A passivator for surface treatment of aluminum foil resistant to heat and moisture, a preparation method and application thereof

Abstract

The application discloses a passivator for treating the surface of aluminum foil resistant to heat and humidity, a preparation method and application. The passivator is suitable for the surface treatment of aluminum foil of aluminum-plastic film for lithium ion battery soft packaging and general soft packaging of food, medicine, daily chemicals and the like. The passivator contains: a trivalent chromium compound (A), a fluorine-containing compound (B) and an epoxy-modified alkyd resin (C). The content of the trivalent chromium compound (A) is 5-60% based on the total mass of the passivator solid, the content of the fluorine-containing compound (B) is 0.01-20%, and the content of the epoxy-modified alkyd resin (C) is preferably 30-90%. The application can form a dense, strongly adhesive passivation film with excellent heat resistance and chemical resistance on the surface of the aluminum foil. The passivation film can meet the affinity requirement of the adhesive for the dry process and can resist the high-temperature compounding condition of the hot process, realizes the general use of the passivator in the dry process and the hot process, and greatly improves the production efficiency and process flexibility.

Description

Technical Field

[0001] This invention relates to the field of metal material surface treatment technology, specifically to a passivating agent for aluminum-plastic film, and more specifically, to a passivating agent for aluminum foil surface treatment with excellent resistance to damp heat, applicable to both dry and hot composite processes of aluminum-plastic film for lithium-ion battery soft packaging and general soft packaging such as food, pharmaceuticals, and daily chemicals, and also to its preparation method and application. Background Technology

[0002] Aluminum-plastic film is widely used in flexible packaging for lithium-ion batteries and general flexible packaging for food, pharmaceuticals, and daily chemicals due to its excellent barrier properties, good mechanical properties, and deep-drawing resistance. The core structure of aluminum-plastic film typically consists of a nylon layer (outer layer), an aluminum foil layer (middle layer), and a polypropylene layer (inner layer). The anti-corrosion treatment (passivation treatment) of the aluminum foil layer directly affects the overall performance of the aluminum-plastic film, particularly its resistance to electrolyte corrosion and damp heat aging in the lithium battery field, and its resistance to media erosion, damp heat aging, and shelf-life stability in the food, pharmaceutical, and daily chemical packaging fields.

[0003] Currently, the production processes for aluminum-plastic film are mainly divided into dry and thermal processes. The dry process involves laminating an aluminum foil layer and a polypropylene layer using an adhesive, without requiring high-temperature treatment. The thermal process, on the other hand, uses modified polypropylene (MPP) as a heat-sealing adhesive layer between an aluminum foil layer and a cast polypropylene (CPP) layer, laminating them under heat and pressure. Because the two processes have different requirements for the passivation film—for example, heat resistance and adhesion to adhesives or MPP—existing aluminum-plastic film passivating agents are typically only suitable for one of the processes and cannot be universally applied (i.e., simultaneously applicable to both dry and thermal lamination processes). This causes inconvenience for inventory management and process switching for lithium battery packaging and general flexible packaging manufacturers in the food, pharmaceutical, and daily chemical industries, impacting production efficiency.

[0004] Furthermore, to meet the stringent requirements of high reliability and long cycle life for packaging in the lithium battery new energy sector, and the core needs of the food, pharmaceutical, and daily chemical sectors for packaging safety, resistance to media, and shelf life, all types of aluminum-plastic films must possess excellent resistance to damp heat aging. In existing technologies, improving damp heat resistance often relies on modifying the adhesive formulation of the outer or inner layer, such as using more expensive specialty resins or adding functional additives. This method not only increases material costs but also offers limited performance improvements, failing to fundamentally solve the problems of corrosion and decreased interfacial adhesion of the aluminum foil substrate in humid and hot environments. It cannot fully meet the electrolyte corrosion protection requirements of lithium batteries, nor can it adapt to the various media erosion protection requirements of food, pharmaceutical, and daily chemical packaging.

[0005] Therefore, developing a passivating agent that is compatible with both dry and thermal composite preparation processes for aluminum-plastic films, can effectively improve the damp heat resistance of aluminum foil through the passivation layer itself, and simultaneously meets the electrolyte resistance requirements of lithium-ion battery soft packaging and the media erosion resistance requirements of general soft packaging for food, pharmaceuticals, and daily chemicals, thereby reducing reliance on expensive adhesives, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] (a) Technical problems to be solved This invention aims to solve the following problems existing in the prior art: First, it provides a universal passivating agent that can be applied to both dry and thermal preparation processes of aluminum-plastic film, thereby improving the flexibility and efficiency of lithium-ion battery soft packaging and general soft packaging for food, pharmaceuticals, and daily chemicals; Second, through the improvement of the passivating agent formulation, it significantly enhances the resistance of aluminum foil to damp heat, while strengthening the aluminum foil's resistance to lithium battery electrolyte corrosion and the erosion of general media in food, pharmaceuticals, and daily chemicals, solving the corrosion protection problem from the aluminum foil substrate level, reducing the dependence on adhesive modification, and thus reducing production costs.

[0007] (II) Technical Solution Option 1: A passivating agent for surface treatment of aluminum foil that is resistant to moisture and heat. To solve the above technical problems, the present invention provides a passivating agent for surface treatment of aluminum foil that is resistant to moisture and heat, the passivating agent containing: a trivalent chromium compound (A), a fluorine-containing compound (B), and an epoxy-modified alkyd resin (C). Based on the total mass of the passivating agent solids, the content of the trivalent chromium compound (A) is 5% to 60%, the content of the fluorine-containing compound (B) is 0.01% to 20%, and the content of the epoxy-modified alkyd resin (C) is preferably 30% to 90%. The epoxy-modified alkyd resin is prepared by reacting acid anhydride S, polyol P and epoxy compound O. The general structural formula of the acid anhydride S is shown in formula (I): (I) And n is an integer from 2 to 7; R1 is independently selected from hydrogen, substituted or unsubstituted hydrocarbon group, alkoxy carbonyl group or amide group; the chemical bond between adjacent carbon atoms forming the anhydride ring skeleton is optionally a single bond or a double bond; The general structural formula of the polyol P is shown in formula (II): (II) And m is an integer from 3 to 10, and R2 is independently selected from hydrogen, alkyl, alkoxycarbonyl, amide or hydroxyl.

[0008] More preferably, the general structural formula of the epoxy compound O is shown in formula (III): (III); Wherein, R3 is a divalent linking group, preferably an alkylene, arylene, alkylene aryl or the above-mentioned group containing an ether bond with 1 to 20 carbon atoms; more preferably, R3 is -CH2-O-C6H4-C(CH3)2-C6H4-O-CH2-.

[0009] Option 2: Preparation method of the above passivating agent The present invention also provides a method for preparing the above-mentioned passivating agent for surface treatment of aluminum foil that is resistant to moisture and heat. The preparation method involves adding a trivalent chromium compound (A) and a fluorine-containing compound (B) to deionized water at room temperature and stirring to dissolve them; then adding an epoxy-modified alkyd resin (C) according to the ratio and continuing to stir and disperse to obtain the passivating agent.

[0010] The above preparation method also includes a step of preparing epoxy-modified alkyd resin, comprising the following steps: Step 1: Mix acid anhydride S, polyol P, and solvent accounting for 10-20% of the total mass of acid anhydride S and polyol P; Step 2: After step 1, heat the mixture at 150°C to 220°C for 4 to 8 hours; Step 3: After step 2, add epoxy compound O and mix, then heat at 180℃~220℃ for 4 to 6 hours.

[0011] In the above preparation method, the solvent is an aromatic hydrocarbon solvent, preferably toluene, with a purity preferably ≥99%; the acid anhydride has a purity preferably ≥99.5%; the polyol P has a purity preferably ≥99%; and the epoxide O has a purity preferably ≥99%.

[0012] Option 3: Manufacturing method of aluminum foil with passivation film and corrosion prevention method of aluminum foil. The present invention further provides a method for manufacturing aluminum foil with a passivation film, the method comprising the steps of contacting the aluminum foil with the aluminum foil passivating agent described in any of the foregoing technical solutions and performing a drying treatment, the aluminum foil with passivation film obtained can be used in the preparation of aluminum-plastic films for soft packaging of lithium-ion batteries and general soft packaging for food, medicine, daily chemicals and other products.

[0013] Meanwhile, the present invention also provides a method for preventing corrosion of aluminum foil. The method involves contacting the aluminum foil with the aforementioned passivating agent to form a dense passivation film on its surface. This passivation film can effectively block the corrosion of aluminum foil by water vapor, lithium battery electrolyte, and common media in food / pharmaceutical / daily chemical products (acids, alcohols, oils, surfactants, pharmaceutical solutions, etc.). Furthermore, trivalent chromium and fluorine-containing compounds form a stable coordination structure in the passivation film, and the migration / dissolution amount meets the mandatory standards of various fields. At the same time, it ensures the interfacial bonding force between the aluminum foil and each layer of the aluminum-plastic film, and is suitable for both dry and thermal composite processes.

[0014] In the above method, the contact method is preferably coating (such as roller coating, spray coating, etc.), the drying temperature is preferably 100℃~250℃, and the time is preferably 1~5 minutes; for food / pharmaceutical applications, the drying temperature is more preferably 150~220℃, and the time is more preferably 3~5 minutes to ensure that the passivation film is completely cured and the degree of crosslinking is ≥90%.

[0015] (III) Beneficial Effects Compared with the prior art, the present invention has the following significant advantages: 1. Achieving process universality and adapting to production needs across all fields: This invention utilizes the synergistic effect of specific ternary components (compliant trivalent chromium compound, food / pharmaceutical grade fluorinated compound, and epoxy-modified alkyd resin) to form a dense, strongly adhesive, and stable passivation film with excellent heat and chemical resistance on the aluminum foil surface. This passivation film meets the affinity requirements of adhesives in dry processes and can withstand the high-temperature composite conditions of thermal processes, achieving universality of the passivating agent in both dry and thermal processes. This significantly improves the efficiency and process flexibility of lithium-ion battery soft packaging and general soft packaging for food, pharmaceuticals, and daily chemicals, solving the inventory management and process switching problems for both types of packaging manufacturers.

[0016] 2. Dual-Effect Corrosion Protection and Compliant Composition, Achieving Performance Standards Across All Fields: This invention uniquely introduces an epoxy-modified alkyd resin with a specific structure. This resin acts as a cross-linking enhancement and barrier in the passivation film, significantly improving the passivation film's ability to block moisture. Simultaneously, it achieves dual corrosion protection against lithium battery electrolytes and general media in food, pharmaceuticals, and daily chemicals. Furthermore, through compliant raw material requirements and optimized process parameters, the migration / dissolution of trivalent chromium and fluorine compounds strictly complies with the GB 4806 series for food, the YBB standard for pharmaceuticals, and the specifications for the daily chemical industry. This achieves the dual goals of corrosion protection and composition compliance in two scenarios at the aluminum foil substrate level. As can be seen from the example data, after applying the passivating agent of this invention, the aluminum-plastic film, after two weeks of damp heat aging at 85℃ / 85%RH, not only shows no blistering or delamination in appearance but also exhibits high peel strength retention (score of 0). It maintains excellent interfacial adhesion even after immersion in electrolytes, food, pharmaceuticals, and daily chemical media, while the migration of components is far below the limits for each field. This makes improving the overall performance of aluminum-plastic film no longer solely dependent on expensive adhesive modifications, effectively reducing the overall production cost of lithium battery soft packaging and general soft packaging.

[0017] 3. Environmentally friendly and safe, meeting environmental standards in both fields: The trivalent chromium compounds used in this invention have a much lower toxicity than hexavalent chromium, and the content of hexavalent chromium impurities is strictly controlled. Highly polluting components such as PFAS are prohibited in fluorinated compounds. All raw materials are of high purity and low impurities. The preparation process enhances solvent removal, with residual amounts ≤3mg / m³. 2 It meets the current environmental protection requirements of industrial production and is an environmentally friendly passivation treatment solution. It not only meets the green production standards in the field of lithium battery new energy, but also adapts to the food contact grade and pharmaceutical grade environmental protection standards for food and pharmaceutical packaging, while meeting the safety requirements of daily chemical packaging.

[0018] 4. High production adaptability, no need to adjust the formula across fields: The passivating agent formula of this invention is a universal formula for all fields. It is only necessary to replace the food-grade / pharmaceutical-grade / industrial-grade aluminum-plastic film raw materials according to the application scenario. There is no need to adjust the passivating agent ratio and core preparation process, which greatly reduces the equipment, process and raw material costs of enterprises for cross-field production and improves production flexibility. Detailed Implementation

[0019] The present invention will now be described in detail through specific embodiments. It should be noted that the numerical range indicated by "~" in the present invention refers to the range including the values ​​before and after "~" as both the lower and upper limits. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer.

[0020] Passivating agent for surface treatment of heat- and moisture-resistant aluminum foil The passivating agent for surface treatment of aluminum foil that is resistant to damp heat provided in this embodiment contains: a trivalent chromium compound (A), a fluorine-containing compound (B), and an epoxy-modified alkyd resin (C).

[0021] In this passivating agent for aluminum foil surface treatment, the content of trivalent chromium compound (A) is preferably 5% to 60% based on the total mass of the passivating agent solids, the content of fluorine-containing compound (B) is preferably 0.01% to 20%, and the content of epoxy-modified alkyd resin (C) is preferably 30% to 90%.

[0022] <Trivalent Chromium Compound (A)> Trivalent chromium compound (A): can be selected from one or more of chromium sulfate, chromium nitrate, chromium acetate, chromium fluoride, and chromium phosphate. Specifically, food-grade raw materials with a purity ≥99.5% are preferred, with hexavalent chromium impurity content ≤0.001% and total heavy metal (lead, cadmium, mercury) impurities ≤0.0005%. Among them, hexavalent chromium (Cr... 6+ Impurity content ≤0.001%, to avoid the introduction of toxic impurities that may affect safety in various fields; total heavy metal (lead, cadmium, mercury) impurities ≤0.0005%, in line with food / pharmaceutical grade raw material standards.

[0023] The trivalent chromium compound (A) exhibits excellent synergistic effects with fluorinated compounds and epoxy-modified alkyd resins, forming a stable chromium salt passivation layer on the aluminum foil surface and improving the density of the passivation film. Furthermore, the content of the trivalent chromium compound (A) is preferably between 5% and 60%. When the content is <5%, a complete passivation substrate cannot be formed, significantly reducing the corrosion resistance of the aluminum foil and failing to prevent corrosion from electrolytes / general media. When the content is >60%, the chromium salt content in the passivation film is too high, easily leading to crystallization and precipitation, resulting in decreased adhesion of the passivation film and increased risk of component migration, failing to meet compliance requirements in the food / pharmaceutical fields. Within the content range of 5% to 60%, examples include 5%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, and 60%, achieving an optimal balance between passivation film density, adhesion, and corrosion resistance, while keeping migration within limits.

[0024] <Fluorine-containing compounds (B)> Fluorine-containing compound (B): selected from one or more of zirconium fluoride, titanium fluoride, hydrofluoric acid, and fluorosilicic acid. Specifically, the purity of the selected fluorine-containing compound (B) is ≥99.0%, the total amount of heavy metal (lead, cadmium, mercury) impurities is ≤0.0005%, and no harmful impurities are leached out.

[0025] The fluorinated compound (B) can form a coordination structure with trivalent chromium compounds, fill the pores of the passivation film, improve the passivation film's barrier ability against various media, and has good compatibility with epoxy-modified alkyd resin.

[0026] Regarding the content of the fluorinated compound (B), when the content is <0.01%, the substrate cannot react effectively, resulting in insufficient density of the passivation film and decreased resistance to electrolyte / general media corrosion. When the content is >20%, the excessive fluorinated compound will reduce the adhesion between the passivation film and the aluminum foil, and the compatibility with epoxy-modified alkyd resin will deteriorate, leading to easy cracking of the passivation film and increasing the risk of fluoride ion migration. The content in the range of 0.01% to 20%, for example, can be 0.01%, 0.05%, 0.1%, 0.5%, 0.8%, 1%, 4%, 6%, 10%, 14%, 15%, 20%, etc., can synergistically form a dense passivation film with trivalent chromium compounds, achieving the best balance between barrier performance and adhesion, and the amount of fluoride ion migration meets the limits of various fields.

[0027] <Epoxy-modified alkyd resin (C)> Epoxy-modified alkyd resin (C) is the core component of this passivating agent for surface treatment of moisture-resistant aluminum foil. Preferably, the epoxy-modified alkyd resin (C) is prepared by reacting raw materials containing acid anhydride S, polyol P, and epoxy compound O. In the passivation film, it plays a role in crosslinking enhancement, barrier protection, and improving interfacial adhesion. This resin structure can simultaneously meet the electrolyte resistance requirements of lithium battery flexible packaging aluminum foil and the dielectric corrosion resistance and composition compliance requirements of food / pharmaceutical / daily chemical general-purpose flexible packaging aluminum foil. It forms a densely crosslinked protective layer in the passivation film, while simultaneously encapsulating trivalent chromium and fluorine-containing compounds, reducing the risk of component migration.

[0028] The general structural formula of the acid anhydride S is shown in formula (I), where n is an integer from 2 to 7, preferably an integer from 2 to 4; R1 is independently selected from hydrogen, substituted or unsubstituted hydrocarbon groups, alkoxycarbonyl groups, or amide groups. In particular, the chemical bonds between adjacent carbon atoms constituting the anhydride ring skeleton are optionally single or double bonds.

[0029] (I) Specifically, when the chemical bond between adjacent carbon atoms forming the anhydride ring is a single bond (i.e., a saturated anhydride), R1 can be located in a saturated sp... 3 On a hybrid carbon atom. If R1 is selected from a substituted or unsubstituted hydrocarbon group, the hydrocarbon group is preferably an alkyl group of C1 to C6, an aryl group of C6 to C12, or an aralkyl group of C7 to C14; if R1 is an alkoxycarbonyl group or an amide group, an ester group or an amide group can be introduced into the anhydride backbone, which helps to adjust the polarity of the final epoxy-modified alkyd resin and its adhesion to the aluminum foil surface.

[0030] When the chemical bond between adjacent carbon atoms forming the anhydride ring is a double bond (i.e., unsaturated anhydrides, such as maleic anhydrides), since the double bond carbon atom is sp... 2The structure is hybridized, with adjacent carbon atoms, carbonyl carbons, and R1 (usually H or a small amount of alkyl / aryl). The presence of this unsaturated structure can introduce crosslinkable carbon-carbon double bonds in the subsequent synthesis of epoxy-modified alkyd resins, further improving the crosslinking density and heat resistance of the passivation film.

[0031] Furthermore, the crosslinking density and flexibility of the final resin can be effectively adjusted by controlling the value of n. Specifically, when n is less than 2, a resin network that combines flexibility and density cannot be obtained; when n > 7, the anhydride chain is too long, the resin molecular chain is too flexible, the spacing between crosslinking points increases, the cohesive strength of the passivation film decreases, the density is insufficient, and the corrosion resistance and adhesion decrease; when n is in the range of 2 to 7, the resin crosslinking density is moderate, and the density and flexibility of the passivation film reach the optimal balance.

[0032] As an example, the anhydride S based on the general structural formula (I) can be succinic anhydride (n=2, single bond, CAS: 108-30-5), maleic anhydride (n=2, double bond, CAS: 108-31-6), glutaric anhydride (n=3, single bond, CAS: 108-55-4), 2-methylsuccinic anhydride (CAS: 4100-80-5), 2-phenylsuccinic anhydride (CAS: 766-96-1), 2-ethoxycarbonylsuccinic anhydride (CAS: 19280-48-9), or 2-carbamoylsuccinic anhydride.

[0033] Specifically, in this scheme, the acid anhydride based on the general structural formula (I) is preferably aliphatic dicarboxylic acid anhydride; more preferably, the purity is ≥99.5%. High-purity aliphatic dicarboxylic acid anhydride can ensure the uniformity of cross-linking in resin synthesis, improve the density of the passivation film, and avoid the introduction of impurities that affect the safety of food / pharmaceutical packaging and the electrolyte compatibility of lithium battery packaging. Furthermore, no harmful impurities are leached, meeting the compliance requirements of various fields. The amount of this acid anhydride used is 30%–50% of the total mass of the resin raw materials. When the content is <30%, the resin carboxyl content is insufficient, resulting in decreased adhesion to the aluminum foil; when the content is >50%, the resin cross-linking is too high, increasing the brittleness of the passivation film and making it prone to cracking.

[0034] The general structural formula of polyol P is shown in formula (II), where m is an integer from 3 to 10; R2 is independently selected from hydrogen, substituted or unsubstituted hydrocarbon group, alkoxycarbonyl group, amide or hydroxyl group.

[0035] (II).

[0036] As an example, in formula (II), when R2 is hydrogen, the corresponding polyol P is preferably: 1,5-pentanediol (m=3, total carbon number 5), 1,6-hexanediol (m=4, total carbon number 6), 1,8-octanediol (m=6, total carbon number 8), 1,10-decanediol (m=8, total carbon number 10), 1,12-dodecanediol (m=10, total carbon number 12), etc. When R2 is a hydrocarbon group, the corresponding polyol P can be selected from 2-methyl-1,5-pentanediol (R2 is methyl, m=3, total carbon number 5), 2-ethyl-1,5-pentanediol (R2 is ethyl, m=3), 2-phenyl-1,5-pentanediol (R2 is phenyl, m=3) or 2-hydroxymethyl-1,5-pentanediol (R2 is hydroxymethyl, belongs to substituted hydrocarbon group, m=4, total carbon number 6), etc. When R2 is an alkoxycarbonyl group, the corresponding polyol P can be selected from 2-ethoxycarbonyl-1,5-pentanediol (R2 is -COOC2H5, m=3), etc. When R2 is a hydroxyl group, the corresponding polyol P can be 2-hydroxy-1,6-hexanediol (R2 is -OH, m=4, total carbon number 6), etc.

[0037] The hydrophilicity and flexibility of the resin can be adjusted by controlling the value of m to meet the needs of different composite processes. Specifically, when m < 3, the polyol chain is too short, the resin is too rigid, the crosslinking density is too high, the passivation film becomes brittle, and it cannot buffer thermal stress in the thermal process, resulting in impaired interfacial bonding. When m > 10, the polyol chain is too long, the density of polar groups in the resin decreases, the hydrogen bonding with the adhesive in the dry process weakens, the peel strength decreases, and the passivation film is not dense enough. When m is in the range of 3 to 10, the resin has both flexibility and rigidity, is suitable for both dry and thermal processes, and achieves optimal adhesion to aluminum foil and film.

[0038] Furthermore, based on the general formula (II) polyol P, a purity of ≥99% is preferred. High-purity polyols can ensure the synthesis efficiency and structural stability of the resin. The resulting resin possesses both flexibility and rigidity, meeting the deep-drawing requirements of lithium battery soft packaging aluminum-plastic film, and also adapting to the processing requirements of food / pharmaceutical irregular-shaped packaging and daily chemical paste packaging. It also exhibits no harmful leaching, complying with food / pharmaceutical compliance requirements. The amount of polyol P used should be 20%–40% of the total mass of the resin raw materials. When the content is <20%, the resin molecular weight is too low, resulting in poor film-forming properties; when the content is >40%, the resin polarity is too low, leading to decreased adhesion to the aluminum foil.

[0039] The general structural formula of epoxy compound O is shown in formula (III); bisphenol A diglycidyl ether is preferred as the epoxy compound O based on general structural formula (III); more preferably, the purity is ≥99%. High-purity epoxy compounds can enhance the crosslinking density and chemical resistance of the resin, improve the barrier ability of the passivation film against lithium battery electrolytes and general media (acids, alcohols, oils, etc.) in food / pharmaceutical / daily chemical products, and the residual amount meets the VOC limit requirements of various fields, with no harmful leaching. The amount of epoxy compound O used is 10% to 30% of the total mass of the resin raw materials. When the content is <10%, the crosslinking degree of the resin is insufficient and the passivation film has poor density; when the content is >30%, the rigidity of the resin is too large and the brittleness of the passivation film increases.

[0040] (III); R3 is a divalent linking group, preferably an alkylene, arylene, alkylene aryl or a divalent linking group containing an ether bond with 1 to 20 carbon atoms.

[0041] To ensure the resin exhibits excellent chemical resistance, R3 is more preferably -CH2-O-C6H4-C(CH3)2-C6H4-O-CH2-, corresponding to the epoxy compound O being bisphenol A diglycidyl ether.

[0042] Preparation method of epoxy-modified alkyd resin (C) The preparation of epoxy-modified alkyd resin (C) includes the following steps: Step 1: Add acid anhydride S to the reactor. Under inert gas protection, nitrogen is preferred here. The mixture is kept at a constant temperature of 75℃~85℃ to remove moisture and impurities, so as to avoid moisture affecting the resin synthesis efficiency and structural stability. Step 2: While stirring, add polyol P. After stirring evenly, add solvent accounting for 10%-20% of the total mass of acid anhydride S and polyol P. Raise the temperature to 150℃-170℃ and react for 3-6 hours. This temperature range is the optimal temperature for the alcohol esterification reaction to ensure a complete reaction without side reactions. Step 3: Continue heating to 180℃-220℃ and react for 1-2 hours until the acid value is less than 50 mgKOH / g to obtain the alkyd resin intermediate. The high temperature stage further promotes the esterification reaction, reduces the acid value, and ensures the film-forming properties of the resin. Step 4: Add epoxy compound O to the alkyd resin intermediate and continue the reaction for 4-6 hours until the acid value is less than 20 mgKOH / g and no longer decreases within 30 minutes, to ensure that the epoxy groups and carboxyl groups react fully and increase the resin crosslinking density; Step 5: After removing the solvent under reduced pressure until the distillate is clear and free of oil droplets (indicating extremely low solvent content), perform a second vacuum drying process, with a vacuum degree ≤ -0.095 MPa, and hold at 75℃ for 1 hour. Then, cool to 70℃-80℃ and slowly add deionized water while stirring to obtain waterborne epoxy-modified alkyd resin. The second vacuum drying ensures that the solvent residue is ≤ 3 mg / m³. 2 This avoids the co-migration of residual solvents with trivalent chromium / fluorine-containing compounds, and complies with compliance requirements in the food / pharmaceutical fields.

[0043] As a supplementary explanation, the resulting product is referred to here as epoxy-modified alkyd resin, where 'epoxy modification' refers to the process of end-capping and crosslinking the end carboxyl groups of the alkyd resin intermediate using epoxy compounds.

[0044] As further explanation, compared to conventional processes that only involve a single vacuum removal of the solvent, resulting in a high residual solvent content and potential component migration, this preparation method innovatively introduces a secondary vacuum drying process. This secondary vacuum drying effectively controls the residual solvent content to within 3 mg / m³. 2 The following approach not only improves the stability of the passivation film but also meets the stringent requirements of the food and pharmaceutical industries.

[0045] Furthermore, when the anhydride S is maleic anhydride or its derivative containing carbon-carbon double bonds, it is preferable to add an inhibitor (such as hydroquinone, 4-methoxyphenol, or 2,6-di-tert-butyl-p-cresol) at a mass of 0.01% to 0.1% of the anhydride S in the mixing system of step 1, and continuously introduce an inert gas (such as nitrogen) throughout the reaction to prevent thermally initiated free radical polymerization of the unsaturated double bonds. Furthermore, in this preparation method, the esterification reaction temperature in step 2 should not be lower than 150°C. If it is lower, the reaction rate will be too slow and the reaction will be incomplete. At the same time, it should not be higher than 170°C. If it is higher, raw material volatilization and side reactions are likely to occur, leading to a decrease in resin performance.

[0046] Furthermore, in step 4 of this preparation method, when adding epoxy compound O to the alkyd resin intermediate, 0.1% to 0.5% of an epoxy ring-opening catalyst (such as triphenylphosphine or tetrabutylammonium bromide) is also added, and the reaction is carried out at 140°C to 160°C for 4 to 6 hours until the acid value is less than 20 mgKOH / g.

[0047] Furthermore, in step 5 of this preparation method, the temperature during the secondary vacuum drying is preferably between 75℃ and 85℃. If the drying temperature is below 75℃, the removal of moisture and impurities will be incomplete, and the resin will be easily hydrolyzed. If the temperature is above 85℃, the acid anhydride will easily decompose, affecting the resin synthesis.

[0048] As further explanation, in this preparation method, the solvent used is an aromatic hydrocarbon solvent, preferably toluene, with a purity ≥99.5%, which is used to promote the reaction. The high purity solvent can reduce residual impurities and ensure that the resin meets the environmental protection requirements of food / pharmaceutical packaging and the electrolyte compatibility of lithium battery packaging.

[0049] As further explanation, in order to ensure reaction efficiency and product purity, and to comply with the safety regulations for food / pharmaceutical packaging, the green production standards for lithium battery new energy fields, and the safety requirements for daily chemical packaging, the purity of acid anhydride is preferably ≥99.5%, the purity of polyol P is preferably ≥99%, and the purity of epoxy compound O is preferably ≥99%.

[0050] Method for manufacturing passivating agents for surface treatment of moisture- and heat-resistant aluminum foil This passivating agent for surface treatment of humid and heat-resistant aluminum foil uses trivalent chromium compound (A), fluorine-containing compound (B), and epoxy-modified alkyd resin (C) as core raw materials. According to the above mass percentage ratio, the trivalent chromium compound and fluorine-containing compound are added to deionized water at room temperature and stirred to dissolve. Then, the epoxy-modified alkyd resin is added and stirred to disperse, resulting in a uniform and stable passivating agent with a total solid content controlled within the range of 3% to 30%.

[0051] During the stirring and dissolving process, the preferred stirring speed is 300–500 r / min, and the preferred stirring time is 60–90 minutes.

[0052] When stirring and dispersing, the rotation speed is preferably 800-1000 r / min, and the stirring time is preferably 90-120 minutes.

[0053] Method for manufacturing aluminum foil with passivation film The method for manufacturing aluminum foil with a passivation film involves contacting the surface of the aluminum foil with a passivating agent for surface treatment that is resistant to moisture and heat, followed by drying. The resulting aluminum foil with a passivation film can be used as a general-purpose substrate for aluminum-plastic films used in soft packaging for lithium-ion batteries and general soft packaging for food, pharmaceuticals, and daily chemicals. It also has excellent resistance to moisture and heat, chemical corrosion, and interfacial adhesion, and the amount of component migration / dissolution meets the mandatory standards of various fields.

[0054] The preferred contact method is coating, such as roller coating or spray coating; the preferred drying temperature is 100℃~250℃, and the preferred drying time is 1~5 minutes; specifically, for industrial / daily chemical applications, the preferred drying temperature is 100~250℃, and the preferred drying time is 1~5 minutes; for food / pharmaceutical applications, the preferred drying temperature is 150~220℃, and the preferred drying time is 3~5 minutes, to ensure that the passivation film is completely cured (crosslinking degree ≥90%), which ensures both density and corrosion resistance, and avoids the film thickness being too thick, affecting the composite adhesion, or too thin, causing component migration.

[0055] Corrosion prevention methods for aluminum foil The corrosion protection method for aluminum foil involves contacting the surface of the aluminum foil with a moisture- and heat-resistant passivating agent to form a dense passivation film. The resulting passivation film is a stable composite protective layer formed by the cross-linking of trivalent chromium salts, fluorides, and epoxy-modified alkyd resin. This effectively blocks the corrosion of the aluminum foil by moisture, lithium battery electrolytes, and common food / pharmaceutical / daily chemical media (such as acids, alcohols, oils, pharmaceutical solutions, surfactants, and fragrances). Simultaneously, trivalent chromium and fluorine compounds form a stable coordination structure within the passivation film, with migration / dissolution rates strictly complying with food GB 4806 series, pharmaceutical YBB standards, and daily chemical industry specifications. This passivation film also ensures the interfacial bonding strength between the aluminum foil and each layer of the aluminum-plastic film, and is suitable for both dry and thermal composite processes.

[0056] The preferred contact method is coating, such as roller coating or spray coating, and the coating process parameters are consistent with the manufacturing method of aluminum foil with passivation film.

[0057] Example The following examples, using aluminum-plastic film for lithium-ion battery soft packaging and general soft packaging in food, pharmaceuticals, and daily chemicals as examples, illustrate the effects of the present invention in detail. However, the scope of the present invention is not limited to the following examples. All trivalent chromium compounds and fluorine-containing compounds used in all examples comply with the above-mentioned compliance requirements. The film raw materials used in the food / pharmaceutical fields are food-grade / pharmaceutical-grade, and all tests include performance testing and component compliance testing.

[0058] <Ingredients> Trivalent chromium compound (A): Selected from one or more of chromium sulfate, chromium nitrate, chromium acetate, chromium fluoride, and chromium phosphate; A1: Food-grade chromium sulfate, purity 99.8%, hexavalent chromium impurity content 0.0005%, total heavy metal impurity 0.0003%; A2: Food-grade chromium phosphate, purity 99.8%, hexavalent chromium impurity content 0.0005%, total heavy metal impurity 0.0003%.

[0059] Fluorine-containing compounds (B): selected from one or more of zirconium fluoride, titanium fluoride, hydrofluoric acid, and fluorosilicic acid; B1: pharmaceutical grade zirconium fluoride, purity 99.5%, total heavy metal impurities 0.0004%, total fluorine content 35ppm, no PFAS monomer detected; B2: pharmaceutical grade titanium fluoride, purity 99.5%, total heavy metal impurities 0.0004%, total fluorine content 35ppm, no PFAS monomer detected.

[0060] Acid anhydride S: Aliphatic dicarboxylic acid anhydride, purchased from Aladdin Reagent, purity ≥99.5%, food grade; Polyols P: such as 1,5-pentanediol (m = 3), 1,8-octanediol (m = 6), 1,12-dodecanediol (m = 10), etc., purchased from Sinopharm Group, with a purity ≥99%; Epoxide O: Bisphenol A diglycidyl ether (epoxide value 0.51-0.54 eq / 100g), purchased from Dow Chemical, purity ≥99%, food grade; Solvent: Toluene, purchased from Sinopharm Group, purity ≥99.5%; Aluminum foil substrate: 8079 O-state soft aluminum foil; Film raw materials: industrial grade ONY / CPP, food grade ONY / CPP, pharmaceutical grade ONY / CPP; Preparation of epoxy-modified alkyd resin <Preparation Example 1: Resin C-1 (n=4, m=6)> The preparation of epoxy-modified alkyd resin C-1 in this example includes the following steps: Step 1: Add 100 parts of aliphatic dicarboxylic anhydride (n=4 in the structural formula) to the reactor, purge with nitrogen for protection, and stir at a constant temperature of 80℃ for 30 minutes to remove moisture and impurities.

[0061] Step 2: While stirring, add 80 parts of composite polyol P (m=6 in the structural formula), stir evenly, then add 27 parts of toluene (accounting for 15% of the total mass of raw materials), heat to 160℃, and keep the temperature for 5 hours.

[0062] Step 3: Continue heating to 200℃, maintain the temperature for 1.5 hours, take a sample and determine the acid value to be 45 mgKOH / g, and obtain the alkyd resin intermediate.

[0063] Step 4: Add 50 parts of bisphenol A diglycidyl ether to the reaction vessel and continue to react with the alkyd resin intermediate at 200℃ for 5 hours until the acid value drops to 15 mgKOH / g.

[0064] Step 5: After removing toluene by vacuum distillation, perform a second vacuum drying (vacuum degree ≤ -0.095MPa, hold at 75℃ for 1 hour), then cool to 75℃, and slowly add deionized water dropwise while stirring at 600 rpm to adjust the solid content to 40%, obtaining waterborne epoxy-modified alkyd resin, denoted as resin C-1, with a solvent residue of 2.5 mg / m³. 2 .

[0065] <Preparation Example 2: Resin C-2 (n=2, m=6)> The preparation method was the same as in Preparation Example 1, except that in step 1, the aliphatic dicarboxylic acid anhydride used had n=2 (i.e., maleic anhydride). All other conditions were the same as in Preparation Example 1. The final resin obtained was C-2, with a solvent residue of 2.3 mg / m³. 2 .

[0066] <Preparation Example 3: Resin C-3 (n=7, m=6)> The preparation method was the same as in Preparation Example 1, except that n=7 was used in the aliphatic dicarboxylic acid anhydride in step 1. All other conditions were the same as in Preparation Example 1. The final resin obtained was C-3 with a solvent residue of 2.6 mg / m³. 2 .

[0067] <Preparation Example 4: Resin C-4 (n=4, m=3)> The preparation method was the same as in Preparation Example 1, except that m=3 was used in polyol P in step 2. All other conditions were the same as in Preparation Example 1. The final resin obtained was C-4 with a solvent residue of 2.4 mg / m³. 2 .

[0068] <Preparation Example 5: Resin C-5 (n=4, m=10)> The preparation method was the same as in Preparation Example 1, except that m=10 was used in polyol P in step 2. All other conditions were the same as in Preparation Example 1. The final resin obtained was C-5 with a solvent residue of 2.5 mg / m³. 2 .

[0069] <Comparative Example 1: Resin D-1 (n=9, m=6)> The preparation method is the same as in Preparation Example 1, except that n=9 (i.e., n>7) is used in the aliphatic dicarboxylic anhydride in step 1. All other conditions are the same as in Preparation Example 1. Resin D-1 is finally obtained.

[0070] <Comparative Example 2: Resin D-2 (n=4, m=2)> The preparation method is the same as in Preparation Example 1, except that in step 2, the polyol P used has m=2 (i.e., m<3). All other conditions are the same as in Preparation Example 1. Resin D-2 is finally obtained.

[0071] <Comparative Example 3: Resin D-3 (n=4, m=12)> The preparation method is the same as in Preparation Example 1, except that in step 2, m=12 (i.e., m>10) is used in polyol P. All other conditions are the same as in Preparation Example 1. Resin D-3 is finally obtained.

[0072] <Comparative Example 4: Resin D-4 (n=9, m=12)> The preparation method is the same as in Preparation Example 1, except that n=9 (n>7) in the aliphatic dicarboxylic anhydride used in step 1, and m=12 (m>10) in the polyol P used in step 2. All other conditions are the same as in Preparation Example 1. Resin D-4 was finally obtained.

[0073] Preparation of passivating agent According to the formulations shown in Table 1, components A, B, and the epoxy-modified alkyd resin (component C, based on solid content) prepared above were formulated using the passivating agent manufacturing method of this invention to obtain the passivating agents for each embodiment and comparative example, with the total solid content controlled within the range of 10%. The formulated passivating agent is a general-purpose passivating agent for lithium-ion battery soft packaging and aluminum foil for food / pharmaceutical / daily chemical general-purpose soft packaging. No formulation adjustment is required for different scenarios; only the drying process parameters need to be controlled according to the scenario.

[0074] Table 1

[0075] Note: The contents of components A, B, and C are the mass percentages of the total mass of the passivating agent solid.

[0076] Preparation of aluminum-plastic film <Pretreatment of Aluminum Foil Substrate> Soft aluminum foil (grade 8079, O state) was selected and subjected to the following treatments in sequence: alkaline degreasing (50g / L solution of Pakase FC-315 from Japan, 50℃, immersion for 60 seconds) → water washing (deionized water, room temperature, spraying for 30 seconds) → hot air drying. This pretreatment process is a common process for aluminum foil used in lithium-ion battery soft packaging and general soft packaging for food / pharmaceutical / daily chemical products. It can effectively remove oil stains from the aluminum foil surface, ensure the adhesion of the passivation film, and leave no harmful residues, meeting the compliance requirements of the food / pharmaceutical industry.

[0077] <Passivation Treatment> Using a wire-bar coating method, the prepared passivating agent is uniformly coated onto both sides of the pretreated aluminum foil. After coating, the aluminum foil is placed in an oven for drying. The process parameters are adjusted according to the application scenario: 200℃ for 2 minutes for industrial / daily chemical applications, and 220℃ for 3 minutes for food / pharmaceutical applications, to ensure complete curing of the passivation film and a crosslinking degree ≥90%. The total dry film thickness of the passivation film is controlled within the range of 0.03~2.0μm. The aluminum foil passivation film obtained by this passivation process can be adapted to both dry and thermal composite processes, meeting the production requirements of aluminum-plastic films for lithium batteries and general packaging in food / pharmaceutical / daily chemical industries, and the component migration / dissolution levels meet the limits for each application.

[0078] <Preparation of Dry-Processed Aluminum-Plastic Film Samples Based on Dry Composite Process> Outer layer lamination: A 4μm thick two-component polyurethane adhesive (food-grade / pharmaceutical-grade adhesive for food / pharmaceutical applications) is coated on one side of the aluminum foil (the side to be laminated with nylon). The solvent is removed by drying at 60°C for 30 seconds. Then, it is dry-laminated with a 20μm thick ONY nylon film of the corresponding grade. The lamination roller temperature is 80°C and the pressure is 0.4MPa.

[0079] Inner layer lamination: A 3μm thick two-component polyurethane adhesive (food-grade / pharmaceutical-grade adhesive for food / pharmaceutical applications) is coated on the other side of the aluminum foil (the side to be laminated with PP). The adhesive is dried at 60℃ for 30 seconds to remove the solvent, and then dry-laminated with a 40μm thick cast polypropylene film (CPP) of the corresponding grade. The lamination roller temperature is 70℃ and the pressure is 0.3MPa. The film raw materials are replaced according to the application: industrial-grade / food-grade CPP is used in the battery / daily chemical industry, GB 4806.7-2016 certified food-grade CPP is used in the food industry, and YBB standard pharmaceutical-grade CPP is used in the pharmaceutical industry.

[0080] Curing: The composite aluminum-plastic film is placed in a curing chamber and cured at 80°C for 3 days to obtain a dry aluminum-plastic film sample. This sample can be used as aluminum-plastic film for lithium-ion battery soft packaging and general soft packaging for food / pharmaceutical / daily chemical products, depending on the film type.

[0081] <Preparation of Thermally Aluminum-Plastic Film Samples Based on Thermal Composite Process> First, following the steps of the dry composite process described above, the passivated aluminum foil is composited with a 20μm nylon film of the corresponding grade, and then cured at 80℃ for 3 days to obtain a nylon / aluminum foil composite film.

[0082] Then, the inner layer is heat-sealed using an extrusion lamination process: The nylon / aluminum foil composite film is conveyed from the unwinding mechanism to the coating mechanism and preheated to a temperature of over 90°C.

[0083] Meanwhile, the screw extruder of the laminating mechanism extrudes a heat-sealing material at 270°C, which is a mixture of corresponding grade CPP resin and aliphatic dicarboxylic anhydride grafted polypropylene hot melt adhesive (food-grade / pharmaceutical-grade raw materials are selected for the food / pharmaceutical field, with a ratio of 7:3), with a total thickness of 70μm.

[0084] The extruded heat-sealing material is heat-bonded with the preheated nylon / aluminum foil composite film at 105℃ and 0.5MPa pressure; in the pharmaceutical field, an additional sterilization process is required: gamma ray irradiation sterilization at a dose of 25kGy.

[0085] Cooling, trimming, and winding yield a thermally processed aluminum-plastic film sample. This sample can be used as aluminum-plastic film for lithium-ion battery soft packaging or general soft packaging for food / pharmaceutical / daily chemical products, depending on the type of raw material.

[0086] Performance evaluation methods All samples were placed in an environment of 23±2℃ and 50±5% relative humidity for 24 hours before testing. The following test methods are divided into basic general performance tests (reusable across all fields), field-specific performance tests, and ingredient compliance tests (focusing on food / pharmaceutical / daily chemical products), referring to the current national standards / industry standards / special standards of each field.

[0087] Part 1: Basic General Performance Testing <Initial peel strength test> The peel strength test shall be conducted according to GB / T 8808-1988 "Peel Test Method for Flexible Composite Plastic Materials": Cut the aluminum-plastic film into 15mm wide strips. Using a universal testing machine, at a tensile speed of 100mm / min, test the T-shaped peel force between the outer layer material (nylon) and aluminum foil, and between the inner layer material (PP or heat-sealing layer) and aluminum foil. Take the smaller of the two values ​​as the initial peel strength of the sample. Each sample shall be tested 5 times, and the average value shall be taken.

[0088] <Depth Drawing Limit Test> Perform according to T / CIAPS0005-2018, using a 40mm×50mm punch and 0.6MPa cold stamping. Inspect the appearance of the stamped sample (for cracks and pinholes), and measure the maximum stamping depth of the sample using a height gauge with an accuracy of 0.01mm, which is the stamping depth limit. Test each sample 10 times and take the minimum value.

[0089] <Damp heat aging resistance test> The sample (the formed cup-shaped object) after the deep drawing limit test was placed in a constant temperature and humidity chamber at 85℃ and 85% relative humidity for 2 weeks. After removal, the appearance of the sample was first visually inspected to observe whether blistering or delamination occurred at the interface of the outer layer material of the aluminum-plastic film / aluminum foil.

[0090] If there is no bubbling or delamination on the surface, the aged sample should be cut into 15mm wide strips according to the method of GB / T 8808-1988, and the peel strength between the outer material (nylon) and aluminum foil should be tested.

[0091] <Residual Solvent Test> According to GB / T 10004-2008, the total amount should be ≤5mg / m³. 2 Gas chromatograph headspace injection, total residual solvent ≤5 mg / m³ 2 It is acceptable.

[0092] Part Two: Domain-Specific Performance Testing <Battery-Specific Testing: Electrolyte Corrosion Resistance Test> Cut the cured aluminum-plastic film into 100mm × 15mm sample strips. Completely immerse the sample strips in an electrolyte solution consisting of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) containing 2000ppm water and 1mol / L lithium hexafluorophosphate (LiPF6) (volume ratio EC:DMC:DEC = 1:1:1). Place the sealed immersion container in an 85℃ constant temperature oven for 30 days. After removal, blot the surface electrolyte with filter paper and immediately test the peel strength between the inner layer material (PP or heat-sealing layer) and aluminum foil according to the method described in GB / T 8808-1988.

[0093] <Battery-Specific Testing: Resistance to Food-Grade Media> The cured aluminum-plastic film was cut into 100mm×15mm sample strips and immersed in 3% acetic acid aqueous solution (acidic), 50% ethanol aqueous solution (alcoholic), and refined peanut oil (oily), respectively. The samples were sealed and immersed at a constant temperature of 60℃ for 30 days. After removal, the surface medium was dried, and the peel strength between the inner layer material and aluminum foil was tested according to GB / T 8808-1988. Each sample was tested 5 times, and the average value was taken.

[0094] <Specific Testing for the Pharmaceutical Industry: Testing for Resistance to Pharmaceutical Media> The cured aluminum-plastic film was cut into 100mm×15mm sample strips and immersed in 3% acetic acid aqueous solution (acidic), 50% ethanol aqueous solution (alcoholic), and refined peanut oil (oily), respectively. The samples were sealed and immersed at a constant temperature of 60℃ for 30 days. After removal, the surface medium was dried, and the peel strength between the inner layer material and aluminum foil was tested according to GB / T 8808-1988. Each sample was tested 5 times, and the average value was taken.

[0095] <Specific Test for the Medical Field: Sterilization Test> The cured aluminum-plastic film was cut into 100mm × 15mm sample strips. After sterilization by steam at 121℃ for 30min / irradiation with 25kGy gamma rays, the presence of blistering or delamination at the aluminum-plastic film / aluminum foil interface was observed.

[0096] <Specific Test for the Daily Chemical Industry: Resistance to Corrosion by Daily Chemical Media> The cured aluminum-plastic film was cut into 100mm×15mm sample strips and immersed in 5% surfactant solution (shampoo simulation solution), 95% ethanol aqueous solution (perfume simulation solution), and fragrance simulation solution, respectively. The strips were sealed and immersed at a constant temperature of 40℃ for 30 days. After removal, the surface medium was blotted dry, and the peel strength between the inner layer material and aluminum foil was tested according to GB / T 8808-1988. Each sample was tested 5 times, and the average value was taken.

[0097] <Specific Test for Daily Chemical Industry: Weather Resistance Test> Perform the procedure according to GB / T 16422.2-2014, age the material under a xenon lamp for 1000 hours, and observe whether the interface between the aluminum-plastic film material and the aluminum foil shows yellowing or cracking.

[0098] Part Three: Ingredient Compliance Testing <Trivalent Chromium Migration / Dissolution Test> 1. Food sector: According to GB 31604.49-2021, a 3% acetic acid aqueous solution is selected as the food simulant. The simulant is soaked at 60℃ for 30 days. The chromium migration is determined by inductively coupled plasma mass spectrometry (ICP-MS). ≤0.25mg / kg is considered qualified.

[0099] 2. Pharmaceutical field: According to YBB00132002, purified water is used as the extraction solution, soaked at 60℃ for 30 days, and the chromium leaching amount is determined by ICP-MS. ≤0.0005% is qualified.

[0100] 3. Daily Chemical Industry: For the daily chemical industry, referencing food industry standards, the chromium migration limit is ≤0.25 mg / kg; 4. In the battery field, in accordance with GB / T 26572-2011, heavy metal residues meet the standards, and no hexavalent chromium is detected.

[0101] <Compliance Testing of Fluorinated Compounds> 1. Food sector: In accordance with EU PPWR regulations, the total fluoride migration is determined by ion chromatography (≤50ppm), and PFAS monomers are determined by liquid chromatography-tandem mass spectrometry (LC-MS / MS) (no detection is considered acceptable).

[0102] 2. Pharmaceutical field: According to the extract test of Part IV of the Chinese Pharmacopoeia, the fluoride ion leaching amount is ≤0.05mg / L; 3. For the daily chemical industry, refer to the food industry; the total fluoride migration limit is ≤50ppm.

[0103] <Heavy Metal Limit Testing> According to GB 4806.7-2016 / YBB00132002, the leaching amounts of lead, cadmium, mercury, and arsenic were tested. The results were ≤0.01mg / kg for food products and ≤0.0005% for pharmaceutical products, both of which are qualified.

[0104] Evaluation and grading standards The specific evaluation and grading standards are shown in Table 2: Table 2

[0105] Evaluation Results and Analysis Following the performance evaluation method described above, the dry and thermal aluminum-plastic film samples prepared in Examples 1-6 and Comparative Examples 1-10 were tested, and the results are summarized in Tables 3 and 4. Table 3

[0106] Table 4

[0107] Results analysis: Analysis of Examples 1-6 As can be seen from Tables 3 and 4, when the content of trivalent chromium compound (A) is 5%–60%, the content of fluorine-containing compound (B) is 0.01%–20%, the content of epoxy-modified alkyd resin (C) is 30%–90%, and the anhydride n of epoxy-modified alkyd resin is in the range of 2–7 and the polyol m is in the range of 3–10 (i.e., the scope protected by this invention), the prepared passivating agent exhibits excellent comprehensive performance in both dry and thermal processes. All evaluation indicators in Examples 1–6 are "0" or "◎", and the component compliance tests are all qualified in the four fields of food, pharmaceuticals, daily chemicals, and batteries. This indicates that within this preferred structural range, the passivating film has a moderate crosslinking density and a balance of rigidity and flexibility. It can form a strong anchoring interface with the adhesive in the dry process and effectively buffer the thermal stress generated during the high-temperature composite and cooling process in the thermal process. Simultaneously, it provides excellent resistance to damp heat aging and barrier capabilities against various media erosion, truly achieving the versatility of the same passivating agent between dry and thermal processes.

[0108] <Analysis of Example 1 (D-1, n=9, m=6, i.e., n>7)> When the anhydride chain is too long (n>7) while the polyol chain length is moderate, the performance of the dry process declines significantly: the initial peel strength, peel strength after damp heat aging, and peel strength after electrolyte and various media all decrease from "0" in the example to "△". This is because the excessively long anhydride chain leads to excessive flexibility of the resin molecular chain, increased spacing between crosslinking points, and decreased cohesive strength and density of the passivation film, weakening its anchoring effect with the dry adhesive and its barrier performance against corrosive media. However, the performance of the thermal process remains "0", indicating that the excessively long flexible chain segment can effectively buffer the thermal stress during thermal lamination, allowing the passivation film of this structure to still withstand high-temperature lamination conditions. This stark contrast of "dry process deterioration, thermal process maintenance" precisely defines the upper limit of the n value necessary to achieve universality of both processes.

[0109] <Analysis of Example 2 (D-2, n=4, m=2, i.e., m<3)> When the polyol chain is too short (m<3) and the anhydride chain is moderate, the performance of the thermal process decreases significantly: the initial peel strength, peel strength after damp heat aging, and peel strength after electrolyte and various media all drop to "△". This is because when the polyol chain is too short, the resin rigidity is too high and the crosslinking density is too high, leading to increased brittleness of the passivation film. During the high-temperature lamination and cooling process of the thermal process, it cannot effectively buffer thermal stress, resulting in damage to the interfacial bonding. In contrast, the dry process, without drastic temperature changes, maintains all properties at "0". This indicates that m must be ≥3 to provide sufficient flexibility for the passivation film to withstand the thermal shock of the thermal process.

[0110] <Analysis of Example 3 (D-3, n=4, m=12, i.e., m>10)> When the polyol chain is too long (m>10), the performance of the dry process declines again: initial peel strength, peel strength after damp heat aging, and peel strength after electrolyte and various media all drop to "△". This is because the longer polyol chain reduces the density of polar groups in the resin, weakening the intermolecular interactions such as hydrogen bonds with the polar adhesive in the dry process, leading to a decrease in peel strength. However, all properties remain "0" under the thermal process. This indicates that m≤10 is a crucial guarantee for maintaining interfacial bonding in the dry process.

[0111] <Analysis of Example 4 (D-4, n=9, m=12, i.e., n>7 and m>10)> When both the anhydride chain and the polyol chain are excessively long (n>7 and m>10), almost all performance indicators decline (all are "△") regardless of whether the process is dry or thermal, and the drawing depth limit also deteriorates to "△". This indicates that when both n and m exceed the protection range, the resin molecular chains become excessively entangled, the cross-linking network becomes severely irregular, and a stable and dense passivation film cannot be formed. The cohesive strength, density, and flexibility of the passivation film deteriorate across the board, completely losing its function as a core component of a general-purpose passivating agent.

[0112] <Analysis of Comparative Example 5 (C-1, A content 1%, B content 20%)> When the content of trivalent chromium compound (A) is below the 5% lower limit specified in this invention, even if the content of fluorine compound (B) is at the upper limit and the resin structure is preferably C-1 (n=4, m=6), a complete and dense chromium salt substrate film cannot be formed. In the dry process, multiple indicators such as initial peel strength, peel strength after damp heat aging, and peel strength after electrolyte and various media resistance are all evaluated as "×" (poor), indicating that the passivation film's barrier ability against corrosive media is seriously insufficient. Although the thermal process has slightly lower requirements for film density due to the high-temperature composite process, most indicators can only reach "△" (good) and fail to reach "〇" (excellent). Although the component compliance test is qualified, the performance defects cannot meet the process compatibility requirements of general-purpose passivating agents.

[0113] <Analysis of Comparative Example 6 (C-1, A content 10%, B content 0.001%)> When the content of fluorinated compound (B) is below the lower limit of 0.01%, although the content of trivalent chromium compound (A) is within a reasonable range and the resin structure is the preferred C-1 (n=4, m=6), the extremely low content of B prevents it from forming an effective coordination structure with A to fill the pores of the passivation film, resulting in severely insufficient film density. In the dry process, key indicators such as initial peel strength, peel strength after damp heat aging, and peel strength after electrolyte and various media are all "×" (poor); in the thermal process, most indicators are only "△" (good), and the performance of electrolyte and media resistance also fails to reach "0". The composition compliance test is qualified, but the film density and barrier performance are significantly deteriorated, and it cannot simultaneously meet the high standard requirements of the dry and thermal processes.

[0114] <Analysis of Comparative Example 7 (C-1, A content 70%, B content 1%)> When the content of trivalent chromium compound (A) exceeds the upper limit of 60%, although the resin structure is the preferred C-1 (n=4, m=6), the excessive chromium salt content in the passivation film leads to easy crystallization and precipitation, increased film brittleness, and decreased adhesion. Consequently, most performance indicators in both dry and thermal processes only reach "△" (good). More critically, due to the excessively low content of resin component (C) (only 29%), the epoxy-modified alkyd resin network is insufficient to adequately physically coat and anchor the high content of inorganic chromium salts and fluorides. This results in the trivalent chromium being exposed and leaching in the medium, causing the migration / dissolution rate to exceed the standard, and the component compliance test is judged as "unqualified". This comparative example shows that an excessively high A content not only impairs overall performance but also fails to meet compliance requirements in multiple fields, thus losing its basis as a general-purpose passivating agent.

[0115] <Analysis of Comparative Example 8 (C-1, A content 20%, B content 40%)> When the content of fluorinated compounds (B) exceeds the upper limit of 20%, although the resin structure is preferably C-1 (n=4, m=6), excessive fluoride will reduce the adhesion between the passivation film and the aluminum foil, and worsen the compatibility with the epoxy-modified alkyd resin, leading to easy cracking and decreased density of the film. In dry and thermal processes, the peel strength after resistance to electrolytes and food media shows "×" (poor), and the compliance tests for fluorinated compounds are all unsatisfactory in the food, pharmaceutical, and daily chemical fields (total fluoride migration or PFAS exceeding the standard). This comparative example illustrates that the B content must be strictly controlled within the range of 0.01% to 20% to balance barrier performance and regulatory safety.

[0116] <Analysis of Comparative Example 9 (C-1, A content 60%, B content 20%)> Although the contents of trivalent chromium compound (A) and fluorine-containing compound (B) are at the boundary values ​​defined in this invention (60% and 20%), respectively, and the resin structure is preferably C-1 (n=4, m=6), when A and B are both at the boundary, the proportion of resin component (C=20%) is too low. The coordination structure of chromium salt and fluoride in the passivation film tends to be saturated, and the skeleton resin is insufficient to effectively coat and anchor the high-content inorganic components. The brittleness of the film increases, and the ternary synergistic effect does not reach the optimal balance. As a result, most performance indicators in the dry and thermal processes only reach "△" (good) and fail to reach "〇" (excellent). The component compliance test is qualified, but the overall performance is limited, and the comprehensive versatility of the dry / thermal process cannot be achieved.

[0117] <Analysis of Comparative Example 10 (C-1, A content 4%, B content 0.5%)> When the content of trivalent chromium compound (A) is slightly below the lower limit of 5% (4%) and the content of fluorine compound (B) is 0.5%, although the resin structure is the preferred C-1 (n=4, m=6), the insufficient content of A prevents the formation of a complete and continuous chromium salt substrate film. Although B is present, it lacks sufficient A to coordinate with it, resulting in severely insufficient density and adhesion of the passivation film. In the dry process, multiple indicators such as initial peel strength, peel strength after damp heat aging, and peel strength after electrolyte and various media are all "×" (poor); in the thermal process, the peel strength after electrolyte and media resistance is also "×", and the remaining indicators are only "△" (good). The composition compliance test is qualified, but the performance defects are significant, and it cannot meet the design requirements for damp heat resistance, media resistance, and process versatility.

[0118] 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 this invention is defined by the appended claims and their equivalents.

Claims

1. A passivating agent for surface treatment of aluminum foil resistant to moisture and heat, characterized in that, The passivating agent contains: a trivalent chromium compound (A), a fluorinated compound (B), and an epoxy-modified alkyd resin (C); Based on the total mass of the passivating agent solids, the content of the trivalent chromium compound (A) is 5% to 60%, the content of the fluorine-containing compound (B) is 0.01% to 20%, and the content of the epoxy-modified alkyd resin (C) is 30% to 90%. The epoxy-modified alkyd resin is prepared by reacting acid anhydride S, polyol P and epoxy compound O. The general structural formula of the acid anhydride S is shown in formula (I): （I） And n is an integer from 2 to 7; R1 is independently selected from hydrogen, substituted or unsubstituted hydrocarbon group, alkoxy carbonyl group or amide group; the chemical bond between adjacent carbon atoms forming the anhydride ring skeleton is optionally a single bond or a double bond; The general structural formula of the polyol P is shown in formula (II): (II) And m is an integer from 3 to 10, and R2 is independently selected from hydrogen, substituted or unsubstituted hydrocarbon group, alkoxycarbonyl group, amide or hydroxyl group.

2. The passivating agent for surface treatment of aluminum foil with moisture and heat resistance according to claim 1, characterized in that, The general structural formula of the epoxy compound O is shown in formula (III): (III); R3 is a divalent linker.

3. A method for preparing a passivating agent for surface treatment of heat-resistant aluminum foil as described in claim 1 or 2, characterized in that, The preparation method involves adding trivalent chromium compound (A) and fluorine-containing compound (B) to deionized water at room temperature and stirring to dissolve them; then adding epoxy-modified alkyd resin (C) according to the ratio and continuing to stir and disperse to obtain a passivating agent.

4. The method for preparing the passivating agent for surface treatment of moisture-resistant aluminum foil according to claim 3, characterized in that, The preparation method further includes a step of preparing epoxy-modified alkyd resin, comprising the following steps: Step 1: Mix acid anhydride S, polyol P, and solvent accounting for 10-20% of the total mass of acid anhydride S and polyol P; Step 2: After step 1, heat the mixture at 150°C to 220°C for 4 to 8 hours; Step 3: After step 2, add epoxy compound O and mix, then heat at 180℃~220℃ for 4 to 6 hours.

5. The method for preparing the passivating agent for surface treatment of moisture-resistant aluminum foil according to claim 4, characterized in that, The solvent is an aromatic hydrocarbon solvent.

6. The method for preparing the passivating agent for surface treatment of moisture-resistant aluminum foil according to claim 4, characterized in that, The purity of the acid anhydride is ≥99.5%, and / or the purity of the polyol P is ≥99%, and / or the purity of the epoxy compound O is ≥99%.

7. A method for manufacturing an aluminum foil with a passivation film, characterized in that, The method includes the steps of contacting aluminum foil with the passivating agent as described in claim 1 or 2 and then drying it.

8. A method for preventing corrosion of aluminum foil, characterized in that, The method involves contacting an aluminum foil with the passivating agent as described in claim 1 or 2 to form a passivation film on its surface.

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