A composite aluminum foil film for food packaging and its preparation method

Abstract

This invention discloses an aluminum foil composite film for food packaging and its preparation method. The aluminum foil composite film comprises an inner layer, a middle layer, and a surface layer arranged sequentially from the inside out. The inner layer is a first base film, the middle layer is aluminum foil, and the surface layer is a modified second base film. The modified second base film comprises, by mass percentage, 70%–80% of the second base film material and 20%–30% of flame-retardant biomass-based aerogel. The flame-retardant biomass-based aerogel in the modified second base film of this invention contains flame-retardant elements such as silicon, copper, and phosphorus, and also introduces carbon nitride, giving the surface layer good thermal conductivity, flame retardancy, and antibacterial properties, thus improving the overall performance of the aluminum foil composite film and showing great promise for food packaging applications.

Description

Technical Field

[0001] This invention relates to the field of food packaging bag technology, and in particular to an aluminum foil composite film for food packaging and its preparation method. Background Technology

[0002] With the continuous improvement of people's living standards, higher requirements have been placed on food packaging, which is characterized by diversity, hygiene, convenience, and high-end design. Aluminum foil composite film is commonly used for packaging high-end fruits, meats, and soy products. Aluminum foil composite film typically consists of three layers, with a typical structure of an outer layer / aluminum foil / inner layer. Generally, the outer and inner layers are made of plastic film. Polypropylene, with its good impact resistance, recyclability, and short production cycle, is the most commonly used plastic film material.

[0003] Currently, the preparation process of aluminum foil composite films can involve bonding the layers with adhesives or extruding and blow molding the materials of each layer followed by hot pressing. For example, CN116215023A discloses a high-temperature resistant flame-retardant aluminum foil bag and its preparation method. The aluminum foil bag is made of an aluminum foil composite film, which includes a surface layer, an intermediate layer, and a substrate layer arranged sequentially from the outside to the inside. The surface layer and the substrate layer are functionalized silica-modified polyethylene flame-retardant composite films, and the intermediate layer is aluminum foil. The functionalized silica-modified polyethylene flame-retardant composite film uses nano-titanium dioxide as an inorganic additive to increase the flame retardancy of the composite film, mitigate the burning rate of the material, and reduce the total heat released by the material. At the same time, the addition of starch increases the mechanical properties of the composite film, while 9,10-dihydro-9oxa-10-phosphaphenanthrene-10-oxide and its derivatives act as flame retardants, improving the flame retardancy of the composite film material. This aluminum foil bag has good mechanical strength and flame retardant properties, but its inner layer contains flame retardants with unknown toxicological components, making it unsuitable for food packaging.

[0004] It remains essential to develop flame-retardant aluminum foil composite films for food packaging. Summary of the Invention

[0005] In order to solve the technical problems existing in the prior art, the present invention provides an aluminum foil composite film for food packaging, comprising an inner layer, a middle layer and a surface layer arranged sequentially from the inside to the outside, wherein the inner layer is a first base film, the middle layer is aluminum foil and the surface layer is a modified second base film;

[0006] The modified second base membrane comprises, by mass percentage, 70% to 80% of the second base membrane material and 20% to 30% of the flame-retardant biomass-based aerogel.

[0007] Furthermore, the preparation method of the flame-retardant biomass-based aerogel includes, by weight, the following:

[0008] Mix 2-5 parts carrageenan, 0.1-0.5 parts silicate, and 80-150 parts water to obtain a solution;

[0009] Add 0.5-2 parts of phytic acid and 0.2-0.5 parts of carbon nitride or dopamine-modified carbon nitride to the solution, stir and mix, and then freeze-dry to obtain flame-retardant biomass-based aerogel.

[0010] Carrageenan is a natural polysaccharide widely found in red algae such as *Euphorbia milii* and *Gelatinum aegyptium*. Carrageenan is widely available, has good water solubility and high viscosity, making it easy to prepare hydrogels. Furthermore, its high molecular weight, rich carbon content, and lack of flame-retardant components make it a suitable carbon source for flame-retardant systems. Silicate groups can interact with carrageenan through electrostatic adsorption and chemical bonding, and the silica formed by its high-temperature decomposition possesses certain flame-retardant properties. Phytic acid, rich in functional groups, promotes the interaction between silicate and carrageenan. Simultaneously, the introduction of phosphorus elements leads to thermal decomposition at high temperatures, producing non-combustible products such as phosphatic acid and phosphate esters, further inhibiting combustion.

[0011] Carbon nitride is a two-dimensional material containing -NH2 and -NH groups remaining after a thermal condensation reaction. These functional groups can react with the -OH groups in phytic acid, allowing carbon nitride to be embedded in flame-retardant biomass-based aerogels. The stable properties of carbon nitride contribute to the formation of a stable carbon layer structure, further inhibiting combustion.

[0012] Furthermore, the method for preparing dopamine-modified carbon nitride includes, by weight, the following:

[0013] Mix 1-3 parts carbon nitride, 0.2-0.5 parts dopamine hydrochloride, and 100-150 parts water and adjust the pH to 8.3-9.5 to obtain a suspension;

[0014] Add 0.5 to 1 part of soluble copper salt to the suspension and stir to react. Collect the insoluble matter to obtain dopamine-modified carbon nitride.

[0015] It should be noted that the type of soluble cobalt salt in this invention is not strictly limited and can be at least one of copper sulfate pentahydrate, copper nitrate trihydrate, copper acetate monohydrate, and copper chloride dihydrate.

[0016] Dopamine readily undergoes self-polymerization in an alkaline liquid environment. Modifying the surface of carbon nitride with a layer of polydopamine not only increases the number of groups on the carbon nitride surface that react with phytic acid, but also increases the number of carbon-forming species. Furthermore, this invention introduces copper ions. Polydopamine, carbon nitride, and phytic acid all have a certain chelating effect on copper ions, further enhancing the interaction. The species produced by copper at high temperatures can also, to some extent, promote the formation of a stable carbon layer, inhibit flue gas formation, and reduce combustion exothermics.

[0017] Furthermore, the method for preparing the carbon nitride includes,

[0018] The precursor was calcined in an oxygen-rich atmosphere at 500-600℃ for 2-5 hours to obtain carbon nitride.

[0019] The precursor includes at least one of urea, melamine, and dicyandiamide.

[0020] Furthermore, the method for preparing the carbon nitride includes,

[0021] The precursor is mixed with oxalic acid at a mass of 0.5 to 1 times that of the precursor and then calcined at 500 to 600°C in an aerobic atmosphere for 2 to 5 hours to obtain carbon nitride.

[0022] The precursor includes at least one of urea, melamine, and dicyandiamide.

[0023] Furthermore, the particle size of the carbon nitride is 300-500 mesh.

[0024] Furthermore, the silicate is at least one of sodium silicate and potassium silicate.

[0025] Furthermore, the particle size of the flame-retardant biomass-based aerogel is 500-800 mesh.

[0026] Furthermore, the thickness of the first base film is 10~50μm, and the material is polypropylene or polyethylene;

[0027] The thickness of the aluminum foil is 15~30μm;

[0028] The modified second base film has a thickness of 10~50μm, and the material of the second base film is polypropylene, polyethylene or polyester resin.

[0029] This invention also provides a method for preparing the above-mentioned aluminum foil composite film for food packaging, comprising,

[0030] The modified second base membrane is obtained by melting, plasticizing, and extruding blow molding the second base membrane material and flame-retardant biomass-based aerogel.

[0031] The modified second base film is hot-pressed onto the surface of aluminum foil, and then the material of the first base film is coated onto the other side of the aluminum foil to obtain an aluminum foil composite film for food packaging.

[0032] It should be noted that the melting, plasticizing, extrusion blow molding, hot pressing and coating processes in the preparation method of the present invention are all commonly used processes in the field and are not strictly limited; adjustments can be made as needed.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The modified second base film in the aluminum foil composite film of the present invention contains flame-retardant biomass-based aerogel with elements such as silicon, copper, and phosphorus, and also introduces carbon nitride, which makes the surface layer have good thermal conductivity, flame retardancy and antibacterial properties, thus improving the overall performance of the aluminum foil composite film and showing great promise in food packaging applications. Detailed Implementation

[0035] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0036] Description of some of the raw materials used in the embodiments of this invention:

[0037] Polypropylene, food grade, brand name F800E, purchased from Sinopec Shanghai Petrochemical Co., Ltd.

[0038] Aluminum foil, 20μm thick, custom-made by Shandong Fengshen Metal Products Co., Ltd.

[0039] Carrageenan, product number 11114-20-8, is type K carrageenan and was purchased from Hubei Xinyuhong Biomedical Technology Co., Ltd.

[0040] Phytic acid, model number JYS14715, was purchased from Wuhan Jiyesheng Chemical Co., Ltd.

[0041] All other unmentioned raw materials are common raw materials. The above content is only for illustrative purposes and should not be construed as a strict limitation of the present invention. Those skilled in the art can directly purchase commercially available raw materials or prepare the same / similar raw materials themselves. These contents will not be repeated in the embodiments.

[0042] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0043] A method for preparing an aluminum foil composite film for food packaging, comprising the following steps:

[0044] Step 1: Weigh out polypropylene and flame-retardant biomass-based aerogel at 80% and 20% by mass percentage, respectively.

[0045] Step 2: Polypropylene and flame-retardant biomass-based aerogel are fed into a two-stage screw extruder for melting and plasticizing, then pelletized, and then extruded and blow-molded to obtain polypropylene containing flame-retardant biomass-based aerogel, which is the modified second base film.

[0046] Step 3: The modified second base film is hot-pressed onto the surface of aluminum foil, and then polypropylene is coated onto the other side of the aluminum foil to obtain a composite film of aluminum foil for food packaging, wherein the inner layer is 15μm polypropylene, the middle layer is 20μm aluminum foil, and the surface layer is 15μm modified second base film.

[0047] The preparation method of flame-retardant biomass-based aerogel is as follows:

[0048] 1. Mix 3g of carrageenan, 0.3g of sodium silicate, and 100g of water to obtain a solution;

[0049] 2. Add 1.5g of phytic acid and 0.3g of carbon nitride to the solution, stir and mix, freeze dry at -55℃ for 36h, grind and sieve to obtain 500-mesh flame-retardant biomass-based aerogel.

[0050] The method for preparing carbon nitride is as follows: melamine is calcined in an air atmosphere at 550°C for 3 hours, ground, and then sieved to obtain 300-mesh carbon nitride. Example 2

[0051] A method for preparing an aluminum foil composite film for food packaging differs from Example 1 in that the carbon nitride is prepared by mixing melamine and oxalic acid in a mass ratio of 1:1, calcining the mixture in an air atmosphere at 550°C for 3 hours, grinding it, and then sieving it to obtain 300-mesh carbon nitride. Example 3

[0052] A method for preparing an aluminum foil composite film for food packaging differs from Example 1 in that, in the method for preparing the flame-retardant biomass-based aerogel, dopamine-modified carbon nitride is used instead of carbon nitride. The method for preparing dopamine-modified carbon nitride is as follows:

[0053] 1. Melamine was calcined at 550°C in air for 3 hours, ground, and then sieved to obtain 300-mesh carbon nitride;

[0054] 2. Stir 2g carbon nitride, 0.3g dopamine hydrochloride, and 120g water at 300rpm for 20min and adjust the pH to 8.5 to obtain a suspension;

[0055] 3. Add 0.5g of copper sulfate pentahydrate to the suspension and stir at 300rpm for 6h. Filter to collect the insoluble matter and wash it three times each with water and ethanol. Then dry it in a constant temperature oven at 120℃ for 8h to obtain dopamine-modified carbon nitride. Example 4

[0056] A method for preparing an aluminum foil composite film for food packaging differs from Example 1 in that, in the method for preparing the flame-retardant biomass-based aerogel, dopamine-modified carbon nitride is used instead of carbon nitride. The method for preparing dopamine-modified carbon nitride is as follows:

[0057] 1. Melamine and oxalic acid were mixed in a mass ratio of 1:1 and calcined in air at 550°C for 3 hours. After grinding, the mixture was sieved to obtain 300-mesh carbon nitride.

[0058] 2. Stir 2g carbon nitride, 0.3g dopamine hydrochloride, and 120g water at 300rpm for 20min and adjust the pH to 8.5 to obtain a suspension;

[0059] 3. Add 0.5g of copper sulfate pentahydrate to the suspension and stir at 300rpm for 6h. Filter to collect the insoluble matter and wash it three times each with water and ethanol. Then dry it in a constant temperature oven at 120℃ for 8h to obtain dopamine-modified carbon nitride.

[0060] Comparative Example 1

[0061] A method for preparing an aluminum foil composite film for food packaging, comprising the following steps:

[0062] Step 1: The polypropylene is fed into a two-stage screw extruder for melting and plasticizing, then pelletized, and then extruded and blow-molded to obtain a polypropylene film.

[0063] Step 2: Press the polypropylene film onto the surface of the aluminum foil, and then coat the other side of the aluminum foil with polypropylene to obtain a composite film for food packaging aluminum foil, wherein the inner layer is 15μm polypropylene, the middle layer is 20μm aluminum foil, and the outer layer is 15μm polypropylene film.

[0064] Comparative Example 2

[0065] A method for preparing an aluminum foil composite film for food packaging differs from Example 1 in that, in the method for preparing the flame-retardant biomass-based aerogel, dopamine-modified carbon nitride is used instead of carbon nitride. The method for preparing dopamine-modified carbon nitride is as follows:

[0066] 1. Melamine and oxalic acid were mixed in a mass ratio of 1:1 and calcined in air at 550°C for 3 hours. After grinding, the mixture was sieved to obtain 300-mesh carbon nitride.

[0067] 2. Stir 2g carbon nitride, 0.3g dopamine hydrochloride and 120g water at 300rpm for 20min and adjust the pH to 8.5 to obtain a suspension. Continue stirring at 300rpm for 6h. Filter to collect the insoluble matter and wash it three times each with water and ethanol. Then dry it in a constant temperature oven at 120℃ for 8h to obtain dopamine-modified carbon nitride.

[0068] According to standard ISO 5660-1-2015, cone calorimetry tests were performed on the surface materials of the aluminum foil composite films in the examples and comparative examples using a cone calorimeter, with a thermal irradiation power of 35 kW / m². 2 The results are shown in Table 1.

[0069] Table 1. Results of cone calorimetry test

[0070] <![CDATA[Total heat release (MJ / m 2 )]]> <![CDATA[Peak CO production rate (10 -4 g / s)]]> Example 1 26.33 25.4 Example 2 23.65 22.1 Example 3 19.28 8.8 Example 4 16.32 4.6 Comparative Example 1 42.98 53.6 Comparative Example 2 21.53 13.5

[0071] As can be seen from the test results in Table 1, compared with Comparative Example 1 containing pure polypropylene, the addition of silicon, phosphorus, and carbon nitride significantly reduced the total heat release and peak CO generation rate. Comparing Examples 1 and 2, and Examples 3 and 4 respectively, the addition of oxalic acid during the preparation of carbon nitride improved the flame retardant effect of the flame retardant system. This is because the decomposition of oxalic acid during calcination increases the specific surface area of ​​carbon nitride, allowing for better dispersion in the solution environment. This results in a more uniform dispersion of carbon nitride in the freeze-dried gel, forming a stable barrier and inhibiting CO release. Example 3 showed a better flame retardant effect than Example 2, indicating that dopamine modification of carbon nitride further improved the compatibility of carbon nitride with the carrageenan and sodium phosphate gel system. Example 4 showed a better flame retardant effect than Comparative Example 2 and Example 3. This is because the introduction of copper ions enhanced the interaction between carbon nitride and the carrageenan and sodium phosphate gel system, promoting carbon nitride dispersion. Furthermore, during high-temperature calcination, the copper species produced catalyzed the formation of a more stable carbon layer structure, inhibiting the release of harmful CO gas and reducing heat release.

[0072] The antibacterial properties of the surface materials in the examples and comparative examples were tested according to standard GB / T 31402-2015 "Test Method for Antibacterial Properties of Plastic Surfaces". Staphylococcus aureus (Staphylococcus aureus) was among the bacteria tested. Staphylococcus aureus ), strain number ATCC6538P; Escherichia coli ( Escherichia coli (Strain number ATCC 8739). The experimental results of the antibacterial rate obtained are shown in Table 2.

[0073] Table 2 Antibacterial Rate Test Results

[0074] Staphylococcus aureus inhibition rate (%) Escherichia coli inhibition rate (%) Example 3 86.3 91.3 Example 4 93.4 96.1 Comparative Example 2 83.1 85.9

[0075] As can be seen from the test results in Table 2, the surface materials of Examples 3 and 4 of the present invention have better antibacterial rates. This is because polydopamine has certain antibacterial properties, and the introduction of copper ions further improves the antibacterial rate of the material.

[0076] The thermal conductivity of the surface material of the aluminum foil composite film in the examples and comparative examples was tested using a thermal conductivity meter, and the results were recorded. The results are shown in Table 3.

[0077] Table 3 Thermal conductivity test results

[0078] Thermal conductivity (W / m·K) Example 1 0.27 Example 2 0.30 Example 3 0.33 Example 4 0.36 Comparative Example 1 0.22 Comparative Example 2 0.29

[0079] A higher thermal conductivity indicates a stronger ability of the material to transfer heat. This means that using it as a packaging material can more effectively dissipate heat and suppress the effects of external conditions, such as heat generated by sunlight, on packaged food. As can be seen from the test results in Table 3, the surface material of the aluminum foil composite film in Example 4 of this invention has the highest thermal conductivity. This is because carbon nitride is well dispersed in the flame-retardant biomass-based aerogel, forming excellent thermal conductivity channels.

[0080] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An aluminum foil composite film for food packaging, characterized in that, It includes an inner layer, a middle layer and a surface layer arranged sequentially from the inside out, wherein the inner layer is a first base film, the middle layer is an aluminum foil and the surface layer is a modified second base film; The modified second base membrane comprises, by mass percentage, 70% to 80% of the second base membrane material and 20% to 30% of the flame-retardant biomass-based aerogel. The preparation method of the flame-retardant biomass-based aerogel includes, by weight, the following: Mix 2-5 parts carrageenan, 0.1-0.5 parts silicate, and 80-150 parts water to obtain a solution; Add 0.5-2 parts of phytic acid and 0.2-0.5 parts of carbon nitride or dopamine-modified carbon nitride to the solution, stir and mix, and then freeze dry to obtain flame-retardant biomass-based aerogel. The method for preparing carbon nitride includes calcining a precursor in an aerobic atmosphere at 500-600°C for 2-5 hours to obtain carbon nitride; the precursor includes at least one of urea, melamine, and dicyandiamide; the method for preparing dopamine-modified carbon nitride, by weight, includes mixing 1-3 parts carbon nitride, 0.2-0.5 parts dopamine hydrochloride, and 100-150 parts water and adjusting the pH to 8.3-9.5 to obtain a suspension; adding 0.5-1 part soluble copper salt to the suspension and stirring to react, collecting the insoluble matter to obtain dopamine-modified carbon nitride; Alternatively, the method for preparing carbon nitride includes mixing a precursor with oxalic acid at a mass of 0.5 to 1 times that of the precursor and calcining the mixture in an aerobic atmosphere at 500 to 600°C for 2 to 5 hours to obtain carbon nitride; the precursor includes at least one of urea, melamine, and dicyandiamide.

2. The aluminum foil composite film for food packaging according to claim 1, characterized in that, The particle size of the carbon nitride is 300-500 mesh.

3. The aluminum foil composite film for food packaging according to claim 1, characterized in that, The silicate is at least one of sodium silicate and potassium silicate.

4. The aluminum foil composite film for food packaging according to claim 1, characterized in that, The flame-retardant biomass-based aerogel has a particle size of 500-800 mesh.

5. The aluminum foil composite film for food packaging according to claim 1, characterized in that, The thickness of the first base film is 10~50μm, and the material is polypropylene or polyethylene; The thickness of the aluminum foil is 15~30μm; The modified second base film has a thickness of 10~50μm, and the material of the second base film is polypropylene, polyethylene or polyester resin.

6. A method for preparing an aluminum foil composite film for food packaging as described in any one of claims 1 to 5, characterized in that, include, The modified second base membrane is obtained by melting, plasticizing, and extruding blow molding the second base membrane material and flame-retardant biomass-based aerogel. The modified second base film is hot-pressed onto the surface of aluminum foil, and then the material of the first base film is coated onto the other side of the aluminum foil to obtain an aluminum foil composite film for food packaging.