Co-extruded film, preparation process and application in new energy battery

Abstract

The present application relates to the technical field of new energy power battery thermal management materials, in particular to a co-extrusion film material for aerogel thermal insulation pad packaging, and discloses a co-extrusion film, a preparation process and application in new energy batteries, wherein the co-extrusion film is prepared from high-performance master batches through a co-extrusion blow molding process, the high-performance master batches are composed of seven-vinyl POSS single-grafted nylon 6 resin, modified expanded vermiculite with octadecenyl and DOPO groups on the surface, and dicumyl peroxide initiator, under the action of the dicumyl peroxide initiator, the vinyl on the POSS cage structure of the seven-vinyl POSS single-grafted nylon 6 resin and the octadecenyl on the surface of the modified expanded vermiculite occur free radical reaction to obtain the high-performance master batches. Through the synergistic modification strategy of double grafting and crosslinking, the present application realizes the synergistic improvement of flame retardation, heat resistance, barrier property and mechanical property, and solves the technical bottlenecks of aerogel packaging materials in high-temperature failure, weak interface bonding and processing performance deterioration.

Description

Technical Field

[0001] This invention relates to the field of thermal management materials technology for new energy power batteries, specifically to co-extruded film materials for aerogel heat insulation pad encapsulation, including co-extruded film, preparation process, and application in new energy batteries. Background Technology

[0002] As new energy vehicles rapidly iterate towards higher energy density, battery safety issues are becoming increasingly prominent. Under extreme conditions such as collisions, overcharging, or external short circuits, the chain reaction caused by thermal runaway of individual cells is a key bottleneck restricting the industry's development. Cell insulation is crucial to preventing heat propagation. Aerogels, with their ultra-low thermal conductivity, are widely recognized as ideal passive insulation materials; however, their low strength, tendency to shed powder, and strong hydrophilicity necessitate encapsulation with a barrier film before engineering applications.

[0003] Currently, aerogel encapsulation mainly employs a non-integrated structure assembled from fiber mat, PET / PI film, and silicone frame through multi-step bonding / dispensing processes. This approach has limitations in ultra-thin battery pack applications, including cumbersome processes and high interfacial thermal resistance. The industry has begun exploring multilayer co-extruded film integrated encapsulation technology. However, traditional polyolefin-based co-extruded films (such as LDPE and PP) have low melting points (<165℃) and are prone to melting and failure under thermal runaway temperatures (typically >500℃); furthermore, their non-polar surfaces have weak adhesion to hydrophilic aerogels, easily leading to interfacial delamination. Improving performance by adding large amounts of flame retardants would severely degrade the material's mechanical properties and processing flowability.

[0004] In contrast, Nylon 6 (PA6), as a polar engineering plastic, has a high melting point (approximately 220°C), good compatibility with polar flame-retardant fillers, and excellent film-forming properties and mechanical properties, making it an ideal substrate for aerogel encapsulation. However, conventional PA6 still suffers from drawbacks such as a low limiting oxygen index (approximately 23%), a low heat distortion temperature (approximately 75°C), and decreased barrier properties under high temperature and humidity environments, making it difficult to meet the requirements for high-temperature shocks during battery thermal runaway and long-term moisture barrier properties. Furthermore, while the introduction of DOPO flame retardant and expanded vermiculite can improve flame retardancy and heat insulation properties, their poor dispersibility and weak interfacial bonding in the PA6 matrix easily lead to film-forming defects and a sharp drop in mechanical properties. At the same time, although cage-like silsesquioxanes (POSS) can improve heat resistance, direct blending easily leads to agglomeration, making it difficult to achieve the nano-reinforcing effect.

[0005] Therefore, this invention aims to achieve a synergistic improvement in flame retardancy, heat resistance, barrier properties, and mechanical properties while ensuring the processing performance of PA6 substrate through molecular structure design and interface regulation, and to solve the problem of weak bonding between the encapsulation film and aerogel interface. Summary of the Invention

[0006] This invention proposes a dual grafting and crosslinking synergistic modification strategy: by molecular design, a multifunctional silane compound containing octadecenyl, DOPO and trimethoxy groups is synthesized, and the compound is used to modify the surface of expanded vermiculite, so that hydrophobic long chains and flame retardant groups are grafted onto the vermiculite surface, thereby solving the problem of hydrophilic aggregation and introducing active sites that can participate in free radical reactions.

[0007] Heptavinyl POSS with a monoepoxy group was synthesized by molecular design. The epoxy functional group of POSS was then used to undergo a ring-opening grafting reaction with the amino group at the end of the nylon 6 molecular chain to prepare heptavinyl POSS single-grafted nylon 6 resin.

[0008] After premixing heptavinyl POSS single-grafted nylon 6 resin with modified expanded vermiculite with octadecene and DOPO groups on the surface, melt grafting crosslinking was carried out under the action of dicumyl peroxide (DCP) initiator. The seven vinyl groups retained on the POSS cage structure serve as multifunctional crosslinking centers, which react with the octadecene groups on the surface of the modified expanded vermiculite to form a three-dimensional network that penetrates the organic matrix and inorganic filler.

[0009] The vermiculite is formed into a co-extruded film through a co-extrusion blow molding process, which ultimately achieves nanoscale dispersion, strong interfacial bonding and polarity interface matching with aerogel in the nylon matrix, thus meeting the requirements of high-performance encapsulation.

[0010] A co-extruded film is prepared by a co-extrusion blow molding process from a high-performance masterbatch, which is prepared by a melt graft crosslinking reaction of the following components:

[0011] Heptavinyl POSS single-grafted nylon 6 resin: 85-95 parts by weight;

[0012] Modified expanded vermiculite with octadecenyl and DOPO groups on the surface: 5-15 parts by weight;

[0013] Dicumyl peroxide initiator: 0.2-0.5 parts by weight;

[0014] Among them, the heptavinyl POSS single-grafted nylon 6 resin is prepared by a ring-opening grafting reaction between the epoxy functional group of the heptavinyl POSS monoepoxy group and the amino group at the end of the nylon 6 molecular chain.

[0015] Modified expanded vermiculite with octadecenyl and DOPO groups was prepared by surface modification of expanded vermiculite with a multifunctional silane compound containing octadecenyl, DOPO and trimethoxy groups;

[0016] Under the action of dicumyl peroxide initiator, the vinyl groups on the POSS cage structure of heptavinyl POSS single-grafted nylon 6 resin undergo a free radical reaction with the octadecene groups on the surface of modified expanded vermiculite to obtain a high-performance masterbatch.

[0017] Preferably, the preparation method of the heptavinyl POSS single-grafted nylon 6 resin is as follows: based on nylon 6 with a terminal amino content of 40-45 mmol / kg, solution grafting modification is performed using a single epoxy group heptavinyl POSS. Under the conditions of epoxy group to terminal amino molar ratio (1.5-1.8):1 and reaction at 100-120℃ for 3-5 h, the grafting rate of the obtained resin is 2.0-3.0 wt%.

[0018] Preferably, the modified expanded vermiculite with octadecenyl and DOPO groups on its surface contains 20-35 wt% of a multifunctional silane compound containing octadecenyl, DOPO and trimethoxy groups.

[0019] A process for preparing a co-extruded film includes the following steps:

[0020] Step 1: Prepare a multifunctional silane compound containing octadecenyl, DOPO and trimethoxy groups, and use it to modify the surface of expanded vermiculite to obtain modified expanded vermiculite;

[0021] Step 2: Prepare monoepoxy heptavinyl POSS and react it with nylon 6 resin to obtain heptavinyl POSS single-grafted nylon 6 resin.

[0022] Step 3: Premix heptavinyl POSS single-grafted nylon 6 resin with modified expanded vermiculite, add initiator, and carry out melt grafting crosslinking reaction to obtain high-performance masterbatch;

[0023] Step four: Add the high-performance masterbatch to the co-extrusion blow molding unit, and obtain the co-extruded film through melt extrusion, blowing, traction and cooling.

[0024] Preferably, the preparation method of the multifunctional silane compound containing octadecenyl, DOPO, and trimethoxy groups is as follows:

[0025] Utilizing a nucleophilic substitution reaction mechanism, an organic base catalyzes a nucleophilic substitution reaction between 1 molar equivalent of oleylamine and 0.95-0.99 molar equivalents of 3-chloropropyltrimethoxysilane via a -NH2 functional group and a chlorine functional group to generate secondary aminooctadecenyltrimethoxysilane.

[0026] An organic base catalyzes a reaction between 1 molar equivalent of acyl-chlorinated [(6-oxo-6H-dibenzo[C,E][1,2]oxophosphorylhexane-6-yl)methyl]succinic acid and 2.01-2.05 molar equivalents of secondary amine octadecenyltrimethoxysilane via an amidation reaction between the acyl chloride functional group and the secondary amine functional group, yielding a multifunctional silane compound containing octadecenyl, DOPO, and trimethoxy groups.

[0027] Preferably, the preparation method of the monoepoxy heptavinyl POSS is as follows:

[0028] Octavinyl POSS, under the action of tetraethylammonium hydroxide, opens a Si-O-Si bond at one vertex to generate an incompletely condensed POSS containing three silanols, namely hepta(vinyl)trisilol POSS;

[0029] The three silanol groups of hepta(vinyl)trisilyl POSS undergo a condensation reaction with 3-(2,3-epoxypropoxy)propyltrimethoxysilane. The three methoxy groups of 3-(2,3-epoxypropoxy)propyltrimethoxysilane react with Si-OH to form Si-O-Si bonds. The cap opens at the apex, introducing an epoxy group to synthesize monoepoxy heptavinyl POSS.

[0030] Preferably, the method for preparing the high-performance masterbatch is as follows:

[0031] Heptavinyl POSS single-grafted nylon 6 resin was premixed with expanded vermiculite with octadecenyl and DOPO groups on its surface to obtain a dry mixture.

[0032] Dicumyl peroxide (DCP) was dissolved in anhydrous acetone and added to the dry mixture by spraying. After mixing evenly and removing the solvent, a pretreated mixture was obtained.

[0033] The pretreated mixture is added to a twin-screw extruder and subjected to a melt grafting crosslinking reaction at a temperature of 210-250℃. The material residence time is controlled to be 1-3 minutes. After extrusion granulation, a high-performance masterbatch is obtained.

[0034] An application of a co-extruded film in the encapsulation of aerogel thermal insulation pads for new energy power batteries, specifically used as an encapsulation barrier film for aerogel thermal insulation pads.

[0035] Beneficial effects:

[0036] This invention is based on a synergistic modification strategy of double grafting and crosslinking:

[0037] By integrating octadecenyl, DOPO groups and trimethoxy groups into a single molecule, vermiculite is surface modified, achieving hydrophobic compatibilization, introduction of reactive sites and flame retardant functionalization of the vermiculite surface, thus solving the problem of nanoscale dispersion of vermiculite in nylon matrix.

[0038] Single grafting modification was achieved by reacting heptavinyl POSS with the 6-terminal amino group of nylon. While ensuring molecular-level dispersion of POSS, the seven vinyl groups were precisely retained as multifunctional crosslinking centers, overcoming the processing gelation problem caused by multifunctional POSS and achieving a balance between nano-reinforcement and processability.

[0039] Under the initiation of DCP, the seven vinyl groups on the POSS cage structure undergo a free radical grafting reaction with the octadecene groups on the modified vermiculite to construct a three-dimensional chemical network that runs through the organic matrix and inorganic filler, and forms a strong interfacial bond with the modified vermiculite. This allows stress to be efficiently transferred from the nylon matrix to the POSS nanoparticles and vermiculite sheets, overcoming the technical bottleneck that physical blending reinforcement is inevitably brittle and flame retardancy is inevitably reduced.

[0040] Experimental data confirms that the co-extruded film products obtained through this strategy can achieve a maximum heat distortion temperature of 117.3℃ (42.5℃ higher than pure nylon 6), a limiting oxygen index of 32.4%, and reach V-0 flame retardancy, while reducing water vapor transmission to a minimum of 4.5 g / (m²). 2 (24h) The tensile strength was simultaneously increased to 79.4MPa, achieving a synergistic improvement in heat resistance, flame retardancy, barrier properties and mechanical properties. Detailed Implementation

[0041] Example 1:

[0042] The preparation process for a multifunctional silane compound containing octadecenyl, DOPO, and trimethoxy groups is as follows:

[0043] Process 1: Utilizing a nucleophilic substitution mechanism, an organic base catalyzes a nucleophilic substitution reaction between 1 molar equivalent of oleylamine and 0.97 molar equivalents of 3-chloropropyltrimethoxysilane via the -NH2 functional group and the chlorine functional group, yielding secondary aminooctadecenyltrimethoxysilane, whose chemical structural formula is as follows:

[0044] ;

[0045] Process 2: An organic base catalyzes a reaction between 1 molar equivalent of acylated [(6-oxo-6H-dibenzo[C,E][1,2]oxophosphorylhexane-6-yl)methyl]succinic acid (CAS No. 63562-33-4) and 2.04 molar equivalent of secondary amine octadecenyltrimethoxysilane via an amidation reaction between the acyl chloride functional group and the secondary amine (-NH-) functional group, yielding a multifunctional silane compound containing octadecenyl, DOPO, and trimethoxy groups. The chemical structural formula of this compound is as follows:

[0046] ;

[0047] The organic base can be selected from pyridine, triethylamine, or tributylamine; in this embodiment, triethylamine is selected.

[0048] The specific experimental steps for preparing multifunctional silane compounds are as follows:

[0049] Under nitrogen protection, 5.4 g of oleylamine and 50 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask and stirred at room temperature until completely dissolved. Then, 30 mL of anhydrous N,N-dimethylformamide solution containing 3.9 g of 3-chloropropyltrimethoxysilane and 1.5 mL of triethylamine were added dropwise to the three-necked flask. The mixture was stirred at room temperature for 30 min, heated to 60 °C and stirred for 8 h. After cooling to room temperature, the solvent was removed by rotary evaporation under reduced pressure. An appropriate amount of anhydrous diethyl ether was added to the residue and stirred to fully dissolve the product. The insoluble triethylamine hydrochloride precipitate was removed by filtration. The filtrate was concentrated under reduced pressure to remove the solvent. The obtained product was dried under vacuum at 60 °C for 5 h to obtain secondary aminooctadecenyltrimethoxysilane.

[0050] 1.5 mL of thionyl chloride and 0.2 mL of anhydrous N,N-dimethylformamide were added dropwise to 20 mL of anhydrous dichloromethane containing 1.7 g of [(6-oxo-6H-dibenzo[C,E][1,2]oxophosphorylhexane-6-yl)methyl]succinic acid. The mixture was heated to 45 °C and stirred for 5 h. After cooling to room temperature, the solvent and residual thionyl chloride were removed by rotary evaporation under reduced pressure to obtain acylated [(6-oxo-6H-dibenzo[C,E][1,2]oxophosphorylhexane-6-yl)methyl]succinic acid. This acylated [(6-oxo-6H-dibenzo[C,E][1,2]oxophosphorylhexane-6-yl)methyl]succinic acid and 30 mL of anhydrous N,N-dimethylformamide were added to... In a three-necked flask, under nitrogen protection, the mixture was stirred at room temperature until completely dissolved. Then, 40 mL of anhydrous N,N-dimethylformamide solution containing 4.3 g of secondary aminooctadecenyltrimethoxysilane and 1.8 mL of triethylamine were added dropwise to the flask. The mixture was stirred at room temperature for 30 min, heated to 70 °C and stirred for 8 h. After cooling to room temperature, the solvent was removed by rotary evaporation under reduced pressure. Dichloromethane was added to the residue and stirred to dissolve the product. The insoluble triethylamine hydrochloride solid was removed by filtration. The filtrate was concentrated under reduced pressure to remove the solvent. The obtained product was dried under vacuum at 60 °C for 5 h to obtain a multifunctional silane compound.

[0051] The proton NMR spectrum of the multifunctional silane compound is characterized as follows: 1 H NMR (CDCl3, 400MHz) δ: 0.64-0.72(m, 4H), 0.87-0.91(t, 6H), 1.19-1.34(m, 44H), 1.57-1.75(m, 8H), 1.94-2.07(m, 8H), 2.59-2.79(m, 4H), 3.16-3.37(m, 9H), 3.57(s, 18H), 5.31-5.35(m, 4H), 7.25-8.13(m, 8H).

[0052] Example 2:

[0053] Preparation of modified expanded vermiculite with octadecenyl and DOPO groups on the surface: A multifunctional silane compound containing octadecenyl, DOPO and trimethoxy groups is used to generate silanol groups under hydrolysis conditions. The silanol groups undergo a dehydration condensation reaction with the hydroxyl groups on the surface of hydrophilic expanded vermiculite, thereby grafting octadecenyl and DOPO groups onto the vermiculite surface to obtain modified expanded vermiculite with octadecenyl and DOPO groups on the surface.

[0054] The specific experimental steps for preparing modified expanded vermiculite are as follows: Hydrophilic expanded vermiculite powder (impurity <0.8%) was placed in a planetary ball mill and ground. The ball mill speed was set to 600 r / min, and the milling time was set to 15 min. The powder was then passed through a 600-mesh sieve to obtain finely milled hydrophilic expanded vermiculite powder. Then, 10 g of the finely milled hydrophilic expanded vermiculite powder and 150 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask, ultrasonically dispersed for 1 h, and stirred at room temperature for 2 hours. h, add 20 mL of N,N-dimethylformamide aqueous solution containing 3 g of multifunctional silane compound (the volume ratio of anhydrous N,N-dimethylformamide to deionized water is 3:1) and 0.5 mL of acetic acid to a three-necked flask, heat to 60 °C and stir for 4 h, cool to room temperature, centrifuge at 8000 rpm for 15 min, wash the precipitate three times with deionized water at 8000 rpm for 15 min each time, and dry under vacuum at 60 °C for 12 h to obtain modified expanded vermiculite.

[0055] Example 3:

[0056] Preparation of high-performance masterbatch I: Based on nylon 6 (F136 type) with a terminal amino content of 40.9 mmol / kg (measured value), solution grafting modification was performed using heptavinyl POSS (molecular weight 721.14) with a single epoxy group. Under the conditions of epoxy group to terminal amino molar ratio of 1.7:1 and reaction at 110℃ for 4 h, after purification and drying, the actual grafting rate of heptavinyl POSS single-grafted nylon 6 resin was determined by terminal amino titration method. The heptavinyl POSS single-grafted nylon 6 resin was then subjected to melt grafting crosslinking reaction with modified expanded vermiculite with octadecenyl and DOPO groups on the surface under the action of an initiator to obtain high-performance masterbatch I.

[0057] The specific experimental steps for preparing high-performance masterbatch I are as follows:

[0058] 100 parts by weight of nylon 6 resin (model F136, terminal amino content 40.9 mmol / kg) and 1000 parts by weight of anhydrous N,N-dimethylformamide were added to a three-necked flask. The mixture was heated to 100°C and stirred for 2 hours to dissolve. After cooling to room temperature, under nitrogen protection, 100 parts by weight of anhydrous N,N-dimethylformamide solution containing 5 parts by weight of monoepoxy heptavinyl POSS was added to the three-necked flask. The mixture was heated to 110°C and stirred for 4 hours. After the reaction was completed, the reaction solution was poured into 10 times its volume of vigorously stirred deionized water to precipitate. The solution was filtered, the solid was collected, and the free POSS was removed by Soxhlet extraction with acetone for 24 hours. The solid was then dried under vacuum at 60°C for 12 hours to obtain heptavinyl POSS-grafted nylon 6 resin.

[0059] 95 parts by weight of heptavinyl POSS single-grafted nylon 6 resin and 5 parts by weight of modified expanded vermiculite with octadecene and DOPO groups on the surface were added to a high-speed mixer and premixed at 1800 rpm for 5 min to obtain a dry mixture.

[0060] Dissolve 0.2 parts by weight of dicumyl peroxide (DCP) in 25 parts by weight of anhydrous acetone, add it to the above dry mixture by spraying, and stir evenly at room temperature. After the acetone has completely evaporated, the pretreated mixture is obtained.

[0061] The pretreated mixture was added to a twin-screw extruder, the speed was set to 200 r / min, the feeding speed was controlled to keep the material residence time at 2 min, the vacuum port was opened at the front of the die head, and the temperatures of zones 1-6 were set to 210℃, 230℃, 235℃, 245℃, 245℃, and 240℃, respectively. The melt grafting crosslinking reaction was carried out and granulation was performed. The extrudate was water-cooled, pelletized, and dried at 80℃ for 6 h to obtain high-performance masterbatch I.

[0062] The chemical structural formula of the monoepoxy heptavinyl POSS is as follows:

[0063] ;

[0064] The preparation method of monoepoxy heptavinyl POSS is as follows:

[0065] (1) Preparation of hepta(vinyl)trisilol POSS: Octavinyl POSS (CAS No. 69655-76-1) under the action of organic base (tetraethylammonium hydroxide) opens the Si-O-Si bond at one vertex to generate an incompletely condensed POSS containing three silanols, namely hepta(vinyl)trisilol POSS. The preparation steps are as follows: under the protection of nitrogen, 6.3g of octavinyl POSS and 60mL of anhydrous N,N-dimethylformamide are added to a three-necked flask and stirred at room temperature until completely dissolved. Then, 10mL of 30wt% tetraethylammonium hydroxide aqueous solution is added to the three-necked flask, the temperature is raised to 70℃ and stirred for 5h, cooled to room temperature, the pH is adjusted to neutral by 0.1mol / L dilute hydrochloric acid, the solvent is removed by rotary evaporation under reduced pressure, the residue is dissolved in 50mL of anhydrous diethyl ether, dried with anhydrous sodium sulfate for 2h, the desiccant is removed by filtration, the diethyl ether is removed by rotary evaporation, and the product is dried under vacuum at 50℃ for 8h to obtain hepta(vinyl)trisilol POSS.

[0066] (2) Preparation of monoepoxy heptavinyl POSS: The three silanol groups of heptavinyltrisilol POSS undergo a condensation reaction with 3-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560). The three methoxy groups of KH-560 react with Si-OH to form Si-O-Si bonds. The cap opens at the apex, introducing an epoxy group to synthesize monoepoxy heptavinyl POSS. The preparation steps are as follows: Under nitrogen protection, 2.9 g of heptavinyltrisilol POSS and 30 mL of anhydrous N,N-dimethylformamide are added. The solution was added to a three-necked flask and stirred at room temperature until completely dissolved. Then, the flask was placed in an ice-water bath, and 10 mL of anhydrous N,N-dimethylformamide solution containing 1.2 g of 3-(2,3-epoxypropoxy)propyltrimethoxysilane was added dropwise. The mixture was stirred in the ice-water bath for 30 min, then the ice-water bath was removed, and the mixture was stirred at room temperature for 12 h. N,N-dimethylformamide and methanol were removed by rotary evaporation under reduced pressure. The residue was dissolved in 40 mL of anhydrous diethyl ether, dried with anhydrous sodium sulfate for 2 h, and then dried under vacuum at 40 °C for 10 h to obtain monoepoxyheptavinyl POSS.

[0067] The 1H NMR characterization of monoepoxyheptavinyl POSS is as follows: 1 H NMR (DMSO-d6, 400MHz) δ: 0.67-0.71 (t, 2H), 1.65-1.72 (m, 2H), 3.23-3.24 (d, 2H), 3.43-3.54 (m, 5H), 5.35-5.44 (t, 7H), 5.72-5.87 (dd, 14H).

[0068] Example 4:

[0069] The preparation method of high-performance masterbatch II differs from that of high-performance masterbatch I only in that the amount of heptavinyl POSS single-grafted nylon 6 resin is adjusted from 95 parts by weight to 90 parts by weight, and the amount of modified expanded vermiculite with octadecene and DOPO groups on the surface is adjusted from 5 parts by weight to 10 parts by weight.

[0070] Example 5:

[0071] The preparation method of high-performance masterbatch III differs from that of high-performance masterbatch I only in that the amount of heptavinyl POSS single-grafted nylon 6 resin is adjusted from 95 parts by weight to 85 parts by weight, and the amount of modified expanded vermiculite with octadecene and DOPO groups on the surface is adjusted from 5 parts by weight to 15 parts by weight.

[0072] Example 6:

[0073] The preparation of co-extruded film I includes the following steps:

[0074] Step 1: Set the co-extruded film I to a five-layer symmetrical film structure, with each layer having a formulation of 100wt% high-performance masterbatch I and a mass ratio of 20:15:30:15:20;

[0075] Step 2: The raw materials for each film layer are fed into the hoppers of the five screw extruders of the five-layer co-extrusion film blow molding unit. The molten resin is combined at the die head through the distributor, and then extruded and blown through the die head (the blow-up ratio is controlled at 2.9). After cooling and winding, a co-extruded film I with a thickness of 100μm is obtained.

[0076] The process parameters for the screw extruders corresponding to each film layer are set as follows: the temperatures of zones 1-3 are 230℃, 240℃, and 245℃, respectively; the flow channel temperature is 248℃; and the rotation speed is 50r / min.

[0077] Example 7:

[0078] The preparation method of co-extruded film II differs from that of co-extruded film I only in that the high-performance masterbatch is changed from high-performance masterbatch I to high-performance masterbatch II.

[0079] Example 8:

[0080] The preparation method of co-extruded film III differs from that of co-extruded film I only in that the high-performance masterbatch is changed from high-performance masterbatch I to high-performance masterbatch III.

[0081] Comparative example:

[0082] The preparation method of the unmodified co-extruded film differs from that of co-extruded film I only in that the high-performance masterbatch is changed from high-performance masterbatch I to nylon 6 resin (model F136).

[0083] Performance testing:

[0084] I. Flame retardant performance test

[0085] (1) Limiting Oxygen Index (LOI)

[0086] According to standard GB / T 2406.2-2009 "Determination of flammability of plastics by oxygen index method - Part 2: Room temperature test", the film was cut into 120 mm long and 10 mm wide, and stacked in the same direction to a thickness of 3 mm. The layers were naturally bonded together without the use of adhesive. The resulting sample was conditioned for 88 h at 25 °C and 50% RH.

[0087] The sample is vertically mounted on the sample holder of the combustion tube. The oxygen and nitrogen flow rates are adjusted to make the gas velocity in the combustion tube 40 mm / s (total flow rate about 10 L / min). The initial oxygen concentration is set. The top surface ignition method is used: the flame height of the igniter is adjusted to 16 mm, and the fuel is propane, butane or natural gas (purity ≥95%). The visible part of the flame contacts the center of the top of the sample and covers the entire top surface. The ignition is continued for 30 seconds, and the igniter is removed. The combustion time and combustion length are recorded.

[0088] The oxygen concentration was adjusted using the Dixon method (step size no greater than 0.5%), and at least 6 experiments were conducted to obtain 6 valid data points (3 "O" combustion and 3 "×" extinguishing alternating). The oxygen concentration was then calculated using the formula OI=C. f The oxygen index was calculated using k·d (k value was obtained from Table 4 of GB / T2406.2-2009), and the result was rounded to 0.1%.

[0089] (2) Vertical flammability rating (UL-94)

[0090] According to standard GB / T 2408-2008 "Determination of the flammability of plastics by horizontal and vertical methods", the film was cut into lengths of 125 mm and widths of 13 mm, and stacked in the same direction to a thickness of 3 mm. The layers were naturally bonded together without the use of adhesives. The resulting sample was conditioned for 88 hours at 25°C and 50%RH.

[0091] The sample is held vertically on the support, with the bottom of the sample 10 mm away from the Bunsen burner nozzle. Degreased cotton is placed 300 mm below the sample. The Bunsen burner is adjusted to produce a blue flame with a height of 20 mm. The flame is applied to the bottom of the sample for 10 seconds and then removed. The first flaming time t1 is recorded. After the flame goes out, the flame is immediately applied again for 10 seconds. The flame time t2 and the flameless time t3 are recorded after the flame is removed. It is observed whether any burning droplets ignite the degreased cotton. Based on the total flaming time of the 5 samples, the single flaming time, and whether the droplets ignite the degreased cotton, the sample is judged as V-0, V-1, V-2, or no grade.

[0092] II. Mechanical Property Testing

[0093] According to standard GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", the specimens were cut into strips with a length of 150 mm, a width of 15 mm, and a gauge length of 50 mm along the longitudinal direction (MD) and transverse direction (TD) respectively, and conditioned at 25℃ and 50%RH for 48 h.

[0094] Measure the thickness of the specimen within the gauge length using a thickness gauge and take the average value. Clamp the specimen on the universal testing machine fixture, ensuring that the specimen axis is consistent with the direction of force. Perform the test at a tensile speed of 50 mm / min until the specimen breaks, and record the force-displacement curve.

[0095] According to formula σ t =F m Calculate the tensile strength using the formula ε (b·d). β =(L-L0) / L0×100% to calculate the elongation at break, where F m The maximum load is given by b, the specimen width is given by d, the specimen thickness is given by L0, the initial gauge length is given by L, and the distance between the gauges at the time of fracture is given by L. The result is the arithmetic mean of 5 specimens.

[0096] III. Thermal Performance Testing

[0097] According to standard GB / T 1634.2-2019 "Determination of Deformation Temperature of Plastics under Load - Part 2: Plastics and Hard Rubber", multilayer films were stacked and hot-pressed into sheets of 80mm×10mm×4mm, and conditioned at 25℃ and 50%RH for 48h.

[0098] The specimen was placed flat on a support with a span of 64 mm, and a bending stress of 0.45 MPa was applied. The temperature was increased at a rate of 2 °C / min. The temperature at which the bending deflection of the specimen reached 0.34 mm was recorded as the heat distortion temperature (HDT). Each group of specimens was measured 3 times, and the arithmetic mean was taken and reported as an integer value in degrees Celsius.

[0099] IV. Barrier Performance Test

[0100] According to standard GB / T 1037-2021 "Determination of Water Vapor Permeability of Plastic Films and Sheets - Cup Method for Weight Gain and Loss", a circular sample with a diameter of 70 mm was cut and conditioned at 25℃ and 50%RH for 48 h.

[0101] Anhydrous calcium chloride (particle size 0.60mm-2.36mm) was added to a permeation cup to a depth of approximately 3mm below the rim. The sample was sealed at the rim and placed in a constant temperature and humidity chamber at 38℃ and 90% relative humidity. Every 24 hours, the sample was removed, cooled at 25℃ for 30 minutes, and weighed. This process was repeated until three consecutive measurements showed a relative change in mass increment of <5% and Δm > 0.02g. The water vapor permeation rate was calculated using the formula WVT = 24 × Δm / (A⋅t), and the result was taken as the average of the three sample groups. Where Δm is the mass increment (in g) and A is the permeation area of ​​the sample (in m²). 2 ), t is the time interval (in hours), and the test results of water vapor transmission rate WVT are expressed in g / (m³). 2 ·24h) indicates;

[0102] The test results are shown in Table 1 below.

[0103] Table 1. Performance test results of co-extruded films

[0104] Performance indicators Co-extruded film I Co-extruded film II Co-extruded film III Comparative Example Limiting Oxygen Index (LOI) (%) 28.7 31.6 32.4 23 UL-94 rating V-1 V-0 V-0 No grade Longitudinal tensile strength (MPa) 70.7 75.2 79.4 62.6 Longitudinal elongation at break (%) 178 141 106 239 Heat distortion temperature (HDT) (°C) 91.2 109.5 117.3 74.8 <![CDATA[Water vapor transmission rate [g / (m 2 ·24 h)]]]> 7.6 5.0 4.5 18.9

[0105] The following conclusions can be drawn from the experimental results:

[0106] By grafting nylon 6 resin with monoepoxy heptavinyl POSS and cross-linking it with modified expanded vermiculite with octadecene and DOPO groups on the surface, a high-performance masterbatch was prepared. Compared with pure nylon 6, the flame retardancy, tensile strength, heat distortion temperature and barrier properties were significantly improved. However, the elongation at break decreased significantly with the increase of vermiculite content.

[0107] Co-extruded film II (with 10wt% modified expanded vermiculite in high-performance masterbatch II) achieves the best balance between flame retardancy, mechanical toughness, and processing performance; co-extruded film III (with 15wt% modified expanded vermiculite in high-performance masterbatch III) is suitable for scenarios with higher requirements for temperature resistance and moisture barrier properties; in practical applications, the filler ratio needs to be optimized according to the comprehensive requirements for toughness, flame retardancy, and temperature resistance.

Claims

1. A co-extruded film, characterized in that, The co-extruded film is produced by co-extrusion blow molding of high-performance masterbatch, which is obtained by melt grafting crosslinking reaction of the following components: Heptavinyl POSS single-grafted nylon 6 resin: 85-95 parts by weight; Modified expanded vermiculite with octadecenyl and DOPO groups on the surface: 5-15 parts by weight; Dicumyl peroxide initiator: 0.2-0.5 parts by weight; Among them, the heptavinyl POSS single-grafted nylon 6 resin is prepared by a ring-opening grafting reaction between the epoxy functional group of the heptavinyl POSS monoepoxy group and the amino group at the end of the nylon 6 molecular chain. Modified expanded vermiculite with octadecenyl and DOPO groups was prepared by surface modification of expanded vermiculite with a multifunctional silane compound containing octadecenyl, DOPO and trimethoxy groups; Under the action of dicumyl peroxide initiator, the vinyl groups on the POSS cage structure of heptavinyl POSS single-grafted nylon 6 resin undergo a free radical reaction with the octadecene groups on the surface of modified expanded vermiculite to obtain a high-performance masterbatch. The chemical structural formula of the multifunctional silane compound containing octadecenyl, DOPO, and trimethoxy groups is as follows: 。 2. The co-extruded film according to claim 1, characterized in that, The chemical structural formula of the monoepoxy heptavinyl POSS is: 。 3. The co-extruded film according to claim 1, characterized in that, The preparation method of the heptavinyl POSS single-grafted nylon 6 resin is as follows: based on nylon 6 with a terminal amino content of 40-45 mmol / kg, solution grafting modification is performed using a single epoxy group heptavinyl POSS. Under the conditions of epoxy group to terminal amino molar ratio (1.5-1.8):1 and reaction at 100-120℃ for 3-5 h, the grafting rate of the obtained resin is 2.0-3.0 wt%.

4. The co-extruded film according to claim 1, characterized in that, The modified expanded vermiculite with octadecenyl and DOPO groups on its surface contains 20-35 wt% of a multifunctional silane compound containing octadecenyl, DOPO and trimethoxy groups.

5. The preparation process of the co-extruded film according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Prepare a multifunctional silane compound containing octadecenyl, DOPO and trimethoxy groups, and use it to modify the surface of expanded vermiculite to obtain modified expanded vermiculite; Step 2: Prepare monoepoxy heptavinyl POSS and react it with nylon 6 resin to obtain heptavinyl POSS single-grafted nylon 6 resin. Step 3: Premix heptavinyl POSS single-grafted nylon 6 resin with modified expanded vermiculite, add initiator, and carry out melt grafting crosslinking reaction to obtain high-performance masterbatch; Step four: Add the high-performance masterbatch to the co-extrusion blow molding unit, and obtain the co-extruded film through melt extrusion, blowing, traction and cooling.

6. The preparation process of the co-extruded film according to claim 5, characterized in that, The preparation method of the multifunctional silane compound containing octadecenyl, DOPO groups and trimethoxy groups is as follows: Utilizing a nucleophilic substitution reaction mechanism, an organic base catalyzes a nucleophilic substitution reaction between 1 molar equivalent of oleylamine and 0.95-0.99 molar equivalents of 3-chloropropyltrimethoxysilane via a -NH2 functional group and a chlorine functional group to generate secondary aminooctadecenyltrimethoxysilane. An organic base catalyzes a reaction between 1 molar equivalent of acyl-chlorinated [(6-oxo-6H-dibenzo[C,E][1,2]oxophosphorylhexane-6-yl)methyl]succinic acid and 2.01-2.05 molar equivalents of secondary amine octadecenyltrimethoxysilane via an amidation reaction between the acyl chloride functional group and the secondary amine functional group, yielding a multifunctional silane compound containing octadecenyl, DOPO, and trimethoxy groups.

7. The preparation process of the co-extruded film according to claim 5, characterized in that, The preparation method of the monoepoxy heptavinyl POSS is as follows: Octavinyl POSS, under the action of tetraethylammonium hydroxide, opens a Si-O-Si bond at one vertex to generate an incompletely condensed POSS containing three silanols, namely hepta(vinyl)trisilol POSS; The three silanol groups of hepta(vinyl)trisilyl POSS undergo a condensation reaction with 3-(2,3-epoxypropoxy)propyltrimethoxysilane. The three methoxy groups of 3-(2,3-epoxypropoxy)propyltrimethoxysilane react with Si-OH to form Si-O-Si bonds. The cap opens at the apex, introducing an epoxy group to synthesize monoepoxy heptavinyl POSS.

8. The preparation process of the co-extruded film according to claim 5, characterized in that, The preparation method of the high-performance masterbatch is as follows: Heptavinyl POSS single-grafted nylon 6 resin was premixed with expanded vermiculite with octadecenyl and DOPO groups on its surface to obtain a dry mixture. Dicumyl peroxide (DCP) was dissolved in anhydrous acetone and added to the dry mixture by spraying. After mixing evenly and removing the solvent, a pretreated mixture was obtained. The pretreated mixture is added to a twin-screw extruder and subjected to a melt grafting crosslinking reaction at a temperature of 210-250℃. The material residence time is controlled to be 1-3 minutes. After extrusion granulation, a high-performance masterbatch is obtained.

9. The application of the co-extruded film according to any one of claims 1-4 in the encapsulation of aerogel heat insulation pads for new energy power batteries, characterized in that, The co-extruded film is used as an encapsulation barrier film for the aerogel heat insulation pad.

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