An ultrathin aluminum foil for liquid packaging and a method for manufacturing the same
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIANGSU ZHONGJI LAMINATION MATERIALS
- Filing Date
- 2026-05-08
- Publication Date
- 2026-08-07
AI Technical Summary
这类聚合物涂层虽然能一定程度降低氧气透过率，但其阻隔性能对湿度敏感（如PVA、EVOH在高湿环境下阻隔性显著下降），且与铝箔的界面结合多依赖物理吸附或弱氢键作用，在长期使用或湿热环境中易发生层间剥离
本发明采用原位生长亚胺COF和 后合成硼氢化钠还原的两步法策略，将刚性易碎的亚胺键还原为柔性可旋转的仲胺键。还原后的柔性胺键连接COF骨架中的碳-氮单键具备自由旋转能力，如同在刚性框架中引入“分子弹簧”，大幅降低了材料的弯曲模量，提高了断裂应变。能够完美适应液体包装铝箔在制袋过程中的高频折叠、卷绕以及后续灌装、运输和存储环节的机械弯折，有效避免了阻隔层因脆性开裂而导致的阻隔失效。
Smart Images
Figure SMS_1
Abstract
Description
Technical Field
[0001] This invention belongs to the field of aluminum foil technology, specifically an ultra-thin aluminum foil for liquid packaging and its preparation method. Background Technology
[0002] Aluminum foil for liquid packaging (such as Tetra Pak and Combibloc aseptic packaging materials) is widely used for the long-term storage and transportation of liquid foods such as fruit juices, dairy products, condiments, and beverages. To protect the contents from oxygen, moisture, and microorganisms, the aluminum foil layer typically needs to possess excellent gas barrier properties. However, while ultra-thin aluminum foil (typically 30-50 μm thick) has some barrier capacity, its surface is prone to pinhole defects, and its barrier performance drops sharply after bending. Therefore, the industry typically laminates it with a polymer coating or an inorganic oxide vapor-deposited layer (such as SiO₂). x AlO x To further improve barrier properties.
[0003] Currently, commonly used polymer barrier coatings mainly include polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer (EVOH), and polyvinylidene chloride (PVDC). Although these polymer coatings can reduce oxygen permeability to a certain extent, their barrier performance is sensitive to humidity (for example, the barrier performance of PVA and EVOH decreases significantly in high humidity environments), and their interfacial bonding with aluminum foil relies mainly on physical adsorption or weak hydrogen bonding, making them prone to interlayer delamination under long-term use or in humid and hot environments. On the other hand, inorganic oxide vapor-deposited layers (such as vacuum-deposited alumina or silicon dioxide) can provide high initial barrier performance, but they are brittle and prone to microcracks during high-frequency folding and winding in the bag-making process, as well as in subsequent filling, transportation, and storage, leading to barrier failure. Summary of the Invention
[0004] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.
[0005] The technical solution adopted by this invention to solve its technical problem is: a method for preparing ultra-thin aluminum foil for liquid packaging, comprising the following steps: S1. Aluminum foil pretreatment: The aluminum foil is ultrasonically cleaned with acetone, anhydrous ethanol and deionized water in sequence to remove surface oil stains, and then plasma treatment is performed to introduce hydroxyl active groups on the surface of the aluminum foil. S2, In-situ growth of imine-linked covalent organic frameworks: Aldehyde and amino monomers are dissolved in a solvent in a certain proportion, a catalyst is added, and the mixture is stirred to obtain a precursor solution; aluminum foil treated with S1 is immersed in the precursor solution, transferred to a high-pressure reactor and sealed, and reacted at 100-150℃ for 24h to form an imine-linked covalent organic framework layer on the surface of the aluminum foil. S3, Post-synthesis reduction: Take out the aluminum foil with imine bond-linked covalent organic framework layer obtained in S2, immerse it in the reducing agent solution, reduce the temperature to 25℃-60℃, reduce the reduction time to 2-6h, reduce the imine bond in the imine bond-linked covalent organic framework to secondary amine bond, and place the reduced aluminum foil material in a nitrogen atmosphere at 150-200℃ for 1-4h. S4. Post-processing and drying: The reduced aluminum foil is taken out, washed, and dried to obtain organic framework composite aluminum foil.
[0006] Preferably, in S1, after the aluminum foil is plasma treated, it is further surface-modified with a silane coupling agent, wherein the silane coupling agent is selected from at least one of 3-aminopropyltriethoxysilane and 3-(2,3-epoxypropoxy)propyltrimethoxysilane.
[0007] Preferably, in S2, the molar ratio of the aldehyde monomer to the amino monomer is 1:0.5-0.5:1.
[0008] Preferably, in S2, the solvent is a mixture of DMAc and mesitylene in a volume ratio of 1:0.5-2.
[0009] Preferably, in S2, the catalyst is selected from at least one of acetic acid, formic acid, and p-toluenesulfonic acid, and the amount of catalyst used is 0.1%-5% of the total mass of the monomer.
[0010] Preferably, in S2, the aldehyde compound monomer is selected from at least one of 1,3,5-tricarboxaldehydebenzene, 1,3,5-tris(4-formylphenyl)benzene, 2,4,6-tris(4-formylphenoxy)-1,3,5-triazine, and trialdehyde-resorcinol.
[0011] Preferably, in S2, the amino compound monomer is selected from at least one of p-phenylenediamine, benzidine, tris(4-aminophenyl)amine, and tris(4-aminophenyl)benzene.
[0012] Preferably, in S3, the reducing agent solution is an ethanol solution of sodium borohydride.
[0013] Preferably, in S3, the amount of reducing agent is 2-5 times the amount of imine bonds in the imine-linked covalent organic framework.
[0014] An ultra-thin aluminum foil for liquid packaging is prepared by the above method.
[0015] The beneficial effects of this invention are as follows: This invention employs a two-step strategy: in-situ growth of imine COF followed by reduction with sodium borohydride. This reduces rigid and brittle imine bonds to flexible, rotatable secondary amine bonds. The reduced flexible amine bonds, connecting the carbon-nitrogen single bonds in the COF framework, possess free rotational capability, much like introducing "molecular springs" into a rigid frame. This significantly reduces the material's flexural modulus and increases its fracture strain. It perfectly adapts to the high-frequency folding and winding of liquid packaging aluminum foil during bag making, as well as the mechanical bending during subsequent filling, transportation, and storage, effectively preventing barrier failure caused by brittle cracking of the barrier layer.
[0016] This invention fundamentally eliminates the possibility of chemical bond hydrolysis and acid / base attack by reducing dynamically reversible imine bonds to quasi-irreversible static secondary amine bonds. Simultaneously, a nitrogen atmosphere heat treatment step at 150-200℃ is added after reduction to induce thermal cross-linking of some secondary amine bonds, forming a denser three-dimensional network structure. This enables its safe application in packaging acidic or alkaline liquids such as fruit juices, dairy products, and condiments, as well as in food packaging requiring high-temperature sterilization, greatly expanding the application scenarios of COF-based barrier materials.
[0017] This invention introduces a surface modification step using a silane coupling agent (3-aminopropyltriethoxysilane or 3-(2,3-epoxypropoxy)propyltrimethoxysilane) in the aluminum foil pretreatment process. The aluminum foil surface, after oxygen plasma activation, is rich in hydroxyl groups, which covalently condense with the silanol groups formed by the hydrolysis of the silane coupling agent, forming a covalent anchoring layer with a thickness of 1-5 nm. The amino or epoxy groups at the ends of this anchoring layer can further participate in the in-situ growth reaction of the COF, forming chemical bonds with the COF backbone. This significantly improves the interfacial bonding strength, ensuring that the composite aluminum foil does not undergo interlayer delamination during long-term use and in humid and hot environments.
[0018] Existing barrier modification methods for liquid packaging aluminum foil mostly employ polymer coatings or inorganic oxide vapor deposition layers. These methods either offer limited barrier enhancement or lack sufficient flexibility, and also lack active antibacterial or molecular sieving functions. This invention combines an innovative material with flexible amine bonds linking COF with ultra-thin aluminum foil, not only solving the brittleness and stability bottlenecks of traditional COF in packaging applications, but also endowing the aluminum foil with higher gas selectivity. Detailed Implementation
[0019] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments. Example 1
[0020] This invention provides an ultrathin aluminum foil for liquid packaging, comprising an aluminum foil substrate and a flexible amine-bonded covalent organic framework barrier layer laminated on at least one surface thereon; The flexible amine-bonded covalent organic framework barrier layer is formed by aldehyde and amino monomers undergoing Schiff base reaction and Eschweiler-Clarke synchronous in-situ reduction reaction under the dual catalysis and reduction of formic acid. The connecting units in the covalent organic framework barrier layer are secondary amine bonds.
[0021] This invention also provides a method for preparing ultrathin aluminum foil for liquid packaging, comprising the following steps: S1. Aluminum foil pretreatment: The aluminum foil is ultrasonically cleaned with acetone, anhydrous ethanol and deionized water in sequence to remove surface oil stains, and then plasma treatment is performed to introduce hydroxyl active groups on the surface of the aluminum foil. In S1, after the aluminum foil is treated with plasma, it is further surface-modified with a silane coupling agent, wherein the silane coupling agent is selected from at least one of 3-aminopropyltriethoxysilane and 3-(2,3-epoxypropoxy)propyltrimethoxysilane. Surface modification steps: Immediately immerse the plasma-treated aluminum foil in the above-mentioned silane coupling agent hydrolysis solution (silane coupling agent ethanol solution with a mass fraction of 0.5% at pH 4.5) for 1-4 hours.
[0022] S2, In-situ growth of imine-linked covalent organic frameworks: Aldehyde monomers and amino monomers are dissolved in a solvent in a certain proportion, a catalyst is added, and the mixture is stirred to obtain a precursor solution; aluminum foil treated with S1 is immersed in the precursor solution, transferred to a high-pressure reactor and sealed, and reacted at 100°C for 24 hours to form an imine-linked covalent organic framework layer on the surface of the aluminum foil. In S2, the molar ratio of aldehyde monomer to amino monomer is 1:0.5, and the total monomer concentration is 5 mg / mL; the solvent is a mixture of DMAc and mesitylene in a volume ratio of 1:0.5; the catalyst is selected from acetic acid, and the amount of catalyst used is 0.1% of the total monomer mass.
[0023] The aldehyde monomer is selected from 1,3,5-tricarboxymethylbenzene; the amino monomer is selected from p-phenylenediamine; S3, Post-synthesis reduction: Take out the aluminum foil with imine bond-linked covalent organic framework layer obtained in S2, immerse it in the reducing agent solution, the reduction temperature is 25℃, the reduction time is 2h, the imine bond in the imine bond-linked covalent organic framework is reduced to secondary amine bond, and the reduced aluminum foil material is placed in a nitrogen atmosphere at 150℃ for 1h for heat treatment. In S3, the reducing agent solution is an ethanol solution of sodium borohydride with a concentration of 0.1M; the amount of reducing agent used is twice the amount of imine bonds in the covalent organic framework linked by imine bonds.
[0024] S4. Post-processing and drying: The reduced aluminum foil is taken out, washed, and dried to obtain organic framework composite aluminum foil.
[0025] In step S4, the aluminum foil was washed five times alternately with anhydrous ethanol and deionized water to remove residual reducing agent and byproducts from the surface. The washed aluminum foil was then placed in a vacuum drying oven and dried at 60°C for 12 hours. Example 2
[0026] This invention provides an ultrathin aluminum foil for liquid packaging, comprising an aluminum foil substrate and a flexible amine-bonded covalent organic framework barrier layer laminated on at least one surface thereon; The flexible amine-bonded covalent organic framework barrier layer is formed by aldehyde and amino monomers undergoing Schiff base reaction and Eschweiler-Clarke synchronous in-situ reduction reaction under the dual catalysis and reduction of formic acid. The connecting units in the covalent organic framework barrier layer are secondary amine bonds.
[0027] This invention also provides a method for preparing ultrathin aluminum foil for liquid packaging, comprising the following steps: S1. Aluminum foil pretreatment: The aluminum foil is ultrasonically cleaned with acetone, anhydrous ethanol and deionized water in sequence to remove surface oil stains, and then plasma treatment is performed to introduce hydroxyl active groups on the surface of the aluminum foil. In S1, after the aluminum foil is treated with plasma, it is further surface-modified with a silane coupling agent, wherein the silane coupling agent is selected from at least one of 3-aminopropyltriethoxysilane and 3-(2,3-epoxypropoxy)propyltrimethoxysilane. Surface modification steps: Immediately immerse the plasma-treated aluminum foil in the above-mentioned silane coupling agent hydrolysis solution (a 3% silane coupling agent ethanol solution with a pH of 5.0) for 2 hours.
[0028] S2, In-situ growth of imine-linked covalent organic frameworks: Aldehyde monomers and amino monomers are dissolved in a solvent in a certain proportion, a catalyst is added, and the mixture is stirred to obtain a precursor solution; the aluminum foil treated with S1 is immersed in the precursor solution, transferred to a high-pressure reactor and sealed, and reacted at 120°C for 24 hours to form an imine-linked covalent organic framework layer on the surface of the aluminum foil. In S2, the molar ratio of aldehyde monomer to amino monomer is 0.8:0.8, and the total monomer concentration is 15 mg / mL; the solvent is a mixture of DMAc and mesitylene at a volume ratio of 1:1.5; the catalyst is selected from formic acid, and the amount of catalyst used is 3% of the total monomer mass.
[0029] The aldehyde monomer is selected from 1,3,5-tris(4-formylphenyl)benzene; the amino monomer is selected from benzidine; S3, Post-synthesis reduction: Take out the aluminum foil with imine bond-linked covalent organic framework layer obtained in S2, immerse it in the reducing agent solution, the reduction temperature is 40℃, the reduction time is 4h, the imine bond in the imine bond-linked covalent organic framework is reduced to secondary amine bond, and the reduced aluminum foil material is placed in a nitrogen atmosphere at 180℃ for 3h. In S3, the reducing agent solution is an ethanol solution of sodium borohydride with a concentration of 0.2 M; the amount of reducing agent used is 2-5 times the amount of imine bonds in the covalent organic framework linked by imine bonds.
[0030] S4. Post-processing and drying: The reduced aluminum foil is taken out, washed, and dried to obtain organic framework composite aluminum foil.
[0031] In step S4, the aluminum foil was washed five times alternately with anhydrous ethanol and deionized water to remove residual reducing agent and byproducts from the surface. The washed aluminum foil was then placed in a vacuum drying oven and dried at 60°C for 12 hours. Example 3
[0032] This invention provides an ultrathin aluminum foil for liquid packaging, comprising an aluminum foil substrate and a flexible amine-bonded covalent organic framework barrier layer laminated on at least one surface thereon; The flexible amine-bonded covalent organic framework barrier layer is formed by aldehyde and amino monomers undergoing Schiff base reaction and Eschweiler-Clarke synchronous in-situ reduction reaction under the dual catalysis and reduction of formic acid. The connecting units in the covalent organic framework barrier layer are secondary amine bonds.
[0033] This invention also provides a method for preparing ultrathin aluminum foil for liquid packaging, comprising the following steps: S1. Aluminum foil pretreatment: The aluminum foil is ultrasonically cleaned with acetone, anhydrous ethanol and deionized water in sequence to remove surface oil stains, and then plasma treatment is performed to introduce hydroxyl active groups on the surface of the aluminum foil. In S1, after the aluminum foil is treated with plasma, it is further surface-modified with a silane coupling agent, wherein the silane coupling agent is selected from at least one of 3-aminopropyltriethoxysilane and 3-(2,3-epoxypropoxy)propyltrimethoxysilane. Surface modification steps: Immediately immerse the plasma-treated aluminum foil in the above-mentioned silane coupling agent hydrolysis solution (5% by mass ethanol solution of silane coupling agent at pH 5.5) for 4 hours.
[0034] S2, In-situ growth of imine-linked covalent organic frameworks: Aldehyde monomers and amino monomers are dissolved in a solvent in a certain proportion, a catalyst is added, and the mixture is stirred to obtain a precursor solution; aluminum foil treated with S1 is immersed in the precursor solution, transferred to a high-pressure reactor and sealed, and reacted at 150°C for 24 hours to form an imine-linked covalent organic framework layer on the surface of the aluminum foil. In S2, the molar ratio of aldehyde monomer to amino monomer is 0.5:1, and the total monomer concentration is 30 mg / mL; the solvent is a mixture of DMAc and mesitylene in a volume ratio of 1:2; the catalyst is selected from at least one of acetic acid, formic acid, and p-toluenesulfonic acid, and the amount of catalyst used is 5% of the total monomer mass.
[0035] The aldehyde monomer is selected from 2,4,6-tris(4-formylphenoxy)-1,3,5-triazine; the amino monomer is selected from tris(4-aminophenyl)amine; S3, Post-synthesis reduction: The aluminum foil with imine bond-linked covalent organic framework layer obtained in S2 is taken out and immersed in reducing agent solution. The reduction temperature is 60℃ and the reduction time is 6h. The imine bond in the imine bond-linked covalent organic framework is reduced to secondary amine bond. The reduced aluminum foil material is placed in a nitrogen atmosphere at 200℃ for 4h for heat treatment. In S3, the reducing agent solution is an ethanol solution of sodium borohydride with a concentration of 0.3 M; the amount of reducing agent used is 5 times the amount of imine bonds in the covalent organic framework linked by imine bonds.
[0036] S4. Post-processing and drying: The reduced aluminum foil is taken out, washed, and dried to obtain organic framework composite aluminum foil.
[0037] In step S4, the aluminum foil was washed five times alternately with anhydrous ethanol and deionized water to remove residual reducing agent and byproducts from the surface. The washed aluminum foil was then placed in a vacuum drying oven and dried at 60°C for 12 hours.
[0038] Comparative Example 1 Commercially available ultra-thin liquid packaging aluminum foil of the same specifications as in the examples (e.g., 30-50 μm thick) is directly selected without any surface cleaning, plasma activation, silane coupling agent modification, or COF in-situ growth or reduction treatment, and is kept in its factory condition.
[0039] Performance testing Oxygen permeability (OTR): Determined according to GB / T 1038-2000 "Test Method for Gas Permeability of Plastic Films and Sheets - Differential Pressure Method". The test gas is high-purity oxygen (99.99%), the test pressure difference is 0.1 MPa, and the result is expressed in cm³ / (m²·24h·0.1MPa). This indicator is used to evaluate the barrier layer's ability to suppress oxygen.
[0040] OTR change after bending: The sample was repeatedly folded 100 times on a 5 mm diameter shaft (folding angle 180°, rate 30 times / min), and the oxygen permeability after folding was determined according to the above OTR test method.
[0041] Citrate buffer (pH 3.0, simulating acidic fruit juice) and sodium carbonate buffer (pH 10.0, simulating alkaline cleaning agent / dairy product environment) were prepared separately. The samples were completely immersed in these media and stored in a 40°C incubator for 30 days. After removal, the samples were rinsed with deionized water, vacuum-dried at 60°C for 12 h, and then the OTR retention rate was tested.
[0042] Based on the above test items, the materials of Examples 1-3 and Comparative Example 1 were tested, and the test results are shown in the table below.
[0043] As can be seen from the table above, the aluminum foil prepared by this invention has excellent gas barrier properties, flexibility, and chemical corrosion resistance.
[0044] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.
Claims
1. A method for preparing ultrathin aluminum foil for liquid packaging, characterized in that, Includes the following steps: S1. Aluminum foil pretreatment: The aluminum foil is ultrasonically cleaned with acetone, anhydrous ethanol and deionized water in sequence to remove surface oil stains, and then plasma treatment is performed to introduce hydroxyl active groups on the surface of the aluminum foil. S2, In-situ growth of imine-linked covalent organic frameworks: Aldehyde and amino monomers are dissolved in a solvent in a certain proportion, a catalyst is added, and the mixture is stirred to obtain a precursor solution; aluminum foil treated with S1 is immersed in the precursor solution, transferred to a high-pressure reactor and sealed, and reacted at 100-150℃ for 24h to form an imine-linked covalent organic framework layer on the surface of the aluminum foil. S3, Post-synthesis reduction: Take out the aluminum foil with imine bond-linked covalent organic framework layer obtained in S2, immerse it in the reducing agent solution, reduce the temperature to 25℃-60℃, reduce the reduction time to 2-6h, reduce the imine bond in the imine bond-linked covalent organic framework to secondary amine bond, and place the reduced aluminum foil material in a nitrogen atmosphere at 150-200℃ for 1-4h. S4. Post-processing and drying: The reduced aluminum foil is taken out, washed, and dried to obtain organic framework composite aluminum foil.
2. The method for preparing an ultra-thin aluminum foil for liquid packaging according to claim 1, characterized in that, In S1, after plasma treatment, the aluminum foil is further surface-modified with a silane coupling agent, wherein the silane coupling agent is selected from at least one of 3-aminopropyltriethoxysilane and 3-(2,3-epoxypropoxy)propyltrimethoxysilane.
3. The method for preparing an ultrathin aluminum foil for liquid packaging according to claim 1, characterized in that, In S2, the molar ratio of aldehyde monomer to amino monomer is 1:0.5-0.5:
1.
4. The method for preparing an ultra-thin aluminum foil for liquid packaging according to claim 1, characterized in that, In S2, the solvent is a mixture of DMAc and mesitylene in a volume ratio of 1:0.5-2.
5. The method for preparing an ultrathin aluminum foil for liquid packaging according to claim 1, characterized in that, In S2, the catalyst is selected from at least one of acetic acid, formic acid, and p-toluenesulfonic acid, and the amount of catalyst used is 0.1%-5% of the total mass of the monomer.
6. The method for preparing an ultrathin aluminum foil for liquid packaging according to claim 1, characterized in that, In S2, the aldehyde compound monomer is selected from at least one of 1,3,5-tricarboxaldehydebenzene, 1,3,5-tris(4-formylphenyl)benzene, 2,4,6-tris(4-formylphenoxy)-1,3,5-triazine, and trialdehyde-resorcinol.
7. The method for preparing an ultrathin aluminum foil for liquid packaging according to claim 1, characterized in that, In S2, the amino compound monomer is selected from at least one of p-phenylenediamine, benzidine, tris(4-aminophenyl)amine, and tris(4-aminophenyl)benzene.
8. The method for preparing an ultrathin aluminum foil for liquid packaging according to claim 1, characterized in that, In S3, the reducing agent solution is an ethanol solution of sodium borohydride.
9. A method for preparing an ultrathin aluminum foil for liquid packaging according to claim 1, characterized in that, In S3, the amount of reducing agent used is 2-5 times the amount of imine bonds in the imine-linked covalent organic framework.
10. An ultra-thin aluminum foil for liquid packaging, characterized in that, The ultrathin aluminum foil for liquid packaging is prepared by the method described in any one of claims 1-9.