Method for improving cracking resistance of thermoplastic low-smoke halogen-free sheath material

Abstract

The invention discloses a method for improving the cracking resistance of a thermoplastic low-smoke halogen-free sheath material. The method comprises the following steps: S1, weighing raw materials according to a mass ratio; s2, stirring and preheating the flame retardant powder, adding long-chain silane, continuously stirring, spraying, melting long-chain fatty acid, putting into a spraying device, and starting an atomizing spraying device while stirring the powder for spraying and cooling; and S3, putting the modified flame retardant powder and other raw materials into an internal mixer for internal mixing, then performing double-cone feeding double-screw mixing, then performing extrusion pelletizing, and performing hot air drying and cooling through a boiling bin to obtain particles. Long-chain silane and long-chain fatty acid are adopted to modify flame retardant powder, a thermal expansion transition layer is constructed, a high-melting-point polypropylene-based elastomer is prepared by selecting a special polymerization process, the heat resistance of the thermoplastic low-smoke halogen-free material is improved, and the good elongation at break is ensured when the filling amount is high, so that the anti-cracking performance is improved, and the service life of the thermoplastic low-smoke halogen-free material is prolonged. And the anti-cracking thermoplastic low-smoke halogen-free sheath material is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of cable materials, and in particular to a method for improving the anti-cracking performance of a thermoplastic low-smoke halogen-free sheath material. Background Art

[0002] Traditional thermoplastic low-smoke, halogen-free sheathing materials are primarily based on polyolefins (EVA, POE, PE) with metal hydroxide flame retardants (aluminum hydroxide, magnesium hydroxide). Especially for low-smoke, halogen-free sheathing materials with high flame retardancy requirements, very high levels of metal hydroxide flame retardants are used to enhance the material's flame retardancy. Due to the poor compatibility between metal hydroxides and resins, adding large amounts can easily degrade the material's mechanical properties, particularly its elongation at break. Improving elongation at break is typically achieved by increasing the amount of polyolefin elastomer. This presents a new problem. Polyolefin elastomers generally have a low melting point (40-70°C). During cable use, the combined heat generated by the cable itself and the ambient temperature can cause the sheath temperature to exceed the elastomer's melting point, causing the material to soften and resulting in a sharp drop in mechanical properties. This softened material is susceptible to microcracks when subjected to external forces, which, over time, can lead to cracking.

[0003] Due to the irradiation of electron beams, the irradiated low-smoke halogen-free sheath material forms a three-dimensional network structure of polymer macromolecular chains, which is dimensionally stable and has significantly improved heat resistance. At the same time, the yield stress of the material is also increased, so there is almost no cracking problem. At present, the main methods to improve the cracking resistance of thermoplastic low-smoke halogen-free materials are: (1) increasing the amount of compatibilizer to improve the interface bonding between filler and resin and reduce stress concentration; (2) increasing the amount of high molecular weight and high melting point polyethylene resin to improve the overall heat resistance of the material, thereby improving the cracking resistance; (3) using the silane cross-linking process to achieve micro-cross-linking of thermoplastic low-smoke halogen-free cable materials to improve physical and mechanical properties, heat resistance and cracking resistance. The compatibilizer added in method (1) improves the interfacial interaction between incompatible components, forms chemical bonds through the reaction of anhydride groups with the hydroxyl groups on the surface of aluminum hydroxide or magnesium hydroxide, improves the interfacial bonding between powder and resin, and thus reduces the risk of cracking. To a certain extent, this method is helpful in improving the overall crack resistance of the material, but it cannot solve the cracking caused by the sudden drop in performance at high temperatures due to the low heat resistance of the matrix, and the cracking caused by the internal stress generated by the different expansion coefficients between the flame retardant and the resin at high temperatures. Method (2) improves the heat resistance of the sheath material to a certain extent by increasing the amount of high molecular weight and high melting point polyethylene in the matrix. However, the crystallinity of this type of polyethylene is relatively high, and the reduction in the proportion of elastomer substrate in the system will inevitably lead to a significant decrease in the elongation at break. In addition, inorganic powders have poor compatibility with non-polar resin polyethylene. An increase in the proportion of polyethylene is more likely to lead to a significant decrease in the mechanical properties of the material and cracking. Method (3), namely, Chinese patent document CN103030917A discloses a crack-resistant thermoplastic low-smoke halogen-free flame-retardant polyolefin cable material, comprising the following components and weight parts: a) base resin: 100; wherein: ethylene-vinyl acetate copolymer: 25-65; metallocene linear low-density polyethylene: 10-40; interfacial compatibilizer: 10-35; b) flame retardant: 160; wherein: aluminum hydroxide: 60-120; magnesium hydroxide: 40-100; c) lubricant: 0-2; d) antioxidant: 0.5-2.5; e) silane coupling agent: 0.05-0.15; f) initiator: 0.01-0.03; g) catalyst: 0.01-0.03; the vinyl acetate content in the ethylene-vinyl acetate copolymer is greater than or equal to 26%. This technical solution introduces DCP and reactive silanes, employing micro-crosslinking technology that can improve the material's crack resistance to a certain extent. However, unlike the extremely low water content of silane-crosslinked polyethylene materials A and B, low-smoke, halogen-free materials contain large amounts of aluminum hydroxide and magnesium hydroxide. The flame retardants contain a high amount of free water, and their own crystal water may be released during processing. This can easily cause localized pre-crosslinking of the material, leading to extrusion surface problems. This partially pre-crosslinked material cannot be plasticized and evenly dispersed with other substrates during extrusion, acting like an impurity, which can easily cause defects and lead to cracking.At the same time, the two-step method’s material production and downstream use are cumbersome and the manufacturing cost is also high.

[0004] Chinese patent document CN109957167A discloses a crack-resistant thermoplastic low-smoke, halogen-free, flame-retardant injection molding compound, its preparation method, and uses, belonging to the field of cable materials. The crack-resistant thermoplastic low-smoke, halogen-free, flame-retardant injection molding compound comprises the following raw materials and parts by weight: 25-40 parts base resin; 0-15 parts compatibilizer; 10-50 parts flame retardant; 0.4-1.2 parts antioxidant; 0.5-1.8 parts lubricant; and 1-3 parts carbon black masterbatch. This technical solution uses conventional methods and does not contain a high-melting-point elastomer. Instead, the powder modification involves a short-chain vinyl silane, which does not improve crack resistance at high temperatures.

[0005] Chinese patent document CN 114456580 A discloses a low-smoke, halogen-free thermoplastic elastomer fire-resistant cable material and production process. The material comprises the following raw materials by weight: 100-150 parts thermoplastic elastomer, 20-35 parts ammonium polyphosphate, 15-25 parts metal oxide smoke suppressant, 10-20 parts carrageenan, 0.5-1.5 parts stearic acid, 0.2-2.5 parts antioxidant, and 0.2-2.5 parts lubricant. The thermoplastic elastomer used in this technical solution uses a TPE flame retardant system based on organic polyphosphates, and the amount of flame retardant filler is relatively low, thus failing to achieve a satisfactory effect.

[0006] Chinese patent document CN116102817A discloses a highly transparent, halogen-free, flame-retardant polyolefin sheathing material and its preparation method. The sheathing material comprises the following raw material components by weight: 9-14 parts polyethylene resin, 20-25 parts ethylene-vinyl acetate copolymer, 10-15 parts ethylene-octene copolymer, 5-10 parts compatibilizer, 1-2 parts carbon black masterbatch, 90-100 parts flame retardant, 3-5 parts smoke suppressant, 3-8 parts shell-forming agent, 0.3-0.7 parts antioxidant, 2-3 parts lubricant, and 0.5-2 parts organopolysiloxane coupling agent. The base elastomer used in this technical solution has a low melting point and does not describe modification of the main flame retardants, aluminum hydroxide and magnesium hydroxide. While long-chain silane-modified powders are used, this is only targeted at difficult-to-disperse powders with a small addition amount. The purpose is to improve the dispersion of such nanopowders, thereby enhancing combustion transmittance, rather than improving cracking resistance at high temperatures.

[0007] Therefore, it is necessary to propose a method for improving the anti-cracking performance of thermoplastic low-smoke halogen-free sheath materials to solve the anti-cracking problem of thermoplastic low-smoke halogen-free sheath materials at high temperatures. Summary of the Invention

[0008] In order to solve the above technical problems, the technical solution of the present invention is: a method for improving the anti-cracking performance of the thermoplastic low-smoke halogen-free sheath material, using long-chain silane and long-chain fatty acid to modify the flame retardant powder, constructing a stable thermal expansion transition layer, improving the anti-cracking performance at high temperature, and obtaining a heat-resistant and crack-resistant thermoplastic low-smoke halogen-free sheath material.

[0009] Research and analysis of the cracking problem of thermoplastic low-smoke halogen-free materials revealed that the main influencing factors on the material side include internal stress at the interface caused by the difference in thermal expansion coefficients between the inorganic flame retardant powder and the resin at high temperatures, the poor heat resistance of the resin matrix, and the self-heating of the cable during use combined with the ambient temperature exceeding the melting point of the elastomer, causing the material to soften, resulting in a sudden drop in mechanical properties. Under external forces, it is prone to yielding, causing microcracks, and ultimately cracking. Therefore, the above technical solution is adopted to modify the flame retardant powder with long-chain silanes and saturated long-chain fatty acids to improve the compatibility of the powder with the resin matrix, while also constructing a stable thermal expansion transition layer. This solves the cracking problem caused by internal stress at the interface caused by the difference in thermal expansion coefficients between the inorganic flame retardant powder and the resin at high temperatures.

[0010] Preferably, the long-chain silane is hexadecyltrimethoxysilane; the long-chain fatty acid is stearic acid. The mass percentage of the modifier stearic acid used is 0.8-1.5%, and the mass percentage of the long-chain silane hexadecyltrimethoxysilane used is 0.6-1.5%. Using the above technical solution, the selected hexadecyltrimethoxysilane has a flash point of 170°C / 0.1KPa and can adapt to high temperatures. At the same time, during the spraying process, the long-chain silane chemically reacts with the flame retardant powder and is grafted onto the flame retardant powder. Due to its long-chain structure, it forms a thermal expansion transition layer, reducing the interfacial stress caused by the thermal expansion difference between the inorganic flame retardant powder and the resin at high temperatures, thereby improving the crack resistance of the thermoplastic low-smoke halogen-free sheathing material. Stearic acid primarily coats the flame retardant powder. As an organic compound, stearic acid, a long 16C chain, promotes bonding between the matrix and the flame retardant powder, further reducing interfacial stress caused by the thermal expansion difference between the inorganic flame retardant powder and the resin at high temperatures. It also improves material extrusion processing.

[0011] Preferably, the specific steps of the improvement method are: S1 weighing raw materials: weigh the raw materials according to the mass ratio and set aside; S2 modified flame retardant powder: stir and preheat the flame retardant powder, add long-chain silane, continue to stir the powder, and start the atomizing spray device for spraying. After the reaction is completed, melt the long-chain fatty acid and place it in the spray device. Stir the powder while starting the atomizing spray device for spraying. After cooling, the modified flame retardant powder is obtained; S3 granulation and molding: The modified flame retardant powder obtained in step S2 and other raw materials are placed in an internal mixer for internal mixing. After the internal mixing is completed, they are fed through a double cone, mixed through a twin screw, and then extruded and pelletized through a single screw. Finally, they are dried and cooled by hot air in a boiling bin to obtain material particles, namely thermoplastic low-smoke halogen-free sheathing materials, which improve the anti-cracking performance. The long-chain silane is grafted with the flame retardant powder by spray atomization. A chemical reaction occurs during the grafting process, and a thermal expansion transition layer is constructed between the inorganic flame retardant powder and the resin, reducing the interfacial stress caused by the thermal expansion difference between the inorganic flame retardant powder and the resin at high temperature; the long-chain fatty acid is coated on the flame retardant powder by spray atomization. This method can be more evenly dispersed in the powder and more efficiently react and coat the flame retardant powder.

[0012] Preferably, the formula of the raw materials in step S1 is as follows by mass ratio: EVA 40~50 parts; 15-30 parts of polypropylene-based elastomer; 20-30 parts of polyethylene; 8~10 parts of compatibilizer; 200~240 parts of flame retardant; 5-15 parts of synergist; 1.5-2 parts of long-chain fatty acids; 1.5-2 parts of long-chain silane; 3~6 parts of lubricant; 1~2 parts of antioxidant; 2~5 parts of masterbatch.

[0013] Preferably, the EVA is a blend of one or more EVAs with a melt flow rate (MFR) of 0.3-6.0 g / 10 min (standard melt flow rate test conditions are 190°C / 2.16 kg) and a VA content of 28-40%. A preferred blend is EVA (6110MC, BASF-Yangzi) and EVA (40L-03, Dow). 6110MC inherently possesses a certain degree of flexibility, while 40L-03, due to its high VA content, offers enhanced flexibility and elasticity. A blend of the two further enhances the flexibility and elasticity of the finished product. Furthermore, 6110MC has a higher melt index and excellent processing fluidity, while 40L-03, despite its lower melt index, offers excellent shape stability during extrusion and blow molding. A blend of the two achieves a balance between processing fluidity and shape retention, ensuring both easy flow and shape retention during processing, improving production efficiency and product quality. The blend is suitable for a variety of processing techniques, such as injection molding and extrusion.

[0014] Preferably, the polypropylene-based elastomer is a LyondellBasell polypropylene-based elastomer with a melt flow rate of 0.5-2.1 g / 10 min (the standard conditions in the melt flow rate test are 230°C / 2.16 kg), a glass transition temperature ≤~40°C, and a melting point ≥140°C.

[0015] The above technical solution, using LyondellBasell's polypropylene-based elastomer, achieves smaller island sizes and more evenly dispersed islands. Produced using a specialized polymerization process, LyondellBasell's polypropylene-based elastomer exhibits an island-in-the-sea structure. Unlike conventional elastomers, this structure features smaller and more evenly distributed islands. This high-melting-point polypropylene-based elastomer, produced using this specialized polymerization process, replaces traditional polyolefin elastomers (POE) to enhance the heat resistance of thermoplastic low-smoke, halogen-free materials while maintaining good elongation at break even under high filler conditions. Compared to the pronounced island-in-the-sea structure of conventional elastomers, this polypropylene-based elastomer features smaller and more evenly distributed islands, reducing thermal expansion of the rubber phase and further minimizing the differential thermal expansion between the base resin and the inorganic flame retardant at high temperatures. Polypropylene-based elastomers also possess a higher yield stress than conventional polyethylene-based POE, enhancing the sheathing material's resistance to yield deformation under external forces.

[0016] Preferably, the polyethylene is metallocene linear low-density polyethylene (LLDPE), and the compatibilizer is a metallocene linear low-density polyethylene grafted maleic anhydride polymer (PE-g-MAH). The melt index of the metallocene is 1.0-3.5 g / 10 min (standard melt index test conditions are 190°C / 2.16 kg), and the maleic anhydride grafting rate is 0.6%-1.2%. Using a metallocene linear low-density polyethylene grafted maleic anhydride polymer further mitigates high-temperature stress and maintains the mechanical properties of the thermoplastic low-smoke, halogen-free sheathing material at high temperatures.

[0017] Preferably, the antioxidant is a mixture of pentaerythritol (1010) and dilauryl thiodipropionate (DLTP), with a mass ratio of 1:1 or 1:2; the flame retardant is modified aluminum hydroxide, modified magnesium hydroxide, or a mixture of modified aluminum hydroxide and modified magnesium hydroxide, with a particle size D50 of 0.8 to 1.5 μm; the synergist is either organic montmorillonite or sepiolite; and the masterbatch is a carbon black masterbatch. Synergists are substances that can significantly enhance the effects of the main additive through synergistic effects. Their core function is to enhance the performance of the main additive through physical or chemical mechanisms, reduce the main additive dosage, or expand the material's comprehensive properties (such as flame retardancy, mechanical strength, and weather resistance).

[0018] Preferably, the specific steps of step S2 are: placing the flame retardant powder in a stirring device and stirring and preheating it to 80~90°C. After reaching the preheating temperature, first placing the long-chain silane in a spray device, continuing to stir the powder, and turning on the atomizing spray device at the same time. The spraying time is 8~12min, the stirrer speed is 500~800rpm, and the stirring time is 20~30min. Then, the long-chain fatty acid is melted and placed in the spray device. While stirring the powder, the atomizing spray device is turned on at the same time. The spraying time is 8~12min, the stirrer speed is 500~800rpm, and the stirring time is 20~30min. After cooling, the modified flame retardant powder is obtained.

[0019] Preferably, the specific steps of step S3 are: placing the modified flame retardant powder and all other raw materials in a banbury mixer, the banburying temperature is 165°C, the banburying time is 15 min, and the discharge temperature is controlled at 160~170°C; after the banburying is completed, the temperature of the double-cone feeding is 100°C; then using a twin-screw mixing, the temperatures of each zone during mixing are 95°C, 95°C, 100°C, 105°C, 105°C, 110°C, and 110°C, and the average speed of the twin screw is 200rpm; then single-screw extrusion and pelletizing, the temperatures of each zone during extrusion are 100°C, 110°C, 130°C, 135°C, and 135°C, and the screw speed is 120rpm; finally, the material particles are obtained after hot air drying and cooling in a boiling bin, and the particle thickness is controlled at 2~4mm.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) The improvement method is simple to implement. It does not require a complicated multi-step material preparation process, packaging, and A / B material mixed extrusion. The cable material can be directly prepared by the traditional mixing and two-stage granulation process, and the downstream can be directly extruded. (2) This improvement method solves the product quality risks caused by the traditional micro-crosslinking process in improving the crack resistance of the sheath material, and the appearance and quality problems caused by poor local pre-crosslinking plasticization; (3) Using a composite modified flame retardant of long-chain saturated fatty acids and long-chain alkane silane to construct a stable thermal expansion transition layer between the resin and the powder, the long-chain alkyl and long-chain fatty acids improve the filler dispersion, while buffering the stress caused by the thermal expansion difference, solving the cracking problem caused by the internal stress at the interface caused by the difference in thermal expansion coefficient between the inorganic flame retardant powder and the resin at high temperature; (4) Introducing a polypropylene-based elastomer with a small-sized, highly dispersed island structure prepared by a special polymerization process to replace the traditional polyolefin elastomer POE. Compared with the significant island-island structure of traditional elastomers, the polypropylene-based elastomer has smaller islands, more uniform distribution, and excellent heat resistance, thereby solving the problem of low elongation at break of the sheath material caused by the traditional method of increasing the amount of high-melting-point polyethylene to improve the low-smoke, halogen-free heat resistance; at the same time, it reduces the thermal expansion of the rubber phase, further reducing the difference in thermal expansion between the base resin and the inorganic flame retardant under high temperature conditions; (5) The thermoplastic low-smoke halogen-free sheath material prepared by this method has a higher yield strength, which improves the material's anti-yield performance. At the same time, the smaller thermal expansion coefficient reduces the interfacial force caused by the large difference in thermal expansion between the resin and the inorganic powder; the synergistic effect with long-chain fatty acids and long-chain silanes further improves the thermoplastic low-smoke halogen-free sheath material's anti-cracking performance at high temperatures. DETAILED DESCRIPTION

[0021] Example: This method for improving the crack resistance of a thermoplastic low-smoke, halogen-free sheathing material uses long-chain silane and long-chain fatty acid to modify a flame retardant powder. This creates a stable thermal expansion transition layer between the inorganic flame retardant powder and the resin, improving crack resistance at high temperatures and resulting in a heat-resistant, crack-resistant thermoplastic low-smoke, halogen-free sheathing material. The long-chain silane is hexadecyltrimethoxysilane, and the long-chain fatty acid is stearic acid. The stearic acid modifier is used in an amount of 0.8-1.5%, and the silane modifier is used in an amount of 0.6-1.5%.

[0022] The specific steps of this improvement method are: S1 weighing raw materials: weigh the raw materials according to the mass ratio and set aside; The formula of the raw materials in step S1 is as follows by mass ratio: EVA 40~50 parts; 15-30 parts of polypropylene-based elastomer; 20-30 parts of polyethylene; Compatibilizer 8~10 parts; 200~240 parts of flame retardant; 5-15 parts of synergist; 1.5-2 parts of long-chain fatty acids; 1.5-2 parts of long-chain silane; 3~6 parts of lubricant; 1~2 parts of antioxidant; 2~5 parts of masterbatch.

[0023] The EVA is a mixture of one or more EVAs having a melt flow rate of 0.3-6.0 g / 10 min (190°C / 2.16kg) and a VA content of 28-40%. Preferably, the mixture is EVA (6110MC, BASF-Yangzi) and EVA (40L-03, Dow). The polypropylene-based elastomer is a LyondellBasell polypropylene-based elastomer having a melt flow rate of 0.5-2.1 g / 10 min (230°C / 2.16 kg), a glass transition temperature ≤~40°C, and a melting point ≥140°C. The polyethylene is metallocene linear low-density polyethylene (LLDPE), and the compatibilizer is a metallocene linear low-density polyethylene grafted maleic anhydride polymer (PE-g-MAH). The melt index of the metallocene is 1.0-3.5 g / 10 min (190°C / 2.16 kg), and the maleic anhydride grafting rate is 0.6%-1.2%. The use of a metallocene linear low-density polyethylene grafted maleic anhydride polymer further mitigates high-temperature stress and maintains the mechanical properties of the thermoplastic low-smoke, halogen-free sheathing material at high temperatures.

[0024] The antioxidant is a mixture of pentaerythritol (1010) and dilauryl thiodipropionate (DLTP), with a mass ratio of 1:1 or 1:2; the flame retardant is modified aluminum hydroxide or modified magnesium hydroxide or a mixture of modified aluminum hydroxide and modified magnesium hydroxide, with a particle size D50 of 0.8-1.5 μm; the synergist is any one of organic montmorillonite and sepiolite; and the masterbatch is carbon black masterbatch; S2 modified flame retardant powder: add long-chain silane, continue to stir the powder, and turn on the atomizing spray device for spraying. After the reaction is completed, melt the long-chain fatty acid and place it in the spray device. Stir the powder while turning on the atomizing spray device for spraying. After cooling, the modified flame retardant powder is obtained; The specific steps of step S2 are: placing the flame retardant powder in a stirring device and stirring and preheating it to 80-90° C. After reaching the preheating temperature, first placing the long-chain silane in a spray device, continuing to stir the powder, and simultaneously turning on the atomizing spray device, the spraying time is 8-12 minutes, the stirrer speed is 500-800 rpm, and the stirring time is 20-30 minutes, then melting the long-chain fatty acid, placing it in the spray device, stirring the powder while turning on the atomizing spray device, the spraying time is 8-12 minutes, the stirrer speed is 500-800 rpm, and the stirring time is 20-30 minutes, and after cooling, the modified flame retardant powder is obtained; S3 granulation molding: The modified flame retardant powder obtained in step S2 and other raw materials are placed in an internal mixer for internal mixing. After the internal mixing is completed, it is fed through a double cone, mixed through a twin screw, and then extruded and pelletized through a single screw. Finally, it is dried and cooled by hot air in a boiling bin to obtain material particles, namely thermoplastic low-smoke halogen-free sheath material, which improves the anti-cracking performance; The specific steps of step S3 are: placing the modified flame retardant powder and all other raw materials in an internal mixer, with a mixing temperature of 165°C, a mixing time of 15 minutes, and a discharge temperature controlled at 160-170°C; after the internal mixing is completed, the temperature of the double-cone feeding is 100°C; then using a twin-screw extruder for mixing, with the temperatures of each zone being 95°C, 95°C, 100°C, 105°C, 105°C, 110°C, and 110°C in sequence during mixing, and the average speed of the twin-screw extruder is 200rpm; then using a single-screw extruder for pelletizing, with the temperatures of each zone being 100°C, 110°C, 130°C, 135°C, and 135°C in sequence during extrusion, and the speed of the screw being 120rpm; finally, drying and cooling the material particles through hot air in a boiling bin, and the particle thickness is controlled at 2-4mm.

[0025] Specific embodiment 1: The specific steps of the lifting method are: S1 weighing raw materials: weigh the raw materials according to the mass ratio and set aside; The formula of the raw materials in step S1 is as follows by mass ratio: EVA (6110MC, BASF-YPC) 25 parts; EVA (40L~03, Dow) 20 parts; PE~g~MAH (TRD~200LM, Sridhar) 10 parts; Polyethylene (FB2230, Borouge) 25 parts; Polypropylene-based elastomer (CA 12A, LyondellBasell) 20 parts; Flame retardant (magnesium hydroxide MDH) 220 parts; Synergist (organically modified montmorillonite I.44P, Nanocor) 5 parts; 2 parts of stearic acid (1842, Lumen Chemical); Silane (9116, Evonik) 2 parts; Lubricant (HMB~0221, DuPont) 4 parts; Antioxidant (1010 / 168 1:1, Lionon) 1.5 parts; Carbon black masterbatch (6269, Cabot) 5 parts; The flame retardant is magnesium hydroxide with a particle size D50 of 0.8-1.5 μm; S2 modified flame retardant powder: The flame retardant powder is stirred and preheated, and after the long-chain fatty acid is melted, it is placed in a spray device, and the powder is stirred while the atomizing spray device is turned on for spraying; then the long-chain silane is added, and the powder is continued to be stirred while the atomizing spray device is turned on for spraying, and the modified flame retardant powder is obtained after cooling; The specific steps of step S2 are: placing the flame retardant powder in a stirring device and stirring and preheating it to 80-90° C. After the preheating temperature reaches the desired level, first placing the long-chain silane in a spray device, continuing to stir the powder, and simultaneously turning on the atomizing spray device, with a spraying time of 10 minutes, a stirrer speed of 700 rpm, and a stirring time of 25 minutes; then melting the long-chain fatty acid, placing it in the spray device, stirring the powder while turning on the atomizing spray device, with a spraying time of 10 minutes, a stirrer speed of 700 rpm, and a stirring time of 25 minutes; and obtaining the modified flame retardant powder after cooling; S3 granulation and molding: the modified flame retardant powder obtained in step S2 and other raw materials are placed in an internal mixer for internal mixing. After the internal mixing is completed, it is fed through a double cone, mixed through a twin screw, and then extruded and pelletized through a single screw. Finally, the material particles are obtained after hot air drying and cooling in a boiling bin; The specific steps of step S3 are: placing the modified flame retardant powder and all other raw materials in an internal mixer, with a mixing temperature of 165°C, a mixing time of 15 minutes, and a discharge temperature controlled at 160-170°C; after the internal mixing is completed, the temperature of the double-cone feeding is 100°C; then using a twin-screw extruder for mixing, with the temperatures of each zone being 95°C, 95°C, 100°C, 105°C, 105°C, 110°C, and 110°C in sequence during mixing, and the average speed of the twin-screw extruder is 200rpm; then using a single-screw extruder for pelletizing, with the temperatures of each zone being 100°C, 110°C, 130°C, 135°C, and 135°C in sequence during extrusion, and the speed of the screw being 120rpm; finally, drying and cooling the material particles through hot air in a boiling bin, and the particle thickness is controlled at 2-4mm.

[0026] Specific embodiment 2: The difference from specific embodiment 1 is that the formula of the raw materials in step S1 is based on the mass ratio; specifically: EVA (6110MC, BASF-YPC) 25 parts; EVA (40L~03, Dow) 20 parts; PE~g~MAH (TRD~200LM, Sridhar) 10 parts; Polyethylene (FB2230, Borouge) 20 parts; Polypropylene-based elastomer (CA 12A, LyondellBasell) 25 parts; Flame retardant (aluminum hydroxide ATH) 220 parts; 5 parts of synergist (I.44P, Nanocor) organically modified montmorillonite; 2 parts of stearic acid (1842, Lumen Chemical); Silane (9116, Evonik) 2 parts; Lubricant (HMB~0221, DuPont) 4 parts; Antioxidant (1010 / 168 1:1, Lionon) 1.5 parts; Carbon black masterbatch (6269, Cabot) 5 parts; Specific embodiment 3: The difference from specific embodiment 1 is that the formula of the raw materials in step S1 is based on the mass ratio; specifically: EVA (6110MC, BASF-YPC) 25 parts; EVA (40L~03, Dow) 20 parts; PE~g~MAH (TRD~200LM, Sridhar) 10 parts; Polyethylene (FB2230, Borouge) 25 parts; Polypropylene-based elastomer (CA 7700A, LyondellBasell) 20 parts; Flame retardant (MDH) 220 parts; Synergist (organically modified special silicate additive Clay20, TOLSA) 5 parts; 2 parts of stearic acid (1842, Lumen Chemical); Silane (9116, Evonik) 2 parts; Lubricant (HMB~0221, DuPont) 4 parts; Antioxidant (1010 / 168 1:1, Lionon) 1.5 parts; Carbon black masterbatch (6269, Cabot) 5 parts.

[0027] Specific embodiment 4: The difference from specific embodiment 1 is that the formula of the raw materials in step S1 is based on the mass ratio; specifically: EVA (6110MC, BASF-YPC) 20 parts; EVA (40L~03, Dow) 20 parts; PE~g~MAH (TRD~200LM, Sridhar) 10 parts; Polyethylene (FB2230, Borouge) 25 parts; Polypropylene-based elastomer (CA 7700A, LyondellBasell) 25 parts; Flame retardant (MDH) 220 parts; Synergist (Clay20, TOLSA) 5 parts; Stearic acid (1842, Lumen Chemical) 1.5 parts; Silane (9116, Evonik) 1.5 parts; Lubricant (HMB~0221, DuPont) 4 parts; Antioxidant (1010 / 168 1:1, Lionon) 1.5 parts; Carbon black masterbatch (6269, Cabot) 5 parts.

[0028] Specific embodiment 5: The difference from specific embodiment 1 is that the formula of the raw materials in step S1 is based on the mass ratio; specifically: EVA (6110MC, BASF-YPC) 25 parts; EVA (40L~03, Dow) 20 parts; PE~g~MAH (TRD~200LM, Sridhar) 10 parts; Polyethylene (FB2230, Borouge) 20 parts; Polypropylene-based elastomer (CA 7700A, LyondellBasell) 25 parts; Flame retardant (MDH) 220 parts; Synergist (Clay20, TOLSA) 5 parts; 2 parts of stearic acid (1842, Lumen Chemical); Silane (9116, Evonik) 2 parts; Lubricant (HMB~0221, DuPont) 4 parts; Antioxidant (1010 / 168 1:1, Lionon) 1.5 parts; Carbon black masterbatch (6269, Cabot) 5 parts.

[0029] Comparative Example 1: The difference from Specific Example 1 is that a common elastomer (8200, Dow) is used, and the flame retardant is not modified with stearic acid, but short-chain silane is used. The formula of the raw materials in step S1 is as follows in terms of mass fraction: EVA (6110MC, BASF-YPC) 25 parts; EVA (40L~03, Dow) 20 parts; PE~g~MAH (TRD~200LM, Sridhar) 10 parts; Polyethylene (FB2230, Borouge) 25 parts; Elastomer (8200, Dow) 20 parts; Flame retardant (MDH) 220 parts; Synergist (I.44P, Nanocor) 5 parts; Silane (A172, Evonik) 2 parts; Lubricant (HMB~0221, DuPont) 4 parts; Antioxidant (1010 / 168 1:1, Lionon) 1.5 parts; Carbon black masterbatch (6269, Cabot) 5 parts.

[0030] Comparative Example 2: The difference from Comparative Example 1 is that a common elastomer (8200, Dow) is used, and the flame retardant is not modified with silane but only with stearic acid. The formula of the raw materials in step S1 is as follows by mass ratio: EVA (6110MC, BASF-YPC) 25 parts; EVA (40L~03, Dow) 20 parts; PE~g~MAH (TRD~200LM, Sridhar) 10 parts; Polyethylene (FB2230, Borouge) 25 parts; Elastomer (8200, Dow) 20 parts; Flame retardant (MDH) 220 parts; Synergist (I.44P, Nanocor) 5 parts; 2 parts of stearic acid (1842, Lumen Chemical); Lubricant (HMB~0221, DuPont) 4 parts; Antioxidant (1010 / 168 1:1, Lionon) 1.5 parts; Carbon black masterbatch (6269, Cabot) 5 parts.

[0031] Comparative Example 3: The difference from Comparative Example 1 is that a common elastomer (8200, Dow) is used, and the flame retardant is modified with long-chain silane and stearic acid. The formula of the raw materials in step S1 is as follows in terms of mass fraction: EVA (6110MC, BASF-YPC) 25 parts; EVA (40L~03, Dow) 20 parts; PE~g~MAH (TRD~200LM, Sridhar) 10 parts; Polyethylene (FB2230, Borouge) 20 parts; Polypropylene-based elastomer (CA 7700A, LyondellBasell) 25 parts; Flame retardant (MDH) 220 parts; Synergist (I.44P, Nanocor) 5 parts; Silane (9116, Evonik) 2 parts; 2 parts of stearic acid (1842, Lumen Chemical); Lubricant (HMB~0221, DuPont) 4 parts; Antioxidant (1010 / 168 1:1, Lionon) 1.5 parts; Carbon black masterbatch (6269, Cabot) 5 parts.

[0032] Comparative Example 4: The difference from Comparative Example 1 is that a polypropylene-based elastomer (CA 7700A, LyondellBasell) is used, and the flame retardant is not modified with stearic acid but only with short-chain silane. The formula of the raw materials in step S1 is as follows by mass ratio: EVA (6110MC, BASF-YPC) 25 parts; EVA (40L~03, Dow) 20 parts; PE~g~MAH (TRD~200LM, Sridhar) 10 parts; Polyethylene (FB2230, Borouge) 20 parts; Polypropylene-based elastomer (CA 7700A, LyondellBasell) 25 parts; Flame retardant (MDH) 220 parts; Synergist (I.44P, Nanocor) 5 parts; Silane (9116, Evonik) 2 parts; Lubricant (HMB~0221, DuPont) 4 parts; Antioxidant (1010 / 168 1:1, Lionon) 1.5 parts; Carbon black masterbatch (6269, Cabot) 5 parts.

[0033] Comparative Example 5: The difference from Comparative Example 1 is that a polypropylene-based elastomer (CA 7700A, LyondellBasell) is used, and the flame retardant is modified only with stearic acid, without modification with long-chain silane. The formula of the raw materials in step S1 is as follows by mass ratio: EVA (6110MC, BASF-YPC) 25 parts; EVA (40L~03, Dow) 20 parts; PE~g~MAH (TRD~200LM, Sridhar) 10 parts; Polyethylene (FB2230, Borouge) 20 parts; Polypropylene-based elastomer (CA 7700A, LyondellBasell) 25 parts; Flame retardant (MDH) 220 parts; Synergist (I.44P, Nanocor) 5 parts; 2 parts of stearic acid (1842, Lumen Chemical); Lubricant (HMB~0221, DuPont) 4 parts; Antioxidant (1010 / 168 1:1, Lionon) 1.5 parts; Carbon black masterbatch (6269, Cabot) 5 parts.

[0034] The performance of the thermoplastic low-smoke halogen-free sheath materials obtained in the above-mentioned specific examples 1 to 5 and comparative examples 1 to 5 was tested, and the test results are shown in Table 1.

[0035] Table 1 Comparative test results of the performance of thermoplastic low-smoke halogen-free sheath materials obtained in specific examples 1 to 5 and comparative examples 1 to 5 The specific test method of the high and low temperature cycle anti-cracking test in the anti-cracking performance test is as follows: Cut the specimens according to the dimensions specified in Appendix A of GB / T 32129-2015 and coil them according to the coiling method, using a 7.5 kg load. Bolt the ends as required and place the specimens in a high-low temperature cycle chamber. Precool the specimens to ~25°C. Allow the coiled specimens to rest for 4 hours. Remove the specimens and transfer them to a high-temperature chamber. Preheat the specimens to 90°C and allow them to rest for 4 hours. Remove the specimens and cool them to room temperature. This is a single high-low temperature cycle cracking test, conducted five times in total. After removal, inspect the coiled specimens for cracks or breaks.

[0036] The high-temperature mechanical properties test method is as follows: Prepare a Type 5 dumbbell plate according to GB / T 1040.1-2018. After measuring its thickness, place the dumbbell plate in the clamp of an electronic tensile testing machine. Close the small air heating box outside the clamp, set the temperature to 90°C, heat for 1 hour, and perform a tensile test at a rate of 25 mm / min. Test tensile strength and elongation at break.

[0037] From the performance comparison test results in Table 1, it can be seen that the flame retardant without modification by long-chain silane and long-chain stearic acid, and the thermoplastic low-smoke halogen-free sheath material obtained by using conventional low-melting-point POE elastomer showed cracking in the high and low temperature cycle anti-cracking test in the crack resistance test, and also showed cracking in the high temperature anti-cracking test. The material after the flame retardant powder was modified by long-chain silane and long-chain stearic acid, and the high melting point propylene elastomer was used to replace the low melting point POE elastomer, showed no significant difference in crack resistance. The materials exhibited no cracking during the high-temperature cyclic cracking test and the high-temperature cracking test. Furthermore, the mechanical properties at high temperatures were half as low as those of Examples 1-5. This suggests that the flame retardant can be modified with long-chain silanes and long-chain stearic acid to create a stable thermal expansion transition layer between the resin and the powder. This high-melting-point polypropylene-based elastomer replaces the traditional polyolefin elastomer (POE), improving the heat resistance of the thermoplastic low-smoke, zero-halogen (LSZH) material while maintaining good elongation at break even under high-fill conditions. Compared to the pronounced sea-island structure of traditional elastomers, the islands of this polypropylene-based elastomer are smaller and more uniformly distributed, reducing the thermal expansion of the rubber phase and further minimizing the differential thermal expansion between the base resin and the inorganic flame retardant at high temperatures. Compared to traditional polyethylene-based POE, polypropylene-based elastomers exhibit a higher yield stress. Their high melting point ensures superior resistance to yield deformation under high temperatures and external forces, effectively improving the crack resistance and mechanical properties of the thermoplastic low-smoke, zero-halogen (LSZH) sheathing material at high temperatures.

[0038] For ordinary technicians in this field, the specific embodiments are only illustrative descriptions of the present invention. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned methods. As long as various non-substantial improvements are made using the method concepts and technical solutions of the present invention, such as changing the weight of a substance or a reaction parameter, or directly applying the concepts and technical solutions of the present invention to other occasions without improvement, they are all within the scope of protection of the present invention.

Claims

1. A method for improving the crack resistance of thermoplastic low-smoke halogen-free sheath material, characterized in that: The flame retardant powder was modified with long-chain silane and long-chain fatty acid, and a thermal expansion transition layer was constructed between the inorganic flame retardant powder and the resin, thereby improving the anti-cracking performance and obtaining a heat-resistant and crack-resistant thermoplastic low-smoke halogen-free sheath material.

2. The method for improving the crack resistance of thermoplastic low-smoke zero-halogen sheath material according to claim 1, characterized in that: The long-chain silane is hexadecyltrimethoxysilane; the long-chain fatty acid is stearic acid; the mass percentage of stearic acid used is 0.8-1.5%, and the mass percentage of the long-chain silane hexadecyltrimethoxysilane used is 0.6-1.5%.

3. The method for improving the crack resistance of thermoplastic low-smoke zero-halogen sheath material according to claim 1, characterized in that: The specific steps of this improvement method are: S1 weighing raw materials: weigh the raw materials according to the mass ratio and set aside; S2 modified flame retardant powder: stir and preheat the flame retardant powder, add long-chain silane, continue to stir the powder, and start the atomizing spray device for spraying. After the reaction is completed, melt the long-chain fatty acid and place it in the spray device. Stir the powder while starting the atomizing spray device for spraying. After cooling, the modified flame retardant powder is obtained; S3 granulation and molding: The modified flame retardant powder obtained in step S2 and other raw materials are placed in an internal mixer for internal mixing. After the internal mixing is completed, it is fed through a double cone, mixed through a twin screw, and then extruded and pelletized through a single screw. Finally, the material particles are obtained after hot air drying and cooling in a boiling bin, which improves the anti-cracking performance.

4. The method for improving the crack resistance of thermoplastic low-smoke zero-halogen sheath material according to claim 3, characterized in that: The formula of the raw materials in step S1 is as follows by mass ratio: EVA 40~50 parts; 15-30 parts of polypropylene-based elastomer; 20-30 parts of polyethylene; Compatibilizer 8~10 parts; 200~240 parts of flame retardant; 5-15 parts of synergist; 1.5-2 parts of long-chain fatty acids; 1.5-2 parts of long-chain silane; 3~6 parts of lubricant; 1~2 parts of antioxidant; 2~5 parts of masterbatch.

5. The method for improving the crack resistance of thermoplastic low-smoke zero-halogen sheath material according to claim 4, characterized in that: The EVA is mixed with one or more EVAs having a melt flow rate of 0.3-6.0 g / 10 min and a VA content of 28-40%.

6. The method for improving the crack resistance of thermoplastic low-smoke zero-halogen sheath material according to claim 4, characterized in that: The polypropylene-based elastomer is selected from polypropylene-based elastomers having a melt flow rate of 0.5-2.1 g / 10 min, a glass transition temperature of ≤~40° C., and a melting point of ≥140° C.

7. The method for improving the crack resistance of thermoplastic low-smoke zero-halogen sheath material according to claim 4, characterized in that: The polyethylene is metallocene linear low-density polyethylene, and the compatibilizer is metallocene linear low-density polyethylene grafted with maleic anhydride polymer; the melt index of the metallocene is 1.0-3.5 g / 10 min, and the grafting rate of maleic anhydride is 0.6%-1.2%.

8. The method for improving the crack resistance of thermoplastic low-smoke zero-halogen sheath material according to claim 4, characterized in that: The antioxidant is a mixture of pentaerythritol (1010) and dilauryl thiodipropionate (DLTP), with a mass ratio of 1:1 or 1:2; the flame retardant is modified aluminum hydroxide or modified magnesium hydroxide or a mixture of modified aluminum hydroxide and modified magnesium hydroxide, with a particle size D50 of 0.8~1.5μm; the synergist is any one of organic montmorillonite and sepiolite; and the masterbatch is a carbon black masterbatch.

9. The method for improving the crack resistance of thermoplastic low-smoke zero-halogen sheath material according to claim 3, characterized in that: The specific steps of step S2 are: placing the flame retardant powder in a stirring device and stirring and preheating it to 80-90°C. After reaching the preheating temperature, first placing the long-chain silane in a spray device, continuing to stir the powder, and simultaneously turning on the atomizing spray device, the spraying time is 8-12 minutes, the stirrer speed is 500-800 rpm, and the stirring time is 20-30 minutes. Then, melting the long-chain fatty acid, placing it in the spray device, stirring the powder while turning on the atomizing spray device, the spraying time is 8-12 minutes, the stirrer speed is 500-800 rpm, and the stirring time is 20-30 minutes. After cooling, the modified flame retardant powder is obtained.

10. The method for improving the crack resistance of thermoplastic low-smoke zero-halogen sheath material according to claim 9, characterized in that: The specific steps of step S3 are: placing the modified flame retardant powder and all other raw materials in an internal mixer, the internal mixing temperature is 170°C, the internal mixing time is 15 minutes, and the discharge temperature is controlled at 170-175°C; after the internal mixing is completed, the temperature of the double-cone feeding is 100°C; then using a twin-screw extruder for mixing, the temperatures of each zone during mixing are 95°C, 95°C, 100°C, 105°C, 105°C, 110°C, and 110°C in sequence, and the average speed of the twin-screw is 200rpm; then using a single-screw extruder for pelletizing, the temperatures of each zone during extrusion are 100°C, 110°C, 130°C, 135°C, and 135°C in sequence, and the speed of the screw is 120rpm; finally, the material particles are obtained after hot air drying and cooling in a boiling bin, and the particle thickness is controlled at 2-4mm.

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