WO2023195251A1

WO2023195251A1 - Surface-treated steel sheet and method for producing same

Info

Publication number: WO2023195251A1
Application number: PCT/JP2023/006069
Authority: WO
Inventors: 卓嗣植野; 祐介中川
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2022-04-08
Filing date: 2023-02-20
Publication date: 2023-10-12
Also published as: TW202342818A

Abstract

The present invention provides a surface-treated steel sheet which can be produced without using hexavalent chromium, and which exhibits excellent film corrosion resistance, coating corrosion resistance, film wet adhesion, coating material secondary adhesion and weldability. The present invention provides a surface-treated steel sheet which comprises, on at least one surface of a steel sheet, an Ni-containing layer, a Cr metal layer that is arranged on the Ni-containing layer, and a Cr oxide layer that is arranged on the Cr metal layer, wherein: the water contact angle is 50° or less; and the sum of the atomic ratios, relative to Cr, of K, Na, Mg and Ca adsorbed on the surface of the steel sheet is 5.0% or less.

Description

Surface treated steel sheet and its manufacturing method

The present invention relates to a surface-treated steel sheet, and particularly to a surface-treated steel sheet that has excellent film corrosion resistance, paint corrosion resistance, film wet adhesion, paint secondary adhesion, and weldability. The surface-treated steel sheet of the present invention can be suitably used for containers such as cans. The present invention also relates to a method for manufacturing the surface-treated steel sheet.

Sn-plated steel sheet (tinplate) has excellent corrosion resistance, weldability, workability, and is easy to manufacture, so it has been used as a material for various metal cans such as beverage cans, food cans, pail cans, and 18-liter cans for 200 years. It has been used for more than a long time.

However, since Sn is an expensive material, tin-free steel sheets (TFS), which are surface-treated steel sheets that do not use Sn, have been developed. A tin-free steel sheet is a surface-treated steel sheet in which a metal Cr layer and an oxidized Cr layer are formed on the surface of the steel sheet, and is usually manufactured by electrolytically treating the steel sheet in an electrolyte containing hexavalent Cr (Patent Document 1-3). Since tin-free steel sheets have excellent corrosion resistance and paint adhesion, they are now extremely commonly used as container steel sheets in place of tinplate. However, this tin-free steel sheet has a chromium oxide layer, which is an insulating film, on its surface, and therefore has poor weldability.

On the other hand, as surface-treated steel sheets that have excellent weldability and do not use Sn, Ni-plated steel sheets that use Ni instead of Sn are known (Patent Documents 4 and 5). However, when using Ni-plated steel sheets as a material for welded cans, it is necessary to apply a chromate treatment film on the Ni-plated steel sheets using an aqueous solution containing hexavalent Cr in order to ensure corrosion resistance and paint adhesion. becomes.

In recent years, due to increasing environmental awareness, the use of hexavalent Cr is being regulated worldwide. Therefore, in the field of surface-treated steel sheets used for containers and the like, there is a need to establish a manufacturing method that does not use hexavalent chromium.

As a method for forming a surface-treated steel sheet without using hexavalent chromium, for example, the methods proposed in Patent Documents 6 and 7 are known. In this method, a surface treatment layer is formed by performing electrolytic treatment in an electrolytic solution containing a trivalent chromium compound such as basic chromium sulfate.

Japanese Patent Application Publication No. 58-110695 Japanese Patent Application Publication No. 55-134197 Japanese Unexamined Patent Publication No. 57-035699 Japanese Patent Application Publication No. 11-117085 Japanese Patent Application Publication No. 2007-231394 Special table 2016-505708 publication Special table 2015-520794 publication

According to the methods proposed in Patent Documents 6 and 7, a surface treatment layer can be formed without using hexavalent chromium. According to Patent Documents 6 and 7, the method allows adhesion to a resin film in a humid environment (hereinafter referred to as "film wet adhesion") and adhesion to a paint in a humid environment (hereinafter referred to as "paint 2"). It is possible to obtain a surface-treated steel sheet with excellent adhesion.

However, although surface-treated steel sheets obtained by conventional methods such as those proposed in Patent Documents 6 and 7 have excellent film wet adhesion and secondary paint adhesion, they have poor weldability and contain hexavalent chromium. The performance was not sufficient to be used as a substitute for surface-treated steel sheets manufactured by the method using the method.

Therefore, there is a need for a surface-treated steel sheet that can be manufactured without using hexavalent chromium and has excellent film corrosion resistance, paint corrosion resistance, film wet adhesion, secondary paint adhesion, and weldability. .

The present invention was made in view of the above-mentioned circumstances, and its purpose is to enable production without using hexavalent chromium, and to provide film corrosion resistance, paint corrosion resistance, film wet adhesion, and paint secondary adhesion. The object of the present invention is to provide a surface-treated steel sheet with excellent properties and weldability.

The inventors of the present invention conducted intensive studies to achieve the above object, and as a result, they obtained the following findings (1) and (2).

(1) In a surface-treated steel sheet having a metal Cr layer and an oxidized Cr layer on the Ni-containing layer, the water contact angle and the sum of the atomic ratios of K, Na, Mg, and Ca adsorbed on the surface to Cr are: By controlling each to a specific range, a surface-treated steel sheet with excellent film corrosion resistance, paint corrosion resistance, film wet adhesion, paint secondary adhesion, and weldability can be obtained.

(2) The above-mentioned surface-treated steel sheet is subjected to cathodic electrolytic treatment in an electrolytic solution containing trivalent chromium ions prepared by a specific method, and then final water washing is performed using water whose electrical conductivity is below a predetermined value. It can be manufactured by performing the following steps.

The present invention has been completed based on the above findings. The gist of the present invention is as follows.

1. steel plate and
a Ni-containing layer disposed on at least one surface of the steel plate;
a metal Cr layer disposed on the Ni-containing layer;
and a Cr oxide layer disposed on the metal Cr layer,
The water contact angle is 50° or less,
A surface-treated steel sheet in which the total atomic ratio of K, Na, Mg, and Ca adsorbed on the surface to Cr is 5.0% or less.

2. The surface-treated steel sheet according to 1 above, wherein the Ni-containing layer has a Ni adhesion amount of 200 mg/m ² or more and 2000 mg/m ² or less per side of the steel sheet.

3. The surface-treated steel sheet according to 1 or 2 above, wherein the metal Cr layer has a Cr adhesion amount of 2 mg/m ² or more and less than 40 mg/m ² per side of the steel sheet.

4. 4. The surface-treated steel sheet according to any one of 1 to 3 above, wherein the Cr oxide layer has a Cr adhesion amount of 0.1 mg/m ² or more and 15.0 mg/m ^{2 or} less per side of the steel sheet.

5. 5. The surface-treated steel sheet according to any one of 1 to 4 above, wherein the atomic ratio of Ni to Cr on the surface of the surface-treated steel sheet is 100% or less.

6. A surface comprising a steel plate, a Ni-containing layer disposed on at least one surface of the steel plate, a metallic Cr layer disposed on the Ni-containing layer, and an oxidized Cr layer disposed on the metallic Cr layer. A method for manufacturing a treated steel sheet, the method comprising:
an electrolytic solution preparation step of preparing an electrolytic solution containing trivalent chromium ions;
a cathodic electrolytic treatment step of cathodic electrolytically treating a steel plate having a Ni-containing layer on at least one surface in the electrolytic solution;
a washing step of washing the steel plate after the cathodic electrolytic treatment at least once with water,
In the electrolyte preparation step,
Mixing a trivalent chromium ion source, a carboxylic acid compound, and water,
The electrolytic solution is prepared by adjusting the pH to 4.0 to 7.0 and the temperature to 40 to 70°C,
In the water washing step,
A method for producing a surface-treated steel sheet, using water with an electrical conductivity of 100 μS/m or less in at least the final washing.

According to the present invention, it is possible to provide a surface-treated steel sheet that has excellent film corrosion resistance, paint corrosion resistance, film wet adhesion, paint secondary adhesion, and weldability without using hexavalent chromium. The surface-treated steel sheet of the present invention can be suitably used as a material for containers and the like.

Hereinafter, a method for implementing the present invention will be specifically described. Note that the following description shows examples of preferred embodiments of the present invention, and the present invention is not limited thereto.

A surface-treated steel sheet in an embodiment of the present invention includes a steel sheet, a Ni-containing layer placed on at least one surface of the steel sheet, a metal Cr layer placed on the Ni-containing layer, and a metal Cr layer placed on the Ni-containing layer. This is a surface-treated steel sheet having a Cr oxide layer disposed thereon. In the present invention, the water contact angle of the surface-treated steel sheet is 50° or less, and the total atomic ratio of K, Na, Mg, and Ca adsorbed on the surface to Cr is 5.0% or less. It is important that there be. Each of the constituent requirements of the surface-treated steel sheet will be explained below.

[Steel plate]
As the steel plate, any steel plate can be used without particular limitation. The steel plate is preferably a steel plate for cans. As the steel plate, for example, an ultra-low carbon steel plate or a low carbon steel plate can be used. The method for manufacturing the steel plate is not particularly limited either, and steel plates manufactured by any method can be used. Usually, a cold-rolled steel plate may be used as the steel plate. The cold-rolled steel sheet can be manufactured by a general manufacturing process that includes, for example, hot rolling, pickling, cold rolling, annealing, and temper rolling.

Although the composition of the steel sheet is not particularly limited, the Cr content is preferably 0.10% by mass or less, more preferably 0.08% by mass or less. If the Cr content of the steel sheet is within the above range, Cr will not be excessively concentrated on the surface of the steel sheet, and as a result, the atomic ratio of Ni to Cr on the surface of the finally obtained surface-treated steel sheet will be 100. % or less. Furthermore, the steel plate may contain C, Mn, P, S, Si, Cu, Ni, Mo, Al, and unavoidable impurities within a range that does not impair the effects of the present invention. In this case, as the steel plate, for example, a steel plate having a composition specified in ASTM A623M-09 can be suitably used.

In one embodiment of the invention, in mass %,
C: 0.0001 to 0.13%,
Si: 0 to 0.020%,
Mn: 0.01-0.60%
P: 0 to 0.020%,
S: 0 to 0.030%,
Al: 0-0.20%,
N: 0 to 0.040%,
Cu: 0 to 0.20%,
Ni: 0 to 0.15%,
Cr: 0 to 0.10%,
Mo: 0 to 0.05%,
Ti: 0 to 0.020%,
Nb: 0 to 0.020%,
B: 0 to 0.020%,
Ca: 0-0.020%,
Sn: 0 to 0.020%,
Sb: 0 to 0.020%,
It is preferable to use a steel plate having a composition consisting of Fe and the remainder Fe and unavoidable impurities. Among the above component compositions, the lower the content of Si, P, S, Al, and N, the more preferable the components are.Cu, Ni, Cr, Mo, Ti, Nb, B, Ca, Sn, and Sb are optional. It is a component that can be added to

The thickness of the steel plate is not particularly limited, but is preferably 0.60 mm or less. Note that "steel plate" is defined here to include "steel strip." On the other hand, the lower limit of the plate thickness is not particularly limited either, but it is preferably 0.10 mm or more.

[Ni-containing layer]
When a surface-treated steel sheet is used as a steel sheet for cans, it is generally welded by resistance welding such as wire seam welding. Since Ni is an element with excellent forge weldability, weldability can be improved by arranging a Ni-containing layer. That is, when a Ni-containing layer is present, excellent welding strength can be obtained from lower resistance heat generation, so the lower limit of the weldable current is widened.

The Ni-containing layer may be provided on at least one surface of the steel plate, and may be provided on both surfaces. The Ni-containing layer only needs to cover at least a portion of the steel plate, and may cover the entire surface on which the Ni-containing layer is provided. Further, the Ni-containing layer may be a continuous layer or a discontinuous layer. Examples of the discontinuous layer include a layer having an island structure.

As the Ni-containing layer, any layer containing nickel can be used, for example, one or both of a Ni layer and a Ni alloy layer can be used. For example, a Ni alloy layer formed by diffusion annealing after Ni plating is also included in the Ni alloy layer. Furthermore, examples of the Ni alloy layer include a Ni--Fe alloy layer.

The Ni-containing layer is preferably a Ni-based plating layer. Here, the term "Ni-based plating layer" is defined as a plating layer having a Ni content of 50% by mass or more. In other words, the Ni-based plating layer is a Ni-plated layer or a plating layer made of a Ni-based alloy.

The Ni-based plating layer may be a dispersed plating layer (composite plating layer) in which solid fine particles are dispersed in Ni or a Ni-based alloy as a matrix. The solid particles are not particularly limited and may be made of any material. The fine particles may be either inorganic fine particles or organic fine particles. Examples of the organic fine particles include fine particles made of resin. Although any resin can be used as the resin, it is preferable to use a fluororesin, and it is more preferable to use polytetrafluoroethylene (PTFE). The inorganic fine particles are not particularly limited, and fine particles made of any inorganic material can be used. The inorganic material may be, for example, a metal (including an alloy), a compound, or another simple substance. Among these, it is preferable to use fine particles made of at least one selected from the group consisting of oxides, nitrides, and carbides, and it is preferable to use fine particles of metal oxides. Examples of the metal oxide include aluminum oxide, chromium oxide, titanium oxide, and zinc oxide.

The particle size of the fine particles used in the dispersion plating is not particularly limited, and particles of any size can be used. However, it is preferable that the diameter of the fine particles does not exceed the thickness of the dispersed plating layer as the Ni-containing layer. Typically, the diameter of the fine particles is preferably 1 nm to 50 μm, more preferably 10 nm to 1000 nm.

The amount of Ni deposited in the Ni-containing layer is not particularly limited and can be any amount. However, from the viewpoint of further improving the weldability and corrosion resistance of the surface-treated steel sheet, the amount of Ni deposited on one side of the steel sheet is preferably 200 mg/m ² or more, and more preferably 250 mg/m ² or more. On the other hand, when the amount of Ni deposited exceeds 2000 mg/m ² , the effect of improving weldability is saturated. Therefore, from the viewpoint of reducing excessive costs, the amount of Ni deposited is preferably 2000 mg/m ² or less, more preferably 1800 mg/m ² or less.

The amount of Ni adhered to the Ni-containing layer is measured by a calibration curve method using fluorescent X-rays. Prepare multiple steel plates with known Ni adhesion amounts, measure the fluorescent X-ray intensity derived from Ni in advance, and linearly approximate the relationship between the measured fluorescent X-ray intensity and the Ni adhesion amount to obtain a calibration curve. do. The intensity of fluorescent X-rays originating from Ni in the surface-treated steel sheet can be measured, and the amount of Ni adhered to the Ni-containing layer can be measured using the above-mentioned calibration curve.

The formation of the Ni-containing layer is not particularly limited, and can be performed by any method such as electroplating. When forming the Ni-containing layer by electroplating, any plating bath can be used. Examples of plating baths that can be used include Watt bath, sulfamic acid bath, and Wood bath. When forming a Ni--Fe alloy layer as the Ni-containing layer, the Ni--Fe alloy layer can be formed by forming the Ni layer on the surface of the steel sheet by a method such as electroplating, and then annealing it.

The surface side of the Ni-containing layer may contain Ni oxide or may not contain it at all, but from the viewpoint of further improving secondary paint adhesion and sulfurization resistance, the Ni-containing layer Preferably, the surface side does not contain Ni oxide. Although Ni oxide can also be formed by dissolved oxygen contained in the washing water after Ni plating, it is preferable to remove the Ni oxide contained in the Ni-containing layer by a pretreatment described below.

[Metal Cr layer]
A metallic Cr layer is present on the Ni-containing layer.

The amount of the metal Cr layer deposited is not particularly limited, and can be set to any value. However, from the viewpoint of further improving corrosion resistance, the amount of Cr deposited on one side of the steel sheet is preferably 2 mg/m ² or more, and preferably 4 mg/m ² or more. More preferred. On the other hand, there is no particular limitation on the upper limit of the amount of the metal Cr layer deposited, but if the amount of the metal Cr layer deposited is excessive, the contact resistance may increase and weldability may be impaired. Therefore, from the viewpoint of ensuring more stable weldability, the amount of Cr deposited on one side of the steel plate is preferably less than 40 mg/m ² , and 35 mg/m ² or less. It is more preferable that

Note that the amount of Cr attached to the metal Cr layer can be measured by a fluorescent X-ray method. Specifically, first, the amount of Cr (total amount of Cr) in the surface-treated steel sheet is measured using a fluorescent X-ray device. Next, the surface-treated steel sheet is subjected to an alkaline treatment by immersing it in 7.5N-NaOH at 90° C. for 10 minutes, and then thoroughly washed with water. Thereafter, the amount of Cr (the amount of Cr after alkali treatment) is measured again using the fluorescent X-ray device. Furthermore, the Cr content (original Cr content) of the steel sheet after the metal Cr layer and the oxidized Cr layer have been peeled off is measured using a fluorescent X-ray device. For example, a commercially available hydrochloric acid-based chromium plating remover can be used to remove the metal Cr layer and the oxidized Cr layer. The value obtained by subtracting the original plate Cr amount from the Cr amount after alkali treatment is defined as the Cr adhesion amount per one side of the steel sheet of the metal Cr layer. Note that the total amount of Cr is used to calculate the amount of Cr deposited as the oxidized Cr layer, which will be described later.

The metal Cr constituting the metal Cr layer may be amorphous Cr or crystalline Cr. That is, the metal Cr layer can contain one or both of amorphous Cr and crystalline Cr. The metal Cr layer manufactured by the method described below generally contains amorphous Cr, and may further contain crystalline Cr. Although the formation mechanism of the metallic Cr layer is not clear, it is thought that when amorphous Cr is formed, crystallization progresses partially, resulting in a metallic Cr layer containing both amorphous and crystalline phases.

The ratio of crystalline Cr to the total of amorphous Cr and crystalline Cr contained in the metal Cr layer is preferably 0% or more and 80% or less, and more preferably 0% or more and 50% or less. Here, the ratio of crystalline Cr can be measured by observing the metal Cr layer with a scanning transmission electron microscope (STEM). Specifically, first, a STEM image is acquired at a magnification of approximately 2 million to 10 million times using a beam diameter that provides a resolution of 1 nm or less. In the obtained STEM image, the area where lattice fringes can be seen is defined as a crystalline phase, and the area where a maize pattern can be seen is defined as amorphous, and the areas of both are determined. From the results, the ratio of the area of crystalline Cr to the total area of amorphous Cr and crystalline Cr is calculated.

[Cr oxide layer]
A Cr oxide layer is present on the metal Cr layer. The amount of the Cr oxide layer deposited is not particularly limited, and can be set to any value. However, from the viewpoint of further improving corrosion resistance, it is preferable that the amount of Cr oxide layer deposited is 0.1 mg/m ² or more in terms of the amount of Cr deposited on one side of the steel sheet. On the other hand, the upper limit of the amount of the Cr oxide layer deposited is not particularly limited, but if the amount of the Cr oxide layer deposited is excessive, the contact resistance may increase and weldability may be impaired. Therefore, from the viewpoint of ensuring more stable weldability, it is preferable that the amount of Cr oxide layer deposited is 15.0 mg/m ² or less in terms of the amount of Cr deposited per one side of the steel plate. Note that the amount of Cr attached to the oxidized Cr layer can be measured by a fluorescent X-ray method. Specifically, the amount of Cr deposited in the oxidized Cr layer can be determined by subtracting the amount of Cr after the alkali treatment from the total amount of Cr measured using the aforementioned fluorescent X-ray device.

One or both of the metal Cr layer and the oxidized Cr layer may contain C. However, if an excessive amount of C is contained in the metal Cr layer and the oxidized Cr layer, the weld heat affected zone may harden during welding and cracks may occur. Therefore, the C content in the metal Cr layer is preferably 40% or less, more preferably 35% or less, as an atomic ratio to Cr. Similarly, the C content in the Cr oxide layer is preferably 40% or less, more preferably 35% or less, as an atomic ratio to Cr. The metal Cr layer and the oxidized Cr layer may not contain C, and therefore, the lower limit of the C content contained in the metal Cr layer and the oxidized Cr layer may be 0% in terms of atomic ratio to Cr, respectively. .

The C content in the metal Cr layer and the C content in the oxidized Cr layer can each be measured by X-ray photoelectron spectroscopy (XPS). Specifically, to measure the C content by XPS, the C atomic ratio and Cr atomic ratio are determined by the relative sensitivity coefficient method from the integrated intensities of the narrow spectra of Cr2p and C1s measured by XPS, and the C atomic ratio/Cr atomic ratio is calculated. This can be done by calculating the ratio.

In addition, since C derived from contamination is detected from the outermost layer of the surface-treated steel sheet, in order to accurately measure the C content in the Cr oxide layer, for example, 0.2 nm in terms of SiO ₂ is removed from the outermost layer. Measurement may be performed after sputtering to a depth greater than or equal to the depth. On the other hand, the C content in the metal Cr layer may be measured after sputtering is performed from the outermost layer after the alkali treatment described above to a depth of 1/2 of the thickness of the metal Cr layer.

The thickness of the metal Cr layer used in the above measurement can be determined by the following procedure. First, XPS measurements are performed every 1 nm in the depth direction from the outermost layer after alkali treatment to measure the Cr atomic ratio and the Ni atomic ratio. Next, a cubic equation that approximates the relationship between the Ni atomic ratio/Cr atomic ratio with respect to the depth from the outermost layer after the alkali treatment is determined by the method of least squares. Using the obtained cubic equation, the depth from the outermost layer at which the Ni atomic ratio/Cr atomic ratio becomes 1 is calculated, and this is taken as the thickness of the metal Cr layer.

For the measurement, for example, a scanning X-ray photoelectron spectrometer PHI X-tool manufactured by ULVAC-PHI can be used. The X-ray source is a monochrome AlKα ray, the voltage is 15 kV, the beam diameter is 100 μmφ, the extraction angle is 45°, the sputtering conditions are Ar ion acceleration voltage 1 kV, and the sputter rate is 1.50 nm/min in terms of SiO ₂ .

The mechanism by which C is contained in the metal Cr layer and the Cr oxide layer is not clear, but in the process of forming the metal Cr layer and the Cr oxide layer on the steel sheet, the carboxylic acid compound contained in the electrolyte is decomposed and the film is formed. It is thought that it will be incorporated.

The form of C present in the metal Cr layer and Cr oxide layer is not particularly limited, but if it exists as a precipitate, corrosion resistance may decrease due to the formation of local batteries. Therefore, it is preferable that the sum of the volume fractions of carbides and clusters having a clear crystal structure is 10% or less, and it is more preferable that they are not contained at all (0%). The presence or absence of carbides can be confirmed, for example, by compositional analysis using energy dispersive X-ray spectroscopy (EDS) or wavelength dispersive X-ray spectroscopy (WDS) attached to a scanning electron microscope (SEM) or transmission electron microscope (TEM). I can do it. The presence or absence of clusters can be confirmed, for example, by performing cluster analysis on data after three-dimensional composition analysis using a three-dimensional atom probe (3DAP).

The metal Cr layer may contain O. The upper limit of the O content in the metal Cr layer is not particularly limited, but if the O content is high, Cr oxide may precipitate and corrosion resistance may deteriorate due to the formation of local batteries. Therefore, the O content is preferably 30% or less, more preferably 25% or less, as an atomic ratio to Cr. The metal Cr layer does not need to contain O, and therefore, the lower limit of the Cr contained in the metal Cr layer is not particularly limited and may be 0%.

The content of O in the metal Cr layer can be measured by compositional analysis such as EDS and WDS attached to SEM or TEM, or 3DAP.

One or both of the metal Cr layer and the oxidized Cr layer may contain Ni. Although the upper limit of the Ni content in the metal Cr layer is not particularly limited, it is preferably less than 100% as an atomic ratio to Cr. Similarly, the upper limit of the Ni content in the Cr oxide layer is not particularly limited, but it is preferably less than 100% as an atomic ratio to Cr. The metal Cr layer and the oxidized Cr layer do not need to contain Ni, so the lower limit of the atomic ratio of Ni to Cr is not particularly limited and may be 0%.

The Ni content on the surface of the surface-treated steel sheet, that is, on the surface of the Cr oxide layer, is not particularly limited, but the lower it is, the better the wet adhesion of the film and the secondary adhesion of the paint will be. Therefore, the atomic ratio of Ni to Cr on the surface of the surface-treated steel sheet is preferably 100% or less, more preferably 80% or less.

The Ni content in the metal Cr layer and the Cr oxide layer can be measured by XPS similarly to the C content. The atomic ratio of Ni to Cr on the surface of the surface-treated steel sheet, that is, on the surface of the Cr oxide layer, can be measured by XPS of the surface of the surface-treated steel sheet. The narrow spectra of Cr2p and Ni2p may be used to calculate the atomic ratio.

The mechanism by which Ni is contained in the metal Cr layer and the Cr oxide layer is not clear, but in the process of forming the metal Cr layer and the Cr oxide layer on the steel sheet, a small amount of Ni contained in the Ni-containing layer is dissolved in the electrolyte. , Ni is considered to be incorporated into the film.

In addition to Cr, O, Ni, and C, as well as K, Na, Mg, and Ca, which will be described later, the metal Cr layer and Cr oxide layer contain metal impurities such as Cu, Zn, Sn, and Fe contained in the aqueous solution. S, N, Cl, Br, etc. may be included. However, the presence of these elements may reduce the wet adhesion of the film and the secondary adhesion of the paint. Therefore, the content of Fe in the metal Cr layer and the Cr oxide layer is preferably 10% or less as an atomic ratio to Cr, and more preferably not contained at all (0%). The total amount of elements other than Cr, O, Ni, C, K, Na, Mg, Ca, and Fe is preferably 3% or less as an atomic ratio to Cr, and more preferably not contained at all (0%). . The content of the above elements is not particularly limited, and can be measured by XPS, for example, similarly to the content of C. In particular, when measuring the content of Fe element by XPS, a narrow spectrum of Fe2p is used, but since it overlaps with the NiLLM peak and the quantitative value of Fe content may be calculated higher than the actual value, as mentioned above, Unlike other elements, the Fe content is preferably controlled to 10% or less as an atomic ratio to Cr.

The metal Cr layer and oxidized Cr layer are preferably crack-free. The presence or absence of cracks can be confirmed by, for example, cutting out a cross section of the film using a focused ion beam (FIB) or the like and directly observing it using a transmission electron microscope (TEM).

Furthermore, the surface roughness of the surface-treated steel sheet of the present invention does not change significantly due to the formation of the metal Cr layer and the oxidized Cr layer, and is generally approximately equivalent to the surface roughness of the underlying steel sheet used. Although the surface roughness of the surface-treated steel sheet is not particularly limited, it is preferable that the arithmetic mean roughness Ra is 0.1 μm or more and 4 μm or less. Moreover, it is preferable that the ten-point average roughness Rz is 0.2 μm or more and 6 μm or less.

[Water contact angle]
In the present invention, it is important that the water contact angle of the surface-treated steel sheet is 50° or less. By making the surface of the surface-treated steel sheet highly hydrophilic so that the water contact angle is 50 degrees or less, strong hydrogen bonds are formed between the resin contained in the paint and the surface-treated steel sheet, and as a result, the wet environment High adhesion can be obtained even at the bottom. From the viewpoint of further improving the secondary paint adhesion, the water contact angle is preferably 48° or less, more preferably 45° or less. Since the water contact angle is preferably as low as possible from the viewpoint of improving adhesion, its lower limit is not particularly limited and may be 0°. However, from the viewpoint of ease of manufacture, etc., the angle is preferably 3° or more, and more preferably 6° or more. Note that the water contact angle can be measured by the method described in Examples.

The mechanism by which the surface of a surface-treated steel sheet becomes hydrophilic is not clear, but when a metal Cr layer and a Cr oxide layer are formed by cathodic electrolysis in an electrolyte, carboxylic acids or carboxylates contained in the electrolyte are This is thought to be because hydrophilic functional groups such as carboxyl groups are imparted to the surface by being decomposed and incorporated into the film. However, if the electrolytic solution is not prepared under specific conditions as described below, even if the electrolytic solution contains a carboxylic acid or a carboxylate salt, the surface of the surface-treated steel sheet will not become hydrophilic. The mechanism by which the preparation conditions of the electrolytic solution affect the hydrophilization of the surface of the surface-treated steel sheet is not clear, but if the electrolytic solution is properly prepared under the conditions described below, hydrophilic functional groups such as carboxyl groups will form on the surface. It is presumed that this is due to the formation of a complex that is easily attached to.

In addition, in surface-treated steel sheets manufactured using conventional hexavalent chromium baths as proposed in Patent Documents 1 to 5, the composition of the chromium hydrated oxide layer present on the surface layer is different from that in a humid environment. It has been reported that it greatly affects the adhesion to paints or films. In a humid environment, water penetrating through the coating or film inhibits adhesion at the interface between the coating or film and the chromium hydrated oxide layer. Therefore, it was thought that if a large amount of hydrophilic OH groups were present in the chromium hydrated oxide layer, the expansion wetting of water at the interface would be promoted and the adhesive force would be reduced. Therefore, in conventional surface-treated steel sheets, the adhesion with paints and films in a humid environment was improved by reducing the number of OH groups, that is, by making the surface hydrophobic, due to the progress of oxation of hydrated chromium oxide.

On the other hand, in the present invention, by making the surface hydrophilic to a level close to superhydrophilicity, strong hydrogen bonds are formed at the interface between the coating film and the surface-treated steel sheet, thereby making the surface highly hydrophilic even in a humid environment. This is based on the technical concept of maintaining adhesion, which is completely opposite to the prior art described above.

[Atomic ratio of adsorbed elements]
As described above, the surface-treated steel sheet of the present invention has high hydrophilicity with a water contact angle of 50° or less, and its surface is chemically active. Therefore, cations of elements such as K, Na, Mg, and Ca are easily adsorbed on the surface of the surface-treated steel sheet. The present inventors have discovered that simply setting the water contact angle to 50° or less does not result in the original adhesion being exhibited due to the influence of the adsorbed cations. In the present invention, by reducing the amount of the cations adsorbed on the surface of the surface-treated steel sheet, it is possible to improve the adhesion to the resin and achieve excellent film wet adhesion and paint secondary adhesion.

Specifically, the total atomic ratio of K, Na, Mg, and Ca adsorbed on the surface of the surface-treated steel sheet to Cr is 5.0% or less, preferably 3.0% or less, and more preferably 1.0% or less. 0% or less. Since the lower the sum of the atomic ratios, the better, the lower limit is not particularly limited and may be 0%. The total atomic ratio can be measured by the method described in Examples.

[Production method]
In a method for manufacturing a surface-treated steel sheet according to an embodiment of the present invention, a surface-treated steel sheet having the above characteristics can be manufactured by the method described below.

A method for manufacturing a surface-treated steel sheet according to an embodiment of the present invention includes, on at least one surface of a steel sheet, a Ni-containing layer, a metal Cr layer disposed on the Ni-containing layer, and a metal Cr layer disposed on the metal Cr layer. A method for manufacturing a surface-treated steel sheet having a Cr oxide layer, which includes the following steps (1) to (3). Each step will be explained below.
(1) An electrolytic solution preparation step of preparing an electrolytic solution containing trivalent chromium ions (2) A cathodic electrolytic treatment step of cathodic electrolytically treating a steel plate having a Ni-containing layer in the electrolytic solution (3) After the cathodic electrolytic treatment A water washing process in which the steel plate is washed at least once with water.

[Electrolyte preparation process]
(i) Mixing In the electrolyte solution preparation step, first, a trivalent chromium ion source, a carboxylic acid compound, and water are mixed to form an aqueous solution.

As the trivalent chromium ion source, any compound that can supply trivalent chromium ions can be used. As the trivalent chromium ion source, for example, at least one selected from the group consisting of chromium chloride, chromium sulfate, and chromium nitrate can be used.

The content of the trivalent chromium ion-containing source in the aqueous solution is not particularly limited, but it is preferably 3 g/L or more and 50 g/L or less, and 5 g/L or more and 40 g/L or less in terms of trivalent chromium ions. More preferred. As the trivalent chromium ion source, Atotech's BluCr (registered trademark) TFS A can be used.

The carboxylic acid compound is not particularly limited, and any carboxylic acid compound can be used. The carboxylic acid compound may be at least one of a carboxylic acid and a carboxylate salt, and is preferably at least one of an aliphatic carboxylic acid and a salt of an aliphatic carboxylic acid. The aliphatic carboxylic acid preferably has 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms. Further, the number of carbon atoms in the aliphatic carboxylate is preferably 1 to 10, more preferably 1 to 5. Although the content of the carboxylic acid compound is not particularly limited, it is preferably 0.1 mol/L or more and 5.5 mol/L or less, and more preferably 0.15 mol/L or more and 5.3 mol/L or less. As the carboxylic acid compound, Atotech's BluCr (registered trademark) TFS B can be used.

In the present invention, water is used as a solvent for preparing the electrolyte. As the water, it is preferable to use ion-exchanged water from which cations have been removed in advance using an ion-exchange resin or the like, or highly purified water such as distilled water. As will be described later, from the viewpoint of reducing the amounts of K, Na, Mg, and Ca contained in the electrolytic solution, it is preferable to use water whose electrical conductivity is 30 μS/m or less.

In order to reduce K, Na, Mg, and Ca adsorbed on the surface of the surface-treated steel sheet, it is preferable that K, Na, Mg, and Ca are not intentionally contained in the above-mentioned aqueous solution. Therefore, it is preferable that the components added to the aqueous solution, such as the above-mentioned trivalent chromium ion source, carboxylic acid compound, and pH adjuster described in detail below, do not contain K, Na, Mg, and Ca. As the pH adjuster, it is preferable to use hydrochloric acid, sulfuric acid, nitric acid, etc. to lower the pH, and use ammonia water, etc. to increase the pH. K, Na, Mg, and Ca that are unavoidably mixed into the aqueous solution or electrolyte are allowed, but the total concentration of K, Na, Mg, and Ca is preferably 2.0 mol/L or less, and 1 It is more preferably .5 mol/L or less, and even more preferably 1.0 mol/L or less.

In order to effectively suppress the production of hexavalent chromium at the anode in the cathodic electrolytic treatment step and improve the stability of the electrolytic solution, it is preferable that the aqueous solution further contains at least one type of halide ion. . The content of halide ions is not particularly limited, but is preferably 0.05 mol/L or more and 3.0 mol/L or less, more preferably 0.10 mol/L or more and 2.5 mol/L or less. In order to contain the halide ions, Atotech's BluCr (registered trademark) TFS C1 and BluCr (registered trademark) TFS C2 can be used.

It is preferable that hexavalent chromium is not added to the above aqueous solution. Except for a very small amount of hexavalent chromium formed at the anode during the cathodic electrolytic treatment process, the electrolytic solution described above does not contain hexavalent chromium. In the cathodic electrolytic treatment process, a trace amount of hexavalent chromium formed at the anode is reduced to trivalent chromium, so the concentration of hexavalent chromium in the electrolyte does not increase.

It is preferable that metal ions other than trivalent chromium ions are not intentionally added to the above-mentioned aqueous solution. The above metal ions are not limited, but include Cu ions, Zn ions, Ni ions, Fe ions, Sn ions, etc., and each is preferably 0 mg/L or more and 40 mg/L or less, and 0 mg/L or more and 20 mg/L. It is more preferably below, and most preferably 0 mg/L or more and 10 mg/L or less. Among the metal ions mentioned above, Ni ions may be dissolved in the electrolyte and eutectoid in the film during the cathodic electrolytic treatment process when the steel plate is immersed in the electrolyte, but this may affect the wet adhesion of the film. It does not affect secondary paint adhesion or weldability. The Ni ion content is preferably 0 mg/L or more and 40 mg/L or less, more preferably 0 mg/L or more and 20 mg/L or less, and most preferably 0 mg/L or more and 10 mg/L or less. Although it is preferable that the Ni ion concentration is within the above range at the time of bath preparation, it is also preferable to maintain the Ni ion concentration in the electrolytic solution within the above range during the cathodic electrolytic treatment step. If Ni ions are controlled within the above range, they will not inhibit the formation of the metal Cr layer and the Cr oxide layer, and the metal Cr layer and the Cr oxide layer can be formed to have the required thickness.

(ii) Adjustment of pH and Temperature Next, the electrolytic solution is prepared by adjusting the pH of the aqueous solution to 4.0 to 7.0 and adjusting the temperature of the aqueous solution to 40 to 70°C. In order to manufacture the above-mentioned surface-treated steel sheet, it is not enough to simply dissolve the trivalent chromium ion source and the carboxylic acid compound in water, and it is important to appropriately control the pH and temperature as described above. .

pH: 4.0-7.0
In the electrolytic solution preparation step, the pH of the mixed aqueous solution is adjusted to 4.0 to 7.0. When the pH is less than 4.0 or more than 7.0, the water contact angle of the surface-treated steel sheet manufactured using the obtained electrolyte becomes higher than 50°. The pH is preferably 4.5 to 6.5.

Temperature: 40-70℃
In the electrolyte solution preparation step, the temperature of the aqueous solution after mixing is adjusted to 40 to 70°C. If the temperature is less than 40°C or more than 70°C, the water contact angle of the surface-treated steel sheet produced using the obtained electrolyte will be greater than 50°. Note that the holding time in the temperature range of 40 to 70°C is not particularly limited.

Through the above procedure, an electrolytic solution to be used in the next cathodic electrolytic treatment step can be obtained. Note that the electrolytic solution produced by the above procedure can be stored at room temperature.

[Cathode electrolytic treatment process]
Next, a steel plate having a Ni-containing layer on at least one surface is subjected to cathodic electrolysis treatment in the electrolytic solution obtained in the electrolytic solution preparation step. By the cathodic electrolytic treatment, a metal Cr layer and a Cr oxide layer can be formed on the Ni-containing layer.

The temperature of the electrolyte during the cathodic electrolytic treatment is not particularly limited, but is preferably in the temperature range of 40° C. or higher and 70° C. or lower in order to efficiently form the metal Cr layer and the oxidized Cr layer. From the viewpoint of stably manufacturing the above-mentioned surface-treated steel sheet, it is preferable to monitor the temperature of the electrolytic solution and maintain it in the above temperature range in the cathodic electrolytic treatment step.

The pH of the electrolyte during cathodic electrolytic treatment is not particularly limited, but is preferably 4.0 or higher, more preferably 4.5 or higher. Further, the pH is preferably 7.0 or less, more preferably 6.5 or less. From the viewpoint of stably manufacturing the above-mentioned surface-treated steel sheet, it is preferable to monitor the pH of the electrolytic solution and maintain it within the above pH range in the cathodic electrolytic treatment step.

The current density in the cathodic electrolytic treatment is not particularly limited, and may be adjusted as appropriate so that a desired surface treatment layer is formed. However, when the current density is excessively high, the C content in the metal Cr layer increases, which may deteriorate weldability. Therefore, the current density is preferably less than 5.0 A/dm ² , more preferably 3.0 A/dm ² or less. The lower limit of the current density is not particularly limited, but if the current density is too low, hexavalent Cr may be generated in the electrolyte, which may disrupt the stability of the bath. Therefore, the current density is preferably 0.01 A/dm ² or more, more preferably 0.03 A/dm ² or more.

The number of times the steel plate is subjected to cathodic electrolysis treatment is not particularly limited, and can be any number of times. In other words, cathodic electrolytic treatment can be performed using an electrolytic treatment apparatus having an arbitrary number of passes of one or more. For example, it is also preferable to carry out cathodic electrolytic treatment continuously by passing a plurality of passes while conveying the steel plate (steel strip). Note that if the number of cathodic electrolytic treatments (that is, the number of passes) is increased, a commensurate number of electrolytic cells will be required, so the number of cathodic electrolytic treatments (the number of passes) is preferably 20 or less.

The electrolysis time per pass is not particularly limited. However, if the electrolysis time per pass is too long, the conveyance speed (line speed) of the steel plate decreases, resulting in a decrease in productivity. Therefore, the electrolysis time per pass is preferably 5 seconds or less, more preferably 3 seconds or less. The lower limit of the electrolysis time per pass is not particularly limited either, but if the electrolysis time is excessively shortened, it becomes necessary to increase the line speed accordingly, making control difficult. Therefore, the electrolysis time per pass is preferably 0.005 seconds or more, more preferably 0.01 seconds or more.

The amount of metallic Cr formed by cathodic electrolytic treatment can be controlled by the total electrical quantity density represented by the product of current density, electrolysis time, and number of passes. As mentioned above, if the amount of metal Cr is too large, the contact resistance will increase and weldability may be impaired, and if the amount of metal Cr is too small, corrosion resistance may be impaired. It is preferable to control the total electricity density so that the amount of Cr deposited on one side of the steel plate is 2 mg/m ² or more and less than 40 mg/m ² . However, since the relationship between the amount of metal Cr layer and the total electrical charge density varies depending on the configuration of the apparatus used in the cathode electrolytic treatment process, the actual electrolytic treatment conditions may be adjusted according to the apparatus.

The type of anode used when performing cathodic electrolysis treatment is not particularly limited, and any anode can be used. As the anode, it is preferable to use an insoluble anode. As the insoluble anode, it is preferable to use at least one selected from the group consisting of an anode in which Ti is coated with one or both of a platinum group metal and an oxide of a platinum group metal, and a graphite anode. More specifically, examples of the insoluble anode include an anode in which the surface of a Ti substrate is coated with platinum, iridium oxide, or ruthenium oxide.

In the cathode treatment step, the concentration of the electrolytic solution constantly changes due to the formation of a metal Cr layer and an oxidized Cr layer on the steel sheet, the removal and introduction of liquid, evaporation of water, etc. The concentration of the electrolyte in the cathodic electrolytic treatment process varies depending on the equipment configuration and manufacturing conditions, so from the perspective of producing surface-treated steel sheets more stably, the concentration of the components contained in the electrolyte in the cathodic electrolytic treatment process is It is preferable to monitor and maintain the concentration within the above-mentioned concentration range.

Note that, prior to the cathodic electrolytic treatment, the steel plate having the Ni-containing layer can be optionally pretreated. By performing the pretreatment, the natural oxide film present on the surface of the Ni-containing layer can be removed and the surface can be activated. The pretreatment method is not particularly limited, and any method can be used. For example, pickling by immersion in dilute sulfuric acid can be performed.

After performing the pretreatment, it is preferable to wash with water in order to remove the pretreatment liquid adhering to the surface.

Furthermore, when forming a Ni-containing layer on the surface of the base steel plate, it is preferable to perform pretreatment on the base steel plate. As the pretreatment, any treatment can be performed, but it is preferable to perform at least one of degreasing, pickling, and water washing.

By degreasing, rolling oil, rust preventive oil, etc. attached to the steel plate can be removed. The degreasing can be carried out by any method without particular limitation. After degreasing, it is preferable to wash the steel plate with water to remove the degreasing solution adhering to the surface of the steel plate.

Additionally, by performing pickling, it is possible to remove the natural oxide film present on the surface of the steel sheet and activate the surface. The pickling can be carried out by any method without particular limitation. After pickling, it is preferable to wash the steel plate with water to remove the pickling solution adhering to the surface of the steel plate.

[Water washing process]
Next, the steel plate after the cathodic electrolytic treatment is washed with water at least once. By washing with water, the electrolyte remaining on the surface of the steel plate can be removed. The water washing can be performed by any method without particular limitation. For example, a water washing tank can be provided downstream of an electrolytic cell for performing cathodic electrolytic treatment, and the steel plate after cathodic electrolytic treatment can be continuously immersed in water. Alternatively, water washing may be performed by spraying water onto the steel plate after cathodic electrolysis treatment.

The number of times the water washing is performed is not particularly limited, and may be once, twice or more. However, in order to avoid an excessive increase in the number of water washing tanks, it is preferable that the number of water washings be 5 times or less. Moreover, when performing the water washing process two or more times, each water washing may be performed by the same method or may be performed by different methods.

In the present invention, it is important to use water with an electrical conductivity of 100 μS/m or less in at least the final water washing of the water washing process. Thereby, the amount of K, Na, Mg, and Ca adsorbed on the surface of the surface-treated steel sheet can be reduced, and as a result, the adhesion can be improved. Water having an electrical conductivity of 100 μS/m or less can be produced by any method. The water having an electrical conductivity of 100 μS/m or less may be, for example, ion exchange water or distilled water. On the other hand, although the lower limit of the electrical conductivity is not particularly limited, excessive reduction will lead to an increase in manufacturing costs. Therefore, from the viewpoint of manufacturing cost, the electrical conductivity is preferably 1 μS/m or more, more preferably 5 μS/m or more, and even more preferably 10 μS/m or more.

In addition, when washing with water twice or more in the water washing process, the above-mentioned effect can be obtained if water with an electrical conductivity of 100 μS/m or less is used for the last washing, so for washing other than the last washing, Any water can be used. Water with an electrical conductivity of 100 µS/m or less may be used for washing other than the final washing, but from the perspective of reducing costs, it is recommended to use water with an electrical conductivity of 100 µS/m or less only in the final washing. It is preferable to use ordinary water such as tap water or industrial water for washing other than the final washing.

From the viewpoint of further reducing the amount of K, Na, Mg, and Ca adsorbed on the surface of the surface-treated steel sheet, the electrical conductivity of the water used for the final washing is preferably 50 μS/m or less, and 30 μS/m or less. /m or less is more preferable.

The temperature of the water used for the washing process is not particularly limited and may be any temperature. However, since an excessively high temperature places an excessive burden on the washing equipment, it is preferable that the temperature of the water used for washing is 95° C. or lower. On the other hand, the lower limit of the temperature of the water used for washing is also not particularly limited, but it is preferably 0° C. or higher. The temperature of the water used for the washing may be room temperature.

The water washing time per water washing treatment is not particularly limited, but from the viewpoint of enhancing the effect of the water washing treatment, it is preferably 0.1 seconds or more, and more preferably 0.2 seconds or more. Further, the upper limit of the water washing time per water washing treatment is not particularly limited, but when manufacturing on a continuous line, the line speed will decrease and productivity will decrease, so it is preferably 10 seconds or less, and 10 seconds or less is preferable. More preferably seconds or less.

After the water washing step, drying may be optionally performed. The drying method is not particularly limited, and for example, a normal dryer or an electric oven drying method can be applied. The temperature during the drying treatment is preferably 100°C or lower. Within the above range, deterioration of the surface treated film can be suppressed. Note that the lower limit is not particularly limited, but is usually about room temperature.

Although the use of the surface-treated steel sheet of the present invention is not particularly limited, it is particularly suitable as a surface-treated steel sheet for containers used for manufacturing various containers such as food cans, beverage cans, pail cans, and 18-liter cans.

In order to confirm the effects of the present invention, a surface-treated steel sheet was manufactured according to the procedure described below, and its characteristics were evaluated.

(Electrolyte preparation process)
First, electrolytic solutions having compositions A to G shown in Table 1 were prepared under the conditions shown in Table 1. That is, each component shown in Table 1 was mixed with water to form an aqueous solution, and then the aqueous solution was adjusted to the pH and temperature shown in Table 1. Note that the electrolytic solution G corresponds to the electrolytic solution used in the example of Patent Document 6. Ammonia water was used to raise the pH, and to lower the pH, sulfuric acid was used for electrolytes A, B, and G, hydrochloric acid was used for electrolytes C and D, and nitric acid was used for electrolytes E and F.

(Formation of Ni-containing layer)
On the other hand, both sides of the steel plate were electrically plated with Ni to obtain a Ni-plated steel plate having Ni plating layers as Ni-containing layers on both sides of the steel plate. A Watts bath was used for the electro-Ni plating. Further, prior to the electrolytic Ni plating, the steel plate was sequentially subjected to electrolytic degreasing, water washing, pickling by immersion in dilute sulfuric acid, and water washing. In the electrolytic Ni plating, the amount of Ni deposited in the Ni plating layer was set to the values shown in Tables 2 and 3 by changing the electrical quantity density. The amount of Ni deposited on the Ni-containing layer was measured by the above-mentioned calibration curve method using fluorescent X-rays. After forming the Ni plating layer, it was washed with water and subjected to the next cathode electrolytic treatment step while kept wet. Note that in some examples, a Ni--Fe alloy layer was formed as the Ni-containing layer. That is, after forming a Ni plating layer by the method described above, a Ni--Fe alloy layer was formed by annealing.

As the steel plate, a steel plate for cans (T4 original plate) having a Cr content of the values shown in Tables 2 and 3 and a plate thickness of 0.17 mm was used.

(Cathode electrolytic treatment process)
Next, the Ni-plated steel sheet was subjected to cathodic electrolysis treatment under the conditions shown in Tables 2 and 3. Note that the electrolytic solution during the cathode electrolytic treatment was maintained at the pH and temperature shown in Table 1. The electric charge density during the cathode electrolysis treatment was the value shown in Tables 2 and 3, and the electrolysis time and number of passes were changed as appropriate. As an anode during the cathodic electrolytic treatment, an insoluble anode in which Ti as a substrate was coated with iridium oxide was used. After the cathodic electrolytic treatment, the sample was washed with water and dried at room temperature using a blower.

(Water washing process)
Next, the steel plate subjected to the cathodic electrolytic treatment was subjected to a water washing treatment. The water washing treatment was performed 1 to 5 times under the conditions shown in Tables 2 and 3. The method of washing each time and the electrical conductivity of the water used were as shown in Tables 2 and 3.

For each of the obtained surface-treated steel sheets, the amount of Cr deposited on one side of the steel sheet in the metal Cr layer and the amount of Cr deposited on one side of the steel sheet in the oxidized Cr layer were measured using the method described above. Similarly, the C atomic ratio of the metal Cr layer was measured using the method described above. Note that the "C atomic ratio" of the metal Cr layer shown in Tables 4 and 5 is a value representing the C content in the metal Cr layer in terms of the atomic ratio to Cr. Further, for each of the obtained surface-treated steel sheets, the water contact angle, the amount of adsorbed elements, and the atomic ratio of Ni on the outermost surface were measured using the following methods. The measurement results are shown in Tables 4 and 5.

(water contact angle)
The water contact angle was measured using an automatic contact angle meter model CA-VP manufactured by Kyowa Interface Science. The surface temperature of the surface-treated steel sheet was set to 20°C ± 1°C, distilled water at 20 ± 1°C was used, and a droplet volume of 2 μl of distilled water was dropped onto the surface of the surface-treated steel sheet, and after 1 second, θ/ The contact angle was measured by method 2, and the arithmetic average value of the contact angles for 5 drops was taken as the water contact angle.

(Amount of adsorbed elements)
The total atomic ratio of K, Na, Mg, and Ca adsorbed on the surface of the surface-treated steel sheet to Cr was measured by XPS. In the measurements, no sputtering was performed. From the integrated intensity of the narrow spectrum of K2p, Na1s, Ca2p, Mg1s, and Cr2p on the outermost surface of the sample, the atomic ratio was quantified by the relative sensitivity coefficient method, and was calculated as (K atomic ratio + Na atomic ratio + Ca atomic ratio + Mg atomic ratio) / Cr atomic ratio. The ratio was calculated. For XPS measurements, a scanning X-ray photoelectron spectrometer PHI X-tool manufactured by ULVAC-PHI was used, the X-ray source was a monochrome AlKα ray, the voltage was 15 kV, the beam diameter was 100 μmφ, and the extraction angle was 45°.

(Ni atomic ratio on the outermost surface)
The atomic ratio of Ni content to Cr on the outermost surface of the surface-treated steel sheet was measured by XPS. In the measurements, no sputtering was performed. From the integrated intensity of the narrow spectrum of Ni2p and Cr2p on the outermost surface of the sample, the atomic ratio was quantified by the relative sensitivity coefficient method, and the Ni atomic ratio/Cr atomic ratio was calculated. For XPS measurements, a scanning X-ray photoelectron spectrometer PHI X-tool manufactured by ULVAC-PHI was used, the X-ray source was a monochrome AlKα ray, the voltage was 15 kV, the beam diameter was 100 μmφ, and the extraction angle was 45°.

Furthermore, the obtained surface-treated steel sheet was evaluated for film wet adhesion, secondary paint adhesion, and weldability using the following methods. The evaluation results are also listed in Tables 4 and 5.

(Preparation of sample)
A laminated steel plate as a sample used for evaluation of film corrosion resistance and film wet adhesion was produced according to the following procedure.

An isophthalic acid copolymerized polyethylene terephthalate film having a stretching ratio of 3.1 x 3.1, a thickness of 25 μm, a copolymerization ratio of 12 mol%, and a melting point of 224°C is laminated on both sides of the obtained surface-treated steel sheet to obtain a laminated steel sheet. was created. The lamination was carried out under conditions such that the crystallinity of the resin film was 10% or less, specifically, the feed speed of the steel plate: 40 m/min, the nip length of the rubber roll: 17 mm, and the time from crimping to water cooling: 1 sec. . The crystallinity of the resin film was determined by the density gradient tube method in accordance with JIS K7112. In addition, the nip length refers to the length of the portion where the rubber roll and the steel plate are in contact with each other in the conveyance direction.

In addition, a coated steel plate as a sample used for evaluation of paint corrosion resistance and paint secondary adhesion was produced according to the following procedure.

An epoxyphenol paint was applied to the surface of the obtained surface-treated steel sheet, and baked at 210° C. for 10 minutes to produce a coated steel sheet. The amount of coating applied was 50 mg/dm ² .

(Film corrosion resistance, paint corrosion resistance)
A cutter was used to make a cross cut deep enough to reach the base iron (steel plate) on the film surface of the produced laminated steel plate and the painted surface of the painted steel plate. A laminated steel plate with cross cuts and a painted steel plate were immersed for 96 hours in a test solution at 55°C consisting of a mixed aqueous solution containing 1.5% by mass citric acid and 1.5% by mass common salt. After dipping, washing and drying, cellophane adhesive tape was applied to the film surface of the laminated steel sheet and the painted surface of the painted steel sheet, and tape peeling was performed by peeling it off. Regarding film corrosion resistance, the film peeling width (the total width of the left and right sides extending from the cut part) was measured at four arbitrary locations on the cross-cut part of the laminated steel plate, and the average value of the four locations was determined and considered as the corrosion width. Regarding paint corrosion resistance, the paint peeling width (the total width of the left and right sides extending from the cut part) was measured at four arbitrary locations on the cross-cut portion of the painted steel plate, and the average value of the four locations was determined and considered as the corrosion width. Film corrosion resistance and paint corrosion resistance were evaluated on the following four levels. In practical terms, if the rating is 1 to 3, it can be said that the material has excellent corrosion resistance.
1: Corrosion width less than 0.3 mm 2: Corrosion width 0.3 mm or more and less than 0.5 mm 3: Corrosion width 0.5 mm or more and less than 1.0 mm 4: Corrosion width 1.0 mm or more

(Film wet adhesion)
Film wet adhesion was evaluated by a 180° peel test in a retort atmosphere at a temperature of 130° C. and a relative humidity of 100% using the laminated steel plate. The specific steps were as follows.

First, a total of six test pieces were cut out from each of the above laminated steel plates: three test pieces with the front side as the target side and three test pieces with the back side as the target side. The size of each test piece was 30 mm in width and 100 mm in length. Next, at a position 15 mm from the top of each test piece in the length direction, the film and steel plate on the opposite side of the target surface were cut, leaving the film on the target surface. After cutting, the test piece was fixed in the longitudinal direction up to 15 mm from the bottom so that the steel plate was perpendicular to the ground, and the part 30 mm wide and 15 mm long above the cutting position was the target I made it hang down while being connected by a film on the surface. Then, a weight of 100 g was attached to the hanging portion of 30 mm in width and 15 mm in length.

The test piece in this state was left in a retort atmosphere at a temperature of 130° and a relative humidity of 100% for 30 minutes, and then opened to the atmosphere. The length by which the film on the target surface was peeled off from the surface-treated steel sheet was defined as the film peeling length, and for each laminated steel sheet, the average value of the film peeling length in six test pieces was determined. Using the average value of the obtained film peel lengths, the film wet adhesion was evaluated on the following four levels. In practical terms, if the evaluation is 1 to 3, it can be said that the film has excellent wet adhesion.
1: Peel length less than 20 mm 2: Peel length 20 mm or more and less than 40 mm 3: Peel length 40 mm or more and less than 60 mm 4: Peel length 60 mm or more

(Paint secondary adhesion)
Two coated steel plates made under the same conditions were laminated with a nylon adhesive film in between so that the coated surfaces faced each other, and then the pressure was 2.94×10 ⁵ Pa, the temperature was 190°C, and the bonding time was 30 seconds. Pasted below. Thereafter, this was divided into test pieces with a width of 5 mm. The divided test pieces were immersed for 168 hours in a test solution at 55°C consisting of a mixed aqueous solution containing 1.5% by mass of citric acid and 1.5% by mass of common salt. After immersion, washing, and drying, the two steel plates of the divided test piece were peeled off using a tensile tester, and the tensile strength when peeled off was measured. The average value of the three test pieces was evaluated on the following four levels. In practical terms, if the rating is 1 to 3, it can be said that the secondary paint adhesion is excellent.
1: 2.5 kgf or more 2: 2.0 kgf or more and less than 2.5 kgf 3: 1.5 kgf or more and less than 2.0 kgf 4: Less than 1.5 kgf

(Weldability)
The obtained surface-treated steel sheets were heat-treated at 210°C for 10 minutes assuming a paint baking process, and then the two samples were heated using a DR type 1 mass% Cr-Cu electrode (tip diameter 2.3 mm, curvature It was sandwiched between electrodes (processed to have an R of 40 mm) and energized under the following conditions.
・Amada Miyachi transistor power supply: MDA-8000A
・Welding head: AH-200
・Pressurization: 40kgf
・Electrification time: 1.6msec. (Slope 0.2msec.)
・Waveform: Square wave

An appropriate current range (=upper limit current - lower limit current) was determined from the lower limit current that provides sufficient strength and the upper limit current that does not cause dusting, and was evaluated using the following four levels. In practical terms, if the evaluation is 1 to 3, it can be said that the weldability is excellent.
1: 2.5kA or more 2: 2.0kA or more, less than 2.5kA 3: 1.5kA or more, less than 2.0kA 4: Less than 1.5kA

As is clear from the results shown in Tables 4 and 5, the surface-treated steel sheets that meet the conditions of the present invention have excellent film corrosion resistance, paint corrosion resistance, and film wetness, even though they were manufactured without using hexavalent chromium. It had excellent adhesion, secondary paint adhesion, and weldability.

Claims

steel plate and
a Ni-containing layer disposed on at least one surface of the steel plate;
a metal Cr layer disposed on the Ni-containing layer;
and a Cr oxide layer disposed on the metal Cr layer,
The water contact angle is 50° or less,
A surface-treated steel sheet in which the total atomic ratio of K, Na, Mg, and Ca adsorbed on the surface to Cr is 5.0% or less.
The surface-treated steel sheet according to claim 1, wherein the Ni-containing layer has a Ni adhesion amount of 200 mg/m 2 or more and 2000 mg/m 2 or less per side of the steel sheet.
The surface-treated steel sheet according to claim 1 or 2, wherein the metal Cr layer has a Cr adhesion amount of 2 mg/m 2 or more and less than 40 mg/m 2 per side of the steel sheet.
The surface-treated steel sheet according to any one of claims 1 to 3, wherein the oxidized Cr layer has a Cr adhesion amount of 0.1 mg/m 2 or more and 15.0 mg/m 2 or less per side of the steel sheet.
The surface-treated steel sheet according to any one of claims 1 to 4, wherein the atomic ratio of Ni to Cr on the surface of the surface-treated steel sheet is 100% or less.
A surface comprising a steel plate, a Ni-containing layer disposed on at least one surface of the steel plate, a metallic Cr layer disposed on the Ni-containing layer, and an oxidized Cr layer disposed on the metallic Cr layer. A method for manufacturing a treated steel sheet, the method comprising:
an electrolytic solution preparation step of preparing an electrolytic solution containing trivalent chromium ions;
a cathodic electrolytic treatment step of cathodic electrolytically treating a steel plate having a Ni-containing layer on at least one surface in the electrolytic solution;
a washing step of washing the steel plate after the cathodic electrolytic treatment at least once with water,
In the electrolyte preparation step,
Mixing a trivalent chromium ion source, a carboxylic acid compound, and water,
The electrolytic solution is prepared by adjusting the pH to 4.0 to 7.0 and the temperature to 40 to 70°C,
In the water washing step,
A method for producing a surface-treated steel sheet, using water with an electrical conductivity of 100 μS/m or less in at least the final washing.