Water-based modified amine curing agent and preparation method thereof

Abstract

The preparation method comprises the following steps: epoxidizing cardanol, sulfonating the epoxidized cardanol by using sodium hydrogen sulfite as a sulfonating agent, and carrying out Mannich reaction on the sulfonated modified cardanol, polyamine, silane coupling agent KH-550 modified nano silicon dioxide and formaldehyde to obtain the waterborne modified amine curing agent. The water-based modified amine curing agent is obtained. The water-based modified amine curing agent is suitable for a water-based epoxy coating system and has the advantages of being good in dispersity and high in curing speed, and a coating formed after curing has excellent mechanical performance and corrosion resistance.

Description

Technical Field

[0001] The invention relates to the technical field of waterborne epoxy curing agents, and in particular to a waterborne modified amine curing agent and a preparation method thereof. Background Art

[0002] Epoxy coatings are a type of coating with epoxy resin as the main film-forming resin, which is widely used in industrial and civil fields. In recent years, with the enhancement of safety, health and environmental awareness, the research and development of water-based epoxy coatings without organic solvents and low VOC values ​​has received more and more attention. Epoxy resin curing agent is an important component in the epoxy coating system. Its function is to promote the curing reaction of epoxy resin and transform the linear epoxy resin into a coating with a cross-linked structure. The curing agent used in water-based epoxy coatings has a crucial influence on the performance of the coating. At present, polyamine curing agents are mainly used in water-based epoxy coatings, but unmodified polyamine curing agents have the problems of long curing time, poor water resistance and low hardness of the coating. Cardanol is a type of phenolic substance extracted from cashew nut shell oil. Modification of polyamine curing agents with cardanol can shorten the curing time of epoxy resin and improve the water resistance and hardness of the coating. However, cardanol-modified polyamine curing agents often have the problem of poor water solubility and are not suitable for water-based epoxy coating systems. Moreover, cardanol introduces more long-chain aliphatic side chains into the system, which reduces the cross-linking density of the system, and its effect on improving the mechanical strength and corrosion resistance of the coating is limited. Summary of the invention

[0003] Based on the technical problems existing in the background technology, the present invention proposes a water-based modified amine curing agent and a preparation method thereof.

[0004] The present invention provides a method for preparing a water-based modified amine curing agent, comprising the following steps:

[0005] S1, adding cardanol, an acid catalyst and a cation exchange resin catalyst to a solvent and mixing them evenly, then dropping hydrogen peroxide to carry out an epoxidation reaction, standing and stratifying after the reaction is completed, removing the aqueous phase, and distilling the obtained organic phase under reduced pressure to obtain epoxidized cardanol;

[0006] S2, mixing the epoxidized cardanol with an aqueous sodium bisulfite solution and performing a sulfonation reaction, and performing reduced pressure distillation after the reaction is completed to obtain a sulfonated modified cardanol;

[0007] S3, uniformly mixing the sulfonated modified cardanol with polyamine and silane coupling agent KH-550 modified nano-silica, then dropping formaldehyde aqueous solution to carry out Mannich reaction, and performing reduced pressure distillation after the reaction is completed to obtain a water-based modified amine curing agent.

[0008] Preferably, in S1, the mass ratio of cardanol, acid catalyst and cation exchange resin catalyst is 1:0.05-0.15:0.01-0.02; the acid catalyst is formic acid, acetic acid or a combination thereof.

[0009] Preferably, in S1, the mass ratio of cardanol to hydrogen peroxide is 1:0.4-1.

[0010] Preferably, in S1, the epoxidation reaction is carried out at a temperature of 50 to 60°C and for a time of 2 to 6 hours.

[0011] Preferably, in S2, the mass ratio of the epoxidized cardanol to sodium bisulfite is 1:0.2-0.3; and the mass concentration of the sodium bisulfite aqueous solution is 30-40%.

[0012] Preferably, in S1, the solvent is ethanol.

[0013] Preferably, in S2, the temperature of the sulfonation reaction is 60-95° C., and the time is 3-8 hours.

[0014] Preferably, in S3, the mass ratio of the sulfonated modified cardanol to the polyamine and the silane coupling agent KH-550 modified nano-silica is 1: 0.2-0.3: 0.02-0.05; and the polyamine is at least one of diethylenetriamine, triethylenetetramine and tetraethylenepentamine.

[0015] The silane coupling agent KH-550 modified nano-silica is obtained by modifying nano-silica with the silane coupling agent KH-550; preferably, the mass ratio of the silane coupling agent KH-550 to the nano-silica is 1 to 3:1.

[0016] In the present invention, the specific method of modifying nano-silica with silane coupling agent KH-550 to obtain nano-silica modified with silane coupling agent KH-550 is not limited, and conventional methods in the art can be used. For example, the silane coupling agent KH-550 is added to ethanol, stirred for 0.5 to 2 hours, and then the nano-silica is added and ultrasonically dispersed uniformly, stirred and reacted at 50 to 60° C. for 2 to 5 hours, and then centrifuged and dried to obtain the nano-silica.

[0017] Preferably, in S3, the mass ratio of the sulfonated modified cardanol to formaldehyde is 1:0.2-0.3; and the mass concentration of the formaldehyde aqueous solution is 35-40%.

[0018] Preferably, in S3, the temperature of the Mannich reaction is 70-90° C., and the time is 5-8 h.

[0019] A water-based modified amine curing agent is prepared by the preparation method.

[0020] The beneficial effects of the present invention are as follows:

[0021] The present invention first epoxidizes the unsaturated long side chain of cardanol, and then sulfonates and modifies it. The obtained sulfonated modified cardanol is subjected to Mannich reaction with polyamine and silane coupling agent KH-550 modified nano-silica, wherein the sulfonated cardanol reacts with the polyamine to form a sulfonated cardanol modified polyamine curing agent, and the nano-silica forms nano-silica grafted with sulfonated cardanol through the reaction of surface amino groups with the sulfonated cardanol, thereby obtaining a water-based modified amine curing agent. In the curing agent, the sulfonated modified cardanol has good emulsification and dispersibility, so that it has good compatibility with the water-based epoxy coating system, and the nano-silica grafted with sulfonated cardanol is uniformly dispersed in the curing agent, and can also participate in the curing reaction of the epoxy resin, which can improve the cross-linking density of the epoxy resin, thereby further improving the mechanical strength and corrosion resistance of the formed coating. The water-based modified amine curing agent of the present invention is suitable for a water-based epoxy coating system, has the characteristics of good dispersibility and fast curing speed, and the coating formed after curing has excellent mechanical properties and anti-corrosion properties. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is described in detail below through specific embodiments.

[0023] In the following examples, the cation exchange resin catalyst used is 732 type strong acid styrene cation exchange resin; the particle size of nano-silicon dioxide is 20 to 50 nm.

[0024] Example 1

[0025] A water-based modified amine curing agent, the preparation method of which comprises the following steps:

[0026] S1. Add cardanol, acetic acid and cation exchange resin catalyst into ethanol at a mass ratio of 1:0.1:0.015 and mix well. Then, dropwise add hydrogen peroxide and react at 60°C for 5 hours. After the reaction is completed, stand and separate, remove the aqueous phase, and distill the obtained organic phase under reduced pressure to obtain epoxidized cardanol, wherein the mass ratio of cardanol to hydrogen peroxide is 1:0.8;

[0027] S2, mixing epoxidized cardanol with a 35% sodium bisulfite aqueous solution, reacting at 90° C. for 6 h, and distilling under reduced pressure after the reaction to obtain sulfonated modified cardanol, wherein the mass ratio of epoxidized cardanol to sodium bisulfite is 1:0.25;

[0028] S3. Evenly mix the sulfonated modified cardanol with diethylenetriamine and nano-silica modified by silane coupling agent KH-550 in a mass ratio of 1:0.24:0.04, then drop a 37% formaldehyde aqueous solution, react at 80°C for 6 hours, and perform reduced pressure distillation after the reaction to obtain a water-based modified amine curing agent, wherein the mass ratio of the sulfonated modified cardanol to formaldehyde is 1:0.25.

[0029] The preparation method of silane coupling agent KH-550 modified nano-silica is as follows: add silane coupling agent KH-550 to ethanol, stir for 1 hour, then add nano-silica for ultrasonic dispersion, stir and react at 55°C for 3 hours, centrifuge and dry to obtain, wherein the mass ratio of silane coupling agent KH-550 to nano-silica is 2:1.

[0030] Example 2

[0031] A water-based modified amine curing agent, the preparation method of which comprises the following steps:

[0032] S1. Add cardanol, acetic acid and cation exchange resin catalyst into ethanol at a mass ratio of 1:0.05:0.01 and mix well. Then, dropwise add hydrogen peroxide and react at 50°C for 6 hours. After the reaction is completed, stand and separate, remove the aqueous phase, and distill the obtained organic phase under reduced pressure to obtain epoxidized cardanol, wherein the mass ratio of cardanol to hydrogen peroxide is 1:0.4;

[0033] S2, mixing epoxidized cardanol with a 30% sodium bisulfite aqueous solution, reacting at 60° C. for 8 h, and distilling under reduced pressure after the reaction to obtain sulfonated modified cardanol, wherein the mass ratio of epoxidized cardanol to sodium bisulfite is 1:0.2;

[0034] S3. Evenly mix the sulfonated modified cardanol with diethylenetriamine and nano-silica modified by silane coupling agent KH-550 in a mass ratio of 1:0.2:0.05, then drop a 37% formaldehyde aqueous solution, react at 70°C for 8h, and perform reduced pressure distillation after the reaction to obtain a water-based modified amine curing agent, wherein the mass ratio of the sulfonated modified cardanol to formaldehyde is 1:0.2.

[0035] The preparation method of silane coupling agent KH-550 modified nano-silica is as follows: add silane coupling agent KH-550 to ethanol, stir for 1 hour, then add nano-silica for ultrasonic dispersion, stir and react at 55°C for 3 hours, centrifuge and dry to obtain, wherein the mass ratio of silane coupling agent KH-550 to nano-silica is 2:1.

[0036] Example 3

[0037] A water-based modified amine curing agent, the preparation method of which comprises the following steps:

[0038] S1. Add cardanol, acetic acid and cation exchange resin catalyst into ethanol at a mass ratio of 1:0.15:0.02 and mix well. Then, dropwise add hydrogen peroxide and react at 60°C for 2h. After the reaction, stand and separate, remove the aqueous phase, and distill the obtained organic phase under reduced pressure to obtain epoxidized cardanol, wherein the mass ratio of cardanol to hydrogen peroxide is 1:1.

[0039] S2, mixing epoxidized cardanol with a 40% sodium bisulfite aqueous solution, reacting at 95° C. for 3 h, and distilling under reduced pressure after the reaction to obtain sulfonated modified cardanol, wherein the mass ratio of epoxidized cardanol to sodium bisulfite is 1:0.3;

[0040] S3. Evenly mix the sulfonated modified cardanol with diethylenetriamine and nano-silica modified by silane coupling agent KH-550 in a mass ratio of 1:0.3:0.02, then drop a 37% formaldehyde aqueous solution, react at 90°C for 5 hours, and perform reduced pressure distillation after the reaction to obtain a water-based modified amine curing agent, wherein the mass ratio of the sulfonated modified cardanol to formaldehyde is 1:0.3.

[0041] The preparation method of silane coupling agent KH-550 modified nano-silica is as follows: add silane coupling agent KH-550 to ethanol, stir for 1 hour, then add nano-silica for ultrasonic dispersion, stir and react at 55°C for 3 hours, centrifuge and dry to obtain, wherein the mass ratio of silane coupling agent KH-550 to nano-silica is 2:1.

[0042] Comparative Example 1

[0043] A water-based modified amine curing agent, the preparation method of which comprises the following steps:

[0044] S1. Add cardanol, acetic acid and cation exchange resin catalyst into ethanol at a mass ratio of 1:0.1:0.015 and mix well. Then, dropwise add hydrogen peroxide and react at 60°C for 5 hours. After the reaction is completed, stand and separate, remove the aqueous phase, and distill the obtained organic phase under reduced pressure to obtain epoxidized cardanol, wherein the mass ratio of cardanol to hydrogen peroxide is 1:0.8;

[0045] S2, mixing epoxidized cardanol with a 35% sodium bisulfite aqueous solution, reacting at 90° C. for 6 h, and distilling under reduced pressure after the reaction to obtain sulfonated modified cardanol, wherein the mass ratio of epoxidized cardanol to sodium bisulfite is 1:0.25;

[0046] S3. Evenly mix the sulfonated modified cardanol and diethylenetriamine at a mass ratio of 1:0.28, then drop a 37% formaldehyde aqueous solution, react at 80°C for 6 hours, and perform reduced pressure distillation after the reaction to obtain a water-based modified amine curing agent, wherein the mass ratio of the sulfonated modified cardanol to formaldehyde is 1:0.25.

[0047] Test example

[0048] The waterborne epoxy coating was prepared according to the following formula (by mass): 45 parts of Hexion waterborne epoxy emulsion EP6520, 5 parts of waterborne curing agent, 16 parts of 1250 mesh barium sulfate, 12 parts of talc, 6 parts of 1250 mesh sericite powder, 2 parts of propylene glycol methyl ether, 2 parts of dipropylene glycol butyl ether, 1 part of RCL-1500 anti-settling agent, 1 part of BYK-190 dispersant, 0.3 parts of BYK-024 defoamer, 1.5 parts of TEGO3030 thickener, 0.2 parts of TEGO270 wetting agent, and 15 parts of deionized water. Among them, the waterborne curing agent used the waterborne modified amine curing agent in Example 1 and Comparative Example 1 respectively. The performance test results of the waterborne epoxy coating obtained by using the waterborne modified amine curing agent in Example 1 and Comparative Example 1 are shown in Table 1:

[0049] Table 1

[0050]

[0051] According to the test results, it can be seen that the water-based modified amine curing agent of the present invention has excellent corrosion resistance and mechanical strength, fast curing speed, good dispersion stability, and is suitable for water-based epoxy coating systems.

[0052] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a water-based modified amine curing agent, characterized in that: The following steps are involved: S1, adding cardanol, an acid catalyst and a cation exchange resin catalyst to a solvent and mixing them evenly, then dropping hydrogen peroxide to carry out an epoxidation reaction, standing and stratifying after the reaction is completed, removing the aqueous phase, and distilling the obtained organic phase under reduced pressure to obtain epoxidized cardanol; S2, mixing the epoxidized cardanol with an aqueous sodium bisulfite solution and performing a sulfonation reaction, and performing reduced pressure distillation after the reaction is completed to obtain a sulfonated modified cardanol; S3, uniformly mixing the sulfonated modified cardanol with polyamine and silane coupling agent KH-550 modified nano-silica, then dropping formaldehyde aqueous solution to carry out Mannich reaction, and performing reduced pressure distillation after the reaction is completed to obtain a water-based modified amine curing agent.

2. The method for preparing a water-based modified amine curing agent according to claim 1, characterized in that: In S1, the mass ratio of cardanol, acid catalyst and cation exchange resin catalyst is 1:0.05-0.15:0.01-0.02; the acid catalyst is formic acid, acetic acid or a combination thereof.

3. The method for preparing a water-based modified amine curing agent according to claim 1, characterized in that: In S1, the mass ratio of cardanol to hydrogen peroxide is 1:0.4-1.

4. The method for preparing a water-based modified amine curing agent according to claim 1, characterized in that: In S1, the epoxidation reaction temperature is 50-60°C and the time is 2-6 hours.

5. The method for preparing a water-based modified amine curing agent according to claim 1, characterized in that: In S2, the mass ratio of the epoxidized cardanol to sodium bisulfite is 1:0.2-0.3; and the mass concentration of the sodium bisulfite aqueous solution is 30-40%.

6. The method for preparing a water-based modified amine curing agent according to claim 1, characterized in that: In S2, the sulfonation reaction is carried out at a temperature of 60 to 95°C and for a time of 3 to 8 hours.

7. The method for preparing a water-based modified amine curing agent according to claim 1, characterized in that: In S3, the mass ratio of the sulfonated modified cardanol to the polyamine and the silane coupling agent KH-550 modified nano-silica is 1:0.2-0.3:0.02-0.05; the polyamine is at least one of diethylenetriamine, triethylenetetramine and tetraethylenepentamine.

8. The method for preparing a water-based modified amine curing agent according to claim 1, characterized in that: In S3, the mass ratio of the sulfonated modified cardanol to formaldehyde is 1:0.2-0.3; and the mass concentration of the formaldehyde aqueous solution is 35-40%.

9. The method for preparing a water-based modified amine curing agent according to claim 1, characterized in that: In S3, the temperature of the Mannich reaction is 70-90° C., and the time is 5-8 hours.

10. A water-based modified amine curing agent, characterized in that: The method is prepared according to any one of claims 1 to 9.

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