An antibacterial high-barrier polyolefin film and a method for preparing the same

Abstract

This invention provides an antibacterial high-barrier polyolefin film and its preparation method, belonging to the field of food packaging. It consists of a polyolefin substrate and a PVA / PEI composite coating applied to the substrate surface. The composite coating comprises the following components in parts by weight: 80-95 parts polyvinyl alcohol (PVA), 5-20 parts polyethyleneimine (PEI), 1-2 parts ε-polylysine, 1-2 parts cinnamaldehyde, 1.6-2 parts propylene glycol, and 0.8-1 parts Tween-80. This invention selects ε-polylysine and cinnamaldehyde as composite antibacterial agents, achieving a broad antibacterial spectrum and high barrier effect, which can reduce production costs and improve production efficiency.

Description

Technical Field

[0001] This invention relates to the field of food packaging materials, and more specifically to an antibacterial high-barrier polyolefin film and its preparation method. Background Technology

[0002] Polyolefin films are widely used in the food packaging industry due to their advantages such as light weight, low cost, and good processability. To meet the oxygen barrier requirements for food preservation, current technologies often employ a method of coating the surface of polyolefin films with a polyvinyl alcohol coating, utilizing the hydroxyl groups of the polyvinyl alcohol molecular chains to form a dense structure that blocks oxygen permeation.

[0003] Japanese Patent JP08245816A discloses a barrier polyolefin film coated with a mixture of polyvinyl alcohol and water-based anchoring agents such as isocyanate and polyethyleneimine. This optimized ratio improves the adhesion between the coating and the substrate, as well as oxygen barrier properties. However, this patent only focuses on oxygen barrier properties and does not consider that the proliferation of residual microorganisms (such as E. coli and mold) inside the packaging can easily lead to food spoilage, thus affecting the food's preservation effect.

[0004] Adding antibacterial agents to the coating can improve the antibacterial properties of the film, but the introduction of new components may adversely affect oxygen barrier properties and interfacial adhesion. Therefore, developing an antibacterial high-barrier film suitable for polyvinyl alcohol and polyethyleneimine coating systems is key to solving the above problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an antibacterial high-barrier polyolefin film and its preparation method, which can simultaneously achieve the combined effects of broad antibacterial spectrum and high barrier properties, meeting the practical needs of specific food packaging.

[0006] Specifically, the present invention provides an antibacterial high-barrier polyolefin film, which is composed of a polyolefin substrate and a composite coating coated on the surface of the substrate. The composite coating contains the following components in parts by weight: 80-95 parts of polyvinyl alcohol (PVA), 5-20 parts of polyethyleneimine (PEI), 1-2 parts of ε-polylysine, 1-2 parts of cinnamaldehyde, 1.6-2 parts of propylene glycol, and 0.8-1 parts of Tween-80.

[0007] The polyolefin substrate is a BOPP, CPP or PE film, and the surface of the substrate is corona treated with a surface tension ≥38mN / m.

[0008] The degree of polymerization of the PVA is 300-1500, and the degree of saponification is 88-99.5%.

[0009] The PEI is branched PEI with a molecular weight between 50,000 and 100,000.

[0010] The present invention also provides a method for preparing the above-mentioned antibacterial high-barrier polyolefin film, comprising the following steps:

[0011] (1) Preparation of composite aqueous solution: PVA aqueous solution and PEI aqueous solution are mixed in proportion and stirred at 300-800 rpm and 20-30℃ for 20-40 min until homogeneous. The pH is adjusted to 7-8. ε-polylysine and cinnamaldehyde are weighed and mixed with propylene glycol and Tween-80 beforehand. After being added dropwise to the above solution, stirring is continued for 30-60 min to obtain a homogeneous and stable composite aqueous solution.

[0012] (2) Coating and drying: The composite aqueous solution is coated onto the surface of the polyolefin substrate by gravure coating. First, the surface moisture is removed by online hot air drying at 50-80℃ for 1-2 min, and then it is transferred to a constant temperature oven at 35-45℃ for 6-8 h to continue drying and curing to obtain an antibacterial high barrier polyolefin film.

[0013] Preferably, the concentrations of both the PVA aqueous solution and the PEI aqueous solution are 5-10 wt%.

[0014] Preferably, in step (2), the coating speed is 60-80 m / min, and the dry coating amount is controlled to be 0.6-1.6 g / m. 2 .

[0015] This invention selects ε-polylysine and cinnamaldehyde as a composite antibacterial agent, which has the following synergistic advantages: (1) Both cinnamaldehyde and ε-polylysine are antibacterial components, and their combination can broaden the antibacterial spectrum; at the same time, the macromolecular chain of ε-polylysine can play a role in coating and stabilizing cinnamaldehyde, reducing its volatilization and migration, and improving the antibacterial durability. (2) The amino group of ε-polylysine forms hydrogen bonds and weak ionic bonds with the hydroxyl group of PVA and the amino group of PEI, and the aldehyde group of cinnamaldehyde forms a weak interaction with the system. The two work together to optimize the barrier properties and adhesion.

[0016] This invention controls the pH at 7-8 and premixes at low temperature to avoid excessive reaction between aldehyde and amino groups, ensuring antibacterial activity and coating stability. Because cinnamaldehyde is highly oil-soluble and hydrophobic, it is difficult to directly and stably disperse in aqueous systems. This invention utilizes the synergistic effect of Tween-80 emulsification and propylene glycol as a solubilizer and stabilizer to efficiently disperse hydrophobic cinnamaldehyde in an aqueous PVA / PEI system, forming a uniform and stable coating solution. This avoids cinnamaldehyde agglomeration that causes coating porosity. Simultaneously, propylene glycol and Tween-80 inhibit the volatilization loss of cinnamaldehyde during high-temperature drying, ensuring barrier properties and long-lasting antibacterial activity.

[0017] Compared with the prior art, the present invention has the following beneficial effects: by selecting specific composite antibacterial agents, the present invention achieves a combination effect of broad antibacterial spectrum and high barrier properties, which can reduce production costs and improve production efficiency. Detailed Implementation

[0018] The specific information of the raw materials used in the embodiments and comparative examples of this invention is as follows:

[0019] The polyolefin substrate is a 25μm BOPP film (surface tension 40mN / m); PVA: degree of polymerization 500, degree of saponification 99%; PEI is selected as a branched PEI with a molecular weight of 70,000; the remaining raw materials are all food grade.

[0020] Example 1

[0021] (1) Preparation of composite aqueous solution: Mix 6 wt% PVA aqueous solution and 6 wt% PEI aqueous solution in a ratio of 90:10, stir at 500 rpm and 25℃ for 30 min until homogeneous, and adjust the pH to 8; weigh 1.5 parts by mass of ε-polylysine and 1.5 parts by mass of cinnamaldehyde, mix them with 1.9 parts by mass of propylene glycol and 1 part by mass of Tween-80 beforehand, add them dropwise to the above solution and continue stirring for 40 min; a homogeneous and stable composite aqueous solution is obtained.

[0022] (2) Coating and drying: Gravure coating was used to coat the surface of the polyolefin substrate at a speed of 65 m / min and the dry coating amount was controlled at 1.2 g / m. 2 First, remove the surface moisture by online hot air drying at 70℃ for 1 min, then transfer it to a constant temperature oven at 40℃ for further drying and curing for 7 hours to obtain an antibacterial high-barrier polyolefin film.

[0023] Example 2

[0024] (1) Preparation of composite aqueous solution: Mix 8 wt% PVA aqueous solution and 8 wt% PEI aqueous solution in a ratio of 93:7, stir at 500 rpm and 25℃ for 30 min until homogeneous, and adjust the pH to 7.5; weigh 1 part by mass of ε-polylysine and 2 parts by mass of cinnamaldehyde, mix them with 2 parts by mass of propylene glycol and 1 part by mass of Tween-80 beforehand, add them dropwise to the above solution and continue stirring for 40 min; a homogeneous and stable composite aqueous solution is obtained.

[0025] (2) Coating and drying: Gravure coating was used to coat the surface of the polyolefin substrate at a speed of 60 m / min and the dry coating amount was controlled at 0.8 g / m. 2 First, remove the surface moisture by online hot air drying at 60℃ for 2 minutes, then transfer it to a constant temperature oven at 36℃ for further drying and curing for 8 hours to obtain an antibacterial high-barrier polyolefin film.

[0026] Example 3

[0027] (1) Preparation of composite aqueous solution: Mix 10wt% PVA aqueous solution and 10wt% PEI aqueous solution at a ratio of 88:12, stir at 500rpm and 25℃ for 30min until homogeneous, and adjust pH to 7; weigh 2 parts by mass of ε-polylysine and 1 part by mass of cinnamaldehyde, mix them with 1.9 parts by mass of propylene glycol and 1 part by mass of Tween-80 beforehand, add them dropwise to the above solution and continue stirring for 40min; a homogeneous and stable composite aqueous solution is obtained.

[0028] (2) Coating and drying: Gravure coating was used to coat the surface of the polyolefin substrate at a speed of 75 m / min and the dry coating amount was controlled at 1 g / m. 2 First, the surface moisture is removed by online hot air drying at 80℃ for 1 min, and then it is transferred to a constant temperature oven at 42℃ for further drying and curing for 6.5 h to obtain an antibacterial high barrier polyolefin film.

[0029] Comparative Example 1

[0030] (1) Preparation of composite aqueous solution: Mix 15wt% PVA aqueous solution and 15wt% PEI aqueous solution at a ratio of 90:10, stir at 500rpm for 30min until uniform, and adjust pH to 8.

[0031] (2) Coating and drying: Gravure coating was used to coat the surface of the polyolefin substrate at a speed of 65 m / min and the dry coating amount was controlled at 1.2 g / m. 2 First, remove the surface moisture by online hot air drying at 70℃ for 1 min, then transfer it to a constant temperature oven at 40℃ for further drying and curing for 7 hours to obtain an antibacterial high-barrier polyolefin film.

[0032] Comparative Example 2

[0033] The antibacterial agent is supplemented with 3 parts by weight of ε-polylysine, and cinnamaldehyde is no longer added. The rest of the formulation and process are the same as in Example 1.

[0034] Comparative Example 3

[0035] The antibacterial agent is made up of 3 parts by weight of cinnamaldehyde, and ε-polylysine is no longer added. The rest of the formulation and process are the same as in Example 1.

[0036] Comparative Example 4

[0037] The antibacterial agent was modified by adding 1.5 parts by weight of nisin to replace ε-polylysine, and the rest of the formulation and process were the same as in Example 1.

[0038] Comparative Example 5

[0039] The difference from Example 1 is that propylene glycol and Tween-80 are not added, while the mass ratio and amount of the remaining components remain unchanged.

[0040] The following tests were conducted on Examples 1-3 and Comparative Examples 1-5. Before the tests, the samples were conditioned for 24 hours in the corresponding temperature and humidity environment. Comparative Example 1 was not tested for antibacterial properties.

[0041] (1) Oxygen permeability: The test was conducted according to the standard method of GB / T 19789-2021. The test temperature was 23.0℃ and the humidity conditions were 60%RH and 85%RH. The test was conducted in parallel three times and the average value was calculated. The unit is cm³ / (m²·24h·atm).

[0042] (2) The heat seal strength is determined by the following method: Select a defect-free film and cut it into a sample 15 mm wide and 100 mm long. Use the coated side as the heat seal surface and heat seal it at 130℃, 0.2 MPa pressure and 2s heat seal time to ensure that the effective heat seal width is ≥5 mm. In an environment of 23℃ and 60%RH, test the maximum tensile force of weld peeling with a tensile testing machine at a speed of 50 mm / min. At least 5 parallel samples are used in each group, and the arithmetic mean is taken as the result. The unit is N / 15 mm.

[0043] (3) Antibacterial properties: inhibition zone method (LB medium for bacteria, Sabouraud dextrose agar for fungi, bacterial concentration) The diameter of the inhibition zone (mm) of Escherichia coli, Staphylococcus aureus, and Candida albicans was determined after a 24-hour incubation period.

[0044] Simultaneously, the antibacterial rate was calculated according to the standard method specified in GB / T 31402-2023: a 10mm × 10mm sterilized film sample was cut, and 0.1mL of a concentration was added. The bacterial suspensions (Escherichia coli and Staphylococcus aureus) were covered with sterile polyethylene film and incubated for 24 h at 37℃±1℃ and relative humidity ≥90%. Subsequently, the bacterial colonies were eluted with physiological saline containing 0.05% Tween-80 (180 times / min, 10 min), and then plated for colony counting. A blank control colony was also included. The test results are shown in Table 1.

[0045]

[0046] Performance testing comparisons show that the oxygen barrier properties, interfacial bonding strength, and antibacterial properties of Comparative Examples 1-5 are significantly inferior to those of Examples 1-3. This demonstrates that the composite antibacterial agent formed by the compounding of ε-polylysine and cinnamaldehyde, combined with the auxiliary optimization effects of propylene glycol and Tween-80, achieves a synergistic effect with the PVA-PEI coating system.

[0047] Comparative Example 1, which did not contain any antibacterial agents or dispersing co-solvents, possessed basic barrier properties and adhesion, but lacked antibacterial function; and due to the absence of antibacterial agents and hydrogen / weak bond interactions in the coating system, the coating density was slightly lower than that of the examples.

[0048] Comparative Example 2, which only added ε-polylysine and did not add cinnamaldehyde, could provide some antibacterial effect, but could not form a compound antibacterial system, with a narrow antibacterial spectrum and low antibacterial efficiency; at the same time, the lack of weak interaction between cinnamaldehyde and the system resulted in insufficient cross-linking density of the coating and a significant decrease in oxygen barrier properties.

[0049] Comparative Example 3 only added cinnamaldehyde and did not add ε-polylysine. Cinnamaldehyde is an oil-soluble small molecule that is prone to agglomeration and phase separation in the aqueous PVA / PEI system. After film formation, it forms microscopic defects and pores, resulting in a significant reduction in coating density, especially in the barrier performance under high humidity. At the same time, it lacks the stabilizing and anchoring effect of macromolecular antibacterial components, resulting in insufficient antibacterial durability and broad spectrum.

[0050] Comparative Example 4 replaced ε-polylysine with nisin. Although nisin has a certain antibacterial effect, it is difficult to form a stable cross-linking network with PVA and PEI, and cannot improve the density of the coating. Therefore, its oxygen barrier properties and interfacial adhesion are inferior to those of the example. Moreover, its synergistic effect with cinnamaldehyde is weak, and its antibacterial effect is not as good as the ε-polylysine and cinnamaldehyde complex system.

[0051] In Comparative Example 5, without the addition of propylene glycol and Tween-80, the oil-soluble cinnamaldehyde was unevenly dispersed in the aqueous system and easily precipitated and volatilized. This not only reduced the antibacterial activity and stability but also caused pores and defects inside the coating, resulting in a significant decrease in oxygen barrier properties and interfacial bonding.

[0052] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An antibacterial high-barrier polyolefin film, characterized in that, It consists of a polyolefin substrate and a composite coating applied to the surface of the substrate. The composite coating contains the following components in parts by weight: 80-95 parts polyvinyl alcohol (PVA), 5-20 parts polyethyleneimine (PEI), 1-2 parts ε-polylysine, 1-2 parts cinnamaldehyde, 1.6-2 parts propylene glycol, and 0.8-1 parts Tween-80.

2. The antibacterial high-barrier polyolefin film according to claim 1, characterized in that, The polyolefin substrate is a BOPP, CPP or PE film, and the surface of the substrate is corona treated with a surface tension ≥38mN / m.

3. The antibacterial high-barrier polyolefin film according to claim 1, characterized in that, The degree of polymerization of the PVA is 300-1500, and the degree of saponification is 88-99.5%.

4. The antibacterial high-barrier polyolefin film according to claim 1, characterized in that, The PEI is branched PEI with a molecular weight between 50,000 and 100,000.

5. The method for preparing the antibacterial high-barrier polyolefin film according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Preparation of composite aqueous solution: PVA aqueous solution and PEI aqueous solution are mixed in proportion and stirred at 300-800 rpm and 20-30℃ for 20-40 min until homogeneous. The pH is adjusted to 7-8. ε-polylysine and cinnamaldehyde are weighed and mixed with propylene glycol and Tween-80 beforehand. After being added dropwise to the above solution, stirring is continued for 30-60 min to obtain a homogeneous and stable composite aqueous solution. (2) Coating and drying: The composite aqueous solution is coated onto the surface of the polyolefin substrate by gravure coating. First, the surface moisture is removed by online hot air drying at 50-80℃ for 1-2 min, and then it is transferred to a constant temperature oven at 35-45℃ for 6-8 h to continue drying and curing to obtain an antibacterial high barrier polyolefin film.

6. The method for preparing the antibacterial high-barrier polyolefin film according to claim 5, characterized in that, The concentrations of both PVA and PEI aqueous solutions were 5-10 wt%.

7. The method for preparing the antibacterial high-barrier polyolefin film according to claim 5, characterized in that, In step (2), the coating speed is 60-80 m / min, and the dry coating amount is controlled at 0.6-1.6 g / m. 2 .

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