Electrophoretic coating with high corrosion resistance and preparation method thereof

Abstract

The invention discloses a high-corrosion-resistance electrophoretic coating and a preparation method thereof, and belongs to the technical field of electrophoretic coatings. The preparation method of the coating comprises the following steps: S1, mixing epoxy resin, a thioether compound with an active group at the end position, a chain extender, triphenylphosphine, an organic solvent 2, an amino catalyst and a neutralizer, and carrying out heat preservation and chain extension to obtain thioether modified epoxy resin; s2, aminating, neutralizing and re-emulsifying the thioether modified epoxy resin in the step S1, an aminating agent, an organic solvent 1, a curing agent, a neutralizing agent and deionized water to obtain a high-corrosion-resistance emulsion; s3, mixing and grinding the thioether modified epoxy resin in the step S1 with pigment, a dispersing agent and deionized water to obtain high-corrosion-resistance color paste; s4, mixing the high-corrosion-resistance emulsion in S2 and the high-corrosion-resistance color paste in S3 according to the mass ratio of 4: 1 to 8: 1 to obtain the high-corrosion-resistance electrophoretic coating. And by adopting the thioether modified epoxy resin, the obtained coating has excellent corrosion resistance, mechanical property and flame retardant property at the same time.

Description

Technical Field

[0001] This invention relates to the field of electrophoretic coating technology, specifically to a high-corrosion-resistant electrophoretic coating and its preparation method. Background Technology

[0002] In the field of metal product protection, epoxy resin electrophoretic coatings have become a key component of anti-corrosion coating systems due to their excellent adhesion, chemical resistance, and mechanical properties. The polar groups in epoxy resin molecules (such as hydroxyl groups, ether bonds, or epoxy groups) can form chemical bonds or hydrogen bonds with the metal surface, ensuring strong adhesion between the coating film and the substrate. The cured epoxy resin film forms a dense three-dimensional network structure, effectively blocking the penetration of water, oxygen, and electrolytes, significantly improving the corrosion resistance of metals in harsh environments such as salt spray and acid / alkali conditions. However, the aromatic rings and easily degradable groups (ether bonds, residual active groups) in the molecular structure of traditional epoxy resins make them susceptible to photo-oxidative degradation under environmental factors such as ultraviolet radiation, humidity, and temperature, leading to coating chalking, cracking, or decreased adhesion, ultimately resulting in loss of protective function. Although adding ultraviolet absorbers, antioxidants, or inorganic fillers can delay aging to some extent, these methods often only improve performance in the short term and cannot fundamentally solve the structural stability problem of epoxy resins.

[0003] In contrast, sulfur-containing resins exhibit superior weather resistance, primarily due to: the high chemical stability of thioether bonds, making them less susceptible to hydrolysis or oxidation; the dense and ordered molecular structure, effectively blocking the penetration of corrosive media; low sensitivity to ultraviolet light, reducing the risk of photodegradation; and the synergistic antioxidant effect of the lone pair electrons of sulfur atoms, which helps delay coating aging. These properties enable sulfur-containing resins to exhibit superior weather resistance, chemical resistance, and heat resistance compared to traditional resins containing ether bonds, ester bonds, or aromatic rings (such as epoxy resins) in harsh environments such as high temperature, high humidity, and strong ultraviolet radiation.

[0004] Therefore, in order to take into account both the excellent adhesion of epoxy resin and the good weather resistance of sulfur-containing resin, flexible or rigid sulfur-containing chains can be introduced into epoxy resin. This can maintain the dense three-dimensional network structure of epoxy resin after curing, and inherit the characteristics of sulfur-containing resin, thereby achieving a controllable balance between the hardness and flexibility of the paint film. Summary of the Invention

[0005] Therefore, the present invention provides a high corrosion-resistant electrophoretic coating and its preparation method to solve the defects of insufficient corrosion resistance of traditional epoxy resins (containing ether bonds, ester bonds or aromatic rings, etc.) in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: According to a first aspect of the present invention, a high-corrosion-resistant electrophoretic coating is provided, which is prepared by mixing a high-corrosion-resistant emulsion and a high-corrosion-resistant pigment in a mass ratio of 4:1 to 8:1.

[0007] Furthermore, the high-preservative emulsion comprises, by weight, the following components: Thioether-modified epoxy resin: 35-40 parts; Amination agent: 3-8 parts; Organic solvent 1:2-4 parts; Hardener: 25-30 parts; Neutralizing agent: 1-2 parts; Deionized water: 30-35 parts; The amination agent is at least one of ketimine, alcohol amine (such as methylethanolamine, diethanolamine, etc.) and alkylamine; the organic solvent 1 is at least one of ketone compounds (such as methyl isobutyl ketone, etc.) and alcohol ether compounds (such as ethylene glycol butyl ether, etc.); the curing agent is a blocked isocyanate; the neutralizing agent is a small organic molecule acid, such as acetic acid, formic acid, lactic acid, methanesulfonic acid, etc. The method for preparing the blocked isocyanate is as follows: The end-capping product was added dropwise to the isocyanate compound at 50-80℃. After the addition was completed, the reaction was maintained at 80℃ for 2-3 hours until no -NCO groups remained in the system. The mass ratio of the end-capping agent to the isocyanate compound is (1-3):(2-4). The end-capping agent is a small molecule compound containing active hydrogen, including but not limited to methyl ethyl ketone oxime, ε-caprolactam, diisopropylamine, dimethylpyrazole, or 1,2,4-triazole. The isocyanate compound is a compound containing -NCO groups, including but not limited to hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), or diphenylmethane diisocyanate (MDI).

[0008] Furthermore, the mass ratio of the end-capping agent to the isocyanate compound is 3:2.

[0009] Furthermore, the high-corrosion-resistant colorant comprises, by weight, the following components: Sulfide-modified epoxy resin: 28-40 parts; Pigment: 22-38 parts; Dispersant: 0.1-0.3 parts; Deionized water: 50-60 parts.

[0010] Furthermore, the pigment comprises 4-8 parts carbon black and 18-30 parts kaolin by weight; the high-corrosion-resistant pigment has a solid content of 40%-60% and is black in color.

[0011] Furthermore, the pigment comprises 4-8 parts carbon black, 15-25 parts kaolin and 15-25 parts titanium dioxide by weight; the high corrosion resistant pigment has a solid content of 50%-60% and a gray color.

[0012] Furthermore, the sulfide-modified epoxy resin comprises, by weight, the following components: Epoxy resin: 20-35 parts; Thioether compounds with active groups at the terminal positions: 4-10 parts; Chain extender: 4-15 parts; Triphenylphosphine: 0.05-0.2 parts; Organic solvent 2: 30-50 parts; Amine catalyst: 2-4 parts; Neutralizing agent: 0.8-1.5 parts; The thioether compound with an active group at the terminal position is at least one of the following: thioether small molecule compounds containing terminal hydroxyl, amino, or carboxyl active groups, and their aliphatic hydrocarbon polymers, such as ethyl-2-hydroxyethyl thioether, o-methylthiophenol, 4,4'-thiodiphenol, 2-aminoanisidine thioether, p-aminoanisidine thioether, and thiodiethylene glycol diamine. N,N' -Di(2-aminoethyl)thiourea, etc.; the chain extender is at least one of bisphenol A and its derivatives (such as bisphenol F, etc.); the organic solvent 2 is at least one of toluene, ketones and ethers; the amine catalyst is at least one of organic amine catalysts and inorganic amine catalysts, such as ketimine, etc.

[0013] According to a second aspect of the present invention, a method for preparing a highly corrosion-resistant electrophoretic coating is provided, comprising the following steps: S1. Preparation of sulfide-modified epoxy resin; S2. Based on the sulfide-modified epoxy resin obtained in step S1, prepare a high-corrosion-resistant emulsion. S3. Based on the sulfide-modified epoxy resin prepared in step S1, prepare a high-corrosion-resistant color paste. S4. Mix the high-corrosion-resistant emulsion and high-corrosion-resistant pigment obtained above at low speed until homogeneous to obtain a high-corrosion-resistant electrophoretic coating.

[0014] Further, the preparation of the sulfide-modified epoxy resin in step S1 is carried out using the following specific method: Epoxy resin, a thioether compound with active terminal groups, a chain extender, and organic solvent 2 were added to a reaction vessel. The temperature was raised to 100°C and stirred continuously. Triphenylphosphine was added, and the reaction was maintained at 100°C for 2 hours. The temperature was raised to 130°C, and an amine catalyst was added. The temperature was further raised to 140-160°C, and the reaction was carried out for 1-3 hours. After the reaction was completed, the temperature was lowered to 90°C, a neutralizing agent was added, and the reaction was maintained at this temperature for 5 minutes to obtain thioether-modified epoxy resin. The epoxy equivalent of the sulfide-modified epoxy resin is 1000-2000.

[0015] Furthermore, the high-preservative emulsion is prepared in step S2, and the specific method is as follows: The sulfide-modified epoxy resin, amination agent, and part of organic solvent 1 are mixed. When the temperature is raised to 100-130℃, the mixture is stirred for 1-2 hours. After cooling to 90℃, the curing agent and the remaining organic solvent 1 are added, and the mixture is stirred for 30 minutes to obtain a mixed resin. The obtained mixed resin is added to a pre-prepared neutralizing agent and sufficient deionized water mixture, and stirred at 55-70℃ for 10-30 minutes. Finally, at 55℃, deionized water is added to adjust the solid content to 35%-40% to obtain a high-corrosion-resistant emulsion.

[0016] Furthermore, in step S3, a highly corrosion-resistant colorant is prepared, and the specific method is as follows: The sulfide-modified epoxy resin, pigment, dispersant and sufficient deionized water are mixed and added to a sand mill. The mixture is ground at 3000 r / min for 2-5 hours until the fineness is <15 μm to obtain a mixture. Then, deionized water is added to adjust the solid content of the mixture to obtain a high corrosion-resistant color paste.

[0017] The present invention has the following advantages: This invention successfully develops a high-performance, corrosion-resistant electrophoretic coating system based on thioether-modified epoxy resin. Thioether compounds with terminal active groups (such as small molecule thioethers containing terminal hydroxyl, amino, or carboxyl groups and their aliphatic hydrocarbon polymers) are used to modify the molecular structure of epoxy resin. Flexible or rigid thioether segments are introduced into the epoxy resin molecular chain. Utilizing the lone pair electron effect and steric hindrance of sulfur atoms, the density of the epoxy resin is significantly improved, while also possessing excellent mechanical properties. The coatings formed by the thioether-modified epoxy resin system have the following advantages: Improved corrosion resistance: Sulfur atoms form coordination bonds with metals to build a dense protective layer. Salt spray tests show that the corrosion resistance time of the coating is more than twice that of traditional electrophoretic coatings. Adjustable mechanical properties: By selecting flexible or rigid sulfide compounds, the sulfide bonds enhance molecular polarity, improving coating adhesion and flexibility, thus achieving flexible adjustment of coating hardness and flexibility: the coating hardness of the coating prepared based on epoxy resin modified with rigid sulfide compounds is increased by one level; the coating adhesion of the coating prepared based on epoxy resin modified with flexible sulfide compounds reaches the highest level (level 0, no peeling). Enhanced flame retardancy: The introduction of sulfide groups significantly enhances the flame retardancy of the coating, increasing its LOI by 23.1%-34.6%. These groups undergo thermal decomposition at high temperatures, releasing gaseous products such as SO2. These products not only dilute the concentration of oxygen and combustible gases but also effectively capture free radicals in the combustion chain reaction, thereby efficiently interrupting the combustion process.

[0018] This invention introduces sulfur-containing compounds to reconstruct the molecular structure of epoxy resin, significantly improving the density and corrosion resistance of the coating, while also increasing the flexibility of the material and possessing excellent mechanical properties to meet the needs of diverse application scenarios. Detailed Implementation

[0019] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] According to a first aspect of the present invention, a high-corrosion-resistant electrophoretic coating is provided, which is prepared by mixing a high-corrosion-resistant emulsion and a high-corrosion-resistant pigment in a mass ratio of 4:1 to 8:1.

[0021] Furthermore, the high-preservative emulsion comprises, by weight, the following components: Thioether-modified epoxy resin: 35-40 parts; Amination agent: 3-8 parts; Organic solvent 1:2-4 parts; Hardener: 25-30 parts; Neutralizing agent: 1-2 parts; Deionized water: 30-35 parts; The amination agent is at least one of ketimine, alcohol amine (such as methylethanolamine, diethanolamine, etc.) and alkylamine; the organic solvent 1 is at least one of ketone compound (such as methyl isobutyl ketone, etc.) and alcohol ether compound (such as ethylene glycol butyl ether, etc.); the curing agent is a blocked isocyanate; the neutralizing agent is a small organic molecule acid, such as acetic acid, formic acid, lactic acid, methanesulfonic acid, etc. The preparation method of blocked isocyanate is as follows: The end-capping product was added dropwise to the isocyanate compound at 50-80℃. After the addition was completed, the reaction was maintained at 80℃ for 2-3 hours until no -NCO groups remained in the system. The mass ratio of the end-capping compound to the isocyanate compound is (1-3):(2-4). The end-capping compound is a small molecule compound containing active hydrogen, including but not limited to methyl ethyl ketone oxime, ε-caprolactam, diisopropylamine, dimethylpyrazole or 1,2,4-triazole. The isocyanate compound is a compound containing -NCO group, including but not limited to hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI).

[0022] Furthermore, the mass ratio of the end-capping compound to the isocyanate compound is 3:2.

[0023] Furthermore, the high-corrosion-resistant colorant, by weight, comprises the following components: Sulfide-modified epoxy resin: 28-40 parts; Pigment: 22-38 parts; Dispersant: 0.1-0.3 parts; Deionized water: 50-60 parts.

[0024] Furthermore, the pigment comprises 4-8 parts carbon black and 18-30 parts kaolin by weight; the high-corrosion-resistant pigment has a solid content of 40%-60% and is black in color.

[0025] Furthermore, the pigment comprises 4-8 parts carbon black, 15-25 parts kaolin and 15-25 parts titanium dioxide by weight; the high-corrosion-resistant pigment has a solid content of 50%-60% and a gray color.

[0026] Furthermore, the sulfide-modified epoxy resin comprises the following components by weight: Epoxy resin: 20-35 parts; Thioether compounds with active groups at the terminal positions: 4-10 parts; Chain extender: 4-15 parts; Triphenylphosphine: 0.05-0.2 parts; Organic solvent 2: 30-50 parts; Amine catalyst: 2-4 parts; Neutralizing agent: 0.8-1.5 parts; Thioether compounds with terminal active groups are at least one of the following: thioether small molecule compounds containing terminal hydroxyl, amino, or carboxyl active groups, and their aliphatic hydrocarbon polymers, such as ethyl-2-hydroxyethyl thioether, o-methylthiophenol, 4,4'-thiodiphenol, 2-aminoanisidine thioether, p-aminoanisidine thioether, and thiodiethylene glycol diamine. N,N' -Di(2-aminoethyl)thiourea, etc.; chain extender is at least one of bisphenol A and its derivatives (such as bisphenol F, etc.); organic solvent 2 is at least one of toluene, ketones and ethers; amine catalyst is at least one of organic amine catalysts and inorganic amine catalysts, such as ketimine, etc.

[0027] According to a second aspect of the present invention, a method for preparing a highly corrosion-resistant electrophoretic coating is provided, comprising the following steps: S1. Preparation of sulfide-modified epoxy resin; S2. Based on the sulfide-modified epoxy resin obtained in step S1, prepare a high-corrosion-resistant emulsion. S3. Based on the sulfide-modified epoxy resin prepared in step S1, prepare a high-corrosion-resistant color paste. S4. Mix the high-corrosion-resistant emulsion and high-corrosion-resistant pigment obtained above at low speed until homogeneous to obtain a high-corrosion-resistant electrophoretic coating.

[0028] Further, the preparation of the sulfide-modified epoxy resin in step S1 is carried out using the following specific method: Epoxy resin, a thioether compound with active terminal groups, a chain extender, and organic solvent 2 were added to a reaction vessel. The temperature was raised to 100°C and stirred continuously. Triphenylphosphine was added, and the reaction was maintained at 100°C for 2 hours. The temperature was raised to 130°C, and an amine catalyst was added. The temperature was further raised to 140-160°C, and the reaction was carried out for 1-3 hours. After the reaction was completed, the temperature was lowered to 90°C, a neutralizing agent was added, and the reaction was maintained at this temperature for 5 minutes to obtain thioether-modified epoxy resin. The epoxy equivalent of sulfide-modified epoxy resin is 1000-2000.

[0029] Furthermore, the high-preservative emulsion is prepared in step S2, and the specific method is as follows: The sulfide-modified epoxy resin, amination agent, and part of organic solvent 1 are mixed. When the temperature is raised to 100-130℃, the mixture is stirred for 1-2 hours. After cooling to 90℃, the curing agent and the remaining organic solvent 1 are added, and the mixture is stirred for 30 minutes to obtain a mixed resin. The obtained mixed resin is added to a pre-prepared neutralizing agent and sufficient deionized water mixture, and stirred at 55-70℃ for 10-30 minutes. Finally, at 55℃, deionized water is added to adjust the solid content to 35%-40% to obtain a high-corrosion-resistant emulsion.

[0030] Furthermore, in step S3, a highly corrosion-resistant colorant is prepared, and the specific method is as follows: The sulfide-modified epoxy resin, pigment, dispersant and sufficient deionized water are mixed and added to a sand mill. The mixture is ground at 3000 r / min for 2-5 hours until the fineness is <15 μm to obtain a mixture. Then, deionized water is added to adjust the solid content of the mixture to obtain a high corrosion-resistant color paste.

[0031] Preparation Example 1: Preparation of blocked isocyanates: 30g of ε-caprolactam was added dropwise to 20g of hexamethylene diisocyanate (HDI) at 70℃. After the addition was completed, the reaction was kept at 80℃ for 2.5h. During the reaction, the reaction was monitored by di-n-butylamine titration until no -NCO groups remained in the system, thus obtaining the blocked isocyanate. Example 1

[0032] (1) Preparation of sulfide-modified epoxy resin: 25g of epoxy resin, 4g of ethyl 2-hydroxyethyl sulfide, 4g of bisphenol A and 30g of toluene were added to a reaction vessel, and the temperature was raised to 100℃ with constant stirring. 0.05g of triphenylphosphine was added, and the reaction was carried out at 100℃ for 2 hours. The temperature was raised to 130℃, and 2g of ketoimine was added. The temperature was further raised to 150℃, and the reaction was carried out for 2 hours. After the reaction was completed, the temperature was lowered to 90℃, 0.8g of acetic acid was added, and the reaction was carried out at this temperature for 5 minutes to obtain a sulfide-modified epoxy resin with an epoxy equivalent of 1200.

[0033] (2) Preparation of high-preservative emulsion: Add 35g of sulfide-modified epoxy resin, 3g of methylethanolamine and 1g of methyl isobutyl ketone obtained in step (1) to a reaction vessel. When the temperature rises to 115°C, stir for 2 hours. After cooling to 90°C, add 25g of blocked isocyanate (prepared in Preparation Example 1) and 1g of methyl isobutyl ketone, and stir for 30 minutes to obtain a mixed resin. Add the obtained mixed resin to a pre-prepared mixture of 1g of acetic acid and 30g of deionized water, and stir at 60°C for 25 minutes. Finally, add deionized water at 55°C to adjust the solid content to 36% to obtain a high-preservative emulsion.

[0034] (3) Preparation of black high-corrosion-resistant pigment: Mix 28g of sulfide-modified epoxy resin, 4g of carbon black, 18g of kaolin, 0.1g of dispersant and 50g of deionized water obtained in step (1), add them to a sand mill, and grind them at 3000r / min for 3h until the fineness is <15um to obtain a mixture; then add deionized water to adjust the solid content of the mixture to 45% to obtain a black high anti-corrosion pigment.

[0035] (4) Preparation of high corrosion resistant electrophoretic coating: The 160g high-corrosion emulsion obtained in step (2) and the 40g black high-corrosion pigment obtained in step (3) are mixed evenly by low-speed stirring to obtain a high-corrosion electrophoretic coating. Example 2

[0036] (1) Preparation of sulfide-modified epoxy resin: 35g of epoxy resin, 5.5g of 4,4'-thiodiphenol, 5.5g of bisphenol A and 50g of toluene were added to a reaction vessel, and the temperature was raised to 100℃ with constant stirring. 0.1g of triphenylphosphine was added, and the reaction was carried out at 100℃ for 2 hours. The temperature was raised to 130℃, and 3g of ketoimine was added. The temperature was further raised to 150℃, and the reaction was carried out for 2 hours. After the reaction was completed, the temperature was lowered to 90℃, 1g of formic acid was added, and the reaction was carried out at this temperature for 5 minutes to obtain a thioether-modified epoxy resin with an epoxy equivalent of 1350.

[0037] (2) Preparation of high-preservative emulsion: Add 35g of sulfide-modified epoxy resin, 4g of ketoimine, 2g of diethanolamine and 1g of methyl isobutyl ketone obtained in step (1) to a reaction vessel. When the temperature rises to 115°C, stir for 2 hours. After cooling to 90°C, add 25g of blocked isocyanate (prepared in Preparation Example 1) and 1g of methyl isobutyl ketone, and stir for 30 minutes to obtain a mixed resin. Add the obtained mixed resin to a pre-prepared mixture of 1g of acetic acid and 30g of deionized water, and stir at 60°C for 25 minutes. Finally, add deionized water at 55°C to adjust the solid content to 36% to obtain a high-preservative emulsion.

[0038] (3) Preparation of black high-corrosion-resistant pigment: Mix 40g of sulfide-modified epoxy resin, 6g of carbon black, 25g of kaolin, 0.2g of dispersant and 50g of deionized water obtained in step (1), add them to a sand mill, and grind them at 3000r / min for 3h until the fineness is <15um to obtain a mixture; then add deionized water to adjust the solid content of the mixture to 45% to obtain a black high anti-corrosion pigment.

[0039] (4) Preparation of high corrosion resistant electrophoretic coating: Mix 180g of high-corrosion-resistant emulsion obtained in step (2) and 30g of black high-corrosion-resistant pigment obtained in step (3) at low speed until homogeneous to obtain a high-corrosion-resistant electrophoretic coating. Example 3

[0040] (1) Preparation of sulfide-modified epoxy resin: 20g of epoxy resin, 10g of 4,4'-thiodiphenol, 15g of bisphenol A and 40g of toluene were added to a reaction vessel, and the temperature was raised to 100℃ with constant stirring. 0.2g of triphenylphosphine was added, and the reaction was carried out at 100℃ for 2 hours. The temperature was raised to 130℃, and 4g of ketoimine was added. The temperature was further raised to 150℃, and the reaction was carried out for 2 hours. After the reaction was completed, the temperature was lowered to 90℃, 1.5g of formic acid was added, and the reaction was carried out at this temperature for 5 minutes to obtain a thioether-modified epoxy resin with an epoxy equivalent of 1800.

[0041] (2) Preparation of high-preservative emulsion: Add 40g of sulfide-modified epoxy resin, 8g of ketoimine and 1g of methyl isobutyl ketone obtained in step (1) to a reaction vessel. When the temperature rises to 115°C, stir for 2 hours. After cooling to 90°C, add 25g of blocked isocyanate (prepared in Preparation Example 1) and 1g of methyl isobutyl ketone, and stir for 30 minutes to obtain a mixed resin. Add the obtained mixed resin to a pre-prepared mixture of 1g of acetic acid and 30g of deionized water, and stir at 60°C for 25 minutes. Finally, add deionized water at 55°C to adjust the solid content to 36% to obtain a high-preservative emulsion.

[0042] (3) Preparation of black high-corrosion-resistant pigment: Mix 30g of sulfide-modified epoxy resin, 8g of carbon black, 30g of kaolin, 0.3g of dispersant and 50g of deionized water obtained in step (1), add them to a sand mill, and grind them at 3000r / min for 3h until the fineness is <15um to obtain a mixture; then add deionized water to adjust the solid content of the mixture to 45% to obtain a black high anti-corrosion pigment.

[0043] (4) Preparation of high corrosion resistant electrophoretic coating: The 160g high-corrosion emulsion obtained in step (2) and the 20g black high-corrosion pigment obtained in step (3) are mixed evenly by low-speed stirring to obtain a high-corrosion electrophoretic coating.

[0044] Comparative example: (1) Preparation of epoxy resin: 20g of epoxy resin, 7.8g of bisphenol A, and 30g of toluene were added to a reaction vessel, and the temperature was raised to 100℃ with constant stirring. 0.05g of triphenylphosphine was added, and the reaction was carried out at 100℃ for 2 hours. The temperature was raised to 130℃, and 2g of ketoimine was added. The temperature was further raised to 150℃, and the reaction was carried out for 2 hours. After the reaction was completed, the temperature was lowered to 90℃, 0.8g of acetic acid was added, and the reaction was carried out at this temperature for 5 minutes to obtain an epoxy resin with an epoxy equivalent of 1200.

[0045] (2) Preparation of emulsion: Add 32g of epoxy resin, 3.5g of methylethanolamine and 1g of methyl isobutyl ketone obtained in step (1) to a reaction vessel. When the temperature rises to 115°C, stir for 2 hours. After cooling to 90°C, add 25g of blocked isocyanate (prepared in Preparation Example 1) and 1g of methyl isobutyl ketone, and stir for 30 minutes to obtain a mixed resin. Add the obtained mixed resin to a pre-prepared mixture of 1.3g of acetic acid and 30g of deionized water, and stir at 60°C for 25 minutes. Finally, add deionized water at 55°C to adjust the solid content to 36% to obtain an emulsion.

[0046] (3) Preparation of black pigment: Mix 30g epoxy resin, 4g carbon black, 18g kaolin, 0.1g dispersant and 50g deionized water obtained in step (1), add them to a sand mill, grind at 3000r / min for 3h, grind and disperse until fineness <15um, and obtain a mixture; then add deionized water to adjust the solid content of the mixture to 45%, and obtain black pigment paste.

[0047] (4) Preparation of traditional electrophoretic coatings: After mixing the 160g emulsion obtained in step (2) and the 40g black pigment obtained in step (3), add 200g deionized water and stir at low speed to mix evenly to obtain a traditional electrophoretic coating.

[0048] Test example: A high-corrosion-resistant electrophoretic coating (prepared in Examples 1-3) and a conventional electrophoretic coating (prepared in the comparative example) were formulated into an electrophoretic coating with a solid content of 20%. The coating was stirred evenly and the temperature of the coating was controlled at 30°C in a constant temperature water bath. Subsequently, the coating was electrophoretically deposited onto a phosphate plate at a uniform speed within 120 seconds under a voltage of 180V. Finally, the phosphate plate was placed in a constant temperature oven at 180°C for 20 minutes to cure, thus obtaining an electrophoretic coating sample.

[0049] The coatings of the electrophoretic coated samples obtained in Examples 1 and 2 and the comparative example were subjected to performance tests. Specific test items are as follows: Thickness test: Refer to GB / T 13452.2-2008 "Determination of film thickness of paints and varnishes"; Salt spray test: Refer to GB / T 1771-2007 "Determination of resistance to neutral salt spray of paints and varnishes"; Limiting Oxygen Index (LOI) Test: Refer to GB / T 2406.1-2008 "Determination of Combustion Behavior by Oxygen Index Method for Plastics"; Hardness test: Refer to GB / T 6739-2006 "Determination of Hardness of Paints and Varnishes by Pencil Method"; Adhesion test: Refer to GB / T 9286-2021 "Cross-cut test for paint and varnish film".

[0050] The table below shows the performance test results of the coatings formed by the high corrosion resistance electrophoretic coatings in Examples 1-3 and the conventional electrophoretic coatings in the comparative examples:

[0051] As can be seen from the data in the table above, compared with traditional electrophoretic coatings (comparative examples), the coatings formed by the sulfide-modified high-corrosion-resistant electrophoretic coatings of the present invention (Examples 1-3) show no significant difference in thickness and appearance, but achieve significant improvements in the following properties: Protective performance: The coatings formed by the high corrosion resistant electrophoretic coatings in Examples 1-3 have a neutral salt spray resistance time (≥2000h) that is more than twice that of the conventional electrophoretic coatings (1000h) in the comparative examples; Flame retardant performance: The LOI (32-35) of the coatings formed by the high corrosion resistant electrophoretic coatings in Examples 1-3 was 23.1%-34.6% higher than that of the conventional electrophoretic coating (26) in the comparative example; Mechanical properties: The hardness (2H) of the coating formed by the high corrosion resistant electrophoretic coating in Examples 1-3 is one grade higher than that of the conventional electrophoretic coating in the comparative example (H); Flexibility: The adhesion of the coatings formed by the high corrosion-resistant electrophoretic coatings in Examples 1-3 (Grade 0, no peeling) is significantly better than that of the conventional electrophoretic coatings in the comparative examples (Grade 1, slight peeling at the edges).

[0052] The improved performance of the coating formed by the aforementioned high-corrosion-resistant electrophoretic coating is attributed to the synergistic enhancement effect of sulfide compounds on the epoxy resin system: In terms of corrosion resistance, the introduction of sulfide groups enhances the hydrophobicity and cross-linking network density of the resin, thereby effectively blocking the penetration of corrosive media such as water, oxygen, and electrolytes; in terms of mechanical properties, the introduction of flexible or rigid sulfide segments optimizes the flexibility and adhesion while maintaining the rigidity of the coating; in terms of flame retardancy, sulfide groups can decompose at high temperatures to produce gaseous products such as SO2, which effectively improve the limiting oxygen index (LOI) of the coating by diluting oxygen, capturing combustion free radicals, and interrupting chain reactions.

[0053] The synergy of these three mechanisms gives the coating excellent corrosion resistance, mechanical properties, and flame retardant safety.

[0054] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A high-corrosion-resistant electrophoretic coating, characterized in that, It is prepared by mixing high-corrosion emulsion and high-corrosion color paste in a mass ratio of 4:1 to 8:

1.

2. The high corrosion-resistant electrophoretic coating as described in claim 1, characterized in that, The high-preservative emulsion comprises the following components by weight: Thioether-modified epoxy resin: 35-40 parts; Amination agent: 3-8 parts; Organic solvent 1:2-4 parts; Hardener: 25-30 parts; Neutralizing agent: 1-2 parts; Deionized water: 30-35 parts; The amination agent is at least one of ketimine, alkanolamine, and alkylamine; the organic solvent 1 is at least one of ketone compound and alcohol ether compound; the curing agent is a blocked isocyanate; and the neutralizing agent is a small organic molecule acid.

3. The high corrosion-resistant electrophoretic coating as described in claim 1, characterized in that, The high-corrosion-resistant pigment, by weight, comprises the following components: Sulfide-modified epoxy resin: 28-40 parts; Pigment: 22-38 parts; Dispersant: 0.1-0.3 parts; Deionized water: 50-60 parts.

4. The high corrosion-resistant electrophoretic coating as described in claim 3, characterized in that, The pigment comprises 4-8 parts carbon black and 18-30 parts kaolin by weight; the high-corrosion-resistant pigment has a solid content of 40%-60% and is black in color.

5. The high corrosion-resistant electrophoretic coating as described in claim 3, characterized in that, The pigment comprises 4-8 parts carbon black, 15-25 parts kaolin and 15-25 parts titanium dioxide by weight; the high corrosion resistant pigment has a solid content of 50%-60% and is gray in color.

6. The high corrosion-resistant electrophoretic coating as described in claim 2 or 3, characterized in that, The sulfide-modified epoxy resin comprises the following components by weight: Epoxy resin: 20-35 parts; Thioether compounds with active groups at the terminal positions: 4-10 parts; Chain extender: 4-15 parts; Triphenylphosphine: 0.05-0.2 parts; Organic solvent 2: 30-50 parts; Amine catalyst: 2-4 parts; Neutralizing agent: 0.8-1.5 parts; The thioether compound with an active group at the terminal position is at least one of a small molecule thioether compound containing a terminal hydroxyl, amino, or carboxyl active group and its aliphatic hydrocarbon polymer; the chain extender is at least one of bisphenol A and its derivatives; the organic solvent 2 is at least one of toluene, ketones, and ether solvents; and the amine catalyst is at least one of organic amine catalysts and inorganic amine catalysts.

7. A method for preparing a highly corrosion-resistant electrophoretic coating, characterized in that, Includes the following steps: S1. Preparation of sulfide-modified epoxy resin; S2. Based on the sulfide-modified epoxy resin obtained in step S1, prepare a high-corrosion-resistant emulsion. S3. Based on the sulfide-modified epoxy resin prepared in step S1, prepare a high-corrosion-resistant color paste. S4. Mix the high-corrosion-resistant emulsion and high-corrosion-resistant pigment obtained above at low speed until homogeneous to obtain a high-corrosion-resistant electrophoretic coating.

8. The method for preparing the high-corrosion-resistant electrophoretic coating as described in claim 7, characterized in that, The preparation of sulfide-modified epoxy resin in step S1 is as follows: Epoxy resin, a sulfide compound with active terminal groups, a chain extender, and organic solvent 2 were added to the reaction vessel. The temperature was raised to 100°C and stirred continuously. Triphenylphosphine was added, and the reaction was carried out at 100°C for 2 hours. The temperature was raised to 130°C, and an amine catalyst was added. Continue heating to 140-160℃ and react for 1-3 hours; after the reaction is complete, lower the temperature to 90℃, add a neutralizing agent, and keep the reaction at this temperature for 5 minutes to obtain sulfide-modified epoxy resin. The epoxy equivalent of the sulfide-modified epoxy resin is 1000-2000.

9. The method for preparing the high-corrosion-resistant electrophoretic coating as described in claim 7, characterized in that, The high-preservative emulsion is prepared in step S2, and the specific method is as follows: The sulfide-modified epoxy resin, amination agent, and part of organic solvent 1 are mixed. When the temperature is raised to 100-130℃, the mixture is stirred for 1-2 hours. After cooling to 90℃, the curing agent and the remaining organic solvent 1 are added, and the mixture is stirred for 30 minutes to obtain a mixed resin. The obtained mixed resin is added to a pre-prepared neutralizing agent and sufficient deionized water mixture, and stirred at 55-70℃ for 10-30 minutes. Finally, at 55℃, deionized water is added to adjust the solid content to 35%-40% to obtain a high-corrosion-resistant emulsion.

10. The method for preparing the high-corrosion-resistant electrophoretic coating as described in claim 7, characterized in that, The high-corrosion-resistant color paste is prepared in step S3, and the specific method is as follows: The sulfide-modified epoxy resin, pigment, dispersant and sufficient deionized water are mixed and added to a sand mill. The mixture is ground at 3000 r / min for 2-5 hours until the fineness is <15 μm to obtain a mixture. Then, deionized water is added to adjust the solid content of the mixture to obtain a high corrosion-resistant color paste.

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