Preparation method of low-voc polyurethane structural adhesive
By introducing modified alumina and flame retardants, low-VOC polyurethane structural adhesives were prepared, solving the problems of flammability and poor UV resistance, and improving safety and environmental performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- 深圳市道丰宁科技有限公司
- Filing Date
- 2025-12-22
- Publication Date
- 2026-07-07
Abstract
Description
Technical Field
[0001] This invention relates to the field of adhesive technology, specifically to a method for preparing a low-VOC polyurethane structural adhesive. Background Technology
[0002] With the development of the modern automotive industry, various profiles are widely used in automobile manufacturing. For example, passenger cars with aluminum alloy body frames use components made of different materials such as aluminum alloy, SMC, ABS, and painted profiles. These materials often cannot be assembled using traditional welding and riveting processes, but must be assembled using structural adhesives. Compared to epoxy and acrylic structural adhesives, two-component polyurethane elastic structural adhesives have both high bonding strength and excellent flexibility. Moreover, their strength, elongation, and other mechanical properties can be adjusted according to user requirements to meet higher usage demands, thus showing great application prospects.
[0003] While polyurethane structural adhesives offer numerous advantages, they also have some drawbacks. Traditional polyurethane structural adhesives have a low limiting oxygen index, classifying them as flammable materials and posing certain safety hazards when used extensively. Furthermore, prolonged exposure to ultraviolet radiation can alter the physical, chemical, and mechanical properties of polyurethane materials, affecting the adhesive's bond strength and lifespan. Therefore, developing polyurethane structural adhesives with excellent flame-retardant and UV-resistant properties is essential.
[0004] Furthermore, when using polyurethane structural adhesives in enclosed spaces such as automobiles, the VOC release of these adhesives must be considered. These volatile organic compounds may adversely affect human health, causing discomfort such as nausea and dizziness, thus impacting the passenger experience. Solvent-free polyurethane structural adhesives can avoid the use of organic solvents, reduce VOC content, and improve the environmental and safety performance of polyurethane structural adhesives. Summary of the Invention
[0005] The purpose of this invention is to provide a method for preparing a low-VOC polyurethane structural adhesive to solve the problems existing in the prior art.
[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:
[0007] A method for preparing a low-VOC polyurethane structural adhesive, the method comprising the following preparation steps:
[0008] (1) Pretreated alumina was prepared by reacting alumina with aminopropyltriethoxysilane; pretreated alumina was prepared by reacting pretreated alumina with triglycidyl isocyanurate; modified alumina was prepared by reacting pretreated alumina with 4-(2H-benzo[D][1,2,3]triazol-2-yl)benzene-1,3-diol.
[0009] (2) Dihydroxyethyl anthracene monomer was prepared by reacting methyl 9-anthracene acrylate and diethanolamine;
[0010] (3) The diethanol composite flame retardant was prepared by reacting 5-(aminomethyl)-2-furan methanol and 5-hydroxymethylfurfural with diethyl phosphite;
[0011] (4) Polytetrahydrofuran diol, dihydroxyethyl anthracene monomer and isophorone diisocyanate are reacted to prepare isocyanate-terminated prepolymer; the isocyanate-terminated prepolymer, polymethylene polyphenyl polyisocyanate and dehydrating agent are mixed to obtain component B;
[0012] (5) Mix castor oil, polyester diol, diethanol composite flame retardant, modified alumina and catalyst to obtain component A;
[0013] (6) Mix component A and component B to obtain a low-VOC polyurethane structural adhesive.
[0014] As an optimization, the particle size of the alumina in step (1) is 800 mesh.
[0015] As an optimization, the preparation method of the pretreated alumina in step (1) is as follows: Alumina, anhydrous ethanol, and deionized water are mixed evenly in a mass ratio of 1:(40~50):(10~14), ultrasonically dispersed for 1~2h, and 0.6~0.8 times the mass of alumina is added. The mixture is stirred and reacted at 70~80℃ for 8~10h, filtered, washed with anhydrous ethanol and deionized water respectively, and vacuum dried at 70~80℃ for 13~15h to obtain pretreated alumina.
[0016] As an optimization, the preparation method of the pre-modified alumina in step (1) is as follows: pretreated alumina, triglycidyl isocyanurate and N,N-dimethylformamide are mixed evenly in a mass ratio of 1:(4~5):(30~40), stirred and reacted at 80~90℃ for 10~12h, filtered, washed with anhydrous ethanol, and vacuum dried at 70~80℃ for 13~15h to obtain pre-modified alumina.
[0017] As an optimization, the preparation method of the modified alumina in step (1) is as follows: pre-modified alumina, 4-(2H-benzo[D][1,2,3]triazol-2-yl)benzene-1,3-diol, and anhydrous ethanol are mixed evenly in a mass ratio of 1:(3~4):(30~40), and 0.1wt% sodium carbonate aqueous solution of 5~6 times the mass of 4-(2H-benzo[D][1,2,3]triazol-2-yl)benzene-1,3-diol is added. Under nitrogen protection, the mixture is stirred and refluxed at 75~85℃ for 7~9h, naturally cooled to room temperature, filtered, washed with anhydrous ethanol, and vacuum dried at 70~80℃ for 13~15h to obtain modified alumina.
[0018] As an optimization, the preparation method of the dihydroxyethyl anthracene monomer in step (2) is as follows: add methyl 9-anthracene acrylate and diethanolamine in a molar ratio of 1:1 to anhydrous ethanol at a mass ratio of 12 to 14 times that of methyl 9-anthracene acrylate, stir and react at 35 to 45°C for 20 to 24 hours, remove the anhydrous ethanol by vacuum distillation, and obtain the dihydroxyethyl anthracene monomer.
[0019] As an optimization, the reaction process of the dihydroxyethyl anthracene monomer in step (2) is as follows:
[0020] .
[0021] As an optimization, the preparation method of the dimethyl methanol composite flame retardant in step (3) is as follows: 5-(aminomethyl)-2-furan methanol and 5-hydroxymethylfurfural are added to anhydrous ethanol at a molar ratio of 1:1, which is 8 to 10 times the mass of 5-(aminomethyl)-2-furan methanol. The mixture is stirred and reacted at 70 to 80°C for 7 to 8 hours. Then, an equimolar amount of diethyl phosphite is added to the mixture, and the mixture is stirred and reacted for another 20 to 24 hours. The anhydrous ethanol is removed by vacuum distillation to obtain the dimethyl methanol composite flame retardant.
[0022] As an optimization, the reaction process of the diethanol composite flame retardant in step (3) is as follows:
[0023] .
[0024] As an optimization, the preparation method of component B in step (4) is as follows: the isocyanate-terminated prepolymer, polymethylene polyphenyl polyisocyanate, and dehydrating agent are mixed evenly in a mass ratio of (10~12):(2~2.4):(0.6~0.8), and vacuum degassing is performed for 30~40 min to obtain component B.
[0025] As an optimization, the preparation method of the isocyanate-terminated prepolymer in step (4) is as follows: weigh polytetrahydrofuran diol, dihydroxyethyl anthracene monomer, and isophorone diisocyanate in a molar ratio of (10~12):(8~10):(24~28); mix polytetrahydrofuran diol, dihydroxyethyl anthracene monomer, and isophorone diisocyanate evenly, add dibutyltin dilaurate at 0.0004~0.0006 times the mass of polytetrahydrofuran diol, and stir and react at 78~82℃ for 2~3h under nitrogen protection to obtain the isocyanate-terminated prepolymer.
[0026] As an optimization, the polytetrahydrofuran diol in step (4) is of type PTMG1000.
[0027] As an optimization, the dehydrating agent in step (4) is one or more of p-benzenesulfonyl isocyanate, sodium aluminosilicate, potassium aluminosilicate, and 1,3-oxazinecyclopentane.
[0028] As an optimization, the polymethylene polyphenyl polyisocyanate in step (4) is of the Wanhua PM200 type.
[0029] As an optimization, the preparation method of component A in step (5) is as follows: weigh 20-24 parts of castor oil, 16-20 parts of polyester diol, 8-10 parts of diethanol composite flame retardant, 0.03-0.05 parts of catalyst, and 5-6 parts of modified alumina by mass. Mix the polyester diol and castor oil evenly, dehydrate under vacuum at 110-120℃ for 1-2 h, cool down to 50-60℃, add diethanol composite flame retardant and modified alumina, mix and stir for 30-40 min, cool down to room temperature, add catalyst and mix evenly, degas under vacuum for 50-60 min to obtain component A.
[0030] As an optimization, the catalyst in step (5) is one or more of dibutyltin dilaurate, zinc sulfosuccinate, stannous octoate, N-methylimidazolium, and tetrabutyl titanate.
[0031] As an optimization, the polyester diol in step (5) is of type PBA2000.
[0032] As an optimization, the mass ratio of component A to component B in step (6) is 1:(1.0~1.2).
[0033] Compared with the prior art, the beneficial effects achieved by the present invention are:
[0034] First, pretreated alumina is prepared by reacting alumina with aminopropyltriethoxysilane, and an amino group is introduced onto the pretreated alumina. The amino group on the pretreated alumina is then reacted with an epoxy group on triglycidyl isocyanurate to prepare pre-modified alumina. Next, the unreacted epoxy group on the pre-modified alumina is reacted with 4-(2H-benzo[D][1,2,3]triazol-2-yl)benzene-1,3-diol to prepare modified alumina. A benzotriazole UV absorber structure and a triazine trione structure are introduced onto the modified alumina. The introduction of the benzoimidazole UV absorber structure improves the UV aging resistance of the structural adhesive; the introduction of the triazine trione structure improves the flame retardant properties of the structural adhesive. Simultaneously, adding alumina as a filler to the structural adhesive improves its thermal conductivity.
[0035] Secondly, dihydroxyethyl anthracene monomer was prepared by reacting methyl 9-anthracene acrylate and diethanolamine; isocyanate-terminated prepolymer was prepared by reacting polytetrahydrofuran glycol, dihydroxyethyl anthracene monomer, and isophorone diisocyanate; anthracene groups were introduced into the structural adhesive; anthracene groups are photosensitive chemical reactive groups, and studies have shown that anthracene groups can undergo cycloaddition reactions under UVA (320-400 nm) wavelength light irradiation. This group can undergo dimerization reactions while UV aging occurs, compensating for the damage to the crosslinking network, thereby maintaining the network crosslinking density and further improving the UV aging resistance of the structural adhesive.
[0036] Finally, a dimethyl phosphite composite flame retardant was prepared by reacting 5-(aminomethyl)-2-furanethanol and 5-hydroxymethylfurfural in a one-pot process, followed by reaction with diethyl phosphite. Castor oil, polyester diol, dimethyl phosphite composite flame retardant, modified alumina, and catalyst were mixed to obtain component A. The five-membered heterocycle of furanyl group has the effect of promoting char formation and can synergistically work with phosphorus in diethyl phosphite to further enhance the flame retardant ability of the structural adhesive.
[0037] In addition, the polyurethane structural adhesive prepared by this invention is solvent-free, contains no organic solvents, and has the advantages of low toxicity, environmental friendliness, and low VOC. Detailed Implementation
[0038] 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.
[0039] Example 1:
[0040] A method for preparing a low-VOC polyurethane structural adhesive, the method comprising the following preparation steps:
[0041] (1) Alumina, anhydrous ethanol, and deionized water were mixed evenly in a mass ratio of 1:40:10 and ultrasonically dispersed for 1 hour. 0.6 times the mass of alumina was added to aminopropyltriethoxysilane, and the mixture was stirred at 70°C for 10 hours. After filtration, the mixture was washed three times each with anhydrous ethanol and deionized water, and then vacuum dried at 70°C for 15 hours to obtain pretreated alumina. Pretreated alumina, triglycidyl isocyanurate, and N,N-dimethylformamide were mixed evenly in a mass ratio of 1:4:30 and stirred at 80°C for 12 hours. After filtration, the mixture was washed three times with anhydrous ethanol and then vacuum dried at 70°C for 15 hours. Pre-modified alumina was obtained by air drying for 15 hours. The pre-modified alumina, 4-(2H-benzo[D][1,2,3]triazol-2-yl)phenyl-1,3-diol, and anhydrous ethanol were mixed evenly in a mass ratio of 1:3:30. A 0.1 wt% sodium carbonate aqueous solution with a mass of 5 times that of 4-(2H-benzo[D][1,2,3]triazol-2-yl)phenyl-1,3-diol was added. The mixture was stirred and refluxed at 75°C for 9 hours under nitrogen protection, naturally cooled to room temperature, filtered, washed 3 times with anhydrous ethanol, and vacuum dried at 70°C for 15 hours to obtain modified alumina.
[0042] (2) Add methyl 9-anthracene acrylate and diethanolamine in a molar ratio of 1:1 to anhydrous ethanol at 12 times the mass of methyl 9-anthracene acrylate, stir and react at 35°C for 24 h, remove anhydrous ethanol by vacuum distillation, and obtain dihydroxyethyl anthracene monomer.
[0043] (3) 5-(aminomethyl)-2-furan methanol and 5-hydroxymethylfurfural were added to anhydrous ethanol at a molar ratio of 1:1 to 8 times the mass of 5-(aminomethyl)-2-furan methanol. The mixture was stirred at 70°C for 8 hours. Then, an equimolar amount of diethyl phosphite was added to the mixture. The mixture was stirred for another 24 hours. The anhydrous ethanol was removed by vacuum distillation to obtain the diethanol composite flame retardant.
[0044] (4) Weigh out polytetrahydrofurandiol, dihydroxyethyl anthracene monomer, and isophorone diisocyanate in a molar ratio of 10:8:24; mix polytetrahydrofurandiol, dihydroxyethyl anthracene monomer, and isophorone diisocyanate evenly, add dibutyltin dilaurate at a mass ratio of 0.0004 times that of polytetrahydrofurandiol, and stir and react at 78°C for 3 hours under nitrogen protection to obtain isocyanate-terminated prepolymer; mix isocyanate-terminated prepolymer, polymethylene polyphenyl polyisocyanate, and sodium aluminosilicate in a mass ratio of 10:2:0.6 evenly, and degas under vacuum for 30 minutes to obtain component B;
[0045] (5) Weigh out 20 parts castor oil, 16 parts polyester diol, 8 parts diethanol composite flame retardant, 0.03 parts dibutyltin dilaurate, and 5 parts modified alumina by mass. Mix polyester diol and castor oil evenly, dehydrate under vacuum at 110°C for 2 h, cool down to 50°C, add diethanol composite flame retardant and modified alumina, mix and stir for 30 min, cool down to room temperature, add dibutyltin dilaurate, mix evenly, degas under vacuum for 50 min, and obtain component A.
[0046] (6) Mix component A and component B at a mass ratio of 1:1 to obtain a low-VOC polyurethane structural adhesive.
[0047] Example 2:
[0048] A method for preparing a low-VOC polyurethane structural adhesive, the method comprising the following preparation steps:
[0049] (1) Alumina, anhydrous ethanol, and deionized water were mixed evenly in a mass ratio of 1:45:12 and ultrasonically dispersed for 1.5 h. 0.7 times the mass of alumina was added, and the mixture was stirred at 75 °C for 9 h. After filtration, the mixture was washed three times each with anhydrous ethanol and deionized water, and then vacuum dried at 75 °C for 14 h to obtain pretreated alumina. Pretreated alumina, triglycidyl isocyanurate, and N,N-dimethylformamide were mixed evenly in a mass ratio of 1:4.5:35 and stirred at 85 °C for 11 h. After filtration, the mixture was washed three times with anhydrous ethanol and then vacuum dried at 75 °C for 14 h to obtain pretreated alumina. Pre-modified alumina was obtained by air drying for 14 hours. The pre-modified alumina, 4-(2H-benzo[D][1,2,3]triazol-2-yl)phenyl-1,3-diol, and anhydrous ethanol were mixed evenly in a mass ratio of 1:3.5:35. A 0.1 wt% sodium carbonate aqueous solution of 5.5 times the mass of 4-(2H-benzo[D][1,2,3]triazol-2-yl)phenyl-1,3-diol was added. The mixture was stirred and refluxed at 80°C for 8 hours under nitrogen protection, naturally cooled to room temperature, filtered, washed three times with anhydrous ethanol, and vacuum dried at 75°C for 14 hours to obtain modified alumina.
[0050] (2) Add methyl 9-anthracene acrylate and diethanolamine in a molar ratio of 1:1 to anhydrous ethanol at 13 times the mass of methyl 9-anthracene acrylate, stir and react at 40°C for 22 h, remove anhydrous ethanol by vacuum distillation, and obtain dihydroxyethyl anthracene monomer.
[0051] (3) 5-(aminomethyl)-2-furan methanol and 5-hydroxymethylfurfural were added to anhydrous ethanol at a molar ratio of 1:1 to 9 times the mass of 5-(aminomethyl)-2-furan methanol. The mixture was stirred at 75°C for 7.5 h. Then, an equimolar amount of diethyl phosphite was added to the mixture. The mixture was stirred for another 22 h. The anhydrous ethanol was removed by vacuum distillation to obtain the diethanol composite flame retardant.
[0052] (4) Weigh out polytetrahydrofurandiol, dihydroxyethyl anthracene monomer, and isophorone diisocyanate in a molar ratio of 11:9:26; mix polytetrahydrofurandiol, dihydroxyethyl anthracene monomer, and isophorone diisocyanate evenly, add dibutyltin dilaurate at a mass ratio of 0.0005 times that of polytetrahydrofurandiol, and stir and react at 80°C for 2.5 h under nitrogen protection to obtain isocyanate-terminated prepolymer; mix isocyanate-terminated prepolymer, polymethylene polyphenyl polyisocyanate, and sodium aluminosilicate in a mass ratio of 11:2.2:0.7 evenly, and degas under vacuum for 35 min to obtain component B;
[0053] (5) Weigh out 22 parts castor oil, 18 parts polyester diol, 9 parts dimethyl alcohol composite flame retardant, 0.04 parts dibutyltin dilaurate, and 5.5 parts modified alumina by mass. Mix polyester diol and castor oil evenly, dehydrate under vacuum at 115°C for 1.5 h, cool down to 55°C, add dimethyl alcohol composite flame retardant and modified alumina, mix and stir for 35 min, cool down to room temperature, add dibutyltin dilaurate, mix evenly, degas under vacuum for 55 min, and obtain component A.
[0054] (6) Mix component A and component B at a mass ratio of 1:1.1 to obtain a low-VOC polyurethane structural adhesive.
[0055] Example 3:
[0056] A method for preparing a low-VOC polyurethane structural adhesive, the method comprising the following preparation steps:
[0057] (1) Alumina, anhydrous ethanol, and deionized water were mixed evenly in a mass ratio of 1:50:14 and ultrasonically dispersed for 2 hours. 0.8 times the mass of alumina was added to aminopropyltriethoxysilane, and the mixture was stirred at 80°C for 8 hours. After filtration, the mixture was washed three times each with anhydrous ethanol and deionized water, and then vacuum dried at 80°C for 13 hours to obtain pretreated alumina. Pretreated alumina, triglycidyl isocyanurate, and N,N-dimethylformamide were mixed evenly in a mass ratio of 1:5:40 and stirred at 90°C for 10 hours. After filtration, the mixture was washed three times with anhydrous ethanol and then vacuum dried at 80°C for 13 hours. Pre-modified alumina was obtained by air drying for 13 hours. The pre-modified alumina, 4-(2H-benzo[D][1,2,3]triazol-2-yl)phenyl-1,3-diol, and anhydrous ethanol were mixed evenly in a mass ratio of 1:4:40. A 0.1 wt% sodium carbonate aqueous solution with a mass of 6 times that of 4-(2H-benzo[D][1,2,3]triazol-2-yl)phenyl-1,3-diol was added. The mixture was stirred and refluxed at 85°C for 7 hours under nitrogen protection, naturally cooled to room temperature, filtered, washed 3 times with anhydrous ethanol, and vacuum dried at 80°C for 13 hours to obtain modified alumina.
[0058] (2) Add methyl 9-anthracene acrylate and diethanolamine in a molar ratio of 1:1 to anhydrous ethanol at 14 times the mass of methyl 9-anthracene acrylate, stir and react at 45°C for 20 h, remove anhydrous ethanol by vacuum distillation, and obtain dihydroxyethyl anthracene monomer.
[0059] (3) 5-(aminomethyl)-2-furan methanol and 5-hydroxymethylfurfural were added to anhydrous ethanol at a molar ratio of 1:1 to 10 times the mass of 5-(aminomethyl)-2-furan methanol. The mixture was stirred at 80°C for 7 hours. Then, an equimolar amount of diethyl phosphite was added to the mixture. The mixture was stirred for another 20 hours. The anhydrous ethanol was removed by vacuum distillation to obtain the diethanol composite flame retardant.
[0060] (4) Weigh out polytetrahydrofurandiol, dihydroxyethyl anthracene monomer, and isophorone diisocyanate in a molar ratio of 12:10:28; mix polytetrahydrofurandiol, dihydroxyethyl anthracene monomer, and isophorone diisocyanate evenly, add dibutyltin dilaurate at a mass ratio of 0.0006 times that of polytetrahydrofurandiol, and stir and react at 82°C for 2 hours under nitrogen protection to obtain isocyanate-terminated prepolymer; mix isocyanate-terminated prepolymer, polymethylene polyphenyl polyisocyanate, and sodium aluminosilicate in a mass ratio of 12:2.4:0.8 evenly, and degas under vacuum for 40 minutes to obtain component B;
[0061] (5) Weigh 24 parts castor oil, 20 parts polyester diol, 10 parts dimethyl alcohol composite flame retardant, 0.05 parts dibutyltin dilaurate, and 6 parts modified alumina by mass. Mix polyester diol and castor oil evenly, dehydrate under vacuum at 120°C for 1 h, cool to 60°C, add dimethyl alcohol composite flame retardant and modified alumina, mix and stir for 40 min, cool to room temperature, add dibutyltin dilaurate, mix evenly, degas under vacuum for 60 min, and obtain component A.
[0062] (6) Mix component A and component B at a mass ratio of 1:1.2 to obtain a low-VOC polyurethane structural adhesive.
[0063] Comparative Example 1:
[0064] The preparation method of the low-VOC polyurethane structural adhesive in Comparative Example 1 differs from that in Example 2 in that step (1) is omitted, and step (5) is modified as follows: 22 parts castor oil, 18 parts polyester diol, 9 parts dimethyl alcohol composite flame retardant, 0.04 parts dibutyltin dilaurate, and 5.5 parts alumina are weighed by mass. The polyester diol and castor oil are mixed evenly, and the mixture is dehydrated under vacuum at 115°C for 1.5 h. After cooling to 55°C, the dimethyl alcohol composite flame retardant and alumina are added and stirred for 35 min. After cooling to room temperature, the dibutyltin dilaurate is added and mixed evenly. The mixture is then degassed under vacuum for 55 min to obtain component A. The remaining steps are the same as in Example 2.
[0065] Comparative Example 2:
[0066] The preparation method of the low-VOC polyurethane structural adhesive in Comparative Example 2 differs from that in Example 2 in that step (2) is omitted, and step (4) is modified as follows: Polytetrahydrofurandiol, 1,4-butanediol, and isophorone diisocyanate are weighed in a molar ratio of 11:9:26; the polytetrahydrofurandiol, 1,4-butanediol, and isophorone diisocyanate are mixed evenly, and dibutyltin dilaurate (0.0005 times the mass of polytetrahydrofurandiol) is added. Under nitrogen protection, the mixture is stirred and reacted at 80°C for 2.5 h to obtain an isocyanate-terminated prepolymer; the isocyanate-terminated prepolymer, polymethylene polyphenyl polyisocyanate, and sodium aluminosilicate are mixed evenly in a mass ratio of 11:2.2:0.7, and vacuum degassed for 35 min to obtain component B. The remaining steps are the same as in Example 2.
[0067] Comparative Example 3:
[0068] The preparation method of the low-VOC polyurethane structural adhesive in Comparative Example 3 differs from that in Example 2 in that step (3) is omitted, and step (5) is modified as follows: 22 parts castor oil, 18 parts polyester diol, 9 parts 1,4-butanediol, 0.04 parts dibutyltin dilaurate, and 5.5 parts modified alumina are weighed by mass. The polyester diol and castor oil are mixed evenly, and the mixture is dehydrated under vacuum at 115°C for 1.5 h. The temperature is then lowered to 55°C, and 1,4-butanediol and modified alumina are added and stirred for 35 min. The mixture is then cooled to room temperature, and dibutyltin dilaurate is added and mixed evenly. The mixture is then degassed under vacuum for 55 min to obtain component A. The remaining steps are the same as in Example 2.
[0069] Test Example 1
[0070] Flame retardant performance testing
[0071] Test method: Standard samples were prepared according to GB / T2406 for the examples and comparative examples, and the limiting oxygen index of the standard samples was tested. The results are shown in Table 1.
[0072] Table 1
[0073] Limiting oxygen index (%) Limiting oxygen index (%) Example 1 30.67 Comparative Example 1 26.75 Example 2 31.58 Comparative Example 2 30.24 Example 3 31.16 Comparative Example 3 25.51
[0074] A comparison of the experimental data of Examples 1-3 and Comparative Examples 1-3 in Table 1 reveals that the low-VOC polyurethane structural adhesive prepared by this invention has good flame retardant properties.
[0075] By comparison, the limiting oxygen index of Examples 1-3 is greater than that of Comparative Example 1, indicating that the pretreated alumina is prepared by reacting alumina with aminopropyltriethoxysilane, and an amino group is introduced onto the pretreated alumina; the amino group on the pretreated alumina is reacted with the epoxy group on triglycidyl isocyanurate to prepare pre-modified alumina; and the unreacted epoxy group on the pre-modified alumina is reacted with 4-(2H-benzo[D][1,2,3]triazol-2-yl)benzene-1,3-diol to prepare modified alumina, and a triazine trione structure is introduced onto the modified alumina. The introduction of the triazine trione structure can improve the flame retardant properties of the structural adhesive.
[0076] By comparison, the limiting oxygen index of Examples 1-3 is greater than that of Comparative Example 3, indicating that the dimethyl alcohol composite flame retardant is prepared by reacting 5-(aminomethyl)-2-furanol and 5-hydroxymethylfurfural in a one-pot process and then reacting them with diethyl phosphite. Castor oil, polyester diol, dimethyl alcohol composite flame retardant, modified alumina, and catalyst are mixed to obtain component A. The five-membered heterocycle of furanyl group has the effect of promoting char formation and can synergistically work with phosphorus in diethyl phosphite to further enhance the flame retardant ability of the structural adhesive.
[0077] Test Example 2
[0078] Testing of UV aging resistance
[0079] Test method: Standard specimens were prepared according to GB / T1040 for the examples and comparative examples, and their tensile strength F1 was tested at a tensile rate of 100 mm / min. The standard specimens were placed in an aging test chamber for accelerated aging test with a UV lamp power of 200W, a wavelength of 365nm, and an aging time of 400h. The tensile strength F2 of the standard specimens after UV aging treatment was tested. The performance retention rate of the standard specimens was calculated as (F2 / F1) × 100%. The results are shown in Table 2.
[0080] Table 2
[0081] Performance retention rate (%) Performance retention rate (%) Example 1 91.67 Comparative Example 1 83.37 Example 2 93.08 Comparative Example 2 78.16 Example 3 92.79 Comparative Example 3 91.58
[0082] A comparison of the experimental data from Examples 1-3 and Comparative Examples 1-3 in Table 2 reveals that the low-VOC polyurethane structural adhesive prepared by this invention has good UV aging resistance.
[0083] By comparison, the performance retention rates of Examples 1-3 were greater than those of Comparative Example 1, indicating that the pretreated alumina was prepared by reacting alumina with aminopropyltriethoxysilane, and an amino group was introduced onto the pretreated alumina. The amino group on the pretreated alumina was then reacted with the epoxy group on triglycidyl isocyanurate to prepare pre-modified alumina. The unreacted epoxy group on the pre-modified alumina was then reacted with 4-(2H-benzo[D][1,2,3]triazol-2-yl)benzene-1,3-diol to prepare modified alumina, and a benzotriazole UV absorber structure was introduced onto the modified alumina. The introduction of the benzimidazole UV absorber structure can improve the UV aging resistance of the structural adhesive.
[0084] By comparison, the performance retention rates of Examples 1-3 were greater than those of Comparative Example 2, indicating that the dihydroxyethyl anthracene monomer was prepared by reacting methyl 9-anthracene acrylate and diethanolamine; the isocyanate-terminated prepolymer was prepared by reacting polytetrahydrofuran glycol, dihydroxyethyl anthracene monomer, and isophorone diisocyanate; and anthracene groups were introduced into the structural adhesive. The anthracene group is a photosensitive chemical reaction group. Studies have shown that the anthracene group can undergo a cycloaddition reaction under UVA (320-400 nm) wavelength light irradiation. This group can undergo a dimerization reaction while the ultraviolet aging reaction occurs, compensating for the damage to the crosslinking network, thereby maintaining the network crosslinking density and further improving the UV aging resistance of the structural adhesive.
[0085] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for preparing a low-VOC polyurethane structural adhesive, characterized in that, The preparation method of the low-VOC polyurethane structural adhesive includes the following preparation steps: (1) Pretreated alumina was prepared by reacting alumina with aminopropyltriethoxysilane; pretreated alumina was prepared by reacting pretreated alumina with triglycidyl isocyanurate; modified alumina was prepared by reacting pretreated alumina with 4-(2H-benzo[D][1,2,3]triazol-2-yl)phenyl-1,3-diol. (2) Dihydroxyethyl anthracene monomer was prepared by reacting methyl 9-anthracene acrylate and diethanolamine; (3) The diethanol composite flame retardant was prepared by reacting 5-(aminomethyl)-2-furan methanol and 5-hydroxymethylfurfural with diethyl phosphite; (4) Polytetrahydrofuran diol, dihydroxyethyl anthracene monomer and isophorone diisocyanate are reacted to prepare isocyanate-terminated prepolymer; the isocyanate-terminated prepolymer, polymethylene polyphenyl polyisocyanate and dehydrating agent are mixed to obtain component B; (5) Mix castor oil, polyester diol, diethanol composite flame retardant, modified alumina and catalyst to obtain component A; (6) Mix component A and component B to obtain a low-VOC polyurethane structural adhesive.
2. The method for preparing the low-VOC polyurethane structural adhesive according to claim 1, characterized in that, The preparation method of the pretreated alumina in step (1) is as follows: alumina, anhydrous ethanol and deionized water are mixed evenly, ultrasonically dispersed, aminopropyltriethoxysilane is added, and the mixture is stirred and reacted at 70~80℃ for 8~10h. After filtration, washing and vacuum drying, pretreated alumina is obtained.
3. The method for preparing a low-VOC polyurethane structural adhesive according to claim 1, characterized in that, The preparation method of the pre-modified alumina in step (1) is as follows: pretreated alumina, triglycidyl isocyanurate and N,N-dimethylformamide are mixed evenly and stirred at 80~90℃ for 10~12h. After filtration, washing and vacuum drying, the pre-modified alumina is obtained.
4. The method for preparing a low-VOC polyurethane structural adhesive according to claim 1, characterized in that, The modified alumina in step (1) is prepared by mixing pre-modified alumina, 4-(2H-benzo[D][1,2,3]triazol-2-yl)benzene-1,3-diol and anhydrous ethanol evenly, adding sodium carbonate aqueous solution, stirring and refluxing at 75~85℃ for 7~9h under nitrogen protection, naturally cooling to room temperature, filtering, washing, and vacuum drying to obtain modified alumina.
5. The method for preparing a low-VOC polyurethane structural adhesive according to claim 1, characterized in that, The preparation method of the dihydroxyethyl anthracene monomer in step (2) is as follows: add methyl 9-anthracene acrylate and diethanolamine to anhydrous ethanol, stir and react at 35~45℃ for 20~24h, remove anhydrous ethanol by vacuum distillation, and obtain dihydroxyethyl anthracene monomer.
6. The method for preparing a low-VOC polyurethane structural adhesive according to claim 1, characterized in that, The preparation method of the diethanol composite flame retardant in step (3) is as follows: 5-(aminomethyl)-2-furan methanol and 5-hydroxymethylfurfural are added to anhydrous ethanol and stirred at 70~80℃ for 7~8h. Diethyl phosphite is added and stirred for 20~24h. Anhydrous ethanol is removed by vacuum distillation to obtain the diethanol composite flame retardant.
7. The method for preparing a low-VOC polyurethane structural adhesive according to claim 1, characterized in that, The method for preparing the isocyanate-terminated prepolymer in step (4) is as follows: polytetrahydrofuran diol, dihydroxyethyl anthracene monomer, and isophorone diisocyanate are mixed evenly, and dibutyltin dilaurate is added. Under nitrogen protection, the mixture is stirred and reacted at 78~82℃ for 2~3h to obtain the isocyanate-terminated prepolymer.
8. The method for preparing a low-VOC polyurethane structural adhesive according to claim 2, characterized in that, The dehydrating agent in step (4) is one or more of p-toluenesulfonyl isocyanate, sodium aluminosilicate, potassium aluminosilicate, and 1,3-oxazinecyclopentane.
9. The method for preparing a low-VOC polyurethane structural adhesive according to claim 2, characterized in that, The catalyst in step (5) is one or more of the following: dibutyltin dilaurate, zinc sulfosuccinate, stannous octoate, N-methylimidazolium, and tetrabutyl titanate.
10. The method for preparing a low-VOC polyurethane structural adhesive according to claim 2, characterized in that, The mass ratio of component A to component B in step (6) is 1:(1.0~1.2).