Composite curing agent for reducing content of free TDI (toluene diisocynate) in polyurethane and preparation method of composite curing agent

Abstract

The invention provides a composite curing agent for reducing the content of free TDI (toluene diisocynate) in polyurethane and a preparation method of the composite curing agent, and belongs to the technical field of polyurethane materials. The preparation method comprises the following steps: mixing a modified metal organic framework, polyether polyol and aliphatic polyol to obtain a suspension, reacting toluene diisocynate with the suspension for 30-60 minutes, adding a catalyst, reacting at 60-70 DEG C for 3-5 hours, adding a polymerization inhibitor, and reacting at 80-90 DEG C for 30-40 minutes to obtain the composite curing agent. The hollow metal organic framework adopted by the invention has a hollow structure and has a higher specific surface area compared with a conventional metal organic framework, more amino groups and carboxyl groups can be modified on the surface of the modified metal organic framework when the modified metal organic framework is synthesized, and the modified metal organic framework can react with more toluene diisocynate to form stable bonding; and the content of free toluene diisocynate is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyurethane materials, and particularly relates to a composite curing agent for reducing the content of free TDI in polyurethane and a preparation method thereof. Background Art

[0002] Polyurethane coatings have a variety of excellent properties: good mechanical properties, hard, flexible, bright and plump film, wear-resistant, corrosion-resistant, and chemical-resistant, so they are widely used in industries such as automobiles, airplanes, machinery, electricity, instruments, floors, and woodware. Polyester coatings (paints) and polyurethane coatings (paints) must be mixed with curing agents to be used. The main raw material for producing curing agents is toluene diisocyanate (TDI). It has two hetero cumulated double bonds and is very active. It can dimerize or trimerize by itself and is also extremely easy to react with other compounds containing active hydrogen atoms. As a commonly used curing agent for polyurethane coatings, it can endow the paint film with various excellent properties. However, TDI is a toxic compound, and its active group isocyanate (R-N=C=O) is harmful to the human body. Long-term inhalation of diisocyanate will damage the lungs, causing headaches, bronchitis, and asthma. For some individuals (such as those with allergic asthma), since isocyanate can react with human proteins to form denatured proteins, it may cause allergic reactions, resulting in symptoms such as difficulty breathing, and in severe cases, it will lead to death. However, due to the limitations of production process technology and equipment level, there is always some TDI remaining in the curing agent eventually. Therefore, when using it to manufacture prepolymers, it is required that its content in the final product be as low as possible.

[0003] Patent CN 101456940A discloses a synthesis method for manufacturing a solvent-based polyurethane curing agent with a low free toluene diisocyanate content. This method prepares the solvent-based polyurethane curing agent through two-stage reactions. The curing agent prepared by this method has the characteristics of a low content of free TDI monomer. However, it may have the problem that the storage time of the curing agent is too long, and reactions can be caused when the environmental temperature changes, resulting in an increase in viscosity and easy formation of gel phenomena.

[0004] Patent CN 105001701A discloses a high-solid-content, uniform molecular weight, non-toxic polyurethane curing agent for matte paint and its preparation method. By separately preparing a TDI trimer reaction solution and a TDI-TMP adduct reaction solution, and separating and diluting them after mixing, a matte TDI curing agent is prepared. However, the trimer reaction solution prepared by it contains solvents, increasing the separation energy consumption. In addition, the curing agent prepared by simple mixing may have problems with compatibility with resins. Summary of the Invention

[0005] To solve the problems existing in the prior art, the present invention provides a composite curing agent for reducing the content of free TDI in polyurethane and a preparation method thereof. Specifically, the technical solution of the present invention includes the following content:

[0006] A preparation method of a composite curing agent for reducing the content of free TDI in polyurethane, the preparation method comprising the following steps:

[0007] Mix a modified metal-organic framework, a polyether polyol, and an aliphatic polyol to obtain a suspension. After reacting toluene diisocyanate with the suspension for 30-60 min, add a catalyst and react at 60-70 °C for 3-5 h, and then add an inhibitor and react at 80-90 °C for 30-40 min to obtain the composite curing agent.

[0008] Furthermore, the preparation method of the modified metal-organic framework comprises the following steps:

[0009] React ammonium cerium nitrate, benzoic acid, and terephthalic acid at 100-110 °C for 16-20 h to obtain a metal-organic framework;

[0010] React zirconium chloride, a polyoxypropylene-polyoxyethylene copolymer solution, the metal-organic framework, hydrochloric acid, and acetic acid at 23-25 °C for 30-50 min, raise the temperature to 75-85 °C, add tetrafluoroterephthalic acid and 2-aminoterephthalic acid and react for 24-28 h to obtain an intermediate. Disperse the intermediate in ethanol and etch at 40-60 °C for 75 h to obtain a hollow metal-organic framework;

[0011] React the hollow metal-organic framework with a hydrochloric acid solution at 55-65 °C for 3-5 h to obtain the modified metal-organic framework.

[0012] Furthermore, the weight ratio of ammonium cerium nitrate, benzoic acid, and terephthalic acid is 1.3-1.7:15-25:1.0-1.5.

[0013] Furthermore, the weight ratio of zirconium chloride, the polyoxypropylene-polyoxyethylene copolymer solution, the metal-organic framework precursor, hydrochloric acid, acetic acid, tetrafluoroterephthalic acid, and 2-aminoterephthalic acid is 9-13:40-60:8-12:0.8-1.1:0.05-0.15:8-12:2-3.

[0014] Furthermore, the weight ratio of the intermediate to ethanol is 10-20:100-400.

[0015] Furthermore, the molar concentration of the hydrochloric acid solution is 0.5 mol / L.

[0016] Furthermore, the weight ratio of the amino-functionalized mesoporous metal-organic framework to the hydrochloric acid solution is 10-20:200-400.

[0017] Furthermore, the polyether polyol includes one of polyether polyol 204, polyether polyol 215, or polyether polyol 220.

[0018] Further, the aliphatic polyol includes one of trimethylolpropane, 1,2,4-butanetriol or trimethylolethane.

[0019] Further, the weight ratio of the modified metal-organic framework, polyether polyol and aliphatic polyol is 0.1-1:10-30:60-90.

[0020] Further, the toluene diisocyanate includes one of 2,4-toluene diisocyanate or 2,6-toluene diisocyanate.

[0021] Further, the catalyst is dibutyltin dilaurate.

[0022] Further, the inhibitor includes one of phosphoric acid, hydrochloric acid or sulfuric acid.

[0023] Further, the weight ratio of the toluene diisocyanate, suspension, catalyst and inhibitor is 40-60:5-15:0.1-0.8:0.1-0.4.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) In the present invention, ammonium cerium nitrate is used to provide metal ions, and benzoic acid and terephthalic acid are used as organic ligands to obtain a metal-organic framework through self-assembly. Subsequently, using the metal-organic framework as a hard template and a polyoxypropylene-polyoxyethylene copolymer solution as a soft template, zirconium chloride, tetrafluoro terephthalic acid and 2-aminoterephthalic acid as shell growth units, and hydrochloric acid and acetic acid as regulators, by regulating the synchronous coordination of shell growth and metal-organic framework dissociation, a dynamic balance of in-situ shell growth and synchronous template dissolution is achieved. Then, the soft template is etched away with ethanol to obtain a hollow metal-organic framework.

[0026] (2) In the present invention, 2-aminoterephthalic acid is used as an amino donor, so that the surface of the hollow metal-organic framework is modified with abundant amino groups; the hollow metal-organic framework is acid-treated with hydrochloric acid, so that part of the Zr-O bonds are hydrolyzed to generate Zr-OH, thereby realizing the hydroxyl modification on the surface of the hollow metal-organic framework, and a modified metal-organic framework with a surface rich in amino and hydroxyl modifications and a hollow structure is prepared; the amino and hydroxyl groups in the modified metal-organic framework react with the isocyanate groups in the toluene diisocyanate to prepare a composite curing agent.

[0027] (3) The hollow metal-organic framework adopted in the present invention has a hollow structure and has a higher specific surface area compared with the conventional metal-organic framework. When synthesizing the modified metal-organic framework, more amino and carboxyl groups can be modified on its surface, and more toluene diisocyanate can react to form stable bonds, reducing the content of free toluene diisocyanate.

[0028] (4) The amino and hydroxyl groups in the composite curing agent react with the free toluene diisocyanate. While avoiding the agglomeration and accumulation of the composite curing agent, the composite curing agent can be integrated into the polyurethane network. While increasing the compatibility between the composite curing agent and the polyurethane matrix, the crosslinking degree of the three-dimensional network is increased, thereby improving the weather resistance of the polyurethane. Specific Embodiments

[0029] The technical solutions of the present invention will be clearly and completely described below through the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention.

[0030] Unless otherwise specified, the raw materials and reagents used in the present invention below are all commercially available products, or can be prepared by known methods.

[0031] Preparation Example 1:

[0032] The preparation method of the modified metal-organic framework includes the following steps:

[0033] 1.5 parts by weight of ammonium cerium nitrate are dispersed in 20 parts by weight of deionized water, and ultrasonic treatment is carried out for 8 min to obtain solution A. 20 parts by weight of benzoic acid and 1.3 parts by weight of terephthalic acid are dispersed in 90 parts by weight of N,N-dimethylformamide, and ultrasonic treatment is carried out for 8 min to obtain solution B. Solution A and solution B are mixed and placed in a hydrothermal reactor. After maintaining the temperature at 105 °C for 18 h, they are washed alternately with deionized water and ethanol, and vacuum dried at 60 °C for 10 h to obtain the metal-organic framework.

[0034] 12 parts by weight of zirconium chloride and 50 parts by weight of polyoxypropylene-polyoxyethylene copolymer solution are dispersed in 300 parts by weight of deionized water. After ultrasonic treatment for 4 min, 10 parts by weight of the metal-organic framework are added and ultrasonic treatment is carried out for 15 min. Then, 0.9 part by weight of hydrochloric acid and 0.1 part by weight of acetic acid are added, and the reaction is stirred at 24 °C for 40 min. Then, the temperature is raised to 80 °C, 9 parts by weight of tetrafluoroterephthalic acid and 3.5 parts by weight of 2-aminoterephthalic acid are added, and the reaction is stirred for 26 h. After that, they are washed alternately with ethanol and deionized water to obtain an intermediate. 15 parts by weight of the intermediate are dispersed in 300 parts by weight of ethanol, and etched at 50 °C for 72 h to obtain a hollow metal-organic framework.

[0035] 15 parts by weight of the hollow metal-organic framework are dispersed in 300 parts by weight of a hydrochloric acid solution with a molar concentration of 0.5 mol / L. After stirring and reacting at 60 °C for 4 h, the solid is collected by centrifugation at a speed of 8000 r / min for 5 min, washed with deionized water until neutral, and vacuum dried at 60 °C for 8 h to obtain the modified metal-organic framework.

[0036] Preparation Example 2:

[0037] The preparation method of the modified metal-organic framework comprises the following steps:

[0038] 1.3 parts by weight of ammonium cerium nitrate is dispersed in 20 parts by weight of deionized water, and ultrasonic treatment is carried out for 5 min to obtain solution A. 15 parts by weight of benzoic acid and 1.0 part by weight of terephthalic acid are dispersed in 90 parts by weight of N,N-dimethylformamide, and ultrasonic treatment is carried out for 5 min to obtain solution B. Solution A and solution B are mixed and placed in a hydrothermal reactor. After heat preservation at 100 °C for 16 h, washing is alternately carried out with deionized water and ethanol, and vacuum drying is carried out at 60 °C for 8 h to obtain the metal-organic framework.

[0039] 9 parts by weight of zirconium chloride and 40 parts by weight of polyoxypropylene polyoxyethylene copolymer solution are dispersed in 300 parts by weight of deionized water. After ultrasonic treatment for 3 min, 8 parts by weight of the metal-organic framework is added and ultrasonic treatment is carried out for 10 min. Then, 0.8 part by weight of hydrochloric acid and 0.05 part by weight of acetic acid are added, and stirring reaction is carried out at 23 °C for 30 min. Then, the temperature is raised to 75 °C, 7 parts by weight of tetrafluoroterephthalic acid and 3 parts by weight of 2-aminoterephthalic acid are added, and stirring reaction is carried out for 24 h. After washing is alternately carried out with ethanol and deionized water to obtain an intermediate, 10 parts by weight of the intermediate is dispersed in 100 parts by weight of ethanol, and etching is carried out at 40 °C for 72 h to obtain the hollow metal-organic framework.

[0040] 10 parts by weight of the hollow metal-organic framework is dispersed in 200 parts by weight of a hydrochloric acid solution with a molar concentration of 0.5 mol / L. After stirring reaction at 55 °C for 3 h, solid is collected by centrifugation at a speed of 8000 r / min for 5 min, washed with deionized water until neutral, and vacuum dried at 60 °C for 6 h to obtain the modified metal-organic framework.

[0041] Preparation Example 3:

[0042] The preparation method of the modified metal-organic framework comprises the following steps:

[0043] 1.4 parts by weight of ammonium cerium nitrate is dispersed in 20 parts by weight of deionized water, and ultrasonic treatment is carried out for 6 min to obtain solution A. 17 parts by weight of benzoic acid and 1.2 part by weight of terephthalic acid are dispersed in 90 parts by weight of N,N-dimethylformamide, and ultrasonic treatment is carried out for 6 min to obtain solution B. Solution A and solution B are mixed and placed in a hydrothermal reactor. After heat preservation at 102 °C for 17 h, washing is alternately carried out with deionized water and ethanol, and vacuum drying is carried out at 60 °C for 9 h to obtain the metal-organic framework.

[0044] 10 parts by weight of zirconium chloride and 45 parts by weight of polyoxypropylene polyoxyethylene copolymer solution are dispersed in 300 parts by weight of deionized water. After ultrasonic treatment for 4 min, 9 parts by weight of metal-organic framework is added and ultrasonic treatment is carried out for 12 min. Then, 0.9 part by weight of hydrochloric acid and 0.07 part by weight of acetic acid are added, and the reaction is stirred at 24 °C for 35 min. Then, the temperature is raised to 77 °C, 8 parts by weight of tetrafluoroterephthalic acid and 3.2 parts by weight of 2-aminoterephthalic acid are added, and the reaction is stirred for 25 h. After that, it is washed alternately with ethanol and deionized water to obtain an intermediate. 12 parts by weight of the intermediate is dispersed in 200 parts by weight of ethanol, and etched at 40-60 °C for 72 h to obtain a hollow metal-organic framework.

[0045] 13 parts by weight of the hollow metal-organic framework is dispersed in 200 parts by weight of hydrochloric acid solution with a molar concentration of 0.5 mol / L. After stirring and reacting at 57 °C for 3.5 h, the solid is collected by centrifugation at a speed of 8000 r / min for 5 min, washed with deionized water until neutral, and vacuum dried at 60 °C for 6.5 h to obtain a modified metal-organic framework.

[0046] Preparation Example 4:

[0047] The preparation method of the modified metal-organic framework includes the following steps:

[0048] 1.6 parts by weight of ammonium cerium nitrate is dispersed in 20 parts by weight of deionized water, and ultrasonic treatment is carried out for 8 min to obtain solution A. 22 parts by weight of benzoic acid and 1.4 parts by weight of terephthalic acid are dispersed in 90 parts by weight of N,N-dimethylformamide, and ultrasonic treatment is carried out for 8 min to obtain solution B. Solution A and solution B are mixed and placed in a hydrothermal reactor. After heat preservation at 108 °C for 19 h, it is washed alternately with deionized water and ethanol, and vacuum dried at 60 °C for 11 h to obtain a metal-organic framework.

[0049] 12 parts by weight of zirconium chloride and 55 parts by weight of polyoxypropylene polyoxyethylene copolymer solution are dispersed in 300 parts by weight of deionized water. After ultrasonic treatment for 6 min, 11 parts by weight of metal-organic framework is added and ultrasonic treatment is carried out for 14 min. Then, 0.9 part by weight of hydrochloric acid and 0.12 part by weight of acetic acid are added, and the reaction is stirred at 25 °C for 45 min. Then, the temperature is raised to 82 °C, 9 parts by weight of tetrafluoroterephthalic acid and 3.7 parts by weight of 2-aminoterephthalic acid are added, and the reaction is stirred for 27 h. After that, it is washed alternately with ethanol and deionized water to obtain an intermediate. 17 parts by weight of the intermediate is dispersed in 320 parts by weight of ethanol, and etched at 40-60 °C for 72 h to obtain a hollow metal-organic framework.

[0050] 17 parts by weight of hollow metal-organic framework are dispersed in 350 parts by weight of hydrochloric acid solution with a molar concentration of 0.5 mol / L. After stirring and reacting at 62 °C for 4.5 h, the solid is collected by centrifugation at a speed of 8000 r / min for 5 min, washed with deionized water until neutral, and vacuum-dried at 60 °C for 7 h to obtain the modified metal-organic framework.

[0051] Preparation Example 5:

[0052] The preparation method of the modified metal-organic framework includes the following steps:

[0053] 1.7 parts by weight of ammonium cerium(IV) nitrate are dispersed in 20 parts by weight of deionized water, and ultrasonic treatment is carried out for 10 min to obtain Solution A. 25 parts by weight of benzoic acid and 1.5 parts by weight of terephthalic acid are dispersed in 90 parts by weight of N,N-dimethylformamide, and ultrasonic treatment is carried out for 10 min to obtain Solution B. Solution A and Solution B are mixed and placed in a hydrothermal reactor. After maintaining the temperature at 110 °C for 20 h, they are washed alternately with deionized water and ethanol, and vacuum-dried at 60 °C for 12 h to obtain the metal-organic framework.

[0054] 13 parts by weight of zirconium chloride and 60 parts by weight of polyoxypropylene-polyoxyethylene copolymer solution are dispersed in 300 parts by weight of deionized water. After ultrasonic treatment for 6 min, 12 parts by weight of the metal-organic framework are added and ultrasonic treatment is carried out for 15 min. Then, 1.1 parts by weight of hydrochloric acid and 0.15 parts by weight of acetic acid are added, and the mixture is stirred and reacted at 25 °C for 50 min. Then, the temperature is raised to 85 °C, 11 parts by weight of tetrafluoroterephthalic acid and 4 parts by weight of 2-aminoterephthalic acid are added, and the mixture is stirred and reacted for 28 h. Then, it is washed alternately with ethanol and deionized water to obtain an intermediate. 20 parts by weight of the intermediate are dispersed in 400 parts by weight of ethanol, and etched at 60 °C for 72 h to obtain the hollow metal-organic framework.

[0055] 20 parts by weight of the hollow metal-organic framework are dispersed in 400 parts by weight of hydrochloric acid solution with a molar concentration of 0.5 mol / L. After stirring and reacting at 65 °C for 5 h, the solid is collected by centrifugation at a speed of 8000 r / min for 5 min, washed with deionized water until neutral, and vacuum-dried at 60 °C for 8 h to obtain the modified metal-organic framework.

[0056] Preparation Example 6:

[0057] The preparation method of the modified metal-organic framework includes the following steps:

[0058] 1.5 parts by weight of ammonium cerium nitrate are dispersed in 20 parts by weight of deionized water, and ultrasonic treatment is carried out for 8 min to obtain solution A. 20 parts by weight of benzoic acid and 1.3 parts by weight of terephthalic acid are dispersed in 90 parts by weight of N,N-dimethylformamide, and ultrasonic treatment is carried out for 8 min to obtain solution B. Solution A and solution B are mixed and placed in a hydrothermal reactor. After heat preservation at 105 °C for 18 h, washing is carried out alternately with deionized water and ethanol, and vacuum drying is carried out at 60 °C for 10 h to obtain a metal-organic framework.

[0059] 12 parts by weight of zirconium chloride and 50 parts by weight of a polyoxypropylene polyoxyethylene copolymer solution are dispersed in 300 parts by weight of deionized water. After ultrasonic treatment for 4 min, 10 parts by weight of the metal-organic framework is added and ultrasonic treatment is carried out for 15 min. Then, 0.9 part by weight of hydrochloric acid and 0.1 part by weight of acetic acid are added, and stirring reaction is carried out at 24 °C for 40 min. Then, the temperature is raised to 80 °C, 9 parts by weight of tetrafluoroterephthalic acid and 3.5 parts by weight of 2-aminoterephthalic acid are added, and stirring reaction is carried out for 26 h. After that, washing is carried out alternately with ethanol and deionized water to obtain an intermediate. 15 parts by weight of the intermediate are dispersed in 300 parts by weight of ethanol, and etching is carried out at 50 °C for 72 h to obtain a modified metal-organic framework.

[0060] Preparation Example 7:

[0061] The preparation method of the modified metal-organic framework comprises the following steps:

[0062] 1.5 parts by weight of ammonium cerium nitrate are dispersed in 20 parts by weight of deionized water, and ultrasonic treatment is carried out for 8 min to obtain solution A. 20 parts by weight of benzoic acid and 1.3 parts by weight of terephthalic acid are dispersed in 90 parts by weight of N,N-dimethylformamide, and ultrasonic treatment is carried out for 8 min to obtain solution B. Solution A and solution B are mixed and placed in a hydrothermal reactor. After heat preservation at 105 °C for 18 h, washing is carried out alternately with deionized water and ethanol, and vacuum drying is carried out at 60 °C for 10 h to obtain a metal-organic framework.

[0063] 12 parts by weight of zirconium chloride and 50 parts by weight of a polyoxypropylene polyoxyethylene copolymer solution are dispersed in 300 parts by weight of deionized water. After ultrasonic treatment for 4 min, 10 parts by weight of the metal-organic framework is added and ultrasonic treatment is carried out for 15 min. Then, 0.9 part by weight of hydrochloric acid and 0.1 part by weight of acetic acid are added, and stirring reaction is carried out at 24 °C for 40 min. Then, the temperature is raised to 80 °C, 9 parts by weight of tetrafluoroterephthalic acid is added, and stirring reaction is carried out for 26 h. After that, washing is carried out alternately with ethanol and deionized water to obtain an intermediate. 15 parts by weight of the intermediate are dispersed in 300 parts by weight of ethanol, and etching is carried out at 50 °C for 72 h to obtain a hollow metal-organic framework.

[0064] 15 parts by weight of hollow metal-organic framework are dispersed in 300 parts by weight of hydrochloric acid solution with a molar concentration of 0.5 mol / L. After stirring and reacting at 60 °C for 4 h, the solid is collected by centrifugation at a speed of 8000 r / min for 5 min, washed with deionized water until neutral, and vacuum dried at 60 °C for 8 h to obtain the modified metal-organic framework.

[0065] Preparation Example 8:

[0066] The preparation method of the modified metal-organic framework includes the following steps:

[0067] 1.5 parts by weight of ammonium cerium nitrate are dispersed in 20 parts by weight of deionized water, and ultrasonic treatment is carried out for 8 min to obtain solution A. 20 parts by weight of benzoic acid and 1.3 parts by weight of terephthalic acid are dispersed in 90 parts by weight of N,N-dimethylformamide, and ultrasonic treatment is carried out for 8 min to obtain solution B. Solution A and solution B are mixed and placed in a hydrothermal reactor. After maintaining the temperature at 105 °C for 18 h, it is washed alternately with deionized water and ethanol, and vacuum dried at 60 °C for 10 h to obtain the metal-organic framework.

[0068] 12 parts by weight of zirconium chloride and 50 parts by weight of polyoxypropylene polyoxyethylene copolymer solution are dispersed in 300 parts by weight of deionized water. After ultrasonic treatment for 4 min, 10 parts by weight of the metal-organic framework is added and ultrasonic treatment is carried out for 15 min. Then, 0.9 parts by weight of hydrochloric acid and 0.1 parts by weight of acetic acid are added, and the mixture is stirred and reacted at 24 °C for 40 min. Then, the temperature is raised to 80 °C, 9 parts by weight of tetrafluoroterephthalic acid is added, and the mixture is stirred and reacted for 26 h. Then, it is washed alternately with ethanol and deionized water to obtain an intermediate. 15 parts by weight of the intermediate are dispersed in 300 parts by weight of ethanol, and etched at 50 °C for 72 h to obtain the modified metal-organic framework.

[0069] Preparation Example 9:

[0070] The preparation method of the modified metal-organic framework includes the following steps:

[0071] 17 parts by weight of zirconium chloride, 1 part by weight of 2-aminoterephthalic acid and 3 parts by weight of acetic acid are dispersed in 100 parts by weight of N,N-dimethylformamide, and stirred and reacted at 120 °C for 12 h to obtain an amino-functionalized metal-organic framework. 15 parts by weight of the amino-functionalized metal-organic framework are dispersed in 300 parts by weight of hydrochloric acid solution with a molar concentration of 0.5 mol / L. After stirring and reacting at 60 °C for 4 h, the solid is collected by centrifugation at a speed of 8000 r / min for 5 min, washed with deionized water until neutral, and vacuum dried at 60 °C for 8 h to obtain the modified metal-organic framework.

[0072] Example 1:

[0073] A preparation method of a composite curing agent for reducing the free TDI content in polyurethane includes the following steps:

[0074] 0.5 parts by weight of the modified metal-organic framework prepared in Preparation Example 1 was dispersed in 20 parts by weight of polyether polyol 204 and 70 parts by weight of trimethylolpropane to obtain a suspension. 50 parts by weight of 2,4-toluene diisocyanate and 10 parts by weight of the suspension were dispersed in 35 parts by weight of ethyl acetate. The temperature was raised to 80 °C in a nitrogen protection environment, and after stirring and reacting for 50 min, the temperature was lowered to 65 °C, 0.4 parts by weight of dibutyltin dilaurate was added, and after stirring and reacting for 4 h, the temperature was raised to 85 °C, 0.3 parts by weight of phosphoric acid was added, and after stirring and reacting for 40 min, the temperature was lowered to 30 °C, and the mixture was filtered and discharged to obtain a composite curing agent.

[0075] Example 2:

[0076] A preparation method of a composite curing agent for reducing the free TDI content in polyurethane, comprising the following steps:

[0077] 0.1 parts by weight of the modified metal-organic framework prepared in Preparation Example 2 was dispersed in 10 parts by weight of polyether polyol 215 and 60 parts by weight of 1,2,4-butanetriol to obtain a suspension. 40 parts by weight of 2,6-toluene diisocyanate and 5 parts by weight of the suspension were dispersed in 30 parts by weight of ethyl acetate. The temperature was raised to 70 °C in a nitrogen protection environment, and after stirring and reacting for 30 min, the temperature was lowered to 60 °C, 0.1 parts by weight of dibutyltin dilaurate was added, and after stirring and reacting for 3 h, the temperature was raised to 80 °C, 0.1 parts by weight of hydrochloric acid was added, and after stirring and reacting for 30 min, the temperature was lowered to 30 °C, and the mixture was filtered and discharged to obtain a composite curing agent.

[0078] Example 3:

[0079] A preparation method of a composite curing agent for reducing the free TDI content in polyurethane, comprising the following steps:

[0080] 0.3 parts by weight of the modified metal-organic framework prepared in Preparation Example 3 was dispersed in 15 parts by weight of polyether polyol 220 and 65 parts by weight of trimethylolethane to obtain a suspension. 45 parts by weight of 2,6-toluene diisocyanate and 7 parts by weight of the suspension were dispersed in 32 parts by weight of ethyl acetate. The temperature was raised to 75 °C in a nitrogen protection environment, and after stirring and reacting for 35 min, the temperature was lowered to 63 °C, 0.2 parts by weight of dibutyltin dilaurate was added, and after stirring and reacting for 3.5 h, the temperature was raised to 82 °C, 0.2 parts by weight of phosphoric acid was added, and after stirring and reacting for 32 min, the temperature was lowered to 32 °C, and the mixture was filtered and discharged to obtain a composite curing agent.

[0081] Example 4:

[0082] A preparation method of a composite curing agent for reducing the free TDI content in polyurethane, comprising the following steps:

[0083] 0.7 parts by weight of the modified metal-organic framework prepared in Preparation Example 4 was dispersed in 25 parts by weight of polyether polyol 204 and 80 parts by weight of trimethylolpropane to obtain a suspension. 55 parts by weight of 2,4-toluene diisocyanate and 12 parts by weight of the suspension were dispersed in 38 parts by weight of ethyl acetate. The temperature was raised to 85 °C in a nitrogen protection environment, and after stirring and reacting for 40 min, the temperature was lowered to 68 °C, 0.6 parts by weight of dibutyltin dilaurate was added, and after stirring and reacting for 3 h, the temperature was raised to 88 °C, 0.2 parts by weight of hydrochloric acid was added, and after stirring and reacting for 38 min, the temperature was lowered to 38 °C, and then filtered and discharged to obtain a composite curing agent.

[0084] Example 5:

[0085] A preparation method of a composite curing agent for reducing the free TDI content in polyurethane, comprising the following steps:

[0086] 1 part by weight of the modified metal-organic framework prepared in Preparation Example 5 was dispersed in 30 parts by weight of polyether polyol 204 and 90 parts by weight of trimethylolpropane to obtain a suspension. 60 parts by weight of 2,4-toluene diisocyanate and 15 parts by weight of the suspension were dispersed in 40 parts by weight of ethyl acetate. The temperature was raised to 90 °C in a nitrogen protection environment, and after stirring and reacting for 60 min, the temperature was lowered to 70 °C, 0.8 parts by weight of dibutyltin dilaurate was added, and after stirring and reacting for 5 h, the temperature was raised to 90 °C, 0.4 parts by weight of sulfuric acid was added, and after stirring and reacting for 40 min, the temperature was lowered to 40 °C, and then filtered and discharged to obtain a composite curing agent.

[0087] Comparative Example 1:

[0088] A preparation method of a composite curing agent for reducing the free TDI content in polyurethane, comprising the following steps:

[0089] The modified metal-organic framework prepared in Preparation Example 1 in Example 1 was replaced with the modified metal-organic framework prepared in Preparation Example 6, and other operations were kept the same as in Example 1.

[0090] Comparative Example 2:

[0091] A preparation method of a composite curing agent for reducing the free TDI content in polyurethane, comprising the following steps:

[0092] The modified metal-organic framework prepared in Preparation Example 1 in Example 1 was replaced with the modified metal-organic framework prepared in Preparation Example 7, and other operations were kept the same as in Example 1.

[0093] Comparative Example 3:

[0094] A preparation method of a composite curing agent for reducing the free TDI content in polyurethane, comprising the following steps:

[0095] Replace the modified metal-organic framework prepared in Preparation Example 1 in Example 1 with the modified metal-organic framework prepared in Preparation Example 8, and keep other operations the same as those in Example 1.

[0096] Comparative Example 4:

[0097] A preparation method of a composite curing agent for reducing the free TDI content in polyurethane, comprising the following steps:

[0098] Replace the modified metal-organic framework prepared in Preparation Example 1 in Example 1 with the modified metal-organic framework prepared in Preparation Example 9, and keep other operations the same as those in Example 1.

[0099] Comparative Example 5:

[0100] A preparation method of a composite curing agent for reducing the free TDI content in polyurethane, comprising the following steps:

[0101] A mixed system is obtained from 20 parts by weight of polyether polyol 204 and 70 parts by weight of trimethylolpropane. 50 parts by weight of 2,4-toluene diisocyanate and 10 parts by weight of the mixed system are dispersed in 35 parts by weight of ethyl acetate. The temperature is raised to 80 °C in a nitrogen protection environment, and after stirring and reacting for 50 min, the temperature is lowered to 65 °C, 0.4 part by weight of dibutyltin dilaurate is added, and after stirring and reacting for 4 h, the temperature is raised to 85 °C, 0.3 part by weight of phosphoric acid is added, and after stirring and reacting for 40 min, the temperature is lowered to 30 °C, and the composite curing agent is obtained by filtration and discharging.

[0102] Comparative Example 6:

[0103] A preparation method of a composite curing agent for reducing the free TDI content in polyurethane, comprising the following steps:

[0104] 0.5 part by weight of the modified metal-organic framework prepared in Preparation Example 1 is dispersed in 90 parts by weight of trimethylolpropane to obtain a suspension. 50 parts by weight of 2,4-toluene diisocyanate and 10 parts by weight of the suspension are dispersed in 35 parts by weight of ethyl acetate. The temperature is raised to 80 °C in a nitrogen protection environment, and after stirring and reacting for 50 min, the temperature is lowered to 65 °C, 0.4 part by weight of dibutyltin dilaurate is added, and after stirring and reacting for 4 h, the temperature is raised to 85 °C, 0.3 part by weight of phosphoric acid is added, and after stirring and reacting for 40 min, the temperature is lowered to 30 °C, and the composite curing agent is obtained by filtration and discharging.

[0105] Comparative Example 7:

[0106] A preparation method of a composite curing agent for reducing the free TDI content in polyurethane, comprising the following steps:

[0107] 0.5 parts by weight of the modified metal-organic framework prepared in Preparation Example 1 was dispersed in 90 parts by weight of polyether polyol 204 to obtain a suspension. 50 parts by weight of 2,4-toluene diisocyanate and 10 parts by weight of the suspension were dispersed in 35 parts by weight of ethyl acetate. The temperature was raised to 80 °C in a nitrogen protection environment, and after stirring and reacting for 50 min, the temperature was lowered to 65 °C, 0.4 parts by weight of dibutyltin dilaurate was added, and after stirring and reacting for 4 h, the temperature was raised to 85 °C, 0.3 parts by weight of phosphoric acid was added, and after stirring and reacting for 40 min, the temperature was lowered to 30 °C, and then filtered and discharged to obtain a composite curing agent.

[0108] Comparative Example 8:

[0109] A preparation method of a composite curing agent for reducing the free TDI content in polyurethane, comprising the following steps:

[0110] 2.5 parts by weight of the modified metal-organic framework prepared in Preparation Example 1 was dispersed in 20 parts by weight of polyether polyol 204 and 70 parts by weight of trimethylolpropane to obtain a suspension. 50 parts by weight of 2,4-toluene diisocyanate and 10 parts by weight of the suspension were dispersed in 35 parts by weight of ethyl acetate. The temperature was raised to 80 °C in a nitrogen protection environment, and after stirring and reacting for 50 min, the temperature was lowered to 65 °C, 0.4 parts by weight of dibutyltin dilaurate was added, and after stirring and reacting for 4 h, the temperature was raised to 85 °C, 0.3 parts by weight of phosphoric acid was added, and after stirring and reacting for 40 min, the temperature was lowered to 30 °C, and then filtered and discharged to obtain a composite curing agent.

[0111] Comparative Example 9:

[0112] A preparation method of a composite curing agent for reducing the free TDI content in polyurethane, comprising the following steps:

[0113] 0.2 parts by weight of the modified metal-organic framework prepared in Preparation Example 1 was dispersed in 20 parts by weight of polyether polyol 204 and 70 parts by weight of trimethylolpropane to obtain a suspension. 50 parts by weight of 2,4-toluene diisocyanate and 10 parts by weight of the suspension were dispersed in 35 parts by weight of ethyl acetate. The temperature was raised to 80 °C in a nitrogen protection environment, and after stirring and reacting for 50 min, the temperature was lowered to 65 °C, 0.4 parts by weight of dibutyltin dilaurate was added, and after stirring and reacting for 4 h, the temperature was raised to 85 °C, 0.3 parts by weight of phosphoric acid was added, and after stirring and reacting for 40 min, the temperature was lowered to 30 °C, and then filtered and discharged to obtain a composite curing agent.

[0114] Performance test:

[0115] Test Example 1: Performance test of the composite curing agent

[0116] Test for the content of isocyanate group (NCO): The content of NCO in the composite curing agents prepared in Examples 1 to 5 and Comparative Examples 1 to 9 was detected by referring to the test method of GB / T 12009.4.

[0117] Solid content test: The solid content of the composite curing agents prepared in Examples 1-5 and Comparative Examples 1-9 was detected by referring to the test method of Standard GB / T 2793-1995;

[0118] Free TDI test: The free TDI content of the composite curing agents prepared in Examples 1-5 and Comparative Examples 1-9 was detected by referring to the test method of Standard GB / T 18446-2009;

[0119] Viscosity test: The viscosity of the composite curing agents prepared in Examples 1-5 and Comparative Examples 1-9 at 25 °C was detected by referring to the test method of Standard GB / T 2794-2013.

[0120] The test results are shown in Table 1.

[0121] Table 1. Performance test of the composite curing agent

[0122] NCO (%) Solid content (%) Free TDI (%) Viscosity (cp) Example 1 13.25 77.6 0.25 26.4 Example 2 13.30 77.1 0.26 26.5 Example 3 13.38 76.5 0.27 26.7 Example 4 13.33 77.3 0.26 26.8 Example 5 13.40 76.7 0.27 26.7 Comparative Example 1 14.52 70.8 0.29 28.9 Comparative Example 2 14.66 70.1 0.29 29.2 Comparative Example 3 16.85 61.1 0.33 33.6 Comparative Example 4 15.47 65.5 0.31 30.8 Comparative Example 5 18.46 55.5 0.37 36.6 Comparative Example 6 13.86 74.3 0.27 27.6 Comparative Example 7 14.05 73.0 0.28 28.2 Comparative Example 8 14.97 68.9 0.30 29.8 Comparative Example 9 14.72 70.1 0.29 29.1

[0123] Test Example 2: Application performance test in paint

[0124] The composite curing agents prepared in Examples 1-5 and Comparative Examples 1-9 of the present invention were used to prepare polyurethane paints. The polyurethane paints consisted of Component A, Component B and a diluent. Component A included alkyd resin with a mass fraction of 60%: hydroxyl acrylic resin with a mass fraction of 15%: aldehyde-ketone resin with a mass fraction of 8%: leveling agent: defoaming agent: polyurethane diluent = 60:15:8:0.5:0.5:16. Component B was the composite curing agent prepared in Examples 1-5 and Comparative Examples 1-9 of the present invention. The polyurethane paint was prepared by mixing Component A, Component B and the diluent in a weight ratio of 1:0.5:0.9.

[0125] The polyurethane paints prepared with the composite curing agents of Examples 1-5 and Comparative Examples 1-9 were respectively subjected to performance tests. The test results are shown in Table 2.

[0126] Surface drying time: The surface drying time was detected by referring to the test method of Standard GB / T 1728-2020.

[0127] Matte gloss test: The matte gloss was detected by referring to the test method of Standard GB / T 9754-2007.

[0128] Hardness test: The hardness was detected by referring to the test method of Standard GB / T 1730-2007.

[0129] Adhesion grade test: The adhesion grade was detected by referring to the test method of Standard GB / T 9286-2021.

[0130] Weather resistance grade test: Detect its comprehensive weather resistance grade with reference to the test methods of Standard GB / T 1865-2009 and Standard GB / T 1766-2008.

[0131] Levelling property test: Prepare a paint film on the surface of tinplate, place the sample plate under the conditions of constant temperature and humidity (30°C, relative humidity range of 35%-40%), and observe the time required for the painted surface to reach a uniform, smooth, and wrinkle-free (no orange peel or goose skin) state; whether the painted surface is qualified in terms of being uniform, smooth, and wrinkle-free (no orange peel or goose skin) is related to the standards specified by users for different products.

[0132] Table 2. Performance test of paint

[0133] Surface drying time / min Matte gloss Hardness Adhesion / grade Comprehensive weather resistance / grade Levelling property Example 1 19 20 2H 0 0 Excellent Example 2 21 21 2H 0 0 Excellent Example 3 23 23 2H 0 0 Excellent Example 4 22 22 2H 0 0 Excellent Example 5 25 23 2H 0 0 Excellent Comparative Example 1 27 30 H 1 1 Qualified Comparative Example 2 27 31 H 1 1 Qualified Comparative Example 3 28 42 B 2 2 Orange peel Comparative Example 4 27 40 B 2 2 Orange peel Comparative Example 5 28 45 2B 2 3 Orange peel Comparative Example 6 27 28 H 1 1 Qualified Comparative Example 7 27 30 H 1 1 Qualified Comparative Example 8 24 35 B 2 2 Orange peel Comparative Example 9 26 33 B 2 2 Orange peel

[0134] From the performance test results in Table 1 and Table 2, it can be seen that the composite curing agents prepared in Examples 1-5 of the present invention have a low free TDI content, and the polyurethane paints prepared with the composite curing agents of Examples 1-5 also have good matting properties, adhesion, weather resistance, etc. The surface of the modified metal framework in Comparative Example 1 only has amino groups, the surface of the modified metal framework in Comparative Example 2 only has hydroxyl groups, and the surface of the modified metal framework in Comparative Example 3 has not been modified with amino or hydroxyl groups. The reduction or absence of amino or hydroxyl groups affects the chemical bonding with toluene diisocyanate, resulting in a high free TDI content; the reason for the low performance of Comparative Example 4 may be that the modified metal-organic framework used is not a hollow structure, with less amino or hydroxyl modification and the lack of a hollow structure, making it impossible to physically adsorb and capture free TDI; the modified curing agent prepared in Comparative Example 5 does not use a modified metal-organic framework and cannot form a dense crosslinked network with toluene diisocyanate, resulting in a reduction in its performance; from the comparison of Comparative Example 1, Comparative Example 6, and Comparative Example 7, it can be seen that polyether polyol and aliphatic polyol act together to adjust the viscosity of the composite curing agent and various properties of the polyurethane paint; in Comparative Example 8, the use of an excessive amount of modified metal-organic framework may lead to the coexistence of local over-crosslinking and unreacted regions, ultimately affecting the uniformity of the polyurethane paint and resulting in an orange peel phenomenon on its surface; in Comparative Example 9, the use of a small amount of modified metal-organic framework cannot perform repeated bonding with toluene diisocyanate, which may cause the self-polymerization of toluene diisocyanate and an increase in viscosity, resulting in poor levelling property of the polyurethane paint.

[0135] The above-described embodiments have detailed the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed.

Claims

1. A preparation method of a composite curing agent for reducing the content of free TDI in polyurethane, characterized in that, The preparation method comprises the following steps: A modified metal-organic framework, a polyether polyol, and an aliphatic polyol are mixed to obtain a suspension. After reacting the toluene diisocyanate with the suspension for 30 - 60 min, a catalyst is added and the reaction is carried out at 60 - 70 °C for 3 - 5 h. Then, an inhibitor is added and the reaction is carried out at 80 - 90 °C for 30 - 40 min to obtain the composite curing agent.

2. The preparation method of the composite curing agent according to claim 1, characterized in that, The preparation method of the modified metal-organic framework comprises the following steps: Ammonium cerium nitrate, benzoic acid, and terephthalic acid are reacted at 100 - 110 °C for 16 - 20 h to obtain a metal-organic framework; Zirconium chloride, a polyoxypropylene polyoxyethylene copolymer solution, the metal-organic framework, hydrochloric acid, and acetic acid are reacted at 23 - 25 °C for 30 - 50 min. Then, the temperature is raised to 75 - 85 °C, and tetrafluoroterephthalic acid and 2-aminoterephthalic acid are added and reacted for 24 - 28 h to obtain an intermediate. The intermediate is dispersed in ethanol and etched at 40 - 60 °C for 75 h to obtain a hollow metal-organic framework; The hollow metal-organic framework and a hydrochloric acid solution are reacted at 55 - 65 °C for 3 - 5 h to obtain the modified metal-organic framework.

3. The preparation method of the composite curing agent according to claim 2, wherein, The weight ratio of the zirconium chloride, the polyoxypropylene polyoxyethylene copolymer solution, the metal-organic framework precursor, hydrochloric acid, acetic acid, tetrafluoroterephthalic acid, and 2-aminoterephthalic acid is 9 - 13:40 - 60:8 - 12:0.8 - 1.1:0.05 - 0.15:8 - 12:2 - 3.

4. The preparation method of the composite curing agent according to claim 2, wherein The molar concentration of the hydrochloric acid solution is 0.5 mol / L.

5. The preparation method of the composite curing agent according to claim 2, wherein, The polyether polyol includes one of polyether polyol 204, polyether polyol 215, or polyether polyol 220.

6. The preparation method of the composite curing agent according to claim 2, wherein, The aliphatic polyol includes one of trimethylolpropane, 1,2,4-butanetriol, or trimethylolethane.

7. The preparation method of the composite curing agent according to claim 1, characterized in that, The weight ratio of the modified metal-organic framework, the polyether polyol, and the aliphatic polyol is 0.1 - 1:10 - 30:60 - 90.

8. The preparation method of the composite curing agent according to claim 1, characterized in that, The toluene diisocyanate includes one of 2,4-toluene diisocyanate or 2,6-toluene diisocyanate.

9. The preparation method of the composite curing agent according to claim 1, wherein, The inhibitor includes one of phosphoric acid, hydrochloric acid, or sulfuric acid.

10. A composite curing agent, characterized in that, It is prepared by the preparation method of the composite curing agent according to any one of claims 1 - 9.