Preparation method of dual-curing cathode electrophoretic coating

Abstract

The invention relates to a preparation method of a dual-curing cathode electrophoretic coating, which comprises the following steps: synthesizing acrylic resin with an epoxy group and a hydroxyl group on a side chain by adopting an acrylate monomer, and grafting monomer semi-terminated isocyanate containing double bonds in molecules to obtain polyurethane modified acrylate capable of being cured by cations and free radicals. Proper photoinitiators and auxiliaries are added into the resin, and the cathode electrophoretic coating capable of being dual-cured is prepared. The introduction of the polyurethane chain segment solves the problems of poor water repellency, low hardness, poor wear resistance and the like of the acrylic resin, the electrophoretic coating prepared after modification has a good curing effect and electrodeposition stability, and after UV curing, the film has good comprehensive performance, is convenient to construct and low in cost, and has a good market prospect.

Description

Technical Field

[0001] This invention relates to a method for preparing a dual-curing cathodic electrophoretic coating, belonging to the field of chemical coating production. Background Technology

[0002] UV-curable coatings utilize ultraviolet light to irradiate the coating resin, causing polymerization and rapid curing at low temperatures. UV-curable electrophoretic coating combines electrophoretic coating with UV curing, offering advantages such as environmental friendliness, high efficiency, and energy saving. Currently, cathodic electrophoretic coatings are widely used in the automotive industry, lighting fixtures, bathroom accessories, and metalworking.

[0003] Photocurable cathodic electrophoretic coatings have attracted much attention in the industry due to their numerous advantages, but their development has been slow, mainly for the following reasons: poor compatibility between photoinitiators and the main resins of photocurable cathodic electrophoretic coatings; and the impact of the flash evaporation process on the curing effect and film performance of photocurable cathodic electrophoretic coatings. Acrylic resins have advantages such as good weather resistance and high gloss, and are commonly used as cathodic electrophoretic coatings. However, the low chemical resistance, poor water resistance, and poor corrosion resistance of acrylic esters have also seriously affected the development of photocurable cathodic electrophoretic coatings.

[0004] This invention addresses the problems existing in cathodic electrophoretic coatings by making a series of improvements to expand their application range. The main improvements include: introducing epoxy groups and vinyl ethers into acrylic resin, enabling the resulting cathodic electrophoretic coating to have both cationic and free radical curing modes. This not only solves a series of problems such as oxygen inhibition in free radical polymerization but also addresses initiator incompatibility, greatly enriching the formulation and process of cathodic electrophoretic coatings; and introducing polyurethane resin into the branches of acrylic resin, improving the resin's solvent resistance, abrasion resistance, adhesion, hardness, and other properties, further expanding the application range of cathodic electrophoretic coatings. Summary of the Invention

[0005] Objective of this invention: This invention synthesizes acrylic resins with epoxy groups and hydroxyl groups on the side chains using acrylate monomers, and then grafts semi-terminated isocyanates containing double bonds into the molecule to obtain polyurethane-modified acrylates that can be cured by both cationic and free radical methods. By adding suitable photoinitiators and additives to this resin, a cathodic electrophoretic coating capable of dual curing is prepared. The introduction of polyurethane segments solves the problems of poor water repellency, low hardness, and poor abrasion resistance of acrylic resins. The modified electrophoretic coating exhibits good curing effect and electrodeposition stability. After UV curing, the film has good overall performance, is easy to apply, and has low cost, showing promising market prospects.

[0006] Technical solution: The technical solution adopted in this invention is: A method for preparing a dual-curing cathodic electrophoretic coating, characterized by comprising the following steps: (1) Preparation of acrylic resin: A certain amount of solvent and initiator are added to a three-necked flask equipped with a stirrer and a thermometer, the temperature is raised, and a mixture of acrylate monomers, vinyl ether monomers and monomers with double bonds at one end and epoxy groups at the other end is added dropwise to the three-necked flask. After the addition is completed, the temperature is maintained for a period of time to obtain acrylic resin. (2) Preparation of semi-closed polyurethane: Add catalyst, monomer with double bond at one end and hydroxyl group at the other end, and polymerization inhibitor to a three-necked flask equipped with a stirrer and thermometer. After heating, add diisocyanate dropwise through a constant pressure funnel. Take a sample and measure the infrared absorption peak. If the hydroxyl absorption peak disappears, stop the reaction and obtain semi-closed polyurethane. (3) Preparation of cathodic electrophoretic coating: Add the acrylic resin obtained in step (1) to a three-necked flask equipped with a stirrer and a thermometer, add the semi-terminated polyurethane obtained in step (2), take a sample after the reaction and measure the infrared absorption peak. The -NCO group absorption peak disappears, stop the reaction, add amine to neutralize to pH=6~8, and obtain polyurethane modified acrylic resin. Take a certain amount of polyurethane-modified acrylic resin, add photoinitiator, defoamer, and reactive diluent, and stir evenly to obtain a dual-cured cathodic electrophoretic coating with a certain solid content.

[0007] As a limited option, a method for preparing a dual-curing cathodic electrophoretic coating includes the following steps: (1) Preparation of acrylic resin: Add a certain amount of solvent and initiator to a three-necked flask equipped with a stirrer and a thermometer, heat to 80~90℃, and add dropwise a mixture of acrylate monomers, vinyl ether monomers and monomers with double bonds at one end and epoxy groups at the other end to the three-necked flask for 2~4 h. After the addition is completed, keep warm for 2~6 h to obtain acrylic resin. (2) Preparation of semi-closed polyurethane: Add catalyst, monomer with double bond at one end and hydroxyl group at the other end, and polymerization inhibitor to a three-necked flask equipped with a stirrer and thermometer. Heat to 40~50℃ and add diisocyanate dropwise using a constant pressure funnel. The dropwise addition time is controlled at 2~4h. After keeping warm for 2~4h, take a sample and measure the infrared absorption peak. If the hydroxyl absorption peak disappears, stop the reaction and obtain semi-closed polyurethane. The amount of acrylic resin and semi-closed polyurethane is the molar ratio of hydroxyl group to isocyanate group (1:1.2~2.2). (3) Preparation of cathodic electrophoretic coating: Add the acrylic resin obtained in step (1) to a three-necked flask equipped with a stirrer and a thermometer, heat to 80~100℃ and add the semi-terminated polyurethane obtained in step (2), react for 4~6 h, take a sample and measure the infrared absorption peak. The -NCO group absorption peak disappears, stop the reaction, add amine to neutralize to pH=6~8, and obtain polyurethane modified acrylic resin.

[0008] Take a certain amount of polyurethane-modified acrylic resin, add photoinitiator, defoamer, and reactive diluent, and stir evenly to obtain a dual-cured cathodic electrophoretic coating with a certain solid content.

[0009] As a preferred embodiment, the preparation method of the dual-curing cathodic electrophoretic coating described above uses a solvent consisting of at least one or a mixture of several of the following: propylene glycol methyl ether acetate, xylene, N,N-dimethylformamide (DMF), toluene, and dipropylene glycol methyl ether acetate, with the solvent accounting for 18-25% of the total mass fraction of the reaction. The initiator is at least one or a mixture of several of the following: azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), potassium persulfate, sodium persulfate, and ammonium persulfate, accounting for 3-6% of the total mass fraction of the reaction. The acrylate monomers include the following raw materials in the following mass percentages: acrylic acid (1~2%), methacrylic acid (1~2%), hydroxyethyl acrylate (HEA) (5~15%), hydroxyethyl methacrylate (HEMA) (5~10%), hydroxypropyl methacrylate (HPMA) (5~8%), tetrahydrofurfuryl acrylate (THFA) (6~9%), benzyl methacrylate (2~4%), polyethylene glycol (400) diacrylate (4~7%), triethylene glycol dimethacrylate (TEGDMA) (8~12%), diethylene glycol diacrylate (4~7%), methyl methacrylate (6~8%), n-butyl methacrylate (3~9%), and a mixture of isooctyl methacrylate (4~10%). Preferably, the vinyl ether monomer is a mixture of vinyl ethoxyethyl acrylate (VEEA) and 4-hydroxybutyl vinyl ether (HBVE) accounting for 5-6% by mass of the whole reaction. Preferably, the monomer having a double bond at one end and an epoxy group at the other end is glycidyl methacrylate (GMA), accounting for 3-5% of the total mass fraction of the reaction. Preferably, the catalyst in step (2) is at least one or a mixture of several of dibutyltin dilaurate, stannous octoate, or organotin compounds; The monomers with a double bond at one end and a hydroxyl group at the other end are: hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), hydroxypropyl acrylate (HPA), hydroxypropyl methacrylate (HPMA), pentaerythritol triacrylate (PETA), and dipentaerythritol pentaacrylate, or a mixture of at least one or more of these. The polymerization inhibitor is at least one or a mixture of several of p-hydroxyanisole, copper chloride, phenothiazine or hydroquinone, and the amount of polymerization inhibitor is 300 to 500 ppm of the total amount of acrylate monomers. Preferably, the diisocyanate is at least one or a mixture of several of the following: isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), hexamethylene diisocyanate (HDI) trimer, diphenylmethane diisocyanate (MDI), and toluene diisocyanate (TDI). Preferably, the amine in step (3) is at least one or a mixture of several of diethylamine, triethylamine, and diethanolamine; The photoinitiator is at least one or a mixture of several of the following: 1173, 184, 2959, 369, 907, diaryliodomonium salt, triarylthionium salt, alkylthionium salt, iron aromatic salt, sulfonyloxy ketone, and triarylsiloxane, accounting for 3-5% of the total coating formulation; The defoamer is at least one or a mixture of several of HT-603, HT-605, and HT-6520; The reactive diluent is at least one or a mixture of several of the following: 2-(2-biphenylethanol) acrylate, 18-ol methacrylate, polyethylene glycol (400) diacrylate (PEG400DA), polyethylene glycol (200) diacrylate (PEG200DA), bis(trimethylolpropane) tetraacrylate (Di-TMPT4A), 5-ethoxylated pentaerythritol tetraacrylate (PPTTA), tetrahydrofurfuryl acrylate (THFA), triethylene glycol dimethacrylate (TEGDMA), 1,6-hexanediol dimethacrylate (HDDMA), dodecyl methacrylate (LMA), 1,4-butanediol dimethacrylate (BDDMA), triethoxylated trimethylolpropane triacrylate (EO3-TMPTA), and nonethoxylated trimethylolpropane triacrylate (EO9-TMPTA), accounting for 10-30% of the entire coating formulation.

[0010] The beneficial effects of this invention are as follows: This invention provides a method for preparing a dual-curing cathodic electrophoretic coating. Addressing the problems existing in cathodic electrophoretic coatings, this invention makes a series of improvements to expand the application range of cathodic electrophoretic coatings. The main improvements are: firstly, introducing epoxy groups and vinyl ethers into acrylic resin, enabling the prepared cathodic electrophoretic coating to have both cationic and free radical curing modes. Cationic curing solves a series of problems associated with free radical curing, such as oxygen inhibition, difficulty in deep curing, large volume shrinkage, and odor generated by initiator decomposition. It also solves the incompatibility problem between the initiator and the resin, greatly enriching the formulation process and application range of cathodic electrophoretic coatings. Secondly, introducing polyurethane resin into the branches of acrylic resin improves the resin's solvent resistance, abrasion resistance, adhesion, hardness, and other properties, greatly enriching the application range of cathodic electrophoretic coatings. This cathodic electrophoretic coating is currently widely used on the surfaces of materials with high weather resistance, high hardness, and high solvent resistance, such as plastics, films, and pharmaceuticals. Detailed Implementation

[0011] The present invention will be further described below with reference to embodiments, but the embodiments do not constitute a limitation on the scope of protection of the present invention: Example

[0012] A method for preparing a dual-curing cathodic electrophoretic coating, comprising the following steps: (1) Preparation of acrylic resin: Add 20g of propylene glycol methyl ether acetate and 3g of azobisisobutyronitrile (AIBN) to a three-necked flask equipped with a stirrer and a thermometer, heat to 80℃, and add dropwise a mixture of 2g acrylic acid, 2g methacrylic acid, 5g hydroxyethyl acrylate (HEA), 8g hydroxyethyl methacrylate (HEMA), 4g hydroxypropyl methacrylate (HPMA), 8g tetrahydrofurfuryl acrylate (THFA), 3g benzyl methacrylate (2~4%), 4g polyethylene glycol (400) diacrylate, 8g triethylene glycol dimethacrylate (TEGDMA), 4g diethylene glycol diacrylate, 6g methyl methacrylate, 3g n-butyl methacrylate, 4g isooctyl methacrylate, 5g vinyl ethoxyethyl acrylate (VEEA), 8g 4-hydroxybutyl vinyl ether (HBVE), and 3g glycidyl methacrylate (GMA), and add dropwise 4g acrylic acid methyl ether acetate (HEA). After the addition of the resin is complete, the mixture is kept at a constant temperature for 4 hours to obtain the acrylic resin.

[0013] (2) Preparation of semi-closed polyurethane: 3.5g dibutyltin dilaurate, 15g hydroxyethyl acrylate (HEA), 15g hydroxyethyl methacrylate (HEMA), 20g hydroxypropyl acrylate (HPA), 0.015g copper chloride and 0.015g p-hydroxyanisole were added to a three-necked flask equipped with a stirrer and a thermometer. The temperature was raised to 50°C, and 115g of isophorone diisocyanate (IPDI) was added dropwise through a constant pressure funnel. The dropwise addition time was controlled at 2h. After keeping the temperature for 4h, a sample was taken and the hydroxyl absorption peak disappeared in the infrared absorption peak. The reaction was stopped, and semi-closed polyurethane was obtained. (3) Preparation of cathodic electrophoretic coating: 100 g of acrylic resin obtained in step (1) was added to a three-necked flask equipped with a stirrer and a thermometer. The temperature was raised to 80°C, and 50 g of semi-terminated polyurethane obtained in step (2) was added. The reaction was carried out for 6 h. The infrared absorption peak of the -NCO group disappeared. The reaction was stopped, and amine was added to neutralize to pH=8 to obtain polyurethane modified acrylic resin.

[0014] (4) Take 100g of polyurethane modified acrylic resin, add 3g of photoinitiator 1173, 4g of defoamer HT-603, 10g of reactive diluent tetrahydrofurfuryl acrylate (THFA), 15g of triethylene glycol dimethacrylate (TEGDMA), and 10g of 1,6-hexanediol dimethacrylate (HDDMA), stir evenly, and a dual-cured cathodic electrophoretic coating with a certain solid content is obtained.

[0015] Take 15g of the prepared cathodic electrophoretic coating and place it in a tetrafluoroethylene tank. Cure it into a film using a 2kW, 20s / cycle crawler-type UV curing machine. Test it according to the standard. The relevant properties of the coating are shown in Table 1 below.

[0016] Table 1. Coating properties are as follows: Testing items Test results Testing standards Impact resistance / cm 60 GB / T 1732-2020 hardness 5H ASTM D 3363-2005 Adhesion Level 0 ASMD 3359-2002 Solvent-resistant bidirectional wipe / time ≥200 GB / T23989-2009 NSS neutral salt spray / h 96 NSS neutral salt spray: No surface corrosion or whitening / peeling of the paint layer was observed. The surface was scratched with a blade at a depth of 45 mm every 24 hours. 。 Make an X shape, then stick 3M tape to the marked area. Rub the tape back and forth 10 times with an eraser to ensure the tape is fully bonded to the product. After 90 seconds, pull it up in the opposite direction. There should be no tearing or peeling of the film at the edges and intersections of the marked lines.

[0017] Example 2 A method for preparing a dual-curing cathodic electrophoretic coating, comprising the following steps: (1) Preparation of acrylic resin: Add 25g of propylene glycol methyl ether acetate and 4g of azobisisobutyronitrile (AIBN) to a three-necked flask equipped with a stirrer and a thermometer, heat to 100℃, and add dropwise a mixture of 1g acrylic acid, 1g methacrylic acid, 6g hydroxyethyl acrylate (HEA), 7g hydroxyethyl methacrylate (HEMA), 5g hydroxypropyl methacrylate (HPMA), 9g tetrahydrofurfuryl acrylate (THFA), 4g benzyl methacrylate (2~4%), 5g polyethylene glycol (400) diacrylate, 9g triethylene glycol dimethacrylate (TEGDMA), 5g diethylene glycol diacrylate, 4g methyl methacrylate, 5g n-butyl methacrylate, 5g isooctyl methacrylate, 6g vinyl ethoxyethyl acrylate (VEEA), 7g 4-hydroxybutyl vinyl ether (HBVE), and 4g glycidyl methacrylate (GMA), and add 2g of acrylic acid resin. After the addition of the resin is complete, the mixture is kept at a constant temperature for 6 hours to obtain the acrylic resin.

[0018] (2) Preparation of semi-closed polyurethane: 2.5g dibutyltin dilaurate, 10g hydroxyethyl acrylate (HEA), 15g hydroxyethyl methacrylate (HEMA), 15g hydroxypropyl acrylate (HPA), 0.013g copper chloride and 0.015g p-hydroxyanisole were added to a three-necked flask equipped with a stirrer and a thermometer. The temperature was raised to 40℃, and 105g isophorone diisocyanate (IPDI) was added dropwise through a constant pressure funnel. The dropwise addition time was controlled at 2h. After keeping the temperature for 4h, a sample was taken and the hydroxyl absorption peak in the infrared absorption peak completely disappeared. The reaction was stopped, and semi-closed polyurethane was obtained. (3) Preparation of cathodic electrophoretic coating: 110 g of acrylic resin obtained in step (1) was added to a three-necked flask equipped with a stirrer and a thermometer. The temperature was raised to 80°C and 50 g of semi-terminated polyurethane obtained in step (2) was added. After reacting for 5 h, the absorption peak of the -NCO group in the infrared absorption peak disappeared. The reaction was stopped and amine was added to neutralize to pH=6 to obtain polyurethane modified acrylic resin.

[0019] (4) Take 100g of polyurethane modified acrylic resin, add 4g of photoinitiator 1173, 4g of defoamer HT-603, 10g of reactive diluent tetrahydrofurfuryl acrylate (THFA), 25g of triethylene glycol dimethacrylate (TEGDMA), and 5g of 1,6-hexanediol dimethacrylate (HDDMA), stir evenly, and a dual-cured cathodic electrophoretic coating with a certain solid content is obtained.

[0020] Take 15g of the prepared cathodic electrophoretic coating and place it in a tetrafluoroethylene tank. Cure it into a film using a 2kW, 20s / cycle crawler-type UV curing machine. Test it according to the standard. The relevant properties of the coating are shown in Table 2 below.

[0021] Table 2. Coating properties are as follows: Testing items Test results Testing standards Impact resistance / cm 50 GB / T 1732-2020 hardness 4H ASTM D 3363-2005 Adhesion Level 0 ASMD 3359-2002 Solvent-resistant bidirectional wipe / time ≥100 GB / T23989-2009 NSS neutral salt spray / h 96 NSS neutral salt spray test method: The surface shows no corrosion or whitening / peeling of the paint layer. Every 24 hours, scratch the surface with a blade at a depth of 45 mm. 。 Make an X shape, then stick 3M tape to the marked area. Rub the tape back and forth 10 times with an eraser to ensure the tape is fully bonded to the product. After 90 seconds, pull it up in the opposite direction. There should be no tearing or peeling of the film at the edges and intersections of the marked lines.

[0022] Example 3 A method for preparing a dual-curing cathodic electrophoretic coating, comprising the following steps: (5) Preparation of acrylic resin: Add 25g of propylene glycol methyl ether acetate and 4g of azobisisobutyronitrile (AIBN) to a three-necked flask equipped with a stirrer and a thermometer, heat to 100℃, and add dropwise a mixture of 1g acrylic acid, 1g methacrylic acid, 6g hydroxyethyl acrylate (HEA), 7g hydroxyethyl methacrylate (HEMA), 5g hydroxypropyl methacrylate (HPMA), 9g tetrahydrofurfuryl acrylate (THFA), 4g benzyl methacrylate (2~4%), 5g polyethylene glycol (400) diacrylate, 9g triethylene glycol dimethacrylate (TEGDMA), 5g diethylene glycol diacrylate, 4g methyl methacrylate, 5g n-butyl methacrylate, 5g isooctyl methacrylate, 6g vinyl ethoxyethyl acrylate (VEEA), 7g 4-hydroxybutyl vinyl ether (HBVE), and 4g glycidyl methacrylate (GMA) to the three-necked flask, and add 2g of acrylic acid methyl ether acetate and 4g of azobisisobutyronitrile (GMA) to the three-necked flask. After the addition of the resin is complete, the mixture is kept at a constant temperature for 6 hours to obtain the acrylic resin.

[0023] (6) Preparation of semi-closed polyurethane: 2.5g dibutyltin dilaurate, 10g hydroxyethyl acrylate (HEA), 15g hydroxyethyl methacrylate (HEMA), 15g hydroxypropyl acrylate (HPA), 0.013g copper chloride and 0.015g p-hydroxyanisole were added to a three-necked flask equipped with a stirrer and a thermometer. The temperature was raised to 40°C. 105g of isophorone diisocyanate (IPDI) was added dropwise through a constant pressure funnel. The dropwise addition time was controlled at 2h. After keeping the temperature for 4h, a sample was taken and the hydroxyl absorption peak in the infrared absorption peak completely disappeared. The reaction was stopped, and semi-closed polyurethane was obtained. (7) Preparation of cathodic electrophoretic coating: 110 g of acrylic resin obtained in step (1) was added to a three-necked flask equipped with a stirrer and a thermometer. The temperature was raised to 80°C and 50 g of semi-terminated polyurethane obtained in step (2) was added. After reacting for 5 h, the absorption peak of the -NCO group in the infrared absorption peak disappeared. The reaction was stopped and amine was added to neutralize to pH=6 to obtain polyurethane modified acrylic resin.

[0024] (8) Take 100g of polyurethane modified acrylic resin, add 4g of photoinitiator diaryliodonium salt, 4g of defoamer HT-603, 10g of reactive diluent tetrahydrofurfuryl acrylate (THFA), 25g of triethylene glycol dimethacrylate (TEGDMA), and 5g of 1,6-hexanediol dimethacrylate (HDDMA), stir evenly, and a dual-cured cathodic electrophoretic coating with a certain solid content is obtained.

[0025] Take 15g of the prepared cathodic electrophoretic coating and place it in a tetrafluoroethylene tank. Cure it into a film using a 2kW, 20s / cycle crawler-type UV curing machine. Test it according to the standard. The relevant properties of the coating are shown in Table 2 below.

[0026] Table 3. Coating properties are as follows: Testing items Test results Testing standards Impact resistance / cm 50 GB / T 1732-2020 hardness 4H ASTM D 3363-2005 Adhesion Level 0 ASMD 3359-2002 Solvent-resistant bidirectional wipe / time ≥100 GB / T23989-2009 NSS neutral salt spray / h 96 NSS neutral salt spray test method: The surface shows no corrosion or whitening / peeling of the paint layer. Every 24 hours, scratch the surface with a blade at a depth of 45 mm. 。 Make an X shape, then stick 3M tape to the marked area. Rub the tape back and forth 10 times with an eraser to ensure the tape is fully bonded to the product. After 90 seconds, pull it up in the opposite direction. There should be no tearing or peeling of the film at the edges and intersections of the marked lines.

[0027] Example 4 Example 2 Example 3 Curing type Free radical curing cationic curing Initiator 1173 Diaryliodomonium salts surface dry 20 seconds (8 times) 30 seconds (8 times) Practical work 80s (15 times) 60s (15 times) Volume shrinkage rate 35% 15% flexibility Level 1 Level 1 Based on the different initiators added in Cases 2 and 3, it can be concluded that: the free radical curing system has faster surface drying but is not conducive to deep curing and has a high volume shrinkage rate; the cationic curing system is more conducive to deep curing and has a low volume shrinkage rate. Therefore, introducing vinyl ether and acrylic groups into this coating can better leverage the advantages of both curing methods.

[0028] The above embodiments are merely preferred embodiments of the present invention. Those skilled in the art can achieve similar technical effects by adjusting the raw material ratio without departing from the principle of the present invention. Such modifications should be considered to fall within the protection scope of this patent.

Claims

1. A method for preparing a dual-curing cathodic electrophoretic coating, characterized in that, Includes the following steps: (1) Preparation of acrylic resin: A certain amount of solvent and initiator are added to a three-necked flask equipped with a stirrer and a thermometer, the temperature is raised, and a mixture of acrylate monomers, vinyl ether monomers and monomers with double bonds at one end and epoxy groups at the other end is added dropwise to the three-necked flask. After the addition is completed, the temperature is maintained for a period of time to obtain acrylic resin. (2) Preparation of semi-closed polyurethane: Add catalyst, monomer with double bond at one end and hydroxyl group at the other end, and polymerization inhibitor to a three-necked flask equipped with a stirrer and thermometer. After heating, add diisocyanate dropwise through a constant pressure funnel. Take a sample and measure the infrared absorption peak. If the hydroxyl absorption peak disappears, stop the reaction and obtain semi-closed polyurethane. (3) Preparation of cathodic electrophoretic coating: Add the acrylic resin obtained in step (1) to a three-necked flask equipped with a stirrer and a thermometer, add the semi-terminated polyurethane obtained in step (2), take a sample after the reaction and measure the infrared absorption peak. The -NCO group absorption peak disappears, stop the reaction, add amine to neutralize to pH=6~8, and obtain polyurethane modified acrylic resin. Take a certain amount of polyurethane-modified acrylic resin, add photoinitiator, defoamer, and reactive diluent, and stir evenly to obtain a dual-cured cathodic electrophoretic coating with a certain solid content.

2. The method for preparing a dual-curing cathodic electrophoretic coating according to claim 1, characterized in that, Includes the following steps: (1) Preparation of acrylic resin: Add a certain amount of solvent and initiator to a three-necked flask equipped with a stirrer and a thermometer, heat to 80~90℃, and add dropwise a mixture of acrylate monomers, vinyl ether monomers and monomers with double bonds at one end and epoxy groups at the other end to the three-necked flask for 2~4 h. After the addition is completed, keep warm for 2~6 h to obtain acrylic resin. (2) Preparation of semi-closed polyurethane: Add catalyst, monomer with double bond at one end and hydroxyl group at the other end, and polymerization inhibitor to a three-necked flask equipped with a stirrer and thermometer. Heat to 40~50℃ and add diisocyanate dropwise using a constant pressure funnel. The dropwise addition time is controlled at 2~4h. After keeping warm for 2~4h, take a sample and measure the infrared absorption peak. If the hydroxyl absorption peak disappears, stop the reaction and obtain semi-closed polyurethane. (3) Preparation of cathodic electrophoretic coating: Add the acrylic resin obtained in step (1) to a three-necked flask equipped with a stirrer and a thermometer, heat to 80~100℃, add the semi-terminated polyurethane obtained in step (2), react for 4~6 h, take a sample to measure the absorption peak of the -NCO group in the infrared absorption peak disappears, stop the reaction, add amine to neutralize to pH=6~8, and obtain polyurethane modified acrylic resin. Take a certain amount of polyurethane-modified acrylic resin, add photoinitiator, defoamer, and reactive diluent, and stir evenly to obtain a dual-cured cathodic electrophoretic coating with a certain solid content.

3. The preparation method according to claim 1 or 2, characterized in that, The solvent mentioned in step (1) is at least one or a mixture of several of the following: propylene glycol methyl ether acetate, xylene, N,N-dimethylformamide, toluene, and dipropylene glycol methyl ether acetate; The initiator is at least one or a mixture of several of the following: azobisisobutyronitrile, benzoyl peroxide, potassium persulfate, sodium persulfate, and ammonium persulfate.

4. The preparation method according to claim 1 or 2, characterized in that, The acrylate monomers described in step (1) comprise the following raw materials in the following mass percentages: 1-2% acrylic acid, 1-2% methacrylic acid, 5-15% hydroxyethyl acrylate, 5-10% hydroxyethyl methacrylate, 5-8% hydroxypropyl methacrylate, 6-9% tetrahydrofurfuryl acrylate, 2-4% benzyl methacrylate, 4-7% polyethylene glycol (400) diacrylate, 8-12% triethylene glycol dimethacrylate, 4-7% diethylene glycol diacrylate, 6-8% methyl methacrylate, 3-9% n-butyl methacrylate, and 4-10% isooctyl methacrylate.

5. The preparation method according to claim 1, characterized in that, The vinyl ether monomers mentioned in step (1) are: a mixture of vinyl ethoxyethyl acrylate and 4-hydroxybutyl vinyl ether, accounting for 5-6% by mass of the whole formulation; The monomer with a double bond at one end and an epoxy group at the other end is glycidyl methacrylate, accounting for 3-5% of the total mass of the formulation.

6. The preparation method according to claim 1, characterized in that, In step (2), the catalyst is at least one or a mixture of several of dibutyltin dilaurate, stannous octoate, or organotin compounds; The monomers with a double bond at one end and a hydroxyl group at the other end are: hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, pentaerythritol triacrylate, and dipentaerythritol pentaacrylate, or a mixture of at least one or more of these. The polymerization inhibitor is at least one or a mixture of several of p-hydroxyanisole, copper chloride, phenothiazine, or hydroquinone; The diisocyanate is at least one or a mixture of several of the following: isophorone diisocyanate, hexamethylene diisocyanate, hexamethylene diisocyanate trimer, diphenylmethane diisocyanate, and toluene diisocyanate.

7. The preparation method according to claim 1, characterized in that, In step (2), the amounts of acrylic resin and semi-capped polyurethane are respectively the molar ratio of hydroxyl to isocyanate groups (1:1.2~2.2).

8. The preparation method according to claim 1, characterized in that, In step (3), the amine is at least one or a mixture of several of diethylamine, triethylamine, and diethanolamine; The photoinitiator is at least one or a mixture of several of the following: 1173, 184, 2959, 369, 907, diaryliodomonium salt, triarylthionium salt, alkylthionium salt, iron aromatic salt, sulfonyloxy ketone and triarylsiloxane; The defoamer is at least one or a mixture of several of HT-603, HT-605, and HT-6520.

9. The preparation method according to claim 1, characterized in that, The active diluent in step (3) is at least one or a mixture of several of the following: 2-(2-biphenylethanol) acrylate, 18-ol methacrylate, polyethylene glycol (400) diacrylate, polyethylene glycol (200) diacrylate, bis(trimethylolpropane) tetraacrylate, 5-ethoxylated pentaerythritol tetraacrylate, tetrahydrofurfuryl acrylate, triethylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, dodecanol methacrylate, 1,4-butanediol dimethacrylate, triethoxylated trimethylolpropane triacrylate, and nonethoxylated trimethylolpropane triacrylate, accounting for 10-30% of the entire coating formulation.