High edge protection type cathode electrophoretic coating and preparation method thereof

Abstract

The invention discloses a high edge protection type cathode electrophoretic coating and a preparation method thereof. Epoxy resin and a cyclic hydroxyl compound are subjected to a chain extension reaction, and a cyclic substituent group is introduced; adding amine chain extension reactants containing multiple active hydrogen into the chain extension product to form a local branched structure; the preparation method comprises the following steps: carrying out amination modification by adopting an aliphatic micromolecular amine mixture to obtain modified epoxy resin with a short-chain comb-type branched structure; sequentially adding a curing agent, a reinforcing material and a neutralizer, and continuously stirring to form a stable resin emulsion; and mixing the color paste, the resin emulsion and pure water according to a mass ratio to obtain the coating. By optimally designing the resin structure, on one hand, coating film flowing in the curing process is inhibited, sufficient film thickness and protection force of the edge are ensured, and on the other hand, when the edge corrosion resistance is improved, the mechanical performance, chemical performance and appearance quality of a coating in a non-edge area are prevented from being sacrificed, the overall performance is cooperatively improved, and the multi-working-condition service requirement of an automobile is met.

Description

Technical Field

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

[0002] As one of the most widely used types of waterborne coatings, cathodic electrophoretic coatings have the characteristics of environmental protection, high efficiency, uniform film coating, excellent anti-corrosion performance, and high degree of automation. Currently, most automotive parts use electrophoretic coatings.

[0003] Automotive parts have complex structures with a large number of edge corners, and the edge corners are often the first to be corroded. If the problem of edge anti-corrosion cannot be well solved, it will not only affect the appearance and lifespan of the vehicle, but may even cause accidents in severe cases.

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

[0005] Patent CN114410178A adds microgels to the coating to reduce the fluidity of the coating during baking, thereby improving the edge anti-corrosion ability of the coating. However, the microgel used is a modified epoxy resin, which, although having good compatibility with the main resin and not affecting the stability of the emulsion, leads to a significant decrease in the anti-corrosion performance at non-edge areas due to its large usage amount and fewer benzene rings relative to the main resin.

[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 anti-corrosion ability of the coating, but the inorganic fillers are prone to sedimentation and have poor usage stability.

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

[0008] To solve the above technical problems, one of the objectives of the present invention is to provide a high-edge protection cathodic electrophoretic coating and its preparation method. By optimizing the resin structure design, on the one hand, it inhibits the film flow during the curing process to ensure sufficient film thickness and protection at the edges. On the other hand, when improving edge corrosion protection, it avoids sacrificing the mechanical properties (hardness, flexibility, adhesion), chemical properties (chemical resistance), and appearance quality (flatness, glossiness) of the non-edge areas of the coating, achieving a synergistic improvement in overall performance and meeting the service requirements of automobiles under various conditions.

[0009] The technical solution adopted by the present invention to solve the above technical problems is as follows: In the first aspect, the present invention provides a preparation method for a high-edge protection cathodic electrophoretic coating, comprising the following steps: (1) Chain extension reaction to introduce cyclic substituents: Using bisphenol A epoxy resin with an epoxy equivalent range of 180 - 330 as the basic raw material, triphenylphosphine with a purity of not less than 98% is selected as the catalytic active substance. The cyclic hydroxyl compound is selected from at least one of bisphenol A and dodecylphenol, and its addition amount is based on the molar ratio of the epoxy groups of the epoxy resin as 0.2 - 0.3:1, and the amount of the catalytic active substance is 0.5 - 1.0% of the mass of the epoxy resin. The chain extension reaction is carried out in a constant temperature environment of 120 - 130 °C for 4 - 6 hours until the epoxy equivalent of the epoxy resin reaches 1000 - 1300.

[0010] By reacting a specific epoxy equivalent epoxy resin with a cyclic hydroxyl compound under the catalysis of triphenylphosphine, cyclic substituents can be accurately introduced. The introduction of cyclic substituents can increase the rigidity and steric hindrance of the resin molecules. During the subsequent curing process, it can effectively inhibit the flow phenomenon of the coating film caused by heat accumulation at the edges, thereby ensuring the coating film thickness at the edges and improving the edge protection ability. At the same time, due to the precise control of the reaction conditions, the introduction amount and position of the cyclic substituents are relatively stable, which is beneficial to the subsequent reaction and the stability of the overall coating performance.

[0011] Chain extension reaction: Under the catalysis of triphenylphosphine, the epoxy resin reacts with bisphenol A, and its reaction formula is as follows:

[0012] The rigidity and steric hindrance of the cyclic substituents restrict the movement of molecular chain segments. According to the glass transition temperature theory, it increases the resin Tg and enhances the heat resistance and deformation resistance ability.

[0013] (2) Form a local branched structure: Cool the above chain-extended product to 80 - 90 °C, add an amine chain extender with multiple active hydrogens, which is selected from at least one of polyetheramine and hexamethylenediamine, and the molar ratio of the amine chain extender to the epoxy groups of the epoxy resin is 1 - 1.5:10. React at 90 - 100 °C for 30 min to 50 min. Within this temperature and molar ratio range, the amine chain extender can fully react with the epoxy groups in the previous chain-extended product to form a local branched structure.

[0014] The formation of the local branched structure further increases the complexity and spatial structure of the resin molecules. On the one hand, it can improve the crosslinking density of the resin and enhance the mechanical properties of the coating film, such as hardness and adhesion; on the other hand, this branched structure can also play a role in hindering the flow of the coating film during the curing process of the coating film, and cooperate with the cyclic substituents to better solve the problem of uneven edge coating film thickness.

[0015] Reactants: Polyetheramine (taking polyetheramine D400 as an example, containing two primary amine groups) In the first step, the polyetheramine ring opens, and its reaction formula is as follows:

[0016] In the second step, the branching reaction formula is as follows:

[0017] The amine groups and hydroxyl groups of the branched chains further react with the epoxy groups of the epoxy resin to form a three-dimensional network structure, improving the anti-corrosion property of the non-edge coating.

[0018] (3) Obtain modified epoxy resin by amination modification: Under the heat preservation state, use an aliphatic small molecule amine mixture composed of primary amines and secondary amines with 3 - 6 carbon atoms mixed in a volume ratio of 1:1 - 2 to carry out amination modification on the above product. The molar ratio of the amine groups of the aliphatic small molecule amine mixture to the remaining epoxy groups is controlled at (1.1 - 1.3):1, the reaction temperature is maintained at 70 - 80 °C, and the reaction duration is 2 - 3 hours. Through this amination modification, a modified epoxy resin with a short-chain comb-shaped branched structure is obtained.

[0019] The short-chain comb-shaped branched structure enables the resin molecules to have a certain flexibility while maintaining a relatively high crosslinking density. In terms of edge anti-corrosion, it can inhibit the flow of the coating film while adapting to the stress generated by the shape change at the edge, avoid the cracking of the coating film, and improve the durability at the edge; in the non-edge area, this structure is also beneficial to improving the flexibility of the coating, so that the coating is not too brittle and hard to affect its comprehensive performance.

[0020] Amination reaction: Taking n-butylamine as an example, its reaction formula is as follows:

[0021] According to the molecular chain entanglement theory, the short branched chains formed by amination have a compact structure and less entanglement, and have high fluidity and low shrinkage at similar molecular weights. High-temperature baking performance retention: At high temperatures, the short branched chain structure results in a small shrinkage amplitude of the coating film, maintaining the thickness and flatness of the sharp-edge coating film and improving the edge corrosion resistance.

[0022] Furthermore, in the present invention, monofunctional glycidyl ethers (such as phenyl glycidyl ether, tertiary carbonate glycidyl ether) can be introduced for bond enhancement.

[0023] The modified epoxy resin contains active groups such as epoxy groups and amino groups (-NH2). The epoxy groups in the monofunctional glycidyl ether have high reactivity. When the reaction starts, the active groups such as amino groups (-NH2) in the modified epoxy resin act as nucleophiles to attack the epoxy groups of the monofunctional glycidyl ether.

[0024] The epoxy groups in the monofunctional glycidyl ether can specifically react with primary amines and polyamines (multiple active hydrogens) in the modified epoxy resin. The high reactivity of the epoxy groups enables it to react preferentially with amino groups under appropriate reaction conditions, thereby achieving the purpose of bond enhancement.

[0025] Through bond enhancement, new chemical bond connections are added to the modified epoxy resin system. The connection between the monofunctional glycidyl ether and the amino group makes the cross-linking between resin molecules tighter and more complex, increasing the cross-linking density. The structure of the monofunctional glycidyl ether can also adjust the flexibility of the coating film to a certain extent. Although the cross-linking density increases, its organic groups (such as the tertiary carbonate group in the tertiary carbonate glycidyl ether) can endow the coating film with certain elasticity and toughness.

[0026] The adhesion between the resin after bond enhancement and the substrate material is optimized. The structure formed after the connection between the monofunctional glycidyl ether and the amino group can better interact with the active groups on the substrate surface, enhancing the binding with the substrate through chemical bonding or physical adsorption, etc.

[0027] The chemical stability of the coating film is improved after bonding. The tight chemical bonding can prevent the penetration of chemical substances (such as acids, bases, solvents, etc.) and reduce the damage of chemical substances to the internal structure of the coating film.

[0028] (4) Stir the modified epoxy resin and the curing agent evenly to form a resin mixture, slowly drop the resin mixture into the mixture of the neutralizing agent 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, then add the second part of water, and carry out emulsifying dispersion on 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 the standard range.

[0029] When the resin mixture is mixed with the neutralizing agent, the neutralization reaction causes the resin molecules to carry charges, and the addition of the first portion of water provides a medium for the dispersion of the resin molecules. Due to the polarity of water, the charged resin molecules can gradually dissociate and be evenly distributed in water, initially forming a dispersion system. A suitable solid content (40 - 50%) ensures sufficient space between the resin molecules for charge interaction and dispersion, and also maintains the viscosity of the system within a range favorable for the dispersion operation, enabling subsequent high-speed dispersion to effectively refine the resin particles and uniformly disperse them in the system.

[0030] After high-speed dispersion, the resin particles have been initially formed and have a certain degree of dispersion stability under the action of the first portion of water. When the second portion of water is added, due to the reduction of the system viscosity, the reinforcing material is more likely to migrate and disperse in the system. At the same time, water as the dispersion medium can help the material overcome its own agglomeration tendency and, through interaction with the dispersion system formed by the resin molecules and the first portion of water, uniformly disperse the material in each part of the resin emulsion. For example, for graphene, water can help it better unfold in the resin emulsion and form an effective interfacial bond with the resin molecules, thereby enhancing the performance of the entire coating system.

[0031] According to the coating formulation design and actual application requirements, a specific standard range of the solid content of the resin emulsion is determined. The addition of the third portion of water is to precisely adjust the concentration of the system to make the resin emulsion reach this standard range. Through dilution, the relative concentrations of the resin molecules, the reinforcing material, and other components in the system are adjusted to ensure that the coating can form a uniform coating film on the substrate surface during the construction process. During the film-forming process, a suitable solid content helps the cross-linking reaction between the resin molecules and the curing process of the coating film, enabling the coating film to have good mechanical properties, chemical properties, and appearance quality, such as hardness, flexibility, adhesion, flatness, and gloss.

[0032] (5) After filtering the above resin emulsion to remove impurities and agglomerates, a high-edge protection type cathodic electrophoretic coating emulsion is obtained.

[0033] (6) The color paste, the coating emulsion, and pure water are mixed in a mass ratio of 1:(4 - 5):(6 - 8), and after continuous stirring for 0.5 - 1 hour, a high-edge protection type cathodic electrophoretic coating is obtained. Through precise proportional mixing and stirring, the color paste is evenly dispersed in the coating emulsion to obtain a cathodic electrophoretic coating with good appearance and performance.

[0034] In a realizable manner of the first aspect, the epoxy equivalent range of the epoxy resin in the step (1) is 180 - 330; and / or, the epoxy resin is bisphenol A type epoxy resin; And / or, at least one of bisphenol A and dodecylphenol is selected as the cyclic hydroxyl compound; And / or, triphenylphosphine is selected as the catalytically active substance, and its purity is not less than 98%.

[0035] In an implementable manner of the first aspect, the addition amount of the cyclic hydroxyl compound is 0.2 - 0.3:1 based on the molar ratio of the epoxy groups of the epoxy resin, and the dosage of the catalytically active substance is 0.5 - 1.0% of the mass of the epoxy resin; And / or, the chain extension reaction is carried out in a constant temperature environment of 120 - 130 °C for 4 - 6 hours until the epoxy equivalent of the epoxy resin reaches 1000 - 1300.

[0036] Under the above conditions, the reaction activity between the amino group and the epoxy group is good and the rate is appropriate, precisely constructing a star-shaped branched chain structure. A reasonable degree of branching increases the crosslinking density and toughness of the coating film, avoiding internal stress caused by excessive crosslinking. At the edge, moderate crosslinking improves the adhesion and impact resistance of the coating film, preventing the corrosion medium from peeling off the coating film; in non-edge areas, a good balance of flexibility and mechanical properties is maintained, because precise regulation inhibits embrittlement caused by excessive crosslinking.

[0037] In an implementable manner of the first aspect, the molar ratio of the amine chain extender with multiple active hydrogens to the epoxy groups of the epoxy resin is 1 - 1.5:10, and the reaction is carried out at 90 - 100 °C for 3 - 5 hours; And / or, at least one of polyetheramine and hexamethylenediamine is selected as the amine chain extender.

[0038] In an implementable manner of the first aspect, the molar ratio of the amino group of the aliphatic small molecule amine mixture in step (3) to the remaining epoxy groups is controlled at (1.1 - 1.3):1, the reaction temperature is maintained at 90 - 100 °C, and the reaction duration is 1 - 3 hours; And / or, the aliphatic small molecule amine mixture is composed of a primary amine and a secondary amine with 3 - 6 carbon atoms mixed in a volume ratio of 1:1 - 2.

[0039] In an implementable manner of the first aspect, the neutralizer is a composite neutralizer, and the composite neutralizer is selected by mixing any two or more of formic acid, acetic acid, lactic acid, amino sulfonic acid, and dimethylolpropionic acid; And / or, the acid value of the composite neutralizer is 20 - 45.

[0040] The compounding of multiple acids in the compound neutralizer can regulate the stability of the emulsion. Different acids have different acid strengths and reaction activities. For example, formic acid has a relatively strong acidity and a relatively fast reaction rate, while lactic acid has a weaker acidity but can provide a certain buffering effect. When they are compounded, the rate and degree of the neutralization reaction can be comprehensively adjusted. An appropriate degree of neutralization can balance the charge interactions between resin molecules, prevent excessive aggregation or precipitation of resin molecules, and thus improve the stability of the emulsion.

[0041] The control of the acid value (20 - 45) also has an important impact on the viscosity of the emulsion. The acid value reflects the acidity degree of the neutralizer. When the acid value is low, the neutralization reaction is incomplete, the charge density of resin molecules is low, and the emulsion may exhibit unstable phenomena such as stratification, and the viscosity is also low. As the acid value increases, the neutralization reaction becomes more complete, the charge density of resin molecules increases, the interaction between molecular chains enhances, and the viscosity of the emulsion will increase accordingly. By controlling the acid value of the compound neutralizer between 20 and 45, the viscosity of the emulsion can be adjusted to an appropriate range, which is beneficial to subsequent process operations such as emulsification and dispersion, and ensures the stability of the emulsion during storage and use.

[0042] In the implementable manner of the first aspect, the curing agent is a composite curing agent, and its preparation method includes the following steps: S1: Select an aromatic curing agent and an aliphatic curing agent for mixing and compounding to form a curing agent mixture; S2: Keep the temperature at 60 - 70 °C, add a capping agent containing active hydrogen according to the molar ratio of isocyanate groups to the capping agent of 1:1.0 - 1.2, and react under the action of a catalyst, with continuous stirring during the reaction process.

[0043] S3: After the reaction ends, stop heating and let the reaction product cool naturally to room temperature to obtain the finished product of the composite curing agent.

[0044] Through the compounding of different types of curing agents and the use of capping agents, the activity and rate of the curing reaction can be controlled. During the curing process of the coating, it can form a good cross - linked network with the modified epoxy resin, improving the cross - linked density and comprehensive performance of the coating film. At the same time, a suitable curing agent system can cooperate with other components in the coating to improve the coating mechanical properties (such as hardness, flexibility), chemical properties (chemical resistance), and appearance quality (flatness, glossiness) of non - edge areas while ensuring the edge anti - corrosion performance.

[0045] Furthermore, in the present invention, the aromatic curing agent 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.

[0046] Toluene diisocyanate (TDI) curing agent is an aromatic curing agent containing a benzene ring structure, which can provide high hardness and good chemical resistance; hexamethylene diisocyanate (HDI) curing agent is an aliphatic curing agent with a relatively flexible molecular chain. When the two are mixed and compounded at a mass ratio of 6:4, during the curing process, the rigid structure of the aromatic part and the flexible structure of the aliphatic part cooperate with each other. When the coating film forms a crosslinked network, the rigid aromatic chain segments can provide sufficient hardness to enable the coating to resist scratching and wear by external forces; while the flexible aliphatic chain segments can relieve the stress concentration inside the coating film, increase the flexibility of the coating film, and prevent the coating film from cracking easily when subjected to external forces.

[0047] Furthermore, the blocking agent is selected from any one or more of trimethylolpropane, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, or ethylene glycol monohexyl ether, and its hydroxyl group (-OH) can react with the isocyanate group (-NCO).

[0048] The activity of the curing agent can be effectively controlled through the blocking reaction. During storage, the active isocyanate groups are blocked, making it less likely to react at room temperature and improving the storage stability of the coating. For example, during the storage of the coating, the situation where the curing agent reacts prematurely with other components and causes the coating to fail is avoided.

[0049] When the coating needs to be cured after construction, by controlling conditions such as the deblocking temperature, the blocking agent can be deblocked to release the active isocyanate groups again, enabling them to react with other components (such as the active groups in the resin) for curing. In this way, the curing process of the coating can be more precisely controlled to obtain a coating film with good performance.

[0050] Furthermore, the catalyst is selected as dibutyltin dilaurate, and the catalyst dosage 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 and reduce the occurrence of other side reactions, thereby improving the quality and performance of the composite curing agent.

[0051] In the achievable manner of the first aspect, the reinforcing material is selected as graphene to further enhance the protection performance of the coating for the edge and non-edge regions; the reinforcing material is pretreated by mixing and grinding the modified epoxy resin and the material, and the mass of the reinforcing material is 5 - 10% of the total mass of the grinding mixture.

[0052] This pretreatment method helps the uniform dispersion of graphene in the resin, significantly improving the compatibility between graphene and the resin. Good compatibility enables graphene to be more evenly dispersed in the modified epoxy resin system. If the compatibility is poor, graphene is prone to agglomerate together, forming large particles, just like oil and water being incompatible and separating. And the uniformly dispersed graphene can fully exert its reinforcing and barrier properties.

[0053] During the grinding process, resin molecules can adsorb on the surface of graphene, forming a good interfacial bond through physical or chemical interactions. On the one hand, resin molecules can overcome the van der Waals forces between graphene, preventing its agglomeration; on the other hand, the functional groups on the surface of graphene (such as carboxyl groups, hydroxyl groups, etc.) can react with the active groups in the resin (such as epoxy groups, amino groups, etc.) to form chemical bonds. This good dispersion and interfacial bond ensure that graphene can fully play its reinforcing and barrier roles in the coating system, rather than existing in the form of aggregates, which affects the performance of the coating.

[0054] In the second aspect, the present invention provides a high-edge protection type cathodic electrophoretic coating, which is prepared by using the preparation method of the above high-edge protection type cathodic electrophoretic coating.

[0055] In an implementable manner of the second aspect, the above electrophoretic coating is subjected to electrophoretic film formation on a phosphated cold-rolled steel sheet. After curing, the film is tested. The coating roughness < 0.3, the neutral salt spray resistance can reach more than 1000 hours, and the number of rust spots in the blade test < 5, meeting the requirements of high-edge protection coatings.

[0056] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) By sequentially introducing cyclic substituents, forming a local branched structure, and amine modification in the resin structure, the present invention obtains a short-chain comb-shaped branched structure, effectively inhibiting the flow of the cured coating film at the edges, ensuring that there is sufficient film thickness and protective force at the edges. After testing, the above electrophoretic coating is subjected to electrophoretic film formation on a phosphated cold-rolled steel sheet. After curing, the film is tested. The coating roughness < 0.3, the neutral salt spray resistance can reach more than 1000 hours, and the number of rust spots in the blade test < 5, meeting the requirements of high-edge protection coatings, greatly improving the anti-corrosion performance at the edges and corners of automotive parts, reducing the damage of automotive spare parts and material waste caused by edge corrosion, extending the service life and appearance retention time of the vehicle, and reducing the risk of traffic accidents caused by edge corrosion.

[0057] (2) While enhancing the anti-corrosion performance of the edges, the coating of the present invention does not sacrifice the mechanical properties (hardness, flexibility, adhesion), chemical properties (chemical resistance), and appearance quality (flatness, glossiness) of the coating in non-edge areas. This is due to the reasonable selection of each component in the coating and precise process control, such as the use of composite curing agents, the addition of reinforcing materials, and the optimization of resin structures. During the multi-condition service process of the automobile, whether it is mechanical wear, chemical substance erosion during daily driving, or environmental impact under different climate conditions, this coating can ensure the good performance of the surface coating of automobile parts, improve the overall reliability and safety of the automobile, and reduce the maintenance cost of the automobile.

[0058] (3) The present invention uses a composite neutralizing agent to neutralize and emulsify the resin, and selects graphene as a reinforcing material and performs pretreatment, so that the coating forms a uniform and stable emulsion phase. Compared with the problems in the prior art that the addition of microgels leads to a decrease in anti-corrosion performance at non-edge areas and the addition of inorganic fillers is prone to sedimentation and poor use stability, the coating of the present invention has better stability and can maintain the consistency of its performance during storage and use, which is convenient for industrial production and application.

[0059] (4) The mechanical properties of the non-edge coating in the present invention are excellent, the pencil hardness is ≥2H, and the Erichsen value is ≥7 mm. The adhesion reaches grade 0, the chemical resistance is strong, and it can withstand a variety of acid, alkali, and salt corrosion media; the appearance quality is good, the roughness is <0.3, and the coating is uniform and flat.

[0060] (5) The present invention develops a stable and efficient composite curing agent and a composite neutralizing agent, overcomes the defects of uneven curing and poor stability of traditional additives, optimizes the curing crosslinking network, improves the denseness, corrosion resistance, and long-term stability of the coating, ensures the reliable storage and construction performance of the coating, extends the shelf life and construction application period, and reduces the production operation and maintenance costs and quality risks.

[0061] In summary, the high-edge protection cathodic electrophoretic coating prepared in the present invention effectively solves the problems of uneven film thickness and weak anti-corrosion caused by the tip effect at the edges and corners of automobile parts, realizes the coordinated improvement of edge protection performance and overall performance, and has good application prospects.

[0062] The present invention will be explained and described in detail below in conjunction with the drawings and specific embodiments. Description of the Drawings

[0063] Figure 1 It is a schematic flow chart of the preparation method of the high-edge protection cathodic electrophoretic coating in the embodiment of the present invention. Specific Embodiments

[0064] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant accompanying 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 disclosed content of the present invention more thorough and comprehensive.

[0065] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are 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.

[0066] Example 1: The embodiment of the present invention provides a preparation method of a high-edge protection type cathodic electrophoretic coating, and the preparation method includes the following steps: (1) Chain extension reaction to introduce cyclic substituents Select E-51 bisphenol A epoxy resin as the basic raw material, use triphenylphosphine with a purity of 98% as the catalytically active substance, select bisphenol A as the cyclic hydroxyl compound, and its addition amount is 0.2:1 based on the molar ratio of the epoxy groups of the epoxy resin. The amount of the catalytically active substance used is 0.5% of the mass of the epoxy resin. The chain extension reaction is carried out in a constant temperature environment of 120°C for 4 hours until the epoxy equivalent of the epoxy resin reaches 1000-1300.

[0067] (2) Formation of a local branched structure Cool the above chain extension product to 80°C, add polyetheramine as an amine chain extender with multiple active hydrogens, and its molar ratio to the epoxy groups of the epoxy resin is 1:10, and react at 90°C for 30 min.

[0068] (3) Amidation modification to obtain modified epoxy resin Use an aliphatic small molecule amine mixture composed of a primary amine and a secondary amine with 3 carbon atoms mixed in a volume ratio of 1:1 to carry out amidation modification on the above product. The molar ratio of the amino groups of the aliphatic small molecule amine mixture to the remaining epoxy groups is controlled at 1.1:1, the reaction temperature is maintained at 90°C, and the reaction duration is 2 hours.

[0069] (4) Bonding enhancement Introduce phenyl glycidyl ether for bonding enhancement, and the addition amount is 5% of the mass of the modified epoxy resin.

[0070] (5) Emulsion preparation The modified epoxy resin after the bonding enhancement treatment is stirred evenly with the composite curing agent to form a resin mixture. The resin mixture is slowly dropped into a mixture of a composite neutralizing agent (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 the standard range.

[0071] The preparation method of the composite curing agent includes the following steps: S1: An aromatic curing agent (toluene diisocyanate curing agent) and an aliphatic curing agent (hexamethylene diisocyanate curing agent) are selected and mixed and compounded according to a mass ratio of 6:4 to form a curing agent mixture; S2: The temperature is maintained at 70°C, a blocking agent is added, and the reaction is carried out under the action of a catalyst. During the reaction process, continuous stirring is carried out, and the molar ratio of the isocyanate group to the blocking agent is 1:1.1.

[0072] S3: After the reaction is completed, heating is stopped, and the reaction product is allowed to cool naturally to room temperature to obtain the finished product of the composite curing agent.

[0073] The catalyst selected is dibutyltin dilaurate, and the catalyst dosage is 0.1% of the total mass of the reactants. The blocking agent selected is trimethylolpropane.

[0074] The above graphene is pretreated, and the modified epoxy resin and graphene are mixed and ground. The mass of graphene is 7% of the total mass of the grinding mixture.

[0075] (6)Preparation of the finished coating The above resin emulsion is filtered to remove impurities and agglomerates, and a high-edge protection type cathodic electrophoretic coating emulsion is obtained. The color paste, the coating emulsion and pure water are mixed according to a mass ratio of 1:4:6, and after continuous stirring for 0.5 hours, a high-edge protection type cathodic electrophoretic coating is obtained.

[0076] It should be noted that the above color paste can use the black color paste of the company's model ZS-891 or the gray color paste of the model ZS-891.

[0077] Table 1 is a comparison table of the coating performance parameters prepared in Examples 1-5 and Comparative Examples 1-5

[0078] In Examples 1-5, a short-chain comb-branched structure was obtained by successively introducing cyclic substituents, forming a local branched structure, and amine modification in the resin structure, effectively suppressing the flow of the cured coating film at the edges and ensuring sufficient film thickness and protection at the edges. At the same time, this structure is also beneficial to improving the flexibility and other properties of the coating in the non-edge regions. The introduction of monofunctional glycidyl ether further increases the flexibility and chemical solvent tolerance of the coating.

[0079] The selection of each raw material and the setting of parameters enable various properties of the coating to reach a better balance. For example, the reasonable compounding of the composite neutralizer and acid value control ensure the stability of the emulsion; the reasonable ratio and use of the composite curing agent improve the crosslinking density and comprehensive properties of the coating film. Graphene, as a reinforcing material, is uniformly dispersed in the coating system after pretreatment, enhancing the protection performance of the coating for the edge and non-edge regions.

[0080] In Comparative Example 1, ordinary epoxy resin was used without modification, and its molecular structure could not effectively inhibit the film flow and improve the edge protection force like the optimized resin structure in the examples, resulting in poor performance indicators.

[0081] In Comparative Example 2, only local branching was carried out without subsequent steps such as amine modification, and the resin structure was imperfect, unable to balance the properties of the edge and non-edge regions well, resulting in poor performance indicators such as coating roughness and neutral salt spray.

[0082] In Comparative Example 3, only amine modification was carried out, lacking previous steps such as local branching, and the resin structure was also imperfect, unable to reach the performance level of the examples, and the performance indicators were poor.

[0083] In Comparative Example 4, the parameters were not within the protection scope of the claims, resulting in an out-of-control reaction process, an unreasonable resin structure, and a serious decline in the coating performance.

[0084] In Comparative Example 5, the parameters were not within the protection scope of the claims, and a single curing agent and neutralizer were used, unable to reasonably adjust the coating performance like the composite curing agent and neutralizer, resulting in poor coating performance.

[0085] Example 2: The embodiment of the present invention provides a preparation method of a high-edge protection type cathodic electrophoretic coating, and the preparation method includes the following steps: (1) Chain extension reaction to introduce cyclic substituents E-51 bisphenol A epoxy resin was selected as the basic raw material, triphenylphosphine with a purity of 98.5% was used as the catalytically active substance, and dodecylphenol was selected as the cyclic hydroxyl compound. Its addition amount was 0.25:1 based on the molar ratio of the epoxy groups of the epoxy resin, and the amount of the catalytically active substance was 0.7% of the mass of the epoxy resin. The chain extension reaction was carried out in a constant temperature environment of 125°C for 5 hours until the epoxy equivalent of the epoxy resin reached 1000 - 1300.

[0086] (2) Formation of a local branched structure The above chain extension product was cooled to 85°C, and hexamethylenediamine was added as an amine chain extender with multiple active hydrogens. Its molar ratio to the epoxy groups of the epoxy resin was 1.2:10, and the reaction was carried out at 95°C for 40 min.

[0087] (3) Amination modification to obtain a modified epoxy resin The above product was subjected to amination modification using a mixture of aliphatic small molecule amines composed of primary amines and secondary amines with 4 carbon atoms in a volume ratio of 1:1.5. The molar ratio of the amino groups of the aliphatic small molecule amine mixture to the remaining epoxy groups was controlled at 1.2:1, the reaction temperature was maintained at 100°C, and the reaction duration was 1 hour.

[0088] (4) Bonding enhancement Glycidyl tert - carbonate was introduced for bonding enhancement, and its addition amount was 8% of the mass of the modified epoxy resin.

[0089] (5) Emulsion preparation The modified epoxy resin after the bonding enhancement treatment was stirred evenly with a composite curing agent to form a resin mixture. The resin mixture was slowly dropped into a mixture of a composite neutralizing agent (acid value of 30) composed of 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 was 45%. After high - speed dispersion for one hour, graphene was added, and then the second part of water was added to emulsify and disperse the resin to form a homogeneous and stable emulsion phase. Finally, the third part of water was added to reduce the solid content in the resin emulsion to the standard range.

[0090] The preparation method steps of the composite curing agent were basically the same as those in Example 1, except that the temperature was maintained at 60°C, trimethylolpropane as a capping agent was added, and the reaction was carried out under the action of a catalyst with continuous stirring during the reaction, and the molar ratio of the isocyanate group to the capping agent was 1:1.0. The amount of the catalyst was 0.2% of the total mass of the reactants.

[0091] The above graphene was pretreated, and the modified epoxy resin and graphene were mixed and ground, where the mass of graphene was 5% of the total mass of the grinding mixture.

[0092] After uniformly stirring the modified epoxy resin and the composite curing agent, a resin mixture is formed. The resin mixture is slowly added dropwise to a mixture of a composite neutralizing agent prepared by mixing lactic acid and sulfamic acid in a ratio of 1:1 and the first portion 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 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 the standard range.

[0093] (6)Preparation of the finished coating The above resin emulsion is subjected to filtration treatment to remove impurities and agglomerates, and a high-edge protection type cathodic electrophoretic coating emulsion is obtained. The color paste, the coating emulsion and pure water are mixed in a mass ratio of 1:4.5:7, and after continuous stirring for 0.7 hours, a high-edge protection type cathodic electrophoretic coating is obtained.

[0094] Example 3: The embodiment of the present invention provides a preparation method of a high-edge protection type cathodic electrophoretic coating, and the preparation method includes the following steps: (1)Chain extension reaction to introduce a cyclic substituent E-44 bisphenol A type epoxy resin is selected as the basic raw material, triphenylphosphine with a purity of 99% is used as the catalytically active substance, the cyclic hydroxyl compound is a mixture of bisphenol A and dodecylphenol in a ratio of 1:1, and its addition amount is 0.3:1 based on the molar ratio of the epoxy groups of the epoxy resin. The amount of the catalytically active substance used is 1.0% of the mass of the epoxy resin. The chain extension reaction is carried out in a constant temperature environment of 130°C for 6 hours until the epoxy equivalent of the epoxy resin reaches 1000 - 1300.

[0095] (2)Form a local branched structure The above chain extension product is cooled to 90°C, and a mixture of polyetheramine and hexamethylenediamine in a ratio of 1:1 is added as an amine-based chain extender with multiple active hydrogens, and its molar ratio to the epoxy groups of the epoxy resin is 1.5:10. The reaction is carried out at 100°C for 50 min.

[0096] (3)Amine modification to obtain a modified epoxy resin An aliphatic small molecule amine mixture composed of a primary amine and a secondary amine with 5 carbon atoms in a volume ratio of 1:2 is used to carry out amine modification on the above product. The molar ratio of the amino groups of the aliphatic small molecule amine mixture to the remaining epoxy groups is controlled at 1.3:1, the reaction temperature is maintained at 95°C, and the reaction duration is 2 hours.

[0097] (4)Bonding enhancement Phenyl glycidyl ether is introduced for bonding enhancement, and the addition amount is 15% of the mass of the modified epoxy resin.

[0098] (5)Emulsion preparation The modified epoxy resin after the bonding enhancement treatment is stirred evenly with the composite curing agent to form a resin mixture. The resin mixture is slowly dropped into a mixture of a composite neutralizing agent (acid value is 45) prepared by mixing acetic acid, lactic acid and sulfamic 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 the standard range.

[0099] The above-mentioned graphene is pretreated, and the modified epoxy resin and graphene are mixed and ground, where the mass of graphene is 10% of the total mass of the grinding mixture.

[0100] The preparation method steps of the composite curing agent are basically the same as those in Example 1, except that a blocking agent ethylene glycol monobutyl ether is added and reacted under the action of a catalyst. During the reaction process, continuous stirring is carried out, and the molar ratio of the isocyanate group to the blocking agent is 1:1.2. The dosage of the catalyst is 0.3% of the total mass of the reactants.

[0101] The aromatic curing agent is selected as a mixture of toluene diisocyanate curing agent and polyphenyl polymethylene polyisocyanate.

[0102] (6)Preparation of the finished coating The above resin emulsion is filtered to remove impurities and agglomerates, and a high-edge protection type cathodic electrophoretic coating emulsion is obtained. The color paste, the coating emulsion and pure water are mixed according to a mass ratio of 1:5:8, and after continuous stirring for 1 hour, a high-edge protection type cathodic electrophoretic coating is obtained.

[0103] Example 4: The embodiment of the present invention provides a preparation method of a high-edge protection type cathodic electrophoretic coating, and the preparation method includes the following steps: (1)Chain extension reaction to introduce a cyclic substituent E-44 bisphenol A type epoxy resin is selected as the basic raw material, triphenylphosphine with a purity of 98.2% is used as the catalytically active substance, the cyclic hydroxyl compound is bisphenol A, and its addition amount is 0.22:1 based on the molar ratio of the epoxy groups of the epoxy resin. The dosage of the catalytically active substance is 0.6% of the mass of the epoxy resin. The chain extension reaction is carried out in a constant temperature environment of 123°C for 4.5 hours until the epoxy equivalent of the epoxy resin reaches 1000 - 1300.

[0104] (2)Form a local branched structure The above chain extension product is cooled to 82°C, and polyetheramine is added as an amine chain extender with multiple active hydrogens, and its molar ratio to the epoxy groups of the epoxy resin is 1.1:10, and the reaction is carried out at 100°C for 35 min.

[0105] (3) Amidation modification to obtain modified epoxy resin The above product was subjected to amidation modification using an aliphatic small molecule amine mixture composed of primary amine and secondary amine with 4 carbon atoms in a volume ratio of 1:1.5. The molar ratio of the amino group of the aliphatic small molecule amine mixture to the remaining epoxy groups was controlled at 1.3:1, the reaction temperature was maintained at 95 °C, and the reaction duration was 3 hours.

[0106] (4)Bonding enhancement Phenyl glycidyl ether was introduced for bonding enhancement, and the addition amount was 12% of the mass of the modified epoxy resin.

[0107] (5)Emulsion preparation The modified epoxy resin after bonding enhancement treatment was stirred evenly with a composite curing agent to form a resin mixture. The resin mixture was slowly added dropwise to a mixture of a composite neutralizing agent (acid value of 25) composed of 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 was 45%. After high-speed dispersion for one hour, graphene was added, and then the second part of water was added to emulsify and disperse the resin to form a uniform and stable emulsion phase. Finally, the third part of water was added to reduce the solid content in the resin emulsion to the standard range.

[0108] The above graphene was pretreated, and the modified epoxy resin and graphene were mixed and ground, where the mass of graphene was 6% of the total mass of the grinding mixture.

[0109] The preparation method steps of the composite curing agent were basically the same as those in Example 1, except that the temperature was maintained at 68 °C, the capping agent diethylene glycol butyl ether was added, and the reaction was carried out under the action of a catalyst. Stirring was continued during the reaction, and the molar ratio of the isocyanate group to the capping agent was 1:1.15. The dosage of the catalyst was 0.15% of the total mass of the reactants.

[0110] (6)Preparation of the finished paint The above resin emulsion was filtered to remove impurities and agglomerates, and a high-edge protection type cathodic electrophoretic coating emulsion was obtained. The color paste, the coating emulsion and pure water were mixed in a mass ratio of 1:4:6, and after continuous stirring for 0.5 hours, a high-edge protection type cathodic electrophoretic coating was obtained.

[0111] Example 5: The embodiment of the present invention provides a preparation method of a high-edge protection type cathodic electrophoretic coating, and the preparation method includes the following steps: (1)Chain extension reaction to introduce a cyclic substituent E-44 bisphenol A epoxy resin was selected as the base raw material, triphenylphosphine with a purity of 98% was used as the catalytically active substance, bisphenol A was selected as the cyclic hydroxyl compound, and its addition amount was 0.26:1 based on the molar ratio of the epoxy groups of the epoxy resin. The amount of the catalytically active substance used was 0.5% of the mass of the epoxy resin. The chain extension reaction was carried out in a constant temperature environment of 126°C for 4 hours until the epoxy equivalent of the epoxy resin reached 1000 - 1300.

[0112] (2) Formation of a local branched structure The above chain extension product was cooled to 86°C, and a polyetheramine and hexamethylenediamine mixture mixed in a ratio of 1:1 was added as an amine chain extender with multiple active hydrogens, and its molar ratio to the epoxy groups of the epoxy resin was 1.3:10. The reaction was carried out at 96°C for 30 min.

[0113] (3) Amination modification to obtain modified epoxy resin An aliphatic small molecule amine mixture composed of a primary amine and a secondary amine with 3 carbon atoms mixed in a volume ratio of 1:1.5 was used to carry out amination modification on the above product. The molar ratio of the amino groups of the aliphatic small molecule amine mixture to the remaining epoxy groups was controlled at 1.2:1, the reaction temperature was maintained at 95°C, and the reaction duration was 2.6 hours.

[0114] (4) Emulsion preparation The modified epoxy resin and the composite curing agent were stirred evenly to form a resin mixture. The resin mixture was slowly added dropwise to a mixture of a composite neutralizing agent (acid value of 20) composed of formic acid and acetic acid mixed in a ratio of 1:1 and the first part of water. At this time, the solid content in the mixture was 45%. After high-speed dispersion for one hour, graphene was added, and then the second part of water was added to emulsify and disperse the resin to form a homogeneous and stable emulsion phase. Finally, the third part of water was added to reduce the solid content in the resin emulsion to the standard range.

[0115] The above graphene was pretreated, and the modified epoxy resin and graphene were mixed and ground, where the mass of graphene was 9% of the total mass of the grinding mixture.

[0116] The preparation method steps of the composite curing agent were basically the same as those in Example 1, except that the temperature was maintained at 68°C, trimethylolpropane as a capping agent was added, and the reaction was carried out under the action of a catalyst. Stirring was continued during the reaction, and the molar ratio of the isocyanate group to the capping agent was 1:1.05. The amount of the catalyst used was 0.1% of the total mass of the reactants.

[0117] (5) Preparation of the finished paint After filtering the above resin emulsion to remove impurities and agglomerates, a high-edge protection cathodic electrophoretic coating emulsion is obtained. The color paste, coating emulsion, and pure water are mixed at a mass ratio of 1:4.5:7 and continuously stirred for 0.7 hours to obtain a high-edge protection cathodic electrophoretic coating.

[0118] Comparative Example 1 The comparative example of the present invention provides a preparation method of a cathodic electrophoretic coating, and its preparation method includes the following steps: (1) The ordinary epoxy resin and the composite curing agent are stirred evenly to form a resin mixture. The resin mixture is slowly dropped into the mixture of the composite neutralizing agent 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 the standard range.

[0119] The composite curing agent and the composite neutralizing agent are the same as those in Example 1.

[0120] The addition amount and pretreatment of the graphene are the same as those in Example 1.

[0121] (2) Preparation of the coating finished product After filtering the above resin emulsion to remove impurities and agglomerates, a coating emulsion is obtained. The color paste, coating emulsion, and pure water are mixed at a mass ratio of 1:4:6 and continuously stirred for 0.5 hours to obtain a coating.

[0122] Comparative Example 2 The comparative example of the present invention provides a preparation method of a cathodic electrophoretic coating, and its basic steps are the same as those in Example 1. The difference is that the epoxy resin only undergoes a chain extension reaction and local branching, without amination modification and without introducing phenyl glycidyl ether to enhance the bonding of the modified resin.

[0123] Comparative Example 3 The comparative example of the present invention provides a preparation method of a cathodic electrophoretic coating, and its basic steps are the same as those in Example 1. The difference is that the epoxy resin only undergoes amination modification, lacking previous steps such as chain extension reaction and local branching.

[0124] Comparative Example 4 The comparative example of the present invention provides a preparation method of a cathodic electrophoretic coating, including the following steps: (1) Introduce a cyclic substituent through a chain extension reaction E-44 bisphenol A epoxy resin was selected as the base raw material, triphenylphosphine with a purity of 98% was used as the catalytically active substance, bisphenol A was selected as the cyclic hydroxyl compound, and its addition amount was 0.4:1 based on the molar ratio of the epoxy groups of the epoxy resin. The amount of the catalytically active substance used was 0.5% of the mass of the epoxy resin. The chain extension reaction was carried out in a constant temperature environment of 140 °C for 7 hours.

[0125] (2) Formation of a local branched structure The above chain extension product was cooled to 80 °C, and polyetheramine was added as an amine chain extender with multiple active hydrogens. The molar ratio of it to the epoxy groups of the epoxy resin was 2:10, and the reaction was carried out at 90 °C for 20 min.

[0126] (3) Amidation modification to obtain modified epoxy resin The above product was subjected to amidation modification with an aliphatic small molecule amine mixture composed of primary amine and secondary amine with 7 carbon atoms in a volume ratio of 1:3. The molar ratio of the amino groups of the aliphatic small molecule amine mixture to the remaining epoxy groups was controlled at 1.1:1, the reaction temperature was maintained at 90 °C, and the reaction duration was 2 hours.

[0127] (4) Bonding enhancement Phenyl glycidyl ether was introduced for bonding enhancement, and the addition amount was 20% of the mass of the modified epoxy resin.

[0128] (5) Emulsion preparation The modified epoxy resin after the bonding enhancement treatment was stirred evenly with a composite curing agent to form a resin mixture. The resin mixture was slowly added dropwise to a mixture of a composite neutralizing agent (acid value of 50) composed of 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 was 40%. After high-speed dispersion for one hour, graphene was added, and then the second part of water was added to emulsify and disperse the resin to form a uniform and stable emulsion phase. Finally, the third part of water was added to reduce the solid content in the resin emulsion to the standard range.

[0129] The preparation method of the composite curing agent includes the following steps: S1: An aromatic curing agent (toluene diisocyanate curing agent) and an aliphatic curing agent (hexamethylene diisocyanate curing agent) were selected and mixed and compounded in a mass ratio of 7:3 to form a curing agent mixture; S2: The temperature was maintained at 70 °C, trimethylolpropane as a blocking agent was added, and the reaction was carried out under the action of a catalyst. During the reaction, continuous stirring was carried out, and the molar ratio of the isocyanate group to the blocking agent was 1:1.5.

[0130] S3: After the reaction ended, heating was stopped, and the reaction product was allowed to cool naturally to room temperature and then filtered to obtain the finished product of the composite curing agent.

[0131] The catalyst selected is dibutyltin dilaurate, and the dosage of the catalyst is 0.4% of the total mass of the reactants.

[0132] The above graphene is pretreated, and the modified epoxy resin and graphene are mixed and ground, where the mass of graphene is 7% of the total mass of the grinding mixture.

[0133] (6)Preparation of the finished paint The above resin emulsion is filtered to remove impurities and agglomerates, and a high-edge protection type cathodic electrophoretic coating emulsion is obtained. The color paste, the coating emulsion and pure water are mixed according to a mass ratio of 1:4:6, and after continuous stirring for 0.5 hours, a high-edge protection type cathodic electrophoretic coating is obtained.

[0134] Comparative Example 5 The comparative example of the present invention provides a preparation method of a cathodic electrophoretic coating, including the following steps: (1)Chain extension reaction to introduce a cyclic substituent E-51 bisphenol A epoxy resin is selected as the basic raw material, triphenylphosphine with a purity of 98% is used as the catalytically active substance, the cyclic hydroxyl compound is bisphenol A, and its addition amount is 0.1:1 based on the molar ratio of the epoxy groups of the epoxy resin. The dosage of the catalytically active substance is 0.3% of the mass of the epoxy resin. The chain extension reaction is carried out in a constant temperature environment of 110°C for 3 hours until the epoxy equivalent of the epoxy resin reaches 600 - 800.

[0135] (2)Form a local branched structure The above chain extension product is cooled to 80°C, and polyetheramine is added as an amine chain extender with multiple active hydrogens. Its molar ratio to the epoxy groups of the epoxy resin is 0.8:10, and the reaction is carried out at 85°C for 2 h.

[0136] (3)Amine modification to obtain a modified epoxy resin The above product is subjected to amine modification using an aliphatic small molecule amine mixture composed of primary amine and secondary amine with 2 carbon atoms in a volume ratio of 1:1.5. The molar ratio of the amino groups of the aliphatic small molecule amine mixture to the remaining epoxy groups is controlled at 0.9:1, the reaction temperature is maintained at 60°C, and the reaction duration is 1.5 hours.

[0137] (4)Bonding enhancement Phenyl glycidyl ether is introduced for bonding enhancement, and the addition amount is 3% of the mass of the modified epoxy resin.

[0138] (5)Emulsion preparation After uniformly stirring the modified epoxy resin after the bonding enhancement treatment with a curing agent (such as toluene diisocyanate curing agent), 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 the standard range.

[0139] The above-mentioned graphene is pretreated, and the modified epoxy resin and graphene are mixed and ground, where the mass of graphene is 3% of the total mass of the grinding mixture.

[0140] (6)Preparation of the finished coating The above resin emulsion is filtered to remove impurities and agglomerates, and a high-edge protection type cathodic electrophoretic coating emulsion is obtained. The color paste, the coating emulsion and pure water are mixed according to a mass ratio of 1:4:6, and after continuous stirring for 0.5 hours, a high-edge protection type cathodic electrophoretic coating is obtained.

[0141] Any numerical values cited in this text include all values from the lower value to the upper value increasing by one unit between the lower limit and the upper limit, as long as there is an interval of at least two units between any lower value and any higher value. For example, if the value of the number of components or process variables (such as temperature, pressure, time, etc.) is stated as ranging from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, then the purpose is to illustrate that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32, etc. are also explicitly listed in this specification. For values less than 1, a unit is appropriately considered to be 0.0001, 0.001, 0.01, 0.1. These are merely examples of what is intended to be clearly expressed, and it can be considered that all possible combinations of the numerical values listed between the lowest value and the highest value are explicitly stated in this specification in a similar manner.

[0142] Unless otherwise specified, all ranges include the endpoints and all numbers between the endpoints. "About" or "approximate" used with a range 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.

[0143] It should be understood that the above description is for illustrative purposes and not for limitation. Upon reading the above description, many embodiments and many applications other than the provided examples will be apparent to those skilled in the art. Therefore, the scope of this teaching should not be determined with reference to the above description, but should be determined with reference to the appended claims and the full scope of the equivalents of these claims. For the sake of completeness, all articles and references, including patent applications and published disclosures, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein from the foregoing claims is not intended to abandon such subject matter, nor should the inventor be regarded as not having considered such subject matter as part of the disclosed inventive subject matter.

[0144] The above exemplary description of the present invention is made in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited by the above methods. As long as such non-substantial improvements are made by adopting 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 protection scope 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 epoxy resin with a specific epoxy equivalent as the basic raw material, a chain extension reaction is carried out with a cyclic hydroxyl compound under the catalysis of a catalytically active substance to introduce a cyclic substituent; (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; (3) Under heat preservation condition, the above product is subjected to amination modification using a mixture of aliphatic small molecule amines to obtain a modified epoxy resin having a short-chain comb-type branched structure; (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 part of water. After high-speed dispersion for one hour, the reinforcing material 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; (5) filtering the resin emulsion to remove impurities and agglomerates to obtain a high edge protection type 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 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; And / or, the epoxy resin is bisphenol A epoxy resin; And / or, the cyclic hydroxy compound is selected from at least one of bisphenol A and dodecylphenol; And / or, the catalytically active substance is triphenylphosphine, and its purity is not less than 98%.

3. The method for preparing the high edge protection cathodic electrophoretic coating according to claim 2, characterized in that: 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 catalytic active substance used is 0.5-1.0% of the mass of the epoxy resin; And / or, the chain extension reaction is continued at a constant temperature of 120-130° C. for 4-6 hours until the epoxy equivalent of the epoxy resin reaches 1000-1300.

4. The method for preparing a high edge protection cathodic electrophoretic coating according to claim 1, characterized in that: 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; And / or, the amine chain extension reactant is selected from at least one of polyetheramine and hexamethylenediamine.

5. The method for preparing a high edge protection cathodic electrophoretic coating according to claim 1, characterized in that: In the step (3), the molar ratio of the amine 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; 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.

6. The method for preparing a high edge protection cathodic electrophoretic coating according to claim 1, characterized in that: 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; And / or, the acid value of the composite neutralizer is 20-45.

7. The method for preparing a high edge protection cathodic electrophoretic coating according to claim 1, characterized in that: The curing agent is a composite curing agent, and its preparation method comprises the following steps: S1: Selecting an aromatic curing agent and an aliphatic curing agent for mixing and compounding 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 the isocyanate group to the 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.

8. The method for preparing a high edge protection cathodic electrophoretic coating according to claim 1, 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; And / or, 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 groups; And / or, the catalyst is dibutyltin dilaurate, and the amount of the catalyst is 0.1-0.3% of the total mass of the reactants.

9. The method for preparing a high edge protection cathodic electrophoretic coating according to any one of claims 1 to 8, characterized in that: Pre-treating the reinforcing material, mixing and grinding the modified epoxy resin and the reinforcing material, wherein the mass of the reinforcing material is 5-10% of the total mass of the ground mixture; And / or, the reinforcing material is graphene.

10. A high edge protection cathodic electrophoretic coating, characterized in that: Prepared by the preparation method of high edge protection cathodic electrophoretic coating according to any one of claims 1 to 9; And / or, the electrophoretic coating is electrophoretically coated on a phosphated cold-rolled steel plate, and the cured paint film is tested, with a coating roughness of <0.3, a neutral salt spray endurance of more than 1000 hours, and a blade test rust point count of <5, meeting the requirements for high edge protection coatings.

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