Surface treatment and pure water washing process of aluminum profile before electrostatic powder spraying

Abstract

The invention belongs to the technical field of profile surface treatment, and particularly relates to a surface treatment and pure water washing process of an aluminum profile before electrostatic powder spraying, and the process comprises degreasing, primary water washing, secondary water washing, passivation, circulating pure water washing and ultraviolet treatment. The repairing agent mercaptoethanol cinnamate is added into the passivation solution, the accelerant ceric ammonium nitrate has an oxidation effect, sulfydryl in the repairing agent is oxidized to form a disulfide bond, and the compactness of a film layer is improved; disulfide bonds formed by oxidation of sulfydryl in the cinnamic acid mercaptoethanol ester form a dynamic structure, so that the generated passivation film has a self-repairing effect, and benzene rings in the cinnamic acid mercaptoethanol ester are non-polar groups and ester groups are close to non-polarity, so that the conductivity error of the surface of the aluminum profile is remarkably reduced. Cinnamic acid groups in the passivation film on the surface of the aluminum profile have double bonds, and the double bonds are further polymerized through ultraviolet treatment, so that the network structure of the passivation film is enhanced, and the corrosion resistance is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of profile surface treatment, in particular to a surface treatment and pure water washing process of aluminum profile before electrostatic powder spraying. BACKGROUND

[0002] With the development of the times and the popularization of environmental protection consciousness, the traditional spraying process has poor processing capacity and is not consistent with the modern environmental protection concept in profile processing. The emerging electrostatic powder spraying process has greatly improved the profile processing problem and the environmental protection problem.

[0003] In the powder spraying process, the coating film performance is not only related to the characteristics of the powder coating, but also closely related to the spraying process parameters and the surface treatment of the profile. If the profile surface cannot be effectively cleaned in the pretreatment process, it will directly affect the spraying quality, resulting in problems such as blistering, peeling, uneven color, etc. Therefore, it is necessary to further remove the impurities on the surface through the pure water washing process, improve the cleaning degree of the workpiece, and reduce the electrical conductivity, thereby laying a foundation for high-quality spraying.

[0004] In the application number "CN201710278757.0" entitled "Powder spraying process of aluminum profile", the profile is not water washed after chromium passivation, and the water-free process can improve production efficiency, but the profile carries residual liquid, which affects the subsequent electrostatic powder spraying effect. In the application number "CN201310101733.X" entitled "Polyester powder spraying process of aluminum alloy profile", the aluminum alloy profile is washed three times, then chromiumized and washed three times. The water washing process is not only complicated, but also consumes a large amount of water. Moreover, the pure water is not used for cleaning, resulting in a high electrical conductivity of the aluminum alloy profile.

[0005] In order to improve the corrosion resistance of the aluminum profile, the existing technology usually adopts chromium-free passivation, but the passivation film formed has lower corrosion resistance than the traditional hexavalent chromium passivation film, and has insufficient self-repairing ability, which easily causes corrosion of the aluminum profile at scratches or cracks. In addition, in the actual aluminum profile surface electrical conductivity detection, in order to improve the detection efficiency and save time, it is not convenient to detect each aluminum profile, and the electrical conductivity of the pure water in the last cleaning tank in the circulating pure water washing is directly tested. However, the error between the electrical conductivity of the pure water after the pure water washing and the surface electrical conductivity of the aluminum profile is large, and the error is about 5 μs / cm. SUMMARY

[0006] In order to solve the problems in the prior art, the present application provides a surface treatment and pure water washing process of aluminum profile before electrostatic powder spraying, which improves the corrosion resistance and self-repairing performance of the profile, improves the surface cleanliness of the profile, reduces the electrical conductivity error of the profile surface, and lays a foundation for high-quality electrostatic powder spraying.

[0007] A surface treatment and pure water washing process of aluminum profile before electrostatic powder spraying, comprising the following steps: S1, degreasing The surface of the aluminum profile is sandblasted, and then the surface of the aluminum profile is sprayed with an acidic degreasing agent diluent for pre-degreasing treatment to remove surface oil stains; then the surface of the aluminum profile is sprayed with an acidic degreasing agent diluent for main degreasing treatment to further remove stubborn oil stains, and after the main degreasing is completed, a water washing link is entered to avoid the influence of residual acid liquid on subsequent processes.

[0008] Preferably, the temperature of the pre-degreasing treatment stage is 50-60°C, the spraying pressure is controlled at 0.1-0.2 MPa, the spraying amount is 8-12 L / (m 2 ·min), and the pre-degreasing time is adjusted according to the contamination degree of the profile, and the time is controlled at 3-8 min.

[0009] Preferably, the temperature of the main degreasing treatment stage is 50-60°C, the spraying pressure is controlled at 0.2-0.3 MPa, the spraying amount is 15-20 L / (m 2 ·min), and the time is 3-5 min.

[0010] Preferably, the acidic degreasing agent is commercially available, and the percentage of each component is: sulfuric acid accounts for 35-42 wt%, hydrofluoric acid accounts for 8-10 wt%, surfactant accounts for 4-6 wt%, metal chelating agent accounts for 4-6 wt%, and the rest is water.

[0011] Preferably, the effective content of the sulfuric acid is 98%.

[0012] Preferably, in the acidic degreasing agent diluent, the mass ratio of the acidic degreasing agent to water is 25:980-1020.

[0013] S2, primary water washing The aluminum profile after main degreasing is sprayed or soaked with tap water for primary water washing to remove residual degreasing agent on the surface of the aluminum profile, and to ensure that the residual acid concentration in the cleaning tank water is ≤1.0‰.

[0014] Preferably, the spraying pressure is controlled at 0.15-0.3 MPa, the spraying amount is 10-15 L / (m 2 ·min), and the time is 1-2 min.

[0015] Preferably, the soaking time is 5-10 min.

[0016] S3, secondary water washing: The aluminum profile after primary water washing is subjected to secondary water washing to further reduce the surface contaminant concentration.

[0017] Preferably, the secondary water washing adopts a countercurrent rinsing design, and the water flow is controlled at 3-5 L / (m 2• min), water washing time 0.5-1 min, ensuring the residual acid concentration in the water of the cleaning tank is ≤0.5 ‰.

[0018] The core of the reverse flow rinsing is that the water flow direction is opposite to the running direction of the aluminum profile, the water is injected from the end of the secondary water cleaning tank (aluminum profile outlet side) and flows to the front end of the secondary water cleaning tank (profile inlet side), and finally flows back from the front end to the cleaning tank of the primary water cleaning to supplement the water of the primary water cleaning.

[0019] S4, passivation The pH of the passivation solution is adjusted to 2.8-3.5, and then the aluminum profile after the secondary water cleaning is immersed in the passivation solution with adjusted pH for passivation treatment.

[0020] Preferably, the percentage of each component in the passivation solution is as follows: hydrofluoric acid accounts for 2-4 wt%, oxalic acid accounts for 1-3 wt%, fluorozirconic acid accounts for 3-5 wt%, film forming aid accounts for 0.1-0.3 wt%, polyacrylic acid accounts for 0.5-0.7 wt%, polyethylene glycol accounts for 0.2-0.4 wt%, chelating agent accounts for 1.5-2.5 wt%, accelerator accounts for 0.4-0.8 wt%, repair agent accounts for 0.5-0.7 wt%, dispersing agent accounts for 0.1-0.2 wt%, and the rest is water.

[0021] Preferably, the chelating agent is one or more of aminotri (methylene) phosphonic acid, ethylenediaminetetraacetic acid disodium salt, aminotri (methylene) phosphonic acid pentasodium salt, and ethylenediaminetetramethylene phosphonic acid.

[0022] Preferably, the film forming aid is one or more of γ-aminopropyl triethoxysilane and γ-glycidyl ether oxypropyl trimethoxysilane.

[0023] Preferably, the accelerator is cerium ammonium nitrate, and the dispersing agent is OP-10 emulsifier.

[0024] Preferably, the preparation method of the repair agent is as follows: cinnamic acid, 2-mercaptoethanol, catalyst, and anhydrous toluene are added to an esterification reactor, heated to reflux under nitrogen protection at 90-110 ℃, and water generated during the reaction is removed, and the reaction is considered to be completed when no water is generated, and the product is cinnamic acid mercaptoethanol ester; the product is washed with saturated sodium bicarbonate solution until it is neutral, and then vacuum dehydration is performed to obtain the repair agent.

[0025] Preferably, the molar ratio of cinnamic acid to 2-mercaptoethanol is 1:1-1.2.

[0026] Preferably, the amount of the catalyst p-toluenesulfonic acid added is 0.8-1.1% of the mass of cinnamic acid.

[0027] Preferably, the volume ratio of 2-mercaptoethanol to anhydrous toluene is 1:5-6.

[0028] Preferably, the temperature of the passivation treatment is 25-30℃, and the time is 3-5 min.

[0029] The functions of the components in the passivation solution are as follows: hydrofluoric acid is used to activate the surface of the aluminum profile; oxalic acid is used to complex Al 3+ and Zr 4+ , to slow down the film formation rate and make the film formation more uniform; fluorozirconic acid is the main film former; silane coupling agent is a film forming aid that improves the adhesion of the passivation film by forming Si-O-Al bonds; polyacrylic acid is used to fill the micropores of the passivation film layer and enhance the interaction between the film and the substrate by coordinating with Al 3+ and Zr 4+ ; the chelating agent prevents the passivation solution from precipitating; the promoter cerium ammonium nitrate not only speeds up film formation and optimizes the film structure, but also preferentially oxidizes the sulfhydryl group in the repair agent mercaptomethyl alcohol ester of cinnamic acid to form a disulfide bond, increasing the compactness of the film layer; the disulfide bond formed by the oxidation of the sulfhydryl group in the mercaptomethyl alcohol ester of cinnamic acid constitutes a dynamic structure, giving the passivation film self-repairing effect; the passivation time is relatively short, and the double bond in the mercaptomethyl alcohol ester of cinnamic acid is less reactive than the sulfhydryl group, so the double bond is basically preserved and further polymerized after subsequent ultraviolet treatment; the addition of polyethylene glycol provides a flexible segment, providing a basis for repair and filling.

[0030] S5, circulating pure water washing The passivated aluminum profile is subjected to circulating pure water washing by immersion or spraying to remove metal ions and small particles, and the surface conductivity is measured after draining.

[0031] Preferably, the conductivity of the pure water is ≤50 μS / cm.

[0032] Preferably, the spraying is provided with multiple stages of series-connected cleaning tanks, and the circulating pure water after washing is reused by entering the pure water tank again for subsequent use; to ensure that the conductivity of the pure water in the pure water tank is ≤50 μS / cm, old water can be discharged regularly and fresh pure water can be supplemented to maintain it; the series-connected cleaning tanks are designed to have 4 stages to ensure cleaning quality; the conductivity and pH value of the water in the pure water tank and the cleaning tank are detected every hour. The pH value of the pure water in the pure water tank is controlled between 6.8 and 8.0 to avoid the influence of excessive acidity or alkalinity on the adhesion of the coating, and the pH value can be adjusted by adding sodium bicarbonate solution.

[0033] Preferably, the spraying pressure is controlled at 0.5-1 MPa, the spraying amount is 10-15 L / (m 2 ·min), and the time is 1-2 min.

[0034] Preferably, the immersion time is 1-3 min, and the temperature is 20-30℃.

[0035] Preferably, the cleaning tank is made of 304 stainless steel or PP material, the inner wall is smooth and has no dead angle, residual dirt is avoided, and the tank is equipped with heating coil and circulating filtration system.

[0036] Preferably, the nozzle spacing and angle of the spray can be adjusted to ensure that the spray covers no blind area and high-pressure spray removes impurities in deep holes or gaps.

[0037] Preferably, the pure water is provided by a pure water preparation system, and the preparation process includes pretreatment and fine treatment.

[0038] Further, the pretreatment is to remove suspended solids and organic matter from tap water through sand filtration and activated carbon filtration, and then remove more than 90% of dissolved salts through an RO membrane; the fine treatment adopts a mixed bed ion exchange resin or an electrodeionization technology.

[0039] After the aluminum profile is washed by the circulating pure water and drained, there is a residual water film on the surface, and the detected conductivity value is actually the conductivity of the pure water in the residual water film. The thinner the residual water film, the closer the conductivity of the aluminum profile washed by the circulating pure water to the conductivity of the pure water, and the smaller the deviation, which is more conducive to production control. Since the benzene ring in the mercaptoethanol ester of cinnamic acid in the passivation film is a nonpolar group, and the ester group is close to nonpolarity, the amount of residual water film on the surface of the aluminum profile washed by the subsequent circulating pure water is significantly reduced, and the conductivity deviation between the pure water after the circulating water washing is smaller. When detecting, the conductivity of the pure water after the circulating water washing can be directly detected, saving detection time.

[0040] S6, ultraviolet treatment The aluminum profile surface washed by the circulating pure water is dried and treated by ultraviolet to obtain a surface-treated aluminum profile.

[0041] Preferably, the drying temperature is 70-80℃, and the time is 30-40min.

[0042] Preferably, the ultraviolet treatment temperature is 50-60℃, the light intensity is 30-40mW / cm 2 , the wavelength is 365nm, and the time is 20-30min.

[0043] The cinnamic acid group in the passivation film on the surface of the aluminum profile has a double bond, which is further polymerized through ultraviolet treatment, enhancing the network structure of the passivation film.

[0044] Due to the adoption of the above technical solutions, the present application has the following advantages: 1. The conductivity of the aluminum profile obtained by the surface treatment and pure water washing process provided by the present application is 20-30μS / cm, while the conductivity of the aluminum profile surface treated by the prior art is usually about 50μS / cm. The appropriate decrease in conductivity makes the subsequent electrostatic powder spraying effect better.

[0045] 2、The passivation film on the surface of the aluminum profile has strong adhesion, and the adhesion detected by the grid method is 0 level (determined according to GB / T9286-2021).

[0046] 3、The passivation film on the surface of the aluminum profile has excellent self-repairing ability, can effectively repair local scratches or cracks of the passivation film, and improves the protection effect of the passivation film on the aluminum profile.

[0047] 4、The passivation film on the surface of the aluminum profile has a dense structure, further improving the corrosion resistance of the aluminum profile.

[0048] 5、The conductivity of the aluminum profile obtained by the surface treatment and pure water washing process provided by the application is controllable, detection is more convenient, error is smaller, and quality control is more beneficial. DETAILED DESCRIPTION

[0049] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined object, the specific embodiments, structures, features and effects according to the present application will be described in detail as follows.

[0050] Example 1: A surface treatment and pure water washing process of an aluminum profile before electrostatic powder spraying, comprising the following steps: S1, degreasing The surface of the aluminum profile is subjected to sand blasting treatment, and then an acidic degreasing agent diluent is sprayed on the surface of the aluminum profile for pre-degreasing treatment to remove surface oil stains. Then, the surface of the aluminum profile is sprayed with an acidic degreasing agent diluent for main degreasing treatment to further remove stubborn oil stains. After the main degreasing is completed, the water washing link is entered to avoid the influence of residual acid liquid on the subsequent process.

[0051] The temperature of the pre-degreasing treatment stage is 55℃, the spraying pressure is controlled at 0.15MPa, the spraying amount is 10L / (m 2 ·min), and the time is 5min.

[0052] The temperature of the main degreasing treatment stage is 55℃, the spraying pressure is controlled at 0.25MPa, the spraying amount is 17L / (m 2 ·min), and the time is 4min.

[0053] The acidic degreasing agent is commercially available, and the percentage of each component is as follows: sulfuric acid accounts for 40wt%, hydrofluoric acid accounts for 10wt%, surfactant sodium dodecyl sulfate accounts for 5wt%, metal chelating agent aminotri-methylene phosphonic acid accounts for 5wt%, and the rest is water.

[0054] The effective content of the sulfuric acid is 98%.

[0055] The mass ratio of the acidic degreasing agent and water in the acidic degreasing agent diluent is 25:1000.

[0056] S2, primary water washing The primary degreased aluminum profile is sprayed with tap water for primary water washing to remove the residual degreasing agent on the surface of the aluminum profile, and the residual acid concentration in the water in the cleaning tank is 0.8 ‰.

[0057] The spraying pressure is controlled at 0.25 MPa, the spraying amount is 12 L / (m 2 ·min), and the time is 1.5 min.

[0058] S3, secondary water washing The primary water washed aluminum profile is subjected to secondary water washing to further reduce the surface contaminant concentration.

[0059] The secondary water washing adopts a countercurrent rinsing design, the water flow is controlled at 4 L / (m 2 ·min), the water washing time is 0.8 min, and the residual acid concentration in the water in the cleaning tank is 0.4 ‰.

[0060] The core of the countercurrent rinsing is that the water flow direction is opposite to the running direction of the aluminum profile, the water is injected from the end of the secondary water washing cleaning tank (the aluminum profile outlet side) and flows to the front end of the secondary water washing cleaning tank (the profile inlet side), and finally flows back from the front end to the cleaning tank of the primary water washing to supplement the water for the primary water washing.

[0061] S4, passivation The pH of the passivation liquid is adjusted to 3, and the secondary water washed aluminum profile is immersed in the passivation liquid with adjusted pH for passivation treatment.

[0062] The percentage of each component in the passivation liquid is as follows: 3wt% of hydrofluoric acid, 2wt% of oxalic acid, 4wt% of fluorozirconic acid, 0.2wt% of film forming aid, 0.6wt% of polyacrylic acid, 0.3wt% of polyethylene glycol, 2wt% of chelating agent, 0.7wt% of promoter, 0.7wt% of repair agent, 0.15wt% of dispersing agent, and the rest is water.

[0063] The chelating agent is aminotri (methylene) phosphonic acid, the film forming aid is γ-aminopropyl triethoxysilane, the promoter is cerium ammonium nitrate, and the dispersing agent is OP-10 emulsifier.

[0064] The molecular weight of the polyacrylic acid is 2000, and the molecular weight of the polyethylene glycol is 600.

[0065] The preparation method of the repair agent is as follows: cinnamic acid, 2-mercaptoethanol, a catalyst, and anhydrous toluene are added into an esterification reactor, heated to reflux at 100℃ under nitrogen protection, water generated in the reaction is removed, and the reaction is considered to be completed when no water is generated, and the product is cinnamic acid mercaptoethanol ester; the product is washed with saturated sodium bicarbonate solution until neutral, and then dehydrated under vacuum to obtain the repair agent.

[0066] The molar ratio of the cinnamic acid to the 2-mercaptoethanol is 1:1.1.

[0067] The catalyst is p-toluenesulfonic acid, and the addition amount is 1% of the mass of the cinnamic acid.

[0068] The volume ratio of the 2-mercaptoethanol to the anhydrous toluene is 1:5.5.

[0069] The temperature of the passivation treatment is 28℃, and the time is 4 min.

[0070] S5, circulating pure water washing The aluminum profile after passivation is washed with circulating pure water by spraying to remove metal ions and small particles, and the surface conductivity is measured after draining.

[0071] The conductivity of the pure water is 20 μS / cm.

[0072] The spraying is provided with four cleaning tanks in series, and the circulating pure water after washing is reused by reverse flow technology; the pure water in the pure water tank is adjusted to a pH value of 7.5 by adding sodium bicarbonate solution.

[0073] The spraying pressure is controlled at 0.7 MPa, the spraying amount is 12 L / (m 2 ·min), and the time is 1.5 min.

[0074] The cleaning tank is made of 304 stainless steel, the inner wall is smooth and has no dead angle to avoid residual dirt, and the tank body is equipped with heating coil and circulating filtration system.

[0075] The nozzle spacing of the spraying is 20 cm, and the angle is 45°.

[0076] The pure water is provided by a pure water preparation system, and the preparation process includes pretreatment and fine treatment.

[0077] The pretreatment is as follows: the tap water is filtered through sand and activated carbon to remove suspended solids and organic matter, and then more than 90% of dissolved salts are removed by an RO membrane; the fine treatment adopts a mixed bed ion exchange resin technology.

[0078] S6, ultraviolet treatment The aluminum profile after circulating pure water washing is dried, and the surface treated aluminum profile is obtained after ultraviolet treatment.

[0079] The temperature of the drying is 75℃, and the time is 35min.

[0080] The temperature of the ultraviolet treatment is 55℃, the light intensity is 35mW / cm 2 , the wavelength is 365nm, and the time is 25min.

[0081] Embodiment 2: A surface treatment and pure water washing process of an aluminum profile before electrostatic powder spraying, comprising the following steps: S1, degreasing The surface of the aluminum profile is subjected to sand blasting treatment, and then the surface of the aluminum profile is sprayed with an acidic degreasing agent diluent for pre-degreasing treatment to remove surface oil stains; then the surface of the aluminum profile is sprayed with an acidic degreasing agent diluent for main degreasing treatment to further remove stubborn oil stains, and after the main degreasing is completed, a water washing link is entered to avoid the influence of residual acid liquid on subsequent processes.

[0082] The temperature of the pre-degreasing treatment stage is 50℃, the spraying pressure is controlled at 0.1MPa, the spraying amount is 12L / (m 2 ·min), and the time is 8min.

[0083] The temperature of the main degreasing treatment stage is 50℃, the spraying pressure is controlled at 0.2MPa, the spraying amount is 20L / (m 2 ·min), and the time is 3min.

[0084] The acidic degreasing agent is commercially available, wherein the percentage of each component is: 35wt% of sulfuric acid, 10wt% of hydrofluoric acid, 4wt% of surfactant sodium dodecyl sulfate, 4wt% of metal chelating agent amino-trimethylene phosphonic acid, and the rest is water.

[0085] The effective content of the sulfuric acid is 98%.

[0086] In the acidic degreasing agent diluent, the mass ratio of the acidic degreasing agent to water is 25:980.

[0087] S2, primary water washing The aluminum profile after the main degreasing is sprayed with tap water for primary water washing to remove the residual degreasing agent on the surface of the aluminum profile, and the residual acid concentration in the cleaning tank is 0.8‰.

[0088] The spraying pressure is controlled at 0.15MPa, the spraying amount is 10L / (m 2 ·min), and the time is 2min.

[0089] S3, secondary water washing: The aluminum profile after the primary water washing is subjected to secondary water washing to further reduce the surface pollutant concentration.

[0090] The secondary water washing adopts a countercurrent rinsing design, and the water flow is controlled at 3 L / (m 2 ·min), and the washing time is 1 min, until the residual acid concentration in the water in the cleaning tank is 0.4 ‰.

[0091] The core of the countercurrent rinsing is that the water flow direction is opposite to the running direction of the aluminum profile, the water is injected from the end of the cleaning tank of the secondary water washing (the aluminum profile outlet side), flows to the front end of the cleaning tank of the secondary water washing (the profile inlet side), and finally flows back from the front end to the cleaning tank of the primary water washing to supplement the water for the primary water washing.

[0092] S4, passivation The pH of the passivation solution is adjusted to 2.8, and then the aluminum profile after the secondary water washing is immersed in the passivation solution with adjusted pH for passivation treatment.

[0093] The percentage of each component in the passivation solution is as follows: 2wt% of hydrofluoric acid, 3wt% of oxalic acid, 3wt% of fluorozirconic acid, 0.1wt% of film forming aid, 0.5wt% of polyacrylic acid, 0.2wt% of polyethylene glycol, 1.5wt% of chelating agent, 0.4wt% of promoter, 0.5wt% of repair agent, 0.1wt% of dispersing agent, and the rest is water.

[0094] The chelating agent is aminotri (methylene) phosphonic acid, the film forming aid is γ-aminopropyl triethoxysilane, the promoter is cerium ammonium nitrate, and the dispersing agent is OP-10 emulsifier.

[0095] The molecular weight of the polyacrylic acid is 2000, and the molecular weight of the polyethylene glycol is 600.

[0096] The preparation method of the repair agent is as follows: cinnamic acid, 2-mercaptoethanol, catalyst, anhydrous toluene are added to an esterification reactor, heated to reflux under nitrogen protection at 90℃, and water generated during the reaction is removed, until no water is generated, which is regarded as the end of the esterification reaction, and the product is cinnamic acid mercaptoethanol ester; the product is washed with saturated sodium bicarbonate solution until neutral, and vacuum dehydration is performed to obtain the repair agent.

[0097] The molar ratio of the cinnamic acid and 2-mercaptoethanol is 1:1.

[0098] The catalyst is p-toluenesulfonic acid, and the addition amount is 0.8% of the mass of the cinnamic acid.

[0099] The volume ratio of the 2-mercaptoethanol and anhydrous toluene is 1:5.

[0100] The temperature of the passivation treatment is 25℃, and the time is 5 min.

[0101] S5, circulating pure water washing The passivated aluminum profiles were washed with pure water by spraying to remove metal ions and tiny particles. After draining, the surface conductivity was measured.

[0102] The conductivity of the pure water is 20 μS / cm.

[0103] The spray system is equipped with four-stage series cleaning tanks. Through countercurrent recycling technology, the pure water used for the pure water washing is recycled back into the pure water tank for reuse. The pH value of the pure water in the pure water tank is adjusted to 7.5 by adding sodium bicarbonate solution.

[0104] The spraying pressure is controlled at 0.5 MPa, and the spraying rate is 10 L / (m³). 2 (min), the time is 2 minutes.

[0105] The cleaning tank is made of 304 stainless steel with a smooth inner wall and no dead corners to avoid residual dirt. The tank is equipped with a heating coil and a circulating filtration system.

[0106] The nozzles of the spray system are spaced 20cm apart and angled at 45°.

[0107] The pure water is provided by a pure water preparation system, the preparation process of which includes pretreatment and fine treatment.

[0108] The pretreatment involves removing suspended solids and organic matter from tap water through sand filtration and activated carbon filtration, and then removing more than 90% of dissolved salts through an RO membrane; the fine treatment uses mixed-bed ion exchange resin technology.

[0109] S6, UV treatment The aluminum profile is dried after being washed with circulating pure water and then subjected to ultraviolet treatment to obtain a surface-treated aluminum profile.

[0110] The drying temperature is 70°C and the time is 30 minutes.

[0111] The ultraviolet treatment temperature was 50℃, and the light intensity was 30mW / cm². 2 The wavelength was 365nm and the time was 30min.

[0112] Example 3: A surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating, including the following steps: S1, degreasing The aluminum profile surface is sandblasted, and then pre-degreased by spraying the surface with diluted acidic degreaser to remove surface oil. Next, the surface of the aluminum profile is sprayed with diluted acidic degreaser for main degreasing to further remove stubborn oil. After the main degreasing is completed, the aluminum profile enters the water washing stage to avoid residual acid affecting subsequent processes.

[0113] The temperature of the pre-degreasing treatment stage is 60°C, the spraying pressure is controlled at 0.2 MPa, the spraying amount is 8 L / (m 2 ·min), and the time is 3 min.

[0114] The temperature of the main degreasing treatment stage is 60°C, the spraying pressure is controlled at 0.3 MPa, the spraying amount is 15 L / (m 2 ·min), and the time is 5 min.

[0115] The acid degreasing agent is commercially available, wherein the percentages of the components are as follows: 42 wt% of sulfuric acid, 8 wt% of hydrofluoric acid, 6 wt% of the surfactant sodium dodecyl sulfate, 6 wt% of the metal chelating agent aminotri(methylene) phosphonic acid, and the rest is water.

[0116] The effective content of the sulfuric acid is 98%.

[0117] In the acid degreasing agent diluent, the mass ratio of the acid degreasing agent to water is 25:1020.

[0118] S2, primary water washing The aluminum profile after the main degreasing is sprayed with tap water for primary water washing to remove the residual degreasing agent on the surface of the aluminum profile, and the residual acid concentration in the cleaning tank is 0.8 ‰.

[0119] The spraying pressure is controlled at 0.3 MPa, the spraying amount is 15 L / (m 2 ·min), and the time is 1 min.

[0120] S3, secondary water washing The aluminum profile after the primary water washing is subjected to secondary water washing to further reduce the surface contaminant concentration.

[0121] The secondary water washing adopts a countercurrent rinsing design, the water flow is controlled at 5 L / (m 2 ·min), the water washing time is 0.5 min, and the residual acid concentration in the cleaning tank is 0.4 ‰.

[0122] The core of the countercurrent rinsing is that the water flow direction is opposite to the running direction of the aluminum profile, the water is injected from the end of the secondary water washing cleaning tank (the aluminum profile outlet side) and flows to the front end of the secondary water washing cleaning tank (the profile inlet side), and finally flows back from the front end to the cleaning tank of the primary water washing to supplement the water for the primary water washing.

[0123] S4, passivation The pH of the passivation liquid is adjusted to 3.5, and then the aluminum profile after the secondary water washing is immersed in the passivation liquid with the adjusted pH for passivation treatment.

[0124] The percentages of each component in the passivation solution are as follows: hydrofluoric acid 4 wt%, oxalic acid 1 wt%, fluorozirconic acid 5 wt%, film-forming aid 0.3 wt%, polyacrylic acid 0.7 wt%, polyethylene glycol 0.4 wt%, chelating agent 2.5 wt%, accelerator 0.8 wt%, repair agent 0.6 wt%, dispersant 0.2 wt%, and the remainder is water.

[0125] The chelating agent is aminotrimethylenephosphonic acid, the film-forming aid is γ-aminopropyltriethoxysilane, the accelerator is cerium ammonium nitrate, and the dispersant is OP-10 emulsifier.

[0126] The polyacrylic acid has a molecular weight of 2000, and the polyethylene glycol has a molecular weight of 600.

[0127] The preparation method of the repair agent is as follows: cinnamic acid, 2-mercaptoethanol, catalyst, and anhydrous toluene are added to an esterification reactor and heated to reflux at 110°C under nitrogen protection. During the reaction, the generated water is removed, and the esterification reaction is considered to be completed when no more water is generated. The product is cinnamic acid mercaptoethanol ester. The product is washed with saturated sodium bicarbonate solution until neutral and dehydrated under vacuum to obtain the repair agent.

[0128] The molar ratio of cinnamic acid to 2-mercaptoethanol is 1:1.2.

[0129] The catalyst is p-toluenesulfonic acid, and the amount added is 1.1% of the mass of cinnamic acid.

[0130] The volume ratio of 2-mercaptoethanol to anhydrous toluene is 1:6.

[0131] The passivation treatment was performed at a temperature of 30°C for 3 minutes.

[0132] S5, Circulating pure water washing The passivated aluminum profiles were washed with pure water by spraying to remove metal ions and tiny particles. After draining, the surface conductivity was measured.

[0133] The conductivity of the pure water is 20 μS / cm.

[0134] The spray system is equipped with four-stage series cleaning tanks. Through countercurrent recycling technology, the pure water used for the pure water washing is recycled back into the pure water tank for reuse. The pH value of the pure water in the pure water tank is adjusted to 7.5 by adding sodium bicarbonate solution.

[0135] The spraying pressure is controlled at 1 MPa, and the spraying rate is 15 L / (m³). 2 (·min), the time is 1min.

[0136] The cleaning tank is made of 304 stainless steel, the inner wall is smooth without dead angle, avoiding residual dirt, the tank is equipped with heating coil and circulating filtration system.

[0137] The nozzle spacing of the spray is 20 cm, and the angle is 45°.

[0138] The pure water is provided by a pure water preparation system, and the preparation process includes pretreatment and fine treatment.

[0139] The pretreatment is to remove suspended solids and organic matter by sand filtration and activated carbon filtration, and then remove more than 90% of dissolved salts by RO membrane; the fine treatment adopts mixed bed ion exchange resin technology.

[0140] S6, ultraviolet treatment The surface of the aluminum profile washed by the circulating pure water is dried, and the surface treated aluminum profile is obtained after ultraviolet treatment.

[0141] The drying temperature is 80℃, and the time is 40min.

[0142] The ultraviolet treatment temperature is 60℃, the light intensity is 40mW / cm 2 , the wavelength is 365nm, and the time is 20min.

[0143] Comparative Example 1: Select a representative of Example 1, remove the repair agent in the passivation solution, and the rest is consistent with Example 1, as Comparative Example 1.

[0144] Comparative Example 2: Select a representative of Example 1, do not do ultraviolet treatment after drying in S6 step, and the rest is consistent with Example 1, as Comparative Example 2.

[0145] Comparative Example 3: Select a representative of Example 1, replace the promoter cerium ammonium nitrate in the passivation solution with an equal amount of triethanolamine, and the rest is consistent with Example 1, as Comparative Example 3.

[0146] The conductivity of the pure water in the last stage cleaning tank after the circulating pure water washing step of Examples 1-3 and Comparative Examples 1-3 is 20μS / cm.

[0147] The surface treated aluminum profiles obtained in Examples 1-3 and Comparative Examples 1-3 are subjected to performance detection, and the specific table is as follows.

[0148] Table 1 Table 2 The self-repairing experiment method is as follows: the samples of examples 1-3 and comparative examples 1-3 are cut with a blade to form a scratch with a depth of 0.5 μm, a width of 3 μm and a length of 1 cm, and then placed in an environment with a temperature of 80 ℃ and a humidity of 60% for 24 h, and then the appearance change is observed, and the corrosion resistance after repair is determined.

[0149] The corrosion resistance test is determined according to the CASS test method in GB / T 10125-2021, and the test period is 24 h, and the corrosion resistance is reflected by calculating the weight loss rate.

[0150] As can be seen from tables 1 and 2, comparative example 1 has no repairing agent, the non-polar group in the passivation film is reduced, resulting in a large error between the surface conductivity of the aluminum profile and the conductivity of pure water; since there is no repairing agent, the passivation film has poor compactness, the corrosion resistance is poor, the scratch on the surface is difficult to repair, the corrosion medium diffuses rapidly, and the weight loss rate after scratch treatment is higher.

[0151] Comparative example 2 removes the ultraviolet treatment, the double bond in the passivation film is difficult to polymerize, the number of pores in the film layer increases, resulting in a higher error between the surface conductivity of the aluminum profile and the conductivity of pure water than example 1, but better than comparative example 1; the corrosion resistance is poor, and the weight loss rate is slightly higher; the scratch repair effect after self-repairing is good, and the weight loss rate after self-repairing is basically unchanged.

[0152] Comparative example 3 replaces the accelerator with triethanolamine, which only promotes film formation but has no oxidizing property, the mercapto group in the repairing agent is difficult to form a disulfide bond, and the subsequent ultraviolet treatment efficiency is low, resulting in a decrease in the compactness of the film layer, a higher error between the surface conductivity of the aluminum profile and the conductivity of pure water than example 1, but better than comparative example 1; the weight loss rate is higher, the repairing ability is poor, the scratch on the surface is difficult to repair, and therefore the weight loss rate after self-repairing is also higher.

[0153] As can be seen from the above, the aluminum profile treated by the method of examples 1-3 has not only a small conductivity error, but also better corrosion resistance and self-repairing ability.

[0154] Unless otherwise specified, the proportions described in the present application are mass proportions, and the percentages are mass percentages; the raw materials are commercially available.

[0155] The above description is only a preferred embodiment of the present application, and does not limit the present application in any form, although the present application has been disclosed as above with a preferred embodiment, however, it is not intended to limit the present application, any person skilled in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the technical solution of the present application, and equivalent embodiments with equivalent changes are equivalent to the above embodiments, but any simple modification, equivalent change and modification made on the basis of the technical essence of the present application to the above embodiments are still within the scope of the technical solution of the present application.

Claims

1. A surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating, characterized in that, The surface treatment and pure water washing process includes degreasing, primary water washing, secondary water washing, passivation, circulating pure water washing, and ultraviolet treatment; The passivation process involves adjusting the pH of the passivation solution to 2.8–3.5, and then immersing the aluminum profile after secondary water washing into the pH-adjusted passivation solution for passivation treatment. The percentages of each component in the passivation solution are as follows: hydrofluoric acid 2-4 wt%, oxalic acid 1-3 wt%, fluorozirconic acid 3-5 wt%, film-forming aid 0.1-0.3 wt%, polyacrylic acid 0.5-0.7 wt%, polyethylene glycol 0.2-0.4 wt%, chelating agent 1.5-2.5 wt%, accelerator 0.4-0.8 wt%, repair agent 0.5-0.7 wt%, dispersant 0.1-0.2 wt%, and the remainder is water; The chelating agent is one or more of the following: aminotrimethylenephosphonic acid, disodium ethylenediaminetetraacetate, pentasodium aminotrimethylenephosphonate, and ethylenediaminetetramethylenephosphonic acid. The film-forming aid is one or more of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; The accelerator is cerium ammonium nitrate, and the dispersant is OP-10 emulsifier; The preparation method of the repair agent is as follows: cinnamic acid, 2-mercaptoethanol, catalyst, and anhydrous toluene are added to an esterification reactor and heated to reflux at 90-110°C under nitrogen protection. During the reaction, the generated water is removed, and the esterification reaction is considered to be complete when no more water is generated. The product is cinnamic acid mercaptoethanol ester. The product is washed with saturated sodium bicarbonate solution until neutral and dehydrated under vacuum to obtain the repair agent. The ultraviolet treatment involves drying the surface of the aluminum profile after it has been washed with circulating pure water, and then performing ultraviolet treatment to obtain a surface-treated aluminum profile.

2. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 1, characterized in that, The molar ratio of cinnamic acid to 2-mercaptoethanol is 1:1 to 1.2; The catalyst is p-toluenesulfonic acid, and the amount added is 0.8-1.1% of the mass of cinnamic acid. The volume ratio of 2-mercaptoethanol to anhydrous toluene is 1:5 to 6; The passivation treatment is performed at a temperature of 25–30°C for 3–5 minutes.

3. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 1, characterized in that, The degreasing process involves sandblasting the surface of the aluminum profile, then spraying the surface of the aluminum profile with a diluted acidic degreasing agent for pre-degreasing treatment; followed by spraying the surface of the aluminum profile with a diluted acidic degreasing agent for main degreasing treatment, and finally, proceeding to the water washing stage after the main degreasing is completed.

4. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 3, characterized in that, The temperature during the pre-degreasing treatment stage is 50–60℃, the spray pressure is controlled at 0.1–0.2 MPa, and the spray volume is 8–12 L / (m³). 2 (min), time is 3-8 minutes; The temperature of the main degreasing stage is 50–60℃, the spray pressure is controlled at 0.2–0.3 MPa, and the spray volume is 15–20 L / (m³). 2 (min), time is 3-5 minutes; In the diluted acidic degreasing agent solution, the mass ratio of acidic degreasing agent to water is 25:980-1020; the acidic degreasing agent is commercially available.

5. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 1, characterized in that, The first-stage water washing involves spraying or immersing the aluminum profile after degreasing with tap water. The spraying pressure is controlled at 0.15–0.3 MPa, and the spraying rate is 10–15 L / (m³). 2 (min), the time is 1 to 2 minutes.

6. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 1, characterized in that, The secondary water washing involves further reducing the concentration of surface contaminants by washing the aluminum profiles after the primary water washing. The secondary water wash adopts a counter-current rinsing design, with the water flow rate controlled at 3-5 L / (m³). 2 (·min), washing time 0.5~1min.

7. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 1, characterized in that, The circulating pure water washing involves using pure water to immerse or spray the passivated aluminum profiles in circulating pure water. The conductivity of the pure water is ≤50μS / cm.

8. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 7, characterized in that, The circulating pure water washing system is equipped with a multi-stage series cleaning tank. The spraying pressure is controlled at 0.5–1 MPa, and the spraying rate is 10–15 L / (m³). 2 (min), the time is 1 to 2 minutes.

9. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 7, characterized in that, The pure water is provided by a pure water preparation system, the preparation process of which includes pretreatment and fine treatment; The pretreatment involves removing suspended solids and organic matter from tap water through sand filtration and activated carbon filtration, and then removing more than 90% of dissolved salts through an RO membrane; the fine treatment uses mixed-bed ion exchange resin or electro-deionization technology.

10. The surface treatment and pure water washing process for aluminum profiles before electrostatic powder coating according to claim 1, characterized in that, The drying temperature is 70-80℃, and the time is 30-40 minutes; The ultraviolet treatment temperature is 50–60℃, and the light intensity is 30–40 mW / cm². 2 The wavelength is 365nm and the time is 20-30min.

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