A method for preparing a composite coating on the surface of a copper piece

Abstract

The present application relates to the technical field of surface treatment, and particularly discloses a preparation method of a composite coating on the surface of a copper piece. The blackening solution and the passivation solution provided by the present application do not contain hexavalent chromium, fluorine, cadmium, lead, mercury and other heavy metals, meet the environmental protection requirements of RoHS / REACH, and avoid environmental pollution and health hazards of the traditional chromate process. The present application forms a dense black composite film (containing CuSe, CuO and the like) through selenium salt blackening, and then is closed by a BTA-phytic acid system chromium-free passivation, so that a dense protective layer is formed on the surface of the blackening film by using the strong complexation of BTA and copper ions, and finally, an organic coating is sprayed to form a triple composite protective structure of "blackening film+passivation film+organic coating", which significantly improves the salt spray corrosion resistance of the copper piece.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, and specifically to a method for preparing a composite coating on the surface of copper parts. Background Technology

[0002] Copper and copper alloys are widely used in electronics, construction, automotive, chemical, and aerospace industries due to their excellent electrical and thermal conductivity, ductility, and corrosion resistance. However, copper parts are prone to oxidation and discoloration during long-term use, affecting their appearance and performance.

[0003] Currently, the main methods for surface treatment of copper parts are as follows:

[0004] (I) Chemical Blackening (Oxidative Blackening). This process generates a dark film, such as black copper oxide (CuO) or copper sulfide (CuS), on the surface of copper parts, giving them a black appearance. Existing blackening processes mainly include selenium salt systems, ammonia systems, and high-temperature alkaline systems. For example, Chinese patent CN119980208B discloses a casting copper blackening agent containing 2-8 parts selenium dioxide and 6-10 parts copper sulfate; Chinese patent CN112111734A discloses a copper product blackening process that uses two blackening steps to form a stable blackened layer. However, the black film formed after existing blackening processes often suffers from high porosity and limited corrosion resistance, usually requiring subsequent sealing treatment.

[0005] (II) Chromate Passivation and Sealing. Traditionally, blackened copper parts are passivated and sealed with chromates to improve corrosion resistance and fingerprint resistance. Chromate passivation films have good isolation properties and self-healing capabilities. However, hexavalent chromium in chromates is highly toxic and carcinogenic, posing serious harm to human health and the environment. With increasingly stringent environmental regulations, the use of chromium-containing processes is facing increasingly strict restrictions.

[0006] (III) Chromium-free passivation technology. In recent years, researchers have developed various chromium-free passivation schemes, such as phytic acid systems and benzotriazole (BTA) systems. As an organic heterocyclic compound, BTA exhibits strong adsorption and complexation with the copper substrate surface in aqueous solution, and can be used as a chromium-free corrosion inhibitor for copper alloys. However, most existing chromium-free passivation technologies only target the anti-discoloration treatment of the original copper color, and a complete solution combining its systematic application to the sealing treatment of the black film layer after blackening and organic coating spraying has not yet been seen.

[0007] (iv) Organic coating spraying. Spraying an organic coating onto the surface of copper parts can further improve the protective performance and decorative effect. However, in the existing technology, blackening treatment, passivation treatment and spraying treatment are often isolated processes, lacking systematic process integration, resulting in insufficient compatibility and synergy between the processes, and the final coating adhesion, corrosion resistance and appearance quality are difficult to achieve ideal state.

[0008] In summary, there is currently a lack of a complete process that can organically combine blackening of copper parts, environmentally friendly chromium-free passivation sealing, and organic coating spraying to achieve a comprehensive improvement in the high corrosion resistance and excellent coating adhesion of copper parts. Summary of the Invention

[0009] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing a composite coating on the surface of copper parts.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A method for preparing a composite coating on the surface of a copper part includes the following steps:

[0012] S1. Preparation of pretreated copper parts

[0013] The copper parts are subjected to chemical degreasing, hot water washing, cold water washing, acid pickling activation, and cold water washing in sequence to obtain pretreated copper parts.

[0014] In this step, the selected copper parts are either red copper or brass.

[0015] In this step, chemical degreasing is performed by immersing the copper parts in an alkaline degreasing agent and treating them at 50-60℃ for 5-10 minutes to remove surface grease.

[0016] Hot water wash: Clean the degreased copper parts in hot water at 60-70℃ for 1-2 minutes.

[0017] Cold water wash: Wash in running cold water at room temperature for 1-2 minutes.

[0018] Pickling and activation: Immerse the copper parts in a 5% (v / v) dilute sulfuric acid solution and treat for 30-60 seconds at room temperature to remove the surface oxide layer.

[0019] Cold water wash: Wash in running cold water at room temperature for 1-2 minutes.

[0020] S2. A black film is formed on the surface of the copper part.

[0021] The pretreated copper parts are immersed in a selenium salt blackening solution and treated at room temperature to form a black film on the surface of the copper parts, thus obtaining blackened copper parts.

[0022] In this step, the selenium salt system blackening solution includes the following components at the following concentrations: copper nitrate 20-25 g / L, selenite 1.5-2.0 g / L, phosphoric acid 10-12 mL / L, sodium citrate 0.5-1 g / L, polyethylene glycol 1.0-1.2 g / L, and deionized water as the solvent.

[0023] In this step, ammonia or phosphoric acid is used to adjust the pH of the selenium salt system blackening solution to 1.5-2.5.

[0024] In this step, after a black film is formed on the surface of the copper part, it is washed in running cold water at room temperature for 1-2 minutes to obtain the blackened copper part.

[0025] S3. Form a passivation layer on the surface of the black film.

[0026] The blackened copper part is immersed in a chromium-free passivation solution and treated at 20-40℃ for 30-60 seconds to form a passivation layer on the surface of the black film, thus obtaining the passivated copper part.

[0027] In this step, the chromium-free passivation solution contains the following components by mass percentage: 5-10% phytic acid, 8-15% citric acid, 1-3% benzotriazole, 2-5% calcium dihydrogen phosphate, 0.5-2% nonionic surfactant, and the balance being deionized water.

[0028] In this step, the passivated copper parts are cleaned with deionized water for 30-60 seconds, and then placed in a hot air circulating oven to dry at 100-120℃.

[0029] S4, Forming a composite coating

[0030] After passivation, primer and topcoat are sprayed sequentially onto the surface of the copper part to form a composite coating.

[0031] In this step, the primer comprises the following components in parts by weight: 40-60 parts epoxy resin, 10-15 parts butyl glycidyl ether, 2-5 parts dispersant, 0.5-2 parts defoamer, 0.5-2 parts leveling agent, 15-20 parts solvent, and 20-35 parts polyamide curing agent.

[0032] In this step, the topcoat comprises the following components in parts by weight: 60-80 parts of fluoropolymer resin, 10-15 parts of modified composite filler, 1-3 parts of dispersant, 0.5-2 parts of defoamer, 0.5-2 parts of leveling agent, and 8-10 parts of isocyanate curing agent.

[0033] The modified composite filler is prepared as follows:

[0034] (1) Disperse silicon carbide in deionized water, then add zinc salt, aluminum salt and cerium salt to it, stir evenly, then add ammonia water to it, adjust the pH of the solution to 8.5-9.5, mix evenly and transfer to a hydrothermal reactor for hydrothermal reaction. After the reaction is completed, centrifuge, wash and dry to obtain composite filler;

[0035] (2) Dissolve 3-amino-4-hydroxybenzoic acid in an aqueous ethanol solution, add carbon disulfide dropwise under nitrogen protection, adjust the pH of the solution to 10-12, stir the reaction, and after the reaction is completed, filter, wash and vacuum dry to obtain dithiocarbamate.

[0036] (3) Under nitrogen protection, dithiocarbamate is dissolved in an aqueous ethanol solution, then the composite filler is added, stirred and treated, and then centrifuged, washed and vacuum dried to obtain the modified composite filler.

[0037] In step (1), the mass ratio of silicon carbide, zinc salt, aluminum salt and cerium salt is 3-5:1-2:1-2:0.2-0.4.

[0038] In step (1), the temperature of the hydrothermal reaction is 120-140℃ and the time of the hydrothermal reaction is 8-12h.

[0039] In step (2), the molar ratio of 3-amino-4-hydroxybenzoic acid to carbon disulfide is 1:1.1-1.3.

[0040] In step (2), the reaction is stirred at room temperature for 3-5 hours.

[0041] In step (3), the mass ratio of dithiocarbamate to composite filler is 1-2:3-5.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) The blackening solution and passivation solution provided by this invention are free of hexavalent chromium, fluorine, cadmium, lead, mercury and other heavy metals, and comply with RoHS / REACH environmental protection requirements, avoiding the environmental pollution and health hazards of traditional chromate processes. This invention forms a dense black composite film (containing CuSe, CuO, etc.) through selenium salt blackening, and then passes it off with a chromium-free BTA-phytic acid system. The strong complexation of BTA with copper ions forms a dense protective layer on the surface of the blackening film. Finally, an organic coating is sprayed to form a triple composite protective structure of "blackening film + passivation film + organic coating", which significantly improves the salt spray corrosion resistance of copper parts.

[0044] (2) The topcoat provided by this invention extends the penetration path of water vapor and corrosive media by growing a two-dimensional LDH layered structure through in-situ hydrothermal growth of Zn-Al-Ce layered hydroxide on the silicon carbide surface. Simultaneously, the doped rare earth element Ce has excellent corrosion inhibition properties, forming a dual barrier of physical and chemical corrosion inhibition with the Zn-Al layer. Then, the generated dithiocarbamate is intercalated into the LDH interlayer and the filler surface. The dithiocarbamate contains polydentate coordinating atoms such as sulfur, nitrogen, and oxygen, which have a strong chelating ability for metal ions, generating an extremely stable complex network, thereby improving the adhesion and corrosion resistance of the coating. Furthermore, the modification with dithiocarbamate improves the wettability and dispersibility of the composite filler in the resin matrix, eliminating interfacial stress concentration defects caused by filler agglomeration, thus improving the wear resistance of the coating.

[0045] (3) The present invention systematically integrates the three processes of blackening, passivation and spraying into a complete process chain. Each process is optimized and matched to ensure the stability and repeatability of the process, which is suitable for industrial mass production. Detailed Implementation

[0046] The present invention will be further described in detail below through specific preferred embodiments, but the present invention is not limited to the following embodiments.

[0047] It should be noted that, unless otherwise specified, all chemical reagents involved in this invention were purchased through commercial channels.

[0048] The alkaline degreasing agent used in this embodiment of the invention is model KM0121, which is sourced from Guangdong Kaimeng Passivation and Rust Prevention Technology Co., Ltd.

[0049] The mass fraction of phosphoric acid is 85%.

[0050] The epoxy resin is model E-51;

[0051] The dispersant is model BYK-163;

[0052] The defoamer's model number is BYK-066N;

[0053] The leveling agent is model BYK-358N;

[0054] The polyamide curing agent, model HY-H115, is sourced from Shenzhen Huiya New Materials Technology Co., Ltd.

[0055] The fluoropolymer resin is a FEVE type fluoropolymer resin, grade: PF501;

[0056] The isocyanate curing agent is model Basonat HW 2100CN;

[0057] The particle size of silicon carbide is 40-60 nm.

[0058] Example 1

[0059] A method for preparing a composite coating on the surface of a copper part includes the following steps:

[0060] S1. Immerse the copper parts in an alkaline degreasing agent and treat them at 50°C for 10 minutes to remove surface grease. Then, wash the degreased copper parts in hot water at 70°C for 1 minute, and then wash them in running cold water at room temperature for 1 minute. Next, immerse the copper parts in a 5% (v / v) dilute sulfuric acid solution and treat them at room temperature for 30 seconds to remove the surface oxide layer. Finally, wash them in running cold water at room temperature for 1 minute to obtain the pretreated copper parts.

[0061] S2. Immerse the pretreated copper parts in a selenium salt blackening solution, which includes the following components at the following concentrations: copper nitrate 20g / L, selenite 1.5g / L, phosphoric acid 10mL / L, sodium citrate 0.5g / L, polyethylene glycol 1.0g / L, and deionized water as the solvent. Adjust the pH of the selenium salt blackening solution to 2.0 and soak at room temperature for 3 minutes, turning the workpiece every 1 minute to ensure uniform blackening. After blackening, a uniform black film with a thickness of 1.5μm is formed on the surface of the copper parts. After blackening, rinse the copper parts in running cold water at room temperature for 1 minute to obtain the blackened copper parts.

[0062] S3. Immerse the blackened copper part in a chromium-free passivation solution, which contains the following components by mass percentage: phytic acid 8%, citric acid 10%, benzotriazole 2%, calcium dihydrogen phosphate 4%, AEO-9 1%, and the balance is deionized water. Treat at 30°C for 45 seconds to form a passivation layer with a thickness of 15 nm on the surface of the black film, and obtain the passivated copper part. Rinse the passivated copper part with deionized water for 30 seconds, and then put it into a hot air circulating oven and dry at 110°C for 12 minutes.

[0063] S4. Mix 40 parts epoxy resin, 10 parts butyl glycidyl ether, 2 parts dispersant, 0.5 parts defoamer, 0.5 parts leveling agent and 20 parts solvent (xylene and n-butanol in a mass ratio of 7:3) evenly, then add 20 parts polyamide curing agent and mix evenly to obtain the primer.

[0064] Mix 60 parts of fluoropolymer resin, 10 parts of modified composite filler, 1 part of dispersant, 0.5 parts of defoamer and 0.5 parts of leveling agent evenly, then add 8 parts of isocyanate curing agent and mix evenly to obtain the topcoat;

[0065] The preparation method of the modified composite filler is as follows:

[0066] (1) Disperse 3g of silicon carbide in 100mL of deionized water, then add 1g of zinc nitrate, 1g of aluminum nitrate and 0.2g of cerium nitrate, stir evenly, then add ammonia water to adjust the pH of the solution to 9.0, mix evenly and transfer to a hydrothermal reactor, and hydrothermally react at 120℃ for 12h. After the reaction is completed, centrifuge, wash and dry to obtain composite filler;

[0067] (2) Dissolve 0.1 mol of 3-amino-4-hydroxybenzoic acid in 100 mL of ethanol-water solution (the volume ratio of ethanol to water is 6:4). Under nitrogen protection, add 0.11 mol of carbon disulfide dropwise, adjust the pH of the solution to 10 with sodium hydroxide solution, stir the reaction at room temperature for 4 h, and after the reaction is completed, filter, wash and vacuum dry to obtain dithiocarbamate.

[0068] (3) Under nitrogen protection, 1g of dithiocarbamate was dissolved in 80mL of ethanol aqueous solution (the volume ratio of ethanol to water was 6:4), and then 3g of composite filler was added. The mixture was stirred at 50℃ for 12h, and then centrifuged, washed and vacuum dried to obtain the modified composite filler.

[0069] First, the primer is sprayed onto the passivated copper surface with a thickness of 20μm and baked at 80℃ for 15min; then the topcoat is sprayed with a thickness of 25μm and cured at 100℃ for 3h to form a composite coating.

[0070] Example 2

[0071] A method for preparing a composite coating on the surface of a copper part includes the following steps:

[0072] S1. Immerse the copper parts in an alkaline degreasing agent and treat them at 50°C for 10 minutes to remove surface grease. Then, wash the degreased copper parts in hot water at 70°C for 1 minute, and then wash them in running cold water at room temperature for 1 minute. Next, immerse the copper parts in a 5% (v / v) dilute sulfuric acid solution and treat them at room temperature for 30 seconds to remove the surface oxide layer. Finally, wash them in running cold water at room temperature for 1 minute to obtain the pretreated copper parts.

[0073] S2. Immerse the pretreated copper parts in a selenium salt blackening solution, which includes the following components at the following concentrations: copper nitrate 20g / L, selenite 1.5g / L, phosphoric acid 10mL / L, sodium citrate 0.5g / L, polyethylene glycol 1.0g / L, and deionized water as the solvent. Adjust the pH of the selenium salt blackening solution to 2.0 and soak at room temperature for 3 minutes, turning the workpiece every 1 minute to ensure uniform blackening. After blackening, a uniform black film with a thickness of 1.5μm is formed on the surface of the copper parts. After blackening, rinse the copper parts in running cold water at room temperature for 1 minute to obtain the blackened copper parts.

[0074] S3. Immerse the blackened copper part in a chromium-free passivation solution, which contains the following components by mass percentage: phytic acid 8%, citric acid 10%, benzotriazole 2%, calcium dihydrogen phosphate 4%, AEO-9 1%, and the balance is deionized water. Treat at 30°C for 45 seconds to form a passivation layer with a thickness of 15 nm on the surface of the black film, and obtain the passivated copper part. Rinse the passivated copper part with deionized water for 30 seconds, and then put it into a hot air circulating oven and dry at 110°C for 12 minutes.

[0075] S4. Mix 60 parts epoxy resin, 15 parts butyl glycidyl ether, 5 parts dispersant, 2 parts defoamer, 2 parts leveling agent and 20 parts solvent (xylene and n-butanol in a mass ratio of 7:3) evenly, then add 35 parts polyamide curing agent and mix evenly to obtain the primer.

[0076] Mix 80 parts of fluoropolymer resin, 15 parts of modified composite filler, 3 parts of dispersant, 2 parts of defoamer and 2 parts of leveling agent evenly, then add 10 parts of isocyanate curing agent and mix evenly to obtain the topcoat.

[0077] The preparation method of the modified composite filler is as follows:

[0078] (1) Disperse 5g of silicon carbide in 100mL of deionized water, then add 2g of zinc nitrate, 2g of aluminum nitrate and 0.4g of cerium nitrate, stir evenly, then add ammonia water to adjust the pH of the solution to 9.0, mix evenly and transfer to a hydrothermal reactor, and hydrothermally react at 120℃ for 12h. After the reaction is completed, centrifuge, wash and dry to obtain composite filler;

[0079] (2) Dissolve 0.1 mol of 3-amino-4-hydroxybenzoic acid in 100 mL of ethanol-water solution (the volume ratio of ethanol to water is 6:4). Under nitrogen protection, add 0.11 mol of carbon disulfide dropwise, adjust the pH of the solution to 10 with sodium hydroxide solution, stir the reaction at room temperature for 4 h, and after the reaction is completed, filter, wash and vacuum dry to obtain dithiocarbamate.

[0080] (3) Under nitrogen protection, 2g of dithiocarbamate was dissolved in 80mL of ethanol aqueous solution (the volume ratio of ethanol to water was 6:4), and then 5g of composite filler was added. The mixture was stirred at 50℃ for 12h, and then centrifuged, washed and vacuum dried to obtain the modified composite filler.

[0081] First, the primer is sprayed onto the passivated copper surface with a thickness of 20μm and baked at 80℃ for 15min; then the topcoat is sprayed with a thickness of 25μm and cured at 100℃ for 3h to form a composite coating.

[0082] Example 3

[0083] A method for preparing a composite coating on the surface of a copper part includes the following steps:

[0084] S1. Immerse the copper parts in an alkaline degreasing agent and treat them at 50°C for 10 minutes to remove surface grease. Then, wash the degreased copper parts in hot water at 70°C for 1 minute, and then wash them in running cold water at room temperature for 1 minute. Next, immerse the copper parts in a 5% (v / v) dilute sulfuric acid solution and treat them at room temperature for 30 seconds to remove the surface oxide layer. Finally, wash them in running cold water at room temperature for 1 minute to obtain the pretreated copper parts.

[0085] S2. Immerse the pretreated copper parts in a selenium salt blackening solution, which includes the following components at the following concentrations: copper nitrate 20g / L, selenite 1.5g / L, phosphoric acid 10mL / L, sodium citrate 0.5g / L, polyethylene glycol 1.0g / L, and deionized water as the solvent. Adjust the pH of the selenium salt blackening solution to 2.0 and soak at room temperature for 3 minutes, turning the workpiece every 1 minute to ensure uniform blackening. After blackening, a uniform black film with a thickness of 1.5μm is formed on the surface of the copper parts. After blackening, rinse the copper parts in running cold water at room temperature for 1 minute to obtain the blackened copper parts.

[0086] S3. Immerse the blackened copper part in a chromium-free passivation solution, which contains the following components by mass percentage: phytic acid 8%, citric acid 10%, benzotriazole 2%, calcium dihydrogen phosphate 4%, AEO-9 1%, and the balance is deionized water. Treat at 30°C for 45 seconds to form a passivation layer with a thickness of 15 nm on the surface of the black film, and obtain the passivated copper part. Rinse the passivated copper part with deionized water for 30 seconds, and then put it into a hot air circulating oven and dry at 110°C for 12 minutes.

[0087] S4. Mix 50 parts epoxy resin, 12 parts butyl glycidyl ether, 3 parts dispersant, 1 part defoamer, 1 part leveling agent and 20 parts solvent (xylene and n-butanol in a mass ratio of 7:3) evenly, then add 30 parts polyamide curing agent and mix evenly to obtain the primer.

[0088] Mix 70 parts of fluoropolymer resin, 12 parts of modified composite filler, 2 parts of dispersant, 1 part of defoamer and 1 part of leveling agent evenly, then add 10 parts of isocyanate curing agent and mix evenly to obtain the topcoat.

[0089] The preparation method of the modified composite filler is as follows:

[0090] (1) Disperse 4g of silicon carbide in 100mL of deionized water, then add 1.5g of zinc nitrate, 1.5g of aluminum nitrate and 0.3g of cerium nitrate, stir evenly, then add ammonia water to adjust the pH of the solution to 9.0, mix evenly and transfer to a hydrothermal reactor, and hydrothermally react at 120℃ for 12h. After the reaction is completed, centrifuge, wash and dry to obtain composite filler;

[0091] (2) Dissolve 0.1 mol of 3-amino-4-hydroxybenzoic acid in 100 mL of ethanol-water solution (the volume ratio of ethanol to water is 6:4). Under nitrogen protection, add 0.12 mol of carbon disulfide dropwise, adjust the pH of the solution to 10 with sodium hydroxide solution, stir the reaction at room temperature for 4 h, and after the reaction is completed, filter, wash and vacuum dry to obtain dithiocarbamate.

[0092] (3) Under nitrogen protection, 1.5g of dithiocarbamate was dissolved in 80mL of ethanol aqueous solution (the volume ratio of ethanol to water was 6:4), and then 4.5g of composite filler was added. The mixture was stirred at 50℃ for 12h, and then centrifuged, washed and vacuum dried to obtain the modified composite filler.

[0093] First, the primer is sprayed onto the passivated copper surface with a thickness of 20μm and baked at 80℃ for 15min; then the topcoat is sprayed with a thickness of 25μm and cured at 100℃ for 3h to form a composite coating.

[0094] Comparative Example 1

[0095] A method for preparing a composite coating on the surface of a copper part includes the following steps:

[0096] S1. Immerse the copper parts in an alkaline degreasing agent and treat them at 50°C for 10 minutes to remove surface grease. Then, wash the degreased copper parts in hot water at 70°C for 1 minute, and then wash them in running cold water at room temperature for 1 minute. Next, immerse the copper parts in a 5% (v / v) dilute sulfuric acid solution and treat them at room temperature for 30 seconds to remove the surface oxide layer. Finally, wash them in running cold water at room temperature for 1 minute to obtain the pretreated copper parts.

[0097] S2. Immerse the pretreated copper parts in a selenium salt blackening solution, which includes the following components at the following concentrations: copper nitrate 20g / L, selenite 1.5g / L, phosphoric acid 10mL / L, sodium citrate 0.5g / L, polyethylene glycol 1.0g / L, and deionized water as the solvent. Adjust the pH of the selenium salt blackening solution to 2.0 and soak at room temperature for 3 minutes, turning the workpiece every 1 minute to ensure uniform blackening. After blackening, a uniform black film with a thickness of 1.5μm is formed on the surface of the copper parts. After blackening, rinse the copper parts in running cold water at room temperature for 1 minute to obtain the blackened copper parts.

[0098] S3. Immerse the blackened copper part in a chromium-free passivation solution, which contains the following components by mass percentage: phytic acid 8%, citric acid 10%, benzotriazole 2%, calcium dihydrogen phosphate 4%, AEO-9 1%, and the balance is deionized water. Treat at 30°C for 45 seconds to form a passivation layer with a thickness of 15 nm on the surface of the black film, and obtain the passivated copper part. Rinse the passivated copper part with deionized water for 30 seconds, and then put it into a hot air circulating oven and dry at 110°C for 12 minutes.

[0099] S4. Mix 40 parts epoxy resin, 10 parts butyl glycidyl ether, 2 parts dispersant, 0.5 parts defoamer, 0.5 parts leveling agent and 20 parts solvent (xylene and n-butanol in a mass ratio of 7:3) evenly, then add 20 parts polyamide curing agent and mix evenly to obtain the primer.

[0100] Mix 60 parts of fluoropolymer resin, 10 parts of silicon carbide, 1 part of dispersant, 0.5 parts of defoamer and 0.5 parts of leveling agent evenly, then add 8 parts of isocyanate curing agent and mix evenly to obtain the topcoat;

[0101] First, the primer is sprayed onto the passivated copper surface with a thickness of 20μm and baked at 80℃ for 15min; then the topcoat is sprayed with a thickness of 25μm and cured at 100℃ for 3h to form a composite coating.

[0102] Compared with Comparative Example 1, no modification treatment was performed on silicon carbide.

[0103] Comparative Example 2

[0104] A method for preparing a composite coating on the surface of a copper part includes the following steps:

[0105] S1. Immerse the copper parts in an alkaline degreasing agent and treat them at 50°C for 10 minutes to remove surface grease. Then, wash the degreased copper parts in hot water at 70°C for 1 minute, and then wash them in running cold water at room temperature for 1 minute. Next, immerse the copper parts in a 5% (v / v) dilute sulfuric acid solution and treat them at room temperature for 30 seconds to remove the surface oxide layer. Finally, wash them in running cold water at room temperature for 1 minute to obtain the pretreated copper parts.

[0106] S2. Immerse the pretreated copper parts in a selenium salt blackening solution, which includes the following components at the following concentrations: copper nitrate 20g / L, selenite 1.5g / L, phosphoric acid 10mL / L, sodium citrate 0.5g / L, polyethylene glycol 1.0g / L, and deionized water as the solvent. Adjust the pH of the selenium salt blackening solution to 2.0 and soak at room temperature for 3 minutes, turning the workpiece every 1 minute to ensure uniform blackening. After blackening, a uniform black film with a thickness of 1.5μm is formed on the surface of the copper parts. After blackening, rinse the copper parts in running cold water at room temperature for 1 minute to obtain the blackened copper parts.

[0107] S3. Immerse the blackened copper part in a chromium-free passivation solution, which contains the following components by mass percentage: phytic acid 8%, citric acid 10%, benzotriazole 2%, calcium dihydrogen phosphate 4%, AEO-9 1%, and the balance is deionized water. Treat at 30°C for 45 seconds to form a passivation layer with a thickness of 15 nm on the surface of the black film, and obtain the passivated copper part. Rinse the passivated copper part with deionized water for 30 seconds, and then put it into a hot air circulating oven and dry at 110°C for 12 minutes.

[0108] S4. Mix 40 parts epoxy resin, 10 parts butyl glycidyl ether, 2 parts dispersant, 0.5 parts defoamer, 0.5 parts leveling agent and 20 parts solvent (xylene and n-butanol in a mass ratio of 7:3) evenly, then add 20 parts polyamide curing agent and mix evenly to obtain the primer.

[0109] Mix 60 parts of fluoropolymer resin, 10 parts of modified composite filler, 1 part of dispersant, 0.5 parts of defoamer and 0.5 parts of leveling agent evenly, then add 8 parts of isocyanate curing agent and mix evenly to obtain the topcoat;

[0110] The preparation method of the modified composite filler is as follows:

[0111] (1) Disperse 3g of silicon carbide in 100mL of deionized water, then add 1g of zinc nitrate and 1g of aluminum nitrate, stir evenly, then add ammonia water to adjust the pH of the solution to 9.0, mix evenly and transfer to a hydrothermal reactor, and hydrothermally react at 120℃ for 12h. After the reaction is completed, centrifuge, wash and dry to obtain composite filler;

[0112] (2) Dissolve 0.1 mol of 3-amino-4-hydroxybenzoic acid in 100 mL of ethanol-water solution (the volume ratio of ethanol to water is 6:4). Under nitrogen protection, add 0.11 mol of carbon disulfide dropwise, adjust the pH of the solution to 10 with sodium hydroxide solution, stir the reaction at room temperature for 4 h, and after the reaction is completed, filter, wash and vacuum dry to obtain dithiocarbamate.

[0113] (3) Under nitrogen protection, 1g of dithiocarbamate was dissolved in 80mL of ethanol aqueous solution (the volume ratio of ethanol to water was 6:4), and then 3g of composite filler was added. The mixture was stirred at 50℃ for 12h, and then centrifuged, washed and vacuum dried to obtain the modified composite filler.

[0114] First, the primer is sprayed onto the passivated copper surface with a thickness of 20μm and baked at 80℃ for 15min; then the topcoat is sprayed with a thickness of 25μm and cured at 100℃ for 3h to form a composite coating.

[0115] Compared to Example 1, Comparative Example 2 did not involve cerium doping in the composite filler.

[0116] Comparative Example 3

[0117] A method for preparing a composite coating on the surface of a copper part includes the following steps:

[0118] S1. Immerse the copper parts in an alkaline degreasing agent and treat them at 50°C for 10 minutes to remove surface grease. Then, wash the degreased copper parts in hot water at 70°C for 1 minute, and then wash them in running cold water at room temperature for 1 minute. Next, immerse the copper parts in a 5% (v / v) dilute sulfuric acid solution and treat them at room temperature for 30 seconds to remove the surface oxide layer. Finally, wash them in running cold water at room temperature for 1 minute to obtain the pretreated copper parts.

[0119] S2. Immerse the pretreated copper parts in a selenium salt blackening solution, which includes the following components at the following concentrations: copper nitrate 20g / L, selenite 1.5g / L, phosphoric acid 10mL / L, sodium citrate 0.5g / L, polyethylene glycol 1.0g / L, and deionized water as the solvent. Adjust the pH of the selenium salt blackening solution to 2.0 and soak at room temperature for 3 minutes, turning the workpiece every 1 minute to ensure uniform blackening. After blackening, a uniform black film with a thickness of 1.5μm is formed on the surface of the copper parts. After blackening, rinse the copper parts in running cold water at room temperature for 1 minute to obtain the blackened copper parts.

[0120] S3. Immerse the blackened copper part in a chromium-free passivation solution, which contains the following components by mass percentage: phytic acid 8%, citric acid 10%, benzotriazole 2%, calcium dihydrogen phosphate 4%, AEO-9 1%, and the balance is deionized water. Treat at 30°C for 45 seconds to form a passivation layer with a thickness of 15 nm on the surface of the black film, and obtain the passivated copper part. Rinse the passivated copper part with deionized water for 30 seconds, and then put it into a hot air circulating oven and dry at 110°C for 12 minutes.

[0121] S4. Mix 40 parts epoxy resin, 10 parts butyl glycidyl ether, 2 parts dispersant, 0.5 parts defoamer, 0.5 parts leveling agent and 20 parts solvent (xylene and n-butanol in a mass ratio of 7:3) evenly, then add 20 parts polyamide curing agent and mix evenly to obtain the primer.

[0122] Mix 60 parts of fluoropolymer resin, 10 parts of composite filler, 1 part of dispersant, 0.5 parts of defoamer and 0.5 parts of leveling agent evenly, then add 8 parts of isocyanate curing agent and mix evenly to obtain the topcoat;

[0123] The preparation method of the composite filler is as follows:

[0124] 3g of silicon carbide was dispersed in 100mL of deionized water, and then 1g of zinc nitrate, 1g of aluminum nitrate and 0.2g of cerium nitrate were added and stirred evenly. Then ammonia water was added to adjust the pH of the solution to 9.0. After mixing evenly, the solution was transferred to a hydrothermal reactor and hydrothermally reacted at 120℃ for 12h. After the reaction was completed, the composite filler was obtained by centrifugation, washing and drying.

[0125] First, the primer is sprayed onto the passivated copper surface with a thickness of 20μm and baked at 80℃ for 15min; then the topcoat is sprayed with a thickness of 25μm and cured at 100℃ for 3h to form a composite coating.

[0126] Compared with Example 1, Comparative Example 3 did not involve loading the composite filler with dithiocarbamate.

[0127] The composite coatings prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention were subjected to performance tests, as detailed below:

[0128] Wear resistance test: The test was conducted according to GB / T1768 "Determination of abrasion resistance of paints and varnishes - Rotary rubber grinding wheel method". The abrasion tester was set at a speed of 60 r / min, a load of 500 g, and a rotation speed of 500 r. The quality of the coating before and after wear was measured using an analytical balance, and the difference in quality before and after wear was calculated as the test data. The test was conducted 3 times, and the average value of the results was taken.

[0129] Adhesion test: The test method is in accordance with GB / T 9286-2021 "Paints and Varnishes Cross-cut Test", and the test is performed 3 times and the average value is taken.

[0130] Neutral salt spray test: The test method is in accordance with GB / T 10125-2012. The test is performed 3 times and the average value is taken.

[0131] Rust prevention performance test: The sample was placed at 60℃ and 90% humidity for 168h, and the rust area on the sample surface was measured. The test was repeated in three parallel tests, and the average value of the results was taken.

[0132] The test results are shown in Table 1.

[0133] Table 1 Performance test results for different groups

[0134]

[0135] As can be seen from the table, compared with comparative examples 1-3, the composite coating prepared in the embodiments of the present invention has the characteristics of strong adhesion, excellent corrosion resistance and wear resistance.

[0136] Finally, it should be noted that the above embodiments do not limit the present invention in any way. Those skilled in the art can make modifications and improvements based on the present invention. Therefore, any modifications or improvements made without departing from the spirit of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a composite coating on the surface of a copper part, characterized in that, Includes the following steps: S1. The copper parts are subjected to chemical degreasing, hot water washing, cold water washing, acid pickling activation, and cold water washing in sequence to obtain pretreated copper parts; S2. Immerse the pretreated copper parts in a selenium salt system blackening solution and treat at room temperature to generate a black film on the surface of the copper parts, thus obtaining blackened copper parts. S3. Immerse the blackened copper part in a chromium-free passivation solution and treat it at 20-40℃ for 30-60 seconds to form a passivation layer on the surface of the black film, thus obtaining the passivated copper part. S4. Apply primer and topcoat sequentially to the passivated copper surface to form a composite coating.

2. The preparation method according to claim 1, characterized in that, In step S2, the selenium salt system blackening solution includes the following components at the following concentrations: copper nitrate 20-25 g / L, selenite 1.5-2.0 g / L, phosphoric acid 10-12 mL / L, sodium citrate 0.5-1 g / L, polyethylene glycol 1.0-1.2 g / L, and deionized water as the solvent.

3. The preparation method according to claim 2, characterized in that, The pH of the blackening solution in the selenium salt system is 1.5-2.

5.

4. The preparation method according to claim 1, characterized in that, In step S3, the chromium-free passivation solution contains the following components by mass percentage: 5-10% phytic acid, 8-15% citric acid, 1-3% benzotriazole, 2-5% calcium dihydrogen phosphate, 0.5-2% nonionic surfactant, and the balance being deionized water.

5. The preparation method according to claim 1, characterized in that, In step S4, the primer comprises the following components in parts by weight: 40-60 parts epoxy resin, 10-15 parts butyl glycidyl ether, 2-5 parts dispersant, 0.5-2 parts defoamer, 0.5-2 parts leveling agent, 15-20 parts solvent, and 20-35 parts polyamide curing agent.

6. The preparation method according to claim 1, characterized in that, In step S4, the topcoat comprises the following components in parts by weight: 60-80 parts of fluoropolymer resin, 10-15 parts of modified composite filler, 1-3 parts of dispersant, 0.5-2 parts of defoamer, 0.5-2 parts of leveling agent, and 8-10 parts of isocyanate curing agent.

7. The preparation method according to claim 6, characterized in that, In step S4, the modified composite filler is prepared as follows: (1) Disperse silicon carbide in deionized water, then add zinc salt, aluminum salt and cerium salt to it, stir evenly, then add ammonia water to it, adjust the pH of the solution to 8.5-9.5, mix evenly and transfer to a hydrothermal reactor for hydrothermal reaction. After the reaction is completed, centrifuge, wash and dry to obtain composite filler; (2) Dissolve 3-amino-4-hydroxybenzoic acid in an aqueous ethanol solution, add carbon disulfide dropwise under nitrogen protection, adjust the pH of the solution to 10-12, stir the reaction, and after the reaction is completed, filter, wash and vacuum dry to obtain dithiocarbamate. (3) Under nitrogen protection, dithiocarbamate is dissolved in an aqueous ethanol solution, then the composite filler is added, stirred and treated, and then centrifuged, washed and vacuum dried to obtain the modified composite filler.

8. The preparation method according to claim 7, characterized in that, In step (1), the mass ratio of silicon carbide, zinc salt, aluminum salt and cerium salt is 3-5:1-2:1-2:0.2-0.

4.

9. The preparation method according to claim 7, characterized in that, In step (2), the molar ratio of 3-amino-4-hydroxybenzoic acid to carbon disulfide is 1:1.1-1.

3.

10. The preparation method according to claim 7, characterized in that, In step (3), the mass ratio of dithiocarbamate to composite filler is 1-2:3-5.

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