Epoxy resin emulsion for high-solubility cathodic electrophoretic paint and preparation method thereof

Abstract

The application discloses an epoxy resin emulsion for high-swimming power cathode electrophoretic paint and a preparation method thereof. The preparation method comprises a preparation step of modified epoxy resin and a preparation step of epoxy resin emulsion. The application improves the flexibility and molecular weight of the resin by simultaneously modifying the epoxy resin with polyester and polyether. The application reduces the solvent content in the emulsion system by increasing the molecular weight of the resin. The application introduces a drier, bismuth neodecanoate, into the resin system, which is low in cost and reduces the potential hydrolysis risk of bismuth hydroxide in the matching color paste. The resin emulsion formed by the application has small particle size, good stability, good curing performance, no abnormality after 40 times of MEK wiping, obviously increased flexibility, cupping and impact resistance of the paint film, and the swimming power of the four-box is more than 50%, the swimming power is obviously improved, and the performance is excellent, so that the application can be suitable for the coating of the body and parts system of a passenger car.

Description

Technical Field

[0001] This invention belongs to the field of electrophoretic coatings, specifically relating to an epoxy resin emulsion for high-penetration cathodic electrophoretic coatings and its preparation method. Background Technology

[0002] Electrophoretic coatings utilize the rapid migration of coating ions to the surface of the object under the influence of an electric field, forming a uniform and dense coating. As a new type of low-pollution coating with excellent anti-corrosion properties, it is widely used in industrial coating fields due to its superior coating performance and high utilization rate. With the rapid development of the automotive industry, epoxy cathodic electrophoretic paint, renowned for its excellent anti-corrosion properties, has achieved complete coverage in the automotive coating industry. However, due to the various shapes of automotive body cavity structures and parts, the interior of body cavities or deep recesses within parts cannot be completely electrophoretically coated, resulting in a loss of corrosion resistance within the cavities. This ability to coat internal cavities is called the electrophoretic paint's penetration power. The higher the penetration power, the stronger the coating ability within internal cavities, the smaller the difference in film thickness between the inner and outer layers, and the better the corrosion resistance of internal cavities and crevices.

[0003] Currently available epoxy cathodic electrocoating coatings on the market have a maximum penetration of only around 40%, such as our FT23-0025 emulsion. Therefore, for coating requirements of complex car bodies and workpieces, electrocoating products with higher penetration are needed to meet customer needs. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned technical deficiencies and to propose an epoxy resin emulsion for high-penetration cathodic electrophoretic coating and its preparation method, thereby solving the technical problem that existing electrophoretic coatings are unable to meet the coating requirements of complex car bodies and workpieces.

[0005] In a first aspect, the present invention provides a method for preparing an epoxy resin emulsion for a high-penetration cathodic electrophoretic coating, comprising the following steps:

[0006] Preparation of modified epoxy resin: Low molecular weight epoxy resin, bisphenol A, polyester diol, bisphenol A polyoxyethylene ether, and xylene formaldehyde resin are mixed evenly. When the temperature is raised to 145-150℃, the first-step alkaline catalyst is added. This reaction is exothermic. After the temperature naturally rises to 180-190℃, the first chain extension reaction is carried out. After the first chain extension reaction is completed, the temperature is lowered to 145-150℃, and the second-step alkaline catalyst is added to carry out the second chain extension reaction. When the epoxy value reaches 0.92-0.93 meq / g, alcohol ether solvent, fully blocked isocyanate crosslinking agent, and amine are added and mixed evenly to carry out the amination reaction to obtain the modified epoxy resin.

[0007] Preparation of epoxy resin emulsion: Modified epoxy resin was mixed evenly with polypropylene glycol 4000, plasticizer, drier, and leveling agent. An organic acid was then added for acidification. Finally, the acidified resin was emulsified with water to obtain the epoxy resin emulsion. The drier was bismuth neodecanoate.

[0008] In a second aspect, the present invention provides an epoxy resin emulsion for high-penetration cathodic electrophoretic coating, which is obtained by the preparation method of the epoxy resin emulsion for high-penetration cathodic electrophoretic coating provided in the first aspect of the present invention.

[0009] Compared with the prior art, the beneficial effects of the present invention include:

[0010] This invention improves the flexibility and molecular weight of epoxy resin by simultaneously modifying it with polyester and polyether. Increasing the molecular weight reduces the solvent content in the emulsion system. Introducing bismuth neodecanoate as a drier into the resin system reduces cost and lowers the risk of potential hydrolysis of bismuth hydroxide in the accompanying color paste. The resulting resin emulsion has small particle size, is stable, and exhibits good curing performance. It withstands 40 MEK wiping cycles without abnormalities. The film's flexibility, cupping, and impact resistance are significantly increased. It can withstand 1000 hours of neutral salt spray testing. The four-element coating achieves over 50% (some reaching 60%) of penetration, demonstrating a significant improvement in penetration. With excellent performance across the board, it is suitable for coating passenger car bodies and their components. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0012] In a first aspect, the present invention provides a method for preparing an epoxy resin emulsion for a high-penetration cathodic electrophoretic coating, comprising the following steps:

[0013] S1. Preparation of modified epoxy resin: Low-molecular-weight epoxy resin, bisphenol A, polyester diol, bisphenol A polyoxyethylene ether, and xyleneform resin are mixed evenly. When the temperature is raised to 145-150℃, the first-step alkaline catalyst is added. This reaction is exothermic. After the temperature naturally rises to 180-190℃, the first chain extension reaction is carried out. After the first chain extension reaction is completed, the temperature is lowered to 145-150℃, and the second-step alkaline catalyst is added to carry out the second chain extension reaction. When the epoxy value reaches 0.92-0.93 meq / g, the modified epoxy resin is then added... Alcohol ether solvents, fully enclosed isocyanate crosslinking agents, and amines are mixed evenly and subjected to an amination reaction to obtain modified epoxy resin. In this process, controlling the temperature of the first chain extension reaction at 180-190℃ is more conducive to the synthesis of polyester diol, bisphenol A polyoxyethylene ether, and low molecular weight epoxy resin. If the epoxy value of the second chain extension product is too high, the throwing power of the high-penetration epoxy cathodic electrophoretic coating product will be low. If the epoxy value of the second chain extension product is too low, it will be difficult to apply the paint film, and the thickness of the paint film will be affected, thus affecting the product's resistance to neutral salt spray.

[0014] S2. Preparation of epoxy resin emulsion: Modified epoxy resin is mixed evenly with polypropylene glycol 4000, plasticizer, drier, and leveling agent. Then, an organic acid is added for acidification. Finally, the acidified resin (a water-emulsifiable cationic resin) is emulsified with water to obtain an epoxy resin emulsion. The drier is bismuth neodecanoate 3[C]. 10 H 19 O2] － Bi 3+ .

[0015] This invention replaces organotin or bismuth hydroxide in the pigment paste grinding system by adding bismuth neodecanoate as a catalyst to the epoxy resin emulsion. Tin-free catalysis is more environmentally friendly, has better catalytic effect, and avoids the potential risk of bismuth hydroxide hydrolysis in the bath. Furthermore, by adding a fully enclosed isocyanate crosslinking agent before the amination reaction, this invention effectively avoids the drawback of poor emulsion opalescence.

[0016] This invention improves the flexibility and molecular weight of epoxy resin by simultaneously modifying it with polyester and polyether. Increasing the molecular weight reduces the solvent content in the emulsion system. Introducing bismuth neodecanoate as a drier into the resin system reduces cost and lowers the risk of potential hydrolysis of bismuth hydroxide in the accompanying color paste. The resulting resin emulsion has small particle size, is stable, and exhibits good curing performance. It withstands 40 MEK wiping cycles without abnormalities. The film flexibility, cupping, and impact resistance are significantly increased. It can withstand 1000 hours of neutral salt spray testing. The four-element coating achieves a penetration rate of over 50%, demonstrating a significant improvement in penetration. With excellent performance across all aspects, it is suitable for coating passenger vehicle bodies and their components.

[0017] Furthermore, the epoxy equivalent of the low molecular weight epoxy resin is 180-190 g / eq.

[0018] Furthermore, the low molecular weight epoxy resin is 128E epoxy resin.

[0019] Furthermore, the polyester diol is one or more of dimer acid polyester diol and polycaprolactone diol.

[0020] Furthermore, the alkaline catalyst is one or more of dimethylbenzylamine, diethanolamine, triethanolamine, dimethylethanolamine, and triethylamine.

[0021] Furthermore, the mass ratio of low molecular weight epoxy resin to bisphenol A, polyester diol, bisphenol A polyoxyethylene ether, and xylene formaldehyde resin is 1:(0.2-0.3):(0.05-0.15):(0.25-0.4):(0.15-0.2).

[0022] Furthermore, the mass ratio of the low molecular weight epoxy resin to the total amount of the first-step alkaline catalyst and the second-step alkaline catalyst is 1:(0.005-0.01).

[0023] Furthermore, the amount of alkaline catalyst used in the first step accounts for 30%-40% of the total amount of alkaline catalyst, and the amount of alkaline catalyst used in the second step accounts for 60%-70% of the total amount of alkaline catalyst.

[0024] Furthermore, the time for the first chain extension reaction is 0.4-0.6 h.

[0025] Furthermore, the amine is one or more of methylethanolamine, diethanolamine, diethylenetriamine ketone imine, and triethylenetetramine ketone imine.

[0026] Preferably, the amine is a mixture of methylethanolamine and diethylenetriamine ketamine imine in a mass ratio of 1:(1.5-2).

[0027] Furthermore, the mass ratio of low molecular weight epoxy resin to amine is 1:(0.15-0.3), and even further, it is 1:(0.2-0.25).

[0028] Furthermore, the amination reaction temperature is 110-120℃, and the amination reaction time is 2.5-3h.

[0029] Furthermore, the alcohol ether solvent is one or more of ethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol phenyl ether, and ethylene glycol hexyl ether.

[0030] Furthermore, the mass ratio of low molecular weight epoxy resin to alcohol ether solvent is 1:(0.25-0.35).

[0031] Furthermore, the mass ratio of low molecular weight epoxy resin to fully closed isocyanate crosslinking agent is 1:(0.8-1.2).

[0032] Further, after the epoxy value reaches 0.92-0.93 meq / g, an alcohol ether solvent, a fully blocked isocyanate crosslinking agent, and an amine are added and mixed evenly to carry out an amination reaction to obtain the modified epoxy resin. The process includes: after the epoxy value reaches 0.92-0.93 meq / g, an alcohol ether solvent is added and the temperature is lowered to 100-110℃, a fully blocked isocyanate curing agent is added, stirring is continued, and the temperature is lowered to 80-90℃, an amine is added, and an amination reaction is carried out at 110-120℃ for 2.5-3 hours.

[0033] Furthermore, the above-mentioned fully enclosed isocyanate crosslinking agent is obtained through the following steps:

[0034] Toluene diisocyanate (TDI), a first ketone solvent, and an organotin catalyst are mixed thoroughly. Then, a mixture of a second ketone solvent and trimethylolpropane is added dropwise while maintaining the temperature at 55-65°C. After the addition is complete, the reaction is maintained at this temperature until the NCO value reaches 160-164 mg / g. Then, an alcohol ether blocking agent is added dropwise while controlling the temperature below 70°C to obtain a fully enclosed isocyanate crosslinking agent. If the NCO value of the fully enclosed isocyanate crosslinking agent is too high, the high-penetration epoxy cathodic electrophoretic coating will not achieve the desired results; if the NCO value is too low, it will affect the curing performance of the product, and consequently, its resistance to neutral salt spray.

[0035] The organotin catalyst is dibutyltin dilaurate.

[0036] The first ketone solvent and the second ketone solvent are one or more of butanone and methyl isobutyl ketone, respectively.

[0037] Among them, the alcohol ether blocking agent is one or more of isooctanol, ethylene glycol butyl ether, and diethylene glycol butyl ether.

[0038] The mass ratio of toluene diisocyanate to organotin catalyst, trimethylolpropane, and alcohol ether blocking agent is 1:(0.0001-0.001):(0.2-0.3):(0.7-0.8).

[0039] The mass ratio of toluene diisocyanate to the total amount of the first ketone solvent and the second ketone solvent is 1:(0.25-0.35).

[0040] In the mixture of the second ketone solvent and trimethylolpropane, the mass ratio of butanone to trimethylolpropane is 1:(1.2-1.6).

[0041] The solid content of the aforementioned fully enclosed isocyanate crosslinking agent is 85-90%.

[0042] Furthermore, the amount of polypropylene glycol 4000 added is 0.3%-0.5% of the modified epoxy resin.

[0043] Furthermore, the plasticizer is Loxanol PL5060 plasticizer.

[0044] Furthermore, the amount of plasticizer added is 1%-3% of the modified epoxy resin.

[0045] Furthermore, the amount of drier added is 0.05%-0.2% of the modified epoxy resin.

[0046] Furthermore, the amount of leveling agent added is 0.2%-0.5% of the modified epoxy resin.

[0047] Furthermore, the organic acid is one or more of formic acid, aminosulfonic acid, acetic acid, lactic acid, and phytic acid.

[0048] Preferably, the organic acid is formic acid.

[0049] Furthermore, the amount of organic acid added is 1-2% of the modified epoxy resin.

[0050] Furthermore, the organic acid is added in the form of an aqueous solution.

[0051] Furthermore, in the organic acid solution, the concentration of organic acid is 10%-30%.

[0052] Furthermore, the organic acid is added dropwise at a temperature of 80-85℃ for 20-40 minutes.

[0053] Furthermore, the acidification reaction temperature is 80-82℃, and the acidification reaction time is 1-1.5h.

[0054] Furthermore, during the emulsification process, the amount of water added is 1.2-1.8 times that of the modified epoxy resin.

[0055] In a second aspect, the present invention provides an epoxy resin emulsion for high-penetration cathodic electrophoretic coating, which is obtained by the preparation method of the epoxy resin emulsion for high-penetration cathodic electrophoretic coating provided in the first aspect of the present invention.

[0056] Example 1

[0057] (1) Preparation of crosslinking agent 1#: 434.7 parts of toluene diisocyanate, 51.2 parts of butanone, and 0.2 parts of dibutyltin dilaurate were added to the reaction flask. At 40°C, a mixture of 76.2 parts of butanone and 108 parts of trimethylolpropane was added dropwise. The reaction temperature was maintained at 55-65°C. After the addition was completed, the temperature was kept warm for 1 hour. When the NCO value reached 161.5±2 mg / g, 329.7 parts of ethylene glycol butyl ether blocking agent were added dropwise. The reaction temperature was controlled below 70°C to obtain a fully blocked crosslinking agent with a solid content of 87.2±2%.

[0058] (2) Preparation of modified epoxy resin: 239.24 parts of epoxy resin (128E epoxy resin), 61.14 parts of bisphenol A, 68.18 parts of bisphenol A polyoxyethylene ether, 17.40 parts of polycaprolactone diol, and 45.3 parts of xyleneform resin were added to a reaction flask and heated to 146℃. 0.52 parts of dimethylbenzylamine were added for the first time. This reaction is exothermic. After the temperature naturally rises to 180-190℃, it is kept at that temperature for half an hour, and then cooled down. At 145-150℃, add 0.94 parts of dimethylbenzylamine for the second time, and continue to keep warm until the epoxy value reaches 0.92-0.93 meq / g. Add 40 parts of ethylene glycol butyl ether and 27 parts of propylene glycol phenyl ether, cool down to 100-110℃, add 241.88 parts of crosslinking agent 1#, mix evenly, add 17.5 parts of methylethanolamine and 31.5 parts of diethylenetriamine ketone imine at 90℃, and heat up to 110-120℃ for amination for 3 hours.

[0059] (3) Preparation of epoxy resin emulsion: After the resin is cooled down, 3.24 parts of polypropylene glycol 4000, 17.24 parts of Loxanol PL5060 plasticizer, 1.1 parts of drying agent (bismuth neodecanoate), and 3.24 parts of leveling agent are added. After mixing evenly, a mixture of 12.06 parts of formic acid and 53.86 parts of deionized water is added dropwise at 85°C. The addition is completed in 0.6 h. Then, the mixture is kept at 80-82°C and stirred for 1.5 h. Finally, the acidified resin is added to 1120 parts of deionized water at 20-25°C to emulsify and obtain the target emulsion 1.

[0060] Example 2

[0061] (1) Preparation of crosslinking agent 1#: Same as in Example 1.

[0062] (2) Preparation of modified epoxy resin: 221.48 parts of epoxy resin (128E epoxy resin), 56.6 parts of bisphenol A, 80.52 parts of bisphenol A polyoxyethylene ether, 15.20 parts of polycaprolactone diol, 14.5 parts of dimer acid polyester diol, and 41.94 parts of xylene-formaldehyde resin were added to a reaction flask and heated to 146°C. 0.48 parts of dimethylbenzylamine were added for the first time. This reaction is exothermic. After the temperature naturally returned to 180-190°C, it was kept at that temperature for half an hour. When the temperature drops to 145-150℃, add 0.86 parts of dimethylbenzylamine for the second time, and continue to keep warm until the epoxy value reaches 0.92-0.93 meq / g. Then add 36.68 parts of ethylene glycol butyl ether and 25.19 parts of propylene glycol phenyl ether, and cool down to 100-110℃. Add 224.58 parts of crosslinking agent 1#, mix well, and add 16.22 parts of methylethanolamine and 29.12 parts of diethylenetriamine ketone imine at 90℃. Raise the temperature to 110-120℃ and keep warm for 3 hours for amination.

[0063] (3) Preparation of epoxy resin emulsion: After the resin is cooled down, 3.00 parts of polypropylene glycol 4000, 16.00 parts of Loxanol PL5060 plasticizer, 1.1 parts of drying agent (bismuth neodecanoate), and 3.00 parts of leveling agent are added. After mixing evenly, a mixture of 11.2 parts of formic acid and 50.00 parts of deionized water is added dropwise at 85°C. The addition is completed in 0.6 hours. Then, the mixture is kept at 80-82°C and stirred for 1.5 hours. Finally, the acidified resin is added to 1183.12 parts of deionized water at 20-25°C to emulsify and obtain the target emulsion 2.

[0064] Comparative Example 1

[0065] (1) Preparation of crosslinking agent 2#: 207.8 parts of toluene diisocyanate, 19.2 parts of methyl isobutyl ketone and 0.1 parts of dibutyltin dilaurate were added to the reaction flask. At 40℃, a mixture of 20.1 parts of methyl isobutyl ketone and 28.4 parts of trimethylolpropane was added dropwise. The reaction temperature was maintained at 55-65℃. After the addition was completed, the temperature was kept for 1 hour. When the NCO value reached 267±2 mg / g, a mixture of 60.5 parts of isooctanol and 152.7 parts of ethylene glycol butyl ether was added dropwise. After the addition was completed, the temperature was kept for 1 hour. Then, 11.3 parts of ethylene glycol butyl ether was added to dilute the mixture, and crosslinking agent 2# with a solid content of 89.0±2% was obtained.

[0066] (2) Preparation of modified epoxy resin: 218 parts of epoxy resin (128E epoxy resin), 56.5 parts of bisphenol A, 80 parts of bisphenol A polyoxyethylene ether, and 33.5 parts of xyleneform resin were added to a reaction flask and heated to 146℃. 0.56 parts of dimethylbenzylamine were added for the first time. This reaction is exothermic. After the temperature naturally rises to 180-190℃, it is kept at that temperature for half an hour. Then, the temperature is lowered to 145-150℃ for the second... Add 1.02 parts of dimethylbenzylamine and continue to heat until the epoxy value reaches 0.98-1.00 meq / g. Add 57.36 parts of ethylene glycol butyl ether and 9.64 parts of propylene glycol phenyl ether. Cool down to 100-110℃. Add 245.4 parts of crosslinking agent 2# and mix evenly. Add 19.08 parts of methylethanolamine and 34.26 parts of diethylenetriamine ketone imine at 90℃. Heat up to 110-120℃ and maintain for amination for 3 hours.

[0067] (3) Preparation of epoxy resin emulsion: After the resin was cooled down, 3.18 parts of polypropylene glycol 4000, 17.5 parts of Loxanol PL5060 plasticizer and 3.16 parts of leveling agent were added. After mixing evenly, a mixture of 11.86 parts of aminosulfonic acid and 48.72 parts of deionized water was added dropwise at 85°C. The addition was completed in 0.6 h. Then, the mixture was kept at 80-82°C and stirred for 1.5 h. Finally, the acidified resin was added to 1126.4 parts of deionized water at 20-25°C to emulsify and obtain control emulsion 1.

[0068] experimental group

[0069] The emulsions obtained in Examples 1-2 and the comparative example were prepared for electrophoresis at a ratio of emulsion: pigment: deionized water of 4:1:5. The pigment used in Examples 1-2 was a ground pigment without drier (based on our FT24-7334 mortar with bismuth hydroxide removed, a laboratory-ground mortar), while Comparative Example 1 used a ground pigment with bismuth hydroxide drier (our FT24-7334 mortar). The electrophoresis penetration test was performed using the four-element test box method, with a curing time of 48 hours and application conditions of 240V / 180s. Table 1 compares the emulsion parameters and film properties of each example and comparative example.

[0070] Table 1

[0071]

[0072] As can be seen from Table 1, in this embodiment of the invention, the NCO value of the fully enclosed polyurethane is 161.5±2 mg / g, indicating a relatively small molecular weight; while the epoxy value of the modified epoxy resin is 0.92-0.93 meq / g, indicating a relatively large molecular weight. This results in a small emulsion particle size and stable emulsion. When combined with the company's epoxy cathodic electrophoretic paint pigment, it exhibits good curing performance, shows no abnormalities after 40 MEK wiping cycles, and significantly increases the flexibility, cupping, and impact resistance of the paint film. It can withstand 1000 hours of neutral salt spray testing, and the penetration of the four-element cartridge is over 50%.

[0073] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing an epoxy resin emulsion for high-penetration cathodic electrophoretic coatings, characterized in that, Includes the following steps: Preparation of fully enclosed isocyanate crosslinking agent: Toluene diisocyanate, a first ketone solvent, and an organotin catalyst are mixed evenly, and then a mixture of a second ketone solvent and trimethylolpropane is added dropwise while maintaining the temperature at 55-65℃. After the addition is complete, the reaction is maintained at this temperature. When the NCO value reaches 160-164 mg / g, an alcohol ether blocking agent is added dropwise while controlling the temperature below 70℃ to obtain a fully enclosed isocyanate crosslinking agent. Preparation of modified epoxy resin: Low molecular weight epoxy resin, bisphenol A, polyester diol, bisphenol A polyoxyethylene ether, and xylene formaldehyde resin are mixed evenly. When the temperature is raised to 145-150℃, the first-step alkaline catalyst is added. This reaction is exothermic. After the temperature naturally rises to 180-190℃, the first chain extension reaction is carried out. After the first chain extension reaction is completed, the temperature is lowered to 145-150℃, and the second-step alkaline catalyst is added to carry out the second chain extension reaction. When the epoxy value reaches 0.92-0.93 meq / g, an alcohol ether solvent, a fully blocked isocyanate crosslinking agent, and an amine are added and mixed evenly to carry out an amination reaction to obtain the modified epoxy resin. The low molecular weight epoxy resin is 128E epoxy resin. Preparation of epoxy resin emulsion: Modified epoxy resin is mixed evenly with polypropylene glycol 4000, plasticizer, drier and leveling agent, then an organic acid is added to carry out an acidification reaction, and finally the acidified resin is emulsified with water to obtain epoxy resin emulsion; wherein, the drier is bismuth neodecanoate.

2. The method for preparing the epoxy resin emulsion for high-penetration cathodic electrophoretic coating according to claim 1, characterized in that, The mass ratio of the low molecular weight epoxy resin to bisphenol A, polyester diol, bisphenol A polyoxyethylene ether, and xylene formaldehyde resin is 1:(0.2-0.3):(0.05-0.15):(0.25-0.4):(0.15-0.2); the mass ratio of the low molecular weight epoxy resin to the total amount of the first-step alkaline catalyst and the second-step alkaline catalyst is 1:(0.005-0.01); the mass ratio of the low molecular weight epoxy resin to alcohol ether solvent is 1:(0.25-0.35); the mass ratio of the low molecular weight epoxy resin to the fully blocked isocyanate crosslinking agent is 1:(0.8-1.2); and the mass ratio of the low molecular weight epoxy resin to the amine is 1:(0.15-0.3).

3. The method for preparing the epoxy resin emulsion for high-penetration cathodic electrophoretic coating according to claim 1, characterized in that, The amount of alkaline catalyst used in the first step accounts for 30%-40% of the total amount of alkaline catalyst, and the amount of alkaline catalyst used in the second step accounts for 60%-70% of the total amount of alkaline catalyst.

4. The method for preparing the epoxy resin emulsion for high-penetration cathodic electrophoretic coating according to claim 1, characterized in that, The polyester diol is one or more of dimerized polyester diol and polycaprolactone diol; the alkaline catalyst is one or more of dimethylbenzylamine, diethanolamine, triethanolamine, dimethylethanolamine, and triethylamine; the alcohol ether solvent is one or more of ethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol phenyl ether, and ethylene glycol hexyl ether; and the amination is one or more of methylethanolamine, diethanolamine, diethylenetriamineketone imine, and triethylenetetramineketone imine.

5. The method for preparing the epoxy resin emulsion for high-penetration cathodic electrophoretic coating according to claim 1, characterized in that, The first chain extension reaction takes 0.4-0.6 h; the amination reaction takes 110-120 °C for 2.5-3 h.

6. The method for preparing the epoxy resin emulsion for high-penetration cathodic electrophoretic coating according to claim 1, characterized in that, The organotin catalyst is dibutyltin dilaurate; the first ketone solvent and the second ketone solvent are one or more of butanone and methyl isobutyl ketone, respectively; the alcohol ether blocking agent is one or more of isooctanol, ethylene glycol butyl ether, and diethylene glycol butyl ether; the mass ratio of toluene diisocyanate to organotin catalyst, trimethylolpropane, and alcohol ether blocking agent is 1:(0.0001-0.001):(0.2-0.3):(0.7-0.8); the mass ratio of toluene diisocyanate to the total amount of the first ketone solvent and the second ketone solvent is 1:(0.25-0.35).

7. The method for preparing the epoxy resin emulsion for high-penetration cathodic electrophoretic coating according to claim 1, characterized in that, The amount of polypropylene glycol 4000 added is 0.3%-0.5% of the modified epoxy resin; the amount of plasticizer added is 1%-3% of the modified epoxy resin; the amount of drying agent added is 0.05%-0.2% of the modified epoxy resin; the amount of leveling agent added is 0.2%-0.5% of the modified epoxy resin; the organic acid is one or more of formic acid, aminosulfonic acid, acetic acid, lactic acid, and phytic acid; the amount of organic acid added is 1-2% of the modified epoxy resin.

8. The method for preparing the epoxy resin emulsion for high-penetration cathodic electrophoretic coating according to claim 1, characterized in that, The acidification reaction is carried out at a temperature of 80-82℃ for 1-1.5 hours; during the emulsification process, the amount of water added is 1.2-1.8 times that of the modified epoxy resin.

9. An epoxy resin emulsion for high-penetration cathodic electrophoretic coating, characterized in that, The epoxy resin emulsion for high-penetration cathodic electrophoretic coating is obtained by the preparation method of the epoxy resin emulsion for high-penetration cathodic electrophoretic coating according to any one of claims 1-8.

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