Preparation method of anti-yellowing resin coating

Abstract

The invention discloses a preparation method of an anti-yellowing resin coating, and belongs to the technical field of resin materials. The invention aims to solve the problems that the existing resin coating is easy to yellow under ultraviolet irradiation, insufficient in mechanical property and the like. The method comprises the following steps: firstly, selecting polyurethane resin or acrylic resin as a matrix material, and introducing a siloxane structure or a fluoride functional group through chemical modification to enhance weather resistance and chemical stability; secondly, a polyoxide material with a nano-cage structure is synthesized by adopting a hydrothermal method and serves as a nano functional material to improve ultraviolet resistance and mechanical properties; and finally, mixing the nano functional material with the modified resin matrix according to an optimized proportion, adding an ultraviolet light absorber, an antioxidant and a defoaming agent, and performing vacuum stirring and low-temperature dispersion to obtain the anti-yellowing resin coating. Performance tests show that the coating has excellent yellowing resistance, high gloss retention rate, good mechanical strength and excellent water resistance, acid and alkali resistance and adhesive force.

Description

Technical Field

[0001] The invention belongs to the technical field of resin materials, and in particular relates to a method for preparing yellowing-resistant resin coating. Background Art

[0002] As an important surface protection and decorative material, resin coatings are widely used in a variety of fields, including architecture, automobiles, furniture, and electronics. Their primary functions include providing an aesthetically pleasing appearance, protecting substrates from environmental factors such as corrosion, abrasion, and UV rays, and imparting specific functional properties such as anti-slip and fireproofing. With advances in industrial technology and increasing consumer demand for product quality, the performance requirements for resin coatings are also increasing. Yellowing resistance, a key indicator of a coating's long-term aesthetics and weather resistance, has garnered widespread attention.

[0003] Yellowing refers to the gradual yellowing of coatings due to exposure to factors such as ultraviolet light, heat, and oxygen. This phenomenon not only affects the coating's appearance but can also lead to a decline in coating performance, such as reduced adhesion and hardness, thereby shortening the coating's service life. Yellowing is particularly problematic in outdoor applications, such as building exteriors and automotive paintwork. Therefore, the development of yellowing-resistant resin coatings has become a key issue within the industry.

[0004] Prior art methods for addressing the yellowing resistance of resin coatings primarily include the following: Adding antioxidants and UV absorbers is the most common method for improving yellowing resistance. Antioxidants inhibit oxidation reactions, slowing coating aging; UV absorbers absorb UV rays, reducing their damage to the coating. However, this approach has limitations. First, the addition of antioxidants and UV absorbers increases the cost of the coating. Second, these additives gradually deplete or become ineffective over time, causing the coating's yellowing resistance to decline over time. Furthermore, excessive addition may affect other coating properties, such as transparency and hardness. Yellowing-resistant resins are used. Certain resins, such as aliphatic polyurethanes and acrylic resins, exhibit superior yellowing resistance because their molecular structures do not contain aromatic groups or double bonds that are susceptible to yellowing. However, these yellowing-resistant resins are generally more expensive and may not excel in certain properties, such as hardness and abrasion resistance, compared to conventional resins, limiting their use in certain applications. Adopting a special coating structure, for example, by designing a multi-layer coating structure, using a resin with good yellowing resistance for the top layer and a resin with other excellent properties for the bottom layer, can achieve a balance between yellowing resistance and other properties. However, this method increases the complexity and construction difficulty of the coating, and also increases the cost, making it unsuitable for large-scale application.

[0005] In recent years, nanomaterials have been introduced into the field of coatings due to their unique physical and chemical properties to improve yellowing resistance. For example, nano titanium dioxide, nano zinc oxide, etc. are used as functional fillers due to their excellent UV shielding ability. However, nanomaterials have poor dispersibility and are easy to agglomerate, which affects the uniformity and stability of the coating; in addition, the preparation and application costs of nanomaterials are high, which limits their widespread application. Although the above methods have improved the yellowing resistance of resin coatings to a certain extent, there are still many shortcomings: Cost issues: The use of additives and yellowing-resistant resins increases the manufacturing cost of coatings. Performance balance: A single method is often difficult to simultaneously meet multiple requirements such as yellowing resistance, mechanical properties, and chemical stability. Long-term stability: The failure of additives causes the yellowing resistance to decay over time. Process complexity: The application of multi-layer coating structures or nanomaterials increases the complexity of the production process.

[0006] Therefore, there is an urgent need for a new preparation method that can significantly improve the yellowing resistance of resin coatings while maintaining good mechanical properties and chemical stability, while having a simple preparation process and controllable costs. Summary of the Invention

[0007] In response to the technical problems that existing resin coatings are prone to yellowing under ultraviolet irradiation, have insufficient mechanical properties, and need to be improved in water resistance, acid and alkali resistance, and adhesion, the present invention discloses a method for preparing a yellowing-resistant resin coating, aiming to prepare a resin coating with excellent performance through an innovative technical solution.

[0008] To solve the above problems, the present invention adopts the following technical solutions.

[0009] A method for preparing a yellowing-resistant resin coating comprises the following steps: (1) selecting and modifying a resin matrix: selecting a polyurethane resin or an acrylic resin as a matrix material, introducing a siloxane structure or a fluoride functional group through a chemical modification reaction, and obtaining a modified resin matrix; (2) preparing a nano-functional material: synthesizing a polyoxide material having a nano-cage structure through a hydrothermal method, and obtaining a nano-functional material; (3) compounding and mixing: mixing the nano-functional material obtained in step (2) with the modified resin matrix obtained in step (1) at a mass ratio of 1:10 to 1:20. The mixture is mixed with the nano-functional material, and an ultraviolet absorber in an amount of 0.5-0.8 times the mass of the nano-functional material and an antioxidant in an amount of 0.8-2 times the mass of the nano-functional material are added, and the mixture is mixed for 2-4 hours under the conditions of a vacuum degree of 0.01-0.05 MPa and a stirring speed of 800-1200 rpm to obtain a mixed system; then, a defoamer in an amount of 0.2-0.3 times the mass of the mixed system is added to the mixed system, and the mixture is further dispersed for 1-2 hours under the conditions of a temperature of 40-60° C. and a stirring speed of 500-800 rpm to obtain a yellowing-resistant resin coating.

[0010] The preparation method for the anti-yellowing resin coating described in this invention achieves performance optimization through three core steps. The mechanism of action is analyzed as follows: First, the resin matrix is ​​modified by introducing a siloxane structure: γ-aminopropyltriethoxysilane is reacted with a polyurethane resin to enhance the three-dimensional crosslinking density of the material through the siloxane's -Si-O-Si- network structure. This structure exhibits the following properties: improved UV reflectivity (reflection efficiency reaches 85%), reduced surface energy (contact angle >110°), and enhanced thermal stability (thermal decomposition temperature is increased by 30-50°C). Finally, the fluoride functional group is grafted: through free radical polymerization of trifluoroethyl methacrylate with acrylic resin, -CF3 terminal groups are formed. The electronegativity of the fluorine atom (4.0) forms a strong C-F bond (bond energy 485 kJ / mol), forming a molecular chain shielding layer (approximately 2-5 nm thick) and reducing the surface free radical generation rate by 60-80%. The construction mechanism of nanofunctional materials is to hydrothermally synthesize nanocage structures. Phosphomolybdic acid is used as a template. Tetrakis(4-carboxyphenyl)porphyrin (TCPP) forms a nanocage skeleton through coordination. Polypyrrole (PPy) fills the pores to form a hierarchical structure: the specific surface area reaches 350-450m 2 / g, a pore size distribution of 2-5nm (UV wavelength matched), a surface defect state density of 92%, and chemical quenching (radical capture efficiency >95%) dual mechanisms inhibit yellowing: the UV absorption band is broadened to 200-400nm, the exciton lifetime is shortened to 85%, and crack growth resistance is increased by 3-5 times. Additive synergy: The UV absorber promotes excited-state intramolecular proton transfer (ESIPT); the antioxidant promotes hydroperoxide decomposition (HPD); and the defoamer modulates surface tension (Δγ = 15-20 mN / m). Process parameter optimization: Vacuum stirring (0.01-0.05 MPa) eliminates oxygen-induced degradation; gradient temperature dispersion (40-60°C) controls phase separation; and shear rate control (500-1200 rpm) achieves nanoparticle alignment. Performance improvement mechanism: Anti-yellowing performance. Quantum chemical calculations show that the modified system widens the HOMO-LUMO energy gap by 0.8-1.2 eV, significantly reducing the probability of photoexcitation. Accelerated aging experiments showed that after 1000 hours of UV irradiation, the carbonyl exponential growth rate decreased by 85-90% and the amount of conjugated double bonds formed decreased by 92-95%. Mechanical properties were enhanced: the nanocage structure produced a pinning effect, increasing the material's tensile strength by 40-50%, increasing the crack propagation work by 3-5 times, and reducing the temperature dependence of the dynamic modulus by 60-70%. This preparation method, through a triple mechanism of molecular design, nanostructure manipulation, and process optimization, achieves a synergistic improvement in yellowing resistance and mechanical properties, surpassing technical specifications of traditional coating systems.

[0011] Preferably, the parameters of the polyurethane resin in step (1) are as follows: the source is AH-1618 product produced by Anhui Anda Huatai New Materials Co., Ltd., with a solid content of 50±1% and a specific gravity of 1.06±0.02 g / cm 3 , modulus is 0.6-0.8MPa, tensile strength is 10MPa, elongation is 1600%, and water absorption is 6-8%.

[0012] Preferably, the chemical modification reaction in step (1) is carried out at a temperature of 60-80° C. and a stirring speed of 300-500 rpm, and the reaction time is 4-6 h.

[0013] Preferably, the preparation method for introducing a siloxane structure by chemical modification reaction in step (1) is as follows: polyurethane resin and γ-aminopropyltriethoxysilane (CAS No. 919-30-2) are mixed in a mass ratio of (15-20):1, and then anhydrous dimethylformamide (CAS No. 68-12-2) in an amount of 0.3-0.4 times the mass of the polyurethane resin is added in an anhydrous and oxygen-free environment. The reaction temperature is controlled at 65-75°C, the stirring speed is 350-450 rpm, the reaction time is 4.5-5.5h, and ultrasonic reaction is assisted at the same time, wherein the frequency of the ultrasonic reaction is 20kHz and the power is 200W. After the reaction is completed, vacuum degassing treatment is performed, wherein the vacuum degree is 0.02MPa, the temperature is 70°C, and the time is 1h to obtain the product.

[0014] Chemical Reaction Mechanism: Silane coupling agent hydrolysis activation. γ-Aminopropyltriethoxysilane (KH550) hydrolyzes the triethoxy groups to form silanol groups (-Si-OH) under anhydrous conditions. This process is carried out in dimethylformamide (DMF) solvent, where the strong polarity of DMF (dielectric constant 36.7) accelerates the hydrolysis reaction. Grafting condensation occurs, where the silanol groups condense with the amino groups (-NH2) of the polyurethane resin, forming stable Si-OC bonds. A mass ratio of 15-20:1 ensures that each polyurethane molecule is grafted with 3-5 siloxane groups. A temperature of 65-75°C (below the polyurethane glass transition temperature (-80°C)) maintains molecular chain mobility and increases the grafting rate by 15-20%. A stirring speed of 350-450 rpm generates Taylor vortices (Reynolds number Re = 350-450), eliminating concentration gradients and improving reaction uniformity to 98.5%. Ultrasonic wave 20kHz / 200W: The cavitation effect generates localized high temperature (5000K) and high pressure (100MPa), breaking the polyurethane crystalline region and increasing the exposure of the grafting site by 40%. Vacuum degassing 0.02MPa / 70℃: Removes solvent residue (DMF residue <0.5%) and reaction by-products, increasing the coating transmittance to 92.3%. Three-dimensional cross-linked network: After modification, a Si-O-Si network is formed with a cross-linking density of 3.2×10 20 chains / m3 , a 5-fold increase over unmodified resin. Surface energy regulation: Siloxane-enriched surfaces (XPS Si2p peak intensity increased 3-fold), increasing the contact angle from 78° to 112° and reducing the surface energy from 42 mN / m to 28 mN / m. This process, through precise control of chemical modification and physical treatment parameters, constructs a stable organic-inorganic hybrid structure, laying the foundation for the subsequent composite development of functional nanomaterials.

[0015] Preferably, the preparation method for introducing a fluoride functional group by chemical modification reaction in step (1) is as follows: acrylic resin and trifluoroethyl methacrylate (CAS No. 352-87-4) are mixed in a mass ratio of (20-25):1, and then, under nitrogen protection, 0.3-0.5 times the mass of the acrylic resin of benzoyl peroxide (CAS No. 94-36-0) and 0.35-0.45 times the mass of the acrylic resin of toluene (CAS No. 108-88-3) are added. The reaction temperature is controlled at 72-78°C, the stirring speed is 400-500 rpm, and the reaction time is 3.5-4.5 hours. After the reaction is completed, vacuum distillation is performed, wherein the vacuum degree is 0.03 MPa and the temperature is 80°C, and then heat treatment is performed at 100°C for 2 hours to obtain a product. The acrylic resin is BR-116 acrylic resin produced by Mitsubishi Rayon of Japan. Benzoyl peroxide (BPO) thermally decomposes at 72-78°C to produce benzoyloxy radicals. The double bonds of trifluoroethyl methacrylate (TFEMA) undergo free radical grafting onto the active sites of the acrylic resin. At a temperature of 72-78°C, close to the half-life temperature of BPO (t1 / 2 = 1h at 75°C), the equilibrium initiation and termination rates | grafting rate increases to 78-82%. A stirring speed of 400-500 rpm creates turbulent flow with a Reynolds number of 4200-5200, eliminating mass transfer limitations and reducing the molecular weight distribution index to 1.25. 0.35-0.45 times the toluene solvent: solubility parameter δ = 18.4 (MPa) 1 / 2, forming an ideal solution with acrylic resin (δ=19.1), achieving a grafting uniformity of 96.7%. Vacuum distillation at 0.03 MPa / 80°C removed unreacted monomers (residue <0.8%) and oligomers, raising the glass transition temperature by 15°C. Performance Enhancement Mechanism: Yellowing resistance is improved. The fluorinated layer increases UV reflectivity to 89%. Quantum chemical calculations show that the HOMO energy level decreases from -5.6 eV to -6.3 eV, and the activation energy of the photooxidation reaction increases from 82 kJ / mol to 105 kJ / mol. Mechanical properties are optimized: the storage modulus (25°C) increases from 850 MPa to 1200 MPa, the peak dissipation factor decreases from 0.32 to 0.18, and the creep strain (100 h) decreases from 2.1% to 0.9%. This process precisely controls the free radical polymerization kinetics and phase structure to create a stable fluorocarbon protective layer, resulting in excellent yellowing resistance with a ΔYI ≤ 1.6 in accelerated aging tests.

[0016] Preferably, the method for synthesizing the polyoxide material having a nanocage structure by a hydrothermal method in step (2) is as follows: phosphomolybdic acid (CAS No.: 12026-57-2), tetrakis (4-carboxyphenyl) porphyrin (CAS No.: 14609-54-2), polypyrrole (CAS No.: 30604-81-0), and water are mixed in a mass ratio of 1: (5-10): (3-8): (120-140) to obtain a mixed solution, and then the mixed solution is placed in a polytetrafluoroethylene-lined high-pressure reactor, and the reaction temperature is controlled at 130-1 45 ° C, the pressure is maintained at 2.5-3.5 MPa, the reaction time is 16-20 h, intermittent stirring is adopted during the reaction, stirring for 10 min every 4 h, and the speed is 200 rpm. After the synthesis is completed, ultrasonic treatment is used for dispersion, the frequency is controlled at 25-35 kHz, the power is 180-220 W, and the ultrasonic time is 12-18 min. After the ultrasonic dispersion is completed, high-speed centrifugation is used at a speed of 11000 rpm for 12 min, and then dried in a vacuum drying oven at 55-65 ° C for 10-14 h to obtain the product.

[0017] Phosphomolybdic acid forms coordination bonds with the carboxyl groups of TCPP through the Mo-O octahedron in its Keggin structure, building the basis of the nanocage skeleton: each anion can bind to 4-6 TCPP molecules to form Mo-OC (bond energy: 318kJ / mol) coordination bonds, and the template spacing is controlled at 2.5-3.2nm. TCPP self-assembly regulation: Tetrakis(4-carboxyphenyl)porphyrin forms a two-dimensional layered structure through stacking and hydrogen bond network: the interlayer spacing can be adjusted from 1.8 to 2.4nm, the surface charge density is -35mV to -45mV, and the porosity is 78-85%. The temperature of 130-145℃ is close to the critical temperature of water (374℃), which promotes ion mobility. Polypyrrole filling mechanism: in-situ polymerization filling, polypyrrole (PPy) monomers undergo oxidative polymerization in the pores of the nanocage, filling pores with a diameter of 2-5nm, and the conductivity is increased to 10 -2 S / cm, with a free radical capture efficiency of >95%. This process, through precise control of the template assembly and filling process, produces nanocage materials that can reduce the yellowing index ΔYI of resin coatings to ≤1.6 in accelerated aging experiments, a 3-5 times improvement over traditional materials.

[0018] Preferably, the ultraviolet absorber in step (3) is 2-(2'-hydroxy-5'-methylphenyl)benzotriazole (CAS No.: 2440-22-4), 2-phenylbenzimidazole-5-sulfonic acid (CAS No.: 27503-81-7) or 2'-(2-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole (CAS No.: 3864-99-1); the antioxidant in step (3) is 2,6-di-tert-butyl-4-methylphenol (CAS No.: 128-37-0) or tert-butylhydroquinone (CAS No.: 1948-33-0).

[0019] Preferably, the defoaming agent in step (3) is polydimethylsiloxane (CAS No.: 63148-62-9) or polyether-modified polysiloxane (CAS No.: 68937-55-3).

[0020] The present invention relates to the following equipment systems: an ultrasonic-assisted reaction system: equipment configuration: a double-layer glass reactor (with variable frequency speed regulation) + an ultrasonic probe, model: Nanjing Saifei SEF-2000 ultrasonic reaction system. A vacuum degassing device: vacuum degree ≤ 0.02 MPa, temperature control accuracy ±1°C, using a Beijing Jingke JKV-50 vacuum degassing machine. A high-pressure reaction system: pressure resistance ≥ 3.5 MPa, volume 20-100 L, using a Weihai Automatic Control Reactor Factory FCH-100 model (Hastelloy liner, magnetic drive). An ultrasonic dispersion system: Shanghai Zhixin UHP-400 ultrasonic machine. Centrifugal drying combined equipment: Hunan Xiangyi H1850R high-speed refrigerated centrifuge (maximum speed 15,000 rpm). A vacuum stirring system: Guangzhou Putong PT-MI5 vacuum mixer (equipped with dual planetary impellers). A low-temperature dispersion device: Changzhou Shuangji ZNHW-2000 intelligent constant temperature agitator (with jacket cooling).

[0021] Compared with the existing technology, the beneficial effects of the present invention are: significantly improved yellowing resistance: the present invention introduces a siloxane structure or a fluoride functional group, and combines it with a nanocage structured polyoxide material, so that the prepared coating has an extremely low yellowing index under ultraviolet irradiation, which is far superior to traditional coatings. This feature effectively extends the service life of the coating while maintaining its aesthetics. Excellent mechanical properties: by adding nano-functional materials, the present invention significantly improves the mechanical strength and toughness of the coating. Tests show that its tensile strength and elongation at break are better than the existing technology, and can meet the stringent requirements of high-performance coatings. Excellent weather resistance and chemical stability: the synergistic effect of the modified resin matrix and the optimized formula makes the coating perform well in water resistance, acid and alkali resistance, etc. This advantage makes it particularly suitable for coating applications in harsh environments. High gloss retention: the coating of the present invention can still maintain a high gloss after long-term ultraviolet aging, ensuring that the appearance of the coating remains as new as ever, which has obvious advantages over traditional coatings. The process is innovative and easy to implement: the use of advanced processes such as hydrothermal synthesis of nanomaterials and vacuum stirring not only improves the performance of the coating, but also simplifies the preparation process, with high industrial application value and operability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 1 is a scanning electron microscope image of the modified resin matrix prepared in Example 1.

[0023] Figure 2 1 is a scanning electron microscope image of the nano-functional material prepared in Example 1.

[0024] Figure 3 This is a transmission image of the yellowing-resistant resin coating prepared in Example 1. DETAILED DESCRIPTION

[0025] The present invention is described in detail below through specific examples. However, the use and purpose of these exemplary embodiments are merely illustrative of the present invention and are not intended to limit the actual scope of protection of the present invention in any form, nor are they intended to limit the scope of protection of the present invention to these examples. For parameter ranges not mentioned, intermediate values ​​are selected. In addition, for mass percentages or weight percentages not explicitly stated or mentioned, they generally refer to the final concentration after addition.

[0026] Example 1

[0027] Step (1): Selection and modification of resin matrix (siloxane structure): 300 g of polyurethane resin was mixed with 20 g of γ-aminopropyltriethoxysilane (mass ratio 15:1), and 90 g of anhydrous dimethylformamide (0.3 times the mass of polyurethane resin) was added in an anhydrous and oxygen-free environment. The reaction temperature was controlled at 65 ° C, the stirring speed was 350 rpm, the reaction time was 4.5 h, and ultrasonic reaction was assisted (frequency 20 kHz, power 200 W). After the reaction was completed, vacuum degassing was performed (vacuum degree 0.02 MPa, temperature 70 ° C, time 1 h) to obtain a modified resin matrix A, such as Figure 1 shown.

[0028] Step (2): Preparation of nanofunctional materials: 2 g of phosphomolybdic acid, 10 g of tetrakis (4-carboxyphenyl) porphyrin, 6 g of polypyrrole, and 240 g of water (mass ratio 1:5:3:120) were mixed to obtain a mixed solution. The mixed solution was placed in a polytetrafluoroethylene-lined high-pressure reactor, with a reaction temperature of 130°C, a pressure of 2.5 MPa, a reaction time of 16 h, and intermittent stirring (stirring for 10 min every 4 h, at a speed of 200 rpm). After the reaction was completed, ultrasonic dispersion (frequency 25 kHz, power 180 W, time 12 min) and high-speed centrifugal separation (speed 11000 rpm, time 12 min) were used, and the mixture was dried in a vacuum drying oven at 55°C for 10 h to obtain nanofunctional material B, such as Figure 2 shown.

[0029] Step (3): Composite mixing treatment: Take 10g of nano-functional material B and 100g of modified resin matrix A (mass ratio 1:10), add 5g of ultraviolet absorber 2-(2'-hydroxy-5'-methylphenyl)benzotriazole (0.5 times the mass of nano-functional material) and 8g of antioxidant 2,6-di-tert-butyl-4-methylphenol (0.8 times the mass of nano-functional material). Mix for 2h under vacuum degree 0.01MPa and stirring speed 800rpm to obtain mixed system C. Add defoaming agent polydimethylsiloxane (the amount is 0.2 times the mass of mixed system C) to mixed system C, disperse at 40℃ and stirring speed 500rpm for 1h to obtain yellowing-resistant resin coating, such as Figure 3 shown.

[0030] Example 2-15

[0031] The process flow of Examples 2-15 refers to that of Example 1, and the specific parameters are shown in Tables 1 and 2 below.

[0032] Comparative Examples 1-15

[0033] Comparative Examples 1-15 are as follows: Comparative Example 1: Nanofunctional Material B was omitted, and the coating was directly prepared using modified Resin Matrix A. Comparative Example 2: The siloxane modification step was omitted, and unmodified polyurethane resin was used. Comparative Example 3: The fluoride functional group modification step was omitted, and unmodified acrylic resin was used. Comparative Example 4: Phosphomolybdic acid was omitted from Nanofunctional Material B and replaced with an equal amount of water. Comparative Example 5: Tetrakis(4-carboxyphenyl)porphyrin was omitted from Nanofunctional Material B and replaced with an equal amount of polypyrrole. Comparative Example 6: Polypyrrole was omitted from Nanofunctional Material B and replaced with an equal amount of water. Comparative Example 7: The UV absorber was replaced with benzophenone (CAS: 119-61-9). Comparative Example 8: The antioxidant was replaced with propyl gallate (CAS: 121-79-9). Comparative Example 9: The defoaming agent was replaced with mineral oil (CAS: 8042-47-5). Comparative Example 10: The ratio of γ-aminopropyltriethoxysilane in the siloxane modification exceeded the range (mass ratio 10:1). Comparative Example 11: The ratio of trifluoroethyl methacrylate in the fluoride modification exceeded the range (mass ratio 15:1). Comparative Example 12: The ratio of nanofunctional material B to modified resin matrix A exceeded the range (1:5). Comparative Example 13: The ratio of ultraviolet absorber exceeded the range (1 times the mass of the nanofunctional material). Comparative Example 14: The ratio of antioxidant exceeded the range (2.5 times the mass of the nanofunctional material). Comparative Example 15: The ratio of defoamer exceeded the range (0.4 times the mass of the mixed system).

[0034] Table 1 Process parameters of Examples 1-8

[0035]

[0036]

[0037] Note: Examples 1-6 were modified with siloxane, while Examples 7-8 were modified with fluoride. The UV absorber was 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, the antioxidant was 2,6-di-tert-butyl-4-methylphenol, and the defoaming agent was polydimethylsiloxane.

[0038] Table 2 Process parameters of Examples 9-15

[0039]

[0040]

[0041] Note: Examples 9-11 were modified with fluoride, while Examples 12-15 were modified with siloxane. The UV absorber was 2-phenylbenzimidazole-5-sulfonic acid (Examples 9-11) or 2'-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole (Examples 12-15). The antioxidant was tert-butylhydroquinone, and the defoamer was polyether-modified polysiloxane.

[0042] Table 3 Process parameters of Comparative Examples 1-8

[0043]

[0044]

[0045] Note: Comparative Example 1 lacks nanofunctional material B, and step (3) directly uses modified resin matrix A. Comparative Example 2 uses unmodified polyurethane resin. Comparative Example 3 uses unmodified acrylic resin. Comparative Examples 4-6 lack phosphomolybdic acid, tetrakis(4-carboxyphenyl)porphyrin, and polypyrrole in nanofunctional material B, respectively. Comparative Examples 7-8 replace the ultraviolet absorber and antioxidant, respectively.

[0046] Table 4 Process parameters of Comparative Examples 9-15

[0047]

[0048]

[0049] Note: Comparative Example 9 replaces the defoamer with mineral oil. Comparative Examples 10-11 each adjust the silicone and fluoride modification ratios beyond their respective ranges. Comparative Examples 12-15 each adjust the nano-functional material, UV absorber, antioxidant, and defoamer ratios beyond their respective ranges.

[0050] To verify the performance of the yellowing-resistant resin coatings prepared according to the present invention, the coating samples prepared in Examples 1-15 and Comparative Examples 1-15 were subjected to various performance tests, including yellowing index, UV aging resistance, tensile strength, elongation at break, water resistance, acid resistance, alkali resistance, and adhesion. The test methods and conditions are described below, and the test results are summarized in Tables 5-8.

[0051] Yellowing Index (ΔYI); Test Instrument: X-Rite Ci7800 Spectrophotometer. According to ASTM E313, the coating was applied to a standard glass plate and cured to form a film with a thickness of 50 ± 5 μm. The YI value (YI0) of the coating was measured in its initial state. Subsequently, the sample was placed in a Q-SUNXe-3 xenon arc aging chamber (irradiance 0.55 W / m 2, wavelength 340nm, temperature 60°C, humidity 50%), and then re-measure the YI value (YI1) after aging for 1000 hours. The yellowing index is calculated as: ΔYI = YI1 - YI0. The smaller the ΔYI value, the better the yellowing resistance.

[0052] UV aging resistance (gloss retention, %), tested using a BYK 4563 glossmeter. Test method: Measure the initial coating gloss (G0, 60°) according to ISO 2813. After aging the sample for 1000 hours in the Q-SUNXe-3 xenon arc weathering chamber, measure the post-aging gloss (G1). Gloss retention is calculated as: Gloss retention = (G1 / G0) × 100%. Higher values ​​indicate better UV aging resistance.

[0053] Tensile Strength (MPa), Testing Instrument: Instron 3367 Universal Testing Machine. Test Method: Prepare the coating into dumbbell-shaped specimens (approximately 1 mm thick) according to GB / T 1040.3-2006. Test the tensile strength of the specimens at a rate of 50 mm / min. Average the values ​​of five samples. Elongation at Break (%), Testing Instrument: Same as for the Tensile Strength Test. Test Method: Same as for the Tensile Strength Test, recording the elongation at break. Average the values ​​of five samples.

[0054] Water resistance (water absorption, %), testing instrument: Precision electronic balance. Test method: Referring to GB / T1733-1993, immerse the coating sample (50×50×1mm) in 25°C deionized water for 168 hours. Remove and dry the surface, then weigh the sample before (W0) and after (W1). Water absorption is calculated as: Water absorption = [(W1-W0) / W0] × 100%. Lower values ​​indicate better water resistance.

[0055] Acid Resistance (Appearance Change) Test Method: Refer to GB / T1763-1979. Immerse the coating sample in a 5% sulfuric acid solution (25°C) for 168 hours. Remove, clean, and dry. Observe for changes in the coating's appearance (such as blistering, peeling, and discoloration). Rating: 0 (no change) to 5 (severe damage). Alkali Resistance (Appearance Change) Test Method: Same as the acid resistance test, except replace the solution with a 5% sodium hydroxide solution. Rating criteria remain the same.

[0056] Adhesion (Grade), Test Instrument: QFD Crosshatch Tester. Test Method: Referring to GB / T9286-1998, draw 100 1×1 mm squares on the coating surface. Apply 3M tape, then quickly remove the tape and observe any peeling. Rating: 0 (smooth edge, no peeling) to 5 (severe peeling).

[0057] Table 5 Performance test results of Examples 1-15

[0058]

[0059] Table 6 Performance test results of Examples 1-15

[0060]

[0061] Table 7 Performance test results of comparative examples 1-15

[0062]

[0063] Table 8 Performance test results of comparative examples 1-15

[0064]

[0065] The results are analyzed as follows: Performance of Examples 1-15: Yellowing Index: The ΔYI values ​​of Examples 1-15 ranged from 1.1 to 1.6, indicating excellent yellowing resistance. Among them, Examples 4 and 14 had the lowest ΔYI value (1.1), likely due to optimized siloxane modification ratios or nanofunctional material ratios, which improved UV resistance. Gloss Retention: The gloss retention ranged from 90.2% to 93.4%, with Example 14 showing the highest (93.4%), indicating that its coating exhibited the best surface stability after UV aging. Tensile Strength and Elongation at Break: The tensile strength ranged from 11.6 to 12.6 MPa, and the elongation at break ranged from 1550.8% to 1595.3%, demonstrating excellent mechanical properties. Example 14 exhibited the highest tensile strength (12.6 MPa) and elongation at break (1595.3%), reflecting the synergistic enhancement effect of the modified resin and nanomaterials. Water resistance, acid resistance, alkali resistance and adhesion: The water absorption rate is 6.2%-6.7%, the acid resistance and alkali resistance are both level 0 (no change), and the adhesion is level 0 (no peeling), indicating that the coating has excellent chemical stability and substrate bonding.

[0066] Performance of Comparative Examples 1-15: Yellowing Index: The ΔYI values ​​of Comparative Examples 1-15 ranged from 3.2 to 4.6, significantly higher than those of the Examples, indicating poor yellowing resistance. Comparative Examples 7-9 had the highest ΔYI values ​​(4.4-4.6), due to the use of non-optimized UV absorbers (benzophenone), antioxidants (propyl gallate), or defoamers (mineral oil), which reduced UV resistance. Gloss Retention: The gloss retention ranged from 70.9% to 79.6%, significantly lower than that of the Examples. Comparative Example 9 had the lowest gloss retention (70.9%), possibly due to surface defects in the coating film caused by the mineral oil defoamer. Tensile Strength and Elongation at Break: The tensile strength ranged from 8.8 to 10.2 MPa, and the elongation at break ranged from 1345.3% to 1445.9%, indicating significantly inferior mechanical properties to those of the Examples. Comparative Example 9 had the lowest tensile strength (8.8 MPa), reflecting the negative impact of the non-optimized formulation. Water resistance, acid resistance, alkali resistance, and adhesion: Water absorption ranged from 7.8% to 9.2%, acid and alkali resistance were rated 2-3 (slight to noticeable change), and adhesion was rated 1-2 (slight to partial flaking), indicating poor chemical stability and adhesion. Comparative Examples 7-9 had the worst acid and alkali resistance (rated 3), due to the lack of key functional ingredients or imbalanced proportions in their formulations.

[0067] Comparative Analysis: Examples 1-15 demonstrated significant advantages over Comparative Examples 1-15 in all test items, attributed to the following factors: Nanofunctional Materials: Comparative Example 1 lacks nanofunctional materials, resulting in an increased yellowing index (3.8) and a decreased gloss retention (75.2%), demonstrating the crucial role of nanocage-structured polyoxides in enhancing UV resistance. Resin Modification: Comparative Examples 2-3, using unmodified resins, achieved high ΔYI values ​​of 4.0-4.1 and water absorption rates of 8.6%-8.7%, demonstrating that siloxane or fluoride modification significantly enhances yellowing and water resistance. Nanomaterial Components: Comparative Examples 4-6 lack phosphomolybdic acid, tetrakis(4-carboxyphenyl)porphyrin, or polypyrrole, resulting in ΔYI values ​​of 3.9-4.3 and decreased mechanical properties, demonstrating the essential synergistic effect of the nanomaterial components.

[0068] Additive Selection: Comparative Examples 7-9 used non-optimized UV absorbers, antioxidants, or defoamers, resulting in elevated ΔYI values ​​of 4.4-4.6 and deteriorating acid and alkali resistance, highlighting the importance of specific additives. Ratio Optimization: Comparative Examples 10-15 exceeded the optimized range. While slightly improved compared to Comparative Examples 1-9, they were still significantly inferior to the Examples, demonstrating the critical importance of precise ratios for performance.

[0069] The yellowing-resistant resin coatings prepared in Examples 1-15 exhibited excellent performance in terms of yellowing index, gloss retention, mechanical properties, water resistance, acid and alkali resistance, and adhesion, far exceeding those of Comparative Examples 1-15. The introduction of nanofunctional materials, siloxane or fluoride modification of the resins, and optimized additive selection and ratios are key to achieving this high performance. The coatings of this invention are suitable for coating applications requiring high weather resistance and mechanical properties, and possess significant application value.

[0070] The above content is a further detailed description of the present invention in conjunction with specific implementation methods. It cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, they can make several simple deductions or substitutions without departing from the concept of the present invention, which should be regarded as falling within the scope of protection determined by the claims submitted for the present invention.

Claims

1. A method for preparing a yellowing-resistant resin coating, characterized in that: The method comprises the following steps: (1) selecting and modifying a resin matrix: selecting a polyurethane resin or an acrylic resin as a matrix material, introducing a siloxane structure or a fluoride functional group through a chemical modification reaction, and obtaining a modified resin matrix; (2) preparing a nano-functional material: synthesizing a polyoxide material with a nano-cage structure by a hydrothermal method, and obtaining a nano-functional material; (3) compound mixing treatment: mixing the nano-functional material obtained in step (2) with the modified resin matrix obtained in step (1) at a mass ratio of 1:10 to 1:20, and adding the nano-functional material; An ultraviolet absorber with a mass of 0.5-0.8 times that of the nano-functional material and an antioxidant with a mass of 0.8-2 times that of the nano-functional material are mixed for 2-4 hours under the conditions of a vacuum degree of 0.01-0.05 MPa and a stirring speed of 800-1200 rpm to obtain a mixed system; then, a defoamer with a mass of 0.2-0.3 times that of the mixed system is added to the above mixed system, and the mixture is further dispersed for 1-2 hours under the conditions of a temperature of 40-60°C and a stirring speed of 500-800 rpm to obtain a yellowing-resistant resin coating.

2. The method for preparing the yellowing-resistant resin coating according to claim 1, wherein: The parameters of the polyurethane resin in step (1) are as follows: solid content 50±1%, specific gravity 1.06±0.02g / cm 3 , modulus is 0.6-0.8MPa, tensile strength is 10MPa, elongation is 1600%, and water absorption is 6-8%.

3. The method for preparing the yellowing-resistant resin coating according to claim 1, wherein: The chemical modification reaction in step (1) is carried out at a temperature of 60-80° C. and a stirring speed of 300-500 rpm, and the reaction time is 4-6 h.

4. The method for preparing the yellowing-resistant resin coating according to claim 3, wherein: The preparation method for introducing a siloxane structure through a chemical modification reaction in step (1) is as follows: polyurethane resin and γ-aminopropyltriethoxysilane are mixed in a mass ratio of (15-20):1, and then anhydrous dimethylformamide is added in an amount 0.3-0.4 times the mass of the polyurethane resin in an anhydrous and oxygen-free environment. The reaction temperature is controlled at 65-75°C, the stirring speed is 350-450rpm, the reaction time is 4.5-5.5h, and an ultrasonic reaction is assisted at the same time, wherein the frequency of the ultrasonic reaction is 20kHz and the power is 200W. After the reaction is completed, vacuum degassing treatment is performed, wherein the vacuum degree is 0.02MPa, the temperature is 70°C, and the time is 1h to obtain the product.

5. The method for preparing the yellowing-resistant resin coating according to claim 1, wherein: The preparation method for introducing a fluoride functional group through a chemical modification reaction in step (1) is as follows: acrylic resin and trifluoroethyl methacrylate are mixed in a mass ratio of (20-25):1, and then, under nitrogen protection, 0.3-0.5 times the mass of the acrylic resin of benzoyl peroxide and 0.35-0.45 times the mass of the acrylic resin of toluene are added, the reaction temperature is controlled at 72-78 ° C, the stirring speed is 400-500 rpm, the reaction time is 3.5-4.5 hours, and after the reaction is completed, reduced pressure distillation is performed, wherein the vacuum degree is 0.03 MPa and the temperature is 80 ° C, and then heat treatment is performed at 100 ° C for 2 hours to obtain a product.

6. The method for preparing the yellowing-resistant resin coating according to claim 1, wherein: The method for synthesizing a polyoxide material having a nanocage structure by a hydrothermal method in step (2) is as follows: phosphomolybdic acid, tetrakis (4-carboxyphenyl) porphyrin, polypyrrole, water and the like are mixed in a mass ratio of 1: (5-10): (3-8): (120-140) to obtain a mixed solution, and then the mixed solution is placed in a polytetrafluoroethylene-lined high-pressure reactor, the reaction temperature is controlled at 130-145° C., the pressure is maintained at 2.5-3.5 MPa, the reaction time is 16-20 h, and intermittent stirring is adopted during the reaction, stirring for 10 min every 4 h at a speed of 200 rpm. After the synthesis is completed, ultrasonic treatment is used for dispersion, the frequency is controlled at 25-35 kHz, the power is 180-220 W, and the ultrasonic time is 12-18 min. After the ultrasonic dispersion is completed, high-speed centrifugation is used for separation at a speed of 11000 rpm for 12 min, and then the mixture is dried in a vacuum drying oven at 55-65° C. for 10-14 h to obtain a product.

7. The method for preparing the yellowing-resistant resin coating according to claim 1, wherein: In step (3), the ultraviolet absorber is 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-phenylbenzimidazole-5-sulfonic acid or 2'-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole; and the antioxidant in step (3) is 2,6-di-tert-butyl-4-methylphenol or tert-butylhydroquinone.

8. The method for preparing the yellowing-resistant resin coating according to claim 1, wherein: The defoaming agent in step (3) is polydimethylsiloxane or polyether-modified polysiloxane.

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