A low heat release, low smoke density flame retardant polyamide material and its preparation method and application

Abstract

The application discloses a low-heat-release, low-smoke-density flame-retardant polyamide material and a preparation method and application thereof, and belongs to the technical field of high polymer materials. The material comprises nylon resin 52-61%, a flame retardant 18-26%, a flame-retardant synergist 6-10%, a plasticizer 8-15%, a coupling agent 0.5-1.0%, an antioxidant 0.3-1.0% and a lubricant 0.3-1.0%, and is prepared through mixing, melt mixing, extrusion and granulation. The application effectively reduces the heat release and the smoke density of the polyamide material during combustion through the synergistic effect of the components such as the flame retardant, and meanwhile, good mechanical properties and processing stability are maintained, thereby meeting the demand of high-safety-grade application scenarios.

Description

Technical Field

[0001] This application relates to a low-heat-release, low-smoke-density flame-retardant polyamide material, its preparation method, and its application, belonging to the field of polymer materials technology. Background Technology

[0002] Polyamide (commonly known as nylon, PA) is the most produced and widely used of the five major general-purpose engineering plastics. With its excellent mechanical strength, toughness, wear resistance, oil resistance, and electrical insulation, it has become an indispensable basic material for pillar industries of the national economy, such as automobiles, electronics, rail transportation, aerospace, new energy, and building materials. Based on the ratio of methylene to amide groups in the molecular chain, polyamide can be divided into short-chain nylon and long-chain nylon. Compared with short-chain nylon, long-chain nylon has a lower amide group density, resulting in extremely low water absorption, excellent dimensional stability, good flexibility, resistance to low-temperature impact, resistance to fuel and chemical corrosion, and a wider processing window. It is particularly suitable for high-end applications with stringent requirements for flexibility, weather resistance, and sealing, such as automotive fuel lines, pneumatic systems, rail transportation cable sheaths, energy storage battery pack harnesses, medical precision instruments, and high-end flexible tubing. Market demand continues to grow rapidly.

[0003] However, long-chain nylon has a limiting oxygen index of only 22%–23%, classifying it as a flammable material. Its high hydrocarbon content in its molecular chain leads to rapid heat release, large total heat release, and high smoke density during combustion, accompanied by severe dripping, making it highly susceptible to flame spread and asphyxiation injuries. With increasingly stringent global requirements for public safety and environmental protection, particularly in emerging fields such as new energy vehicles, rail transportation, and energy storage power stations where fire safety standards for materials are constantly being upgraded, traditional pure nylon can no longer meet the multiple stringent standards of "low smoke, non-toxicity, low heat release, and high flame retardancy," severely limiting its application in high-safety scenarios. Therefore, developing high-performance halogen-free flame-retardant long-chain nylon materials has become a critical technical problem urgently needing to be solved by the industry.

[0004] While current mainstream halogen-free flame retardant systems (phosphorus-based, nitrogen-based, phosphorus-nitrogen synergistic, etc.) can achieve halogen-free flame retardancy, they still have significant drawbacks: 1) High heat release and smoke density: Existing halogen-free flame-retardant polyamides still have high heat release rate (HRR), total heat release (THR), and smoke density (Ds) under open flame or high heat irradiation, which makes it difficult to meet the high-level fire protection standards for low smoke and low heat release in rail transit, new energy battery packs, etc. 2) It is difficult to balance flame retardant efficiency and mechanical properties: In order to reduce smoke density and heat release, it is often necessary to significantly increase the amount of flame retardant added, which leads to a significant decrease in material strength and toughness, and at the same time causes problems such as flame retardant precipitation, blooming, poor hydrolysis resistance, and insufficient processing stability. 3) Poor compatibility and processing stability: Phosphorus-based (such as red phosphorus, ammonium polyphosphate) and nitrogen-based (such as MCA) flame retardants have limited compatibility with polyamide matrix. They are prone to decomposition, volatilization and migration during high-temperature processing, resulting in yellowing, scale buildup and poor flame retardancy. The problems are more prominent in glass fiber reinforced, high-temperature flame retardant and light-colored / white products. 4) It is difficult to balance low heat release and low smoke density: Existing research focuses on improving single flame retardant properties, and there are few halogen-free flame retardant polyamide solutions that simultaneously take into account low smoke, low heat release, high flame retardant efficiency, and good mechanical and processing stability, which makes it difficult to meet the comprehensive needs of high-end application scenarios.

[0005] Therefore, developing a halogen-free, environmentally friendly, low-heat-release, low-smoke-density, high-flame-retardant-efficiency, good mechanical property retention, and excellent processing stability flame-retardant polyamide material is of great practical significance and application value for meeting the high safety and environmental protection requirements of new energy, rail transportation, and electronic and electrical fields. Summary of the Invention

[0006] To address the aforementioned issues, this invention provides a low-heat-release, low-smoke-density flame-retardant polyamide material, its preparation method, and its applications. By optimizing the selection of a long-chain nylon matrix and the synergistic ratio of a halogen-free flame-retardant system, this invention achieves a synergistic improvement in high flame-retardant efficiency, low heat release, low smoke density, excellent ductility, and impact strength. It also possesses good processing stability and environmental friendliness, and can be widely applied in high-end fields with stringent requirements for fire safety and flexibility.

[0007] According to one aspect of this application, a low heat release, low smoke density flame-retardant polyamide material is provided, comprising the following raw material components in the following mass fractions: 52-61% nylon resin, 18-26% flame retardant, 6-10% flame retardant synergist, 8-15% plasticizer, 0.5-1.0% coupling agent, 0.3-1.0% antioxidant, and 0.3-1.0% lubricant.

[0008] Optionally, the nylon resin has a relative viscosity ≥2.0 and a terminal amino content ≥40mmol / kg; Preferably, the nylon resin has a relative viscosity of 2.0 to 2.4 and a terminal amino content of 40 to 60 mmol / kg.

[0009] Specifically, the inventors discovered that relative viscosity affects the degree of molecular chain entanglement and melt flowability of the nylon matrix. By limiting the relative viscosity range, they ensured that the material had sufficient tensile strength and impact toughness, while maintaining good processing flowability, which facilitated the uniform dispersion of flame retardants.

[0010] The terminal amino group can chemically bond with acidic organic phosphonate flame retardants, significantly improving the interfacial bonding force between the two phases, reducing the aggregation and precipitation of flame retardants, and extending the flame retardant durability. By limiting the content of terminal amino groups, a balance can be achieved between interfacial bonding force and material water absorption rate, avoiding the decrease in dimensional stability caused by excessive water absorption rate.

[0011] Optionally, the nylon resin is selected from at least one of PA612 and PA12.

[0012] Optionally, the flame retardant is selected from at least one of aluminum hypophosphite, aluminum dimethylphosphite, aluminum diethylphosphite, zinc diethylphosphite, calcium diethylphosphite, magnesium diethylphosphite, and aluminum diisobutylphosphite.

[0013] Specifically, by selecting organic phosphonate flame retardants, which decompose upon heating during combustion, PO is released. PO2 Free radicals, capturing H in the gas phase OH Active free radicals interrupt the combustion chain reaction; at the same time, they promote the dehydration of the matrix into carbon in the condensed phase, forming a dense carbon layer to block heat and oxygen transfer.

[0014] Optionally, the flame retardant synergist is selected from at least one of melamine polyphosphate, triazine charring agent, aluminum phosphite, zinc borate, and organomontmorillonite.

[0015] Specifically, melamine polyphosphate decomposes upon heating to generate inert gases such as ammonia, which dilutes the concentration of combustible gases and promotes char formation. Triazine charring agent can form a dense and continuous expanded char layer during combustion, which can effectively block the transfer of heat and flue gas. The lamellar structure of organomontmorillonite is oriented during combustion to form a composite char layer with a "brick-mud" structure, which further enhances the blocking effect and adsorbs toxic particles in the flue gas.

[0016] Optionally, the mass ratio of the flame retardant to the flame retardant synergist is (1.8~4.5):1.

[0017] Specifically, by limiting the ratio of the two, the synergistic effect of gas-phase free radical capture and condensed-phase char formation is excellent, and the PO produced by the decomposition of organic phosphonates is reduced. PO2 Free radicals can rapidly capture H in the gas phase OH Active free radicals interrupt the combustion chain reaction; at the same time, the inert gas produced by the decomposition of the synergist can dilute the concentration of combustible gas and promote the dehydration of the nylon matrix into carbon, forming a dense and continuous expanded carbon layer, which blocks heat, oxygen and combustible gas inside the material, achieving highly efficient flame retardancy with integrated chain breaking, dilution and barrier.

[0018] When the mass ratio of flame retardant to synergist is less than 1.8:1, excessive synergist dilutes the matrix, leading to a significant decrease in the tensile strength and impact toughness of the material. Furthermore, due to excessive char formation in the condensed phase but insufficient gas-phase free radical capture capacity, it cannot effectively suppress flame propagation in the early stages of combustion. Additionally, excessive synergist decomposes prematurely in the early stages of combustion, resulting in premature and porous char layer formation, which fails to effectively block heat and oxygen transfer in the later stages, thus increasing the total heat release. When the mass ratio is greater than 4.5:1, insufficient synergist leads to inadequate char formation, failing to form an effective barrier layer, thereby significantly increasing the heat release rate and smoke density, and lowering the flame retardant rating.

[0019] Optionally, the plasticizer is selected from at least one of N-butylbenzenesulfonamide and p-toluenesulfonamide; the coupling agent is selected from at least one of γ-aminopropyltriethoxysilane and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane. The antioxidant is selected from at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N,N'-1,6-hexene-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamide], bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, and bis(2,4-dicumylphenyl)pentaerythritol diphosphite; The lubricant is selected from at least one of ethylene bis-stearamide and pentaerythritol stearate.

[0020] Specifically, benzenesulfonamide plasticizers, with their polarity matching that of long-chain nylon, can insert themselves between nylon molecular chains to weaken hydrogen bonding forces and enhance chain segment mobility, thereby improving the material's ductility and low-temperature toughness without negatively impacting flame retardant properties. Ethylene bis-stearamide and pentaerythritol stearate lubricants can improve melt flowability, reduce screw wear and die fouling, and ensure the stability of continuous extrusion molding.

[0021] According to another aspect of this application, a method for preparing a low-heat-release, low-smoke-density flame-retardant polyamide material is also provided, comprising the following steps: mixing nylon resin, flame retardant, flame retardant synergist, plasticizer, coupling agent, antioxidant and lubricant in proportion to obtain a premix; The premixed material is then fed into a twin-screw extruder, where it is melt-mixed, extruded, cooled, and pelletized to obtain a flame-retardant polyamide composite material.

[0022] Optionally, the temperatures of heating zones 2# to 10# and the die head of the twin-screw extruder are 210℃, 230℃, 230℃, 230℃, 230℃, 230℃, 225℃, 225℃, 225℃ and 230℃ respectively.

[0023] According to another aspect of this application, the application of a low-heat-release, low-smoke-density flame-retardant polyamide material in new energy vehicles, rail transit, and energy storage power stations is also provided; preferably, its application in flame-retardant electric pipes, flame-retardant corrugated pipes, and flame-retardant cable coatings is also provided.

[0024] The beneficial effects of this application include, but are not limited to: 1. This application combines nylon resin, flame retardant, flame retardant synergist, plasticizer, coupling agent, antioxidant and lubricant in specific mass fractions. By utilizing the synergistic effect of flame retardant and flame retardant synergist, it promotes the rapid formation of a dense char layer and releases non-combustible gas when the material is heated and burned, thereby effectively isolating heat transfer and oxygen diffusion, and significantly reducing the heat release rate and total heat release.

[0025] 2. This application utilizes plasticizers to improve the mobility of polymer chain segments and coupling agents to enhance the interfacial bonding between inorganic flame-retardant particles and the nylon matrix. This allows the material to maintain a high flame retardancy rating while avoiding embrittlement caused by excessive filling, thus maintaining excellent elongation at break and impact strength.

[0026] 3. This application, through the auxiliary effects of antioxidants and lubricants, inhibits thermo-oxidative degradation during high-temperature processing and improves melt fluidity, ensuring the uniformity and stability of the internal structure of the material, thus avoiding the generation of large amounts of dense smoke and the occurrence of molten droplets during combustion.

[0027] 4. This application improves the interfacial compatibility between the flame retardant and the matrix by limiting the relative viscosity and terminal amino content of the nylon resin, reducing the precipitation and migration of the flame retardant, extending the service life of the material, and ensuring good processing fluidity. It also employs highly efficient synergists such as triazine charring agents and organomontmorillonite to work synergistically with organophosphinate flame retardants, improving charring efficiency and char layer density. Compared with the traditional melamine polyphosphate synergistic system, the smoke density and total heat release are reduced, significantly improving the fire safety of the material.

[0028] 5. The flame-retardant polyamide material of this application is halogen-free and environmentally friendly, and can be widely used in high-end fields with stringent fire safety and environmental protection requirements, such as new energy vehicles, rail transit, and energy storage power stations. It has broad market prospects and important application value. Attached Figure Description

[0029] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a photograph of the flame-retardant polyamide material prepared in Example 1 of this application after being granulated. Figure 2The images show combustion test results of flame-retardant polyamide material samples prepared in the various embodiments and comparative examples of this application (from left to right: Examples 1-6 and Comparative Examples 1-9). Detailed Implementation

[0030] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they shall be used in accordance with conventional methods in the art or as per the product instructions. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described in this patent are for illustrative purposes only.

[0032] The nylon resin, flame retardant, flame retardant synergist, plasticizer, coupling agent, antioxidant, and lubricant used in this application are all commercially available products. The main instruments and equipment include: a high-speed mixer (SHR-10A); a twin-screw extruder (SHJ-35, L / D ratio 40:1); an injection molding machine (MA900); a universal electronic tensile testing machine (CMT5105); a cantilever beam impact testing machine (XJUD-5.5); an oxygen index meter (JF-3); a horizontal and vertical combustion tester (CZF-5); a smoke density meter (JCY-3); a cone calorimeter (FTT 0007); and a terminal amine content analyzer (potential titration method). Terminal amine content: determined by potentiometric titration, using phenol-ethanol as the solvent and hydrochloric acid standard solution for titration.

[0033] The embodiments and comparative examples in this application use a uniform preparation method: (1) Dry the nylon resin in a vacuum drying oven at 80°C for 12 hours to remove moisture; weigh the dried nylon resin, flame retardant, flame retardant synergist, plasticizer, coupling agent, antioxidant and lubricant according to the formula ratio, add them to a high-speed mixer, and mix at 1500r / min for 5 minutes at room temperature to obtain a uniform premix. (2) The premixed material is fed into a twin-screw extruder for melt mixing and extrusion. The temperatures of heating zones 2# to 10# and the die head are 210℃, 230℃, 230℃, 230℃, 230℃, 225℃, 225℃, 225℃, and 230℃ respectively. The screw speed is 300r / min and the feeding speed is 15kg / h. The extruded strip is cooled by water and air-dried before being fed into a pelletizer to obtain flame-retardant polyamide composite material particles. The particles are dried in an 80℃ vacuum drying oven for 12 hours and then injection molded into standard test strips by an injection molding machine. The injection temperature is 220~240℃, the mold temperature is 40℃, and the holding time is 15 seconds.

[0034] Example 1 This embodiment provides a low-heat-release, low-smoke-density flame-retardant polyamide material. The total feed amount is 100 kg, and the amounts of each component are as follows: PA12 (relative viscosity 2.2, terminal amino group 45 mmol / kg) 59.3 kg, zinc diethylphosphite 22 kg, organomontmorillonite 8 kg, N-butylbenzenesulfonamide 9 kg, KH-550 0.5 kg, antioxidant 1010 0.2 kg, antioxidant 626 0.4 kg, and PETS 0.6 kg. The composite material is prepared according to the above-described unified preparation process, and its performance is tested.

[0035] Example 2 This embodiment provides a low-heat-release, low-smoke-density flame-retardant polyamide material. The total feed amount is 100 kg, and the amounts of each component are as follows: PA612 (relative viscosity 2.3, terminal amino group 52 mmol / kg) 56.0 kg, diethylaluminum hypophosphite 20 kg, triazine charring agent 10 kg, p-toluenesulfonamide 12 kg, KH-792 0.8 kg, antioxidant 1098 0.4 kg, antioxidant 9228 0.3 kg, and EBS 0.5 kg. The composite material is prepared according to the above-described unified preparation process, and its performance is tested.

[0036] Example 3 This embodiment provides a low-heat-release, low-smoke-density flame-retardant polyamide material. The total feed amount is 100 kg, and the amounts of each component are as follows: PA12 (relative viscosity 2.2, terminal amino group 45 mmol / kg) 60.3 kg, aluminum diethylphosphite 18 kg, aluminum phosphite 10 kg, N-butylbenzenesulfonamide 10 kg, KH-792 0.6 kg, antioxidant 1098 0.5 kg, antioxidant 626 0.5 kg, and PETS 0.4 kg. The composite material is prepared according to the above-described unified preparation process, and its performance is tested.

[0037] Example 4 This embodiment provides a low-heat-release, low-smoke-density flame-retardant polyamide material. The total feed amount is 100 kg, and the amounts of each component are as follows: PA12 (relative viscosity 2.2, terminal amino group 45 mmol / kg) 58.5 kg, zinc diethylphosphite 25 kg, organomontmorillonite 7 kg, p-toluenesulfonamide 8 kg, KH-550 0.6 kg, antioxidant 1098 0.6 kg, antioxidant 626 0.2 kg, and EBS 0.3 kg. The composite material is prepared according to the above-described unified preparation process, and its performance is tested.

[0038] Example 5 This embodiment provides a low-heat-release, low-smoke-density flame-retardant polyamide material. The total feed amount is 100 kg, and the amounts of each component are as follows: PA612 (relative viscosity 2.3, terminal amino group 52 mmol / kg) 53.4 kg, aluminum diethylphosphite 26 kg, melamine polyphosphate 6 kg, N-butylbenzenesulfonamide 12 kg, KH-550 1.0 kg, antioxidant 1010 0.3 kg, antioxidant 9228 0.3 kg, and PETS 1.0 kg. The composite material is prepared according to the above-described unified preparation process, and its performance is tested.

[0039] Example 6 This embodiment provides a low-heat-release, low-smoke-density flame-retardant polyamide material. The total feed amount is 100 kg, and the amounts of each component are as follows: PA612 (relative viscosity 2.3, terminal amino group 52 mmol / kg) 52.8 kg, diethylaluminum hypophosphite 8 kg, diethylzinc hypophosphite 12 kg, zinc borate 5 kg, organomontmorillonite 5 kg, p-toluenesulfonamide 15 kg, KH-792 0.7 kg, antioxidant 1098 0.3 kg, antioxidant 1010 0.3 kg, antioxidant 9228 0.4 kg, and PETS 0.5 kg. The composite material is prepared according to the above-described unified preparation process, and its performance is tested.

[0040] Comparative Example 1 This comparative example provides a flame-retardant polyamide material with a total feed amount of 100 kg. The amounts of each component are as follows: PA12 (relative viscosity 2.2, terminal amino group 45 mmol / kg) 65.0 kg, aluminum diethylphosphite 30 kg, organomontmorillonite 10 kg, N-butylbenzenesulfonamide 3 kg, KH-550 0.5 kg, antioxidant 1098 0.3 kg, antioxidant 1010 0.3 kg, antioxidant 9228 0.4 kg, and PETS 0.5 kg. The preparation process and testing methods are the same as in Example 1.

[0041] Comparative Example 2 This comparative example provides a flame-retardant polyamide material with a total feed amount of 100 kg. The amounts of each component are as follows: PA612 (relative viscosity 2.3, terminal amino group 52 mmol / kg) 64.9 kg, zinc diethylphosphite 25 kg, melamine polyphosphate 8 kg, KH-792 0.6 kg, antioxidant 1098 0.3 kg, antioxidant 1010 0.3 kg, antioxidant 9228 0.4 kg, and PETS 0.5 kg. The preparation process and testing methods are the same as in Example 1.

[0042] Comparative Example 3 This comparative example provides a flame-retardant polyamide material with a total feed amount of 100 kg. The amounts of each component are as follows: PA12 (relative viscosity 2.2, terminal amino group 45 mmol / kg) 57.8 kg, zinc diethylphosphite 30 kg, N-butylbenzenesulfonamide 10 kg, KH-550 0.7 kg, antioxidant 1098 0.3 kg, antioxidant 1010 0.3 kg, antioxidant 9228 0.4 kg, and PETS 0.5 kg. The preparation process and testing methods are the same as in Example 1.

[0043] Comparative Example 4 This comparative example provides a flame-retardant polyamide material with a total feed amount of 100 kg. The amounts of each component are as follows: PA612 (relative viscosity 2.3, terminal amino group 52 mmol / kg) 60.5 kg, diethylaluminum hypophosphite 20 kg, organomontmorillonite 10 kg, p-toluenesulfonamide 8 kg, antioxidant 1098 0.3 kg, antioxidant 1010 0.3 kg, antioxidant 9228 0.4 kg, and PETS 0.5 kg. The preparation process and testing methods are the same as in Example 1.

[0044] Comparative Example 5 This comparative example provides a flame-retardant polyamide material, which differs from Example 3 only in that the PA12 resin is replaced with PA12 with a relative viscosity of 1.7 and a terminal amino content of 32 mmol / kg. The dosage of other components and the preparation process are exactly the same.

[0045] Comparative Example 6 This comparative example provides a flame-retardant polyamide material, which differs from Example 3 only in that the PA12 resin is replaced with PA12 with a relative viscosity of 3.0 and a terminal amino content of 68 mmol / kg. The dosage of other components and the preparation process are exactly the same.

[0046] Comparative Example 7 This comparative example provides a flame-retardant polyamide material, which differs from Example 2 only in that the PA612 resin is replaced with PA612 with a relative viscosity of 2.3 and a terminal amino content of 35 mmol / kg, while the dosage of other components and the preparation process are exactly the same.

[0047] Comparative Example 8 This comparative example provides a flame-retardant polyamide material, which differs from Example 2 only in that the PA612 resin is replaced with PA612 with a relative viscosity of 2.3 and a terminal amino content of 72 mmol / kg. The dosage of other components and the preparation process are exactly the same.

[0048] Comparative Example 9 This comparative example provides a flame-retardant polyamide material, which differs from Example 5 only in that the amount of melamine polyphosphate is adjusted to 5.2 kg, the amount of PA612 resin is adjusted accordingly to 54.2 kg, and the amounts of other components and the preparation process are exactly the same.

[0049] Experimental Example The following performance tests were conducted on the low heat release, low smoke density flame-retardant polyamide materials prepared in each embodiment and comparative example. The composite materials prepared in each embodiment and comparative example were dried and injection molded into standard specimens. The test methods are as follows: Elongation at break: determined according to GB / T 1040.2-2006 standard, with a tensile rate of 50 mm / min and a type I specimen.

[0050] Notched impact strength: Determined according to GB / T 1843-2008 standard, using cantilever beam notched impact, notch radius 0.25mm, and sample size 80mm×10mm×4mm.

[0051] Limiting Oxygen Index (LOI): Determined according to GB / T 2406.2-2009 standard, with a sample size of 150mm × 6.5mm × 3mm.

[0052] Maximum smoke density: determined according to GB / T 8627-2007 standard, using flaming combustion mode, with sample size of 75mm×75mm×3mm.

[0053] Total heat release (THR): Measured according to GB / T 16172-2007 standard using a cone calorimeter with a thermal radiation power of 50 kW / m² and sample dimensions of 100 mm × 100 mm × 3 mm. The final results are shown in Table 1.

[0054] Table 1 Performance test results of Examples 1-6 and Comparative Examples 1-9

[0055] As shown in Table 1, the flame-retardant polyamide materials prepared in Examples 1-6 of this application all achieved excellent comprehensive properties: elongation at break was greater than 260%, with a maximum of 322%; notched impact strength was greater than 35 kJ / m², with a maximum of 46.9 kJ / m²; limiting oxygen index was greater than 32%, with a maximum of 33.6%; maximum smoke density was less than 50, with a minimum of 35; and total heat release was less than 85 kW / m², with a minimum of 72 kW / m². This indicates that by optimizing the formulation system and preparation process, this invention has solved the problem of balancing flame-retardant performance with mechanical properties, low heat release, and low smoke density. The prepared materials meet the stringent requirements of flexible flame-retardant materials in high-end fields such as new energy vehicles and rail transit.

[0056] Among them, Example 2 has the best overall performance, with an oxygen index of 33.3%, a maximum smoke density of 39, and a total heat release of 73 kW / m². Compared with the MPP system (Example 5), the smoke density is reduced by 11.4% and the total heat release is reduced by 14.1%. Examples 1 and 4 have the lowest smoke densities (36~39) and the highest mechanical property retention rate, making them suitable for scenarios with high flexibility requirements. Example 6 has the lowest heat release (72 kW / m²) and also has a good smoke suppression effect.

[0057] Regarding the comparative examples, compared to Example 1 (insufficient plasticizer), Comparative Example 1 (with insufficient plasticizer) showed that after the plasticizer addition was reduced from 9 kg to 3 kg, the elongation at break decreased from 295% to 10.5%, and the notched impact strength decreased from 42.5 kJ / m² to 3.2 kJ / m², indicating that benzenesulfonamide plasticizers play a key role in the high ductility and flexibility of the material. Comparative Example 2, lacking plasticizer, although achieving a V0 rating, had an impact strength of only 6.7 kJ / m², failing to meet application requirements. Comparative Example 3, lacking a flame retardant synergist, resulted in poor char quality, a smoke density as high as 76, a heat release of 144 kW / m², and a flame retardant rating of V1. Comparing Comparative Example 4 (without coupling agent) with Example 2: Without the addition of coupling agent, the elongation at break decreased from 284% to 154%, and the notched impact strength decreased from 36.5 kJ / m² to 20.3 kJ / m², indicating that aminosilane coupling agent can improve the interfacial compatibility between inorganic flame retardant and organic matrix, and enhance the mechanical properties of the material.

[0058] Comparative Experiment 3, Comparative Example 5, and Comparative Example 6 (only the relative viscosity of the nylon resin differs, the rest are completely the same): When the relative viscosity drops to 1.7 (below 2.0), the mechanical properties of the material decrease significantly, the elongation at break drops to 194% (a decrease of 27.3%), the notched impact strength drops to 21.9 kJ / m² (a decrease of 45.5%), the oxygen index drops to 31.3%, and the smoke density rises to 50; when the relative viscosity rises to 3.0 (above 2.4), the processing fluidity of the material deteriorates, the flame retardant is unevenly dispersed, resulting in the elongation at break dropping to 166% (a decrease of 37.8%), and the total heat release rising to 77 kW / m².

[0059] Comparative Examples 2, 7, and 8 (only the nylon resin terminal amino content differed, the rest were identical). When the terminal amino content decreased to 35 mmol / kg (below 40 mmol / kg), the flame retardant and mechanical properties of the material deteriorated simultaneously. The oxygen index decreased to 31.1%, the smoke density increased to 53 (an increase of 35.9%), the total heat release increased to 91 kW / m² (an increase of 24.7%), and the notched impact strength decreased to 25.0 kJ / m² (a decrease of 31.5%). When the terminal amino content increased to 72 mmol / kg (above 60 mmol / kg), the water absorption rate of the material increased significantly, the long-term dimensional stability deteriorated, and yellowing easily occurred during processing. However, the decrease in mechanical and flame retardant properties was relatively small. The reason for this is that when the terminal amino content is insufficient, the flame retardant mainly relies on physical adsorption to bond with the matrix. The interfacial bonding force is weak, and phase separation easily occurs, leading to flame retardant agglomeration and precipitation. This not only reduces mechanical properties but also causes discontinuous char layer during combustion, increasing heat release and smoke density. When the content of terminal amino groups is too high, the density of amide groups increases, the water absorption rate of the material increases, and the dimensional stability and hydrolysis resistance are affected.

[0060] Comparing Experiment 3, Experiment 5, and Comparative Example 9: When the ratio of flame retardant to synergist is 4.33:1 (close to the upper limit), it still maintains excellent overall performance, with an oxygen index of 33.5%, smoke density of 35, heat release of 85 kW / m², and no significant decrease in mechanical properties; when the ratio is increased to 5:1 (exceeding the upper limit of 4.5:1 as defined in the claims), the flame retardant-related performance deteriorates: the oxygen index drops to 30.8%, the maximum smoke density jumps sharply from 35 to 65 (an increase of 85.7%), and the total heat release increases from 85 kW / m² to 115 kW / m² (an increase of 35.3%), while only the mechanical properties remain basically unchanged.

[0061] The above results demonstrate that the material prepared by this invention exhibits very low smoke generation and heat release rates in simulated fire scenarios, while maintaining good flexibility and impact resistance. It can be used in applications such as the preparation of flame-retardant automotive parts, rail transit cable sheaths, and new energy battery pack connection components to prevent and / or mitigate personnel asphyxiation and equipment damage caused by material combustion in fire accidents.

[0062] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A low-heat-release, low-smoke-density flame-retardant polyamide material, characterized in that, The raw material composition includes the following components by mass fraction: nylon resin 52-61%, flame retardant 18-26%, flame retardant synergist 6-10%, plasticizer 8-15%, coupling agent 0.5-1.0%, antioxidant 0.3-1.0%, and lubricant 0.3-1.0%. The nylon resin is selected from at least one of PA612 and PA12.

2. The low heat release, low smoke density flame-retardant polyamide material according to claim 1, characterized in that, The nylon resin has a relative viscosity ≥2.0 and a terminal amino content ≥40mmol / kg.

3. The low heat release, low smoke density flame-retardant polyamide material according to claim 2, characterized in that, The relative viscosity of the nylon resin is 2.0~2.4, and the content of terminal amino groups is 40~60 mmol / kg.

4. The low heat release, low smoke density flame-retardant polyamide material according to claim 1, characterized in that, The flame retardant is selected from at least one of aluminum hypophosphite, aluminum dimethylphosphite, aluminum diethylphosphite, zinc diethylphosphite, calcium diethylphosphite, magnesium diethylphosphite, and aluminum diisobutylphosphite.

5. The low heat release, low smoke density flame-retardant polyamide material according to claim 1, characterized in that, The flame retardant synergist is selected from at least one of melamine polyphosphate, triazine charring agent, aluminum phosphite, zinc borate, and organomontmorillonite.

6. The low heat release, low smoke density flame-retardant polyamide material according to claim 1, characterized in that, The mass ratio of the flame retardant to the flame retardant synergist is (1.8~4.5):

1.

7. The low heat release, low smoke density flame-retardant polyamide material according to claim 1, characterized in that, The plasticizer is selected from at least one of N-butylbenzenesulfonamide and p-toluenesulfonamide; The coupling agent is selected from at least one of γ-aminopropyltriethoxysilane and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane; The antioxidant is selected from at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N,N'-1,6-hexene-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamide], bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, and bis(2,4-dicumylphenyl)pentaerythritol diphosphite; The lubricant is selected from at least one of ethylene bis-stearamide and pentaerythritol stearate.

8. A method for preparing a low-heat-release, low-smoke-density flame-retardant polyamide material as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Nylon resin, flame retardant, flame retardant synergist, plasticizer, coupling agent, antioxidant and lubricant are mixed evenly in proportion to obtain a premix; The premixed material is then fed into a twin-screw extruder, where it is melt-mixed, extruded, cooled, and pelletized to obtain a flame-retardant polyamide composite material.

9. The preparation method according to claim 8, characterized in that, The temperatures of heating zones 2# to 10# and the die head of the twin-screw extruder are 210℃, 230℃, 230℃, 230℃, 230℃, 230℃, 225℃, 225℃, 225℃ and 230℃ respectively.

10. The application of a low-heat-release, low-smoke-density flame-retardant polyamide material as described in any one of claims 1 to 7 in new energy vehicles, rail transit, and energy storage power stations.

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