High-barrier BOPET (Biaxially Oriented Polyester) film and preparation method thereof

Abstract

The invention discloses a high-barrier BOPET (Biaxially Oriented Polyethylene Terephthalate) film and a preparation method thereof. Comprising the following steps: carrying out melt extrusion on dried polyester chips, cooling cast sheets, and then carrying out longitudinal stretching; after corona treatment, double surfaces are coated with a coating liquid, and the thickness of the coating is controlled to be 0.5-1 [mu] m; then transversely stretching and shaping at high temperature, so that the coating is fully crosslinked and cured; and finally, carrying out sectional cooling and rolling to obtain the BOPET film. The preparation method has the beneficial effects that the modified monomer with a quaternary ammonium salt structure is chemically synthesized and is applied to a coating liquid system of the BOPET film, so that the comprehensive performance of the film is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of film preparation, and in particular relates to a high-barrier BOPET film and a preparation method thereof. Background Art

[0002] In the traditional BOPET film preparation field, polyester film is widely used in packaging, electronics, medical and other industries due to its excellent mechanical strength, transparency and chemical stability.

[0003] However, the BOPET films prepared by existing technologies still have obvious deficiencies in terms of barrier properties, antibacterial properties and antistatic properties. Ordinary BOPET films have limited barrier capabilities against oxygen and water vapor, making it difficult to meet the long-term preservation needs of high-end food and pharmaceutical packaging. At the same time, traditional films lack effective antibacterial functions and are prone to breeding bacteria in humid environments, limiting their application in medical and food packaging. In addition, ordinary BOPET films have high surface resistance and are prone to accumulate static electricity, which not only affects printing and composite processing performance, but may also cause safety hazards. Current methods to improve these properties mainly include surface coating and adding modifiers, but conventional coating technologies often have problems with poor coating adhesion and easy peeling, and the addition of small molecule antibacterial agents or antistatic agents is prone to performance degradation due to migration and loss. Although the use of nanomaterials such as carbon nanotubes in existing technologies can partially improve conductivity, due to poor dispersibility, it often leads to a decrease in the mechanical properties of the film.

[0004] Therefore, in order to solve the above problems, the present invention provides a high-barrier BOPET film and a preparation method thereof. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a high-barrier BOPET film and a preparation method thereof.

[0006] The purpose of the present invention can be achieved through the following technical solutions: A method for preparing a high-barrier BOPET film comprises the following steps: melt-extruding dried polyester chips and cooling the cast sheets, followed by longitudinal stretching; corona treatment, double-sided coating with a coating liquid, with the coating thickness controlled at 0.5-1 μm; transverse stretching and shaping at high temperature to fully crosslink and solidify the coating; and finally, segmented cooling and winding to obtain the BOPET film.

[0007] More optimally, the preparation process of the coating solution is: A1: Under a nitrogen atmosphere, the modified monomer, bio-based polycarbonate diol, isophorone diisocyanate, and N,N-dimethylacetamide were mixed, the temperature was raised to 90-100°C, and the reaction was carried out for 3-4 hours. The temperature was then lowered to 60°C, and isophorone diamine and N-methyldiethanolamine were added. The temperature was raised to 70-80°C, and the reaction was carried out for 3-4 hours to obtain a modified polyurethane emulsion. A2: Mix the modified polyurethane emulsion, carbon nanotubes, N,N-dimethylacetamide, leveling agent, and defoaming agent, and stir evenly to obtain a coating solution.

[0008] More optimally, the modified polyurethane emulsion raw materials include the following components: by weight, 20-30 parts of modified monomer, 30-40 parts of bio-based polycarbonate diol, 15-20 parts of isophorone diisocyanate, 40-60 parts of N,N-dimethylacetamide, 8-10 parts of isophorone diamine, and 3-5 parts of N-methyldiethanolamine.

[0009] More optimally, the coating liquid raw materials include the following components: by weight, 60-70 parts of modified polyurethane emulsion, 5-6 parts of carbon nanotubes, 10-25 parts of N,N-dimethylacetamide, 0.1-0.2 parts of leveling agent, and 0.1-0.2 parts of defoaming agent.

[0010] More optimally, the preparation process of the modified monomer is: S1: Under a protective atmosphere, 1-pyreneboronic acid, α-thioglycerol and anhydrous tetrahydrofuran were mixed, p-toluenesulfonic acid was added, and the temperature was raised to 40-50°C. The reaction was carried out for 1-2 hours. After the reaction was completed, the mixture was purified by column chromatography and dried to obtain intermediate A; S2: Under a protective atmosphere, intermediate A, N-allylimidazole, and anhydrous tetrahydrofuran are mixed and stirred evenly, 2,2-dimethoxy-2-phenylacetophenone is added, and the mixture is irradiated with ultraviolet light at room temperature for 1-2 hours. After the reaction is completed, post-treatment is performed to obtain intermediate B; S3: Under nitrogen protection, intermediate B, 2-chloro-1,3-propanediol, and anhydrous acetonitrile were mixed, potassium carbonate was added, and the mixture was stirred in an oil bath at 60°C for 6-8 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, and dried to obtain a modified monomer.

[0011] In the scheme, the boronic acid group in 1-pyreneboronic acid undergoes a dehydration reaction with the hydroxyl group in α-thioglycerol to obtain intermediate A. The specific reaction process is shown below: More optimally, the intermediate A raw material includes the following components: by weight, 10-12 parts of 1-pyreneboric acid, 6-8 parts of α-thioglycerol, 50-80 parts of anhydrous tetrahydrofuran, and 0.5-1 part of p-toluenesulfonic acid.

[0012] In the scheme, the thiol group of intermediate A undergoes a click reaction with the double bond of N-allylimidazole to obtain intermediate B. The specific synthesis process is as follows: More optimally, the intermediate B raw material includes the following components: by weight, 10-12 parts of intermediate A, 4-6 parts of N-allylimidazole, 40-60 parts of anhydrous tetrahydrofuran, and 0.1-0.2 parts of 2,2-dimethoxy-2-phenylacetophenone.

[0013] In the scheme, the imidazole group in intermediate B acts as a nucleophile to attack the β-carbon atom of 2-chloro-1,3-propanediol, resulting in nucleophilic substitution. The specific synthesis process is shown below: More optimally, the modified monomer raw material includes the following components: by weight, 8-10 parts of intermediate B, 5-7 parts of 2-chloro-1,3-propanediol, 50-70 parts of anhydrous acetonitrile, and 3-5 parts of potassium carbonate.

[0014] Beneficial effects of the present invention: The present invention chemically synthesizes a modified monomer with a quaternary ammonium salt structure and applies it to the coating liquid system of BOPET film, significantly improving the comprehensive performance of the film. The details are as follows: First: In the scheme, the rigid pyrene group (a large π-conjugated system of four benzene rings fused together) contained in the synthesized modified monomer can form a strong interfacial bond with the surface of carbon nanotubes through π-π stacking, effectively improving the dispersion of the nanofiller and enhancing the stress transfer efficiency, thereby improving the mechanical properties of the film; moreover, the rigid structure of the pyrene group can hinder the expansion of microcracks and improve the fracture toughness of the film.

[0015] Second: In this scheme, the quaternary ammonium cations in the modified monomer destroy the bacterial cell membrane through electrostatic adsorption; moreover, the quaternary ammonium salt is chemically bonded to the polyurethane chain segment, which can effectively prevent the migration and loss of small molecule antimicrobial agents and achieve long-lasting antimicrobial properties; at the same time, the quaternary ammonium salt group can also work synergistically with the carbon nanotubes to improve the antistatic ability of the film.

[0016] Third: In the scheme, the polyurethane coating obtained contains hydrogen bonds and ion cross-linking network structures, which improves the density and crystallinity of the material and increases the complexity of the gas or water vapor diffusion path, thereby effectively reducing the water vapor permeability; in addition, the hydrophobic chain segments contained in the modified monomer further enhance the hydrophobicity of the material and hinder the penetration of water molecules; at the same time, the rigid pyrene groups in the modified monomer form a tight bond with the carbon nanotubes through π-π stacking, increasing the tortuosity of the water vapor molecule penetration path, forcing the diffusing molecules to take a longer detour. DETAILED DESCRIPTION

[0017] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0018] Example 1: A method for preparing a high-barrier BOPET film, comprising the following steps: melt-extruding dried polyester chips and cooling the cast sheet, followed by longitudinal stretching; corona treatment, double-sided coating with a coating liquid, with the coating thickness controlled to be 0.5 μm; transverse stretching and shaping at high temperature to fully crosslink and solidify the coating; and finally, cooling in sections and winding to obtain the BOPET film. Wherein, the preparation process of the coating liquid is: A1: Under a nitrogen atmosphere, 20 parts of the modified monomer, 30 parts of bio-based polycarbonate diol, 15 parts of isophorone diisocyanate, and 40 parts of N,N-dimethylacetamide were mixed, the temperature was raised to 90°C, and the reaction was carried out for 3 hours. The mixture was then cooled to 60°C, 8 parts of isophorone diamine and 3 parts of N-methyldiethanolamine were added, and the temperature was raised to 70°C. The mixture was reacted for 3 hours to obtain a modified polyurethane emulsion. A2: Mix 60 parts of modified polyurethane emulsion, 5 parts of carbon nanotubes, 10 parts of N,N-dimethylacetamide, 0.1 parts of leveling agent, and 0.1 parts of defoaming agent, and stir evenly to obtain a coating solution; Wherein, the preparation process of the modified monomer is: S1: Under a protective atmosphere, 10 parts of 1-pyreneboronic acid, 6 parts of α-thioglycerol and 50 parts of anhydrous tetrahydrofuran were mixed, 0.5 parts of p-toluenesulfonic acid were added, the temperature was raised to 40°C, and the reaction was carried out for 1 hour. After the reaction, the mixture was purified by column chromatography and dried to obtain intermediate A; S2: Under a protective atmosphere, 10 parts of intermediate A, 4 parts of N-allylimidazole, and 40 parts of anhydrous tetrahydrofuran were mixed and stirred evenly. 0.1 parts of 2,2-dimethoxy-2-phenylacetophenone was added and the mixture was irradiated with ultraviolet light at room temperature for 1 hour. After the reaction was completed, the intermediate B was obtained by post-treatment. S3: Under nitrogen protection, 8 parts of intermediate B, 5 parts of 2-chloro-1,3-propanediol, and 50 parts of anhydrous acetonitrile were mixed, 3 parts of potassium carbonate were added, and the mixture was stirred in an oil bath at 60°C for 6 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, and dried to obtain a modified monomer.

[0019] Example 2: A method for preparing a high-barrier BOPET film, comprising the following steps: melt-extruding dried polyester chips and cooling the cast sheet, followed by longitudinal stretching; corona treatment, double-sided coating with a coating liquid, with the coating thickness controlled to be 1 μm; transverse stretching and shaping at high temperature to fully crosslink and solidify the coating; and finally, cooling in sections and winding to obtain the BOPET film. Wherein, the preparation process of the coating liquid is: A1: Under a nitrogen atmosphere, 30 parts of the modified monomer, 40 parts of bio-based polycarbonate diol, 20 parts of isophorone diisocyanate, and 60 parts of N,N-dimethylacetamide were mixed, the temperature was raised to 100°C, and the reaction was carried out for 4 hours. The mixture was then cooled to 60°C, 10 parts of isophorone diamine and 5 parts of N-methyldiethanolamine were added, and the temperature was raised to 80°C. The mixture was reacted for 4 hours to obtain a modified polyurethane emulsion. A2: Mix 70 parts of modified polyurethane emulsion, 6 parts of carbon nanotubes, 25 parts of N,N-dimethylacetamide, 0.2 parts of leveling agent, and 0.2 parts of defoaming agent, and stir evenly to obtain a coating solution; Wherein, the preparation process of the modified monomer is: S1: Under a protective atmosphere, 12 parts of 1-pyreneboronic acid, 8 parts of α-thioglycerol, and 80 parts of anhydrous tetrahydrofuran were mixed, 1 part of p-toluenesulfonic acid was added, the temperature was raised to 50°C, and the reaction was carried out for 2 hours. After the reaction, the mixture was purified by column chromatography and dried to obtain intermediate A; S2: Under a protective atmosphere, 12 parts of intermediate A, 6 parts of N-allylimidazole, and 60 parts of anhydrous tetrahydrofuran were mixed and stirred evenly. 0.2 parts of 2,2-dimethoxy-2-phenylacetophenone was added and the mixture was irradiated with ultraviolet light at room temperature for 2 hours. After the reaction was completed, the intermediate B was obtained by post-treatment. S3: Under nitrogen protection, 10 parts of intermediate B, 7 parts of 2-chloro-1,3-propanediol, and 70 parts of anhydrous acetonitrile were mixed, 5 parts of potassium carbonate were added, and the mixture was stirred in an oil bath at 60°C for 8 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, and dried to obtain a modified monomer.

[0020] Example 3: A method for preparing a high-barrier BOPET film, comprising the following steps: melt-extruding dried polyester chips and cooling the cast sheet, followed by longitudinal stretching; corona treatment, double-sided coating with a coating liquid, with the coating thickness controlled to be 0.8 μm; transverse stretching and shaping at high temperature to fully crosslink and solidify the coating; and finally, cooling in sections and winding to obtain the BOPET film. Wherein, the preparation process of the coating liquid is: A1: Under a nitrogen atmosphere, 25 parts of the modified monomer, 35 parts of bio-based polycarbonate diol, 17.5 parts of isophorone diisocyanate, and 50 parts of N,N-dimethylacetamide were mixed, the temperature was raised to 95°C, and the reaction was carried out for 3.5 hours. The mixture was then cooled to 60°C, 9 parts of isophorone diamine and 4 parts of N-methyldiethanolamine were added, and the temperature was raised to 75°C. The mixture was reacted for 3.5 hours to obtain a modified polyurethane emulsion. A2: 65 parts of modified polyurethane emulsion, 5.5 parts of carbon nanotubes, 17.5 parts of N,N-dimethylacetamide, 0.15 parts of leveling agent, and 0.15 parts of defoaming agent were mixed and stirred to obtain a coating solution; Wherein, the preparation process of the modified monomer is: S1: Under a protective atmosphere, 11 parts of 1-pyreneboronic acid, 7 parts of α-thioglycerol, and 65 parts of anhydrous tetrahydrofuran were mixed, 0.75 parts of p-toluenesulfonic acid were added, the temperature was raised to 45°C, and the reaction was carried out for 1.5 hours. After the reaction, the mixture was purified by column chromatography and dried to obtain intermediate A; S2: Under a protective atmosphere, 11 parts of intermediate A, 5 parts of N-allylimidazole, and 50 parts of anhydrous tetrahydrofuran were mixed and stirred evenly. 0.15 parts of 2,2-dimethoxy-2-phenylacetophenone was added and the mixture was irradiated with ultraviolet light at room temperature for 1.5 hours. After the reaction was completed, the intermediate B was obtained by post-treatment. S3: Under nitrogen protection, 9 parts of intermediate B, 6 parts of 2-chloro-1,3-propanediol, and 60 parts of anhydrous acetonitrile were mixed, 4 parts of potassium carbonate were added, and the mixture was stirred in an oil bath at 60°C for 7 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, and dried to obtain a modified monomer.

[0021] Comparative Example 1: No modified monomer was introduced, and the rest was the same as Example 3, specifically as follows: A method for preparing a high-barrier BOPET film comprises the following steps: melt-extruding dried polyester chips and cooling the cast sheets, followed by longitudinal stretching; corona treatment, double-sided coating with a coating liquid, with the coating thickness controlled to be 0.8 μm; transverse stretching and shaping at high temperature to fully crosslink and solidify the coating; and finally, cooling in sections and winding to obtain the BOPET film. Wherein, the preparation process of the coating liquid is: A1: Under a nitrogen atmosphere, 35 parts of bio-based polycarbonate diol, 17.5 parts of isophorone diisocyanate, and 50 parts of N,N-dimethylacetamide were mixed, the temperature was raised to 95°C, and the reaction was carried out for 3.5 hours. The mixture was then cooled to 60°C, 9 parts of isophorone diamine and 4 parts of N-methyldiethanolamine were added, and the temperature was raised to 75°C. The mixture was reacted for 3.5 hours to obtain a polyurethane emulsion. A2: 65 parts of polyurethane emulsion, 5.5 parts of carbon nanotubes, 17.5 parts of N,N-dimethylacetamide, 0.15 parts of leveling agent, and 0.15 parts of defoaming agent were mixed and stirred uniformly to obtain a coating liquid.

[0022] Comparative Example 2: No polyurethane coating is added, as follows: A method for preparing a high-barrier BOPET film comprises the following steps: melting and extruding dried polyester chips and cooling them to form sheets, followed by biaxial stretching and heat setting, and cooling and corona treating the stretched film before winding it up to obtain the BOPET film.

[0023] Detection test: (1) Using a high resistance meter and measuring electrodes, measure the surface resistance of the film after applying a voltage of 100V for 1 minute at 23°C and 50% RH, after sufficient humidity adjustment. Evaluate the antistatic properties based on the surface resistance. (2) Test the tensile strength of the film according to ASTM D882; (3) According to GB / T21529-2008 standard, the film was tested using a water vapor transmission rate tester (38°C, 90% RH); (4) Use a pipette to draw an appropriate amount of bacterial suspension (the test strains are Escherichia coli and Staphylococcus aureus), carefully add it to the surface of the film, and then place it in a constant temperature incubator and incubate it at 37°C for 4 hours. After the incubation, use a sterile pipette to draw 10 μL of bacterial liquid and transfer it to a sterile culture dish and continue to culture it at 37°C for 24 hours. After the incubation, count the number of colonies in each culture dish and compare it with the blank control group to calculate the antibacterial rate; The obtained data is shown in the following table: Conclusion: This invention significantly improves the overall performance of BOPET film by chemically synthesizing a modified monomer with a quaternary ammonium salt structure and applying it to the coating solution system. Experimental data show that compared with Comparative Example 1, which did not introduce the modified monomer, and Comparative Example 2, which did not add a polyurethane coating, the films prepared in Examples 1 to 3 exhibit significant advantages in mechanical properties, barrier properties, antibacterial properties, and antistatic properties.

[0024] Specifically, the surface resistance of the film of the embodiment was reduced to 6.3×10 6 Ω to 7.4×10 6 Ω, much lower than 4.5×10 12Ω, showing excellent antistatic properties; the tensile strength reaches a maximum of 242N / mm² in the MD direction and a maximum of 225N / mm² in the TD direction, which are significantly higher than those of the comparative example, reflecting the synergistic enhancement of the mechanical properties by the modified monomer and carbon nanotubes; the water vapor permeability is only 0.73-0.78g / (m²·day), much lower than 3.5g / (m²·day) of comparative example 1 and 10.2g / (m²·day) of comparative example 2, indicating that the density of the coating significantly improves the barrier performance; in terms of antibacterial rate, the inhibition rates against Escherichia coli and Staphylococcus aureus are both over 91%, with the highest reaching 96.5%, while the antibacterial rate of the comparative example is less than 60%, proving the long-lasting antibacterial effect of the quaternary ammonium salt structure.

[0025] In summary, the present invention achieves comprehensive improvements in the mechanical, barrier, antibacterial and antistatic properties of BOPET film by introducing modified monomers and optimizing the coating liquid system, and has broad application prospects.

[0026] Throughout the specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0027] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high barrier BOPET film, characterized in that: The process comprises the following steps: melt-extruding dried polyester chips and cooling the cast sheet, followed by longitudinal stretching; After corona treatment, the coating liquid is coated on both sides, and the coating thickness is controlled at 0.5-1μm; then it is stretched horizontally and shaped at high temperature to make the coating fully cross-linked and cured; finally, it is cooled in sections and rolled up to obtain BOPET film.

2. The method for preparing a high barrier BOPET film according to claim 1, wherein: The preparation process of the coating solution is: A1: Under a nitrogen atmosphere, the modified monomer, bio-based polycarbonate diol, isophorone diisocyanate, and N,N-dimethylacetamide were mixed, the temperature was raised to 90-100°C, and the reaction was carried out for 3-4 hours. The temperature was then lowered to 60°C, and isophorone diamine and N-methyldiethanolamine were added. The temperature was raised to 70-80°C, and the reaction was carried out for 3-4 hours to obtain a modified polyurethane emulsion. A2: Mix the modified polyurethane emulsion, carbon nanotubes, N,N-dimethylacetamide, leveling agent, and defoaming agent, and stir evenly to obtain a coating solution.

3. The method for preparing a high barrier BOPET film according to claim 2, wherein: The modified polyurethane emulsion raw materials include the following components: by weight, 20-30 parts of modified monomers, 30-40 parts of bio-based polycarbonate diols, 15-20 parts of isophorone diisocyanate, 40-60 parts of N,N-dimethylacetamide, 8-10 parts of isophorone diamine, and 3-5 parts of N-methyldiethanolamine.

4. The method for preparing a high barrier BOPET film according to claim 2, wherein: The coating liquid raw materials include the following components: by weight, 60-70 parts of modified polyurethane emulsion, 5-6 parts of carbon nanotubes, 10-25 parts of N,N-dimethylacetamide, 0.1-0.2 parts of leveling agent, and 0.1-0.2 parts of defoaming agent.

5. The method for preparing a high barrier BOPET film according to claim 2, wherein: The preparation process of the modified monomer is: S1: Under a protective atmosphere, 1-pyreneboronic acid, α-thioglycerol and anhydrous tetrahydrofuran were mixed, p-toluenesulfonic acid was added, and the temperature was raised to 40-50°C. The reaction was carried out for 1-2 hours. After the reaction was completed, the mixture was purified by column chromatography and dried to obtain intermediate A; S2: Under a protective atmosphere, intermediate A, N-allylimidazole, and anhydrous tetrahydrofuran are mixed and stirred evenly, 2,2-dimethoxy-2-phenylacetophenone is added, and the mixture is irradiated with ultraviolet light at room temperature for 1-2 hours. After the reaction is completed, post-treatment is performed to obtain intermediate B; S3: Under nitrogen protection, intermediate B, 2-chloro-1,3-propanediol, and anhydrous acetonitrile were mixed, potassium carbonate was added, and the mixture was stirred in an oil bath at 60°C for 6-8 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, and dried to obtain a modified monomer.

6. The method for preparing a high barrier BOPET film according to claim 5, characterized in that: The intermediate A raw material comprises the following components: by weight, 10-12 parts of 1-pyreneboric acid, 6-8 parts of α-thioglycerol, 50-80 parts of anhydrous tetrahydrofuran, and 0.5-1 part of p-toluenesulfonic acid.

7. The method for preparing a high barrier BOPET film according to claim 5, characterized in that: The intermediate B raw material comprises the following components: by weight, 10-12 parts of intermediate A, 4-6 parts of N-allylimidazole, 40-60 parts of anhydrous tetrahydrofuran, and 0.1-0.2 parts of 2,2-dimethoxy-2-phenylacetophenone.

8. The method for preparing a high barrier BOPET film according to claim 5, characterized in that: The modified monomer raw material comprises the following components: by weight, 8-10 parts of intermediate B, 5-7 parts of 2-chloro-1,3-propylene glycol, 50-70 parts of anhydrous acetonitrile, and 3-5 parts of potassium carbonate.

9. A BOPET film obtained according to the method for preparing a high-barrier BOPET film according to any one of claims 1 to 8.

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