Halogen-free flame-retardant polyolefin sheath material for flexible fireproof cable and preparation method of halogen-free flame-retardant polyolefin sheath material

Abstract

The invention relates to the technical field of cable materials, and particularly discloses a halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable and a preparation method thereof.According to the halogen-free flame-retardant polyolefin sheath material, low-density polyethylene serves as a main base material, and the molecular structure of the low-density polyethylene has many long-chain branches; meanwhile, by adding the composite copolymer and the flame-retardant filler, the mechanical property, the high and low temperature resistance and the flame-retardant property of the sheath material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of cable materials, and in particular to a halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable and a preparation method thereof. Background Art

[0002] As a key carrier for electrical energy transmission and distribution, the sheath structure of power cables is crucial for ensuring the safe and reliable operation of the cables. The sheath, wrapped around the conductor and insulation, primarily provides mechanical protection, resists environmental degradation (such as chemical corrosion, moisture penetration, and UV aging), and extends the cable's service life. It is an essential component for ensuring stable power delivery to end-user devices. Therefore, selecting the appropriate sheath material directly impacts the cable's long-term performance and safety in complex environments.

[0003] Currently, polyethylene (PE) is commonly used as a sheathing material for power cables due to its good chemical stability, excellent electrical insulation properties, low density, ease of installation and maintenance, and relatively economical cost. However, this polyethylene material still has significant defects in key performance. First, polyethylene's high-temperature resistance is insufficient. When the temperature rises due to current load or external heat sources during cable operation, the sheath is prone to softening, deformation, or even melting, exposing the internal conductor and significantly increasing the risk of short circuits and electrical fires. Second, polyethylene's inherent flame retardancy is poor. In the event of a fire, it is difficult to effectively prevent the spread of flames along the cable, which can deprive valuable time for personnel evacuation and fire rescue, posing a serious threat to life and property.

[0004] For example, Chinese patent document CN202310413407.6 discloses a halogen-free, low-smoke flame-retardant polyolefin sheathing material and its preparation process, comprising the following steps: Step 1: Preparation of a halogen-free flame retardant; Step 2: Preparation of a flame retardant synergist: dispersing montmorillonite in N,N-dimethylformamide and modifying it with octadecyl isocyanate to obtain a flame retardant synergist; Step 3: Ethylene-octene copolymer elastomer, high-density polyethylene, ethylene-octene copolymer grafted maleic anhydride copolymer, halogen-free flame retardant, flame retardant synergist, lubricant, and organic peroxide, stirring, mixing, kneading, extruding and granulating to obtain a polyolefin sheathing material. Although the mechanical properties and flame retardant properties of the prepared sheathing material have been improved to a certain extent, further improvement is still needed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the object of the present invention is to provide a halogen-free flame-retardant polyolefin sheath material for flexible fire-resistant cables and a preparation method thereof.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable comprises the following components in parts by weight: 20-40 parts of low-density polyethylene, 10-15 parts of a composite copolymer, 5-10 parts of PE-grafted maleic anhydride, 10-15 parts of a flame-retardant filler, 2-4 parts of a lubricant, 1-3 parts of an antioxidant, 1-2 parts of an ultraviolet absorber, 0.2-0.4 parts of a heat stabilizer, and 0.1-0.2 parts of lauroyl peroxide.

[0007] In the technical solution disclosed in the present invention, the preparation method of the composite copolymer is as follows: 1,4-butenediol is added to an organic solvent, stirred to dissolve, and then phosphonic acid-B-phenylenediol ester and benzoyl peroxide are added, heated and stirred to react, and after the reaction is completed, vacuum distillation and drying are performed to obtain a composite copolymer.

[0008] Specifically, the mass ratio of the 1,4-butenediol, B-styryl phosphonate and benzoyl peroxide is 3-6:5-10:0.05-0.1. For example, 3:5:0.05, 3:5:0.08, 3:5:0.1, 5:5:0.05, 5:8:0.05, 5:10:0.1, 6:5:0.05, 6:8:0.08, and 6:10:0.1 can be selected, but the above values ​​are not limited to those listed. Other values ​​not listed within the numerical range are also applicable.

[0009] Specifically, the temperature of the heating and stirring reaction is 60-80°C, for example, 60°C, 65°C, 70°C, 75°C, or 80°C can be selected, and the time of the heating and stirring reaction is 3-5h, for example, 3h, 3.5h, 4h, 4.5h, or 5h can be selected, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0010] In the technical solution disclosed in the present invention, 1,4-butenediol and phosphonic acid-B-styryl ester are copolymerized to form a composite copolymer through an addition reaction between double bonds, and the composite copolymer is introduced into a sheath material. The molecular structure of phosphonic acid-B-styryl ester contains a benzene ring structure and a phosphonic acid group. The benzene ring structure can improve the thermal stability of the molecular chain, making the material less likely to undergo thermal decomposition at high temperatures, thereby improving the heat resistance of the material. The phosphonic acid group has good flame retardancy, thereby improving the flame retardant performance of the material. The flexible long-chain alkyl structure in 1,4-butenediol improves the low-temperature resistance of the material. At the same time, the hydroxyl group in 1,4-butenediol can react with PE-grafted maleic anhydride, thereby improving the mechanical properties of the material.

[0011] In the technical solution disclosed in the present invention, the preparation method of the flame retardant filler is as follows: S1. Add alkali lignin to deionized water, stir and dissolve, then add bentonite thereto, disperse uniformly by ultrasonication, filter, dry and grind to obtain a composite bentonite material; S2. Dispersing the composite bentonite material in carbon tetrachloride, then adding 5-amino-2-mercaptobenzimidazole and epichlorohydrin, heating and stirring to react, after the reaction is completed, filtering, washing, and drying to obtain a flame retardant filler.

[0012] Specifically, in step S1, the mass ratio of alkali lignin to bentonite is 4-8:10-15, for example, 4:10, 4:12, 4:15, 6:10, 6:12, 6:15, 8:10, 8:12, 8:15 can be selected, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0013] Specifically, in step S2, the mass ratio of the composite bentonite material, 5-amino-2-mercaptobenzimidazole and epichlorohydrin is 5-10:3-5:4-6.

[0014] Specifically, in step S2, the temperature of the heating and stirring reaction is 50-60° C., and the time of the heating and stirring reaction is 2-4 hours.

[0015] In the present invention, alkali lignin is first dissolved in deionized water. The alkali lignin molecules contain a large number of phenolic hydroxyl groups. The alkali lignin is loaded on the surface and interlayers of bentonite through hydrogen bonding to obtain a composite bentonite material. Subsequently, under the action of a crosslinking agent, epichlorohydrin, 5-amino-2-mercaptobenzimidazole is grafted onto the composite bentonite material to obtain a flame retardant filler. The present invention loads the alkali lignin on the surface and interlayers of the bentonite so that the alkali lignin forms a dense carbon layer at high temperature, which can isolate oxygen and prevent heat transfer, thereby improving the flame retardant performance of the bentonite. Subsequently, 5-amino-2-mercaptobenzimidazole is grafted onto the composite bentonite material, thereby improving the dispersibility of the flame retardant filler in the raw material. The benzimidazole group in the 5-amino-2-mercaptobenzimidazole further improves the heat resistance of the material. The 5-amino-2-mercaptobenzimidazole contains a mercapto group. Under the action of an initiator, dodecyl peroxide, the mercapto group reacts with a small amount of double bonds contained in low-density polyethylene, thereby further improving the mechanical properties of the material.

[0016] In the technical solution disclosed in the present invention, the lubricant is selected from any one of calcium stearate, polyethylene wax, stearic acid, and stearic acid monoglyceride.

[0017] In the technical solution disclosed in the present invention, the antioxidant is selected from antioxidant 1010 or antioxidant 1076.

[0018] In the technical solution disclosed in the present invention, the ultraviolet absorber is selected from one or more of titanium dioxide, UV328, UV327, and UV326.

[0019] In the technical solution disclosed in the present invention, the heat stabilizer is selected from calcium zinc heat stabilizer CZ-113 or calcium zinc heat stabilizer CZ-116.

[0020] The present invention also provides a method for preparing the halogen-free flame-retardant polyolefin sheath material for the flexible fire-resistant cable, comprising the following steps: adding low-density polyethylene, a composite copolymer, PE-grafted maleic anhydride, a flame-retardant filler, a lubricant, an antioxidant, an ultraviolet absorber, a heat stabilizer, and lauroyl peroxide according to the formula amount into a high-speed mixer, mixing for 30-60 minutes, and then adding the mixture into a twin-screw extruder, setting the temperature to 160-180°C and the screw speed to 150-300 r / min, and melt-extruding and granulating to obtain the sheath material composite material.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) The halogen-free flame-retardant polyolefin sheathing material provided by the present invention uses low-density polyethylene as the main base material. The molecular structure of low-density polyethylene has a large number of long chain branches, which gives the material excellent flexibility and elasticity. At the same time, by adding composite copolymers and flame-retardant fillers, the mechanical properties, high and low temperature resistance and flame retardant properties of the sheathing material are improved.

[0022] (2) The present invention forms a composite copolymer by copolymerizing 1,4-butenediol and phosphonic acid-B-phenylenediol through an addition reaction between double bonds, and introduces the composite copolymer into the sheath material. The molecular structure of phosphonic acid-B-phenylenediol contains a benzene ring structure and a phosphonic acid group. The benzene ring structure can improve the thermal stability of the molecular chain, making the material less likely to undergo thermal decomposition at high temperatures, thereby improving the heat resistance of the material. The phosphonic acid group has good flame retardancy, thereby improving the flame retardancy of the material. The flexible long chain structure of the alkyl group in 1,4-butenediol improves the low-temperature resistance of the material. At the same time, the hydroxyl group in 1,4-butenediol can react with PE-grafted maleic anhydride, thereby improving the mechanical properties of the material.

[0023] (3) The present invention loads alkali lignin on the surface and interlayers of bentonite. Alkali lignin forms a dense carbon layer at high temperature, which can isolate oxygen and prevent heat transfer, thereby improving the flame retardant properties of bentonite. Subsequently, 5-amino-2-mercaptobenzimidazole is grafted onto the composite bentonite material, thereby improving the dispersion performance of the flame retardant filler in the raw material. The benzimidazole group in 5-amino-2-mercaptobenzimidazole further improves the heat resistance of the material. 5-amino-2-mercaptobenzimidazole contains mercapto groups. Under the action of the initiator dodecyl peroxide, the mercapto groups react with a small amount of double bonds contained in low-density polyethylene, further improving the mechanical properties of the material. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below through specific preferred embodiments, but the present invention is not limited to the following embodiments.

[0025] It should be noted that, unless otherwise specified, all chemical reagents involved in the present invention were purchased through commercial channels.

[0026] The low-density polyethylene used in the embodiments of the present invention is VL8005; the PE grafted maleic anhydride is DuPont 40E529; the CAS number of phosphonic acid-B-phenylphenyl ester is 1707-08-0; and the bentonite is calcium-based bentonite with a mesh size of 400 mesh.

[0027] Example 1

[0028] A method for preparing a halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable comprises the following steps: 30 parts of low-density polyethylene, 12 parts of composite copolymer, 8 parts of PE grafted maleic anhydride, 12 parts of flame retardant filler, 3 parts of polyethylene wax, 2 parts of antioxidant 1010, 1 part of ultraviolet absorber UV327, 0.3 parts of calcium zinc heat stabilizer CZ-113 and 0.1 part of lauryl peroxide were added to a high-speed mixer and mixed for 30 minutes to obtain a mixture; then the mixture was added to a twin-screw extruder, the temperature was set to 170°C, the screw speed was set to 200 r / min, and melt-extruded and granulated to obtain a sheath material composite material.

[0029] The preparation method of the composite copolymer is as follows: 3 g of 1,4-butenediol is added to 100 mL of an organic solvent, DMF, and stirred to dissolve. Then, 5 g of phosphonic acid-B-phenylenediol and 0.05 g of benzoyl peroxide are added, and the mixture is heated and stirred at 60° C. for 5 h. After the reaction is completed, the mixture is distilled under reduced pressure and dried to obtain a composite copolymer.

[0030] The preparation method of the flame retardant filler is as follows: S1. Add 4 g of alkali lignin to 100 mL of deionized water and stir to dissolve. Then add 10 g of bentonite and disperse evenly by ultrasonication. After suction filtration, drying, and grinding through a 400-mesh sieve, a composite bentonite material is obtained. S2. Disperse 5 g of the composite bentonite material in 100 mL of carbon tetrachloride, then add 3 g of 5-amino-2-mercaptobenzimidazole and 4 g of epichlorohydrin, heat and stir at 50°C for 3 h, and after the reaction is completed, filter, wash, and dry to obtain a flame retardant filler.

[0031] Example 2

[0032] A method for preparing a halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable comprises the following steps: 20 parts of low-density polyethylene, 10 parts of composite copolymer, 5 parts of PE grafted maleic anhydride, 10 parts of flame retardant filler, 2 parts of calcium stearate, 2 parts of antioxidant 1010, 1 part of ultraviolet absorber UV327, 0.2 parts of calcium zinc heat stabilizer CZ-113 and 0.1 part of lauryl peroxide were added to a high-speed mixer and mixed for 30 minutes to obtain a mixture; then the mixture was added to a twin-screw extruder, the temperature was set to 170°C, the screw speed was set to 200 r / min, and melt-extruded and granulated to obtain a sheath material composite material.

[0033] The preparation method of the composite copolymer is as follows: 6 g of 1,4-butenediol is added to 100 mL of an organic solvent, DMF, and stirred to dissolve. Then, 10 g of phosphonic acid-B-phenylphenyl ester and 0.1 g of benzoyl peroxide are added, and the mixture is heated and stirred at 60° C. for 5 h. After the reaction is completed, the mixture is distilled under reduced pressure and dried to obtain a composite copolymer.

[0034] The preparation method of the flame retardant filler is as follows: S1. Add 6 g of alkali lignin to 100 mL of deionized water and stir to dissolve. Then add 12 g of bentonite and disperse evenly by ultrasonication. After suction filtration, drying, and grinding through a 400-mesh sieve, a composite bentonite material is obtained. S2. Disperse 10 g of the composite bentonite material in 100 mL of carbon tetrachloride, then add 5 g of 5-amino-2-mercaptobenzimidazole and 6 g of epichlorohydrin, heat and stir at 50°C for 3 h, and after the reaction is completed, filter, wash, and dry to obtain a flame retardant filler.

[0035] Example 3

[0036] A method for preparing a halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable comprises the following steps: 40 parts of low-density polyethylene, 15 parts of composite copolymer, 10 parts of PE grafted maleic anhydride, 15 parts of flame retardant filler, 4 parts of calcium stearate, 3 parts of antioxidant 1010, 2 parts of ultraviolet absorber UV327, 0.4 parts of calcium zinc heat stabilizer CZ-113 and 0.2 parts of lauryl peroxide were added to a high-speed mixer and mixed for 30 minutes to obtain a mixture; then the mixture was added to a twin-screw extruder, the temperature was set to 170°C, the screw speed was set to 200 r / min, and melt-extruded and granulated to obtain a sheath material composite material.

[0037] The preparation method of the composite copolymer is as follows: 5 g of 1,4-butenediol is added to 100 mL of an organic solvent, DMF, and stirred to dissolve. Then, 8 g of phosphonic acid-B-phenylenediol and 0.1 g of benzoyl peroxide are added. The mixture is heated and stirred at 80° C. for 3 h. After the reaction is completed, the mixture is distilled under reduced pressure and dried to obtain a composite copolymer.

[0038] The preparation method of the flame retardant filler is as follows: S1, 8g of alkali lignin was added to 100mL of deionized water, stirred to dissolve, and then 15g of bentonite was added thereto, ultrasonically dispersed evenly, filtered, dried, and ground through a 400-mesh sieve to obtain a composite bentonite material; S2. Disperse 8 g of the composite bentonite material in 100 mL of carbon tetrachloride, then add 4 g of 5-amino-2-mercaptobenzimidazole and 5 g of epichlorohydrin, heat and stir at 50°C for 3 h, and after the reaction is completed, filter, wash, and dry to obtain a flame retardant filler.

[0039] Example 4

[0040] A method for preparing a halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable comprises the following steps: 25 parts of low-density polyethylene, 10 parts of composite copolymer, 6 parts of PE grafted maleic anhydride, 10 parts of flame retardant filler, 2 parts of calcium stearate, 2 parts of antioxidant 1076, 1 part of ultraviolet absorber UV327, 0.2 parts of calcium zinc heat stabilizer CZ-113 and 0.1 part of lauryl peroxide were added to a high-speed mixer and mixed for 30 minutes to obtain a mixture; then the mixture was added to a twin-screw extruder, the temperature was set to 170°C, the screw speed was set to 200 r / min, and melt-extruded and granulated to obtain a sheath material composite material.

[0041] The preparation method of the composite copolymer is as follows: 4 g of 1,4-butenediol is added to 100 mL of an organic solvent, DMF, and stirred to dissolve. Then, 6 g of phosphonic acid-B-phenylenediol and 0.08 g of benzoyl peroxide are added, and the mixture is heated and stirred at 80° C. for 3 h. After the reaction is completed, the mixture is distilled under reduced pressure and dried to obtain a composite copolymer.

[0042] The preparation method of the flame retardant filler is as follows: S1. Add 5 g of alkali lignin to 100 mL of deionized water and stir to dissolve. Then add 10 g of bentonite and disperse evenly by ultrasonication. After suction filtration, drying, and grinding through a 400-mesh sieve, a composite bentonite material is obtained. S2. Disperse 6 g of the composite bentonite material in 100 mL of carbon tetrachloride, then add 4 g of 5-amino-2-mercaptobenzimidazole and 4 g of epichlorohydrin, heat and stir at 50°C for 3 h, and after the reaction is completed, filter, wash, and dry to obtain a flame retardant filler.

[0043] Comparative Example 1

[0044] A method for preparing a halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable comprises the following steps: 30 parts of low-density polyethylene, 8 parts of PE grafted maleic anhydride, 12 parts of flame retardant filler, 3 parts of polyethylene wax, 2 parts of antioxidant 1010, 1 part of ultraviolet absorber UV327, 0.3 parts of calcium zinc heat stabilizer CZ-113 and 0.1 part of lauryl peroxide were added to a high-speed mixer and mixed for 30 minutes to obtain a mixture; then the mixture was added to a twin-screw extruder, the temperature was set to 170°C, the screw speed was set to 200 r / min, and melt-extruded and granulated to obtain a sheath material composite material.

[0045] Wherein, the preparation method of the flame retardant filler is as follows: S1. Add 4 g of alkali lignin to 100 mL of deionized water and stir to dissolve. Then add 10 g of bentonite and disperse evenly by ultrasonication. After suction filtration, drying, and grinding through a 400-mesh sieve, a composite bentonite material is obtained. S2. Disperse 5 g of the composite bentonite material in 100 mL of carbon tetrachloride, then add 3 g of 5-amino-2-mercaptobenzimidazole and 4 g of epichlorohydrin, heat and stir at 50°C for 3 h, and after the reaction is completed, filter, wash, and dry to obtain a flame retardant filler.

[0046] Compared with Example 1, Comparative Example 1 does not add the composite copolymer.

[0047] Comparative Example 2

[0048] A method for preparing a halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable comprises the following steps: 30 parts of low-density polyethylene, 12 parts of composite copolymer, 8 parts of PE grafted maleic anhydride, 12 parts of flame retardant filler, 3 parts of polyethylene wax, 2 parts of antioxidant 1010, 1 part of ultraviolet absorber UV327, 0.3 parts of calcium zinc heat stabilizer CZ-113 and 0.1 part of lauryl peroxide were added to a high-speed mixer and mixed for 30 minutes to obtain a mixture; then the mixture was added to a twin-screw extruder, the temperature was set to 170°C, the screw speed was set to 200 r / min, and melt-extruded and granulated to obtain a sheath material composite material.

[0049] The preparation method of the composite copolymer is as follows: 3 g of 1,4-butenediol is added to 100 mL of an organic solvent, DMF, and stirred to dissolve. Then, 5 g of phosphonic acid-B-phenylenediol and 0.05 g of benzoyl peroxide are added, and the mixture is heated and stirred at 60° C. for 5 h. After the reaction is completed, the mixture is distilled under reduced pressure and dried to obtain a composite copolymer.

[0050] The preparation method of the flame retardant filler is as follows: 5 g of bentonite was dispersed in 100 mL of carbon tetrachloride, and then 3 g of 5-amino-2-mercaptobenzimidazole and 4 g of epichlorohydrin were added thereto. The mixture was heated and stirred at 50° C. for 3 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain a flame retardant filler.

[0051] Compared with Example 1, in Comparative Example 2, the bentonite was not treated with alkali lignin loading.

[0052] Comparative Example 3

[0053] A method for preparing a halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable comprises the following steps: 30 parts of low-density polyethylene, 12 parts of composite copolymer, 8 parts of PE grafted maleic anhydride, 12 parts of flame retardant filler, 3 parts of polyethylene wax, 2 parts of antioxidant 1010, 1 part of ultraviolet absorber UV327, 0.3 parts of calcium zinc heat stabilizer CZ-113 and 0.1 part of lauryl peroxide were added to a high-speed mixer and mixed for 30 minutes to obtain a mixture; then the mixture was added to a twin-screw extruder, the temperature was set to 170°C, the screw speed was set to 200 r / min, and melt-extruded and granulated to obtain a sheath material composite material.

[0054] The preparation method of the composite copolymer is as follows: 3 g of 1,4-butenediol is added to 100 mL of an organic solvent, DMF, and stirred to dissolve. Then, 5 g of phosphonic acid-B-phenylenediol and 0.05 g of benzoyl peroxide are added, and the mixture is heated and stirred at 60° C. for 5 h. After the reaction is completed, the mixture is distilled under reduced pressure and dried to obtain a composite copolymer.

[0055] The preparation method of the flame retardant filler is as follows: S1. Add 4 g of alkali lignin to 100 mL of deionized water and stir to dissolve. Then add 10 g of bentonite and disperse evenly by ultrasonication. After suction filtration, drying, and grinding through a 400-mesh sieve, a composite bentonite material is obtained. S2. Disperse 5 g of the composite bentonite material in 100 mL of carbon tetrachloride, then add 3 g of 4-aminobenzimidazole and 4 g of epichlorohydrin, heat and stir at 50°C for 3 h, and after the reaction is completed, filter, wash, and dry to obtain a flame retardant filler.

[0056] Compared with Example 1, Comparative Example 3 uses 4-aminobenzimidazole to replace 5-amino-2-mercaptobenzimidazole.

[0057] The sheath materials prepared in Examples 1-2 and Comparative Examples 1-3 were made into samples that met the test standards, and then performance tests were performed, as follows: Tensile strength test: tested according to GB / T 1040.1-2018 standard, with a tensile speed of 100 mm / min; Oxygen index test: tested according to GB / T 2406.2-2009 standard; Heat aging resistance test: Heat aging was performed in a heat aging oven according to the standard GBT 7141-2008 at 135°C for 168 hours, and then the tensile strength retention was tested. Unnotched impact strength test: tested in accordance with GB / T 1843-2008 standard, temperature is -40℃; The test results are shown in Table 1.

[0058] Table 1 Performance test results of different groups

[0059] As can be seen from Table 1, the present invention improves the mechanical properties, high and low temperature resistance and flame retardancy of the sheath material through the cooperation of the composite copolymer and the flame retardant filler.

[0060] Finally, it should be noted that the above embodiments do not limit the present invention in any form. Those skilled in the art will appreciate that modifications and improvements can be made based on the present invention. Therefore, any modifications or improvements made without departing from the spirit of the present invention are intended to fall within the scope of protection claimed in the present invention.

Claims

1. A halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable, characterized in that: The invention comprises the following components in parts by weight: 20-40 parts of low-density polyethylene, 10-15 parts of composite copolymer, 5-10 parts of PE grafted maleic anhydride, 10-15 parts of flame retardant filler, 2-4 parts of lubricant, 1-3 parts of antioxidant, 1-2 parts of ultraviolet absorber, 0.2-0.4 parts of heat stabilizer and 0.1-0.2 parts of lauroyl peroxide.

2. The halogen-free flame-retardant polyolefin sheath material for flexible fireproof cables according to claim 1, characterized in that: The preparation method of the composite copolymer is as follows: 1,4-butenediol is added to an organic solvent, stirred to dissolve, then phosphonic acid-B-phenylenediol ester and benzoyl peroxide are added, heated and stirred to react, and after the reaction is completed, vacuum distillation and drying are performed to obtain the composite copolymer.

3. The halogen-free flame-retardant polyolefin sheath material for flexible fireproof cables according to claim 2, characterized in that: The mass ratio of the 1,4-butenediol, B-styryl phosphonate and benzoyl peroxide is 3-6:5-10:0.05-0.

1.

4. The halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable according to claim 2, characterized in that: The temperature for the heating and stirring reaction is 60-80°C, and the time for the heating and stirring reaction is 3-5h.

5. The halogen-free flame-retardant polyolefin sheath material for flexible fireproof cables according to claim 1, characterized in that: The preparation method of the flame retardant filler is as follows: S1. Add alkali lignin to deionized water, stir and dissolve, then add bentonite thereto, disperse uniformly by ultrasonication, filter, dry and grind to obtain a composite bentonite material; S2. Dispersing the composite bentonite material in carbon tetrachloride, then adding 5-amino-2-mercaptobenzimidazole and epichlorohydrin, heating and stirring to react, after the reaction is completed, filtering, washing, and drying to obtain a flame retardant filler.

6. The halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable according to claim 5, characterized in that: In step S1, the mass ratio of alkali lignin to bentonite is 4-8:10-15.

7. The halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable according to claim 5, characterized in that: In step S2, the mass ratio of the composite bentonite material, 5-amino-2-mercaptobenzimidazole and epichlorohydrin is 5-10:3-5:4-6.

8. The halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable according to claim 1, characterized in that: The lubricant is selected from any one of calcium stearate, polyethylene wax, stearic acid, and stearic acid monoglyceride; and the antioxidant is selected from antioxidant 1010 or antioxidant 1076.

9. The halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable according to claim 1, characterized in that: The ultraviolet absorber is selected from one or more of titanium dioxide, UV328, UV327, and UV326; and the heat stabilizer is selected from calcium zinc heat stabilizer CZ-113 or calcium zinc heat stabilizer CZ-116.

10. The method for preparing the halogen-free flame-retardant polyolefin sheath material for a flexible fireproof cable according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: adding low-density polyethylene, composite copolymer, PE grafted maleic anhydride, flame retardant filler, lubricant, antioxidant, ultraviolet absorber, heat stabilizer and lauroyl peroxide into a high-speed mixer according to the formula amount, mixing for 30-60 minutes, adding the mixture into a twin-screw extruder, setting the temperature to 160-180°C, setting the screw speed to 150-300 r / min, and melt-extruding and granulating to obtain the sheath material composite material.

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