Antibacterial master batch and preparation method thereof as well as polylactic acid film and preparation method thereof

Abstract

The invention relates to the field of application of a thin film flexible package technology, in particular to an antibacterial master batch and a preparation method thereof as well as a polylactic acid thin film and a preparation method thereof. The antibacterial master batch is prepared from the following components in parts by mass: 0.5 to 15 parts of an antibacterial agent, 0.5 to 8 parts of a coupling agent, 0.5 to 5 parts of a dispersing agent and 72 to 98.5 parts of polylactic resin, the antibacterial agent is modified graphene, and the modified graphene is obtained by modifying graphene with sodium dodecyl benzene sulfonate. Surface modification is carried out on graphene through sodium dodecyl benzene sulfonate, the dispersity and antibacterial activity of the graphene are remarkably improved, and no metal ion residue risk exists. Meanwhile, the film is endowed with excellent tensile strength and barrier property due to the addition of the antibacterial master batch, and the film has the characteristics of environmental protection and degradability. The master batch is suitable for the fields of food packaging, medical treatment and the like, and an innovative solution is provided for packaging materials which have efficient antibacterial and mechanical properties and are green and environment-friendly.

Description

[0001] This application is a divisional application of the application with the application number 202211492638.2, the application date of November 25, 2022, and the title of "A Polylactic Acid Film and Its Preparation Method". Technical Field

[0002] The present invention relates to the technical application field of thin film soft packaging, and particularly relates to an antibacterial masterbatch and its preparation method, a polylactic acid film and its preparation method. Background Art

[0003] The use of plastic packaging products has brought great convenience to people's lives and has become an indispensable packaging material for human survival and social development. In order to meet packaging requirements, it is a commonly used method to compound packaging materials with various material structures. For example, in order to make the film have heat-sealing performance, a layer of CPP or IPE film is usually compounded as a heat-sealing layer in the inner layer structure of the film. Although this combination method can meet the packaging requirements of different occasions, it increases the difficulty of subsequent recycling after completing the packaging mission. With the implementation of the "plastic limit order" and the improvement of environmental protection requirements, single-material, environmentally friendly, recyclable, and degradable materials have attracted much attention. It has gradually become a trend for single-material films to have heat-sealing performance. Moreover, with the improvement of people's health and hygiene awareness, packaging films applied in fields such as packaging not only require the packaging material to have good heat-sealing performance but also should have good antibacterial properties.

[0004] At present, antibacterial materials mainly achieve antibacterial functions by adding some metal ions or organic compounds. However, organic compounds are not heat-resistant or prone to color change problems, and the use of metal ion antibacterial agents such as silver ions, zinc ions, or copper ions will cause metal ions to directly enter the natural environment and cause pollution after the packaging material is processed or degraded.

[0005] Therefore, how to provide an antibacterial material that is environmentally friendly and has good antibacterial performance for use in films has become an urgent problem to be solved currently. Summary of the Invention

[0006] To solve the problems mentioned in the prior art, an antibacterial masterbatch provided by the present invention, by mass, comprises 0.5 - 15 parts of an antibacterial agent, 0.5 - 8 parts of a coupling agent, 0.5 - 5 parts of a dispersant, and 72 - 98.5 parts of a polylactic acid resin; The antibacterial agent is modified graphene; the modified graphene is obtained by modifying graphene with sodium dodecylbenzenesulfonate.

[0007] In one embodiment, the modified graphene is prepared by the following method: S1: Dissolve graphene in deionized water with the mass ratio of water to graphene being 1:5 - 1:50. Stir for 10 - 60 minutes under the condition of a rotation speed of 100 - 300 r / min, then centrifuge at a speed of 200 - 800 r / min for 5 - 20 minutes. Take the upper-layer mixture, remove the large-particle-size particles at the bottom of the centrifuge tube, and then centrifuge the collected upper-layer mixture at a speed of 3000 - 8000 r / min. Remove the supernatant, scrape out the graphene at the bottom layer of the centrifuge tube, dry it at 50 - 100 °C, and then pass it through a sieve. S2: Add it to the reaction kettle according to the mass ratio of graphene to deionized water being 1:1 - 1:10. At the same time, add sodium dodecylbenzenesulfonate, and then stir and react in a water bath at 50 - 100 °C for 1 - 5 h. After centrifugation, wash it with deionized water. Then dry it at 50 - 100 °C, pass it through a sieve, and finally activate it at 100 - 120 °C for 1 - 5 h to obtain modified graphene.

[0008] In one embodiment, the added mass fraction of sodium dodecylbenzenesulfonate is 20% - 300% of that of graphene.

[0009] In one embodiment, the coupling agent includes γ-glycidoxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane.

[0010] In one embodiment, the mass ratio of γ-glycidoxypropyltrimethoxysilane to γ-methacryloxypropyltrimethoxysilane is (50 - 70):(30 - 50).

[0011] In one embodiment, first, put the modified graphene, coupling agent, and dispersant into a stirrer and stir at a speed of 200 - 1000 r / min for 3 - 15 minutes, then add polylactic acid resin, and under the high-speed stirring mode, mix highly for 10 - 25 min to obtain a mixture. Then add the mixture to a twin-screw extruder, melt-extrude, draw into strips, cool, pelletize, and dry at 180 - 215 °C to obtain an antibacterial masterbatch.

[0012] The present invention also provides a polylactic acid film, which sequentially includes an upper surface layer, a middle layer, and a lower surface layer. By mass fraction, the upper surface layer includes 1 - 5 parts of an anti-sticking masterbatch, 1 - 15 parts of an antibacterial masterbatch, and 80 - 98 parts of polylactic acid resin. The middle layer is 100 parts of polylactic acid resin. The lower surface layer includes 1 - 5 parts of an anti-sticking masterbatch, 1 - 15 parts of an antibacterial masterbatch, 1 - 10 parts of a compatibilizer, 25 - 65 parts of a functional resin, and 5 - 72 parts of polylactic acid resin. The functional resin includes poly(butylene succinate-co-adipate) and polyethylene terephthalate-1,4-cyclohexanedimethanol ester; the mass ratio of poly(butylene succinate-co-adipate) to polyethylene terephthalate-1,4-cyclohexanedimethanol ester is (50-90):(10-50); The compatibilizer is selected from any one or at least two of ethylene-methyl acrylate-glycidyl methacrylate random terpolymer, ethylene-acrylate-maleic anhydride copolymer, ethylene-vinyl acetate copolymer, maleic anhydride grafted ethylene-octene copolymer, ethylene-acrylic acid copolymer, and glycidyl methacrylate grafted ethylene-octene copolymer in any proportion mixture; The antibacterial masterbatch uses the antibacterial masterbatch as described above or the antibacterial masterbatch prepared by the preparation method of the antibacterial masterbatch as described above.

[0013] Furthermore, the thickness of the polylactic acid film is 10-80 μm; among them, the thickness of the upper surface layer and the lower surface layer is 1-4 μm; the thickness of the middle barrier layer is 2-72 μm.

[0014] In one embodiment, by mass, the anti-sticking masterbatch includes 0.5-5 parts of lubricant, 3-10 parts of antiblocking agent, 0.5-5 parts of antioxidant, and 80-96 parts of polylactic acid resin; The lubricant is selected from one or a combination of erucamide, silicone, PE wax, and ethylene bisstearamide; The antioxidant is selected from antioxidant 1010 and antioxidant 168 mixed in a ratio of 2:1; The antiblocking agent is selected from one or a combination of diatomite, kaolin, calcium carbonate, talc, silica, polymethyl methacrylate microspheres, and polystyrene microspheres.

[0015] In one embodiment, the anti-sticking masterbatch is obtained by melting and extruding, strand drawing, cooling, pelletizing, and drying through a twin-screw extruder at a temperature of 180-215 °C.

[0016] The present invention also provides a preparation method of the polylactic acid film as described above, S1: Dry all the raw materials and control the moisture content of the raw materials below 200 ppm; S2: Mix the raw materials of the upper surface layer, the middle layer, and the lower surface layer according to the formula ratio respectively, and then melt and plasticize and extrude through their respective extruders at a temperature of 170-210 °C, and flow out through a T-die head; S3: Use a low-pressure air knife to attach the melt to a cold drum to form a thick sheet, where the thickness of the thick sheet is 100-350 μm and the temperature of the cold drum is 10-50 °C; S4: Immerse the thick sheet in a water bath at 20-80 °C for pretreatment; S5: After heating the thick sheet, synchronously biaxially stretch the polylactic acid film using a Bruckner magnetic levitation synchronous biaxial stretching device, where the stretching temperature is 90 - 180 °C and the stretching ratio is 3.5×3.5 - 5.5×5.5; S6: Perform heat setting on the stretched film, where the setting temperature is 140 - 190 °C and the setting time is 5 - 40 s. Then, cool and corona-treat the film. The corona treatment power is 10 - 15 Wmin / m², and then wind it up; S7: Slit the wound biaxially stretched polylactic acid film as required to finally obtain the described polylactic acid film.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The antibacterial masterbatch of the present invention contains modified graphene. Its antibacterial effect mainly utilizes graphene. Specifically, as a two-dimensional material, graphene is a single-layer structure with a thickness of only one carbon atom. Usually, there are 3 million layers of single-layer graphene in 1 mm of graphite, and the smallest bacteria currently discovered are about 0.2 mm. When bacteria move on such sharp nano-scale two-dimensional materials, their cell walls are instantly cut and they die, playing an antibacterial role; graphene can also kill bacteria by directly extracting a large number of phospholipid molecules on the cell membrane to destroy the cell membrane. Therefore, the antibacterial performance of graphene is very prominent, and there will be no problem of metal ion residues. It is a very promising material; After the present invention modifies graphene with sodium dodecylbenzenesulfonate, the antibacterial performance of graphene is significantly improved. Specifically, due to its high specific surface area, edge effect, and surface non-polarity, the interaction force between graphene, such as van der Waals force, is much greater than that between ordinary molecules, and it is very easy to agglomerate by itself, resulting in uneven dispersion in the polymer matrix and affecting the antibacterial effect. As an anionic surfactant, sodium dodecylbenzenesulfonate can be attached to the surface of graphene through physical adsorption or chemical bonding. Its hydrophilic sulfonic acid group significantly improves the hydrophilicity of graphene, making it evenly dispersed in the solution, ensuring that the graphene nanosheets are fully exposed in the film and maximizing the contact area with bacteria; in addition, the sulfonic acid group (-SO3⁻) of sodium dodecylbenzenesulfonate can combine with the surface defects or oxygen-containing functional groups on the graphene surface to form a stable surface modification layer, endowing graphene with stronger chemical activity. For example, through surface charge regulation, it promotes the electrostatic attraction between it and the negatively charged bacterial cell membrane, thereby enhancing the ability to destroy the bacterial cell membrane.

[0018] 2. As a nano-scale material, graphene also has an obvious strengthening effect and can significantly improve the mechanical properties of the film.

[0019] In addition, under the action of the screw shear force, the sheet structure of graphene is peeled off, and the layered structure is dispersed in the polymer film, forming numerous two-dimensional flakes that are parallel to each other and stacked. Small molecule substances such as oxygen cannot directly penetrate the film and can only pass through the gaps between the layers. Therefore, the addition of graphene can hinder the penetration of small molecule substances such as oxygen, producing a tortuous maze effect, which is equivalent to extending the path of small molecule substances such as oxygen through the film, ultimately resulting in a decrease in the permeation amount of small molecule substances such as oxygen.

[0020] 3. The polylactic acid film provided by the present invention uses poly(butylene succinate-co-adipate) and poly(ethylene terephthalate-co-1,4-cyclohexanedimethanol) as functional resins in the lower surface layer to ensure the heat-sealing performance of the film. This is mainly because this substance is an amorphous resin, and after blending with polylactic acid, it reduces the softening point and melting point of the blend, achieving excellent heat-sealing performance. Both the upper surface layer and the lower surface layer of the film provided by the present invention have antibacterial materials. When it is made into a packaging bag, it has a double insurance of antibacterial properties. The outer surface layer can resist and kill foreign bacteria, and the inner layer can kill the bacteria generated under internal conditions, protecting the health and safety of the packaged contents.

[0021] 4. The film prepared by the present invention has good antibacterial properties and heat-sealing performance, is widely used and has good performance, and is easy to process. The production process is simple, the production efficiency is high, and it is easy to realize industrialization. It is a completely biodegradable material, non-toxic, harmless, and hygienic, and is a green and environmentally friendly packaging material, meeting the environmental protection trend and tendency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0023] Figure 1 It is a schematic structural diagram of a polylactic acid film provided by an embodiment of the present invention.

[0024] Reference numerals: 10 Lower surface layer; 20 Core layer; 30 Upper surface layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] For a better understanding of the present invention, the present invention will be described in detail below with reference to specific embodiments and comparative examples, without limiting the present invention in any way.

[0027] The present invention provides an antibacterial masterbatch as described below: By mass parts, it includes 0.5 - 15 parts of antibacterial agent, 0.5 - 8 parts of coupling agent, 0.5 - 5 parts of dispersant, and 72 - 98.5 parts of polylactic acid resin; The antibacterial agent is modified graphene; The modified graphene is obtained by modifying graphene with sodium dodecylbenzenesulfonate.

[0028] The modified graphene is prepared by the following method: S1: Dissolve graphene in deionized water, with the mass ratio of water to graphene being 1:5 - 1:50. Stir for 10 - 60 min under the condition of a rotation speed of 100 - 300 r / min, then centrifuge at a speed of 200 - 800 r / min for 5 - 20 min. Take the upper-layer mixture, remove the large-particle-size particles at the bottom of the centrifuge tube, and then centrifuge the collected upper-layer mixture at a speed of 3000 - 8000 r / min. Remove the supernatant, scrape out the graphene at the bottom layer of the centrifuge tube, dry it at 50 - 100 °C, and then sieve it; S2: Add it to the reaction kettle according to the mass ratio of graphene to deionized water being 1:1 - 1:10. At the same time, add sodium dodecylbenzenesulfonate, and then stir and react in a water bath at 50 - 100 °C for 1 - 5 h. After centrifugation, wash it with deionized water. Then dry it at 50 - 100 °C, sieve it, and finally activate it at 100 - 120 °C for 1 - 5 h to obtain modified graphene.

[0029] The added mass parts of the sodium dodecylbenzenesulfonate are 20% - 300% of graphene.

[0030] The coupling agent includes γ-glycidoxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane.

[0031] The mass ratio of the γ-glycidoxypropyltrimethoxysilane to the γ-methacryloxypropyltrimethoxysilane is (50 to 70):(30 to 50).

[0032] The dispersant is Lubrizol DP310.

[0033] The preparation method of the antibacterial masterbatch provided by the present invention is as follows: S1: Dissolve graphene in deionized water. The mass fraction ratio of water to graphene is 1:5 to 1:50. Stir for 10 to 60 minutes under the condition of a rotation speed of 100 to 300 r / min, then centrifuge at a speed of 200 to 800 r / min for 5 to 20 minutes. Take the upper-layer mixture, remove the large-particle-size particles at the bottom of the centrifuge tube, and then centrifuge the collected upper-layer mixture at a speed of 3000 to 8000 r / min, remove the supernatant, scrape the graphene at the bottom layer of the centrifuge tube, dry it at 50 to 100 °C, and then sieve it.

[0034] S2: Add it to the reaction kettle according to the mass fraction ratio of graphene to deionized water of 1:1 to 1:10. At the same time, add sodium dodecylbenzenesulfonate. The added mass fraction of sodium dodecylbenzenesulfonate is 20% to 300% of graphene. Then stir and react in a water bath at 50 to 100 °C for 1 to 5 h, wash with deionized water after centrifugation. Then dry it at 50 to 100 °C, sieve it through a 500-mesh sieve, and finally activate it at 100 to 120 °C for 1 to 5 h to obtain modified graphene; S3: Put the treated graphene, coupling agent, and dispersant into a stirrer, stir at a speed of 200 to 1000 r / min for 3 to 15 minutes, then add polylactic acid resin, and perform high-speed mixing for 10 to 25 minutes in the high-speed stirring mode to obtain a mixture; S4: Add the mixture to a twin-screw extruder, melt-extrude, draw into strips, cool, pelletize, and dry it at 180 to 215 °C to obtain the antibacterial masterbatch.

[0035] The present invention provides the following examples of the application of the antibacterial masterbatch.

[0036] Example 1 A polylactic acid film, referring to Figure 1 , the polylactic acid film is composed of a three-layer structure, which are the upper surface layer, the middle layer, and the lower surface layer from top to bottom. Among them, the upper surface layer and the lower surface layer have antibacterial properties, and at the same time, the lower surface layer also has heat-sealing properties. By mass fraction, the upper surface layer includes 3 parts of anti-sticking masterbatch, 5 parts of antibacterial masterbatch, and 92 parts of polylactic acid resin; the middle layer is 100 parts of polylactic acid resin; the lower surface layer includes 3 parts of anti-sticking masterbatch, 5 parts of antibacterial masterbatch, 5 parts of compatibilizer, 40 parts of functional resin, and 47 parts of polylactic acid resin.

[0037] Among them, the functional resin is composed of poly(butylene succinate-co-adipate) and poly(ethylene terephthalate-co-1,4-cyclohexanedimethanol) in a mass ratio of 60:40.

[0038] By mass, the antibacterial masterbatch includes 10 parts of graphene, 5 parts of coupling agent, 3 parts of Lubrizol DP310, and 82 parts of polylactic acid resin. The coupling agent is composed of γ-glycidoxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane in a mass ratio of 60:40.

[0039] The antibacterial masterbatch of this example is obtained by twin-screw blending modification, and its preparation method is as follows: S1: Dissolve graphene in deionized water. The mass ratio of water to graphene is 1:20. Stir at a speed of 200 r / min for 20 min, then centrifuge at a speed of 600 r / min for 10 min. Take the upper-layer mixture, remove the large-particle-size particles at the bottom of the centrifuge tube, then centrifuge the collected upper-layer mixture at a speed of 5000 r / min, remove the supernatant, scrape out the graphene at the bottom layer of the centrifuge tube, dry it at 80 °C, and then screen it. S2: Add it to the reaction kettle according to the mass ratio of graphene to deionized water of 1:5. At the same time, add sodium dodecylbenzenesulfonate. The added mass of sodium dodecylbenzenesulfonate is 50% of that of graphene. Then stir and react in a water bath at 80 °C for 2 h, centrifuge and wash with deionized water. Then dry it at 80 °C, sieve it through a 500-mesh sieve, and finally activate it at 105 °C for 3 h to obtain organically treated graphene. S3: Put the treated graphene, coupling agent, and dispersant into a stirrer, stir at a speed of 500 r / min for 8 minutes, then add polylactic acid resin, and high-speed mix for 15 min in the high-speed stirring mode to obtain a mixture. S4: Add the mixture to a twin-screw extruder, melt extrude, draw, cool, pelletize, and dry it at 200 °C to obtain the antibacterial masterbatch.

[0040] By mass, the anti-sticking masterbatch includes 3 parts of ethylene bis-stearamide, 6 parts of silica, 2 parts of antioxidant, and 89 parts of polylactic acid resin. The antioxidant is selected from antioxidant 1010 and antioxidant 168 and mixed in a mass ratio of 2:1.

[0041] The anti-sticking masterbatch of this example is obtained by melting extrusion, drawing, cooling, pelletizing, and drying with a twin-screw extruder at a temperature of 200 °C.

[0042] The compatibilizer is selected from glycidyl methacrylate grafted ethylene-octene copolymer.

[0043] The thickness of the polylactic acid film in this embodiment is 25 μm, among which, the thicknesses of the upper surface layer and the lower surface layer are 2 μm; the thickness of the middle barrier layer is 21 μm.

[0044] The preparation method of the polylactic acid film in this embodiment includes the following preparation steps: S1: Dry all the raw materials and control the moisture content of the raw materials below 200 ppm; S2: Mix the raw materials of the upper surface layer, the middle layer and the lower surface layer respectively according to the formula ratio, then melt and plasticize and extrude them through their respective extruders at a temperature of 200 °C, and flow out through a T-shaped die head; S3: Use a low-pressure air knife to attach the melt to a cold drum to form a thick sheet, where the thickness of the thick sheet is 265 μm and the temperature of the cold drum is 15 °C; S4: Immerse the thick sheet in a water bath at 50 °C for pretreatment; S5: Heat the thick sheet and then perform synchronous biaxial stretching of the polylactic acid film using a Bruckner magnetic levitation synchronous biaxial stretching device, where the stretching temperature is 105 °C and the stretching ratio is 4×4; S6: Perform heat setting treatment on the stretched film, where the setting temperature is 125 °C and the setting time is 8 s, then cool and corona-treat the film, the corona treatment power is 10 Wmin / m², and wind it up; S7: Slit the wound biaxially stretched polylactic acid film as required, and finally obtain the polylactic acid film, and the film thickness is 25 μm.

[0045] Example 2 A polylactic acid film, the polylactic acid film is composed of a three-layer structure, which are an upper surface layer, a middle layer and a lower surface layer from top to bottom in sequence, where the upper surface layer and the lower surface layer have antibacterial properties, and at the same time the lower surface layer also has heat-sealing properties. By mass, the upper surface layer includes 4 parts of anti-sticking masterbatch, 6 parts of antibacterial masterbatch, and 90 parts of polylactic acid resin; the middle layer is 100 parts of polylactic acid resin; the lower surface layer includes 4 parts of anti-sticking masterbatch, 6 parts of antibacterial masterbatch, 6 parts of compatibilizer, 50 parts of functional resin, and 34 parts of polylactic acid resin.

[0046] Among them, the functional resin is composed of polybutylene succinate-adipate butanediol ester and polyethylene terephthalate-1,4-cyclohexanedimethanol ester in a mass ratio of 70:30.

[0047] By mass, the antibacterial masterbatch includes 12 parts of graphene, 6 parts of coupling agent, 4 parts of Lubrizol DP310 and 78 parts of polylactic acid resin, and the coupling agent is composed of γ-glycidyl ether oxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane in a mass ratio of 55:45.

[0048] The antibacterial masterbatch of this embodiment is obtained by twin-screw blending modification, and its preparation method is as follows: S1: Dissolve graphene in deionized water, with the mass ratio of water to graphene being 1:30. Stir at 250 r / min for 30 min, then centrifuge at 650 r / min for 15 min. Take the upper-layer mixture, remove the large-particle-size particles at the bottom of the centrifuge tube, and then centrifuge the collected upper-layer mixture at 6000 r / min. Remove the supernatant, scrape out the graphene at the bottom layer of the centrifuge tube, dry it at 85 °C, and then screen it; S2: Add it to the reaction kettle according to the mass ratio of graphene to deionized water of 1:6. At the same time, add sodium dodecylbenzenesulfonate, and the added mass fraction of sodium dodecylbenzenesulfonate is 80% of that of graphene. Then stir and react in a water bath at 90 °C for 3 h, wash with deionized water after centrifugation. Then dry it at 85 °C, sieve it through a 500-mesh sieve, and finally activate it at 110 °C for 3.5 h to obtain organically treated graphene; S3: Put the treated graphene, coupling agent, and dispersant into a stirrer, stir at 600 r / min for 10 min, and then add polylactic acid resin. Under the high-speed stirring mode, mix it at high speed for 20 min to obtain a mixture; S4: Add the mixture to a twin-screw extruder, melt-extrude, draw, cool, pelletize, and dry it at 205 °C to obtain the antibacterial masterbatch.

[0049] By mass, the anti-sticking masterbatch includes 4 parts of erucamide, 8 parts of polystyrene microspheres, 3 parts of antioxidant, and 85 parts of polylactic acid resin. The antioxidant is selected from antioxidant 1010 and antioxidant 168 and is mixed according to a mass ratio of 2:1.

[0050] The anti-sticking masterbatch of this embodiment is obtained by melting, extruding, drawing, cooling, pelletizing, and drying through a twin-screw extruder at a temperature of 205 °C.

[0051] The compatibilizer is selected from ethylene-acrylate-maleic anhydride copolymer.

[0052] The thickness of the polylactic acid film of this embodiment is 25 μm; among them, the thicknesses of the upper surface layer and the lower surface layer are 2.5 μm; the thickness of the middle barrier layer is 20 μm.

[0053] The preparation method of the polylactic acid film of this embodiment includes the following steps: S1: Dry all the raw materials and control the moisture content of the raw materials below 200 ppm; S2: Mix the raw materials of the upper surface layer, the middle layer, and the lower surface layer according to the formula ratio respectively, and then melt and plasticize and extrude them through their respective extruders at a temperature of 205 °C and flow out through a T-shaped die head; S3: Attach the melt to the cold drum using a low-pressure air knife to form a thick sheet, where the thickness of the thick sheet is 280 μm and the temperature of the cold drum is 18°C; S4: Immerse the thick sheet in a water bath at 55°C for pretreatment; S5: Heat the thick sheet and then perform synchronous biaxial stretching of the polylactic acid film using a Bruckner magnetic levitation synchronous biaxial stretching device, where the stretching temperature is 110°C and the stretching ratio is 4.5×4.5; S6: Perform heat setting on the stretched film, where the setting temperature is 130°C and the setting time is 10 s. Then, cool and corona-treat the film. The power of the corona treatment is 11 Wmin / m², and then wind up the film; S7: Slit the wound biaxially stretched polylactic acid film as required to finally obtain the polylactic acid film, and the thickness of the film is 25 μm.

[0054] Example 3 A polylactic acid film, which is composed of a three-layer structure, including an upper surface layer, a middle layer, and a lower surface layer from top to bottom. The upper surface layer and the lower surface layer have antibacterial properties, and at the same time, the lower surface layer also has heat-sealability. By mass fraction, the upper surface layer includes 3 parts of anti-sticking masterbatch, 9 parts of antibacterial masterbatch, and 88 parts of polylactic acid resin; the middle layer is 100 parts of polylactic acid resin; the lower surface layer includes 3 parts of anti-sticking masterbatch, 9 parts of antibacterial masterbatch, 8 parts of compatibilizer, 55 parts of functional resin, and 25 parts of polylactic acid resin.

[0055] Among them, the functional resin is composed of poly(butylene succinate-co-adipate) and poly(ethylene terephthalate-co-1,4-cyclohexanedimethanol terephthalate) in a mass ratio of 80:20.

[0056] By mass fraction, the antibacterial masterbatch includes 14 parts of graphene, 7 parts of coupling agent, 4 parts of Lubrizol DP310, and 75 parts of polylactic acid resin. The coupling agent is composed of γ-glycidoxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane in a mass ratio of 60:40.

[0057] The antibacterial masterbatch of this example is obtained by twin-screw blending modification, and its preparation method is as follows: S1: Dissolve graphene in deionized water, and the mass fraction ratio of water to graphene is 1:15. Stir at a speed of 250 r / min for 40 min, then centrifuge at a speed of 700 r / min for 15 min. Take the upper mixed solution, remove the large-particle-size particles at the bottom of the centrifuge tube, and then centrifuge the collected upper mixed solution at a speed of 7000 r / min, remove the supernatant, scrape the graphene at the bottom layer of the centrifuge tube, dry it at 90°C, and then screen it; S2: Add them to the reactor according to the mass ratio of graphene to deionized water of 1:5. Meanwhile, add sodium dodecylbenzenesulfonate, and the added mass fraction of sodium dodecylbenzenesulfonate is 80% of that of graphene. Then, stir and react in a water bath at 90 °C for 4 h, wash with deionized water after centrifugation. Then, dry at 90 °C, sieve through a 500-mesh sieve, and finally activate at 115 °C for 4 h to obtain organically treated graphene; S3: Put the treated graphene, coupling agent, and dispersant into a stirrer, stir at a speed of 700 r / min for 10 minutes, then add polylactic acid resin, and mix at high speed for 20 min in the high-speed stirring mode to obtain a mixture; S4: Add the mixture to a twin-screw extruder, melt extrude, draw into strands, cool, pelletize, and dry at 205 °C to obtain an antibacterial masterbatch.

[0058] By mass, the anti-sticking masterbatch includes 4 parts of lubricant, 8 parts of silica, 3 parts of antioxidant, and 85 parts of polylactic acid resin. The lubricant is selected from erucamide and ethylene bisstearamide mixed at a mass ratio of 1:1, and the antioxidant is selected from antioxidant 1010 and antioxidant 168 mixed at a mass ratio of 2:1.

[0059] The anti-sticking masterbatch of this example is obtained by melt extruding, drawing into strands, cooling, pelletizing, and drying through a twin-screw extruder at a temperature of 205 °C.

[0060] The compatibilizer is selected from maleic anhydride grafted ethylene-octene copolymer and glycidyl methacrylate grafted ethylene-octene copolymer mixed at a ratio of 1:1.

[0061] The thickness of the polylactic acid film in this example is 25 μm; among them, the thickness of the upper surface layer and the lower surface layer is 3 μm; the thickness of the middle barrier layer is 19 μm.

[0062] The preparation method of the polylactic acid film in this example includes the following preparation steps: S1: Dry all the raw materials and control the moisture content of the raw materials below 200 ppm; S2: Mix the raw materials of the upper surface layer, the middle layer, and the lower surface layer respectively according to the formula ratio, then melt and plasticize and extrude through their respective extruders at a temperature of 205 °C, and flow out through a T-shaped die head; S3: Use a low-pressure air knife to attach the melt to a cold drum to form a thick sheet, where the thickness of the thick sheet is 270 μm and the temperature of the cold drum is 16 °C; S4: Immerse the thick sheet in a water bath at 60 °C for pretreatment; S5: Heat the thick sheet and then perform synchronous biaxial stretching of the polylactic acid film using a Bruckner magnetic levitation synchronous biaxial stretching device, where the stretching temperature is 105 °C and the stretching ratio is 4.2×4.2; S6: The stretched film is subjected to heat setting treatment, where the setting temperature is 130 °C and the setting time is 12 s. Then the film is cooled and corona post-treated with a corona treatment power of 10 Wmin / m², and then wound up. S7: The wound biaxially stretched polylactic acid film is slit as required, and finally the described polylactic acid film is obtained, with a film thickness of 25 μm.

[0063] Comparative Example 1 A polylactic acid film, which from top to bottom in sequence includes an upper surface layer, a middle layer, and a lower surface layer. By mass fraction, the upper surface layer includes 3 parts of an anti-sticking masterbatch and 97 parts of polylactic acid resin; the middle layer is 100 parts of polylactic acid resin; the lower surface layer includes 3 parts of an anti-sticking masterbatch and 97 parts of polylactic acid resin. Among them, the anti-sticking masterbatch, polylactic acid resin used in this comparative example, as well as the thickness of each layer of the film and the preparation method are all the same as those in Example 1.

[0064] Comparative Example 2 A polylactic acid film, which from top to bottom in sequence includes an upper surface layer, a middle layer, and a lower surface layer, where the lower surface layer has heat-sealing performance. By mass fraction, the upper surface layer includes 3 parts of an anti-sticking masterbatch, 97 parts of polylactic acid resin; the middle layer is 100 parts of polylactic acid resin; the lower surface layer includes 3 parts of an anti-sticking masterbatch, 5 parts of a compatibilizer, 40 parts of a functional resin, and 52 parts of polylactic acid resin. Among them, the anti-sticking masterbatch, polylactic acid resin, functional resin, and compatibilizer used in this comparative example, as well as the thickness of each layer of the film and the preparation method are all the same as those in Example 1.

[0065] Comparative Example 3 A polylactic acid film, which from top to bottom in sequence includes an upper surface layer, a middle layer, and a lower surface layer, where the upper surface layer and the lower surface layer have antibacterial properties. By mass fraction, the upper surface layer includes 3 parts of an anti-sticking masterbatch, 5 parts of an antibacterial masterbatch, and 92 parts of polylactic acid resin; the middle layer is 100 parts of polylactic acid resin; the lower surface layer includes 3 parts of an anti-sticking masterbatch, 5 parts of an antibacterial masterbatch, and 92 parts of polylactic acid resin. Among them, the anti-sticking masterbatch, polylactic acid resin, and antibacterial masterbatch used in this comparative example, as well as the thickness of each layer of the film and the preparation method are all the same as those in Example 1.

[0066] Comparative Example 4.1 A polylactic acid film, which successively includes an upper surface layer, an intermediate layer, and a lower surface layer from top to bottom. The upper surface layer and the lower surface layer have antibacterial properties, and at the same time, the lower surface layer also has heat-sealing properties. By mass fraction, the upper surface layer includes 3 parts of anti-sticking masterbatch, 5 parts of antibacterial masterbatch, and 92 parts of polylactic acid resin; the intermediate layer is 100 parts of polylactic acid resin; the lower surface layer includes 3 parts of anti-sticking masterbatch, 5 parts of antibacterial masterbatch, 5 parts of compatibilizer, 40 parts of functional resin, and 47 parts of polylactic acid resin; By mass fraction, the antibacterial masterbatch of this comparative example includes 10 parts of silver-based antibacterial agent (model AntibacMax P203 produced by Langyi New Materials), 5 parts of coupling agent, 3 parts of Lubrizol DP310, and 82 parts of polylactic acid resin. The coupling agent is composed of γ-glycidyl ether oxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane in a mass ratio of 60:40.

[0067] The antibacterial masterbatch of this comparative example is obtained by twin-screw blending modification, and its preparation method is as follows: S1: Dissolve the silver-based antibacterial agent in deionized water. The mass ratio of water to the silver-based antibacterial agent is 1:20. Stir at a speed of 200 r / min for 20 min, then centrifuge at a speed of 600 r / min for 10 min. Take the upper-layer mixture, remove the large-particle-size particles at the bottom of the centrifuge tube, and then centrifuge the collected upper-layer mixture at a speed of 5000 r / min. Remove the supernatant, scrape out the silver-based antibacterial agent at the bottom layer of the centrifuge tube, dry it at 80 °C, and then pass through a sieve; S2: Add to the reaction kettle according to the mass ratio of the silver-based antibacterial agent to deionized water of 1:5. At the same time, add sodium dodecylbenzenesulfonate. The added mass fraction of sodium dodecylbenzenesulfonate is 50% of the silver-based antibacterial agent. Then stir and react in a water bath at 80 °C for 2 h, and wash with deionized water after centrifugation. Then dry at 80 °C, pass through a 500-mesh sieve, and finally activate at 105 °C for 3 h to obtain an organically treated silver-based antibacterial agent; S3: Put the treated silver-based antibacterial agent, coupling agent, and dispersant into a stirrer, stir at a speed of 500 r / min for 8 minutes, then add polylactic acid resin, and in the high-speed stirring mode, high-mix for 15 min to obtain a mixture; S4: Add the mixture to a twin-screw extruder, melt-extrude, draw, cool, pelletize, and dry at 200 °C to obtain the antibacterial masterbatch.

[0068] The anti-sticking masterbatch, polylactic acid resin, functional resin, compatibilizer used in this comparative example, as well as the thickness of each layer of the film and the preparation method are all the same as those in Example 1.

[0069] Comparative Example 4.2 Replace the silver-based antibacterial agent in Comparative Example 4.1 with a copper-based antibacterial agent, specifically AntibacMax B401 produced by Langyi New Materials, and the rest is the same as Comparative Example 4.1.

[0070] Comparative Example 4.3 Replace the silver-based antibacterial agent in Comparative Example 4.1 with a zinc-based antibacterial agent, specifically AntibacMax B201 produced by Langyi New Materials, and the rest is the same as Comparative Example 4.1.

[0071] Comparative Example 5 A polylactic acid film, which successively comprises an upper surface layer, a middle layer and a lower surface layer from top to bottom. The upper surface layer and the lower surface layer have antibacterial properties, and at the same time, the lower surface layer also has heat-sealing properties. By mass, the upper surface layer comprises 3 parts of an anti-sticking masterbatch, 5 parts of an antibacterial masterbatch, and 92 parts of polylactic acid resin; the middle layer is 100 parts of polylactic acid resin; the lower surface layer comprises 3 parts of an anti-sticking masterbatch, 5 parts of an antibacterial masterbatch, 5 parts of a compatibilizer, 40 parts of a functional resin, and 47 parts of polylactic acid resin; Among them, the functional resin of this comparative example is polybutylene adipate / terephthalate; The anti-sticking masterbatch, polylactic acid resin, antibacterial masterbatch and compatibilizer used in this comparative example, as well as the thickness of each layer of the film and the preparation method are all the same as those in Example 1.

[0072] Comparative Example 6 A polylactic acid film, which successively comprises an upper surface layer, a middle layer and a lower surface layer from top to bottom. The upper surface layer and the lower surface layer have antibacterial properties, and at the same time, the lower surface layer also has heat-sealing properties. By mass, the upper surface layer comprises 3 parts of an anti-sticking masterbatch, 5 parts of an antibacterial masterbatch, and 92 parts of polylactic acid resin; the middle layer is 100 parts of polylactic acid resin; the lower surface layer comprises 3 parts of an anti-sticking masterbatch, 5 parts of an antibacterial masterbatch, 5 parts of a compatibilizer, 40 parts of a functional resin, and 47 parts of polylactic acid resin; Among them, the functional resin of this comparative example is polyethylene terephthalate-1,4-cyclohexanedimethanol ester; The anti-sticking masterbatch, polylactic acid resin, antibacterial masterbatch and compatibilizer used in this comparative example, as well as the thickness of each layer of the film and the preparation method are all the same as those in Example 1.

[0073] Comparative Example 7 A polylactic acid film, from top to bottom, successively includes an upper surface layer, a middle layer, and a lower surface layer, wherein the upper surface layer and the lower surface layer have antibacterial properties, and at the same time, the lower surface layer also has heat-sealing properties. By mass fraction, the upper surface layer includes 3 parts of an anti-sticking masterbatch, 5 parts of an antibacterial masterbatch, and 92 parts of polylactic acid resin; the middle layer is 100 parts of polylactic acid resin; the lower surface layer includes 3 parts of an anti-sticking masterbatch, 5 parts of an antibacterial masterbatch, 5 parts of a compatibilizer, 40 parts of a functional resin, and 47 parts of polylactic acid resin; Among them, the functional resin of this comparative example is poly(butylene succinate-co-adipate); The anti-sticking masterbatch, polylactic acid resin, antibacterial masterbatch, and compatibilizer used in this comparative example, as well as the thickness of each layer of the film and the preparation method, are all the same as those in Example 1.

[0074] Comparative Example 8 A polylactic acid film, from top to bottom, successively includes an upper surface layer, a middle layer, and a lower surface layer, wherein the upper surface layer and the lower surface layer have antibacterial properties, and at the same time, the lower surface layer also has heat-sealing properties. By mass fraction, the upper surface layer includes 3 parts of an anti-sticking masterbatch, 5 parts of an antibacterial masterbatch, and 92 parts of polylactic acid resin; the middle layer is 100 parts of polylactic acid resin; the lower surface layer includes 3 parts of an anti-sticking masterbatch, 5 parts of an antibacterial masterbatch, 5 parts of a compatibilizer, 40 parts of a functional resin, and 47 parts of polylactic acid resin.

[0075] By mass fraction, the antibacterial masterbatch of this comparative example includes 10 parts of graphene, 5 parts of a coupling agent, 3 parts of Lubrizol DP310, and 82 parts of polylactic acid resin. The coupling agent is composed of γ-glycidoxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane in a mass ratio of 60:40.

[0076] The antibacterial masterbatch of this comparative example is obtained by twin-screw blending modification, and its preparation method is as follows: S1: Put graphene, a coupling agent, and a dispersant into a stirrer, stir at a speed of 500 r / min for 8 minutes, then add polylactic acid resin, and under the high-speed stirring mode, high-mix for 15 min to obtain a mixture; S2: Add the mixture to a twin-screw extruder, melt-extrude, draw into strands, cool, pelletize, and dry at 200 °C to obtain the antibacterial masterbatch.

[0077] The anti-sticking masterbatch, polylactic acid resin, functional resin, and compatibilizer used in this comparative example, as well as the thickness of each layer of the film and the preparation method, are all the same as those in Example 1.

[0078] It should be noted that the specific parameters or some common reagents in the above embodiments are specific embodiments or preferred embodiments under the concept of the present invention, rather than limitations thereof; those skilled in the art can make adaptive adjustments within the concept and protection scope of the present invention. In addition, unless otherwise specified, the raw materials used can be conventional commercially available products in the art or prepared by conventional methods in the art.

[0079] The present invention tests the relevant performances of the above-mentioned various embodiments and comparative examples, and the specific result data are shown in the following table: Table 1

[0080] Note: (1) Test of heat-sealing performance: The test is carried out in accordance with the standard requirements of QB / T 2358 "Test Method for Heat-sealing Strength of Plastic Film Packaging Bags". Among them, "○" is used to represent the quality of the heat-sealing performance. The more the number of "○", the better the heat-sealing performance, and "×" represents extremely poor heat-sealing performance or inability to test.

[0081] (2) Tensile strength performance test: The test is carried out in accordance with the standard requirements of GB / T 1040.3 "Plastics - Determination of Tensile Properties - Part 3: Test Conditions for Films and Sheets".

[0082] (3) Antibacterial performance test: The test is carried out in accordance with the standard requirements of GB / T 31402-2015 "Plastics - Test Method for Antibacterial Properties of Plastic Surfaces".

[0083] (4) The barrier performance is judged by detecting the oxygen transmission rate. Among them, the oxygen transmission rate performance test: The test is carried out in accordance with the standard requirements of ASTM D3985 "Standard Test Method for Oxygen Gas Transmission Rate Through Plastic Film and Sheeting Using a Coulometric Sensor". In Table 1, "☆" is used to represent the quality of the barrier performance. The more the number of "☆", the better the barrier performance, and "×" represents extremely poor barrier performance or inability to test.

[0084] It can be seen from the test results in Table 1 that compared with the film prepared in the comparative example, the polylactic acid film prepared in the example has better antibacterial and heat-sealing performances, and at the same time has excellent tensile strength and degradability.

[0085] Specifically, no functional resin was added in Comparative Example 1 and Comparative Example 3, and polybutylene adipate / terephthalate was used to replace the functional resin of the present invention in Comparative Example 5. The heat-sealing properties of all three were extremely poor. In Comparative Example 6 and Comparative Example 7, only one component of the functional resin of the present invention was used, and their heat-sealing properties also decreased to some extent, indicating that the functional resin provided by the present invention plays a key role in improving the heat-sealing properties of the finished film.

[0086] No antibacterial masterbatch was added in Comparative Example 1 and Comparative Example 2, and they hardly had antibacterial properties, and there were obvious decreases in barrier properties and mechanical properties. In Comparative Example 4.1, Comparative Example 4.2 and Comparative Example 4.3, commonly used silver-based antibacterial agents, copper-based antibacterial agents and zinc-based antibacterial agents in the art were used to replace the antibacterial masterbatch used in the present invention. Although their antibacterial properties were similar to those of the film prepared by the present invention, their barrier properties and mechanical properties had obvious decreases. Thus, it can be seen that adding conventional metal ion antibacterial agents (including silver-based, copper-based and zinc-based) to the system of the present invention can ensure the antibacterial properties of the film, but at the same time will also cause a decrease in other properties of the film and there is a problem of metal ion residue, which is not conducive to environmental protection.

[0087] The graphene used in the antibacterial masterbatch of Comparative Example 8 was not pre-modified, and its performance in terms of antibacterial properties, barrier properties and mechanical properties was significantly lower than that of the examples. Thus, it can be seen that modifying graphene has a significant impact on the performance of the subsequent film.

[0088] In summary, the film prepared by the present invention has good heat-sealing properties, and both the upper surface layer and the lower surface layer have antibacterial materials. When it is made into a packaging bag, it has a double antibacterial insurance. The outer surface layer can resist and kill foreign bacteria, and the inner surface layer can kill the bacteria generated under internal conditions, protecting the health and safety of the packaged contents. At the same time, it also has excellent tensile strength and degradability, and is a green and environmentally friendly packaging material.

[0089] Although terms such as upper surface layer, middle layer, lower surface layer, etc. are used more in this article, the possibility of using other terms is not excluded. Using these terms is only for more convenient description and explanation of the essence of the present invention; interpreting them as any additional limitation is contrary to the spirit of the present invention.

[0090] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An antibacterial masterbatch, characterized in that: By mass parts, it includes 0.5 to 15 parts of an antibacterial agent, 0.5 to 8 parts of a coupling agent, 0.5 to 5 parts of a dispersant, and 72 to 98.5 parts of a polylactic acid resin; The antibacterial agent is modified graphene; The modified graphene is obtained by modifying graphene with sodium dodecylbenzenesulfonate.

2. The antibacterial masterbatch according to claim 1, characterized in that: The modified graphene is prepared by the following method: S1: Dissolve graphene in deionized water, the mass ratio of water to graphene is 1:5 to 1:50, stir for 10 to 60 minutes under the condition of a rotation speed of 100 to 300 r / min, then centrifuge at a speed of 200 to 800 r / min for 5 to 20 minutes, take the upper-layer mixture, remove the large-particle-size particles at the bottom of the centrifuge tube, and then centrifuge the collected upper-layer mixture at a speed of 3000 to 8000 r / min, remove the supernatant, scrape out the graphene at the bottom layer of the centrifuge tube, dry it at 50 to 100 °C, and then sieve it; S2: Add it to the reaction kettle according to the mass ratio of graphene to deionized water of 1:1 to 1:

10. At the same time, add sodium dodecylbenzenesulfonate, and then stir and react in a water bath at 50 to 100 °C for 1 to 5 h, wash it with deionized water after centrifugation. Then dry it at 50 to 100 °C, sieve it, and finally activate it at 100 to 120 °C for 1 to 5 h to obtain modified graphene.

3. The antibacterial masterbatch according to claim 2, characterized in that: The added mass parts of the sodium dodecylbenzenesulfonate are 20% to 300% of graphene.

4. The antibacterial masterbatch according to claim 1, characterized in that: The coupling agent includes γ-glycidoxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane.

5. The antibacterial masterbatch according to claim 4, characterized in that: The mass ratio of γ-glycidoxypropyltrimethoxysilane to γ-methacryloxypropyltrimethoxysilane is (50 to 70):(30 to 50).

6. A preparation method of the antibacterial masterbatch according to any one of claims 1-5, characterized in that: First, put the modified graphene, the coupling agent, and the dispersant into a stirrer, stir at a speed of 200 to 1000 r / min for 3 to 15 minutes, then add the polylactic acid resin, and under the high-speed stirring mode, high-mix for 10 to 25 min to obtain a mixture; Then add the mixture to a twin-screw extruder, melt-extrude, draw into strips, cool, pelletize, and dry at 180 to 215 °C to obtain the antibacterial masterbatch.

7. A polylactic acid film, characterized in that: It sequentially includes an upper surface layer, a middle layer, and a lower surface layer, By mass parts, the upper surface layer includes 1 to 5 parts of an anti-sticking masterbatch, 1 to 15 parts of an antibacterial masterbatch, and 80 to 98 parts of a polylactic acid resin; The middle layer is 100 parts of a polylactic acid resin; The lower surface layer includes 1 to 5 parts of an anti-sticking masterbatch, 1 to 15 parts of an antibacterial masterbatch, 1 to 10 parts of a compatibilizer, 25 to 65 parts of a functional resin, and 5 to 72 parts of a polylactic acid resin; The functional resin includes polybutylene succinate-adipate and polyethylene terephthalate-1,4-cyclohexanedimethanol ester; the mass ratio of polybutylene succinate-adipate to polyethylene terephthalate-1,4-cyclohexanedimethanol ester is (50 to 90):(10 to 50); The compatibilizer is selected from any one or at least two of ethylene-methyl acrylate-glycidyl methacrylate random terpolymer, ethylene-acrylate-maleic anhydride copolymer, ethylene-vinyl acetate copolymer, maleic anhydride grafted ethylene-octene copolymer, ethylene-acrylic acid copolymer and glycidyl methacrylate grafted ethylene-octene copolymer in any proportion mixture; The antibacterial masterbatch is the antibacterial masterbatch described in any one of claims 1 to 5 or the antibacterial masterbatch prepared by the preparation method of the antibacterial masterbatch described in claim 6.

8. The polylactic acid film according to claim 7, characterized in that: By mass parts, the anti-sticking masterbatch comprises 0.5-5 parts of lubricant, 3-10 parts of antiblocking agent, 0.5-5 parts of antioxidant and 80-96 parts of polylactic acid resin.

9. The polylactic acid film according to claim 8, wherein: The lubricant is selected from one or a combination of several of erucamide, silicone, PE wax, ethylene bisstearamide; The antioxidant is selected from antioxidant 1010 and antioxidant 168 mixed in a ratio of 2:1; The antiblocking agent is selected from one or a combination of several of diatomite, kaolin, calcium carbonate, talc powder, silica, polymethyl methacrylate microspheres, polystyrene microspheres; The anti-sticking masterbatch is obtained by melting and extruding, pelletizing, cooling, granulating and drying through a twin-screw extruder at a temperature of 180-215 °C.

10. A preparation method of a polylactic acid film according to any one of claims 7-9, wherein: S1: Dry all the raw materials, and control the moisture content of the raw materials to be below 200 ppm; S2: Mix the raw materials of the upper surface layer, the middle layer and the lower surface layer according to the formula ratio respectively, and then melt and plasticize and extrude through their respective extruders at a temperature of 170-210 °C, and flow out through a T-die; S3: Use a low-pressure air knife to attach the melt to a cold drum to form a thick sheet, wherein the thickness of the thick sheet is 100-350 μm, and the temperature of the cold drum is 10-50 °C; S4: Immerse the thick sheet in a water bath at 20-80 °C for pretreatment; S5: Heat the thick sheet and then use a Bruckner magnetic levitation synchronous biaxial stretching device to perform synchronous biaxial stretching of the polylactic acid film, wherein the stretching temperature is 90-180 °C, and the stretching ratio is 3.5×3.5-5.5×5.5; S6: Perform heat setting treatment on the stretched film, wherein the setting temperature is 140-190 °C, the setting time is 5-40 s, then the film is cooled and corona post-treated, the corona treatment power is 10-15 Wmin / m², and it is wound up; S7: Slit the wound biaxially stretched polylactic acid film as required, and finally obtain the polylactic acid film.

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