Sn-PLATED CLAD MATERIAL AND METHOD FOR PRODUCING Sn-PLATED CLAD MATERIAL

Abstract

To provide an Sn-plated clad material in which the crack area ratio generated on the surface of the Sn plating layer after tensile testing with the elongation set at 17% is 0.016 or less.　An Sn-plated clad material having a Cu layer made of Cu on at least one surface of a base material made of Fe or an Fe alloy and further having an Sn plating layer on the surface of the Cu layer, wherein the crack area ratio determined by Sc / S is 0.016 or less when the area of the observation region is taken as S and the total area of cracks is taken as Sc in an observation image in which the surface of the Sn plating layer side of the test piece is viewed in plan after performing tensile testing with the elongation set at 17% using a test piece cut from the Sn-plated clad material.

Description

Sn-plated clad material and method for manufacturing Sn-plated clad material

[0001] The present invention relates to a Sn-plated clad material and a method for manufacturing the Sn-plated clad material, and more particularly to a Sn-plated clad material suitable for, for example, a negative electrode case of a button-shaped zinc-air battery, and a method for manufacturing the Sn-plated clad material.

[0002] Conventionally, a button-shaped zinc-air battery has been known (Patent Document 1).

[0003] The air-zinc battery disclosed in Patent Document 1 includes a negative electrode containing a zinc alloy as a negative electrode active material and an alkaline electrolyte, a negative electrode case that also serves as a current collector for the negative electrode, a positive electrode case fixed to the negative electrode case via an insulating member, and a positive electrode housed within the positive electrode case and using oxygen as a positive electrode active material. The negative electrode case is, for example, composed of a multilayer structure material in which a Sn layer, a Cu layer, an Fe layer, and a Ni layer are stacked in this order. The multilayer structure material is, for example, a Sn-plated clad material formed by forming a Sn-plated layer on the surface of the Cu layer by Sn plating on a three-layer clad material formed by laminating and pressure-welding (clad rolling) a Cu plate, a stainless steel plate, and a Ni plate. The Cu layer functions as a negative electrode current collector. The Fe layer is made of stainless steel and serves as a substrate that provides the mechanical strength of the negative electrode case. The Ni layer provides low contact resistance and corrosion resistance in the operating environment. The Sn layer (Sn plated layer) is a layer that has the function of suppressing the generation of hydrogen gas during the battery reaction.

[0004] In batteries (primary batteries) including the above-mentioned air-zinc battery, hydrogen gas generation during the battery reaction can cause problems such as deterioration of power generation, expansion due to an increase in internal battery pressure, and electrolyte leakage. Previously, mercury was added to the negative electrode active material to increase the hydrogen overvoltage of zinc, thereby suppressing hydrogen gas generation upon contact between the electrolyte and the current collector (Cu layer). However, in recent years, environmental concerns, regulations such as the RoHS Directive and the Minamata Convention have led to the trend toward mercury-free batteries, including air-zinc batteries. In the examples of Patent Document 1, it is described that by forming a Sn plating layer with a thickness of approximately 0.2 μm on the surface of the current collector (Cu layer) of the negative electrode case using an electroless substitution Sn plating process, the hydrogen overvoltage of the Cu layer can be increased, thereby suppressing hydrogen gas generation during the battery reaction.

[0005] Japanese Patent Application Laid-Open No. 2006-261042

[0006] Recently, not only secondary batteries but also primary batteries have become smaller and have higher capacities, and improved drawing workability for the negative electrode cases of the above-mentioned zinc-air batteries is also required. In the case of negative electrode cases using Sn-plated clad materials, increasing the degree of drawing can cause cracks in the Sn-plated layer and Cu layer, exposing the Fe layer through the cracks. When a negative electrode case with an exposed Fe layer is used, the Fe contained in the Fe layer and the Zn (zinc) contained in the negative electrode active material come into contact with each other through the electrolyte, increasing the possibility of hydrogen gas generation. Therefore, there is a need for a Sn-plated clad material that exhibits minimal cracking in the Sn-plated layer and Cu layer, even when drawing to an elongation of approximately 17% (equivalent to a degree of drawing of 7.0%), as described below.

[0007] An object of the present invention is to provide a Sn-plated clad material and a method for manufacturing the Sn-plated clad material that can sufficiently reduce cracks that occur on the surface of the Sn plating layer when, for example, forming a negative electrode case of a button-shaped air zinc battery by drawing.

[0008] The inventors investigated and analyzed actual negative electrode cases and discovered that cracks occur in the Sn plating layer before cracks occur in the Cu layer underlying the Sn plating layer. Through subsequent ingenuity, they discovered a configuration for the Sn plating layer that can follow the plastic deformation of the underlying Cu layer, and arrived at the present invention.

[0009] The Sn-plated clad material according to the present invention comprises a substrate made of Fe or an Fe alloy, a Cu layer made of Cu on at least one surface thereof, and a Sn-plated layer on the surface of the Cu layer, and a test piece cut out from the Sn-plated clad material is subjected to a tensile test with an elongation set to 17%, and then, in an observation image of the test piece when the surface of the Sn-plated layer side is viewed in plan, the crack area ratio calculated from Sc / S is 0.016 or less, where S is the area of ​​the observation region and Sc is the total area of ​​crack locations. The reason for setting the elongation to 17% will be described later.

[0010] In the Sn-plated clad material according to the present invention, in an observation image when the surface of the Sn-plated layer side of the test specimen is viewed in plan before the tensile test, the average grain size of the crystal grains constituting the Sn-plated layer is preferably 0.8 μm or more, more preferably 1.0 μm or more, and even more preferably 1.2 μm or more.

[0011] In the Sn-plated clad material according to the present invention, preferably, the average thickness of the Sn-plated layer is 0.5 μm or more in an observation image when the Sn-plated layer of the test specimen is viewed in cross section before the tensile test is performed.

[0012] The above-mentioned Sn-plated clad material can be obtained by the following method for producing a Sn-plated clad material.

[0013] The method for manufacturing a Sn-plated clad material according to the present invention includes the steps of: (1) preparing a clad material having a Cu layer made of Cu on at least one surface of a substrate made of Fe or an Fe alloy; and (2) forming a Sn plating layer on the surface of the Cu layer of the clad material, wherein in the step (2), an electrolytic Sn plating process is used to form the Sn plating layer such that the average grain size of the crystal grains constituting the Sn plating layer is 0.8 μm or more when observed in a planar view of the surface on the Sn plating layer side.

[0014] The method for manufacturing a Sn-plated clad material according to the present invention preferably forms the Sn-plated layer so that the average grain size of the crystal grains constituting the Sn-plated layer is 1.0 μm or more, and more preferably forms the Sn-plated layer so that the average grain size of the crystal grains constituting the Sn-plated layer is 1.2 μm or more.

[0015] The method for manufacturing a Sn-plated clad material according to the present invention preferably forms the Sn-plated layer so that the average thickness of the Sn-plated layer is 0.5 μm or more in an observed cross-sectional image of the Sn-plated layer.

[0016] According to the present invention, it is possible to provide a Sn-plated clad material and a method for manufacturing the Sn-plated clad material, in which the area ratio of cracks generated on the surface of the Sn plating layer after a tensile test with an elongation set to 17% is 0.016 or less, which can contribute to the practical application of anode cases and the like suitable for air zinc batteries, which have few cracks generated in the Sn plating layer.

[0017] 1 is a diagram showing a cross-sectional configuration of a button-shaped zinc-air battery. 2 is a diagram showing a configuration of a Sn-plated clad material 1A having a substrate 11, a Cu layer 12, and a Sn-plated layer 10. 3 is a diagram showing a configuration of a Sn-plated clad material 1B having a substrate 11, a Cu layer 12, a Sn-plated layer 10, and a Ni layer 13. 4 is a diagram showing the elongation amount, working degree, and an observation image (plan view) of the Sn-plated layer of a test specimen after a tensile test. 5 is a diagram (graph) showing the relationship between the average grain size of the Sn-plated layer of the test specimen before the tensile test and the crack area ratio of the Sn-plated layer of the test specimen after the tensile test. 6 is a diagram (graph) showing the relationship between the x value and y value of a first model, the relationship between the p value and q value of a second model, and the absolute value of the difference between the y value and the q value.

[0018] Hereinafter, embodiments of the Sn-plated clad material and the method for manufacturing the Sn-plated clad material according to the present invention will be described with specific examples.

[0019] The Sn-plated clad material according to an embodiment of the present invention is used, for example, in the negative electrode case of a button-shaped air-zinc battery. The button-shaped air-zinc battery uses oxygen in the air for the positive electrode and zinc for the negative electrode, and has, for example, a cross-sectional configuration as shown in FIG. 1. As shown in FIG. 1, the air-zinc battery 100 is composed of a negative electrode case 101, a positive electrode case 102, a separator 103, a negative electrode 104, a positive electrode 105, a water-repellent film 106, a diffusion paper 107, a gasket 108, and an air hole 109. When oxygen in the air is taken into the battery through the air hole 109, the air-zinc battery 100 enters a discharge state and functions as a battery.

[0020] The negative electrode case 101 has a Sn plating layer 10 (see Figures 2 and 3) on its inside (inside the battery) and serves as a structural component of the battery, serving as the negative electrode terminal. The positive electrode case 102 serves as a structural component of the battery, serving as the positive electrode terminal. The separator 103 separates the negative electrode 104 from the positive electrode 105. The negative electrode 104 contains zinc and an alkali metal hydroxide such as potassium hydroxide. The positive electrode 105 is an air electrode that utilizes oxygen in the air taken in through the air hole 109. The water-repellent film 106 prevents moisture in the air taken in through the air hole 109 from entering the battery. The diffusion paper 107 helps ensure that the oxygen in the air taken in through the air hole 109 is evenly absorbed into the battery.

[0021] The negative electrode case 101 is formed into a desired shape by drawing using a Sn-plated clad material with the Sn-plated layer facing inward. The positive electrode case 102 is formed into a desired shape by drawing using a rolled material such as a stainless steel plate or a three-layer positive electrode clad material having Ni layers on both sides of a stainless steel substrate. While the negative electrode case 101 shown in FIG. 1 has a substantially rectangular cross section, the cross-sectional shape of a negative electrode case using a Sn-plated clad material is not limited to this. The negative electrode case 101 shown in FIG. 1 is an example of a product (drawn product) using a "Sn-plated clad material" as defined in the claims.

[0022] As described above, a Sn-plated clad material is used for the negative electrode case 101. The Sn-plated clad materials 1A and 1B shown in FIGS. 2 and 3 are configuration examples according to embodiments of the Sn-plated clad material of the present invention. The Sn-plated clad material 1A (hereinafter referred to as clad material 1A) shown in FIG. 1 has a Cu layer 12 on one side (Z1 side) of the substrate 11, and a Sn-plated layer 10 on the surface (Z1 side) of the Cu layer 12. The Sn-plated clad material 1B (hereinafter referred to as clad material 1B) shown in FIG. 3 has a Cu layer 12 on one side (Z1 side) of the substrate 11, a Sn-plated layer 10 on the surface (Z1 side) of the Cu layer 12, and a Ni layer 13 on the surface (Z2 side) of the substrate 11. The clad material 1B has a practical advantage over the clad material 1A because it has the Ni layer 13, which performs the function described below.

[0023] 2 and 3 have a Cu layer 12 on at least one surface side (Z1 side) of the substrate 11. The Sn-plated clad material according to the present invention can have the Cu layer 12 on both one surface side (Z1 side) and the other surface side (Z2 side) of the substrate 11. Although not shown, the Sn-plated clad material having a Cu layer (referred to as Cu layer 12') on the other surface side (Z2 side) of the substrate 11 can further have a Ni layer on the other surface side (Z2 side) of the Cu layer 12'.

[0024] In the clad materials 1A and 1B described above, the substrate 11 (Fe layer) is made of Fe (iron) or an Fe alloy, which has excellent mechanical strength, and is a metal layer that functions to maintain the structure of the clad materials 1A and 1B. The substrate 11 may be a rolled material made of Fe or an Fe alloy. When the substrate 11 is made of an Fe alloy, the Fe alloy may be, for example, stainless steel such as SUS304 or SUS316L according to the JIS standard.

[0025] In the clad materials 1A and 1B described above, the Cu layer 12 is made of Cu (copper), which has excellent electrical conductivity, and is a metal layer that functions as a current collector for the clad materials 1A and 1B. The Cu layer 12 may be a rolled material made of Cu. In this case, the Cu constituting the Cu layer 12 may be oxygen-free copper such as JIS C1020. The Cu layer 12 may also be a Cu plated film formed by electrolytic plating or electroless plating.

[0026] In the clad materials 1A and 1B described above, the Sn plating layer 10 is a Sn plating film made of Sn (tin) or a Sn alloy plating film made of a Sn alloy, and is a metal plating layer that improves the hydrogen overvoltage of the Cu layer 12 and suppresses the generation of hydrogen gas during a battery reaction. The Sn plating layer 10 may be a Sn plating film or a Sn alloy plating film (hereinafter collectively referred to as "Sn plating film") formed by electrolytic plating. The Sn alloy may be, for example, an alloy with Zn (zinc), In (indium), Bi (bismuth), Cu (copper), Ag (silver), or the like, and may be an Sn-Zn-based, Sn-In-based, Sn-Bi-based, Sn-Cu-based, or Sn-Ag-based alloy.

[0027] Furthermore, in the clad material 1B, the Ni layer 13 is made of Ni (nickel) or a Ni alloy, which is electrically conductive and has excellent corrosion resistance, and is a metal layer that provides the clad material 1B with low contact resistance and corrosion resistance in the usage environment. The Ni layer 13 may be a rolled material made of Ni, a Ni plating film formed by electrolytic plating, or a NiP plating film formed by electroless plating. The NiP plating film contains P (phosphorus) derived from the electroless plating solution. In the case of a rolled material, the Ni constituting the Ni layer 13 may be NW2200 or NW2201 according to the JIS standard. Because the clad material 1B has the Ni layer 13 that provides the above-mentioned functions, it is preferable to the clad material 1A from the viewpoint of practicality.

[0028] Clad materials 1A and 1B were subjected to a tensile test with an elongation set to 17% using specimens 1A and 1B cut from the clad materials 1A and 1B. In the observation image of the surface of the Sn-plated layer 10 side (Z1 side) of the specimens 1A and 1B after the tensile test, where S is the area of ​​the observation area and Sc is the total area of ​​the cracked portions, the crack area ratio calculated by Sc / S is 0.016 or less. The planar view of the surface of the Sn-plated layer 10 means observation from the Z1 side shown in Figures 2 and 3 . The reason for setting the elongation to 17% during the tensile test will be described later, but will be briefly explained here. When a 0.128 mm thick Sn-plated clad material was drawn to form a cup-shaped case, the thickness of the thinnest part of the case was 0.119 mm. In this case, the drawing degree V Ｐ The elongation of the 0.128 mm Sn-plated clad material was 7%. Furthermore, when the 0.128 mm Sn-plated clad material was stretched to a thickness of 0.119 mm in a tensile test, the elongation was 17%. From the results of the drawing process and the tensile test, it can be understood that the elongation of the 0.128 mm Sn-plated clad material during the tensile test (17%) corresponds to the degree of drawing (7%) and also to the elongation of the thinnest part of the case. From this perspective, the elongation during the tensile test was used as a substitute for the degree of drawing. The comparison standard for the degree of drawing was set to 7%, and the comparison standard for the corresponding elongation during the tensile test was set to 17%.

[0029] The Sn plating layer 10 having a crack area ratio Sc / S of 0.016 or less can follow the plastic deformation of the underlying Cu layer 12 during drawing of the clad materials 1A and 1B. Therefore, even in drawing that involves such large plastic deformation that cracks may occur in the Cu layer 12, the Sn plating layer 10 follows the plastic deformation of the Cu layer 12, and can prevent cracks from occurring in the Sn plating layer 10 before they occur in the Cu layer 12. As a result, even if cracks occur in the Sn plating layer 10 due to drawing, excessive exposure of the substrate 11 to the surface of the Sn plating layer 10 is prevented because the crack area ratio Sc / S is 0.016 or less.

[0030] Specifically, the clad materials 1A and 1B (specimens 1A and 1B), in which the crack area ratio Sc / S of specimens 1A and 1B after a tensile test at an elongation of 17% was 0.016 or less, exhibited sufficiently small cracks in the Sn plating layer 10 even when subjected to drawing, which involves large plastic deformation of approximately 17% elongation. Therefore, the anode case 101 formed using the clad materials 1A and 1B by drawing at an elongation of approximately 17% exhibits sufficiently smaller cracks on the surface of the Sn plating layer 10 than conventional cases. Anode cases 101 with sufficiently smaller cracks on the surface of the Sn plating layer 10 than conventional cases can suppress hydrogen gas generation during battery reactions more effectively than conventional cases. As a result, the clad materials 1A and 1B can contribute to the practical application of anode cases 101 for air-zinc batteries 100 because the anode cases 101 using them enhance the reliability of the air-zinc batteries 100. The relationship between the elongation amount during the tensile test and the crack area ratio Sc / S of the Sn plating layer 10 has been confirmed by experiment, and will be described in detail later.

[0031] Specimen 1A cut out from clad material 1A for use in tensile tests and the like has the same layer structure as clad material 1A shown in Fig. 2, and includes substrate 11, Cu layer 12, and Sn plating layer 10. Similarly, specimen 1B cut out from clad material 1B has the same layer structure as clad material 1B shown in Fig. 3, and includes substrate 11, Cu layer 12, Ni layer 13, and Sn plating layer 10.

[0032] In the clad materials 1A and 1B, in an observation image when the surface on the Sn plating layer 10 side (Z1 side) of the specimens 1A and 1B is viewed in plan view before the above-described tensile test is performed, the average grain size of the crystal grains constituting the Sn plating layer 10 is preferably 0.8 μm or more, more preferably 1.0 μm or more, and even more preferably 1.2 μm or more. The average grain size of the crystal grains constituting the Sn plating layer 10 is preferably 3.0 μm or less, and more preferably 2.5 μm or less.

[0033] Clad materials 1A and 1B (specimens 1A and 1B) having an average grain size of 0.8 μm or more constituting the Sn plating layer 10 are likely to have a crack area ratio Sc / S of 0.016 or less after a tensile test at an elongation of 17%. Furthermore, when the reference value for the crack area ratio Sc / S of the Sn plating layer 10 of clad materials 1A and 1B (specimens 1A and 1B) is 0.016, clad materials 1A and 1B (specimens 1A and 1B) having an average grain size of 1.0 μm or more constituting the Sn plating layer 10 are likely to have a crack area ratio Sc / S that is reduced by a further 30% to 40% from the reference value. Furthermore, in clad materials 1A and 1B (specimens 1A and 1B) in which the average grain size of the crystal grains constituting the Sn plating layer 10 is 1.2 μm or more, there is a high possibility that the crack area ratio Sc / S will be reduced by a further 45% to 55% from the reference value. Note that the relationship between the average grain size of the Sn plating layer 10 and the crack area ratio Sc / S has been confirmed by prediction based on experimental results, and will be described in detail later.

[0034] In the clad materials 1A and 1B, in an observation image of the Sn plating layer 10 of the specimens 1A and 1B before the tensile test described above, the average thickness of the Sn plating layer 10 is preferably 0.5 μm or more, more preferably 1.0 μm or more. In the clad materials 1A and 1B, in an observation image of the Sn plating layer 10 of the specimens 1A and 1B before the tensile test described above, the average thickness of the Sn plating layer 10 is preferably 5.0 μm or less, more preferably 2.0 μm or less. Note that the cross-sectional view of the Sn plating layer 10 means observing the cross section along the Z1 and Z2 directions from any of the X1, X2, Y1, and Y2 directions shown in FIGS. 2 and 3 .

[0035] Clad materials 1A and 1B (specimens 1A and 1B) having an average thickness of the Sn plating layer 10 of 0.5 μm or more are preferred because the Sn plating layer 10 is less likely to fracture due to moderate plastic deformation and can be drawn at a practical degree of working. Clad materials 1A and 1B (specimens 1A and 1B) having an Sn plating layer 10 with an average thickness exceeding 5.0 μm can also be drawn at a practical degree of working. Therefore, if drawing at a practical degree of working is important, the average thickness of the Sn plating layer 10 may exceed 5.0 μm. On the other hand, if the average thickness of the Sn plating layer 10 exceeds 5 μm, the electrolytic Sn plating process takes longer, which may reduce production efficiency. Therefore, the average thickness of the Sn plating layer 10 that is likely to be effective and efficient for achieving the above-mentioned crack area ratio of 0.016 or less is 0.5 μm or more and 5.0 μm or less. Therefore, the average thickness of the Sn plating layer 10 of the clad materials 1A and 1B (specimens 1A and 1B) is preferably 0.5 μm or more, more preferably 1.0 μm or more. Also, the average thickness of the Sn plating layer 10 of the clad materials 1A and 1B (specimens 1A and 1B) is preferably 5.0 μm or less, more preferably 2.0 μm or less.

[0036] Next, an embodiment of a method for manufacturing a Sn-plated clad material according to the present invention will be described, taking the method for manufacturing the above-mentioned Sn-plated clad materials 1A and 1B (clad materials 1A and 1B) as an example.

[0037] The clad material 1A shown in FIG. 2 can be efficiently produced by a manufacturing method that includes a step (1) of preparing a clad material (intermediate material A) having a Cu layer 12 made of Cu on the surface of one side (Z1 side) of a base material 11 made of Fe or an Fe alloy, and a step (2) of forming a Sn plating layer 10 on the surface of the Cu layer 12 of the clad material (intermediate material A). In the step (2), an electrolytic Sn plating process is used to form the Sn plating layer 10 such that the average grain size of the crystal grains constituting the Sn plating layer 10 is 0.8 μm or more in an observation image when the surface on the Sn plating layer 10 side (Z1 side) is viewed in plan.

[0038] Similarly, the clad material 1B shown in FIG. 3 includes a step (1-1) of forming a Cu layer 12 made of Cu on one side (Z1 side) of a substrate 11 made of Fe or an Fe alloy, and a step (1-2) of forming a Ni layer 13 made of Ni on the other side (Z2 side) of the substrate 11. The clad material 1B can be efficiently produced by a manufacturing method including a step (1) of preparing a clad material (intermediate material B) having the Cu layer 12 on one side (Z1 side) of the substrate 11 and the Ni layer 13 on the other side (Z2 side) of the substrate 11, and a step (2) of forming a Sn plating layer 10 on the surface of the Cu layer 12 of the clad material (intermediate material B). In the step (2), an electrolytic Sn plating process is performed to form the Sn plating layer 10 such that the average grain size of the crystal grains constituting the Sn plating layer 10 is 0.8 μm or more in an observation image when the surface on the Sn plating layer 10 side (Z1 side) is viewed in plan.

[0039] As described above, in the method for manufacturing clad materials 1A and 1B, by forming an Sn plating layer 10 in which the average grain size of the crystal grains constituting the Sn plating layer 10 is 0.8 μm or more in an observation image when the surface on the Sn plating layer 10 side (Z1 side) is viewed in plan, clad materials 1A and 1B having an Sn plating layer 10 with the crack area ratio Sc / S of 0.016 or less can be manufactured. Furthermore, in the method for manufacturing clad materials 1A and 1B, by forming an Sn plating layer 10 in which the average grain size of the crystal grains constituting the Sn plating layer 10 is 1.0 μm or more, clad materials 1A and 1B having an Sn plating layer 10 with a high possibility of reducing the crack area ratio Sc / S by a further 30% to 40% from the reference value (0.016) can be manufactured. Furthermore, by forming the Sn plating layer 10 so that the average grain size of the crystal grains constituting the Sn plating layer 10 is 1.2 μm or more, it is possible to manufacture clad materials 1A and 1B having the Sn plating layer 10, which is highly likely to reduce the crack area ratio Sc / S by a further 45% to 55% from the reference value (0.016). Note that the relationship between the average grain size of the Sn plating layer 10 and the crack area ratio Sc / S has been confirmed by prediction based on experimental results, and will be described in detail later.

[0040] Furthermore, in the manufacturing method of the clad materials 1A and 1B, the Sn plating layer 10 is preferably formed so that the average thickness of the Sn plating layer 10 is 0.5 μm or more (more preferably, 0.5 μm or more and 5.0 μm or less) in a cross-sectional image of the Sn plating layer 10. Note that the cross-sectional view of the Sn plating layer 10 refers to observing the cross section along the Z1 and Z2 directions from any of the X1, X2, Y1, and Y2 directions shown in FIGS. 2 and 3 . A Sn plating layer 10 having an average thickness of 0.5 μm or more (more preferably, 0.5 μm or more and 5.0 μm or less) is moderately plastically deformed and less likely to fracture, and therefore is likely to have a crack area ratio of 0.016 or less when drawn at a practical working rate. The average thickness of the Sn plating layer 10 may exceed 5 μm, but this may result in a longer electrolytic Sn plating process time, which may reduce production efficiency. In the following, steps (1) and (2) are shown. The term "clad material" refers to the intermediate material before Sn plating. To distinguish the laminated structure, intermediate materials A, B, etc. are sometimes referred to in parentheses.

[0041] <Step (1)> In the case of clad material 1A, step (1) is a step of preparing a clad material (intermediate material A) having a Cu layer 12 made of Cu on at least one surface (Z1 side) of a substrate 11 made of Fe or an Fe alloy. The substrate 11 made of Fe or an Fe alloy can be made of a rolled material made of a corresponding Fe or an Fe alloy. The Cu layer 12 made of Cu can be made of a corresponding copper material made of Cu. In this case, a copper material to become the Cu layer 12 is laminated on one surface of the rolled material to become the substrate 11, and the resulting material is rolled (clad rolling) to produce a two-layer clad material (intermediate material A) in which the rolled material and the copper material are laminated in the thickness direction. After clad rolling, diffusion annealing may be further performed to increase the bonding strength between the substrate 11 and the Cu layer 12 that constitute the two-layer clad material (intermediate material A).

[0042] If it is desired to form a Cu layer (Cu layer 12' not shown) on the other surface of the rolled material that becomes the substrate 11, a three-layer clad material (intermediate material A') in which the rolled material and the copper material are laminated in the thickness direction can be produced by rolling (clad rolling) in a state in which copper material is laminated on both sides of the rolled material (one side and the other side). After clad rolling, diffusion annealing may be further performed to increase the bonding strength between the substrate 11 and the Cu layer 12 and between the substrate 11 and the Cu layer 12' that constitute the three-layer clad material (intermediate material A').

[0043] In the case of clad material 1B, step (1) includes a step (1-1) of forming a Cu layer 12 made of Cu on one side (Z1 side) of a substrate 11 made of Fe or an Fe alloy, and a step (1-2) of forming a Ni layer 13 made of Ni on the other side (Z2 side) of the substrate 11, thereby preparing a clad material (intermediate material B) having a Cu layer 12 on one side (Z1 side) of the substrate 11 and a Ni layer 13 on the other side (Z2 side) of the substrate 11. In the case of clad material 1B, in step (1-1), similar to clad material 1A, a rolled material made of a corresponding Fe or Fe alloy can be used for the substrate 11. Furthermore, a copper material made of a corresponding Cu can be used for the Cu layer 12. In the case of clad material 1B, unlike clad material 1A, preferably, step (1-1) is positioned as a pre-step (preparation step) for forming a clad material with a two-layer structure made of copper material and rolled material, and in the next step (1-2), a clad material with a three-layer structure (intermediate material B) made of copper material, rolled material, and nickel material is produced.

[0044] In the case of clad material 1B, a Ni layer 13 made of Ni is formed in the above step (1-2). A corresponding nickel material made of Ni can be used for the Ni layer 13. In this case, instead of producing a two-layer clad material in the above step (1-1), preferably, a copper material that will become the Cu layer 12 is laminated on one surface of a rolled material that will become the substrate 11, and a nickel material that will become the Ni layer 13 is laminated on the other surface of the substrate 11 of the rolled material, and then the resulting material is rolled (clad rolling) to produce a three-layer clad material (intermediate material B) in which the copper material, the rolled material, and the nickel material are laminated in the thickness direction. After clad rolling, diffusion annealing may be further performed to increase the bonding strength between the substrate 11 and the Cu layer 12 and between the substrate 11 and the Ni layer 13 that constitute the three-layer clad material (intermediate material B).

[0045] If it is desired to form a Cu layer (Cu layer 12' not shown) on the other surface of the rolled material that becomes the substrate 11, copper material is laminated on both sides of one side and the other side of the rolled material, and nickel material is further laminated on the surface of the Cu layer 12' (or Cu layer 12), and the rolled material is then rolled (clad rolling) in this state, thereby producing a four-layer clad material (intermediate material B') in which copper material, rolled material, copper material, and nickel material are laminated in the thickness direction. After clad rolling, diffusion annealing may be further performed to increase the bonding strength between the substrate 11 and the Cu layer 12, the substrate 11 and the Cu layer 12', and the Cu layer 12' (or Cu layer 12) and the Ni layer 13 that constitute the four-layer clad material (intermediate material B').

[0046] In the above step (1), in the case of a clad material having any of the above layer structures, instead of the copper material, a Cu plating film can be formed on one surface of the rolled material that will become the base material 11 by Cu plating, and the Cu plating film can be made into the Cu layer 12 or the Cu layer 12'. In this case, the clad material having the Cu layer 12 or the Cu layer 12' made of the Cu plating film may be further subjected to surface cleaning, drying, strip processing, etc.

[0047] Furthermore, in the above step (1), when the Ni layer 13 is formed, instead of the nickel material, a Ni plating film can be formed by Ni plating on the surface of a rolled material that will become the base material 11, or a Ni plating film can be formed on the surface of a copper material that will become the Cu layer 12 or the Cu layer 12', and the Ni plating film can be used as the Ni layer 13. In this case, the clad material having the Ni layer 13 made of the Ni plating film may be further subjected to surface cleaning, drying, stripping, etc. Note that the Cu layer 12 or the Cu layer 12' may be formed by Cu plating, and the Ni layer 13 may be formed by Ni plating, after which surface cleaning, drying, stripping, etc. may be performed.

[0048] <Step (2)> In the case of clad materials having any of the layer structures described above, step (2) involves forming a Sn plating layer 10 on the surface of the Cu layer 12 (or Cu layer 12') of the clad material. Specifically, in the case of clad materials having any of the layer structures described above, step (2) involves forming a Sn plating layer 10 on the surface of the Cu layer 12 (or Cu layer 12' (not shown)) of the clad material by electrolytic Sn plating, such that the average grain size of the crystal grains constituting the Sn plating layer 10 is 0.8 μm or more in an observation image when the surface on the Sn plating layer 10 side (Z1 side) is viewed in plan. The Sn plating layer 10 formed by electrolytic Sn plating consists of Sn and unavoidable impurities derived from the plating solution. While the Sn plating layer 10 can also be formed by electroless Sn plating, it is formed by electrolytic Sn plating in this invention. Compared with electroless Sn plating, electrolytic Sn plating allows for easier control of the thickness of the Sn plating film and allows for easier formation of a relatively thick Sn plating film. Therefore, electrolytic Sn plating is highly practical and more effective than electroless Sn plating for obtaining a Sn plating layer 10 of a desired thickness (film thickness) while ensuring productivity in forming the Sn plating layer 10.

[0049] As described above, in step (2), the Sn plating layer 10 is formed by electrolytic Sn plating, with the average grain size of the crystal grains being 0.8 μm or more. In this invention, the average grain size of the crystal grains constituting the Sn plating layer 10 is the average value of the circle-equivalent diameter. Specifically, in an observation image when the surface on the Sn plating layer 10 side (Z1 side) is viewed in plan, the diameter of a circle having an area equivalent to the area within the grain boundary determined for one crystal grain is defined as the grain size (circle-equivalent diameter) of that crystal grain. Then, in the observation image, the grain sizes (circle-equivalent diameters) of the individual crystal grains are determined, and their average value is calculated to define the average grain size of the crystal grains constituting the Sn plating layer 10.

[0050] By forming a Sn plating layer 10 having an average grain size of 0.8 μm or more as determined above, a tensile test is performed using specimens 1A and 1B cut from clad materials 1A and 1B having the Sn plating layer 10, with an elongation set to 17%. Then, in a planar observation image of the surface of specimen 1A or 1B facing the Sn plating layer 10, the likelihood of the crack area ratio Sc / S being 0.016 or less can be increased. Furthermore, by forming a Sn plating layer 10 having an average grain size of 1.0 μm or more, the likelihood of the crack area ratio Sc / S being reduced by a further 30% to 40% from the reference value (0.016) can be increased. Furthermore, by forming a Sn plating layer 10 having an average grain size of 1.2 μm or more, the likelihood of the crack area ratio Sc / S being reduced by a further 45% to 55% from the reference value (0.016) can be increased. The relationship between the average grain size of the Sn plating layer 10 and the crack area ratio Sc / S has been confirmed by prediction based on experimental results, and will be described in detail later.

[0051] <Confirmation Experiment> Next, as described above, a clad material having a Ni layer (see FIG. 3), which is more practically advantageous than a clad material not having a Ni layer (see FIG. 2), was produced, and the relationship between the elongation amount during a tensile test and the crack area ratio Sc / S of the Sn plating layer, and the relationship between the average grain size of the Sn plating layer and the crack area ratio Sc / S were confirmed by experiment.

[0052] In the experiment, to produce a Sn-plated clad material having a Ni layer as shown in Figure 3, a rolled material made of SUS304, a well-known austenitic stainless steel, a copper material made of oxygen-free copper (equivalent to C1020) that is widely used as a highly conductive metal material, and a nickel material made of high-purity Ni (99.0 mass% or more equivalent to NW2200 or NW2201) that has low contact resistance and excellent corrosion resistance were prepared. The copper material, rolled material, and nickel material were then laminated in this order in the thickness direction, and cold-rolled (clad rolling) was performed to pressure-weld the layers, followed by diffusion annealing. Further cold-rolling and annealing were performed to thin the material to a predetermined thickness, producing a three-layer clad material (intermediate material B) having a Cu layer, a substrate, and a Ni layer. The three-layer clad material (intermediate material B) is a clad material (intermediate material B) having a thickness of 0.127 mm and not Sn-plated, and having a Cu layer having a thickness of 13 μm, a base material having a thickness of 108 μm, and a Ni layer having a thickness of 6 μm.

[0053] Next, using the three-layer clad material (intermediate material B) prepared as described above, a Sn plating layer of a predetermined thickness was formed on one surface of the Cu layer by electrolytic Sn plating to form clad material 1B. This resulted in the production of clad materials for drawing and tensile testing (Experiments 1 to 4) with a four-layer structure (see Figure 3) having a 1 μm-thick Sn plating layer, a 13 μm-thick Cu layer, a 108 μm-thick substrate, and a 6 μm-thick Ni layer, each with a thickness of 0.128 mm. The thicknesses are all average values ​​(average thicknesses) of multiple measurements. The thickness of the Sn plating layer can be measured using an X-ray fluorescence analyzer. The thicknesses of the Cu layer, substrate, and Ni layer can be measured using a stereomicroscope or a FE-SEM (Field Emission-Scanning Electron Microscope). We also attempted to measure the surface hardness of a 1 μm-thick Sn-plated layer. However, even though we used a nanoindenter (a device that employs the nanoindentation method, which is suitable for measuring the hardness of thin films), the measured values ​​varied greatly due to the influence of the surface morphology of the substrate (rolled material). This phenomenon was also observed when measuring the hardness of the Sn-plated layer on a cup-shaped case, as described below. Therefore, we abandoned the hardness measurement of the Sn-plated layer.

[0054] Next, a hydrogen gas generation test was conducted simulating an air-zinc battery using a cup-shaped case simulating the approximately rectangular negative electrode case 101 shown in FIG. 1. For the hydrogen gas generation test, a cup-shaped case was used in which the Sn-plated clad material prepared as described above and having a thickness (average thickness) of 0.128 mm was drawn to simulate the approximately rectangular negative electrode case 101 shown in FIG. 1. In both cases, the Sn-plated layer 10 was drawn to the inside of the cup shape, and the thinnest part was near the edge of the opening of the cup shape. In both cases, the thickness (minimum thickness) of the thinnest part was 0.119 mm. Here, the thickness (average thickness) of the clad material 1B before drawing was T Ｐ The thickness of the thinnest part of the case after drawing (minimum thickness) is T Ｃ Let (T Ｐ -T Ｃ ) / T Ｐ The value obtained by multiplying by 100 is V Ｐ Then, as above, T Ｐ is 0.128 mm and T Ｃ is 0.119 mm, so V Ｐ = (0.128 - 0.119) / 0.128 x 100, V Ｐ In this invention, the V Ｐ The value was taken as the degree of drawing of the cup-shaped case, and the comparison standard for the degree of drawing was set at 7%.

[0055] The above-mentioned drawing degree V Ｐ A hydrogen gas generation test was conducted using a cup-shaped case with a 7.0% Sn content to confirm whether or not hydrogen gas was generated from the inner surface (Sn plating layer) of the cup-shaped case. The hydrogen gas generation test simulating an air-zinc battery was conducted by immersing a cup-shaped case filled with zinc (Zn) powder, which served as the negative electrode active material, in a potassium hydroxide solution (30% aqueous solution), which served as the electrolyte, for 10 minutes. During immersion, the presence or absence of hydrogen gas generation on the surface of the Sn plating layer was visually observed (by magnifying glass), and then the hydrogen gas generation portion on the surface of the Sn plating layer of the cup-shaped case, which was then removed from the electrolyte, was observed in plan view using a stereomicroscope.

[0056] As a result of the hydrogen gas generation test, relatively large cracks were confirmed in the observation image (plan view) of the hydrogen gas generation area on the surface of the Sn plating layer of the cup-shaped case. During the immersion, hydrogen gas generation could be confirmed visually from the vicinity of the observed cracks. The area with the relatively large cracks was cross-sectionally processed using a FIB (Focused Ion Beam) device, and the cross section of the cracked area was observed in detail using a SEM (Scanning Electron Microscope).

[0057] As a result, it was found that cracks occurred in the Sn plating layer and the Cu layer, but not in the substrate. Furthermore, it was found that in the cracked area, the Cu layer extended and thinned toward the bottom of the crack, while no change in the thickness of the Sn plating layer was observed, indicating that it had not extended or thinned. This indicates that, because cracks occur in the Sn plating layer before cracks occur in the Cu layer, a Sn plating layer that can follow the plastic deformation of the Cu layer is likely to reduce cracks that occur on its surface.

[0058] Next, using test specimens cut out from the Sn-plated clad materials for tensile tests (Test Nos. 1 to 4) with a thickness (average thickness) of 0.128 mm prepared as described above, tensile tests were carried out with varying amounts of elongation of the test specimens (test pieces). The tensile test method referred to JIS-Z2241:2011. The test specimen (test piece) shape used was a plate-shaped test piece No. 13B. The tensile speed was 10 mm / min. The comparison standard for the elongation of the test specimens was the same as that described above (T Ｐ -T Ｃ ) / T Ｐ × 100 to calculate the degree of drawing V Ｐ The thickness T of the experimental clad material when Ｐ (0.128 mm) and the thickness of the thinnest part of the cup-shaped case T ＣThe elongation was determined taking into consideration the relationship with the thickness of the thinnest part of the 0.128 mm specimen (0.119 mm). Specifically, a tensile test was performed to determine the elongation amount at the point when a specimen with a thickness of 0.128 mm was elongated and the thickness of the thinnest part of the elongated specimen reached 0.119 mm. The elongation amount was 17%. This value (17%) was set as the comparison standard for the elongation amount in the tensile test and also as a substitute for the comparison standard (7%) for the degree of drawing of the cup-shaped case described above. The changes in elongation amount in the tensile test were set at 7%, 10%, 17% (comparison standard), and 22%.

[0059] In this invention, the "crack area ratio" is an index indicating the degree of cracks occurring on the surface of the Sn plating layer in the planar observation image of the surface of the Sn plating layer of the test specimen after the tensile test. The crack area ratio is calculated by Sc / S, where S is the area of ​​the observation region and Sc is the total area of ​​the cracked portions. Table 1 shows the elongation of the test specimen in the tensile test, the thickness (average thickness) before the tensile test, the thickness (minimum thickness) of the thinnest part after the tensile test, and the crack area ratio of the Sn plating layer surface calculated from the planar observation image of the Sn plating layer surface. Furthermore, Figure 4 shows examples of planar observation images of the Sn plating layer surface of test specimens with elongations of 7%, 10%, 17%, and 22%. The crack area ratio recommended in this invention is 0.016 or less (upper limit).

[0060]

[0061] The crack area ratios shown in Table 1 and Figure 4 were determined by the following steps (1) to (5): (1) The surface of the Sn-plated layer of the test specimen after the tensile test was observed in plan view using an SEM, and the observed image (1000x magnification) was recorded as digital data. (2) The digital data was binarized using commercially available image processing software or the like, and recorded as binarized data. (3) From the binarized data, cells corresponding to the crack locations and the number of cells were extracted and recorded as crack data. (4) The number of cells x the cell area was calculated from the crack data and the cell size (cell area), and this was used to determine the total area Sc of the crack locations. (5) Sc / S was calculated from the total area Sc of the crack locations and the observed area S of the observed image, and this was used to determine the crack area ratio.

[0062] As shown in Table 1 and Figure 4, in the specimen with an elongation of 7% in Experiment No. 1, relatively small cracks were detected on the surface of the Sn-plated layer, resulting in a relatively small crack area ratio of 0.013. In the specimen with an elongation of 10% in Experiment No. 2, relatively large cracks were detected on the surface of the Sn-plated layer, resulting in a relatively large crack area ratio of 0.040. In the specimen with an elongation of 17% in Experiment No. 3, relatively large cracks were detected on the surface of the Sn-plated layer, resulting in a relatively large crack area ratio of 0.050. In the specimen with an elongation of 22% in Experiment No. 4, multiple fairly large cracks were detected on the surface of the Sn-plated layer, resulting in a fairly large crack area ratio of 0.109. As a result, it was found that the crack area ratio on the surface of the Sn-plated layer increased as the degree of deformation of the specimen in the tensile test increased. Furthermore, it was found that when the elongation amount of Experiment No. 1 was 7%, the upper limit of the crack area ratio recommended in this invention (0.016) was not exceeded. On the other hand, when the elongation amount of Experiment Nos. 2 and 3 was 10% or more, it was found that the upper limit of the crack area ratio (0.016) was greatly exceeded.

[0063] The specimen in Experiment No. 3 with an elongation of 17% had a crack area ratio of 0.050, which corresponds to a cup-shaped case with a drawing ratio of 7.0%, as described above. Therefore, if a cup-shaped case with a drawing ratio of 7.0% is produced using a Sn-plated clad material equivalent to the specimen in Experiment No. 3, it is predicted that the crack area ratio on the surface of the Sn-plated layer of the case will be approximately 0.050. As a result, it is predicted that the specimen in Experiment No. 3 with an elongation of 17% has a sufficiently high possibility of hydrogen gas generation.

[0064] Next, using the three-layer clad material (intermediate material B) prepared as described above, an Sn plating layer with different crystal grain diameters (circle-equivalent diameters) was formed on one surface of the Cu layer by electrolytic Sn plating, resulting in clad material 1B. In the electrolytic Sn plating, the crystal grain diameters of the Sn plating layer were controlled according to the desired grain diameter by setting various conditions, such as the concentration and temperature of the plating solution, the type and concentration of additives, and the current density. This resulted in four-layer clad materials for tensile testing (Experiments Nos. 11 to 16) with a thickness of 0.128 mm and a Sn plating layer composed of crystal grains with a diameter (circle-equivalent diameter) of 0.2 μm to 2.2 μm in plan view. The clad materials for tensile testing were identical to the clad materials for drawing and tensile testing described above in terms of the Cu layer, substrate, and Ni layer, except for the Sn plating layer. For details on how to determine the diameter (circle-equivalent diameter) of the crystal grains in the Sn plating layer, please refer to the above explanation. Hereinafter, the diameter of the crystal grains constituting the Sn plating layer is the circle-equivalent diameter unless otherwise specified.

[0065] Tensile tests were conducted using test specimens cut from the tensile test clad materials (Test Nos. 11 to 16) with different grain sizes constituting the Sn-plated layer, with the elongation of the test specimens fixed at a comparison standard (17%). The tensile test method, test specimen shape, tensile speed, and method for determining the comparison standard for the elongation of the test specimens were the same as those for the tensile tests of Test Nos. 1 to 4 described above. Table 2 shows the grain size and crack area ratio of the grains constituting the Sn-plated layer, determined from the planar observation image of the surface of the Sn-plated layer. In Table 2, the crack area ratio is displayed to four decimal places to clearly distinguish between Test Nos. 11 to 16. Figure 5 (graph) shows the crack area ratio versus grain size of the Sn-plated layer. In Figure 5, the crack area ratio is indicated by a "●", the polynomial (cubic) approximation line is indicated by a solid line, the power approximation line is indicated by a dashed line, and the upper limit value of the crack area ratio recommended in this invention (0.016) is indicated by a dotted-dash line.

[0066]

[0067] As shown in Table 2 and Figure 5, the crack area ratio of the surface of the Sn-plated layer in the specimen with Experiment No. 11, in which the grain size of the Sn-plated layer was 0.2 μm, was 0.05 (0.0499). The crack area ratio of the surface of the Sn-plated layer in the specimen with Experiment No. 12, in which the grain size of the Sn-plated layer was 1.0 μm, was less than 0.01 (0.0084). Similarly, the crack area ratio of the surface of the Sn-plated layer in the specimens with Experiment Nos. 13, 14, 15, and 16, in which the grain sizes of the Sn-plated layer were 1.4 μm, 1.7 μm, 2.0 μm, and 2.2 μm, was less than 0.01 (0.0084, 0.0079, 0.0069, 0.0031, and 0.0027). As a result, it was found that the crack area ratio of the surface of the Sn-plated layer decreased as the grain size of the crystal grains constituting the Sn-plated layer increased.

[0068] In Sn-plated clad materials, the larger the grain size of the crystal grains constituting the Sn plating layer, as determined from a planar observation image of the surface of the Sn plating layer, the smaller the crack area ratio on the surface of the Sn plating layer. This phenomenon occurs because, when a tensile load is applied to the Sn plating layer, the larger the grain size of the crystal grains constituting the Sn plating layer, the greater the relative amount of elongation occurring within the crystal grains. As the grain size of the crystal grains increases, the number of crystal grains decreases in a given surface area, resulting in a smaller total length of the crystal grain boundaries. On the other hand, as the number of crystal grains decreases, the total area within the crystal grains increases. Therefore, when a tensile load is applied to the crystal grains, the larger the grain size of the crystal grains, the greater the relative amount of elongation occurring within the crystal grains compared to the amount occurring at the grain boundaries. Furthermore, the fracture stress within the crystal grains is usually greater than the fracture stress at the grain boundaries. Therefore, as the grain size of the crystal grains increases, the relative amount of elongation occurring within the crystal grains increases, resulting in a greater fracture stress, which reduces the occurrence of cracks and reduces the crack area ratio. If the grain size of the crystal grains constituting the Sn plating layer (Sn plating film) is made large, it takes time for the grains to grow, and therefore the production efficiency of the Sn plating layer decreases.

[0069] Therefore, taking into consideration the production efficiency of the Sn plating layer, this invention recommends that the grain size (circle equivalent diameter) of the crystal grains constituting the Sn plating layer be 0.5 μm or more and 3.0 μm or less. The effectiveness of the recommended grain size range of the Sn plating layer (0.5 μm or more and 3.0 μm or less), particularly the effectiveness of 0.8 μm or more, 1.0 μm or more, and 1.2 μm or more will be described in detail based on the results of predictions in the following section.

[0070] 5, it is particularly noteworthy that the crack area ratio on the surface of the Sn plating layer decreases extremely significantly as the grain size of the Sn plating layer increases from 0.2 μm (Experiment No. 11) to 1.0 μm (Experiment No. 12). Furthermore, the upper limit of the crack area ratio recommended in this invention (0.016) exists between the grain size of the Sn plating layer of 0.2 μm and 1.0 μm.

[0071] Therefore, predictions 1 and 2 were performed based on the polynomial (cubic) approximation line shown by the solid line and the power approximation line shown by the dashed line in Figure 5. Then, based on the results of predictions 1 and 2, the range of grain size of the crystal grains constituting the Sn plating layer, in which the crack area ratio on the surface of the Sn plating layer is equal to or less than the upper limit value (0.016), was determined. The polynomial (cubic) approximation line is calculated using the coefficient of determination R ２ is 0.9956, so its reliability is sufficiently high. ２ is 0.9943, so its reliability is sufficiently high.

[0072] In prediction 1, a polynomial (cubic) approximation line is used as the first model: y = Ax ３ +Bx ２ +Cx+D (A, B, C, and D are coefficients). Table 3 shows the first model. Using this first model, the grain size of the Sn plating layer was used as the independent variable x, and the x value was assigned in the range of 0.2 to 3.3 to determine the crack area ratio (y value) of the Sn plating layer, which was the dependent variable y. Table 4 and FIG. 6 show the y value for each x value and the absolute value |y value - experimental value| of the difference between the y value and the experimental value shown in Table 2 (crack area ratios for Experiments 11 to 16). The range of x values ​​corresponding to a specific range of y values ​​was then determined to be the result of Prediction 1 by the first model, i.e., the appropriate range of grain size of the Sn plating layer. Furthermore, based on Table 4 and FIG. 6, the range of grain size of the Sn plating layer for which the first model is applicable was confirmed.

[0073] In prediction 2, the power approximation line is the second model: p = Aq Ｂ (A and B are coefficients). Table 3 shows the second model. Using this second model, the grain size of the Sn plating layer was used as the independent variable p, and p was assigned a value between 0.2 and 3.3 to determine the crack area ratio (q value) of the Sn plating layer, which was the dependent variable q. Table 4 and FIG. 6 show the q value for each p value, the absolute value |y value - q value| of the difference between the y value and the q value, and the absolute value |q value - experimental value| of the difference between the q value and the experimental value shown in Table 2 (crack area ratios for Experiments 11 to 16). The range of q values ​​corresponding to a specific range of p values ​​was then determined to be the result of Prediction 2 by the second model, i.e., the appropriate range of grain size of the Sn plating layer. Furthermore, based on Table 4 and FIG. 6, the range of grain size of the Sn plating layer for which the second model is applicable was confirmed.

[0074] Subsequently, the results of Prediction 1 and Prediction 2 were considered, and an appropriate range of the grain size of the crystal grains constituting the Sn plating layer was determined as the result of a more reliable prediction. Specifically, |y value - experimental value| and |q value - experimental value| shown in Table 4 were confirmed. Furthermore, for |y value - q value| shown in Table 4 and Figure 6, the minimum value and the x value (p value) that gave that minimum value were confirmed. Furthermore, the gentleness and stability of the gradient of change in the y value (q value) relative to the x value (p value) were confirmed for the two approximation lines shown in Figure 6. Based on these results, the grain size range of the Sn plating layer for which the first model is appropriate and the grain size range of the Sn plating layer for which the second model is appropriate were confirmed, and finally, an appropriate range of the grain size of the crystal grains constituting the Sn plating layer was determined. In Figure 6 (graph), the relationship between the x value and y value of the first model is shown by a solid line, the relationship between the p value and q value of the second model is shown by a dashed line, the absolute value of the difference between the y value and the q value |y value - q value| is shown by a dotted line, the upper limit value of the crack area ratio recommended in this invention (0.016) is shown by a dotted-dotted line, and the crack area ratios of experiment numbers 11 to 16 shown in Table 2 are shown by ``●''.

[0075]

[0076]

[0077] As shown in Table 4, |y value - experimental value| and |q value - experimental value| were confirmed. |y value - experimental value| was less than 0.002 for the x value range of 0.2 to 2.2, and is therefore considered to be sufficiently reliable. Furthermore, |q value - experimental value| was less than 0.004 for the x value range of 0.2 to 2.2, and is therefore considered to be reasonably reliable. However, for the small x value range (near 0.2), the q value is considered to be less reliable than the y value.

[0078] Furthermore, as shown in Table 4 and FIG. 6, the y value (q value) changes relatively significantly and decreases with respect to a change in the x value (p value) from 0.2 to 1.0. The decrease in the y value is more gradual and stable than the decrease in the q value. Furthermore, with a change in the x value (p value) from 1.0 to 2.2, the y value (q value) changes very little and decreases slightly. Furthermore, with a change in the x value (p value) from 2.2 to 3.3, the y value changes significantly and decreases, while the q value changes very little and decreases slightly. From the above perspective, it can be determined that when the x value (p value) is in the range of 1.0 to 2.2, both the results of Prediction 1 and Prediction 2 are reliable, when the x value (p value) is in the range of 0.2 to 1.0, the result of Prediction 1 is more reliable than the result of Prediction 2, and when the x value (p value) is in the range of 2.2 to 3.3, the result of Prediction 2 is more reliable than the result of Prediction 1.

[0079] Furthermore, in Table 4 and FIG. 6, the minimum value of the difference |y-q| between the y value and the q value is 0.000083 (83 ppm), and the x value (p value) at that time is 1.2. Therefore, the error (prediction error) of the y value (q value) when the x value (p value) is 1.2 is considered to be extremely small. Furthermore, in the range of x value (p value) 1.2 or less (0.2≦x value (p value) ≦1.2), the decrease in the y value is gentler and more stable than the decrease in the q value, while in the range of x value (p value) 1.2 or more (1.2≦x value (p value) ≦3.3), the decrease in the q value is gentler and more stable than the decrease in the y value. Furthermore, in the range of x value (p value) 1.0 to 1.4, the difference |y-q| is less than 0.001, so the error (prediction error) of the y value (q value) is considered to be relatively small. From this, it can be determined that it is appropriate to apply the results of Prediction 1 when the x value (p value) is in the range of 1.2 or less (0.2 to 1.2), and that it is appropriate to apply the results of Prediction 2 when the x value (p value) is in the range of 1.2 or more (1.2 to 3.3). Note that when the x value (p value) is in the range of 1.0 to 1.2, the difference |y-q| is less than 0.001, so it can be determined that the results of Prediction 2 can be applied.

[0080] Based on the results of the above predictions, the range of grain size of the crystal grains constituting the Sn plating layer, within which the crack area ratio on the surface of the Sn plating layer is equal to or less than the upper limit (0.016), was determined. When the grain size of the crystal grains constituting the Sn plating layer was 0.2 μm to 1.0 μm, the result of Prediction 1 (crack area ratio) was considered preferentially. When the grain size was in the range of 1.0 μm to 1.2 μm, the result of Prediction 1 or 2 (crack area ratio) was considered. When the grain size was in the range of 1.2 μm to 3.3 μm, the result of Prediction 2 (crack area ratio) was considered preferentially. This confirmed that when the grain size of the crystal grains constituting the Sn plating layer was in the range of 0.5 μm to 3.0 μm, the crack area ratio on the surface of the Sn plating layer was likely to be equal to or less than 0.016. It was also confirmed that there is a sufficiently high possibility that the crack area ratio of the Sn plating layer will be 0.016 or less when the grain size of the Sn plating layer is 0.8 μm or more, that the crack area ratio of the Sn plating layer will be reduced by 30% to 40% from the reference value (0.016) when the grain size of the Sn plating layer is 1.0 μm or more, and that the crack area ratio of the Sn plating layer will be reduced by 45% to 55% from the reference value (0.016) when the grain size of the Sn plating layer is 1.2 μm or more. The details are as follows.

[0081] <Reference value of crack area ratio: 0.016> As described above, the reference value for the crack area ratio on the surface of the Sn plating layer was set to 0.016. According to the results of Prediction 1, the grain size of the Sn plating layer at which the crack area ratio reaches the reference value of 0.016 is in the range of 0.7 μm to 0.8 μm, and according to the results of Prediction 2, it is in the range of 0.5 μm to 0.6 μm. In both predictions, as the grain size of the Sn plating layer increases, the crack area ratio of the Sn plating layer decreases. Here, as described above, when the grain size of the Sn plating layer is in the range of 0.2 μm to 1.0 μm, the results of Prediction 1 are given priority. This confirms that when the grain size of the Sn plating layer is 0.8 μm or more, there is a sufficiently high possibility that the crack area ratio of the Sn plating layer will be 0.016 or less.

[0082] <Crack Area Ratio 0.0112> The crack area ratio of the Sn plating layer of 0.0112 is a value 30% lower than the reference value of 0.016. The grain size of the Sn plating layer at which the crack area ratio is 0.0112 is in the range of 0.9 μm to 1.0 μm according to the results of Prediction 1, and in the range of 0.7 μm to 0.8 μm according to the results of Prediction 2. In both predictions, as the grain size of the Sn plating layer increases, the crack area ratio of the Sn plating layer decreases. Here, as described above, when the grain size of the Sn plating layer is in the range of 0.2 μm to 1.0 μm, the results of Prediction 1 are given priority. This confirms that a grain size of the Sn plating layer of 1.0 μm or greater is highly likely to reduce the crack area ratio of the Sn plating layer by a further 30% from the reference value.

[0083] <Crack Area Ratio 0.0096> The crack area ratio of the Sn plating layer of 0.0096 is a value that is 40% lower than the reference value of 0.016. According to the results of Prediction 1, the grain size of the Sn plating layer that results in a crack area ratio of 0.0096 is in the range of 0.9 μm to 1.0 μm, and according to the results of Prediction 2, it is in the range of 0.9 μm to 1.0 μm. In both predictions, as the grain size of the Sn plating layer increases, the crack area ratio of the Sn plating layer decreases. This confirms that, including the case of the crack area ratio of 0.0112 described above, when the grain size of the Sn plating layer is 1.0 μm or greater, there is a sufficiently high possibility that the crack area ratio of the Sn plating layer will be reduced by a further 30% to 40% from the reference value.

[0084] <Crack Area Ratio 0.0088> The crack area ratio of the Sn plating layer of 0.0088 is a value that is 45% lower than the reference value of 0.016. According to the results of Prediction 1, the grain size of the Sn plating layer that results in a crack area ratio of 0.0088 is in the range of 1.0 μm to 1.1 μm, and according to the results of Prediction 2, it is in the range of 0.9 μm to 1.0 μm. In both predictions, as the grain size of the Sn plating layer increases, the crack area ratio of the Sn plating layer decreases. This confirms that a grain size of the Sn plating layer of 1.1 μm or more (1.2 μm or more if the difference in prediction of 0.1 μm is taken into account) is highly likely to reduce the crack area ratio of the Sn plating layer by a further 45% from the reference value.

[0085] <Crack Area Ratio 0.0072> The crack area ratio of the Sn plating layer of 0.0072 is a value that is 55% reduced from the reference value of 0.016. According to the results of Prediction 1, the grain size of the Sn plating layer that results in a crack area ratio of 0.0072 is in the range of 1.1 μm to 1.2 μm, and according to the results of Prediction 2, it is in the range of 1.1 μm to 1.2 μm. In both predictions, as the grain size of the Sn plating layer increases, the crack area ratio of the Sn plating layer decreases. This confirms that, including the case of the crack area ratio of 0.0088 described above, when the grain size of the Sn plating layer is 1.2 μm or more, there is a sufficiently high possibility that the crack area ratio of the Sn plating layer will be reduced by a further 45% to 55% from the reference value.

[0086] From the above, the effectiveness of a Sn-plated clad material was confirmed, which has a Cu layer made of Cu on at least one surface of a substrate made of Fe or an Fe alloy, and further has a Sn-plated layer on the surface of the Cu layer, and after a tensile test set to an elongation of 17% was performed using a test specimen cut from the Sn-plated clad material, the surface of the test specimen facing the Sn-plated layer had a crack area ratio of 0.016 or less, calculated as Sc / S, where S is the area of ​​the observed region and Sc is the total area of ​​crack locations. Furthermore, it was confirmed that, in the Sn-plated clad material, the average grain size of the Sn-plated layer was preferably 0.8 μm or more, more preferably 1.0 μm or more, and even more preferably 1.2 μm or more, in an observation image of the surface of the Sn-plated layer of the test specimen before the tensile test.

[0087] The Sn-plated clad material according to the present invention is sufficiently free from cracks on the surface of the Sn-plated layer when subjected to drawing at a practical level, and is therefore suitable for use as a metal material for drawing to form cup-shaped negative electrode cases for button-type batteries.

[0088] 1A Clad material (Sn-plated clad material) 10 Sn-plated layer 11 Base material (Fe layer) 12 Cu layer 13 Ni layer 100 Air zinc battery 101 Negative electrode case (negative electrode terminal) 102 Positive electrode case (positive electrode terminal) 103 Separator 104 Negative electrode (zinc) 105 Positive electrode (air electrode) 106 Water-repellent film 107 Diffusion paper 108 Gasket 109 Air hole

Claims

1. A clad material with Sn plating, having a Cu layer made of Cu on at least one surface of a base material made of Fe or an Fe alloy, and further having a Sn plating layer on the surface of the Cu layer, wherein after a tensile test with an elongation set to 17% is performed using a test piece cut out from the clad material with Sn plating, in an observation image when the surface on the Sn plating layer side of the test piece is viewed in a plan view, when the area of the observation region is S and the total area of the cracked portions is Sc, the crack area ratio obtained by Sc / S is 0.016 or less.

2. The clad material with Sn plating according to claim 1, wherein in an observation image when the surface on the Sn plating layer side of the test piece before the tensile test is viewed in a plan view, the average grain size of the crystal grains constituting the Sn plating layer is 0.8 μm or more.

3. The clad material with Sn plating according to claim 2, wherein the average grain size of the crystal grains constituting the Sn plating layer is 1.0 μm or more.

4. The clad material with Sn plating according to claim 2, wherein the average grain size of the crystal grains constituting the Sn plating layer is 1.2 μm or more.

5. The clad material with Sn plating according to any one of claims 1 to 4, wherein in an observation image when the Sn plating layer of the test piece before the tensile test is viewed in a cross section, the average thickness of the Sn plating layer is 0.5 μm or more.

6. A method for manufacturing a clad material with Sn plating, comprising: step (1) of preparing a clad material having a Cu layer made of Cu on at least one surface of a base material made of Fe or an Fe alloy; and step (2) of forming a Sn plating layer on the surface of the Cu layer of the clad material, wherein in step (2), an Sn plating layer is formed by electrolytic Sn plating treatment such that the average grain size of the crystal grains constituting the Sn plating layer is 0.8 μm or more in an observation image when the surface on the Sn plating layer side is viewed in a plan view.

7. The method for manufacturing a clad material with Sn plating according to claim 6, wherein an Sn plating layer is formed such that the average grain size of the crystal grains constituting the Sn plating layer is 1.0 μm or more.

8. The method for manufacturing a clad material with Sn plating according to claim 6, wherein an Sn plating layer is formed such that the average grain size of the crystal grains constituting the Sn plating layer is 1.2 μm or more.

9. The method for manufacturing a clad material with Sn plating according to any one of claims 6 to 8, wherein the Sn plating layer having an average thickness of 0.5 µm or more is formed in an observation image when the Sn plating layer is viewed in cross section.

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