Bio-based ultraviolet-resistant polyurethane pressure-sensitive adhesive as well as preparation method and application thereof

Abstract

The invention relates to the technical field of adhesives, in particular to a bio-based ultraviolet-resistant polyurethane pressure-sensitive adhesive as well as a preparation method and application thereof. A bio-based epoxy monomer is prepared from a bio-based raw material containing a phenolic hydroxyl group and epoxy chloropropane through epoxidation reaction; introducing the bio-based epoxy monomer and dicarboxymethyl propionic acid into a cross-linking site through a ring-opening esterification reaction of carboxyl and an epoxy group to obtain a bio-based cross-linking agent containing polyfunctional groups; the bio-based cross-linking agent participates in a cross-linking reaction in a polyurethane system, so that the density of a network structure is improved, an aromatic conjugated skeleton of the bio-based cross-linking agent endows a material with intrinsic ultraviolet absorption capacity, integration of anti-ultraviolet and cross-linking functions is realized, and a traditional petroleum-based additive type auxiliary agent is effectively replaced; meanwhile, the bio-based ultraviolet-resistant polyurethane pressure-sensitive adhesive obtained by reacting the bio-based cross-linking agent with a polyurethane prepolymer has excellent weather resistance, bonding stability and environmental friendliness, and is suitable for high-reliability bonding scenes such as aerospace and the like.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and in particular to a bio-based UV-resistant polyurethane pressure-sensitive adhesive, its preparation method, and its application. Background Technology

[0002] In the aerospace field, pressure-sensitive adhesives (PSAs) are used in critical components such as structural bonding and sealing, requiring long-term resistance to harsh environments such as strong ultraviolet radiation and extreme temperature variations. However, traditional polyurethane PSAs are prone to UV aging, with tensile strength decreasing by up to 38.6% and tear strength by approximately 7% after UV aging. They also exhibit color darkening, surface cracking, roughening, and microscopic cracks and pores. Furthermore, the benzene ring structure is highly susceptible to oxidation under UV light, forming quinone chromophores, leading to severe yellowing. Therefore, traditional polyurethane PSAs are prone to UV aging, resulting in yellowing, embrittlement, and adhesive failure.

[0003] Existing UV protection methods mostly rely on additives, such as UV absorbers or nano-oxides, but these suffer from problems such as migration, precipitation, and uneven dispersion, making it difficult to achieve long-term stable protection. For example, small-molecule UV absorbers can migrate from the interior of the adhesive layer to the surface during storage or use, forming white hazy or powdery precipitates that severely affect transparency and appearance. Furthermore, additives that migrate to the adhesive layer can transfer to the surface of the adhered substrate, causing substrate contamination or optical surface hazing, making them unsuitable for applications such as electronic protective films and optical tapes.

[0004] Currently, the UV-resistant additives used in polyurethane pressure-sensitive adhesives are mainly derived from petroleum-based systems, such as benzotriazoles and benzophenones, which are organic UV absorbers. These additives are not only non-renewable, but some are also toxic or photoinstable, and are prone to volatilization or degradation during long-term service, affecting the protective effect.

[0005] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a bio-based UV-resistant polyurethane pressure-sensitive adhesive, its preparation method and application, aiming to solve the problem that existing UV-resistant polyurethane pressure-sensitive adhesives are prone to UV aging, resulting in yellowing, embrittlement and adhesion failure.

[0007] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing a bio-based UV-resistant polyurethane pressure-sensitive adhesive, comprising the steps of: A bio-based raw material containing phenolic hydroxyl groups, epichlorohydrin, and a first catalyst are mixed and subjected to a first reaction to obtain a bio-based epoxy monomer. The bio-based epoxy monomer, dimethylolpropionic acid, and the second catalyst are mixed and subjected to a second reaction to obtain a bio-based crosslinking agent. Polyester polyol or polyether polyol is mixed with diisocyanate and subjected to a third reaction to obtain a polyurethane prepolymer with terminal isocyanate groups. The bio-based crosslinking agent is mixed with the polyurethane prepolymer, and after coating and curing, a bio-based UV-resistant polyurethane pressure-sensitive adhesive is obtained.

[0008] Preferably, in the preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive, the bio-based raw material containing phenolic hydroxyl groups is selected from one or more of eugenol, 4-vinylphenol, cashew phenol, vanillin, demethylated lignin, and monobutyric acid.

[0009] Preferably, in the preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive, the mass ratio of the bio-based raw material containing phenolic hydroxyl groups, the epichlorohydrin, and the first catalyst is 1:(0.2-1):(0.01-0.2).

[0010] As a preferred embodiment, in the preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive, the temperature of the first reaction is 50℃-80℃, and the time of the first reaction is 2h-5h.

[0011] As a preferred embodiment, in the preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive, the temperature of the second reaction is 90℃-120℃, and the time of the second reaction is 3h-6h.

[0012] Preferably, in the preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive, the first catalyst is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and organic tertiary amines.

[0013] Preferably, in the preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive, the second catalyst is selected from one or more of tetrabutylammonium bromide, tetrabutylammonium chloride, triethylamine, dibutyltin dilaurate, and tetrabutyl titanate.

[0014] Preferably, in the preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive, the mass ratio of the bio-based epoxy monomer, the dimethylolpropionic acid and the second catalyst is 1:(0.1-1):(0.01-0.1).

[0015] Preferably, in the preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive, the mass fraction of the bio-based crosslinking agent in the bio-based UV-resistant polyurethane pressure-sensitive adhesive is 0.5%-15%.

[0016] Secondly, the present invention also provides a bio-based UV-resistant polyurethane pressure-sensitive adhesive, which is prepared using the preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive.

[0017] Thirdly, the present invention also provides the application of a bio-based UV-resistant polyurethane pressure-sensitive adhesive in aircraft skin sealant, floor and composite material interlayer adhesive, wire harness covering adhesive, or sensor fixing adhesive.

[0018] Beneficial Effects: This invention provides a bio-based UV-resistant polyurethane pressure-sensitive adhesive, its preparation method, and its application. The preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive includes the following steps: mixing a bio-based raw material containing phenolic hydroxyl groups, epichlorohydrin, and a first catalyst, and undergoing a first reaction to obtain a bio-based epoxy monomer; mixing the bio-based epoxy monomer, dimethylolpropionic acid, and a second catalyst, and undergoing a second reaction to obtain a bio-based crosslinking agent; mixing a polyester polyol or polyether polyol with a diisocyanate, and undergoing a third reaction to obtain a polyurethane prepolymer with isocyanate-terminated groups; mixing the bio-based crosslinking agent with the polyurethane prepolymer, and after coating and curing, obtaining the bio-based UV-resistant polyurethane pressure-sensitive adhesive. This invention utilizes a bio-based raw material containing phenolic hydroxyl groups to epoxidize epichlorohydrin to obtain a bio-based epoxy monomer. Then, the bio-based epoxy monomer is reacted with dimethyl carboxylic acid (DMPA) through a ring-opening esterification reaction of carboxyl and epoxy groups to introduce crosslinking sites, resulting in a bio-based crosslinking agent containing multiple functional groups. This crosslinking agent participates in the crosslinking reaction in the polyurethane system, not only increasing the network structure density but also endowing the material with intrinsic UV absorption capabilities through its aromatic conjugated skeleton, achieving integrated UV protection and crosslinking functions, effectively replacing traditional petroleum-based additives. Simultaneously, the bio-based UV-resistant polyurethane pressure-sensitive adhesive obtained by reacting this bio-based crosslinking agent with a polyurethane prepolymer exhibits excellent weather resistance, bonding stability, and environmental friendliness, making it suitable for high-reliability bonding scenarios such as aerospace. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the process flow for preparing a bio-based UV-resistant polyurethane pressure-sensitive adhesive according to the present invention. Figure 2 This is a synthetic route diagram for bio-based crosslinking agents. Detailed Implementation

[0020] This invention provides a bio-based UV-resistant polyurethane pressure-sensitive adhesive, its preparation method, and its application. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0021] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0022] Eugenol, 4-vinylphenol, and other bio-based monomers contain natural benzene ring conjugated structures and active double bonds, exhibiting excellent UV absorption capabilities. Furthermore, they are renewable and low in toxicity, making them promising candidates for incorporating green UV-resistant units into polymer backbones. However, limitations in reaction controllability, compatibility, and cost mean that the technology for converting bio-based monomers into highly efficient reactive crosslinking polyurethane UV-resistant agents is still immature, and related research is weak. Therefore, there is an urgent need to develop a polyurethane UV-resistant crosslinking agent based on bio-based monomers to form a polyurethane pressure-sensitive adhesive with a polyurethane prepolymer, replacing traditional petroleum-based additives to achieve green and long-lasting UV protection.

[0023] Based on this, such as Figure 1 and Figure 2 As shown, this invention provides a method for preparing a bio-based UV-resistant polyurethane pressure-sensitive adhesive, comprising the following steps: Step S10: The bio-based raw material containing phenolic hydroxyl groups, epichlorohydrin and the first catalyst are mixed and subjected to a first reaction to obtain a bio-based epoxy monomer; Step S20: The bio-based epoxy monomer, dimethylolpropionic acid, and the second catalyst are mixed and subjected to a second reaction to obtain a bio-based crosslinking agent; Step S30: Mix polyester polyol or polyether polyol with diisocyanate, and then react in the third step to obtain polyurethane prepolymer with isocyanate-terminated groups. Step S40: The bio-based crosslinking agent is mixed with the polyurethane prepolymer, and after coating and curing, a bio-based UV-resistant polyurethane pressure-sensitive adhesive is obtained.

[0024] In this embodiment, a bio-based epoxy monomer is prepared by epoxidation of a bio-based raw material containing phenolic hydroxyl groups and epichlorohydrin. Then, the bio-based epoxy monomer is reacted with dimethyl carboxylic acid (DMPA) through a ring-opening esterification reaction of carboxyl and epoxy groups to introduce crosslinking sites, thereby obtaining a bio-based crosslinking agent containing multiple functional groups. This crosslinking agent participates in the crosslinking reaction in the polyurethane system, which not only increases the network structure density, but also endows the material with intrinsic UV absorption capability through its aromatic conjugated skeleton, realizing the integration of UV protection and crosslinking functions, effectively replacing traditional petroleum-based additives. At the same time, the bio-based UV-resistant polyurethane pressure-sensitive adhesive obtained by reacting this bio-based crosslinking agent with polyurethane prepolymer has excellent weather resistance, adhesion stability and environmental friendliness, and is suitable for high-reliability bonding scenarios such as aerospace.

[0025] Specifically, this invention utilizes the bio-based raw material containing phenolic hydroxyl groups to prepare an epoxy intermediate with an aromatic conjugated structure through an epoxidation reaction. This intermediate utilizes its own structure to achieve intrinsic UV resistance, replacing traditional easily migrating additive UV absorbers and significantly improving the weather resistance and stability of the pressure-sensitive adhesive. Simultaneously, the bio-based epoxy monomer is reacted with dimethylolpropionic acid (DMPA) to introduce hydroxyl groups and construct a multifunctional bio-based crosslinking agent. This agent can participate in the polyurethane crosslinking reaction to enhance the network structure and also impart UV resistance to the material, achieving functional integration. Furthermore, the raw materials for the bio-based crosslinking agent are derived from renewable resources, replacing traditional petroleum-based raw materials. Combined with a mild and controllable synthesis process, the final pressure-sensitive adhesive exhibits excellent environmental friendliness, aligning with green and sustainable development principles and making it suitable for reliability-related fields such as aerospace.

[0026] In some embodiments, the phenolic hydroxyl-containing bio-based raw material is selected from, but is not limited to, one or more of eugenol, 4-vinylphenol, cashew phenol, vanillin, demethylated lignin, and monobutyric acid. The bio-based crosslinking agent prepared using the above-mentioned phenolic hydroxyl-containing bio-based raw material has free radical quenching properties, achieving a UV shielding effect. Furthermore, through the vibrational relaxation of the phenolic hydroxyl group and aromatic ring, the absorbed UV photon energy is converted into heat energy release, rather than initiating a photochemical reaction. The phenolic hydroxyl group is a natural hydrogen donor, capable of quenching UV-excited free radicals and blocking oxidation chain reactions. Simultaneously, the above-mentioned phenolic hydroxyl-containing bio-based raw material reacts with epichlorohydrin under the action of a first catalyst to form an aromatic conjugated structure. This structure significantly enhances the UV resistance and weather resistance of the bio-based crosslinking agent in polyurethane pressure-sensitive adhesives through a triple mechanism of chromophore-auxochrome synergistic absorption, photothermal conversion, and free radical quenching. In addition, the bio-based source avoids the toxicity problem of bisphenol A, aligning with the trend of green materials development.

[0027] In some embodiments, the mass ratio of the phenolic hydroxyl-containing bio-based raw material, the epichlorohydrin, and the first catalyst is 1:(0.2-1):(0.01-0.2). By controlling the mass ratio of the phenolic hydroxyl-containing bio-based raw material, the epichlorohydrin, and the first catalyst within the above range, a bio-based epoxy monomer can be obtained after substitution, providing an aromatic ring structure for the bio-based crosslinking agent. This structure can conjugate with the phenolic hydroxyl group obtained in subsequent ring-opening reactions through lone pair electrons, producing a redshift effect, enhancing the absorption capacity of long-wave ultraviolet light, and simultaneously improving the conversion efficiency of light energy to heat energy.

[0028] In some embodiments, the mass ratio of the phenolic hydroxyl-containing bio-based raw material, the epichlorohydrin, and the first catalyst may be 1:0.2:0.02, 1:0.3:0.04, 1:0.4:0.05, 1:0.5:0.07, 1:0.6:0.08, 1:0.7:0.1, 1:0.8:0.11, 1:0.9:0.12, 1:1.0:0.2, 1:0.3:0.08, or 1:0.5:0.1, but is not limited to these ratios.

[0029] In a preferred embodiment, the phenolic hydroxyl-containing bio-based raw material has the structural formula R-OH, wherein R is selected from... , , One of them.

[0030] In some embodiments, the temperature of the first reaction is 50°C-80°C, and the reaction time is 2h-5h. At this temperature and time, a substitution reaction occurs between the phenolic hydroxyl-containing bio-based raw material and the epichlorohydrin. The phenolic hydroxyl-containing bio-based raw material removes hydrogen from its phenolic hydroxyl group and undergoes a substitution reaction with the chlorine atom in the epichlorohydrin, thereby obtaining a bio-based epoxy monomer.

[0031] In some embodiments, the first reaction may be carried out at 50°C for 2 hours, at 55°C for 3 hours, at 60°C for 3.5 hours, at 65°C for 4 hours, at 70°C for 4 hours, at 75°C for 4.5 hours, or at 80°C for 5 hours, but is not limited thereto.

[0032] In some embodiments, the temperature of the second reaction is 90℃-120℃, and the reaction time is 3h-6h. Controlling the temperature and time of the second reaction within these ranges allows the bio-based epoxy monomer and the dimethylolpropionic acid to undergo a ring-opening reaction under the conditions of the second catalyst, thereby obtaining a bio-based crosslinking agent. Furthermore, the bio-based crosslinking agent obtained through the ring-opening reaction contains both hydroxyl and aromatic conjugated structures in its molecular structure, which can be used to achieve a synergistic function of crosslinking curing and intrinsic ultraviolet absorption in polyurethane systems.

[0033] In some embodiments, the second reaction may be carried out at 90°C for 3 hours, at 95°C for 3 hours, at 100°C for 3.5 hours, at 105°C for 3.5 hours, at 110°C for 4 hours, at 115°C for 5 hours, or at 120°C for 6 hours, but is not limited thereto.

[0034] In some embodiments, the first catalyst is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and organic tertiary amines. Using these substances as alkaline catalysts can promote the reaction between the phenolic hydroxyl-containing bio-based raw material and the epichlorohydrin, and increase the reaction rate, thereby producing a bio-based epoxy monomer.

[0035] In a preferred embodiment, the first catalyst is sodium hydroxide, which has the advantages of low cost and convenient storage, and its moderate alkalinity can avoid excessive deprotonation leading to excessive nucleophilicity of phenolate anions and reduce side reactions in the etherification stage.

[0036] In some embodiments, the second catalyst is selected from one or more of tetrabutylammonium bromide, tetrabutylammonium chloride, triethylamine, dibutyltin dilaurate, and tetrabutyl titanate. These catalysts can precisely control the ring-opening rate, regioselectivity, and stereoselectivity in the ring-opening reaction by lowering the activation energy and altering the reaction pathway, thereby promoting the rapid ring-opening reaction between the bio-based epoxy monomer and dimethylolpropionic acid.

[0037] Specifically, under the action of the second catalyst, the bio-based epoxy monomer and the dimethylolpropionic acid introduce crosslinking sites through the ring-opening esterification reaction of carboxyl and epoxy groups to obtain a bio-based crosslinking agent containing multiple functional groups. This crosslinking agent participates in the crosslinking reaction in the polyurethane system, which not only improves the network structure density, but also endows the material with intrinsic ultraviolet absorption capability through its aromatic conjugated skeleton, thus realizing the integration of anti-ultraviolet and crosslinking functions.

[0038] In a preferred embodiment, the second catalyst is tetrabutylammonium bromide.

[0039] In some embodiments, the mass ratio of the bio-based epoxy monomer, the dimethylolpropionic acid, and the second catalyst is 1:(0.1-1):(0.01-0.1). By controlling the mass ratio of the bio-based epoxy monomer, the dimethylolpropionic acid, and the second catalyst within the above range, a bio-based crosslinking agent can be obtained after a ring-opening reaction. The molecular structure of the bio-based crosslinking agent simultaneously contains hydroxyl and aromatic conjugated structures, which can be used to achieve a synergistic function of crosslinking curing and intrinsic ultraviolet absorption in polyurethane systems.

[0040] In some embodiments, the mass ratio of the bio-based epoxy monomer, the dimethylolpropionic acid, and the second catalyst is 1:0.1:0.01, 1:0.2:0.02, 1:0.3:0.03, 1:0.4:0.04, 1:0.5:0.05, 1:0.6:0.06, 1:0.7:0.07, 1:0.8:0.08, 1:0.9:0.09, or 1:0.1:0.1, but is not limited thereto.

[0041] In some embodiments, the mass ratio of the polyester polyol or polyether polyol to the diisocyanate is 100:(5-20). At this mass ratio, the diisocyanate can be used as a linker to sequentially link the polyester polyol or the polyether polyol to form a macromolecular polyurethane prepolymer, namely a polyurethane prepolymer with terminal isocyanate groups (-NCO).

[0042] In some embodiments, the mass ratio of the polyester polyol or polyether polyol to the diisocyanate is 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, 100:11, 100:12, 100:13, 100:14, 100:15, 100:16, 100:17, 100:18, 100:19, or 100:20, but is not limited thereto.

[0043] In some embodiments, the temperature of the third reaction is 60°C-100°C, and the time of the third reaction is 1 hour-4 hours; at this temperature and time, the polyester polyol or polyether polyol is reacted with the diisocyanate, and the diisocyanate can be used to sequentially link the polyester polyol or polyether polyol to form a macromolecular polyurethane prepolymer.

[0044] In some embodiments, the polyurethane prepolymer includes, but is not limited to, one or more of IPDI-type polyester prepolymers, HDI-type polyester prepolymers, IPDI-type polyether prepolymers, and HDI-type polyether prepolymers. Using the above-mentioned polyurethane prepolymers allows the bio-based crosslinking agent to participate in the crosslinking reaction in the polyurethane system, which not only increases the network structure density, but also endows the material with intrinsic UV absorption capability through its aromatic conjugated skeleton, realizing the integration of UV protection and crosslinking functions, and significantly improving the weather resistance and stability of the pressure-sensitive adhesive.

[0045] In some embodiments, the diisocyanate includes, but is not limited to, one or more of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), and naphthalene diisocyanate (NDI); the above diisocyanate can be used as a binder for obtaining polyurethane prepolymers by polymerization of polyester polyols or polyether polyols, wherein the polyester polyols or polyether polyols are sequentially linked to form macromolecular polyurethane prepolymers.

[0046] In some embodiments, the bio-based crosslinking agent has a mass fraction of 0.5%-15% in the bio-based UV-resistant polyurethane pressure-sensitive adhesive. In the bio-based UV-resistant polyurethane pressure-sensitive adhesive, if the amount of bio-based crosslinking agent is too small, the UV resistance of the adhesive is weak; while if the amount of bio-based crosslinking agent is too large, it will affect the performance of the adhesive, causing it to become brittle. Therefore, controlling the mass fraction of the bio-based crosslinking agent in the bio-based UV-resistant polyurethane pressure-sensitive adhesive between 0.5% and 15% allows the multifunctional bio-based crosslinking agent to participate in the polyurethane crosslinking reaction to enhance the network structure and impart UV resistance to the material, achieving an integration of UV resistance and crosslinking functions. Furthermore, controlling the mass fraction of the bio-based crosslinking agent within the above range allows the bio-based UV-resistant polyurethane pressure-sensitive adhesive obtained from the reaction of the bio-based crosslinking agent and the polyurethane prepolymer to have excellent weather resistance, adhesive stability, and environmental friendliness, making it suitable for high-reliability bonding scenarios such as aerospace.

[0047] In some embodiments, the mass fraction of the bio-based crosslinking agent in the bio-based UV-resistant polyurethane pressure-sensitive adhesive can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, or 15%, but is not limited thereto.

[0048] In some embodiments, in step S40, the bio-based crosslinking agent is stirred with the polyurethane prepolymer for 30 minutes, coated onto a substrate, and cured at 60-120°C for 0.5-4 hours to obtain a bio-based UV-resistant polyurethane pressure-sensitive adhesive. Through the curing process, the bio-based crosslinking agent participates in the crosslinking reaction within the polyurethane system, not only increasing the network structure density but also endowing the material with intrinsic UV absorption capabilities through its aromatic conjugated skeleton, thus achieving an integrated UV resistance and crosslinking function.

[0049] In a preferred embodiment, the curing temperature is 80°C and the curing time is 2 hours.

[0050] In addition, the present invention also provides a bio-based UV-resistant polyurethane pressure-sensitive adhesive, which is prepared using the preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive.

[0051] In this embodiment, the preparation method utilizes a bio-based raw material containing phenolic hydroxyl groups to epoxidize epichlorohydrin to obtain a bio-based epoxy monomer. Then, the bio-based epoxy monomer is reacted with dimethyl carboxylic acid (DMPA) through a ring-opening esterification reaction of carboxyl and epoxy groups to introduce crosslinking sites, resulting in a bio-based crosslinking agent containing multiple functional groups. This bio-based crosslinking agent participates in the crosslinking reaction in the polyurethane system, not only increasing the network structure density but also endowing the material with intrinsic UV absorption capabilities through its aromatic conjugated skeleton, achieving integrated UV protection and crosslinking functions, effectively replacing traditional petroleum-based additives. The bio-based UV-resistant polyurethane pressure-sensitive adhesive prepared using this method exhibits excellent weather resistance, bonding stability, and environmental friendliness, making it suitable for high-reliability bonding scenarios such as aerospace.

[0052] In addition, the present invention also provides an application of a bio-based UV-resistant polyurethane pressure-sensitive adhesive in aircraft skin sealants, floor and composite material interlayer adhesives, wire harness overlay adhesives, or sensor fixing adhesives.

[0053] In this embodiment, the preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive utilizes the bio-based raw material containing phenolic hydroxyl groups to obtain an epoxy intermediate with an aromatic conjugated structure through an epoxidation reaction. This intermediate utilizes its own structure to achieve intrinsic UV resistance, replacing traditional easily migrating additive UV absorbers and significantly improving the weather resistance and stability of the pressure-sensitive adhesive. Simultaneously, the bio-based epoxy monomer is reacted with dimethylolpropionic acid (DMPA) to introduce hydroxyl groups and construct a multifunctional bio-based crosslinking agent. This agent can participate in the polyurethane crosslinking reaction to enhance the network structure and also impart UV resistance to the material, achieving functional integration. Furthermore, the raw materials for the bio-based crosslinking agent are derived from renewable resources, replacing traditional petroleum-based raw materials. Combined with a mild and controllable synthesis process, the final pressure-sensitive adhesive exhibits excellent environmental friendliness, aligning with green and sustainable development principles. It is suitable for reliability applications such as aerospace, including aircraft skin sealing, flooring, interlayer bonding of composite materials, wire harness wrapping, or sensor fixation.

[0054] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.

[0055] Example 1 This embodiment provides a bio-based UV-resistant polyurethane pressure-sensitive adhesive, and the specific preparation steps are as follows: 100g of eugenol was mixed with 50g of epichlorohydrin and 10g of sodium hydroxide, and reacted at 70℃ for 3h under sodium hydroxide catalysis to obtain a bio-based epoxy monomer. The bio-based epoxy monomer was mixed with 80g of dimethylolpropionic acid and tetrabutylammonium bromide, and reacted at 110℃ for 4h under catalysis to obtain a bio-based crosslinking agent. 25g of the bio-based crosslinking agent was added to a polyurethane prepolymer prepared by reacting 500g of polyester polyol and 48g of TDI at 80℃ for 2h. After stirring for 30min, the mixture was coated onto a PET substrate and cured at 80℃ for 2h to obtain a bio-based UV-resistant polyurethane pressure-sensitive adhesive.

[0056] Example 2 This embodiment provides a bio-based UV-resistant polyurethane pressure-sensitive adhesive, and the specific preparation steps are as follows: 100g of 4-vinylphenol was mixed with 50g of epichlorohydrin and 10g of sodium hydroxide, and reacted at 70℃ for 3h under sodium hydroxide catalysis to obtain a bio-based epoxy monomer. The bio-based epoxy monomer was mixed with 80g of dimethylolpropionic acid and tetrabutylammonium bromide, and reacted at 110℃ for 4h under catalysis to obtain a bio-based crosslinking agent. 20g of the bio-based crosslinking agent was added to a polyurethane prepolymer prepared by reacting 500g of polyether polyol and 110g of IPDI at 75℃ for 3h. After stirring for 30min, the mixture was coated onto a PET substrate and cured at 80℃ for 2h to obtain a bio-based UV-resistant polyurethane pressure-sensitive adhesive.

[0057] Example 3 This embodiment provides a bio-based UV-resistant polyurethane pressure-sensitive adhesive, and the specific preparation steps are as follows: 100g of eugenol was mixed with 50g of epichlorohydrin and 10g of sodium hydroxide, and reacted at 70℃ for 3h under sodium hydroxide catalysis to obtain a bio-based epoxy monomer. The bio-based epoxy monomer was mixed with 80g of dimethylolpropionic acid and tetrabutylammonium bromide, and reacted at 110℃ for 4h under catalysis to obtain a bio-based crosslinking agent. 40g of the bio-based crosslinking agent was added to a polyurethane prepolymer prepared by reacting 500g of polyester polyol and 48g of TDI at 80℃ for 2h. After stirring for 30min, the mixture was coated onto a PET substrate and cured at 80℃ for 2h to obtain a bio-based UV-resistant polyurethane pressure-sensitive adhesive.

[0058] Comparative Example 1 This comparative example provides a petroleum-based polyurethane pressure-sensitive adhesive, and the specific preparation steps are as follows: 30g of the non-biological crosslinking agent trimethylolpropane triacrylate (TMPTA) was added to a polyurethane prepolymer prepared by reacting 500g of polyester polyol and 48g of TDI at 80℃ for 2h. After stirring for 30min, the mixture was coated onto a PET substrate and cured at 80℃ for 2h to obtain a petroleum-based polyurethane pressure-sensitive adhesive.

[0059] Comparative Example 2 This comparative example provides a polyurethane pressure-sensitive adhesive without a UV crosslinking agent. The specific preparation steps are as follows: 30g of non-biological crosslinking agent trimethylolpropane triacrylate (TMPTA) and 10g of UV-9 were added to a polyurethane prepolymer prepared by reacting 500g of polyester polyol and 48g of TDI at 80℃ for 2h. After stirring for 30min, the mixture was coated onto a PET substrate and cured at 80℃ for 2h to obtain a polyurethane pressure-sensitive adhesive without UV crosslinking agent.

[0060] The polyurethane pressure-sensitive adhesives prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were characterized in terms of performance. The specific characterization data are shown in Table 1.

[0061]

[0062] Examples 1-3 of this invention are bio-based UV-resistant polyurethane pressure-sensitive adhesives prepared using the aforementioned method. As shown in Table 1, the peel strength did not decrease significantly after 24 hours of UV aging, and no small-molecule UV stabilizer precipitated. Comparative Example 1, a polyurethane pressure-sensitive adhesive prepared with a common crosslinking agent, lacked a UV stabilizer and exhibited a significant performance decline under UV irradiation. Comparative Example 2, a polyurethane pressure-sensitive adhesive with added small-molecule UV stabilizers, showed good UV resistance, but the small-molecule UV stabilizer easily precipitated during the double 85 thermo-oxidative aging test, affecting the adhesive's performance.

[0063] Performance characterization data from the polyurethane pressure-sensitive adhesives prepared in Examples 1 to 3 and Comparative Examples 1 to 2 show that the entire chain—from bio-based functional monomer design to crosslinking agent synthesis to polyurethane pressure-sensitive adhesive construction—not only solves the core pain points of traditional pressure-sensitive adhesives, such as poor aging resistance and reliance on petroleum resources, but also achieves a balance between high performance and green sustainability. The bio-based UV-resistant polyurethane pressure-sensitive adhesive prepared using the aforementioned method is a breakthrough in terms of technological advancement, environmental friendliness, economic feasibility, and wide applicability. It is an ideal upgrade solution for traditional pressure-sensitive adhesives, possessing broad market prospects and industrialization value.

[0064] In summary, this invention provides a bio-based UV-resistant polyurethane pressure-sensitive adhesive, its preparation method, and its application. The preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive includes the following steps: mixing a bio-based raw material containing phenolic hydroxyl groups, epichlorohydrin, and a first catalyst, and undergoing a first reaction to obtain a bio-based epoxy monomer; mixing the bio-based epoxy monomer, dimethylolpropionic acid, and a second catalyst, and undergoing a second reaction to obtain a bio-based crosslinking agent; mixing a polyester polyol or polyether polyol with a diisocyanate, and undergoing a third reaction to obtain a polyurethane prepolymer with isocyanate-terminated groups; mixing the bio-based crosslinking agent with the polyurethane prepolymer, and then coating and curing the mixture to obtain the bio-based UV-resistant polyurethane pressure-sensitive adhesive. This invention utilizes a bio-based raw material containing phenolic hydroxyl groups to epoxidize epichlorohydrin to obtain a bio-based epoxy monomer. Then, the bio-based epoxy monomer is reacted with dimethyl carboxylic acid (DMPA) through a ring-opening esterification reaction of carboxyl and epoxy groups to introduce crosslinking sites, resulting in a bio-based crosslinking agent containing multiple functional groups. This crosslinking agent participates in the crosslinking reaction in the polyurethane system, not only increasing the network structure density but also endowing the material with intrinsic UV absorption capabilities through its aromatic conjugated skeleton, achieving integrated UV protection and crosslinking functions, effectively replacing traditional petroleum-based additives. Simultaneously, the bio-based UV-resistant polyurethane pressure-sensitive adhesive obtained by reacting this bio-based crosslinking agent with a polyurethane prepolymer exhibits excellent weather resistance, bonding stability, and environmental friendliness, making it suitable for high-reliability bonding scenarios such as aerospace.

[0065] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a bio-based UV-resistant polyurethane pressure-sensitive adhesive, characterized in that, Including the following steps: A bio-based raw material containing phenolic hydroxyl groups, epichlorohydrin, and a first catalyst are mixed and subjected to a first reaction to obtain a bio-based epoxy monomer. The bio-based epoxy monomer, dimethylolpropionic acid, and the second catalyst are mixed and subjected to a second reaction to obtain a bio-based crosslinking agent. Polyester polyol or polyether polyol is mixed with diisocyanate and subjected to a third reaction to obtain a polyurethane prepolymer with terminal isocyanate groups. The bio-based crosslinking agent is mixed with the polyurethane prepolymer, and after coating and curing, a bio-based UV-resistant polyurethane pressure-sensitive adhesive is obtained.

2. The preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive according to claim 1, characterized in that, The phenolic hydroxyl-containing bio-based raw material is selected from one or more of eugenol, 4-vinylphenol, cashew phenol, vanillin, demethylated lignin, and monobutyric acid.

3. The preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive according to claim 1, characterized in that, The mass ratio of the phenolic hydroxyl-containing bio-based raw material, the epichlorohydrin, and the first catalyst is 1:(0.2-1):(0.01-0.2).

4. The preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive according to claim 1, characterized in that, The temperature of the first reaction is 50℃-80℃, and the reaction time is 2h-5h.

5. The method for preparing the bio-based UV-resistant polyurethane pressure-sensitive adhesive according to claim 1, characterized in that, The temperature of the second reaction is 90℃-120℃, and the reaction time is 3h-6h.

6. The preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive according to claim 1, characterized in that, The first catalyst is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and organic tertiary amines; And / or, the second catalyst is selected from one or more of tetrabutylammonium bromide, tetrabutylammonium chloride, triethylamine, dibutyltin dilaurate, and tetrabutyl titanate.

7. The preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive according to claim 1, characterized in that, The mass ratio of the bio-based epoxy monomer, the dimethylolpropionic acid, and the second catalyst is 1:(0.1-1):(0.01-0.1).

8. The method for preparing the bio-based UV-resistant polyurethane pressure-sensitive adhesive according to claim 1, characterized in that, The bio-based crosslinking agent has a mass fraction of 0.5%-15% in the bio-based UV-resistant polyurethane pressure-sensitive adhesive.

9. A bio-based UV-resistant polyurethane pressure-sensitive adhesive, characterized in that, It is prepared using the preparation method of the bio-based UV-resistant polyurethane pressure-sensitive adhesive as described in any one of claims 1-8.

10. The application of the bio-based UV-resistant polyurethane pressure-sensitive adhesive as described in claim 9 in aircraft skin sealants, floor and composite material interlayer adhesives, wire harness overlay adhesives, or sensor fixing adhesives.

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