A method for producing puncture-resistant dairy product packaging film

Abstract

The invention discloses a puncture-resistant dairy product packaging film and a production method thereof. The film comprises the following steps: subjecting a base film to ultrasonic treatment, and then subjecting the base film to plasma treatment, wherein during the ion treatment, the electrode distance is 3-4 cm, the oxygen flow rate is 0.5-1.5 mL / min, the vacuum degree is 12-15 Pa, the discharge time is 10-20 s, and the discharge voltage is 100-200 V, so as to obtain a pre-treated base film; adding nano cellulose to tetrahydrofuran and dispersing the film uniformly, and then adding styrene-butadiene-styrene block copolymer, dendritic polyamide-amine and nano graphene oxide and stirring the film uniformly to obtain a spraying liquid; spraying the spraying liquid on the outer side of the pre-treated base film in an ethanol vapor atmosphere, waiting for the tetrahydrofuran to completely volatilize to obtain a protective layer, and drying the film at room temperature; exhausting the air, subjecting the inner side of the pre-treated base film to corona treatment, heat treating the film at 100-130° C. for 5-10 min, and cooling the film to room temperature to obtain the puncture-resistant dairy product packaging film.

Description

Technical Field

[0001] The invention relates to the technical field of packaging films, in particular to a puncture-resistant dairy product packaging film and a production method thereof. Background Art

[0002] China's dairy industry is developing rapidly, and consumers' increasing concern for health has driven the development of the dairy industry. Dairy products have long been considered to be foods rich in high-quality protein, calcium, vitamins, and other trace elements such as zinc and magnesium. The best nutritional preservation of dairy products is pasteurized form. Although road conditions are improving in transportation, the transportation process is still challenging. Due to the complexity of dairy production, packaging, transportation and storage, the sales growth of dairy products has been affected to a certain extent, mainly reflected in the limited inventory cycle and imperfect cold chain.

[0003] At present, the main forms of domestic liquid dairy product packaging are paper-plastic-aluminum composite packaging and multi-layer co-extruded film packaging. Aluminum foil is used as a barrier layer. Although it has good barrier properties, the cost is relatively high, and the large-scale use of aluminum foil will also have a certain impact on the environment. The cost of multi-layer co-extruded packaging film is relatively low. At present, five-layer co-extruded film is generally used, with a high barrier layer in the middle. However, domestic dairy companies generally use three-layer co-extruded film based on cost considerations and when storage conditions permit. However, for pure milk, due to its high content of nutrients such as fat, protein and some aromatic components, and the three-layer co-extruded film, there is no high barrier material in the middle, and its barrier performance is worse than that of the five-layer film. The low barrier property of the packaging material will lead to the increase of oxygen and water vapor infiltrating into the package, or the speed of the filling gas in the package seeping out of the package will increase, which will eventually lead to the increase of oxygen content and humidity in the package. The performance of maintaining product quality is also greatly limited. At the same time, it is greatly affected by puncture, has poor puncture resistance, and is prone to product breakage, deterioration, odor and other problems, which damages the interests of consumers.

[0004] The most commonly used three-layer co-extruded composite film is polypropylene film, which is made of ordinary polypropylene raw materials through three-layer co-extrusion by a cast film machine. As a result, the three-layer co-extruded composite film has poor low-temperature resistance and puncture resistance. Especially when used for dairy product packaging, it is very easy to be punctured and ruptured by sharp objects, which easily causes air leakage, poor thermal insulation, and short shelf life, which greatly limits its use. Summary of the invention

[0005] Based on the technical problems existing in the background technology, the present invention proposes a puncture-resistant dairy product packaging film and a production method thereof.

[0006] A method for producing a puncture-resistant dairy product packaging film comprises the following steps:

[0007] S1, ultrasonically treating the basement membrane, and then plasma treating it. During the ion treatment, the electrode distance is 3-4 cm, the oxygen flow rate is 0.5-1.5 mL / min, the vacuum degree is 12-15 Pa, the discharge time is 10-20 s, and the discharge voltage is 100-200 V to obtain a pretreated basement membrane;

[0008] S2, adding nanocellulose to tetrahydrofuran and dispersing it evenly, then adding styrene-butadiene-styrene block copolymer, dendritic polyamide-amine and nano-graphene oxide and stirring them evenly to obtain a spraying liquid;

[0009] S3. In an ethanol vapor atmosphere, spray the spray liquid on the outside of the pretreated base film, wait for the tetrahydrofuran to completely evaporate to obtain a protective layer, and dry at room temperature; exhaust the air, perform corona treatment on the inside of the pretreated base film, perform heat treatment at 100-130°C for 5-10 minutes, and cool to room temperature to obtain a puncture-resistant dairy product packaging film.

[0010] Preferably, in S1, the base film includes, from the inside to the outside, an inner layer, a middle layer, and an outer layer; the raw materials of the inner layer are composed of high-density polyethylene, low-density polyethylene, polylactic acid, and PPA masterbatch in a mass ratio of 20-40:10-20:1-3:1-2; the raw materials of the middle layer are composed of low-density polyethylene, ethylene-octene polymer, and PPA masterbatch in a mass ratio of 10-20:20-30:1-3; the raw materials of the outer layer include: high-density polyethylene, ethylene-propylene-butadiene terpolymer polypropylene material, low-density polyethylene, ethylene-octene polymer, polylactic acid, dendritic polyamide-amine, and PPA masterbatch, and the mass ratio of high-density polyethylene, ethylene-propylene-butadiene terpolymer polypropylene material, low-density polyethylene, ethylene-octene polymer, polylactic acid, dendritic polyamide-amine, and PPA masterbatch is 20-40:1-3:5-15:5-15:1-2:1-3:1-2.

[0011] Preferably, the base film has a thickness of 160-220 μm, wherein the thickness ratio of the inner layer, the middle layer and the outer layer is 1:2-2.5:0.5-1.5.

[0012] Preferably, in S1, the base film is prepared by the following specific operations: the outer layer raw material, the middle layer raw material and the inner layer raw material are mixed evenly, added to the multi-layer co-extruder through the hopper for melt extrusion, wherein the melt temperature is 170-180°C, and enter the annular co-extrusion die to form a three-layer film extrusion, and compressed air is blown into the cooling air duct in the center of the die to inflate the film into a cylindrical film to obtain the base film.

[0013] Preferably, in S1, during the film blowing process, the blowing ratio is 2-2.5 and the pulling ratio is 1:5-10.

[0014] Preferably, in S1, the specific operation of ultrasonic treatment is as follows: immerse the basement membrane in ethanol and ultrasonically treat it for 1-3 minutes, wash it with distilled water, and dry it at 30-40°C.

[0015] Preferably, in S2, the mass ratio of nanocellulose, styrene-butadiene-styrene block copolymer, dendritic polyamide-amine, and nano-graphene oxide is 1-2:5-15:1-2:0.1-1.

[0016] Preferably, in S3, the thickness of the protective layer is 2-5 μm.

[0017] Preferably, in S3, the corona voltage is 340-360V.

[0018] Preferably, the dendritic polyamidoamine is an amino-terminated dendritic polyamidoamine.

[0019] A puncture-resistant dairy product packaging film is produced by adopting the puncture-resistant dairy product packaging film production method.

[0020] Beneficial effects:

[0021] (1) The present invention adopts a three-layer co-extrusion process to prepare the base film, wherein by adding polylactic acid and dendritic polyamide-amine to the outer layer of the base film, the tensile strength of the obtained dairy product packaging film can reach above 52 MPa, and the tensile strain at break can reach above 825%, and the puncture resistance is excellent; and the middle layer and the inner layer of the base film are coordinated, not only the heat sealing temperature can be reduced to below 85°C, but also the heat sealing speed can be increased, and it is convenient and quick to use.

[0022] (2) After the base film of the present invention is treated with plasma, the carbon-hydrogen bonds in the methyl groups on its surface are destroyed, causing the hydrogen atoms to detach and react with the active oxygen generated by oxygen during the plasma treatment to form free radicals in a plasma state that recombine with the methylene groups on the surface, thereby forming hydroxyl and carboxyl hydrophilic groups on the surface of the base film. The coating liquid is coated on the surface, and then the protective layer and the base film are chemically bonded by heat treatment. The nano-scale graphene oxide has a large specific surface area, which can provide abundant fixing positions for the phase separation of styrene-butadiene-styrene block copolymers, thereby enhancing the bonding strength between the protective layer and the pretreated base film.

[0023] The test found that plasma treatment will not affect the mechanical properties of the material. This is because the shallow surface layer of the material is etched, and the treatment depth is extremely low, which will not have a significant impact on the mechanical properties of the material. On the contrary, under the synergistic effect of the protective layer, the multi-dimensional strength superposition of the film can be achieved, which greatly enhances the puncture resistance of the dairy packaging film and has excellent low-temperature toughness. At the same time, after multi-layer composite, the distance of small molecules passing through both sides of the packaging film is effectively extended, and the barrier performance is also greatly improved.

[0024] (3) The three layers of the base film of the present invention have similar thermal shrinkage rates and good compatibility with each other, ensuring that no wrinkles are generated during the molding of the three layers of the film. The three layers of the film are not easy to peel off after molding and cooling, and further cooperate with the coating film, so that the mechanical properties are stable, the high temperature stability is good, and the heat sealing strength is high.

[0025] Compared with common packaging films, the packaging film of the present invention has high mechanical strength and good puncture resistance. In addition to significantly improved puncture resistance, it also has excellent barrier properties, can significantly increase the shelf life of dairy products, has a simple production process, and is easy to promote and apply on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a comparison chart of the barrier properties of the dairy product packaging films obtained in Example 5 and Comparative Examples 1-2.

[0027] Figure 2 This is a comparison of the residual bacterial colonies on the surface of cheese after the cheese slices were packaged with the dairy product packaging films obtained in Example 5 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is described in detail below through specific embodiments.

[0029] Example 1

[0030] A method for producing a puncture-resistant dairy product packaging film comprises the following steps:

[0031] S1. Soak a base film with a thickness of 161 μm in ethanol and ultrasonically treat it for 1 minute. After washing with distilled water, dry it at 30°C, and then subject it to plasma treatment. During the ion treatment, the electrode distance is 3 cm, the oxygen flow rate is 0.5 mL / min, the vacuum degree is 12 Pa, the discharge time is 10 s, and the discharge voltage is 100 V to obtain a pretreated base film;

[0032] The basement membrane includes, from the inside to the outside, an inner layer, a middle layer, and an outer layer; the thickness ratio of the inner layer, the middle layer, and the outer layer is 1:2:0.5;

[0033] The raw materials of the inner layer are composed of high-density polyethylene, low-density polyethylene, polylactic acid, and PPA masterbatch in a mass ratio of 20:10:1:1; the raw materials of the middle layer are composed of low-density polyethylene, ethylene-octene polymer, and PPA masterbatch in a mass ratio of 10:20:1; the raw materials of the outer layer include: 2000g of high-density polyethylene, 100g of ethylene-propylene-butadiene terpolymer polypropylene material, 500g of low-density polyethylene, 500g of ethylene-octene polymer, 100g of polylactic acid, 100g of amino-terminated dendritic polyamide-amine, and 100g of PPA masterbatch;

[0034] The base film is prepared by the following specific operation: the outer layer raw material, the middle layer raw material and the inner layer raw material are mixed evenly, added to the multi-layer co-extruder through the hopper for melt extrusion, wherein the melt temperature is 170°C, and enter the annular co-extrusion die to form a three-layer film extrusion, and compressed air is blown into the cooling air duct at the center of the die to inflate the film into a cylindrical film, the blowing ratio is 2, and the pulling ratio is 1:5, so as to obtain the base film;

[0035] S2, adding nanocellulose to tetrahydrofuran and dispersing it evenly, then adding styrene-butadiene-styrene block copolymer, amino-terminated dendritic polyamide-amine and nano-graphene oxide and stirring to obtain a spraying liquid;

[0036] The mass ratio of nanocellulose, styrene-butadiene-styrene block copolymer, amino-terminated dendritic polyamide-amine, and nanographene oxide is 1:5:1:0.1;

[0037] S3. In an ethanol vapor atmosphere, spray the spray liquid on the outside of the pretreated base film, wait for the tetrahydrofuran to completely evaporate to obtain a protective layer with a thickness of 2 μm, and dry at room temperature; exhaust the air, perform corona treatment on the inside of the pretreated base film, the corona voltage is 340V, heat treatment is performed at 100°C for 5 minutes, and then the temperature is cooled to room temperature to obtain a puncture-resistant dairy product packaging film.

[0038] Example 2

[0039] A method for producing a puncture-resistant dairy product packaging film comprises the following steps:

[0040] S1. Soak a 220 μm thick base film in ethanol for ultrasonic treatment for 3 min, wash with distilled water, dry at 40°C, and then subject it to plasma treatment. During the ion treatment, the electrode distance is 4 cm, the oxygen flow rate is 1.5 mL / min, the vacuum degree is 15 Pa, the discharge time is 20 s, and the discharge voltage is 200 V to obtain a pretreated base film;

[0041] The basement membrane includes, from the inside to the outside, an inner layer, a middle layer, and an outer layer; the thickness ratio of the inner layer, the middle layer, and the outer layer is 1:2.5:1.5;

[0042] The raw materials of the inner layer are composed of high-density polyethylene, low-density polyethylene, polylactic acid, and PPA masterbatch in a mass ratio of 40:20:3:2; the raw materials of the middle layer are composed of low-density polyethylene, ethylene-octene polymer, and PPA masterbatch in a mass ratio of 20:30:3; the raw materials of the outer layer include: 4000g of high-density polyethylene, 300g of ethylene-propylene-butadiene terpolymer polypropylene material, 1500g of low-density polyethylene, 1500g of ethylene-octene polymer, 200g of polylactic acid, 300g of terminal amino dendritic polyamide-amine, and 200g of PPA masterbatch;

[0043] The base film is prepared by the following specific operation: the outer layer raw material, the middle layer raw material and the inner layer raw material are mixed evenly, added to the multi-layer co-extruder through the hopper for melt extrusion, wherein the melt temperature is 180°C, and enter the annular co-extrusion die to form a three-layer film extrusion, and compressed air is blown into the cooling air duct at the center of the die to inflate the film into a cylindrical film, the blowing ratio is 2.5, and the pulling ratio is 1:10, so as to obtain the base film;

[0044] S2, adding nanocellulose to tetrahydrofuran and dispersing it evenly, then adding styrene-butadiene-styrene block copolymer, amino-terminated dendritic polyamide-amine and nano-graphene oxide and stirring to obtain a spraying liquid;

[0045] The mass ratio of nanocellulose, styrene-butadiene-styrene block copolymer, amino-terminated dendritic polyamide-amine, and nanographene oxide is 2:15:2:1;

[0046] S3. In an ethanol vapor atmosphere, spray the spray liquid on the outside of the pretreated base film, wait for the tetrahydrofuran to completely evaporate to obtain a protective layer with a thickness of 5 μm, and dry at room temperature; exhaust the air, perform corona treatment on the inside of the pretreated base film, the corona voltage is 360V, heat treatment is performed at 130°C for 10 minutes, and then the temperature is cooled to room temperature to obtain a puncture-resistant dairy product packaging film.

[0047] Example 3

[0048] A method for producing a puncture-resistant dairy product packaging film comprises the following steps:

[0049] S1. Soak a base film with a thickness of 180 μm in ethanol and perform ultrasonic treatment for 2.5 min. After washing with distilled water, dry it at 33° C., and then perform plasma treatment on it. During the ion treatment, the electrode distance is 3.5 cm, the oxygen flow rate is 1.2 mL / min, the vacuum degree is 13 Pa, the discharge time is 18 s, and the discharge voltage is 130 V to obtain a pretreated base film.

[0050] The basement membrane includes, from the inside to the outside, an inner layer, a middle layer, and an outer layer; the thickness ratio of the inner layer, the middle layer, and the outer layer is 1:2.4:0.6;

[0051] The raw materials of the inner layer are composed of high-density polyethylene, low-density polyethylene, polylactic acid, and PPA masterbatch in a mass ratio of 35:13:2.5:1.2; the raw materials of the middle layer are composed of low-density polyethylene, ethylene-octene polymer, and PPA masterbatch in a mass ratio of 18:22:2.5; the raw materials of the outer layer include: 2500g of high-density polyethylene, 250g of ethylene-propylene-butadiene terpolymer polypropylene material, 800g of low-density polyethylene, 1200g of ethylene-octene polymer, 130g of polylactic acid, 250g of terminal amino dendritic polyamide-amine, and 130g of PPA masterbatch;

[0052] The base film is prepared by the following specific operation: the outer layer raw material, the middle layer raw material and the inner layer raw material are mixed evenly, added to the multi-layer co-extruder through the hopper for melt extrusion, wherein the melt temperature is 177°C, and enter the annular co-extrusion die to form a three-layer film extrusion, and compressed air is blown into the cooling air duct at the center of the die to inflate the film into a cylindrical film, the blowing ratio is 2.2, and the pulling ratio is 1:6, so as to obtain the base film;

[0053] S2, adding nanocellulose to tetrahydrofuran and dispersing it evenly, then adding styrene-butadiene-styrene block copolymer, amino-terminated dendritic polyamide-amine and nano-graphene oxide and stirring to obtain a spraying liquid;

[0054] The mass ratio of nanocellulose, styrene-butadiene-styrene block copolymer, amino-terminated dendritic polyamide-amine, and nanographene oxide is 1.7:8:1.7:0.2;

[0055] S3. In an ethanol vapor atmosphere, spray the spray liquid on the outside of the pretreated base film, wait for the tetrahydrofuran to completely evaporate to obtain a protective layer with a thickness of 4 μm, and dry at room temperature; exhaust the air, perform corona treatment on the inside of the pretreated base film, the corona voltage is 345V, heat treatment is performed at 120°C for 3 minutes, and then the temperature is cooled to room temperature to obtain a puncture-resistant dairy product packaging film.

[0056] Example 4

[0057] A method for producing a puncture-resistant dairy product packaging film comprises the following steps:

[0058] S1. Soak a base film with a thickness of 189 μm in ethanol and perform ultrasonic treatment for 1.5 min. After washing with distilled water, dry it at 37° C., and then perform plasma treatment on it. During the ion treatment, the electrode distance is 3.5 cm, the oxygen flow rate is 0.8 mL / min, the vacuum degree is 14 Pa, the discharge time is 12 s, and the discharge voltage is 170 V to obtain a pretreated base film.

[0059] The basement membrane includes, from the inside to the outside, an inner layer, a middle layer, and an outer layer; the thickness ratio of the inner layer, the middle layer, and the outer layer is 1:2.2:1.3;

[0060] The raw materials of the inner layer are composed of high-density polyethylene, low-density polyethylene, polylactic acid, and PPA masterbatch in a mass ratio of 25:17:1.5:1.8; the raw materials of the middle layer are composed of low-density polyethylene, ethylene-octene polymer, and PPA masterbatch in a mass ratio of 12:28:1.5; the raw materials of the outer layer include: 3500g of high-density polyethylene, 150g of ethylene-propylene-butadiene terpolymer polypropylene material, 1200g of low-density polyethylene, 800g of ethylene-octene polymer, 170g of polylactic acid, 150g of terminal amino dendritic polyamide-amine, and 170g of PPA masterbatch;

[0061] The base film is prepared by the following specific operation: the outer layer raw material, the middle layer raw material and the inner layer raw material are mixed evenly, added to the multi-layer co-extruder through the hopper for melt extrusion, wherein the melt temperature is 172°C, and enter the annular co-extrusion die to form a three-layer film extrusion, and compressed air is blown into the cooling air duct at the center of the die to inflate the film into a cylindrical film, the blowing ratio is 2.2, and the pulling ratio is 1:8, so as to obtain the base film;

[0062] S2, adding nanocellulose to tetrahydrofuran and dispersing it evenly, then adding styrene-butadiene-styrene block copolymer, amino-terminated dendritic polyamide-amine and nano-graphene oxide and stirring to obtain a spraying liquid;

[0063] The mass ratio of nanocellulose, styrene-butadiene-styrene block copolymer, amino-terminated dendritic polyamide-amine, and nanographene oxide is 1.3:12:1.3:0.8;

[0064] S3. In an ethanol vapor atmosphere, spray the spray liquid on the outside of the pretreated base film, wait for the tetrahydrofuran to completely evaporate to obtain a protective layer with a thickness of 3 μm, and dry at room temperature; exhaust the air, perform corona treatment on the inside of the pretreated base film, the corona voltage is 355V, heat treatment is performed at 110°C for 8 minutes, and then the temperature is cooled to room temperature to obtain a puncture-resistant dairy product packaging film.

[0065] Example 5

[0066] A method for producing a puncture-resistant dairy product packaging film comprises the following steps:

[0067] S1. Soak a 200 μm thick base film in ethanol for ultrasonic treatment for 2 min, wash with distilled water, dry at 35° C., and then subject it to plasma treatment. During the ion treatment, the electrode distance is 3.5 cm, the oxygen flow rate is 1 mL / min, the vacuum degree is 13.5 Pa, the discharge time is 15 s, and the discharge voltage is 150 V to obtain a pretreated base film.

[0068] The basement membrane includes, from the inside to the outside, an inner layer, a middle layer, and an outer layer; the thickness ratio of the inner layer, the middle layer, and the outer layer is 1:2.3:0.7;

[0069] The raw materials of the inner layer are composed of high-density polyethylene, low-density polyethylene, polylactic acid, and PPA masterbatch in a mass ratio of 30:15:2:1.5; the raw materials of the middle layer are composed of low-density polyethylene, ethylene-octene polymer, and PPA masterbatch in a mass ratio of 15:25:2; the raw materials of the outer layer include: 3000g of high-density polyethylene, 200g of ethylene-propylene-butadiene terpolymer polypropylene material, 1000g of low-density polyethylene, 1000g of ethylene-octene polymer, 150g of polylactic acid, 200g of terminal amino dendritic polyamide-amine, and 150g of PPA masterbatch;

[0070] The base film is prepared by the following specific operation: the outer layer raw material, the middle layer raw material and the inner layer raw material are mixed evenly, added to the multi-layer co-extruder through the hopper for melt extrusion, wherein the melt temperature is 175°C, and enter the annular co-extrusion die to form a three-layer film extrusion, and compressed air is blown into the cooling air duct at the center of the die to inflate the film into a cylindrical film, the blowing ratio is 2.2, and the pulling ratio is 1:7, so as to obtain the base film;

[0071] S2, adding nanocellulose to tetrahydrofuran and dispersing it evenly, then adding styrene-butadiene-styrene block copolymer, amino-terminated dendritic polyamide-amine and nano-graphene oxide and stirring to obtain a spraying liquid;

[0072] The mass ratio of nanocellulose, styrene-butadiene-styrene block copolymer, amino-terminated dendritic polyamide-amine, and nanographene oxide is 1.5:10:1.5:0.5;

[0073] S3. In an ethanol vapor atmosphere, spray the spray liquid on the outside of the pretreated base film, wait for the tetrahydrofuran to completely evaporate to obtain a protective layer with a thickness of 3.5 μm, and dry at room temperature; exhaust the air, perform corona treatment on the inside of the pretreated base film, the corona voltage is 350V, heat treatment is performed at 115°C for 5 minutes, and then the temperature is cooled to room temperature to obtain a puncture-resistant dairy product packaging film.

[0074] Comparative Example 1

[0075] A method for producing a dairy product packaging film comprises the following steps:

[0076] i. Add nanocellulose to tetrahydrofuran and disperse evenly, then add styrene-butadiene-styrene block copolymer, amino-terminated dendritic polyamide-amine and nano-graphene oxide and stir evenly to obtain a spraying liquid;

[0077] The mass ratio of nanocellulose, styrene-butadiene-styrene block copolymer, amino-terminated dendritic polyamide-amine, and nanographene oxide is 1.5:10:1.5:0.5;

[0078] ii. In an ethanol vapor atmosphere, spray the coating liquid on the outer side of the base film obtained in Example 5, wait for the tetrahydrofuran to completely evaporate to obtain a protective layer with a thickness of 3.5 μm, and dry at room temperature; exhaust the air, perform corona treatment on the inner side of the pretreated base film, the corona voltage is 350 V, heat treatment is performed at 115° C. for 5 min, and then the temperature is cooled to room temperature to obtain a dairy product packaging film.

[0079] Comparative Example 2

[0080] A method for producing a puncture-resistant dairy product packaging film comprises the following steps:

[0081] i. The base film obtained in Example 5 was immersed in ethanol and ultrasonically treated for 2 minutes, washed with distilled water, dried at 35° C., and then subjected to plasma treatment. During the ion treatment, the electrode distance was 3.5 cm, the oxygen flow rate was 1 mL / min, the vacuum degree was 13.5 Pa, the discharge time was 15 s, and the discharge voltage was 150 V to obtain a pretreated base film;

[0082] ii. adding nanocellulose to tetrahydrofuran and dispersing the nanocellulose evenly, and then adding styrene-butadiene-styrene block copolymer and amino-terminated dendritic polyamide-amine and stirring to obtain a spraying liquid;

[0083] The mass ratio of nanocellulose, styrene-butadiene-styrene block copolymer, and amino-terminated dendritic polyamide-amine is 1.5:10:1.5;

[0084] iii. In an ethanol vapor atmosphere, spray the spray liquid on the outside of the pretreated base film, wait for the tetrahydrofuran to completely evaporate to obtain a protective layer with a thickness of 3.5 μm, and dry at room temperature; exhaust the air, perform corona treatment on the inside of the pretreated base film, the corona voltage is 350V, heat treatment is performed at 115°C for 5 minutes, and then cool to room temperature to obtain a puncture-resistant dairy product packaging film.

[0085] The mechanical properties of the dairy product packaging films obtained in Example 5 and Comparative Examples 1-2 were measured as follows: tensile strength and elongation at break were tested with reference to GB / T 1040.3-2006 "Determination of tensile properties of plastics Part 3: Test conditions for thin plastics and sheets"; after the packaging film was aged for 48 hours, samples were cut and placed in a -10°C freezer for 24 hours, and immediately taken out and subjected to a low-temperature dart impact strength test with reference to Method A in GB / T 9639.1-2008 "Test method for impact resistance of plastic films and sheets - Free-falling dart method - Part 1: Step method"; puncture strength test and peel force test were performed with reference to GB / T 10004-2008 "Plastic composite films for packaging, dry composite bags, and extrusion composites".

[0086]

[0087]

[0088] As can be seen from the table above: the dairy packaging films obtained in Example 5 and Comparative Examples 1-2 all have excellent tensile properties and low-temperature toughness, but the tensile strength, elongation at break and low-temperature dart impact strength of the three are similar, with no significant difference (P>0.05). This is because the plasma treatment will not affect the mechanical properties of the material, because the shallow surface layer of the material is etched, and the treatment depth is extremely low, which will not have a significant impact on the mechanical properties of the material; while nano-scale graphene oxide has a large specific surface area, which can provide abundant fixed positions for the phase separation of styrene-butadiene-styrene block copolymers, and enhance the bonding strength between the protective layer and the pre-treated base film.

[0089] The puncture resistance and peel strength of the dairy product packaging film obtained in Example 5 are significantly better than those of Comparative Examples 1-2 (P < 0.05). This is because, on the one hand, under the synergistic effect of the protective layer, the packaging film achieves multi-dimensional strength superposition, greatly enhancing its puncture resistance. On the other hand, the base film is treated with plasma, and the carbon-hydrogen bonds in the methyl groups on its surface are destroyed, causing the hydrogen atoms to detach and react with the active oxygen generated by oxygen during the plasma treatment to form plasma-state free radicals that recombine with the methylene groups on the surface, thereby forming hydroxyl and carboxyl hydrophilic groups on the surface of the base film. The coating liquid is coated on its surface, and then the protective layer and the base film are chemically bonded through heat treatment, further enhancing the bonding strength between the protective layer and the pretreated base film.

[0090] The barrier properties of the dairy product packaging films obtained in Example 5 and Comparative Examples 1-2 were measured, and the water vapor transmission rate and oxygen transmission rate were used to characterize the barrier properties of the materials.

[0091] The water vapor permeability test was carried out according to the weight gain method in GB / T1037-2021 "Determination of Water Vapor Permeability of Plastic Films and Sheets - Cup Weight Gain and Weight Loss Method". The test temperature was 38°C, the humidity was 90% RH, the preheating time was 2h, the rotation interval was 10min, and 3 parallels were set for each group.

[0092] Refer to GB / T1038.1-2022 "Plastic film and sheet gas permeability test method Part 1: Differential pressure method" for oxygen permeability test, the test temperature is 23℃, the humidity is 50%RH, and the vacuum time is 4h. Ensure that the sample surface is free of pollution and scratches, and set 3 parallels for each group.

[0093] like Figure 1 As shown, the water barrier and oxygen barrier properties of the dairy product packaging films obtained in Example 5 and Comparative Example 1 are significantly better than those in Comparative Example 2, while the difference between Example 5 and Comparative Example 1 is not significant (P>0.05). The applicant believes that this is because Example 5 and Comparative Example 1 are coated with the same coating liquid, so that the multi-layer composite packaging film can effectively extend the distance for small molecules to pass through both sides of the packaging film, and the barrier performance is greatly improved.

[0094] The inner surface of the dairy product packaging film obtained in Example 5 and Comparative Examples 1-2 was placed under ultraviolet light for 40 minutes for ultraviolet sterilization. 3 cfu / mL of Listeria monocytogenes solution for 1 minute and then immediately taken out. The inoculated cheese samples were vacuum packed with each group of packaging film samples and stored in a refrigerator at 4°C for a certain period of time (0d, 3d, 6d, 9d, 12d, 15d, 18d, 21d). Then, the total number of residual colonies on the surface of each group of cheese samples was determined by the plate colony counting method and Listeria chromogenic medium. The experiment was repeated three times and the average value was taken.

[0095] like Figure 2 As shown, at 4°C, with the extension of storage time, the total bacterial colony count of the cheeses in the comparative examples 1-2 groups increased almost linearly, while the growth of the total bacterial colony count of the cheeses in the comparative example 1 group was slightly slower than that in the comparative example 2 group, but the total bacterial count of the cheeses in the example 5 group increased slowly, which confirmed that the packaging film obtained by the present invention has excellent barrier properties and can significantly improve the shelf life of dairy products.

[0096] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for producing a puncture-resistant dairy product packaging film, characterized in that: The steps include: S1, ultrasonically treating the basement membrane, and then plasma treating it. During the ion treatment, the electrode distance is 3-4 cm, the oxygen flow rate is 0.5-1.5 mL / min, the vacuum degree is 12-15 Pa, the discharge time is 10-20 s, and the discharge voltage is 100-200 V to obtain a pretreated basement membrane; The basement membrane includes, from inside to outside, an inner layer, a middle layer, and an outer layer; The inner layer material is composed of high-density polyethylene, low-density polyethylene, polylactic acid, and PPA masterbatch in a mass ratio of 20-40:10-20:1-3:1-2; The middle layer raw material is composed of low-density polyethylene, ethylene-octene polymer, and PPA masterbatch in a mass ratio of 10-20:20-30:1-3; The outer layer raw materials include: high-density polyethylene, ethylene-propylene-butadiene terpolymer polypropylene material, low-density polyethylene, ethylene-octene polymer, polylactic acid, dendritic polyamide-amine, PPA masterbatch, and the mass ratio of high-density polyethylene, ethylene-propylene-butadiene terpolymer polypropylene material, low-density polyethylene, ethylene-octene polymer, polylactic acid, dendritic polyamide-amine, and PPA masterbatch is 20-40:1-3:5-15:5-15:1-2:1-3:1-2; S2, adding nanocellulose to tetrahydrofuran and dispersing it evenly, then adding styrene-butadiene-styrene block copolymer, dendritic polyamide-amine and nano-graphene oxide and stirring them evenly to obtain a spraying liquid; S3. In an ethanol vapor atmosphere, spray the spray liquid on the outside of the pretreated base film, wait for the tetrahydrofuran to completely evaporate to obtain a protective layer, and dry at room temperature; exhaust the air, perform corona treatment on the inside of the pretreated base film, perform heat treatment at 100-130°C for 5-10 minutes, and cool to room temperature to obtain a puncture-resistant dairy product packaging film.

2. The method for producing puncture-resistant dairy product packaging film according to claim 1, characterized in that: In S1, the base film is prepared by the following specific operations: the outer layer raw material, the middle layer raw material, and the inner layer raw material are mixed evenly, added to the multi-layer co-extruder through the hopper for melt extrusion, wherein the melting temperature is 170-180°C, and enter the annular co-extrusion die to form a three-layer film extrusion, and compressed air is blown into the cooling air duct in the center of the die to inflate the film into a cylindrical film to obtain the base film.

3. The method for producing puncture-resistant dairy product packaging film according to claim 2, characterized in that: In S1, during the film blowing process, the blowing ratio is 2-2.5 and the pulling ratio is 1:5-10.

4. The method for producing puncture-resistant dairy product packaging film according to claim 1, characterized in that: In S1, the specific operation of ultrasonic treatment is as follows: the basement membrane is immersed in ethanol and ultrasonically treated for 1-3 minutes, washed with distilled water, and then dried at 30-40°C.

5. The method for producing puncture-resistant dairy product packaging film according to claim 1, characterized in that: In S2, the mass ratio of nanocellulose, styrene-butadiene-styrene block copolymer, dendritic polyamide-amine, and nanographene oxide is 1-2:5-15:1-2:0.1-1.

6. The method for producing puncture-resistant dairy product packaging film according to claim 1, characterized in that: In S3, the thickness of the protective layer is 2-5 μm.

7. The method for producing puncture-resistant dairy product packaging film according to claim 1, characterized in that: In S3, the corona voltage is 340-360V.

8. The method for producing a puncture-resistant dairy product packaging film according to any one of claims 1 to 7, characterized in that: The dendritic polyamidoamine is an amino-terminated dendritic polyamidoamine.

9. A puncture-resistant dairy product packaging film, characterized in that: The film is prepared by the method for producing the puncture-resistant dairy product packaging film according to any one of claims 1 to 8.

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