A drop-resistant dairy product packaging film and preparation method thereof

Abstract

The present invention discloses a drop-resistant dairy product packaging film, comprising a base film, an ink layer printed on the outside of the base film, and a protective layer coated on the outside of the base film and the ink layer; the protective layer is obtained by spraying a spray liquid on the outside of the base film and the ink layer and then drying; the raw materials of the spray liquid include: nano-calcium carbonate, polystyrene nanoparticles, styrene-butadiene-styrene block copolymer, and dendritic polyamide-amine, and the mass ratio of nano-calcium carbonate, polystyrene nanoparticles, styrene-butadiene-styrene block copolymer, and dendritic polyamide-amine is 1-5:1-2:2-8:1-2. The present invention discloses a method for preparing the above-mentioned drop-resistant dairy product packaging film. The dairy product packaging film obtained by the present invention has excellent barrier properties, high mechanical strength, good drop resistance, and excellent surface hydrophobicity and excellent self-cleaning function. It can also ensure extremely high cleanliness after falling, thereby improving the shelf life of dairy products and facilitating large-scale promotion and application.

Description

Technical Field

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

[0002] Dairy product packaging is the process of filling, loading, or wrapping dairy products with appropriate packaging materials to maintain their value and original state during transportation and storage. As the final step in dairy production, dairy product packaging is the guarantee for the circulation and sales of dairy products, and has a direct impact on the development of the dairy industry.

[0003] Dairy product packaging materials must meet two basic requirements. First, they must protect dairy products from external contamination and ensure that dairy products do not deteriorate under storage conditions. Second, they must meet safety and hygiene requirements. The chemical substances in the packaging material itself do not migrate into the dairy products, and no chemical reactions that cause harm to the human body will occur when dairy products come into contact with the packaging material, thus preventing secondary pollution to the dairy products.

[0004] Traditional dairy product packaging film has three layers and uses a simple traditional production process. Due to the imperfect refrigeration methods in my country in the early days, packaging with a long shelf life was required. The product protection provided by the packaging has a very limited period of time, and the packaging material has poor impact resistance, resulting in the product being likely to deteriorate within a very short time after the filling time.

[0005] Therefore, there is still a need in the art for a simple, cost-effective dairy product packaging film that not only does not compromise the purity of the product during storage, but also has high impact resistance and is not easily broken when dropped, compared to existing packaging. Summary of the Invention

[0006] Based on the technical problems existing in the background technology, the present invention proposes a drop-resistant dairy product packaging film and a preparation method thereof.

[0007] A drop-resistant dairy product packaging film comprises a base film, an ink layer printed on the outside of the base film, and a protective layer coated on the outside of the base film and the ink layer; the protective layer is obtained by spraying a spray liquid on the outside of the base film and the ink layer and then drying; the raw materials of the spray liquid include: nano-calcium carbonate, polystyrene nanoparticles, styrene-butadiene-styrene block copolymer, and dendritic polyamide-amine, and the mass ratio of the nano-calcium carbonate, polystyrene nanoparticles, styrene-butadiene-styrene block copolymer, and dendritic polyamide-amine is 1-5:1-2:2-8:1-2.

[0008] Preferably, the thickness of the heat-sealing layer is 20-40 μm, the thickness of the barrier layer is 4-8 μm, the thickness of the outer layer is 5-15 μm, and the thickness of the protective layer is 2-3 μm.

[0009] Preferably, the base film includes, from the inside to the outside, a heat-sealing layer, a barrier layer, and an outer layer. The raw material of the heat-sealing layer is low-density polyethylene, the raw materials of the barrier layer include low-density polyethylene, epoxy soybean oil, and a solubilizer, and the raw materials of the outer layer include low-density polyethylene, polyamide, and oleamide.

[0010] More preferably, the density of the low-density polyethylene is 0.9 g / cm 3 , the melt index is 0.35g / 10min.

[0011] More preferably, in the barrier layer raw material, the mass ratio of low-density polyethylene, epoxy soybean oil, and solubilizer is 20-40:1-2:1-2.

[0012] More preferably, in the outer layer raw material, the mass ratio of low-density polyethylene, polyamide, and oleamide is 20-30:1-5:1-2.

[0013] Preferably, the dendritic polyamidoamine is an amino-terminated dendritic polyamidoamine with a generation number of 3-4.

[0014] Preferably, the styrene-butadiene-styrene block copolymer has a weight average molecular weight of 220 kg / mol and a glass transition temperature of 102-105°C.

[0015] Preferably, the particle size of nano calcium carbonate is 50-150 nm.

[0016] Preferably, the particle size of the polystyrene nanoparticles is 100-200 nm.

[0017] Preferably, the spraying liquid is prepared by the following specific steps: adding nano-calcium carbonate and polystyrene nanoparticles into tetrahydrofuran and dispersing them evenly, adding styrene-butadiene-styrene block copolymer and dendritic polyamide-amine and stirring evenly to obtain the spraying liquid.

[0018] The method for preparing the drop-resistant dairy product packaging film comprises the following steps:

[0019] S1. Add the raw materials of the heat seal layer, barrier layer, and outer layer into the hopper of the screw extruder respectively, set the processing temperature of each extruder, and when the temperature reaches the set temperature, start the extruders at the same time, and sequentially go through film drawing, inflation, stretching, pulling, trimming, and winding to obtain the base film;

[0020] S2. Print an ink layer on the outside of the base film and solidify it. Load the spray liquid into a spray gun and spray it on the base film and the outer wall of the ink layer in an ethanol vapor atmosphere. After the spray liquid solvent is completely evaporated, a protective layer is formed on the outside of the base film and the ink layer. Heat treatment is performed at 105-110°C for 10-20 minutes, and then cooled to room temperature to obtain a drop-resistant dairy product packaging film.

[0021] The present invention adopts a heat seal layer, a barrier layer and an outer layer, and then prints an ink layer on the outside of the base film and sprays a coating liquid to form a protective layer. This can not only effectively enhance the impact resistance of the film layer and have a good drop resistance effect, but also has an excellent self-cleaning effect on the surface. Even after falling, it can effectively reduce surface stains and ensure the shelf life of dairy products. At the same time, it can effectively improve the barrier performance. Even in an environment with a relative humidity of 90%, its water vapor transmission rate is not higher than 1.54g / (m 2 d), and the oxygen transmission rate is not higher than 0.87cm 3 / (m 2 ·d·0.1Mpa), meeting the barrier requirements of dairy product packaging.

[0022] The spraying liquid dissolves styrene-butadiene-styrene block copolymer in tetrahydrofuran, and with the action of nano-calcium carbonate particles, is sprayed on the surface of the ink layer in an ethanol atmosphere. Since the volatilization of tetrahydrofuran reduces the surface temperature of the system, the ethanol atmosphere condenses and enters the solution spraying liquid, causing the styrene-butadiene-styrene block copolymer to phase separate in the system. When the tetrahydrofuran is completely volatilized, a rough porous film structure can be formed on the surface of the film, and the surface has excellent super-hydrophobic properties. After heat treatment, the styrene-butadiene-styrene block copolymer particles melt and adhere, which can effectively enhance the mechanical strength of the film while ensuring good super-hydrophobic properties, and will not peel off.

[0023] The styrene-butadiene-styrene block copolymer is compounded with dendritic polyamide-amine and polystyrene nanoparticles. The dendritic polyamide-amine has an excellent spatial structure, which can effectively limit the movement of the styrene-butadiene-styrene block copolymer during the heat treatment process. At the same time, the polystyrene nanoparticles have a high affinity with the styrene-butadiene-styrene block copolymer, and can effectively enhance the impact strength of the film after heat treatment.

[0024] The dairy product packaging film obtained by the present invention has excellent barrier properties, which extends the shelf life of the product. In addition, the packaging film has high mechanical strength and good drop resistance. At the same time, the surface is extremely hydrophobic and has excellent self-cleaning function. It can also ensure extremely high cleanliness after falling, which significantly improves the shelf life of dairy products. The production process is simple and is convenient for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 1 is a comparison chart of the barrier properties of the dairy product packaging films obtained in Example 5 and Comparative Examples 1-3.

[0026] Figure 2 The figure is a comparison of the static contact angle and the rolling angle of the dairy product packaging films obtained in Example 5 and Comparative Examples 2-3.

[0027] Figure 3This is a comparison chart of the static contact angles of the dairy product packaging films obtained in Example 5 and Comparative Examples 2-3 after friction cycles. DETAILED DESCRIPTION

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

[0029] The density of the low-density polyethylene used below is 0.9 g / cm 3 The melt index is 0.35 g / 10 min. The generation number of the amino-terminated dendritic polyamide-amine is 4. The weight average molecular weight of the styrene-butadiene-styrene block copolymer is 220 kg / mol, and the glass transition temperature is 102-105°C.

[0030] Example 1

[0031] A drop-resistant dairy product packaging film comprises a base film, an ink layer printed on the outside of the base film, and a protective layer. The protective layer is formed by spraying a coating liquid on the outside of the base film and the ink layer and then drying it.

[0032] The base film includes, from the inside to the outside, a heat-sealing layer, a barrier layer, and an outer layer. The raw material of the heat-sealing layer is low-density polyethylene, the raw material of the barrier layer is low-density polyethylene, epoxy soybean oil, and a solubilizer in a mass ratio of 20:1:1, and the raw material of the outer layer is low-density polyethylene, polyamide, and oleamide in a mass ratio of 20:1:1.

[0033] The raw materials for the spraying liquid include: 100g of nano-calcium carbonate, 100g of polystyrene nanoparticles, 200g of styrene-butadiene-styrene block copolymer, and 100g of amino-terminated dendritic polyamide-amine. The spraying liquid is prepared by adding the nano-calcium carbonate and polystyrene nanoparticles to tetrahydrofuran and uniformly dispersing them. Then, the styrene-butadiene-styrene block copolymer and amino-terminated dendritic polyamide-amine are added to the mixture, and the mixture is stirred at 1000 rpm for 5 minutes to obtain the spraying liquid.

[0034] The method for preparing the drop-resistant dairy product packaging film comprises the following steps:

[0035] S1. Add the raw materials of the heat seal layer, barrier layer, and outer layer into the hopper of the screw extruder respectively, set the processing temperature of each extruder, and when the temperature reaches the set temperature, start the extruders at the same time, and sequentially go through film drawing, inflation, stretching, pulling, trimming, and winding to obtain the base film;

[0036] The processing temperature of the heat seal layer is 150°C, the processing temperature of the barrier layer is 180°C, the processing temperature of the outer layer is 195°C, and the head temperature is 200°C;

[0037] S2. Print an ink layer on the outside of the base film and solidify it. Load the spray liquid into a spray gun and spray it on the base film and the outer wall of the ink layer in an ethanol vapor atmosphere. After the spray liquid solvent is completely evaporated, a protective layer is formed on the outside of the base film and the ink layer. Heat treatment is performed at 105°C for 10 minutes, and then the temperature is cooled to room temperature to obtain a drop-resistant dairy product packaging film.

[0038] Example 2

[0039] A drop-resistant dairy product packaging film comprises a base film, an ink layer printed on the outside of the base film, and a protective layer. The protective layer is formed by spraying a coating liquid on the outside of the base film and the ink layer and then drying it.

[0040] The base film includes, from the inside to the outside, a heat-sealing layer, a barrier layer, and an outer layer. The raw material of the heat-sealing layer is low-density polyethylene, the raw material of the barrier layer is low-density polyethylene, epoxy soybean oil, and solubilizer in a mass ratio of 40:2:2, and the raw material of the outer layer is low-density polyethylene, polyamide, and oleamide in a mass ratio of 30:5:2.

[0041] The raw materials for the spraying liquid include: 500g of nano-calcium carbonate, 200g of polystyrene nanoparticles, 800g of styrene-butadiene-styrene block copolymer, and 200g of amino-terminated dendritic polyamide-amine. The spraying liquid is prepared by adding the nano-calcium carbonate and polystyrene nanoparticles to tetrahydrofuran and uniformly dispersing them. Then, the styrene-butadiene-styrene block copolymer and amino-terminated dendritic polyamide-amine are added to the mixture, and the mixture is stirred at 2000 rpm for 15 minutes to obtain the spraying liquid.

[0042] The method for preparing the drop-resistant dairy product packaging film comprises the following steps:

[0043] S1. Add the raw materials of the heat seal layer, barrier layer, and outer layer into the hopper of the screw extruder respectively, set the processing temperature of each extruder, and when the temperature reaches the set temperature, start the extruders at the same time, and sequentially go through film drawing, inflation, stretching, pulling, trimming, and winding to obtain the base film;

[0044] The processing temperature of the heat seal layer is 160°C, the processing temperature of the barrier layer is 190°C, the processing temperature of the outer layer is 205°C, and the head temperature is 210°C;

[0045] S2. Print an ink layer on the outside of the base film and solidify it. Load the spray liquid into a spray gun and spray it on the base film and the outer wall of the ink layer in an ethanol vapor atmosphere. After the spray liquid solvent is completely evaporated, a protective layer is formed on the outside of the base film and the ink layer. Heat treatment is performed at 110°C for 20 minutes and then cooled to room temperature to obtain a drop-resistant dairy product packaging film.

[0046] Example 3

[0047] A drop-resistant dairy product packaging film comprises a base film, an ink layer printed on the outside of the base film, and a protective layer with a thickness of 2 μm. The protective layer is obtained by spraying a coating liquid onto the base film and the outside of the ink layer and then drying it.

[0048] The base film consists, from the inside out, of a 40μm-thick heat-seal layer, a 4μm-thick barrier layer, and a 15μm-thick outer layer. The heat-seal layer is made of low-density polyethylene (LDPE), while the barrier layer comprises LDPE, epoxidized soybean oil, and a solubilizer in a mass ratio of 25:1.7:1.2. The outer layer is made of LDPE, polyamide, and oleamide in a mass ratio of 28:2:1.8.

[0049] The raw materials for the spraying liquid include: 200g of nano-calcium carbonate, 170g of polystyrene nanoparticles, 300g of styrene-butadiene-styrene block copolymer, and 180g of amino-terminated dendritic polyamide-amine. The spraying liquid is prepared by adding the nano-calcium carbonate and polystyrene nanoparticles to tetrahydrofuran and uniformly dispersing them. Then, the styrene-butadiene-styrene block copolymer and amino-terminated dendritic polyamide-amine are added, and the mixture is stirred at 1300 rpm for 12 minutes to obtain the spraying liquid.

[0050] The method for preparing the drop-resistant dairy product packaging film comprises the following steps:

[0051] S1. Add the raw materials of the heat seal layer, barrier layer, and outer layer into the hopper of the screw extruder respectively, set the processing temperature of each extruder, and when the temperature reaches the set temperature, start the extruders at the same time, and sequentially go through film drawing, inflation, stretching, pulling, trimming, and winding to obtain the base film;

[0052] The processing temperature of the heat seal layer is 152°C, the processing temperature of the barrier layer is 187°C, the processing temperature of the outer layer is 198°C, and the head temperature is 208°C;

[0053] S2. Print an ink layer on the outside of the base film and solidify it. Load the spray liquid into a spray gun and spray it on the base film and the outer wall of the ink layer in an ethanol vapor atmosphere. After the spray liquid solvent is completely evaporated, a protective layer is formed on the outside of the base film and the ink layer. Heat treatment is performed at 107°C for 18 minutes, and then the temperature is cooled to room temperature to obtain a drop-resistant dairy product packaging film.

[0054] Example 4

[0055] A drop-resistant dairy product packaging film comprises a base film, an ink layer printed on the outside of the base film, and a protective layer with a thickness of 3 μm. The protective layer is obtained by spraying a coating liquid on the base film and the outside of the ink layer and then drying it.

[0056] The base film consists, from the inside out, of a 20μm-thick heat-seal layer, an 8μm-thick barrier layer, and a 5μm-thick outer layer. The heat-seal layer is made of low-density polyethylene (LDPE), while the barrier layer comprises LDPE, epoxidized soybean oil, and a solubilizer in a mass ratio of 35:1.3:1.8. The outer layer is made of LDPE, polyamide, and oleamide in a mass ratio of 22:4:1.2.

[0057] The raw materials for the spraying liquid include: 400g of nano-calcium carbonate, 130g of polystyrene nanoparticles, 700g of styrene-butadiene-styrene block copolymer, and 120g of amino-terminated dendritic polyamide-amine. The spraying liquid is prepared by adding the nano-calcium carbonate and polystyrene nanoparticles to tetrahydrofuran and uniformly dispersing them. Then, the styrene-butadiene-styrene block copolymer and amino-terminated dendritic polyamide-amine are added, and the mixture is stirred at 1700 rpm for 8 minutes to obtain the spraying liquid.

[0058] The method for preparing the drop-resistant dairy product packaging film comprises the following steps:

[0059] S1. Add the raw materials of the heat seal layer, barrier layer, and outer layer into the hopper of the screw extruder respectively, set the processing temperature of each extruder, and when the temperature reaches the set temperature, start the extruders at the same time, and sequentially go through film drawing, inflation, stretching, pulling, trimming, and winding to obtain the base film;

[0060] The processing temperature of the heat seal layer is 158°C, the processing temperature of the barrier layer is 183°C, the processing temperature of the outer layer is 202°C, and the head temperature is 202°C;

[0061] S2. Print an ink layer on the outside of the base film and solidify it. Load the spray liquid into a spray gun and spray it on the base film and the outer wall of the ink layer in an ethanol vapor atmosphere. After the spray liquid solvent is completely evaporated, a protective layer is formed on the outside of the base film and the ink layer. Heat treatment is performed at 109°C for 12 minutes and then cooled to room temperature to obtain a drop-resistant dairy product packaging film.

[0062] Example 5

[0063] A drop-resistant dairy product packaging film comprises a base film, an ink layer printed on the outside of the base film, and a protective layer with a thickness of 2.5 μm. The protective layer is obtained by spraying a coating liquid onto the base film and the outside of the ink layer and then drying it.

[0064] The base film consists, from the inside out, of a 30μm-thick heat-seal layer, a 6μm-thick barrier layer, and a 10μm-thick outer layer. The heat-seal layer is made of low-density polyethylene (LDPE), while the barrier layer comprises LDPE, epoxidized soybean oil, and a solubilizer in a mass ratio of 30:1.5:1.5. The outer layer is made of LDPE, polyamide, and oleamide in a mass ratio of 25:3:1.5.

[0065] The raw materials for the spraying liquid include: 300g of nano-calcium carbonate, 150g of polystyrene nanoparticles, 500g of styrene-butadiene-styrene block copolymer, and 150g of amino-terminated dendritic polyamide-amine. The spraying liquid is prepared by adding the nano-calcium carbonate and polystyrene nanoparticles to tetrahydrofuran and uniformly dispersing them. Then, the styrene-butadiene-styrene block copolymer and amino-terminated dendritic polyamide-amine are added, and the mixture is stirred at 1500 rpm for 10 minutes to obtain the spraying liquid.

[0066] The method for preparing the drop-resistant dairy product packaging film comprises the following steps:

[0067] S1. Add the raw materials of the heat seal layer, barrier layer, and outer layer into the hopper of the screw extruder respectively, set the processing temperature of each extruder, and when the temperature reaches the set temperature, start the extruders at the same time, and sequentially go through film drawing, inflation, stretching, pulling, trimming, and winding to obtain the base film;

[0068] The processing temperature of the heat seal layer is 155°C, the processing temperature of the barrier layer is 185°C, the processing temperature of the outer layer is 200°C, and the head temperature is 205°C;

[0069] S2. Print an ink layer on the outside of the base film and solidify it. Load the spray liquid into a spray gun and spray it on the base film and the outer wall of the ink layer in an ethanol vapor atmosphere. After the spray liquid solvent is completely evaporated, a protective layer is formed on the outside of the base film and the ink layer. Heat treatment is performed at 108°C for 15 minutes, and then the temperature is cooled to room temperature to obtain a drop-resistant dairy product packaging film.

[0070] Comparative Example 1

[0071] A dairy product packaging film comprises: the base film obtained in Example 5, an ink layer printed on the outside of the base film, and a protective layer with a thickness of 2.5 μm. The protective layer is formed by casting polyethylene on the outside of the base film and the ink layer.

[0072] The above-mentioned method for preparing the dairy product packaging film includes the following steps: printing an ink layer on the outside of the base film, curing it, then using polyethylene to cast the base film and the outside of the ink layer to form a protective layer, heat treating at 108°C for 15 minutes, and cooling to room temperature to obtain the dairy product packaging film.

[0073] Comparative Example 2

[0074] A dairy product packaging film comprises: the base film obtained in Example 5, an ink layer printed on the outside of the base film, and a protective layer with a thickness of 2.5 μm. The protective layer is obtained by spraying a coating liquid on the base film and the outside of the ink layer and then drying it.

[0075] The raw materials for the spraying liquid include: 300g of nano-calcium carbonate, 150g of polystyrene nanoparticles, and 500g of styrene-butadiene-styrene block copolymer. The spraying liquid is prepared by adding the nano-calcium carbonate and polystyrene nanoparticles to tetrahydrofuran and uniformly dispersing them. Then, the styrene-butadiene-styrene block copolymer is added and stirred at 1500 rpm for 10 minutes to obtain the spraying liquid.

[0076] The above-mentioned method for preparing the dairy product packaging film includes the following steps: printing an ink layer on the outside of the base film, curing it, loading the spray liquid into a spray gun, spraying it on the base film and the outer wall of the ink layer in an ethanol vapor atmosphere, waiting for the spray liquid solvent to completely evaporate, forming a protective layer on the outside of the base film and the ink layer, heat treating at 108°C for 15 minutes, and cooling to room temperature to obtain the dairy product packaging film.

[0077] Comparative Example 3

[0078] A dairy product packaging film comprises: the base film obtained in Example 5, an ink layer printed on the outside of the base film, and a protective layer with a thickness of 2.5 μm. The protective layer is obtained by spraying a coating liquid on the base film and the outside of the ink layer and then drying it.

[0079] The raw materials for the spraying liquid include: 300g of nano-calcium carbonate, 150g of polystyrene nanoparticles, 500g of styrene-butadiene-styrene block copolymer, and 150g of amino-terminated dendritic polyamide-amine. The spraying liquid is prepared by adding the nano-calcium carbonate and polystyrene nanoparticles to tetrahydrofuran and uniformly dispersing them. Then, the styrene-butadiene-styrene block copolymer and amino-terminated dendritic polyamide-amine are added, and the mixture is stirred at 1500 rpm for 10 minutes to obtain the spraying liquid.

[0080] The above-mentioned method for preparing the dairy product packaging film includes the following steps: printing an ink layer on the outside of the base film, curing it, loading the spray liquid into a spray gun, spraying it on the base film and the outer wall of the ink layer in an ethanol vapor atmosphere, and waiting for the spray liquid solvent to completely evaporate, forming a protective layer on the outside of the base film and the ink layer to obtain the dairy product packaging film.

[0081] The mechanical properties of the dairy product packaging films obtained in Example 5 and Comparative Examples 1-3 were measured as follows: tensile strength and elongation at break were tested with reference to GB / T1040.3-2006 "Determination of tensile properties of plastics Part 3: Test conditions for thin plastics and sheets"; dart impact strength test was performed with reference to Method A in GB / T9639.1-2008 "Test method for impact resistance of plastic film and sheeting - Free-fall dart method Part 1: Ladder method"; and drop test was performed with reference to GB / T4857.5-1992 "Drop test method for packaging and transport packages".

[0082]

[0083]

[0084] As can be seen from the table above, the dairy product packaging film obtained in Comparative Example 1 has poor mechanical properties and low impact strength, making it difficult to withstand a free fall from a height of 3 meters. However, the dairy product packaging film obtained in Example 5 has excellent mechanical properties and high impact strength, effectively extending the shelf life of liquid dairy product packaging bags.

[0085] The applicant believes that this is because Example 5 uses a composite heat-seal layer, barrier layer, and outer layer as a base film, and then uses a spray coating liquid to form a protective layer after printing an ink layer on the outside of the base film, which effectively enhances the film's impact resistance and provides excellent drop resistance. Furthermore, the styrene-butadiene-styrene block copolymer is compounded with a dendritic polyamide-amine and polystyrene nanoparticles. The dendritic polyamide-amine has an excellent spatial structure that effectively restricts the movement of the styrene-butadiene-styrene block copolymer during heat treatment. The styrene-butadiene-styrene block copolymer particles melt and adhere to each other during heat treatment. Furthermore, the polystyrene nanoparticles have a high affinity for the styrene-butadiene-styrene block copolymer, effectively enhancing the film's mechanical strength, particularly its impact resistance.

[0086] The barrier properties of the dairy product packaging films obtained in Example 5 and Comparative Examples 1-3 were measured, and the water vapor transmission rate and oxygen transmission rate were used to characterize the barrier properties of the materials.

[0087] The water vapor transmission rate test was carried out according to the weight gain method in GB / T1037-2021 "Plastic Film and Sheeting - Determination of Water Vapor Transmission Properties - Cup Weight Gain and Weight Loss Method". The test temperature was 38°C, the humidity was 90% RH, the preheating time was 2 hours, the rotation interval was 10 minutes, and 3 parallels were set for each group.

[0088] Oxygen transmission rate tests were conducted according to GB / T1038.1-2022, "Plastic Film and Sheeting Gas Permeability Test Method - Part 1: Differential Pressure Method." The test temperature was 23°C, the humidity was 50% RH, and the vacuum was applied for 4 hours. Ensure that the sample surface was free of contamination and scratches. Three parallel samples were set for each group.

[0089] 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 3 were significantly better than those of the other two groups, while the difference between Example 5 and Comparative Example 3 was not significant (P>0.05). The applicant believes that this is because both Example 5 and Comparative Example 3 use a composite heat seal layer, barrier layer, and outer layer as the base film, and then use a spray coating liquid to form a protective layer after printing an ink layer on the outer surface of the base film, which can effectively improve the barrier performance and meet the barrier requirements of dairy product packaging.

[0090] Based on the above results, the applicant believes that the performance of the dairy product packaging film obtained in Comparative Example 1 cannot meet the corresponding requirements for dairy product packaging and will no longer participate in subsequent tests.

[0091] The static contact angle and rolling angle of the dairy product packaging films obtained in Example 5 and Comparative Examples 2-3 were measured using a contact angle meter. Water droplets were carefully dropped onto the surface of each group of packaging films, and the static contact angle was measured. Five parallel drops were placed on each group of packaging films. Each group of packaging films was then placed on a custom-made, adjustable inclined surface, and the angle of the inclined surface was recorded as the water droplet rolled. Five parallel drops were placed on each group of packaging films.

[0092] like Figure 2 As shown, the dairy product packaging film obtained in Comparative Example 3 has the highest static contact angle and the lowest rolling angle; while the static contact angle of the dairy product packaging film obtained in Example 5 is not as good as that in Comparative Example 3, but still reaches 152.2°, and still maintains good superhydrophobic properties.

[0093] The applicant believes that this is because the styrene-butadiene-styrene block copolymer is dissolved in tetrahydrofuran, combined with the action of nano-calcium carbonate particles, and sprayed on the surface of the ink layer under an ethanol atmosphere. Since the volatilization of tetrahydrofuran lowers the surface temperature of the system, the ethanol atmosphere condenses and enters the solution spray liquid, causing the styrene-butadiene-styrene block copolymer to phase separate in the system. When the tetrahydrofuran is completely volatilized, a rough porous film structure can be formed on the surface of the film, and the surface super-hydrophobicity is excellent. After heat treatment, the styrene-butadiene-styrene block copolymer particles melt and adhere, resulting in an increase in the surface energy of the protective layer and a slight decrease in the super-hydrophobicity, but still maintaining good super-hydrophobicity.

[0094] The dairy product packaging films obtained in Example 5 and Comparative Examples 2-3 were rubbed on sandpaper to test their wear resistance. The friction distance was 10 cm, and one horizontal and vertical friction was counted as one cycle. After every five cycles, the contact angle of the sample surface was measured.

[0095] like Figure 3 As shown, the contact angles of each group of packaging films stabilized as the friction cycles progressed. The dairy product packaging film obtained in Example 5 showed the smallest decrease in contact angle. The dairy product packaging film obtained in Comparative Example 3 experienced a significant decrease in contact angle after friction, reaching 146.8° after 15 friction cycles. However, since the protective layer in Comparative Example 3 was not heat-treated, the styrene-butadiene-styrene block copolymer particles did not melt-adhere. Continued friction would have resulted in significant peeling of the protective layer, resulting in poor durability.

[0096] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A drop-resistant dairy product packaging film, characterized in that: The invention comprises a base film, an ink layer printed on the outside of the base film, and a protective layer coated on the outside of the base film and the ink layer; The base film includes, from the inside out, a heat seal layer, a barrier layer, and an outer layer; The protective layer is obtained by spraying the coating liquid on the outside of the base film and the ink layer and then drying; The raw materials of the spraying liquid include: nano calcium carbonate, polystyrene nanoparticles, styrene-butadiene-styrene block copolymer, dendritic polyamide-amine and tetrahydrofuran, and the mass ratio of nano calcium carbonate, polystyrene nanoparticles, styrene-butadiene-styrene block copolymer and dendritic polyamide-amine is 1-5:1-2:2-8:1-2; Prepared by the following steps: S1. Add the raw materials of the heat seal layer, barrier layer, and outer layer into the hopper of the screw extruder respectively, set the processing temperature of each extruder, and when the temperature reaches the set temperature, start the extruders at the same time, and sequentially go through film drawing, inflation, stretching, pulling, trimming, and winding to obtain the base film; S2. Print an ink layer on the outside of the base film and solidify it. Load the spray liquid into a spray gun and spray it on the base film and the outer wall of the ink layer in an ethanol vapor atmosphere. Wait until the tetrahydrofuran is completely volatilized to form a protective layer on the outside of the base film and the ink layer. Heat treat at 105-110°C for 10-20 minutes and cool to room temperature to obtain a drop-resistant dairy product packaging film.

2. The drop-resistant dairy product packaging film according to claim 1, characterized in that: The raw material of the heat sealing layer is low-density polyethylene, the raw materials of the barrier layer include low-density polyethylene, epoxy soybean oil, and solubilizer, and the raw materials of the outer layer include low-density polyethylene, polyamide, and oleamide.

3. The drop-resistant dairy product packaging film according to claim 2, characterized in that: The density of low-density polyethylene is 0.9 g / cm 3 , the melt index is 0.35g / 10min.

4. The drop-resistant dairy product packaging film according to claim 2, characterized in that: In the barrier layer raw materials, the mass ratio of low-density polyethylene, epoxy soybean oil and solubilizer is 20-40:1-2:1-2.

5. The drop-resistant dairy product packaging film according to claim 2, characterized in that: In the outer layer raw materials, the mass ratio of low-density polyethylene, polyamide and oleamide is 20-30:1-5:1-2.

6. The drop-resistant dairy product packaging film according to claim 1, characterized in that: The dendritic polyamidoamine is an amino-terminated dendritic polyamidoamine with a generation number of 3-4.

7. The drop-resistant dairy product packaging film according to claim 1, characterized in that: The weight average molecular weight of the styrene-butadiene-styrene block copolymer is 220 kg / mol, and the glass transition temperature is 102-105°C.

8. The drop-resistant dairy product packaging film according to claim 1, characterized in that: The particle size of nano calcium carbonate is 50-150nm.

9. The drop-resistant dairy product packaging film according to claim 1, characterized in that: The particle size of polystyrene nanoparticles is 100-200nm.

10. A method for preparing the drop-resistant dairy product packaging film according to any one of claims 1 to 9, characterized in that: The steps include: S1. Add the raw materials of the heat seal layer, barrier layer, and outer layer into the hopper of the screw extruder respectively, set the processing temperature of each extruder, and when the temperature reaches the set temperature, start the extruders at the same time, and sequentially go through film drawing, inflation, stretching, pulling, trimming, and winding to obtain the base film; S2. Print an ink layer on the outside of the base film and solidify it. Load the spray liquid into a spray gun and spray it on the base film and the outer wall of the ink layer in an ethanol vapor atmosphere. Wait until the tetrahydrofuran is completely volatilized to form a protective layer on the outside of the base film and the ink layer. Heat treat at 105-110°C for 10-20 minutes and cool to room temperature to obtain a drop-resistant dairy product packaging film.

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