AQUEOUS COMPOSITION, AND MANUFACTURING METHOD AND THINNING PROCESSING METHOD FOR STAINLESS STEEL USING SAME

Description

TECHNICAL FIELD

The present invention relates to an aqueous composition, and a manufacturing method for stainless steel and a method for thinning treatment of stainless steel, each using the aqueous composition, and particularly relates to an aqueous composition for thinning stainless steel, etc.

BACKGROUND ART

Because of its properties excellent in durability and weather resistance, stainless steel has recently been considered for application in various fields. For example, stainless steel is coming into widespread use in electronic components, battery current collector foils and automotive component housings.

For use in various products, stainless steel is known to be treated to increase its surface area (e.g., Patent Literature 1) and/or treated to form asperities on the surface of stainless steel (e.g., Patent Literature 2), etc.

CITATION LIST

Patent Literatures

• Patent Literature 1: JP 2011-168017 A
• Patent Literature 2: JP 2015-183239 A

SUMMARY OF INVENTION

Technical Problem

Stainless steel is desired to be thinned depending on the purpose of its use. In particular, there is a demand in some cases for stainless steel which has been thinned while maintaining its surface smoothness. Moreover, even when using conventional methods for manufacturing or surface treatment of stainless steel, etc., it was difficult to obtain stainless steel which has been thinned while sufficiently minimizing its surface roughness.

Solution to Problem

The present invention provides an aqueous composition, a manufacturing method for stainless steel, a method for thinning treatment of stainless steel, etc., as shown below.

Namely, the present invention encompasses the following embodiments.

• • [1] An aqueous composition for thinning stainless steel, comprising 0.01% to 10% by mass of hydrogen peroxide, 12.5% to 40% by mass of halide ions and 0% to 3.0% by mass of copper ions.
  • [2] The aqueous composition according to [1] above, comprising 0.1% to 5% by mass of hydrogen peroxide, 15% to 30% by mass of halide ions and 0% to 1.0% by mass of copper ions.
  • [3] A manufacturing method for stainless steel, comprising a thinning treatment step for thinning stainless steel with the aqueous composition according to [1] or [2] above.
  • [4] The manufacturing method for stainless steel according to [3] above, wherein the surface of the stainless steel after the thinning treatment has a mean roughness (Ra) of 0.35 μm or less and a maximum height (Rz) of 2.5 μm or less.
  • [5] The manufacturing method for stainless steel according to [3] or [4] above, wherein the density of the stainless steel after the thinning treatment is 4.5 g/cm³ or more.
  • [6] The manufacturing method for stainless steel according to any one of [3] to [5] above, wherein the density (g/cm³) of the stainless steel after the thinning treatment is 0.60-fold or more of the density (g/cm³) of the stainless steel before the thinning treatment.
  • [7] The manufacturing method for stainless steel according to any one of [3] to [6] above, wherein the thickness of the stainless steel after the thinning treatment is 100 μm or less.
  • [8] The manufacturing method for stainless steel according to any one of [3] to [7] above, wherein the thickness (μm) of the stainless steel after the thinning treatment is 0.95-fold or less of the thickness (μm) of the stainless steel before the thinning treatment.
  • [9] A method for thinning treatment of stainless steel, comprising a thinning treatment step wherein stainless steel is treated using the aqueous composition according to [1] above.

Advantageous Effects of Invention

According to the present invention, it is possible to achieve an aqueous composition which allows the thinning of stainless steel by simple procedures, and a manufacturing method for stainless steel and a method for thinning treatment of stainless steel, each involving the step of such thinning treatment. According to the present invention, for example, foil-shaped or plate-shaped stainless steel can be thinned while minimizing its surface roughness.

DESCRIPTION OF EMBODIMENTS

The present invention will be further described in more detail below. The present invention is not limited to the following descriptions, and various modifications may be made without departing from the spirit of the present invention.

[1. Aqueous Composition]

The aqueous composition of the present invention is used for thinning stainless steel, and comprises 0.01% to 10% by mass of hydrogen peroxide, 12.5% to 40% by mass of halide ions and 0% to 3.0% by mass of copper ions, each based on the total amount of the aqueous composition. In addition to these components, the aqueous composition of the present invention may comprise water, etc., especially ion exchanged water or ultrapure water.

Each component of the aqueous composition will be explained below.

<1-1. Hydrogen Peroxide>

The concentration of hydrogen peroxide in the aqueous composition is 0.01% to 10% by mass based on the total amount (total mass) of the aqueous composition, but it is preferably 0.05% to 7% by mass, 0.1% to 5% by mass or 0.15% to 7% by mass, more preferably 0.2% to 3% by mass or 0.3% to 4% by mass, even more preferably 0.3% to 2% by mass or 0.4% to 1.5% by mass, and particularly preferably 0.5% to 1% by mass, based on the total amount (total mass) of the aqueous composition.

Moreover, the lower limit of the concentration of hydrogen peroxide in the aqueous composition may be, for example, 0.001% by mass, 0.01% by mass, 0.05% by mass, 0.10% by mass, 0.15% by mass, 0.2% by mass, 0.25% by mass, 0.3% by mass, 0.35% by mass, 0.4% by mass, 0.45% by mass, based on the total amount (total mass) of the aqueous composition, while the upper limit of the concentration of hydrogen peroxide contained in the aqueous composition may be, for example, 9% by mass, 8% by mass, 7% by mass, 6% by mass, 5% by mass, 4% by mass, 4.0% by mass, 3.5% by mass, 3% by mass, 3.0% by mass, 2.5% by mass, 2% by mass, 2.0% by mass, 1.5% by mass, 1% by mass, 1.0% by mass, etc., based on the total amount (total mass) of the aqueous composition.

The concentration range of hydrogen peroxide may be selected from the above lower and upper limits combined as appropriate.

As a result of selecting the concentration of hydrogen peroxide from among the ranges mentioned above, the effect of the present invention tends to be achieved in a more preferred manner, and even when copper ions, halide ions and others described later are also contained in the aqueous composition, the possibility of heat generation or bubble formation associated with the decomposition of hydrogen peroxide can be suppressed to thereby ensure the safety of operation.

<1-2. Halide Ions (Halogen Ions)>

Halide ions to be contained in the aqueous composition may be of any type, and examples include fluoride ions, chloride ions, bromide ions and iodide ions, with chloride ions being more preferred in terms of easy handling and cost effectiveness.

Halogen compounds supplying halide ions are not limited in any way, and examples include hydrochloric acid, alkali metal halides (e.g., sodium halides and potassium halides), alkaline earth metal halides (e.g., calcium halides), ammonium halides, copper halides, and hydrogen halides. Among them, preferred are hydrochloric acid, alkali metal halides or hydrogen halides in terms of more effectively and reliably providing the effect of the present invention, and more preferred is hydrochloric acid or sodium chloride.

Such halogen compounds are used either alone or in combination. It should be noted that halogen compounds may overlap with copper compounds described later. For example, when a copper halide is used as a source of halide ions, this copper halide also falls within copper compounds described later, which serve as a copper ion source. Copper chloride is preferred as a copper halide. Halogen compounds (halide ions) are deemed to cause pitting corrosion on the passive film during the thinning treatment of the stainless steel surface.

The concentration of halide ions in the aqueous composition is 12.5% to 30% by mass based on the total amount (total mass) of the aqueous composition, but it is preferably 13% to 28% by mass or 14% to 29% by mass or 15% to 30% by mass, more preferably 16% to 26% by mass or 17% to 27% by mass, and particularly preferably 18% to 25% by mass, 19% to 26% by mass, or 20% to 25% by mass, based on the total amount (total mass) of the aqueous composition.

Moreover, the lower limit of the concentration of halide ions in the aqueous composition may be any of 8% by mass, 10% by mass, 12% by mass, 14% by mass, 15% by mass, 16% by mass, 17% by mass, 18% by mass, 19% by mass and 20% by mass, based on the total amount (total mass) of the aqueous composition, while the upper limit of the concentration of halide ions may be any of 30% by mass, 29% by mass, 28% by mass, 27% by mass, 26% by mass and 25% by mass, based on the total amount of the aqueous composition.

The concentration range of halide ions may be selected as appropriate from the above lower and upper limits combined as appropriate.

As a result of selecting the concentration of halide ions from among the ranges mentioned above, the effect of the present invention tends to be achieved in a more preferred manner. In more detail, in the aqueous composition whose concentration of halide ions is within the above range, thinning is attempted while preventing the progression of pitting corrosion reaction on stainless steel, and the decomposition reaction of hydrogen peroxide can also be prevented to ensure safety.

<1-3. Copper Ions>

The concentration of copper ions in the aqueous composition is 0% to 3% by mass based on the total amount (total mass) of the aqueous composition. Namely, the aqueous composition intended in the present invention is free from copper ions or has a copper ion content of 3% by mass or less based on the total amount (total mass) of the aqueous composition. Copper ions in the aqueous composition can be generated by mixing a copper compound serving as a copper ion source with other components. The copper ion source may be of any type, as long as it is a copper compound capable of supplying copper ions in the aqueous composition.

Examples of such a copper compound include copper sulfate (e.g., cupric sulfate), copper chloride (e.g., cupric chloride), copper tetrafluoroborate, cupric bromide, cupric oxide, copper phosphate, copper acetate, copper formate, copper nitrate and so on, which may be in anhydride form or in pentahydrate form. Among them, preferred is copper sulfate or copper chloride in terms of more effectively and reliably providing the effect of the present invention and in terms of easy handling and cost effectiveness, more preferred is cupric sulfate or cupric chloride, and even more preferred is cupric sulfate. These members may be used either alone or in combination.

It is inferred that copper ions contained in the aqueous composition will cause substitution reaction for nickel and chromium, which are components of stainless steel, during the thinning treatment, and substitution reaction products derived from copper ions are then removed to obtain an appropriate roughened pattern.

Moreover, in terms of the quality of stainless steel after the thinning treatment, particularly when the aqueous composition is used in the treatment of a stainless steel foil whose thickness is small, the content of copper ions is preferably adjusted to prevent the occurrence of extremely thin regions or pinholes, as described later.

The concentration of copper ions contained in the aqueous composition is 3% by mass or less, preferably 2% by mass or less, less than 1.5% by mass or 1.5% by mass or less, and more preferably 1.2% by mass or less or 1.0% by mass or less, and may be 0.75% by mass or less, 0.5% by mass or less, or less than 0.25% by mass. The concentration range of copper ions is 0% to 3% by mass, preferably 0% to 2% by mass or 0% to 1.5% by mass, more preferably 0% to 1.5% by mass or 0.1% to 1.2% by mass, and even more preferably 0.2% to 1.0% by mass, and may be 0.3% to 1.5% by mass.

The lower limit of the concentration of copper ions in the aqueous composition is 0% by mass based on the total amount (total mass) of the aqueous composition, but may be for example 0.00001% by mass (0.1 mass ppm), 0.0001% by mass (1 mass ppm), 0.001% by mass, 0.01% by mass, 0.02% by mass, 0.03% by mass, 0.05% by mass, 0.07% by mass, or 0.1% by mass, based on the total amount (total mass) of the aqueous composition.

Likewise, the upper limit of the concentration of copper ions in the aqueous composition may be, for example, 3% by mass, 2.5% by mass, 2% by mass, 1.7% by mass, 1.5% by mass, 1% by mass, 0.5% by mass, 0.3% by mass, 0.22% by mass, 0.16% by mass, 0.14% by mass, etc., based on the total amount of the aqueous composition. The concentration range of copper ions may be selected as appropriate from the above lower and upper limits combined as appropriate, for example, 0.0001% to 3% by mass, 0.001% to 3% by mass, 0.01% to 2% by mass, 0.01% to 1.7% by mass, 0.01% to 1.5% by mass, 0.02% to 1% by mass, 0.03% to 0.25% by mass, 0.03% to 0.20% by mass, 0.05% to 0.15% by mass, 0.05% to 0.12% by mass, etc.

As a result of selecting the concentration of copper ions from among the ranges mentioned above, the effect of the present invention tends to be achieved in a more preferred manner.

On the other hand, if the concentration of copper ions in the aqueous composition is too high, pinholes or extremely thin regions are more likely to occur on stainless steel after the thinning treatment. If the concentration of copper ions is too low, the thinning treatment will probably not proceed efficiently.

<1-4. Additives Contained in the Aqueous Composition>

The aqueous composition of the present invention may comprise additives as components other than hydrogen peroxide, copper ions and halide ions mentioned above, as long as the effect of the present invention is exerted. Examples of such additives include heterocyclic nitrogen compounds (azole compounds), organic solvents and so on. These additives are used either alone or in combination. Moreover, additives also include a surfactant, a pH adjuster and so on, but they are preferably not contained in the aqueous composition of the present invention.

The concentration of additives which may be contained in the aqueous composition is preferably 10% by mass or less, more preferably 5.0% by mass or less, even more preferably 2.0% by mass or less, and particularly preferably 1.0% by mass or less.

<1-5. Water>

The aqueous composition of the present invention may comprise water, and preferably comprises water. The water intended here is not limited in any way, but it is preferably water which has been treated to remove metal ions, organic impurities, particles and so on by distillation, ion exchange treatment, filter treatment, various adsorption treatments, etc., and it is more preferably pure water, and particularly preferably ultrapure water.

The content of water in the aqueous composition of the present invention is the balance of the composition (i.e., other than the individual components described above and additives described in detail later), and is not limited in any way, but it is preferably 50% to 98% by mass, more preferably 60% to 95% by mass, even more preferably 75% to 93% by mass, and particularly preferably 85% to 90% by mass, based on the total amount (total mass) of the aqueous composition.

It should be noted that the aqueous composition of the present invention is preferably in the form of a solution, and is preferably free from components which are non-soluble in the composition in the form of a solution, as exemplified by solid particles such as abrasive particles.

<1-6. Function and Properties of the Aqueous Composition>

The aqueous composition comprising the above individual components is considered to efficiently pursue thinning while preventing an extreme increase in roughness on the surface of stainless steel, i.e., the occurrence of a significantly uneven pattern, as shown below.

Halide ions are responsible for pitting corrosion of the oxide film which is usually formed on the surface of stainless steel. Copper ions have the effect of causing substitution reaction for nickel and chromium, which are components of stainless steel, as described above, and substitution reaction products derived from copper ions are then removed to allow thinning while forming some asperities on the surface of stainless steel.

Likewise, hydrogen peroxide serves to remove the above substitution reaction products derived from copper ions after the substitution reaction.

Moreover, the aqueous composition comprising copper ions and others whose content is adjusted within an appropriate range can prevent the occurrence of extremely thin regions or pinholes on stainless steel after the thinning treatment, particularly on a stainless steel foil after the thinning treatment.

The aqueous composition of the present invention may be prepared by stirring the hydrogen peroxide-containing component, the halide ion-supplying component and water mentioned above, optionally together with the copper ion-supplying component and other components, until a uniform mixture is obtained.

The properties of the aqueous composition are not limited in any way, but its pH value is preferably −1.0 to 4.0, more preferably −0.5 to 3.0, even more preferably −0.25 to 2.5, and particularly preferably −0.1 to 2.0, 0.0 to 1.5, 0.005 to 1.0, or 0.01 to 0.5. The pH value may be measured by the method described in the Example section.

[2. Manufacturing Method for Stainless Steel]

The manufacturing method for stainless steel of the present invention comprises a thinning treatment step wherein stainless steel is treated using the above aqueous composition. According to the manufacturing method for stainless steel of the present invention, for example, plate-shaped or foil-shaped stainless steel can be thinned, i.e., its thickness can be reduced while mostly maintaining its surface smoothness.

<2-1. Surface Roughness of Stainless Steel>

According to the manufacturing method for stainless steel of the present invention, the arithmetical mean roughness (Ra) on the surface of stainless steel (a stainless steel foil (film or sheet) also falls within stainless steel) after the thinning treatment can be kept at 0.35 μm or less. Namely, although surface roughness is often increased during the surface treatment of stainless steel, the value of arithmetical mean roughness (Ra) on the treated surface can be kept at 0.35 μm or less in the manufacturing method for stainless steel of the present invention. The value of arithmetical mean roughness (Ra) on the surface of stainless steel after the thinning treatment is preferably 0.34 μm or less, 0.33 μm or less, 0.32 μm or less, 0.31 μm or less, 0.30 μm or less, 0.29 μm or less or 0.28 μm or less, more preferably 0.27 μm or less or 0.26 μm or less, and particularly preferably 0.25 μm or less, 0.24 μm or less or 0.23 μm or less. Alternatively, the value of arithmetical mean roughness (Ra) on the stainless steel surface after the thinning treatment may be 0.4 μm or less, 0.5 μm or less or 0.6 μm or less.

The lower limit of arithmetical mean roughness (Ra) on the surface of stainless steel after the thinning treatment is not limited in any way, but it is for example 0.03 μm or more, and may be 0.05 μm or more, or 0.07 μm or more.

It should be noted that the arithmetical mean roughness (Ra) of untreated stainless steel is not limited in any way, but it is for example 0.02 to 0.15 μm or 0.03 to 0.10 μm, and preferably 0.04 to 0.08 μm.

In the method for thinning treatment of stainless steel of the present invention, an increment in the value A₁ of arithmetical mean roughness (Ra) on the surface of stainless steel after the thinning treatment relative to the value A₂ of arithmetical mean roughness (Ra) on the flat surface of untreated stainless steel, i.e., A₁-A₂ (μm) can be 0.3 μm or less. Preferably, the increment of Ra is 0.27 μm or less or 0.25 μm or less. More preferably, the increment of Ra is 0.23 μm or less or 0.20 μm or less. Particularly preferably, the increment of Ra is 0.18 μm or less or 0.16 μm or less.

In the method for thinning treatment of stainless steel of the present invention, the maximum height (Rz) on the surface of stainless steel after the thinning treatment can be kept at 2.5 μm or less. Namely, although surface roughness is often increased during the surface treatment of stainless steel, the value of maximum height (Rz) on the treated surface can be kept at 2.5 μm or less in the manufacturing method for stainless steel of the present invention. The value of maximum height (Rz) on the surface of stainless steel after the thinning treatment is preferably 2.4 μm or less, 2.3 μm or less, 2.2 μm or less, 2.1 μm or less, 2.0 μm or less, 1.9 μm or less or 1.8 μm or less, more preferably 1.7 μm or less or 1.6 μm or less, and particularly preferably 1.5 μm or less, 1.4 μm or less or 1.3 μm or less. Alternatively, the value of maximum height (Rz) on the stainless steel surface after the thinning treatment may be 3.0 μm or less, 3.5 μm or less or 4.0 μm or less.

The lower limit of maximum height (Rz) on the surface of stainless steel after the thinning treatment is not limited in any way, but it is for example 0.6 μm or more, and may be 0.8 μm or more, or 1.0 μm or more.

It should be noted that the maximum height (Rz) of untreated stainless steel is not limited in any way, but it is for example 0.2 to 1.8 μm or 0.3 to 1.6 μm, and preferably 0.35 to 1.3 μm.

In the method for thinning treatment of stainless steel of the present invention, an increment in the value Zi of maximum height (Rz) on the surface of stainless steel after the thinning treatment relative to the value Z₂ of maximum height (Rz) on the flat surface of untreated stainless steel, i.e., Z₁-Z₂ (μm) can be 2.2 μm or less. Preferably, the increment of Rz is 1.8 μm or less or 1.7 μm or less. More preferably, the increment of Rz is 1.6 μm or less or 1.5 μm or less. Particularly preferably, the increment of Rz is 1.4 μm or less, 1.3 μm or less, 1.2 μm or less, 1.1 μm or less or 1.0 μm or less.

The above arithmetical mean roughness (Ra) and maximum height (Rz) are calculated according to JIS B 0601-2001. The apparatus used for measurement of these parameters is not limited in any way, and a laser microscope may be used for this purpose, by way of example.

It should be noted that the surface of stainless steel after the thinning treatment on which deposits have been generated after the thinning treatment may be treated with a physical means (e.g., an adhesive tape) to remove the deposits, prior to the measurement of the arithmetical mean roughness (Ra) and maximum height (Rz) after the thinning treatment step. However, such a physical means is not always practical as a part of the manufacturing process.

<2-2. Density of Stainless Steel>

Stainless steel undergoing the thinning treatment step, i.e., stainless steel after the thinning treatment has a density of preferably 4.5 g/cm³ or more. Although there is a tendency to reduce the density of stainless steel by the action of the aqueous composition, the thinning treatment step also serves to prevent an extreme reduction in density. The density of stainless steel after the thinning treatment is more preferably 5.0 g/cm³ or more, 5.3 g/cm³ or more or 5.5 g/cm³ or more, even more preferably 5.6 g/cm³ or more, 5.7 g/cm³ or more or 5.8 g/cm³ or more, still even more preferably 5.9 g/cm³ or more, 6.0 g/cm³ or more or 6.1 g/cm³ or more, and particularly preferably 6.2 g/cm³ or more, 6.3 g/cm³ or more or 6.4 g/cm³ or more. The density of stainless steel after the thinning treatment is usually 7.3 g/cm³ or less without being limited in any way.

The density D₁ (g/cm³) of stainless steel undergoing the thinning treatment compared with the density D₂ (g/cm³) of the same stainless steel without undergoing the thinning treatment is preferably 0.60-fold or more (i.e., D₁/D₂≥0.60), more preferably 0.65-fold or more, 0.70-fold or more or 0.72-fold or more, even more preferably 0.74-fold or more, 0.76-fold or more or 0.78-fold or more, and particularly preferably 0.80-fold or more, 0.82-fold or more or 0.85-fold or more. The ratio of densities before and after the thinning treatment (D₁/D₂) is usually 0.98-fold or less without being limited in any way.

The difference between the density Di (g/cm³) of stainless steel undergoing the thinning treatment and the density D₂ (g/cm³) of the same stainless steel without undergoing the thinning treatment, i.e., D₂-D₁ (g/cm³) is preferably 3.0 (g/cm³) or less, more preferably 2.8 (g/cm³) or less, 2.6 (g/cm³) or less or 2.4 (g/cm³) or less, even more preferably 2.2 (g/cm³) or less, 2.0 (g/cm³) or less or 1.8 (g/cm³) or less, and particularly preferably 1.6 (g/cm³) or less, 1.4 (g/cm³) or less or 1.2 (g/cm³) or less. The difference between densities before and after the thinning treatment, i.e., D₂-D₁ (g/cm³) is usually 0.1 (g/cm³) or more without being limited in any way.

<2-3. Thickness of Stainless Steel>

There is no particular limitation on the shape and thickness of stainless steel to be subjected to the thinning treatment, but foil-shaped or plate-shaped stainless steel is preferred for use. When foil-shaped stainless steel, i.e., a stainless foil is subjected to the thinning treatment, the thickness is for example 100 μm or less, preferably 50 μm or less or 25 μm or less, more preferably 20 μm or less or 18 μm or less, even more preferably 15 μm or less or 12 μm or less, and particularly preferably 10 μm or less. The lower limit of the above thickness will vary depending on the intended purpose of use and is not limited in any way, but it is preferably 1 μm or more in terms of durability and weather resistance.

When plate-shaped stainless steel is subjected to the thinning treatment, the thickness is for example 2.0 mm or less, preferably 1.5 mm or less, more preferably 1.2 mm or less, or less than 1.2 mm, even more preferably 1.1 mm or less, less than 1.1 mm, or 1.0 mm or less, and particularly preferably 0.8 mm or less. The lower limit of the above thickness will vary depending on the intended purpose of use and is not limited in any way, but it is preferably 0.1 mm or more in terms of durability and weather resistance.

The thickness T₁ (μm) of stainless steel undergoing the thinning treatment compared with the thickness T₂ (μm) of the same stainless steel without undergoing the thinning treatment is preferably 0.95-fold or less (i.e., T₁/T₂≤0.95), more preferably 0.9-fold or less or 0.85-fold or less, even more preferably 0.8-fold or less or 0.75-fold or less, and particularly preferably 0.7-fold or less, 0.65-fold or less or 0.6-fold or less.

<2-4. Type of Stainless Steel>

There is no particular limitation on the type of stainless steel to be subjected to the thinning treatment using the aqueous composition of the present invention, but examples include the following.

Namely, examples include those defined in JIS G4305, as exemplified by chromium-nickel stainless steel including SUS304, SUS316, SUS321, SUS347, and SUS329J1; ferrite stainless steel (chromium stainless steel) including SUS405, SUS430, SUS434, SUS444, SUS447, and SUSXM27; and precipitation hardening stainless steel (chromium-nickel stainless steel) including SUS630, SUS631, and SUH660.

Among the above stainless steels, SUS304, SUS430 series (e.g., SUS430 and SUS430LX) and SUS444 are more preferred as those to be subjected to the thinning treatment with the aqueous composition.

<2-5. Aqueous Composition>

In the manufacturing method for stainless steel, the above aqueous composition is preferred for use. Namely, an aqueous composition comprising 0.1% to 5% by mass of hydrogen peroxide, 1% to 30% by mass of halide ions and 0% to 40% by mass of copper ions, each based on the total amount of the aqueous composition, is preferred for use in the thinning treatment step. Details on the components of the aqueous composition are as described above. The aqueous composition forms fine asperities on the surface of stainless steel, but excessive roughening is prevented and the thickness of stainless steel can be extremely reduced.

In the method for thinning treatment for thinning the surface of stainless steel according to the present invention, a thinning treatment step is conducted. Namely, the method for thinning treatment of the present invention comprises a thinning treatment step in which the above aqueous composition is used to perform thinning treatment on the surface of stainless steel. In the context of the present invention, performing thinning treatment on the surface of stainless steel using the aqueous composition is intended to mean bringing the aqueous composition for use in the treatment into contact with the surface of stainless steel. As can be seen from this, the method for thinning treatment of stainless steel of the present invention comprises at least the step of bringing the aqueous composition into contact with the surface of stainless steel.

<2-6. Conditions for Thinning Treatment>

In the thinning treatment step, the above aqueous composition is brought into contact with stainless steel to be treated.

In the thinning treatment step, the temperature required for thinning treatment is preferably 20° C. to 60° C., more preferably 25° C. to 55° C., and particularly preferably 30° C. to 50° C. Thus, the method for thinning treatment of stainless steel of the present invention is advantageous in that the surface thinning of stainless steel proceeds even at not so high temperature, for example, even at room temperature of 25° C. In the context of the present invention, the temperature required for thinning treatment is intended to mean the temperature at which the aqueous composition is brought into contact with the surface of stainless steel, particularly the solution temperature of the aqueous composition to be brought into contact with the surface of stainless steel.

Moreover, in the thinning treatment step, the time required for thinning treatment is preferably 30 seconds to 180 seconds, more preferably 40 seconds to 150 seconds, and particularly preferably 50 seconds to 130 seconds. Thus, the method for thinning treatment of stainless steel of the present invention is advantageous in that the thinning of stainless steel proceeds even within not so long time. In the context of the present invention, the time required for thinning treatment is intended to mean the time during which the aqueous composition is in contact with the surface of stainless steel. For example, it means the time during which stainless steel is soaked in the aqueous composition, or the time required from spraying the aqueous composition over the surface of stainless steel until removing the aqueous composition by water washing, etc.

Any method may be used to bring the aqueous composition into contact with the surface of stainless steel. For example, it is possible to select a method in which the aqueous composition is brought into contact with stainless steel in a dropwise manner or in a spraying (spray treatment) manner, etc., or a method in which stainless steel is soaked in the aqueous composition. In the present invention, either of these methods may be selected for this purpose. For example, the aqueous composition may be sprayed over stainless steel processed into a specific shape to obtain thinned stainless steel, or alternatively, an apparatus for adding dropwise, spraying or soaking the aqueous composition is provided between stainless steel foil rolls, and a stainless steel foil is passed near the above apparatus to supply the aqueous composition during being conveyed in a roll-to-roll fashion from the roll around which the untreated stainless steel foil has been wound, and the thinned stainless steel foil is then wound around the other roll.

It should be noted that the stainless steel thinned in the thinning treatment step may be subjected to water washing or other treatment (i.e., a washing step).

According to the method for thinning treatment of stainless steel described above, stainless steel with a reduced thickness can be obtained while preventing asperities on the surface, simply by a substantially single-step treatment, i.e., thinning treatment alone in which the aqueous composition of the present invention is brought into contact with the surface of stainless steel to be treated, or optionally in combination with appropriate washing (e.g., water washing).

Moreover, as described above, the treatment conditions used in the thinning treatment are mild, and the time required for this treatment is also short, so that the present invention enables the efficient thinning treatment of stainless steel.

[3. Thinning Treatment Method for Stainless Steel]

The above thinning treatment step not only serves as a part of the manufacturing method for stainless steel, but is also useful as a post-treatment for the manufactured stainless steel, etc., by way of example. The method for thinning treatment of stainless steel of the present invention comprises the thinning treatment step described above. Thus, in the thinning treatment used in the thinning treatment method, the properties and type of stainless steel, the components of the aqueous composition, and conditions for the thinning treatment are as described above.

[4. Applications of Stainless Steel after Thinning Treatment]

According to the thinning treatment step described above, stainless steel with a reduced thickness, e.g., a stainless foil can be easily manufactured while preventing an uneven pattern on the surface. Namely, according to the thinning treatment step described above, thinned stainless steel whose surface pattern remains almost unchanged can be obtained simply by a substantially single-step treatment, i.e., thinning treatment alone in which the aqueous composition of the present invention is brought into contact with the surface of stainless steel to be treated, or optionally in combination with appropriate washing (e.g., water washing).

Moreover, as described above, the treatment conditions used in the thinning treatment are mild, and the time required for this treatment is also short, so that thinned stainless steel can be efficiently obtained.

Thinned stainless steel thus obtained can be used, for example, in battery current collector foils for solid-state batteries or lithium-ion batteries, etc., solar battery substrates, flexible substrates for electronic devices, substrates for electric accumulator devices, carriers for exhaust gas purification catalysts, etc., electromagnetic wave shielding members, heat radiating members, and other applications. Thinned stainless steel foils obtained by the manufacturing method for stainless steel of the present invention are preferred for use as battery current collector foils, by way of example.

EXAMPLES

The present invention will be further described in more detail by way of the following examples, which are not intended to limit the scope of the invention.

<Measurement of Surface Roughness of Stainless Steel Foil>

The stainless steel foil used as a starting material, and the surface-treated foils obtained in the following examples and comparative examples were measured for their maximum height (Rz) and arithmetical mean roughness (Ra) according to JIS B 0601-2001 with a laser microscope (manufactured by Keyence Corporation, Japan; product name: “VK-X250”).

<Thickness>

The surface-treated stainless foils in the examples and comparative examples, and the untreated stainless foils in Reference Examples 1 to 4 were measured for their thickness with a digital micrometer (manufactured by Mitutoyo Corporation, Japan; MDC-25MXT).

<Density>

The surface-treated stainless foils in the examples and comparative examples, and the untreated stainless foils in Reference Examples 1 to 4 were calculated for their density by the following equation (1) using the weight (D) of the stainless foil used, the area(S) of the stainless foil used, and the thickness (T) of the stainless foil measured as described above.

[ Math . 1 ] Density ⁢ ( g / cm 3 ) = Weight ⁢ D ⁢ ( g ) ⁢ of ⁢ stain ⁢ less ⁢ foil Area ⁢ S ⁢ ( cm 2 ) ⁢ of ⁢ stainless ⁢ foil × Thickness ⁢ T ⁢ ( µm ) ⁢ of ⁢ stainless ⁢ foil × 1 ⁢ 0 4 ( 1 )

Example 1

A stainless steel (foil) was provided which had a thickness of 10 μm and a length and width of 30 mm×30 mm and whose material was SUS444 (Reference Example 1).

To 130 ml of ultrapure water, hydrogen peroxide in a final amount of 0.5% by mass (1.7 g of a 60 wt % aqueous hydrogen peroxide solution) and 72% by mass (143 g) of a 35 wt % aqueous hydrochloric acid solution were added to prepare an aqueous composition. The concentration of halide ions (Cl⁻) derived from hydrochloric acid in this composition was 25% by mass based on the total amount of the aqueous composition.

The above stainless steel foil was soaked for 60 seconds in the above aqueous composition at a solution temperature of 30° C. Then, the soaked stainless steel foil was washed well with ultrapure water, and then dried well to obtain the surface-treated foil. The resulting surface-treated foil was found to have a thickness of 9 μm, a surface Ra value of 0.17 (μm), a surface Rz value of 1.53 (μm) and a density of 6.6 g/cm³, as measured in accordance with the procedures described above.

Examples 2 to 9 and Comparative Examples 1 to 9

The same thinning treatment as shown in Example 1 was performed on stainless steel foils to obtain surface-treated foils, except that the stainless steel to be treated, the properties of the aqueous composition and/or the conditions for the thinning treatment method were changed as indicated in Table 1 below.

It should be noted that copper sulfate pentahydrate (CuSO₄·5H₂O) was used as a source of copper ions (Cu²⁺) in an amount of 3.9 g, 12 g and 12 g, respectively, in Comparative Examples 3, 7 and 8, while iron (III) chloride hexahydrate (FeCl₃·6H₂O) was used in an amount of 133 g and 133 g, respectively, in Comparative Examples 5 and 6.

The results including the values of thickness, surface roughness and density obtained for the resulting surface-treated foils are shown in Tables 1 to 4. In Tables 1 to 4, changes in the measured values after the treatment are calculated based on the values of the reference examples (untreated), and these changes are shown together with the measured values.

	TABLE 1
	Properties of stainless foil obtained

Aqueous composition

Treatment method

Ra

Rz

Density

Metal

H2O2

Cu2+

Cl−

FeCl3

Temperature

Time

Thickness

Change

Change

Change

foil

[wt %]

[wt %]

[wt %]

[wt %]

[° C.]

[sec]

[μm]

[μm]

[μm]

[μm]

[μm]

[g/cm3]

[%]

Example 1	SUS444	0.5	0	25	0	30	60	9	0.17	0.12	1.53	1.10	6.6	86.1
Example 2	SUS444	0.5	0	25	0	30	90	8	0.22	0.17	1.77	1.34	5.7	74.5
Example 3	SUS444	0.5	0	25	0	30	120	6	0.18	0.13	1.31	0.88	5.7	74.0
Comparative	SUS444	0.1	0	12	0	30	60	10	0.33	0.28	3.85	3.42	7.7	100.3
Example 1
Comparative	SUS444	1.0	0	12	0	30	60	10	0.45	0.40	2.54	2.11	6.4	83.0
Example 2
Comparative	SUS444	0.5	0.5	12	0	35	60	10	0.63	0.58	3.82	3.39	6.9	90.4
Example 3
Comparative	SUS444	0.0	0	25	0	30	60	10	0.05	0.00	0.35	−0.08	7.6	99.2
Example 4
Comparative	SUS444	0.0	0	0	40	30	30	10	0.60	0.55	7.17	6.74	7.4	96.6
Example 5
Comparative	SUS444	0.0	0	0	40	30	60	10	0.59	0.54	7.68	7.25	5.3	68.8
Example 6
Reference	SUS444	—	—	—	—	—	—	10	0.05	—	0.43	—	7.7	—
Example 1
(untreated)

	TABLE 2
	Properties of stainless foil obtained

Aqueous composition

Treatment method

Ra

Rz

Density

Metal

H2O2

Cu2+

Cl−

FeCl3

Temperature

Time

Thickness

Change

Change

Change

foil

[wt %]

[wt %]

[wt %]

[wt %]

[° C.]

[sec]

[μm]

[μm]

[μm]

[μm]

[μm]

[g/cm3]

[%]

Example 4	SUS430	0.5	0	25	0	30	30	8	0.20	0.16	1.62	1.25	6.8	86.9
Example 5	SUS430	0.5	0	25	0	30	90	6	0.21	0.17	1.59	1.22	5.3	67.6
Reference	SUS430	—	—	—	—	—	—	10	0.04	—	0.37	—	7.8	—
Example 2
(untreated)

	TABLE 3
	Properties of stainless foil obtained

Aqueous composition

Treatment method

Ra

Rz

Density

H2O2

Cu2+

Cl−

FeCl3

Temperature

Time

Thickness

Change

Change

Change

Metal foil

[wt %]

[wt %]

[wt %]

[wt %]

[° C.]

[sec]

[μm]

[μm]

[μm]

[μm]

[μm]

[g/cm3]

[%]

Example 6	SUS430LX	0.5	0	25	0	30	30	8	0.22	0.16	1.68	1.18	6.6	88.3
Example 7	SUS430LX	0.5	0	25	0	30	90	6	0.28	0.22	1.85	1.35	5.9	79.5
Reference	SUS430LX	—	—	—	—	—	—	10	0.06	—	0.50	—	7.4	—
Example 3
(untreated)

	TABLE 4
	Properties of stainless foil obtained

Aqueous composition

Treatment method

Ra

Rz

Density

H2O2

Cu2+

Cl−

FeCl3

Temperature

Time

Thickness

Change

Change

Change

Metal foil

[wt %]

[wt %]

[wt %]

[wt %]

[° C.]

[sec]

[μm]

[μm]

[μm]

[μm]

[μm]

[g/cm3]

[%]

Example 8	SUS304	1.0	0	20	0	35	60	8	0.14	0.06	1.23	−0.03	7.2	90.5
Comparative	SUS304	0.5	1.5	12	0	35	60	8	0.38	0.30	2.34	1.08	6.3	79.3
Example 6
Comparative	SUS304	1.0	1.5	20	0	35	60	6	0.45	0.37	2.44	1.18	4.4	55.3
Example 7
Comparative	SUS304	9.0	0	9	0	35	60	10	0.80	0.72	10.51	9.25	7.9	98.3
Example 8
Reference	SUS304	—	—	—	—	—	—	10	0.08	—	1.26	—	8.0	—
Example 4
(untreated)

INDUSTRIAL APPLICABILITY

In each example mentioned above using an aqueous composition of particular composition, it was confirmed that stainless steel could be efficiently thinned with few steps and in a short time, and the thickness of stainless steel was reduced before and after the treatment. Moreover, there was no significant increase in the uneven pattern on the surface of stainless steel after the treatment. When stainless steel, particularly a stainless steel foil, thus thinned while maintaining a good appearance is used in battery current collector foils, automotive component housings, etc., dielectric substances or organic materials can be effectively adhered or held. Also in the case of members for heat radiation, thinned stainless steel may be preferred for use.

Accordingly, the present invention is recognized to have industrial applicability in the field of treating stainless steel as a material member, e.g., as a material member for use in the above products.