An antibacterial heat-sealable biaxially oriented polylactic acid film and its preparation method

Abstract

The present invention provides an antibacterial heat-sealable biaxially stretched polylactic acid film and a preparation method thereof. Among them, the antibacterial heat-sealable biaxially stretched polylactic acid film successively includes an upper surface layer, an intermediate layer, and a lower surface layer. The composition of the upper surface layer includes an anti-sticking masterbatch, an antibacterial masterbatch, and a polylactic acid resin; the composition of the intermediate layer includes a polylactic acid resin; the composition of the lower surface layer includes an anti-sticking masterbatch, an antibacterial masterbatch, a compatibilizer, a functional resin, and a polylactic acid resin. Among them, the functional resin includes poly(butylene succinate-co-adipate) and polyethylene terephthalate-1,4-cyclohexanedimethanol ester. The film prepared by the present invention has good antibacterial properties and heat-sealing properties, 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. It is a green and environmentally friendly packaging material, meeting the environmental protection trend and tendency.

Description

Technical Field

[0001] The present invention relates to the technical application field of thin film soft packaging, and particularly relates to an antibacterial heat-sealable biaxially oriented polylactic acid film and a preparation method thereof. Background Art

[0002] 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 currently a common method to use packaging materials with various material structures in combination. 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 adds difficulties to subsequent recycling after completing the packaging mission. With the implementation of the "Plastic Restriction 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 awareness of health and hygiene, 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.

[0003] At present, antibacterial materials mainly achieve antibacterial functions by adding some metal ions or organic compounds. However, organic compounds are not temperature-resistant or prone to discoloration 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.

[0004] Therefore, how to obtain an antibacterial heat-sealable degradable film has become an urgent problem to be solved currently. Summary of the Invention

[0005] To solve the problems mentioned in the prior art, the present invention provides an antibacterial heat-sealable biaxially oriented polylactic acid film, which sequentially includes an upper surface layer, an intermediate layer, and a lower surface layer;

[0006] The composition of the upper surface layer includes an anti-sticking masterbatch, an antibacterial masterbatch, and a polylactic acid resin;

[0007] The composition of the intermediate layer includes a polylactic acid resin;

[0008] The composition of the lower surface layer includes an anti-sticking masterbatch, an antibacterial masterbatch, a compatibilizer, a functional resin, and a polylactic acid resin, wherein the functional resin includes polybutylene adipate-co-butylene succinate and polyethylene terephthalate-1,4-cyclohexanedimethanol ester.

[0009] In one embodiment, the mass ratio of the poly(butylene succinate - adipate) to the poly(ethylene terephthalate - 1,4 - cyclohexanedimethanol) is (50 - 90):(10 - 50).

[0010] In one embodiment, by mass parts, the upper surface layer comprises 1 - 5 parts of an anti - sticking masterbatch, 1 - 15 parts of an antibacterial masterbatch, and 80 - 98 parts of a polylactic acid resin;

[0011] The middle layer is 100 parts of a polylactic acid resin;

[0012] The lower surface layer comprises 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 a polylactic acid resin.

[0013] In one embodiment, the antibacterial masterbatch is composed of an antibacterial agent, a coupling agent, a dispersant, and a polylactic acid resin; the antibacterial agent is modified graphene, and the modified graphene is obtained by modifying graphene with sodium dodecylbenzenesulfonate.

[0014] In one embodiment, the coupling agent includes γ - glycidoxypropyltrimethoxysilane and γ - methacryloxypropyltrimethoxysilane.

[0015] In one embodiment, the mass ratio of γ - glycidoxypropyltrimethoxysilane to γ - methacryloxypropyltrimethoxysilane is (50 - 70):(30 - 50).

[0016] In one embodiment, by mass parts, the antibacterial masterbatch includes 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.

[0017] In one embodiment, the antibacterial masterbatch is obtained by twin - screw blending modification, and its preparation method is as follows:

[0018] First, put the modified graphene, the coupling agent, and the dispersant into a stirrer, stir at a speed of 200 - 1000 r / min for 3 - 15 minutes, then add the polylactic acid resin, and under the high - speed stirring mode, mix at high speed for 10 - 25 min to obtain a mixture;

[0019] Then add the mixture to a twin - screw extruder, and melt - extrude, draw into strands, cool, pelletize, and dry at 180 - 215 °C to obtain the antibacterial masterbatch.

[0020] In one embodiment, the preparation method of the modified graphene includes the following preparation steps:

[0021] 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 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 under the condition of 50 to 100 °C, and then sieve it.

[0022] 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. The added mass fraction of sodium dodecylbenzenesulfonate is 20% to 300% of that 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 under the condition of 50 to 100 °C, sieve it through a 500-mesh sieve, and finally activate it under the condition of 100 to 120 °C for 1 to 5 h to obtain modified graphene.

[0023] In one embodiment, by mass, the anti-sticking masterbatch comprises 0.5 to 5 parts of lubricant, 3 to 10 parts of antiblocking agent, 0.5 to 5 parts of antioxidant, and 80 to 96 parts of polylactic acid resin.

[0024] In one embodiment, the lubricant is selected from one or a combination of erucamide, silicone, PE wax, and ethylene bisstearamide;

[0025] The antioxidant is selected from a mixture of antioxidant 1010 and antioxidant 168 in a ratio of 2:1.

[0026] The antiblocking agent is selected from one or a combination of diatomite, kaolin, calcium carbonate, talc powder, silica, polymethyl methacrylate microspheres, and polystyrene microspheres.

[0027] In one embodiment, the anti-sticking masterbatch is obtained by melt extrusion, strand drawing, cooling, pelletizing, and drying through a twin-screw extruder at a temperature of 180 to 215 °C.

[0028] In one embodiment, the compatibilizer is selected from any one or a mixture of at least two in any proportion 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.

[0029] In one embodiment, the thickness of the antibacterial heat-sealable biaxially oriented polylactic acid film of the solution 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 intermediate barrier layer is 2-72 μm.

[0030] The present invention also provides a preparation method of an antibacterial heat-sealable biaxially oriented polylactic acid film, melting and co-extruding each layer component to obtain an unstretched cast sheet;

[0031] Biaxially stretching the unstretched cast sheet to obtain an antibacterial heat-sealable biaxially oriented polylactic acid film.

[0032] In one embodiment, the preparation method specifically includes the following steps:

[0033] S1: Dry all raw materials and control the moisture content of the raw materials below 200 ppm;

[0034] S2: Mix the raw materials of the upper surface layer, the intermediate layer and the lower surface layer respectively according to the formula ratio, and then melt and plasticize and extrude through their respective extruders at a temperature of 170-210 °C, and flow out through a T-shaped die head;

[0035] 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;

[0036] S4: Immerse the thick sheet in a water bath at 20-80 °C for pretreatment;

[0037] S5: Heat the thick sheet and then perform synchronous biaxial stretching of the polyamide film using a Brückner 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;

[0038] S6: Perform heat setting treatment on the stretched film, where the setting temperature is 140-190 °C and the setting time is 5-40 s, and then the film is cooled and corona post-treated, the corona treatment power is 10-15 W·min / m², and it is wound up;

[0039] S7: Slice the wound biaxially oriented polyamide film as required, and finally obtain the antibacterial heat-sealable biaxially oriented polylactic acid film, and the film thickness is 10-80 μm.

[0040] Compared with the prior art, the antibacterial heat-sealable biaxially oriented polylactic acid film provided by the present invention has the following technical principles and effects:

[0041] (1) In the present invention, poly(butylene succinate-co-adipate) and poly(ethylene terephthalate-co-1,4-cyclohexanedimethanol) are used as functional resins in the lower surface layer to ensure the heat-sealing performance of the film. This is mainly because these substances are amorphous resins. After blending with polylactic acid, they reduce the softening point and melting point of the blend, achieving excellent heat-sealing performance.

[0042] (2) The antibacterial masterbatch of the present invention contains modified graphene. Its antibacterial effect mainly utilizes graphene. Specifically, as a two-dimensional crystal, graphene is a single-layer structure with only one carbon atom thickness. 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 swim on such sharp nanoscale two-dimensional materials, their cell walls are instantly cut and they die, thus playing an antibacterial role. Graphene can also kill bacteria by directly extracting a large amount of phospholipid molecules on the cell membrane to destroy the cell membrane. Therefore, the antibacterial performance of the film under this formulation is very prominent, and there will be no problem of metal ion residues. It is a very promising material.

[0043] At the same time, as a nanoscale material, graphene also has an obvious strengthening effect and can significantly improve the mechanical properties of the film.

[0044] In addition, under the action of the screw shear force, the lamellar structure of graphene is peeled off, and the layered structure is dispersed in the polymer film, forming many parallel and stacked two-dimensional thin sheets. Small molecules such as oxygen cannot directly penetrate the film and can only penetrate through the gaps between the layers. Therefore, the addition of graphene can hinder the penetration of small molecules such as oxygen, playing a tortuous maze effect, which is equivalent to extending the path of small molecules such as oxygen through the film, ultimately resulting in a reduction in the permeation amount of small molecules such as oxygen.

[0045] (3) Both the upper surface layer and the lower surface layer of the film prepared by the present invention have antibacterial materials. When it is made into a packaging bag, it has double antibacterial protection. The outer surface layer can resist and kill foreign bacteria, and the inner layer can kill the bacteria generated under internal conditions, protecting the hygienic safety of the packaged contents.

[0046] (4) The film prepared by the present invention has good antibacterial performance and heat-sealing performance. It has a wide range of uses and good performance. It is easy to process, with a simple production process, high production efficiency, and easy to realize industrialization. It is a completely biodegradable material, non-toxic, harmless, and hygienic. It is a green and environmentally friendly packaging material, meeting the environmental protection trend and tendency. Brief Description of the Drawings

[0047] 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.

[0048] Figure 1 It is a schematic structural diagram of an antibacterial heat-sealable biaxially stretched polylactic acid film provided by an embodiment of the present invention.

[0049] Reference numerals:

[0050] Detailed implementation manners

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, 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 belong to the scope of protection of the present invention.

[0052] To better understand the present invention, the following will describe the present invention in detail with specific embodiments and comparative examples without limiting the present invention in any way.

[0053] Example 1

[0054] An antibacterial heat-sealable biaxially stretched polylactic acid film, referring to Figure 1 The antibacterial heat-sealable biaxially stretched polylactic acid film is composed of three layers, namely, 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 the lower surface layer also has heat-sealing properties. By mass, 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 intermediate 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.

[0055] 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 60:40.

[0056] By mass fraction, the antibacterial masterbatch comprises 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.

[0057] The antibacterial masterbatch of this example is obtained by twin-screw blending modification, and its preparation method is as follows:

[0058] S1: Dissolve graphene in deionized water. The mass fraction ratio of water to graphene is 1:20. Stir at 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 graphene at the bottom layer of the centrifuge tube, dry it at 80 °C, and then screen it.

[0059] S2: Add to the reaction kettle according to the mass fraction ratio of graphene to deionized water of 1:5. At the same time, add sodium dodecylbenzenesulfonate. The added mass fraction 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 at 80 °C, screen through a 500-mesh sieve, and finally activate at 105 °C for 3 h to obtain organically treated graphene.

[0060] 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 perform high-speed mixing for 15 min in the high-speed stirring mode to obtain a mixture.

[0061] S4: 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.

[0062] By mass fraction, the anti-sticking masterbatch comprises 3 parts of ethylene bisstearamide, 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.

[0063] 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 200 °C.

[0064] The compatibilizer is selected from glycidyl methacrylate grafted ethylene-octene copolymer.

[0065] The thickness of the antibacterial heat-sealable biaxially oriented polylactic acid film in this example is 25 μm, wherein the thickness of the upper surface layer and the lower surface layer is 2 μm; the thickness of the middle barrier layer is 21 μm.

[0066] The preparation method of the antibacterial heat-sealable biaxially oriented polylactic acid film of this embodiment includes the following preparation steps:

[0067] S1: Dry all raw materials and control the moisture content of the raw materials below 200 ppm;

[0068] 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 200 °C, and flow out through a T-shaped die head;

[0069] 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;

[0070] S4: Immerse the thick sheet in a water bath at 50 °C for pretreatment;

[0071] S5: After heating the thick sheet, use a Bruckner magnetic levitation synchronous biaxial stretching device to perform synchronous biaxial stretching of the polyamide film, where the stretching temperature is 105 °C and the stretching ratio is 4×4;

[0072] S6: Perform heat setting treatment on the stretched film, where the setting temperature is 125 °C and the setting time is 8 s, then the film is cooled and corona post-treated, the corona treatment power is 10 Wmin / m², and it is wound up;

[0073] S7: Slit the wound biaxially oriented polyamide film as required, and finally obtain the antibacterial heat-sealable biaxially oriented polylactic acid film, and the film thickness is 25 μm.

[0074] Example 2

[0075] An antibacterial heat-sealable biaxially oriented polylactic acid film, the antibacterial heat-sealable biaxially oriented 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 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-sealable 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.

[0076] Among them, the functional resin is composed of polybutylene adipate-co-butylene succinate and polyethylene terephthalate-1,4-cyclohexanedimethanol ester in a mass ratio of 70:30.

[0077] By mass fraction, the antibacterial masterbatch comprises 12 parts of graphene, 6 parts of coupling agent, 4 parts of Lubrizol DP310 and 78 parts of polylactic acid resin. The coupling agent is composed of γ-glycidoxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane in a mass ratio of 55:45.

[0078] The antibacterial masterbatch of this example is obtained by twin-screw blending modification, and its preparation method is as follows:

[0079] S1: Dissolve graphene in deionized water. The mass ratio of water to graphene is 1:30. Stir at 250 r / min for 30 min, then centrifuge at a speed of 650 r / min for 15 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 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 sieve it.

[0080] S2: Add to the reaction kettle according to the mass ratio of graphene to deionized water of 1:6. At the same time, add sodium dodecylbenzenesulfonate. 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 at 85 °C, sieve through a 500-mesh sieve, and finally activate at 110 °C for 3.5 h to obtain organically treated graphene.

[0081] S3: Put the treated graphene, coupling agent, and dispersant into a stirrer, stir at a speed of 600 r / min for 10 minutes, then add polylactic acid resin, and high-speed mix for 20 min in the high-speed stirring mode to obtain a mixture.

[0082] S4: Add the mixture to a twin-screw extruder, melt-extrude, draw, cool, pelletize, and dry at 205 °C to obtain the antibacterial masterbatch.

[0083] By mass fraction, the anti-sticking masterbatch comprises 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 mixed in a mass ratio of 2:1.

[0084] The anti-sticking masterbatch of this example is obtained by melt-extruding, drawing, cooling, pelletizing, and drying with a twin-screw extruder at a temperature of 205 °C.

[0085] The compatibilizer is selected from ethylene-acrylate-maleic anhydride copolymer.

[0086] The thickness of the antibacterial heat-sealable biaxially oriented polylactic acid film in this example is 25 μm; among them, the thickness of the upper surface layer and the lower surface layer is 2.5 μm; the thickness of the middle barrier layer is 20 μm.

[0087] The preparation method of the antibacterial heat-sealable biaxially oriented polylactic acid film of this embodiment includes the following steps:

[0088] S1: Dry all raw materials and control the moisture content of the raw materials below 200 ppm;

[0089] S2: Mix the raw materials of the upper surface layer, the middle layer and the lower surface layer according to the formula ratio respectively, then melt and plasticize and extrude through their respective extruders at a temperature of 205 °C, and flow out through a T-die head;

[0090] 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 280 μm and the temperature of the cold drum is 18 °C;

[0091] S4: Immerse the thick sheet in a water bath at 55 °C for pretreatment;

[0092] S5: Heat the thick sheet and then perform synchronous biaxial stretching of the polyamide 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;

[0093] S6: Perform heat setting treatment 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 corona treatment power is 11 Wmin / m², and wind up;

[0094] S7: Slit the wound biaxially oriented polyamide film as required, and finally obtain the antibacterial heat-sealable biaxially oriented polylactic acid film, and the film thickness is 25 μm.

[0095] Example 3

[0096] An antibacterial heat-sealable biaxially oriented polylactic acid film, the antibacterial heat-sealable biaxially oriented 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-sealable properties. By mass, 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.

[0097] Among them, the functional resin is composed of polybutylene succinate-adipate and polyethylene terephthalate-1,4-cyclohexanedimethanol ester in a mass ratio of 80:20.

[0098] By mass fraction, the antibacterial masterbatch comprises 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.

[0099] The antibacterial masterbatch of this example is obtained by twin-screw blending modification, and its preparation method is as follows:

[0100] S1: Dissolve graphene in deionized water. The mass ratio of water to graphene is 1:15. Stir at 250 r / min for 40 min, then centrifuge at 700 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 7000 r / min. Remove the supernatant, scrape the graphene at the bottom layer of the centrifuge tube, dry it at 90 °C, and then sieve it.

[0101] 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 fraction of sodium dodecylbenzenesulfonate is 80% of that of graphene. Then stir and react in a 90 °C water bath 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.

[0102] S3: Put the treated graphene, coupling agent, and dispersant into a stirrer, stir at 700 r / min for 10 minutes, then add polylactic acid resin, and high-speed mix for 20 min in the high-speed stirring mode to obtain a mixture.

[0103] S4: Add the mixture to a twin-screw extruder, melt extrude, draw, cool, pelletize, and dry at 205 °C to obtain the antibacterial masterbatch.

[0104] By mass fraction, the anti-sticking masterbatch comprises 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 in a mass ratio of 1:1. The antioxidant is selected from antioxidant 1010 and antioxidant 168 mixed in a mass ratio of 2:1.

[0105] 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 205 °C.

[0106] The compatibilizer is selected from maleic anhydride grafted ethylene-octene copolymer and glycidyl methacrylate grafted ethylene-octene copolymer mixed in a ratio of 1:1.

[0107] The thickness of the antibacterial heat-sealable biaxially oriented polylactic acid film in this embodiment is 25 μm; among them, the thicknesses of the upper surface layer and the lower surface layer are 3 μm; the thickness of the middle barrier layer is 19 μm.

[0108] The preparation method of the antibacterial heat-sealable biaxially oriented polylactic acid film in this embodiment includes the following preparation steps:

[0109] S1: Dry all raw materials and control the moisture content of the raw materials to be below 200 ppm;

[0110] S2: Mix the raw materials of the upper surface layer, the middle layer, and the lower surface layer respectively according to the formula ratio, 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;

[0111] 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;

[0112] S4: Immerse the thick sheet in a water bath at 60 °C for pretreatment;

[0113] S5: After heating the thick sheet, use a Brückner magnetic levitation synchronous biaxial stretching device to perform synchronous biaxial stretching of the polyamide film, where the stretching temperature is 105 °C and the stretching ratio is 4.2×4.2;

[0114] S6: Perform heat setting on the stretched film, where the setting temperature is 130 °C and the setting time is 12 s, then cool and corona-treat the film, the corona treatment power is 10 Wmin / m², and wind it up;

[0115] S7: Slit the wound biaxially oriented polyamide film as required, and finally obtain the antibacterial heat-sealable biaxially oriented polylactic acid film, and the film thickness is 25 μm.

[0116] Comparative Example 1

[0117] A polylactic acid film, which successively includes an upper surface layer, a middle layer, and a lower surface layer from top to bottom. By mass, 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;

[0118] Among them, the anti-sticking masterbatch, polylactic acid resin used in this comparative example, as well as the thicknesses and preparation methods of each layer of the film are all the same as those in Example 1.

[0119] Comparative Example 2

[0120] A polylactic acid film, which from top to bottom successively includes an upper surface layer, a middle layer and a lower surface layer, wherein the lower surface layer has heat-sealing performance. By mass parts, the upper surface layer includes 3 parts of 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 anti-sticking masterbatch, 5 parts of compatibilizer, 40 parts of functional resin and 52 parts of polylactic acid resin;

[0121] Wherein, the anti-sticking masterbatch, polylactic acid resin, functional resin and compatibilizer used in this comparative example, as well as the thicknesses and preparation methods of each layer of the film are all the same as those in Example 1.

[0122] Comparative Example 3

[0123] A polylactic acid film, which 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 performance. By mass parts, 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 and 92 parts of polylactic acid resin;

[0124] Wherein, the anti-sticking masterbatch, polylactic acid resin and antibacterial masterbatch used in this comparative example, as well as the thicknesses and preparation methods of each layer of the film are all the same as those in Example 1.

[0125] Comparative Example 4.1

[0126] A polylactic acid film, which 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 performance, and at the same time the lower surface layer also has heat-sealing performance. By mass parts, 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;

[0127] By mass parts, 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.

[0128] The antibacterial masterbatch of this comparative example is obtained by twin-screw blending modification, and its preparation method is as follows:

[0129] 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 for 20 min under the condition of 200 r / 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 screen it;

[0130] 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, wash with deionized water after centrifugation. Then dry at 80 °C, sieve through a 500-mesh sieve, and finally activate at 105 °C for 3 h to obtain the organically treated silver-based antibacterial agent;

[0131] 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 min, then add polylactic acid resin, and high-speed mix for 15 min in the high-speed stirring mode to obtain a mixture;

[0132] S4: Add the mixture to a twin-screw extruder, melt-extrude, draw into strips, cool, pelletize, and dry at 200 °C to obtain the antibacterial masterbatch.

[0133] The anti-sticking masterbatch, polylactic acid resin, functional resin, compatibilizer used in this comparative example, and the thickness of each layer of the film and the preparation method are all the same as those in Example 1.

[0134] Comparative Example 4.2

[0135] Use a copper-based antibacterial agent to replace the silver-based antibacterial agent in Comparative Example 4.1. The specific model is AntibacMax B401 produced by Langyi New Materials, and the rest is the same as Comparative Example 4.1.

[0136] Comparative Example 4.3

[0137] Use a zinc-based antibacterial agent to replace the silver-based antibacterial agent in Comparative Example 4.1. The specific model is AntibacMax B201 produced by Langyi New Materials, and the rest is the same as Comparative Example 4.1.

[0138] Comparative Example 5

[0139] 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 parts, 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;

[0140] Among them, the functional resin of this comparative example is polybutylene adipate / terephthalate;

[0141] 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.

[0142] Comparative Example 6

[0143] 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 parts, 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;

[0144] Among them, the functional resin of this comparative example is polyethylene terephthalate-1,4-cyclohexanedimethanol ester;

[0145] 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.

[0146] Comparative Example 7

[0147] 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 parts, 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;

[0148] Among them, the functional resin of this comparative example is polybutylene succinate-adipate;

[0149] 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.

[0150] Comparative Example 8

[0151] 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 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 comprises 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.

[0152] By mass, the antibacterial masterbatch of this comparative example comprises 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-glycidyl ether oxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane in a mass ratio of 60:40.

[0153] The antibacterial masterbatch of this comparative example is obtained by twin-screw blending modification, and its preparation method is as follows:

[0154] S1: Put 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 under the high-speed stirring mode, high-mix for 15 min to obtain a mixture;

[0155] S2: Add the mixture to a twin-screw extruder, melt-extrude, draw into strips, cool, pelletize and dry at 200 °C to obtain the antibacterial masterbatch.

[0156] 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.

[0157] 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 thereto; 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.

[0158] The present invention tests the relevant properties of the above-mentioned examples and comparative examples, and the specific result data are shown in the following table:

[0159] Table 1

[0160]

[0161] Note:

[0162] (1)Testing of heat-sealing performance: The test was 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 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.

[0163] (2)Testing of tensile strength performance: The test was 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".

[0164] (3)Testing of antibacterial performance: The test was carried out in accordance with the standard requirements of GB / T 31402-2015 "Plastics - Test method for antibacterial performance on the surface of plastics".

[0165] (4)The barrier performance was judged by detecting the oxygen transmission rate. Among them, the performance test of oxygen transmission rate: The test was 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 barrier performance. The more the number of "☆", the better the barrier performance, and "×" represents extremely poor barrier performance or inability to test.

[0166] It can be seen from the test results in Table 1 that compared with the film prepared in the comparative example, the antibacterial heat-sealable biaxially oriented polylactic acid film prepared in the example has better antibacterial and heat-sealing performance, and at the same time has excellent tensile strength and degradability.

[0167] Specifically, no functional resin was added in Comparative Example 1 and Comparative Example 3, and polybutylene adipate / terephthalate was used instead of the functional resin of the present invention in Comparative Example 5. The heat-sealing performance of the three is extremely poor, while only one component of the functional resin of the present invention was used in Comparative Example 6 and Comparative Example 7, and their heat-sealing performance also decreased, indicating that the functional resin provided by the present invention plays a key role in improving the heat-sealing performance of the finished film.

[0168] In Comparative Example 1 and Comparative Example 2, the antibacterial masterbatch was not added, and they hardly had antibacterial properties, and the barrier properties and mechanical properties decreased significantly. In Comparative Example 4.1, Comparative Example 4.2 and Comparative Example 4.3, the silver-based antibacterial agent, copper-based antibacterial agent and zinc-based antibacterial agent commonly used in the art were used to replace the antibacterial masterbatch used in the present invention. Although the antibacterial properties were similar to those of the film prepared by the present invention, their barrier properties and mechanical properties decreased significantly. 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 the existence of metal ion residues, which is not conducive to environmental protection.

[0169] The graphene used in the antibacterial masterbatch of Comparative Example 8 was not pre-modified, and its antibacterial properties, barrier properties and mechanical properties decreased significantly compared with the examples. Thus, it can be seen that the modification treatment of graphene has a significant impact on the performance of the subsequent film.

[0170] 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 inside 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.

[0171] Although terms such as upper surface layer, intermediate layer, lower surface layer, etc. are used more in this article, the possibility of using other terms is not excluded. These terms are only used to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitation is contrary to the spirit of the present invention.

[0172] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, not 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 heat-sealable biaxially stretched polylactic acid film, characterized in that, it successively includes an upper surface layer, an intermediate layer and a lower surface layer, the composition of the upper surface layer includes an anti-sticking masterbatch, an antibacterial masterbatch and polylactic acid resin; the composition of the intermediate layer includes polylactic acid resin; the composition of the lower surface layer includes an anti-sticking masterbatch, an antibacterial masterbatch, a compatibilizer, a functional resin and polylactic acid resin, wherein 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 antibacterial masterbatch is composed of an antibacterial agent, a coupling agent, a dispersant and polylactic acid resin, the antibacterial agent is modified graphene, and the modified graphene is obtained by modifying graphene with sodium dodecylbenzenesulfonate; the coupling agent includes γ-glycidoxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane.

2. The antibacterial heat-sealable biaxially stretched polylactic acid film according to claim 1, characterized in that: by mass parts, the upper surface layer includes 1-5 parts of anti-sticking masterbatch, 1-15 parts of antibacterial masterbatch, 80-98 parts of polylactic acid resin; the intermediate layer is 100 parts of polylactic acid resin; the lower surface layer includes 1-5 parts of anti-sticking masterbatch, 1-15 parts of antibacterial masterbatch, 1-10 parts of compatibilizer, 25-65 parts of functional resin, 5-72 parts of polylactic acid resin.

3. The antibacterial heat-sealable biaxially stretched polylactic acid film according to claim 1, characterized in that: the mass ratio of γ-glycidoxypropyltrimethoxysilane to γ-methacryloxypropyltrimethoxysilane is (50-70):(30-50).

4. The antibacterial heat-sealable biaxially stretched polylactic acid film according to claim 1, characterized in that: by mass parts, the anti-sticking masterbatch includes 0.5-5 parts of lubricant, 3-10 parts of opening agent, 0.5-5 parts of antioxidant and 80-96 parts of polylactic acid resin.

5. The antibacterial heat-sealable biaxially stretched polylactic acid film according to claim 1, characterized in that: 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.

6. The antibacterial heat-sealable biaxially stretched polylactic acid film according to claim 1, characterized in that: the thickness of the antibacterial heat-sealable biaxially stretched polylactic acid film is 10-80 μm, and the thicknesses of the upper surface layer and the lower surface layer are both 1-4 μm; the thickness of the intermediate barrier layer is 2-72 μm.

7. An antibacterial heat-sealable biaxially stretched polylactic acid film according to any one of claims 1-6, characterized in that: each layer component is respectively melted and co-extruded to obtain an unstretched cast sheet; The unstretched cast film is biaxially stretched to obtain an antibacterial heat-sealable biaxially stretched polylactic acid film.

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