A double-sided aluminum-plated film and preparation method thereof

Abstract

The invention discloses a double-sided coated aluminum film and a preparation method thereof, and relates to the field of aluminum film products, including a base layer and a spray layer, wherein the spray layer is arranged on opposite sides of the base layer, and the spray layer is made of the following raw materials: 40-60 parts of waterborne polyurethane; 5-15 parts of modified coconut shell powder; 20-30 parts of polytetrahydrofuran; 2-6 parts of silane coupling agent; 5-10 parts of curing agent; 60-80 parts of ethanol; the modified coconut shell powder is made of the following raw materials: coconut shell powder, isopropyl alcohol, epichlorohydrin, hydroxypropyl chitosan and triethylenetetramine. The present application has the effect of improving the tensile strength of the aluminum film.

Description

Technical Field

[0001] The invention relates to the field of aluminum-plated film products, in particular to a double-sided coated aluminum-plated film and a preparation method thereof. Background Art

[0002] Aluminum-coated film is a composite flexible packaging material that is formed by coating an extremely thin layer of metal aluminum on the surface of a plastic film using a special process. The most commonly used processing method is vacuum aluminizing, which is to melt and evaporate the metal aluminum at high temperature under a high vacuum state, so that the aluminum vapor precipitates and accumulates on the surface of the plastic film, thereby giving the surface of the plastic film a metallic luster.

[0003] However, when the aluminized film is used for packaging, the aluminized film is not strong enough and is easy to break during the stretching process. Summary of the invention

[0004] In order to improve the tensile strength of an aluminum-plated film, the present application provides a double-sided coated aluminum-plated film and a preparation method thereof.

[0005] In the first aspect, the double-sided coated aluminum film provided in the present application adopts the following technical solution:

[0006] A double-sided coated aluminum-plated film comprises a base layer and a spray layer, wherein the spray layer is arranged on opposite sides of the base layer, and the spray layer is made of the following raw materials: 40-60 parts of waterborne polyurethane; 5-15 parts of modified coconut shell powder; 20-30 parts of polytetrahydrofuran; 2-6 parts of silane coupling agent; 5-10 parts of curing agent; and 60-80 parts of ethanol; the modified coconut shell powder is made of the following raw materials: coconut shell powder, isopropyl alcohol, epichlorohydrin, hydroxypropyl chitosan and triethylenetetramine.

[0007] By adopting the above technical scheme, the present application mixes water-based polyurethane, modified coconut shell powder, polytetrahydrofuran and other components and then coats them on the base layer to form a spray layer. Ethanol as a solvent helps to mix other components, while polytetrahydrofuran and modified coconut shell powder can enhance the mechanical strength of water-based polyurethane and further improve flexibility. The silane coupling agent improves the interface bonding between modified coconut shell powder and water-based polyurethane and polytetrahydrofuran, further improving the tensile strength of the spray layer.

[0008] Preferably, the preparation method of the modified coconut shell powder is: after mixing 10-20 parts by weight of coconut shell powder and 20-40 parts by weight of isopropanol, 2-6 parts by weight of epichlorohydrin, 3-9 parts by weight of hydroxypropyl chitosan and 2-8 parts by weight of triethylenetetramine are added in sequence, and the modified coconut shell powder is obtained after washing and drying.

[0009] By adopting the above technical scheme, the present application modifies the coconut shell powder, and epichlorohydrin and hydroxypropyl chitosan are attached to the surface of the coconut shell powder to form a three-dimensional network structure. The modified coconut shell powder is added as a component to the spray layer, which can improve the mechanical strength of the aluminum-plated film, make the spray layer tightly bonded to the substrate, and improve the overall performance of the film. At the same time, the coconut shell powder can improve the barrier properties of the film, reduce the permeability of oxygen and moisture, and thereby improve the stability of the aluminum-plated film.

[0010] Preferably, the weight ratio of the coconut shell powder, epichlorohydrin and hydroxypropyl chitosan is (2.4-3):1:(1.4-1.6).

[0011] By adopting the above technical scheme, when coconut shell powder, epichlorohydrin and hydroxypropyl chitosan are in a specific weight ratio, epichlorohydrin reacts with the hydroxyl group of hydroxypropyl chitosan to form a chemical cross-linked structure, which is then mixed with coconut shell powder, thereby further improving the adsorption performance of the coconut shell powder, thereby enabling the spray layer to better adhere to the base layer and improving the adhesion between the two.

[0012] Preferably, the polytetrahydrofuran is modified polytetrahydrofuran, and the preparation method of the modified polytetrahydrofuran is: 10-15 parts by weight of lignin, 10-20 parts by weight of polytetrahydrofuran, 6-10 parts by weight of methylenebisacrylamide, 3-12 parts by weight of KH550 and 10-20 parts by weight of dodecanol are mixed and stirred, washed and dried to obtain the modified polytetrahydrofuran.

[0013] By adopting the above technical scheme, the present application modifies polytetrahydrofuran, which is a polyether polyol with good flexibility. Methylenebisacrylamide is used as a cross-linking agent to cross-link lignin with polytetrahydrofuran. Lignin is filled on the surface of polytetrahydrofuran, further improving the stability and barrier properties of polytetrahydrofuran, thereby improving the barrier properties of the film and reducing the water permeability.

[0014] Preferably, the weight ratio of the polytetrahydrofuran, lignin and methylenebisacrylamide is 1:(0.8-1):(0.53-0.6).

[0015] By adopting the above technical scheme, when polytetrahydrofuran, lignin and methylenebisacrylamide are in a specific weight ratio, methylenebisacrylamide reacts with polytetrahydrofuran to form a three-dimensional network structure, and lignin is dispersed on the surface of polytetrahydrofuran, thereby improving the stability of polytetrahydrofuran and improving the mechanical strength of the modified polytetrahydrofuran, thereby improving the tensile strength and barrier properties of the film.

[0016] Preferably, the weight ratio of the waterborne polyurethane, modified coconut shell powder and modified polytetrahydrofuran is 1:(0.48-0.52):(0.24-0.3).

[0017] By adopting the above technical scheme, when the waterborne polyurethane, modified coconut shell powder and modified polytetrahydrofuran are in a specific weight ratio, the modified coconut shell powder can improve the compatibility between the components, enable the waterborne polyurethane and modified polytetrahydrofuran to be better combined, and further improve the tensile strength of the components, thereby improving the tensile strength and barrier properties of the film.

[0018] Preferably, the curing agent is selected from one of maleic anhydride and pyromellitic anhydride.

[0019] By adopting the above technical solution and selecting a suitable curing agent, the cross-linking between the hydroxyl groups in the waterborne polyurethane and the curing agent can be promoted, thereby improving the tensile strength of the film.

[0020] Preferably, the thickness of the sprayed layer is 30-50 μm.

[0021] By adopting the above technical solution, controlling the thickness of the spray layer can make the adhesion between the layers of the aluminum-plated film higher and improve the flatness of the aluminum-plated film.

[0022] Preferably, the preparation method of the waterborne polyurethane is as follows: 10-20 parts by weight of isophorone diisocyanate, 5-10 parts by weight of 4,4'-diphenylmethane diisocyanate, 20-40 parts by weight of polyvinyl alcohol and 1-2 parts by weight of a catalyst are heated and stirred; then 1-2 parts by weight of 2,2-dihydroxymethylpropionic acid and 10-30 parts by weight of acetone are added and stirred continuously, and then 1-3 parts by weight of triethylamine and 100-150 parts by weight of water are added and stirred uniformly to obtain the waterborne polyurethane.

[0023] By adopting the above technical scheme, the water-based polyurethane prepared by the method of the present application can improve the compatibility of the modified coconut shell powder and the water-based polyurethane, and make the modified coconut shell powder and polytetrahydrofuran in the water-based polyurethane uniform, thereby further improving the barrier properties of the film.

[0024] In the second aspect, the present application provides a method for preparing a double-sided coated aluminum film using the following technical solution:

[0025] A method for preparing a double-sided coated aluminum film comprises the following steps:

[0026] S1. Mix waterborne polyurethane, modified coconut shell powder, polytetrahydrofuran, silane coupling agent and ethanol, add curing agent, spray on the base layer, and cure naturally;

[0027] S2. Vacuum coating the sprayed layer.

[0028] By adopting the above technical solution, a protective layer is first sprayed on the base layer, and then an aluminum oxide layer is plated, so as to improve the stability of the film, thereby improving the mechanical strength and barrier properties of the film.

[0029] In summary, this application has the following beneficial technical effects:

[0030] 1. In the present application, waterborne polyurethane, modified coconut shell powder, polytetrahydrofuran and other components are mixed and coated on a base layer to form a spray coating. Ethanol as a solvent helps to mix other components, while polytetrahydrofuran and modified coconut shell powder can enhance the mechanical strength of waterborne polyurethane and further improve flexibility. Silane coupling agent improves the interface bonding between modified coconut shell powder and waterborne polyurethane and polytetrahydrofuran, further improving the tensile strength of the spray coating.

[0031] 2. The present application modifies the coconut shell powder, and epichlorohydrin and hydroxypropyl chitosan are attached to the surface of the coconut shell powder to form a three-dimensional network structure. The modified coconut shell powder is added as a component to the spray layer, which can improve the mechanical strength of the aluminum-plated film, make the spray layer tightly bonded to the substrate, and improve the overall performance of the film. At the same time, the coconut shell powder can improve the barrier properties of the film, reduce the permeability of oxygen and moisture, and thereby improve the stability of the aluminum-plated film. DETAILED DESCRIPTION

[0032] The present application is further described in detail below in conjunction with embodiments and comparative examples.

[0033] Preparation Example

[0034] Preparation Example 1

[0035] A method for preparing waterborne polyurethane comprises the following steps: heating 10g of isophorone diisocyanate, 5g of 4,4'-diphenylmethane diisocyanate, 20g of polyvinyl alcohol and 1g of dibutyltin dilaurate catalyst to 80°C, stirring for 60min at a rotation speed of 150r / min; then adding 1g of 2,2-dihydroxymethylpropionic acid and 10g of acetone, stirring for 30min, then adding 1g of triethylamine and 100g of water, stirring evenly for 10min at a rotation speed of 1000r / min, and obtaining waterborne polyurethane.

[0036] Preparation Example 2

[0037] A method for preparing waterborne polyurethane

[0038] 20g of isophorone diisocyanate, 10g of 4,4'-diphenylmethane diisocyanate, 40g of polyvinyl alcohol and 2g of dibutyltin dilaurate catalyst were heated to 80°C and stirred at a speed of 150r / min for 60min; then 2g of 2,2-dihydroxymethylpropionic acid and 30g of acetone were added and stirring was continued for 30min, then 3g of triethylamine and 150g of water were added and stirred evenly at a speed of 1000r / min for 10min to obtain waterborne polyurethane.

[0039] Example

[0040] Example 1

[0041] A method for preparing a double-sided coated aluminum film comprises the following steps:

[0042] S1. 40g of the waterborne polyurethane prepared in Preparation Example 1, 5g of modified coconut shell powder, 20g of polytetrahydrofuran, 2g of KH560 silane coupling agent and 60g of ethanol were mixed and stirred, and then 5g of maleic anhydride curing agent was added and sprayed on the base layer. The thickness of the spray layer was 30μm and the coating amount was 5g / m 2 After natural curing for 6 hours, it was sent to the oven for drying for 1 hour at a drying temperature of 100°C; the relative molecular weight of polytetrahydrofuran is 2000;

[0043] S2. The spray coating is vacuum coated in a vacuum evaporation machine, wherein the wire feeding speed of the aluminum wire is 210 mm / min, and the vacuum is evacuated until the evaporation vacuum degree is 4×10-4 mbar, and then the evaporation boat of the vacuum aluminum coating machine is heated to 1180°C, and oxygen is introduced at a flow rate of 13000 sccm. The substrate is polyethylene terephthalate.

[0044] The preparation method of the modified coconut shell powder is as follows: 10g coconut shell powder and 20g isopropanol are mixed and stirred at a temperature of 50°C for 4h, 2g epichlorohydrin, 3g hydroxypropyl chitosan and 2g triethylenetetramine are added in sequence and mixed and stirred at a temperature of 50°C for 4h, and then the mixture is washed and transferred to an oven and dried at a temperature of 80°C for 1h to obtain the modified coconut shell powder. Hydroxypropyl chitosan is purchased from lullaby23876.

[0045] Example 2

[0046] A method for preparing a double-sided coated aluminum film comprises the following steps:

[0047] S1. 60g of the waterborne polyurethane prepared in Preparation Example 2, 15g of modified coconut shell powder, 30g of polytetrahydrofuran, 6g of KH560 silane coupling agent and 80g of ethanol were mixed and stirred, and then 10g of pyromellitic anhydride curing agent was added and sprayed on the base layer. The thickness of the spray layer was 50μm and the coating amount was 5g / m 2 After natural curing for 6 hours, it was sent to the oven for drying for 1 hour at a drying temperature of 100°C; the relative molecular weight of polytetrahydrofuran is 2000;

[0048] S2. The spray coating is vacuum coated in a vacuum evaporation machine, wherein the wire feeding speed of the aluminum wire is 210 mm / min, and the vacuum is evacuated until the evaporation vacuum degree is 4×10-4 mbar, and then the evaporation boat of the vacuum aluminum coating machine is heated to 1180°C, and oxygen is introduced at a flow rate of 13000 sccm. The substrate is polyethylene terephthalate.

[0049] The preparation method of the modified coconut shell powder is as follows: 10g coconut shell powder and 20g isopropanol are mixed and stirred at a temperature of 50°C for 4h, 2g epichlorohydrin, 3g hydroxypropyl chitosan and 2g triethylenetetramine are added in sequence and mixed and stirred at a temperature of 50°C for 4h, and then the mixture is washed and transferred to an oven and dried at a temperature of 80°C for 1h to obtain the modified coconut shell powder. Hydroxypropyl chitosan is purchased from lullaby23876.

[0050] Example 3

[0051] A method for preparing a double-sided coated aluminum film comprises the following steps:

[0052] S1. 50g of the waterborne polyurethane prepared in Preparation Example 1, 10g of modified coconut shell powder, 25g of polytetrahydrofuran, 4g of KH560 silane coupling agent and 70g of ethanol were mixed and stirred, and then 7.5g of maleic anhydride curing agent was added and sprayed on the base layer. The thickness of the spray layer was 40μm and the coating amount was 5g / m 2 After natural curing for 6 hours, it was sent to the oven for drying for 1 hour at a drying temperature of 100°C; the relative molecular weight of polytetrahydrofuran is 2000;

[0053] S2. The spray coating is vacuum coated in a vacuum evaporation machine, wherein the wire feeding speed of the aluminum wire is 210 mm / min, and the vacuum is evacuated until the evaporation vacuum degree is 4×10-4 mbar, and then the evaporation boat of the vacuum aluminum coating machine is heated to 1180°C, and oxygen is introduced at a flow rate of 13000 sccm. The substrate is polyethylene terephthalate.

[0054] The preparation method of the modified coconut shell powder is as follows: 10g coconut shell powder and 20g isopropanol are mixed and stirred at a temperature of 50°C for 4h, 2g epichlorohydrin, 3g hydroxypropyl chitosan and 2g triethylenetetramine are added in sequence and mixed and stirred at a temperature of 50°C for 4h, and then the mixture is washed and transferred to an oven and dried at a temperature of 80°C for 1h to obtain the modified coconut shell powder. Hydroxypropyl chitosan is purchased from lullaby23876.

[0055] Example 4

[0056] A method for preparing a double-sided coated aluminum-plated film, which is different from Example 3 in that: the preparation method of the modified coconut shell powder is as follows: 20g of coconut shell powder and 40g of isopropanol are mixed and stirred at a temperature of 50°C for 4h, and then 6g of epichlorohydrin, 9g of hydroxypropyl chitosan and 8g of triethylenetetramine are added in sequence and mixed and stirred at a temperature of 50°C for 4h, and after washing, the mixture is transferred to an oven and dried at a temperature of 80°C for 1h to obtain the modified coconut shell powder.

[0057] Example 5

[0058] A method for preparing a double-sided coated aluminum-plated film, which is different from Example 4 in that: in the process of preparing the modified coconut shell powder, the input amount of coconut shell powder is 12g, the input amount of epichlorohydrin is 5g, and the input amount of hydroxypropyl chitosan is 7g.

[0059] Example 6

[0060] A method for preparing a double-sided coated aluminum-plated film, which is different from Example 3 in that: in the process of preparing the modified coconut shell powder, the input amount of coconut shell powder is 15g, the input amount of epichlorohydrin is 5g, and the input amount of hydroxypropyl chitosan is 8g.

[0061] Example 7

[0062] A method for preparing a double-sided coated aluminum-plated film, which is different from Example 6 in that: polytetrahydrofuran is replaced with modified polytetrahydrofuran in equal amounts, wherein the preparation method of the modified polytetrahydrofuran is as follows: 10g of lignin, 10g of polytetrahydrofuran, 6g of methylenebisacrylamide, 3g of KH550 and 10g of dodecanol are put into an ultrasonic cleaner, mixed and stirred at a temperature of 45°C for 30min, transferred to a constant temperature drying oven and dried at a temperature of 70°C for 8h, washed with anhydrous ethanol and dried in an oven at a temperature of 80°C for 1h to obtain modified polytetrahydrofuran.

[0063] Example 8

[0064] A method for preparing a double-sided coated aluminum-plated film, which is different from Example 6 in that: polytetrahydrofuran is replaced with modified polytetrahydrofuran in equal amounts, wherein the preparation method of the modified polytetrahydrofuran is as follows: 15g of lignin, 20g of polytetrahydrofuran, 10g of methylenebisacrylamide, 12g of KH550 and 20g of dodecanol are put into an ultrasonic cleaner, mixed and stirred at a temperature of 45°C for 30min, transferred to a constant temperature drying oven and dried at a temperature of 70°C for 8h, washed with anhydrous ethanol and dried in an oven at a temperature of 80°C for 1h to obtain modified polytetrahydrofuran.

[0065] Example 9

[0066] A method for preparing a double-sided coated aluminum-plated film, which is different from Example 7 in that: in the preparation method of modified polytetrahydrofuran, the input amount of polytetrahydrofuran is 15g, the input amount of lignin is 12g, and the input amount of methylenebisacrylamide is 8g.

[0067] Example 10

[0068] A method for preparing a double-sided coated aluminum-plated film, which is different from Example 7 in that: in the preparation method of modified polytetrahydrofuran, the input amount of polytetrahydrofuran is 15g, the input amount of lignin is 15g, and the input amount of methylenebisacrylamide is 9g.

[0069] Embodiment 11

[0070] A method for preparing a double-sided coated aluminum-plated film, which is different from Example 10 in that: the input amount of the water-based polyurethane prepared in Preparation Example 1 is 50g, the input amount of modified polytetrahydrofuran is 24g, and the input amount of modified coconut shell powder is 12g.

[0071] Example 12

[0072] A method for preparing a double-sided coated aluminum-plated film, which is different from Example 10 in that: the input amount of the water-based polyurethane prepared in Preparation Example 1 is 50g, the input amount of modified polytetrahydrofuran is 26g, and the input amount of modified coconut shell powder is 15g.

[0073] Comparative Example

[0074] Comparative Example 1

[0075] A method for preparing a double-sided coated aluminum-plated film, which is different from Example 3 in that an equal amount of modified coconut shell powder is replaced by coconut shell powder.

[0076] Comparative Example 2

[0077] A method for preparing a double-sided coated aluminum-plated film, which is different from Example 3 in that an equal amount of modified coconut shell powder is replaced with silicon dioxide.

[0078] Comparative Example 3

[0079] A method for preparing a double-sided coated aluminum film, which is different from Example 3 in that: polytetrahydrofuran is replaced with polyacrylamide in equal amounts, and the polyacrylamide is selected from Chongqing Haikuo Environmental Protection Technology Co., Ltd., model HK-5318.

[0080] Comparative Example 4

[0081] A method for preparing a double-sided coated aluminum-plated film, which is different from Example 3 in that an equal amount of polytetrahydrofuran is replaced with the water-based polyurethane prepared in Preparation Example 1.

[0082] Performance testing:

[0083] Light transmittance test: According to GB / T 2410-2008 “Determination of light transmittance and haze of transparent plastics”, the light transmittance of the films of Examples 1-12 and Comparative Examples 1-4 was tested.

[0084] Water vapor barrier property: According to ASTM F 1249, the water vapor permeability of the films of Examples 1 to 12 and Comparative Examples 1 to 4 was tested.

[0085] Tensile strength and aluminum coating adhesion test: Examples 1-12 and Comparative Examples 1-4 were tested for tensile strength and aluminum coating adhesion (expressed as the area of ​​aluminum coating shedding) in accordance with BB / T 0030-2019 "Aluminum-coated film for packaging".

[0086] Transmittance % Moisture permeability% Tensile strength MPa Adhesion % Example 1 85.9 0.7 226 0.4 Example 2 85.4 0.8 227 0.5 Example 3 85.7 0.7 227 0.3 Example 4 85.8 0.7 228 0.3 Example 5 88.3 0.5 233 0.1 Example 6 88.5 0.4 235 0.1 Example 7 90.8 0.4 239 No shedding Example 8 90.4 0.4 239 No shedding Example 9 92.4 0.4 244 No shedding Example 10 92.5 0.4 242 No shedding Embodiment 11 94.1 0.1 259 No shedding Example 12 94.3 0.1 261 No shedding Comparative Example 1 84.8 1.3 208 1.2 Comparative Example 2 80.7 1.6 215 5.6 Comparative Example 3 82.4 1.0 203 2.7 Comparative Example 4 82.6 1.2 211 1.6

[0087] According to the data comparison of Examples 1-4 and Comparative Examples 1-4, the present application mixes waterborne polyurethane, modified coconut shell powder, polytetrahydrofuran and other components and then applies them on the base layer to form a spray layer. Ethanol as a solvent helps to mix other components, while polytetrahydrofuran and modified coconut shell powder can enhance the mechanical strength of the waterborne polyurethane and further improve the flexibility. The silane coupling agent improves the interface bonding between the modified coconut shell powder and the waterborne polyurethane and polytetrahydrofuran, further improving the tensile strength of the spray layer. According to the data comparison of Examples 3 and 5-6, when coconut shell powder, epichlorohydrin and hydroxypropyl chitosan are in a specific weight ratio, epichlorohydrin reacts with the hydroxyl group of hydroxypropyl chitosan to form a chemical cross-linked structure, which is then mixed with coconut shell powder, which can further improve the adsorption performance of the coconut shell powder, thereby allowing the spray layer to better adhere to the base layer and improve the adhesion between the two.

[0088] According to the data comparison between Example 5 and Example 7-8, the present application modifies polytetrahydrofuran, which is a polyether polyol with good flexibility. Methylene bisacrylamide is used as a cross-linking agent to cross-link lignin with polytetrahydrofuran. Lignin is filled on the surface of polytetrahydrofuran, which further improves the stability and barrier properties of polytetrahydrofuran, thereby improving the barrier properties of the film and reducing the water permeability.

[0089] According to the data comparison of Example 7 and Examples 9-10, it can be obtained that when polytetrahydrofuran, lignin and methylenebisacrylamide are in a specific weight ratio, methylenebisacrylamide reacts with polytetrahydrofuran to form a three-dimensional network structure, and lignin is dispersed on the surface of polytetrahydrofuran, thereby improving the stability of polytetrahydrofuran and improving the mechanical strength of the modified polytetrahydrofuran, thereby improving the tensile strength and barrier properties of the film.

[0090] According to the data comparison of Examples 10-12, when the waterborne polyurethane, modified coconut shell powder and modified polytetrahydrofuran are in a specific weight ratio, the modified coconut shell powder can improve the compatibility between the components, enable a better combination of the waterborne polyurethane and the modified polytetrahydrofuran, and further improve the tensile strength of the components, thereby improving the tensile strength and barrier properties of the film.

[0091] The specific embodiments are merely explanations of the present application and are not limitations of the present application. After reading this specification, those skilled in the art may make modifications to the embodiments without any creative contribution as needed. However, as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A double-sided coated aluminum film, characterized in that: The invention comprises a base layer and a spray layer, wherein the spray layer is arranged on two opposite sides of the base layer, and the spray layer is made of the following raw materials: 40-60 parts of waterborne polyurethane; 5-15 parts of modified coconut shell powder; 20-30 parts of polytetrahydrofuran; 2-6 parts of silane coupling agent; 5-10 parts of curing agent; 60-80 parts of ethanol; the modified coconut shell powder is made of the following raw materials: coconut shell powder, isopropyl alcohol, epichlorohydrin, hydroxypropyl chitosan and triethylenetetramine; the preparation method of the modified coconut shell powder is as follows: 10-20 parts by weight of coconut shell powder and 20-40 parts by weight of isopropyl After the alcohol is mixed and stirred, 2-6 weight parts of epichlorohydrin, 3-9 weight parts of hydroxypropyl chitosan and 2-8 weight parts of triethylenetetramine are added in sequence, and the mixture is washed and dried to obtain the modified coconut shell powder; the polytetrahydrofuran is modified polytetrahydrofuran, and the preparation method of the modified polytetrahydrofuran is as follows: 10-15 weight parts of lignin, 10-20 weight parts of polytetrahydrofuran, 6-10 weight parts of methylenebisacrylamide, 3-12 weight parts of KH550 and 10-20 weight parts of dodecanol are mixed and stirred, washed and dried to obtain the modified polytetrahydrofuran.

2. A double-sided coated aluminum film according to claim 1, characterized in that: The weight ratio of the coconut shell powder, epichlorohydrin and hydroxypropyl chitosan is (2.4-3):1:(1.4-1.6).

3. The double-sided coated aluminum film according to claim 1, characterized in that: The weight ratio of the polytetrahydrofuran, lignin and methylenebisacrylamide is 1:(0.8-1):(0.53-0.6).

4. The double-sided coated aluminum film according to claim 1, characterized in that: The weight ratio of the waterborne polyurethane, the modified coconut shell powder and the modified polytetrahydrofuran is 1: (0.48-0.52): (0.24-0.3).

5. The double-sided coated aluminum film according to claim 1, characterized in that: The curing agent is selected from one of maleic anhydride and pyromellitic anhydride.

6. The double-sided coated aluminum film according to claim 1, characterized in that: The thickness of the sprayed layer is 30-50 μm.

7. The double-sided coated aluminum film according to claim 1, characterized in that: The preparation method of the waterborne polyurethane comprises: heating and stirring 10-20 parts by weight of isophorone diisocyanate, 5-10 parts by weight of 4,4'-diphenylmethane diisocyanate, 20-40 parts by weight of polyvinyl alcohol and 1-2 parts by weight of a catalyst; then adding 1-2 parts by weight of 2,2-dihydroxymethylpropionic acid and 10-30 parts by weight of acetone and continuing to stir, then adding 1-3 parts by weight of triethylamine and 100-150 parts by weight of water and stirring evenly to obtain the waterborne polyurethane.

8. A method for preparing a double-sided coated aluminum film, characterized in that: The method for preparing the double-sided coated aluminum film according to any one of claims 1 to 6 comprises the following steps: S1. Mix waterborne polyurethane, modified coconut shell powder, polytetrahydrofuran, silane coupling agent and ethanol, add curing agent, spray on the base layer, and cure naturally; S2. Vacuum coating the sprayed layer.