A low-smoke halogen-free flame-retardant wire and its preparation method

Abstract

This invention discloses a low-smoke halogen-free flame-retardant network cable and its preparation method, comprising a conductor, an insulation layer, a foamed filler strip, an aluminum-plastic composite film wrapping layer, a non-woven fabric wrapping layer, and a halogen-free flame-retardant outer sheath layer. The halogen-free flame-retardant sheath layer is prepared from the following components: ethylene-vinyl acetate copolymer, POE, pretreated magnesium hydroxide, ammonium polyphosphate, modified lignin, attapulgite, zinc borate, maleic anhydride-grafted ethylene-vinyl acetate copolymer, antioxidant, and calcium stearate. This low-smoke halogen-free flame-retardant network cable uses an EVA / POE blend as the sheath matrix and employs a ternary composite flame-retardant system of magnesium hydroxide, ammonium polyphosphate, and modified lignin, synergistically using zinc borate and attapulgite as functional additives. Without introducing halogens, the sheath material simultaneously possesses B1-level flame-retardant performance, low-smoke and low-toxicity characteristics, and transmission performance meeting the Category 6 network cable standard. The overall solution balances the requirements of flame-retardant safety and communication functionality.

Description

Technical Field

[0001] This invention belongs to the field of wire mesh manufacturing technology, specifically relating to a low-smoke halogen-free flame-retardant wire mesh and its manufacturing method. Background Technology

[0002] Category 6 unshielded twisted-pair cable is currently the most widely used data transmission medium in structured cabling projects. According to standards such as GB / T 18015.4 and IEC 61156-5, it is required to meet specified transmission performance indicators such as insertion loss, near-end crosstalk attenuation, and return loss within the 250MHz frequency range. In the field of building cabling, especially in public buildings, rail transit, and data centers, relevant fire protection codes have clearly defined requirements for the flame retardant rating of cables. According to GB 31247-2014, Class B1 flame-retardant cables must simultaneously meet multiple assessment indicators such as combustion performance, smoke density, and toxic gas release, which places high demands on the flame-retardant system design of the sheath material.

[0003] Traditional cable sheathing materials are primarily polyvinyl chloride (PVC). PVC itself contains chlorine, which releases large amounts of hydrogen chloride and other toxic halogenated hydrocarbons during combustion, resulting in high smoke concentrations. This poses a threat to personnel escape and secondary firefighting, failing to meet the requirements for low-smoke halogen-free flame-retardant cables. Therefore, the industry has generally shifted to halogen-free flame-retardant systems based on polyolefins such as ethylene-vinyl acetate copolymer and polyethylene. However, the limiting oxygen index of polyolefin matrices is only 17%-19%, insufficient for flame retardancy, necessitating the introduction of large amounts of flame-retardant fillers to meet the B1 rating requirement.

[0004] In the field of halogen-free flame-retardant fillers, magnesium hydroxide and aluminum hydroxide are currently the most widely used inorganic flame retardants. Both exert gas-phase dilution and endothermic cooling effects by releasing water vapor through endothermic decomposition, and their decomposition products are halogen-free and non-toxic. However, these fillers have relatively low flame-retardant efficiency, and usually require large additions to the polyolefin matrix to meet flame-retardant requirements. High filler content significantly reduces the elongation at break and processing fluidity of the material, adversely affecting the extrusion coating process and mechanical properties of cable sheaths. Based on this, intumescent flame retardants such as ammonium polyphosphate have been introduced into composite flame-retardant systems due to their advantages in condensed phase char formation. This can reduce the amount of inorganic fillers used to some extent. However, ammonium polyphosphate has strong hygroscopicity, which can easily lead to a decline in the electrical insulation performance of the material after long-term use, and the smoke suppression effect of a single intumescent system is limited.

[0005] Lignin, a major industrial byproduct generated during papermaking and biomass refining, contains benzene rings and various active hydroxyl groups in its molecular skeleton, theoretically possessing the potential to serve as a carbon source for char formation and flame retardancy. However, the direct addition of natural or industrial lignin to polymer matrices presents challenges such as poor compatibility with nonpolar polyolefins, insufficient thermal stability, and limited char formation efficiency, thus hindering its practical application in the flame retardant field.

[0006] In summary, existing low-smoke halogen-free flame-retardant network cable products still have shortcomings in the overall balance of flame-retardant efficiency, smoke suppression performance, and sheath mechanical properties, and need further improvement. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a low-smoke, halogen-free flame-retardant wire and its preparation method.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A low-smoke halogen-free flame-retardant network cable includes a conductor, an insulation layer, a foam filler strip, an aluminum-plastic composite film wrapping layer, a non-woven fabric wrapping layer, and a halogen-free flame-retardant outer sheath layer. The conductor is covered with an insulation layer, and the conductor and the insulation layer form an insulated core. Every two insulated cores are twisted together to form a twisted pair. Four pairs of twisted pairs are twisted together to form a cable core. The inside of the cable core is provided with a foam filler strip. The outside of the cable core is covered with an aluminum-plastic composite film wrapping layer, the outside of the aluminum-plastic composite film wrapping layer is covered with a non-woven fabric wrapping layer, and the outside of the non-woven fabric wrapping layer is covered with a halogen-free flame-retardant sheath layer. The halogen-free flame-retardant sheath layer is prepared from the following components in parts by mass: 90-100 parts of ethylene-vinyl acetate copolymer, 10-20 parts of POE, 65-75 parts of pretreated magnesium hydroxide, 20-25 parts of ammonium polyphosphate, 20-25 parts of modified lignin, 5-10 parts of attapulgite, 5-8 parts of zinc borate, 8-10 parts of maleic anhydride-grafted ethylene-vinyl acetate copolymer, 2-3 parts of antioxidant, and 1-2 parts of calcium stearate.

[0009] Preferably, the conductor is made of 7 strands of annealed soft copper monofilaments with a diameter of 0.191 mm twisted together, with an outer diameter of 0.574 mm and a twisting pitch ratio of 12-16; the insulation layer is made of high-density polyethylene with a thickness of 0.2-0.25 mm.

[0010] Preferably, the pitch of the twisted pair is 8-13 mm, the pitch of the cable core is 60-80 mm, and the thickness of the halogen-free flame-retardant sheath is 1-1.3 mm.

[0011] Preferably, the method for preparing the modified lignin includes the following steps: S1. Add alkali lignin to deionized water, stir, then add ammonium dihydrogen phosphate and stir until completely dissolved. Then, perform rotary evaporation under reduced pressure, heat-treat the solid product, and then wash and dry to obtain phosphorylated lignin. S2. Add the phosphorylated lignin from S1 to dimethyl sulfoxide, then add boric acid, pentaerythritol and p-toluenesulfonic acid, and heat the reaction. After the reaction is complete, add 4 times the volume of deionized water to precipitate, filter and dry to obtain phosphorylated boron lignin. S3. Add the phosphoboryl lignin from step S2 to deionized water, then add ammonium molybdate, zinc acetate and citric acid, adjust the pH to 6-6.5, carry out a constant temperature reaction, filter after the reaction is completed, and perform heat treatment to obtain composite lignin. S4. Add the composite lignin from step S3 to an ethanol aqueous solution, adjust the pH to 4-5, then add γ-glycidyl etheroxypropyltrimethoxysilane, stir for 20-30 minutes, and then filter, wash and dry to obtain modified lignin.

[0012] Preferably, in step S1, the mass ratio of alkali lignin to ammonium dihydrogen phosphate is 100:10-15, the vacuum degree of the reduced pressure rotary evaporation is -(0.08~0.09) MPa, and the temperature is 55-65℃; the temperature of the heat treatment is 150-160℃, and the time is 1.5-2.5h.

[0013] In this invention, a method is adopted to dehydrate alkali lignin and ammonium dihydrogen phosphate in a mixed solution under reduced pressure by rotary evaporation, followed by solid-phase heat treatment. This allows the ammonium dihydrogen phosphate to be uniformly dispersed in the lignin solid during the low-temperature dehydration stage, and to undergo deammoniation activation during heat treatment at 150-160℃. The phosphate group then undergoes a solid-phase esterification reaction with the phenolic and aliphatic hydroxyl groups of the lignin. This process has a simple reaction system, and the byproducts (NH3, H2O) are all gaseous and easily escape. The product can directly enter the subsequent modification steps without further purification, making the operation process simple.

[0014] Preferably, in step S2, the mass ratio of phosphorylated lignin, dimethyl sulfoxide, boric acid, pentaerythritol, and p-toluenesulfonic acid is 100:800-1000:8-12:10-15:0.5-1, and the heating reaction temperature is 90-95℃ for 5-6 hours.

[0015] In this invention, p-toluenesulfonic acid is used as a catalyst to induce an esterification reaction between boric acid and pentaerythritol in a DMSO system. Simultaneously, the polyhydroxy properties of pentaerythritol are utilized to graft borate ester groups onto the hydroxyl sites of the phosphorylated lignin, forming PB synergistic structural units. Compared to directly adding inorganic borates to the formulation, introducing boron into the lignin framework via covalent bonding avoids the migration and precipitation of inorganic components in the matrix, resulting in a more durable and stable flame-retardant function of boron. Furthermore, the PB binding sites provide complementary thermal stabilization during char formation, helping to increase the oxidation initiation temperature of the char layer.

[0016] Preferably, in step S3, the mass ratio of phosphobic borate lignin, deionized water, ammonium molybdate, zinc acetate, and citric acid is 100:500-600:4-6:3-5:3-5, the isothermal reaction temperature is 60-70℃ and the time is 4-5h, and the heat treatment temperature is 120-130℃ and the time is 2-3h.

[0017] In this invention, in a weakly acidic aqueous medium, citric acid is used as a coordination modifier to introduce ammonium molybdate and zinc acetate onto the surface of phosphobically borated lignin, forming a Mo-Zn bimetallic complex structure. Subsequently, heat treatment at 120-130°C decomposes and solidifies the metal salt precursor. During combustion, the molybdenum compounds catalyze the gas-phase oxidation of organic matter, promoting the oxidation of combustible volatiles into char at low temperatures rather than direct combustion, thereby reducing smoke particle formation. The zinc compounds, synergistically with phosphorus and boron, promote the formation of a cross-linked char layer in the condensed phase, further reducing smoke density and CO emissions, enabling the sheath material to meet the smoke density requirements of the low-smoke halogen-free flame-retardant standard.

[0018] Preferably, in step S4, the volume fraction of ethanol in the aqueous ethanol solution is 90-95%, the mass ratio of the composite lignin to γ-glycidoxypropyltrimethoxysilane is 100:5-8, the temperature of the stirring reaction is 55-65℃, and the time is 2-3h.

[0019] In this invention, composite lignin is dispersed in an ethanol-water solution, allowing γ-glycidyl etheroxypropyltrimethoxysilane to condense with the hydroxyl groups on the lignin surface and the supported metal oxides to form Si-O covalent bonds, thus constructing an organosilicon coating layer on the particle surface, with free epoxy groups retained at the outer ends. KH560, containing epoxy groups, is chosen instead of amino or vinyl silanes because the epoxy groups can chemically react with the polar groups of the EVA segments during subsequent melt mixing, establishing a covalent interface between the modified lignin and the polymer matrix, eliminating particle stress concentration effects, and preventing the sudden drop in elongation at break common in high-filler flame-retardant systems. Simultaneously, the combustion of the organosilicon layer generates SiO2 inorganic residues, further covering the char layer surface, forming a four-layer synergistic flame-retardant system together with phosphorus-catalyzed char formation, borosilicate glass film, and Mo / Zn gas-phase inhibition.

[0020] Preferably, the method for preparing the pretreated magnesium hydroxide is as follows: Add 1.5-2 parts by weight of vinyltrimethoxysilane to 45-55 parts by weight of ethanol in a 90% aqueous solution, adjust the pH to 4.0-4.5, and stir at room temperature for 30-40 minutes to obtain a silane solution; add 100 parts by weight of magnesium hydroxide to a high-speed mixer, and spray the above silane solution evenly, stir at 1000-1200 rpm for 30 minutes, dry at 110-120℃ for 2-3 hours, depolymerize using a high-speed pulverizer, and pass through a 200-mesh sieve to obtain the final product.

[0021] This invention also protects a method for preparing a low-smoke halogen-free flame-retardant wire as described above, comprising the following steps: Step 1: Add ethylene-vinyl acetate copolymer, POE, pretreated magnesium hydroxide, ammonium polyphosphate, modified lignin, attapulgite, zinc borate, maleic anhydride-grafted ethylene-vinyl acetate copolymer, antioxidant, and calcium stearate to a high-speed mixer according to the formula ratio and mix evenly. Then, melt-blend and granulate the mixture using a twin-screw extruder to obtain a low-smoke halogen-free flame-retardant sheath material. The extrusion temperature is controlled at 150-180℃, and the screw speed is 80-120 rpm. Step 2: Twist 7 annealed soft copper monofilaments with a diameter of 0.191 mm to obtain a conductor, and use high-density polyethylene as the insulating material to extrude and coat the conductor to prepare an insulated wire core; Step 3: Twist the two insulated wire cores together to obtain twisted wires. Twist the four pairs of twisted wires together and fill the gap in the center of the cable core with foam filler strips to form the cable core. Step 4: Wrap an aluminum-plastic composite film around the cable core, then wrap it with non-woven fabric. Using an extruder, cover the surface of the non-woven fabric wrapping layer with a sheath layer to obtain the low-smoke halogen-free flame-retardant network cable.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) The low-smoke halogen-free flame-retardant network cable provided by the present invention uses EVA / POE blend as the sheath matrix and adopts a ternary composite flame-retardant system of magnesium hydroxide, ammonium polyphosphate and modified lignin, and uses zinc borate and attapulgite as functional additives. Without introducing halogens, the sheath material has B1-level flame retardant performance, low smoke and low toxicity characteristics and transmission performance that meets the Category 6 network cable standard. The action mechanism of each flame-retardant component in the sheath layer formula covers both the gas phase and the condensed phase, and there is a clear synergistic relationship between them, rather than a simple superposition of components. The conductor structure and cable core stranding parameters are designed according to relevant standards. The overall solution takes into account the requirements of flame retardant safety and communication functionality.

[0023] (2) This invention introduces phosphate ester groups, borate ester groups, and molybdenum / zinc metal complex sites onto the alkali lignin skeleton through four-step chemical modification, and improves its interfacial compatibility with the EVA matrix by KH560 (γ-glycidyl etheroxypropyltrimethoxysilane) silanization treatment. This allows it to form a multi-level, cross-dimensional synergistic flame retardant system with other flame retardant components in the sheath formulation, with condensed phase charring as the core. In the condensed phase, the phosphate ester groups decompose to produce phosphoric acid / metaphophosphate during combustion, which synergistically provides an acid source with ammonium polyphosphate, catalyzing the lignin skeleton. The covalently linked pentaerythritol dehydrates to form char, creating a continuously expanding char layer. As temperature increases, the pyrolysis of borate esters generates B2O3 glassy melt, which covers the char layer surface, sealing pores and inhibiting the outward escape of combustible gases, significantly enhancing the gas barrier continuity of the char layer. The crystal water released from the decomposition of magnesium hydroxide further dilutes the combustible gas and absorbs heat to lower the temperature, superimposing this char formation mechanism in time and space, compensating for the shortcomings of the loose char layer caused by the pulverization of magnesium oxide, a product of magnesium hydroxide decomposition alone. In the gas phase, the loaded molybdenum enters the flame zone in the form of molybdenum trioxide, inhibiting… Gas-phase chain combustion compensates for the limited contribution of the pure condensed phase mechanism to the limiting oxygen index. Regarding smoke suppression, the lignin aromatic skeleton is solidified into char residue through efficient char formation rather than being decomposed into volatile polycyclic aromatic hydrocarbons. The molybdenum / zinc bimetallic system further catalyzes the oxidation of the generated soot, simultaneously exerting a smoke-suppressing effect from both the generation and elimination of smoke particles. The organosilicon layer introduced by KH560 generates silica inorganic residues after combustion, which are superimposed on the char layer, further enhancing the thermal oxidation stability of the char layer. Simultaneously, its surface free epoxy groups copolymerize with ethylene-vinyl acetate. The formation of a covalent interface in the matrix improves the dispersibility of modified lignin in the matrix and eliminates the stress concentration effect of particles. It is precisely because of the complementary synergy of four functional components—phosphate ester group catalytic char formation, borosilicate glass membrane sealing, molybdenum / zinc gas phase inhibition and smoke suppression, and organosilicon carbon layer reinforcement—that the flame retardant contributions of each functional group of modified lignin are superimposed rather than simply added together. This allows modified lignin to play a flame retardant role in this composite flame retardant system that exceeds its addition ratio, thereby maintaining the processing fluidity and mechanical properties of the sheath material while controlling the total filler content.

[0024] (3) The low-smoke halogen-free flame-retardant mesh provided by the present invention has magnesium hydroxide surface treated with vinyltrimethoxysilane, which introduces vinyl groups on the particle surface and can form a certain degree of chemical bonding with the EVA matrix, improve the dispersion state of inorganic particles in the polymer, and reduce the mechanical property degradation caused by filler agglomeration; magnesium hydroxide begins to decompose and absorb heat and release water vapor at about 330°C, which plays a physical flame-retardant role of cooling and dilution; ammonium polyphosphate generates phosphoric acid after thermal decomposition, which can work together with lignin and EVA pyrolysis products to dehydrate and form carbon. The two action stages are connected to each other, so that the flame-retardant mechanism plays a continuous role throughout the combustion process. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the cross-sectional structure of the low-smoke halogen-free flame-retardant wire mesh provided by the present invention.

[0026] In the diagram, 1 is the conductor; 2 is the insulation layer; 3 is the foam filler strip; 4 is the aluminum-plastic composite film wrapping layer; 5 is the non-woven fabric wrapping layer; and 6 is the halogen-free flame-retardant sheath layer. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] In the following embodiments, the vinyl acetate copolymer in the ethylene-vinyl acetate copolymer has a content of 26-33 wt%, preferably DuPont Elvax 260; the POE is an ethylene-octene copolymer, with an octene content of 20-35 wt%, preferably Dow Engage 8150; the maleic anhydride-grafted ethylene-vinyl acetate copolymer is Mitsui ADMER VE300; the attapulgite has a mesh size of 325 mesh; and the antioxidant is a mixture of antioxidant 1098 and antioxidant 168 in a mass ratio of 2:1.

[0029] Example 1 A low-smoke halogen-free flame-retardant network cable includes a conductor 1, an insulation layer 2, a foam filler strip 3, an aluminum-plastic composite film wrapping layer 4, a non-woven fabric wrapping layer 5, and a halogen-free flame-retardant outer sheath layer 6. The conductor 1 is covered with the insulation layer 2, and the conductor 1 and the insulation layer 2 form an insulated wire core. Every two insulated wire cores are twisted together to form a twisted pair. Four pairs of twisted pairs are twisted together to form a cable core. The cable core is provided with a foam filler strip 3 inside. The cable core is covered with an aluminum-plastic composite film wrapping layer 4. The aluminum-plastic composite film wrapping layer 4 is covered with a non-woven fabric wrapping layer 5. The non-woven fabric wrapping layer 5 is covered with a halogen-free flame-retardant sheath layer 6. The halogen-free flame-retardant sheath layer 6 is prepared from the following components in parts by mass: 95 parts of ethylene-vinyl acetate copolymer, 15 parts of POE, 70 parts of pretreated magnesium hydroxide, 22 parts of ammonium polyphosphate, 23 parts of modified lignin, 8 parts of attapulgite, 7 parts of zinc borate, 9 parts of maleic anhydride-grafted ethylene-vinyl acetate copolymer, 2.5 parts of antioxidant, and 1.5 parts of calcium stearate.

[0030] The method for preparing the modified lignin includes the following steps: S1. Add 100g of alkali lignin to 2L of deionized water, stir for 25min, then add 13g of ammonium dihydrogen phosphate and stir until completely dissolved. Then perform rotary evaporation under reduced pressure at a vacuum of -0.085MPa and a temperature of 60℃. Heat-treat the solid product at 155℃ for 2h, then wash with deionized water 4 times and dry to obtain phosphorylated lignin. S2. Add 100g of phosphorylated lignin from S1 to 900g of dimethyl sulfoxide, then add 10g of boric acid, 13g of pentaerythritol and 0.8g of p-toluenesulfonic acid, and react at 95℃ for 5.5h. After the reaction is complete, add 4 times the volume of deionized water to precipitate, filter and dry to obtain phosphorylated boron lignin. S3. Add 100g of phosphoribobated lignin from step S2 to 550g of deionized water, then add 5g of ammonium molybdate, 4g of zinc acetate and 4g of citric acid. Adjust the pH to 6.5 with dilute ammonia water and react at a constant temperature of 65℃ for 4.5h. After the reaction is completed, filter and heat treat at 125℃ for 2.5h to obtain composite lignin. S4. Add 100g of the composite lignin from step S3 to 1L of ethanol aqueous solution (ethanol volume fraction of 95%), adjust the pH to 4.5 with dilute hydrochloric acid, then add 7g of γ-glycidoxypropyltrimethoxysilane, stir for 25min, and then stir and react at 60℃ for 2.5h. After completion, filter, wash and dry to obtain modified lignin. The preparation method of the pretreated magnesium hydroxide is as follows: 1.8 parts by weight of vinyltrimethoxysilane are added to 50 parts by weight of an aqueous ethanol solution with a mass fraction of 90%, the pH is adjusted to 4.5, and the mixture is stirred at room temperature for 35 min to obtain a silane solution; 100 parts by weight of magnesium hydroxide are added to a high-speed mixer, and the above silane solution is added evenly by spraying. After stirring at 1100 rpm for 30 min, the mixture is dried at 115℃ for 2.5 h, depolymerized by a high-speed pulverizer, and passed through a 200-mesh sieve to obtain the final product.

[0031] A method for preparing a low-smoke halogen-free flame-retardant wire includes the following steps: Step 1: Ethylene-vinyl acetate copolymer, POE, pretreated magnesium hydroxide, ammonium polyphosphate, modified lignin, attapulgite, zinc borate, maleic anhydride-grafted ethylene-vinyl acetate copolymer, antioxidant, and calcium stearate are added to a high-speed mixer according to the formula ratio and mixed evenly. The mixture is then melt-blended and granulated using a twin-screw extruder to obtain a low-smoke halogen-free flame-retardant sheath material. The extrusion temperature is controlled at 170℃ and the screw speed is 100rpm. Step 2: Twist 7 annealed soft copper monofilaments with a diameter of 0.191 mm to obtain a conductor with an outer diameter of 0.574 mm and a twisting pitch ratio of 14. Use high-density polyethylene as the insulation material to extrude and coat the conductor to prepare an insulated wire core. The thickness of the insulation layer is 0.2-0.25 mm. Step 3: Twist the two insulated wire cores together to obtain a twisted wire with a pitch of 10 mm. Twist the four pairs of twisted wires together and fill the gap in the center of the cable core with foam filler strips to form the cable core with a pitch of 770 mm. Step 4: Wrap the cable core with an aluminum-plastic composite film, then wrap it with non-woven fabric. Using an extruder, cover the surface of the non-woven fabric wrapping layer with a sheath layer. The thickness of the halogen-free flame-retardant sheath layer is 1-1.3 mm, thus obtaining the low-smoke halogen-free flame-retardant network cable.

[0032] Example 2 A low-smoke halogen-free flame-retardant network cable includes a conductor 1, an insulation layer 2, a foam filler strip 3, an aluminum-plastic composite film wrapping layer 4, a non-woven fabric wrapping layer 5, and a halogen-free flame-retardant outer sheath layer 6. The conductor 1 is covered with the insulation layer 2, and the conductor 1 and the insulation layer 2 form an insulated wire core. Every two insulated wire cores are twisted together to form a twisted pair. Four pairs of twisted pairs are twisted together to form a cable core. The cable core is provided with a foam filler strip 3 inside. The cable core is covered with an aluminum-plastic composite film wrapping layer 4. The aluminum-plastic composite film wrapping layer 4 is covered with a non-woven fabric wrapping layer 5. The non-woven fabric wrapping layer 5 is covered with a halogen-free flame-retardant sheath layer 6. The halogen-free flame-retardant sheath layer 6 is prepared from the following components in parts by mass: 90 parts of ethylene-vinyl acetate copolymer, 20 parts of POE, 65 parts of pretreated magnesium hydroxide, 20 parts of ammonium polyphosphate, 20 parts of modified lignin, 5 parts of attapulgite, 5 parts of zinc borate, 8 parts of maleic anhydride-grafted ethylene-vinyl acetate copolymer, 2 parts of antioxidant, and 1 part of calcium stearate.

[0033] The method for preparing the modified lignin includes the following steps: S1. Add 100g of alkali lignin to 2L of deionized water, stir for 20min, then add 10g of ammonium dihydrogen phosphate and stir until completely dissolved. Then perform rotary evaporation under reduced pressure at a vacuum of -0.08MPa and a temperature of 65℃. Heat-treat the solid product at 150℃ for 2.5h, then wash with deionized water 4 times and dry to obtain phosphorylated lignin. S2. Add 100g of phosphorylated lignin from S1 to 800g of dimethyl sulfoxide, then add 8g of boric acid, 10g of pentaerythritol and 0.5g of p-toluenesulfonic acid, and react at 90℃ for 6h. After the reaction is complete, add 4 times the volume of deionized water to precipitate, filter and dry to obtain phosphorylated boron lignin. S3. Add 100g of phosphoroborated lignin from step S2 to 500g of deionized water, then add 4g of ammonium molybdate, 3g of zinc acetate and 3g of citric acid. Adjust the pH to 6 with dilute ammonia water, and react at a constant temperature of 60℃ for 5h. After the reaction is completed, filter and heat treat at 120℃ for 3h to obtain composite lignin. S4. Add 100g of the composite lignin from step S3 to 1L of ethanol aqueous solution (ethanol volume fraction of 90%), adjust the pH to 4 with dilute hydrochloric acid, then add 5g of γ-glycidoxypropyltrimethoxysilane, stir for 20min, and then stir and react at 55℃ for 3h. After completion, filter, wash and dry to obtain modified lignin. The preparation method of the pretreated magnesium hydroxide is as follows: 1.5 parts by weight of vinyltrimethoxysilane are added to 45 parts by weight of an aqueous ethanol solution with a mass fraction of 90%, the pH is adjusted to 4.0, and the mixture is stirred at room temperature for 30 min to obtain a silane solution; 100 parts by weight of magnesium hydroxide are added to a high-speed mixer, and the above silane solution is added evenly by spraying. After stirring at 1000 rpm for 30 min, the mixture is dried at 110℃ for 3 h, depolymerized by a high-speed pulverizer, and passed through a 200-mesh sieve to obtain the final product.

[0034] A method for preparing a low-smoke halogen-free flame-retardant wire includes the following steps: Step 1: Ethylene-vinyl acetate copolymer, POE, pretreated magnesium hydroxide, ammonium polyphosphate, modified lignin, attapulgite, zinc borate, maleic anhydride-grafted ethylene-vinyl acetate copolymer, antioxidant, and calcium stearate are added to a high-speed mixer according to the formula ratio and mixed evenly. The mixture is then melt-blended and granulated using a twin-screw extruder to obtain a low-smoke halogen-free flame-retardant sheath material. The extrusion temperature is controlled at 170℃ and the screw speed is 100rpm. Step 2: Twist 7 annealed soft copper monofilaments with a diameter of 0.191 mm to obtain a conductor with an outer diameter of 0.574 mm and a twisting pitch ratio of 14. Use high-density polyethylene as the insulation material to extrude and coat the conductor to prepare an insulated wire core. The thickness of the insulation layer is 0.2-0.25 mm. Step 3: Twist the two insulated wire cores together to obtain a twisted wire with a pitch of 10 mm. Twist the four pairs of twisted wires together and fill the gap in the center of the cable core with foam filler strips to form the cable core with a pitch of 770 mm. Step 4: Wrap the cable core with an aluminum-plastic composite film, then wrap it with non-woven fabric. Using an extruder, cover the surface of the non-woven fabric wrapping layer with a sheath layer. The thickness of the halogen-free flame-retardant sheath layer is 1-1.3 mm, thus obtaining the low-smoke halogen-free flame-retardant network cable.

[0035] Example 3 A low-smoke halogen-free flame-retardant network cable includes a conductor 1, an insulation layer 2, a foam filler strip 3, an aluminum-plastic composite film wrapping layer 4, a non-woven fabric wrapping layer 5, and a halogen-free flame-retardant outer sheath layer 6. The conductor 1 is covered with the insulation layer 2, and the conductor 1 and the insulation layer 2 form an insulated wire core. Every two insulated wire cores are twisted together to form a twisted pair. Four pairs of twisted pairs are twisted together to form a cable core. The cable core is provided with a foam filler strip 3 inside. The cable core is covered with an aluminum-plastic composite film wrapping layer 4. The aluminum-plastic composite film wrapping layer 4 is covered with a non-woven fabric wrapping layer 5. The non-woven fabric wrapping layer 5 is covered with a halogen-free flame-retardant sheath layer 6. The halogen-free flame-retardant sheath layer 6 is prepared from the following components in parts by mass: 100 parts of ethylene-vinyl acetate copolymer, 10 parts of POE, 75 parts of pretreated magnesium hydroxide, 25 parts of ammonium polyphosphate, 25 parts of modified lignin, 10 parts of attapulgite, 8 parts of zinc borate, 10 parts of maleic anhydride-grafted ethylene-vinyl acetate copolymer, 3 parts of antioxidant, and 2 parts of calcium stearate.

[0036] The method for preparing the modified lignin includes the following steps: S1. Add 100g of alkali lignin to 2L of deionized water, stir for 30min, then add 15g of ammonium dihydrogen phosphate and stir until completely dissolved. Then perform rotary evaporation under reduced pressure at a vacuum of -0.09MPa and a temperature of 55℃. Heat-treat the solid product at 160℃ for 1.5h, then wash with deionized water 4 times and dry to obtain phosphorylated lignin. S2. Add 100g of phosphorylated lignin from S1 to 1000g of dimethyl sulfoxide, then add 12g of boric acid, 15g of pentaerythritol and 1g of p-toluenesulfonic acid, and react at 95℃ for 5h. After the reaction is complete, add 4 times the volume of deionized water to precipitate, filter and dry to obtain phosphorylated boron lignin. S3. Add 100g of phosphoribobated lignin from step S2 to 600g of deionized water, then add 6g of ammonium molybdate, 5g of zinc acetate and 5g of citric acid. Adjust the pH to 6.5 with dilute ammonia water, and react at a constant temperature of 70℃ for 4h. After the reaction is completed, filter and heat treat at 130℃ for 2h to obtain composite lignin. S4. Add 100g of the composite lignin from step S3 to 1L of ethanol aqueous solution (ethanol volume fraction is 95%), adjust the pH to 5 with dilute hydrochloric acid, then add 8g of γ-glycidoxypropyltrimethoxysilane, stir for 30min, and then stir and react at 65℃ for 2h. After completion, filter, wash and dry to obtain modified lignin. The preparation method of the pretreated magnesium hydroxide is as follows: 2 parts by weight of vinyltrimethoxysilane are added to 55 parts by weight of ethanol aqueous solution with a mass fraction of 90%, the pH is adjusted to 4.5, and the mixture is stirred at room temperature for 40 min to obtain a silane solution; 100 parts by weight of magnesium hydroxide are added to a high-speed mixer, and the above silane solution is added evenly by spraying. After stirring at 1200 rpm for 30 min, the mixture is dried at 120℃ for 2 h, depolymerized by a high-speed pulverizer, and passed through a 200-mesh sieve to obtain the final product.

[0037] A method for preparing a low-smoke halogen-free flame-retardant wire includes the following steps: Step 1: Ethylene-vinyl acetate copolymer, POE, pretreated magnesium hydroxide, ammonium polyphosphate, modified lignin, attapulgite, zinc borate, maleic anhydride-grafted ethylene-vinyl acetate copolymer, antioxidant, and calcium stearate are added to a high-speed mixer according to the formula ratio and mixed evenly. The mixture is then melt-blended and granulated using a twin-screw extruder to obtain a low-smoke halogen-free flame-retardant sheath material. The extrusion temperature is controlled at 170℃ and the screw speed is 100rpm. Step 2: Twist 7 annealed soft copper monofilaments with a diameter of 0.191 mm to obtain a conductor with an outer diameter of 0.574 mm and a twisting pitch ratio of 14. Use high-density polyethylene as the insulation material to extrude and coat the conductor to prepare an insulated wire core. The thickness of the insulation layer is 0.2-0.25 mm. Step 3: Twist the two insulated wire cores together to obtain a twisted wire with a pitch of 10 mm. Twist the four pairs of twisted wires together and fill the gap in the center of the cable core with foam filler strips to form the cable core with a pitch of 770 mm. Step 4: Wrap the cable core with an aluminum-plastic composite film, then wrap it with non-woven fabric. Using an extruder, cover the surface of the non-woven fabric wrapping layer with a sheath layer. The thickness of the halogen-free flame-retardant sheath layer is 1-1.3 mm, thus obtaining the low-smoke halogen-free flame-retardant network cable.

[0038] Comparative Example 1 Compared with Example 1, this comparative example replaces the modified lignin in the halogen-free flame-retardant sheath layer with an equal amount of alkali lignin, while all other aspects remain unchanged.

[0039] Comparative Example 2 Compared with Example 1, this comparative example replaces the modified lignin in the halogen-free flame-retardant sheath layer with an equal amount of phosphated lignin, while all other aspects remain unchanged.

[0040] The method for preparing the phosphorylated lignin includes the following steps: 100g of alkali lignin was added to 2L of deionized water and stirred for 25min. Then, 13g of ammonium dihydrogen phosphate was added and stirred until completely dissolved. Subsequently, rotary evaporation was performed under reduced pressure at a vacuum of -0.085MPa and a temperature of 60℃. The solid product was then heat-treated at 155℃ for 2h, followed by washing with deionized water four times and drying to obtain phosphorylated lignin.

[0041] Comparative Example 3 Compared with Example 1, this comparative example replaces the modified lignin in the halogen-free flame-retardant sheath layer with an equal amount of phosphobic boronized lignin, while all other aspects remain unchanged.

[0042] The method for preparing the phosphobic borylated lignin includes the following steps: S1. Add 100g of alkali lignin to 2L of deionized water, stir for 25min, then add 13g of ammonium dihydrogen phosphate and stir until completely dissolved. Then perform rotary evaporation under reduced pressure at a vacuum of -0.085MPa and a temperature of 60℃. Heat-treat the solid product at 155℃ for 2h, then wash with deionized water 4 times and dry to obtain phosphorylated lignin. S2. Add 100g of phosphorylated lignin from S1 to 900g of dimethyl sulfoxide, then add 10g of boric acid, 13g of pentaerythritol and 0.8g of p-toluenesulfonic acid, and react at 95℃ for 5.5h. After the reaction is complete, add 4 times the volume of deionized water to precipitate, filter and dry to obtain phosphorylated boron lignin.

[0043] Comparative Example 4 Compared with Example 1, this comparative example replaces the modified lignin in the halogen-free flame-retardant sheath layer with an equal amount of composite lignin, while all other aspects remain unchanged.

[0044] The preparation method of the composite lignin includes the following steps: S1. Add 100g of alkali lignin to 2L of deionized water, stir for 25min, then add 13g of ammonium dihydrogen phosphate and stir until completely dissolved. Then perform rotary evaporation under reduced pressure at a vacuum of -0.085MPa and a temperature of 60℃. Heat-treat the solid product at 155℃ for 2h, then wash with deionized water 4 times and dry to obtain phosphorylated lignin. S2. Add 100g of phosphorylated lignin from S1 to 900g of dimethyl sulfoxide, then add 10g of boric acid, 13g of pentaerythritol and 0.8g of p-toluenesulfonic acid, and react at 95℃ for 5.5h. After the reaction is complete, add 4 times the volume of deionized water to precipitate, filter and dry to obtain phosphorylated boron lignin. S3. Add 100g of phosphoribobated lignin from step S2 to 550g of deionized water, then add 5g of ammonium molybdate, 4g of zinc acetate and 4g of citric acid. Adjust the pH to 6.5 with dilute ammonia water, and react at a constant temperature of 65℃ for 4.5h. After the reaction is complete, filter and heat treat at 125℃ for 2.5h to obtain composite lignin.

[0045] Comparative Example 5 Compared with Example 1, the modified lignin in the halogen-free flame-retardant sheath layer in this comparative example was prepared by physical blending of alkali lignin with ammonium dihydrogen phosphate, boric acid, ammonium molybdate, and zinc acetate, while the rest remained unchanged.

[0046] The method for preparing the modified lignin includes the following steps: 100g of alkali lignin, 13g of ammonium dihydrogen phosphate, 10g of boric acid, 5g of ammonium molybdate, and 4g of zinc acetate were mixed evenly to obtain modified lignin.

[0047] The low-smoke halogen-free flame-retardant sheath materials prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to performance tests. The limiting oxygen index (LOI) was tested according to GB / T 2406.2-2009 "Determination of flammability by oxygen index method for plastics - Part 2: Room temperature test". The sample size was 150mm × 10mm × 4mm, prepared by compression molding at a temperature of 170-180℃ and a pressure of 10MPa. After holding the pressure for 5 minutes, the sample was cooled and demolded. The test was conducted at room temperature (23±2℃) and relative humidity of 50±5%. The sample was held vertically and ignited from the top to determine the minimum oxygen volume fraction required to sustain combustion. The vertical flammability rating (UL94) was determined according to GB / T The test was conducted according to GB / T 2408-2021 "Determination of Burning Performance of Plastics - Horizontal and Vertical Methods". The vertical burning method was used. The sample size was 125mm × 13mm × 3.2mm. After molding, the sample was conditioned for 48 hours at (23±2℃, 50±5% relative humidity). The sample was vertically suspended, with the lower end 300mm from the absorbent cotton. A 20mm flame was applied for ignition, and the flame was removed after 10 seconds. The flaming time t1 was recorded. If the flame extinguished, it was re-ignited for 10 seconds, and the flameless time t2 and t3 were recorded. It was observed whether molten droplets ignited the absorbent cotton. Five samples were used per group. The V-0, V-1, or V-2 rating was determined based on t1, t2, t3, and the dripping situation. The peak heat release rate, total heat release, and total smoke release were determined according to GB / T The test was conducted according to 16172-2007 "Test Method for Heat Release Rate of Building Materials". The sample size was 100mm×100mm, the thickness was 4mm, and it was molded. The bottom surface was covered with aluminum foil to simulate single-sided exposure to combustion. An external radiant heat flux density of 50kW / m³ was applied. 2(Equivalent to a moderate intensity real fire condition), placed horizontally, continuously ignited by an igniter, and the complete curve of heat release rate over time was recorded. The peak heat release rate, the total heat release during the entire combustion process, and the total smoke release were extracted from the curve. Tensile strength and elongation at break were tested according to GB / T 1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics" standard, using a 180mm×10mm×4mm specimen with a tensile rate of 50mm / min. The test results are shown in Table 1 below.

[0048] Table 1 As can be seen from Table 1 above, the low-smoke halogen-free flame-retardant sheath material prepared by this invention has significantly better flame-retardant and mechanical properties than all five comparative examples. Comparative example 1 (alkali lignin) has the worst flame-retardant index, indicating the overall necessity of the four-step modification. From comparative examples 2 to 4, as the modification steps are gradually improved, the limiting oxygen index increases sequentially, while the peak heat release rate and total smoke release decrease sequentially, showing a clear progressive trend, which confirms the independent contribution of each step of phosphate esterification, borate esterification, and molybdenum / zinc bimetallic complex loading. Comparative example 5 (physical blend) has the worst comprehensive performance, indicating that the covalent modification route is inherently superior to physical blending in both flame-retardant efficiency and interfacial compatibility.

[0049] The above description is a further detailed explanation of the present invention in conjunction with specific implementation examples. It should not be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the protection scope of the present invention.

[0050] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-smoke, halogen-free, flame-retardant network cable, characterized in that, The cable core includes a conductor (1), an insulation layer (2), a foam filler strip (3), an aluminum-plastic composite film wrapping layer (4), a non-woven fabric wrapping layer (5), and a halogen-free flame-retardant outer sheath layer (6). The conductor (1) is covered with an insulation layer (2). The conductor (1) and the insulation layer (2) form an insulated wire core. Every two insulated wire cores are twisted together to form a twisted wire. Four pairs of twisted wires are twisted together to form a cable core. The inside of the cable core is provided with a foam filler strip (3). The outside of the cable core is covered with an aluminum-plastic composite film wrapping layer (4). The outside of the aluminum-plastic composite film wrapping layer (4) is covered with a non-woven fabric wrapping layer (5). The outside of the non-woven fabric wrapping layer (5) is covered with a halogen-free flame-retardant sheath layer (6). The halogen-free flame-retardant sheath layer (6) is prepared from the following components in parts by mass: 90-100 parts of ethylene-vinyl acetate copolymer, 10-20 parts of POE, 65-75 parts of pretreated magnesium hydroxide, 20-25 parts of ammonium polyphosphate, 20-25 parts of modified lignin, 5-10 parts of attapulgite, 5-8 parts of zinc borate, 8-10 parts of maleic anhydride-grafted ethylene-vinyl acetate copolymer, 2-3 parts of antioxidant, and 1-2 parts of calcium stearate.

2. The low-smoke halogen-free flame-retardant wire according to claim 1, characterized in that, The conductor is made of 7 strands of annealed soft copper monofilaments with a diameter of 0.191 mm, an outer diameter of 0.574 mm, and a stranding pitch ratio of 12-16; the insulation layer is made of high-density polyethylene with a thickness of 0.2-0.25 mm.

3. The low-smoke halogen-free flame-retardant wire according to claim 1, characterized in that, The twisted pair has a pitch of 8-13 mm, the cable core has a pitch of 60-80 mm, and the halogen-free flame-retardant sheath has a thickness of 1-1.3 mm.

4. The low-smoke halogen-free flame-retardant wire according to claim 1, characterized in that, The method for preparing the modified lignin includes the following steps: S1. Add alkali lignin to deionized water, stir, add ammonium dihydrogen phosphate, stir until completely dissolved, then perform rotary evaporation under reduced pressure, heat treat the solid product, then wash and dry to obtain phosphorylated lignin. S2. Add the phosphorylated lignin from S1 to dimethyl sulfoxide, then add boric acid, pentaerythritol and p-toluenesulfonic acid, and heat the reaction. After the reaction is complete, add 4 times the volume of deionized water to precipitate, filter and dry to obtain phosphorylated boron lignin. S3. Add the phosphoboryl lignin from step S2 to deionized water, then add ammonium molybdate, zinc acetate and citric acid, adjust the pH to 6-6.5, carry out a constant temperature reaction, filter after the reaction is completed, and perform heat treatment to obtain composite lignin. S4. Add the composite lignin from step S3 to an ethanol aqueous solution, adjust the pH to 4-5, then add γ-glycidyl etheroxypropyltrimethoxysilane, stir for 20-30 minutes, and then filter, wash and dry to obtain modified lignin.

5. The low-smoke halogen-free flame-retardant wire according to claim 4, characterized in that, In step S1, the mass ratio of alkali lignin to ammonium dihydrogen phosphate is 100:10-15, the vacuum degree of the rotary evaporation is -(0.08~0.09) MPa, and the temperature is 55-65℃; the temperature of the heat treatment is 150-160℃, and the time is 1.5-2.5h.

6. The low-smoke halogen-free flame-retardant wire according to claim 4, characterized in that, In step S2, the mass ratio of phosphorylated lignin, dimethyl sulfoxide, boric acid, pentaerythritol, and p-toluenesulfonic acid is 100:800-1000:8-12:10-15:0.5-1, and the heating reaction is carried out at a temperature of 90-95°C for 5-6 hours.

7. The low-smoke halogen-free flame-retardant wire according to claim 4, characterized in that, In step S3, the mass ratio of phosphobically borated lignin, deionized water, ammonium molybdate, zinc acetate, and citric acid is 100:500-600:4-6:3-5:3-5. The isothermal reaction is carried out at a temperature of 60-70℃ for 4-5 hours, and the heat treatment is carried out at a temperature of 120-130℃ for 2-3 hours.

8. The low-smoke halogen-free flame-retardant wire according to claim 4, characterized in that, In step S4, the volume fraction of ethanol in the aqueous ethanol solution is 90-95%, the mass ratio of the composite lignin to γ-glycidoxypropyltrimethoxysilane is 100:5-8, the temperature of the stirring reaction is 55-65℃, and the time is 2-3h.

9. The low-smoke halogen-free flame-retardant wire according to claim 1, characterized in that, The method for preparing the pretreated magnesium hydroxide is as follows: Add 1.5-2 parts by weight of vinyltrimethoxysilane to 45-55 parts by weight of ethanol in a 90% aqueous solution, adjust the pH to 4.0-4.5, and stir at room temperature for 30-40 minutes to obtain a silane solution; add 100 parts by weight of magnesium hydroxide to a high-speed mixer, and spray the above silane solution evenly, stir at 1000-1200 rpm for 30 minutes, dry at 110-120℃ for 2-3 hours, depolymerize using a high-speed pulverizer, and pass through a 200-mesh sieve to obtain the final product.

10. A method for preparing a low-smoke halogen-free flame-retardant wire according to any one of claims 1-9, characterized in that, Includes the following steps: Step 1: Add ethylene-vinyl acetate copolymer, POE, pretreated magnesium hydroxide, ammonium polyphosphate, modified lignin, attapulgite, zinc borate, maleic anhydride-grafted ethylene-vinyl acetate copolymer, antioxidant, and calcium stearate to a high-speed mixer according to the formula ratio and mix evenly. Then, melt-blend and granulate the mixture using a twin-screw extruder to obtain a low-smoke halogen-free flame-retardant sheath material. The extrusion temperature is controlled at 150-180℃, and the screw speed is 80-120 rpm. Step 2: Twist 7 annealed soft copper monofilaments with a diameter of 0.191 mm to obtain a conductor, and use high-density polyethylene as the insulating material to extrude and coat the conductor to prepare an insulated wire core; Step 3: Twist the two insulated wire cores together to obtain twisted wires. Twist the four pairs of twisted wires together and fill the gap in the center of the cable core with foam filler strips to form the cable core. Step 4: Wrap an aluminum-plastic composite film around the cable core, then wrap it with non-woven fabric. Using an extruder, cover the surface of the non-woven fabric wrapping layer with a sheath layer to obtain the low-smoke halogen-free flame-retardant network cable.

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