A multipurpose corrosion-resistant electrophoretic paint and a method for preparing the same

Abstract

The present application belongs to the technical field of paint, and relates to a multipurpose corrosion-resistant electrophoretic paint and a preparation method thereof. The present application uses methyl benzoate as a starting raw material, introduces hydrazide through ester exchange, reacts with aldehyde to generate acyl hydrazone, reacts with acid anhydride to generate an oxadiazole ring, introduces the oxadiazole modified polybenzimidazole resin into polybenzimidazole by using 3-chlorophenol, and prepares the electrophoretic paint with good corrosion resistance, water resistance and impact resistance by using fillers, additives and cross-linking agents, which can be quickly cured at low temperature.

Description

Technical Field

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

[0002] Electrophoretic coating is a coating system that uses electrophoretic coating technology to uniformly deposit coating particles onto the surface of a workpiece to form a paint film. Its core principle is that under the action of a direct current electric field, charged coating particles move towards an electrode with an opposite charge and are deposited on the surface of the workpiece to form a paint film.

[0003] Current technologies face challenges such as high curing temperatures and poor corrosion resistance in coatings. For example, battery components for new energy vehicles require low-temperature coating (e.g., 80°C) to ensure the materials do not deform or break due to high temperatures. However, traditional epoxy resins have high curing temperatures, necessitating the development of low-temperature crosslinking resins. Chinese Patent Publication No. CN112322146B discloses a low-temperature curing cathodic electrophoretic coating, its preparation process, and its applications. This invention uses an epoxy resin modified with hydrogenated bisphenol A, dimethyl benzylamine, and methyl isobutyl ketone as a base, adding a modified isocyanate-based low-temperature curing agent and colorant to prepare a low-temperature curing cathodic electrophoretic coating, applicable to the automotive, motorcycle, home appliance, elevator, furniture, and hardware lighting industries. The coating prepared using this method requires 25-30 minutes to cure at 130-140°C. Summary of the Invention

[0004] The present invention aims to provide a multi-purpose corrosion-resistant electrophoretic coating and its preparation method. The coating has good corrosion resistance, water resistance and mechanical strength, and can be cured quickly at low temperature (80℃) to ensure that the material will not be deformed or damaged due to high temperature. It can be used for corrosion protection and appearance coating of automotive body, engine, battery and other parts, coating of hardware parts, protection and aesthetics of home appliance shells and other fields.

[0005] To achieve the above objectives, this invention provides a multi-purpose corrosion-resistant electrophoretic coating, comprising a modified resin, deionized water, pigment, filler, additives, co-solvent, and crosslinking agent; the mass ratio of the modified resin, deionized water, pigment, filler, additives, co-solvent, and crosslinking agent is 1:(5~10):(0.01~0.05):(0.015~0.035):(0.25~0.45):(0.5~1):(0.03~0.05); the modified resin is a modified polybenzimidazole resin, prepared by grafting polybenzimidazole with a bis(oxadiazole) derivative and then introducing sulfonic acid groups; the structural formula of the modified polybenzimidazole resin is as follows:

[0006] ;

[0007] Where n takes the value of an integer between 128 and 162.

[0008] Preferably, the filler is hollow glass microspheres.

[0009] The cosolvent is propylene glycol butyl ether.

[0010] The crosslinking agent is sulfonyl succinimide ester.

[0011] Preferably, the additives include corrosion inhibitors, leveling agents, and defoamers.

[0012] Preferably, the pigment is chromium oxide green.

[0013] Preferably, the mass ratio of the corrosion inhibitor, leveling agent, and defoamer is 1:(0.75~1):(1~1.25).

[0014] Preferably, the corrosion inhibitor is any one or more of sodium molybdate, zinc phosphate, and mercaptobenzothiazole.

[0015] Preferably, the leveling agent is any one or more of fluorinated acrylate EFKA-3777, polyester modified siloxane Tego Flow300, and polyether modified polydimethylsiloxane BYK-331.

[0016] Preferably, the defoamer is any one or more of the following: organosilicon-polyether copolymer Tego Foamex 1488 and fluorinated defoamer BYK-1790.

[0017] This invention also provides a method for preparing a multi-purpose corrosion-resistant electrophoretic coating, comprising:

[0018] Step S1: Dissolve methyl benzoate in anhydrous ethanol, add hydrazine hydrate and catalyst, react to obtain crude benzoyl hydrazine product, recrystallize from anhydrous ethanol to obtain benzoyl hydrazine.

[0019] Step S2: Dissolve benzoyl hydrazine in anhydrous ethanol, add chloroacetaldehyde, react to obtain the crude product of the first intermediate, recrystallize from anhydrous ethanol to obtain the first intermediate;

[0020] Step S3: Mix the first intermediate with acetic anhydride and react to obtain a reaction solution. After cooling, pour the reaction solution into ice water and stir. Filter to obtain the crude product of the second intermediate. Wash to obtain the second intermediate.

[0021] Step S4: Mix 3-chlorophenol and catalyst, dissolve in anhydrous ethanol, stir, remove anhydrous ethanol to obtain intermediate product, dissolve intermediate product in first solvent, add second intermediate, react, cool, add water to precipitate, filter to obtain crude third intermediate product, recrystallize from anhydrous ethanol to obtain third intermediate.

[0022] Step S5: Dissolve the third intermediate in the second solvent, add sulfite, adjust the pH to 5-7, and react to obtain the sulfonated third intermediate;

[0023] Step S6: Disperse polybenzimidazole in the first solvent, pass in an inert gas to remove oxygen, add sulfonated third intermediate and sodium hydride, and react under ice bath and inert gas protection to obtain modified polybenzimidazole resin.

[0024] Step S7: The modified polybenzimidazole resin is dispersed in deionized water, and a cosolvent, crosslinking agent, additive, filler and pigment are added to obtain an electrophoretic coating.

[0025] Preferably, the first solvent is any one or more of N-methylpyrrolidone and dimethyl sulfoxide.

[0026] Preferably, the catalyst is any one or more of sodium carbonate and potassium carbonate.

[0027] Preferably, in step S1, the reaction temperature is 60~80℃ and the reaction time is 4~6 h; the mass ratio of methyl benzoate, hydrazine hydrate, anhydrous ethanol and catalyst is 1:(0.52~0.6):(2~3):(0.075~0.11).

[0028] Preferably, in step S2, the reaction temperature is 60~80℃ and the reaction time is 8~12 h; the mass ratio of benzoyl hydrazine, chloroacetaldehyde and anhydrous ethanol is 1:(0.55~1):(5~10).

[0029] Preferably, in step S3, the mass ratio of the first intermediate, acetic anhydride, and ice water is 1:(5~12):(20~25); the washing solvent is deionized water and anhydrous ethanol in sequence; the reaction temperature is 120~130℃, the reaction time is 3~5 h, and the stirring time is 10~12 h.

[0030] Preferably, in step S4, the stirring temperature is 40~60℃ and the stirring time is 20~60 min; the reaction temperature is 120~150℃ and the reaction time is 2~4 h; the mass ratio of 3-chlorophenol, catalyst and anhydrous ethanol is 1:(1~1.5):(10~15); and the mass ratio of intermediate product, first solvent and second intermediate is 1:(10~15):(0.75~0.9).

[0031] Preferably, in step S5, the second solvent is any one or more of anhydrous ethanol aqueous solution and acetone aqueous solution, wherein the mass ratio of anhydrous ethanol to water is 1:(0.75~1.5), and the mass ratio of acetone to water is 1:(0.75~1.5); the sulfite is any one or more of sodium bisulfite and sodium sulfite; the mass ratio of the third intermediate, the sulfite, and the second solvent is 1:(1~1.5):(10~15); the reaction temperature is 50~70℃, and the reaction time is 8~12 h.

[0032] Preferably, in step S6, the reaction temperature is 80~100℃ and the reaction time is 8~12 h; the mass ratio of polybenzimidazole, the first solvent, the sulfonated third intermediate and sodium hydride is 1:(5~10):(1.5~2):(0.1~0.2).

[0033] Preferably, in step S7, the stirring temperature is 40~60℃ and the stirring time is 2~3 h.

[0034] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0035] This application uses methyl benzoate as a starting material, introduces acyl hydrazine through transesterification, reacts with aldehyde to generate acylhydrazone, reacts with acid anhydride to generate oxadiazole ring, and uses 3-chlorophenol to introduce the compound into polybenzimidazole resin. After sulfonation treatment, oxadiazole-modified polybenzimidazole resin is prepared. The coating prepared has significantly improved hardness, impact resistance, corrosion resistance, and water resistance, and significantly reduced curing temperature (80℃), achieving rapid curing at low temperature.

[0036] (1) Hardness and impact resistance: The oxadiazole ring has a planar rigid structure and contains heteroatoms such as nitrogen and oxygen, which can change the structure of polymer molecular chains and the distribution of electron clouds, further improving the regularity and rigidity of molecular chains, forming a cross-linked network, reducing stress concentration points, making it less prone to cracking when impacted, increasing the way in which molecules interact, and improving the hardness of the resin.

[0037] (2) Corrosion resistance and water resistance: The introduction of the oxadiazole ring structure into the polybenzimidazole resin forms a stable conjugated system, which improves chemical inertness. The nitrogen and oxygen atoms in the oxadiazole ring can act as hydrogen bond acceptors and form intermolecular hydrogen bonds with amino and imino groups in the resin molecular chain, thereby increasing the crosslinking density of the resin and forming a tighter network structure, which hinders the diffusion and penetration of corrosive media. Furthermore, the aryl substitution in the oxadiazole ring can improve the water resistance of the coating.

[0038] (3) Lower curing temperature and curing time: Oxadiazole is a strong electron conjugated system. Through π-π conjugation, it forms a large conjugated structure of imidazole-oxadiazole with the imidazole ring, which enhances electron delocalization. The sulfonic acid group is a strong electron-withdrawing group. Its electron-withdrawing effect is indirectly transmitted through the conjugated system of the oxadiazole ring. It does not directly reduce the electron cloud density of the imidazole ring, but rather makes the lone pair electrons of the N atom on the imidazole ring more easily exposed through electron-withdrawing induction, ultimately increasing the electron cloud density of the nucleophilic site of the imidazole ring. Sulfonate succinimide ester is a crosslinking agent with higher reactivity than ordinary esters, such as carboxylic acid esters. In the structure of sulfonate succinimide ester, the sulfonate succinimide linked to the ester group is a strongly stable leaving group. According to the rules of nucleophilic substitution reaction, the more stable the leaving group, the easier the reaction occurs, that is, the lower the activation energy. The ester carbon group is subject to a dual electron-withdrawing effect from the adjacent sulfonic acid group and succinimide ring, resulting in a significantly reduced electron cloud density. This makes it more susceptible to nucleophilic attacks from imidazole derivatives, leading to a substantial increase in the reaction rate. Compared to traditional crosslinking agents, sulfonic acid succinimide esters directly lower the energy barrier of the reaction, enabling rapid crosslinking with imidazole derivatives at lower temperatures. The modified polybenzimidazole resin exhibits increased electron cloud density in the imidazole ring, enhancing its nucleophilicity. Consequently, the activation energy for the nucleophilic substitution reaction with sulfonic acid succinimide esters is significantly reduced, allowing the reaction to begin without high temperatures (i.e., a lower curing temperature) and increased collision success rate (i.e., a faster curing speed). While ordinary polybenzimidazole resins require temperatures above 250°C to promote slow intermolecular crosslinking, sulfonic acid succinimide esters can facilitate the process at around 80-100°C. The synergistic effect of the sulfonic acid group optimizing electronic effects, the energy barrier reduction achieved by the highly active crosslinking agent, and the intermolecular interactions promoting contact ultimately results in both a lower curing temperature and a faster curing speed. Attached Figure Description

[0039] Figure 1 This is a flowchart of a method for preparing a multi-purpose corrosion-resistant electrophoretic coating.

[0040] Figure 2 This is a synthetic route diagram for modified polybenzimidazole resin.

[0041] Figure 3 For benzoyl hydrazine 1 H NMR spectrum.

[0042] Figure 4 For the first intermediate 1 H NMR spectrum.

[0043] Figure 5 For the second intermediate 1 H NMR spectrum.

[0044] Figure 6 As a third intermediate 1 H NMR spectrum.

[0045] Figure 7 Comparison of FTIR spectra of the third intermediate and the sulfonated third intermediate.

[0046] Figure 8 This is a photograph of a multi-purpose corrosion-resistant electrophoretic coating. Detailed Implementation

[0047] The following embodiments are only used to illustrate the technical solutions of the present invention more clearly, and should not be used to limit the scope of protection of the present invention.

[0048] The polybenzimidazole used in the examples and comparative examples was purchased from Maclean Reagents (Shanghai Maclean Biochemical Technology Co., Ltd.), also known as: diphenyl isophthalate-3,3',4,4'-tetraaminodiphenyl polymer; CAS No.: 25928-81-8; Product No.: P909984.

[0049] The fluorinated acrylate leveling agent used in the examples and comparative examples is Hyperlev F81 (Guangdong Core Chemical).

[0050] The polyether-modified polydimethylsiloxane leveling agent used in the examples and comparative examples is BYK-331 (BYK, Germany).

[0051] The polyether-modified silicone defoamer used in the examples and comparative examples is model BYK-034 (BYK, Germany).

[0052] The polyether defoamer used in the examples and comparative examples is Antifoam 429 (Dow Chemical).

[0053] Unless otherwise specified, all reagents and equipment used in the following examples were purchased from commercial channels.

[0054] Example 1

[0055] like Figure 1 As shown, a multi-purpose corrosion-resistant electrophoretic coating is prepared by means of:

[0056] Step S1: Dissolve 10 g of methyl benzoate in 20 g of anhydrous ethanol, add 5.2 g of hydrazine hydrate and 0.75 g of sodium carbonate, react at 60 °C for 6 h to obtain crude benzoyl hydrazine. Recrystallize from anhydrous ethanol to obtain benzoyl hydrazine. 1 H NMR spectrum as shown Figure 3 As shown.

[0057] Step S2: Dissolve 10 g of benzoyl hydrazine in 50 g of anhydrous ethanol, add 5.5 g of chloroacetaldehyde, react at 60 °C for 12 h to obtain the crude first intermediate product. Recrystallize from anhydrous ethanol to obtain the first intermediate.1 H NMR spectrum as shown Figure 4 As shown.

[0058] Step S3: Mix 10 g of the first intermediate with 50 g of acetic anhydride and react at 120°C for 5 h to obtain a reaction solution. After cooling, pour the reaction solution into 200 g of ice water and stir for 12 h. Filter to obtain the crude product of the second intermediate. Wash the crude product of the second intermediate with deionized water and anhydrous ethanol to obtain the second intermediate. 1 H NMR spectrum as shown Figure 5 As shown.

[0059] Step S4: Mix 20 g of 3-chlorophenol and 20 g of sodium carbonate, dissolve in 200 g of anhydrous ethanol, stir at 40°C for 60 min, remove anhydrous ethanol by rotary evaporation to obtain an intermediate product. Dissolve 10 g of the intermediate product in 100 g of dimethyl sulfoxide, add 7.5 g of the second intermediate, react at 120°C for 4 h, cool to room temperature, add water to precipitate, filter to obtain the crude third intermediate product, recrystallize from anhydrous ethanol to obtain the third intermediate. 1 H NMR spectrum as shown Figure 6 As shown.

[0060] Step S5: Dissolve 10 g of the third intermediate in 100 g of anhydrous ethanol aqueous solution (57 g anhydrous ethanol and 43 g water), add 10 g of sodium sulfite, adjust the pH to 5, and react at 50℃ for 12 h to obtain the sulfonated third intermediate. A comparison of the FTIR spectra of the third intermediate and the sulfonated third intermediate is shown below. Figure 7 As shown.

[0061] Step S6: Disperse 10 g of polybenzimidazole in 50 g of N-methylpyrrolidone, add 15 g of sulfonated third intermediate, purge oxygen from the reaction system with inert gas, and slowly add 1 g of sodium hydride under continuous inert gas protection in an ice bath. React at 80°C for 12 h to obtain modified polybenzimidazole resin, as shown below. Figure 2 As shown.

[0062] Step S7: Disperse 10 g of modified polybenzimidazole resin in 50 g of deionized water, add 5 g of propylene glycol butyl ether, 0.3 g of sulfonated succinimide ester, 2.5 g of additives (0.91 g of sodium molybdate, 0.68 g of fluorinated acrylate leveling agent, and 0.91 g of polyether-modified silicone defoamer), 0.15 g of hollow glass microspheres, and 0.1 g of chromium oxide green. Stir at 40°C for 3 h to obtain an electrophoretic coating, as shown below. Figure 8 As shown.

[0063] Example 2

[0064] like Figure 1 As shown, a multi-purpose corrosion-resistant electrophoretic coating is prepared by means of:

[0065] Step S1: Dissolve 10 g of methyl benzoate in 25 g of anhydrous ethanol, add 5.8 g of hydrazine hydrate and 0.9 g of potassium carbonate, react at 70 °C for 5 h to obtain crude benzoyl hydrazine. Recrystallize from anhydrous ethanol to obtain benzoyl hydrazine. 1 H NMR spectrum as shown Figure 3 As shown.

[0066] Step S2: Dissolve 10 g of benzoyl hydrazine in 75 g of anhydrous ethanol, add 7.5 g of chloroacetaldehyde, react at 70 °C for 10 h to obtain the crude first intermediate product. Recrystallize from anhydrous ethanol to obtain the first intermediate. 1 H NMR spectrum as shown Figure 4 As shown.

[0067] Step S3: Mix 10 g of the first intermediate with 100 g of acetic anhydride and react at 125 °C for 4 h to obtain a reaction solution. After cooling, pour the reaction solution into 220 g of ice water and stir for 10 h. Filter to obtain the crude product of the second intermediate. Wash the crude product of the second intermediate with deionized water and anhydrous ethanol to obtain the second intermediate. 1 H NMR spectrum as shown Figure 5 As shown.

[0068] Step S4: Mix 20 g of 3-chlorophenol and 24 g of potassium carbonate, dissolve in 240 g of anhydrous ethanol, stir at 50°C for 40 min, remove anhydrous ethanol by rotary evaporation to obtain an intermediate product. Dissolve 10 g of the intermediate product in 120 g of N-methylpyrrolidone, add 8.5 g of the second intermediate, react at 130°C for 3 h, cool to room temperature, add water to precipitate, filter to obtain the crude third intermediate product, recrystallize from anhydrous ethanol to obtain the third intermediate. 1 H NMR spectrum as shown Figure 6 As shown.

[0069] Step S5: Dissolve 10 g of the third intermediate in 120 g of acetone aqueous solution (60 g acetone and 60 g water), add 12 g of sodium bisulfite, adjust the pH to 6, and react at 60℃ for 10 h to obtain the sulfonated third intermediate. A comparison of the FTIR spectra of the third intermediate and the sulfonated third intermediate is shown below. Figure 7 As shown.

[0070] Step S6: Disperse 10 g of polybenzimidazole in 75 g of dimethyl sulfoxide, add 18 g of sulfonated third intermediate, purge oxygen from the reaction system with inert gas, and slowly add 1.5 g of sodium hydride under ice bath and continuous inert gas protection. React at 90°C for 10 h to obtain modified polybenzimidazole resin, as shown below. Figure 2 As shown.

[0071] Step S7: Disperse 10 g of modified polybenzimidazole resin in 75 g of deionized water, add 7.5 g of propylene glycol butyl ether, 0.4 g of sulfonated succinimide ester, 3.5 g of additives (1.21 g of zinc phosphate, 0.96 g of fluorinated acrylate leveling agent and 1.33 g of polyether defoamer), 0.25 g of hollow glass microspheres and 0.3 g of chromium oxide green, stir at 50°C for 2.5 h to obtain an electrophoretic coating, as shown below. Figure 8 As shown.

[0072] Example 3

[0073] like Figure 1 As shown, a multi-purpose corrosion-resistant electrophoretic coating is prepared by means of:

[0074] Step S1: Dissolve 10 g of methyl benzoate in 30 g of anhydrous ethanol, add 6 g of hydrazine hydrate and 1.1 g of sodium carbonate, react at 80 °C for 4 h to obtain crude benzoyl hydrazine. Recrystallize from anhydrous ethanol to obtain benzoyl hydrazine. 1 H NMR spectrum as shown Figure 3 As shown.

[0075] Step S2: Dissolve 10 g of benzoyl hydrazine in 100 g of anhydrous ethanol, add 10 g of chloroacetaldehyde, react at 80 °C for 8 h to obtain the crude product of the first intermediate. Recrystallize from anhydrous ethanol to obtain the first intermediate. 1 H NMR spectrum as shown Figure 4 As shown.

[0076] Step S3: Mix 10 g of the first intermediate with 120 g of acetic anhydride and react at 130 °C for 3 h to obtain a reaction solution. After cooling, pour the reaction solution into 250 g of ice water and stir for 12 h. Filter to obtain the crude product of the second intermediate. Wash the crude product of the second intermediate with deionized water and anhydrous ethanol to obtain the second intermediate. 1 H NMR spectrum as shown Figure 5 As shown.

[0077] Step S4: Mix 20 g of 3-chlorophenol and 30 g of sodium carbonate, dissolve in 300 g of anhydrous ethanol, stir at 60 °C for 20 min, remove anhydrous ethanol by rotary evaporation to obtain an intermediate product. Dissolve 10 g of the intermediate product in 150 g of dimethyl sulfoxide, add 9 g of the second intermediate, react at 150 °C for 2 h, cool to room temperature, add water to precipitate, filter to obtain the crude third intermediate product, recrystallize from anhydrous ethanol to obtain the third intermediate. 1 H NMR spectrum as shown Figure 6 As shown.

[0078] Step S5: Dissolve 10 g of the third intermediate in 150 g of anhydrous ethanol aqueous solution (60 g of anhydrous ethanol and 90 g of water), add 15 g of sodium sulfite, adjust the pH to 7, and react at 70℃ for 8 h to obtain the sulfonated third intermediate. A comparison of the FTIR spectra of the third intermediate and the sulfonated third intermediate is shown below. Figure 7 As shown.

[0079] Step S6: Disperse 10 g of polybenzimidazole in 100 g of dimethyl sulfoxide, add 20 g of sulfonated third intermediate, purge oxygen from the reaction system with inert gas, and slowly add 2 g of sodium hydride under ice bath and continuous inert gas protection. React at 100°C for 8 h to obtain modified polybenzimidazole resin, as shown below. Figure 2 As shown.

[0080] Step S7: Disperse 10 g of modified polybenzimidazole resin in 100 g of deionized water, add 10 g of propylene glycol butyl ether, 0.5 g of sulfonated succinimide ester, 4.5 g of additives (1.4 g of mercaptobenzothiazole, 1.4 g of polyether-modified polydimethylsiloxane leveling agent, and 1.7 g of polyether defoamer), 0.35 g of hollow glass microspheres, and 0.5 g of chromium oxide green. Stir at 60°C for 2 h to obtain an electrophoretic coating, as shown below. Figure 8 As shown.

[0081] Comparative Example 1

[0082] A multi-purpose corrosion-resistant electrophoretic coating is prepared in a way that differs from that in Example 3, the third intermediate in step S5 is not modified by sulfonation with sodium sulfite, and the third intermediate without sulfonation modification is reacted with polybenzimidazole in step S6.

[0083] Comparative Example 2

[0084] A multi-purpose corrosion-resistant electrophoretic coating is prepared in a way that differs from that in Example 3, in step S7, polybenzimidazole resin is used instead of modified polybenzimidazole resin.

[0085] Performance testing:

[0086] (1) Curing time: Record the appearance of the coating after curing and the curing time at 80℃.

[0087] (2) Gloss: The coating was coated on a black matte substrate and cured. The gloss of the coating was measured using a Gz-1 gloss meter.

[0088] (3) Impact resistance test: Coating is applied to a metal substrate, and after curing, the substrate is fixed on an impact tester. A 1kg hammer is dropped from a certain height to impact the punch. The drop height is gradually increased, and the maximum impact height at which the coating film does not crack or peel off is tested. Three tests are conducted at the same height position.

[0089] (4) Corrosion resistance: Grind the substrate, wash it with industrial gasoline, dry it and then coat it. After curing, immerse 2 / 3 of the substrate vertically in a 5% hydrochloric acid solution or sodium hydroxide solution. Check it every 24 hours and observe whether the paint film has lost its gloss, changed color, small bubbles, spots, or peeling.

[0090] (5) Salt water resistance: After coating and curing, 2 / 3 of the substrate is vertically immersed in a 5% sodium chloride solution at a temperature of 25℃±1. Check every 24 hours to observe whether the coating film peels off, wrinkles, bubbles, rusts, discoloration and loss of gloss.

[0091] (6) Water resistance: After coating and curing, 2 / 3 of the substrate is vertically immersed in water at a temperature of 25℃±1℃. Check every 24 hours to observe whether the coating film peels off, wrinkles, bubbles, rusts, discoloration and loss of gloss.

[0092] Table 1. Results of Coating Appearance and Gloss Tests

[0093]

[0094] As shown in Table 1, the coatings prepared in Examples 1-3, Comparative Examples 1 and 2 all exhibited a glossy and smooth appearance after curing. The gloss of the coatings prepared in Examples 1-3 and Comparative Example 1 was above 80%, while the gloss of the coating prepared in Comparative Example 2 was only 74%, significantly lower than the other groups. Experiments demonstrate that embedding the rigid planar structure of the oxadiazole ring into the polybenzimidazole structure enhances the regularity of the molecular chain through π-π conjugation, reducing the degree of freedom of chain segment movement and resulting in a smoother surface after curing. The coatings prepared in Examples 1-3 and Comparative Example 1 cured to form a film in approximately 20 minutes at a low temperature (80°C), while the coating prepared in Comparative Example 2 required 45 minutes to cure.

[0095] Table 2 Impact strength test results of coatings

[0096]

[0097] As shown in Table 2, the coatings prepared in Examples 1-3 all exhibited impact strengths above 65 cm, demonstrating excellent impact resistance. The coatings prepared in Comparative Examples 1 and 2 showed significantly lower impact resistance and hardness compared to Examples 1-3. Experiments demonstrate that the ring-opening polymerization of oxadiazole rings with polybenzimidazole increases crosslinking density, restricts molecular chain movement, enhances coating rigidity, and improves network uniformity, reducing stress concentration points and optimizing impact resistance.

[0098] Table 3. Corrosion resistance test results of coatings

[0099]

[0100] Table 4. Test results of salt water resistance and water resistance of coatings

[0101]

[0102] According to the data in Tables 3 and 4, the coatings prepared in Examples 1 to 3 showed no significant changes after 48 hours in both acidic and alkaline environments, and after 7 days in water and salt water. However, the coating prepared in Comparative Example 1 developed rust spots and lost gloss after 48 hours in an acidic environment, and also developed rust spots, lost gloss, and small blisters after 48 hours in an alkaline environment. After 7 days in water, the coating lost gloss and developed localized wrinkles. In salt water, the coating also lost gloss, developed rust spots, and developed localized wrinkles. Similarly, the coating prepared in Comparative Example 2 lost gloss, changed color, and developed rust spots after 48 hours in an acidic environment, and also developed rust spots and localized peeling after 48 hours in an alkaline environment. After 7 days in water, the coating also lost gloss, developed rust spots, and developed localized peeling. In salt water, the coating also lost gloss, developed rust spots, and developed localized peeling after 7 days. Experiments have shown that ordinary polybenzimidazole resin has a low crosslinking density, and solvent molecules can easily penetrate into the interchain space, causing volume expansion. Modified polybenzimidazole resin can block corrosive media and inhibit swelling.

[0103] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A multi-purpose corrosion-resistant electrophoretic coating, characterized in that, The coating comprises modified resin, deionized water, pigment, filler, additives, co-solvent, and crosslinking agent; the mass ratio of the modified resin, deionized water, pigment, filler, additives, co-solvent, and crosslinking agent is 1:(5~10):(0.01~0.05):(0.015~0.035):(0.25~0.45):(0.5~1):(0.03~0.05); the modified resin is a modified polybenzimidazole resin, and the preparation method of the modified polybenzimidazole resin is: grafting polybenzimidazole with a bisoxadiazole derivative, and then introducing sulfonic acid groups; the structural formula of the modified polybenzimidazole resin is as follows: ； Where n takes the value of an integer between 128 and 162.

2. The multi-purpose corrosion-resistant electrophoretic coating according to claim 1, characterized in that, The filler is hollow glass microspheres; the cosolvent is propylene glycol butyl ether; the crosslinking agent is sulfonated succinimide ester; the additives include corrosion inhibitors, leveling agents and defoamers; the pigment is chromium oxide green; the mass ratio of the corrosion inhibitor, leveling agent and defoamer is 1:(0.75~1):(1~1.25).

3. The multi-purpose corrosion-resistant electrophoretic coating according to claim 2, characterized in that, The corrosion inhibitor is any one or more of sodium molybdate, zinc phosphate, and mercaptobenzothiazole; the leveling agent is any one or more of fluorinated acrylate and polyether-modified polydimethylsiloxane; and the defoamer is any one or more of polyether-modified silicone defoamer and polyether defoamer.

4. The method for preparing a multi-purpose corrosion-resistant electrophoretic coating according to any one of claims 1 to 3, characterized in that, include: Step S1: Dissolve methyl benzoate in anhydrous ethanol, add hydrazine hydrate and catalyst, react to obtain crude benzoyl hydrazine product, recrystallize from anhydrous ethanol to obtain benzoyl hydrazine. Step S2: Dissolve benzoyl hydrazine in anhydrous ethanol, add chloroacetaldehyde, react to obtain the crude product of the first intermediate, recrystallize from anhydrous ethanol to obtain the first intermediate; Step S3: Mix the first intermediate with acetic anhydride and react to obtain a reaction solution. After cooling, pour the reaction solution into ice water and stir. Filter to obtain the crude product of the second intermediate. Wash to obtain the second intermediate. Step S4: Mix 3-chlorophenol and catalyst, dissolve in anhydrous ethanol, stir, remove anhydrous ethanol to obtain intermediate product, dissolve intermediate product in first solvent, add second intermediate, react, cool, add water to precipitate, filter to obtain crude third intermediate product, recrystallize from anhydrous ethanol to obtain third intermediate. Step S5: Dissolve the third intermediate in the second solvent, add sulfite, adjust the pH to 5-7, and react to obtain the sulfonated third intermediate; Step S6: Disperse polybenzimidazole in the first solvent, pass in an inert gas to remove oxygen, add sulfonated third intermediate and sodium hydride, and react under ice bath and inert gas protection to obtain modified polybenzimidazole resin. Step S7: The modified polybenzimidazole resin is dispersed in deionized water, and a cosolvent, crosslinking agent, additives, filler and pigment are added to obtain an electrophoretic coating.

5. The method for preparing a multi-purpose corrosion-resistant electrophoretic coating according to claim 4, characterized in that, The first solvent is any one or more of N-methylpyrrolidone and dimethyl sulfoxide; the catalyst is any one or more of sodium carbonate and potassium carbonate; in step S1, the reaction temperature is 60~80℃ and the reaction time is 4~6 h; the mass ratio of methyl benzoate, hydrazine hydrate, anhydrous ethanol and catalyst is 1:(0.52~0.6):(2~3):(0.075~0.11).

6. The method for preparing a multi-purpose corrosion-resistant electrophoretic coating according to claim 4, characterized in that, In step S2, the reaction temperature is 60~80℃ and the reaction time is 8~12 h; the mass ratio of benzoyl hydrazine, chloroacetaldehyde and anhydrous ethanol is 1:(0.55~1):(5~10).

7. The method for preparing a multi-purpose corrosion-resistant electrophoretic coating according to claim 4, characterized in that, In step S3, the mass ratio of the first intermediate, acetic anhydride, and ice water is 1:(5~12):(20~25); the washing solvents are deionized water and anhydrous ethanol in sequence; the reaction temperature is 120~130℃, the reaction time is 3~5 h, and the stirring time is 10~12 h.

8. The method for preparing a multi-purpose corrosion-resistant electrophoretic coating according to claim 4, characterized in that, In step S4, the stirring temperature is 40~60℃ and the stirring time is 20~60 min; the reaction temperature is 120~150℃ and the reaction time is 2~4 h; the mass ratio of 3-chlorophenol, catalyst and anhydrous ethanol is 1:(1~1.5):(10~15); the mass ratio of intermediate product, first solvent and second intermediate is 1:(10~15):(0.75~0.9).

9. The method for preparing a multi-purpose corrosion-resistant electrophoretic coating according to claim 4, characterized in that, In step S5, the second solvent is any one or more of anhydrous ethanol aqueous solution and acetone aqueous solution, wherein the mass ratio of anhydrous ethanol to water is 1:(0.75~1.5) and the mass ratio of acetone to water is 1:(0.75~1.5); the sulfite is any one or more of sodium bisulfite and sodium sulfite; the mass ratio of the third intermediate, the sulfite and the second solvent is 1:(1~1.5):(10~15); the reaction temperature is 50~70℃ and the reaction time is 8~12 h.

10. The method for preparing a multi-purpose corrosion-resistant electrophoretic coating according to claim 4, characterized in that, In step S6, the reaction temperature is 80~100℃ and the reaction time is 8~12 h; the mass ratio of polybenzimidazole, first solvent, sulfonated third intermediate and sodium hydride is 1:(5~10):(1.5~2):(0.1~0.2).

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