Intrinsic anti-aging solvent-free polyurethane adhesive and preparation method thereof

Abstract

The invention discloses an intrinsic anti-aging solvent-free polyurethane adhesive and a preparation method thereof, and belongs to the field of bio-based functional polymer materials. The adhesive is composed of a component A and a component B, wherein the component A is aliphatic polyisocyanate; the component B is prepared from the following raw materials in parts by weight: 20 to 50 parts of tea polyphenol derivative polyol and 50 to 80 parts of conventional polyether polyol or polyester polyol; the tea polyphenol derivative polyol is prepared from tea polyphenol and a cyclic carbonate compound through a synthetic reaction, and at least one catechol structure is reserved. The adhesive has intrinsic, lasting and efficient thermal oxidation resistance and ultraviolet aging resistance, keeps high-strength adhesion to plastic films, is excellent in aging test performance, is green and environment-friendly, and can be widely applied to the fields of packaging, automotive trim, outdoor advertising films, electronic element packaging and the like.

Description

Technical Field

[0001] This invention belongs to the field of bio-based functional polymer materials technology, and particularly relates to an intrinsically anti-aging solvent-free polyurethane adhesive and its preparation method. Background Technology

[0002] Polyurethane adhesives are prone to aging under the influence of light, heat, and oxygen, leading to decreased bond strength, yellowing, and even failure. Traditional anti-aging methods mainly rely on adding antioxidants (such as hindered phenols and phosphites) and ultraviolet absorbers. However, these small-molecule additives have problems such as not meeting food safety requirements, easy migration, volatility, and extraction, resulting in insufficient long-term protection and potential contamination of the adhered materials or the environment.

[0003] Tea polyphenols are a collective term for polyhydroxyphenolic compounds in tea, mainly including catechins. Their structure contains multiple ortho- and posterior phenolic hydroxyl groups, and they are recognized as strong natural antioxidants and ultraviolet absorbers. Currently, research on the application of tea polyphenols in polymer materials mainly focuses on physical blending, such as adding them to films or coatings. However, research on their use in adhesives, especially the introduction of them into the polyurethane backbone through chemical bonding to achieve permanent, non-migratory anti-aging effects, has not been publicly reported domestically or internationally.

[0004] Currently, simply blending tea polyphenols into polyurethane adhesives faces at least the following fundamental challenges: (1) Poor compatibility: The highly polar tea polyphenols have poor compatibility with the weakly polar polyurethane matrix, easily agglomerating and causing defects in the adhesive layer. (2) Impact on curing: Phenolic hydroxyl groups react with isocyanates, interfering with normal curing stoichiometry, which can lead to unstable performance if not controlled. (3) Waste of function: Physically dispersed tea polyphenol molecules cannot fully utilize their multi-site synergistic antioxidant capacity, and there is still a possibility of slow migration.

[0005] Therefore, how to develop a polyurethane adhesive that can stably, efficiently, and persistently utilize the anti-aging function of tea polyphenols is a technical problem that needs to be solved.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide an intrinsically anti-aging solvent-free polyurethane adhesive and its preparation method. Through molecular design, tea polyphenols can be converted into components of a polyurethane network when solvents are required, thereby endowing the adhesive with intrinsic, durable, and highly efficient resistance to heat, oxygen, and ultraviolet aging, while maintaining high-strength adhesion to plastic films, thus solving the problems existing in the prior art.

[0008] The objective of this invention is achieved through the following technical solution: An intrinsically anti-aging solvent-free polyurethane adhesive is disclosed, comprising component A and component B. Component A is an aliphatic polyisocyanate. Component B comprises the following raw materials in parts by weight: 20-50 parts by weight of tea polyphenol derivative polyol and 50-80 parts by weight of conventional polyether polyol or polyester polyol. The tea polyphenol derivative polyol is prepared by a synthetic reaction of tea polyphenols and cyclic carbonate compounds, and retains at least one catechol structure.

[0009] Preferably, in the above adhesive, the tea polyphenols in the tea polyphenol derivative polyol of component B are catechin compounds.

[0010] Preferably, in the above adhesive, the catechin compound is epigallocatechin gallate.

[0011] Preferably, in the above adhesive, the cyclic carbonate compound in the tea polyphenol derivative polyol is ethylene carbonate or propylene carbonate.

[0012] Preferably, in the above-mentioned adhesive, the alkaline catalyst used in the synthesis reaction of the tea polyphenol derivative polyol is at least one of potassium carbonate, sodium carbonate, or sodium hydroxide.

[0013] Preferably, in the above adhesive, the aliphatic polyisocyanate of component A is at least one of a mixed trimer of HDI and IPDI, an HDI trimer, and an IPDI trimer.

[0014] Preferably, in the above-mentioned adhesive, when the A component and B component of the adhesive are cured together, the NCO / OH ratio is 1.05 to 1.6.

[0015] A method for preparing the intrinsically anti-aging solvent-free polyurethane adhesive of the present invention includes: Take the raw materials for components A and B according to the above formula; Preparation of component B: Add the tea polyphenol derivative polyol in the raw material of component B and conventional polyether polyol or polyester polyol into a reaction vessel, and the product obtained after vacuum dehydration is component B. During curing, the aliphatic polyisocyanate of component A and component B are reacted and cured at an NCO / OH ratio of 1.05 to 1.6. The cured network contains tea polyphenol structural units derived from tea polyphenol derivative polyols that are linked by chemical bonds.

[0016] Preferably, in the above method, the tea polyphenol derivative polyol used for component B is synthesized in the following manner: The product, which retains at least one catechol structure, is a polyol derived from tea polyphenols, synthesized by reacting tea polyphenols with cyclic carbonate compounds at 80–100°C for 4–8 hours under the action of an alkaline catalyst.

[0017] Compared with the prior art, the intrinsically anti-aging solvent-free polyurethane adhesive and its preparation method provided by the present invention have the following beneficial effects: By selectively chemically modifying tea polyphenols, a tea polyphenol derivative polyol is prepared that retains the antioxidant core structure and can undergo a controllable reaction with polyurethane raw materials. This polyol can be chemically anchored in the cross-linked network, and when solvents are required, the tea polyphenols can be converted into components of the polyurethane network. This endows the adhesive with intrinsic, durable, and highly efficient resistance to heat, oxidation, and UV aging, while maintaining high-strength adhesion to plastic films. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the specific content of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments, which do not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0019] First, the following explanations are provided for the terms that may be used in this article: The term "and / or" means that either or both can be achieved simultaneously. For example, X and / or Y means that it includes both "X" or "Y" as well as the three cases of "X and Y".

[0020] The terms "comprising," "including," "containing," "having," or other similar semantic descriptions should be interpreted as non-exclusive inclusion. For example, including a technical feature element (such as raw material, component, ingredient, carrier, dosage form, material, size, part, component, mechanism, device, step, process, method, reaction conditions, processing conditions, parameter, algorithm, signal, data, product or article of manufacture, etc.) should be interpreted as including not only the expressly listed technical feature element, but also other technical feature elements that are not expressly listed and are well-known in the art.

[0021] The term "composed of" excludes any technical features not expressly listed. When used in a claim, it closes the claim to exclude all technical features other than those expressly listed, except for associated conventional impurities. If the term appears only in a clause of a claim, it limits the claim to the elements expressly listed in that clause; elements recited in other clauses are not excluded from the overall claim.

[0022] The term "parts by mass" indicates the mass ratio between multiple components. For example, if component X is described as x parts by mass and component Y as y parts by mass, then the mass ratio of component X to component Y is x:y. One part by mass can represent any mass; for example, one part by mass can be expressed as 1 kg or 3.1415926 kg, etc. The sum of the parts by mass of all components is not necessarily 100 parts; it can be greater than 100 parts, less than 100 parts, or equal to 100 parts. Unless otherwise stated, parts, proportions, and percentages mentioned herein are all measured by mass.

[0023] When concentration, temperature, pressure, size, or other parameters are expressed as numerical ranges, such ranges should be understood to specifically disclose all ranges formed by any pairing of upper limits, lower limits, or preferred values ​​within that range, regardless of whether the range is explicitly stated; for example, if the numerical range "2 to 8" is stated, then that range should be interpreted to include ranges such as "2 to 7", "2 to 6", "5 to 7", "3 to 4 and 6 to 7", "3 to 5 and 7", "2 and 5 to 7", etc. Unless otherwise stated, the numerical ranges described herein include both their endpoints and all integers and fractions within that range.

[0024] The solution provided by this invention will be described in detail below. Contents not described in detail in the embodiments of this invention are prior art known to those skilled in the art. Where specific conditions are not specified in the embodiments of this invention, they shall be performed according to conventional conditions in the art or conditions recommended by the manufacturer. Reagents or instruments used in the embodiments of this invention whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0025] This invention provides an intrinsically anti-aging solvent-free polyurethane adhesive, which is composed of component A and component B. Component A is an aliphatic polyisocyanate. Component B is composed of the following raw materials in parts by weight: 20-50 parts by weight of tea polyphenol derivative polyol and 50-80 parts by weight of conventional polyether polyol or polyester polyol. The tea polyphenol derivative polyol is prepared by a synthetic reaction of tea polyphenols and cyclic carbonate compounds, and retains at least one catechol structure.

[0026] When this adhesive cures, its cured network contains tea polyphenol structural units derived from polyols and linked by chemical bonds. It can convert tea polyphenols into components of a polyurethane network when solvents are required, thereby endowing the adhesive with intrinsic, durable, and highly effective resistance to heat, oxidation, and UV aging, while maintaining high-strength adhesion to plastic films.

[0027] In some specific embodiments, in component B of the above-mentioned adhesive, the tea polyphenols in the tea polyphenol derivative polyol are catechin compounds.

[0028] In some specific embodiments, the catechin compound in the above adhesive is epigallocatechin gallate.

[0029] In some specific embodiments, the cyclic carbonate compound in the tea polyphenol derivative polyol of the above adhesive is ethylene carbonate or propylene carbonate.

[0030] In some specific embodiments, in the above-mentioned adhesive, the alkaline catalyst used in the synthesis reaction of the tea polyphenol derivative polyol is at least one of potassium carbonate, sodium carbonate, or sodium hydroxide.

[0031] In some specific embodiments, in the above-mentioned adhesive, the aliphatic polyisocyanate of component A is at least one of a mixed trimer of HDI and IPDI, an HDI trimer, and an IPDI trimer.

[0032] In some specific embodiments, when the adhesive A and B components are cured together, the NCO / OH ratio is 1.05 to 1.6.

[0033] The present invention also provides a method for preparing the above-mentioned intrinsically anti-aging solvent-free polyurethane adhesive, comprising: Take the raw materials for components A and B according to the above formula;

[0034] Preparation of component B: Add the tea polyphenol derivative polyol in the raw material of component B and conventional polyether polyol or polyester polyol into a reaction vessel, and the product obtained after vacuum dehydration is component B. During curing, the aliphatic polyisocyanate of component A and component B are reacted and cured at an NCO / OH ratio of 1.05 to 1.6. The cured network contains tea polyphenol structural units derived from tea polyphenol derivative polyols that are linked by chemical bonds.

[0035] In some specific embodiments, the tea polyphenol derivative polyol used in component B of the above method is synthesized in the following manner: The product, which retains at least one catechol structure, is a polyol derived from tea polyphenols, synthesized by reacting tea polyphenols with cyclic carbonate compounds at 80–100°C for 4–8 hours under the action of an alkaline catalyst.

[0036] The core innovation of this invention lies in selectively chemically modifying tea polyphenols to prepare a multifunctional monomer that retains the core structure of antioxidants and can undergo a controllable reaction with polyurethane raw materials, and chemically anchoring it in the cross-linking network.

[0037] Step 1: Synthesis of the key monomer—tea polyphenol derivative polyol (TP-polyol): Tea polyphenol extracts (rich in epigallocatechin gallate ester EGCG) were reacted with cyclic carbonate compounds (such as ethylene carbonate) under a mild alkaline catalyst. This reaction was selective: it primarily occurred at the non-ortho- ortho-phenolic or alcoholic hydroxyl groups of the tea polyphenols, forming hydroxyformate bonds through ring-opening, thereby introducing one or more terminal primary hydroxyl groups onto the tea polyphenol molecule. The key catechol structure (two adjacent phenolic hydroxyl groups), which determines its antioxidant and UV absorption capabilities, was preserved.

[0038] The above reaction equation is illustrated as: TP-(OH) n + m (cyclic carbonate compound) → TP-(O-CO-O-CH2-CH2-OH) m , where n > m, to ensure that at least one catechol unit is retained.

[0039] This yields TP-polyol, which simultaneously possesses: 1) a primary hydroxyl group that can react with -NCO and 2) an unreacted catechol group.

[0040] Step 2: Preparation of adhesive: Component A (isocyanate component): Aliphatic isocyanates (such as HDI trimer, IPDI trimer) are used because their resistance to yellowing is superior to that of aromatic isocyanates, which synergizes with the anti-aging target.

[0041] Component B (polyol component): Contains 20-50 parts by weight of the above-mentioned TP-polyol, mixed with 50-80 parts by weight of conventional polyether or polyester polyol. The hydroxyl groups of the TP-polyol participate in the polymerization, making them part of the polyurethane backbone or side chain.

[0042] Curing: After components A and B are mixed, the hydroxyl groups of TP-polyol react with the -NCO of component A, permanently fixing the tea polyphenol structural units in the three-dimensional cross-linked network by covalent bonds, thereby endowing the adhesive with intrinsic, durable, and highly efficient resistance to heat, oxygen and UV aging, while maintaining high-strength adhesion to plastic films.

[0043] The innovative mechanism and application effects of this invention: (1) "Anchored" permanent anti-aging mechanism: Traditional antioxidants migrate. The TP-polyol of this invention becomes part of the polyurethane network itself and is never lost. When attacked by free radicals or ultraviolet light, the catechol units on the network immediately come into play.

[0044] (2) Multi-layered collaborative protection: (21) Highly efficient free radical quenching: The fixed catechol groups can continuously and efficiently capture peroxy radicals (ROO·) generated by the thermo-oxidative aging of polyurethane, interrupting the chain reaction.

[0045] (22) Ultraviolet shielding and conversion: The catechol structure is an excellent ultraviolet absorbing group, which can dissipate harmful ultraviolet light energy in the form of harmless heat energy, and protect the urethane and urea bonds of polyurethane from photodegradation.

[0046] (23) Metal ion passivation: Catechol can also chelate trace metal ions (such as Fe³⁺ and Cu²⁺) that may be mixed into the adhesive layer. These ions are catalysts for oxidation reactions, and passivation further delays aging.

[0047] (3) Overall performance improvement: (31) Significant improvement in durability: After 1000 hours of high temperature and humidity aging at 85℃ / 85% RH, the peel strength retention rate of the adhesive layer to the PET film is ≥85%, while that of the control group without added or physically added tea polyphenols is ≤50%. The accelerated UV aging (QUV) test shows the same advantage.

[0048] (32) Enhanced adhesive strength: The polar phenolic hydroxyl groups on TP-polyol increase the surface interaction force with polar plastic films (such as PET, PA), and the initial peel strength is increased by 10-20%.

[0049] (33) Safety and environmental friendliness: It is derived from nature and has no risk of migration of toxic small molecules, which is in line with the trend of food contact materials and green products.

[0050] To more clearly demonstrate the technical solution and its effects provided by the present invention, the following detailed description of the solution provided by the embodiments of the present invention is provided with reference to specific examples.

[0051] Example 1 This embodiment provides an intrinsically anti-aging solvent-free polyurethane adhesive, the preparation method of which is as follows: Step 1, TP-polyol synthesis: 10 parts by weight of tea polyphenols (EGCG content > 90%), 15 parts by weight of ethylene carbonate, and 0.1 parts by weight of potassium carbonate (alkaline catalyst) are reacted at 90℃ for 6 hours. After purification, a viscous liquid with a hydroxyl value of approximately 280 mg KOH / g is obtained, which is the TP-polyol.

[0052] Step 2, Preparation of Component B: 40 parts by weight of TP-polyol and 60 parts by weight of polytetrahydrofuran ether diol (Mn=2000) are added to the reactor and dehydrated under vacuum to obtain Component B.

[0053] Step 3, Component A: HDI trimer is used.

[0054] Step 4, Performance Testing: A and B are mixed at a ratio of NCO / OH = 1:1, coated onto a PA film, and then laminated with an RCPP film. Post-curing testing: Initial peel strength 8.8 N / 15 mm; after 1000 hours of double 85 aging, peel strength is 7.6 N / 15 mm (retention rate 86.4%); the yellowing index (Δb) change is significantly smaller than that of the control group using existing polyurethane adhesives that do not utilize the intrinsic antioxidant properties of this invention.

[0055] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. The information disclosed in the background section is intended only to enhance the understanding of the overall background technology of the present invention and should not be construed as an admission or implication in any way that such information constitutes prior art known to those skilled in the art.

Claims

1. An intrinsic anti-aging solvent-free polyurethane adhesive, characterized in that, The adhesive is composed of component A and component B; wherein component A is an aliphatic polyisocyanate; component B is composed of the following raw materials in parts by weight: 20-50 parts by weight of tea polyphenol derivative polyol and 50-80 parts by weight of conventional polyether polyol or polyester polyol; wherein the tea polyphenol derivative polyol is obtained by the synthesis reaction of tea polyphenol and cyclic carbonate compound, and retains at least one catechol structure.

2. The intrinsic age resistant solvent-free polyurethane adhesive according to claim 1, wherein, In component B, the tea polyphenols in the tea polyphenol derivative polyol are catechin compounds.

3. The intrinsic age resistant solvent-free polyurethane adhesive according to claim 2, wherein, The catechin compound is epigallocatechin gallate.

4. The intrinsic age-resistant solvent-free polyurethane adhesive according to any one of claims 1-3, characterized in that, The cyclic carbonate compound in the polyol of the tea polyphenol derivative is ethylene carbonate or propylene carbonate.

5. The intrinsic age-resistant solvent-free polyurethane adhesive according to any one of claims 1-3, characterized in that, In the synthesis reaction of the tea polyphenol derivative polyol, the alkaline catalyst used is at least one of potassium carbonate, sodium carbonate, or sodium hydroxide.

6. The intrinsically anti-aging solvent-free polyurethane adhesive according to any one of claims 1-3, characterized in that, The aliphatic polyisocyanate of component A is at least one of the following: a mixed trimer of HDI and IPDI, an HDI trimer, and an IPDI trimer.

7. The adhesive according to any one of claims 1-3, characterized in that, When the adhesive is cured in combination with its components A and B, the NCO / OH ratio is 1.05 to 1.

6.

8. A method for preparing the intrinsically anti-aging solvent-free polyurethane adhesive according to any one of claims 1-7, comprising: The formulation according to any one of claims 1-7 comprises the raw materials of components A and B; Preparation of component B: Add the tea polyphenol derivative polyol in the raw material of component B and conventional polyether polyol or polyester polyol into a reaction vessel, and the product obtained after vacuum dehydration is component B. During curing, the aliphatic polyisocyanate of component A and component B are reacted and cured at an NCO / OH ratio of 1.05 to 1.

6. The cured network contains tea polyphenol structural units derived from tea polyphenol derivative polyols that are linked by chemical bonds.

9. The method for preparing the intrinsic anti-aging solvent-free polyurethane adhesive according to claim 8, wherein the tea polyphenol derivative polyol used in component B is synthesized in the following manner, comprising: The product, which retains at least one catechol structure, is a polyol derived from tea polyphenols, synthesized by reacting tea polyphenols with cyclic carbonate compounds at 80–100°C for 4–8 hours under the action of an alkaline catalyst.