Waterborne epoxy curing agent as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of curing agents, and particularly relates to a waterborne epoxy curing agent as well as a preparation method and application thereof. The water-based epoxy curing agent is prepared from the following raw materials: polyamine, epoxy resin, an epoxy prepolymer and alkyl polyoxyethylene epoxy ether. The functionality of the epoxy prepolymer is greater than 2. By introducing the epoxy prepolymer with specific functionality and the hydrophilic alkyl polyoxyethylene epoxy ether into an epoxy curing agent system, the surface tension of the system can be greatly reduced, so that the epoxy curing agent has good wetting dispersity and storage stability. The epoxy curing agent contains a branched structure, can be stably dispersed in water, and has better compatibility with epoxy emulsion, so that the epoxy coating can be cured at room temperature and is high in drying speed, and the coating has good flexibility, adhesive force, water resistance and salt fog resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of curing agents, and particularly relates to an aqueous epoxy curing agent, a preparation method thereof, and an application thereof. Background Art

[0002] Waterborne epoxy coatings are an environmentally friendly type of coating. Due to their low odor, low toxicity, easy construction, excellent adhesion, and good chemical resistance, they are increasingly favored by people. As an important part of waterborne epoxy coatings, the composition and structure of epoxy curing agents play a decisive role in the physical and chemical properties of waterborne epoxy coatings.

[0003] Currently, common waterborne epoxy curing agent products are mainly modified with polyamines. For synthetic research, waterborne epoxy curing agents can be divided into ionic and non-ionic types. Ionic curing agents generally modify polyamines with epoxy resins to generate polyamine-epoxy adducts, improving the compatibility of the curing agent with another epoxy resin component, and adding acid to neutralize and form salts, thereby enhancing the water solubility and water dispersion ability of the curing agent. Ionic curing agents are sensitive to the pH of the system. When formulating coatings by adding pigments and fillers, they are prone to losing stability. Non-ionic curing agents regulate the hydrophilicity of epoxy-polyamine adducts by introducing non-ionic hydrophilic segments, avoiding the disadvantages brought by adding acids in ionic curing agents. However, the curing agents prepared by such methods are mostly linear polymers, with limited structural designability. After mixing with waterborne epoxy resins, the toughness of the coating film is insufficient, and defects are prone to occur during the film-forming process, resulting in problems such as blistering of the coating, reduced adhesion, and even peeling off from the substrate.

[0004] In the process of coating production, the wetting and dispersion of pigments and fillers is a very important production link, which is directly related to the storage, construction, appearance, and performance of the coating. Currently, most waterborne epoxy curing agents on the market have poor wetting and dispersion effects. During the coating preparation process, it is often necessary to additionally add wetting and dispersing agents to improve the dispersion efficiency of pigments and fillers and shorten the grinding time. However, this not only increases costs but also increases the process flow and reduces production efficiency.

[0005] Therefore, there is an urgent need to provide an epoxy curing agent that has good wetting and dispersion effects, can reduce or even avoid the use of wetting and dispersing agents, reduce costs, and at the same time can improve the toughness, water resistance, and adhesion of the resulting coating. Summary of the Invention

[0006] The present invention aims to solve one or more of the above-mentioned technical problems existing in the prior art and at least provide a beneficial option. Specifically, the present invention provides an aqueous epoxy curing agent that has good wetting and dispersion effects, can reduce or even avoid the use of wetting and dispersing agents, reduce costs; and at the same time can improve the toughness, water resistance, and adhesion of the resulting coating.

[0007] Inventive concept of the present invention: The raw materials for preparing the epoxy curing agent of the present invention include polyamine, epoxy resin, epoxy prepolymer, and alkyl polyoxyethylene epoxy ether; the functionality of the epoxy prepolymer is greater than 2. By introducing an epoxy prepolymer with a specific functionality and a hydrophilic alkyl polyoxyethylene epoxy ether into the epoxy curing agent system of the present invention, an amphiphilic (hydrophilic and lipophilic) macromolecule with a long-chain branched structure can be obtained, which can greatly reduce the surface tension of the system and make it easier for pigments and fillers to be wetted and dispersed. At the same time, the long-chain branched molecular structure can coat the pigment and filler particles or increase the steric hindrance, thereby preventing the aggregation and sedimentation of pigment and filler particles, improving the dispersibility of pigments and fillers, and enabling the epoxy curing agent to have both wetting and dispersing effects. During the actual use of waterborne coatings, when the epoxy curing agent is co-ground with pigments and fillers, less or even no wetting and dispersing agent needs to be added, which can shorten the grinding time, improve the grinding efficiency, and reduce costs. Moreover, due to the reduction or even non-use of the wetting and dispersing agent, the negative impacts of the use of the wetting and dispersing agent on the gloss, durability, and adhesion of the coating can be reduced. In addition, the waterborne epoxy curing agent of the present invention contains a branched structure and can be stably dispersed in water. When combined with another component, epoxy emulsion, in the epoxy coating, it has good compatibility, making the epoxy coating easy to cure at room temperature and having a fast drying speed, and can improve the flexibility, adhesion, and salt spray resistance of the coating. Furthermore, the synergistic advantages of the Si-O-Si cyclic structure and benzene ring structure in the epoxy curing agent not only endow the finally prepared coating with the high hardness and strength of epoxy resin but also the good toughness and dense structure of branched polymers, making the coating have good anti-corrosion ability, adhesion, water resistance, and flexibility.

[0008] Therefore, in the first aspect of the present invention, a waterborne epoxy curing agent is provided.

[0009] Specifically, the raw materials for preparing the waterborne epoxy curing agent include polyamine, epoxy resin, epoxy prepolymer, and alkyl polyoxyethylene epoxy ether;

[0010] The functionality of the epoxy prepolymer is greater than 2.

[0011] Preferably, the functionality of the epoxy prepolymer is 3 - 6.

[0012] More preferably, the functionality of the epoxy prepolymer is 4.

[0013] Preferably, the polyamine includes at least one of diethylenetriamine, ethylenediamine, triethylenetetramine, tetraethylenepentamine, m-xylenediamine, isophoronediamine, 1,2-propanediamine, 1,3-propanediamine, 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, cyclohexanediamine.

[0014] Preferably, the epoxy resin includes at least one of phenolic epoxy resin, bisphenol A epoxy resin, and bisphenol F epoxy resin; more preferably, the epoxy resin includes at least one of epoxy resin E51, epoxy resin E44, and epoxy resin E20.

[0015] Preferably, the epoxy equivalent of the epoxy resin is 150 - 550 g / eq; more preferably, the epoxy equivalent of the epoxy resin is 180 - 500 g / eq.

[0016] Preferably, the epoxy group prepolymer includes at least one of epoxy group organosilicon prepolymer and trimethylolpropane triglycidyl ether; more preferably, the epoxy group prepolymer is epoxy group organosilicon prepolymer; even more preferably, the epoxy group organosilicon prepolymer is selected from at least one of Silok3597 and Silok3590F4 of Guangzhou Silok Polymer Co., Ltd.

[0017] The structural formula of the epoxy group organosilicon prepolymer is:

[0018]

[0019] Preferably, the alkyl polyoxyethylene epoxy ether includes methyl polyoxyethylene epoxy ether.

[0020] Preferably, the weight average molecular weight of the alkyl polyoxyethylene epoxy ether is 270 - 4500; more preferably, the weight average molecular weight of the alkyl polyoxyethylene epoxy ether is 300 - 4000.

[0021] Preferably, the aqueous epoxy curing agent further includes a solvent, and by weight, the preparation raw materials of the aqueous epoxy curing agent include 4.5 - 40 parts of polyamine, 9 - 55 parts of epoxy resin, 3.5 - 28 parts of epoxy group prepolymer, 9 - 33 parts of alkyl polyoxyethylene epoxy ether, and 18 - 65 parts of solvent.

[0022] More preferably, the aqueous epoxy curing agent further includes a solvent, and by weight, the preparation raw materials of the aqueous epoxy curing agent include 5 - 35 parts of polyamine, 10 - 50 parts of epoxy resin, 4 - 25 parts of epoxy group prepolymer, 10 - 30 parts of alkyl polyoxyethylene epoxy ether, and 20 - 60 parts of solvent.

[0023] Preferably, in the aqueous epoxy curing agent, the ratio of the total molar number of amino groups to the total molar number of epoxy groups is (1.0 - 2.2):1; more preferably, in the aqueous epoxy curing agent, the ratio of the total molar number of amino groups to the total molar number of epoxy groups is (1.2 - 2.0):1.

[0024] The second aspect of the present invention provides a method for preparing the aqueous epoxy curing agent described in the first aspect of the present invention.

[0025] Specifically, the method for preparing the aqueous epoxy curing agent includes the following steps:

[0026] (1) Mix the epoxy resin and polyamine, and react to obtain Intermediate Product 1;

[0027] (2) Mix the epoxy group prepolymer with Intermediate Product 1 obtained in step (1), and react to obtain Intermediate Product 2;

[0028] (3) Mix the alkyl polyoxyethylene epoxy ether with Intermediate Product 2 obtained in step (2), and react to prepare the aqueous epoxy curing agent.

[0029] Specifically, Intermediate Product 1 is an amine-epoxy-amine adduct, and Intermediate Product 2 is a branched modified polymer.

[0030] Preferably, in step (1), the reaction temperature is 50-70 °C, and the reaction time is 1-4 h; more preferably, in step (1), the reaction temperature is 60-65 °C, and the reaction time is 2.5-3.5 h.

[0031] Preferably, in step (1), first heat up the polyamine, and then slowly dropwise add the propylene glycol methyl ether solution of epoxy resin under stirring. After the dropwise addition is completed, react to obtain Intermediate Product 1.

[0032] Preferably, the duration of the dropwise addition is 30-60 min; more preferably, the duration of the dropwise addition is 40-60 min.

[0033] Preferably, in step (2), the reaction temperature is 60-80 °C, and the reaction time is 1-4 h; more preferably, in step (2), the reaction temperature is 65-80 °C, and the reaction time is 2-3 h.

[0034] Preferably, in step (2), slowly dropwise add the epoxy group prepolymer to Intermediate Product 1 obtained in step (1). After the dropwise addition is completed, react to obtain Intermediate Product 2.

[0035] Preferably, the duration of the dropwise addition is 20-40 min; more preferably, the duration of the dropwise addition is 25-40 min.

[0036] Preferably, in step (3), the temperature of the reaction is 60 - 80 °C, and the time of the reaction is 1 - 3 h; more preferably, in step (3), the temperature of the reaction is 65 - 80 °C, and the time of the reaction is 2 - 3 h.

[0037] Preferably, in step (3), the alkyl polyoxyethylene epoxy ether is slowly added dropwise to the intermediate product 2 obtained in step (2), and after the addition is completed, the reaction is carried out to obtain the aqueous epoxy curing agent.

[0038] Preferably, the duration of the dropwise addition is 20 - 40 min; more preferably, the duration of the dropwise addition is 25 - 40 min.

[0039] Preferably, in step (3), after the reaction, a process of adding a solvent is further included.

[0040] Preferably, the solvent is added under stirring, the stirring speed is 1200 - 2500 rpm, and the stirring time is 30 - 60 min; more preferably, the stirring speed is 1500 - 2500 rpm, and the stirring time is 30 - 55 min.

[0041] Preferably, in step (3), after the reaction, a process of removing the organic solvent by vacuum distillation and cooling is further included.

[0042] Preferably, the temperature after cooling is 40 - 60 °C.

[0043] Specifically, after removing the organic solvent by vacuum distillation and cooling, the solvent is added again.

[0044] Specifically, in steps (1) - (3), the reaction time is calculated from the completion of the dropwise addition.

[0045] The third aspect of the present invention provides a coating.

[0046] Specifically, the coating includes the aqueous epoxy curing agent described in the first aspect of the present invention.

[0047] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows:

[0048] (1) In the epoxy curing agent system of the present invention, an epoxy prepolymer with a specific functionality and a hydrophilic alkyl polyoxyethylene epoxy ether are introduced, and an amphiphilic macromolecule with a long-chain branched structure can be obtained, which can greatly reduce the surface tension of the system, making it easier for pigments and fillers to be wetted and dispersed. At the same time, the long-chain branched molecular structure can coat the pigment and filler particles or increase the steric hindrance, thereby preventing the aggregation and sedimentation of pigment and filler particles, improving the dispersibility of pigments and fillers, enabling the epoxy curing agent to have the function of wetting and dispersing, while maintaining the stable state of the system and having good storage stability. During the actual use of waterborne coatings, when the epoxy curing agent is co-ground with pigments and fillers, less or even no wetting and dispersing agent needs to be added, which can shorten the grinding time, improve the grinding efficiency, and reduce costs. Moreover, due to the reduction or even non-use of the wetting and dispersing agent, the negative impacts of the use of the wetting and dispersing agent on the gloss, durability, and adhesion of the coating can be reduced.

[0049] (2) The waterborne epoxy curing agent of the present invention contains a branched structure and can be stably dispersed in water. It has good compatibility with epoxy emulsions, making the epoxy coating easy to cure at room temperature and having a fast drying speed, and can improve the flexibility, adhesion, and salt spray resistance of the paint film. Moreover, the synergistic advantages of the Si-O-Si cyclic structure and the benzene ring structure in the epoxy curing agent not only endow the epoxy coating with the advantages of high hardness and high strength of epoxy resin, but also have the good toughness and dense structure of branched polymers, making the coating have good anti-corrosion ability, adhesion, water resistance, and flexibility.

[0050] (3) The preparation method of the present invention is simple, easy to produce, safe, and environmentally friendly. And the raw materials are selected from commercially available mature raw materials, which are rich in sources, stable in composition, and sufficient in supply, providing quality assurance for the large-scale production and application of waterborne epoxy curing agents. Detailed implementation mode

[0051] In order to make those skilled in the art more clearly understand the technical solutions described in the present invention, the following examples are listed for illustration. It should be noted that the following examples do not limit the scope of protection required by the present invention.

[0052] Unless otherwise specified, the raw materials, reagents, or devices used in the following examples can be obtained from conventional commercial channels or can be obtained by existing known methods.

[0053] Example 1

[0054] A preparation method of a waterborne epoxy curing agent, comprising the following steps:

[0055] (1) Place 24.51 g of m - xylylenediamine, 8.17 g of 1,5 - pentanediamine, 19.63 g of triethylenetetramine, and 4.49 g of diethylenetriamine into a 500 mL three - necked flask equipped with a thermometer, a stirrer, and a condenser reflux tube. While stirring, slowly heat up to 50 °C, and slowly add dropwise a propylene glycol methyl ether solution of 145.45 g of epoxy resin E - 44 with a solid content of 50 wt%. The dropping time is 60 min. After the dropping is completed, keep the temperature at 65 °C and react for 4 h to obtain an amine - epoxy - amine adduct;

[0056] (2) Pour 29.44 g of epoxy - based organosilicon prepolymer Silok 3590F4 (functionality is 4) into a constant - pressure dropping funnel, and slowly add it dropwise to the amine - epoxy - amine adduct obtained in step (1) for 30 min. After the dropping is completed, keep the temperature at 65 °C and react for 2.5 h to obtain a branched - modified polymer;

[0057] (3) Pour 64 g of methyl polyoxyethylene epoxy ether with a molecular weight of 800 (Hangzhou Danwei Technology Co., Ltd.) into a constant - pressure dropping funnel, and slowly add it dropwise to the branched - modified polymer obtained in step (2) for 40 min. After the dropping is completed, react for 2 h under a 75 °C atmosphere, distill off the organic solvent under reduced pressure, cool down to 50 °C, and then add dropwise 103.85 g of deionized water under the stirring condition of 1200 rpm. The dropping is completed in 30 min, and then discharge the product to obtain a light - yellow transparent aqueous epoxy curing agent.

[0058] In Example 1, the solid content of the aqueous epoxy curing agent is 50 wt%, the active hydrogen equivalent is 253 g / eq, and the amine value is 247 mgKOH / g.

[0059] Example 2

[0060] A preparation method of an aqueous epoxy curing agent, comprising the following steps

[0061] (1) Place 24.33 g of isophorone diamine, 12.23 g of cyclohexanediamine, 12.52 g of triethylenetetramine, and 10.02 g of diethylenetriamine into a 500 mL three - necked flask equipped with a thermometer, a stirrer, and a condenser reflux tube. While stirring, slowly heat up to 50 °C, and slowly add dropwise a propylene glycol methyl ether solution of 105.71 g of epoxy resin E - 51 with a solid content of 50 wt%. The dropping time is 60 min. After the dropping is completed, keep the temperature at 65 °C and react for 4 h to obtain an amine - epoxy - amine adduct;

[0062] (2) Pour 26.29 g of epoxy - based organosilicon prepolymer Silok 3590F4 (functionality is 4) into a constant - pressure dropping funnel, and slowly add it dropwise to the amine - epoxy - amine adduct obtained in step (1) for 30 min. After the dropping is completed, keep the temperature at 65 °C and react for 2.5 h to obtain a branched - modified polymer;

[0063] (3) Pour 85.71 g of methyl polyoxyethylene epoxy ether with a molecular weight of 1200 (Hangzhou Danwei Technology Co., Ltd.) into a constant-pressure dropping funnel, and slowly add it dropwise to the branched modified polymer obtained in step (2) for 40 min. After the addition is completed, react for 2 h in an atmosphere of 75 °C. Remove the organic solvent by vacuum distillation, cool to 50 °C, and then add 103.65 g of deionized water dropwise under stirring at 1200 rpm. The addition is completed in 30 min, and then discharge to obtain a light yellow transparent water-based epoxy curing agent.

[0064] In Example 2, the solid content of the water-based epoxy curing agent is 50 wt%, the active hydrogen equivalent is 313 g / eq, and the amine value is 171 mgKOH / g.

[0065] Example 3

[0066] A preparation method of a water-based epoxy curing agent includes the following steps:

[0067] (1) Place 16.76 g of m-xylenediamine, 16.37 g of isophorone diamine, 16.18 g of triethylenetetramine, and 10.89 g of cyclohexanediamine in a 500 mL three-necked flask equipped with a thermometer, a stirrer, and a condenser reflux tube. Slowly heat to 50 °C while stirring, and slowly add dropwise a propylene glycol methyl ether solution of 139.86 g of epoxy resin E-44 with a solid content of 50 wt%. The dropping time is 50 min. After the addition is completed, keep the temperature at 65 °C and react for 4 h to obtain an amine-epoxy-amine adduct.

[0068] (2) Pour 28.31 g of epoxy-functional silicone prepolymer Silok 3590F4 (functionality 4) into a constant-pressure dropping funnel, and slowly add it dropwise to the amine-epoxy-amine adduct obtained in step (1) for 30 min. After the addition is completed, keep the temperature at 65 °C and react for 2.5 h to obtain a branched modified polymer.

[0069] (3) Pour 76.93 g of methyl polyoxyethylene epoxy ether with a molecular weight of 1000 (Hangzhou Danwei Technology Co., Ltd.) into a constant-pressure dropping funnel, and slowly add it dropwise to the branched modified polymer obtained in step (2) for 40 min. After the addition is completed, react for 2 h in an atmosphere of 75 °C. Remove the organic solvent by vacuum distillation, cool to 50 °C, and then add 177.67 g of deionized water dropwise under stirring at 1500 rpm. The addition is completed in 30 min, and then discharge to obtain a light yellow transparent water-based epoxy curing agent.

[0070] In Example 3, the solid content of the water-based epoxy curing agent is 50 wt%, the active hydrogen equivalent is 290 g / eq, and the amine value is 197 mgKOH / g.

[0071] Comparative Example 1

[0072] The difference between Comparative Example 1 and Example 1 is only that in Comparative Example 1, 29.44 g of epoxy-functional silicone prepolymer Silok3590F4 was replaced with 160 g of epoxy-functional silicone prepolymer Silok 3596F2 (purchased from Guangzhou Silok Polymer Co., Ltd.). The functionality of the epoxy-functional silicone prepolymer Silok 3596F2 is 2, and the molecular weight is 2000. Other conditions are the same as those in Example 1.

[0073] The structural formula of the epoxy-functional silicone prepolymer Silok 3596F2 is as follows:

[0074]

[0075] The solid content of the epoxy curing agent in Comparative Example 1 is 50 wt%, the active hydrogen equivalent is 437 g / eq, and the amine value is 174 mgKOH / g.

[0076] Comparative Example 2

[0077] The difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, 29.44 g of epoxy-functional silicone prepolymer Silok3590F4 was replaced with 560 g of epoxy-functional silicone prepolymer Silok 3591F (purchased from Guangzhou Silok Polymer Co., Ltd.). The functionality of the epoxy-functional silicone prepolymer Silok 3591F is 1, and the molecular weight is 3500. Other conditions are the same as those in Example 1.

[0078] The structural formula of the epoxy-functional silicone prepolymer Silok 3591F is as follows:

[0079]

[0080] The solid content of the epoxy curing agent in Comparative Example 2 is 55 wt%, the active hydrogen equivalent is 473 g / eq, and the amine value is 131 mgKOH / g.

[0081] Comparative Example 3

[0082] Comparative Example 3 is a commercially available epoxy curing agent Aradur38-1, whose main component is a polyamine-modified polymer, purchased from Dalian Liansheng Trading Co., Ltd.

[0083] Comparative Example 4

[0084] Comparative Example 4 is a commercially available wetting and dispersing agent, whose main component is a polymer block copolymer.

[0085] Performance Test

[0086] The surface tension and storage stability of the epoxy curing agents of Examples 1-3, Comparative Examples 1-3, and the wetting and dispersing agent of Comparative Example 4 were tested. The test methods are as follows:

[0087] Surface tension: The epoxy curing agents of Examples 1-3 and Comparative Examples 1-3 and the wetting and dispersing agent of Comparative Example 4 were formulated into 0.5 wt% aqueous solutions, and then the static surface tension and dynamic surface tension of the epoxy curing agents of Examples 1-3 and Comparative Examples 1-3 and the wetting and dispersing agent of Comparative Example 4 were tested using a BP100 dynamic surface tension meter respectively.

[0088] Storage stability: At room temperature, the epoxy curing agents of Examples 1-3 and Comparative Examples 1-3 and the wetting and dispersing agent of Comparative Example 4 were centrifuged at 4000 rpm for 20 minutes, and whether they were layered was observed.

[0089] The test results of the surface tension and storage stability of the epoxy curing agents of Examples 1-3 and Comparative Examples 1-3 and the wetting and dispersing agent of Comparative Example 4 are shown in Table 1.

[0090] Table 1: Test results of the surface tension and storage stability of the epoxy curing agents of Examples 1-3 and Comparative Examples 1-3 and the wetting and dispersing agent of Comparative Example 4

[0091]

[0092] As can be seen from Table 1, the epoxy curing agent prepared by the present invention has a lower surface tension and good storage stability.

[0093] Comparative Example 1 used an epoxy-based silicone prepolymer with a functionality of 2, which made the surface tension of the epoxy curing agent in Comparative Example 1 significantly higher than that in Example 1, and the storage stability was also worse than that in Example 1. Comparative Example 2 used an epoxy-based silicone prepolymer with a functionality of 1, which made the surface tension of the epoxy curing agent in Comparative Example 2 significantly higher than that in Example 1.

[0094] The action mechanism of the wetting agent is mainly to reduce the surface tension of the solvent (water) so that the surface energy of the solid pigment and filler can be wetted by water; the action mechanism of the dispersing agent is on the one hand to reduce the interfacial tension between liquid-liquid or solid-liquid, and on the other hand to form an adsorption layer on the surface of the solid particles, increasing the charge on the surface of the solid particles and improving the steric hindrance. Therefore, the epoxy curing agent of the present invention has both wetting and dispersing functions. This may be because the long-chain polyether chain segment in the aqueous epoxy curing agent of the present invention can provide strong hydrophilicity, and the silicone group can greatly reduce the surface tension of the system, making it easier to wet and disperse the pigment and filler. When the epoxy curing agent is co-ground with the pigment and filler, the grinding time can be shortened and the grinding efficiency can be improved with little or no addition of wetting and dispersing agents. At the same time, the long-chain branched molecular structure can coat the pigment and filler or increase the steric hindrance, thereby preventing the aggregation and sedimentation of particles and maintaining the stable state of the system with good storage stability.

[0095] Comparative Example 3 uses the existing epoxy curing agent, and its surface tension is significantly higher than that of Example 1, which means that the epoxy curing agent of Comparative Example 3 only has curing performance and poor wetting and dispersion effect.

[0096] Comparative Example 4 is an existing wetting and dispersing agent. By comparing Comparative Example 4 with the embodiment, it is shown that the epoxy curing agent of the present invention also has the effect of a wetting and dispersing agent. Like the wetting and dispersing agent, it can reduce the surface tension and has a wetting and dispersing effect.

[0097] The water-based epoxy curing agents prepared in Examples 1-3 and Comparative Examples 1-3 were respectively prepared into pigment and filler slurries, the grinding fineness was controlled to be below 35 μm, and then each group of pigment and filler slurries was prepared into component A of epoxy coating. The epoxy coating consists of component A and component B, component B is a water-based epoxy emulsion, the ratio of the number of active hydrogen moles of component A to the number of epoxy group moles of component B is 1:1.2, component A and component B are mixed and stirred evenly to obtain epoxy coatings corresponding to each embodiment and comparative example.

[0098] The preparation method of the pigment and filler slurry is to mix and grind various raw material components to obtain the pigment and filler slurry; the preparation method of component A in the epoxy coating is to mix and stir various raw material components to obtain the pigment and filler slurry.

[0099] The raw material components and dosage of the pigment and filler slurry are shown in Table 2, and the raw material components and dosage of component A in the epoxy coating are shown in Table 3.

[0100] Table 2: Raw material components and dosage of pigment and filler slurry (mass percentage)

[0101]

[0102]

[0103] Table 3: Raw material components and dosage of epoxy coating component A (mass percentage)

[0104]

[0105] The epoxy coatings prepared by the water-based epoxy curing agents of the above Examples 1-3 and Comparative Examples 1-3 were sprayed on the polished tinplate and cold-rolled steel plates, respectively. After the paint film was left to level for 20 minutes, it was placed in a 70°C oven for curing for 3 hours, and then the performance test was performed after 24 hours. Among them, the tinplate was used for pencil hardness, adhesion, and flexibility tests, and other tests were performed on cold-rolled steel plates. The test items and methods are as follows:

[0106] Drying time: According to the requirements of national standard GB / T 1728-1979, the surface drying time of various paint films is tested by finger touch method;

[0107] Pencil hardness: Tested according to the requirements of the national standard GB / T 6739-2006, using the method of "Determination of film hardness by pencil method for paints and varnishes".

[0108] Adhesion: Tested by the cross-hatch method according to the requirements of the national standard GB / T 9286-1998.

[0109] Flexibility: Tested according to the requirements of the national standard GB / T 1731-2020.

[0110] Water resistance: Tested according to the requirements of the national standard GB / T 1733-1993.

[0111] Neutral salt spray resistance: Tested according to the requirements of the national standard GB / T 1771-2007.

[0112] The properties of the epoxy coatings prepared from the waterborne epoxy curing agents of Examples 1-3 and Comparative Examples 1-3 are shown in Table 4.

[0113] Table 4: Performance test results of the epoxy coatings of Examples 1-3 and Comparative Examples 1-3

[0114]

[0115] As can be seen from Table 4, under the conditions of meeting the resistance to 40°C water and neutral salt spray, the epoxy coating of the present invention also has a faster surface drying time, better flexibility performance and adhesion.

[0116] In Comparative Example 1, an epoxy-based organosilicon prepolymer with a functionality of 2 was used, resulting in the surface drying time of the epoxy coating prepared from the epoxy curing agent of Comparative Example 1 being significantly longer than that of Example 1, and the pencil hardness, flexibility and neutral salt spray resistance being worse than those of Example 1. In Comparative Example 2, an epoxy-based organosilicon prepolymer with a functionality of 1 was used, resulting in the surface drying time of the epoxy coating prepared from the epoxy curing agent of Comparative Example 2 being significantly longer than that of Example 1, and the pencil hardness, adhesion, water resistance and neutral salt spray resistance being significantly worse than those of Example 1. It shows that the use of a specific epoxy-based organosilicon prepolymer in the present invention can improve the pencil hardness, adhesion, flexibility, water resistance and neutral salt spray resistance of the coating and reduce the surface drying time. This is because the branched modified waterborne epoxy curing agent prepared in the present invention can give full play to the synergistic advantages of the Si-O-Si ring structure and the benzene ring structure, not only having the advantages of high hardness and high strength of epoxy resin, but also having the good toughness and dense structure of branched polymers, greatly improving the adhesion and anti-corrosion ability of the coating.

[0117] In Comparative Example 3, a commercially available epoxy curing agent was used, resulting in the surface drying time of the epoxy coating prepared from the epoxy curing agent of Comparative Example 3 being significantly longer than that of Example 1, and the pencil hardness, flexibility and neutral salt spray resistance being significantly worse than those of Example 1.

[0118] In summary, by introducing an epoxy prepolymer with a specific functionality and a hydrophilic alkyl polyoxyethylene epoxy ether into the epoxy curing agent system of the present invention, the surface tension of the system can be greatly reduced, so that the epoxy curing agent has good wetting and dispersibility and storage stability. In addition, the aqueous epoxy curing agent of the present invention contains a branched structure, can be stably dispersed in water, and has good compatibility with the epoxy emulsion, so that the epoxy coating can be cured at room temperature with a fast drying speed, and the film has good flexibility, adhesion and salt spray resistance. At the same time, the synergistic advantages of the Si-O-Si cyclic structure and the benzene ring structure in the epoxy curing agent not only endow the epoxy coating with the advantages of high hardness and high strength, but also can obtain a coating with good resistance to neutral salt spray, water resistance, adhesion and flexibility.

[0119] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An epoxy curing agent, characterized in that The raw materials for its preparation include polyamine, epoxy resin, epoxy prepolymer, alkyl polyoxyethylene epoxy ether; The functionality of the epoxy prepolymer is greater than 2.

2. The epoxy curing agent according to claim 1, characterized in that The polyamine includes at least one of diethylenetriamine, ethylenediamine, triethylenetetramine, tetraethylenepentamine, meta-xylylenediamine, isophoronediamine, 1,2-propylenediamine, 1,3-propylenediamine, 1,4-butylenediamine, 1,5-pentanediamine, 1,6-hexanediamine, and cyclohexanediamine.

3. The epoxy curing agent according to claim 1, characterized in that The epoxy resin includes at least one of novolac epoxy resin, bisphenol A epoxy resin and bisphenol F epoxy resin; and / or the epoxy equivalent of the epoxy resin is 150-550 g / eq.

4. The epoxy curing agent according to claim 1, characterized in that The epoxy prepolymer includes at least one of epoxy silicone prepolymer and trimethylolpropane triglycidyl ether.

5. The epoxy curing agent according to claim 1, characterized in that The alkyl polyoxyethylene epoxy ether includes methyl polyoxyethylene epoxy ether; and / or the weight average molecular weight of the alkyl polyoxyethylene epoxy ether is 270-4500.

6. The epoxy curing agent according to any one of claims 1 to 5, characterized in that The epoxy curing agent also includes a solvent; and in parts by weight, the raw materials for preparing the epoxy curing agent include 4.5-40 parts of polyamine, 9-55 parts of epoxy resin, 3.5-28 parts of epoxy prepolymer, 9-33 parts of alkyl polyoxyethylene epoxy ether, and 18-65 parts of solvent.

7. The epoxy curing agent according to any one of claims 1 to 5, characterized in that In the epoxy curing agent, the ratio of the total molar number of amine groups to the total molar number of epoxy groups is (1.0-2.2):

1.

8. The method for preparing the epoxy curing agent according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) mixing the epoxy resin and the polyamine, and reacting them to obtain an intermediate product 1; (2) mixing the epoxy prepolymer with the intermediate product 1 obtained in step (1), and reacting the mixture to obtain an intermediate product 2; (3) mixing the alkyl polyoxyethylene epoxy ether with the intermediate product 2 obtained in step (2), and reacting them to obtain the epoxy curing agent.

9. The preparation method according to claim 8, characterized in that: In step (1), the reaction temperature is 50-70°C, and the reaction time is 1-4h; and / or, in step (2), the reaction temperature is 60-80°C, and the reaction time is 1-4h; and / or, in step (3), the reaction temperature is 60-80°C, and the reaction time is 1-3h; and / or, in step (3), the reaction further includes a process of adding a solvent after the reaction.

10. A coating, characterized in that: The invention comprises the epoxy curing agent according to any one of claims 1 to 7.

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