Aqueous polyurethane adhesive, its preparation method and use

Abstract

The application discloses a kind of water-based polyurethane adhesive and its preparation method and application.The water-based polyurethane adhesive of the application includes the following components by mass fraction: water-based polyurethane: 100 parts;Silanized carbon dots: 0.02 parts-0.2 parts;Tackifying resin: 10 parts-30 parts;Auxiliary agent: 0.2 parts-1.5 parts.The preparation method of the water-based polyurethane adhesive of the application includes the following steps: ultrasonic dispersion is carried out in water-based polyurethane with silanized carbon dots, then tackifying resin and auxiliary agent are added and mixed uniformly, and the water-based polyurethane adhesive is obtained.The water-based polyurethane adhesive of the application has large bonding strength and low VOC content, the adhesive film formed therefrom has good water resistance, good solvent resistance, good thermal stability and good softness adjustability, and the preparation method is simple, the production cost is low, and it is suitable for large-scale industrial application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of adhesives, in particular to a water-based polyurethane adhesive and a preparation method and application thereof. BACKGROUND

[0002] The water-based polyurethane adhesive refers to an adhesive formed by dissolving or dispersing polyurethane in water, and the adhesive film formed by the water-based polyurethane adhesive has the advantages of good adjustability of softness and hardness, low-temperature resistance, and good flexibility, and has attracted widespread attention. However, the single water-based polyurethane has low solid content, small bonding strength, and low initial adhesion, and since the molecular chain of the water-based polyurethane is mostly linear structure, it lacks chemical cross-linking bonds, resulting in poor water resistance, heat resistance, and solvent resistance of the formed adhesive film, which cannot completely meet the actual application requirements.

[0003] Therefore, it is of great significance to develop a water-based polyurethane adhesive with large bonding strength, low VOC content, and good water resistance / solvent resistance / thermal stability of the formed adhesive film. SUMMARY

[0004] The present application aims to provide a water-based polyurethane adhesive and a preparation method and application thereof.

[0005] The technical solution adopted by the present application is as follows:

[0006] A water-based polyurethane adhesive comprises the following components by mass:

[0007] Water-based polyurethane: 100 parts;

[0008] Silanized carbon dots: 0.02 parts to 0.2 parts;

[0009] Tackifying resin: 10 parts to 30 parts;

[0010] Auxiliary agent: 0.2 parts to 1.5 parts.

[0011] Preferably, the water-based polyurethane is made by a preparation method comprising the following steps:

[0012] 1) mixing polypropylene glycol, diisocyanate, and a catalyst to perform a polycondensation reaction, then adding 2,2-dimethylol propionic acid to perform a first chain extension reaction, then adding 1,4-butanediol to perform a second chain extension reaction, and then adding triethylamine to perform a neutralization reaction to obtain a water-based polyurethane prepolymer;

[0013] 2) dispersing the water-based polyurethane prepolymer in water, then adding ethylenediamine to perform a third chain extension reaction, and then performing vacuum rotary evaporation to obtain the water-based polyurethane.

[0014] Preferably, the molar ratio of the polypropylene glycol to the diisocyanate in step 1) is 1:2.5 to 3.5.

[0015] Preferably, the number average molecular weight of the polypropylene glycol in step 1) is 1000-3000.

[0016] Preferably, the diisocyanate in step 1) is at least one of 2,4-toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate.

[0017] Preferably, the catalyst in step 1) is an organic tin catalyst.

[0018] Further preferably, the catalyst in step 1) is at least one of dibutyltin dilaurate (DBTDL), dibutyltin oxide, dioctyltin oxide.

[0019] Preferably, the polycondensation reaction in step 1) is carried out at a temperature of 60-90°C, and the reaction time is 2-6h.

[0020] Preferably, the amount of 2,2-dimethylol propionic acid in step 1) is 3%-5% of the total mass of polypropylene glycol and diisocyanate.

[0021] Preferably, the first chain extension reaction in step 1) is carried out at a temperature of 70-90°C, and the reaction time is 2-4h.

[0022] Preferably, the amount of 1,4-butanediol in step 1) is 1%-1.5% of the total mass of polypropylene glycol and diisocyanate.

[0023] Preferably, the second chain extension reaction in step 1) is carried out at a temperature of 50-80°C, and the reaction time is 1-4h.

[0024] Preferably, the molar ratio of 2,2-dimethylol propionic acid to triethylamine in step 1) is 1:0.95-1.05.

[0025] Preferably, the neutralization reaction in step 1) is carried out at room temperature (25°C±5°C), and the reaction time is 20-40min.

[0026] Preferably, the amount of ethylenediamine in step 2) is 0.01%-0.1% of the total mass of polypropylene glycol and diisocyanate.

[0027] Preferably, the dispersion in step 2) is carried out at a blender speed of 1000-2000r / min.

[0028] Preferably, the third chain extension reaction in step 2) is carried out at room temperature, and the reaction time is 20-40min.

[0029] Preferably, the vacuum rotary evaporation in step 2) is performed under the conditions of a vacuum degree of 0.07-0.09 MPa and a temperature of 30-50°C, and the rotary evaporation time is 30-60 min.

[0030] Preferably, the silanized carbon dots are made by a preparation method comprising the following steps:

[0031] a) dispersing citric acid and ethylenediamine in water to perform a hydrothermal reaction, to obtain carbon dots;

[0032] b) dispersing the carbon dots in water, and then adding a silane coupling agent to perform a reaction, to obtain the silanized carbon dots.

[0033] Preferably, the molar ratio of citric acid to ethylenediamine in step a) is 1.67-1.73:1.

[0034] Preferably, the hydrothermal reaction in step a) is performed at a temperature of 150-200°C, and the reaction time is 4-6 h.

[0035] Preferably, the mass ratio of the carbon dots to the silane coupling agent in step b) is 1:1-15.

[0036] Preferably, the silane coupling agent in step b) is at least one of 3-aminopropyl triethoxysilane (silane coupling agent KH-550) and γ-glycidoxypropyltrimethoxysilane (silane coupling agent KH-560).

[0037] Preferably, the reaction in step b) is performed at a temperature of 40-60°C, and the reaction time is 4-6 h.

[0038] Preferably, after the reaction in step b) is completed, the reaction solution is subjected to centrifugation, and the solid product obtained by centrifugation is subjected to washing and drying.

[0039] Preferably, the centrifugation is performed at a centrifuge speed of 8000-12000 r / min, and the centrifugation time is 5-15 min.

[0040] Preferably, the washing solvent used in the washing is at least one of benzene, toluene, anhydrous ethanol, and acetone.

[0041] Preferably, the tackifying resin is at least one of a water-based rosin tackifying emulsion and a water-based terpene tackifying emulsion.

[0042] Preferably, the auxiliary agent is at least one of a leveling agent, a defoaming agent, and a wetting agent.

[0043] A preparation method of the water-based polyurethane adhesive as described above comprises the following steps:

[0044] The silanized carbon dots are ultrasonically dispersed in the water-based polyurethane, and then a tackifying resin and an additive are added and uniformly mixed to obtain the water-based polyurethane adhesive.

[0045] The application of the water-based polyurethane adhesive as described above in automobile manufacturing or automobile repair.

[0046] The water-based polyurethane adhesive has the advantages of high bonding strength, low VOC content, good water resistance, good solvent resistance, good thermal stability, good softness adjustability, simple preparation method, low production cost, and suitability for large-scale industrial application.

[0047] Specifically,

[0048] 1) The water-based polyurethane adhesive contains silanized carbon dots, which are successfully grafted in the water-based polyurethane polymer chain through chemical reaction, so that the hydrogen bonding and crosslinking of the water-based polyurethane are enhanced, and the cohesive strength, tensile strength, and bonding strength of the water-based polyurethane can be effectively improved by adding a small amount of silanized carbon dots, so that the adhesive film formed by the prepared water-based polyurethane adhesive has good water resistance, solvent resistance, thermal stability, and other properties.

[0049] 2) The water bath reaction grafts a layer of silane network chain on the surface of the carbon dots, which weakens the mutual attraction between the carbon dot molecules, solves the problems of easy agglomeration and poor dispersibility of the carbon dots in the water-based polyurethane, effectively improves the dispersibility of the nano-scale carbon dot particles in the water-based polyurethane adhesive layer, and thus improves the bonding strength, mechanical properties, and solvent resistance of the adhesive layer.

[0050] 3) The carbon dots are applied in the field of water-based polyurethane adhesives by taking advantage of the rich functional groups on the surface of the carbon dots and the easy functionalization of the carbon dots, which expands the application range of carbon dot and water-based polyurethane composite materials.

[0051] 4) The preparation method of the water-based polyurethane adhesive is simple and convenient, and uses environmentally friendly carbon dots and water-based polyurethane as the main modification body, and reduces the emission of VOC through the vacuum rotary evaporation process. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 The infrared spectra of the carbon dots, silane coupling agent KH-550, silanized carbon dots, water-based polyurethane, and water-based polyurethane adhesive in Example 1.

[0053] Figure 2 The XPS graph of the water-based polyurethane adhesive in Example 1.

[0054] Figure 3Stress-strain relationship curves of the adhesive films formed by the waterborne polyurethane adhesives in Example 7 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0055] The application will be further explained and described with reference to the following specific examples.

[0056] Example 1

[0057] A waterborne polyurethane adhesive, the composition of which is shown in the following table:

[0058] Table 1 Composition table of a waterborne polyurethane adhesive

[0059]

[0060] Note:

[0061] The preparation method of the waterborne polyurethane is as follows:

[0062] 1) 19.14 mmol of polypropylene glycol 2000, 57.42 mmol of 2,4-toluene diisocyanate and 2 drops of dibutyltin dilaurate were mixed, reacted at 75°C for 2.5 h, then 12.6 mmol of 2,2-dimethylol propionic acid was added, reacted at 87°C for 2 h, then 8.77 mmol of 1,4-butanediol was added, reacted at 80°C for 1 h, cooled to room temperature, then 7.37 mmol of triethylamine was added, stirred at room temperature for 30 min, to obtain a waterborne polyurethane prepolymer;

[0063] 2) The waterborne polyurethane prepolymer was dispersed in 80 mL of deionized water under the condition that the stirring speed of the blender was 2000 r / min, then 0.5 g of ethylenediamine was added, reacted at room temperature for 30 min, then rotary evaporation was performed under the condition that the vacuum degree was 0.085 MPa and the temperature was 35°C for 40 min (to remove most of the VOC), to obtain the waterborne polyurethane.

[0064] The preparation method of the silanized carbon dots is as follows:

[0065] a) 3.15 g of citric acid and 975 μL of ethylenediamine were dispersed in 30 mL of deionized water, then transferred to an autoclave, reacted at 200°C for 5 h, naturally cooled to room temperature, then the reaction liquid was added to a dialysis bag with a molecular weight cut-off of 1000 Da, dialyzed in 1 L of deionized water for 24 h (the deionized water was replaced every 8 h), then the solid product obtained by dialysis was placed in a vacuum drying oven and dried at 60°C, to obtain the carbon dots;

[0066] b) 20 mg of carbon dots were dispersed in 6 mL of deionized water to prepare a carbon dot dispersion, and 21 μL of silane coupling agent KH-550 was dispersed in 20 mL of anhydrous ethanol to prepare a silane coupling agent solution, the silane coupling agent solution was added to the carbon dot dispersion, stirred at room temperature for 30 min, then placed in a 60°C water bath and stirred for 5 h, naturally cooled to room temperature, centrifuged at 12000 rpm for 10 min, the solid product obtained by centrifugation was washed with anhydrous ethanol and centrifuged several times, and then dried to obtain silanized carbon dots.

[0067] The preparation method of the above waterborne polyurethane adhesive is as follows:

[0068] The silanized carbon dots were ultrasonically dispersed in the waterborne polyurethane (utilizing the chemical reaction between the active groups on the surface of the silanized carbon dots and the groups in the molecular chain of the waterborne polyurethane), then waterborne rosin tackifying emulsion 958, leveling agent WSS-304, defoaming agent WSS-353 and wetting agent WSS-718 were added, and stirred at room temperature for 30 min to obtain the waterborne polyurethane adhesive.

[0069] Performance test:

[0070] 1) The infrared spectra of the carbon dots (denoted as CD), silane coupling agent KH-550, silanized carbon dots (denoted as K-CD), waterborne polyurethane (denoted as WPU) and waterborne polyurethane adhesive (denoted as KCD-WPU) in this example are shown in Figure 1 .

[0071] It can be seen from Figure 1 :

[0072] a) K-CD not only retains the O-H group stretching vibration peak at 3450 cm -1 and the -C=O stretching vibration peak at 1700 cm -1 of CD, but also strengthens the N-H bending vibration peak at 1556 cm -1 , because the grafting of silane coupling agent on the surface of CD introduces more -NH2;

[0073] b) K-CD appears Si-O-Si stretching vibration absorption peak at 1100 cm -1 , which verifies that the silicon hydroxyl after hydrolysis of KH-550 condenses with the hydroxyl on the surface of CD to form a silicon-oxygen bond, confirming the success of grafting;

[0074] c) KCD-WPU strengthens the -C=O stretching vibration peak at 1700 cm -1 , and adds a Si-O-Si stretching vibration absorption peak at 1100 cm -1 , indicating that the carbon dots are successfully grafted in WPU through chemical bonds.

[0075] 2) The X-ray photoelectron spectroscopy (XPS) spectrum of the waterborne polyurethane adhesive (denoted as KCD-WPU) in this example is shown in Figure Figure 2 (Full spectrum).

[0076] From Figure Figure 2 , it can be seen that four peaks appearing at 282.7 eV, 398.7 eV, 528.7 eV and 100.0 eV are attributed to C1s, N 1s, O 1s and Si 2p, respectively, in which the relatively weak Si 2p peak comes from the silanized carbon dots, and the presence of this element verifies the formation of a new chemical structure between KCD and WPU.

[0077] Example 2:

[0078] A waterborne polyurethane adhesive, the composition of which is shown in the following table:

[0079] Table 2 Composition table of a waterborne polyurethane adhesive

[0080]

[0081]

[0082] Note:

[0083] The preparation method of the silanized carbon dots is as follows:

[0084] 20 mg of carbon dots (same as in Example 1) were dispersed in 6 mL of deionized water to form a carbon dot dispersion, and 106 μL of silane coupling agent KH-550 was dispersed in 20 mL of anhydrous ethanol to form a silane coupling agent solution, then the silane coupling agent solution was added to the carbon dot dispersion, stirred at room temperature for 30 min, then placed in a 60°C water bath for stirring reaction for 5 h, naturally cooled to room temperature, centrifuged at 12000 rpm for 10 min, and the solid product obtained by centrifugation was washed and centrifuged with anhydrous ethanol several times, and then dried to obtain the silanized carbon dots.

[0085] The preparation method of the above waterborne polyurethane adhesive is as follows:

[0086] The silanized carbon dots were ultrasonically dispersed in the waterborne polyurethane, and then the waterborne rosin tackifying emulsion 958, the leveling agent WSS-304, the defoaming agent WSS-353 and the wetting agent WSS-718 were added, and stirred at room temperature for 30 min to obtain the waterborne polyurethane adhesive.

[0087] Example 3:

[0088] A waterborne polyurethane adhesive, the composition of which is shown in the following table:

[0089] Table 3 Composition table of a waterborne polyurethane adhesive

[0090]

[0091]

[0092] Note:

[0093] The preparation method of the silanized carbon dots is as follows:

[0094] 20 mg of carbon dots (same as in Example 1) were dispersed in 6 mL of deionized water to prepare a carbon dot dispersion, and 211 μL of silane coupling agent KH-550 was dispersed in 20 mL of anhydrous ethanol to prepare a silane coupling agent solution, then the silane coupling agent solution was added to the carbon dot dispersion, stirred at room temperature for 30 min, then placed in a 60°C water bath for stirring reaction for 5 h, naturally cooled to room temperature, centrifuged at 12000 rpm for 10 min, and the solid product obtained by centrifugation was washed with anhydrous ethanol for several times and centrifuged, and then dried to obtain silanized carbon dots.

[0095] The preparation method of the above waterborne polyurethane adhesive is as follows:

[0096] The silanized carbon dots were ultrasonically dispersed in the waterborne polyurethane, then the waterborne rosin tackifying emulsion 958, the leveling agent WSS-304, the defoaming agent WSS-353 and the wetting agent WSS-718 were added, and stirred at room temperature for 30 min to obtain the waterborne polyurethane adhesive.

[0097] Example 4:

[0098] A waterborne polyurethane adhesive, the composition of which is shown in the following table:

[0099] Table 4 Composition table of a waterborne polyurethane adhesive

[0100]

[0101] Note:

[0102] The preparation method of the silanized carbon dots is as follows:

[0103] 20 mg of carbon dots (same as in Example 1) were dispersed in 6 mL of deionized water to prepare a carbon dot dispersion, and 317 μL of silane coupling agent KH-550 was dispersed in 20 mL of anhydrous ethanol to prepare a silane coupling agent solution, then the silane coupling agent solution was added to the carbon dot dispersion, stirred at room temperature for 30 min, then placed in a 60°C water bath for stirring reaction for 5 h, naturally cooled to room temperature, centrifuged at 12000 rpm for 10 min, and the solid product obtained by centrifugation was washed with anhydrous ethanol for several times and centrifuged, and then dried to obtain silanized carbon dots.

[0104] The preparation method of the above waterborne polyurethane adhesive is as follows:

[0105] Silanized carbon dots were ultrasonically dispersed in the aqueous polyurethane, and then the aqueous rosin tackifying emulsion 958, the leveling agent WSS-304, the defoaming agent WSS-353 and the wetting agent WSS-718 were added. After stirring at room temperature for 30 min, an aqueous polyurethane adhesive was obtained.

[0106] Example 5:

[0107] An aqueous polyurethane adhesive had the composition shown in the following table:

[0108] Table 5 Composition table of an aqueous polyurethane adhesive

[0109]

[0110] Note:

[0111] The preparation method of the aqueous polyurethane was as follows:

[0112] 1) 19.14 mmol of polypropylene glycol 2000, 57.42 mmol of 2,4-toluene diisocyanate and 3 drops of dibutyltin dilaurate were mixed, and reacted at 70°C for 2 h. Then 12.6 mmol of 2,2-dimethylol propionic acid was added, and reacted at 87°C for 2 h. Then 8.77 mmol of 1,4-butanediol was added, and reacted at 70°C for 2 h. After cooling to room temperature, 7.37 mmol of triethylamine was added, and stirred at room temperature for 30 min to obtain an aqueous polyurethane prepolymer;

[0113] 2) The aqueous polyurethane prepolymer was dispersed in 70 mL of deionized water at a stirring speed of 2000 r / min, and then 0.5 g of ethylenediamine was added, and reacted at room temperature for 30 min. Then rotary evaporation was performed at a vacuum degree of 0.07 MPa and a temperature of 50°C for 40 min (to remove most of the VOCs) to obtain an aqueous polyurethane.

[0114] The preparation method of the above-mentioned aqueous polyurethane adhesive was as follows:

[0115] Silanized carbon dots were ultrasonically dispersed in the aqueous polyurethane, and then the aqueous rosin tackifying emulsion 958, the leveling agent WSS-304, the defoaming agent WSS-353 and the wetting agent WSS-718 were added. After stirring at room temperature for 30 min, an aqueous polyurethane adhesive was obtained.

[0116] Example 6:

[0117] An aqueous polyurethane adhesive had the composition shown in the following table:

[0118] Table 6 Composition table of an aqueous polyurethane adhesive

[0119]

[0120] The preparation method of the above-mentioned water-based polyurethane adhesive is as follows:

[0121] The silanized carbon dots are ultrasonically dispersed in the water-based polyurethane, and then the water-based rosin tackifying emulsion 958, the leveling agent WSS-304, the defoaming agent WSS-353 and the wetting agent WSS-718 are added. After stirring at room temperature for 30 min, the water-based polyurethane adhesive is obtained.

[0122] Example 7:

[0123] A water-based polyurethane adhesive, the composition of which is shown in the following table:

[0124] Table 7 Composition table of a water-based polyurethane adhesive

[0125]

[0126]

[0127] The preparation method of the above-mentioned water-based polyurethane adhesive is as follows:

[0128] The silanized carbon dots are ultrasonically dispersed in the water-based polyurethane, and then the water-based rosin tackifying emulsion 958, the leveling agent WSS-304, the defoaming agent WSS-353 and the wetting agent WSS-718 are added. After stirring at room temperature for 30 min, the water-based polyurethane adhesive is obtained.

[0129] Example 8:

[0130] A water-based polyurethane adhesive, the composition of which is shown in the following table:

[0131] Table 8 Composition table of a water-based polyurethane adhesive

[0132]

[0133] Note:

[0134] The preparation method of the above-mentioned water-based polyurethane adhesive is as follows:

[0135] The silanized carbon dots are ultrasonically dispersed in the water-based polyurethane, and then the water-based rosin tackifying emulsion 958, the leveling agent WSS-304, the defoaming agent WSS-353 and the wetting agent WSS-718 are added. After stirring at room temperature for 30 min, the water-based polyurethane adhesive is obtained.

[0136] Comparative Example 1:

[0137] A water-based polyurethane adhesive, the composition of which is shown in the following table:

[0138] Table 9 Composition table of a water-based polyurethane adhesive

[0139]

[0140] Note:

[0141] The preparation method of the waterborne polyurethane is as follows:

[0142] 1) 19.14 mmol of polypropylene glycol 2000, 57.42 mmol of 2,4-toluene diisocyanate and 3 drops of dibutyltin dilaurate were mixed, reacted at 75°C for 1.5 h, then 12.6 mmol of 2,2-dimethylol propionic acid was added, reacted at 87°C for 2.5 h, then 8.77 mmol of 1,4-butanediol was added, reacted at 80°C for 1 h, cooled to room temperature, then 7.37 mmol of triethylamine was added, stirred at room temperature for 30 min, to obtain a waterborne polyurethane prepolymer;

[0143] 2) The waterborne polyurethane prepolymer was dispersed in 80 mL of deionized water under the condition that the stirring speed of the blender was 2000 r / min, then 0.5 g of ethylenediamine was added, reacted at room temperature for 30 min, then rotary evaporation was performed under the condition that the vacuum degree was 0.085 MPa and the temperature was 35°C for 40 min (to remove most of the VOC), to obtain the waterborne polyurethane.

[0144] The preparation method of the carbon dots is as follows:

[0145] 2.1 g of citric acid and 650 μL of ethylenediamine were dispersed in 20 mL of deionized water, then transferred to a hydrothermal reaction kettle, reacted at 150°C for 5 h, naturally cooled to room temperature, then the reaction liquid was added to a dialysis bag with a molecular weight cut-off of 1000 Da, dialyzed in 1 L of deionized water for 24 h (the deionized water was replaced every 8 h), then the solid product obtained by dialysis was placed in a vacuum drying oven and dried at 60°C, to obtain the carbon dots.

[0146] The preparation method of the waterborne polyurethane adhesive is as follows:

[0147] The carbon dots were ultrasonically dispersed in the waterborne polyurethane (physical blending), then the waterborne rosin tackifying emulsion 958, the leveling agent WSS-304, the defoaming agent WSS-353 and the wetting agent WSS-718 were added and stirred uniformly, to obtain the waterborne polyurethane adhesive.

[0148] Comparative Example 2:

[0149] A waterborne polyurethane adhesive, the composition of which is shown in the following table:

[0150] Table 10 Composition table of a waterborne polyurethane adhesive

[0151]

[0152] Note:

[0153] The preparation method of the waterborne polyurethane is as follows:

[0154] 1) Mix 19.14 mmol of polypropylene glycol 2000, 57.42 mmol of 2,4-toluene diisocyanate and 2 drops of dibutyl tin dilaurate, react at 70°C for 2 h, then add 12.6 mmol of 2,2-dimethylol propionic acid, react at 87°C for 2 h, then add 8.77 mmol of 1,4-butanediol, react at 70°C for 2 h, cool to room temperature, then add 7.37 mmol of triethylamine, stir at room temperature for 30 min, to obtain an aqueous polyurethane prepolymer;

[0155] 2) Disperse the aqueous polyurethane prepolymer in 80 mL of deionized water at a stirring speed of 2000 r / min, then add 0.5 g of ethylenediamine, react at room temperature for 30 min, then rotary evaporate at a vacuum degree of 0.07 MPa and a temperature of 50°C for 40 min (to remove most of the VOC), to obtain an aqueous polyurethane.

[0156] The preparation method of the above aqueous polyurethane adhesive is as follows:

[0157] Mix the aqueous polyurethane, the aqueous rosin tackifying emulsion 958, the leveling agent WSS-304, the defoaming agent WSS-353 and the wetting agent WSS-718, stir at room temperature for 30 min, to obtain the aqueous polyurethane adhesive.

[0158] Performance test:

[0159] 1) Use a nanoparticle size analyzer (Malvern Instruments Ltd) to determine the dispersion particle size of the silanized carbon dots in Examples 1-4 and the carbon dots in Comparative Example 1, and the test results are shown in the following table:

[0160] Table 11 Test results of dispersion particle size of silanized carbon dots and carbon dots

[0161] Test item Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Dispersed particle size (nm) 475.2 344.0 160.0 248.5 447.7

[0162] As can be seen from Table 11, Examples 1-4 graft a layer of silane network chain on the surface of the carbon dots through water bath reaction, which weakens the mutual attraction between the carbon dots molecules, and can effectively improve the dispersibility of the nanometer carbon dots particles in the aqueous polyurethane adhesive; when the mass ratio of the carbon dots to the silane coupling agent is 1:10 (Example 3), the dispersibility of the silanized carbon dots is the best.

[0163] 2) Test the adhesion performance of the aqueous polyurethane adhesives of Examples 1-8 and Comparative Examples 1-2 according to “GB / T 2792-2014 Test method for adhesive tape peel strength”, and the obtained 180° peel strength test results (the adherend is a steel plate) are shown in the following table:

[0164] Table 12 Results of 180° peel strength test for waterborne polyurethane adhesives of Examples 1-8 and Comparative Examples 1-2

[0165]

[0166] As shown in Table 12, the poor dispersibility of carbon dots leads to a slight decrease in the peel strength of the adhesive. However, the addition of silanized carbon dots improves the bonding strength of the waterborne polyurethane adhesive. For example, the 180° peel strength of the waterborne polyurethane adhesive with 0.1 wt% silanized carbon dots (Example 7) is 510 N / m, which is 31.8% higher than that of the waterborne polyurethane adhesive without carbon dots (Comparative Example 2).

[0167] 3) The tensile strength of the adhesive films formed by the waterborne polyurethane adhesives in Examples 1-8 and Comparative Examples 1-2 was tested according to "GB / T 1040-1992 Plastics Tensile Testing Method" (the stress-strain curves of the adhesive films formed by the waterborne polyurethane adhesives in Example 7 and Comparative Examples 1-2 are shown in Figure 1-2). Figure 3 As shown in the table below, the test results were obtained:

[0168] Table 13 Tensile strength test results of the adhesive film

[0169]

[0170]

[0171] From Table 13 and Figure 3 It can be seen that: because the silanized carbon dots are successfully grafted onto the molecular chain of waterborne polyurethane, the hydrogen bonding and cross-linking effects of waterborne polyurethane are enhanced, thus the tensile strength of the film formed by the waterborne polyurethane adhesive is significantly improved. For example, compared with the waterborne polyurethane adhesive without added carbon dots (Comparative Example 2), the tensile strength of the film formed by the waterborne polyurethane adhesive in Example 7 is increased by 62.6%.

[0172] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An aqueous polyurethane adhesive, characterized by, Components comprising the following parts by mass: Water-based polyurethane: 100 parts; Silanized carbon dots: 0.02 parts to 0.2 parts; Tackifying resin: 10 parts to 30 parts; Auxiliary agent: 0.2 parts to 1.5 parts; The water-based polyurethane is made by a preparation method comprising the following steps: 1) mixing polypropylene glycol, diisocyanate and catalyst for polycondensation reaction, then adding 2,2-dimethylol propionic acid for first chain extension reaction, then adding 1,4-butanediol for second chain extension reaction, then adding triethylamine for neutralization reaction, to obtain water-based polyurethane prepolymer; 2) dispersing water-based polyurethane prepolymer in water, then adding ethylenediamine for third chain extension reaction, then performing vacuum rotary evaporation, to obtain water-based polyurethane; In step 1), the molar ratio of polypropylene glycol to diisocyanate is 1:2.5 to 3.5; In step 1), the amount of 2,2-dimethylol propionic acid is 3% to 5% of the total mass of polypropylene glycol and diisocyanate; In step 1), the amount of 1,4-butanediol is 1% to 1.5% of the total mass of polypropylene glycol and diisocyanate; In step 2), the amount of ethylenediamine is 0.01% to 0.1% of the total mass of polypropylene glycol and diisocyanate; The silanized carbon dots are made by a preparation method comprising the following steps: a) dispersing citric acid and ethylenediamine in water for hydrothermal reaction, to obtain carbon dots; b) dispersing carbon dots in water, then adding silane coupling agent for reaction, to obtain silanized carbon dots; In step b), the silane coupling agent is at least one of 3-aminopropyltriethoxysilane and gamma-glycidoxypropyltrimethoxysilane.

2. The aqueous polyurethane adhesive according to claim 1, characterized in that: In step 1), the number average molecular weight of polypropylene glycol is 1000 to 3000; in step 1), the diisocyanate is at least one of 2,4-toluene diisocyanate, isophorone diisocyanate and hexamethylene diisocyanate; in step 1), the molar ratio of 2,2-dimethylol propionic acid to triethylamine is 1:0.95 to 1.

05.

3. The waterborne polyurethane adhesive according to claim 1 or 2, characterized in that: In step 1), the polycondensation reaction is performed at a temperature of 60°C to 90°C, and the reaction time is 2h to 6h; in step 1), the first chain extension reaction is performed at a temperature of 70°C to 90°C, and the reaction time is 2h to 4h; in step 1), the second chain extension reaction is performed at a temperature of 50°C to 80°C, and the reaction time is 1h to 4h; in step 1), the neutralization reaction is performed at room temperature, and the reaction time is 20min to 40min; in step 2), the third chain extension reaction is performed at room temperature, and the reaction time is 20min to 40min.

4. The aqueous polyurethane adhesive according to claim 1, characterized in that: In step a), the molar ratio of citric acid to ethylenediamine is 1.67 to 1.73:1; in step b), the mass ratio of carbon dots to silane coupling agent is 1:1 to 15.

5. The waterborne polyurethane adhesive according to claim 1 or 4, characterized in that: In step a), the hydrothermal reaction is performed at a temperature of 150°C to 200°C, and the reaction time is 4h to 6h; in step b), the reaction is performed at a temperature of 40°C to 60°C, and the reaction time is 4h to 6h.

6. The aqueous polyurethane adhesive of claim 1, wherein: The tackifying resin is at least one of a water-based rosin tackifying emulsion and a water-based terpene tackifying emulsion; and the auxiliary agent is at least one of a leveling agent, a defoaming agent, and a wetting agent.

7. A process for producing the waterborne polyurethane adhesive according to any one of claims 1 to 6, characterized by, The method comprises the following steps: The silanized carbon dots are ultrasonically dispersed in the water-based polyurethane, and then the tackifying resin and the auxiliary agent are added and uniformly mixed to obtain the water-based polyurethane adhesive.

8. Use of the water-based polyurethane adhesive according to any one of claims 1-6 in automobile manufacturing or automobile repair.

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