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

Abstract

The invention relates to the technical field of organic polymer materials, and particularly discloses a low-smoke halogen-free flame-retardant material and a preparation method thereof. The low-smoke halogen-free flame-retardant material is prepared from the following raw materials in parts by weight: polyolefin, an ethylene-butyl acrylate copolymer, polyurethane, dicumyl peroxide, melamine polyphosphate, a reinforced wear-resistant filler, a double-layer shell structure microcapsule, a compatilizer and an antioxidant, the reinforced wear-resistant filler is silicon carbide micro powder of which the surface is plated with a metal oxide; the microcapsule with the double-layer shell structure comprises a core material, an inner shell layer and an outer shell layer from inside to outside, the core material is molybdenum disulfide nanoparticles, the inner shell layer is a copolymer of polyester polyol and isocyanate, and the outer shell layer is poly N-isopropylacrylamide. The low-smoke halogen-free flame-retardant material disclosed by the invention can be applied to many fields such as electronic appliances, electric wires and cables, rail transit and buildings, and has the advantages of high flame retardance, less combustion smoke and high wear resistance.

Description

Technical Field

[0001] The present application relates to the technical field of organic polymer materials, and more specifically, to a low-smoke and halogen-free flame retardant material and a preparation method thereof. Background Art

[0002] In the technical field of organic polymer materials, low-smoke and halogen-free flame retardant materials are attracting increasing attention. With the continuous improvement of the requirements for fire safety and environmental protection in modern society, traditional halogen-containing flame retardant materials are gradually restricted in their applications because they release a large amount of toxic hydrogen halide gas and produce thick smoke when burning, posing a serious threat to life safety and the environment. Low-smoke and halogen-free flame retardant materials have emerged. These materials produce less smoke and do not release halogens when burning, greatly reducing the harm to the human body and environmental pollution during a fire. In many fields such as electronic appliances, wires and cables, rail transit, and construction, the application demand for low-smoke and halogen-free flame retardant materials continues to grow. For example, in electronic and electrical products, in order to prevent electrical failures from causing fires, the internal wiring and housing materials need to have good flame retardant properties; as a key carrier for power transmission and signal transmission, wires and cables using low-smoke and halogen-free flame retardant materials can effectively improve the power supply safety and stability and reduce secondary disasters during a fire.

[0003] In the related art, a patent application document with the publication number CN105924729A discloses a flame retardant cable material, which includes the following components by mass parts: 80-100 parts of low-density polyethylene resin, 40-60 parts of PVC resin, 50-60 parts of aluminum hydroxide flame retardant, 1-2 parts of coupling agent, 6-8 parts of melamine cyanurate, 2-3 parts of dimethyl disulfide, 6-10 parts of dioctyl phthalate, 0.1-0.3 parts of ultraviolet absorber, 10-15 parts of active nano calcium carbonate, 4-6 parts of paraffin wax, 0.2-0.4 parts of stearic acid, and 2-4 parts of epoxidized soybean oil.

[0004] In the above solution, aluminum hydroxide is added as a flame retardant to increase the smokeless flame retardant performance of the cable material, so that the cable material has good flame retardant and heat resistance properties. However, due to the relatively low hardness of aluminum hydroxide itself and the limited interfacial bonding force with the resin matrix, the addition of a large amount of aluminum hydroxide flame retardant forms many relatively weak interfacial regions inside the material. When the material is subjected to frictional external forces, these regions are prone to being damaged first, resulting in poor wear resistance of the flame retardant material. Especially for the application scenarios of the outer insulation protection of wires and cables that need to be frequently rubbed and scratched, poor wear resistance will cause rapid surface wear of the material, reduce the insulation performance, and lead to potential electrical safety hazards. Therefore, the flame retardant materials in the related art have the defect of poor wear resistance. Summary of the Invention

[0005] In order to improve the wear resistance of the flame retardant material while ensuring good flame retardant effect, the present application provides a low-smoke and halogen-free flame retardant material and its preparation method.

[0006] The low-smoke and halogen-free flame retardant material provided by the present application adopts the following technical solution: A low-smoke and halogen-free flame retardant material, which is made of the following raw materials in parts by weight: 50-60 parts of polyolefin, 40-50 parts of ethylene-butyl acrylate copolymer, 20-30 parts of polyurethane, 5-10 parts of dicumyl peroxide, 12-18 parts of melamine polyphosphate, 10-20 parts of enhanced wear-resistant filler, 10-15 parts of double-layer shell structure microcapsule, 1-5 parts of compatibilizer, and 1-5 parts of antioxidant; The enhanced wear-resistant filler is silicon carbide micropowder with a surface coated with metal oxide; The double-layer shell structure microcapsule includes a core material, an inner shell layer and an outer shell layer from the inside to the outside. The core material is molybdenum disulfide nanoparticles, the inner shell layer is a copolymer of polyester polyol and isocyanate, and the outer shell layer is poly-N-isopropylacrylamide.

[0007] By adopting the above technical solution, polyolefin, ethylene-butyl acrylate copolymer and polyurethane constitute the matrix of the material, providing the basic mechanical properties of the material. Dicumyl peroxide as a cross-linking agent can form a cross-linked structure between polymer molecular chains, enhancing the overall strength and stability of the material, which has a positive effect on improving wear resistance. Melamine polyphosphate is an efficient flame retardant, which can form an expanded carbon layer during combustion to isolate oxygen and heat, achieving a flame retardant effect.

[0008] Silicon carbide micropowder with a surface coated with metal oxide (such as titanium dioxide) is used as the enhanced wear-resistant filler. Silicon carbide itself has high hardness and wear resistance, providing the basic wear resistance of the material. The surface-coated titanium dioxide metal oxide can, on the one hand, improve the wettability and interfacial bonding force between the silicon carbide micropowder and the resin matrix, making it better dispersed in the resin matrix and evenly bearing the frictional external force; on the other hand, the characteristics of the metal oxide itself also help to improve the surface hardness and wear resistance of the material.

[0009] By adding microcapsules with a double-shell structure, the molybdenum disulfide nanoparticles selected as the core material of the double-shell structure microcapsules have good lubricating properties. Molybdenum disulfide has a typical layered structure, and the binding force between layers is weak. During the friction process, these layered structures are prone to relative sliding, and can form a continuous lubricating film on the friction surface, reducing the direct contact and friction coefficient between the friction pairs, thereby reducing the wear of the material. When tiny pits and scratches appear on the material surface due to friction, the molybdenum disulfide nanoparticles released by the microcapsules can fill these defective parts. They can fill the unevenness of the material surface, make the friction surface smoother, reduce the stress concentration phenomenon, avoid further aggravation of wear, and thus improve the wear resistance of the material surface.

[0010] By designing a double-sided layer structure, when the microcapsules are not subjected to external stimuli such as friction, the double-shell structure provides good protection for the core material. The inner polyurethane-isocyanate shell has a certain strength and sealing performance, which can prevent the premature leakage of the core material during storage and use. The outer shell further enhances the stability and durability of the microcapsules, avoids the damage of the microcapsules in the normal environment, and ensures the effectiveness of the core material and the service life of the microcapsules. The outer shell is made of temperature-sensitive poly(N-isopropylacrylamide) (PNIPAAm). When the material is subjected to friction, the heat generated by friction raises the temperature around the microcapsules, exceeding the lower critical solution temperature (LCST) of PNIPAAm. The outer shell undergoes a phase transition from hydrophilic to hydrophobic, with a volume contraction, and the conformation of its molecular chain also changes, making the carboxyl groups that were originally in a "hidden" state and had low activity exposed and have higher reactivity, so that they can undergo transesterification reactions with the polyurethane of the inner shell, destroying the structure of the inner shell and enabling the core material to be released to the friction surface in a timely manner. The extrusion effect of the outer shell helps to promote the release of the core material outward, and the structural changes caused by the volume contraction of the outer shell can also promote the reaction between the outer shell and the inner shell, further facilitating the release of the core material. This temperature-sensitive triggered release mechanism ensures that the core material will be released to play a role only when the material is truly worn and needs wear-resistant repair, thus effectively enhancing the wear resistance of the material. As the friction continues, more and more microcapsules release the core material due to the increase in temperature, continuously repairing and lubricating the friction surface. This self-repair cycle mechanism can continuously play a role during the entire use process of the material, maintaining and improving the wear resistance of the material in the long term.

[0011] Optionally, the metal oxide coated on the surface of the wear-resistant filler is titanium dioxide.

[0012] By adopting the above technical solution, titanium dioxide has good chemical stability and optical properties. In the filler, it can tightly combine with the surface of silicon carbide micropowder to form a hard and chemically stable coating. On the one hand, this coating improves the wear resistance of the silicon carbide micropowder itself; on the other hand, titanium dioxide has a good affinity with the resin matrix, which can enhance the interfacial bonding force between the silicon carbide micropowder and the matrix. When subjected to frictional external forces, the silicon carbide micropowder can better disperse stress, thereby improving the wear resistance of the entire material. At the same time, titanium dioxide also helps to improve the flame retardancy of the material to a certain extent. It can participate in the reaction during material combustion, promote the formation of a carbon layer, and enhance the flame retardant effect.

[0013] Optionally, the enhanced wear-resistant filler is obtained through the following preparation steps: A1. Mix tetrabutyl titanate and an ethanol solution, then add hydrochloric acid dropwise to adjust the pH value of the solution to 2 - 3, and continue stirring for 1 - 2 hours to obtain a sol-like plating solution; A2. Add silicon carbide micropowder to the plating solution, place it on a magnetic stirrer, stir at room temperature for 4 - 6 h, then filter the mixture, take the solid and place it in a crucible, put it into a muffle furnace, heat it at a heating rate of 5 - 10 °C / min to 450 - 550 °C, and keep it at this temperature for 2 - 3 h. After cooling, the enhanced wear-resistant filler is obtained.

[0014] By adopting the above technical solution, in step A1, by mixing tetrabutyl titanate and an ethanol solution and adjusting the pH value, a sol-like plating solution is prepared. The tetrabutyl titanate in this solution will undergo hydrolysis and polycondensation reactions to form an active titanium dioxide precursor. In step A2, after adding silicon carbide micropowder to the plating solution, the titanium dioxide precursor gradually deposits on the surface of the silicon carbide micropowder and reacts to form a uniform titanium dioxide coating. After high-temperature treatment in a muffle furnace, the structure of the titanium dioxide coating is more dense and stable. The silicon carbide micropowder with a titanium dioxide coating on its surface obtained through this specific preparation method has greatly improved hardness and bonding force with the matrix, thereby effectively improving the wear resistance of the material. In terms of flame retardancy, the titanium dioxide coating participates in the combustion reaction, which helps to improve the flame retardancy efficiency of the material.

[0015] Optionally, the mass ratio of tetrabutyl titanate to the ethanol solution in step A1 is 1:(5 - 7); the mass concentration of the ethanol solution is 25 - 45%.

[0016] Optionally, the mass ratio of silicon carbide micropowder to the plating solution in step A2 is 1:(3 - 5).

[0017] By adopting the above technical solution, when the mass ratio of silicon carbide micropowder to the plating solution is 1:(3 - 5), the titanium dioxide precursor in the plating solution can fully contact the surface of the silicon carbide micropowder, forming a titanium dioxide coating with sufficient thickness and uniformity. If the ratio is inappropriate, it may lead to a too thin or uneven coating, affecting the improvement effect of the wear resistance of the silicon carbide micropowder on the material. The appropriate coating thickness and uniformity enable the silicon carbide micropowder to better withstand frictional external forces in the material, improving the wear resistance of the material. In terms of flame retardancy, a sufficient amount of titanium dioxide coating can more effectively participate in the reaction during combustion, enhancing the flame retardant performance.

[0018] Optionally, the double-layer shell structure microcapsule is obtained through the following preparation steps: B1. Disperse molybdenum disulfide nanoparticles in toluene, then add sodium dodecyl sulfate, and ultrasonically disperse for 20 - 30 min to obtain a core material dispersion liquid. Add polyester polyol and toluene diisocyanate to the core material dispersion liquid, and stir and react at 50 - 60 °C for 30 - 60 min. After the reaction ends, centrifuge to separate the inner microcapsules, and then wash the inner microcapsules. B2. Dissolve N-isopropylacrylamide in deionized water, then add N,N'-methylenebisacrylamide and ammonium persulfate, and stir for 10 - 30 min to obtain a polymer solution. Then add the inner microcapsules to the polymer solution, and stir and react at 20 - 25 °C for 3 - 6 h. After the reaction ends, centrifuge to separate the solid product, and then wash and dry the solid product to obtain the double-layer structure microcapsule.

[0019] Optionally, in step B1, the mass ratio of the molybdenum disulfide nanoparticles, toluene, and sodium dodecyl sulfate is 1:(10 - 15):(0.1 - 0.3); the mass ratio of the polyester polyol to the molybdenum disulfide nanoparticles is (2 - 3):1; the mass ratio of the toluene diisocyanate to the molybdenum disulfide nanoparticles is (1.5 - 2):1.

[0020] Optionally, in step B2, the mass ratio of the N-isopropylacrylamide, N,N'-methylenebisacrylamide, and ammonium persulfate is 10:(1 - 3):(0.5 - 1.5).

[0021] By adopting the above technical solution, N-isopropylacrylamide, as the main monomer of the outer shell layer, can control the rate and degree of the polymerization reaction with a specific mass ratio of N,N'-methylenebisacrylamide (crosslinking agent) and ammonium persulfate (initiator). At this ratio, the polymerization reaction can form a poly-N-isopropylacrylamide outer shell layer with appropriate crosslinking degree and molecular weight. The appropriate crosslinking degree endows the outer shell layer with good mechanical properties and stability, which can effectively protect the inner microcapsules and molybdenum disulfide nanoparticles. At the same time, the formed poly-N-isopropylacrylamide outer shell layer has good temperature sensitivity, and can release molybdenum disulfide nanoparticles to fill and repair the worn area when the material generates heat due to friction.

[0022] Optionally, in step B2, the mass ratio of the inner microcapsules to N-isopropylacrylamide is 1:(5 - 10).

[0023] The present application also provides a preparation method of a low-smoke and halogen-free flame retardant material, adopting the following technical solution: A preparation method of a low-smoke and halogen-free flame retardant material includes the following steps: S1. Add polyolefin, ethylene-butyl acrylate copolymer, and polyurethane into a high-speed mixer, and mix at 80 - 100 °C for 10 - 15 min; then add dicumyl peroxide, melamine polyphosphate, compatibilizer, and antioxidant into the mixer, and continue to stir and mix for 40 - 60 min to obtain a premix. S2. Add the enhanced wear-resistant filler and the double-shell structure microcapsules into the premix, and stir at a speed of 300 - 500 r / min for 20 - 30 min to obtain a mixture. S3. Transfer the mixture to a twin-screw extruder for melt blending and extrusion, and the extrudate is cooled by water and pelletized to obtain the low-smoke and halogen-free flame retardant material.

[0024] In summary, the present application has the following beneficial effects: 1. This application uses a variety of raw materials in synergistic cooperation, significantly improving the material properties. Polyolefin, ethylene-butyl acrylate copolymer, and polyurethane form the material matrix, endowing the material with basic mechanical properties. Diisopropylbenzene peroxide is used as a crosslinking agent to promote the crosslinking of polymer molecular chains, enhancing the overall strength and stability of the material, and playing a significant role in improving wear resistance. Melamine polyphosphate forms an expanded carbon layer during combustion, effectively isolating oxygen and heat, ensuring good flame retardant effect. Silicon carbide micropowder with a titanium dioxide coating is used as an enhanced wear-resistant filler. The high hardness and wear resistance of silicon carbide are the basis. The titanium dioxide coating not only improves its own wear resistance but also enhances the interfacial bonding force with the matrix, effectively resisting frictional external forces. The molybdenum disulfide nanoparticle core material in the double-shell structure microcapsule has good lubrication performance, which can reduce the friction coefficient and reduce wear. The cooperation of each raw material greatly improves the wear resistance of the material while ensuring the flame retardant performance.

[0025] 2. The double-shell structure microcapsule adopted in this application is exquisitely designed, greatly enhancing the wear resistance of the material. When not stimulated by friction, the inner polyurethane-isocyanate shell and the outer poly(N-isopropylacrylamide) (PNIPAAm) shell provide reliable protection for the molybdenum disulfide nanoparticle core material, preventing premature leakage and ensuring the effectiveness of the core material and the service life of the microcapsule. When the material is subjected to friction, the heat generated by friction raises the temperature around the microcapsule above the lower critical solution temperature of PNIPAAm. The outer shell undergoes a phase transition, and its volume shrinks. The originally hidden and low-activity carboxyl groups are exposed and their activity is enhanced, and an ester exchange reaction occurs with the isocyanate of the inner shell, destroying the inner shell structure and promoting the release of the core material to the friction surface. The released molybdenum disulfide nanoparticles fill the pits and scratches on the material surface, making the surface smoother, reducing stress concentration, and avoiding exacerbation of wear. This temperature-sensitive trigger release and self-healing cycle mechanism continuously plays a role throughout the use process of the material, effectively maintaining and enhancing the wear resistance of the material in the long term.

[0026] 3. This application ensures the full integration of each component of the material through a preparation method with specific process parameters, obtaining a low-smoke and halogen-free flame retardant material with excellent and stable performance. When preparing the enhanced wear-resistant filler, the conditions such as the ratio of tetrabutyl titanate and ethanol solution, pH value, and reaction time are strictly controlled, so that the titanium dioxide precursor is evenly deposited on the surface of silicon carbide micropowder, and a dense and stable coating is formed after high-temperature treatment, improving the performance of silicon carbide micropowder. When preparing the double-shell structure microcapsule, the raw material ratios and reaction conditions of each step are accurately controlled to ensure the reliability of the microcapsule structure and performance. During the material preparation process, the matrix materials such as polyolefin are first fully mixed in a high-speed mixer, then other additives are added and stirred evenly, then the enhanced wear-resistant filler and microcapsules are added with low-speed stirring, and finally, they are melt-blended and extruded through a twin-screw extruder. This method ensures the uniform mixing of each component of the material, enables each component to fully exert its wear-resistant and flame retardant properties, and improves the stability of the overall material performance. Detailed implementation manners

[0027] The following further elaborates on the present application in conjunction with embodiments.

[0028] In the technical solution of the present application, the polyolefin can be any one of polyethylene, polypropylene, and polybutene. Without special instructions, all raw materials used in the embodiments of the present application are obtained through ordinary commercial channels. Among them, the polyolefin used in the embodiments of the present application is the MH-L20 brand low-density polyethylene purchased from Jiangyin Ximalun Environmental Protection Technology Co., Ltd.; the ethylene-butyl acrylate copolymer is the B28N230 brand ethylene-butyl acrylate copolymer purchased from Shanghai Jiejun Plastic Technology Co., Ltd.; the polyurethane is the shp105 brand polyurethane purchased from Yantai Caihua Polyurethane Technology Co., Ltd.; the polyethylene adipate and polybutylene succinate are purchased from Shanghai Aoji Chemical Industry Co., Ltd.

[0029] Preparation examples of the enhanced wear-resistant filler Preparation example 1 The enhanced wear-resistant filler is prepared by the following method: A1. Mix 10 kg of tetrabutyl titanate with 50 kg of an ethanol solution with a mass concentration of 45%, then add hydrochloric acid dropwise to adjust the pH value of the solution to 2.5, and continue stirring for 1 hour to obtain a sol-like plating solution; A2. Add 10 kg of silicon carbide micropowder to 30 kg of the plating solution, place it on a magnetic stirrer, stir at room temperature for 4 h, then filter the mixed solution, take the solid and place it in a crucible, put it into a muffle furnace, heat it to 450 °C at a heating rate of 5 °C / min, and keep it at this temperature for 2 h. After the heat preservation is completed, cool it to obtain the enhanced wear-resistant filler.

[0030] Preparation example 2 The enhanced wear-resistant filler is prepared by the following method: A1. Mix 10 kg of tetrabutyl titanate with 60 kg of an ethanol solution with a mass concentration of 35%, then add hydrochloric acid dropwise to adjust the pH value of the solution to 2.5, and continue stirring for 1.5 hours to obtain a sol-like plating solution; A2. Add 10 kg of silicon carbide micropowder to 40 kg of the plating solution, place it on a magnetic stirrer, stir at room temperature for 5 h, then filter the mixed solution, take the solid and place it in a crucible, put it into a muffle furnace, heat it to 500 °C at a heating rate of 8 °C / min, and keep it at this temperature for 2.5 h. After the heat preservation is completed, cool it to obtain the enhanced wear-resistant filler.

[0031] Preparation example 3 The enhanced wear-resistant filler is prepared by the following method: A1. Mix 10 kg of tetrabutyl titanate with 70 kg of an ethanol solution with a mass concentration of 25%, then add hydrochloric acid dropwise to adjust the pH value of the solution to 2.5, and continue stirring for 2 hours to obtain a sol-like plating solution; A2. Add 10 kg of silicon carbide micropowder to 50 kg of the plating solution, place it on a magnetic stirrer, stir at room temperature for 6 h, then filter the mixture, take the solid and place it in a crucible, put it into a muffle furnace, heat it to 550 °C at a heating rate of 10 °C / min, and keep it at this temperature for 3 h. After the heat preservation is completed, cool it to obtain the enhanced wear-resistant filler.

[0032] Preparation example of double-layer shell structure microcapsules Preparation example 4 The double-layer shell structure microcapsules are prepared by the following method: B1. Disperse 1 kg of molybdenum disulfide nanoparticles in 10 kg of toluene, add 0.1 kg of sodium dodecyl sulfate, and ultrasonically disperse for 20 min to obtain a core material dispersion. Add 2 kg of polyethylene adipate and 1.5 kg of toluene diisocyanate to the core material dispersion, stir and react at 50 °C for 30 min. After the reaction is completed, centrifuge to separate the inner layer of microcapsules, and then wash the inner layer of microcapsules; B2. Dissolve 10 kg of N-isopropylacrylamide in 30 L of deionized water, then add 1 kg of N,N'-methylenebisacrylamide and 0.5 kg of ammonium persulfate, stir for 10 min to obtain a polymer solution. Then add 1 kg of the inner layer of microcapsules to the polymer solution, stir and react at 20 °C for 3 h. After the reaction is completed, centrifuge to separate the solid product, and then wash and dry the solid product to obtain the double-layer structure microcapsules.

[0033] Preparation example 5 The double-layer shell structure microcapsules are prepared by the following method: B1. Disperse 1 kg of molybdenum disulfide nanoparticles in 13 kg of toluene, add 0.2 kg of sodium dodecyl sulfate, and ultrasonically disperse for 25 min to obtain a core material dispersion. Add 2.5 kg of polybutylene succinate and 1.8 kg of toluene diisocyanate to the core material dispersion, stir and react at 55 °C for 45 min. After the reaction is completed, centrifuge to separate the inner layer of microcapsules, and then wash the inner layer of microcapsules; B2. Dissolve 10 kg of N-isopropylacrylamide in 30 L of deionized water, then add 2 kg of N,N'-methylenebisacrylamide and 1.0 kg of ammonium persulfate, stir for 20 min to obtain a polymer solution. Then add 1.5 kg of inner microcapsules to the polymer solution, stir and react at 22 °C for 4 h. After the reaction is completed, centrifuge to separate the solid product, and then wash and dry the solid product to obtain the double-layer structure microcapsules.

[0034] Preparation Example 6 Double-layer shell structure microcapsules are prepared by the following method: B1. Disperse 1 kg of molybdenum disulfide nanoparticles in 15 kg of toluene, then add 0.3 kg of sodium dodecyl sulfate, and ultrasonically disperse for 30 min to obtain a core material dispersion. Add 3 kg of polyethylene adipate and 2 kg of toluene diisocyanate to the core material dispersion, stir and react at 60 °C for 60 min. After the reaction is completed, centrifuge to separate the inner microcapsules, and then wash the inner microcapsules. B2. Dissolve 10 kg of N-isopropylacrylamide in 30 L of deionized water, then add 3 kg of N,N'-methylenebisacrylamide and 1.5 kg of ammonium persulfate, stir for 30 min to obtain a polymer solution. Then add 2 kg of inner microcapsules to the polymer solution, stir and react at 25 °C for 6 h. After the reaction is completed, centrifuge to separate the solid product, and then wash and dry the solid product to obtain the double-layer structure microcapsules.

[0035] Preparation Example 7 The double-layer shell structure microcapsules are different from those in Preparation Example 4 in that the B2 step is different. In this preparation example, the outer shell layer of the double-layer shell structure microcapsules is polymethyl methacrylate. Specifically, the B2 step in this preparation example is as follows: B2. Dissolve 10 kg of methyl methacrylate in 30 L of toluene, then add 1 kg of ethylene glycol dimethacrylate and 0.5 kg of azobisisobutyronitrile, stir for 20 min to obtain a polymer solution. Then add 1 kg of inner microcapsules to the polymer solution, stir and react at 60 °C for 3 h. After the reaction is completed, centrifuge to separate the solid product, and then wash and dry the solid product with toluene to obtain the double-layer structure microcapsules.

[0036] Preparation Example 8 The double-layer shell structure microcapsules are different from those in Preparation Example 4 in that in this preparation example, an equal amount of nano-graphite powder is used instead of molybdenum disulfide nanoparticles as the core material in B1.

[0037] Preparation Example 9 Single-layer shell polyurethane microcapsules are prepared by the following method: B1. Disperse 1 kg of molybdenum disulfide nanoparticles in 13 kg of toluene, then add 0.2 kg of sodium dodecyl sulfate and ultrasonically disperse for 25 min to obtain a core material dispersion. Add 2.5 kg of polybutylene succinate and 1.8 kg of toluene diisocyanate to the core material dispersion, and stir and react at 55 °C for 45 min. After the reaction, centrifuge to separate the inner microcapsules, and then wash the inner microcapsules to obtain single-layer shell polyurethane microcapsules.

[0038] Example Example 1 A low-smoke and halogen-free flame retardant material, the raw material components and dosages of which are shown in Table 1. Among them, the polyolefin is polyethylene; the enhanced wear-resistant filler is the enhanced wear-resistant filler prepared in Preparation Example 1; the double-layer shell structure microcapsule is the double-layer shell structure microcapsule prepared in Preparation Example 4; the compatibilizer is maleic anhydride grafted polyethylene; the antioxidant is the hindered phenol antioxidant 1010.

[0039] The preparation method of the low-smoke and halogen-free flame retardant material comprises the following steps: S1. Add the polyolefin, ethylene-butyl acrylate copolymer, and polyurethane to a high-speed mixer and mix at 80 °C for 15 min; then add dicumyl peroxide, melamine polyphosphate, compatibilizer, and antioxidant to the mixer and continue to stir and mix for 40 min to obtain a premix. S2. Add the enhanced wear-resistant filler and the double-layer shell structure microcapsule to the premix and stir at a speed of 300 r / min for 30 min to obtain a mixture. S3. Transfer the mixture to a twin-screw extruder for melt blending and extrusion. The barrel temperature is set at 180 °C, and the head temperature is set at 200 °C. The extrudate is cooled by water and pelletized to obtain the low-smoke and halogen-free flame retardant material.

[0040] Example 2 A low-smoke and halogen-free flame retardant material, the raw material components and dosages of which are shown in Table 1. Among them, the polyolefin is polyethylene; the enhanced wear-resistant filler is the enhanced wear-resistant filler prepared in Preparation Example 2; the double-layer shell structure microcapsule is the double-layer shell structure microcapsule prepared in Preparation Example 4; the compatibilizer is maleic anhydride grafted polyethylene; the antioxidant is the hindered phenol antioxidant 1010.

[0041] The preparation method of the low-smoke and halogen-free flame retardant material comprises the following steps: S1. Add the polyolefin, ethylene-butyl acrylate copolymer, and polyurethane to a high-speed mixer and mix at 90 °C for 13 min; then add dicumyl peroxide, melamine polyphosphate, compatibilizer, and antioxidant to the mixer and continue to stir and mix for 50 min to obtain a premix. S2. Add the enhanced wear-resistant filler and the double-layer shell structure microcapsules to the premix, and stir for 25 min at a speed of 400 r / min to obtain a mixed material. S3. Transfer the mixed material to a twin-screw extruder for melt blending and extrusion. Set the barrel temperature to 180 °C and the head temperature to 200 °C. Cool the extrudate with water and pelletize it to obtain the low-smoke and halogen-free flame retardant material.

[0042] Example 3 A low-smoke and halogen-free flame retardant material, the raw material components and dosages of which are shown in Table 1. Among them, the polyolefin is polyethylene; the enhanced wear-resistant filler is the enhanced wear-resistant filler prepared in Preparation Example 3; the double-layer shell structure microcapsules are the double-layer shell structure microcapsules prepared in Preparation Example 4; the compatibilizer is maleic anhydride grafted polyethylene; the antioxidant is the hindered phenol antioxidant 1010.

[0043] A preparation method of a low-smoke and halogen-free flame retardant material, comprising the following steps: S1. Add the polyolefin, ethylene-butyl acrylate copolymer, and polyurethane to a high-speed mixer and mix at 100 °C for 10 min; then add dicumyl peroxide, melamine polyphosphate, compatibilizer, and antioxidant to the mixer and continue to stir and mix for 60 min to obtain a premix. S2. Add the enhanced wear-resistant filler and the double-layer shell structure microcapsules to the premix, and stir for 20 min at a speed of 500 r / min to obtain a mixed material. S3. Transfer the mixed material to a twin-screw extruder for melt blending and extrusion. Set the barrel temperature to 180 °C and the head temperature to 200 °C. Cool the extrudate with water and pelletize it to obtain the low-smoke and halogen-free flame retardant material.

[0044] Table 1 Raw material components and dosages (kg) of the flame retardant materials in Examples 1-3

[0045] Example 4 A low-smoke and halogen-free flame retardant material, which is different from Example 1 in that: in this example, the double-layer shell structure microcapsules are the double-layer shell structure microcapsules prepared in Preparation Example 5.

[0046] Example 5 A low-smoke and halogen-free flame retardant material, which is different from Example 1 in that: in this example, the double-layer shell structure microcapsules are the double-layer shell structure microcapsules prepared in Preparation Example 6.

[0047] Comparative Example Comparative Example 1 A flame retardant material was prepared according to Example 1 in the patent document with the announcement number CN105924729 and the name "Flame Retardant Cable Material". Its components include low-density polyethylene resin, PVC resin, aluminum hydroxide flame retardant, coupling agent, melamine cyanurate, dimethyl disulfide, dioctyl phthalate, ultraviolet absorber, active nano calcium carbonate, paraffin, stearic acid and epoxy soybean oil.

[0048] Comparative Example 2 A low-smoke and halogen-free flame retardant material, which is different from Example 1 in that: in this comparative example, an equal amount of silicon nitride micropowder is used to replace the reinforcing and wear-resistant material.

[0049] Comparative Example 3 A low-smoke and halogen-free flame retardant material, which is different from Example 1 in that: in this comparative example, the double-layer shell structure microcapsules selected are the double-layer shell structure microcapsules prepared in Preparation Example 7.

[0050] Comparative Example 4 A low-smoke and halogen-free flame retardant material, which is different from Example 1 in that: in this comparative example, the double-layer shell structure microcapsules selected are the double-layer shell structure microcapsules prepared in Preparation Example 8.

[0051] Comparative Example 5 A low-smoke and halogen-free flame retardant material, which is different from Example 1 in that: in this comparative example, an equal amount of single-layer shell polyurethane microcapsules prepared in Preparation Example 9 is used to replace its double-layer shell structure microcapsules.

[0052] Performance Detection Test 1. Flame retardancy: The limiting oxygen index (LOI) of the flame retardant materials in Examples 1-5 and Comparative Examples 1-5 was tested in accordance with "GB / T2406.1-2008". LOI is the lowest oxygen concentration (volume percentage) required for the material to self-ignite in an oxygen-nitrogen mixed gas. The higher the LOI value, the stronger the flame retardancy of the material and the more difficult it is to be ignited. The test results are shown in Table 2.

[0053] 2. Smoke density: Tested in accordance with "GB / T8323.2-2008", using a flameless combustion mode, the radiation intensity was 25 kW / m, and the test time was 20 min. The test results are shown in Table 2.

[0054] 3. Abrasion resistance: The volume abrasion of the flame retardant materials prepared in Examples 1-5 and Comparative Examples 1-5 was tested with reference to the standard GB / T9867-2008 "Determination of Abrasion Resistance of Vulcanized Rubber or Thermoplastic Rubber (Rotating Drum Abrasion Machine Method)". The test results are shown in Table 2.

[0055] Table 2 Performance Test Results of the Flame Retardant Materials in Examples 1-5 and Comparative Examples 1-5

[0056] According to Table 2, the various indicators of Examples 1-5 of the present application remain stable, indicating that the flame retardant materials prepared in the examples of the present application have good flame retardant properties, low smoke density and excellent wear resistance. From the perspective of the limiting oxygen index (LOI), all reached more than 57%, indicating that the material is difficult to ignite in an oxygen-nitrogen mixed gas and has good flame retardancy; the smoke density (Dm) is all below 16, indicating that the material produces less smoke when burning; the volume wear is all below 26 mm³, and the wear-resistant material shows outstanding wear resistance.

[0057] Comparative Example 1 uses aluminum hydroxide flame retardant. Although its LOI reaches 57.6% and has good flame retardant properties, its volume wear is as high as 132.5mm³. Since aluminum hydroxide itself has a low hardness and limited interfacial bonding strength with the resin matrix, a large number of relatively weak interface areas are formed inside the material after a large amount of aluminum hydroxide is added. When the material is subjected to external friction force, these areas are prone to be damaged first, so the wear resistance is poor.

[0058] Comparative Example 2 uses untreated silicon nitride powder instead of reinforced wear-resistant material. Although it has a certain hardness, its wettability and interface bonding with the resin matrix are poor. From the test data, its LOI is 54.6%, the smoke density is 16.9, and the volume wear loss is 55.3mm³. Although it has certain flame retardant properties and the smoke density control is acceptable, due to the unsatisfactory bonding with the matrix, the wear resistance is significantly reduced compared with the embodiment, and the wear resistance of the material cannot be effectively improved.

[0059] The double-shell microcapsules in Comparative Example 3 use the product of Preparation Example 7 with polymethyl methacrylate as the outer shell layer. Its LOI is 53.1%, the smoke density is 16.7, and the volume wear loss is 95.6 mm³. Polymethyl methacrylate does not have the temperature sensitivity of poly-N-isopropylacrylamide, and when the material is heated by friction, it cannot accurately and effectively trigger the release of the core material. This makes it difficult for molybdenum disulfide nanoparticles to be released at the right time to play a lubricating and repairing role, resulting in a significant reduction in the wear resistance of the material, and also has a certain degree of negative impact on the flame retardant performance.

[0060] The double-shell structure microcapsules in Comparative Example 4 use the product of Preparation Example 8 with nanographite powder as the core material. Its LOI is 55.2%, smoke density is 16.4, and volume wear is 107.9 mm³. Although nanographite powder has a certain lubricity, compared with molybdenum disulfide nanoparticles, its crystal structure and interlayer force and other factors lead to poor effects in forming a continuous lubricating film, reducing friction coefficient, and reducing wear. When the material is subjected to friction, it cannot effectively fill surface defects and reduce stress concentration like molybdenum disulfide nanoparticles, so the wear resistance is obviously not as good as the flame retardant material in the embodiment.

[0061] In Comparative Example 5, the single-shell polyurethane microcapsules prepared in Preparation Example 9 in equal amounts were used to replace the double-shell structure microcapsules. Its LOI was 55.7%, the smoke density was 16.2, and the volume wear was 101.2 mm³. The single-shell structure cannot provide good protection when the material is not rubbed like the double-shell structure, and when heat is generated by friction, the outer shell lacks a temperature-sensitive trigger release mechanism. This results in the core material being difficult to release at the appropriate time, unable to repair the wear on the material surface in a timely manner, thereby significantly reducing the wear resistance of the material, and at the same time, the improvement effect on the overall performance is also inferior to that of the double-shell structure microcapsules.

[0062] This specific embodiment is only an interpretation of the present application and does not limit the present application. Those skilled in the art can make modifications to this embodiment without creative contributions according to needs after reading this specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A low-smoke halogen-free flame retardant material, characterized in that: The invention is made of the following raw materials in parts by weight: 50-60 parts of polyolefin, 40-50 parts of ethylene-butyl acrylate copolymer, 20-30 parts of polyurethane, 5-10 parts of dicumyl peroxide, 12-18 parts of melamine polyphosphate, 10-20 parts of reinforcing wear-resistant filler, 10-15 parts of double-shell structure microcapsules, 1-5 parts of compatibilizer and 1-5 parts of antioxidant; The reinforcing wear-resistant filler is silicon carbide powder with metal oxide coated on the surface; The double-shell structure microcapsule comprises a core material, an inner shell layer and an outer shell layer from inside to outside, the core material is molybdenum disulfide nanoparticles, the inner shell layer is a copolymer of polyester polyol and isocyanate, and the outer shell layer is poly-N-isopropylacrylamide.

2. The low-smoke halogen-free flame retardant material according to claim 1, characterized in that: The metal oxide plated on the surface of the reinforced wear-resistant filler is titanium dioxide.

3. The low-smoke halogen-free flame retardant material according to claim 2, characterized in that: The reinforced wear-resistant filler is obtained by the following preparation steps: A1. Mix butyl titanate and ethanol solution, then add hydrochloric acid to adjust the pH value of the solution to 2-3, and continue stirring for 1-2 hours to obtain a sol-like plating solution; A2. Add silicon carbide powder to the plating solution, place it on a magnetic stirrer, stir it at room temperature for 4-6 hours, then filter the mixed solution, take the solid and put it in a crucible, put it in a muffle furnace, heat it to 450-550℃ at a heating rate of 5-10℃ / min, and keep it at this temperature for 2-3 hours. After the insulation is completed, cool it to obtain a reinforced wear-resistant filler.

4. The low-smoke halogen-free flame retardant material according to claim 3, characterized in that: In step A1, the mass ratio of butyl titanate to the ethanol solution is 1:(5-7); the mass concentration of the ethanol solution is 25-45%.

5. The low-smoke halogen-free flame retardant material according to claim 3, characterized in that: In step A2, the mass ratio of silicon carbide powder to plating solution is 1:(3-5).

6. The low-smoke halogen-free flame retardant material according to claim 1, characterized in that: The double-shell structure microcapsules are obtained by the following preparation steps: B1. Dispersing molybdenum disulfide nanoparticles in toluene, adding sodium dodecyl sulfate, and ultrasonically dispersing for 20-30 minutes to obtain a core material dispersion, adding polyester polyol and toluene diisocyanate to the core material dispersion, stirring and reacting at 50-60° C. for 30-60 minutes, and after the reaction is completed, separating the inner layer microcapsules by centrifugation, and then washing the inner layer microcapsules; B2. Dissolve N-isopropylacrylamide in deionized water, then add N,N'-methylenebisacrylamide and ammonium persulfate, stir for 10-30 minutes to obtain a polymer solution, then add inner-layer microcapsules to the polymer solution, stir and react at 20-25°C for 3-6 hours, after the reaction is completed, separate the solid product by centrifugation, and then wash and dry the solid product to obtain double-layer structure microcapsules.

7. The low-smoke halogen-free flame retardant material according to claim 6, characterized in that: In step B1, the mass ratio of the molybdenum disulfide nanoparticles, toluene and sodium dodecyl sulfate is 1:(10-15):(0.1-0.3); the mass ratio of the polyester polyol to the molybdenum disulfide nanoparticles is (2-3):1; the mass ratio of the toluene diisocyanate to the molybdenum disulfide nanoparticles is (1.5-2):

1.

8. The low-smoke halogen-free flame retardant material according to claim 6, characterized in that: In step B2, the mass ratio of N-isopropylacrylamide, N,N'-methylenebisacrylamide and ammonium persulfate is 10:(1-3):(0.5-1.5).

9. The low-smoke halogen-free flame retardant material according to claim 6, characterized in that: In step B2, the mass ratio of the inner layer microcapsules to N-isopropylacrylamide is 1:(5-10).

10. A method for preparing a low-smoke halogen-free flame retardant material according to any one of claims 1 to 9, characterized in that: The steps include: S1. Add polyolefin, ethylene-butyl acrylate copolymer and polyurethane into a high-speed mixer and mix at 80-100° C. for 10-15 min. Then add dicumyl peroxide, melamine polyphosphate, compatibilizer and antioxidant into the mixer and continue stirring and mixing for 40-60 min to obtain a premix. S2, adding the reinforcing wear-resistant filler and the double-shell structure microcapsules to the premix, stirring at a speed of 300-500 r / min for 20-30 min to obtain a mixture; S3, transferring the mixed material to a twin-screw extruder for melt blending and extrusion, and the extrudate is water-cooled and pelletized to obtain a low-smoke halogen-free flame retardant material.

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