An environmentally friendly water-based adhesive and its preparation method

Abstract

The present invention relates to the technical field of adhesives, and discloses an environmentally friendly water-based adhesive and a preparation method thereof. The water-based adhesive prepared by the present invention comprises the following raw materials in parts by weight: 20-30 parts of polyethylene adipate glycol, 3-8 parts of modified polyacrylic acid, 13-18 parts of isophorone diisocyanate, 3-6 parts of modified chain extender, 0.005-0.02 part of catalyst, 0.2-0.5 part of propylene glycol, 0.1-0.3 part of triethylamine, 3-6 parts of acetone, and 50-70 parts of deionized water; it is a water-based polyurethane adhesive, and is synthesized by adding auxiliaries such as modified polyacrylic acid and modified chain extender, which improves the adhesion, heat resistance, water resistance and other properties of the adhesive, and at the same time has certain environmental protection performance.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and particularly to an environmentally friendly water-based adhesive and a preparation method thereof. Background Art

[0002] Due to the strong polarity and strong chemical reactivity of the urethane group and isocyanate group contained in polyurethane adhesives, they can form good adhesions with materials containing active hydrogen and a variety of porous materials, such as wood, leather, paper, fabric, foam plastics, ceramics, etc. Compared with solvent-based polyurethane adhesives, water-based polyurethane adhesives with water as the dispersion medium are non-toxic, harmless, safe and environmentally friendly, safer for storage and transportation, and water-based polyurethane adhesives are easy to use and the residues are easy to clean, while solvent-based polyurethane adhesives consume a large amount of organic solvents and the residues are not easy to clean.

[0003] However, at present, water-based polyurethane adhesives have the disadvantages of poor heat resistance and water resistance. Therefore, it is necessary to carry out modification treatment for these disadvantages to improve the heat resistance and water resistance of the adhesives. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides an environmentally friendly water-based adhesive and a preparation method thereof.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] An environmentally friendly water-based adhesive, comprising the following raw materials in parts by weight: 20-30 parts of polyethylene adipate glycol (molecular weight 2000), 3-8 parts of modified polyacrylic acid, 13-18 parts of isophorone diisocyanate, 3-6 parts of modified chain extender, 0.005-0.02 part of catalyst (dibutyltin dilaurate), 0.2-0.5 part of propylene glycol, 0.1-0.3 part of triethylamine, 3-6 parts of acetone, 50-70 parts of deionized water;

[0007] The modified chain extender is prepared by the following steps:

[0008] Step A1: Disperse ethylenediamine and sodium hydroxide in acetonitrile, denoted as solution 1; mix cyanuric chloride and acetonitrile evenly at 0-5°C, slowly add half of the volume of solution 1, maintain the temperature and react for 1-2 h, then raise the temperature to 45-55°C, add the remaining volume of solution 1, and continue to react for 2-3 h to obtain an intermediate product;

[0009] Further, in step A1, the dosage ratio of cyanuric chloride, acetonitrile and solution 1 is 0.01-0.02 mol: 100 mL: 100 mL, and the dosage ratio of ethylenediamine, sodium hydroxide and acetonitrile in solution 1 is 0.02-0.04 mol: 0.08-0.16 g: 100 mL;

[0010] Step A2: Disperse β-alanine and sodium hydroxide in acetonitrile, denoted as Solution 2; heat the intermediate product to 90 °C, slowly add Solution 2, react for 4 - 5 h, adjust the pH to 6 - 7, filter, wash, and dry to obtain the modified chain extender;

[0011] Furthermore, in Step A2, the dosage ratio of β-alanine, sodium hydroxide, and acetonitrile in Solution 2 is 0.01 - 0.02 mol : 0.04 - 0.08 g : 50 mL.

[0012] The modified polyacrylic acid is prepared by the following steps:

[0013] Step B1: Mix maleic anhydride evenly in N,N-dimethylformamide, denoted as Mixture 1; under nitrogen conditions, stir and mix p-aminobenzoic acid and N,N-dimethylformamide, slowly add Mixture 1, continuously stir at room temperature for 24 h, then pour into distilled water and let it stand for 30 min, filter, wash, and dry to obtain Intermediate Product 1;

[0014] Furthermore, in Step B1, the dosage ratio of p-aminobenzoic acid, N,N-dimethylformamide, and Mixture 1 is 0.01 - 0.03 mol : 100 mL : 100 mL, and the dosage ratio of maleic anhydride and N,N-dimethylformamide in Mixture 1 is 0.01 - 0.03 mol;

[0015] Step B2: Mix Intermediate Product 1, sodium acetate, and acetic anhydride, heat to 50 - 60 °C and stir for 2 - 4 h, then cool to room temperature in an ice-water bath, filter, wash, recrystallize, and dry to obtain Intermediate Product 2;

[0016] Furthermore, in Step B2, the dosage ratio of Intermediate Product 1, sodium acetate, and acetic anhydride is 0.01 - 0.03 mol : 0.16 - 0.5 g : 30 - 60 mL;

[0017] Step B3: Disperse Intermediate Product 2 in tetrahydrofuran, successively add 1-hydroxybenzotriazole and N,N-dimethylpyridin-2-amine, then stir at 0 °C for 25 - 35 min, slowly add dicyclohexylcarbodiimide, and vigorously stir at room temperature for 12 - 16 h, concentrate under reduced pressure, then add ethyl acetate, filter and collect the filtrate, and distill under reduced pressure to obtain the functional monomer;

[0018] Furthermore, in Step B3, the dosage ratio of Intermediate Product 2, tetrahydrofuran, 1-hydroxybenzotriazole, N,N-dimethylpyridin-2-amine, dicyclohexylcarbodiimide, and ethyl acetate is 0.01 - 0.03 mol : 100 mL : 0.014 - 0.036 mol : 0.3 - 0.9 g : 0.012 - 0.033 mol : 20 - 40 mL;

[0019] Step B4: After dispersing the emulsifier (SE-10N) in deionized water, add acrylic acid, methyl methacrylate, 2-hydroxyethyl methacrylate and the functional monomer and stir for 20-40 min to form a pre-emulsion; disperse ammonium persulfate in deionized water, heat up to 55-65 °C and stir for 10 min, then slowly dropwise add the pre-emulsion within 1-2 h, and then heat up to 80-90 °C and react for 2-3 h, and filter to obtain the modified polyacrylic acid;

[0020] Further, in step B4, the mass ratio of ammonium persulfate, deionized water and the pre-emulsion is 0.01-0.06:50:43-77, and the mass ratio of the emulsifier, deionized water, acrylic acid, methyl methacrylate, 2-hydroxyethyl methacrylate and the functional monomer in the pre-emulsion is 1-2:30-50:2-6:5-10:4-6:1-3.

[0021] A preparation method of an environment-friendly water-based adhesive includes the following steps:

[0022] Step S1: Weigh the raw materials by weight. Vacuum dehydrate the polyethylene adipate glycol at 100-120 °C for 1 h, add isophorone diisocyanate, propylene glycol and the modified chain extender at 80-90 °C and react for 1.5-2.5 h, and then add the catalyst (dibutyltin dilaurate) and react for 3-4 h to obtain a polyurethane prepolymer;

[0023] Step S2: Add the modified polyacrylic acid to the polyurethane prepolymer, react at 50-60 °C for 30-50 min, then add acetone and triethylamine and continue to stir for 10-15 min, and then add deionized water and stir for 30-60 min to obtain the environment-friendly water-based adhesive.

[0024] The beneficial effects of the present invention:

[0025] The water-based adhesive prepared by the present invention is synthesized with polyurethane as the matrix and adding auxiliaries such as modified polyacrylic acid and modified chain extender, which improves the adhesion, heat resistance, water resistance and other properties of the adhesive, and at the same time has certain environmental protection performance.

[0026] The modified chain extender is synthesized with cyanuric chloride intermediate by reacting with the amino groups in ethylenediamine and β-alanine; the terminal amino groups contained in the modified chain extender react with the isocyanate groups to form urea bonds, reducing the content of urethane in the polyurethane molecular chain, effectively reducing the decomposition of urethane in high-temperature and high-humidity environments, improving the comprehensive performance of the adhesive, and at the same time the strongly polar urea bonds can also enhance the intermolecular force, making the molecular chain segment structure more compact, reducing the surface free energy of the adhesive film, and enhancing the hydrophobicity and water resistance; the introduction of the hydrophilic group carboxyl in the chain extender can alleviate the poor wetting performance caused by the large surface tension of the matrix; in addition, the presence of the triazine structure also improves the heat resistance of the matrix.

[0027] In the modified polyacrylic acid, the anhydride group in maleic anhydride undergoes a ring-opening reaction with the amino group in p-aminobenzoic acid to form intermediate 1; intermediate 1 is then dehydrated and cyclized under the action of acetic anhydride and sodium acetate to form intermediate 2; then, an esterification reaction between intermediate 2 and 1-hydroxybenzotriazole is used to generate a functional monomer; finally, acrylic acid, methyl methacrylate, 2-hydroxyethyl methacrylate, and the functional monomer are used as raw materials, and a reaction is carried out under the action of an emulsifier and ammonium persulfate to synthesize the modified polyacrylic acid. After the modified polyacrylic acid is introduced into the matrix, it grafts onto the polyurethane molecular chain, not only retaining its own excellent adhesion, but also improving the water resistance, heat resistance, etc. of the adhesive; among them, the active groups contained in the modified polyacrylic acid can undergo chemical bonding with the terminal isocyanate groups in the polyurethane prepolymer, improving the compatibility between the two, making the structure more compact, and water molecules can diffuse into the interior of the film, reducing the water absorption rate, thereby improving the water resistance of the film; the introduction of the functional monomer in the modified polyacrylic acid improves the comprehensive performance of the film. For example, the imide ring with good heat resistance improves the heat resistance of the matrix, and the benzotriazole structure with ultraviolet absorption function improves the anti-yellowing performance of the film, while avoiding the migration and precipitation of small molecule substances such as traditional ultraviolet absorbers and heat-resistant agents in the film. Specific embodiments

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0029] Example 1

[0030] The modified chain extender is prepared by the following steps:

[0031] Step A1: Disperse 0.02 mol of ethylenediamine and 0.08 g of sodium hydroxide in 100 mL of acetonitrile, denoted as solution 1; mix 0.01 mol of cyanuric chloride and 100 mL of acetonitrile evenly at 0 °C, slowly add 50 mL of solution 1, maintain the temperature and react for 1 h, then raise the temperature to 45 °C, add the remaining 50 mL of solution 1, and continue to react for 2 h to obtain the intermediate;

[0032] Step A2: Disperse 0.01 mol of β-alanine and 0.04 g of sodium hydroxide in 50 mL of acetonitrile, denoted as solution 2; raise the temperature of the intermediate to 90 °C, slowly add solution 2, react for 4 h, adjust the pH to 6, filter, wash, and dry to obtain the modified chain extender.

[0033] The modified polyacrylic acid is prepared by the following steps:

[0034] Step B1: Mix 0.01 mol of maleic anhydride evenly in 100 mL of N,N-dimethylformamide, denoted as mixture 1; under nitrogen conditions, stir and mix 0.01 mol of p-aminobenzoic acid and 100 mL of N,N-dimethylformamide, slowly add 100 mL of mixture 1, continuously stir at room temperature for 24 h, then pour it into distilled water, let it stand for 30 min, filter, wash, and dry to obtain intermediate 1;

[0035] Step B2: Mix 0.01 mol of intermediate 1, 0.16 g of sodium acetate, and 30 mL of acetic anhydride, heat up to 50 °C and stir for 2 h, then cool it to room temperature in an ice-water bath, filter, wash, recrystallize, and dry to obtain intermediate 2;

[0036] Step B3: Disperse 0.01 mol of intermediate 2 in 100 mL of tetrahydrofuran, sequentially add 0.014 mol of 1-hydroxybenzotriazole and 0.3 g of N,N-dimethylpyridin-2-amine, then stir at 0 °C for 25 min, slowly add 0.012 mol of dicyclohexylcarbodiimide, and vigorously stir at room temperature for 12 h, concentrate under reduced pressure, then add 20 mL of ethyl acetate, filter and collect the filtrate, distill under reduced pressure to obtain the functional monomer;

[0037] Step B4: After dispersing 1 g of emulsifier (SE-10N) in 30 g of deionized water, add 2 g of acrylic acid, 5 g of methyl methacrylate, 4 g of 2-hydroxyethyl methacrylate, and 1 g of the functional monomer and stir for 20 min to form a pre-emulsion; disperse 0.01 g of ammonium persulfate in 50 g of deionized water, heat up to 55 °C and stir for 10 min, then slowly drip 43 g of the pre-emulsion within 1 h, then heat up to 80 °C and react for 2 h, filter to obtain the modified polyacrylic acid.

[0038] Example 2

[0039] The modified chain extender is prepared by the following steps:

[0040] Step A1: Disperse 0.03 mol of ethylenediamine and 0.12 g of sodium hydroxide in 100 mL of acetonitrile, denoted as solution 1; mix 0.015 mol of cyanuric chloride and 100 mL of acetonitrile evenly at 2 °C, slowly add 50 mL of solution 1, maintain the temperature and react for 1.5 h, then heat up to 50 °C, add the remaining 50 mL of solution 1, and continue to react for 2.5 h to obtain the intermediate;

[0041] Step A2: Disperse 0.015 mol of β-alanine and 0.06 g of sodium hydroxide in 50 mL of acetonitrile, denoted as solution 2; heat the intermediate up to 90 °C, slowly add solution 2, react for 4.5 h, adjust the pH to 6.5, filter with suction, wash, and dry to obtain the modified chain extender.

[0042] The modified polyacrylic acid is prepared by the following steps:

[0043] Step B1: Mix 0.02 mol of maleic anhydride evenly in 100 mL of N,N-dimethylformamide, denoted as mixture 1; under nitrogen conditions, stir and mix 0.02 mol of p-aminobenzoic acid and 100 mL of N,N-dimethylformamide, slowly add 100 mL of mixture 1, and continuously stir at room temperature for 24 h, then pour it into distilled water and let it stand for 30 min, filter, wash, and dry to obtain intermediate 1;

[0044] Step B2: Mix 0.02 mol of intermediate 1, 0.3 g of sodium acetate, and 45 mL of acetic anhydride, heat up to 55 °C and stir for 3 h, then place it in an ice-water bath and cool to room temperature, filter, wash, recrystallize, and dry to obtain intermediate 2;

[0045] Step B3: Disperse 0.02 mol of intermediate 2 in 100 mL of tetrahydrofuran, sequentially add 0.025 mol of 1-hydroxybenzotriazole and 0.6 g of N,N-dimethylpyridin-2-amine, then stir at 0 °C for 30 min, slowly add 0.022 mol of dicyclohexylcarbodiimide, and stir vigorously at room temperature for 14 h, concentrate under reduced pressure, then add 30 mL of ethyl acetate, filter and collect the filtrate, and distill under reduced pressure to obtain the functional monomer;

[0046] Step B4: After dispersing 1.5 g of emulsifier (SE-10N) in 40 g of deionized water, add 4 g of acrylic acid, 7 g of methyl methacrylate, 5 g of 2-hydroxyethyl methacrylate, and 2 g of the functional monomer and stir for 30 min to form a pre-emulsion; disperse 0.04 g of ammonium persulfate in 50 g of deionized water, heat up to 60 °C and stir for 10 min, then slowly dropwise add 59.5 g of the pre-emulsion within 1.5 h, then heat up to 85 °C and react for 2.5 h, filter to obtain the modified polyacrylic acid.

[0047] Example 3

[0048] The modified chain extender is prepared by the following steps:

[0049] Step A1: Disperse 0.04 mol of ethylenediamine and 0.16 g of sodium hydroxide in 100 mL of acetonitrile, denoted as solution 1; mix 0.02 mol of cyanuric chloride and 100 mL of acetonitrile evenly at 5 °C, slowly add 50 mL of solution 1, maintain the temperature and react for 2 h, then heat up to 55 °C, add the remaining 50 mL of solution 1, and continue to react for 3 h to obtain the intermediate;

[0050] Step A2: Disperse 0.02 mol of β-alanine and 0.08 g of sodium hydroxide in 50 mL of acetonitrile, denoted as Solution 2; heat the intermediate product to 90 °C, slowly add Solution 2, react for 5 h, adjust the pH to 7, filter, wash, and dry to obtain the modified chain extender.

[0051] The modified polyacrylic acid is prepared by the following steps:

[0052] Step B1: Mix 0.03 mol of maleic anhydride evenly in 100 mL of N,N-dimethylformamide, denoted as Mixture 1; under nitrogen conditions, stir and mix 0.03 mol of p-aminobenzoic acid and 100 mL of N,N-dimethylformamide, slowly add 100 mL of Mixture 1, and continuously stir at room temperature for 24 h, then pour it into distilled water and let it stand for 30 min, filter, wash, and dry to obtain Intermediate Product 1;

[0053] Step B2: Mix 0.03 mol of Intermediate Product 1, 0.5 g of sodium acetate, and 60 mL of acetic anhydride, heat to 60 °C and stir for 4 h, then cool to room temperature in an ice-water bath, filter, wash, recrystallize, and dry to obtain Intermediate Product 2;

[0054] Step B3: Disperse 0.03 mol of Intermediate Product 2 in 100 mL of tetrahydrofuran, sequentially add 0.036 mol of 1-hydroxybenzotriazole and 0.9 g of N,N-dimethylpyridin-2-amine, then stir at 0 °C for 35 min, slowly add 0.033 mol of dicyclohexylcarbodiimide, and vigorously stir at room temperature for 16 h, concentrate under reduced pressure, add 40 mL of ethyl acetate, filter and collect the filtrate, and distill under reduced pressure to obtain the functional monomer;

[0055] Step B4: After dispersing 2 g of emulsifier (SE-10N) in 50 g of deionized water, add 6 g of acrylic acid, 10 g of methyl methacrylate, 6 g of 2-hydroxyethyl methacrylate, and 3 g of the functional monomer and stir for 40 min to form a pre-emulsion; disperse 0.06 g of ammonium persulfate in 50 g of deionized water, heat to 65 °C and stir for 10 min, then slowly add 77 g of the pre-emulsion within 2 h, then heat to 90 °C and react for 3 h, filter to obtain the modified polyacrylic acid.

[0056] Example 4

[0057] A preparation method of an environmentally friendly water-based adhesive includes the following steps:

[0058] 20 parts of polyethylene adipate glycol (molecular weight 2000), 3 parts of the modified polyacrylic acid prepared in Example 1, 13 parts of isophorone diisocyanate, 3 parts of the modified chain extender prepared in Example 1, 0.005 part of catalyst (dibutyltin dilaurate), 0.2 part of propylene glycol, 0.1 part of triethylamine, 3 parts of acetone, 50 parts of deionized water;

[0059] Step S1: Weigh the raw materials according to parts by weight. Vacuum dehydrate the polyethylene adipate glycol at 100 °C for 1 h, add isophorone diisocyanate, propylene glycol and the modified chain extender prepared in Example 1 at 80 °C and react for 1.5 h, then add the catalyst (dibutyltin dilaurate) and react for 3 h to obtain the polyurethane prepolymer;

[0060] Step S2: Add the modified polyacrylic acid prepared in Example 1 to the polyurethane prepolymer, react at 50 °C for 30 min, then add acetone and triethylamine and continue stirring for 10 min, and then add deionized water and stir for 30 min to obtain the environmentally friendly water-based adhesive.

[0061] Example 5

[0062] A preparation method of an environmentally friendly water-based adhesive comprises the following steps:

[0063] 25 parts of polyethylene adipate glycol (molecular weight 2000), 5 parts of the modified polyacrylic acid prepared in Example 2, 16 parts of isophorone diisocyanate, 4.5 parts of the modified chain extender prepared in Example 2, 0.01 part of catalyst (dibutyltin dilaurate), 0.3 part of propylene glycol, 0.2 part of triethylamine, 5 parts of propanone, 60 parts of deionized water;

[0064] Step S1: Weigh the raw materials according to parts by weight. Vacuum dehydrate the polyethylene adipate glycol at 110 °C for 1 h, add isophorone diisocyanate, propylene glycol and the modified chain extender prepared in Example 2 at 85 °C and react for 2 h, then add the catalyst (dibutyltin dilaurate) and react for 3.5 h to obtain the polyurethane prepolymer;

[0065] Step S2: Add the modified polyacrylic acid prepared in Example 2 to the polyurethane prepolymer, react at 55 °C for 40 min, then add acetone and triethylamine and continue stirring for 12 min, and then add deionized water and stir for 45 min to obtain the environmentally friendly water-based adhesive.

[0066] Example 6

[0067] A preparation method of an environmentally friendly water-based adhesive comprises the following steps:

[0068] 30 parts of polyethylene adipate glycol (molecular weight 2000), 8 parts of modified polyacrylic acid prepared in Example 3, 18 parts of isophorone diisocyanate, 6 parts of modified chain extender prepared in Example 3, 0.02 part of catalyst (dibutyltin dilaurate), 0.5 part of propylene glycol, 0.3 part of triethylamine, 6 parts of acetone, 70 parts of deionized water;

[0069] Step S1: Weigh the raw materials according to parts by weight. Vacuum dehydrate polyethylene adipate glycol at 120 °C for 1 h, and add isophorone diisocyanate, propylene glycol and the modified chain extender prepared in Example 3 at 90 °C and react for 2.5 h. Then add the catalyst (dibutyltin dilaurate) and react for 4 h to obtain a polyurethane prepolymer;

[0070] Step S2: Add the modified polyacrylic acid prepared in Example 3 to the polyurethane prepolymer, react at 60 °C for 50 min, then add acetone and triethylamine and continue stirring for 15 min, and then add deionized water and stir for 60 min to obtain an environmentally friendly water-based adhesive.

[0071] Comparative Example 1

[0072] This comparative example is a water-based adhesive. The difference from Example 6 is that ethylenediamine is used instead of the modified chain extender prepared in Example 3, and the rest are the same.

[0073] Comparative Example 2

[0074] This comparative example is a water-based adhesive. The difference from Example 6 is that commercially available polyacrylic acid is used instead of the modified polyacrylic acid prepared in Example 3, and the rest are the same.

[0075] Perform performance tests on the products prepared in Examples 4 - 6 and Comparative Examples 1 - 2:

[0076] Peel strength test: Refer to GB / T2941 - 2006 for execution, and test the peel strength. Among them, the adherend of the test sample is PVC;

[0077] Heat and water resistance performance test: Place the sample at a temperature of 23 ± 2 °C and a relative humidity of 50 ± 5% for 5 days, then place it at a temperature of 70 ± 2 °C for 5 days, and then soak it in water at 25 °C for 5 days, and perform a peel strength test. The test method is carried out according to GB / T532 - 2008;

[0078] Yellowing test: Lay the rubber strip flat on white cardboard, place it in a yellowing resistance test chamber (50 °C, 300W lamp), and observe the yellowing situation after 24 hours;

[0079] The test results are shown in the following table:

[0080]

[0081]

[0082] As can be seen from the above table, the waterborne polyurethane adhesive prepared by the present invention has been tested for performance. The peel strength is in the range of 94.3 N / cm - 99.1 N / cm, and the peel strength after heat and water resistance tests is in the range of 86.6 N / cm - 90.2 N / cm, and no yellowing occurs, indicating that the adhesive has excellent comprehensive properties.

[0083] The above content is only an example and illustration of the concept of the present invention. Those skilled in the art of the present technology can make various modifications or supplements to the described specific embodiments or use similar ways to replace them. As long as they do not deviate from the scope defined by the concept of the invention, they should all fall within the protection scope of the present invention.

Claims

1. An aqueous adhesive, characterized in that, It comprises the following raw materials in parts by weight: 20 - 30 parts of polyethylene adipate glycol, 3 - 8 parts of modified polyacrylic acid, 13 - 18 parts of isophorone diisocyanate, 3 - 6 parts of modified chain extender, 0.005 - 0.02 part of catalyst, 0.2 - 0.5 part of propylene glycol, 0.1 - 0.3 part of triethylamine, 3 - 6 parts of acetone, and 50 - 70 parts of deionized water; The said modified chain extender is prepared by the following steps: Step A1: Disperse ethylenediamine and sodium hydroxide in acetonitrile, denoted as solution 1; mix cyanuric chloride and acetonitrile evenly at 0 - 5°C, slowly add half of the volume of solution 1, maintain the temperature for reaction for 1 - 2 h, then raise the temperature to 45 - 55°C, add the remaining volume of solution 1, and continue the reaction for 2 - 3 h to obtain an intermediate product; Step A2: Disperse β-alanine and sodium hydroxide in acetonitrile, denoted as solution 2; raise the temperature of the intermediate product to 90°C, slowly add solution 2, react for 4 - 5 h, adjust the pH to 6 - 7, filter, wash, and dry to obtain the modified chain extender; The modified polyacrylic acid is prepared by the following steps: Step B1: Mix maleic anhydride evenly in N,N-dimethylformamide, denoted as mixture 1; under nitrogen condition, stir and mix p-aminobenzoic acid and N,N-dimethylformamide, slowly add mixture 1, and continuously stir at room temperature for 24 h, then pour it into distilled water and let it stand for 30 min, filter, wash, and dry to obtain intermediate product 1; Step B2: Mix intermediate product 1, sodium acetate, and acetic anhydride, and raise the temperature to 50 - 60°C and stir for 2 - 4 h, then place it in an ice-water bath and cool to room temperature, filter, wash, recrystallize, and dry to obtain intermediate product 2; Step B3: Disperse intermediate product 2 in tetrahydrofuran, successively add 1-hydroxybenzotriazole and N,N-dimethylpyridin-2-amine, then stir at 0°C for 25 - 35 min, slowly add dicyclohexylcarbodiimide, and stir vigorously at room temperature for 12 - 16 h, concentrate under reduced pressure, add ethyl acetate, filter and collect the filtrate, and distill under reduced pressure to obtain the functional monomer; Step B4: After dispersing the emulsifier in deionized water, add acrylic acid, methyl methacrylate, 2-hydroxyethyl methacrylate, and the functional monomer and stir for 20 - 40 min to form a pre-emulsion; Disperse ammonium persulfate in deionized water, raise the temperature to 55 - 65°C and stir for 10 min, then slowly dropwise add the pre-emulsion within 1 - 2 h, then raise the temperature to 80 - 90°C and react for 2 - 3 h, filter to obtain the modified polyacrylic acid.

2. The water-based adhesive according to claim 1, characterized in that, In step A1, the dosage ratio of cyanuric chloride, acetonitrile, and solution 1 is 0.01 - 0.02 mol: 100 mL: 100 mL, and the dosage ratio of ethylenediamine, sodium hydroxide, and acetonitrile in solution 1 is 0.02 - 0.04 mol: 0.08 - 0.16 g: 100 mL.

3. The water-based adhesive according to claim 1, characterized in that, In step A2, the dosage ratio of β-alanine, sodium hydroxide, and acetonitrile in solution 2 is 0.01 - 0.02 mol: 0.04 - 0.08 g: 50 mL.

4. The aqueous adhesive according to claim 1, characterized in that, In step B2, the dosage ratio of intermediate 1, sodium acetate and acetic anhydride is 0.01 - 0.03 mol : 0.16 - 0.5 g : 30 - 60 mL.

5. A water-based adhesive according to claim 1, characterized in that, In step B3, the dosage ratio of intermediate 2, tetrahydrofuran, 1 - hydroxybenzotriazole, N,N - dimethylpyridin - 2 - amine, dicyclohexylcarbodiimide and ethyl acetate is 0.01 - 0.03 mol : 100 mL : 0.014 - 0.036 mol : 0.3 - 0.9 g : 0.012 - 0.033 mol : 20 - 40 mL.

6. The water-based adhesive according to claim 1, characterized in that, In step B4, the mass ratio of ammonium persulfate, deionized water and the pre - emulsion is 0.01 - 0.06 : 50 : 43 - 77, and in the pre - emulsion, the mass ratio of emulsifier, deionized water, acrylic acid, methyl methacrylate, 2 - hydroxyethyl methacrylate and functional monomer is 1 - 2 : 30 - 50 : 2 - 6 : 5 - 10 : 4 - 6 : 1 - 3.

7. A method for preparing the aqueous adhesive according to any one of claims 1-6, characterized in that, It includes the following steps: Step S1, weigh raw materials according to parts by weight, vacuum - dehydrate polyethylene adipate glycol at 100 - 120 °C for 1 h, add isophorone diisocyanate, propylene glycol and modified chain extender at 80 - 90 °C and react for 1.5 - 2.5 h, then add a catalyst and react for 3 - 4 h to obtain a polyurethane prepolymer; Step S2, add modified polyacrylic acid to the polyurethane prepolymer, react at 50 - 60 °C for 30 - 50 min, then add acetone and triethylamine and continue stirring for 10 - 15 min, and then add deionized water and stir for 30 - 60 min to obtain an aqueous adhesive.

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