Low-smoke halogen-free flame-retardant cable and preparation method thereof

Abstract

The invention relates to the technical field of cables, and provides a low-smoke halogen-free flame-retardant cable and a preparation method thereof.The low-smoke halogen-free flame-retardant cable comprises a cable core, an insulating layer, a shielding layer, a belting layer, an armor layer and a low-smoke halogen-free sheath layer from inside to outside; an inorganic flame-retardant material is filled between the belting layer and the shielding layer; the cable core comprises a plurality of wire cores, and the inorganic flame-retardant material is glass fiber filaments; and the low-smoke halogen-free sheath layer is prepared from the following raw materials in parts by weight: 100 parts of polyethylene resin, 25-30 parts of ethylene-vinyl acetate copolymer and 20-25 parts of inorganic flame retardant. According to the technical scheme, the problems that the flame retardance and the mechanical property of the cable cannot be well combined and the smoke density control is poor in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of cable technology, specifically to a low-smoke halogen-free flame-retardant cable and its preparation method. Background Technology

[0002] With the rapid development of the power industry, construction engineering, rail transportation, and new energy sectors, cables, as the core carriers of energy transmission and signal transmission, are facing increasingly complex application scenarios and ever-increasing demands for safety performance. Traditional PVC cables release large amounts of toxic and harmful gases (such as hydrogen chloride) and dense smoke when burning, which can cause poisoning and suffocation, hinder rescue efforts, and pose a serious threat to life and property. Therefore, low-smoke halogen-free flame-retardant cables, with their core advantages of "low smoke, halogen-free, low toxicity, and flame retardancy" during combustion, are gradually replacing traditional PVC cables and are widely used in high-rise buildings, hospitals, subways, nuclear power plants, and other locations with stringent safety requirements.

[0003] Currently, existing low-smoke halogen-free flame-retardant cables mainly achieve flame-retardant effects by adding inorganic flame retardants (such as magnesium hydroxide and aluminum hydroxide) to the sheath layer. Some products also add a flame-retardant wrapping layer between the insulation layer and the armor layer to enhance flame-retardant performance. However, existing technologies still suffer from insufficient flame retardancy and mechanical strength in cables.

[0004] Therefore, developing a low-smoke halogen-free flame-retardant cable with a reasonable structural design, high flame retardancy, excellent mechanical properties, and low smoke density has become a technical problem that the industry urgently needs to solve. Summary of the Invention

[0005] This invention proposes a low-smoke halogen-free flame-retardant cable and its preparation method, which solves the problems in related technologies where the flame retardancy and mechanical properties of the cable cannot be well combined, and the smoke density control is poor.

[0006] The technical solution of the present invention is as follows: This invention proposes a low-smoke halogen-free flame-retardant cable, comprising, from the inside out, a cable core, an insulation layer, a shielding layer, a wrapping layer, an armor layer, and a low-smoke halogen-free sheath layer; the wrapping layer and the shielding layer are filled with an inorganic flame-retardant material; the cable core comprises multiple wire cores, and the inorganic flame-retardant material is glass fiber filament; the raw material of the low-smoke halogen-free sheath layer comprises the following components in parts by weight: 100 parts of polyethylene resin, 25-30 parts of ethylene-vinyl acetate copolymer, and 20-25 parts of inorganic flame retardant.

[0007] As a further technical solution, the wire core includes a copper conductor made of twisted copper wires and a cross-linked polyethylene material covering the copper conductor.

[0008] As a further technical solution, the material used for the wrapping layer is mica tape.

[0009] As a further technical solution, the shielding layer is a metal wire braided layer.

[0010] As a further technical solution, the armor layer is an aluminum wire armor layer or a steel wire armor layer.

[0011] As a further technical solution, the insulation layer is a cross-linked polyethylene insulation layer.

[0012] As a further technical solution, the raw materials of the low-smoke halogen-free sheath layer, by weight, also include 1 to 1.5 parts of antioxidant and 0.5 to 0.8 parts of light stabilizer.

[0013] As a further technical solution, the antioxidant includes one or more of antioxidant 1010, antioxidant 168, and antioxidant 1076.

[0014] As a further technical solution, the light stabilizer includes one or both of the light stabilizer UV-770 and the light stabilizer UV-865.

[0015] As a further technical solution, the inorganic flame retardant comprises the following raw materials in parts by weight: 100 parts of silane-modified magnesium hydroxide and 30-50 parts of magnesium hydroxide modified with anhydride compounds; the raw materials for the silane-modified magnesium hydroxide include an amino-containing silane coupling agent and magnesium hydroxide; wherein the magnesium hydroxide modified with anhydride compounds can be 30 parts, 35 parts, 40 parts, 45 parts, or 50 parts, preferably 40 parts.

[0016] The addition of inorganic flame retardants in this invention has the following problems: (1) It is difficult to balance flame retardant performance and mechanical performance: In order to achieve the ideal flame retardant level, existing cables often need to add inorganic flame retardants to the sheath layer, which leads to a decrease in the flexibility of the sheath layer, an increase in processing difficulty, and a significant reduction in the mechanical properties of the cable. During laying and use, cracking and damage are likely to occur, affecting the service life. (2) Poor material compatibility: The inorganic flame retardant is not compatible with the sheath substrate (such as polyethylene, EVA), which leads to uneven dispersion of the flame retardant in the material. This not only affects the flame retardant effect of the inorganic flame retardant, but also reduces the mechanical properties of the sheath layer. (3) Poor smoke density control: Although some existing low-smoke halogen-free cables can meet the halogen-free requirements, the smoke density is still high when burning. When used in enclosed spaces (such as subway tunnels and underground machine rooms), the dense smoke will still affect visibility and rescue efficiency.

[0017] The inorganic flame retardants in this invention include silane-modified magnesium hydroxide and magnesium hydroxide modified with anhydride compounds. Compared with directly adding magnesium hydroxide as a flame retardant to the cable sheath, this method can improve the dispersibility of magnesium hydroxide during the sheath preparation process and its compatibility with the sheath base material. This not only better leverages the flame retardant effect of magnesium hydroxide, but also improves the mechanical strength of the sheath layer and allows for better control of smoke density. This solves the problems of difficulty in achieving both flame retardant and mechanical properties in cable sheath layers, as well as poor smoke density control.

[0018] As a further technical solution, the amino-containing silane coupling agent includes one or both of silane coupling agent KH-550 and silane coupling agent KH-792, preferably silane coupling agent KH-550.

[0019] In this invention, by specifying that the silane coupling agent in the raw material of silane-modified magnesium hydroxide is an aminosilane coupling agent, the introduction of amino groups can not only improve the compatibility between magnesium hydroxide and polyethylene resin, but also form hydrogen bonding forces with the carbonyl groups in the ethylene-vinyl acetate copolymer during the preparation process. It can also better construct a stable inorganic flame retardant system with magnesium hydroxide modified with acid anhydride compounds. While improving the flame retardancy of the sheath layer, it can also further improve the mechanical properties of the sheath layer.

[0020] As a further technical solution, the raw material for the modified magnesium hydroxide containing anhydride compounds includes anhydride compounds, which include one or two of trimellitic anhydride and phenylmaleic anhydride.

[0021] In this invention, the acid anhydride compound in the raw material for modifying magnesium hydroxide with anhydride compounds can preferably be one or two of trimellitic anhydride and phenyl maleic anhydride. When the acid anhydride compound is one or two of trimellitic anhydride and phenyl maleic anhydride, the flame retardancy and mechanical strength of the sheath layer can be further improved. The reason is that when the acid anhydride compound is one or two of trimellitic anhydride and phenyl maleic anhydride, the carbonyl group in its molecular structure can better form hydrogen bond forces with the groups on the surface of magnesium hydroxide. This not only improves the compatibility with polyethylene resin in the sheath layer base material, but also better forms a stable inorganic flame retardant system with silane-modified magnesium hydroxide. While providing flame retardancy to the sheath layer, it can also further improve the mechanical properties of the sheath layer.

[0022] As a further technical solution, the acid-containing anhydride compound is composed of trimellitic anhydride and phenylmaleic anhydride.

[0023] As a further technical solution, the mass ratio of trimellitic anhydride to phenylmaleic anhydride is 3:1 to 2. For example, it can be 3:1, 2:1, or 3:2, but is not limited to the listed ratios; preferably, it is 2:1.

[0024] As a further technical solution, the preparation method of the silane-modified magnesium hydroxide includes the following steps: adding an amino-containing silane coupling agent to water and mixing it evenly, then adding magnesium hydroxide I and mixing, filtering and drying to obtain silane-modified magnesium hydroxide.

[0025] As a further technical solution, in the preparation method of silane-modified magnesium hydroxide, the amino-containing silane coupling agent is 2% to 3% of the mass of magnesium hydroxide I, for example, it can be 2%, 2.2%, 2.4%, 2.6%, 2.8%, or 3%, preferably 2.2%.

[0026] As a further technical solution, the preparation method of the acid anhydride-modified magnesium hydroxide includes the following steps: adding the acid anhydride compound to a solvent and mixing evenly, then adding magnesium hydroxide II and mixing, followed by filtration and drying to obtain the acid anhydride-modified magnesium hydroxide.

[0027] As a further technical solution, the solvent is one of acetone and ethyl acetate.

[0028] As a further technical solution, magnesium hydroxide I and magnesium hydroxide II are the same.

[0029] As a further technical solution, in the preparation method of magnesium hydroxide modified with anhydride compound, the anhydride compound is 2% to 3% of the mass of magnesium hydroxide II, for example, it can be 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%, preferably 2.4%.

[0030] This invention also proposes a method for preparing a low-smoke halogen-free flame-retardant cable, comprising the following steps: S1. After extruding the insulating material onto the outside of the cable core to form an insulating layer, a shielding layer is set on the outside of the insulating layer, and then an inorganic flame-retardant material is wrapped inside with a wrapping layer material to form a wrapping layer. S2. After setting an armor layer outside the wrapping layer, a semi-finished cable is obtained; S3. After the raw materials of the low-smoke halogen-free sheath layer are mixed evenly, they are extruded and wrapped on the outside of the cable semi-finished product to obtain a low-smoke halogen-free flame-retardant cable. In step S1, the cable core is obtained by twisting together multiple wire cores.

[0031] The working principle and beneficial effects of this invention are as follows: The low-smoke halogen-free flame-retardant cable of the present invention comprises, from the inside out, a cable core, an insulation layer, a shielding layer, a wrapping layer, an armor layer, and a low-smoke halogen-free sheath layer. An inorganic flame-retardant material, namely glass fiber, is filled between the wrapping layer and the shielding layer. The glass fiber is non-combustible and heat-resistant, thus able to withstand high temperatures in a fire. Combined with the wrapping layer, it forms a dual protection of physical barrier and chemical flame retardancy within the cable. Furthermore, the filling of the inorganic flame-retardant material reduces the porosity of the wrapping layer and the shielding layer, allowing the shielding layer, inorganic flame-retardant material, and wrapping layer to fit tightly together, improving the overall mechanical properties of the cable. The sheath layer uses a low-smoke halogen-free material, avoiding the halogen gas released during the combustion of traditional halogen-containing materials. The sheath layer uses a mixture of polyethylene and ethylene-vinyl acetate copolymer, which improves the comprehensive mechanical properties of the sheath layer. Therefore, the low-smoke halogen-free flame-retardant cable of the present invention has high flame retardancy, mechanical properties, and low smoke density, further expanding the application scenarios of the cable. Detailed Implementation

[0032] 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.

[0033] In the following embodiments and comparative examples: Polyethylene resin: Model 1I2A-1, manufacturer: Yanshan Petrochemical; Ethylene-vinyl acetate copolymer; model 7470, manufactured by Formosa Plastics, Taiwan.

[0034] Example 1 A method for preparing a low-smoke halogen-free flame-retardant cable includes the following steps: S1. After extruding the insulating material onto the outside of the cable core to form an insulating layer, a shielding layer is woven with metal wires on the outside of the insulating layer, and then glass fiber filaments are wrapped inside with mica tape to form a wrapping layer; wherein the cable core is a copper conductor made of copper wire stranded together; wherein the cable core is obtained by stranding multiple wire cores, the wire cores include a copper conductor made of copper wire stranded together and cross-linked polyethylene material wrapped around the copper conductor; S2. After setting an aluminum wire armor layer outside the wrapping layer, a semi-finished cable is obtained; S3. After the raw materials of the low-smoke halogen-free sheath layer are mixed evenly, they are extruded and wrapped on the outside of the cable semi-finished product to obtain a low-smoke halogen-free flame-retardant cable. The raw materials for the low-smoke halogen-free sheath layer include the following components in parts by weight: 100 parts of polyethylene resin, 25 parts of ethylene-vinyl acetate copolymer, 20 parts of inorganic flame retardant, 1 part of antioxidant 1010, and 0.5 parts of light stabilizer UV-770. The inorganic flame retardant comprises the following components in parts by weight: 100 parts of silane-modified magnesium hydroxide and 40 parts of magnesium hydroxide modified with anhydride compounds. The preparation method of silane-modified magnesium hydroxide includes the following steps: adding silane coupling agent A-172 to water and mixing evenly, then adding magnesium hydroxide I, mixing at 40℃ for 2.5h, filtering, and drying to obtain silane-modified magnesium hydroxide; wherein the amount of silane coupling agent A-172 added is 2.2% of the mass of magnesium hydroxide I, and the mass-volume ratio of magnesium hydroxide I to water is 1g:5mL; A method for preparing magnesium hydroxide modified with an anhydride compound includes the following steps: adding the anhydride compound to acetone and mixing evenly, then adding magnesium hydroxide II, mixing at 40°C for 2.5 h, filtering, and drying to obtain magnesium hydroxide modified with anhydride compound; wherein the amount of the anhydride compound added is 2.4% of the mass of magnesium hydroxide II, and the mass-to-volume ratio of magnesium hydroxide II to acetone is 1 g: 6 mL; the anhydride compound is trimellitic anhydride; Magnesium hydroxide I is the same as magnesium hydroxide II, with an average particle size of 800 mesh.

[0035] Example 2 A method for preparing a low-smoke halogen-free flame-retardant cable includes the following steps: S1. After extruding the insulating material onto the outside of the cable core to form an insulating layer, a shielding layer is woven with metal wires on the outside of the insulating layer, and then glass fiber filaments are wrapped inside with mica tape to form a wrapping layer; wherein the cable core is a copper conductor made of copper wire stranded together; wherein the cable core is obtained by stranding multiple wire cores, the wire cores include a copper conductor made of copper wire stranded together and cross-linked polyethylene material wrapped around the copper conductor; S2. After setting an aluminum wire armor layer outside the wrapping layer, a semi-finished cable is obtained; S3. After the raw materials of the low-smoke halogen-free sheath layer are mixed evenly, they are extruded and wrapped on the outside of the cable semi-finished product to obtain a low-smoke halogen-free flame-retardant cable. The raw materials for the low-smoke halogen-free sheath layer include the following components in parts by weight: 100 parts of polyethylene resin, 30 parts of ethylene-vinyl acetate copolymer, 25 parts of inorganic flame retardant, 1.5 parts of antioxidant 1010, and 0.8 parts of light stabilizer UV-770. The inorganic flame retardant comprises the following components in parts by weight: 100 parts of silane-modified magnesium hydroxide and 40 parts of magnesium hydroxide modified with anhydride compounds. The preparation method of silane-modified magnesium hydroxide includes the following steps: adding silane coupling agent A-172 to water and mixing evenly, then adding magnesium hydroxide I, mixing at 40℃ for 2.5h, filtering, and drying to obtain silane-modified magnesium hydroxide; wherein the amount of silane coupling agent A-172 added is 2.2% of the mass of magnesium hydroxide I, and the mass-volume ratio of magnesium hydroxide I to water is 1g:5mL; A method for preparing magnesium hydroxide modified with an anhydride compound includes the following steps: adding the anhydride compound to acetone and mixing evenly, then adding magnesium hydroxide II, mixing at 40°C for 2.5 h, filtering, and drying to obtain magnesium hydroxide modified with anhydride compound; wherein the amount of the anhydride compound added is 2.4% of the mass of magnesium hydroxide II, and the mass-to-volume ratio of magnesium hydroxide II to acetone is 1 g: 6 mL; the anhydride compound is trimellitic anhydride; Magnesium hydroxide I is the same as magnesium hydroxide II, with an average particle size of 800 mesh.

[0036] Example 3 Compared with Example 1, the only difference in this example is that the inorganic flame retardant is silane-modified magnesium hydroxide, and the preparation method of silane-modified magnesium hydroxide in this example is the same as that in Example 1.

[0037] Example 4 Compared with Example 1, the only difference in this example is that the inorganic flame retardant is magnesium hydroxide modified with an acid anhydride compound. The preparation method of magnesium hydroxide modified with an acid anhydride compound in this example is the same as that in Example 1.

[0038] Example 5 Compared with Example 1, the only difference in this example is that the silane coupling agent A-172 is replaced with an equal amount of silane coupling agent KH-550.

[0039] Example 6 Compared with Example 1, the only difference in this example is that the silane coupling agent A-172 is replaced with an equal amount of silane coupling agent KH-792.

[0040] Example 7 Compared with Example 6, the only difference in this example is that the anhydride compound is phenylmaleic anhydride.

[0041] Example 8 Compared with Example 6, the only difference in this example is that the anhydride compound is composed of trimellitic anhydride and phenylmaleic anhydride in a mass ratio of 3:1.

[0042] Example 9 Compared with Example 6, the only difference in this example is that the anhydride compound is composed of trimellitic anhydride and phenylmaleic anhydride in a mass ratio of 2:1.

[0043] Example 10 Compared with Example 6, the only difference in this example is that the anhydride compound is composed of trimellitic anhydride and phenylmaleic anhydride in a mass ratio of 3:1.5.

[0044] Experimental Example The performance of the sheath layer in the low-smoke halogen-free flame-retardant cables in Examples 1-10 was determined using the following methods: (1) Oxygen index: The test was conducted in accordance with the test method in GB / T 2406.1-2008 "Determination of combustion behavior of plastics by oxygen index method - Part 1: Guidelines"; (2) Tensile strength: The test shall be conducted in accordance with the test method 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 Properties". (3) Smoke density (minimum transmittance): The test shall be conducted in accordance with the test method in GB / T17651.1-2021 "Determination of smoke density of cables or optical cables under specific conditions"; The measurement results are shown in Tables 1, 2, and 3 below.

[0045] Table 1. Results of oxygen index determination of the sheath layer in low-smoke halogen-free flame-retardant cables in Examples 1-6

[0046] As shown in Table 1, the oxygen index of the sheath layer in low-smoke halogen-free flame-retardant cables can be improved by using amino-containing silane coupling agents to modify magnesium hydroxide and using acid anhydride compounds to modify magnesium hydroxide.

[0047] Table 2. Tensile strength test results of the sheath layer in low-smoke halogen-free flame-retardant cables in Examples 1-10

[0048] As shown in Table 2, the tensile strength of the sheath layer in low-smoke halogen-free flame-retardant cables can be improved by using amino-containing silane coupling agents to modify magnesium hydroxide and using acid anhydride compounds to modify magnesium hydroxide.

[0049] Table 3. Test results of smoke density (minimum light transmittance) of the sheath layer in low-smoke halogen-free flame-retardant cables in Examples 1 and 2.

[0050] As shown in Table 3, the low-smoke halogen-free flame-retardant cable of the present invention has a high minimum light transmittance.

[0051] 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 low-smoke, halogen-free, flame-retardant cable, characterized in that, The cable consists of, from the inside out, a cable core, an insulation layer, a shielding layer, a wrapping layer, an armor layer, and a low-smoke halogen-free sheath layer. The wrapping layer and the shielding layer are filled with an inorganic flame-retardant material. The cable core comprises multiple wires, and the inorganic flame-retardant material is glass fiber. The raw material for the low-smoke halogen-free sheath layer includes the following components by weight: 100 parts polyethylene resin, 25-30 parts ethylene-vinyl acetate copolymer, and 20-25 parts inorganic flame retardant.

2. The low-smoke halogen-free flame-retardant cable according to claim 1, characterized in that, The core comprises a copper conductor made of twisted copper wires and a cross-linked polyethylene material covering the copper conductor.

3. The low-smoke halogen-free flame-retardant cable according to claim 1, characterized in that, The material used for the wrapping layer is mica tape.

4. The low-smoke halogen-free flame-retardant cable according to claim 1, characterized in that, The shielding layer is a braided metal wire layer.

5. The low-smoke halogen-free flame-retardant cable according to claim 1, characterized in that, The armor layer is an aluminum wire armor layer or a steel wire armor layer.

6. The low-smoke halogen-free flame-retardant cable according to claim 1, characterized in that, The insulation layer is a cross-linked polyethylene insulation layer.

7. The low-smoke halogen-free flame-retardant cable according to claim 1, characterized in that, The raw materials of the low-smoke halogen-free sheath layer, by weight, also include 1 to 1.5 parts of antioxidant and 0.5 to 0.8 parts of light stabilizer.

8. The low-smoke halogen-free flame-retardant cable according to claim 1, characterized in that, The inorganic flame retardant comprises the following raw materials in parts by weight: 100 parts of silane-modified magnesium hydroxide and 30-50 parts of magnesium hydroxide modified with anhydride compounds; the raw materials for the silane-modified magnesium hydroxide include an amino-containing silane coupling agent and magnesium hydroxide.

9. A low-smoke halogen-free flame-retardant cable according to claim 8, characterized in that, The raw material for the modified magnesium hydroxide containing acid anhydride compounds includes acid anhydride compounds, which include one or two of trimellitic anhydride and phenylmaleic anhydride.

10. A method for preparing a low-smoke halogen-free flame-retardant cable, used to prepare the low-smoke halogen-free flame-retardant cable as described in any one of claims 1 to 9, characterized in that, Includes the following steps: S1. After extruding the insulating material onto the outside of the cable core to form an insulating layer, a shielding layer is set on the outside of the insulating layer, and then an inorganic flame-retardant material is wrapped inside with a wrapping layer material to form a wrapping layer. S2. After setting an armor layer outside the wrapping layer, a semi-finished cable is obtained; S3. After the raw materials of the low-smoke halogen-free sheath layer are mixed evenly, they are extruded and wrapped on the outside of the cable semi-finished product to obtain a low-smoke halogen-free flame-retardant cable. In step S1, the cable core is obtained by twisting together multiple wire cores.

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