CN107636207B - Surface-treated steel sheet - Google Patents

Abstract

The surface-treated steel sheet is provided with: a steel plate; and a plating layer formed on one or both sides of the steel sheet and containing zinc and vanadium or zirconium, wherein the plating layer has: a zinc metal-containing dendrite; and an intercrystalline filling region which fills the dendrites and shows an amorphous diffraction pattern when electron beam diffraction is performed, wherein the intercrystalline filling region contains a hydrated vanadium oxide or vanadium hydroxide when the plating layer contains vanadium, and contains a hydrated zirconium oxide or zirconium hydroxide when the plating layer contains zirconium.

Description

Surface-treated steel sheet

Technical Field

The present invention relates to a surface-treated steel sheet having excellent corrosion resistance (barrier property) and coating film adhesion of a plating layer in a corrosive environment.

The present application claims priority based on Japanese application No. 2015-116554 and No. 2015-116604 filed on 9/6/2015 and applies the contents thereof.

Background

In the past, electrogalvanized steel sheets have been used in various fields such as home electric appliances, building materials, and automobiles. Further improvement in corrosion resistance (hereinafter referred to as barrier property) of a plating layer in a corrosive environment is required for the electrogalvanized steel sheet.

As a method for improving the barrier property of the electrogalvanized steel sheet, it is conceivable to increase the plating amount (weight per unit area) of the zinc plating layer. However, when the weight per unit area of the zinc plating layer is increased, there are problems that the production cost is increased and workability and weldability are lowered.

In addition, as a method for improving the barrier property and appearance of the electrogalvanized steel sheet, a technique of forming a coating film on the surface has been widely used. However, if the adhesion between the plating layer and the coating film (coating film adhesion, also referred to as coating film adhesion) of the electrogalvanized steel sheet is insufficient, the effect resulting from the formation of the coating film cannot be sufficiently obtained even if the coating film is formed on the surface. Therefore, it is required to improve the barrier property of the electrogalvanized steel sheet and to improve the coating film adhesion.

In recent years, it has been studied to improve barrier properties by incorporating vanadium into a zinc plating layer of an electrogalvanized steel sheet. For example, non-patent documents 1 to 4 describe a technique of performing composite electrodeposition of a Zn — V oxide on the surface of a copper plate as a cathode.

Patent document 1 describes a technique of forming a V-concentrated layer on a surface layer portion of a plating layer of a zinc-based plated steel sheet.

Patent document 2 describes a technique relating to a plating layer containing zinc and vanadium and having a plurality of dendritic arms.

Patent document 3 describes that a plating layer containing zinc and vanadium formed on a steel sheet has dendrites in which vanadium oxide is present in zinc; it is described that a phase having a higher vanadium content than that in the dendrite exists in a portion other than the dendrite.

Patent document 4 describes that in a zinc-based composite plated steel sheet containing zinc and vanadium hydroxide, vanadium hydroxide is eutectoid in zinc.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2013-185199

Patent document 2: japanese patent No. 5273316

Patent document 3: japanese patent laid-open publication No. 2013-108183

Patent document 4: japanese patent laid-open publication No. 2011-

Non-patent document

Non-patent document 1: volume 22 (2009) -933-936 to 936 of CAMP-ISIJ

Non-patent document 2: no. 11, pages 49 to 54 of No. 93 volume (2007) of iron and steel

Non-patent document 3: 115 th lecture meeting gist set of surface technology association, 9A-26, 139 pages to 140 pages

Non-patent document 4: ferrum (Japanese: ふぇらむ) volume 13, No.4, page 245, 2008.4.1

Disclosure of Invention

Problems to be solved by the invention

However, in conventional surface-treated steel sheets having a plating layer containing zinc and vanadium on the surface of the steel sheet, further improvement in barrier properties is required.

Further, since V (vanadium) is a rare element, a plating layer having excellent barrier properties is desired instead of the zinc-vanadium plating layer.

The present invention has been made in view of such circumstances, and an object thereof is to provide a surface-treated steel sheet having excellent barrier properties and coating film adhesion of a plating layer containing zinc and vanadium or zirconium formed on the surface of the steel sheet.

Means for solving the problems

The present inventors have made extensive studies to solve the above problems as described below.

That is, the inventors of the present invention formed a plating layer containing zinc and vanadium or zirconium on the surface of a steel sheet under various conditions by using the steel sheet as a cathode by an electroplating method, and examined the barrier property and coating film adhesion.

As a result, the inventors of the present invention have found that: the plating layer may be formed as a plating layer containing zinc and vanadium, having dendrites containing metallic zinc, and intercrystalline filled regions containing hydrated vanadium oxide or vanadium hydroxide. Such a plating layer has an intercrystalline filled region containing a hydrated vanadium oxide or vanadium hydroxide, and therefore has a higher corrosion potential and more excellent barrier properties than, for example, a plated steel sheet in which a zinc plating layer is provided in place of the plating layer.

In addition, the inventors of the present invention have found that: under certain conditions, a phase containing hydrated zirconium oxide or zirconium hydroxide is formed around dendrites formed from metallic zinc. The following conditions are judged: such a plating layer has barrier properties equal to or higher than those of a zinc-vanadium plating layer and has excellent coating film adhesion, and the present invention has been completed. Aspects of the invention are described below.

(1) A surface-treated steel sheet according to one aspect of the present invention comprises: a steel plate; and a plating layer formed on one or both sides of the steel sheet and containing zinc and vanadium or zirconium, wherein the plating layer has: a zinc metal-containing dendrite; and an intercrystalline filling region which fills the dendrites and shows an amorphous diffraction pattern when electron beam diffraction is performed, wherein the intercrystalline filling region contains a hydrated vanadium oxide or vanadium hydroxide when the plating layer contains vanadium, and contains a hydrated zirconium oxide or zirconium hydroxide when the plating layer contains zirconium.

(2) The surface-treated steel sheet according to the above (1) may have the following structure: when the plating layer contains the vanadium, V/Zn, which is the molar ratio of the vanadium to the zinc, in the intercrystalline filling regions is 0.10 to 2.00, and when the plating layer contains the zirconium, Zr/Zn, which is the molar ratio of the zirconium to the zinc, in the intercrystalline filling regions is 1.00 to 3.00.

(3) The surface-treated steel sheet according to the above (1) or (2), which has the following structure: in the case where the plating layer contains the vanadium, the surface layer of the dendrite contains zinc oxide or zinc hydroxide.

(4) The surface-treated steel sheet according to any one of the above (1) to (3), which has a structure comprising: a base coating layer having a Zn/V ratio of 8.00 or more, which is a molar ratio of Zn to the vanadium, is further provided between the steel sheet and the coating layer.

(5) The surface-treated steel sheet according to any one of the above (1) to (4), which has a structure comprising: the surface of the plating layer is further provided with an organic resin coating film containing a polyurethane resin and 1-20 mass% of carbon black.

(6) A method for producing a surface-treated steel sheet according to one aspect of the present invention is a method for producing a surface-treated steel sheet according to any one of (1) to (5) above, the method including: a substrate forming step of forming a substrate by using a composition containing 0.10 to 4.00mol/l of Zn²⁺Ions and 0.01 to 2.00mol/l of V ions or 0.10 to 4.00molA plating bath of 0 to 18A/dm of Zr ions²The current density of (a) is controlled so that hydrated vanadium oxide or vanadium hydroxide is precipitated on the steel sheet to form irregularities; and an upper layer plating step of using the plating bath at 21 to 200A/dm for the steel sheet having the irregularities formed thereon²Electroplating is performed at the current density of (1).

ADVANTAGEOUS EFFECTS OF INVENTION

According to the above aspects, a surface-treated steel sheet having excellent barrier properties and coating film adhesion can be provided.

Drawings

Fig. 1 is a schematic cross-sectional view for explaining an example of a surface-treated steel sheet according to embodiment 1.

Fig. 2 is a schematic cross-sectional view for explaining an example of the surface-treated steel sheet according to embodiment 2.

Fig. 3 is a schematic view showing an example of a plating apparatus used in the production of the surface-treated steel sheet of the present embodiment.

Fig. 4A is a schematic view for explaining the precipitation of vanadium compounds in the process of producing the surface-treated steel sheet shown in fig. 1.

Fig. 4B is a schematic view for explaining the growth of dendrites in the process of manufacturing the surface-treated steel sheet shown in fig. 1.

Fig. 4C is a schematic view for explaining generation of hydrogen at the tip of the branch portion of the dendrite in the process of manufacturing the surface-treated steel sheet shown in fig. 1.

FIG. 5A is a photograph of a cross-section taken in the entire thickness direction of the plated layer of the surface-treated steel sheet of example V4 using a Transmission Electron Microscope (TEM).

Fig. 5B is an enlarged photograph of the interface portion between the steel sheet and the plating layer in the cross section of fig. 5A.

Fig. 5C is an enlarged photograph of the dendrite and its surrounding portion in the cross section of fig. 5A.

FIG. 6 is a Scanning Electron Microscope (SEM) photograph of the plated layer of the surface-treated steel sheet of example V4.

FIG. 7 is a Scanning Electron Microscope (SEM) photograph of the plated layer of the surface-treated steel sheet of comparative example x 2.

FIG. 8 is a photograph showing an electron beam diffraction pattern of the plated layer of the surface-treated steel sheet of example V4.

FIG. 9 is a Transmission Electron Microscope (TEM) photograph of the plated layer of the surface-treated steel sheet of example Z4.

Detailed Description

"embodiment 1, surface-treated Steel sheet 10"

The surface-treated steel sheet 10 according to embodiment 1 will be described in detail below with reference to the drawings in the case where the plating layer contains vanadium.

Fig. 1 is a schematic cross-sectional view for explaining an example of a surface-treated steel sheet 10 according to the present embodiment. The surface-treated steel sheet 10 shown in fig. 1 has a base layer 20, a plating layer 30, and a surface layer 40 formed on both sides of the steel sheet 1 in this order from the steel sheet 1 side. In fig. 1, only the base layer 20, the plating layer 30, and the surface layer 40 formed on one surface (upper surface) side of the steel sheet 1 are shown, and the other surface (lower surface) side is not shown.

In the present embodiment, the steel sheet 1 having the plating layer 30 formed on the surface thereof is not particularly limited. For example, as the steel sheet 1, any type of steel sheet such as an extremely low C type (ferrite main structure), an Al — k type (structure containing pearlite in ferrite), a 2-phase structure type (for example, structure containing martensite in ferrite, structure containing bainite in ferrite), a work induction transformation type (structure containing retained austenite in ferrite), a fine crystal type (ferrite main structure), or the like can be used.

As shown in fig. 1, a base layer 20 may be disposed between the steel sheet 1 and the plating layer 30. The base layer 20 is provided as necessary to improve adhesion between the steel sheet 1 and the plating layer 30. In the present embodiment, it is preferable to provide the underlayer 20 made of nickel-containing crystal having a thickness of 1 to 300 nm.

The plating layer 30 has, as shown in fig. 1: a dendrite 31; and an intercrystalline filling region 32 which is arranged between the dendrites 31 and shows an amorphous diffraction pattern when electron beam diffraction is performed.

The "amorphous" in the present invention means: electron beam diffraction was performed on each layer from the cross-sectional direction using a Transmission Electron Microscope (TEM), and a diffraction pattern due to the crystal structure could not be obtained.

The intercrystalline fill region 32 comprises hydrated vanadium oxide or vanadium hydroxide. In order to improve the coating film adhesion, it is preferable that the intercrystalline filling region 32 contain vanadium hydroxide.

In addition, it is preferable that the intercrystalline filling region 32 contains zinc. The inter-crystal filling region 32 contains zinc, thereby improving corrosion resistance.

In the case where the intercrystalline filling region 32 contains hydrated vanadium oxide or vanadium hydroxide and zinc, the molar ratio (V/Zn) of vanadium to zinc in the intercrystalline filling region 32 is preferably 0.10 to 2.00. When the molar ratio (V/Zn) is in the above range and electron beam diffraction is performed, the intercrystalline filling regions show an amorphous diffraction pattern, and thus excellent corrosion resistance (barrier property) and coating film adhesion can be obtained. If the molar ratio (V/Zn) of vanadium to zinc in the intercrystalline filler region 32 is less than 0.10, an amorphous diffraction pattern may not be stably obtained, resulting in poor corrosion resistance. On the other hand, if the above molar ratio exceeds 2.00, the sacrificial corrosion resistance of the plating layer deteriorates.

As shown in fig. 1, a plurality of dendrites 31 are formed in the plating layer 30. The shape of the plurality of dendrites 31 may be completely different or may include the same shape. Each dendrite 31 may be needle-like or rod-like in shape. Further, each dendrite 31 may extend linearly in the longitudinal direction or may extend in a curved line. The cross-sectional shape of each dendrite 31 is not particularly limited, and examples thereof include: circular, elliptical, polygonal, etc. The cross-sectional shape of each dendrite 31 may be uniform or non-uniform in the longitudinal direction. Further, the outer peripheral dimensions of the respective dendrites 31 may be uniform or non-uniform in the longitudinal direction.

As shown in fig. 1, in the surface-treated steel sheet 10 of the present embodiment, each dendrite 31 has: an inner portion 3a of the dendrite, and a surface layer 3b formed on the surface of the dendrite 31. The dendrite 31 grows from the steel plate 1 side to the outside, and has a plurality of branched parts. The surface layer 3b is formed to have a substantially uniform thickness so as to cover the surface of the inner portion 3a of the dendrite 31.

The dendrite 31 shown in fig. 1 having the inner portion 3a and the surface layer 3b of the dendrite 31 is preferably 4.0 μm or less in the maximum length and 0.5 μm or less in the maximum width when viewed in cross section. When the maximum length and the maximum width of the dendrite 31 are within the above ranges, the dense plating layer 30 having the fine dendrite 31 is formed. Therefore, the barrier effect of the plating layer 30 is improved, and further excellent barrier property can be obtained. In order to further improve the barrier property, the maximum length of the dendrite 31 is more preferably 3.0 μm or less. Further, the maximum width of the dendrite 31 in the cross-sectional view is more preferably 0.4 μm or less.

In the present embodiment, the "maximum length of the dendrite 31" is determined by observing a cross section of the plating layer using a Scanning Electron Microscope (SEM), measuring the maximum length of 50 dendrites 31, and calculating the average value thereof.

The "maximum width of the dendrite 31 in cross-sectional observation" is obtained by observing the cross-section of the plating layer using a Transmission Electron Microscope (TEM), measuring the maximum widths of 50 dendrites 31, and calculating the average value thereof.

The inner portion 3a of the dendrite 31 preferably contains metallic zinc. The interior 3a of the dendrite 31 may contain other metal components such as nickel having a higher deposition potential than zinc, in addition to metallic zinc.

In addition, the surface layer 3b preferably contains crystals containing zinc oxide or zinc hydroxide. The surface layer 3b more preferably contains crystals of zinc oxide. The thickness of the surface layer 3b is preferably 0.1 to 500 nm.

In addition, as shown in fig. 1, granular crystals 3c may be contained in the interior 3a of the dendrite 31. The granular crystals 3c contain zinc and nickel. The particle diameter of the granular crystal 3c is preferably 0.1 to 500 nm. When the particle diameter of the granular crystals 3c is within the above range, more excellent coating film adhesion can be obtained.

In the surface-treated steel sheet 10 of the present embodiment, Zn/V, which is a molar ratio of zinc to vanadium contained in the plating layer 30, is preferably 0.50 or more and less than 8.00. It is preferable that the Zn/V is 0.50 or more and less than 8.00 because an excellent barrier function by the vanadium can be obtained.

In the case of the surface-treated steel sheet 10, a base plating layer (not shown) containing zinc may be formed between the steel sheet 1 and the plating layer 30 (between the base layer 20 and the plating layer 30 in the case of forming the base layer 20). This is because, by forming the base plating layer (not shown), an excellent corrosion resistance improving effect by sacrificial corrosion prevention of zinc can be obtained.

The base coating (not shown) may contain zinc and vanadium and the molar ratio of the zinc to the vanadium, i.e., Zn/V, may be 8.00 or more. Alternatively, the base plating (not shown) may be composed of zinc alone.

An upper plating layer (not shown) containing zinc may also be formed on the upper layer of the plating layer 30. The formation of the upper plating layer (not shown) is preferable because an excellent corrosion resistance improving effect by sacrificial corrosion prevention of zinc can be obtained.

The upper layer (not shown) may also consist of zinc only. In addition, the upper plating layer (not shown) may contain zinc and vanadium and a molar ratio of the zinc to the vanadium, i.e., Zn/V, may be 8.00 or more.

By controlling the current density of the plating and adjusting the molar ratio of zinc to vanadium, a base plating layer (not shown) can be formed between the steel sheet 1 and the plating layer 30 (between the base layer 20 and the plating layer 30 in the case where the base layer 20 is formed).

An upper plating layer (not shown) may be formed on the plating layer 30 in the same manner as the base plating layer (not shown).

The molar ratio (a/b) of the amount of zinc (a) contained in the interior 3a of the dendrite 31 to the total (b) of the amount of zinc contained in the intercrystalline filling region 32 and the surface layer 3b of the dendrite 31 is preferably in the range of 0.10 to 3.00.

If the molar ratio (a/b) is 0.10 or more, when damage occurs on the surface of the plating layer 30, the sacrificial corrosion preventing effect by the metallic zinc contained in the dendrites 31 can be effectively obtained, and more excellent barrier properties can be obtained. In order to more effectively obtain the sacrificial corrosion preventing effect by the metallic zinc contained in the dendrites 31, it is more preferable to set the above molar ratio (a/b) to 0.20 or more.

In addition, when the above molar ratio (a/b) is 3.00 or less, the effect of improving the barrier property of the steel sheet 1 due to the fact that the zinc oxide or zinc hydroxide contained in the surface layer of the dendrite 31 is difficult to pass air or water can be effectively obtained, and more excellent barrier property can be obtained. In order to more effectively obtain the barrier property-improving effect by the surface layer 3b of the dendrite 31, the molar ratio (a/b) is more preferably 0.25 or less.

Further, the molar ratio (a/B) of the total (a) of the amount of zinc contained in the dendrite 31 and the amount of zinc contained in the surface layer 3B of the dendrite 31 to the amount of vanadium (B) contained in the inter-crystal filling region 32 is preferably 0.05 to 6.00. When the above molar ratio (a/B) is 0.05 or more, the sacrificial anticorrosion action by the metal zinc contained in the dendrites 31 and the barrier property-improving action by the zinc oxide or zinc hydroxide contained in the surface layer 3B of the dendrites 31 can be effectively obtained, and more excellent barrier properties can be obtained.

In order to more effectively obtain the sacrificial etching effect by the dendrites 31 and the barrier property improving effect by the surface layer 3B of the dendrites 31, the above molar ratio (a/B) is more preferably 0.10 or more. When the molar ratio (a/B) is 6.00 or less, the corrosion potential due to the vanadium content is set to a high potential, and the effect of improving the barrier property can be more effectively exhibited. In order to further improve the barrier property-improving effect by the vanadium content, the above molar ratio (a/B) is more preferably 5.00 or less, and still more preferably 4.50 or less.

In the present embodiment, the vanadium content in the plating layer 30 is preferably 1 to 20 mass%. If the amount of vanadium in the plating layer 30 is 1 mass% or more, more excellent barrier properties can be obtained. In order to further improve the barrier property and the coating film adhesion, the vanadium content in the plating layer 30 is more preferably 4 mass% or more. When the vanadium content in the plating layer 30 is 20 mass% or less, the content of the dendrites 31 and the surface layer 3b of the dendrites 31 is relatively increased, and the sacrificial corrosion prevention effect by the dendrites 31 and the barrier property improving effect by the surface layer 3b of the dendrites 31 can be effectively obtained.

In order to secure the content of the dendrites 31 and the surface layer 3b of the dendrites 31, the vanadium content of the plating layer 30 is more preferably 15 mass% or less.

The amount of the plating layer 30 to be attached is preferably 1g/m for the purpose of improving the barrier property²Above, more preferably 3g/m²The above. The amount of deposit of the plating layer 30 is preferably 90g/m²Hereinafter, more preferably 50g/m²Hereinafter, it is more preferably 15g/m²The following. The amount of the deposit on the plating layer 30 was 15g/m²In the following cases, the zinc alloy is similar to conventional electrogalvanizing (usually 20 g/m)²Left and right), etc., and is economically superior from the viewpoint of metal cost and electric power cost for forming the plating layer 30.

The surface-treated steel sheet 10 of the present embodiment preferably has a natural immersion potential (corrosion potential) of-0.8V or more when immersed in a 5% NaCl aqueous solution at 25 ℃ with the plating layer 30 as a working electrode. The corrosion potential is preferably higher by 0.2V or more than that of a plated steel sheet (corrosion potential of about-1.0V) provided with a zinc plating layer in place of the plating layer 30. In order to further improve the barrier property, the corrosion potential is more preferably-0.7V or more.

As shown in fig. 1, a surface layer 40 composed of 1 or more coating films is formed on the surface of the plating layer 30. The surface layer 40 is provided as required. By forming the surface layer 40, the corrosion resistance is improved.

The 1 or more coating films on which the surface layer 40 is formed preferably contain an organic resin (R).

The organic resin (R) contained in the coating is not particularly limited, and examples thereof include: a polyurethane resin.

As the organic resin (R) contained in the film, 1 or 2 or more kinds of organic resins (unmodified organic resins) may be mixed and used, or 1 or 2 or more kinds of organic resins obtained by modifying at least 1 other organic resin may be mixed and used in the presence of at least 1 kind of organic resin.

Examples of the urethane resin used for the organic resin (R) include: and products obtained by reacting a polyol compound with a polyisocyanate compound and then extending the chain with a chain extender.

The polyol compound used as a raw material of the polyurethane resin is not particularly limited as long as it contains 2 or more hydroxyl groups per 1 molecule, and examples thereof include: ethylene glycol, propylene glycol, diethylene glycol, 1, 6-hexanediol, neopentyl glycol, triethylene glycol, glycerin, trimethylolethane, trimethylolpropane, polycarbonate polyol, polyester polyol, polyether polyol such as bisphenol hydroxypropyl ether, polyesteramide polyol, acrylic polyol, polyurethane polyol, or a mixture thereof.

As the polyisocyanate compound used as a raw material of the polyurethane resin, a compound containing 2 or more isocyanate groups per 1 molecule is used, and examples thereof include: aliphatic isocyanates such as Hexamethylene Diisocyanate (HDI), alicyclic diisocyanates such as isophorone diisocyanate (IPDI), aromatic diisocyanates such as Toluene Diisocyanate (TDI), aromatic aliphatic diisocyanates such as diphenylmethane diisocyanate (MDI), or mixtures thereof.

As the chain extender used in the production of the polyurethane resin, a compound containing 1 or more active hydrogen in the molecule is used, and examples thereof include: aliphatic polyamines such as ethylenediamine, propylenediamine, hexamethylenediamine, diethylenetriamine, dipropylenetriamine, triethylenetetramine and tetraethylenepentamine, aromatic polyamines such as tolylenediamine, xylylenediamine and diaminodiphenylmethane, alicyclic polyamines such as diaminocyclohexylmethane, piperazine, 2, 5-dimethylpiperazine and isophoronediamine, hydrazines such as hydrazine, succinic dihydrazide, adipic dihydrazide and terephthalic dihydrazide, and alkanolamines such as hydroxyethyldiethylenetriamine, 2- [ (2-aminoethyl) amino ] ethanol and 3-aminopropanediol. These compounds used as a chain extender may be used singly or in admixture of 2 or more.

The urethane resin used for the organic resin (R) may be obtained by: heating a raw material solution containing a blocked isocyanate compound and the polyol compound to a temperature at which the blocking agent is dissociated, and reacting the regenerated isocyanate group with a polyol component of the polyol compound contained in the raw material solution.

The blocked isocyanate compound is regenerated by heating to a temperature higher than the dissociation temperature of the blocking agent. As the blocked isocyanate compound, for example, a blocked isocyanate compound obtained by masking the isocyanate group of the polyisocyanate compound with a conventionally known blocking agent can be used. Examples of the blocking agent include Dimethylpyrazole (DMP) and methyl ethyl ketone oxime.

The 1 or more coating films forming the surface layer 40 preferably contain 1 or 2 or more raw materials selected from the group consisting of phosphoric acid compounds (P), organosilicon compounds (W), carbon black (C), metal fluoro complexes (F), and polyethylene wax (Q) in addition to the organic resin (R).

The phosphoric acid compound (P) contained in the coating is more preferably a compound which emits a phosphate ion in the coating. When the phosphoric acid compound (P) is a compound (P) that releases phosphate ions in the coating, the phosphoric acid compound (P) reacts with vanadium oxide present on the surface of the plating layer 30 when a coating composition for forming the coating comes into contact with the plating layer 30 during the formation of the coating or when phosphate ions derived from the phosphoric acid compound are eluted from the coating after the formation of the coating, thereby forming a poorly soluble phosphate-vanadium coating on the surface of the plating layer 30. This can greatly improve the white rust resistance.

In the case where the phosphoric acid compound (P) is a non-soluble compound that does not emit phosphoric acid ions in the environment, the phosphoric acid compound (P) contained in the coating film inhibits the movement of corrosive factors such as water and oxygen, and therefore, excellent barrier properties can be obtained.

Examples of the phosphate compound (P) contained in the coating film include phosphoric acids such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid and tetraphosphoric acid, and ammonium dihydrogen phosphate. These phosphoric acid compounds (P) may be used alone, or 2 or more kinds thereof may be used in combination.

The content of the phosphoric acid compound (P) in the coating is preferably 1 to 20% by mass, more preferably 6 to 18% by mass, and most preferably 10 to 15% by mass, in terms of phosphate ions. When the concentration of phosphate ions contained in the coating film is 1% by mass or more, excellent barrier properties can be obtained. Further, if the phosphate ion concentration in the coating film is 20% by mass or less, swelling of the coating film due to elution of phosphoric acid can be prevented.

In the case where the phosphate compound (P) is contained in the coating, a barrier layer (not shown) having excellent barrier properties against corrosion factors (water, oxygen, etc.) including vanadium in the plating layer 30 and the phosphate compound in the coating is formed on the surface of the steel sheet 1. As a result, compared with the case where the surface layer 40 is not formed on the surface of the plating layer 30, the effect of delaying the red rust formation while having excellent white rust resistance can be obtained, and the barrier property is remarkably improved.

Examples of the organosilicon compound (W) contained in the coating film include: hydrolysis and condensation products of silane coupling agents, and the like.

Examples of the silane coupling agent used for the formation of the organosilicon compound (W) in the coating film include: 3-glycidoxypropyltrimethoxysilane and 3-aminopropyltriethoxysilane. The silane coupling agent may be used alone, or 2 or more of them may be used in combination.

The organosilicon compound (W) in the coating film is preferably obtained by the reaction of an amino group-containing silane coupling agent (W1) and an epoxy group-containing silane coupling agent (W2). In this case, a dense coating film having a high crosslinking density is formed by the reaction between the amino group and the epoxy group and the reaction between the alkoxysilyl group or the partial hydrolysis product thereof contained in each of the silane coupling agent (W1) and the silane coupling agent (W2). As a result, the surface-treated steel sheet has further improved barrier properties, scratch resistance, and stain resistance.

Examples of the amino group-containing silane coupling agent (W1) include: 3-aminopropyltriethoxysilane. Examples of the epoxy group-containing silane coupling agent (W2) include: 3-Glycidoxypropyltrimethoxysilane (3-Glycidoxypropyltrimethoxysilane).

The molar ratio [ (W1)/(W2) ] of the amino group-containing silane coupling agent (W1) to the epoxy group-containing silane coupling agent (W2) is preferably 0.5 to 2.5, more preferably 0.7 to 1.6. When the molar ratio [ (W1)/(W2) ] is 0.5 or more, a sufficient film-forming property can be obtained, and therefore, the barrier property is improved. Further, if the above molar ratio is 2.5 or less, sufficient water resistance can be obtained, and therefore, excellent barrier properties can be obtained.

The organosilicon compound (W) contained in the coating film is preferably an organosilicon compound having a number average molecular weight of 1000 to 10000, more preferably 2000 to 10000. When the number average molecular weight of the organosilicon compound (W) is 1000 or more, a coating film having excellent water resistance is formed, and the alkali resistance and barrier property are further improved. On the other hand, if the number average molecular weight of the organosilicon compound (W) is 10000 or less, the organosilicon compound (W) can be stably dissolved or dispersed in an aqueous medium containing water as a main component, and the storage stability may be lowered.

The number average molecular weight of the organosilicon compound (W) can be measured directly by the Time of flight mass spectrometry (TOF-MS) method or by conversion using chromatography.

The mass ratio (R/W) of the organic resin (R) to the organosilicon compound (W) in the coating film is preferably 1.0 to 3.0. When R/W is 1.0 or more, cohesive failure is less likely to occur in the film during processing, and processing adhesion is improved. Further, if R/W is 3.0 or less, the effect of containing the organosilicon compound (W) can be sufficiently obtained, and a coating film having high hardness can be obtained.

The organosilicon compound (W) can be produced, for example, by the following method: the above silane coupling agent is dissolved or dispersed in water, and stirred at a predetermined temperature for a predetermined time to obtain a hydrolytic condensate.

The coating film containing the organosilicon compound (W) can be formed, for example, by the following method: an aqueous liquid or an alcohol liquid containing an organosilicon compound (W) is produced as a raw material of a coating composition for forming a coating film, and the coating composition containing the aqueous liquid or the alcohol liquid is applied onto a plating layer and dried.

The aqueous liquid or the alcohol-based liquid containing the organosilicon compound (W) can be produced, for example, by the following method: a method in which an organic silicon compound such as a hydrolytic condensate of a silane coupling agent is dissolved or dispersed in water to obtain an aqueous liquid; and a method of dissolving an organic silicon compound such as a hydrolytic condensate of a silane coupling agent in an alcohol-based organic solvent such as methanol, ethanol, or isopropyl alcohol to obtain an alcohol-based liquid.

In the production of the aqueous liquid or the alcohol-based liquid containing the organosilicon compound (W), in addition to the organosilicon compound (W) and the water or the alcohol-based organic solvent, an acid, a base, an organic solvent, a surfactant, or the like may be added in order to dissolve or disperse the silane coupling agent or the hydrolysis condensate thereof in the aqueous liquid or the alcohol-based liquid. In particular, from the viewpoint of storage stability of the aqueous liquid or the alcohol liquid, it is preferable to adjust the pH of the aqueous liquid or the alcohol liquid to 3 to 6 by adding an organic acid in addition to water or the alcohol organic solvent.

The solid content concentration of the organosilicon compound (W) in the aqueous liquid or the alcohol-based liquid of the organosilicon compound (W) is preferably 25% by mass or less. If the solid content concentration of the organosilicon compound (W) is 25% by mass or less, the storage stability of the aqueous liquid or the alcohol-based liquid becomes good.

The coating film preferably contains carbon black (C) as a coloring pigment. When the coating contains carbon black, fine spots present on the surface of the plating layer are concealed, and a beautiful black appearance is obtained, thereby achieving excellent design.

Examples of the carbon black (C) contained in the coating include: known carbon blacks such as furnace black, ketjen black, acetylene black and channel black. As the carbon black (C) contained in the coating, carbon black subjected to known ozone treatment, plasma treatment, or liquid phase oxidation treatment can be used.

The particle size of the carbon black (C) contained in the coating film is not particularly limited as long as it is within a range that does not cause any problem in dispersibility in the coating composition for forming the coating film, quality of the coating film, and coatability. When carbon black is dispersed in an aqueous solvent, the carbon black is aggregated in the course of dispersion. Therefore, it is generally difficult to disperse carbon black in an aqueous solvent in a state of a primary particle diameter. Therefore, the carbon black contained in the coating composition for forming a coating film is present in the form of secondary particles having a larger particle diameter than the primary particle diameter. Therefore, the carbon black in the coating film formed using the coating composition is also present in the form of secondary particles, as in the coating composition.

As carbon black used as a raw material of the coating film, for example, carbon black having a primary particle diameter of 10nm to 120nm can be used. The particle diameter of the carbon black contained in the coating film is preferably 10nm to 50nm in consideration of the design property and barrier property of the coating film.

In order to ensure the design and barrier properties of the coating film, the particle size of the carbon black in the form of secondary particles dispersed in the coating film is important. The average particle diameter of the carbon black in the coating is preferably 20nm to 300 nm.

The content of the carbon black (C) in the coating is preferably, for example, 1 to 20 mass%, more preferably 3 to 15 mass%, and most preferably 5 to 13 mass%. When the content of the carbon black (C) contained in the coating film is 1% by mass or more, a uniform black appearance can be obtained. In addition, if the content of the carbon black (C) contained in the film is 20% by mass or less, the content of the raw material other than the carbon black (C) contained in the film can be secured, and therefore, excellent barrier properties can be obtained.

The coating film may contain a metal fluoro complex (F). The metal fluoro complex (F) acts as a crosslinking agent in the coating film to improve the cohesive force of the coating film. The metal fluoro complex (F) is not particularly limited, and a metal fluoro complex having titanium is preferably used from the viewpoint of barrier properties. Examples of the metal fluoro complex (F) include: titanium hydrofluoric acid.

The coating film may contain polyethylene wax (Q). The polyethylene wax (Q) can improve the scratch resistance of the coating film. Therefore, if the polyethylene wax (Q) is contained in the coating film, the lubricity of the surface-treated steel sheet is improved, and for example, the frictional resistance caused by the contact between the steel sheet and the press die is reduced, so that damage at the processed portion of the steel sheet and scratches when the steel sheet is disposed can be prevented.

The polyethylene wax (Q) contained in the film is not particularly limited, and a known lubricant can be used. Specifically, as the polyethylene wax (Q), a polyolefin resin-based lubricant is preferably used.

The polyolefin resin-based lubricant used as the polyethylene wax (Q) is not particularly limited, and examples thereof include: hydrocarbon waxes such as polyethylene.

The content of the polyethylene wax (Q) contained in the coating film is preferably 0.5 to 10% by mass, more preferably 1 to 5% by mass, in the coating film. If the polyethylene wax (Q) content is 0.5% by mass or more, the effect of improving scratch resistance can be obtained. When the content of the polyethylene wax (Q) is 10% by mass or less, the content of the raw material other than the polyethylene wax (Q) contained in the coating film can be secured, and therefore, excellent barrier properties can be obtained.

Method for producing surface-treated steel sheet 10 "

Next, a method for manufacturing the surface-treated steel sheet 10 will be described.

The method for producing a surface-treated steel sheet according to the present embodiment is characterized by comprising: a substrate forming step of forming a substrate by using a composition containing 0.10 to 4.00mol/l of Zn²⁺A plating bath of 0 to 18A/dm of ions and 0.01 to 2.00mol/l of V ions or 0.10 to 4.00mol/l of Zr ions²The current density of (a) is plated to precipitate hydrated vanadium oxide or vanadium hydroxide on the steel sheet 1 to form irregularities; and an upper layer plating step of applying the plating bath to 21 to 200A/dm of the steel sheet 1 having the irregularities formed thereon²Electroplating is performed at the current density of (1). The base formation step is a factor that affects the molar ratio of the vanadium to the zinc, i.e., V/Zn, in the intercrystalline filling region in the coating layer. The current density in the substrate forming step is more than 18A/dm²In the case of (3), V/Zn which is the molar ratio of vanadium to zinc in the intercrystalline filled region isBelow 0.10.

In the present embodiment, both surfaces of the steel sheet 1 on which the plating layer 30 is formed are pretreated as necessary. As the pretreatment, it is preferable to form the underlayer 20 by plating nickel with a thickness of 1 to 300nm on both sides of the steel sheet 1.

Next, a plating layer 30 is formed on one surface or both surfaces of the steel sheet 1. In the present embodiment, a method of forming the plating layers 30 on both surfaces of the steel sheet 1 by the electroplating method using the plating apparatus shown in fig. 3 will be described as an example.

FIG. 3 is a schematic view showing an example of a plating apparatus. In the present embodiment, among the rollers 4a, 4b, 5a, and 5b, the rollers 4a and 4b disposed above the steel plate 1 function as a connecting member (conductor) for electrically connecting a power source (not shown) to the steel plate 1. The steel sheet 1 becomes a cathode by being electrically connected to the rollers 4a and 4 b. When the plating is performed, a plurality of plating apparatuses shown in fig. 3 are used in series. The substrate forming process is performed in the plating apparatus shown in fig. 3 or in the region surrounded by the rollers 4a, 5a and the intermediate branch lines 2d, 2f in fig. 3. The upper layer plating step is performed in the plating apparatus shown in fig. 3 or in the region surrounded by the intermediate branch lines 2d and 2f and the rollers 4b and 5b in fig. 3.

The plating tank 21 includes an upper tank 21a disposed above the steel plate 1 and a lower tank 21b disposed below the steel plate 1.

As shown in fig. 3, a plurality of anodes 3 made of platinum or the like are disposed in the upper tank 21a and the lower tank 21b at positions adjacent to the steel plate 1 with a predetermined interval from the steel plate 1. The surface of each anode 3 facing the steel plate 1 is disposed substantially parallel to the surface of the steel plate 1. Each anode 3 is electrically connected to a power supply (not shown) through a connecting member (not shown).

The inside of the upper tank 21a and the inside of the lower tank 21b are filled with the plating bath 2. As shown in fig. 3, the steel sheet 1, which moves substantially horizontally in the planar direction, is disposed between the upper tank 21a and the lower tank 21b of the plating tank 21. Then, the steel sheet 1 passed through the plating tank 21 in the direction of the arrow by the rollers 4a, 4b, 5a, and 5b is immersed in the plating bath 2 in the upper tank 21a and the lower tank 21 b. Therefore, in the present embodiment, the steel sheet 1 is moved in the plating bath 2 by conveying the steel sheet 1 by the rollers 4a, 4b, 5a, 5b, and the plating bath 2 becomes a fluid plating bath 2 in which the steel sheet 1 flows relatively.

As shown in fig. 3, an upper supply pipe 2a for supplying the plating bath 2 to the upper tank 21a is provided in the upper tank 21a so as to penetrate the upper surface of the upper tank 21 a. The upper supply pipe 2a branches into a plurality of outer branch passages 2c and a plurality of intermediate branch passages 2d (only 1 is shown in fig. 3) in the upper tank 21 a. The plurality of intermediate branch paths 2d are arranged along the width direction of the steel plate 1 between the adjacent anodes 3 in a plan view. The intermediate branch path 2d has an opening for supplying the plating bath 2 between the anodes 3 on both sides and the steel sheet 1. The outer circumferential branch path 2c is disposed in plurality along the width direction of the steel plate 1 between the anode 3 and the rollers 4a and 4b in a plan view. The outer peripheral branch passage 2c has an opening for supplying the plating bath 2 between the anode 3 and the steel sheet 1.

A discharge port (not shown) for discharging the plating bath 2 is provided in the upper tank 21a, and is connected to the upper supply pipe 2a via a pipe (not shown) provided with a pump. Therefore, the plating bath 2 supplied from the upper supply pipe 2a and discharged from the discharge port in the upper tank 21a is a flowing plating bath 2 which is again supplied from the upper supply pipe 2a by a pump via a pipe and circulated.

A lower supply pipe 2b for supplying the plating bath 2 to the lower tank 21b is provided in the lower tank 21b so as to penetrate the lower surface of the lower tank 21 b. The lower supply pipe 2b is branched into a plurality of outer branch passages 2e and a plurality of intermediate branch passages 2f (only 1 is shown in fig. 3) in the lower groove 21 b. The plurality of intermediate branch paths 2f are arranged along the width direction of the steel plate 1 between the adjacent anodes 3 in a plan view. The intermediate branch path 2f has an opening for supplying the plating bath 2 between the anodes 3 on both sides and the steel sheet 1. The outer circumferential branch path 2e is disposed in plurality along the width direction of the steel plate 1 between the anode 3 and the rollers 5a and 5b in a plan view. The outer peripheral branch passage 2e has an opening for supplying the plating bath 2 between the anode 3 and the steel sheet 1.

A discharge port (not shown) for discharging the plating bath 2 is provided in the lower tank 21b, and is connected to the lower supply pipe 2b via a pipe (not shown) provided with a pump. Therefore, the plating bath 2 supplied from the lower supply pipe 2b and discharged from the discharge port in the lower tank 21b is a plating bath 2 in a flowing state which is supplied again from the lower supply pipe 2b by a pump via a pipe and circulated.

When the energization time in the base formation step is adjusted to 0.05 to 8.00 seconds, an amorphous diffraction pattern is stably displayed in the intercrystalline filling region 32.

In the present embodiment, it is assumed that: the plating layer 30 is formed on the surface of the steel sheet 1 by the following mechanism. Fig. 4A to 4C are schematic views for explaining the state of the surface of the steel sheet 1 in the process of manufacturing the surface-treated steel sheet 10 shown in fig. 1.

In the plating apparatus shown in FIG. 3, the steel sheet 1 having the nickel plating layer (base layer) 20a formed on the surface thereof is brought into contact with the plating bath 2 in order from the portion thereof passing between the rolls 4a and 5a, and at a rate of 18A/dm²The plating was started at the following current density.

That is, the rollers 4a and 5a are rollers for conducting electricity, and are also called conductive rollers (Conductor rollers). The steel sheet and the plating solution pass between the conductive rollers 4a and 5a and then contact each other.

In the present embodiment, before zinc is deposited on the surface (solid-liquid interface) of the steel sheet 1 having the nickel plating layer 20a formed thereon passing between the rolls 4A and 5a, as shown in fig. 4A, a base formation step is started in which a vanadium compound 6 containing a hydrated vanadium oxide or vanadium hydroxide is deposited to form irregularities.

It is presumed that this is because: at 18A/dm²At the current density below, vanadium having a high deposition potential was reduced and deposited, but zinc having a low deposition potential was not deposited. In the base formation step, the vanadium compound 6 containing a hydrated vanadium oxide or vanadium hydroxide is precipitated. Which is different from the substrate layer 20. The substrate is ultimately received in the plating 30.

In the base formation step, if the precipitation of the vanadium compound 6 on the surface of the steel sheet 1 is started, a plurality of current concentrated portions 61 are formed on the surface of the steel sheet 1 as shown in fig. 4A. It can be presumed that: the current concentrating portion 61 is a current flowing portion formed of a portion of the surface of the steel sheet 1 where the vanadium compound 6 is not precipitated and a portion where the amount of precipitation is small.

If set to 21A/dm²When the current density is as above, the potential for deposition of Zn is reached, and the reductive deposition reaction of Zn is started. As shown in fig. 4B, the current concentration portion 61 becomes a starting point, the dendrite 3a containing metallic zinc grows, and the upper layer plating process starts. It is presumed that: if the dendrite 3a grows, crystals become easier to grow at the tip portion of the dendrite 3 a.

In the upper plating step, as the dendrite 3a grows, the current becomes concentrated at the tips of the plurality of branch portions branched from the dendrite 3a, and it is estimated that: as shown in fig. 4C, hydrogen 62 is generated at the solid-liquid interface between the tip of the branch portion and the plating bath 2.

The hydrogen 62 thus generated raises the pH of the solid-liquid interface between the surface of the dendrite 3a and the plating bath 2. The estimated result is: crystals containing zinc oxide or zinc hydroxide are precipitated so as to cover the surface of the dendrite 31, forming the dendrite 31 having the surface layer 3b shown in fig. 1. In addition, it is presumed that: due to the increase in the pH of the plating bath 2, an amorphous containing hydrated vanadium oxide or vanadium hydroxide is precipitated between the adjacent dendrites 31, forming intercrystalline filled regions 32 shown in fig. 1.

In the present embodiment, as described above, in the base forming step, the energization time is controlled to be in the range of 0.05 to 8.00 seconds. Therefore, before zinc is deposited on the surface of the steel sheet 1, the deposition of the vanadium compound 6 is started, and a plurality of current concentrated portions 61 are formed on the surface of the steel sheet 1. The estimated result is: by the above-described mechanism, the dendrite 31 can be obtained, and the intercrystalline filled region 32 showing an amorphous diffraction pattern when electron beam diffraction is performed can be obtained. The moving time of the steel plate 1 passing through the interval D is more preferably in the range of 1.00 to 6.00 seconds.

If the energization time in the substrate forming step is less than 0.05 seconds, the amount of the vanadium compound 6 deposited before the zinc is deposited on the surface of the steel sheet 1 is insufficient. Therefore, the dendrite 31 formed of the metallic zinc becomes difficult to grow on the current concentrated portion 61 formed on the surface of the steel sheet 1. In addition, the intercrystalline filled region 32 containing a hydrated vanadium oxide or vanadium hydroxide cannot be obtained or even if the intercrystalline filled region 32 is obtained, the amorphous diffraction pattern becomes unstable.

If the energization time in the base formation step exceeds 8.00 seconds, the amount of the vanadium compound 6 deposited before the zinc is deposited on the surface of the steel sheet 1 becomes too large, and the number of the current concentrated portions 61 formed on the surface of the steel sheet 1 becomes small or disappears. Therefore, the dendrite 31 formed of the metallic zinc becomes difficult to grow or the dendrite 31 and the intercrystalline filling region 32 cannot be obtained, or even if the intercrystalline filling region 32 is obtained, the amorphous diffraction pattern becomes unstable.

In the present embodiment, in the base forming step, the current density is preferably 0 to 18A/dm²Under the condition (2), more preferably 2 to 15A/dm²Electroplating is performed under the conditions of (1). The current density in the substrate forming step is set to 18A/dm²The molar ratio (V/Zn) of vanadium to zinc in the inter-crystal filling regions 32 is set to 0.10 to 2.00, and the inter-crystal filling regions 32 exhibit an amorphous diffraction pattern when electron beam diffraction is performed, and as a result, the barrier properties and the coating film adhesion can be improved. On the other hand, if the current density in the base forming step is not within the above range, the inter-crystal filling region 32 cannot be formed, or even if the inter-crystal filling region 32 is formed, the amorphous diffraction pattern becomes unstable.

In the upper layer plating step, the current density is preferably 21 to 200A/dm²Electroplating is performed under the conditions of (1). By setting the current density to 21A/dm²As described above, hydrogen 62 can be sufficiently generated at the solid-liquid interface between the tip of the branch portion of the dendrite 31 and the plating bath 2. Therefore, the precipitation amount of the hydrated vanadium oxide or vanadium hydroxide contained in the intercrystalline filling region 32 increases. Therefore, the plating layer 30 having a large vanadium content and excellent barrier properties can be formed. In addition, if the current density exceeds 200A/dm²Since the plating layer structure becomes coarse and cracks are likely to occur, the adhesion between the plating layer 30 and the steel sheet 1 may be reduced.

The average flow rate of the plating bath 2 in the plating tank 21 during plating is preferably in the range of 20 to 300 m/min, and more preferably in the range of 40 to 200 m/min. When the average flow rate of the plating bath 2 is in the range of 20 to 300 m/min, the generation of cracks in the plating layer 30 can be prevented, and the supply of ions from the plating bath 2 to the surface of the steel sheet 1 can be performed without hindrance.

As the plating bath 2, a plating bath containing a V compound and a Zn compound is used. In addition, in the plating bath 2, a pH adjuster, a metal compound other than the V compound and the Zn compound, and an additive may be added as necessary in addition to the V compound and the Zn compound.

Examples of the pH adjuster include: h₂SO₄NaOH, etc.

Examples of additives include: na for stabilizing the conductivity of the plating bath 2₂SO₄And the like.

Examples of the other metal compounds include: NiSO₄·6H₂And nickel compounds such as O. When the plating bath 2 contains a nickel compound, it is preferable that the plating bath 2 contains 0.01mol/l or more of Ni²⁺. This enables formation of the plating layer 30 containing sufficient nickel. The nickel-containing plating layer 30 is preferable because excellent plating adhesion can be obtained.

Examples of the Zn compound used in the plating bath 2 include: metal Zn, ZnSO₄·7H₂O、ZnCO₃And the like. These may be used alone, or 2 or more of them may be used in combination.

Further, examples of the V compound used in the plating bath 2 include: ammonium metavanadate (V), potassium metavanadate (V), sodium metavanadate (V), VO (C)₅H₇O₂)₂(vanadyl (IV) acetylacetonate), VOSO₄·5H₂O (vanadyl (IV) sulfate), and the like. These may be used alone, or 2 or more of them may be used in combination.

As the plating bath 2, it is preferable to use one containing Zn²⁺And VO²⁺The plating bath of (1).

Containing Zn in the plating bath 2²⁺In the case (1), it is preferable that 0.10 to 4.00mol/l of Zn is contained²⁺More preferably, the content of the compound is 0.35 to 2.00 mol/l.

VO in plating bath 2²⁺In the case of (2), it is preferable that VO is contained in the plating bath 2 in an amount of 0.01mol/l or more and less than 2.00mol/l²⁺. By using a composition containing VO in the above range²⁺The plating bath 2 in (2) can easily form a plating layer 30 having a large vanadium content and excellent barrier properties. VO contained in plating bath 2²⁺If the content of (b) is less than the above range, it becomes difficult to secure the vanadium content in the plating layer 30. In addition, if VO is contained in the plating bath 2²⁺If the content of (b) exceeds the above range, expensive vanadium is used in a large amount in the plating bath 2, which is economically disadvantageous.

In addition, it is preferable to use a plating bath 2 containing 0.10mol/l or more of Na in the plating bath 2⁺The plating bath of (1). In this case, the conductivity of the plating bath 2 can be improved, and the plating layer 30 of the present embodiment can be easily formed.

The temperature of the plating bath 2 is not particularly limited, but is preferably in the range of 40 to 60 ℃ in order to easily and efficiently form the plating layer 30 of the present embodiment.

In order to easily form the plating layer 30 of the present embodiment, the pH of the plating bath 2 is preferably in the range of 1 to 5, and more preferably in the range of 1.5 to 4.

In the present embodiment, it is preferable that: after the plating layer 30 is formed, a treatment agent for improving barrier properties, fingerprint resistance, scratch resistance, lubricity, design properties, and the like is applied to the plating layer 30 as necessary to form the surface layer 40.

Through the above steps, the surface-treated steel sheet 10 shown in fig. 1 can be obtained.

"embodiment 2, surface-treated Steel sheet 210"

The surface-treated steel sheet 210 according to embodiment 2 will be described below in the case where the plated layer 230 contains zirconium.

The surface-treated steel sheet 210 of the present embodiment includes: a steel plate 201; and a plated layer 230 formed on one or both surfaces of the steel sheet. The plating layer 230 contains zinc and zirconium. The plating layer 230 further includes: dendrites 231, which comprise metallic zinc; and an intercrystalline fill region 232 comprising one or both of a hydrated zirconium oxide or zirconium hydroxide. The surface-treated steel sheet 210 will be described in detail below.

The steel sheet 201 is the same as the steel sheet 1 of embodiment 1, and therefore, description thereof is omitted.

As described above, the plating layer 230 has: dendrites 231, which comprise metallic zinc; and an intercrystalline fill region 232 comprising one or both of a hydrated zirconium oxide or zirconium hydroxide.

The dendrite 231 is a dendritic crystal phase containing metallic zinc, and the intercrystalline filling region 232 contains one or both of hydrated zirconium oxide and zirconium hydroxide, is formed around the dendrite 231, and has an amorphous pattern by electron beam diffraction.

The plating layer 230 has the following form: the dendrite 231 is precipitated first, and then the intercrystalline filling region 232 is precipitated around the dendrite 231.

As described above, the dendrite 31 of embodiment 1 has the inner portion 3a and the surface layer 3 b. As described above, the inner portion 3a of the dendrite 31 preferably contains metallic zinc, but may contain other metal components such as nickel. On the other hand, the surface layer 3b of the dendrite 31 preferably contains zinc oxide or zinc hydroxide, more preferably contains crystals of hydrated zinc oxide. On the other hand, the dendrite 231 of the present embodiment does not have an inner portion and a surface layer.

The dendrite 231 may be formed of only metallic zinc, or may contain metallic zinc and other metal components such as nickel having a higher deposition potential than zinc. In addition, the dendrite 231 has the following structure: the plating layer 230 grows from the steel sheet 201 side to the surface side of the plating layer 230 in the thickness direction of the plating layer 230, and branches off toward the surface of the plating layer 230. The dendrite 231 contains metallic zinc, and thus sacrificial corrosion resistance can be given to the plating layer 230.

The intercrystalline fill region 232 may also comprise zinc oxide in addition to one or both of hydrated zirconium oxide or zirconium hydroxide. By including these inclusions in the intercrystalline filler region 232, barrier properties can be imparted to the plating layer 230. Further, since the inter-crystal filling region 232 is mainly composed of a hydrated oxide or hydroxide, when a coating film is formed in the inter-crystal filling region 232, the coating film adhesion can be secured.

The inter-crystal filling region 232 shows an amorphous diffraction pattern when electron beam diffraction is performed.

In the case where the intercrystalline fill region 232 contains a hydrated zirconium oxide or a zirconium hydroxide and a zinc oxide, the molar ratio of zirconium to zinc (Zr/Zn) in the intercrystalline fill region 232 is preferably 1.00 to 3.00. When the molar ratio (Zr/Zn) is in the above range and electron beam diffraction is performed, the inter-crystal filling region 232 shows an amorphous diffraction pattern, and thus excellent corrosion resistance (barrier property) and coating film adhesion can be obtained.

An amorphous layer 250 exhibiting an amorphous diffraction pattern when electron beam diffraction is performed may be formed on the upper layer of the plating layer 230.

Presumably: the amorphous layer 250 is initially formed when the plating layer 230 is formed. Namely, it is presumed that: an amorphous layer 250 is initially formed on the steel sheet 201, and then a plating layer 230 including dendrites 231 and intercrystalline filling regions 232 is grown between the steel sheet 201 and the amorphous layer 250.

The amorphous layer 250 is a layer mainly composed of zirconia, and may contain a small amount of zinc. The amorphous layer 250 exerts barrier properties by being formed on the upper layer of the plating layer 230.

After the plating layer 230 is formed, the amorphous layer 250 can be removed by immersing the steel sheet 201 having the plating layer 230 in an acidic solution. Through such a step, the amorphous layer 250 can be removed from the surface-treated steel sheet 201.

The plating layer 230 is exposed by removing the amorphous layer 250. The surface of the plating layer 230 has a higher surface roughness than the amorphous layer 250, and the coating film adhesion is more excellent than the case where the amorphous layer 250 is formed.

In order to improve the barrier property, the amount of adhesion of the plating layer 230 is preferably 1g/m²Above, more preferably 3g/m²The above.The amount of deposit of the plating layer 230 is preferably 60g/m²Hereinafter, more preferably 40g/m²Hereinafter, it is more preferably 20g/m²The following. The amount of deposit on the plating layer 230 was 20g/m²In the following cases, the zinc alloy is similar to conventional electrogalvanizing (usually 20 g/m)²Left and right), etc., the amount of metal precipitated can be reduced. In addition, if the amount of adhesion is too large, cracks are likely to occur in the plating layer 230.

The thickness of the plating layer 230 is preferably in the range of 0.5 to 40 μm, more preferably in the range of 1.0 to 20 μm, and still more preferably in the range of 2.0 to 15 μm. If the thickness of the plating layer 230 is not less than the lower limit, the barrier property can be improved. Further, if the thickness of the plated layer 230 is not more than the upper limit, cracks are less likely to occur in the plated layer 230. The thickness of the plating layer 230 can be controlled by adjusting the amount of power applied during plating.

The thickness of the amorphous layer 250 is preferably in the range of 0.20 to 2.00. mu.m, more preferably in the range of 0.30 to 1.50. mu.m, and still more preferably in the range of 0.50 to 1.00. mu.m. If the thickness of the amorphous layer 250 is not less than the lower limit, barrier properties can be imparted to the plating layer 230. In addition, if the thickness of the amorphous layer 250 is not more than the upper limit, it is possible to prevent the occurrence of cracks and to secure barrier properties. The thickness of the amorphous layer 250 can be controlled by adjusting the Zr concentration in the plating bath during electroplating. That is, the thickness of the amorphous layer 250 can be increased as the Zr concentration in the plating bath is increased during the plating.

The plating layer 230 contains Zr: 3-40 atomic%, Zn: 3-40 atomic%, the remainder comprising oxygen and impurities. If Zr in the plating layer 230 is 3 atomic% or more, barrier properties can be improved. Further, if Zr in the plating layer 230 is 40 atomic% or less, it is possible to prevent the occurrence of cracks in the plating layer 230 and ensure barrier properties. In addition, if Zn in the plating layer 230 is 3 atomic% or more, a sacrificial corrosion prevention effect can be imparted to the plating layer 230. Further, if Zn in the plating layer 230 is 40 atomic% or less, the amount of Zr can be relatively secured, and the barrier property of the plating layer 230 can be improved.

As described above, the dendrite 231 contains metal Zn, and may also contain Ni or the like.

When electron beam diffraction is performed on the cross section of the plating layer 230 using a Transmission Electron Microscope (TEM), the dendrite 231 can obtain a diffraction pattern due to the crystal structure.

For the intercrystalline fill region 232, Zr: 10-80 atomic%, Zn: 3-40 atomic%, the remainder comprising oxygen and impurities. If Zr in the intercrystalline filling region 232 is 10 atomic% or more, barrier properties can be improved. Further, if Zr in the intercrystalline filling region 232 is 80 atomic% or less, it is possible to prevent the occurrence of cracks in the plating layer 230 and ensure barrier properties. Further, if Zn in the intercrystalline filling region 232 is 3 atomic% or more, barrier properties can be improved. Further, if Zn in the intercrystalline filler region 232 is 40 atomic% or less, the amount of Zr can be relatively secured, and the barrier property of the plating layer 230 can be improved.

The amorphous layer 250 contains Zr: 10-60 atomic%, Zn: 0 to 15 atomic%, the remainder comprising oxygen and impurities. If Zr in the amorphous layer 250 is 10 atomic% or more, barrier properties can be improved. In addition, if Zr in the amorphous layer 250 is 60 atomic% or less, it is possible to prevent the occurrence of cracks and ensure barrier properties. The amorphous layer 250 may contain a small amount of Zn or may not contain Zn.

The same as in embodiment 1 can be applied to the point that the base layer 220 can be formed between the steel sheet 201 and the plated layer 230.

The surface layer 240 can be formed on the plating layer 230 (or on the amorphous layer 250 in the case where the amorphous layer 250 is formed) in the same manner as in embodiment 1.

The surface-treated steel sheet 210 of the present embodiment has an appearance of black, and the L value indicating brightness is 40 or less. By having a black appearance, the resin composition can be used for various purposes. When the value of L exceeds 40, it is difficult to use the material as a material having a black appearance. In particular, by setting the Zr concentration in the plating layer 230 to 5 mass% or more, the L value can be reliably set to 40 or less.

In addition, in the surface-treated steel sheet 210 of the present embodiment, an example in which the plating layer 230 is formed on the steel sheet 201 is described, but the present embodiment is not limited thereto, and the plating layer 230 of the present embodiment may be formed on a zinc plating layer of an electrogalvanized steel sheet, a hot-dip galvanized steel sheet, or an alloyed hot-dip galvanized steel sheet. That is, a 2 nd zinc plating layer (not shown) containing zinc may be further formed between the steel sheet 201 and the plating layer 230. By further forming the 2 nd zinc plating layer (not shown), the corrosion resistance of the surface-treated steel sheet 210 can be further improved. For example, even when corrosive substances pass through the plated layer 230, the sacrificial corrosion prevention effect can be exerted by the 2 nd zinc plated layer (not shown), and the corrosion resistance of the surface-treated steel sheet 210 can be improved.

"method for manufacturing surface-treated Steel sheet 210"

Next, a method for manufacturing the surface-treated steel sheet 210 will be described. The method for producing the surface-treated steel sheet 210 is different from the method for producing the surface-treated steel sheet 1 according to embodiment 1 only in the composition of the plating bath, and is otherwise the same.

The method for manufacturing the surface-treated steel sheet 210 includes a base forming step and an upper-layer plating step, as in embodiment 1. The same plating bath is used in the substrate forming step and the upper layer plating step, and a compound containing Zr (ZrO) is used²⁺) And Zn compound (Zn)²⁺) The plating bath of (1).

As the Zr compound, ZrO is preferably formed in the plating bath²⁺Ionic compounds, for example, can be exemplified by: soluble salts such as zirconyl nitrate, zirconyl sulfate, zirconyl nitrate chloride, and the like. These may be used alone, or 2 or more of them may be used in combination.

The plating bath preferably contains 0.10 to 4.00mol/l of Zn²⁺More preferably, the content of the organic solvent is 0.50 to 2.00 mol/l. In addition, it is preferable that ZrO is contained in an amount of 0.10 to 4.00mol/l²⁺More preferably, the content of the organic solvent is 0.50 to 2.00 mol/l. By using a ZrO containing range within the above range²⁺The plating bath of (3) has a high Zr content, and thus the plating layer 230 having excellent barrier properties can be easily formed. ZrO contained in plating bath²⁺When the content of (b) is less than the above range, it is difficult to secure the Zr content in the plating layer 230. In addition, if in the plating bathZrO contained²⁺If the content of (b) exceeds the above range, Zr is used in the plating bath 2 in a large amount, which is economically disadvantageous.

In addition to the Zr compound and the Zn compound, a pH adjuster, other metal compounds than the Zr compound and the Zn compound, additives, and the like may be added to the plating bath as necessary.

The current densities in the base formation step and the upper plating step are the same as those in embodiment 1, and therefore, the description thereof is omitted.

"other examples"

The present invention is not limited to the above-described embodiments.

In the present embodiment, the case where the plating layers are formed on both surfaces of the steel sheet is described as an example, but the plating layers may be formed only on one surface of the steel sheet.

Further, the base layer is preferably formed between the steel sheet and the plating layer, but the base layer may not be formed. When plating layers are formed on both surfaces of the steel sheet, a base layer may be formed only between the plating layer and one surface of the steel sheet.

In the present embodiment, the case where the plating layer contains vanadium and the case where the plating layer contains zirconium are described separately, but these embodiments may be provided together.

In the present embodiment, the case where the surface layer is formed on the surface of the plating layer is described as an example, but the surface layer may not be formed. Since the surface-treated steel sheet of the present embodiment has excellent barrier properties, a surface layer for improving the barrier properties may not be formed on the surface of the plating layer. When plating layers are formed on both surfaces of the steel sheet, a surface layer may be formed only on one surface of the plating layer.

In addition, in the present embodiment, the case where the surface-treated steel sheet is manufactured by using the plating apparatus shown in fig. 3 is described as an example, but the plating apparatus for manufacturing the surface-treated steel sheet is not limited to the plating apparatus shown in fig. 3. For example, 4 anodes 3 are arranged in the plating apparatus shown in FIG. 3, but several anodes 3 are possible in terms of the number of anodes 3. The size and shape of the plating tank 21, the steel sheet 1, and the anode 3, and the arrangement and shape of the upper supply pipe 2a and the lower supply pipe 2b are not particularly limited, and may be appropriately determined according to the application of the surface-treated steel sheet 10, and the like.

Example 1

Test results of surface-treated Steel sheet containing vanadium "

A surface-treated steel sheet having vanadium-containing plating layers on both sides of the steel sheet was produced by the following method using the plating apparatus shown in fig. 3, and evaluated.

A plating bath in a flowing state was prepared by circulating the plating baths having the plating bath compositions, temperatures, and pH shown in table 1 at a relative average flow rate of 100 m/min.

TABLE 1

As the steel sheet, a steel sheet having a thickness of 0.5mm as SPCD for drawing a cold-rolled steel sheet prescribed in JIS G3141 was used.

The steel sheet was pretreated (nickel-plated) and used as a cathode.

In the pretreatment, first, the following plating bath was prepared as a plating bath for nickel plating: ion exchange water, concentrated sulfuric acid and NiSO₄·6H₂O is mixed as Ni²⁺Contains 60g/L, and has a pH of 2.0 at 60 ℃. Then, the steel sheet was immersed in a plating bath, the steel sheet was used as a cathode, a platinum electrode was used as an anode, and the amount of Ni deposited was 200mg/m²The electrolytic treatment was performed.

In the base forming step and the upper layer plating step, the energization times were set to the times shown in tables 2 and 3, and the plating layer was formed by the electroplating method.

TABLE 2

TABLE 3

It should be noted that, in the plating bath composition shown in Table 1, ZnSO was used₄·7H₂O as Zn compound, using VOSO₄·5H₂O as a V compound, and further Na is used as required₂SO₄NiSO as other metal compound₄·6H₂And O. By adjusting their contents, Zn shown in Table 1 was adjusted to²⁺、V(V⁴⁺、VO²⁺)、Na⁺、Ni²⁺The concentration of (c).

The plating layers of the examples and comparative examples thus obtained were observed with a field emission transmission electron microscope (FE-TEM) (JED-2100F, Japan Electron Co., Ltd.).

FIGS. 5A to 5C are Transmission Electron Microscope (TEM) photographs of the plated layer of the surface-treated steel sheet of example V4. Fig. 5A is a photograph of a cross section of the plating layer 30 formed on the steel sheet 1 in the entire thickness direction, fig. 5B is an enlarged photograph of the interface portion of the steel sheet and the plating layer in the cross section of fig. 5A, and fig. 5C is an enlarged photograph of dendrites and their surrounding portions in the cross section of fig. 5A.

In fig. 5B, reference numeral 51 denotes a base layer, and reference numeral 52 denotes an intercrystalline filling region in the vicinity of the interface between the steel sheet and the plating layer. In fig. 5C, reference numeral 53 denotes a dendrite, reference numeral 54 denotes an intercrystalline filling region, and reference numeral 55 denotes a surface layer formed on the surface of the dendrite.

As shown in fig. 5A to 5C, in the surface-treated steel sheet of example V4, dendrites, intercrystalline filled regions, and a surface layer of dendrites were formed in the plating layer.

The plating layers of the surface-treated steel sheets of examples V1 to V3 and V5 to V20 were also observed by TEM in the same manner as in example V4. As a result, dendrites, regions filled between the dendrites, and a surface layer of the dendrites are formed in the plating layer.

The plated layer of the surface-treated steel sheet of example V4 was observed from the cross-sectional direction using a scanning electron microscope (SEM: A-4300SE, manufactured by Hitachi Ltd.). In order to easily observe the surface shape of the plating layer, the observation of the plating layer is performed after the gold film is deposited on the surface of the plating layer.

FIG. 6 is a Scanning Electron Microscope (SEM) photograph of the plated layer of the surface-treated steel sheet of example V4. In fig. 6, reference numeral 56 denotes dendrites, reference numeral 57 denotes inter-crystal filling regions disposed between the dendrites, and reference numeral 58 denotes a surface layer covering the surfaces of the dendrites. In the photograph shown in fig. 6, the white portion of the surface of the plating layer is a gold film deposited for observing the plating layer.

The plating layers of the surface-treated steel sheets of examples V1 to V3 and V5 to V20 also formed dendrites, intercrystalline filler regions, and the surface layer of dendrites in the same manner as the plating layer of example V4.

The plating layers of the surface-treated steel sheets of comparative examples x1 to x7 were observed by SEM in the same manner as in example V4. FIG. 7 is a Scanning Electron Microscope (SEM) photograph of a plated layer of a surface-treated steel sheet of comparative example x 2. As shown in fig. 7, the plating layer of comparative example x2 was a single phase formed of dendrites.

Elemental analyses of the dendrites, the intercrystalline filled regions, and the surface layers of the dendrites were performed on the plating layers of examples V1 to V20 using an energy dispersive X-ray spectrometer (EDS) (JED-2300T, manufactured by japan electronics corporation). Then, the element (composition) contained in the dendrite, the element (composition) contained in the intercrystalline filling region, and the amount of vanadium and zinc thereof, and the element (composition) contained in the surface layer of the dendrite were examined.

Further, the molar ratio (V/Zn) of the amount of vanadium to the amount of zinc in the intercrystalline filling region was calculated using the results of elemental analysis.

The elemental analyses of the dendrites, the intercrystalline filled regions, and the surface layers of the dendrites were also performed for the plating layers of comparative example x1 to comparative example x7 in the same manner as in example V1 to example V20.

The results are shown in tables 4 and 5.

TABLE 4

TABLE 5

In addition, it was confirmed that the plated layers of the surface-treated steel sheets of examples V1 to V20 each had a crystal structure or were amorphous by using an electron beam diffraction image obtained by TEM from the cross-sectional direction.

FIG. 8 is a photograph showing an electron beam diffraction pattern of the plating layer of example V4. The symbols marked in the photograph shown in fig. 8 correspond to the intercrystalline filling regions 52, dendrites 53, intercrystalline filling regions 54, surface layers 55 of dendrites shown in fig. 5B and 5C, respectively.

As can be seen from the electron beam diffraction image shown in fig. 8: the dendrite 53 and the dendrite surface layer 55 have a crystal structure. In addition, it can be seen that: the inter-crystal filled regions 52 and 54 do not obtain a diffraction pattern due to the crystal structure, and are amorphous.

The plating layers of the surface-treated steel sheets of examples V1 to V3 and V5 to V20 also confirmed that the dendrites, the intercrystalline filled regions, and the surface layer of the dendrites each had a crystalline structure or were amorphous, in the same manner as in example V4. The results show that: the surface layer of the dendrite and the dendrite has a crystal structure, and the filling area between the dendrites is amorphous.

Further, impurities in the dendritic crystal were examined, and as a result, C, Si, S, Fe, and N were each about 0.1 to 5 atomic%.

The plating layers of the surface-treated steel sheets of comparative examples X1 to X7 were analyzed using an X-ray diffraction apparatus (XRD: RINT2500 manufactured by Rigaku corporation). As a result, the plating layers of comparative examples x1 to x7 were confirmed to be: dendrites have the crystal structure of Zn. In addition, it was confirmed that: except for comparative example x7, no intercrystalline filler regions were formed (comparative examples x4 and x6), and even when formed, only unstable amorphous diffraction patterns were obtained (comparative examples x1 to x3 and x 5).

The following items were evaluated for the plating layers of examples and comparative examples by the following methods.

(amount of adhesion and vanadium content in plating layer)

The amount of deposit of the plating layer was set to the total mass per unit area of the Zn element and the V element detected by a fluorescent X-ray device (simulx 14 manufactured by Rigaku Corporation). The vanadium content in the plating layer was calculated as a percentage by dividing the amount of the V element detected by a fluorescent X-ray device by the above adhesion amount.

Barrier property "

The edge and the back of the test piece cut out from the surface-treated steel sheet were sealed with a tape, and subjected to a salt water spray test (JIS-Z-2371). Then, the white rust generation area ratio of the non-sealed portion after 72 hours was visually observed and evaluated by the following criteria. The white rust occurrence area ratio is a percentage of the area of the white rust occurrence portion with respect to the area of the observation portion.

(Standard)

5: the area ratio of white rust generation is less than 10 percent,

4: the white rust area ratio is 10-25%

3: the white rust generation area ratio is more than 25% and less than 50%

2: the white rust generation area ratio is 50% or more and less than 75%

1: the white rust generation area ratio is more than 75%

Sacrificial Corrosion protection "

A coating material (Amilac #1000, manufactured by Kansai paint Co., Ltd.) was applied to a test piece cut out from a surface-treated steel sheet in a bar coating manner, and baked at 140 ℃ for 20 minutes to form a coating film having a dry film thickness of 25 μm. Then, the edge and the back surface of the coated test piece were sealed with a tape, and a scratch was applied to the surface in an X shape by an NT cutter. Then, a salt water spray test (JIS-Z-2371) was performed, and the time until red rust was generated from the scratched portion was measured and evaluated by the following criteria.

(Standard)

5: the time until red rust is generated is more than 960 hours

4: the time until red rust is generated is more than 720 hours and less than 960 hours

3: the time until red rust is generated is more than 480 hours and less than 720 hours

2: the time until red rust is generated is more than 120 hours and less than 480 hours

1: the time until red rust is generated is less than 120 hours

(powdering Property (adhesion between plating layer and Steel sheet))

A 60V bend die was used in the powdering test. The test piece cut out from the surface-treated steel sheet was bent at 60 ° using a die having a radius of curvature of 1mm at the tip, so that the evaluation surface of the test piece was located inside the bent portion, and the tape was peeled off. Powdering (peeling width (mm)) was evaluated from the state of peeling of the plating layer peeled together with the tape.

(film adhesion)

A coating (Amilac #1000, manufactured by Kansai paint Co., Ltd.) was applied to a test piece cut out from a surface-treated steel sheet in a bar coating manner, and baked at 140 ℃ for 20 minutes to form a coating film having a dry film thickness of 25 μm. The coated plate thus obtained was immersed in boiling water for 30 minutes and then left to stand at room temperature for 24 hours. Then, 100 checkerboards 1mm square were cut out from the test piece using an NT cutter, the checkerboards were pushed out by an ericsson tester by 7mm, and then a peel test using an adhesive tape was performed on the pushed-out convex portions, and the adhesion (number of peeled off portions) of the coating film was evaluated.

TABLE 6

TABLE 7

As shown in tables 6 and 7, it can be seen that: the surface-treated steel sheets of examples V1 to V20 all satisfied the scope of the present invention, and were superior in barrier property and coating film adhesion to the surface-treated steel sheets of comparative examples x1 to x 7.

In addition, the current density in the substrate forming process is 0 to 18A/dm²The plating layers of the surface-treated steel sheets of examples V1 to V20 had a current density of 25A/dm in the step of forming a base²The surface-treated steel sheets of comparative examples x2 and x3 had different plating layers, and the molar ratio (V/Zn) of vanadium to zinc in the intercrystalline filler regions was 0.10 to 2.00, and the intercrystalline filler regions exhibited an amorphous diffraction pattern when subjected to electron beam diffraction. In addition, it can be seen that: the barrier property and coating film adhesion are more excellent.

Example 2

"test results of surface-treated Steel sheet containing vanadium with coating formation"

The coating compositions for forming a coating film were prepared by dispersing the organic resin (R), the phosphoric acid compound (P), the carbon black (C), the organosilicon compound (W), the metal fluoro complex compound (F), the isocyanate compound (I), and the polyethylene wax (Q) shown in table 8 in water as a solvent at the contents (mass% of solid content) shown in tables 9 and 10 by stirring with a coating dispersion machine.

TABLE 8

TABLE 9

Watch 10

In the preparation of the coating composition, an aqueous liquid containing a hydrolytic condensate produced by dissolving 3-aminopropyltriethoxysilane (W1) and 3-glycidoxypropyltrimethoxysilane (W2) shown in table 8 in water in the ratio [ (W1)/(W2) ] shown in table 9 and table 10 was added as the organosilicon compound (W) in the amounts shown in tables 9 and 10.

(paint stability)

The coating composition thus prepared was stirred at room temperature for 30 minutes, and the presence or absence of generation of precipitates was visually observed.

The case where no precipitates were generated was evaluated as "OK" and the case where precipitates were generated was evaluated as "NG" for paint stability. The results of coating stability are shown in tables 9 and 10.

As shown in tables 9 and 10, the coating compositions used in examples t1 to t14 and comparative examples w1 to w5 exhibited "OK" as a result of coating stability and excellent stability.

Next, a coating film was formed on the surface of the plated layer of the surface-treated steel sheet of example V4 or comparative example x3 produced in example 1 by the following method using each of the above-described coating compositions.

First, on the surface of the surface-treated steel sheet, the coating composition was applied using a roll coater so as to be film thicknesses shown in tables 11 and 12. Then, the surface-treated steel sheet coated with the coating composition was dried by heating so that the steel sheet reached a temperature of 150 ℃, and was spray-cooled with water to obtain a coating film. It should be noted that hydrated oxides are present in the coating even after heating to 150 ℃.

Next, each of the surface-treated steel sheets having a coating film formed on the surface of the plating layer was evaluated for uniformity in appearance, corrosion resistance, conductivity, work adhesion, and scratch resistance. Further, as reference example e2, the surface-treated steel sheet of example V4 produced in example 1 was evaluated for uniformity of appearance, corrosion resistance, conductivity, work adhesion, and scratch resistance.

The evaluation results of the respective items are shown in tables 11 and 12.

TABLE 11

TABLE 12

The evaluation methods and evaluation criteria for each item are shown below.

(uniformity of appearance)

The L value of the surface-treated steel sheet was measured using a colorimeter (CR-400) manufactured by Konika Mingta, and evaluated according to the following evaluation criteria.

(evaluation criteria)

5: l value less than 24

4: l value is 24 or more and less than 27

3: l value is 27 or more and less than 28

2: l value is more than 28 and less than 30

1: l value exceeds 30

(Corrosion resistance)

The edge and the back of the test piece cut out from the surface-treated steel sheet were sealed with a tape, and subjected to a salt water spray test (JIS Z2371). Then, the white rust generation area ratio of the non-sealed portion after 240 hours was visually observed and evaluated by the following criteria. The white rust occurrence area ratio is a percentage of the area of the white rust occurrence portion with respect to the area of the observation portion.

(evaluation criteria)

6: the white rust generation rate is less than 3 percent

5: the white rust generation rate is more than 3% and less than 10%

4: the white rust generation rate is more than 10% and less than 25%

3: the white rust generation rate is more than 25% and less than 50%

2: the white rust generation rate is more than 50 percent and less than 75 percent

1: white rust generation rate of 75% or more

(conductivity)

Using a test piece cut out from the surface-treated steel sheet, the interlayer resistance value (Ω · cm) was measured by the measurement method prescribed in JIS C2550²) The conductivity was evaluated by the following criteria.

(evaluation criteria)

6: interlayer resistance value of less than 1.0 omega cm²

5: the interlayer resistance value was 1.0. omega. cm²Above and below 1.5 omega cm²

4: the interlayer resistance value was 1.5. omega. cm²Above and below 2.0 omega cm²

3: the interlayer resistance value was 2.0. omega. cm²Above and below 2.5 omega cm²

2: the interlayer resistance value was 2.5. omega. cm²Above and below 3.0 omega cm²

1: the interlayer resistance value was 3.0. omega. cm²The above

(working adhesion)

After a test piece cut out from the surface-treated steel sheet was bent at 180 °, a tape peeling test was performed on the outer side of the bent portion. The appearance of the tape-peeled portion was observed with a magnifying glass having a magnification of 10 times, and evaluated by the following evaluation criteria. The bending was performed by holding a 0.5mm separator therebetween in an atmosphere of 20 ℃.

(evaluation criteria)

5: no peeling was found in the coating film

4: peeling was found in a very small part of the coating film (peeling area. ltoreq.2%)

3: peeling was found in a part of the coating film (2% < peeled area. ltoreq.10%)

2: peeling was observed in the coating film (10% < peeled area. ltoreq.20%)

1: peeling was observed in the coating film (peeling area > 20%)

(scratch resistance)

The test piece cut out from the surface-treated steel sheet was brought into close contact with the electrogalvanized steel sheet (no treatment material), and the test piece was rotated by 90 ° in a pressurized state. Pressurization is set to 0.2kg/cm²The test temperature was set at 25 ℃. Then, the appearance of the test material was evaluated by visual observation.

(evaluation criteria)

6: no scratch was seen at all.

5: with fine scratches but no exposure of the substrate

4: the substrate was slightly exposed (exposed area: less than 3%)

3: the substrate is exposed (exposed area: 3% or more and less than 10%)

2: the substrate is exposed (exposed area: 10% or more and less than 30%)

1: exposing the substrate (exposed area: more than 30%)

As shown in tables 11 and 12, examples t1 to t14, which had an overcoat film on the plating surface of the surface-treated steel sheet of example V4, exhibited excellent uniformity of appearance, corrosion resistance, conductivity, work adhesion and scratch resistance, in all evaluation items, which were 2 or more of the evaluation criteria. Further, examples t1 to t14 were superior in corrosion resistance and electrical conductivity to those of reference example e2 in which no coating was formed on the surface.

On the other hand, the evaluation results of the appearance uniformity, corrosion resistance after 240 hours, work adhesion and scratch resistance of comparative examples w1 to w5 in which the coating surface of the surface-treated steel sheet of comparative example x3 had a coating film were 1, and the performance was poor.

Example 3

Test results of surface-treated Steel sheet containing zirconium "

Using the plating apparatus shown in fig. 2, a surface-treated steel sheet having zirconium-containing plating layers on both surfaces of the steel sheet was produced by the following method, and evaluated.

Note that the same matters as in example 1 will not be described.

A plating bath in a flowing state was prepared by circulating the plating baths having the plating bath compositions, temperatures, and pH shown in table 13 at an average relative flow rate of 100 m/min.

Watch 13

Then, the steel sheet was used as a cathode by pretreatment (nickel plating). In the base forming step and the upper layer plating step, the energization time was set to the times shown in tables 14 and 15, the current density was set to the values shown in tables 14 and 15, and the plating layer was formed by the electroplating method.

TABLE 14

Watch 15

In the plating bath composition shown in Table 13, ZnSO was used₄·7H₂O as Zn Compound, ZrO (NO)₃)₂Aqueous solution or ZrOSO₄The aqueous solution used as the Zr compound further contains Na as required₂SO₄NiSO as other metal compound₄·6H₂And O. By adjusting their contents, Zn shown in Table 1 was adjusted to²⁺、Zr(Zr⁴⁺、ZrO²⁺)、Na⁺、Ni²⁺The concentration of (c).

The plating layers of the examples and comparative examples thus obtained were observed with a field emission transmission electron microscope (FE-TEM) (JED-2100F, Japan Electron Co., Ltd.).

FIG. 9 is a Transmission Electron Microscope (TEM) photograph of the plated layer of the surface-treated steel sheet of example Z4.

As shown in fig. 9, it is understood that: in the plating layer of the present embodiment, dendrites, an intercrystalline filling region formed around the dendrites, and an amorphous layer in the surface layer portion are formed. It was confirmed that the dendrite was formed of metallic Zn by elemental analysis and electron beam diffraction analysis using an energy dispersive X-ray analyzer (EDS (JED-2300T, Japan Electron Ltd.). The region filled with the intercrystalline region was composed of zirconium oxide and zirconium hydroxide, and further, it was confirmed that the amorphous layer in the surface layer part was composed of zirconium oxide.

In the plating layers of the other examples, dendrites, intercrystalline filling regions formed around the dendrites, and an amorphous layer of the surface layer portion were formed in the same manner as in example Z4. Further, there is also a plating layer obtained by removing the amorphous layer in the surface layer portion.

Elemental analyses of "dendrites", "inter-crystal filling regions" and "surface layers of dendrites" were performed on the plating layers of examples Z1 to Z20 using an energy dispersive X-ray spectrometer (EDS) (JED-2300T, manufactured by japan electronics corporation). Then, the element (composition) contained in the dendrite, the element (composition) contained in the intercrystalline filling region, and the amounts of zirconium and zinc thereof, and the element (composition) contained in the surface layer of the dendrite were examined.

Further, the molar ratio of the amount of zirconium to the amount of zinc (Zr/Zn) in the intercrystalline filling region was calculated using the results of elemental analysis.

In the plating layers of comparative examples x11 to x16, the elemental analyses of "dendrites", "inter-crystal filling regions", and "surface layers of dendrites" were also performed in the same manner as in examples Z1 to Z20.

The results are shown in tables 16 to 17.

TABLE 16

TABLE 17

It was confirmed that the "dendrites", "inter-crystal filled regions", and "surface layers of dendrites" had a crystal structure or were amorphous in the plated layers of the surface-treated steel sheets of examples Z1 to Z20. As a result, it was found that the dendrites and the surface layer of the dendrite had a crystal structure, and the region filled between the dendrites was amorphous.

Further, impurities in the dendritic crystal were examined, and as a result, C, Si, S, Fe, and N were each about 0.1 to 5 atomic%.

The plating layers of the surface-treated steel sheets of comparative examples X11 to X16 were analyzed using an X-ray diffraction apparatus (XRD: RINT2500 manufactured by Rigaku Corporation). As a result, it was confirmed that: the dendrite had a crystal structure of Zn in the plating layers of comparative examples x11 to x 16. In addition, it was confirmed that: in the case where no intercrystalline filler region was formed (comparative example x15), only unstable amorphous diffraction patterns were obtained even when formed (comparative examples x11 to x14 and x 16).

The following items were evaluated for the plating layers of examples and comparative examples by the following methods.

(amount of adhesion in plating layer, zirconium content)

The amount of deposit of the plating layer was set to the total mass per unit area of the Zn element and the Zr element detected by a fluorescent X-ray device (simulx 14 manufactured by Rigaku Corporation). The zirconium content in the plating layer was calculated as a percentage by dividing the amount of Zr element detected by a fluorescent X-ray device by the above adhesion amount.

Watch 18

Watch 19

As shown in tables 18 and 19, it can be seen that: examples Z1 to Z20 all satisfied the scope of the present invention, and were superior in barrier properties and coating film adhesion to the surface-treated steel sheets of comparative examples x11 to x 16.

In addition, the current density in the substrate forming process is 0 to 18A/dm²The plating layers of the surface-treated steel sheets of examples Z1 to Z20 had a current density of 25A/dm in the step of forming a base²Ratio of (A to (B)The surface-treated steel sheets of comparative examples x12 to x13 had a molar ratio of zirconium to zinc (Zr/Zn) of 1.00 to 3.00 in the intercrystalline filler regions, and the intercrystalline filler regions exhibited an amorphous diffraction pattern when subjected to electron beam diffraction. In addition, it can be seen that: the barrier property and coating film adhesion are more excellent.

Example 4

"test results of film-formed zirconium-containing surface-treated Steel sheet"

The coating compositions for forming a coating film were prepared by dispersing the organic resin (R), the phosphoric acid compound (P), the carbon black (C), the organosilicon compound (W), the metal fluoro complex compound (F), the isocyanate compound (I), and the polyethylene wax (Q) shown in table 8 in water as a solvent at the contents (mass% of solid content) shown in tables 20 and 21 by stirring with a coating dispersion machine.

Note that the same matters as in example 2 will not be described.

Watch 20

TABLE 21

As shown in tables 20 and 21, the coating compositions used in examples u1 to u14 and comparative examples y1 to y5 exhibited "OK" as a result of coating stability and excellent stability.

Next, a coating film was formed on the plated surface of the surface-treated steel sheet of example Z4 or comparative example x13 produced in example 3 by the following method using the above-described coating composition.

First, on the surface of the surface-treated steel sheet, the coating composition was applied using a roll coater so as to be film thicknesses shown in tables 22 and 23. Then, the surface-treated steel sheet coated with the coating composition was dried by heating so that the steel sheet reached a temperature of 150 ℃, and was spray-cooled with water to obtain a coating film. It should be noted that hydrated oxides are present in the coating even after heating to 150 ℃.

Next, each of the surface-treated steel sheets having a coating film formed on the surface of the plating layer was evaluated for uniformity in appearance, corrosion resistance, conductivity, work adhesion, and scratch resistance. In addition, as reference example f1, the surface-treated steel sheet of example Z4 produced in example 3 was evaluated for uniformity of appearance, corrosion resistance, conductivity, work adhesion, and scratch resistance.

The evaluation results of the respective items are shown in tables 22 and 23.

TABLE 22

TABLE 23

As shown in tables 22 and 23, examples u1 to u14, in which the surface of the plating layer of the surface-treated steel sheet of example Z4 had a coating film, exhibited excellent uniformity of appearance, corrosion resistance, conductivity, work adhesion and scratch resistance, in all evaluation items, which were 2 or more of the evaluation criteria. Further, examples u1 to u14 were superior in corrosion resistance and electrical conductivity to those of reference example f1 in which no coating was formed on the surface.

On the other hand, the evaluation results of the uniformity of appearance, corrosion resistance after 240 hours, work adhesion and scratch resistance of comparative examples y1 to y5 in which the surface of the plating layer of the surface-treated steel sheet of comparative example x13 had a coating were 1, and the performance was poor.

While the preferred embodiments of the present invention have been described above, it is needless to say that the present invention is not limited to these examples. It is obvious to those skilled in the art that various modifications and variations can be made within the scope of the claims, and it is understood that these matters also naturally fall within the technical scope of the present invention.

Industrial applicability

According to the above embodiments, a surface-treated steel sheet having a plating layer containing zinc and vanadium formed on the surface of the steel sheet and having excellent barrier properties and coating film adhesion can be provided.

Description of the symbols

1. 201 steel plate

2 plating bath

2a upper supply pipe

2b lower supply pipe

2c, 2e peripheral branch line

2d, 2f intermediate branch

3 Anode

Interior of 3a dendrite

3b, 55, 58 dendrite surface layer

3c granular crystals

4a, 5a, 4b, 5b rollers

6 vanadium compounds

10. 210 surface-treated steel sheet

20. 51, 220 base layer

20a nickel plating

21 plating bath

21a upper groove

21b lower groove

30. 230 plating layer

31. 53, 56, 231 dendrites

32. 52, 54, 57, 232 crystal inter-filling region

40. 240 surface layer

61 current concentration part

62 hydrogen

250 amorphous layer

Spacing between D rollers 4a, 5a and anode 3

Claims (7)

1. A surface-treated steel sheet, characterized by comprising:

a steel plate; and

a plating layer formed on one or both surfaces of the steel sheet and containing zinc and vanadium or zirconium,

wherein the plating layer has:

a zinc metal-containing dendrite; and

an intercrystalline filling region which is filled between the dendrites and shows an amorphous diffraction pattern when electron beam diffraction is performed,

in the case where the plating layer contains the vanadium, the intercrystalline filling regions contain hydrated vanadium oxide or vanadium hydroxide,

in the case where the plating layer contains zirconium, the intercrystalline fill regions contain hydrated zirconium oxide or zirconium hydroxide,

a base layer formed of a crystal containing nickel is further provided between the steel sheet and the plating layer.

2. The surface-treated steel sheet according to claim 1, wherein when the plating layer contains the vanadium, a molar ratio of the vanadium to the zinc in the intercrystalline filling regions, V/Zn, is 0.10 to 2.00,

when the plating layer contains the zirconium, the Zr/Zn ratio in the intergranular filling region is 1.00 to 3.00 in terms of the molar ratio of the zirconium to the zinc.

3. The surface-treated steel sheet according to claim 1, wherein in the case where the plating layer contains the vanadium, the surface layer of the dendrite contains zinc oxide or zinc hydroxide.

4. The surface-treated steel sheet according to claim 1, wherein a base coating layer having a molar ratio of zinc to vanadium, i.e., Zn/V, of 8.00 or more is further provided between the steel sheet and the coating layer.

5. The surface-treated steel sheet according to claim 1, wherein a base plating layer having a Zn/V molar ratio of zinc to vanadium of 8.00 or more is further provided between the base layer and the plating layer.

6. The surface-treated steel sheet according to claim 1, further comprising an organic resin coating film comprising a urethane resin and 1 to 20 mass% of carbon black on the surface of the plating layer.

7. A method for producing a surface-treated steel sheet according to claim 1 or claim 2, comprising:

a substrate forming step of forming a substrate by using a composition containing 0.10 to 4.00mol/l of Zn²⁺A plating bath of ions and 0.01 to 2.00mol/l of V ions or 0.10 to 4.00mol/l of Zr ions at an average flow rate of 40 to 200 m/min and 0 to 18A/dm²Performing electroplating at a current density such that when the plating bath contains V ions, hydrated vanadium oxide or vanadium hydroxide is precipitated on the steel sheet to form irregularities, or when the plating bath contains Zr ions, hydrated zirconium oxide or zirconium hydroxide is precipitated on the steel sheet to form irregularities; and

an upper layer plating step of using the plating bath at an average flow rate of 40 to 200 m/min and 21 to 200A/dm for the steel sheet having the irregularities formed thereon²The current density of (a) is used for electroplating,

further comprising a step of forming a base by using Ni²⁺And a step of plating the steel sheet with an ion plating bath to deposit nickel-containing crystals.

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