Anionic epoxy resin-based polyol aqueous dispersion and preparation method thereof

Abstract

The invention discloses an anionic epoxy resin-based polyol aqueous dispersion and a preparation method thereof, and belongs to the technical field of waterborne epoxy resin preparation. Comprising the following steps: 1) adding a mixed solution of a chain extender and a catalyst into an epoxy resin solution at 0-40 DEG C, preserving heat for 1-4 hours to obtain an intermediate, and 2) adding a mixed solution of a hydroxyl end-capping reagent and a carboxyl end-capping reagent into the intermediate, reacting at 20-60 DEG C for 1-4 hours, adding pure water under high-speed stirring, and dispersing to obtain the aqueous dispersion. According to the polyhydric alcohol prepared by the invention, high-activity primary hydroxyl groups can be introduced to the tail end and the middle of a resin main chain, so that the polyhydric alcohol is more suitable for a polyurethane coating system without high-temperature baking, and is completely compatible with anionic hydroxy acrylic latex / dispersion; and the water resistance, the salt fog resistance and the interlayer adhesive force of the water-based two-component acrylic coating can be effectively improved through cold splicing use. The preparation process is simple, the reaction conditions are mild, and the product is more flexible in use mode.

Description

Technical Field

[0001] This invention relates to the field of waterborne epoxy resin preparation technology, and particularly to a polyol aqueous dispersion and its preparation method. Background Technology

[0002] Two-component acrylic resins, with their excellent weather resistance, are widely used in decorative coatings. However, they generally suffer from poor water resistance, salt spray resistance, and poor adhesion after recoating. Epoxy resins, on the other hand, complement these properties in many ways. Although epoxy primer + acrylic topcoat solutions can solve most problems, there are still many applications where high performance is required using only acrylic coatings. Therefore, how to use epoxy resins for cold blending or chemical modification of acrylic resins has become a research hotspot.

[0003] Integrating epoxy and acrylic resins during the synthesis stage has been a popular research topic, including the preparation of two-component epoxy-acrylic hybrid emulsions using emulsion polymerization (a typical product is Dow MAINCOTE AEH-20), and the preparation of epoxy-grafted acrylic dispersions using solution polymerization. These technologies generally suffer from drawbacks such as complex processes, high costs, and the inability to adjust the epoxy resin content in coating formulations. On the other hand, these hybrid resins typically retain epoxy groups or use amines to open the epoxy groups, making them suitable for amine-curing systems, air-drying systems (for epoxy esters), or blocked isocyanate-curing systems (cathodic electrophoretic coatings), but unsuitable for common anionic waterborne hydroxyl acrylic polyurethane or amino baking varnish curing systems.

[0004] Modifying epoxy resin into a polyol aqueous dispersion and then cold-blending it with waterborne hydroxypropyl resin is obviously the simplest application method, but it places stricter requirements on the compatibility of the two resins: most waterborne hydroxyacrylic resins (including hydroxyacrylic latex and hydroxyacrylic dispersion) are anionic, and the resin backbone or the emulsifier that plays a stabilizing role contains a large number of acid groups. Therefore, the hydrophilic groups of the modified epoxy resin must be anionic or nonionic, and the backbone cannot contain amine basic groups. Otherwise, the resins will form salts with each other, which will seriously affect the storage stability. Therefore, the chemical methods for preparing epoxy resin-based polyols are very limited.

[0005] Patent CN201110407743.7 discloses a self-emulsifying nonionic terpene-based epoxy resin polyol emulsion and its preparation method. The method involves blending polyethylene glycol, a small-molecule polyol, and epoxy resin, followed by ring-opening via a strong acid catalyst to obtain a self-emulsifying block copolymer. However, this technical route has several drawbacks: after ring-opening with the epoxy resin, the main chain hydroxyl groups are mostly highly hindered secondary hydroxyl groups generated during ring-opening, while highly active primary hydroxyl groups are only present at the very end, easily leading to slow drying speed and low crosslinking density in polyurethane coatings. Using ternary or polyols may introduce primary hydroxyl groups into the resin to some extent, but the amount used is extremely limited, otherwise it is easy to cause excessive molecular weight or gelation. On the other hand, this invention uses sulfuric acid or boron trifluoride ether as a catalyst, and there is no neutralization or elimination step in the later stage of the reaction. It is easy to affect the stability when mixed with weakly alkaline aqueous hydroxypropyl resin. Patent CN101914194A discloses an anionic terpene-based epoxy resin polyol amine aqueous dispersion and preparation method, which uses aminocarboxylic acid to introduce carboxyl groups at the resin end to form salts. Not only does it contain basic groups in the main chain, which are incompatible with anionic acrylic resins, but all the hydroxyl groups in the structure are secondary hydroxyl groups generated by ring opening, resulting in low reactivity. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an anionic epoxy resin-based polyol aqueous dispersion and its preparation method. Based on the efficient ring-opening reaction between thiol groups and epoxy, highly active primary hydroxyl groups are simultaneously introduced into the middle and end of the resin chain segments through chain extenders and hydroxyl end-capping agents. This can accelerate the curing speed or reduce the curing temperature, while the higher crosslinking density leads to better paint film performance. On the other hand, the introduction of carboxyl groups to form anionic hydrophilic groups with the catalyst results in good compatibility with commonly used anionic hydroxyl acrylic latex / aqueous dispersions. Cold blending can improve the corrosion resistance and interlayer adhesion of acrylic coatings.

[0007] The objective of this invention is achieved as follows: an anionic epoxy resin-based polyol aqueous dispersion, prepared from raw materials comprising the following parts by mass: 20-40 parts epoxy resin, 2-10 parts chain extender, 2-10 parts hydroxyl end-capping agent, 1-8 parts carboxyl end-capping agent, 2-8 parts catalyst, 0-10 parts co-solvent, and 30-70 parts water.

[0008] Furthermore, the epoxy resin comprises one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin and bisphenol S type epoxy resin with an epoxy equivalent of 100~400 g / eq.

[0009] Furthermore, the chain extender is a compound whose chemical structure contains at least one primary hydroxyl group and two thiol groups; The hydroxyl capping agent is a compound containing at least one primary hydroxyl group and one thiol group in its chemical structure; The carboxyl end-capping agent is a compound containing at least one primary hydroxyl group and one thiol group in its chemical structure; The molar ratio of epoxy resin to chain extender is 1.5~2.5:1, and the ratio of the total amount of epoxy groups in epoxy resin to the total amount of mercapto groups in chain extender / capping agent is 0.9~1.1:1.

[0010] Furthermore, the chain extender is selected from one or more of dimercaprol, 2,2-bis(mercaptomethyl)-1,3-propanediol, and trimethylolpropane di(3-mercaptopropionate).

[0011] Furthermore, the hydroxyl end-capping agent is selected from one or more of 2-mercaptoethanol, 3-mercaptopropanol, 3-mercapto-1,2-propanediol, 3-mercapto-3-methyl-1-butanol, and 4-mercapto-1-butanol; the carboxyl end-capping agent is selected from one or more of 2-mercaptoacetic acid, 3-mercaptopropionic acid, and mercaptosuccinic acid.

[0012] Furthermore, the catalyst is selected from any one of N,N-dimethylethanolamine, triethanolamine, and triethylamine; the co-solvent is selected from one or more of propylene glycol methyl ether, ethylene glycol butyl ether, and diethylene glycol butyl ether.

[0013] A method for preparing an anionic epoxy resin-based polyol aqueous dispersion includes the following steps: Step 1) Mix epoxy resin and cosolvent to form a bottom solution, add a mixture of end-capping agent and catalyst, and keep warm for a period of time to obtain an intermediate; Step 2) At a certain temperature, add a mixture of hydroxyl end-capping agent and carboxyl end-capping agent to the intermediate, keep it warm for a period of time, and then add water to disperse it to obtain epoxy resin-based polyol aqueous dispersion.

[0014] Furthermore, the specific process of the reaction in step 1) is as follows: the temperature of the material inside the reactor is maintained at 0~40℃ for 1~4 hours; The specific process of the reaction in step 2) is as follows: the temperature of the material in the reactor is maintained at 20~60℃ for 1~4h, and then the required pure water is added at once. The mixture is dispersed at 50℃ for at least 30min to obtain an epoxy resin-based polyol aqueous dispersion.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Taking advantage of the high reactivity of thiol and epoxy groups under the action of tertiary amine catalyst, hydroxyl and carboxyl groups can be introduced into the resin structure under low temperature conditions, avoiding the side reactions of carboxyl, hydroxyl and epoxy groups in high temperature environment; at the same time, the tertiary amine catalyst itself is also a neutralizing agent of carboxyl groups, and can be directly added with water for self-emulsification without the need for a post-neutralization step, making the process simple.

[0016] (2) The thioether structure generated after the mercapto reaction is neutral in water. The hydrophilic group is a carboxyl group that forms a salt with a monotertiary amine. The hydrophilic system is a typical anionic system, so it has good compatibility with anionic waterborne acrylic latex / dispersion.

[0017] (3) By using a thiol chain extender and end-capping agent containing primary hydroxyl groups, highly active primary hydroxyl groups are introduced into the middle and end of the resin, which effectively ensures the curing speed and crosslinking density of the polyol in the two-component coating.

[0018] (4) The epoxy resin-based polyol water dispersion obtained in this invention is particularly suitable for blending with waterborne hydroxy acrylic latex / dispersion for use in polyurethane and amino baking paints. The introduction of epoxy resin structure can significantly improve the performance of coatings in terms of corrosion resistance and adhesion, and the amount added can be flexibly adjusted in the coating formulation according to the requirements. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 A method for preparing an anionic epoxy resin-based polyol aqueous dispersion A includes the following steps: (1) Add 27 parts by weight of bisphenol A type epoxy resin with an epoxy equivalent of 196 g / eq and 7 parts by weight of propylene glycol methyl ether to the reactor and mix them as the bottom liquid for later use; then add 4 parts by weight of dimercaptopropanol and 5 parts by weight of triethanolamine mixture, and keep the material in the reactor at 25°C for 4 hours to obtain the intermediate. (2) Add 3 parts by weight of a mixture of 2-mercaptoethanol and 5 parts by weight of mercaptosuccinic acid to the intermediate, heat to 50°C and keep warm for 4 hours, then add 49 parts by weight of pure water under high-speed stirring, and continue stirring at 50°C for 30 minutes to obtain an anionic epoxy resin-based polyol aqueous dispersion A with a solid content of 45% and an appearance of milky white with a bluish tint. (3) According to the waterborne two-component acrylic polyurethane formulation shown in Table 1, replace 10% by weight of hydroxyl acrylic dispersion with anionic epoxy resin-based polyol water dispersion A. Take a portion of component A and seal it in a 50℃ oven to test its storage stability. Add the remaining component B according to the formulation ratio to make a varnish and apply it to a tinplate substrate. Prepare a single-layer coating and test its water resistance (refer to national standard GB / T 1733-1993). Take another substrate to prepare a single layer coating. After it is completely dry, apply another layer. After it is completely dry, test the interlayer adhesion (refer to national standard GB / T 9286-2021). Example 2 A method for preparing an anionic epoxy resin-based polyol aqueous dispersion B includes the following steps: (1) Add 28 parts by weight of bisphenol A type epoxy resin with an epoxy equivalent of 196 g / eq and 6 parts by weight of propylene glycol methyl ether to the reactor and mix them as the bottom liquid for later use; then add 5 parts by weight of a mixture of 2,2-bis(mercaptomethyl)-1,3-propanediol and 3 parts by weight of N,N-dimethylethanolamine, and keep the material in the reactor at 25°C for 4 hours to obtain the intermediate; (2) Add 4 parts by weight of a mixture of 2-mercaptoethanol and 3 parts by weight of mercaptosuccinic acid to the intermediate, heat to 50°C and keep warm for 4 hours, then add 51 parts by weight of pure water under high-speed stirring, and continue stirring at 50°C for 30 minutes to obtain anionic epoxy resin-based polyol aqueous dispersion B with a solid content of 45% and an appearance of milky white with a bluish tint. (3) According to the waterborne two-component acrylic polyurethane formulation shown in Table 1, replace 10% by weight of hydroxyl acrylic dispersion with anionic epoxy resin-based polyol water dispersion B. Take a portion of component A and seal it in a 50℃ oven to test its storage stability. Add the remaining component B according to the formulation ratio to make a varnish and apply it to a tinplate substrate. Prepare a single-layer coating and test its water resistance (refer to national standard GB / T 1733-1993). Take another substrate to prepare a single layer coating. After it is completely dry, apply another layer. After it is completely dry, test the interlayer adhesion (refer to national standard GB / T 9286-2021). Example 3 A method for preparing an anionic epoxy resin-based polyol aqueous dispersion C includes the following steps: (1) Add 29 parts by weight of bisphenol A type epoxy resin with an epoxy equivalent of 196 g / eq and 6 parts by weight of propylene glycol methyl ether to the reactor and mix them as the bottom liquid for later use; then add 6 parts by weight of a mixture of 2,2-bis(mercaptomethyl)-1,3-propanediol and 3 parts by weight of N,N-dimethylethanolamine, and keep the material in the reactor at 25°C for 4 hours to obtain the intermediate; (2) Add 3 parts by weight of a mixture of 2-mercaptoethanol and 4 parts by weight of 3-mercaptopropionic acid to the intermediate, heat to 50°C and keep warm for 4 hours, then add 50 parts by weight of pure water under high-speed stirring, and continue stirring at 50°C for 30 minutes to obtain an anionic epoxy resin-based polyol aqueous dispersion C with a solid content of 45% and an appearance of milky white with a bluish tint. (3) According to the waterborne two-component acrylic polyurethane formulation shown in Table 1, replace 10% by weight of hydroxyl acrylic dispersion with anionic epoxy resin-based polyol water dispersion C. Take a portion of component A and seal it in a 50℃ oven to test its storage stability. Add the remaining component B according to the formulation ratio to make a varnish and apply it to a tinplate substrate. Prepare a single-layer coating and test its water resistance (refer to national standard GB / T 1733-1993). Take another substrate to prepare a single layer and apply another layer after it is completely dry. After it is completely dry, test the interlayer adhesion (refer to national standard GB / T 9286-2021). Example 4 A method for preparing an anionic epoxy resin-based polyol aqueous dispersion D includes the following steps: (1) Add 31 parts by weight of bisphenol A type epoxy resin with an epoxy equivalent of 227 g / eq and 7 parts by weight of propylene glycol methyl ether to the reactor and mix them as the bottom liquid for later use; then add 5 parts by weight of a mixture of 2,2-bis(mercaptomethyl)-1,3-propanediol and 2 parts by weight of N,N-dimethylethanolamine, and keep the material in the reactor at 25°C for 4 hours to obtain the intermediate; (2) Add 4 parts by weight of a mixture of 3-mercapto-1,2-propanediol and 3 parts by weight of 3-mercaptopropionic acid to the intermediate, heat to 50°C and keep warm for 4 hours, then add 49 parts by weight of pure water under high speed stirring, and continue stirring at 50°C for 30 minutes to obtain an anionic epoxy resin-based polyol aqueous dispersion D with a solid content of 45% and an appearance of milky white with blue light; (3) According to the waterborne two-component acrylic polyurethane formulation shown in Table 1, replace 10% by weight of hydroxyl acrylic dispersion with anionic epoxy resin-based polyol water dispersion D. Take a portion of component A and seal it in a 50℃ oven to test its storage stability. Add the remaining component B according to the formulation ratio to make a varnish and apply it to a tinplate substrate. Prepare a single-layer coating and test its water resistance (refer to national standard GB / T 1733-1993). Take another substrate to prepare a single layer coating. After it is completely dry, apply another layer. After it is completely dry, test the interlayer adhesion (refer to national standard GB / T 9286-2021). Example 5 A method for preparing an anionic epoxy resin-based polyol aqueous dispersion E includes the following steps: (1) Add 29 parts by weight of bisphenol A type epoxy resin with an epoxy equivalent of 227 g / eq and 10 parts by weight of ethylene glycol butyl ether to the reactor and mix them as the bottom liquid for later use; then add 5 parts by weight of a mixture of 2,2-bis(mercaptomethyl)-1,3-propanediol and 3 parts by weight of N,N-dimethylethanolamine, and keep the material in the reactor at 25°C for 4 hours to obtain the intermediate; (2) Add 5 parts by weight of a mixture of 3-mercapto-1,2-propanediol and 2 parts by weight of mercaptosuccinic acid to the intermediate, heat to 50°C and keep warm for 4 hours, then add 45 parts by weight of pure water under high speed stirring, and continue stirring at 50°C for 30 minutes to obtain an anionic epoxy resin-based polyol aqueous dispersion E with a solid content of 45% and an appearance of milky white with blue light; (3) According to the waterborne two-component acrylic polyurethane formulation shown in Table 1, replace 10% by weight of hydroxyl acrylic dispersion with anionic epoxy resin-based polyol water dispersion E. Take a portion of component A and seal it in a 50℃ oven to test its storage stability. Add the remaining component B according to the formulation ratio to make a varnish and apply it to a tinplate substrate. Prepare a single-layer coating and test its water resistance (refer to national standard GB / T 1733-1993). Take another substrate to prepare a single layer coating. After it is completely dry, apply another layer. After it is completely dry, test the interlayer adhesion (refer to national standard GB / T 9286-2021). Example 6 A method for preparing an anionic epoxy resin-based polyol aqueous dispersion F includes the following steps: (1) Add 30 parts by weight of bisphenol A type epoxy resin with an epoxy equivalent of 227 g / eq and 10 parts by weight of ethylene glycol butyl ether to the reactor and mix them as the bottom liquid for later use; then add 5 parts by weight of a mixture of 2,2-bis(mercaptomethyl)-1,3-propanediol and 3 parts by weight of N,N-dimethylethanolamine, and keep the material in the reactor at 25°C for 4 hours to obtain the intermediate; (2) Add 4 parts by weight of a mixture of 3-mercapto-1,2-propanediol and 3 parts by weight of 3-mercaptopropionic acid to the intermediate, heat to 50°C and keep warm for 4 hours, then add 45 parts by weight of pure water under high speed stirring, and continue stirring at 50°C for 30 minutes to obtain an anionic epoxy resin-based polyol aqueous dispersion F with a solid content of 45% and an appearance of milky white with blue light; (3) According to the waterborne two-component acrylic polyurethane formulation shown in Table 1, replace 10% by weight of hydroxyl acrylic dispersion with anionic epoxy resin-based polyol water dispersion F. Take a portion of component A and seal it in a 50℃ oven to test its storage stability. Add the remaining component B according to the formulation ratio to make a varnish. Apply it to a tinplate substrate and prepare a single-layer coating to test its water resistance (refer to national standard GB / T 1733-1993). Take another substrate to prepare a single layer coating. After it is completely dry, apply another layer. After it is completely dry, test the interlayer adhesion (refer to national standard GB / T 9286-2021). Comparative Example 1 According to the waterborne two-component acrylic polyurethane formulation shown in Table 1, without adding the epoxy resin-based polyol aqueous dispersion in the examples, a portion of component A was sealed in a 50°C oven to test its storage stability. The remaining component was added to component B according to the formulation ratio to make a varnish, which was then applied to a tinplate substrate to prepare a single-layer coating for water resistance testing (refer to national standard GB / T 1733-1993). Another substrate was used to prepare a single-layer coating, which was allowed to dry completely before being coated again. After drying, the interlayer adhesion was tested (refer to national standard GB / T 9286-2021). The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

[0021] Table 1: Formulation of Waterborne Two-Component Acrylic Polyurethane Clearvarnish

[0022] The performance test results of the above embodiments and comparative examples are shown in Table 2: Table 2: Performance of epoxy resin-based polyol aqueous dispersions and hydroxypropyl dispersions when combined

[0023] As shown in Table 2, the two-component waterborne polyurethane coating using only hydroxyl acrylic dispersion has poor water resistance and poor interlayer adhesion after recoating. However, the water resistance and adhesion are significantly improved after adding a small amount of epoxy resin-based polyol. Furthermore, the addition of epoxy resin-based polyol has no adverse effect on the thermal storage stability of component A, demonstrating the high compatibility of the product of this invention with waterborne hydroxyl acrylic resin. It is very suitable as a modifier for waterborne two-component hydroxyl acrylic coatings.

[0024] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. An anionic epoxy resin-based polyol aqueous dispersion, characterized in that, It is prepared from raw materials comprising the following parts by weight: 20-40 parts epoxy resin, 2-10 parts chain extender, 2-10 parts hydroxyl end-capping agent, 1-8 parts carboxyl end-capping agent, 2-8 parts catalyst, 0-10 parts co-solvent, and 30-70 parts water.

2. The anionic epoxy resin-based polyol aqueous dispersion according to claim 1, characterized in that, The epoxy resin comprises one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin and bisphenol S type epoxy resin with an epoxy equivalent of 100~400 g / eq.

3. The anionic epoxy resin-based polyol aqueous dispersion according to claim 2, characterized in that, The chain extender is a compound whose chemical structure contains at least one primary hydroxyl group and two thiol groups; The hydroxyl capping agent is a compound containing at least one primary hydroxyl group and one thiol group in its chemical structure; The carboxyl end-capping agent is a compound containing at least one primary hydroxyl group and one thiol group in its chemical structure; The molar ratio of epoxy resin to chain extender is 1.5~2.5:1, and the ratio of the total amount of epoxy groups in epoxy resin to the total amount of mercapto groups in chain extender / capping agent is 0.9~1.1:

1.

4. An anionic epoxy resin-based polyol aqueous dispersion according to any one of claims 1-3, characterized in that, The chain extender is selected from one or more of dimercaprol, 2,2-bis(mercaptomethyl)-1,3-propanediol, and trimethylolpropane di(3-mercaptopropionate).

5. An anionic epoxy resin-based polyol aqueous dispersion according to any one of claims 1-3, characterized in that, The hydroxyl end-capping agent is selected from one or more of 2-mercaptoethanol, 3-mercaptopropanol, 3-mercapto-1,2-propanediol, 3-mercapto-3-methyl-1-butanol, and 4-mercapto-1-butanol; the carboxyl end-capping agent is selected from one or more of 2-mercaptoacetic acid, 3-mercaptopropionic acid, and mercaptosuccinic acid.

6. An anionic epoxy resin-based polyol aqueous dispersion according to any one of claims 1-3, characterized in that, The catalyst is selected from any one of N,N-dimethylethanolamine, triethanolamine, and triethylamine; the co-solvent is selected from one or more of propylene glycol methyl ether, ethylene glycol butyl ether, and diethylene glycol butyl ether.

7. A method for preparing an anionic epoxy resin-based polyol aqueous dispersion as described in any one of claims 1-6, characterized in that, Includes the following steps: Step 1) Mix epoxy resin and cosolvent to form a bottom solution, add a mixture of end-capping agent and catalyst, and keep warm for a period of time to obtain an intermediate; Step 2) At a certain temperature, add a mixture of hydroxyl end-capping agent and carboxyl end-capping agent to the intermediate, keep it warm for a period of time, and then add water to disperse it to obtain epoxy resin-based polyol aqueous dispersion.

8. The method for preparing anionic epoxy resin-based polyol aqueous dispersion according to claim 7, characterized in that, The specific process of the reaction in step 1) is as follows: the temperature of the material in the reactor is maintained at 0~40℃ for 1~4 hours; The specific process of the reaction in step 2) is as follows: the temperature of the material in the reactor is maintained at 20~60℃ for 1~4h, and then the required pure water is added at once. The mixture is dispersed at 50℃ for at least 30min to obtain an epoxy resin-based polyol aqueous dispersion.

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