Environment-friendly water-based adhesive and preparation method thereof

Abstract

The invention relates to the technical field of adhesives, and discloses an environment-friendly water-based adhesive and a preparation method thereof. The water-based adhesive prepared by the preparation method disclosed by the invention is prepared from the following raw materials in parts by weight: 20 to 30 parts of polyethylene glycol adipate glycol, 3 to 8 parts of modified polyacrylic acid, 13 to 18 parts of isophorone diisocyanate, 3 to 6 parts of a modified chain extender, 0.005 to 0.02 part of a catalyst, 0.2 to 0.5 part of propylene glycol, 0.1 to 0.3 part of triethylamine, 3 to 6 parts of acetone and 50 to 70 parts of deionized water. The waterborne polyurethane adhesive is synthesized by adding auxiliaries such as modified polyacrylic acid and a modified chain extender, so that the adhesion, heat resistance, water resistance and the like of the adhesive are improved, and meanwhile, the waterborne polyurethane adhesive has certain environmental protection performance.

Description

Technical Field

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

[0002] Polyurethane adhesives, due to their strong polarity and chemical activity of urethane and isocyanate groups, can form good bonds 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 to store and transport, and easy to use and easy to clean the residue, while solvent-based polyurethane adhesives consume a lot of organic solvents and the residue is not easy to clean.

[0003] However, the current water-based polyurethane adhesive has the disadvantages of poor heat resistance and water resistance. Therefore, it is necessary to improve the heat resistance and water resistance of the adhesive by modifying these disadvantages. 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: An environmentally friendly water-based adhesive comprises 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 isophorol diisocyanate, 3-6 parts of modified chain extender, 0.005-0.02 parts of catalyst (dibutyltin dilaurate), 0.2-0.5 parts of propylene glycol, 0.1-0.3 parts of triethylamine, 3-6 parts of acetone, and 50-70 parts of deionized water; The modified chain extender is prepared by the following steps: Step A1, dispersing ethylenediamine and sodium hydroxide in acetonitrile, recorded as solution 1; mixing cyanuric chloride and acetonitrile at 0-5°C, slowly adding half the volume of solution 1, maintaining the temperature for reaction for 1-2h, then heating to 45-55°C, adding the remaining volume of solution 1, and continuing the reaction for 2-3 to obtain an intermediate product; Further, in step A1, the usage ratio of cyanuric chloride, acetonitrile and solution 1 is 0.01-0.02 mol: 100 mL: 100 mL, and the usage ratio of ethylenediamine, sodium hydroxide and acetonitrile in solution 1 is 0.02-0.04 mol: 0.08-0.16 g: 100 mL; Step A2, dispersing β-alanine and sodium hydroxide in acetonitrile, recorded as solution 2; heating the intermediate product to 90° C., slowly adding solution 2, reacting for 4-5 hours, adjusting the pH to 6-7, filtering, washing, and drying to obtain a modified chain extender; Furthermore, the dosage ratio of β-alanine, sodium hydroxide and acetonitrile in solution 2 of step A2 is 0.01-0.02 mol: 0.04-0.08 g: 50 mL.

[0006] The modified polyacrylic acid is prepared by the following steps: Step B1, maleic anhydride was mixed evenly in N, N-dimethylformamide, recorded as mixed solution 1; under nitrogen conditions, p-aminobenzoic acid and N, N-dimethylformamide were stirred and mixed, and the mixed solution 1 was slowly added, and the mixture was stirred continuously at room temperature for 24 hours, and then poured into distilled water and allowed to stand for 30 minutes, filtered, washed, and dried to obtain intermediate product 1; Further, in step B1, the amount ratio of p-aminobenzoic acid, N,N-dimethylformamide and mixed solution 1 is 0.01-0.03 mol:100 mL:100 mL, and the amount ratio of maleic anhydride and N,N-dimethylformamide in mixed solution 1 is 0.01-0.03 mol; Step B2, the intermediate product 1, sodium acetate and acetic anhydride are mixed, and the mixture is heated to 50-60° C. and stirred for 2-4 hours, and then cooled to room temperature in an ice water bath, filtered, washed, recrystallized and dried to obtain the intermediate product 2; Further, in step B2, the usage ratio of the intermediate product 1, sodium acetate and acetic anhydride is 0.01-0.03 mol: 0.16-0.5 g: 30-60 mL; Step B3, disperse the intermediate product 2 in tetrahydrofuran, add 1-hydroxybenzotriazole and N,N-dimethylpyridine in sequence, and then stir at 0°C for 25-35 minutes, then slowly add dicyclohexylcarbodiimide, and vigorously stir at room temperature for 12-16 hours, concentrate under reduced pressure, then add ethyl acetate, filter and collect the filtrate, and distill under reduced pressure to obtain a functional monomer; Further, in step B3, the usage ratio of intermediate product 2, tetrahydrofuran, 1-hydroxybenzotriazole, N,N-dimethylpyridine, 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; Step B4, after dispersing the emulsifier (SE-10N) in deionized water, add acrylic acid, methyl methacrylate, hydroxyethyl methacrylate and functional monomers and stir for 20-40 minutes to form a pre-emulsion; disperse ammonium persulfate in deionized water, heat to 55-65°C and stir for 10 minutes, then slowly drop the pre-emulsion within 1-2 hours, heat to 80-90°C and react for 2-3 hours, filter, and obtain modified polyacrylic acid; Furthermore, in step B4, the mass ratio of ammonium persulfate, deionized water and pre-emulsion is 0.01-0.06:50:43-77, and the mass ratio of emulsifier, deionized water, acrylic acid, methyl methacrylate, hydroxyethyl methacrylate and functional monomer in the pre-emulsion is 1-2:30-50:2-6:5-10:4-6:1-3.

[0007] A method for preparing an environmentally friendly water-based adhesive comprises the following steps: Step S1, weighing raw materials according to weight, vacuum dehydrating polyethylene adipate diol at 100-120° C. for 1 h, adding isophorol diisocyanate, propylene glycol and a modified chain extender at 80-90° C. for reaction for 1.5-2.5 h, and then adding a catalyst (dibutyltin dilaurate) for reaction for 3-4 h to obtain a polyurethane prepolymer; Step S2, adding modified polyacrylic acid to the polyurethane prepolymer, reacting at 50-60° C. for 30-50 minutes, then adding acetone and triethylamine and stirring for 10-15 minutes, then adding deionized water and stirring for 30-60 minutes to obtain an environmentally friendly water-based adhesive.

[0008] Beneficial effects of the present invention: The water-based adhesive prepared by the invention is synthesized by using polyurethane as a matrix and adding auxiliary agents such as modified polyacrylic acid and modified chain extender, thereby improving the adhesive's adhesion, heat resistance, water resistance and other properties, and having certain environmental protection properties.

[0009] The modified chain extender is synthesized by reacting the intermediate cyanuric chloride with the amino groups in ethylenediamine and β-alanine; the terminal amino group contained in the modified chain extender reacts with the isocyanate group to form a urea bond, which reduces the content of carbamate in the polyurethane molecular chain, effectively reduces the decomposition of carbamate in high temperature and high humidity environments, and improves the comprehensive performance of the adhesive. At the same time, the highly polar urea bond can also enhance the intermolecular force, make the molecular chain segment structure more compact, reduce the surface free energy of the film, and enhance the hydrophobicity and water resistance; the introduction of the hydrophilic group carboxyl in the chain extender can alleviate the poor wetting performance of the substrate caused by the large surface tension; in addition, the presence of the triazine structure also improves the heat resistance of the substrate.

[0010] In the modified polyacrylic acid, the anhydride group in maleic anhydride and the amino group in p-aminobenzoic acid undergo a ring-opening reaction to generate an intermediate product 1; the intermediate product 1 is then dehydrated and ring-closed under the action of acetic anhydride and sodium acetate to generate an intermediate product 2; the intermediate product 2 is then subjected to an esterification reaction with 1-hydroxybenzotriazole to generate a functional monomer; finally, acrylic acid, methyl methacrylate, hydroxyethyl methacrylate and the functional monomer are used as raw materials to react and synthesize the modified polyacrylic acid under the action of an emulsifier and ammonium persulfate. After the modified polyacrylic acid is introduced into the matrix, it is grafted into the polyurethane molecular chain, which not only retains its own excellent adhesion, but also improves the water resistance and heat resistance of the adhesive. Among them, the active groups contained in the modified polyacrylic acid can chemically bond with the terminal isocyanate groups in the polyurethane prepolymer, so that the compatibility of the two is improved, the structure is tighter, and water molecules can diffuse into the interior of the film, the water absorption rate is reduced, and the water resistance of the film is improved. The introduction of functional monomers in the modified polyacrylic acid improves the comprehensive performance of the film, such as: 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 molecular substances such as traditional ultraviolet absorbers and heat resistors in the film. DETAILED DESCRIPTION

[0011] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example

[0012] The modified chain extender is prepared by the following steps: Step A1, 0.02 mol of ethylenediamine and 0.08 g of sodium hydroxide were dispersed in 100 mL of acetonitrile, recorded as solution 1; 0.01 mol of cyanuric chloride and 100 mL of acetonitrile were mixed at 0°C, 50 mL of solution 1 was slowly added, the temperature was maintained for reaction for 1 hour, then the temperature was raised to 45°C, the remaining 50 mL of solution 1 was added, and the reaction was continued for 2 hours to obtain an intermediate product; Step A2, disperse 0.01 mol β-alanine and 0.04 g sodium hydroxide in 50 mL acetonitrile, recorded as solution 2; heat the intermediate product to 90° C., slowly add solution 2, react for 4 h, adjust the pH to 6, filter, wash, and dry to obtain a modified chain extender.

[0013] Modified polyacrylic acid is prepared by the following steps: Step B1, 0.01 mol of maleic anhydride was mixed uniformly in 100 mL of N, N-dimethylformamide, recorded as mixed solution 1; under nitrogen conditions, 0.01 mol of p-aminobenzoic acid and 100 mL of N, N-dimethylformamide were stirred and mixed, 100 mL of mixed solution 1 was slowly added, and stirring was continued at room temperature for 24 hours, then poured into distilled water and allowed to stand for 30 minutes, filtered, washed, and dried to obtain intermediate product 1; Step B2, 0.01 mol of intermediate product 1, 0.16 g of sodium acetate and 30 mL of acetic anhydride were mixed, and the mixture was heated to 50° C. and stirred for 2 h, then placed in an ice-water bath and cooled to room temperature, filtered, washed, recrystallized and dried to obtain intermediate product 2; Step B3, 0.01 mol of the intermediate product 2 was dispersed in 100 mL of tetrahydrofuran, 0.014 mol of 1-hydroxybenzotriazole and 0.3 g of N, N-dimethylpyridine were added in sequence, and then stirred at 0°C for 25 min, and then 0.012 mol of dicyclohexylcarbodiimide was slowly added, and vigorously stirred at room temperature for 12 h, and concentrated under reduced pressure, and then 20 mL of ethyl acetate was added, and the filtrate was filtered and collected, and distilled under reduced pressure to obtain a functional monomer; Step B4: Disperse 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 hydroxyethyl methacrylate and 1 g of 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 to 55 ° C and stir for 10 min, then slowly add 43 g of the pre-emulsion within 1 h, heat to 80 ° C and react for 2 h, filter, and obtain modified polyacrylic acid. Example

[0014] The modified chain extender is prepared by the following steps: Step A1, 0.03 mol of ethylenediamine and 0.12 g of sodium hydroxide were dispersed in 100 mL of acetonitrile, recorded as solution 1; 0.015 mol of cyanuric chloride and 100 mL of acetonitrile were mixed at 2°C, 50 mL of solution 1 was slowly added, the temperature was maintained for reaction for 1.5 hours, then the temperature was raised to 50°C, the remaining 50 mL of solution 1 was added, and the reaction was continued for 2.5 hours to obtain an intermediate product; Step A2, disperse 0.015 mol β-alanine and 0.06 g sodium hydroxide in 50 mL acetonitrile, recorded as solution 2; heat the intermediate product to 90° C., slowly add solution 2, react for 4.5 hours, adjust the pH to 6.5, filter, wash, and dry to obtain a modified chain extender.

[0015] Modified polyacrylic acid is prepared by the following steps: Step B1, 0.02 mol of maleic anhydride was mixed uniformly in 100 mL of N, N-dimethylformamide, recorded as mixed solution 1; under nitrogen conditions, 0.02 mol of p-aminobenzoic acid and 100 mL of N, N-dimethylformamide were stirred and mixed, 100 mL of mixed solution 1 was slowly added, and stirring was continued at room temperature for 24 hours, then poured into distilled water and allowed to stand for 30 minutes, filtered, washed, and dried to obtain intermediate product 1; Step B2, 0.02 mol of intermediate product 1, 0.3 g of sodium acetate and 45 mL of acetic anhydride were mixed, and the mixture was heated to 55° C. and stirred for 3 h, then placed in an ice water bath and cooled to room temperature, filtered, washed, recrystallized and dried to obtain intermediate product 2; Step B3, 0.02 mol of the intermediate product 2 was dispersed in 100 mL of tetrahydrofuran, 0.025 mol of 1-hydroxybenzotriazole and 0.6 g of N, N-dimethylpyridine were added in sequence, and then stirred at 0°C for 30 min, and then 0.022 mol of dicyclohexylcarbodiimide was slowly added, and vigorously stirred at room temperature for 14 h, and concentrated under reduced pressure, and then 30 mL of ethyl acetate was added, and the filtrate was filtered and collected, and distilled under reduced pressure to obtain a functional monomer; Step B4, after dispersing 1.5g of emulsifier (SE-10N) in 40g of deionized water, add 4g of acrylic acid, 7g of methyl methacrylate, 5g of hydroxyethyl methacrylate and 2g of functional monomer and stir for 30min to form a pre-emulsion; disperse 0.04g of ammonium persulfate in 50g of deionized water, heat to 60°C and stir for 10min, then slowly add 59.5g of the pre-emulsion within 1.5h, heat to 85°C and react for 2.5h, filter to obtain modified polyacrylic acid. Example

[0016] The modified chain extender is prepared by the following steps: Step A1, 0.04 mol of ethylenediamine and 0.16 g of sodium hydroxide were dispersed in 100 mL of acetonitrile, which was recorded as solution 1; 0.02 mol of cyanuric chloride and 100 mL of acetonitrile were mixed at 5°C, 50 mL of solution 1 was slowly added, the temperature was maintained for reaction for 2 hours, and then the temperature was raised to 55°C, the remaining 50 mL of solution 1 was added, and the reaction was continued for 3 hours to obtain an intermediate product; Step A2, disperse 0.02 mol β-alanine and 0.08 g sodium hydroxide in 50 mL acetonitrile, recorded 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 a modified chain extender.

[0017] Modified polyacrylic acid is prepared by the following steps: Step B1, 0.03 mol of maleic anhydride was mixed uniformly in 100 mL of N, N-dimethylformamide, recorded as mixed solution 1; under nitrogen conditions, 0.03 mol of p-aminobenzoic acid and 100 mL of N, N-dimethylformamide were stirred and mixed, 100 mL of mixed solution 1 was slowly added, and stirring was continued at room temperature for 24 hours, then poured into distilled water and allowed to stand for 30 minutes, filtered, washed, and dried to obtain intermediate product 1; Step B2, 0.03 mol of intermediate product 1, 0.5 g of sodium acetate and 60 mL of acetic anhydride were mixed, and the mixture was heated to 60° C. and stirred for 4 h, then placed in an ice water bath and cooled to room temperature, filtered, washed, recrystallized and dried to obtain intermediate product 2; Step B3, 0.03 mol of the intermediate product 2 was dispersed in 100 mL of tetrahydrofuran, 0.036 mol of 1-hydroxybenzotriazole and 0.9 g of N, N-dimethylpyridine were added in sequence, and then stirred at 0°C for 35 min, and then 0.033 mol of dicyclohexylcarbodiimide was slowly added, and vigorously stirred at room temperature for 16 h, and concentrated under reduced pressure, and then 40 mL of ethyl acetate was added, and the filtrate was filtered and collected, and distilled under reduced pressure to obtain a functional monomer; Step B4, after dispersing 2g of emulsifier (SE-10N) in 50g of deionized water, add 6g of acrylic acid, 10g of methyl methacrylate, 6g of hydroxyethyl methacrylate and 3g of functional monomer and stir for 40min to form a pre-emulsion; disperse 0.06g of ammonium persulfate in 50g of deionized water, heat to 65°C and stir for 10min, then slowly add 77g of the pre-emulsion dropwise within 2h, heat to 90°C and react for 3h, filter to obtain modified polyacrylic acid. Example

[0018] A method for preparing an environmentally friendly water-based adhesive comprises the following steps: 20 parts of polyethylene adipate glycol (molecular weight 2000), 3 parts of modified polyacrylic acid prepared in Example 1, 13 parts of isophorol diisocyanate, 3 parts of modified chain extender prepared in Example 1, 0.005 parts of catalyst (dibutyltin dilaurate), 0.2 parts of propylene glycol, 0.1 parts of triethylamine, 3 parts of acetone, and 50 parts of deionized water; Step S1, weighing raw materials according to weight parts, vacuum dehydrating polyethylene adipate glycol at 100° C. for 1 h, adding isophorol diisocyanate, propylene glycol and the modified chain extender prepared in Example 1 at 80° C. for 1.5 h, and then adding a catalyst (dibutyltin dilaurate) for 3 h to obtain a polyurethane prepolymer; Step S2, adding the modified polyacrylic acid prepared in Example 1 to the polyurethane prepolymer, reacting at 50° C. for 30 minutes, then adding acetone and triethylamine and stirring for 10 minutes, then adding deionized water and stirring for 30 minutes to obtain an environmentally friendly water-based adhesive. Example

[0019] A method for preparing an environmentally friendly water-based adhesive comprises the following steps: 25 parts of polyethylene adipate glycol (molecular weight 2000), 5 parts of modified polyacrylic acid prepared in Example 2, 16 parts of isophorol diisocyanate, 4.5 parts of modified chain extender prepared in Example 2, 0.01 parts of catalyst (dibutyltin dilaurate), 0.3 parts of propylene glycol, 0.2 parts of triethylamine, 5 parts of propane, and 60 parts of deionized water; Step S1, weighing raw materials according to weight parts, vacuum dehydrating polyethylene adipate diol at 110° C. for 1 h, adding isophorol diisocyanate, propylene glycol and the modified chain extender prepared in Example 2 at 85° C. for reaction for 2 h, and then adding a catalyst (dibutyltin dilaurate) for reaction for 3.5 h to obtain a polyurethane prepolymer; Step S2, adding the modified polyacrylic acid prepared in Example 2 to the polyurethane prepolymer, reacting at 55° C. for 40 minutes, then adding acetone and triethylamine and stirring for 12 minutes, then adding deionized water and stirring for 45 minutes, to obtain an environmentally friendly water-based adhesive. Example

[0020] A method for preparing an environmentally friendly water-based adhesive comprises the following steps: 30 parts of polyethylene adipate glycol (molecular weight 2000), 8 parts of modified polyacrylic acid prepared in Example 3, 18 parts of isophorol diisocyanate, 6 parts of modified chain extender prepared in Example 3, 0.02 parts of catalyst (dibutyltin dilaurate), 0.5 parts of propylene glycol, 0.3 parts of triethylamine, 6 parts of acetone, and 70 parts of deionized water; Step S1, weighing raw materials according to weight parts, vacuum dehydrating polyethylene adipate diol at 120° C. for 1 h, adding isophorol diisocyanate, propylene glycol and the modified chain extender prepared in Example 3 at 90° C. for reaction for 2.5 h, and then adding a catalyst (dibutyltin dilaurate) for reaction for 4 h to obtain a polyurethane prepolymer; Step S2, adding the modified polyacrylic acid prepared in Example 3 to the polyurethane prepolymer, reacting at 60° C. for 50 min, then adding acetone and triethylamine and stirring for 15 min, then adding deionized water and stirring for 60 min, to obtain an environmentally friendly water-based adhesive.

[0021] Comparative Example 1 This comparative example is a water-based adhesive, which differs from Example 6 in that ethylenediamine is used instead of the modified chain extender prepared in Example 3, and the rest are the same.

[0022] Comparative Example 2 This comparative example is a water-based adhesive, which differs from Example 6 in that commercially available polyacrylic acid is used instead of the modified polyacrylic acid prepared in Example 3, and the rest is the same.

[0023] The performance tests were performed on the samples prepared in Examples 4-6 and Comparative Examples 1-2: Peel strength test: refer to GB / T2941-2006 to test the peel strength, where the bonded material of the test sample is PVC; Heat and water resistance test: Place the sample at 23±2℃ and relative humidity 50±5% for 5 days, then at 70±2℃ for 5 days, and then soak it in 25℃ water for 5 days for peel strength test. The test method is in accordance with GB / T532-2008. Yellowing test: Lay the adhesive strip flat on white paper and place it in a yellowing resistance test box (50°C, 300W bulb). Observe the yellowing after 24 hours. The test results are shown in the following table: As can be seen from the above table, the water-based polyurethane adhesive prepared by the present invention has a peel strength in the range of 94.3N / cm-99.1N / cm after performance testing, and a peel strength in the range of 86.6N / cm-90.2N / cm after heat resistance and water resistance testing, and no yellowing occurs, indicating that the adhesive has excellent comprehensive performance.

[0024] The above contents are merely examples and explanations of the concept of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. 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 environmentally friendly water-based adhesive, characterized in that: The 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 isophorol diisocyanate, 3-6 parts of modified chain extender, 0.005-0.02 parts of catalyst, 0.2-0.5 parts of propylene glycol, 0.1-0.3 parts of triethylamine, 3-6 parts of acetone and 50-70 parts of deionized water; The modified chain extender is prepared by the following steps: Step A1, dispersing ethylenediamine and sodium hydroxide in acetonitrile, recorded as solution 1; mixing cyanuric chloride and acetonitrile at 0-5°C, slowly adding half the volume of solution 1, maintaining the temperature for reaction for 1-2h, then heating to 45-55°C, adding the remaining volume of solution 1, and continuing the reaction for 2-3 to obtain an intermediate product; Step A2, disperse β-alanine and sodium hydroxide in acetonitrile, recorded as solution 2; heat the intermediate product to 90° C., slowly add solution 2, react for 4-5 hours, adjust the pH to 6-7, filter, wash and dry to obtain a modified chain extender.

2. The environmentally friendly water-based adhesive according to claim 1, characterized in that: In step A1, the usage ratio of cyanuric chloride, acetonitrile and solution 1 is 0.01-0.02 mol:100 mL:100 mL, and the usage 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 environmentally friendly water-based adhesive according to claim 1, characterized in that: The dosage ratio of β-alanine, sodium hydroxide and acetonitrile in solution 2 of step A2 is 0.01-0.02 mol: 0.04-0.08 g: 50 mL.

4. The environmentally friendly water-based adhesive according to claim 1, characterized in that: The modified polyacrylic acid is prepared by the following steps: Step B1, maleic anhydride was mixed evenly in N, N-dimethylformamide, recorded as mixed solution 1; under nitrogen conditions, p-aminobenzoic acid and N, N-dimethylformamide were stirred and mixed, and the mixed solution 1 was slowly added, and the mixture was stirred continuously at room temperature for 24 hours, and then poured into distilled water and allowed to stand for 30 minutes, filtered, washed, and dried to obtain intermediate product 1; Step B2, the intermediate product 1, sodium acetate and acetic anhydride are mixed, and the mixture is heated to 50-60° C. and stirred for 2-4 hours, and then cooled to room temperature in an ice water bath, filtered, washed, recrystallized and dried to obtain the intermediate product 2; Step B3, disperse the intermediate product 2 in tetrahydrofuran, add 1-hydroxybenzotriazole and N,N-dimethylpyridine in sequence, and then stir at 0°C for 25-35 minutes, then slowly add dicyclohexylcarbodiimide, and vigorously stir at room temperature for 12-16 hours, concentrate under reduced pressure, then add ethyl acetate, filter and collect the filtrate, and distill under reduced pressure to obtain a functional monomer; Step B4, after dispersing the emulsifier in deionized water, add acrylic acid, methyl methacrylate, hydroxyethyl methacrylate and functional monomer and stir for 20-40 minutes to form a pre-emulsion; Disperse ammonium persulfate in deionized water, heat to 55-65°C and stir for 10 minutes, then slowly add the pre-emulsion dropwise within 1-2 hours, heat to 80-90°C and react for 2-3 hours, filter, and obtain modified polyacrylic acid.

5. The environmentally friendly water-based adhesive according to claim 4, characterized in that: In step B1, the amount ratio of p-aminobenzoic acid, N,N-dimethylformamide and mixed solution 1 is 0.01-0.03 mol:100 mL:100 mL, and the amount ratio of maleic anhydride and N,N-dimethylformamide in mixed solution 1 is 0.01-0.03 mol.

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

7. The environmentally friendly water-based adhesive according to claim 4, characterized in that: In step B3, the usage ratio of intermediate product 2, tetrahydrofuran, 1-hydroxybenzotriazole, N,N-dimethylpyridine, 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.

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

9. A method for preparing the environmentally friendly water-based adhesive according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step S1, weighing raw materials according to weight, vacuum dehydrating polyethylene adipate diol at 100-120° C. for 1 h, adding isophorol diisocyanate, propylene glycol and a modified chain extender at 80-90° C. for reaction for 1.5-2.5 h, and then adding a catalyst for reaction for 3-4 h to obtain a polyurethane prepolymer; Step S2, adding modified polyacrylic acid to the polyurethane prepolymer, reacting at 50-60° C. for 30-50 minutes, then adding acetone and triethylamine and stirring for 10-15 minutes, then adding deionized water and stirring for 30-60 minutes to obtain an environmentally friendly water-based adhesive.

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