Two-component polyurethane adhesive as well as preparation method and application thereof

Abstract

The invention discloses a two-component polyurethane adhesive as well as a preparation method and application thereof, and the adhesive comprises a component A and a component B in parts by weight, the component A is prepared from 15 to 30 parts of hydroxyl-terminated polybutadiene, 20 to 40 parts of polyester polyol, 5 to 15 parts of epoxy modified polyether polyol, 1 to 5 parts of phosphate ester, 1 to 5 parts of micromolecular dihydric alcohol chain extender, 2 to 10 parts of silane coupling agent, 1 to 5 parts of thixotropic agent, 20 to 50 parts of filler, 5 to 15 parts of flame retardant and 0.1 to 0.5 part of catalyst; the component B is prepared from the following components in parts by weight: 60 to 80 parts of polyisocyanate and 20 to 40 parts of polyurethane prepolymer. The bi-component polyurethane adhesive is used for bonding SMC or metal, has high strength and high elasticity, balances the thermal expansion coefficient difference between the SMC and the metal, and can realize reliable bonding of the SMC without complex surface treatment.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and in particular to a two-component polyurethane adhesive, its preparation method, and its application. Background Technology

[0002] Sheet molding compounds (SMCs), as fiber-reinforced thermosetting composites, possess advantages such as lightweight, high strength, corrosion resistance, and high design freedom, and are widely used in automotive, aerospace, and construction industries. In practical applications, SMC components often need to be connected and assembled with other SMC components or metal components, but problems such as release agent residue and low surface energy on the SMC surface make bonding difficult.

[0003] Currently, commonly used adhesives for SMC bonding include epoxy resin adhesives, acrylic adhesives, and polyurethane adhesives. Epoxy resin adhesives offer high bonding strength but are brittle after curing and have poor impact resistance; acrylic adhesives cure quickly but have high shrinkage and insufficient durability; polyurethane adhesives, due to their excellent toughness, fatigue resistance, and overall mechanical properties, have become the preferred solution for SMC bonding.

[0004] However, existing polyurethane adhesives still have shortcomings in SMC bonding: First, they have poor adaptability to SMC surfaces and require complex surface treatments (such as sanding and primer) to ensure bonding effect; second, when bonding SMC with dissimilar metal materials, the large difference in thermal expansion coefficients can easily lead to internal stress under thermal cycling conditions, resulting in bonding failure; and third, it is difficult to achieve both high strength and high elasticity at the same time.

[0005] Chinese patent CN117106406A discloses a vegetable oil-based flame-retardant two-component polyurethane adhesive, which can bond substrates including SMC and metals. The bonding strength of aluminum sheets / aluminum sheets reaches more than 15MPa and has excellent flame-retardant properties, but it does not solve the stress problem caused by the difference in thermal expansion coefficients between SMC and metals. Beijing Gaomeng New Materials Co., Ltd. disclosed a delayed-temperature heat-sensitive two-component polyurethane adhesive (CN120209768A), which has a long operating time at room temperature and rapid curing after heating. The bonding substrates include wood, SMC, and metals, but it also does not solve the problem of thermal stress compatibility between SMC and metals.

[0006] Therefore, developing a two-component polyurethane adhesive that adapts to the surface properties of SMC, balances the thermal stress between SMC and metal, and possesses both high strength and high elasticity has significant technical and application value. Summary of the Invention

[0007] Objectives of the Invention: The first objective of this invention is to provide a two-component polyurethane adhesive for bonding SMCs to SMCs or between metals, which combines high strength and high elasticity, balances the difference in thermal expansion coefficients between SMCs and metals, and achieves reliable bonding of SMCs without complex surface treatment; the second objective of this invention is to provide a method for preparing the two-component polyurethane adhesive; the third objective of this invention is to provide applications of the two-component polyurethane adhesive.

[0008] The two-component polyurethane adhesive of the present invention comprises component A and component B. By weight, component A comprises: 15-30 parts of hydroxyl-terminated polybutadiene, 20-40 parts of polyester polyol, 5-15 parts of epoxy-modified polyether polyol, 1-5 parts of phosphate ester, 1-5 parts of small molecule diol chain extender, 2-10 parts of silane coupling agent, 1-5 parts of thixotropic agent, 20-50 parts of filler, 5-15 parts of flame retardant, and 0.1-0.5 parts of catalyst; component B comprises: 60-80 parts of polyisocyanate and 20-40 parts of polyurethane prepolymer.

[0009] In the two-component polyurethane adhesive, components A and B are mixed with an isocyanate index of 1 to 1.5. The preferred mass ratio of components A to B is 3:1 to 5:1.

[0010] Preferably, the phosphate ester is one or more of trimethyl phosphate, triethyl phosphate, and tributyl phosphate. Phosphate esters can reduce the viscosity of the system, improve the wetting of the filler, effectively enhance the dispersibility of the filler, and have strong penetration ability against commonly used release agents, effectively reducing the impact of release agents on adhesion. Furthermore, the groups of phosphate esters can form stable bonds with the substrate surface, effectively increasing the chemical bonding force with the substrate.

[0011] Preferably, the hydroxyl-terminated polybutadiene has a hydroxyl value of 35-115 mg KOH / g and a molecular weight of 1000-3000. If the hydroxyl value is too high or the molecular weight is too low, the system becomes significantly brittle; if the hydroxyl value is too low or the molecular weight is too high, the bulk strength is significantly insufficient. More preferably, the hydroxyl-terminated polybutadiene has a hydroxyl value of 44-51 KOH / g.

[0012] Preferably, the polyester polyol is a dimer acid-modified polyester polyol with a hydroxyl value of 35-65 mg KOH / g and a molecular weight of 2000-2500. Introducing polar groups into the polyester polyol significantly improves the wettability of the substrate surface. Simultaneously, the flexible long carbon chains of the dimer acid greatly reduce the rigidity of the polyester chain segments and enhance diffusion with the micropores on the substrate surface, promoting close contact with the substrate.

[0013] Preferably, the epoxy value of the epoxy-modified polyether polyol is 0.08–0.12 mol / 100g. The flexible long-chain structure of the polyether significantly reduces the brittleness of the cured epoxy resin, while maintaining the original high adhesive strength and modulus of the epoxy resin while toughening it. The epoxy-modified polyether polyol is obtained by modifying a polyether polyol with propylene oxide, wherein the hydroxyl value of the polyether polyol is 54–58 mgKOH / g, and the molecular weight is 1500–2500.

[0014] The epoxy-modified polyether polyol was prepared in the laboratory. The specific preparation method was as follows: the polyether polyol was added to a dry reaction vessel, purged with nitrogen three times, and then a catalyst and propylene oxide (ECH) were added. The mixture was stirred at 55±2℃ for 4 hours. After the reaction was completed, the system was cooled to 45℃, and a 30% NaOH aqueous solution was slowly added dropwise. The mixture was then stirred vigorously at 45±2℃ for 4 hours. Activated carbon was added, and the mixture was stirred for 30 min to adsorb the catalyst and impurities. The solid catalyst and activated carbon were removed by vacuum filtration. Unreacted ECH, water, and solvent were removed by vacuum distillation at 80-100℃ / -0.095MPa. The mixture was then filtered through a 0.45 μm filter membrane to obtain the final product.

[0015] Preferably, the silane coupling agent is one or more of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane. The silane coupling agent forms chemical bonds with the difficult-to-bond glass fibers in the SMC substrate, effectively improving the adhesion between the colloid and the substrate and significantly enhancing the bonding performance.

[0016] Preferably, the small molecule diol chain extender is one or more combinations of 1,4-butanediol, ethylene glycol, or diethylene glycol.

[0017] Preferably, the thixotropic agent is fumed silica.

[0018] Preferably, the filler is one or more of calcium carbonate and talc.

[0019] Preferably, the flame retardant is a phosphorus-based flame retardant (such as ammonium polyphosphate or triphenyl phosphate).

[0020] Preferably, the catalyst is a delayed-temperature thermosensitive catalyst. The delayed-temperature thermosensitive catalyst is Evonik SA-8 or SA-102, etc. Delayed-temperature thermosensitive catalysts can achieve long operating times at room temperature and rapid curing when heated to above 60°C.

[0021] Preferably, the polyisocyanate is one or more of diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), or hexamethylene diisocyanate (HDI). Preferably, the polyurethane prepolymer is an MDI-type prepolymer with an NCO content of 10% to 11%.

[0022] The MDI-type prepolymer is obtained by reacting dimer acid polyol and MDI. The preparation method is as follows: add dimer acid polyol to the reaction and dehydrate under vacuum conditions; cool down to below 80 degrees, add MDI, and stir the reaction at 70~90 degrees to obtain polyurethane prepolymer for later use.

[0023] The preparation method of the two-component polyurethane adhesive of the present invention includes the following steps:

[0024] (1) Preparation of component A: Hydroxyl-terminated polybutadiene, polyester polyol, epoxy-modified polyether polyol, phosphate ester and small molecule diol chain extender are added to the reactor and dehydrated under vacuum; the temperature is lowered to below 50°C, silane coupling agent, thixotropic agent, filler, flame retardant and catalyst are added, and after stirring evenly, the mixture is discharged and packaged as component A.

[0025] (2) Preparation of component B: Add polyisocyanate and polyurethane prepolymer to the reactor, stir and react at 60-70°C, and package as component B after cooling;

[0026] (3) Adhesive preparation: When using, mix component A and component B evenly to obtain a two-component polyurethane adhesive.

[0027] Preferably, in step (1), the conditions for vacuum dehydration are: 100~110℃, vacuum degree -0.095MPa.

[0028] Preferably, in step (2), the reaction time is 1.5 to 2.5 h.

[0029] The application of the two-component polyurethane adhesive of the present invention in bonding SMC to SMC or metal.

[0030] Preferably, the application method is as follows: during bonding, the thickness of the adhesive layer is controlled to be 0.1~0.3 mm, and it can be cured at room temperature or medium temperature. The medium temperature curing temperature is 80~100℃, the curing time is 30 min~1 h, and then it is cured at room temperature for more than 24 h.

[0031] Mechanism of Invention: In this invention, hydroxyl-terminated polybutadiene imparts excellent elasticity to the adhesive, while polyester polyol and epoxy-modified polyether polyol ensure sufficient strength, solving the technical challenge of traditional polyurethane adhesives in balancing strength and elasticity. The high-elasticity design effectively absorbs and disperses thermal stress caused by the difference in thermal expansion coefficients between SMC and metal, significantly improving the durability of the bonded joint under thermal cycling conditions.

[0032] Phosphate esters reduce system viscosity, improve filler wetting, and effectively enhance filler dispersibility. They also exhibit strong penetration into commonly used release agents, effectively reducing their impact on adhesion. Furthermore, the groups in phosphate esters can form stable bonds with the substrate surface, effectively increasing chemical bonding strength. Silane coupling agents form chemical bonds with the difficult-to-bond glass fibers in the SMC substrate, effectively improving the adhesion between the colloid and the substrate, significantly enhancing bonding performance. The synergistic effect of silane coupling agents and phosphate esters allows the adhesive to be adapted to different brands and formulations of SMC materials, even enabling direct bonding of certain SMCs without sanding.

[0033] Beneficial effects: Compared with the prior art, the present invention has the following advantages: (1) The two-component polyurethane adhesive of the present invention is used for bonding between SMC and SMC or between metals, and has both high strength and high elasticity. It balances the difference in thermal expansion coefficients between SMC and metal, and can achieve reliable bonding of SMC without complex surface treatment; (2) The adhesive of the present invention has excellent bonding strength for both SMC and metal. The shear strength of SMC / SMC bonding reaches more than 9 MPa, and the shear strength of SMC / steel bonding reaches more than 11 MPa. Both achieve 100% destruction of SMC substrate; (3) With the addition of phosphorus flame retardant, the limiting oxygen index of the adhesive reaches more than 30. It extinguishes within 5 seconds after being removed from the flame after 10 seconds of ignition and without dripping. The flame retardant rating reaches UL94 V0. (3) Adjusting the type and content of catalyst can achieve room temperature curing or medium temperature rapid curing to meet the needs of different production cycles; (4) The preparation method is simple; (5) The two-component polyurethane adhesive of the present invention is used for bonding between SMC and SMC or between metals to meet the stringent requirements of structural bonding in the fields of automobiles, aerospace and other fields. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments.

[0035] Example 1

[0036] The two-component polyurethane adhesive of the present invention is prepared by means of the following steps:

[0037] (1) Preparation of component A

[0038] Prepare the raw materials according to the following weight ratio: 20 parts of hydroxyl-terminated polybutadiene (Poly bd R-45M, hydroxyl value 38~44 mg KOH / g, molecular weight 2800, Cary Valley), 30 parts of dimer acid modified polyester polyol (model BY3022, hydroxyl value 50~60 mg KOH / g, molecular weight 2000, Beijing Baiyuan Chemical Co., Ltd.), 10 parts of epoxy modified polyether polyol (epoxy value 0.08~0.12 mol / 100 g), 3 parts of trimethyl phosphate, 3 parts of 1,4-butanediol, 5 parts of γ-aminopropyltriethoxysilane, 3 parts of fumed silica, 35 parts of calcium carbonate, 10 parts of ammonium polyphosphate, and 0.3 parts of SA-8.

[0039] The preparation method of the epoxy-modified polyether polyol is as follows: 100 parts of polyether polyol (DL-2000 hydroxyl value 54~58 mg KOH / g, molecular weight 2000, purchased from Shandong Lanxing Dongda Co., Ltd.) are added to a dry reaction vessel according to the mass ratio. The mixture is purged with nitrogen three times. 1 part of boron trifluoride ethylamine complex catalyst (Shanghai Aladdin Biochemical Technology Co., Ltd.) and 30 parts of ECH are added. The mixture is stirred at 55±2℃ for 4 hours. After the reaction is completed, the system is cooled to 45℃, and 20 parts of 30% NaOH aqueous solution are slowly added dropwise. The mixture is stirred vigorously at 45±2℃ for 4 hours. 3 parts of activated carbon are added, and the mixture is stirred for 30 min to adsorb the catalyst and impurities. The solid catalyst and activated carbon are removed by vacuum filtration. The mixture is then distilled under reduced pressure at 80-100℃ / -0.095MPa to remove unreacted ECH, water, and solvent. The mixture is filtered through a 0.45 μm filter membrane to obtain the finished product with an epoxy value of 0.08~0.12 mol / 100 g.

[0040] Preparation process of component A: Hydroxyl-terminated polybutadiene, polyester polyol, epoxy-modified polyether polyol, triethyl phosphate and 1,4-butanediol are added to a reaction vessel and dehydrated for 1 hour at 100-110℃ and -0.095MPa vacuum. After cooling to below 50℃, silane coupling agent, fumed silica, calcium carbonate, ammonium polyphosphate and catalyst are added. After thorough mixing, the mixture is discharged and packaged as component A.

[0041] (2) Preparation of component B

[0042] Prepare the raw materials according to the following weight ratio: 70 parts of diphenylmethane diisocyanate (MDI) and 30 parts of MDI-type polyurethane prepolymer (NCO content 10.5%).

[0043] Preparation method of MDI type polyurethane prepolymer: According to the mass ratio, 60 parts of dimer acid polyol (DA-2110, hydroxyl value 50~60 mg KOH / g, molecular weight 2000, Shanghai Jingri New Material Technology Co., Ltd.) were added to the reaction under vacuum conditions for dehydration; the temperature was lowered to below 80 degrees, 40 parts of MDI were added, and the mixture was stirred and reacted at 75~85 degrees for 2 h to obtain polyurethane prepolymer with NCO content of 10.5%.

[0044] Preparation process of component B: MDI and polyurethane prepolymer are added to a reactor and stirred at 60-70°C for 2 hours. After cooling, it is packaged as component B.

[0045] (3) Adhesive preparation: Mix component A and component B evenly at a mass ratio of 4:1.

[0046] Example 2

[0047] The two-component polyurethane adhesive of the present invention is prepared by means of the following steps:

[0048] (1) Preparation of component A

[0049] Prepare the raw materials according to the following weight ratio: 25 parts of hydroxyl-terminated polybutadiene (Poly bd R-45HTLO, hydroxyl value 44~51 mgKOH / g, molecular weight 2800, Cray Valley), 25 parts of dimer acid modified polyester polyol (DA-2110, hydroxyl value 50~60 mgKOH / g, molecular weight 2000, purchased from Shanghai Jingri New Material Technology Co., Ltd.), 12 parts of epoxy modified polyether polyol (same as Example 1), 5 parts of triethyl phosphate, 2 parts of ethylene glycol, 6 parts of γ-glycidyl etheroxypropyltrimethoxysilane, 2 parts of fumed silica, 40 parts of talc, 8 parts of triphenyl phosphate, and 0.2 parts of SA-8.

[0050] The preparation process of component A is the same as in Example 1.

[0051] (2) Preparation of component B

[0052] Prepare the raw materials according to the following weight ratio: 60 parts of hexamethylene diisocyanate (HDI) and 40 parts of MDI-type polyurethane prepolymer (same as in Example 1).

[0053] The preparation process for component B is the same as in Example 1.

[0054] (3) Adhesive preparation: Mix component A and component B evenly at a mass ratio of 3.5:1.

[0055] Example 3

[0056] The two-component polyurethane adhesive of the present invention is prepared by means of the following steps:

[0057] (1) Preparation of component A

[0058] Prepare the raw materials according to the following weight ratios: 18 parts of hydroxyl-terminated polybutadiene (Poly bd R-20LM, hydroxyl value 90~112 mg KOH / g, molecular weight 1200, Cray Valley), 35 parts of dimer acid modified polyester polyol (BY3026, hydroxyl value 37~43 mg KOH / g, molecular weight 2500, Beijing Baiyuan Chemical Co., Ltd.), 8 parts of epoxy modified polyether polyol (same as Example 1), 5 parts of tributyl phosphate, 4 parts of diethylene glycol, 7 parts of a mixture of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane (mass ratio 1:1), 4 parts of fumed silica, 32 parts of a mixture of calcium carbonate and talc (mass ratio 1:1), 12 parts of ammonium polyphosphate, and 0.4 parts of SA-102.

[0059] The preparation process of component A is the same as in Example 1.

[0060] (2) Preparation of component B

[0061] Prepare the raw materials according to the following weight ratio: 65 parts of toluene diisocyanate (TDI) and 35 parts of MDI-type polyurethane prepolymer (same as in Example 1).

[0062] The preparation process for component B is the same as in Example 1.

[0063] (3) Adhesive preparation: Mix component A and component B evenly at a mass ratio of 4.5:1.

[0064] Comparative Example 1

[0065] Commercially available two-component polyurethane structural adhesive (brand: Zhijiang JS-3020) was used. After mixing according to the instructions, SMC / SMC, SMC / steel, and SMC / aluminum bonding tests were conducted using the same process. The results are shown in Table 1.

[0066] Comparative Example 2

[0067] Based on Example 2, no phosphate ester was added to component A, and all other conditions remained unchanged.

[0068] Comparative Example 3

[0069] Based on Example 2, no silane coupling agent was added to component A, and all other conditions remained unchanged.

[0070] Comparative Example 4

[0071] Based on Example 2, the dimer acid modified polyester polyol in component A was replaced with the same amount of polyester polyol N-112 (BGI Chemical), while the other conditions remained unchanged.

[0072] Performance testing

[0073] (1) Adhesion performance test

[0074] The adhesives prepared in Examples 1-3 and Comparative Example 1 were applied to the surface of SMC test pieces that had undergone simple cleaning treatment (wiping with a dry cloth or blowing with dry air), and then bonded to another SMC test piece, a steel sheet, and an aluminum test piece, respectively (test piece size 25mm × 100mm, bonding area 25mm × 12.5mm, adhesive layer thickness 0.2mm). The adhesives were cured at 80℃ for 1 h, and then cured at room temperature for 24 h. Shear strength was tested according to GB / T 7124-2008 standard, and the results are shown in Table 1.

[0075] (2) Thermal stress relaxation ability test

[0076] To verify the thermal stress relaxation ability of the adhesive of the present invention in bonding SMC to metal, the adhesives prepared in Examples 1-3 and Comparative Examples 1-4 were used for bonding SMC to steel sheets. The sample size was 25mm × 100mm, the bonding area was 25mm × 12.5mm, and the adhesive layer thickness was 0.2mm. The samples were cured at 80℃ for 1 h, and then cured at room temperature for 24 h. The cured samples were placed in a thermal cycling chamber at -40℃ to 80℃ for 1000 cycles (1 h per cycle). The bond strength retention rate before and after thermal cycling was tested, and the bond interface condition was observed. The results are shown in Table 1.

[0077] Table 1. Test results of adhesive performance of the examples and comparative examples.

[0078]

[0079] Note: Thermal cycling conditions are -40℃ to 80℃, 1000 cycles; strength retention rate is compared with initial strength.

[0080] As shown in Table 1, the two-component polyurethane adhesives prepared in Examples 1-3 of this invention exhibit excellent performance in SMC / SMC and SMC / metal bonding, significantly outperforming commercially available ordinary products. Comparative Example 2, compared to Example 1, shows decreased bond strength and fails to achieve the UL94 V-0 flame retardant rating. This is because the absence of phosphate ester results in insufficient penetration into the substrate, and the flame retardant component is also insufficient. Comparative Example 3, compared to Example 2, shows decreased bond strength due to the lack of a silane coupling agent, leading to insufficient adhesion to the substrate surface. Comparative Example 4, compared to Example 3, shows decreased bond strength because the absence of dimer acid-modified polyester polyol is due to the lack of polar groups, which cannot improve the wettability of the substrate surface, and the absence of the flexible long carbon chains of dimer acid, which cannot reduce the rigidity of the polyester chain segments and improve diffusion to the micropores on the substrate surface.

[0081] As shown in Table 1, after 1000 thermal cycles, the adhesive strength retention rates of Examples 1-3 were 95%, 96%, and 93%, respectively, all above 90%, with intact bonding interfaces, no cracks, and no debonding. In contrast, the adhesive strengths of Comparative Examples 1-4 were 75%, 62%, 69%, and 50%, respectively, with retention rates all below 80%, and interfacial debonding occurred. The decrease in adhesive strength of Comparative Examples 2 and 3 was due to the lack of phosphate ester or coupling agent penetration or bonding at the interface, resulting in reduced interfacial bonding strength after cycling. The decrease in adhesive strength of Comparative Example 4 was due to the lower thermal stability of conventional polyester polyols compared to dimer acid-modified polyester polyols, leading to a decrease in overall adhesive layer strength after cycling. These test results fully demonstrate the excellent thermal stress relaxation ability and durability of the adhesive of this invention, making it particularly suitable for bonding dissimilar materials such as SMC and metals with large differences in thermal expansion coefficients.

Claims

1. A two-component polyurethane adhesive, characterized in that, The product comprises component A and component B. By weight, component A includes: 15-30 parts of hydroxyl-terminated polybutadiene, 20-40 parts of polyester polyol, 5-15 parts of epoxy-modified polyether polyol, 1-5 parts of phosphate ester, 1-5 parts of small molecule diol chain extender, 2-10 parts of silane coupling agent, 1-5 parts of thixotropic agent, 20-50 parts of filler, 5-15 parts of flame retardant, and 0.1-0.5 parts of catalyst; component B includes: 60-80 parts of polyisocyanate and 20-40 parts of polyurethane prepolymer.

2. The two-component polyurethane adhesive according to claim 1, characterized in that, The phosphate ester is one or more of trimethyl phosphate, triethyl phosphate, and tributyl phosphate.

3. The two-component polyurethane adhesive according to claim 1, characterized in that, The hydroxyl-terminated polybutadiene has a hydroxyl value of 35~115 mg KOH / g.

4. The two-component polyurethane adhesive according to claim 1, characterized in that, The polyester polyol is a dimer acid-modified polyester polyol with a molecular weight of 2000-2500.

5. The two-component polyurethane adhesive according to claim 1, characterized in that, The epoxy value of the epoxy-modified polyether polyol is 0.08–0.12 mol / 100g.

6. The two-component polyurethane adhesive according to claim 1, characterized in that, The silane coupling agent is one or more of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane.

7. The two-component polyurethane adhesive according to claim 1, characterized in that, The polyisocyanate is one or more of diphenylmethane diisocyanate, toluene diisocyanate, or hexamethylene diisocyanate.

8. The two-component polyurethane adhesive according to claim 1, characterized in that, The polyurethane prepolymer is an MDI-type prepolymer with an NCO content of 10% to 11%.

9. A method for preparing a two-component polyurethane adhesive according to any one of claims 1 to 8, characterized in that, Includes the following steps: (1) Preparation of component A: Hydroxyl-terminated polybutadiene, polyester polyol, epoxy-modified polyether polyol, phosphate ester and small molecule diol chain extender are added to the reactor and dehydrated under vacuum; the temperature is lowered to below 50°C, silane coupling agent, thixotropic agent, filler, flame retardant and catalyst are added, and after stirring evenly, the mixture is discharged and packaged as component A. (2) Preparation of component B: Polyisocyanate and polyurethane prepolymer are added to the reactor and stirred at 60-70°C. After cooling, they are packaged as component B. (3) Adhesive preparation: When using, mix component A and component B evenly to obtain a two-component polyurethane adhesive.

10. The use of a two-component polyurethane adhesive according to any one of claims 1 to 8 in bonding SMC to SMC or metal.

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