Plastic wrap and preparation method therefor and application thereof

Abstract

Disclosed are a plastic wrap and a preparation method therefor and an application thereof. The plastic wrap comprises a supporting layer and a functional layer that is arranged on the surface and at least parts of holes on one side of the supporting layer; the functional layer comprises a polymer A and a polymer B; the molecular structure of the polymer A contains hydroxyl; the polymer B comprises a polymeric ammonium salt; the molar ratio of the hydroxyl in the polymer A to an ammonium salt group in the polymer B is greater than 0.1:1 and less than 10:1. In the present application, the plastic wrap has a high selectivity for the permeation of gases such as water vapor, carbon dioxide, and oxygen, and can intelligently adjust the moisture permeation rate on the basis of humidity changes in a box, thereby achieving intelligent preservation; the plastic wrap has good barrier properties against oxygen and carbon dioxide, and can inhibit the emission of carbon dioxide inside the box and the entry of oxygen outside the box, thus inhibiting the aerobic respiration of fruits and vegetables and prolonging preservation time; in addition, the plastic wrap further has good antibacterial properties, avoiding the risk of dissolution of an antibacterial agent.

Description

A kind of fresh-keeping film and its preparation method and application Technical Field

[0001] The embodiments of the present application relate to the technical field of cling film, for example, a cling film and a preparation method and application thereof. Background Art

[0002] Food wrap is primarily used for heating food in microwaves, preserving food in refrigerators, and packaging fresh and cooked food. It is widely used in household applications, supermarkets, hotels, restaurants, and industrial food packaging. Depending on the material used and the plasticizers added, cling film comes in various types, including paper-based and polymer-based ones.

[0003] At present, on the one hand, plastic wrap does not have high selectivity for the permeability of gases such as water vapor and carbon dioxide, and cannot effectively block carbon dioxide, thereby failing to inhibit the aerobic respiration of fruits and vegetables, resulting in the inability to keep food fresh; on the other hand, plastic wrap cannot adjust the moisture permeability according to the humidity in the fresh-keeping box, resulting in excessively rapid water loss in fruits and vegetables, or the inability of moisture to pass through to form supersaturated liquid water, which accelerates food decay.

[0004] For example, CN111378216A discloses a fruit and vegetable fresh-keeping film, which includes the following components: high-density ethylene, low-density ethylene, linear low-density ethylene, EVA resin, lubricant, antibacterial and mildew-proof agent, ethylene adsorbent, antioxidant and sodium citrate. The film can replace the gas that affects the deterioration of fruits and vegetables in the fresh-keeping packaging, inhibit the respiration of the storage cells to slow their metabolic process, thereby achieving longer storage of the products with minimal nutrient loss; however, the fresh-keeping film cannot achieve intelligent preservation and has poor preservation effect; and the addition of multiple additives, such as antibacterial and mildew-proof agents with antibacterial functions, may cause the antibacterial agent to dissolve during use, resulting in potential toxic side effects.

[0005] Therefore, it is an urgent problem to be solved in this field to develop a cling film that has high selectivity for the permeation of water vapor, carbon dioxide and oxygen, can effectively block carbon dioxide, can achieve intelligent preservation according to environmental changes, has good antibacterial effect without the need to add additional antibacterial agents, and has no risk of antibacterial agent dissolution.

[0006] Summary of the Invention

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0008] The present application provides a cling film, a preparation method, and an application thereof. The cling film has a high selectivity for permeability to gases such as water vapor, carbon dioxide, and oxygen, and can intelligently adjust its moisture permeability according to changes in humidity within the box, thereby achieving intelligent preservation and dynamically maintaining the humidity within the box at a relative humidity of more than 90% but less than 100% saturation humidity. The cling film also has excellent barrier properties to oxygen and carbon dioxide, inhibiting the emission of carbon dioxide from the box and the ingress of oxygen from outside the box, thereby inhibiting aerobic respiration of fruits and vegetables and extending their shelf life. Furthermore, the cling film has excellent antibacterial properties, avoiding the risk of antibacterial agent dissolution.

[0009] In a first aspect, an embodiment of the present application provides a cling film, which includes a support layer and a functional layer, and is provided on at least a portion of the surface and pores of one side of the support layer; the functional layer includes polymer A and polymer B; the molecular structure of polymer A contains hydroxyl groups; the polymer B includes a polymer ammonium salt; the molar ratio of the hydroxyl groups in polymer A to the ammonium salt groups in polymer B is greater than 0.1:1 and less than 10:1.

[0010] In the present application, polymer A with specific functional groups and polymer B with specific functional groups can produce ion-specific effects under specific conditions; wherein polymer A is a film-forming polymer, constituting the main body of the functional layer, and has a constant moisture permeability and a low moisture permeability; its functional group hydroxyl group provides a binding and diffusion site for water molecules, which can carry out mass transfer of water molecules, but has a low permeability to carbon dioxide and oxygen, thereby improving the selective permeability of the cling film to water vapor, carbon dioxide and oxygen, thereby inhibiting the aerobic respiration of fruits and vegetables in the box and prolonging the preservation effect; polymer B is a functional switch polymer, which can give the cling film dual functions; wherein the concentration of the acid anion in polymer B will affect the binding of the hydroxyl group in the structure of polymer A with water molecules; therefore, the cling film can achieve intelligent preservation according to changes in humidity; that is Under low humidity conditions, the concentration of acid radical ions is high, and the acid radical ions destroy the hydrogen bonds between the hydroxyl groups and the hydrated water molecules of polymer A, forming hydrogen bonds between the acid radical anions and the hydroxyl groups, resulting in fewer water molecule binding sites and a low water vapor transmission rate, thereby inhibiting the moisture permeability of the functional film layer; under saturated humidity conditions, liquid condensation is formed and absorbed on the surface of the plastic wrap film, and the concentration of acid radical ions in polymer B decreases. Under low concentration conditions, the acid radical ions cannot destroy the hydrogen bonds between the hydroxyl groups and the hydrated water molecules of polymer A, and the water vapor molecules and the hydroxyl groups in the structure of polymer A combine normally, and the moisture permeability of the functional layer is greatly improved, thereby preventing the water vapor from being oversaturated to form liquid water and causing the fruits and vegetables to rot; such a dynamic balance causes the box to maintain a higher humidity level but no condensation is generated, thereby ensuring that the fruits and vegetables do not lose water quickly, and will not rot faster due to the generation of condensation due to humidity saturation. In addition, the ammonium salt introduced by polymer B has a highly effective antibacterial effect and is itself a film-forming component that interacts with polymer A. Unlike added small molecules or inorganic antibacterial agents, it will not precipitate during use, making the antibacterial effect of the plastic wrap long-lasting and non-fading. Moreover, the effect is even better at a specific molar ratio of polymer A to polymer B.

[0011] In the present application, the molar ratio of the hydroxyl group in the polymer A to the ammonium salt group in the polymer B is greater than 0.1:1 and less than 10:1, wherein the range of greater than 0.1 and less than 10 can be 0.2, 0.22, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 9.8, 9.9 or a range consisting of any two thereof.

[0012] In the present application, if the molar ratio of the hydroxyl group to the ammonium salt group is too low, the anionic acid radicals in polymer B are excessive, and under saturated humidity conditions, they cannot quickly respond to the influence of the concentration of condensed water, resulting in the moisture permeability rate not being able to change quickly according to the humidity; if the molar ratio of the hydroxyl group to the ammonium salt group is too high, the acid radical ions in polymer B cannot well exert the ion-specific effect, the proportion of hydrogen bonding with polymer A is small, and the water molecule binding sites of polymer A are less affected by changes in its concentration, resulting in the moisture permeability rate also not being able to change quickly according to the humidity.

[0013] Preferably, the molar percentage of the hydroxyl-containing repeating units in the polymer A is ≥40%, for example, it can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99%, 100% or a range consisting of any two thereof.

[0014] In the present application, the molar percentage of the hydroxyl-containing repeating units is within the above range, so that the number of water molecule binding sites on the surface of the functional layer is large, and effective water molecule channels can be formed.

[0015] Preferably, the polymer A includes at least one of hydroxypropyl methylcellulose (HPMC), hydroxymethyl cellulose (HMC), hydroxypropyl cellulose (HPC), hydroxyethyl cellulose (HEC), polyhydroxyethyl methacrylate (PHEMA), polyhydroxyethyl acrylate (PHEA), polyvinyl alcohol (PVA), polydextrose (PD), starch (AMY), dextrin, carrageenan, guar gum, xanthan gum, pectin, gum arabic (AS), hyaluronic acid (HA), gelatin (Gel), sodium alginate (SA) or agarose (AG).

[0016] Preferably, the number average molecular weight of the polymer A is 4-200KDa, for example, it can be 4KDa, 8KDa, 12KDa, 16KDa, 20KDa, 25KDa, 30KDa, 35KDa, 40KDa, 50KDa, 60KDa, 70KDa, 80KDa, 90KDa, 100KDa, 110KDa, 120KDa, 130KDa, 140KDa, 150KDa, 160KDa, 170KDa, 180KDa, 190KDa, 200KDa or a range consisting of any two of them.

[0017] In this application, the number average molecular weight is obtained by testing in accordance with GB / T36241.5-2018 standard.

[0018] In the present application, the number average molecular weight of the polymer A is within the above-defined range, which is conducive to good film density and film forming properties.

[0019] Preferably, the ammonium salt group in the polymer ammonium salt is located in at least one of the side chain and the main chain of the polymer.

[0020] Preferably, the polymer ammonium salt comprises at least one of a compound having a structure represented by Formula I and a compound having a structure represented by Formula II:

[0021] Wherein, R1, R2, and R3 are each independently selected from any one of H, C1-C6 straight-chain or branched alkyl (for example, C1, C2, C3, C4, C5, C6 straight-chain or branched alkyl, etc.); and X is selected from any one of carbonate ion, nitrate ion, chloride ion, bromide ion, iodide ion, sulfate ion, sulfonate ion, acetate ion, citrate ion, hypochlorite ion, or hypobromite ion.

[0022] Preferably, the molar percentage of repeating units containing ammonium salt groups in the polymer B is ≥40%, for example, it can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99%, 100% or a range consisting of any two of them.

[0023] In the present application, the molar percentage of the repeating units containing ammonium salt groups is within the above-defined range, which is beneficial to the long-lasting antibacterial effect and the ion-specific effect of the acid radical ion.

[0024] Preferably, the polymer in the polymer ammonium salt includes at least one of polyacrylamide (PAM), polyethyleneimine (PEI), polymethacrylamide (PMAM), chitosan (CS), polyaminoethyl methacrylate (PAEM), polyaminoethyl acrylate (PEA), poly N,N-dimethylaminoethyl methacrylate (PDMAEMA), poly N,N-diethylaminoethyl methacrylate (PDEAEMA), poly N,N-dimethylaminoethyl acrylate (PDMAEA), poly N,N-diethylaminoethyl acrylate (PDEAEA) or amino-terminated hyperbranched polymer (HBPNH2), or a block copolymer of at least two of the above polymers.

[0025] Preferably, the number average molecular weight of the polymer B is 1 to 100 KDa, for example, it can be 1 KDa, 2 KDa, 5 KDa, 10 KDa, 15 KDa, 20 KDa, 25 KDa, 30 KDa, 35 KDa, 40 KDa, 45 KDa, 50 KDa, 55 KDa, 60 KDa, 65 KDa, 70 KDa, 75 KDa, 80 KDa, 85 KDa, 90 KDa, 95 KDa, 100 KDa or a range consisting of any two of them.

[0026] In the present application, the number average molecular weight of the polymer B is between 1-100KDa, and the polymer B can be more fully and evenly dispersed in the solution, so that the ammonium salt on its molecular chain segment effectively forms hydrogen bonds with the polymer A, and the molecular chain is within a suitable length range, avoiding the instability of the hydrogen bond formed, thereby further ensuring the density of the film layer.

[0027] In the present application, the preparation method of the polymer ammonium salt includes: dissolving an amino polymer having a primary amine, secondary amine, or tertiary amine group in a side chain or main chain in water, then adding acid, stirring at room temperature, and monitoring the pH change of the solution using a pH meter during the acid addition process. When the solution pH reaches 7.0, the addition of acid is stopped, and a polymer ammonium salt solution is formed.

[0028] In the present application, the acid includes at least one of carbonic acid (H2CO3), acetic acid (AcOH), sulfuric acid (H2SO4), nitric acid (HNO3), sulfonic acid (H2SO3), hydrochloric acid (HCl), citric acid (CA), hydrobromic acid (HBr) or hypochlorous acid (HClO).

[0029] As the optimal technical solution of the present application, the molar ratio of the hydroxyl groups in the polymer A to the ammonium salt groups in the polymer B is (0.25-5):1.

[0030] Preferably, the support layer comprises a porous support layer.

[0031] Preferably, the material of the support layer includes at least one of polyethylene, polypropylene, polystyrene, polyimide, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene terephthalate or polycaprolactam.

[0032] Preferably, the thickness of the support layer is 5 to 100 μm, for example, it can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm or a range consisting of any two of them.

[0033] Preferably, the thickness of the functional layer is 0.2 to 10 μm, for example, it can be 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm or a range consisting of any two of them.

[0034] In this application, the thickness of the support layer and the thickness of the functional layer are tested according to GB / T 6672-2001 standard.

[0035] Preferably, the cling film satisfies at least one of the following requirements:

[0036] a) Maintain humidity above 90% but less than 100%;

[0037] b) Antibacterial rate ≥ 90%;

[0038] c) Air permeability ≥ 20000sec / 100ml.

[0039] In a second aspect, an embodiment of the present application provides a method for preparing the cling film according to the first aspect, the preparation method specifically comprising the following steps:

[0040] The functional layer is provided on the surface of one side of the support layer and at least a part of the hole to obtain the preservative film.

[0041] Preferably, the preparation method comprises: mixing polymer A with a solvent to obtain a polymer A solution; mixing polymer B with a solvent to obtain a polymer B solution; mixing the polymer A solution with the polymer B solution to obtain a polymer mixed solution; and then coating the polymer mixed solution on the surface of a support layer and drying to obtain the cling film.

[0042] Preferably, the mass fraction of polymer A in the polymer A solution is 0.2-15%, for example, it can be 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or any two thereof; preferably, it is 1-10%.

[0043] In the present application, if the mass fraction of the polymer A is too low, it is not conducive to the density of the fresh-keeping film. If the mass fraction of the polymer A is too high, the viscosity of the solution is too high, which is not conducive to the uniformity and processing of the film preparation.

[0044] Preferably, the mass fraction of polymer B in the polymer B solution is 0.3-10%, for example, it can be 0.3%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any two thereof, more preferably 0.5-10%.

[0045] In this application, if the mass fraction of polymer B is too low, it is impossible to respond to humidity changes by changing the acid ion concentration and thus control the speed of moisture permeability; if the mass fraction of polymer B is too high, the introduced ammonium salt content is too high, affecting the flexibility and density of the membrane.

[0046] Preferably, the coating method includes at least one of slot coating, knife coating, roller coating, dip coating or extrusion coating.

[0047] In the present application, the preparation method is simple and does not require complicated cross-linking, modification and other processes.

[0048] In a third aspect, an embodiment of the present application provides a food cling film, wherein the food cling film includes the cling film as described in the first aspect or the cling film prepared by the preparation method of the cling film as described in the second aspect.

[0049] Preferably, the food preservative film includes fruit and vegetable preservative film.

[0050] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to limited space and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0051] Compared with the related art, the beneficial effects of the embodiments of the present application are:

[0052] The cling film provided in the embodiment of the present application uses a polymer A having a specific functional group and a polymer B having a specific functional group to form a functional layer, which can change the water molecule content in the functional layer according to the change of humidity, thereby realizing the change of the concentration of acid radical anions, realizing the alternating change of hydrated water molecule-hydroxyl hydrogen bonding and acid radical anion-hydroxyl hydrogen bonding, thereby realizing the control of hydroxyl-water binding sites and the adjustment of moisture permeability; realizing intelligent preservation; and the cling film has high selective permeability to water molecules, carbon dioxide and oxygen, and has a high barrier effect on carbon dioxide and oxygen, thereby inhibiting aerobic respiration and prolonging the preservation effect; in addition, the natural antibacterial effect of the polymer ammonium salt is non-dissolution and non-toxic side effects.

[0053] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0054] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0055] In this application, polymer ammonium salts are represented by the abbreviation of polymer and acid, such as polyethyleneimine hydrochloride: PEI-HCl; chitosan acetate: CS-AcOH; polymethacrylate N,N-dimethylaminoethyl ester hydrochloride: PDMAEMA-HCl; amino-terminated hyperbranched polymer nitrate: HBPNH2-HNO3.

[0056] In the present application, the thickness of the support layer is 20 μm, and the thickness of the functional layer is 1.5 μm.

[0057] Example 1

[0058] This embodiment provides a cling film, which includes a support layer and a functional layer, wherein the functional layer is distributed on the surface and in the pore structure of the support layer; the support layer is made of a polyethylene porous film; the functional layer includes HPMC (number average molecular weight of 18 kDa, hydroxyl repeating unit ratio of 88%) and chitosan hydrochloride CS-HCl (chitosan number average molecular weight of 5 kDa); the molar ratio of hydroxyl groups in the HPMC to ammonium salt groups in the CS-HCl is 1:1.

[0059] This embodiment provides a method for preparing a fresh-keeping film, which specifically includes the following steps:

[0060] HPMC is dispersed in water to obtain a 4% by mass HPMC aqueous solution; chitosan is dispersed and dissolved in water, HCl is added, and the mixture is stirred at room temperature. During the acid addition process, a pH change of the solution is monitored using a pH meter. When the pH of the solution reaches 7.0, the acid addition is stopped to form a 2% by mass CS-HCl solution; the HPMC aqueous solution and the CS-HCl solution are then mixed, and the obtained mixed solution is coated on one surface of a polyethylene porous film and dried to obtain the preservative film.

[0061] Examples 2-21, Comparative Examples 1-10

[0062] Examples 2-21 and Comparative Examples 1-10 respectively provide a fresh-keeping film, whose raw material formula, process parameters, etc. are shown in Table 1 (including Example 1), and the other steps are the same as Example 1.

[0063] Table 1 Note: “ / ” indicates that the substance is not added to the raw materials; Table 1 contains only the abbreviations of polymers or acids, which means that only polymers or acids are added, not salts formed by the two.

[0064] Performance Testing

[0065] The air permeability test of cling film is carried out according to GB / T36363-2018 standard. If the air permeability value of cling film is above 20000s / 100mL, it is considered to have good barrier properties to gas, that is, good barrier properties to O2 and CO2.

[0066] Moisturizing evaluation and testing methods:

[0067] The test was conducted using the following method: a water-soaked sponge was placed inside a plastic box. The moisturizing film sample was mounted on a matching box lid, which was sealed tightly against the box. A humidity sensor was placed inside the box to monitor the humidity in real time. The entire box was then placed in a 5°C environment for 72 hours. The humidity inside the box was recorded from the 24th to the 72nd hour, and the average moisturizing effect was calculated. The surface of the moisturizing film was also observed for condensation.

[0068] The antibacterial performance of the moisturizing film was determined with reference to GB21551.2-2010 standard.

[0069] The specific test results are shown in Table 2:

[0070] Table 2 Note: “-” means the test cannot be performed or the test is meaningless.

[0071] As can be seen from the above table, the cling film provided by the present application uses a polymer A having a specific functional group and a polymer B having a specific functional group to form a functional layer, which can intelligently adjust the moisture permeability of the cling film according to changes in humidity. Under low humidity conditions, the moisture permeability is low, which inhibits water loss; under high humidity conditions, the moisture permeability is high, which avoids food decay caused by supersaturation of water vapor, thereby achieving efficient preservation; and the cling film has high barrier properties to carbon dioxide and oxygen, can inhibit aerobic respiration, and prolong the preservation effect; in addition, the use of polymer ammonium salts not only has a good antibacterial effect, but also avoids the risk of dissolution of small molecule antibacterial agents, and the preparation method is simple and does not require cross-linking modification.

[0072] When polymer ammonium salt is not added, it has no antibacterial effect and cannot intelligently adjust humidity, and the moisturizing effect is poor, less than 90%.

[0073] The addition of polymer ammonium salt B imparts antibacterial properties and enables intelligent humidity regulation. Furthermore, when the molar ratio of hydroxyl groups to ammonium salt groups is within an optimal range, condensation is eliminated. Furthermore, when the molecular weights of polymers A and B, as well as the mass fractions of their solutions, are within optimal ranges, the moisturizing effect is further enhanced.

[0074] Examples 1-21 are preferred examples, with good structural performance parameters. Polymer B and the main film-forming polymer A form strong hydrogen bonds, and the resulting composite membrane has better air tightness than the HPMC membrane alone (Comparative Examples 1 and 2), resulting in a significant increase in its air permeability. Because all key parameters are within the set range, their moisturizing properties are all above 90%, meeting the target setting requirements; at the same time, due to the presence of the polymer ammonium salt, the antibacterial effect reaches 99.9%. Comparative Examples 1-2 and 4 have poor antibacterial properties, only 73.4%; 74.1% and 74.3% due to the lack of the addition of polymer ammonium salt B or amino polymer, and their moisturizing and breathability effects are also poor. The moisturizing properties of Comparative Examples 1-2 and 4 reflect the characteristics of the HPMC membrane itself, all exceeding 80%. Comparative Example 3 incorporates an amino polymer, namely, CS, into HPMC. CS is insoluble in water, resulting in poor dispersion and compatibility within the HPMC membrane structure. This results in poor membrane density and a lower air permeability than the HPMC membrane, at 12,600. Its moisturizing effect is also impaired. Due to the introduction of the antibacterial component of CS, the antibacterial performance of the composite membrane reaches 95.7%, but falls short of the optimal 99.9%, possibly due to the inability of CS to be well dispersed within the composite membrane structure.

[0075] Among them, Example 3-4 is a main membrane structure, that is, polymer A is replaced by HPMC to PVA, and the ammonium salt system is replaced by hydrochloride to acetate, and it also has good structural properties.

[0076] Comparative Examples 5-6 lack a film-forming main structure and contain only polymer ammonium salt B or amino polymers. Consequently, they fail to form a dense composite film layer, exhibit low air permeability, poor film-forming properties, and poor moisturizing effects. In Comparative Example 6, CS is insoluble, preventing film formation, resulting in poor composite effects, low air permeability, and no moisturizing properties due to the inability to form a dense structure. However, the presence of the polymer ammonium salt or amino polymer allows the composite film to achieve an antibacterial performance exceeding 90%.

[0077] Comparative Examples 7 and 8 show that the mass fraction of polymer ammonium salt B was not within the optimal range. Too high a mass fraction resulted in excessive polymer ammonium salt B, which affected the film's density, reduced air permeability, and impaired its moisturizing effect. Too low a mass fraction prevented the ion-specific effect from being fully realized, similarly resulting in poor moisturizing effect. In both cases, a moisturizing effect exceeding 90% was not achieved.

[0078] Comparative Examples 9 and 10, where the hydroxyl / ammonium salt molar ratio was not within the optimal range, also failed to achieve a moisturizing effect exceeding 90%. A too low molar ratio of hydroxyl to ammonium salt resulted in an excess of acid ions, which prevented a rapid response to changes in saturated humidity and resulted in condensation. A too high molar ratio of hydroxyl to ammonium salt resulted in a low acid ion content, a weak ion-specific effect, and similarly poor moisturizing effect.

[0079] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of this application. It should be understood that the above is only a specific embodiment of this application and is not intended to limit this application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this application should be included in the scope of protection of this application.

Claims

1. A fresh-keeping film comprising a support layer and A functional layer, disposed on the surface of one side of the support layer and at least a portion of the hole; The functional layer includes polymer A and polymer B; The polymer A contains hydroxyl groups in its molecular structure; The polymer B comprises a polymer ammonium salt; The molar ratio of the hydroxyl groups in the polymer A to the ammonium salt groups in the polymer B is greater than 0.1:1 and less than 10:

1.

2. The cling film according to claim 1, wherein The molar percentage of the hydroxyl repeating units in the polymer A is ≥40%.

3. The cling film according to claim 1 or 2, wherein: The polymer A includes at least one of hydroxypropyl methylcellulose, hydroxymethyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, polyhydroxyethyl methacrylate, polyhydroxyethyl acrylate, polyvinyl alcohol, polydextrose, starch, dextrin, carrageenan, guar gum, xanthan gum, pectin, gum arabic, hyaluronic acid, gelatin, sodium alginate or agarose.

4. The cling film according to any one of claims 1 to 3, wherein: The number average molecular weight of the polymer A is 4-200 KDa.

5. The cling film according to any one of claims 1 to 4, wherein The ammonium salt group in the polymer ammonium salt is located at least one of the side chain and the main chain of the polymer.

6. The cling film according to any one of claims 1 to 5, wherein: The polymer ammonium salt includes at least one of a compound having a structure shown in Formula I and a compound having a structure shown in Formula II: Wherein, R1, R2, and R3 are each independently selected from any one of H, C1-C6 straight chain or branched alkyl; X is selected from any one of carbonate ion, nitrate ion, chloride ion, bromide ion, iodide ion, sulfate ion, sulfonate ion, acetate ion, citrate ion, hypochlorite ion or hypobromite ion.

7. The cling film according to any one of claims 1 to 6, wherein The molar percentage of repeating units containing ammonium salt groups in the polymer B is ≥40%.

8. The cling film according to any one of claims 1 to 7, wherein The polymer in the polymer ammonium salt includes at least one of polyacrylamide, polyethyleneimine, polymethacrylamide, chitosan, polyaminoethyl methacrylate, polyaminoethyl acrylate, polyN,N-dimethylaminoethyl methacrylate, polyN,N-diethylaminoethyl methacrylate, polyN,N-dimethylaminoethyl acrylate, polyN,N-diethylaminoethyl acrylate or amino-terminated hyperbranched polymer, or a block copolymer of at least two of the above polymers; Preferably, the number average molecular weight of the polymer B is 1 to 100 KDa.

9. The cling film according to any one of claims 1 to 8, wherein The molar ratio of the hydroxyl groups in the polymer A to the ammonium salt groups in the polymer B is (0.25-5):

1.

10. The cling film according to any one of claims 1 to 9, wherein The support layer comprises a porous support layer; Preferably, the material of the support layer includes at least one of polyethylene, polypropylene, polystyrene, polyimide, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene terephthalate or polycaprolactam; Preferably, the thickness of the support layer is 5 to 100 μm; Preferably, the thickness of the functional layer is 0.2 to 10 μm; Preferably, the cling film satisfies at least one of the following: a) Maintain humidity above 90% but less than 100%; b) Antibacterial rate ≥ 90%; c) Air permeability ≥ 20000sec / 100ml.

11. A method for preparing a fresh-keeping film according to any one of claims 1 to 10, comprising the following steps: The functional layer is disposed on the surface of one side of the support layer and at least a part of the holes to obtain the preservative film.

12. The method for preparing a fresh-keeping film according to claim 11, wherein: The preparation method comprises: mixing polymer A with a solvent to obtain a polymer A solution; mixing polymer B with a solvent to obtain a polymer B solution; mixing the polymer A solution with the polymer B solution to obtain a polymer mixed solution; and then coating the polymer mixed solution on the surface of a support layer and drying to obtain the preservative film.

13. The method for preparing a fresh-keeping film according to claim 12, wherein: The mass fraction of polymer A in the polymer A solution is 0.2-15%, preferably 1-10%.

14. The method for preparing a fresh-keeping film according to claim 12 or 13, wherein: The mass fraction of polymer B in the polymer B solution is 0.3 to 10%, and more preferably 0.5 to 10%.

15. A food preservative film, wherein: The food preservative film comprises the preservative film according to any one of claims 1 to 10 or the preservative film prepared by the preparation method of the preservative film according to any one of claims 11 to 14.

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