Strong acid-resistant ionic waterborne epoxy curing agent as well as preparation method and application thereof

Abstract

The invention provides a strong acid-resistant ionic waterborne epoxy curing agent as well as a preparation method and application thereof, and belongs to the technical field of epoxy coatings. The waterborne epoxy curing agent is prepared from the following raw materials in parts by mass: 10 to 20 parts of taurine, 20 to 35 parts of amine, 65 to 70 parts of binary epoxy resin, 6 to 12 parts of monoglycidyl ether compound, 35 to 40 parts of organic solvent and 80 to 95 parts of water. The binary epoxy resin comprises a diglycidyl ether compound and epoxy resin with double epoxy groups. The preparation method comprises the following steps: neutralizing taurine by amine to obtain hydrophilic ammonium salt, dropwise adding binary epoxy resin to carry out chain extension on amine and taurine, and finally sealing redundant primary amine in a system by using a monoglycidyl ether compound to obtain the strong acid-resistant ionic waterborne epoxy curing agent. The obtained strong-acid-resistant ionic waterborne epoxy curing agent has hydrophilicity, a paint film formed by mixing and curing the strong-acid-resistant ionic waterborne epoxy curing agent and epoxy emulsion has excellent adhesive force and corrosion resistance, and the preparation cost is low.

Description

Technical Field

[0001] The invention relates to the technical field of epoxy coatings, and in particular to a strong acid-resistant ionic water-based epoxy curing agent and a preparation method and application thereof. Background Art

[0002] Epoxy resin has a series of excellent properties and is widely used in the coating industry. Among them, water-based epoxy curing agent is an important component of the water-based epoxy system. Its composition and structure directly affect the physical and chemical properties of the coating film. According to the type of groups introduced during the synthesis process, water-based epoxy curing agents can be divided into ionic and non-ionic types. Water-based non-ionic epoxy curing agents have the advantages of good storage stability and excellent salt spray resistance of the paint film formed by compounding with water-based epoxy resin, but their production cost is high and their application is limited; the production cost of water-based ionic epoxy curing agents is relatively low, and they have better practical application prospects.

[0003] Most of the existing water-based ionic epoxy curing agents use organic acids to neutralize a portion of primary or secondary amines in the final adduct to form salts to form water-based epoxy systems. However, the organic acid added during the salt formation process will react with the metal substrate, and the formed carboxylate is a weak acid and weak base salt with poor hydrophilicity. It is also sensitive to the pH value of the environment, thereby reducing the corrosion resistance of the coating. In addition, traditional water-based ionic epoxy curing agents are sensitive to acidity and alkalinity, and are prone to lose stability when adding pigments and fillers to formulate coatings. In addition, there are defects such as poor matching between epoxy emulsions and curing agents, which makes it difficult to meet practical application requirements. Therefore, it is of great significance to develop an ionic water-based epoxy curing agent with good storage stability and excellent anti-corrosion properties of the paint film formed by compounding with epoxy emulsions. Summary of the invention

[0004] The purpose of the present invention is to provide a strong acid-resistant ionic water-based epoxy curing agent and a preparation method and application thereof. The obtained strong acid-resistant ionic water-based epoxy curing agent has good stability, and the paint film formed by compounding with epoxy emulsion has excellent anti-corrosion properties such as water resistance, acid resistance, and neutral salt spray resistance.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a strong acid-resistant ionic water-based epoxy curing agent, which comprises the following raw materials by weight: 10 to 20 parts of taurine, 20 to 35 parts of amine, 65 to 70 parts of binary epoxy resin, 6 to 12 parts of monoglycidyl ether compound, 35 to 40 parts of organic solvent, and 80 to 95 parts of water;

[0007] The binary epoxy resin includes diglycidyl ether compounds and diepoxy group epoxy resins;

[0008] The preparation method of the strong acid-resistant ionic water-based epoxy curing agent comprises the following steps:

[0009] The taurine, the amine and the organic solvent are mixed and subjected to a neutralization reaction to obtain an ammonium salt mixture;

[0010] The ammonium salt mixture is mixed with the diglycidyl ether compound and the diepoxy group epoxy resin to carry out a chain extension reaction to obtain an intermediate;

[0011] The monoglycidyl ether compound is mixed with the intermediate, and after a capping reaction, water is added to obtain a strong acid-resistant ionic water-based epoxy curing agent.

[0012] Preferably, the amine includes one or more of aliphatic amines and aromatic amines, the aliphatic amine includes one or more of ethylenediamine, 1,3-propylenediamine, 1,4-butylenediamine, 1,5-pentanediamine, 1,6-hexanediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, N-(2-aminoethyl)piperazine, 1,3-cyclohexanedimethylamine, 1,2-cyclohexanediamine and isophoronediamine; the aromatic amine includes one or more of meta-phenylenediamine, p-phenylenediamine, meta-phenylenediamine and 4,4'-diaminobiphenyl.

[0013] Preferably, the structural formula of the diglycidyl ether compound is as shown in Formula I:

[0014]

[0015] In formula I, 2≤n≤20, n is an integer;

[0016] The structural formula of the diepoxy epoxy resin is shown in Formula II:

[0017]

[0018] In formula II, 1≤m≤10, and m is an integer.

[0019] Preferably, the molar ratio of the diglycidyl ether compound to the diepoxy group epoxy resin is 1:10-25.

[0020] Preferably, the monoglycidyl ether compound includes one or more of C1-C14 alkyl glycidyl ether, phenyl glycidyl ether and benzyl glycidyl ether.

[0021] Preferably, the solid content of the strong acid-resistant ionic water-based epoxy curing agent is ≥50wt.%.

[0022] The present invention also provides a method for preparing a strong acid-resistant ionic water-based epoxy curing agent, comprising the following steps:

[0023] The taurine, the amine and the organic solvent are mixed and subjected to a neutralization reaction to obtain an ammonium salt mixture;

[0024] The ammonium salt mixture is mixed with the diglycidyl ether compound and the diepoxy group epoxy resin to carry out a chain extension reaction to obtain an intermediate;

[0025] The monoglycidyl ether compound is mixed with the intermediate, and after a capping reaction, water is added to obtain a strong acid-resistant ionic water-based epoxy curing agent.

[0026] Preferably, the neutralization reaction temperature is 40-60°C, and the time is 0.5-2h; the chain extension reaction temperature is 50-100°C, and the time is 3-5h; the end-capping reaction temperature is 50-100°C, and the time is 1-3h.

[0027] Preferably, the organic solvent includes one or more of propylene glycol methyl ether, dipropylene glycol methyl ether, propylene glycol butyl ether, ethylene glycol butyl ether and diethylene glycol butyl ether.

[0028] The present invention also provides the use of the above-mentioned strong acid-resistant ion-type water-based epoxy curing agent or the strong acid-resistant ion-type water-based epoxy curing agent prepared by the above-mentioned preparation method in epoxy coatings.

[0029] Beneficial effects:

[0030] The invention firstly conducts a neutralization reaction between taurine and amine to form a salt, and then conducts a neutralization reaction between the sulfonic acid group in taurine and polyamine to obtain a hydrophilic ammonium salt, thereby improving the hydrophilicity of the curing agent, obtaining a stable water-based epoxy resin, and greatly reducing the cost of the ionic water-based epoxy curing agent; the invention conducts a chain extension reaction between the obtained hydrophilic ammonium salt and a diglycidyl ether compound and a diepoxy group epoxy resin, and adjusts the hydrophilic-lipophilic balance value of the curing agent by the diglycidyl ether compound, thereby adjusting the hydrophilicity of the ionic water-based epoxy curing agent. The lipophilicity value is improved by grafting and ring-opening the epoxy resin with amino groups, thereby increasing the cross-linking density of the curing agent and the density of the molecular network structure, thereby improving the compatibility of the curing agent with the epoxy emulsion and improving the anti-corrosion performance of the paint film. The dense network structure also improves the water resistance of the curing agent; finally, monoglycidyl ether compounds are used to cap the residual primary amines in the system, which can not only improve the compatibility of the curing agent with the epoxy resin, but also reduce the content of primary amine hydrogen, thereby extending the storage time of the strong acid-resistant ion water-based epoxy curing agent.

[0031] The present invention adds taurine, and the obtained ionic water-based epoxy curing agent is acidic. When the obtained paint film is tested for acid resistance in a 0.5% H2SO4 solution, the acidic condition of the system is conducive to hydrogen-hydrogen exchange with hydrogen ions in sulfuric acid, and the acid resistance of the curing agent paint film is greatly improved through ion exchange; at the same time, the sulfonic acid structure in taurine can react chemically with the surface of the plate when the paint film is made, forming a chemical protective layer to further improve the anti-corrosion performance of the paint film, and also improve the adhesion between the paint film and the equipment; in the test of the salt spray resistance of the paint film, the ammonium salt formed by the neutralization of taurine and amine is unstable when encountering the cationic component in the salt spray, and anions are formed by aminolysis, and the free anions are combined with the cations in the salt spray, thereby improving the salt spray resistance of the paint film. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The results of taking out the waterborne epoxy curing agents of Examples 1 to 5 and Comparative Examples 1 to 5 after being put into a 50° C. electric heated air drying oven for 30 days are shown in the figure. DETAILED DESCRIPTION

[0033] The present invention provides a strong acid-resistant ionic water-based epoxy curing agent, which comprises the following raw materials by weight: 10 to 20 parts of taurine, 20 to 35 parts of amine, 65 to 70 parts of binary epoxy resin, 6 to 12 parts of monoglycidyl ether compound, 35 to 40 parts of organic solvent, and 80 to 95 parts of water;

[0034] The binary epoxy resin includes diglycidyl ether compounds and diepoxy group epoxy resins;

[0035] The preparation method of the strong acid-resistant ionic water-based epoxy curing agent comprises the following steps:

[0036] The taurine, the amine and the organic solvent are mixed and subjected to a neutralization reaction to obtain an ammonium salt mixture;

[0037] The ammonium salt mixture is mixed with the diglycidyl ether compound and the diepoxy group epoxy resin to carry out a chain extension reaction to obtain an intermediate;

[0038] The monoglycidyl ether compound is mixed with the intermediate, and after a capping reaction, water is added to obtain a strong acid-resistant ionic water-based epoxy curing agent.

[0039] In the present invention, the mass fraction of taurine is preferably 10 to 20 parts, more preferably 15 to 20 parts, and even more preferably 18.8 parts. Taurine (2-aminoethanesulfonic acid) itself has fewer active groups and is difficult to dissolve in organic solvents such as acetone and ether. The prior art does not use taurine as the main component to prepare an ionic water-based epoxy curing agent. However, taurine has good water solubility and contains relatively active amino groups and sulfonic acid groups in its structure. The present invention utilizes the amino groups in the taurine molecule to open the epoxy groups on the main chain of the epoxy resin, and introduces the hydrophilic sulfonate group into the main chain to form a salt. The sulfonic acid group is a strong acid group. After the salt is formed, it is a weak base salt with strong hydrophilic ability, which can adjust the hydrophilic-lipophilic balance value of the curing agent, and is easy to prepare a stable water-based epoxy resin. At the same time, the ring-opening reaction also increases the crosslinking density and improves the compatibility of the curing agent with the epoxy emulsion. The sulfonate group is a strong polar group, and its introduction can increase the molecular Coulomb force and hydrogen bond, thereby improving the compatibility of the epoxy resin segment, so that the cured film has good mechanical properties.

[0040] In the present invention, the mass fraction of the amine is preferably 20 to 35 parts, more preferably 25 to 35 parts, and more preferably 31.5 parts. The amine preferably includes one or more of aliphatic amines and aromatic amines. The aliphatic amine preferably includes ethylenediamine, 1,3-propylenediamine, 1,4-butylenediamine, 1,5-pentanediamine, 1,6-hexanediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, N-(2-aminoethyl)piperazine, 1,3-cyclohexanedimethylamine, 1,2-cyclohexanediamine and isoflavone. One or more of oxadiamine, preferably one or more of ethylenediamine, 1,6-hexanediamine, diethylenetriamine, 1,3-cyclohexanediamine and isophoronediamine, more preferably one or two of isophoronediamine and diethylenetriamine; the aromatic amine preferably includes one or more of m-phenylenediamine, p-phenylenediamine, m-phenylenediamine and 4,4'-diaminobiphenyl, more preferably one or two of m-phenylenediamine and m-phenylenediamine, more preferably m-phenylenediamine. When the amine is two or more of the above, the present invention has no special restrictions on the ratio of different types of amines, and any ratio is acceptable. In the present invention, the amine can react with taurine to form an ammonium salt to improve the hydrophilicity of the system; on the other hand, it reacts with the binary epoxy resin to form a ring-opening reaction to increase the crosslinking density of the system, which is conducive to the synthesis of an ionic waterborne epoxy curing agent with excellent anti-corrosion performance.

[0041] In the present invention, the mass fraction of the binary epoxy resin is preferably 65 to 70 parts, and more preferably 69.5 parts; the binary epoxy resin preferably includes a diglycidyl ether compound and a diepoxy group epoxy resin, and the structural formula of the diglycidyl ether compound is preferably as shown in Formula I:

[0042]

[0043] In formula I, n is preferably 2≤n≤20 and is an integer, n is further preferably 2≤n≤10 and is an integer, and n is more preferably 2≤n≤5 and is an integer; the diglycidyl ether compound preferably includes polyethylene glycol glycidyl ether or 1,4-butanediol diglycidyl ether, and further preferably includes polyethylene glycol diglycidyl ether; both ends of the diglycidyl ether compound can be ring-opened, and the amine and taurine can be linked to achieve chain extension of the organic amine, adjust its hydrophilic-lipophilic balance value, and then adjust the hydrophilic-lipophilic balance value of the ionic waterborne epoxy curing agent, and the molecular weight of the diglycidyl ether compound is low, which will not affect the anticorrosive performance of the curing agent;

[0044] The structural formula of the diepoxy epoxy resin is preferably as shown in Formula II:

[0045]

[0046] In formula II, m is preferably 1≤m≤10 and is an integer, m is further preferably 1≤m≤8 and is an integer, and m is more preferably 1≤m≤5 and is an integer; the diepoxy group epoxy resin preferably includes epoxy resin E51 or epoxy resin E28, and further preferably includes epoxy resin E28; the diepoxy group epoxy resin can be linked to the carbon chain of the organic amine after ring opening to improve the crosslinking density of the system, and can react with the amino group in taurine on the other hand, thereby improving the compatibility of the ionic water-based epoxy curing agent and the epoxy emulsion; according to the principle of like dissolves like, the ionic water-based epoxy curing agent containing the epoxy resin can be better soluble in the epoxy emulsion, and the crosslinking density of the curing agent system is improved by the crosslinking reaction between the hydrophobic compound of the diepoxy group and the amine, thereby improving the comprehensive performance of the paint film formed by the strong acid-resistant ionic water-based epoxy curing agent and the epoxy emulsion.

[0047] In the present invention, the molar ratio of the diglycidyl ether compound to the diepoxy group epoxy resin is preferably 1:10-25, further preferably 1:10-23, and more preferably 1:10-15; the specific amount of the diglycidyl ether compound and the diepoxy group epoxy resin can modify taurine on the one hand to make it suitable for ionic waterborne epoxy curing agent, and on the other hand, can also undergo a ring-opening reaction with amines to increase the crosslinking density of the curing agent, thereby improving the anti-corrosion performance of the ionic waterborne epoxy curing agent.

[0048] In the present invention, the mass fraction of the monoglycidyl ether compound is preferably 6 to 12 parts, further preferably 6 to 10 parts, and more preferably 6.5 parts. The monoglycidyl ether compound preferably includes one or more of C1 to C14 alkyl glycidyl ether, phenyl glycidyl ether, and benzyl glycidyl ether, and further preferably includes one or more of n-butyl glycidyl ether and phenyl glycidyl ether, and more preferably n-butyl glycidyl ether; the monoglycidyl ether compound is used as a capping agent, which can react with the primary amine hydrogen of the strong acid-resistant ion-type water-based epoxy curing agent to block excess primary amine hydrogen, thereby improving the compatibility of the curing agent with the epoxy resin and reducing the content of primary amine hydrogen, thereby extending the trial period of the strong acid-resistant ion-type water-based epoxy curing agent system and extending the storage time of the strong acid-resistant ion-type water-based epoxy curing agent.

[0049] In the present invention, the solid content of the strong acid-resistant ionic water-based epoxy curing agent is preferably ≥50wt.%; the specific solid content is limited mainly to ensure that taurine can be fully dissolved while ensuring the stability of the water-based epoxy curing agent, thereby optimizing the performance and cost-effectiveness of the curing agent.

[0050] The present invention also provides a method for preparing a strong acid-resistant ionic water-based epoxy curing agent, comprising the following steps:

[0051] The taurine, the amine and the organic solvent are mixed and subjected to a neutralization reaction to obtain an ammonium salt mixture;

[0052] The ammonium salt mixture is mixed with the diglycidyl ether compound and the diepoxy group epoxy resin to carry out a chain extension reaction to obtain an intermediate;

[0053] The monoglycidyl ether compound is mixed with the intermediate, and after a capping reaction, water is added to obtain a strong acid-resistant ionic water-based epoxy curing agent.

[0054] In the present invention, the temperature of the neutralization reaction is preferably 40-60°C, more preferably 50-60°C, more preferably 60°C, and the time is preferably 0.5-2h, more preferably 0.5-1.5h, more preferably 0.5-1h; the temperature of the chain extension reaction is preferably 50-100°C, more preferably 60-80°C, more preferably 60°C, and the time is preferably 3-5h, more preferably 3-4h, more preferably 4h; the temperature of the end-capping reaction is 50-100°C, more preferably 60-90°C, more preferably 60°C, and the time is preferably 1-3h, more preferably 1-2h, more preferably 1h.

[0055] In the present invention, the mass fraction of the organic solvent is preferably 35-40 parts, further preferably 36-38 parts, and more preferably 37-38 parts; the organic solvent preferably includes one or more of propylene glycol methyl ether, dipropylene glycol methyl ether, propylene glycol butyl ether, dipropylene glycol butyl ether, propylene glycol phenyl ether, ethylene glycol butyl ether and diethylene glycol butyl ether, further preferably one or more of propylene glycol methyl ether, dipropylene glycol methyl ether, propylene glycol butyl ether, dipropylene glycol butyl ether and propylene glycol phenyl ether, more preferably one or more of propylene glycol methyl ether, dipropylene glycol methyl ether, propylene glycol butyl ether and propylene glycol phenyl ether; the role of the organic solvent is to provide a homogeneous reaction system and reduce the viscosity of the curing agent.

[0056] In the present invention, the mass fraction of water is preferably 80 to 95 parts, more preferably 85 to 95 parts, and more preferably 88 to 95 parts; water is used in the reaction system to adjust the solid content of the waterborne epoxy curing agent.

[0057] The present invention also provides the use of the above-mentioned strong acid-resistant ion-type water-based epoxy curing agent or the strong acid-resistant ion-type water-based epoxy curing agent prepared by the above-mentioned preparation method in epoxy coatings.

[0058] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0059] Example 1

[0060] Weigh 18.8 parts of taurine, 12.77 parts of isophorone diamine, 5.15 parts of diethylenetriamine, 13.6 parts of meta-xylylenediamine, 1.6 parts of polyethylene glycol diglycidyl ether, 67.9 parts of epoxy resin E286, 6.5 parts of n-butyl glycidyl ether, 37.89 parts of propylene glycol methyl ether, and 88.43 parts of water by mass;

[0061] In a 500 mL three-necked flask equipped with a stirrer, a reflux condenser and a thermometer, 18.8 parts of taurine, 12.77 parts of isophorone diamine, 5.15 parts of diethylenetriamine, 13.36 parts of m-xylylenediamine and 37.89 parts of propylene glycol methyl ether were added, and a neutralization reaction was carried out at 60° C. with stirring for 0.5 h to obtain an ammonium salt mixture;

[0062] Use a constant pressure dropping funnel to drop 1.6 parts of a mixture of polyethylene glycol glycidyl ether and 67.9 parts of epoxy resin E28 into the flask, control the reaction temperature at 60°C, and after the dropwise addition, carry out a chain extension reaction at 60°C, and react for 4 hours to obtain an intermediate;

[0063] 6.5 parts of n-butyl glycidyl ether were added dropwise to the flask using a constant pressure dropping funnel. After constant temperature reaction at 60°C for 1 hour, 88.43 parts of water were added and stirred for 0.5 hour to obtain the strong acid-resistant ionic water-based epoxy curing agent of Example 1, which was recorded as A1 with a solid content of 50 wt.%, an amine value of 196 mgKOH / g, and an active hydrogen equivalent of 200 g / mol.

[0064] Example 2

[0065] The only difference from Example 1 is:

[0066] Replace 12.77 parts of isophoronediamine with 4.5 parts of ethylenediamine;

[0067] Other conditions remain unchanged;

[0068] The strong acid-resistant ionic water-based epoxy curing agent of Example 2 was obtained, which was recorded as A2, with a solid content of 50 wt.%, an amine value of 236 mgKOH / g, and an active hydrogen equivalent of 182 g / mol.

[0069] Example 3

[0070] The only difference from Example 1 is:

[0071] 13.6 parts of m-xylylenediamine were replaced with 14.23 parts of 1,3-cyclohexylenediamine;

[0072] Other conditions remain unchanged;

[0073] The strong acid-resistant ionic water-based epoxy curing agent of Example 3 was obtained, which was recorded as A3, with a solid content of 50 wt.%, an amine value of 218 mgKOH / g, and an active hydrogen equivalent of 193 g / mol.

[0074] Example 4

[0075] The only difference from Example 1 is:

[0076] Replace 6.5 parts of n-butyl glycidyl ether with 6.51 parts of phenyl glycidyl ester;

[0077] Other conditions remain unchanged;

[0078] The strong acid-resistant ionic water-based epoxy curing agent of Example 4 was obtained, which was recorded as A4, with a solid content of 50 wt.%, an amine value of 193 mgKOH / g, and an active hydrogen equivalent of 203 g / mol.

[0079] Example 5

[0080] The only difference from Example 1 is:

[0081] Replace 1.6 parts of polyethylene glycol diglycidyl ether with 1.85 parts of 1,4-butanediol diglycidyl ether;

[0082] Other conditions remain unchanged;

[0083] The strong acid-resistant ionic water-based epoxy curing agent of Example 5 was obtained, which was recorded as A5, with a solid content of 50 wt.%, an amine value of 175 mgKOH / g, and an active hydrogen equivalent of 226 g / mol.

[0084] Comparative Example 1

[0085] The only difference from Example 1 is:

[0086] Replace 18.8 parts of taurine with 8.87 parts of n-propylamine;

[0087] Other conditions remain unchanged;

[0088] The strong acid-resistant ionic water-based epoxy curing agent of Comparative Example 1 was obtained, which was recorded as B1, with a solid content of 50 wt.%, an amine value of 215 mgKOH / g, and an active hydrogen equivalent of 194 g / mol.

[0089] Comparative Example 2

[0090] The only difference from Example 1 is:

[0091] Replace 18.8 parts of taurine with 20.86 parts of 2-(methylamino)ethanesulfonic acid;

[0092] Other conditions remain unchanged;

[0093] The strong acid-resistant ionic water-based epoxy curing agent of Comparative Example 2 was obtained, which was recorded as B2, with a solid content of 50 wt.%, an amine value of 236 mgKOH / g, and an active hydrogen equivalent of 182 g / mol.

[0094] Comparative Example 3

[0095] The only difference from Example 1 is:

[0096] Replace 18.8 parts of taurine with 21.02 parts of 3-hydroxypropanesulfonic acid;

[0097] Other conditions remain unchanged;

[0098] The strong acid-resistant ionic water-based epoxy curing agent of Comparative Example 3 was obtained, which was recorded as B3, with a solid content of 50 wt.%, an amine value of 218 mgKOH / g, and an active hydrogen equivalent of 198 g / mol.

[0099] Comparative Example 4

[0100] The only difference from Example 1 is:

[0101] Taurine was not added in the neutralization reaction;

[0102] The end-capping reaction is:

[0103] Use a constant pressure dropping funnel to slowly add 6.5 parts of n-butyl glycidyl ether into the flask, and react at a constant temperature of 60°C for 1 hour. Then, mix 11.11 parts of propionic acid with 88.43 parts of water to obtain a propionic acid aqueous solution, add the propionic acid aqueous solution into the flask, and react with stirring for 0.5 hour to obtain the strong acid-resistant ionic water-based epoxy curing agent of Comparative Example 4, recorded as B4, with a solid content of 50wt.%, an amine value of 294mgKOH / g, and an active hydrogen equivalent of 134g / mol.

[0104] Comparative Example 5

[0105] The only difference from Example 1 is:

[0106] Taurine was not added in the neutralization reaction;

[0107] The end-capping reaction is:

[0108] 6.5 parts of n-butyl glycidyl ether were slowly added dropwise into the flask using a constant pressure dropping funnel, and the reaction was carried out at a constant temperature of 60°C for 1 hour. Then, 18.8 parts of taurine were mixed with 88.43 parts of water to obtain a taurine aqueous solution, which was added into the flask and stirred for 0.5 hour to obtain a strong acid-resistant ionic water-based epoxy curing agent of Comparative Example 5, which was recorded as B5, with a solid content of 50 wt.%, an amine value of 263 mgKOH / g, and an active hydrogen equivalent of 126 g / mol.

[0109] Performance Testing

[0110] 1. Stability of waterborne epoxy curing agent

[0111] Method: Take equal amounts of the waterborne epoxy curing agents of Examples 1 to 5 and Comparative Examples 1 to 5, place them in 100 mL transparent plastic bottles, and mark them with serial numbers;

[0112] Put the transparent plastic bottle into an electric blast drying oven at 50°C, the model of the electric blast drying oven is DHG-101;

[0113] Starting from the first day of placing in the electric hot air drying oven, the transparency of the water-based epoxy curing agent in each plastic bottle was observed and recorded regularly every day for more than 30 days (more than 15 days in the prior art practice measurement).

[0114] Judgment criteria: Transparency is qualified, turbidity is unqualified.

[0115] The transparency of the waterborne epoxy curing agent of Examples 1 to 5 and Comparative Examples 1 to 5 was recorded every day, and the results of the number of days of maintaining transparency are shown in Tables 1 and Figure 1 .

[0116] Table 1 Stability of waterborne epoxy curing agent

[0117]

[0118] Combining Table 1 and Figure 1 It can be seen that the number of days that the waterborne epoxy curing agents of Examples 1 to 5 of the present invention and Comparative Examples 1 to 5 remain transparent is greater than 30 days, indicating that the waterborne epoxy curing agents prepared in Examples 1 to 5 and Comparative Examples 1 to 5 have good stability, can remain transparent for a long time, can be used normally, and will not affect subsequent performance measurements.

[0119] 2. Performance of waterborne epoxy curing agent and the formed gray primer

[0120] The strong acid-resistant ionic water-based epoxy curing agent obtained in Examples 1 to 5 and Comparative Examples 1 to 5 was respectively compounded with a commercially available epoxy emulsion (BANCO-2092 epoxy emulsion, solid content of 60wt.%, epoxy equivalent of 990g / mol) at a mass ratio of 100:12 to obtain a gray primer. The cold-rolled steel plate was used as the substrate, dried at 80°C for 120min, and then air-dried at room temperature for 3 days. The performance test was performed according to the following method. The results are shown in Table 2.

[0121] Performance testing method:

[0122] Hardness: GB / T6739-2006 "Paint and varnish pencil method for determination of film hardness"

[0123] Adhesion: GBT9286-1998 "Scratch test for paint and varnish films"

[0124] Pull-off method: GB / T 5210-1985 "Determination of adhesion of coatings - Pull-off method"

[0125] Impact: GB / T 1732-2020 "Determination of impact resistance of paint films"

[0126] Water resistance at 40°C: GB / T 1733-1993 "Determination of water resistance of paint films"

[0127] Resistant to 0.5% H2SO4: GB1763-1979 "Determination of chemical resistance of paint films"

[0128] Neutral salt spray resistance: GB1763-1979 "Determination of paint film resistance to chemical reagents"

[0129] Table 2 Performance test results of gray primer

[0130]

[0131]

[0132] It can be seen from Example 1, Comparative Example 1 and Comparative Example 4 in combination with Table 2 that the gray primer formed by compounding A1 with epoxy emulsion is significantly better than the gray primer formed by B1 and B4 in terms of water resistance, acid resistance and neutral salt spray resistance, indicating that the anti-corrosion performance of the strong acid-resistant ionic waterborne epoxy curing agent provided by the present invention is closely related to the raw material taurine. Compared with propylamine and propionic acid having similar structures, the sulfonic acid group in taurine can react with the amine group in the system to form a salt to adjust the hydrophilicity of the curing agent; at the same time, the amine group in taurine can be grafted with epoxy resin to increase the crosslinking density of the curing agent, thereby improving the anti-corrosion performance of the strong acid-resistant ionic waterborne epoxy curing agent. When testing the acid resistance, the cations combined with the sulfonic acid group of taurine in the A1 curing agent system can undergo ion exchange with the hydrogen ions in the 0.5% H2SO4 solution, thereby improving the acid resistance of the curing agent. In testing the salt spray resistance of the paint film, the ammonium salt formed by the neutralization of taurine and amine in the A1 curing agent system encounters water in the salt spray and undergoes ion exchange with NaCl at the scratch site to produce amine salts, and the sulfonic acid obtained by the exchange will corrode the surface of the substrate and cause rust accumulation at the scratch site, thereby improving the neutral salt spray resistance of the paint film.

[0133] It can also be seen from Example 1, Comparative Example 1 and Comparative Example 4 in combination with Table 2 that the adhesion of the gray primer formed by compounding A1 with epoxy emulsion is better than that of the gray primer formed by B1 and B4, indicating that the oxygen atoms in taurine can form hydrogen bonds with the substrate metal, thereby improving the adhesion of the paint film; at the same time, the pulling data can further determine that the gray primer formed by compounding A1 with epoxy emulsion has excellent adhesion.

[0134] It can be seen from Examples 1 to 5 and Comparative Example 5 in combination with Table 2 that the adhesion and anti-corrosion performance of the gray primer formed by compounding A1 to A5 with epoxy emulsion are better than those of the gray primer formed by B5, indicating that taurine that has not undergone high cross-linking cannot improve the anti-corrosion performance of the paint film. The amine group in taurine and epoxy resin undergo ring opening to form a network structure to increase the cross-linking density of the curing agent, so taurine needs to be added before adding epoxy to allow it to participate in the cross-linking reaction. When preparing B5, taurine is added in the last step. At this time, the reaction mechanism of taurine is that the sulfonic acid group reacts with the residual amine group in the system to form a salt, and the formed curing agent has good hydrophilicity, but the cross-linking density and network structure of the curing agent are not as good as A1 to A5, so the performance of B5 in all aspects is not as good as A1 to A5.

[0135] It can be seen from Example 1, Comparative Example 2 and Comparative Example 3 in combination with Table 2 that the acid resistance and neutral salt spray resistance of the gray primer formed by compounding A1 with epoxy emulsion are significantly better than those of the gray primer formed by Comparative Example 2 and Comparative Example 3, and the anticorrosion performance of the gray primer formed by compounding Comparative Example 3 with epoxy emulsion is the worst. Analysis of the reasons: Although 2-(methylamino)ethanesulfonic acid and 3-hydroxypropanesulfonic acid both contain sulfonic acid groups, which can form ammonium salts with polyamines in the system, they can be aminolyzed with cationic ammonium salts in the neutral salt spray system and then combined with cations in the salt spray to form a more stable structure, so that the neutral salt spray resistance of the paint film is improved, but there are no active primary amine groups in 2-(methylamino)ethanesulfonic acid and 3-hydroxypropanesulfonic acid. Compared with A1 to A5, when compounding B2 and B3 with epoxy emulsion to prepare gray primer, B2 and B3 have poor compatibility, which makes the prepared film less dense, and thus the water resistance and acid resistance of the primer formed are reduced.

[0136] It can be seen from Examples 1 to 5, Comparative Examples 2 and 3 in combination with Table 2 that the adhesion of the gray primers formed by compounding A1 to A5, B2 and B3 with epoxy emulsions respectively meets the standard, because taurine, 2-(methylamino)ethanesulfonic acid and 3-hydroxypropanesulfonic acid all contain sulfonic acid groups, which can form hydrogen bonds with the metal on the surface of the substrate, thereby making the paint film have better adhesion. The acid resistance of the gray primers compounded with A1 to A5 and epoxy emulsions is significantly better than that of the gray primer formed by B4. The reason is analyzed as follows: although taurine and propionic acid both contain hydroxyl groups, taurine itself has more active reaction sites, and the cross-linking density of the formed curing agent is higher, while propionic acid only participates in the acidification and salting process, and does not participate in the highly cross-linked reaction, so the molecular chain of the B4 curing agent is shorter and the network structure is sparse, so the anti-corrosion performance of the gray primer formed by B4 is poor.

[0137] It can be seen from Examples 1 to 5 and Comparative Examples 1 to 5 that the present invention provides a strongly acid-resistant ionic water-based epoxy curing agent with a storage stability of more than 30 days at 50°C, indicating good storage stability; the obtained ionic water-based epoxy curing agent is compounded with a water-based epoxy resin to form a paint film with good adhesion and excellent anti-corrosion performance, a simple preparation process, and low production cost, and is suitable for large-scale industrial applications.

[0138] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A strong acid-resistant ionic water-based epoxy curing agent, characterized in that: The preparation raw materials include the following by weight: 10 to 20 parts of taurine, 20 to 35 parts of amine, 65 to 70 parts of binary epoxy resin, 6 to 12 parts of monoglycidyl ether compound, 35 to 40 parts of organic solvent, and 80 to 95 parts of water; The binary epoxy resin includes diglycidyl ether compounds and diepoxy group epoxy resins; The preparation method of the strong acid-resistant ionic water-based epoxy curing agent comprises the following steps: The taurine, the amine and the organic solvent are mixed and subjected to a neutralization reaction to obtain an ammonium salt mixture; The ammonium salt mixture is mixed with the diglycidyl ether compound and the diepoxy group epoxy resin to carry out a chain extension reaction to obtain an intermediate; The monoglycidyl ether compound is mixed with the intermediate, and after a capping reaction, water is added to obtain a strong acid-resistant ionic water-based epoxy curing agent.

2. The strong acid-resistant ionic water-based epoxy curing agent according to claim 1, characterized in that: The amine includes one or more of aliphatic amines and aromatic amines. The aliphatic amine includes one or more of ethylenediamine, 1,3-propylenediamine, 1,4-butylenediamine, 1,5-pentanediamine, 1,6-hexanediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, N-(2-aminoethyl)piperazine, 1,3-cyclohexanedimethylamine, 1,2-cyclohexanediamine and isophoronediamine; the aromatic amine includes one or more of meta-phenylenediamine, p-phenylenediamine, meta-phenylenediamine and 4,4'-diaminobiphenyl.

3. The strong acid-resistant ionic water-based epoxy curing agent according to claim 1, characterized in that: The structural formula of the diglycidyl ether compound is shown in Formula I: In formula I, 2≤n≤20, n is an integer; The structural formula of the diepoxy epoxy resin is shown in Formula II: In formula II, 1≤m≤10, and m is an integer.

4. The strong acid-resistant ionic water-based epoxy curing agent according to claim 1, characterized in that: The molar ratio of the diglycidyl ether compound to the diepoxy group epoxy resin is 1:10-25.

5. The strong acid-resistant ionic water-based epoxy curing agent according to claim 1, characterized in that: The monoglycidyl ether compound includes one or more of C1-C14 alkyl glycidyl ether, phenyl glycidyl ether and benzyl glycidyl ether.

6. The strong acid-resistant ionic water-based epoxy curing agent according to claim 1, characterized in that: The solid content of the strong acid-resistant ionic water-based epoxy curing agent is ≥50wt.%.

7. The method for preparing the strong acid-resistant ionic water-based epoxy curing agent according to claims 1 to 6, characterized in that: The following steps are involved: The taurine, the amine and the organic solvent are mixed and subjected to a neutralization reaction to obtain an ammonium salt mixture; The ammonium salt mixture is mixed with the diglycidyl ether compound and the diepoxy group epoxy resin to carry out a chain extension reaction to obtain an intermediate; The monoglycidyl ether compound is mixed with the intermediate, and after a capping reaction, water is added to obtain a strong acid-resistant ionic water-based epoxy curing agent.

8. The preparation method according to claim 7, characterized in that: The temperature of the neutralization reaction is 40-60°C, and the time is 0.5-2h; the temperature of the chain extension reaction is 50-100°C, and the time is 3-5h; the temperature of the end-capping reaction is 50-100°C, and the time is 1-3h.

9. The preparation method according to claim 7, characterized in that: The organic solvent includes one or more of propylene glycol methyl ether, dipropylene glycol methyl ether, propylene glycol butyl ether, ethylene glycol butyl ether and diethylene glycol butyl ether.

10. Use of the strong acid-resistant ionic waterborne epoxy curing agent according to any one of claims 1 to 6 or the strong acid-resistant ionic waterborne epoxy curing agent prepared by the preparation method according to any one of claims 7 to 9 in epoxy coatings.

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