A high edge protection cathodic electrophoretic coating and preparation method thereof

Abstract

The present invention discloses a high edge protection type cathode electrophoretic coating and its preparation method, epoxy resin and cyclic hydroxyl compound are subjected to chain extension reaction, and cyclic substituents are introduced; amine chain extension reactants containing multiple active hydrogens are added to the chain extension product to form a local branched structure; aliphatic small molecule amine mixture is used to implement amination modification to obtain a modified epoxy resin with a short branched comb-type branched structure; curing agent, reinforcing material, neutralizing agent are added in sequence, and continuous stirring is performed to form a stable resin emulsion; color paste, resin emulsion and pure water are mixed in a mass ratio to obtain a coating. The present invention, by optimizing the design of the resin structure, on the one hand suppresses the flow of the coating film during the curing process, ensures sufficient film thickness and protective power at the edge, and on the other hand avoids sacrificing the mechanical properties, chemical properties and appearance quality of the coating in the non-edge area when improving the edge anti-corrosion, thereby achieving a synergistic improvement in overall performance and meeting the multi-condition service requirements of the automobile.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of cathode electrophoretic coatings, in particular to a high-edge protection cathode electrophoretic coating and a preparation method thereof. Background Art

[0002] Cathodic electrophoretic coating is one of the most widely used types of water-based coatings. It has the characteristics of environmental protection, high efficiency, uniform coating film, excellent anti-corrosion performance, and high degree of automation. Currently, most automotive parts use electrophoretic coating.

[0003] Automotive parts are complex structures with numerous sharp edges and corners, which are often the first to corrode. Failure to properly address edge corrosion can not only affect the vehicle's appearance and lifespan, but can even lead to accidents.

[0004] The main reason for the poor corrosion resistance at the edges is that there is often a tip effect at sharp parts such as edge corners. During the curing heating process, a tip thermal effect occurs, and heat accumulates faster at the edge, causing the temperature of the tip to rise faster. There is a local surface tension difference, and the coating flows from the edge with low surface tension to the non-edge area with higher surface tension, reducing the thickness of the coating at the edge. In order to solve the problem of poor edge corrosion resistance, most of the existing technologies achieve the purpose of inhibiting the flow of the coating during the curing process by adding microgels and using inorganic fillers such as silica.

[0005] Patent CN114410178A adds microgel to the coating to reduce the fluidity of the coating during the baking process to improve the edge corrosion resistance of the coating. However, the microgel used is a modified epoxy resin. Although it has good compatibility with the main resin and does not affect the stability of the emulsion, due to its large usage and fewer benzene rings compared to the main resin, the corrosion resistance of the coating film at non-edge locations is significantly reduced.

[0006] Patent CN113881310A adds inorganic fillers such as silica and olivine to the main resin, which not only reduces the fluidity of the coating during baking to improve the edge corrosion resistance of the coating, but the inorganic fillers are easy to settle and have poor stability in use.

[0007] The above technical solutions are all good explorations of cathodic electrophoretic coatings, but there is still room for improvement. Therefore, this application proposes a high-edge protection cathodic electrophoretic coating and a preparation method thereof, which can effectively solve the problems of uneven coating thickness and weak corrosion protection caused by the tip effect at the edges and corners of automotive parts. Summary of the Invention

[0008] In order to solve the above technical problems, one of the purposes of the present invention is to provide a high-edge protection cathodic electrophoretic coating and a preparation method thereof. By optimizing the resin structure, on the one hand, the flow of the coating film during the curing process is suppressed to ensure sufficient film thickness and protection at the edge; on the other hand, when improving edge corrosion protection, the mechanical properties (hardness, flexibility, adhesion), chemical properties (chemical resistance) and appearance quality (flatness, glossiness) of the coating in the non-edge area are avoided from being sacrificed, thereby achieving a synergistic improvement in overall performance and meeting the multi-condition service requirements of automobiles.

[0009] The technical solution adopted by the present invention to solve the above technical problems is:

[0010] In a first aspect, the present invention provides a method for preparing a high edge protection cathodic electrophoretic coating, comprising the following steps:

[0011] (1) Chain extension reaction introduces cyclic substituents:

[0012] The catalyst is based on a bisphenol A epoxy resin with an epoxy equivalent weight (EPW) of 180-330. Triphenylphosphine with a purity of at least 98% is used as the catalytic active substance. The cyclic hydroxyl compound is selected from at least one of bisphenol A and dodecylphenol, with a molar ratio of 0.2-0.3:1 based on the epoxy groups in the epoxy resin. The amount of the catalytic active substance is 0.5-1.0% of the weight of the epoxy resin. The chain extension reaction is carried out at a constant temperature of 120-130°C for 4-6 hours until the EPW of the epoxy resin reaches 1000-1300.

[0013] By reacting a specific epoxy resin with an epoxy equivalent weight and a cyclic hydroxy compound, catalyzed by triphenylphosphine, a cyclic substituent can be precisely introduced. The introduction of the cyclic substituent increases the rigidity and steric hindrance of the resin molecule. During the subsequent curing process, it effectively inhibits the flow of the coating film at the edges caused by heat accumulation, thereby maintaining the coating thickness at the edges and improving edge protection. Furthermore, due to the precise control of the reaction conditions, the amount and position of the cyclic substituent introduced are relatively stable, which facilitates the subsequent reaction and the stability of the overall coating performance.

[0014] Chain extension reaction: Epoxy resin reacts with bisphenol A under the catalysis of triphenylphosphine. The reaction formula is as follows:

[0015]

[0016] The rigidity and steric hindrance of the cyclic substituents limit the movement of molecular chain segments. According to the glass transition temperature theory, the Tg of the resin is increased, and the heat resistance and deformation resistance are enhanced.

[0017] (2) Formation of local branched structure:

[0018] The chain-extended product is cooled to 80-90°C, and a polyactive hydrogen amine chain-extending reactant is added. The amine chain-extending reactant is selected from at least one of polyetheramine and hexamethylenediamine, and the molar ratio of the amine chain-extending reactant to the epoxy group of the epoxy resin is 1-1.5:10. The reaction is carried out at 90-100°C for 30-50 minutes. Within this temperature and molar ratio range, the amine chain-extending reactant can fully react with the epoxy groups in the previously extended product to form a locally branched structure.

[0019] The formation of local branched structures further increases the complexity and spatial structure of the resin molecules. On the one hand, it can improve the cross-linking density of the resin and enhance the mechanical properties of the coating, such as hardness and adhesion. On the other hand, this branched structure can also play a certain role in hindering the flow of the coating during the curing process of the coating, and synergize with the cyclic substituents to better solve the problem of uneven coating thickness at the edge.

[0020] Reactants: Polyetheramine (taking polyetheramine D400 as an example, containing two primary amino groups)

[0021] In the first step, the polyetheramine ring is opened, and the reaction formula is as follows:

[0022]

[0023] In the second step, the branching reaction formula is as follows:

[0024]

[0025] The side chain amino and hydroxyl groups further react with the epoxy groups of the epoxy resin to form a three-dimensional network structure, thereby improving the corrosion resistance of the non-edge coating.

[0026] (3) Amination modification to obtain modified epoxy resin:

[0027] While incubating, the product is subjected to amination modification using an aliphatic small amine mixture composed of a primary amine having 3 to 6 carbon atoms and a secondary amine in a volume ratio of 1:1-2. The molar ratio of amine groups to residual epoxy groups in the aliphatic small amine mixture is controlled at (1.1-1.3):1. The reaction temperature is maintained at 70-80°C for 2-3 hours. This amination modification yields a modified epoxy resin having a short-chain comb-shaped branched structure.

[0028] The short-chain comb-shaped branching structure imparts a degree of flexibility to the resin molecules while maintaining a high crosslink density. For edge corrosion protection, it inhibits film flow while adapting to stresses caused by shape changes at the edges, preventing cracking and improving durability at the edges. In non-edge areas, this structure also enhances the coating's flexibility, preventing it from becoming too brittle and affecting its overall performance.

[0029] Amination reaction: Taking n-butylamine as an example, the reaction formula is as follows:

[0030]

[0031] According to the theory of molecular chain entanglement, the short-chain branched structure formed by amination is compact and has few entanglements. When the molecular weight is similar, it has high fluidity and low shrinkage. High-temperature baking performance is maintained: at high temperatures, the short-chain branched structure minimizes the shrinkage of the coating, maintains the thickness and flatness of the sharp-edge coating, and improves edge corrosion resistance.

[0032] Furthermore, in the present invention, monofunctional glycidyl ether (such as phenyl glycidyl ether and versatile carbonic acid glycidyl ether) can be introduced to enhance bonding.

[0033] Modified epoxy resins contain reactive groups such as epoxy and amine (-NH2). The epoxy groups in monofunctional glycidyl ethers are highly reactive. When the reaction begins, the amine (-NH2) and other reactive groups in the modified epoxy resin act as nucleophiles to attack the epoxy groups in the monofunctional glycidyl ether.

[0034] The epoxy groups in monofunctional glycidyl ethers react specifically with primary amines and polyamines (multiple active hydrogen atoms) in modified epoxy resins. The high reactivity of the epoxy group allows it to preferentially react with amine groups under appropriate reaction conditions, thereby achieving bond strengthening.

[0035] Through bond enhancement, new chemical bonds are added to the modified epoxy resin system. The connection between monofunctional glycidyl ether and amine groups creates tighter and more complex crosslinks between resin molecules, increasing the crosslink density. The structure of the monofunctional glycidyl ether can also modulate the flexibility of the coating to a certain extent. Despite the increased crosslink density, its organic groups (such as the versatile carbonic acid group in versatile glycidyl ether) can impart a certain degree of elasticity and toughness to the coating.

[0036] The enhanced bonding optimizes the adhesion between the resin and the substrate. The structure formed by the monofunctional glycidyl ether and the amino group can better interact with the active groups on the substrate surface, enhancing the bond with the substrate through chemical bonding or physical adsorption.

[0037] The bonded structure improves the chemical stability of the coating. Tight chemical bonding can prevent the penetration of chemical substances (such as acids, bases, solvents, etc.), reducing the damage to the internal structure of the coating.

[0038] (4) Stir the modified epoxy resin and curing agent evenly to form a resin mixture, and slowly add the resin mixture dropwise to the mixture of the neutralizer and the first part of water. At this time, the solid content in the mixture is 40-50%. After high-speed dispersion for one hour, add the reinforcing material, and then add the second part of water to emulsify and disperse the resin to form a uniform and stable emulsion phase. Finally, add the third part of water to reduce the solid content in the resin emulsion to within the standard range.

[0039] When the resin mixture is mixed with the neutralizer, the neutralization reaction causes the resin molecules to become charged. The initial addition of water provides a medium for the dispersion of the resin molecules. Due to the polarity of water, the charged resin molecules gradually dissociate and become evenly distributed in the water, initially forming a dispersed system. An appropriate solids content (40-50%) ensures sufficient space between the resin molecules for charge interaction and dispersion, while also maintaining the system's viscosity within a range conducive to dispersion operations. This allows the subsequent high-speed dispersion to effectively refine the resin particles and evenly disperse them throughout the system.

[0040] After high-speed dispersion, the resin particles have been initially formed and have achieved a certain degree of dispersion stability under the action of the first portion of water. When the second portion of water is added, the system viscosity decreases, making it easier for the reinforcing material to migrate and disperse within the system. At the same time, water, as a dispersion medium, can help the material overcome its inherent tendency to agglomerate. By interacting with the dispersion system formed by the resin molecules and the first portion of water, the material is evenly dispersed throughout the resin emulsion. For example, for graphene, water can help it better spread within the resin emulsion and form an effective interfacial bond with the resin molecules, thereby enhancing the performance of the entire coating system.

[0041] Based on the coating formulation and actual application requirements, a specific standard range of solids content for the resin emulsion is established. The addition of water in the third portion precisely adjusts the system concentration to bring the resin emulsion within this standard range. This dilution adjusts the relative concentrations of the resin molecules, reinforcements, and other components in the system, ensuring that the coating forms a uniform film on the substrate during application. During film formation, an appropriate solids content facilitates cross-linking reactions between the resin molecules and the curing process of the coating, resulting in a film with excellent mechanical and chemical properties and aesthetic qualities, such as hardness, flexibility, adhesion, smoothness, and gloss.

[0042] (5) The resin emulsion is filtered to remove impurities and agglomerates, thereby obtaining a high edge protection cathodic electrophoretic coating emulsion.

[0043] (6) The color paste, coating emulsion, and pure water are mixed in a mass ratio of 1:(4-5):(6-8) and stirred for 0.5-1 hour to obtain a high-edge protection cathodic electrophoretic coating. By precisely mixing and stirring, the color paste is evenly dispersed in the coating emulsion, resulting in a cathodic electrophoretic coating with good appearance and performance.

[0044] In an achievable manner of the first aspect, the epoxy equivalent weight of the epoxy resin in step (1) is in the range of 180 to 330;

[0045] And / or, the epoxy resin is bisphenol A epoxy resin;

[0046] And / or, the cyclic hydroxy compound is selected from at least one of bisphenol A and dodecylphenol;

[0047] And / or, the catalytically active substance is triphenylphosphine, and its purity is not less than 98%.

[0048] In an achievable manner of the first aspect, the amount of the cyclic hydroxyl compound added is 0.2-0.3:1 based on the epoxy group molar ratio of the epoxy resin, and the amount of the catalytically active substance used is 0.5-1.0% of the mass of the epoxy resin;

[0049] And / or, the chain extension reaction is continued at a constant temperature of 120-130° C. for 4-6 hours until the epoxy equivalent weight of the epoxy resin reaches 1000-1300.

[0050] Under these conditions, the amine and epoxy groups react with excellent activity and moderate rate, precisely constructing a star-shaped branched structure. A reasonable degree of branching increases the coating's crosslink density and toughness, while avoiding internal stress caused by excessive crosslinking. Moderate crosslinking at the edges enhances adhesion and impact resistance, preventing peeling from corrosive media. Non-edges maintain a good balance of flexibility and mechanical properties, and precise control suppresses embrittlement caused by excessive crosslinking.

[0051] In an achievable manner of the first aspect, the molar ratio of the polyactive hydrogen amine chain extension reactant to the epoxy group of the epoxy resin is 1-1.5:10, and the reaction is carried out at 90-100° C. for 3-5 hours;

[0052] And / or, the amine chain extension reactant is selected from at least one of polyetheramine and hexamethylenediamine.

[0053] In a manner that can be implemented in the first aspect, in step (3), the molar ratio of the amino group to the remaining epoxy group of the aliphatic small molecule amine mixture is controlled to be (1.1-1.3):1, the reaction temperature is maintained at 90-100°C, and the reaction time is 1-3 hours;

[0054] And / or, the aliphatic small molecule amine mixture is formed by mixing primary amines having 3 to 6 carbon atoms and secondary amines in a volume ratio of 1:1 to 2.

[0055] In an achievable manner of the first aspect, the neutralizer is a composite neutralizer, and the composite neutralizer is a mixture of any two or more of formic acid, acetic acid, lactic acid, aminosulfonic acid, and dimethylolpropionic acid;

[0056] And / or, the acid value of the composite neutralizer is 20-45.

[0057] The combination of multiple acids in a composite neutralizer can adjust the stability of the emulsion. Different acids have varying acid strengths and reactivities. For example, formic acid is more acidic and reacts relatively quickly, while lactic acid is less acidic but provides a certain buffering effect. When these acids are combined, the speed and extent of the neutralization reaction can be comprehensively adjusted. The appropriate degree of neutralization can balance the charge interactions between resin molecules, preventing excessive aggregation or precipitation, thereby improving the stability of the emulsion.

[0058] Controlling the acid value (20-45) also has a significant impact on the viscosity of the emulsion. The acid value reflects the acidity of the neutralizer. When the acid value is low, the neutralization reaction is incomplete, the charge density of the resin molecules is low, and the emulsion may exhibit instability such as stratification, while also having a low viscosity. As the acid value increases, the neutralization reaction becomes more complete, the charge density of the resin molecules increases, and the interaction between the molecular chains is strengthened, resulting in a corresponding increase in the viscosity of the emulsion. By controlling the acid value of the composite neutralizer between 20-45, the viscosity of the emulsion can be adjusted to an appropriate range, facilitating subsequent emulsification and dispersion processes, and ensuring the stability of the emulsion during storage and use.

[0059] In an achievable manner of the first aspect, the curing agent is a composite curing agent, and a preparation method thereof comprises the following steps:

[0060] S1: An aromatic curing agent and an aliphatic curing agent are mixed and compounded to form a curing agent mixture;

[0061] S2: maintaining the temperature at 60-70° C., adding an active hydrogen-containing blocking agent at a molar ratio of isocyanate group to blocking agent of 1:1.0-1.2, and reacting under the action of a catalyst, with continuous stirring during the reaction.

[0062] S3: After the reaction is completed, stop heating and allow the reaction product to cool naturally to room temperature to obtain a finished composite curing agent.

[0063] By combining different curing agents and using end-capping agents, the activity and speed of the curing reaction can be controlled. During the coating curing process, a well-developed cross-linking network can be formed with the modified epoxy resin, improving the cross-link density and overall performance of the coating film. Furthermore, a suitable curing agent system can synergize with other coating components to enhance the mechanical properties (such as hardness and flexibility), chemical properties (chemical resistance), and appearance quality (smoothness and gloss) of the coating in non-edge areas while maintaining edge corrosion resistance.

[0064] Furthermore, the aromatic curing agent in the present invention is selected from at least one of toluene diisocyanate curing agent and polyphenyl polymethylene polyisocyanate, the aliphatic curing agent is selected from hexamethylene diisocyanate curing agent, and the mass ratio of the toluene diisocyanate curing agent to the hexamethylene diisocyanate curing agent is 6:4.

[0065] Toluene diisocyanate (TDI) is an aromatic curing agent containing a benzene ring structure, which provides high hardness and good chemical resistance. Hexamethylene diisocyanate (HDI) is an aliphatic curing agent with good molecular flexibility. When the two are mixed and compounded in a mass ratio of 6:4, the rigid structure of the aromatic portion and the flexible structure of the aliphatic portion complement each other during the curing process. When the coating forms a cross-linked network, the rigid aromatic segments provide sufficient hardness to make the coating resistant to scratches and abrasion; while the flexible aliphatic segments relieve stress concentration within the coating, increase the film's flexibility, and prevent the coating from cracking when subjected to external forces.

[0066] Furthermore, the blocking agent is selected from any one or more of trimethylolpropane, ethylene glycol butyl ether, diethylene glycol butyl ether or ethylene glycol hexyl ether, and the hydroxyl group (-OH) thereof can react with the isocyanate group (-NCO).

[0067] The end-capping reaction effectively controls the activity of the curing agent. During storage, the active isocyanate groups are blocked, making them less likely to react at room temperature, thereby improving the storage stability of the coating. For example, during storage, this prevents the curing agent from prematurely reacting with other ingredients, which could lead to coating failure.

[0068] When the coating needs to be cured after application, controlling the deblocking temperature and other conditions can deblock the blocking agent, releasing the active isocyanate groups, which react with other ingredients (such as the active groups in the resin) to cure. This allows for more precise control of the coating's curing process, resulting in a coating film with excellent performance.

[0069] Furthermore, the catalyst is dibutyltin dilaurate, and the amount of the catalyst is 0.1-0.3% of the total mass of the reactants, which helps to improve the selectivity of the reaction between the isocyanate group and the blocking agent, reduce the occurrence of other side reactions, and thus improve the quality and performance of the composite curing agent.

[0070] In a method that can be implemented in the first aspect, the reinforcing material is graphene to further enhance the protective performance of the coating on the edge and non-edge areas; the reinforcing material is pretreated, and the modified epoxy resin and the material are mixed and ground, wherein the mass of the reinforcing material is 5 to 10% of the total mass of the ground mixture.

[0071] This pretreatment helps evenly disperse graphene in the resin, significantly improving compatibility between the two. Good compatibility allows graphene to be more evenly dispersed in the modified epoxy resin system. If compatibility is poor, graphene tends to clump together, forming large particles, much like the separation of oil and water due to incompatibility. However, evenly dispersed graphene can fully demonstrate its reinforcing and barrier properties.

[0072] During the grinding process, resin molecules can adsorb onto the graphene surface, forming a good interfacial bond through physical or chemical interactions. On the one hand, the resin molecules overcome the van der Waals forces between the graphene particles, preventing aggregation. On the other hand, the functional groups on the graphene surface (such as carboxyl and hydroxyl groups) react with the active groups in the resin (such as epoxy and amino groups) to form chemical bonds. This excellent dispersion and interfacial bonding ensures that the graphene can fully exert its reinforcing and barrier properties in the coating system, rather than existing as aggregates and affecting the coating's performance.

[0073] In a second aspect, the present invention provides a high edge protection type cathode electrophoretic coating, which is prepared using the above-mentioned method for preparing the high edge protection type cathode electrophoretic coating.

[0074] In the method that can be implemented in the second aspect, the above-mentioned electrophoretic coating is electrophoretically coated on a phosphated cold-rolled steel plate. The cured paint film is tested and the coating roughness is less than 0.3, the neutral salt spray can reach more than 1000 hours, and the number of rust points in the blade test is less than 5, which meets the requirements of high edge protection coating.

[0075] Compared with the prior art, the present invention has the following beneficial effects:

[0076] (1) The present invention introduces cyclic substituents into the resin structure in sequence, forms a local branched structure, and obtains a short-chain comb-type branched structure through amination modification, thereby effectively inhibiting the flow of the cured coating at the edge, ensuring that the edge has sufficient film thickness and protection. After testing, the electrophoretic coating was electrophoretically coated on a phosphated cold-rolled steel plate. The cured paint film was tested and the coating roughness was less than 0.3, the neutral salt spray test time could reach more than 1000 hours, and the number of rust points in the blade test was less than 5, which met the requirements of high edge protection coatings. It greatly improved the anti-corrosion performance of the edges and corners of automotive parts, reduced damage to automotive parts and material waste caused by edge corrosion, extended the service life and appearance retention time of the car, and reduced the risk of traffic accidents caused by edge corrosion.

[0077] (2) While improving the edge corrosion resistance, the coating of the present invention does not sacrifice the mechanical properties (hardness, flexibility, adhesion), chemical properties (chemical resistance), and appearance quality (smoothness, gloss) of the coating in the non-edge area. This is due to the rational selection of the various components in the coating and precise process control, such as the use of composite curing agents, the addition of reinforcing materials, and the optimization of the resin structure. During the multi-operating service of the vehicle, whether it is subjected to mechanical wear and chemical corrosion during daily driving or environmental influences under different climatic conditions, the coating can ensure the good performance of the surface coating of the vehicle parts, improve the overall reliability and safety of the vehicle, and reduce the maintenance cost of the vehicle.

[0078] (3) The present invention uses a composite neutralizer to neutralize and emulsify the resin, and uses graphene as a reinforcing material and pre-treats it, so that the coating forms a uniform and stable emulsion phase. Compared with the existing technology, which has problems such as the addition of microgels leading to reduced corrosion resistance at non-edge locations and the addition of inorganic fillers that easily settle and have poor stability in use, the coating of the present invention has better stability and can maintain its performance consistency during storage and use, making it easier to industrialize and apply.

[0079] (4) The non-edge coating of the present invention has excellent mechanical properties, with a pencil hardness of ≥2H and a cupping ≥7mm.

[0080] The adhesion reaches level 0, and it has strong chemical resistance and can withstand a variety of acid, alkali and salt corrosion media; the appearance quality is good, the roughness is less than 0.3, and the coating is uniform and smooth.

[0081] (5) The present invention develops a stable and efficient composite curing agent and composite neutralizing agent to overcome the defects of uneven curing and poor stability of traditional additives, optimize the curing cross-linking network, improve the density, corrosion resistance and long-term stability of the coating, ensure the reliable storage and construction performance of the coating, extend the shelf life and construction application period, and reduce production and operation costs and quality risks.

[0082] In summary, the high-edge protection cathodic electrophoretic coating prepared in the present invention effectively solves the problems of uneven coating thickness and weak corrosion protection caused by the tip effect at the edge corners of automotive parts, achieves a synergistic improvement in edge protection performance and overall performance, and has good application prospects.

[0083] The present invention will be explained in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] Figure 1 Schematic diagram of the process for preparing a high edge protection cathodic electrophoretic coating according to an embodiment of the present invention. DETAILED DESCRIPTION

[0085] To facilitate understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are given in the drawings. However, the present invention can be implemented in different forms and is not limited to the embodiments described in the text. On the contrary, these embodiments are provided to make the content disclosed in the present invention more thorough and comprehensive.

[0086] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly used by those skilled in the art to which the present invention pertains. The terminology used in the specification of the present invention is for the purpose of describing specific embodiments and is not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0087] Example 1: The present invention provides a method for preparing a high edge protection cathodic electrophoretic coating, the preparation method comprising the following steps:

[0088] (1) Introduction of cyclic substituents by chain extension reaction

[0089] E-51 bisphenol A epoxy resin was used as the base raw material, and 98% pure triphenylphosphine was used as the catalytic active substance. Bisphenol A was used as the cyclic hydroxyl compound, with a molar ratio of 0.2:1 based on the epoxy group of the epoxy resin. The amount of catalytic active substance was 0.5% of the epoxy resin mass. The chain extension reaction was carried out at a constant temperature of 120°C for 4 hours until the epoxy equivalent weight of the epoxy resin reached 1000-1300.

[0090] (2) Formation of local branched structure

[0091] The chain extension product was cooled to 80°C, and polyetheramine was added as a multi-active hydrogen amine chain extension reactant with a molar ratio of epoxy groups of polyetheramine to epoxy resin of 1:10, and the reaction was carried out at 90°C for 30 min.

[0092] (3) Amination modification to obtain modified epoxy resin

[0093] The above product was subjected to amination modification using an aliphatic small molecule amine mixture composed of a primary amine with a carbon number of 3 and a secondary amine in a volume ratio of 1:1. The molar ratio of amino groups to residual epoxy groups in the aliphatic small molecule amine mixture was controlled at 1.1:1. The reaction temperature was maintained at 90°C and the reaction time was 2 hours.

[0094] (4) Bonding enhancement

[0095] Phenyl glycidyl ether was introduced for bonding reinforcement, with the addition amount being 5% of the mass of the modified epoxy resin.

[0096] (5) Emulsion preparation

[0097] The modified epoxy resin after bonding enhancement treatment is evenly stirred with the composite curing agent to form a resin mixture, and the resin mixture is slowly added dropwise to a mixture of a composite neutralizer (acid value of 20) prepared by mixing formic acid and acetic acid in a ratio of 1:1 and the first part of water. At this time, the solid content in the mixture is 40%. After high-speed dispersion for one hour, graphene is added, and then the second part of water is added to emulsify and disperse the resin to form a uniform and stable emulsion phase. Finally, the third part of water is added to reduce the solid content in the resin emulsion to within the standard range.

[0098] The preparation method of the composite curing agent comprises the following steps:

[0099] S1: An aromatic curing agent (toluene diisocyanate curing agent) and an aliphatic curing agent (hexamethylene diisocyanate curing agent) are mixed and compounded in a mass ratio of 6:4 to form a curing agent mixture;

[0100] S2: maintaining the temperature at 70°C, adding a blocking agent, and reacting under the action of a catalyst, stirring continuously during the reaction, and the molar ratio of isocyanate group to blocking agent is 1:1.1.

[0101] S3: After the reaction is completed, stop heating and allow the reaction product to cool naturally to room temperature to obtain a finished composite curing agent.

[0102] The catalyst is dibutyltin dilaurate, and the amount of the catalyst is 0.1% of the total mass of the reactants. The end-capping agent is trimethylolpropane.

[0103] The graphene is pretreated, and the modified epoxy resin and the graphene are mixed and ground, wherein the mass of the graphene is 7% of the total mass of the ground mixture.

[0104] (6) Preparation of finished coatings

[0105] The resin emulsion was filtered to remove impurities and agglomerates to obtain a high edge protection cathodic electrophoretic coating emulsion. The color paste, coating emulsion, and pure water were mixed in a mass ratio of 1:4:6 and stirred for 0.5 hours to obtain a high edge protection cathodic electrophoretic coating.

[0106] It should be noted that the above-mentioned color paste can be the black color paste of model ZS-891 or the gray color paste of model ZS-891 produced by our company.

[0107] Table 1 is a comparison table of coating performance parameters prepared in Examples 1-5 and Comparative Examples 1-5

[0108]

[0109] In Examples 1-5, by sequentially introducing cyclic substituents into the resin structure, forming a localized branching structure, and then aminating the resin, a short-chain comb-shaped branched structure was achieved. This effectively inhibited the flow of the cured coating at the edges, ensuring sufficient film thickness and protective strength at the edges. Furthermore, this structure also improved the coating's flexibility and other properties in non-edge areas. The introduction of a monofunctional glycidyl ether further enhanced the coating's flexibility and resistance to chemical solvents.

[0110] The selection of raw materials and parameter settings achieve a well-balanced performance profile for the coating. For example, the rational blending of the composite neutralizer and the control of the acid value ensure the stability of the emulsion; the rational proportioning and use of the composite curing agent enhance the crosslinking density and overall performance of the coating. Graphene, as a reinforcing material, is uniformly dispersed in the coating system after pretreatment, enhancing the coating's protective properties in both edge and non-edge areas.

[0111] Comparative Example 1 uses ordinary epoxy resin without modification, and its molecular structure cannot effectively inhibit the flow of the coating and improve the edge protection as the optimized resin structure in the embodiment, resulting in poor performance indicators.

[0112] Comparative Example 2 was only partially branched without subsequent steps such as amination modification. The resin structure was imperfect and could not well balance the performance of the edge and non-edge areas, resulting in poor performance indicators such as coating roughness and neutral salt spray.

[0113] Comparative Example 3 was only modified by amination, lacking preliminary steps such as local branching, and the resin structure was also imperfect, unable to reach the performance level of the examples, and various performance indicators were poor.

[0114] The parameters in Comparative Example 4 are not within the scope of protection of the claims, resulting in a loss of control over the reaction process, an unreasonable resin structure, and a serious degradation of coating performance.

[0115] The parameters of Comparative Example 5 are not within the scope of protection of the claims, and a single curing agent and neutralizer are used, which cannot reasonably adjust the coating performance like a composite curing agent and neutralizer, resulting in poor coating performance.

[0116] Example 2: The present invention provides a method for preparing a high-edge protection cathodic electrophoretic coating, the preparation method comprising the following steps:

[0117] (1) Introduction of cyclic substituents by chain extension reaction

[0118] E-51 bisphenol A epoxy resin was used as the base raw material, triphenylphosphine with a purity of 98.5% was used as the catalytic active substance, and dodecylphenol was used as the cyclic hydroxyl compound. The molar ratio of the cyclic hydroxyl compound to the epoxy group of the epoxy resin was 0.25:1, and the amount of the catalytic active substance was 0.7% of the epoxy resin mass. The chain extension reaction was carried out at a constant temperature of 125°C for 5 hours until the epoxy equivalent weight of the epoxy resin reached 1000-1300.

[0119] (2) Formation of local branched structure

[0120] The chain-extended product was cooled to 85° C., and hexamethylenediamine was added as a polyactive hydrogen amine chain-extending reactant at a molar ratio of 1.2:10 to the epoxy group of the epoxy resin. The reaction was continued at 95° C. for 40 min.

[0121] (3) Amination modification to obtain modified epoxy resin

[0122] The above product was subjected to amination modification using an aliphatic small molecule amine mixture composed of a primary amine with a carbon number of 4 and a secondary amine in a volume ratio of 1:1.5. The molar ratio of amino groups to residual epoxy groups in the aliphatic small molecule amine mixture was controlled at 1.2:1. The reaction temperature was maintained at 100°C and the reaction time was 1 hour.

[0123] (4) Bonding enhancement

[0124] Tert-butyl glycidyl ether was introduced for bonding reinforcement, with the addition amount being 8% of the mass of the modified epoxy resin.

[0125] (5) Emulsion preparation

[0126] The modified epoxy resin after bonding enhancement treatment is evenly stirred with the composite curing agent to form a resin mixture, and the resin mixture is slowly added dropwise to a mixture of a composite neutralizer (acid value of 30) prepared by mixing formic acid, acetic acid and lactic acid in a ratio of 1:1:1 and the first part of water. At this time, the solid content in the mixture is 45%. After high-speed dispersion for one hour, graphene is added, and then the second part of water is added to emulsify and disperse the resin to form a uniform and stable emulsion phase. Finally, the third part of water is added to reduce the solid content in the resin emulsion to within the standard range.

[0127] The steps for preparing the composite curing agent were substantially the same as those in Example 1, except that the temperature was maintained at 60° C., trimethylolpropane (TMP) was added as a blocking agent, and the reaction was carried out in the presence of a catalyst. Stirring was continued during the reaction, and the molar ratio of isocyanate groups to blocking agent was 1:1.0. The catalyst was used in an amount of 0.2% of the total mass of the reactants.

[0128] The graphene is pretreated, and the modified epoxy resin and the graphene are mixed and ground, wherein the mass of the graphene is 5% of the total mass of the ground mixture.

[0129] The modified epoxy resin and the composite curing agent are stirred evenly to form a resin mixture, and the resin mixture is slowly added dropwise to a mixture of a composite neutralizer prepared by mixing lactic acid and aminosulfonic acid in a ratio of 1:1 and the first part of water. At this time, the solid content in the mixture is 45%. After high-speed dispersion for one hour, graphene is added, and then the second part of water is added to emulsify and disperse the resin to form a uniform and stable emulsion phase. Finally, the third part of water is added to reduce the solid content in the resin emulsion to within the standard range.

[0130] (6) Preparation of finished coatings

[0131] The resin emulsion was filtered to remove impurities and agglomerates to obtain a high edge protection cathodic electrophoretic coating emulsion. The color paste, coating emulsion, and pure water were mixed in a mass ratio of 1:4.5:7 and stirred for 0.7 hours to obtain a high edge protection cathodic electrophoretic coating.

[0132] Example 3: The present invention provides a method for preparing a high edge protection cathodic electrophoretic coating, the preparation method comprising the following steps:

[0133] (1) Introduction of cyclic substituents by chain extension reaction

[0134] E-44 bisphenol A epoxy resin was used as the base raw material, and 99% pure triphenylphosphine was used as the catalytic active substance. The cyclic hydroxyl compound was a 1:1 mixture of bisphenol A and dodecylphenol, with a molar ratio of 0.3:1 based on the epoxy group content of the epoxy resin. The amount of catalytic active substance was 1.0% of the epoxy resin mass. The chain extension reaction was carried out at a constant temperature of 130°C for 6 hours until the epoxy resin's epoxy equivalent weight reached 1000-1300.

[0135] (2) Formation of local branched structure

[0136] The chain extension product was cooled to 90°C, and a mixture of polyetheramine and hexamethylenediamine in a ratio of 1:1 was added as a multi-active hydrogen amine chain extension reactant with a molar ratio of epoxy groups of 1.5:10 to the epoxy resin, and the mixture was reacted at 100°C for 50 min.

[0137] (3) Amination modification to obtain modified epoxy resin

[0138] The above product was subjected to amination modification using an aliphatic small molecule amine mixture composed of a primary amine with a carbon number of 5 and a secondary amine in a volume ratio of 1:2. The molar ratio of the amino group to the residual epoxy group of the aliphatic small molecule amine mixture was controlled at 1.3:1. The reaction temperature was maintained at 95°C and the reaction time was 2 hours.

[0139] (4) Bonding enhancement

[0140] Phenyl glycidyl ether was introduced for bonding reinforcement, with the addition amount being 15% of the mass of the modified epoxy resin.

[0141] (5) Emulsion preparation

[0142] The modified epoxy resin after bonding enhancement treatment is evenly stirred with the composite curing agent to form a resin mixture, and the resin mixture is slowly added dropwise to a mixture of a composite neutralizer (acid value of 45) prepared by mixing acetic acid, lactic acid and aminosulfonic acid in a ratio of 1:1:1 and the first part of water. At this time, the solid content in the mixture is 45%. After high-speed dispersion for one hour, graphene is added, and then the second part of water is added to emulsify and disperse the resin to form a uniform and stable emulsion phase. Finally, the third part of water is added to reduce the solid content in the resin emulsion to within the standard range.

[0143] The graphene is pretreated, and the modified epoxy resin and the graphene are mixed and ground, wherein the mass of the graphene is 10% of the total mass of the ground mixture.

[0144] The steps for preparing the composite curing agent are essentially the same as those in Example 1, except that ethylene glycol butyl ether, a capping agent, is added, the reaction is carried out in the presence of a catalyst, stirring is continued during the reaction, and the molar ratio of isocyanate groups to capping agent is 1:1.2. The catalyst is used in an amount of 0.3% of the total mass of the reactants.

[0145] The aromatic curing agent is a mixture of toluene diisocyanate curing agent and polyphenyl polymethylene polyisocyanate.

[0146] (6) Preparation of finished coatings

[0147] The resin emulsion was filtered to remove impurities and agglomerates to obtain a high edge protection cathodic electrophoretic coating emulsion. The color paste, coating emulsion, and pure water were mixed in a mass ratio of 1:5:8 and stirred for 1 hour to obtain a high edge protection cathodic electrophoretic coating.

[0148] Example 4: The present invention provides a method for preparing a high edge protection cathodic electrophoretic coating, the preparation method comprising the following steps:

[0149] (1) Introduction of cyclic substituents by chain extension reaction

[0150] E-44 bisphenol A epoxy resin was used as the base raw material, and triphenylphosphine with a purity of 98.2% was used as the catalytic active substance. Bisphenol A was used as the cyclic hydroxyl compound, with a molar ratio of 0.22:1 based on the epoxy group of the epoxy resin. The amount of catalytic active substance was 0.6% of the epoxy resin mass. The chain extension reaction was carried out at a constant temperature of 123°C for 4.5 hours until the epoxy equivalent weight of the epoxy resin reached 1000-1300.

[0151] (2) Formation of local branched structure

[0152] The chain extension product was cooled to 82°C, and polyetheramine was added as a multi-active hydrogen amine chain extension reactant with a molar ratio of epoxy groups of polyetheramine to epoxy resin of 1.1:10, and the reaction was carried out at 100°C for 35 minutes.

[0153] (3) Amination modification to obtain modified epoxy resin

[0154] The above product was subjected to amination modification using an aliphatic small molecule amine mixture composed of a primary amine with a carbon number of 4 and a secondary amine in a volume ratio of 1:1.5. The molar ratio of amino groups to residual epoxy groups in the aliphatic small molecule amine mixture was controlled at 1.3:1. The reaction temperature was maintained at 95°C and the reaction time was 3 hours.

[0155] (4) Bonding enhancement

[0156] Phenyl glycidyl ether was introduced for bonding reinforcement, with the addition amount being 12% of the mass of the modified epoxy resin.

[0157] (5) Emulsion preparation

[0158] The modified epoxy resin after bonding enhancement treatment is evenly stirred with the composite curing agent to form a resin mixture, and the resin mixture is slowly added dropwise to a mixture of a composite neutralizer (acid value of 25) prepared by mixing formic acid, acetic acid and aminosulfonic acid in a ratio of 1:1:1 and the first part of water. At this time, the solid content in the mixture is 45%. After high-speed dispersion for one hour, graphene is added, and then the second part of water is added to emulsify and disperse the resin to form a uniform and stable emulsion phase. Finally, the third part of water is added to reduce the solid content in the resin emulsion to within the standard range.

[0159] The graphene is pretreated, and the modified epoxy resin and the graphene are mixed and ground, wherein the mass of the graphene is 6% of the total mass of the ground mixture.

[0160] The steps for preparing the composite curing agent were substantially the same as those in Example 1, except that the temperature was maintained at 68° C., a capping agent, diethylene glycol butyl ether, was added, and the reaction was carried out in the presence of a catalyst. Stirring was continued during the reaction, and the molar ratio of isocyanate group to capping agent was 1:1.15. The catalyst was used in an amount of 0.15% of the total mass of the reactants.

[0161] (6) Preparation of finished coatings

[0162] The resin emulsion was filtered to remove impurities and agglomerates to obtain a high edge protection cathodic electrophoretic coating emulsion. The color paste, coating emulsion, and pure water were mixed in a mass ratio of 1:4:6 and stirred for 0.5 hours to obtain a high edge protection cathodic electrophoretic coating.

[0163] Example 5: The present invention provides a method for preparing a high-edge protection cathodic electrophoretic coating, the preparation method comprising the following steps:

[0164] (1) Introduction of cyclic substituents by chain extension reaction

[0165] E-44 bisphenol A epoxy resin was used as the base material, with 98% pure triphenylphosphine as the catalytic active substance. Bisphenol A was used as the cyclic hydroxyl compound, with a molar ratio of 0.26:1 based on the epoxy group of the epoxy resin. The amount of catalytic active substance was 0.5% of the epoxy resin mass. The chain extension reaction was carried out at a constant temperature of 126°C for 4 hours until the epoxy equivalent weight of the epoxy resin reached 1000-1300.

[0166] (2) Formation of local branched structure

[0167] The chain extension product was cooled to 86°C, and polyetheramine and hexamethylenediamine were added in a 1:1 ratio as a multi-active hydrogen amine chain extension reactant, with a molar ratio of epoxy groups of the polyetheramine and epoxy resin being 1.3:10, and the reaction was carried out at 96°C for 30 minutes.

[0168] (3) Amination modification to obtain modified epoxy resin

[0169] The above product was subjected to amination modification using an aliphatic small molecule amine mixture composed of a primary amine with a carbon number of 3 and a secondary amine in a volume ratio of 1:1.5. The molar ratio of the amino group to the residual epoxy group of the aliphatic small molecule amine mixture was controlled at 1.2:1. The reaction temperature was maintained at 95°C and the reaction time was 2.6 hours.

[0170] (4) Emulsion preparation

[0171] The modified epoxy resin and the composite curing agent are stirred evenly to form a resin mixture, which is then slowly added dropwise to a mixture of a composite neutralizer (acid value of 20) prepared by mixing formic acid and acetic acid in a ratio of 1:1 and the first portion of water. At this point, the solid content in the mixture is 45%. After high-speed dispersion for one hour, graphene is added, followed by the second portion of water to emulsify and disperse the resin to form a uniform and stable emulsion phase. Finally, the third portion of water is added to reduce the solid content in the resin emulsion to within the standard range.

[0172] The graphene is pretreated, and the modified epoxy resin and the graphene are mixed and ground, wherein the mass of the graphene accounts for 9% of the total mass of the ground mixture.

[0173] The steps for preparing the composite curing agent were substantially the same as those in Example 1, except that the temperature was maintained at 68° C., trimethylolpropane (TMP) was added as a capping agent, and the reaction was carried out in the presence of a catalyst. Stirring was continued during the reaction, and the molar ratio of isocyanate groups to capping agent was 1:1.05. The catalyst was used in an amount of 0.1% of the total mass of the reactants.

[0174] (5) Preparation of finished coatings

[0175] The resin emulsion was filtered to remove impurities and agglomerates to obtain a high edge protection cathodic electrophoretic coating emulsion. The color paste, coating emulsion, and pure water were mixed in a mass ratio of 1:4.5:7 and stirred for 0.7 hours to obtain a high edge protection cathodic electrophoretic coating.

[0176] Comparative Example 1

[0177] The comparative example of the present invention provides a method for preparing a cathode electrophoretic coating, and the preparation method comprises the following steps:

[0178] (1) Stir the ordinary epoxy resin and the composite curing agent evenly to form a resin mixture, and slowly add the resin mixture dropwise to the mixture of the composite neutralizer and the first part of water. At this time, the solid content in the mixture is 40%. After high-speed dispersion for one hour, add graphene, and then add the second part of water to emulsify and disperse the resin to form a uniform and stable emulsion phase. Finally, add the third part of water to reduce the solid content in the resin emulsion to within the standard range.

[0179] The composite curing agent and composite neutralizing agent are consistent with those in Example 1.

[0180] The addition amount of the graphene and the pretreatment are consistent with those in Example 1.

[0181] (2) Preparation of finished coatings

[0182] The resin emulsion was filtered to remove impurities and agglomerates to obtain a coating emulsion. The color paste, coating emulsion and pure water were mixed in a mass ratio of 1:4:6 and stirred for 0.5 hours to obtain a coating.

[0183] Comparative Example 2

[0184] The comparative example of the present invention provides a method for preparing a cathode electrophoretic coating, the basic steps of which are consistent with those of Example 1, except that the epoxy resin is only subjected to chain extension reaction and local branching, without amination modification and without introduction of phenyl glycidyl ether to strengthen the bonding of the modified resin.

[0185] Comparative Example 3

[0186] The comparative example of the present invention provides a method for preparing a cathode electrophoretic coating, the basic steps of which are consistent with those of Example 1, except that the epoxy resin is only modified by amination, and the early steps such as chain extension reaction and local branching are missing.

[0187] Comparative Example 4

[0188] The comparative example of the present invention provides a method for preparing a cathode electrophoretic coating, comprising the following steps:

[0189] (1) Introduction of cyclic substituents by chain extension reaction

[0190] E-44 bisphenol A epoxy resin was used as the base material, with 98% pure triphenylphosphine as the catalytic active substance. Bisphenol A was used as the cyclic hydroxyl compound, with a molar ratio of 0.4:1 based on the epoxy group of the epoxy resin. The amount of catalytic active substance was 0.5% of the epoxy resin mass. The chain extension reaction was carried out at a constant temperature of 140°C for 7 hours.

[0191] (2) Formation of local branched structure

[0192] The chain extension product was cooled to 80°C, and polyetheramine was added as a multi-active hydrogen amine chain extension reactant with a molar ratio of epoxy groups of polyetheramine to epoxy resin of 2:10, and the reaction was carried out at 90°C for 20 min.

[0193] (3) Amination modification to obtain modified epoxy resin

[0194] The above product was subjected to amination modification using an aliphatic small molecule amine mixture composed of a primary amine with a carbon number of 7 and a secondary amine in a volume ratio of 1:3. The molar ratio of the amino group to the residual epoxy group of the aliphatic small molecule amine mixture was controlled at 1.1:1. The reaction temperature was maintained at 90°C and the reaction time was 2 hours.

[0195] (4) Bonding enhancement

[0196] Phenyl glycidyl ether was introduced for bonding reinforcement, with the addition amount being 20% ​​of the mass of the modified epoxy resin.

[0197] (5) Emulsion preparation

[0198] The modified epoxy resin after bonding enhancement treatment is evenly stirred with the composite curing agent to form a resin mixture, and the resin mixture is slowly added dropwise to a mixture of a composite neutralizer (acid value of 50) prepared by mixing formic acid and acetic acid in a ratio of 1:1 and the first part of water. At this time, the solid content in the mixture is 40%. After high-speed dispersion for one hour, graphene is added, and then the second part of water is added to emulsify and disperse the resin to form a uniform and stable emulsion phase. Finally, the third part of water is added to reduce the solid content in the resin emulsion to within the standard range.

[0199] The preparation method of the composite curing agent comprises the following steps:

[0200] S1: An aromatic curing agent (toluene diisocyanate curing agent) and an aliphatic curing agent (hexamethylene diisocyanate curing agent) are mixed and compounded in a mass ratio of 7:3 to form a curing agent mixture;

[0201] S2: maintaining the temperature at 70°C, adding the blocking agent trimethylolpropane, and reacting under the action of a catalyst, stirring continuously during the reaction, and the molar ratio of isocyanate group to blocking agent is 1:1.5.

[0202] S3: After the reaction is completed, heating is stopped, the reaction product is allowed to cool naturally to room temperature, and filtered to obtain a finished composite curing agent.

[0203] The catalyst is dibutyltin dilaurate, and the amount of the catalyst is 0.4% of the total mass of the reactants.

[0204] The graphene is pretreated, and the modified epoxy resin and the graphene are mixed and ground, wherein the mass of the graphene is 7% of the total mass of the ground mixture.

[0205] (6) Preparation of finished coatings

[0206] The resin emulsion was filtered to remove impurities and agglomerates to obtain a high edge protection cathodic electrophoretic coating emulsion. The color paste, coating emulsion, and pure water were mixed in a mass ratio of 1:4:6 and stirred for 0.5 hours to obtain a high edge protection cathodic electrophoretic coating.

[0207] Comparative Example 5

[0208] The comparative example of the present invention provides a method for preparing a cathode electrophoretic coating, comprising the following steps:

[0209] (1) Introduction of cyclic substituents by chain extension reaction

[0210] E-51 bisphenol A epoxy resin was used as the base raw material, and 98% pure triphenylphosphine was used as the catalytic active substance. Bisphenol A was used as the cyclic hydroxyl compound, with a molar ratio of 0.1:1 based on the epoxy group of the epoxy resin. The amount of catalytic active substance was 0.3% of the epoxy resin mass. The chain extension reaction was carried out at a constant temperature of 110°C for 3 hours until the epoxy equivalent weight of the epoxy resin reached 600-800.

[0211] (2) Formation of local branched structure

[0212] The chain extension product was cooled to 80°C, and polyetheramine was added as a multi-active hydrogen amine chain extension reactant with a molar ratio of epoxy groups of polyetheramine to epoxy resin of 0.8:10, and the reaction was carried out at 85°C for 2h.

[0213] (3) Amination modification to obtain modified epoxy resin

[0214] The above product was subjected to amination modification using an aliphatic small molecule amine mixture composed of a primary amine with a carbon number of 2 and a secondary amine in a volume ratio of 1:1.5. The molar ratio of the amino group to the residual epoxy group of the aliphatic small molecule amine mixture was controlled at 0.9:1. The reaction temperature was maintained at 60°C and the reaction time was 1.5 hours.

[0215] (4) Bonding enhancement

[0216] Phenyl glycidyl ether was introduced for bonding reinforcement, with the addition amount being 3% of the mass of the modified epoxy resin.

[0217] (5) Emulsion preparation

[0218] The modified epoxy resin after bonding enhancement treatment is evenly stirred with a curing agent (such as toluene diisocyanate curing agent) to form a resin mixture, and the resin mixture is slowly added dropwise to a mixture of formic acid (acid value is 15) and the first part of water. At this time, the solid content in the mixture is 40%. After high-speed dispersion for one hour, graphene is added, and then the second part of water is added to emulsify and disperse the resin to form a uniform and stable emulsion phase. Finally, the third part of water is added to reduce the solid content in the resin emulsion to within the standard range.

[0219] The graphene is pretreated, and the modified epoxy resin and the graphene are mixed and ground, wherein the mass of the graphene is 3% of the total mass of the ground mixture.

[0220] (6) Preparation of finished coatings

[0221] The resin emulsion was filtered to remove impurities and agglomerates to obtain a high edge protection cathodic electrophoretic coating emulsion. The color paste, coating emulsion, and pure water were mixed in a mass ratio of 1:4:6 and stirred for 0.5 hours to obtain a high edge protection cathodic electrophoretic coating.

[0222] Any numerical value cited herein includes all values ​​of the lower and upper values ​​in increments of one unit from the lower limit to the upper limit, and there is an interval of at least two units between any lower value and any higher value. For example, if the value of the quantity of a component or a process variable (such as temperature, pressure, time, etc.) is set forth to be from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, the purpose is to illustrate that values ​​such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 are also explicitly listed in this specification. For values ​​less than 1, one unit is appropriately considered to be 0.0001, 0.001, 0.01, 0.1. These are merely examples that are intended to be clearly expressed, and it can be considered that all possible combinations of the numerical values ​​listed between the minimum and maximum values ​​are explicitly set forth in this specification in a similar manner.

[0223] Unless otherwise indicated, all ranges include the endpoints and all numbers between the endpoints. When used with a range, "about" or "approximately" applies to both endpoints of the range. Thus, "about 20 to 30" is intended to cover "about 20 to about 30," including at least the specified endpoints.

[0224] It should be understood that the above description is for illustration and not for limitation. Many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of the present teachings should not be determined with reference to the above description, but rather with reference to the appended claims and the full scope of equivalents to which such claims are entitled. For the purpose of comprehensiveness, all articles and references, including disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein from the foregoing claims is not intended to be a disclaimer of such subject matter, nor should it be assumed that the inventors did not consider such subject matter to be part of the disclosed inventive subject matter.

[0225] The above description of the present invention is exemplified in conjunction with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as such non-substantial improvements are made using the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the scope of protection of the present invention.

Claims

1. A method for preparing a high edge protection cathodic electrophoretic coating, characterized in that: The following steps are involved: (1) using an epoxy resin having a specific epoxy equivalent as a base material, carrying out a chain extension reaction with a cyclic hydroxyl compound under the catalysis of a catalytically active substance to introduce a cyclic substituent, wherein the cyclic hydroxyl compound is selected from at least one of bisphenol A and dodecylphenol; (2) cooling the chain extension product to 80-90° C., adding an amine chain extension reactant containing multiple active hydrogens, and reacting at 90-100° C. for 30-50 minutes to form a local branched structure, wherein the amine chain extension reactant is selected from at least one of polyetheramine and hexamethylenediamine, and the molar ratio of the amine chain extension reactant to the epoxy resin is 1-1.5:10; (3) Under heat preservation, the above product is subjected to amination modification using an aliphatic small molecule amine mixture, the reaction temperature is maintained at 90-100° C., and the reaction time is 1-3 hours to obtain a modified epoxy resin having a short-chain comb-type branched structure, wherein the aliphatic small molecule amine mixture is composed of a primary amine having 3-6 carbon atoms and a secondary amine having 3-6 carbon atoms in a volume ratio of 1:1-2, and the molar ratio of the amino group to the remaining epoxy group is (1.1-1.3):1; (4) The modified epoxy resin and the curing agent are stirred evenly to form a resin mixture, and the resin mixture is slowly added dropwise to the mixture of the neutralizer and the first portion of water. After high-speed dispersion for one hour, the reinforcing material graphene is added, and then the second portion of water is added to emulsify and disperse the resin to form a uniform and stable emulsion phase. Finally, the third portion of water is added to reduce the solid content in the resin emulsion to within the standard range; (5) filtering the resin emulsion to remove impurities and agglomerates to obtain a high edge protection cathode electrophoretic coating emulsion; (6) The color paste, the coating emulsion and pure water are mixed in a mass ratio of 1:(4-5):(6-8) and stirred continuously for 0.5-1 hour to obtain a high edge protection cathodic electrophoretic coating.

2. The method for preparing a high edge protection cathodic electrophoretic coating according to claim 1, characterized in that: The epoxy equivalent weight of the epoxy resin in step (1) is in the range of 180 to 330; The epoxy resin is bisphenol A epoxy resin; The catalytically active substance is triphenylphosphine, and its purity is not less than 98%.

3. The method for preparing a high edge protection cathodic electrophoretic coating according to claim 2, wherein: The amount of the cyclic hydroxyl compound added is 0.2 to 0.3:1 based on the epoxy group molar ratio of the epoxy resin, and the amount of the catalytic active substance used is 0.5 to 1.0% of the mass of the epoxy resin; The chain extension reaction is continued for 4 to 6 hours at a constant temperature of 120 to 130° C. until the epoxy equivalent weight of the epoxy resin reaches 1000 to 1300.

4. The method for preparing a high edge protection cathodic electrophoretic coating according to claim 1, wherein: The neutralizer is a composite neutralizer, which is a mixture of any two or more of formic acid, acetic acid, lactic acid, aminosulfonic acid and dimethylolpropionic acid; The acid value of the composite neutralizer is 20 to 45 mgKOH / g.

5. The method for preparing a high edge protection cathodic electrophoretic coating according to claim 1, wherein: The curing agent is a composite curing agent, and its preparation method comprises the following steps: S1: An aromatic curing agent and an aliphatic curing agent are mixed and compounded to form a curing agent mixture; S2: maintaining the temperature at 60-70° C., adding a blocking agent, and reacting under the action of a catalyst, stirring continuously during the reaction, and the molar ratio of isocyanate group to blocking agent is 1:1.0-1.2; S3: After the reaction is completed, stop heating and allow the reaction product to cool naturally to room temperature to obtain a finished composite curing agent.

6. The method for preparing a high edge protection cathodic electrophoretic coating according to claim 5, characterized in that: The aromatic curing agent is selected from at least one of toluene diisocyanate curing agent and polyphenyl polymethylene polyisocyanate, and the aliphatic curing agent is selected from hexamethylene diisocyanate curing agent, and the mass ratio of the aromatic curing agent to the aliphatic curing agent is 6:4; The end-capping agent is selected from any one or more of trimethylolpropane, ethylene glycol butyl ether, diethylene glycol butyl ether or ethylene glycol hexyl ether to block the active group; The catalyst is dibutyltin dilaurate, and the amount of the catalyst is 0.1-0.3% of the total mass of the reactants.

7. The method for preparing a high edge protection cathodic electrophoretic coating according to any one of claims 1 to 6, characterized in that: The reinforcing material is pretreated, and the modified epoxy resin and the reinforcing material are mixed and ground, wherein the mass of the reinforcing material is 5-10% of the total mass of the ground mixture.

8. A high edge protection cathodic electrophoretic coating, characterized in that: The high edge protection cathodic electrophoretic coating is prepared by the preparation method of any one of claims 1 to 7.

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