Low-temperature fast-curing weather-resistant polyurethane adhesive and preparation method thereof

Abstract

The application provides a low-temperature fast-curing weather-resistant polyurethane adhesive and a preparation method thereof, and belongs to the technical field of adhesives. The adhesive is of a two-component structure, which is obtained by mixing component A and component B in proportion. Component A comprises 35-45 parts of an alicyclic isocyanate composition, 33-47 parts of a polyol composition, 10-18 parts of a filler and 0.5-2 parts of an auxiliary composition. Component B comprises 60-80 parts of polyaspartic ester, 8-15 parts of a small-molecule chain extender, 15-25 parts of a polyether polyol, 1.0-2.0 parts of a composite catalyst and 0.2-1.0 parts of a dispersion aid. When components A and B are mixed, the equivalent ratio of isocyanate groups to total active hydrogen is 1.05-1.1:1, and a polyurea-polyurethane hybrid crosslinked structure is formed. The polyurethane adhesive of the application can be rapidly cured to reach practical strength without heating in a low-temperature environment of 0-15 DEG C, and simultaneously has excellent UV aging resistance and wet heat aging resistance.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and in particular to a low-temperature, rapid-curing, weather-resistant polyurethane adhesive and its preparation method. Background Technology

[0002] Polyurethane adhesives are widely used in construction, transportation, electronics, and outdoor engineering due to their wide bonding range, adjustable mechanical properties, and excellent resistance to various media. With the expansion of outdoor applications, higher demands are placed on the weather resistance and low-temperature application performance of adhesives: on the one hand, long-term outdoor use requires resistance to aging effects such as ultraviolet light and alternating hot and humid conditions to avoid yellowing and strength reduction; on the other hand, construction in winter or extremely cold environments requires adhesives to reach practical strength quickly without additional heating, thus shortening the construction cycle.

[0003] Existing polyurethane adhesives can be divided into two categories based on their performance focus. One category aims to improve heat resistance by using aromatic isocyanates combined with aromatic ring-containing polyols to construct rigid molecular chains, supplemented with various inorganic fillers to enhance thermal stability. Although this type of solution can improve the performance retention rate at high temperatures, the aromatic structure is prone to photo-oxidation under ultraviolet irradiation, generating quinone chromophores that lead to yellowing and molecular chain degradation, resulting in insufficient reliability for long-term outdoor use. At the same time, the high rigidity of the molecular structure results in high material viscosity, high steric hindrance of functional group reactions, weak chain segment diffusion ability at low temperatures, and a significant decrease in curing rate, requiring heating conditions to ensure sufficient cross-linking. Another approach aims to improve water-resistant bonding strength by using a blend of polyether and polyester polyols with modified aromatic isocyanates to prepare prepolymers. This involves chain extension with small-molecule diols to enhance cohesive strength, and the addition of nanofillers and silane coupling agents to improve interfacial water resistance. However, this approach still relies primarily on aromatic isocyanates, resulting in inherent limitations in UV aging resistance. Furthermore, the crosslinking reaction depends on the addition reaction between hydroxyl groups and isocyanates, and the reaction rate decreases exponentially at low temperatures. Optimal performance can only be achieved through a post-curing process at around 80°C, which fails to meet the construction requirements for low-temperature, heat-free, and rapid curing.

[0004] In summary, existing technologies cannot simultaneously achieve rapid curing at low temperatures without heating and long-term weather resistance, making them unsuitable for long-term use in outdoor low-temperature environments. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a low-temperature rapid curing weather-resistant polyurethane adhesive and its preparation method. The adhesive can be rapidly cured to practical strength without heating in a low-temperature environment of 0~15℃, and at the same time has excellent resistance to ultraviolet aging and damp heat aging.

[0006] To achieve the above objectives, the present invention provides the following solution: On the one hand, the present invention provides a low-temperature fast-curing weather-resistant polyurethane adhesive, wherein the polyurethane adhesive has a two-component structure, which is cured by mixing component A and component B in a certain proportion; Component A comprises the following components in parts by weight: 35-45 parts of alicyclic isocyanate composition; 33-47 parts of polyol composition; 10-18 parts of filler; and 0.5-2 parts of auxiliary agent composition; Component B comprises the following components in parts by weight: 60-80 parts of polyaspartic acid ester; 8-15 parts of small molecule chain extender; 15-25 parts of polyether polyol; 1.0-2.0 parts of composite catalyst; and 0.2-1.0 parts of dispersant. When components A and B are mixed, the equivalent ratio of isocyanate groups to total active hydrogen is 1.05~1.1:1, and the isocyanate groups undergo addition reactions with amino and hydroxyl groups to form a polyurea-polyurethane hybrid crosslinked structure.

[0007] Preferably, the alicyclic isocyanate composition is obtained by compounding hydrogenated diphenylmethane diisocyanate and isophorone diisocyanate in a mass ratio of 7~8:2~3.

[0008] Preferably, the polyol composition is obtained by compounding high-primary-hydroxyl polyoxypropylene triol and polycarbonate diol in a mass ratio of 2.5 to 3.5:1.

[0009] Preferably, the filler is a modified composite nanofiller, which is obtained by in-situ modification of coated rutile nano-TiO2 and gaseous nano-SiO2 with a silane coupling agent, and the mass ratio of the two is 1:1.2~1.5.

[0010] Preferably, in the modified composite nanofiller, the silane coupling agent is a complex coupling agent, which is a mixture of γ-mercaptopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 1:1.

[0011] Preferably, the additive composition is a mixture of polyether-modified silicone defoamer, polyacrylate leveling agent, and molecular sieve dehydrating agent in a mass ratio of 1:1:1; the composite catalyst is a mixture of organic bismuth catalyst and triethylenediamine in a mass ratio of 2:1.

[0012] Preferably, the small molecule chain extender is 1,4-butanediol, the polyether polyol is polyoxypropylene glycol with a molecular weight of 1000, and the dispersing agent is a polyether-type dispersant.

[0013] On the other hand, the present invention also provides a method for preparing the above-mentioned low-temperature rapid-curing weather-resistant polyurethane adhesive, comprising the following steps: S1. After dehydrating the polyol composition, add the alicyclic isocyanate composition for prepolymerization until the isocyanate group content reaches the preset value. Then add filler to disperse the fineness of the material, add the auxiliary composition and mix evenly. After degassing under vacuum, discharge the material to obtain component A. S2. Mix polyaspartic acid ester, small molecule chain extender, and polyether polyol evenly, then add composite catalyst and dispersant and continue stirring until completely dispersed. Degas under vacuum and discharge to obtain component B. S3. Mix component A and component B in a certain proportion until uniform, and after curing, the low-temperature fast-curing weather-resistant polyurethane adhesive is obtained.

[0014] Preferably, in step S1, the dehydration treatment temperature is 110~120℃, and vacuum dehydration is performed until the moisture content is no more than 0.05%; the prepolymerization reaction is carried out under nitrogen protection at 80~85℃ for 2.5~3h until the isocyanate group content reaches 4.5%~5.5%; the filler is added in batches and dispersed at high speed at 1200~1500rpm for 20~40min, and then treated by horizontal sand milling until the material fineness is no more than 20μm.

[0015] Preferably, in steps S1 and S2, the vacuum degree of the vacuum degassing is not higher than -0.095 MPa, and the degassing time is 3 to 10 min; in step S2, each component is stirred at a speed of 300 to 500 rpm for 5 to 20 min until uniform, and after adding the composite catalyst and dispersing agent, stirring is continued for 10 to 20 min.

[0016] Compared with the prior art, the present invention discloses at least the following technical effects: (1) This invention uses alicyclic isocyanate instead of traditional aromatic isocyanate, which avoids the formation of quinone chromophores under ultraviolet light irradiation from the molecular structure perspective. The yellowing resistance and UV aging resistance of the material are significantly better than those of aromatic solutions. At the same time, the polyol component is a compound of high primary hydroxyl polyoxypropylene triol and polycarbonate diol. The polyether backbone can still maintain good flexibility at low temperature, ensuring the mobility of macromolecular chain segments. The reactivity of high primary hydroxyl groups is much higher than that of ordinary secondary hydroxyl groups, which can effectively compensate for the low reactivity of alicyclic isocyanates and create conditions for rapid curing under low temperature conditions.

[0017] (2) Regarding the crosslinking reaction, component B uses the secondary amino group of polyaspartic acid ester as the main crosslinking functional group. The secondary amino group has a much higher reactivity with isocyanate groups than hydroxyl groups at low temperatures, solving the problem of slow reaction rate at low temperatures in the traditional pure hydroxyl crosslinking route. The compound catalyst has high selectivity for the NCO-NH reaction and can still effectively promote the crosslinking reaction at low temperatures, avoiding over-catalysis of side reactions such as moisture. The addition of small molecule chain extenders and polyether polyols can flexibly adjust the crosslinking density and the flexibility of the adhesive layer, so that both the curing speed and the operating window are within a suitable range. The amino and hydroxyl groups participate in the reaction together, and finally form a polyurea-polyurethane hybrid crosslinking network, giving the adhesive layer rapid crosslinking ability and good mechanical properties.

[0018] (3) Regarding the filler treatment, this invention modifies the composite nanofiller by in-situ grafting with silane coupling agents, giving the filler surface active functional groups that can react with isocyanate groups, thereby forming chemical bonds with the resin matrix, further improving the interfacial bonding force between the filler and the matrix, and reducing interfacial defects. Simultaneously, the coated rutile nano-TiO2 surface is covered with an inert inorganic layer, effectively inhibiting its photocatalytic activity and preventing accelerated aging of the resin matrix; the introduction of vapor-phase nano-SiO2 further enhances the barrier effect against water vapor and oxygen. Thus, this invention achieves rapid low-temperature curing while maintaining excellent long-term weather resistance, meeting the requirements for use in outdoor low-temperature environments. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of a method for preparing a low-temperature, rapid-curing, weather-resistant polyurethane adhesive according to the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] like Figure 1 As shown, this invention provides a method for preparing a low-temperature, rapid-curing, weather-resistant polyurethane adhesive, comprising the following steps: S1. After dehydrating the polyol composition, add the alicyclic isocyanate composition for prepolymerization until the isocyanate group content reaches the preset value. Then add filler to disperse until the material fineness meets the standard. Add the auxiliary composition and mix evenly. After degassing under vacuum, discharge the material to obtain component A.

[0024] Specifically, the polyol composition in step S1 is obtained by compounding high primary hydroxyl polyoxypropylene triol and polycarbonate diol at a mass ratio of 2.5~3.5:1, and the amount used is 33~47 parts. The high primary hydroxyl polyoxypropylene triol has a molecular weight of 3000, and the proportion of primary hydroxyl groups is not less than 85%. Its molecular chain ends with primary hydroxyl groups, and its reactivity is much higher than that of ordinary secondary hydroxyl polyethers. It can react rapidly with isocyanate groups to form urethane bonds in the prepolymerization reaction. At the same time, the ether bonds in the polyether backbone endow it with good flexibility and low-temperature chain segment mobility, so that the prepolymer still maintains low viscosity and good flowability and wettability at low temperatures.

[0025] In addition, polycarbonate diol has a molecular weight of 2000 and contains carbonate bonds in its molecular structure. Compared with polyester polyol, it has better hydrolytic stability and can significantly improve the adhesive's resistance to humid heat aging. At the same time, the polar carbonate groups in its molecular chain can enhance the adhesion to metal substrates. Both polyols were heated at 110~120℃ under vacuum and continuously dehydrated under vacuum for 2 hours to reduce the moisture content of the system to below 0.05%, preventing the reaction of moisture with isocyanate to form urea bonds and carbon dioxide bubbles, and ensuring that the prepolymerization reaction proceeds according to the stoichiometric ratio.

[0026] Further, after dehydration, the temperature is lowered to 60°C, and 35-45 parts of an alicyclic isocyanate composition are added under nitrogen protection. This alicyclic isocyanate composition is obtained by compounding hydrogenated diphenylmethane diisocyanate and isophorone diisocyanate in a mass ratio of 7-8:2-3. The hydrogenated diphenylmethane diisocyanate molecule contains two alicyclic isocyanate groups, which have moderate reactivity and impart good initial tack strength and cohesive strength to the prepolymer. The isophorone diisocyanate molecule has two isocyanate groups located on a cyclohexane ring, and their reactivity differs. One of them is significantly affected by the steric hindrance of the methyl group and the cyclohexane ring, which is beneficial to the gradual increase of molecular weight and the steady increase of prepolymer viscosity during the reaction process. The compounding of the two makes the molecular weight distribution of the prepolymer more uniform. The temperature is raised to 80-85°C and stirred for 2.5-3 hours. At this temperature, the addition reaction rate of the isocyanate groups and hydroxyl groups is suitable and there are few side reactions.

[0027] In addition, NCO content was measured every 30 minutes during the reaction, and the reaction was stopped when the measured value reached 4.5%~5.5%. This NCO content range corresponds to a suitable molecular weight of the prepolymer, which can ensure sufficient crosslinking point density when crosslinking with component B, without causing excessive viscosity due to excessive molecular weight, which would be detrimental to filler dispersion.

[0028] Subsequently, 10-18 parts of modified composite nanofiller were added to the prepolymer. The preparation method of the filler is as follows: Coated rutile nano-TiO2 and fumed nano-SiO2 are added to anhydrous ethanol at a mass ratio of 1:1.2~1.5 to prepare a suspension with a solid content of 15%~20%. A compound silane coupling agent accounting for 2%~3% of the total mass of the filler is added. The compound coupling agent is a mixture of γ-mercaptopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane at a mass ratio of 1:1. The pH is adjusted to 4~5 with glacial acetic acid to hydrolyze the silane coupling agent to generate silanol groups. The mixture is ultrasonically dispersed for 30 min to break up the nanofiller agglomerates. The temperature is raised to 60℃ and stirred for 2 h to allow the hydrolyzed silanol groups to undergo a dehydration condensation reaction with the hydroxyl groups on the surface of the filler, thereby achieving covalent grafting of the silane coupling agent. After centrifugation, the mixture is washed three times with anhydrous ethanol to remove unreacted coupling agent. The mixture is then vacuum dried at 80℃ for 12 h, ground, and sieved to obtain the final product.

[0029] Among them, the surface of the coated rutile nano-TiO2 is coated with an inert layer of alumina / silica, which can effectively shield the photocatalytic activity of TiO2 and prevent it from catalytically degrading the surrounding resin matrix under ultraviolet irradiation; the gas phase nano-SiO2 has a high specific surface area and nano-sized particle size, which can fill the gaps between nano-TiO2 particles to form a dense filler stacking structure.

[0030] In addition, the filler was added in three batches and dispersed at high speed by shearing at 1200-1500 rpm for 20-40 minutes. Then, it was subjected to horizontal sand milling to ensure the material fineness was no greater than 20 μm, guaranteeing that the filler was uniformly dispersed in the prepolymer at the nanoscale, preventing agglomerates from becoming stress concentration points and penetration channels for aging media. Finally, 0.5-2 parts of an auxiliary composition were added. This auxiliary composition consisted of polyether-modified silicone defoamer, polyacrylate leveling agent, and molecular sieve dehydrating agent in a mass ratio of 1:1:1. The mixture was stirred at low speed at 200-300 rpm for 15 minutes. The defoamer reduced the surface tension of the system, promoting bubble escape; the leveling agent improved the wetting and spreading properties of the adhesive on the substrate surface; and the dehydrating agent further captured trace amounts of moisture in the system. Afterward, the mixture was defoamed for 3-10 minutes under a vacuum degree not exceeding -0.095 MPa, discharged, and stored under nitrogen purging and sealing to obtain component A.

[0031] S2. Mix polyaspartic acid ester, small molecule chain extender, and polyether polyol evenly, then add composite catalyst and dispersant and continue stirring until completely dispersed. After degassing under vacuum, discharge to obtain component B.

[0032] Specifically, in step S2, the amount of polyaspartic acid ester is 60-80 parts. Its two secondary amino groups are located on the side groups of the diethyl succinate backbone, regulated by the steric hindrance effect of adjacent ester groups and side alkyl groups. The secondary amino groups have moderate reactivity, ensuring that the pot life after mixing is not too short due to excessive reactivity, while still maintaining a reaction rate much higher than that of hydroxyl groups at low temperatures. The amount of small molecule chain extender is 8-15 parts, using 1,4-butanediol. Its simple molecular structure and high reactivity of the primary hydroxyl groups at both ends allow it to react rapidly with isocyanate groups during curing, playing a role in chain extension and regulating crosslinking density, increasing the content of hard segments in polyurethane, and improving the cohesive strength and modulus of the adhesive layer. The amount of polyether polyol is 15-25 parts, using polypropylene glycol with a molecular weight of 1000. Its low molecular weight and good chain flexibility allow it to adjust the viscosity of component B and the flexibility of the cured product, avoiding excessive crosslinking density that could increase the brittleness of the adhesive layer.

[0033] The three components were added to a stirred tank in the specified proportions and stirred at 300-500 rpm for 5-20 minutes until homogeneous. Then, 1.0-2.0 parts of the composite catalyst and 0.2-1.0 parts of the dispersant were added. The composite catalyst was a mixture of an organobismuth catalyst and triethylenediamine in a 2:1 mass ratio. The organobismuth catalyst exhibits high selectivity for the NCO-NH reaction, directionally accelerating the addition reaction between isocyanate groups and amino groups, while showing lower catalytic activity for the NCO-OH reaction and the NCO-H2O side reaction, thus reducing side reactions while ensuring the low-temperature curing rate. Triethylenediamine is a tertiary amine catalyst, and its synergistic effect with organobismuth further enhances the NCO-NH reaction rate at low temperatures. The catalytic activity of the mixture is superior to that of traditional organotin catalysts in the low-temperature range.

[0034] In addition, the dispersant is a polyether-type dispersant, whose anchoring groups in its molecular chain can be adsorbed onto the surface of the filler, and the solvated segments extend into the medium, preventing flocculation and sedimentation of the filler during storage through steric hindrance. After addition, continue stirring at 300~500 rpm for 10~20 min to ensure that the catalyst and dispersant are fully and uniformly dispersed in component B. Then, degas under a vacuum degree not exceeding -0.095 MPa for 3~10 min and discharge the material. Store in a sealed and dry environment to obtain component B.

[0035] In component B, primary and secondary amino groups coexist, as well as amino and hydroxyl groups. During storage, the polyether-type dispersant can effectively isolate the active components, inhibit the reaction of amino groups with CO2 in the air and the side reactions caused by trace amounts of moisture, and ensure that component B has sufficient storage stability.

[0036] S3. Mix component A and component B in a certain proportion until uniform, and after curing, the low-temperature fast-curing weather-resistant polyurethane adhesive is obtained.

[0037] Specifically, in step S3, components A and B are mixed in proportion, and the equivalent ratio of isocyanate groups to total active hydrogen (the sum of amino and hydroxyl groups) is controlled to be 1.05~1.1:1, that is, the isocyanate groups are slightly in excess. The excess isocyanate groups can compensate for the trace water consumption in the system, while ensuring that the crosslinking reaction proceeds fully and avoiding residual active hydrogen from affecting the water resistance of the adhesive layer.

[0038] After mixing, the isocyanate groups simultaneously undergo addition reactions with the secondary amino groups in polyaspartic acid ester and the primary hydroxyl groups in 1,4-butanediol. The NCO-NH reaction rate is significantly faster than the NCO-OH reaction. The secondary amino groups of polyaspartic acid ester preferentially react with the isocyanate groups to form urea bonds, rapidly forming the primary structure of the crosslinked network and imparting early strength to the adhesive layer. Subsequently, 1,4-butanediol reacts with the remaining isocyanate groups and unreacted NCO-terminated prepolymers in the system to form urethane bonds, further increasing the crosslinking density and refining the network structure, ultimately forming a polyurea-polyurethane hybrid crosslinked network.

[0039] Furthermore, the urea bonds in this hybrid network are more polar than the urethane bonds, enabling stronger intermolecular hydrogen bonding and imparting higher cohesive strength and heat resistance to the adhesive layer. Simultaneously, the polyether segments provide flexibility and low-temperature toughness, preventing the adhesive layer from becoming brittle at low temperatures. In addition, the silane coupling agent grafted onto the filler surface contains thiol and epoxy groups. The thiol groups can react with isocyanate groups in the system to form thiourethane bonds, while the epoxy groups can be ring-opened by trace amounts of active hydrogen in the system during curing. This results in a covalent bond between the filler and the resin matrix, rather than a simple physical coating. This chemically bonded interface effectively eliminates interfacial defects between the filler and the matrix, allowing stress to be effectively transferred at the interface while blocking the channels for aging media such as water vapor and oxygen to penetrate along the interface. The entire reaction process maintains a sufficient reaction rate even at low temperatures of 0–15°C, gelling within 30–60 minutes after application and reaching practical bonding strength within 24 hours, meeting the requirements for rapid assembly and positioning under outdoor low-temperature conditions.

[0040] The above content will be further described below through specific implementation methods, wherein all raw materials used are commercially available industrial-grade products.

[0041] Example 1 This embodiment aims to provide a low-temperature, rapid-curing, weather-resistant polyurethane adhesive, with the following component composition: Component A, comprising 100 parts of raw materials, includes: 40 parts of an alicyclic isocyanate composition consisting of 30 parts of hydrogenated diphenylmethane diisocyanate and 10 parts of isophorone diisocyanate; 42 parts of a polyol composition consisting of 32 parts of high-primary-hydroxyl polyoxypropylene triol and 10 parts of polycarbonate diol; 16 parts of a modified composite nanofiller consisting of 7 parts of coated rutile nano-titanium dioxide and 9 parts of fumed nano-silica; and 2 parts of an additive composition consisting of 0.7 parts of polyether-modified silicone defoamer, 0.7 parts of polyacrylate leveling agent, and 0.6 parts of molecular sieve dehydrating agent.

[0042] Component B, consisting of 100 parts of raw materials, includes: 70 parts of polyaspartic acid ester; 10 parts of 1,4-butanediol; 18 parts of polypropylene glycol (molecular weight 1000); 1.5 parts of composite catalyst, composed of 1 part of organic bismuth catalyst and 0.5 parts of triethylenediamine; and 0.5 parts of dispersant.

[0043] When using, components A and B are mixed at a mass ratio of 100:25, with the corresponding isocyanate group to total active hydrogen equivalent ratio being 1.08:1.

[0044] The modified composite nanofiller is prepared as follows: coated rutile nano-titanium dioxide and fumed nano-silica are added to anhydrous ethanol at a mass ratio of 1:1.2~1.5 to prepare a suspension with a solid content of 15%~20%. A compound silane coupling agent accounting for 2%~3% of the total mass of the filler is added. γ-mercaptopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane are mixed at a mass ratio of 1:1. The pH is adjusted to 4~5 with glacial acetic acid, and the mixture is ultrasonically dispersed for 30 min. The mixture is heated to 60℃ and stirred for 2 h. After centrifugation, the mixture is washed 3 times with anhydrous ethanol, vacuum dried at 80℃ for 12 h, and then ground and sieved to obtain the final product.

[0045] The polyurethane adhesive preparation method provided in this embodiment is as follows: Preparation of Component A: High-primary-hydroxyl polyoxypropylene triol and polycarbonate diol were added to a reaction vessel in proportion, heated to 120°C, and dehydrated for 2 hours under a vacuum of not less than 0.095 MPa. After the moisture content was found to be no more than 0.05%, the temperature was lowered to 60°C. Nitrogen gas was introduced for protection, and the alicyclic isocyanate composition was slowly added. After stirring evenly, the temperature was raised to 85°C and reacted at a constant temperature for 3 hours. During this period, the isocyanate group content was titrated every 30 minutes. The reaction was stopped when the measured value reached 5.5%. The modified composite nanofiller was added to the prepolymer in 3 batches and dispersed at high speed at 1500 rpm for 30 minutes. Then, it was treated by horizontal sand milling to a fineness of no more than 20 μm. Defoamer, leveling agent, and dehydrating agent were added, and the mixture was stirred at low speed at 300 rpm for 15 minutes. After vacuum degassing for 5 minutes, the mixture was discharged, sealed with nitrogen, and stored.

[0046] Preparation of Component B: Polyaspartic acid ester, 1,4-butanediol and polypropylene glycol were added to a stirred tank in proportion and stirred at 300 rpm for 10 min at room temperature until homogeneous; the composite catalyst and dispersant were added and stirred for another 15 min until completely dispersed; after vacuum degassing for 5 min, the material was discharged and stored in a sealed and dry environment.

[0047] Example 2 The component ratios in this embodiment are basically the same as those in Embodiment 1, except that: Component A contains 35 parts of an alicyclic isocyanate composition, consisting of approximately 27 parts of hydrogenated diphenylmethane diisocyanate and approximately 8 parts of isophorone diisocyanate; 47 parts of a polyol composition, consisting of approximately 36 parts of high-primary-hydroxyl polypropylene triol and approximately 11 parts of polycarbonate diol; 16 parts of modified composite nanofiller; and 2 parts of additives. Component B contains 65 parts of polyaspartic acid ester, 12 parts of 1,4-butanediol, 21 parts of polypropylene diol, 1.5 parts of composite catalyst, and 0.5 parts of dispersant. Components A and B are mixed at a mass ratio of 100:27, corresponding to an isocyanate group to total active hydrogen equivalent ratio of 1.05:1.

[0048] Example 3 The component ratios in this embodiment are basically the same as those in Embodiment 1, except that: Component A contains 45 parts of an alicyclic isocyanate composition, consisting of approximately 35 parts of hydrogenated diphenylmethane diisocyanate and approximately 10 parts of isophorone diisocyanate; 37 parts of a polyol composition, consisting of approximately 28 parts of high-primary-hydroxyl polyoxypropylene triol and approximately 9 parts of polycarbonate diol; 16 parts of modified composite nanofiller; and 2 parts of additives. Component B contains 75 parts of polyaspartic acid ester, 8 parts of 1,4-butanediol, 15 parts of polyoxypropylene diol, 1.5 parts of composite catalyst, and 0.5 parts of dispersant. Components A and B are mixed at a mass ratio of 100:23, corresponding to an isocyanate group to total active hydrogen equivalent ratio of 1.1:1.

[0049] Comparative Example 1 This comparative example uses an aromatic isocyanate as the main component, combined with aromatic ring polyols and pure hydroxyl crosslinking, corresponding to the main characteristics of existing heat-resistant solutions: the isocyanate used is pure diphenylmethane diisocyanate, the polyol is a mixture of resorcinol diglycidyl ether and polytetrahydrofuran ether diol, the crosslinking agent is trimethylolpropane, and the catalyst is a mixture of organotin and triethylenediamine; the preparation process uses the prepolymer method, the filler is a physically blended fumed silica and ordinary titanium dioxide; and the curing method is room temperature curing.

[0050] Comparative Example 2 This comparative example employs a pure hydroxyl crosslinking design using a modified diphenylmethane diisocyanate, a polyether and polyester polyol blend, and 1,4-butanediol chain extension. This design corresponds to the main characteristics of existing water-resistant, high-strength solutions: the isocyanate used is modified diphenylmethane diisocyanate; the polyol is a blend of polyether and polyester polyol; the chain extender is 1,4-butanediol; and the catalyst is dibutyltin dilaurate. The preparation process uses a prepolymer plus chain extender process, with the filler being a simple blend of fumed silica and silane coupling agent KH-550. The curing method is initial curing at 25℃ for 24 hours, followed by post-curing at 80℃ for 2 hours.

[0051] Comparative Example 3 This comparative example retains the all-alicyclic isocyanate backbone and modified weather-resistant filler of the present invention, only removing polyaspartic acid ester and replacing it with a pure hydroxyl crosslinking system to verify the necessity of amino crosslinking for low-temperature rapid curing. Component A is exactly the same as in Example 1; Component B does not contain polyaspartic acid ester, and uses 1,4-butanediol and trimethylolpropane in a mass ratio of 7:3 as a pure hydroxyl crosslinking agent. The total active hydrogen equivalent of the crosslinking agent is equivalent to that of Component B in Example 1. Polypropylene glycol, composite catalyst and dispersant are retained, and the dosage is the same as in Example 1. When using, components A and B are mixed at an isocyanate group to hydroxyl equivalent ratio of 1.08:1, and the preparation process is the same as in Example 1.

[0052] Comparative Example 4 This comparative example retains the rapid-curing crosslinking system of polyaspartic acid ester of the present invention, but replaces it with aromatic isocyanate and ordinary unmodified filler to verify that high weather resistance cannot be achieved simultaneously by polyaspartic acid ester alone. Component A replaces the alicyclic isocyanate with pure diphenylmethane diisocyanate, and the amount is adjusted so that the content of isocyanate groups in the prepolymer is equivalent to that of component A in Example 1; the polyol composition is the same as in Example 1; the filler is replaced with uncoated ordinary rutile nano-titanium dioxide and unmodified fumed nano-silica through physical blending, without in-situ silane modification, and the total amount of filler is the same as in Example 1; component B is exactly the same as in Example 1; when using, components A and B are mixed at an isocyanate group to total active hydrogen equivalent ratio of 1.08:1, and the preparation process is the same as in Example 1.

[0053] Comparative Example 5 This comparative example retains the all-alicyclic isocyanate backbone and polyaspartic acid ester fast-curing crosslinking system of the present invention, only replacing the filler with physical blending instead of in-situ silane modification, to verify the contribution of filler interfacial chemical bonding to weather resistance and water resistance. The isocyanate and polyol composition and dosage in component A are completely consistent with those in Example 1; the filler uses the same proportion of coated rutile nano-titanium dioxide and fumed nano-silica, without in-situ modification with silane coupling agent, and is directly added to the prepolymer by physical blending, and the total filler dosage is consistent with that in Example 1; the composition and dosage of the additives are the same as in Example 1; component B is completely the same as in Example 1; when using, components A and B are mixed at an isocyanate group to total active hydrogen equivalent ratio of 1.08:1, and the preparation process is the same as in Example 1 except for the filler modification step.

[0054] For Examples 1-3 and Comparative Examples 1-5 above, the low-temperature curing performance, weather resistance, substrate adhesion performance, and water resistance were tested respectively. The test methods are as follows: Gel time: After mixing components A and B in a certain proportion at a constant temperature of 10℃, the gel time of the mixture was tested using the glass rod method.

[0055] Low-temperature curing strength: After curing at 10℃ for 24 hours, the aluminum-aluminum tensile shear strength was tested.

[0056] Yellowing resistance: The yellowing index ΔYI was tested after 1000 hours of UV aging under QUV-A (340nm) conditions.

[0057] Aging strength retention rate: After 1000h of UV aging under QUV-A (340nm) conditions, the tensile shear strength of the fully cured specimen was tested, and the percentage of the strength before aging was calculated.

[0058] Room temperature curing strength: After curing at 25℃ for 24 hours, the aluminum-aluminum tensile shear strength was tested. Comparative Example 2 was tested after curing at 80℃.

[0059] Water resistance strength retention rate: After immersion in deionized water at room temperature for 168 hours, the tensile shear strength of the fully cured sample was tested, and the percentage of the strength before immersion was calculated.

[0060] The test results are shown in Tables 1 and 2 below: Table 1 Performance test results of Examples 1-3 of the present invention

[0061] Table 2 Performance test results of Comparative Examples 1-5 of the present invention

[0062] *Note: The values ​​in Comparative Example 2 are test results after curing at 80℃. Its shear strength is 6.8 MPa after curing at room temperature for 24 hours.

[0063] As shown in Table 1, the gel time of Examples 1-3 of the present invention was no more than 52 min at a low temperature of 10℃, and the shear strength after 24 h was all above 4.7 MPa, indicating that the adhesive can quickly establish practical strength without heating at low temperatures. After 1000 h of QUV aging, the yellowing index was all below 4.1, the aging strength retention rate was no less than 79.2%, and the strength retention rate after water immersion was no less than 88.5%, indicating that while achieving rapid curing at low temperatures, the material also has excellent weather resistance and water resistance. Among the three examples, Example 3 had the highest isocyanate group content, the shortest gel time, and the highest crosslinking density, thus having the highest low-temperature strength and room-temperature strength, but a relatively short pot life. Example 2 had the lowest isocyanate group content, and its gel time and various strength indicators were slightly lower than those of Example 3, but its operating window was the widest. The above results show that within an equivalent ratio range of 1.05 to 1.1:1, Examples 1-3 can achieve a good balance between rapid curing at low temperatures and high weather resistance.

[0064] Table 2 shows that Comparative Example 1 and Comparative Example 2 represent two typical solutions in the prior art, both employing aromatic isocyanates and pure hydroxyl crosslinking systems. Both exhibit gel times exceeding 300 min at 10℃ and shear strengths below 2.1 MPa after 24 hours of low-temperature curing, indicating severely insufficient reactivity of the traditional pure hydroxyl crosslinking system at low temperatures. Furthermore, after UV aging, the yellowing index is above 11, and the aging strength retention rate is less than 56%, indicating poor weather resistance of aromatic structures in long-term outdoor use. Although Comparative Example 2 achieves a room-temperature shear strength of 18.2 MPa after curing at 80℃, it cannot be cured by heating in actual low-temperature construction scenarios. Its strength after only 24 hours of room-temperature curing is only 6.8 MPa, failing to meet the requirements for rapid assembly and positioning.

[0065] Comparative Example 3 replaced aromatic isocyanate with alicyclic isocyanate, retaining the pure hydroxyl crosslinking system. Its yellowing index of 4.0 and aging strength retention rate of 78.9% were significantly better than those of Comparative Examples 1 and 2, indicating that the alicyclic skeleton plays a decisive role in improving weather resistance. However, its gel time at 10℃ was still as long as 230 min, and its shear strength after 24 h of low-temperature curing was only 2.6 MPa, indicating that simply replacing the alicyclic skeleton cannot solve the problem of slow low-temperature curing rate.

[0066] Comparative Example 4 retains the rapid-curing crosslinking system of polyaspartic acid ester, but the isocyanate is still aromatic and the filler is not coated or modified. Its gel time at 10℃ is only 32 min and its low-temperature strength reaches 5.5 MPa, indicating that amino crosslinking is the key to achieving rapid curing at low temperature. However, the yellowing index of 11.9 and the aging strength retention rate of 54.2% are comparable to those of Comparative Examples 1 and 2, indicating that polyaspartic acid ester alone cannot overcome the weather resistance defects of aromatic structures.

[0067] The filler in Comparative Example 5, which was not modified in situ with silane, had an aging strength retention rate of 71.8% and a water resistance retention rate of 83.5%, both lower than those of Example 1 (80.5% and 89.2%). This demonstrates that the chemical bonding interface between the filler and the matrix can be used to block the penetration path of aging media and improve the long-term performance retention rate.

[0068] Based on the comparison results of Comparative Examples 3-5 and Example 1, it can be seen that the secondary amine crosslinking system mainly contributes to the low-temperature rapid curing capability, the full alicyclic isocyanate skeleton mainly contributes to the weather resistance, and the filler interface chemical bonding mainly contributes to the long-term performance retention rate. Thus, the present invention can simultaneously solve the technical problem that it is difficult to achieve both low-temperature rapid curing and long-term weather resistance in the prior art.

[0069] Using Example 1 as a sample, the gelation time (application period) under different ambient temperatures was tested, and the results are shown in Table 3 below: Table 3. Gel time of Sample 1 in Example 1 at different ambient temperatures.

[0070] Table 3 shows that the gelation time of this invention is 75-85 min at 0℃ and 18-45 min at room temperature (15-25℃), with the gelation time gradually decreasing as the temperature increases. The fact that it can still gel within 85 min at 0℃ indicates that the secondary amino group of the polyaspartic acid ester maintains high reactivity towards the isocyanate group at low temperatures. This gelation time range also meets the requirements for outdoor low-temperature application. At 25℃, the gelation time is shortened to 18-25 min, still within the operable applicable range, and will not affect the application process due to excessively rapid curing. These results demonstrate that this invention has a controllable applicable period within a wide temperature range of 0-25℃, adaptable to the outdoor application needs of different seasons and regions, and does not have the limitation of being effective only at a single temperature.

[0071] In addition, to address the storage stability issue of the coexistence of amino groups and catalysts in component B, accelerated storage tests were conducted: component B was sealed in an aluminum foil composite bag and stored at a constant temperature of 25°C for 6 months and at a constant temperature of 50°C for 7 days. The gel time at 10°C and the shear strength after 24 hours of curing at room temperature were tested after mixing with component A before and after storage. The viscosity change at 25°C was also tested. The results are shown in Table 4 below. Table 4 Storage stability verification results

[0072] Table 4 shows that after 6 months of storage at 25℃, the gel time change rate at 10℃ did not exceed 8%, the shear strength change rate at room temperature did not exceed 7%, and the viscosity increase did not exceed 10%, while the system remained homogeneous, transparent, and free of gelation. After 7 days of accelerated storage at 50℃, the gel time change rate did not exceed 12%, the shear strength change rate did not exceed 10%, and the viscosity increased from approximately 1200 mPa·s to approximately 1416 mPa·s, an increase of approximately 18%, while the system again remained homogeneous and free of gelation. The secondary amino group of polyaspartic acid ester and the primary hydroxyl group of 1,4-butanediol coexist in component B, theoretically presenting a possibility of slow side reactions. However, the above results indicate that the polyether-type dispersant effectively isolated the active components through steric hindrance, inhibiting the side reactions of amino and hydroxyl groups during storage, as well as the reaction of amino groups with CO2 in the air. This ensured the chemical stability of component B under normal temperature storage and accelerated aging conditions, meeting the storage and transportation requirements of industrial products.

[0073] If a further extension of the high-temperature storage period is required, 0.1 to 0.5 parts of a stabilizer (such as benzoyl chloride or p-toluenesulfonyl isocyanate) can be added to component B. By consuming trace amounts of moisture and free alkali in the system, side reactions can be further suppressed, thus extending the storage period.

[0074] Therefore, the above-mentioned low-temperature rapid curing weather-resistant polyurethane adhesive and its preparation method can be used to achieve practical strength by rapidly curing at a low temperature of 0~15℃ without heating, while also possessing excellent resistance to ultraviolet aging and damp heat aging.

[0075] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0076] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A low-temperature, rapid-curing, weather-resistant polyurethane adhesive, characterized in that, The polyurethane adhesive has a two-component structure, consisting of component A and component B mixed in a certain proportion and then cured for use. Component A comprises the following components in parts by weight: 35-45 parts of alicyclic isocyanate composition; 33-47 parts of polyol composition; 10-18 parts of filler; and 0.5-2 parts of auxiliary agent composition; Component B comprises the following components in parts by weight: 60-80 parts of polyaspartic acid ester; 8-15 parts of small molecule chain extender; 15-25 parts of polyether polyol; 1.0-2.0 parts of composite catalyst; and 0.2-1.0 parts of dispersant. When components A and B are mixed, the equivalent ratio of isocyanate groups to total active hydrogen is 1.05~1.1:1, and the isocyanate groups undergo addition reactions with amino and hydroxyl groups to form a polyurea-polyurethane hybrid crosslinked structure.

2. The polyurethane adhesive according to claim 1, characterized in that, The alicyclic isocyanate composition is obtained by compounding hydrogenated diphenylmethane diisocyanate and isophorone diisocyanate in a mass ratio of 7~8:2~3.

3. The polyurethane adhesive according to claim 1, characterized in that, The polyol composition is obtained by compounding high-primary-hydroxyl polyoxypropylene triol and polycarbonate diol in a mass ratio of 2.5 to 3.5:

1.

4. The polyurethane adhesive according to claim 1, characterized in that, The filler is a modified composite nanofiller, which is obtained by in-situ modification of coated rutile nano-TiO2 and gaseous nano-SiO2 with a silane coupling agent, and the mass ratio of the two is 1:1.2~1.

5.

5. The polyurethane adhesive according to claim 4, characterized in that, In the modified composite nanofiller, the silane coupling agent is a complex coupling agent, which is a mixture of γ-mercaptopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 1:

1.

6. The polyurethane adhesive according to claim 1, characterized in that, The additive composition is a compound of polyether modified silicone defoamer, polyacrylate leveling agent, and molecular sieve dehydrating agent in a mass ratio of 1:1:1; the composite catalyst is a compound of organic bismuth catalyst and triethylenediamine in a mass ratio of 2:

1.

7. The polyurethane adhesive according to claim 1, characterized in that, The small molecule chain extender is 1,4-butanediol, the polyether polyol is polyoxypropylene glycol with a molecular weight of 1000, and the dispersing agent is a polyether-type dispersant.

8. A method for preparing a low-temperature rapid-curing weather-resistant polyurethane adhesive as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. After dehydrating the polyol composition, add the alicyclic isocyanate composition for prepolymerization until the isocyanate group content reaches the preset value. Then add filler to disperse the fineness of the material, add the auxiliary composition and mix evenly. After degassing under vacuum, discharge the material to obtain component A. S2. Mix polyaspartic acid ester, small molecule chain extender, and polyether polyol evenly, then add composite catalyst and dispersant and continue stirring until completely dispersed. Degas under vacuum and discharge to obtain component B. S3. Mix component A and component B in a certain proportion until uniform, and after curing, the low-temperature fast-curing weather-resistant polyurethane adhesive is obtained.

9. The preparation method according to claim 8, characterized in that, In step S1, the dehydration treatment temperature is 110~120℃, and vacuum dehydration is carried out until the moisture content is no more than 0.05%; the prepolymerization reaction is carried out at 80~85℃ for 2.5~3h under nitrogen protection until the isocyanate group content reaches 4.5%~5.5%; the filler is added in batches and dispersed at high speed at 1200~1500rpm for 20~40min, and then treated by horizontal sand milling until the material fineness is no more than 20μm.

10. The preparation method according to claim 8, characterized in that, In steps S1 and S2, the vacuum degree of the vacuum degassing is not higher than -0.095MPa, and the degassing time is 3~10min; in step S2, each component is stirred at 300~500rpm for 5~20min until uniform, and after adding the composite catalyst and dispersing agent, stirring is continued for 10~20min.

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