A cathodic electrophoretic paint and a method for its preparation

Abstract

The application belongs to the technical field of paint, and provides a cathode electrophoretic paint and a preparation method thereof.The preparation method comprises the following steps: S1, 50 parts of epoxy resin, 13-15 parts of polyethylene glycol and 27-32 parts of solvent are added into a flask according to weight parts, and then the mixture is subjected to warming reaction, 7.5-8.5 parts of bisphenol A is added, and then the mixture is subjected to reaction, so that a chain extension resin is obtained; S2, the chain extension resin and the solvent are added into the flask, and then acrylic monomer and an initiator are added dropwise in a warming mode, and then the mixture is subjected to reaction, and then diethanolamine is added in a cooling mode after the reaction, and then a composite additive, lactic acid and deionized water are added after the reaction, so that the cathode electrophoretic paint is obtained; the acrylic monomer comprises methyl methacrylate, styrene, butyl acrylate and acrylamide, and the mass of the four substances is 5-5.3%, 6.2-6.6%, 5-5.3% and 3.3-3.4% of the mass of the epoxy resin respectively; the composite additive comprises a wetting agent, modified silicon dioxide and water. The application reduces the amount of acrylamide to avoid yellowing of the paint film, reduce the density of the paint film shrinkage, avoid the appearance of orange stripes and improve the quality of the paint film.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, and in particular relates to a cathodic electrophoretic coating and its preparation method. Background Technology

[0002] Electrophoretic coatings originated in the 1930s, and subsequently, high-performance cathodic electrophoretic coatings were gradually developed. Due to their excellent corrosion resistance, high leveling properties, high decorative properties, high degree of automation in coating, and low coating pollution, they are widely used in the automotive industry.

[0003] Epoxy resins are commonly used in electrophoretic coatings due to their good adhesion and strong corrosion resistance, making them suitable for primers. However, they suffer from a hard, brittle film with poor flexibility. To address these shortcomings, existing technologies first use polypropylene glycol (PPG), a flexible chain extender, to toughen and modify the epoxy resin, using this resin as the base. Then, acrylic monomers are grafted onto the epoxy resin to form the main resin, which is then subjected to an ionization reaction to obtain the cathodic electrophoretic coating. The acrylic monomers include acrylamide, an unsaturated amide that can crosslink with hydroxyl groups at high temperatures. Amides are hydrophilic groups, allowing acrylamide to both replace the curing agent and introduce hydrophilic groups into the epoxy resin, making it water-soluble or water-dispersible. Increasing the amount of acrylamide within a certain range can effectively improve the film appearance, reduce the film pore density, and prevent orange peel texture.

[0004] However, amides are prone to coloring under the action of initiators (benzoyl peroxide), and excessive use can easily lead to yellowing of the paint film, which will have a certain impact on the quality of the final paint film. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a cathodic electrophoretic coating and its preparation method. By reducing the amount of acrylamide, the coating film is prevented from yellowing, while the pore density is reduced to avoid orange peel texture and improve the quality of the coating film.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a cathodic electrophoretic coating, comprising the following steps:

[0007] S1. By weight, add 50 parts epoxy resin, 13-15 parts polyethylene glycol and 27-32 parts solvent to a four-necked flask, heat to 125-130℃, and react at a constant temperature for 2-2.5h. Then add 7.5-8.5 parts chain extender bisphenol A and react at a constant temperature for 2.8-3.2h to obtain chain extender resin.

[0008] S2. Add the chain extender resin and solvent obtained in S1 to a four-necked flask, heat to 115±2℃, keep the temperature constant for 30-35 min, add acrylic monomers and initiator benzoyl peroxide (BPO) dropwise. After the dropwise addition is complete, react for 2 h, add a small amount of initiator azobisisobutyronitrile (AIBN), then cool to 80±2℃, add diethanolamine, react for 2-2.5 h, add composite additives, lactic acid and deionized water, cool down and discharge the material to obtain the cathodic electrophoretic coating.

[0009] The acrylic monomers include methyl methacrylate, styrene, butyl acrylate, and acrylamide, with the mass percentages of the four monomers being 5-5.3%, 6.2-6.6%, 5-5.3%, and 3.3-3.4% of the epoxy resin, respectively.

[0010] The composite additive includes a wetting agent, modified silica, and deionized water. The modified silica is prepared by modifying nano-silica with a silane coupling agent.

[0011] Furthermore, in S2, the mass of the composite additive is 1.2-1.5% of the mass of the epoxy resin.

[0012] Furthermore, the mass ratio of the wetting agent, modified silica, and deionized water is 11:(5-7):1.

[0013] Further, the preparation method of the modified silica is as follows: 30 parts of nano silica slurry (solid content 20%) are added to a reaction vessel equipped with a condenser. A mixture of vinyltrimethoxysilane (KH-171) and ethanol solution (8 parts KH-171 + 40 parts anhydrous ethanol + 22 parts deionized water) is slowly added dropwise under stirring, with the dropping rate controlled at 1 mL / min. The temperature is raised to 65±2℃ and the reaction is maintained at this temperature for 4-5 h, during which the pH is maintained at 4-5 (adjusted with acetic acid). At this time, the silane coupling agent hydrolyzes to generate Si-OH groups, which undergo a condensation reaction with the hydroxyl groups on the surface of nano silica. The mixture is cooled to room temperature, centrifuged (8000 rpm × 10 min), washed 3 times with ethanol / water, and vacuum dried (60℃ / 24 h) to obtain the modified silica.

[0014] Further, in S1, the epoxy resin (low molecular weight) is 6101 epoxy resin; the polyethylene glycol is PEG-400.

[0015] Further, in S2, the mass of the initiator is 0.15-0.2% of the mass of the epoxy resin.

[0016] Furthermore, the initiator comprises benzoyl peroxide (BPO) and azobisisobutyronitrile (AIBN) in a mass ratio of 3:1.

[0017] Furthermore, in S2, the mass of diethanolamine added is 37-39% of the mass of the epoxy resin.

[0018] Furthermore, in S2, the mass of lactic acid added is 16-17% of the mass of epoxy resin; deionized water is added to adjust the pH value to 5.8-6.0.

[0019] Secondly, the present invention provides a cathodic electrophoretic coating, which is prepared by the above-described cathodic electrophoretic coating preparation method.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention reduces the amount of acrylamide used (from 4.35% to 3.35% of the epoxy resin mass). On the one hand, this has a negative impact: the density of polar groups in the system decreases, the contact angle between the coating and the substrate increases, wettability decreases, and poor wetting in local areas easily leads to the formation of "fish-eye" shaped pinholes, resulting in an increased pinhole density in the paint film. On the other hand, it also has a positive impact: it avoids excessive cross-linking, prevents the paint film from being too rigid and lacking elasticity, which is not conducive to the deformation and escape of bubbles, ensures a balance between hardness and ductility, and is more conducive to reducing the pinhole density of the paint film.

[0022] Meanwhile, this invention also incorporates a composite additive (wetting agent + modified silica). On one hand, the fluorocarbon segments of the SN-210 water-based wetting agent are directionally adsorbed onto the substrate surface, reducing the static / dynamic surface tension of the coating, enhancing its wetting and penetration capabilities, weakening / offsetting the negative impact of reducing acrylamide dosage (positive effects are retained), and forcing the coating to spontaneously spread and fill micro-pits. On the other hand, the polyether segments in the SN-210 water-based wetting agent form hydrogen bonds with acrylamide residues, compensating for the polarity loss caused by the reduction in acrylamide dosage; the modified silica is uniformly distributed on the surface of the paint film, forming a dense arrangement, generating a capillary negative pressure effect, actively drawing the coating towards the depressions; the surface groups of the modified silica can also covalently bond with the epoxy resin, forming an "anchoring effect," preventing the effective components of the composite additive from precipitating and migrating; thus synergistically reducing the pinhole density of the paint film. Attached Figure Description

[0023] Figure 1 This is a comparative trend chart showing the pinhole rate data of the cathodic electrophoretic coatings prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0026] Example 1: (I) Preparation of modified silica, the preparation method is as follows: 30 parts by weight of nano silica slurry (solid content 20%) were added to a reaction vessel equipped with a condenser. A mixture of vinyltrimethoxysilane (KH-171) and ethanol solution containing 8 parts vinyltrimethoxysilane (KH-171), 40 parts anhydrous ethanol and 22 parts deionized water was slowly added dropwise under stirring. The dropwise addition rate was controlled at 1 mL / min. The temperature was raised to 65℃ and the reaction was kept at this temperature for 4.5 h. During this period, the pH was maintained at 4-5 (adjusted with acetic acid). At this time, the silane coupling agent was hydrolyzed to generate Si-OH groups, which condensed with the hydroxyl groups on the surface of nano silica. The mixture was cooled to room temperature, centrifuged (8000 rpm × 10 min), washed 3 times with ethanol / water, and vacuum dried (60℃ / 24 h) to obtain modified silica.

[0027] (II) Preparation of the composite additive, the preparation method is as follows: SN-210 aqueous wetting agent is mixed with deionized water to obtain a wetting solution; modified silica is slowly added to the wetting solution and dispersed for 30 minutes using a high-speed disperser (8000 rpm) to form a homogeneous premix. This premix is ​​then transferred to a sand mill (zirconia beads Φ0.1 mm) and circulated for 2 hours. 0.5% of sodium polyacrylate dispersant by total mass is added, and stirring continues for 1 hour. The mixture is then filtered through a 300-mesh filter cloth to obtain a uniform suspension, which is the composite additive. The mass ratio of SN-210 aqueous wetting agent, modified silica, and deionized water is 11:6:1.

[0028] (III) A method for preparing a cathodic electrophoretic coating, comprising the following steps:

[0029] S1. By weight, add 50 parts epoxy resin, 14 parts polyethylene glycol, and 30 parts toluene solvent to a four-necked flask. Heat to 128°C and react at this temperature for 2.2 hours. Then add 8 parts bisphenol A chain extender and react at this temperature for 3 hours to obtain the chain-extended resin. The epoxy resin is 6101 epoxy resin; the polyethylene glycol is PEG-400.

[0030] S2. Add the chain extender resin obtained in S1 and the solvent toluene in a four-necked flask with a mass ratio of 1:1. Heat to 115℃ and hold for 32 min. Add acrylic monomers and initiator benzoyl peroxide (BPO) dropwise. After the addition is complete, react for 2 h and then add the initiator azobisisobutyronitrile (AIBN).

[0031] The acrylic monomers include methyl methacrylate, styrene, butyl acrylate, and acrylamide, with their respective mass percentages being 5.2%, 6.5%, 5.2%, and 3.35% of the epoxy resin mass.

[0032] The total mass of the initiator is 0.2% of the mass of the epoxy resin, and the mass ratio of benzoyl peroxide (BPO) to azobisisobutyronitrile (AIBN) is 3:1, that is, the mass of benzoyl peroxide (BPO) is 0.15% of the mass of the epoxy resin, and the mass of azobisisobutyronitrile (AIBN) is 0.05% of the mass of the epoxy resin.

[0033] The temperature was then lowered to 80°C, and diethanolamine was added. The mass of diethanolamine was 38% of the mass of the epoxy resin. After reacting for 2.2 hours, composite additives, lactic acid, and deionized water were added. The mass of the composite additives was 1.4% of the mass of the epoxy resin, the mass of the lactic acid was 16.5% of the mass of the epoxy resin, and the pH was adjusted to 5.9 with deionized water. Finally, the mixture was cooled and discharged to obtain the cathodic electrophoretic coating.

[0034] Example 2: The difference between this example and Example 1 is that: a method for preparing a cathodic electrophoretic coating includes the following steps:

[0035] S1. By weight, add 50 parts epoxy resin, 14 parts polyethylene glycol, and 30 parts toluene solvent to a four-necked flask. Heat to 128°C and react at this temperature for 2.2 hours. Then add 8 parts bisphenol A chain extender and react at this temperature for 3 hours to obtain the chain-extended resin. The epoxy resin is 6101 epoxy resin; the polyethylene glycol is PEG-400.

[0036] S2. Add the chain extender resin obtained in S1 and the solvent toluene to a four-necked flask, heat to 115°C, keep the temperature constant for 32 min, add acrylic monomers and initiator benzoyl peroxide (BPO) dropwise, react for 2 h after the addition is complete, and then add the initiator azobisisobutyronitrile (AIBN).

[0037] The acrylic monomers include methyl methacrylate, styrene, butyl acrylate, and acrylamide, with their respective mass percentages being 5.2%, 6.5%, 5.2%, and 3.3% of the epoxy resin mass.

[0038] The total mass of the initiator is 0.2% of the mass of the epoxy resin, and the mass ratio of benzoyl peroxide (BPO) to azobisisobutyronitrile (AIBN) is 3:1, that is, the mass of benzoyl peroxide (BPO) is 0.15% of the mass of the epoxy resin, and the mass of azobisisobutyronitrile (AIBN) is 0.05% of the mass of the epoxy resin.

[0039] The temperature was then lowered to 80°C, and diethanolamine was added. The mass of diethanolamine was 38% of the mass of the epoxy resin. After reacting for 2.2 hours, composite additives, lactic acid, and deionized water were added. The mass of the composite additives was 1.5% of the mass of the epoxy resin, the mass of the lactic acid was 16.5% of the mass of the epoxy resin, and the pH was adjusted to 5.9 with deionized water. Finally, the mixture was cooled and discharged to obtain the cathodic electrophoretic coating.

[0040] Example 3: The difference between this example and Example 1 is that: a method for preparing a cathodic electrophoretic coating includes the following steps:

[0041] S1. By weight, add 50 parts epoxy resin, 14 parts polyethylene glycol, and 30 parts toluene solvent to a four-necked flask. Heat to 128°C and react at this temperature for 2.2 hours. Then add 8 parts bisphenol A chain extender and react at this temperature for 3 hours to obtain the chain-extended resin. The epoxy resin is 6101 epoxy resin; the polyethylene glycol is PEG-400.

[0042] S2. Add the chain extender resin obtained in S1 and the solvent toluene to a four-necked flask, heat to 115°C, keep the temperature constant for 32 min, add acrylic monomers and initiator benzoyl peroxide (BPO) dropwise, react for 2 h after the addition is complete, and then add the initiator azobisisobutyronitrile (AIBN).

[0043] The acrylic monomers include methyl methacrylate, styrene, butyl acrylate, and acrylamide, with their respective mass percentages being 5.2%, 6.5%, 5.2%, and 3.4% of the epoxy resin mass.

[0044] The total mass of the initiator is 0.2% of the mass of the epoxy resin, and the mass ratio of benzoyl peroxide (BPO) to azobisisobutyronitrile (AIBN) is 3:1, that is, the mass of benzoyl peroxide (BPO) is 0.15% of the mass of the epoxy resin, and the mass of azobisisobutyronitrile (AIBN) is 0.05% of the mass of the epoxy resin.

[0045] The temperature was then lowered to 80°C, and diethanolamine was added. The mass of diethanolamine was 38% of the mass of the epoxy resin. After reacting for 2.2 hours, composite additives, lactic acid, and deionized water were added. The mass of the composite additives was 1.2% of the mass of the epoxy resin, the mass of the lactic acid was 16.5% of the mass of the epoxy resin, and the pH was adjusted to 5.9 with deionized water. Finally, the mixture was cooled and discharged to obtain the cathodic electrophoretic coating.

[0046] Comparative Example 1: The difference between this comparative example and Example 1 is that in the preparation of the cathodic electrophoretic coating, the mass of acrylamide is 4.35% of the mass of epoxy resin; and no composite additives are added.

[0047] Specifically, a method for preparing a cathodic electrophoretic coating includes the following steps:

[0048] S1. By weight, add 50 parts epoxy resin, 14 parts polyethylene glycol, and 30 parts toluene solvent to a four-necked flask. Heat to 128°C and react at this temperature for 2.2 hours. Then add 8 parts bisphenol A chain extender and react at this temperature for 3 hours to obtain the chain-extended resin. The epoxy resin is 6101 epoxy resin; the polyethylene glycol is PEG-400.

[0049] S2. Add the chain extender resin obtained in S1 and the solvent toluene to a four-necked flask, heat to 115°C, keep the temperature constant for 32 min, add acrylic monomers and initiator benzoyl peroxide (BPO) dropwise, react for 2 h after the addition is complete, and then add the initiator azobisisobutyronitrile (AIBN).

[0050] The acrylic monomers include methyl methacrylate, styrene, butyl acrylate, and acrylamide, with their respective mass percentages being 5.2%, 6.5%, 5.2%, and 4.35% of the epoxy resin mass.

[0051] The total mass of the initiator is 0.2% of the mass of the epoxy resin, and the mass ratio of benzoyl peroxide (BPO) to azobisisobutyronitrile (AIBN) is 3:1, that is, the mass of benzoyl peroxide (BPO) is 0.15% of the mass of the epoxy resin, and the mass of azobisisobutyronitrile (AIBN) is 0.05% of the mass of the epoxy resin.

[0052] The temperature was then lowered to 80°C, and diethanolamine (38% of the epoxy resin mass) was added. After reacting for 2.2 hours, lactic acid (16.5% of the epoxy resin mass) and deionized water were added, and the pH was adjusted to 5.9 with deionized water. Finally, the mixture was cooled and discharged to obtain the cathodic electrophoretic coating.

[0053] Comparative Example 2: The difference between this comparative example and Example 1 is that no composite additives are added in the preparation of the cathodic electrophoretic coating.

[0054] Specifically, a method for preparing a cathodic electrophoretic coating includes the following steps:

[0055] S1. By weight, add 50 parts epoxy resin, 14 parts polyethylene glycol, and 30 parts toluene solvent to a four-necked flask. Heat to 128°C and react at this temperature for 2.2 hours. Then add 8 parts bisphenol A chain extender and react at this temperature for 3 hours to obtain the chain-extended resin. The epoxy resin is 6101 epoxy resin; the polyethylene glycol is PEG-400.

[0056] S2. Add the chain extender resin obtained in S1 and the solvent toluene to a four-necked flask, heat to 115°C, keep the temperature constant for 32 min, add acrylic monomers and initiator benzoyl peroxide (BPO) dropwise, react for 2 h after the addition is complete, and then add the initiator azobisisobutyronitrile (AIBN).

[0057] The acrylic monomers include methyl methacrylate, styrene, butyl acrylate, and acrylamide, with their respective mass percentages being 5.2%, 6.5%, 5.2%, and 3.35% of the epoxy resin mass.

[0058] The total mass of the initiator is 0.2% of the mass of the epoxy resin, and the mass ratio of benzoyl peroxide (BPO) to azobisisobutyronitrile (AIBN) is 3:1, that is, the mass of benzoyl peroxide (BPO) is 0.15% of the mass of the epoxy resin, and the mass of azobisisobutyronitrile (AIBN) is 0.05% of the mass of the epoxy resin.

[0059] The temperature was then lowered to 80°C, and diethanolamine (38% of the epoxy resin mass) was added. After reacting for 2.2 hours, lactic acid (16.5% of the epoxy resin mass) and deionized water were added, and the pH was adjusted to 5.9 with deionized water. Finally, the mixture was cooled and discharged to obtain the cathodic electrophoretic coating.

[0060] Comparative Example 3: The difference between this comparative example and Example 1 is that in the preparation of the cathodic electrophoretic coating, the mass of acrylamide is 4.35% of the mass of epoxy resin.

[0061] Specifically, a method for preparing a cathodic electrophoretic coating includes the following steps:

[0062] S1. By weight, add 50 parts epoxy resin, 14 parts polyethylene glycol, and 30 parts toluene solvent to a four-necked flask. Heat to 128°C and react at this temperature for 2.2 hours. Then add 8 parts bisphenol A chain extender and react at this temperature for 3 hours to obtain the chain-extended resin. The epoxy resin is 6101 epoxy resin; the polyethylene glycol is PEG-400.

[0063] S2. Add the chain extender resin obtained in S1 and the solvent toluene to a four-necked flask, heat to 115°C, keep the temperature constant for 32 min, add acrylic monomers and initiator benzoyl peroxide (BPO) dropwise, react for 2 h after the addition is complete, and then add the initiator azobisisobutyronitrile (AIBN).

[0064] The acrylic monomers include methyl methacrylate, styrene, butyl acrylate, and acrylamide, with their respective mass percentages being 5.2%, 6.5%, 5.2%, and 4.35% of the epoxy resin mass.

[0065] The total mass of the initiator is 0.2% of the mass of the epoxy resin, and the mass ratio of benzoyl peroxide (BPO) to azobisisobutyronitrile (AIBN) is 3:1, that is, the mass of benzoyl peroxide (BPO) is 0.15% of the mass of the epoxy resin, and the mass of azobisisobutyronitrile (AIBN) is 0.05% of the mass of the epoxy resin.

[0066] The temperature was then lowered to 80°C, and diethanolamine was added. The mass of diethanolamine was 38% of the mass of the epoxy resin. After reacting for 2.2 hours, composite additives, lactic acid, and deionized water were added. The mass of the composite additives was 1.4% of the mass of the epoxy resin, the mass of the lactic acid was 16.5% of the mass of the epoxy resin, and the pH was adjusted to 5.9 with deionized water. Finally, the mixture was cooled and discharged to obtain the cathodic electrophoretic coating.

[0067] Experimental Example: Experimental Subjects: Cathodic electrophoretic coatings (films) prepared in Examples 1-3 and Comparative Examples 1-3. Method for obtaining the film: Low-carbon stainless steel plate was selected as the anode, and treated tinplate plate as the cathode. The anode plate and cathode workpiece were hung, and the anode and cathode plates were adjusted to be basically parallel. The circuit was connected, timed for 3 minutes, and the voltage was 150V. The prepared film was washed with tap water to remove the floating paint adhering to its surface due to impregnation. Then, the workpiece was placed in the air at room temperature for a period of time, and then transferred to an oven and baked at 170℃ for 0.5 hours. After cooling, various performance tests were conducted.

[0068] Test items and methods: 1. Paint film appearance - observe whether it yellows. 2. Paint film pinhole rate / density - observe the number of pinholes (diameter 0.5-3.0mm) on the paint film surface and calculate the average number per cm. 2 The number of shrinkage cavities.

[0069] Experimental results: see Table 1.

[0070] Table 1. Test data for the experimental cases

[0071]

[0072] Results Analysis: Combining the data in Table 1 and... Figure 1 Analysis of Examples 1-3 shows that the cathodic electrophoretic coating film prepared by the present invention (Examples 1-3) is free of craters and orange peel, and is smooth and does not turn yellow.

[0073] Combining the data in Table 1 and Figure 1 Analysis was conducted on Example 1 and Comparative Examples 1-3, specifically on Comparative Examples 1 and 2. It was found that, compared to Comparative Example 1 (where the amount of acrylamide was 4.35% of the epoxy resin mass), the paint film in Comparative Example 1 was yellowish and had a pore rate of 0.05 pores / cm. 2In Comparative Example 2, the amount of acrylamide was reduced to 3.35% of the epoxy resin mass. As a result, the paint film of Comparative Example 2 did not yellow, but the pore rate increased to 0.07 pores / cm. 2 This indicates that reducing the amount of acrylamide (from 4.35% to 3.35% of the epoxy resin mass) can prevent the paint film from yellowing, but at the same time, it will also lead to an increase in the pore rate / density of the paint film.

[0074] This is mainly because reducing the amount of acrylamide has two negative effects. On the one hand, it reduces the density of polar groups in the system, increases the contact angle between the coating and the substrate, reduces wettability, and makes it easy for "fish-eye" craters to form in local areas due to poor wetting, resulting in an increase in the crater density of the paint film. On the other hand, it also has a positive effect, avoiding excessive cross-linking and preventing the paint film from being too rigid and lacking elasticity, which is not conducive to the deformation and escape of bubbles. It ensures a balance between hardness and extensibility, which is more conducive to reducing the crater density of the paint film. Here, the negative effects outweigh the positive effects, ultimately leading to an increase in the crater rate / density of the paint film.

[0075] Specifically, analysis of Comparative Examples 1 and 3 shows that, compared to Comparative Example 1 (where the amount of acrylamide was 4.35% of the epoxy resin mass), the paint film in Comparative Example 1 was yellowish and had a pore rate of 0.05 pores / cm. 2 In Comparative Example 3, the composite additive of the present invention was introduced. As a result, the paint film of Comparative Example 3 was still yellowish, but the pore rate was reduced to 0.02 pores / cm. 2 This indicates that introducing the composite additive of the present invention can reduce the pinhole rate / density of the paint film.

[0076] In comparison with Example 1, it can be seen that when the amount of acrylamide is reduced to 3.35% of the epoxy resin mass, the addition of the composite additive of the present invention can ensure that the paint film does not yellow, while synergistically reducing the pore rate / density of the paint film.

[0077] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the preparation of a cathodic electrocoat material, characterized in that, The method comprises the following steps: S1, adding 50 parts of epoxy resin, 13-15 parts of polyethylene glycol and 27-32 parts of solvent into a flask by weight fraction, heating to 125-130 DEG C, constant temperature reaction for 2-2.5 h, then adding 7.5-8.5 parts of chain extender bisphenol A, constant temperature reaction for 2.8-3.2 h, to obtain chain extension resin; S2, adding the chain extension resin and solvent obtained in S1 into a flask, heating to 115±2 DEG C, constant temperature for 30-35 min, adding acrylic monomer and initiator dropwise, reaction for 2 h, cooling to 80±2 DEG C, adding diethanolamine, reaction for 2-2.5 h, adding composite additive, lactic acid and deionized water, to obtain the cathodic electrophoretic paint; the mass of the composite additive is 1.2-1.5% of the mass of the epoxy resin; The acrylic monomer comprises methyl methacrylate, styrene, butyl acrylate and acrylamide, and the mass of the four is 5-5.3%, 6.2-6.6%, 5-5.3% and 3.3-3.4% of the mass of the epoxy resin respectively; The composite additive comprises wetting agent, modified silica and deionized water, the wetting agent is SN-210 water-based wetting agent; the modified silica is prepared by modifying nano-silica with silane coupling agent; the mass ratio of the wetting agent, modified silica and deionized water is 11: (5-7) :1; The preparation method of the modified silica is as follows: adding nano-silica slurry into a reaction kettle, adding the mixture of vinyl trimethoxysilane and ethanol solution dropwise under stirring, heating to 65±2 DEG C, maintaining pH=4-5, reaction for 4-5 h, cooling to room temperature, centrifugation, washing and drying.

2. The method for preparing a cathodic electrodeposition paint according to claim 1, characterized in that, In S1, the epoxy resin is 6101 epoxy resin; the polyethylene glycol is PEG-400.

3. The method for preparing a cathodic electrodeposition paint according to claim 1, characterized in that, In S2, the mass of the initiator is 0.15-0.2% of the mass of the epoxy resin.

4. The method for producing a cathodic electrodeposition paint according to claim 3, characterized in that, The initiator comprises benzoyl peroxide and azobisisobutyronitrile, and the mass ratio of the two is 3:

1.

5. The method of preparing a cathodic electrodeposition paint according to claim 1, characterized in that, In S2, the mass of diethanolamine added is 37-39% of the mass of the epoxy resin.

6. The method of preparing a cathodic electrodeposition paint according to claim 1, characterized in that, In S2, the mass of lactic acid added is 16-17% of the mass of the epoxy resin; deionized water is added to adjust the pH value to 5.8-6.

0.

7. A cathodic electrodeposition coating characterized by The cathodic electrophoretic paint is prepared by the preparation method of any one of claims 1-6.

Images