Fruit and vegetable fresh-keeping film based on high polymer material and preparation method thereof

Abstract

The invention provides a fruit and vegetable fresh-keeping film based on a high polymer material and a preparation method of the fruit and vegetable fresh-keeping film, a corona layer comprises the following components: isotactic homo-polypropylene, polylactic acid, nano aluminum oxide and polyvinyl alcohol in a mass ratio of 6: 1.5: 1: 1.5; the middle layer is prepared from the following components in percentage by mass: 90 to 97 percent of base material, 0.1 to 3 percent of humectant, 0.1 to 2 percent of antioxidant, 0.1 to 2 percent of antibacterial agent, 0.1 to 1.0 percent of light stabilizer, 2 to 5 percent of plasticizer and 0.1 to 0.5 percent of nanoscale impact modifier; the heat sealing layer comprises the following components in percentage by mass: 85-90% of copolymerized polyethylene, 5-10% of bamboo fibers, 1-5% of a deodorant and 1-5% of an antifogging agent. According to the invention, the polymer composite material with a multi-layer structure is adopted, and each layer has a specific function and jointly acts on the preservation of fruits and vegetables; wherein the corona layer has good tensile strength and toughness, and the middle layer has the moisturizing, antioxidant and antibacterial effects and also improves the affinity and impact resistance at the same time; and the heat sealing layer realizes good deodorization and fog prevention.

Description

Technical Field

[0001] The invention relates to the technical field of fruit and vegetable fresh-keeping films, in particular to a fruit and vegetable fresh-keeping film based on a polymer material and a preparation method thereof. Background Art

[0002] Fruit and vegetable fresh-keeping film is a plastic film specially used for packaging and protecting fresh fruits and vegetables. Its main purpose is to extend the shelf life of fruits and vegetables and maintain their freshness, color and taste. Fruit and vegetable fresh-keeping film usually has the following key characteristics: breathability, allowing appropriate gas exchange, especially the exchange of oxygen and carbon dioxide, to maintain the respiration and water balance of fruits and vegetables; moisture barrier: preventing excessive water evaporation, helping to keep fruits and vegetables fresh; antibacterial property, the antibacterial agent contained can inhibit the growth of microorganisms and reduce the occurrence of decay.

[0003] Existing composite cling film generally adopts PET / PE / PET composite film; PET (polyethylene terephthalate) provides good mechanical strength and moisture barrier properties; PE as an intermediate layer provides good heat sealing and gas barrier properties; however, the existing composite cling film has poor mechanical properties, and fruits and vegetables are closely attached to the cling film when the cling film is used, which is not easy to breathe, and when multiple cling films are used, the fruits and vegetables are easily damaged due to friction and collision. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention aims to provide a fruit and vegetable fresh-keeping film based on a polymer material and a preparation method thereof, which can solve the existing problems.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows:

[0006] The present invention is realized by the following technical scheme: a fruit and vegetable fresh-keeping film based on polymer materials and a preparation method thereof, comprising a corona layer, an intermediate layer and a heat-sealing layer, wherein the intermediate layer is located between the corona layer and the heat-sealing layer;

[0007] The corona layer comprises the following components in a mass ratio: isotactic homopolypropylene, polylactic acid, nano-alumina and polyvinyl alcohol = 6:1.5:1:1.5;

[0008] The middle layer comprises the following components in percent by mass: 90-97% of base material, 0.1-3% of moisturizer, 0.1-2% of antioxidant, 0.1-2% of antibacterial agent, 0.1-1.0% of light stabilizer, 2-5% of plasticizer and 0.1-0.5% of nano-scale impact resistant agent;

[0009] The heat sealing layer comprises the following components in percent by weight: 85-90 percent of copolymerized polyethylene, 5-10 percent of bamboo fiber, 1-5 percent of deodorant, and 1-5 percent of antifogging agent.

[0010] Furthermore, the base material includes components in the following mass ratio: low-density polyethylene, metallocene polyethylene, starch, chitosan and gelatin = 3.5:3.5:2:0.5:0.5.

[0011] Furthermore, the moisturizer includes one or more of sorbitol, sodium alginate, sunflower oil, soybean oil, polyethylene glycol and propylene glycol; the antioxidant includes one or more of vitamin C, vitamin E, tocopherol, tea polyphenols, butylated hydroxyanisole and butylated hydroxytoluene; the antibacterial agent includes silver ions and quaternary ammonium salts; the light stabilizer includes ultraviolet absorbers, ultraviolet shielding agents or free radical scavengers; the plasticizer includes phthalates, aliphatic dibasic acid esters, epoxy compounds or epoxy compounds; the nano-scale impact resistant agent includes one or more of nano-calcium carbonate, nano-silicon dioxide, nano-cellulose and nano-clay.

[0012] Furthermore, the deodorant includes one or more of activated carbon, zeolite, tea extract and eucalyptus oil; the antifogging agent includes one or more of organic silane, fluorocarbon, polyacrylate and polyethylene oxide.

[0013] Furthermore, the thickness of the corona layer is 5-15 microns, the thickness of the intermediate layer is 10-50 microns, and the thickness of the heat sealing layer is 5-15 microns.

[0014] Furthermore, the middle layer and the heat-sealing layer form a wave structure, and the surface of the fruit and vegetable preservative film is provided with micropores with a trapezoidal cross-section.

[0015] The method for preparing a fruit and vegetable fresh-keeping film based on a polymer material is characterized in that the method for preparing a fruit and vegetable fresh-keeping film based on a polymer material according to any one of claims 1 to 6 comprises:

[0016] Mixing and melting the components of the middle layer according to mass percentage and extruding them, and cooling them to form a primary middle layer;

[0017] The two sides of the primary intermediate layer are treated with plasma to introduce hydroxyl groups and carboxyl groups on the surface to form an intermediate layer;

[0018] Mix and melt the components of the corona layer according to the mass ratio, and apply them on one side of the intermediate layer to form a primary corona layer;

[0019] Performing corona treatment on the primary corona layer to form a corona layer;

[0020] The components of the heat-sealing layer are melted according to the mass percentage and coated on the other side of the middle layer to form the heat-sealing layer; after cooling, the whole fresh-keeping film is formed.

[0021] Furthermore, a plurality of micropores with a trapezoidal cross-section are marked on the surface of the fresh-keeping film using laser marking technology.

[0022] Furthermore, the method further comprises coating a nano coating on the surface of the corona layer.

[0023] Compared with the prior art, the beneficial effects of the present invention include:

[0024] The fruit and vegetable fresh-keeping film of the present invention adopts a multi-layered polymer composite material, each layer has its specific function, and they work together to keep the fruits and vegetables fresh; the corona layer has good tensile strength and toughness, and effectively improves its barrier performance and mechanical strength; the middle layer has moisturizing, anti-oxidation and antibacterial effects, and also improves affinity and impact resistance; the heat-sealing layer achieves good deodorization and anti-fogging, and the components derived from bamboo fiber increase the sustainability of the product and reduce the impact on the environment; the fresh-keeping period of fruits and vegetables can be significantly extended, losses can be reduced, and economic benefits can be improved.

[0025] The fruit and vegetable fresh-keeping film of the present invention adopts a special structure. When in contact with fruits and vegetables, the contact area is reduced, which prevents the fresh-keeping film from directly adhering to the surface of fruits and vegetables, further improving the antibacterial effect, and is convenient for deodorizing and moisturizing the inside. In addition, the heat-sealing layer of the arc structure has a better buffering effect than the flat fresh-keeping film, further improving the impact resistance of the fruit and vegetable fresh-keeping film; the microporous design facilitates the circulation of internal air and prevents interference from external water. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The disclosure of the present invention is described with reference to the accompanying drawings. It should be understood that the drawings are only for illustrative purposes and are not intended to limit the scope of protection of the present invention. In the drawings, the same reference numerals are used to refer to the same components. Among them:

[0027] Figure 1 The figure is a schematic diagram of the overall structure of the fruit and vegetable fresh-keeping film based on polymer materials of the present invention.

[0028] Notes in the figure: 1. Corona layer; 2. Middle layer; 3. Micropores; 4. Heat sealing layer. DETAILED DESCRIPTION

[0029] It is easy to understand that according to the technical solution of the present invention, without changing the essential spirit of the present invention, a person skilled in the art can propose a variety of interchangeable structural modes and implementation modes. Therefore, the following specific implementation modes and drawings are only exemplary descriptions of the technical solution of the present invention, and should not be regarded as the whole of the present invention or as a limitation or restriction to the technical solution of the present invention.

[0030] The present invention provides a fruit and vegetable fresh-keeping film based on a polymer material, wherein the fruit and vegetable fresh-keeping film is provided with three layers, including a corona layer, an intermediate layer and a heat-sealing layer, wherein the intermediate layer is located between the corona layer and the heat-sealing layer;

[0031] The corona layer comprises components in the following mass ratio: isotactic homopolypropylene, polylactic acid, nano-alumina and polyvinyl alcohol=6:1.5:1:1.5.

[0032] Homopolymer polypropylene is the main synthetic matrix. Homopolymer polypropylene has high tensile strength and toughness, which makes the cling film made of it not easy to break during use and can better protect fruits and vegetables. During the preservation of fruits and vegetables, the film may be affected by environmental factors such as moisture, oxygen, and carbon dioxide. Homopolymer polypropylene has good resistance to environmental stress cracking and can effectively extend the service life of the cling film. In addition, homopolymer polypropylene has good resistance to most chemicals, which means that when the cling film comes into contact with fruit and vegetable juice, detergents, etc., it will not easily react chemically, maintaining the integrity of the film.

[0033] The added polylactic acid has moderate air permeability and moisture permeability, which can effectively regulate the carbon dioxide and water produced by the respiration of fruits and vegetables, maintain a suitable internal environment, thereby delaying the ripening process of fruits and vegetables and extending the shelf life; polylactic acid is a natural polymer material, harmless to the human body and the environment, suitable for food contact materials, ensuring food safety; polylactic acid film has good transparency, allowing consumers to clearly see the state of fruits and vegetables, which is conducive to the display and sales of goods.

[0034] The added nano-alumina can improve the shortcomings of insufficient mechanical properties of homopolymer polypropylene as the main synthetic matrix. Adding nano-alumina in the corona layer can significantly enhance the mechanical properties of polyvinyl alcohol film, improve the strength, toughness and wear resistance of the film, and make the film more durable and less prone to damage; the tiny size of the nano-alumina particles increases the density of the film, thereby enhancing the film's barrier ability to gases (such as oxygen, carbon dioxide), steam and aroma, which is beneficial to maintaining the freshness and taste of fruits and vegetables; the addition of nano-alumina can improve the thermal stability of the film, making the plastic wrap film less likely to deform or melt at high temperatures, and more suitable for heat-sealed packaging.

[0035] Polyvinyl alcohol (PVA) is added to the corona layer. The polyvinyl alcohol film has good water vapor permeability and can adjust the water evaporation rate according to the needs of different fruits and vegetables. It not only avoids the loss of water and shrinkage of fruits and vegetables caused by excessive evaporation of water, but also prevents corruption and deterioration caused by excessive water accumulation.

[0036] Therefore, the corona layer of the present invention is formed by composite combination mixing and corona treatment; the corona layer of the present invention uses regular homopolymer polypropylene with good tensile strength and toughness as the main raw material, and adds certain polylactic acid, nano-alumina and polyvinyl alcohol, effectively improving the shortcomings of insufficient mechanical properties of regular homopolymer polypropylene as the main raw material, and further improving the air permeability and moisture permeability of the corona layer.

[0037] The intermediate layer comprises the following components in percent by mass: 90-97% of base material, 0.1-3% of moisturizing agent, 0.1-2% of antioxidant, 0.1-2% of antibacterial agent, 0.1-1.0% of light stabilizer, 2-5% of plasticizer and 0.1-0.5% of nano-scale impact resistant agent; preferably, the intermediate layer comprises the following components in percent by mass: 95% of base material, 1% of moisturizing agent, 0.5% of antioxidant, 0.5% of antibacterial agent, 0.5% of light stabilizer, 2% of plasticizer and 0.5% of nano-scale impact resistant agent;

[0038] The basic material includes the following components in the following mass ratio: low-density polyethylene, metallocene polyethylene, starch, chitosan and gelatin = 3.5:3.5:2:0.5:0.5; low-density polyethylene (LDPE) has good toughness and puncture resistance, and can effectively protect fruits and vegetables; LDPE has relatively low cost and is suitable for large-scale production and wide application.

[0039] Metallocene polyethylene (mPE) can maintain good flexibility and mechanical properties at lower temperatures and is also suitable for packaging frozen foods. Compared with traditional LDPE, mPE has better oxygen and carbon dioxide barrier properties, which helps maintain the freshness of fruits and vegetables.

[0040] Starch is a natural material that is easily biodegradable, reducing the impact on the environment; starch can absorb and retain water, helping to maintain the freshness of fruits and vegetables.

[0041] Chitosan has good antibacterial properties, which can inhibit the growth of microorganisms on the surface of fruits and vegetables and extend the shelf life. Chitosan is a natural biopolymer that is friendly to the human body and the environment.

[0042] Gelatin has good film-forming properties, and the film it forms has good transparency and certain strength. Gelatin can absorb moisture, helping to maintain the moisture of fruits and vegetables, while also increasing the viscosity and consistency of the film and improving its mechanical properties.

[0043] The use of natural and biodegradable materials helps reduce the impact on the environment and meets the requirements of sustainable development.

[0044] In the above, the moisturizing agent includes one or more of sorbitol, sodium alginate, sunflower oil, soybean oil, polyethylene glycol and propylene glycol; preferably, the moisturizing agent includes sorbitol and sunflower oil; sorbitol is a substance naturally present in fruits, which is easily metabolized by the human body after ingestion and is harmless to the body; it can be used not only as a moisturizing agent, but also as a sweetener and preservative, reducing the use of other additives; the sunflower oil is relatively stable at high temperature and is not easy to produce harmful substances, and is suitable for fresh-keeping bags that require heating treatment.

[0045] The antioxidant includes one or more of vitamin C, vitamin E, tocopherol, tea polyphenols, butylated hydroxyanisole and butylated hydroxytoluene; preferably, the antioxidant includes vitamin C and tea polyphenols; vitamin C has a strong reducing property, can neutralize free radicals, prevent oil oxidation, and extend the shelf life of food; vitamin C is easily soluble in water, can be evenly distributed on the surface of food or the inner layer of the fresh-keeping bag, and improve the antioxidant effect of food. Tea polyphenols can prevent protein denaturation, inhibit microbial growth, and protect food quality in all directions; under different conditions, the antioxidant activity of tea polyphenols is relatively stable and not easily destroyed.

[0046] The antibacterial agent includes silver ions and quaternary ammonium salts; silver ions can achieve good antibacterial effects;

[0047] The light stabilizer includes a UV absorber, a UV shielding agent or a free radical scavenger; preferably, the light stabilizer includes a UV absorber;

[0048] The plasticizer includes phthalates, aliphatic dibasic acid esters, epoxy compounds or epoxy compounds; preferably, the plasticizer includes aliphatic dibasic acid esters. Aliphatic dibasic acid ester plasticizers are a type of environmentally friendly plasticizers with less impact on the environment and human health. This type of plasticizer can be used to produce food contact materials, mainly including dioctyl adipate (DOA), which is a widely used aliphatic dibasic acid ester plasticizer. It has good heat resistance, cold resistance and chemical stability, and is suitable for various plastic films, including fresh-keeping bags. Diisodecyl sebacate (DOS), DOS has good transparency and compatibility, and is a high-performance environmentally friendly plasticizer suitable for food packaging materials, such as plastic wrap, food-grade plastic containers, etc. New dioctyl sebacate (DNOP, has good cold resistance, weather resistance and low volatility, suitable for food contact materials, such as fresh-keeping bags and food-grade plastic products, diisononyl adipate (DINCH): is a high-performance environmentally friendly plasticizer, widely used in food contact materials, such as fresh-keeping bags, baby bottles, toys, etc. Diisononyl azelate (DINN), is a new environmentally friendly plasticizer, with good compatibility, transparency and cold resistance, suitable for food contact materials.

[0049] The nano-scale impact-resistant agent includes one or more of nano-calcium carbonate, nano-silicon dioxide, nano-cellulose and nano-clay. Preferably, the nano-scale impact-resistant agent includes nano-calcium carbonate, which has small particles, large surface area, strong interfacial interaction with the polymer matrix, and can significantly improve the toughness of the fresh-keeping bag and increase its impact resistance; the addition of nano-calcium carbonate can enhance the tensile strength of the fresh-keeping bag, making the bag less likely to break when impacted by external forces, thereby improving the safety of the packaging.

[0050] The heat-sealing layer comprises the following components in 100% by weight: 85-90% copolymerized polyethylene, 5-10% bamboo fiber, 1-5% deodorant, and 1-5% antifogging agent. Preferably, the heat-sealing layer comprises the following components in 100% by weight: 90% copolymerized polyethylene, 5% bamboo fiber, 3% deodorant, and 2% antifogging agent.

[0051] The deodorant includes one or more of activated carbon, zeolite, tea extract and eucalyptus oil; preferably includes tea extract and activated carbon; activated carbon has a strong adsorption capacity, which can not only absorb the odor produced by fruits and vegetables, but also absorb ethylene gas, thereby slowing down the ripening process of fruits and vegetables; the antifogging agent includes one or more of organic silane, fluorocarbon compound, polyacrylate and polyethylene oxide. Preferably, the antifogging agent includes organic silane.

[0052] The copolymer polyethylene has good toughness and wear resistance, which can effectively protect fruits and vegetables from physical damage; the air permeability and moisture permeability of the film can be adjusted to maintain the freshness of fruits and vegetables.

[0053] Bamboo fiber comes from renewable resources and is easily biodegradable, which is beneficial to the environment. Bamboo fiber contains natural antibacterial ingredients that help inhibit the growth of microorganisms on the surface of fruits and vegetables and extend the shelf life. Bamboo fiber has good moisture absorption and air permeability, which can keep the surface of fruits and vegetables dry and reduce the chance of mold growth.

[0054] Deodorants can absorb and neutralize the odors produced by fruits and vegetables, keeping the air inside the package fresh; deodorants can also inhibit the production of ethylene during the ripening process of fruits and vegetables, thereby extending the shelf life.

[0055] Anti-fog agents can reduce condensed water droplets on the inner surface of the packaging, avoid the appearance of water droplets on the surface of fruits and vegetables, and maintain a clean and fresh appearance; reducing the formation of fog helps improve the visibility of fruits and vegetables, making it easier for consumers to select.

[0056] Therefore, the composite cling film of the heat-sealing layer of the present invention can provide protection from multiple aspects such as physical protection, antibacterial, deodorizing, and anti-fogging, creating a better storage environment for fruits and vegetables; the components derived from bamboo fiber increase the sustainability of the product and reduce the impact on the environment; it can significantly extend the shelf life of fruits and vegetables, reduce losses, and improve economic benefits.

[0057] In the fruit and vegetable fresh-keeping film of the present invention, the thickness of the corona layer is 5-15 microns, the thickness of the middle layer is 10-50 microns, and the thickness of the heat-sealing layer is 5-15 microns.

[0058] like Figure 1 As shown, the intermediate layer 2 and the heat sealing layer 4 form a wave structure. When the heat sealing layer 4 with the wave structure contacts with fruits and vegetables, the contact area is reduced, which prevents the fresh-keeping film from directly adhering to the surface of fruits and vegetables, further improving the antibacterial effect, and is convenient for deodorizing and moisturizing the inside. In addition, the heat sealing layer 4 with an arc structure has an improved buffering effect compared with the flat fresh-keeping film, further improving the impact resistance of the fruit and vegetable fresh-keeping film; a corona layer 1 with a flat surface is formed on the other side of the intermediate layer 2; micropores 3 with a trapezoidal cross-section are opened on the surface of the fruit and vegetable fresh-keeping film, and the design of the micropores 3 facilitates the circulation of internal air and prevents interference from external water.

[0059] The fruit and vegetable fresh-keeping film of the present invention adopts a multi-layered polymer composite material, each layer has its specific function, and they work together to keep the fruits and vegetables fresh; the corona layer has good tensile strength and toughness, and effectively improves its barrier performance and mechanical strength; the middle layer has moisturizing, anti-oxidation and antibacterial effects, and also improves affinity and impact resistance; the heat-sealing layer achieves good deodorization and anti-fogging, and the components derived from bamboo fiber increase the sustainability of the product and reduce the impact on the environment; the fresh-keeping period of fruits and vegetables can be significantly extended, losses can be reduced, and economic benefits can be improved.

[0060] The fruit and vegetable fresh-keeping film of the present invention adopts a special structure. When in contact with fruits and vegetables, the contact area is reduced, which prevents the fresh-keeping film from directly adhering to the surface of fruits and vegetables, further improving the antibacterial effect, and is convenient for deodorizing and moisturizing the inside. In addition, the heat-sealing layer of the arc structure has a better buffering effect than the flat fresh-keeping film, further improving the impact resistance of the fruit and vegetable fresh-keeping film; the microporous design facilitates the circulation of internal air and prevents interference from external water.

[0061] The present invention also provides a method for preparing a fruit and vegetable fresh-keeping film based on a polymer material, the preparation method comprising the following steps:

[0062] Step 1: Mix and melt the components of the middle layer according to the mass percentage, extrude them, and cool them to form a primary middle layer;

[0063] Step 2: using plasma treatment technology to introduce hydroxyl groups and carboxyl groups on the surfaces of both sides of the primary intermediate layer to form an intermediate layer;

[0064] Step 3: Mix and melt the components of the corona layer according to the mass ratio, and apply them on one side of the intermediate layer to form a primary corona layer;

[0065] Step 4: performing corona treatment on the primary corona layer to form a corona layer;

[0066] Step 5: Melt the components of the heat-sealing layer according to the mass percentage, and apply them on the other side of the middle layer to form a heat-sealing layer; after cooling, the entire fresh-keeping film is formed.

[0067] In order to further increase the air permeability, laser marking technology is used to mark multiple micropores with a trapezoidal cross-section on the surface of the cling film.

[0068] In order to further improve the antibacterial effect, a nano coating is coated on the surface of the corona layer.

[0069] Implementation case 1:

[0070] The corona layer comprises the following components in a mass ratio: isotactic homopolymer polypropylene, polylactic acid, nano-alumina and polyvinyl alcohol = 6:1.5:1:1.5;

[0071] The middle layer includes the following components in percent by weight: 95% of base material, 1% of moisturizer, 0.5% of antioxidant, 0.5% of antibacterial agent, 0.5% of light stabilizer, 2% of plasticizer and 0.5% of nano-scale impact resistant agent; the base material includes the following components in the following mass ratios: low-density polyethylene, metallocene polyethylene, starch, chitosan and gelatin = 3.5:3.5:2:0.5:0.5;

[0072] The heat sealing layer comprises the following components in 100% by mass: 90% of copolymer polyethylene, 5% of bamboo fiber, 3% of deodorant and 2% of antifogging agent; and is used to prepare a fruit and vegetable fresh-keeping film.

[0073] Implementation case 2:

[0074] The corona layer comprises the following components in the following weight ratios: polypropylene;

[0075] The middle layer includes the following components in percent by weight: 95% polyethylene, 0.5% antioxidant, 0.5% light stabilizer, and 4% plasticizer;

[0076] The heat sealing layer comprises the following components in 100% by mass: polyethylene; and is used to prepare a film for preserving fruits and vegetables.

[0077] Implementation case three:

[0078] The corona layer comprises the following components in a mass ratio: isotactic homopolymer polypropylene, polylactic acid, nano-alumina and polyvinyl alcohol = 8:0.5:1:0.5;

[0079] The middle layer includes the following components in percent by weight: 90% of base material, 2% of moisturizer, 1% of antioxidant, 1% of antibacterial agent, 1% of light stabilizer, 4% of plasticizer and 1% of nano-scale impact resistant agent; the base material includes the following components in the following mass ratio: low-density polyethylene, metallocene polyethylene, starch, chitosan and gelatin = 3.0:3.0:2:1:1;

[0080] The heat sealing layer comprises the following components in 100% by mass: 95% of copolymer polyethylene, 1% of bamboo fiber, 2% of deodorant and 2% of antifogging agent; and is used to prepare a fruit and vegetable fresh-keeping film.

[0081] Performance Testing

[0082] Antibacterial property: tested according to QB / T2591-2003 method, testing Staphylococcus aureus;

[0083] Tensile strength: Tested according to the method of GB / T4456-2008 to test the transverse tensile strength;

[0084] Four bananas on the same branch were placed indoors, wrapped with the fresh-keeping films prepared in Implementation Case 1, Implementation Case 2, and Implementation Case 3, and placed indoors for 10 days, and the outer surfaces were observed to test the fresh-keeping performance;

[0085] After testing, the antibacterial properties of Implementation Case 1, Implementation Case 2, and Implementation Case 3 were 99.9%, 94.5%, and 98.7%, respectively.

[0086] The tensile strengths of Implementation Case 1, Implementation Case 2, and Implementation Case 3 are 29 MPa, 19 MPa, and 24 MPa, respectively.

[0087] The test results of four bananas showed that the black spots on the rubber surface were almost all over the outer surface. The color of the banana in the first implementation case turned slightly yellow, with little change. The color of the rubber in the second implementation case turned dark yellow, with large areas of black spots. The color of the banana in the third implementation case turned yellow. It can be seen that the fresh-keeping film of the present invention can achieve good antibacterial, anti-stretching and fresh-keeping effects.

[0088] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0089] In the description of this patent, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", and "set" should be understood in a broad sense, for example, it can be fixedly connected or set, or it can be detachably connected or set, or connected or set in one piece. For ordinary technicians in this field, the specific meanings of the above terms in this patent can be understood according to specific circumstances.

[0090] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "several" is two or more, unless otherwise clearly and specifically defined.

[0091] The technical scope of the present invention is not limited to the contents in the above description. Those skilled in the art can make various deformations and modifications to the above embodiments without departing from the technical idea of ​​the present invention, and these deformations and modifications should all fall within the protection scope of the present invention.

Claims

1. Fruit and vegetable fresh-keeping film based on polymer materials, characterized by: include A corona layer, an intermediate layer and a heat-sealing layer, wherein the intermediate layer is between the corona layer and the heat-sealing layer; The corona layer comprises the following components in a mass ratio: isotactic homopolypropylene, polylactic acid, nano-alumina and polyvinyl alcohol = 6:1.5:1:1.5; The middle layer comprises the following components in percent by mass: 90-97% of base material, 0.1-3% of moisturizer, 0.1-2% of antioxidant, 0.1-2% of antibacterial agent, 0.1-1.0% of light stabilizer, 2-5% of plasticizer and 0.1-0.5% of nano-scale impact resistant agent; The heat sealing layer comprises the following components in percent by weight: 85-90 percent of copolymerized polyethylene, 5-10 percent of bamboo fiber, 1-5 percent of deodorant, and 1-5 percent of antifogging agent.

2. The fruit and vegetable fresh-keeping film based on polymer materials according to claim 1, characterized in that: The base material includes components in the following mass ratio: low-density polyethylene, metallocene polyethylene, starch, chitosan and gelatin = 3.5:3.5:2:0.5:0.

5.

3. The fruit and vegetable fresh-keeping film based on polymer materials according to claim 1, characterized in that: The moisturizer includes one or more of sorbitol, sodium alginate, sunflower oil, soybean oil, polyethylene glycol and propylene glycol; the antioxidant includes one or more of vitamin C, vitamin E, tocopherol, tea polyphenols, butylated hydroxyanisole and butylated hydroxytoluene; the antibacterial agent includes silver ions and quaternary ammonium salts; the light stabilizer includes ultraviolet absorbers, ultraviolet shielding agents or free radical scavengers; the plasticizer includes phthalates, aliphatic dibasic acid esters, epoxy compounds or epoxy compounds; the nano-scale impact resistant agent includes one or more of nano calcium carbonate, nano silicon dioxide, nano cellulose and nano clay.

4. The fruit and vegetable fresh-keeping film based on polymer materials according to claim 1, characterized in that: The deodorant includes one or more of activated carbon, zeolite, tea extract and eucalyptus oil; the antifogging agent includes one or more of organic silane, fluorocarbon compound, polyacrylate and polyethylene oxide.

5. The fruit and vegetable fresh-keeping film based on polymer materials according to claim 1, characterized in that: The thickness of the corona layer is 5-15 microns, the thickness of the intermediate layer is 10-50 microns, and the thickness of the heat sealing layer is 5-15 microns.

6. The fruit and vegetable fresh-keeping film based on polymer materials according to claim 1, characterized in that: The middle layer and the heat-sealing layer form a wave structure, and the surface of the fruit and vegetable fresh-keeping film is provided with micropores with a trapezoidal cross-section.

7. A method for preparing a fruit and vegetable fresh-keeping film based on a polymer material, characterized in that: The method for preparing the fruit and vegetable fresh-keeping film based on polymer materials according to any one of claims 1 to 6 comprises: Mixing and melting the components of the middle layer according to mass percentage and extruding them, and cooling them to form a primary middle layer; The two sides of the primary intermediate layer are treated with plasma to introduce hydroxyl groups and carboxyl groups on the surface to form an intermediate layer; Mix and melt the components of the corona layer according to the mass ratio, and apply them on one side of the intermediate layer to form a primary corona layer; Performing corona treatment on the primary corona layer to form a corona layer; The components of the heat-sealing layer are melted according to the mass percentage and coated on the other side of the middle layer to form the heat-sealing layer; after cooling, the whole fresh-keeping film is formed.

8. The fruit and vegetable fresh-keeping film based on polymer materials and the preparation method thereof according to claim 7, characterized in that: Laser marking technology is used to mark multiple micropores with a trapezoidal cross-section on the surface of the cling film.

9. The fruit and vegetable fresh-keeping film based on polymer materials and the preparation method thereof according to claim 7, characterized in that: The method also includes coating a nano coating on the surface of the corona layer.

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