High-temperature-resistant cathode electrophoresis emulsion and preparation method thereof

Abstract

The invention relates to the field of cathode electrophoresis emulsions, and particularly discloses a high-temperature-resistant cathode electrophoresis emulsion and a preparation method thereof. The emulsion is prepared from the following raw materials: amine modified epoxy resin and blocked isocyanate, wherein the amine modified epoxy resin is prepared from the following raw materials: DOPO type modified novolac epoxy resin, bisphenol A type epoxy resin E-20, bisphenol S, nonyl phenol, monobasic secondary amine and diaminodiphenyl sulfone. The cathode electrophoresis emulsion provided by the invention has excellent high-temperature resistance, and the cathode electrophoresis paint prepared by matching the cathode electrophoresis emulsion with corresponding cathode electrophoresis paint color paste components has obvious high-temperature resistance advantage compared with the conventional cathode electrophoresis paint after the obtained coating is dried to form a film; meanwhile, various properties such as good chemical stability, deformation stability and the like are also realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of cathodic electrophoretic emulsion, more particularly, it relates to a high-temperature-resistant cathodic electrophoretic emulsion and a preparation method thereof. BACKGROUND

[0002] With the continuous development of industry, cathodic electrophoretic coating has been widely used in many fields such as automobiles, new energy, machinery manufacturing, electronics and electrical appliances, etc. due to its unique advantages such as good corrosion resistance, penetration and coating efficiency. In the automotive industry, cathodic electrophoretic coating can provide good protection and decoration effect for the vehicle body, effectively prolonging the service life of the vehicle; in the new energy field, it plays an important role in ensuring the stability and safety of energy equipment, in addition, it can also meet the functional requirements of different industries for the coating.

[0003] With the rapid development of the energy market, new energy technology is innovating day by day. Compared with the traditional fuel vehicle system, the demand for high-temperature resistance and flame retardance has significantly increased. As an important part of supporting materials, electrophoretic coating plays an indispensable role in the field of new energy and automotive lamps. High-temperature-resistant coatings have important significance in real-world environments, such as occasional fires after car collisions, and the presence of high-temperature-resistant coatings can reduce the severity of accidents, so the market's demand for heat-resistant coatings is increasing.

[0004] Currently, in the field of cathodic electrophoretic coating, the conventional method is to use ordinary epoxy resin as the base material to prepare a cathodic electrophoretic emulsion. Ordinary epoxy resin is widely available and relatively low in cost, and is commonly used as a base material for preparing cathodic electrophoretic emulsion. However, the molecular structure and properties of ordinary epoxy resin limit the improvement of the heat resistance of the coating, and cannot meet the higher requirements for high-temperature resistance in new energy technology and real-world environments. In high-temperature environments, the existing cathodic electrophoretic coating is prone to discoloration, powdering, and even peeling, which leads to a decrease in the protective performance of the coating and cannot effectively protect the workpiece. SUMMARY

[0005] In order to solve the above technical problems, the present application provides a high-temperature-resistant cathodic electrophoretic emulsion and a preparation method thereof.

[0006] In a first aspect, the present application provides a high-temperature-resistant cathodic electrophoretic emulsion, which adopts the following technical solution: A high-temperature-resistant cathodic electrophoretic emulsion, the raw materials used include amine-modified epoxy resin and blocked isocyanate, the raw materials used for the amine-modified epoxy resin include DOPO-modified phenolic epoxy resin, bisphenol A type epoxy resin E-20, bisphenol S, nonylphenol, monobasic secondary amine and diamino diphenyl sulfone.

[0007] By adopting the technical scheme, the amine modified epoxy resin and the blocked isocyanate are used as raw materials, and a cathodic electrophoretic emulsion with excellent high-temperature resistance can be prepared, the cathodic electrophoretic coating prepared by using the cathodic electrophoretic emulsion and corresponding cathodic electrophoretic coating color paste components has obvious high-temperature resistance advantage compared with conventional cathodic electrophoretic coating, and the coating obtained by baking and film forming has the advantages of not being easy to discolor, powdering and falling off in a high-temperature environment, and can provide stable protection for the workpiece.

[0008] Specifically, the DOPO type modified phenolic epoxy resin is used in the amine modified epoxy resin, compared with the conventional epoxy system, more rigid structures and phosphorus heterocycles can be introduced, and the heat resistance of the resin matrix is effectively improved; the bisphenol S is used for chain extension, the sulfone group can be introduced to the small molecule epoxy resin in priority, the introduction of the sulfone group not only improves the thermal stability of the coating film, but also enhances the chemical stability and deformation stability; the nonyl phenol is grafted on the resin, which can bring certain flexibility to the resin and effectively improve the appearance of the coating film; the mono secondary amine and the diamino diphenyl sulfone are used for amination, a small amount of diamino diphenyl sulfone can improve the heat stability while improving the penetration of the cathodic electrophoretic solution.

[0009] Preferably, the weight ratio of the DOPO type modified phenolic epoxy resin and the bisphenol A type epoxy resin E-20 is (0.15-0.20):1.

[0010] By adopting the technical scheme, the ratio of the DOPO type modified phenolic epoxy resin and the bisphenol A type epoxy resin E-20 is optimized, the content of the rigid structure and the phosphorus heterocycle in the system reaches a suitable ratio, and the heat resistance of the resin matrix is effectively improved. If the ratio is lower than the ratio, the amount of the rigid structure and the phosphorus heterocycle introduced in the system is insufficient, and the heat resistance of the resin matrix cannot be fully improved; if the ratio is higher than the ratio, too much rigid structure will cause the flexibility of the resin to decrease, and affect the appearance and other properties of the coating film.

[0011] Preferably, the weight ratio of the nonyl phenol and the bisphenol S is (0.3-0.4):1.

[0012] By adopting the technical scheme, the ratio of the nonyl phenol and the bisphenol S is optimized, the nonyl phenol can bring suitable flexibility to the resin on the basis of ensuring that the bisphenol S introduces the sulfone group to improve the thermal stability, chemical stability and deformation stability of the coating film, and effectively improve the appearance of the coating film. If the ratio is lower than the ratio, the amount of the nonyl phenol is too small, the resin toughness is insufficient, and the appearance of the coating film cannot be effectively improved, and the leveling property of the finished paint film is poor; if the ratio is higher than the ratio, the content of the nonyl phenol is too high, the effect of improving the thermal stability of the coating film brought by the introduction of the sulfone group by the bisphenol S is weakened, and the storage stability of the finished paint is poor.

[0013] Secondly, this application provides a method for preparing a high-temperature resistant cathodic electrophoretic emulsion, which adopts the following technical solution: A method for preparing a high-temperature resistant cathodic electrophoretic emulsion includes the following steps: S1. Preparation of amine-modified epoxy resin DOPO-type modified phenolic epoxy resin, bisphenol A-type epoxy resin E-20, bisphenol S, nonylphenol and inert solvent are mixed and heated to melt. Then a catalyst is added to carry out chain extension reaction. After chain extension is completed, the temperature is lowered and a monoamine is added for amine modification. Then diaminodiphenyl sulfone is added to continue amination to obtain amine-modified epoxy resin. S2. Preparation of high-temperature resistant cathodic electrophoretic emulsion Blocked isocyanate and film-forming aid are added to the amine-modified epoxy resin obtained in step S1 and mixed evenly. Then, after neutralization, emulsification, and vacuum distillation, the solid content is adjusted to obtain a high-temperature cathodic electrophoresis emulsion with a solid content of 33-35%.

[0014] Preferably, the inert solvent in S1 is a toluene-based solvent or a ketone-based solvent.

[0015] Preferably, the toluene solvent is one or more of toluene, o-xylene, and m-xylene.

[0016] Preferably, the ketone solvent is butanone and / or methyl isobutyl ketone.

[0017] Preferably, the amount of the inert solvent is 15-20% of the total mass of all resins.

[0018] Preferably, the epoxy equivalent of the resin after chain extension in S1 is 800-1100.

[0019] By adopting the above technical solution, this application controls the epoxy equivalent after chain extension to 800-1100 to ensure good workability voltage and emulsion storage stability. If the epoxy equivalent is too low, the molecular weight will be too small, and the electrophoretic coating bath will be easily broken down by the electric field, resulting in abnormal coating film; if the epoxy equivalent is too high, the storage stability of the finished coating will be poor.

[0020] Preferably, the monovalent secondary amine is one or more of methylethanolamine, diethanolamine, and ethylethanolamine.

[0021] Preferably, the amount of the monovalent secondary amine added in S1 is 75-85% of the molar number of epoxy groups in the resin after chain extension.

[0022] Preferably, the amount of diaminodiphenyl sulfone added in S1 is 2-3% of the molar number of epoxy groups in the resin after chain extension.

[0023] Preferably, the neutralization process in S2 specifically involves neutralization using small molecule organic acids.

[0024] Preferably, the small molecule organic acid is one or more of lactic acid, acetic acid, formic acid, and aminosulfonic acid.

[0025] In summary, this application has the following beneficial technical effects: 1. The cathodic electrophoretic emulsion of this application has excellent high temperature resistance. The cathodic electrophoretic coating prepared by the cathodic electrophoretic emulsion in combination with the corresponding cathodic electrophoretic coating pigment components has a significant advantage in high temperature resistance after drying and film formation compared with conventional cathodic electrophoretic coatings. At the same time, it also has good chemical stability, deformation stability and other properties. 2. The coating made from the cathodic electrophoretic emulsion of this application has high storage stability and good flexibility, which effectively improves the appearance of the coating film and has good leveling properties; 3. The preparation method of the cathodic electrophoretic emulsion of this application is simple, easy to operate, and the raw materials are readily available, making it suitable for large-scale industrial production. Detailed Implementation

[0026] In some specific embodiments of high-temperature cathodic electrophoretic emulsions, the weight ratio of DOPO-type modified phenolic epoxy resin to bisphenol A-type epoxy resin E-20 is (0.15-0.20):1. In some specific embodiments of high-temperature cathodic electrophoretic emulsions, the weight ratio of nonylphenol to bisphenol S is (0.3-0.4):1; In some specific embodiments of high-temperature cathodic electrophoretic emulsions, the inert solvent is a toluene-based solvent or a ketone-based solvent, wherein the toluene-based solvent is one or more of toluene, o-xylene, and m-xylene, and the ketone-based solvent is butanone and / or methyl isobutyl ketone. In some specific embodiments of high-temperature cathodic electrophoretic emulsions, the amount of inert solvent used is 15-20% of the total mass of all resins; In some specific embodiments of high-temperature cathodic electrophoretic emulsions, the epoxy equivalent of the resin after chain extension is 800-1100. In some specific embodiments of high-temperature cathodic electrophoretic emulsions, the monovalent secondary amine is one or more of methylethanolamine, diethanolamine, and ethylethanolamine; In some specific embodiments of high-temperature cathodic electrophoretic emulsions, the amount of monovalent secondary amine added is 75-85% of the molar number of epoxy groups in the resin after chain extension. In some specific embodiments of high-temperature cathodic electrophoretic emulsions, the amount of diaminodiphenyl sulfone added is 2-3% of the molar number of epoxy groups in the resin after chain extension. In some specific embodiments of high-temperature cathodic electrophoretic emulsions, the neutralization process specifically involves neutralization using small-molecule organic acids; wherein, the small-molecule organic acids are one or more of lactic acid, acetic acid, formic acid, and aminosulfonic acid; In some specific embodiments of high-temperature cathodic electrophoretic emulsions, the above raw materials, proportions, and process conditions are used, and the preparation method is as follows: S1. Preparation of amine-modified epoxy resin DOPO-type modified phenolic epoxy resin, bisphenol A-type epoxy resin E-20, bisphenol S, nonylphenol, and an inert solvent were mixed and heated to 100-110℃. After all the resins were completely melted, a catalyst was added, and the temperature was raised to 130-140℃ and kept for 2 hours. Then, the epoxy equivalent was tested. When the epoxy equivalent met the standard, the temperature was lowered to 100℃, and a monohydric secondary amine was added for amine modification. After keeping the temperature at 100-120℃ for 1 hour, diaminodiphenyl sulfone was added to continue amination. After amination was completed, the amine-modified epoxy resin was obtained and cooled to 90-100℃ for later use. S2. Preparation of high-temperature resistant cathodic electrophoretic emulsion Blocked isocyanate and film-forming aid are added to the amine-modified epoxy resin obtained in step S1, and the mixture is stirred and mixed evenly. Then the temperature is lowered to 55-60℃, and small molecule organic acid is added for neutralization. Deionized water is added for emulsification under high-speed dispersion. After emulsification, low-boiling-point solvent is removed by vacuum distillation, and then deionized water is added to adjust the solid content. The obtained high-temperature resistant cathodic electrophoretic emulsion with a solid content of 33-35% has excellent high-temperature resistance. The cathodic electrophoretic coating prepared by matching the cathodic electrophoretic coating pigment components with this cathodic electrophoretic emulsion has a significant advantage in high-temperature resistance after drying and film formation compared with conventional cathodic electrophoretic coatings. At the same time, it also has good chemical stability, deformation stability and other properties.

[0027] Based on the above, the applicant will further describe this application in detail using the following embodiments.

[0028] Unless otherwise specified, the raw materials used in this application are those that can be regularly purchased from commercial channels.

[0029] The DOPO-type modified phenolic epoxy resin used in this application was purchased from Tongyu New Materials, model TER520K75; The bisphenol A type epoxy resin E-20 used in this application was purchased from Nantong Xingchen. The blocked isocyanate in this application is a semi-finished product manufactured by our company, model number DP-05. This product is formed by blocking MDI-type isocyanate with ethylene glycol monobutyl ether and diethylene glycol monobutyl ether. Since its preparation process is a conventional preparation process in this field, its specific preparation process will not be described in detail in this application.

[0030] Example 1.1 A method for preparing a high-temperature resistant cathodic electrophoretic emulsion includes the following steps: S1. Preparation of amine-modified epoxy resin 40g of DOPO-modified phenolic epoxy resin, 200g of bisphenol A-type epoxy resin E-20, 22g of bisphenol S, 8g of nonylphenol, and 50g of methyl isobutyl ketone were mixed and heated to 105℃. After all the resins were completely melted, 0.3g of triphenylphosphine catalyst was added, and the temperature was raised to 135℃ and kept for 2 hours. Then, the epoxy equivalent was tested. When the epoxy equivalent met the standard, the temperature was lowered to 100℃, and 21.4g of methylethanolamine was added for amine modification. After keeping at 110℃ for 1 hour, 2.2g of diaminodiphenyl sulfone was added to continue amination. After amination was completed, amine-modified epoxy resin was obtained and cooled to 95℃ for use. S2. Preparation of high-temperature resistant cathodic electrophoretic emulsion Add 55g of blocked isocyanate and 4g of film-forming aid propylene glycol phenyl ether to 200g of amine-modified epoxy resin obtained in step S1, stir and mix evenly, then cool to 55℃, add 8g of lactic acid to neutralize, add deionized water to emulsify under high-speed dispersion, after emulsification, remove low-boiling-point solvent by vacuum distillation, add deionized water to adjust solid content, and obtain high-temperature resistant cathodic electrophoresis emulsion.

[0031] Example 1.2 A method for preparing a high-temperature resistant cathodic electrophoretic emulsion differs from Example 1.1 in that the weight ratio of DOPO-modified phenolic epoxy resin and bisphenol A-type epoxy resin E-20 is 0.15:1, specifically, 30g of DOPO-modified phenolic epoxy resin and 200g of bisphenol A-type epoxy resin E-20 are used, while the rest is the same as in Example 1.1.

[0032] Example 1.3 A method for preparing a high-temperature resistant cathodic electrophoretic emulsion differs from Example 1.1 in that the weight ratio of DOPO-modified phenolic epoxy resin and bisphenol A-type epoxy resin E-20 is 0.1:1, specifically, 20g of DOPO-modified phenolic epoxy resin and 200g of bisphenol A-type epoxy resin E-20 are used, while the rest is the same as in Example 1.1.

[0033] Example 1.4 A method for preparing a high-temperature resistant cathodic electrophoretic emulsion differs from Example 1.1 in that the weight ratio of DOPO-modified phenolic epoxy resin and bisphenol A-type epoxy resin E-20 is 0.3:1, specifically, 60g of DOPO-modified phenolic epoxy resin and 200g of bisphenol A-type epoxy resin E-20 are used, while the rest is the same as in Example 1.1.

[0034] Example 2.1 A method for preparing a high-temperature resistant cathodic electrophoretic emulsion differs from Example 1.1 in that the weight ratio of nonylphenol to bisphenol S is 0.3:1, specifically, nonylphenol is 6.6g and bisphenol S is 22g, while the rest is the same as in Example 1.1.

[0035] Example 2.2 A method for preparing a high-temperature resistant cathodic electrophoretic emulsion differs from Example 1.1 in that the weight ratio of nonylphenol to bisphenol S is 0.4:1, specifically, nonylphenol is 8.8g and bisphenol S is 22g, while the rest is the same as in Example 1.1.

[0036] Example 2.3 A method for preparing a high-temperature resistant cathodic electrophoretic emulsion differs from Example 1.1 in that the weight ratio of nonylphenol to bisphenol S is 0.1:1, specifically, nonylphenol is 2.2g and bisphenol S is 22g, while the rest is the same as in Example 1.1.

[0037] Example 2.4 A method for preparing a high-temperature resistant cathodic electrophoretic emulsion differs from Example 1.1 in that the weight ratio of nonylphenol to bisphenol S is 0.6:1, specifically, nonylphenol is 13.2g and bisphenol S is 22g, while the rest is the same as in Example 1.1.

[0038] Example 3.1 A method for preparing a high-temperature resistant cathodic electrophoretic emulsion differs from Example 1.1 in that the epoxy equivalent of the resin after chain extension is 560, specifically consisting of 35g of DOPO-type modified phenolic epoxy resin, 175g of bisphenol A-type epoxy resin E-20, 11g of bisphenol S1, 4g of nonylphenol, and 50g of methyl isobutyl ketone. The rest is the same as in Example 1.1.

[0039] Example 3.2 A method for preparing a high-temperature resistant cathodic electrophoretic emulsion differs from Example 1.1 in that the epoxy equivalent of the resin after chain extension is 1490, specifically consisting of 70g of DOPO-modified phenolic epoxy resin, 350g of bisphenol A-type epoxy resin E-20, 58g of bisphenol S, 21g of nonylphenol, and 50g of methyl isobutyl ketone. The rest is the same as in Example 1.1.

[0040] Comparative Example 1 The difference from Example 1.1 is that DOPO-type modified phenolic epoxy resin is not added in step S1, and bisphenol A type epoxy resin E-20 is changed to 240g. The rest is the same as in Example 1.1.

[0041] Comparative Example 2 The difference from Example 1.1 is that nonylphenol is not added in step S1, and bisphenol S is changed to 28g. The rest is the same as in Example 1.1.

[0042] Comparative Example 3 The difference from Example 1.1 is that diaminodiphenyl sulfone is not added in step S1, and methylethanolamine is changed to 24g. The rest is the same as in Example 1.1.

[0043] Performance testing 1. The cathodic electrophoretic emulsions prepared in the above examples and comparative examples, as well as conventional cathodic electrophoretic emulsion products, were mixed with conventional color paste products and deionized water to prepare cathodic electrophoretic coatings. After being placed in an electrophoresis tank and matured for 24 hours, the coating film was obtained by electrophoresis on the workpiece for 90 seconds under the conditions of 180V construction voltage and 30℃ tank temperature. The coating was then baked at 180℃ for 30 minutes, and relevant performance tests were performed. The results are shown in Table 1.

[0044] The amount of electrophoretic emulsion used is 700g, the amount of conventional pigment product used is 100g, and the amount of deionized water used is 800g. The conductivity of the deionized water is controlled below 1µs / cm. The conventional cathodic electrophoretic emulsion is a self-made product of our company, model HS1607. The conventional pigment product is a self-made conventional black pigment product of our company, model HL-1600. The workpiece uses a standard phosphate plate.

[0045] Relevant performance tests include appearance, adhesion, film thickness, cupping, flexibility, pencil hardness, impact, acid resistance, alkali resistance, corrosion resistance, heat resistance, and penetration (four-piece box). Appearance is determined visually. Adhesion testing follows the cross-cut test in GB / T 9286-1998, with grade 0 being the best and grade 5 the worst. Film thickness follows the relevant methods in GB / T 1345.2-2008. Cupping follows the relevant methods in GB / T 9753-2007. Flexibility follows the relevant methods in GB / T 1731-1993. Pencil hardness follows the relevant methods in GB / T 6739-2006. Impact testing follows the relevant methods in GB / T 1732-1993. Acid and alkali resistance follow the relevant methods in GB / T 1763-1979. Corrosion resistance follows the relevant methods in GB / T 1771. Heat resistance testing follows GB / T... The relevant methods are in 1735-2009; for permeability, refer to the relevant methods in HG / T 3334-2012.

[0046] Table 1. Test Results of Relevant Performance of Paint As shown in Table 1, the cathodic electrophoretic coating obtained by using the cathodic electrophoretic emulsion and matching color paste prepared in the embodiments of this application has a smooth and even appearance, with adhesion reaching grade 0, bottom adhesion (acrylic color) reaching grade 0, an average film thickness of 21 μm, an average cupping thickness of 8.56 mm, a flexibility of 1 mm (axis radius of curvature), a pencil hardness of 2H, completely OK impact performance, OK acid resistance on the board surface after 72 hours, grade 0 secondary adhesion, OK alkali resistance on the board surface after 72 hours, grade 0 secondary adhesion, corrosion resistance greater than 1000 hours, heat resistance not less than 300℃, and penetration not less than 65%. In contrast, the cathodic electrophoretic coating obtained by using the conventional cathodic electrophoretic emulsion product HS1607 and matching color paste has a heat resistance of only 260℃. Therefore, the cathodic electrophoretic emulsion prepared in this application has excellent high temperature resistance. The cathodic electrophoretic coating prepared with the corresponding cathodic electrophoretic coating pigment components has a significant advantage in high temperature resistance after drying and film formation compared with conventional cathodic electrophoretic coatings. It also has good chemical stability, deformation stability and other properties.

[0047] The difference between Examples 1.3-1.4 and Example 1.1 lies in the different ratios of DOPO-type modified phenolic epoxy resin and bisphenol A-type epoxy resin E-20. As can be seen from Table 1, if the amount of DOPO-type modified phenolic epoxy resin added is too low, the effect on improving heat resistance will be insufficient; if the amount added is too high, it will affect the flexibility of the coating film.

[0048] The difference between Examples 2.3-2.4 and Example 1.1 lies in the different ratio of nonylphenol and bisphenol S. As can be seen from Table 1, if the amount of nonylphenol added is too low, the effect on improving flexibility will be insufficient; if the amount added is too high, the effect on heat resistance will be affected.

[0049] The difference between Examples 3.1-3.2 and Example 1.1 lies in the epoxy equivalent of the resin after chain extension. As can be seen from Table 1, if the epoxy equivalent is controlled too low, the breakdown voltage will be too low and the coating will be abnormal; if the epoxy equivalent is controlled too high, the coating will be too brittle and both adhesion and flexibility will be affected.

[0050] The difference between Comparative Examples 1-3 and Example 1.1 is that DOPO-modified phenolic epoxy resin, nonylphenol, and diaminodiphenyl sulfone were not added, respectively. As can be seen from Table 1, the absence of DOPO-modified phenolic epoxy resin significantly reduces the heat resistance of the coating film, the lack of nonylphenol results in insufficient flexibility and appearance of the coating film, and the lack of further amination with diaminodiphenyl sulfone slightly reduces the throwing power. Therefore, it can be seen that the use of DOPO-modified phenolic epoxy resin, nonylphenol, and diaminodiphenyl sulfone in combination with other raw materials in this application can significantly improve the high temperature resistance, chemical stability, deformation stability, flexibility, and throwing power of the emulsion.

[0051] 2. The cathodic electrophoretic emulsions prepared in Examples 1.1 and Comparative Examples 1-3, as well as conventional cathodic electrophoretic emulsion products, were mixed with deionized water to prepare cathodic electrophoretic coatings (varnishes). After being placed in an electrophoresis tank and matured for 24 hours, the coating film was obtained by electrophoresis on the workpiece for 60 seconds under the conditions of 180V construction voltage and 30℃ tank temperature. The coating was then baked at 180℃ for 30 minutes, and relevant performance tests were performed. The results are shown in Table 2.

[0052] The amount of electrophoretic emulsion used is 800g, the amount of deionized water used is 800g, the conductivity of the deionized water is controlled below 1µs / cm, the conventional cathodic electrophoretic emulsion is a self-made product of our company, model HS1607, and the workpiece is a standard phosphate plate.

[0053] The relevant performance tests include appearance, adhesion and heat resistance. Appearance is determined by visual inspection; adhesion is tested according to the cross-cut test in GB / T 9286-1998, with 0 being the best and 5 being the worst; heat resistance is tested according to the relevant methods in GB / T 1735-2009.

[0054] Table 1. Test Results of Relevant Performance of Clear Varnish Item Appearance Adhesion (grade) Heat resistance (°C) Example 1.1 Smooth and glossy 0 grade 270 Example 1.2 Smooth and glossy 0 grade 320 Comparative Example 1 Smooth and glossy 0 grade 300 Comparative Example 2 Smooth and glossy 0 grade 320 Comparative Example 3 Smooth and glossy 0 grade 300 As shown in Table 2, the varnish obtained using the cathodic electrophoretic emulsion prepared in this application also has a smooth and even appearance, an adhesion rating of 0, and a heat resistance of 320℃. In contrast, the varnish made using conventional cathodic electrophoretic emulsions only has a heat resistance of 270℃. This demonstrates that the cathodic electrophoretic emulsion of this application has excellent heat resistance. Comparative Example 1, without the addition of DOPO-modified phenolic epoxy resin, produced a varnish film with a heat resistance of 300℃, significantly lower than that of Example 1.1. Comparative Example 3, without further amination using diaminodiphenyl sulfone, also produced a varnish film with a heat resistance of 300℃, similarly lower than that of Example 1.1. The experimental results further demonstrate that the use of DOPO-modified phenolic epoxy resin in the amine-modified epoxy resin of this application, compared to conventional epoxy systems, can introduce more rigid structures and phosphorus heterocycles, effectively improving the heat resistance of the resin matrix; a small amount of diaminodiphenyl sulfone can introduce sulfone groups to improve thermal stability.

[0055] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A high-temperature resistant cathodic electrophoretic emulsion, characterized in that, The raw materials used include amine-modified epoxy resin and blocked isocyanate. The raw materials used for the amine-modified epoxy resin include DOPO-type modified phenolic epoxy resin, bisphenol A-type epoxy resin E-20, bisphenol S, nonylphenol, monohydric secondary amine and diaminodiphenyl sulfone.

2. The high-temperature resistant cathodic electrophoretic emulsion according to claim 1, characterized in that, The weight ratio of the DOPO-type modified phenolic epoxy resin and the bisphenol A-type epoxy resin E-20 is (0.15-0.20):

1.

3. The high-temperature resistant cathodic electrophoretic emulsion according to claim 1, characterized in that, The weight ratio of nonylphenol to bisphenol S is (0.3-0.4):

1.

4. A method for preparing the high-temperature resistant cathodic electrophoretic emulsion according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Preparation of amine-modified epoxy resin DOPO-type modified phenolic epoxy resin, bisphenol A-type epoxy resin E-20, bisphenol S, nonylphenol and inert solvent are mixed and heated to melt. Then a catalyst is added to carry out chain extension reaction. After chain extension is completed, the temperature is lowered and a monoamine is added for amine modification. Then diaminodiphenyl sulfone is added to continue amination to obtain amine-modified epoxy resin. S2. Preparation of high-temperature resistant cathodic electrophoretic emulsion Blocked isocyanate and film-forming aid are added to the amine-modified epoxy resin obtained in step S1 and mixed evenly. Then, after neutralization, emulsification, and vacuum distillation, the solid content is adjusted to obtain a high-temperature cathodic electrophoresis emulsion with a solid content of 33-35%.

5. The method for preparing a high-temperature resistant cathodic electrophoretic emulsion according to claim 4, characterized in that, The inert solvent in S1 is a toluene-based solvent or a ketone-based solvent.

6. The method for preparing a high-temperature resistant cathodic electrophoretic emulsion according to claim 4, characterized in that, The epoxy equivalent of the resin after chain extension in S1 is 800-1100.

7. The method for preparing a high-temperature resistant cathodic electrophoretic emulsion according to claim 4, characterized in that, The amount of the monovalent secondary amine added in S1 is 75-85% of the molar number of epoxy groups in the resin after chain extension.

8. The method for preparing a high-temperature resistant cathodic electrophoretic emulsion according to claim 4, characterized in that, The amount of diaminodiphenyl sulfone added in S1 is 2-3% of the molar number of epoxy groups in the resin after chain extension.

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