Corrosion-inhibiting epoxy resin curing agent for use in low-temperature humid environments, method of preparation and use thereof

Abstract

The present application relates to a kind of epoxy resin curing agent for low temperature humid environment and its preparation method, the epoxy resin curing agent structure as shown in formula (I) is as follows: The epoxy resin curing agent of the present application contains ketimine structure, reacts with water in humid environment, releases primary amine on one hand, and cures epoxy resin;On one hand, acyl thiourea class substance is released, and reacts with epoxy resin quickly to release a large amount of heat, further promotes the reaction of amine and epoxy, so that curing reaction can be carried out quickly in humid, low temperature environment;O, S and N atom in acyl thiourea and the π electron of benzene ring are adsorbed on the surface of metal, greatly improve the adhesion of coating, and form strong and dense adsorption film simultaneously, which can prevent corrosion reaction and will not migrate to cause pollution.The curing agent of the present application is especially suitable for the coating of large steel structure in cold and humid environment.

Description

Technical Field

[0001] This invention belongs to the field of epoxy resin curing agent technology, specifically relating to an epoxy resin curing agent for corrosion inhibition in low-temperature and humid environments, its preparation method, and its application. Background Technology

[0002] Epoxy resin is commonly used as a primer for large steel structures, such as ships, bridges, and industrial equipment and installations. However, slow curing at low temperatures significantly reduces coating efficiency. Furthermore, when humidity is high, a water film forms on the substrate surface. This water film has several advantages: first, it dissolves amine curing agents, preventing them from reacting with the epoxy resin and reducing the coating's mechanical properties; second, it promotes corrosion of the steel substrate; and third, the presence of the water film further reduces coating adhesion. Ultimately, this exacerbates paint film peeling, and the steel components corrode, losing their mechanical properties.

[0003] Chinese invention patents CN103044266A, CN101747205A, CN101555310A, and CN101173086A all disclose low-temperature curing agents and their preparation methods, but none of them address the treatment of water films on substrate surfaces in humid environments (>95% RH). While known ketimine curing agents for humid conditions can cure epoxy resins under high humidity or water-containing conditions, their reactivity is limited, making them unsuitable for use in low-temperature environments (<5℃), and they have no beneficial effect on adhesion or delaying corrosion of steel. Summary of the Invention

[0004] In view of the above-mentioned problems in the prior art, the purpose of this invention is to provide a corrosion-inhibiting epoxy resin curing agent for low-temperature and humid environments, which enables the curing reaction to proceed rapidly in humid and low-temperature environments, greatly improves the adhesion of the coating, and forms a strong and dense adsorption film that can prevent corrosion reaction and will not migrate and cause pollution.

[0005] Another object of the present invention is to provide a method for preparing such a corrosion-inhibiting epoxy resin curing agent for use in low-temperature and humid environments.

[0006] Another object of the present invention is to provide the use of this corrosion-inhibiting epoxy resin curing agent in low-temperature and humid environments.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] An epoxy resin curing agent for corrosion inhibition in low-temperature and humid environments, with the structure shown in formula (Ⅰ):

[0009]

[0010] Wherein: R is selected from C2-C12 straight-chain or branched alkyl groups, preferably C2-C6 straight-chain or branched alkyl groups; R1 is selected from --CH3 or R2 is selected from Or -NH-; R3 is selected from H or Furthermore, at least one of R1, R2, and R3 has a benzene ring structure.

[0011] On the other hand, the aforementioned method for preparing an epoxy resin curing agent for corrosion inhibition in low-temperature and humid environments involves reacting a compound with the structure shown in formula (II) with a compound with the structure shown in formula (III):

[0012]

[0013] Among them, R, R1, R2, and R3 are the same as those in equation (Ⅰ).

[0014] In one specific embodiment, the compound with the structure shown in formula (III) is selected from any one of 1-benzyl-2-thiourea, 1-benzoyl-3-phenylthiourea, N-(4-acetylphenyl)thiourea, and 1-(3-acetylphenyl)-2-thiourea.

[0015] In one specific embodiment, the molar ratio of the compound with the structure shown in formula (II) to the compound with the structure shown in formula (III) is 1:1.9-2.1, preferably 1:1.95-2.05.

[0016] In one specific implementation, at room temperature, a solution containing the compound with the structure shown in formula (II) and the compound with the structure shown in formula (III) is added to a reaction vessel, nitrogen is used to purge the mixture, the reaction vessel is heated to the reaction temperature, and after the reaction, cooling water is introduced to cool down the vessel and obtain the product.

[0017] In one specific implementation, the solvent for dissolving the compound with the structure shown in formula (II) and the compound with the structure shown in formula (III) is at least one of carbon tetrachloride, ethyl acetate, butanone, toluene, and xylene.

[0018] In one specific implementation, the reaction temperature is 30-120°C, preferably 50-110°C.

[0019] In one specific implementation, the reaction time is 0.5h-10h, preferably 2h-5h.

[0020] On the other hand, the aforementioned or the aforementioned method of preparing corrosion-inhibiting epoxy resin curing agents for low-temperature and humid environments is particularly suitable for the application of epoxy resin curing in low-temperature and humid environments, especially for the coating of large steel structures.

[0021] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0022] 1) The epoxy resin curing agent of the present invention contains a ketimine structure, which can absorb the water film adhering to the surface of the metal substrate in a humid environment, reduce the dissolution loss of the amine curing agent by the water film, and react with it to release amine-cured epoxy resin.

[0023] 2) The epoxy resin curing agent of the present invention releases acyl thiourea substances when it reacts with water. The thiourea structure contained therein reacts with the epoxy resin to release a large amount of heat, which further promotes the curing reaction, enabling the reaction to proceed rapidly at low temperatures.

[0024] 3) The acylthiourea substances released by the epoxy resin curing agent of the present invention when reacting with water contain abundant ketone structures, benzene ring structures and S and N atoms. By forming feedback bonds and covalent bonds with iron atoms, they can be tightly adsorbed on the surface of metal substrates, effectively inhibiting the corrosion reaction. Moreover, as a corrosion inhibitor, it will not migrate and cause environmental pollution.

[0025] 4) The acyl thiourea substances released by the epoxy resin curing agent of the present invention react with water can be adsorbed on the metal surface by acyl thiourea, which can greatly improve the adhesion of the coating to the metal substrate and improve the protective effect of the coating. Detailed Implementation

[0026] To better understand the technical solution of the present invention, the following embodiments will further illustrate the method provided by the present invention. However, the present invention is not limited to the listed embodiments, but should also include any other known modifications within the scope of the claims of the present invention.

[0027] A method for preparing an epoxy resin curing agent for corrosion inhibition in low-temperature and humid environments, characterized in that it is prepared by reacting a compound with the structure shown in formula (II) with a compound with the structure shown in formula (III):

[0028]

[0029] Wherein, R is selected from C2-C12 straight-chain or branched alkyl groups, preferably C2-C6 straight-chain or branched alkyl groups; R1 is selected from --CH3 or R2 is selected from Or -NH-; R3 is selected from H or Furthermore, at least one of R1, R2, and R3 has a benzene ring structure.

[0030] Specifically, the compound with the structure shown in formula (II) is selected from any one of ethylenediamine, propylenediamine, butylenediamine, pentanediamine, isobutylenediamine, hexanediamine, heptamethamine, octanediamine, nonanediamine, decanediamine, and 1,12-diaminododecane.

[0031] The compound with the structure shown in formula (III) is selected from any one of 1-benzyl-2-thiourea, 1-benzoyl-3-phenylthiourea, N-(4-acetylphenyl)thiourea, and 1-(3-acetylphenyl)-2-thiourea.

[0032] Specifically, the preparation method includes adding a solution containing the compound with the structure shown in formula (II) and the compound with the structure shown in formula (III) to a reaction vessel at room temperature, purging with nitrogen, heating the reaction vessel to a certain temperature, maintaining the reaction for a certain time, then introducing cooling water to cool down, and discharging the product.

[0033] The compounds with the structure shown in formula (II) and the compounds with the structure shown in formula (III) are preferably dissolved in a solvent. There are no particular limitations on the solvent used, such as at least one selected from carbon tetrachloride, ethyl acetate, butanone, toluene, and xylene.

[0034] The molar ratio of the compound represented by formula (II) to the compound represented by formula (III) is 1:1.9-2.1, for example, including but not limited to 1:1.9, 1:1.95, 1:2.0, 1:2.05, 1:2.1, preferably 1:1.95-2.05.

[0035] The reaction temperature is 30-120℃, including but not limited to 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, and 120℃, preferably 50-110℃. The reaction time is 0.5h-10h, including but not limited to 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, and 10h, preferably 2h-5h.

[0036] There are no special restrictions on the temperature of the condensate; for example, room temperature cooling water can be used to cool the reaction products to room temperature.

[0037] The epoxy resin curing agent for low-temperature and humid environments of the present invention contains a ketimine structure. In a humid environment, it reacts with water to release a primary amine, which cures the epoxy resin. At the same time, it releases an acylthiourea compound, which reacts rapidly with the epoxy resin, releasing a large amount of heat and further promoting the reaction between the amine and the epoxy, so that the curing reaction can proceed rapidly in a humid and low-temperature environment. The O, S, and N atoms in the acylthiourea and the π electrons of the benzene ring are adsorbed on the metal surface, which greatly improves the adhesion of the coating. At the same time, it forms a strong and dense adsorption film that can prevent corrosion reaction and will not migrate and cause pollution.

[0038] The present invention will be further illustrated below with more specific embodiments, but these do not constitute any limitation.

[0039] Unless otherwise specified, the raw materials used in the following examples and comparative examples were all obtained through commercial purchases.

[0040] The main testing methods of this invention are as follows:

[0041] 1) Curing time test: According to GB / T 1728—1979(1989) Determination of drying time of paint film and putty film, the actual drying time of epoxy paint at 5℃ was tested.

[0042] 2) Adhesion test: GB / T 9286-1998 Cross-cut test for paint and varnish film.

[0043] 3) Salt spray resistance test: GB / T1771—2007 "Determination of resistance to neutral salt spray of paints and varnishes".

[0044] Example 1: Preparation of a low-temperature, moisture-induced corrosion inhibitor and curing agent:

[0045] 1-Benzyl-2-thiourea and ethylenediamine were added to a 100 mL three-necked flask in a molar ratio of 2:1, with carbon tetrachloride as the solvent. The flask was then placed in a jacketed magnetic stirrer, and the stirrer, water separator, and condenser were connected. The stirrer was turned on and the reaction was carried out at 80°C for 3 hours. The product was then discharged to obtain a low-temperature moisture curing agent.

[0046] A low-temperature moisture curing agent was mixed with epoxy resin in an equimolar ratio and applied to a steel surface with a water film adhering to it. The surface drying and hard drying speeds, paint film adhesion, and salt spray resistance were then tested.

[0047] Examples 2-7

[0048] The preparation method of the curing agent and the test method of the paint film performance are basically the same as those in Example 1. The formula table and reaction conditions are detailed in Table 1, and the test paint film performance parameters are shown in Table 2.

[0049] Table 1. Process parameters for preparing curing agents in Examples 1-5

[0050]

[0051] Preparation of Low-Temperature Curing Agent (Comparative Example 1)

[0052] A low-temperature curing agent was prepared according to the method of Example 4 disclosed in patent CN101747205A. The low-temperature curing agent was mixed with epoxy resin in an equimolar ratio and applied to a steel surface with a water film adhering to it. The surface drying speed, hard drying speed, paint film adhesion, and salt spray resistance were then tested.

[0053] Comparative Example 2: Preparation of Moisture Curing Agent

[0054] Add MIBK and 1,3-BAC in a molar ratio of 2:1 to the 100mL three-necked flask, with toluene as the solvent. Place the three-necked flask in a jacketed magnetic stirrer, connect the stirrer, water separator and condenser, turn on the stirrer and stir, control the reaction at 80℃ for 3h, and discharge the material to obtain the curing agent under humid conditions.

[0055] The above curing agent was mixed with epoxy resin in an equimolar ratio and applied to the surface of steel with a water film adhering to it. The surface drying and hard drying speeds, paint film adhesion and salt spray resistance were then tested.

[0056] Table 2. Coating film performance test data for the examples and comparative examples.

[0057]

[0058]

[0059] Although the present invention has been described in detail through the preferred embodiments described above, it should be understood that the above description should not be considered as a limitation of the present invention. Those skilled in the art will understand that modifications or adjustments can be made to the present invention based on the teachings of this specification. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A corrosion-inhibiting epoxy resin curing agent for use in low-temperature and humid environments, characterized in that, The structure is shown in equation (I): Wherein: R is selected from C2-C12 straight-chain or branched alkyl groups; R1 is selected from --CH3 or R2 is selected from R3 is selected from H or Furthermore, at least one of R1, R2, and R3 has a benzene ring structure.

2. The epoxy resin curing agent for corrosion inhibition in low-temperature and humid environments as described in claim 1, characterized in that, R is a C2-C6 straight-chain or branched alkyl group.

3. The preparation method of the corrosion-inhibiting epoxy resin curing agent for low-temperature and humid environments as described in claim 1 or 2, characterized in that, The compound with the structure shown in formula (II) is prepared by reacting it with the compound with the structure shown in formula (III). H2N-R-NH2 Formula (II) Among them, R, R1, R2, and R3 are the same as in equation (I).

4. The preparation method according to claim 3, characterized in that, The compound with the structure shown in formula (III) is selected from any one of 1-benzyl-2-thiourea, 1-benzoyl-3-phenylthiourea, N-(4-acetylphenyl)thiourea, and 1-(3-acetylphenyl)-2-thiourea.

5. The preparation method according to claim 3, characterized in that, The molar ratio of the compound with the structure shown in formula (II) to the compound with the structure shown in formula (III) is 1:1.9-2.

1.

6. The preparation method according to claim 5, characterized in that, The molar ratio of the compound with the structure shown in formula (II) to the compound with the structure shown in formula (III) is 1:1.95-2.

05.

7. The preparation method according to claim 3, characterized in that, At room temperature, a solution containing the compound with the structure shown in formula (II) and the compound with the structure shown in formula (III) is added to a reaction vessel, nitrogen is used to purge the mixture, the reaction vessel is heated to the reaction temperature, and after the reaction, cooling water is introduced to cool it down to obtain the product.

8. The preparation method according to claim 7, characterized in that, The solvent for dissolving the compound with the structure shown in formula (II) and the compound with the structure shown in formula (III) is at least one of carbon tetrachloride, ethyl acetate, butanone, toluene, and xylene.

9. The preparation method according to claim 3, characterized in that, The reaction temperature is 30-120℃.

10. The preparation method according to claim 9, characterized in that, The reaction temperature is 50-110℃.

11. The preparation method according to claim 3, characterized in that, The reaction time is 0.5h-10h.

12. The preparation method according to claim 11, characterized in that, The reaction time is 2-5 hours.

13. The application of the corrosion-inhibiting epoxy resin curing agent for low-temperature and humid environments as described in claim 1 or 2, or the epoxy resin curing agent for low-temperature and humid environments prepared by any one of claims 3 to 12, in curing epoxy resin in low-temperature and humid environments.

14. The application of the corrosion-inhibiting epoxy resin curing agent according to claim 13 for curing epoxy resin in a low-temperature and humid environment, characterized in that, Used for painting large steel structures.

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