Ionic aqueous epoxy curing agent, preparation method therefor and use thereof

Abstract

An ionic aqueous epoxy curing agent, a preparation method therefor and the use thereof. The aqueous epoxy curing agent is prepared by reacting the following raw materials in parts by weight: a) 1 part of a polyepoxy compound, b) 1.3-6 parts of a multifunctional compound, c) 0.2 to 1.25 parts of a monoepoxy compound, and d) 0.01 to 0.23 parts of a sultone, wherein the multifunctional compound has four or more active hydrogens. The curing agent obtained has a good hydrophilic effect and very good thinning performance, the paint film prepared by mixing same with an epoxy dispersion has the following advantages: excellent salt spray resistance and water resistance, strong adhesion, high hardness, etc.; in addition, the preparation process of the curing agent is simple, the conditions are mild, and room temperature curing is carried out.

Claims

1. An ionic aqueous epoxy curing agent, prepared by reacting the following raw materials in parts by weight: a) 1 part of a polyepoxy compound; b) 1.3 to 6 parts of a multifunctional compound; c) 0.2 to 1.25 parts of a monoepoxy compound; and d) 0.01 to 0.23 parts of a sultone; wherein the multifunctional compound has four or more active hydrogens.

2. The aqueous epoxy curing agent according to claim 1, wherein the multifunctional compound is a polyamine compound; the polyamine compound is selected from one or more of aliphatic polyamines, cycloaliphatic polyamines, and aromatic polyamines, whose molar mass does not exceed 1000 g/mol.

3. The aqueous epoxy curing agent according to claim 1, wherein the polyepoxy compound is an aliphatic epoxy resin and/or an aromatic epoxy resin; the epoxide equivalent of the polyepoxy compound is 150 g/mol to 4000 g/mol.

4. The aqueous epoxy curing agent according to claim 1, wherein the monoepoxy compound is selected from one or more of epoxy ethers of phenols, epoxy esters of unsaturated alcohols, epoxy esters of unsaturated carboxylic acids, aliphatic glycidyl ethers, and aromatic glycidyl ethers.

5. The aqueous epoxy curing agent according to claim 1, wherein the sultone is an unsaturated sultone and/or a saturated sultone.

6. The aqueous epoxy curing agent according to claim 1, wherein the reaction raw materials of the aqueous epoxy curing agent further comprise: e) 0 to 0.075 parts of an alkaline-neutralizing agent; f) 0.4 to 2 parts of water; and g) 0 to 0.5 parts of an unmodified polyetheramine; the alkaline-neutralizing agent is selected from one or more of sodium hydroxide, potassium hydroxide, trimethylamine, and diethylamine; and the unmodified polyetheramine is a polyetheramine with a molar mass of 200 g/mol to 5000 g/mol, and the functionality of the unmodified polyetheramine is 2 or 3.

7. The aqueous epoxy curing agent according to claims 1, wherein the aqueous epoxy curing agent further comprises a compound having sulfonic acid or sulfonate groups, which constitutes 2 wt % to 7 wt %, of the total weight of the aqueous epoxy curing agent.

8. A preparation method for the aqueous epoxy curing agent according to claims 1, comprising the following steps: subjecting the polyepoxy compound to a ring-opening reaction with the multifunctional compound to obtain an intermediate product i; and subjecting the intermediate product i to an end-capping reaction with the monoepoxy compound and the sultone to obtain the aqueous epoxy curing agent.

9. The preparation method according to claim 8, wherein in the ring-opening reaction, the polyepoxy compound is added dropwise to the multifunctional compound, wherein the reaction duration of the ring-opening reaction is 0.5 hours to 4 hours, and the reaction temperature of the ring-opening reaction is 60° C. to 100; and/or the reaction raw materials of the aqueous epoxy curing agent further comprise 0.4 to 2 parts of water; in the end-capping reaction, water is added for dispersion and viscosity reduction, then the monoepoxy compound is added dropwise to the reaction system, and finally the sultone is added and reacted for 10 minutes to 30 minutes, wherein the reaction duration for adding the monoepoxy compound is 0.5 hours to 2 hours, and the reaction temperature of the end-capping reaction is 60° C. to 100° C.

10. The preparation method according to claim 8, further comprising: after the competition of the ring-opening reaction, subjecting the reaction system to reduced pressure distillation; and/or the reaction raw materials of the aqueous epoxy curing agent further comprise 0 to 0.075 parts of an alkaline-neutralizing agent and 0 to 0.5 parts of an unmodified polyetheramine, and after the competition of the end-capping reaction, the alkaline-neutralizing agent is added to perform a neutralization reaction, or the alkaline-neutralizing agent and the unmodified polyetheramine are added.

11. The preparation method according to claims 8, wherein the amine value of the aqueous epoxy curing agent is 100 mgKOH/g to 500 mgKOH/g; the solid content of the aqueous epoxy curing agent is 60 wt % to 80 wt %; and the pH value of the aqueous epoxy curing agent is 8 to 11.5.

12. The preparation method according to claim 8, wherein the amine value of the aqueous epoxy curing agent is 150 mgKOH/g to 350 mgKOH/g.

13. A formulation method of coatings using the aqueous epoxy curing agent prepared by the preparation method according to claim 8 in the formulation of coatings and the curing of an epoxy resin system.

14. The preparation method according to claim 8, wherein the pH value of the aqueous epoxy curing agent is 9 to 11.

15. A formulation method of coatings using of the aqueous epoxy curing agent according to claim 1 in the formulation of coatings and the curing of an epoxy resin system.

16. The aqueous epoxy curing agent according to claim 1, wherein the multifunctional compound is a polyamine compound comprising at least one member selected from the group consisting of ethylenediamine, propylenediamine, butanediamine, 2-methyl-1, 5-pentanediamine, 1,6-hexanediamine, diethylenetriamine, m-xylylenediamine, 1,3-bisaminomethylcyclohexane, 1-ethyl-1,3-propylenediamine, p-aminodicyclohexylmethane, 2,2,4-trimethyl-1,6-hexanediamine, p-xylylenediamine, polyetheramine, triethylenetetramine, tetraethylenepentamine, isophorondiamine, polyethylenimine and diethyltoluenediamine.

17. The aqueous epoxy curing agent according to claim 1, wherein the multifunctional compound comprises at least one member selected from the group consisting of m-xylylenediamine, diethylenetriamine, polyetheramine, isophorondiamine and triethylenetetramine.

18. The aqueous epoxy curing agent according to claim 1, wherein the multifunctional compound comprises a bisamine polyetheramine having a molar mass of 200 g/mol to 1000 g/mol.

19. The aqueous epoxy curing agent according to claim 1, wherein the sultone comprises at least one member selected from the group consisting of propanesultone and butanesultone.

20. The aqueous epoxy curing agent according to claim 1, wherein the aqueous epoxy curing agent further comprises a compound having sulfonic acid or sulfonate groups, which constitutes 2.5 wt % to 6 wt %, of the total weight of the aqueous epoxy curing agent.

Description

DETAILED DESCRIPTION

(1) To provide a clearer understanding of the technical features and contents of the present disclosure, a detailed description of the preferred embodiments of the present disclosure will be given below. The examples illustrate the preferred embodiments of the present disclosure, but it should be understood that the present disclosure may be implemented in various ways and should not be limited to the embodiments set forth herein.

(2) <The Sources of Reaction Raw Materials>

(3) TABLE-US-00001 Material name Form Supplier CAS No. Isophorondiamine Liquid BASF 2855-13-2 Diethylenetriamine Liquid Dow Chemical 111-40-0 m-xylylenediamine Liquid Ningbo Guomao 1477-55-0 Chemical Epoxy resin E51/E44 Viscous Sinopec (Baling) 25068-38-6 liquid Diethylene glycol Liquid Anhui Hengyuan 4206-61-5 diglycidyl ether Group Butyl glycidyl ether Liquid Anhui Hengyuan 2426-08-06 Group Phenyl glycidyl ether Liquid Anhui Hengyuan 122-60-1 Group Cardanol glycidyl ether Liquid Anhui Hengyuan 171263-25-5 Group Polyetheramine Liquid Huntsman 9046-10-0, D400/T403/T5000 39423-51-3 Propanesultone White TCI 1120-71-4 crystal Butanesultone Liquid Aladdin 1633-83-6 Sodium hydroxide Solid Sinopharm 1310-73-2

(4) <Test Methods>

(5) The pendulum hardness was tested with reference to Determination of hardness of the paint films—Pendulum damping test (GB/T 1730).

(6) The adhesion was tested with reference to Paints and varnishes—Cross cut test for films (GB/T 9286).

(7) The water resistance was tested with reference to Determination of resistance to water of films (GB/T 1733).

(8) The salt spray resistance was tested with reference to Method of producing of paint films for testing heat and humidity resistance, salt fog resistance and accelerated weathering (GB/T 1765).

(9) The 30-day thermal storage stability of curing agents or coatings was tested in the following manner: a sample to be tested was placed in a constant temperature oven at 50° C. and tested for 30 days to see whether there was delamination.

(10) The amine value of the curing agent was tested by titration: a sample to be tested was dissolved in methanol, a solution of di-n-butylamine-chlorobenzene was added thereto, potentiometric titration was carried out with hydrochloric acid standard solution until there was mutation occurring, then blank titration was carried out in the same manner, and the final result was calculated based on the mass of KOH equivalent to the sample, in units of mg KOH/g.

(11) The infrared spectroscopy test was carried out in the following manner: in the process of the reaction for preparing an aqueous epoxy curing agent, a sample which was taken from the reaction system was used as the sample to be tested, the sample to be tested was then measured with a Fourier infrared spectrometer until the peak at a wavenumber of 913 cm.sup.−1 disappeared, and after that, the reaction was considered to be completed.

(12) The nuclear magnetic test was carried out in the following manner: in the process of the reaction for preparing an aqueous epoxy curing agent, a sample which was taken from the reaction system was used as the sample to be tested, the sample to be tested was dissolved with a deuterated reagent and then subjected to hydrogen spectrum analysis by nuclear magnetic, the hydrogen of the epoxy group had an absorption peak at a chemical shift of about 4.3, and after the signal peak at this chemical shift disappeared completely, the reaction was considered to be completed.

(13) In each of the following Examples and Comparative Examples, the reaction endpoint of the preparation process of the curing agent was determined by both infrared spectroscopy and nuclear magnetic method.

Example 1

(14) 300 g of isophoronediamine was added into a reaction flask, and the temperature was preheated to 80° C. 160 g of epoxy resin E51 was gradually dripped into the reaction flask by a peristaltic pump, and then a ring-opening reaction was carried out, wherein the addition continued for 1 hour and the temperature continued to be maintained for half an hour. After the completion of the ring-opening reaction, the material in the reaction flask was distilled under reduced pressure by a vacuum pump, 120 g of deionized water was added to the reaction system for dispersion after excess isophoronediamine in the reaction system was removed, and 100 g of butyl glycidyl ether was gradually dripped into the reaction flask by a peristaltic pump for reaction, wherein the addition duration was 1 hour and the temperature was maintained for half an hour. 5 g of propanesultone was added to the reaction system slowly and reacted for 10 minutes, after the reaction, 1.7 g of NaOH was added therein for neutralization, and then 15 g of polyetheramine D400 was added therein. After the material in the reaction flask was stirred evenly, a curing agent was obtained. The resulting curing agent had a solid content of 73.9 wt %, an amine value of 275 mg KOH/g, and a pH of 9.7. The compound having sulfonate groups in the resulting curing agent constituted 3.7 wt % of the total weight of the aqueous epoxy curing agent.

Example 2

(15) 280 g of diethylenetriamine was added into a reaction flask, and the temperature was preheated to 80° C. 150 g of epoxy resin E51 was gradually dripped into the reaction flask by a peristaltic pump, and then a ring-opening reaction was carried out, wherein the addition continued for 1 hour and the temperature continued to be maintained for half an hour. After the completion of the ring-opening reaction, the material in the reaction flask was distilled under reduced pressure by a vacuum pump, 130 g of deionized water was added to the reaction system for dispersion after excess diethylenetriamine in the reaction system was removed, and 95 g of phenyl glycidyl ether was gradually dripped into the reaction flask by a peristaltic pump for reaction, wherein the addition duration was 1 hour and the temperature was maintained for half an hour. 6 g of propanesultone was added to the reaction system slowly and reacted for half an hour, and after the reaction, 2 g of NaOH was added therein for neutralization. After the material in the reaction flask was stirred evenly, a curing agent was obtained. The resulting curing agent had a solid content of 75.2 wt %, an amine value of 325 mg KOH/g, and a pH of 10.1. The compound having sulfonate groups in the resulting curing agent constituted 4.6 wt % of the total weight of the aqueous epoxy curing agent.

Example 3

(16) 350 g of diethylenetriamine was added into a reaction flask, and the temperature was preheated to 80° C. 150 g of epoxy resin E51 was gradually dripped into the reaction flask by a peristaltic pump, and then a ring-opening reaction was carried out, wherein the addition continued for 1 hour and the temperature continued to be maintained for half an hour. After the completion of the ring-opening reaction, the material in the reaction flask was distilled under reduced pressure by a vacuum pump, 140 g of deionized water was added to the reaction system for dispersion after excess diethylenetriamine in the reaction system was removed, and 110 g of phenyl glycidyl ether was gradually dripped into the reaction flask by a peristaltic pump for reaction, wherein the addition duration was 1 hour and the temperature was maintained for half an hour. 6 g of propanesultone was added to the reaction system slowly and reacted for half an hour. After the reaction, the material in the reaction flask was stirred evenly, and a curing agent was obtained. The resulting curing agent had a solid content of 76.2 wt %, an amine value of 295 mg KOH/g, and a pH of 9.2. The compound having sulfonate groups in the resulting curing agent constituted 2.9 wt % of the total weight of the aqueous epoxy curing agent.

Example 4

(17) 312 g of triethylenetetramine was added into a reaction flask, and the temperature was preheated to 80° C. 148 g of epoxy resin E51 was gradually dripped into the reaction flask by a peristaltic pump, and then a ring-opening reaction was carried out, wherein the addition continued for 1 hour and the temperature continued to be maintained for half an hour. After the completion of the ring-opening reaction, the material in the reaction flask was distilled under reduced pressure by a vacuum pump, 120 g of deionized water was added to the reaction system for dispersion after excess triethylenetetramine in the reaction system was removed, and 105 g of phenyl glycidyl ether was gradually dripped into the reaction flask by a peristaltic pump for reaction, wherein the addition duration was 1 hour and the temperature was maintained for half an hour. 8 g of propanesultone was added to the reaction system slowly and reacted for half an hour, and after the reaction, 2.6 g of NaOH was added therein for neutralization. After the material in the reaction flask was stirred evenly, a curing agent was obtained. The resulting curing agent had a solid content of 78.2 wt %, an amine value of 329 mg KOH/g, and a pH of 9.6. The compound having sulfonate groups in the resulting curing agent constituted 3.6 wt % of the total weight of the aqueous epoxy curing agent.

Example 5

(18) 280 g of diethylenetriamine was added into a reaction flask, and the temperature was preheated to 80° C. 120 g of diethylene glycol diglycidyl ether was gradually dripped into the reaction flask by a peristaltic pump, and then a ring-opening reaction was carried out, wherein the addition continued for 1 hour and the temperature continued to be maintained for half an hour. After the completion of the ring-opening reaction, the material in the reaction flask was distilled under reduced pressure by a vacuum pump, 130 g of deionized water was added to the reaction system for dispersion after excess diethylenetriamine in the reaction system was removed, and 100 g of phenyl glycidyl ether was gradually dripped into the reaction flask by a peristaltic pump for reaction, wherein the addition duration was 1 hour and the temperature was maintained for half an hour. 6 g of propanesultone was added to the reaction system slowly and reacted for half an hour, and after the reaction, 2 g of NaOH was added therein for neutralization. After the material in the reaction flask was stirred evenly, a curing agent was obtained. The resulting curing agent had a solid content of 74.8 wt %, an amine value of 257 mg KOH/g, and a pH of 10.4. The compound having sulfonate groups in the resulting curing agent constituted 4.1 wt % of the total weight of the aqueous epoxy curing agent.

Example 6

(19) 280 g of diethylenetriamine was added into a reaction flask, and the temperature was preheated to 80° C. 150 g of a mixture of epoxy resin E51 and diethylene glycol diglycidyl ether was gradually dripped into the reaction flask by a peristaltic pump, and then a ring-opening reaction was carried out, wherein the addition duration continued for 1 hour and the temperature continued to be maintained for half an hour. After the completion of the ring-opening reaction, the material in the reaction flask was distilled under reduced pressure by a vacuum pump, 130 g of deionized water was added to the reaction system for dispersion after excess diethylenetriamine in the reaction system was removed, and 95 g of phenyl glycidyl ether was gradually dripped into the reaction flask by a peristaltic pump for reaction, wherein the addition duration was 1 hour and the temperature was maintained for half an hour. 6 g of propanesultone was added to the reaction system slowly and reacted for half an hour, and after the reaction, 2 g of NaOH was added therein for neutralization. After the material in the reaction flask was stirred evenly, a curing agent was obtained. The resulting curing agent had a solid content of 75.6 wt %, an amine value of 280 mg KOH/g, and a pH of 9.4. The compound having sulfonate groups in the resulting curing agent constituted 5.2 wt % of the total weight of the aqueous epoxy curing agent.

Example 7

(20) 320 g of m-xylylenediamine was added into a reaction flask, and the temperature was preheated to 80° C. 150 g of epoxy resin E51 was gradually dripped into the reaction flask by a peristaltic pump, and then a ring-opening reaction was carried out, wherein the addition continued for 1 hour and the temperature continued to be maintained for half an hour. After the completion of the ring-opening reaction, the material in the reaction flask was distilled under reduced pressure by a vacuum pump, 120 g of deionized water was added to the reaction system for dispersion after excess m-xylylenediamine in the reaction system was removed, and 95 g of phenyl glycidyl ether was gradually dripped into the reaction flask by a peristaltic pump for reaction, wherein the addition duration was 1 hour and the temperature was maintained for half an hour. 6 g of propanesultone was added to the reaction system slowly and reacted for half an hour, and after the reaction, 2 g of NaOH was added therein for neutralization. After the material in the reaction flask was stirred evenly, a curing agent was obtained. The resulting curing agent had a solid content of 77.2 wt %, an amine value of 253 mg KOH/g, and a pH of 9.0. The compound having sulfonate groups in the resulting curing agent constituted 2.6 wt % of the total weight of the aqueous epoxy curing agent.

Example 8

(21) 300 g of triethylenetetramine was added into a reaction flask, and the temperature was preheated to 80° C. 120 g of diethylene glycol diglycidyl ether was gradually dripped into the reaction flask by a peristaltic pump, and then a ring-opening reaction was carried out, wherein the addition continued for 1 hour and the temperature continued to be maintained for half an hour. After the completion of the ring-opening reaction, the material in the reaction flask was distilled under reduced pressure by a vacuum pump, 130 g of deionized water was added to the reaction system for dispersion after excess triethylenetetramine in the reaction system was removed, and 115 g of cardanol glycidyl ether was gradually dripped into the reaction flask by a peristaltic pump for reaction, wherein the addition duration was 1 hour and the temperature was maintained for half an hour. 6 g of propanesultone was added to the reaction system slowly and reacted for half an hour, and after the reaction, 2 g of NaOH was added therein for neutralization. After the material in the reaction flask was stirred evenly, a curing agent was obtained. The resulting curing agent had a solid content of 74.1 wt %, an amine value of 307 mg KOH/g, and a pH of 9.5. The compound having sulfonate groups in the resulting curing agent constituted 2.8 wt % of the total weight of the aqueous epoxy curing agent.

Example 9

(22) 280 g of diethylenetriamine was added into a reaction flask, and the temperature was preheated to 80° C. 120 g of diethylene glycol diglycidyl ether was gradually dripped into the reaction flask by a peristaltic pump, and then a ring-opening reaction was carried out, wherein the addition continued for 1 hour and the temperature continued to be maintained for half an hour. After the completion of the ring-opening reaction, the material in the reaction flask was distilled under reduced pressure by a vacuum pump, 130 g of deionized water was added to the reaction system for dispersion after excess diethylenetriamine in the reaction system was removed, and 75 g of butyl glycidyl ether was gradually dripped into the reaction flask by a peristaltic pump for reaction, wherein the addition duration was 1 hour and the temperature was maintained for half an hour. 10 g of propanesultone was added to the reaction system slowly and reacted for half an hour. After the reaction, the material in the reaction flask was stirred evenly, a curing agent was obtained. The resulting curing agent had a solid content of 73.8 wt %, an amine value of 265 mg KOH/g, and a pH of 9.2. The compound having sulfonate groups in the resulting curing agent constituted 6.2 wt % of the total weight of the aqueous epoxy curing agent.

Example 10

(23) 400 g of diethylenetriamine was added into a reaction flask, and the temperature was preheated to 80° C. 150 g of epoxy resin E51 was gradually dripped into the reaction flask by a peristaltic pump, and then a ring-opening reaction was carried out, wherein the addition continued for 1 hour and the temperature continued to be maintained for half an hour. After the completion of the ring-opening reaction, the material in the reaction flask was distilled under reduced pressure by a vacuum pump, 130 g of deionized water was added to the reaction system for dispersion after excess diethylenetriamine in the reaction system was removed, and 95 g of phenyl glycidyl ether was gradually dripped into the reaction flask by a peristaltic pump for reaction, wherein the addition duration was 1 hour and the temperature was maintained for half an hour. 6 g of propanesultone was added to the reaction system slowly and reacted for half an hour, after the reaction, 2 g of NaOH was added therein for neutralization, and then 20 g of polyetheramine T403 was added therein. After the material in the reaction flask was stirred evenly, a curing agent was obtained. The resulting curing agent had a solid content of 75.2 wt %, an amine value of 365 mg KOH/g, and a pH of 9.6. The compound having sulfonate groups in the resulting curing agent constituted 2.9 wt % of the total weight of the aqueous epoxy curing agent.

Example 11

(24) 280 g of diethylenetriamine was added into a reaction flask, and the temperature was preheated to 80° C. 170 g of epoxy resin E44 was gradually dripped into the reaction flask by a peristaltic pump, and then a ring-opening reaction was carried out, wherein the addition continued for 1 hour and the temperature continued to be maintained for half an hour. After the completion of the ring-opening reaction, the material in the reaction flask was distilled under reduced pressure by a vacuum pump, 130 g of deionized water was added to the reaction system for dispersion after excess diethylenetriamine in the reaction system was removed, and 110 g of cardanol glycidyl ether was gradually dripped into the reaction flask by a peristaltic pump for reaction, wherein the addition duration was 1 hour and the temperature was maintained for half an hour. 8 g of butanesultone was added to the reaction system slowly and reacted for half an hour, and after the reaction, 2.5 g of NaOH was added therein for neutralization. After the material in the reaction flask was stirred evenly, a curing agent was obtained. The resulting curing agent had a solid content of 74.7 wt %, an amine value of 271 mg KOH/g, and a pH of 9.6. The compound having sulfonate groups in the resulting curing agent constituted 6.6 wt % of the total weight of the aqueous epoxy curing agent.

Comparative Example 1

(25) Step 1: a solution of 187 g of toluene and 187 g of epoxy resin (Yueyang Baling Sinopec E51) was added to an excess amount of m-xylylenediamine at 100° C., the mixture was maintained at 100° C. and reacted for 5 hours, and then excess toluene was removed by reduced pressure distillation and excess m-xylylenediamine was recovered.

(26) Step 2: 229.5 g of the product obtained in Step 1 was reacted with 50 g of methoxy PEG acetic acid at 200° C. for 4 hours under a nitrogen atmosphere and then cooled to 100° C., 220.5 g of phenyl glycidyl ether was added at 140° C., the temperature was maintained at 100° C. for two hours after the addition, and a curing agent was prepared.

(27) Step 3: 400 g of the curing agent prepared in Step 2 and 44.4 g of toluene were added to a glass bottle and stirred, 111 g of water was then added to the glass bottle, and after the addition, an oil-in-water emulsion was formed. 26.2 g of toluene and 187 g of water were added to form an emulsion of the curing agent having a solid content of 49.7 wt %. The resulting curing agent had an amine value of 176 mg KOH/g and a pH of 9.6.

Comparative Example 2

(28) Step 1: 30 g of epoxy resin E51, 200 g of polyether (PEG4000), and 20 g of acetone were added into a reaction flask, and with the temperature heated to 60° C., mixed evenly and refluxed. 4.76 wt % of a catalyst solution consisting of 1 g of boron trifluoride ethyl ether and 20 g of acetone was added dropwise for half an hour. After the completion of the addition, the reaction was continued at this temperature for 1 hour. After the product was dissolved in water, 15 g of deionized water was added to terminate the reaction to obtain a condensate.

(29) Step 2: 38.8 g epoxy resin E51 and 25 g of diethylenetriamine were weighted, epoxy resin E51 was added once for all to a mixture of diethylenetriamine and 25 g of acetone at normal temperature, heated with stirring, and reacted at 60° C. for half an hour to obtain a polyamine adduct. The condensate obtained in Step 1 and the polyamine adduct were mixed at a mass ratio of 3.6:1 and then stirred for 3 hours to obtain a modified polyamine compound. After acetone was removed by reduced pressure distillation, deionized water was added dropwise to adjust the solid content to 50.2 wt % to obtain a non-ionic curing agent. The resulting curing agent had an amine value of 109 mg KOH/g and a pH of 9.1.

Comparative Example 3

(30) 280 g of diethylenetriamine was added to a reaction flask, and the temperature was preheated to 80° C. 150 g of epoxy resin E51 was gradually dripped into the reaction flask by a peristaltic pump, and then a ring-opening reaction was carried out, wherein the addition continued for 1 hour and the temperature continued to be maintained for half an hour. After the completion of the ring-opening reaction, the material in the reaction flask was distilled under reduced pressure by a vacuum pump, and 95 g of phenyl glycidyl ether was gradually dripped into the reaction flask by a peristaltic pump after excess diethylenetriamine in the reaction system was removed, wherein the addition duration was 1 hour and the temperature was maintained for half an hour. After that, 120 g of deionized water was added to the reaction system for dispersion, 6 g of propanesultone was added to the reaction system slowly and reacted for half an hour, and after the reaction, 2 g of NaOH was added therein for neutralization. After the material in the reaction flask was stirred evenly, a curing agent was obtained. The resulting curing agent had a solid content of 75.9 wt %, an amine value of 299 mg KOH/g, and a pH of 9.8. The compound having sulfonate groups in the resulting curing agent constituted 3.1 wt % of the total weight of the aqueous epoxy curing agent.

(31) Each of the aqueous epoxy curing agents obtained in the Examples and Comparative Examples was mixed with an aqueous epoxy emulsion to prepare a paint film, wherein the formulations of Component A and Component B for preparing the paint film were shown in Table 1 and Table 2.

(32) TABLE-US-00002 TABLE 1 Formulation of Component A Component A Mass fraction Composition Supplier (wt %) H.sub.2O — 12 Dispersant ADDITOL VXW BYK 2 6208 pH adjuster AMP-95 Angus Chemical 0.2 Barium sulfate Linke Chemical 13 Zinc phosphate Xinjing Chemical 9 Wollastonite Mineral product from Shanggao 25 Yueliang Mountain Black carbon Evonik 0.8 Epoxy emulsion 6520 Hexion 36 Wetting agent BYK346 BYK 0.5 Foamstar 2410 BASF 0.5 Flash rust inhibitor FA179 Elementis 0.2 Thickener U905 Wanhua 0.8 Total 100

(33) TABLE-US-00003 TABLE 2 Formulation of Component B Component B Mass fraction Composition Supplier (wt %) H.sub.2O 30 DPnB Dow Chemical 30 Curing agent Curing agents prepared in 40 Examples 1 to 11 and Curing agents prepared in Comparative Examples 1 to 3 Total 100

(34) The main paint (component A) obtained in Table 1 and each of the curing agents (component B) obtained in Table 2 were mixed according to a mass ratio of 10:1 and stirred for 15 minutes, and after that, a small amount of deionized water was added to adjust the mixture to a construction viscosity to obtain a mixed paint solution. The mixed paint was then plastered according to industry operating standards (flash leveling for 10 minutes and baking at 80° C. for 30 minutes) to obtain a paint film. The paint film was allowed to stand for 7 days under standard conditions of 23±2° C. and a humidity of 50±5%, and after that, each test was carried out according to the test method described above.

(35) The resulting paint films were tested according to the test methods described above and the performance test results are shown in Table 3.

(36) TABLE-US-00004 TABLE 3 Test results of thermal stability of Curing agents and paint performance VOC content (deducting 30-day thermal Activation pendulum water) of Examples of storage stability water salt spray period hardness pain system curing agents of curing agents adhesion resistance resistance (h) (s) (g/L) Example 1 Transparent and 0 5 5 4 82 105 unlayered Example 2 Transparent and 0 5   5− 4.5 77 105 unlayered Example 3 Transparent and 0 5 5 4 73 105 unlayered Example 4 Transparent and 0 5   4+ 5 81 105 unlayered Example 5 Transparent and 0 5 5 5 78 105 unlayered Example 6 Transparent and 0 5 5 4.5 69 105 unlayered Example 7 Transparent and 0 5 5 4 78 105 unlayered Example 8 Transparent and 0 5   5− 4 80 105 unlayered Example 9 Transparent and 0 5 5 5 84 105 unlayered Example 10 Transparent and 0 5 5 5 76 105 unlayered Example 11 Transparent and 0 5 5 4 69 105 unlayered Comparative non-transparent 2   4+ 2 6.5 61 269 Example 1 Comparative Solid precipitation 3 3   1+ 3.5 55 197 Example 2 Comparative Transparent and 2 4 2 4 63 178 Example 3 layered

(37) Each test was carried out in accordance with the national standards, as described specifically in <Test methods>. The endurance data were test results after 20 days of tracking observation.

(38) The grade of the adhesion test results is 0 to 5, wherein grade 0 means that the adhesion is the best and grade 5 means that the adhesion is the worst.

(39) The grade of the water-resistance test results is 0 to 5, wherein grade 5 means that the water resistance is the best and grade 0 means that the water resistance is the worst.

(40) The grade of the salt spray resistance test results is 0 to 5, wherein grade 5 means that the salt spray resistance is the best and grade 0 means that the salt spray resistance is the worst.

(41) From the results of Table 1, it can be seen that the thermal storage stability of the curing agents obtained in Examples 1 to 11 was good, and no delamination occurred, which indicates that the introduction of ionic groups (sulfonic acid groups or sulfonate groups) had positive effects on the stability of the curing agent system. When the curing agent was too hydrophilic, the water resistance performance of the obtained paint film became weak, and therefore, the hydrophilicity of the curing agent and the water resistance of the obtained paint film needed to be balanced. In the present disclosure, hydrophilicity was improved by introducing a certain proportion of compounds having sulfonic acid groups or sulfonate groups into the curing agent. When the curing agent was used in the curing system, the performance indicators of the paint films in each test were great, that is, after the aqueous epoxy curing agents prepared in each Example were applied to the paint film prepared from a dispersion, data such as adhesion, water resistance, salt spray resistance, activation period, and paint film hardness were excellent. However, in Comparative Examples 1 to 2, no ionic group was introduced into the curing agent, and after 30 days, the thermal storage stability of these curing agents was poor, and the hydrophilicity of the prepared curing agents was not superior to that of the curing agents prepared in each Example of the present disclosure. The addition sequence of water (for the purpose of viscosity reduction) and the monoepoxy compound in Comparative Example 3 was opposite to the sequence in Example 2, which seriously affected the salt spray resistance of the curing agent. Meanwhile, the synthesis conditions of the aqueous epoxy curing agents prepared in each Example were mild, the preparation steps were simple, and thus these aqueous epoxy curing agents could meet the market requirements and be particularly suitable for applying in the field of heavy corrosion protection.

(42) The above have described various embodiments of the present disclosure. The above description is illustrative, and not exhaustive, and not limited to the disclosed various embodiments. Without departing from the scope and spirit of the described various embodiments, various modifications and variations are apparent to those skilled in the art.