Preparation method and application of waterproof and electrolyte-resistant aluminum-plastic film

Abstract

The present invention discloses a method for preparing a waterproof, electrolyte-resistant aluminum-plastic film and its application. This method belongs to the technical field of polymer materials. The method sequentially laminates an aluminum foil layer and a polyamide layer onto the surface of a CPP film layer. 100 parts of epoxy resin, 10-80 parts of amino-terminated polyether, 5-50 parts of amino-terminated polyurethane, and 1-30 parts of glycidyl ether are dissolved in ethyl acetate. After sufficient and uniform dissolution, the resulting mixture is applied to the surface of the polyamide layer to a thickness of 2-3 μm. The film is then baked and cured to produce a waterproof, electrolyte-resistant aluminum-plastic film suitable for lithium battery packaging. This film exhibits adequate waterproofing and electrolyte corrosion resistance while maintaining its drawing depth limit.

Description

Technical Field

[0001] The present invention relates to the technical field related to lithium battery packaging, and in particular to a preparation method and application of a waterproof and electrolyte-resistant aluminum-plastic film. Background Art

[0002] Lithium battery packaging is becoming an increasingly common packaging format. Its main structure, from the inside out, consists of an inner protective layer, an aluminum foil layer, and an outer protective layer. The outer protective layer is primarily made of polyamide. Polyamide has high requirements for impact resistance, puncture resistance, heat resistance, and friction resistance. Its function is to protect the aluminum foil from scratches and provide sufficient deformation strength to prevent it from breaking during the molding process.

[0003] Since polyamide (PA) itself has strong hygroscopicity, its water barrier performance is poor. Therefore, water vapor can easily pass through the polyamide layer and contact the aluminum foil, causing corrosion of the aluminum foil layer over time, posing a safety hazard. At the same time, during the production of battery packs, there is a risk of electrolyte leakage to the polyamide surface, causing corrosion, affecting subsequent use. The existing technical solutions mainly improve and solve the problem by compounding PET on the polyamide surface. PET has many advantages such as wear resistance, high hardness, and strong solvent resistance, but its crystallization leads to high brittleness and low elongation at break, and the impact on the depth limit of the composite outer layer is much lower than that of pure polyamide, which greatly affects the size specifications of the battery, reduces the efficiency of use, and further increases the cost of raw materials.

[0004] Therefore, under the premise of controlling costs, a battery packaging material that is waterproof and resistant to electrolyte corrosion while not affecting the depth of punching is needed. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for preparing a waterproof and electrolyte-resistant aluminum-plastic film and its application. As a lithium battery package, the film has certain waterproof and electrolyte corrosion resistance properties while not affecting the drawing depth limit.

[0006] The present invention provides a method for preparing a waterproof and electrolyte-resistant aluminum-plastic film, comprising the following steps:

[0007] Ⅰ. Laminating a polyurethane adhesive layer on one side of the aluminum foil layer, and coating a polyolefin adhesive layer on the other side of the aluminum foil layer and then curing;

[0008] Ⅱ. A polypropylene film is applied to the surface of the aluminum foil layer coated with the polyolefin adhesive layer;

[0009] Ⅲ. In parts by weight, 100 parts of epoxy resin, 10 to 80 parts of amino-terminated polyether, 5 to 50 parts of amino-terminated polyurethane, and 1 to 30 parts of glycidyl ether were dissolved in ethyl acetate and fully dissolved to obtain a first composition;

[0010] Ⅳ. The first composition is applied to the surface of the aluminum foil layer coated with a polyurethane adhesive layer side, with a thickness of 2 to 3 μm, baked in an oven at 130 to 170 ℃ for 1 to 2 minutes, and then aged at 75 to 85 ℃ for 3 to 5 days to obtain a waterproof and electrolyte-resistant aluminum-plastic film.

[0011] Preferably or optionally, the polyurethane adhesive layer in step I is composed of a base polyol and a curing agent. The polyurethane is composed of a base polyol and a curing agent. The polyols include polyester polyols, polyether polyols, and polyurethane prepolymers derived from polyester polyols or polyether polyols. Aromatic diols and aliphatic diols may be added to adjust the hardness of the main structure. Curing agents include general-purpose isocyanates such as TDI, MDI, and PAPI; methylene isocyanates such as XDI, m-TMXDI, and p-TMXDI; aliphatic isocyanates, alicyclic isocyanates, and blocked isocyanates.

[0012] Preferably or optionally, the polyolefin adhesive layer in step I is selected from maleic anhydride grafted polypropylene, maleic anhydride grafted propylene-ethylene copolymer, maleic anhydride grafted propylene-butene copolymer, and maleic anhydride grafted propylene-octene copolymer.

[0013] Preferably or optionally, the epoxy resin in step III includes bisphenol A epoxy resin, bisphenol F epoxy resin, polyphenol glycidyl ether epoxy resin, aliphatic glycidyl ether epoxy resin, glycidyl ester epoxy resin, glycidyl amine epoxy resin, epoxidized olefin compound, heterocyclic epoxy resin, and mixed epoxy resin.

[0014] Preferably or optionally, the amino-terminated polyether in step III has a molecular weight of 100 to 10,000 and a functionality of 2.

[0015] Preferably or optionally, the amino-terminated polyurethane in step III is a linear polyurethane oligomer with a molecular weight of 500 to 10,000.

[0016] Preferably or optionally, the glycidyl ether in step III includes ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, butanediol diglycidyl ether, hexanediol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, bisphenol A diglycidyl ether, and bisphenol F diglycidyl ether.

[0017] Preferably or optionally, the glycidyl ether further includes glycerol triglycidyl ether, castor oil triglycidyl ether, trimethylolpropane triglycidyl ether, and propoxyglycerol triglycidyl ether.

[0018] A waterproof and electrolyte-resistant aluminum-plastic film based on any one of the above items is used for lithium battery packaging.

[0019] Beneficial Effects: The present invention produces a waterproof, electrolyte-resistant aluminum-plastic film. The first composition is prepared by dissolving an epoxy resin, an amino-terminated polyether, an amino-terminated polyurethane, and a glycidyl ether in ethyl acetate, and then coating the first composition on the surface of the battery packaging for curing. The present invention uses epoxy resin and amino-terminated polyurethane as the matrix resin materials. The epoxy resin can impart a higher base strength to the first composition, and the high density of polar groups on the surface imparts excellent adhesion to the coated polyamide. The other monomer, a linear oligomeric amino-terminated polyurethane, can achieve higher toughness by sacrificing some mechanical strength. Glycidyl ether can be used to weaken the forces between molecular chains and synergize with the amino-terminated polyether with a functionality of 2, significantly improving its processing performance without affecting the heat-sealing process. The waterproof, electrolyte-resistant aluminum-plastic film produced by the present invention is coated with the polyamide layer using the cured first composition, effectively preventing moisture from entering the interior of the packaging material, which could cause hydrolysis of the polyamide layer and corrosion of the aluminum foil layer. DETAILED DESCRIPTION

[0020] In the following description, numerous specific details are provided to provide a more thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without one or more of these details. In other instances, certain technical features well known in the art are not described to avoid confusion with the present invention.

[0021] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0022] The present invention will be further described below in conjunction with the examples. The examples are intended to explain the present invention and are not to be construed as limiting the present invention. Where specific techniques and reaction conditions are not specified in the examples, the techniques or conditions described in the literature in the art or the product instructions may be used. Any reagent, instrument or equipment not specified by manufacturer may be obtained commercially. Example

[0023] 100 parts of bisphenol A epoxy resin, 40 parts of amino-terminated polyether with a molecular weight of 2000, 15 parts of polyethylene glycol amino-terminated polyurethane, and 10 parts of butanediol diglycidyl ether were dissolved in ethyl acetate. After a polyamide with a thickness of 25 μm was applied to the surface of an aluminum foil, the mixture was applied to the polyamide surface with a thickness of 2 μm. The modified epoxy resin was initially cured in an oven at 150°C, and then placed in an 80°C environment and aged for 4 days with the outer polyurethane adhesive to fully cure the modified epoxy resin. In this embodiment, due to the excessive cross-linking caused by excessive epoxy groups in the molecular chain segments, the elongation at break was reduced, so diglycidyl ether was preferred. Taking into account the control of molecular weight and the improvement of elasticity of the molecular chain flexibility after polymerization, butanediol diglycidyl ether was further preferred. Example

[0024] 100 parts of epoxy resin, 50 parts of amino-terminated polyether with a molecular weight of 2000, 15 parts of polyethylene glycol type amino-terminated polyurethane,

[0025] 10 parts of butanediol diglycidyl ether were dissolved in ethyl acetate. After a 25 μm thick polyamide was applied to the surface of aluminum foil, the mixture was applied to the polyamide surface with a thickness of 2 μm. The mixture was baked in an oven at 150°C to initially cure the modified epoxy resin. It was then placed in an environment of 80°C and aged for 4 days with the outer layer of polyurethane adhesive to fully cure the modified epoxy resin. Example

[0026] 100 parts of epoxy resin, 50 parts of amino-terminated polyether with a molecular weight of 2000, 20 parts of polyethylene glycol amino-terminated polyurethane,

[0027] 10 parts of butanediol diglycidyl ether were dissolved in ethyl acetate. After a 25 μm thick polyamide was applied to the surface of aluminum foil, the mixture was applied to the polyamide surface with a thickness of 2 μm. The mixture was baked in an oven at 150°C to initially cure the modified epoxy resin. It was then placed in an environment of 80°C and aged for 4 days with the outer layer of polyurethane adhesive to fully cure the modified epoxy resin.

[0028] Comparative Example 1

[0029] The outer layer is made of pure polyamide with a thickness of 25μm. It is applied to the surface of aluminum foil according to our existing process and placed in an environment of 80℃.

[0030] Medium ripening 4 days.

[0031] Comparative Example 2

[0032] The outer layer is a combination of polyamide and PET, with PET on the outside, with a total thickness of 27μm, including 15μm polyamide and 12μm PET. It is adhered to the surface of aluminum foil according to our company's existing process and placed in an 80℃ environment for 4 days.

[0033] In the above examples and comparative examples, the thickness of the CPP layer is 45 μm, the thickness of the aluminum foil is 40 μm, and the thickness of the outer layer is 25-27 μm. Test method:

[0034] Forming limit test: Cut the aluminum-plastic film into 200mm*150mm samples and place them in the forming machine for deep punching;

[0035] Forming floatation: Deepen the mold to 80% of the limit, and place it in 50℃ water and 75℃, 90% RH oven for 1 week, 2 weeks, 4 weeks, and 9 weeks respectively;

[0036] Corrosion resistance of the outer surface: Use a dropper to drop a drop of electrolyte at five different locations on the outer surface. After leaving it at room temperature for 1 hour, wipe off the surface electrolyte and observe whether there is corrosion on the surface.

[0037] The test data is shown in Table 1 below:

[0038] Table 1

[0039] Pig: —No abnormality; ▲—Discoloration other than the horn; ▲▲—Discoloration at the horn; ●—Surface abnormality

[0040] The evaluation results demonstrate that the waterproof, electrolyte-resistant aluminum-plastic films produced in Examples 1-3 of the present invention offer significant advantages over existing packaging methods with pure polyamide and PET outer layers. Examples 1-3 maintain comparable waterproof performance to PET while maintaining a superior drawing depth limit. Furthermore, the aluminum-plastic films produced using this novel process exhibit a certain degree of corrosion resistance against electrolyte spills on the outer surface during battery pack production.

[0041] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

Claims

1. A method for preparing a waterproof and electrolyte-resistant aluminum-plastic film, characterized in that: The following steps are involved: Ⅰ. Laminating a polyurethane adhesive layer on one side of the aluminum foil layer, and coating a polyolefin adhesive layer on the other side of the aluminum foil layer and then curing; Ⅱ. A polypropylene film is applied to the surface of the aluminum foil layer coated with the polyolefin adhesive layer; III. In parts by weight, 100 parts of an epoxy resin, 10 to 80 parts of an amino-terminated polyether, 5 to 50 parts of an amino-terminated polyurethane, and 1 to 30 parts of a glycidyl ether are dissolved in ethyl acetate and dissolved uniformly to obtain a first composition; Ⅳ. The first composition is applied to the surface of the aluminum foil layer coated with a polyurethane adhesive layer side, having a thickness of 2 to 3 μm, baked in an oven at 130 to 170 ℃ for 1 to 2 minutes, and then aged at 75 to 85 ℃ for 3 to 5 days to obtain a waterproof and electrolyte-resistant aluminum-plastic film; The amino-terminated polyether in step III has a molecular weight of 100 to 10,000 and a functionality of 2; The amino-terminated polyurethane in step III is a linear polyurethane oligomer with a molecular weight of 500 to 10,000.

2. The method for preparing a waterproof and electrolyte-resistant aluminum-plastic film according to claim 1, wherein: The polyurethane bonding layer in step I is composed of a main agent polyol and a curing agent. The polyol includes polyester polyol, polyether polyol, and polyurethane prepolymer; the curing agent includes universal isocyanate, methylene isocyanate, aliphatic isocyanate, alicyclic isocyanate, and blocked isocyanate.

3. The method for preparing the waterproof and electrolyte-resistant aluminum-plastic film according to claim 1, wherein: The polyolefin adhesive layer in step I includes maleic anhydride grafted polypropylene, maleic anhydride grafted propylene-ethylene copolymer, maleic anhydride grafted propylene-butene copolymer, and maleic anhydride grafted propylene-octene copolymer.

4. The method for preparing the waterproof and electrolyte-resistant aluminum-plastic film according to claim 1, wherein: The epoxy resin in step III includes bisphenol A epoxy resin, bisphenol F epoxy resin, polyphenol glycidyl ether epoxy resin, aliphatic glycidyl ether epoxy resin, glycidyl ester epoxy resin, glycidyl amine epoxy resin, epoxidized olefin compound, heterocyclic epoxy resin, and mixed epoxy resin.

5. The method for preparing the waterproof and electrolyte-resistant aluminum-plastic film according to claim 1, wherein: The glycidyl ether in step III includes ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, butanediol diglycidyl ether, hexanediol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, bisphenol A diglycidyl ether, and bisphenol F diglycidyl ether.

6. The method for preparing the waterproof and electrolyte-resistant aluminum-plastic film according to claim 5, wherein: The glycidyl ethers also include glycerol triglycidyl ether, castor oil triglycidyl ether, trimethylolpropane triglycidyl ether, and propoxyglycerol triglycidyl ether.

7. An application of the waterproof and electrolyte-resistant aluminum-plastic film according to any one of claims 1 to 6, characterized in that: Used in lithium battery packaging.

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