Preparation method of new energy battery pack cover plate flame-retardant PP material

Abstract

The invention discloses a preparation method of a new energy battery pack cover plate flame-retardant PP material, and relates to the technical field of polymer flame-retardant materials. The preparation method comprises the following steps: sequentially adding phosphate esterified polypropylene, a maleic anhydride grafted polyolefin elastomer, polyether block amide, modified nano clay, a B-P-triazinyl charring agent, a carbodiimide type anti-hydrolysis agent, a hindered phenol antioxidant, short carbon fibers, polytetrafluoroethylene micro powder and modified hollow glass beads into a mixing mill; and adding the obtained premix into a twin-screw extruder, extruding, pelletizing, and carrying out injection molding to obtain the flame-retardant PP material for the cover plate of the new energy battery pack. The prepared new energy battery pack cover plate flame-retardant PP material has excellent mechanical performance, flame retardance, thermal stability, dimensional stability and antistatic performance, is light in weight, and has wide application prospects in the fields of new energy automobiles, energy storage systems, consumer electronics, aerospace and industrial equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer flame retardant materials, and specifically to a preparation method of a flame retardant PP material for a new energy battery pack cover plate. Background Art

[0002] In recent years, with the rapid development of new energy vehicles and energy storage devices, higher requirements have been put forward for the flame retardancy, heat resistance, and lightweight properties of battery pack encapsulation materials. Traditional polypropylene (PP)-based materials are widely used due to their excellent processing performance and cost advantages, but their inherent flammability limits their application in high-safety scenarios. Existing technologies mostly improve the flame retardancy level by adding halogen-based, phosphorus-nitrogen-based, or intumescent flame retardants. However, such externally added components are prone to cause problems such as deterioration of the mechanical properties of the material, decrease in processing fluidity, and migration and precipitation of the flame retardant during long-term use. Especially in high-humidity or electrolyte-exposed environments, hygroscopic flame retardants (such as ammonium polyphosphate) are prone to side reactions with the electrolyte, resulting in the failure of the electrical insulation of the material and even the risk of short-circuiting the battery system. In addition, there is a contradiction between conventional flame retardant modification and lightweight design. High-filled flame retardant systems often lead to a significant increase in the density of the material, making it difficult to meet the urgent need of new energy vehicles for component weight reduction.

[0003] On the other hand, the battery pack cover plate material needs to balance rigidity, creep resistance, and fatigue resistance under complex working conditions, and traditional modification technologies are difficult to achieve the co-optimization of multiple properties. For example, when enhancing rigidity with inorganic fillers, the toughness may drop suddenly, while elastomer toughening may sacrifice dimensional stability and heat resistance. Existing material systems are prone to problems such as interface delamination and stress cracking under harsh conditions such as long-term electrolyte infiltration, mechanical vibration, and thermal cycling, affecting the overall reliability of the battery system. In addition, single-functional design is difficult to simultaneously meet the composite property requirements such as antistatic and chemical corrosion resistance, and the poor interfacial compatibility during multi-component compounding further restricts the improvement of the comprehensive properties of the material. Therefore, developing a polypropylene-based composite material with intrinsic flame retardancy, lightweight, and balanced multiple properties has become a technical problem that urgently needs to be solved in the battery encapsulation field. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a flame retardant PP material for a new energy battery pack cover plate to solve the problems raised in the background art.

[0005] To achieve the above purpose, the present invention provides the following technical solutions: A flame retardant PP material for a new energy battery pack cover plate is made of the following raw materials counted by weight parts: Phosphoric acid esterified polypropylene 60 - 70 parts; B-P-triazine-based charring agent 5 - 8 parts; Modified nano-clay 3 - 5 parts; 8 - 12 parts of chopped carbon fiber; 5 - 8 parts of maleic anhydride grafted polyolefin elastomer; 1 - 2 parts of polytetrafluoroethylene micro powder; 2 - 4 parts of polyether block amide; 5 - 8 parts of modified hollow glass microspheres; 0.5 - 1 part of carbodiimide type anti - hydrolytic agent; 0.3 - 0.5 part of hindered phenol antioxidant.

[0006] The preparation steps of the phosphorylated polypropylene are as follows: A1. Under an inert atmosphere, at 70 °C, mix Rac - ethylenebis(4,5,7 - trihydroxy - 1 - indenyl) zirconium dichloride, methylaluminoxane, triisobutylaluminum, hexane and toluene, add 11 - bromo - 1 - undecene and introduce propylene gas, and react for 0.5 - 2 h to obtain PP - Br; Further, the dosage ratio of Rac - ethylenebis(4,5,7 - trihydroxy - 1 - indenyl) zirconium dichloride, methylaluminoxane, triisobutylaluminum, hexane, 11 - bromo - 1 - undecene, propylene and toluene is (0.02 - 0.05) g:(35 - 70) mL:(5 - 10) mL:(400 - 500) mL:(15 - 20) g:(32.5 - 72.2) mL:(50 - 100) mL.

[0007] A2. Under an inert atmosphere, at 120 - 180 °C, PP - Br and phosphite compound are melt - copolymerized under stirring at a speed of 500 - 800 r / min to undergo the Arbuzov reaction, and react for 6 - 60 h to obtain phosphorylated polypropylene.

[0008] Further, the mass ratio of PP - Br to phosphite compound is 100:(38.4 - 77.6).

[0009] Further, the phosphite compound is triisopropyl phosphite or triphenyl phosphite.

[0010] Further, when the phosphite compound is triisopropyl phosphite (alkyl phosphite), the reaction conditions are reaction at 120 - 140 °C for 6 - 8 h; when the phosphite compound is triphenyl phosphite, the reaction conditions are reaction at 160 - 180 °C for 48 - 60 h.

[0011] It should be noted that in step A1, propylene and 11-bromo-1-undecene undergo copolymerization under the action of a metallocene catalyst to introduce a bromoalkyl side chain, obtaining PP-Br; in step A2, the C-Br bond of PP-Br reacts with the phosphite of a phosphite compound through the Arbuzov reaction, and nucleophilic substitution generates a phosphate bond, introducing a -PO(OR)2 group (R = isopropyl or phenyl) into the side chain, obtaining a phosphate-functionalized polypropylene.

[0012] It should be noted that the phosphate groups in the phosphorylated polypropylene can be rapidly catalytically carbonized at the battery thermal runaway temperature (300 - 500 °C) to form an expanded carbon layer, isolating oxygen and heat; the non-polar main chain of PP is resistant to the electrolyte, and the phosphate groups reduce the surface energy (the contact angle increases), reducing the penetration of the electrolyte; the nanoclay platelets and the phosphate esters cooperate to inhibit size shrinkage, and the coefficient of thermal expansion decreases, meeting the tolerance requirements of precision components.

[0013] It should be noted again that compared with directly physically adding traditional flame retardants such as ammonium polyphosphate (APP) to polypropylene plastics, the phosphorylated polypropylene prepared in the present invention is covalently bonded with phosphorus elements, has a high catalytic carbonization efficiency, no small molecule migration, and more persistent flame retardancy. However, APP is easy to migrate and precipitate in polypropylene, and a high addition amount is required to ensure the flame retardancy efficiency, and the flame retardancy performance will decline over time; the polar groups in the phosphorylated polypropylene enhance the interfacial bonding force and improve the mechanical strength of the plastic matrix, while the addition of APP will cause a decrease in the mechanical strength of the matrix; there are no moisture-absorbing groups in the phosphorylated polypropylene, and the heat aging performance is stable, while APP has strong hygroscopicity and is easy to cause plastic failure; the melt fluidity of the phosphorylated polypropylene is controllable and has good compatibility with inorganic fillers, while a high addition amount of APP (to ensure the flame retardancy efficiency) in polypropylene will lead to poor fluidity and difficult processing.

[0014] Furthermore, the preparation steps of the B-P-triazine-based charring agent are as follows: B1. Dissolve hydroxyvanillin in methanol, heat to 60 °C under stirring, slowly drop the aminophenylboronic acid / methanol solution within 15 min, adjust the pH to 5 - 6, reflux for 4 - 8 h, naturally cool to room temperature, filter, wash, and dry in an air circulation oven at 120 °C for 2 h and then in a vacuum oven at 160 °C for 4 h to obtain an intermediate; Furthermore, in step B1, the dosage ratio of the hydroxyvanillin, methanol, and aminophenylboronic acid / methanol solution is (125 - 130) g:500 mL:100 mL; Furthermore, in step B1, the aminophenylboronic acid / methanol solution is prepared by dissolving aminophenylboronic acid in methanol, and the dosage ratio of the aminophenylboronic acid and methanol is (90 - 96) g:100 mL; B2. Disperse the intermediate in N,N-dimethylformamide, add sodium carbonate, stir for 10 min, slowly dropwise add the cyanuric chloride / N,N-dimethylformamide solution within 10 min, and react at 0 - 5 °C for 2 h; Further, in step B2, the dosage ratio of the intermediate, N,N-dimethylformamide, sodium carbonate and the cyanuric chloride / N,N-dimethylformamide solution is (180 - 220) g : (180 - 220) mL : (45 - 55) g : 100 mL; Further, in step B2, the cyanuric chloride / N,N-dimethylformamide solution is prepared by dissolving cyanuric chloride in N,N-dimethylformamide, and the dosage ratio of cyanuric chloride and N,N-dimethylformamide is (25 - 30) g : 100 mL; B3. Heat the reaction system to 65 °C, dissolve bis[4-(3-aminophenoxy)phenyl]phenylphosphine oxide in N,N-dimethylformamide, slowly dropwise add it to the mixed solution obtained in B2 within 15 min, and react at 65 °C for 2 h; Further, in step B3, the dosage ratio of bis[4-(3-aminophenoxy)phenyl]phenylphosphine oxide, N,N-dimethylformamide and the mixed solution obtained in B2 is (6 - 7) g : 100 mL : (560 - 640) mL; B4. Heat the reaction system to 95 °C, dissolve bis[4-(3-aminophenoxy)phenyl]phenylphosphine oxide in N,N-dimethylformamide, slowly dropwise add it to the mixed solution obtained in B3 within 10 min, react at 95 °C for 4 h, cool to room temperature, filter, wash with deionized water at 80 °C until neutral, dry in an air circulation oven at 120 °C for 2 h, and dry in a vacuum oven at 165 °C for 2 h to obtain the B-P-triazine-based charring agent.

[0015] Further, in step B4, the dosage ratio of bis[4-(3-aminophenoxy)phenyl]phenylphosphine oxide, N,N-dimethylformamide and the mixed solution obtained in B3 is (12.4 - 13.4) g : 100 mL : (660 - 740) mL.

[0016] It should be noted that in step B1, the aldehyde group of hydroxyvanillin and the amino group of aminophenylboronic acid undergo Schiff base condensation to obtain an intermediate; in step B2, the hydroxy group of the intermediate undergoes a monosubstitution reaction with cyanuric chloride; in steps B3 and B4, the monosubstituted product obtained in B2 undergoes a nucleophilic substitution reaction with the amino groups on two bis[4-(3-aminophenoxy)phenyl]phenylphosphine oxide molecules to generate a B-P-triazine-based charring agent with alternating phosphorus-triazine and boron-containing side-chain repeating units. The triazine ring serves as the flame-retardant core of the B-P-triazine-based charring agent, decomposing at high temperatures to release nitrogen-containing free radicals, catalyzing char formation and diluting combustible gases; the phosphorus-triazine bridging structure forms a chain-like / lamellar structure, inhibiting melt dripping and enhancing the strength of the char layer; the imine bond and benzene ring are also further destroyed during combustion and transformed into a carbon skeleton. In addition, during high-temperature combustion, the boric acid group in the side chain dehydrates to form boron oxide, forming a molten glass layer that combines with the PO· free radicals released by the decomposition of phosphorus-triazine to form a B-P-O crosslinked network, inhibiting soot release.

[0017] Further, the modified nano-clay is surface-modified with a long-chain quaternary ammonium salt, with a particle size of 50 - 200 nm and a lamellar thickness of 2 - 5 nm.

[0018] It should be noted that after modification, the interlayer spacing of the nano-clay is enlarged, the compatibility with the PP matrix is improved, an intercalated-crosslinked char layer is formed with phosphoric acid esterified polypropylene, and at the same time, the lamellar structure can delay thermal decomposition and thermal shrinkage, improving the thermal stability and dimensional stability of the flame-retardant PP material.

[0019] Further, the short carbon fiber has a fiber length of 3 - 6 mm and an aspect ratio of 50 - 100.

[0020] It should be noted that the short carbon fiber can ensure uniform dispersion of the matrix during injection molding, improve the mechanical properties of the flame-retardant PP material, and disperse the matrix stress.

[0021] Further, the grafting rate of the maleic anhydride-grafted polyolefin elastomer is 0.8 - 1.2%.

[0022] It should be noted that the maleic anhydride-grafted polyolefin elastomer can effectively improve the interfacial bonding between the flame-retardant PP material and non-polar fillers, improve toughness to avoid brittle fracture, and enhance the impact resistance.

[0023] Further, the particle size of the polytetrafluoroethylene micropowder is 5 - 30 μm.

[0024] It should be noted that the polytetrafluoroethylene micropowder can inhibit the melt dripping phenomenon during combustion in the plastic matrix, and at the same time, its low surface energy can reduce the penetration of the new energy battery electrolyte.

[0025] Further, the polyether / polyamide block ratio in the polyether block amide is (6 - 7):(3 - 4).

[0026] It should be noted that the polyether block amide can eliminate the static electricity risk in the plastic matrix, improve the antistatic performance, and enhance the toughness of the flame-retardant PP material at low temperatures (above -40°C). Furthermore, the modified hollow glass microspheres are surface-modified with a silane coupling agent and have a particle size of 65 - 125 μm.

[0027] It should be noted that surface modification enhances the compatibility with the plastic matrix, reduces the density of the plastic matrix to make it lightweight, and at the same time, the rigid microspheres inhibit the shrinkage and deformation of the plastic matrix.

[0028] Furthermore, the molecular weight of the hindered phenol antioxidant is greater than 1000.

[0029] It should be noted that antioxidants with a large molecular weight can reduce the migration and precipitation of antioxidants in the plastic matrix and improve the thermal stability of the flame-retardant PP material.

[0030] A preparation method of a flame-retardant PP material for a new energy battery pack cover plate includes the following steps: S1. Add phosphoric acid esterified polypropylene, maleic anhydride grafted polyolefin elastomer, and polyether block amide into a mixer at 180°C and mix for 5 min at a rotation speed of 50 - 300 r / min; S2. Under a nitrogen atmosphere, add the modified nano-clay in batches, premix and add the B-P-triazine-based charring agent and the carbodiimide type anti-hydrolysis agent, add the hindered phenol antioxidant, and mix for 8 min at a rotation speed of 200 r / min; S3. Cool down to 160°C, add the short carbon fiber through a side feeder, premix the polytetrafluoroethylene micro-powder and the modified hollow glass microspheres and evenly sprinkle them through a vibrating sieve, mix for 3 min at a rotation speed of 100 r / min, and carry out vacuum degassing for 30 - 60 s to obtain a premixed material; S4. Add the premixed material into a twin-screw extruder at a temperature of 170 - 200°C and a screw rotation speed of 200 - 300 rpm, cool and pelletize with 25°C water, centrifuge, and screen to obtain a blended pellet; S5. Add the blended pellet into a servo-electric injection molding machine, set the melt temperature at 190 - 200°C, the mold temperature at 60°C, the injection speed at 30 - 50 mm / s, the holding pressure at 60 - 80 MPa, the holding time at 8 s, and the cooling time at 25 s, demold after injection molding to obtain the flame-retardant PP material for the new energy battery pack cover plate.

[0031] Compared with the prior art, the present invention has the following beneficial effects: The flame-retardant PP material for the cover plate of the new energy battery pack prepared by the present invention has excellent mechanical properties, flame retardancy, thermal stability, dimensional stability and antistatic properties, and is lightweight. Through the synergy of phosphoric acid esterified polypropylene and B-P-triazine-based charring agent, intrinsic flame retardancy is achieved without adding traditional flame retardant APP, avoiding hygroscopicity, migration and side reactions with the electrolyte, and having broad application prospects in the fields of new energy vehicles, energy storage systems, consumer electronics, aerospace and industrial equipment. Detailed implementation manners

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] (1) The preparation steps of phosphoric acid esterified polypropylene are as follows: A1. Under an inert atmosphere, at 70 °C, 0.05 g of Rac-ethylenebis(4,5,7-trihydroxy-1-indenyl)zirconium dichloride, 70 mL of methylaluminoxane, 10 mL of triisobutylaluminum, 500 mL of hexane and 20 mL of toluene are mixed, 72.2 mL of 11-bromo-1-undecene is added and 100 mL of propylene gas is introduced, and the reaction is carried out for 1 h to obtain PP-Br; A2. Under an inert atmosphere, at 140 °C, 100 g of PP-Br and 38.4 g of triisopropyl phosphite are reacted under stirring at a rotation speed of 600 r / min for 8 h to obtain phosphoric acid esterified polypropylene.

[0034] (2) The preparation steps of the B-P-triazine-based charring agent are as follows: B1. 93 g of aminophenylboronic acid is dissolved in 100 mL of methanol to prepare an aminophenylboronic acid / methanol solution. 128 g of hydroxyvanillin is dissolved in 500 mL of methanol, heated to 60 °C under stirring, 100 mL of the aminophenylboronic acid / methanol solution is slowly added dropwise within 15 min, the pH is adjusted to 5.5, refluxed for 6 h, naturally cooled to room temperature, filtered, washed, dried in an air circulation oven at 120 °C for 2 h, and dried in a vacuum oven at 160 °C for 4 h to obtain an intermediate; B2. 28 g of cyanuric chloride is dissolved in 100 mL of N,N-dimethylformamide to prepare a cyanuric chloride / N,N-dimethylformamide solution. 200 g of the intermediate is dispersed in 200 mL of N,N-dimethylformamide, 50 g of sodium carbonate is added, stirred for 10 min, 100 mL of the cyanuric chloride / N,N-dimethylformamide solution is slowly added dropwise within 10 min, and the reaction is carried out at 0 °C for 2 h; B3. Heat the reaction system to 65 °C. Dissolve 6.5 g of bis[4-(3-aminophenoxy)phenyl]phenylphosphine oxide in 100 mL of N,N-dimethylformamide, and slowly drop the resulting mixed solution into 560 mL of B2 within 15 min. React at 65 °C for 2 h. B4. Heat the reaction system to 95 °C. Dissolve 12.9 g of bis[4-(3-aminophenoxy)phenyl]phenylphosphine oxide in 100 mL of N,N-dimethylformamide, and slowly drop the resulting mixed solution into 660 mL of B3 within 10 min. React at 95 °C for 4 h, cool to room temperature, filter, wash with deionized water at 80 °C until neutral, dry in an air circulation oven at 120 °C for 2 h, and dry in a vacuum oven at 165 °C for 2 h to obtain the B-P-triazine-based charring agent.

[0035] (3) The preparation steps of the modified nano-clay are as follows: Dissolve 8.5 g of cetyltrimethylammonium bromide in a mixed solution of 100 mL of ethanol and deionized water with a volume ratio of 1:1 under a water bath at 60 °C, and adjust the pH to 5 to obtain a quaternary ammonium salt solution. Disperse 50 g of nano-clay in 500 mL of deionized water, stir at a speed of 1000 r / min at 60 °C for 2 h, centrifuge, and take the upper suspension. Slowly add 20 mL of the quaternary ammonium salt solution to 100 mL of the suspension, stir and react for 12 h, centrifuge, wash, dry at 60 °C for 24 h, pulverize with a ball mill, and pass through a 200-mesh sieve to obtain the modified nano-clay.

[0036] (4) The preparation steps of the modified hollow glass microspheres are as follows: Disperse 10 g of hollow glass microspheres in 100 mL of a hydrochloric acid solution with a mass fraction of 5%, perform ultrasonic treatment for 30 min, centrifuge, wash until neutral, and dry at 80 °C for 12 h. Add 3 g of silane coupling agent KH550 to a mixed solution of 100 mL of ethanol and deionized water with a volume ratio of 9:1, adjust the pH to 4, and stir for 1 h to prepare a hydrolysis solution. Add the pretreated 10 g of hollow glass microspheres to 100 mL of the hydrolysis solution, stir at 60 °C under a water bath for 6 h, centrifuge, wash, dry at 60 °C for 12 h, and dry at 120 °C for 2 h to obtain the modified hollow glass microspheres. Example 1

[0037] A preparation method of a flame-retardant PP material for a new energy battery pack cover plate includes the following steps: S1. Add 65 parts of phosphoric acid esterified polypropylene, 6.5 parts of maleic anhydride grafted polyolefin elastomer, and 3 parts of polyether block amide to a mixer at 180 °C, and mix at a speed of 150 r / min for 5 min. S2. Under a nitrogen atmosphere, add 4 parts of modified nano-clay in batches. Premix and add 6.5 parts of B-P-triazine-based charring agent and 0.8 part of carbodiimide-based anti-hydrolysis agent, and add 0.4 part of hindered phenol antioxidant. Knead at a speed of 200 r / min for 8 min; S3. Cool down to 160 °C, add 10 parts of short carbon fiber through a side feeder. Premix 1.5 parts of polytetrafluoroethylene micro-powder and 6.5 parts of modified hollow glass microspheres, and evenly sprinkle them through a vibrating sieve. Knead at a speed of 100 r / min for 3 min, and degas under vacuum for 60 s to obtain a premix; S4. Add the premix to a twin-screw extruder, with the feeding section at 170 °C, the melting section at 185 °C, the mixing section at 200 °C, the exhaust section at 180 °C, the homogenizing section at 190 °C, and the die head at 175 °C. The screw speed is 250 rpm. Cool and pelletize with 25 °C water, centrifuge, and screen to obtain blended pellets; S5. Add the blended pellets to a servo-electric injection molding machine, set the melt temperature at 190 °C, the mold temperature at 60 °C, the injection speed at 40 mm / s, the holding pressure at 60 MPa, the holding time at 8 s, and the cooling time at 25 s. Demold after injection molding to obtain a flame-retardant PP material for the cover plate of a new energy battery pack. Example 2

[0038] A preparation method of a flame-retardant PP material for the cover plate of a new energy battery pack includes the following steps: S1. Add 60 parts of phosphoric acid esterified polypropylene, 5 parts of maleic anhydride grafted polyolefin elastomer, and 2 parts of polyether block amide to a kneader at 180 °C, and knead at a speed of 150 r / min for 5 min; S2. Under a nitrogen atmosphere, add 3 parts of modified nano-clay in batches. Premix and add 5 parts of B-P-triazine-based charring agent and 0.5 part of carbodiimide-based anti-hydrolysis agent, and add 0.3 part of hindered phenol antioxidant. Knead at a speed of 200 r / min for 8 min; S3. Cool down to 160 °C, add 8 parts of short carbon fiber through a side feeder. Premix 1 part of polytetrafluoroethylene micro-powder and 5 parts of modified hollow glass microspheres, and evenly sprinkle them through a vibrating sieve. Knead at a speed of 100 r / min for 3 min, and degas under vacuum for 60 s to obtain a premix; S4. Add the premix to a twin-screw extruder, with the feeding section at 170 °C, the melting section at 185 °C, the mixing section at 200 °C, the exhaust section at 180 °C, the homogenizing section at 190 °C, and the die head at 175 °C. The screw speed is 250 rpm. Cool and pelletize with 25 °C water, centrifuge, and screen to obtain blended pellets; S5. Add the blended pellets into a servo-electric injection molding machine, set the melt temperature at 190 °C, the mold temperature at 60 °C, the injection speed at 40 mm / s, the holding pressure at 60 MPa, the holding time at 8 s, and the cooling time at 25 s. Demold after injection molding to obtain the flame-retardant PP material for the cover plate of the new energy battery pack. Example 3

[0039] A preparation method of a flame-retardant PP material for the cover plate of a new energy battery pack includes the following steps: S1. Add 70 parts of phosphorylated polypropylene, 8 parts of maleic anhydride-grafted polyolefin elastomer, and 4 parts of polyether block amide into a mixer at 180 °C, and mix at a speed of 150 r / min for 5 min; S2. Under a nitrogen atmosphere, add 5 parts of modified nano-clay in batches, premix and add 8 parts of B-P-triazine-based charring agent and 1 part of carbodiimide-type anti-hydrolysis agent, add 0.5 part of hindered phenol antioxidant, and mix at a speed of 200 r / min for 8 min; S3. Cool down to 160 °C, add 12 parts of short carbon fiber through a side feeder, premix 2 parts of polytetrafluoroethylene micro-powder and 8 parts of modified hollow glass microspheres, and evenly sprinkle them through a vibrating sieve, mix at a speed of 100 r / min for 3 min, and vacuum degas for 60 s to obtain a premix; S4. Add the premix into a twin-screw extruder, with the feeding section at 170 °C, the melting section at 185 °C, the mixing section at 200 °C, the exhaust section at 180 °C, the homogenizing section at 190 °C, and the die head at 175 °C, the screw speed at 250 rpm, cool and pelletize with 25 °C water, centrifuge, and screen to obtain the blended pellets; S5. Add the blended pellets into a servo-electric injection molding machine, set the melt temperature at 190 °C, the mold temperature at 60 °C, the injection speed at 40 mm / s, the holding pressure at 60 MPa, the holding time at 8 s, and the cooling time at 25 s. Demold after injection molding to obtain the flame-retardant PP material for the cover plate of the new energy battery pack.

[0040] Comparative Example 1 A preparation method of a flame-retardant PP material for the cover plate of a new energy battery pack includes the following steps: S1. Add 47 parts of polypropylene, 18 parts of ammonium polyphosphate, 6.5 parts of maleic anhydride-grafted polyolefin elastomer, and 3 parts of polyether block amide into a mixer at 180 °C, and mix at a speed of 150 r / min for 5 min; S2. Under a nitrogen atmosphere, add 4 parts of modified nano-clay in batches, premix and add 6.5 parts of B-P-triazine-based charring agent and 0.8 part of carbodiimide-type anti-hydrolysis agent, add 0.4 part of hindered phenol antioxidant, and mix at a speed of 200 r / min for 8 min; S3. Cool down to 160 °C, add 10 parts of chopped carbon fiber through a side feeder, premix 1.5 parts of polytetrafluoroethylene micropowder and 6.5 parts of modified hollow glass microspheres and evenly sprinkle them through a vibrating sieve, knead at a speed of 100 r / min for 3 min, and conduct vacuum degassing for 60 s to obtain a premix; S4. Add the premix to a twin-screw extruder, with the feeding section at 170 °C, the melting section at 185 °C, the mixing section at 200 °C, the exhaust section at 180 °C, the homogenizing section at 190 °C, and the die head at 175 °C. The screw speed is 250 rpm. Cool and pelletize with 25 °C water, centrifuge, and screen to obtain blended pellets; S5. Add the blended pellets to a servo-electric injection molding machine, set the melt temperature at 190 °C, the mold temperature at 60 °C, the injection speed at 40 mm / s, the holding pressure at 60 MPa, the holding time at 8 s, and the cooling time at 25 s. Demold after injection molding to obtain a flame-retardant PP material for the cover plate of a new energy battery pack.

[0041] The difference between this comparative example and Example 1 is that instead of adding phosphoric acid esterified polypropylene, polypropylene and ammonium polyphosphate are added.

[0042] Comparative Example 2 A preparation method of a flame-retardant PP material for the cover plate of a new energy battery pack includes the following steps: S1. Add 65 parts of phosphoric acid esterified polypropylene, 6.5 parts of maleic anhydride grafted polyolefin elastomer, and 3 parts of polyether block amide to a kneader at 180 °C and knead at a speed of 150 r / min for 5 min; S2. Under a nitrogen atmosphere, add 4 parts of modified nano-clay in batches, add 0.8 part of carbodiimide type anti-hydrolysis agent, and add 0.4 part of hindered phenol antioxidant, and knead at a speed of 200 r / min for 8 min; S3. Cool down to 160 °C, add 10 parts of chopped carbon fiber through a side feeder, premix 1.5 parts of polytetrafluoroethylene micropowder and 6.5 parts of modified hollow glass microspheres and evenly sprinkle them through a vibrating sieve, knead at a speed of 100 r / min for 3 min, and conduct vacuum degassing for 60 s to obtain a premix; S4. Add the premix to a twin-screw extruder, with the feeding section at 170 °C, the melting section at 185 °C, the mixing section at 200 °C, the exhaust section at 180 °C, the homogenizing section at 190 °C, and the die head at 175 °C. The screw speed is 250 rpm. Cool and pelletize with 25 °C water, centrifuge, and screen to obtain blended pellets; S5. Add the blended pellets to a servo-electric injection molding machine, set the melt temperature at 190 °C, the mold temperature at 60 °C, the injection speed at 40 mm / s, the holding pressure at 60 MPa, the holding time at 8 s, and the cooling time at 25 s. Demold after injection molding to obtain a flame-retardant PP material for the cover plate of a new energy battery pack.

[0043] The difference between this comparative example and Example 1 is that no B-P-triazine-based charring agent is added.

[0044] Comparative Example 3 A preparation method of a flame-retardant PP material for a new energy battery pack cover plate includes the following steps: S1. At 180 °C, add 65 parts of phosphorylated polypropylene, 6.5 parts of maleic anhydride grafted polyolefin elastomer and 3 parts of polyether block amide into a mixer, and mix at a speed of 150 r / min for 5 min; S2. Under a nitrogen atmosphere, add 4 parts of modified nano-clay in batches, premix and add 6.5 parts of pentaerythritol phosphate and 0.8 part of carbodiimide type anti-hydrolysis agent, add 0.4 part of hindered phenol antioxidant, and mix at a speed of 200 r / min for 8 min; S3. Cool down to 160 °C, add 10 parts of short carbon fiber through a side feeder, premix 1.5 parts of polytetrafluoroethylene micro-powder and 6.5 parts of modified hollow glass microspheres, and evenly sprinkle them through a vibrating sieve, mix at a speed of 100 r / min for 3 min, and degas under vacuum for 60 s to obtain a premix; S4. Add the premix into a twin-screw extruder, with the feeding section at 170 °C, the melting section at 185 °C, the mixing section at 200 °C, the exhaust section at 180 °C, the homogenizing section at 190 °C, the die head at 175 °C, the screw speed at 250 rpm, cool and pelletize with 25 °C water, centrifuge and screen to obtain blended pellets; S5. Add the blended pellets into a servo-electric injection molding machine, set the melt temperature at 190 °C, the mold temperature at 60 °C, the injection speed at 40 mm / s, the holding pressure at 60 MPa, the holding time at 8 s, the cooling time at 25 s, demold after injection molding to obtain the flame-retardant PP material for the new energy battery pack cover plate.

[0045] The difference between this comparative example and Example 1 is that no B-P-triazine-based charring agent is added, but pentaerythritol phosphate charring agent is added.

[0046] Test: I. Mechanical properties Impact resistance: "Determination of Plastics - Izod Impact Strength - Part 1: Non-Instrumented Impact Test (GB / T 1843-2018)" Flexural properties: "Determination of Flexural Properties of Plastics (GB / T 9341-2008)" Tensile properties: "Test Method for Tensile Properties of Plastics - Part 1: General Principles (GB / T 1040.1-2018)"

[0047] As can be seen from Table 1, the mechanical properties of the samples in Examples 1-3 are excellent, meeting the mechanical requirements for the production, assembly and use scenarios of the battery pack.

[0048] II. Flame Retardancy Performance Vertical Burning Rating (UL 94): "GB / T 2408-2021 Plastics - Determination of burning behaviour - Horizontal and vertical methods" Heat Release Capacity (HRC): "ISO 5660-1:2015 Fire reaction tests - Heat release, smoke production and mass loss rate - Part 1: Heat release rate (cone calorimeter method)" Peak Heat Release Rate (PHRR): "ISO 5660-1:2015 Fire reaction tests - Heat release, smoke production and mass loss rate - Part 1: Heat release rate (cone calorimeter method)" Total Heat Release (THR): "ISO 5660-1:2015 Fire reaction tests - Heat release, smoke production and mass loss rate - Part 1: Heat release rate (cone calorimeter method)" Residual Carbon Rate (W): "GB / T 33047.1-2016 Plastics - Polymer thermogravimetry (TG) - Part 1: General principles" Limiting Oxygen Index (LOI): "GB / T 2406.2-2009 Plastics - Determination of burning behaviour by the oxygen index method - Part 2: Ambient temperature test" The test results are shown in Table 2 as follows:

[0049] It can be seen from Table 2 that the samples of Examples 1-3 all have excellent flame retardancy performance, meet the safety standards of industrial lithium batteries and power battery packs, and provide fire safety protection for the covers of new energy battery packs.

[0050] III. Thermal Stability Vicat Softening Temperature (VST): "GB / T 1633-2000 Plastics - Determination of Vicat softening temperature (VST) of thermoplastics" Decomposition Temperature (T S ): "GB / T 33047.1-2016 Plastics - Polymer thermogravimetry (TGA) - Part 1: General principles"

[0051] It can be seen from Table 3 that the samples of Examples 1-3 all have excellent thermal stability and meet the requirements of IEC 62619:2022, Article 8.3.3, that is, VST≥150°C and T S ≥250°C for the battery case materials.

[0052] IV. Dimensional Stability Coefficient of linear thermal expansion (CLTE): "ISO 11359-2:2021 Plastics - Thermomechanical analysis (TMA) - Part 2: Determination of coefficient of linear thermal expansion and glass transition temperature" Creep strain: "ISO 899-1:2017 Plastics - Determination of creep properties - Part 1: Tensile creep"

[0053] As can be seen from Table 4, the samples of Examples 1-3 all have good dimensional stability and all meet the requirements of IEC 62619:2022, Article 8.3.4 regarding the battery enclosure material passing the ISO 11359-2 test: CLTE ≤ 6×10 -5 / °C in the range of -40°C to 85°C, and the requirements for passing the ISO 899-1 test: creep strain < 1%.

[0054] V. Physical Properties Density: "GB / T 1033.1-2008 Plastics - Determination of the density of non-cellular plastics - Part 1: Immersion method, pycnometer method and titration method"

[0055] As can be seen from Table 5, the density of the samples of Examples 1-3 is all ≤ 1.05 g / cm 3 , meeting the requirements of the lightweight scenario for the cover plate of new energy battery packs.

[0056] VI. Antistatic Performance Surface resistivity: "GB / T 31838.2-2019 Solid insulating materials - Dielectric and resistive properties - Part 2: Resistive properties (DC method) - Tests for volume resistance and volume resistivity, surface resistance and surface resistivity"

[0057] As can be seen from Table 6, the surface resistivity of the samples of Examples 1-3 all meets the recommendations for material electrostatic control in Appendix C.3 of SAE J2344:2020 (the surface resistivity of the battery pack encapsulation material is controlled at 10 9 -10 11 Ω / sq), which can prevent the electrolyte from catching fire and exploding due to electrostatic accumulation.

[0058] In the description of the specification, the description referring to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0059] The above content is only an illustration and explanation of the present invention. Those skilled in the art of the present technology can make various modifications or supplements to the described specific embodiments or use similar ways to replace them. As long as they do not deviate from the invention or exceed the scope defined by the claims of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A preparation method of a flame-retardant PP material for a cover plate of a new energy battery pack, characterized in that: The flame-retardant PP material for the new energy battery pack cover is made of the following raw materials counted in parts by weight: 60-70 parts of phosphated polypropylene; BP-triazine-based carbon-forming agent 5-8 parts; 3-5 parts of modified nanoclay; 8-12 parts of chopped carbon fiber; 5-8 parts of maleic anhydride grafted polyolefin elastomer; 1-2 parts of polytetrafluoroethylene powder; 2-4 parts of polyether block amide; 5-8 parts of modified hollow glass microspheres; 0.5-1 part of carbodiimide type anti-hydrolysis agent; 0.3-0.5 parts of hindered phenol antioxidant; The preparation method of the flame-retardant PP material for the new energy battery pack cover comprises the following steps: S1. Add phosphated polypropylene, maleic anhydride grafted polyolefin elastomer and polyether block amide into a mixer at 180° C. and mix at a speed of 50-300 r / min for 5 minutes; S2. Under a nitrogen atmosphere, the modified nanoclay was added in batches, the BP-triazine carbonizing agent and the carbodiimide type anti-hydrolysis agent were pre-mixed and added, and the hindered phenol antioxidant was added, and the mixture was mixed at a speed of 200 r / min for 8 min; S3. Cooling to 160° C., adding chopped carbon fibers through a side feeder, premixing polytetrafluoroethylene powder and modified hollow glass microspheres, and evenly adding them through a vibrating screener, mixing at a speed of 100 r / min for 3 min, and vacuum degassing for 30-60 s to obtain a premix; S4, adding the premix to a twin-screw extruder at a temperature of 170-200°C and a screw speed of 200-300 rpm, cooling with water at 25°C, pelletizing, centrifuging, and sieving to obtain blended pellets; S5. Add the blended pellets into a servo electric injection molding machine, set the melt temperature to 190-200°C, the mold temperature to 60°C, the injection speed to 30-50 mm / s, the holding pressure to 60-80 MPa, the holding time to 8 s, and the cooling time to 25 s. After injection molding, demold the material to obtain a flame-retardant PP material for the new energy battery pack cover.

2. The preparation method of a flame-retardant PP material for the cover plate of a new energy battery pack according to claim 1, characterized in that: The preparation steps of the phosphated polypropylene are as follows: A1. Under an inert atmosphere, Rac-ethylenebis(4,5,7-tetrahydroxy-1-indenyl)zirconium dichloride, methylaluminoxane, triisobutylaluminum, hexane, and toluene were mixed at 70°C, 11-bromo-1-undecene was added, and propylene gas was introduced. The reaction was carried out for 0.5-2 hours to obtain PP-Br; In the step A1, the amount ratio of Rac-ethylenebis(4,5,7-tetrahydroxy-1-indenyl)zirconium dichloride, methylaluminoxane, triisobutylaluminum, hexane, 11-bromo-1-undecene, propylene and toluene is (0.02-0.05) g:(35-70) mL:(5-10) mL:(400-500) mL:(15-20) g:(32.5-72.2) mL:(50-100) mL; A2. Under an inert atmosphere, PP-Br and a phosphite compound are melt-copolymerized at 120-180° C. with stirring at a speed of 500-800 r / min to produce an Eberzov reaction for 6-60 hours to obtain phosphated polypropylene; In the step A2, the mass ratio of the PP-Br to the phosphite compound is 100:(38.4 - 77.6); In the step A2, the phosphite compound is triisopropyl phosphite or triphenyl phosphite; In the step A2, when the phosphite compound is triisopropyl phosphite, the reaction conditions are reacting at 120 - 140 °C for 6 - 8 h; when the phosphite compound is triphenyl phosphite, the reaction conditions are reacting at 160 - 180 °C for 48 - 60 h.

3. The preparation method of a flame-retardant PP material for a new energy battery pack cover plate according to claim 1, characterized in that: The preparation steps of the B-P-triazine-based charring agent are as follows: B1. Dissolve hydroxyvanillin in methanol, heat to 60 °C with stirring, slowly dropwise add the aminophenylboronic acid / methanol solution within 15 min, adjust the pH to 5 - 6, reflux for 4 - 8 h, naturally cool to room temperature, filter, wash, dry in an air circulation oven at 120 °C for 2 h, and dry in a vacuum oven at 160 °C for 4 h to obtain an intermediate; In the step B1, the dosage ratio of the hydroxyvanillin, methanol, and aminophenylboronic acid / methanol solution is (125 - 130) g:500 mL:100 mL; In the step B1, the aminophenylboronic acid / methanol solution is prepared by dissolving aminophenylboronic acid in methanol, and the dosage ratio of the aminophenylboronic acid and methanol is (90 - 96) g:100 mL; B2. Disperse the intermediate in N,N-dimethylformamide, add sodium carbonate, stir for 10 min, slowly dropwise add the cyanuric chloride / N,N-dimethylformamide solution within 10 min, and react at 0 - 5 °C for 2 h; In the step B2, the dosage ratio of the intermediate, N,N-dimethylformamide, sodium carbonate, and cyanuric chloride / N,N-dimethylformamide solution is (180 - 220) g:(180 - 220) mL:(45 - 55) g:100 mL; In the step B2, the cyanuric chloride / N,N-dimethylformamide solution is prepared by dissolving cyanuric chloride in N,N-dimethylformamide, and the dosage ratio of the cyanuric chloride and N,N-dimethylformamide is (25 - 30) g:100 mL; B3. Heat the reaction system to 65 °C, dissolve bis[4-(3-aminophenoxy)phenyl]phenylphosphine oxide in N,N-dimethylformamide, slowly dropwise add it to the mixed solution obtained in B2 within 15 min, and react at 65 °C for 2 h; In the step B3, the dosage ratio of the bis[4-(3-aminophenoxy)phenyl]phenylphosphine oxide, N,N-dimethylformamide, and the mixed solution obtained in B2 is (6 - 7) g:100 mL:(560 - 640) mL; B4. Heat the reaction system to 95 °C, dissolve bis[4-(3-aminophenoxy)phenyl]phenylphosphine oxide in N,N-dimethylformamide, slowly dropwise add it to the mixed solution obtained in B3 within 10 min, react at 95 °C for 4 h, cool to room temperature, filter, wash with deionized water at 80 °C until neutral, dry in an air circulation oven at 120 °C for 2 h, and dry in a vacuum oven at 165 °C for 2 h to obtain the B-P-triazine-based charring agent; In the step B4, the dosage ratio of the bis[4-(3-aminophenoxy)phenyl]phenylphosphine oxide, N,N-dimethylformamide and the mixed solution obtained in B3 is (12.4-13.4) g: 100 mL: (660-740) mL.

4. The preparation method of a flame-retardant PP material for a cover plate of a new energy battery pack according to claim 1, characterized in that: The modified nano-clay is surface-modified with a long-chain quaternary ammonium salt, with a particle size of 50-200 nm and a lamellar thickness of 2-5 nm.

5. The preparation method of a flame-retardant PP material for a cover plate of a new energy battery pack according to claim 1, characterized in that: The chopped carbon fiber has a fiber length of 3-6 mm and an aspect ratio of 50-100.

6. The preparation method of a flame-retardant PP material for a new energy battery pack cover plate according to claim 1, characterized in that: The grafting rate of the maleic anhydride grafted polyolefin elastomer is 0.8-1.2%.

7. The preparation method of a flame-retardant PP material for a cover plate of a new energy battery pack according to claim 1, characterized in that: The particle size of the polytetrafluoroethylene micropowder is 5-30 μm.

8. The preparation method of a flame-retardant PP material for a cover plate of a new energy battery pack according to claim 1, wherein: The polyether / polyamide block ratio in the polyether block amide is (6-7):(3-4).

9. The preparation method of a flame-retardant PP material for the cover plate of a new energy battery pack according to claim 1, wherein: The modified hollow glass microspheres are surface-modified with a silane coupling agent, with a particle size of 65-125 μm.

10. The preparation method of a flame-retardant PP material for a cover plate of a new energy battery pack according to claim 1, characterized in that: The molecular weight of the hindered phenol antioxidant is greater than 1000.

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