A waterborne polyurethane curing agent with high water resistance, its preparation method and application

Abstract

The present invention belongs to the technical field of coatings, and specifically discloses a waterborne polyurethane curing agent with high water resistance, its preparation method and application. The raw material components of the waterborne polyurethane curing agent, by weight, include: 1.5 - 5 parts of amino sulfonate; 95.0 - 97.5 parts of hexamethylene diisocyanate trimer; 6 - 16 parts of silane coupling agent; 0.15 - 0.5 part of catalyst; the silane coupling agent includes 3-mercaptopropyltriethoxysilane and mercaptopropyltrimethoxysilane. The present invention first synthesizes with amino sulfonate and hexamethylene diisocyanate trimer to ensure that the waterborne polyisocyanate curing agent has excellent dispersibility without dilution with solvent; then, 3-mercaptopropyltriethoxysilane and mercaptopropyltrimethoxysilane react chemically with part of the isocyanate groups under the action of the catalyst in the original waterborne polyisocyanate system, and the siloxy groups are grafted onto the molecular chain to obtain a waterborne polyurethane curing agent with high water resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of coatings, and particularly relates to a waterborne polyurethane curing agent with high water resistance, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, the country has continuously raised environmental protection requirements. Undoubtedly, waterborne coatings have become one of the important development directions of current coating technologies. Among them, a film obtained by using a waterborne polyurethane coating crosslinked with an isocyanate compound can have very excellent abrasion resistance, chemical resistance, and stain resistance.

[0003] Waterborne isocyanate curing agents have excellent performance. Due to the high reactivity of the isocyanate group, they can crosslink and cure with polymers having active hydrogen atoms such as alcohols and amines at room temperature. However, because a large number of hydrophilic groups are introduced, after film formation in the later stage, there is still a certain difference in water resistance compared with oil-based polyurethanes, which greatly limits the application and popularization of polyurethane technology. To solve this technical problem, a waterborne polyurethane curing agent with high water resistance has emerged. By introducing siloxane groups into the waterborne polyurethane curing agent and adjusting an appropriate ratio, the bite force between the polyurethane and the substrate is greatly increased during film formation, and finally the purpose of greatly improving the water resistance of the paint film is achieved.

[0004] Currently, for waterborne polyurethane curing agents on the market, in order to improve their water resistance, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane or 3-aminopropyltriethoxysilane is mostly used as an additive, and it needs to be used immediately after being mixed with the polyurethane system. Although the water resistance is improved to a certain extent, it also has a greater impact on the pot life and the appearance of the paint film.

[0005] Therefore, it is urgent to develop a waterborne polyurethane curing agent that can effectively avoid its impact on the pot life of the system and the appearance of the paint film, and at the same time improve the water resistance of the paint film. Summary of the Invention

[0006] The present invention aims to solve the technical problems existing in the existing waterborne polyurethane curing agents, such as the need for immediate preparation and use, resulting in a short pot life of the system, poor aesthetics and water resistance of the paint film. For this purpose, the present invention provides a waterborne polyurethane curing agent with high water resistance, a preparation method thereof, and an application thereof.

[0007] The inventive concept of the present invention is as follows: First, by synthesizing with sulfamic acid salt and hexamethylene diisocyanate trimer, hydrophilic properties are provided for the polyisocyanate, thereby ensuring that the aqueous polyisocyanate curing agent has excellent dispersibility without being diluted with a solvent; then, 3-mercaptopropyltriethoxysilane and mercaptopropyltrimethoxysilane react chemically with some isocyanate groups under the action of the catalyst in the original aqueous polyisocyanate system, and the siloxy groups are grafted onto the molecular chain to obtain a highly water-resistant aqueous polyurethane curing agent. This curing agent can be stored stably for a long time and does not require additional addition of other silane coupling agents during use, and greatly improves the water resistance of the system while ensuring good gloss stability.

[0008] To solve the above technical problems, in the first aspect of the present invention, an aqueous polyurethane curing agent is provided. The raw material components of the aqueous polyurethane curing agent, by weight, include:

[0009]

[0010] The silane coupling agent includes 3-mercaptopropyltriethoxysilane and mercaptopropyltrimethoxysilane.

[0011] Specifically, in the present invention, first, sulfamic acid salt and hexamethylene diisocyanate trimer are synthesized. Since the sulfonic acid group is a very hydrophilic group, when combined with the isocyanate trimer, it can act as an internal emulsifying hydrophilic group, thereby providing hydrophilicity for the system and further ensuring that the aqueous polyisocyanate curing agent has excellent dispersibility without being diluted with a solvent; then, -SH groups are introduced through 3-mercaptopropyltriethoxysilane and mercaptopropyltrimethoxysilane. Under the influence of the catalyst in the original aqueous polyisocyanate system, the hydrogen therein reacts with the isocyanate, so that the siloxy groups are attached to the molecular chain to improve the water resistance of the aqueous polyurethane curing agent.

[0012] At the same time, the present invention uses the catalyst in the original system to promote the rapid grafting of the two silane coupling agents, 3-mercaptopropyltriethoxysilane and mercaptopropyltrimethoxysilane, onto the isocyanate molecular chain without additional addition of a catalyst. During the film-forming process, silicon atoms are enriched on the surface, and the siloxy groups are more likely to hydrolyze into silanol groups when the polyurethane is dispersed in water. During the film-forming process, dehydration forms a three-dimensional silicon-silicon cross-linked network, which spreads over the surface of the paint film and tightly bites the substrate, thereby greatly improving the mechanical properties, water resistance and weather resistance of the paint film.

[0013] Therefore, the present invention uses sulfamic acid salt, hexamethylene diisocyanate trimer and a specific silane coupling agent as the main raw materials. Under a specific raw material ratio, an aqueous polyurethane curing agent with high water resistance, good mechanical properties and long-term stable storage can be prepared.

[0014] As a further improvement of the above solution, the NCO content of the hexamethylene diisocyanate trimer is 21-24%.

[0015] As a further improvement of the above solution, the mass ratio of the 3-mercaptopropyltriethoxysilane to the mercaptopropyltrimethoxysilane is (0.3-2.7):1.

[0016] Preferably, the addition amount of the 3-mercaptopropyltriethoxysilane is 3-8 parts by weight.

[0017] More preferably, the addition amount of the 3-mercaptopropyltriethoxysilane is 4-6 parts by weight.

[0018] Preferably, the addition amount of the mercaptopropyltrimethoxysilane is 3-8 parts by weight.

[0019] More preferably, the addition amount of the mercaptopropyltrimethoxysilane is 4-6 parts by weight.

[0020] Preferably, the amino sulfonate is selected from at least one of sodium 2-tert-butyl-4-(cyclohexylamino)-1-butanesulfonate, sodium 2-tert-butyl-3-(cyclohexylamino)-1-propanesulfonate, and sodium 2-isopentyl-3-(cyclohexylamino)-1-propanesulfonate.

[0021] Preferably, the catalyst is N,N-dimethylbenzylamine.

[0022] The second aspect of the present invention provides a preparation method of an aqueous polyurethane curing agent, which is used to prepare the aqueous polyurethane curing agent described in the first aspect of the present invention, and includes the following steps:

[0023] (1) Mix the amino sulfonate, hexamethylene diisocyanate trimer and catalyst, and carry out a reaction to obtain a reaction product;

[0024] (2) Add a siloxane compound to the reaction product, and carry out a secondary reaction to obtain the aqueous polyurethane curing agent.

[0025] As a further improvement of the above solution, in step (1), the temperature of the reaction is 80-100 °C, and the reaction time is 3-10 hours.

[0026] As a further improvement of the above solution, in step (2), the temperature of the secondary reaction is 40-80 °C, and the reaction is carried out until the NCO content is 15-18%.

[0027] Specifically, the reaction end point of preparing the high water-resistant aqueous polyurethane curing agent of the present invention is based on the isocyanate group content dropping to the theoretical value. The isocyanate group content of the isocyanate is measured by the toluene-di-n-butylamine titration method, and the difference from the theoretical content of the isocyanate group needs to be less than 0.05 wt%.

[0028] As a further improvement of the above scheme, both step (1) and step (2) are carried out under the protection of inert gas.

[0029] Preferably, the inert gas is nitrogen.

[0030] As a further improvement of the above solution, the solid content of the waterborne polyurethane curing agent is 99-100%.

[0031] The third aspect of the present invention provides a waterborne polyurethane coating, which comprises the waterborne polyurethane curing agent described in the first aspect of the present invention.

[0032] Compared with the prior art, the above technical solution of the present invention has at least the following technical effects or advantages:

[0033] (1) The waterborne polyurethane curing agent of the present invention utilizes 3-mercaptopropyltriethoxysilane and mercaptopropyltrimethoxysilane to modify the waterborne polyisocyanate curing agent obtained by reacting aminosulfonate with hexamethylene diisocyanate trimer. The obtained waterborne polyurethane curing agent has high water resistance.

[0034] (2) During the preparation of the present invention, the catalyst existing in the aqueous polyisocyanate system of the first reaction is used as 3-mercaptopropyltriethoxysilane and mercaptopropyltrimethoxysilane catalyst to modify the isocyanate group of the aqueous polyisocyanate. The reaction conditions are mild and no additional catalyst is required, making the system more stable during subsequent storage.

[0035] (3) The waterborne polyurethane curing agent prepared by the present invention has high gloss, the overall paint film is hard and not brittle, and has high wear resistance, and greatly improves the final water resistance of the paint film, and can be used in various industrial coatings. DETAILED DESCRIPTION

[0036] The present invention is described in detail below with reference to the examples to facilitate understanding of the present invention by those skilled in the art. It is necessary to point out that the examples are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above-mentioned invention should still fall within the scope of protection of the present invention. At the same time, the raw materials mentioned below that are not described in detail are all commercially available products; the process steps or preparation methods that are not mentioned in detail are all process steps or preparation methods known to those skilled in the art.

[0037] Example 1

[0038] A water-based polyurethane curing agent, the raw material components of which include, by weight:

[0039]

[0040] A preparation method of an aqueous polyurethane curing agent, comprising the following steps:

[0041] (1) Put hexamethylene diisocyanate trimer into a four-necked flask equipped with a stirrer, a thermometer and a nitrogen inlet. Under nitrogen protection, heat up to 60 °C, and while stirring, add sodium 2-tert-butyl-4-(cyclohexylamino)-1-butanesulfonate and N,N-dimethylbenzylamine. After reacting at 80 °C for 6 hours, sample and detect the isocyanate group content until it is close to the theoretical value (the difference from the theoretical value content does not exceed 0.5%); obtain the reaction product;

[0042] (2) Add 3-mercaptopropyltriethoxysilane and mercaptopropyltrimethoxysilane to the reaction product obtained in step (1). After reacting at 45 °C for 5 hours, sample and detect the isocyanate group content to reach the theoretical value (17.5 wt%), and prepare the aqueous polyurethane curing agent of this example. The determination of the isocyanate group content adopts the toluene-di-n-butylamine titration method in HGT 2409-1992.

[0043] Example 2

[0044] An aqueous polyurethane curing agent, calculated by weight, its raw material components include:

[0045]

[0046] A preparation method of an aqueous polyurethane curing agent, comprising the following steps:

[0047] (1) Put hexamethylene diisocyanate trimer into a four-necked flask equipped with a stirrer, a thermometer and a nitrogen inlet. Under nitrogen protection, heat up to 60 °C, and while stirring, add sodium 2-tert-butyl-3-(cyclohexylamino)-1-propanesulfonate and N,N-dimethylbenzylamine. After reacting at 90 °C for 4.5 hours, sample and detect the isocyanate group content until it is close to the theoretical value (the difference from the theoretical value content does not exceed 0.5%); obtain the reaction product;

[0048] (2) Add 3-mercaptopropyltriethoxysilane and mercaptopropyltrimethoxysilane to the reaction product obtained in step (1). After reacting at 80 °C for 5 hours, sample and detect the isocyanate group content to reach the theoretical value (18.5 wt%), and prepare the aqueous polyurethane curing agent of this example. The determination of the isocyanate group content adopts the toluene-di-n-butylamine titration method in HGT 2409-1992.

[0049] Example 3

[0050] An aqueous polyurethane curing agent, calculated by weight, its raw material components include:

[0051]

[0052] A preparation method of an aqueous polyurethane curing agent, comprising the following steps:

[0053] (1) Put hexamethylene diisocyanate trimer into a four-necked flask equipped with a stirrer, a thermometer and a nitrogen inlet. Under nitrogen protection, heat up to 60°C, and while stirring, add sodium 2-isopentyl-3-(cyclohexylamino)-1-propane sulfonate and N,N-dimethylbenzylamine. After reacting for 5.5 hours at 80°C, sample and detect the isocyanate group content until it is close to the theoretical value (the difference from the theoretical value is not more than 0.5%); obtain the reactant;

[0054] (2) Add 3-mercaptopropyltriethoxysilane and mercaptopropyltrimethoxysilane to the reactant obtained in step (1). After reacting for 5 hours at 80°C, sample and detect that the isocyanate group content reaches the theoretical value (16.5 wt%), and obtain the aqueous polyurethane curing agent of this example. The determination of the isocyanate group content uses the toluene-di-n-butylamine titration method in HGT 2409-1992.

[0055] Comparative Example 1

[0056] An aqueous polyurethane curing agent, by weight, its raw material components include:

[0057]

[0058] A preparation method of an aqueous polyurethane curing agent, comprising the following steps:

[0059] (1) Put hexamethylene diisocyanate trimer into a four-necked flask equipped with a stirrer, a thermometer and a nitrogen inlet. Under nitrogen protection, heat up to 60°C, and while stirring, add sodium 2-tert-butyl-4-(cyclohexylamino)-1-butane sulfonate and N,N-dimethylbenzylamine. After reacting for 5.5 hours at 80°C, sample and detect the isocyanate group content until it is close to the theoretical value (the difference from the theoretical value is not more than 0.5%); obtain the reactant;

[0060] (2) Add 3-mercaptopropyltriethoxysilane and mercaptopropyltrimethoxysilane to the reactant obtained in step (1). After reacting for 5 hours at 80°C, sample and detect that the isocyanate group content reaches the theoretical value (16.5 wt%), and obtain the aqueous polyurethane curing agent of this comparative example. The determination of the isocyanate group content uses the toluene-di-n-butylamine titration method in HGT 2409-1992.

[0061] The difference between Comparative Example 1 and Example 3 is that mercaptopropyltrimethoxysilane is not added to the raw material components of the aqueous polyurethane curing agent, and the total addition amount of the catalyst remains unchanged.

[0062] Comparative Example 2

[0063] The commercially available waterborne polyurethane curing agent is Covestro XP2655.

[0064] Performance testing

[0065] 1. Preparation of waterborne polyurethane coatings

[0066] Using the waterborne polyurethane curing agents of Examples 1-3 and Comparative Examples 1-2 as Component B, waterborne polyurethane coatings were prepared. The preparation steps are as follows:

[0067] (1) By mass percentage, take 80% waterborne polyurethane dispersion Bayhydrol@2470, 0.25% wetting agent Twin 4100, 0.15% wetting agent Twin 810, 2.5% dipropylene glycol butyl ether, 2.5% dipropylene glycol monomethyl ether, 0.25% thickener COAPUR XS71, 0.35% waterborne leveling agent BYK-333, and 14% water, mix to obtain Component A;

[0068] (2) Weigh Component A and Component B prepared in step (1) according to the mass ratio of A to B being 8:1. Add Component B to Component A, and after mixing evenly, obtain the waterborne polyurethane coating.

[0069] 2. Coating performance testing

[0070] The waterborne polyurethane coatings prepared using the waterborne polyurethane curing agents of Examples 1-3 and Comparative Examples 1-2 as Component B were subjected to performance testing. The test results are shown in Table 1. Among them:

[0071] Water resistance test: Use a 100μm wet film applicator to prepare a paint film on the substrate with the waterborne polyurethane coating. After surface drying, cure it at 23°C and 60% humidity for 7 days. After edge sealing, soak it in clear water at 25°C and observe whether film defects such as whitening and pitting occur;

[0072] Pot life test: After mixing Components A and B, place them in an environment at 35°C, with the viscosity not doubling and the film properties not deteriorating;

[0073] Hardness test: According to GBT6739-1996;

[0074] Storage stability test: At room temperature and after storage at 50°C, the viscosity increase < 5% and the NCO decrease < 2.5%.

[0075] Table 1: Performance comparison table of waterborne polyurethane coatings

[0076]

[0077]

[0078] As can be seen from Table 1, the waterborne polyurethane curing agents prepared in Examples 1-3 of the present invention have excellent water solubility under the influence of hydrophilic groups, and often form extremely fine particles after being dispersed in water, thereby improving the transparency and gloss of the polyurethane. At the same time, 3-mercaptopropyltriethoxysilane and mercaptopropyltrimethoxysilane are used as addition materials, making the polyurethane paint film have an appropriate crosslinking density and excellent bite force with the substrate, thus greatly improving the excellent water resistance, mechanical properties and storage stability of the paint film.

[0079] Compared with the commercially available conventional polyisocyanate curing agent in Comparative Example 2, the waterborne polyurethane curing agents in Examples 1-3 have significantly improved gloss, water resistance, activation period, hardness and storage stability.

[0080] In Comparative Example 1, since only 3-mercaptopropyltriethoxysilane, a silane coupling agent, is used, its water resistance and hardness are lower than those in Examples 1-3.

[0081] For those of ordinary skill in the art to which the present invention pertains, several simple deductions or substitutions can be made without departing from the concept of the present invention, without the need for creative labor. Therefore, simple improvements made by those skilled in the art based on the disclosure of the present invention should fall within the protection scope of the present invention. The above embodiments are the preferred embodiments of the present invention, and all processes similar to the present invention and equivalent changes made thereto shall fall within the protection scope of the present invention.

Claims

1. An aqueous polyurethane curing agent, characterized in that, The raw material components of the aqueous polyurethane curing agent include, by weight parts: The silane coupling agent includes 3-mercaptopropyltriethoxysilane and mercaptopropyltrimethoxysilane; The aqueous polyurethane curing agent is prepared by a preparation method including the following steps: (1) Mix an amino sulfonate, a hexamethylene diisocyanate trimer and a catalyst, and carry out a reaction to obtain a reaction product; (2) Add a silane coupling agent to the reaction product, and carry out a secondary reaction to obtain the aqueous polyurethane curing agent.

2. The aqueous polyurethane curing agent according to claim 1, wherein The NCO content of the hexamethylene diisocyanate trimer is 21-24%.

3. The aqueous polyurethane curing agent according to claim 1, wherein By weight parts, the mass ratio of the 3-mercaptopropyltriethoxysilane to the mercaptopropyltrimethoxysilane is (0.3-2.7):

1.

4. The aqueous polyurethane curing agent according to claim 1, wherein The amino sulfonate is selected from at least one of sodium 2-tert-butyl-4-(cyclohexylamino)-1-butanesulfonate, sodium 2-tert-butyl-3-(cyclohexylamino)-1-propanesulfonate, and sodium 2-isopentyl-3-(cyclohexylamino)-1-propanesulfonate.

5. The aqueous polyurethane curing agent according to claim 1, wherein The catalyst is N,N-dimethylbenzylamine.

6. The aqueous polyurethane curing agent according to claim 1, characterized in that, In step (1), the temperature of the reaction is 80-100°C, and the reaction time is 3-10 hours.

7. The aqueous polyurethane curing agent according to claim 1, wherein In step (2), the temperature of the secondary reaction is 40-80°C, and the reaction ends when the NCO content reaches 15-18%.

8. The aqueous polyurethane curing agent according to claim 1, wherein Both step (1) and step (2) are carried out under the protection of an inert gas.

9. An aqueous polyurethane coating, characterized in that, The aqueous polyurethane coating contains the aqueous polyurethane curing agent according to any one of claims 1 to 8.

Images