A waterborne anion blocked isocyanate curing agent, its preparation method and application

Abstract

This invention relates to an aqueous anionic blocked isocyanate curing agent, its preparation method, and its application. The preparation method includes the following steps: (1) reacting isocyanate with a crosslinking agent to obtain modified isocyanate; (2) adding a capping agent to the system after the reaction in step (1) to obtain an intermediate; (3) adding a hydrophilic modifier and a solvent to the system after the reaction in step (2) to react; (4) adding a neutralizing agent to the system after the reaction in step (3) and mixing to obtain an aqueous anionic blocked isocyanate curing agent. The preparation method of the aqueous anionic blocked isocyanate curing agent provided by this invention is simple and convenient to operate. Through a specific preparation method, the obtained aqueous anionic blocked isocyanate curing agent can have excellent thermal storage stability, unsealing temperature, pot life, anti-yellowing performance, adhesion, and mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of waterborne coatings technology, and in particular to a waterborne anionic blocked isocyanate curing agent, its preparation method, and its application. Background Technology

[0002] With the increasing awareness of environmental protection and the increasingly stringent regulatory requirements, the emissions of volatile organic compounds (VOCs) from traditional solvent-based coatings have become increasingly harmful to the environment and human health. In order to replace traditional coatings, water-based coatings have attracted much attention due to their advantages such as being non-toxic, non-polluting, and having excellent mechanical properties. However, current water-based coatings still have some shortcomings in terms of performance, such as poor water resistance, low hardness, and poor chemical resistance. Specifically, these include: (1) Insufficient water resistance and chemical resistance, which can easily lead to problems such as coating delamination and precipitation, affecting the long-term performance of the coating; (2) Insufficient stability of the water-based curing agents used, especially in terms of thermal storage stability and service life; (3) While maintaining good performance, current water-based coatings are difficult to achieve lower unsealing temperatures and higher weather resistance, which limits their promotion and use in certain special application areas; (4) Difficulty in achieving a balance between hardness, abrasion resistance and flexibility, which affects the overall performance of the coating; (5) Poor adhesion to substrates such as metals and plastics, especially on complex-shaped parts, where insufficient adhesion is likely to occur.

[0003] To improve the performance of waterborne coatings, polyurethane modification and acrylate modification are commonly used. Polyurethane modification can improve the abrasion resistance and flexibility of the coating, but it tends to reduce the coating hardness; while acrylate modification can improve the water resistance and chemical resistance of the coating, but it affects the crosslinking density and hardness of the coating. Furthermore, to further improve the performance of waterborne coatings, novel polymers and crosslinking agents have been developed. For example, the physical properties of coatings are improved by introducing branched structures and increasing functionality; hydrophilic modifiers and crosslinking agents are used to improve the hydrophilicity and chemical resistance of the coating. However, there are still significant shortcomings in achieving lower unblocking temperatures, higher weather resistance, and superior adhesion while maintaining good coating performance.

[0004] CN110423323A discloses a water-soluble blocked polyurethane curing agent, its preparation method, and its application. It primarily uses a trifunctional isocyanate prepolymer. The isocyanate is partially blocked and then reacted with dimethylolcarboxylic acid to generate product A. The remaining -NCO groups in product A are then completely blocked to obtain the water-soluble blocked polyurethane curing agent. This curing agent has advantages such as a relatively small molecular weight, high solid content, high NCO%, and good water solubility (dissolving in water in any proportion). It is mainly used in conjunction with water-based resins to produce water-based baking paints and water-based high-temperature adhesives. However, its curing agent performance and stability are unsatisfactory.

[0005] CN108929427A discloses a method for preparing blocked isocyanates to improve the film-forming properties of cathodic electrophoretic coatings. The method includes preparing an isocyanate trimer under nitrogen protection, chain-extending it with a polyhydroxy monomer to prepare an isocyanate-terminated polyisocyanate prepolymer, and then blocking the prepolymer with a composite blocking agent to prepare a branched polyisocyanate crosslinking agent. In another method, diisocyanate is added to the branched system, and chain-extending it with a polyester polyol to prepare an isocyanate-terminated diisocyanate prepolymer, which is then hydrophilically modified with an alkynyl surfactant, and finally blocked with a composite blocking agent to obtain a blocked polyisocyanate crosslinking agent. However, its stability and deblocking performance are poor.

[0006] Therefore, designing and providing a water-based anionic blocked isocyanate curing agent with excellent thermal storage stability, pot life and adhesion has become an urgent problem to be solved. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a water-based anionic blocked isocyanate curing agent, its preparation method, and its application. When applied to water-based coatings, this water-based anionic blocked isocyanate curing agent effectively solves the problems of poor water resistance, insufficient thermal stability, high unsealing temperature, and difficulty in achieving strong adhesion to the substrate found in existing water-based coatings.

[0008] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing an aqueous anionic blocked isocyanate curing agent, the method comprising the following steps: (1) The isocyanate is reacted with a crosslinking agent to obtain a modified isocyanate; (2) Add a capping agent to the system after the reaction described in step (1) to carry out the reaction and obtain an intermediate; (3) Add a hydrophilic modifier and a solvent to the system after the reaction described in step (2) to carry out the reaction; (4) After adding a neutralizing agent to the system after the reaction in step (3) and mixing, an aqueous anionic blocked isocyanate curing agent is obtained.

[0009] The waterborne anionic blocked isocyanate curing agent provided by this invention has a simple and convenient preparation method. Through its specific preparation method, the resulting waterborne anionic blocked isocyanate curing agent exhibits excellent thermal storage stability, unsealing temperature, pot life, anti-yellowing performance, adhesion, and mechanical properties. When applied to waterborne coatings, the prepared waterborne anionic blocked isocyanate curing agent enables the coating to possess a good "rigidity-toughness balance," ensuring both the strength of the hard segments and the flexibility of the soft segments, thus solving the problem of traditional coatings' difficulty in simultaneously achieving both hardness and flexibility. Furthermore, the waterborne anionic blocked isocyanate curing agent provided by this invention exhibits strong adhesion to metals, plastics, and old paint films, and is particularly suitable for aluminum powder paints, significantly improving coating adhesion and metallic appearance.

[0010] Specifically, this invention first modifies the isocyanate with a crosslinking agent to form a branched structure, thereby increasing the functionality of the resin when applied to water-based coatings. This effectively improves the water resistance and chemical resistance of the coating, solving the problems of layering and sedimentation that are common in traditional water-based coatings, and ensuring the stability of the coating during long-term use. Next, a sealing agent is added to block some of the isocyanate groups (-NCO), forming tertiary NCO-blocked products, thus lowering the deblocking temperature (10-15°C lower than traditional IPDI / HDI), achieving energy saving, reducing energy consumption, and minimizing thermal damage to the substrate. This is particularly suitable for low-temperature curing of automotive plastic parts and intermediate / topcoats. Then, a hydrophilic modifier is used for hydrophilic modification, giving the resin excellent hydrophilic properties when applied to water-based coatings. Finally, a neutralizing agent is used for neutralization treatment, significantly improving the hydrolytic stability of the resulting water-based coating, thereby giving the coating excellent water resistance, damp heat resistance, and salt spray resistance.

[0011] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0012] As a preferred technical solution of the present invention, the isocyanate in step (1) includes any one of aromatic diisocyanate, aliphatic diisocyanate or aryl aliphatic diisocyanate, preferably aryl aliphatic diisocyanate.

[0013] In this invention, the isocyanate is preferably an araliphatic diisocyanate. This allows the resulting waterborne anionic blocked isocyanate curing agent to contain a benzene ring in its structure, but the NCO group is not conjugated with the benzene ring. Therefore, when applied to waterborne coatings, the resulting coating exhibits excellent weather resistance, superior UV stability, and long-term non-yellowing, meeting the 10-year weather resistance requirements of automotive original equipment manufacturer (OEM) paints. Furthermore, by selecting this specific isocyanate as a raw material, the resulting waterborne coating also possesses a lower unsealing temperature, superior mechanical properties, and stronger adhesion.

[0014] Preferably, the aromatic diisocyanate includes any one or a combination of at least two of diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), phenylene diisocyanate (PDI / PPDI), or dimethylbiphenyl diisocyanate (TODI).

[0015] Preferably, the aliphatic isocyanate includes any one or a combination of at least two of isophorone diisocyanate (IPDI), dimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), methylcyclohexane diisocyanate (HTDI), or dicyclohexylmethane diisocyanate (HMDI).

[0016] Preferably, the arylita-based diisocyanate comprises tetramethyl phenyl diisocyanate (TMXDI) and / or phenyl diisocyanate (XDI). Preferably, the crosslinking agent in step (1) comprises trimethylolpropane and / or trimethylolpropane (TMP).

[0017] Preferably, the molar ratio of isocyanate to crosslinking agent in step (1) is 1:(0.1-0.5), wherein (0.1-0.5) can be, for example, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0018] This invention optimizes the molar ratio of isocyanate to crosslinking agent, thereby increasing the functionality of the curing agent. This allows the curing agent to form a higher crosslinking density with the resin, ultimately improving the adhesion and chemical resistance of the resin after film formation. When the molar ratio is high, meaning the crosslinking agent content is low, the functionality is too low, resulting in poor adhesion and chemical resistance of the cured film. Conversely, when the molar ratio is low, meaning the crosslinking agent content is high, gelation is likely to occur during preparation, making it impossible to obtain the aqueous anionic blocked isocyanate curing agent of this invention.

[0019] Preferably, the reaction in step (1) is carried out in an organic solvent.

[0020] Preferably, the organic solvent includes acetone and / or butanone.

[0021] It should be noted that the organic solvent used in this invention mainly serves to reduce viscosity, and its addition amount is adjusted according to the actual situation, including but not limited to 8-15% of the total mass of isocyanate and crosslinking agent.

[0022] Preferably, the reaction temperature in step (1) is 75-85℃, for example, it can be 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, 81℃, 82℃, 83℃ or 85℃, and specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0023] Preferably, the reaction time in step (1) is 1.5-2.5 h, for example, it can be 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h, 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h or 2.5 h, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0024] Preferably, the capping agent in step (2) includes any one or a combination of at least two of imidazole, 2-methylimidazolium, 3,5-dimethylpyrazole, butanone oxime, methyl isobutyl ketone oxime, or diethyl malonate.

[0025] Preferably, the amount of capping agent added in step (2) is 25-45% of the mass of the modified isocyanate in step (1), for example, it can be 25%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42% or 45%, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0026] Preferably, the reaction temperature in step (2) is 70-90℃, for example, it can be 70℃, 72℃, 74℃, 76℃, 78℃, 80℃, 82℃, 84℃, 86℃ or 90℃, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0027] Preferably, the reaction time in step (2) is 1-3 h, for example, it can be 1 h, 1.2 h, 1.5 h, 1.8 h, 2 h, 2.2 h, 2.5 h, 2.8 h or 3 h, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific point values ​​included in the range.

[0028] Preferably, the hydrophilic modifier in step (3) includes dimethylolpropionic acid (DMPA) and / or dimethylolbutyric acid (DMBA).

[0029] Preferably, the solvent in step (3) includes acetone and / or butanone.

[0030] Preferably, the amount of hydrophilic modifier added in step (3) is 5-10% of the mass of the intermediate in step (2), for example, it can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0031] Preferably, the amount of solvent added in step (3) is 5-20% of the mass of the intermediate in step (2), for example, it can be 5%, 8%, 10%, 12%, 14%, 15%, 16%, 18% or 20%, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0032] Preferably, the reaction temperature in step (3) is 60-80℃, for example, it can be 60℃, 62℃, 65℃, 68℃, 70℃, 72℃, 75℃, 78℃ or 80℃, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0033] Preferably, the reaction time in step (3) is 2-5 h, for example, it can be 2 h, 2.3 h, 2.5 h, 2.8 h, 3 h, 3.2 h, 3.5 h, 3.8 h, 4 h, 4.2 h, 4.5 h or 5 h, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0034] Preferably, the neutralizing agent in step (4) includes any one or a combination of at least two of ammonia, diethylamine, triethylamine, diethanolamine, or triethanolamine.

[0035] Preferably, the molar ratio of the neutralizing agent in step (4) to the hydrophilic modifier in step (3) is (1-1.2):1, wherein (1-1.2 can be, for example, 1, 1.02, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18 or 1.2, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0036] Preferably, the mixing in step (4) is carried out under stirring.

[0037] Preferably, the mixing temperature in step (4) is 40-60°C, for example, it can be 40°C, 42°C, 45°C, 48°C, 50°C, 52°C, 55°C, 58°C or 60°C, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0038] Preferably, the mixing time in step (4) is 1-2 h, for example, it can be 1 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h or 2 h, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific point values ​​included in the range.

[0039] Preferably, the specific preparation method of the aqueous anionic blocked isocyanate curing agent includes the following steps: (1) The isocyanate and the crosslinking agent are reacted at 75-85℃ for 1.5-2.5 h to obtain the modified isocyanate; (2) Add a capping agent to the system after the reaction described in step (1) and react at 70-90℃ for 1-3 h to obtain an intermediate; (3) Add a hydrophilic modifier and solvent to the system after the reaction described in step (2), and react at 60-80℃ for 2-5 hours; (4) Add a neutralizing agent to the system after the reaction described in step (3) and mix at 40-60℃ for 1-2 h to obtain an aqueous anionic blocked isocyanate curing agent.

[0040] In a second aspect, the present invention provides an aqueous anionic blocked isocyanate curing agent prepared by the preparation method of the aqueous anionic blocked isocyanate curing agent as described in the first aspect.

[0041] Thirdly, the present invention provides an application of the waterborne anionic blocked isocyanate curing agent as described in the second aspect in waterborne coatings.

[0042] Preferably, the water-based coating includes water-based automotive paint. When the water-based anionic blocked isocyanate curing agent of the present invention is used in water-based coatings, it has excellent automotive paint performance and is particularly suitable for low-temperature curing of automotive plastic parts, intermediate coats and topcoats.

[0043] Compared with the prior art, the present invention has at least the following beneficial effects: The waterborne anionic blocked isocyanate curing agent provided by this invention has a simple and convenient preparation method. Through its specific preparation method, the resulting waterborne anionic blocked isocyanate curing agent can have suitable viscosity (100-200 mPa·s) and particle size (100-130 nm), excellent thermal storage stability (viscosity and particle size change rate <10%) and unsealing temperature (≤125℃). When used in waterborne paints, it can enable the resulting waterborne paints to have excellent pot life (no stratification, no sedimentation), high adhesion (≤1 grade), and good mechanical properties (tensile strength ≥10 MPa, elongation ≥250%). Furthermore, through optimization of raw material components, the resulting waterborne paint can also have excellent anti-yellowing properties. Detailed Implementation

[0044] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0045] Unless otherwise specified, the materials and equipment involved in the following detailed embodiments are all conventional materials and equipment in the art and will not affect the technical effects of the present invention.

[0046] Unless otherwise specified, all reagents and raw materials used in the following examples and comparative examples are commercially available products.

[0047] Example 1 This embodiment provides an aqueous anionic blocked isocyanate curing agent and its preparation method, the preparation method comprising the following steps: (1) Tetramethylphenyl dimethyl diisocyanate (TMXDI) and trimethylolpropane (TMP) were mixed at a molar ratio of 1:0.1, and acetone (10% of the total mass of TMXDI and TMP) was added as an organic solvent to reduce viscosity. The mixture was reacted at 78°C for 1.8 h to obtain modified isocyanate. (2) 3,5-Dimethylpyrazole was added to the system after the reaction described in step (1), and the mixture was stirred at 72°C for 2.5 h to obtain an intermediate in which some -NCO was blocked; wherein, the amount of 3,5-dimethylpyrazole added was 45% of the mass of the modified isocyanate described in step (1); (3) Add dimethylolpropionic acid (DMPA) and acetone to the system after the reaction described in step (2), and stir the reaction at 68°C for 2.5 h to obtain a uniformly mixed reaction solution; wherein, the amount of DMPA added is 9% of the mass of the intermediate described in step (2), and the amount of acetone added is 15% of the mass of the intermediate described in step (2); (4) Triethylamine is added to the system after the reaction in step (3) and stirred and dispersed at 55°C for 1.5 h to obtain the aqueous anionic blocked isocyanate curing agent; wherein the molar ratio of triethylamine to DMPA in step (2) is 1.1:1.

[0048] Example 2 This embodiment provides an aqueous anionic blocked isocyanate curing agent and its preparation method, the preparation method comprising the following steps: (1) Tetramethylphenyl dimethyl diisocyanate (TMXDI) and trimethylolpropane (TMP) were mixed at a molar ratio of 1:0.2. Acetone (10% of the total mass of TMXDI and TMP) was added as an organic solvent to reduce viscosity. The mixture was reacted at 85°C for 2.5 h to obtain modified isocyanate. (2) Methyl isobutyl ketone oxime was added to the system after the reaction described in step (1) and the mixture was stirred at 80°C for 1.5 h to obtain an intermediate in which some -NCO was blocked; wherein, the amount of methyl isobutyl ketone oxime added was 35% of the mass of the modified isocyanate described in step (1); (3) Add dimethylolpropionic acid (DMPA) and acetone to the system after the reaction described in step (2), and stir the reaction at 65°C for 4 h to obtain a uniformly mixed reaction solution; wherein, the amount of DMPA added is 7% of the mass of the intermediate described in step (2), and the amount of acetone added is 20% of the mass of the intermediate described in step (2); (4) Triethylamine is added to the system after the reaction in step (3) and stirred and dispersed at 45°C for 2 h to obtain the aqueous anionic blocked isocyanate curing agent; wherein the molar ratio of triethylamine to DMPA in step (2) is 1:1.

[0049] Example 3 This embodiment provides an aqueous anionic blocked isocyanate curing agent and its preparation method, the preparation method comprising the following steps: (1) Tetramethylphenyl dimethyl diisocyanate (TMXDI) and trimethylolethane were mixed at a molar ratio of 1:0.3, and methyl ethyl ketone (10% of the total mass of TMXDI and TMP) was added as an organic solvent to reduce viscosity. The mixture was reacted at 75°C for 1.5 h to obtain modified isocyanate. (2) Diethyl malonate was added to the system after the reaction described in step (1), the temperature was controlled at 90°C, and the reaction was stirred for 1 h to obtain an intermediate in which some -NCO was blocked; wherein, the amount of diethyl malonate added was 27% of the mass of the modified isocyanate described in step (1); (3) Add dimethylolbutyric acid (DMBA) and butanone to the system after the reaction described in step (2), and stir the reaction at 78°C for 2 hours to obtain a uniformly mixed reaction solution; wherein, the amount of DMBA added is 5% of the mass of the intermediate described in step (2), and the amount of butanone added is 12% of the mass of the intermediate described in step (2); (4) Triethanolamine is added to the system after the reaction in step (3) and stirred and dispersed at 60°C for 1 h to obtain the aqueous anionic blocked isocyanate curing agent; wherein the molar ratio of triethanolamine to DMPA in step (2) is 1.2:1.

[0050] Example 4 This embodiment provides an aqueous anionic blocked isocyanate curing agent and its preparation method. The only difference between this embodiment and Example 1 is that tetramethylphenyl dimethyl diisocyanate (TMXDI) is replaced with an equimolar amount of diphenylmethane diisocyanate (MDI). All other raw materials, addition amounts, and preparation methods are the same as in Example 1.

[0051] Example 5 This embodiment provides an aqueous anionic blocked isocyanate curing agent and its preparation method. The only difference between this embodiment and Example 1 is that tetramethylphenyl dimethyl diisocyanate (TMXDI) is replaced with an equimolar amount of isophorone diisocyanate (IPDI). All other raw materials, addition amounts, and preparation methods are the same as in Example 1.

[0052] Example 6 This embodiment provides an aqueous anionic blocked isocyanate curing agent and its preparation method. The only difference between this embodiment and Example 1 is that tetramethylphenyl dimethyl diisocyanate (TMXDI) is replaced with an equimolar amount of hexamethylene diisocyanate (HDI). All other raw materials, addition amounts, and preparation methods are the same as in Example 1.

[0053] Example 7 This embodiment provides an aqueous anionic blocked isocyanate curing agent and its preparation method. The only difference between this embodiment and Example 1 is that the mass ratio of TMXDI to TMP in step (1) is adjusted from 1:0.1 to 1:0.08. The other raw materials, addition amounts and preparation methods are the same as in Example 1.

[0054] Comparative Example 1 This comparative example provides an isocyanate curing agent and its preparation method, the preparation method comprising the following steps: (1) Add 12 g of trimethylolpropane, 2 g of neopentyl glycol, 98 g of isophorone diisocyanate (IPDI), and 40 g of N-methylpyrrolidone to a 500 mL flask equipped with a thermometer, stirrer, and reflux condenser. React at 85 °C for 3 h under nitrogen protection to obtain branched polyisocyanate. (2) Add 12 g of dimethylolpropionic acid and 0.05 g of dibutyltin dilaurate to the system after the reaction in step (1), react at 75°C for 2 h, and take samples to analyze the free isocyanate content; add 10.6 g of 2-methylimidazole, and after isocyanate blocking reaction at 65°C for 1 h, the free isocyanate blocking rate is 80%; at room temperature, add 5.4 g of triethylamine for neutralization, with a neutralization degree of 0.6; add 60 g of butyl acetate under stirring to obtain the isocyanate curing agent.

[0055] Comparative Example 2 This comparative example provides an isocyanate curing agent and its preparation method, the preparation method comprising the following steps: 1 g of isophorone diisocyanate (IPDI), 1.1 g of trimethylolpropane (TMP), 0.1 g of dimethylolpropionic acid (DMPA) and 0.6 g of acetone were mixed and reacted at 70 °C for 3 h. After adding 0.2 g of 3,5-dimethylpyrazole, the reaction was continued for another 2 h. The mixture was then cooled to 30 °C, and 0.08 g of triethylamine was added and stirred until homogeneous to obtain the isocyanate curing agent.

[0056] The isocyanate curing agents provided in Examples 1-7 and Comparative Examples 1-2 were subjected to performance tests, and the test methods / standards are as follows: (1) Thermal storage stability: Stored in a 50℃ oven for 4 months, and tested in accordance with GB / T 11175-2021 standard; (2) Unsealing temperature: DSC test was used. Temperature range: 30-300℃, heating rate: 5℃ / min.

[0057] The isocyanate curing agents provided in Examples 1-7 and Comparative Examples 1-2 were blended with an equal mass of water-based anionic polyol main agent (Shanghai Tuxin Chemical Co., Ltd., AOH 412) to obtain a water-based paint. The performance of the water-based paint was tested using the following methods / standards: (3) Shelf life: After storing in a 50℃ oven for 2 months, observe the changes in appearance; (4) Anti-yellowing performance: Observe the appearance changes after 4 hours of ultraviolet light irradiation; (5) Adhesion: Tested in accordance with GB / T 9286-2021 standard; (6) Tensile strength and elongation at break: Tested in accordance with GB / T 528-2009 standard.

[0058] The test results are shown in Table 1.

[0059] Table 1 According to the test results in Table 1: (1) As can be seen from Examples 1 to 7, the waterborne anionic blocked isocyanate curing agent prepared by the preparation method provided by the present invention has suitable viscosity (100-200 mPa·s) and particle size (100-130 nm), excellent thermal storage stability (viscosity and particle size change rate <10%) and unsealing temperature (≤125℃). When used in waterborne paint, it can make the resulting waterborne paint have excellent pot life (no stratification, no sedimentation), high adhesion (≤1 grade) and good mechanical properties (tensile strength ≥10 MPa, elongation ≥250%).

[0060] (2) By comparing Examples 4-6 with Example 1, it can be seen that by selecting and optimizing isocyanates, the present invention can make the obtained waterborne anionic blocked isocyanate curing agent have a lower unblocking temperature, and when applied to waterborne paint, it can make the waterborne paint have stronger adhesion, better mechanical properties and anti-yellowing properties.

[0061] (3) By comparing Example 7 with Examples 1-3, it can be seen that by optimizing the molar ratio of isocyanate to crosslinking agent, the present invention can make the waterborne anionic blocked isocyanate curing agent have stronger adhesion when applied to waterborne paint. When the molar ratio of the two is high (Example 7), that is, the crosslinking agent content is low, the adhesion of the resulting waterborne paint decreases.

[0062] (4) By comparing Comparative Examples 1-2 with Examples 1-7, it can be seen that, compared with the existing methods for preparing isocyanate curing agents, the water-based anionic blocked isocyanate curing agent prepared by the specific preparation method of the present invention has better thermal stability, lower unsealing temperature, higher adhesion and better mechanical properties, based on suitable viscosity and particle size.

[0063] In summary, by optimizing the raw materials and their content in the preparation method provided by this invention, the resulting waterborne anionic blocked isocyanate curing agent can have a more suitable viscosity (150-180 mPa·s) and particle size (110-130 nm), and a lower unblocking temperature (≤115℃). When used in waterborne paints, it can make the resulting waterborne paints have stronger adhesion (adhesion grade 0) and better mechanical properties (tensile strength ≥15 MPa, elongation ≥300%).

[0064] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for producing an aqueous anionically blocked isocyanate curing agent, characterized by, The preparation method includes the following steps: (1) The isocyanate is reacted with a crosslinking agent to obtain a modified isocyanate; (2) Add a capping agent to the system after the reaction described in step (1) to carry out the reaction and obtain an intermediate; (3) Add a hydrophilic modifier and a solvent to the system after the reaction described in step (2) to carry out the reaction; (4) After adding a neutralizing agent to the system after the reaction in step (3) and mixing, an aqueous anionic blocked isocyanate curing agent is obtained.

2. The production method according to claim 1, characterized by, The isocyanate in step (1) includes any one of aromatic diisocyanate, aliphatic diisocyanate or aryl aliphatic diisocyanate, preferably aryl aliphatic diisocyanate; Preferably, the aromatic diisocyanate includes any one or a combination of at least two of diphenylmethane diisocyanate, toluene diisocyanate, phenylene diisocyanate or dimethylbiphenyl diisocyanate; Preferably, the aliphatic isocyanate includes any one or a combination of at least two of isophorone diisocyanate, dimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, methylcyclohexane diisocyanate or dicyclohexylmethane diisocyanate. Preferably, the arylita diisocyanate includes tetramethyl phthalimide diisocyanate and / or phthalimide diisocyanate; Preferably, the crosslinking agent in step (1) includes trimethylolpropane and / or trimethylolpropane; Preferably, the molar ratio of isocyanate to crosslinking agent in step (1) is 1:(0.1-0.5); Preferably, the reaction in step (1) is carried out in an organic solvent; Preferably, the organic solvent includes acetone and / or butanone.

3. The production method according to claim 1 or 2, characterized by, The reaction in step (1) is carried out at a temperature of 75-85℃ for 1.5-2.5 h.

4. The production method according to any one of claims 1 to 3, characterized by, The capping agent in step (2) includes any one or a combination of at least two of the following: imidazole, 2-methylimidazolium, 3,5-dimethylpyrazole, butanone oxime, methyl isobutyl ketone oxime, or diethyl malonate; Preferably, the amount of capping agent added in step (2) is 25-45% of the mass of the modified isocyanate in step (1).

5. The method of any one of claims 1-4, wherein, The reaction in step (2) is carried out at a temperature of 70-90℃ for 1-3 hours.

6. The preparation method according to any one of claims 1-5, characterized in that, The hydrophilic modifier in step (3) includes dimethylolpropionic acid and / or dimethylolbutyric acid; Preferably, the solvent in step (3) includes acetone and / or butanone; Preferably, the amount of hydrophilic modifier added in step (3) is 5-10% of the mass of the intermediate in step (2); Preferably, the amount of solvent added in step (3) is 5-20% of the mass of the intermediate in step (2); Preferably, the reaction in step (3) is carried out at a temperature of 60-80°C for 2-5 hours.

7. The preparation method according to any one of claims 1-6, characterized in that, The neutralizing agent in step (4) includes any one or a combination of at least two of ammonia, diethylamine, triethylamine, diethanolamine, or triethanolamine; Preferably, the molar ratio of the neutralizing agent in step (4) to the hydrophilic modifier in step (3) is (1-1.2):1; Preferably, the mixing in step (4) is carried out under stirring; Preferably, the mixing temperature in step (4) is 40-60℃ and the time is 1-2 h.

8. The preparation method according to any one of claims 1-7, characterized in that, The preparation method includes the following steps: (1) The isocyanate and the crosslinking agent are reacted at 75-85℃ for 1.5-2.5 h to obtain the modified isocyanate; (2) Add a capping agent to the system after the reaction described in step (1) and react at 70-90℃ for 1-3 h to obtain an intermediate; (3) Add a hydrophilic modifier and solvent to the system after the reaction described in step (2), and react at 60-80℃ for 2-5 h; (4) Add a neutralizing agent to the system after the reaction described in step (3) and mix at 40-60℃ for 1-2 h to obtain an aqueous anionic blocked isocyanate curing agent.

9. A water-based anionic blocked isocyanate curing agent prepared by the method described in any one of claims 1-8.

10. The application of the waterborne anionic blocked isocyanate curing agent as described in claim 9 in waterborne coatings.

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