Polyamide flame-retardant composite material, preparation method and battery box cover

Abstract

The invention provides a polyamide flame-retardant composite material, a preparation method and a battery box cover, the composite material comprises a resin matrix and a fiber fabric, the resin matrix comprises a lactam monomer, DOPO derivative modified fullerene, montmorillonite and graphite; the fiber fabric comprises one or more of glass fibers, carbon fibers, basalt fibers, aramid fibers and organic fibers. Through the synergistic effect of the specific DOPO derivative modified fullerene, montmorillonite and graphite, the flame retardant property of the polyamide composite material is remarkably improved, meanwhile, good mechanical property is kept, and the problem that in the prior art, the mechanical property is reduced due to the fact that the adding amount of a flame retardant is large is solved.

Description

Technical Field

[0001] The present application relates to the technical field of automobile battery box covers, and in particular to a polyamide flame-retardant composite material, a preparation method, and a battery box cover. Background Art

[0002] In recent years, the penetration rate of electric vehicles has increased rapidly, and the sales of new electric vehicles in China have reached 47.3% of the total sales of new cars. However, issues such as battery safety of electric vehicles are still widely concerned. Traditional battery box covers are mainly made of metal materials. However, due to their high weight, metal materials cannot meet the lightweight requirements of electric vehicles. Lightweight composite materials have become an important technological development trend for battery shells, especially composite top covers, which have been widely mass-produced and applied in mass-produced models on the market. Currently, the mainstream composite battery box covers on the market are mostly thermosetting composite materials. As the requirements for "carbon emission reduction" become increasingly stringent, the automotive industry will also be more inclined to use low-carbon materials. And as the technology development of the thermoplastic composite material industry becomes more mature, thermoplastic composite materials will become a key new material in the automotive industry.

[0003] Cast nylon (MC nylon) is a high-performance engineering plastic made from caprolactam monomer. It is poured into a mold under normal pressure in the presence of an alkaline catalyst and activator, where it rapidly polymerizes and cures through an anionic polymerization reaction. MC nylon exhibits high mechanical strength, good chemical resistance, and high thermal stability, making it widely used in many fields. Thermoplastic polyamide composites prepared by reinforcing MC nylon with fibers significantly improve its mechanical properties, such as tensile strength and flexural strength, and its application range is further expanding to load-bearing components. However, polyamides have poor inherent flame retardancy and are prone to burning at high temperatures, posing a fire hazard. Therefore, how to significantly improve the flame retardancy of polyamide while maintaining its excellent mechanical properties has become a pressing issue for researchers.

[0004] Currently, there are many patent reports on continuous fiber reinforced polyamide flame retardant composite materials, but there are still problems such as unsatisfactory flame retardant effect, significant reduction in mechanical properties of the flame retardant material, low molding efficiency, and high cost. Patent CN109957235B discloses a halogen-free flame retardant polyamide 6 polymer and its composite material and its preparation method. It uses a phosphazene flame retardant to prepare a continuous fiber reinforced flame retardant anionic polyamide 6 composite material with a flame retardancy rating of UL 94-V0 through an RTM process. However, the amount of phosphazene flame retardant added in this application is large, which will affect the mechanical properties of the material, and the molding process is relatively inefficient, which cannot meet the large-scale demand for automotive industry products. Summary of the Invention

[0005] The present application is made in view of the above-mentioned problems, and its purpose is to provide a polyamide flame-retardant composite material, a preparation method and a battery box cover. The composite material has excellent flame retardant properties and mechanical properties while maintaining the processability of thermoplastic composite materials, and can meet the requirements of automobile battery box covers for lightweight, high strength and flame retardancy.

[0006] Specifically as follows, the first aspect of the present application provides a polyamide flame retardant composite material, the composite material comprising a resin matrix and a fiber fabric, the resin matrix comprising a lactam monomer, a DOPO derivative-modified fullerene, montmorillonite, and graphite; The fiber fabric includes one or more of glass fiber, carbon fiber, basalt fiber, aramid fiber, and organic fiber.

[0007] Furthermore, the raw materials for preparing the DOPO derivative-modified fullerene include amino-modified fullerene and DOPO derivative.

[0008] Furthermore, the preparation method of the DOPO derivative-modified fullerene is as follows: fullerene is reacted with liquid ammonia to obtain a modified fullerene, and the surface of the modified fullerene is grafted with a DOPO derivative (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide), wherein the molar ratio of the modified fullerene to the DOPO derivative is 1:1.2.

[0009] Furthermore, the surface of the montmorillonite is covered with a tannic acid-iron ion chelate coating.

[0010] Furthermore, the modified montmorillonite is prepared by dispersing montmorillonite in a tannic acid aqueous solution, adding a FeCl3 solution to react, and forming a tannic acid-iron ion chelate coating.

[0011] Furthermore, the graphite includes modified expandable graphite.

[0012] Furthermore, the preparation method of the modified expandable graphite is: immersing the modified expandable graphite in a sodium lignin sulfonate solution, drying it, and then carbonizing it under nitrogen protection.

[0013] Furthermore, the lactam is caprolactam and / or laurolactam.

[0014] Furthermore, the mass percentage of the resin matrix is ​​30-60%; the mass percentage of the fiber fabric is 40-70%; and / or In the resin matrix, the mass percentage of DOPO derivative-modified fullerene is 0.1-5%, the mass percentage of montmorillonite is 0.1-5%, and the mass percentage of graphite is 15-30%.

[0015] The second aspect of the present application provides a method for preparing the polyamide flame retardant composite material, comprising the following steps: Mixing DOPO derivative-modified fullerene, montmorillonite, and a portion of lactam monomers, and adding a catalyst to prepare a first mixture; mixing graphite and the remaining portion of the lactam monomer, and then adding an activator to prepare a second mixture; Laying the fiber fabric into the mold, heating and pressurizing it to obtain a preform; The first mixture and the second mixture are mixed and then impregnated into a fiber preform, and then pressurized and cured.

[0016] Furthermore, the catalyst is one or more of lactam magnesium halide, alkali metal aluminum dilactam salt, alkali metal and / or alkali metal lactam salt, alkali metal hydroxide; and / or The activator is one or more of isocyanate, isocyanurate, biuret, allophanate, uretdione and carbodiimide, or a compound of the above activators and caprolactam.

[0017] Furthermore, the pressure of the pressurized curing is 10-20 MPa; and / or The temperature of press curing is 140~180℃; and / or The time for pressurized curing is 5 to 30 minutes.

[0018] The third aspect of the present application provides an application of the polyamide flame retardant composite material on a car battery box cover.

[0019] The present invention has the following beneficial effects: (1) This application significantly improves the flame retardant properties of polyamide composite materials through the synergistic effect of DOPO derivative-modified fullerene, modified montmorillonite and modified expandable graphite, while maintaining good mechanical properties, thereby solving the problem in the prior art of reduced mechanical properties due to the large amount of flame retardant added.

[0020] (2) This application uses modified fullerene, modified montmorillonite and modified expandable graphite as flame retardants. These flame retardants have good dispersibility and compatibility in the polyamide resin matrix. DOPO derivative-modified fullerene improves its dispersibility through amino modification and DOPO derivative grafting, introduces phosphorus and nitrogen elements, and forms an effective flame retardant barrier; modified montmorillonite improves its thermal stability and barrier properties through tannic acid-iron ion chelate coating; modified expandable graphite has a higher expansion multiple and better flame retardant effect after carbonization treatment. The synergistic effect of these flame retardants enables the composite material to form a dense carbon layer during combustion, effectively isolating oxygen and heat, thereby improving the flame retardant performance. These flame retardants work together in the resin matrix to form a multi-level and multi-dimensional flame retardant system, thereby significantly improving the flame retardant performance of the polyamide composite material.

[0021] Furthermore, the addition amounts of the DOPO derivative-modified fullerene, modified montmorillonite, and modified expandable graphite are precisely controlled, and exhibit excellent dispersibility and compatibility within the polyamide resin matrix. The synergistic flame retardant effect of these three flame retardants reduces the amount of flame retardant added and mitigates its impact on the mechanical properties of the composite. Furthermore, these flame retardants form strong interfacial interactions with the polyamide resin matrix, enhancing the overall mechanical properties of the composite.

[0022] (3) The polyamide flame-retardant composite material prepared in this application has excellent lightweight, high strength and flame-retardant properties, which can meet the high requirements of automobile battery box covers on material properties and provide a strong guarantee for the safety performance of electric vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present drawings or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present drawings. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0024] Figure 1 It is a structural diagram of the battery box cover.

[0025] The purpose, features and advantages of this drawing will be further described with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is described and illustrated below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are merely used to explain this application and are not intended to limit this application. Based on the embodiments provided in this application, all other embodiments obtained by those of ordinary skill in the art without making any creative work are within the scope of protection of this application.

[0027] Obviously, the following descriptions are merely some examples or embodiments of the present application. Those skilled in the art can apply the present application to other similar scenarios without inventive effort. Furthermore, it is also understood that, although the effort involved in such a development process may be complex and lengthy, for those skilled in the art related to the content disclosed in the present application, changes in design, manufacturing, or production based on the technical content disclosed in the present application are merely conventional technical means and should not be construed as an insufficiency of the content disclosed in the present application.

[0028] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0029] The first aspect of the present application provides a polyamide flame retardant composite material, which includes a resin matrix and a fiber fabric, wherein the resin matrix includes a lactam monomer, a DOPO derivative-modified fullerene, montmorillonite and graphite; the continuous fiber is one or more of glass fiber, carbon fiber, basalt fiber, aramid fiber and organic fiber.

[0030] The DOPO derivative-modified fullerene, montmorillonite, and graphite used as flame retardants in the resin matrix described above exhibit excellent dispersibility and compatibility within the polyamide resin matrix. The DOPO derivative-modified fullerene, through grafting with a DOPO derivative, introduces phosphorus and nitrogen, forming an effective flame-retardant barrier. The modified montmorillonite is enhanced with a tannic acid-iron ion chelate coating for improved thermal stability and barrier properties. The modified expandable graphite, after carbonization, exhibits a higher expansion ratio and enhanced flame retardancy. The synergistic effect of these flame retardants enables the composite material to form a dense char layer during combustion, effectively isolating oxygen and heat, thereby enhancing flame retardancy. These flame retardants work synergistically within the resin matrix, forming a multi-layered, multi-dimensional flame retardant system, significantly improving the flame retardancy of the polyamide composite.

[0031] Furthermore, the addition amounts of DOPO derivative-modified fullerenes, modified montmorillonite, and modified expandable graphite are precisely controlled, and exhibit excellent dispersibility and compatibility within the polyamide resin matrix. These flame retardants are uniformly distributed within the resin matrix, avoiding localized stress concentrations and thus maintaining the mechanical properties of the composite without degrading them. Furthermore, these flame retardants form strong interfacial interactions with the polyamide resin matrix, enhancing the overall mechanical properties of the composite.

[0032] In this embodiment, the raw materials for preparing the DOPO derivative-modified fullerene include amino-modified fullerene and DOPO derivative.

[0033] The preparation method of the DOPO derivative-modified fullerene is as follows: first, fullerene powder and liquid ammonia are placed in a sealed reactor and stirred at 20-80°C for 50-70 hours to ensure smooth modification reaction. After the reaction, excess ammonia is removed under reduced pressure, the solid product is washed three times with deionized water, and vacuum-dried at 40°C to obtain the modified fullerene. The modified fullerene is dispersed in anhydrous DMF, and the DOPO derivative is added at a molar ratio of 1:1.2. Triethylamine is added to maintain the pH at 7.8-8.3. Under nitrogen protection, the reaction is stirred at 120-130°C for 10-12 hours. The reaction solution is centrifuged, washed three times with ethanol and then acetone to remove unreacted DOPO derivative, and vacuum-dried at 60°C to obtain the DOPO derivative-modified fullerene.

[0034] The DOPO derivative was purchased from Shanghai Woentropy New Materials Co., Ltd., CAS NO: 99208-50-1.

[0035] In this embodiment, the surface of the montmorillonite is covered with a tannic acid-iron ion chelate coating.

[0036] The preparation method of montmorillonite comprises the following steps: adding 5 g of montmorillonite to 495 g of deionized water (solid content 1 wt%), and ultrasonically dispersing the mixture at 500 W for 30 minutes until no agglomerates are formed, thereby obtaining a montmorillonite dispersion; dissolving 25 g of tannic acid in 475 g of deionized water (solid content 5 wt%), and preheating the mixture at 60° C. until the mixture is completely dissolved; pouring the preheated tannic acid solution into the montmorillonite dispersion to obtain a mixed solution, and adding FeCl3 solution (2 g of FeCl3 dissolved in 20 mL of water) dropwise in a water bath at 60-62° C., continuously stirring the mixture for 2 hours, maintaining the pH at 3.5-4.0, vacuum filtering the mixture, and drying the mixture to obtain the modified montmorillonite.

[0037] In this embodiment, the graphite includes modified expandable graphite. The modified expandable graphite is prepared by: weighing 10g of sodium lignin sulfonate and dissolving it in 90g of deionized water, stirring in a 60°C water bath for 30 minutes until completely dissolved, and ultrasonically degassing for 10 minutes; immersing 20g of the modified expandable graphite in the sodium lignin sulfonate solution, dispersing it with 300W ultrasonic assisted technology for 15 minutes, stirring it at a low speed (200 rpm) at 60°C for 2 hours to ensure sufficient adsorption, vacuum filtering, and drying it at 80°C for 12 hours to constant weight; spreading the coated modified expandable graphite flat on an alumina crucible, heating it at a rate of 5°C / min to 300°C at a nitrogen flow rate of 50mL / min, holding it at that temperature for 1 hour, and then cooling it naturally to obtain the modified expandable graphite.

[0038] Furthermore, the lactam is caprolactam and / or laurolactam, preferably caprolactam.

[0039] The fiber fabric is woven from any one or more of glass fiber, carbon fiber, basalt fiber, aramid fiber, and organic fiber, and the weaving form is a mixture of any one or more of 2D, 2.5D, and 3D.

[0040] The second aspect of the present application provides a method for preparing the polyamide flame retardant composite material, comprising the following steps: Mixing DOPO derivative-modified fullerene, montmorillonite, and a portion of lactam monomers, and adding a catalyst to prepare a first mixture; mixing graphite and the remaining portion of the lactam monomer, and then adding an activator to prepare a second mixture; Laying the fiber fabric into the mold, heating and pressurizing it to obtain a preform; The first mixture and the second mixture are mixed and then impregnated into a fiber preform, and then pressurized and cured.

[0041] Specifically, (1) lactam monomers are added to reactors A and B respectively, heated to melt, and vacuum dehydrated; (2) Add the catalyst, DOPO derivative modified fullerene and montmorillonite to kettle A, stir evenly, and continue vacuum dehydration; add the activator and modified expandable graphite to kettle B, stir evenly, and continue vacuum dehydration; (3) Laying the fiber fabric into the preforming mold, heating and pressurizing to obtain a preform, and then transferring it to the forming mold; (4) The melts in kettles A and B are mixed evenly by a spray gun and then injected into a heated molding die under high pressure to fully infiltrate the fiber preform, and then pressurized and cured to obtain a polyamide flame retardant composite material.

[0042] The mass content of the above-mentioned resin matrix is ​​30-60%, the mass content of the catalyst in the resin matrix is ​​0.1-4%, the mass content of the activator in the resin matrix is ​​0.1-4%, the mass content of the DOPO derivative-modified fullerene in the resin matrix is ​​0.1-5%, the mass content of montmorillonite in the resin matrix is ​​0.1-5%, the mass content of graphite in the resin matrix is ​​15-30%, and the mass content of the fiber fabric is 40-70%.

[0043] In step (1), lactam monomers are added to reactors A and B respectively, wherein the mass ratio of the lactam monomers in reactor A to reactor B is 1:0.8-1.2. Preferably, the amount ratio of the lactam monomers in reactor A to reactor B is 1:1.

[0044] The melting temperature of the lactam monomer ranges from 80°C to 140°C. Specifically, the resin mixture should be heated to any temperature before injection, ranging from 80°C, 85°C, 90°C, 100°C, 110°C, 120°C, 130°C, or 140°C. Too low a temperature will result in poor resin fluidity and difficulty fully penetrating the fiber layer; too high a temperature may cause the resin to cure prematurely, affecting the overall performance of the composite material. During the injection process, temperature and pressure must be strictly controlled to ensure uniform resin distribution and form a dense structure.

[0045] In this embodiment, the catalyst in step (2) is one or more of lactam magnesium halide, alkali metal aluminum dilactam salt, alkali metal and / or alkali metal lactam salt, alkali metal hydroxide; and / or Furthermore, the lactam magnesium halide is preferably lactam magnesium bromide; the alkali metal aluminum dilactam salt is preferably sodium dilactam; the alkali metal and / or alkali metal lactam salt is preferably sodium lactam, potassium lactam and / or magnesium lactam; and the alkali metal hydroxide is preferably a mixture of one or more of sodium hydroxide and magnesium hydroxide.

[0046] In this embodiment, the activator is one or more of isocyanate, isocyanurate, biuret, allophanate, uretdione and carbodiimide, or a compound of the above activators and caprolactam.

[0047] The lactam monomer was added into a reactor, melted at 80-140°C, then vacuumed to -0.098 MPa, dehydrated for 30 minutes, and nitrogen was filled into the reactor to normal pressure; then the catalyst, modified fullerene and modified montmorillonite were added into reactor A; the activator and modified expandable graphite were added into reactor B, and the mixtures were stirred evenly, vacuumed to -0.098 MPa, dehydrated for 30 minutes, and nitrogen was filled into the reactor to normal pressure to obtain material A and material B respectively.

[0048] In step (3), the fiber fabric is laid in a specific order into the preforming mold to prepare the preform. The specific preparation process of the preform is as follows: a 600g / m 2 Warp-knitted fabrics such as ±45° glass fiber, carbon fiber, or basalt fiber are cut into specific shapes and quantities and laid in a pre-forming mold in the order of layering. A setting agent is used between each layer of fabric to set the shape, ensuring that the fibers are arranged in the mold according to the predetermined direction and density, thereby optimizing the mechanical properties and structural stability of the composite material. Through this step, a preform with a predetermined shape and structure is obtained for subsequent thermoplastic resin infiltration and curing molding. The pre-forming mold is closed, heated to 105-115°C, and pressurized to 1.8-2.2MPa. The molding time is 15-30 minutes, so that the multiple layers of fabric are bonded into a whole to obtain a preform.

[0049] In an embodiment of the present invention, the resin melt in the A and B reactors is infiltrated into the preform, and the resin temperature and injection pressure are precisely controlled to ensure that the resin can be evenly and quickly infiltrated into every part of the fiber preform. A high-pressure glue injection machine is used to mix the A material and the B material in the A and B reactors in the injection gun head. The temperature of the injection gun head is 80~140℃. After the A material and the B material are mixed, they are immediately injected into the mold. After the injection is completed, the molding pressure is increased to 10~20MPa to ensure that the resin is tightly combined with the fiber preform. Finally, through the pressurized curing process, the composite material battery box cover is cured at a temperature of 140~180℃ for 5~30min to fully cure the resin and form a battery box cover with excellent mechanical properties.

[0050] Furthermore, in step (4), the mold clamping pressure before injection is lower than 0.5 MPa, the mold is evacuated to a vacuum degree of -0.098 MPa, and the injection pressure is 0.1-20 MPa; after the injection is completed, the molding pressure is increased to 10-20 MPa. The vacuuming process effectively eliminates bubbles and ensures that there are no defects inside the material. The pressurization after injection allows the resin to fully penetrate, further improving the density and strength of the composite material.

[0051] The pressurized curing process is performed at a pressure of 10-20 MPa, a temperature of 140-180°C, and a duration of 5-30 minutes. The curing temperature is preferably 165°C for 10 minutes. Under these conditions, the resin is fully cured and the fiber structure is stable, ensuring the battery case cover has excellent mechanical properties and long-term stability. After curing, the product is cooled to room temperature and demolded.

[0052] The third aspect of the present application provides an application of the polyamide flame retardant composite material on a car battery box cover.

[0053] The polyamide flame retardant composite material can be made into an automobile battery box cover by a mold, and can then be used in an automobile battery box.

[0054] The battery box cover is made of the above-mentioned polyamide flame-retardant composite material, and has the characteristics of light weight, high strength, excellent flame retardant performance, etc., and can meet the high requirements of electric vehicles for battery box covers.

[0055] Example The following examples describe the present disclosure in more detail and are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight. Unless otherwise stated, all reagents used in the examples are available through conventional commercial sources or synthesized according to conventional methods and can be used directly without further processing. Unless otherwise stated, all instruments used in the examples are available through conventional commercial sources.

[0056] Example 1 The preparation method of the polyamide flame retardant composite material comprises the following steps: S1: Use the blanking machine to cut 600g / m 2 The glass fibers with an angle of ±45° are cut into specific shapes and quantities and laid in a pre-formed mold in a specific laying order. A setting agent is used between each layer of fabric to set the shape. S2: The preforming mold is closed, heated to 110°C, pressurized to 2.2 MPa, and formed for 20 minutes to bond the multiple layers of fabric into a whole to obtain a preform; S3: Divide 1225g of caprolactam into two equal parts, add them into reactors A and B respectively, heat to 125℃ for melting, then evacuate to remove moisture, the vacuum degree is -0.098MPa, the evacuation time is 30min, and then fill the reactor with nitrogen to normal pressure.

[0057] S4: Add sodium hydroxide, DOPO derivative-modified fullerene, and montmorillonite to kettle A, stir evenly, and continue vacuum dehydration with a vacuum degree of -0.098 MPa for 30 minutes; add 2,4-diisocyanate toluene and graphite to kettle B, stir evenly, and continue vacuum dehydration with a vacuum degree of -0.098 MPa for 30 minutes; then fill kettles A and B with nitrogen to normal pressure.

[0058] S5: Heat the mold to 165°C and spray a release agent inside the mold; S6: Place the preform into the cavity of the preheated mold and close the mold. Control the closing pressure at 0.45 MPa, then evacuate the mold cavity to a vacuum degree of -0.098 MPa. Use a high-pressure injection machine to mix material A and material B in the A and B kettles in a ratio of 1:1 in the injection gun head. The injection gun head temperature is 90°C. After the material A and material B are mixed, they are immediately injected into the mold at an injection pressure of 5 MPa. After the injection is completed, the molding pressure is increased to 15 MPa to solidify the preform. S6: The molding temperature is 165°C, the molding time is 10 minutes, and the mold is removed.

[0059] Example 2 This embodiment uses substantially the same raw materials and molding process as that of embodiment 1, with the following differences: the weight of the caprolactam monomer is 1155 g; the weight of the graphite is 210 g, and its mass content in the resin melt is 15%.

[0060] Example 3 This embodiment uses substantially the same raw materials and molding process as that of embodiment 1, with the following differences: the weight of the caprolactam monomer is 1085 g; the weight of the graphite is 280 g, and its mass content in the resin melt is 20%.

[0061] Example 4 This embodiment uses substantially the same raw materials and molding process as that of embodiment 1, except that the monomer is bis-acylated lactam-1,6-hexanediamine, which weighs 1155 g; the weight of graphite is 210 g, and its mass content in the resin melt is 15%.

[0062] Example 5 This embodiment uses the same raw materials and molding process as embodiment 1, except that: the weight of the caprolactam monomer is 906g; the continuous fiber is 600g / m 2 ±45° carbon fiber; the weight of DOPO derivative modified fullerene is 5.5g, and its mass content in the resin melt is 0.5%; the weight of montmorillonite is 11g, and its mass content in the resin melt is 1%; the weight of graphite is 165g, and its mass content in the resin melt is 15%.

[0063] Comparative Example 1 This comparative example uses substantially the same raw materials and molding process as Example 1, except that the weight of the caprolactam monomer is 1386 g; and no DOPO derivative-modified fullerene, montmorillonite, or graphite is added.

[0064] Comparative Example 2 This comparative example uses substantially the same raw materials and molding process as Example 1, except that: the weight of the caprolactam monomer is 1365 g; the weight of the DOPO derivative-modified fullerene is 7 g, and its mass content in the resin melt is 0.5%; the weight of montmorillonite is 14 g, and its mass content in the resin melt is 1%; and no graphite is added.

[0065] Comparative Example 3 This comparative example uses substantially the same raw materials and molding process as Example 1, except that: the weight of the caprolactam monomer is 1176 g; no DOPO derivative-modified fullerene and montmorillonite are added; and the weight of graphite is 210 g, with its mass content in the resin melt being 15%.

[0066] Comparative Example 4 This comparative example uses substantially the same raw materials and molding process as Example 1, except that: the weight of the caprolactam monomer is 966 g; no DOPO derivative-modified fullerene and montmorillonite are added; and the weight of graphite is 420 g, with its mass content in the resin melt being 30%.

[0067] Comparative Example 5 This comparative example is basically the same as Example 2, except that unmodified fullerene, montmorillonite and graphite are used instead of DOPO derivative modified fullerene, modified montmorillonite and modified expandable graphite.

[0068] Composite materials were prepared according to the methods of Examples 1-5 and Comparative Examples 1-5. The amounts of raw materials used in each example are shown in Table 1. Corresponding performance tests were performed according to national standards. The results are shown in Table 2.

[0069]

[0070] The mechanical properties and flame retardant properties of the composite battery box covers of the embodiments and comparative examples are shown in Table 2.

[0071]

[0072] Combining Table 1 and Table 2, it can be seen from Examples 1-5 that as the amount of expandable graphite as a flame retardant increases, the flame retardant properties of the composite material improve, but the mechanical properties of the material decrease.

[0073] As can be seen from Examples 1-4 and Comparative Example 1, while no flame retardant was added in Comparative Example 1, the flame retardant content added in Examples 1-4 significantly improved the flame retardant properties of the composite material, but the mechanical properties were correspondingly reduced. Comparative Examples 1-4 show that the flame retardant effect of the composite material was poor when no flame retardant was added, when only DOPO derivative-modified fullerenes and modified montmorillonite were added, or when only expandable graphite was added. Furthermore, as can be seen from Comparative Examples 3 and 4, increasing the amount of expandable graphite added did not improve the flame retardant effect, remaining at only V2. Instead, the mechanical properties significantly decreased. This is because expandable graphite has poor dispersibility in the composite material, and excessive addition can cause it to agglomerate in the matrix resin, thereby affecting the mechanical properties of the composite material. In Example 2-3, the flame retardants DOPO derivative-modified fullerene, modified montmorillonite, and expandable graphite were added simultaneously, achieving a flame retardant effect of V0 while maintaining essentially unchanged mechanical properties. This may be due to the synergistic flame retardancy of the modified fullerene and modified montmorillonite within the composite material, effectively improving the thermal stability and flame retardancy of the composite material. Due to its unique structure and chemical properties, the DOPO derivative-modified fullerene can form a char layer at high temperatures, isolating oxygen and thus preventing the spread of flames. The modified montmorillonite absorbs heat, lowering the combustion temperature of the composite material, while its layered structure also prevents flame penetration. The synergistic effect between the DOPO derivative-modified fullerene, modified montmorillonite, and expandable graphite significantly improves the flame retardancy while maintaining a low dosage of expandable graphite, while not significantly impacting the mechanical properties of the composite material.

[0074] Furthermore, the addition of DOPO derivative-modified fullerene and modified montmorillonite had little effect on the mechanical properties of the composites. This may be because the modified fullerenes and modified montmorillonite have better dispersion in the composites, forming a good interface with the matrix resin, thus maintaining the mechanical properties of the composites.

[0075] From Comparative Example 5, it can be seen that when unmodified fullerene, montmorillonite and expandable graphite are used as flame retardants, the mechanical properties of the material are reduced and the flame retardant effect is poor because the fullerene, montmorillonite and expandable graphite cannot be well dispersed in the resin.

[0076] In summary, the combined use of modified fullerene, modified montmorillonite and expandable graphite can achieve the purpose of synergistic flame retardancy, reduce the amount of expandable graphite added, reduce the impact on the mechanical properties of the material, and balance the flame retardancy level and mechanical properties.

[0077] The polyamide flame-retardant composite battery box cover and its preparation method provided by the present invention not only solve the problem of balancing the mechanical properties and flame-retardant properties of the battery box cover in the prior art, but also achieve the goal of recyclable, environmentally friendly and efficient production, which is of great significance for promoting the lightweight process and energy conservation and emission reduction in the automotive industry.

[0078] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A polyamide flame retardant composite material, characterized in that: The composite material comprises a resin matrix and fiber fabrics, wherein the resin matrix comprises lactam monomer, DOPO derivative-modified fullerene, montmorillonite and graphite.

2. The polyamide flame retardant composite material according to claim 1, characterized in that: The raw materials for preparing the DOPO derivative-modified fullerene include amino-modified fullerene and DOPO derivative.

3. The polyamide flame retardant composite material according to claim 1, characterized in that: The surface of the montmorillonite is covered with a tannic acid-iron ion chelate coating.

4. The polyamide flame retardant composite material according to claim 1, characterized in that: The graphite includes modified expandable graphite.

5. The polyamide flame retardant composite material according to claim 1, characterized in that: The lactam is caprolactam and / or laurolactam.

6. The polyamide flame retardant composite material according to claim 1, characterized in that: The mass percentage of the resin matrix is ​​30-60%; the mass percentage of the fiber fabric is 40-70%; and / or In the resin matrix, the mass percentage of DOPO derivative-modified fullerene is 0.1-5%, the mass percentage of montmorillonite is 0.1-5%, and the mass percentage of graphite is 15-30%.

7. A method for preparing the polyamide flame retardant composite material according to any one of claims 1 to 6, characterized in that: The following steps are involved: Mixing DOPO derivative-modified fullerene, montmorillonite, and a portion of lactam monomers, and adding a catalyst to prepare a first mixture; mixing graphite and the remaining portion of the lactam monomer, and then adding an activator to prepare a second mixture; Laying the fiber fabric into the mold, heating and pressurizing it to obtain a preform; The first mixture and the second mixture are mixed and then impregnated into a fiber preform, and then pressurized and cured.

8. The method for preparing the polyamide flame retardant composite material according to claim 7, characterized in that: The catalyst is one or more of lactam magnesium halide, alkali metal aluminum dilactam salt, alkali metal and / or alkali metal lactam salt, alkali metal hydroxide; and / or The activator is one or more of isocyanate, isocyanurate, biuret, allophanate, uretdione and carbodiimide, or a compound of the above activators and caprolactam.

9. The method for preparing the polyamide flame retardant composite material according to claim 7, characterized in that: The pressure of the pressurized curing is 10-20 MPa; and / or The temperature of press curing is 140~180℃; and / or The time for pressurized curing is 5 to 30 minutes.

10. Use of the polyamide flame retardant composite material according to any one of claims 1 to 6 in a car battery box cover.

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