Medium voltage fire resistant cable and method of making same

Abstract

The application relates to the technical field of electric wire and cable, and discloses a medium-voltage fireproof cable and a preparation method thereof; the medium-voltage fireproof cable comprises, from inside to outside, a conductor, a conductor shielding layer, an insulation layer, an insulation shielding layer, an oxygen isolation layer, a fire-resistant layer, a metal shielding layer, an armoring layer and an outer sheath layer; the raw material of the outer sheath layer comprises low-density polyethylene, modified zinc borate, an ethylene-acrylic acid copolymer, an antioxidant, a plasticizer and a heat stabilizer; the modified zinc borate is obtained by modifying zinc borate with a vinyl silicone resin; the vinyl silicone resin comprises first vinyl silicone resin and second vinyl silicone resin; the mass content of vinyl in the first vinyl silicone resin is 0.94%-0.98%, and the mass content of vinyl in the second vinyl silicone resin is 1.29%-1.33%. The technical scheme solves the problem of poor flame-retardant performance of the outer sheath layer of the medium-voltage cable in the related art.

Description

Technical Field

[0001] This invention relates to the field of wire and cable technology, specifically to a medium-voltage fire-resistant cable and its preparation method. Background Technology

[0002] Medium-voltage fire-resistant cables, as core components of power transmission systems, are widely used in densely populated or critical infrastructure scenarios such as high-rise buildings, rail transit, nuclear power plants, data centers, and petrochemical plants. They not only need to ensure the stable transmission of medium-voltage power, but also need to have excellent fire-resistant and flame-retardant performance under extreme conditions such as fires. The fire-resistant effect of the outer sheath of existing medium-voltage cables mostly relies on traditional flame-retardant materials such as zinc borate. However, zinc borate particles are prone to agglomeration, and when directly added to the outer sheath material, it is difficult to achieve uniform dispersion and fully exert its flame-retardant effect, which restricts its application in high-end scenarios. Therefore, it is necessary to propose a medium-voltage fire-resistant cable with excellent fire resistance and suitable for medium-voltage transmission requirements, as well as its preparation method. Summary of the Invention

[0003] This invention proposes a medium-voltage fire-resistant cable and its preparation method, which solves the problem of poor flame-retardant performance of the outer sheath of medium-voltage cables in related technologies.

[0004] The technical solution of the present invention is as follows:

[0005] This invention proposes a medium-voltage fireproof cable, which, from the inside out, comprises a conductor, a conductor shielding layer, an insulation layer, an insulation shielding layer, an oxygen barrier layer, a fire-resistant layer, a metal shielding layer, an armor layer, and an outer sheath layer.

[0006] The raw materials for the outer sheath layer include the following components by weight: 70-90 parts of low-density polyethylene, 25-30 parts of modified zinc borate, 8-10 parts of ethylene-acrylic acid copolymer, 0.5-1.5 parts of antioxidant, 8-12 parts of plasticizer, and 2-5 parts of heat stabilizer; the modified zinc borate is obtained by modifying zinc borate with vinyl silicone resin.

[0007] The vinyl silicone resin includes a first vinyl silicone resin and a second vinyl silicone resin; the first vinyl silicone resin has a vinyl content of 0.94% to 0.98% by mass, and the second vinyl silicone resin has a vinyl content of 1.29% to 1.33% by mass.

[0008] As a further technical solution, the mass ratio of the first vinyl silicone resin to the second vinyl silicone resin is 1~3:1.

[0009] As a further technical solution, the preparation method of the modified zinc borate includes the following steps: mixing zinc borate, vinyl silicone resin and solvent evenly and then drying to obtain modified zinc borate.

[0010] As a further technical solution, the mass of the vinyl silicone resin is 1.5% to 2.5% of the mass of zinc borate.

[0011] As a further technical solution, the solvent is isopropanol.

[0012] As a further technical solution, the mixing is carried out at 60~70℃ for 7~9 hours.

[0013] As a further technical solution, the ethylene-acrylic acid copolymer is composed of a first ethylene-acrylic acid copolymer and a second ethylene-acrylic acid copolymer, wherein the melt indexes of the first ethylene-acrylic acid copolymer and the second ethylene-acrylic acid copolymer are different.

[0014] As a further technical solution, the melt index of the first ethylene-acrylic acid copolymer is 7.9 g / 10 min, and the test conditions are 190℃ and 2.16 kg; the melt index of the second ethylene-acrylic acid copolymer is 9.0 g / 10 min, and the test conditions are 190℃ and 2.16 kg.

[0015] The outer sheath layer of the medium-voltage fire-resistant cable of this invention improves the mechanical strength of the cable by compounding a first ethylene-acrylic acid copolymer with melt indices of 7.9 g / 10 min and a second ethylene-acrylic acid copolymer, respectively. On one hand, the lower melt index of the first ethylene-acrylic acid copolymer results in longer molecular chains, enabling more stable physical entanglement within the material and providing a fundamental support for mechanical strength. On the other hand, the higher melt index of the second ethylene-acrylic acid copolymer offers better flowability, improving the interfacial integration of components during processing and reducing phase separation defects, thereby synergistically enhancing the mechanical strength of the outer sheath material.

[0016] As a further technical solution, the mass ratio of the first ethylene-acrylic acid copolymer to the second ethylene-acrylic acid copolymer is 3~6:2.

[0017] As a further technical solution, the antioxidant includes one or more of antioxidant 1010, antioxidant 168, and antioxidant BHT.

[0018] As a further technical solution, the plasticizer includes one or both of dioctyl phthalate and tributyl acetyl citrate.

[0019] As a further technical solution, the heat stabilizer includes one or both of zinc stearate and calcium stearate.

[0020] This invention also proposes a method for preparing a medium-voltage fire-resistant cable, comprising the following steps:

[0021] S1. Extruding conductor shielding material onto the outside of the conductor to form a conductor shielding layer;

[0022] S2. An insulating layer material is extruded onto the outside of the conductor shielding layer to form an insulating layer;

[0023] S3. An insulating shielding layer material is extruded onto the outside of the insulating layer to form an insulating shielding layer;

[0024] S4. A fireproof strip is wrapped around the outside of the insulating shielding layer to form an oxygen barrier layer;

[0025] S5. Wrap refractory mica tape around the outside of the oxygen barrier layer to form a refractory layer;

[0026] S6. Braid tin-plated copper wires on the outside of the fire-resistant layer to form a metal shielding layer;

[0027] S7. Wrap an armor layer material around the outside of the metal shielding layer to form an armor layer;

[0028] S8. After mixing the outer sheath material, it is extruded onto the outside of the armor layer to form the outer sheath layer, thus obtaining the medium-voltage fireproof cable.

[0029] As a further technical solution, the conductor is made of 50 copper wires with a diameter of 2mm twisted together.

[0030] As a further technical solution, the conductor shielding layer material is cross-linked polyethylene; the insulation layer material is high-density cross-linked polyethylene; and the insulation shielding layer material is cross-linked polyethylene.

[0031] As a further technical solution, the fireproof belt is an aramid fiber fireproof webbing.

[0032] As a further technical solution, the armor layer material is galvanized steel strip.

[0033] The working principle and beneficial effects of this invention are as follows:

[0034] This invention uses vinyl silicone resin to coat and modify zinc borate. On the one hand, this effectively reduces the tendency of zinc borate particles to agglomerate, improves its dispersion uniformity in the polyethylene matrix, and ensures that it can fully exert its function. On the other hand, vinyl silicone resin can form a dense siloxane heat-insulating char layer during combustion, which, together with zinc borate, constructs a double fire barrier, further improving the flame retardancy of the outer sheath layer. At the same time, a first vinyl silicone resin with a vinyl content of 0.94%~0.98% and a second vinyl silicone resin with a vinyl content of 1.29%~1.33% are selected as modifiers. The first vinyl silicone resin with a low vinyl content can improve the compatibility between the coating layer and the matrix, while the second vinyl silicone resin with a high vinyl content can enhance the crosslinking density and char layer stability after combustion. The synergistic effect of the two can optimize the dispersion and flame retardant efficiency of modified zinc borate in the polyethylene matrix, thereby further improving the fire resistance of medium-voltage fire-resistant cables. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] In the following examples and comparative examples, low-density polyethylene, grade 2426H, was purchased from Suzhou Weipai Plastics Co., Ltd.; the first vinyl silicone resin, with a vinyl content of 0.94%~0.98% by mass, model RH-S11, was purchased from Ningbo Runhe High-Tech Materials Technology Co., Ltd.; the second vinyl silicone resin, with a vinyl content of 1.29%~1.33% by mass, model RH-S0826H, was purchased from Ningbo Runhe High-Tech Materials Technology Co., Ltd.; zinc borate, with a particle size of 45μm; and the first ethylene-acrylic acid copolymer, with a melt index of 7.9g / 10min (test conditions: 190℃, 2.16kg), grade DuPont 2014. Purchased from Shenzhen Mait Plastic Products Co., Ltd.; Secondary ethylene-acrylic acid copolymer, melt index 9.0 g / 10 min (test conditions 190℃, 2.16 kg), grade Arkema 4403, from Shenzhen Mait Plastic Products Co., Ltd.; Cross-linked polyethylene, item number XHF1500X04, from LyondellBasell Polyolefins (Shanghai) Co., Ltd.; High-density cross-linked polyethylene, grade XL1800, from Dongguan Jinshixiang Plastic Raw Materials Co., Ltd.; Fire-resistant mica tape, model 65, from Yangzhou Shengkai Electrical Insulation Co., Ltd.; Aramid fiber fireproof webbing, item number HFS-001, from Hephaestus Weaving (Guangdong) Co., Ltd.

[0037] Example 1

[0038] A medium-voltage fire-resistant cable comprises, from the inside out, a conductor, a conductor shielding layer, an insulation layer, an insulation shielding layer, an oxygen barrier layer, a fire-resistant layer, a metal shielding layer, an armor layer, and an outer sheath layer.

[0039] The raw materials for the outer sheath layer include the following components by weight: 70 parts low-density polyethylene, 25 parts modified zinc borate, 8 parts ethylene-acrylic acid copolymer, 0.5 parts antioxidant 1010, 8 parts dioctyl phthalate, and 2 parts zinc stearate; wherein, the ethylene-acrylic acid copolymer is the first ethylene-acrylic acid copolymer;

[0040] The preparation method of modified zinc borate includes the following steps: zinc borate, vinyl silicone resin and isopropanol are mixed at 65°C for 8 hours and then dried to obtain modified zinc borate; the mass of vinyl silicone resin is 2% of the mass of zinc borate; the mass ratio of zinc borate to isopropanol is 1:5; the vinyl silicone resin is composed of a first vinyl silicone resin and a second vinyl silicone resin in a mass ratio of 1:1.

[0041] A method for preparing a medium-voltage fire-resistant cable includes the following steps:

[0042] S1. A conductor is formed by twisting 50 copper wires with a diameter of 2mm together, and cross-linked polyethylene material is extruded on the outside of the conductor to form a conductor shielding layer.

[0043] S2. High-density cross-linked polyethylene material is extruded onto the outside of the conductor shield core to form an insulation layer;

[0044] S3. Extruding cross-linked polyethylene onto the outside of the insulation layer to form an insulating shielding layer;

[0045] S4. Wrap aramid fiber fireproof webbing around the outside of the insulating shielding layer to form an oxygen barrier layer;

[0046] S5. Wrap refractory mica tape around the outside of the oxygen barrier layer to form a refractory layer;

[0047] S6. Tin-plated copper wire is braided on the outside of the refractory layer to form a metal shielding layer;

[0048] S7. A galvanized steel strip is wrapped around the outside of the metal shielding layer to form an armor layer;

[0049] S8. After mixing the outer sheath material, it is extruded onto the outside of the armor layer to form the outer sheath layer, thus obtaining a medium-voltage fireproof cable.

[0050] Example 2

[0051] Compared with Example 1, the only difference in this example is that the raw materials of the outer sheath layer in this example include the following components by weight: 80 parts of low-density polyethylene, 28 parts of modified zinc borate, 9 parts of ethylene-acrylic acid copolymer, 1 part of antioxidant 168, 10 parts of acetylsicitrin tributyl ester, and 3 parts of calcium stearate; wherein, the ethylene-acrylic acid copolymer is the first ethylene-acrylic acid copolymer.

[0052] Example 3

[0053] Compared with Example 1, the only difference in this example is that the raw materials of the outer sheath layer in this example include the following components by weight: 90 parts of low-density polyethylene, 30 parts of modified zinc borate, 10 parts of ethylene-acrylic acid copolymer, 1.5 parts of antioxidant BHT, 12 parts of acetylsicitrin tributyl ester, and 5 parts of zinc stearate; wherein, the ethylene-acrylic acid copolymer is the first ethylene-acrylic acid copolymer.

[0054] Example 4

[0055] Compared with Example 1, the only difference in this example is that in the preparation method of modified zinc borate in this example, the vinyl silicone resin is composed of a first vinyl silicone resin and a second vinyl silicone resin with a mass ratio of 2:1.

[0056] Example 5

[0057] Compared with Example 1, the only difference in this example is that in the preparation method of modified zinc borate in this example, the vinyl silicone resin is composed of a first vinyl silicone resin and a second vinyl silicone resin in a mass ratio of 3:1.

[0058] Example 6

[0059] Compared with Example 1, the only difference in this example is that the ethylene-acrylic acid copolymer in the outer sheath layer of this example is composed of a first ethylene-acrylic acid copolymer and a second ethylene-acrylic acid copolymer with a mass ratio of 3:2.

[0060] Example 7

[0061] Compared with Example 1, the only difference in this example is that the ethylene-acrylic acid copolymer in the outer sheath layer of this example is composed of a first ethylene-acrylic acid copolymer and a second ethylene-acrylic acid copolymer with a mass ratio of 5:2.

[0062] Example 8

[0063] Compared with Example 1, the only difference in this example is that the ethylene-acrylic acid copolymer in the outer sheath layer of this example is composed of a first ethylene-acrylic acid copolymer and a second ethylene-acrylic acid copolymer with a mass ratio of 3:1.

[0064] Example 9

[0065] Compared with Example 1, the only difference in this example is that the ethylene-acrylic acid copolymer in the raw material of the outer sheath layer in this example is a second ethylene-acrylic acid copolymer.

[0066] Comparative Example 1

[0067] Compared with Example 1, the only difference in this comparative example is that, in the preparation method of the modified zinc borate in this comparative example, the vinyl silicone resin is only the first vinyl silicone resin.

[0068] Comparative Example 2

[0069] Compared with Example 1, the only difference in this comparative example is that in the preparation method of modified zinc borate in this comparative example, the vinyl silicone resin is only the second vinyl silicone resin.

[0070] Comparative Example 3

[0071] Compared with Example 1, the only difference in this comparative example is that the modified zinc borate is replaced with an equal amount of zinc borate in the raw material of the sheath layer.

[0072] The outer sheaths of the medium-voltage fire-resistant cables prepared in Examples 1-9 and Comparative Examples 1-3 were tested according to the following method:

[0073] 1. Fire resistance test: The oxygen index of the outer sheath of the medium-voltage fireproof cable was determined according to the test method specified in GB / T 2406.2-2009 "Determination of burning behavior by oxygen index method for plastics - Part 2: Room temperature test"; the sample type was type V, and the ignition method was method B, diffusion ignition method;

[0074] 2. Mechanical property testing: The tensile strength of the outer sheath of the medium-voltage fireproof cable was determined according to the test methods in GB / T 2951.11-2008 "General test methods for insulation and sheath materials of cables and optical cables - Part 11: General test methods for thickness and dimensional measurement and mechanical property testing". The specimen was a dumbbell specimen with a thickness of 1.5 mm, the total distance between the clamps was 50 mm, and the clamp moving speed was 250 mm / min.

[0075] The test results are shown in Tables 1 and 2.

[0076] Table 1. Test results of fire resistance performance of the outer sheath of medium-voltage fire-resistant cables

[0077]

[0078] According to the data in Table 1, the addition of zinc borate modified with vinyl silicone resin (composed of first vinyl silicone resin and second vinyl silicone resin) can improve the fire resistance of medium-voltage fire-resistant cables.

[0079] Table 2. Test results of the mechanical properties of the outer sheath of medium-voltage fire-resistant cables

[0080]

[0081] According to the data in Table 2, the present invention can improve the tensile strength of medium-voltage fireproof cables by using a combination of first ethylene-acrylic acid copolymers and second ethylene-acrylic acid copolymers with different melt indices.

[0082] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A medium-voltage fire-resistant cable, characterized in that, From the inside out, it includes a conductor, a conductor shielding layer, an insulation layer, an insulation shielding layer, an oxygen barrier layer, a fire-resistant layer, a metal shielding layer, an armor layer, and an outer sheath layer. The raw materials for the outer sheath layer include the following components by weight: 70-90 parts of low-density polyethylene, 25-30 parts of modified zinc borate, 8-10 parts of ethylene-acrylic acid copolymer, 0.5-1.5 parts of antioxidant, 8-12 parts of plasticizer, and 2-5 parts of heat stabilizer; the modified zinc borate is obtained by modifying zinc borate with vinyl silicone resin. The vinyl silicone resin includes a first vinyl silicone resin and a second vinyl silicone resin; the first vinyl silicone resin has a vinyl content of 0.94% to 0.98% by mass, and the second vinyl silicone resin has a vinyl content of 1.29% to 1.33% by mass.

2. The medium-voltage fire-resistant cable according to claim 1, characterized in that, The mass ratio of the first vinyl silicone resin to the second vinyl silicone resin is 1 to 3:

1.

3. A medium-voltage fire-resistant cable according to claim 1, characterized in that, The method for preparing the modified zinc borate includes the following steps: mixing zinc borate, vinyl silicone resin and solvent evenly and then drying to obtain modified zinc borate.

4. A medium-voltage fire-resistant cable according to claim 3, characterized in that, The mass of the vinyl silicone resin is 1.5% to 2.5% of the mass of zinc borate.

5. A medium-voltage fire-resistant cable according to claim 3, characterized in that, The solvent is isopropanol.

6. A medium-voltage fire-resistant cable according to claim 3, characterized in that, The mixing temperature is 60~70℃.

7. A medium-voltage fire-resistant cable according to claim 1, characterized in that, The ethylene-acrylic acid copolymer is composed of a first ethylene-acrylic acid copolymer and a second ethylene-acrylic acid copolymer, wherein the first ethylene-acrylic acid copolymer and the second ethylene-acrylic acid copolymer have different melt indices.

8. A medium-voltage fire-resistant cable according to claim 7, characterized in that, The melt index of the first ethylene-acrylic acid copolymer was 7.9 g / 10 min, and the test conditions were 190 °C and 2.16 kg; the melt index of the second ethylene-acrylic acid copolymer was 9.0 g / 10 min, and the test conditions were 190 °C and 2.16 kg.

9. A medium-voltage fire-resistant cable according to claim 8, characterized in that, The mass ratio of the first ethylene-acrylic acid copolymer to the second ethylene-acrylic acid copolymer is 3~6:

2.

10. A method for preparing a medium-voltage fire-resistant cable, used to prepare a medium-voltage fire-resistant cable as described in any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Extruding conductor shielding material onto the outside of the conductor to form a conductor shielding layer; S2. An insulating layer material is extruded onto the outside of the conductor shielding layer to form an insulating layer; S3. An insulating shielding layer material is extruded onto the outside of the insulating layer to form an insulating shielding layer; S4. A fireproof strip is wrapped around the outside of the insulating shielding layer to form an oxygen barrier layer; S5. Wrap refractory mica tape around the outside of the oxygen barrier layer to form a refractory layer; S6. Braid tin-plated copper wires on the outside of the fire-resistant layer to form a metal shielding layer; S7. Wrap an armor layer material around the outside of the metal shielding layer to form an armor layer; S8. After mixing the outer sheath material, it is extruded onto the outside of the armor layer to form the outer sheath layer, thus obtaining the medium-voltage fireproof cable.

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