A high-barrier polyvinyl alcohol coated film and a method for preparing the same

Abstract

This invention discloses a high-barrier polyvinyl alcohol coated film and its preparation method. The coated film structure sequentially includes: a film substrate, a primer layer, and a high-barrier coating layer. The high-barrier coating layer is prepared and coated from the following raw materials in the indicated mass percentages: 4-10% water-resistant modified polyvinyl alcohol, 2-6% acidic aluminum sol, 0.2-0.5% melamine resin prepolymer, 0.5-1% stabilizer, 0.05-0.5% leveling agent, 0.05-0.1% defoamer, and 83-93% deionized water. This invention provides the market with a packaging film material suitable for boiling, possessing high oxygen barrier properties and transparency.

Description

Technical Field

[0001] This invention relates to the field of packaging film technology, specifically to a high-barrier polyvinyl alcohol coated film and its preparation method. Background Technology

[0002] Currently, the mainstream high-barrier packaging materials on the market mainly include aluminum foil composite film, polyvinylidene chloride (PVDC) coated composite film, ethylene-vinyl alcohol copolymer (EVOH) co-extruded film, and aluminized film, but each has its own technical shortcomings and application limitations. Firstly, while aluminum foil composite films possess light-blocking, high oxygen barrier, and high moisture barrier properties, their production costs are high. Furthermore, microscopic defects such as pinholes in the aluminum foil layer can significantly reduce the overall oxygen barrier performance of the composite film. Secondly, PVDC-coated composite films offer good oxygen and moisture barrier performance at a low cost, but due to the large amount of chlorine atoms in the material, incineration after disposal releases harmful gases, polluting the ecological environment and contradicting green and sustainable development policies. Thirdly, EVOH co-extruded films also possess excellent oxygen barrier performance, but due to technological limitations, the core raw material EVOH resin is mainly imported, resulting in high material costs. Moreover, its moisture barrier performance is poor in high humidity environments, requiring special moisture-proof treatment. Fourthly, while aluminized films offer high barrier effects and are much cheaper than aluminum foil, their coating is thin and easily damaged by mechanical means, and their barrier effect is easily compromised by friction and folding.

[0003] Polyvinyl alcohol (PVA), as a water-soluble polymer, forms coatings with excellent oxygen barrier properties, making it a potential application in the packaging materials field. However, pure PVA coatings have significant hydrophilicity; their oxygen barrier properties decrease noticeably with increasing ambient humidity, and they are easily dissolved in boiling water at 100°C. This greatly limits the application scenarios and service life of pure PVA-based high-barrier films.

[0004] Chinese patent CN200410034455.1 discloses a modified polyvinyl alcohol coating liquid and its manufacturing process. By adding additives such as nano-silica, coupling agents, tackifiers, and plasticizers, the oxygen and moisture barrier properties of the polyvinyl alcohol coating layer are significantly improved, but its high-temperature boiling resistance is poor. Chinese patent CN200810000935.4 discloses an aqueous high-barrier coating liquid and a method for manufacturing a water-resistant high-barrier coating obtained therefrom. By adding nano-inorganic substances and aliphatic aldehyde compounds to barrier resins such as polyvinyl alcohol, the water-resistant and high-temperature boiling resistance is improved. However, the proportion of added aldehyde small molecules and other chemical additives is too high, which can easily lead to excessive chemical residues and affect food safety.

[0005] In summary, there is still a need in this field for a high-barrier packaging film material that combines environmental friendliness, cost advantages, high oxygen barrier properties, high transparency, and water resistance. Summary of the Invention

[0006] Therefore, the purpose of this invention is to provide a green, environmentally friendly, and low-cost high-barrier polyvinyl alcohol coated film and its preparation method, providing the market with a packaging film material suitable for boiling, with high oxygen barrier properties and transparency.

[0007] The specific technical solution of the present invention is as follows:

[0008] A high-barrier polyvinyl alcohol coated film, the structure of which comprises, in sequence: a film substrate, a primer layer, and a high-barrier coating layer; the high-barrier coating layer is prepared and coated from the following raw materials in the indicated mass percentages: 4-10% water-resistant modified polyvinyl alcohol, 2-6% acidic aluminum sol, 0.2-0.5% melamine resin prepolymer, 0.5-1% stabilizer, 0.05-0.5% leveling agent, 0.05-0.1% defoamer, and 83-93% deionized water.

[0009] Furthermore, the water-resistant modified polyvinyl alcohol is prepared by adding 2 mol of ethyl vinyl ether with a hydrophobic ether segment during polymerization, followed by alkaline alcoholysis; the degree of polymerization of the water-resistant modified polyvinyl alcohol is 1700-1900, and the degree of alcoholysis is 89-99%.

[0010] Furthermore, the acidic aluminum sol has a solid content of 10-20% and a pH value of 4-5.5.

[0011] Furthermore, the melamine resin prepolymer is modified by methanol etherification, retaining 20-40% hydroxymethyl groups on the molecular chain, while introducing methoxymethyl groups, with a pH value of 8-10.

[0012] Furthermore, the stabilizer is a nonionic surfactant of polyoxyethylene ether and / or polyol fatty acid ester; the leveling agent is BYK-345; and the defoamer is AFE-1510.

[0013] Furthermore, the base layer is coated with a high-temperature resistant A / B two-component polyurethane adhesive, wherein the main component of component A is polyester polyol and the main component of component B is isocyanate.

[0014] Furthermore, the dry weight of the adhesive layer is 1.8-2.2 g / m³. 2 The coating amount of the high-barrier coating is 0.8-1.5 g / m³. 2 .

[0015] Furthermore, the film substrate includes BOPP film, CPP film, PET film, and PA film; the thickness of the film substrate is 12-30 μm.

[0016] A method for preparing a high-barrier polyvinyl alcohol coated film includes the following steps:

[0017] Step 1, Preparation of high barrier coating liquid: (1) First, add 83-93% deionized water to the reactor, and add 4-10% water-resistant modified polyvinyl alcohol while stirring to prevent it from sticking together. Heat to 95-98℃ and continue stirring for 2-3 hours until it becomes a stable modified polyvinyl alcohol emulsion. Then cool to room temperature to obtain emulsion a; (2) While stirring, slowly add 0.2-0.5% melamine resin prepolymer to emulsion a. After that, add 0.5-1% stabilizer and continue stirring for 0.5 hours to obtain emulsion b; (3) Add 2-6% acidic aluminum sol to emulsion b. After stirring evenly, add 0.05-0.5% leveling agent and 0.05-0.1% defoamer. After stirring evenly, the high barrier coating liquid is obtained.

[0018] Step 2, Preparation of high-barrier polyvinyl alcohol coated film: (1) Unwind the film substrate onto the machine and perform corona treatment on one of the surfaces of the substrate to make the dyne value ≥52 in order to improve the surface energy and roughness; (2) Use a coating equipment to coat a layer of A / B two-component polyurethane adhesive on the surface of the corona-treated substrate, dry it to obtain a base layer, and then coat a layer of high-barrier coating liquid on the surface of the base layer, and dry it to obtain a high-barrier coating layer; (3) Roll up the film and place it in a curing chamber to cure at 45°C for 48-72 hours to obtain a high-barrier polyvinyl alcohol coated film.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] The high-barrier coating liquid of this invention incorporates melamine resin prepolymer, in which the hydroxymethyl and methoxymethyl groups react with the hydroxyl groups of water-resistant modified polyvinyl alcohol. This not only blocks some hydroxyl groups, reducing the hydrophilic swelling of polyvinyl alcohol, but also forms a stable ether crosslinking structure, constructing a three-dimensional network polymer, significantly improving the coating's water resistance, barrier properties, and thermal stability. The added acidic aluminum sol provides an acidic environment, promoting the forward crosslinking reaction. Through crosslinking, the polymer chains transform from linear to a three-dimensional network structure, forming a stable spatial network. Simultaneously, the alumina formed after drying the acidic aluminum sol is encapsulated and fixed by the three-dimensional network structure, filling the gaps in the three-dimensional network and forming a dense coating, further improving the oxygen barrier effect.

[0021] The high-barrier polyvinyl alcohol coated film of this invention possesses excellent properties such as high oxygen barrier, high transparency, water resistance, and environmental friendliness. Furthermore, the coating process is simple, adaptable to existing coating equipment, and requires no significant equipment investment or technical adjustments. The high-barrier polyvinyl alcohol coated film prepared using BOPP film substrate can be laminated with high-temperature retortable CPP film to form a single-material recyclable composite film suitable for boil-out packaging applications. Detailed Implementation

[0022] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0023] Example 1

[0024] A high-barrier polyvinyl alcohol coated film, the structure of which comprises, in sequence: a film substrate, a primer layer, and a high-barrier coating layer. The film substrate is a PET film with a thickness of 12 μm; the primer layer is coated with a high-temperature resistant A / B two-component polyurethane adhesive, where component A is mainly composed of polyester polyols and component B is mainly composed of isocyanates; the high-barrier coating layer is prepared and coated from the following raw materials in the indicated mass percentages:

[0025]

[0026] Specifically, the water-resistant modified polyvinyl alcohol in this embodiment is prepared by adding 2 mol of ethyl vinyl ether with a hydrophobic ether segment during polymerization, followed by alkaline alcoholysis; the degree of polymerization of the water-resistant modified polyvinyl alcohol is 1700, and the degree of alcoholysis is 89%. The acidic aluminum sol has a solid content of 10% and a pH of 5.5. The melamine resin prepolymer is modified by methanol etherification, retaining 20% ​​hydroxymethyl groups on the molecular chain, while introducing methoxymethyl groups, with a pH of 8.

[0027] In addition, the stabilizer in this embodiment is a nonionic surfactant of polyol fatty acid ester; the leveling agent is BYK-345; and the defoamer is AFE-1510. The dry weight of the primer layer is 1.8 g / m³. 2 The coating weight of the high-barrier coating is 0.8 g / m². 2 .

[0028] A method for preparing a high-barrier polyvinyl alcohol coated film includes the following steps:

[0029] Step 1, Preparation of high barrier coating liquid: (1) According to the ratio of each raw material, first add deionized water to the reaction vessel, add water-resistant modified polyvinyl alcohol while stirring to prevent it from sticking together, heat to 98°C, and continue stirring for 3 hours until it becomes a stable modified polyvinyl alcohol emulsion, and then cool to room temperature to obtain emulsion a; (2) Under stirring, slowly drop an amine resin prepolymer into emulsion a, and then add a stabilizer after it is finished, and continue stirring for 0.5 hours to obtain emulsion b; (3) Add acidic aluminum sol to emulsion b, stir evenly, and then add leveling agent and defoamer. After stirring evenly, the high barrier coating liquid is obtained.

[0030] Step 2, Preparation of high-barrier polyvinyl alcohol coated film: (1) Unwind the film substrate onto the machine and perform corona treatment on one of the surfaces of the substrate to make the dyne value ≥52 in order to improve the surface energy and roughness; (2) Use a coating equipment to coat a layer of A / B two-component polyurethane adhesive on the surface of the corona-treated substrate, dry to obtain a base layer, and then coat a layer of high-barrier coating liquid on the surface of the base layer and dry to obtain a high-barrier coating layer; (3) Roll up the film and place it in a curing chamber to cure at 45°C for 72 hours to obtain a high-barrier polyvinyl alcohol coated film.

[0031] Example 2

[0032] A high-barrier polyvinyl alcohol coated film, the structure of which comprises, in sequence: a film substrate, a primer layer, and a high-barrier coating layer. The film substrate is a BOPP film with a thickness of 25 μm; the primer layer is coated with a high-temperature resistant A / B two-component polyurethane adhesive, where component A is mainly composed of polyester polyols and component B is mainly composed of isocyanates; the high-barrier coating layer is prepared and coated from the following raw materials in the indicated mass percentages:

[0033]

[0034] Specifically, the water-resistant modified polyvinyl alcohol in this embodiment is prepared by adding 2 mol of ethyl vinyl ether with a hydrophobic ether segment during polymerization, followed by alkaline alcoholysis; the degree of polymerization of the water-resistant modified polyvinyl alcohol is 1800, and the degree of alcoholysis is 92%. The acidic aluminum sol has a solid content of 13% and a pH of 5. The melamine resin prepolymer is modified by methanol etherification, retaining 40% hydroxymethyl groups on the molecular chain, while introducing methoxymethyl groups, with a pH of 8.7.

[0035] In addition, the stabilizer in this embodiment is a nonionic surfactant of polyoxyethylene ether; the leveling agent is BYK-345; and the defoamer is AFE-1510. The dry weight of the primer layer is 2.0 g / m³. 2 The coating weight of the high-barrier coating is 1.2 g / m². 2 .

[0036] The preparation method of a high-barrier polyvinyl alcohol coated film is consistent with that in Example 1.

[0037] Example 3

[0038] A high-barrier polyvinyl alcohol coated film, the structure of which comprises, in sequence: a film substrate, a primer layer, and a high-barrier coating layer. The film substrate is a CPP film with a thickness of 30 μm; the primer layer is coated with a high-temperature resistant A / B two-component polyurethane adhesive, where component A is mainly composed of polyester polyols and component B is mainly composed of isocyanates; the high-barrier coating layer is prepared and coated from the following raw materials in the indicated mass percentages:

[0039]

[0040] Specifically, the water-resistant modified polyvinyl alcohol in this embodiment is prepared by adding 2 mol of ethyl vinyl ether with a hydrophobic ether segment during polymerization, followed by alkaline alcoholysis; the degree of polymerization of the water-resistant modified polyvinyl alcohol is 1900, and the degree of alcoholysis is 99%. The acidic aluminum sol has a solid content of 18% and a pH of 4.3. The melamine resin prepolymer is modified by methanol etherification, retaining 30% hydroxymethyl groups on the molecular chain, while introducing methoxymethyl groups, with a pH of 10.

[0041] In addition, the stabilizer in this embodiment is a nonionic surfactant of polyoxyethylene ether; the leveling agent is BYK-345; and the defoamer is AFE-1510. The dry weight of the primer layer is 2.2 g / m². 2 The coating weight of the high-barrier coating is 1.5 g / m². 2 .

[0042] The preparation method of a high-barrier polyvinyl alcohol coated film is consistent with that in Example 1.

[0043] Example 4

[0044] A high-barrier polyvinyl alcohol coated film, the structure of which comprises, in sequence: a film substrate, a primer layer, and a high-barrier coating layer. The film substrate is a PA film with a thickness of 15 μm; the primer layer is coated with a high-temperature resistant A / B two-component polyurethane adhesive, where component A is mainly composed of polyester polyols and component B is mainly composed of isocyanates; the high-barrier coating layer is prepared and coated from the following raw materials in the indicated mass percentages:

[0045]

[0046] Specifically, the water-resistant modified polyvinyl alcohol in this embodiment is prepared by adding 2 mol of ethyl vinyl ether with a hydrophobic ether segment during polymerization, followed by alkaline alcoholysis; the degree of polymerization of the water-resistant modified polyvinyl alcohol is 1900, and the degree of alcoholysis is 96%. The acidic aluminum sol has a solid content of 20% and a pH of 4. The melamine resin prepolymer is modified by methanol etherification, retaining 20% ​​hydroxymethyl groups on the molecular chain, while introducing methoxymethyl groups, with a pH of 9.3.

[0047] In addition, the stabilizer in this embodiment is a nonionic surfactant of polyoxyethylene ether; the leveling agent is BYK-345; and the defoamer is AFE-1510. The dry weight of the primer layer is 2.0 g / m³. 2 The coating weight of the high-barrier coating is 1.0 g / m². 2 .

[0048] The preparation method of a high-barrier polyvinyl alcohol coated film is consistent with that in Example 1.

[0049] Comparative Example 1

[0050] The acidic aluminum sol in the high-barrier coating solution formulation of Example 1 was removed, while the preparation methods of the remaining raw materials, coating solution, and coating film remained unchanged.

[0051] Comparative Example 2

[0052] The melamine resin prepolymer in the high-barrier coating liquid formulation of Example 2 was removed, while the preparation methods of the remaining raw materials, coating liquid, and coating film remained unchanged.

[0053] Comparative Example 3

[0054] The melamine resin prepolymer and acidic aluminum sol in the high-barrier coating liquid formulation of Example 3 were removed, while the preparation methods of the remaining raw materials, coating liquid, and coating film remained unchanged.

[0055] The coated films prepared in each embodiment and comparative example were subjected to performance tests, and the test results are shown in the table below:

[0056] Coated film test results

[0057]

[0058] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high barrier polyvinyl alcohol coated film, characterized by, The structure of the coated film comprises, in sequence: a film substrate, a primer layer, and a high-barrier coating; the high-barrier coating is prepared and coated from the following raw materials in the indicated mass percentages: 4-10% water-resistant modified polyvinyl alcohol, 2-6% acidic aluminum sol, 0.2-0.5% melamine resin prepolymer, 0.5-1% stabilizer, 0.05-0.5% leveling agent, 0.05-0.1% defoamer, and 83-93% deionized water.

2. The high barrier polyvinyl alcohol coated film according to claim 1, characterized in that, The water-resistant modified polyvinyl alcohol is prepared by adding 2 mol of ethyl vinyl ether with a hydrophobic ether segment during polymerization, followed by alkaline alcoholysis; the degree of polymerization of the water-resistant modified polyvinyl alcohol is 1700-1900, and the degree of alcoholysis is 89-99%.

3. The high barrier polyvinyl alcohol coated film according to claim 2, characterized in that, The acidic aluminum sol has a solid content of 10-20% and a pH value of 4-5.

5.

4. The high barrier polyvinyl alcohol coated film according to claim 3, characterized in that, The melamine resin prepolymer is modified by methanol etherification, retaining 20-40% hydroxymethyl on the molecular chain, while introducing methoxymethyl, with a pH value of 8-10.

5. The high barrier polyvinyl alcohol coated film according to claim 1, characterized in that, The stabilizer is a nonionic surfactant of polyoxyethylene ether and / or polyol fatty acid ester; the leveling agent is BYK-345; and the defoamer is AFE-1510.

6. The high barrier polyvinyl alcohol coated film according to claim 5, characterized in that, The base layer is coated with a high-temperature resistant A / B two-component polyurethane adhesive. The main component of component A is polyester polyol, and the main component of component B is isocyanate.

7. The high barrier polyvinyl alcohol coated film according to claim 6, characterized in that, The glue amount of the primer layer is 1.8-2.2 g / m 2 ; the coating amount of the high-barrier coating layer is 0.8-1.5 g / m 2 .

8. The high barrier polyvinyl alcohol coated film according to claim 7, characterized in that, The film substrate includes BOPP film, CPP film, PET film, and PA film; the thickness of the film substrate is 12-30μm.

9. The method of claim 1-8, wherein the high barrier polyvinyl alcohol coating film is prepared by the steps of: a) preparing a polyvinyl alcohol solution; b) coating the polyvinyl alcohol solution on a substrate; c) drying the polyvinyl alcohol solution; d) stretching the polyvinyl alcohol solution; and e) annealing the polyvinyl alcohol solution. Includes the following steps: Step 1, Preparation of high barrier coating liquid: (1) First, add 83-93% deionized water to the reactor, and add 4-10% water-resistant modified polyvinyl alcohol while stirring to prevent it from sticking together. Heat to 95-98℃ and continue stirring for 2-3 hours until it becomes a stable modified polyvinyl alcohol emulsion. Then cool to room temperature to obtain emulsion a; (2) While stirring, slowly add 0.2-0.5% melamine resin prepolymer to emulsion a. After that, add 0.5-1% stabilizer and continue stirring for 0.5 hours to obtain emulsion b; (3) Add 2-6% acidic aluminum sol to emulsion b. After stirring evenly, add 0.05-0.5% leveling agent and 0.05-0.1% defoamer. After stirring evenly, the high barrier coating liquid is obtained. Step 2, Preparation of high-barrier polyvinyl alcohol coated film: (1) Unwind the film substrate onto the machine and perform corona treatment on one of the surfaces of the substrate to make the dyne value ≥52 in order to improve the surface energy and roughness; (2) Use a coating equipment to coat a layer of A / B two-component polyurethane adhesive on the surface of the corona-treated substrate, dry it to obtain a base layer, and then coat a layer of high-barrier coating liquid on the surface of the base layer, and dry it to obtain a high-barrier coating layer; (3) Roll up the film and place it in a curing chamber to cure at 45°C for 48-72 hours to obtain a high-barrier polyvinyl alcohol coated film.

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