Preparation method of aziridine closed isocyanate cross-linking agent

Abstract

The invention relates to the technical field of organic synthesis, and discloses a preparation method of an aziridine closed isocyanate cross-linking agent, which adopts an aziridine aqueous solution and an MDI toluene solution as raw materials to prepare the aziridine closed isocyanate cross-linking agent. The aziridine aqueous solution is prepared from ethanolamine, a sulfuric acid aqueous solution and a sodium hydroxide solution, and is low in toxicity, safe and simple in process; an MDI toluene solution is adopted as a raw material, toluene, water and the aziridine closed type isocyanate cross-linking agent are immiscible, so that the toluene, the water and the aziridine closed type isocyanate cross-linking agent can be layered, and the water and the aziridine closed type isocyanate cross-linking agent can be quickly separated; in addition, side reaction impurities generated in the aziridine and MDI reaction process can be dissolved in methylbenzene, and the technical effect of impurity removal is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of organic synthesis, and in particular to a preparation method of a nitrogen propyleneimine-closed isocyanate crosslinking agent. Background Art

[0002] Isocyanate compounds are excellent adhesive preparations, which have excellent adhesive properties, no formaldehyde, strong water resistance and aging resistance. However, isocyanate groups have relatively active chemical properties and are prone to react with water vapor. Especially in an aqueous solution system, their stability is extremely poor, resulting in the inability of isocyanate compounds to be stored for a long time. Therefore, how to achieve stable dispersion of isocyanates in an aqueous solution and maintain reaction activity has become a key issue in the development of isocyanate adhesives.

[0003] Currently, for the dispersion problem of isocyanates in an aqueous solution, it is mostly solved by preparing isocyanate prepolymer water emulsions or dispersions through an emulsification method. Although this method can disperse isocyanates in an aqueous solution, due to the presence of free isocyanate groups, there are still problems such as poor stability, short pot life, and difficult storage. The prior art points out that using a blocking agent to modify isocyanates can improve the stability of isocyanates. Nitrogen propyleneimine in the blocking agent can be used as a modifier for cyanates. For example, a nitrogen propyleneimine-based waterborne blocked polyisocyanate curing agent and its preparation method disclosed in Publication No. CN107828049A. In this technical solution, the amine groups and hydroxyl groups produced after the ring-opening and deblocking of the obtained nitrogen propyleneimine-based waterborne blocked polyisocyanate curing agent can both react with isocyanate groups to form a dense paint film.

[0004] When the present invention uses nitrogen propyleneimine to modify diphenylmethane diisocyanate (MDI), it is found that when using high-purity nitrogen propyleneimine, high-purity nitrogen propyleneimine has problems such as high toxicity, strong allergenicity, low safety, large hydrolysis degree, difficult recovery, and complex process. Summary of the Invention

[0005] In view of the problems of low safety, difficult recovery, and complex process in using high-purity nitrogen propyleneimine to modify MDI in the prior art, the present invention provides a preparation method of a nitrogen propyleneimine-closed isocyanate crosslinking agent. This method uses an aqueous solution of nitrogen propyleneimine and a toluene solution of MDI as raw materials to prepare a nitrogen propyleneimine-closed isocyanate crosslinking agent. The aqueous solution of nitrogen propyleneimine is made from ethanolamine, sulfuric acid aqueous solution, and sodium hydroxide solution, which has low toxicity, is safe, and has a simple process. The present invention also uses a toluene solution of MDI as a raw material. Toluene is immiscible with water and the nitrogen propyleneimine-closed isocyanate crosslinking agent. Therefore, toluene, water, and the nitrogen propyleneimine-closed isocyanate crosslinking agent will form layers, enabling rapid separation of water and the nitrogen propyleneimine-closed isocyanate crosslinking agent. In addition, the side reaction impurities generated during the reaction between nitrogen propyleneimine and MDI can be dissolved in toluene, and using toluene can also achieve the technical effect of impurity removal.

[0006] The specific technical solution of the present invention is as follows: A preparation method of a nitrogen-propyleneimine-closed isocyanate crosslinking agent, comprising the following steps: (1) Put ethanolamine and a solvent into a reaction vessel for inerting treatment to make a reaction raw material, carry out an esterification reaction on the reaction raw material with an aqueous sulfuric acid solution to make an esterified product, and then react the esterified product with an aqueous sodium hydroxide solution to make an aqueous solution of nitrogen-propyleneimine; (2) Dropwise add an MDI toluene solution to the aqueous solution of nitrogen-propyleneimine for reaction. After the reaction is completed, let it stand for stratification and add toluene to the lower-layer liquid for washing. After standing for stratification again, take the lower-layer liquid to obtain a material, and use a stabilizer to adjust the pH of the material to make an emulsion of the nitrogen-propyleneimine-closed isocyanate crosslinking agent.

[0007] The present invention provides a preparation method of a nitrogen-propyleneimine-closed isocyanate crosslinking agent. This method uses ethanolamine, an aqueous sulfuric acid solution and a sodium hydroxide solution as raw materials to prepare an aqueous solution of nitrogen-propyleneimine, and then uses the aqueous solution of nitrogen-propyleneimine and an MDI toluene solution to prepare the nitrogen-propyleneimine-closed isocyanate crosslinking agent. Compared with using high-purity nitrogen-propyleneimine as a raw material, using the aqueous solution of nitrogen-propyleneimine has higher safety, does not require purification, the process is simpler, and the cost is lower.

[0008] The present invention also uses an MDI toluene solution as a raw material. MDI can be dissolved in toluene, while the reaction product nitrogen-propyleneimine-closed isocyanate crosslinking agent formed by nitrogen-propyleneimine and MDI is immiscible with toluene, and the by-product impurities generated during the reaction of nitrogen-propyleneimine and MDI can also be miscible with toluene. Therefore, toluene in the present invention is both a solvent for MDI and an extractant for the by-product impurities generated during the reaction of nitrogen-propyleneimine and MDI. Therefore, when using the MDI toluene solution, the generated by-product impurities can be separated, achieving the technical effects of removing impurities from the product and purifying the product.

[0009] The purpose of inerting treatment of ethanolamine and the solvent is to prevent carbon dioxide in the air from reacting with the product and ensure the purity of the product.

[0010] Preferably, the mass ratio of ethanolamine to the solvent is 1:3.5 - 5.

[0011] Preferably, the molar ratio of ethanolamine to sulfuric acid is 1:1 - 1.05.

[0012] Preferably, the solvent is one or more of benzene, cyclohexane, toluene and xylene.

[0013] Preferably, the mass percentage of the aqueous sulfuric acid solution is 95 - 98%.

[0014] Preferably, the concentration of the aqueous sodium hydroxide solution is 16 - 17%.

[0015] Preferably, the concentration of the MDI toluene solution is 10-15%.

[0016] Preferably, the stabilizer is an organic amine, and the organic amine is one or more of diethanolamine, tetramethylethylenediamine, 2-hydroxyethylpropylamine, and N-(2-hydroxyethyl)ethylenediamine.

[0017] Preferably, the pH is 8.5-10, and the aziridine-blocked isocyanate crosslinking agent emulsion adjusts the water content in the emulsion by evaporation, and the evaporation temperature is 50-60°C.

[0018] The present invention uses evaporation to adjust the water content in the aziridine-blocked isocyanate crosslinking agent emulsion and controls the evaporation temperature so that water can be gradually separated from the aziridine-blocked isocyanate crosslinking agent emulsion and ensure that the aziridine-blocked isocyanate crosslinking agent is not affected.

[0019] Preferably, the molar ratio of aziridine to MDI is 1:0.4-0.45.

[0020] Compared with the prior art, the present application has the following technical effects: This method uses an aziridine aqueous solution and an MDI toluene solution as raw materials to prepare an aziridine-blocked isocyanate crosslinking agent. The aziridine aqueous solution is made from ethanolamine, sulfuric acid aqueous solution, and sodium hydroxide solution. It has low toxicity, is safe, and has a simple process. The present invention also uses an MDI toluene solution as a raw material. Toluene is immiscible with water and the aziridine-blocked isocyanate crosslinking agent. Therefore, toluene, water, and the aziridine-blocked isocyanate crosslinking agent will form layers, enabling rapid separation of water and the aziridine-blocked isocyanate crosslinking agent. In addition, the side reaction impurities generated during the reaction of aziridine and MDI can dissolve in toluene to achieve the technical effect of impurity removal. Specific Embodiments

[0021] The present invention will be further described below with reference to the embodiments.

[0022] Example 1: A method for preparing an aziridine-blocked isocyanate crosslinking agent includes the following steps: (1) Add 596 g of ethanolamine and 2100 g of toluene to a reaction flask and inertize it twice with nitrogen to make the reaction raw materials; (2) Slowly add 975 g of concentrated sulfuric acid to the reaction raw materials for an esterification reaction. The heat of reaction is relatively large, and the temperature needs to be controlled at 30-40°C. After the reaction is completed, the reaction flask is heated to 90-105°C for reflux dehydration until anhydrous to make the esterified product; (3) Cool the esterified product to 25°C, then add 5350 g of sodium hydroxide aqueous solution (concentration 15%) for reaction. After the reaction, let it stand for stratification. Heat the lower aqueous layer to above 100°C for steam stripping to obtain an aqueous solution of aziridine (aziridine content is 378 g); (4) Cool the aqueous solution of aziridine to 10°C and stir. Slowly add dropwise the MDI toluene solution at 40°C (containing 989 g of MDI). After the addition, slowly raise the temperature to 20°C and continue the reaction. After the reaction is completed, let it stand for stratification. Inject toluene into the lower layer of the material for washing, and separate the lower liquid by standing for stratification to make the material; (5) Add 2-hydroxyethylpropylamine to the material to adjust the pH to 9.5 to make an aziridine-blocked isocyanate crosslinking agent emulsion. Place the aziridine-blocked isocyanate crosslinking agent emulsion at 50°C for evaporation to adjust the water content in the emulsion.

[0023] Example 2: A preparation method of an aziridine-blocked isocyanate crosslinking agent, comprising the following steps: (1) Add 596 g of ethanolamine and 2300 g of xylene to a reaction flask and inertize it twice with nitrogen to make the reaction raw materials; (2) Slowly add 1000 g of concentrated sulfuric acid to the reaction raw materials for esterification reaction. Since the heat of reaction is relatively large, the temperature needs to be controlled at 30 - 40°C. After the reaction is completed, raise the temperature of the reaction flask to 115 - 140°C for reflux dehydration until anhydrous to make the esterified product; (3) Cool the esterified product to 25°C, then add 5740 g of sodium hydroxide aqueous solution (concentration 15%) for reaction. After the reaction, let it stand for stratification. Heat the lower aqueous layer to above 100°C for steam stripping to obtain an aqueous solution of aziridine (aziridine content is 391 g); (4) Cool the aqueous solution of aziridine to 10°C and stir. Slowly add dropwise the MDI toluene solution at 40°C (containing 977 g of MDI). After the addition, slowly raise the temperature to 20°C and continue the reaction. After the reaction is completed, let it stand for stratification. Inject toluene into the lower layer of the material for washing, and separate the lower liquid by standing for stratification to make the material; (5) Add 2-hydroxyethylpropylamine to the material to adjust the pH to 9.5 to make an aziridine-blocked isocyanate crosslinking agent emulsion. Place the aziridine-blocked isocyanate crosslinking agent emulsion at 50°C for evaporation to adjust the water content in the emulsion.

[0024] Example 3: A preparation method of an aziridine-blocked isocyanate crosslinking agent, comprising the following steps: (1) Add 596 g of ethanolamine and 2900 g of cyclohexane to a reaction flask and inertize it twice with nitrogen to make the reaction raw materials; (2) Slowly add 975 g of concentrated sulfuric acid to the reaction raw materials for esterification reaction. Since the heat released during the reaction is relatively large, the temperature needs to be controlled at 30 - 40 °C. After the reaction is completed, raise the temperature of the reaction flask to 73 - 80 °C for reflux dehydration until anhydrous to form an esterified product; (3) Cool the esterified product to 25 °C, then add 5550 g of sodium hydroxide aqueous solution (concentration 15%) for reaction. After the reaction is completed, let it stand for stratification. Heat the lower aqueous layer to above 100 °C for steam stripping to obtain an aqueous solution of aziridine (aziridine content is 361 g); (4) Cool the aqueous solution of aziridine to 10 °C and stir. Slowly add a toluene solution of MDI at 40 °C (containing 945 g of MDI). After the addition is complete, slowly raise the temperature to 25 °C and continue the reaction. After the reaction is completed, let it stand for stratification. Inject toluene into the lower layer of the material for washing, and separate the lower liquid by standing for stratification to form the material; (5) Add N-(2-hydroxyethyl)ethylenediamine to the material to adjust the pH to 10 to form an aziridine-blocked isocyanate crosslinking agent emulsion. Place the aziridine-blocked isocyanate crosslinking agent emulsion at 50 °C for evaporation to adjust the water content in the emulsion.

[0025] Example 4: (Benzene to be supplemented) A preparation method of an aziridine-blocked isocyanate crosslinking agent, comprising the following steps: (1) Add 596 g of ethanolamine and 2600 g of benzene to a reaction flask and inertize it twice with nitrogen to form reaction raw materials; (2) Slowly add 975 g of concentrated sulfuric acid to the reaction raw materials for esterification reaction. Since the heat released during the reaction is relatively large, the temperature needs to be controlled at 30 - 40 °C. After the reaction is completed, raise the temperature of the reaction flask to [temperature value missing] °C for reflux dehydration until anhydrous to form an esterified product; (3) Cool the esterified product to 25 °C, then add 5350 g of sodium hydroxide aqueous solution (concentration 15%) for reaction. After the reaction is completed, let it stand for stratification. Heat the lower aqueous layer to above 100 °C for steam stripping to obtain an aqueous solution of aziridine (aziridine content is 378 g); (4) Cool the aqueous solution of aziridine to 10 °C and stir. Slowly add a toluene solution of MDI at 40 °C (containing 989 g of MDI). After the addition is complete, slowly raise the temperature to 20 °C and continue the reaction. After the reaction is completed, let it stand for stratification. Inject toluene into the lower layer of the material for washing, and separate the lower liquid by standing for stratification to form the material; (5) Add 2-hydroxyethylpropylamine to the material to adjust the pH to 9.5 to form an aziridine-blocked isocyanate crosslinking agent emulsion. Place the aziridine-blocked isocyanate crosslinking agent emulsion at 50 °C for evaporation to adjust the water content in the emulsion.

[0026] Example 5: A preparation method of aziridine - closed isocyanate cross - linker, comprising the following steps: (1) Add 596 g of ethanolamine and 2100 g of toluene into a reaction flask and inertize it twice with nitrogen to make reaction raw materials; (2) Slowly drop 975 g of concentrated sulfuric acid into the reaction raw materials for esterification reaction. Since the heat release of the reaction is relatively large, the temperature needs to be controlled at 30 - 40 °C. After the reaction is completed, raise the temperature of the reaction flask to 90 - 105 °C for reflux dehydration until anhydrous to make an esterified product; (3) Cool the esterified product to 25 °C and then add 5350 g of sodium hydroxide aqueous solution (concentration 15%) for reaction. After the reaction ends, let it stand for layering. Heat the lower water layer to above 100 °C for steam stripping to obtain an aziridine aqueous solution (aziridine content is 378 g); (4) Cool the aziridine aqueous solution to 10 °C and stir. Slowly drop the MDI toluene solution at 40 °C (containing 989 g of MDI). After dropping, slowly raise the temperature to 20 °C and continue the reaction. After the reaction is completed, let it stand for layering. Inject toluene into the lower - layer material for washing, and separate the lower - layer liquid by standing layering to make a material; (5) Add diethanolamine to the material to adjust the pH to 9.5 to make an aziridine - closed isocyanate cross - linker emulsion, and place the aziridine - closed isocyanate cross - linker emulsion at 50 °C for evaporation to adjust the water content in the emulsion.

[0027] Example 6: A preparation method of aziridine - closed isocyanate cross - linker, comprising the following steps: (1) Add 596 g of ethanolamine and 2100 g of toluene into a reaction flask and inertize it twice with nitrogen to make reaction raw materials; (2) Slowly drop 975 g of concentrated sulfuric acid into the reaction raw materials for esterification reaction. Since the heat release of the reaction is relatively large, the temperature needs to be controlled at 30 - 40 °C. After the reaction is completed, raise the temperature of the reaction flask to 90 - 105 °C for reflux dehydration until anhydrous to make an esterified product; (3) Cool the esterified product to 25 °C and then add 5350 g of sodium hydroxide aqueous solution (concentration 15%) for reaction. After the reaction ends, let it stand for layering. Heat the lower water layer to above 100 °C for steam stripping to obtain an aziridine aqueous solution (aziridine content is 378 g); (4) Cool the aziridine aqueous solution to 10 °C and stir. Slowly drop the MDI toluene solution at 40 °C (containing 989 g of MDI). After dropping, slowly raise the temperature to 20 °C and continue the reaction. After the reaction is completed, let it stand for layering. Inject toluene into the lower - layer material for washing, and separate the lower - layer liquid by standing layering to make a material; (5) Add tetramethylethylenediamine to the material to adjust the pH to 9.5 to prepare an aziridine-blocked isocyanate crosslinker emulsion, and place the aziridine-blocked isocyanate crosslinker emulsion at 50 °C to adjust the water content in the emulsion by evaporation.

[0028] Example 7: A preparation method of an aziridine-blocked isocyanate crosslinker, comprising the following steps: (1) Add 596 g of ethanolamine and 2100 g of toluene to a reaction flask and inertize twice with nitrogen to prepare a reaction raw material; (2) Slowly add 975 g of concentrated sulfuric acid to the reaction raw material for an esterification reaction. The heat released during the reaction is relatively large, and the temperature needs to be controlled at 30-40 °C. After the reaction is completed, heat the reaction flask to 90-105 °C for reflux dehydration until anhydrous to obtain an esterified product; (3) Cool the esterified product to 25 °C and then add 5350 g of sodium hydroxide aqueous solution (concentration 15%) for reaction. After the reaction is completed, let it stand for stratification, heat the lower water layer to above 100 °C for steam stripping to obtain an aziridine aqueous solution (aziridine content is 378 g); (4) Cool the aziridine aqueous solution to 10 °C and stir, slowly add a toluene solution of MDI at 40 °C (containing 989 g of MDI). After the addition is completed, slowly heat up to 20 °C and continue the reaction. After the reaction is completed, let it stand for stratification, inject toluene into the lower material for washing, and separate the lower liquid by standing for stratification to obtain a material; (5) Add N-(2-hydroxyethyl)ethylenediamine to the material to adjust the pH to 10 to prepare an aziridine-blocked isocyanate crosslinker emulsion, and place the aziridine-blocked isocyanate crosslinker emulsion at 50 °C to adjust the water content in the emulsion by evaporation.

[0029] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that ethanolamine and the solvent were not subjected to a nitrogen inerting reaction; it includes the following steps: (1) Add 596 g of ethanolamine and 2100 g of toluene to a reaction flask to prepare a reaction raw material; (2) Slowly add 975 g of concentrated sulfuric acid to the reaction raw material for an esterification reaction. The heat released during the reaction is relatively large, and the temperature needs to be controlled at 30-40 °C. After the reaction is completed, heat the reaction flask to 90-105 °C for reflux dehydration until anhydrous to obtain an esterified product; (3) Cool the esterified product to 25 °C and then add 5350 g of sodium hydroxide aqueous solution (concentration 15%) for reaction. After the reaction is completed, let it stand for stratification, heat the lower water layer to above 100 °C for steam stripping to obtain an aziridine aqueous solution (aziridine content is 353 g); (4) Cool the aziridine aqueous solution to 10 °C and stir. Slowly add dropwise the toluene solution of MDI (containing 989 g of MDI) at 40 °C. After the addition is complete, slowly raise the temperature to 20 °C and continue the reaction. After the reaction is completed, let it stand for layering. Inject toluene into the lower-layer material for washing, and let it stand for layering to separate the lower-layer liquid to make the material; (5) Add 2-hydroxyethylpropylamine to the material to adjust the pH to 9.5 to make an aziridine-closed isocyanate crosslinking agent emulsion. Place the aziridine-closed isocyanate crosslinking agent emulsion at 50 °C to adjust the water content in the emulsion by evaporation.

[0030] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that MDI is directly used without using toluene, including the following steps: (1) Add 596 g of ethanolamine and 2100 g of toluene to a reaction flask and inertize it twice with nitrogen to make a reaction raw material; (2) Slowly add dropwise 975 g of concentrated sulfuric acid to the reaction raw material for an esterification reaction. The heat released during the reaction is relatively large, and the temperature needs to be controlled at 30 - 40 °C. After the reaction is completed, raise the temperature of the reaction flask to 90 - 105 °C for reflux dehydration until anhydrous to make an esterified product; (3) Cool the esterified product to 25 °C and then add 5350 g of sodium hydroxide aqueous solution (concentration 15%) for reaction. After the reaction is completed, let it stand for layering. Heat the lower-layer water layer to above 100 °C for steam distillation to obtain an aziridine aqueous solution (aziridine content is 378 g); (4) Cool the aziridine aqueous solution to 10 °C and stir. Slowly add dropwise 989 g of MDI at 40 °C. After the addition is complete, slowly raise the temperature to 20 °C and continue the reaction to make the material; (5) Add 2-hydroxyethylpropylamine to the material to adjust the pH to 9.5 to make an aziridine-closed isocyanate crosslinking agent emulsion. Place the aziridine-closed isocyanate crosslinking agent emulsion at 50 °C to adjust the water content in the emulsion by evaporation.

[0031] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that toluene is not used to wash the material, including the following steps: (1) Add 596 g of ethanolamine and 2100 g of toluene to a reaction flask and inertize it twice with nitrogen to make a reaction raw material; (2) Slowly add dropwise 975 g of concentrated sulfuric acid to the reaction raw material for an esterification reaction. The heat released during the reaction is relatively large, and the temperature needs to be controlled at 30 - 40 °C. After the reaction is completed, raise the temperature of the reaction flask to 90 - 105 °C for reflux dehydration until anhydrous to make an esterified product; (3) Cool down the esterified product to 25°C, then add 5350 g of sodium hydroxide aqueous solution (concentration 15%) for reaction. After the reaction ends, let it stand for layering. Heat the lower aqueous layer to above 100°C for steam stripping to obtain an aqueous solution of aziridine (aziridine content is 378 g); (4) Cool down the aqueous solution of aziridine to 10°C and stir. Slowly add dropwise the MDI toluene solution at 40°C (containing 989 g of MDI). After the addition is complete, slowly raise the temperature to 20°C and continue the reaction. After the reaction is completed, let it stand for layering and separate the lower liquid to make the material; (5) Add 2-hydroxyethylpropylamine to the material to adjust the pH to 9.5 to make an aziridine-blocked isocyanate crosslinking agent emulsion. Place the aziridine-blocked isocyanate crosslinking agent emulsion at 50°C for evaporation to adjust the water content in the emulsion.

[0032] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that the evaporation temperature of the aziridine-blocked isocyanate crosslinking agent emulsion is too high, including the following steps: (1) Add 596 g of ethanolamine and 2100 g of toluene to the reaction flask and inertize it twice with nitrogen to make the reaction raw material; (2) Slowly add dropwise 975 g of concentrated sulfuric acid to the reaction raw material for esterification reaction. Since the heat of reaction is large, the temperature needs to be controlled at 30 - 40°C. After the reaction is completed, raise the temperature of the reaction flask to 90 - 105°C for reflux dehydration until anhydrous to make the esterified product; (3) Cool down the esterified product to 25°C, then add 5350 g of sodium hydroxide aqueous solution (concentration 15%) for reaction. After the reaction ends, let it stand for layering. Heat the lower aqueous layer to above 100°C for steam stripping to obtain an aqueous solution of aziridine (aziridine content is 378 g); (4) Cool down the aqueous solution of aziridine to 10°C and stir. Slowly add dropwise the MDI toluene solution at 40°C (containing 989 g of MDI). After the addition is complete, slowly raise the temperature to 20°C and continue the reaction. After the reaction is completed, let it stand for layering, inject toluene into the lower material for washing, and separate the lower liquid by standing for layering to make the material; (5) Add 2-hydroxyethylpropylamine to the material to adjust the pH to 9.5 to make an aziridine-blocked isocyanate crosslinking agent emulsion. Place the aziridine-blocked isocyanate crosslinking agent emulsion at 100°C for evaporation to adjust the water content in the emulsion.

[0033] Detection Example: Test the aziridine-blocked isocyanate crosslinking agent emulsions prepared in Examples 1 to 7 and Comparative Examples 1 to 4; The test items include: water content and crosslinking agent purity, The test method is as follows: Moisture content determination steps: Open the weighing bottle with its lid and place them together in a constant temperature drying oven at 105 ± 2 °C for 1 hour. Then, put the weighing bottle and its lid into a desiccator and cool them to room temperature, weigh them accurately to 0.1 mg. Repeat the operation until the difference in mass between the last two times is less than 0.3 mg. Take about 5 g of the test sample, place it in the weighing bottle, weigh it precisely, dry it to a constant weight at 105 °C, and conduct parallel tests simultaneously. Calculate the loss on drying of the test sample from the weight loss after constant weight and the sample size. Crosslinking agent purity determination method (HPLC): Packed column specifications (C18, 250 mm × 4.6 mm × 5 μm), wavelength (254 nm), mobile phase (acetonitrile: deionized water is 50:50, flow rate 1 ml / min); The test results are shown in Table 1.

[0034] Table 1 Test Results As shown in Table 1, the purity of the aziridine - closed isocyanate crosslinking agent emulsion prepared in Examples 1 to 7 is 98.71 - 99.13%, and the impurity content is 0.87 - 1.29%. Through testing, it is found that the main impurity by - product generated is diphenylmethane diamine. The above results indicate that the prepared aziridine - closed isocyanate crosslinking agent emulsion has high purity, low impurity content, and high product quality.

[0035] In Comparative Example 1, nitrogen was not used to inertize the raw materials made of ethanolamine and solvent. As a result, it was found that the product contained impurities generated by the reaction of carbon dioxide with the product, and these impurities led to a decrease in the purity of the product and made it difficult to separate the subsequent crosslinking agent emulsion.

[0036] In Comparative Example 2, MDI was directly used without using toluene. As a result, it was found that the impurity content in the aziridine - closed isocyanate crosslinking agent emulsion prepared in Comparative Example 2 reached 32.6%, and the impurity content in Comparative Example 2 was significantly higher than that in Example 1.

[0037] In Comparative Example 3, toluene was not used to wash the materials. As a result, it was found that the impurity content in the aziridine - closed isocyanate crosslinking agent emulsion prepared in Comparative Example 3 was higher than that in Example 1. The results show that using toluene to wash the materials can further remove the by - product impurities generated, ensure the purity of the emulsion product, and improve the product quality.

[0038] In Comparative Example 4, the evaporation temperature of the aziridine - closed isocyanate crosslinking agent emulsion was too high. As a result, it was found that too high an evaporation temperature would cause the prepared product to deteriorate rapidly and polymers would form between the products.

[0039] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent transformations made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing an aziridine blocked isocyanate crosslinking agent, characterized in that: The following steps are involved: (1) Ethanolamine and a solvent are placed in a reaction container for inertization to prepare a reaction raw material, a sulfuric acid aqueous solution is used to carry out an esterification reaction with the reaction raw material to prepare an esterified product, and a sodium hydroxide aqueous solution is used to react with the esterified product to prepare an aziridine aqueous solution; (2) Add MDI toluene solution dropwise to aziridine aqueous solution for reaction. After the reaction is completed, stand and separate the layers and add toluene to the lower layer of liquid for washing. After standing and separating the layers, take out the lower layer of liquid to obtain the material. Use a stabilizer to adjust the pH of the material to prepare an aziridine blocked isocyanate crosslinker emulsion.

2. The preparation method according to claim 1, characterized in that: The mass ratio of ethanolamine to solvent is 1:3.5~5.

3. The preparation method according to claim 1, characterized in that: The molar ratio of ethanolamine to sulfuric acid is 1:1~1.

05.

4. The preparation method according to claim 1 or 2, characterized in that: The solvent is one or more of benzene, cyclohexane, toluene and xylene.

5. The preparation method according to claim 1, characterized in that: The mass percentage of the aqueous sulfuric acid solution is 95-98%.

6. The preparation method according to claim 1, characterized in that: The concentration of the sodium hydroxide aqueous solution is 15%.

7. The preparation method according to claim 1, characterized in that: The concentration of the MDI toluene solution is 10-15%.

8. The preparation method according to claim 1, characterized in that: The stabilizer is an organic amine, and the organic amine is one or more of diethanolamine, tetramethylethylenediamine, 2-hydroxyethylaminepropylamine, and N-(2-hydroxyethyl)ethylenediamine.

9. The preparation method according to claim 1, characterized in that: The pH is 8.5-10, and the water content in the aziridine blocked isocyanate crosslinking agent emulsion is regulated by evaporation, and the evaporation temperature is 50-60°C.

10. The preparation method according to claim 1, characterized in that: The molar ratio of aziridine to MDI is 1:0.4~0.45.

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