Metal surface anti-oxidation anti-discoloration bright lasting gloss retention agent as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of metal protection, and provides a metal surface anti-oxidation anti-discoloration bright lasting gloss retention agent and a preparation method and application thereof.The gloss retention agent comprises waterborne polyurethane resin, a composite corrosion inhibitor, a composite passivator, a flatting agent, a pH regulator and deionized water; the composite corrosion inhibitor is a molybdenum-tungsten heteropoly acid-phytic acid chelate prepared by reacting ammonium molybdate, sodium tungstate and phytic acid; the composite passivator is prepared by sequentially carrying out silicon dioxide in-situ coating and rare earth element doping modification on nano titanium dioxide. The anti-oxidation anti-discoloration bright lasting gloss retention agent for the metal surface provided by the invention realizes multiple protection and long-acting protection on the metal surface, and has the core advantages of synergistic interaction of the composite corrosion inhibitor and the composite passivator and complementarity of the components in the aspects of film forming, corrosion inhibition, passivation, self-cleaning and the like; and a stable and lasting protection system on the metal surface is jointly constructed.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal protection, and relates to a light preservative for antioxidation and anti-discoloration with long-lasting brightness on the metal surface, its preparation method and application. Background Art

[0002] The antioxidation and anti-discoloration treatment of the metal surface is a core technical issue that has been long concerned in the industrial field. Traditional methods mostly rely on electroplating, organic coatings or inorganic passivation processes, but these technologies generally have functional defects and environmental hazards. For example, although chromate passivation can form a dense protective film, the toxicity and carcinogenicity of hexavalent chromium have gradually led to its elimination; although organic coatings can provide a certain isolation effect, the release of volatile organic compounds is not friendly to the environment, and long-term exposure is prone to coating cracking due to ultraviolet aging or mechanical wear, which in turn causes corrosion of the metal substrate. In recent years, inorganic corrosion inhibition systems represented by molybdates and tungstates have received attention due to their low toxicity and environmental compatibility. However, single-component corrosion inhibitors have limited ability to inhibit oxygen corrosion and electrochemical corrosion under complex working conditions, and are prone to dissolution and loss in humid environments, resulting in attenuation of the protection effect. At the same time, the nano-material modified passivation technology attempts to improve the denseness of the film layer by introducing particles such as titanium dioxide and silicon dioxide, but the dispersion stability of nano-particles in a highly polar aqueous system is poor, and they are prone to agglomeration to form microporous defects, which instead accelerate local corrosion.

[0003] More critically, existing technical solutions often optimize a single performance index, such as corrosion resistance or appearance brightness, in isolation, but ignore the synergistic improvement of comprehensive properties such as the interfacial bonding force between the protective coating and the metal substrate, environmental adaptability and self-healing ability. In fields with strict surface protection requirements such as high-end electronic devices and automotive parts, the existing processes are difficult to balance the contradictions between long-term antioxidation, anti-discoloration and surface finish, resulting in limited product service life and high maintenance costs. This technical bottleneck urgently requires the development of a metal surface protection system with environmental friendliness, functional durability and process compatibility to break through the limitations of existing technologies. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a light preservative for antioxidation and anti-discoloration with long-lasting brightness on the metal surface, its preparation method and application. The light preservative for antioxidation and anti-discoloration with long-lasting brightness on the metal surface provided by the present invention realizes multiple protections and long-term protection of the metal surface. Its core advantages are reflected in the synergistic effect of the composite corrosion inhibitor and the composite passivator, as well as the complementary effects of each component in aspects such as film formation, corrosion inhibition, passivation and self-cleaning, jointly constructing a stable and long-lasting protection system for the metal surface.

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

[0006] In a first aspect, the present invention provides a light-protecting agent for antioxidation and anti-discoloration with long-lasting brightness on a metal surface. The light-protecting agent includes: aqueous polyurethane resin, a composite corrosion inhibitor, a composite passivator, a leveling agent, a pH regulator, and deionized water;

[0007] The composite corrosion inhibitor is a molybdenum-tungsten heteropolyacid-phytic acid chelate prepared by reacting ammonium molybdate, sodium tungstate, and phytic acid; the composite passivator is prepared by in-situ coating of silica and doping modification with rare earth elements on nano-titanium dioxide in sequence.

[0008] The light-protecting agent for antioxidation and anti-discoloration with long-lasting brightness on a metal surface provided by the present invention realizes multiple protection and long-term protection of the metal surface. Its core advantages are reflected in the synergistic effect of the composite corrosion inhibitor and the composite passivator, as well as the complementary effects of each component in aspects such as film formation, corrosion inhibition, passivation, and self-cleaning, jointly constructing a stable and long-lasting protection system for the metal surface.

[0009] The composite corrosion inhibitor adopts a molybdenum-tungsten heteropolyacid-phytic acid chelate formed by reacting ammonium molybdate, sodium tungstate, and phytic acid. This design breaks through the limitations of traditional single corrosion inhibitors. Molybdenum-tungsten heteropolyacid has surface activity with a polyacid cluster structure, which can form multi-point coordination chelation with the metal surface through oxygen atoms, forming a dense adsorption layer on the metal surface and effectively blocking the contact of oxygen and water molecules. The introduction of phytic acid further enhances the stability of the chelation network. The multiple ortho-hydroxy groups and phosphorus atoms in its molecule cooperate to preferentially form stable complexes with metal ions, inhibiting the corrosion reaction caused by metal dissolution. This chelation structure not only improves the coverage density of the corrosion inhibitor on the metal surface but also reduces the local corrosion potential through the charge balance effect, thereby significantly delaying the oxidation reaction. Compared with single corrosion inhibitors, the molybdenum-tungsten heteropolyacid-phytic acid chelate has more stable corrosion inhibition efficiency in complex environments, especially maintaining excellent performance under high humidity or electrolyte-containing conditions.

[0010] The composite passivator is prepared by in-situ coating of silica and doping modification with rare earth elements on nano-titanium dioxide. Nano-titanium dioxide itself has photocatalytic activity, but its direct exposure easily leads to agglomeration and photocorrosion. The in-situ coating of silica not only solves the dispersion problem of nano-particles but also forms an intermediate layer with a gradient structure, alleviating the film layer peeling caused by external force impact. The doping of rare earth elements significantly improves the light absorption range and carrier separation efficiency of titanium dioxide through lattice doping and surface hydroxyl modification. The modified nano-titanium dioxide can generate reactive oxygen species under visible light excitation, continuously decompose the adsorbed organic matter and corrosion medium on the surface, and at the same time promote the chemical bonding between metal oxides and the substrate in the passivation coating, forming a denser titanium-oxygen-silicon-oxygen composite passivation film. This passivation film not only has higher hardness and wear resistance, but its porous structure can also store corrosion inhibition components through capillary action to achieve self-repair function.

[0011] The synergistic effect of the composite corrosion inhibitor and the composite passivator is reflected in spatial distribution and complementary functions. The titanium-silicon composite passivation film formed by the composite passivator acts as a physical barrier, blocking the penetration paths of most external corrosive media. The chelating components of the composite corrosion inhibitor can penetrate into the microscopic defect areas of the passivation film and form a second protective network on the metal surface through chemical adsorption. When the passivation film is mechanically worn or locally damaged, the composite corrosion inhibitor can quickly migrate to the exposed metal surface and generate a dense corrosion product layer through chelation reactions to inhibit the further expansion of corrosion. This dual protection mechanism of "physical barrier + chemical adsorption" enables the light stabilizer to exhibit excellent anti-cycle corrosion ability during long-term use.

[0012] The overall protective effect of the light stabilizer shows multi-level synergistic enhancement: The waterborne polyurethane resin serves as a film-forming matrix and forms a continuous and transparent organic protective layer through crosslinking and curing. The urethane bonds in its molecular chain segments form hydrogen bond interactions with the metal surface, enhancing the film adhesion; The inorganic passivation film formed by the composite passivator is embedded in the organic resin network, and the photocatalytic properties of titanium dioxide are used to continuously decompose surface pollutants to maintain the bright appearance of the metal; The composite corrosion inhibitor exists in the film layer gaps in the form of dynamic adsorption, inhibits the anodic process of electrochemical corrosion by chelating metal ions, and at the same time its decomposition products can participate in the self-repair of the passivation film. The light response characteristics brought about by rare earth element doping cause the passivation film to produce a surface hydrophobic effect under light conditions, further reducing the probability of water vapor attachment. This multi-component synergistic mechanism not only realizes the basic functions of antioxidant and anti-discoloration, but also endows the light stabilizer with additional properties such as self-cleaning and wear resistance, enabling the metal surface to still maintain high gloss and corrosion resistance during long-term exposure.

[0013] The light stabilizer provided by the present invention can be well matched with a variety of metal substrates (such as aluminum, magnesium, copper and their alloys), and is particularly suitable for precision surface treatment in high-end fields such as aerospace, automotive parts, and electronic appliances. Its construction process is simple, and it can be flexibly applied by spraying, brushing or dipping, etc., and has a fast drying speed, which is suitable for large-scale assembly line operations.

[0014] As a preferred technical solution of the present invention, taking the mass fraction of the light stabilizer as 100 wt%, it comprises the following components in mass fractions:

[0015]

[0016] The balance is deionized water.

[0017] The present invention specifically limits the addition amount of the composite corrosion inhibitor to 5-10 wt%. The composite corrosion inhibitor forms a chelating network structure through the synergistic effect of ammonium molybdate, sodium tungstate and phytic acid, and its addition amount directly affects the coverage density of the coating on the metal surface, the interfacial bonding strength and the corrosion inhibition function.

[0018] When the addition amount of the composite corrosion inhibitor is in the range of 5-10 wt%, the chelating network can cover the metal surface with sufficient density to form a continuous physical barrier layer, and at the same time avoid micro-defects caused by excessive accumulation. The molecular segments of the composite corrosion inhibitor and the waterborne polyurethane resin are uniformly dispersed through interactions such as hydrogen bonds and van der Waals forces, which not only maintain the flexibility of the coating but also enhance the interfacial adhesion, preventing the film from cracking due to mechanical deformation or environmental stress during service.

[0019] When the addition amount of the composite corrosion inhibitor is less than 5 wt%, the adsorption density of the chelating network on the metal surface is insufficient, making it difficult to form a continuous and dense barrier layer, resulting in an accelerated penetration rate of oxygen and corrosive media. Local oxidation reactions are likely to occur on the metal surface, manifested as a shortened antioxidant aging time and an increased risk of discoloration. At the same time, the too low content of the composite corrosion inhibitor cannot effectively inhibit the active sites of the electrochemical reaction on the metal surface, and the corrosion inhibition efficiency is significantly reduced due to incomplete adsorption coverage, making it difficult to meet the long-term protection requirements.

[0020] When the addition amount of the composite corrosion inhibitor is higher than 10 wt%, the excessive accumulation of the chelating network per unit area will lead to densification of the structure and an increase in brittleness. The too high content of the composite corrosion inhibitor will also cause micro-cracks or peeling tendencies due to concentrated internal stress during the curing process of the coating, damaging the integrity of the coating and accelerating the intrusion of corrosive media instead. At the same time, the excessive composite corrosion inhibitor will change the rheological properties of the waterborne polyurethane resin, affect the leveling property of the coating, resulting in an increase in surface roughness, a decrease in light reflection efficiency, and a decline in the brightness persistence of the metal surface. In addition, the excessive introduction of components such as phytic acid in the composite corrosion inhibitor will damage the stability of the composite passivator, interfere with the function of the passivation film formed by cerium doping modification, and lead to an imbalance in the synergistic effect between the corrosion inhibition and passivation functions.

[0021] The present invention specifically limits the addition amount of the composite passivator to 10-15 wt%. The composite passivator forms a core-shell structure by modifying nano-titanium dioxide with a silane coupling agent and enhances the surface activity through cerium doping modification. Its addition amount directly determines the densification, uniformity of the passivation film and the synergistic effect efficiency with the matrix coating.

[0022] When the addition amount of the composite passivator is in the range of 10-15 wt%, the distribution density of the composite passivator is sufficient to form a continuous and dense passivation coating, blocking the penetration of corrosive media. In addition, a moderate addition amount can also ensure that the passivation coating formed by the composite passivator and the primary adsorption layer formed by the composite corrosion inhibitor are complementary at the interface: the physical barrier of the passivation coating reduces external erosion, and the chemical adsorption of the corrosion inhibitor blocks internal electrochemical reactions. The two work together to extend the corrosion resistance period of the metal. In addition, the composite passivator within this addition amount range can maintain the film-forming fluidity and surface smoothness of the waterborne polyurethane resin, making the light reflection uniform and maintaining a long-term bright appearance. It not only avoids the problems of difficult dispersion and phase separation caused by excessive composite passivator, but also ensures the full fusion of the composite passivator and the resin matrix, improving the mechanical flexibility and adhesion of the passivation coating, and preventing the failure of protection caused by stress cracking during service.

[0023] When the addition amount of the composite passivator is less than 10 wt%, the distribution density of the composite passivator in the passivation coating is insufficient, resulting in pores and defects on the surface of the passivation coating, weakening the physical barrier ability to oxygen, water molecules and corrosive ions. In addition, too low a content of the composite passivator will lead to insufficient interfacial bonding strength between the passivation coating and the primary adsorption layer formed by the composite corrosion inhibitor, and the synergistic protection effect is weakened. The metal surface is prone to discoloration or loss of luster due to local corrosion. At the same time, too low a content of the composite passivator will also cause abnormal leveling of the waterborne polyurethane resin matrix, an increase in the surface roughness of the passivation coating, and an aggravation of light scattering.

[0024] When the addition amount of the composite passivator is higher than 15 wt%, the excessive accumulation of the composite passivator causes densification and embrittlement of the structure of the passivation coating. Excessive composite passivator generates internal stress due to volume shrinkage during the curing process, resulting in the formation of microcracks or peeling tendencies inside the passivation coating, destroying the continuity of the passivation coating, and instead providing a channel for the penetration of corrosive media. In addition, excessive passivator will interfere with the film-forming process of the waterborne polyurethane resin, change its rheological properties, cause orange peel phenomenon or a decrease in adhesion on the surface of the passivation coating, and affect the long-term weather resistance.

[0025] In the second aspect, the present invention provides a preparation method of a light-protecting agent for antioxidant, anti-discoloration and long-lasting brightness on the metal surface described in the first aspect, and the preparation method includes:

[0026] (I) Ammonium molybdate, sodium tungstate and water are mixed to obtain a mixed solution, and the pH is adjusted; phytic acid is added, mixed, stirred and heated under a nitrogen atmosphere to obtain a product solution, and a mixed solvent is added for chelation precipitation. After centrifugation, washing and drying, a composite corrosion inhibitor is obtained;

[0027] (II) The nano-titanium dioxide is modified with a silane coupling agent to obtain modified titanium dioxide, which is then dispersed in a nitric acid solution to obtain a modified titanium dioxide dispersion. Tetraethyl orthosilicate is added, and the mixture is stirred and heated to react. After centrifugation, washing, and drying, coated titanium dioxide is obtained; the coated titanium dioxide is modified by cerium doping to obtain a composite passivator;

[0028] (III) An aqueous polyurethane resin, a composite corrosion inhibitor, a leveling agent, and a wetting agent are sequentially added to a reaction kettle, mixed, stirred, and heated to obtain a prepolymer solution; the composite passivator is mixed with water to obtain a dispersion, and the dispersion is added to the prepolymer solution, mixed, stirred, and heated to obtain an intermediate solution. A pH regulator is added, and the mixture is mixed, stirred, and heated to obtain the light stabilizer.

[0029] Furthermore, the preparation method of the light stabilizer includes:

[0030] (I) Ammonium molybdate and sodium tungstate are dissolved in deionized water to obtain a mixed solution, and a nitric acid solution is added dropwise to the mixed solution to adjust the pH value; phytic acid is added to the mixed solution, and after mixing evenly, a reaction solution is obtained. The reaction solution is mixed, stirred, and heated under a nitrogen atmosphere to obtain a product solution. A mixed solvent is added to the product solution for chelation precipitation, and after centrifugal separation, washing, and vacuum drying, the composite corrosion inhibitor is obtained;

[0031] (II) The nano-titanium dioxide is modified with a silane coupling agent to obtain modified titanium dioxide, and the modified titanium dioxide is dispersed in a nitric acid solution to obtain a modified titanium dioxide dispersion; tetraethyl orthosilicate is added to the modified titanium dioxide dispersion, and the mixture is mixed, stirred, and heated to react. Subsequently, after centrifugation, washing, and drying, coated titanium dioxide powder is obtained; the coated titanium dioxide powder is modified by cerium doping to obtain the composite passivator;

[0032] (III) An aqueous polyurethane resin, a composite corrosion inhibitor, a leveling agent, and a wetting agent are sequentially added to a reaction kettle, and the mixture is mixed, stirred, and heated under a nitrogen atmosphere to obtain a prepolymer solution; the composite passivator is mixed with deionized water to obtain a dispersion, and the dispersion is added to the prepolymer solution, mixed, stirred, and heated to obtain an intermediate solution; a pH regulator is added dropwise to the intermediate solution, and the mixture is mixed, stirred, and heated to obtain the light stabilizer.

[0033] The present invention organically combines a composite corrosion inhibitor, a composite passivator, and an aqueous polyurethane resin to form a multi-layered and multi-functional protective coating, thereby showing excellent effects in aspects such as antioxidant property, anti-discoloration property, light retention property, and durability.

[0034] The composite corrosion inhibitor is prepared by using a mixed solution of ammonium molybdate and sodium tungstate, and a molybdenum-tungsten heteropolyacid system is formed by adjusting the pH value. The introduction of phytic acid not only acts as a chelating agent to promote the complexation reaction between the heteropolyacid and the metal surface, but also forms a dense primary adsorption layer on the metal surface, effectively blocking the penetration of oxygen and corrosive media. The heating and stirring process under nitrogen protection ensures the stability of the reaction system, avoids the occurrence of oxidation side reactions, and at the same time promotes the deep cross-linking of phytic acid with molybdenum and tungsten ions to form a chelate with a three-dimensional network structure. The subsequent chelation precipitation and vacuum drying steps further regulate the nano-scale dispersibility of the corrosion inhibitor, making it evenly distributed during the subsequent coating process, so as to form a continuous and dense protective coating on the metal surface. The composite corrosion inhibitor prepared by the present invention not only enhances the adhesion to the substrate through chemical bonding, but also can delay the corrosion reaction through physical barrier effects, significantly prolonging the corrosion resistance period of the metal.

[0035] The composite passivator is prepared by modifying nano-titanium dioxide with a silane coupling agent, optimizing its dispersibility in nitric acid solution. The modified titanium dioxide reacts with tetraethyl orthosilicate to form a silica coating layer, forming a core-shell structure TiO2@SiO2 composite material. This coating structure not only prevents the aggregation of nano-titanium dioxide, but also enhances its chemical stability, avoiding the decline of the protective performance caused by the migration or aggregation of nano-titanium dioxide in subsequent applications. The cerium doping modification further improves the performance of the composite passivator. The introduction of cerium ions promotes the formation of oxides on the surface of the coated titanium dioxide powder, increases the density and crystallinity of the passivation coating. At the same time, the variable valence characteristics of cerium can participate in the redox cycle, effectively inhibiting the generation of free radicals, thereby delaying photocatalytic degradation and oxidation discoloration.

[0036] The synthesis of the light stabilizer uses a waterborne polyurethane resin as the matrix, and a composite protective coating is constructed through the synergistic effect of the composite corrosion inhibitor and the composite passivator. The environmental protection characteristics and high adhesion of the waterborne polyurethane provide excellent flexibility and wear resistance for the protective coating, while the introduction of the composite corrosion inhibitor and the composite passivator endows it with multiple protective effects: the composite corrosion inhibitor blocks the penetration of corrosive media through chelation, and the composite passivator blocks the oxidation reaction by forming a dense passivation coating. The synergistic effect of the two significantly improves the corrosion resistance of the protective coating. The addition of a leveling agent and a wetting agent optimizes the microscopic morphology of the surface of the protective coating, reduces the generation of pinholes and microcracks, makes the light reflection more uniform, and thus maintains a long-term bright appearance. The step-by-step mixing process under nitrogen protection ensures the uniform dispersion of each component, avoids phase separation or film formation defects caused by excessive local concentration, and finally forms a dense, smooth and weather-resistant composite protective coating.

[0037] As a preferred technical solution of the present invention, in step (Ⅰ), the molar ratio of ammonium molybdate to sodium tungstate is 1:(0.8 - 1.2). For example, it can be 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1, 1:1.05, 1:1.1, 1:1.15 or 1:1.2. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0038] The present invention specifically defines that the molar ratio of ammonium molybdate to sodium tungstate is 1:(0.8 - 1.2). As the precursors of molybdenum-tungsten heteropolyacid, the molar ratio of ammonium molybdate to sodium tungstate directly affects the structural symmetry, charge density of the heteropolyacid anion and the chelation efficiency with phytic acid.

[0039] When the molar ratio of ammonium molybdate to sodium tungstate is within the range of 1:(0.8 - 1.2), the coordination numbers of molybdenum and tungsten are close to the stoichiometric balance, and the heteropolyacid skeleton shows a highly delocalized electron cloud distribution. It not only retains the strong coordination ability of molybdenum but also enhances the hydrolysis resistance stability of the primary adsorption layer by using the stabilizing effect of tungsten. The chelation site matching degree between the heteropolyacid clusters formed within this molar ratio range and phytic acid is the highest, and chelates with moderate molecular weight and dense structure can be generated. Such chelates form strong coordination bonds with the metal surface through oxygen atoms, and at the same time form a porous but discontinuous primary adsorption layer on the surface, providing a chemical bonding interface for the passivation coating formed by the subsequent composite passivator. The appropriate porosity of the primary adsorption layer allows the composite passivator to be embedded therein, enhancing the overall mechanical interlocking effect of the coating, while the continuous organic-inorganic hybrid interface effectively blocks the penetration of corrosive media. In addition, within this molar ratio range, it can ensure the balanced distribution of acidic sites of the heteropolyacid, making the chelation reaction of phytic acid proceed stably under nitrogen protection, avoiding the generation of by-products, and thus obtaining a composite corrosion inhibitor with high purity and high dispersibility. The appropriate molybdenum-tungsten molar ratio also optimizes the compatibility between the primary adsorption layer and the waterborne polyurethane resin, enabling the coating to form a uniform microstructure during the curing process, reducing microcracks caused by stress concentration, and maintaining a long-term bright appearance and flexibility.

[0040] If the addition amount of ammonium molybdate exceeds the upper limit of the range defined by the present invention, it will lead to an excess of the coordination number of molybdenum in the heteropolyacid, forming a highly symmetric heteropolyacid structure centered on Mo. In this structure, the doping ratio of tungsten is insufficient, which will weaken the electron delocalization effect of the heteropolyacid skeleton and reduce its chelation stability with phytic acid. Excessive ammonium molybdate will also trigger the competitive coordination of phytic acid, resulting in a non-ideal oxygen vacancy distribution in the heteropolyacid clusters, causing a decrease in the bonding density of the primary adsorption layer to the metal surface and being unable to effectively block the penetration of oxygen and corrosive media.

[0041] When the addition amount of sodium tungstate exceeds the upper limit of the range defined in the present invention, the coordination number of tungsten dominates, forming a heteropolyacid cluster with W as the core. The strong electronegativity of tungsten causes the electron cloud distribution of the heteropolyacid skeleton to deviate towards the tungsten site, reducing its coordination activity with phytic acid and decreasing the rate and efficiency of the chelation reaction. At this time, the molecular weight of the chelate formed by the heteropolyacid and phytic acid is relatively small, making it difficult to form a continuous coating on the metal surface, and the exposed metal active sites are prone to local corrosion. At the same time, the excessive amount of tungsten will also cause excessive consumption of phytic acid, resulting in insufficient concentration of free phytic acid in the reaction solution, which cannot effectively stabilize the polycondensation process of the heteropolyacid and generate by-products of oxygen-containing acid radicals with non-target structures. These by-products are prone to form loose flocculent precipitates during the subsequent chelation precipitation process, reducing the purity and dispersion uniformity of the composite corrosion inhibitor, and further affecting the adhesion strength of the coating to the metal substrate.

[0042] In some alternative examples, the mass fractions of ammonium molybdate and sodium tungstate in the mixed solution are 10 - 15 wt%, for example, it can be 10 wt%, 10.5 wt%, 11 wt%, 11.5 wt%, 12 wt%, 12.5 wt%, 13 wt%, 13.5 wt%, 14 wt%, 14.5 wt% or 15 wt%, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0043] In some alternative examples, the concentration of the nitric acid solution is 1 - 2 mol / L, for example, it can be 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L or 2.0 mol / L, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0044] In some alternative examples, a nitric acid solution is added dropwise to the mixed solution to adjust its pH value to 3.5 - 4.5, for example, it can be 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4 or 4.5, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0045] In some alternative examples, the mass ratio of ammonium molybdate and sodium tungstate in the mixed solution to the mass of phytic acid is 1:(3 - 3.5), for example, it can be 1:3.0, 1:3.05, 1:3.1, 1:3.15, 1:3.2, 1:3.25, 1:3.3, 1:3.35, 1:3.4, 1:3.45 or 1:3.5, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0046] The present invention specifically defines that the mass ratio of ammonium molybdate and sodium tungstate in the mixed solution to the mass of phytic acid is 1:(3 - 3.5). As a polydentate ligand, the dosage of phytic acid directly affects the stability of the chelation network and the compactness of the metal surface protective layer.

[0047] When the mass ratio of ammonium molybdate and sodium tungstate to the mass of phytic acid is within the range of 1:(3 - 3.5), the dosage of phytic acid can ensure that molybdenum and tungsten ions form stable chelate ring structures in a six-tooth or eight-tooth coordination mode. Such structures achieve deep bonding through the strong interaction of oxygen atoms with the metal surface, effectively blocking the diffusion paths of oxygen and water molecules. At the same time, the appropriately added phytic acid keeps the molecular chain segments of the chelate at an appropriate length, which can not only form a dense monomolecular adsorption layer but also avoid the increase in brittleness caused by excessive cross-linking. The primary adsorption layer formed within this range and the passivation coating formed by the subsequent composite passivator have a complementary effect: the primary adsorption layer blocks the corrosion electrochemical reaction through chemical bonding, and the passivation coating delays oxidation discoloration through physical barrier, and the two work together to extend the corrosion resistance period of the metal.

[0048] If the addition amount of phytic acid is lower than the lower limit of the range defined in the present invention, the chelation sites of molybdenum and tungsten ions with phytic acid cannot be fully saturated, resulting in a relatively small molecular weight and loose structure of the formed chelate. Such chelates are difficult to form a continuous and dense primary adsorption layer when adsorbed on the metal surface, and the exposed metal active sites are prone to react with oxygen or water molecules, accelerating the penetration of the corrosion medium and weakening the inhibitory ability of the composite corrosion inhibitor against oxidation discoloration and electrochemical corrosion. At the same time, insufficient phytic acid will also increase the concentration of free molybdenum and tungsten ions in the reaction solution, causing local supersaturated precipitation during the subsequent chelation precipitation process, resulting in uneven product particle sizes and affecting the dispersion uniformity of the primary adsorption layer. In addition, too low phytic acid content will also disrupt the charge balance of the reaction system, leading to fluctuations in the pH of the solution during heating and stirring under nitrogen protection, and then triggering the polycondensation side reaction of molybdenum and tungsten heteropolyacids to generate oxygen-containing acid radicals with non-target structures, weakening the chemical stability of the primary adsorption layer.

[0049] When the addition amount of phytic acid is higher than the upper limit of the range defined in the present invention, excessive phytic acid molecules will competitively occupy the coordination sites of molybdenum and tungsten ions to form supramolecular chelates with a high crosslinking density. Although such chelates can increase the coverage density of the metal surface through intensive adsorption, their over-crosslinked network structure will significantly reduce the flexibility of the primary adsorption layer, resulting in microcracks or peeling tendencies due to stress concentration during the coating curing process, and destroying the continuity of the physical barrier function. At the same time, excessive phytic acid will also remain in the primary adsorption layer, interfering with the interfacial combination of the subsequent composite passivator and the composite corrosion inhibitor, resulting in the inability to form a gradient synergistic structure between the passivation coating and the primary adsorption layer, and weakening the synergistic effect of photocatalytic inhibition and chemical passivation. In addition, excessive phytic acid will also change the pH environment of the reaction system, causing the hydrolysis degree of molybdenum-tungsten heteropolyacid to deviate from the optimal range, generating hydroxylated intermediate products, which are prone to form a loose honeycomb structure during drying and film formation, reducing the denseness and corrosion resistance of the coating.

[0050] In some alternative examples, the temperature for mixing and stirring the reaction solution is 70-80 °C, for example, it can be 70 °C, 71 °C, 72 °C, 73 °C, 74 °C, 75 °C, 76 °C, 77 °C, 78 °C, 79 °C or 80 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0051] In some alternative examples, the time for mixing and stirring the reaction solution is 2-3 h, for example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or 3.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0052] As a preferred technical solution of the present invention, in step (Ⅰ), the volume ratio of the product solution to the mixed solvent is 1:(1-1.5), for example, it can be 1:1.0, 1:1.05, 1:1.1, 1:1.15, 1:1.2, 1:1.25, 1:1.3, 1:1.35, 1:1.4, 1:1.45 or 1:1.5, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0053] In some alternative examples, the mixed solvent is composed of ethanol and acetone.

[0054] In some alternative examples, the volume ratio of ethanol to acetone in the mixed solvent is (3 to 4):1. For example, it can be 3.0:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, 3.6:1, 3.7:1, 3.8:1, 3.9:1 or 4.0:1. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0055] In some alternative examples, the rotation speed of the centrifugal separation is 6000 to 8000 rpm. For example, it can be 6000 rpm, 6200 rpm, 6400 rpm, 6600 rpm, 6800 rpm, 7000 rpm, 7200 rpm, 7400 rpm, 7600 rpm, 7800 rpm or 8000 rpm. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0056] In some alternative examples, the time of the centrifugal separation is 15 to 20 min. For example, it can be 15 min, 15.5 min, 16 min, 16.5 min, 17 min, 17.5 min, 18 min, 18.5 min, 19 min, 19.5 min or 20 min. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0057] In some alternative examples, the temperature of the vacuum drying is 60 to 80 °C. For example, it can be 60 °C, 62 °C, 64 °C, 66 °C, 68 °C, 70 °C, 72 °C, 74 °C, 76 °C, 78 °C or 80 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0058] In some alternative examples, the time of the vacuum drying is 4 to 6 h. For example, it can be 4.0 h, 4.2 h, 4.4 h, 4.6 h, 4.8 h, 5.0 h, 5.2 h, 5.4 h, 5.6 h, 5.8 h or 6.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0059] As a preferred technical solution of the present invention, in step (II), the steps of the modification treatment of the nano-titanium dioxide include:

[0060] Disperse the nano-titanium dioxide in an ethanol aqueous solution to obtain a titanium dioxide dispersion liquid. Add a silane coupling agent to the titanium dioxide dispersion liquid, mix and stir and heat, and then obtain modified titanium dioxide after centrifugation, washing and drying.

[0061] In some alternative examples, the volume ratio of absolute ethanol to deionized water in the aqueous ethanol solution is (6 - 8):1. For example, it can be 6.0:1, 6.2:1, 6.4:1, 6.6:1, 6.8:1, 7.0:1, 7.2:1, 7.4:1, 7.6:1, 7.8:1 or 8.0:1. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0062] In some alternative examples, the mass fraction of nano-titanium dioxide in the titanium dioxide dispersion is 4 - 5 wt%. For example, it can be 4.0 wt%, 4.1 wt%, 4.2 wt%, 4.3 wt%, 4.4 wt%, 4.5 wt%, 4.6 wt%, 4.7 wt%, 4.8 wt%, 4.9 wt% or 5.0 wt%. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0063] In some alternative examples, the mass ratio of nano-titanium dioxide to the silane coupling agent in the titanium dioxide dispersion is (10 - 20):1. For example, it can be 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1 or 20:1. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0064] The present invention specifically defines that the mass ratio of nano-titanium dioxide to the silane coupling agent in the titanium dioxide dispersion is (10 - 20):1. The silane coupling agent, as a modifier for nano-titanium dioxide, improves the dispersibility of nano-titanium dioxide through chemical bonding and enhances the interfacial bonding strength between it and the resin matrix and the passivation coating.

[0065] When the mass ratio of nano-titanium dioxide to the silane coupling agent is within the range of (10 - 20):1, the silane coupling agent can uniformly cover the surface of nano-titanium dioxide in the form of a monolayer or a small number of multilayers. It not only effectively reduces the van der Waals force between nano-titanium dioxide particles to prevent agglomeration but also retains sufficient active sites to react with the cerium nitrate solution, promoting the dense growth of the silica coating layer. The modified composite passivator forms stable hydrogen bonds and covalent bonds with the aqueous polyurethane resin matrix through the bridging action of the silane coupling agent, maintaining the flexibility of the coating while enhancing the interfacial adhesion and preventing particle detachment caused by stress cracking during service. In addition, an appropriate amount of the silane coupling agent optimizes the dispersion fluidity of nano-titanium dioxide, enabling tetraethyl orthosilicate to uniformly penetrate into the gaps between nano-titanium dioxide particles, thereby forming a continuous and defect-free silica coating layer on the surface of the modified titanium dioxide. The silica coating layer and cerium doping act synergistically to not only delay the penetration of corrosive media through physical barrier but also continuously consume free radicals through the variable valence characteristics of cerium oxide to inhibit the photocatalytic oxidation reaction.

[0066] When the dosage of the silane coupling agent is lower than the lower limit of the range defined in the present invention, the surface coverage rate of the silane coupling agent on the surface of nano-titanium dioxide is insufficient, resulting in agglomeration between particles due to van der Waals forces or electrostatic attraction, forming loose aggregates. Such agglomeration will not only reduce the dispersion uniformity of the composite passivator in the coating, but also cause phase separation due to excessive local concentration during the curing process, destroying the denseness of the coating. In addition, the deficiency of the silane coupling agent will weaken the interfacial adhesion between titanium dioxide and the waterborne polyurethane resin, resulting in the easy detachment of the composite passivator particles from the coating during service, exposing the unmodified surface of nano-titanium dioxide and reactivating its photocatalytic activity, accelerating the oxidation and discoloration of the metal under ultraviolet light irradiation. At the same time, the low dosage of the silane coupling agent cannot effectively block the hydroxyl active sites on the surface of nano-titanium dioxide, leading to an imbalance in its reaction activity with the cerium nitrate solution, affecting the uniformity of cerium doping modification, and further weakening the dense structure of the passivation coating.

[0067] When the dosage of the silane coupling agent is higher than the upper limit of the range defined in the present invention, excessive coupling agent molecules will form multi-layer adsorption on the surface of nano-titanium dioxide, resulting in too high surface charge density of nano-titanium dioxide, triggering excessive electrostatic repulsion, and instead inhibiting the effective dispersion between nano-titanium dioxides. Such over-modification will change the surface energy distribution of nano-titanium dioxide, reducing its dispersion stability in the solution, resulting in uneven growth of the silica layer during the coating process, with local looseness or pores appearing. In addition, the excessive silane coupling agent will remain on the surface of the composite passivator particles, interfering with the subsequent blending process with the waterborne polyurethane resin, reducing the leveling property of the coating, increasing the surface roughness, and intensifying light scattering. Secondly, the excessive silane coupling agent will introduce redundant organic functional groups, which are prone to hydrolysis or oxidation reactions in a humid and hot environment, releasing volatile small molecules, resulting in micro-cracks in the passivation coating and destroying its physical barrier function. At the same time, the excess of the silane coupling agent will also change the interfacial interaction between the composite passivator and the composite corrosion inhibitor, weakening the synergistic protection effect of the two in the coating, making the primary adsorption layer formed by the composite corrosion inhibitor and the passivation coating formed by the composite passivator unable to form a gradient complementary structure, and ultimately reducing the overall protection durability.

[0068] In some optional examples, the temperature of the mixing and stirring of the titanium dioxide dispersion liquid and the silane coupling agent is 60 - 70 °C. For example, it can be 60 °C, 61 °C, 62 °C, 63 °C, 64 °C, 65 °C, 66 °C, 67 °C, 68 °C, 69 °C or 70 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0069] In some alternative examples, the mixing and stirring time of the titanium dioxide dispersion and the silane coupling agent is 40 to 50 minutes, for example, it can be 40 minutes, 41 minutes, 42 minutes, 43 minutes, 44 minutes, 45 minutes, 46 minutes, 47 minutes, 48 minutes, 49 minutes or 50 minutes, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0070] As a preferred technical solution of the present invention, in step (Ⅱ), the concentration of the nitric acid solution is 1 to 2 mol / L, for example, it can be 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L or 2.0 mol / L, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0071] In some alternative examples, the mass fraction of the modified titanium dioxide in the modified titanium dioxide dispersion is 8 to 10 wt%, for example, it can be 8.0 wt%, 8.2 wt%, 8.4 wt%, 8.6 wt%, 8.8 wt%, 9.0 wt%, 9.2 wt%, 9.4 wt%, 9.6 wt%, 9.8 wt% or 10.0 wt%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0072] In some alternative examples, the mass ratio of the modified titanium dioxide to tetraethyl orthosilicate in the modified titanium dioxide dispersion is 1:(3 to 4), for example, it can be 1:3.0, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9 or 1:4.0, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0073] The present invention specifically defines that the mass ratio of the modified titanium dioxide to tetraethyl orthosilicate in the modified titanium dioxide dispersion is 1:(3 to 4). As a silica precursor, the amount of tetraethyl orthosilicate directly affects the compactness, thickness of the silica coating layer and the interfacial bonding strength with the modified titanium dioxide particles.

[0074] When the mass ratio of modified titanium dioxide to tetraethyl orthosilicate is within the range of 1:(3 - 4), the hydrolysis and polycondensation reaction of tetraethyl orthosilicate can proceed at a controllable rate, thereby forming a silica coating layer with a uniform thickness on the surface of modified titanium dioxide. This coating layer can not only effectively fill the gaps between titanium dioxide particles and block the penetration path of corrosive media, but also provide a stable substrate for cerium doping modification through a dense silica network, promoting the uniform growth of the cerium oxide layer. The dense and continuous silica coating layer and the cerium oxide active layer form a gradient passivation structure. The former delays the initiation of the oxidation reaction through physical shielding, and the latter continuously consumes free radicals through its variable valence characteristics, blocking the photocatalytic oxidation chain reaction. At the same time, an appropriate amount of silicon source can ensure that the molecular chains of silane coupling agents on the surface of titanium dioxide are fully extended after surface modification, forming an interfacial combination synergistically of hydrogen bonds and covalent bonds with the waterborne polyurethane resin matrix, which not only maintains the flexibility of the coating but also enhances the anchoring strength of the composite passivator, preventing peeling caused by mechanical deformation or environmental stress during service.

[0075] If the dosage of tetraethyl orthosilicate is higher than the upper limit of the range defined in the present invention, the excessive silicon source will accelerate the hydrolysis and polycondensation reaction, forming an overly thick silica coating layer, increasing the brittleness of the silica coating layer, and causing microcracks due to stress concentration during subsequent curing or service, destroying the continuity of the passivation coating and providing a channel for the penetration of corrosive media. In addition, the overly thick silica coating layer will hinder the effective contact between the cerium oxide active layer formed by cerium doping modification and the surface of titanium dioxide particles, weaken the charge transfer synergistic effect between the two, and reduce the inhibitory ability against photocatalytic oxidation reactions. At the same time, the excessive tetraethyl orthosilicate will also change the rheological properties of the modified titanium dioxide dispersion, resulting in excessive repulsion between modified titanium dioxide particles due to too high surface charge density, triggering a tendency of particle agglomeration, increasing the surface roughness of the coating layer, reducing the light reflection efficiency, and accelerating the light brightness attenuation.

[0076] If the dosage of tetraethyl orthosilicate is lower than the lower limit of the range defined in the present invention, the concentration of silica sol is too low, and the growth of the silica coating layer cannot reach the critical thickness. The silica coating layer has a large number of pores and defects due to insufficient thickness, and oxygen and water molecules can easily penetrate, weakening the physical barrier effect. Electrochemical corrosion is likely to occur on the metal surface, manifested as the spread of rust spots and the shortening of the antioxidant aging time. In addition, the overly thin silica coating layer is difficult to support the continuous crystal structure formed by the cerium oxide active layer, resulting in a decrease in the chemical stability of the passivation coating, a weakening of the free radical scavenging ability, and an increased risk of photocatalytic discoloration. In addition, at a low silicon source concentration, the silane coupling agent modification layer on the surface of titanium dioxide particles may not be fully extended and cannot effectively bridge the resin matrix, resulting in a decrease in the dispersion compatibility of the composite passivator and the composite corrosion inhibitor. Eventually, microscopic interfacial defects are likely to form inside the protective coating, and particles are likely to fall off during service, exposing the unpassivated metal surface.

[0077] In some alternative examples, the temperature for mixing and stirring the modified titanium dioxide dispersion and tetraethyl orthosilicate is 80 to 90 °C. For example, it can be 80 °C, 81 °C, 82 °C, 83 °C, 84 °C, 85 °C, 86 °C, 87 °C, 88 °C, 89 °C or 90 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0078] In some alternative examples, the time for mixing and stirring the modified titanium dioxide dispersion and tetraethyl orthosilicate is 6 to 8 h. For example, it can be 6.0 h, 6.2 h, 6.4 h, 6.6 h, 6.8 h, 7.0 h, 7.2 h, 7.4 h, 7.6 h, 7.8 h or 8.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0079] As a preferred technical solution of the present invention, in step (Ⅱ), the process of cerium-doped modification of the coated titanium dioxide powder includes:

[0080] Disperse the coated titanium dioxide powder in a nitric acid solution to obtain a coated titanium dioxide dispersion. Add a cerium nitrate solution to the coated titanium dioxide dispersion, mix, stir and heat. Subsequently, filter, wash, dry and calcine to obtain a composite passivator.

[0081] In some alternative examples, the concentration of the nitric acid solution is 1 to 2 mol / L. For example, it can be 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L or 2.0 mol / L. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0082] In some alternative examples, the mass fraction of the coated titanium dioxide powder in the coated titanium dioxide dispersion is 10 to 15 wt%. For example, it can be 10 wt%, 10.5 wt%, 11 wt%, 11.5 wt%, 12 wt%, 12.5 wt%, 13 wt%, 13.5 wt%, 14 wt%, 14.5 wt% or 15 wt%. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0083] In some optional examples, the mass fraction of the cerium nitrate solution is 1-2 wt%, for example, it can be 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt% or 2.0 wt%, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0084] In some optional examples, the mass ratio of the coated titanium dioxide powder in the coated titanium dioxide dispersion to cerium nitrate in the cerium nitrate solution is 1:(0.3-0.5), for example, it can be 1:0.3, 1:0.32, 1:0.34, 1:0.36, 1:0.38, 1:0.4, 1:0.42, 1:0.44, 1:0.46, 1:0.48 or 1:0.5, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0085] The present invention specifically limits the mass ratio of the coated titanium dioxide powder in the coated titanium dioxide dispersion to cerium nitrate in the cerium nitrate solution to 1:(0.3-0.5). The introduction of cerium forms a cerium oxide active layer on the surface of titanium dioxide through a redox reaction, and its content directly affects the compactness, chemical stability and photocatalytic inhibition ability of the passivation coating.

[0086] When the mass ratio of the coated titanium dioxide powder to cerium nitrate is within the range of 1:(0.3-0.5), an appropriate amount of cerium ions can replace some titanium ions in the titanium dioxide lattice to form a cerium oxide thin layer with oxygen vacancies on the surface. These oxygen vacancies can not only serve as active sites to adsorb water molecules and oxygen in the environment, enhance the physical barrier effect by forming a dense cerium hydroxide / cerium oxide mixed layer, but also utilize the variable valence property of cerium (Ce 3+ / Ce 4+ ) to participate in the redox cycle, continuously consume free radical intermediates, and block the photocatalytic oxidation chain reaction. At the same time, this mass ratio range can ensure the integrity of the TiO2@SiO2 core-shell structure. The silica coating layer can not only block the excessive diffusion of cerium ions to avoid phase separation caused by too high local concentration, but also improve the interfacial compatibility between the modified titanium dioxide particles and the resin matrix, so that the passivation coating formed by the composite passivator and the primary adsorption layer formed by the composite corrosion inhibitor form a synergistic protection. In addition, moderate cerium doping optimizes the surface energy distribution of the passivation coating, reduces its hydrophilicity, reduces the capillary penetration of water molecules under the film, and the uniformly distributed cerium oxide particles maintain a high reflectivity of light through the scattering effect, delaying the light decay.

[0087] When the dosage of cerium nitrate is higher than the upper limit of the range defined in the present invention, the excessive cerium nitrate will cause excessive enrichment of cerium ions on the surface of the coated titanium dioxide powder. The excessive cerium ions will destroy the uniformity of the silica coating layer, resulting in rupture or increased porosity in local areas of the silica coating layer, weakening the physical barrier effect of the passivation coating. In addition, the high concentration of cerium ions will also cause increased lattice distortion of titanium dioxide, forming a non-stoichiometric titanium oxide phase. The instability of these phase structures will accelerate the recombination of photo-generated carriers, reduce their ability to capture free radicals, and instead weaken the inhibitory effect on the photocatalytic oxidation reaction. At the same time, excessive cerium doping will also change the surface charge distribution of the passivation coating, resulting in a decrease in the interfacial bonding force between it and the waterborne polyurethane resin matrix, causing the finally obtained protective coating to be prone to microcracks due to stress concentration during service, providing a channel for the penetration of corrosive media.

[0088] When the dosage of cerium nitrate is lower than the lower limit of the range defined in the present invention, the insufficient cerium nitrate will result in too low a cerium doping concentration to form a continuous and uniform cerium oxide active layer on the surface of the coated titanium dioxide powder. At this time, the photocatalytic activity of titanium dioxide is not effectively inhibited, and it may still undergo a water photolysis reaction to generate hydroxyl radicals under ultraviolet light irradiation, accelerating the oxidation and discoloration of the metal surface. In addition, too low cerium doping cannot induce the formation of a dense crystalline oxide layer on the surface of titanium dioxide, resulting in an increase in the porosity of the passivation coating and an accelerated penetration rate of oxygen and water molecules, making the metal matrix prone to electrochemical corrosion in a humid and hot environment, manifested as the spread of rust spots and a rapid loss of gloss.

[0089] In some alternative examples, the temperature for mixing and stirring the coated titanium dioxide dispersion liquid and the cerium nitrate solution is 70 - 80 °C, for example, it can be 70 °C, 71 °C, 72 °C, 73 °C, 74 °C, 75 °C, 76 °C, 77 °C, 78 °C, 79 °C or 80 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0090] In some alternative examples, the time for mixing and stirring the coated titanium dioxide dispersion liquid and the cerium nitrate solution is 60 - 80 min, for example, it can be 60 min, 62 min, 64 min, 66 min, 68 min, 70 min, 72 min, 74 min, 76 min, 78 min or 80 min, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0091] In some alternative examples, the calcination temperature is 250 to 350 °C, for example, it can be 250 °C, 260 °C, 270 °C, 280 °C, 290 °C, 300 °C, 310 °C, 320 °C, 330 °C, 340 °C or 350 °C, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0092] In some alternative examples, the calcination time is 0.5 to 1.5 h, for example, it can be 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h or 1.5 h, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0093] As a preferred technical solution of the present invention, in step (Ⅲ), the mixing and stirring time of the aqueous polyurethane resin, the leveling agent and the composite corrosion inhibitor is 40 to 50 min, for example, it can be 40 min, 41 min, 42 min, 43 min, 44 min, 45 min, 46 min, 47 min, 48 min, 49 min or 50 min, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0094] In some alternative examples, the mixing and stirring temperature of the aqueous polyurethane resin, the leveling agent and the composite corrosion inhibitor is 60 to 70 °C, for example, it can be 60 °C, 61 °C, 62 °C, 63 °C, 64 °C, 65 °C, 66 °C, 67 °C, 68 °C, 69 °C or 70 °C, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0095] In some alternative examples, the mixing and stirring time of the dispersion liquid and the prepolymer solution is 20 to 30 min, for example, it can be 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min or 30 min, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0096] In some alternative examples, the mixing and stirring temperature of the dispersion liquid and the prepolymer solution is 40 to 50 °C, for example, it can be 40 °C, 41 °C, 42 °C, 43 °C, 44 °C, 45 °C, 46 °C, 47 °C, 48 °C, 49 °C or 50 °C, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0097] In some alternative embodiments, the mixing and stirring time of the intermediate solution and the pH regulator is 1 to 2 hours. 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. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0098] In some alternative embodiments, the mixing and stirring temperature of the intermediate solution and the pH regulator is 50 to 60 °C. For example, it can be 50 °C, 51 °C, 52 °C, 53 °C, 54 °C, 55 °C, 56 °C, 57 °C, 58 °C, 59 °C or 60 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0099] In some alternative embodiments, the pH regulator is triethanolamine.

[0100] In a third aspect, the present invention provides an application of the light protection agent for antioxidation, anti-discoloration, bright and long-lasting on the metal surface described in the first aspect, and the light protection agent is used on the metal surface.

[0101] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0102] The light protection agent for antioxidation, anti-discoloration, bright and long-lasting on the metal surface provided by the present invention realizes multiple protection and long-term protection of the metal surface. Its core advantages are reflected in the synergistic effect of the composite corrosion inhibitor and the composite passivator, as well as the complementary effects of each component in aspects such as film formation, corrosion inhibition, passivation and self-cleaning, jointly constructing a stable and long-lasting protection system for the metal surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0103] Figure 1 It is a process flow chart of the preparation of the light protection agent provided in Examples 1-19 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0104] The technical solution of the present invention will be described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments recorded herein are specific specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are all explanatory and exemplary, and should not be construed as a limitation on the embodiments of the present invention and the protection scope of the present invention. Except for the embodiments recorded herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of the present application. These technical solutions include technical solutions that make any obvious substitutions and modifications to the embodiments recorded herein.

[0105] The chemical reagents used in the embodiments of the present invention are all commercially available products, and their specifications, models, manufacturers and other information are as follows:

[0106] Waterborne polyurethane resin: JS2024120514, solid content 35 ± 1%, purchased from Wuhan Jushun Chemical Co., Ltd.;

[0107] Triethanolamine: purity 99.9%, industrial grade, purchased from Nanjing Kerunjiang Chemical Co., Ltd.;

[0108] Ammonium molybdate: purity 99%, industrial grade, purchased from Hubei Xinrunde Chemical Co., Ltd.;

[0109] Sodium tungstate: purity 99%, industrial grade, purchased from Shanghai Nuotai Chemical Co., Ltd.;

[0110] Nitric acid: industrial grade, purchased from Tianjin Damao Chemical Reagent Factory;

[0111] Phytic acid: purity 99%, industrial grade, purchased from Beijing Hailiyang Chemical Technology Co., Ltd.;

[0112] Ethanol: purity 99.9%, industrial grade, purchased from Nanjing Chemical Reagent Co., Ltd.;

[0113] Acetone: industrial grade, purchased from Lihuayi Weiyuan Chemical Co., Ltd.;

[0114] Nano-titanium dioxide: purity 99%, particle size D90 = 100 nm, purchased from Sichuan Juchun Materials Technology Co., Ltd.;

[0115] Silane coupling agent KH550: S15028, purchased from Shanghai Yuanye Bio-Technology Co., Ltd.;

[0116] Silane coupling agent KH560: S15029, purchased from Shanghai Yuanye Bio-Technology Co., Ltd.;

[0117] Silane coupling agent KH570: S15030, purchased from Shanghai Yuanye Bio-Technology Co., Ltd.;

[0118] Tetraethyl orthosilicate: S30585, purchased from Shanghai Yuanye Bio-Technology Co., Ltd.;

[0119] Cerium nitrate: MKR4, purity 99.9%, purchased from Jining Mike Rui Rare Earth Co., Ltd.;

[0120] Leveling agent: BYK333, BYK306, purchased from Shanghai Puhao Chemical Co., Ltd.;

[0121] Wetting agent: BYK163, BYK111, purchased from Shanghai Puhao Chemical Co., Ltd.

[0122] Example 1

[0123] This embodiment provides a light preservative for antioxidation and anti-discoloration with long-lasting brightness on the metal surface. Calculated based on the mass fraction of the light preservative being 100 wt%, it includes the following components in parts by weight:

[0124]

[0125] The balance is deionized water.

[0126] This embodiment also provides a preparation method of a light preservative for antioxidation and anti-discoloration with long-lasting brightness on the metal surface. As Figure 1 shown, the preparation method includes the following steps:

[0127] (1) Dissolve ammonium molybdate and sodium tungstate in deionized water. The molar ratio of ammonium molybdate to sodium tungstate is 1:0.8 to obtain a mixed solution. The mass fractions of ammonium molybdate and sodium tungstate in the mixed solution are 10 wt%. Dropwise add a nitric acid solution with a concentration of 1 mol / L to the mixed solution to adjust its pH value to 4.5;

[0128] Add phytic acid to the mixed solution. The mass ratio of ammonium molybdate and sodium tungstate in the mixed solution to the mass of phytic acid is 1:3. After mixing evenly, obtain a reaction solution. Under a nitrogen atmosphere and at a heating temperature of 70 °C, mix and stir the reaction solution for 3 h to obtain a product solution. Add a mixed solvent to the product solution. The mixed solvent consists of ethanol and acetone with a volume ratio of 3:1. The volume ratio of the product solution to the mixed solvent is 1:1. Mix and stir to cause chelation precipitation, and then centrifuge at a speed of 6000 rpm for 20 min. Wash the precipitate obtained by centrifugation with deionized water, and finally conduct vacuum drying at 60 °C for 6 h to obtain a composite corrosion inhibitor;

[0129] (2) Disperse nano-titanium dioxide in an ethanol aqueous solution (the volume ratio of absolute ethanol to deionized water in the ethanol aqueous solution is 6:1) to obtain a titanium dioxide dispersion. The mass fraction of nano-titanium dioxide in the titanium dioxide dispersion is 4 wt%. Add silane coupling agent KH550 to the titanium dioxide dispersion. The mass ratio of nano-titanium dioxide to silane coupling agent KH550 in the titanium dioxide dispersion is 10:1. Then mix and stir at 60 °C for 50 min, and then obtain modified titanium dioxide after centrifugation, washing and drying;

[0130] Disperse the modified titanium dioxide in a 1 mol / L nitric acid solution to obtain a modified titanium dioxide dispersion. The mass fraction of the modified titanium dioxide in the modified titanium dioxide dispersion is 8 wt%. Add tetraethyl orthosilicate to the modified titanium dioxide dispersion. The mass ratio of the modified titanium dioxide to tetraethyl orthosilicate is 1:3. Mix and stir at 80 °C for 8 h, and then obtain coated titanium dioxide powder after centrifugation, washing and drying;

[0131] Disperse the titanium dioxide-coated powder in a 1 mol / L nitric acid solution to obtain a titanium dioxide-coated dispersion. The mass fraction of the titanium dioxide-coated powder in the titanium dioxide-coated dispersion is 10 wt%. Add a cerium nitrate solution to the titanium dioxide-coated dispersion. The mass fraction of the cerium nitrate solution is 1 wt%. The mass ratio of the titanium dioxide-coated powder in the titanium dioxide-coated dispersion to the cerium nitrate in the cerium nitrate solution is 1:0.3. Mix and stir at 70 °C for 80 min, then filter, wash, and dry. Calcinate the dried product at 250 °C for 1.5 h to obtain a composite passivator;

[0132] (3) Sequentially add waterborne polyurethane resin, the composite corrosion inhibitor obtained in step (1), leveling agent BYK333, and wetting agent BYK163 to the reaction kettle. Under a nitrogen atmosphere, mix and stir at 60 °C for 50 min to obtain a prepolymer solution; Mix the composite passivator obtained in step (2) with deionized water to obtain a dispersion, add the dispersion to the prepolymer solution, and mix and stir at 40 °C for 30 min to obtain an intermediate solution; Dropwise add triethanolamine to the intermediate solution, and mix and stir at 50 °C for 2 h to obtain the light stabilizer.

[0133] Example 2

[0134] This example provides a light stabilizer for metal surface anti-oxidation, anti-discoloration, bright and durable. Calculated based on the mass fraction of the light stabilizer being 100 wt%, it includes the following components in parts by weight:

[0135]

[0136]

[0137] The balance is deionized water.

[0138] This example also provides a preparation method of a light stabilizer for metal surface anti-oxidation, anti-discoloration, bright and durable, as Figure 1 shown. The preparation method includes the following steps:

[0139] (1) Dissolve ammonium molybdate and sodium tungstate in deionized water. The molar ratio of ammonium molybdate to sodium tungstate is 1:0.9 to obtain a mixed solution. The mass fraction of ammonium molybdate and sodium tungstate in the mixed solution is 11 wt%; Dropwise add a 1.2 mol / L nitric acid solution to the mixed solution to adjust its pH value to 4.2;

[0140] Phytic acid was added to the mixed solution, and the mass ratio of ammonium molybdate and sodium tungstate in the mixed solution to the mass of phytic acid was 1:3.1. After mixing evenly, a reaction solution was obtained. The reaction solution was mixed and stirred under a nitrogen atmosphere at a heating temperature of 72 °C for 2.8 h to obtain a product solution. A mixed solvent was added to the product solution. The mixed solvent was composed of ethanol and acetone with a volume ratio of 3.2:1. The volume ratio of the product solution to the mixed solvent was 1:1.2. Mixing and stirring were carried out to cause chelation precipitation. Subsequently, centrifugal separation was carried out at a speed of 6500 rpm for 18 min. The precipitate obtained by centrifugal separation was washed with deionized water, and finally vacuum dried at 65 °C for 5.5 h to obtain a composite corrosion inhibitor;

[0141] (2) Nano-titanium dioxide was dispersed in an ethanol aqueous solution (the volume ratio of absolute ethanol and deionized water in the ethanol aqueous solution was 6.5:1) to obtain a titanium dioxide dispersion. The mass fraction of nano-titanium dioxide in the titanium dioxide dispersion was 4.2 wt%. Silane coupling agent KH550 was added to the titanium dioxide dispersion. The mass ratio of nano-titanium dioxide in the titanium dioxide dispersion to silane coupling agent KH550 was 12:1. Subsequently, mixing and stirring were carried out at 62 °C for 48 min. Then, after centrifugation, washing and drying, modified titanium dioxide was obtained;

[0142] The modified titanium dioxide was dispersed in a 1.2 mol / L nitric acid solution to obtain a modified titanium dioxide dispersion. The mass fraction of modified titanium dioxide in the modified titanium dioxide dispersion was 8.5 wt%. Tetraethyl orthosilicate was added to the modified titanium dioxide dispersion. The mass ratio of modified titanium dioxide to tetraethyl orthosilicate was 1:3.2. Mixing and stirring were carried out at 82 °C for 7.5 h. Then, after centrifugation, washing and drying, coated titanium dioxide powder was obtained;

[0143] The coated titanium dioxide powder was dispersed in a 1.2 mol / L nitric acid solution to obtain a coated titanium dioxide dispersion. The mass fraction of coated titanium dioxide powder in the coated titanium dioxide dispersion was 11 wt%. A cerium nitrate solution was added to the coated titanium dioxide dispersion. The mass fraction of the cerium nitrate solution was 1.2 wt%. The mass ratio of coated titanium dioxide powder in the coated titanium dioxide dispersion to cerium nitrate in the cerium nitrate solution was 1:0.35. Mixing and stirring were carried out at 72 °C for 75 min. Subsequently, filtration, washing and drying were carried out, and the dried product was calcined at 280 °C for 1.2 h to obtain a composite passivator;

[0144] (3) Add aqueous polyurethane resin, the composite corrosion inhibitor obtained in step (1), leveling agent BYK333, and wetting agent BYK163 into the reaction kettle in sequence. Under a nitrogen atmosphere, mix and stir at 62 °C for 48 min to obtain a prepolymer solution; mix the composite passivator obtained in step (2) with deionized water to obtain a dispersion, add the dispersion into the prepolymer solution, and mix and stir at 42 °C for 28 min to obtain an intermediate solution; add triethanolamine dropwise to the intermediate solution, and mix and stir at 52 °C for 1.8 h to obtain the light stabilizer.

[0145] Example 3

[0146] This example provides a light stabilizer for anti-oxidation, anti-discoloration, bright and durable on the metal surface. Calculated based on the mass fraction of the light stabilizer being 100 wt%, it includes the following components in parts by weight:

[0147]

[0148] The balance is deionized water.

[0149] This example also provides a preparation method of a light stabilizer for anti-oxidation, anti-discoloration, bright and durable on the metal surface. As Figure 1 shown, the preparation method includes the following steps:

[0150] (1) Dissolve ammonium molybdate and sodium tungstate in deionized water. The molar ratio of ammonium molybdate to sodium tungstate is 1:1 to obtain a mixed solution. The mass fractions of ammonium molybdate and sodium tungstate in the mixed solution are 12 wt%; add a nitric acid solution with a concentration of 1.5 mol / L dropwise to the mixed solution to adjust its pH value to 4;

[0151] Add phytic acid to the mixed solution. The mass ratio of ammonium molybdate and sodium tungstate in the mixed solution to the mass of phytic acid is 1:3.2. After mixing evenly, obtain a reaction solution. Under a nitrogen atmosphere and at a heating temperature of 75 °C, mix and stir the reaction solution for 2.5 h to obtain a product solution. Add a mixed solvent to the product solution. The mixed solvent consists of ethanol and acetone with a volume ratio of 3.5:1. The volume ratio of the product solution to the mixed solvent is 1:1.3. Mix and stir to cause chelation precipitation, and then centrifuge at a speed of 7000 rpm for 17 min. Wash the precipitate obtained by centrifugation with deionized water, and finally conduct vacuum drying at 70 °C for 5 h to obtain the composite corrosion inhibitor;

[0152] (2) Disperse nano-titanium dioxide in an ethanol aqueous solution (the volume ratio of absolute ethanol to deionized water in the ethanol aqueous solution is 7:1) to obtain a titanium dioxide dispersion. The mass fraction of nano-titanium dioxide in the titanium dioxide dispersion is 4.5 wt%. Add silane coupling agent KH560 to the titanium dioxide dispersion. The mass ratio of nano-titanium dioxide to silane coupling agent KH560 in the titanium dioxide dispersion is 15:1. Then mix and stir at 65 °C for 45 min, and then obtain modified titanium dioxide after centrifugation, washing and drying;

[0153] Disperse the modified titanium dioxide in a 1.5 mol / L nitric acid solution to obtain a modified titanium dioxide dispersion. The mass fraction of modified titanium dioxide in the modified titanium dioxide dispersion is 9 wt%. Add tetraethyl orthosilicate to the modified titanium dioxide dispersion. The mass ratio of modified titanium dioxide to tetraethyl orthosilicate is 1:3.5. Mix and stir at 85 °C for 7 h, and then obtain coated titanium dioxide powder after centrifugation, washing and drying;

[0154] Disperse the coated titanium dioxide powder in a 1.5 mol / L nitric acid solution to obtain a coated titanium dioxide dispersion. The mass fraction of coated titanium dioxide powder in the coated titanium dioxide dispersion is 12 wt%. Add a cerium nitrate solution to the coated titanium dioxide dispersion. The mass fraction of the cerium nitrate solution is 1.5 wt%. The mass ratio of coated titanium dioxide powder to cerium nitrate in the cerium nitrate solution in the coated titanium dioxide dispersion is 1:0.4. Mix and stir at 75 °C for 70 min, then filter, wash and dry, and calcine the dried product at 300 °C for 1 h to obtain a composite passivator;

[0155] (3) Sequentially add waterborne polyurethane resin, the composite corrosion inhibitor obtained in step (1), leveling agent BYK306 and wetting agent BYK111 to the reaction kettle. Under a nitrogen atmosphere, mix and stir at 65 °C for 45 min to obtain a prepolymer solution; Mix the composite passivator obtained in step (2) with deionized water to obtain a dispersion, add the dispersion to the prepolymer solution, and mix and stir at 45 °C for 25 min to obtain an intermediate solution; Dropwise add triethanolamine to the intermediate solution, and mix and stir at 55 °C for 1.5 h to obtain the light stabilizer.

[0156] Example 4

[0157] This example provides a light stabilizer for metal surface anti-oxidation, anti-discoloration, bright and durable. Calculated based on 100 wt% of the mass fraction of the light stabilizer, it includes the following components in parts by weight:

[0158]

[0159] The balance is deionized water.

[0160] This embodiment also provides a preparation method of a light-protecting agent for antioxidation, anti-discoloration, and long-lasting brightness on a metal surface, as Figure 1 shown. The preparation method includes the following steps:

[0161] (1) Dissolve ammonium molybdate and sodium tungstate in deionized water. The molar ratio of ammonium molybdate to sodium tungstate is 1:1.1 to obtain a mixed solution, and the mass fractions of ammonium molybdate and sodium tungstate in the mixed solution are 13 wt%. Dropwise add a nitric acid solution with a concentration of 1.8 mol / L to the mixed solution to adjust its pH value to 3.8;

[0162] Add phytic acid to the mixed solution. The mass ratio of ammonium molybdate and sodium tungstate in the mixed solution to the mass of phytic acid is 1:3.3. After mixing evenly, a reaction solution is obtained. Under a nitrogen atmosphere and at a heating temperature of 78 °C, mix and stir the reaction solution for 2.2 h to obtain a product solution. Add a mixed solvent to the product solution. The mixed solvent is composed of ethanol and acetone with a volume ratio of 3.8:1. The volume ratio of the product solution to the mixed solvent is 1:1.4. Mix and stir to cause chelation precipitation, and then centrifuge at a speed of 7500 rpm for 16 min. Wash the precipitate obtained by centrifugation with deionized water, and finally conduct vacuum drying at 75 °C for 4.5 h to obtain a composite corrosion inhibitor;

[0163] (2) Disperse nano-titanium dioxide in an ethanol aqueous solution (the volume ratio of absolute ethanol to deionized water in the ethanol aqueous solution is 7.5:1) to obtain a titanium dioxide dispersion liquid. The mass fraction of nano-titanium dioxide in the titanium dioxide dispersion liquid is 4.8 wt%. Add silane coupling agent KH560 to the titanium dioxide dispersion liquid. The mass ratio of nano-titanium dioxide in the titanium dioxide dispersion liquid to silane coupling agent KH560 is 18:1. Then mix and stir at 68 °C for 42 min, and then obtain modified titanium dioxide after centrifugation, washing, and drying;

[0164] Disperse the modified titanium dioxide in a 1.8 mol / L nitric acid solution to obtain a modified titanium dioxide dispersion liquid. The mass fraction of the modified titanium dioxide in the modified titanium dioxide dispersion liquid is 9.5 wt%. Add tetraethyl orthosilicate to the modified titanium dioxide dispersion liquid. The mass ratio of the modified titanium dioxide to tetraethyl orthosilicate is 1:3.8. Mix and stir at 88 °C for 6.5 h, and then obtain coated titanium dioxide powder after centrifugation, washing, and drying;

[0165] Disperse the titanium dioxide-coated powder in a 1.8 mol / L nitric acid solution to obtain a titanium dioxide-coated dispersion. The mass fraction of the titanium dioxide-coated powder in the titanium dioxide-coated dispersion is 13 wt%. Add a cerium nitrate solution to the titanium dioxide-coated dispersion. The mass fraction of the cerium nitrate solution is 1.8 wt%. The mass ratio of the titanium dioxide-coated powder in the titanium dioxide-coated dispersion to cerium nitrate in the cerium nitrate solution is 1:0.45. Mix and stir at 78 °C for 65 min, then filter, wash, and dry. Calcinate the dried product at 320 °C for 0.8 h to obtain a composite passivator;

[0166] (3) Sequentially add waterborne polyurethane resin, the composite corrosion inhibitor obtained in step (1), leveling agent BYK306, and wetting agent BYK111 to the reaction kettle. Under a nitrogen atmosphere, mix and stir at 68 °C for 42 min to obtain a prepolymer solution; Mix the composite passivator obtained in step (2) with deionized water to obtain a dispersion, add the dispersion to the prepolymer solution, and mix and stir at 48 °C for 22 min to obtain an intermediate solution; Dropwise add triethanolamine to the intermediate solution and mix and stir at 58 °C for 1.2 h to obtain the light stabilizer.

[0167] Example 5

[0168] This example provides a light stabilizer for metal surface anti-oxidation, anti-discoloration, bright and durable. Calculated based on the mass fraction of the light stabilizer being 100 wt%, it includes the following components in parts by weight:

[0169]

[0170]

[0171] The balance is deionized water.

[0172] This example also provides a preparation method of a light stabilizer for metal surface anti-oxidation, anti-discoloration, bright and durable, as Figure 1 shown. The preparation method includes the following steps:

[0173] (1) Dissolve ammonium molybdate and sodium tungstate in deionized water. The molar ratio of ammonium molybdate to sodium tungstate is 1:1.2 to obtain a mixed solution. The mass fraction of ammonium molybdate and sodium tungstate in the mixed solution is 15 wt%; Dropwise add a 2 mol / L nitric acid solution to the mixed solution to adjust its pH value to 3.5;

[0174] Phytic acid was added to the mixed solution, and the mass ratio of ammonium molybdate and sodium tungstate in the mixed solution to the mass of phytic acid was 1:3.5. After mixing evenly, a reaction solution was obtained. The reaction solution was mixed and stirred for 2 h under a nitrogen atmosphere and at a heating temperature of 80 °C to obtain a product solution. A mixed solvent was added to the product solution. The mixed solvent was composed of ethanol and acetone with a volume ratio of 4:1. The volume ratio of the product solution to the mixed solvent was 1:1.5. Mixing and stirring were carried out to cause chelation precipitation. Subsequently, centrifugal separation was carried out at a speed of 8000 rpm for 15 min. The precipitate obtained by centrifugal separation was washed with deionized water, and finally vacuum dried at 80 °C for 4 h to obtain a composite corrosion inhibitor;

[0175] (2) Nano-titanium dioxide was dispersed in an ethanol aqueous solution (the volume ratio of absolute ethanol and deionized water in the ethanol aqueous solution was 8:1) to obtain a titanium dioxide dispersion. The mass fraction of nano-titanium dioxide in the titanium dioxide dispersion was 5 wt%. Silane coupling agent KH570 was added to the titanium dioxide dispersion. The mass ratio of nano-titanium dioxide in the titanium dioxide dispersion to silane coupling agent KH570 was 20:1. Subsequently, mixing and stirring were carried out at 70 °C for 40 min. Then, after centrifugation, washing and drying, modified titanium dioxide was obtained;

[0176] The modified titanium dioxide was dispersed in a 2 mol / L nitric acid solution to obtain a modified titanium dioxide dispersion. The mass fraction of modified titanium dioxide in the modified titanium dioxide dispersion was 10 wt%. Tetraethyl orthosilicate was added to the modified titanium dioxide dispersion. The mass ratio of modified titanium dioxide to tetraethyl orthosilicate was 1:4. Mixing and stirring were carried out at 90 °C for 6 h. Then, after centrifugation, washing and drying, coated titanium dioxide powder was obtained;

[0177] The coated titanium dioxide powder was dispersed in a 2 mol / L nitric acid solution to obtain a coated titanium dioxide dispersion. The mass fraction of coated titanium dioxide powder in the coated titanium dioxide dispersion was 15 wt%. A cerium nitrate solution was added to the coated titanium dioxide dispersion. The mass fraction of the cerium nitrate solution was 2 wt%. The mass ratio of coated titanium dioxide powder in the coated titanium dioxide dispersion to cerium nitrate in the cerium nitrate solution was 1:0.5. Mixing and stirring were carried out at 80 °C for 60 min. Then, filtration, washing and drying were carried out, and the dried product was calcined at 350 °C for 0.5 h to obtain a composite passivator;

[0178] (3) Add aqueous polyurethane resin, the composite corrosion inhibitor obtained in step (1), leveling agent BYK306 and wetting agent BYK111 into the reaction kettle in sequence. Under a nitrogen atmosphere, mix and stir at 70 °C for 40 min to obtain a prepolymer solution; mix the composite passivator obtained in step (2) with deionized water to obtain a dispersion, add the dispersion into the prepolymer solution, and mix and stir at 50 °C for 20 min to obtain an intermediate solution; add triethanolamine dropwise to the intermediate solution, and mix and stir at 60 °C for 1 h to obtain the light stabilizer.

[0179] Example 6

[0180] This example provides a light stabilizer for anti-oxidation, anti-discoloration, bright and durable on the metal surface. The difference from Example 1 is that the addition amount of the composite corrosion inhibitor is adjusted to 3 wt%, and other operation steps and process parameters are exactly the same as those in Example 1.

[0181] Example 7

[0182] This example provides a light stabilizer for anti-oxidation, anti-discoloration, bright and durable on the metal surface. The difference from Example 1 is that the addition amount of the composite corrosion inhibitor is adjusted to 13 wt%, and other operation steps and process parameters are exactly the same as those in Example 1.

[0183] Example 8

[0184] This example provides a light stabilizer for anti-oxidation, anti-discoloration, bright and durable on the metal surface. The difference from Example 1 is that the addition amount of the composite passivator is adjusted to 8 wt%, and other operation steps and process parameters are exactly the same as those in Example 1.

[0185] Example 9

[0186] This example provides a light stabilizer for anti-oxidation, anti-discoloration, bright and durable on the metal surface. The difference from Example 1 is that the addition amount of the composite passivator is adjusted to 18 wt%, and other operation steps and process parameters are exactly the same as those in Example 1.

[0187] Example 10

[0188] This example provides a preparation method of a light stabilizer for anti-oxidation, anti-discoloration, bright and durable on the metal surface. The difference from Example 1 is that in step (1), the molar ratio of ammonium molybdate to sodium tungstate is adjusted to 1:0.5, and other operation steps and process parameters are exactly the same as those in Example 1.

[0189] Example 11

[0190] This embodiment provides a preparation method of a light-protecting agent for anti-oxidation, anti-discoloration, bright and durable on the metal surface. The difference from Embodiment 1 is that in step (1), the molar ratio of ammonium molybdate to sodium tungstate is adjusted to 1:1.5, and other operation steps and process parameters are exactly the same as those in Embodiment 1.

[0191] Embodiment 12

[0192] This embodiment provides a preparation method of a light-protecting agent for anti-oxidation, anti-discoloration, bright and durable on the metal surface. The difference from Embodiment 1 is that in step (1), the mass ratio of ammonium molybdate and sodium tungstate in the mixed solution to the mass of phytic acid is adjusted to 1:2.5, and other operation steps and process parameters are exactly the same as those in Embodiment 1.

[0193] Embodiment 13

[0194] This embodiment provides a preparation method of a light-protecting agent for anti-oxidation, anti-discoloration, bright and durable on the metal surface. The difference from Embodiment 1 is that in step (1), the mass ratio of ammonium molybdate and sodium tungstate in the mixed solution to the mass of phytic acid is adjusted to 1:4, and other operation steps and process parameters are exactly the same as those in Embodiment 1.

[0195] Embodiment 14

[0196] This embodiment provides a preparation method of a light-protecting agent for anti-oxidation, anti-discoloration, bright and durable on the metal surface. The difference from Embodiment 1 is that in step (2), the mass ratio of nano-titanium dioxide to silane coupling agent in the titanium dioxide dispersion liquid is adjusted to 8:1, and other operation steps and process parameters are exactly the same as those in Embodiment 1.

[0197] Embodiment 15

[0198] This embodiment provides a preparation method of a light-protecting agent for anti-oxidation, anti-discoloration, bright and durable on the metal surface. The difference from Embodiment 1 is that in step (2), the mass ratio of nano-titanium dioxide to silane coupling agent in the titanium dioxide dispersion liquid is adjusted to 23:1, and other operation steps and process parameters are exactly the same as those in Embodiment 1.

[0199] Embodiment 16

[0200] This embodiment provides a preparation method of a light-protecting agent for anti-oxidation, anti-discoloration, bright and durable on the metal surface. The difference from Embodiment 1 is that in step (2), the mass ratio of modified titanium dioxide to tetraethyl orthosilicate in the modified titanium dioxide dispersion liquid is adjusted to 1:2, and other operation steps and process parameters are exactly the same as those in Embodiment 1.

[0201] Embodiment 17

[0202] This embodiment provides a preparation method of a light-preserving agent for antioxidation, anti-discoloration, bright and durable metal surfaces. The difference from Example 1 is that in step (2), the mass ratio of modified titanium dioxide in the modified titanium dioxide dispersion liquid to tetraethyl orthosilicate is adjusted to 1:5, and other operation steps and process parameters are exactly the same as those in Example 1.

[0203] Example 18

[0204] This embodiment provides a preparation method of a light-preserving agent for antioxidation, anti-discoloration, bright and durable metal surfaces. The difference from Example 1 is that in step (2), the mass ratio of coated titanium dioxide powder in the coated titanium dioxide dispersion liquid to cerium nitrate in the cerium nitrate solution is adjusted to 1:0.1, and other operation steps and process parameters are exactly the same as those in Example 1.

[0205] Example 19

[0206] This embodiment provides a preparation method of a light-preserving agent for antioxidation, anti-discoloration, bright and durable metal surfaces. The difference from Example 1 is that in step (2), the mass ratio of coated titanium dioxide powder in the coated titanium dioxide dispersion liquid to cerium nitrate in the cerium nitrate solution is adjusted to 1:0.8, and other operation steps and process parameters are exactly the same as those in Example 1.

[0207] Apply the light-preserving agents provided in Examples 1 - 19 to the surface of a steel plate with a coating thickness of 30 μm. After air-drying, a protective coating is formed on the surface of the steel plate. Test the coating hardness, adhesion grade, corrosion rate, and color difference ΔE of the protective coating. The specific test steps are as follows:

[0208] (1) Coating hardness

[0209] Use pencil hardness test to evaluate the coating hardness of the protective coating (such as 2H - 6H), referring to GB / T 6739 - 202 "Paints and varnishes - Determination of film hardness by pencil test".

[0210] (2) Adhesion grade

[0211] Test the adhesion grade (0 - 5 levels) by the cross-cut method, referring to GB / T 9286 - 2021 "Paints and varnishes - Cross-cut test for films".

[0212] (3) Corrosion rate

[0213] First, prepare test specimens. Prepare 19 completely identical steel plates and cut them into sizes of 10 mm × 10 mm × 3 mm. Polish the surface to Ra ≤ 0.8 μm, clean the oil stain with acetone, rinse with deionized water, and then apply the light-preserving agents provided in Examples 1 - 19 to the surface of the cleaned steel plates respectively. After air-drying, 19 specimens are obtained.

[0214] The corrosive medium is a 3.5 wt% sodium chloride solution (simulating seawater), and the temperature is controlled at 35 ± 2 °C. Before the test, weigh 19 specimens respectively, record as m0 (accurate to 0.1 mg), vertically suspend all specimens in the corrosive medium, ensure that the specimens are completely immersed in the corrosive medium but do not contact the container wall, take out the specimens after 168 h, rinse with deionized water, gently brush with a soft brush to remove the corrosion products, dry and then weigh, record the mass as m t (accurate to 0.1 mg).

[0215] The corrosion rate of each specimen is calculated by the following formula:

[0216]

[0217] where A is the exposed area of the specimen (cm 2 ), t is the immersion time (h), and ρ is the density of the steel plate (g / cm 3 ).

[0218] (4) Color difference ΔE

[0219] Irradiate the protective coating on the steel plate surface with a xenon lamp to simulate full-spectrum sunlight (including ultraviolet, visible, and infrared rays). The irradiation intensity of the xenon lamp is set to 0.35 - 0.55 W / m 2 (simulating outdoor sunlight), the test environmental temperature is 65 ± 3 °C, and the test environmental humidity is 60% RH. The test time is 1000 h. The color difference ΔE of the protective coating before and after the xenon lamp aging test is calculated by the following formula:

[0220]

[0221] where L1 * is the brightness of the protective coating before the aging test, a1 * is the red-green chromaticity of the protective coating before the aging test, b1 * is the yellow-blue chromaticity of the protective coating before the aging test; L2 * is the brightness of the protective coating after the aging test, a2 * is the red-green chromaticity of the protective coating after the aging test, b2 * is the yellow-blue chromaticity of the protective coating after the aging test.

[0222] The test results are shown in Table 1.

[0223] Table 1 Test results of the protective coating

[0224]

[0225]

[0226] From the test data of Example 1, Example 6 and Example 7, it can be seen that the corrosion rate of Example 1 is only 0.008 g / (m 2 ·h), and the adhesion remains at level 0. In Example 6, the addition amount of the composite corrosion inhibitor is insufficient, resulting in the corrosion rate of the protective coating increasing to 0.312 g / (m 2 ·h), and the adhesion decreasing to level 4. This is because when the composite corrosion inhibitor is insufficient, a continuous protective coating cannot be formed on the surface of the metal matrix, making it easy for corrosive media such as chloride ions to invade the substrate and cause pitting corrosion. In Example 7, the addition amount of the composite corrosion inhibitor is excessive, resulting in the corrosion rate of the protective coating increasing to 0.205 g / (m 2 ·h), and the adhesion decreasing to level 3. This is because the excessive composite corrosion inhibitor will cause stress concentration inside the protective coating, resulting in microcracks in the protective coating during the curing process, but not completely destroying the bonding force between the protective coating and the matrix.

[0227] From the test data of Example 1, Example 8 and Example 9, it can be seen that the excellent performance of Example 1 benefits from the dense passivation coating formed by the composite passivator. In Example 8, the addition amount of the composite passivator is insufficient, resulting in the corrosion rate of the protective coating increasing to 0.187 g / (m 2 ·h), and the adhesion decreasing to level 4. This is because the insufficient addition amount of the composite passivator leads to too high porosity of the passivation coating, and the corrosive medium can directly contact the substrate through the pores to form a corrosion cell. In Example 9, the addition amount of the composite passivator is excessive, resulting in the corrosion rate of the protective coating increasing to 0.124 g / (m 2 ·h), and the adhesion decreasing to level 3. This is because the excessive composite passivator will increase the brittleness of the protective coating, making it easy to crack under external force and destroying the integrity of the protective coating.

[0228] From the test data of Example 1, Example 10 and Example 11, it can be seen that the addition amount of sodium tungstate in Example 1 is appropriate, and the corrosion rate remains at 0.008 g / (m 2 ·h). In Example 10, the addition amount of sodium tungstate is insufficient, resulting in the corrosion rate of the protective coating increasing to 0.057 g / (m 2 ·h), and the adhesion decreasing to level 3. This is because the symmetry of the heteropolyacid cluster is destroyed, resulting in a decrease in the corrosion inhibition efficiency. In Example 11, the addition amount of sodium tungstate is excessive, resulting in the corrosion rate of the protective coating increasing to 0.073 g / (m 2 ·h), and the adhesion decreasing to level 2. The excessive sodium tungstate causes the collapse of the heteropolyacid structure, reduces the flexibility of the passivation film, and further increases the corrosion rate.

[0229] From the test data of Example 1, Example 12 and Example 13, it can be seen that in Example 1, complete chemical bonding was achieved by adding an appropriate amount of phytic acid. In Example 12, the addition amount of phytic acid was insufficient, resulting in the corrosion rate of the protective coating increasing to 0.062 g / (m 2 ·h), and the adhesion decreasing to Grade 4. This is because the insufficient addition amount of phytic acid led to insufficient chelating sites, and the composite corrosion inhibitor could not uniformly cover the substrate. In Example 13, the addition amount of phytic acid was excessive, resulting in the corrosion rate of the protective coating increasing to 0.081 g / (m 2 ·h), and the adhesion decreasing to Grade 3. This is because excessive phytic acid would cause swelling of the resin matrix and destroy the cohesive strength of the protective coating. Although there was still a certain anti-corrosion ability, the coating life would be shortened due to the accumulation of internal stress.

[0230] From the test data of Example 1, Example 14 and Example 15, it can be seen that in Example 1, by precisely controlling the ratio of nano-titanium dioxide to silane coupling agent, the uniform dispersion and high photocatalytic activity of nano-titanium dioxide were achieved. In Example 14, the addition amount of nano-titanium dioxide was too small, and the addition amount of silane coupling agent was relatively too large, resulting in the corrosion rate of the protective coating increasing to 0.021 g / (m 2 ·h), and the adhesion decreasing to Grade 2. This is because the excessive amount of silane coupling agent underwent self-polymerization, resulting in the formation of a dense but brittle silicone network on the surface of the protective coating. In Example 15, the addition amount of nano-titanium dioxide was too large, and the addition amount of silane coupling agent was relatively too small, resulting in the corrosion rate of the protective coating increasing to 0.033 g / (m 2 ·h), and the adhesion decreasing to Grade 3. This is because the insufficient amount of silane coupling agent could not fully coat all nano-titanium dioxide, resulting in uneven dispersion of nano-titanium dioxide and interfacial defects.

[0231] From the test data of Example 1, Example 16 and Example 17, it can be seen that in Example 1, an appropriate amount of tetraethyl orthosilicate was added, enabling the formed silica coating layer to form a uniform nano-scale pore structure, which could not only block the penetration of corrosive media but also maintain the flexibility of the coating. In Example 16, the addition amount of tetraethyl orthosilicate was insufficient, resulting in the corrosion rate of the protective coating increasing to 0.019 g / (m 2 ·h), and the adhesion decreasing to Grade 4. This is because the too low addition amount of tetraethyl orthosilicate led to insufficient formation of silica, and the silica coating layer was too thin to effectively block corrosive media, causing the physical barrier function to fail. In Example 17, the addition amount of tetraethyl orthosilicate was excessive, resulting in the corrosion rate of the protective coating increasing to 0.028 g / (m 2·h), the adhesion decreased to level 2 because the excessive addition of tetraethyl orthosilicate led to excessive generation of silicon dioxide, significantly increasing the brittleness of the coating. The excessive silicon dioxide caused stress concentration, making the protective coating prone to cracking. Meanwhile, the too-thick silicon dioxide coating layer hindered the chemical bonding between the composite corrosion inhibitor and the substrate.

[0232] From the test data of Example 1, Example 18, and Example 19, it can be seen that Example 1 achieved the best photocatalytic efficiency through appropriate Ce 3+ doping. In Example 18, the Ce 3+ doping was insufficient, resulting in the corrosion rate of the protective coating increasing to 0.015 g / (m 2 ·h), and the adhesion decreasing to level 3 because the incomplete coverage of the cerium oxide active layer limited the photocatalytic function. In Example 19, the Ce 3+ doping was excessive, resulting in the corrosion rate of the protective coating increasing to 0.017 g / (m 2 ·h), and the adhesion decreasing to level 4 because the excessive cerium ions would cause lattice distortion of TiO2, leading to stress concentration and accelerating the coating aging. Although the increase in the corrosion rate was limited, the adhesion decreased significantly, and the integrity of the protective coating was damaged.

[0233] The applicant declares that the above description is only the specific implementation mode 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 the disclosure scope of the present invention.

Claims

1. A light preservative for antioxidation and anti-discoloration with long-lasting brightness on the metal surface, characterized in that The light stabilizer includes: aqueous polyurethane resin, composite corrosion inhibitor, composite passivator, leveling agent, pH regulator and deionized water; The composite corrosion inhibitor is a molybdenum-tungsten heteropolyacid-phytic acid chelate prepared by reacting ammonium molybdate, sodium tungstate and phytic acid; the composite passivator is prepared by in-situ coating of silica and doping modification with rare earth elements on nano-titanium dioxide in sequence.

2. The light retention agent according to claim 1, characterized in that, Based on the mass fraction of the light stabilizer being 100 wt%, it includes the following components with the following mass fractions:

3. A preparation method of a light-preserving agent for antioxidation, anti-discoloration, and long-lasting brightness of a metal surface according to claim 1, characterized in that, The preparation method includes: (Ⅰ) Dissolve ammonium molybdate and sodium tungstate in deionized water to obtain a mixed solution, add a nitric acid solution to the mixed solution to adjust the pH value; add phytic acid to the mixed solution, mix evenly to obtain a reaction solution, mix and stir the reaction solution under a nitrogen atmosphere and heat to obtain a product solution, add a mixed solvent to the product solution, carry out chelation precipitation, and obtain the composite corrosion inhibitor after centrifugal separation, washing and vacuum drying; (Ⅱ) Modify nano-titanium dioxide with a silane coupling agent to obtain modified titanium dioxide, disperse the modified titanium dioxide in a nitric acid solution to obtain a modified titanium dioxide dispersion; add tetraethyl orthosilicate to the modified titanium dioxide dispersion, mix and stir and heat to react, and then obtain coated titanium dioxide powder after centrifugation, washing and drying; carry out cerium doping modification on the coated titanium dioxide powder to obtain the composite passivator; (Ⅲ) Add aqueous polyurethane resin, composite corrosion inhibitor, leveling agent and wetting agent to the reaction kettle in sequence, mix and stir and heat under a nitrogen atmosphere to obtain a prepolymer solution; mix the composite passivator with deionized water to obtain a dispersion, add the dispersion to the prepolymer solution, mix and stir and heat to obtain an intermediate solution; add a pH regulator dropwise to the intermediate solution, mix and stir and heat to obtain the light stabilizer.

4. The preparation method according to claim 3, characterized in that, In step (Ⅰ), the molar ratio of ammonium molybdate to sodium tungstate is 1:(0.8 - 1.2); The mass fraction of ammonium molybdate and sodium tungstate in the mixed solution is 10 - 15 wt%; The concentration of the nitric acid solution is 1 - 2 mol / L; Add a nitric acid solution to the mixed solution to adjust its pH value to 3.5 - 4.5; The mass ratio of ammonium molybdate and sodium tungstate in the mixed solution to the mass of phytic acid is 1:(3 - 3.5); The temperature of the mixed stirring of the reaction solution is 70 - 80 °C; The time of the mixed stirring of the reaction solution is 2 - 3 h.

5. The preparation method according to claim 3, characterized in that, In step (Ⅰ), the volume ratio of the product solution to the mixed solvent is 1:(1 - 1.5); The mixed solvent is composed of ethanol and acetone; The volume ratio of ethanol to acetone in the mixed solvent is (3 - 4):1; The rotation speed of the centrifugal separation is 6000 - 8000 rpm; The time of the centrifugal separation is 15 - 20 min; The temperature of the vacuum drying is 60 - 80 °C; The time of the vacuum drying is 4 - 6 h.

6. The preparation method according to claim 3, characterized in that, In step (Ⅱ), the steps of the modification treatment of the nano-titanium dioxide include: Disperse nano-titanium dioxide in an ethanol aqueous solution to obtain a titanium dioxide dispersion liquid. Add a silane coupling agent to the titanium dioxide dispersion liquid, mix and stir, and heat. Then, after centrifugation, washing, and drying, modified titanium dioxide is obtained. The volume ratio of absolute ethanol to deionized water in the ethanol aqueous solution is (6 - 8):

1. The mass fraction of nano-titanium dioxide in the titanium dioxide dispersion liquid is 4 - 5 wt%. The mass ratio of nano-titanium dioxide to the silane coupling agent in the titanium dioxide dispersion liquid is (10 - 20):

1. The temperature for mixing and stirring the titanium dioxide dispersion liquid and the silane coupling agent is 60 - 70 °C. The time for mixing and stirring the titanium dioxide dispersion liquid and the silane coupling agent is 40 - 50 min.

7. The preparation method according to claim 3, characterized in that In step (Ⅱ), the concentration of the nitric acid solution is 1 - 2 mol / L. The mass fraction of the modified titanium dioxide in the modified titanium dioxide dispersion liquid is 8 - 10 wt%. The mass ratio of the modified titanium dioxide to tetraethyl orthosilicate in the modified titanium dioxide dispersion liquid is 1:(3 - 4). The temperature for mixing and stirring the modified titanium dioxide dispersion liquid and tetraethyl orthosilicate is 80 - 90 °C. The time for mixing and stirring the modified titanium dioxide dispersion liquid and tetraethyl orthosilicate is 6 - 8 h.

8. The preparation method according to claim 3, characterized in that, In step (Ⅱ), the process of cerium doping modification of the coated titanium dioxide powder includes: Disperse the coated titanium dioxide powder in a nitric acid solution to obtain a coated titanium dioxide dispersion liquid. Add a cerium nitrate solution to the coated titanium dioxide dispersion liquid, mix and stir, and heat. Then, after filtration, washing, drying, and calcination, a composite passivator is obtained. The concentration of the nitric acid solution is 1 - 2 mol / L. The mass fraction of the coated titanium dioxide powder in the coated titanium dioxide dispersion liquid is 10 - 15 wt%. The mass fraction of the cerium nitrate solution is 1 - 2 wt%. The mass ratio of the coated titanium dioxide powder in the coated titanium dioxide dispersion liquid to cerium nitrate in the cerium nitrate solution is 1:(0.3 - 0.5). The temperature for mixing and stirring the coated titanium dioxide dispersion liquid and the cerium nitrate solution is 70 - 80 °C. The time for mixing and stirring the coated titanium dioxide dispersion liquid and the cerium nitrate solution is 60 - 80 min. The temperature of the calcination is 250 - 350 °C. The time of the calcination is 0.5 - 1.5 h.

9. The preparation method according to claim 3, characterized in that, In step (Ⅲ), the time for mixing and stirring the waterborne polyurethane resin, the leveling agent, and the composite corrosion inhibitor is 40 - 50 min. The temperature for mixing and stirring the waterborne polyurethane resin, the leveling agent, and the composite corrosion inhibitor is 60 - 70 °C. The time for mixing and stirring the dispersion liquid and the prepolymer solution is 20 - 30 min. The temperature for mixing and stirring the dispersion liquid and the prepolymer solution is 40 - 50 °C. The time for mixing and stirring the intermediate solution and the pH regulator is 1 - 2 h. The temperature for mixing and stirring the intermediate solution and the pH regulator is 50 - 60 °C. The pH regulator is triethanolamine.

10. Use of a light protection agent for anti-oxidation, anti-discoloration, bright and long-lasting protection of a metal surface according to claim 1, characterized in that, The light stabilizer is used on the metal surface.

Images