Aqueous epoxy curing agent, its preparation method and application

Abstract

The application discloses a water-based epoxy curing agent, a preparation method and application thereof. The water-based epoxy curing agent is obtained by adding a water-based epoxy resin water solution into an ethylenediamine water solution for reaction. The preparation process is simple, easy to control, and mild. The water-based epoxy curing agent has the characteristics of low toxicity, good surface activity, etc. The water-based epoxy curing agent can be used as a water-based curing agent alone. After the water-based epoxy curing agent is cured with a water-based epoxy resin, the cured product has small brittleness and excellent impact resistance.

Description

Technical Field

[0001] This invention relates to a curing agent, particularly to a waterborne epoxy curing agent, and also to a method for preparing and applying the waterborne epoxy curing agent, belonging to the field of waterborne epoxy resin curing agent preparation. Background Technology

[0002] Ethylenediamine is a commonly used epoxy resin curing agent. It has low viscosity and can cure rapidly at room temperature. It is used in bonding, casting, coating and other fields, and has a large market demand.

[0003] However, ethylenediamine is highly volatile and hygroscopic, forming a white fumes in the air. It is highly toxic and can easily cause allergies and poisoning among construction workers, harming their health. Furthermore, epoxy resin systems formulated with ethylenediamine release a large amount of heat, easily triggering explosive polymerization reactions. The cured epoxy resin is brittle, has poor impact resistance, and cannot meet seismic requirements.

[0004] To reduce the volatility and toxicity of ethylenediamine, it is often modified with phenols and formaldehyde. While this method is effective, it tends to result in a higher concentration of free amines, phenols, and aldehydes in the curing agent, increasing its toxicity. Furthermore, phenol and formaldehyde-modified ethylenediamine molecules have fewer flexible groups, failing to address the high brittleness of epoxy cured products. Currently, there are also methods that modify ethylenediamine with macromolecules, reacting it with epoxy compounds containing epoxy groups to increase its molecular weight and reduce toxicity. Chinese patent CN112175487A discloses an anti-whitening epoxy floor coating curing agent, characterized by the following components and weight ratios: epoxy resin 45-55 parts; n-butanol 22.5-27.5 parts; xylene 22.5-27.5 parts; ethylenediamine 11.7-14.3 parts; cyclohexanone 45-55 parts. Among these, n-butanol, xylene, and cyclohexanone are all organic solvents. However, this method requires organic solvents, and the performance of the modified curing agent is generally poor. Summary of the Invention

[0005] To address the shortcomings of existing waterborne epoxy curing agents, the first objective of this invention is to provide a waterborne epoxy curing agent containing multiple functional groups. This curing agent can provide a stepped curing reaction rate during the coating curing process, ensuring stable exothermic curing reaction, exhibiting low toxicity, good surface activity, and improving the curing film-forming effect. It also provides the cured product with good flexibility properties and can be used alone as a waterborne curing agent. Furthermore, the cured product after curing with waterborne epoxy resin exhibits low brittleness and excellent impact resistance.

[0006] The second objective of this invention is to provide a method for preparing a waterborne epoxy curing agent that is simple and easy to control, and does not require the use of organic solvents. This method obtains a high-performance waterborne epoxy curing agent through the stepwise polymerization reaction of small molecule ethylenediamine on waterborne epoxy resin.

[0007] The third objective of this invention is to provide an application of a waterborne epoxy curing agent, which, when applied to a waterborne epoxy resin varnish, results in a cured product with low brittleness and excellent impact resistance after curing with the epoxy resin.

[0008] To achieve the above technical objectives, the present invention provides a water-based epoxy curing agent with the following structural formula:

[0009]

[0010] Where x ranges from 15 to 60; y ranges from 2 to 10;

[0011] R3 is selected from hydrogen or methyl;

[0012] R1 and R2 are structural units introduced into the epoxy compound, and R1 and R2 can be the same or different.

[0013] As a preferred embodiment, the epoxy compound is a bisphenol A type epoxy resin, hydrogenated bisphenol A epoxy resin, bisphenol F epoxy resin, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, hexanediol diglycidyl ether, bisphenol A phenolic epoxy resin, phenolic epoxy resin, o-cresol phenolic epoxy resin, or glycerol triglycidyl ether.

[0014] This structural formula contains symmetrical primary, secondary, and tertiary amino groups, which can provide a step-wise curing reaction rate during the coating curing process, making the exothermic curing reaction stable. It also contains multiple hydroxyl groups, and the primary, secondary, and tertiary amino groups can form new hydroxyl groups after curing, which enables it to form good adhesion to a variety of substrates. In addition, the long-chain structure containing amino and hydroxyl groups and the polyethylene glycol and / or polypropylene glycol structure on the branches give this curing agent good surface activity, which is beneficial to improving the curing film-forming effect and providing good flexibility to the cured product.

[0015] The present invention also provides a method for preparing a waterborne epoxy curing agent, wherein an aqueous solution of an aqueous epoxy resin is added dropwise to an aqueous solution of ethylenediamine to carry out reaction I, thereby obtaining the curing agent.

[0016] This invention introduces flexible segments into the ethylenediamine structure through the reaction of the epoxy groups of waterborne epoxy resin with the amino groups of ethylenediamine, thereby improving the brittleness of the cured ethylenediamine and epoxy resin. Simultaneously, the reaction is carried out using water as a solvent, making the reaction stable and easily controlled. As a preferred embodiment, the dripping time of the aqueous epoxy resin solution is controlled within 1–5 hours. If the dripping time of the aqueous epoxy resin solution in this invention is too short, the reaction between the epoxy resin and ethylenediamine will be too vigorous, increasing the exothermic reaction and causing gel solidification; if the dripping time is too long, it will affect production efficiency.

[0017] As a preferred embodiment, the temperature of the ethylenediamine aqueous solution is controlled to be below 100°C during the process of adding the aqueous epoxy resin solution dropwise to the ethylenediamine aqueous solution. In this invention, the reaction between the aqueous epoxy resin and ethylenediamine is exothermic; if the temperature is too high, gel solidification may easily occur.

[0018] As a preferred embodiment, after the aqueous epoxy resin solution is completely added dropwise to the ethylenediamine aqueous solution, the reaction is carried out at 50–80°C for 1–5 hours. This invention effectively controls the reaction rate and efficiency by controlling the reaction temperature. If the reaction temperature is too high, the reaction is too fast and prone to gelation; while if the reaction temperature is too low, the reaction is too slow and takes too long, affecting production efficiency.

[0019] As a preferred embodiment, the mass ratio of the waterborne epoxy resin to ethylenediamine is 1.5–4.0:1. This invention obtains a waterborne epoxy curing agent with low toxicity and low brittleness by controlling the mass ratio of the waterborne epoxy resin to ethylenediamine. If the mass ratio of the waterborne epoxy resin to ethylenediamine is too high, the reaction is prone to gelation; if the mass ratio is too low, the content of long-chain groups in the waterborne epoxy curing agent is low, resulting in a brittle and poorly impact-resistant cured product.

[0020] As a preferred embodiment, the waterborne epoxy resin is obtained by reacting an epoxy compound with a polyether unit amine in reaction II.

[0021] As a preferred embodiment, the mass percentage of the epoxy compound to the polyether unit amine is 15-50% : 15-85%; the sum of the mass percentages of the epoxy compound and the polyether unit amine is 100%.

[0022] As a preferred option, the conditions for reaction II are: temperature of 60–150°C and time of 1–6 h.

[0023] The structural formula of the polyether unit amine is:

[0024]

[0025] Wherein, R3 is selected from hydrogen or methyl; the value of x ranges from 15 to 60, and the value of y ranges from 2 to 10.

[0026] The polyether monoamine of this invention is a polyether chain compound with a monoamine group attached to one end. The polyether backbone is composed of polyethylene glycol segments and polypropylene glycol segments. The monoamine group provides easy reactivity with epoxy groups, the polyethylene glycol segments provide hydrophilicity, and the polypropylene glycol segments provide good mechanical properties. The monoamine group is attached to the methyl group of the polypropylene glycol to ensure the storage stability of the waterborne epoxy resin.

[0027] The present invention also provides an application of a waterborne epoxy curing agent, which is applied to a waterborne epoxy resin varnish.

[0028] The waterborne epoxy curing agent provided by this invention has the advantages of low toxicity and good surface activity. It can be used alone as a waterborne curing agent. After curing with waterborne epoxy resin, the cured product has low brittleness and excellent impact resistance.

[0029] Compared with the prior art, the technical solution of the present invention brings the following beneficial technical effects:

[0030] 1) The ethylenediamine-modified waterborne epoxy curing agent of the present invention has low toxicity, good flexibility, and excellent surface activity. It can be used alone as a waterborne curing agent, and after curing with waterborne epoxy resin, the cured product has low brittleness and excellent impact resistance. This solves the problems of high toxicity and high brittleness and poor impact resistance of ethylenediamine when used as an epoxy resin curing agent.

[0031] 2) The preparation process of the ethylenediamine-modified waterborne epoxy curing agent of the present invention is simple and easy to control. In the technical solution of the present invention, the epoxy component is a waterborne resin, and the amine has good water solubility and can react directly in water. The amount of water added can be adjusted according to the designed solid content. On the one hand, water can reduce the concentration of reactants; on the other hand, water has a large latent heat of vaporization, which can prevent the accumulation of heat generated by the reaction to the greatest extent, thus effectively solving the problem of large heat release and difficulty in controlling the reaction between ethylenediamine and epoxy resin. Detailed Implementation

[0032] The following embodiments are only specific descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. For those skilled in the art, any improvements made without departing from the present invention should be considered within the scope of protection of the present invention.

[0033] Example 1:

[0034] The structural formula of the water-based epoxy curing agent in this embodiment is as follows:

[0035]

[0036] Where x = 19, y = 3;

[0037] R3 is a methyl group;

[0038]

[0039] n = 0.14.

[0040] The preparation method of the water-based epoxy curing agent in this embodiment is as follows:

[0041] 1) Preparation of waterborne epoxy resin:

[0042] 48g of bisphenol A type epoxy resin (epoxy equivalent 190g / eq) and 50g of polyether monoamine M-1000 (Hennessmann) were added to a four-necked reaction flask. Stirring was started, and the mixture was slowly heated to 90℃ and maintained for 3 hours to obtain the waterborne epoxy resin. The structural formula of the polyether monoamine is as follows:

[0043]

[0044] In this case, R3 is a methyl group, x = 19, and y = 3.

[0045] 2) Preparation of water-based curing agents

[0046] Weigh 40g of waterborne epoxy resin and dissolve it in 40g of water to obtain an aqueous solution of waterborne epoxy resin. Add this aqueous solution dropwise to a mixed solution of 10g ethylenediamine and 10g water to carry out the reaction. Stirring is turned on during both the dropwise addition and the reaction. The dropwise addition time is controlled at 2.5h, and the temperature of the mixed solution is 75℃ during the dropwise addition. After the dropwise addition is completed, the reaction time is 2h, and the reaction temperature is controlled at 65℃. After the reaction is completed, the waterborne epoxy curing agent is obtained.

[0047] Example 2:

[0048] The structural formula of the water-based epoxy curing agent in this embodiment is as follows:

[0049]

[0050] Where x = 31; y = 10;

[0051] R3 is a methyl group;

[0052]

[0053] m = 1.6.

[0054] The preparation method of the water-based epoxy curing agent in this embodiment is as follows:

[0055] 1) Preparation of waterborne epoxy resin:

[0056] 45g of phenolic epoxy resin (epoxy equivalent 180g / eq) and 100g of polyether monoamine M-2070 (Hennessmann) were added to a four-necked reaction flask. Stirring was started, and the mixture was slowly heated to 95℃ and maintained for 3 hours to obtain the waterborne epoxy resin. The structural formula of the polyether monoamine is as follows:

[0057]

[0058] Where R3 is a methyl group, x = 31; y = 10.

[0059] 2) Preparation of water-based curing agent: Weigh 35g of water-based epoxy resin and dissolve it in 35g of water to obtain an aqueous solution containing water-based epoxy resin. Add this aqueous solution dropwise to a mixed solution of 15g ethylenediamine and 15g water to carry out the reaction. Stirring is turned on during both the dropwise addition and the reaction. The dropwise addition time is controlled at 2.5h, and the temperature of the mixed solution is 75℃ during the dropwise addition. After the dropwise addition is completed, the reaction time is 2h, and the reaction temperature is controlled at 65℃. After the reaction is completed, the water-based epoxy curing agent is obtained.

[0060] Example 3:

[0061] The structural formula of the water-based epoxy curing agent in this embodiment is as follows:

[0062]

[0063] Where x = 41; y = 4;

[0064] R3 is a methyl group;

[0065] R1 is R2 is z = 3, m = 0.2;

[0066] The preparation method of the water-based epoxy curing agent in this embodiment is as follows:

[0067] 1) Preparation of waterborne epoxy resin:

[0068] 25g of phenolic epoxy resin (epoxy equivalent 180g / eq), 28g of polyethylene glycol glycidyl ether (epoxy equivalent 200g / eq), and 100g of polyether monoamine M-2095 (Hennessmann) were added to a four-necked reaction flask. The mixture was stirred and slowly heated to 100℃, maintaining the reaction for 3 hours to obtain the waterborne epoxy resin. The structural formula of the polyether monoamine is as follows:

[0069]

[0070] Where R3 is a methyl group, x = 41; y = 4.

[0071] 2) Preparation of water-based curing agents

[0072] Weigh 30g of waterborne epoxy resin and dissolve it in 30g of water to obtain an aqueous solution containing the epoxy resin. Add this aqueous solution dropwise to a mixed solution of 20g ethylenediamine and 20g water to carry out the reaction. Stirring is turned on during both the dropwise addition and the reaction. The dropwise addition time is controlled at 2.5h, and the temperature of the mixed solution is 75℃ during the dropwise addition. After the dropwise addition is completed, the reaction time is 2h, and the reaction temperature is controlled at 65℃. After the reaction is completed, the waterborne epoxy curing agent is obtained.

[0073] Comparative Example 1:

[0074] The preparation method of the waterborne epoxy curing agent in this comparative example is as follows:

[0075] 1) The preparation of the waterborne epoxy resin is the same as in Example 1;

[0076] 2) Preparation of water-based curing agents

[0077] Weigh 25g of waterborne epoxy resin and dissolve it in 25g of water to obtain an aqueous solution containing the epoxy resin. Add this aqueous solution dropwise to a mixed solution of 25g of ethylenediamine and 25g of water to carry out the reaction. Stirring is turned on during both the dropwise addition and the reaction. The dropwise addition time is controlled at 2.5h, and the temperature of the mixed solution is 75℃ during the dropwise addition. After the dropwise addition is completed, the reaction time is 2h, and the reaction temperature is controlled at 65℃. After the reaction is completed, the waterborne epoxy curing agent is obtained.

[0078] Comparative Example 2:

[0079] The preparation method of the waterborne epoxy curing agent in this comparative example is as follows:

[0080] 1) The preparation of the waterborne epoxy resin is the same as in Example 1;

[0081] 2) Preparation of water-based curing agents

[0082] Weigh 45g of waterborne epoxy resin and dissolve it in 45g of water to obtain an aqueous solution containing the epoxy resin. Add this aqueous solution dropwise to a mixed solution of 5g ethylenediamine and 5g water to carry out the reaction. Stirring is turned on during both the dropwise addition and the reaction. The dropwise addition time is controlled at 2.5h, and the temperature of the mixed solution is 75℃ during the dropwise addition. After the dropwise addition is completed, the reaction time is 2h, and the reaction temperature is controlled at 65℃. After the reaction is completed, the viscosity of the reactant is too high and close to that of a gel.

[0083] Comparative Example 3:

[0084] The preparation method of the waterborne epoxy curing agent in this comparative embodiment is as follows: 80g of waterborne epoxy resin (Hansen 3510) was weighed and added dropwise to a mixed solution of 10g ethylenediamine and 10g water for reaction. Stirring was turned on during both the dropwise addition and the reaction. The dropwise addition time was controlled at 2.5h, and the temperature of the mixed solution was 75℃ during the dropwise addition. After the dropwise addition was completed, the reaction time was 2h, and the reaction temperature was controlled at 65℃. The waterborne epoxy curing agent was obtained after the reaction was completed.

[0085] The waterborne epoxy curing agents prepared in Examples 1-3 and Comparative Examples 1-3 were mixed with commercially available American Hansen 3510 epoxy resin at an equivalent ratio of 1:1 to form a waterborne epoxy resin varnish. After complete curing, the impact resistance was tested using the CJQ-Ⅱ impact tester of standard GB / T 1732-93 "Determination of Impact Resistance of Coating Films". The results are shown in Table 1.

[0086] Table 1: Impact resistance of waterborne epoxy curing agents and epoxy cured products prepared in Examples 1-3 and Comparative Examples 1-3

[0087]

[0088]

[0089] Note: * indicates that the ethylenediamine ratio is too high, the curing agent synthesis reaction is close to gel, and the viscosity is too high to use.

[0090] Table 1 shows that the curing agents prepared in Examples 1-3, when compounded with commercially available Hansen 3510 epoxy resin in an equivalent ratio of 1:1, produced waterborne epoxy resin varnishes with excellent impact resistance. In Comparative Example 1, the proportion of the modifier waterborne epoxy resin was too small, resulting in poor impact resistance. In Comparative Example 2, the proportion of the modifier waterborne epoxy resin was too large, causing the curing agent synthesis reaction to approach gelation, resulting in excessive viscosity that rendered it unusable. In Comparative Example 3, commercially available Hansen 3510 epoxy resin was used to modify ethylenediamine. Because the flexibility of 3510 was inferior to that of the waterborne epoxy resin in this invention, the varnish prepared by the modified curing agent also had poor impact resistance.

Claims

1. A water-based epoxy curing agent, characterized in that: The structure is as follows: ； Where x is 15~60; y is 2~10; R3 is selected from hydrogen or methyl; R1 and R2 are structural units introduced by the epoxy compound, and R1 and R2 may be the same or different. The waterborne epoxy curing agent is prepared by adding an aqueous solution of waterborne epoxy resin dropwise to an aqueous solution of ethylenediamine to carry out reaction I; the mass ratio of the waterborne epoxy resin to ethylenediamine is 1.5~4.0:

1.

2. The water-based epoxy curing agent according to claim 1, characterized in that: The epoxy compound is bisphenol A type epoxy resin, hydrogenated bisphenol A epoxy resin, bisphenol F epoxy resin, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, hexanediol diglycidyl ether, bisphenol A phenolic epoxy resin, phenolic epoxy resin, o-cresol phenolic epoxy resin, or glycerol triglycidyl ether.

3. The method for preparing a waterborne epoxy curing agent according to claim 1, characterized in that: The aqueous epoxy resin solution is added dropwise to the aqueous ethylenediamine solution to carry out reaction I, thus obtaining the product; The mass ratio of the waterborne epoxy resin to ethylenediamine is 1.5~4.0:

1.

4. The method for preparing a waterborne epoxy curing agent according to claim 3, characterized in that: The dripping time of the aqueous epoxy resin solution is controlled within 1 to 5 hours.

5. The method for preparing a waterborne epoxy curing agent according to claim 4, characterized in that: During the process of adding the aqueous epoxy resin solution dropwise into the ethylenediamine aqueous solution, the temperature of the ethylenediamine aqueous solution is controlled to be less than 100°C.

6. The method for preparing a waterborne epoxy curing agent according to claim 3, characterized in that: After the aqueous epoxy resin solution is completely added dropwise to the ethylenediamine aqueous solution, the reaction is carried out at 50-80°C for 1-5 hours.

7. The method for preparing a waterborne epoxy curing agent according to claim 3, characterized in that: The aqueous epoxy resin is obtained by reacting an epoxy compound with a polyether unit amine.

8. The method for preparing a waterborne epoxy curing agent according to claim 7, characterized in that: The mass percentage of the epoxy compound to the polyether monoamine is 15-50%: 15-85%; the sum of the mass percentages of the epoxy compound and the polyether monoamine is 100%.

9. The method for preparing a waterborne epoxy curing agent according to claim 8, characterized in that: The conditions for reaction II are: temperature 60~150℃, time 1~6h.

10. The method for preparing a waterborne epoxy curing agent according to claim 8, characterized in that: The structural formula of the polyether unit amine is: ； Wherein, R3 is selected from hydrogen or methyl; the value of x ranges from 15 to 60, and the value of y ranges from 2 to 10.

11. Use of the aqueous epoxy curing agent according to claim 1, characterized in that: It is used in water-based epoxy resin varnishes.

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