Oxidation discoloration resistant electro-optical silver coating and preparation method thereof

Abstract

The invention relates to the field of electro-optical silver coatings, in particular to an electro-optical silver coating resistant to oxidative discoloration and a preparation method thereof, and aims at solving the problems that traditional metal silver powder is prone to oxidation, so that gloss is reduced, and the anti-oxidation effect of a conventional antioxidant is low. Firstly, an electro-optic silver coloring layer is composed of composite coating silver powder, an oxidation inhibitor, acrylic resin, pearl powder, a polycarboxylate dispersing agent and xylene, and then the oxidation and discoloration resistant electro-optic silver coating is composed of a bottom layer, the electro-optic silver coloring layer and a protective layer. The oxidation and discoloration resistant electro-optical silver coating not only keeps the high-end appearance of electro-optical silver cold light flow from oxidation and discoloration for a long time, but also has practical protection performance such as excellent wear resistance, scratch resistance and high adhesive force, is further suitable for industrial production, and perfectly meets the double high requirements of scenes such as high-end automobile color change and industrial scratch-resistant film pasting on appearance texture and durability.

Description

Technical Field

[0001] This invention relates to the field of electro-optic silver coatings, specifically to an electro-optic silver coating resistant to oxidation and discoloration and its preparation method. Background Technology

[0002] Electro-silver, a metallic silver tone that combines a sense of technology and sophistication, boasts a unique appearance. It's not pure white, but rather enhanced with special processes like electro-optical treatment to create a flowing, cool-light visual effect. It closely resembles the understated luxury and refinement emphasized by classic GT silver, and its high-gloss silver-gray quality has earned it the title of "timeless classic color." In terms of color matching, electro-silver is closest to the metallic versions of RAL 9006 (aluminum white) or RAL 9010 (pure white) in the RAL color chart. RAL 9006 (aluminum white) belongs to the RAL E3 / E4 series of metallic colors, and its "silver-gray + high gloss" characteristics perfectly match electro-silver. The RAL 9010 (pure white) metallic version achieves high gloss and a lighter tone through a coating process, with only a slightly higher brightness than electro-silver, resulting in minimal visual difference.

[0003] In application fields, electroplated silver has become the preferred color for high-end scenarios. In the automotive industry, it is used for color changes on high-end models, and when paired with design elements such as black and red color blocking and aluminum alloy rear swingarms, it can significantly enhance the vehicle's technological and premium feel. In the industrial sector, it is often used as a color for scratch-resistant body wraps, meeting surface protection needs with its wear-resistant and stain-resistant properties. However, existing electroplated silver coatings are susceptible to oxidation and discoloration due to environmental factors such as air, moisture, and ultraviolet radiation during long-term use. This manifests as loss of metallic luster and a dulling of the color, which not only destroys the original cool, flowing visual effect of electroplated silver but also reduces the coating's protective performance on the substrate, shortens the product's lifespan, and fails to meet users' needs for electroplated silver coatings to maintain their appearance and durability over a long period.

[0004] The core problem of oxidation and discoloration in existing coatings lies in two aspects: firstly, traditional metallic silver powder is prone to oxidation upon contact with air and moisture, generating substances such as silver oxide, leading to a decrease in gloss; secondly, conventional antioxidants lack sufficient dispersibility and long-lasting effect in coatings, making it difficult to continuously inhibit the oxidation chain reaction. Therefore, developing an oxidation-resistant, discoloration-resistant electro-optic silver coating that can fundamentally solve the problem of silver powder oxidation and has highly efficient antioxidant action has become a key direction urgently needing breakthroughs in the field of coating materials. Summary of the Invention

[0005] In order to overcome the above-mentioned technical problems, the purpose of this invention is to provide an electro-optic silver coating resistant to oxidation and discoloration and its preparation method.

[0006] The objective of this invention can be achieved through the following technical solutions: In a first aspect, this application provides an electro-silver coating resistant to oxidation and discoloration, comprising an underlayer, an electro-silver coloring layer, and a protective layer; The bottom layer comprises the following components in parts by weight: The composition includes 18-22 parts epoxy resin, 9-11 parts polyurethane modified resin, 12-14 parts ethyl acetate, 3-4 parts silane coupling agent, and 1.5-2.5 parts organosilicon defoamer. The electro-optic silver coloring layer comprises the following components in parts by weight: The composition includes 24-26 parts acrylic resin, 7-9 parts composite coated silver powder, 3-4 parts pearlescent powder, 1.5-2.5 parts polycarboxylate dispersant, 4-5 parts oxidation inhibitor, and 14-16 parts xylene. The protective layer comprises the following components in parts by weight: 28-32 parts of fluorocarbon resin, 5-7 parts of nano-silica, 3-4 parts of benzotriazole UV absorber, 1.2-1.8 parts of polysiloxane leveling agent, and 12-14 parts of methyl ethyl ketone (MEK); The oxidation inhibitor is prepared by the following steps: Step a1: Add methanol and butanediamine to a three-necked flask equipped with a stirrer, thermometer, and constant pressure dropping funnel. Stir the reaction at 25-30℃ and 250-300 r / min for 10-15 min. Then, add methyl acrylate dropwise while stirring at 400-500 r / min, controlling the dropping rate to 1-2 drops / s. After the addition is complete, continue stirring for 24-26 h. After the reaction is complete, transfer the mixture to a rotary evaporator and distill under reduced pressure at 45-50℃ and 130-133 Pa for 2 h. Then dry with anhydrous sodium sulfate for 12-14 h to obtain the intermediate product. Step a2: Add methanol and intermediate product to a three-necked flask equipped with a stirrer, thermometer and constant pressure dropping funnel. Stir the reaction for 20-25 min at a temperature of 25-30℃ and a stirring rate of 250-300 r / min. Then, add ethylenediamine dropwise while stirring at a stirring rate of 400-500 r / min, controlling the dropping rate to 1-2 drops / s. After the addition is complete, continue stirring the reaction for 24-26 h. After the reaction is complete, transfer the mixture to a rotary evaporator and distill under reduced pressure for 3 h at a water bath temperature of 70-72℃ and a vacuum degree of 130-133 Pa. Then dry with anhydrous sodium sulfate for 12-14 h to obtain dendritic macromolecules. Step a3: Add the dendritic macromolecule and anhydrous dichloromethane to a three-necked flask equipped with a stirrer, thermometer, gas delivery tube, and constant-pressure dropping funnel. Purge with nitrogen for protection. Stir the reaction at 25-30℃ and a stirring rate of 350-400 rpm for 15-20 min. Add anhydrous potassium carbonate and stir for 10-12 min. Then, while stirring at 450-500 rpm, add the 3,5-di-tert-butylhydroxyphenylpropionyl chloride / anhydrous dichloromethane solution dropwise, controlling the dropping rate at 1-2 drops / s. After the addition is complete, raise the temperature to 30-35℃ and continue stirring for 24-26 h. After the reaction is complete, transfer to a container... The mixture was transferred to a Buchner funnel and filtered. The filter cake was washed 3-4 times with anhydrous dichloromethane. The filtrates were combined and washed with deionized water until the pH of the aqueous phase was 7. The aqueous phase was discarded, and the organic phase was dried with anhydrous magnesium sulfate for 12-13 hours. The desiccant was removed by filtration, and the organic phase was transferred to a rotary evaporator and distilled under reduced pressure at 35-40℃ and 130-133 Pa. The resulting product was then purified by silica gel chromatography with 200-300 mesh silica gel as the stationary phase and ethyl acetate / petroleum ether solution as the mobile phase. The main fraction was collected and the solvent was removed by distillation under reduced pressure again. The product was then placed in a vacuum drying oven and dried at 55-60℃ for 8-9 hours to obtain the oxidation inhibitor.

[0007] In a preferred embodiment of the present invention, the ratio of methanol, butanediamine and methyl acrylate used in step a1 is 40-44.5g: 17.6-19.6g: 137.6-153.2g.

[0008] In a preferred embodiment of the present invention, the ratio of methanol, intermediate product and ethylenediamine used in step a2 is 60-75g: 8-10g: 9.6-12g.

[0009] In a preferred embodiment of the present invention, the ratio of the dendritic macromolecule, anhydrous dichloromethane, anhydrous potassium carbonate, and 3,5-di-tert-butylhydroxyphenylpropionyl chloride / anhydrous dichloromethane solution in step a3 is 4-6g:80-120mL:11-16g:37-55mL.

[0010] In a preferred embodiment of the present invention, the 3,5-di-tert-butylhydroxyphenylpropionyl chloride / anhydrous dichloromethane solution in step a3 is a solution prepared by mixing 3,5-di-tert-butylhydroxyphenylpropionyl chloride and anhydrous dichloromethane in a ratio of 17.13 g: 20 mL.

[0011] In a preferred embodiment of the present invention, the ethyl acetate / petroleum ether solution in step a3 is a solution composed of ethyl acetate and petroleum ether mixed in a volume ratio of 1:4.

[0012] The composite coated silver powder is prepared by the following steps: Step b1: Place the silver powder and anhydrous ethanol 1 in an ultrasonic cleaner and ultrasonically disperse them for 30-35 minutes at a power of 280-300W. Then centrifuge the product and transfer the precipitate to a three-necked flask equipped with a stirrer, thermometer, and constant-pressure dropping funnel. Add anhydrous ethanol 2 and stir the mixture for 10-15 minutes at a temperature of 25-30℃ and a stirring rate of 200-300 r / min. Then, while stirring, add tetraethyl orthosilicate dropwise at a rate of 1-2 drops / s. After the addition is complete... After the reaction is complete, continue stirring for 15-20 minutes. Then, while stirring, add the ammonia-ethanol mixture dropwise at a rate of 1-2 drops / s. Stop adding the mixture when the pH of the system reaches 8.5-9.0. Then, raise the temperature to 35-40℃ and continue stirring for 4-5 hours. After the reaction is complete, centrifuge the product and wash the precipitate 3-4 times with anhydrous ethanol. Then, place it in a vacuum drying oven and dry it at 55-60℃ for 8-9 hours to obtain silicon oxide coated silver powder. Step b2: Add the dendritic macromolecules to anhydrous ethanol and stir magnetically for 30-35 minutes at a stirring rate of 300-400 r / min to obtain a dendritic macromolecule-ethanol solution. Step b3: Add silica-coated silver powder and anhydrous ethanol to a three-necked flask equipped with a stirrer, thermometer, and constant-pressure dropping funnel. Stir the reaction at 25-30℃ and a stirring rate of 350-400 r / min for 15-20 min. Then, ultrasonically disperse the mixture at a power of 270-300 W for 20-25 min. While stirring, add the dendritic macromolecule-ethanol solution dropwise at a rate of 1-2 drops / s. After the addition is complete, raise the temperature to 45-50℃ and continue stirring for 3-4 h. After the reaction is complete, centrifuge the reaction product and wash the precipitate 2-3 times with anhydrous ethanol. Then, place the precipitate in a vacuum drying oven and dry it at 45-50℃ for 6-7 h to obtain composite coated silver powder.

[0013] In a preferred embodiment of the present invention, the ratio of the amount of silver powder, anhydrous ethanol 1, anhydrous ethanol 2 and tetraethyl orthosilicate in step b1 is 10-14g: 100-140mL: 150-210mL: 5-7mL.

[0014] In a preferred embodiment of the present invention, the particle size of the metallic silver powder in step b1 is 5-20 μm.

[0015] In a preferred embodiment of the present invention, the ammonia-ethanol mixture in step b1 is a solution of ammonia and anhydrous ethanol mixed in a volume ratio of 3.0 mL: 20 mL; the mass fraction of the ammonia is 25%.

[0016] In a preferred embodiment of the present invention, the ratio of the dendritic macromolecule to anhydrous ethanol in step b2 is 1-3g: 50-150mL.

[0017] In a preferred embodiment of the present invention, the ratio of the amount of silicon dioxide-coated silver powder, anhydrous ethanol, and dendritic macromolecule-ethanol solution used in step b3 is 10-12g: 150-180mL: 50-60mL.

[0018] Secondly, this application provides a method for preparing an electro-optic silver coating resistant to oxidation and discoloration, comprising the following steps: Step 1: Add epoxy resin, polyurethane modified resin, ethyl acetate, silane coupling agent and organosilicon defoamer to a mixing tank and stir for 40-50 minutes at a speed of 900-1100 r / min to obtain the base coat. Then, apply the base coat to the pretreated substrate surface by air spraying, with the spray thickness controlled at 35-45 μm. After that, bake in an oven at a temperature of 85-95℃ for 35-40 minutes to form the base coat. Step 2: Add acrylic resin, composite coated silver powder, pearlescent powder, polycarboxylate dispersant, oxidation inhibitor, and xylene to a mixing tank and stir for 50-70 minutes at a speed of 1200-1400 r / min. Then grind the mixture to a particle size of <5μm using a three-roll mill to obtain an electro-optic silver coloring layer coating. Apply the coating to the bottom surface using an airless spraying method to a thickness of 25-35μm. Then bake it in an oven at a temperature of 130-140℃ for 22-28 minutes to form an electro-optic silver coloring layer. Step 3: Add fluorocarbon resin, nano silica, benzotriazole UV absorber, polysiloxane leveling agent, and methyl ethyl ketone to a mixing tank and stir for 40-50 minutes at a speed of 1000-1200 r / min to obtain a protective coating. Apply the protective coating to the surface of the electro-silver coloring layer by air spraying to a thickness of 30-40 μm. Then bake in an oven at 140-150℃ for 45-55 minutes to form an electro-silver coating resistant to oxidation and discoloration.

[0019] In a preferred embodiment of the present invention, the epoxy resin in step one is of type E-51; the polyurethane modified resin is EPU-133L from Complex High-Tech Materials (Shanghai) Co., Ltd.; the silane coupling agent is KH-570; and the silicone defoamer is BYK-052.

[0020] In a preferred embodiment of the present invention, the acrylic resin in step two is 7860A from Zhishang Chemical (Shanghai) Co., Ltd.; the pearlescent powder has a particle size of 20-50μm; and the polycarboxylate dispersant is polycarboxylate dispersant 5040 from Jingzhou Yinjie Chemical Co., Ltd.

[0021] In a preferred embodiment of the present invention, the fluorocarbon resin in step three is of type GK 570; the nano-silica has a particle size of 12-14 nm; the benzotriazole UV absorber has a CAS number of 70321-86-7; and the polysiloxane leveling agent is BYK-333.

[0022] The beneficial effects of this invention are: This invention discloses an oxidation-resistant electro-optic silver coating and its preparation method. First, an electro-optic silver coloring layer is composed of composite-coated silver powder, an oxidation inhibitor, acrylic resin, pearlescent powder, polycarboxylate dispersant, and xylene. Then, an oxidation-resistant electro-optic silver coating is formed by a base layer, the electro-optic silver coloring layer, and a protective layer. The oxidation inhibitor, through dendritic macromolecules bridging four hindered phenolic units, can efficiently capture oxidative free radicals in the coating, actively terminating the oxidation chain reaction of the silver powder. Simultaneously, it exhibits good compatibility with the resin and is not easily migrated, extending the coating's antioxidant lifespan. The silica layer of the composite-coated silver powder physically isolates the silver powder from air and moisture, while the dendritic macromolecule layer enhances its dispersibility with the resin. This dual passive protection prevents the silver powder from oxidizing and turning black. The oxidation-resistant electro-optic silver coating not only maintains the high-end appearance of electro-optic silver's cool, flowing light without oxidation or discoloration, but also possesses excellent wear resistance, scratch resistance, and high adhesion, making it suitable for industrial production and perfectly meeting the dual high requirements of appearance and durability for high-end automotive color changes and industrial anti-scratch films.

[0023] In the preparation of the oxidation-resistant electro-optic silver coating, an oxidation inhibitor was first prepared. Butylenediamine (containing two primary amine groups) acts as a nucleophile, attacking the electron-deficient double-bonded carbon of methyl acrylate (containing a carbon-carbon double bond). Addition is completed through double bond opening and new bond formation. One molecule of butylenediamine can react with four molecules of methyl acrylate, ultimately generating an intermediate with an ester group at the end. This intermediate then undergoes nucleophilic substitution with the primary amine group of ethylenediamine. The -OCH3 group of the ester group leaves the ester group, forming a stable amide bond. One molecule of the intermediate (containing four ester groups) can react with four molecules of ethylenediamine. The unreacted ethylenediamine remains at the molecule's end, ultimately generating a dendritic macromolecule with an amine group at the end. The terminal amine group of this dendritic macromolecule then attacks the electron-deficient carbonyl carbon of 3,5-di-tert-butylhydroxyphenylpropionyl chloride. The -Cl group leaves the dendritic macromolecule, forming an amide bond, thus removing the blocked ester group. Phenolic units (containing -OH antioxidant groups) are bridged to the dendritic framework. One dendritic macromolecule (containing 4 amino groups) can react with 4 acyl chloride molecules to ultimately generate an oxidation inhibitor containing 4 hindered phenolic units. Anhydrous potassium carbonate acts as an acid-binding agent to absorb the hydrogen chloride generated in the reaction. After modification, each dendritic macromolecule can bridge 4 hindered phenolic units. Compared with traditional small-molecule hindered phenols, the symmetrical branched structure of the dendritic macromolecule allows the 4 antioxidant units to be evenly dispersed in space, which can capture more oxidative free radicals at the same time, improving the antioxidant efficiency by 2-3 times. It can more quickly terminate the oxidation chain reaction of metallic silver powder in the electro-optic silver coating. The highly branched structure of the dendritic macromolecule forms a three-dimensional barrier in the coating. On the one hand, it can physically block oxygen and moisture from contacting the silver powder. On the other hand, it can coat the surface of the silver powder and reduce the catalytic effect of impurity metal ions on the oxidation reaction, thus doubly improving the coating's resistance to oxidation and discoloration.

[0024] In the preparation of the oxidation-resistant electro-optic silver coating, a composite coated silver powder was first prepared. Initially, under the action of ammonia, the siloxane bonds of tetraethyl orthosilicate broke, reacting with water molecules to generate silanol. Due to adsorption, hydroxyl groups were present on the silver powder surface. The -OH groups of the silanol underwent dehydration condensation with the -OH groups on the silver powder surface, forming Si-O-Si covalent bonds. Simultaneously, silanol molecules also aggregated, gradually growing into a continuous and dense silicon oxide film on the silver powder surface, ultimately forming silicon oxide coated silver powder. Subsequently, a large number of silanol groups were present on the surface of the silicon oxide coated silver powder. The end groups -NH2 and -Si-OH of the dendritic macromolecules bonded through two interactions: hydrogen bonding (the N atom of -NH2 forms a strong hydrogen bond with the H atom of -Si-OH) and electrostatic interaction (the -Si-OH on the silicon oxide surface is negatively charged due to ionization, and the -NH2 of the dendritic macromolecules is protonated (-NH3). +The silver powder is positively charged and then combines with the silicon oxide layer through electrostatic attraction, ultimately forming an organic dendritic macromolecular film on the outside of the silicon oxide coating layer, resulting in composite coated silver powder. The silicon oxide forms a dense inorganic film on the surface of the silver powder, directly blocking the contact between air, moisture, sulfides and the silver powder, reducing oxidation reactions at the source. The branched structure of the dendritic macromolecules can form a three-dimensional barrier on the outside of the silicon oxide layer, further blocking the penetration of oxidizing media. At the same time, its end group -NH2 can combine with oxidation inhibitors in the coating, anchoring the antioxidant units around the silver powder, efficiently capturing oxidizing free radicals, and doubly enhancing the oxidation resistance. The composite coated silver powder also has optimized compatibility, which can solve the dispersion problem, ensure the coating texture, and the two coating steps do not change the lamellar structure and metallic properties of the silver powder. The composite coated silver powder can still present a cool light flow effect close to RAL 9006 / RAL 9010, meeting the appearance requirements of high-end car color change and industrial film application. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. Example 1:

[0026] This embodiment describes a method for preparing an electro-optic silver coating resistant to oxidation and discoloration, comprising the following steps: Step s1: Add 40g methanol and 17.6g butanediamine to a three-necked flask equipped with a stirrer, thermometer and constant pressure dropping funnel. Stir the reaction at 25℃ and 250r / min for 10min. Then, add 137.6g methyl acrylate dropwise while stirring at 400r / min, controlling the dropping rate to 1 drop / s. After the addition is complete, continue stirring for 24h. After the reaction is complete, transfer to a rotary evaporator and distill under reduced pressure at 45℃ and 130Pa for 2h. Then dry with anhydrous sodium sulfate for 12h to obtain the intermediate product. Step s2: 60g methanol and 8g intermediate were added to a three-necked flask equipped with a stirrer, thermometer and constant pressure dropping funnel. The mixture was stirred for 20min at 25℃ and 250r / min. Then, 9.6g ethylenediamine was added dropwise while stirring at 400r / min, with the dropping rate controlled at 1 drop / s. After the addition was completed, the mixture was stirred for 24h. After the reaction was completed, the mixture was transferred to a rotary evaporator and distilled under reduced pressure for 3h at 70℃ and 130Pa. The product was then dried with anhydrous sodium sulfate for 12h to obtain dendritic macromolecules. Step s3: Add 4g of dendritic macromolecules and 80mL of anhydrous dichloromethane to a three-necked flask equipped with a stirrer, thermometer, gas delivery tube, and constant pressure dropping funnel. Purge with nitrogen for protection and stir for 15min at 25℃ and a stirring rate of 350r / min. Add 11g of anhydrous potassium carbonate and stir for 10min. Then, while stirring at 450r / min, add 37mL of anhydrous potassium carbonate dropwise. 3,5-Di-tert-butylhydroxyphenylpropionyl chloride / anhydrous dichloromethane solution (the 3,5-di-tert-butylhydroxyphenylpropionyl chloride / anhydrous dichloromethane solution is a solution prepared by mixing 3,5-di-tert-butylhydroxyphenylpropionyl chloride and anhydrous dichloromethane at a ratio of 17.13 g: 20 mL), with a dropping rate controlled at 1 drop / s. After the addition is complete, the temperature is raised to 30 °C, and the reaction is continued with stirring for 24 h. After the reaction is completed, the mixture is transferred to a Buchner funnel for vacuum filtration. The filter cake is washed three times with anhydrous dichloromethane, and the filtrates are combined. The filtrate is washed with deionized water until the pH of the aqueous phase is 7, and then the aqueous phase is discarded. The organic phase was dried with anhydrous magnesium sulfate for 12 h, the desiccant was removed by filtration, and the organic phase was transferred to a rotary evaporator and distilled under reduced pressure at 35 °C and 130 Pa. After purification by silica gel chromatography, the stationary phase was 200 mesh silica gel, and the mobile phase was ethyl acetate / petroleum ether solution (ethyl acetate / petroleum ether solution is a solution of ethyl acetate and petroleum ether mixed in a volume ratio of 1:4). The main fraction was collected, and the solvent was removed by reduced pressure distillation again. Then it was placed in a vacuum drying oven and dried at 55 °C for 8 h to obtain the oxidation inhibitor. Step s4: Place 10g of metallic silver powder (particle size 5μm) and 100mL of anhydrous ethanol 1 in an ultrasonic cleaner and ultrasonically disperse for 30min at 280W. Centrifuge the product and transfer the precipitate to a three-necked flask equipped with a stirrer, thermometer, and constant-pressure dropping funnel. Add 150mL of anhydrous ethanol 2 and stir for 10min at 25℃ and 200r / min. Then, while stirring, add 5mL of tetraethyl orthosilicate dropwise at a rate of 1 drop / s. After the addition is complete, continue stirring for 15 minutes. After a min, an ammonia-ethanol mixture (ammonia-ethanol mixture is a solution of ammonia and anhydrous ethanol mixed in a volume ratio of 3.0 mL: 20 mL; the mass fraction of ammonia is 25%) was added dropwise while stirring. The dropping rate was controlled at 1 drop / s. The dropping was stopped when the pH of the system was adjusted to 8.5. Then, the temperature was raised to 35℃ and the stirring was continued for 4 h at a speed of 450 r / min. After the reaction was completed, the reaction product was centrifuged, the precipitate was washed 3 times with anhydrous ethanol, and then placed in a vacuum drying oven and dried at a temperature of 55℃ for 8 h to obtain silicon oxide coated silver powder. Step s5: Add 1g of dendritic macromolecule to 50mL of anhydrous ethanol and stir magnetically for 30min at a stirring rate of 300r / min to obtain a dendritic macromolecule-ethanol solution. Step s6: Add 10g of silica-coated silver powder and 150mL of anhydrous ethanol to a three-necked flask equipped with a stirrer, thermometer and constant pressure dropping funnel. Stir the reaction at 25℃ and 350r / min for 15min. Then, ultrasonically disperse the mixture at 270W for 20min. Then, add 50mL of dendritic macromolecule-ethanol solution dropwise while stirring, controlling the dropping rate to 1 drop / s. After the addition is complete, raise the temperature to 45℃ and continue stirring for 3h. After the reaction is complete, centrifuge the reaction product, wash the precipitate twice with anhydrous ethanol, and then place it in a vacuum drying oven and dry it at 45℃ for 6h to obtain composite coated silver powder. Step s7: Add 18 parts epoxy resin (epoxy resin type E-51), 9 parts polyurethane modified resin (polyurethane modified resin is EPU-133L from Complex High-Tech Materials Shanghai Co., Ltd.), 12 parts ethyl acetate, 3 parts silane coupling agent (silane coupling agent is KH-570) and 1.5 parts organosilicon defoamer (organosilicon defoamer is BYK-052) to a mixing tank and stir for 40 minutes at a speed of 900 r / min to obtain the base coat. Then, apply the base coat to the pretreated substrate surface by air spraying, with the spray thickness controlled at 35 μm. Then, bake in an oven at 85℃ for 35 minutes to form the base coat. Step s8: Add 24 parts of acrylic resin (7860A from Zhishang Chemical (Shanghai) Co., Ltd.), 7 parts of composite coated silver powder, 3 parts of pearl powder (pearl powder with a particle size of 20μm), 1.5 parts of polycarboxylate dispersant (polycarboxylate dispersant 5040 from Jingzhou Yinjie Chemical Co., Ltd.), 4 parts of oxidation inhibitor and 14 parts of xylene to a stirring tank and stir for 50 minutes at a speed of 1200 r / min. Then grind the mixture to a particle size of <5μm using a three-roll mill to obtain an electro-optic silver coloring layer coating. Apply the coating to the bottom surface using an airless spraying method with a spray thickness of 25μm. Then bake it in an oven at 130℃ for 22 minutes to form an electro-optic silver coloring layer. Step s9: Add 28 parts of fluorocarbon resin (model GK 570), 5 parts of nano silica (particle size of nano silica is 12nm), 3 parts of benzotriazole UV absorber (CAS number of benzotriazole UV absorber is 70321-86-7), 1.2 parts of polysiloxane leveling agent (polysiloxane leveling agent is BYK-333) and 12 parts of methyl ethyl ketone to a mixing tank and stir for 40 minutes at a speed of 1000 r / min to obtain a protective coating. Apply the protective coating to the surface of the electro-silver coloring layer by air spraying to a thickness of 30μm. Then bake in an oven at 140℃ for 45 minutes to form an electro-silver coating resistant to oxidation and discoloration. Example 2:

[0027] This embodiment describes a method for preparing an electro-optic silver coating resistant to oxidation and discoloration, comprising the following steps: Step s1: Add 42g methanol and 18.6g butanediamine to a three-necked flask equipped with a stirrer, thermometer and constant pressure dropping funnel. Stir the reaction at 27℃ and 270r / min for 12min. Then, add 145.4g methyl acrylate dropwise while stirring at 450r / min, controlling the dropping rate to 1 drop / s. After the addition is complete, continue stirring for 25h. After the reaction is complete, transfer to a rotary evaporator and distill under reduced pressure at 47℃ and 131Pa for 2h. Then dry with anhydrous sodium sulfate for 13h to obtain the intermediate product. Step s2: 67g methanol and 9g intermediate were added to a three-necked flask equipped with a stirrer, thermometer and constant pressure dropping funnel. The mixture was stirred at 27℃ and 270r / min for 23min. Then, 10.8g ethylenediamine was added dropwise while stirring at 450r / min, with the dropping rate controlled at 1 drop / s. After the addition was completed, the mixture was stirred and reacted for 25h. After the reaction was completed, the mixture was transferred to a rotary evaporator and distilled under reduced pressure at 71℃ and 131Pa for 3h. The product was then dried with anhydrous sodium sulfate for 13h to obtain dendritic macromolecules. Step s3: Add 5g of dendritic macromolecules and 100mL of anhydrous dichloromethane to a three-necked flask equipped with a stirrer, thermometer, gas delivery tube, and constant-pressure dropping funnel. Purge with nitrogen for protection and stir for 17min at 27℃ and a stirring rate of 370r / min. Add 13.5g of anhydrous potassium carbonate and stir for 11min. Then, while stirring at 470r / min, add 46mL of anhydrous potassium carbonate dropwise. 3,5-Di-tert-butylhydroxyphenylpropionyl chloride / anhydrous dichloromethane solution (the 3,5-di-tert-butylhydroxyphenylpropionyl chloride / anhydrous dichloromethane solution is a solution prepared by mixing 3,5-di-tert-butylhydroxyphenylpropionyl chloride and anhydrous dichloromethane at a ratio of 17.13 g: 20 mL), with a dropping rate controlled at 1 drop / s. After the addition is complete, the temperature is raised to 33°C, and the reaction is continued with stirring for 25 h. After the reaction is complete, the mixture is transferred to a Buchner funnel for filtration. The filter cake is washed three times with anhydrous dichloromethane. The filtrates are combined, and the filtrates are washed with deionized water until the pH of the aqueous phase is 7. The aqueous phase is discarded, and the organic phase is retained. The organic phase was dried with anhydrous magnesium sulfate for 12.5 h, filtered to remove the desiccant, and transferred to a rotary evaporator. It was then distilled under reduced pressure at 37 °C and 131 Pa, followed by purification by silica gel chromatography. The stationary phase was 200-mesh silica gel, and the mobile phase was an ethyl acetate / petroleum ether solution (a solution of ethyl acetate and petroleum ether mixed in a volume ratio of 1:4). The main fraction was collected, and the solvent was removed by another reduced pressure distillation. The resulting product was then placed in a vacuum drying oven and dried at 570 °C for 8.5 h to obtain the oxidation inhibitor. Step s4: Place 12g of metallic silver powder (particle size 10μm) and 120mL of anhydrous ethanol 1 in an ultrasonic cleaner and ultrasonically disperse for 33min at 290W. Centrifuge the product and transfer the precipitate to a three-necked flask equipped with a stirrer, thermometer, and constant-pressure dropping funnel. Add 180mL of anhydrous ethanol 2 and stir for 12min at 27℃ and 250r / min. Then, while stirring, add 6mL of tetraethyl orthosilicate dropwise at a rate of 1 drop / s. After the addition is complete, continue stirring for 17min. Then, while stirring, a mixture of ammonia and ethanol (the ammonia-ethanol mixture is a solution of ammonia and anhydrous ethanol mixed in a volume ratio of 3.0 mL: 20 mL; the mass fraction of ammonia is 25%) was added dropwise, controlling the dropping rate to 1 drop / s. The dropping was stopped when the pH of the system was adjusted to 8.7. Then, the temperature was raised to 37°C and the stirring was continued for 4.5 h. After the reaction was completed, the reaction product was centrifuged, the precipitate was washed three times with anhydrous ethanol, and then placed in a vacuum drying oven and dried at 57°C for 8.5 h to obtain silicon oxide coated silver powder. Step s5: Add 2g of dendritic macromolecules to 100mL of anhydrous ethanol and stir magnetically for 33min at a stirring rate of 350r / min to obtain a dendritic macromolecule-ethanol solution. Step s6: Add 11g of silica-coated silver powder and 165mL of anhydrous ethanol to a three-necked flask equipped with a stirrer, thermometer, and constant pressure dropping funnel. Stir the mixture at 27℃ and a stirring rate of 370r / min for 17min. Then, ultrasonically disperse the mixture at 290W for 23min. While stirring, add 55mL of dendritic macromolecule-ethanol solution dropwise at a rate of 1 drop / s. After the addition is complete, raise the temperature to 47℃ and continue stirring for 3.5h. After the reaction is complete, centrifuge the reaction product, wash the precipitate twice with anhydrous ethanol, and then place it in a vacuum drying oven at 47℃ for 6.5h to obtain composite coated silver powder. Step s7: Add 20 parts epoxy resin (epoxy resin type E-51), 10 parts polyurethane modified resin (polyurethane modified resin is EPU-133L from Complex High-Tech Materials Shanghai Co., Ltd.), 13 parts ethyl acetate, 3.5 parts silane coupling agent (silane coupling agent is KH-570) and 2 parts organosilicon defoamer (organosilicon defoamer is BYK-052) to a mixing tank and stir for 45 minutes at a speed of 1000 r / min to obtain the base coat. Then, apply the base coat to the pretreated substrate surface by air spraying, with the spray thickness controlled at 40 μm. Then, bake in an oven at 90℃ for 37 minutes to form the base coat. Step s8: Add 25 parts of acrylic resin (7860A from Zhishang Chemical (Shanghai) Co., Ltd.), 8 parts of composite coated silver powder, 3.5 parts of pearl powder (pearl powder with a particle size of 35μm), 2 parts of polycarboxylate dispersant (polycarboxylate dispersant 5040 from Jingzhou Yinjie Chemical Co., Ltd.), 4.5 parts of oxidation inhibitor and 15 parts of xylene to a mixing tank and stir for 60 minutes at a speed of 1300 r / min. Then grind the mixture to a particle size of <5μm using a three-roll mill to obtain an electro-optic silver coloring layer coating. Apply the coating to the bottom surface using an airless spraying method with a spray thickness of 30μm. Then bake it in an oven at 135℃ for 25 minutes to form an electro-optic silver coloring layer. Step s9: Add 30 parts of fluorocarbon resin (model GK 570), 6 parts of nano silica (particle size of nano silica is 13nm), 3.5 parts of benzotriazole UV absorber (CAS number of benzotriazole UV absorber is 70321-86-7), 1.5 parts of polysiloxane leveling agent (polysiloxane leveling agent is BYK-333) and 13 parts of methyl ethyl ketone to a mixing tank and stir for 45 minutes at a speed of 1100 r / min to obtain a protective coating. Apply the protective coating to the surface of the electro-silver coloring layer by air spraying to a thickness of 35μm. Then bake in an oven at 145℃ for 50 minutes to form an electro-silver coating resistant to oxidation and discoloration. Example 3:

[0028] This embodiment describes a method for preparing an electro-optic silver coating resistant to oxidation and discoloration, comprising the following steps: Step s1: 44.5g methanol and 19.6g butanediamine were added to a three-necked flask equipped with a stirrer, thermometer and constant pressure dropping funnel. The mixture was stirred at 30℃ and 300r / min for 15min. Then, 153.2g methyl acrylate was added dropwise while stirring at 500r / min, with a dropping rate of 2 drops / s. After the addition was complete, the mixture was stirred for 26h. After the reaction was completed, the mixture was transferred to a rotary evaporator and distilled under reduced pressure at 50℃ and 133Pa for 2h. The product was then dried with anhydrous sodium sulfate for 14h to obtain the intermediate product. Step s2: 75g methanol and 10g intermediate were added to a three-necked flask equipped with a stirrer, thermometer and constant pressure dropping funnel. The mixture was stirred at 30℃ and 300r / min for 25min. Then, 12g ethylenediamine was added dropwise while stirring at 500r / min, with the dropping rate controlled at 2 drops / s. After the addition was completed, the mixture was stirred and reacted for 26h. After the reaction was completed, the mixture was transferred to a rotary evaporator and distilled under reduced pressure at 72℃ and 133Pa for 3h. The product was then dried with anhydrous sodium sulfate for 14h to obtain dendritic macromolecules. Step s3: Add 6g of dendritic macromolecules and 120mL of anhydrous dichloromethane to a three-necked flask equipped with a stirrer, thermometer, gas delivery tube, and constant pressure dropping funnel. Purge with nitrogen for protection and stir for 20min at 30℃ and a stirring rate of 400r / min. Add 16g of anhydrous potassium carbonate and stir for 12min. Then, while stirring at 500r / min, add 55mL of anhydrous potassium carbonate dropwise. 3,5-Di-tert-butylhydroxyphenylpropionyl chloride / anhydrous dichloromethane solution (the 3,5-di-tert-butylhydroxyphenylpropionyl chloride / anhydrous dichloromethane solution is a solution prepared by mixing 3,5-di-tert-butylhydroxyphenylpropionyl chloride and anhydrous dichloromethane at a ratio of 17.13 g: 20 mL), with a dropping rate controlled at 2 drops / s. After the addition is complete, the temperature is raised to 35°C, and the reaction is continued with stirring for 26 h. After the reaction is completed, the mixture is transferred to a Buchner funnel for vacuum filtration. The filter cake is washed four times with anhydrous dichloromethane, and the filtrates are combined. The filtrate is washed with deionized water until the pH of the aqueous phase is 7, and then the aqueous phase is discarded. The organic phase was dried with anhydrous magnesium sulfate for 13 h, the desiccant was removed by filtration, and the organic phase was transferred to a rotary evaporator and distilled under reduced pressure at 40 °C and 133 Pa. After purification by silica gel chromatography, the stationary phase was 300 mesh silica gel, and the mobile phase was ethyl acetate / petroleum ether solution (ethyl acetate / petroleum ether solution is a solution of ethyl acetate and petroleum ether mixed in a volume ratio of 1:4). The main fraction was collected, and the solvent was removed by reduced pressure distillation again. Then it was placed in a vacuum drying oven and dried at 60 °C for 9 h to obtain the oxidation inhibitor. Step s4: Place 14g of metallic silver powder (particle size 20μm) and 140mL of anhydrous ethanol 1 in an ultrasonic cleaner and ultrasonically disperse for 35min at 300W. Centrifuge the product and transfer the precipitate to a three-necked flask equipped with a stirrer, thermometer, and constant-pressure dropping funnel. Add 210mL of anhydrous ethanol 2 and stir for 15min at 30℃ and 300r / min. Then, while stirring, add 7mL of tetraethyl orthosilicate dropwise at a rate of 2 drops / s. After the addition is complete, continue stirring. After 0 min, an ammonia-ethanol mixture (ammonia-ethanol mixture is a solution of ammonia and anhydrous ethanol mixed in a volume ratio of 3.0 mL: 20 mL; the mass fraction of ammonia is 25%) was added dropwise while stirring. The dropping rate was controlled at 2 drops / s. The dropping was stopped when the pH of the system was adjusted to 9.0. Then the temperature was raised to 40℃ and the stirring was continued for 5 h at a speed of 500 r / min. After the reaction was completed, the reaction product was centrifuged, the precipitate was washed 4 times with anhydrous ethanol, and then placed in a vacuum drying oven and dried at 60℃ for 9 h to obtain silicon oxide coated silver powder. Step s5: Add 3g of dendritic macromolecules to 150mL of anhydrous ethanol and stir magnetically for 35min at a stirring rate of 400r / min to obtain a dendritic macromolecule-ethanol solution. Step s6: Add 12g of silica-coated silver powder and 180mL of anhydrous ethanol to a three-necked flask equipped with a stirrer, thermometer and constant pressure dropping funnel. Stir the reaction at 30℃ and 400r / min for 20min. Then, ultrasonically disperse the mixture at 300W for 25min. Then, add 60mL of dendritic macromolecule-ethanol solution dropwise while stirring, controlling the dropping rate to 2 drops / s. After the addition is complete, raise the temperature to 50℃ and continue stirring for 4h. After the reaction is complete, centrifuge the reaction product, wash the precipitate three times with anhydrous ethanol, and then place it in a vacuum drying oven and dry it at 50℃ for 7h to obtain composite coated silver powder. Step s7: Add 22 parts epoxy resin (epoxy resin type E-51), 11 parts polyurethane modified resin (polyurethane modified resin is EPU-133L from Complex High-Tech Materials Shanghai Co., Ltd.), 14 parts ethyl acetate, 4 parts silane coupling agent (silane coupling agent is KH-570) and 2.5 parts organosilicon defoamer (organosilicon defoamer is BYK-052) to a mixing tank and stir for 50 minutes at a speed of 1100 r / min to obtain the base coat. Then, apply the base coat to the pretreated substrate surface by air spraying, with the spray thickness controlled at 45 μm. Then, bake in an oven at 95℃ for 40 minutes to form the base coat. Step s8: Add 26 parts of acrylic resin (7860A from Zhishang Chemical (Shanghai) Co., Ltd.), 9 parts of composite coated silver powder, 4 parts of pearl powder (particle size of pearl powder is 20-50μm), 2.5 parts of polycarboxylate dispersant (polycarboxylate dispersant 5040 from Jingzhou Yinjie Chemical Co., Ltd.), 5 parts of oxidation inhibitor and 16 parts of xylene to a mixing tank and stir for 70 minutes at a speed of 1400 r / min. Then grind the mixture to a particle size of <5μm using a three-roll mill to obtain an electro-optic silver coloring layer coating. Apply the coating to the bottom surface using an airless spraying method with a spray thickness of 35μm. Then bake it in an oven at 140℃ for 28 minutes to form an electro-optic silver coloring layer. Step s9: Add 32 parts of fluorocarbon resin (model GK 570), 7 parts of nano silica (particle size of nano silica is 14nm), 4 parts of benzotriazole UV absorber (CAS number of benzotriazole UV absorber is 70321-86-7), 1.8 parts of polysiloxane leveling agent (polysiloxane leveling agent is BYK-333) and 14 parts of methyl ethyl ketone to a mixing tank and stir for 50 minutes at a speed of 1200 r / min to obtain a protective coating. Apply the protective coating to the surface of the electro-optic silver coloring layer by air spraying to a thickness of 40μm. Then bake in an oven at 150℃ for 55 minutes to form an electro-optic silver coating resistant to oxidation and discoloration.

[0029] Comparative Example 1: This comparative example illustrates a method for preparing an electro-optic silver coating resistant to oxidation and discoloration, comprising the following steps: Step s1: Place 10g of metallic silver powder (particle size 5μm) and 100mL of anhydrous ethanol 1 in an ultrasonic cleaner and ultrasonically disperse for 30min at 280W. Centrifuge the product and transfer the precipitate to a three-necked flask equipped with a stirrer, thermometer, and constant-pressure dropping funnel. Add 150mL of anhydrous ethanol 2 and stir for 10min at 25℃ and 200r / min. Then, while stirring, add 5mL of tetraethyl orthosilicate dropwise at a rate of 1 drop / s. After the addition is complete, continue stirring for 15 minutes. After a min, an ammonia-ethanol mixture (ammonia-ethanol mixture is a solution of ammonia and anhydrous ethanol mixed in a volume ratio of 3.0 mL: 20 mL; the mass fraction of ammonia is 25%) was added dropwise while stirring. The dropping rate was controlled at 1 drop / s. The dropping was stopped when the pH of the system was adjusted to 8.5. Then, the temperature was raised to 35℃ and the stirring was continued for 4 h at a speed of 450 r / min. After the reaction was completed, the reaction product was centrifuged, the precipitate was washed 3 times with anhydrous ethanol, and then placed in a vacuum drying oven and dried at a temperature of 55℃ for 8 h to obtain silicon oxide coated silver powder. Step s2: Add 1g of dendritic macromolecule to 50mL of anhydrous ethanol and stir magnetically for 30min at a stirring rate of 300r / min to obtain a dendritic macromolecule-ethanol solution. Step s3: Add 10g of silica-coated silver powder and 150mL of anhydrous ethanol to a three-necked flask equipped with a stirrer, thermometer and constant pressure dropping funnel. Stir the reaction at 25℃ and 350r / min for 15min. Then, ultrasonically disperse the mixture at 270W for 20min. Then, add 50mL of dendritic macromolecule-ethanol solution dropwise while stirring, controlling the dropping rate to 1 drop / s. After the addition is complete, raise the temperature to 45℃ and continue stirring for 3h. After the reaction is complete, centrifuge the reaction product, wash the precipitate twice with anhydrous ethanol, and then place it in a vacuum drying oven and dry it at 45℃ for 6h to obtain composite coated silver powder. Step s4: Add 18 parts epoxy resin (epoxy resin type E-51), 9 parts polyurethane modified resin (polyurethane modified resin is EPU-133L from Complex High-Tech Materials Shanghai Co., Ltd.), 12 parts ethyl acetate, 3 parts silane coupling agent (silane coupling agent is KH-570) and 1.5 parts organosilicon defoamer (organosilicon defoamer is BYK-052) to a mixing tank and stir for 40 minutes at a speed of 900 r / min to obtain the base coat. Then, apply the base coat to the pretreated substrate surface by air spraying, with the spray thickness controlled at 35 μm. Then, bake in an oven at 85℃ for 35 minutes to form the base coat. Step s5: Add 24 parts of acrylic resin (7860A from Zhishang Chemical (Shanghai) Co., Ltd.), 7 parts of composite coated silver powder, 3 parts of pearl powder (pearl powder with a particle size of 20μm), 1.5 parts of polycarboxylate dispersant (polycarboxylate dispersant 5040 from Jingzhou Yinjie Chemical Co., Ltd.) and 14 parts of xylene to a mixing tank and stir for 50 minutes at a speed of 1200 r / min. Then grind the mixture to a particle size of <5μm using a three-roll mill to obtain an electro-optic silver coloring layer coating. Apply the coating to the bottom surface using an airless spraying method with a spray thickness of 25μm. Then bake it in an oven at 130℃ for 22 minutes to form an electro-optic silver coloring layer. Step s6: Add 28 parts of fluorocarbon resin (model GK 570), 5 parts of nano silica (particle size of nano silica is 12nm), 3 parts of benzotriazole UV absorber (CAS number of benzotriazole UV absorber is 70321-86-7), 1.2 parts of polysiloxane leveling agent (polysiloxane leveling agent is BYK-333) and 12 parts of methyl ethyl ketone to a mixing tank and stir for 40 minutes at a speed of 1000 r / min to obtain a protective coating. Apply the protective coating to the surface of the electro-silver coloring layer by air spraying to a thickness of 30μm. Then bake in an oven at 140℃ for 45 minutes to form an electro-silver coating resistant to oxidation and discoloration.

[0030] Comparative Example 2: This comparative example illustrates a method for preparing an electro-optic silver coating resistant to oxidation and discoloration, comprising the following steps: Step s1: Add 40g methanol and 17.6g butanediamine to a three-necked flask equipped with a stirrer, thermometer and constant pressure dropping funnel. Stir the reaction at 25℃ and 250r / min for 10min. Then, add 137.6g methyl acrylate dropwise while stirring at 400r / min, controlling the dropping rate to 1 drop / s. After the addition is complete, continue stirring for 24h. After the reaction is complete, transfer to a rotary evaporator and distill under reduced pressure at 45℃ and 130Pa for 2h. Then dry with anhydrous sodium sulfate for 12h to obtain the intermediate product. Step s2: 60g methanol and 8g intermediate were added to a three-necked flask equipped with a stirrer, thermometer and constant pressure dropping funnel. The mixture was stirred for 20min at 25℃ and 250r / min. Then, 9.6g ethylenediamine was added dropwise while stirring at 400r / min, with the dropping rate controlled at 1 drop / s. After the addition was completed, the mixture was stirred for 24h. After the reaction was completed, the mixture was transferred to a rotary evaporator and distilled under reduced pressure for 3h at 70℃ and 130Pa. The product was then dried with anhydrous sodium sulfate for 12h to obtain dendritic macromolecules. Step s3: Add 4g of dendritic macromolecules and 80mL of anhydrous dichloromethane to a three-necked flask equipped with a stirrer, thermometer, gas delivery tube, and constant pressure dropping funnel. Purge with nitrogen for protection and stir for 15min at 25℃ and a stirring rate of 350r / min. Add 11g of anhydrous potassium carbonate and stir for 10min. Then, while stirring at 450r / min, add 37mL of anhydrous potassium carbonate dropwise. 3,5-Di-tert-butylhydroxyphenylpropionyl chloride / anhydrous dichloromethane solution (the 3,5-di-tert-butylhydroxyphenylpropionyl chloride / anhydrous dichloromethane solution is a solution prepared by mixing 3,5-di-tert-butylhydroxyphenylpropionyl chloride and anhydrous dichloromethane at a ratio of 17.13 g: 20 mL), with a dropping rate controlled at 1 drop / s. After the addition is complete, the temperature is raised to 30 °C, and the reaction is continued with stirring for 24 h. After the reaction is completed, the mixture is transferred to a Buchner funnel for vacuum filtration. The filter cake is washed three times with anhydrous dichloromethane, and the filtrates are combined. The filtrate is washed with deionized water until the pH of the aqueous phase is 7, and then the aqueous phase is discarded. The organic phase was dried with anhydrous magnesium sulfate for 12 h, the desiccant was removed by filtration, and the organic phase was transferred to a rotary evaporator and distilled under reduced pressure at 35 °C and 130 Pa. After purification by silica gel chromatography, the stationary phase was 200 mesh silica gel, and the mobile phase was ethyl acetate / petroleum ether solution (ethyl acetate / petroleum ether solution is a solution of ethyl acetate and petroleum ether mixed in a volume ratio of 1:4). The main fraction was collected, and the solvent was removed by reduced pressure distillation again. Then it was placed in a vacuum drying oven and dried at 55 °C for 8 h to obtain the oxidation inhibitor. Step s4: Add 18 parts epoxy resin (epoxy resin type E-51), 9 parts polyurethane modified resin (polyurethane modified resin is EPU-133L from Complex High-Tech Materials Shanghai Co., Ltd.), 12 parts ethyl acetate, 3 parts silane coupling agent (silane coupling agent is KH-570) and 1.5 parts organosilicon defoamer (organosilicon defoamer is BYK-052) to a mixing tank and stir for 40 minutes at a speed of 900 r / min to obtain the base coat. Then, apply the base coat to the pretreated substrate surface by air spraying, with the spray thickness controlled at 35 μm. Then, bake in an oven at 85℃ for 35 minutes to form the base coat. Step s5: Add 24 parts of acrylic resin (7860A from Zhishang Chemical (Shanghai) Co., Ltd.), 7 parts of silver powder, 3 parts of pearl powder (particle size of pearl powder is 20μm), 1.5 parts of polycarboxylate dispersant (polycarboxylate dispersant 5040 from Jingzhou Yinjie Chemical Co., Ltd.), 4 parts of oxidation inhibitor and 14 parts of xylene to a mixing tank and stir for 50 minutes at a speed of 1200 r / min. Then grind the mixture to a particle size of <5μm using a three-roll mill to obtain an electro-optic silver coloring layer coating. Apply the coating to the bottom surface using an airless spraying method with a spray thickness of 25μm. Then bake it in an oven at 130℃ for 22 minutes to form an electro-optic silver coloring layer. Step s6: Add 28 parts of fluorocarbon resin (model GK 570), 5 parts of nano silica (particle size of nano silica is 12nm), 3 parts of benzotriazole UV absorber (CAS number of benzotriazole UV absorber is 70321-86-7), 1.2 parts of polysiloxane leveling agent (polysiloxane leveling agent is BYK-333) and 12 parts of methyl ethyl ketone to a mixing tank and stir for 40 minutes at a speed of 1000 r / min to obtain a protective coating. Apply the protective coating to the surface of the electro-silver coloring layer by air spraying to a thickness of 30μm. Then bake in an oven at 140℃ for 45 minutes to form an electro-silver coating resistant to oxidation and discoloration.

[0031] Comparative Example 3: This comparative example illustrates a method for preparing an electro-optic silver coating resistant to oxidation and discoloration, comprising the following steps: Step s1: Add 18 parts epoxy resin (epoxy resin type E-51), 9 parts polyurethane modified resin (polyurethane modified resin is EPU-133L from Complex High-Tech Materials Shanghai Co., Ltd.), 12 parts ethyl acetate, 3 parts silane coupling agent (silane coupling agent is KH-570) and 1.5 parts organosilicon defoamer (organosilicon defoamer is BYK-052) to a mixing tank and stir for 40 minutes at a speed of 900 r / min to obtain the base coat. Then, apply the base coat to the pretreated substrate surface by air spraying, with the spray thickness controlled at 35 μm. Then, bake in an oven at 85℃ for 35 minutes to form the base coat. Step s2: Add 24 parts of acrylic resin (7860A from Zhishang Chemical (Shanghai) Co., Ltd.), 7 parts of silver powder, 3 parts of pearl powder (pearl powder with a particle size of 20μm), 1.5 parts of polycarboxylate dispersant (polycarboxylate dispersant 5040 from Jingzhou Yinjie Chemical Co., Ltd.), and 14 parts of xylene to a mixing tank and stir for 50 minutes at a speed of 1200 r / min. Then, grind the mixture to a particle size of <5μm using a three-roll mill to obtain an electro-optic silver coloring layer coating. Apply the coating to the bottom surface using an airless spraying method with a spray thickness of 25μm. Then, bake it in an oven at 130℃ for 22 minutes to form an electro-optic silver coloring layer. Step s3: Add 28 parts of fluorocarbon resin (model GK 570), 5 parts of nano silica (particle size of nano silica is 12nm), 3 parts of benzotriazole UV absorber (CAS number of benzotriazole UV absorber is 70321-86-7), 1.2 parts of polysiloxane leveling agent (polysiloxane leveling agent is BYK-333) and 12 parts of methyl ethyl ketone to a mixing tank and stir for 40 minutes at a speed of 1000 r / min to obtain a protective coating. Apply the protective coating to the surface of the electro-optic silver coloring layer by air spraying to a thickness of 30μm. Then bake in an oven at a temperature of 140℃ for 45 minutes to form an electro-optic silver coating resistant to oxidation and discoloration.

[0032] Performance testing The electro-optic silver coatings of Examples 1-3 and Comparative Examples 1-3 were tested for corrosion resistance and oxidation stability according to GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test"; weather resistance and long-term oxidation stability according to GB / T 1865-2009 "Paints and Varnishes - Artificial Climate Aging and Artificial Radiation Exposure - Filtered Xenon Arc Radiation"; adhesion performance according to GB / T9286-2021 "Paints and Varnishes - Cross-cut Test"; and abrasion resistance according to GB / T 1768-2006 "Determination of Abrasion Resistance of Paints and Varnishes - Rotating Rubber Grinding Wheel Method".

[0033] The test results are shown in the table below:

[0034] Referring to the table above, based on the comparison between Examples 1-3 and Comparative Examples 1-3, it can be seen that the electro-optic silver coating resistant to oxidation and discoloration has excellent oxidation resistance and corrosion resistance, while also taking into account adhesion and wear resistance.

[0035] Based on the comparison between Example 1 and Comparative Example 1, it can be seen that the electro-optic silver coating with added composite coated silver powder and oxidation inhibitor during the preparation process has better performance than the electro-optic silver coating with added composite coated silver powder during the preparation process.

[0036] Based on the comparison between Example 1 and Comparative Example 2, it can be seen that the electro-optic silver coating with added composite coated silver powder and oxidation inhibitor during the preparation process has better performance than the electro-optic silver coating with added ordinary silver powder and oxidation inhibitor during the preparation process.

[0037] Based on the comparison between Example 1 and Comparative Example 3, it can be seen that the electro-optic silver coating with added composite coated silver powder and oxidation inhibitor during the preparation process has better performance than the electro-optic silver coating with added ordinary silver powder during the preparation process.

[0038] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0039] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in this application, they should all fall within the protection scope of the present invention.

Claims

1. An oxidation tarnish resistant electro-optic silver coating characterized by, The coating includes a bottom layer, an electro-optic silver coloring layer and a protective layer. The bottom layer includes the following components by weight: epoxy resin 18-22 parts, polyurethane modified resin 9-11 parts, ethyl acetate 12-14 parts, silane coupling agent 3-4 parts and silicone defoaming agent 1.5-2.5 parts; The electro-optic silver coloring layer includes the following components by weight: acrylic resin 24-26 parts, composite coated silver powder 7-9 parts, pearl powder 3-4 parts, polycarboxylate dispersant 1.5-2.5 parts, oxidation inhibitor 4-5 parts and dimethylbenzene 14-16 parts; The protective layer includes the following components by weight: fluorocarbon resin 28-32 parts, nano-silicon dioxide 5-7 parts, benzotriazole ultraviolet absorber 3-4 parts, polysiloxane leveling agent 1.2-1.8 parts and butanone 12-14 parts; The oxidation inhibitor is prepared by the following steps: Step a1: methanol, butanediamine are added to a three-necked flask and stirred, methyl acrylate is added for reaction, vacuum distillation is performed, and drying is performed to obtain an intermediate product; Step a2: methanol and the intermediate product are added to a three-necked flask and stirred, ethylenediamine is added for reaction, vacuum distillation is performed, and drying is performed to obtain a dendrimer; Step a3: the dendrimer and anhydrous dichloromethane are added to a three-necked flask and stirred, anhydrous potassium carbonate is added and stirred, 3,5-di-tert-butylhydroxybenzyl chloride / anhydrous dichloromethane solution is added for reaction, suction filtration is performed, the organic phase is dried, filtration is performed, vacuum distillation is performed, and then purification is performed by a silica gel chromatographic column, vacuum distillation is performed again, and drying is performed to obtain the oxidation inhibitor.

2. The tarnish and discoloration resistant electro-optic silver coating of claim 1, wherein, The amount ratio of the methanol, butanediamine and methyl acrylate in step a1 is 40-44.5g:17.6-19.6g:137.6-153.2g; the amount ratio of the methanol, the intermediate product and ethylenediamine in step a2 is 60-75g:8-10g:9.6-12g; and the amount ratio of the dendrimer, anhydrous dichloromethane, anhydrous potassium carbonate and 3,5-di-tert-butylhydroxybenzyl chloride / anhydrous dichloromethane solution in step a3 is 4-6g:80-120mL:11-16g:37-55mL.

3. The tarnish and discoloration resistant electro-optic silver coating of claim 1, wherein, The 3,5-di-tert-butylhydroxybenzyl chloride / anhydrous dichloromethane solution in step a3 is a solution prepared by mixing 3,5-di-tert-butylhydroxybenzyl chloride and anhydrous dichloromethane in an amount ratio of 17.13g:20mL; and the ethyl acetate / petroleum ether solution is a solution prepared by mixing ethyl acetate and petroleum ether in a volume ratio of 1:

4.

4. The tarnish and discoloration resistant electro-optic silver coating of claim 1, wherein, The composite coated silver powder is prepared by the following steps: Step b1: metal silver powder and anhydrous ethanol 1 are ultrasonically dispersed, then centrifuged, the precipitate is added to a three-necked flask, anhydrous ethanol 2 is added and stirred for reaction, tetraethyl orthosilicate is added for reaction, ammonia-ethanol mixed solution is added, the system pH is adjusted to 8.5-9.0 to stop dropping, the reaction is continued, centrifuged, washed, and dried to obtain silica-coated silver powder; Step b2: the dendrimer is added to anhydrous ethanol and stirred to obtain a dendrimer-ethanol solution; Step b3: the silica-coated silver powder, anhydrous ethanol were added into a three-necked flask and stirred, then ultrasonic dispersed, the dendrimer-ethanol solution was added for reaction, centrifuged, washed, dried to obtain the composite coated silver powder.

5. An electro-optic silver coating resistant to discoloration by oxidation according to claim 4, characterized in that The amount ratio of the silver powder, anhydrous ethanol 1, anhydrous ethanol 2 and tetraethyl orthosilicate in step b1 was 10-14g: 100-140mL: 150-210mL: 5-7mL; the amount ratio of the dendrimer, anhydrous ethanol in step b2 was 1-3g: 50-150mL; the amount ratio of the silica-coated silver powder, anhydrous ethanol, dendrimer-ethanol solution in step b3 was 10-12g: 150-180mL: 50-60mL.

6. The tarnish and discoloration resistant electro-optic silver coating of claim 4, wherein, The particle size of the silver powder in step b1 was 5-20μm; the ammonia-ethanol mixed solution was a solution prepared by mixing ammonia water and anhydrous ethanol according to the amount ratio of 3.0mL: 20mL; the mass fraction of the ammonia water was 25%.

7. A process for the preparation of an oxidation tarnish resistant electro-optic silver coating characterized by, A method for preparing an oxidation discoloration resistant electro-optic silver coating according to any one of claims 1-6, comprising the following steps: Step one: epoxy resin, polyurethane modified resin, ethyl acetate, silane coupling agent and silicone defoaming agent were added into a stirring kettle and stirred to obtain a primer, then the primer was coated on the surface of a pretreated substrate and baked to form a primer layer; Step two: acrylic resin, composite coated silver powder, pearl powder, polycarboxylate dispersant, oxidation inhibitor and dimethylbenzene were added into a stirring kettle and stirred and ground to obtain an electro-optic silver colored layer coating, which was coated on the surface of the primer layer and baked to form an electro-optic silver colored layer; Step three: fluorocarbon resin, nano-silicon dioxide, benzotriazole ultraviolet absorber, polysiloxane leveling agent and butanone were added into a stirring kettle and stirred to obtain a protective layer coating, which was coated on the surface of the electro-optic silver colored layer and baked to form a protective layer, thereby obtaining an oxidation discoloration resistant electro-optic silver coating.

8. A process for the preparation of an electro-optic silver coating resistant to discoloration by oxidation according to claim 7, characterized in that, The model of the epoxy resin in step one was E-51; the brand of the polyurethane modified resin was EPU-133L; the silane coupling agent was KH-570; the silicone defoaming agent was BYK-052.

9. A process for the preparation of an electro-optic silver coating resistant to discoloration by oxidation according to claim 7, characterized in that, The model of the acrylic resin in step two was 7860A; the particle size of the pearl powder was 20-50μm; the polycarboxylate dispersant was 5040.

10. A process for the preparation of an electro-optic silver coating resistant to discoloration by oxidation according to claim 7, characterized in that, The model of the fluorocarbon resin in step three was GK 570; the particle size of the nano-silicon dioxide was 12-14nm; the CAS number of the benzotriazole ultraviolet absorber was 70321-86-7; the polysiloxane leveling agent was BYK-333.

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