Edge corrosion resistant auxiliary agent for cathode electrophoretic coating and preparation method of edge corrosion resistant auxiliary agent

Abstract

The invention provides an edge-corrosion-resistant auxiliary agent for a cathode electrophoretic coating and a preparation method of the edge-corrosion-resistant auxiliary agent, and belongs to the technical field of cathode electrophoretic paints.The preparation method comprises the following steps that amino-terminated nitrile rubber and polypropylene glycol diglycidyl ether are subjected to an addition reaction in a solvent, and epoxy resin modified amino-terminated nitrile rubber is obtained; mixing the epoxy resin modified amino-terminated nitrile rubber with a solvent, adding a mixture of the solvent and benzoyl peroxide into the mixture, and carrying out polymerization reaction to obtain repolymerized epoxy resin modified amino-terminated nitrile rubber; and sequentially adding acid water and deionized water, and stirring to obtain the edge corrosion resistant auxiliary agent. According to the cathode electrophoretic paint, the amino-terminated nitrile rubber is modified by the polypropylene glycol diglycidyl ether, so that the mechanical property and the flexibility of the cathode electrophoretic paint are improved; and then benzoyl peroxide is used for initiating repolymerization of the epoxy modified nitrile rubber to reduce the fluidity of the electrophoretic paint in the baking process, so that the edge corrosion resistance of the cathode electrophoretic paint is improved.

Description

Technical Field

[0001] This invention relates to the field of cathodic electrophoretic coating technology, and more specifically to an edge corrosion resistant additive for cathodic electrophoretic coating and its preparation method. Background Technology

[0002] Cathodic electrophoretic coatings utilize the rapid migration of coating ions to the surface of the substrate on the cathode under the influence of an electric field, forming a uniform and dense coating. As a novel type of coating with low pollution and excellent anti-corrosion properties, it is widely used in the automotive industry and other industrial coating fields due to its high degree of automation and high coating utilization.

[0003] Cathodic electrophoretic coatings require baking, during which they retain fluidity. During leveling, the coating film easily separates from sharp edges due to surface tension, resulting in lower film thickness at the edges. Consequently, when testing the coating's resistance to neutral salt spray, the edges are more susceptible to corrosion. Therefore, improving the edge corrosion resistance of electrophoretic coatings is crucial for enhancing the overall corrosion resistance of metal workpieces. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides an edge corrosion resistant additive for cathodic electrophoretic coatings and its preparation method, aiming to solve the technical problem of weak edge corrosion resistance of electrophoretic coatings.

[0005] In a first aspect, embodiments of this application provide a method for preparing an edge corrosion resistant additive for cathodic electrophoretic coatings, comprising the following steps: S1. An addition reaction is carried out between amino-terminated butadiene nitrile rubber and polypropylene glycol diglycidyl ether in a solvent to obtain epoxy resin modified amino-terminated butadiene nitrile rubber. S2. Mix epoxy resin modified amino-terminated nitrile rubber with solvent, cool down, and then add a mixture of solvent and benzoyl peroxide to carry out a polymerization reaction to obtain repolymerized epoxy resin modified amino-terminated nitrile rubber. S3. Add acid water and deionized water sequentially to the repolymerized epoxy resin modified amino-terminated nitrile rubber, and stir to obtain an edge corrosion resistant additive.

[0006] Secondly, embodiments of this application provide an edge corrosion resistant additive for cathodic electrophoretic coatings, which is prepared using the above-described method.

[0007] Thirdly, embodiments of this application provide a cathodic electrophoretic coating, which, by weight, includes 2-4 parts of an edge corrosion resistant additive and 100 parts of an epoxy cathodic electrophoretic paint emulsion.

[0008] The advantages of this application, which differ from existing technical solutions, include: This invention modifies amino-terminated nitrile butadiene rubber with polypropylene glycol diglycidyl ether. The "C≡N groups" introduced into the resin increase the dipole-dipole interactions between molecular chains, forming stronger cohesive energy, thereby improving tensile strength, tear resistance, and abrasion resistance, and enhancing the mechanical properties and flexibility of cathodic electrophoretic coatings. Furthermore, benzoyl peroxide is used to initiate the repolymerization of epoxy-modified nitrile butadiene rubber. The increased molecular weight of the resin makes it less prone to migration during baking, which can be used to reduce the flowability of electrophoretic coatings during baking. The cathodic electrophoretic coating formed by this invention has a small particle size and stable emulsion for edge corrosion resistance. Add this additive to FT23-0033 epoxy cathodic electrophoretic paint emulsion at a mass ratio of 2% to 4%. During the electrophoretic coating process, the epoxy cathodic electrophoretic paint and the additive can be coated on the metal surface in equal proportions. The resulting epoxy electrophoretic coating film, at a thickness of 20±2μm, exhibits significantly improved cupping and impact resistance, increased flexibility by more than 20%, and can withstand neutral salt spray for up to 1000 hours. When tested for edge corrosion resistance with a blade, no more than 10 rust spots of 0.1 to 0.4 mm are observed after 168 hours. This coating is suitable for the coating requirements of passenger car bodies and their component systems.

[0009] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Detailed Implementation

[0010] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0011] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0012] Cathodic electrophoretic coatings require baking, during which they retain fluidity. During leveling, the coating film easily separates from sharp edges due to surface tension, resulting in lower film thickness at the edges. Consequently, when testing the coating's resistance to neutral salt spray, the edges are more susceptible to corrosion. Therefore, improving the edge corrosion resistance of electrophoretic coatings is crucial for enhancing the overall corrosion resistance of metal workpieces.

[0013] To address the technical problem of weak edge corrosion resistance in electrophoretic coatings, this application provides an edge corrosion resistant additive for cathodic electrophoretic coatings and its preparation method. In this method, the mechanical properties and flexibility of the cathodic electrophoretic coating are improved by modifying the amino-terminated nitrile rubber with polypropylene glycol diglycidyl ether. Further polymerization with epoxy-modified nitrile rubber can reduce the flowability of the electrophoretic coating during the baking process.

[0014] In a first aspect, embodiments of this application provide a method for preparing an edge corrosion resistant additive for cathodic electrophoretic coatings, comprising the following steps: S1. An addition reaction is carried out between amino-terminated butadiene nitrile rubber and polypropylene glycol diglycidyl ether in a solvent to obtain epoxy resin modified amino-terminated butadiene nitrile rubber. S2. Mix epoxy resin modified amino-terminated nitrile rubber with solvent, cool down, and then add a mixture of solvent and benzoyl peroxide to carry out a polymerization reaction to obtain repolymerized epoxy resin modified amino-terminated nitrile rubber. S3. Add acid water and deionized water sequentially to the repolymerized epoxy resin modified amino-terminated nitrile rubber, and stir to obtain an edge corrosion resistant additive.

[0015] In the technical solution of this application embodiment, polypropylene glycol diglycidyl ether is first used to modify the amino-terminated nitrile rubber. Polypropylene glycol diglycidyl ether is a type of epoxy resin. By introducing "C≡N groups" into the amino-terminated nitrile rubber, epoxy resin modified amino-terminated nitrile rubber is obtained, which increases the dipole-dipole interaction between molecular chains, forms stronger cohesive energy, thereby improving tensile strength, tear resistance and abrasion resistance, and improving the mechanical properties and flexibility of cathodic electrophoretic paint.

[0016] The epoxy resin-modified amino-terminated nitrile rubber still contains some double bonds. It undergoes polymerization under the initiator of benzoyl peroxide to obtain repolymerized epoxy resin-modified amino-terminated nitrile rubber, which further increases the molecular weight. The resin with increased molecular weight is less prone to migration during baking and can be used to reduce the fluidity of electrophoretic coatings during baking.

[0017] Acid water is added to the repolymerized epoxy resin modified with amino-terminated nitrile rubber to cationize the coating, making it easier to use for cathodic electrophoretic coating; then deionized water is added, stirred and diluted, and emulsified to obtain an emulsion-like edge corrosion resistant additive.

[0018] In some embodiments, the mass ratio of amino-terminated nitrile rubber, polypropylene glycol diglycidyl ether, benzoyl peroxide, acidic water, and deionized water is (10-18):(4-8):(0.3-0.8):(0.5-1.0):(40-70).

[0019] In some embodiments, the acidic water is a 30% to 80% acetic acid solution.

[0020] In some embodiments, the solvent includes at least one of ethylene glycol butyl ether, propylene glycol methyl ether, sec-butanol, and methyl isobutyl ketone.

[0021] In some embodiments, the addition reaction conditions in step S1 are as follows: the amino-terminated nitrile rubber and solvent are added to the reaction vessel, the temperature is raised to 60-65°C, polypropylene glycol diglycidyl ether is added, nitrogen gas is introduced, the temperature is further raised to 95-105°C, and the addition reaction is carried out at the set temperature until the set viscosity is reached, thereby obtaining epoxy resin modified amino-terminated nitrile rubber.

[0022] In some embodiments, the mass ratio of amino-terminated nitrile rubber to solvent is (10-18):(5-10).

[0023] In some embodiments, in step S2, after the epoxy resin-modified amino-terminated nitrile rubber is mixed with the solvent, the temperature is lowered to 60-70°C, and then the solvent and benzoyl peroxide are added within 10 minutes. The polymerization reaction is carried out at 60-70°C for 20-60 minutes to obtain the repolymerized epoxy resin-modified amino-terminated nitrile rubber.

[0024] In some embodiments, the reaction conditions for adding acidic water in step S3 are: at 60-70°C, for 15-60 min.

[0025] In some embodiments, the step of adding deionized water in step S3 is as follows: adding deionized water dropwise into the reaction vessel over 30 to 60 minutes and continuing to stir the reaction for another 30 to 60 minutes.

[0026] Secondly, embodiments of this application provide an edge corrosion resistant additive for cathodic electrophoretic coatings, which is prepared using the above-described method.

[0027] Thirdly, embodiments of this application provide a cathodic electrophoretic coating, which, by weight, includes 2-4 parts of an edge corrosion resistant additive and 100 parts of an epoxy cathodic electrophoretic paint emulsion.

[0028] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0029] I. Preparation Method Example 1 A method for preparing an edge corrosion resistant additive for epoxy cathodic electrophoretic coating includes the following steps: S1. Before production, place the amino-terminated nitrile rubber in a drying oven below 100℃ until the raw material is flowable. During production, add 15.5 parts of amino-terminated nitrile rubber and 7.7 parts of ethylene glycol butyl ether to the reactor. When the temperature reaches 65℃, add 5.5 parts of polypropylene glycol diglycidyl ether, purge with nitrogen, and continue heating to 98℃ and holding for 1 hour. Measure the viscosity every half hour until the viscosity reaches 2.0 dPas, obtaining epoxy resin modified amino-terminated nitrile rubber. Turn on the coolant in the reactor to lower the temperature, and add 5.9 parts of propylene glycol methyl ether to the reactor.

[0030] S2. When the temperature of the epoxy resin-modified amino-terminated nitrile rubber drops to 65°C, add a mixture of 5.0 parts of ethylene glycol butyl ether and 0.6 parts of benzoyl peroxide (BPO) within 10 minutes, and keep it at 60°C for 60 minutes to obtain the repolymerized epoxy resin-modified amino-terminated nitrile rubber.

[0031] S3. Add 0.7 parts of acidic water to the repolymerized epoxy resin modified amino-terminated nitrile rubber and keep it at 70°C for 15 minutes. Then add 60 parts of deionized water dropwise into the reactor over 60 minutes and continue stirring for 30 minutes to obtain an edge corrosion resistant additive.

[0032] Example 2 A method for preparing an edge corrosion resistant additive for epoxy cathodic electrophoretic coating includes the following steps: S1. Before production, place the amino-terminated nitrile rubber in a drying oven below 100℃ until the raw material is flowable. During production, add 10 parts of amino-terminated nitrile rubber and 10 parts of ethylene glycol butyl ether to the reactor. When the temperature reaches 65℃, add 4 parts of sec-butanol, purge with nitrogen, and continue heating to 95℃ and holding for 1 hour. Measure the viscosity every half hour until the viscosity reaches 8.0 dPas, obtaining epoxy resin modified amino-terminated nitrile rubber. Turn on the coolant in the reactor to lower the temperature, and add 4 parts of propylene glycol methyl ether to the reactor.

[0033] S2. When the temperature of the epoxy resin-modified amino-terminated nitrile rubber drops to 65°C, add a mixture of 8 parts ethylene glycol butyl ether and 0.3 parts benzoyl peroxide (BPO) within 10 minutes, and keep it at 60°C for 60 minutes to obtain the repolymerized epoxy resin-modified amino-terminated nitrile rubber.

[0034] S3. Add 1.0 part of acidic water to the repolymerized epoxy resin modified amino-terminated nitrile rubber and keep it at 60°C for 60 minutes. Then add 40 parts of deionized water dropwise into the reactor over 60 minutes and continue stirring for 30 minutes to obtain an edge corrosion resistant additive.

[0035] Example 3 A method for preparing an edge corrosion resistant additive for epoxy cathodic electrophoretic coating includes the following steps: S1. Before production, place the amino-terminated nitrile rubber in a drying oven below 100℃ until the raw material is flowable. During production, add 18 parts of amino-terminated nitrile rubber and 5 parts of methyl isobutyl ketone to the reactor. When the temperature reaches 65℃, add 4 parts of polypropylene glycol diglycidyl ether, purge with nitrogen, and continue heating to 105℃ and holding for 1 hour. Measure the viscosity every half hour until the viscosity reaches 2.0 dPas, obtaining epoxy resin modified amino-terminated nitrile rubber. Turn on the coolant in the reactor to lower the temperature, and add 8 parts of propylene glycol methyl ether to the reactor.

[0036] S2. When the temperature of the epoxy resin-modified amino-terminated nitrile rubber drops to 65°C, add a mixture of 4 parts ethylene glycol butyl ether and 0.8 parts benzoyl peroxide (BPO) within 10 minutes, and keep it at 60°C for 60 minutes to obtain the repolymerized epoxy resin-modified amino-terminated nitrile rubber.

[0037] S3. Add 0.5 parts of acidic water to the repolymerized epoxy resin modified amino-terminated nitrile rubber and keep it at 70°C for 15 minutes. Then add 70 parts of deionized water dropwise into the reactor over 60 minutes and continue stirring for 30 minutes to obtain an edge corrosion resistant additive.

[0038] Example 4 A method for preparing a cathodic electrophoretic coating includes the following steps: Two parts of the edge corrosion resistant additive of the epoxy cathodic electrophoretic coating prepared in Example 1 were added to 100 parts of FT23-0033 epoxy cathodic electrophoretic paint emulsion to prepare the cathodic electrophoretic coating.

[0039] Example 5 A method for preparing a cathodic electrophoretic coating includes the following steps: Four parts of the edge corrosion resistant additive of the epoxy cathodic electrophoretic coating prepared in Example 1 were added to 100 parts of FT23-0033 epoxy cathodic electrophoretic paint emulsion to prepare the cathodic electrophoretic coating.

[0040] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that polypropylene glycol diglycidyl ether was not used for modification when preparing the edge corrosion resistant additive for the epoxy cathodic electrophoretic coating. A method for preparing a cathodic electrophoretic coating includes the following steps: S1. When the amino-terminated nitrile rubber is heated to 65°C, a mixture of 5.0 parts of ethylene glycol butyl ether and 0.6 parts of benzoyl peroxide (BPO) is added within 10 minutes, and the mixture is kept at 60°C for 60 minutes to obtain the repolymerized amino-terminated nitrile rubber.

[0041] S3. Add 0.7 parts of acidic water to the repolymerized end-aminobutyronitrile rubber and keep it at 70°C for 15 minutes. Then add 60 parts of deionized water dropwise into the reactor over 60 minutes and continue stirring for 30 minutes to obtain an edge corrosion resistant additive.

[0042] S3. Add 2 parts of edge corrosion resistant additive to 100 parts of FT23-0033 epoxy cathodic electrophoretic paint emulsion to prepare cathodic electrophoretic coating.

[0043] Comparative Example 2 The difference between Comparative Example 1 and Example 1 is that no repolymerization was performed during the preparation of the edge corrosion resistant additive for the epoxy cathodic electrophoretic coating. A method for preparing a cathodic electrophoretic coating includes the following steps: S1. Before production, place the amino-terminated nitrile rubber in a drying oven at below 100°C until the raw material is flowable. During production, add 15.5 parts of amino-terminated nitrile rubber and 7.7 parts of ethylene glycol butyl ether to the reactor. When the temperature rises to 65°C, add 5.5 parts of polypropylene glycol diglycidyl ether, purge with nitrogen, and continue heating to 98°C and holding for 1 hour. Measure the viscosity every half hour until the viscosity reaches 2.0 dPas, thus obtaining epoxy resin modified amino-terminated nitrile rubber.

[0044] S2. Add 0.7 parts of acidic water to the epoxy resin-modified amino-terminated nitrile rubber and keep it at 70°C for 15 minutes. Then add 60 parts of deionized water dropwise into the reactor over 60 minutes and continue stirring for 30 minutes to obtain an edge corrosion resistant additive.

[0045] S3. Add 2 parts of edge corrosion resistant additive to 100 parts of FT23-0033 epoxy cathodic electrophoretic paint emulsion to prepare cathodic electrophoretic coating.

[0046] Comparative Example 3 Comparative Example 3 used FT23-0033 epoxy cathodic electrophoretic paint emulsion as the cathodic electrophoretic coating.

[0047] II. Testing Methods 1. Test method for edge corrosion resistance of cathodic electrophoretic coating: First, phosphate the paper cutter blade, then apply the electrophoretic coating, and dry it according to the product requirements. Finally, place the blade vertically in a 5% salt spray chamber for 168 hours, rinse with water, and then air dry. Observe the number of rust spots on the blade using a 30x magnifying glass. Currently, the automotive industry requires no more than 30 rust spots of 0.1–0.4 mm.

[0048] 2. Gloss test method: The standard GB / T 9754 is used to determine the specular gloss of paint films without metallic pigments at 20°, 60° and 85°.

[0049] 3. Hardness testing method: The hardness of the paint film was determined by the pencil method of standard GB / T 6739 for paints and varnishes.

[0050] 4. Flexibility testing method: The flexibility of paint film and putty film shall be tested according to the standard GB / T 1731.

[0051] 5. Impact strength test method: The impact strength test shall be conducted in accordance with the standard GB / T 1732 Test Method for Impact Resistance of Coating Film.

[0052] 6. Adhesion test method: The adhesion test shall be conducted according to the standard GB / T 9286 paint and varnish cross-cut test.

[0053] 7. Neutral salt spray test method: The test shall be conducted using the standard GB / T 10125 Artificial Atmosphere Corrosion Test Salt Spray Test.

[0054] III. Analysis of Test Results for Each Embodiment and Comparative Example The edge corrosion resistance properties of the cathodic electrophoretic coatings prepared in Examples 1-3 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1 below.

[0055] Table 1. Test results of the edge corrosion resistance additives for cathodic electrophoretic coatings

[0056] As shown in Table 1, the emulsions obtained in Examples 1-3 of this invention have small particle sizes and are stable. In Comparative Example 1, no polypropylene glycol diglycidyl ether was used for modification. The terminal amino groups in the amino-terminated nitrile rubber did not react with the epoxy resin, resulting in insufficient neutralization of the amino groups in the subsequent acid treatment. This led to reduced stability of the edge corrosion resistant additive in the prepared cathodic electrophoretic coating, indicating that modification with polypropylene glycol diglycidyl ether can improve coating stability.

[0057] The cathodic electrophoretic coatings prepared in Examples 4-5 and Comparative Examples 1-3 were subjected to performance testing, and the test results are shown in Table 2 below.

[0058] Table 2 Performance test results of cathodic electrophoretic coating

[0059] As shown in Table 2, when the edge corrosion resistance additive for cathodic electrophoretic coatings prepared in Example 1 is combined with the epoxy cathodic electrophoretic paint pigment of our company, the flexibility of the coating film is significantly increased, the cupping effect increases by more than 20%, and the resistance to neutral salt spray test can reach 1000h. The edge corrosion resistance of the comparative examples 1-3 is significantly reduced, indicating that the edge corrosion resistance additive for epoxy cathodic electrophoretic coatings prepared by modification with polypropylene glycol diglycidyl ether followed by polymerization can significantly improve the edge corrosion resistance of the electrophoretic coating.

[0060] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing an edge corrosion resistant additive for cathodic electrophoretic coatings, characterized in that, Includes the following steps: S1. An addition reaction is carried out between amino-terminated butadiene nitrile rubber and polypropylene glycol diglycidyl ether in a solvent to obtain epoxy resin modified amino-terminated butadiene nitrile rubber. S2. After mixing the epoxy resin modified amino-terminated nitrile rubber with a solvent, a mixture of solvent and benzoyl peroxide is added to it to carry out a polymerization reaction to obtain a repolymerized epoxy resin modified amino-terminated nitrile rubber. S3. Add acid water and deionized water sequentially to the repolymerized epoxy resin modified amino-terminated nitrile rubber, and stir to obtain an edge corrosion resistant additive.

2. The method for preparing the edge corrosion resistant additive for cathodic electrophoretic coating according to claim 1, characterized in that, The mass ratio of the amino-terminated nitrile rubber, polypropylene glycol diglycidyl ether, benzoyl peroxide, acidic water, and deionized water is (10-18):(4-8):(0.3-0.8):(0.5-1.0):(40-70).

3. The method for preparing the edge corrosion resistant additive for cathodic electrophoretic coating according to claim 1, characterized in that, The acidic water is a 30%–80% acetic acid solution.

4. The method for preparing the edge corrosion resistant additive for cathodic electrophoretic coating according to claim 1, characterized in that, The solvent includes at least one of ethylene glycol butyl ether, propylene glycol methyl ether, sec-butanol, and methyl isobutyl ketone.

5. The method for preparing the edge corrosion resistant additive for cathodic electrophoretic coating according to claim 1, characterized in that, The addition reaction conditions described in step S1 are as follows: add the amino-terminated nitrile rubber and solvent to the reaction vessel, heat to 60-65°C, add polypropylene glycol diglycidyl ether, introduce nitrogen gas, continue to heat to 95-105°C, and keep warm to carry out the addition reaction to the set viscosity to obtain epoxy resin modified amino-terminated nitrile rubber. The mass ratio of the amino-terminated butyronitrile rubber to the solvent is (10-18):(5-10).

6. The method for preparing the edge corrosion resistant additive for cathodic electrophoretic coating according to claim 1, characterized in that, In step S2, the epoxy resin-modified amino-terminated nitrile rubber is mixed with a solvent and then cooled to 60-70°C. Within 10 minutes, the solvent and benzoyl peroxide are added, and the polymerization reaction is carried out at 60-70°C for 20-60 minutes to obtain the repolymerized epoxy resin-modified amino-terminated nitrile rubber.

7. The method for preparing the edge corrosion resistant additive for cathodic electrophoretic coating according to claim 1, characterized in that, The reaction conditions for adding acidic water in step S3 are: 60-70℃, reaction time 15-60 min.

8. The method for preparing the edge corrosion resistant additive for cathodic electrophoretic coating according to claim 1, characterized in that, The steps for adding deionized water in step S3 are as follows: add deionized water dropwise into the reaction vessel over 30 to 60 minutes and continue stirring the reaction for another 30 to 60 minutes.

9. An edge corrosion resistant additive for cathodic electrophoretic coatings, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 8.

10. A cathodic electrophoretic coating, characterized in that, The product comprises, by weight, 2 to 4 parts of the edge corrosion resistant additive as described in claim 7 and 100 parts of epoxy cathodic electrophoretic paint emulsion.

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