A salt spray resistant epoxy modified waterborne acrylic resin emulsion and its preparation method and application

Abstract

The present invention relates to the technical field of acrylic resins, and discloses a salt-fog-resistant epoxy-modified water-based acrylic resin emulsion and a preparation method and application thereof, wherein the water-based acrylic resin emulsion comprises 100 parts by weight of a vinyl monomer, 0.4-0.5 parts by weight of an initiator, 2-2.8 parts by weight of an emulsifier, and 10-35 parts by weight of a cationic Schiff base-modified epoxy resin; after the epoxy resin of the present invention is cationically modified, an antibacterial cationic quaternary ammonium salt group is introduced into the molecular chain, which can play a good bactericidal effect and show a good antibacterial rate to Escherichia coli and Staphylococcus aureus. The acrylic resin is endowed with excellent antibacterial properties. At the same time, the adhesion, water resistance, salt-fog resistance and other properties of the paint film are improved, and better anticorrosion properties are shown.

Description

Technical Field

[0001] The invention relates to the technical field of acrylic resins, in particular to a salt-spray resistant epoxy-modified waterborne acrylic resin emulsion and a preparation method and application thereof. Background Art

[0002] Water-based acrylic resin uses water as solvent, is green and environmentally friendly, has good weather resistance and excellent chemical resistance, can be made into coatings, inks and other materials, and is widely used in the fields of automobiles, machinery, construction, etc. It is of great significance to improve the adhesion and bonding performance between water-based acrylic resin and metal substrates, and improve its salt spray resistance and anti-corrosion performance.

[0003] Epoxy resin is a resin material with good mechanical properties, good heat resistance and excellent anti-corrosion performance. The performance of acrylic resin can be effectively improved by modifying acrylic resin with epoxy resin. The common method is mainly to react acrylic acid with epoxy resin to obtain epoxy acrylate, and then polymerize with acrylate monomers to obtain epoxy acrylate. The invention patent with publication number CN116855119A discloses a light-cured epoxy resin quaternary ammonium salt antibacterial coating and its preparation method. The light-cured epoxy resin quaternary ammonium salt is obtained by reacting olefinic acid compounds, epoxy resin and triethylamine hydrochloride as an antibacterial agent, and the light-cured polymer emulsion is used as a base material. The obtained antibacterial coating has excellent antibacterial performance, mechanical properties, aging resistance, chemical corrosion resistance and other properties. The present invention uses cationic Schiff base modified epoxy resin to improve the adhesion, antibacterial property, water resistance and salt spray resistance of acrylic resin. Summary of the invention

[0004] The invention solves the problem that the water-based acrylic resin has poor salt spray resistance, corrosion resistance and other performances.

[0005] The technical solution of the present invention is: a salt spray resistant epoxy modified waterborne acrylic resin emulsion, the raw materials comprising 100 parts by weight of vinyl monomer, 0.4-0.5 parts by weight of initiator, 2-2.8 parts by weight of emulsifier, 10-35 parts by weight of cationic Schiff base modified epoxy resin, 0.5-1 parts by weight of defoamer, and 0.3-0.6 parts by weight of leveling agent;

[0006] Preferably, the salt spray resistant epoxy modified waterborne acrylic resin emulsion is used in anti-corrosion coatings.

[0007] Preferably, the preparation method of the salt-fog resistant epoxy-modified water-based acrylic resin emulsion comprises: adding vinyl monomer and emulsifier to water, heating to 70-80° C. in a nitrogen atmosphere, adding initiator, stirring and reacting for 40-60 minutes, then adding more vinyl monomer and initiator, stirring and reacting for 2.5-3.5 hours, adding sodium hydroxide to adjust the pH to 7-7.5, adding cationic Schiff base-modified epoxy resin, defoamer, leveling agent, stirring and mixing, and obtaining the salt-fog resistant epoxy-modified water-based acrylic resin emulsion.

[0008] Preferably, the preparation method of the cationic Schiff base modified epoxy resin comprises: adding epoxy resin to anhydrous ethanol, adding dimethylamine hydrochloride modifier after stirring, heating to 75-80°C, condensing and refluxing for 6-10h, adding anhydrous ethanol to dilute, and centrifuging to obtain the cationic Schiff base modified epoxy resin.

[0009] Preferably, the vinyl monomer includes any one or a combination of methyl acrylate, methyl methacrylate, acrylic acid, methacrylic acid, butyl acrylate, and butyl methacrylate.

[0010] Preferably, the initiator is ammonium persulfate or potassium persulfate; and the emulsifier is OP-10 and sodium dodecyl sulfate.

[0011] Preferably, the mass ratio of dimethylamine hydrochloride modifier to epoxy resin is (1.4-1.8):1.

[0012] Preferably, the preparation method of the dimethylamine hydrochloride modifier comprises:

[0013] (1) Add 3,5-dinitrobenzoyl chloride, N,N-dimethylethylenediamine, and sodium carbonate in a molar ratio of 1:(1-1.1):(1-1.1) to tetrahydrofuran, add water, react at 35-40°C for 10-12h, remove tetrahydrofuran by vacuum distillation, filter and wash with water, add the product to anhydrous ethanol, add tin powder, and concentrated hydrochloric acid with a mass fraction of 35-37%, heat to 70-80°C, condense and reflux for 1-2h, cool and add sodium hydroxide solution to adjust the pH to 8-9, then extract with ethyl acetate, separate and add anhydrous sodium sulfate to the organic phase for drying, filter and concentrate the filtrate by evaporation, cool and recrystallize to obtain an intermediate. The reaction formula is:

[0014] .

[0015] (2) Add the intermediate, salicylaldehyde, in a molar ratio of 1:(2-2.4) to anhydrous ethanol, heat to 40-50°C, react for 5-8h, add hydrochloric acid solution to adjust the pH to 5-6, distill under reduced pressure, wash with petroleum ether, and recrystallize the product in an ethanol aqueous solution with a volume fraction of 80% to obtain a dimethylamine hydrochloride modifier. The reaction formula is:

[0016] .

[0017] Technical effect: The present invention utilizes the tertiary amine hydrochloride group of the dimethylamine hydrochloride modifier to react with the epoxy group of the epoxy resin to generate a quaternary ammonium salt group to obtain a cationic Schiff base modified epoxy resin.

[0018] The present invention uses monomers such as methyl acrylate, acrylic acid, and butyl methacrylate for polymerization reaction, and then mixes with cationic Schiff base modified epoxy resin, defoamer, etc. to obtain salt spray resistant epoxy modified waterborne acrylic resin emulsion. After being cationically modified, the epoxy resin has good hydrophilicity and water solubility, and its cationic group can electrostatically interact with the sodium carboxylate anion group in the acrylic resin, thereby improving the interface compatibility between the epoxy resin and the acrylic resin, so that the epoxy resin has good dispersibility in the waterborne acrylic resin emulsion, the emulsion is not stratified, has no precipitation, and has excellent storage stability.

[0019] After the epoxy resin of the present invention is cation-modified, an antibacterial cationic quaternary ammonium salt group is introduced into the molecular chain, which can play a good bactericidal role and show a good antibacterial rate against Escherichia coli and Staphylococcus aureus, thereby giving the acrylic resin excellent antibacterial properties.

[0020] The cationic Schiff base modified epoxy resin of the present invention contains salicylaldehyde Schiff base groups, which can coordinate with the surface of substrates such as tinplate, so that the paint film is firmly attached to the surface of the substrate, the paint film is not easy to bubble and crack, the adhesion level reaches level 0, and the adhesion performance and bonding performance are very good. At the same time, the cationic group of the epoxy resin and the sodium carboxylate anion group in the acrylic resin have an electrostatic interaction, and the two form a cross-linked network, which increases the cross-linking density inside the paint film, is conducive to preventing corrosive media such as water and salt from entering the paint film, thereby improving the water resistance and salt spray resistance of the paint film, and showing better anti-corrosion performance. DETAILED DESCRIPTION

[0021] In order to better understand the technical solution of the present invention, the above content of the present invention is further described in detail below through specific implementation methods in the form of embodiments, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples. All technologies realized based on the above content of the present invention belong to the scope of the present invention.

[0022] Example 1

[0023] (1) Add 60 mmol of 3,5-dinitrobenzoyl chloride, 60 mmol of N,N-dimethylethylenediamine, and 60 mmol of sodium carbonate to 150 mL of tetrahydrofuran, add 120 mL of water, react at 35°C for 12 h, remove tetrahydrofuran by vacuum distillation, filter and wash with water, add the product to 400 mL of anhydrous ethanol, add 38 g of tin powder and 30 mL of 37% concentrated hydrochloric acid, heat to 75°C, condense and reflux for 2 h, cool and add sodium hydroxide solution to adjust the pH to 8, then extract with ethyl acetate, separate and add anhydrous sodium sulfate to the organic phase for drying, filter and concentrate the filtrate by evaporation, cool and recrystallize to obtain an intermediate.

[0024] (2) Add 40 mmol of the intermediate and 80 mmol of salicylaldehyde to 350 mL of anhydrous ethanol, heat to 50 °C, react for 5 h, add 20% by mass hydrochloric acid solution to adjust the pH to 6, distill under reduced pressure, wash with petroleum ether, and recrystallize the product in 80% by volume ethanol aqueous solution to obtain a dimethylamine hydrochloride modifier.

[0025] (3) Add 5 g of epoxy resin E51 to 20 mL of anhydrous ethanol, stir, add 7 g of dimethylamine hydrochloride modifier, heat to 80 °C, condense and reflux for 6 h, add anhydrous ethanol to dilute, centrifuge and separate to obtain cationic Schiff base modified epoxy resin.

[0026] (4) Add 7.2 g of methyl acrylate, 1.7 g of methacrylic acid, 21.1 g of butyl methacrylate, 0.9 g of OP-10 and 1.9 g of sodium dodecyl sulfate as emulsifier to 120 mL of water, heat to 75 °C in a nitrogen atmosphere, add 0.1 g of initiator ammonium persulfate, stir and react for 60 min, then add 16.6 g of methyl acrylate, 4 g of methacrylic acid, 49.4 g of butyl methacrylate and 0.3 g of initiator ammonium persulfate, stir and react for 3.5 h, add sodium hydroxide to adjust the pH to 7.5, add 10 g of cationic Schiff base modified epoxy resin, 0.8 g of defoamer Surfynol 104E and 0.6 g of leveling agent BYK-333, stir and mix to obtain a salt spray resistant epoxy modified waterborne acrylic resin emulsion.

[0027] Example 2

[0028] (1) Add 60 mmol of 3,5-dinitrobenzoyl chloride, 66 mmol of N,N-dimethylethylenediamine, and 66 mmol of sodium carbonate to 180 mL of tetrahydrofuran, add 120 mL of water, react at 40°C for 10 h, remove tetrahydrofuran by vacuum distillation, filter and wash with water, add the product to 400 mL of anhydrous ethanol, add 35 g of tin powder and 30 mL of 37% concentrated hydrochloric acid, heat to 70°C, condense and reflux for 2 h, cool, add sodium hydroxide solution to adjust the pH to 9, then extract with ethyl acetate, separate, add anhydrous sodium sulfate to the organic phase, dry, filter, evaporate and concentrate the filtrate, cool and recrystallize to obtain an intermediate.

[0029] (2) Add 40 mmol of the intermediate and 96 mmol of salicylaldehyde to 400 mL of anhydrous ethanol, heat to 40 °C, react for 8 h, add 20% by mass hydrochloric acid solution to adjust the pH to 5, distill under reduced pressure, wash with petroleum ether, and recrystallize the product in 80% by volume ethanol aqueous solution to obtain a dimethylamine hydrochloride modifier.

[0030] (3) Add 5 g of epoxy resin E51 to 20 mL of anhydrous ethanol, stir, add 8.2 g of dimethylamine hydrochloride modifier, heat to 75 °C, condense and reflux for 10 h, add anhydrous ethanol to dilute, centrifuge and separate to obtain cationic Schiff base modified epoxy resin.

[0031] (4) Add 7.7 g of methyl methacrylate, 1.8 g of methacrylic acid, 20.5 g of butyl acrylate, 0.7 g of OP-10 emulsifier and 1.3 g of sodium dodecyl sulfate to 150 mL of water, heat to 80 °C in a nitrogen atmosphere, add 0.15 g of initiator potassium persulfate, stir and react for 40 min, then add 17.4 g of methyl methacrylate, 4.2 g of methacrylic acid, 48.4 g of butyl acrylate and 0.35 g of initiator potassium persulfate, stir and react for 2.5 h, add sodium hydroxide to adjust the pH to 7, add 15 g of cationic Schiff base modified epoxy resin, 1 g of defoamer Surfynol 104E and 0.3 g of leveling agent BYK-333, stir and mix to obtain a salt spray resistant epoxy modified waterborne acrylic resin emulsion.

[0032] Example 3

[0033] (1) Add 60 mmol of 3,5-dinitrobenzoyl chloride, 60 mmol of N,N-dimethylethylenediamine, and 60 mmol of sodium carbonate to 180 mL of tetrahydrofuran, add 100 mL of water, react at 40°C for 10 h, remove tetrahydrofuran by vacuum distillation, filter and wash with water, add the product to 300 mL of anhydrous ethanol, add 33 g of tin powder and 40 mL of 35% concentrated hydrochloric acid, heat to 80°C, condense and reflux for 1 h, cool and add sodium hydroxide solution to adjust the pH to 9, then extract with ethyl acetate, separate and add anhydrous sodium sulfate to the organic phase for drying, filter and concentrate the filtrate by evaporation, cool and recrystallize to obtain an intermediate.

[0034] (2) Add 40 mmol of the intermediate and 88 mmol of salicylaldehyde to 400 mL of anhydrous ethanol, heat to 45 °C, react for 8 h, add 20% by mass hydrochloric acid solution to adjust the pH to 5, distill under reduced pressure, wash with petroleum ether, and recrystallize the product in 80% by volume ethanol aqueous solution to obtain a dimethylamine hydrochloride modifier.

[0035] (3) Add 5 g of epoxy resin E51 to 20 mL of anhydrous ethanol, stir, add 9 g of dimethylamine hydrochloride modifier, heat to 80 °C, condense and reflux for 10 h, add anhydrous ethanol to dilute, centrifuge and separate to obtain cationic Schiff base modified epoxy resin.

[0036] (4) Add 7.9 g of methyl methacrylate, 1.8 g of acrylic acid, 20.3 g of butyl methacrylate, 0.7 g of OP-10 emulsifier and 1.5 g of sodium dodecyl sulfate to 150 mL of water, heat to 70 °C in a nitrogen atmosphere, add 0.1 g of initiator potassium persulfate, stir and react for 60 min, then add 18.2 g of methyl methacrylate, 4.2 g of acrylic acid, 47.6 g of butyl methacrylate and 0.32 g of initiator potassium persulfate, stir and react for 3 h, add sodium hydroxide to adjust the pH to 7.5, add 25 g of cationic Schiff base modified epoxy resin, 0.5 g of defoamer Surfynol 104E and 0.6 g of leveling agent BYK-333, stir and mix to obtain a salt spray resistant epoxy modified waterborne acrylic resin emulsion.

[0037] Example 4

[0038] (1) Add 8.1 g of methyl acrylate, 1.6 g of methacrylic acid, 20.3 g of butyl methacrylate, 0.9 g of OP-10 and 1.9 g of sodium dodecyl sulfate as emulsifier to 120 mL of water, heat to 75°C in a nitrogen atmosphere, add 0.1 g of initiator ammonium persulfate, stir and react for 60 min, then add 18.6 g of methyl acrylate, 3.7 g of methacrylic acid, 47.7 g of butyl methacrylate and 0.3 g of initiator ammonium persulfate, stir and react for 3.5 h, add sodium hydroxide to adjust the pH to 7.5, add 35 g of cationic Schiff base modified epoxy resin (prepared in Example 1), 0.8 g of defoamer Surfynol 104E and 0.6 g of leveling agent BYK-333, stir and mix to obtain a salt spray resistant epoxy modified waterborne acrylic resin emulsion.

[0039] Comparative Example 1

[0040] (1) Add 7.2g methyl acrylate, 1.7g methacrylic acid, 21.1g butyl methacrylate, 0.9g OP-10 and 1.9g sodium dodecyl sulfate to 120mL water, heat to 75°C in a nitrogen atmosphere, add 0.1g initiator ammonium persulfate, stir and react for 60min, then add 16.6g methyl acrylate, 4g methacrylic acid, 49.4g butyl methacrylate, 0.3g initiator ammonium persulfate, stir and react for 3.5h, add sodium hydroxide to adjust the pH to 7.5, add 0.8g defoamer Surfynol 104E and 0.6g leveling agent BYK-333, stir and mix to obtain a salt spray resistant epoxy modified waterborne acrylic resin emulsion.

[0041] Comparative Example 2

[0042] (1) Add 7.2 g of methyl acrylate, 1.7 g of methacrylic acid, 21.1 g of butyl methacrylate, 0.9 g of OP-10 and 1.9 g of sodium dodecyl sulfate as emulsifier to 120 mL of water, heat to 75 °C in a nitrogen atmosphere, add 0.1 g of initiator ammonium persulfate, stir and react for 60 min, then add 16.6 g of methyl acrylate, 4 g of methacrylic acid, 49.4 g of butyl methacrylate and 0.3 g of initiator ammonium persulfate, stir and react for 3.5 h, add sodium hydroxide to adjust the pH to 7.5, add 10 g of epoxy resin E51, 0.8 g of defoamer Surfynol 104E and 0.6 g of leveling agent BYK-333, stir and mix to obtain a salt spray resistant epoxy modified waterborne acrylic resin emulsion.

[0043] Comparative Example 3

[0044] (1) Add 5 g of epoxy resin E51 to 20 mL of water, stir, add 7 g of triethylamine hydrochloride, heat to 80 °C, react for 6 h, dry and remove water to obtain a cationic modified epoxy resin.

[0045] (2) Add 7.2 g of methyl acrylate, 1.7 g of methacrylic acid, 21.1 g of butyl methacrylate, 0.9 g of OP-10 and 1.9 g of sodium dodecyl sulfate as emulsifier to 120 mL of water, heat to 75 °C in a nitrogen atmosphere, add 0.1 g of initiator ammonium persulfate, stir and react for 60 min, then add 16.6 g of methyl acrylate, 4 g of methacrylic acid, 49.4 g of butyl methacrylate and 0.3 g of initiator ammonium persulfate, stir and react for 3.5 h, add sodium hydroxide to adjust the pH to 7.5, add 10 g of cationic modified epoxy resin, 0.8 g of defoamer Surfynol 104E and 0.6 g of leveling agent BYK-333, stir and mix to obtain a salt spray resistant epoxy modified waterborne acrylic resin emulsion.

[0046] The acrylic resin emulsion was placed at room temperature for 60 days and the storage condition of the emulsion was observed.

[0047] Pour the water-based acrylic resin emulsion onto the mold surface and dry it at 80°C for 12 hours to form a paint film.

[0048] Carry out cross-cut test and adhesion grade test according to GB / T 9286-2021 method.

[0049] The pencil hardness of the paint film was tested according to GB / T 6739-2022.

[0050] The salt spray resistance test was carried out according to GB / T 1771-2007 for 480 hours. The water resistance test was carried out according to GB / T 1733-1993 for 720 hours. The substrate was tinplate.

[0051] The test strains were cultured and activated to prepare a bacterial solution with a concentration of 10 6 cfu / mL bacterial suspension. Pipette 0.2mL of bacterial suspension and drop it on the surface of the paint film in the experimental group and the blank group respectively, and cover it with a sterilized polyethylene film. Incubate it at 37℃ for 24h in a constant temperature and humidity incubator. After incubation, wash the paint film and polyethylene film with a 0.8% sodium chloride solution. Take 0.2mL of washing solution and inoculate it in nutrient agar medium. Incubate it at 37℃ for 48h in a constant temperature and humidity incubator. After incubation, count the viable bacteria. Calculate the inhibition rate R. R=(BC) / B×100%.

[0052] B is the average number of recovered bacteria (cfu / piece) in the paint film samples of the blank group. C is the average number of recovered bacteria (cfu / piece) in the paint film samples of the test group.

[0053] The paint film made of the water-based acrylic resin emulsion in Comparative Example 1 is a blank group. The paint films of Examples 1-4 and Comparative Examples 2-3 are test groups. The test bacteria are Escherichia coli or Staphylococcus aureus. The test results are shown in Tables 1 and 2.

[0054] Table 1: Test results

[0055]

[0056] Table 2: Test results

[0057]

[0058] Compared with Comparative Example 1, cationic Schiff base modified epoxy resin is added to the aqueous acrylic resin emulsion of Examples 1-4. After the epoxy resin is cationically modified, it has good hydrophilicity and water solubility, and its cationic group can electrostatically interact with the sodium carboxylate anion group in the acrylic resin, thereby improving the interfacial compatibility between the epoxy resin and the acrylic resin, so that the epoxy resin has good dispersibility in the aqueous acrylic resin emulsion, the emulsion is not stratified, has no precipitation, and has excellent storage stability. In addition, after the epoxy resin is cationically modified, an antibacterial cationic quaternary ammonium salt group is introduced into the molecular chain, which can play a good bactericidal effect and show a good antibacterial rate against Escherichia coli and Staphylococcus aureus.

[0059] And the cationic Schiff base modified epoxy resin contains salicylaldehyde Schiff base group

[0060] ( ), can coordinate with the surface of substrates such as tinplate, so that the paint film is firmly attached to the surface of the substrate, the paint film is not easy to bubble and crack, and the adhesion level reaches level 0. At the same time, the cationic group of the epoxy resin and the anionic group of the sodium carboxylate in the acrylic resin interact electrostatically, and the two form a cross-linked network, which increases the cross-linking density inside the paint film, which is conducive to preventing corrosive media such as water and salt from entering the paint film, thereby improving the water resistance and salt spray resistance of the paint film, showing better anti-corrosion performance.

[0061] Comparative Example 2: Epoxy resin is added to the aqueous acrylic resin emulsion. Since the epoxy resin has poor water solubility, poor dispersibility in the aqueous acrylic resin emulsion, poor storage stability of the emulsion, and easy stratification and precipitation. In addition, the epoxy resin does not contain quaternary ammonium salt cationic groups and salicylaldehyde Schiff base groups, and its water resistance and salt spray resistance are poor, the adhesion grade is 1, and the antibacterial performance is very poor.

[0062] In Comparative Example 3, triethylamine hydrochloride is reacted with epoxy resin to obtain a cationically modified epoxy resin. The aqueous acrylic resin emulsion has good storage stability, and has excellent water resistance, salt spray resistance and antibacterial properties. However, the cationically modified epoxy resin does not contain a salicylaldehyde Schiff base group and cannot coordinate with the surface of a substrate such as tinplate, resulting in lower adhesion performance between the epoxy resin and the group than in the embodiments.

Claims

1. A salt spray resistant epoxy modified waterborne acrylic resin emulsion, characterized in that: The raw materials of the salt spray resistant epoxy modified waterborne acrylic resin emulsion include 100 parts by weight of vinyl monomer, 0.4-0.5 parts by weight of initiator, 2-2.8 parts by weight of emulsifier, 10-35 parts by weight of cationic Schiff base modified epoxy resin, 0.5-1 parts by weight of defoamer, and 0.3-0.6 parts by weight of leveling agent; The preparation method of the cationic Schiff base modified epoxy resin comprises: Add epoxy resin to anhydrous ethanol, stir and add the structural formula: The dimethylamine hydrochloride modifier is heated to 75-80°C, condensed and refluxed for 6-10 hours, anhydrous ethanol is added for dilution, and centrifuged to obtain a cationic Schiff base modified epoxy resin; The vinyl monomer includes one of acrylic acid and methacrylic acid, and any one or a combination of methyl acrylate, methyl methacrylate, butyl acrylate, and butyl methacrylate.

2. The salt spray resistant epoxy modified aqueous acrylic resin emulsion according to claim 1, characterized in that: The initiator is ammonium persulfate or potassium persulfate; the emulsifier is OP-10 and sodium dodecyl sulfate.

3. The salt spray resistant epoxy modified aqueous acrylic resin emulsion according to claim 1, characterized in that: The mass ratio of the dimethylamine hydrochloride modifier to the epoxy resin is (1.4-1.8):

1.

4. The salt-fog resistant epoxy-modified aqueous acrylic resin emulsion according to claim 3, characterized in that: The preparation method of the dimethylamine hydrochloride modifier comprises: (1) Add 3,5-dinitrobenzoyl chloride, N,N-dimethylethylenediamine, and sodium carbonate in a molar ratio of 1:(1-1.1):(1-1.1) to tetrahydrofuran, add water, react at 35-40°C for 10-12h, remove tetrahydrofuran by vacuum distillation, filter and wash, add the product to anhydrous ethanol, add tin powder and concentrated hydrochloric acid, heat to 70-80°C, condense and reflux for 1-2h, cool, add sodium hydroxide solution, extract, and recrystallize to obtain an intermediate; (2) Add the intermediate, salicylaldehyde, in a molar ratio of 1:(2-2.4) to anhydrous ethanol, heat to 40-50°C, react for 5-8h, add hydrochloric acid solution, distill under reduced pressure, wash, and recrystallize to obtain a dimethylamine hydrochloride modifier.

5. The salt-fog resistant epoxy-modified aqueous acrylic resin emulsion according to claim 4, characterized in that: The mass fraction of concentrated hydrochloric acid in (1) is 35-37%.

6. The salt-fog resistant epoxy-modified aqueous acrylic resin emulsion according to claim 4, characterized in that: In the step (1), sodium hydroxide solution is added to adjust the pH of the reaction solution to 8-9.

7. The salt-fog resistant epoxy-modified aqueous acrylic resin emulsion according to claim 4, characterized in that: In the step (2), hydrochloric acid solution is added to adjust the pH of the reaction solution to 5-6.

8. A method for preparing the salt-fog resistant epoxy-modified waterborne acrylic resin emulsion according to any one of claims 1 to 7, characterized in that: The preparation method comprises: adding vinyl monomer and emulsifier into water, heating to 70-80°C in a nitrogen atmosphere, adding initiator, stirring and reacting for 40-60 minutes, then adding more vinyl monomer and initiator, stirring and reacting for 2.5-3.5 hours, adding sodium hydroxide to adjust the pH to 7-7.5, adding cationic Schiff base modified epoxy resin, defoamer, leveling agent, stirring and mixing, and obtaining salt spray resistant epoxy modified waterborne acrylic resin emulsion.

9. Use of the salt-spray resistant epoxy-modified waterborne acrylic resin emulsion obtained by the preparation method as claimed in claim 8 in anti-corrosion coatings.

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