TW202342818A - Surface-treated steel sheet and method for producing same - Google Patents

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 DEG 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 plate and manufacturing method thereof

The present invention relates to a surface-treated steel plate, and in particular to a surface-treated steel plate having excellent film corrosion resistance, coating corrosion resistance, film wetting adhesion, secondary paint adhesion, and weldability. The surface-treated steel plate of the present invention can be applied to containers such as cans. Furthermore, the present invention relates to a method for manufacturing the above-mentioned surface-treated steel plate.

Sn-plated steel plate (blik) has excellent corrosion resistance, weldability, and processability and is easy to manufacture. It has been used for 200 years as a material for various metal cans such as beverage cans, food cans, pail cans (pails), and 18-liter cans. years and above.

However, since Sn is an expensive material, tin-free steel sheets (TFS), surface-treated steel sheets that do not use Sn, were developed. Tin-free steel plates are surface-treated steel plates in which a metal Cr layer and an oxide Cr layer are formed on the surface of the steel plate. They are usually produced by subjecting the steel plate to an electrolytic treatment in an electrolytic solution containing hexavalent Cr (Patent Documents 1 to 3). Since tin-free steel plates have excellent corrosion resistance and paint adhesion, they are now very commonly used as steel plates for containers instead of tin-plated steel plates. However, this tin-free steel plate lacks weldability due to the chromium oxide layer of the insulating film on its surface.

In addition, surface-treated steel sheets that are excellent in weldability and do not use Sn are known, and Ni-plated steel sheets that use Ni instead of Sn are known (Patent Documents 4 and 5). However, when Ni-plated steel plates are used as materials for welded cans, in order to ensure corrosion resistance and paint adhesion, an aqueous solution containing hexavalent Cr must be used on the Ni-plated steel plates to provide a chromate treatment film.

In recent years, as environmental awareness has increased, the world has moved towards restricting the use of hexavalent Cr. Therefore, even in the field of surface-treated steel plates used in containers and the like, it is required to establish a manufacturing method that does not use hexavalent chromium.

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

Patent Document 1: Japanese Patent Application Publication No. Sho 58-110695 Patent Document 2: Japanese Patent Application Publication No. Sho 55-134197 Patent Document 3: Japanese Patent Application Publication No. Sho 57-035699 Patent Document 4: Japanese Patent Application Publication No. 11-117085 Patent Document 5: Japanese Patent Application Publication No. 2007-231394 Patent Document 6: Japanese Patent Publication No. 2016-505708 Patent Document 7: Japanese Patent Publication No. 2015-520794

Invent the problem to be solved

According to the methods proposed in Patent Documents 6 and 7, the surface treatment layer can be formed without using hexavalent chromium. In addition, according to Patent Documents 6 and 7, by the above-mentioned method, the adhesion to a resin film in a humid environment (hereinafter referred to as "film wet adhesion") and the adhesion to a paint in a humid environment can be obtained. Surface-treated steel plate with excellent adhesion (hereinafter referred to as "paint secondary adhesion").

However, surface-treated steel sheets produced by conventional methods such as those proposed in Patent Documents 6 and 7 have excellent film wetting adhesion and secondary paint adhesion, but have poor weldability. When used as a replacement for steel plates, it has full performance.

Therefore, there is a demand for surface-treated steel plates that can be produced without using hexavalent chromium and have excellent film corrosion resistance, coating corrosion resistance, film wetting and adhesion, secondary paint adhesion, and weldability.

The present invention was completed in view of the above actual situation, and the object of the present invention is to provide a method that can be manufactured without using hexavalent chromium and has excellent film corrosion resistance, coating corrosion resistance, film wetting adhesion, and secondary coating adhesion. , and surface-treated steel plates with excellent weldability. means to solve problems

As a result of careful examination in order to achieve the above object, the inventors of the present invention have obtained the following findings (1) and (2).

(1) In the surface-treated steel plate with a metallic Cr layer and an oxidized Cr layer on the Ni-containing layer, the water contact angle and the atomic ratio of K, Na, Mg, and Ca adsorbed on the surface to Cr are respectively controlled. Within a specific range, surface-treated steel plates with excellent film corrosion resistance, coating corrosion resistance, film wetting adhesion, secondary paint adhesion, and weldability can be obtained.

(2) The above-mentioned surface-treated steel plate is produced by subjecting it to cathodic electrolysis in an electrolytic solution prepared by a specific method containing trivalent chromium ions, and then using water with a conductivity below a predetermined value for final washing.

The present invention was completed based on the above findings. The main contents of the present invention are as follows.

1. A surface-treated steel plate, which has a steel plate, 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 an oxide Cr layer disposed on the metal Cr layer, The water contact angle is below 50°, The total atomic ratio of K, Na, Mg, and Ca adsorbed on the surface relative to Cr is 5.0% or less.

2. For the surface-treated steel plate as described in 1 above, the Ni adhesion amount of the Ni-containing layer is 200 mg/m ² or more and 2000 mg/m ² or less per side of the steel plate.

3. The surface-treated steel plate as described in 1 or 2 above, wherein the Cr adhesion amount of the aforementioned metal Cr layer is 2 mg/m 2 or ^more and less than 40 mg/m ² per single side of the aforementioned steel plate.

4. The surface-treated steel plate according to any one of the above 1 to 3, wherein the Cr adhesion amount of the aforementioned Cr oxide layer is not less than 0.1 mg/m 2 and not ^more than 15.0 mg/m ² per single side of the aforementioned steel plate.

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

A method of manufacturing a surface-treated steel plate, which includes a steel plate, 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 an oxide Cr layer disposed on the metal Cr layer. The manufacturing method of surface-treated steel plate has the following steps: The electrolyte preparation step of preparing an electrolyte containing trivalent chromium ions, the cathodic electrolytic treatment step of cathodic electrolytic treatment of a steel plate having a Ni-containing layer on at least one side in the aforementioned electrolytic solution, and the cathodic electrolytic treatment step of subjecting the steel plate after the aforementioned cathodic electrolytic treatment to at least 1 water washing step, In the aforementioned electrolyte preparation step, a trivalent chromium ion source, a carboxylic acid compound, and water are mixed, the pH is adjusted to 4.0~7.0, and the temperature is adjusted to 40~70°C to prepare the aforementioned electrolyte, and the aforementioned water washing step , at least in the final water wash, use water with a conductivity of less than 100 μS/m. Invention effect

According to the present invention, a surface-treated steel plate is provided that does not use hexavalent chromium and has excellent film corrosion resistance, coating corrosion resistance, film wetting adhesion, secondary paint adhesion, and weldability. The surface-treated steel plate of the present invention can be suitably used as a material for containers and the like.

Form of carrying out the invention

Hereinafter, the method of carrying out the present invention will be specifically described. In addition, the following description shows examples of preferred embodiments of the present invention, and the present invention is not limited thereto.

The surface-treated steel plate in one embodiment of the present invention includes a steel plate, 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 an oxide layer disposed on the metal Cr layer. Surface treated steel plate with Cr layer. In the present invention, it is important that the water contact angle of the surface-treated steel sheet is 50° or less, and that the total atomic ratio of K, Na, Mg, and Ca adsorbed on the surface to Cr is 5.0% or less. Hereinafter, the components of the surface-treated steel plate will be explained respectively.

[steel plate] The steel plate is not particularly limited, and any steel plate can be used. The aforementioned steel plate is preferably a steel plate for cans. As the steel plate, for example, a very low carbon steel plate or a low carbon steel plate can be used. The manufacturing method of the aforementioned steel plate is not particularly limited, and steel plates manufactured by any method can be used. Usually, cold-rolled steel plates can be used as the aforementioned steel plates. The aforementioned cold-rolled steel plate can be produced by, for example, general manufacturing steps of hot rolling, pickling, cold rolling, and tempering and rolling.

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

In one embodiment of the present invention, it is preferable to have, in terms of mass %, and the remaining part of Fe and unavoidable impurities. Among the above components, the lower the content of Si, P, S, Al, and N, the better. Cu, Ni, Cr, Mo, Ti, Nb, B, Ca, Sn, and Sb can be added arbitrarily. ingredients.

The thickness of the aforementioned steel plate is not particularly limited, but is preferably 0.60 mm or less. Moreover, here, "steel plate" is defined as including "steel strip". In addition, the lower limit of the aforementioned plate thickness is not particularly limited, but is preferably 0.10 mm or more.

[Ni-containing layer] When surface-treated steel plates are used as tank steel plates, they are generally welded by resistance welding such as wire seam welding. Ni is an element with excellent forge welding properties, so by arranging a Ni-containing layer, weldability can be improved. That is, when the Ni-containing layer is present, heat can be generated with lower resistance and excellent welding strength can be obtained, so the lower limit of the welding current can be expanded.

The aforementioned Ni-containing layer may be provided on at least one side of the steel plate, or may be provided on both sides. The Ni-containing layer may cover at least a part of the steel plate, or may cover the entire surface on which the Ni-containing layer is provided. In addition, 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.

The aforementioned Ni-containing layer may be any layer containing nickel. For example, one or both of a Ni layer and a Ni alloy layer may be used. For example, when a Ni alloy layer is formed through diffusion annealing treatment after Ni plating, it is also included in the Ni alloy layer. In addition, the Ni alloy layer may be, for example, a Ni-Fe alloy layer.

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

The Ni-based plating layer may be a dispersion plating layer (composite plating layer) in which solid microparticles are dispersed in Ni or Ni-based alloy as a matrix. The solid fine particles are not particularly limited, and fine particles of any material can be used. The aforementioned fine particles may be any of inorganic fine particles and organic fine particles. Examples of the organic fine particles include fine particles made of resin. Any resin can be used as the aforementioned resin, but fluorine resin is preferably used, and polytetrafluoroethylene (PTFE) is more preferably used. The aforementioned inorganic fine particles are not particularly limited, and fine particles made of any inorganic material can be used. The aforementioned inorganic material may be, for example, a metal (including an alloy), a compound, or other monomers. Among them, it is preferable to use fine particles composed of at least one selected from the group consisting of oxides, nitrides, and carbides, and it is more preferable to use fine particles of metal oxides. Examples of the metal oxide include aluminum oxide, chromium oxide, titanium oxide, zinc oxide, and the like.

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 aforementioned microparticles is preferably 1 nm to 50 μm, and more preferably 10 nm to 1000 nm.

The Ni adhesion amount in the Ni-containing layer is not particularly limited and can be any amount. However, from the perspective of further improving the weldability and corrosion resistance of the surface-treated steel plate, the Ni adhesion amount per side of the steel plate is 200 mg/m ² or more, and more preferably 250 mg/m ² or more. In addition, when the aforementioned Ni adhesion amount exceeds 2000 mg/ ^m2 , the effect of improving weldability is saturated. Therefore, from the viewpoint of reducing excessive costs, the Ni adhesion amount is preferably 2000 mg/m ² or less, more preferably 1800 mg/m ² or less.

The Ni adhesion amount of the Ni-containing layer is measured by the fluorescent X-ray calibration line method. Prepare a steel plate with a known Ni adhesion amount and measure the fluorescence X-ray intensity from Ni in advance. The relationship between the measured fluorescence X-ray intensity and the Ni adhesion amount is linearly approximated and used as a calibration line. The intensity of fluorescent X-rays derived from Ni is measured on the surface-treated steel plate, and the Ni adhesion amount of the Ni-containing layer can be measured using the above calibration line.

The formation of the Ni-containing layer is not particularly limited, and any method such as electroplating can be used. When forming a Ni-containing layer by electroplating, any plating bath can be used. Examples of plating baths that can be used include Watts nickel plating bath (Watts bath), sulfamic acid bath, or nickel plating bath. When forming a Ni-Fe alloy layer as a Ni-containing layer, a Ni layer is formed on the surface of a steel plate by a method such as electroplating, and then the Ni-Fe alloy layer is formed by annealing.

The surface side of the Ni-containing layer may contain Ni oxide or may not contain it at all. However, from the viewpoint of improving the secondary adhesion of the paint and the resistance to sulfide blackening, it is preferable that the surface side of the Ni-containing layer does not contain Ni oxide. Ni oxide. Ni oxide is formed by dissolved oxygen and the like contained in the washing water after Ni plating. However, it is preferable to remove the Ni oxide contained in the Ni-containing layer in a pre-treatment to be described later.

[Metal Cr layer] There is a metallic Cr layer on the aforementioned Ni-containing layer.

The adhesion amount of the aforementioned metal Cr layer is not particularly limited and can be any value. However, from the viewpoint of further improving the corrosion resistance, the adhesion amount of the metal Cr layer is preferably 2 mg/m ² or more, and more preferably 4 mg/m ² or more based on the Cr adhesion amount per single side of the steel plate. In addition, the upper limit of the adhesion amount of the metal Cr layer is not particularly limited. When the adhesion amount of the metal Cr layer is too large, the contact resistance increases, which may impair the weldability. Therefore, from the viewpoint of ensuring weldability more stably, the adhesion amount of the metal Cr layer is preferably less than 40 mg/m ² and more preferably less than 35 mg/m ² based on the Cr adhesion amount per single side of the steel plate.

In addition, the Cr adhesion amount in the metal Cr layer can be measured by fluorescence X-ray method. Specifically, first, the Cr content (total Cr content) in the surface-treated steel plate was measured using a fluorescent X-ray device. Next, the surface-treated steel plate was subjected to an alkali treatment by immersing it in 7.5N-NaOH at 90° C. for 10 minutes, and then thoroughly washed with water. Then, the Cr amount (Cr amount after alkali treatment) was measured using a fluorescent X-ray device. Furthermore, about the steel plate after peeling off the metallic Cr layer and the oxidized Cr layer, the amount of Cr (the amount of Cr in the original plate) was measured using a fluorescent X-ray device. To peel off the metal Cr layer and the oxide Cr layer, for example, a commercially available chromium plating stripper such as hydrochloric acid series can be used. The value obtained by subtracting the Cr content of the original plate from the Cr content after alkali treatment is used as the Cr adhesion content of the metal Cr layer per single side of the steel plate. In addition, the aforementioned total Cr amount is used to calculate the Cr adhesion amount as the Cr oxide layer described later.

The metal Cr constituting the metal Cr layer may be amorphous Cr or crystalline Cr. That is, the metal Cr layer may contain one or both of amorphous Cr and crystalline Cr. The metal Cr layer produced by the method described below generally contains amorphous Cr, and may also contain crystalline Cr. Although the formation mechanism of the metal Cr layer is unknown, it is considered that when amorphous Cr is formed, it is partially crystallized and becomes a metal Cr layer containing both amorphous and crystalline phases.

The proportion of crystalline Cr in the total of amorphous Cr and crystalline Cr contained in the metal Cr layer is preferably 0% or more and 80% or less, more preferably 0% or more and 50% or less. Here, the proportion 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 obtained at a magnification of about 2 million times to 10 million times using a beam diameter that can obtain a resolution energy of 1 nm or less. In the obtained STEM image, the area where the lattice fringe can be seen is regarded as the crystal phase, and the area where the maze pattern can be seen is regarded as the amorphous phase, and the areas of the two are calculated. From the results, the ratio of the area of crystalline Cr to the total area of amorphous Cr and crystalline Cr was calculated.

[Cr Oxide Layer] A Cr oxide layer exists on the metal Cr layer. The adhesion amount of the aforementioned Cr oxide layer is not particularly limited and can be any value. However, from the perspective of further improving corrosion resistance, the amount of Cr oxide layer attached is preferably 0.1 mg/m ² or more based on the amount of Cr attached to each side of the steel plate. In addition, the upper limit of the adhesion amount of the Cr oxide layer is not particularly limited. When the adhesion amount of the Cr oxide layer is too large, the contact resistance increases, which may impair the weldability. Therefore, from the viewpoint of ensuring more stable weldability, the adhesion amount of the oxidized Cr layer is preferably 15.0 mg/m ² or less based on the Cr adhesion amount per single side of the steel plate. In addition, the Cr adhesion amount in the oxidized Cr layer can be measured by fluorescence X-ray method. Specifically, the Cr adhesion amount in the oxidized Cr layer can be obtained by subtracting the Cr amount after alkali treatment from the total Cr amount measured using the aforementioned fluorescent X-ray device.

One or both of the metal Cr layer and the oxide Cr layer may contain C. However, if too much C is contained in the metallic Cr layer and the oxidized Cr layer, the welding heat-affected zone will harden during welding and cracks may occur. Therefore, the atomic ratio of C content to Cr in the metal Cr layer is preferably 40% or less, more preferably 35% or less. Similarly, regarding the C content in the oxidized Cr layer, the atomic ratio to Cr is preferably 40% or less, more preferably 35% or less. The metal Cr layer and the oxide Cr layer may not contain C. Therefore, the lower limit of the C content contained in the metal Cr layer and the oxide Cr layer may be 0% in terms of the atomic ratio of each to Cr.

The C content in the metallic Cr layer and the C content in the oxidized Cr layer can be measured by X-ray photoelectron spectroscopy (XPS) respectively. The measurement of C content by XPS, specifically, by using the integrated intensity of the narrow spectrum of Cr2p and C1s measured by XPS, the C atomic ratio and the Cr atomic ratio are calculated using the relative sensitivity coefficient method. Atomic ratio/Cr atomic ratio can be implemented.

In addition, since C from contamination is detected in the outermost layer of the surface-treated steel plate, in order to accurately measure the C content in the oxidized Cr layer, sputtering is performed from the outermost layer to a depth of 0.2 nm or more in terms of SiO ₂ conversion, for example. Just measure after plating. In addition, the C content in the metal Cr layer can be measured from the surface layer after the above-mentioned alkali treatment and sputtering to a depth of 1/2 of the thickness of the metal Cr layer.

The thickness of the metal Cr layer used for the above measurement can be obtained using the following steps. First, the Cr atomic ratio and Ni atomic ratio were measured by XPS every 1 nm in the depth direction from the alkali-treated outermost layer. Next, the cubic equation that approximates the relationship between the Ni atomic ratio/Cr atomic ratio of the outermost surface layer to the depth after alkali treatment is obtained by the least squares method. Using the obtained cubic formula, the depth of the outermost layer where the Ni atomic ratio/Cr atomic ratio becomes 1 is calculated, and this is taken as the thickness of the metallic Cr layer.

For the aforementioned measurement, for example, a scanning X-ray photoelectron spectroscopic analyzer PHI X-tool manufactured by ULVAC-PHI Co., Ltd. can be used. The X-ray source is a monochromatic AlKα line, the voltage is 15kV, the beam diameter is 100μmφ, the take-off angle is 45°, the sputtering conditions are Ar ions at an acceleration voltage of 1kV, and the sputtering rate is SiO ₂ Just convert it to 1.50nm/min.

Although the mechanism why the metallic Cr layer and the oxidized Cr layer contain C is unknown, it can be considered that in the steps of forming the metallic Cr layer and the oxidized Cr layer on the steel plate, the carboxylic acid compound contained in the electrolyte is decomposed and incorporated into the film.

The existence form of C in the metal Cr layer and the oxidized Cr layer is not particularly limited. If it exists as a precipitate, the corrosion resistance may be reduced due to the formation of local cells. Therefore, the total volume fraction of carbides or clusters having a clear crystal structure is preferably 10% or less, and more preferably does not contain it at all (0%). The presence or absence of carbides can be determined by, for example, energy dispersive X-ray spectroscopy (EDS) or wavelength dispersion X-ray spectroscopy (WDS) attached to a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Analyze to confirm. Regarding the presence or absence of clusters, for example, cluster analysis can be performed on data analyzed by three-dimensional composition using a three-dimensional atom probe (3DAP).

The metallic Cr layer may contain O. The upper limit of the O content in the metal Cr layer is not particularly limited. When the O content is high, Cr oxide will precipitate, and the corrosion resistance may be reduced due to the formation of local cells. Therefore, the atomic ratio of O content to Cr is preferably 30% or less, more preferably 25% or less. The metal Cr layer does not need to contain O. Therefore, the lower limit of Cr contained in the metal Cr layer is not particularly limited and may be 0%.

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

One or both of the metal Cr layer and the oxide Cr layer may contain Ni. The upper limit of the Ni content in the metal Cr layer is not particularly limited, but the atomic ratio of Cr is preferably less than 100%. Similarly, the upper limit of the Ni content in the oxidized Cr layer is not particularly limited, but the atomic ratio of Cr is preferably less than 100%. The metal Cr layer and the oxide Cr layer do not need to contain Ni. Therefore, 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 plate, that is, the surface of the Cr oxide layer, is not particularly limited. The lower the Ni content, the better the film wetting adhesion and the secondary coating adhesion. Therefore, the atomic ratio of Ni to Cr in the surface of the surface-treated steel plate is preferably 100% or less, more preferably 80% or less.

The Ni content in the metallic Cr layer and the oxidized Cr layer is the same as the C content and can be measured by XPS. The surface of the surface-treated steel plate, that is, the atomic ratio of Ni to Cr in the surface of the oxidized Cr layer, can be measured by XPS. To calculate the atomic ratio, the narrow spectrum of Cr2p and Ni2p can be used.

The mechanism why the metallic Cr layer and the oxidized Cr layer contain Ni is not clear, but it can be considered that the steps of forming the metallic Cr layer and the oxidized Cr layer on the steel plate are such that trace amounts of Ni contained in the Ni-containing layer are dissolved in the electrolyte, and Ni is incorporated into the film.

In addition to Cr, O, Ni, C, and K, Na, Mg, and Ca described below, the above metal Cr layer and oxidized Cr layer also contain metal impurities including Cu, Zn, Sn, Fe, etc. contained in the aqueous solution, or S , N, Cl, Br, etc. However, when these elements are present, the wet adhesion of the film and the secondary adhesion of the paint may be reduced. Therefore, the Fe content in the metallic Cr layer and the oxidized Cr layer is preferably 10% or less relative to the atomic ratio of Cr, and more preferably does not contain it at all (0%). The total atomic ratio of elements other than Cr, O, Ni, C, K, Na, Mg, Ca, and Fe to Cr is preferably 3% or less, and more preferably does not contain it at all (0%). The content of the above-mentioned elements is not particularly limited. For example, it can be measured by XPS like the content of C. Especially when measuring the content of Fe element using XPS, the narrow spectrum of Fe2p is used, but it overlaps with the NiLLM peak, and the quantitative value of Fe content is calculated to be higher than the actual value. As mentioned above, the Fe content is different from other elements. The atomic ratio of Cr is preferably controlled below 10%.

The above metal Cr layer and oxide Cr layer are preferably free of cracks. The presence or absence of cracks can be confirmed by directly observing the cross-section of the film with a focused ion beam (FIB) or the like, and directly observing it with a transmission electron microscope (TEM).

In addition, the surface roughness of the surface-treated steel plate of the present invention will not change greatly due to the formation of the metallic Cr layer and the oxidized Cr layer, and is usually approximately the same as the surface roughness of the base steel plate used. The surface roughness of the surface-treated steel plate is not particularly limited, but the arithmetic mean roughness Ra is preferably 0.1 μm or more and 4 μm or less. In addition, the ten-point average roughness Rz is preferably 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 plate is 50° or less. By setting the water contact angle to 50° or less, the surface of the surface-treated steel plate is highly hydrophilic, and strong hydrogen bonds are formed between the resin contained in the paint and the surface-treated steel plate. As a result, even in a humid environment, High adhesion can be obtained. From the viewpoint of further improving the secondary adhesion of the paint, the water contact angle is preferably 48° or less, more preferably 45° or less. From the viewpoint of improving adhesion, the lower the aforementioned water contact angle, the better. Therefore, the lower limit is not particularly limited and may be 0°. However, from the viewpoint of ease of production, etc., it is preferably 3° or more, and more preferably 6° or more. In addition, the water contact angle can be measured by the method described in the Examples.

Although the mechanism of hydrophilization of the surface of the surface-treated steel plate is unknown, when cathodic electrolysis is performed in the electrolyte to form a metal Cr layer and an oxide Cr layer, the carboxylic acid or carboxylate contained in the electrolyte is decomposed and is This is because hydrophilic functional groups such as carboxyl groups are given to the surface when incorporated into the film. However, as will be described later, if the electrolyte is not prepared under specific conditions, the surface of the surface-treated steel sheet will not become hydrophilic even if the electrolyte contains carboxylic acid or carboxylate. The mechanism by which the conditions for preparing the electrolyte solution affect the hydrophilization of the surface of the surface-treated steel sheet is unknown, but it is presumed that when the electrolyte solution is appropriately prepared under the conditions described below, hydrophilic functional groups such as carboxyl groups form complexes that are easily imparted to the surface. things.

In addition, the composition of the hydrated chromium oxide layer present on the surface of surface-treated steel sheets produced using conventional hexavalent chromium baths proposed in Patent Documents 1 to 5 greatly affects the adhesion to coatings or films in a humid environment. impact reporting. In a humid environment, water penetrating into the coating or film will hinder the interface between the coating or film and the hydrated chromium oxide layer. Therefore, when many h of hydrophilic OH groups exist in the hydrated chromium oxide layer, the expansion and wetting of water in the interface is promoted, and the adhesion force is reduced. Therefore, in conventional surface-treated steel sheets, the OH groups are reduced due to the carbonylation (oxo) of hydrated chromium oxide, that is, the surface is hydrophobicized, which improves the adhesion to coatings or films in a humid environment.

In this regard, the present invention hydrophilizes the surface to a level close to superhydrophilicity to form strong hydrogen bonds at the interface between the coating film and the surface-treated steel plate. Therefore, it can maintain a high level of moisture even in a humid environment. The so-called closeness is based on technical thinkers that are completely opposite to the previous technologies mentioned above.

[Atomic ratio of adsorbed elements] As mentioned above, the surface-treated steel plate of the present invention has high hydrophilicity with a water contact angle of 50° or less, and its surface is chemically active. Therefore, the surface of the aforementioned surface-treated steel plate easily adsorbs cations of elements such as K, Na, Mg, and Ca. The present inventors found that when the water contact angle was simply set to 50° or less, the original adhesion could not be exerted due to the influence of the above-mentioned cations before adsorption. In the present invention, by reducing the amount of the cations adsorbed on the surface of the surface-treated steel plate and improving the adhesion to the resin, excellent film wetting adhesion and secondary coating adhesion can be achieved.

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

[Manufacturing method] A method for manufacturing a surface-treated steel plate according to an embodiment of the present invention uses the method described below to produce a surface-treated steel plate having the above characteristics.

A method for manufacturing a surface-treated steel plate according to an embodiment of the present invention is a surface treatment of a steel plate having a Ni-containing layer on at least one surface, a metal Cr layer disposed on the Ni-containing layer, and an oxide Cr layer disposed on the metal Cr layer. The manufacturing method of the steel plate has the following steps (1) to (3). Each step is explained below. (1) Electrolyte preparation steps for preparing an electrolyte containing trivalent chromium ions (2) The cathodic electrolytic treatment step of subjecting the steel plate having a Ni-containing layer to cathodic electrolytic treatment in the aforementioned electrolytic solution (3) The steel plate after the aforementioned cathodic electrolytic treatment is subjected to a water washing step of at least once

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

Any source of trivalent chromium ions can be used as long as it is a compound that can supply trivalent chromium ions. 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 source containing trivalent chromium ions in the aqueous solution is not particularly limited. In terms of trivalent chromium ions, it is preferably 3 g/L or more and 50 g/L or less, and more preferably 5 g/L or more and 40 g/L or less. As the aforementioned trivalent chromium ion source, Atotech's BluCr (registered trademark) TFSA can be used.

The carboxylic acid compound is not particularly limited, and any carboxylic acid compound can be used. The aforementioned carboxylic acid compound may be at least one of carboxylic acid and carboxylate, and is preferably at least one of aliphatic carboxylic acid and aliphatic carboxylate. The number of carbon atoms in the aliphatic carboxylic acid is preferably 1 to 10, more preferably 1 to 5. Furthermore, the carbon number of the aliphatic carboxylate is preferably 1 to 10, more preferably 1 to 5. The content of the carboxylic acid compound is not particularly limited, but is preferably 0.1 mol/L or more and 5.5 mol/L or less, more preferably 0.15 mol/L or more and 5.3 mol/L or less. As the aforementioned carboxylic acid compound, BluCr (registered trademark) TFS B from Atotech Co., Ltd. can be used.

In the present invention, water is used as a solvent for preparing the electrolyte solution. The aforementioned water is an ion exchange resin, etc., and it is preferable to use ion exchange water from which cations have been removed in advance, or water with high purity 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 with a conductivity of 30 μS/m or less.

In order to reduce K, Na, Mg, and Ca adsorbed on the surface of the surface-treated steel plate, it is preferable that the above-mentioned aqueous solution deliberately does not contain K, Na, Mg, and Ca. Therefore, it is preferable that the components added to the aqueous solution of the trivalent chromium ion source, the carboxylic acid compound, and the pH adjuster described in detail below do not contain K, Na, Mg, and Ca. As a pH adjuster, when the pH is lowered, hydrochloric acid, sulfuric acid, nitric acid, etc. are used; when the pH is raised, ammonia water, etc. is preferably used. Unavoidable mixing of K, Na, Mg, and Ca is allowed in the aqueous solution or electrolyte, but the total concentration of K, Na, Mg, and Ca is preferably 2.0 mol/L or less, more preferably 1.5 mol/L or less. More preferably, it is 1.0 mol/L or less.

In order to effectively suppress the generation of hexavalent chromium on the anode in the cathodic electrolysis treatment step and improve the stability of the electrolyte, the aqueous solution preferably contains at least one halide ion. The content of halide ions is not particularly limited, but is preferably from 0.05 mol/L to 3.0 mol/L, more preferably from 0.10 mol/L to 2.5 mol/L. In order to contain the aforementioned 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-mentioned aqueous solution. In the cathodic electrolysis treatment step, a very small amount of hexavalent chromium formed on the anode is removed, and the electrolyte does not contain hexavalent chromium. During the cathodic electrolysis treatment step, a very small amount of hexavalent chromium formed on the anode is reduced to trivalent chromium, so the concentration of hexavalent chromium in the electrolyte will not increase.

It is preferable that metal ions other than trivalent chromium ions are not intentionally added to the aqueous solution. The above-mentioned metal ions are not limited, and examples thereof include Cu ions, Zn ions, Ni ions, Fe ions, Sn ions, etc., each of which is preferably 0 mg/L or more and 40 mg/L or less, and more preferably 0 mg/L or more and 20 mg/L or less. The optimum value is 0 mg/L or more and 10 mg/L or less. Among the above-mentioned metal ions, Ni ions dissolve in the electrolyte when the steel plate is immersed in the electrolyte during the cathodic electrolysis treatment step, causing eutectoid formation in the film, but this does not affect the film. Wetting adhesion, secondary paint adhesion and weldability. Ni ion 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, most preferably 0 mg/L or more and 10 mg/L or less. In addition, the Ni ion concentration is preferably in the above range when establishing the bath. However, even in the cathode electrolytic treatment step, the Ni ion concentration in the electrolyte is preferably maintained in the above range. When Ni ions are controlled within the above range, it will not hinder the formation of the metal Cr layer and the oxide Cr layer, and the metal Cr layer and the oxide Cr layer of necessary thickness can be formed.

(ii) Adjustment of pH and temperature Next, the pH of the aqueous solution is adjusted to 4.0~7.0, and the temperature of the aqueous solution is adjusted to 40~70°C to prepare the electrolyte. In order to produce 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. It is important to appropriately control the pH and temperature as mentioned above.

pH: 4.0~7.0 The aforementioned electrolyte preparation step is to adjust the pH of the mixed aqueous solution to 4.0~7.0. When the pH is less than 4.0 or exceeds 7.0, the water contact angle of the surface-treated steel plate produced using the obtained electrolyte is higher than 50°. The preferred pH is 4.5~6.5.

Temperature: 40~70℃ In the aforementioned electrolyte preparation step, the temperature of the mixed aqueous solution is adjusted to 40~70°C. When the temperature is less than 40°C or exceeds 70°C, the water contact angle of the surface-treated steel plate produced by using the obtained electrolyte is higher than 50°. In addition, the holding time in the temperature range of 40 to 70°C is not particularly limited.

Through the above steps, the electrolyte solution used in the following cathode electrolytic treatment steps can be obtained. In addition, the electrolyte solution prepared in the above steps can be stored at room temperature.

[Cathode electrolysis treatment steps] Next, the steel plate having a Ni-containing layer on at least one side is subjected to cathodic electrolysis treatment in the electrolyte obtained in the above electrolyte preparation step. Through the aforementioned cathode electrolysis treatment, a metallic Cr layer and an oxide Cr layer can be formed on the aforementioned Ni-containing layer.

The temperature of the electrolyte during cathodic electrolysis is not particularly limited. In order to efficiently form the metal Cr layer and the oxide Cr layer, a temperature range of 40° C. to 70° C. is preferred. From the viewpoint of stably producing the above-mentioned surface-treated steel sheet, it is preferable to monitor the temperature of the electrolyte solution during the cathodic electrolytic treatment step and maintain the above-mentioned temperature range.

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

The current density in the above-mentioned cathodic electrolytic treatment is not particularly limited and can be appropriately adjusted to form a desired surface treatment layer. However, when the current density is too high, the C content in the metal Cr layer increases and the weldability may deteriorate. Therefore, the current density is preferably less than 5.0A/dm ² and more preferably less than 3.0A/dm ² . The lower limit of the current density is not particularly limited. When the current density is too low, hexavalent Cr is generated in the electrolyte, which may cause the stability of the bath to collapse. Therefore, the current density is preferably 0.01A/dm ² or more, more preferably 0.03A/dm ² or more.

The number of times the cathodic electrolytic treatment is applied to the steel plate is not particularly limited and can be any number of times. In other words, cathodic electrolytic treatment can be performed using an electrolytic treatment device having an arbitrary number of passes of 1 or 2 or more. For example, it is preferable to carry out the cathodic electrolytic treatment continuously while conveying the steel plate (steel strip) through a plurality of paths. In addition, when increasing the number of cathodic electrolytic treatments (that is, the number of passes), a corresponding number of electrolytic cells are required. Therefore, the number of cathodic electrolytic treatments (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 conveying speed (linear speed) of the steel plate will decrease, resulting in a decrease in productivity. Therefore, the electrolysis time per pass is preferably 5 seconds or less, more preferably 3 seconds or less. There is no particular limit on the lower limit of the electrolysis time per pass. However, if the electrolysis time is shortened excessively, it will be necessary to increase the linear 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 electrolysis can be controlled by the total charge density expressed as the product of the current density and the electrolysis time and the number of passes. As mentioned above, if the amount of metal Cr is too much, the contact resistance increases, which may impair the weldability. If the amount of metal Cr is too small, the corrosion resistance may be impaired. Therefore, each of the above-mentioned steel plates in front of the metal Cr layer The Cr adhesion amount on one side should be more than 2mg/ ^m2 and less than 40mg/ ^m2 , which is better to control the total electric density. However, the relationship between the amount of metal Cr layer and the total charge density changes due to the structure of the equipment used in the cathode electrolysis treatment step. Therefore, the actual electrolysis treatment conditions only need to be adjusted according to the equipment.

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

In the above-mentioned cathodic electrolytic treatment steps, the metal Cr layer and the oxidized Cr layer are formed on the steel plate. Due to the influence of the liquid being carried out or brought in, the evaporation of water, etc., the concentration of the electrolyte solution often changes. The concentration of the electrolyte in the cathodic electrolytic treatment step changes depending on the structure of the device and the manufacturing conditions. From the perspective of more stable production of surface-treated steel sheets, the concentration of components contained in the electrolytic solution is monitored during the cathodic electrolytic treatment step. And it is better to maintain it within the above concentration range.

In addition, before the aforementioned cathodic electrolytic treatment, the steel plate having the Ni-containing layer can be arbitrarily subjected to pre-treatment. By performing pretreatment to remove the natural oxide film existing on the surface of the Ni-containing layer, the surface can be activated. The method of the aforementioned pretreatment is not particularly limited, and any method may be used. For example, pickling by immersing in dilute sulfuric acid may be performed.

After the aforementioned pretreatment, it is preferred to perform water washing from the viewpoint of removing the pretreatment liquid adhering to the surface.

In addition, when a Ni-containing layer is formed on the surface of the base steel plate, it is better to perform pre-treatment on the base steel plate. As the aforementioned pretreatment, any treatment may be performed, but it is preferable to perform at least one of degreasing, pickling, and water washing.

By degreasing, rolling oil, anti-rust oil, etc. attached to the steel plate can be removed. The aforementioned degreasing is not particularly limited and can be performed by any method. After degreasing, in order to remove the degreasing treatment liquid adhering to the surface of the steel plate, it is preferably washed with water.

In addition, by pickling, the natural oxide film existing on the surface of the steel plate is removed, and the surface can be activated. The aforementioned pickling is not particularly limited and can be performed by any method. After pickling, in order to remove the pickling solution adhering to the surface of the steel plate, it is best to perform water washing.

[Washing steps] 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 aforementioned water washing is not particularly limited and can be performed by any method. For example, a water washing tank is installed downstream of an electrolytic tank for cathodic electrolytic treatment, and the steel plate after cathodic electrolytic treatment can be continuously immersed in water. In addition, the steel plate after cathode electrolysis treatment can also be washed by spraying water.

The number of times of water washing is not particularly limited, it may be once, or it may be two or more times. However, in order to avoid too many water washing tanks, the number of water washing times is preferably less than 5 times. Moreover, when water-washing is performed two or more times, each water-washing may be performed by the same method, or may be performed by a different method.

In the present invention, it is important to use water having a conductivity of 100 μS/m or less in at least the final water washing step. This can reduce the amount of K, Na, Mg, and Ca adsorbed on the surface of the surface-treated steel plate, and as a result, the adhesion can be improved. Water with a conductivity of less than 100 μS/m can be produced by any method. The water having a conductivity of 100 μS/m or less may be, for example, ion-exchanged water or distilled water. In addition, the lower limit of the aforementioned conductivity is not particularly limited, but excessive reduction may lead to an increase in manufacturing costs. Therefore, from the viewpoint of manufacturing cost, the conductivity is preferably 1 μS/m or more, more preferably 5 μS/m or more, and still more preferably 10 μS/m or more.

In addition, in the above-mentioned water washing treatment step, when water washing is performed two or more times, the above effect can be obtained if water with a conductivity of 100 μS/m or less is used for the last water washing. Therefore, any water can be used for the water washing other than the last water washing. . Although water with a conductivity of less than 100 μS/m can also be used for water washing other than the last water washing, from the perspective of cost reduction, only water with a conductivity of less than 100 μS/m is used for the last water washing. For water washing other than the last water washing, tap water is preferably used. , industrial water and other general water.

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

The temperature of the water used for the water washing treatment is not particularly limited and can be any temperature. However, if the temperature is too high, it will cause excessive burden on the washing equipment, so the temperature of the water used for washing is preferably below 95°C. In addition, the lower limit of the temperature of water used for water washing is not particularly limited, but it is preferably 0° C. or higher. The temperature of the water used in the aforementioned water washing may also be room temperature.

The washing time of each water washing treatment is not particularly limited, but from the viewpoint of improving the effect of the water washing treatment, it is preferably 0.1 seconds or more, and more preferably 0.2 seconds or more. In addition, the upper limit of the water washing time for each water washing process is not particularly limited. When manufacturing in a continuous production line, since a decrease in line speed will reduce productivity, it is preferably 10 seconds or less, and more preferably 8 seconds or less.

After the above-mentioned water washing step, optional drying can also be performed. The drying method is not particularly limited, and common dryers and electric furnace drying methods can be used, for example. The temperature during drying treatment is preferably 100°C or lower. If it is within the above range, the deterioration of the surface treatment film can be suppressed. In addition, the lower limit is not particularly limited, but is usually around room temperature.

The use of the surface-treated steel sheet of the present invention is not particularly limited, but it is particularly suitable as a surface-treated steel sheet for containers used in the manufacture of various containers such as food cans, beverage cans, barrel cans, and 18-liter cans. Example

In order to confirm the effects of the present invention, surface-treated steel plates were produced using the following procedures, and their characteristics were evaluated.

(Electrolyte preparation step) First, an electrolyte solution having the compositions A to G shown in Table 1 was prepared under the conditions shown in Table 1. That is, each component shown in Table 1 is mixed with water to prepare an aqueous solution, and then the aqueous solution is adjusted to the pH and temperature shown in Table 1. In addition, the electrolytic solution G corresponds to the electrolytic solution used in the Example of Patent Document 6. When raising the pH, ammonia water was used. When lowering the pH, sulfuric acid was used for the electrolyte solutions A, B, and G, hydrochloric acid was used for the electrolyte solutions C and D, and nitric acid was used for the electrolyte solutions E and F.

(Formation of Ni-containing layer) Furthermore, Ni electroplating was applied to both surfaces of the steel plate to obtain a Ni-plated steel plate having Ni plating layers as Ni-containing layers on both surfaces of the steel plate. For the aforementioned Ni electroplating, Watts bath was used. In addition, before the aforementioned Ni electroplating, the steel plate is sequentially subjected to electrolytic degreasing, water washing, pickling by immersing in dilute sulfuric acid, and water washing. The aforementioned Ni electroplating is performed by changing the electric charge density, and the Ni adhesion amount of the Ni plating layer is set as the value shown in Tables 2 and 3. The Ni adhesion amount of the Ni-containing layer is measured by the above-mentioned fluorescent X-ray calibration line method. After the Ni plating layer is formed, it is washed with water and kept in a wet state for the subsequent cathode electrolysis treatment step. In some embodiments, a Ni-Fe alloy layer is formed as a Ni-containing layer. That is, after the Ni plating layer is formed by the above method, the Ni-Fe alloy layer is formed by annealing.

As the aforementioned steel plate, a steel plate for tanks (T4 original plate) with a Cr content as shown in Tables 2 and 3 and a plate thickness of 0.17 mm was used.

(Cathode electrolysis treatment step) Next, the Ni-plated steel sheet was subjected to cathodic electrolysis treatment under the conditions shown in Tables 2 and 3. In addition, the pH and temperature of the electrolyte solution during the cathodic electrolysis treatment were maintained as shown in Table 1. The electric charge density during cathodic electrolysis treatment is the value shown in Tables 2 and 3, so that the electrolysis time and the number of passes can be appropriately changed. As the anode during the cathodic electrolysis treatment, an insoluble anode in which Ti as a base is coated with iridium oxide is used. After the cathodic electrolytic treatment, it was washed with water and dried at room temperature using a hair dryer.

(washing step) Next, the steel plate after the cathode electrolysis treatment is subjected to water washing treatment. The aforementioned water washing treatment was performed 1 to 5 times under the conditions shown in Table 2 and Table 3. The method of each water washing and the conductivity of the water used are shown in Table 2 and Table 3.

For each of the obtained surface-treated steel plates, the Cr adhesion amount of the metal Cr layer per one side of the steel plate and the Cr adhesion amount of the oxidized Cr layer per one side of the steel plate were measured by the method described above. Similarly, the C atomic ratio of the metallic Cr layer was measured using the method described above. In addition, 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 relative to the atomic ratio of Cr. Furthermore, for each of the obtained surface-treated steel sheets, the water contact angle, the amount of adsorbed elements, and the atomic ratio of Ni in the outermost surface were measured by 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 Co., Ltd. The surface temperature of the surface-treated steel plate is set to 20℃±1℃. The water system uses distilled water of 20±1℃. The distilled water is dropped to the surface of the surface-treated steel plate with a droplet volume of 2μl. After 1 second, the distilled water is dropped by θ/2 The contact angle is measured using the method, and the average value of the contact angles of 5 drops is used 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 plate to Cr was measured by XPS. Sputtering was not performed during the measurement. From the integrated intensity of the narrow spectrum of K2p, Na1s, Ca2p, Mg1s and Cr2p on the surface of the sample, the atomic ratio is quantified by the relative sensitivity coefficient method, and the (K atomic ratio + Na atomic ratio + Ca atomic ratio + Mg atomic ratio )/Cr atomic ratio. The XPS measurement system uses the scanning X-ray photoelectric spectroscopic analysis device PHI X-tool manufactured by Ulvac-Phi Company. The X-ray source is monochromatic AlKα ray, the voltage is 15kV, the beam diameter is 100μmφ, and the grazing angle is 45°.

(Atomic ratio of Ni on the surface) The atomic ratio of Ni content to Cr on the outermost surface of the surface-treated steel plate was measured by XPS. Sputtering was not performed during the measurement. From the integrated intensity of the narrow spectrum of Ni2p and Cr2p on the surface of the sample, the atomic ratio is quantified by the relative sensitivity coefficient method, and the Ni atomic ratio/Cr atomic ratio is calculated. The XPS measurement system uses the scanning X-ray photoelectric spectroscopic analysis device PHI X-tool manufactured by Ulvac-Phi Company. The X-ray source is monochromatic AlKα ray, the voltage is 15kV, the beam diameter is 100μmφ, and the grazing angle is 45°.

Furthermore, the obtained surface-treated steel plate was evaluated for film wet adhesion, paint secondary adhesion, and weldability by the following methods. The evaluation results are listed in Table 4 and Table 5 together.

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

A phthalic acid copolymerized polyethylene terephthalate film was laminated on both surfaces of the obtained surface-treated steel plate with an elongation ratio of 3.1×3.1, a thickness of 25 μm, a copolymerization ratio of 12 mol%, and a melting point of 224°C to produce a laminated steel plate. The above-mentioned lamination is based on the conditions that the crystallization degree of the resin film becomes 10% or less. Specifically, the steel plate feeding speed is: 40m/min, the nip length of the rubber roller: 17mm, and the time until water cooling after pressing: 1 sec. implementation. In addition, the degree of crystallization of the resin film was determined by the density gradient tube method according to JIS K7112. In addition, the nip length refers to the length of the portion where the rubber roller and the steel plate meet in the conveying direction.

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

The surface of the obtained surface-treated steel plate was coated with an epoxy phenol-based paint, and dried at 210° C. for 10 minutes to produce a coated steel plate. The coating adhesion amount is 50mg/dm ² .

(Thin film corrosion resistance, coating corrosion resistance) On the film side of the laminated steel plate and the painted side of the painted steel plate, use a cutting knife to make a cross cut as deep as the bottom metal (steel plate). Cross-cut laminated steel plates and coated steel plates were immersed in a 55°C test solution containing a mixed aqueous solution of 1.5 mass% citric acid and 1.5 mass% salt for 96 hours. After immersion, cleaning and drying, apply cellophane adhesive tape to the film side of the laminated steel plate and the coating side of the coated steel plate, and peel off the tape by pulling it off. For the film corrosion resistance, the film peeling width (the total width of the left and right extensions from the cut portion) of any four locations of the cross-cut portion of the laminated steel plate was measured, and the average value of the four locations was calculated and regarded as the corrosion width. Regarding the coating corrosion resistance, the film peeling width (the total width of the left and right extensions from the cut section) was measured at any four locations of the cross-cut portion of the coated steel plate, and the average value of the four locations was calculated and regarded as the corrosion width. The film corrosion resistance and coating corrosion resistance were evaluated based on the following 4 standards. Practically speaking, when the evaluation is 1 to 3, it means excellent corrosion resistance. 1: The corrosion width is less than 0.3mm 2: The corrosion width is more than 0.3mm but less than 0.5mm. 3: The corrosion width is more than 0.5mm but less than 1.0mm 4: Corrosion width is more than 1.0mm

(Film wetting and adhesion) The film wettability and adhesion were evaluated by a 180° peeling test in a cooking environment with a temperature of 130°C and a relative humidity of 100% using the above-mentioned laminated steel plate. The specific order is as follows.

First, from each of the above-mentioned laminated steel plates, three test pieces with the front surface as the target surface and three test pieces with the back surface as the target surface were cut out, for a total of six test pieces. The dimensions of each test piece are 30mm in width and 100mm in length. Next, the film on the target surface was left at a position 15 mm from the upper part in the longitudinal direction of each test piece, and the film on the opposite side to the target surface was cut from the steel plate. With the steel plate perpendicular to the ground, fix the cut test piece from the bottom to 15mm in the direction of the length of the test piece. The part with a width of 30mm and a length of 15mm above the cutting position is placed on the film on the object surface. The state of connection hangs down. Then, install a 100g hammer on the hanging portion with a width of 30mm and a length of 15mm.

The test piece in this state was placed in a cooking environment with a temperature of 130°C and a relative humidity of 100% for 30 minutes, and then opened to the atmosphere. The length of the film peeling off the surface-treated steel plate from the surface-treated steel plate was defined as the film peeling length. For each laminated steel plate, the average value of the film peeling length among the six test pieces was calculated. Using the average value of the film peeling length obtained, the film wet adhesion was evaluated based on the following 4 criteria. Practically speaking, when the evaluation is 1 to 3, it means that the film has excellent wet adhesion. 1: The peeling length does not reach 20mm 2: The peeling length is more than 20mm and less than 40mm 3: The peeling length is more than 40mm and less than 60mm 4: The peeling length is more than 60mm

(Secondary paint adhesion) Two coated steel plates produced under the same conditions were sandwiched between nylon adhesive films and laminated with the painted surfaces facing each other. Then, the pressure was 2.94×10 ⁵ Pa and the temperature was 190°C. Carry out lamination under pressing conditions with a pressing time of 30 seconds. Subsequently, this was divided into 5 mm wide test pieces. The divided test pieces were immersed in a 55°C test solution containing a mixed aqueous solution containing 1.5% by mass citric acid and 1.5% by mass salt for 168 hours. After immersion, washing and drying, the two steel plates of the divided test pieces were peeled off using a tensile testing machine, and the tensile strength during peeling was measured. The average value of three test pieces was evaluated based on the following criteria. Practically speaking, when the evaluation is 1 to 3, it means that the secondary adhesion of the paint is excellent. 1: More than 2.5kgf 2: More than 2.0kgf but less than 2.5kgf 3: More than 1.5kgf but less than 2.0kgf ×: Less than 1.5kgf

(Weldability) The obtained surface-treated steel plate was subjected to a heat treatment at 210°C for 10 minutes assuming a coating and baking step, and then two samples were processed with a DR type 1 mass % Cr-Cu electrode (tip diameter 2.3mm, curvature R40mm electrode) and apply electricity using the following conditions. ･Transistor power supply made by Amada Miyachi Co., Ltd.: MDA-8000A ･Soldering head: AH-200 ･Pressure: 40kgf ･Power-on time: 1.6msec. (slope 0.2msec.) ･Waveform: Rectangular wave

From the lower limit current with sufficient strength and the upper limit current without scattering, find the appropriate current range (=upper limit current - lower limit current), and evaluate based on the following 4 criteria. Practically speaking, when the evaluation is 1 to 3, it means excellent weldability. 1: 2.5kA or more 2: Above 2.0kA, less than 2.5kA 3: 1.5kA or more, 2 less than .0kA 4: Less than 1.5kA

From the results shown in Tables 4 and 5, it can be seen that the surface-treated steel plates that meet the conditions of the present invention still have excellent film corrosion resistance, coating corrosion resistance, and film wettability even if they are not produced using hexavalent chromium. Adhesion, secondary paint adhesion, and weldability.

Claims (6)

A surface-treated steel plate, which has a steel plate, a Ni-containing layer arranged on at least one surface of the steel plate, a metal Cr layer arranged on the Ni-containing layer, and an oxide Cr layer arranged on the metal Cr layer, wherein water The contact angle is below 50°, The total atomic ratio of K, Na, Mg, and Ca adsorbed on the surface relative to Cr is 5.0% or less. For example, for the surface-treated steel plate in claim 1, the Ni adhesion amount of the Ni-containing layer is 200 mg/m ² or more and 2000 mg/m ² or less per side of the steel plate. For example, the surface-treated steel plate of claim 1 or 2, wherein the Cr adhesion amount of the aforementioned metal Cr layer is 2 mg/m 2 or ^more but not 40 mg/m ² per single side of the aforementioned steel plate. For example, the surface-treated steel plate according to any one of claims 1 to 3, wherein the Cr adhesion amount of the aforementioned Cr oxide layer is not less than 0.1 mg/m 2 and not ^more than 15.0 mg/m ² per single side of the aforementioned steel plate. The surface-treated steel plate according to any one of claims 1 to 4, wherein the atomic ratio of Ni to Cr in the surface of the surface-treated steel plate is less than 100%. A method of manufacturing a surface-treated steel plate, which includes a steel plate, 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 an oxide Cr layer disposed on the metal Cr layer. The manufacturing method of surface-treated steel plate has the following steps: The electrolyte preparation step of preparing an electrolyte containing trivalent chromium ions, the cathodic electrolytic treatment step of cathodic electrolytic treatment of a steel plate having a Ni-containing layer on at least one side in the aforementioned electrolytic solution, and the cathodic electrolytic treatment step of subjecting the steel plate after the aforementioned cathodic electrolytic treatment to at least 1 water washing step, In the aforementioned electrolyte preparation step, a trivalent chromium ion source, a carboxylic acid compound, and water are mixed, the pH is adjusted to 4.0~7.0, and the temperature is adjusted to 40~70°C to prepare the aforementioned electrolyte, and the aforementioned water washing step , at least in the final water wash, use water with a conductivity of less than 100 μS/m.