JP2020117748A - Steel sheet for can, and method of manufacturing the same - Google Patents

Abstract

To provide a steel sheet for a can excellent in coating material adhesion, and a method of manufacturing the steel sheet.SOLUTION: A steel sheet for a can has, on a surface of the steel sheet, a metallic chromium layer and a chromium hydration oxide layer in this order from a side of the steel sheet. A coating amount of the chromium hydration oxide layer in terms of chromium is 3.0 mg/mor more and 10.0 mg/mor less. A peak area ratio of chromium hydroxide to chromium oxide, acquired by X-ray photoelectron spectroscopy on a top surface of the chromium hydration oxide layer is 1.00 or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a steel sheet for cans and a method for manufacturing the steel sheet.

Cans, which are containers applied to beverages and foods, are used all over the world because they can store contents for a long time. The can is squeezed on a metal plate, ironed, stretched, and bent to integrally mold the bottom and the body of the can, and then a two-piece can that is tightened with an upper lid and the metal plate is processed into a tubular shape, It is roughly divided into a can body welded by a seam method and a three-piece can in which both ends thereof are wound with a lid.

Conventionally, Sn-plated steel sheets (so-called tinplate) have been widely used as steel sheets for cans.
In recent years, an electrolytic chromate-treated steel sheet having a metal chromium layer and a hydrated chromium oxide layer (hereinafter, also referred to as tin-free steel (TFS)) is cheaper than tinplate, and thus its application range is expanding. ..

On the other hand, TFS may be inferior in weldability as compared with tinplate. The reason is that the surface chrome hydrated oxide layer undergoes a dehydration condensation reaction due to a baking treatment after coating or a heat treatment after laminating an organic resin film, thereby increasing the contact resistance.
Therefore, the current TFS enables welding by mechanically polishing and removing the chromium hydrated oxide layer immediately before welding.
However, in industrial production, there are many problems such as a risk that the metal powder after polishing is mixed into the contents, an increase in maintenance load such as cleaning of the can making device, and a risk of a fire caused by the metal powder.

Therefore, a technique for welding TFS without polishing has been proposed in Patent Document 1, for example. According to the technique disclosed in Patent Document 1, the granular protrusions made of metallic chromium destroy the chromium hydrated oxide layer, which is a welding inhibitor of the surface layer, during welding, thereby reducing the contact resistance and improving the weldability. Expected to improve.

JP, 11-189898, A

However, when the inventors of the present invention have examined the steel sheet for cans (Invention Example 4) specifically described in paragraphs [0035] to [0037] of Patent Document 1, as a result, the paint adhesion is insufficient. was there.

Therefore, an object of the present invention is to provide a steel sheet for cans having excellent paint adhesion and a method for producing the same.

As a result of earnest studies by the present inventors, they found that the above object can be achieved when the outermost surface of the hydrated chromium oxide layer satisfies specific parameters, and completed the present invention.

That is, the present invention provides the following [1] to [9].
[1] A metal chromium layer and a chromium hydrated oxide layer are sequentially provided on the surface of the steel sheet from the steel sheet side, and the chromium-deposited amount of the chromium hydrated oxide layer is 3.0 mg/m ² or more. The can is 10.0 mg/m ² or less, and the peak area ratio of chromium hydroxide to chromium oxide is 1.00 or less, which is determined by X-ray photoelectron spectroscopy of the outermost surface of the hydrated chromium oxide layer. Steel plate.
[2] The steel sheet for a can according to [1], wherein the peak area ratio is 0.80 or more.
[3] The steel sheet for a can according to [1] or [2], wherein the amount of the metal chromium layer deposited is 50 mg/m ² or more and 200 mg/m ² or less.
[4] The steel sheet for a can according to any one of [1] to [3], wherein the metal chromium layer includes a base and granular projections provided on the base.
[5] The steel plate for a can according to [4], wherein the granular projections have a maximum particle size of 150 nm or less and a number density per unit area of 10 particles/μm ² or more.
[6] A method for producing a steel sheet for a can, which comprises obtaining the steel sheet for a can according to any one of [1] to [5], wherein an aqueous solution containing a hexavalent chromium compound is used to produce a steel sheet. The cathodic electrolysis treatment C1, the anodic electrolysis treatment A1, the cathodic electrolysis treatment C2, and the anodic electrolysis treatment A2 are performed in this order, and the electric quantity density of the anodic electrolysis treatment A2 is 0.1 C/dm ² or more and 5.0 C/dm2. The manufacturing method of the steel plate for cans which is ² or less.
[7] The aqueous solution contains a hexavalent chromium compound, a fluorine-containing compound, and a first aqueous solution containing SO ₄ ²⁻ , a hexavalent chromium compound, and a fluorine-containing compound, and SO ₄ ²⁻ A second aqueous solution which does not substantially contain, and is subjected to the cathodic electrolysis treatment C1 using the first aqueous solution, and the anodic electrolysis treatment A1 and the cathodic electrolysis treatment are performed using the second aqueous solution. The method for producing a steel sheet for a can according to [6] above, wherein C2 and the anodic electrolytic treatment A2 are performed.
[8] The first aqueous solution has a Cr amount of 0.5 mol/L or more, an F amount of 0.20 mol/L or more, and an SO ₄ ²⁻ amount of 0.009 mol/L or more, and the second aqueous solution. Is the method for producing a steel sheet for a can according to the above [7], wherein the Cr amount is 0.5 mol/L or more and the F amount is 0.05 mol/L or more.
[9] The method for producing a steel sheet for a can according to any of [6] to [8], wherein the anodic electrolytic treatment A2 is the final electrolytic treatment.

ADVANTAGE OF THE INVENTION According to this invention, the steel plate for cans excellent in paint adhesiveness, and its manufacturing method can be provided.

It is sectional drawing which shows an example of the steel plate for cans of this invention typically.

[Steel plate]
FIG. 1 is a cross-sectional view schematically showing an example of the steel plate for a can of the present invention.
As shown in FIG. 1, it has a steel plate 2. The steel plate 1 for a can further has a metal chromium layer 3 and a chromium hydrate oxide layer 4 on the surface of the steel plate 2 in order from the steel plate 2 side.
The metallic chrome layer 3 preferably includes a flat plate-shaped base portion 3a that covers the steel plate 2, and granular projections 3b provided on the base portion 3a. In this case, the chromium hydrated oxide layer 4 is arranged on the metallic chromium layer 3 so as to follow the shape of the granular protrusions 3b. The amount of chromium equivalent adhesion on the hydrated chromium oxide layer 4 is 3.0 mg/m ² or more and 10.0 mg/m ² or less. The amount of adhesion is the amount of adhesion per one side of the steel sheet (the same applies hereinafter).
The peak area ratio of chromium hydroxide to chromium oxide (chromium hydroxide/chromium oxide) determined by X-ray photoelectron spectroscopy on the outermost surface of chromium hydrated oxide layer 4 is 1.00 or less. ..

Such a steel sheet for cans of the present invention has excellent paint adhesion. The reason is presumed as follows.
First, the hydrated chromium oxide forming the hydrated chromium oxide layer contains chromium oxide and chromium hydroxide. Of these, chromium hydroxide (particularly, the hydroxy group contained in chromium hydroxide) is effective for paint adhesion. For this reason, a certain amount of hydrated chromium oxide (chromium hydroxide) is required for paint adhesion, and the amount of chromium equivalent adhered to the hydrated chromium oxide layer should be 3.0 mg/m ² or more. To do.
However, if the amount of chromium hydrated oxide (chromium hydroxide) is too large, the chromium hydrated oxide layer itself may cause cohesive failure, and good paint adhesion may not be obtained.
Therefore, the adhesion amount in terms of chromium of the hydrated chromium oxide layer is set to 10.0 mg/m ² or less, and the peak area ratio (chromium hydroxide) obtained by X-ray photoelectron spectroscopy of the outermost surface of the hydrated chromium oxide layer. Substance/chromium oxide) to 1.00 or less.
As a result, an appropriate amount of hydrated chromium oxide (chrome hydroxide) is obtained, and good paint adhesion is obtained.

Hereinafter, each structure of the steel sheet for a can of the present invention will be described in more detail.

<Steel plate>
The type of steel sheet is not particularly limited. Generally, a steel plate used as a container material (for example, a low carbon steel plate or an ultra low carbon steel plate) can be used. The manufacturing method and material of the steel sheet are not particularly limited. It is manufactured through the steps of hot rolling, pickling, cold rolling, annealing, temper rolling, etc. from the usual billet manufacturing process.

<Metal chrome layer>
The steel plate for a can of the present invention has a metal chromium layer on the surface of the above-mentioned steel plate.
The role of metallic chromium in general TFS is to suppress the surface exposure of the steel sheet and improve the corrosion resistance.
For the reason that corrosion resistance of a steel sheet for cans is excellent, the adhesion amount of the metal chromium layer, 50 mg / ^{m 2} or more preferably, 60 mg / ^{m 2} or more preferably, 65 mg / ^{m 2} or more is more preferable, 70 mg / ^{m 2} or more Is particularly preferable.

On the other hand, when the amount of metallic chromium is too large, the metallic chromium having a high melting point covers the entire surface of the steel sheet, and the welding strength may be lowered and dust may be significantly generated during welding, which may deteriorate the weldability.
The adhesion amount of the metal chromium layer is preferably 200 mg/m ² or less, more preferably 180 mg/m ² or less, still more preferably 160 mg/m ² or less, because the steel plate for a can has excellent weldability.

<<Measurement method of adhesion amount>>
The adhesion amount of the metallic chromium layer and the adhesion amount of chromium hydrate oxide layer, which will be described later, in terms of chromium are measured as follows.
First, the amount of chromium (total amount of chromium) is measured using a fluorescent X-ray device for the steel sheet for cans on which the metallic chromium layer and the hydrated chromium oxide layer have been formed. Then, the steel plate for a can is subjected to an alkali treatment of being immersed in 7.5N-NaOH at 90° C. for 10 minutes, and then the amount of chromium (the amount of chromium after the alkali treatment) is measured again using the fluorescent X-ray device. .. The amount of chromium after alkali treatment is defined as the amount of metal chromium layer deposited.
Next, (amount of alkali-soluble chromium)=(amount of total chromium)−(amount of chromium after alkali treatment) is calculated, and the amount of alkali-soluble chromium is defined as the amount of chromium equivalent adhered to the hydrated chromium oxide layer.

Such a metallic chromium layer preferably includes a base and granular projections provided on the base. Next, each of these parts included in the metal chromium layer will be described in detail.

<Base of metal chrome layer>
The base of the metal chromium layer mainly plays a role of covering the surface of the steel sheet and improving the corrosion resistance.
In addition to the corrosion resistance generally required for TFS, the base portion of the metal chromium layer in the present invention has a granular projection provided on the surface layer that breaks the base portion when the steel sheets for cans inevitably come into contact with each other during handling. It is preferable to ensure a sufficient uniform thickness so that the steel sheet is not exposed.

From such a viewpoint, the present inventors conducted a rubbing test between steel sheets for cans and investigated the rust resistance. As a result, it has been found that if the thickness of the base of the metal chromium layer is 7.0 nm or more, the rust resistance is excellent. That is, the thickness of the base of the metal chromium layer is preferably 7.0 nm or more, more preferably 9.0 nm or more, and further preferably 10.0 nm or more, because the can steel sheet has excellent rust resistance.
On the other hand, the upper limit of the thickness of the base of the metal chromium layer is not particularly limited, but is, for example, 20.0 nm or less, preferably 15.0 nm or less.

(Method of measuring thickness)
The thickness of the base of the metallic chromium layer is measured as follows.
First, a cross-sectional sample of a steel plate for a can on which a metal chromium layer and a hydrated chromium oxide layer were formed was prepared by a focused ion beam (FIB) method and observed with a scanning transmission electron microscope (TEM) at 20,000 times. To do. Next, by observing the cross-sectional shape with a bright field image, paying attention to the part where there is no granular protrusion and only the base part, line analysis by energy dispersive X-ray spectroscopy (EDX), and the intensity curves of chromium and iron : Distance, vertical axis: strength) to obtain the thickness of the base. At this time, more specifically, in the strength curve of chromium, the point where the strength is 20% of the maximum value is the outermost layer, and the cross point with the strength curve of iron is the boundary point with iron. Is the thickness of the base.

For reasons of rust resistance of the steel sheet for cans is excellent, the adhesion amount of the base of the metallic chromium layer, 10 mg / ^{m 2} or more preferably, 30 mg / ^{m 2} or more preferably, 40 mg / ^{m 2} or more is more preferable.

<<Granular protrusions of metal chrome layer>>
The granular protrusions of the metal chromium layer are formed on the surface of the base described above, and mainly play a role of reducing the contact resistance between the steel sheets for cans and improving the weldability. The presumed mechanism by which the contact resistance decreases is described below.
Since the chromium hydrated oxide layer coated on the metallic chromium layer is a non-conductive film, it has a larger electric resistance than metallic chromium and becomes a hindrance factor for welding. When granular projections are formed on the surface of the base of the metallic chromium layer, the granular projections destroy the chromium hydrate oxide layer due to the surface pressure when the steel sheets for cans are brought into contact during welding, and the welding current conduction point And the contact resistance is significantly reduced.

If the metallic chrome layer has too few granular projections, the number of current-carrying points during welding may be reduced and contact resistance may not be reduced, resulting in poor weldability.
The number density of the granular projections per unit area is preferably 10 pieces/μm ² or more because the steel plate for a can has excellent weldability. 15 pieces/μm ² or more is preferable, 20 pieces/μm ² or more is more preferable, 30 pieces/μm ² or more is further preferable, and 50 pieces/μm ² or more is used because the weldability of the steel sheet for cans is more excellent. Particularly preferable, and 100/μm ² or more is most preferable.

On the other hand, if the number density of the granular protrusions per unit area is too high, the color tone may be affected. The number density of the granular projections per unit area is preferably 10,000 pieces/μm ² or less, more preferably 5,000 pieces/μm ² or less, and 1,000 pieces because the surface appearance of the steel sheet for cans is excellent. /Μm ² or less is more preferable, and 800/μm ² or less is particularly preferable.

If the maximum particle size of the granular projections of the metal chromium layer is too large, it may affect the color tone of the steel sheet for cans, resulting in a brown pattern and inferior surface appearance. The reason is that the granular projections absorb light on the short wavelength side (blue system) and the reflected light is attenuated to give a reddish brown color; the granular projections scatter reflected light. , It becomes dark due to the reduction of the overall reflectance;

Therefore, the maximum particle size of the granular protrusions of the metal chromium layer is preferably 150 nm or less, more preferably 140 nm or less, further preferably 130 nm or less, and particularly preferably 110 nm or less. Thereby, the surface appearance of the steel sheet for cans is excellent. It is considered that this is because the particle diameter of the granular protrusions is reduced, whereby absorption of light on the short wavelength side is suppressed and scattering of reflected light is suppressed.
The lower limit of the maximum particle size is not particularly limited, but is preferably 10 nm or more.

(Measurement method of particle size of granular projections and number density per unit area)
The particle size and the number density per unit area of the granular protrusions of the metallic chromium layer are measured as follows.
First, carbon is vapor-deposited on the surface of the steel plate for a can on which the metal chromium layer and the hydrated chromium oxide layer have been formed, and a sample for observation is prepared by the extraction replica method. A photograph was taken at 1,000 times, the photographed picture was binarized using software (trade name: ImageJ), and image analysis was performed. And the number density per unit area is calculated. The maximum particle size is the maximum particle size in the observation field of view captured in 5 fields of view at 20,000 times, and the number density per unit area is the average of 5 fields.

<Chromium hydrate oxide layer>
Chromium hydrate oxide is deposited on the surface of the steel sheet at the same time as metallic chromium, and plays a role of improving corrosion resistance. In addition, the hydrated chromium oxide improves the paint adhesion, as described above.

<<Adhesion amount>>
In order to secure the corrosion resistance of the steel sheet for cans and the adhesiveness of the coating material, the chromium-emulsion amount of the hydrated chromium oxide layer is 3.0 mg/m ² or more.

On the other hand, chromium hydrated oxide has inferior conductivity as compared with metallic chromium, and if the amount is too large, it causes excessive resistance during welding, and various welding defects such as blowholes due to the occurrence of dust and splash and excessive fusion welding. In some cases, resulting in poor weldability of the steel sheet for cans.
Further, as described above, if the amount of hydrated chromium oxide is too large, good paint adhesion may not be obtained.
Therefore, the adhesion amount of chromium hydrated oxide layer in terms of chromium is 10.0 mg/m ² or less because the weldability of the steel sheet for cans and the coating adhesion are excellent, and the weldability of the steel sheet for cans and From the reason that the paint adhesion is more excellent, it is preferably 9.0 mg/m ² or less, more preferably 8.0 mg/m ² or less, and further preferably 7.0 mg/m ² or less.

The method for measuring the amount of chromium equivalent attached to the hydrated chromium oxide layer is as described above.

<Peak area ratio>
Then, as described above, the peak area ratio of chromium hydroxide to chromium oxide, which is obtained by X-ray photoelectron spectroscopy of the outermost surface of the chromium hydrate oxide layer, is obtained because the paint adhesion of the steel sheet for cans is excellent. (Hereinafter, simply referred to as "peak area ratio (chromium hydroxide/chromium oxide)") is 1.00 or less.
The peak area ratio (chromium hydroxide/chromium oxide) of the hydrated chromium oxide layer is preferably 0.98 or less, and more preferably 0.95 or less, because the paint adhesion of the steel sheet for cans is more excellent. , 0.90 or less is more preferable.

On the other hand, as described above, a certain amount of chromium hydroxide is required for paint adhesion, and because the paint adhesion of the steel sheet for cans is more excellent, the peak area of the hydrated chromium oxide layer is The ratio (chromium hydroxide/chromium oxide) is preferably 0.70 or more, more preferably 0.75 or more, still more preferably 0.80 or more.

The peak area ratio (chromium hydroxide/chromium oxide) of the hydrated chromium oxide layer is determined by X-ray photoelectron spectroscopy of the outermost surface of the hydrated chromium oxide layer.
More specifically, first, a can steel sheet on which a metal chromium layer and a chromium hydrate oxide layer are formed is placed in an ultrahigh vacuum, and the chromium hydrate oxide layer of the chromium hydrate oxide layer is analyzed by X-ray photoelectron spectroscopy under the following conditions. Obtain the O(1s) spectrum of the outermost surface. After the background correction of the obtained O(1s) spectrum, the peak of chromium oxide appearing at 530.3±0.5 eV, the peak of chromium hydroxide appearing at 531.8±0.5 eV, and Separated into H ₂ O peaks appearing at 532.5±0.5 eV. The peaks are separated by the curve fitting method by the nonlinear least squares method using the Gauss-Lorentz composite function. Next, the area of each separated peak is calculated.
Thus, the ratio of the peak area of chromium hydroxide to the peak area of chromium oxide, that is, the peak area ratio (chromium hydroxide/chromium oxide) of the outermost surface of the hydrated chromium oxide layer is determined.

(Conditions for X-ray photoelectron spectroscopy)
・Measuring device: X-tool manufactured by Ulvac-PHI
・Excitation source: monoAl Kα 25W×15kV
・Analysis size: 100μmφ
・Take-out angle: 45°
・Pass Energy
Survey scan: 280.0 eV
Narrow scan: 112.0 eV

[Method of manufacturing steel sheet for cans]
Next, a method for manufacturing a steel sheet for a can of the present invention will be described.
The method for producing a steel sheet for cans of the present invention (hereinafter, also simply referred to as "the production method of the present invention") is a method for producing the steel sheet for cans of the present invention described above, and is a hexavalent chromium compound. Is a method for producing a steel sheet for cans, in which a steel sheet is subjected to cathodic electrolysis treatment C1, anodic electrolysis treatment A1, cathodic electrolysis treatment C2, and anodic electrolysis treatment A2 in this order using an aqueous solution containing.

Generally, in cathodic electrolysis in an aqueous solution containing a hexavalent chromium compound, a reduction reaction occurs on the surface of the steel sheet, and chromium metal and chromium hydrate oxide, which is an intermediate product to metallic chromium, are formed on the surface. Is deposited. This hydrated chromium oxide is non-uniformly dissolved by intermittent electrolytic treatment or long immersion in an aqueous solution of a hexavalent chromium compound. Granular projections are formed.

By performing the anodic electrolysis treatment between the cathodic electrolysis treatments, the metallic chromium is dissolved over the entire surface of the steel sheet and becomes the starting point of the granular projections made of metallic chromium formed by the subsequent cathodic electrolysis treatment. The base portion of the metal chromium layer is deposited by the cathode electrolysis treatment C1 before the anode electrolysis treatment A1, and the granular projections of the metal chromium layer are deposited by the cathode electrolysis treatment C2 after the anode electrolysis treatment A1.
Then, by performing the anode electrolysis treatment A2 after the cathode electrolysis treatment C2, the excessively formed chromium hydrated oxide layer is scraped (dissolved), and the chromium hydroxide on the outermost surface is appropriately reduced.

The amount of each deposited can be controlled by the electrolysis conditions in each electrolytic treatment.
Hereinafter, the aqueous solution and each electrolytic treatment used in the production method of the present invention will be described in detail.

<Aqueous solution>
The aqueous solution used in the production method of the present invention contains at least a hexavalent chromium compound.
The aqueous solution used in the production method of the present invention is an aqueous solution used for the cathodic electrolysis treatment C1 (first aqueous solution), and an aqueous solution used for the anodic electrolysis treatment A1, the cathodic electrolysis treatment C2, and the anodic electrolysis treatment A2 (second aqueous solution). It is preferable to include and.

<First aqueous solution>
As described above, it is preferable to perform the cathodic electrolysis treatment C1 using the first aqueous solution.
It is preferable that the first aqueous solution contains a hexavalent chromium compound, a fluorine-containing compound, and SO ₄ ²⁻ .

Ions (for example, F ⁻ , SiF ₆ ²⁻ ) and SO ₄ ²⁻ dissociated from the fluorine-containing compound participate in the reduction reaction and the oxidation reaction of the hexavalent chromium ion in the electrolytic treatment.
SO ₄ ²⁻ improves the deposition efficiency of metallic chromium in the cathodic electrolysis treatment. In the cathodic electrolysis treatment, the base of the metal chromium layer is deposited with high efficiency and stably for a long time, as compared with the case of using an aqueous solution containing no SO ₄ ²⁻ .

Examples of the hexavalent chromium compound include chromium trioxide (CrO ₃ ); potassium dichromate (K ₂ Cr ₂ O ₇ ) and other dichromates; and potassium chromate (K ₂ CrO ₄ ) and other chromates. And the like.
Examples of the fluorine-containing compound include hydrofluoric acid (HF), potassium fluoride (KF), sodium fluoride (NaF), hydrosilicofluoric acid (H ₂ SiF ₆ ), and/or a salt thereof. Examples of the hydrosilicofluoric acid salt include sodium silicofluoride (Na ₂ SiF ₆ ), potassium silicofluoride (K ₂ SiF ₆ ), ammonium silicofluoride ((NH ₄ ) ₂ SiF ₆ ), and the like.
SO ₄ ²⁻ is blended in the form of sulfuric acid (H ₂ SO ₄ ); sulfate such as sodium sulfate (Na ₂ SO ₄ ), calcium sulfate (CaSO ₄ ); It is preferable.

(Cr amount)
In the first aqueous solution, the amount of Cr is preferably 0.5 mol/L or more, more preferably 0.7 mol/L or more, still more preferably 1.0 mol/L or more.
On the other hand, in the first aqueous solution, the amount of Cr is preferably 5.0 mol/L or less, more preferably 3.0 mol/L or less.

(F amount)
In the first aqueous solution, the amount of F is preferably 0.10 mol/L or more, more preferably 0.15 mol/L or more, further preferably 0.20 mol/L or more, particularly preferably 0.25 mol/L or more.
On the other hand, in the first aqueous solution, the amount of F is preferably 5.00 mol/L or less, more preferably 4.00 mol/L or less, and further preferably 3.00 mol/L or less.

(SO ₄ ^2- amount)
In the first aqueous solution, the SO ₄ ²⁻ amount is preferably 0.003 mol/L or more, more preferably 0.005 mol/L or more, and further preferably 0.009 mol/L or more.
On the other hand, in the first aqueous solution, the SO ₄ ²⁻ amount is preferably 0.090 mol/L or less, more preferably 0.080 mol/L or less, and further preferably 0.070 mol/L or less.

<<Second aqueous solution>>
As described above, it is preferable to perform the anodic electrolysis treatment A1, the cathodic electrolysis treatment C2, and the anodic electrolysis treatment A2 using the second aqueous solution.
It is preferable that the second aqueous solution contains a hexavalent chromium compound and a fluorine-containing compound and does not substantially contain SO ₄ ²⁻ .
Suitable examples of the hexavalent chromium compound and the fluorine-containing compound include the hexavalent chromium compound and the fluorine-containing compound described as the components contained in the first aqueous solution.

In the second aqueous solution, the fluorine-containing compound affects the dissolution of the hydrated chromium oxide during immersion, and the dissolution of the metallic chromium and the hydrated chromium oxide during the anodic electrolysis treatment (anodic electrolysis treatment A1). It has a great influence on the form of metallic chromium deposited in the cathodic electrolysis treatment (cathodic electrolysis treatment C2).
The same effect can be obtained with SO ₄ ²⁻ , but the effect becomes excessive, and a huge granular projection is locally formed due to the non-uniform dissolution of hydrated chromium oxide. In some cases, the dissolution of metallic chromium in A1) progresses violently, making it difficult to form fine granular projections.
Therefore, the second aqueous solution does not contain SO ₄ ²⁻ , except for SO ₄ ²⁻ which is inevitably mixed. That is, the second aqueous solution does not substantially contain SO ₄ ²⁻ .

(Cr amount)
In the second aqueous solution, the amount of Cr is preferably 0.1 mol/L or more, more preferably 0.3 mol/L or more, still more preferably 0.5 mol/L or more.
On the other hand, in the second aqueous solution, the amount of Cr is preferably 5.0 mol/L or less, more preferably 3.0 mol/L or less.

(F amount)
In the second aqueous solution, the amount of F is preferably 0.01 mol/L or more, more preferably 0.03 mol/L or more, still more preferably 0.05 mol/L or more. As a result, in the anodic electrolytic treatment A1, fine metal chromium is uniformly dissolved over the entire surface, and it is easy to obtain fine granular protrusion generation sites in the cathodic electrolytic treatment C2.
On the other hand, in the second aqueous solution, the amount of F is preferably 0.50 mol/L or less, more preferably 0.40 mol/L or less, and further preferably 0.30 mol/L or less.

The second aqueous solution contains substantially no SO ₄ ²⁻ . Specifically, the SO ₄ ²⁻ amount in the second aqueous solution is preferably less than 0.0010 mol/L, more preferably less than 0.0001 mol/L.

The liquid temperature of each aqueous solution in each electrolytic treatment is preferably 20° C. or higher and 80° C. or lower, and more preferably 40° C. or higher and 60° C. or lower.

<Cathode electrolytic treatment C1>
In the cathodic electrolysis treatment C1, it is preferable to use the above-mentioned first aqueous solution.
In the cathodic electrolysis treatment C1, metallic chromium and chromium hydrate oxide are deposited.
In this case, from the viewpoint of a proper precipitation amount, the electric charge density of the cathode electrolytic treatment C1 (the product of the current density and the current time), 5C / dm ² or more preferably, 10C / dm ² or more is more preferable. On the other hand, the electric quantity density of the cathodic electrolysis treatment C1 is preferably 50 C/dm ² or less, and more preferably 45 C/dm ² or less.
The current density (unit: A/dm ² ) and energization time (unit: sec.) of the cathodic electrolysis treatment C1 are appropriately set from the above-mentioned electricity amount density.

<Anodic electrolytic treatment A1>
In the anodic electrolytic treatment A1, it is preferable to use the above-mentioned second aqueous solution.
The anodic electrolysis treatment A1 plays a role of dissolving the metal chromium deposited in the cathodic electrolysis treatment C1 and forming the generation sites of the granular protrusions of the metal chrome layer in the cathodic electrolysis treatment C2.
At this time, if the dissolution in the anodic electrolysis treatment A1 is too strong or too weak, the number of generated sites is reduced, the number density of the granular projections is decreased, or the dissolution progresses unevenly, and the distribution of the granular projections varies. It may occur or the thickness of the base of the metal chromium layer may be reduced. In particular, if the electricity quantity density of the anodic electrolytic treatment A1 is too low, the particle size of the granular projections formed by the cathodic electrolytic treatment C2 may become too small.
From the above point of view, the electric charge density of the anodic electrolysis treatment A1 (product of current density and power supply time) is preferably from 0.1 C / dm ² or more, 0.3 C / dm ² or more, more preferably, 1.0 C / More preferably dm ² or more. On the other hand, the electric charge density of the anodic electrolysis treatment A1 is preferably less than 5.0C / dm ^2, more preferably not more than 3.0C / dm ^2.
The current density (unit: A/dm ² ) and energization time (unit: sec.) of the anodic electrolysis treatment A1 are appropriately set from the above-mentioned electricity amount density.

<Cathode electrolytic treatment C2>
In the cathodic electrolysis treatment C2, it is preferable to use the above-mentioned second aqueous solution.
In the cathodic electrolysis treatment C2, the granular projections of the metal chromium layer are generated starting from the above-mentioned generation site. At this time, if the electricity density is too high, the granular projections of the metal chromium layer may grow rapidly and the grain size may become coarse.
From the above point of view, the electric charge density of the cathode electrolytic treatment C2 (the product of the current density and power supply time) is preferably less than 50.0C / dm ^2, and more preferably at most 45.0C / dm ^2. On the other hand, the electric charge density of the cathode electrolytic treatment C2 is, for example, 1.0 C / dm ² or more, preferably 2.0 C / dm ² or more, 5.0C / dm ² or more, more preferably, 10.0c / dm ² or more is more preferable, 15.0 C/dm ² or more is particularly preferable, and 20.0 C/dm ² or more is the most preferable.
The current density (unit: A/dm ² ) and energization time (unit: sec.) of the cathodic electrolysis treatment C2 are appropriately set from the above-mentioned electricity amount density.

<Anodic electrolytic treatment A2>
In the anodic electrolytic treatment A2, it is preferable to use the above-mentioned second aqueous solution.
The anodic electrolytic treatment A2 plays a role of dissolving a part of the chromium hydrate oxide deposited in the cathodic electrolytic treatment C2.
At this time, if the electricity density of the anodic electrolytic treatment A2 is too high, the chromium hydrate oxide may be excessively dissolved or may be unevenly dissolved. On the other hand, if the electricity amount density of the anodic electrolysis treatment A2 is too low, the hydrated chromium oxide may not be sufficiently dissolved, and the above-mentioned effect may not be easily obtained.
From the above point of view, the electric charge density of the anodic electrolysis treatment A2 (the product of the current density and the current time) is 0.1 C / dm ² or more 5.0C / dm ² or less.
Electric charge density of the anodic electrolysis treatment A2, the reason that the paint adhesion of the can steel sheet for more excellent, preferably 0.5 C / dm ² or more, 1.0 C / dm ² or more, more preferably, 2.0 C / More preferably dm ² or more.
On the other hand, the electric quantity density of the anodic electrolytic treatment A2 is preferably 4.0 C/dm ² or less.
The current density (unit: A/dm ² ) and energization time (unit: sec.) of the anodic electrolysis treatment A2 are appropriately set from the above-mentioned electricity amount density.

The anodic electrolytic treatment A2 is preferably the final electrolytic treatment. That is, it is preferable that no further electrolytic treatment (particularly cathodic electrolytic treatment) is performed after the anodic electrolytic treatment A2.

The number of passes of the cathodic electrolysis treatment C1, the anodic electrolysis treatment A1, the cathodic electrolysis treatment C2, and the anodic electrolysis treatment A2 may be one or two or more. When the number of passes is two or more, the total electricity density is within the above range.
Further, the cathodic electrolysis treatment C1, the anodic electrolysis treatment A1, the cathodic electrolysis treatment C2, and the anodic electrolysis treatment A2 may not be continuous electrolysis treatments. That is, in industrial production, the electrolysis may be intermittent electrolysis in which the electroless dipping time is inevitably present by performing electrolysis separately on a plurality of electrodes. In the case of intermittent electrolysis treatment, the total electricity quantity density is within the above range.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these.

<Production of steel sheet for cans>
Normal degreasing and pickling were performed on a steel plate with a tempering degree T4CA manufactured with a plate thickness of 0.22 mm, and then the aqueous solution shown in Table 1 below was circulated at 100 mpm by a pump in a flow cell to obtain a lead electrode. Was used and subjected to electrolytic treatment under the conditions shown in Table 2 below to produce a steel sheet for cans that was TFS. The steel plate for a can thus produced was washed with water and dried at room temperature using a blower.

More specifically, the cathodic electrolysis treatment C1 was performed using the first aqueous solution, and then the anodic electrolysis treatment A1, the cathodic electrolysis treatment C2, and the anodic electrolysis treatment A2 were performed in this order using the second aqueous solution.
In some comparative examples, some electrolytic treatment was not performed. In that case, "-" is described in Table 2 below.

<Adhesion amount, etc.>
With respect to the produced steel sheet for cans, the adhesion amount of the metal chromium layer and the adhesion amount of chromium hydrate oxide layer in terms of chromium (in the following Table 2, simply referred to as “adhesion amount”) were measured. The measuring method is as described above.
Further, the maximum grain size of the granular protrusions and the number density per unit area of the metal Cr layer of the manufactured can steel sheet were measured. The measuring method is as described above.
The results are shown in Table 2 below. When the measurement was not performed, "-" is shown in Table 2 below.

<Peak area ratio>
The peak area ratio (chromium hydroxide/chromium oxide) was determined by X-ray photoelectron spectroscopy on the outermost surface of the hydrated chromium oxide layer in the manufactured can steel sheet according to the method described above (only in Table 2 below). Notated as "peak area ratio"). The results are shown in Table 2 below.

<Evaluation>
The following evaluation was performed on the manufactured can steel sheet. The evaluation results are shown in Table 2 below. When not evaluated, "-" is described in Table 2 below.

<Surface appearance>
The L value of the manufactured steel sheet for cans was measured based on the Hunter color difference measurement specified in the old JIS Z 8730 (1980), and evaluated according to the following criteria. Practically, it can be evaluated that the surface appearance is excellent if it is "◎", "◎" or "○".
◎ ◎: L value 70 or more ◎: L value 67 or more and less than 70 ○: L value 63 or more and less than 67 △: L value 60 or more and less than 63 ×: L value less than 60

<< Weldability >>
The produced steel sheet for cans was subjected to heat treatment simulating thermocompression bonding of an organic resin film laminate and post-heating, and then the contact resistance was measured.
More specifically, first, the prepared steel sheet for cans was passed through a film laminating apparatus under the conditions that the roll pressure was 4 kg/cm ² , the plate feed rate was 40 mpm, and the surface temperature of the plate after passing the roll was 160° C. Then, it was post-heated in the batch furnace (maintained plate temperature was 210° C. for 120 seconds). Thus, the steel sheet for cans was heat-treated. The heat-treated can steel sheets were stacked. The stacked steel sheets for cans were sandwiched between electrodes (DR type 1 mass% Cr-Cu electrode processed with a tip diameter of 6 mm and a curvature of R40 mm), and a pressing force of 1 kgf/cm ² was maintained for 15 seconds. Then, the contact resistance between the steel sheets for cans was measured. The average value measured at 10 points was taken as the contact resistance value and evaluated according to the following criteria.
Practically, if "◎◎", "◎" or "○", excellent weldability can be evaluated.
◎ ◎: Contact resistance 50μΩ or less ◎: Contact resistance 50μΩ or more, 100μΩ or less ○: Contact resistance 100μΩ or more, 300μΩ or less △: Contact resistance 300μΩ or more, 1000μΩ or less ×: Contact resistance 1000μΩ or more

<<Paint adhesion>>
The prepared can steel sheet was coated with an epoxyphenol-based coating material at 50 mg/m ² and baked at 210° C. for 10 minutes. A nylon film was sandwiched between the coated surfaces of the two baked steel sheets for cans, preheated at 190° C. for 1 minute, then pressure-bonded at 3 kgf/cm for 30 seconds, and then sheared to a width of 5 mm. The peel strength between the steel sheets for cans was 3.33 mm/sec. Was measured at the pulling speed and evaluated according to the following criteria.
Practically, it can be evaluated that the coating adhesion is excellent if it is “◎◎”, “◎” or “○”.
◎ ◎: Peel strength 4.0 kgf/5 cm or more, less than 4.5 kgf/5 cm ◎: Peel strength 3.5 kgf/5 cm or more, less than 4.0 kgf/5 cm ○: Peel strength 3.0 kgf/5 cm or more, 3.5 kgf/ Less than 5 cm Δ: Peel strength 2.5 kgf/5 cm or more, less than 3.0 kgf/5 cm ×: Peel strength less than 2.5 kgf/5 cm

As is clear from the results shown in Table 2 above, the steel sheets for cans of Inventive Examples 1 to 8 were excellent in coating material adhesion, surface appearance and weldability.

On the other hand, in Comparative Example 1 in which the amount of chromium hydrated oxide adhered was large and the peak area ratio (chromium hydroxide/chromium oxide) was large, the paint adhesion was insufficient.
Further, in Comparative Example 2 in which the amount of hydrated chromium oxide was small, the paint adhesion was insufficient.
Further, in Comparative Example 3 in which the peak area ratio (chromium hydroxide/chromium oxide) was large, the paint adhesion was insufficient.
Further, Comparative Example 4 (corresponding to Invention Example 4 of Patent Document 1) in which the amount of hydrated chromium oxide adhered was large and the peak area ratio (chromium hydroxide/chromium oxide) was large The sex was insufficient.

1: Steel plate for cans 2: Steel plate 3: Metal chromium layer 3a: Base part 3b: Granular projections 4: Chromium hydrated oxide layer

Claims (9)

On the surface of the steel sheet, in order from the steel sheet side, having a metal chromium layer and a chromium hydrate oxide layer,
The amount of chromium equivalent adhered to the hydrated chromium oxide layer is 3.0 mg/m ² or more and 10.0 mg/m ² or less,
A steel sheet for a can having a peak area ratio of chromium hydroxide to chromium oxide of 1.00 or less, which is determined by X-ray photoelectron spectroscopy on the outermost surface of the hydrated chromium oxide layer. The steel plate for a can according to claim 1, wherein the peak area ratio is 0.80 or more. The steel plate for a can according to claim 1 or 2, wherein an adhesion amount of the metal chromium layer is 50 mg/m ² or more and 200 mg/m ² or less. The steel plate for a can according to any one of claims 1 to 3, wherein the metal chrome layer includes a base portion and granular projections provided on the base portion. The steel plate for a can according to claim 4, wherein the granular projections have a maximum particle size of 150 nm or less and a number density per unit area of 10 particles/μm ² or more. A method for producing a steel sheet for a can, comprising obtaining the steel sheet for a can according to claim 1.
Using an aqueous solution containing a hexavalent chromium compound, the steel sheet was subjected to cathodic electrolysis treatment C1, anodic electrolysis treatment A1, cathodic electrolysis treatment C2, and anodic electrolysis treatment A2 in this order,
Said electric charge density of the anodic electrolysis treatment A2 is at 0.1 C / dm ² or more 5.0C / dm ² or less, the manufacturing method of a steel sheet for cans. The aqueous solution is
A hexavalent chromium compound, a fluorine-containing compound, and a first aqueous solution containing SO ₄ ²⁻ ,
A hexavalent chromium compound, and a second aqueous solution containing a fluorine-containing compound and substantially not containing SO ₄ ²⁻ ,
Performing the cathodic electrolysis treatment C1 using the first aqueous solution,
The method for manufacturing a steel sheet for a can according to claim 6, wherein the anodic electrolysis treatment A1, the cathodic electrolysis treatment C2, and the anodic electrolysis treatment A2 are performed using the second aqueous solution. The first aqueous solution has a Cr amount of 0.5 mol/L or more, an F amount of 0.20 mol/L or more, and an SO ₄ ²⁻ amount of 0.009 mol/L or more,
The method for producing a steel sheet for a can according to claim 7, wherein the second aqueous solution has a Cr amount of 0.5 mol/L or more and an F amount of 0.05 mol/L or more. The method for manufacturing a steel sheet for a can according to claim 6, wherein the anodic electrolytic treatment A2 is a final electrolytic treatment.