A TDI curing agent with low free monomer and good matte property, preparation method and application thereof

Abstract

The present invention discloses a polyisocyanate curing agent with storage stability, a preparation method and an application thereof, wherein the curing agent is obtained by reacting toluene diisocyanate with a hydroxyl compound; in the curing agent component, the molar ratio of isocyanurate group to toluene diisocyanate is 3%-9%, and the molar ratio of allophanate group to toluene diisocyanate is less than 1%. The TDI curing agent prepared by the method of the present invention is used in the field of polyurethane coatings or adhesives.

Description

Technical Field

[0001] The invention relates to a method for preparing a TDI curing agent with low free monomer content, and further relates to the application of the TDI curing agent in the fields of polyurethane coatings and polyurethane adhesives. Background Art

[0002] Polyurethane coatings have the advantages of high hardness, good toughness, strong chemical resistance and fast drying. They are one of the most widely used solvent-based coatings with excellent performance. They dominate furniture and wood coatings. Polyurethane coatings are composed of two components, one is a hydroxyl component such as alkyd resin, polyester resin or acrylic resin, and the other key component is a polyurethane curing agent.

[0003] Polyurethane curing agents are widely used in high-performance coatings, paints, adhesives, decorative building materials, elastomers, and household products. The flexible and varied polyurethane chemical reactions give these products excellent properties, such as compatibility with other components, outstanding thermal stability, and mechanical properties.

[0004] Commonly used curing agents for polyurethane coatings on wood coatings can be divided into: TDI and TMP adducts, TDI and hydroxyl-containing substances adducts and TDI trimers. TMP-TDI adducts are important members of the polyurethane coating industry. Because of their excellent properties such as good film gloss, good elasticity and good toughness, they have become the mainstream of the coating market. Therefore, domestic and foreign countries are competing to carry out research on this.

[0005] In the furniture coating market, wood coatings mainly include glossy paint and matte paint. Among them, with the improvement of people's material and cultural living standards and the pursuit of fashion and individuality, matte wood coatings occupy a large market share. Wood coatings mainly include matte wood coatings, which occupy a large market share.

[0006] CN201610736354 mentions that the matting of glossy paint film is mainly achieved by using matting powder. However, due to the characteristics of matting powder itself, it is greatly affected by factors such as construction process, drying time, ambient temperature and humidity, and anti-settling effect. Especially in the production of low-gloss clear topcoat, if the amount of matting powder is large, the paint film is prone to paint defects such as poor transparency, uneven gloss, and floweriness.

[0007] If the prepared curing agent itself has a good matting effect, the amount of matting powder used can be reduced, thereby solving the disadvantages caused by the large amount of matting powder used and reducing costs.

[0008] CN201510424566 prepares TDI trimer reaction liquid and TDI-TMP adduct reaction liquid respectively, mixes and separates them to prepare matte TDI curing agent. However, the trimer reaction liquid prepared contains solvent, which increases separation energy consumption. In addition, the curing agent prepared by simple mixing may have compatibility problems with resin. Summary of the invention

[0009] The invention relates to a TDI curing agent with low free monomer and good matte property. The matte property of the TDI curing agent itself is improved by controlling the contents of isocyanurate and allophanate during the synthesis of the TDI curing agent, thereby reducing the amount of matting powder in the prepared matte paint.

[0010] The present invention adopts the following technical solution:

[0011] On the one hand, the present invention provides a TDI curing agent with low free monomer content and good matte properties, wherein the curing agent is obtained by reacting toluene diisocyanate with a hydroxyl compound; in the curing agent component, the molar ratio of isocyanurate group to toluene diisocyanate group is 3-9:100, and the molar ratio of allophanate group to toluene diisocyanate group is less than 1:100;

[0012] The toluene diisocyanate group refers to the sum of carbamate, allophanate, isocyanurate and free TDI in the structure

[0013] The toluene diisocyanate described in the present invention is 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, or a mixture of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate, preferably a mixture of 65%-80% by weight of 2,4-toluene diisocyanate and 20%-35% by weight of 2,6-toluene diisocyanate.

[0014] The hydroxy compound in the present invention comprises trimethylolpropane and polyol, and the molar ratio of the hydroxyl groups of the trimethylolpropane to the polyol is (0.1-5):1, preferably (0.2-2):1.

[0015] In the present invention, the hydroxy compound is selected from a polyol with a molecular weight of 60-200; the polyol is selected from one or more of ethylene glycol, propylene glycol, methyl propylene glycol, 1,3-butanediol, 1,4-butanediol, diethylene glycol and dipropylene glycol, 2-methyl-1,3-propanediol, glycerol, 1,2,6-hexanetriol, trimethylolethane and pentaerythritol.

[0016] The molar ratio of the isocyanate groups in the toluene diisocyanate to the hydroxyl groups in the hydroxyl compound described in the present invention is (1-10):1, preferably (3-5):1.

[0017] In the present invention, the free toluene diisocyanate content in the TDI curing agent is ≤1.0%, preferably ≤0.5%, based on the total mass of the curing agent;

[0018] On the other hand, the present invention also provides a method for preparing a free monomer low matte TDI curing agent, comprising the following steps: a) adding a catalyst to toluene diisocyanate to react; b) adding a terminator to terminate the reaction when a predetermined NCO value is reached to obtain a reaction solution containing an isocyanurate group; c) adding a hydroxyl compound to the reaction solution to carry out an amination reaction to obtain a prepolymer reaction solution; d) separating and removing unreacted toluene diisocyanate in the prepolymer reaction solution obtained in step c); and e) adding an organic solvent to dilute the reaction solution to obtain the TDI curing agent.

[0019] The reaction temperature in step a) is 40-80° C., preferably 50-60° C.; the catalyst is one or more of Mannich bases, hydroxides of hydroxyalkylammonium, phosphorus compounds or metal salts of alkyl carboxylic acids, preferably Mannich bases; and the amount of the catalyst is 0.001%-1.0% ppm, preferably 0.005%-0.2% ppm, based on the total weight of toluene diisocyanate in step a).

[0020] In the present invention, the hydroxide of the hydroxyalkylammonium is preferably trimethylhydroxypropylammonium hydroxide, trimethylhydroxyethylammonium hydroxide, triethylhydroxypropylammonium hydroxide, triethylhydroxyethylammonium hydroxide; the phosphorus compound is preferably tributylphosphine; the metal salt of the alkyl carboxylic acid is preferably potassium acetate, tin octoate, zinc octoate and salt of tin acetate; the Mannich base catalyst is preferably a catalyst containing a hydroxyl group and a dialkylaminomethyl group in one molecule, and particularly preferably a catalyst whose dialkylaminomethyl group (alkyl = C1 to C3 chain) is located in the ortho position relative to the aromatic hydroxyl group.

[0021] The preparation method step b) the terminator is a proton acid, an acylating agent or an alkylating agent; the proton acid is preferably one or more of phosphoric acid, hydrochloric acid and sulfuric acid; the acylating agent is preferably benzoyl chloride; the alkylating agent is preferably one or two of methyl p-toluenesulfonate and di-n-butyl phosphate; and / or the amount of the terminator is 1.0-5.0 times the weight of the catalyst in step a).

[0022] The preparation method step c) the urea reaction time is 0.5-2h, the reaction temperature is 40-70°C;

[0023] The separation and removal of unreacted toluene diisocyanate in step d) of the preparation method is carried out by thin film evaporation or short path evaporation, wherein the first stage separation temperature of thin film evaporation is 120-180°C and the pressure is 100-1000Pa, the second stage separation temperature is 150°C-210°C and the vacuum degree is 0-100Pa; the short path evaporator separation temperature is 140-200°C and the pressure is 1-50Pa.

[0024] The organic solvent in step e) of the preparation method is one or more of ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate and propylene glycol methyl ether acetate, preferably ethyl acetate; the dilution degree is such that the solid content of the curing agent is 30-80%, preferably 74-76%.

[0025] It should be noted that the molar ratio of isocyanurate group and allophanate group to toluene diisocyanate can be obtained by measuring 13C-NMR. The proton nuclear magnetic resonance spectrum was measured using Bruker's AVANCE NEO 600MHz, deuterated DMSO as a solvent, 600MHz, and 16 cumulative times to confirm the molar ratio of allophanate group, urea group and toluene diisocyanate. The molar ratio of isocyanurate group and allophanate group to toluene diisocyanate was determined by measuring the signal area of ​​methyl carbon atoms bonded to toluene diisocyanate near 13ppm and 17ppm (1C), the signal area of ​​carbon atoms derived from isocyanurate group near 148ppm (3C) and the signal area of ​​carbon atoms bonded to nitrogen of allophanate near 156ppm (1C).

[0026] The invention also provides application of the TDI curing agent in the field of polyurethane coating or adhesive.

[0027] Finally, the present invention also provides an application of the TDI curing agent in matte paint: the obtained curing agent is mixed with a TDI trimer at a mass ratio of 2:1 to obtain a curing agent mixture, and the obtained mixture is then mixed with a polyol (matte varnish, HS-129) at an NCO / OH molar ratio of 1:1, and then a mixed solvent of butyl acetate / xylene is added for dilution, wherein the content of the curing agent in the solution formed by the curing agent and butyl acetate / xylene is 38-42wt%, and a paint is finally obtained.

[0028] The beneficial effects of the present invention are as follows: the polyisocyanate curing agent of the present invention has a high NCO content and good storage stability, and can be stored at -20°C for 12 months without precipitation. DETAILED DESCRIPTION

[0029] The following examples will further illustrate the method provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the claims of the present invention. The specific application of the present invention is not limited to the application mentioned in the examples, and those familiar with the art can make any modifications and further development within the scope of the claims of the present invention.

[0030] Trimethylolpropane, purchased from Weifang Pasto Co., Ltd.;

[0031] Diethylene glycol was purchased from Yanshan Petrochemical Co., Ltd.;

[0032] Methylpropanediol was purchased from Aladdin Reagents;

[0033] Neopentyl glycol was purchased from Wanhua Chemical Group Co., Ltd.;

[0034] TDI-80, containing approximately 80% 2,4-toluene diisocyanate and 20% 2,6-toluene diisocyanate, was purchased from Wanhua Chemical Group Co., Ltd.;

[0035] Mannich base catalysts: (1) Mannich base based on bisphenol A / formalin / dimethylamine, synthesized by referring to lines 5-10 on page 6 of US 4115373; (2) Mannich base based on phenol / formalin / dimethylamine, synthesized by referring to lines 5-40 on page 8 of US 4115373.

[0036] Unless otherwise specified, other raw materials and reagents can be purchased through commercial channels.

[0037] NCO content test is in accordance with standard GB / T 12009.4;

[0038] The dynamic viscosity was measured at 25 °C using a rotor viscometer (Brookfield DV-II);

[0039] The Hazen color value was determined using a colorimetric device (BYK LCS IV);

[0040] Solid content is tested according to GB / T2793-1995;

[0041] The free TDI content is tested according to GB / T18446-2009;

[0042] Example 1

[0043] 800g TDI-80 was added to the reactor, heated and stirred at 60°C, 0.04g catalyst (Mannich base based on bisphenol A / formalin / dimethylamine) was added to initiate trimerization, when NCO% = 43.7%, 0.2g dibutyl phosphate was added to terminate the reaction, and then 60.9g diethylene glycol and 51.3g trimethylolpropane were added dropwise to the reactor. After the addition was completed, the reaction was continued under stirring for 1 hour; the obtained prepolymer reaction liquid was separated from the reaction liquid in the tank by a short-path evaporator (separation temperature 165°C, pressure 18Pa); the separated reaction liquid entered the dilution kettle and was diluted with ethyl acetate to obtain TDI curing agent. The obtained curing agent had the following parameters after measurement:

[0044] NCO content: 13.58%

[0045] Solid content 75.5%

[0046] Free monomer content 0.38%

[0047] Color value 27Hazen.

[0048] Example 2

[0049] 800g TDI-80 was added to the reactor, heated and stirred at 50℃, 0.01g of potassium carbonate catalyst was added to initiate trimerization reaction, when NCO% = 41.4%, 0.04g of benzoyl chloride was added to terminate the reaction, and then 77.4g of diethylene glycol and 52.2g of trimethylolpropane were added dropwise to the reactor. After the addition was completed, the reaction was continued under stirring for 1 hour; the obtained prepolymer reaction liquid was separated from the reaction liquid in the tank by a short-path evaporator (separation temperature 170℃, pressure 13Pa); the separated reaction liquid was put into the dilution kettle and diluted with ethyl acetate to obtain TDI curing agent. The obtained curing agent has the following parameters after measurement:

[0050] NCO content 13.52%

[0051] Solid content 75.3%

[0052] Free monomer content 0.36%

[0053] Color value 30 Hazen.

[0054] Example 3

[0055] 800g TDI-80 was added to the reactor, heated and stirred at 40°C, 0.16g catalyst (Mannich base based on phenol / formalin / dimethylamine) was added to initiate trimerization reaction, when NCO% = 42.5%, 0.16g dibutyl phosphate was added to terminate the reaction, and then 68.9g methyl propanediol and 13.7g trimethylolpropane were added dropwise to the reactor. After the addition was completed, the reaction was continued under stirring for 0.5 hours; the obtained prepolymer reaction liquid was separated from the reaction liquid in the tank by a short-path evaporator (separation temperature 162°C, pressure 17Pa); the separated reaction liquid entered the dilution kettle and was diluted with ethyl acetate to obtain TDI curing agent. The obtained curing agent had the following parameters after measurement:

[0056] NCO content: 13.48%

[0057] Solid content 75.4%

[0058] Free monomer content 0.36%

[0059] Color value 35 Hazen.

[0060] Example 4

[0061] 800g TDI-80 was added to the reactor, heated and stirred at 50°C, 0.048g catalyst (Mannich base based on phenol / formalin / dimethylamine) was added to initiate trimerization, when NCO% = 46%, 0.144g dibutyl phosphate was added to terminate the reaction, and then a mixed alcohol consisting of 108.3g diethylene glycol and 45.6g trimethylolpropane was added dropwise to the reactor, and after the addition was completed, the reaction was continued under stirring for 2 hours; the obtained prepolymer reaction liquid was separated from the reaction liquid in the tank by a short-path evaporator (separation temperature 165°C, pressure 19Pa); the separated reaction liquid entered the dilution kettle and was diluted with ethyl acetate to obtain TDI curing agent. The obtained curing agent had the following parameters after measurement:

[0062] NCO content 13.51%

[0063] Solid content 75.2%

[0064] Free monomer content 0.33%

[0065] Color value 29 Hazen.

[0066] Example 5

[0067] 800g TDI-80 was added to the reactor, heated and stirred at 50°C, 0.08g catalyst (Mannich base based on phenol / formalin / dimethylamine) was added to initiate trimerization, when NCO% = 45%, 0.24g dibutyl phosphate was added to terminate the reaction, and then a mixed alcohol consisting of 32g neopentyl glycol and 54.8g trimethylolpropane was added to the reactor. After completion, the reaction was continued under stirring for 2 hours; the obtained prepolymer reaction liquid was separated from the reaction liquid in the tank by a short-path evaporator (separation temperature 150°C, pressure 11Pa); the separated reaction liquid entered the dilution kettle and was diluted with ethyl acetate to obtain TDI curing agent. The obtained curing agent had the following parameters after measurement:

[0068] NCO content: 13.39%

[0069] Solid content 75.0%

[0070] Free monomer content 0.42%

[0071] Color value 27Hazen.

[0072] Example 6

[0073] 800g TDI-80 was added to the reactor, heated and stirred at 60°C, 0.056g of catalyst tributylphosphine was added to initiate trimerization, when NCO% = 44.3%, 0.224g of methyl p-toluenesulfonate was added to terminate the reaction, and then a mixed alcohol consisting of 52g of diethylene glycol and 65.8g of trimethylolpropane was added to the reactor. After completion, the reaction was continued under stirring for 1.5 hours; the obtained prepolymer reaction liquid was separated from the reaction liquid in the tank by a short-path evaporator (separation temperature 172°C, pressure 20Pa); the separated reaction liquid entered the dilution kettle and was diluted with ethyl acetate to obtain TDI curing agent. The obtained curing agent had the following parameters after measurement:

[0074] NCO content: 13.44%

[0075] Solid content 75.3%

[0076] Free monomer content 0.41%

[0077] Color value 26Hazen.

[0078] Comparative Example 1

[0079] 800g TDI-80 was added to the reactor, heated and stirred at 60°C, and then a mixed alcohol consisting of 60.9g diethylene glycol and 51.3g trimethylolpropane was added dropwise to the reactor. After the addition was completed, the reaction was continued under stirring for 1 hour, and 0.04g catalyst (Mannich base based on bisphenol A / formalin / dimethylamine) was added to initiate trimerization. When NCO% = 35.3%, 0.2g dibutyl phosphate was added to terminate the reaction; the obtained prepolymer reaction liquid was separated from the reaction liquid in the tank using a short-path evaporator (separation temperature 165°C, pressure 18Pa); the separated reaction liquid entered the dilution kettle and was diluted with ethyl acetate to obtain a TDI curing agent. The obtained curing agent had the following parameters after measurement:

[0080] NCO content 13.54%

[0081] Solid content 75.3%

[0082] Free monomer content 0.36%

[0083] Color value 29 Hazen.

[0084] Comparative Example 2

[0085] 800g TDI-80 was added to the reactor, heated and stirred at 60°C, and then 0.04g catalyst (Mannich base based on bisphenol A / formalin / dimethylamine) was added to initiate trimerization. When NCO% = 46.8%, 0.2g dibutyl phosphate was added to terminate the reaction, and then 60.9g diethylene glycol and 51.3g trimethylolpropane were added dropwise to the reactor. After the addition was completed, the reaction was continued under stirring for 1 hour; the obtained prepolymer reaction liquid was separated from the reaction liquid in the tank by a short-path evaporator (separation temperature 165°C, pressure 18Pa); the separated reaction liquid entered the dilution kettle and was diluted with ethyl acetate to obtain TDI curing agent. The obtained curing agent had the following parameters after measurement:

[0086] NCO content 13.60%

[0087] Solid content 75.6%

[0088] Free monomer content 0.44%

[0089] Color value 25Hazen.

[0090] Comparative Example 3

[0091] 800g TDI-80 was added to the reactor, heated and stirred at 60°C, 0.04g catalyst (Mannich base based on bisphenol A / formalin / dimethylamine) was added to initiate trimerization, when NCO% = 38%, 0.2g dibutyl phosphate was added to terminate the reaction, and then 60.9g diethylene glycol and 51.3g trimethylolpropane were added dropwise to the reactor. After the addition was completed, the reaction was continued under stirring for 1 hour; the obtained prepolymer reaction liquid was separated from the reaction liquid in the tank by a short-path evaporator (separation temperature 165°C, pressure 18Pa); the separated reaction liquid entered the dilution kettle and was diluted with ethyl acetate to obtain TDI curing agent. The obtained curing agent had the following parameters after measurement:

[0092] NCO content 13.52%

[0093] Solid content 75.4%

[0094] Free monomer content 0.39%

[0095] Color value 28 Hazen.

[0096] The performance indicators of the products are shown in Table 1

[0097]

[0098] The preparation method of the paint in this embodiment comprises the following steps: mixing the prepared TDI curing agent with Wanhua TT-350B was mixed at a mass ratio of 2:1 to prepare a curing agent mixture, and the obtained mixture was then mixed with a common commercial polyol (matte varnish, HS-129) at a NCO / OH molar ratio of 1:1, and then a mixed solvent of butyl acetate / xylene was added to dilute it, wherein the content of the curing agent in the solution formed by the curing agent and butyl acetate / xylene was 40wt%, and finally a paint was prepared.

[0099] The prepared paints were tested for adhesion and other properties according to the following methods: (1) Drying (surface drying) test: GB / T 1728; (2) Matt gloss test: GB / T 9754; (3) Leveling test: Prepare a paint film on the tinplate surface, place the sample under constant temperature and humidity (30°C, 35%-40% relative humidity), and observe the time required for the painted surface to reach a uniform, smooth, wrinkle-free (no orange peel or goose skin) state; whether the uniform, smooth, wrinkle-free (no orange peel or goose skin) state of the painted surface is qualified depends on the user's standard requirements for different products; (4) Hardness test: GB / T1730; (5) Adhesion grade test: GB / T 9286. The test results are shown in Table 2.

[0100] Table 2 Test results of paint properties

[0101]

[0102]

[0103] It can be seen from the performance test results of Table 1 and Table 2 that the embodiments have good matte properties. Comparative Example 1 has poor matte properties (>30) due to the high content of allophanate, and Comparative Example 2 has poor matte properties (>30) due to the low content of isocyanurate; Comparative Example 3 has good matte properties, but the isocyanurate content is higher than 10%, resulting in poor leveling, hardness and adhesion of its coating; it can be seen that the molar ratio of isocyanurate group to toluene diisocyanate in the preparation of TDI curing agent is 3%-9%, and the molar ratio of allophanate group to toluene diisocyanate is less than 1%, and a TDI curing agent with good matte properties can be obtained.

[0104] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A TDI curing agent, characterized in that The curing agent is obtained by reacting toluene diisocyanate with a hydroxyl compound; in the curing agent component, the molar ratio of isocyanurate group to toluene diisocyanate group is 3-9:100, and the molar ratio of allophanate group to toluene diisocyanate group is less than 1:100, the hydroxyl compound comprises trimethylolpropane and polyol, the molar ratio of hydroxyl group of trimethylolpropane to polyol is (0.1-5):1, the polyol is selected from one or more of ethylene glycol, propylene glycol, methyl propanediol, 1,3-butanediol, 1,4-butanediol, diethylene glycol and dipropylene glycol, glycerol, 1,2,6-hexanetriol, trimethylolethane and pentaerythritol, and the toluene diisocyanate group refers to the sum of carbamate, allophanate, isocyanurate and free TDI in the structure.

2. The TDI curing agent according to claim 1, characterized in that The toluene diisocyanate is 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, or a mixture of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate.

3. The TDI curing agent according to claim 2, characterized in that The toluene diisocyanate is a mixture of 65% to 80% by weight of 2,4-toluene diisocyanate and 20% to 35% by weight of 2,6-toluene diisocyanate.

4. The TDI curing agent according to claim 1, characterized in that The molar ratio of the trimethylolpropane to the hydroxyl group of the polyol is (0.2-2):

1.

5. The TDI curing agent according to any one of claims 1 to 4, characterized in that The molar ratio of the isocyanate group in the toluene diisocyanate to the hydroxyl group in the hydroxyl compound is (3-10):

1.

6. The method for preparing the TDI curing agent according to any one of claims 1 to 4, characterized in that: The following steps are involved: a) adding a catalyst to toluene diisocyanate to react; b) adding a terminator to terminate the reaction when a predetermined NCO value is reached to obtain a reaction solution containing isocyanurate groups; c) adding a hydroxy compound to the reaction solution for amination reaction to obtain a prepolymer reaction solution; d) separating and removing unreacted toluene diisocyanate in the prepolymer reaction solution obtained in step c); and e) adding an organic solvent for dilution to obtain the TDI curing agent.

7. The preparation method according to claim 6, characterized in that: The reaction temperature in step a) is 40-80° C.; the catalyst is one or more of Mannich bases, hydroxides of hydroxyalkylammonium, phosphorus compounds or metal salts of alkyl carboxylic acids; and the amount of the catalyst is 0.001%-1.0% ppm based on the total weight of toluene diisocyanate in step a).

8. The preparation method according to claim 6, characterized in that: The reaction temperature in step a) is 50-60° C.; the amount of the catalyst used is 0.005%-0.2% ppm based on the total weight of toluene diisocyanate in step a).

9. The preparation method according to any one of claims 6 to 8, characterized in that: The terminator in step b) is a protonic acid, an acylating agent or an alkylating agent; the protonic acid is selected from one or more of phosphoric acid, hydrochloric acid and sulfuric acid; the acylating agent is benzoyl chloride; the alkylating agent is selected from one or both of methyl p-toluenesulfonate and di-n-butyl phosphate; and / or the amount of the terminator is 1.0-5.0 times the weight of the catalyst in step a).

10. The preparation method according to any one of claims 6 to 8, characterized in that: The amination reaction time of step c) is 0.5-2h, and the reaction temperature is 40-70°C; and / or, the separation and removal of unreacted toluene diisocyanate in step d) is carried out by thin film evaporation or short path evaporation, wherein the first stage separation temperature of thin film evaporation is 120-180°C, the pressure is 100-1000Pa, the second stage separation temperature is 150°C-210°C, and the vacuum degree is 0-100Pa; the short path evaporator separation temperature is 140-200°C, and the pressure is 1-50Pa.

11. Use of the TDI curing agent according to any one of claims 1 to 5 or the TDI curing agent prepared by the preparation method according to any one of claims 6 to 10 in the field of polyurethane coatings or adhesives.

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