Semi-conductive three-dimensional mesh cable buffer layer material and preparation method thereof

Abstract

The invention discloses a semi-conductive three-dimensional mesh cable buffer layer material. Comprising the following components in parts by weight: 40-50 parts of an ethylene-vinyl acetate copolymer, 30-40 parts of low-density polyethylene, 10-25 parts of an olefin block copolymer, 8-12 parts of a foaming agent, 1-3 parts of a foaming aid, 1-3 parts of a crosslinking sensitizer, 0.5-3 parts of a sensitizing aid, 2-5 parts of polyethylene wax, 15-25 parts of conductive carbon black, 0.1-0.5 part of an antioxidant, 4-8 parts of a filler and 6-10 parts of a special aid. The invention also discloses a preparation method of the semi-conductive three-dimensional mesh cable buffer layer material. The master slice to be crosslinked can be prepared through one-step forming, the technological process is greatly simplified, the cost is saved, and the comprehensive cost of 550-850 yuan can be reduced for each ton of products. The prepared semi-conductive three-dimensional mesh cable buffer layer material plays a role in buffering between a high-voltage cable insulation shield and a metal sheath, is excellent in discharge ablation resistance, current impact resistance and transverse water resistance, does not need additional moisture-proof treatment compared with the prior art, remarkably reduces the numerical values of volume resistance and surface resistance, and is suitable for large-scale production. And the problems of cable radial power concentration and discharge ablation caused by material falling in the later stage of moisture-proof treatment are greatly solved.

Description

Technical Field

[0001] The invention relates to the technical field of high-voltage cables and foamed polyolefin products, and in particular to a semi-conductive three-dimensional mesh cable buffer layer material and a preparation method thereof. Background Art

[0002] So far, 66-500kV power cables have been basically all domestically produced, and more than 10,000 kilometers of high-voltage cables are buried underground every year. From the analysis of production equipment, raw material selection, product characteristics and production process, one of the main factors affecting the quality of high-voltage cross-linked polyethylene insulated power cables is the sheath structure, raw material performance and sheath processing technology. The main problem that currently plagues high-voltage cross-linked polyethylene insulated power cables in China is the ablation of the buffer layer. How to solve the ablation of the buffer layer has become one of the technical research topics of major domestic cable companies, and it is also an urgent problem that needs to be solved.

[0003] Chinese patent CN105304180A provides a semi-conductive buffer water-blocking tape, which includes a substrate structure layer, a material structure layer, an environmentally friendly polyester film and a mica tape. The substrate structure layer is formed by uniformly coating a non-woven fabric or polyester fabric with a semi-conductive adhesive by a roller dyeing method. The material structure layer is mainly prepared with rubber and thermoplastic elastomer. The substrate structure layer and the material structure layer are calendered to form a semi-conductive shielding buffer water-blocking tape. However, the production process of the semi-conductive buffer water-blocking tape is complicated, and in the cable production process, the compatibility problem of the semi-conductive water-blocking tape easily causes radial current concentration in the cable, or the hygroscopicity of the semi-conductive water-blocking tape causes ablation in the cable buffer layer or accelerates the formation of white powder, thereby forming a cable electric field stress concentration, which becomes a safety hazard for high-voltage power cables. At present, most high-voltage cable failures occur in the cable buffer layer.

[0004] This is because the semi-conductive buffer water-blocking tapes currently used in the market are all non-woven fabrics made of textile fibers, and then the semi-conductive carbon black is made into a conductive slurry, and the conductive liquid is coated on the non-woven fabric using a dyeing process, and then squeezed and dried (the specific drying process is shown in Chinese patent CN204918988 U).

[0005] In the existing technology of semi-conductive buffer water-blocking tape processing, since the conductive carbon black is coated on the non-woven fabric, the water-blocking tape manufactured by the coating process may fall off during long-term exposure to moisture, thereby causing electric field stress concentration in the cable buffer layer, and then discharge ablation. Summary of the invention

[0006] In order to overcome the biggest technical defect in the prior art, the purpose of the present invention is to provide a semi-conductive three-dimensional mesh cable buffer layer material and a preparation method thereof.

[0007] Compared with the prior art, the invention improves the formula and does not use the processing technology of coating the non-woven fabric with conductive carbon black.

[0008] The mother sheet to be cross-linked can be obtained by molding in one step, which greatly simplifies the process flow. The obtained product has stable semi-conductive performance, light weight, non-toxicity, no odor, and excellent moisture-repellent performance and mechanical properties.

[0009] The prepared semi-conductive three-dimensional mesh cable buffer layer material plays a buffering role between the insulation shield and the metal sheath of the high-voltage cable. It has excellent resistance to discharge erosion, current shock and lateral water blocking. It does not require additional moisture-proof treatment, which greatly solves the problem of radial power concentration and discharge erosion of the cable caused by the shedding of materials after moisture-proof treatment.

[0010] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0011] The present invention provides a semi-conductive three-dimensional mesh cable buffer layer material, comprising the following components in parts by weight:

[0012]

[0013] The melt index MI of the ethylene-vinyl acetate copolymer and low-density polyethylene at 190°C×2.16kg is 1-3g / 10min; the olefin block copolymer is an ethylene-octene copolymer, wherein the octene content is 20-30% and the density is 0.865-0.895g / cm3.

[0014] Further, the foaming agent is azodicarbonamide, diisopropyl azodicarboxylate or azobisisobutyl cyanide. Preferably, the foaming agent is azodicarbonamide, the mesh number of which is 300-1000, and the pH value is 5-8. More preferably, the mesh number of the azodicarbonamide is 500-700, and the pH value is 6-7.

[0015] Furthermore, the foaming aid is a compound of zinc oxide and stearic acid. Preferably, in the compound, the mass ratio of zinc oxide to stearic acid is 1:1-10.

[0016] Furthermore, the sensitizing agent is dibasic lead phosphite, tribasic lead sulfate, calcium stearate or zinc stearate, preferably zinc stearate. The addition of the sensitizing agent is conducive to lowering the foaming temperature, thereby reducing the influence of high temperature on the properties of the foaming material.

[0017] Furthermore, the crosslinking agent is one or more of triallyl isocyanurate (TAIC), triallyl cyanurate (TAC) and trimethylolpropane trimethacrylate (TMPTMA). In the present invention, by adding a crosslinking agent, the irradiation dose and irradiation cost are reduced, and the damage of irradiation to material properties is reduced.

[0018] Furthermore, the filler is calcium carbonate or talcum powder. Adding calcium carbonate or talcum powder can help improve the dimensional stability and processability of the product.

[0019] Furthermore, the conductive carbon black is in powder form, with a particle size of 15-45 nm and a pH value of 6-9. Conductive carbon black within this particle size range has a better conductive effect, and due to the excellent conductive properties of the conductive carbon black itself, the amount of conductive carbon black added can be reduced as much as possible on the basis of satisfying the conductive capacity of the product, thereby improving the foaming effect of the product.

[0020] Furthermore, the antioxidant consists of a main antioxidant and an auxiliary antioxidant, the main antioxidant is a phenolic main antioxidant 1010 or 1076, and the auxiliary antioxidant is a thioester auxiliary antioxidant such as dilauryl thiodipropionate (DLTP), ditetradecyl thiodipropionate (DMTP) or distearyl thiodipropionate (DSTP).

[0021] Furthermore, the special additive is one or more of metal powder, graphene or carbon fiber with excellent conductive properties, such as copper powder, amorphous iron, carbon fiber powder, nano iron powder, and graphene powder.

[0022] The present invention also provides a method for preparing the semi-conductive three-dimensional mesh cable buffer layer material, comprising the following steps:

[0023] The first step is to mix the formulated amount of ethylene-vinyl acetate copolymer, low-density polyethylene, olefin block copolymer, crosslinking agent, polyethylene wax and antioxidant, conductive carbon black, filler and special additives in an internal mixer, liquid-cool the internal mixer, and then add a foaming agent and heat and mix to 120-130°C;

[0024] In the second step, the kneaded material and the foaming sensitizer in the first step are added into an extruder and extruded to obtain a master sheet;

[0025] The third step is to irradiate the master sheet obtained in the second step at a radiation dose of 8-14 Mrad to obtain a cross-linked sheet;

[0026] The fourth step is to foam the cross-linked sheet obtained in the third step at 230-260° C. to obtain the semi-conductive three-dimensional mesh cable buffer layer material.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The mother sheet to be cross-linked can be obtained in one step, which greatly simplifies the process flow and saves costs, which can reduce the overall cost by 550-850 yuan per ton of product.

[0029] The prepared semi-conductive three-dimensional mesh cable buffer layer material plays a buffering role between the insulation shield and the metal sheath of the high-voltage cable. It has excellent resistance to discharge erosion, current impact and lateral water resistance. Compared with the existing technology, it does not require additional moisture-proof treatment, significantly reduces the values ​​of volume resistance and surface resistance, and greatly solves the problems of radial power concentration and discharge erosion of the cable caused by the shedding of materials in the later stage of moisture-proof treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention is a process roadmap for preparing the semi-conductive three-dimensional mesh cable buffer layer material.

[0031] Figure 2 A physical comparison diagram of the water-blocking tape in the prior art and the water-blocking tape made of the semi-conductive three-dimensional mesh cable buffer layer material of the present invention. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0034] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods, and the materials, reagents, etc. used are all available from commercial sources unless otherwise specified.

[0035] Examples 1 to 3: Preparation of semi-conductive three-dimensional mesh cable buffer layer material

[0036] This embodiment provides a semi-conductive three-dimensional mesh cable buffer layer material and a preparation method thereof, comprising the following steps:

[0037] Step 1: Mixing

[0038] According to the formula in Table 1, ethylene-vinyl acetate copolymer, low-density polyethylene, olefin block copolymer, crosslinking agent, polyethylene wax and antioxidant, conductive carbon black, filler and special additives are mixed evenly in an internal mixer, the internal mixer is liquid-cooled, and then a foaming agent is added and heated to a temperature range of 120 to 130° C. to obtain a foamed internal mixer product.

[0039] Step 2: One-step molding to obtain the master sheet

[0040] The material kneaded in step 1 is directly put into the main feeding hopper of the single screw extruder. There is a feeding section in the middle section of the single screw extruder. The foaming sensitizer is added in proportion from the feeding section. A die head that meets the requirements is installed at the end of the single screw extruder to extrude the mother sheet.

[0041] Step 3: Irradiation cross-linking

[0042] The master sheet obtained in step 2 was irradiated at a dose of 12 Mrad to obtain a cross-linked sheet.

[0043] Step 4: High temperature foaming

[0044] The cross-linked sheet obtained in step 3 is subjected to high-temperature foaming in a foaming furnace with a foaming ratio of 5 to 10 times to obtain a semi-conductive foamed buffer layer material molded product with a thickness of 2 mm.

[0045] Table 1 Formula of semi-conductive three-dimensional mesh cable buffer layer material of Examples 1-5

[0046]

[0047]

[0048] In the above embodiments:

[0049] In embodiment 1 or 4:

[0050] The melt index of ethylene vinyl acetate is MI = 2 g / 10 min;

[0051] The melt index of low-density polyethylene is MI = 1.5 g / 10 min;

[0052] The foaming agent is azodicarbonamide with a mesh size of 500-700 and a pH value of 6-7;

[0053] The foaming aid is zinc oxide;

[0054] The sensitizing agent is zinc stearate;

[0055] The particle size of conductive carbon black is 15-25nm, pH = 6-7.5;

[0056] The antioxidant is the main antioxidant 1076 + the auxiliary antioxidant DSTP. The mixing ratio is 2:1. The cross-linking agent is a mixture of TAIC and TAC, and the mixing ratio is 2:1.

[0057] In embodiment 2 or 5:

[0058] The melt index of ethylene vinyl acetate is MI = 1.5 g / 10 min;

[0059] The melt index of low-density polyethylene is MI = 2g / 10min;

[0060] The foaming agent is azodicarbonamide with a mesh size of 500-700 and a pH value of 6-7;

[0061] The foaming aid is a mixture of zinc oxide and stearic acid in a mass ratio of 1:5;

[0062] The sensitizing agent is zinc stearate;

[0063] The particle size of conductive carbon black is 15-25nm, pH = 6-7.5;

[0064] The antioxidant is a main antioxidant 1076 + an auxiliary antioxidant DSTP, the mixing ratio is 2:1. The crosslinking agent is a mixture of TAIC and TMPTMA, the mixing ratio is 2:1. In Example 3:

[0065] The melt index of ethylene vinyl acetate is MI = 2 g / 10 min;

[0066] The melt index of low-density polyethylene is MI = 2g / 10min;

[0067] The foaming agent is azodicarbonamide with a mesh size of 500-700 and a pH value of 6-7;

[0068] The foaming aid is a mixture of zinc oxide and stearic acid in a mass ratio of 1:5;

[0069] The sensitizing agent is zinc stearate;

[0070] The particle size of conductive carbon black is 25-40nm, pH = 7.5-8.5;

[0071] The antioxidant is the main antioxidant 1010 and the auxiliary antioxidant DSTP; the mixing ratio is 2:1. The cross-linking agent is a mixture of TAC and TMPTMA, the mixing ratio is 2:1. In comparative example 6:

[0072] The melt index of ethylene vinyl acetate is MI = 1.5 g / 10 min;

[0073] The melt index of low-density polyethylene is MI = 2g / 10min;

[0074] The foaming agent is azodicarbonamide with a mesh size of 500-700 and a pH value of 6-7;

[0075] The foaming aid is a mixture of zinc oxide and stearic acid in a mass ratio of 1:5;

[0076] The sensitizing agent is zinc stearate;

[0077] The particle size of conductive carbon black is 15-25nm, pH = 6-7.5;

[0078] The antioxidant is the main antioxidant 1076 + the auxiliary antioxidant DSTP, and the mixing ratio is 2:1. The cross-linking agent is a mixture of TAIC and TMPTMA, and the mixing ratio is 2:1.

[0079] Performance Test:

[0080] The semi-conductive polyolefin foam material prepared in the example was tested for performance, and the results are shown in Table 2.

[0081] Table 2 Performance test results of semi-conductive shielding polyolefin foam products prepared in Examples 1 to 5 and Comparative Example 6

[0082]

[0083] As can be seen from Table 2, the semi-conductive radiation cross-linked polyolefin foamed buffer layer products prepared in Examples 1-5 meet the requirements of the JB / T 10259 standard on semi-conductive buffer water-blocking layer materials in terms of tensile strength, elongation at break, volume resistivity and surface resistance compared with the foamed antistatic materials in the comparative example in various performance tests, and have excellent moisture-repellent properties, excellent discharge ablation resistance, current impact resistance and lateral water-blocking properties.

[0084] In particular, the present invention optimizes and reduces the amount of conductive carbon black added (an amount less than 10% can significantly save the cost of adding conductive carbon black), and compounds it with metal powder (copper powder and / or nano iron powder), thereby significantly reducing the values ​​of volume resistance and surface resistance (the volume resistance is less than 10 to the cube, while the volume resistance of the prior art is greater than 10 to the fifth power).

[0085] In addition, compared with the prior art, the mechanical properties of the conventional semi-conductive buffer layer are relatively low, with an elongation of only about 10%, and the volume resistivity and surface resistivity are better than those of the foamed buffer layer material. Since the conductive carbon black is directly coated on the surface, it is easy to lose and corona is easily generated on the surface of the buffer layer. Therefore, the conventional semi-conductive buffer layer will generate sparks when the voltage is applied to about 24kV, while the buffer layer material of the present invention needs to be pressurized to about 30kV before sparks will occur.

[0086] There are also obvious differences in heat resistance and stability. After heat shock treatment at 280°C / 3min, the conventional semi-conductive buffer layer water-blocking tape has obvious curling and delamination, while the buffer layer material of the present invention can still retain the original shape characteristics.

[0087] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A semi-conductive three-dimensional mesh cable buffer layer material, characterized in that: It includes the following components by weight:

2. A semi-conductive three-dimensional mesh cable buffer layer material as claimed in claim 1, characterized in that: The melt index MI of the ethylene-vinyl acetate copolymer and low-density polyethylene at 190°C×2.16kg is 1-3g / 10min; the olefin block copolymer is an ethylene-octene copolymer, wherein the octene content is 20-30% and the density is 0.865-0.895g / cm3.

3. A semi-conductive three-dimensional mesh cable buffer layer material as claimed in claim 1, characterized in that: The foaming agent is azodicarbonamide, diisopropyl azodicarboxylate or azobisisobutylcyanide.

4. A semi-conductive three-dimensional mesh cable buffer layer material as claimed in claim 1, characterized in that: The foaming auxiliary agent is a compound of zinc oxide and stearic acid.

5. A semi-conductive three-dimensional mesh cable buffer layer material as claimed in claim 1, characterized in that: The sensitizing aid is dibasic lead phosphite, tribasic lead sulfate, calcium stearate or zinc stearate.

6. A semi-conductive three-dimensional mesh cable buffer layer material as claimed in claim 1, characterized in that: The crosslinking agent is one or more of triallyl isocyanurate, triallyl cyanurate and trimethylolpropane trimethacrylate.

7. A semi-conductive three-dimensional mesh cable buffer layer material as claimed in claim 1, characterized in that: The filler is calcium carbonate or talc.

8. The semi-conductive three-dimensional mesh cable buffer layer material according to claim 1, characterized in that: The conductive carbon black is in powder form, has a particle size of 15-45 nm, and a pH value of 6-9.

9. A semi-conductive three-dimensional mesh cable buffer layer material as claimed in claim 1, characterized in that: The antioxidant is composed of a main antioxidant and an auxiliary antioxidant, wherein the main antioxidant is a phenolic main antioxidant 1010 or 1076, and the auxiliary antioxidant is a thioester auxiliary antioxidant such as dilauryl thiodipropionate, ditetradecyl thiodipropionate or dioctadecyl thiodipropionate; The special additive is one or more of metal powder, graphene or carbon fiber.

10. A method for preparing a semi-conductive three-dimensional mesh cable buffer layer material as claimed in any one of claims 1 to 9, characterized in that: The following steps are involved: The first step is to mix the formulated amount of ethylene-vinyl acetate copolymer, low-density polyethylene, olefin block copolymer, crosslinking agent, polyethylene wax and antioxidant, conductive carbon black, filler and special additives in an internal mixer, liquid-cool the internal mixer, and then add a foaming agent and heat and mix to 120-130°C; In the second step, the kneaded material and the foaming sensitizer in the first step are added into an extruder and extruded to obtain a master sheet; The third step is to irradiate the master sheet obtained in the second step at a radiation dose of 8-14 Mrad to obtain a cross-linked sheet; The fourth step is to foam the cross-linked sheet obtained in the third step at 230-260° C. to obtain the semi-conductive three-dimensional mesh cable buffer layer material.

Images