Coating and method for its production, coating, battery case

Abstract

The application belongs to the field of water-based industrial anticorrosive coatings, and particularly relates to a coating, a preparation method of the coating, a coating layer and a battery shell. The coating comprises: a modified epoxy resin comprising an epoxy resin and silane groups grafted on the epoxy resin; an emulsifier; and a latent curing agent. The coating has long-term stable storage, and the coating layer formed from the coating has strong mechanical strength, corrosion resistance or strong bonding strength with a base material.

Description

Technical Field

[0001] This application belongs to the field of water-based industrial anti-corrosion coatings, specifically involving coatings and their preparation methods, coatings, and battery casings. Background Technology

[0002] Waterborne epoxy resins are the mainstream anti-corrosion system, but they suffer from significant problems during the curing stage: amine curing agents are prone to side reactions with water and carbon dioxide or are encapsulated by residual moisture, leading to incomplete epoxy group reactions, defective crosslinking networks, and significantly reduced coating density, adhesion, and corrosion resistance. Polyether amine curing agents are affected by water and oxygen in aqueous environments, resulting in low crosslinking efficiency and coating performance that fails to meet the requirements of high-end equipment such as battery steel casings, necessitating the introduction of hydrolyzable crosslinking reinforcing components. Among related technologies, directly adding silane coupling agents easily leads to problems such as silane self-polymerization and storage instability; the "silane-modified amine curing agent" technology faces inherent drawbacks such as complex processes, high costs, easy hydrolysis and gelation of silane groups, and poor compatibility with epoxy. Therefore, coatings require further improvement. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention proposes a coating, its preparation method, a coating layer, and a battery casing. The coating exhibits long-term stable storage properties, and the coating formed by the coating possesses strong mechanical strength, corrosion resistance, or strong bonding strength with the substrate.

[0004] A first aspect of this application provides a coating comprising: Modified epoxy resin, comprising epoxy resin and silane groups grafted onto said epoxy resin; Emulsifier; Latent curing agent.

[0005] This application successfully prepared a stable one-component waterborne coating by chemically grafting silane groups onto the epoxy resin backbone and pre-compositing it with a latent curing agent. This method utilizes the spatial shielding effect of the epoxy resin polymer chain on the silane groups to effectively inhibit premature hydrolysis and self-condensation reactions of silanes during storage, thereby achieving long-term stable storage of the coating while also providing ease of application. The coating formed by this method exhibits strong mechanical strength, corrosion resistance, or strong adhesion to the substrate.

[0006] According to embodiments of this application, the above-mentioned coating satisfies at least one of the following conditions: The epoxy resin includes bisphenol A type epoxy resin, and the bisphenol A type epoxy resin includes at least one of E-51 and E-44; The silane group includes an alkoxysilane functional group; The emulsifier includes a nonionic surfactant, and the nonionic surfactant includes at least one of NP-10 and TX-10; The latent curing agent includes at least one of dicyandiamide and adipate dihydrazide; The mass ratio of the modified epoxy resin, the emulsifier, and the latent curing agent is 100:(1.5-4):(4-8), and the mass percentage of the modified epoxy resin is 40%-60% based on the total mass of the coating.

[0007] According to embodiments of this application, the coating further includes at least one of the following: A curing accelerator, wherein the accelerator comprises at least one of 4,4'-methylenediphenylbisurea, 2-phenylimidazole, and 2-ethyl-4-methylimidazole; The dispersant includes at least one of the polymeric block copolymer dispersants BYK-190, BYK-184, and BYK-154; The leveling agent includes at least one of BYK-333, BYK-306, TEGO Glide 410, BYK-354, and BYK-358; The defoamer includes at least one of the following: silicone defoamers BYK-024, BYK-022, TEGO Foamex 810, and BYK-066 N.

[0008] According to embodiments of this application, the above-mentioned coating satisfies at least one of the following conditions: The mass of the accelerator is 30%-40% of the mass of the latent curing agent; Based on the total mass of the coating, the leveling agent has a mass percentage content of 0.05%-0.3%; Based on the total mass of the coating, the defoamer has a mass percentage content of 0.1%-0.6%. Based on the total mass of the coating, the mass percentage of the dispersant is 0.3% - 2.0%.

[0009] A second aspect of this application provides a method for preparing a coating, comprising: Epoxy resin and silane coupling agent are mixed in a solvent and reacted to graft silane groups in the silane coupling agent onto the main chain of the epoxy resin, thereby obtaining a modified epoxy resin. The modified epoxy resin, deionized water, and emulsifier are mixed and emulsified to obtain an oil-in-water emulsion. The latent curing agent is dispersed in the oil-in-water emulsion to obtain a coating.

[0010] The above method is simple to operate, avoids the need for complex chemical modification of the curing agent in traditional processes, significantly simplifies the production process, and reduces the difficulty of quality control.

[0011] According to embodiments of this application, the mixing and reaction includes: The epoxy resin and solvent are first mixed at 60°C-70°C to obtain a first solution; The first solution, the silane coupling agent, and the catalyst are mixed in a second mixture and reacted at 110℃-120℃ for 3-4 hours to obtain the modified epoxy resin.

[0012] According to embodiments of this application, the above method satisfies at least one of the following conditions: The solvent includes at least one of propylene glycol methyl ether, propylene glycol butyl ether, and ethylene glycol butyl ether; The silane coupling agent includes at least one of KH-560, KH-570, and GEO-602; The catalyst includes at least one of triphenyl phosphate, tetramethylammonium chloride, and tetraethylammonium bromide. The mass ratio of the epoxy resin, the silane coupling agent, the catalyst, and the solvent is 100:(3-12):(0.1-1.0):(5-20).

[0013] According to embodiments of this application, the mixing and emulsification of the modified epoxy resin, deionized water, and emulsifier includes: The modified epoxy resin and emulsifier are mixed for the third time at 50℃-60℃ to obtain a second solution; Deionized water was added dropwise to the second solution at a shear rate of 3000 rpm-4000 rpm, and emulsification occurred to obtain an oil-in-water emulsion.

[0014] According to an embodiment of this application, after dispersing the latent curing agent in the oil-in-water emulsion, the method further includes adding at least one of an accelerator, a leveling agent, and an antifoaming agent to the oil-in-water emulsion.

[0015] A third aspect of this application provides a coating formed by heating and curing the coating described in the first aspect at 100°C-130°C.

[0016] According to embodiments of this application, the coating comprises an organic network composed of epoxy-amine crosslinking and an inorganic network composed of siloxane condensation.

[0017] A fourth aspect of this application provides a battery casing comprising the coating described in the third aspect. Attached Figure Description

[0018] Figure 1This is a performance test diagram of the coating in Embodiment 1 of this application.

[0019] Figure 2 This is a performance test diagram of the coating in Embodiment 2 of this application.

[0020] Figure 3 This is a performance test diagram of the coating in Embodiment 3 of this application.

[0021] Figure 4 This is a performance test diagram of the coating in Embodiment 4 of this application.

[0022] Figure 5 This is a performance test diagram of the coating of Comparative Example 1 of this application.

[0023] Figure 6 This is a performance test diagram of the coating of Comparative Example 2 of this application. Detailed Implementation

[0024] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0025] As one of the core systems in the current anti-corrosion field, waterborne epoxy resin still faces significant technical bottlenecks in practical applications. During its curing stage, amine curing agents are prone to side reactions with water and carbon dioxide, or are encapsulated by residual moisture in the system, leading to incomplete reactions of the epoxy groups in the epoxy resin and structural defects in the crosslinking network. These problems directly result in insufficient coating density, weakened adhesion, and ultimately severely reduced long-term corrosion resistance. Currently, polyether amine curing agents widely used in industry are more susceptible to water and oxygen interference in aqueous environments—the problem of low crosslinking efficiency is particularly pronounced, making it difficult for the coating's salt spray resistance and mechanical strength to meet the stringent protection requirements of high-end equipment such as battery steel casings. Therefore, introducing hydrolyzable crosslinking reinforcing components into the coating system can both compensate for the defects of incomplete curing reactions and strengthen the interfacial bonding between the coating and the substrate.

[0026] Currently, related technologies use silane coupling agents to modify curing agents to improve weak boundary layers at the interface. While this can enhance adhesion and shielding, it still faces challenges such as silane self-polymerization, poor storage stability, and poor synchronization with the curing of the substrate, hindering its large-scale application in high-quality battery casing protection. The "silane-modified amine curing agent" technology, while effectively improving the adhesion and corrosion resistance of waterborne epoxy coatings, still has several inherent drawbacks, stemming from the chemical characteristics and process complexity of its technical route. First, this technology requires multi-step organic synthesis modification of the curing agent (such as Michael addition reaction), a complex process with demanding conditions, resulting in high production costs and difficulty in controlling batch stability. Second, and most importantly, the introduced hydrolyzable alkoxysilane group (-Si(OR)3) is a double-edged sword: while it enhances interfacial bonding during curing, it slowly hydrolyzes and undergoes self-condensation during storage, leading to increased system viscosity or even gelation, severely affecting product storage stability. Furthermore, the polarity change of the modified curing agent may lead to poor compatibility with epoxy resin emulsions, making it prone to microphase separation during film formation, affecting the uniformity of the crosslinking network, and introducing microscopic defects. These problems essentially stem from the instability of silane chemistry in aqueous environments and the inherent thermodynamic sensitivity of multi-component systems, which are inherent limitations that are difficult to completely avoid at the molecular design level.

[0027] Based on the above, this application considers directly grafting silane coupling agents onto the epoxy resin backbone. This design provides steric protection for the silane groups through the resin backbone, fundamentally inhibiting their hydrolytic self-condensation reaction and ensuring the long-term storage stability of the coating. Simultaneously, the covalent bonding between silane and epoxy significantly improves system compatibility, promoting the formation of a uniform and dense organic-inorganic hybrid crosslinking network. Ultimately, this results in a waterborne epoxy anti-corrosion coating with superior overall performance, suitable for industrial production, systematically overcoming the three core bottlenecks of existing silane-modified amine curing agent technologies: complex processes, unstable storage, and poor compatibility. The coating formed by this method exhibits strong mechanical strength, corrosion resistance, or strong adhesion to the substrate.

[0028] In view of the above, a first aspect of this application provides a coating comprising: a modified epoxy resin, including an epoxy resin and silane groups grafted onto the epoxy resin; an emulsifier; and a latent curing agent.

[0029] This application successfully prepared a stable one-component waterborne coating by chemically grafting silane groups onto the epoxy resin backbone and pre-compositing it with a latent curing agent. This method utilizes the steric shielding effect of the epoxy resin polymer chain on the silane groups to effectively inhibit premature hydrolysis and self-condensation reactions of silanes during storage, thereby achieving long-term stable storage of the coating while also providing ease of application. The coating formed by this method exhibits strong mechanical strength, corrosion resistance, or strong adhesion to the substrate.

[0030] According to embodiments of this application, the epoxy resin comprises a bisphenol A type epoxy resin, wherein the bisphenol A type epoxy resin includes at least one of E-51 and E-44. The above-mentioned epoxy resin has a suitable epoxy value and viscosity, providing a good film-forming basis and reactivity for the coating.

[0031] According to embodiments of this application, the silane group includes a hydrolyzable alkoxysilane functional group, such as at least one of trimethoxysilane and methyldimethoxysilane. The aforementioned silane group can crosslink with epoxy resin, thereby improving the hydrolysis problem of silanes, and can also condense in situ within the coating to form a siloxane (Si-O-Si) network, ultimately constructing a dense organic-inorganic hybrid protective structure.

[0032] According to embodiments of this application, the emulsifier comprises a nonionic surfactant, which includes at least one of NP-10 and TX-10. The aforementioned emulsifier effectively reduces interfacial tension, promotes the formation of a fine and stable emulsion, and ensures the uniformity of the coating during storage and use.

[0033] According to embodiments of this application, the latent curing agent includes at least one of dicyandiamide and adipic acid dihydrazide. The aforementioned latent curing agent is inert at room temperature and only crosslinks with the modified epoxy resin under specific conditions, enabling the coating to be stored stably.

[0034] According to embodiments of this application, the mass ratio of the modified epoxy resin, the emulsifier, and the latent curing agent is 100:(1.5-4):(4-8), and based on the total mass of the coating, the mass percentage content of the modified epoxy resin is 40%-60%. Within the above range, the coating can simultaneously achieve excellent storage stability, good emulsification effect, and excellent curing ability. The synergistic effect of each component ensures the reliability of the coating performance.

[0035] According to embodiments of this application, the aforementioned coating further includes a curing accelerator, said accelerator comprising at least one of 4,4'-methylenediphenylbisurea, 2-phenylimidazole, and 2-ethyl-4-methylimidazole. The aforementioned accelerator can effectively reduce the activation energy of the curing reaction between the modified epoxy resin and the latent curing agent, enabling the coating to cure rapidly into a coating layer.

[0036] According to embodiments of this application, the mass of the curing accelerator is 30%-40% of the mass of the latent curing agent, specifically within the range of 30%, 32%, 34%, 36%, 38%, 40%, or any two of these ranges. Within this range, rapid activation of the curing reaction after construction can be ensured, shortening the curing cycle.

[0037] According to embodiments of this application, the aforementioned coating further includes a dispersant, said dispersant comprising at least one of polymeric block copolymer dispersants BYK-190, BYK-184, and BYK-154. The above dispersants can improve the dispersibility of the coating and enhance its storage stability.

[0038] According to embodiments of this application, based on the total mass of the coating, the mass percentage of the dispersant is 0.3% - 2.0%, specifically such as 0.3%, 0.5%, 1%, 1.5%, 2%, or any two of these ranges. Within the above range, the various substances in the coating can be sufficiently dispersed.

[0039] According to embodiments of this application, the aforementioned coating further includes a leveling agent, wherein the leveling agent includes at least one of BYK-333, BYK-306, TEGO Glide 410, and acrylic leveling agents BYK-354 and BYK-358. The above-mentioned leveling agents possess both good compatibility and surface tension regulating capabilities, effectively improving the flow and spreading properties of the coating during application.

[0040] According to an embodiment of this application, based on the total mass of the coating, the mass percentage content of the leveling agent is 0.05% - 0.3%, specifically such as 0.05%, 0.1%, 0.2%, 0.3%, or any two of these ranges. Within the above range, defects such as pores caused by differences in surface tension during construction can be reduced, resulting in a smooth and even coating appearance on the substrate surface.

[0041] According to embodiments of this application, the aforementioned coating further includes a defoamer, wherein the defoamer includes at least one of silicone defoamers BYK-024, BYK-022, TEGO Foamex 810, and mineral oil defoamer BYK-066 N. The aforementioned defoamer can quickly penetrate to the bubble interface in the coating, disrupting bubble stability and promoting its collapse, thereby reducing or avoiding defects such as voids and rough coating surfaces caused by bubbles.

[0042] According to an embodiment of this application, based on the total mass of the coating, the mass percentage of the defoamer is 0.1% - 0.6%, specifically such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or any two of these ranges. Within the above range, it can efficiently and effectively eliminate air bubbles introduced during coating application due to stirring, spraying, and other operations.

[0043] According to embodiments of this application, the coating further includes a remaining amount of solvent, which includes, but is not limited to, deionized water.

[0044] A second aspect of this application provides a method for preparing a coating, comprising: S10: Epoxy resin and silane coupling agent are mixed in a solvent and reacted to graft silane groups in the silane coupling agent onto the main chain of the epoxy resin, thereby obtaining a modified epoxy resin.

[0045] As an example, the epoxy resin and solvent are first mixed at 60°C-70°C to obtain a first solution; the first solution, the silane coupling agent and the catalyst are second mixed and reacted at 110°C-120°C for 3-4 hours to obtain a modified epoxy resin.

[0046] In this step, there is no specific time limit for the first mixing; it is sufficient to dissolve the epoxy resin and the silane coupling agent. Under the above reaction conditions, the grafting reaction is facilitated to proceed fully and efficiently, allowing the silane groups to be fully grafted onto the epoxy resin backbone.

[0047] According to embodiments of this application, the solvent includes at least one selected from propylene glycol methyl ether, propylene glycol butyl ether, and ethylene glycol butyl ether. These solvents can effectively dissolve raw materials and reduce the viscosity of the reaction system, and are low in cost, thus contributing to cost reduction.

[0048] According to embodiments of this application, the silane coupling agent includes at least one of KH-560, KH-570, and GEO-602. The aforementioned silane coupling agent can be grafted onto epoxy resin, thereby improving the problem of easy hydrolysis of silanes. The aforementioned silane coupling agent contains hydrolyzable alkoxysilane functional groups, such as at least one of trimethoxysilyl and methyldimethoxysilyl. The silane coupling agent chemically bonds to the epoxy resin skeleton through its hydrolyzable alkoxysilane functional groups, forming a self-silanized modified epoxy resin. This structural design can effectively slow down the hydrolysis and self-condensation rate of alkoxysilanes during coating storage, thereby significantly improving the storage stability of the system. During the subsequent heating and curing process, the protected alkoxysilane functional groups can undergo controlled hydrolysis and participate in the reaction. On the one hand, they form strong siloxane (Si-OM) interfacial bonds with the metal substrate, and on the other hand, they condense in situ inside the coating to form a siloxane (Si-O-Si) network, ultimately constructing a dense organic-inorganic hybrid protective structure.

[0049] According to embodiments of this application, the catalyst includes at least one selected from triphenyl phosphate, tetramethylammonium chloride, and tetraethylammonium bromide. The above-mentioned catalyst can accelerate the grafting reaction, enabling the grafting reaction to proceed efficiently.

[0050] According to embodiments of this application, the mass ratio of the epoxy resin, the silane coupling agent, the catalyst, and the solvent is 100:(3-12):(0.1-1.0):(5-20). Within this range, silane groups can be sufficiently grafted onto the main chain of the epoxy resin, and the reaction can proceed efficiently.

[0051] S20: The modified epoxy resin, deionized water and emulsifier are mixed and emulsified to obtain an oil-in-water emulsion.

[0052] As an example, the modified epoxy resin and emulsifier are mixed for the third time at 50°C-60°C to obtain a second solution; deionized water is added dropwise to the second solution at a shear rate of 3000rpm-4000rpm to emulsify and obtain an oil-in-water emulsion.

[0053] In this step, the modified epoxy resin system is a continuous oil-phase system. After adding the emulsifier, it is uniformly dispersed and adsorbed onto the surface of the oil phase under high-speed stirring conditions (e.g., 1000 rpm-1500 rpm). When adding deionized water dropwise at a higher shear rate (3000 rpm-4000 rpm), the deionized water is added dropwise to the oil phase system. After the system emulsification stabilizes, it is added continuously. During this process, the deionized water, as the dispersed phase, gradually penetrates into the oil phase to form tiny droplets. Initially, the viscosity of the system increases due to droplet accumulation. When the water volume reaches the phase inversion point, the aqueous phase transforms into the continuous phase, and the oil phase becomes the dispersed phase, causing the viscosity of the system to drop sharply. Continued addition of water allows the oil phase to be fully dispersed into nano-sized droplets, and the emulsifier molecules form a stable adsorption layer at the oil-water interface, ultimately resulting in a uniform, fine, water-in-oil emulsion with a milky white and bluish tint.

[0054] According to embodiments of this application, an emulsifying aid may also be added to the above emulsification process. The emulsifying aid includes at least one of NP-10 and TX-10, and its mass accounts for 1.5%–4% of the total mass of the coating. As a wetting and dispersing aid, the above-mentioned aid can further optimize interfacial compatibility, inhibit the aggregation of oil phase droplets, and improve the fineness of the emulsion.

[0055] According to embodiments of this application, the emulsification method further includes at least one of ultrasonic emulsification and D-phase emulsification.

[0056] Ultrasonic emulsification refers to the use of ultrasonic cavitation to generate extremely fine emulsion particles, thereby achieving efficient dispersion and emulsification of oily components in the aqueous phase, resulting in a narrower distribution and better stability.

[0057] D-phase emulsification is a high-efficiency, low-energy emulsification process. It involves forming a "D phase (i.e., intermediate gel state)" through surfactant-polyol, followed by oil phase swelling and water dilution to prepare a stable water-in-oil nanoemulsion. The core technology is to utilize the self-assembly structure of the D phase to achieve high-efficiency emulsification with low energy consumption and narrow distribution. It is suitable for high-viscosity systems and can be used to prepare emulsions with high internal phase and low viscosity.

[0058] S30: Disperse the latent curing agent in the oil-in-water emulsion to obtain a coating.

[0059] In this step, the latent curing agent is uniformly dispersed in the oil-in-water emulsion in the form of tiny particles. The emulsifier in the emulsion forms an adsorption layer on the surface of the latent curing agent particles, which prevents particle aggregation and keeps the latent curing agent stably suspended in the continuous aqueous phase. This ensures that it is not prematurely activated during storage and can fully contact the modified epoxy resin in the oil phase after construction.

[0060] According to embodiments of this application, after dispersing the latent curing agent in the oil-in-water emulsion, the method further includes adding at least one of a curing accelerator, a leveling agent, a defoamer, and a dispersant to the oil-in-water emulsion. The curing accelerator, after uniform dispersion, adsorbs onto the surface of the curing agent or modified epoxy resin particles, reserving activity for subsequent curing reactions; the leveling agent and defoamer adsorb onto the oil-water interface and the surface of air bubbles in the system, respectively, adjusting the surface tension of the emulsion and disrupting bubble stability; the dispersant enables uniform dispersion of all substances in the coating, improving the stability of the coating.

[0061] According to an embodiment of this application, the above method further includes: adjusting the viscosity of the system after adding the latent curing agent to the spraying requirements (usually 80KU-100KU) with deionized water, then filtering with a 200-mesh filter cloth, sealing and packaging, and finally obtaining the coating.

[0062] A third aspect of this application provides a coating formed by heating and curing the coating described in the first aspect at 100°C-130°C, the coating comprising an organic network composed of epoxy-amine crosslinking and an inorganic network composed of siloxane condensation.

[0063] When the coating is applied to the substrate and heated to a temperature sufficient to activate the latent curing agent, the aqueous phase in the coating rapidly evaporates, breaking the stable structure of the water-in-oil emulsion and causing demulsification. The modified epoxy resin in the oil phase and the dispersed latent curing agent particles aggregate together. Simultaneously, under the catalysis of the accelerator, the latent curing agent and the hydrolysis products (hydroxyl groups) of the epoxy groups and silane groups on the main chain of the modified epoxy resin rapidly undergo cross-linking reactions, forming a dense and stable organic-inorganic hybrid protective coating. In addition, the silane groups further hydrolyze and condense, forming strong covalent bonds with the surface of the substrate (e.g., battery casing, cold-rolled steel sheet, and electrophoretic steel sheet) to improve interfacial adhesion, and building a dense cross-linked network inside the coating to reduce the coating porosity. The leveling agent continuously regulates the surface tension to help the resin spread evenly, and the defoamer breaks up residual microbubbles, ultimately forming a dense, highly adhesive, and corrosion-resistant coating.

[0064] A fourth aspect of this application provides a battery casing comprising the coating described in the third aspect. This battery casing includes all the features and advantages of the coating described in the third aspect, which will not be repeated here.

[0065] In the design of battery casing coatings, a comprehensive balance must be struck between insulation, corrosion protection, welding and assembly compatibility, and cost. Due to requirements for welding processes (such as laser welding) and the reliability of electrical connections, coatings typically cover only selected areas rather than the entire surface.

[0066] In selective coating schemes, the preferred locations for coating should be concentrated on the parts that are most critical to the long-term safety and protection of the casing: (1) Outer surface of the casing body: This is the most important coating area, which aims to provide basic environmental corrosion protection for the battery casing (such as salt spray resistance and oxidation prevention) and ensure structural integrity; (2) Side walls and bottom surfaces with non-welded and non-conductive connections: These areas may come into contact with adjacent structural components when the battery is assembled. The coating can provide necessary insulation protection and play a certain buffering role when the battery expands slightly; (3) Inner surface (depending on the material and process): For materials such as steel casing that are susceptible to electrolyte corrosion, coating the inner surface can improve its chemical corrosion resistance; when coating, the sealing surface and areas that may affect electrolyte wetting should be avoided.

[0067] The embodiments of this application are described in detail below.

[0068] Example 1 (1) Preparation of modified epoxy resin: In a dry four-necked flask, add 100g of epoxy resin E-51 and 10g of propylene glycol methyl ether PM cosolvent, heat to 60℃ and stir until uniform, add 5g of KH-560 silane coupling agent, then add the catalyst triphenyl phosphate TPP (0.3g), slowly raise the temperature to 115℃, and react at this temperature for 4h. After the reaction is completed, cool down to 70℃ to obtain the modified epoxy resin; (2) The modified resin was cooled to 50°C, and emulsifier NP-10 (4g) and additive BYK-190 (2g) were added. The system was stirred at high speed (1500 rpm) to make it uniform. Then, deionized water (80g) was slowly added dropwise at a shear rate of 3000 rpm to carry out phase inversion emulsification (dropping rate 1 drop / second). The system will thicken initially and then suddenly become thinner (phase inversion point). Water was added continuously until a milky white, bluish-green, fine emulsion was obtained. (3) Continue shearing for 15 minutes to ensure emulsion stability. Finally, add 0.5g of defoamer BYK-024, defoam at low speed, and discharge the material. Transfer the above base emulsion to a low-speed stirring tank (600 rpm). Slowly add 7.0g of ultrafine dicyandiamide (DICY) powder to the above system, followed by 2.5g of accelerator UR powder. Increase the speed to 1500 rpm, add 2g of dispersant, and continue dispersing for 40 minutes. Reduce the speed to 500 rpm, and add 0.3g of leveling agent BYK-333 and 0.5g of defoamer BYK-024 in sequence. After stirring for 15 minutes, adjust the viscosity to 100 KU with deionized water. Finally, filter the coating with a 200-mesh filter cloth, seal and package to obtain the coating, in which the modified epoxy resin accounts for 48% of the total mass of the coating. (4) Clean and dry the battery casing steel shell for later use. Immerse the battery casing steel shell sample completely in the coating for 10 seconds. After taking it out, drain it at 25°C for 15 minutes, and then transfer it to a 120°C forced-air oven for curing for 30 minutes.

[0069] The specific parameters for Examples 2-4 are shown in Table 1, and the other parameters are the same as those for Example 1.

[0070] Comparative Example 1 (1) Preparation of epoxy resin emulsion: In a dry four-necked flask, add 100g of epoxy resin E-51 and 10g of propylene glycol methyl ether (PM) cosolvent, heat to 60℃ and stir for 20 minutes until completely homogeneous. Then add emulsifier NP-10 (4g) and wetting and dispersing agent BYK-190 (2g), and shear and stir at 1500rpm for 15 minutes to obtain a homogeneous solution. Maintaining a shear rate of 3000rpm, slowly add 80g of deionized water to the above solution at a rate of about 1 drop / second to carry out phase transition emulsification. After the viscosity of the system first increases and then suddenly decreases (phase inversion point), continue to add the remaining water. After the addition is complete, continue shearing for 15 minutes to obtain a stable epoxy resin emulsion. Finally, add 0.5g of defoamer BYK-024, defoam at low speed and discharge the material. The solid content of the emulsion is about 55%. (2) Preparation of two-component coating: Take 100g of the above epoxy resin emulsion and place it in a container. Add 28g of polyetheramine curing agent D230 (calculated based on an epoxy group to amino hydrogen molar ratio of 1:1, accounting for 21% of the total coating mass), followed by 0.3g of leveling agent BYK-333 and 0.2g of defoamer BYK-024. Stir at 500rpm for 15 minutes to obtain a uniform two-component coating; (3) Coating and curing: Clean and dry the battery steel shell for later use. Immerse the battery steel shell sample completely in the coating for 10 seconds. After removal, drain at 25°C for 15 minutes, and then transfer to an 80°C forced-air oven for curing for 30 minutes.

[0071] Comparative Example 2 Same as Example 1, except that the epoxy resin was not modified with a silane coupling agent. The specific operation is as follows: (1) Preparation of unmodified epoxy resin emulsion: In a dry four-necked flask, add 100g of epoxy resin E-51 and 10g of propylene glycol methyl ether (PM) cosolvent, heat to 60℃ and stir for 20 minutes to obtain a completely homogeneous resin solution. Cool the above resin solution to 55℃, add emulsifier NP-10 (4g) and wetting and dispersing agent BYK-190 (2g), and shear stir at 1500rpm for 15 minutes. Maintain a shear rate of 3000rpm and slowly add 80g of deionized water at a rate of about 1 drop / second to carry out phase inversion emulsification. After the addition is complete, continue shearing for 15 minutes to obtain a stable unmodified epoxy resin emulsion. Finally, add 0.5g of defoamer BYK-024, defoam at low speed and discharge the emulsion. The solid content of the emulsion is about 55%. (2) Preparation of a single-component latent curing coating: Transfer 100g of the above unmodified epoxy resin emulsion to a low-speed stirring tank (600rpm). Slowly add 7.0g of ultrafine dicyandiamide (DICY) powder (particle size D90<5μm), followed by 2.5g of accelerator 4,4'-methylenediphenylbisurea (UR) powder. Increase the stirring speed to 1500rpm and continue dispersing for 40 minutes. Reduce the stirring speed to 500rpm and add 0.3g of leveling agent BYK-333 and 0.5g of defoamer BYK-024 in sequence. After stirring for 15 minutes, adjust the viscosity to 100 KU with deionized water. Finally, filter the coating through a 200-mesh filter cloth, seal and package to obtain a single-component coating; (3) Coating and curing: Clean and dry the battery steel shell for later use. Immerse the battery steel shell sample completely in the coating for 10 seconds. After removal, drain at 25°C for 15 minutes, and then transfer to an 80°C forced-air oven for curing for 30 minutes.

[0072] Performance testing (1) Bond strength between coating and substrate: Coating pull-off adhesion test scheme (based on Chinese national standard GB / T 5210-2006).

[0073] (2) Corrosion resistance: The steel casing of the coated battery was subjected to a neutral salt spray test (NSS) at 35°C in 5% NaCl solution according to ISO 9227 standard to evaluate its corrosion resistance.

[0074] (3) Mechanical strength: Coating hardness test – pencil hardness test (according to standard ASTM D3363). Pencil hardness refers to the depth and hardness of the mark left by the pencil lead on the coating (this application performs multi-point hardness tests on different locations of the same sample, and the hardness value with the highest frequency in the test results is used as the final judgment result). Hardness from high to strong is: 9H<8H<7H<6H<5H<4H<3H<2H <H<F<HB<B<2B<3B<4B<5B<6B<7B<8B<9B。

[0075] Table 1

[0076] Note: Failure type: A / B represents failure between the substrate and the coating, B / Y represents failure between the coating and the adhesive (the adhesive is the reagent required in the test standard, using 3M epoxy structural adhesive DP420), with results accurate to 10%.

[0077] Conclusion: This application significantly improves the mechanical properties, interfacial adhesion, and corrosion resistance of coatings by using silane coupling agents to chemically graft and modify epoxy resins and applying them to coating systems. Figures 1-6 These are corrosion resistance test diagrams, adhesion test diagrams, and hardness test diagrams of the coatings in Examples 1-4 and Comparative Examples 1-2 of this application. A comparison of the experimental data shows that: 1. The key role of silane modification was verified: Examples 1-4 modified with silane showed significantly better bond strength (2MPa-4MPa) and pencil hardness (2H-7H) than the unmodified Comparative Example 2 (1 MPa, 2B). Example 1 (KH-560 modified) showed only slight corrosion after 48 hours in the corrosion resistance test, while the conventional two-component system (Comparative Example 1) showed more severe corrosion after 12 hours, proving that silane modification plays a decisive role in improving the overall protective performance of the coating.

[0078] 2. The influence of silane type and content on performance is clearly defined: Comparing Example 1 (KH-560) and Example 2 (KH-570), it is evident that the coating modified with KH-560 exhibits superior corrosion resistance (48h vs 12h) and mechanical strength (7H vs HB) at the same content, indicating that epoxy-based silane (KH-560) is more suitable for this system. Furthermore, within the modified epoxy resin content range of 40%-60% (Examples 1, 3, and 4), the coatings maintain high mechanical strength (6H-7H) and basic rust prevention ability (24h-48h), demonstrating that this content range is reasonably designed, and the intermediate value of 48% (Example 1) exhibits the best performance balance.

[0079] 3. The present invention has comprehensive advantages over the prior art: Compared with the two-component system using conventional polyetheramine curing agent (Comparative Example 1), the single-component latent curing system of the present invention maintains the convenience of construction while significantly improving key indicators such as bonding strength, corrosion resistance and mechanical hardness, which reflects the innovation of the present invention in material design and process integration.

[0080] In summary, this invention, through chemical modification of epoxy resin with silane and rational formulation design, has successfully developed a water-based epoxy protective coating that combines high strength, high adhesion, long corrosion resistance, and ease of application and storage. Its overall performance is significantly superior to existing technical solutions.

[0081] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0082] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0083] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A coating, characterized in that, include: Modified epoxy resin, comprising epoxy resin and silane groups grafted onto said epoxy resin; Emulsifier; Latent curing agent.

2. The coating according to claim 1, characterized in that, At least one of the following conditions must be met: The epoxy resin includes bisphenol A type epoxy resin, and the bisphenol A type epoxy resin includes at least one of E-51 and E-44; The silane group is an alkoxysilane functional group; The emulsifier includes a nonionic surfactant, and the nonionic surfactant includes at least one of NP-10 and TX-10; The latent curing agent includes at least one of dicyandiamide and adipate dihydrazide; The mass ratio of the modified epoxy resin, the emulsifier, and the latent curing agent is 100:(1.5-4):(4-8), and the mass percentage of the modified epoxy resin is 40%-60% based on the total mass of the coating.

3. The coating according to claim 1 or 2, characterized in that, It also includes at least one of the following: A curing accelerator, wherein the accelerator comprises at least one of 4,4'-methylenediphenylbisurea, 2-phenylimidazole, and 2-ethyl-4-methylimidazole; The dispersant includes at least one of BYK-190, BYK-184, and BYK-154; The leveling agent includes at least one of BYK-333, BYK-306, TEGO Glide 410, BYK-354, and BYK-358; The defoamer includes at least one of BYK-024, BYK-022, TEGO Foamex 810, and BYK-066 N.

4. The coating according to claim 3, characterized in that, At least one of the following conditions must be met: The mass of the curing accelerator is 30%-40% of the mass of the latent curing agent; Based on the total mass of the coating, the leveling agent has a mass percentage content of 0.05%-0.3%; Based on the total mass of the coating, the defoamer has a mass percentage content of 0.1%-0.6%. Based on the total mass of the coating, the mass percentage of the dispersant is 0.3% - 2.0%.

5. A method for preparing a coating, characterized in that, include: Epoxy resin and silane coupling agent are mixed in a solvent and reacted to graft silane groups in the silane coupling agent onto the main chain of the epoxy resin, thereby obtaining a modified epoxy resin. The modified epoxy resin, deionized water, and emulsifier are mixed and emulsified to obtain an oil-in-water emulsion. The latent curing agent is dispersed in the oil-in-water emulsion to obtain a coating.

6. The method according to claim 5, characterized in that, The mixing and reaction include: The epoxy resin and solvent are first mixed at 60°C-70°C to obtain a first solution; The first solution, the silane coupling agent, and the catalyst are mixed in a second mixture and reacted at 110℃-120℃ for 3-4 hours to obtain the modified epoxy resin.

7. The method according to claim 6, characterized in that, At least one of the following conditions must be met: The solvent includes at least one of propylene glycol methyl ether, propylene glycol butyl ether, and ethylene glycol butyl ether; The silane coupling agent includes at least one of KH-560, KH-570, and GEO-602; The catalyst includes at least one of triphenyl phosphate, tetramethylammonium chloride, and tetraethylammonium bromide. The mass ratio of the epoxy resin, the silane coupling agent, the catalyst, and the solvent is 100:(3-12):(0.1-1.0):(5-20).

8. The method according to claim 5, characterized in that, The process of mixing and emulsifying the modified epoxy resin, deionized water, and emulsifier includes: The modified epoxy resin and emulsifier are mixed for the third time at 50℃-60℃ to obtain a second solution; Deionized water was added dropwise to the second solution at a shear rate of 3000 rpm-4000 rpm, and emulsification occurred to obtain an oil-in-water emulsion.

9. The method according to claim 5, characterized in that, After dispersing the latent curing agent in the oil-in-water emulsion, the method further includes adding at least one of a curing accelerator, a leveling agent, an antifoaming agent, and a dispersant to the oil-in-water emulsion.

10. A coating, characterized in that, It is formed by heating and curing the coating according to any one of claims 1-9 at 100℃-130℃.

11. The coating according to claim 10, characterized in that, The coating comprises an organic network composed of epoxy-amine crosslinking and an inorganic network composed of siloxane condensation.

12. A battery casing, characterized in that, Including the coating as described in claim 10 or 11.

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