JP2017030205A - Surface-treated stainless steel foil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface-treated stainless steel foil which is excellent in electrolyte resistance even when the surface shape has changed by thinning of a stainless steel foil, and has good adhesiveness with a resin even when the resin has been formed on a surface-treated film.SOLUTION: There is provided a surface-treated stainless steel foil 1 having a surface-treated film 20 with a thickness of 2-500 nm formed on the surface of a stainless steel foil 10 with a thickness of 100 μm or less, where the surface on which the surface-treated film 20 is formed in the foil has such a surface property that Ra measured by a probe of which a radius of curvature of a tip is 6-15 nm of 30-100 nm, and Pc measured by a probe in a square area of one side of 30 μm on the surface is 20 or more, and the surface-treated film 20 contains element groups A, C, O, Cr and F constituted of one or more selected from P, Zr, Ti and N in a molar ratio of A:C:O:Cr:F=1 to 5:3 to 15:30 to 50:15 to 35:15 to 35.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a surface-treated stainless steel foil having a surface-treated film formed on at least one surface of a stainless steel foil. In particular, the present invention relates to a surface-treated stainless steel foil having excellent resistance to an electrolytic solution used for a secondary battery.

  Secondary devices such as nickel-cadmium batteries, nickel-hydrogen batteries, lithium-ion batteries, etc. for electronic devices such as mobile phones, smart phones, notebook personal computers, digital cameras, video cameras, portable game machines, hybrid cars, and electric cars Batteries are widely used. Such a secondary battery is configured by accommodating a positive electrode, a negative electrode, a separator, an electrolytic solution, and the like in a container.

  Such containers are required to be able to prevent electrolyte leakage without deformation or breakage even when an external force or the like is applied. As a material for the container, plastic foil or aluminum foil has been used.

  On the other hand, with the miniaturization of electronic devices, secondary batteries are also required to be small and light. In response to such demands, attempts have been made to increase the battery capacity by reducing the thickness of the secondary battery container and storing more electrolytic solution even if the volume is the same.

  However, if the thickness of the plastic foil or aluminum foil is reduced to, for example, 200 μm or less, the strength is lowered and it becomes unsuitable as a container material for a secondary battery.

  Therefore, it has been studied to use a stainless steel foil instead of these materials. However, since stainless steel is inferior in corrosion resistance to the corrosive substance contained in the electrolytic solution, it is necessary to form a resin capable of blocking the corrosive substance on the surface of the stainless steel foil. And in order to ensure the adhesion between the formed resin and the stainless steel foil, the surface of the stainless steel foil is chromated to form a surface treatment film, thereby ensuring the adhesion with the resin and preventing the electrolysis. Liquidity is improved (see Patent Document 1).

  By the way, since hexavalent chromium used for chromate treatment has a high environmental load, chemical conversion treatment is performed using a trivalent chromium compound as an alternative substance (see Patent Document 2).

JP 2007-168184 A JP 2013-23706 A

  However, when the thickness of the stainless steel foil is reduced, there are the following problems. That is, the surface treatment film formed by the specific surface treatment on the surface of the stainless steel foil having a relatively large thickness has good adhesion and resistance to electrolytic solution, but the thickness of the stainless steel advances. Even if the surface film formed on the surface has the same composition, there is a problem that good adhesion and resistance to electrolytic solution cannot be obtained.

  As a result of studies by the present inventors on such a problem, as the thinning progresses, the surface properties of the stainless steel foil change, and a surface having characteristic irregularities is formed. It has been found that the surface treatment film is affected, and the superiority or inferiority of the electrolytic solution resistance or adhesion changes. Conventionally, in the surface treatment of stainless steel foil, it is considered that the components of the surface treatment agent for surface treatment or the characteristics of the formed surface treatment film are important, and the surface properties of the stainless steel foil have been almost studied. It wasn't.

  The present invention has been made in view of the above situation, and as a result of promoting the thinning of the stainless steel foil, even when the surface properties of the stainless steel foil have changed, the electrolytic solution is excellent in resistance to electrolytes and on the surface treatment film. It is an object of the present invention to provide a surface-treated stainless steel foil having good adhesion to the resin even when laminated with a resin or the like.

  In order to solve the above-mentioned problems, the present inventors have identified the surface properties of the stainless steel foil and also studied the composition of the components contained in the surface treatment film. As a result, it has been found that unless the composition of the specific component contained in the surface treatment film is optimized according to the surface properties of the thinned stainless steel foil, good electrolytic solution resistance cannot be obtained. It came to complete.

That is, the aspect of the present invention is
(1) A surface-treated stainless steel foil in which a surface-treated film is formed on at least one surface of the stainless steel foil,
The stainless steel foil has a thickness of 100 μm or less,
In the stainless steel foil, the surface on which the surface treatment film is formed has an arithmetic average roughness Ra measured by a probe having a radius of curvature of the tip portion of 6 nm to 15 nm of 30 nm to 100 nm, Having a surface property in which a peak count Pc measured by the probe is 20 or more in a quadrangular region having a side of 30 μm on the surface;
The surface treatment film has a thickness of 2 nm to 500 nm,
The surface treatment film is an element group A composed of at least one or two or more selected from phosphorus (P), zirconium (Zr), titanium (Ti) and nitrogen (N), carbon (C), Oxygen (O), chromium (Cr), and fluorine (F) at a molar ratio of A: C: O: Cr: F = 1 to 5: 3 to 15:30 to 50:15 to 35: It is a surface-treated stainless steel foil characterized by containing in the ratio of 15-35.
(2) The surface-treated stainless steel foil according to (1), wherein at least a part of the carbon is derived from an organic compound.
(3) The surface-treated stainless steel foil according to (1) or (2), wherein at least a part of the chromium is derived from a trivalent chromium compound.
(4) The surface-treated stainless steel foil according to any one of (1) to (3), which has a polyolefin-based resin layer containing a functional group having polarity on the surface-treated film.
(5) The surface treatment film comprises a trivalent chromium compound, at least one or two or more resins selected from a polyolefin resin, a urethane resin, a vinyl resin, and an acrylic resin, a phosphate group, and / or (1) characterized by having a phosphorus compound having a phosphonic group, a nitrogen compound having an amino group and / or an amide group, a zirconium compound, and one or more crosslinkable compounds selected from titanium compounds The surface-treated stainless steel foil according to any one of (4).

  According to the present invention, as a result of promoting the thinning of the stainless steel foil, even when the surface properties of the stainless steel foil are changed, the electrolyte solution is excellent in resistance to the electrolyte, and the surface treatment film is laminated with a resin or the like. Even when it is performed, a surface-treated stainless steel foil having good adhesion to the resin can be provided.

FIG. 1 is a schematic cross-sectional view of a surface-treated stainless steel foil according to this embodiment. FIG. 2 is a schematic diagram for explaining the procedure for calculating the peak count Pc on the surface of the stainless steel foil. FIG. 3 is a schematic diagram for explaining a process performed when calculating the peak count Pc on the surface of the stainless steel foil. FIG. 4 is a depth profile regarding the XPS spectrum of the element contained in the surface-treated stainless steel foil. FIG. 5 is an image obtained by performing image processing for calculating an observation image with an atomic force microscope and a peak count Pc with respect to Examples and Comparative Examples of the present invention.

Hereinafter, the present invention will be described in detail in the following order based on embodiments shown in the drawings.
1. 1. Surface-treated stainless steel foil 1-1 Stainless steel foil 1-2 Surface-treated film 1-3 Polyolefin resin layer Measuring method of surface properties of stainless steel foil 2-1 Arithmetic average roughness Ra
2-2 Peak count Pc
3. 3. Method for analyzing surface treatment film 4. Method for producing surface-treated stainless steel foil Effects of the present embodiment 6. Modified example

(1. Surface-treated stainless steel foil)
As shown in FIG. 1, the surface-treated stainless steel foil 1 according to the present embodiment has a surface-treated film 20 formed on one surface of the stainless steel foil 10, and further a polyolefin-based resin layer 30 formed thereon. It has the composition which is. This surface-treated stainless steel foil is suitable as a material for a container that accommodates a secondary battery because it has excellent resistance to electrolytic solution and good adhesion to a resin layer. Hereinafter, each component will be described in detail.

(1-1 stainless steel foil)
In this embodiment, the stainless steel constituting the stainless steel foil is not particularly limited, and may be any of austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, austenite-ferritic duplex stainless steel. Also good.

  Further, the thickness of the stainless steel foil is 100 μm or less, preferably 10 to 60 μm, in order to realize an increase in capacity of the secondary battery. In this embodiment, since the stainless steel foil is such a very thin foil, the surface property of the stainless steel changes when the stainless steel is processed into a foil. And, the inventors have a special surface property of stainless steel foil in the case of an extremely thin foil of 100 μm or less, and if the surface treatment film is not formed according to this surface property, the electrolytic solution resistance, It was found that the adhesiveness with the resin layer cannot be compatible.

  In the present embodiment, the surface properties of the stainless steel foil are defined by the arithmetic average roughness Ra and the peak count Pc. Specifically, Ra is in the range of 30 to 100 nm, preferably in the range of 35 to 70 nm. Pc in a square region with one side of stainless steel foil being 30 μm is 20 or more, preferably 25 or more. The upper limit of Pc is not particularly limited, but Pc is a parameter that depends on the processing conditions such as rolling when stainless steel is used as the stainless steel foil, and the processing conditions for forming a thin foil are limited. About 100.

  As described above, in the present embodiment, the surface property of the stainless steel foil is formed from nanoscale irregularities, and therefore the probe can follow the irregularities unless measured using a very small probe. Therefore, the unevenness is not accurately reflected in the measurement result. Therefore, the above Ra and Pc are values measured using a probe having a radius of curvature of the tip portion of 6 nm to 15 nm. A specific measurement method will be described later.

  Since the effects of the present invention can be obtained by forming a surface treatment film to be described later on the surface having such a surface property, the surface property of the surface on which the surface treatment film is formed has the above surface property. It only has to be. Therefore, the surface on which the surface treatment film is not formed may or may not have the above surface properties. In addition, this surface property hardly changes before and after formation of the surface treatment film mentioned later.

(1-2 Surface treatment film)
In the present embodiment, the surface treatment film 20 is a film formed by surface-treating the surface of a stainless steel foil, and includes the following elements within a specific range. That is, the surface treatment film 20 includes an element group A composed of at least one or two or more selected from phosphorus (P), zirconium (Zr), titanium (Ti), and nitrogen (N), and carbon (C). And oxygen (O), chromium (Cr), and fluorine (F) in a molar ratio of A: C: O: Cr: F = 1 to 5: 3 to 15:30 to 50:15. 35: In a ratio of 15-35. Preferably, A: C: O: Cr: F = 2 to 4: 3 to 10:35 to 45:20 to 30:20 to 30.

  The elements constituting the element group A can form a dense film in the surface treatment film 20 because the compound containing the element has high film forming properties. As an element constituting the element group A, phosphorus (P) is preferable. By the presence of phosphorus in the surface treatment film 20, the activity of phosphorus in the film can be increased and the electrolyte containing phosphorus can be prevented from entering the surface treatment film 20. it can.

  Carbon (C) is mainly a component derived from an organic compound, and the amount of the organic compound to be present in the surface treatment film 20 can be defined by setting the molar ratio of carbon within the above range. As described above, in the surface-treated stainless steel foil according to this embodiment, the surface properties of the stainless steel foil are special. Therefore, when the amount of carbon is too small, that is, when the film derived from the organic compound is small, the film derived from the inorganic compound alone cannot follow the special surface properties, and the film has cracks, defects, etc. The barrier property against the corrosive substances contained in can not be ensured. On the other hand, when the amount of carbon is too large, that is, when there are too many films derived from an organic compound, the inorganic compound components are relatively reduced, so that the corrosion resistance is deteriorated. Moreover, since the ion permeability of the film increases, the barrier property tends to deteriorate. Therefore, the amount of carbon is controlled within the above range.

  Oxygen (O), chromium (Cr), and fluorine (F) mainly form a mixed film of chromium oxide and chromium fluoride, and by making these element amounts within the above ranges, The surface can be effectively protected.

  Therefore, in the present embodiment, the surface treatment film 20 is a composite film of a film made of an inorganic compound and a film made of an organic compound because the element is contained in the above ratio. Conceivable. Specifically, it is considered that a network structure derived from an inorganic compound and a network structure derived from an organic compound are formed in a composite manner. By having such a configuration, it is possible to follow the special surface properties of the stainless steel foil without causing cracks and the like, and it is possible to sufficiently suppress the entry of corrosive substances contained in the electrolytic solution. .

  In addition, although elements other than the above elements may be included in the surface treatment film, the total number of moles of elements other than the above elements (excluding the number of moles of hydrogen (H)) is the total of the surface treatment film. Preferably it is 10 mol% or less with respect to 100% of the total number of moles of an element, More preferably, it is 5 mol% or less. In addition, the molar ratio of said element (element group A, C, O, Cr, F) is calculated without considering content of elements other than said element.

  The coating liquid before the surface treatment film 20 is formed contains various inorganic compounds and organic compounds. Specifically, it has a trivalent chromium compound, at least one resin selected from polyolefin resin, urethane resin, vinyl resin and acrylic resin, and a phosphate group and / or a phosphone group. It is preferable that one or two or more crosslinkable compounds selected from a phosphorus compound, a nitrogen compound having an amino group and / or an amide group, a zirconium compound, and a titanium compound are included.

  As will be described later, the surface treatment film 20 is formed by heat-treating the coating solution. Therefore, the compound of the element contained in the coating liquid may be altered in the surface treatment film 20, but is contained in the surface treatment film 20 by using an analysis method such as FTIR, for example. Can be identified.

  Therefore, at least a part of the carbon contained in the surface treatment film 20 is derived from an organic compound such as a resin component. Further, at least a part of the chromium contained in the surface treatment film 20 is derived from a trivalent chromium compound.

  The ratio of each element in the surface treatment film 20 is calculated based on the concentration profile of each element obtained from the result of depth direction analysis by XPS (X-ray Photoelectron Spectroscopy). The calculation method of the element content ratio will be described later.

  In the present embodiment, the thickness of the surface treatment film 20 is 2 nm to 500 nm, preferably 5 nm to 100 nm. If the thickness is too thin, the ratio of the surface treatment film that actually covers the stainless steel foil (coverage ratio) decreases, and corrosive substances contained in the electrolyte solution easily enter the film. Sex tends to get worse. The thickness of the surface treatment film 20 is calculated from the result of depth direction analysis by XPS (X-ray Photoelectron Spectroscopy), similarly to the element content ratio. A method for measuring the thickness will be described later.

(1-3 Polyolefin resin layer)
The polyolefin resin layer 30 is formed on the surface treatment film 20 and may be a single layer or a plurality of layers. The polyolefin-based resin layer 30 is in close contact with the stainless steel foil 10 through the surface treatment film 20, so that even if the surface-treated stainless steel foil 1 is used as a material for a secondary battery container, the 2 Good corrosion resistance can be shown with respect to the electrolyte solution used for a secondary battery.

  Examples of the polyolefin resin constituting the polyolefin resin layer 30 include polyethylene, polypropylene, polybutene, polypentene, polyhexene, polyoctenylene, polyisoprene, polybutadiene, aliphatic polyolefin, and aromatic polyolefin. Examples of the aliphatic polyolefin include an ethylene-propylene copolymer, an ethylene-butene copolymer, an ethylene-propylene-hexadiene copolymer, and an ethylene-propylene-5-ethylidene-2-norbornene copolymer. Examples of aromatic polyolefins include styrene copolymers. Furthermore, acrylic acid and its derivatives, methacrylic acid and its derivatives, imide and its derivatives, vinyl chloride and the like may be contained to the extent that the corrosion resistance to the electrolytic solution is maintained.

In the present embodiment, the polyolefin-based resin layer 30 includes a functional group having polarity in order to achieve good adhesion with the stainless steel foil. The functional group having polarity is a functional group to which elements having a Pauling electronegativity difference of 0.33 eV ^0.5 or more are bonded. Specific examples include acid anhydride groups, hydroxyl groups, carboxyl groups, amide groups, amino groups, urethane groups, ester groups, imide groups, maleimide groups, halogen groups, ether groups, thiol groups, and epoxy groups.

  The polyolefin resin layer 30 preferably has a thickness in the range of 10 to 100 μm.

(2. Method for measuring surface properties of stainless steel foil)
The method for measuring the surface properties of the stainless steel foil will be specifically described below.

(2-1 arithmetic average roughness Ra)
In the present embodiment, the arithmetic average roughness Ra is calculated in accordance with the provisions of JIS B601. That is, when calculating Ra, it may be based on the definition defined in JIS B601, but the numerical conditions defined in JIS B601 are not necessarily used.

  As described above, since the surface properties of the stainless steel foil are composed of very small irregularities, the arithmetic average roughness Ra of the stainless steel foil is at the nanometer level. In order to measure such Ra at the nanometer level, the probe with the tip having a radius of curvature at the micrometer level cannot accurately trace the unevenness at the nanometer level, and the tip is at the nanometer level. It is necessary to use a probe having a curvature radius of. Specifically, Ra is measured using a probe whose tip has a radius of curvature of 6 to 15 nm.

  In the present embodiment, the measuring device is not particularly limited as long as the tip has a probe having a curvature radius of 6 to 15 nm, but in reality, using a scanning probe microscope (Scanning Probe Microscope). Measure. Hereinafter, an explanation will be given using an atomic force microscope (AFM) as a scanning probe microscope.

  In the atomic force microscope, when the sample surface is expressed as an XY plane using the X axis and the Y axis, the surface irregularities can be expressed as displacement in the Z axis direction perpendicular to the XY plane. That is, with the atomic force microscope, the unevenness of the sample can be measured as a three-dimensional (X, Y, Z) shape. Therefore, in the atomic force microscope, two-dimensional data (XZ plane and YZ plane) is obtained as a cross-sectional profile. Based on this data, the arithmetic average roughness is obtained according to the method defined in JIS B601. What is necessary is just to calculate Ra. At this time, Ra may be calculated by performing data processing using analysis software attached to the atomic force microscope or commercially available analysis software.

  The obtained measurement data includes shape data resulting from noise other than the surface properties of the stainless steel foil, such as deflection of the stainless steel foil, wrinkles on the surface of the stainless steel foil, and the like. Therefore, this measurement data does not correctly reflect the surface properties of the stainless steel foil. Therefore, by removing such noise, it is possible to calculate Ra with high accuracy reflecting the surface properties of the stainless steel foil. As a method for removing noise, a known method may be used, but when Ra is calculated, flattening (Flatten) processing or the like is exemplified.

  In the flattening process, a polynomial (about 0th to 3rd order) is fitted to the cross-sectional curve constituting the cross-sectional profile, and the best-fit polynomial is selected. Then, the cross-section curve is flattened by subtracting the best fitting polynomial from the cross-section curve. By applying this operation to the entire cross-sectional curve constituting the cross-sectional profile, a noise-removed and flattened cross-sectional profile can be obtained.

  The size of the area for measuring Ra is not particularly limited, but in the measurement of peak count Pc, which will be described later, since a square area having a side of 30 μm is scanned and measured, the size of the area for measuring Ra is also one side. Is preferably a square region of 30 μm.

  In the present embodiment, Ra is calculated by measuring the surface properties of five fields of view on a surface of a stainless steel foil, with an arbitrarily selected rectangular region having a side of 30 μm as one field of view. That is, the average value of Ra calculated in each visual field is defined as the arithmetic average roughness Ra of the stainless steel foil surface.

(2-2 Peak count Pc)
In the present embodiment, the peak count Pc is calculated in accordance with JIS B601 regulations. That is, when calculating Pc, it may be based on the definition prescribed in JIS B601, but the numerical condition prescribed in JIS B601 is not necessarily used.

  In the measurement of the peak count Pc as well as the measurement of Ra, since the tip portion is measured using a probe having a curvature radius of 6 to 15 nm, hereinafter, an atomic force microscope (AFM) is used. An explanation will be given using.

  In the present embodiment, as shown in FIG. 2, the peak count Pc refers to the number of peak regions (convex portions) that exceed a threshold value (Threshold) set in a predetermined region. As this Pc is larger, it indicates that the number of convex portions is larger in a certain period, and that irregularities are formed in a shorter period. In the present embodiment, a square having a side of 30 μm is set as the predetermined area. Also, the threshold (Threshold) is 50 nm in the present invention, unlike the average height line. It has been found empirically that undulations of less than this height do not contribute to the performance as a surface-treated stainless steel foil, and furthermore, by providing this threshold value, it has been found that a value well correlated with the performance can be obtained. This is because the. As described above, the peak count Pc on the surface of the stainless steel foil according to this embodiment is 20 or more, preferably 25 or more.

  Similar to Ra, two-dimensional data is obtained as a cross-sectional profile. Based on this data, the peak count Pc may be calculated in accordance with the provisions of JIS B601. At this time, Pc may be calculated by performing data processing using analysis software attached to the atomic force microscope or commercially available analysis software.

  Moreover, since Pc is easily influenced by factors other than the surface properties of the stainless steel foil, such as wrinkles on the surface of the stainless steel foil, it is preferable to remove these factors. Specifically, it is preferable to perform a median process in addition to the flattening process. In the median processing, first, for an arbitrary pixel having a displacement in the Z-axis direction as numerical information (pixel value) and a position defined on the XY plane, a predetermined number (for example, 7 × 7, 11 × 11) matrix is assumed, and the median value (median value) is calculated for the pixel values of all the pixels in the matrix. Then, the calculated median value is replaced with the pixel value of the pixel located at the center of the matrix. This operation is performed for all the pixels in the measurement region. By performing such processing, pixels that show abnormal pixel values in a specific range can be removed. That is, factors other than the surface properties of the stainless steel foil can be removed as noise.

  Further, when the peak count Pc is calculated in consideration of all regions up to the peripheral portion of the measurement region (a square having a side of 30 μm), the displacement of the peripheral portion is considered to be larger than actual in data processing. The Pc calculated in this way does not reflect actual surface properties. Therefore, as shown in FIG. 3, processing that is not taken into account when calculating Pc can be performed on the peripheral edge E that is a part of the measurement region. That is, in this embodiment, Pc is calculated without taking into account the peripheral edge E of about 0.5 μm. In this case, the actual region where Pc is calculated is a quadrangle with a side of 29 μm.

(3. Analysis method of surface treatment film)
In the present embodiment, the thickness and the component composition of the surface treatment film are defined within a specific range. Therefore, a method for analyzing the thickness and composition of the surface treatment film will be described in detail.

  In the present embodiment, the thickness and component composition of the surface treatment film are measured by depth direction analysis by X-ray photoelectron spectroscopy (XPS). XPS obtains elemental information on the sample surface (a few nanometers deep from the surface) and information about its binding state by analyzing the kinetic energy of photoelectrons excited by the photoelectric effect when X-rays are incident on the sample. It is a possible analytical method.

  On the other hand, sputtering is a technique in which Ar atoms and the like are ionized, accelerated by applying a voltage to collide with the surface of the sample, and the surface of the sample is scraped off.

  A depth direction analysis can be performed by combining XPS and sputtering. That is, the depth direction analysis can be performed by repeating the operation of performing XPS measurement on the sample surface after performing sputtering for a certain time. After the analysis, a profile of each element as shown in FIG. 4 can be obtained in the depth direction of the surface-treated stainless steel foil. In FIG. 4, the vertical axis represents the element ratio contained in the sample, and the horizontal axis represents the sputtering time.

In addition, in order to convert the sputtering time on the horizontal axis into depth, sputtering is performed using a standard sample having a known thickness (for example, SiO ₂ ), and the depth (sputter rate) sputtered per unit time is calculated. The sputtering rate may be converted by multiplying the sputtering time. Strictly speaking, the sputter rate of the standard sample is different from the sputter rate of the surface treatment film made of a material different from the standard sample. However, in the present invention, it is important to specify the thickness of the surface treatment film on the basis of a predetermined standard, instead of obtaining the exact thickness of the surface treatment film. Therefore, in the present invention, there is no problem even if the thickness of the surface treatment film is calculated by the above method.

  First, the thickness of the surface treatment film is calculated based on the obtained FIG. In this embodiment, as shown in FIG. 4, the concentration of Fe, which is the main component of the stainless steel foil, increases in the depth direction from the outermost surface of the surface treatment film, and the concentration is saturated and becomes substantially constant. The depth at which the concentration is half that of the measured concentration is defined as the thickness of the surface treatment film. That is, the region indicating the depth corresponds to the boundary between the surface treatment film and the stainless steel foil.

  Since Fe, which is the main component of the stainless steel foil, hardly diffuses into the surface treatment film, in FIG. 4, the Fe concentration is expected to increase rapidly at the interface between the stainless steel foil and the surface treatment film. Actually, as shown in FIG. 4, the concentration of Fe increases with a predetermined slope. This is probably because the X-ray spot diameter irradiated in the XPS measurement is relatively large, and the stainless steel foil itself is not flat but uneven in the spot diameter range. As a result, it is considered that the position of the interface changes in the measurement depth direction.

  After calculating the thickness of the surface treatment film, it is composed of at least one or two or more selected from phosphorus (P), zirconium (Zr), titanium (Ti), and nitrogen (N), which are components of the surface treatment film. The content ratio of element group A, carbon (C), oxygen (O), chromium (Cr), and fluorine (F) is calculated.

  Specifically, in the depth direction, from the peak strength and sensitivity coefficient of the binding energy of each element measured from the surface of the surface treatment film to the interface between the film and the stainless steel foil determined above, the element The molar ratio of each element is calculated so that the sum of group A, carbon (C), oxygen (O), chromium (Cr), and fluorine (F) is 100 mol%.

  At this time, the concentration information of each element at the outermost surface of the surface treatment film and the boundary between the surface treatment film and the stainless steel foil is not considered. Normally, contaminants such as organic substances are attached to the outermost surface of the surface treatment film, and it is difficult to completely remove them. Therefore, when the molar ratio of each element on the outermost surface of the surface treatment film is calculated, both carbon constituting the contaminants adhering to the outermost surface and carbon contained in the surface treatment film are particularly detected. The amount of carbon on the outermost surface of the treated film is detected more than the actual amount. Therefore, the concentration information of each element on the outermost surface is not considered.

  On the other hand, regarding the concentration information of each element at the interface between the surface treatment film and the stainless steel foil, the concentration information of each element at the interface is Do not consider.

  Moreover, the following methods are illustrated as a method of specifying the compound contained in the surface treatment film.

  About the compound containing carbon and oxygen, the said compound can be specified from IR spectrum obtained by the highly sensitive Fourier transform infrared spectroscopy (FTIR) by the RAS (reflection absorption) method, for example.

  For trivalent chromium compounds, phosphorus compounds, nitrogen compounds, zirconium compounds, and titanium compounds, for example, the valence can be estimated and estimated from the peak shift of each element in XPS. Further, when a crystalline compound is formed, the compound can be specified by specifying the element and the crystal structure with a transmission electron microscope.

(4. Method for producing surface-treated stainless steel foil)
Below, the method to manufacture said surface-treated stainless steel foil is demonstrated.

  First, a stainless steel foil having the surface properties described above is manufactured. The manufacturing process of the stainless steel foil is substantially the same as the manufacturing process of a normal stainless steel foil. That is, the stainless steel foil having the above-described surface properties can be obtained by foil rolling the stainless steel strip, then cleaning the surface, performing final annealing, and performing temper rolling (tension leveler) as necessary.

When producing a normal stainless steel foil, in rolling a stainless steel strip, a rolled material having a width of 1000 mm or more is usually rolled with good shape controllability. It is performed by applying a tension of about 300 N / mm ² .

On the other hand, when manufacturing the stainless steel foil having the above-mentioned surface properties, a work roll having a diameter of about 30 to 60 mm, which is much smaller than the above, is used, and the longitudinal tension is about 500 N / mm ² . Rolling is performed. In the case of stainless steel having a large deformation resistance in rolling, in order to obtain a stainless steel foil having a thickness of 100 μm or less with high productivity, the contact area between the material to be rolled and the work roll is reduced, and as much rolling load as possible is obtained. This is because it is necessary to transmit to the material to be rolled and to set the tension in the rolling direction high.

  In addition, although a KT mill, a Sendzimir mill, etc. can be used for a rolling mill, especially the kind of rolling mill and the number of rolls are not limited. Moreover, high-speed steel, cemented carbide or ceramics can be used as the material of the work roll for rolling, and the surface roughness (Ra) is preferably 0.1 to 0.4 μm. When the surface roughness is 0.1 μm or less, the surface roughness of the obtained stainless steel foil becomes smooth and the adhesion strength with the resin layer to be laminated decreases. This is because, when the surface roughness is 0.4 μm or more, the deformation resistance of the stainless steel foil during rolling increases and the productivity decreases.

  As described above, when the stainless steel strip is processed into a foil, the surface properties of the stainless steel change. Therefore, the amount of foil rolling using a work roll having a small diameter and applying a high tension is related to the surface properties of the stainless steel foil.

  As described above, the thickness of the stainless steel foil is 100 μm or less, preferably 10 to 60 μm, in order to realize an increase in the capacity of the secondary battery. The plate thickness is 200 μm or more, preferably 300 μm or more. If the amount of rolling is within this range, a stainless steel foil having the special surface properties as described above can be obtained.

  It should be noted that the foil rolling process may be divided into a plurality of times (multi-stage rolling) according to the thickness of the stainless steel strip used for foil rolling, and intermediate annealing may be performed between the foil rolling processes.

  Next, the coating liquid in which the component composition is prepared so that the molar ratio of each element in the surface treatment film to be formed is within the above-described range on one or both surfaces of the obtained stainless steel foil. Is coated by a known coating means. Then, a surface treatment film is formed on the surface of the stainless steel foil by drying at a predetermined temperature. What is necessary is just to determine the temperature to dry suitably according to the component composition of a coating liquid. Moreover, what is necessary is just to change a coating amount suitably according to the thickness of a desired surface treatment film.

  The coating liquid can contain the following compounds as compounds that serve as the supply source of the above elements.

(Element group A)
Examples of phosphorus (P) include phosphorus compounds having a phosphate group and / or a phosphone group, and a crosslinkable compound is preferable. Specifically, tripolyphosphoric acid, chromium (III) phosphate, aminotri (methylenephosphonic acid), 1-hydroxyethane-1,1-diphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediamine-N, N, N ′, N′-tetra (methylenephosphonic acid), hexamethylenediamine-N, N, N ′, N′-tetra (methylenephosphonic acid), diethylenetriamine-N, N, N ′, N ″, N '' -Penta (methylenephosphonic acid), 2-phosphonobutane-1,2,4-tricarboxylic acid and the like are exemplified. When such a compound is used, not only a phosphorus source but also a nitrogen source, a carbon source, a chromium source, and an oxygen source can be used.

Zirconium (Zr) is exemplified by zirconium carbonate, oxide, hydroxide, nitrate, sulfate, phosphate, fluoride, fluoro acid (salt), organic acid salt, organic complex compound, and the like. It is preferable that it is an ionic compound. Specifically, basic zirconium carbonate, zirconium oxycarbonate, ammonium zirconium carbonate (NH ₄ ) ₂ [Zr (CO ₃ ) ₂ (OH) ₂ ], zirconium oxide (IV) (zirconia), zirconium nitrate, zirconyl nitrate ZrO (NO ₃ ) ₂ , zirconium (IV) sulfate, zirconyl sulfate, zirconium oxyphosphate, zirconium pyrophosphate, zirconyl dihydrogen phosphate, zirconium fluoride, hexafluorozirconic acid H ₂ ZrF ₆ , ammonium hexafluorozirconate [(NH ₄ ) ₂ ZrF ₆ ], zirconyl acetate, zirconium acetylacetonate Zr (OC (═CH ₂ ) CH ₂ COCH ₃ ) _{4 and the} like. When such a compound is used, not only a zirconium source but also a phosphorus source, a nitrogen source, a carbon source, an oxygen source, and a fluorine source can be used.

Examples of titanium (Ti) include titanium carbonates, oxides, hydroxides, nitrates, sulfates, phosphates, fluorides, fluoro acids (salts), organic acid salts, and organic complex compounds. It is preferable that it is an ionic compound. Specifically, titanium oxide (IV) (titania), titanium nitrate, titanium sulfate (III), titanium sulfate (IV), titanyl sulfate TiOSO ₄ , titanium fluoride (III), titanium fluoride (IV), hexafluoro Titanate H ₂ TiF ₆ , ammonium hexafluorotitanate [(NH ₄ ) ₂ TiF ₆ ], titanium laurate, diisopropoxytitanium bisacetone (C ₅ H ₇ O ₂ ) ₂ Ti [OCH (CH ₃ ) ₂ ] ₂ , titanium acetylacetonate Ti (OC (═CH ₂ ) CH ₂ COCH ₃ ) _{3 and the} like can be exemplified. When such a compound is used, not only a titanium source but also a phosphorus source, a nitrogen source, a carbon source, an oxygen source, and a fluorine source can be used.

  Nitrogen (N) is exemplified by nitrogen compounds having an amino group and / or an amide group, and is preferably a crosslinkable compound. Specifically, ethylenediamine, N, N-dimethylformamide, 1,3-diamino-2-propanol-N, N, N ′, N′-tetraacetic acid, aminotri (methylenephosphonic acid), 1-hydroxyethane-1 , 1-diphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediamine-N, N, N ′, N′-tetra (methylenephosphonic acid), hexamethylenediamine-N, N, N ′, N ′ -Tetra (methylenephosphonic acid), diethylenetriamine-N, N, N ′, N ″, N ″ -penta (methylenephosphonic acid) and the like can be exemplified. When such a compound is used, not only a nitrogen source but also a phosphorus source, a carbon source, and an oxygen source can be used.

  Examples of carbon (C) include polyolefin resins, urethane resins, vinyl resins, and acrylic resins. When such a resin is used, not only a carbon source but also a nitrogen source and an oxygen source can be used. Moreover, the component derived from the compound which is another element source is illustrated.

  Examples of oxygen (O) include various resins added as a carbon source or phosphoric acid compounds added as a phosphorus source. Moreover, the oxygen derived from the water contained in a coating liquid may be sufficient.

As for chromium (Cr), a chromium compound not containing hexavalent chromium is exemplified from the viewpoint of environmental problems, and in this embodiment, it is a trivalent chromium compound. Specific examples include chromium sulfate, chromium nitrate, chromium fluoride, chromium phosphate, chromium oxalate, chromium acetate, chromium biphosphate, chromium acetylacetonate (Cr (C ₅ H ₇ O ₂ ) ₃ ) and the like. When such a compound is used, not only a chromium source but also a phosphorus source, a nitrogen source, a carbon source, an oxygen source, and a fluorine source can be used.

  About fluorine (F), it is preferable to use the compound containing a fluorine among the compounds of the other element sources mentioned above. Specifically, chromium fluoride is exemplified.

  As a solvent used in the coating solution, water is preferably the main component. Further, if necessary, an alcohol-based, ketone-based, or cellosolve-based water-soluble organic solvent may be used. Moreover, as long as the above-mentioned surface treatment film can be formed and the effects of the present invention are obtained, known surfactants, antifoaming agents, leveling agents, antibacterial and antifungal agents, coloring agents, curing agents, and the like are added. It may be added.

  When forming a polyolefin resin layer on the formed surface treatment film, a polyolefin resin film having a predetermined thickness may be prepared, laminated on the surface treatment film, and thermocompression bonded.

  By doing in this way, the surface treatment stainless steel foil which concerns on this embodiment can be manufactured.

(5. Effects of the present embodiment)
In this embodiment, a surface treatment film having a specific component composition is formed on a stainless steel foil having a special surface property. In this way, the surface properties of stainless steel foil, which has not been paid attention to in the past, are specified, and the component composition suitable for the surface properties is optimized to form a surface treatment film, thereby improving the resistance to electrolyte. Can do.

  In particular, by forming the surface treatment film on a stainless steel foil having a thickness of 100 μm or less, the organic compound component and the inorganic compound component contained in the surface treatment film cooperate to form a composite network structure. Due to this composite network structure, it is possible to achieve both a high barrier property against the corrosive substance contained in the electrolytic solution and a followability that can flexibly cope with the deformation of the stainless steel foil.

(6. Modifications)
In the above embodiment, the surface treatment film is formed on one surface of the stainless steel foil, but the surface treatment film may be formed on both surfaces of the stainless steel foil.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the embodiment mentioned above at all, and can be variously modified within the range which does not deviate from the summary of this invention.

  Hereinafter, the present invention will be described based on further detailed examples, but the present invention is not limited to these examples.

(Test 1)
The stainless steel foil is 0.3 mm (300 μm) thick stainless steel (SUS304, SUS316L, SUS444, SUS430) manufactured by Nippon Steel & Sumikin Stainless Steel Co., Ltd. Except for Comparative Example 31, a stainless steel foil having a thickness of 30 μm was produced. In Comparative Example 31, a cold-rolled SUS304 steel plate having a thickness of 300 μm was used as the stainless steel foil.

As a rolling mill, a KT mill was used, the diameter of the work roll was 30 to 60 mm, and the longitudinal tension was 400 to 600 N / mm ² . Further, intermediate annealing was appropriately performed to avoid a decrease in productivity due to work hardening of the rolled material.

  For the rolled material, a work roll having a surface roughness Ra of 0.25 μm was used. However, only the comparative example 32 used the work roll whose surface roughness is 0.02 micrometer.

(Surface property measurement of stainless steel foil)
The surface properties of the obtained stainless steel foil were measured as follows. An atomic force microscope (Bruker AXS Nanoscope 5) was used as a measuring device. The cantilever used was MPP11100 manufactured by the same company, and the radius of curvature of the tip of the probe was 8 nm.

  In order to obtain measurement data that reflects the surface properties inherent to the stainless steel foil, the measurement mode of the atomic force microscope is set to the tapping mode. Was arbitrarily selected a 30 μm square region, and measurement was performed on the region. The measurement was repeated 5 times. That is, measurement was performed on arbitrary five regions on the stainless steel foil.

  In addition, using the software attached to the atomic force microscope, flatten processing was performed on the obtained measurement data of the five regions, and the arithmetic average roughness Ra in each region was calculated. Further, a median process was performed with an 11 × 11 matrix, a threshold value was set to 50 nm, and a peak count Pc in each region was calculated. The peak count Pc was calculated by cutting the peripheral edge with a width of 0.45 μm from a square region with a side of 30 μm. That is, the peak count Pc was calculated in a square region with a side of 29.1 μm. Was calculated. The average values of Ra and Pc in each obtained region were defined as the arithmetic average roughness Ra and peak count Pc of the stainless steel foil. The results are shown in Table 1. FIG. 5 shows an image obtained by performing image processing for calculating the observation image with the atomic force microscope and the peak count Pc for the inventive example 31 and the comparative example 31.

(Formation of surface treatment film)
The coating solution was applied to one surface of the stainless steel foil obtained above using a spin coater. The amount of adhesion at the time of coating was adjusted by the rotation speed of the spin coater. After coating, a surface treatment film was formed by heating at a temperature range of 170 to 200 ° C. for 10 to 30 seconds. For heating, a box-type heating furnace having a substantially cubic space with a side of 25 cm or more set at a predetermined temperature was used.

  The coating solution was prepared by controlling the amount of the compound (element supply source) shown below so that the element ratio in the surface treatment film formed after coating became the value shown in Table 1.

(Element group A)
Phosphorus (P): tripolyphosphoric acid (P1), chromium (III) phosphate (P2), 1-hydroxy-ethylidene-1,1-diphosphonic acid (HEDP) (P3)
All of the above compounds are also sources of oxygen. Chromium phosphate is also a source of chromium, and HEDP is also a source of carbon.

Zirconium (Zr): Zirconium ammonium carbonate (Z)
Since the carbonic acid component and the ammonium component are not taken into the surface treatment film, the same molar amount as the required Zr molar amount was used.

Titanium (Ti): Titanium acetylacetonate (T)
The above compounds are also sources of carbon and oxygen.

  Nitrogen (N): 1,3-diamino-2-propanol-N, N, N ′, N′-tetraacetic acid (DPTA) (N)

Carbon (C): polyolefin resin (PO), polyurethane resin (PU), polyvinyl resin (PV), polyacrylic resin (PA)
The amount added was calculated by excluding the amount added from other additives.

  As the polyolefin resin, a copolymer of ethylene (80% by mass) and acrylic acid (20% by mass) (average molecular weight: 100,000, neutralized ammonia product) was used.

  As the polyurethane resin, one produced by the following procedure was used. That is, 100 parts of polyester polyol (adipic acid / 3-methyl-1,5-pentanediol, number average molecular weight 1000, number of functional groups 2, hydroxyl value 112.2), 3 parts of trimethylolpropane, 2 parts of dimethylolpropionic acid, 85 parts of isophorone diisocyanate was reacted in methyl ethyl ketone to obtain a urethane prepolymer. This was mixed with 9.4 parts of triethylamine, poured into water, the urethane prepolymer was dispersed in water, and elongated with ethylenediamine to obtain a dispersion. Methyl ethyl ketone was distilled off to obtain an aqueous urethane resin dispersion containing 30% by mass of non-volatile content, which was used.

  As the polyvinyl resin, a partially saponified product of polyvinyl acetate (average molecular weight: 50000, 5 mass% acetoacetylated) was used. The polyvinyl resin was produced by polymerizing vinyl acetate, partially saponifying 90%, and then acetoacetylating 5% by mass with respect to 100% by mass of the copolymer.

  As a polyacrylic resin, what was produced by the procedure shown below was used. That is, 20 parts of methyl methacrylate, 40 parts of butyl acrylate, 10 parts of 2-hydroxypropyl methacrylate, 10 parts of styrene, and 20 parts of N, N-dimethylaminopropyl methacrylate were used as the monomer composition. In the synthesis method, the above monomer was mixed with 100 parts of a 10% by mass aqueous emulsifier solution in which a reactive nonionic emulsifier and polyoxyethylene octylphenyl ether (HLB17.9) were mixed at 6: 4, and the mixture was mixed at 5000 rpm using a homogenizer. Was emulsified for 10 minutes to obtain a monomer emulsion. Subsequently, 150 parts of an emulsifier aqueous solution was added to a four-necked flask equipped with a stirrer, a reflux condenser, a thermometer, and a monomer supply pump, and kept at 40 to 50 ° C., and a 5 mass% aqueous solution of ammonium persulfate (50 parts) and Each of the monomer emulsions was placed in a dropping funnel, attached to another mouth of the flask, dropped over about 2 hours, the temperature was raised to 60 ° C., and the mixture was stirred for about 1 hour. The mixture was cooled to room temperature while stirring to obtain an aqueous dispersion of an acrylic resin, which was used.

  Oxygen (O): In addition to the amount derived from the additive of other elements, the deficiency is taken in from the water in the coating solution, so if the amount of additive of other elements is determined, the mole of oxygen The ratio is also determined.

Chromium (Cr): One or more selected from chromium sulfate / n hydrate, chromium nitrate nonahydrate, chromium fluoride trihydrate, and chromium (III) phosphate hexahydrate Since the anion components of sulfate and nitrate are hardly taken into the surface treatment film, there is no need to consider them. Chromium fluoride is also a fluorine source, and chromium phosphate is also a phosphorus source.

  Fluorine (F): Chromium fluoride

(Analysis of surface treatment film)
(Thickness of surface treatment film)
The thickness of the surface treatment film was measured by X-ray photoelectron spectroscopy (XPS). Using a Quantum 2000 XPS analyzer manufactured by PHI, 15 kV and 25 W X-rays from an Al Kα X-ray source were used as the radiation source. The measurement area is a 0.1 mm square area, and the surrounding 2 mm square area is sputtered at a speed that gives a sputter rate of 4.26 nm / min when SiO ₂ as a standard sample is sputtered. Measurements were taken. Based on the peak intensity and sensitivity coefficient of each component element, the element ratio was calculated. Sputtering was carried out until the sputtering reached the stainless steel foil and the Fe strength contained in the stainless steel foil became substantially constant.

  In this example, the sputtering depth at which the Fe concentration at which the Fe strength was stabilized decreased to half the concentration in the surface-treated film was used as the interface between the surface-treated film and the stainless steel foil for convenience. And the sputtering depth calculated | required from the sputtering time from the outermost layer of a surface treatment film to the said interface and the sputtering rate of a standard sample was made into the thickness of a surface treatment film. The results are shown in Table 1.

(Molar ratio of each element)
XPS was also used for analysis for calculating the molar ratio of elements contained in the surface treatment film. In the thickness of the surface treatment film, depth direction analysis was performed so that five or more XPS measurement points were obtained between the outermost layer and the interface between the surface treatment film and the stainless steel foil. Of the obtained measurement data, element group A, carbon (C), oxygen (O), chromium (Cr) and fluorine (F), except for the measurement data at the outermost surface layer of the surface treatment film and the measurement data at the interface The element ratio was calculated so that the total of these elements was 100 mol%. The results are shown in Table 1.

(Identification of organic compounds)
In order to specify the organic compound contained in the surface-treated film, the RAS method FTIR was used. As a result, it was confirmed that the surface treatment film contained the organic compound added to the coating solution.

(Lamination of polyolefin resin layer)
A polyolefin-based resin layer was formed on the surface treatment film to obtain a resin-coated stainless steel foil. Specifically, a polyolefin resin film having a thickness of 30 μm (Admer QE060 manufactured by Mitsui Chemicals Tosero Co., Ltd.) is laminated on the surface treatment film and held for 10 seconds under the conditions of temperature: 200 ° C. and pressure: 1 MPa, and the surface treated stainless steel. The foil and the polyolefin resin film were thermocompression bonded.

  The characteristic evaluation shown below was performed to the obtained resin-coated stainless steel foil.

(Primary adhesion)
Cut out 15 mm x 100 mm samples in pairs from resin-coated stainless steel foil, match the ends of the two coated resins together, thermocompression bond, create a T-peel test piece, and bond strength to T-peel It was measured by a test (23 ° C., T peel: same type as JIS K6854-3, pulling speed 300 mm / min). Each level N was measured at 5 and the five data were averaged to determine the adhesion strength. In units of [N / 15 mm], a rating of 40 or more was rated 4, a score of less than 40 was 30 or more, a score of less than 30 was 20 or more, a score of 2, and an adhesion strength of less than 20 was rated 1. The results are shown in Table 1.

(Electrolytic solution resistance)
As an evaluation of the resistance to electrolytic solution, a 10 mm × 100 mm sample was cut out from the resin-coated stainless steel foil, completely immersed in the electrolyte solution for a simulated deteriorated battery in a sealed container, and held at 85 ° C. for 7 days. As an electrolytic solution for a simulated deteriorated battery, lithium hexafluorophosphate (LiPF ₆ ) is used as an electrolyte, and a solvent in which ethylene carbonate and diethyl carbonate are mixed in a 1: 1 ratio is diluted to a concentration of 1 mol / L, and ion-exchanged water. Was added at 0.1% by weight.

  After holding, the sample was taken out from the electrolytic solution, the peel strength was measured by the following peel test, and compared with the peel strength of the sample before immersion. As for the peel strength, the peel strength before immersion and that after immersion were peel-tested with an N number of 5, and the five data were averaged to obtain the adhesion strength. The peel test was conducted at 23 ° C. and 180 ° peel: the same format as JIS K6854-2, at a pulling speed of 20 mm / min.

  The obtained peel strength after immersion was compared with the peel strength before immersion, and the strength reduction was calculated and evaluated as the strength maintenance rate. If there is no decrease in strength, it is 100%, and if the tensile strength is 0 after immersion, it is 0%. A score of 95% or more, a score of 90% or more, a score of 4, a score of 70% or more, a score of 3, a score of 50% or more, a score of 2, and a score of less than 50% were rated 1. The results are shown in Table 1.

  Table 1 shows the influence of the component composition contained in the surface treatment film on the effect of the present invention. That is, when the molar ratio of each element is within the range of the present invention, it was confirmed that the electrolytic solution resistance was good. Moreover, when the molar ratio of each element was made into the especially preferable range, it has confirmed that it showed the further outstanding electrolyte solution resistance.

  On the other hand, when the molar ratio of each element deviated from the scope of the present invention, it was confirmed that the electrolytic solution resistance could not be obtained. Further, in the comparative example in which only phosphorus (P) is higher than the range of the present invention, it was confirmed that the primary adhesion strength was low although the minimum electrolytic solution resistance could be secured.

(Test 2)
A resin-coated stainless steel foil was prepared in the same manner as in Test Example 1, except that the stainless steel foil was prepared by changing the steel type, presence / absence of annealing, foil rolling conditions, etc. The characteristics of the resulting resin-coated stainless steel foil were evaluated. In addition, the rolling conditions in which Pc exceeds 100 were not practically obtained. The results are shown in Table 2.

  Table 2 shows the influence of the surface properties of the stainless steel foil on the effects of the present invention. In Test 1, it was confirmed that even a sample having good electrolytic solution resistance caused a difference in electrolytic solution resistance due to a change in the surface properties of the stainless steel foil. In particular, when the surface property of the stainless steel foil defined in the present invention is deviated, it was confirmed that good electrolytic solution resistance was not obtained and the primary adhesion strength was slightly low.

(Test 3)
A resin-coated stainless steel foil was prepared in the same manner as in Example 2 of Test 1 except that the thickness of the surface treatment film was changed by adjusting the amount of adhesion during coating. The characteristics of the obtained resin-coated stainless steel foil were evaluated. The results are shown in Table 3.

  Table 3 shows the influence of the thickness of the surface treatment film on the effect of the present invention. When the thickness of the surface treatment film is thin, the electrolytic solution resistance tends to deteriorate, and when the thickness is less than 2 nm, it has been confirmed that sufficient electrolytic solution resistance cannot be obtained.

  On the other hand, when the thickness of the surface treatment film was large, it was confirmed that the primary adhesion strength tends to be low although the electrolytic solution resistance is good. In addition, when the thickness of the surface treatment film was increased, coating unevenness occurred when the concentration of the coating liquid was not increased during the formation of the surface treatment film. On the other hand, a coating solution having such a concentration that unevenness does not occur may cause precipitation in about two weeks, and there may be a problem in pot life. When the thickness exceeded 500 nm, it was confirmed that, in addition to the fact that the primary adhesion strength could not be obtained, coating unevenness was caused in the first place, and the electrolytic solution resistance deteriorated.

DESCRIPTION OF SYMBOLS 1 ... Surface treatment stainless steel foil 10 ... Stainless steel foil 20 ... Surface treatment film 30 ... Polyolefin resin layer

Claims (5)

A surface-treated stainless steel foil in which a surface-treated film is formed on at least one surface of the stainless steel foil,
The stainless steel foil has a thickness of 100 μm or less,
In the stainless steel foil, the surface on which the surface treatment film is formed has an arithmetic average roughness Ra measured by a probe having a radius of curvature of the tip portion of 6 nm to 15 nm of 30 nm to 100 nm, Having a surface property in which a peak count Pc measured by the probe is 20 or more in a quadrangular region having a side of 30 μm on the surface;
The surface treatment film has a thickness of 2 nm to 500 nm,
The surface treatment film is an element group A composed of at least one or two or more selected from phosphorus (P), zirconium (Zr), titanium (Ti) and nitrogen (N), carbon (C), Oxygen (O), chromium (Cr), and fluorine (F) at a molar ratio of A: C: O: Cr: F = 1 to 5: 3 to 15:30 to 50:15 to 35: A surface-treated stainless steel foil, which is contained at a ratio of 15 to 35.   The surface-treated stainless steel foil according to claim 1, wherein at least a part of the carbon is derived from an organic compound.   The surface-treated stainless steel foil according to claim 1, wherein at least a part of the chromium is derived from a trivalent chromium compound.   The surface-treated stainless steel foil according to any one of claims 1 to 3, further comprising a polyolefin-based resin layer containing a functional group having polarity on the surface-treated film.   The surface treatment film comprises a trivalent chromium compound, at least one resin selected from a polyolefin resin, a urethane resin, a vinyl resin, and an acrylic resin, and a phosphate group and / or a phosphone group. 5. One or more crosslinkable compounds selected from a phosphorus compound having an amino group and / or an amide group, a zirconium compound, and a titanium compound. The surface-treated stainless steel foil according to item 1.