Preservative film as well as preparation method and application thereof

Abstract

The invention provides a preservative film as well as a preparation method and application thereof. The preservative film comprises a supporting layer, a functional layer, a surface arranged on one side of the supporting layer and at least one part of holes, the functional layer comprises a polymer A and a polymer B; the molecular structure of the polymer A contains hydroxyl; the polymer B comprises polymer ammonium salt; the molar ratio of hydroxyl in the polymer A to ammonium salt groups in the polymer B is greater than 0.1: 1 and less than 10: 1. According to the intelligent fresh-keeping box disclosed by the invention, the fresh-keeping film has relatively high selectivity on permeability of gases such as water vapor, carbon dioxide and oxygen, and the moisture permeation rate can be intelligently adjusted according to the change of humidity in the box, so that intelligent fresh-keeping is realized; the fruit and vegetable packaging box has good barrier performance on oxygen and carbon dioxide and can restrain carbon dioxide in the box from being exhausted and oxygen outside the box from entering, so that aerobic respiration of fruits and vegetables is restrained, and the preservation time is prolonged. In addition, the coating also has good antibacterial performance, and the risk of dissolution of an antibacterial agent is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of cling film, and in particular relates to a cling film and a preparation method and application thereof. Background Art

[0002] Food cling film is mainly used for heating food in microwave ovens, preserving food in refrigerators, packaging fresh and cooked food, etc. It is widely used in food packaging fields such as family life, supermarkets, hotels and restaurants, and industrial production. According to the different materials used and the added plasticizers, cling film is divided into many types, including paper-based and polymer-based cling film.

[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 rate according to the humidity in the fresh-keeping box, resulting in fruits and vegetables losing water too quickly, or moisture cannot pass through to form supersaturated liquid water, accelerating food decay.

[0004] For example, CN111378216A discloses a fruit and vegetable cling 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, which 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 delay their metabolic process, thereby achieving a longer storage time of the product with less nutrient loss; however, the cling film cannot achieve intelligent preservation and has a poor preservation effect; and a variety of additives are added, such as antibacterial and mildew-proof agents with antibacterial function, but this may cause the antibacterial agent to dissolve during use, and there are potential toxic side effects.

[0005] Therefore, it is an urgent problem to be solved in this field to develop a cling film that is highly selective for the permeation of water vapor, carbon dioxide and oxygen, can effectively block carbon dioxide, can achieve intelligent preservation according to environmental changes, has a good antibacterial effect without the risk of antibacterial agent dissolution without the need for additional antibacterial agents. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a fresh-keeping film and its preparation method and application. The fresh-keeping film has high selectivity for the permeability of gases such as water vapor, carbon dioxide and oxygen, and can intelligently adjust the moisture permeability according to the humidity changes in the box, thereby realizing intelligent preservation, and dynamically maintaining the humidity in the fresh-keeping box at a relative humidity of more than 90%, but less than 100% saturated humidity; and has good barrier properties for oxygen and carbon dioxide, can inhibit the discharge of carbon dioxide in the box and the entry of oxygen outside the box, thereby inhibiting the aerobic respiration of fruits and vegetables and extending the storage time; in addition, it also has good antibacterial properties to avoid the risk of dissolution of antibacterial agents.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a cling film, comprising a supporting layer and a functional layer, and at least a portion of the surface and holes of one side of the supporting layer is arranged; the functional layer comprises polymer A and polymer B; the molecular structure of polymer A contains hydroxyl groups; the polymer B comprises polymer ammonium salt; the molar ratio of hydroxyl groups in polymer A to ammonium salt groups in polymer B is greater than 0.1:1 and less than 10:1.

[0009] In the present invention, 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 being able to inhibit 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 a dual function; 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. 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 permeability rate, thereby inhibiting the moisture permeability of the functional film layer; under saturated humidity conditions, liquid condensed water 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 are normally combined, 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 high humidity level but does not produce condensed water, thereby ensuring that the fruits and vegetables do not lose water quickly and do not accelerate decay due to the production of condensed water due to humidity saturation. In addition, the ammonium salt introduced by polymer B has a highly effective antibacterial effect, and is a film-forming component that interacts with polymer A. It will not precipitate during use like added small molecules or inorganic antibacterial agents, making the antibacterial effect of the plastic wrap lasting and not declining. Moreover, the effect of polymer A and polymer B is better at a specific molar ratio.

[0010] In the present invention, 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 of them.

[0011] In the present invention, if the molar ratio of the hydroxyl group to the ammonium salt group is too low, the anionic acid radicals in the polymer B are too many, and under saturated humidity conditions, the concentration of condensed water cannot be quickly responded to, resulting in the moisture permeability rate not being able to change quickly according to humidity; if the molar ratio of the hydroxyl group to the ammonium salt group is too high, the acid radical ions in the polymer B cannot play a good ion-specific effect, the proportion of hydrogen bonding with the polymer A is small, and the water molecule binding sites of the polymer A are less affected by the change of its concentration, resulting in the moisture permeability rate also not being able to change quickly according to humidity.

[0012] 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 the range of any two thereof.

[0013] In the present invention, the molar percentage of the hydroxyl-containing repeating unit 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.

[0014] 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).

[0015] 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.

[0016] In the present invention, 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.

[0017] 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.

[0018] Preferably, the polymer ammonium salt comprises at least one of a compound having a structure shown in Formula I and a compound having a structure shown in Formula II:

[0019] 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.); 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.

[0020] 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 the range of any two thereof.

[0021] In the present invention, the molar percentage of the repeating unit containing the ammonium salt group is within the above-defined range, which is beneficial to the durability of the antibacterial effect and the ion-specific effect of the acid radical ion.

[0022] 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), polyN,N-dimethylaminoethyl methacrylate (PDMAEMA), polyN,N-diethylaminoethyl methacrylate (PDEAEMA), polyN,N-dimethylaminoethyl acrylate (PDMAEA), polyN,N-diethylaminoethyl acrylate (PDEAEA) or amino-terminated hyperbranched polymer (HBPNH2), or a block copolymer of at least two of the above polymers.

[0023] 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.

[0024] In the present invention, the number average molecular weight of the polymer B is between 1-100 KDa, 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, and further ensuring the density of the film layer.

[0025] In the present invention, the preparation method of the polymer ammonium salt comprises: dissolving an amino polymer having a primary amine, a secondary amine or a tertiary amine group in a side chain or a main chain in water, then adding an acid, stirring at room temperature, and monitoring the pH change of the solution by a pH meter during the acid addition process. When the pH of the solution becomes 7.0, the addition of the acid is stopped, and a polymer ammonium salt solution is formed.

[0026] In the present invention, 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).

[0027] As the most optimal technical solution of the present invention, 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.

[0028] Preferably, the support layer comprises a porous support layer.

[0029] Preferably, the material of the support layer includes at least one of polyethylene, polypropylene, polystyrene, polyimide, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene terephthalate or polycaprolactam.

[0030] 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.

[0031] 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.

[0032] Preferably, the cling film satisfies at least one of the following:

[0033] a) Maintain humidity above 90% but less than 100%;

[0034] b) Antibacterial rate ≥ 90%;

[0035] c) Air permeability ≥ 20000sec / 100ml.

[0036] In a second aspect, the present invention provides a method for preparing the cling film according to the first aspect, the preparation method specifically comprising the following steps:

[0037] 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.

[0038] 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.

[0039] 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%.

[0040] In the present invention, if the mass fraction of the polymer A is too low, it is not conducive to the compactness of the cling 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.

[0041] 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%.

[0042] In the present invention, if the mass fraction of polymer B is too low, it is impossible to respond to humidity changes by changing the acid radical ion concentration to control the speed of moisture permeability; if the mass fraction of polymer B is too high, the ammonium salt content introduced is too high, which affects the flexibility and density of the membrane.

[0043] Preferably, the coating method includes at least one of slot coating, knife coating, roller coating, dip coating or extrusion coating.

[0044] In the present invention, the preparation method is simple and does not require complicated cross-linking, modification and other processes.

[0045] In a third aspect, the present invention provides a food preservative film, wherein the food preservative film comprises the preservative film as described in the first aspect or the preservative film prepared by the preparation method of the preservative film as described in the second aspect.

[0046] Preferably, the food preservative film includes fruit and vegetable preservative film.

[0047] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The fresh-keeping film provided by the present invention adopts a polymer A with a specific functional group and a polymer B with a specific functional group to form a functional layer, and can change the water molecule content in the functional layer according to the change of humidity, thereby realizing the concentration change of acid radical anions, realizing the alternating change of hydrated water molecules-hydroxyl hydrogen bonding and acid radical anion-hydroxyl hydrogen bonding, thereby realizing the control of hydroxyl-water binding sites, realizing the adjustment of moisture permeability, realizing intelligent fresh-keeping, and the fresh-keeping film has high selective permeability to water molecules, carbon dioxide and oxygen, and has high barrier effect to carbon dioxide and oxygen, thereby inhibiting aerobic respiration and prolonging the fresh-keeping effect; in addition, the natural antibacterial effect of the polymer ammonium salt is non-dissolving and non-toxic and side effects. DETAILED DESCRIPTION

[0050] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0051] In the present invention, the polymer ammonium salt is represented by the abbreviation of the polymer and the 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.

[0052] In the present invention, the thickness of the support layer is 20 μm, and the thickness of the functional layer is 1.5 μm.

[0053] Example 1

[0054] The present 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 material of the support layer is a polyethylene porous film; the functional layer includes HPMC (number average molecular weight of 18KDa, hydroxyl repeating unit ratio of 88%) and chitosan hydrochloride CS-HCl (chitosan number average molecular weight of 5KDa); the molar ratio of hydroxyl groups in the HPMC to ammonium salt groups in the CS-HCl is 1:1.

[0055] This embodiment provides a method for preparing a fresh-keeping film, which specifically comprises the following steps:

[0056] HPMC is dispersed in water to obtain a 4% 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 meter is used to monitor the pH change of the solution. When the pH of the solution becomes 7.0, the acid is stopped from being added to form a CS-HCl solution with a mass fraction of 2%; the HPMC aqueous solution is then mixed with the CS-HCl solution, and the obtained mixed solution is coated on one surface of a polyethylene porous film, and the mixture is dried to obtain the preservative film.

[0057] Examples 2-21, Comparative Examples 1-10

[0058] 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.

[0059] Table 1

[0060]

[0061]

[0062]

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

[0064] Performance Testing

[0065] The air permeability of cling film is tested according to GB / T36363-2018 standard. If the air permeability 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 according to the following method: a water-soaked sponge was placed in a plastic square box, and the moisturizing film sample was installed on the matching square box cover. The square box cover and the box were relatively well sealed. A humidity sensor was placed inside the square box to detect the humidity inside the box in real time. The entire square box was placed in a 5°C environment for 72 hours, and the humidity inside the box from the 24th to the 72nd hour was recorded to calculate the average moisturizing effect. At the same time, observe whether there is condensation on the surface of the moisturizing film.

[0068] The antibacterial property 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

[0071]

[0072]

[0073]

[0074] Note: “-” means the test cannot be performed or the test is meaningless.

[0075] As can be seen from the above table, the cling film provided by the present invention uses a polymer A having a specific functional group and a polymer B having a specific functional group to form a functional layer, and can intelligently adjust the moisture permeability of the cling film according to changes in humidity. Under low humidity conditions, the moisture permeability is low, and water loss is suppressed; under high humidity conditions, the moisture permeability is high, and food decay caused by supersaturation of water vapor is avoided, 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 no cross-linking modification is required.

[0076] When no polymer ammonium salt is added, it has no antibacterial properties and cannot intelligently adjust humidity, and the moisturizing effect is poor, less than 90%.

[0077] After adding polymer ammonium salt B, it has antibacterial properties and can achieve intelligent humidity regulation. Furthermore, when the molar ratio of hydroxyl group to ammonium salt group is limited to the optimal range, no condensation water will be generated; the molecular weight of polymer A and polymer B and the mass fraction of the solution of the two are within the optimal range, which can further improve the moisturizing effect.

[0078] Embodiment 1-21 is a preferred example, and the structural performance parameters are good. Polymer B and the main film-forming high molecular polymer A form a strong hydrogen bond, and the air tightness of the obtained composite membrane is better than that of the single HPMC membrane (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 higher than 90%, meeting the target setting requirements; at the same time, due to the presence of polymer ammonium salts, the antibacterial effect reaches 99.9%. Comparative Examples 1-2, 4 have poor antibacterial properties, only 73.4; 74.1 and 74.3%, because there is no addition of polymer ammonium salt B or amino polymer, and their moisturizing and breathable effects are also poor. The moisturizing properties of Comparative Examples 1-2, 4 reflect the characteristics of the HPMC membrane itself, all of which are more than 80%. Comparative Example 3 is to add an amino polymer, namely CS, to HPMC. CS is insoluble in water, resulting in poor dispersion and compatibility in the main film-forming structure of HPMC, resulting in poor density of the membrane, poor air permeability of 12600 compared with the HPMC membrane, and poor moisturizing effect. Due to the introduction of the antibacterial component of CS, the antibacterial performance of the composite membrane reaches 95.7%, but does not reach the optimal effect of 99.9%, which is also because CS cannot be well dispersed in the composite membrane structure.

[0079] Among them, Example 3-4 is a main membrane structure, that is, polymer A is replaced by PVA from HPMC, and the ammonium salt system is replaced by acetate from hydrochloride, and it also has good structural properties.

[0080] Comparative Examples 5-6, which have no film-forming main structure and only contain polymer ammonium salt B or amino polymer, cannot form a dense composite film layer, have very low air permeability, poor film-forming performance, and poor moisturizing effect; among them, in Comparative Example 6, CS is insoluble, cannot form a film, has poor composite effect, has very low air permeability, and has no moisturizing performance because it cannot form a dense structure. However, due to the presence of polymer ammonium salt or amino polymer, the antibacterial performance of the composite film reaches more than 90%.

[0081] In comparative examples 7-8, the mass fraction of polymer ammonium salt B is not within the optimal range. The mass fraction is too high, and there is too much polymer ammonium salt B, which affects the density of the cling film, reduces the air permeability, and deteriorates the moisturizing effect; the mass fraction is too low, and the ion-specific effect cannot be exerted, and similarly, the moisturizing effect deteriorates. In both cases, the moisturizing effect of more than 90% cannot be achieved.

[0082] Comparative Examples 9 and 10 are that the molar ratio of hydroxyl group to ammonium salt group is not within the optimal range, and the moisturizing effect cannot reach more than 90%. The molar ratio of hydroxyl group to ammonium salt group is too low, and there are too many acid radical ions, which cannot quickly respond to changes in saturated humidity and produce condensed water. The molar ratio of hydroxyl group to ammonium salt is too high, and there are fewer acid radical ions, the ion-specific effect is not obvious, and the moisturizing effect is also poor.

[0083] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A cling film, characterized in that: The fresh-keeping film comprises a supporting 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, characterized in that: The molar percentage of hydroxyl-containing repeating units in the polymer A is ≥40%; Preferably, the polymer A comprises 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; Preferably, the number average molecular weight of the polymer A is 4-200 KDa.

3. The cling film according to claim 1 or 2, characterized in that: 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; Preferably, the polymer ammonium salt comprises 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.

4. The cling film according to any one of claims 1 to 3, characterized in that: The molar percentage of repeating units containing ammonium salt groups in the polymer B is ≥40%; Preferably, the polymer in the polymer ammonium salt comprises 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.

5. The cling film according to any one of claims 1 to 4, characterized in that: 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.

6. The cling film according to any one of claims 1 to 5, characterized in that: 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.

7. A method for preparing a fresh-keeping film according to any one of claims 1 to 6, characterized in that: The preparation method specifically comprises 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.

8. The method for preparing the cling film according to claim 7, characterized in that: 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.

9. The method for preparing the fresh-keeping film according to claim 7 or 8, characterized in that: The mass fraction of polymer A in the polymer A solution is 0.2 to 15%, preferably 1 to 10%; Preferably, the mass fraction of polymer B in the polymer B solution is 0.3 to 10%, more preferably 0.5 to 10%; Preferably, the coating method includes at least one of slot coating, knife coating, roller coating, dip coating or extrusion coating.

10. A food preservative film, characterized in that: The food preservative film comprises the preservative film according to any one of claims 1 to 6 or the preservative film prepared by the preparation method of the preservative film according to any one of claims 7 to 9.

Images