Sterile milk packaging bag and preparation process thereof

Abstract

The invention relates to the technical field of research and development of sterile milk packaging materials, and discloses a sterile milk packaging bag and a preparation process thereof. The preparation method comprises the following steps: carrying out a grafting modification effect on chitosan based on a hydroxyl-epoxy ring-opening reaction mechanism or / and an amino-epoxy ring-opening reaction mechanism by utilizing an epoxy-based antibacterial monomer, so as to prepare an antibacterial agent; a film structure of a nine-layer co-extrusion film is arranged, an antibacterial agent is introduced into a first layer and a ninth layer of the nine-layer co-extrusion film, and the antibacterial composite film is prepared by adopting a multi-layer co-extrusion blow molding film forming process and an ultraviolet sterilization process. According to the preparation technology of the nine-layer composite structure film, the prepared nine-layer composite structure film has excellent antibacterial performance and barrier performance and can be used as a raw material in manufacturing of sterile milk packaging bags.

Description

Technical Field

[0001] The invention relates to the technical field of research and development of aseptic milk packaging materials, in particular to an aseptic milk packaging bag and a preparation process thereof. Background Art

[0002] Aseptic milk packaging is basically composed of the following three parts: first, pre-sterilization of milk materials, second, sterilization of packaging containers, and third, aseptic filling and sealing environment. Aseptically packaged milk has little nutritional loss, its flavor and color remain basically unchanged, and it can be stored for a long time without refrigeration. This is an inevitable trend in the development of milk packaging. However, aseptic packaging materials are still easy to become carriers of microorganisms during storage, circulation, transportation and use. Pathogenic microorganisms not only threaten human life and health, but also cause serious public environmental problems. Therefore, antibacterial materials have a high use value in food packaging.

[0003] The main method to improve the antibacterial properties of food packaging materials is to add antibacterial agents. For example, the patent with publication number CN118003733A discloses an antibacterial multi-layer co-extruded PE film doped with metal ions and a preparation method thereof. By adding bactericidal metal ions to one or several layers of the multi-layer co-extruded PE film, the packaging can obtain bactericidal properties, eliminate bacteria or fungi that cause food spoilage, and thus extend the shelf life of the food.

[0004] The search found that chitosan has excellent natural antibacterial effects and is used as an antibacterial preservative in the fields of food, medicine, feed additives, etc. However, the antibacterial activity of chitosan is seriously affected by pH and has the best antibacterial effect under acidic conditions. Therefore, it is often necessary to modify it to improve its antibacterial properties. Geraniol is a product extracted from natural essential oils and has good antibacterial properties, but it has poor water solubility, is easily volatile and oxidized when used alone, and is inconvenient to use. Summary of the invention

[0005] The present invention provides a newly developed nine-layer composite structure film with antibacterial properties, and provides a process for producing the nine-layer composite structure film with antibacterial properties. The nine-layer composite structure film with antibacterial properties prepared in this way can be used as a raw material in the manufacture of aseptic milk packaging bags.

[0006] A preparation process of an antibacterial composite film comprises the following steps:

[0007] Step 1: preparing an epoxy antibacterial monomer, wherein the epoxy antibacterial monomer is an epoxy antibacterial monomer M1 or an epoxy antibacterial monomer M2;

[0008] The chemical structure of the epoxy antibacterial monomer M1 is:

[0009]

[0010] The chemical structure of the epoxy antibacterial monomer M2 is:

[0011]

[0012] Step 2: using epoxy antibacterial monomers to carry out grafting modification on chitosan based on the hydroxyl-epoxy ring-opening or / and amino-epoxy ring-opening reaction mechanism to prepare an antibacterial agent;

[0013] Step 3: Set up a nine-layer co-extruded film structure, introduce the antibacterial agent into the first layer and the ninth layer of the nine-layer co-extruded film, respectively, and adopt a multi-layer co-extrusion blow molding process and an ultraviolet sterilization process to prepare an antibacterial composite film.

[0014] Preferably, the preparation method of the epoxy antibacterial monomer M1 is:

[0015] Step S2-1: a phase transfer catalyst is used to catalyze a nucleophilic substitution reaction between the hydroxyl functional group of geraniol and the bromine functional group of (3-bromopropyl)dimethylamine to generate a geraniol-based tertiary amine monomer;

[0016] Step S2-2: utilizing the nucleophilic substitution reaction mechanism, the tertiary amine group of the geraniol-based tertiary amine monomer undergoes a quaternization reaction with the chlorine functional group of epichlorohydrin to generate an epoxy-based antibacterial monomer M1.

[0017] Preferably, the preparation method of the epoxy antibacterial monomer M2 is:

[0018] Step S3-1: a phase transfer catalyst is used to catalyze a nucleophilic substitution reaction between the hydroxyl functional group of geraniol and the bromine functional group of 2-bromo-N-(bromoethyl)ethylamine to generate a di(geraniol-based) secondary amine monomer;

[0019] Step S3-2: using the Mannich reaction mechanism, condensing α-H-containing acetophenone with formaldehyde and di(geraniol) secondary amine monomer to generate di(geraniol) tertiary amine monomer;

[0020] Step S3-3: utilizing the nucleophilic substitution reaction mechanism, the tertiary amine group of the di(geraniol-based) tertiary amine monomer undergoes a quaternization reaction with the chlorine functional group of epichlorohydrin to generate an epoxy antibacterial monomer M2.

[0021] Preferably, the phase transfer catalyst is one of benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride and tetrabutylammonium hydrogen sulfate.

[0022] Preferably, the preparation method of the antibacterial composite film in step three is:

[0023] Step S5-1: Setting the film structure of a nine-layer co-extruded film, the formula and dosage of each film layer of the nine-layer co-extruded film are as follows:

[0024] The first layer: 20 to 30 parts by weight of a PE outer layer made of 85 to 95 wt% low-density polyethylene resin and 5 to 15 wt% antibacterial agent;

[0025] The second layer: 3 to 8 parts by weight of a HDPE layer prepared from 100 wt% high-density polyethylene resin;

[0026] The third layer: 3 to 8 parts by weight of LDPE layer prepared from 100 wt% low-density polyethylene resin;

[0027] The fourth layer: an adhesive layer prepared from 100wt% maleic anhydride grafted polyethylene resin, 3 to 8 parts by weight;

[0028] Ninth layer: 10 to 30 parts by weight of a barrier layer prepared from 30 to 70 wt% low-density polyethylene resin and 30 to 70 wt% ethylene-vinyl alcohol copolymer resin;

[0029] The sixth layer: an adhesive layer prepared from 100wt% maleic anhydride grafted polyethylene resin, 3 to 8 parts by weight;

[0030] The seventh layer: 3 to 8 parts by weight of LDPE layer prepared from 100 wt% low-density polyethylene resin;

[0031] The eighth layer: 3 to 8 parts by weight of a HDPE layer made from 100 wt% high-density polyethylene resin;

[0032] Ninth layer: 20 to 30 parts by weight of a PE inner layer made of 85 to 95 wt% low-density polyethylene resin and 5 to 15 wt% antibacterial agent;

[0033] Step S5-2: The raw materials of each layer of the film are sequentially put into the corresponding hoppers of the nine screw extruders of the nine-layer co-extrusion film blow molding unit. After stirring and mixing, the molten resin is converged at the head of the machine through the diverter, blown and extruded through the die head, and then sterilized by ultraviolet light to obtain an antibacterial composite film.

[0034] Preferably, the wavelength of the ultraviolet rays is 250-280 nm.

[0035] The antibacterial composite film prepared according to the above process is a nine-layer co-extruded film with a thickness of 50 to 200 μm.

[0036] Beneficial Effects

[0037] The present invention designs and synthesizes a novel epoxy antibacterial monomer, utilizes the epoxy antibacterial monomer and chitosan to achieve compounding through grafting, prepares an antibacterial agent, uses the antibacterial agent as the functional modifier of the outer layer and the inner layer in the nine-layer co-extruded film, adopts a multi-layer co-extrusion blow molding film forming process and an ultraviolet sterilization process, and prepares an antibacterial composite film. Experimental results show that the antibacterial composite film prepared by the present invention exhibits an inhibitory effect on Staphylococcus aureus and Escherichia coli, shows excellent antibacterial and barrier properties, and its mechanical properties are also slightly improved, and it can be used in aseptic packaging of milk. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is the synthetic route of epoxy antibacterial monomer M1;

[0039] Figure 2 It is the hydrogen spectrum of epoxy antibacterial monomer M1;

[0040] Figure 3 This is the synthetic route of epoxy antibacterial monomer M2;

[0041] Figure 4 It is the hydrogen spectrum of epoxy antibacterial monomer M2;

[0042] Figure 5 It is a line graph of the experimental results of the antibacterial properties of the composite membrane. DETAILED DESCRIPTION

[0043] Experimental Example 1:

[0044] Synthesize epoxy antibacterial monomer M1, such as Figure 1 As shown, the synthesis process is as follows:

[0045] (1) Synthesizing a geraniol-based tertiary amine monomer, wherein the synthesis method comprises: catalyzing a nucleophilic substitution reaction between a hydroxyl functional group of geraniol and a bromine functional group of (3-bromopropyl)dimethylamine with a phase transfer catalyst to generate a geraniol-based tertiary amine monomer, wherein the specific experimental steps are: adding 1.5 g of geraniol, 20 mL of a 30 wt% sodium hydroxide aqueous solution and 20 mL of N,N-dimethylformamide into a three-necked flask, heating the flask to 30° C. and stirring the flask until all the tertiary amine monomers are dissolved, then dropping 2.0 mL of tetrabutylammonium hydrogen sulfate and 10 mL of a (3-bromopropyl)dimethylamine solution (prepared with 1.7 g of (3-bromopropyl)dimethylamine and 10 mL of N,N-dimethylformamide) into the three-necked flask in sequence, heating the flask to 70° C. and stirring the flask for 10 h, cooling the flask and filtering the flask, washing the flask with ethanol and deionized water in sequence, and vacuum drying the flask to obtain a geraniol-based tertiary amine monomer;

[0046] The phase transfer catalyst is one of benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride and tetrabutylammonium hydrogen sulfate; in this experimental example, tetrabutylammonium hydrogen sulfate is selected;

[0047] (2) Synthesis of epoxy antibacterial monomer M1. The synthesis method is as follows: using the nucleophilic substitution reaction mechanism, the tertiary amine group of the geraniol-based tertiary amine monomer reacts with the chlorine functional group of epichlorohydrin to produce the epoxy antibacterial monomer M1. The specific experimental steps are as follows: 1.2 g of geraniol-based tertiary amine monomer and 30 mL of cyclohexane are added to a three-necked flask, and the temperature is raised to 40°C under nitrogen protection and mechanical stirring. After the temperature stabilizes, 10 mL of epichlorohydrin solution (prepared with 0.5 g of epichlorohydrin and 10 mL of cyclohexane) is added dropwise to the three-necked flask, and the reaction is maintained at 40°C with stirring for 12 hours. After cooling, the epoxy antibacterial monomer M1 is obtained by rotary evaporation, washing with ethyl acetate, and vacuum drying. The hydrogen spectrum (test conditions: 400 Hz, DMSOd6) characterization results are as follows: Figure 2 shown.

[0048] Experimental Example 2:

[0049] Synthesize epoxy antibacterial monomer M2, such as Figure 3 As shown, the synthesis process is as follows:

[0050] (1) Synthesizing a di(geraniol-based) secondary amine monomer, wherein the synthesis method comprises: catalyzing a nucleophilic substitution reaction between a hydroxyl functional group of geraniol and a bromine functional group of 2-bromo-N-(bromoethyl)ethylamine with a phase transfer catalyst to generate a di(geraniol-based) secondary amine monomer, wherein the specific experimental steps refer to the preparation experiment of a geraniol-based tertiary amine monomer, and the difference between the preparation experiment of the di(geraniol-based) secondary amine monomer and the tertiary amine monomer is that 1.7 g of (3-bromopropyl) dimethylamine is replaced by 1.2 g of 2-bromo-N-(bromoethyl)ethylamine;

[0051] The phase transfer catalyst is one of benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride and tetrabutylammonium hydrogen sulfate; in this experimental example, tetrabutylammonium hydrogen sulfate is selected;

[0052] (2) Synthesizing di(geraniol) tertiary amine monomer, wherein the synthesis method is as follows: utilizing the Mannich reaction mechanism, a condensation reaction of α-H-containing acetophenone with formaldehyde and di(geraniol) secondary amine monomer occurs to generate di(geraniol) tertiary amine monomer, wherein the specific experimental steps are as follows: adding 1.8 g of di(geraniol) secondary amine monomer, 0.6 g of acetophenone, 0.2 g of formaldehyde and 50 mL of anhydrous ethanol into a three-necked flask, slowly adding 5 drops of concentrated hydrochloric acid into the three-necked flask under nitrogen protection and mechanical stirring, heating to 85° C. and reflux reaction for 4 h, cooling to room temperature, removing the solvent by rotary evaporation, suction filtering and drying to obtain di(geraniol) tertiary amine monomer;

[0053] (2) Synthesize epoxy antibacterial monomer M2. The synthesis method is as follows: utilize nucleophilic substitution reaction mechanism to generate epoxy antibacterial monomer M2 by quaternization reaction of tertiary amine group of di(geraniol) tertiary amine monomer and chlorine functional group of epichlorohydrin. The specific experimental steps refer to the preparation experiment of epoxy antibacterial monomer M1. The difference between the preparation experiment of epoxy antibacterial monomer M2 and epoxy antibacterial monomer M1 is that 2.5g of di(geraniol) tertiary amine monomer is used to replace 1.2g of geraniol tertiary amine monomer. The characterization results of hydrogen spectrum (test conditions: 400Hz, DMSOd6) are as follows: Figure 4 shown.

[0054] Embodiment 1:

[0055] (1) preparing antibacterial agent A1, the preparation method of which is: subjecting chitosan (chitosan contains hydroxyl and amino functional groups) to graft modification based on hydroxyl-epoxy ring-opening and amino-epoxy ring-opening reaction mechanisms by epoxy antibacterial monomer M1 to obtain antibacterial agent A1, the specific experimental steps of which are: adding 3 g of chitosan, 0.5 g of triethylamine and 100 mL of dimethyl sulfoxide to a three-necked flask, stirring at room temperature until all dissolved, then adding 10 mL of epoxy antibacterial monomer M1 solution (prepared with 0.3 g of epoxy antibacterial monomer M1 and 10 mL of dimethyl sulfoxide) to the three-necked flask, heating to 70° C. and stirring for 6 h, cooling to room temperature, pouring into acetone, filtering, and vacuum drying to obtain antibacterial agent A1;

[0056] (2) Antimicrobial agent A2 was prepared by the following method: chitosan was subjected to grafting modification based on the hydroxyl-epoxy ring-opening and amino-epoxy ring-opening reaction mechanisms by epoxy antimicrobial monomer M2 to obtain antimicrobial agent A2. The specific experimental steps were referred to the preparation experiment of antimicrobial agent A1. The only difference between antimicrobial agent A2 and antimicrobial agent A1 was that epoxy antimicrobial monomer M2 was used to replace epoxy antimicrobial monomer M1.

[0057] Embodiment 2:

[0058] (1) Preparing an antibacterial composite film I, comprising the following steps:

[0059] Step 1: Set the antibacterial composite film I as a nine-layer co-extruded film, and its film structure is as follows:

[0060] The first layer: 25 parts by weight of a PE outer layer made from 90 wt% low-density polyethylene resin and 10 wt% antibacterial agent A1;

[0061] The second layer: 5 parts by weight of a HDPE layer made from 100 wt% high-density polyethylene resin;

[0062] The third layer: 5 parts by weight of LDPE layer prepared from 100 wt% low-density polyethylene resin;

[0063] The fourth layer: an adhesive layer prepared from 100 wt % maleic anhydride grafted polyethylene resin, 5 parts by weight;

[0064] Ninth layer: a barrier layer prepared from 50wt% low-density polyethylene resin + 50wt% ethylene-vinyl alcohol copolymer resin, 20 parts by weight;

[0065] The sixth layer: an adhesive layer prepared from 100 wt % maleic anhydride grafted polyethylene resin, 5 parts by weight;

[0066] The seventh layer: 5 parts by weight of LDPE layer prepared from 100 wt% low-density polyethylene resin;

[0067] The eighth layer: 5 parts by weight of a HDPE layer made from 100 wt% high-density polyethylene resin;

[0068] Ninth layer: PE inner layer made of 90wt% low-density polyethylene resin + 10wt% antibacterial agent A1, 25 parts by weight;

[0069] Step 2, respectively putting the raw materials in step 1 into a nine-layer co-extrusion film blowing unit, melt extruding, merging at the mouth of the nine-layer die head through their respective flow channels, and then undergoing inflation molding, with the inflation ratio controlled at 2.5, cooling, sterilizing with 260nm ultraviolet rays, and winding to obtain an antibacterial composite film I with a thickness of 120μm;

[0070] Among them, the process parameters of the screw extruder corresponding to the PE outer layer and the PE inner layer are set as follows: the temperatures of zones 1-3 are 120°C, 150°C, and 170°C, respectively, the flow channel temperature is 165°C, and the rotation speed is 30r / min;

[0071] The process parameters of the screw extruder corresponding to the bonding layer were set as follows: the temperatures of zones 1-3 were 125°C, 150°C, and 165°C, respectively, the flow channel temperature was 160°C, and the rotation speed was 15 r / min;

[0072] The process parameters of the screw extruder corresponding to the barrier layer were set as follows: the temperatures of zones 1-3 were 170°C, 190°C, and 205°C, respectively, the flow channel temperature was 200°C, and the rotation speed was 40 r / min.

[0073] Among them, low-density polyethylene resin was purchased from CNOOC Shell Petrochemical Co., Ltd. with the brand name 2420H; maleic anhydride grafted polyethylene resin was purchased from Dongguan Taotao Plastic Raw Materials Co., Ltd. with the brand name 4288; ethylene-vinyl alcohol copolymer resin was purchased from Dongguan Kaisi Li Plastic Raw Materials Co., Ltd. with the brand name E105B.

[0074] (2) Preparation of antibacterial composite film II: using antibacterial agent A2 instead of the above antibacterial agent A1, referring to the preparation steps and experimental conditions of antibacterial composite film I, to prepare antibacterial composite film II;

[0075] (3) Preparation of composite membrane: Referring to the preparation steps and experimental conditions of antibacterial composite membrane I, a composite membrane was prepared without using antibacterial agent A1 as a comparative example.

[0076] Performance Test:

[0077] (1) The antibacterial performance test was carried out using an MJ-250I mold incubator. The specific test steps were as follows: the sample was cut into a disc with a diameter of 6 mm and irradiated with ultraviolet light for 2 h to fully sterilize it. Then, 100 μL of bacterial solution (concentration of 1.0×10 6 CFU / mL), place the sterile sample flat on the culture medium, place it in an incubator at 37℃ and invert it for 24h, and observe the bacterial growth on the film surface and the diameter of the inhibition ring;

[0078] The bacterial liquid was ATCC6538 Staphylococcus aureus and ATCC25922 Escherichia coli purchased from Shanghai Luwei Technology Co., Ltd.

[0079] (2) The oxygen permeability test and water vapor permeability test of the samples were carried out in accordance with GB / T 1038-2000 and GB / T 1037-2021, respectively. The specific test steps are as follows: a 30 cm round sample was placed in a glass desiccator at an ambient temperature of 25°C and anhydrous calcium chloride was used as a desiccant for 72 hours. Then, the barrier properties of the sample were tested using a Y110 oxygen permeability tester and a TC-03 water vapor permeability tester;

[0080] (3) The tensile strength of the sample was tested using an Instron 5565 universal tensile testing machine. The specific test steps are as follows: a 150 mm × 20 mm sample was fixed on the tensile testing machine, and a tensile test was performed at a tensile rate of 5 mm / min. The longitudinal and transverse tensile strengths of the sample were recorded. The specific method is as follows:

[0081] Tensile strength (MPa) = tensile stress / (sample width × sample thickness);

[0082] The above experimental results are shown in Table 1-2.

[0083] Table 1 Experimental results of antibacterial properties of composite films

[0084]

[0085] Table 2 Experimental results of barrier properties and mechanical properties of composite films

[0086]

[0087]

[0088] The hygienic properties of the samples were tested according to GB / T 5009.60-2003 "Analysis Method for Hygienic Standards of Polyethylene, Polystyrene and Polypropylene Molded Products for Food Packaging", and the experimental results confirmed that the composite film prepared by the present invention can meet the requirements of the hygienic standards;

[0089] According to the experimental data in Table 1, Figure 5 , through comprehensive analysis of the above experimental results, we can draw the following conclusions:

[0090] (1) Both antimicrobial agents showed inhibitory effects on Staphylococcus aureus and Escherichia coli, and both endowed the composite film with excellent antimicrobial ability, among which the antimicrobial effect of antimicrobial agent A2 was significantly better than that of antimicrobial agent A1;

[0091] (2) The antibacterial composite films prepared by the present invention all exhibit relatively excellent barrier properties.

Claims

1. A process for preparing an antibacterial composite film, characterized in that: The following steps are involved: Step 1: preparing an epoxy antibacterial monomer, wherein the epoxy antibacterial monomer is an epoxy antibacterial monomer M1 or an epoxy antibacterial monomer M2; The chemical structure of the epoxy antibacterial monomer M1 is: The chemical structure of the epoxy antibacterial monomer M2 is: Step 2: using epoxy antibacterial monomers to carry out grafting modification on chitosan based on the hydroxyl-epoxy ring-opening or / and amino-epoxy ring-opening reaction mechanism to prepare an antibacterial agent; Step 3: Set up a nine-layer co-extruded film structure, introduce the antibacterial agent into the first layer and the ninth layer of the nine-layer co-extruded film, respectively, and adopt a multi-layer co-extrusion blow molding process and an ultraviolet sterilization process to prepare an antibacterial composite film.

2. The process for preparing an antibacterial composite film according to claim 1, characterized in that: The preparation method of the epoxy antibacterial monomer M1 is as follows: Step S2-1: a phase transfer catalyst is used to catalyze a nucleophilic substitution reaction between the hydroxyl functional group of geraniol and the bromine functional group of (3-bromopropyl)dimethylamine to generate a geraniol-based tertiary amine monomer; Step S2-2: utilizing the nucleophilic substitution reaction mechanism, the tertiary amine group of the geraniol-based tertiary amine monomer undergoes a quaternization reaction with the chlorine functional group of epichlorohydrin to generate an epoxy-based antibacterial monomer M1.

3. The process for preparing an antibacterial composite film according to claim 1, characterized in that: The preparation method of the epoxy antibacterial monomer M2 is: Step S3-1: a phase transfer catalyst is used to catalyze a nucleophilic substitution reaction between the hydroxyl functional group of geraniol and the bromine functional group of 2-bromo-N-(bromoethyl)ethylamine to generate a di(geraniol-based) secondary amine monomer; Step S3-2: using the Mannich reaction mechanism, condensing α-H-containing acetophenone with formaldehyde and di(geraniol) secondary amine monomer to generate di(geraniol) tertiary amine monomer; Step S3-3: utilizing the nucleophilic substitution reaction mechanism, the tertiary amine group of the di(geraniol-based) tertiary amine monomer undergoes a quaternization reaction with the chlorine functional group of epichlorohydrin to generate an epoxy antibacterial monomer M2.

4. A process for preparing an antibacterial composite film according to claim 2 or 3, characterized in that: The phase transfer catalyst is one of benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride and tetrabutylammonium hydrogen sulfate.

5. The process for preparing an antibacterial composite film according to claim 1, characterized in that: The preparation method of the antibacterial composite film in step 3 is: Step S5-1: Setting the film structure of a nine-layer co-extruded film, the formula and dosage of each film layer of the nine-layer co-extruded film are as follows: The first layer: 20 to 30 parts by weight of a PE outer layer made of 85 to 95 wt% low-density polyethylene resin and 5 to 15 wt% antibacterial agent; The second layer: 3 to 8 parts by weight of a HDPE layer prepared from 100 wt% high-density polyethylene resin; The third layer: 3 to 8 parts by weight of LDPE layer prepared from 100 wt% low-density polyethylene resin; The fourth layer: an adhesive layer prepared from 100wt% maleic anhydride grafted polyethylene resin, 3 to 8 parts by weight; Ninth layer: 10 to 30 parts by weight of a barrier layer prepared from 30 to 70 wt% low-density polyethylene resin and 30 to 70 wt% ethylene-vinyl alcohol copolymer resin; The sixth layer: an adhesive layer prepared from 100wt% maleic anhydride grafted polyethylene resin, 3 to 8 parts by weight; The seventh layer: 3 to 8 parts by weight of LDPE layer prepared from 100 wt% low-density polyethylene resin; The eighth layer: 3 to 8 parts by weight of a HDPE layer made from 100 wt% high-density polyethylene resin; Ninth layer: 20 to 30 parts by weight of a PE inner layer made of 85 to 95 wt% low-density polyethylene resin and 5 to 15 wt% antibacterial agent; Step S5-2: The raw materials of each layer of the film are sequentially put into the corresponding hoppers of the nine screw extruders of the nine-layer co-extrusion film blow molding unit. After stirring and mixing, the molten resin is converged at the head of the machine through the diverter, blown and extruded through the die head, and then sterilized by ultraviolet light to obtain an antibacterial composite film.

6. The process for preparing an antibacterial composite film according to claim 5, characterized in that: The wavelength of the ultraviolet rays is 250-280 nm.

7. An antibacterial composite membrane prepared by the process according to any one of claims 1 to 3, characterized in that: The antibacterial composite film is a nine-layer co-extruded film with a thickness of 50 to 200 μm.

8. Use of the antibacterial composite film according to claim 7 in aseptic packaging bags for milk.

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