant and modified graphene oxide were added to a reciprocating mixer for mixing, filtered in a screen changer, extruded under pressure by a melt pump, and the melt was granulated through an underwater granulation system and dried by forced air to obtain a resin composite material; then the resin composite material was subjected to a post-absorption process with a crosslinking agent to obtain the semiconductive shielding material.

[0082] The mixing and feeding section temperature is 80℃, the melting section temperature is 180℃, the plasticizing section temperature is 190℃, the extrusion section temperature is 190℃, and the screw speed is 300rpm. In the extrusion granulation, the die head temperature is 200℃, the melt pressure is 7~7.5MPa, the underwater pelletizing temperature is 40℃, the forced-air drying temperature is 60℃, the post-absorption temperature is 70℃, and the time is 2.5h.

[0083] The semiconductive shielding material is inspected for surface protrusions, and then the finished product is packaged.

[0084] Examples 4-6

[0085] The preparation methods for Examples 4-6 are the same as those for Example 3, and the raw material composition is as shown in Table 2.

[0086] Comparative Examples 2-4

[0087] The preparation methods for Comparative Examples 2-4 are the same as those in Example 3, and the raw material composition is as shown in Table 2.

[0088] Table 2 Composition of Semiconductor Shielding Material

[0089] Example 3 Example 4 Example 5 Example 6 Comparative Example 2 Comparative Example 3 Comparative Example 4 EBA 60 60 60 60 60 60 60 Crosslinking agent 1.2 1.2 1.2 1.2 1.2 1.2 1.2 antioxidants 0.7 0.7 0.7 0.7 0.7 0.7 0.7 Conductive carbon black 34.5 36 34.5 36 34.5 34.5 37.5 lubricant 0.6 0.6 0.6 0.6 0.6 0.6 0.6 BPBA-GO-1 3 1.5 BPBA-GO-1 3 1.5 PBA-GO-1 3 GO 3

[0090] The modified graphene oxide prepared in Examples 1, 2 and Comparative Example 1 was dissolved and filtered through a microporous membrane. The test results of the polybutyl acrylate obtained in the filtrate are shown in Table 1.

[0091] Branched structures result in more compact polymer molecules with smaller hydrodynamic volumes; the higher the degree of branching, the more compact the structure. Compared to linear polymers of the same molecular weight, they exhibit lower intrinsic viscosity and lower MH equation parameter α.

[0092] It is known that no branched monomer was added in Comparative Example 1, while DVB was added as a branched monomer in the examples. As shown in Table 1, compared with Comparative Example 1, the polybutyl acrylate in the modified graphene oxide prepared in the examples has a lower weight-average intrinsic viscosity, a smaller hydrodynamic volume in GPC, and a lower MH equation parameter. This indicates that the polymer in the modified graphene oxide in Example 1 has a higher degree of branching.

[0093] Table 3 Test Results of Ultra-Smooth Semiconductor Shielding Material

[0094]

[0095] As can be seen from the data in Table 3, the basic properties of the cable shielding material prepared by the composition in the examples all meet the indicators specified for cable shielding materials of 220kV voltage level in Q / GDW 11883.2—2018 "Materials for AC Extruded Insulated Cables with Rated Voltage of 110kV to 220kV Part 2: Crosslinkable Semiconductor Shielding Materials".

[0096] Compared to the comparative examples, the comparative examples exhibited poorer resistivity at both room temperature and high temperature, and their surface protrusions did not meet the standards. This was because the conductive carbon black was difficult to disperse in the polar matrix resin, leading to a deterioration in various properties. Example 3, on the other hand, showed the lowest resistivity while significantly reducing the number of surface protrusions smaller than 50 μm. This was because the presence of highly branched structures improved the compatibility of fillers such as carbon black and graphene oxide with the polar resin. Furthermore, the establishment of a long-range conductive network and the introduction of aromatic branched structures enhanced the stability of electrical properties.

[0097] The above embodiments are only used to describe preferred embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that various modifications and improvements made to the technical solutions of the present invention by means of modifications or equivalent substitutions should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A semiconductive shielding material, comprising the following components: 55 to 68 parts by weight of the matrix resin; 30 to 35 parts by weight of conductive carbon black; 0.4 parts by weight to 1 part by weight of antioxidant; 0.5 to 1.5 parts by weight of lubricant; 0.8 to 1.3 parts by weight of crosslinking agent; 1.5 to 4 parts by weight of modified graphene oxide.

2. The semiconductive shielding material according to claim 1, characterized in that, The matrix resin comprises one or more of the following: ethylene-vinyl acetate copolymer, ethylene-butyl acrylate copolymer, ethylene-methyl acrylate copolymer, and ethylene-ethyl acrylate copolymer.

3. The semiconductive shielding material according to claim 1 or 2, characterized in that, The vinyl acetate monomer unit in the ethylene-vinyl acetate copolymer has a mass fraction of 15-30%, preferably 16-20%, and more preferably 16-19%; the butyl acrylate monomer unit in the ethylene-butyl acrylate copolymer has a mass fraction of 15-25%, preferably 16-20%, and more preferably 16-19%; the methyl acrylate monomer unit in the ethylene-methyl acrylate copolymer has a mass fraction of 15-25%, preferably 16-20%, and more preferably 16-19%.

4. The semiconductive shielding material according to any one of claims 1-3, characterized in that, The method for preparing the modified graphene oxide includes the following steps: (1) Graphene oxide was ultrasonically dispersed in a solvent to obtain dispersion 1; (2) Add the polymerizing monomer and the branching monomer to the dispersion 1 and perform ultrasonic dispersion to obtain dispersion 2; (3) Under a nitrogen atmosphere, the dispersion 2 is reacted with the initiator and chain transfer agent; (4) Separate the product from step (3), freeze it, and dry it.

5. The semiconductive shielding material according to any one of claims 1-4, characterized in that, The graphene oxide has a thickness of 0.8–1.2 nm and a sheet diameter of 0.5–5 μm; it contains no more than 44% carbon and no less than 50% oxygen.

6. The semiconductive shielding material according to any one of claims 1-5, characterized in that, The graphene oxide has a thickness of 0.8–1.2 nm and a sheet diameter of 0.5–5 μm; it contains no more than 44% carbon and no less than 50% oxygen.

7. The semiconductive shielding material according to any one of claims 1-6, characterized in that, The polymeric monomer comprises (meth)acrylic acid and its esters, preferably one or more of acrylic acid, methyl acrylate, ethyl acrylate, isooctyl acrylate, butyl acrylate, methyl methacrylate, butyl acrylate, and vinyl acetate.

8. The semiconductive shielding material according to any one of claims 1-7, characterized in that, The branched monomer is an aromatic compound with two or more carbon-carbon double bond functional groups, preferably divinylbenzene.

9. The semiconductive shielding material according to claim 4, characterized in that, In the method for preparing modified graphene oxide, the mass concentration of each raw material is: based on the mass of the raw materials for preparing modified graphene oxide, including the solvent.

10. A method for preparing the semiconductive shielding material according to any one of claims 1-9, comprising the following steps: The matrix resin, conductive carbon black, lubricant, antioxidant, and modified graphene oxide are added to a reciprocating mixer for mixing, filtering, extrusion, granulation using an underwater pelletizing system, and drying to obtain a resin composite material; the resin composite material is then subjected to a post-absorption process with a crosslinking agent to obtain the semiconductive shielding material.

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