Special polyurethane adhesive and its preparation method and application

Abstract

The present application relates to the technical field of polyurethane adhesive, and particularly discloses a special polyurethane adhesive as well as a preparation method and application thereof.The special polyurethane adhesive comprises the following raw materials in parts by weight: 40-45 parts of castor oil, 25-30 parts of polycaprolactone glycol, 30-35 parts of isophorone diisocyanate, 0.05-0.1 parts of dibutyltin dilaurate, 5-8 parts of dimethylol propionic acid, 3-5 parts of a sulfur-containing chain extender, 4-6 parts of a functional filler, 3-5 parts of hexadecyl trimethoxysilane, 8-12 parts of hydroxyethyl methacrylate, 0.8-1.2 parts of a photoinitiator, and 60-70 parts of deionized water.The special polyurethane adhesive prepared by the present application has unique raw material formula and process, and has the characteristics of photocuring and water dispersion;after curing, a dense crosslinked network is formed, and the adhesive exhibits excellent moisture resistance, interfacial bonding strength and mechanical stability, and is suitable for the surface of materials with high-performance bonding requirements in the fields of automobiles, electronics, construction and aerospace.

Description

Technical Field

[0001] This invention relates to the field of polyurethane adhesives, and specifically discloses a special polyurethane adhesive, its preparation method, and its application. Background Technology

[0002] Polyurethane adhesives are widely used in automotive, electronics, construction, and aerospace industries, where high-performance bonding is critical, due to their excellent flexibility, low-temperature resistance, and good adhesion properties. However, with increasingly stringent requirements for material performance across industries, particularly in the context of humid and hot environments, high-reliability connections, and increasingly stringent environmental regulations, developing novel polyurethane adhesives that combine efficient curing characteristics, excellent resistance to humid and hot conditions, high-strength interfacial adhesion, and environmental friendliness has become a pressing technical challenge for the industry.

[0003] While traditional solvent-based polyurethane adhesives possess excellent overall performance, the environmental pollution and health risks posed by solvent evaporation are significant, making them unsuitable for current green manufacturing trends. Waterborne polyurethane adhesives, using water as the dispersion medium, offer the advantage of low VOC emissions; however, their curing process relies on water evaporation, leading to low curing efficiency and insufficient resistance to damp heat aging in humid environments. Furthermore, a single water-based dispersion system struggles to form a highly dense cross-linked network, resulting in a significant decrease in interfacial bond strength under long-term damp heat cycling. In addition, while conventional UV-cured polyurethane systems can achieve rapid curing through UV irradiation, the single-stage UV curing reaction is often limited by insufficient functional group reactivity and cross-linking density, resulting in the cured adhesive layer's mechanical stability and chemical resistance failing to meet the demands of high-requirement applications such as aerospace.

[0004] In terms of functional filler modification, one-dimensional nanomaterials such as halloysite nanotubes, due to their unique tubular structure and large specific surface area, have become ideal choices for improving the mechanical properties of adhesives. However, the compatibility issues between their surface polar groups and the polyurethane matrix lead to poor filler dispersion and insufficient interfacial bonding, making it difficult to fully exert the reinforcing and toughening effects. The introduction of sulfur-containing chain extenders can improve the crosslinking network structure through the special bonding effect of sulfur, but the synthesis of traditional chain extenders suffers from problems such as low reaction efficiency and imprecise functional group control, making it difficult to effectively control the balance between the crosslinking density and toughness of the adhesive layer. Therefore, to address the problems of insufficient resistance to humid heat, limited interfacial bonding strength, single curing method, and poor compatibility of functional fillers in existing technologies, this invention provides a special polyurethane adhesive, its preparation method, and its application to solve the aforementioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a special polyurethane adhesive, its preparation method and application. The prepared polyurethane adhesive adopts a unique raw material formulation and process, and has both photocuring and water dispersibility characteristics. After curing, it forms a dense cross-linked network, exhibiting excellent resistance to damp heat, interfacial bonding strength and mechanical stability. It is suitable for material surfaces in the automotive, electronics, construction and aerospace fields that require high-performance bonding.

[0006] This invention provides a special polyurethane adhesive, employing the following technical solution:

[0007] A special polyurethane adhesive is composed of the following raw materials in parts by weight: 40-45 parts castor oil, 25-30 parts polycaprolactone diol, 30-35 parts isophorone diisocyanate, 0.05-0.1 parts dibutyltin dilaurate, 5-8 parts dimethylolpropionic acid, 3-5 parts sulfur-containing chain extender, 4-6 parts functional filler, 3-5 parts hexadecyltrimethoxysilane, 8-12 parts hydroxyethyl methacrylate, 0.8-1.2 parts photoinitiator, and 60-70 parts deionized water.

[0008] A second objective of this invention is to provide a method for preparing the special polyurethane adhesive, comprising the following steps:

[0009] S1. Castor oil and polycaprolactone diol are vacuum dehydrated at 110-120℃ for 1-2 hours, cooled to 78-82℃, and isophorone diisocyanate and dibutyltin dilaurate are added. The mixture is reacted in a nitrogen atmosphere for 2-4 hours to obtain polyurethane prepolymer.

[0010] S2. The polyurethane prepolymer is cooled to 65-70℃, and dimethylolpropionic acid and sulfur-containing chain extender are added in sequence. The reaction is carried out at 75-80℃ for 1-2 hours. Functional filler and hexadecyltrimethoxysilane are added, and the reaction is carried out at 60-65℃ for 2-4 hours to obtain the modified prepolymer.

[0011] S3. Add hydroxyethyl methacrylate and photoinitiator to the modified prepolymer, react at 60-65℃ until the -NCO content is ≤2%, add triethylamine to adjust the pH to neutral, add deionized water at high speed of 10000-15000rpm for 20-30min, and finally degas under vacuum to obtain a special polyurethane adhesive.

[0012] Preferably, the preparation step of the sulfur-containing chain extender in step S2 is as follows: 2,2-dihydroxymethylbutyric acid and thioglycolic acid are dissolved in acetone, triethylamine is added, and the mixture is refluxed at 75-80°C for 4-6 hours under nitrogen protection, followed by vacuum distillation, and the resulting product is the sulfur-containing chain extender.

[0013] Preferably, the preparation steps of the sulfur-containing chain extender are, by weight, 10-15 parts of 2,2-dihydroxymethylbutyric acid, 5-8 parts of thioglycolic acid, 40-45 parts of acetone and 0.5-0.8 parts of triethylamine.

[0014] Preferably, the preparation step of the functional filler in step S2 is as follows:

[0015] A1. Halloysite nanotubes were dispersed in toluene and sonicated for 30-35 min. Hexadecyltrimethoxysilane and concentrated hydrochloric acid were added, and the mixture was refluxed at 78-84℃ under nitrogen protection for 20-24 h. After centrifugation, washing and drying, modified halloysite nanotubes were obtained.

[0016] A2. Vanillin and bis(4-hydroxyphenyl) disulfide were dissolved in toluene, p-toluenesulfonic acid was added, and the mixture was refluxed at 105-110℃ for 6-8 hours. After vacuum distillation, recrystallization and drying were performed to obtain vanillin-grafted disulfide.

[0017] A3. Modified halloysite nanotubes and vanillin-grafted disulfide are mixed at a mass ratio of (5-8):(1-3), stirred at 68-75℃ for 1-2 hours, and then filtered and dried to obtain the functional filler.

[0018] Preferably, step A1 comprises, by weight, 8-12 parts halloysite nanotubes, 30-35 parts toluene, 3-5 parts hexadecyltrimethoxysilane, and 0.5-1 parts concentrated hydrochloric acid.

[0019] Preferably, step A2 comprises, by weight, 5-8 parts vanillin, 3-6 parts bis(4-hydroxyphenyl) disulfide, 30-35 parts toluene, and 0.2-0.5 parts p-toluenesulfonic acid.

[0020] Preferably, the photoinitiator in step S3 is 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0021] The special polyurethane adhesive designed in this invention is used in the automotive, electronics, construction or aerospace fields for bonding material surfaces that require resistance to moisture and heat and high-strength adhesion.

[0022] In summary, the present invention has the following beneficial effects:

[0023] 1. This invention combines sulfur-containing chain extenders, functional fillers, modified prepolymers, and other raw materials with deionized water to construct a special polyurethane adhesive system that combines photocuring and water dispersibility. The sulfur-containing chain extender, through its unique bonding ability, forms stable chemical bonds between polyurethane molecular chains, optimizing the cross-linking network structure. The functional filler undergoes special modification treatment, effectively improving its compatibility with the polyurethane matrix and enhancing the system's stability. The modified prepolymer, under the synergistic effect of multiple raw materials, endows the adhesive with excellent mechanical properties and environmental adaptability. The photoinitiator and hydroxyethyl methacrylate work synergistically to enable the adhesive to rapidly initiate a free radical polymerization reaction under light irradiation, achieving rapid curing and significantly improving production efficiency. Furthermore, the use of castor oil, polycaprolactone diol, and other raw materials to prepare the polyurethane prepolymer reduces dependence on traditional petrochemical resources, lowering production costs and environmental impact.

[0024] 2. The functional filler of this invention is prepared by silane coupling modification of halloysite nanotubes and composite with vanillin-grafted disulfide. The unique tubular structure of the modified halloysite nanotubes forms physical cross-linking points in the polyurethane matrix, while the active groups in the vanillin-grafted disulfide chemically react with the polyurethane molecular chains, forming a stable interfacial bond. This structure allows the functional filler to be uniformly dispersed in the matrix, giving the adhesive excellent cohesive strength and toughness, enabling it to adapt to the bonding requirements of different material surfaces. Simultaneously, the functional filler effectively inhibits degradation reactions under humid and hot environments, maintains the stability of the adhesive's physicochemical properties, and significantly improves its resistance to humid and hot conditions.

[0025] 3. The sulfur-containing chain extender designed in this invention introduces thioether bonds and carboxyl active groups into the molecular structure through the esterification reaction of thioglycolic acid and 2,2-dihydroxymethylbutyric acid. The unique electronic structure of sulfur significantly enhances the polar interactions between polyurethane molecular chains, forming a denser network structure during crosslinking. This chain extender not only precisely controls the chain length and crosslinking point distribution of the polyurethane prepolymer, endowing the adhesive with excellent flexibility and impact resistance, but also effectively inhibits molecular chain breakage and hydrolysis reactions under humid and hot environments through the chemical stability of the thioether bonds, thereby significantly improving the adhesive layer's resistance to humid and hot aging and its long-term service reliability. Furthermore, the synergistic effect of the sulfur-containing groups and the active sites on the surface of the functional filler further enhances the interfacial bonding force between the filler and the matrix, enabling the adhesive to form a high-strength bonding interface on various material surfaces. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the experimental materials used, unless otherwise specified, were all purchased from conventional biochemical reagent stores. All quantitative experiments in the following examples were performed in triplicate, and the data are the average of the three replicates or the average ± standard deviation.

[0028] Example 1

[0029] A method for preparing a special polyurethane adhesive includes the following preparation steps:

[0030] Preparation of sulfur-containing chain extender: 10g of 2,2-dihydroxymethylbutyric acid, 5g of thioglycolic acid, 40g of acetone and 0.5g of triethylamine were added to a three-necked flask and refluxed at 75°C for 6h with stirring at 300rpm under nitrogen protection. Then, acetone and excess triethylamine were removed by vacuum distillation to obtain sulfur-containing chain extender.

[0031] Preparation of functional fillers: A1. 8g halloysite nanotubes were dispersed in 30g toluene and treated with ultrasound at 200W and 40kHz for 30min. Then, 3g hexadecyltrimethoxysilane and 0.5g concentrated hydrochloric acid were added, and the mixture was refluxed at 250rpm for 24h under nitrogen protection at 78℃. After centrifugation, washing and drying, modified halloysite nanotubes were obtained. A2. 5g vanillin, 3g bis(4-hydroxyphenyl) disulfide, 30g toluene and 0.2g p-toluenesulfonic acid were mixed and refluxed at 200rpm for 8h at 105℃. After vacuum distillation, recrystallization and drying, vanillin-grafted disulfide was obtained. A3. 5g modified halloysite nanotubes and 1g vanillin-grafted disulfide were mixed and stirred at 300rpm for 2h at 68℃. After filtration and drying, functional fillers were obtained.

[0032] Preparation of adhesive: S1, 40g castor oil and 25g polycaprolactone diol were added to a reaction vessel and dehydrated for 2h at 110℃ and vacuum degree -0.1MPa. The temperature was then lowered to 78℃, and 30g isophorone diisocyanate and 0.05g dibutyltin dilaurate were added. The mixture was reacted for 4h at a stirring rate of 200rpm in a nitrogen atmosphere to obtain a polyurethane prepolymer. S2: The polyurethane prepolymer was cooled to 65℃, and 5g dimethylolpropionic acid and 3g sulfur-containing chain extender were added sequentially. The mixture was reacted for 2h at 75℃ and stirring rate of 200rpm. Then, 4g functional filler and 3g hexadecyltrimethoxysilane were added. The mixture was reacted for 4h at 60℃ and stirring rate of 200rpm to obtain a modified prepolymer. S3: Add 8g of hydroxyethyl methacrylate and 0.8g of 2-hydroxy-2-methyl-1-phenyl-1-propanone to the modified prepolymer. React at 60℃ and 200rpm until the -NCO content is ≤2%. Add triethylamine dropwise to adjust the pH to neutral. Then add 60g of deionized water under high-speed emulsification at 10000rpm and emulsify for 30min. Finally, degas at a vacuum of -0.1MPa and 60℃ for 1h to obtain a special polyurethane adhesive.

[0033] Example 2

[0034] A method for preparing a special polyurethane adhesive includes the following preparation steps:

[0035] Preparation of sulfur-containing chain extender: 12g of 2,2-dihydroxymethylbutyric acid, 6g of thioglycolic acid, 42g of acetone and 0.6g of triethylamine were refluxed at 78℃ for 5h with a stirring rate of 350rpm under nitrogen protection, and then the sulfur-containing chain extender was obtained by vacuum distillation.

[0036] Preparation of functional fillers: A1. 10g halloysite nanotubes were dispersed in 32g toluene and treated with ultrasound at 250W and 40kHz for 33min. 4g hexadecyltrimethoxysilane and 0.7g concentrated hydrochloric acid were added, and the mixture was refluxed at 280rpm for 22h under nitrogen protection at 80℃. After centrifugation, washing, and drying, modified halloysite nanotubes were obtained. A2. 6g vanillin, 4g bis(4-hydroxyphenyl) disulfide, 32g toluene, and 0.3g p-toluenesulfonic acid were mixed and refluxed at 220rpm for 7h at 108℃. After vacuum distillation, recrystallization, and drying, vanillin-grafted disulfide was obtained. A3. 6g modified halloysite nanotubes were mixed with 2g vanillin-grafted disulfide and stirred at 320rpm for 1.5h at 70℃. After filtration and drying, functional fillers were obtained.

[0037] Preparation of adhesive: S1, 42g castor oil and 27g polycaprolactone diol were dehydrated at 115℃ and vacuum degree -0.1MPa for 1.5h, then cooled to 80℃, and 32g isophorone diisocyanate and 0.07g dibutyltin dilaurate were added. The mixture was reacted at a stirring rate of 220rpm for 3h in a nitrogen atmosphere to obtain a polyurethane prepolymer; S2, the polyurethane prepolymer was cooled to 67℃, and 6g dimethylolpropionic acid and 4g sulfur-containing chain extender were added sequentially. The mixture was reacted at 78℃ and stirring at 220rpm for 1.5h, and then 5g functional filler and 4g hexadecyl sulfate were added. Alkyltrimethoxysilane was reacted at 62℃ and 220 rpm for 3 h to obtain a modified prepolymer; S3, 10 g of hydroxyethyl methacrylate and 1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone were added to the modified prepolymer and reacted at 62℃ and 220 rpm until the -NCO content was ≤2%. Triethylamine was added dropwise to adjust the pH value to neutral. Then, 65 g of deionized water was added under high-speed emulsification at 12000 rpm and emulsified for 25 min. Finally, degassing was carried out at a vacuum of -0.1 MPa and 60℃ for 0.8 h to obtain a special polyurethane adhesive.

[0038] Example 3

[0039] A method for preparing a special polyurethane adhesive includes the following preparation steps:

[0040] Preparation of sulfur-containing chain extender: 15g of 2,2-dihydroxymethylbutyric acid, 8g of thioglycolic acid, 45g of acetone and 0.8g of triethylamine were reacted under nitrogen protection at 80℃ with stirring at 400rpm for 4h, and the sulfur-containing chain extender was obtained by vacuum distillation.

[0041] Preparation of functional fillers: A1. 12g halloysite nanotubes were dispersed in 35g toluene and treated with ultrasound at 300W and 40kHz for 35min. 5g hexadecyltrimethoxysilane and 1g concentrated hydrochloric acid were added, and the mixture was refluxed at 300rpm for 20h under nitrogen protection at 84℃. After centrifugation, washing and drying, modified halloysite nanotubes were obtained. A2. 8g vanillin, 6g bis(4-hydroxyphenyl) disulfide, 35g toluene and 0.5g p-toluenesulfonic acid were mixed and refluxed at 250rpm for 6h at 110℃. After vacuum distillation, recrystallization and drying, vanillin-grafted disulfide was obtained. A3. Modified halloysite nanotubes (8g) and vanillin-grafted disulfide (3g) were mixed and stirred at 350rpm for 1h at 75℃. After filtration and drying, functional fillers were obtained.

[0042] Preparation of adhesive: S1. Place 45g castor oil and 30g polycaprolactone diol in a reactor and dehydrate for 1h at 120℃ and a vacuum of -0.1MPa. Cool to 82℃, add 35g isophorone diisocyanate and 0.1g dibutyltin dilaurate, and react for 2h at a stirring rate of 250rpm under a nitrogen atmosphere to obtain a polyurethane prepolymer; S2. Cool the polyurethane prepolymer to 70℃, add 8g dimethylolpropionic acid and 5g sulfur-containing chain extender sequentially, and react for 1h at 80℃ and a stirring rate of 250rpm. Then add 6g functional filler and 5g hexadecane. Trimethoxysilane was reacted at 65℃ and 250 rpm for 2 h to obtain a modified prepolymer; S3, 12 g of hydroxyethyl methacrylate and 1.2 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone were added to the modified prepolymer, and the reaction was carried out at 65℃ and 250 rpm until the -NCO content was ≤2%. Triethylamine was added dropwise to adjust the pH to neutral, and then 70 g of deionized water was added under high-speed emulsification at 15000 rpm for 20 min. Finally, the mixture was degassed at a vacuum of -0.1 MPa and 60℃ for 0.5 h to obtain a special polyurethane adhesive.

[0043] Example 4

[0044] A method for preparing a special polyurethane adhesive includes the following preparation steps:

[0045] Preparation of sulfur-containing chain extender: 13g of 2,2-dihydroxymethylbutyric acid, 6.5g of thioglycolic acid, 43g of acetone and 0.65g of triethylamine were refluxed at 77℃ for 5h with a stirring rate of 330rpm under nitrogen protection, and the sulfur-containing chain extender was obtained by vacuum distillation.

[0046] Preparation of functional fillers: A1. 10g halloysite nanotubes were dispersed in 33g toluene and treated with ultrasound at 250W and 40kHz for 33min. 4g hexadecyltrimethoxysilane and 0.7g concentrated hydrochloric acid were added, and the mixture was refluxed at 270rpm for 23h under nitrogen protection at 81℃. After centrifugation, washing, and drying, modified halloysite nanotubes were obtained. A2. 6.5g vanillin, 4.5g bis(4-hydroxyphenyl) disulfide, 33g toluene, and 0.35g p-toluenesulfonic acid were mixed and refluxed at 230rpm for 7h at 107℃. After vacuum distillation, recrystallization, and drying, vanillin-grafted disulfide was obtained. A3. 6.5g modified halloysite nanotubes were mixed with 2.5g vanillin-grafted disulfide and stirred at 330rpm for 1.5h at 72℃. After filtration and drying, functional fillers were obtained.

[0047] Preparation of adhesive: S1, 43g castor oil and 28g polycaprolactone diol were dehydrated at 118℃ and vacuum degree -0.1MPa for 1.2h, then cooled to 81℃, and 33g isophorone diisocyanate and 0.08g dibutyltin dilaurate were added. The mixture was reacted at a stirring rate of 230rpm for 2.5h in a nitrogen atmosphere to obtain a polyurethane prepolymer; S2, the polyurethane prepolymer was cooled to 68℃, and 6.5g dimethylolpropionic acid and 4g sulfur-containing chain extender were added sequentially. The mixture was reacted at 77℃ and stirring at 230rpm for 1.5h, and then 5g functional filler and 4g... Hexadecyltrimethoxysilane was reacted at 63℃ and 230 rpm for 3 h to obtain a modified prepolymer; S3, 10 g of hydroxyethyl methacrylate and 1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone were added to the modified prepolymer and reacted at 63℃ and 230 rpm until the -NCO content was ≤2%. Triethylamine was added dropwise to adjust the pH value to neutral. Then, 68 g of deionized water was added under high-speed emulsification at 13000 rpm and emulsified for 25 min. Finally, degassing was carried out at a vacuum of -0.1 MPa and 60℃ for 0.7 h to obtain a special polyurethane adhesive.

[0048] Comparative Example 1

[0049] A method for preparing a special polyurethane adhesive differs from Example 4 in that the sulfur-containing chain extender does not incorporate thioglycolic acid. Specifically, the preparation steps of the sulfur-containing chain extender are as follows: 13g of 2,2-dihydroxymethylbutyric acid, 6.5g of glycolic acid, 43g of acetone, and 0.65g of triethylamine are added to a three-necked flask. Under nitrogen protection, the mixture is refluxed at 77°C with a stirring rate of 330rpm for 5 hours. Then, acetone and excess triethylamine are removed by vacuum distillation to obtain a chain extender without sulfur structure. The composition of the remaining raw materials and the preparation method are the same as in Example 4.

[0050] Comparative Example 2

[0051] A method for preparing a special polyurethane adhesive differs from Example 4 in that modified halloysite nanotubes are not used. Specifically, the preparation steps of the functional filler are as follows: A1. 10g of halloysite nanotubes, without modification by hexadecyltrimethoxysilane, are directly used in subsequent steps. A2. 6.5g of vanillin, 4.5g of bis(4-hydroxyphenyl) disulfide, 33g of toluene, and 0.35g of p-toluenesulfonic acid are mixed and refluxed at 107°C with a stirring rate of 230 rpm for 7 hours. The mixture is then distilled under reduced pressure, recrystallized, and dried to obtain vanillin-grafted disulfide. A3. 10g of unmodified halloysite nanotubes are mixed with 2.5g of vanillin-grafted disulfide and stirred at 72°C with a stirring rate of 330 rpm for 1.5 hours. The mixture is then filtered and dried to obtain the functional filler. The composition of the remaining raw materials and the preparation method are the same as in Example 4.

[0052] Comparative Example 3

[0053] A method for preparing a special polyurethane adhesive differs from Example 4 in that the functional filler is not modified with vanillin grafting. Specifically, the preparation steps of the functional filler are as follows: A1. 10g of halloysite nanotubes are dispersed in 33g of toluene and treated with ultrasound at 250W and 40kHz for 33min. Then, 4g of hexadecyltrimethoxysilane and 0.7g of concentrated hydrochloric acid are added, and the mixture is refluxed at 270rpm for 23h under nitrogen protection at 81℃. After centrifugation, washing, and drying, modified halloysite nanotubes are obtained and used directly as the functional filler. The composition of the remaining raw materials and the preparation method are the same as in Example 4.

[0054] Comparative Example 4

[0055] A method for preparing a special polyurethane adhesive differs from Example 4 in that the photoinitiator is prepared by physical mixing. Specifically, the preparation steps of the adhesive are as follows: S1, 43g of castor oil and 28g of polycaprolactone diol are dehydrated at 118°C and a vacuum of -0.1MPa for 1.2h, then cooled to 81°C, and 33g of isophorone diisocyanate and 0.08g of dibutyltin dilaurate are added. The mixture is reacted at a stirring rate of 230rpm in a nitrogen atmosphere for 2.5h to obtain a polyurethane prepolymer. S2, the polyurethane prepolymer is cooled to 68°C, and 6.5g of dimethylolpropionic acid and 4g of sulfur-containing chain extender are added sequentially. The mixture is reacted at 77°C and a stirring rate of 230rpm for 1.5h, then 5g of functional filler and 4g of hexadecyltrimethoxysilane are added. The mixture is reacted at 63°C and a stirring rate of 230rpm for 3h to obtain a modified prepolymer. S3: 1g of 2-hydroxy-2-methyl-1-phenyl-1-propanone was mechanically blended with the modified prepolymer. After stirring at 63℃ and 230rpm for 30min, triethylamine was added dropwise to adjust the pH to neutral. Then, 68g of deionized water was added under high-speed emulsification at 13000rpm, and emulsification was carried out for 25min. Finally, the mixture was degassed at -0.1MPa and 60℃ for 0.7h to obtain a special polyurethane adhesive. The composition of the remaining raw materials and the preparation method were the same as in Example 4.

[0056] Comparative Example 5

[0057] A method for preparing a special polyurethane adhesive differs from Example 4 in that no sulfur-containing chain extender is added. Specifically, the preparation steps of the adhesive are as follows: S1, 43g of castor oil and 28g of polycaprolactone diol are dehydrated at 118°C and a vacuum of -0.1MPa for 1.2h, then cooled to 81°C, and 33g of isophorone diisocyanate and 0.08g of dibutyltin dilaurate are added. The mixture is reacted at a stirring rate of 230rpm for 2.5h in a nitrogen atmosphere to obtain a polyurethane prepolymer; S2, the polyurethane prepolymer is cooled to 68°C, and 6.5g of dimethylolpropionic acid is added sequentially. The mixture is reacted at 77°C and a stirring rate of 230rpm for 1.5h, and then 5g of functional filler and 4g of hexadecyltrimethylolpropionic acid are added. Methoxysilane was reacted at 63°C and 230 rpm for 3 hours to obtain a modified prepolymer. In step S3, 10 g of hydroxyethyl methacrylate and 1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone were added to the modified prepolymer, and the reaction was carried out at 63°C and 230 rpm until the -NCO content was ≤2%. Triethylamine was added dropwise to adjust the pH to neutral. Then, 68 g of deionized water was added under high-speed emulsification at 13000 rpm, and emulsification was carried out for 25 minutes. Finally, degassing was performed at -0.1 MPa and 60°C for 0.7 hours to obtain a special polyurethane adhesive without added sulfur-containing chain extenders. The remaining raw material composition and preparation method were the same as in Example 4.

[0058] Comparative Example 6

[0059] A method for preparing a special polyurethane adhesive differs from Example 4 in that the polyurethane prepolymer is not modified with functional fillers. Specifically, the preparation steps of the adhesive are as follows: S1, 43g of castor oil and 28g of polycaprolactone diol are dehydrated at 118°C and a vacuum of -0.1MPa for 1.2h, then cooled to 81°C, and 33g of isophorone diisocyanate and 0.08g of dibutyltin dilaurate are added. The mixture is reacted at a stirring rate of 230rpm in a nitrogen atmosphere for 2.5h to obtain the polyurethane prepolymer. S2: The polyurethane prepolymer is cooled to 68°C, and 6.5g of dimethylolpropionic acid and 4g of sulfur-containing chain extender are added sequentially. The mixture is reacted at 77°C and a stirring rate of 230rpm for 1.5h, and then 4g of hexadecyltrimethoxysilane is added. The mixture is reacted at 63°C and a stirring rate of 230rpm for 3h to obtain the prepolymer without added functional fillers. S3: 10g of hydroxyethyl methacrylate and 1g of 2-hydroxy-2-methyl-1-phenyl-1-propanone were added to the prepolymer. The mixture was reacted at 63°C and 230rpm until the -NCO content was ≤2%. Triethylamine was added dropwise to adjust the pH to neutral. Then, 68g of deionized water was added under high-speed emulsification at 13000rpm, and emulsification was carried out for 25min. Finally, the mixture was degassed at -0.1MPa and 60°C for 0.7h to obtain a special polyurethane adhesive that had not been modified with functional fillers. The composition of the remaining raw materials and the preparation method were the same as in Example 4.

[0060] Performance testing

[0061] The performance of the special polyurethane adhesives prepared in Examples 1-4 and Comparative Examples 1-6 was tested:

[0062] 1. Moist heat resistance: The tensile strength retention rate (85℃ / 95%RH, 500h) after damp heat aging of the special polyurethane adhesives prepared in Examples 1-4 and Comparative Examples 1-6 was tested according to GB / T1740-2007 standard. The test results are shown in Table 1.

[0063] 2. Mechanical properties: The tensile strength and elongation at break of the special polyurethane adhesives prepared in Examples 1-4 and Comparative Examples 1-6 were tested according to GB / T6329-1996 standard. The test results are shown in Table 1.

[0064] 3. Interface bond strength test: The interface bond strength of the special polyurethane adhesives prepared in Examples 1-4 and Comparative Examples 1-6 was tested in accordance with GB / T7124-2008 standard. The test results are shown in Table 1.

[0065] Table 1

[0066] Test Project Moist heat resistance % Tensile strength MPa Tensile strength at break % Curing time (s) Bond strength MPa Example 1 88 35.2 480 35 15.6 Example 2 91 37.8 510 34 16.8 Example 3 89 36.5 495 36 16.2 Example 4 93 39.0 525 35 17.3 Comparative Example 1 71 28.1 380 62 11.2 Comparative Example 2 68 30.5 350 60 9.80 Comparative Example 3 75 32.0 410 61 12.5 Comparative Example 4 82 34.5 430 58 13.4 Comparative Example 5 65 25.0 310 70 9.10 Comparative Example 6 73 27.5 365 72 10.7

[0067] The special polyurethane adhesives prepared in Examples 1-4 of this invention significantly outperform Comparative Examples 1-6 in terms of moisture heat resistance, tensile strength, elongation at break, curing time, and bond strength. The examples exhibit the highest moisture heat resistance (93%), a highest tensile strength of 39.0 MPa, a highest elongation at break of 525%, a shortest curing time of 34 seconds, and a highest bond strength of 17.3 MPa. In contrast, the comparative examples show a maximum moisture heat resistance of only 82%, a maximum tensile strength of 34.5 MPa, a maximum elongation at break of 430%, a shortest curing time of 58 seconds, and a highest bond strength of 13.4 MPa. This invention achieves a balance between high moisture heat resistance, high-strength adhesion, and rapid curing through synergistic optimization, meeting the engineering application requirements in harsh environments.

[0068] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A special polyurethane adhesive, characterized in that, Composed of the following raw materials in parts by weight: 40-45 parts castor oil, 25-30 parts polycaprolactone diol, 30-35 parts isophorone diisocyanate, 0.05-0.1 parts dibutyltin dilaurate, 5-8 parts dimethylolpropionic acid, 3-5 parts sulfur-containing chain extender, 4-6 parts functional filler, 3-5 parts hexadecyltrimethoxysilane, 8-12 parts hydroxyethyl methacrylate, 0.8-1.2 parts photoinitiator, and 60-70 parts deionized water; The preparation steps of the sulfur-containing chain extender are as follows: 2,2-dihydroxymethylbutyric acid and thioglycolic acid are dissolved in acetone, triethylamine is added, and the mixture is refluxed at 75-80℃ for 4-6 hours under nitrogen protection and then distilled under reduced pressure to obtain the sulfur-containing chain extender. The preparation steps of the functional filler are as follows: A1. Halloysite nanotubes were dispersed in toluene and sonicated for 30-35 min. Hexadecyltrimethoxysilane and concentrated hydrochloric acid were added, and the mixture was refluxed at 78-84℃ under nitrogen protection for 20-24 h. After centrifugation, washing and drying, modified halloysite nanotubes were obtained. A2. Vanillin and bis(4-hydroxyphenyl) disulfide were dissolved in toluene, p-toluenesulfonic acid was added, and the mixture was refluxed at 105-110℃ for 6-8 hours. After vacuum distillation, recrystallization and drying were performed to obtain vanillin-grafted disulfide. A3. Modified halloysite nanotubes and vanillin-grafted disulfide are mixed at a mass ratio of (5-8):(1-3), stirred at 68-75℃ for 1-2 hours, and then filtered and dried to obtain the functional filler.

2. The method for preparing the special polyurethane adhesive according to claim 1, characterized in that, Includes the following steps: S1. Castor oil and polycaprolactone diol are vacuum dehydrated at 110-120℃ for 1-2 hours, cooled to 78-82℃, and isophorone diisocyanate and dibutyltin dilaurate are added. The mixture is reacted in a nitrogen atmosphere for 2-4 hours to obtain polyurethane prepolymer. S2. The polyurethane prepolymer is cooled to 65-70℃, and dimethylolpropionic acid and sulfur-containing chain extender are added in sequence. The reaction is carried out at 75-80℃ for 1-2 hours. Functional filler and hexadecyltrimethoxysilane are added, and the reaction is carried out at 60-65℃ for 2-4 hours to obtain the modified prepolymer. S3. Add hydroxyethyl methacrylate and photoinitiator to the modified prepolymer, react at 60-65℃ until the -NCO content is ≤2%, add triethylamine to adjust the pH to neutral, add deionized water at high speed of 10000-15000rpm for 20-30min, and finally degas under vacuum to obtain a special polyurethane adhesive.

3. The method for preparing the special polyurethane adhesive according to claim 2, characterized in that, The composition is 10-15 parts by weight of 2,2-dihydroxymethylbutyric acid, 5-8 parts of thioglycolic acid, 40-45 parts of acetone and 0.5-0.8 parts of triethylamine.

4. The method for preparing the special polyurethane adhesive according to claim 2, characterized in that, Step A1 consists of 8-12 parts by weight of halloysite nanotubes, 30-35 parts of toluene, 3-5 parts of hexadecyltrimethoxysilane, and 0.5-1 parts of concentrated hydrochloric acid.

5. The method for preparing the special polyurethane adhesive according to claim 2, characterized in that, In step A2, the ingredients are 5-8 parts by weight of vanillin, 3-6 parts by weight of bis(4-hydroxyphenyl) disulfide, 30-35 parts by weight of toluene, and 0.2-0.5 parts by weight of p-toluenesulfonic acid.

6. The method for preparing the special polyurethane adhesive according to claim 2, characterized in that, In step S3, the photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone.

7. The application of the polyurethane adhesive according to claim 1 or the polyurethane adhesive prepared by the method according to any one of claims 2-6, characterized in that, The polyurethane adhesive is used in the automotive, electronics, construction, or aerospace industries for bonding material surfaces that require resistance to moisture and heat and high-strength adhesion.