Microporous composite film for dynamic controlled atmosphere fresh-keeping and preparation method thereof

Abstract

The invention discloses a microporous composite film for dynamic controlled atmosphere fresh-keeping and a preparation method thereof. The preparation method comprises the following steps: carrying out multi-layer co-extrusion film blowing on a polyolefin raw material, and carrying out two-way stretching treatment on an obtained co-extrusion barrier base material film to obtain a microporous base material film which at least comprises an outer barrier layer and an inner functional layer; carrying out gradient dip-coating on the inner functional layer by adopting a hydrophilic functional solution containing a humidity control agent, and carrying out heavy ion punching on the outer barrier layer of the composite membrane after dip-coating to obtain a serial hole composite membrane; carrying out electrostatic spinning treatment on an outer barrier layer of the serial hole composite membrane based on a spinning solution containing water-repellent nanofibers to form a dynamic breathable composite membrane with a function of preventing liquid water from flowing backwards; the dynamic breathable composite film is subjected to multi-section progressive heat sealing, and the microporous composite film for dynamic controlled atmosphere fresh keeping is obtained; according to the invention, continuous adjustment and stable control of gas transmission in a high-humidity fluctuation environment are realized, and the dynamic air conditioning performance and the use reliability of the membrane material are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer materials, in particular to a microporous composite film for dynamic modified atmosphere packaging and a preparation method thereof. BACKGROUND

[0002] In the field of fresh food packaging such as fruits, vegetables, flowers and aquatic products, modified atmosphere packaging (MAP) is widely used because it can effectively delay the metabolic process and inhibit microbial growth. In recent years, with the development of cold chain transportation and the acceleration of global agricultural product circulation, traditional static modified atmosphere films have gradually been transformed into dynamic modified atmosphere films with "responsiveness" and "self-regulating ability". Such film materials require the ability to perceive environmental humidity and gas concentration, and can independently adjust the permeation rate of O2, CO2 and other gases through changes in film structure or material properties, thereby maintaining the stability of the packaging atmosphere. To achieve this function, scientific research and industry have explored various paths including multilayer co-extrusion films, porous materials, and stimulus-responsive coatings.

[0003] Currently, some research and commercial preservation composite films use degradable polymer coatings to adjust the gas permeability to achieve dynamic modified atmosphere function, such as applying a temperature and humidity responsive coating on the surface of a polylactic acid (PLA) substrate, or forming a humidity regulating functional layer by cross-linking water-soluble materials such as starch polysaccharides and polyvinyl alcohol (PVA) to achieve response and adjustment to humidity changes. However, the functional layer is mostly a continuous and dense coating structure, lacks gas "directional channels", and is prone to swelling and blocking gas diffusion paths due to water absorption, resulting in a dramatic fluctuation in film permeability in a high humidity environment, losing the stability of the adjustment. In addition, the blocking ability of such functional layers to liquid water penetration is limited, especially in a cold storage environment, which is prone to condensation penetration, humidity-sensitive layer swelling and damage, ultimately affecting the dynamic modified atmosphere effect and mechanical stability of the film material.

[0004] Therefore, it is necessary to provide a microporous composite film for dynamic modified atmosphere packaging and a preparation method thereof to solve the problems of easy loss of adjustment stability and poor dynamic modified atmosphere effect of existing preservation composite films. SUMMARY

[0005] The main purpose of the present application is to provide a microporous composite film for dynamic modified atmosphere packaging and a preparation method thereof, which aims to solve the technical problems mentioned in the background.

[0006] The present application adopts the following technical solutions: A microporous composite film for dynamic modified atmosphere packaging and a preparation method thereof, comprising: The polyolefin raw material is subjected to multi-layer co-extrusion blown film, and the obtained co-extrusion barrier substrate film is subjected to two-way stretching treatment to obtain a microporous substrate film, which at least includes an outer barrier layer and an inner functional layer; The inner functional layer is subjected to gradient dip coating with a hydrophilic functional solution containing a humidity regulator, and the outer barrier layer of the dip-coated composite film is subjected to heavy ion punching to obtain a string hole composite film; The outer barrier layer of the string hole composite film is subjected to electrospinning treatment based on a spinning solution containing water-repellent nanofibers to form a dynamic breathable composite film with liquid water backflow prevention function; The dynamic breathable composite film is subjected to multi-section gradual heat sealing to obtain a microporous composite film for dynamic modified atmosphere packaging.

[0007] Further, the hydrophilic functional solution is a mixture of polyvinyl alcohol and poly-N-isopropyl acrylamide, and the mass ratio of polyvinyl alcohol to poly-N-isopropyl acrylamide is 60-65:35.

[0008] Further, the spinning solution includes a preset solute and a preset solution, and the preset solute accounts for 15-20% of the mass of the spinning solution; In the preset solute, 18-20% of n-eicosane / silica shell phase change microcapsules and 10-15% of long-chain fluorosilane water-repellent modifier are included, and the balance is thermoplastic polyurethane; The preset solution is at least one of tetrahydrofuran or N,N-dimethylformamide.

[0009] Further, the step of co-extrusion blown film of the polyolefin raw material includes: The polyethylene copolymer and the fluoropolymer processing aid are mixed and then melt plasticized to form an outer barrier layer material, and the polyethylene and the organically modified nano-montmorillonite are subjected to melt intercalation to form a core layer material; The polyethylene, hydroxyl-terminated polyethylene oxide, and polyethylene glycol monomethyl ether are subjected to blending and melt treatment to form an inner functional layer material; The outer barrier layer material, the core layer material, and the inner functional layer material are subjected to layered convergence co-extrusion to obtain a co-extrusion barrier substrate film.

[0010] Further, the step of two-way stretching treatment of the obtained co-extrusion barrier substrate film to obtain a microporous substrate film includes: The co-extrusion barrier substrate film is subjected to longitudinal stretching and transverse stretching to obtain a two-way gradient microporous substrate film, wherein the preheating temperature of the longitudinal stretching is 115-120°C, and the temperature of the transverse stretching is 135-140°C; The two-way gradient microporous substrate film is subjected to heat setting and then rapid cooling treatment to form a microporous substrate film with an inner dense and outer sparse microporous structure.

[0011] Further, the step of gradiently immersing the inner functional layer in the hydrophilic functional solution containing the moisture regulating agent comprises: performing low-pressure oxygen plasma treatment on the microporous substrate film to form hydroxyl and carboxyl groups on the surface of the inner functional layer, thereby obtaining an activated substrate film; gradiently immersing the activated substrate film in the hydrophilic functional solution, thereby obtaining a functional coating composite film with asymmetric permeability; performing in-situ cross-linking and curing on the functional coating composite film, thereby forming a gradiently immersed composite film.

[0012] Further, the step of perforating the outer barrier layer of the immersed composite film with heavy ions to obtain a string-hole composite film comprises: perforating the outer barrier layer of the immersed composite film with heavy ion irradiation to obtain a latent track composite film; gradiently chemically etching the latent track composite film to obtain a through-hole string composite film, wherein each micropore in the through-hole string composite film has one end opening on the surface of the outer barrier layer and the other end terminating at the core layer; depositing a positive functional group on the micropore wall of the through-hole string composite film, thereby obtaining a string-hole composite film.

[0013] Further, the step of electrospinning the outer barrier layer of the string-hole composite film based on the spinning solution containing water-repellent nanofibers to form a dynamic air-permeable composite film with the function of preventing liquid water from backflowing comprises: etching a ring-shaped positioning mark on the micropore of the string-hole composite film, and electrospinning the string-hole composite film with the ring-shaped positioning mark using the spinning solution, thereby obtaining a fiber composite film; performing pulse heat pressing on the fiber composite film, and then performing gas phase deposition in a hexafluoroisopropanol vapor atmosphere, thereby obtaining a dynamic air-permeable composite film.

[0014] Further, the step of performing multi-section progressive heat sealing on the dynamic air-permeable composite film to obtain a microporous composite film for dynamic modified atmosphere packaging comprises: cutting the dynamic air-permeable composite film, and performing multi-section progressive heat sealing on the cut composite film based on ultrasonic waves, thereby forming a heat-sealed composite film with a ring-shaped sealing band; folding the ring-shaped sealing band of the heat-sealed composite film inward for secondary heat sealing, thereby obtaining a microporous composite film for dynamic modified atmosphere packaging.

[0015] A microporous composite film for dynamic modified atmosphere packaging is prepared by the preparation method of any one of the above microporous composite films for dynamic modified atmosphere packaging.

[0016] Beneficial effects: In this invention, a microporous substrate membrane with a multi-layer functional structure is obtained by multi-layer co-extrusion blown film processing of polyolefin raw materials and supplementing it with biaxial stretching treatment. The outer barrier layer provides basic gas barrier properties and mechanical strength, while the inner functional layer serves as a functional carrier for moisture and gas regulation. By using a hydrophilic functional solution containing a moisture regulator to perform gradient dip-coating on the inner functional layer, a gradient structure with gradually decreasing moisture absorption capacity from the inside to the outside can be constructed in the membrane thickness direction. This allows the membrane to maintain a relatively stable moisture absorption / release balance under fluctuating humidity conditions, avoiding membrane deformation or functional degradation caused by local oversaturation. Heavy ion perforation is performed on the outer barrier layer to establish a transparent and stable "tandem microporous channel". Combined with the gradient moisture absorption layer, this improves the sensitivity and controllability of gas exchange and enhances the dynamic response capability of the membrane material. In addition, electrospinning treatment of the surface of the perforated outer barrier layer using a spinning solution containing water-repellent nanofibers can effectively prevent liquid water such as condensate and free water in the packaging contents from entering the microporous channels and causing damage to the functional layer or blockage of the channels; multi-stage progressive heat sealing enables the layers of the composite film to fully bond at different temperature zones and maintain structural stability, making it suitable for preservation scenarios such as fruits and vegetables that are sensitive to changes in the ambient atmosphere. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of a method for preparing a microporous composite membrane for dynamic modified atmosphere preservation according to the present invention. The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0018] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0019] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, a direct connection, or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0021] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0022] Reference Figure 1 This invention proposes a method for preparing a microporous composite membrane for dynamic modified atmosphere preservation, comprising: S1: Multi-layer co-extrusion blown film is made from polyolefin raw material, and the resulting co-extruded barrier substrate film is subjected to biaxial stretching treatment to obtain microporous substrate film. The microporous substrate film includes at least an outer barrier layer and an inner functional layer. In step S1, polyolefin raw materials refer to polymeric materials with polyethylene, polypropylene and other olefin polymers as the main components. In this embodiment, a combination of various polyolefins with different densities and modifications is used to construct a three-layer asymmetric structure. The three-layer structure consists of an outer barrier layer, a core layer and an inner functional layer from the outside to the inside.

[0023] Three different polyolefin feedstocks were simultaneously extruded and merged at the die to form a complete preform. The outer barrier layer is mainly composed of high-density polyethylene, with the addition of ethylene-vinyl alcohol copolymer short-grafted modified particles and fluoropolymer processing aids, resulting in an extremely low coefficient of friction on the outer surface. The strong polarity of the ethylene-vinyl alcohol copolymer segments significantly improves oxygen barrier performance. The core layer is mainly composed of linear low-density polyethylene, with the addition of organically modified nano-montmorillonite (i.e., layered silicate filler with quaternary ammonium salt surface treatment) and ethylene-octene copolymer elastomer. The highly filled nano-montmorillonite can undergo interfacial delamination with the polymer matrix during stretching, generating numerous micropores. The ethylene-octene copolymer elastomer improves the core layer's toughness, preventing brittle fracture during stretching. The inner functional layer uses pure linear low-density polyethylene premixed with hydrophilic polyethylene oxide, providing good wettability. The three material streams converge to form a flat three-layer co-extruded substrate film with a thickness of about 90μm. At this time, the initial oxygen permeability of the entire film is extremely low, and the inner and outer sides show obvious performance asymmetry: the outer side is smooth and has high barrier properties, while the inner side is slightly rough and hydrophilic.

[0024] After obtaining the co-extruded barrier substrate film, it enters the biaxial stretching process. Here, "biaxial stretching" specifically refers to asynchronous biaxial stretching in both longitudinal and transverse directions. Specifically, longitudinal stretching occurs first, followed by transverse stretching, rather than simultaneous biaxial stretching. The aim is to induce a large number of oriented micropores in the core layer while maintaining the relative integrity of the outer barrier layer. In actual operation, the substrate film is first preheated and then subjected to high-speed longitudinal stretching in a longitudinal stretching machine. At this time, the highly filled nano-montmorillonite in the core layer begins to delaminate against the polyolefin matrix, forming microcracks that elongate longitudinally. Immediately afterwards, the film enters the chain-track oven of the transverse stretching machine for transverse stretching. The superposition of longitudinal and transverse stresses further expands and connects the microcracks in the core layer, forming a large number of three-dimensionally interconnected microporous networks. Because the outer barrier layer contains rigid ethylene-vinyl alcohol copolymer graft segments and is relatively thin, very few micropores are generated during stretching, and the pore sizes are extremely small (mostly closed or necked channels). In contrast, the inner functional layer contains flexible ethylene-octene copolymer elastomer segments and has weaker interfacial bonding with the core layer, resulting in a high micropore density and large opening size on the inner side. This ultimately creates an asymmetrical micropore distribution characterized by "dense inside and sparse outside, large inside and small outside." After stretching, the micropores are immediately heat-set and then rapidly cooled to lock in the micropore morphology and prevent shrinkage. Most of the micropore channels have a large opening at one end on the inner energy layer surface, while the other end is partially closed or leaves only a very fine necked channel in the outer barrier layer, ensuring that the membrane as a whole still maintains a certain level of mechanical strength.

[0025] S2: The inner functional layer is gradient dip-coated with a hydrophilic functional solution containing a humectant, and the outer barrier layer of the composite film after dip-coating is perforated with heavy ions to obtain a perforated composite film. In step S2, a hydrophilic functional solution containing a humectant is prepared. This is a polymeric blend system with significant temperature-humidity dual response. Polyvinyl alcohol and poly(N-isopropylacrylamide) can be used as the main components, with their mass ratio controlled between 60:40 and 70:30. Polyvinyl alcohol provides excellent film-forming properties and hydrophilicity, while poly(N-isopropylacrylamide) imparts significant temperature-sensitive properties to the coating, exhibiting low-temperature hydrophilic expansion and high-temperature hydrophobic shrinkage. The solid content of the solution is controlled at 18-22 wt%, and polyethylene glycol diglycidyl ether is added. Oil ethers or polyisocyanates are used as crosslinking agents to improve water resistance. Nanocellulose whiskers or nano-SiO2 are added to enhance the anchoring force between the coating and the substrate. The most crucial step is to add latent humidity-regulating components, such as menthol / β-cyclodextrin inclusion complexes, lauryl alcohol / cyclodextrin inclusion complexes, or octadecyl phosphate. At low temperatures (≤15℃), the humidity regulator can slowly release bound water, causing the hydrophilic network to expand further and thus significantly reducing gas permeability. At higher temperatures (≥25℃), it can quickly volatilize or desorb, reopening the channels. The microporous substrate film obtained in step S1 is fed into a gradient dip coating device with the inner functional layer facing upwards. The roller speed and immersion depth decrease in a progressively decreasing manner. For example, the first dip coating roller has a linear speed of 8-12 m / min and an immersion depth of 6-10 mm, while the second dip coating roller has a linear speed of 14-18 m / min and an immersion depth of only 2-4 mm. This allows the hydrophilic functional solution to first form a continuous coating on the surface of the inner functional layer. At the same time, the strong capillary action generated by the large-opening micropores on the inner side allows the solution to penetrate directionally into the interior of the film along the micropore channels, forming a continuous hydrophilic network on the inner wall of the micropores. The outer barrier layer is almost not penetrated by the solution due to the extremely fine micropores, thus achieving true single-sided gradient anchoring. After dip coating is completed, the film immediately enters the drying tunnel to obtain a temperature-sensitive hydrophilic functional layer that is extremely firmly bonded to the substrate.

[0026] After the gradient dip coating and curing of the hydrophilic functional layer are completed, heavy ion drilling is performed on the outer barrier layer. During drilling, the composite membrane is continuously operated with the hydrophilic functional layer facing down and the outer barrier layer facing up. Krypton or xenon ions are used to irradiate the outer barrier layer at the terminal of the high vacuum heavy ion accelerator, creating a micropore array in the area 8-15 mm away from the edge, thus forming a downhole channel in the outer barrier layer. After irradiation, the entire membrane is immersed in a sodium hydroxide solution for chemical etching. The depth of each micropore is just enough to penetrate the outer barrier layer and part of the core layer, but without damaging the hydrophilic coating of the inner functional layer, thus forming a composite gas passage with micropores with extremely narrow outer diameters and wide channels formed by stretched micropores at the inner end.

[0027] It is worth emphasizing that heavy ion drilling must be carried out after the hydrophilic functional layer has been completely cured and before electrospinning. At this time, the inner micropores have been filled by the hydrophilic network and have a certain back pressure, which can effectively prevent the trace debris generated by heavy ion drilling from contaminating the inner layer, while the surface of the outer barrier layer remains clean and flat.

[0028] S3: The outer barrier layer of the perforated composite membrane is electrospun based on a spinning solution containing water-repellent nanofibers to form a dynamic breathable composite membrane with anti-liquid water backflow function. In step S3, an electrospinning solution with water repellency, air permeability, and certain phase change temperature regulation functions is prepared. Thermoplastic polyurethane is used as the main fiber-forming polymer and dissolved in a mixed solvent of tetrahydrofuran and N,N-dimethylformamide in a 1:1 volume ratio to prepare a transparent spinning solution with a solid content of 14%–16%. Phase change microcapsules are added, which can be core-shell structured microcapsules with an eicosane core and a silica shell. These microcapsules absorb or release latent heat during temperature fluctuations in the packaging cold chain, mitigating drastic changes in temperature and humidity inside the bag. A long-chain fluorosilane coupling agent or a fluoropolymer, such as heptadecafluorodecyltriethoxysilane, is then added for water repellency modification, reducing the final fiber surface energy to below 15 mN / m. The perforated composite membrane is mounted in a continuous roll on the receiving roller of the electrospinning machine, with the outer barrier layer facing upwards. A water-repellent nanofiber membrane with a thickness of only 4–7 micrometers is directly deposited on the surface of the outer barrier layer of the perforated composite membrane. The resulting nanofibers exhibit a random three-dimensional stacked network structure, resulting in a porosity of over 90% between fibers, while the permeability coefficients for oxygen and carbon dioxide remain almost unaffected. Due to the effect of the high-voltage electrostatic field, the charged jet is repelled by the local electric field distortion at the micropore opening when it approaches the area with pre-drilled micropores. This causes the nanofibers to automatically form "fiber sparse regions" or "bare pore regions" directly above the micropores, ensuring that the outer opening of each micropore remains unobstructed and is not completely covered by fibers. Simultaneously, during the spinning process, the newly deposited thermoplastic polyurethane nanofibers undergo micro-melting anchoring with the surface of the polyolefin outer barrier layer, forming a strong local spot weld. This prevents large-area pore blockage and ensures that the nanofiber layer does not detach or become fuzzy during subsequent packaging, use, friction, and folding. The resulting hydrophobic nanofiber membrane is so strong that even when placed horizontally and water droplets are placed on its surface, the droplets quickly roll off without penetrating the micropores. Furthermore, even when the membrane is inverted and a column of liquid water is applied to the outside of the micropores (simulating the most extreme scenario of condensation backflow), the liquid water forms stable liquid bridges due to the dual barrier of the superhydrophobic nanofibers and the extremely narrow pores, preventing it from penetrating the membrane and achieving a true "anti-liquid water backflow" function. Simultaneously, because the nanofiber membrane is extremely thin and has extremely large pores, it offers almost no resistance to gas molecule diffusion. The entire membrane can achieve a dynamic controlled atmosphere effect, allowing water vapor to escape rapidly when humidity inside the packaging increases, CO2 to leak out quickly when concentration is high, and oxygen to be replenished rapidly when oxygen is insufficient. This prevents liquid water from completely blocking the ventilation channels caused by water seepage from fruits and vegetables or condensation in the cold chain.

[0029] S4: Perform multi-stage progressive heat sealing on the dynamic breathable composite membrane to obtain a microporous composite membrane for dynamic modified atmosphere preservation.

[0030] In step S4, the dynamic breathable composite membrane obtained after electrospinning has the following structure from the inside out: a thick hydrophilic coating with temperature-sensitive humidity control function, an inner functional layer and inner large-opening stretched micropores, a core layer with a high-density stretched microporous network, an outer barrier layer and extremely narrow channels formed by heavy ion perforation, and an outermost ultra-thin water-repellent and breathable nanofiber membrane. The material properties of each functional layer are quite different, with melting points ranging from about 180°C for polyvinyl alcohol hydrophilic layers, 220-260°C for polyolefin matrices, to about 190°C for thermoplastic polyurethane nanofibers. Moreover, the nanofiber layer is extremely thin, has high porosity, and the fibers are only bonded at points. Therefore, a multi-stage progressive heat sealing is required, which decomposes the entire heat sealing process into multiple energy-increasing stages in time and space, so that heat is transferred layer by layer from the outside to the inside, and finally, each layer reaches the optimal melt flow state simultaneously.

[0031] Specifically, the dynamically breathable composite film, cut to the required packaging size, is placed in a dedicated five- or six-segment variable frequency ultrasonic heat-sealing machine. Pulse hot air heat sealing or infrared gradient heating heat sealing can also be used. Taking a 12-15mm wide sealing area as an example, only the outermost water-repellent nanofibers and the surface of the outer barrier layer undergo slight melting and spot welding, forming a bridge for initial positioning and preventing subsequent heat conduction. In the second stage, the frequency is increased, at which point the high-density polyethylene body of the outer barrier layer begins to soften sufficiently, and the residual polar functional groups around the micropores generate stronger interfacial entanglement with the fluorosilane segments in the nanofibers. In the third stage, the frequency is further increased... The process involves several steps: First, heat is effectively transferred to the core layer. The residual nano-montmorillonite filler in the core layer acts as a thermal bridge due to its high thermal conductivity, causing the interface between the core layer and the outer barrier layer to quickly reach a viscous flow state. Simultaneously, the hydrophilic coating on the surface of the inner functional layer begins to pre-soften. Second, the polyvinyl alcohol-polyN-isopropylacrylamide blend in the fourth hydrophilic functional layer has completely entered the transition range from a high-elasticity state to a viscous flow state, achieving good compatibility and fusion with the polyolefin of the inner functional layer. Third, the fifth stage undergoes final strengthening welding, forming a homogeneous fusion band with a thickness of approximately 80-100 micrometers at the edge region of all five or six layers, completely eliminating the interlayer interface and presenting a single phase.

[0032] In another embodiment, referring to Table 1, comparative examples were selected for performance testing. All performance tests were conducted under uniform conditions: the effective air permeability area of ​​the sample was 100 cm². 2 The sample was placed in a standard controlled atmosphere test chamber, with a temperature cycle of 25℃ (room temperature for 2 hours) to 5℃ (refrigerated for 4 hours), and a relative humidity of 95%±3%. The initial gas composition inside the chamber was O2 5%, CO2 8%, and N2 in equilibrium. The liquid water backflow test was conducted by inverting the membrane sample and applying a gradually increasing water column to the outside until leakage occurred. The heavy ion perforation density and air permeability data were converted to standard 1m. 2 The baseline test was repeated 5 times and the average value was taken.

[0033] Comparative Example 1 is a "biodegradable dynamic modified atmosphere membrane" with biaxially oriented polylactic acid as the substrate and a continuous cross-linked polyvinyl alcohol / polyN-isopropylacrylamide temperature-sensitive coating on both sides. The coating thickness is about 15μm. It has no physical micropores or laser-drilled perforations and relies entirely on the coating to absorb water and expand / contract to achieve air permeability regulation. Comparative Example 2 is an "ordinary PE microporous food storage bag" which uses synchronous biaxial stretching to form symmetrical micropores. It is coated with ordinary hydrophilic PVA desiccant only on one side. It has no heavy ion perforation, no water-repellent nanofiber layer, no asymmetric micropore design, no phase change microcapsules, and no latent desiccant, which makes the micropores easily blocked by liquid water under high humidity.

[0034] The biggest difference between this invention and the two comparative examples lies in the construction of a novel composite structure characterized by "extreme internal and external asymmetry, multi-level serial channels, and triple dynamic response": First, through asynchronous bi-stretching and nano-montmorillonite interface exfoliation, an asymmetric stretched microporous network with a larger inner core and a smaller outer core is formed, ensuring a balance between mechanical strength and air permeability; second, through single-sided gradient impregnation and latent moisture-regulating agent, a non-clogging temperature-sensitive hydrophilic network is constructed on the inner side, reducing the air permeability by only 18% under high humidity (instead of the drastic 78% fluctuation in Comparative Example 1), achieving true "mild regulation"; third, through the precise application of heavy ions to the outer barrier layer, an extremely dense microporous network with a density of up to 20,000 / cm² is formed. The narrow-necked constricted pores, connected in series with the wide inner channels, combined with the self-avoiding deposition of water-repellent nanofibers only 4-7 μm thick on the outermost layer, completely solve the global problem of condensation backflow in the cold chain. This significantly increases the resistance to liquid water backflow from 12 cm water column in Comparative Example 1 and 28 cm water column in Comparative Example 2 to over 180 cm, more than 15 times that of ordinary plastic wrap. Simultaneously, the phase change microcapsules added to the electrospinning solution and the rapid low-temperature recovery characteristics allow the O2 permeability to return to normal within 8 minutes after a sudden temperature drop, compared to up to 2 hours in Comparative Example 1 and 45 minutes in Comparative Example 2. This greatly reduces the risk of suffocation and anaerobic respiration of fruits and vegetables under the impact of temperature differences in the cold chain. It is this triple synergistic mechanism of "physical microporous directional channels, chemical temperature-sensitive network, and surface super-water-repellent nanofibers" that enables the membrane of this invention to maintain a high initial air permeability (850 cm⁻¹). 3 / m 2 While maintaining a moderate to high 24h atm (suitable for most fruits and vegetables), it also achieves highly sensitive adaptive regulation of humidity, temperature, and gas concentration, CO2. 2 / O 2 With a selectivity of up to 4.8, it completely solves the industry pain points mentioned in the background technology, such as "high humidity runaway, liquid water clogging, and poor regulation stability". In actual cold chain preservation tests of high-breathing fruits and vegetables such as strawberries, blueberries, lychees, and fresh-cut vegetables, the shelf life is generally extended by 35% to 70%, and the phenomenon of fogging and water leakage is almost eliminated.

[0035] Table 1: In one embodiment, the hydrophilic functional solution is a mixture of polyvinyl alcohol and poly(N-isopropylacrylamide), wherein the mass ratio of polyvinyl alcohol to poly(N-isopropylacrylamide) is 60-65:35.

[0036] In the above embodiments, polyvinyl alcohol and poly(N-isopropylacrylamide) are blended at a mass ratio of 60-65:35 as the main component of the hydrophilic functional solution. When the ambient temperature is below 32°C, the poly(N-isopropylacrylamide) segments form strong hydrogen bonds with water molecules, causing the polymer network to expand dramatically, effectively blocking the large-opening micropores on the inner side and significantly reducing the permeation rates of O2 and CO2. When the temperature rises above 35°C due to heat generated by the respiration of fruits and vegetables, the hydrogen bonds of the poly(N-isopropylacrylamide) segments break, the hydrophobic effect is enhanced, the network rapidly shrinks and expels adsorbed water, and the micropores reopen, achieving an adaptive increase in gas flux with temperature. Maintaining a polyvinyl alcohol ratio of 60-65% provides sufficient hydroxyl groups to form covalent bonds and hydrogen bonds with subsequent crosslinking agents and hydroxyl / carboxyl groups on the substrate surface, ensuring that the coating does not peel off in high humidity environments. The 35% poly(N-isopropylacrylamide) ensures sufficient temperature response range and response speed. In one example, the spinning solution includes a preset solute and a preset solution, wherein the preset solute accounts for 15% to 20% of the mass of the spinning solution. The preset solute, by mass ratio, contains 18%~20% n-eicosane / silica shell phase change microcapsules and 10%~15% long-chain fluorosilane water-repellent modifier, with the balance being thermoplastic polyurethane. The preset solution is at least one of tetrahydrofuran or N,N-dimethylformamide.

[0037] In the above embodiments, the preset solute is the total solid content of the spinning solution, controlled at 15%–20%. The solute consists of 18%–20% n-eicosane / silica shell phase change microcapsules, 10%–15% long-chain fluorosilane water-repellent modifier, and the balance thermoplastic polyurethane. The n-eicosane phase change microcapsules undergo a solid-liquid phase change at 32–36°C, which is endothermic and can delay the further increase of local high temperature in fruits and vegetables. At the same time, liquid n-eicosane slowly seeps out along the microcracks in the silica shell, further enhancing the hydrophobicity of the fiber surface. During spinning and subsequent hexafluoroisopropanol vapor deposition, the long-chain fluorosilane reacts with the polar groups on the molecular chains and micropore walls of the thermoplastic polyurethane to form low surface energy -CF3 and -CF3- densely arranged groups, which makes the static water contact angle stable >150° and has a roll-off angle <10°, achieving a super strong anti-liquid water backflow capability. Thermoplastic polyurethane, as a continuous phase, ensures the mechanical strength of the fibers and their thermal adhesion to the substrate. The ratio of the three components allows the nanofiber layer to maintain extremely high water vapor permeability while completely blocking the penetration of condensate or fruit and vegetable surface juices, ensuring that the micropores and stretched micropores are not blocked by liquid water for a long time, thereby maintaining the long-term unobstructed flow of the dynamic modified atmosphere channel.

[0038] In one example, the step of performing multilayer co-extrusion blown film extrusion on the polyolefin raw material includes: The outer barrier layer is formed by mixing polyethylene copolymer and fluoropolymer processing aid and then melting and plasticizing it. The core layer is formed by melting and intercalating polyethylene with organically modified nano-montmorillonite. Polyethylene is blended and melt-treated with hydroxyl-terminated polyethylene oxide and polyethylene glycol monomethyl ether to form an inner functional layer material; The outer barrier layer material, core layer material and inner functional layer material are layered and co-extruded to obtain a co-extruded barrier substrate film.

[0039] In the above embodiments, the outer barrier layer material is mainly polyethylene copolymer with a small amount of fluoropolymer processing aids added, making the surface of the melt extremely smooth and the coefficient of friction extremely low when it is cast in the die. At the same time, the migration characteristics of fluoropolymers form an extremely thin low surface energy layer on the outer surface, which can provide a clean interface. The core layer uses linear polyethylene as the matrix and is pre-melted and intercalated with organically modified nano-montmorillonite through a high-shear twin-screw extruder. This allows the montmorillonite sheets to be fully peeled and dispersed between the polymer chains, which can serve as a "sacrificial template" for interface peeling and pore formation during stretching. At the same time, an appropriate amount of elastomer is added to improve the toughness of the core layer and prevent macroscopic fracture during stretching. The inner functional layer is made of polyethylene blended with hydroxyl-terminated polyethylene oxide and polyethylene glycol monomethyl ether, which rapidly enriches a large number of polar segments on its surface, resulting in a surface energy that is significantly higher than that of the outer layer, providing strong adhesion for the hydrophilic coating. The three material streams converge in layers without mixing within the coat hanger-type die head. The melt curtain is rapidly cooled and shaped by a high-pressure air knife, resulting in differences in crystallinity and orientation between the inner and outer layers. This ultimately yields a substrate film with uniform thickness and distinctly different internal and external properties. The asymmetry provides a material basis for selective microporousization and functional modification. The process does not require complex interlayer adhesives; the structural foundation is completed in a single co-extrusion step, making the process simple and efficient.

[0040] In one example, the step of biaxially stretching the obtained co-extruded barrier substrate film to obtain a microporous substrate film includes: The co-extruded barrier substrate film is subjected to longitudinal stretching and transverse stretching to obtain a bidirectional gradient microporous substrate film, wherein the preheating temperature for longitudinal stretching is 115~120℃ and the temperature for transverse stretching is 135~140℃. After heat setting, the bidirectional gradient microporous substrate film is rapidly cooled to form a microporous substrate film with a dense inner and sparse outer microporous structure.

[0041] In the above embodiments, asymmetric micropores are induced in the core layer through asynchronous longitudinal and transverse stretching, while maintaining the outer layer as relatively dense. The co-extruded substrate film is subjected to high-speed longitudinal stretching at a relatively low temperature, with a preheating temperature of 115~120℃. The outer barrier layer, containing grafted segments with high rigidity, does not undergo significant deformation, while the nano-montmorillonite in the core layer begins to generate stress concentration with the matrix, causing the interface to peel off first along the machine direction, forming a large number of slender microcracks. Immediately, the process is switched to transverse stretching at a higher temperature, with the transverse stretching temperature increased to 135~140℃. At this time, the inner functional layer, containing flexible hydrophilic segments, is more likely to soften and deform. The microcracks further expand and interconnect under transverse stress, while the outer barrier layer, due to its high melting point, remains relatively intact, forming only extremely fine necking channels, naturally forming a gradient microporous structure of "dense inside and sparse outside, large inside and small outside". After stretching, the hole shape is locked by high-temperature short-time heat setting, followed by rapid cooling to prevent the hole channel from shrinking. Finally, one end of the micropore channel is open in the inner functional layer, and the other end is partially closed by the outer barrier layer. The resulting asymmetric channel provides a perfect structural basis for the precise "windowing" of the outer layer and the "blocking and releasing" of the inner hydrophilic coating. The whole process does not rely on filler extraction or foaming agent, but relies entirely on the difference of tensile stress to achieve selective pore formation. The pore size distribution is narrow, the connectivity is good, and the process is stable and controllable.

[0042] In one example, the step of gradient dip-coating the inner functional layer with a hydrophilic functional solution containing a humectant includes: The microporous substrate membrane is subjected to low-pressure oxygen plasma treatment to form hydroxyl and carboxyl groups on the surface of the inner functional layer, thereby obtaining an activated substrate membrane. The activated substrate membrane was subjected to gradient dip coating with a hydrophilic functional solution to obtain an asymmetric permeation functional coating composite membrane. The functional coating composite film is cross-linked and cured in situ to form a gradient dip-coated composite film.

[0043] In the above embodiments, gradient dip coating is not simply applying a layer of hydrophilic material; rather, it involves establishing a temperature-sensitive hydrogel network with a continuously varying depth of 20-25 micrometers from the surface to the interior of the membrane within the large-aperture micropores on the inner side. The microporous substrate membrane is subjected to low-pressure oxygen plasma treatment, introducing a large number of active sites such as hydroxyl and carboxyl groups onto the surface of the inner functional layer and the pore walls. This transforms the originally hydrophobic polyolefin pore walls into hydrophilic ones, significantly improving the wetting and spreading ability of the solution. Further, a two-stage differential dip coating is performed using a mixed solution primarily composed of polyvinyl alcohol and poly(N-isopropylacrylamide) (mass ratio approximately 63:37). The first stage involves a slow, deep dip to allow the solution to fully penetrate deep into the micropores, while the second stage involves a rapid, shallow dip to primarily supplement the surface coating thickness, forming a gradient structure that gradually thins from the inside out. The membrane then enters a multi-zone gradient drying tunnel. The low-temperature zone slowly removes the solvent to avoid bubble formation, the medium-temperature zone initiates the reaction between the crosslinking agent and the hydroxyl groups, and the high-temperature zone completes in-situ crosslinking and curing, enabling the hydrophilic network to form chemical bonds with the pore walls rather than physical adsorption. The resulting coating swells and absorbs water at temperatures below 32°C, almost completely blocking the large pores on the inside and restricting gas passage. At higher temperatures, the chain segments shrink and dehydrate, reopening the pores and achieving "breathing" dynamic atmosphere regulation. Because the coating thickness and pore size are gradient-matched, it does not sacrifice air permeability and can accurately respond to temperature and humidity changes caused by the respiration of fruits and vegetables. The entire process utilizes the synergistic effect of the microporous asymmetric structure and the temperature-sensitive polymer to achieve adaptive regulation without the need for mechanical valves.

[0044] In one embodiment, the step of performing heavy ion perforation on the outer barrier layer of the dip-coated composite film to obtain a perforated composite film includes: The outer barrier layer of the dip-coated composite film was perforated by heavy ion irradiation to obtain a latent trajectory composite film. Gradient chemical etching is performed on the latent trajectory composite film to obtain a through-hole series composite film, wherein each micropore in the through-hole series composite film opens at one end to the surface of the outer barrier layer and terminates at the other end to the core layer. Positive functional groups are deposited on the micropore walls of the through-hole series composite membrane to obtain a series-hole composite membrane.

[0045] In the above embodiments, heavy ion perforation of the outer barrier layer opens extremely narrow gas channels on the originally almost dense barrier layer on the outside and precisely connects them with the existing stretched microporous network on the inside, thereby forming a composite channel structure that is "narrow on the outside and wide on the inside", achieving high selective air permeability while maintaining extremely high barrier background.

[0046] Specifically, the composite membrane, after being gradient-coated and cured with a hydrophilic functional solution, is fixed with the outer barrier layer facing upwards in a vacuum target chamber, and vertically irradiated using a krypton or xenon heavy ion beam with an energy of 2.2 GeV, with the irradiation flux controlled at 5 × 10⁻⁶. 5 ~1×10 7 ions / cm 2Within a certain range, high-energy heavy ions penetrate the outer barrier layer one by one, leaving nanometer-sized latent trajectory damage regions in the polymer molecular chains without producing significant thermal effects or carbide residues. The irradiated latent trajectory composite film is then placed in a gradient chemical etching system, first at 50–60 °C with a concentration of 6–9 mol / L... Etching in sodium hydroxide solution for 20–40 minutes allows the latent tracks on the surface of the outer barrier layer to preferentially expand and form openings. Then, the concentration of the etching solution is gradually reduced and ultrasonic vibration is applied to gradually slow down the etching rate from the surface inwards, ultimately forming cylindrical through-holes in the outer barrier layer. One end of the micropore opens onto the outer surface, while the other end does not completely penetrate, terminating in the core layer. It naturally merges and connects with the interfacial delamination micropores generated by the previous biaxial stretching in the core layer region, forming a series channel. This constitutes a stepped perforated structure with extremely narrow outer ends and wide inner ends. After etching, selective deposition is performed on the pore walls in a weakly alkaline solution containing silane coupling agent or dopamine. This enriches the pore wall surface with a large number of active functional groups such as hydroxyl and amino groups, which not only significantly improves the solubility-diffusion selectivity of carbon dioxide relative to oxygen, but also provides chemical bonding sites for the positioning and anchoring of the water-repellent nanofiber layer. Finally, a perforated composite membrane is obtained, whose gas channels have both extremely high selective permeability and excellent structural stability, fully meeting the dual requirements of dynamic modified atmosphere preservation for precise O2 / CO2 control and prevention of liquid water backflow.

[0047] In one embodiment, the step of electrospinning the outer barrier layer of the perforated composite membrane with anti-liquid water backflow function based on the spinning solution containing water-repellent nanofibers includes: The micropores of the perforated composite membrane are etched with annular positioning marks, and the perforated composite membrane with annular positioning marks is spun and deposited using spinning solution to obtain a fiber composite membrane. After the fiber composite membrane is subjected to pulse hot pressing treatment, it is vapor-deposited in a hexafluoroisopropanol vapor atmosphere to obtain a dynamic breathable composite membrane.

[0048] In the above embodiments, electrospinning rapidly constructs an ultrathin water-repellent nanofiber membrane on the surface of the outer barrier layer. This membrane completely covers the area surrounding the micropores to prevent liquid water backflow while ensuring that the micropores themselves are not completely blocked by the fibers, forming a dynamically permeable "selectively open" structure. The outer barrier layer of the perforated composite membrane undergoes rapid UV or plasma etching to form shallow annular grooves with a diameter of approximately 30-50 μm around each micropore opening as positioning markers. During spinning using a spinning solution containing water-repellent functional components, the composite membrane is laid flat or rolled up onto a receiving roller with the outer barrier layer facing upwards. At a voltage of 28-32 kV and a receiving distance of 15-20 cm, the annular positioning markers around the micropores and the oxygen-rich functional groups at the pore edges result in a higher local electric field intensity. The charged jet actively avoids the center of the pore and deposits densely around it, forming an adaptive pattern of "exposed pores and high-density surrounding coverage." Immediately after spinning, a short-duration pulsed hot-pressing process (temperature 90-110℃, pressure 0.2-0.5MPa, time 3-8s) is performed to allow the fibers and substrate to undergo moderate melting and solidification. Finally, a brief vapor-phase deposition is carried out in a hexafluoroisopropanol vapor atmosphere to further enhance the orientation and cross-linking of the water-repellent long chains on the fiber surface. The entire nanofiber membrane is only 4-6μm thick, with a water contact angle >150°, yet it maintains extremely high water vapor permeability. At refrigerated temperatures, the phase change microcapsules absorb heat and expand, further opening the fiber gaps to achieve temperature-controlled enhanced breathability, perfectly meeting the dual requirements of preventing liquid water backflow and dynamic breathability.

[0049] In one embodiment, the step of performing multi-stage progressive heat sealing on the dynamic breathable composite membrane to obtain a microporous composite membrane for dynamic modified atmosphere preservation includes: The dynamic breathable composite membrane is cut, and the cut composite membrane is heat-sealed in multiple stages based on ultrasonic waves to form a heat-sealed composite membrane with an annular sealing strip. The annular sealing strip of the heat-sealed composite film is folded inward for secondary heat sealing to obtain a microporous composite film for dynamic modified atmosphere preservation.

[0050] In the above embodiments, multi-segment progressive heat sealing achieves absolute airtightness at the edge of the final product, eliminating side leakage, and also separates the multifunctional microporous area from the sealing edge area. The dynamically breathable composite membrane with completed nanofiber spinning is cut to the required size and fed into a multi-segment variable frequency ultrasonic heat sealing machine. The heat sealing head has five or more segments, with the frequency of each segment gradually increasing from 20kHz to 28kHz, and the amplitude and energy density increasing synchronously. This allows the outermost water-repellent nanofiber layer to first slightly melt and flatten at a lower energy level, while the outer barrier layer, the core microporous area, and the inner functional hydrophilic coating layer successively achieve molecular chain interpenetration and fusion welding at higher energies, forming a completely closed annular sealing band with a width of 10-15mm. Because ultrasonic vibration can generate extremely high instantaneous temperature and shear force at the interface of different materials, even if the surface energy difference between the water-repellent nanofiber and the polyolefin substrate is huge, a firm bond can be achieved in a short time without damaging the central microporous functional area. After the first heat sealing, the film edge is folded inward 180° and then subjected to a second heat sealing at a higher frequency and with higher energy. This allows the folded portion to fuse with the inner side again, forming a three-dimensional sealing structure with double protection. This multi-stage, progressive combination of folding and secondary sealing steps avoids fiber layer peeling or thermal damage to micropore areas that may occur with traditional heat sealing. It also ensures zero edge leakage of the final product under extreme conditions such as transportation, bagging, and vacuuming. This achieves a complete and highly reliable seal that can be implemented from the laboratory to industrialization. The finished product can be directly used for dynamic modified atmosphere packaging bags or box lid films for high-end fruits and vegetables.

[0051] This application also discloses a microporous composite membrane for dynamic modified atmosphere preservation, which is prepared by any of the above-described methods for preparing a microporous composite membrane for dynamic modified atmosphere preservation, and includes the corresponding technical features in the above-described preparation methods, which will not be repeated here.

[0052] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a microporous composite film for dynamic controlled atmosphere packaging, characterized by, The application relates to a method for preparing a micro-porous composite film for dynamic modified atmosphere packaging. The method comprises the following steps: performing multi-layer co-extrusion blown film on a polyolefin raw material, performing bidirectional stretching treatment on the obtained co-extrusion barrier base film to obtain a micro-porous base film, and the micro-porous base film at least comprises an outer barrier layer and an inner functional layer; A hydrophilic functional solution containing a humidity regulator is used to perform gradient dip coating on the inner functional layer, and heavy ion punching is performed on the outer barrier layer of the dip-coated composite film to obtain a string-hole composite film; Based on a spinning solution containing water-repellent nanofibers, electrospinning treatment is performed on the outer barrier layer of the string-hole composite film to form a dynamic air-permeable composite film with a liquid water backflow prevention function; The dynamic air-permeable composite film is subjected to multi-section gradual heat sealing to obtain a micro-porous composite film for dynamic modified atmosphere packaging.

2. The method for preparing a microporous composite membrane for dynamic modified atmosphere preservation according to claim 1, characterized in that, The hydrophilic functional solution is a mixture of polyvinyl alcohol and poly-N-isopropyl acrylamide, and the mass ratio of the polyvinyl alcohol and the poly-N-isopropyl acrylamide is 60-65:

35.

3. The method for preparing a microporous composite membrane for dynamic modified atmosphere preservation according to claim 1, characterized in that, The spinning solution comprises a preset solute and a preset solution, and the preset solute accounts for 15%-20% of the mass of the spinning solution. In the preset solute, 18%-20% of n-eicosane / silica shell phase change microcapsules and 10%-15% of long-chain fluorosilane water-repellent modifier are contained, and the rest is thermoplastic polyurethane. The preset solution is at least one of tetrahydrofuran or N,N-dimethylformamide.

4. The method for preparing a microporous composite membrane for dynamic modified atmosphere preservation according to claim 1, characterized in that, The step of performing multi-layer co-extrusion blown film on the polyolefin raw material comprises the following steps: Polyethylene copolymer and fluoropolymer processing aids are mixed and then melt-plasticized to form an outer barrier layer material, and polyethylene and organically modified nano-montmorillonite are subjected to melt intercalation compounding to form a core layer material; Polyethylene, hydroxyl-terminated polyethylene oxide and polyglycol monomethyl ether are subjected to blending melt treatment to form an inner functional layer material; The outer barrier layer material, the core layer material and the inner functional layer material are subjected to layered convergence co-extrusion to obtain a co-extrusion barrier base film.

5. The method for preparing a microporous composite membrane for dynamic modified atmosphere preservation according to claim 1, characterized in that, The step of performing bidirectional stretching treatment on the obtained co-extrusion barrier base film to obtain a micro-porous base film comprises the following steps: The co-extrusion barrier base film is subjected to longitudinal stretching and transverse stretching to obtain a bidirectional gradient micro-porous base film, wherein the preheating temperature of the longitudinal stretching is 115-120 DEG C, and the temperature of the transverse stretching is 135-140 DEG C; After the bidirectional gradient micro-porous base film is heat set, rapid cooling treatment is performed to form a micro-porous base film with an inner dense and outer sparse micro-porous structure.

6. The method for preparing a microporous composite membrane for dynamic modified atmosphere preservation according to claim 1, characterized in that, The step of performing gradient dip coating on the inner functional layer by using the hydrophilic functional solution containing a humidity regulator comprises the following steps: Low-pressure oxygen plasma treatment is performed on the micro-porous base film to form hydroxyl and carboxyl on the surface of the inner functional layer to obtain an activated base film; The activated base film is subjected to gradient dip coating by using the hydrophilic functional solution to obtain a functional coating composite film with asymmetric permeation; In-situ cross-linking and curing are performed on the functional coating composite film to form a gradient dip-coated composite film.

7. The method for preparing a microporous composite membrane for dynamic modified atmosphere preservation according to claim 4, characterized in that, The step of performing heavy ion punching on the outer barrier layer of the dip-coated composite film to obtain a string-hole composite film comprises the following steps: Heavy ion irradiation punching is performed on the outer barrier layer of the dip-coated composite film to obtain a latent track composite film; Gradient chemical etching is performed on the potential track composite film to obtain a through-hole series composite film, and each micropore in the through-hole series composite film has one end opening on the surface of the outer barrier layer and the other end terminating in the core layer; Deposition of a positive functional group on the micropore wall of the through-hole series composite film to obtain a string-hole composite film.

8. The method for preparing a microporous composite membrane for dynamic modified atmosphere preservation according to claim 1, characterized in that, The step of electrospinning treatment of the outer barrier layer of the string-hole composite film based on the spinning solution containing water-repellent nanofibers to form a dynamic breathable composite film with a liquid water backflow prevention function, includes: Etching a ring-shaped positioning mark on the micropore of the string-hole composite film, and using a spinning solution to spin and deposit the string-hole composite film with the ring-shaped positioning mark to obtain a fiber composite film; After pulse heat pressing treatment of the fiber composite film, gas phase deposition is performed in a hexafluoroisopropanol vapor atmosphere to obtain a dynamic breathable composite film.

9. The method for preparing a microporous composite membrane for dynamic modified atmosphere preservation according to claim 1, characterized in that, The step of performing multi-stage progressive heat sealing on the dynamic breathable composite film to obtain a microporous composite film for dynamic modified atmosphere packaging, includes: Cutting the dynamic breathable composite film, and performing multi-stage progressive heat sealing on the cut composite film based on ultrasonic waves to form a heat-sealed composite film with a ring-shaped sealing band; Inward folding the ring-shaped sealing band of the heat-sealed composite film for secondary heat sealing to obtain a microporous composite film for dynamic modified atmosphere packaging.

10. The microporous composite film for dynamic controlled atmosphere packaging according to claim 1, wherein Made by a method for preparing a microporous composite film for dynamic modified atmosphere packaging according to any one of claims 1-9. Made by a method for preparing a microporous composite film for dynamic modified atmosphere packaging according to any one of claims 1-9.

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