Aqueous polyurethane adhesive, process for its preparation and use

Abstract

This invention belongs to the field of adhesive technology, specifically relating to waterborne polyurethane adhesives, their preparation methods, and applications. The waterborne polyurethane adhesive comprises a polyurethane prepolymer, an oligomer containing an epoxy-containing silane coupling agent, a carboxyl-containing silica sol, and a quaternary ammonium salt compound. Addressing issues of heat resistance, damp heat resistance, and thermal cycling shock, it constructs an inorganic-organic hybrid crosslinked network within the polyurethane matrix through the ring-opening reaction of epoxy and carboxyl groups. This network combines the toughness of organic resins with the thermal stability of silica, preventing adhesive failure in damp heat environments and during thermal cycling shocks.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, and relates to waterborne polyurethane adhesives, their preparation methods and uses. Background Technology

[0002] In the automotive interior trim sector, solvent-based polyurethane has long held a dominant market position due to its advantages such as strong initial tack and fast drying. However, in recent years, with increasing environmental awareness and stricter VOC requirements in the automotive industry, low-VOC waterborne polyurethane automotive interior adhesives are showing a trend of gradually replacing similar solvent-based polyurethanes.

[0003] However, waterborne polyurethane adhesives exhibit a decline in bonding performance compared to similar solvent-based products. Due to the typically high coefficient of thermal expansion of their molecular chains, they are prone to reduced bond strength and interface damage when bonding to substrates with low coefficients of thermal expansion, such as metals, glass, or plastics, due to cyclical temperature changes. This is particularly problematic under prolonged high-temperature and high-humidity environments and cyclical heating and cooling conditions, posing a significant risk of adhesive failure. Therefore, targeted improvements are necessary. Furthermore, waterborne polyurethane adhesives are often composed of neutralized waterborne resins dispersed in water. As thermodynamically unstable dispersions, their storage stability must be considered. While meeting the performance requirements of waterborne polyurethane adhesives, their storage stability and shelf-life requirements must also be taken into account. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to improve the heat resistance, damp heat resistance and thermal shock stability of waterborne polyurethane adhesives by introducing carboxyl-containing silica sol, epoxy-containing silane coupling agent oligomers and quaternary ammonium salt compounds, while improving the antibacterial properties of waterborne polyurethane adhesives and taking into account their storage stability.

[0005] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, a waterborne polyurethane adhesive comprises:

[0007] Polyurethane prepolymers, oligomers containing epoxy-containing silane coupling agents, silica sols containing carboxyl groups, and quaternary ammonium salt compounds;

[0008] The polyurethane prepolymer contains a polyol chain extender, a hydrophilic chain extender, a polyol, a diisocyanate, and a catalyst. The polyurethane prepolymer is end-capped with -NCO groups. The hydrophilic chain extender is a polyol or polyamine containing at least one -COOH or -SO3H group.

[0009] Preferably, the polyol chain extender is selected from any one or a combination of two of 1,4-butanediol, 1,6-hexanediol, 1,3-butanediol and polycarbonate diol;

[0010] Preferably, the hydrophilic chain extender is selected from one or more combinations of dimethylolpropionic acid, dimethylolbutyric acid, sodium 1,4-butanediol-2-sulfonate and sodium ethylenediamine ethanesulfonate;

[0011] Preferably, the polyol is selected from one or two of polyester polyols or polyether polyols;

[0012] The polyester polyol is selected from one or more of the following: adipic acid-based polyester polyol, phthalic acid-based polyester polyol, aliphatic polyester polyol or polycaprolactone polyol.

[0013] The polyether polyol is selected from one or more of the following: polytetrahydrofuran ether diol and polypropylene glycol;

[0014] More preferably, the polyol is selected from one or more combinations of polybutylene adipate diol, polyisopropylene adipate, polypentylene adipate diol, polytetrahydrofuran ether diol, and polypropylene glycol.

[0015] Preferably, the diisocyanate is selected from one or more of the following: isophorone diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and 1,6-hexanediisocyanate.

[0016] The diisocyanate is preferably isophorone diisocyanate or diphenylmethane diisocyanate.

[0017] Preferably, the catalyst is selected from any one or more of organobismuth catalysts and organotin catalysts;

[0018] More preferably, the catalyst is selected from dibutyltin dilaurate (DBTDL).

[0019] Further, the polyurethane prepolymer comprises the following raw materials in parts by weight: 110-150 parts of polyol, 45-70 parts of diisocyanate, 3-10 parts of hydrophilic chain extender, 10-20 parts of polyol chain extender, and 0.001-0.01 parts of catalyst.

[0020] The epoxy-containing silane coupling agent oligomer is selected from oligomers of γ-glycidyl etheroxypropyltrimethoxysilane or oligomers of γ-glycidyl etheroxypropyltriethoxysilane.

[0021] The carboxyl-containing silica sol is prepared by a sol-gel reaction of a carboxyl-containing silane coupling agent and an orthosilicate organic ester.

[0022] Preferably, the carboxyl-containing silane coupling agent is obtained by Michael addition reaction of piperazine methyltriethoxysilane with acrylic acid.

[0023] Preferably, the organic ester of orthosilicate is selected from any one of methyl orthosilicate, ethyl orthosilicate, or propyl orthosilicate.

[0024] Furthermore, the sol-gel reaction process of the carboxyl-containing silane coupling agent and the orthosilicate organic ester includes: adding 20-30 parts of the carboxyl-containing silane coupling agent, 1-10 parts of the orthosilicate organic ester, 60-70 parts of the alcohol solvent and 1-10 parts of deionized water into the reaction vessel, adjusting the pH of the reaction system to 7-9, then heating to 50-70℃ and reacting for 1-4 hours, and after the reaction is completed, cooling to room temperature and aging for 12-48 hours to obtain the carboxyl-containing silica sol.

[0025] Preferably, the alcohol solvent is selected from any one of methanol, ethanol, n-propanol, or isopropanol.

[0026] The quaternary ammonium salt compound is selected from tetraalkylammonium halides.

[0027] Preferably, the quaternary ammonium salt compound is selected from hexadecyltrimethylammonium halide.

[0028] Preferably, the quaternary ammonium salt compound is selected from either hexadecyltrimethylammonium chloride or hexadecyltrimethylammonium bromide.

[0029] Furthermore, the method for preparing the polyurethane prepolymer includes:

[0030] S1. The polyol is dehydrated under vacuum, and then polyol, hydrophilic chain extender, acetone and diisocyanate are added to the reaction vessel and mixed and reacted. Then polyol chain extender is added and reacted, and then catalyst is added and reacted until the -NCO content of the reaction mixture is <10wt%.

[0031] S2, Neutralization reaction: The polyurethane prepolymer is cooled to 30-60°C, and a neutralizing agent is added under the shearing action of a high-speed disperser, and the reaction is carried out for 5-60 minutes;

[0032] S3, the deketolization process, sets the temperature to 40-60℃ and the pressure inside the container to no more than 0.1Pa, and removes acetone by vacuum.

[0033] The neutralizing agent is selected from any one of ammonia, triethylamine (TEA), N,N-dimethylethanolamine (DMEA), or triethanolamine (TEOA).

[0034] Preferably, after cooling in step S2, 60-100 parts of acetone are added to dilute the prepolymer to reduce the viscosity of the polyurethane prepolymer, and then a neutralizing agent is added under the shearing action of a high-speed disperser to carry out a neutralization reaction.

[0035] Preferably, the neutralizing agent is selected from triethylamine.

[0036] Secondly, the preparation method of the above-mentioned waterborne polyurethane adhesive includes: mixing polyurethane prepolymer, diamine, oligomer containing epoxy silane coupling agent, silica sol containing carboxyl groups and quaternary ammonium salt compound and then dispersing them evenly by mechanical means.

[0037] The diamine is selected from either diamine or ethylenediamine.

[0038] Preferably, the polyurethane prepolymer is first mechanically mixed with diamine and carboxyl-containing silica sol until homogeneous, and then oligomers containing epoxy-containing silane coupling agents and quaternary ammonium salt compounds are added and mixed mechanically until homogeneous.

[0039] Furthermore, by weight, the polyurethane prepolymer comprises 90-110 parts, the diamine 1-10 parts, the oligomer containing epoxy silane coupling agent 3-15 parts, the silica sol containing carboxyl groups 5-20 parts, and the quaternary ammonium salt compound 0.1-0.5 parts.

[0040] Preferably, the mechanical method specifically involves dispersing using a high-speed disperser at a rotation speed of 500-5000 rpm;

[0041] Preferably, the dispersion time is 10-120 min.

[0042] Thirdly, the above-mentioned waterborne polyurethane adhesives are used for bonding polyurethane substrates to plastic substrates, and for bonding polyvinyl chloride substrates to plastic substrates.

[0043] The polyurethane substrate is selected from polyurethane (PU) semi-rigid foam substrate;

[0044] The polyvinyl chloride material is selected from polyvinyl chloride (PVC) leather;

[0045] The plastic substrate includes any one of polybutylene terephthalate (PBT), polycarbonate (PC), polyamide (PA), acrylonitrile-butadiene-styrene copolymer (ABS), and polyphenylene sulfide (PPS).

[0046] Fourthly, the application of the above-mentioned waterborne polyurethane adhesives in automotive interior bonding.

[0047] The beneficial effects of the technical solution of this invention are:

[0048] Polycarbonate diol is used as a chain extender in the synthesis of polyurethane prepolymer, thereby replacing part of the polyester diol. The main chain of polycarbonate molecules is composed of carbonate-O-(C=O)-O-, which is more stable than the -(C=O)-O- ester group of polyester, especially with higher chemical stability under humid and hot conditions, thus avoiding hydrolysis problems.

[0049] To address issues related to heat resistance, damp heat resistance, and thermal cycling shock, a multi-layer crosslinking network was designed through the ring-opening reaction of epoxy and carboxyl groups. This network tightly binds carboxyl-containing silica sol, KH560 coupling agent oligomer, and polyurethane prepolymer through strong chemical bonds, thereby constructing an inorganic-organic hybrid crosslinking network within the polyurethane matrix. This network combines the toughness of organic resins with the thermal stability of silica. Simultaneously, silica with a low coefficient of thermal expansion (CTE) is introduced into the waterborne adhesive system. After chemical crosslinking, the overall CTE of the adhesive is reduced, preventing failure during thermal cycling shock.

[0050] To address the stability issues of waterborne polyurethane, the use of highly reactive amino / epoxy groups should be avoided. Instead, a crosslinking network constructed using carboxyl / epoxy groups can maintain better storage stability. At the same time, the introduction of quaternary ammonium salt catalysts provides long-lasting antibacterial properties, which is beneficial for the long-term use of waterborne polyurethane adhesives in humid and hot environments.

[0051] Introducing quaternary ammonium salt compounds into waterborne polyurethane adhesives, in addition to acting as catalysts for epoxy ring opening, also provides long-lasting antibacterial properties due to the inherent characteristics of quaternary ammonium salt compounds. This prevents waterborne polyurethane adhesives from aging, degrading, or developing odors due to microbial growth, making them particularly suitable for protection against microbial erosion in humid and hot environments. Detailed Implementation

[0052] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0053] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0054] Unless otherwise specified, the experimental conditions used in the examples are generally in accordance with conventional conditions in the art or the conditions recommended by the reagent company. Unless otherwise specified, the materials and reagents used in the examples can be purchased commercially.

[0055] Example 1

[0056] Carboxyl-containing silica sol was synthesized by sol-gel method. The carboxyl-containing silane coupling agent was obtained by Michael addition reaction of piperazine methyltriethoxysilane and acrylic acid according to the method of 202310240825X. 24 parts of the carboxyl-containing silane coupling agent, 65 parts of ethanol, 5 parts of deionized water and 6 parts of tetraethyl orthosilicate were added to a flask, the pH was adjusted to 8 with ammonia water, the temperature was raised to 60°C and reacted for 3 hours, and then the temperature was lowered to room temperature and aged for 24 hours to obtain the carboxyl-containing silica sol.

[0057] Example 2

[0058] Waterborne polyurethane is synthesized according to the following steps (wherein the raw materials are in parts by weight):

[0059] S1. Preparation of polyurethane prepolymer containing hydrophilic monomers: 15 parts of poly(neopentyl adipate) glycol and 105 parts of poly(butylene adipate) glycol were added to a three-necked flask. The polyols were dehydrated under vacuum at 120°C for 2 hours. The temperature was then lowered to 80-85°C. 6 parts of dimethylolpropionic acid and 8 parts of acetone were added and stirred for 20 minutes. 55 parts of isophorone diisocyanate were added and reacted at 80-85°C for 2 hours. Then 15 parts of polycarbonate diol PCD-260 were added and reacted at 80-85°C for 1 hour. 0.003 parts of catalyst DBTDL were added and reacted at 70-80°C until the -NCO content decreased to 5 wt%, thus obtaining a polyurethane prepolymer containing hydrophilic monomers.

[0060] S2, Neutralization reaction: Cool the polyurethane prepolymer to 40-45℃, add 75 parts of acetone to reduce the viscosity of the polyurethane prepolymer, and then add 7 parts of triethylamine under the shearing action of a high-speed disperser, and react for 15-20 minutes.

[0061] S3, Deketone process: Set the temperature to 55℃ and remove acetone by vacuum for 1-3 hours until the acetone content is <200ppm, thereby obtaining waterborne polyurethane prepolymer;

[0062] S4. Take 100 parts of the waterborne polyurethane prepolymer prepared above, add 4 parts of chain extender ethylenediamine and 10 parts of carboxyl-containing silica hydrosol prepared in Example 1 in sequence, disperse at 1000 rpm for 15 min in a high-speed disperser, then add 6 parts of KH560 oligomer (Jiangxi Hongbai New Materials, brand name HP187 oligomer) and 0.2 parts of hexadecyltrimethylammonium bromide, disperse at 1000 rpm for 30 min in a high-speed disperser to obtain waterborne polyurethane adhesive.

[0063] Example 3

[0064] The synthesis steps of waterborne polyurethane are the same as in Example 2, except that in S4, 100 parts of waterborne polyurethane are taken, and 4 parts of chain extender ethylenediamine and 15 parts of carboxyl-containing silica hydrosol prepared in Example 1 are added in sequence. The mixture is dispersed at 1000 rpm for 15 min in a high-speed disperser. Then, 6 parts of KH560 oligomer (Jiangxi Hongbai New Materials, brand name HP187 oligomer) and 0.2 parts of hexadecyltrimethylammonium chloride are added. The mixture is dispersed at 1000 rpm for 30 min in a high-speed disperser to obtain waterborne polyurethane adhesive.

[0065] Example 4

[0066] Waterborne polyurethane is synthesized according to the following steps (wherein each raw material is in parts by weight):

[0067] S1. Preparation of polyurethane prepolymer containing hydrophilic monomers: In a three-necked flask, add 110 parts of polybutylene adipate diol, 15 parts of polypentyl adipate diol, and 10 parts of polytetrahydrofuran ether diol. Dehydrate the polyols under vacuum at 120°C for 2 hours. Cool to 80-85°C, add 5 parts of dimethylolpropionic acid and 6 parts of acetone, stir for 20 minutes, add 20 parts of diphenylmethane diisocyanate and 30 parts of isophorone diisocyanate, and react at 80-85°C for 2 hours. Then add 5 parts of 1,4-butanediol and 10 parts of polycarbonate diol PCD-260, and react at 80-85°C for 1 hour. Add 0.003 parts of catalyst DBTDL and react at 70-80°C until the -NCO content decreases to 5 wt%, thereby obtaining a polyurethane prepolymer containing hydrophilic monomers.

[0068] S2, Neutralization reaction: Cool the polyurethane prepolymer to 40-45°C, add 76 parts of acetone to reduce the viscosity of the polyurethane prepolymer, and then add 6 parts of triethylamine under the shearing action of a high-speed disperser, and react for 15-20 minutes.

[0069] S3. Deketation process: Set the temperature to 55℃, the pressure to 0.098Pa, deketate for 1-3 hours, and the acetone content to <200ppm, thereby obtaining a water-based polyurethane adhesive with a solid content of 50%.

[0070] S4. Take 100 parts of the waterborne polyurethane prepared above, add 4 parts of chain extender ethylenediamine and 10 parts of carboxyl-containing silica hydrosol prepared in Example 1 in sequence, disperse at 1000 rpm for 15 min in a high-speed disperser, then add 6 parts of KH560 oligomer (Jiangxi Hongbai New Materials, brand name HP187 oligomer) and 0.2 parts of hexadecyltrimethylammonium bromide, disperse at 1000 rpm for 30 min in a high-speed disperser to obtain waterborne polyurethane adhesive.

[0071] Example 5

[0072] The synthesis steps of waterborne polyurethane are the same as in Example 4, except that in S4, 100 parts of waterborne polyurethane are taken, and 4 parts of chain extender ethylenediamine and 15 parts of carboxyl-containing silica hydrosol prepared in Example 1 are added in sequence. The mixture is dispersed at 1000 rpm for 15 min in a high-speed disperser. Then, 6 parts of KH560 oligomer (Jiangxi Hongbai New Materials, brand name HP187 oligomer) and 0.2 parts of hexadecyltrimethylammonium chloride are added. The mixture is dispersed at 1000 rpm for 30 min in a high-speed disperser to obtain waterborne polyurethane adhesive.

[0073] Comparative Example 1

[0074] The synthesis steps of waterborne polyurethane are the same as in Example 2, except that in S4, 100 parts of waterborne polyurethane are taken, 4 parts of chain extender ethylenediamine are added, and the mixture is directly dispersed in a high-speed disperser at 1000 rpm for 30 minutes to obtain waterborne polyurethane adhesive.

[0075] Comparative Example 2

[0076] The synthesis steps of waterborne polyurethane are the same as in Example 2, except that in S4, 100 parts of waterborne polyurethane are taken, 4 parts of chain extender ethylenediamine and 10 parts of carboxyl-containing silica hydrosol prepared in Example 1 are added in sequence, dispersed at 1000 rpm for 15 min in a high-speed disperser, and then 0.2 parts of hexadecyltrimethylammonium bromide are added, and dispersed at 1000 rpm for 30 min in a high-speed disperser to obtain waterborne polyurethane adhesive.

[0077] Comparative Example 3

[0078] The synthesis steps of waterborne polyurethane are the same as in Example 6, except that in S4, 100 parts of waterborne polyurethane are taken, 4 parts of chain extender ethylenediamine are added, and the mixture is dispersed at 1000 rpm for 15 min in a high-speed disperser. Then, 6 parts of KH560 oligomer (Jiangxi Hongbai New Materials, brand name HP187 oligomer) and 0.2 parts of hexadecyltrimethylammonium bromide are added, and the mixture is dispersed at 1000 rpm for 30 min in a high-speed disperser to obtain waterborne polyurethane adhesive.

[0079] Comparative Example 4

[0080] Amino-containing silica sol was synthesized by sol-gel method. 24 parts of amino-containing silane coupling agent γ-aminopropyltriethoxysilane (KH550) were added to a flask along with 65 parts of ethanol, 5 parts of deionized water and 6 parts of tetraethyl orthosilicate. The mixture was heated to 60°C and reacted for 3 hours, then cooled to room temperature and aged for 24 hours to obtain amino-containing silica sol.

[0081] Comparative Example 5

[0082] The synthesis steps of waterborne polyurethane are the same as in Example 2, except that in S4, 100 parts of waterborne polyurethane are taken, 4 parts of chain extender ethylenediamine and 10 parts of amino-containing silica hydrosol prepared in Comparative Example 4 are added sequentially, dispersed at 1000 rpm for 15 min in a high-speed disperser, and then 6 parts of KH560 oligomer (Jiangxi Hongbai New Materials, brand name HP187 oligomer) are added, and dispersed at 1000 rpm for 30 min in a high-speed disperser to obtain waterborne polyurethane adhesive.

[0083] Testing: The performance of the waterborne polyurethane adhesive samples prepared in the above examples and comparative examples was tested, and the test results are listed in Table 1.

[0084] Sample preparation: The prepared waterborne polyurethane adhesive samples were uniformly brushed onto the surfaces of 25*20mm polyvinyl chloride (PVC) leather, ABS sheets, and polyurethane (PU) semi-rigid foam substrates, and baked at 80℃ for 15 minutes. The ABS sheets coated with adhesive were then bonded together with the polyurethane (PU) semi-rigid foam substrate and the PVC leather, respectively, and a pressure of 0.2MPa was applied for 15 seconds to obtain the bonded samples.

[0085] Adhesion strength test: The bonded ABS sheet and polyurethane (PU) semi-rigid foam substrate, and the ABS sheet and polyvinyl chloride (PVC) leather were heat-cured at 105°C for 30 minutes, and then left at room temperature for 72 hours before performance testing.

[0086] Heat resistance test: Place the laminated ABS sheet with polyurethane (PU) semi-rigid foam substrate and ABS sheet with polyvinyl chloride (PVC) leather in a 100℃ oven for 24 hours and observe whether the glue comes off.

[0087] Moisture and heat resistance test: The laminated ABS sheet and polyurethane (PU) semi-rigid foam substrate, and ABS sheet and polyvinyl chloride (PVC) leather were placed in a test chamber at 85% humidity and 85°C for 24 hours to test their peel strength.

[0088] Thermal cycling test: The laminated ABS sheet with polyurethane (PU) semi-rigid foam substrate and ABS sheet with polyvinyl chloride (PVC) leather were subjected to the following conditions at 80% relative humidity: the temperature was raised from 30°C to 80°C and maintained for 4 hours; the temperature was lowered from 80°C to -40°C and maintained for 4 hours at 30% relative humidity; the temperature was raised from -40°C to 25°C and maintained for 1 hour at 30% relative humidity. This process constitutes one cycle. After three cycles, the peel strength of the laminated sheets was tested.

[0089] Storage stability test of waterborne polyurethane: The prepared waterborne polyurethane adhesive sample was placed in a sample bottle and sealed. It was then placed in an oven at 60±2℃ for 7 days. After being taken out and cooled to room temperature, the flowability of the adhesive was observed to see if it was normal and whether there was any sediment at the bottom of the sample bottle.

[0090] The results of the above tests are listed in Table 1.

[0091] Table 1

[0092]

[0093] Analysis of the results in Table 1 shows that the waterborne polyurethane adhesives prepared in Examples 2-5, through the addition of carboxyl-containing silica sol, KH560 oligomer, and hexadecyltrimethylammonium chloride or hexadecyltrimethylammonium bromide, catalyze the reaction between the epoxy groups in the KH560 oligomer and the carboxyl groups in the carboxyl-containing silica sol and the dimethylolpropionic acid introduced into the polyurethane molecule. This catalyzes the construction of a multi-linked network, tightly binding the carboxyl-containing silica sol and the polyurethane prepolymer through strong chemical bonds, forming a polyurethane-KH560 oligomer-nano silica chemical bond network. The nano silica is firmly fixed in the crosslinked network, preventing agglomeration and greatly improving the cohesive strength, heat resistance, and water resistance of the waterborne polyurethane adhesive system. Simultaneously, the KH560 oligomer contains multiple repeating Si-O-Si bonds, which can act as flexible bridges in the crosslinked network to disperse stress, preventing cohesive breakdown during alternating hot and cold cycles that could lead to the failure of the waterborne polyurethane adhesive.

[0094] Finally, in addition to acting as a catalyst for epoxy ring opening, hexadecyltrimethylammonium chloride or hexadecyltrimethylammonium bromide also provides long-lasting antibacterial ability, preventing waterborne polyurethane adhesives from aging, degrading, or producing odors due to microbial growth. They are particularly suitable for protection against microbial erosion in humid and hot environments.

[0095] Comparative Example 1 did not use KH560 oligomer and carboxyl-containing nano-silica. The corresponding waterborne polyurethane adhesive had significantly worse heat resistance, damp heat resistance, and thermal cycling resistance. The adhesive was unreliable and difficult to use for bonding automotive interiors.

[0096] Comparative Example 2 did not use KH560 oligomers containing epoxy groups. It was difficult to form a stable chemical bond cross-linking network by relying solely on nano-silica containing carboxyl groups and waterborne polyurethane. Therefore, it also had the problem of poor heat resistance, damp heat resistance and cold and heat cycling resistance.

[0097] Comparative Example 3 did not use carboxyl-containing silica sol, relying solely on KH560 oligomer and waterborne polyurethane for crosslinking. The lack of silica sol resulted in a decrease in the strength of the crosslinked network and the absence of a component with a low coefficient of thermal expansion (CTE). The destructive force of high- and low-temperature cycling on the adhesive stems from the internal stress generated by the different CTEs of each component. Connecting low-CTE silica sol to the adhesive matrix through chemical bonds reduces the overall CTE, effectively transferring and dispersing internal stress from the organic phase to the high-modulus inorganic network, thus preventing stress concentration. Therefore, the lack of silica sol in Comparative Example 3 led to a significant reduction in its resistance to thermal cycling.

[0098] Comparative Example 5 uses the amino-containing silica sol prepared in Comparative Example 4 instead of the carboxyl-containing silica sol prepared in Example 1. It can also achieve the same heat resistance, damp heat resistance and thermal cycling resistance of waterborne polyurethane adhesives. However, since amino and epoxy groups can react at room temperature and are difficult to control, the stability of waterborne polyurethane adhesives is poor.

[0099] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of them. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention. Although the specific embodiments of the present invention have been described above, they are not intended to limit the protection scope of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A water-based polyurethane adhesive, characterized in that, Waterborne polyurethane adhesives include: Polyurethane prepolymers, diamines, oligomers containing epoxy-containing silane coupling agents, carboxyl-containing silica sols, and quaternary ammonium salt compounds; The raw materials of the polyurethane prepolymer include polyol chain extender, hydrophilic chain extender, polyol, diisocyanate and catalyst. The polyurethane prepolymer is end-capped with -NCO groups. The hydrophilic chain extender is a polyol or polyamine containing at least one -COOH or -SO3H group. The epoxy-containing silane coupling agent oligomer is selected from oligomers of γ-glycidyl etheroxypropyltrimethoxysilane or oligomers of γ-glycidyl etheroxypropyltriethoxysilane. The carboxyl-containing silica sol is prepared by a sol-gel reaction between a carboxyl-containing silane coupling agent and an organic ester of orthosilicate. The quaternary ammonium salt compound is selected from tetraalkylammonium halides; The polyurethane prepolymer comprises the following raw materials in parts by weight: 110-150 parts of polyol, 45-70 parts of diisocyanate, 3-10 parts of hydrophilic chain extender, 10-20 parts of polyol chain extender, and 0.001-0.01 parts of catalyst. The polyol chain extender is any one of polycarbonate diol and 1,4-butanediol, 1,6-hexanediol, and 1,3-butanediol; By weight, the polyurethane prepolymer comprises 90-110 parts, the diamine 1-10 parts, the oligomer containing epoxy silane coupling agent 3-15 parts, the silica sol containing carboxyl groups 5-20 parts, and the quaternary ammonium salt compound 0.1-0.5 parts.

2. The waterborne polyurethane adhesive according to claim 1, characterized in that, The hydrophilic chain extender is selected from one or more combinations of dimethylolpropionic acid, dimethylolbutyric acid, sodium 1,4-butanediol-2-sulfonate and sodium ethylenediaminoethanesulfonate; And / or, the diisocyanate is selected from one or more of the following: isophorone diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and 1,6-hexanediisocyanate; And / or, the catalyst is selected from any one or more of organobismuth catalysts and organotin catalysts.

3. The waterborne polyurethane adhesive according to claim 1, characterized in that, The polyol is selected from one or two of polyester polyols or polyether polyols.

4. The waterborne polyurethane adhesive according to claim 3, characterized in that, The polyester polyol is selected from aliphatic polyester polyols.

5. The waterborne polyurethane adhesive according to claim 3, characterized in that, The polyester polyol is selected from one or more of the following: acetic acid-based polyester polyol, phthalic acid-based polyester polyol, or polycaprolactone polyol.

6. The waterborne polyurethane adhesive according to claim 3, characterized in that, The polyether polyol is selected from one or more of the following: polytetrahydrofuran ether diol and polypropylene glycol.

7. The waterborne polyurethane adhesive according to claim 1, characterized in that, The carboxyl-containing silane coupling agent is obtained by Michael addition reaction of piperazine methyltriethoxysilane with acrylic acid; And / or, the organic ester of orthosilicate is selected from any one of methyl orthosilicate, ethyl orthosilicate, or propyl orthosilicate.

8. The waterborne polyurethane adhesive according to claim 1, characterized in that, The sol-gel reaction process of the carboxyl-containing silane coupling agent and orthosilicate organic ester includes: adding 20-30 parts of carboxyl-containing silane coupling agent, 1-10 parts of orthosilicate organic ester, 60-70 parts of alcohol solvent and 1-10 parts of deionized water into a reaction vessel, adjusting the pH of the reaction system to 7-9, then heating to 50-70℃ and reacting for 1-4 hours, and after the reaction is completed, cooling to room temperature and aging for 12-48 hours to obtain carboxyl-containing silica sol.

9. The waterborne polyurethane adhesive according to claim 1, characterized in that, The method for preparing the polyurethane prepolymer includes: S1. The polyol is dehydrated under vacuum, and then polyol, hydrophilic chain extender, acetone and diisocyanate are added to the reaction vessel and mixed and reacted. Then polyol chain extender is added and reacted, and then catalyst is added and reacted until the -NCO content of the reaction mixture is <10wt%. S2, Neutralization reaction: The polyurethane prepolymer is cooled to 30-60°C, and a neutralizing agent is added under the shearing action of a high-speed disperser, and the reaction is carried out for 5-60 minutes; S3, the deketolization process, sets the temperature to 40-60℃, and the pressure inside the container to no more than 0.1Pa, removing acetone through vacuum; The neutralizing agent is selected from any one of ammonia, triethylamine, N,N-dimethylethanolamine, or triethanolamine.

10. The method for preparing the waterborne polyurethane adhesive according to any one of claims 1-9, characterized in that, The polyurethane prepolymer, diamine, oligomer containing epoxy silane coupling agent, silica sol containing carboxyl groups, and quaternary ammonium salt compound are mixed and then dispersed uniformly by mechanical methods. The diamine is selected from either diamine or ethylenediamine.

11. The method for preparing the waterborne polyurethane adhesive according to claim 10, characterized in that, The polyurethane prepolymer is first mechanically mixed with diamine and carboxyl-containing silica sol until homogeneous. Then, oligomers containing epoxy-containing silane coupling agents and quaternary ammonium salt compounds are added and mixed mechanically until homogeneous.

12. An application characterized in that, The use of the waterborne polyurethane adhesive as described in any one of claims 1-9 for bonding between a polyurethane substrate and a plastic substrate, and between a polyvinyl chloride substrate and a plastic substrate; Wherein, the polyurethane substrate is selected from polyurethane semi-rigid foam substrate; The polyvinyl chloride material is selected from polyvinyl chloride leather; The plastic substrate includes any one of polybutylene terephthalate, polycarbonate, polyamide, acrylonitrile-butadiene-styrene copolymer, and polyphenylene sulfide.

13. An application characterized in that, The application of the waterborne polyurethane adhesive as described in any one of claims 1-9 in the bonding of automotive interior trim.

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