A kind of waterborne epoxy curing agent modified by small molecule corrosion inhibitor and preparation method thereof

Abstract

The present invention discloses a waterborne epoxy curing agent modified by a small molecule corrosion inhibitor and a preparation method thereof, comprising the following steps: heating a cycloaliphatic amine to 65°C to 75°C; uniformly mixing polyether alcohol diglycidyl ether with epoxy resin, slowly dropping into the cycloaliphatic amine, reacting for 4 to 5 hours, and obtaining an epoxy-polyamine adduct; adding a small molecule corrosion inhibitor, reacting for 3 to 4 hours at 70°C to 80°C, and obtaining a waterborne epoxy curing agent modified by a corrosion inhibitor. The process flow of the present invention is simple, and the prepared waterborne epoxy curing agent can give the waterborne epoxy coating excellent water resistance, corrosion resistance and high mechanical properties.

Description

Technical Field

[0001] The invention belongs to the technical field of waterborne epoxy resin curing agents, and particularly relates to a small molecule corrosion inhibitor-modified waterborne epoxy curing agent and a preparation method thereof. Background Art

[0002] As one of the three general thermosetting resins, epoxy resin has no use value when it forms a film alone. Only when epoxy curing agent is added can it form a three-dimensional network cross-linked structure and show its excellent performance. Two-component epoxy resin coatings have the advantages of excellent mechanical properties, chemical resistance, corrosion resistance and high adhesion, and are widely used in the field of metal corrosion protection. However, traditional epoxy resin anti-corrosion coatings are typical solvent-based systems, containing a certain proportion of volatile compounds, which will release a large amount of organic solvents during construction and curing film formation, causing great harm to the environment and human health. In recent years, with the development of coating technology, out of consideration for health and the environment, water-based epoxy resin coatings have occupied an increasing market share. However, the current two-component water-based epoxy resin coatings still have a certain gap in water resistance and corrosion resistance compared with traditional solvent-based epoxy systems, especially in the field of heavy corrosion protection.

[0003] At present, waterborne epoxy curing agents are usually epoxy-polyamine adducts made from aliphatic polyamines. For example, CN109161001A discloses a waterborne epoxy resin curing agent of epoxy-polyamine adducts made from aliphatic polyamines, and end-capsulated with benzaldehyde phenol polyoxyethylene ether (obtained from oxidized styrene phenol polyoxyethylene ether), giving the coating better anti-corrosion performance; CN10604632A discloses a waterborne epoxy resin curing agent of epoxy-polyamine adducts made from triethylenetetramine, and improves the problem of poor hardness of waterborne epoxy coatings by introducing silane coupling agents. Although aliphatic polyamines can give curing agents better hydrophilicity and toughness, the coating film made from such curing agents has low hardness, poor water resistance, and poor corrosion resistance, and cannot protect metals for a long time.

[0004] There are many types of organic corrosion inhibitors, one of which is heterocyclic compounds containing nitrogen, sulfur, oxygen, phosphorus and other heteroatoms. Thanks to the presence of electronegative elements such as N, S, O, and P, this type of corrosion inhibitor has the ability to quickly adsorb on the metal surface and can react with transition metals containing empty orbitals to produce a passivation layer, thereby delaying the progress of metal corrosion. Adding trace or small amounts of such chemicals can significantly reduce the corrosion rate of metal materials in the medium, while maintaining the original physical and mechanical properties of the metal materials.

[0005] Adding corrosion inhibitors is a feasible means to improve the corrosion resistance of coatings, but directly adding corrosion inhibitors cannot provide long-term protection. A common solution is to encapsulate corrosion inhibitors with nano-microspheres. For example, CN111253831A discloses a scheme for encapsulating corrosion inhibitors using lignin microspheres. The corrosion inhibitor encapsulated by lignin microspheres is released under pH changes caused by corrosion, successfully giving the epoxy coating the ability to self-repair; CN110105843A discloses a method for encapsulating corrosion inhibitors using CuO microcapsules, successfully constructing an anti-corrosion coating material with dual functions of pH response and self-repair. However, this type of method is not only relatively complex and has high process requirements, but also may cause the adhesion of the coating to decrease due to the introduction of nano-microspheres in the coating. Summary of the invention

[0006] The present invention aims to provide a method for preparing a small molecule corrosion inhibitor modified waterborne epoxy curing agent for corrosion protection with simple process and good stability, which is used to improve the problems of poor water resistance and insufficient long-term corrosion resistance of the coating film obtained by curing waterborne epoxy resin with existing curing agent.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A method for preparing a small molecule corrosion inhibitor modified waterborne epoxy curing agent, characterized in that it comprises the following steps:

[0009] (1) mixing polyether alcohol diglycidyl ether with epoxy resin to obtain an epoxy prepolymer; adding the epoxy prepolymer to alicyclic polyamine for reaction to obtain an epoxy adduct;

[0010] (2) adding small molecule corrosion inhibitor to continue the reaction;

[0011] (3) adding a solvent to adjust the solid content to obtain a water-based epoxy curing agent modified with a small molecule corrosion inhibitor;

[0012] The small molecule corrosion inhibitor has two molecular structure characteristics at the same time: (a) the molecular structure contains a nitrogen and / or sulfur heterocycle; and (b) the molecular structure contains a primary amine or epoxy group.

[0013] Preferably, in step (1), the epoxy resin is one or more of bisphenol A epoxy resin and bio-based epoxy resin.

[0014] Preferably, the bisphenol A type epoxy resin is E-20, E-44, E-51; and the bio-based epoxy resin is NC-514s.

[0015] Preferably, in step (1), the epoxy prepolymer is slowly dripped into the alicyclic polyamine, and the reaction is stirred at 65-75° C. for 4-5 hours; in step (2), the reaction temperature is increased to 75-85° C., a small molecule corrosion inhibitor is slowly added, and the reaction is stirred for 3-4 hours; in step (3), the solvent is slowly dripped, and the reaction is stirred for 1±0.5 hours.

[0016] Preferably, in step (1), the polyether alcohol diglycidyl ether is one or more of polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polyhexylene glycol diglycidyl ether; the epoxy value of the polyether alcohol diglycidyl ether is 0.2 to 0.4; and the molar ratio of the epoxy resin to the polyether alcohol diglycidyl ether is 4:6 to 8:2.

[0017] Preferably, in step (1), the alicyclic polyamine is one of 1,2-cyclohexanediamine, 1-methyl-2,4-cyclohexanediamine, isophoronediamine, and 1,8-diamino-p-menthane; and the molar ratio of the alicyclic polyamine to the epoxy prepolymer is 2:1 to 2.2:1.

[0018] Preferably, in step (2), the small molecule corrosion inhibitor is one of 2-aminothiazole, 2-aminobenzothiazole, 4-(2-aminoethyl)pyridine, benzotriazole, 5-methyl-1H-benzotriazole, and 4-epoxypropaneoxycarbazole; and the added mass of the small molecule corrosion inhibitor accounts for 3% to 30% of the mass of the epoxy adduct.

[0019] Preferably, in step (3), the solvent is one or more of water, propylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol butyl ether, and ethylene glycol propyl ether; and the solid content of the water-based epoxy curing agent modified by the small molecule corrosion inhibitor is 55% to 75%.

[0020] Preferably, the molar ratio of the epoxy resin to the polyether alcohol diglycidyl ether is 6:4 to 7:3; and the molar ratio of the alicyclic polyamine to the epoxy prepolymer is 2.1:1.

[0021] A small molecule corrosion inhibitor modified waterborne epoxy curing agent prepared by the preparation method.

[0022] The principle of the present invention is to introduce different proportions of epoxy resin and polyol ether diglycidyl ether into the polyamine, adjust the hydrophilicity and lipophilicity of the epoxy resin, and make the curing agent and the water-based epoxy resin component have better compatibility. At the same time, the selected alicyclic polyamine can give the cured coating better mechanical properties and water resistance. In addition, the present invention also introduces a small molecule corrosion inhibitor in the form of a covalent bond. Compared with the corrosion inhibitor existing in a free state, the grafted corrosion inhibitor small molecule not only does not have an adverse effect on the compatibility of the curing agent and the epoxy resin, but also consumes the primary amine of the curing agent, prevents the reaction rate from being too fast and causing incomplete curing, and is beneficial to improving the strength and water resistance of the coating; the introduced corrosion inhibitor small molecule is enriched on the surface side of the metal substrate during the curing stage, and forms a passivation layer with the metal after corrosion occurs, delaying the continued occurrence of corrosion. The entire process is simple, and the prepared small molecule corrosion inhibitor modified water-based epoxy curing agent gives the water-based epoxy excellent water resistance and long-term corrosion resistance.

[0023] The preparation method of the present invention and the obtained product have the following advantages and beneficial effects:

[0024] (1) Based on the epoxy-polyamine addition method, the synthesis process is simple, the stability is good, and it is highly compatible with water-based epoxy resin.

[0025] (2) By selecting alicyclic polyamines, the cured coating has high hardness and good toughness.

[0026] (3) Small molecule corrosion inhibitors are introduced in the form of covalent bonds to give the coating better water resistance and long-term corrosion resistance. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0028] Example 1

[0029] Add 10.7g of isophorone diamine to a 250mL three-necked flask equipped with a stirrer and a condenser, heat to 65°C, then slowly add a mixture of 9.54g of bisphenol A epoxy resin E-44 and 5.63g of polyethylene glycol diglycidyl ether (epoxy value = 0.32), continue stirring, and react for 5h. Heat to 75°C, slowly add 0.81g of 4-epoxypropyleneoxycarbazole, continue stirring, and react for 4h. Slowly add deionized water, stir at 65°C for 1h, and adjust to obtain a small molecule corrosion inhibitor waterborne epoxy curing agent with a solid content of 60%.

[0030] Example 2

[0031] Add 10.7g of isophorone diamine to a 250mL three-necked flask equipped with a stirrer and a condenser, heat to 65°C, then slowly add a mixture of 9.54g of bisphenol A epoxy resin E-44 and 5.63g of polyethylene glycol diglycidyl ether (epoxy value = 0.32), continue stirring, and react for 5h. Heat to 75°C, slowly add 2.25g of 4-epoxypropyleneoxycarbazole, continue stirring, and react for 4h. Slowly add deionized water, stir at 65°C for 1h, and adjust to obtain a small molecule corrosion inhibitor waterborne epoxy curing agent with a solid content of 65%.

[0032] Example 3

[0033] Add 10.7g of isophorone diamine to a 250mL three-necked flask equipped with an agitator and a condenser, heat to 65°C, then slowly add a mixture of 15.54g of cashew nut shell oil-based epoxy resin NC-514s and 5.63g of polyethylene glycol diglycidyl ether (epoxy value = 0.32), continue stirring, and react for 5h. Heat to 75°C, slowly add 2.77g of 4-epoxypropyleneoxycarbazole, continue stirring, and react for 4h. Slowly add deionized water, stir at 65°C for 1h, and adjust to obtain a small molecule corrosion inhibitor waterborne epoxy curing agent with a solid content of 65%.

[0034] Example 4

[0035] Add 8.16g of 1-methyl-2,4-cyclohexanediamine to a 250mL three-necked flask equipped with a stirrer and a condenser, heat to 65°C, then slowly add a mixture of 15.54g of cashew nut shell oil-based epoxy resin NC-514s and 5.63g of polyethylene glycol diglycidyl ether (epoxy value = 0.32), continue stirring, and react for 5h. Heat to 75°C, slowly add 2.55g of 4-epoxypropyleneoxycarbazole, continue stirring, and react for 4h. Slowly add deionized water, stir at 65°C for 1h, and adjust to obtain a small molecule corrosion inhibitor waterborne epoxy curing agent with a solid content of 65%.

[0036] Example 5

[0037] Add 8.16g of 1-methyl-2,4-cyclohexanediamine to a 250mL three-necked flask equipped with a stirrer and a condenser, heat to 65°C, then slowly add a mixture of 15.54g of cashew nut shell oil-based epoxy resin NC-514s and 5.63g of polyethylene glycol diglycidyl ether (epoxy value = 0.32), continue stirring, and react for 5h. Heat to 75°C, slowly add 4.77g of 4-epoxypropyleneoxycarbazole, continue stirring, and react for 4h. Slowly add deionized water, stir at 65°C for 1h, and adjust to obtain a small molecule corrosion inhibitor waterborne epoxy curing agent with a solid content of 70%.

[0038] Example 6

[0039] Add 8.16g of 1-methyl-2,4-cyclohexanediamine to a 250mL three-necked flask equipped with a stirrer and a condenser, heat to 65°C, then slowly add a mixture of 8.28g of bisphenol A epoxy resin E-44 and 7.5g of polyethylene glycol diglycidyl ether (epoxy value = 0.32), continue stirring, and react for 5h. Heat to 75°C, slowly add 5.98g of 4-epoxypropyleneoxycarbazole, continue stirring, and react for 4h. Slowly add deionized water, stir at 65°C for 1h, and adjust to obtain a small molecule corrosion inhibitor waterborne epoxy curing agent with a solid content of 75%.

[0040] Comparative Example 1

[0041] 12.26g of triethylenetetramine was added to a 250mL three-necked flask equipped with a stirrer and a condenser, heated to 65°C, then 9.54g of bisphenol A epoxy resin E-44 and 5.63g of polyethylene glycol diglycidyl ether (epoxy value = 0.32) were slowly added, and the mixture was stirred for 5 hours. Deionized water was slowly added, stirred for 1 hour at 65°C, and a water-based epoxy curing agent with a solid content of 60% was obtained.

[0042] Comparative Example 2

[0043] Add 10.7g of isophorone diamine to a 250mL three-necked flask equipped with a stirrer and a condenser, heat to 65°C, then slowly add a mixture of 15.54g of cashew nut shell oil-based epoxy resin NC-514s and 5.63g of polyethylene glycol diglycidyl ether (epoxy value = 0.32), continue stirring, and react for 5h. Heat to 75°C and react for 4h. Slowly add deionized water, stir at 65°C for 1h, and adjust to obtain a water-based epoxy curing agent with a solid content of 60%.

[0044] The waterborne epoxy curing agent obtained in the above Examples 1 to 6 and Comparative Examples 1 to 2 was mixed evenly with a commercially available waterborne epoxy resin (3EE104W from Foshan Gaoming Tongde Resin Co., Ltd.) according to the theoretical chemical reaction stoichiometry, that is, the ratio of the molar number of carboxyl / amine hydrogen to the molar number of epoxy group in the waterborne curing agent was 0.9:1. Then, a film was applied on a steel plate, left at room temperature for 1 day, and cured at 150°C for 3 hours. The test results of the film properties corresponding to different curing agents are shown in Table 1.

[0045] Table 1: Performance test results of various examples

[0046]

[0047] The above test results refer to the following test methods or standards:

[0048] Determine the surface drying time, GB / T1728-1779;

[0049] Adhesion test by cross-cut method, GB / T9286-1998;

[0050] Determination of pencil hardness of paint film, GB / T6739-1996;

[0051] Determination of paint film flexibility, GB / T1731-1993;

[0052] Water absorption test method: After weighing the cured film, completely immerse it in deionized water. After 24 hours at room temperature, take it out, carefully wipe the surface with filter paper, and then weigh it. The ratio of the weight difference before and after immersion to the weight before immersion is the water absorption rate.

[0053] Determination of water resistance, GB / 1733-1993;

[0054] The test method for salt water resistance is: immerse the coated steel plate in a 3.5wt% sodium chloride solution for 30 days, observe whether the coating surface has blistering and whitening, whether the iron substrate surface has corrosion and the severity of corrosion;

[0055] It can be seen from the comparison results that the waterborne epoxy coating prepared by the waterborne epoxy curing agent modified with the small molecule corrosion inhibitor adopted in the present invention has been significantly improved in terms of hardness, water resistance and corrosion resistance.

[0056] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a small molecule corrosion inhibitor modified waterborne epoxy curing agent, characterized in that: The steps include: (1) mixing polyether alcohol diglycidyl ether with epoxy resin to obtain epoxy prepolymer; adding the epoxy prepolymer to alicyclic polyamine to react to obtain epoxy adduct; (2) Add small molecule corrosion inhibitor to continue the reaction; (3) adding a solvent to adjust the solid content to obtain a water-based epoxy curing agent modified with a small molecule corrosion inhibitor; In step (1), the epoxy prepolymer is slowly dripped into the alicyclic polyamine, and the reaction is stirred at 65-75° C. for 4-5 hours; the molar ratio of the epoxy resin to the polyether alcohol diglycidyl ether is 4:6-8:2; the molar ratio of the alicyclic polyamine to the epoxy prepolymer is 2:1-2.2:1; In step (2), the reaction temperature is increased to 75-85°C, a small molecule corrosion inhibitor is slowly added, and the reaction is stirred for 3-4 hours; the mass of the small molecule corrosion inhibitor added accounts for 3%-30% of the mass of the epoxy adduct; In step (3), slowly add the solvent dropwise and stir the reaction for 1±0.5h; The small molecule corrosion inhibitor has two molecular structure characteristics at the same time: (a) a nitrogen and / or sulfur-containing heterocyclic ring is contained in the molecular structure; (b) a primary amine or epoxy group is contained in the molecular structure; The epoxy resin is a bio-based epoxy resin.

2. The preparation method according to claim 1, characterized in that: The bio-based epoxy resin is NC-514s.

3. The preparation method according to claim 1, characterized in that: In step (1), the polyether alcohol diglycidyl ether is one or more of polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polyhexylene glycol diglycidyl ether; and the epoxy value of the polyether alcohol diglycidyl ether is 0.2 to 0.

4.

4. The preparation method according to claim 1, characterized in that: In step (1), the alicyclic polyamine is one of 1,2-cyclohexanediamine, 1-methyl-2,4-cyclohexanediamine, isophoronediamine, and 1,8-diamino-p-menthane.

5. The preparation method according to claim 1, characterized in that: In step (2), the small molecule corrosion inhibitor is one of 2-aminothiazole, 2-aminobenzothiazole, 4-(2-aminoethyl)pyridine, and 4-epoxypropaneoxycarbazole.

6. The preparation method according to claim 1, characterized in that: In step (3), the solvent is one or more of water, propylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol butyl ether, and ethylene glycol propyl ether; and the solid content of the water-based epoxy curing agent modified by the small molecule corrosion inhibitor is 55% to 75%.

7. The preparation method according to claim 1, characterized in that: The molar ratio of the epoxy resin to the polyether alcohol diglycidyl ether is 6:4-7:3; the molar ratio of the alicyclic polyamine to the epoxy prepolymer is 2.1:

1.

8. A small molecule corrosion inhibitor modified waterborne epoxy curing agent prepared by the preparation method according to any one of claims 1 to 7.

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