JP7669028B2 - Method for producing metal plate having layered double hydroxide on its surface - Google Patents

Description

The present invention relates to a method for producing a metal plate having a layered double hydroxide on its surface.

Magnesium alloys and aluminum alloys are expected to be used as lightweight components for transportation equipment (automobiles, trains, etc.), home appliances, portable electronic devices, and welfare materials (wheelchairs, canes, etc.), but they have a problem of low corrosion resistance, especially in environments containing chloride ions. Transportation equipment and home appliances are exposed to rain, seawater splashes, and human sweat that contain chloride ions. For this reason, the formation of a highly corrosion-resistant coating and, depending on the component, painting in addition to the highly corrosion-resistant coating are required.
Conventional corrosion-resistant coatings for magnesium materials mainly contain elements that have a high environmental impact, such as chromium, manganese, and fluorine, but as environmental regulations such as RoHS and REACH have been strengthened, the use of chromate treatment has been prohibited or eliminated. For this reason, there is a demand for corrosion-resistant coatings that are composed of elements that have a small environmental impact during the manufacturing process and are highly safe for the environment during use.

There has been a report of a highly corrosion-resistant coating formed by anodizing in a solution composed of environmentally friendly elements, mainly phosphoric acid (Patent Document 1). However, anodizing has the disadvantage of consuming a large amount of power.
In addition, chemical conversion solutions and anodizing electrolytes containing phosphoric acid, manganic acid, and calcium oxide have been developed (Non-Patent Documents 1 to 4), and the films produced therefrom exhibit high corrosion resistance and adhesion to paint. However, since manganic acid is a substance that requires wastewater treatment, there is a need for a corrosion-resistant film with even lower environmental impact and a method for producing the same.

In recent years, layered double hydroxide (LDH: general formula [M ²⁺ _1-x M ³⁺ _x (OH) ₂ ][A ^n- _x/n ·mH ₂ O]) coatings have attracted attention as corrosion-resistant coatings for magnesium alloys and aluminum alloys (see Patent Documents 2, 3 and 4).
LDH is a compound in which a host layer of metal hydroxide layers such as Mg or Al and a guest layer consisting of anions and water molecules are alternately laminated, and it can incorporate not only anions but also organic molecules between the layers. For this reason, it is expected that forming a coating with LDH with a corrosion inhibitor for magnesium alloys or aluminum alloys inserted between the layers will promote self-repair of scratches in the coating. To date, coatings have been formed on the surfaces of AZ31 alloys and Mg-Al-Zn-Ca alloys by autoclave (high temperature/high pressure steam) treatment, coatings by electrolytic deposition on the surfaces of AZ91 in metal nitrate solutions such as Zn(NO ₃ ) ₂ -Al(NO ₃ ) ₃ , coatings by immersion in LDH slurry and heat treatment, and LDH coatings by chemical conversion treatment in an Al(NO ₃ ) ₃ solution.

The autoclave treatment has the advantage of high adhesion because it is a method of growing LDH from the surface of the substrate magnesium alloy, but it takes a long time to process and is costly because a large high-pressure steam furnace must be installed for large components. The slurry immersion method also has the disadvantage of a long processing time. Electrolytic deposition can form a film in a short time, but the pH of the metal nitrate solution is low, so there is a concern that the substrate may corrode during processing, and there are problems with application to Mg alloys and pure Mg, which have relatively low corrosion resistance. A treatment method that can be performed in a relatively short time has been developed for chemical conversion treatment, but the composition and form of the LDH layer are highly dependent on the substrate Mg alloy because Mg ions eluted from the substrate become the main component of the LDH layer. In addition, whether electrolytic deposition or chemical conversion treatment, it is difficult to insert any anion or organic molecule between the LDH layers after the coating is formed. This is because the ion exchange reaction between the LDH layers takes place in an aqueous solution, so there is a high possibility that the substrate magnesium alloy will be corroded during the ion exchange treatment.

Patent No. 5517024 Patent No. 4303948 WO2019-069841 Special table number 2015-520018

Shulha, et al., Sci. Rep., 8: 16409 (2018). Wu et al., Appl. Surf. Sci., 313 834 (2014) Light Metals Vol. 67 No. 10 (2017), 511-517 Electrochimica Acta, 283 (2018) 1845-1857

Conventional methods for coating the surfaces of magnesium alloys or aluminum alloys with layered double hydroxides (LDHs) have issues such as long processing times of several hours to several days, high corrosiveness of the processing solution restricting the alloy compositions that can be processed, high costs, and restrictions on the LDH composition and the ions that can be inserted between layers.

As a result of intensive research, the inventors of the present invention came up with the idea that the use of electrophoretic deposition may enable the processing time to be shortened and the LDH composition and ions to be inserted between layers to be freely selected. The electrophoretic deposition method is a method in which ceramic particles are charged and dispersed in an electrolyte, an electrode substrate is immersed in the suspension, and an electric field is applied between the counter electrode to directly deposit the ceramic particles on the electrode substrate. The inventors focused on the advantages of the electrophoretic deposition method, such as the ability to deposit LDH powders of various compositions and the ability to deposit LDH powders with any anion or organic molecule inserted between layers.
On the other hand, it is known that the electrophoretic deposition method generally has a problem in adhesion between the ceramic particle deposition layer and the electrode substrate. The present inventor discovered that the adhesion of the deposition layer can be improved by adding metal ions to the electrolyte and electrolytically depositing them as hydroxides together with the LDH powder, and thus completed the present invention.

In other words, the present invention solves the above-mentioned problems by providing a method for forming films of layered double hydroxide powders and metal hydroxides of various compositions in a short period of time, such as one minute to several tens of minutes, and a method for forming films containing layered double hydroxide powders with any anion or organic molecule (inhibitor) inserted between the layers.

[1] As shown in Figs. 1 and 2, the method for producing a metal plate having a layered double hydroxide on its surface includes the steps of: dispersing a layered double hydroxide powder in a first electrolytic solution containing water (S100); immersing an electrode substrate and a first counter electrode plate in a suspension containing the first electrolytic solution and the layered double hydroxide powder, the electrode substrate being a metal plate to be coated (S102); and applying an electric field between the first electrode substrate and the first counter electrode plate to electrophoretically deposit the layered double hydroxide powder on the electrode substrate (S104, S106).
The method includes the steps of: adding metal ions to a second electrolytic solution containing water (S110); immersing an electrode substrate on which the layered double hydroxide powder has been deposited and a second counter electrode plate in the second electrolytic solution containing the added metal ions (S112); and applying an electric field between the electrode substrate on which the layered double hydroxide powder has been deposited and the second counter electrode plate, thereby electrolytically depositing the metal ions as hydroxides on the electrode substrate on which the layered double hydroxide powder has been deposited (S114, S116).
Preferably, the method includes a step (S108) of continuing electrophoretic deposition until the thickness of the deposited layer of layered double hydroxide powder on the electrode substrate 12 reaches a predetermined value, and then removing the electrode substrate 12 coated with layered double hydroxide from the first electrolytic solution.

[2] The method for producing a metal plate having a layered double hydroxide on its surface according to the present invention includes, as shown in Figs. 1 and 5, a step of adding metal ions to a third electrolytic solution containing water (S200), a step of immersing an electrode substrate and a third counter electrode plate in the third electrolytic solution containing the added metal ions (S202), the electrode substrate being a metal plate to be coated (S204, S206), and a step of applying an electric field between the electrode substrate and the third counter electrode plate to electrolytically deposit the metal ions as hydroxides on the electrode substrate (S205, S206).
The method includes the steps of: dispersing a layered double hydroxide powder in a fourth electrolytic solution containing water (S210); immersing an electrode substrate on which the hydroxide of the metal ion is electrolytically deposited and a fourth counter electrode plate in a suspension consisting of the fourth electrolytic solution and the layered double hydroxide powder (S212); and electrophoretically depositing the layered double hydroxide powder on the electrode substrate by applying an electric field between the electrode substrate on which the hydroxide of the metal ion is electrolytically deposited and the fourth counter electrode plate (S214, S216).
Preferably, the electrolytic deposition is continued until the thickness of the metal hydroxide on the electrode substrate 12 reaches a predetermined value, and then the electrode substrate 12 coated with the metal hydroxide is removed from the third electrolytic solution (S208). The metal hydroxide is a hydroxide of the metal ion.

[3] A method for producing a metal plate having a layered double hydroxide on its surface according to the present invention includes, as shown in, for example, Figs. 1, 7 and 8, a step of adding metal ions to a fifth electrolytic solution containing water and dispersing a layered double hydroxide powder in the fifth electrolytic solution (S300), or a step of dispersing a layered double hydroxide powder in the fifth electrolytic solution containing water and adding metal ions to the fifth electrolytic solution (S300), a step of immersing an electrode substrate 12 and a fifth counter electrode plate in a suspension consisting of the fifth electrolytic solution containing the added metal ions and the layered double hydroxide powder, the electrode substrate 12 being a metal plate to be coated (S302), and a step of electrophoretically depositing a complex of the hydroxide of the metal ions and the layered double hydroxide powder on the electrode substrate 12 by applying an electric field between the electrode substrate 12 and the fifth counter electrode (S304, S306).
The method includes the steps of: adding metal ions to a sixth electrolytic solution containing water (S310); immersing an electrode substrate on which a complex of the hydroxide of the metal ion and the layered double hydroxide powder has been deposited and a sixth counter electrode plate in the sixth electrolytic solution containing the added metal ions (S312); and applying an electric field between the electrode substrate 12 and the sixth counter electrode plate to electrolytically deposit the hydroxide of the metal ion on the electrode substrate on which the complex of the hydroxide of the metal ion and the layered double hydroxide powder has been deposited (S314, S316).
Preferably, the electrophoretic deposition is continued until the thickness of the composite deposition layer of the metal hydroxide and the layered double hydroxide powder on the electrode substrate 12 reaches a predetermined value, and then the electrode substrate 12 covered with the composite deposition layer is removed from the fifth electrolyte (S308).

[4] A method for producing a metal plate having a layered double hydroxide on its surface according to the present invention includes, as shown in, for example, Figs. 1, 7 and 10, a step of adding metal ions to a seventh electrolytic solution containing water (S400), a step of immersing an electrode substrate and a seventh counter electrode plate in the seventh electrolytic solution containing the added metal ions (S402), the electrode substrate 12 being the metal plate to be coated (S404, S406), and a step of applying an electric field between the electrode substrate 12 and the seventh counter electrode plate to electrolytically deposit the metal ions as hydroxides on the electrode substrate 12 (S404, S406).
The method includes the steps of adding metal ions to an eighth electrolytic solution containing water and dispersing a layered double hydroxide powder in the eighth electrolytic solution, or dispersing a layered double hydroxide powder in the eighth electrolytic solution containing water and adding metal ions to the eighth electrolytic solution (S410); immersing an electrode substrate on which the hydroxide of the metal ions is electrolytically deposited and an eighth counter electrode plate in a suspension consisting of the eighth electrolytic solution containing the added metal ions and the layered double hydroxide powder (S412); and applying an electric field between the electrode substrate on which the hydroxide of the metal ions is electrolytically deposited and the eighth counter electrode plate, thereby electrophoretically depositing a complex of the hydroxide of the metal ions and the layered double hydroxide powder on the electrode substrate 12 (S414, S416).
Preferably, the electrophoretic deposition is continued until the thickness of the metal hydroxide on the electrode substrate 12 reaches a predetermined value, and then the electrode substrate 12 coated with the metal hydroxide is removed from the seventh electrolyte (S408).

[5] In the method [1] to [4] for producing a metal plate having a layered double hydroxide on its surface according to the present invention, the first to eighth electrolytic solutions are preferably mixed solvents of an organic solvent and water.
[6] In the method [5] for producing a metal plate having a layered double hydroxide on its surface according to the present invention, the volume ratio of the organic solvent to the water is preferably from 99:1 to 70:30 (organic solvent:water).
If the volumetric percentage of water exceeds 30%, corrosion of the substrate magnesium alloy or aluminum alloy in the coating treatment solution increases, and hydrogen gas generated by the reduction reaction of water increases, resulting in more defects in the coating. If the volumetric percentage of water is less than 1%, the concentration of the organic solvent is too high to obtain the electrical conductivity required for electrophoretic deposition. If the volumetric percentage of water is 1% or more and 30% or less, with the remainder being an organic solvent, a dense layered double hydroxide layer can be produced.
[7] In the method [5] or [6] for producing a metal plate having a layered double hydroxide on its surface according to the present invention, the organic solvent preferably includes any one of ethanol, methanol, butanol, propanol, isopropanol, glycerin, ethylene glycol, acetone, dimethyl ketone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, diethyl ether, dimethyl sulfoxide, dimethylformamide, and chloroform.
[8] In the methods [1] to [7] for producing a metal plate having a layered double hydroxide on its surface according to the present invention, preferably, the metal ion is a metal ion containing any one of Mg, Al, Zn, Mn, Fe, Co, Ni, Cu, Ca, Cr, and In, and the metal salt generating the metal ion is a nitrate, sulfate, carbonate, carboxylate, phosphate, or chloride.

[9] In the method [1] to [8] for producing a metal plate having a layered double hydroxide on the surface thereof according to the present invention, the layered double hydroxide powder 40 is preferably represented by the general formula: [M ²⁺ _(1-x) M ³⁺ _x (OH) ₂ ][A ^n- _x/ n.yH ₂ O],
M2 ⁺ is a divalent metal ion selected from any one of Mg (magnesium), Zn (zinc), Ca (calcium), Mn (manganese), Pd (palladium), Sr (strontium), Fe (iron), Co (cobalt), Ni (nickel), and Cu (copper);
M3 ⁺ is a trivalent metal ion selected from any one of Al (aluminum), Bi (bismuth), Ga (gallium), Ni, Mn, V (vanadium), Ce (cerium), La (lanthanum), Cr (chromium), Fe (iron), Co (cobalt), and In (indium);
A may be an n-valent (n=1, 2, 3, or 4) anion selected from any one of NO ₃ ⁻ , CO ₃ ²⁻ , OH ⁻ , Cl ⁻ , SO ₄ ²⁻ , SiO ₄ ⁴⁻ , phosphoric acid, chromic acid, permanganic acid, vanadic acid, selenic acid, boric acid, fluoride, and carboxylic acid.
[10] In the method [9] for producing a metal plate having a layered double hydroxide on its surface according to the present invention, preferably, the trivalent metal ions in the layered double hydroxide powder 40 are substituted with divalent metal ions up to a maximum molar ratio of M ²⁺ :M ³⁺ =2:1. When the proportion of M ³⁺ is zero, it is called Mg(OH) ₂ (brucite). The lower limit is a state where no substitution is present, but preferably the molar ratio of divalent to trivalent metal ions is in the range of 4:1 to 2:1.

[11] In the method for producing a metal plate having a layered double hydroxide on its surface according to the present invention [9] or [10], the volume ratio of layered double hydroxide powder 40 to metal hydroxide in the deposited layer electrolytically deposited on the electrode substrate 12 is preferably layered double hydroxide powder:metal hydroxide=90:10 to 10:90.
The volume ratio of the layered double hydroxide powder and the metal hydroxide in the sediment layer will be described. The upper limit of the powder ratio is layered double hydroxide powder:metal hydroxide=90:10 (volume ratio). This is because the maximum packing ratio is about 90% in a simulation in which two types of lenticular particles of different sizes are mixed randomly. The lower limit of the widest range is layered double hydroxide powder:metal hydroxide=10:90 (volume ratio). This is the ratio in a sediment layer produced by EPD in an electrolyte with a low voltage or low metal ion concentration. The lower limit of the preferred range is layered double hydroxide powder:metal hydroxide=55:45 (volume ratio). This is because the lowest packing ratio is about 55% in a simulation in which spherical particles of uniform size are randomly packed. The lower limit of the more preferred range is layered double hydroxide powder:metal hydroxide=68:32 (volume ratio). This is the case in which the layered double hydroxide powder is spherical and packed in a body-centered cubic shape with uniform size. The lower limit of the optimum range is layered double hydroxide powder:metal hydroxide=74:26 (volume ratio), in which the layered double hydroxide powder is packed closely in the form of uniformly sized spheres, with the metal hydroxide filling the gaps.
Widest range: Layered double hydroxide powder: Metal hydroxide = 90:10 to 10:90
Preferred range: layered double hydroxide powder: metal hydroxide=90:10 to 55:45
More preferred range: 90:10 to 68:32
Optimum range: layered double hydroxide powder: metal hydroxide = 90:10 to 74:26
[12] In the methods [1] to [11] for producing a metal plate having a layered double hydroxide on its surface according to the present invention, the electrode substrate 12 is preferably made of pure Mg or any one of an AZ31 (Mg-3Al-1Zn) alloy, an AZ91 (Mg-9Al-1Zn) alloy, an AM60 (Mg-6Al-0.4Mn) alloy, an AXM (Mg-Al-(Zn)-Ca) alloy, a WE43 (Mg-4Y-3RE) alloy, and a ZK60 (Mg-6Zn-0.5Zr) alloy.
[13] In the method [1] to [12] for producing a metal plate having a layered double hydroxide on its surface according to the present invention, the electric field applied to the electrode substrate 12 is preferably a pulse voltage or a constant voltage.

In the method of manufacturing a metal plate having a layered double hydroxide on its surface according to the present invention, the effect of carrying out a coating treatment in two stages, namely, a step of electrolytic deposition of a metal hydroxide in an electrolyte solution containing added metal nitrate as a metal ion and a step of electrophoretic deposition of a layered double hydroxide powder, and the effect of finally depositing a complex of layered double hydroxide powder and a metal hydroxide, will be explained in comparison with the prior art.
1) In electrophoretic deposition, the force with which the powder is pressed against the substrate is proportional to the surface charge of the powder. Therefore, in determining the deposition conditions for the layered double hydroxide powder, it is not necessary to take into account the effect of added metal ions on the surface charge of the powder, which is an advantage in forming a dense powder deposition layer.
2) If a metal hydroxide is precipitated after the powder is deposited, the metal hydroxide will penetrate into the gaps between the powder particles, thereby increasing the adhesion between the powder particles and sealing the pores in the deposited layer.
3) When the powder is deposited after the metal hydroxide is precipitated, the metal hydroxide between the substrate surface and the powder acts as glue to increase the adhesion of the powder. In addition, the metal hydroxide layer is denser than the powder deposition layer, which reduces defects in the coating.
4) Layered double hydroxide powder is used as the main raw material. This allows for a high degree of freedom in the composition of the layered double hydroxide powder and the anions and organic molecules between the layers.
5) Electrophoretic deposition is a technique that can form a thick coating of several micrometers or more in a relatively short time, so the coating time can be shortened.
6) Electrophoretic deposition can form layered double hydroxide coatings regardless of the alloy composition. In contrast, chemical conversion coating and autoclave treatment incorporate Mg and Al from the magnesium alloy substrate into the coating to form layered double hydroxide, so the composition of the coating depends on the composition of the substrate alloy.
7) When metal nitrates are added to the electrolyte as metal ions as in the examples, the electrolytic deposition method and the electrophoretic deposition method are combined. The adhesion of the powder can be improved by the deposition and deposition of the metal hydroxide and layered double hydroxide powder.

FIG. 1 is a schematic diagram of an electrophoretic deposition apparatus used to manufacture a metal plate having the layered double hydroxide of the present invention on its surface; (A) shows an electrophoretic deposition process using layered double hydroxide (LDH) powder, and (B) shows an electrolytic deposition process using added metal ions. 1 is a flow chart illustrating a process for producing a metal plate having a layered double hydroxide on its surface according to a first embodiment of the present invention. Electron microscope images of AZ31 surfaces subjected to electrophoretic deposition (EPD) in ethanol-water electrolytes containing only hydrotalcite (HT) powder at various concentrations. 1 is an electron microscope photograph of a surface electrophoretically deposited with metal hydroxides after electrophoretic deposition of hydrotalcite (HT) powder according to a first aspect of the present invention. 3 is a flow chart illustrating the steps of producing a metal plate having a layered double hydroxide on its surface according to the second embodiment of the present invention. 4 is an electron microscope photograph of a surface where a metal hydroxide has been electrolytically deposited followed by electrophoretic deposition of hydrotalcite (HT) powder according to the second aspect of the present invention. FIG. 1 is a schematic diagram of an electrophoretic deposition apparatus used to manufacture a metal plate having a layered double hydroxide of the present invention on its surface, showing an electrophoretic deposition process with layered double hydroxide (LDH) powder and added metal ions. 4 is a flow diagram illustrating a process for producing a metal plate having a layered double hydroxide (LDH) on its surface according to a third embodiment of the present invention. 1 is an electron microscope photograph of a surface on which metal hydroxide has been electrolytically deposited after electrophoretic deposition of a hydrotalcite (HT) powder-metal hydroxide composite according to a third embodiment of the present invention. 4 is a flow chart illustrating a process for producing a metal plate having a layered double hydroxide (LDH) on its surface according to the fourth embodiment of the present invention. 1 is an electron microscope photograph of a surface on which a hydrotalcite (HT) powder-metal hydroxide composite is electrophoretically deposited after electrolytic deposition of a metal hydroxide according to the fourth embodiment of the present invention.

The present invention will now be described with reference to the drawings.
Fig. 1 is a schematic diagram of an electrophoretic deposition apparatus used to manufacture a metal plate having a layered double hydroxide (LDH) on its surface according to the present invention, in which (A) shows the electrophoretic deposition process of LDH powder, and (B) shows the electrolytic deposition process of added metal ions. In Fig. 1 (A) and (B), the electrophoretic deposition apparatus is provided with an electrolytic cell 10, a stirrer 20, a DC power source 30, and a function generator 36.
1(A), an electrolytic cell 10 contains a surface treatment solution 16a in which LDH powder 40 is dispersed, a substrate 12 as a metal substrate to be treated, and a counter electrode plate 14 are immersed in the surface treatment solution 16a, and a stirrer 22 is positioned below the surface treatment solution 16a. As treatment by electrophoretic deposition progresses, an electrophoretic deposit 18a of LDH powder is present on the surface of the substrate 12. One pole of a DC power source 30 is connected to the substrate 12 by an electric wire 32. The other pole of the DC power source 30 is connected to the counter electrode plate 14 by an electric wire 34.
Due to the potential difference between the substrate 12 and the counter electrode 14, the LDH powder 40 moves from the counter electrode 14 to the substrate 12 in the surface treatment solution 16a, forming a layer of deposited LDH powder 40. The voltage of the DC power supply 30 is set to a voltage required for electrophoretic deposition. In electrophoretic deposition, the charged powder is pressed onto the electrode substrate by the force of an electric field (F=qE.F: force, q: charge coulomb, E: voltage).

1(B), the electrolytic cell 10 contains a surface treatment solution 16b to which metal ions 42 have been added, and a substrate 12 as a metal substrate to be treated and a counter electrode plate 14 are immersed in the surface treatment solution 16b, with a stirrer 22 positioned below the surface treatment solution 16b. As the treatment by electrophoretic deposition progresses, a deposition layer of metal ion hydroxides 18b is present on the surface of the substrate 12 on which electrophoretic deposits 18a of LDH powder 40 have been deposited. One pole of a DC power source 30 is connected to the substrate 12 by an electric wire 32. The other pole of the DC power source 30 is connected to the counter electrode plate 14 by an electric wire 34.
Due to the potential difference generated between the substrate 12 and the counter electrode 14, the added metal ions 42 in the surface treatment solution 16b migrate from the counter electrode 14 to the substrate 12, forming a layer of deposited metal hydroxide 18. The voltage of the DC power supply 30 is set to a voltage required for electrolytic deposition.

The operation of the electrophoretic deposition apparatus thus configured will now be described.
In the electrophoretic deposition apparatus, an electric field is applied between the substrate 12, which is the substrate on which the powder is deposited, as the cathode and the counter electrode plate 14, such as a stainless steel plate, as the anode. As a result, the powder and positively charged ions (cations) in the electrolyte are attracted to the cathode, and the negative ions (anions) are attracted to the anode. The powder attracted to the cathode is pressed against it by the electric field. At the same time, water is electrolyzed on the surface of the cathode, generating hydrogen and increasing the pH. As a result, the positive ions (cations) attracted to the cathode are precipitated on the surface of the cathode as hydroxides in a high pH environment.
In the electrophoretic deposition apparatus of the present invention, in FIG. 1(A), the LDH powder is pressed by the electric field on the cathode Mg alloy surface. On the other hand, in FIG. 1(B), the Mg ions and/or Al ions are precipitated as hydroxides due to an increase in pH, or as organometallic compounds which are compounds with organic solvents. If a layer of LDH powder 40 has already been formed on the substrate 12, the hydroxides due to an increase in pH of Mg ions and/or Al ions, or organometallic compounds which are compounds with organic solvents, are precipitated in a state of being adsorbed on the surface of the LDH powder or on the Mg alloy surface exposed in the gaps between the LDH powder. The metal ions adsorbed on the LDH powder or Mg alloy surface react with water in the air to become hydroxides or oxides, and the organometallic compounds are hydrolyzed to become hydroxides or oxides. For this reason, the LDH powder can be fixed to the Mg alloy surface using the metal hydroxide as a binder (glue).

Layered double hydroxides are represented by the general formula: [M ²⁺ _(1-x) M ³⁺ _x (OH) ₂ ][A ^n- _x/n ·yH ₂ O] (see Eiichi Narita, Clay Science, 46(4), 207-218 (2007)).
Here, M2 ⁺ in the basic layer is a divalent metal ion such as Mg (magnesium), Zn (zinc), Ca (calcium), Mn (manganese), Pd (palladium), Sr (strontium), Fe (iron), Co (cobalt), Ni (nickel), or Cu (copper).
The M3 ⁺ in the basic layer is a trivalent metal ion such as Al (aluminum), Bi (bismuth), Ga (gallium), Ni, Mn, V (vanadium), Ce (cerium), La (lanthanum), Cr (chromium), Fe (iron), Co (cobalt), or In (indium).
Trivalent metal ions in the hydroxide based layer can replace divalent metal ions up to a maximum molar ratio M ²⁺ :M ³⁺ =2:1.
The anion A in the intermediate layer is an n-valent anion such as NO ₃ ⁻ , CO ₃ ²⁻ , OH ⁻ , Cl ⁻ , SO ₄ ²⁻ , SiO ₄ ⁴⁻ , phosphate, chromate, permanganate, vanadate, selenate, borate, fluoride, or carboxylate.

The surface treatment solution 16 is an electrolyte for surface treatment, and has the following composition as an electrophoretic solution:
Organic solvent-water mixed solvent: Organic solvents include alcohols such as ethanol, methanol, butanol, propanol, isopropanol, glycerin, and ethylene glycol. Ketones include acetone, dimethyl ketone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Ethers include diethyl ether. Others include dimethyl sulfoxide, dimethylformamide, and chloroform.

The concentration of the LDH powder dispersed in the electrolyte is preferably 0% or more and 10% or less in volume ratio to the electrolyte. If the concentration of the LDH powder exceeds 10%, the distance between particles in the suspension becomes short, causing aggregation and making the particles more likely to settle, which is a technical problem.
When metal nitrates are added as metal ions to the electrolyte, the concentration ranges of Mg(NO ₃ ) ₂ and Al(NO ₃ ) ₃ may be, for example, in the following ratio.
Mg(NO ₃ ) ₂ :Al(NO ₃ ) ₃ =1:0 to 0:1
When metal ions and LDH powder coexist, magnesium ions are adsorbed to the surface of the LDH powder and migrate to the negative electrode side together with the LDH powder, and precipitate as gel-like magnesium hydroxide on the negative electrode surface, resulting in the technical effect that magnesium hydroxide acts as a glue to adhere the LDH powder to the negative electrode surface and to other powders. Aluminum ions, like magnesium ions, are adsorbed to the surface of the LDH powder and migrate, resulting in the technical effect that they act as a glue to adhere the LDH powder to the negative electrode surface and to other powders. When magnesium ions and aluminum ions are added simultaneously, they precipitate as double hydroxides of magnesium and aluminum on the negative electrode surface, and act as a glue to adhere the LDH powder to the negative electrode surface and to other powders.

FIG. 2 is a flow chart illustrating the process for producing a metal plate having a layered double hydroxide (LDH) on its surface according to the first embodiment of the present invention.
First, the LDH powder 40 is dispersed in the electrolytic solution 16a (S100). In this case, the dispersion is stirred using a stirrer, for example. The LDH powder 40 spontaneously becomes charged in the electrolytic solution 16a.
Next, the electrode substrate 12 and the counter electrode plate 14 are immersed in a suspension consisting of the electrolytic solution 16a and the LDH powder 40 (S102). Then, an electric field is applied between the electrode substrate 12 and the counter electrode plate 14 (S104). For example, the electric field is applied by connecting one pole of a DC power source 30 and the substrate 12 with an electric wire 32, connecting the other pole of the DC power source 30 and the counter electrode plate 14 with an electric wire 34, and applying an electric field by a constant voltage or a pulse voltage of a predetermined potential from the DC power source 30. Then, the LDH powder 40 is electrophoretically deposited on the electrode substrate 12 (S106).
Electrophoretic deposition is continued until the thickness of the LDH powder 40 on the electrode substrate 12 reaches a predetermined value (S108). The time for which electrophoretic deposition is continued may be determined by directly measuring the thickness of the LDH powder 40 on the electrode substrate 12, or may be determined from the total amount of charge supplied from the DC power source 30 or the change in weight of the substrate before and after electrophoretic deposition. Then, the electrode substrate 12 coated with the LDH powder 40 is removed from the electrolytic solution 16a (S108).

Next, metal ions 42 are added to the second electrolytic solution 16b (S110). Next, the electrode substrate 12 and the counter electrode plate 14 are immersed in the electrolytic solution 16b containing the added metal ions 42 (S112). An electric field is applied between the electrode substrate 12 and the counter electrode plate 14 (S114). Then, hydroxides of the metal ions 42 are electrolytically deposited on the electrode substrate 12 coated with the LDH powder 40 (S116). Electrolytic deposition is continued until the film thickness of the metal hydroxide on the electrode substrate 12 reaches a predetermined value (S118). Then, the electrode substrate 12 having the deposition layer 18b coated with the hydroxides of the metal ions 42 on the electrophoretic deposition layer of the LDH powder 40 is taken out from the electrolytic solution 16b (S218).

In the examples, commercially available hydrotalcite (HT) powder was used as the LDH powder. HT is a Mg-Al-based LDH with CO ₃ ^2- ions inserted between layers. For the substrate, Mg-3 mass% Al-1 mass% Zn (AZ31) alloy was used. AZ31 alloy is a general-purpose magnesium alloy currently used in components for automobiles, cameras, personal computers, mobile phones, etc.

Example 1-1: Electrophoretic deposition of HT powder only The surface of an Mg-3mass% Al-1mass% Zn (AZ31) plate was finished with #1200 waterproof abrasive paper to form a substrate. For the electrolyte, a solution was used in which commercially available hydrotalcite (HT) powder with a particle size of about 1 μm was suspended at 1 to 5 w/v% (weight/volμme%) in a solvent of ethanol:water = 4:1 (volume ratio). While stirring the suspension, the substrate AZ31 plate was inserted as the working electrode and a stainless steel mesh plate as the counter electrode. A pulse voltage of peak-peak (pp) voltage 10V, frequency 0.1Hz, and duty ratio 98% was applied between the AZ31 plate as the cathode and the counter electrode for 10 minutes to perform electrophoretic deposition (EPD). The AZ31 plate after EPD was dried at 100°C for 1 hour, and then ultrasonically cleaned with an isopropanol solution to obtain an LDH-deposited surface. Before the ultrasonic cleaning, the surface was found to be uniformly covered with HT powder when observed visually.

Figure 3 shows electron microscope photographs of the HT deposition surface when the HT concentration in the EPD was 1 w/v%, 2 w/v%, 3 w/v%, and 5 w/v%. Aggregates of HT powder were found attached to the surface. The amount of HT powder attached increased with an increase in the HT powder concentration in the electrolyte.

Example 1-2: Electrophoretic deposition of HT powder → Electrolytic deposition of metal hydroxide The surface of an Mg-3 mass% Al-1 mass% Zn (AZ31) plate was finished with #1200 waterproof abrasive paper to be used as a substrate. For the electrophoretic deposition of the first stage of hydrotalcite (HT) powder, a solution was used in which commercially available HT powder with a particle size of about 1 μm was suspended at 2 w/v% (weight/volμme%) in a solvent of isopropanol:water = 40:1 (volume ratio). The substrate AZ31 plate was inserted as the working electrode and a stainless steel plate as the counter electrode into the electrolytic solution. A constant voltage of 100 V was applied between the AZ31 plate as the cathode and the counter electrode for 1 minute to perform electrophoretic deposition (EPD).
The electrolytic solution for the electrolytic deposition of the second metal hydroxide was a solution in which 0.002 mol/L magnesium nitrate and 0.0005 mol/L aluminum nitrate were added to a solvent of isopropanol:water = 40:1 (volume ratio). The substrate AZ31 on which the HT powder was deposited in the first electrophoretic deposition was inserted into the electrolytic solution as the working electrode and a stainless steel plate as the counter electrode. A constant voltage of 100V was applied between the cathode and the counter electrode for 1 minute to perform electrolytic deposition. Then, it was dried at 100°C for 1 hour.
An electron microscope photograph of the prepared surface is shown in Figure 4. Metal hydroxide was observed on the outermost surface, and HT powder was found between the substrate and the metal hydroxide. A composite deposition layer of HT powder and metal hydroxide was formed on the substrate surface.

5 is a flow chart for explaining the process for producing a metal plate having a layered double hydroxide (LDH) on the surface thereof according to the second embodiment of the present invention. In the second embodiment, the order of electrophoretic deposition of the LDH powder 40 on the electrode substrate 12 and electrolytic deposition of the hydroxide of the metal ions is reversed compared to the first embodiment.
First, metal ions 42 are added to the electrolytic solution 16b (S200). Next, the electrode substrate 12 and the counter electrode plate 14 are immersed in the electrolytic solution 16b containing the added metal ions 42 (S202). An electric field is applied between the electrode substrate 12 and the counter electrode plate 14 (S204). For example, the electric field is applied by connecting one pole of the DC power source 30 to the substrate 12 with an electric wire 32, connecting the other pole of the DC power source 30 to the counter electrode plate 14 with an electric wire 34, and applying an electric field from the DC power source 30 by a constant voltage or pulse voltage of a predetermined potential. Then, hydroxides of the metal ions are electrolytically deposited on the electrode substrate 12 (S206).
The electrolytic deposition is continued until the thickness of the metal hydroxide film on the electrode substrate 12 reaches a predetermined value (S208). The time for which the electrolytic deposition is continued may be determined by directly measuring the thickness of the metal hydroxide film on the electrode substrate 12, or may be determined from the total amount of charge supplied from the DC power source 30 or the change in weight of the substrate before and after the electrolytic deposition. Then, the electrode substrate 12 coated with the metal hydroxide is removed from the electrolytic solution 16b (S208).

Next, the LDH powder 40 is dispersed in another electrolytic solution 16a (S210). In this case, the dispersion is stirred using a stirrer, for example. The LDH powder 40 spontaneously becomes charged in the electrolytic solution 16a.
Next, the electrode substrate 12 and the counter electrode plate 14 coated with the hydroxide of the metal ions 42 are immersed in a suspension consisting of the electrolytic solution 16a and the LDH powder 40 (S212). Then, an electric field is applied between the electrode substrate 12 and the counter electrode plate 14 (S214). Then, the LDH powder 40 is electrophoretically deposited on the electrode substrate 12 (S216). The electrophoretic deposition is continued until the film thickness of the LDH powder 40 on the electrode substrate 12 reaches a predetermined value (S218). Then, the treated electrode substrate 12, in which the surface of the electrode substrate 12 coated with the metal hydroxide is covered with an electrophoretically deposited layer of the LDH powder 40, is taken out from the electrolytic solution 16a (S218).

Example 2: Electrolytic deposition of metal hydroxide → electrophoretic deposition of HT powder The surface of an Mg-3 mass% Al-1 mass% Zn (AZ31) plate was finished with #1200 waterproof abrasive paper to prepare a substrate. For the electrolytic deposition of the first stage of metal hydroxide, a solution was used in which 0.002 mol/L of magnesium nitrate and 0.0005 mol/L of aluminum nitrate were added to a solvent of isopropanol:water = 40:1 (volume ratio). An AZ31 substrate plate was inserted as a working electrode and a stainless steel plate as a counter electrode into the electrolytic solution. A constant voltage of 100V was applied between the AZ31 plate as a cathode and the counter electrode for 1 minute to perform electrolytic deposition.

The electrolytic solution for electrophoretic deposition of hydrotalcite (HT) powder in the second stage was a solution in which commercially available HT powder with a particle size of about 1 μm was suspended at 2 w/v% (weight/volume μme%) in a solvent of isopropanol:water = 40:1 (volume ratio). The substrate AZ31 on which metal hydroxide was deposited in the first stage electrolytic deposition was inserted into the electrolytic solution as the working electrode and a stainless steel plate as the counter electrode. A constant voltage of 100 V was applied between the cathode and the counter electrode for 1 minute to perform electrophoretic deposition. Then, it was dried at 100 ° C for 1 hour.
An electron microscope photograph of the prepared surface is shown in Figure 6. The HT powder was attached to the upper surface of the metal hydroxide deposition layer. A composite deposition layer of HT powder and metal hydroxide was formed on the substrate surface.

Fig. 7 is a schematic diagram of an electrophoretic deposition apparatus used for producing a metal plate having a layered double hydroxide on its surface according to the present invention, showing an electrophoretic deposition process in the simultaneous presence of LDH powder and added metal ions. In Fig. 7, components having the same functions as those in Fig. 1 are given the same reference numerals and will not be described.
In FIG. 1(A), the electrolytic cell 10 contains a surface treatment solution 16a in which LDH powder 40 is dispersed, whereas in FIG. 7, the electrolytic cell 10 contains a surface treatment solution 16 to which metal ions 42 have been added, in which LDH powder 40 is dispersed.
In the process shown in FIG. 1(B), which is a separate process, a surface treatment solution 16b to which metal ions 42 have been added is contained in an electrolytic cell 10. In the process shown in FIG. 7, a coating process for an electrode substrate is performed in the same combination as in the process shown in FIG. 1(A).

In the operation shown in FIG. 7, the potential difference between the substrate 12 and the counter electrode 14 causes the LDH powder 40 and added metal ions 42 to move from the counter electrode 14 to the substrate 12 inside the surface treatment solution 16, forming an electrophoretic deposition layer of the LDH powder 40 and metal hydroxide 18. The voltage of the DC power supply 30 is set to the voltage required for electrophoretic deposition. In electrophoretic deposition, the charged powder is pressed onto the electrode substrate by the force of an electric field (F=qE.F: force, q: charge coulomb, E: voltage).

In the electrophoretic deposition process shown in Figure 7, the LDH powder is pressed against the cathode Mg alloy surface by the electric field, and simultaneously, Mg ions and/or Al ions are precipitated as hydroxides due to an increase in pH, precipitated while adsorbed to the LDH powder, or precipitated as organometallic compounds that are compounds with organic solvents. Metal ions adsorbed to the LDH powder react with water in the air to become hydroxides or oxides, and organometallic compounds become hydroxides or oxides when hydrolyzed. This allows the LDH powder to adhere to the Mg alloy surface using the metal hydroxide as a binder (glue).

FIG. 8 is a flow diagram illustrating the process for producing a metal plate having a layered double hydroxide (LDH) on its surface according to the third embodiment of the present invention.
The third embodiment of the present invention for producing a metal plate having a layered double hydroxide on its surface is different from the first embodiment in that, instead of electrophoretically depositing only HT powder on the electrode substrate 12, in the third embodiment, a complex of HT powder and a metal hydroxide is electrophoretically deposited on the electrode substrate 12, followed by electrolytic deposition of the hydroxide of the metal ion.

First, the LDH powder 40 is dispersed in the electrolytic solution 16 to which metal ions have been added (S300). The LDH powder 40 is dispersed by stirring, for example, with a stirrer. The LDH powder 40 is spontaneously charged in the electrolytic solution 16. The order of adding the metal ions to the electrolytic solution and dispersing the LDH powder may be reversed. That is, the order may be such that the metal ions are added to the electrolytic solution 16 in which the LDH powder has been dispersed.
Next, the electrode substrate 12 and the counter electrode plate 14 are immersed in a suspension consisting of the electrolytic solution 16 with added metal ions and the LDH powder 40 (S302). Then, an electric field is applied between the electrode substrate 12 and the counter electrode plate 14 (S304). Then, a complex of the LDH powder 40 and the hydroxide of the metal ions 42 is electrophoretically deposited on the electrode substrate 12 (S306).
Electrophoretic deposition is continued until the thickness of the complex of the hydroxides of the LDH powder 40 and the metal ions 42 on the electrode substrate 12 reaches a predetermined value (S308). The time for which electrophoretic deposition is continued may be determined by directly measuring the thickness of the complex of the hydroxides of the LDH powder 40 and the metal ions 42 on the electrode substrate 12, or may be determined from the total amount of charge supplied from the DC power source 30 or the change in weight of the base material 12 before and after electrophoretic deposition. Then, the electrode substrate 12 coated with the LDH powder 40 is removed from the electrolyte solution 16 (S308).
The second step, steps S310 to S318 for electrolytically depositing hydroxides of metal ions 42 onto electrode substrate 12, are similar to steps S110 to S118 shown in FIG.

Example 3: Electrophoretic deposition of a complex of HT powder and metal hydroxide → Electrolytic deposition of metal hydroxide The surface of an Mg-3mass% Al-1mass% Zn (AZ31) plate was finished with #1200 waterproof abrasive paper to form a substrate. For the electrolytic solution for electrophoretic deposition of a complex of hydrotalcite (HT) powder and metal hydroxide in the first stage, a solution was used in which commercially available HT powder with a particle size of about 1 μm was suspended at 2 w/v% (weight/volμme%) in a solvent of isopropanol:water = 40:1 (volume ratio) to which 0.002 mol/L magnesium nitrate and 0.0005 mol/L aluminum nitrate were added. An AZ31 substrate plate was inserted as a working electrode and a stainless steel plate was inserted as a counter electrode into the electrolytic solution. A constant voltage of 100 V was applied between the AZ31 plate as a cathode and the counter electrode for 1 minute to perform electrophoretic deposition (EPD).

The electrolytic solution for the electrolytic deposition of the metal hydroxide in the second stage was a solution in which 0.002 mol/L magnesium nitrate and 0.0005 mol/L aluminum nitrate were added to a solvent of isopropanol:water = 40:1 (volume ratio). The substrate AZ31 on which the composite of HT powder and metal hydroxide was deposited in the first stage electrophoretic deposition was inserted as the working electrode and a stainless steel plate as the counter electrode into the electrolytic solution. A constant voltage of 100V was applied between the cathode and the counter electrode for 1 minute to perform electrolytic deposition. Then, it was dried at 100°C for 1 hour.
An electron microscope photograph of the prepared surface is shown in Figure 9. The substrate surface was covered with a composite deposition layer of HT powder and metal hydroxide in an amount that did not show any polishing marks, and the metal oxide precipitated on the surface layer was observed. A composite deposition layer of HT powder and metal hydroxide was formed on the substrate surface.

The fourth embodiment of the present invention for producing a metal plate having a layered double hydroxide on its surface is different from the second embodiment in that electrolytic deposition of hydroxides of metal ions is carried out, and then, instead of electrophoretic deposition of only HT powder on the electrode substrate 12 in the second embodiment, a composite electrophoretic deposition of HT powder and metal hydroxide is carried out on the electrode substrate 12 in the fourth embodiment.
FIG. 10 is a flow chart illustrating the steps of producing a metal plate having a layered double hydroxide on its surface according to the fourth embodiment of the present invention.
The first steps, steps S400 to S408 for electrolytically depositing hydroxides of metal ions 42 on electrode substrate 12, are similar to steps S200 to S208 shown in FIG.

Next, the LDH powder 40 is dispersed in another electrolytic solution 16 to which metal ions have been added (S410). In this case, stirring is performed using a stirrer, for example. The LDH powder 40 spontaneously becomes charged in the electrolytic solution 16. The order of adding the metal ions to the electrolytic solution and dispersing the LDH powder may be reversed. In other words, the order may be such that the metal ions are added to the electrolytic solution 16 in which the LDH powder has been dispersed.
Next, the electrode substrate 12 and the counter electrode plate 14 coated with the hydroxide of the metal ion 42 are immersed in a suspension consisting of the electrolytic solution 16 to which the metal ions have been added and the LDH powder 40 (S412). Then, an electric field is applied between the electrode substrate 12 and the counter electrode plate 14 (S414). Then, a complex of the LDH powder 40 and the hydroxide of the metal ion 42 is electrophoretically deposited on the electrode substrate 12 (S416). The electrophoretic deposition is continued until the film thickness of the LDH powder 40 on the electrode substrate 12 reaches a predetermined value (S418). Then, the treated electrode substrate 12, in which the surface of the electrode substrate 12 coated with the metal hydroxide is covered with an electrophoretically deposited layer of the complex of the LDH powder 40 and the hydroxide of the metal ion 42, is taken out from the electrolytic solution 16 (S418).

Example 4: Electrolytic deposition of metal hydroxide → composite electrophoretic deposition of HT powder and metal hydroxide The surface of an Mg-3mass% Al-1mass% Zn (AZ31) plate was finished with #1200 waterproof abrasive paper to be used as a substrate. For the electrolytic deposition of the first stage of metal hydroxide, a solution was used in which 0.002 mol/L of magnesium nitrate and 0.0005 mol/L of aluminum nitrate were added to a solvent of isopropanol:water = 40:1 (volume ratio). The substrate AZ31 plate was inserted as the working electrode and a stainless steel plate as the counter electrode into the electrolytic solution. A constant voltage of 100V was applied between the AZ31 plate as the cathode and the counter electrode for 1 minute to perform electrolytic deposition.

The electrolytic solution for the composite electrophoretic deposition of hydrotalcite (HT) powder and metal hydroxide in the second stage was prepared by suspending commercially available HT powder with a particle size of about 1 μm at 2 w/v% (weight/volume μme%) in a solvent of isopropanol:water = 40:1 (volume ratio) to which 0.002 mol/L magnesium nitrate and 0.0005 mol/L aluminum nitrate were added. The substrate AZ31 on which metal hydroxide was deposited in the first stage electrolytic deposition was inserted into the electrolytic solution as the working electrode and a stainless steel plate as the counter electrode. A constant voltage of 100 V was applied between the cathode and the counter electrode for 1 minute to perform electrophoretic deposition. The solution was then dried at 100 ° C. for 1 hour.
An electron microscope photograph of the prepared surface is shown in Figure 11. A metal hydroxide was precipitated on the substrate in an amount that did not show any polishing marks, and a composite of HT powder and metal hydroxide was deposited on top of it. A composite deposition layer of HT powder and metal hydroxide was formed on the substrate surface.

As explained in detail above, the method for producing a metal plate having a layered double hydroxide on the surface of the present invention makes it easy to form a highly corrosion-resistant coating on magnesium alloys and aluminum alloys, and depending on the application, paint can also be applied in addition to the highly corrosion-resistant coating. Therefore, when these light alloys are used in transportation equipment or home appliances, their durability is increased even when they are exposed to rain or seawater containing chloride ions or human sweat.

10: Electrolytic cell 12: Base material (metal substrate to be treated, electrode substrate)
14: Counter electrode plate 16a, 16b: Surface treatment solution (electrolyte)
18a, 18b: deposited metal hydroxide 20: stirrer 22: stirring bar 30: DC power supply 36: function generator 40: LDH (layered double hydroxide) powder 42: added metal ions

Claims (16)

Dispersing a layered double hydroxide powder in a first electrolytic solution containing water;
a step of immersing an electrode substrate and a first counter electrode plate in a suspension containing the first electrolytic solution and the layered double hydroxide powder, the electrode substrate being a metal plate to be coated;
applying an electric field between the electrode substrate and the first counter electrode plate to electrophoretically deposit the layered double hydroxide powder onto the electrode substrate;
adding metal ions to a second electrolytic solution containing water;
immersing the electrode substrate on which the layered double hydroxide powder has been deposited and a second counter electrode in the second electrolytic solution containing the added metal ions;
applying an electric field between the electrode substrate on which the layered double hydroxide powder is deposited and the second counter electrode plate, thereby electrolytically depositing the metal ions as hydroxides on the electrode substrate on which the layered double hydroxide powder is deposited;
A method for producing a metal plate having a layered double hydroxide on its surface. adding metal ions to a third electrolytic solution containing water;
a step of immersing an electrode substrate and a third counter electrode plate in the third electrolytic solution containing the added metal ions, the electrode substrate being a metal plate to be coated;
applying an electric field between the electrode substrate and the third counter electrode plate to electrolytically deposit the metal ions as hydroxides on the electrode substrate;
dispersing a layered double hydroxide powder in a fourth electrolytic solution containing water;
a step of immersing an electrode substrate on which the hydroxide of the metal ion is electrolytically deposited and a fourth counter electrode plate in a suspension containing the fourth electrolytic solution and the layered double hydroxide powder;
a step of electrophoretically depositing the layered double hydroxide powder on the electrode substrate by applying an electric field between the electrode substrate on which the hydroxide of the metal ions is electrolytically deposited and the fourth counter electrode plate;
A method for producing a metal plate having a layered double hydroxide on its surface. a step of adding metal ions to a fifth electrolytic solution containing water and dispersing a layered double hydroxide powder in the fifth electrolytic solution, or a step of dispersing a layered double hydroxide powder in the fifth electrolytic solution containing water and adding metal ions to the fifth electrolytic solution;
a step of immersing an electrode substrate and a fifth counter electrode plate in a suspension composed of the fifth electrolytic solution containing the added metal ions and the layered double hydroxide powder, the electrode substrate being a metal plate to be coated;
applying an electric field between the electrode substrate and the fifth counter electrode plate to electrophoretically deposit a complex of the hydroxide of the metal ion and the layered double hydroxide powder on the electrode substrate;
adding metal ions to a sixth electrolytic solution containing water;
a step of immersing the electrode substrate on which the complex of the hydroxide of the metal ion and the layered double hydroxide powder is deposited and a sixth counter electrode plate in the sixth electrolytic solution containing the added metal ions;
applying an electric field between the electrode substrate and the sixth counter electrode plate to electrolytically deposit the metal ions as hydroxides on the electrode substrate on which a complex of the hydroxides of the metal ions and the layered double hydroxide powder has been deposited;
A method for producing a metal plate having a layered double hydroxide on its surface. adding metal ions to a seventh electrolyte solution containing water;
a step of immersing an electrode substrate and a seventh counter electrode plate in the seventh electrolytic solution containing the added metal ions, the electrode substrate being a metal plate to be coated;
applying an electric field between the electrode substrate and the seventh counter electrode plate to electrolytically deposit the metal ions as hydroxides on the electrode substrate;
a step of adding metal ions to an eighth electrolytic solution containing water and dispersing a layered double hydroxide powder in the eighth electrolytic solution, or a step of dispersing a layered double hydroxide powder in the eighth electrolytic solution containing water and adding metal ions to the eighth electrolytic solution;
a step of immersing an electrode substrate on which the hydroxide of the metal ion is electrolytically deposited and an eighth counter electrode plate in a suspension composed of the eighth electrolytic solution containing the added metal ion and the layered double hydroxide powder;
a step of electrophoretically depositing a complex of the hydroxide of the metal ion and the layered double hydroxide powder on the electrode substrate by applying an electric field between the electrode substrate on which the hydroxide of the metal ion is electrolytically deposited and the eighth counter electrode plate;
A method for producing a metal plate having a layered double hydroxide on its surface. The method for producing a metal plate having a layered double hydroxide on its surface, as described in claim 1, characterized in that the first and second electrolytic solutions are mixed solvents of an organic solvent and water. The method for producing a metal plate having a layered double hydroxide on its surface, as described in claim 2, characterized in that the third and fourth electrolytic solutions are mixed solvents of an organic solvent and water. The method for producing a metal plate having a layered double hydroxide on its surface according to claim 3, characterized in that the fifth and sixth electrolytic solutions are mixed solvents of an organic solvent and water. The method for producing a metal plate having a layered double hydroxide on its surface, as described in claim 4, characterized in that the seventh and eighth electrolytic solutions are mixed solvents of an organic solvent and water. The method for producing a metal plate having a layered double hydroxide on its surface according to any one of claims 5 to 8, characterized in that the volume ratio of the organic solvent to water is organic solvent:water = 99:1 to 70:30. The method for producing a metal plate having a layered double hydroxide on its surface according to any one of claims 5 to 9, characterized in that the organic solvent contains one of the following: ethanol, methanol, butanol, propanol, isopropanol, glycerin, ethylene glycol, acetone, dimethyl ketone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, diethyl ether, dimethyl sulfoxide, dimethylformamide, and chloroform. The metal ion is any one of Mg, Al, Zn, Mn, Fe, Co, Ni, Cu, Ca, Cr, and In,
The metal salt that generates the metal ion is a nitrate, sulfate, carbonate, carboxylate, phosphate or chloride.
A method for producing a metal plate having the layered double hydroxide according to any one of claims 1 to 10 on its surface. The layered double hydroxide powder is represented by the general formula: [M ²⁺ _(1-x) M ³⁺ _x (OH) ₂ ][A ^n- _x/n · _y H ₂ O],
M2 ⁺ is a divalent metal ion selected from any one of Mg (magnesium), Zn (zinc), Ca (calcium), Mn (manganese), Pd (palladium), Sr (strontium), Fe (iron), Co (cobalt), Ni (nickel), and Cu (copper);
M3 ⁺ is a trivalent metal ion selected from any one of Al (aluminum), Bi (bismuth), Ga (gallium), Ni, Mn, V (vanadium), Ce (cerium), La (lanthanum), Cr (chromium), Fe (iron), Co (cobalt), and In (indium);
The A is an anion having a valence of n (n=1, 2, 3, or 4) selected from any one of NO ₃ ⁻ , CO ₃ ²⁻ , OH ⁻ , Cl ⁻ , SO ₄ ²⁻ , SiO ₄ ⁴⁻ , phosphoric acid, chromic acid, permanganic acid, vanadic acid, selenic acid, boric acid, fluoride, and carboxylic acid;
A method for producing a metal plate having the layered double hydroxide according to any one of claims 1 to 11 on its surface. 13. The method for producing a metal plate having a layered double hydroxide on a surface thereof according to claim 12, characterized in that the trivalent metal ions in the layered double hydroxide powder are substituted for divalent metal ions up to a maximum molar ratio of ^{M2+ :} M3+ = 2:1. the volume ratio of the layered double hydroxide powder to the metal hydroxide in the deposition layer formed by the step of electrophoretically depositing a complex of the hydroxide of the metal ion and the layered double hydroxide powder is layered double hydroxide powder:metal hydroxide=90:10 to 10:90;
A method for producing a metal plate having the layered double hydroxide according to claim 3, 4, 7 or 8 on its surface. 15. The method for producing a metal plate having a layered double hydroxide on a surface thereof according to any one of claims 1 to 14, wherein the electrode substrate is a pure Mg material, an AZ31 (Mg-3Al-1Zn) alloy, an AZ91 (Mg-9Al-1Zn) alloy, an AM60 (Mg-6Al-0.4Mn) alloy, an AXM (Mg-Al-(Zn)-Ca) alloy, a WE43 (Mg-4Y- 3RE ) alloy, or a ZK60 (Mg-6Zn-0.5Zr) alloy. 16. The method for producing a metal plate having a layered double hydroxide on a surface thereof according to claim 1, wherein the electric field applied to the electrode substrate is a constant voltage or a pulse voltage.