Copper-plated steel sheet

Abstract

A copper-plated steel sheet (10) is provided with a base steel sheet (20) and a copper-plated film (30) formed on at least one surface of the base steel sheet (20). The copper plating film (30) has, in a cross-section parallel to the thickness direction in a cross-sectional view, a base film section (31) that continuously covers the base steel sheet (20), and a protruding section (32) that grows in a dendritic shape from the base film section (31). The volume fraction of the protrusions (32) in a region from the base film portion (31) to a height of 10 [mu] m is 0.10% or more.

Description

TECHNICAL FIELD

[0001] The present application relates to a copper-plated steel sheet. BACKGROUND

[0002] A copper-plated steel sheet provided with a copper-plated layer on a base steel sheet is widely used for various products such as a double-wound pipe (an automobile brake pipe, an oil supply pipe, etc.), a welded pipe (a ground rod, etc.), an oil cooler, and the like, because of good brazing and soldering properties. In addition, a copper-plated steel sheet is also used as a base material for a cylindrical rolled bushing (a sliding bearing) or the like, which is a sliding member for a transmission or the like.

[0003] For example, Patent Literature 1 proposes a sliding member (copper-plated steel sheet) provided with a sliding base material such as a steel sheet, a pure copper-plated layer formed on the surface of the sliding base material, and a composite copper-plated layer formed on the pure copper-plated layer, which contains a plurality of block-shaped portions containing copper and graphite and has a Vickers hardness of 120 or less. However, this sliding member incurs costs for forming the composite copper-plated layer, and in the case of a large load, the maintenance ability of the sliding property (maintenance time of the coefficient of friction) is sometimes insufficient.

[0004] In addition, Patent Literature 2 proposes a multi-layer bearing composed of a metal base material, a porous layer formed on the surface thereof, and a resin composition impregnated and covered on the porous layer (for example, claim 1). This Patent Literature 2 describes a method of using a copper-plated steel sheet as the metal base material and using a sintered layer of copper as the porous layer (paragraphs 0045, 0046, 0051). It is said that by providing such a base material and a porous layer, the anti-seizure effect is improved. This bearing is excellent in product performance, but in terms of manufacturing, since copper plating and sintering are different processes, sometimes it becomes somewhat disadvantageous in terms of manufacturing costs.

[0005] Further, as a coating film excellent in sliding property, a sliding resin coating film formed of a lubricant resin or the like is known. For example, Patent Literature 3 proposes a sliding resin coating film (a coated article) obtained by applying a sliding property-improving paint containing, as main components, a base resin 95 to 50% by weight having a film formation temperature lower than the melting point of a polytetrafluoroethylene resin and a polytetrafluoroethylene resin 5 to 50% by weight having an average particle diameter of 2 to 40 μm to the surface of a metal sheet or the like and baking it. However, such a sliding resin coating film has low adhesion to a metal sheet or the like, and is easily peeled from the base material in a sliding environment, so sometimes the maintenance ability of the sliding property is insufficient.

[0006] On the other hand, as a technique for reducing the unevenness of the plated copper film surface, Patent Literature 4 describes a method in which, when forming a plated copper film on an insulating substrate having a metal film for power supply formed on the surface, the stirring speed V of the plating solution is increased in accordance with the increase in the current density Dk. In addition, it is known from Non-Patent Literature 1 that a technique for forming a dendritic plated copper film on a Zn-Al substrate.

[0007] Prior Art Documents

[0008] Patent Literature

[0009] Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 2018-197387

[0010] Patent Literature 2: International Publication No. 2010 / 079719

[0011] Patent Literature 3: Japanese Patent (JP-B) No. 4339960

[0012] Patent Literature 4: Japanese Patent Application Laid-Open (JP-A) No. 2013-95968

[0013] Non-Patent Literature

[0014] Non-Patent Literature 1: H Tanabe et al., "Cu Dendrite Crystal Ball Formation on a Zn-Al Substrate by Electroplating Method", e-Journal of Surface Science and Nanotechnology, Vol. 20, No. 4, pp. 232-236, 2022 SUMMARY

[0015] PROBLEMS TO BE SOLVED BY THE INVENTION

[0016] An object of the present application is to provide a plated copper steel sheet in which a sliding resin film is less likely to peel off when the sliding resin film is provided on a plated copper film.

[0017] SOLUTION TO PROBLEM

[0018] The present inventors have intensively studied a plated copper steel sheet, and as a result, have found that a plated copper film having a specific surface shape has excellent adhesion to a sliding resin film when the sliding resin film is provided on the plated copper film, and thus completed the present application.

[0019] That is, the present application provides a plated copper steel sheet including a base steel sheet and a plated copper film formed on at least one surface of the base steel sheet,

[0020] The copper-plated film has a base film portion that continuously covers the base steel sheet, and a protrusion portion that grows from the base film portion in a dendritic shape,

[0021] The volume fraction of the protrusion portion in a region from the base film portion to a height of 10 μm is 0.10% or more.

[0022] Effects of the Invention

[0023] According to the present application, a copper-plated steel sheet in which a sliding resin film is less likely to peel off when the sliding resin film is provided on a copper-plated film can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a schematic cross-sectional view of a copper-plated steel sheet of an embodiment of the present application.

[0025] Figure 2 is a schematic cross-sectional view of a copper-plated steel sheet of an embodiment of the present application further provided with a sliding resin film.

[0026] Figure 3 is an example of a three-dimensional image of a protrusion portion in a copper-plated steel sheet measured by X-ray CT.

[0027] Figure 4 is a schematic view for explaining a process of forming a copper-plated film. DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the present application will be specifically described. It should be understood that the present application is not limited to the following embodiments, and that solutions obtained by appropriately modifying, improving, and the like of the following embodiments based on common knowledge of those skilled in the art within a scope not departing from the gist of the present application also fall within the scope of the present application.

[0029] Note that in the present specification, "%" relating to a component means "mass %" unless otherwise specified.

[0030] Figure 1 is a schematic cross-sectional view of a copper-plated steel sheet of an embodiment of the present application.

[0031] As Figure 1 shown, a copper-plated steel sheet 10 of an embodiment of the present application includes a base steel sheet 20 and a copper-plated film 30 formed on one face of the base steel sheet 20. Note that, Figure 1 Examples in which the copper-plated film 30 is formed on one face of the base steel sheet 20 are shown in FIGS. 1 to 3, but the copper-plated film 30 can be formed on both faces of the base steel sheet 20.

[0032] The plated copper steel sheet 10 of the embodiment of the present application can further have a sliding property resin coating film. Here, a schematic cross-sectional view of the plated copper steel sheet of the embodiment of the present application further having a sliding property resin coating film is shown in Figure 2 .

[0033] As shown in Figure 2 , the sliding property resin coating film 40 is provided on the plated copper coating film 30.

[0034] Here, in the present specification, "steel sheet" means a steel material in a sheet shape (including a strip shape).

[0035] As the base steel sheet 20, there is no particular limitation, and various steel sheets such as a hot-rolled steel sheet, a cold-rolled steel sheet, and the like can be used. Among them, as the base steel sheet 20, a cold-rolled steel sheet is preferably used.

[0036] As for the composition of the base steel sheet 20, there is no particular limitation, and appropriate selection can be made depending on the use.

[0037] The plated copper coating film 30 is a coating film having good adhesion to the base steel sheet 20 and the sliding property resin coating film 40. Therefore, by providing the plated copper coating film 30, in the case where the sliding property resin coating film 40 is provided on the plated copper coating film 30, the sliding property resin coating film 40 can be prevented from being easily peeled off from the plated copper steel sheet 10. As a result, the sliding property can be maintained for a long period even in a sliding environment where a large load is applied.

[0038] When a cross section parallel to the thickness direction is sectioned, the plated copper coating film 30 has a base coating film portion 31 continuously covering the base steel sheet 20, and a protrusion portion 32 growing from the base coating film portion 31 in a dendritic shape.

[0039] Here, in the present specification, "the base coating film portion 31 continuously covering the base steel sheet 20" means a portion uniformly covering the base steel sheet 20 without exposing the base steel sheet 20. Therefore, the base coating film portion 31 is a region until a portion where the plated copper coating film 30 is not found is found when a line parallel to the surface of the base steel sheet 20 is drawn from the surface of the base steel sheet 20 in a cross section parallel to the thickness direction. For example, in Figure 1 , the dotted line portion becomes the boundary between the base coating film portion 31 and the protrusion portion 32, and the thickness T of the base coating film portion 31 is the height from the base steel sheet 20 to the dotted line portion.

[0040] The thickness T of the base coating film portion 31 is not particularly limited, and is preferably 1.0 μm or more, more preferably 1.3 μm or more, and further preferably 1.5 μm or more.

[0041] By continuously covering the base steel sheet 20 with the base film portion 31 having the thickness T as described above, the sliding resin film 40 becomes less likely to peel off even in a sliding environment where the load is large, in the case where the sliding resin film 40 is provided on the copper-plated film 30. Note that the upper limit of the thickness T of the base film portion 31 is not particularly limited, but is typically 10.0 μm or less, and preferably 8.0 μm or less, in consideration of manufacturing costs and the like.

[0042] The thickness T of the base film portion 31 can be measured by observing in a cross section parallel to the thickness direction of the copper-plated steel sheet 10 using a microscope (e.g., SEM).

[0043] In the case where the sliding resin film 40 is provided on the copper-plated film 30, the protrusion portion 32 growing dendritically (dendritically) from the base film portion 31 generates an anchoring effect between the copper-plated film 30 and the sliding resin film 40, thereby imparting an effect of making the sliding resin film 40 less likely to peel off even in a sliding environment where the load is large.

[0044] In order to obtain this effect, the volume fraction of the protrusion portion 32 in the region from the base film portion 31 to a height of 10 μm is 0.10% or more. By controlling the volume fraction of the protrusion portion 32 within this range, the state where there is a sufficient amount of the protrusion portion 32 to obtain the anchoring effect is achieved. From the viewpoint of stably ensuring this effect, the volume fraction of the protrusion portion 32 is preferably 0.20% or more, and more preferably 0.30% or more. Note that the volume fraction of the protrusion portion 32 is not particularly limited, but is typically 50.0% or less, since a larger volume fraction makes it easier to obtain the anchoring effect.

[0045] The volume fraction of the protrusion portion 32 in the region from the base film portion 31 to a height of 10 μm can be measured using X-ray CT. X-ray CT obtains a transmission image by irradiating X-rays while rotating the measurement target (copper-plated steel sheet 10), and performs a reconstruction process on the obtained image, thereby enabling three-dimensional observation of the internal structure of the copper-plated steel sheet 10.

[0046] Here, an example of a three-dimensional image of the protrusion portion 32 in the copper-plated steel sheet 10 measured using X-ray CT is shown in FIG. 6. Figure 3 .

[0047] The substrate steel plate 20 and the base coating portion 31 of the copper-plated film 30 (the continuously covered portion) are uniformly flat. When the object to be measured (copper-plated steel plate 10) is rotated, the X-ray absorption contrast changes uniformly with the thickness. Therefore, the X-ray absorption contrast of the substrate steel plate 20 and the base coating portion 31 of the copper-plated film 30 becomes the same and indistinguishable. On the other hand, the area where the protrusion 32 is formed has unevenness on its surface. When the object to be measured (copper-plated steel plate 10) is rotated, the X-ray absorption contrast in the uneven area changes according to its shape. Therefore, by setting a threshold for the X-ray absorption contrast of the entire three-dimensional image of the copper-plated steel plate 10 obtained by X-ray CT, it is possible to extract only the three-dimensional image of the protrusion 32. That is, the brightness value of the X-ray CT is different between the protrusion 32 and the substrate steel plate 20 and the base coating portion 31 of the copper-plated film 30 due to the difference in X-ray absorption contrast. Figure 3 As shown, it is possible to easily extract only the three-dimensional image of the protrusion 32.

[0048] The volume fraction of the protrusions 32 in the region from the base coating portion 31 to a height of 10 μm can be determined from a three-dimensional image obtained using X-ray CT. Figure 3 And calculated. Figure 3 Since only the region where the protrusion 32 is formed was extracted, the starting point of the height of the region where the volume fraction of the protrusion 32 is measured (the surface of the substrate coating 31) becomes the lowest point.

[0049] It should be noted that even in the presence of the sliding resin coating 40, by performing X-ray CT measurements in the same manner as described above, it is possible to extract only the three-dimensional image of the protrusion 32.

[0050] There is no particular limitation on the amount of copper adhering to the copper-plated coating 30, but it is preferably 10 to 150 g / m². 2 More preferably, it is 13–120 g / m 2 More preferably, it is 15–60 g / m 2 By controlling the amount of copper adhesion within such a range, it is possible to obtain a copper-plated coating 30 with good adhesion to the substrate steel plate 20 and the sliding resin coating 40.

[0051] An anti-discoloration treatment layer can also be formed on the copper plating film 30 to inhibit discoloration of the copper plating film 30. The anti-discoloration treatment layer is effective in inhibiting discoloration of the copper plating film 30 over time, especially in inhibiting discoloration within a few days after the copper plating film 30 is formed.

[0052] As an anti-discoloration treatment layer, there are no particular limitations as long as it does not impair the adhesion of the subsequently formed sliding resin coating 40. For example, an anti-discoloration treatment layer can be formed by immersing the substrate steel plate 20 in an aqueous solution / dispersion of a commercially available anti-discoloration agent and then drying it. Examples of commercially available anti-discoloration agents include: VERZONE See-You Guard D manufactured by Yamato Kasei Corporation; silane coupling agents containing benzotriazole groups manufactured by Shin-Etsu Chemical Industry Co., Ltd.; GOSPEL (C-30, C-70, or C-220) manufactured by GOSPEL Chemical Co., Ltd.; TOP RINSE CU-5 manufactured by Okuno Pharmaceutical Co., Ltd.; KPC-2003 manufactured by Metal Chemical Technology Research Institute Co., Ltd.; CU-5600 manufactured by Meltex Inc.; and BTZ-M manufactured by Kyodo Pharmaceutical Co., Ltd.

[0053] It should be noted that the anti-discoloration treatment layer can be formed entirely on the copper-plated film 30, or it can be formed locally.

[0054] The sliding resin coating 40 is a coating formed from a resin with sliding properties. Here, "sliding resin coating 40" in this specification refers to a resin coating with a dynamic friction coefficient of 0.2 or less when a flat portion of a plated steel sheet with a resin coating is collected as the test material and subjected to a friction and wear test using a surface roughness measuring instrument (HEIDON-TYPE14) manufactured by Shin-To Science Co., Ltd., under the conditions of a load of 1N, a 10mmφ SUS ball as the test material, a sliding (moving) speed of 150mm / min, and a test material temperature of 20-30°C.

[0055] The sliding resin coating 40 is not particularly limited, and any sliding resin coating known in the art can be used. For example, a resin coating with added lubricant or a self-lubricating resin coating can be used as the sliding resin coating 40. Among these, a coating in which polytetrafluoroethylene (PTFE) resin is dispersed in a matrix resin is preferred as the sliding resin coating 40. The matrix resin is not particularly limited, and examples include polyester resin, linear polymer polyester resin, acrylic resin, epoxy resin, polyurethane resin, phenoxy resin, phenolic resin, polyvinylidene fluoride (PVdF) / acrylic resin, and vinyl chloride resin.

[0056] The thickness of the sliding resin coating 40 is not particularly limited, and is 3 to 40 μm. By controlling the thickness of the sliding resin coating 40 within this range, the sliding properties can be stably ensured.

[0057] The aforementioned anti-discoloration treatment layer can also be formed between the copper plating film 30 and the sliding resin film 40.

[0058] The manufacturing method of the copper-plated steel sheet 10 according to the embodiments of the present invention is not particularly limited as long as it is a method capable of manufacturing the copper-plated steel sheet 10 having the above-described characteristics, and can be carried out according to known methods. Hereinafter, an example of the manufacturing method of the copper-plated steel sheet 10 according to the embodiments of the present invention will be described.

[0059] The manufacturing method of the copper-plated steel plate 10 according to the embodiments of the present invention includes an electroplating process in which a copper-plated coating 30 is formed on at least one side of the base steel plate 20 by electroplating.

[0060] The preferred electroplating process is to perform copper sulfate plating after copper pyrophosphate plating.

[0061] Copper pyrophosphate plating is performed by immersing the base steel plate 20 in a copper pyrophosphate plating solution.

[0062] There are no particular limitations on the conditions for copper pyrophosphate plating; they can be appropriately set according to known methods. Typical conditions are as follows.

[0063] Composition of copper pyrophosphate plating solution: 50 g / L copper pyrophosphate, 250 g / L potassium pyrophosphate, 10 g / L oxalic acid

[0064] The pH of the copper pyrophosphate plating solution is 9.2.

[0065] Temperature of copper pyrophosphate plating solution: 20~60℃

[0066] Current density: 1~10A / dm 2

[0067] Time: 5-100 seconds

[0068] It should be noted that copper pyrophosphate plating can be done once or multiple times under different conditions.

[0069] For copper sulfate plating, it is preferable to immerse the substrate steel plate 20 in a copper sulfate plating solution while varying the flow rate of the solution. More specifically, it is even more preferable to alternately repeat copper sulfate plating at low flow rates (e.g., flow rates below 0.30 m / s) and high flow rates (e.g., flow rates above 0.50 m / s).

[0070] Here, a schematic diagram illustrating the formation process of the copper plating film 30 is shown. Figure 4 .

[0071] When copper sulfate plating is performed at a low flow rate, insufficient copper ion supply to the plating surface is easily caused, and the deposited copper is easily destroyed by bubbles generated by hydrogen during the plating process. As a result, particulate copper adheres to the surface (state A). On the other hand, when copper sulfate plating is performed at a high flow rate, copper ions are easily and sufficiently supplied to the plating surface. As a result, the plating layer grows along the surface, thereby forming a copper plating film 30 that covers the entire surface with attached particulate copper (state B). Next, if copper sulfate plating is performed again at a low flow rate, particulate copper adheres in the same way as in state A, and the copper grows into dendritic crystals (dendritic crystals) (state C). Next, if copper sulfate plating is performed again at a high flow rate, a copper plating film 30 is formed that covers the entire surface, thereby strengthening the dendritic copper and increasing the thickness of the copper plating film 30 (state D). By alternating between copper sulfate plating at low flow rates and copper sulfate plating at high flow rates, a copper plating film 30 with the protrusions 32 described above can be formed.

[0072] The number of repetitions of copper sulfate plating at low flow rates and high flow rates, as well as the energizing time for each repetition, can be adjusted appropriately based on the composition of the copper sulfate plating solution, the current density, and the desired plating adhesion. Typically, the current density is 20–60 A / dm³. 2 The energizing time for each cycle (the energizing time for plating at low flow rate and plating at high flow rate) is 1 to 30 seconds, and the number of cycles is 5 to 50.

[0073] It should be noted that copper sulfate plating can be performed using electroplating equipment that allows the plating solution to flow (such as a flow bath).

[0074] Apart from these conditions, there are no particular limitations on the copper sulfate plating process; they can be appropriately set according to known methods. Typical conditions are as follows.

[0075] Composition of copper sulfate plating solution: 220 g / L copper sulfate, 45 g / L sulfuric acid

[0076] The pH of the copper sulfate plating solution is 1.0.

[0077] Temperature of copper sulfate plating solution: 20~50℃

[0078] The manufacturing method of the copper-plated steel sheet 10 according to the embodiments of the present invention may further include a resin coating forming step of forming a sliding resin coating 40 on the copper-plated coating 30.

[0079] The resin coating formation process is not particularly limited as long as it can form a sliding resin coating 40, and can be carried out according to known methods. In a typical resin coating formation process, a sliding resin coating 40 can be formed by coating a resin composition comprising a matrix resin and a polytetrafluoroethylene (PTFE) resin onto a copper-plated coating 30 and allowing it to dry.

[0080] There are no particular limitations on the coating method for the resin composition; for example, known methods such as dip coating, rod coating, roller coating, spin coating, and spray coating can be used. The coating of the resin composition can be performed once or multiple times to form a sliding resin film of a specified thickness. Furthermore, the drying temperature can be appropriately set according to the composition of the resin composition, etc., and is not particularly limited.

[0081] When an anti-discoloration treatment layer is provided on the copper plating film 30 or between the copper plating film 30 and the sliding resin film 40, the anti-discoloration treatment process can be performed after the electroplating process or between the electroplating process and the resin film formation process.

[0082] The anti-discoloration treatment process simply involves applying a solution containing anti-discoloration agents such as benzotriazole onto the copper-plated film 30 and allowing it to dry.

[0083] There are no particular limitations on the coating method for the solution containing the anti-discoloration agent, and the known methods described above can be used. Furthermore, the drying temperature can be set appropriately according to the type of solution, and there are no particular limitations.

[0084] Example

[0085] The following examples illustrate the content of the present invention in detail, but the present invention is not limited to these examples.

[0086] (Examples 1-3)

[0087] A 0.5mm thick cold-rolled steel sheet was prepared as the base steel plate. This cold-rolled steel sheet was then subjected to electrolytic degreasing, water washing, and pickling in sequence. Electrolytic degreasing involved immersing the cold-rolled steel sheet as the anode in a 5% Na-based degreasing agent (at 60°C) with a current density set to 2A / dm³. 2 The pickling process is performed with a timer set to 10 seconds. Additionally, the steel sheet is immersed in a 2% hydrochloric acid aqueous solution (at 20°C) for 30 seconds. Next, the cold-rolled steel sheet is immersed in a 60°C copper pyrophosphate plating solution with a current density set to 5 A / dm³. 2The copper pyrophosphate plating process was performed for 13 seconds. Next, the cold-rolled steel sheet coated with copper pyrophosphate was immersed in a copper sulfate plating solution at 35°C. Under the conditions of current density and copper sulfate plating solution flow rate shown in Table 1, copper sulfate plating was alternately performed at low flow rate and high flow rate, for a total of 21 cycles (11 cycles at high flow rate and 10 cycles at low flow rate). This resulted in a copper-plated steel sheet with a copper coating. It should be noted that the composition and pH of the pyrophosphate and copper sulfate plating solutions used are as described below.

[0088] Composition of copper pyrophosphate plating solution: 50 g / L copper pyrophosphate, 250 g / L potassium pyrophosphate, 10 g / L oxalic acid

[0089] The pH of the copper pyrophosphate plating solution is 9.2.

[0090] Composition of copper sulfate plating solution: 220 g / L copper sulfate, 45 g / L sulfuric acid

[0091] The pH of the copper sulfate plating solution is 1.0.

[0092] In addition, the flow rate in this embodiment refers to the speed of the plating solution flowing between the electrodes (cold-rolled steel sheet - anode) along the direction of the cold-rolled steel sheet.

[0093] Next, the copper-plated steel sheet with the copper coating was immersed in a 2 g / L benzotriazole aqueous solution (60°C) for 3 seconds and then dried to form an anti-discoloration treatment layer. Then, a resin composition containing 25% PTFE particles with an average particle size of 10 μm was coated onto the copper-plated steel sheet with the anti-discoloration treatment layer and dried at 200°C to form a 20 μm thick sliding resin coating. In a portion of the copper-plated steel sheets (Example 3), a sliding resin coating was formed without the anti-discoloration treatment layer. Here, the average particle size refers to the particle size at which the cumulative value in the particle size distribution determined by laser diffraction / scattering method reaches 50%.

[0094] (Comparative Example 1)

[0095] Instead of alternating between 21 copper sulfate plating operations performed at high flow rates and 21 copper sulfate plating operations at low flow rates, only 21 high flow rate copper sulfate plating operations were performed. Then, an anti-discoloration treatment layer and a sliding resin coating were formed, similar to the embodiments described above.

[0096] The copper-plated steel sheets obtained in the above embodiments were evaluated as follows.

[0097] <Copper adhesion amount of copper plating film>

[0098] A copper-plated steel sheet with only a copper coating was immersed in a mixed aqueous solution of ammonia (28% ammonia concentration) and hydrogen peroxide to dissolve the copper coating. The mass difference [g] before and after dissolution was measured, and the mass difference was divided by the area [m] of the region with the copper coating. 2 From this, the amount of copper adhering [g / m] can be calculated. 2 ].

[0099] <Thickness T of the substrate coating>

[0100] A copper-plated steel sheet with only a copper coating was cut in a manner that allows observation of a section parallel to the thickness direction, and resin filling was performed with the cut surface serving as the observation surface. Next, the resin-filled test piece was mirror-finished by wet grinding. The mirror-finished surface was observed using a SEM (Hitachi High Technology Co., Ltd. SU6600 model). In the 2000x SEM image, the thickness T [μm] of the substrate coating portion at a length of approximately 1000 μm in a direction orthogonal to the thickness direction was measured.

[0101] <Volume fraction of protrusions>

[0102] A copper-plated steel sheet with only a copper coating was machined into a circular plate-shaped sample with a diameter of 10 mm. X-ray CT was performed using an Xradia 520 Versa camera manufactured by Carl Zeiss. The pixel size of the X-ray transmission image was 1 μm / pixel, the magnification was 28x (4x objective lens), and the observation area was 1.0 mm × 1.0 mm × 0.5 mm. The tube voltage was set to 140 kV.

[0103] Next, the obtained X-ray CT images were reconstructed to obtain a three-dimensional image of the protrusion. Then, using Avizo (ver. 2022.2) manufactured by FEI as image analysis software, the protrusion within a region (1000μm × 1000μm × 10μm) from the basement membrane to a height of 10μm was identified, and its volume fraction was calculated.

[0104] <Evaluation of the Adhesion of Sliding Resin Coating>

[0105] A copper-plated steel sheet with a sliding resin coating was punched into a disc shape with a diameter of 6 mm. The clearance was set to 0.1 mm. Next, the punched copper-plated steel sheet was cut so that a cross-section parallel to the thickness direction could be observed, and resin filling was performed with the cut surface as the observation surface. Then, the resin-filled test piece was mirror-finished by wet grinding. For the mirror-finished surface, the peeling length of the sliding resin coating from the punched end face was measured. The evaluation criteria are as follows.

[0106] Peel length less than 20 μm: Excellent adhesion of the sliding resin coating (◎)

[0107] Peel length greater than 20 μm and less than 100 μm: The sliding resin coating exhibits good adhesion (○).

[0108] Peeling length exceeding 100 μm: Poor adhesion of the sliding resin coating (×)

[0109] The evaluation results are shown in Table 1.

[0110] [Table 1]

[0111]

[0112] As shown in Table 1, the copper-plated steel sheets of Examples 1 to 3 have good adhesion of the sliding resin coating because the volume ratio of the protrusions in the area from the substrate coating to a height of 10 μm is within a suitable range.

[0113] In contrast, the copper-plated steel sheet of Comparative Example 1 had insufficient adhesion of the sliding resin coating because the volume fraction of the protrusions in the area from the substrate coating to a height of 10 μm was not within a suitable range.

[0114] As can be seen from the above results, according to the present invention, a copper-plated steel sheet can be provided in which the sliding resin coating is not easily peeled off when the sliding resin coating is provided on the copper-plated coating. Therefore, the copper-plated steel sheet with the sliding resin coating provided on the copper-plated coating can maintain its sliding properties for a long time.

[0115] Explanation of reference numerals in the attached figures

[0116] 10 Copper-plated steel sheet

[0117] 20 Base steel plate

[0118] 30 Copper plating coating

[0119] 31. Substrate coating

[0120] 32. Protrusion

[0121] 40 Sliding resin coating.

Claims

1. A copper-plated steel sheet comprising a base steel sheet and a copper-plated coating formed on at least one side of the base steel sheet. When viewed in a cross-section parallel to the thickness direction, the copper plating film has: a base coating portion that continuously covers the substrate steel plate, and protrusions that grow from the base coating portion in a dendritic manner. The volume fraction of the protrusions in the region from the substrate coating to a height of 10 μm is 0.10% or more.

2. The copper-plated steel sheet according to claim 1, wherein, The thickness of the substrate coating is 1.0 μm or more.

3. The copper-plated steel sheet according to claim 1 or 2, further comprising a sliding resin coating disposed on the copper-plated coating.

4. The copper-plated steel sheet according to claim 1 or 2, further comprising an anti-discoloration treatment layer disposed on the copper-plated coating.

5. The copper-plated steel sheet according to claim 3, further comprising an anti-discoloration treatment layer disposed between the copper plating film and the slip-resistant resin film.

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