Adhesive additive and preparation method thereof and structural adhesive

Abstract

The present invention provides an adhesive agent, a preparation method thereof and a structural adhesive. The adhesive agent is firstly prepared by polymerizing HDI biuret with monoaminosilane coupling agent and bisaminosilane coupling agent in sequence, and then reacting with binary functional group small molecules and diethanolamine; in terms of molar parts: 100 parts of HDI biuret, 20-50 parts of bisaminosilane coupling agent, 100-200 parts of monoaminosilane coupling agent, 20-150 parts of binary functional group small molecules, and 20-150 parts of diethanolamine. The above-mentioned adhesive agent has a macromolecule with 1-4 hydroxyl groups, a large number of urea groups and a large number of silicon-oxygen-carbon bonds. When applied to polyurethane structural adhesive, it not only participates in the polyurethane chain extension reaction to improve the bulk strength of the structural adhesive, but also because it contains a large number of siloxane structures and urea groups, it can improve the bonding strength and low-temperature initial adhesion performance of the structural adhesive to substrates such as glass, stainless steel, and anodized aluminum, which is beneficial to shorten the construction period of window manufacturing in a low-temperature environment, and even improve the construction quality.

Description

Technical Field

[0001] The invention relates to the technical field of bonding aids, and in particular to a bonding aid used in structural adhesives, a preparation method thereof, and the structural adhesive. Background Art

[0002] In addition to the adhesive, the existing adhesive also includes an adhesive aid for enhancing the adhesive's bonding strength and other properties. For example, Chinese patent application CN113717213A discloses an adhesive aid for foam plastics, a preparation method and an application thereof, wherein the adhesive aid is prepared by reacting 1,6-hexanediisocyanate biuret with a silane coupling agent; the adhesive aid is directly added to the adhesive component and then mixed with the curing component during the construction process, so that the isocyanate group in the molecule reacts with the hydroxyl group in the foam plastic stock solution to form a part of the foam main chain, and then the foam plastic main chain contains a carbon-oxygen-silicon bond structure that can assist bonding, thereby making the foam plastic's bonding performance more stable.

[0003] Two-component raw material system polyurethane is widely used due to its unique properties. When in use, the two-component raw materials need to be mixed in proportion to achieve its bonding function. When using two-component adhesives, it is usually necessary to use a glue gun to extrude and mix the two components at the same time. If the viscosity of the component is relatively high, the user needs to apply a large force to extrude the component, especially when constructing in winter or in a low temperature environment, which increases the construction difficulty of the user; moreover, the high viscosity of the component is not conducive to the uniform mixing of the two components.

[0004] In addition, during the construction process, the curing speed of the adhesive is closely related to the ambient temperature. During construction in winter or in a low temperature environment, the polyurethane system adhesive often has poor initial adhesion performance and low initial bonding strength. This is especially true when using polyurethane structural adhesive to bond car windows (bonding the car window glass to the electrophoretic paint frame). This will result in a long construction period and even unqualified car window manufacturing. Summary of the invention

[0005] In view of this, it is necessary for the present invention to provide an adhesive additive and a preparation method and application thereof.

[0006] Specifically, the technical solution provided by the present invention is: an adhesive agent, which is mainly prepared by first polymerizing HDI biuret with a monoaminosilane coupling agent and a bisaminosilane coupling agent in sequence, and then reacting with a binary functional group small molecule and diethanolamine to obtain a macromolecular adhesive agent having 1 to 4 hydroxyl groups, urea groups and silicon-oxygen-carbon bonds, wherein, in terms of molar parts: 100 parts of HDI biuret, 20 to 50 parts of bisaminosilane coupling agent, 100 to 200 parts of monoaminosilane coupling agent, 20 to 150 parts of binary functional group small molecules, 20 to 150 parts of diethanolamine, and the binary functional group small molecules contain one hydroxyl group and one amino group.

[0007] The "HDI biuret" in this article refers to 1,6-hexamethylene diisocyanate biuret. The "binary functional group small molecule" in this article refers to a compound with a molecular weight of less than 110 and containing one hydroxyl group and one amino group.

[0008] Based on the above, n(HDI biuret)×3=n(bisaminosilane coupling agent)×2+n(monoaminosilane coupling agent)+n(binary functional group small molecule)+n(diethanolamine), wherein n(HDI biuret), n(bisaminosilane coupling agent), n(monoaminosilane coupling agent), n(diethanolamine) and n(binary functional group small molecule) represent the molar fractions of the corresponding raw materials respectively; because one HDI biuret molecule contains three isocyanate groups, the amounts of the five are limited in this way, so that the isocyanate groups in the HDI biuret are completely reacted and blocked, and the prepared product does not contain isocyanate groups.

[0009] Based on the above, the bisaminosilane coupling agent is N-aminoethyl-γ-aminopropyltrimethoxysilane or N-aminoethyl-γ-aminopropyltriethoxysilane.

[0010] Based on the above, the monoaminosilane coupling agent is bis(3-trimethoxysilylpropyl)amine, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane or 3-(phenylamino)propyltrimethoxysilane; preferably bis(3-trimethoxysilylpropyl)amine.

[0011] Based on the above, the binary functional group small molecule is an amine compound containing a hydroxyl group or an alcohol compound containing an amino group such as monoethanolamine, n-propanolamine, 3-amino-n-butanol or 2-amino-n-butanol.

[0012] The present invention provides a method for preparing the above-mentioned bonding aid, comprising:

[0013] Under inert gas conditions, HDI biuret and a first solvent are uniformly mixed to form a first mixture, and then the monoaminosilane coupling agent is gradually added dropwise to the first mixture under stirring at 20° C. to 25° C. until the addition is complete, and then the reaction is continued for 30 to 60 minutes, and then the bisaminosilane coupling agent is added dropwise, and the reaction is continued for 30 to 60 minutes after the addition is completed, and then the temperature is raised to 50° C. to 70° C. and the reaction is continued for 30 to 60 minutes to prepare a first prepolymer;

[0014] First, the binary functional group small molecule, diethanolamine and the second solvent are uniformly mixed to form a second mixture, and then the first prepolymer is added dropwise to the second mixture at 25°C to 30°C, a rotation speed of 80 to 120 r / min and inert gas protection conditions until the addition is completed and the reaction is continued for 30 to 60 minutes, and then the temperature is raised to 50°C to 60°C and the reaction is continued for 60 to 90 minutes to obtain the bonding agent.

[0015] Specifically, the solid content of the bonding agent is 34% to 36%. During the preparation process, the solid content in the formula is calculated. If the solid content is below 34%, the solvent is removed by vacuum and adjusted to 34% to 36%. If the solid content is above 36%, a second solvent is added to adjust the solid content to 34% to 36%.

[0016] Based on the above, the mass ratio of the total mass of HDI biuret, the bisaminosilane coupling agent and the monoaminosilane coupling agent to the first solvent is (50-100):100.

[0017] Based on the above, the mass ratio of the total mass of the binary functional group small molecule and diethanolamine to the mass ratio of the second solvent is (5-20):100.

[0018] Based on the above, the first solvent and the second solvent are butyl acetate, butanone, toluene or xylene respectively.

[0019] The present invention also provides a polyurethane structural adhesive, the raw materials of which include the above-mentioned bonding aid. Preferably, the polyurethane structural adhesive is a low-density polyurethane structural adhesive.

[0020] Based on the polyurethane structural adhesive, the raw materials of the polyether phase component include the above-mentioned bonding aid. Specifically, the polyurethane structural adhesive is mainly composed of the following raw materials in parts by weight:

[0021] Component A: PAPI (polymethylene polyphenyl isocyanate)

[0022] Component B, i.e., the polyether phase component, is obtained by the following method: 100 parts of polyether polyol are added to a dehydration kettle, and dehydrated for 2 to 3 hours at a temperature below -0.095 MPa and 80°C to 100°C, then cooled to 30°C to 40°C, 0.5 to 5 parts of the bonding aid are added thereto, and the mixture is stirred under vacuum for 0.5 to 1 hour to remove the solvent; 5 to 30 parts of dehydrated glass microbeads, 2 to 5 parts of fumed silica, and 0.05 to 0.2 parts of a catalyst are added thereto, and the mixture is stirred for 10 to 20 minutes. The polyether polyol is composed of 12 to 25 parts of a small molecule polyether polyol and 75 to 88 parts of a polyether polyol 330N.

[0023] The small molecule polyether polyol is a combination of one or more of YD303, YD304 and YD305. The catalyst is dibutyltin dilaurate or dibutyltin dichloride.

[0024] Glass beads have a true density of 0.15 g / cm 3 ~0.70g / cm 3 , hollow microspheres with a particle size D90 between 15 microns and 110 microns, preferably glass microspheres produced by Zhengzhou Shenglait Hollow Microsphere New Materials Co., Ltd.

[0025] The components A and B in the polyurethane structural adhesive are uniformly mixed according to the molar ratio of the isocyanate group in the component A to the hydroxyl group in the component B (0.98-1.05):1, and then cured.

[0026] If the above-mentioned bonding aid is added to the adhesive component A of the polyurethane adhesive, the hydroxyl group contained in it will react with the isocyanate group in the A component, causing the viscosity of the A component to increase and the storage performance to deteriorate, increasing the extrusion force of the A component during the construction process and increasing the construction difficulty. However, the above-mentioned bonding aid should be added to the polyether phase of the B component of the adhesive, and the viscosity of this component does not change much. Therefore, adding the above-mentioned bonding aid to the polyether phase of the polyurethane structural adhesive can avoid a sharp change in the viscosity of the component and enhance the workability of the structural adhesive.

[0027] The above-mentioned bonding aid provided by the present invention is mainly prepared by reacting HDI biuret, bisaminosilane coupling agent, monoaminosilane coupling agent, difunctional small molecule and diethanolamine, and the monoaminosilane coupling agent is first added to react part of the isocyanate group in the HDI biuret, and then the bisaminosilane coupling agent is added to better control the reaction and reduce the situation that some molecular chains are too large, and finally the difunctional small molecule and diethanolamine are added mainly to block the isocyanate group, so that the bonding aid does not contain isocyanate group, contains 1 to 4 hydroxyl groups, a large number of urea groups and a large number of silicon-oxygen-carbon bonds, and the macromolecular bonding aid is not only beneficial to improving the bonding strength of the polyurethane adhesive, but also because the multifunctional molecules (molecules containing more than two hydroxyl groups) therein can play a cross-linking role, which is beneficial to subsequently improving the strength of the polyurethane colloid itself, and at the same time, because the isocyanate group is completely blocked, its use method is also changed.

[0028] When the macromolecular bonding agent having 1 to 4 hydroxyl groups provided by the present invention is applied to polyurethane structural adhesive, on the one hand, it participates in the polyurethane chain extension reaction and reacts into the polyurethane chain segment with a larger bonding group. Moreover, since it contains multifunctional molecules (molecules containing more than two hydroxyl groups), it can play a cross-linking role, thereby improving the bulk strength of the final polyurethane structural adhesive. On the other hand, since the bonding agent contains a large amount of siloxane structures and a large amount of urea groups, the bonding strength and low-temperature initial adhesion performance of the polyurethane structural adhesive to substrates such as glass, stainless steel, and anodized aluminum are improved, which is beneficial to shortening the construction period of window manufacturing in a low-temperature environment and even improving the construction quality. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described in detail below through specific implementation methods.

[0030] Examples 1 to 5

[0031] The raw materials of the bonding aids provided in Examples 1 to 5 of the present invention and Comparative Example 1 are shown in Table 1 below.

[0032] Table 1 Molar ratio of raw materials of adhesive additives

[0033]

[0034] The bonding aids provided in Examples 1 to 5 are mainly prepared by the following steps:

[0035] The first step is to mix HDI biuret and the first solvent butyl acetate evenly under nitrogen protection to prepare a first mixture, and then gradually add bis(3-trimethoxysilylpropyl)amine to the first mixture under stirring at 25°C, and continue to react for 45 minutes after the addition is complete, and then continue to gradually add the bisaminosilane coupling agent to the above substances, and continue to react for 45 minutes after the addition is complete, and then heat to 60°C and continue to react for 45 minutes, so that bis(3-trimethoxysilylpropyl)amine and HDI biuret react completely to prepare a first prepolymer, and the total mass ratio of butyl acetate solvent to HDI biuret, N-aminoethyl-γ-aminopropyltrimethoxysilane and bis(3-trimethoxysilylpropyl)amine is 100:75;

[0036] The second step is to evenly mix the monoethanolamine and diethanolamine and dehydrate them in a nitrogen atmosphere at 105° C. for 90 minutes, then cool them to room temperature and add the second solvent butyl acetate to prepare a second mixture, slowly drop the first prepolymer into the second mixture at 25° C., a rotation speed of 100 r / min and nitrogen protection, and continue to react for 90 minutes after the addition, then raise the temperature to 55° C. and continue to react for 75 minutes, so that the remaining isocyanate groups in the HDI biuret completely react with the amino groups in the monoethanolamine and diethanolamine, and then adjust the solid content to 35% to obtain the above-mentioned bonding agent, and the mass ratio of the butyl acetate solvent to the total mass of the monoethanolamine and diethanolamine is 100:13.

[0037] The bonding agent provided in Comparative Example 1 is mainly prepared by the following steps:

[0038] 1) First, diethanolamine is dehydrated, and then HDI biuret and butyl acetate (25% by weight of the total weight of the bonding agent) are added thereto at 25° C. and in an inert atmosphere, and stirred at 300 r / min for 30 minutes, and then the temperature is raised to 75° C. and stirred for 60 minutes, and then 0.3 parts by weight of dibutyltin dioxysilicate is added and the reaction is continued for 45 minutes, at which time butyl acetate is added to dilute the product, and the amount of butyl acetate added is 25% by weight of the total weight of the bonding agent;

[0039] 2) Add N-aminoethyl-γ-aminopropyltrimethoxysilane dropwise to the diluted product of step 1) at a stirring speed of 400 r / min and below 20° C. for 45 min. After the addition is complete, continue the reaction for 1.5 h;

[0040] 3) Continue to add bis(3-trimethoxysilylpropyl)amine to the product in step 2) in batches, keep the temperature and speed unchanged, and stir the reaction for 45 minutes after the addition is completed. At this time, reduce the speed to 300r / min, increase the temperature to 65°C and continue stirring for 1.5h, then adjust the solid content to 35% to obtain the bonding agent.

[0041] Structural adhesives of embodiments 1 to 5 of the present invention

[0042] (1) Examples 1 to 5 of the present invention and Comparative Example 1 each provide a polyurethane structural adhesive, each comprising the following raw materials in parts by weight:

[0043] Component A: PAPI

[0044] Component B: obtained by the following method: add 18 parts of polyether polyol (YD305) and 82 parts of polyether polyol (330n) into a dehydration kettle, and dehydrate at a temperature below -0.095 MPa and 90°C for 2.5 hours, then cool to 35°C and add 3 parts of the bonding agent provided in Examples 1 to 5, and continue stirring under vacuum for 0.5 to 1 hour to remove the solvent; add 18 parts of dehydrated glass microspheres (HL42), 3 parts of fumed silica, and 0.12 parts of dibutyltin dilaurate, and stir for 15 minutes to obtain component B.

[0045] Evenly mix component A and component B in the polyurethane adhesive in a mass ratio of 1:561 and allow to cure.

[0046] (2) Comparative Examples 2 to 6 of the present invention each provide a polyurethane structural adhesive, wherein the bonding aid provided in Examples 1 to 5 is added to Component A of the polyurethane structural adhesive provided in Examples 1 to 5, respectively, but not to Component B, and the other components and processes remain unchanged.

[0047] Embodiments 6 to 8

[0048] The raw materials of the bonding aid provided in Examples 6 to 8 of the present invention are shown in Table 2.

[0049] Table 2 Molar ratio of raw materials of adhesive additives

[0050]

[0051] The preparation methods of the bonding aids provided in Examples 6 to 8 are substantially the same as the preparation methods of the bonding aids provided in Examples 1 to 5, with the main difference being:

[0052] The first solvent used in Example 6 is xylene, and the ratio of its mass to the total mass of HDI biuret, N-aminoethyl-γ-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane is 100:80; the second solvent used is xylene, and the ratio of its mass to the total mass of n-propanolamine and diethanolamine is 100:30.

[0053] The first solvent used in Example 7 is toluene, and the ratio of the total mass of toluene to HDI biuret, N-aminoethyl-γ-aminopropyltriethoxysilane and 3-aminopropyltriethoxysilane is 100:100; the second solvent used is toluene, and the ratio of the total mass of toluene to 3-aminobutanol and diethanolamine is 100:20.

[0054] The first solvent used in Example 8 is butanone, and the ratio of the total mass of butanone to HDI biuret, N-aminoethyl-γ-aminopropyltriethoxysilane and 3-(phenylamino)propyltrimethoxysilane is 100:75; the second solvent used is butanone, and the ratio of the total mass of butanone to 2-amino-n-butanol and diethanolamine is 100:50.

[0055] Embodiments 6 to 8 of the present invention also provide a polyurethane structural adhesive, and the raw materials respectively include:

[0056] Component A: PAPI

[0057] Component B: by mass, 17 parts of polyether polyol YD304, 83 parts of polyether polyol 330n, 4 parts of bonding agent provided in Examples 6 to 8, 17 parts of glass microspheres HL40, 4 parts of fumed silica, and 0.15 parts of dibutyltin dilaurate. The treatment process of component B is basically the same as the corresponding treatment process provided in Examples 1 to 5.

[0058] Evenly mix component A and component B in the polyurethane structural adhesive in a mass ratio of 100:515 and then cure.

[0059] Performance Testing

[0060] Density measurement method: After the polyurethane structural adhesives provided by Examples 1 to 8 and Comparative Examples 1 to 6 were cured for 5 days under standard conditions of 23°C*50% RH, they were mixed evenly according to the mixing ratio of component A and component B respectively, and scraped into 2mm×40mm×40mm thin sheets. After curing for 7 days under standard conditions of 23°C×50% RH, their densities were tested by the drainage method. The results are shown in Table 3.

[0061] Viscosity measurement method: The polyurethane structural adhesive sealant using the bonding aid provided in the above Examples 1 to 8 and Comparative Examples 1 to 6 was stored and cured under standard conditions of 23°C × 50% RH for 24 hours, and then the viscosity of the A and B components was tested using a rotational viscometer, and the viscosity of the A component was tested after 10 days of curing. The results are shown in Table 3.

[0062] Shear strength measurement method: After curing for 5 days under the standard conditions of 23°C*50%RH for 5 days, the polyurethane structural adhesives provided by the bonding aids of Examples 1 to 8 and Comparative Examples 1 to 6 are mixed evenly according to the mixing ratio of the respective components A and B, and the respective mixtures are used to coat the surface of a 25mm×100mm×2mm electrophoretic painted steel sheet with a thickness of 1mm and a bonding area of ​​25mm×12.5mm with the corresponding structural adhesive, and the sheet is pasted on a 50mm×40mm×6mm glass sheet treated with a toluene dilution of a silane coupling agent KH550, and cured for 7 days under the standard conditions of 23°C*50%RH and at a low temperature of -5°C, and the bonding strength is tested. The results are shown in Table 3.

[0063] Table 3 Performance test table of polyurethane structural adhesive

[0064]

[0065] It can be seen from Table 3 that compared with the polyurethane structural adhesive provided by Comparative Example 1, the standard shear strength of the polyurethane structural adhesive provided by Examples 1 to 5 is relatively large, which shows that the bonding aid provided by this embodiment is beneficial to enhancing the bonding strength and body strength of the polyurethane structural adhesive.

[0066] From the perspective of low-temperature shear strength, the low-temperature shear strength of the polyurethane structural adhesive provided by Examples 1 to 5 is much higher than that of Comparative Examples 1 to 6. This shows that the bonding aid provided by this embodiment is beneficial to enhancing the initial bonding strength of the polyurethane structural adhesive under low temperature conditions, increasing the construction performance under low temperature environment, and is beneficial to shortening the construction period.

[0067] In terms of the viscosity of the components, the viscosity of component A of the polyurethane structural adhesive provided in Examples 1 to 5 and Comparative Example 1 is basically unchanged, but the viscosity of its component B is much lower than that of component B of Comparative Example 1, which shows that the viscosity of each component of the polyurethane structural adhesive provided in the embodiment of the present invention is relatively small, which is conducive to construction. Comparing the viscosity data of components A and B provided in Examples 1 to 5 and Comparative Examples 2 to 6, the addition of the bonding agent provided in the embodiment of the present invention to component A of the polyurethane structural adhesive will significantly increase its viscosity, and will cause the storage of component A to deteriorate, which is not conducive to construction; the addition of the polyurethane bonding agent provided in Examples 1 to 5 of the present invention to component B will have little effect on its viscosity. Therefore, when the bonding agent provided in the embodiment of the present invention is added to component B of the polyurethane adhesive, the viscosity of each component is relatively small and the workability is good under the premise of ensuring the bonding performance and colloid strength of the polyurethane structural adhesive.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention, which should be included in the scope of the technical solution for protection of the present invention.

Claims

1. An adhesive aid, Features: The invention is a macromolecular bonding auxiliary agent having 1 to 4 hydroxyl groups, urea groups and silicon-oxygen-carbon bonds, prepared by first polymerizing HDI biuret with a monoaminosilane coupling agent and a bisaminosilane coupling agent in sequence, and then reacting with a binary functional group small molecule and diethanolamine to terminate the isocyanate group, wherein the macromolecular bonding auxiliary agent comprises, by mole, 100 parts of HDI biuret, 20 to 50 parts of a bisaminosilane coupling agent, 100 to 200 parts of a monoaminosilane coupling agent, 20 to 150 parts of a binary functional group small molecule and 20 to 150 parts of diethanolamine, and the binary functional group small molecule contains one hydroxyl group and one amino group.

2. The bonding aid according to claim 1, Features: The amounts of HDI biuret, bisaminosilane coupling agent, monoaminosilane coupling agent, binary functional group small molecule and diethanolamine are represented by n (HDI biuret), n (bisaminosilane coupling agent), n (monoaminosilane coupling agent), n (binary functional group small molecule) and n (diethanolamine), respectively, and n (HDI biuret) × 3 = n (bisaminosilane coupling agent) × 2 + n (monoaminosilane coupling agent) + n (binary functional group small molecule) + n (diethanolamine).

3. The bonding aid according to claim 1 or 2, Features: The bisaminosilane coupling agent is N-aminoethyl-γ-aminopropyltrimethoxysilane or N-aminoethyl-γ-aminopropyltriethoxysilane.

4. The bonding aid according to claim 1 or 2, Features: The monoaminosilane coupling agent is bis(3-trimethoxysilylpropyl)amine, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane or 3-(phenylamino)propyltrimethoxysilane.

5. The bonding aid according to claim 1 or 2, Features: The binary functional group small molecule is monoethanolamine, n-propanolamine, 3-amino n-butanol or 2-amino n-butanol.

6. A method for preparing the bonding aid according to any one of claims 1 to 5, include: Under inert gas conditions, HDI biuret and the first solvent are uniformly mixed to form a first mixture, and then the monoaminosilane coupling agent is gradually added dropwise to the first mixture under stirring at 20° C. to 25° C. until the addition is complete, and then the reaction is continued for 30 to 60 minutes, and then the bisaminosilane coupling agent is added dropwise, and the reaction is continued for 30 to 60 minutes after the addition is completed, and then the temperature is raised to 50° C. to 70° C. and the reaction is continued for 30 to 60 minutes to prepare a first prepolymer; First, the binary functional group small molecule, diethanolamine and the second solvent are uniformly mixed to form a second mixture, and then the first prepolymer is added dropwise to the second mixture at 25°C to 30°C, a rotation speed of 80 to 120 r / min and inert gas protection conditions until the addition is completed and the reaction is continued for 30 to 60 minutes, and then the temperature is raised to 50°C to 60°C and the reaction is continued for 60 to 90 minutes to obtain the bonding agent.

7. The preparation method according to claim 6, Features: The mass ratio of the total mass of HDI biuret, the bisaminosilane coupling agent and the monoaminosilane coupling agent to the first solvent is (50-100):

100.

8. The preparation method according to claim 6 or 7, Features: The mass ratio of the total mass of the binary functional group small molecule and diethanolamine to the mass ratio of the second solvent is (5-20):

100.

9. The preparation method according to claim 8, Features: The first solvent and the second solvent are butyl acetate, butanone, toluene or xylene respectively.

10. A polyurethane structural adhesive, the raw material of which comprises the bonding aid according to any one of claims 1 to 5.

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