A water-based modified amine curing agent and preparation method thereof

Abstract

The invention discloses a water-based modified amine curing agent and a preparation method thereof. Cardanol is first epoxidized, then sodium bisulfite is used as a sulfonating agent to sulfonate the epoxidized cardanol, and then the sulfonated modified cardanol, polyamine, silane coupling agent KH-550 modified nano-silica and formaldehyde are subjected to a Mannich reaction to obtain a water-based modified amine curing agent. 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.

Description

Technical Field

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

[0002] Epoxy coatings are a type of coating based on epoxy resin as the primary film-forming resin and are widely used in both industrial and residential applications. In recent years, with growing awareness of safety, health, and environmental protection, the development of waterborne epoxy coatings that are solvent-free and low in VOC has garnered increasing attention. Epoxy resin curing agents are crucial components in epoxy coating systems, promoting the curing reaction of the epoxy resin, transforming the linear structure into a cross-linked coating. The curing agent used in waterborne epoxy coatings has a crucial impact on the performance of the coating. Currently, polyamine curing agents are primarily used in waterborne epoxy coatings. However, unmodified polyamine curing agents suffer from long curing times, poor water resistance, and low film hardness. Cardanol, a phenolic compound extracted from cashew nut shell liquid, can be modified with cardanol to shorten the curing time of epoxy resins and improve the water resistance and hardness of the coating. However, cardanol-modified polyamine curing agents often suffer from poor water solubility, making them unsuitable for waterborne epoxy coating systems. Moreover, cardanol introduces a large number of 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 adding hydrogen peroxide dropwise to carry out an epoxidation reaction, and after the reaction is completed, standing and stratifying, 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 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 dropwise adding formaldehyde aqueous solution to carry out Mannich reaction, and performing reduced pressure distillation after the reaction 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 temperature is 50-60° C., and the time is 2-6 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 sulfonation reaction is carried out at a temperature of 60 to 95° C. and for a time of 3 to 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 nano-silica modified with silane coupling agent KH-550 is obtained by modifying nano-silica with silane coupling agent KH-550; preferably, the mass ratio of the silane coupling agent KH-550 to nano-silica is 1 to 3:1.

[0016] In the present invention, the specific method for modifying nano-silica with the silane coupling agent KH-550 to obtain the silane coupling agent KH-550-modified nano-silica is not limited, and conventional methods in the art can be used. For example, the silane coupling agent KH-550 can be added to ethanol and stirred for 0.5 to 2 hours, then the nano-silica is added and ultrasonically dispersed uniformly, and the mixture is stirred at 50 to 60° C. for 2 to 5 hours, followed by centrifugation and drying 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 chains of cardanol and then sulfonates and modifies them. The resulting sulfonated modified cardanol undergoes a Mannich reaction with a polyamine and nano-silica modified with a silane coupling agent KH-550. The sulfonated cardanol reacts with the polyamine to form a sulfonated cardanol-modified polyamine curing agent. The nano-silica reacts with the sulfonated cardanol through surface amino groups to form nano-silica grafted with the sulfonated cardanol, thereby obtaining a water-based modified amine curing agent. The sulfonated modified cardanol in this curing agent has good emulsification and dispersibility, making it highly compatible with water-based epoxy coating systems. The nano-silica grafted with the sulfonated cardanol is evenly dispersed in the curing agent and can also participate in the curing reaction of the epoxy resin, thereby increasing the crosslinking density of the epoxy resin and further enhancing the mechanical strength and corrosion resistance of the resulting 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 the nano-silica 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. Cardanol, acetic acid, and a cation exchange resin catalyst were added to ethanol in a mass ratio of 1:0.1:0.015 and mixed evenly. Then, hydrogen peroxide was added dropwise and reacted at 60° C. for 5 h. After the reaction, the mixture was allowed to stand and stratify, the aqueous phase was removed, and the obtained organic phase was distilled under reduced pressure to obtain epoxidized cardanol, wherein the mass ratio of cardanol to hydrogen peroxide was 1:0.8;

[0027] S2. Mixing epoxidized cardanol with a 35% aqueous sodium bisulfite solution, reacting the mixture at 90° C. for 6 h, and performing reduced pressure distillation 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 dropwise add 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: adding silane coupling agent KH-550 to ethanol, stirring for 1 hour, then adding nano-silica and ultrasonically dispersing it evenly, stirring and reacting at 55°C for 3 hours, centrifuging and drying to obtain the product, 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. Cardanol, acetic acid, and a cation exchange resin catalyst were added to ethanol in a mass ratio of 1:0.05:0.01 and mixed evenly. Then, hydrogen peroxide was added dropwise and reacted at 50° C. for 6 h. After the reaction, the mixture was allowed to stand for stratification, the aqueous phase was removed, and the obtained organic phase was distilled under reduced pressure to obtain epoxidized cardanol, wherein the mass ratio of cardanol to hydrogen peroxide was 1:0.4;

[0033] S2. Mixing epoxidized cardanol with a 30% aqueous sodium bisulfite solution, reacting the mixture at 60° C. for 8 h, and performing reduced pressure distillation 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 dropwise add a 37% formaldehyde aqueous solution, react at 70°C for 8 hours, and distill under reduced pressure after the reaction to obtain a water-based modified amine curing agent, wherein the mass ratio of 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: adding silane coupling agent KH-550 to ethanol, stirring for 1 hour, then adding nano-silica and ultrasonically dispersing it evenly, stirring and reacting at 55°C for 3 hours, centrifuging and drying to obtain the product, 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. Cardanol, acetic acid, and a cation exchange resin catalyst were added to ethanol in a mass ratio of 1:0.15:0.02 and mixed evenly. Then, hydrogen peroxide was added dropwise and reacted at 60° C. for 2 h. After the reaction, the mixture was allowed to stand for stratification, the aqueous phase was removed, and the obtained organic phase was distilled under reduced pressure to obtain epoxidized cardanol, wherein the mass ratio of cardanol to hydrogen peroxide was 1:1;

[0039] S2. Mixing epoxidized cardanol with a 40% aqueous sodium bisulfite solution, reacting the mixture at 95° C. for 3 h, and performing reduced pressure distillation 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 dropwise add a 37% formaldehyde aqueous solution, and react at 90°C for 5 hours. After the reaction is completed, perform reduced pressure distillation to obtain a water-based modified amine curing agent, wherein the mass ratio of 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: adding silane coupling agent KH-550 to ethanol, stirring for 1 hour, then adding nano-silica and ultrasonically dispersing it evenly, stirring and reacting at 55°C for 3 hours, centrifuging and drying to obtain the product, 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. Cardanol, acetic acid, and a cation exchange resin catalyst were added to ethanol in a mass ratio of 1:0.1:0.015 and mixed evenly. Then, hydrogen peroxide was added dropwise and reacted at 60° C. for 5 h. After the reaction, the mixture was allowed to stand and stratify, the aqueous phase was removed, and the obtained organic phase was distilled under reduced pressure to obtain epoxidized cardanol, wherein the mass ratio of cardanol to hydrogen peroxide was 1:0.8;

[0045] S2. Mixing epoxidized cardanol with a 35% aqueous sodium bisulfite solution, reacting the mixture at 90° C. for 6 h, and performing reduced pressure distillation 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 dropwise add a 37% formaldehyde aqueous solution, and react at 80°C for 6 hours. After the reaction is completed, perform reduced pressure distillation 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] A water-based epoxy coating was prepared according to the following formula (by mass): 45 parts of Hexion water-based epoxy emulsion EP6520, 5 parts of water-based 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 water-based curing agent used was the water-based modified amine curing agent in Example 1 and Comparative Example 1 respectively. The performance test results of the water-based epoxy coatings obtained using the water-based modified amine curing agents in Example 1 and Comparative Example 1 are shown in Table 1:

[0049] Table 1

[0050]

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

[0052] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection 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 adding hydrogen peroxide dropwise to carry out an epoxidation reaction, and after the reaction is completed, standing and stratifying, removing the aqueous phase, and distilling the obtained organic phase under reduced pressure to obtain epoxidized cardanol; S2, mixing the epoxidized cardanol with a sodium bisulfite aqueous solution having a mass concentration of 30-40% and performing a sulfonation reaction, and performing reduced pressure distillation after the reaction to obtain sulfonated modified cardanol, wherein the mass ratio of epoxidized cardanol to sodium bisulfite is 1:0.2-0.3, the sulfonation reaction temperature is 60-95° C., and the time is 3-8 h; S3. Evenly mix the sulfonated modified cardanol with polyamine and nano-silica modified with silane coupling agent KH-550, then dropwise add formaldehyde aqueous solution to carry out Mannich reaction, and perform reduced pressure distillation after the reaction to obtain a water-based modified amine curing agent; the mass ratio of the sulfonated modified cardanol to polyamine and nano-silica modified with silane coupling agent KH-550 is 1:0.2-0.3:0.02-0.

05.

2. The method for preparing a water-based modified amine curing agent according to claim 1, wherein 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 preparation method of the 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 preparation method of the 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, wherein In S3, the polyamine is at least one of diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

6. The method for preparing a water-based modified amine curing agent according to claim 1, wherein: 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%.

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

8. A water-based modified amine curing agent, characterized in that The invention is prepared by the preparation method according to any one of claims 1 to 7.

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