JP7307337B2 - Method for producing plating solution and method for producing plated steel sheet using the same - Google Patents

Description

The present invention relates to a method for producing a plating solution, a plating solution, and a method for producing a plated steel sheet using the same.

Zinc-based plated steel sheets are used in various applications such as automobiles, electrical equipment, and construction. Zinc-based plated steel sheets are usually obtained by a hot-dip plating method or an electroplating method. In particular, the electroplating method allows the temperature of the plating solution to be lower than that of the hot-dip plating method, which makes it difficult for the steel sheet to deform due to thermal strain, and makes it easy to form a uniform plating layer even if the thickness is thin. Therefore, it is desired to obtain a zinc-based plated steel sheet by an electroplating method. Zinc-based plated steel sheets used for the above applications are required to be improved in corrosion resistance, workability, and the like.

Zirconium (Zr) and zirconium oxides such as zirconium hydroxide and zirconium oxide (hereinafter also referred to as Zr oxides) are known as components added to improve corrosion resistance and workability.

For example, there is known a method (dispersion plating method) of electro-Zn—Mn plating using a plating solution in which ZrO ₂ particles as a zirconium source are dispersed together with Al ₂ O ₃ particles and SiO ₂ particles (for example, patent Reference 1). It is said that a Zn--Mn plating layer in which these particles are dispersed is thereby obtained.

However, in the dispersion plating method as shown in Patent Document 1, the ZrO ₂ particles have a high density and do not have the ionic or hydrophilic groups necessary for dispersion in an aqueous solution, so there is a problem that they tend to settle. . As a result, not only is it impossible to obtain a desired plating layer, but there is also the danger that deposition will occur in the low-flow-velocity portion of the tank and that valve opening/closing problems will occur.

To solve this problem, the pH is raised by generating hydrogen on the plated surface of the steel sheet that serves as the cathode ( ^cathode ) during electroplating. A method of precipitating it as a hydroxide has been proposed (see Patent Documents 2 and 3, for example). In the document, a plating solution to which a sulfate (soluble metal salt) such as zirconium sulfate is added is used, and Zr is precipitated as a hydroxide from the state of zirconium ion (Zr ⁴⁺ ) due to the pH increase in the vicinity of the plating surface. is stated.

In addition to increasing the pH during electroplating, there is also known a method of further adding an oxidizing agent such as nitrate ions as a method for facilitating precipitation of metal ions dissolved in the plating solution as hydroxide (for example, patent References 2 and 3).

There is also a method of performing Zn—Zr oxide plating under conditions of pH 1 or 2 using a plating solution containing zirconium sulfate hydrate (Zr(SO ₄ ) _{2.4H 2} O) as a zirconium source. known (see, for example, Non-Patent Document 1).

JP-A-2-11799 JP-A-64-00298 JP-A-1-272796

Hiroaki Nakano et al., Journal of the Japan Institute of Metals, 80 (2016), p.151-156

As described above, Patent Literatures 2 and 3 disclose that a sulfate such as zirconium sulfate is added to the plating solution as a zirconium source to dissolve Zr ions (Zr ⁴⁺ ). However, in order to actually dissolve Zr ions, the pH of the plating solution must be lowered to zero or less, which may cause dissolution of the steel sheet and the formed plating layer.

Further, as shown in Patent Documents 2 and 3, when an oxidizing agent such as nitric acid ions is added in order to facilitate the deposition of Zr ions during electroplating, the oxidizing agent is decomposed during electroplating, resulting in harmful by-products. Substances (for example, nitrite ions, NOx gas, ammonia gas, etc.) are likely to be generated.

Further, in Non-Patent Document 1, since zirconium sulfate is used as the zirconium source, sulfuric acid tends to accumulate excessively in the plating solution due to replenishment. When sulfuric acid accumulates excessively in the plating solution, the viscosity of the plating solution increases due to the high viscosity of sulfuric acid, which reduces the fluidity of the plating solution and increases the power required to flow the plating solution. It's easy to do. Also, when sulfuric acid is excessively accumulated in the plating solution, the pH of the plating solution tends to be low. As a result, when zirconium sulfate or the like is replenished while the plating solution is flowing, hydrogen ions are continuously supplied to the interface of the cathode electrode, making it difficult to increase the pH of the interface of the cathode electrode. Zr hydroxide could not be precipitated by raising the pH. That is, even in the method of Non-Patent Document 1, a plating solution containing zirconium sulfate and zinc sulfate could not actually form a plating layer containing Zr oxide.

In addition, when a plating solution is prepared from zirconium sulfate, zirconium sulfate itself exhibits strong acidity, so it is necessary to add a large amount of an alkali chemical such as sodium hydroxide in order to adjust the pH within a predetermined range. Since the solubility of the cation (eg, Na) of the alkaline chemical and the salt of the sulfate ion limits the amount of the alkaline chemical to be used, it has sometimes been impossible to adjust the pH to a predetermined value.

Furthermore, zirconium oxychloride (ZrOCl ₂ ) and zirconium oxynitrate (ZrO(NO ₃ ) ₂ ) are also known as zirconium sources other than those disclosed in Patent Documents 1 to 3 and Non-Patent Document 1. These zirconium compounds are also soluble in an acidic aqueous solution, but when the plating solution is continuously replenished, chloride ions and nitrate ions accumulate in the plating solution, producing hydrochloric acid and nitric acid decomposition products. It is easy to produce harmful by-products such as A method of dissolving metallic zirconium in the plating solution is also conceivable, but since zirconium is a metal with extremely high acid resistance, it does not dissolve even if the pH of the plating solution is lowered to near zero.

Thus, in the conventional method, in practice, a zinc-based coating layer containing Zr components (Zr and Zr oxides) on the steel sheet can be obtained while suppressing the generation of harmful by-products and excessive accumulation of sulfuric acid components. could not be stably formed.

The present invention has been made in view of the above circumstances, and stably forms a zinc-based plating layer containing a Zr component on a steel sheet while suppressing the generation of harmful by-products and excessive accumulation of sulfuric acid components. It is an object of the present invention to provide a method for producing a plating solution, a plating solution, and a method for producing a plated steel sheet using the same.

The present invention relates to the following method for producing a plating solution, a plating solution, and a method for producing a plated steel sheet using the same.

A method for producing a plating solution of the present invention includes a step of mixing a zinc source, a basic zirconium carbonate, a sulfuric acid source, and water to obtain a plating solution having a pH of 3.0 or less.

The plating solution of the present invention is obtained by the method for producing a plating solution of the present invention.

The plating solution of the present invention contains a zinc source, colloidal particles containing a polymer in which two or more zirconium atoms are bonded via hydroxyl groups, a sulfuric acid source, and water, and a dynamic light scattering method for the colloidal particles. The cumulant mean particle size measured at is between 0.5 and 500 nm.

The method for producing a plated steel sheet of the present invention includes a step of forming a plated layer on the steel sheet by performing electroplating using the plating solution of the present invention.

According to the present invention, a method for producing a plating solution capable of stably forming a zinc-based plating layer containing a Zr component on a steel sheet while suppressing the generation of harmful by-products and excessive accumulation of sulfuric acid components, A plating solution and a method for producing a plated steel sheet using the same can be provided.

As a result of intensive studies, the present inventors found that by using "basic zirconium carbonate" as a zirconium source, the basic zirconium carbonate can be satisfactorily dispersed as predetermined colloidal particles in an aqueous sulfuric acid solution. It has been found that a plated layer stably containing a Zr component can be formed by performing electroplating using Zr. In addition, since basic zirconium carbonate does not contain chloride ions or nitrate ions as constituents, it is less likely to produce harmful by-products during electroplating. It was found that it is difficult to generate The configuration of the present invention will be described below.

1. Method for Producing Plating Solution The method for producing the plating solution of the present invention comprises: 1) mixing a zinc source, a basic zirconium carbonate, a sulfuric acid source, and water to obtain a plating solution; It is preferable to further include the step of aging the liquid.

About Step 1) In this step, a zinc source, a basic zirconium carbonate, a sulfuric acid source, and water are mixed to obtain a plating solution (aqueous solution).

(zinc source)
The zinc source is zinc (metallic zinc (Zn)) or a zinc compound that is the main component of the plating layer. Examples of zinc compounds include _zinc sulfate ( _ZnSO4.7H2O , _ZnSO4 , or _ZnSO4.nH2O (n=1-6) ₎ , zinc oxide (ZnO), zinc chloride (( _ZnCl2 ), Zinc nitrate (Zn(NO ₃ ) _{2 or} Zn(NO ₃ ) 2.6H ₂ O) is included.In particular, not only can it be used as a sulfuric acid source, but also the molar ratio SO ₄ /Zr described later can be adjusted within a predetermined range. From the viewpoint of facilitating the formation of colloidal particles derived from basic zirconium carbonate, the zinc source is zinc sulfate (ZnSO ₄ .7H ₂ O, ZnSO ₄ , or ZnSO ₄ .nH ₂ O (n = 1 to 6). ) is preferably included.

One zinc source may be used, or two or more zinc sources may be used. For example, in addition to zinc sulfate heptahydrate (ZnSO ₄ .7H ₂ O), the zinc source may be a small amount of zinc chloride (ZnCl ₂ ) or zinc nitrate ( Zn(NO ₃ ) ₂ ) may further be included.

(basic zirconium carbonate)
Basic zirconium carbonate is a compound in which OH and _CO3 are coordinated to a Zr atom, specifically a polymer in which two or more Zr atoms are bonded via coordinated OH (Zr-OH bond). and CO ₃ or OH may be further coordinated to the Zr atoms constituting the polymer. Basic zirconium carbonate may be a hydrate.

Specifically, basic zirconium carbonate can have a composition represented by the following formula (1).
Formula ₍ 1): Zr(OH) _x ( _CO3 ) _yzH2O
In formula (1), 0<x≦6, 0.1≦y≦4, and 0≦z≦10. Note that x, y and z may each be a decimal number or an integer.

The basic zirconium carbonate may further contain small amounts of hafnium (Hf). The Hf concentration of the basic zirconium carbonate can be usually 0.05 or less in Hf/Zr molar ratio. The reason why basic zirconium carbonate contains Hf is that Hf is contained in raw materials for industrial production, and Hf and Zr have almost the same chemical and electrochemical properties and are difficult to separate. .

Although the form of the basic zirconium carbonate is not particularly limited, it can usually be particulate. The average particle size of basic zirconium carbonate is not particularly limited, but is, for example, 0.5 to 100 μm.

However, it is preferable that ammonium (NH ₄ ) is not coordinated to basic zirconium carbonate. That is, the basic zirconium carbonate is preferably not ammonium zirconium carbonate. This is because when ammonium is coordinated, the pH range in which zirconium oxide precipitates becomes excessively high, so even if the pH is raised by generating hydrogen on the plated surface, zirconium oxide is less likely to precipitate. In addition, if other components other than the constituent elements of water are coordinated, the components may be decomposed during electroplating to generate harmful by-products, contaminate the plating solution, or damage the plating equipment. Adhesion of products may occur. Further, when such basic zirconium carbonate is replenished to the plating solution, ammonium tends to accumulate in the plating solution and increase the viscosity of the plating solution.

ｐＨ２．１以下では、ＨＳＯ^４－が相対的に多く生成され、ｐＨ２．１以上ではＳＯ_４ ^２－が相対的に多く生成される。 (sulfuric acid source)
A sulfuric acid source is a compound that, when added to water, produces sulfate ions (SO ₄ ²⁻ ) or hydrogen sulfate ions (HSO ₄ ²⁻ ) (hereinafter collectively referred to as “sulfate ions”). Sulfate ions produce the following equilibrium reaction in an aqueous solution.

A relatively large amount of HSO ^4- is produced at a pH of 2.1 or lower, and a relatively large amount of SO ₄ ^2- is produced at a pH of 2.1 or higher.

Examples of sulfuric acid sources include sulfuric acid, sulfates (zinc sulfate, sodium sulfate, aluminum sulfate, magnesium sulfate, nickel sulfate, cobalt sulfate, tin sulfate, iron sulfate, vanadium sulfate, etc.). These sulfates can also be used as zinc sources or conductive aids.

The sulfuric acid source may be added separately from the zinc source and the conductive aid, or may be added together with the zinc source and the conductive aid. Above all, the sulfuric acid source preferably contains sulfuric acid from the viewpoint of facilitating adjustment of the pH to the range described below.

(other ingredients)
In addition, if necessary, other components than those described above may be further added. Examples of other components include alloying components that alloy with zinc and conductive aids.

Examples of alloying components include Ni or its compounds, Co or its compounds, Sn or its compounds, Fe or its compounds.

The conductive aid can be added from the viewpoint of lowering the voltage during electroplating, reducing the cost of electroplating power supply equipment, and reducing the power required for plating. The type of conductive aid is not particularly limited, but examples thereof include sodium sulfate, aluminum sulfate, magnesium sulfate, ammonium sulfate, potassium chloride and sodium chloride. Among them, sulfates such as sodium sulfate, aluminum sulfate, and magnesium sulfate are preferable from the viewpoint of being able to be used as a sulfuric acid source. This is because, like zinc sulfate described above, sulfate facilitates adjustment of the later-described molar ratio (SO ₄ /Zr) within a predetermined range, and facilitates formation of colloidal particles.

(mixture)
Then, these zinc source, basic zirconium carbonate, sulfuric acid source, water and, if necessary, other components are mixed.

When basic zirconium carbonate is added to an aqueous solution in which sulfate ions are present, the _CO3 coordinated to the Zr atom of the basic zirconium carbonate is dissolved in the aqueous solution in which sulfate ions are present, preferably at pH 3.0 where sulfate ions are present. It becomes unstable in the following aqueous solutions, desorbs from the basic zirconium carbonate, and is discharged out of the system as carbon dioxide gas.

That is, destabilized CO ₃ desorbs from basic zirconium carbonate. Then, sulfate ions in the aqueous solution are coordinated (covalently bonded) to Zr atoms in place of the desorbed _CO3 , or electrostatically attached to the ionized polymer (Zr-OH polymer) due to the desorption of _CO3 . It is thought that addition of sulfate ions (ionic bonding) to , or both, stabilizes the polymer (Zr—OH polymer) microscopic colloidal particles. Such a polymer in which two or more Zr atoms are bonded via OH and stabilized by sulfate ions is referred to as Zr hydroxide sulfate colloidal particles (hereinafter simply referred to as "colloidal particles"). That is, the polymer that constitutes the colloidal particles maintains the structure of the polymer that constitutes the basic zirconium carbonate (polymer in which two or more Zr atoms are bonded via coordinated OH) before being added to water. it seems to do.

When the Zr-OH polymer constituting the colloidal particles is a dimer, it is considered to have the following structure, for example.

Since the colloidal particles thus produced are positively charged, they can be well dispersed in the plating solution due to electrostatic repulsion. Also, the positively charged colloidal particles are attracted to the plated surface of the steel sheet, which has a negative potential at the cathode during electroplating. At this time, if the pH of the plating solution in the vicinity of the plated surface of the steel sheet rises due to hydrogen generation, the surface charge of the colloidal particles is deprived and sulfate ions are detached, and Zr constituting the colloidal particles is taken into the plating layer. be Zr constituting the colloidal particles is incorporated into the plating layer as Zr oxide when hydrogen (H) is desorbed while being incorporated into the plating layer. When hydrogen is not desorbed, it is incorporated into the plating layer as Zr hydroxide. As a result, Zr oxide (Zr oxide or Zr hydroxide) or hydrated Zr oxide is incorporated into the plating layer.

In addition, when the basic zirconium carbonate further contains Hf, it is considered that colloidal particles produced include colloidal particles in which some of the Zr atoms are replaced with Hf atoms. That is, even when the basic zirconium carbonate contains Hf, it produces colloidal particles in the same way as when it does not contain Hf. As a result, the resulting plated layer may contain Hf oxide as well as Zr oxide.

Then, the _CO3 detached from the Zr atom of the basic zirconium carbonate is discharged outside the system as _CO2 gas, and the OH and _H2O coordinated to the Zr atom of the basic zirconium carbonate are converted into Zr It is taken into the plating layer as a constituent element (OH or O) of the oxide. Therefore, since unnecessary components are less likely to accumulate in the plating solution, changes in the composition of the plating solution can be reduced, and work for adjusting the components of the plating solution can be reduced. Thus, a plating solution containing colloidal particles derived from basic zirconium carbonate is less likely to cause decomposition of components not involved in plating or generation of by-products during electroplating, so that the composition of the plating solution is stable.

The zinc source, basic zirconium carbonate, sulfuric acid source and water are preferably mixed so that the composition of the plating solution satisfies the following.

That is, the amount of zinc source to be added is preferably set so that the Zn concentration in the plating solution is 0.3 to 1.9 mol/L. When the Zn concentration is 0.3 mol/L or more, it is easy to supply a sufficient amount of Zn ions to the plating surface during electroplating, so electroplating can be stably continued. When the Zn concentration is 1.9 mol/L or less, precipitation of the zinc source can be easily suppressed when the plating solution is stored at room temperature (about 25°C). From the same point of view, the amount of zinc source to be added is more preferably set so that the Zn concentration in the plating solution is 0.5 to 1.6 mol/L.

The amount of basic zirconium carbonate to be added can be set according to the amount to be contained in the plating layer. Specifically, the amount of basic zirconium carbonate to be added is preferably set so that the Zr concentration in the plating solution is 0.02 to 1.6 mol/L. When the Zr concentration in the plating solution is 0.02 mol/L or more, not only is it easy to adjust the SO ₄ /Zr molar ratio of the plating solution within the range described later, but also the average particle size of the colloidal particles can be appropriately increased. It is easy to obtain a sufficient amount of Zr in the resulting plating layer. When the Zr concentration in the plating solution is 1.6 mol/L or less, not only is it easy to adjust the SO ₄ /Zr molar ratio of the plating solution within the range described below, but gelation of the plating solution can be avoided. In addition, since the average particle size of the particles does not become too large, precipitation can be prevented. From the same point of view, the amount of basic zirconium carbonate to be added is more preferably set so that the Zr concentration in the plating solution is 0.1 to 1.2 mol/L.

The Zn concentration or Zr concentration in the plating solution is the number of moles of Zn or Zr per volume corresponding to the amount of added zinc source or basic zirconium carbonate, regardless of whether it is ionic or non-ionic. The Zn concentration or Zr concentration in the plating solution can be measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

The sulfuric acid source is added so that the pH of the plating solution is within a predetermined range.

That is, the pH of the plating solution is not particularly limited as long as the colloidal particles to be generated can exist in a stably dispersed state and the elution of the steel sheet and the plating layer can be suppressed, and the pH is 3.0 or less. , preferably 0.1 to 3.0. When the pH of the plating solution is 0.1 or more, the elution of Fe from the steel sheet can be further reduced, so that a plating layer with higher corrosion resistance can be easily obtained. For example, after the steel sheet is immersed in the plating solution, Fe is eluted from the steel sheet into the plating solution before plating is started, and becomes Fe ²⁺ ions that are electroplated together to reduce the corrosion resistance of the plating layer. can be suppressed. On the other hand, when the pH is 3.0 or less, the basic zirconium carbonate is easily dissolved in water, and colloidal particles are easily generated. In addition, the colloidal particles that are produced are less likely to aggregate or settle, and are easier to stably disperse in the plating solution.

Reasons why the pH is preferably 3.0 or less include the following points. That is, when the plating solution contains eluted Fe ions, since the plating solution is fluid, the contact with oxygen in the air is substantially large, and the divalent Fe ions (Fe ²⁺ ) are in contact with the air. It is easily oxidized by the oxygen inside. Bivalent Fe ions (Fe ²⁺ ) become trivalent Fe ions (Fe ³⁺ ) when oxidized with oxygen. If the pH is too high in a state where there are many trivalent Fe ions (Fe ³⁺ ), the trivalent Fe ions are likely to change to Fe hydroxide (Fe(OH) ₃ ) or Fe oxyhydroxide (FeOOH). Since these have low solubility, they tend to precipitate as particles in the plating solution, and the particles of precipitated Fe hydroxide (Fe(OH) ₃ ) and Fe oxyhydroxide (FeOOH) aggregate over time to form sludge. Prone. As a result, the dispersion of the generated colloidal particles of Zr hydroxide sulfate is hindered, and the amount of colloidal particles that can be dispersed in the plating solution is substantially reduced, which may reduce the amount of colloidal particles entering the plating layer. In addition, sludge adheres to the plated layer, and there is a possibility that molding defects may occur due to deterioration of the appearance or catching during mold molding. In addition, sludge may accumulate in tanks, pipes, valves, etc. due to sedimentation of sludge, resulting in deterioration of workability. Also from the viewpoint of making such inconvenience less likely to occur, it is preferable to set the pH to 3.0 or less.

From the same viewpoint, the pH of the plating solution is more preferably 0.5 to 2.8. The pH of the plating solution can be measured with a composite electrode in which a glass electrode and a reference electrode are integrated, or a composite electrode in which a temperature compensation electrode is also integrated.

The pH of the plating solution can be adjusted, for example, by adjusting the amount of sulfuric acid source added or the amount of zinc source containing sulfate ions added.

In order to stably disperse the colloidal particles in the plating solution, it is preferable that the SO ₄ and Zr molar ratio (SO ₄ /Zr) in the plating solution is 1.5 or more. When the SO ₄ /Zr ratio is 1.5 or more, the average particle size of the colloidal particles does not become excessively large, so that it is difficult to precipitate or settle in the plating solution, and the proportion of colloidal particles that do not contribute to plating can be reduced. . For the same reason, SO ₄ /Zr is more preferably 2.0 or more, more preferably 2.5 or more. Although the upper limit of SO ₄ /Zr is not particularly limited, it can be set to 200, for example, from the viewpoint of easiness of preparation and blending of the plating solution.

Note that SO ₄ in SO ₄ /Zr includes all those that exist as SO ₄ in the plating solution regardless of whether they are ions or nonions. Therefore, SO ₄ in SO ₄ /Zr includes not only sulfate ions (SO ₄ ²⁻ ) but also hydrogen sulfate ions HSO ₄ ²⁻ and SO in sulfates such as undissociated zinc sulfate (ZnSO ₄ ). ₄ is also included. The reason why SO ₄ in sulfate such as undissociated zinc sulfate (ZnSO ₄ ) is included is that when the concentration of sulfate ions in the plating solution decreases, the sulfate dissociates to generate sulfate ions. It is for

The SO ₄ /Zr ratio of the plating solution can be calculated from the SO ₄ concentration and Zr concentration of the plating solution. The SO ₄ concentration in the plating solution can be measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

SO ₄ /Zr can be adjusted by the amount of sulfuric acid source added and the amount of basic zirconium carbonate added. In order to increase SO ₄ /Zr, for example, it is preferable to increase the amount of the sulfuric acid source and decrease the amount of basic zirconium carbonate.

In addition to the above components, when a conductive additive is further mixed, the content of the conductive additive in the plating solution varies depending on the type. L or less is preferable. When the sulfuric acid concentration is 2.9 mol/L or less, the conductive aid is less likely to precipitate even when stored at room temperature (about 25°C), and it is possible to suppress hindrance during the next electroplating after rest. . The sulfuric acid concentration is the number of moles per volume of sulfuric acid corresponding to the added sulfate, regardless of whether it is ionic or nonionic. (In the case of sodium sulfate, the concentration of sodium) can be measured, and the concentration of sulfuric acid, which becomes an anion, can be obtained from the chemical formula of the sulfate.

In this step, an aqueous solution in which colloidal particles are well dispersed, that is, a plating solution can be obtained. It is preferable to further perform the step 2) from the viewpoint of making the

2) Step In this step, the plating solution obtained in 1) above is further aged.

Aging is preferably carried out so that the particle size of the colloidal particles produced in step 1) is appropriately reduced. Specifically, the colloidal particles are composed of a polymer in which two or more Zr atoms are bonded via coordinated OH. ₄ to lower the molecular weight. As a result, the colloidal particles have a smaller particle size than immediately after generation, so that a plating solution containing highly dispersed colloidal particles can be obtained.

The average particle size of the colloidal particles in the plating solution after aging is not particularly limited as long as it can be dispersed more stably in the plating solution and the Zr component can be stably contained in the plating layer. For example, from the viewpoint of stably containing the Zr component in the plating layer and preventing the colloidal particles from precipitating even when the plating solution is stored in a non-fluid state, the colloidal particles measured by the dynamic light scattering method The cumulant average particle size of is preferably 0.5 to 500 nm. When the cumulant average particle size of the colloidal particles is 0.5 nm or more, the colloidal particles are easily incorporated into the plating layer, and when it is 500 nm or less, the colloidal particles are less likely to precipitate without flowing the plating solution. From the same point of view, the colloidal particles preferably have a cumulant average particle size of 0.7 to 350 nm.

The cumulant average particle size of colloidal particles can be measured as the cumulant average particle size at 25° C. by a dynamic light scattering method conforming to JIS Z 8828:2019 (ISO 22412:2017). JIS Z 8828:2019 corresponds to ISO22412:2017.

The average particle size of the colloidal particles can be adjusted by adjusting the amount of basic zirconium carbonate added in step 1) and the aging conditions (temperature, time) in this step. In order to reduce the average particle size of the colloidal particles, for example, the amount of basic zirconium carbonate added in step 1) above may be reduced, the aging temperature may be raised, and the aging time may be lengthened. is preferred.

Aging may be performed at room temperature or under heating. From the viewpoint of making the colloidal particles have a desired average particle size in a relatively short time, aging is preferably carried out under heating.

Specifically, the aging temperature is not particularly limited as long as it is set so that the average particle size of the produced colloidal particles is within a predetermined range. 80° C. is more preferred.

Similarly to the above, the aging time may be set so that the average particle size of the produced colloidal particles is within a predetermined range. It is preferably up to 200 hours, and in the case of aging at 50-70° C., it is preferably 0.3-20 hours.

Aging is carried out by examining the relationship between the aging conditions (temperature and time) and the average particle size of the colloidal particles in advance, and allowing the colloidal particles to stand still under predetermined conditions until the desired average particle size is achieved. Alternatively, aging may be continued until the desired average particle size is reached while measuring the average particle size of the colloidal particles in the plating solution at predetermined intervals.

2. Plating Solution The plating solution of the present invention is obtained by the method for producing the plating solution of the present invention. That is, the plating solution of the present invention is obtained by mixing a zinc source, basic zirconium carbonate, a sulfuric acid source, and water. Contains colloidal particles containing coalescence, a source of sulfuric acid, and water.

Colloidal particles are composed of a polymer in which zirconium atoms are bonded together via hydroxyl groups, and are derived from basic zirconium carbonate. The average particle size of colloidal particles in the plating solution is the same as described above. The Zn concentration, Zr concentration, SO ₄ /Zr and pH of the plating solution are also the same as described above.

The plating solution of the present invention can be used for various electroplating, and is preferably used as a zinc-based plating solution for zinc-based plating on the surface of a steel sheet.

3. Method for producing plated steel sheet The method for producing a plated steel sheet of the present invention includes a step of forming a plating layer on a steel sheet by performing electroplating using the plating solution of the present invention.

Specifically, a plating layer is formed on the surface of the steel sheet (material to be plated), which is the cathode, by energizing the steel sheet, which is the cathode, with the anode arranged so as to face it in the plating solution. do.

The type of steel sheet used as the cathode is not particularly limited, but examples thereof include cold-rolled steel sheets and stainless steel sheets (including austenitic, martensitic, ferritic, and ferrite-martensite two-phase systems).

The thickness of the steel plate can be appropriately set according to the application. For example, when a plated steel sheet is used as a material for electrical equipment, the thickness of the steel sheet is preferably, for example, 0.2 to 4.0 mm, and from the viewpoint of weight reduction, it is 0.2 to 2.0 mm. is preferred.

As the anode, for example, a titanium electrode coated with iridium oxide is used.

The electroplating may be performed with the steel sheet (cathode) fixed (batch type) or may be performed while the steel sheet (cathode) is conveyed (continuous type). Electroplating may be performed while continuously supplying a plating solution between the steel sheet (cathode) and the anode, or may be performed without supplying the solution. Furthermore, the electroplating cell structure may be horizontal (horizontal), vertical, or radial.

Electroplating may be performed without flowing the plating solution, or may be performed while flowing. In particular, when electroplating is performed by a batch method, it is preferable to flow the plating solution from the viewpoint of facilitating continuous supply of consumed Zn ions, colloidal particles, and other components to the vicinity of the plated surface of the steel sheet.

Specifically, the flow velocity (relative velocity) of the plating solution to the steel sheet is preferably 0.1 to 10 m/s. When the relative velocity of the plating solution is 10 m/s or less, the supply rate of hydrogen ions to the vicinity of the plating surface is unlikely to be excessive, so it is difficult to lower the pH of the plating solution in the vicinity of the plating surface, and the precipitation of Zr oxide is inhibited. hard to be Further, when the relative flow velocity is 0.1 m/s or more, plating components and the like can be stably supplied to the plating surface. In addition, in a plating apparatus in which a plating solution is supplied between the steel plate and the anode, Zn, colloidal particles, and other components consumed during electroplating are continuously supplied to the plating surface, so the plating solution and the steel plate can be zero.

The temperature of the plating solution is not particularly limited as long as it is a temperature at which a plating layer can be stably formed on the plated surface of the steel sheet, but is preferably 20 to 80°C. When the temperature of the plating solution is 20° C. or higher, diffusion of plating components such as Zn ions and colloidal particles to the plating surface is less likely to decrease, and these are easily supplied sufficiently, so that electroplating can be stably continued. When the temperature of the plating solution is 80° C. or lower, excessive evaporation of water from the plating solution is less likely to occur, so that changes in the composition of the plating solution due to thickening of the plating components are less likely to occur, and the quality of the plating is more likely to be stable. The temperature of the plating solution is more preferably 40 to 70° C. for the same reason.

The current density is not particularly limited, but from the viewpoint of facilitating the deposition of Zr oxide at the same time as Zn on the plated surface of the steel sheet during electroplating, that is, from the viewpoint of facilitating the increase of the pH of the plated surface due to hydrogen generation, It is preferably 10 A/dm ² or more. When the current density is 10 A/dm ² or more, the amount of hydrogen generated on the plated surface of the steel sheet increases sufficiently, so that the pH tends to moderately rise substantially directly above the plated surface. The upper limit of the current density can be, for example, 500 A/dm ² or less from the viewpoint of suppressing the generation of Zn hydroxide due to an excessive increase in pH, the contamination of the Zn hydroxide into the plating layer, and the resulting deterioration of the appearance. .

4. Plated Steel Sheet The plated steel sheet obtained by the method for producing a plated steel sheet of the present invention has a steel sheet and a plating layer formed on at least one surface of the steel sheet.

The plating layer contains Zn and Zr or its oxide.

The content of Zr or Zr derived from its oxide in the plating layer is not particularly limited, but is preferably 0.1 to 30% by mass, more preferably 0.2 to 15% by mass with respect to the plating layer. is more preferred.

The Zr content in the plating layer can be measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) or energy dispersive X-ray spectroscopy using an electron beam as the primary beam.

The plated layer may further contain components other than those described above, such as alloy components and components derived from conductive aids (Na, Al, Mg, etc.). The total content of other components may preferably be 5% by mass or less with respect to the plating layer.

The coating weight of the plating layer is not particularly limited, but is preferably 1 to 60 g/m ² per side, more preferably 2 to 30 g/m ² .

Plated steel sheets can be preferably used as base sheets for automobiles, electrical equipment, building materials, and coated steel sheets, for example.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited by these examples.

1. Components of plating solution (1) Zirconium source (Zr source)
Zr basic carbonate: basic zirconium carbonate (Zr(OH)x( _CO3 ) _yzH2O , x=3.1, y=0.45, z=7.2), Zr(Hf) _O2 Converted concentration 40.3% by mass, Hf/Zr = 0.01 (molar ratio), average particle size 12 µm
Zr hydroxide: hydrated zirconium hydroxide, Zr(OH) _4.n ( _H2O ), Zr(Hf) _O2 conversion concentration 29.8% by mass, average particle size 3.0 μm
Zr oxide: zirconium oxide (ZrO ₂ ), average particle size 1.6 μm
Zr sulfate: zirconium sulfate tetrahydrate (Zr( _SO4 ) _2.4H2O ), average particle _size 2.4 µm

The composition and average particle size of the Zr source were each measured by the following methods.

(Zr, Hf concentration)
The concentrations of Zr and Hf in the Zr source were measured by the EDTA titration method and converted to Zr(Hf)O ₂ concentrations.

(Composition of basic Zr carbonate)
1) First, the amount of CO ₃ (M1) was measured from the weight loss due to the generation of CO ₂ when dissolved in dilute sulfuric acid. At this time, the pH of the dilute sulfuric acid was adjusted to be zero or less even after the basic Zr carbonate was dissolved.
2) Next, basic Zr carbonate was heated to 600° C., and the total amount of H ₂ O and CO ₃ (M2) was measured from the weight loss when H ₂ O and CO ₂ were desorbed.
3) The amount of H 2 O was calculated by subtracting the amount of CO ₃ (M1) obtained with dilute sulfuric acid obtained in 1) above from the total amount (M2) obtained in ₂ ) above. The composition (x, y, z in formula (1)) was identified from these quantitative ratios and molar masses.

(Average particle size)
The average particle size of the zirconium source was measured by a laser diffraction/scattering method. Ethanol was used as the dispersion medium. The median diameter was defined as the average particle diameter.

(2) Zinc source (Zn source)
Zn sulfate: zinc sulfate heptahydrate ( _ZnSO4.7H2O , average particle _size 0.4 mm)
Metal Zn: Metal zinc (Zn), particle size 3 to 7 mm
Zn oxide: Zinc oxide (ZnO), average particle size 1 μm

(3) Sulfuric acid source Sulfuric acid (H ₂ SO ₄ ), zinc sulfate heptahydrate (when used as zinc source), conductive aid (when conductive aid is used)

(4) Conductive agent Na sulfate: sodium sulfate anhydride, Na ₂ SO ₄ , solid (powder)
Al sulfate: aluminum sulfate hydrate, Al ₂ (SO ₄ ) _{3.nH 2} O, Al concentration: 16.5% by mass in terms of Al ₂ O ₃ , solid (powder)
Mg sulfate: magnesium sulfate heptahydrate, _MgSO4.7H2O , solid ( _powder )

(5) pH adjuster sulfuric acid, sodium hydroxide

2. Preparation and Evaluation of Plating Solution <Tests 1-2, 4-6 and 10>
Each component and ion-exchanged water were mixed at the temperature shown in Table 1 so as to have the composition and pH shown in Table 1 to obtain a plating solution (mixing step).

<Tests 3, 7-9 and 11-31>
Each component and ion-exchanged water were mixed at the temperature shown in Table 1 so as to obtain the composition and pH shown in Table 1 (mixing step). The pH was adjusted by the amount of sulfuric acid added. Next, the resulting aqueous solution was allowed to stand at the temperature shown in Table 1 for 2 hours (aging step) to obtain a plating solution.

<Evaluation>
The pH of the obtained plating solution, the average particle size of the colloidal particles and the dispersibility thereof were measured by the following methods.

(pH)
The pH of the resulting plating solution was measured after aging at the same temperature as during mixing shown in Table 1 using a composite electrode in which three electrodes, a glass electrode, a reference electrode and a temperature compensation electrode, were integrated.

(Average particle size of colloidal particles)
The average particle size (cumulant average particle size) of the colloidal particles in the obtained plating solution was measured by the dynamic scattering method (JIS Z 8828). Measurements were made at 25°C.

(dispersibility)
The resulting plating solution was placed in a container and stored at room temperature for 48 hours, after which the dispersibility of the colloidal particles was visually observed. Then, the dispersibility was evaluated according to the following criteria.
A: All the added Zr source was stably dispersed without precipitating, and the state of the bottom of the container could be determined when the plating solution was placed in the container and raised to a height of 100 mm. In addition, the colloidal particles have an average particle size of 10 nm or less, and the plating solution has a lower degree of white turbidity than the criteria indicated by ◯ below and a high degree of transparency.
◯: All the added Zr source was stably dispersed without sedimentation, and when the plating solution was placed in a container and raised to a height of 100 mm, the degree of cloudiness was low and the state of the bottom of the container could be determined.
Δ: The added Zr source is stably dispersed without precipitating, but when the plating solution is placed in a container and raised to a height of 100 mm, the state of the bottom of the container cannot be determined due to cloudiness.
x: Even part of the added Zr source precipitates or aggregates.

Table 1 shows the preparation conditions and evaluation results of the plating solutions obtained in Tests 1 to 31. The concentrations of Zr, Zn, Na, Al, Mg, and SO ₄ in Table 1 are expressed as molar concentrations (mol/L) of the added amounts of each component. That is, for each component, regardless of whether it is dispersed or not, the number of moles of each component added divided by the volume of the solution is listed. All of the zinc source and conductive aid dissolved.

As shown in Table 1, tests 1-26 (invention) using basic Zr carbonate as the zirconium source show good dispersion even at room temperature.

In particular, when the molar ratio of SO ₄ /Zr is 1.5 or more, the average particle size becomes small and the dispersibility is further enhanced (comparison between Tests 9 and 11).

Further, it can be seen that when the pH is 3.0 or less, the particles are dispersed, and when the pH is 2.8 or less, the particle size decreases and the dispersibility is further enhanced (comparison between Tests 19 and 20).

It can also be seen that the higher the mixing temperature and the aging temperature, the higher the dispersibility (compare Tests 5, 12 and 16).

On the other hand, in Tests 27 to 29 (comparative examples) using Zr hydroxide as a zirconium source _, dispersion did not occur even when heated to 60° C. sedimentation). In addition, in Tests 30 and 31 using Zr oxide as the zirconium source, even if SO ₄ /Zr is increased to around 3600, it is found that the particles do not disperse (settle).

<Tests 32-35>
A plating solution was obtained in the same manner as in Test 1 except that each component and ion-exchanged water were mixed (mixing step) and aged so that the composition and pH shown in Table 2 were obtained. In Test 35, since Zr sulfate (strongly acidic) was used as both the Zr source and the sulfuric acid source, the pH was adjusted by adding Na hydroxide.

<Evaluation>
The pH of the plating solutions obtained in Tests 32 to 35, the average particle size of colloidal particles and their dispersibility were measured in the same manner as described above.

Table 2 shows the preparation conditions and evaluation results of the plating solutions obtained in Tests 32-35.

As shown in Table 2, in tests 32 to 34 (invention) using basic Zr carbonate as the zirconium source, the dispersibility was high even when the molar ratio ( _SO /Zr) was low. I understand.

In contrast, in Test 35 (comparative example) using Zr sulfate as the zirconium source, there were no colloidal particles themselves, and the particle size was not measured.

3. Preparation of plated steel sheet <Tests 36 to 44>
(Preprocessing)
An annealed cold-rolled steel sheet (low-carbon aluminum-killed steel) was prepared as the steel sheet. This was electrolytically degreased in a 2.5% by mass sodium hydroxide aqueous solution, and then pickled in a 5% by mass sulfuric acid aqueous solution.

(Electroplating)
As a plating apparatus, a vertical plating apparatus was prepared in which a rectangular tube was arranged in the vertical direction and an anode and a steel sheet could be set therein so as to face the anode. Then, 8 L of the plating solution shown in Table 3 was circulated (thrown in and flowed) in the rectangular tube of the plating apparatus. Then, the pickled steel plate was immersed in the plating solution. The anode electrodes were arranged at intervals of 10 mm so as to face the steel plate. As the anode electrode, titanium coated with iridium oxide was used. Then, electroplating was performed under the conditions of the current density and the flow rate of the plating solution shown in Table 3 to obtain a plated steel sheet. The amount of plating deposited was 20 g/m ² .

<Evaluation>
The Zr concentration in the obtained plating layer was measured by the following method.

(Zr concentration)
The Zr concentration was measured by energy dispersive X-ray spectroscopy using an electron beam of 15 keV as the primary beam.

Table 3 shows the evaluation results of Tests 36-44.

As shown in Table 3, in Tests 36 to 43 using the plating solutions (present invention) prepared in Tests 32 to 34, Zr, specifically Zr oxide, was contained in the plating layer in an amount of 1% by mass or more. I understand. Also, it can be seen that the higher the current density, the higher the Zr concentration in the plating layer.

On the other hand, in Test 44 using the plating solution (comparative example) prepared in Test 35, the content of Zr contained in the plating layer was less than 0.1% by mass, indicating that it is hardly contained.

According to the present invention, a method for producing a plating solution capable of stably forming a zinc-based plating layer containing a Zr component on a steel sheet while suppressing the generation of harmful by-products and excessive accumulation of sulfuric acid components, A plating solution and a method for producing a plated steel sheet using the same can be provided.

Claims (8)

mixing a zinc source, a basic zirconium carbonate, a sulfuric acid source, and water to obtain a plating solution having a pH of 3.0 or less ;
A step of heating and aging the plating solution so that the colloidal particles generated from the basic zirconium carbonate have a cumulant average particle size measured by a dynamic light scattering method of 0.5 to 500 nm;
including
The basic zirconium carbonate is represented by the following formula (1) and ammonium is not bound,
A method for producing a plating solution.
Formula ( 1): _Zr ( OH) _x ( _CO3 ) _yzH2O
(In formula (1), 0 < x ≤ 6, 0.1 ≤ y ≤ 4, 0 ≤ z ≤ 10) the zinc source comprises zinc sulfate;
The method for producing the plating solution according to claim 1 . the sulfuric acid source comprises sulfuric acid;
A method for producing a plating solution according to claim 1 or 2 . The molar ratio SO ₄ /Zr between SO ₄ and Zr in the plating solution is 1.5 or more.
A method for producing a plating solution according to any one of claims 1 to 3 . The plating solution has a pH of 0.1 to 3.0.
A method for producing a plating solution according to any one of claims 1 to 4 . Further comprising a step of aging the plating solution at 40 to 100 ° C.
A method for producing a plating solution according to any one of claims 1 to 5 . A step of obtaining a plating solution by the method for producing a plating solution according to any one of claims 1 to 6;
A step of forming a plating layer on the steel sheet by performing electroplating using the plating solution,
A method for producing a plated steel sheet. The electroplating is performed at a current density of 10 A / dm ² or more,
A method for producing a plated steel sheet according to claim 7 .