Trivalent chromium passivation solution and preparation method thereof

Abstract

The invention discloses a trivalent chromium passivation solution and a preparation method thereof, and relates to the field of surface treatment. The trivalent chromium passivation solution comprises trivalent chromium salt, a bluing agent, a dispersing agent, a solvent and an auxiliary agent, wherein the bluing agent comprises cobalt salt and acid blue dye; the dispersing agent comprises isomeric alcohol ether succinic acid monoester sodium sulfonate and polyethylene glycol 20000. The bluing agent and the dispersing agent are added, so that the problem that a blue-white passivation film of traditional trivalent chromium blue-white passivation is unstable and uneven is solved; cobalt salt and zinc are replaced on the surface of a plating layer to form Zn-Co alloy, the corrosion resistance is enhanced, but due to the fact that a zinc plating layer is affected by current gradient and concentration polarization in the electroplating process, metal deposition distribution is not uniform, cobalt salt is not uniform in distribution in the plating layer, blue dye and cobalt salt jointly form a bluing agent, the dye in a passivating agent solution has a bluing effect, and the bluing effect is good. Adsorption belongs to diffusion control, after fine gaps are formed in a zinc coating through acid etching, dye is adsorbed by the surfaces of the gaps, and then the gaps are sealed by auxiliaries.

Description

Technical Field

[0001] The present application relates to the field of surface treatment technology, and in particular to a trivalent chromium passivation solution and a preparation method thereof. Background Art

[0002] Hexavalent chromium conversion coating is widely used in the anti-corrosion protection of zinc coating, but Cr 6+ It is a carcinogen with high toxicity. At the same time, due to the continuous progress of environmental protection policies, Cr 6+ Its application has been greatly restricted. Summary of the invention

[0003] The present application provides a trivalent chromium passivation solution and a preparation method thereof, so as to solve the problems of high toxicity and uneven blueing of the existing passivation film.

[0004] In a first aspect, the present application provides a trivalent chromium passivation solution, including a trivalent chromium salt, a bluing agent, a dispersant, a solvent and an auxiliary agent, wherein:

[0005] The bluing agent includes a cobalt salt and an acid blue dye;

[0006] The dispersant comprises sodium isomeric alcohol ether succinic acid monoester sulfonate and polyethylene glycol 20000.

[0007] The traditional hexavalent chromium passivation film is formed by the dissolution of zinc, the reduction of chromate and the precipitation of trivalent chromium gel. The formation of the conversion film is a dynamic process. Therefore, the passivation film has the ability to repair itself, also known as self-healing ability. 6+ In the conversion film, Cr actually plays the role of isolating corrosion. 6+ Cr generated after reduction 3+ ,Cr 3+ Directly react with zinc ions, hydroxide, etc. to form insoluble compounds that precipitate on the zinc surface, and Cr 3+ The only toxicity is Cr 6+ 1%, but with Cr 6+ In comparison, Cr 3+ The passivation solution should make up for Cr 6+ The oxidizability of Cr 3+ Not oxidized to Cr 6+ In addition, the related reaction of chromium ion is a first-order reaction. 6+ Reduction to Cr 3+ In the reaction, Cr 3+ The formation of Cr(OH)3 is slow, so the Cr(OH)3 gel and other insoluble substances are dispersed evenly in the generated passivation film; 3+ In the passivation solution, Cr 3+It exists in the form of hydrated complex ions, and its reaction kinetic constant is extremely small, the reaction is slow, and the conversion film formed is poorly stable and dull; therefore, a certain amount of complexing agent must be added to increase the kinetic constant of the complex ion reaction with chromium ions, which is conducive to the reaction. 3+ The composition of the passivation solution is complex and the stability is poor. Especially in the blue-white passivation solution, the blue conversion film often appears uneven blue or even no blue. At the same time, because the formation of the conversion film is one-time, the Cr 6+ The self-healing ability of Cr 6+ .

[0008] In this application, by adding bluing agent and dispersant, the problem of instability and unevenness of the blue-white passivation film of traditional trivalent chromium blue-white passivation is solved. Cobalt salt is electrochemically controlled on the surface of the coating, and replaces with zinc to form Zn-Co alloy, which enhances corrosion resistance. However, due to the influence of current gradient and concentration polarization on the zinc coating during electroplating, the metal deposition distribution is uneven, so the cobalt salt is also unevenly distributed in the coating. The blueing agent is composed of blue dye and cobalt salt. The dye is in the passivator solution, and its adsorption belongs to diffusion control. When the zinc coating is etched with fine gaps, the dye is adsorbed on the surface of the gap, and then the gap is sealed by the auxiliary agent to form a nano-sized organic-inorganic hybrid blue-white film, which improves the uniformity of the blue-white film, and the trivalent chromium salt reduces the toxicity of the passivation solution. The cobalt salt in the bluing agent replaces with zinc to form a Zn-Co alloy, which enhances corrosion resistance. The blue dye in the bluing agent makes up for the uneven blue part, improves the uniformity of blue, and the dispersant assists in dispersing the blue dye, further improving the uniformity of blue.

[0009] In some embodiments, the mass proportion of the bluing agent in the trivalent chromium passivation solution is 0.6% to 5.5%. The mass proportion of the bluing agent in the trivalent chromium passivation solution within this range can provide a suitable blue dye, present a good visual effect, and can synergize with the dispersant to improve the problem of instability and unevenness of the blue film; and / or,

[0010] In some embodiments, the mass proportion of the dispersant in the trivalent chromium passivation solution is 1.0% to 2.5%. The mass proportion of the dispersant in the trivalent chromium passivation solution is within this range, which can evenly disperse the blue dye and synergize with the bluing agent to solve the problem of unstable and uneven blue film.

[0011] In some embodiments, the trivalent chromium salt includes at least one of chromium nitrate nonahydrate and chromium chloride hexahydrate, which can provide a suitable trivalent chromium salt; and / or,

[0012] The mass proportion of the trivalent chromium salt in the trivalent chromium passivation solution is 20.0% to 40.0%. Within this range, the trivalent chromium salt can serve as a skeleton to form a network structure in the passivation solution, providing a key component for film formation.

[0013] In some embodiments, the auxiliary agent includes nitrate, complexing agent, reducing agent, film-forming promoter and sealing agent. The auxiliary agent can help the surface treatment process of the passivation solution and improve the passivation effect. Nitrate can accelerate the film-forming speed, prevent the passivation film from atomizing, and improve the brightness of the passivation film. The complexing agent can activate the zinc layer and form a complex with trivalent chromium, which is conducive to the trivalent chromium ions forming a uniform and dense passivation film on the surface of the zinc-plated layer. The reducing agent can stabilize the trivalent chromium, the film-forming promoter can use anions to accelerate the micro-anode reaction, activate the solid-liquid interface to promote film formation, and the sealing agent can improve the corrosion resistance of the passivation film.

[0014] In some embodiments, the nitrate includes at least one of sodium nitrate, ammonium nitrate and potassium nitrate. Using at least one of the above nitrates can accelerate the film forming speed, prevent the passivation film from being atomized, and improve the brightness of the passivation film; and / or,

[0015] The complexing agent includes at least one of oxalic acid, malonic acid, tartaric acid and citric acid. At least one of the complexing agents can form a complex with trivalent chromium, which is conducive to the formation of a uniform and dense passivation film of trivalent chromium ions on the surface of the zinc-plated layer; and / or,

[0016] The reducing agent includes at least one of sodium hypophosphite, potassium hypophosphite and ammonium hypophosphite. At least one of the reducing agents can stabilize trivalent chromium. When the pH of the passivation solution rises to 4-5, Zn in the solution 2+ ,Cr 3+ , and PO4 3- It will react on the surface of the zinc coating to form insoluble zinc phosphate and chromium phosphate, which together with the trivalent chromium skeleton form a passivation film; and / or,

[0017] The film-forming promoter includes at least one of nickel nitrate and nickel chloride. By using at least one of the above film-forming promoters, anions can be used to accelerate the micro-anode reaction and activate the solid-liquid interface to promote film formation. - Can improve the brightness of the passivation film, Cl - It is beneficial to form a reactive passivation film with a certain thickness and shorten the passivation time; and / or,

[0018] The sealant includes fluorozirconate and silane coupling agent. The use of the sealant can improve the corrosion resistance of the passivation film without the need for subsequent sealing treatment.

[0019] In some embodiments, the mass ratio of trivalent chromium salt, nitrate, complexing agent, reducing agent, bluing agent, dispersant, film-forming promoter and sealing agent is (20-40): (1-5): (0.5-5): (2-5): (0.6-5.5): (1-2.5): (1-5): (0.7-2). When the mass ratio of trivalent chromium salt, nitrate, complexing agent, reducing agent, bluing agent, dispersant, film-forming promoter and sealing agent is within this range, a uniformly distributed, bright and dense blue-white passivation film can be obtained, thereby effectively improving the performance of the passivation film.

[0020] In a second aspect, the present application proposes a method for preparing a trivalent chromium passivation solution, comprising the following steps:

[0021] The trivalent chromium salt, bluing agent, dispersant, solvent and auxiliary agent are mixed to obtain a trivalent chromium passivation solution.

[0022] By adding bluing agent and dispersant, the problem of unstable and uneven blue film is solved. Cobalt salt is electrochemically controlled on the surface of the coating and replaces with zinc to form Zn-Co alloy, which enhances corrosion resistance. However, due to the influence of current gradient and concentration polarization during the electroplating process, the metal deposition distribution of the zinc coating is uneven, so the distribution of cobalt salt in the coating is also uneven. The blueing agent is composed of blue dye and cobalt salt. The adsorption of dye in the passivation solution is diffusion controlled. When the zinc coating is etched with fine gaps, the dye is adsorbed on the surface of the gaps, and then the gaps are sealed by the auxiliary agent to form a nano-sized organic-inorganic hybrid blue-white film, which improves the uniformity of the blue-white film. At the same time, trivalent chromium salt reduces the toxicity of the passivation solution. The cobalt salt in the bluing agent replaces with zinc to form Zn-Co alloy, which enhances corrosion resistance. The blue dye in the bluing agent makes up for the uneven blueing parts and improves the uniformity of blue. The dispersant assists the uniformity of blue dye dispersion, further improving the uniformity of blueing. The passivation solution of the present application does not need to be sealed after passivation. The conversion film formed can self-repair in humid air after being damaged, and has the same performance as Cr 6+ Considerable self-healing ability.

[0023] In some embodiments, the step of mixing a trivalent chromium salt, a bluing agent, a dispersant, a solvent and an auxiliary agent to obtain a trivalent chromium passivation solution comprises:

[0024] Mixing the cobalt salt nitrate, the complexing agent, the film-forming promoter and the first part of the solvent to obtain a first mixed solution;

[0025] Mixing the trivalent chromium salt, the reducing agent and the second part of the solvent to obtain a second mixed solution;

[0026] Mixing the acid blue dye, the dispersant and the blocking agent to obtain a third mixed solution;

[0027] Mixing the third mixed solution with the first mixed solution to obtain a fourth mixed solution;

[0028] The fourth mixed solution is mixed with the second mixed solution to obtain a trivalent chromium passivation solution.

[0029] The trivalent chromium passivation solution is prepared by a step-by-step mixing method, so that the trivalent chromium passivation solution can be mixed more evenly and the generation of precipitation can be reduced.

[0030] In some embodiments, the cobalt salt nitrate, the complexing agent, the film-forming promoter and the first part of the solvent are mixed to obtain a first mixed solution:

[0031] The mixing temperature is 50-70° C. Within this range, the first mixed solution can be mixed more evenly; and / or,

[0032] The mixing time is 1 to 3 hours. Within this range, the first mixed liquid can be mixed more evenly.

[0033] In some embodiments, the fourth mixed solution is mixed with the second mixed solution to obtain a trivalent chromium passivation solution:

[0034] The mixing temperature is 30-40°C. The mixing temperature within this range can make the trivalent chromium passivation solution mix more evenly; and / or,

[0035] The mixing time is 0.5 to 2 hours. Within this range, the trivalent chromium passivation solution can be mixed more evenly. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 The appearance color of the galvanized layer passivated with the trivalent chromium passivation solution of Example 3 of the present application, the galvanized layer passivated with the trivalent chromium passivation solution of Comparative Example 1, and the galvanized layer not passivated.

[0038] Figure 2 These are electron microscope images of the zinc-plated layer passivated with the trivalent chromium passivation solution of Example 3 of the present application, the zinc-plated layer passivated with the trivalent chromium passivation solution of Comparative Example 1, and the zinc-plated layer that has not been passivated.

[0039] Figure 3 The anodic potentiodynamic polarization curves of the trivalent chromium passivation solution of Example 3 of the present application, the galvanized layer passivated with the trivalent chromium passivation solution of Comparative Example 1, and the galvanized layer not passivated in a 5% NaCl solution. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0041] Hexavalent chromium conversion coating is widely used in the anti-corrosion protection of zinc coating, but Cr 6+ It is a carcinogen with high toxicity. At the same time, due to the continuous progress of environmental protection policies, Cr 6+ Its application has been greatly restricted.

[0042] The traditional hexavalent chromium passivation film is formed by the dissolution of zinc, the reduction of chromate and the precipitation of trivalent chromium gel. The formation of the conversion film is a dynamic process. Therefore, the passivation film has the ability to repair itself, also known as self-healing ability. 6+ In the conversion film, Cr actually plays the role of isolating corrosion. 6+ Cr generated after reduction 3+ ,Cr 3+ Directly react with zinc ions, hydroxide, etc. to form insoluble compounds that precipitate on the zinc surface, and Cr 3+ The only toxicity is Cr 6+ 1%, but with Cr 6+ In comparison, Cr 3+ The passivation solution should make up for Cr 6+ The oxidizability of Cr 3+ Not oxidized to Cr 6+ In addition, the related reaction of chromium ion is a first-order reaction. 6+ Reduction to Cr 3+ In the reaction, Cr 3+ The formation of Cr(OH)3 is slow, so the Cr(OH)3 gel and other insoluble substances are dispersed evenly in the generated passivation film; 3+ In the passivation solution, Cr 3+ It exists in the form of hydrated complex ions, and its reaction kinetic constant is extremely small, the reaction is slow, and the conversion film formed is poorly stable and dull; therefore, a certain amount of complexing agent must be added to increase the kinetic constant of the complex ion reaction with chromium ions, which is conducive to the reaction. 3+ The composition of the passivation solution is complex and the stability is poor. Especially in the blue-white passivation solution, the blue conversion film often appears uneven blue or even no blue. At the same time, because the formation of the conversion film is one-time, the Cr 6+ The self-healing ability of Cr6+ .

[0043] In view of this, the present application provides a trivalent chromium passivation solution and a preparation method thereof to solve the problems of high toxicity and uneven blueing of the existing passivation film.

[0044] In a first aspect, the present application provides a trivalent chromium passivation solution, including a trivalent chromium salt, a bluing agent, a dispersant, a solvent and an auxiliary agent, wherein:

[0045] The bluing agent includes a cobalt salt and an acid blue dye;

[0046] The dispersant comprises sodium isomeric alcohol ether succinic acid monoester sulfonate and polyethylene glycol 20000.

[0047] In this application, by adding bluing agent and dispersant, the problem of instability and unevenness of the blue-white passivation film of traditional trivalent chromium blue-white passivation is solved. Cobalt salt is electrochemically controlled on the surface of the coating, and replaces with zinc to form Zn-Co alloy, which enhances corrosion resistance. However, due to the influence of current gradient and concentration polarization on the zinc coating during electroplating, the metal deposition distribution is uneven, so the cobalt salt is also unevenly distributed in the coating. The blueing agent is composed of blue dye and cobalt salt. The dye is in the passivator solution, and its adsorption belongs to diffusion control. When the zinc coating is etched with fine gaps, the dye is adsorbed on the surface of the gap, and then the gap is sealed by the auxiliary agent to form a nano-sized organic-inorganic hybrid blue-white film, which improves the uniformity of the blue-white film, and the trivalent chromium salt reduces the toxicity of the passivation solution. The cobalt salt in the bluing agent replaces with zinc to form a Zn-Co alloy, which enhances corrosion resistance. The blue dye in the bluing agent makes up for the uneven blue part, improves the uniformity of blue, and the dispersant assists the uniformity of the blue dye dispersion, further improving the uniformity of blue.

[0048] The dispersant is prepared by mixing sodium isomeric alcohol ether succinic acid monoester sulfonate and polyethylene glycol 20000 in a mass ratio of (6-8): (2-4). The isomeric alcohol ether (decanol or tridecanol) EO addition can be selected according to the chain length of the isomeric alcohol with the same carbon number. After melting, the mixture is added into a reaction kettle, the temperature is raised to 100°C±5°C, and equimolar maleic anhydride that has been pre-selected and crushed is added, and then the mixture is kept warm for 6 hours. After the reaction is completed, water of the same mass as the maleic anhydride is added into the kettle to quench the unreacted maleic anhydride, the temperature is lowered to 85°C±5°C, a prepared sodium pyrosulfite solution is added dropwise, and after the addition, a sodium hydroxide solution is added dropwise into the kettle to adjust the pH value to 6.0-7.0, the mixture is kept warm for 2 hours, the temperature is lowered to about 60°C, and then a PEG-20000 tablet is added, the mixture is stirred until the PEG-20000 is completely dissolved, and then the mixture is kept warm for half an hour, and the mixture is cooled and discharged to obtain the dispersant.

[0049] The cobalt salt includes at least one of cobalt nitrate and cobalt chloride hexahydrate, the acid blue dye can be Milliken X3LV model, and the solvent can be water.

[0050] In combination with the first aspect, in some embodiments provided in the present application, the mass proportion of the bluing agent in the trivalent chromium passivation solution is 0.6% to 5.5%. The mass proportion of the bluing agent in the trivalent chromium passivation solution is within this range, and can synergize with the dispersant to improve the problem of instability and unevenness of the blue film.

[0051] In combination with the first aspect, in some embodiments provided in the present application, the mass proportion of the dispersant in the trivalent chromium passivation solution is 1.0% to 2.5%. The mass proportion of the dispersant in the trivalent chromium passivation solution is within this range, which can evenly disperse the blue dye and synergize with the bluing agent to improve the problem of instability and unevenness of the blue film.

[0052] In combination with the first aspect, in some embodiments provided in the present application, the trivalent chromium salt includes at least one of chromium nitrate nonahydrate and chromium chloride hexahydrate, which can provide a suitable trivalent chromium salt.

[0053] In combination with the first aspect, in some embodiments provided in the present application, the mass proportion of the trivalent chromium salt in the trivalent chromium passivation solution is 20.0% to 40.0%. Within this range, the trivalent chromium salt can serve as a skeleton to form a network structure in the passivation solution, providing a key component for film formation.

[0054] In conjunction with the first aspect, in some embodiments provided in the present application, the auxiliary agent includes nitrate, complexing agent, reducing agent, film-forming promoter and sealing agent. The auxiliary agent can help the surface treatment process of the passivation solution and improve the passivation effect. Nitrate can accelerate the film-forming speed, prevent the passivation film from atomizing, and improve the brightness of the passivation film. The complexing agent can activate the zinc layer and form a complex with trivalent chromium, which is conducive to the trivalent chromium ions forming a uniform and dense passivation film on the surface of the zinc coating. The reducing agent can stabilize the trivalent chromium, the film-forming promoter can utilize anions to accelerate the micro-anodic reaction, activate the solid-liquid interface to promote film formation, and the sealing agent can improve the corrosion resistance of the passivation film.

[0055] In combination with the first aspect, in some embodiments provided in the present application, the nitrate includes at least one of sodium nitrate, ammonium nitrate and potassium nitrate. Using at least one of the above nitrates can accelerate the film formation speed, prevent the passivation film from being atomized, and improve the brightness of the passivation film.

[0056] In combination with the first aspect, in some embodiments provided in the present application, the complexing agent includes at least one of oxalic acid, malonic acid, tartaric acid and citric acid. The use of at least one of the above complexing agents can form a complex with trivalent chromium, which is conducive to the formation of a uniform and dense passivation film of trivalent chromium ions on the surface of the zinc-plated layer.

[0057] In combination with the first aspect, in some embodiments provided in the present application, the reducing agent includes at least one of sodium hypophosphite, potassium hypophosphite and ammonium hypophosphite. At least one of the above reducing agents can stabilize trivalent chromium, and when the pH of the passivation solution rises to 4-5, Zn in the solution 2+ ,Cr 3+ , and PO4 3- It will react on the surface of the galvanized layer to form insoluble zinc phosphate and chromium phosphate, which together with the trivalent chromium skeleton form a passivation film.

[0058] In combination with the first aspect, in some embodiments provided in the present application, the film-forming promoter includes at least one of nickel nitrate and nickel chloride. By using at least one of the above film-forming promoters, anions can be used to accelerate the micro-anode reaction and activate the solid-liquid interface to promote film formation, wherein NO3 - Can improve the brightness of the passivation film, Cl - It is beneficial to form a reactive passivation film with a certain thickness and shorten the passivation time.

[0059] In combination with the first aspect, in some embodiments provided in the present application, the sealant includes fluorozirconate and a silane coupling agent. The use of the above-mentioned sealant can improve the corrosion resistance of the passivation film without the need for subsequent sealing treatment.

[0060] In combination with the first aspect, in some embodiments provided in the present application, the mass ratio of trivalent chromium salt, nitrate, complexing agent, reducing agent, bluing agent, dispersant, film-forming promoter and sealing agent is (20-40): (1-5): (0.5-5): (2-5): (0.6-5.5): (1-2.5): (1-5): (0.7-2). When the mass ratio of trivalent chromium salt, nitrate, complexing agent, reducing agent, bluing agent, dispersant, film-forming promoter and sealing agent is within this range, a uniformly distributed, bright and dense blue-white passivation film can be obtained, which effectively improves the performance of the passivation film.

[0061] In a second aspect, the present application proposes a method for preparing a trivalent chromium passivation solution, comprising the following steps:

[0062] The trivalent chromium salt, bluing agent, dispersant, solvent and auxiliary agent are mixed to obtain a trivalent chromium passivation solution.

[0063] By adding bluing agent and dispersant, the problem of unstable and uneven blue film is solved. Cobalt salt is electrochemically controlled on the surface of the coating and replaces with zinc to form Zn-Co alloy, which enhances corrosion resistance. However, due to the influence of current gradient and concentration polarization during the electroplating process, the metal deposition distribution of the zinc coating is uneven, so the distribution of cobalt salt in the coating is also uneven. The blueing agent is composed of blue dye and cobalt salt. The adsorption of dye in the passivation solution is diffusion controlled. When the zinc coating is etched with fine gaps, the dye is adsorbed on the surface of the gaps, and then the gaps are sealed by the auxiliary agent to form a nano-sized organic-inorganic hybrid blue-white film, which improves the uniformity of the blue-white film. At the same time, trivalent chromium salt reduces the toxicity of the passivation solution. The cobalt salt in the bluing agent replaces with zinc to form Zn-Co alloy, which enhances corrosion resistance. The blue dye in the bluing agent makes up for the uneven blueing parts and improves the uniformity of blue. The dispersant assists the uniformity of blue dye dispersion, further improving the uniformity of blueing. The passivation solution of the present application does not need to be sealed after passivation. The conversion film formed can self-repair in humid air after being damaged, and has the same performance as Cr 6+ Considerable self-healing ability.

[0064] In combination with the second aspect, in some embodiments provided in the present application, the mixing of the trivalent chromium salt, the bluing agent, the dispersant, the solvent and the auxiliary agent to obtain the trivalent chromium passivation solution comprises:

[0065] Mixing the cobalt salt nitrate, the complexing agent, the film-forming promoter and the first part of the solvent to obtain a first mixed solution;

[0066] Mixing the trivalent chromium salt, the reducing agent and the second part of the solvent to obtain a second mixed solution;

[0067] Mixing the acid blue dye, the dispersant and the blocking agent to obtain a third mixed solution;

[0068] Mixing the third mixed solution with the first mixed solution to obtain a fourth mixed solution;

[0069] The fourth mixed solution is mixed with the second mixed solution to obtain a trivalent chromium passivation solution.

[0070] The trivalent chromium passivation solution is prepared by a step-by-step mixing method, so that the trivalent chromium passivation solution can be mixed more evenly and the generation of precipitation can be reduced.

[0071] In combination with the second aspect, in some embodiments provided in the present application, cobalt salt nitrate, a chelating agent, a film-forming promoter and a first part of the solvent are mixed to obtain a first mixed liquid: the mixing temperature is 50 to 70°C. The mixing temperature within this range can make the first mixed liquid more evenly mixed.

[0072] In combination with the second aspect, in some embodiments provided in the present application, cobalt salt nitrate, a chelating agent, a film-forming promoter and a first part of the solvent are mixed to obtain a first mixed liquid: the mixing time is 1 to 3 hours. Within this mixing time range, the first mixed liquid can be mixed more evenly.

[0073] In combination with the second aspect, in some embodiments provided in the present application, the fourth mixed liquid is mixed with the second mixed liquid to obtain a trivalent chromium passivation solution: the mixing temperature is 30 to 40° C., which can make the trivalent chromium passivation solution more evenly mixed.

[0074] In combination with the second aspect, in some embodiments provided in the present application, the fourth mixed liquid is mixed with the second mixed liquid to obtain a trivalent chromium passivation solution: the mixing time is 0.5 to 2 hours, which can make the trivalent chromium passivation solution more uniform.

[0075] The technical solution provided in this application is described in detail below in conjunction with embodiments.

[0076] Example 1

[0077] Example 1 of the present application provides a trivalent chromium passivation solution, the raw materials of which include:

[0078] The mass ratio of trivalent chromium salt, nitrate, complexing agent, reducing agent, bluing agent, dispersant, film-forming accelerator and sealing agent is 20:1:0.5:2:0.6:1:1:0.7;

[0079] The trivalent chromium salt is chromium chloride hexahydrate; the nitrate is potassium nitrate; the complexing agent is composed of malonic acid and tartaric acid in a mass ratio of 1:0.5; the reducing agent is composed of sodium hypophosphite and ammonium hypophosphite in a mass ratio of 2:4; the bluing agent is composed of cobalt nitrate, cobalt chloride hexahydrate, and acid blue dye (Milliken X3LV) in a mass ratio of 2:3:2; the dispersant is composed of sodium isocyanate sulfonate and polyethylene glycol 20000 in a mass ratio of 7:3; the film-forming promoter is nickel chloride; the sealing agent is composed of sodium fluorozirconate and a silane coupling agent (Shanghai Mingjie Chemical IP0943) in a mass ratio of 6:2.

[0080] Example 2

[0081] Example 2 of the present application provides a trivalent chromium passivation solution, the raw materials of which include:

[0082] The mass ratio of trivalent chromium salt, nitrate, complexing agent, reducing agent, bluing agent, dispersant, film-forming accelerator and sealing agent is 40:5:5:5:5.5:2.5:5:2;

[0083] The trivalent chromium salt is chromium nitrate nonahydrate; the nitrate is ammonium nitrate; the complexing agent is composed of malonic acid and citric acid in a mass ratio of 1:3; the reducing agent is composed of sodium hypophosphite and potassium hypophosphite in a mass ratio of 2:5; the bluing agent is composed of cobalt nitrate, cobalt chloride hexahydrate, and acid blue dye (Milliken X3LV) in a mass ratio of 2:4:3; the dispersant is composed of sodium isocyanate sulfonate and polyethylene glycol 20000 in a mass ratio of 8:2; the film-forming promoter is nickel nitrate; the sealing agent is composed of sodium fluorozirconate and a silane coupling agent (Shanghai Mingjie Chemical IP0943) in a mass ratio of 4:2.

[0084] Example 3

[0085] Example 3 of the present application provides a trivalent chromium passivation solution, the raw materials of which include:

[0086] The mass ratio of trivalent chromium salt, nitrate, complexing agent, reducing agent, bluing agent, dispersant, film-forming accelerator and sealing agent is 30:3:3:3.5:3:2:3:1.5;

[0087] The trivalent chromium salt is chromium chloride; the nitrate is sodium nitrate; the complexing agent is composed of malonic acid and tartaric acid in a mass ratio of 1:1; the reducing agent is composed of sodium hypophosphite and ammonium hypophosphite in a mass ratio of 2:3; the bluing agent is composed of cobalt nitrate, cobalt chloride hexahydrate, and acid blue dye (Milliken X3LV) in a mass ratio of 2:3:2; the dispersant is composed of sodium isocyanate sulfonate and polyethylene glycol 20000 in a mass ratio of 7:3; the film-forming promoter is nickel chloride; the sealing agent is composed of sodium fluorozirconate and a silane coupling agent (Shanghai Mingjie Chemical IP0943) in a mass ratio of 5:2.

[0088] Example 4

[0089] Example 4 of the present application provides a method for preparing a trivalent chromium passivation solution, comprising the following steps:

[0090] Add cobalt salt, nitrate, complexing agent and film-forming accelerator into a preparation kettle, add twice the mass of water, stir at 60°C until dissolved, keep warm for 2 hours, and obtain the first mixed solution;

[0091] Dissolving the trivalent chromium salt and the reducing agent in water to obtain a second mixed solution;

[0092] Add the acid blue dye in the bluing agent to the dispersant, stir evenly, and then add the blocking agent to obtain a third mixed solution;

[0093] At 30° C., adding the third mixed solution to the first mixed solution and stirring evenly to obtain a fourth mixed solution;

[0094] Then, at 35° C., the second mixed solution was added to the fourth mixed solution and stirred for 1 hour to obtain a trivalent chromium blue-white passivation solution.

[0095] Comparative Example 1

[0096] Comparative Example 1 of the present application provides a trivalent chromium passivation solution, comprising:

[0097] The mass ratio of trivalent chromium salt, nitrate, complexing agent, reducing agent, cobalt salt and film-forming accelerator is 30:3:3:3.5:3:3.

[0098] The trivalent chromium salt is chromium chloride; the nitrate is sodium nitrate; the complexing agent is composed of malonic acid and tartaric acid in a mass ratio of 1:1; the reducing agent is composed of sodium hypophosphite and ammonium hypophosphite in a mass ratio of 2:3; the cobalt salt is cobalt chloride hexahydrate; and the film-forming accelerator is nickel chloride.

[0099] Performance Testing

[0100] The trivalent chromium passivation solutions of Examples 1 to 3 and the trivalent chromium passivation solution of Comparative Example 1 were prepared by the preparation method of Example 4, and the surfaces of galvanized sheets of the same size were immersed in the trivalent chromium passivation solutions of Examples 1 to 3 and Comparative Example 1, respectively. The passivation treatment temperature was controlled at 25° C., and the passivation treatment time was controlled at 30 s. The galvanized sheets were then taken out, washed, dried, and subjected to a neutral salt spray test. The method for the neutral salt spray test was as follows:

[0101] At a temperature of 25°C ± 2°C, dissolve sodium chloride in distilled water or deionized water with a conductivity of no more than 20μS / cm to prepare a solution with a concentration of 50g / L ± 5g / L. The collected spray liquid concentration is 50g / L ± 5g / L. At 25°C, the relative density of the prepared solution is in the range of 1.029 to 1.036.

[0102] The pH value of the test solution (5.1) should be adjusted so that the pH value of the spray solution collected in the salt spray chamber (6.2) is between 6.5 and 7.2 at 25℃±2℃. The pH value is measured with a potentiometric pH meter using an electrode suitable for weakly buffered sodium chloride solution (dissolved in deionized water). The pH value of the solution is adjusted with a solution prepared with analytical grade hydrochloric acid, sodium hydroxide or sodium bicarbonate.

[0103] Test piece production

[0104] Preparation of base liquid: Add the calculated amount of solid sodium hydroxide into the plating tank, add about 1 / 3 of the tank volume of water, stir to dissolve, then slowly add the calculated amount of zinc oxide into the sodium hydroxide solution, stirring while adding to completely dissolve it, then add water to the specified volume, and after a period of low current electrolysis, you can try plating.

[0105] The concentration of each component in the plating solution is as follows:

[0106] Zinc (g / L) 8.0;

[0107] Caustic soda (g / L) 125.0;

[0108] Alkaline cyanide-free zinc plating brightener (mL / L) 20.0;

[0109] WT(g / L)2.0;

[0110] Take 500 mL of the above plating solution and add it into the Hull cell, use No. 0 zinc plate as the anode, and use a copper sheet (6.5 cm×20 cm) with a thickness of 0.3 mm and polished into a mirror surface by a cloth wheel as the cathode. Place the Hull cell in a constant temperature water bath, control the temperature of the test piece to 25°C, the current density to 0.5 A / dm2, and electroplating for 15 minutes to obtain a uniform bright coating on the entire piece. Based on this test piece, passivation of Examples 1 to 3 and Comparative Example 1 was carried out.

[0111] The test results are shown in Table 1 and Figures 1 to 3 shown.

[0112] Table 1 Performance test results of trivalent chromium passivation solution of Examples 1 to 3 and Comparative Example 1

[0113] Neutral salt spray test white rust time (h) Appearance Galvanized layer 2.5 Bright and uniform white, with darker edges Example 1 124.0 Blue-white film, evenly distributed, bright and dense Example 2 120.5 Blue-white film, evenly distributed, bright and dense Example 3 126.0 Blue-white film, evenly distributed, bright and dense Comparative Example 1 48.5 Grayish white with light blue, uneven distribution Comparative Example 2 72.5 Grayish white with light blue, uniform and dense

[0114] Figure 1 (a) shows the appearance and color of the galvanized layer without passivation treatment. It can be seen that the zinc layer is relatively uniform, but the edge presents a darker color, which may be attributed to the gas escape during the electroplating of the zinc coating, resulting in uneven coating. Figure 1 (b) is the appearance color of the zinc-plated layer passivated with trivalent chromium passivation solution in comparative example 1. The surface of the zinc layer is grayish white with light blue appearance, and the color is not obvious. Figure 1 (c) is the appearance color of the zinc-plated layer passivated with trivalent chromium passivation solution in Example 3. It can be seen that the zinc layer has a uniform light blue appearance.

[0115] The microstructures before and after passivation were observed using field emission scanning electron microscopy. Figure 2 (a) is the zinc layer without passivation or sealing treatment, showing a porous structure. Figure 2 (b) is the Cr formed on the surface of the zinc layer after the trivalent chromium passivation treatment in Comparative Example 1. 3+ The SEM image of the passivation film shows that the surface is still relatively rough and has many pores. Figure 2 (c) is the zinc-plated layer passivated with the trivalent chromium passivation solution of Example 3. It can be clearly seen that after being treated with the trivalent chromium blue-white passivation solution of Example 3, a dense passivation film with fewer pores is formed.

[0116] Figure 3 (a) is the anodic potentiodynamic polarization curve of the trivalent chromium passivated zinc layer in 5% NaCl solution of comparative example 1, Figure 3 (b) is the anodic potentiodynamic polarization curve of the zinc layer passivated with trivalent chromium passivation solution in 5% NaCl solution in Example 3 of the present application, Figure 3 (c) is the anodic potential polarization curve of the unpassivated galvanized layer in 5% NaCl solution. After the trivalent chromium passivation of comparative example 1, the corrosion potential of the galvanized layer increased significantly, and when the trivalent chromium passivation solution of Example 3 of the present application was used for treatment, the corrosion potential increased further, indicating that the passivation solution of the present application can make the zinc layer have better corrosion resistance. Passivation is an anodic dissolution process. Under the action of an oxidant, a metal forms a metal oxide, and a very thin, dense, and well-covering passivation film is formed on the metal surface. The passivation film is firmly adsorbed on the metal surface. This film exists as an independent phase, usually a compound of oxidized metals, which plays a role in completely isolating the metal from the corrosive medium, preventing the metal from contacting the corrosive medium, thereby causing the metal to basically stop dissolving and form a passive state to achieve an anti-corrosion effect. This film is usually a loose and porous structure. In the trivalent chromium passivation solution of the present application, Cr 3+ It directly reacts with zinc ions, hydroxide, etc. to form insoluble compounds that precipitate on the zinc surface, making the passivation film denser and thus improving corrosion resistance.

[0117] The passivation solution of the present application does not need sealing treatment after passivation. Fluorozirconate and silane coupling agent release zirconium oxide and cross-linked silicon dioxide as sealing agents under acidic conditions to generate zirconium oxide particles that enter the gaps and seal the pores. The silane coupling agent is hydrolyzed to generate Si─OH, which combines with the active OH- in the inorganic matter to form a three-dimensional network structure similar to Si─O─Si on the metal surface through dehydration condensation. The formed conversion film can self-repair in humid air after being damaged, and has the same performance as Cr 6+ Considerable self-healing ability.

[0118] In summary, by adding bluing agent and dispersant, the problem of unstable and uneven blue film is solved. Cobalt salt is electrochemically controlled on the surface of the coating and replaces with zinc to form Zn-Co alloy, which enhances corrosion resistance. However, due to the influence of current gradient and concentration polarization during the electroplating process, the metal deposition distribution of the zinc coating is uneven, so the distribution of cobalt salt in the coating is also uneven. The blueing agent is composed of blue dye and cobalt salt. The adsorption of dye in the passivation solution is diffusion controlled. When the zinc coating is etched with fine gaps, the dye is adsorbed on the surface of the gaps, and then the gaps are sealed by the auxiliary agent to form a nano-sized organic-inorganic hybrid blue-white film, which improves the uniformity of the blue-white film. At the same time, trivalent chromium salt reduces the toxicity of the passivation solution. The cobalt salt in the bluing agent replaces with zinc to form Zn-Co alloy, which enhances corrosion resistance. The blue dye in the bluing agent makes up for the uneven blueing parts and improves the uniformity of blue. The dispersant assists in dispersing the blue dye and further improves the uniformity of blueing.

[0119] In the description of this specification, the description with reference to the terms "one embodiment / method", "some embodiments / methods", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment / method or example are included in at least one embodiment / method or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment / method or example. Moreover, the specific features, structures, materials or characteristics described may be combined in a suitable manner in any one or more embodiments / methods or examples. In addition, those skilled in the art may combine and combine the different embodiments / methods or examples described in this specification and the features of the different embodiments / methods or examples, unless they are contradictory.

[0120] It should be noted that, in the present application, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of more restrictions, the elements defined by the sentence "comprise one..." do not exclude the existence of other identical elements in the process, method, article or equipment including the elements. In the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically stipulated.

[0121] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A trivalent chromium passivation solution, characterized in that: Including trivalent chromium salts, bluing agents, dispersants, solvents and auxiliary agents, including: The bluing agent includes a cobalt salt and an acid blue dye; The dispersant comprises sodium isomeric alcohol ether succinic acid monoester sulfonate and polyethylene glycol 20000.

2. The trivalent chromium passivation solution according to claim 1, characterized in that: The mass proportion of the bluing agent in the trivalent chromium passivation solution is 0.6% to 5.5%; and / or, The mass proportion of the dispersant in the trivalent chromium passivation solution is 1.0% to 2.5%.

3. The trivalent chromium passivation solution according to claim 1, characterized in that: The trivalent chromium salt comprises at least one of chromium nitrate nonahydrate and chromium chloride hexahydrate; and / or, The mass proportion of the trivalent chromium salt in the trivalent chromium passivation solution is 20.0% to 40.0%.

4. The trivalent chromium passivation solution according to claim 1, characterized in that: The auxiliary agent includes nitrate, complexing agent, reducing agent, film-forming accelerator and sealing agent.

5. The trivalent chromium passivation solution according to claim 4, characterized in that: The nitrate comprises at least one of sodium nitrate, ammonium nitrate and potassium nitrate; and / or, The complexing agent comprises at least one of oxalic acid, malonic acid, tartaric acid and citric acid; and / or, The reducing agent comprises at least one of sodium hypophosphite, potassium hypophosphite and ammonium hypophosphite; and / or, The film-forming promoter comprises at least one of nickel nitrate and nickel chloride; and / or, The sealing agent includes fluorozirconate and a silane coupling agent.

6. The trivalent chromium passivation solution according to claim 4, characterized in that: The mass ratio of trivalent chromium salt, nitrate, complexing agent, reducing agent, bluing agent, dispersant, film-forming promoter and sealing agent is (20-40): (1-5): (0.5-5): (2-5): (0.6-5.5): (1-2.5): (1-5): (0.7-2).

7. A method for preparing a trivalent chromium passivation solution according to any one of claims 1 to 6, characterized in that: The following steps are involved: The trivalent chromium salt, bluing agent, dispersant, solvent and auxiliary agent are mixed to obtain a trivalent chromium passivation solution.

8. The method for preparing a trivalent chromium passivation solution according to claim 7, wherein: The trivalent chromium salt, bluing agent, dispersant, solvent and auxiliary agent are mixed to obtain a trivalent chromium passivation solution, which comprises: Mixing the cobalt salt, the nitrate, the complexing agent, the film-forming accelerator and the first part of the solvent to obtain a first mixed solution; Mixing the trivalent chromium salt, the reducing agent and the second part of the solvent to obtain a second mixed solution; Mixing the acid blue dye, the dispersant and the blocking agent to obtain a third mixed solution; Mixing the third mixed solution with the first mixed solution to obtain a fourth mixed solution; The fourth mixed solution is mixed with the second mixed solution to obtain a trivalent chromium passivation solution.

9. The method for preparing a trivalent chromium passivation solution according to claim 8, wherein: The cobalt salt, nitrate, complexing agent, film-forming accelerator and the first part of solvent are mixed to obtain the first mixed solution: The mixing temperature is 50 to 70°C; and / or, The mixing time is 1 to 3 hours.

10. The method for preparing a trivalent chromium passivation solution according to claim 8, wherein: The fourth mixed solution is mixed with the second mixed solution to obtain a trivalent chromium passivation solution: The mixing temperature is 30-40°C; and / or, The mixing time is 0.5 to 2 hours.

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