Semi-conductive shielding material based on dynamic vulcanization and preparation method thereof

Abstract

The invention relates to a semi-conductive shielding material based on dynamic vulcanization and a preparation method thereof, and belongs to the technical field of cable materials. The semi-conductive shielding material comprises a continuous phase, a dispersed phase, a cross-linking agent, a functional additive and a conductive filler, the dispersed phase is ethylene propylene diene monomer and is dispersed in the continuous phase; the conductive filler is limited to be dispersed in the continuous phase and is lapped to form a conductive network; the continuous phase is polyethylene. According to the scheme provided by the invention, selective dispersion of the conductive filler can be realized, the electrical performance and mechanical performance of the semi-conductive shielding material can be improved while the use amount of the conductive filler is reduced, and the semi-conductive shielding material has the advantage of being recyclable.

Description

Technical Field

[0001] The present application relates to the technical field of cable materials, and in particular to a semi-conductive shielding material based on dynamic vulcanization and a preparation method thereof. Background Art

[0002] With the rapid development of urbanization, urban loads are becoming increasingly dense and the grid structure is becoming increasingly complex. Major cities in China have formed large-capacity concentrated power load centers, and it is urgent to build ultra-high voltage and large-capacity power transmission and transformation projects to realize the centralized transmission of large-scale electric energy. However, urban land resources are very limited and the cost of use is very high. At the same time, it is necessary to meet the requirements of modern cities for clean and beautiful construction. Traditional large-capacity overhead line transmission can no longer meet the various needs of modern urban power transmission and supply. Therefore, the increase in electricity consumption, the centralized transmission of large-scale urban electric energy, and the requirements for environmentally friendly conversion have brought new development opportunities for the application of high-voltage and large-capacity transmission cables. As a key raw material for the production of high-voltage cables, the quality of semi-conductive shielding materials for high-voltage cables is crucial to the safety of use and service life of high-voltage cables.

[0003] In the related art, in the manufacturing process of wires and cables, in order to improve the anti-interference ability and safety of the cable, a semi-conductive shielding layer is usually used to wrap the inner and outer insulating layers. The cable semi-conductive shielding material is made of ethylene-vinyl acetate copolymer (EVA), ethylene-butyl acrylate (EBA) or ethylene-ethyl acrylate (EEA) as the base resin, and conductive materials and functional additives are added and melt-blended. In order to meet the electrical performance requirements, a large amount of conductive materials need to be added to the semi-conductive shielding material, and a large amount of conductive materials will reduce the mechanical properties such as tensile strength and elongation at break of the semi-conductive shielding material, which is difficult to meet the mechanical properties of the cable. A small amount of conductive material is difficult to form a connected conductive network, which is difficult to meet the electrical properties of the cable, and even at high temperatures, the resistivity will show a significant increase trend, affecting the safety of the cable. Therefore, while ensuring the mechanical properties of the semi-conductive shielding material, how to take into account the anti-interference ability of the semi-conductive shielding material should be a key problem that needs to be solved. Summary of the invention

[0004] One of the purposes of the present invention is to avoid the shortcomings of the prior art and provide a semi-conductive shielding material based on dynamic vulcanization, which can achieve selective dispersion of conductive fillers, reduce the amount of conductive fillers, and improve the electrical and mechanical properties of the semi-conductive shielding material, and has the advantage of being recyclable.

[0005] A second object of the present invention is to provide a method for preparing a semi-conductive shielding material based on dynamic vulcanization.

[0006] One of the purposes of the present invention is achieved through the following technical solutions:

[0007] Provided is a semi-conductive shielding material based on dynamic vulcanization, comprising a continuous phase, a dispersed phase, a cross-linking agent, a functional additive and a conductive filler;

[0008] The dispersed phase is EPDM rubber, which is dispersed in the continuous phase;

[0009] The conductive filler is dispersed in the continuous phase and overlaps to form a conductive network;

[0010] The continuous phase is polyethylene.

[0011] In some embodiments, the ratio of the polyethylene to the EPDM rubber is (50-70): (35-45); the amount of the cross-linking agent is 1% to 2% of the mass of the EPDM rubber; and the amount of the conductive filler is 10% to 40% of the sum of the mass of the polyethylene and the EPDM rubber.

[0012] In some embodiments, the functional additives include a dispersant, a lubricant, and an antioxidant;

[0013] The conductive filler includes one or more of conductive carbon black, carbon nanotubes, graphene, flaky silver powder and silver-coated copper powder;

[0014] The crosslinking agent is one or more organic peroxide vulcanizing agents.

[0015] In some embodiments, the organic peroxide curing agent includes one or more of tert-butyl perbenzoate, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, and dibenzoyl peroxide;

[0016] The dispersant is one or both of oleamide and vinyl bisstearamide;

[0017] The lubricant is one or both of zinc stearate and pentaerythritol;

[0018] The antioxidant includes one or more of antioxidant 168, antioxidant 1076, antioxidant 1010, antioxidant 2246, antioxidant 1098, antioxidant B102, antioxidant B900 and antioxidant DLTP.

[0019] The second object of the present invention is achieved by the following technical solutions:

[0020] A method for preparing the above-mentioned semi-conductive shielding material based on dynamic vulcanization is provided, comprising the following steps:

[0021] The polyethylene and the functional additive are melt-blended at a temperature of 160 to 200° C., and then the EPDM rubber is added and mixed evenly to obtain an uncrosslinked mixture;

[0022] adding a crosslinking agent to the uncrosslinked mixture to initiate dynamic vulcanization to obtain a dynamically vulcanized mixture;

[0023] The conductive filler is added into the dynamic vulcanization mixture for blending to obtain a semi-conductive shielding material based on dynamic vulcanization.

[0024] In some embodiments, if the conductive filler includes conductive carbon black and carbon nanotubes, the melt blending of polyethylene and functional additives at a temperature of 160 to 200° C. is specifically as follows:

[0025] The polyethylene is melted and plasticized at a temperature of 150 to 190° C., and then carbon nanotubes are added and mixed evenly, and then the mixture is cooled to room temperature and crushed to obtain polyethylene composite carbon nanotube masterbatch;

[0026] The polyethylene composite carbon nanotube masterbatch, polyethylene and functional additives are melt-blended at a temperature of 160-200°C.

[0027] In some embodiments, the mass ratio of the carbon nanotubes to the conductive carbon black is (2-5):(30-33).

[0028] In some embodiments, the carbon nanotube has a diameter of 10 to 50 nm and a length of 20 to 50 μm; and the carbon nanotube is a multi-walled carbon nanotube.

[0029] In some embodiments, the melt blending is performed at a rotation speed of 60 to 150 rpm for 2 to 15 min; the reaction time of the dynamic vulcanization is 0.5 to 10 min; and the melt plasticization is performed at a rotation speed of 60 to 500 rpm for 2 to 15 min.

[0030] In some embodiments, the melt blending machine includes any one or a combination of an internal mixer and an extruder.

[0031] The technical solution provided by this application may have the following beneficial effects:

[0032] (1) The semi-conductive shielding material based on dynamic vulcanization provided by the present application has the high elasticity of rubber and the thermoplasticity of plastic. The EPDM rubber dispersed phase is dispersed in the polyethylene continuous phase to form an island structure. The conductive network formed by the overlapping of the conductive filler is separately distributed in the continuous phase, realizing the selective dispersion of the conductive filler. Since the conductive filler is only distributed in the polyethylene continuous phase, the packing density of the conductive filler is increased, thereby improving the electrical properties of the semi-conductive shielding material. Under the same electrical performance requirements, the amount of conductive filler used can be reduced, and the influence of the conductive filler on the mechanical properties of the semi-conductive shielding material can be reduced.

[0033] (2) The present application adopts dynamic vulcanization to prepare semi-conductive shielding materials. The vulcanizer captures hydrogen atoms from the EPDM rubber molecular chain to form macromolecular free radicals, so that the linear structure of the EPDM rubber is transformed into a network structure. Under the action of shear, the EPDM rubber is broken into particles and dispersed in molten polyethylene together with the conductive filler. The formed network structure is combined with the olefin chain of the polyethylene, which can improve the mechanical properties of the material. Compared with thermosetting polymer resins, the polyethylene / EPDM rubber prepared in the present application has better product performance.

[0034] (3) The polyethylene continuous phase in the present application has the characteristic of being re-meltable. When the recycled semi-conductive shielding material is melted and recycled, the polyethylene can be converted back into a molten state. Since the EPDM rubber has a network structure, the EPDM rubber is still dispersed in the molten polyethylene in the form of particles when the polyethylene is in a molten state. Therefore, the conductive filler dispersed in the molten polyethylene is still unable to enter the interior of the EPDM rubber, thus achieving circular recycling and utilization, which is in line with the development trend and requirements of green, low-carbon and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The above and other objects, features and advantages of the present application will become more apparent by describing in more detail the exemplary embodiments of the present application in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the present application.

[0036] Figure 1 A flowchart of a specific implementation method provided by the present invention;

[0037] Figure 2 is a scanning electron microscope image of Example 2;

[0038] Figure 3 This is a scanning electron microscope image of Example 3. DETAILED DESCRIPTION

[0039] The preferred embodiments of the present application will be described in more detail below with reference to the accompanying drawings. Although the preferred embodiments of the present application are shown in the accompanying drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to make the present application more thorough and complete, and to fully convey the scope of the present application to those skilled in the art.

[0040] With the rapid development of urbanization, the increase in electricity consumption, the centralized transmission of large-scale urban electricity, and the requirements for environmentally friendly conversion have brought new development opportunities for the application of high-voltage and large-capacity transmission cables. As a key raw material for the production of high-voltage cables, the quality of semi-conductive shielding materials for high-voltage cables is crucial to the safety of use and service life of high-voltage cables.

[0041] In order to meet the electrical performance requirements, a large amount of conductive materials need to be added to the semi-conductive shielding material, and a large amount of conductive materials will reduce the tensile strength and elongation at break of the semi-conductive shielding material, making it difficult to meet the mechanical properties of the cable. A small amount of conductive materials will make it difficult to form a connected conductive network, making it difficult to meet the electrical properties of the cable, and even at high temperatures, the resistivity will show a significant increase trend, that is, a significant PTC effect will be shown, affecting the safety of the cable.

[0042] In view of the above problems, the present invention provides a semi-conductive shielding material based on dynamic vulcanization and a preparation method thereof.

[0043] The present invention is further described in detail below in conjunction with the examples. The components described in the present invention are all commercially available, and the components described in the specific implementation manner or examples are mass ratios or mass parts.

[0044] In a typical embodiment of the present invention, a semi-conductive shielding material based on dynamic vulcanization is provided, which can achieve selective dispersion of conductive fillers, and can still improve the electrical and mechanical properties of the semi-conductive shielding material while reducing the amount of conductive fillers, and has the advantage of being recyclable.

[0045] In one embodiment of the present invention, a semi-conductive shielding material based on dynamic vulcanization is provided, comprising a continuous phase, a dispersed phase, a cross-linking agent, a functional additive and a conductive filler;

[0046] The dispersed phase is EPDM rubber, which is dispersed in the continuous phase;

[0047] The conductive filler is dispersed in the continuous phase and overlaps to form a conductive network;

[0048] The continuous phase is polyethylene.

[0049] A system formed by one or more substances dispersed in another (or more) substances is a dispersed system. Among them, the dispersed substance is called a dispersed phase, and the continuous medium is called a continuous phase. In the present invention, EPDM rubber is used as a dispersed phase, and polyethylene is used as a continuous phase. The EPDM rubber used as a dispersed phase is composed of multiple particles and dispersed in the continuous phase. A particle in the dispersed phase can be used as an independent unit, and a particle and another particle can be regarded as different dispersed internal phases in the dispersed phase. The semi-conductive shielding material provided in this application is similar to a sea-island structure in structure. The conductive filler is dispersed in the continuous phase and overlapped in an undirected manner to form a conductive network. The conductive network formed by the overlap is relative to the dispersion technology in the prior art. Since the conductive filler is only dispersed in the continuous phase, the density of the conductive network formed by the conductive filler in the continuous phase can be increased, thereby improving the electrical properties of the semi-conductive shielding material. The dispersed phase is dispersed in the continuous phase in the form of particles, and the dispersed phase does not contain a conductive filler, which can avoid the conductive filler from interfering with the bonding strength between the EPDM rubber and the polyethylene in the dispersed phase, and ensure the mechanical properties of the semi-conductive shielding material.

[0050] In a preferred embodiment of the present invention, the ratio of the amount of polyethylene and EPDM rubber in the above-mentioned dynamically vulcanized semi-conductive shielding material is (50-70):(35-45); the amount of the cross-linking agent is 1%-2% of the mass of the EPDM rubber; the amount of the conductive filler is 10%-40% of the sum of the mass of the polyethylene and the EPDM rubber.

[0051] Specifically, polyethylene serves as the continuous phase, and the ratio between polyethylene and EPDM rubber determines the packing density of the conductive filler in the continuous phase when the conductive filler is added in a fixed amount. In other words, the present application can obtain a semi-conductive shielding material with a specific resistivity by regulating the addition ratio between polyethylene and EPDM rubber, the addition amount of the conductive filler, and the composition of the conductive filler.

[0052] In the present invention, the usage ratio of polyethylene to EPDM rubber is (50-70):(35-45), specifically 50:35, 50:40, 50:45, 60:35, 60:40, 60:45, 70:35, 70:40, 70:45.

[0053] In the present invention, the amount of the crosslinking agent is 1% to 2% of the mass of the EPDM rubber, specifically 1%, 1.2%, 1.4%, 1.6%, 1.8% or 2%.

[0054] In the present invention, the amount of conductive filler is 10% to 40% of the sum of the mass of polyethylene and EPDM rubber, specifically 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 45%.

[0055] In the present invention, the functional additives include dispersants, lubricants and antioxidants. In specific implementation, one or more of conductive carbon black, carbon nanotubes, graphene, flaky silver powder, and silver-coated copper powder can be selected according to the electrical performance requirements of the cable; one or more of phenolic system vulcanizers, sulfur system vulcanizers and organic peroxide vulcanizers can be selected according to the dynamic vulcanization requirements of EPDM rubber.

[0056] The present invention has no particular limitation on polyethylene, EPDM rubber, dispersant, lubricant and antioxidant. The polyethylene, EPDM rubber, dispersant, lubricant and antioxidant known to those skilled in the art may be used, and may be prepared according to conventional methods or purchased commercially.

[0057] The conductive filler of the present invention includes one or more combinations of conductive carbon black, carbon nanotubes, furnace black, acetylene black, graphene, flaky silver powder, and silver-coated copper powder. Typical but non-limiting examples of the combination include conductive carbon black and carbon nanotubes, conductive carbon black and graphene, conductive carbon black and flaky silver powder, carbon nanotubes and flaky silver powder, flaky silver powder and silver-coated copper powder, etc.

[0058] The present invention has no particular restriction on the amount of the conductive filler added. In order to improve the dispersion and conductivity of the present invention, the conductive filler is 10% to 40% of the sum of the mass of the polyethylene and the EPDM rubber. Exemplarily, when the conductive filler is conductive carbon black, the amount of the conductive filler can be 20%, 25%, 30%, 32%, 35%, 37%, or 40%. Furthermore, the oil absorption value of the conductive carbon black is 130mL / 100g to 200mL / 100g. For example, the oil absorption value of the conductive carbon black is 140mL / 100g, 150mL / 100g, 180mL / 100g, etc. The particle size distribution of the conductive carbon black is 30nm to 70nm, and the surface area is 60 to 90m 2 When the conductive filler is a combination of conductive carbon black and carbon nanotubes, the conductive carbon black is used as the main conductive component, and the carbon nanotubes are used as the conductive performance enhancement phase to enhance the conductive performance of the semiconductor shielding material. Specifically, the amount of carbon nanotubes is 1% to 5% of the main conductive component.

[0059] The crosslinking agent of the present invention includes an amine vulcanizing agent, a bisphenol vulcanizing agent or a peroxide vulcanizing agent, and more preferably a peroxide vulcanizing agent. Peroxide refers to a compound containing one or more oxygen-oxygen bonds (ROOR') in the structure. Under the action of heat energy, peroxide forms alkoxy radicals or alkyl radicals through homolysis, and the free radicals can capture hydrogen atoms from the ethylene propylene diene monomer (EPDM) molecular chain to form EPDM macromolecular free radicals. The peroxide vulcanizing agent of the present invention includes one or more of tert-butyl perbenzoate, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, diisopropylbenzene peroxide, di-tert-butyl peroxide and dibenzoyl peroxide, and more preferably diisopropylbenzene peroxide.

[0060] The dispersant of the present invention comprises one or both of oleic acid amide and vinyl bisstearic acid amide, more preferably oleic acid amide; the lubricant of the present invention comprises one or both of zinc stearate and pentaerythritol, more preferably zinc stearate; the antioxidant of the present invention comprises one or more combinations of antioxidant 168, antioxidant 1076, antioxidant 1010, antioxidant 2246, antioxidant 1098, antioxidant B102, antioxidant B900 and antioxidant DLTP, typical but non-limiting examples of the combination include combinations of antioxidant 168 and antioxidant 1076, antioxidant 1076 and antioxidant 1010, and antioxidant DLTP and antioxidant B102.

[0061] The semi-conductive shielding material based on dynamic vulcanization provided by the present application has the high elasticity of rubber and the thermoplasticity of plastic compared with the existing EVA, EBA and EEA. The EPDM dispersed phase is dispersed in the polyethylene continuous phase to form an island structure. The conductive network formed by the overlap of the conductive filler is separately distributed in the continuous phase, realizing the selective dispersion of the conductive filler. Since the conductive filler is only distributed in the polyethylene continuous phase, the packing density of the conductive filler in the semi-conductive shielding material is increased, thereby improving the electrical properties of the semi-conductive shielding material. Under the same electrical performance requirements, the amount of conductive filler used can be reduced, and the influence of the conductive filler on the mechanical properties of the semi-conductive shielding material can be reduced.

[0062] Please refer to Figure 1 , Figure 1 The present invention provides a flowchart of a specific implementation method.

[0063] In another embodiment of the present invention, a method for preparing a semiconductive shielding material based on dynamic vulcanization is provided, the preparation method comprising:

[0064] The polyethylene and the functional additive are melt-blended at a temperature of 160 to 200° C., and then the EPDM rubber is added and mixed evenly to obtain an uncrosslinked mixture;

[0065] adding a crosslinking agent to the uncrosslinked mixture to initiate dynamic vulcanization to obtain a dynamically vulcanized mixture;

[0066] The conductive filler is added into the dynamic vulcanization mixture for blending to obtain a semi-conductive shielding material based on dynamic vulcanization.

[0067] Polyethylene can be LDPE, MDPE and HDPE. Polyethylene, dispersant, lubricant and antioxidant are added to the torque rheometer for melting and plasticization, EPDM rubber is added and mixed evenly, and vulcanizing agent is added to initiate dynamic vulcanization. At this time, the EPDM rubber undergoes a cross-linking reaction, and is broken into particles and dispersed in the polyethylene continuous phase under the temperature of 160 to 200°C and shear force to form a thermoplastic elastomer with a "sea-island" structure. Specifically, the temperature of the heating treatment is 160°C to 200°C. Optionally, the temperature of the heating treatment is 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C or 200°C, etc. In specific implementation, the temperature of the heating treatment can be adjusted according to the actual production situation, for example, the heating treatment time is 10min to 60min. After the vulcanization reaction is completed, a conductive filler is added. Since EPDM rubber is in a high-viscosity viscoelastic state when polyethylene is in a molten state, EPDM rubber can be regarded as a solid relative to the conductive filler. Therefore, even under the action of shear dispersion, the conductive filler cannot enter the interior of the EPDM rubber, so the conductive filler can only be filled and dispersed in the polyethylene continuous phase. The conductive filler filled in the polyethylene continuous phase is evenly dispersed by a dispersant and a lubricant, so that the semi-conductive shielding material provided by the present invention has the advantages of reducing the amount of conductive filler and improving mechanical properties under the same electrical performance requirements. The semi-conductive shielding material prepared by this method eliminates the high-temperature vulcanization process in the subsequent co-extrusion process with the insulating layer, reduces energy consumption, and has good recyclability.

[0068] In a preferred embodiment of the present invention, in the above preparation method, if the conductive filler includes conductive carbon black and carbon nanotubes, the melt blending of polyethylene and functional additives at a temperature of 160 to 200° C. is specifically as follows:

[0069] The polyethylene is melted and plasticized at a temperature of 160 to 200° C., and then carbon nanotubes are added and mixed evenly, and then the mixture is cooled to room temperature and crushed to obtain polyethylene composite carbon nanotube masterbatch;

[0070] The polyethylene composite carbon nanotube masterbatch, polyethylene and functional additives are melt-blended at a temperature of 160-200°C.

[0071] Furthermore, the mass ratio of carbon nanotubes to conductive carbon black in the above preparation method is (2-5):(30-33).

[0072] Furthermore, the carbon nanotubes prepared by the above method have a diameter of 10 to 50 nm and a length of 20 to 50 μm; the carbon nanotubes are multi-walled carbon nanotubes.

[0073] Specifically, the mass ratios of carbon nanotubes to conductive carbon black are 2:33, 3.5:31.5, and 5:30. The conductive carbon black and carbon nanotubes are compounded to synergistically improve the conductivity of the material.

[0074] In a preferred embodiment of the present invention, the melt blending of the preparation method is mixed at a rotation speed of 60-150 rpm for 2-15 min; the reaction time of the dynamic vulcanization is 0.5-10 min; and the melt plasticization is mixed at a rotation speed of 60-500 rpm for 2-15 min.

[0075] In a preferred embodiment of the present invention, the melt blending machine in the above preparation method includes any one or a combination of an internal mixer and an extruder.

[0076] The beneficial effects of the present invention will be further described below in conjunction with embodiments.

[0077] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0078] The embodiments of the present invention can use the test methods in (GB / T 18890.2-2015) to test the corresponding items: tensile strength (MPa), elongation at break (%), tear strength (kN / m), volume resistivity at 23°C (Ω·cm), and volume resistivity at 90°C (Ω·cm).

[0079] Examples 1 to 5 and Comparative Examples 1 to 2

[0080] 1. Raw material formula:

[0081] The raw materials for preparing Examples 1 to 5 and Comparative Examples 1 to 2 are shown in Table 1:

[0082]

[0083]

[0084] 2. Preparation of semi-conductive shielding materials

[0085] 2.1 Preparation

[0086] 2.1.1 Among them, Examples 1 to 5 and Comparative Example 1 were prepared using the preparation method of the present application, specifically as follows:

[0087] Weigh the raw materials according to the amount, add polyethylene, dispersant, lubricant and antioxidant into the torque rheometer, melt and mix evenly at 160°C and 90rpm; add EPDM rubber and mix evenly; then add a cross-linking agent to initiate dynamic vulcanization, and continue mixing until the torque is balanced; finally, add the conductive filler and blend evenly, discharge the material, cool it to room temperature, and then crush it to obtain a semi-conductive shielding material; wherein, in Examples 1 to 5 and Comparative Example 1, the conductive filler is conductive carbon black or a conductive carbon black / carbon nanotube composite component; the cross-linking agent is diisopropyl peroxide; and the polyethylene is all LDPE.

[0088] 2.1.2 Comparative Example 2 was prepared using the conventional method, as follows:

[0089] Weigh the raw materials according to the amount, add polyethylene, EPDM rubber, conductive carbon black, dispersant, lubricant, antioxidant and cross-linking agent into the torque rheometer, melt mix evenly at 160°C and 90rpm, the total time is the same as that of Examples 1 to 5, discharging and cooling to room temperature and then crushing to obtain the semi-conductive shielding material of Comparative Example 2.

[0090] 2.2 Product testing: tensile strength, elongation at break, tear strength, 23℃ volume resistivity, and 90℃ volume resistivity tests are carried out in accordance with (GB / T 18890.2-2015).

[0091] 2.3 The test parameters of Examples 1 to 5 and Comparative Examples 1 to 2 are shown in Table 2:

[0092]

[0093] 2.4 Conclusion Analysis:

[0094] In Examples 1 to 5 and Comparative Examples 1 to 2, the amount of polyethylene, EPDM rubber and functional additives used is the same. When the composition of the above three components remains unchanged, we examine the mechanical properties and electrical properties of the semi-conductive shielding material by the amount of crosslinking agent, conductive filler and the composition of the conductive filler. From Table 2, we can see that in Examples 1 to 3, the amount of conductive carbon black used increases successively, the elongation at break of the three embodiments gradually decreases, the volume resistivity also gradually decreases, and the difference in tensile strength and tear strength is small, which shows that the higher the content of conductive carbon black, the more conducive the carbon black dispersed in the polyethylene continuous phase is to form a conductive network. In Examples 1 and Examples 4 to 5, the amount of conductive filler added is the same, and the main difference is that a small amount of carbon nanotubes is used to replace conductive carbon black in Example 4 and Example 5. It can be seen that the synergistic enhancement effect of carbon nanotubes on the electrical properties of semi-conductive shielding materials also shows that under certain volume resistivity requirements, the amount of conductive filler used can be reduced by selective dispersion, and carbon nanotubes can be used to replace part of the conductive carbon black, further reducing the amount of conductive carbon black, thereby improving the mechanical properties of the semi-conductive shielding material.

[0095] The difference between Comparative Example 1 and Example 1 is that no cross-linking agent is used. The tensile strength, elongation at break, tear strength, and volume resistivity at 23°C and 90°C of Comparative Example 1 are all worse than those of Example 1. The reason is that when EPDM rubber and polyethylene are melt-blended, the EPDM rubber is not dynamically vulcanized, and the EPDM rubber cannot play a role in volume exclusion. The conductive carbon black can be freely dispersed in the EPDM rubber dispersed phase, which reduces the packing density of the conductive carbon black, reduces the overlap density of the conductive network, and reduces the conductive properties and mechanical properties of the semi-conductive shielding material.

[0096] The method used in Comparative Document 2 is a conventional existing preparation method, which is to melt and plasticize by feeding the materials at one time and combining the temperature designed in this application. The experimental results of Comparative Example 2 show that the mechanical properties of the semi-conductive shielding material prepared by this method are slightly worse than those of Example 5, and the volume resistivity at 23°C and 90°C is quite different from that of Example 5. Specifically, the vulcanization process of rubber can generally be divided into an induction period, a vulcanization reactor and a pervulcanization period. After the material is put into the torque rheometer at one time, each component needs a certain amount of time to heat up. At this time, the EPDM rubber is in the induction period and appears as a fluid with a certain viscosity. Under the action of shear force, it is broken into small droplets, and the conductive carbon black is adsorbed on the surface of the droplets. However, since the EPDM rubber is still in the induction period at this time, the droplets agglomerate into large droplets under the action of shear force, and then continue to break into small droplets. At this time, the EPDM rubber and polyethylene are both continuous phases, so the mixed conductive carbon black can be dispersed in the EPDM rubber until the carbon black is completely dispersed in the system to reach equilibrium or the EPDM rubber enters the vulcanization reaction period, causing the broken small droplets to undergo a cross-linking reaction, prompting the linear structure of the EPDM rubber to be transformed into a network structure, and the EPDM rubber is solidified into granular form.

[0097] It can be seen that the reason why the EPDM rubber without cross-linking in Comparative Document 1 cannot achieve selective dispersion of conductive carbon black is that the EPDM rubber acts as a continuous phase together with polyethylene during melt blending, and the conductive carbon black can freely enter the EPDM rubber. Comparative Example 2 uses one-time feeding. When the EPDM rubber undergoes the vulcanization induction period, the cross-linking reaction is weak at this time. The EPDM rubber and polyethylene act as a continuous phase together, so that the conductive carbon black can be freely mixed with the EPDM rubber during the vulcanization induction period. After entering the vulcanization reaction period, the EPDM rubber acts as a dispersed phase. Although it can prevent the conductive carbon black from entering the interior of the EPDM rubber particles, due to the dispersion effect of the previous vulcanization induction period, part of the conductive carbon black is filled in the EPDM rubber, thereby reducing the filling density of the conductive carbon black in the polyethylene, thereby affecting the electrical properties of the semi-conductive shielding material.

[0098] In summary, the semi-conductive shielding material with dynamic vulcanization provided by the present application, the selective dispersion of conductive fillers enhances the conductivity of the semi-conductive shielding material and maintains good mechanical properties. Its application in high-voltage cables can well protect cable facilities.

[0099] In addition, the present application also carried out electron microscope scanning on the semi-conductive shielding materials prepared in Examples 2 and 3. The electron microscope scanning photos are shown in Figure 2 and Figure 3 .

[0100] like Figure 2 and Figure 3As shown, the conductive carbon black is evenly dispersed in the polyethylene continuous phase. The area selected by the red circle in the figure is the cross-linked EPDM phase, and there are fewer carbon black particles, indicating that the selective dispersion of the conductive carbon black is achieved by the technology of the present invention.

[0101] The embodiments of the present application have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A semi-conductive shielding material based on dynamic vulcanization, characterized in that: It includes continuous phase, dispersed phase, cross-linking agent, functional additive and conductive filler; The dispersed phase is EPDM rubber, which is dispersed in the continuous phase; The conductive filler is dispersed in the continuous phase and overlaps to form a conductive network; The continuous phase is polyethylene.

2. The semi-conductive shielding material based on dynamic vulcanization according to claim 1, characterized in that: The dosage ratio of polyethylene to EPDM rubber is (50-70):(35-45); the dosage of the cross-linking agent is 1%-2% of the mass of the EPDM rubber; and the dosage of the conductive filler is 10%-40% of the sum of the mass of polyethylene and EPDM rubber.

3. The semi-conductive shielding material based on dynamic vulcanization according to claim 1, characterized in that: The functional additives include dispersants, lubricants and antioxidants; The conductive filler includes one or more of conductive carbon black, carbon nanotubes, graphene, flaky silver powder, and silver-coated copper powder; The crosslinking agent is an organic peroxide vulcanizing agent.

4. The semi-conductive shielding material based on dynamic vulcanization according to claim 3, characterized in that: The organic peroxide vulcanizing agent includes one or more of tert-butyl perbenzoate, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide and dibenzoyl peroxide; The dispersant is one or both of oleamide and vinyl bisstearamide; The lubricant is one or both of zinc stearate and pentaerythritol; The antioxidant includes one or more of antioxidant 168, antioxidant 1076, antioxidant 1010, antioxidant 2246, antioxidant 1098, antioxidant B102, antioxidant B900 and antioxidant DLTP.

5. A method for preparing a semi-conductive shielding material based on dynamic vulcanization according to any one of claims 1 to 4, characterized in that: The preparation method comprises: The polyethylene and the functional additive are melt-blended at a temperature of 160 to 200° C., and then the EPDM rubber is added and mixed evenly to obtain an uncrosslinked mixture; adding a crosslinking agent to the uncrosslinked mixture to initiate dynamic vulcanization to obtain a dynamically vulcanized mixture; The conductive filler is added into the dynamic vulcanization mixture for blending to obtain a semi-conductive shielding material based on dynamic vulcanization.

6. The method for preparing a semi-conductive shielding material based on dynamic vulcanization according to claim 5, characterized in that: If the conductive filler includes conductive carbon black and carbon nanotubes, the melt blending of polyethylene and functional additives at a temperature of 160 to 200° C. is specifically as follows: The polyethylene is melted and plasticized at a temperature of 150 to 190° C., and then carbon nanotubes are added and mixed evenly, and then the mixture is cooled to room temperature and crushed to obtain polyethylene composite carbon nanotube masterbatch; The polyethylene composite carbon nanotube masterbatch, polyethylene and functional additives are melt-blended at a temperature of 160-200°C.

7. The method for preparing a semi-conductive shielding material based on dynamic vulcanization according to claim 6, characterized in that: The mass ratio of the carbon nanotubes to the conductive carbon black is (2-5):(30-33).

8. The method for preparing a semi-conductive shielding material based on dynamic vulcanization according to claim 7, characterized in that: The carbon nanotubes have a diameter of 10 to 50 nm and a length of 20 to 50 μm; the carbon nanotubes are multi-walled carbon nanotubes.

9. The method for preparing a semi-conductive shielding material based on dynamic vulcanization according to claim 6, characterized in that: The melt blending is mixed at a rotation speed of 60 to 150 rpm for 2 to 15 minutes; the reaction time of the dynamic vulcanization is 0.5 to 10 minutes; and the melt plasticization is mixed at a rotation speed of 60 to 500 rpm for 2 to 15 minutes.

10. The method for preparing a semi-conductive shielding material based on dynamic vulcanization according to claim 5, characterized in that: The melt blending machine includes any one or a combination of an internal mixer and an extruder.

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