A free amine-free nonionic waterborne epoxy curing agent and a preparation method thereof

Abstract

This invention provides a free amine-free nonionic waterborne epoxy curing agent and its preparation method, relating to the field of epoxy curing agent technology. The method includes the following steps: 1) mixing and reacting a small molecule aldehyde and hydroxyethyldiethylenetriamine to obtain an oxazolidine- and aldolimide-terminated modified amine; 2) reacting the modified amine and polyether amine-modified multifunctional epoxy resin to obtain a hydrophilic oxazolidine- and aldolimide-terminated modified resin amine; 3) mixing and reacting the hydrophilic oxazolidine- and aldolimide-terminated modified resin amine, a monofunctional glycidyl ether, and water to obtain the free amine-free nonionic waterborne epoxy curing agent. The nonionic waterborne epoxy curing agent of this invention, when combined with a waterborne epoxy emulsion to form a film, can impart excellent resistance to boiling water, acids and alkalis, and neutral salt spray, etc., and the preparation process is simple and the production cost is low, making it suitable for large-scale industrial applications.

Description

Technical Field

[0001] This invention relates to the field of epoxy curing agent technology, specifically to a non-ionic waterborne epoxy curing agent without free amines and its preparation method. Background Technology

[0002] Epoxy resins are increasingly used in water-based epoxy coatings, adhesives, reactive diluents, cement mortar repair materials, sizing agents for glass fiber or carbon fiber, and anti-corrosion primers. Epoxy resin itself has a thermoplastic linear structure and cannot be used directly. A curing agent must be added to the epoxy resin to form a three-dimensional network structure (three-dimensional mesh structure) before it can be used. The type and structure of the curing agent directly determine the performance of the epoxy resin. Currently, most water-based epoxy curing agents on the market contain a large amount of free small-molecule amines due to manufacturing processes. This not only significantly weakens the epoxy resin's resistance to acids, alkalis, and salt spray, but also poses a great hazard to construction workers and the environment.

[0003] For example, CN202211644892.X uses ketimine modification to obtain a nonionic waterborne epoxy curing agent. The resulting hyperbranched structure endows it with excellent chemical resistance. However, it only uses dual-tube epoxy resin modification and does not further use a large amount of polyfunctional epoxy resin to enhance the hyperbranched structure. Similarly, patent CN202211646020.7 uses ketimine modification to obtain a cationic waterborne epoxy curing agent. It also only uses dual-tube epoxy resin modification and has excellent chemical resistance. In summary, resin-like curing agents with highly hyperbranched structures and no small molecule free amines will have excellent chemical resistance properties such as resistance to boiling water, acids and alkalis, and neutral salt spray.

[0004] Therefore, it is of great significance to develop a non-ionic waterborne epoxy curing agent that is free of free amines, has a simple preparation process, low production cost, and can impart excellent properties such as resistance to boiling water, acid and alkali, and neutral salt spray when compounded with waterborne epoxy emulsions. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a nonionic waterborne epoxy curing agent without free amines and its preparation method, by introducing oxazolidine and aldimine structures during the synthesis process, as shown in the reaction formula of the modified amine formation mechanism of oxazolidine and aldimine end-capped:

[0006]

[0007] Further reaction with multifunctional epoxy resins forms resin-modified resin amines with hyperbranched structures, such as the resin amines with oxazolidine and aldehyde-imine-terminated ends, as shown in the reaction formula:

[0008]

[0009] Subsequently, by observing that the oxazolidine and aldolimine structures in the modified resin amine have different hydrolysis rates with water and that the corresponding primary and secondary amines after hydrolysis have different reactivity, and by using an excess of polyfunctional epoxy resin in the reaction, the primary amine corresponding to the aldolimine was cleverly designed to participate in the reaction, while the secondary amine corresponding to the oxazolidine was designed to protect it and avoid participating in the reaction as much as possible. Then, a larger molecular weight hyperbranched structure was further formed in the original resin-like modified resin amine with a hyperbranched structure, which effectively avoided the gel phenomenon caused by the secondary amine group at the other end of the molecular structure participating in the reaction and resulting in intramolecular chain extension.

[0010] This invention, through its ingenious oxazolidinyl and aldehyde-imine structures, balances the reaction rates of different amine hydrogens participating in the reaction process, thereby enabling the incorporation of multifunctional epoxy resins to form high-molecular-weight hyperbranched structures. Compared to the commonly used dual-functionality modified epoxy curing agents on the market, multifunctional epoxy resins exhibit more pronounced hyperbranched structures, significantly increasing the crosslinking density and chemical resistance of the curing agent.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a nonionic waterborne epoxy curing agent without free amines, comprising the following steps:

[0013] 1) A small molecule aldehyde and hydroxyethyldiethylenetriamine are mixed and reacted to obtain a modified amine with oxazolidine and aldehyde imine-terminated ends;

[0014] 2) The modified amine and polyether amine were reacted to the multifunctional epoxy resin to obtain the modified resin amine with hydrophilic modified oxazolidine and aldehyde imine end capping.

[0015] 3) A mixture of hydrophilic modified oxazolidine and aldehyde-imine-terminated modified resin amine, monofunctional glycidyl ether and water is reacted to obtain a nonionic waterborne epoxy curing agent without free amine.

[0016] As a further aspect of the present invention, in step 1), the small molecule aldehyde is at least one of formaldehyde aqueous solution, paraformaldehyde, and isobutyraldehyde.

[0017] As a further aspect of the present invention, in step 1), the molar ratio of the small molecule aldehyde to hydroxyethyldiethylenetriamine is 2.8 to 4.0:1.0.

[0018] As a further embodiment of the present invention, in step 1), the small molecule aldehyde and hydroxyethyldiethylenetriamine are mixed and reacted at 80°C to 120°C for 6 to 12 hours.

[0019] As a further aspect of the present invention, in step 1), the small molecule aldehyde and hydroxyethyldiethylenetriamine are mixed and reacted, including:

[0020] Small molecule aldehydes and hydroxyethyldiethylenetriamine are mixed and reacted. Water produced during the reaction is removed in time. Then, vacuum operation is carried out for 1h to 3h at a temperature of 100℃~120℃ and a vacuum degree of -0.1MPa~-0.06MPa (to remove excess small molecule aldehydes) to obtain modified amines with oxazolidine and aldimine-terminated ends.

[0021] As a further aspect of the present invention, in step 2), the polyetheramine is M1000 with a concentration of 1000 g / mol.

[0022] As a further aspect of the present invention, in step 2), the multifunctional epoxy resin is an epoxy resin with an epoxy group functionality ≥3, and the corresponding product model is at least one of F51 phenolic epoxy resin, triglycidyl isocyanate (TGIC), and trimethylolpropane triglycidyl ether (XY-636).

[0023] As a further aspect of the present invention, in step 2), the molar ratio of the modified amine with oxazolidine and aldehyde imine end-capped to the total epoxy groups in the multifunctional epoxy resin is 1.0:1.05-1.2.

[0024] As a further embodiment of the present invention, in step 2), the mass ratio of multifunctional epoxy resin to polyetheramine is 1.14 to 1.57:1.0; the modified amine and polyetheramine-modified multifunctional epoxy resin are reacted at 60°C to 90°C for 2 to 4 hours.

[0025] As a further aspect of the present invention, in step 3), the monofunctional glycidyl ether is C1 to C2. 14 At least one of alkyl glycidyl ether, phenyl glycidyl ether, benzyl glycidyl ether, and o-tolyl glycidyl ether.

[0026] As a further embodiment of the present invention, in step 3), the mass ratio of the hydrophilic modified oxazolidine and aldimine-terminated modified resin amine to water is 1.26 to 1.44:1.0.

[0027] As a further embodiment of the present invention, in step 3), the molar ratio of the epoxy groups in the hydrophilic modified oxazolidine and aldehyde imine-terminated modified resin amine and the monofunctional glycidyl ether is 1.0:0.2-1.0.

[0028] As a further embodiment of the present invention, in step 3), the reaction is carried out at 60°C to 90°C for 2 hours to 5 hours.

[0029] Secondly, the present invention also provides a non-ionic waterborne epoxy curing agent without free amines, which is prepared by the above-mentioned preparation method of the non-ionic waterborne epoxy curing agent without free amines.

[0030] Compared with existing technologies, the present invention proposes a free amine-free nonionic waterborne epoxy curing agent and its preparation method. The prepared free amine-free nonionic waterborne epoxy curing agent, when compounded with waterborne epoxy emulsion, can impart excellent properties to the coating film, such as resistance to boiling water, acids and alkalis, and neutral salt spray. Moreover, the preparation process is simple and the production cost is low, making it suitable for large-scale industrial applications. It has the following beneficial effects:

[0031] This invention is based on aldehyde-modified hydroxyethyl diethylenetriamine to prepare a non-ionic waterborne epoxy curing agent without free amines (aldehyde-imine method). By introducing oxazolidine and aldehyde-imine structures during the synthesis process, and then reacting them with multifunctional epoxy resin to form a modified resin amine with a hyperbranched structure, the oxazolidine and aldehyde-imine structures in the modified resin amine exhibit different hydrolysis rates with water and different reactivity of the primary and secondary amines after hydrolysis. With the participation of excess multifunctional epoxy resin, the primary amine corresponding to the aldehyde-imine is cleverly designed to participate in the reaction, while the secondary amine corresponding to the oxazolidine plays a protective role and does not participate in the reaction as much as possible. A higher molecular weight hyperbranched structure is further formed in the original hyperbranched resin amine, effectively avoiding the gel phenomenon caused by the participation of the secondary amine group at the other end of the molecular structure in the reaction and resulting in intramolecular chain extension. It crosslinks with multifunctional epoxy resin to form a regular dendritic supramolecular structure. This supramolecular dendritic structure can effectively shield acid and alkali ions and other chemical media, ultimately endowing the coating film with excellent properties such as resistance to boiling water, acid and alkali, and neutral salt spray.

[0032] The raw materials of the free amine-free nonionic waterborne epoxy curing agent of the present invention are inexpensive and readily available, the preparation cost is low, the process is simple, and it is suitable for mass industrial production.

[0033] These or other aspects of this application will become more apparent from the following description of embodiments. It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the application. Detailed Implementation

[0034] The present application will be further described below with reference to specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0035] Example 1

[0036] This embodiment provides a non-ionic, water-based epoxy curing agent that does not contain free amines, and its preparation method includes the following steps:

[0037] Synthesis of intermediates:

[0038] Add 784.31g of epoxy resin F51 and 500g of M1000 polyetheramine (mass ratio of epoxy resin to polyetheramine 1.57:1.0) to a 2L reactor, heat to 80-85℃ and keep at that temperature for 4h, take a sample and measure the epoxy equivalent to 430±50g / eq, and discharge the material for later use.

[0039] The preparation method of this non-ionic waterborne epoxy curing agent without free amine also includes the following steps:

[0040] 1) Paraformaldehyde and hydroxyethyldiethylenetriamine were mixed at a molar ratio of 2.8:1.0 and reacted at 80°C for 6 hours. During the reaction, the water produced was removed in time. Then, a vacuum operation was performed at 100°C and a vacuum degree of -0.06MPa for 2 hours (to remove excess aldehyde) to obtain modified amine A.

[0041] 2) Add 450g of the intermediate described in Example 1 (molar ratio of modified amine A to intermediate: 1.0:1.05) to the modified amine A in step 1), and react at 60-70℃ for 4h to obtain the hydrophilic modified amine.

[0042] 3) Mix hydrophilic modified amine, 108.7g benzyl glycidyl ether and 520g water (the mass ratio of hydrophilic modified amine to water is 1.26:1, and the molar ratio of epoxy groups in modified amine and benzyl glycidyl ether is 1.0:0.5), and react at 70℃ for 5h to obtain a nonionic waterborne epoxy curing agent without free amine.

[0043] Example 2

[0044] This embodiment provides a non-ionic, water-based epoxy curing agent that does not contain free amines, and its preparation method includes the following steps:

[0045] Synthesis of intermediates:

[0046] Add 693.6g TGIC1 and 500g M1000 polyetheramine (the mass ratio of epoxy resin to polyetheramine is 1.39:1.0) to a 2L reactor, heat to 120-130℃ and keep at that temperature for 4 hours. Take a sample and measure the epoxy equivalent, which is 170±20g / eq. Discharge the material for later use.

[0047] The preparation method of this non-ionic waterborne epoxy curing agent without free amine also includes the following steps:

[0048] 1) Isobutyraldehyde and hydroxyethyl diethylenetriamine were mixed at a molar ratio of 3.95:1 and reacted at 100°C for 6 hours. During the reaction, the water produced was removed in time. Then, a vacuum operation was performed at 110°C and a vacuum degree of -0.07MPa for 1 hour (to remove excess aldehyde) to obtain isobutyraldehyde-modified hydroxyethyl diethylenetriamine, i.e., modified amine B.

[0049] 2) Add 187.57g of the intermediate described in Example 2 (molar ratio of modified amine AB to intermediate: 1.0:1.1) to the modified amine B in step 1) in 5 portions, and keep the temperature at 60-70℃ for 3h to obtain hydrophilic modified amine;

[0050] 3) Mix 406.9g of hydrophilic modified amine, 66.67g of carbododecyl glycidyl ether, 44.25g of phenyl glycidyl ether and 300g of water (the mass ratio of modified amine to water is 1.0:1.35:1.35:1, and the molar ratio of epoxy groups in modified amine, carbododecyl glycidyl ether and phenyl glycidyl ether is 1.0:0.25:0.25), and react at 80℃ for 3h to obtain a nonionic waterborne epoxy curing agent without free amine.

[0051] Example 3

[0052] This embodiment provides a non-ionic, water-based epoxy curing agent that does not contain free amines, and its preparation method includes the following steps:

[0053] Synthesis of intermediates:

[0054] Add 571.43g XY-636 (trimethylolpropane triglycidyl ether) and 500g M1000 polyetheramine (the mass ratio of epoxy resin to polyetheramine is 1.14:1.0) to a 2L reactor, heat to 85℃ and hold for 4 hours. Take a sample and measure the epoxy equivalent, which is 270±30g / eq. Discharge the material for later use.

[0055] The preparation method of this non-ionic waterborne epoxy curing agent without free amine also includes the following steps:

[0056] 1) Mix 37% formaldehyde aqueous solution and hydroxyethyl diethylenetriamine at a molar ratio of 4.0:1, react at 90℃ for 12h, remove the water produced during the reaction in time, and then perform a vacuum operation at 120℃ and a vacuum degree of -0.09MPa for 3h (to remove excess aldehyde) to obtain modified amine C;

[0057] 2) Add 267.86g of the intermediate from Example 3 (molar ratio of modified amine AC to intermediate: 1.0:1.2) to the modified amine C from step 1), and react at 80°C for 3 hours to obtain a hydrophilic modified amine;

[0058] 3) Mix hydrophilic modified amine, 97g o-tolyl glycidyl ether and 400g water (the mass ratio of modified amine to water is 1.44:1.0, and the molar ratio of epoxy groups in modified amine to o-tolyl glycidyl ether is 1.0:0.5), and react at 80℃ for 32h to obtain a nonionic waterborne epoxy curing agent without free amine.

[0059] Comparative Example 1

[0060] A non-ionic, waterborne epoxy curing agent without free amines is synthesized by replacing the polyfunctional epoxy resin F51 with the difunctional epoxy resin E51 intermediate. The process involves adding 784.31 g of epoxy resin E51 and 500 g of M1000 polyetheramine (epoxy resin to polyetheramine mass ratio 1.57:1.0) to a 2 L reactor, heating to 80-85℃ and holding for 4 hours. A sample is taken and the epoxy equivalent is measured to be 430±50 g / eq. The material is then discharged for later use. The preparation method of this non-ionic, waterborne epoxy curing agent without free amines includes the following steps:

[0061] 1) Paraformaldehyde and hydroxyethyldiethylenetriamine were mixed at a molar ratio of 2.8:1.0 and reacted at 80°C for 6 hours. During the reaction, the water produced was removed in time. Then, a vacuum operation was performed at 100°C and a vacuum degree of -0.06MPa for 2 hours (to remove excess aldehyde) to obtain modified amine A.

[0062] 2) Add 450g of the intermediate from Example 1 (molar ratio of modified amine A to intermediate: 1.0:1.05) to the modified amine A from step 1), and react at 60-70℃ for 4h to obtain the hydrophilic modified amine.

[0063] 3) Mix hydrophilic modified amine, 108.7g benzyl glycidyl ether and 520g water (the mass ratio of hydrophilic modified amine to water is 1.26:1.0, and the molar ratio of epoxy groups in modified amine and benzyl glycidyl ether is 1.0:0.5), and react at 70℃ for 5h to obtain a nonionic waterborne epoxy curing agent without free amine.

[0064] Comparative Example 2

[0065] A non-ionic, waterborne epoxy curing agent without free amines, wherein hydroxyethyl diethylenetriamine is replaced with diethylenetriamine, is prepared by the following steps:

[0066] 1) Paraformaldehyde and diethylenetriamine were mixed at a molar ratio of 3.8:1 and reacted at 80°C for 6 hours. During the reaction, the water produced was removed in time. Then, a vacuum operation was carried out at 100°C and a vacuum degree of -0.06MPa for 2 hours (to remove excess aldehyde) to obtain modified amine E.

[0067] 2) Add 428.1g of the intermediate from Example 1 to the modified amine E in step 1), and react at 70°C for 4 hours. During the addition, gelation occurred due to excessive viscosity.

[0068] Performance testing:

[0069] The performance of the waterborne epoxy curing agents of Examples 1-3 and Comparative Examples 1-2 was tested, and the test results are shown in Table 1 below:

[0070] Table 1. Performance test results of the waterborne epoxy curing agents of Examples 1-3 and Comparative Examples 1-2

[0071]

[0072]

[0073] Note:

[0074] Solid content: Tested according to "GB 1725-1979 Determination of Solid Content in Coatings";

[0075] Amine hydrogen equivalent: Tested according to "GB / T 7383-2020 Determination of hydroxyl value of nonionic surfactants";

[0076] Viscosity: Tested according to "GB / T 22235-2008 Determination of viscosity of liquids";

[0077] Adhesion: Tested according to "GB / T 9286-2021 Paints and Varnishes Cross-cut Test";

[0078] Boiling water resistance: Tested according to "GB / T 4893.1-2005 Furniture surface cold liquid resistance test method";

[0079] Resistance to 5% sulfuric acid: Tested according to "GB / T 4893.1-2005 Furniture surface cold liquid resistance test method";

[0080] Resistance to 5% sodium hydroxide: Tested according to "GB / T 4893.1-2005 Test method for cold resistance of furniture surfaces";

[0081] Hardness: The test was conducted according to "ASTM D3363-2000 Pencil Test for Determination of Hardness of Paint Film";

[0082] Neutral salt spray resistance time: Tested according to "GB / T 1771-1991 Determination of neutral salt spray resistance of paints and varnishes".

[0083] Preparation of the coating film: The epoxy emulsion EP101 of Guangdong Huaguoshan Environmental Protection Technology Co., Ltd. and the water-based epoxy curing agent of Examples 1-3 and Comparative Example 1 were mixed evenly according to the epoxy value and active hydrogen equivalent ratio of 1:0.8, and then sprayed on the sandblasted steel plate and cured at room temperature for 168 hours.

[0084] As shown in Table 1, the free amine-free nonionic waterborne epoxy curing agent of the present invention exhibits excellent properties, especially in terms of resistance to boiling water, acids and alkalis, and salt spray, which are superior to those of Comparative Example 1 modified with E51. This demonstrates that multifunctional epoxy resins, compared to dual-functional epoxy resins, impart superior resistance to boiling water, acids and alkalis, and neutral salt spray to the coating film.

[0085] As shown in Table 1, the modified amine prepared by hydroxyethyl diethylenetriamine in this invention contains oxazolidine and aldehyde imine structures. It can cleverly design the primary amine to participate in the hyperbranching structure, and the secondary amine corresponding to oxazolidine plays a protective role and does not participate in the reaction as much as possible. Compared with the pure aldehyde imine structure of diethylenetriamine (Comparative Example 2), it can successfully prepare a highly hyperbranched nonionic waterborne epoxy curing agent without free amine.

[0086] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A process for the preparation of a free amine-free non-ionic aqueous epoxy curing agent, characterized in that, The method comprises the following steps: 1) mixing and reacting a small molecule aldehyde and a hydroxyethyl diethylene triamine to obtain an oxazolidine and aldimine capped modified amine; 2) reacting the modified amine, a polyether amine modified multifunctional epoxy resin to obtain a hydrophilic modified oxazolidine and aldimine capped modified resin amine; 3) mixing and reacting the hydrophilic modified oxazolidine and aldimine capped modified resin amine, a monofunctional glycidyl ether and water to obtain the non-ionic waterborne epoxy curing agent without free amine.

2. The method of making a free amine-free non-ionic aqueous epoxy curing agent according to claim 1, wherein, In step 1), the small molecule aldehyde is at least one of an aqueous formaldehyde solution, paraformaldehyde and isobutyl aldehyde.

3. The process for preparing a free amine-free non-ionic aqueous epoxy curing agent according to claim 2, characterized in that, In step 1), the molar ratio of the small molecule aldehyde and the hydroxyethyl diethylene triamine is 2.8-4.0:1.0; the small molecule aldehyde and the hydroxyethyl diethylene triamine are mixed and reacted at 80-120 DEG C for 6-12 hours.

4. The method of making a free amine-free non-ionic aqueous epoxy curing agent according to claim 3, wherein, In step 1), the mixing and reacting of the small molecule aldehyde and the hydroxyethyl diethylene triamine comprises: The small molecule aldehyde and the hydroxyethyl diethylene triamine are mixed and reacted, and the water produced in the reaction is removed in time, and then vacuumizing operation is carried out under the conditions of a temperature of 100-120 DEG C and a vacuum degree of -0.1 to -0.06 MPa for 1-3 hours to obtain the oxazolidine and aldimine capped modified amine.

5. The process for preparing a free amine-free non-ionic aqueous epoxy curing agent according to claim 1, characterized in that, In step 2), the polyether amine is M1000 with a molecular weight of 1000 g / mol; the multifunctional epoxy resin is at least one of F51 phenolic epoxy resin, isocyanuric acid triglycidyl ester and trimethylolpropane triglycidyl ether with an epoxy group functionality of not less than 3.

6. The method of making a free amine-free non-ionic aqueous epoxy curing agent according to claim 1 or 5, wherein, In step 2), the molar ratio of the oxazolidine and aldimine capped modified amine to the total epoxy groups in the multifunctional epoxy resin is 1.0:1.05-1.2; the mass ratio of the multifunctional epoxy resin to the polyether amine is 1.14-1.57:1.0; the modified amine and the polyether amine modified multifunctional epoxy resin are reacted at 60-90 DEG C for 2-4 hours.

7. The process for preparing a free amine-free non-ionic aqueous epoxy curing agent according to claim 1, characterized in that, In step 3), the monofunctional glycidyl ether is at least one of a C1-C 14 alkyl glycidyl ether, a phenyl glycidyl ether, a benzyl glycidyl ether, an o-tolyl glycidyl ether.

8. The method of making a free amine-free non-ionic aqueous epoxy curing agent according to claim 1 or 7, wherein, In step 3), the mass ratio of the hydrophilic modified oxazolidine and aldimine capped modified resin amine to water is 1.26-1.44:1.0; the molar ratio of the epoxy groups in the hydrophilic modified oxazolidine and aldimine capped modified resin amine to the monofunctional glycidyl ether is 1.0:0.2-1.

0.

9. The process for preparing a free amine-free non-ionic aqueous epoxy curing agent according to claim 8, characterized in that, In step 3), the reaction is carried out at 60-90 DEG C for 2-5 hours.

10. A nonionic aqueous epoxy curing agent free of free amine, characterized in that, The non-ionic waterborne epoxy curing agent without free amine is prepared by the method of any one of claims 1-9.

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