Yellowing-resistant antioxidant melamine resin and preparation method thereof

Abstract

The invention belongs to the technical field of melamine resin preparation, and provides yellowing-resistant antioxidant melamine resin and a preparation method thereof. The preparation method comprises the following steps: firstly, by taking melamine, formaldehyde and a modifying reagent as raw materials, preparing a melamine prepolymer by adjusting reaction conditions; secondly, a quinone-phenol hybrid antioxidant is designed and prepared, and through introduction of a hybrid molecular structure, the quinone-phenol hybrid antioxidant has excellent free radical capture ability and oxidation inhibition effect; then, a multifunctional light stabilizer containing hindered amine, phosphine and triazine groups is synthesized, and the light stability and weather resistance of the material are remarkably improved by utilizing an intermolecular synergistic effect; and finally, uniformly dispersing and curing the melamine prepolymer, an antioxidant, a light stabilizer and other auxiliaries, and carrying out multi-step temperature regulation and curing treatment to prepare the melamine resin material with excellent performance.

Description

Technical Field

[0001] The invention belongs to the technical field of melamine resin preparation, and relates to a yellowing-resistant and antioxidant melamine resin and a preparation method thereof. Background Art

[0002] Melamine resin is an important thermosetting resin material. Due to its excellent performance, it is widely used in decorative laminates, tableware, coatings, and adhesives. However, with long-term use or in certain environments, melamine resin is prone to yellowing and oxidation, which not only affects its appearance but also significantly reduces its performance, thus limiting its further promotion in high-end decorative materials and outdoor applications. The yellowing of melamine resin is mainly related to its molecular structure and environmental factors. Oxidation is one of the main causes of yellowing. Unreacted hydroxyl groups or free formaldehyde in melamine resin are easily oxidized in air, producing darker oxidation products. In addition, ultraviolet radiation can break chemical bonds in the molecular structure, forming free radicals, which further trigger photodegradation reactions and produce colored compounds. High temperatures can also cause thermal degradation of melamine resin's chemical bonds, producing yellow-brown or dark-colored degradation byproducts. These reactions work together to cause melamine resin to yellow under the combined influence of light, heat, and oxygen.

[0003] Therefore, the development of melamine resins with antioxidant and yellowing resistance has become a hot topic and an important research direction. Summary of the Invention

[0004] In response to the shortcomings of the prior art, the present invention aims to provide a yellowing-resistant, antioxidant melamine resin and a preparation method thereof. First, a prepolymer is prepared using melamine and formaldehyde as the main raw materials. Subsequently, a quinone-phenol hybrid antioxidant is prepared. This antioxidant improves antioxidant properties and suppresses yellowing caused by oxidative degradation by introducing the free radical scavenging ability of the quinone-phenol structure and the synergistic effect of the multifunctional groups in the hybrid molecule. Simultaneously, the present invention also synthesizes a hindered amine-phosphine-triazine light stabilizer. This light stabilizer combines the free radical scavenging effect of the hindered amine, the antioxidant properties of the phosphine group, and the ultraviolet absorption capacity of the triazine group. Through intermolecular synergy, this light stabilizer significantly improves the light stability and weather resistance of the resin. Finally, the prepolymer, antioxidant, light stabilizer, and other additives are mixed and cured through multi-step temperature control to produce a yellowing-resistant, antioxidant melamine resin with excellent comprehensive performance. This meets the needs of actual production.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a yellowing-resistant and antioxidant melamine resin, the preparation method comprising:

[0007] S1, mixing melamine, formaldehyde solution, and deionized water, adjusting the pH of the solution to 8.5-9.0 for reaction, adjusting the pH of the solution to 6.5-7.0, adding a GPTMS n-butanol mixture and n-butyl p-toluenesulfonate to obtain a prepolymer;

[0008] S2, dispersing catechol and 2-aminophenylboronic acid pinacol ester in a methanol aqueous solution for reaction, adjusting the pH to 3.5-4.0 at room temperature, adding ammonium cerium nitrate for reaction, and adding ascorbic acid to terminate the reaction to obtain a quinone-phenol hybrid antioxidant;

[0009] S3, mixing 2,2,6,6-tetramethylpiperidinamine, triphenyl phosphite and 4-dimethylaminopyridine to react to obtain a phosphine ester product, and adding the phosphine ester product, 2,4,6-trichloro-1,3,5-triazine and pyridine to toluene to react to obtain a hindered amine-phosphine-triazine light stabilizer;

[0010] S4, octavinyl-POSS, PEEK powder, quinone-phenol hybrid antioxidant and hindered amine-phosphine-triazine light stabilizer are dispersed in ethanol by ultrasonic dispersion, prepolymer, polyether-modified silicone oil and fluorocarbon leveling agent are added, and cured to obtain a yellowing-resistant and antioxidant melamine resin.

[0011] Specifically include:

[0012] S1, mixing melamine, formaldehyde solution, and deionized water, adjusting the temperature to a first temperature, adjusting the pH of the solution to 8.5-9.0, keeping the mixture warm for reaction, adjusting the temperature to a second temperature, adjusting the pH of the solution to 6.5-7.0, adding a GPTMS n-butanol mixture, stirring for reaction, then adding n-butyl p-toluenesulfonate, mixing well, and filtering to obtain a prepolymer;

[0013] S2, dispersing catechol and 2-aminophenylboronic acid pinacol ester in a methanol aqueous solution, adjusting the temperature to a third temperature under a nitrogen atmosphere for reaction, adjusting the pH to 3.5-4.0 at room temperature, adding ammonium cerium nitrate, stirring the reaction, adding ascorbic acid to terminate the reaction, filtering and drying to obtain a quinone-phenol hybrid antioxidant;

[0014] S3, mixing 2,2,6,6-tetramethylpiperidinamine, triphenyl phosphite and 4-dimethylaminopyridine, adjusting the temperature to a first temperature for reaction to obtain a phosphinate product, adding the phosphinate product, 2,4,6-trichloro-1,3,5-triazine and pyridine to toluene, reacting at a fourth temperature, and filtering, concentrating and purifying after completion of the reaction to obtain a hindered amine-phosphine-triazine light stabilizer;

[0015] S4, dispersing octavinyl-POSS, PEEK powder, quinone-phenol hybrid antioxidant and hindered amine-phosphine-triazine light stabilizer in ethanol by ultrasonic dispersion, adding prepolymer, polyether modified silicone oil and fluorocarbon leveling agent, adjusting the temperature to the fourth temperature and stirring evenly, placing it at the fifth temperature for vacuum curing, and then adjusting the temperature to the sixth temperature for curing to obtain a yellowing-resistant and antioxidant melamine resin.

[0016] During the initial synthesis of melamine resin, the polycondensation reaction between melamine and formaldehyde follows a classic amino-carbonyl nucleophilic addition mechanism. The electron-rich amino nitrogen atom in the melamine molecule initiates a nucleophilic attack on the carbonyl carbon of formaldehyde, forming an unstable hydroxymethyl intermediate. Under alkaline catalysis, the hydroxymethyl groups further undergo intermolecular dehydration condensation to form a methylene-bridged network with a triazine ring as its core structure. γ-Glycidyloxypropyltrimethoxysilane (GPTMS) is subsequently introduced as a functional modifier. Its intramolecular epoxy groups undergo selective ring-opening in a weakly acidic medium. The epoxy groups covalently bond with unreacted hydroxymethyl or primary amino groups in the prepolymer via a nucleophilic ring-opening mechanism, anchoring the siloxane segments to the melamine resin backbone. Simultaneously, the trimethoxysilane termini of the GPTMS are gradually hydrolyzed to silanols in the system, and a condensation reaction initially constructs a localized siloxane cross-linked network. n-Butanol, acting as a reaction medium and proton acceptor, stabilizes the intermediate through a solvation effect and promotes the etherification of the hydroxymethyl group, thereby reducing the risk of free formaldehyde release. The introduction of the latent catalyst n-butyl p-toluenesulfonate demonstrates the regulation of the cure. This compound exists as an ester at low temperatures, maintaining chemical inertness. When the system is heated to the cure threshold, the ester bond undergoes thermal cleavage, releasing p-toluenesulfonic acid, which catalyzes the deep condensation of the siloxane network. This staged curing strategy enables the construction of a melamine-siloxane interpenetrating network: the melamine resin provides a rigid three-dimensional skeleton, while the siloxane phase imparts a toughening effect to the material interface through dynamic Si-O-Si bonds. Its hydrophobic properties also effectively block water molecule penetration, inhibiting hydrolytic aging of the resin.

[0017] 2-Aminophenylboronic acid pinacol ester undergoes hydrolysis in the protic solvent of methanol, removing the pinacol protecting group and exposing the active boronic acid group. This boronic acid group coordinates with the ortho-phenolic hydroxyl group of catechol to form a stable boronate ester ring structure. This coordination process occurs through the interaction of the boron atom's unoccupied p orbital with the lone pair of electrons of the phenolic hydroxyl group, forming a transition state that enhances the electron delocalization of the phenolic hydroxyl group, thereby improving its antioxidant activity. Subsequently, under nitrogen protection, heating to high temperature further allows the boronate ring to form a highly conjugated quinone-boron hybrid structure with the aromatic skeleton of catechol through π-π stacking and a hydrogen bonding network. The introduction of ammonium cerium nitrate initiates the oxidation phase. The highly oxidizing cerium ion preferentially attacks the phenolic hydroxyl groups of catechol in acidic medium, oxidizing some of the phenolic hydroxyl groups to quinoid structures via a single electron transfer mechanism. During the oxidation process, the presence of the boronic acid coordination ring, through steric hindrance, ensures that the quinone groups and the remaining phenolic hydroxyl groups form an alternating quinone-phenol conjugated system. The addition of ascorbic acid, through its reductive quinol structure, captures residual oxidizing species (such as cerium ions or free radical intermediates) in the system, terminating the oxidation chain reaction and preventing excessive formation of quinone radicals. The resulting quinone-phenol hybrid antioxidant combines the electron acceptor properties of quinone with the electron donor capacity of phenol. Its extended conjugated system stabilizes free radicals through an intramolecular charge transfer mechanism, while the boric acid coordination ring further anchors free radicals through Lewis acidic sites, achieving a synergistic antioxidant effect. This hybrid structure effectively inhibits the initiation and propagation of the oxidation chain reaction in a melamine resin matrix, thereby imparting long-lasting yellowing resistance to the material.

[0018] 2,2,6,6-Tetramethylpiperidinamine reacts with triphenyl phosphite under catalytic conditions to undergo a phosphinoesterification reaction. The primary amine group in the 2,2,6,6-Tetramethylpiperidinamine molecule acts as a strong nucleophile, attacking the phosphorus center of the phosphite, displacing the phenoxy group to form a stable phosphoamide bond. This introduces the rigid piperidine ring structure of the hindered amine into the molecular backbone. The synergistic interaction between the lone pair of electrons of the phosphorus atom and the amine group enhances intramolecular charge transfer, providing an active site for subsequent free radical capture. Subsequently, the phosphinoesterified product reacts with 2,4,6-trichloro-1,3,5-triazine in a toluene medium for a nucleophilic substitution reaction. The highly reactive chlorine atom in the 2,4,6-trichloro-1,3,5-triazine molecule is activated in the alkaline environment of pyridine and subsequently displaces the amine or hydroxyl groups of the phosphinoesterified product, forming a covalent linkage between the triazine ring and the phosphoamide structure. The strong electron-withdrawing properties of the triazine ring enhance the affinity of the hindered amine unit for free radicals through a conjugated effect. At the same time, the introduction of the phosphine group not only provides additional free radical stabilization through its lone pair of electrons, but also forms intramolecular coordination with the triazine ring, constructing a rigid coplanar structure and inhibiting the thermal motion of the molecular chain, thereby improving thermal stability. The resulting hindered amine-phosphine-triazine hybrid molecule has both light and thermal stabilization functions. The hindered amine unit effectively captures and neutralizes free radicals through the steric effect of its tetramethylpiperidine ring; the phosphine group stabilizes high-energy intermediates through electron delocalization; and the triazine ring inhibits photodegradation through ultraviolet absorption and energy dissipation mechanisms. The three, through the synergistic interaction of covalent bonds and intramolecular interactions, form a multi-level stable network, improving the durability of melamine resin in complex environments.

[0019] The active hydroxymethyl and siloxane groups in the prepolymer are activated at high temperatures, forming an interpenetrating network structure with both chemical bonds and physical entanglements with the functional additives. The introduction of octavinyl-POSS nanoparticles, through their cage-like siloxane structure, interacts with the resin matrix to form crosslinking nodes, effectively dissipating stress and inhibiting crack propagation. Quinone-phenol hybrid antioxidants form dynamic covalent bonds with amino or hydroxymethyl groups in the resin via boric acid coordination centers, achieving uniform dispersion and anchoring of the antioxidant component. The extended quinone-phenol conjugated system quenches free radicals through an intramolecular charge transfer mechanism, blocking the oxidative chain reaction. Hindered amine-phosphine-triazine light stabilizers shield high-energy photons through the UV absorption properties of the triazine ring. The hindered amine units capture free radicals generated by photoexcitation, while the phosphine groups stabilize the excited molecules through electron transfer, forming a multi-stage light protection mechanism. Fluorocarbon leveling agents, due to their low surface energy, align themselves on the resin surface, forming a dense molecular film, reducing interfacial tension and eliminating surface defects, thereby improving the material's gloss and stain resistance. Polyether-modified silicone oil, a defoamer, disrupts the stability of the bubble film layer through its amphiphilic molecular structure, promoting bubble merging and escape, and ensuring a homogeneous and dense curing process. A gradient temperature increase strategy during the curing phase enables the controllable construction of the network structure by activating different reaction pathways in stages. During the pre-curing stage, at a relatively low temperature, the hydroxymethyl condensation of the melamine resin is preferentially initiated to form a primary cross-linked network. Volatile small molecules are simultaneously removed by vacuum removal to reduce internal defects. The subsequent high-temperature stage strengthens the self-condensation of the siloxane network and the chemical bonding of the functional additives, forming a melamine-siloxane interpenetrating network. This multi-scale synergistic cross-linking not only gives the material a highly rigid skeleton and a dynamic interface, but also inhibits the initiation and propagation of aging reactions through the steric hindrance and electronic effects of the functional components, ultimately improving the melamine resin's antioxidant and yellowing resistance.

[0020] As a preferred technical solution of the present invention, in S1, the mass ratio of the melamine, formaldehyde solution, deionized water, GPT MS n-butanol mixture and n-butyl p-toluenesulfonate is (100-110): (150-160): 50: (35-40): (0.3-0.5), for example, it can be (100, 101, 102, 103, 104, 105, 106, 107, 108, 109 or 110): (150, 151, 152, 153, 154, 155, 156, 157, 158, 159 or 160):50:(35.0, 35.5, 36.0, 36.5, 37.0, 37.5, 38.0, 38.5, 39.0, 39.5 or 40.0):(0.30, 0.32, 0.34, 0.36, 0.38, 0.40, 0.42, 0.44, 0.46, 0.48 or 0.50), but are not limited to the listed values, other values ​​not listed within the numerical range are also applicable.

[0021] In some optional examples, the mass fraction of the formaldehyde solution is 30-35wt.%, for example, it can be 30.0wt.%, 30.5wt.%, 31.0wt.%, 31.5wt.%, 32.0wt.%, 32.5wt.%, 33.0wt.%, 33.5wt.%, 34.0wt.%, 34.5wt.% or 35.0wt.%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0022] In some optional examples, the first temperature is 80-85°C, for example, it can be 80.0°C, 80.5°C, 81.0°C, 81.5°C, 82.0°C, 82.5°C, 83.0°C, 83.5°C, 84.0°C, 84.5°C or 85.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] In some optional examples, the insulation reaction time is 1.5-2h, for example, it can be 1.50h, 1.55h, 1.60h, 1.65h, 1.70h, 1.75h, 1.80h, 1.85h, 1.90h, 1.95h or 2.00h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] In some optional examples, the second temperature is 40-45°C, for example, it can be 40.0°C, 40.5°C, 41.0°C, 41.5°C, 42.0°C, 42.5°C, 43.0°C, 43.5°C, 44.0°C, 44.5°C or 45.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] In some optional examples, the mass ratio of GPTMS to n-butanol in the GPTMS-n-butanol mixture is 4.5:30.

[0026] In some optional examples, the stirring reaction time is 1-2h, for example, it can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] As a preferred technical solution of the present invention, in S2, the mass ratio of catechol, 2-aminophenylboronic acid pinacol ester, methanol aqueous solution, ceric ammonium nitrate and ascorbic acid is (10-12): (6-7): 100: (5-6): 0.5, for example, it can be (10.0, 10.2, 10.4, 10.6, 10.8, 11.0, 11.2, 11.4, 11.6, 11 .8 or 12.0): (6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9 or 7.0): 100: (5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9 or 6.0): 0.5, but is not limited to the listed values, other values ​​not listed within the numerical range are also applicable.

[0028] In some optional examples, the volume ratio of methanol to deionized water in the methanol aqueous solution is 4:1.

[0029] In some optional examples, the third temperature is 85-90°C, for example, it can be 85.0°C, 85.5°C, 86.0°C, 86.5°C, 87.0°C, 87.5°C, 88.0°C, 88.5°C, 89.0°C, 89.5°C or 90.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] In some optional examples, the time of the third temperature reaction is 4-5h, for example, it can be 4.0h, 4.1h, 4.2h, 4.3h, 4.4h, 4.5h, 4.6h, 4.7h, 4.8h, 4.9h or 5.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] In some optional examples, the stirring reaction time is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] As a preferred technical solution of the present invention, in S3, the mass ratio of 2,2,6,6-tetramethylpiperidinamine, triphenyl phosphite and 4-dimethylaminopyridine is (10-11): (19-20): (0.1-0.2), for example, it can be (10.0, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9 or 11.0): (19.0, 19.1, 19.2, 19.3, 19.4, 19.5, 19.6, 19.7, 19.8, 19.9 or 20.0): (0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19 or 0.20), but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] In some optional examples, the time of the first temperature reaction is 8-9h, for example, it can be 8.0h, 8.1h, 8.2h, 8.3h, 8.4h, 8.5h, 8.6h, 8.7h, 8.8h, 8.9h or 9.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] In some optional examples, the mass ratio of the phosphinodide product, 2,4,6-trichloro-1,3,5-triazine, pyridine and toluene is (10-11): (6-7): (5-6): 150, for example, it can be (10.0, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9 or 11.0): (6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9 or 7.0): (5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9 or 6.0): 150, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] In some optional examples, the fourth temperature is 60-65°C, for example, it can be 60.0°C, 60.5°C, 61.0°C, 61.5°C, 62.0°C, 62.5°C, 63.0°C, 63.5°C, 64.0°C, 64.5°C or 65.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] In some optional examples, the fourth temperature reaction time is 6-7h, for example, it can be 6.0h, 6.1h, 6.2h, 6.3h, 6.4h, 6.5h, 6.6h, 6.7h, 6.8h, 6.9h or 7.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] As a preferred technical solution of the present invention, in S4, the mass ratio of the octaethylene-POSS, PEEK powder, quinone-phenol hybrid antioxidant, hindered amine-phosphine-triazine light stabilizer, prepolymer, polyether-modified silicone oil and fluorocarbon leveling agent is (0.5-1): (2-3): (3-4): (2-3): (100-110): (0.4-0.6): (0.2-0.3), for example, it can be (0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95 or 1.00): (2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3.0): (3.0, 3.1, 3.2, 3.3, 3. 4, 3.5, 3.6, 3.7, 3.8, 3.9 or 4.0): (2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3.0): (100, 101, 102, 103, 104, 105, 106, 107, 108, 109 or 110): (0.40, 0.42, 0. 44, 0.46, 0.48, 0.50, 0.52, 0.54, 0.56, 0.58 or 0.60): (0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29 or 0.30), but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] In some optional examples, the fifth temperature is 100-105°C, for example, it can be 100.0°C, 100.5°C, 101.0°C, 101.5°C, 102.0°C, 102.5°C, 103.0°C, 103.5°C, 104.0°C or 104.5°C, 105.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] In some optional examples, the vacuum curing time is 30-40 minutes, for example, it can be 30 minutes, 31 minutes, 32 minutes, 33 minutes, 34 minutes, 35 minutes, 36 minutes, 37 minutes, 38 minutes, 39 minutes or 40 minutes, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] In some optional instances, the sixth temperature is 140-145°C, for example, it can be 140.0°C, 140.5°C, 141.0°C, 141.5°C, 142.0°C, 142.5°C, 143.0°C, 143.5°C, 144.0°C or 144.5°C, 145.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] In some optional examples, the sixth temperature curing time is 60-70 min, for example, it can be 60 min, 61 min, 62 min, 63 min, 64 min, 65 min, 66 min, 67 min, 68 min, 69 min or 70 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] In a second aspect, the present invention provides a yellowing-resistant and antioxidant melamine resin prepared by the preparation method described in the first aspect.

[0043] Compared with the prior art, the present invention has the following beneficial effects: (1) Traditional melamine resin relies on a single antioxidant to inhibit oxidation, which is easily ineffective due to molecular migration or self-degradation. The present invention constructs a dynamic electron transfer network through a quinone phenol-boric acid coordination hybrid structure: the quinone group acts as an electron acceptor to stabilize free radicals, the phenolic hydroxyl group regenerates antioxidant activity through proton transfer, and the boric acid coordination center anchors free radicals through Lewis acid action. At the same time, the hindered amine-phosphine-triazine hybrid molecule achieves synchronous inhibition of multi-factor aging through the triple synergy of triazine ring ultraviolet absorption, phosphine group electron delocalization and hindered amine free radical capture; (2) Through the directional bonding of the epoxy group of the silane coupling agent and the melamine hydroxymethyl group, the molecular-level dispersion of the siloxane chain segment in the resin skeleton is achieved. During the curing process, the siloxane network and the melamine network form interpenetration, the Si-O-Si bond of the siloxane effectively dissipates stress, and the melamine triazine ring maintains a rigid skeleton, so that the material has both high hardness and impact resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A flow chart of a method for preparing a yellowing-resistant and antioxidant melamine resin is provided for Examples 1-4 of the present invention. DETAILED DESCRIPTION

[0045] The technical solutions of the present invention are described in detail below in conjunction with specific embodiments and the accompanying drawings. The embodiments described herein are specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be understood as limiting the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the contents disclosed in the claims of this application and its specification, including technical solutions that adopt any obvious replacements and modifications to the embodiments described herein.

[0046] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products and have not been subjected to any further purification treatment.

[0047] Example 1

[0048] This embodiment provides a yellowing-resistant and antioxidant melamine resin and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0049] S1, 100g of melamine, 150g of a 30wt.% formaldehyde solution, and 50g of deionized water were mixed, the temperature was adjusted to 80°C, the pH of the solution was adjusted to 8.5, and the mixture was kept warm for 1.5h. The temperature was then adjusted to 40°C, the pH of the solution was adjusted to 6.5, 35g of a GPTM S n-butanol mixture was added, the mixture was stirred for 1h, and 0.3g of n-butyl p-toluenesulfonate was added. The mixture was mixed evenly and filtered to obtain a prepolymer;

[0050] S2, dispersing 10 g of catechol and 6 g of 2-aminophenylboronic acid pinacol ester in 100 g of methanol aqueous solution, adjusting the temperature to 85°C under nitrogen atmosphere and reacting for 4 h. At room temperature, adjusting the pH to 3.5 and adding 5 g of ammonium cerium nitrate and stirring to react for 2 h. Adding 0.5 g of ascorbic acid to terminate the reaction, filtering and drying to obtain a quinone-phenol hybrid antioxidant; the volume ratio of methanol to deionized water in the methanol aqueous solution is 4:1;

[0051] S3, 10g of 2,2,6,6-tetramethylpiperidinamine, 19g of triphenyl phosphite and 0.1g of 4-dimethylaminopyridine were mixed, and the temperature was adjusted to 80°C for reaction for 8h to obtain a phosphinodine product. 10g of the phosphinodine product, 6g of 2,4,6-trichloro-1,3,5-triazine and 5g of pyridine were added to 150g of toluene, and the mixture was reacted at 60°C for 6h. After the reaction was completed, the mixture was filtered, concentrated and purified to obtain a hindered amine-phosphine-triazine light stabilizer;

[0052] S4, 0.5g of octavinyl-POSS, 2g of PEEK powder, 3g of quinone-phenol hybrid antioxidant and 2g of hindered amine-phosphine-triazine light stabilizer are dispersed in ethanol by ultrasonic dispersion, 100g of prepolymer, 0.4g of polyether-modified silicone oil and 0.2g of fluorocarbon leveling agent are added, the temperature is adjusted to 60°C and stirred evenly, and the mixture is placed at 100°C for vacuum curing for 30min, and then the temperature is adjusted to 140°C for curing for 60min to obtain a yellowing-resistant and antioxidant melamine resin.

[0053] Example 2

[0054] This embodiment provides a yellowing-resistant and antioxidant melamine resin and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0055] S1, 110g of melamine, 160g of 35wt.% formaldehyde solution, and 50g of deionized water were mixed, the temperature was adjusted to 82°C, the pH of the solution was adjusted to 9.0, and the mixture was kept warm for 2h. The temperature was adjusted to 45°C, the pH of the solution was adjusted to 6.8, 40g of GPTMS n-butanol mixed solution was added, the mixture was stirred for 1.4h, and 0.4g of n-butyl p-toluenesulfonate was added. The mixture was mixed well and filtered to obtain a prepolymer;

[0056] S2, dispersing 11.5 g of catechol and 7 g of 2-aminophenylboronic acid pinacol ester in 100 g of methanol aqueous solution, adjusting the temperature to 90°C under nitrogen atmosphere and reacting for 4.3 h. At room temperature, adjusting the pH to 4.0 and adding 5.3 g of ammonium cerium nitrate and stirring for 3 h. The reaction was terminated by adding 0.5 g of ascorbic acid, and the mixture was filtered and dried to obtain a quinone-phenol hybrid antioxidant; the volume ratio of methanol to deionized water in the methanol aqueous solution was 4:1;

[0057] S3, 11 g of 2,2,6,6-tetramethylpiperidinamine, 19.2 g of triphenyl phosphite, and 0.2 g of 4-dimethylaminopyridine were mixed, and the temperature was adjusted to 84° C. for reaction for 9 h to obtain a phosphinodine product. 10.7 g of the phosphinodine product, 6.3 g of 2,4,6-trichloro-1,3,5-triazine, and 5.2 g of pyridine were added to 150 g of toluene, and the mixture was reacted at 65° C. for 6.2 h. After the reaction was completed, the mixture was filtered, concentrated, and purified to obtain a hindered amine-phosphine-triazine light stabilizer;

[0058] S4, 0.7g of octavinyl-POSS, 3g of PEEK powder, 3.2g of quinone-phenol hybrid antioxidant and 3g of hindered amine-phosphine-triazine light stabilizer were dispersed in ethanol by ultrasonic dispersion, 110g of prepolymer, 0.5g of polyether-modified silicone oil and 0.3g of fluorocarbon leveling agent were added, the temperature was adjusted to 65°C and stirred evenly, and the mixture was placed at 101°C for vacuum curing for 33min, and then the temperature was adjusted to 142°C for curing for 66min to obtain a yellowing-resistant and antioxidant melamine resin.

[0059] Example 3

[0060] This embodiment provides a yellowing-resistant and antioxidant melamine resin and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0061] S1, 103g of melamine, 152g of a 32wt.% formaldehyde solution, and 50g of deionized water were mixed, the temperature was adjusted to 85°C, the pH of the solution was adjusted to 8.7, and the mixture was kept warm for 1.7h. The temperature was then adjusted to 44°C, the pH of the solution was adjusted to 7.0, 39g of a GPTM S n-butanol mixture was added, the mixture was stirred for 2h, and 0.5g of n-butyl p-toluenesulfonate was added. The mixture was mixed evenly and filtered to obtain a prepolymer;

[0062] S2, dispersing 12 g of catechol and 6.2 g of 2-aminophenylboronic acid pinacol ester in 100 g of methanol aqueous solution, adjusting the temperature to 88°C under nitrogen atmosphere and reacting for 5 h. At room temperature, adjusting the pH to 3.8 and adding 6 g of ammonium cerium nitrate and stirring to react for 2.4 h. Adding 0.5 g of ascorbic acid to terminate the reaction, filtering and drying to obtain a quinone-phenol hybrid antioxidant; the volume ratio of methanol to deionized water in the methanol aqueous solution is 4:1;

[0063] S3, 10.4 g of 2,2,6,6-tetramethylpiperidinamine, 20 g of triphenyl phosphite and 0.13 g of 4-dimethylaminopyridine were mixed, and the temperature was adjusted to 85° C. for reaction for 8.7 h to obtain a phosphinodine product. 11 g of the phosphinodine product, 7 g of 2,4,6-trichloro-1,3,5-triazine and 6 g of pyridine were added to 150 g of toluene, and the mixture was reacted at 62° C. for 7 h. After the reaction was completed, the mixture was filtered, concentrated and purified to obtain a hindered amine-phosphine-triazine light stabilizer;

[0064] S4, 1g of octavinyl-POSS, 2.4g of PEEK powder, 4g of quinone-phenol hybrid antioxidant and 2.4g of hindered amine-phosphine-triazine light stabilizer were dispersed in ethanol by ultrasonic dispersion, 103g of prepolymer, 0.6g of polyether-modified silicone oil and 0.22g of fluorocarbon leveling agent were added, the temperature was adjusted to 62°C and stirred evenly, and the mixture was placed at 105°C for vacuum curing for 40min, and then the temperature was adjusted to 145°C for curing for 70min to obtain a yellowing-resistant and antioxidant melamine resin.

[0065] Example 4

[0066] This embodiment provides a yellowing-resistant and antioxidant melamine resin and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0067] S1, 107g of melamine, 156g of a 34wt.% formaldehyde solution, and 50g of deionized water were mixed, the temperature was adjusted to 83°C, the pH of the solution was adjusted to 8.6, and the mixture was kept warm for 1.9h. The temperature was then adjusted to 41°C, the pH of the solution was adjusted to 6.6, 36g of a GPTM S n-butanol mixture was added, the mixture was stirred for 1.8h, and 0.35g of n-butyl p-toluenesulfonate was added. The mixture was mixed evenly and filtered to obtain a prepolymer;

[0068] S2, dispersing 10.5 g of catechol and 6.6 g of 2-aminophenylboronic acid pinacol ester in 100 g of methanol aqueous solution, adjusting the temperature to 86°C under nitrogen atmosphere and reacting for 4.9 h. At room temperature, adjusting the pH to 3.6 and adding 5.8 g of ammonium cerium nitrate and stirring to react for 2.8 h. Adding 0.5 g of ascorbic acid to terminate the reaction, filtering and drying to obtain a quinone-phenol hybrid antioxidant; the volume ratio of methanol to deionized water in the methanol aqueous solution is 4:1;

[0069] S3, 10.7 g of 2,2,6,6-tetramethylpiperidinamine, 19.8 g of triphenyl phosphite and 0.18 g of 4-dimethylaminopyridine were mixed, the temperature was adjusted to 81° C. and the reaction was carried out for 8.2 h to obtain a phosphinodine product, 10.4 g of the phosphinodine product, 6.5 g of 2,4,6-trichloro-1,3,5-triazine and 5.8 g of pyridine were added to 150 g of toluene, and the mixture was reacted at 64° C. for 6.7 h. After the reaction was completed, the mixture was filtered, concentrated and purified to obtain a hindered amine-phosphine-triazine light stabilizer;

[0070] S4, 0.9g of octavinyl-POSS, 2.6g of PEEK powder, 3.7g of quinone-phenol hybrid antioxidant and 2.8g of hindered amine-phosphine-triazine light stabilizer were dispersed in ethanol by ultrasonic dispersion, 107g of prepolymer, 0.45g of polyether-modified silicone oil and 0.26g of fluorocarbon leveling agent were added, the temperature was adjusted to 64°C and stirred evenly, and the mixture was placed at 104°C for vacuum curing for 37min, and then the temperature was adjusted to 144°C for curing for 63min to obtain a yellowing-resistant and antioxidant melamine resin.

[0071] Comparative Example 1

[0072] This comparative example provides a yellowing-resistant, antioxidant melamine resin and a preparation method thereof. The difference between it and Example 1 is that the mass g of 2-aminophenylboronic acid pinacol ester in S2 is 1 g, which is 5 g less than that in Example 1. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0073] Comparative Example 2

[0074] This comparative example provides a yellowing-resistant and antioxidant melamine resin and a preparation method thereof. The difference between it and Example 1 is that the mass g of the phosphinolyzed product in S3 is 2g, which is 8g less than that in Example 1. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0075] Comparative Example 3

[0076] This comparative example provides a yellowing-resistant and antioxidant melamine resin and a preparation method thereof. The difference between it and Example 1 is that the mass g of 2,4,6-trichloro-1,3,5-triazine in S3 is 2g, which is 4g less than that in Example 1. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0077] Equal amounts of the melamine resins prepared in the Examples and Comparative Examples were melt-extruded and cooled on a casting drum to form melamine resin films. The films were then tested for weather resistance. The UV resistance test method followed GB / T 14522-2008; the comprehensive aging test method followed GB / T 16422.2-2014; the yellowing index test method followed ASTM E313-20; and the tensile test method followed GB / T 1040.3-2006. The test results are shown in Table 1.

[0078] Table 1 Test results of yellowing-resistant and antioxidant melamine resins of Examples 1-4 and Comparative Examples 1-3

[0079]

[0080] As shown in Table 1, compared to Example 1, Comparative Example 1 exhibits reduced UV resistance and comprehensive aging test performance, while exhibiting an increased yellowing index. This is due to insufficient 2-aminophenylboronic acid pinacol ester in Comparative Example 1, which reduces the number of boronic acid coordination centers. Boric acid coordination stabilizes free radicals and enhances the UV absorption capacity of the quinone-phenol conjugated system. Insufficient phosphinate products in Comparative Example 2 reduce the formation of triazine-phosphine hybrid molecules, weakening the UV absorption efficiency of the triazine ring and triggering photooxidation of the resin bulk. In Comparative Example 3, insufficient 2,4,6-trichloro-1,3,5-triazine reduces the triazine ring density in the light stabilizer, narrowing the UV shielding range and inducing chain breakage and oxidation.

[0081] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a yellowing-resistant and antioxidant melamine resin, characterized in that: The preparation method comprises: S1, mixing melamine, formaldehyde solution, and deionized water, adjusting the pH of the solution to 8.5-9.0 for reaction, adjusting the pH of the solution to 6.5-7.0, adding a GPTMS n-butanol mixture and n-butyl p-toluenesulfonate to obtain a prepolymer; S2, dispersing catechol and 2-aminophenylboronic acid pinacol ester in a methanol aqueous solution for reaction, adjusting the pH to 3.5-4.0 at room temperature, adding ammonium cerium nitrate for reaction, and adding ascorbic acid to terminate the reaction to obtain a quinone-phenol hybrid antioxidant; S3, mixing 2,2,6,6-tetramethylpiperidinamine, triphenyl phosphite and 4-dimethylaminopyridine to react to obtain a phosphine ester product, and adding the phosphine ester product, 2,4,6-trichloro-1,3,5-triazine and pyridine to toluene to react to obtain a hindered amine-phosphine-triazine light stabilizer; S4, octavinyl-POSS, PEEK powder, quinone-phenol hybrid antioxidant and hindered amine-phosphine-triazine light stabilizer are dispersed in ethanol by ultrasonic dispersion, prepolymer, polyether-modified silicone oil and fluorocarbon leveling agent are added, and cured to obtain a yellowing-resistant and antioxidant melamine resin.

2. The method for preparing a yellowing-resistant and antioxidant melamine resin according to claim 1, wherein: In S1: The mass ratio of the melamine, formaldehyde solution, deionized water, GPTMS n-butanol mixed solution and n-butyl p-toluenesulfonate is (100-110):(150-160):50:(35-40):(0.3-0.5).

3. The method for preparing a yellowing-resistant and antioxidant melamine resin according to claim 1, wherein: In S1: The mass fraction of the formaldehyde solution is 30-35 wt.%.

4. The method for preparing a yellowing-resistant and antioxidant melamine resin according to claim 1, wherein: In S1: The mass ratio of GPTMS to n-butanol in the GPTMS-n-butanol mixed solution is 4.5:

30.

5. The method for preparing a yellowing-resistant and antioxidant melamine resin according to claim 1, wherein: In S2: The mass ratio of the catechol, 2-aminophenylboronic acid pinacol ester and methanol aqueous solution is (10-12): (6-7):

100.

6. The method for preparing a yellowing-resistant and antioxidant melamine resin according to claim 1, wherein: In S2: The mass ratio of catechol, ammonium cerium nitrate and ascorbic acid is (10-12): (5-6): 0.

5.

7. The method for preparing a yellowing-resistant and antioxidant melamine resin according to claim 1, wherein: In S3: The mass ratio of the 2,2,6,6-tetramethylpiperidinamine, triphenyl phosphite and 4-dimethylaminopyridine is (10-11): (19-20): (0.1-0.2).

8. The method for preparing a yellowing-resistant and antioxidant melamine resin according to claim 1, wherein: In S3: The mass ratio of the phosphinodated product, 2,4,6-trichloro-1,3,5-triazine, pyridine and toluene is (10-11):(6-7):(5-6):

150.

9. The method for preparing a yellowing-resistant and antioxidant melamine resin according to claim 1, wherein: In S4: The mass ratio of the octaethylene-POSS, PEEK powder, quinone-phenol hybrid antioxidant, hindered amine-phosphine-triazine light stabilizer, prepolymer, polyether-modified silicone oil and fluorocarbon leveling agent is (0.5-1): (2-3): (3-4): (2-3): (100-110): (0.4-0.6): (0.2-0.3).

10. A yellowing-resistant and antioxidant melamine resin obtained according to the preparation method according to any one of claims 1 to 9.

Images