Preparation device and method of micro-modified atmosphere fruit and vegetable preservation film

Abstract

The application discloses a kind of micro-fruit and vegetable fresh-keeping film preparation device and method, the device includes forming cylinder assembly, feeding coating component, dust generation and settlement component, air cooling device and film winding collection component;Forming cylinder assembly includes rotatable self-heating forming cylinder, feeding coating component is used to coat film-forming liquid on the left upper surface of self-heating forming cylinder, dust generation and settlement component is used to settle nano antibacterial catalyst dust on the film surface on self-heating forming cylinder;Air cooling device is used to cold blow setting on the film surface of the right lower part of self-heating forming cylinder, and film winding collection component is used to winding collection of the film formed.The device of the application utilizes the time window period of film not completely solidified to load nano catalytic functional powder, so that the powder is firmly attached to the film surface layer, the contact area of catalytic powder and oxygen is increased, the catalytic efficiency is improved, and the migration risk of catalytic powder is reduced.

Description

Technical Field

[0001] This invention relates to the field of fruit and vegetable preservation film technology, specifically to a device and method for preparing a modified atmosphere fruit and vegetable preservation film. Background Technology

[0002] Fruits and vegetables maintain a high level of respiratory metabolism during post-harvest storage and distribution, and continuously exchange water and gases, making them susceptible to problems such as dehydration and wilting, softening of texture, decline in flavor and nutritional components, and microbial spoilage. Studies have shown that appropriately controlling the concentration of oxygen and carbon dioxide within packaging and inhibiting water loss helps reduce the respiration intensity of fruits and vegetables, delay ripening and senescence, and maintain commercial quality. Therefore, in addition to basic physical isolation and mechanical protection, fruit and vegetable preservation packaging materials should also, to a certain extent, achieve synergistic regulation of water vapor and gas transport behavior to create a suitable micro-atmosphere environment.

[0003] Currently, petroleum-based films such as polyethylene (PE) are still the main materials used for fruit and vegetable preservation packaging. While these materials have mature manufacturing processes and low costs, their non-degradability creates an environmental burden, and their adjustable range in gas and moisture transport properties is limited, making it difficult to precisely match them to the different respiratory characteristics of various fruits and vegetables. Polyvinyl alcohol (PVA), as a water-soluble polymer, has advantages such as good film-forming properties, high transparency, good moisture permeability, and adjustable mechanical properties, and has attracted widespread attention in the field of biodegradable packaging. However, the large number of hydroxyl groups in the PVA molecular chain makes it too hydrophilic in high-humidity environments, resulting in a high water vapor permeability and accelerated water loss from fruits and vegetables. This limits its direct application in fruit and vegetable preservation packaging where moisture retention is crucial.

[0004] On the other hand, for the preservation of fruits and vegetables with climacteric respiration, the content of oxygen and ethylene has a significant impact on preservation. Studies have shown that using nano-metal catalysts can effectively catalyze the conversion of oxygen into reactive oxygen species, which is beneficial for promoting ethylene degradation and improving antibacterial effects. In existing technologies, nano-catalysts are generally prepared by blending with a thin film matrix and then casting or casting to form a film. This blending and incorporation route is relatively simple, but after the film solidifies, most of the nano-catalyst inside the film is isolated by the film matrix. Oxygen cannot contact the nano-catalyst, and the catalytic effect of this part of the internal nano-catalyst cannot be exerted. This process exposes relatively little catalyst on the surface of the film, resulting in very limited catalytic capacity. To obtain a better antibacterial effect, it is often necessary to increase the overall amount of nano-catalyst added, which not only increases costs but also seriously reduces the physical properties of the film.

[0005] While existing publicly available information has laid out some groundwork regarding the "PVA + cyclodextrin" direction, its technological focus does not align with the claims to be protected in this application. For example, patent CN102585412A discloses an "active packaging film based on essential oil / β-cyclodextrin inclusion complex," whose main idea is to use β-cyclodextrin as an embedding wall material to slowly release and migrate essential oils to the food surface to exert antibacterial effects; the packaging film is primarily a polyvinyl alcohol film. Patent CN102604292B... The patent CN114059234B discloses a PVA / PLA active packaging film, which slowly releases natural antibacterial agents after encapsulation with β-cyclodextrin, while PLA is used to improve the water resistance of PVA. Patent CN114059234B discloses a fruit and vegetable preservation film containing polyvinyl alcohol and cyclodextrin, which uses electrospinning to form a high-porosity fiber film, focusing on essential oil encapsulation and active release. Patent CN106751280A uses β-cyclodextrin to encapsulate garlic oil to improve the dispersibility of bentonite in the PVA substrate and improve water resistance. Another patent CN104356569B uses cyclodextrin as part of the PVA film composite plasticizing system to inhibit the migration of small molecule plasticizers and improve tensile and optical properties. The above disclosure states that in the prior art, the main role of β-cyclodextrin in the PVA system is mainly concentrated on inclusion, sustained release, plasticizer stabilization, or filler dispersion. This invention patent directly uses β-cyclodextrin as the key regulating component. PVA can easily permeate water molecules, but it has an obstructive effect on non-polar gases such as oxygen. The addition of cyclodextrin is mainly to generate trace gas channels. By utilizing the partial hydrophobic effect of its central pores, the purpose of oxygen permeability can be achieved, thus establishing a synergistic regulation mechanism for water permeability and oxygen permeability in fruit and vegetable packaging.

[0006] In their paper "The Influence of Packaging Materials on the Modified Atmosphere Preservation Effect of Cherry Tomatoes," Wang Yu et al. disclosed that when using PA / PE film and EHA / PE film for packaging, the O2 content inside the cherry tomato packaging dropped to 0 on the 3rd day, while the CO2 rose to over 30% on the 6th day. This indicates that when the barrier properties of the packaging material are too strong, it is very easy to create an excessively low-oxygen / high-carbon dioxide environment, which can induce adverse physiological reactions. This publication demonstrates the feasibility of spontaneous modified atmosphere packaging, but it also shows that simply relying on the barrier properties of a given film material makes it difficult to balance the different needs of fruits and vegetables in terms of water retention, oxygen supply, and metabolic inhibition.

[0007] In terms of functional catalytic / antibacterial components, nano-zinc oxide is one of the most widely disclosed materials. Public reviews have summarized the antibacterial mechanism of ZnO in food packaging as the generation of surface reactive oxygen species and Zn... 2+ The pathways include dissolution, direct cellular action, and photocatalysis; further mechanistic studies have shown that ZnO can be generated through reactive oxygen species and Zn... 2+It releases damaged cell membranes and induces oxidative stress. Meanwhile, many existing methods still directly incorporate ZnO into the membrane through blending, casting, casting, or blow molding. For example, the 2021 Foods publication, "Preparation and Characterization of Chitosan-Nano-ZnO Composite Film and Its Preservation Effect on Cherry Tomatoes," shows that chitosan / nano-ZnO composite films can maintain soluble solids in cherry tomatoes and inhibit respiration; patent CN101497702A discloses a "food nano-preservation film" which involves coating a nano-zinc oxide dispersion onto a PE / EVA base film after blow molding; and Gao Yanli et al.'s "Zinc Migration in Nano-Zinc Oxide Composite Coatings and Its Effect on Postharvest Oranges" further suggests that after ZnO nanoparticles are introduced into the coating, the migration of Zn to the peel is affected by the amount added and the storage temperature.

[0008] The aforementioned disclosure demonstrates the application potential of ZnO in fruit and vegetable preservation, but also highlights that blending or conventional coating methods still face challenges such as particle agglomeration, intrafilm embedding, insufficient utilization, and migration risk assessment. This invention patent provides a device for preparing a nano-catalyst composite preservation film, using nano-ZnO as an example. The active oxygen (ROS) generated by nano-ZnO and the zinc ions (ZnO) released... 2+ The non-contact mechanism dominated by ) can play a role in inhibiting bacteria and catalyzing ethylene, increasing the contact area between nanocatalysts and oxygen, improving catalytic efficiency, and reducing the risk of migration of catalytic powder.

[0009] Besides ZnO, publicly available information also covers other catalytic or adsorption systems related to fruit and vegetable preservation. Patent CN109912876B discloses an antibacterial microporous preservation film using ZSM-5 molecular sieve as an ethylene scavenger and TiO2 as an antibacterial agent, noting that when the TiO2 content reaches a good antibacterial level, the elongation at break decreases significantly, making it difficult to maintain mechanical properties. Patent CN112831070B discloses using 1-MCP and palladium-loaded activated carbon together in the middle layer of a fruit and vegetable preservation film to achieve humidity-responsive release and catalytic removal of ethylene after adsorption. An earlier patent, CN101578978A, discloses an ethylene absorbent using activated carbon, diatomaceous earth, or zeolite as a carrier and palladium compounds as the main reactant, primarily used in the form of independent granules or small bags. Additionally, CN108424579B discloses the preparation of preservation films by doping visible light-responsive photocatalysts into polymer base materials. The above disclosures indicate that existing technologies utilize catalysts / adsorbents in various forms, including integral blending, independent carrier, and sandwich construction. However, there is still a lack of clear and systematic disclosures regarding technical approaches that ensure the catalyst is stably attached directly to the membrane surface while simultaneously considering adhesion, surface exposure, preservation effect, and membrane physical properties.

[0010] Based on the publicly available information, it can be seen that although existing technologies have conducted considerable research on PVA modification, β-cyclodextrin active encapsulation, ZnO / TiO2 and other functional particle blending or surface coating, and ethylene adsorption catalytic systems, the following problems still exist: First, existing PVA / cyclodextrin-related disclosures mostly use β-cyclodextrin as an encapsulation, slow-release, or plasticizing auxiliary component, and there is a lack of fruit and vegetable micro-atmosphere control technology solutions that use β-cyclodextrin as a key regulating factor to simultaneously achieve water permeability and oxygen permeability regulation in the PVA system; Second, existing nanocatalysts or antibacterial particles are mostly introduced through blending, ordinary coating, or post-treatment methods, making it difficult to simultaneously ensure the effective exposure, adhesion, migration control, and recycling of particles on the membrane surface; Third, existing disclosures often only solve one or some of the problems of antibacterial, ethylene removal, water blocking, or oxygen blocking, and it is still difficult to simultaneously ensure physical property stability and practical application effects.

[0011] This invention provides a method for preparing a micro-atmosphere modified fruit and vegetable preservation film, which significantly improves various indicators compared with traditional preservation films, and can solve the problem of nanocatalyst migration and effectively recover nanocatalysts. Summary of the Invention

[0012] In view of the above-mentioned technical problems existing in the prior art, the purpose of the present invention is to provide a device and method for preparing a micro-modified atmosphere fruit and vegetable preservation film.

[0013] The technical solution adopted in this invention is as follows: A device for preparing a modified atmosphere fruit and vegetable preservation film includes a forming cylinder assembly, a feeding and coating assembly, a dust generation and settling assembly, an air cooling device, and a film hoisting and collecting assembly. A molding cylinder assembly, including a rotatable, self-heating molding cylinder; The feeding coating assembly is used to coat the film-forming liquid onto the upper left surface of the self-heating forming cylinder; The dust generation and settling assembly includes a settling cylinder and a dust pneumatic conveying device. The bottom of the settling cylinder is provided with an opening that is spaced out and located directly above the self-heating forming cylinder. The dust pneumatic conveying device is used to transport the nano antibacterial catalyst into the settling cylinder by wind to form a dust cloud, so that the dust settles on the film surface on the self-heating forming cylinder. The air-cooling device is used to blow out cold air to cool and shape the film surface on the lower right side of the self-heating forming cylinder. The film winch collection assembly is used to winch and collect the formed film.

[0014] Furthermore, the feeding and coating assembly includes a coating cylinder, a coating nozzle at the bottom of the coating cylinder, and an electric heater on the outer wall of the coating nozzle; multiple diversion pipes are provided at the top of the coating cylinder, and a peristaltic pump is fixedly connected to the side of the coating cylinder. The inlet of the peristaltic pump is supplied with film-forming liquid, and the outlet of the peristaltic pump is connected to the multiple diversion pipes respectively.

[0015] Furthermore, the settling cylinder is trumpet-shaped, narrow at the top and wide at the bottom, with the side of the bottom opening of the settling cylinder being arc-shaped. The bottom opening of the settling cylinder is close to the upper surface of the self-heating forming cylinder, and the distance between the bottom opening of the settling cylinder and the upper surface of the self-heating forming cylinder is 0.5-2cm, preferably 0.5-1.0cm.

[0016] Furthermore, the dust pneumatic conveying device includes a feed pipe, a feeding cylinder, a conical hopper, a nano antibacterial catalyst feeding component, and a dust generating component. The top outlet of the feeding cylinder is connected to a settling cylinder through the feed pipe, and the bottom of the feeding cylinder is connected to the conical hopper. A filter screen is installed inside the bottom of the conical hopper and connected to the dust generating component. The nano-antibacterial catalyst feeding assembly is used to feed the nano-antibacterial catalyst into the feeding cylinder; The dust generating component is used to input gas into the conical hopper and feeding cylinder. The gas carries the nano-antibacterial catalyst to disperse, thereby forming stable dust.

[0017] Furthermore, the nano-antibacterial catalyst feeding assembly includes a feeding funnel containing the nano-antibacterial catalyst and a screw conveyor, the screw conveyor being used to transport the nano-antibacterial catalyst in the feeding funnel into the feeding cylinder; The dust generating component includes an air inlet pipe fixedly connected to the bottom of the conical hopper. The lower end of the air inlet pipe is fixedly connected to a pulse control valve. The air inlet of the pulse control valve is fixedly connected to an air pump. The air pump supplies air into the air inlet pipe through the pulse control valve, and the gas then enters the conical hopper and the feeding cylinder.

[0018] Furthermore, the air-cooling device includes an air cooler, the air outlet of which is angled upward toward the lower right side of the self-heating forming cylinder.

[0019] A method for preparing a modified atmosphere fruit and vegetable preservation film, using the apparatus described in this invention, includes the following steps: Step 1: Polyvinyl alcohol (PVA) and β-cyclodextrin (β-CD) are dissolved sequentially in deionized water under heating to obtain a PVA / β-CD composite film-forming solution; Step 2: While the self-heating molding cylinder is rotating, it is self-heating. The PVA / β-CD composite film-forming liquid obtained in Step 1 is coated onto the upper left surface of the self-heating molding cylinder through the feeding coating assembly to form a film. The film gradually solidifies under the heating effect during the rotation and conveying process of the self-heating molding cylinder. Step 3: The dust pneumatic conveying device uses conveying gas to disperse the nano antibacterial catalyst into stable dust, and then conveys the dust into the settling cylinder to form a dust cloud; when the film is conveyed to the bottom of the settling cylinder along with the self-heating forming cylinder, the film surface is in a semi-cured state that is not completely dried, and the dust in the settling cylinder settles and adheres to the film surface. Step 4: The film with dust adhering to its surface is dried and cured by air cooling device to obtain PVA / β-CD / nano antibacterial catalyst composite preservation film, and finally collected by film hoisting collection component.

[0020] Furthermore, in step 1, the mass of β-cyclodextrin (β-CD) is 5%-10% of the mass of polyvinyl alcohol (PVA).

[0021] Furthermore, in step 2, the self-heating forming cylinder is self-heated to a surface temperature of 40-50℃.

[0022] Furthermore, the nano-antibacterial catalyst mentioned in step 3 is nano-ZnO, nano-TiO2, or nano-SiO2; in the PVA / β-CD / nano-antibacterial catalyst composite preservation film in step 4, the loading of the nano-antibacterial catalyst is 1-3 wt%.

[0023] Compared with the prior art, the beneficial effects achieved by the present invention are: 1. By miscibly dissolving β-cyclodextrin in PVA film, the oxygen permeability of PVA base film is improved, while the water vapor permeability is reduced, thus meeting the micro-modified atmosphere preservation requirements of non-climacteric fruits and vegetables. 2. By utilizing the time window during which the thin film is not fully solidified, nano-catalytic functional powders are loaded, allowing the powders to adhere firmly to the film surface. This increases the contact area between the catalytic powders and oxygen, thereby improving catalytic efficiency and reducing the risk of powder migration. The nano-catalytic functional powders are not limited to ZnO and can be extended to various functional materials such as TiO2, SiO2, and nanoclay. 3. The apparatus for preparing the modified atmosphere fruit and vegetable preservation film of the present invention has a continuous structure and controllable parameters, making it suitable for industrial continuous preparation of modified atmosphere fruit and vegetable preservation film. Attached Figure Description

[0024] Figure 1 This is one of the overall structural schematic diagrams of the preparation device for the micro-atmosphere modified fruit and vegetable preservation film of the present invention; Figure 2 This is the second schematic diagram of the overall structure of the preparation device for the micro-atmosphere fruit and vegetable preservation film of the present invention; Figure 3 This is a front view of the apparatus for preparing the micro-atmosphere modified fruit and vegetable preservation film of the present invention; Figure 4 yes Figure 1 Schematic diagram of the structure of the intermediate forming cylinder assembly; Figure 5 yes Figure 1 A partial structural schematic diagram of the thin-film hoisting collection assembly; Figure 6 yes Figure 1 Schematic diagram of the structure of the in-feed coating assembly; Figure 7 yes Figure 1 Schematic diagram of the connection structure between the mid-distance adjustment component and the coating cylinder; Figure 8 yes Figure 1 Schematic diagram of the dust generation component; Figure 9 These are SEM images comparing the cling film prepared in Example 3 and Comparative Example 1 of this invention. Figures 1-8In the middle section: 1. Molding cylinder assembly; 11. First support frame; 12. Self-heating molding cylinder; 13. First motor; 2. Feeding and coating assembly; 21. Second support frame; 22. Distance adjustment assembly; 221. Guide plate; 222. Guide groove; 223. Slider; 224. Adjusting screw; 23. Coating cylinder; 24. Coating nozzle; 25. Peristaltic pump; 26. Diverter pipe; 3. Dust generation and settling assembly; 31. Settling cylinder; 32. Suspension assembly; 321. Fixing frame; 322. Threaded rod; 323. Locking nut; 324. Hanger 33. Feeding plate; 34. Feeding cylinder; 35. Conical hopper; 36. Filter screen; 37. Screw conveyor; 38. Feeding funnel; 39. Dust generating assembly; 391. Air inlet pipe; 392. Pulse control valve; 393. Air pump; 4. Film hoisting and collecting assembly; 41. Third support frame; 42. Semi-circular groove; 43. Rotating shaft; 44. Take-up roller; 45. Fixing plate; 46. Mounting base; 47. Second motor; 5. Vibration motor; 6. Fourth support frame; 7. Support roller; 8. Electric heater; 9. Horizontal plate; 10. Air cooler. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0026] Please see Figure 1-8 The present invention provides a device for preparing a micro-atmosphere modified fruit and vegetable preservation film, comprising a forming cylinder assembly 1, a feeding and coating assembly 2, a dust generation and settling assembly 3, and a film hoisting and collecting assembly 4.

[0027] The molding cylinder assembly 1 includes two first support frames 11, and the same self-heating molding cylinder 12 is rotatably connected between the two first support frames 11. A first motor 13 is fixedly connected to one of the first support frames 11, and the output end of the first motor 13 is fixedly connected to the self-heating molding cylinder 12. Under the drive of the first motor 13, the self-heating molding cylinder 12 can be rotated.

[0028] The feeding coating assembly 2 includes two second support frames 21 respectively fixedly connected to two first support frames 11. A distance adjustment assembly 22 is fixedly connected to each of the two second support frames 21. A coating cylinder 23 is fixedly connected between the two distance adjustment assemblies 22. A coating nozzle 24 is provided at the bottom of the coating cylinder 23. An electric heater 8 is provided on the outer wall of the coating nozzle 24. The electric heater 8 can heat the coating nozzle 24 as needed, thereby flexibly adjusting the coating temperature. Multiple diversion pipes 26 are provided at the top of the coating cylinder 23. A peristaltic pump 25 is fixedly connected to the side of the coating cylinder 23. The inlet of the peristaltic pump 25 is filled with film-forming liquid, and the outlet of the peristaltic pump 25 is connected to the multiple diversion pipes 26.

[0029] The distance adjustment assembly 22 includes a guide plate 221 fixedly connected to the second support frame 21. A guide groove 222 is formed on the side of the guide plate 221 near the coating cylinder 23. An adjusting screw 224 is rotatably connected to the guide groove 222 via a bearing, with one end of the adjusting screw 224 extending to the outside of the guide plate 221. A slider 223 is fixedly connected to the side of the coating cylinder 23 near the adjacent guide groove 222. The slider 223 is located within the guide groove 222 and is threaded onto the adjusting screw 224. By turning the adjusting screw 224, the position of the slider 223 within the guide groove 222 can be adjusted, thereby adjusting the distance between the coating nozzle 24 and the self-heating forming cylinder 12, allowing for flexible adjustment of the coating distance as needed.

[0030] The dust generation and settling assembly 3 includes a settling cylinder 31 and a dust wind conveying device. The settling cylinder 31 has an opening at the bottom and is located directly above the self-heating forming cylinder 12. The dust wind conveying device is used to transport the nano antibacterial catalyst into the settling cylinder 31 by wind to form a dust cloud, so that the dust settles on the film surface on the self-heating forming cylinder 12.

[0031] Comparison chart Figure 1 and Figure 3 The settling cylinder 31 is funnel-shaped, narrow at the top and wide at the bottom. The side of the bottom opening of the settling cylinder 31 is arc-shaped. The bottom opening of the settling cylinder 31 is close to the upper surface of the self-heating forming cylinder 12. Thus, there is a gap between the bottom opening of the settling cylinder 31 and the film on the upper surface of the self-heating forming cylinder 12. The gas inside the settling cylinder 31 flows out through this gap. Under the carrying effect of the gas flow, the rate of dust settling on the film surface can be increased. In addition, the gap is small, which is conducive to the dust settling fully on the film surface and the amount of dust carried away by the gas is small.

[0032] The dust pneumatic conveying device includes a feed pipe 33, a feeding cylinder 34, a conical hopper 35, a nano-antibacterial catalyst feeding assembly, and a dust generating assembly 39. The top outlet of the feeding cylinder 34 is connected to a settling cylinder 31 via the feed pipe 33. The bottom of the feeding cylinder 34 is connected to the conical hopper 35, and a filter screen 36 is installed inside the bottom of the conical hopper 35 and connected to the dust generating assembly 39. The nano-antibacterial catalyst feeding assembly is used to feed the nano-antibacterial catalyst into the feeding cylinder 34. The dust generating assembly 39 is used to input gas into the conical hopper 35 and the feeding cylinder 34. The gas drives the nano-antibacterial catalyst to disperse, thereby forming stable dust.

[0033] The nano-antibacterial catalyst feeding assembly includes a feeding funnel 38 containing the nano-antibacterial catalyst and a screw conveyor 37, which is used to transport the nano-antibacterial catalyst in the feeding funnel 38 into the feeding cylinder 34.

[0034] The dust generating assembly 39 includes an air inlet pipe 391 fixedly connected to the bottom of the conical hopper 35. The lower end of the air inlet pipe 391 is fixedly connected to a pulse control valve 392. The air inlet of the pulse control valve 392 is fixedly connected to an air pump 393. The air pump 393 supplies air into the air inlet pipe 391 through the pulse control valve 392. The gas then enters the conical hopper 35 and the feeding cylinder 34, thereby enabling the nano antibacterial catalyst powder to disperse and form stable dust.

[0035] Comparison Figures 1-3 A suspension assembly 32 is fixedly connected to the outer wall of the settling cylinder 31. The suspension assembly 32 includes two symmetrically fixed brackets 321 fixed to the side walls of the settling cylinder 31. Each bracket 321 is movably threaded with a threaded rod 322. The rod wall of each threaded rod 322 is threaded with two locking nuts 323. The bracket 321 is located between the two locking nuts 323. A lifting plate 324 is fixedly connected to the upper end of the threaded rod 322. The lifting plate 324 is fixedly connected to the support bracket by screws, thereby enabling the settling cylinder 31 to be fixedly installed. The height of the trumpet-shaped settling cylinder 31 can be adjusted by loosening the two locking nuts 323, thereby allowing the distance between the settling cylinder 31 and the self-heating forming cylinder 12 to be flexibly adjusted according to actual needs.

[0036] Comparison Figure 3 A vibration motor 5 is fixedly connected to the lower side of the feed tube 33. The vibration motor 5 is turned on at regular intervals to drive the feed tube 33 to vibrate, thereby preventing dust from adhering to the inner wall of the feed tube 33 and causing accumulation and blockage.

[0037] The film winding and collecting assembly 4 includes two third support frames 41. Each of the two third support frames 41 has a semi-circular groove 42 on its top. A rotating shaft 43 is movably inserted into each of the two semi-circular grooves 42. A take-up roller 44 is connected between the two rotating shafts 43. A fixing plate 45 is fixedly connected to one of the third support frames 41. A mounting base 46 is fixedly connected to the upper side of the fixing plate 45 by multiple bolts. A second motor 47 is fixedly connected to the mounting base 46. The output end of the second motor 47 is engaged in the rotating shaft 43. The second motor 47 drives the rotating shaft 43 to rotate, and the rotating shaft 43 drives the take-up roller 44 to rotate.

[0038] The film winding and collecting assembly 4 also includes two fourth support frames 6 and a support roller 7 rotatably connected between them. The support roller 7 is located between the winding roller 44 and the self-heating forming cylinder 12. The support roller 7 can support the film, thereby improving the smoothness of film winding.

[0039] The air-cooling device includes an air cooler 10, as shown in the comparison. Figure 1A horizontal plate 9 is fixedly connected between the two first support frames 11, and an air cooler 10 is fixedly connected to the horizontal plate 9. The air outlet of the air cooler 10 is angled upward toward the lower right side of the self-heating forming cylinder 12. The air cooler 10 can accelerate the cooling of the film, thereby increasing the forming speed of the film and improving the production efficiency of the film.

[0040] The preparation process of the modified atmosphere fruit and vegetable preservation film using the equipment includes the following stages: Stage I: The film-forming liquid is extruded from the coating nozzle 24 and adheres to the outer wall of the self-heating forming cylinder 12. The film formed by the film-forming liquid reaching the outer wall of the self-heating forming cylinder 12 in this stage is still in a fluid / high-flow state.

[0041] Stage II: When the film on the outer wall surface of the self-heating forming cylinder 12 reaches below the settling cylinder 31 as it rotates, the film surface is in a semi-flowing and semi-solidified state, which facilitates the embedding and adhesion of nano-antibacterial catalyst dust on the film in this state.

[0042] Stage III: As the film continues to rotate with the self-heating forming cylinder 12, when it reaches the continuous heating section near the middle of the right side of the self-heating forming cylinder 12, the film needs to be basically solidified to resist sagging caused by gravity.

[0043] Stage IV: The film continues to rotate with the self-heating forming cylinder 12 to the lower right side of the self-heating forming cylinder 12. Under the action of the air-cooling device, it is dried and cured to complete the cooling and shaping. Under the winding action of the film hoisting and collecting assembly 4, it is peeled off and enters the film hoisting and collecting assembly to form the finished film roll.

[0044] In the embodiments and comparative examples of this invention, the polyvinyl alcohol (PVA) raw material used has a degree of polymerization of 3588.

[0045] In a specific embodiment of the present invention, the testing method for the plastic wrap is as follows: 1. Determination of water vapor permeability The water vapor permeability of thin films was determined according to the cup method principle of GB / T 1037-2021. This standard specifies the cup method for determining the weight gain and weight loss of water vapor permeability of plastic films and sheets, and is applicable to the moisture permeability characterization of film materials.

[0046] This study employed a modified cup-type weight gain method to determine water vapor transmission rate (WVTR). An appropriate amount of anhydrous calcium chloride was placed in a permeation cup, the rim of which was covered with the membrane sample to be tested, and secured with a sealing ring and sealing material to ensure a constant effective test area and no leakage at the edges. The permeation cup was then placed in a 75% RH environment and equilibrated at 25°C. The mass of the permeation cup was weighed every 24 hours, and the data was recorded continuously for at least 7 days. The water vapor transmission rate (WVTR) was calculated by plotting the increase in the permeation cup's mass per unit time against time and taking the slope of the straight line during the steady-state phase. ; WVTR is the water vapor transmission rate, in g·m³. -2 ·d -1 ; Δm is the change in mass during the steady-state phase, expressed in grams. A is the effective transmittance area, in meters. 2 ; Δt is the measurement time, d.

[0047] 2. Determination of oxygen permeability The oxygen permeability of the thin film was determined using a combination of static diffusion and headspace gas analysis. Methods for determining the gas permeability behavior of packaging materials based on changes in headspace gas concentration have been reported in relevant studies and can be used for the quantitative analysis of oxygen and carbon dioxide permeability in flexible packaging materials.

[0048] The membrane sample to be tested was heat-sealed and fixed in a self-made sealed diffusion cell, ensuring that independent upper and lower cavities were formed on both sides of the membrane, and the effective permeation area was accurately measured. Before testing, one cavity was kept in an air environment, while the other cavity was purged with high-purity nitrogen to bring its initial oxygen volume fraction close to 0. Both cavities were kept at atmospheric pressure. The device was then placed in a constant temperature environment, and the change in oxygen volume fraction in the low-oxygen side cavity was measured at predetermined time intervals using an F950 portable ethylene / oxygen / carbon dioxide analyzer. The oxygen permeability (OTR) was calculated using the slope of the linear phase of the oxygen concentration change over time on the low-oxygen side. ; OTR is oxygen permeability, in cm. 3 ·m -2 ·d -1 ; V is the volume of the receiving cavity on the hypoxic side, in cm. 3 ; A is the effective transmittance area, in meters. 2 ; dC / dt represents the rate of change of oxygen volume fraction during the steady-state phase. Each sample was measured in triplicate.

[0049] 3. Determination of the ethylene removal performance of the composite membrane The ethylene removal performance of composite membranes with different ZnO introduction methods was determined using a closed headspace method. ZnO is a typical semiconductor photocatalytic material, and its photoresponse is mainly located in the ultraviolet region. Under ultraviolet irradiation, ZnO can generate electron-hole pairs, thereby promoting the oxidative removal of ethylene. Therefore, this experiment was conducted at 25 °C under UV-A irradiation.

[0050] During testing, membrane samples were cut to 10 cm × 10 cm pieces, with one sample placed in each sealed reaction vessel. The vessels used were 1000 mL sealed glass containers with a silica gel sampling port at the top to ensure good airtightness and the feasibility of repeated sampling. Ethylene standard gas was then injected into the containers to achieve an initial ethylene volume fraction of 50 μL / L. Once the initial ethylene concentration reached 50 ppm, the containers were immediately sealed. To minimize environmental interference, all test vessels were placed in a constant temperature environment at 25℃ and continuously irradiated with a 365 nm UV-A lamp above them, with the light intensity controlled at 1.0 mW / cm². 2 .

[0051] Headspace gas was sampled through the sampling port at 0 h, 6 h, 12 h, and 24 h, and the ethylene concentration in the container was measured using an F-950 portable gas analyzer. The instrument was calibrated before testing to ensure the comparability of data from different time points. Three replicates were set up for each sample group, and results are expressed as mean ± standard deviation.

[0052] The ethylene removal rate of the composite membrane is calculated using the following formula: ; C0 represents the initial ethylene concentration in the container, in μL / L; C t The concentration of ethylene in the container after time t of light exposure is expressed in μL / L.

[0053] 4. Antibacterial performance test of Escherichia coli The antibacterial properties of the composite film were determined using the Oxford cup diffusion method, with *Escherichia coli* as the test strain and the diameter of the inhibition zone as the evaluation index. This method is widely used in antibacterial packaging film research and can directly reflect the inhibitory effect of the active components in the film sample on bacterial growth.

[0054] The preserved bacterial strain was inoculated into nutrient broth medium and incubated at 37 °C for 18–24 h to allow it to recover growth and reach the logarithmic growth phase. The bacterial suspension was then collected, diluted with sterile physiological saline, and the concentration was adjusted to approximately 1.0 × 10⁻⁶. 7CFU / mL, for later use. Spread 100 μL of bacterial suspension evenly onto the surface of a solidified nutrient agar plate, allowing the bacteria to form a uniform bacterial film on the culture medium surface. After the bacterial suspension has been largely absorbed, gently place a sterile Oxford cup on the plate surface. Cut the test film sample into round pieces with a diameter of 0.7 cm and add them to the Oxford cup under aseptic conditions. Then, incubate the plate at 37 ℃ for 24 h. Measure the diameter of the inhibition zone using calipers. Set up three replicates for each sample, with at least two measurements per replicate. Take the average value as the diameter of the inhibition zone for that sample. Results are expressed as mean ± standard deviation.

[0055] Example 1: A method for preparing a modified atmosphere fruit and vegetable preservation film, comprising the following steps: Step 1: Preparation of film-forming solution: Weigh polyvinyl alcohol (PVA) and add it to deionized water. Heat to 90°C and stir to dissolve to obtain PVA film-forming solution. The mass concentration of PVA in the PVA film-forming solution is 9%. After the solution cools to 60°C, add β-cyclodextrin (β-CD) and continue stirring until homogeneous (the mass of β-CD added is 5% of the mass of PVA) to obtain PVA / β-CD composite film-forming solution. Step 2, Roller Coating and Thickness Control: The self-heating forming cylinder 12 is internally heated to raise the surface temperature of the self-heating forming cylinder 12 and maintain its surface temperature at 45±2℃; the PVA / β-CD composite film-forming liquid described in Step 1 is coated onto the upper left surface of the self-heating forming cylinder 12 through the feeding coating assembly 2 to form a thin film. The film gradually solidifies under the heating action during the rotation and conveying process of the self-heating forming cylinder 12. By controlling the gap between the coating nozzle of the feeding coating assembly 2 and the upper left surface of the self-heating forming cylinder 12, the dry film thickness is controlled to be 0.05 mm; the linear speed v of the film rotation on the surface of the self-heating forming cylinder 12 is controlled to be 2 mm / s.

[0056] Step 3, film formation: The film is dried and cured by the air cooler 10 to finally obtain a PVA / β-CD-5% composite food preservation film with a dry film thickness of 0.05 mm. The composite food preservation film is then wound up by the film hoisting and collecting assembly 4.

[0057] Compared to the preservation film prepared according to the method of Example 1 but without the addition of β-CD, the PVA / β-CD-5% composite preservation film obtained in Example 1 has a 31.8% lower water vapor transmission rate and an 11.5% higher oxygen transmission rate, resulting in better preservation effect.

[0058] Example 2: A method for preparing a micro-atmosphere modified fruit and vegetable preservation film. The experimental steps are repeated in Example 1, except that the amount of β-CD is changed so that the added mass of β-CD is 10% of the mass of PVA. All other conditions remain unchanged, and a PVA / β-CD-10% composite preservation film is finally obtained.

[0059] Compared to the preservation film prepared according to the method of Example 2 but without the addition of β-CD, the preservation film obtained in Example 2 has a 15.9% lower water vapor transmission rate and an 86.7% higher oxygen transmission rate, resulting in better preservation effect.

[0060] Example 3: A method for preparing a modified atmosphere fruit and vegetable preservation film, comprising the following steps: Step 1: Preparation of film-forming solution: Weigh polyvinyl alcohol (PVA) and add it to deionized water. Heat to 90°C and stir to dissolve to obtain PVA film-forming solution. After the solution cools to 60°C, add β-cyclodextrin (β-CD) and continue stirring until homogeneous (the mass of β-CD added is 5% of the mass of PVA) to obtain PVA / β-CD composite film-forming solution. Step 2, Roller Coating and Thickness Control: The self-heating forming cylinder 12 is internally heated to raise the surface temperature of the self-heating forming cylinder 12 and maintain its surface temperature at 45±2℃; the PVA / β-CD composite film-forming liquid described in Step 1 is coated onto the upper left surface of the self-heating forming cylinder 12 through the feeding coating assembly 2 to form a thin film. The film gradually solidifies under the heating action during the rotation and conveying process of the self-heating forming cylinder 12. The dry film thickness is controlled to 0.05 mm by adjusting the gap between the coating nozzle of the feeding coating assembly 2 and the upper left surface of the self-heating forming cylinder 12. Furthermore, the catalyst loading on the film surface can be controlled by adjusting the rotation speed of the self-heating forming cylinder 12. The linear velocity v of the film rotation on the surface of the self-heating forming cylinder 12 is controlled to be 2 mm / s.

[0061] Step 3, ZnO dust formation and settling spraying: The width of the bottom opening of the settling cylinder 31 is about 40 cm. When the film on the outer wall surface of the self-heating forming cylinder 12 reaches the bottom of the settling cylinder 31 as it rotates, the film surface is in a semi-flowing and semi-cured state that is not completely dry. Nano ZnO powder is fed into the feeding cylinder 34 at a feeding rate of F = 0.9 g / min. The dust generating component 39 disperses the nano ZnO powder to form stable dust, which is then conveyed to the upper part of the settling zone through the feed pipe 33 to form a dust cloud. The dust settles and adheres to the surface of the film below the settling cylinder 31. Step 4: Film Formation: The ZnO-coated film is dried and cured using an air cooler 10, resulting in a PVA / β-CD / ZnO composite preservation film with a dry film thickness of 0.05 mm. The PVA / β-CD / ZnO composite preservation film is then wound up using a film hoisting and collecting assembly 4. The Zn content is determined (according to national standard GB 5009.268-2016, pretreatment using microwave digestion combined with inductively coupled plasma mass spectrometry (ICP-MS)). The ZnO loading on the PVA / β-CD / ZnO composite preservation film is 2.04 wt%.

[0062] The composite preservation film obtained in Example 3 showed an inhibition rate of 96.85% against Escherichia coli, which was 6.6% higher than that of the blend film in Comparative Example 1; the ethylene removal rate after 24 hours was 70%-78%, which was 84.5% higher than that of the blend film in Comparative Example 1; the tensile strength was 67.97 MPa, which was 19.6% higher than that of the PVA / β-CD-5% composite preservation film in Example 1; in the preservation experiment, the PVA / β-CD / ZnO composite preservation film of Example 3 showed a more significant ability to inhibit water loss, with a mass loss of only 10.2% after 28 days, which was significantly lower than that of the PVA group and the PVA / β-CD group. The PVA group refers to the preservation film PVA prepared according to the method of Example 1 but without the addition of β-CD, and the PVA / β-CD group refers to the PVA / β-CD-5% composite preservation film of Example 1. It maintains optimal firmness at the end of storage (21 N at 28 days); it has excellent retention of soluble solids content (TSS) (6.8% at 28 days) and better preservation effect.

[0063] Example 4: A method for preparing a micro-atmosphere modified atmosphere fruit and vegetable preservation film The experimental steps of Example 4 were repeated in Example 3, except that the linear speed of the film rotation on the surface of the self-heating forming cylinder 12 was controlled to be v=5mm / s, and the other conditions remained unchanged. Finally, a PVA / β-CD / ZnO composite food preservation film was obtained.

[0064] The Zn content of the PVA / β-CD / ZnO composite food preservation film obtained in Example 4 was determined, and the ZnO loading on the PVA / β-CD / ZnO composite food preservation film was 1.56 wt%. The composite preservation film of Example 4 showed an inhibition rate of 94.25% against Escherichia coli, which was 4.1% higher than that of the blend film of Comparative Example 1; the ethylene removal rate after 24 hours was 45%-50%, which was 18.8% higher than that of the blend film of Comparative Example 1; and the tensile strength was 71.2 MPa, which was 27.1% higher than that of the PVA / β-CD-5% composite preservation film of Example 1.

[0065] Example 5: A method for preparing a micro-atmosphere modified atmosphere fruit and vegetable preservation film The experimental steps of Example 5 were repeated in Example 3, except that the linear speed of the film rotation on the surface of the self-heating forming cylinder 12 was controlled to be v=7.5mm / s, and the other conditions remained unchanged. Finally, a PVA / β-CD / ZnO composite food preservation film was obtained.

[0066] The Zn content of the PVA / β-CD / ZnO composite food preservation film obtained in Example 5 was determined, and the ZnO loading on the PVA / β-CD / ZnO composite food preservation film was 1.07 wt%.

[0067] The composite preservation film can inhibit Escherichia coli by 92.12%, which is 2.0% higher than the blend film of Comparative Example 1; the ethylene removal rate after 24 hours is 55%-62%, which is 43.8% higher than the blend film of Comparative Example 1; and the tensile strength is 73.7 MPa, which is 31.6% higher than the PVA / β-CD-5% composite preservation film of Example 1.

[0068] Comparative Example 1: A method for preparing a micro-atmosphere modified atmosphere fruit and vegetable preservation film This comparative example uses a commonly used method in the literature—pVA solution casting and nano-ZnO solution co-dispersion—to prepare the composite film. Specifically, ZnO nanoparticles are directly added to the film-forming solution and fully dispersed before casting to obtain a blended PVA / β-CD / ZnO composite film. This type of route is widely used in the preparation of PVA-ZnO composite films. The co-solution method is as follows: (1) Preparation of film-forming solution Weigh PVA and add it to deionized water, heat to 80 °C and stir continuously to dissolve, preparing a 5 wt% PVA aqueous solution. Then add β-cyclodextrin (β-CD) and continue stirring for 30 min to allow it to swell fully and disperse evenly, obtaining the PVA / β-CD composite film-forming solution.

[0069] (2) Nano ZnO blend dispersion Weigh out nano ZnO powder at a mass fraction of 2 wt% of the total solids in (PVA+β-CD), add it to a small amount of deionized water, and then use ultrasonic dispersion for 30 min to obtain a uniform ZnO dispersion.

[0070] The ZnO dispersion was slowly added to the PVA / β-CD film-forming solution, and magnetic stirring was continued for 1 h to form a PVA / β-CD / ZnO blend film-forming solution (i.e., ZnO is dispersed inside the membrane).

[0071] (3) Casting film formation and thickness control The above film-forming solution was cast onto a glass plate, and the wet film thickness was controlled by a doctor blade casting process. It was then placed in a 40 ℃ constant temperature drying oven to dry to constant weight, and the film was peeled off. The dry film thickness was controlled to be 0.05 mm by adjusting the doctor blade gap and casting volume.

[0072] The blended PVA / β-CD / ZnO composite film has a ZnO loading of approximately 2 wt%. Compared with the composite preservation film in Example 3, it showed a 6.6% decrease in inhibition of Escherichia coli, an 84.5% decrease in 24-hour ethylene removal rate, and a 19.6% decrease in tensile strength.

[0073] Comparative Example 2: A method for preparing a micro-atmosphere modified atmosphere fruit and vegetable preservation film The experimental steps of Comparative Example 2 were repeated in Example 3, except that "nano ZnO powder was replaced with nano TiO2 powder and the TiO2 feeding rate F = 0.9 g / min" and the other conditions remained unchanged. Finally, a PVA / β-CD / TiO2 composite preservation film with a TiO2 loading of 1.96% was obtained.

[0074] The composite preservation film of Comparative Example 2 showed an inhibition rate of 94.32% against Escherichia coli, a 24-hour ethylene removal rate of 61%-68%, and a tensile strength of 68.32 MPa, which was 21.2% higher than that of the PVA / β-CD-5% composite preservation film of Example 1.

[0075] Comparative Example 3: A method for preparing a micro-atmosphere modified atmosphere fruit and vegetable preservation film The experimental steps of Comparative Example 3 were repeated in Example 3, except that "nano ZnO powder was replaced with nano SrTiO3 powder and the SrTiO3 feeding rate F = 0.9 g / min" and the other conditions remained unchanged. Finally, a PVA / β-CD / SrTiO3 composite preservation film with an SrTiO3 loading of 2.07% was obtained.

[0076] The composite preservation film of Comparative Example 3 showed an inhibition rate of 93.29% against Escherichia coli, a 24-hour ethylene removal rate of 54%-58%, and a tensile strength of 72.45 MPa, which was 28.5% higher than that of the PVA / β-CD-5% composite preservation film of Example 1.

[0077] Verification of the effects of food preservation films prepared in different embodiments and comparative examples: 1. Water permeability and oxygen permeability test Following the experimental procedure of Example 1, the amount of β-CD was varied to make the added mass of β-CD 0%, 2.5%, 5.0%, 7.5%, and 10% of the PVA mass, resulting in a series of PVA / β-CD composite films with different β-CD addition amounts. Experiments were then conducted on the prepared films using different parameters.

[0078] Water and oxygen permeability tests were conducted, and all results are expressed as mean ± standard deviation, with error bars representing ±SD. Film thickness was measured using a micrometer at 10 different locations on each film and the average was taken. Samples were equilibrated at 23°C and 50%RH for 48 hours prior to testing.

[0079] Water vapor transmission rate (WVTR) was characterized under the following environmental conditions: temperature 25 ℃ / 75%RH, closely simulating the high humidity application scenario for fruits and vegetables. The unit for WVTR is g·m. -2 ·d -1Under all conditions, the same method and humidity gradient were used. The WVTR was calculated within the steady-state linear interval, and the mean ± SD (n=3) was reported. The test results are shown in Table 1. The oxygen permeability test results are shown in Table 2. The OTR unit is cm. 3 ·m -2 ·d -1 The error is the standard deviation of 3 independently fabricated films (±SD).

[0080] Table 1. Effect of different β-CD addition amounts on the water vapor transmission rate (WVTR) of PVA / β-CD composite membranes. .

[0081] Table 2. Effect of different β-CD addition amounts on oxygen permeability of PVA / β-CD composite membranes .

[0082] Conclusion: The addition of β-CD can control the water and oxygen permeability of plastic wrap.

[0083] 2. Antibacterial test Antibacterial experiments were conducted on the plastic wrap prepared in Examples 3, 4, 5, Comparative Examples 1, 2, and 3, as shown in Table 3. The antibacterial rate of the plastic wrap prepared using the process of the present invention meets the national standard requirements. The antibacterial performance of the plastic wrap was tested in accordance with the national standard GB / T 31402-2015 and showed a significant improvement in antibacterial rate compared with the plastic wrap prepared by the traditional process.

[0084] Table 3 .

[0085] 3. Ethylene Removal Experiment Ethylene removal experiments were conducted on the plastic wraps prepared in Examples 3, 4, 5, Comparative Examples 1, 2, and 3. The experimental results are shown in Table 4. The experimental data show that the plastic wraps prepared using the process method of the present invention have significantly reduced ethylene permeability and increased ethylene removal rate, thereby improving the preservation time of the plastic wraps and extending the preservation time of fruits and vegetables.

[0086] Table 4 .

[0087] 4. Determination of nano-element content in thin films Take the prepared composite membrane sample (randomly selected points within the effective width), cut it into small pieces using clean scissors, and place it in a polytetrafluoroethylene digestion vessel. Weigh 0.1000 g (accurate to 0.1 mg) of each sample, add 38 mL of analytical grade HNO3 + 2 mL of H2O2, let it stand for 10 min for pre-reaction, and then perform microwave digestion. After digestion, cool to room temperature, transfer the digestion solution to a polypropylene volumetric flask, and make up to 50.0 mL with 1% (v / v) nitric acid solution. Mix well and then test using an instrument.

[0088] The quantitative determination of nano-elements is performed using ICP-MS in accordance with GB 5009.268.

[0089] 5. Mechanical properties of thin films Mechanical property tests were conducted on the plastic wraps prepared in Examples 1, 3, 4, 5, Comparative Examples 1, 2, and 3. Sample preparation and testing were performed according to GB / T 1040.3: the film was cut into strips of specified size, the thickness was measured (average of multiple points), and the film was stretched on a tensile testing machine at the specified clamping distance and tensile speed. The maximum force and elongation at break were recorded, and the tensile strength (TS) and elongation at break (EB) were calculated. The test results are shown in Table 5.

[0090] Table 5 Mechanical properties of different samples .

[0091] The results show that the mechanical properties of the composite preservation film prepared by this patent method are improved.

[0092] In Table 5, PVA refers to the plastic wrap PVA prepared according to the method of Example 1 but without the addition of β-CD.

[0093] 6. Nanoscale distribution and adhesion state of thin film surface (SEM-EDS) Taking Zn as an example, film samples (10 mm × 10 mm) of the plastic wrap prepared in Example 3 and Comparative Example 1 were taken and observed by scanning electron microscopy after vacuum sputtering with gold, and the surface and cross-sectional morphology were collected. The surface of the plastic wrap was characterized by SEM, and the SEM images are shown below. Figure 9 , Figure 9 The sub-figures (a) and (b) correspond to the food preservation films prepared in Example 1 and Example 3, respectively. The observation results of the Zn catalyst morphology on the surface are shown in Table 6.

[0094] Table 6 .

[0095] According to the electron microscopy characterization experiments in the table above, the nano-ZnO particles of the preservation film prepared by the process method of the present invention are embedded in the polymer matrix to form a good filling structure, which is beneficial to improving the barrier and mechanical properties of the film.

[0096] 7. Food safety experiments Taking Zn as an example, film samples of the plastic wrap prepared in Examples 3, 4, 5 and Comparative Example 1 were tested using the GB 31604.49 method, which involves immersing the plastic wrap in a 4% acetic acid aqueous solution at 40°C for 10 days. The test results are shown in Table 7.

[0097] Table 7 .

[0098] Zinc oxide nanoparticles exhibit low toxicity to biological systems. Furthermore, zinc is an essential element for human physiological activities. The experimental data in the table above show that the Zn migration of the food preservation film prepared according to this invention is far below the national standard of 1.0 mg / kg, and the film meets food safety standards.

[0099] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A device for preparing a micro-modified atmosphere fruit and vegetable preservation film, characterized in that, It includes a molding cylinder assembly (1), a feeding and coating assembly (2), a dust generation and settling assembly (3), an air-cooling device, and a film hoisting and collecting assembly (4). The molding cylinder assembly (1) includes a rotatable self-heating molding cylinder (12). The feeding coating assembly (2) is used to coat the film-forming liquid onto the upper left surface of the self-heating forming cylinder (12); The dust generation and settling assembly (3) includes a settling cylinder (31) and a dust wind conveying device. The settling cylinder (31) has an opening at the bottom and is located at intervals directly above the self-heating forming cylinder (12). The dust wind conveying device is used to transport the nano antibacterial catalyst into the settling cylinder (31) by wind to form a dust cloud so that the dust settles on the film surface on the self-heating forming cylinder (12). The air-cooling device is used to blow out cold air to cool and shape the film surface on the lower right side of the self-heating forming cylinder (12); The film hoisting and collecting assembly (4) is used to hoist and collect the formed film.

2. The apparatus for preparing a micro-modified atmosphere fruit and vegetable preservation film as described in claim 1, characterized in that, The feeding coating assembly (2) includes a coating cylinder (23), a coating nozzle (24) is provided at the bottom of the coating cylinder (23), and an electric heater (8) is provided on the outer wall of the coating nozzle (24); multiple diversion pipes (26) are provided at the top of the coating cylinder (23), and a peristaltic pump (25) is fixedly connected to the side of the coating cylinder (23). The inlet of the peristaltic pump (25) is filled with film-forming liquid, and the outlet of the peristaltic pump (25) is connected to the multiple diversion pipes (26) respectively.

3. The apparatus for preparing a micro-atmosphere modified atmosphere fruit and vegetable preservation film as described in claim 1, characterized in that, The settling cylinder (31) is trumpet-shaped, narrow at the top and wide at the bottom. The side of the bottom opening of the settling cylinder (31) is arc-shaped. The bottom opening of the settling cylinder (31) is close to the upper surface of the self-heating forming cylinder (12). The distance between the bottom opening of the settling cylinder (31) and the upper surface of the self-heating forming cylinder (12) is 0.5-2cm.

4. The apparatus for preparing a micro-modified atmosphere fruit and vegetable preservation film as described in claim 1, characterized in that, The dust pneumatic conveying device includes a feed pipe (33), a feeding cylinder (34), a conical hopper (35), a nano antibacterial catalyst feeding component, and a dust generating component (39). The top outlet of the feeding cylinder (34) is connected to the settling cylinder (31) through the feed pipe (33). The bottom of the feeding cylinder (34) is connected to the conical hopper (35). A filter screen (36) is installed in the bottom of the conical hopper (35) and connected to the dust generating component (39). The nano-antibacterial catalyst feeding assembly is used to feed the nano-antibacterial catalyst into the feeding cylinder (34); The dust generating component (39) is used to input gas into the conical hopper (35) and the feeding cylinder (34), and the gas drives the nano antibacterial catalyst to disperse, thereby forming stable dust.

5. The apparatus for preparing a micro-modified atmosphere fruit and vegetable preservation film as described in claim 4, characterized in that, The nano-antibacterial catalyst feeding assembly includes a feeding funnel (38) containing the nano-antibacterial catalyst and a screw conveyor (37). The screw conveyor (37) is used to transport the nano-antibacterial catalyst in the feeding funnel (38) into the feeding cylinder (34). The dust generating assembly (39) includes an air inlet pipe (391) fixedly connected to the bottom of the conical hopper (35). The lower end of the air inlet pipe (391) is fixedly connected to a pulse control valve (392). The air inlet of the pulse control valve (392) is fixedly connected to an air pump (393). The air pump (393) supplies air into the air inlet pipe (391) through the pulse control valve (392), and the gas then enters the conical hopper (35) and the feeding cylinder (34).

6. The apparatus for preparing a micro-modified atmosphere fruit and vegetable preservation film as described in claim 1, characterized in that, The air-cooling device includes an air cooler (10), the air outlet of which is angled upward toward the lower right side of the self-heating forming cylinder (12).

7. A method for preparing a modified atmosphere packaging film for fruits and vegetables, characterized in that, Using the apparatus as described in any one of claims 1-6, the method includes the following steps: Step 1: Polyvinyl alcohol (PVA) and β-cyclodextrin are dissolved sequentially in deionized water under heating to obtain a PVA / β-cyclodextrin composite film-forming solution; Step 2: While keeping the self-heating molding cylinder (12) rotating, it is self-heated. The PVA / β-cyclodextrin composite film-forming liquid obtained in step 1 is coated onto the upper left surface of the self-heating molding cylinder (12) through the feeding coating component (2) to form a film. The film gradually solidifies under the heating action during the rotation and conveying process of the self-heating molding cylinder (12). Step 3: The dust wind conveying device drives the nano antibacterial catalyst to disperse and form stable dust by conveying gas, and conveys the dust to the settling cylinder (31) to form a dust cloud; when the film is conveyed to the bottom of the settling cylinder (31) along with the self-heating forming cylinder (12), the surface of the film is in a semi-cured state that is not completely dried, and the dust in the settling cylinder (31) settles and adheres to the surface of the film; Step 4: The film with dust adhering to its surface is dried and cured by air cooling device to obtain PVA / β-cyclodextrin / nano antibacterial catalyst composite preservation film, and finally collected by film hoisting collection component (4).

8. The method for preparing a micro-atmosphere modified atmosphere fruit and vegetable preservation film as described in claim 7, characterized in that, In step 1, the mass of β-cyclodextrin is 5%-10% of the mass of polyvinyl alcohol (PVA).

9. The method for preparing a micro-modified atmosphere fruit and vegetable preservation film as described in claim 7, characterized in that, In step 2, the self-heating forming cylinder (12) is self-heated to make its surface temperature 40-50℃.

10. The method for preparing a micro-atmosphere modified atmosphere fruit and vegetable preservation film as described in claim 7, characterized in that, The nano-antibacterial catalyst mentioned in step 3 is nano-ZnO, nano-TiO2, or nano-SiO2; in the PVA / β-cyclodextrin / nano-antibacterial catalyst composite preservation film in step 4, the loading of the nano-antibacterial catalyst is 1-3 wt%.

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