Iron-plated metal foil and method for producing iron-plated metal foil

Abstract

An iron-plated metal foil including: a metal foil having a thickness of 100 μm or less; and an iron-plated film provided on the metal foil and having a thickness of 10 μm or less, wherein a KAM value obtained when the iron-plated film is analyzed at 3000x magnification by using an EBSD method is 0.70 or less.

Description

Iron-plated metal foil and method for producing the same

[0001] The present invention relates to an iron-plated metal foil and a method for producing the same.

[0002] Materials with iron plating on the surface of metals are used as materials for electromagnetic shielding of electronic devices. In particular, in recent years, electronic devices have been miniaturized, and it has been required to reduce the thickness of the metal foil that is the base material for plating.

[0003] On the other hand, as the base material becomes thinner, the shape of the material after plating is likely to be affected by the internal stress of the plating. Specifically, when tensile stress is generated in the plating film, the material will warp toward the plated surface. In particular, since tensile stress is likely to occur in the iron plating film, this warping (curl) problem is likely to occur, and materials with curl cannot be used as raw materials for electronic components.

[0004] As an example of iron plating, for example, Patent Document 1 describes plating containing 0.02 to 0.5% by mass of nitrogen in the iron plating film. Also, as a technique for preventing the generation of precipitation in the iron plating solution, Patent Document 2 describes an iron plating solution.

[0005] Japanese Patent Application Laid-Open No. 9-228092 Japanese Patent Application Laid-Open No. 10-204674

[0006] However, the iron plating containing nitrogen described in Patent Document 1 has characteristics such as no rust generation, but there is no explanation regarding the warping of the plating. Probably because the hardness of the plating is as high as 1000 to 1100 Hv, it is expected that the plating stress is high.

[0007] Also, Patent Document 2 describes a method of adding an organic compound for preventing precipitation in the iron plating solution, and it is described that the appearance of the iron plating becomes good, but the stress of the plating film is not mentioned.

[0008] Therefore, even when iron plating is applied to a thin material such as a metal foil, it is desired to develop a material with low plating stress and, as a result, good suppression of warping.

[0009] In view of these problems, embodiments of the present invention provide an iron-plated metal foil with well suppressed warping and a method for manufacturing an iron-plated metal foil.

[0010] Embodiments of the present invention that solve the above problems are defined below. 1. An iron-plated metal foil comprising a metal foil with a thickness of 100 μm or less and an iron plating film with a thickness of 10 μm or less provided on the metal foil, wherein the KAM value obtained when the iron plating film is analyzed by EBSD at a magnification of 3000x is 0.70 or less. 2. The iron-plated metal foil according to 1, wherein the iron plating film contains columnar crystals that are columnar in a cross section perpendicular to the direction of elongation of the metal foil, and the average length of the short side of the columnar crystals is 0.5 μm or more. 3. The iron-plated metal foil according to 1 or 2, wherein the thickness of the iron plating film is 3 μm or less. 4. The iron-plated metal foil according to any one of 1 to 3, wherein the metal foil is nickel foil. 5. A method for manufacturing an iron-plated metal foil, wherein an iron plating film is formed on the surface of a metal foil by electroplating, wherein the temperature of the iron plating solution in the electroplating is 40°C or higher.

[0011] According to embodiments of the present invention, it is possible to provide an iron-plated metal foil with well suppressed warping and a method for manufacturing an iron-plated metal foil.

[0012] This is a diagram showing a method for measuring the short side width of columnar crystals. This is a schematic diagram for explaining a method for measuring the amount of warping of iron-plated metal foil. This is the KAM map of Comparative Example 1. This is the KAM map of Example 1. This is the KAM map of Example 2. This is a cross-sectional SIM image of Comparative Example 1. This is a cross-sectional SIM image of Example 1. This is a cross-sectional SIM image of Example 2.

[0013] Preferred embodiments of the present invention will be described below, but the present invention should not be construed as being limited thereto, and various modifications and improvements can be made based on the knowledge of those skilled in the art, without departing from the spirit of the invention. The multiple components disclosed in this embodiment can be combined in appropriate ways to form various inventions. For example, some components may be removed from all the components shown in this embodiment.

[0014] <Iron-plated metal foil> The iron-plated metal foil according to the embodiment of the present invention includes a metal foil and an iron-plated film provided on the metal foil. In addition, the iron-plated metal foil according to the embodiment of the present invention may have an intermediate layer such as an iron strike plating layer or a nickel plating layer between the metal foil and the iron-plated film, to the extent that it does not hinder the effects of the present invention, and a rust-preventive layer, an iron compound layer, an iron alloy layer, etc. may be provided on the surface of the iron-plated film.

[0015] (Metal foil) The metal foil of the iron-plated metal foil according to the embodiment of the present invention has a thickness of 100 μm or less. When the iron-plated metal foil according to the embodiment of the present invention is used in a small electronic device, having a metal foil thickness of 100 μm or less has the effect of reducing both mass and volume. The metal foil of the iron-plated metal foil according to the embodiment of the present invention preferably has a thickness of 3 to 100 μm, and more preferably 4 to 50 μm.

[0016] The metal foil used in the iron-plated metal foil according to the embodiment of the present invention is not particularly limited, but examples include nickel foil, nickel alloy foil, copper foil, copper alloy foil, titanium foil, titanium alloy foil, stainless steel foil, permalloy foil, 42 alloy foil, Kovar foil, Inconel foil, or Hastelloy foil.

[0017] (Iron Plating Film) The iron plating film of the iron-plated metal foil according to the embodiment of the present invention has a thickness of 10 μm or less. When the iron-plated metal foil according to the embodiment of the present invention is used in a small electronic device, a thickness of 10 μm or less of the iron plating film has the effect of reducing both mass and volume. The iron plating film of the iron-plated metal foil according to the embodiment of the present invention is preferably 5 μm or less in thickness, and more preferably 3 μm or less. The lower limit of the iron plating film of the iron-plated metal foil according to the embodiment of the present invention is not particularly limited, but may be, for example, 0.1 μm or more, 0.2 μm or more, or 0.4 μm or more. The thickness of the iron plating film of the iron-plated metal foil can be measured with an X-ray fluorescence film thickness gauge (SFT9550X: manufactured by Hitachi High-Tech Corporation), etc.

[0018] The composition of the iron plating film on the iron-plated metal foil according to the embodiment of the present invention is not particularly limited, but in terms of plating corrosion resistance, it is desirable to have a low amount of impurities other than iron, such as 99.9% iron.

[0019] (Crystal Structure) The iron plating film of the iron-plated metal foil according to the embodiment of the present invention contains columnar crystals that are columnar in shape in a cross section perpendicular to the direction of elongation (longitudinal direction) of the metal foil, and the average length of the short side of the columnar crystals is 0.5 μm or more. When the cross section of the iron plating film, that is, the cross section perpendicular to the direction of elongation (longitudinal direction) of the base metal foil is observed with a FIB (Focused Ion Beam) device, the crystal grains of the iron plating can be confirmed. In the iron plating film of metal foil with low residual stress as in the present invention, these crystal grains are columnar crystals, and by controlling the average length of the short side of the columnar crystals to 0.5 μm or more, an iron-plated metal foil with better suppression of warping can be obtained. The average length of the short side of the columnar crystals is more preferably 0.6 μm or more, and even more preferably 0.7 μm or more. Figure 1 shows a method for measuring the width of the short side of the columnar crystals (length of the short side of the columnar crystals). First, the plating film is cut with FIB and a cross-sectional image is taken. In this cross-sectional image, the length in the short-side direction at the halfway point of the long side of the columnar crystal is read from the cross-sectional image. The short-side width is measured for five or more columnar crystals, and the average value is calculated from the obtained data and defined as the average columnar crystal short-side width (average length of the short side of the columnar crystal).

[0020] (EBSD) Electron Back Scatter Diffraction (EBSD) is an analytical method that measures microscopic crystal orientation and crystal system based on the Kikuchi pattern obtained by irradiating a sample with an electron beam. EBSD provides information for each crystal grain, and from the crystal orientation data, the orientation distribution of crystal grains and the orientation difference distribution of each crystal grain can be understood. The orientation difference of crystal grains corresponds to the strain of the metal, and in metals with greater strain, the stress also increases. The KAM value is data that represents this orientation difference. In the embodiment of the present invention, it was found that there is a correlation between the KAM value and the plating stress, and it was discovered that the plating stress can be kept low by controlling the KAM value to a specific value. In the embodiment of the present invention, a method of evaluating the amount of warpage of the material, as described later, was adopted as a means of evaluating the plating stress. That is, in the iron-plated metal foil according to the embodiment of the present invention, the KAM value obtained when the iron plating film is analyzed by the EBSD method at a magnification of 3000 times is controlled to be 0.70 or less. This configuration makes it possible to provide iron-plated metal foil with well suppressed warping. The KAM value is preferably 0.60 or less, and more preferably 0.50 or less.

[0021] (Warping Amount) In the embodiment of the present invention, it is preferable that the thickness of the metal foil is 5 μm, the thickness of the iron plating film is 1 μm, and the amount of warping when the iron plated metal foil is processed to a size of length × width = 50 mm × 50 mm is 25 mm or less. The amount of warping of the iron plated metal foil in the embodiment of the present invention is more preferably 20 mm or less, even more preferably 10 mm or less, even more preferably 8 mm or less, even more preferably 6 mm or less, and even more preferably 4 mm or less.

[0022] The amount of warpage of the iron-plated metal foil according to the embodiment of the present invention can be measured as follows. First, the iron-plated metal foil is processed to a thickness of 5 μm, an iron plating film thickness of 1 μm, and a size of 50 mm x 50 mm (length x width). When the thickness of the iron-plated metal foil is greater than 5 μm, or when the thickness of the iron plating film is greater than 1 μm, the thickness can be reduced to 5 μm and 1 μm, respectively, by etching or mechanical polishing. When the thickness of the iron-plated metal foil is less than 5 μm, or when the thickness of the iron plating film is less than 1 μm, the thickness can be increased to 5 μm and 1 μm, respectively, by deposition or sputtering. These methods require a long time for film deposition, but since almost no stress is generated, the amount of warpage of the iron-plated metal foil can be accurately measured. Processing the iron-plated metal foil to its length x width size can be done by cutting, etc. When iron-plated metal foil warps, the iron-plated film always curves inward. As shown in Figure 2, when the iron-plated metal foil is placed on a horizontal surface with the metal foil side down, both ends (edges) of the metal foil surface will be slightly lifted. The distance between the edge of the metal foil and the horizontal surface at this time is measured and defined as the amount of warping. If the edge of the metal foil is not straight (e.g., the edge is wavy), the distance between the edge of the metal foil and the horizontal surface will vary depending on the measurement position. In this case, the "amount of warping" of the iron-plated metal foil in this invention is defined as the distance at the position where the distance between the edge of the metal foil and the horizontal surface is maximum. Note that the "distance between the edge of the metal foil and the horizontal surface" refers to the distance between the starting point of a perpendicular line drawn from the horizontal surface (a point on the horizontal surface) and the intersection point of the perpendicular line and the edge. This distance can be obtained, for example, by measuring the distance between the edge of the metal foil and the intersection point of a ruler (straight ruler) placed vertically on a horizontal surface.

[0023] (Applications) As described above, the iron-plated metal foil according to the embodiment of the present invention exhibits excellent warping suppression. Therefore, the iron-plated metal foil according to the embodiment of the present invention can be used in many industrial fields, such as electronic components and electromagnetic shielding materials.

[0024] <Method for Manufacturing Iron-Plated Metal Foil> In the method for manufacturing iron-plated metal foil according to the embodiment of the present invention, first, a metal foil is prepared. The metal foil can be manufactured, for example, by rolling a metal ingot to obtain a metal foil (rolled foil), or by an electroplating method to obtain a metal foil (electrolytic foil). However, it is not limited to these, and in the embodiment of the present invention, the metal foil may be manufactured by any method.

[0025] Next, an iron plating film is formed on the surface of the metal foil by electroplating. Internal stress is usually generated in the plated film; for example, compressive stress is generated in zinc plating and cadmium plating, and tensile stress is generated in iron, nickel, and chromium plating. When plating is applied to a thin metal foil as in the present invention, internal stress in the plating tends to cause the metal foil to warp (curl). In the method for manufacturing iron-plated metal foil according to the embodiment of the present invention, this curl can be effectively suppressed.

[0026] Iron plating solutions can utilize inorganic chemicals such as iron(II) sulfate, iron sulfamate, iron(II) chloride, and ammonium chloride, as well as organic additives. For example, sulfur-containing compounds such as iron sulfate and iron sulfamate have the effect of reducing internal stress in the plating film, so it is preferable to increase the proportion of these compounds added. Similarly, benzothiazole compounds such as sodium saccharin also have the effect of easing internal stress in the plating film, as described later, so they may be added in small amounts. However, if the amount added is too high, the corrosion resistance of the plating will decrease and rust will be more likely to occur, so it is necessary to adjust the amount added. As for other additives, it is also possible to add small amounts of nonionic surfactants as a pitting inhibitor for the plating.

[0027] Examples of the concentrations of the chemicals that make up the iron plating solution include: iron(II) sulfate heptahydrate: 150-300 g / L, iron(II) chloride tetrahydrate: 10-100 g / L, and ammonium chloride: 4-50 g / L.

[0028] In electroplating, the temperature of the iron plating solution is controlled to 40°C or higher. If a large amount of hydrogen is generated during plating, it will be incorporated into the plating film. As time passes, the hydrogen incorporated into the plating film escapes from the plating film, causing tensile stress within the plating. This tensile stress causes curling in the metal foil on which the iron plating film is formed, leading to problems such as difficulty in handling after plating. In contrast, in the method for manufacturing iron-plated metal foil according to the embodiment of the present invention, by controlling the temperature of the iron plating solution to 40°C or higher, the generation of hydrogen during plating can be suppressed, and the amount of hydrogen incorporated into the plating film can be suppressed. The temperature of the iron plating solution is preferably 40 to 70°C, and more preferably 40 to 55°C.

[0029] In the method for manufacturing iron-plated metal foil according to the embodiment of the present invention, it is preferable that the pH of the iron plating solution is controlled to 1.0 to 5.5. By controlling the pH of the iron plating solution to 1.0 to 5.5, the generation of insoluble iron hydroxide in the plating solution can be suppressed, thereby suppressing the occurrence of defects in the plating appearance. Furthermore, by adjusting the pH and controlling the temperature of the iron plating solution as described above, the average length of the short side of the columnar crystals, which are columnar in a cross section perpendicular to the direction of elongation (longitudinal direction) of the metal foil, can be controlled to 0.5 μm or more. The pH of the iron plating solution is preferably 1.25 to 4.75.

[0030] The current density for electroplating is 0.1 to 20 A / dm². 2 It is preferable that the current density of the electroplating is 0.1 A / dm 2 The above conditions can suppress the occurrence of unplated areas in the plating. The electroplating current density is 20 A / dm². 2The following conditions can suppress plating scorching and prevent the plating film from becoming unsightly. Note that if plating scorching occurs, the unevenness of the plating film increases at the site of scorching, leading to increased moisture adhesion, making drying after plating difficult and causing rust. The current density for electroplating is preferably 2 to 15 A / dm². 2 More preferably, 3 to 10 A / dm 2 That is the case.

[0031] In electroplating, it is preferable that the concentration of trivalent iron ions in the iron plating solution is 0.7 g / L or less. When the concentration of trivalent iron ions is 0.7 g / L or less, it is possible to effectively suppress the occurrence of plating charring in high current density regions, such as when the metal foil is at the edge of a strip material, and to suppress the occurrence of rust in the plating and the increase in internal stress of the plating film. It is more preferable that the concentration of trivalent iron ions in the iron plating solution in electroplating is 0.05 g to 0.6 g / L, and even more preferable that it is 0.05 to 0.5 g / L.

[0032] In the method for manufacturing iron-plated metal foil according to an embodiment of the present invention, iron plating is applied to the surface of the metal foil, and it is preferable to use pure iron as the anode for electroplating. An insoluble anode made of titanium plated with platinum can be used as the anode for electroplating, but while using an insoluble anode has the advantage of avoiding the problem of impurities originating from the anode being mixed into the plating film, it is prone to the problem of trivalent iron ion generation. In contrast, these problems can be avoided with a soluble anode such as iron. Furthermore, by using a high-purity iron anode, it is possible to further reduce the amount of impurities deposited in the iron plating film.

[0033] In electroplating, it is preferable that the iron plating solution contains a benzothiazole compound. Examples of benzothiazole compounds include sodium salts of benzothiazole, saccharin, and sodium saccharin. For example, the amount of sodium saccharin added is preferably 0 to 1.0 g / L, and more preferably 0 to 0.4 g / L. The benzothiazole compound functions as a stress relaxant in the iron plating solution, and the addition of this compound can reduce internal stress in the plating, thereby effectively suppressing warping of the iron-plated metal foil.

[0034] In the method for manufacturing iron-plated metal foil according to the embodiment of the present invention, iron plating is applied to the surface of the metal foil. Iron plating may be applied to both the front and back surfaces of the metal foil, or to only one surface. For example, in conventional plating, an electric current is passed through a pair of anodes (placed outside the plating material) installed in a plating tank to plate both the front and back surfaces of the metal foil. On the other hand, by supplying an electric current to only one side of the anode and performing electroplating so that the electric current flows to one surface of the metal foil in the plating solution, it is possible to manufacture iron-plated metal foil with different compositions on the front and back, where one side is iron and the other side is the metal foil material. As another example, it is also possible to manufacture foil in which an iron-plated film is formed on only one side by contacting a film or resin with one side of the metal foil before plating.

[0035] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples.

[0036] <Preparation of Samples for Comparative Example 1, Example 1 and Example 2> (Metal Foil) A nickel foil with a thickness of 5 μm was prepared as the metal foil. The nickel foil was manufactured by rolling and had a glossy appearance. This nickel foil was cut to a width of 110 mm x a length of 200 mm to be used as metal foil for iron plating in a beaker.

[0037] (Iron plating solution, electroplating method) As an iron plating solution, the following iron plating solution was prepared. For electroplating, a 2-liter beaker containing the iron plating solution and an anode was used, and the solution was stirred with a stirrer. Next, the nickel foil was placed in the iron plating solution, and the nickel foil and the anode were connected to a DC power supply. Next, the current was turned on, and electroplating was performed at a current density of 5 A / dm 2 2 , and an iron plating (iron plating film) with a thickness of 1 μm was formed on one side of the nickel foil. The liquid temperature of the iron plating solution was 30 to 50 °C, and the pH was 5.5. A soluble anode (iron plate) was used for the anode. Table 1 shows the sample preparation conditions for Comparative Example 1, Example 1, and Example 2.

[0038] ・ Iron plating solution Ferrous sulfate heptahydrate: 250 g / L Ferrous chloride tetrahydrate: 50 g / L Ammonium chloride: 20 g / L

[0039]

[0040] <Composition of iron plating film> For the samples of Comparative Example 1, Example 1, and Example 2, the composition of the iron plating film was evaluated by the following method. The composition was measured by TOF-SIMS 4S manufactured by ION-TOF, and it was confirmed that all samples were pure iron with a purity of 99.9% or more.

[0041] <EBSD measurement> For the samples of Comparative Example 1, Example 1, and Example 2, a KAM map was measured by using JXA8500F manufactured by JEOL Ltd. as an EBSD measuring device and analyzing at a magnification of 3000 times. The KAM map measured a 30 μm × 30 μm portion of the sample surface, and the results are shown in FIGS. 3A, 3B, and 3C. In this figure, the dark gray portion indicates a location where the crystal orientation difference of each iron crystal is small. It was confirmed that in Comparative Example 1, the dark gray portion was narrower compared to other test examples. Next, based on the KAM map data of FIGS. 3A, 3B, and 3C, the KAM value was calculated. The results are shown in Table 2. The KAM value becomes smaller as the orientation difference between each crystal becomes smaller. The KAM values of Example 1 and Example 2 were smaller compared to Comparative Example 1.

[0042]

[0043] <Electroplating Cross-Section Measurement>For observing the cross-sectional structure of the electroplating film, SMI3050SE manufactured by SII Technology Co., Ltd. was used. First, the electroplating film was cut with FIB, and then the cross-sectional SIM image was observed. The obtained cross-sectional images are shown in FIGS. 4A, 4B, and 4C. When comparing the sizes of the electroplating film crystals, it was confirmed that the crystals in Comparative Example 1 were smaller than those in Example 1 and Example 2. Next, based on the cross-sectional SIM images in FIGS. 4A, 4B, and 4C, the length in the short-side direction at the midpoint of the long side of the columnar crystals was read by the measurement method shown in FIG. 1. The measurement of the short-side width was performed on five or more columnar crystals, and the average value was obtained from the obtained data, which was defined as the average short-side width of the columnar crystals (average length of the short side of the columnar crystals). The results are shown in Table 3. The average short-side width of the columnar crystals in Comparative Example 1 was smaller than those in Example 1 and Example 2.

[0044]

[0045] <Amount of Warping of Iron-Plated Metal Foil>The samples of Comparative Example 1, Example 1, and Example 2 were cut into a size of length × width = 50 mm × 50 mm. Next, as shown in FIG. 2, the samples processed so that the metal foil side was downward were placed on a horizontal table. At this time, both ends (edge portions) of the surface of the metal foil of the sample were slightly lifted. The distance between the edge portion of the metal foil and the horizontal table at this time was measured and defined as the amount of warping. The evaluation results are shown in Table 4. In Comparative Example 1, the amount of warping was large, the sample curled up (like a spring shape), and the measurement became impossible.

[0046]

[0047] As described above, in Comparative Example 1, the KAM value was larger, the average crystal grain size was smaller, and the amount of warping was larger compared to Example 1 and Example 2. On the other hand, in Example l and Example 2, the KAM value was 0.70 or less, the average short-side width of the columnar crystals (average length of the short side of the columnar crystals) was 0.5 μm or more, the amount of warping was small, and it was confirmed that the residual stress of the electroplating film was small. Furthermore, it was also confirmed that these iron-plated metal foils of Example 1 and Example 2 can be obtained by electroplating at a temperature of the electroplating solution of 40°C or higher.

[0048] <Potential Contribution to SDGs> According to the embodiment described above, it is possible to provide iron-plated metal foil with well suppressed warping and a method for manufacturing iron-plated metal foil, which may improve the yield and performance of products manufactured using iron-plated metal foil. For this reason, this embodiment may contribute to Goal 9 "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation" and Goal 12 "Ensure sustainable consumption and production patterns" of the United Nations-led Sustainable Development Goals (SDGs).

Claims

1. An iron-plated metal foil comprising a metal foil with a thickness of 100 μm or less and an iron plating film with a thickness of 10 μm or less provided on the metal foil, wherein the KAM value obtained when the iron plating film is analyzed by EBSD at a magnification of 3000x is 0.70 or less.

2. The iron-plated metal foil according to claim 1, wherein the iron-plated film contains columnar crystals that are columnar in a cross-section perpendicular to the direction in which the metal foil elongates, and the average length of the short side of the columnar crystals is 0.5 μm or more.

3. The iron-plated metal foil according to claim 1, wherein the thickness of the iron-plated film is 3 μm or less.

4. The iron-plated metal foil according to claim 1, wherein the metal foil is nickel foil.

5. A method for manufacturing iron-plated metal foil, wherein an iron plating film is formed on the surface of the metal foil by electroplating, the temperature of the iron plating solution in the electroplating is 40°C or higher, according to any one of claims 1 to 4.

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