Conductive film and method for manufacturing the same

Abstract

The objective is to provide a conductive film that is lightweight and does not undergo cracking of the metal layer even after molding, making it useful as an electromagnetic wave shielding material. [Solution] A copper layer and a tin layer are laminated in this order on at least one side of a resin film, and the amount of copper added per unit area (g / m²) 2 ) and the amount of tin deposited per unit area (g / m²) 2 The conductive film is characterized in that the ratio [Cu / Sn] to ) is 0.15 or less, and the average particle size of the tin crystals constituting the tin layer is 5.0 μm or more.

Description

[Technical Field] 【0001】 This invention relates to a conductive film. More specifically, this invention relates to a conductive film that is useful as an electromagnetic wave shielding material, is lightweight, and does not undergo cracking of the metal layer even when molded. [Background technology] 【0002】 In recent years, with the rapid development of IT and office automation equipment, the impact of electromagnetic waves generated by electronic devices, cables, motors, and inverters on other electronic and information equipment has become a growing concern. 【0003】 Electromagnetic waves not only cause malfunctions in precision equipment, but also raise concerns about their effects on the human body. For this reason, various technologies have been developed to mitigate the effects of electromagnetic waves using electromagnetic shielding materials. One example of such a technology is a laminate made by laminating a metal layer with electromagnetic shielding properties, such as copper foil, onto a resin film. 【0004】 However, laminates formed by laminating a metal layer onto a resin film are prone to cracking during molding. Therefore, there is a need to suppress cracking and improve moldability. On the other hand, methods such as increasing the thickness of the metal layer or increasing the number of metal layers can be considered to suppress cracking, but such methods increase weight, making weight reduction difficult. It is not easy to satisfy both weight reduction and moldability simultaneously. 【0005】 Various proposals have been made regarding electromagnetic wave shielding materials that laminate a metal layer onto a resin film. For example, Patent Document 1 discloses an electromagnetic wave shielding material in which resin layers are tightly laminated on both sides of a metal foil to suppress breakage during molding. This material incorporates measures to enhance the ductility of the metal foil, but it has the disadvantage that it cannot be soldered because the metal foil is sandwiched between resin layers. 【0006】 Patent Document 2 discloses that an electromagnetic wave shielding material with excellent three-dimensional moldability and lightweight properties can be obtained by laminating a resin layer on a copper foil and limiting the degree of orientation of the copper foil surface and the relationship between the thickness of the copper foil and the thickness of the resin layer. However, this method has the disadvantage of requiring the creation of copper foil with a specific degree of orientation and thickness, and then laminating multiple layers of copper foil and resin, which complicates the process. 【0007】 Patent Document 3 discloses an electromagnetic shielding material in which multiple metal layers and insulating layers are alternately laminated to suppress the occurrence of cracks in the metal layers due to molding. However, this material tends to be thicker and involves more manufacturing steps. 【0008】 Furthermore, Patent Document 4 discloses a conductive film obtained by laminating copper and tin in that order on a film substrate, but this film improves solderability by providing a barrier layer made of an organic compound between the copper layer and the tin layer. [Prior art documents] [Patent Documents] 【0009】 [Patent Document 1] Japanese Patent Publication No. 2018-152466 [Patent Document 2] Japanese Patent Publication No. 2021-163789 [Patent Document 3] Japanese Patent Publication No. 2022-091579 [Patent Document 4] International release 2022 / 085374 [Overview of the Initiative] [Problems that the invention aims to solve] 【0010】 The present invention aims to provide a conductive film that is lightweight and does not undergo cracking of the metal layer even after molding, making it useful as an electromagnetic wave shielding material. [Means for solving the problem] 【0011】 In order to solve the above problems, the inventors have found that when a laminate in which a copper layer and a tin layer are laminated in this order on a resin film satisfies certain conditions for the ratio of the amount of copper applied and the amount of tin applied and the average particle diameter of the tin crystals constituting the tin layer, the above problems can be solved, and the present invention has been completed. 【0012】 That is, the present invention relates to a conductive film shown below. (1) A metal layer in which a copper layer and a tin layer are laminated in this order on at least one side of a resin film, and the ratio [Cu / Sn] of the amount of copper applied per unit area (g / m 2 ) and the amount of tin applied per unit area (g / m 2 ) is 0.15 or less, and the average particle diameter of the tin crystals constituting the tin layer is 5.0 μm or more. A conductive film characterized by this. 【0013】 (2) The conductive film according to (1), wherein the amount of copper applied per unit area in the copper layer is 10 g / m 2 or less. (3) The conductive film according to (1), wherein the arithmetic mean roughness Ra of the surface of the tin layer is 0.25 μm or more. (4) The conductive film according to (1), wherein the thickness of the resin film is 100 to 200 μm. 【0014】 (5) A method for manufacturing the conductive film according to any one of (1) to (4), including a step of forming a copper layer on a resin film and a step of forming a tin layer on the copper layer formed in the above step by an electro-tin plating method. A method for manufacturing a conductive film. (6) The method for manufacturing a conductive film according to (5), wherein in the electro-tin plating method, a tin plating solution that is not for gloss is used as the plating solution. 【Effects of the Invention】 【0015】 According to the present invention, a conductive film useful as an electromagnetic wave shielding material, which is excellent in lightness and does not crack in the metal layer even when subjected to molding processing, can be obtained. 【Brief Description of the Drawings】 【0016】 [Figure 1] It is a cross-sectional view showing an outline of an example of the conductive film of the present invention. [Figure 2] It is a plan view showing an outline of a jig and a sample used in the method for evaluating formability in the examples. [Figure 3] It is a cross-sectional view and a schematic view showing an outline of a sample fixing jig for evaluation used in the method for evaluating formability in the examples. [Figure 4] Regarding the method for evaluating formability in the examples, it is a cross-sectional view schematically showing a forming process. [Figure 5] It is a schematic view showing the conductive film (evaluation sample molded product) after molding in the examples. [Figure 6] It is a digital microscope image observing the presence or absence of metal cracks in the evaluation of formability for the conductive film produced in Example 1. [Figure 7] It is a digital microscope image used for measuring the crystal grain size of the tin layer for the conductive film produced in Example 1. [Figure 8] It is a digital microscope image observing the presence or absence of metal cracks in the evaluation of formability for the conductive film produced in Comparative Example 5. [Figure 9] It is a digital microscope image observing the presence or absence of light leakage in the evaluation of formability for the conductive film produced in Comparative Example 5. 【Modes for Carrying Out the Invention】 【0017】 The conductive film of the present invention comprises at least a resin film and a metal layer formed on the resin film. 【0018】 1. Resin Film As the resin film, a film made of synthetic resin is preferably used. The synthetic resin is not particularly limited, but examples include films made of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polyimide, polyetherimide, and polyphenylene sulfide. 【0019】 A more desirable resin film is one with an elastic modulus of 3.0 GPa or higher. Furthermore, a tensile strength of 70 MPa or higher, more preferably 75 MPa or higher, and particularly preferably 100 MPa or higher is used. A glass transition temperature of 90°C or higher, more preferably 150°C or higher, is used. Finally, a melting point of 270°C or higher, more preferably 300°C or higher is used. 【0020】 A resin film that satisfies these conditions has advantages such as high film strength, resistance to breakage, excellent heat resistance, and resistance to thermal distortion during the reflow process after molding. Therefore, it can be preferably used in the present invention as a material that is easy to mold and has high strength. Specifically, polyetherimide (PEI) and polyphenylene sulfide (PPS) are particularly preferred. 【0021】 The thickness of the resin film is not particularly limited, but it is preferably 100 to 200 μm. If the resin film thickness is within this range, moldability is improved. If the thickness is 100 μm or more, the film is less likely to break and handling is not reduced. Furthermore, sufficient strength after molding can be maintained. If the thickness is 200 μm or less, the film does not become difficult to conform to the mold during molding. 【0022】 2. Metal layer The metal layer formed on the resin film includes at least a copper layer and a tin layer. The metal layer may be formed on only one side of the resin film or on both sides. 【0023】 (1) Copper layer The copper layer is formed on at least one side of the resin film in contact with the resin film. In this invention, the copper layer includes not only a layer made of metallic copper but also a layer made of a copper alloy. That is, the metal forming the copper layer may be either copper or a copper alloy. Examples of copper alloys include alloys of copper with metals such as nickel, zinc, and tin. The proportion of copper in the copper alloy is not particularly limited. Preferably, it consists of copper only. 【0024】 Amount of copper added per unit area in a copper layer (g / m²) 2 ) is not particularly limited, but preferably 10.0 g / m 2 The following applies: When the amount of copper added is within this range, metal cracking during molding tends to be less likely. The lower limit of the amount of copper added is not particularly limited, but preferably 3.0 g / m 2 That's all. 【0025】 The thickness of the copper layer is not particularly limited, but is preferably 1.0 μm or less. The lower limit of the thickness is not particularly limited, but is preferably 0.1 μm or more, more preferably 0.3 μm or more. If the thickness of the copper layer is within this range, a conductive film with sufficient conductivity, flexibility, and excellent moldability can be obtained. 【0026】 The copper layer may be a single layer or two or more layers may be laminated. The number of laminated copper layers is preferably 1 to 2. When multiple copper layers are laminated, they may have the same or different properties and formation methods. However, if the composition of the constituent materials of the layers is the same, they are considered as a single layer. When multiple copper layers are laminated, the preferred amount of metal added to the copper layer and the range of thickness are the total thickness of the laminated copper layers. 【0027】 As a method for forming the copper layer, known methods can be adopted without limitation. For example, methods such as attaching a copper foil using an adhesive, dry film forming methods such as vacuum evaporation and sputtering, and wet film forming methods such as electroless plating and electroplating can be mentioned. Also, the copper layer may be formed by combining these methods. Preferred methods are dry film forming methods or wet film forming methods. Further, a resin film (including commercially available products) on which a copper layer has already been formed can also be used. 【0028】 When there is only one copper layer, the amount of copper applied per unit area in the copper layer (g / m 2 ) is not particularly limited, but is preferably 10.0 g / m 2 or less, more preferably 5.0 g / m 2 or less. The lower limit of the applied amount is not particularly limited, but is preferably 3.0 g / m 2 or more. 【0029】 The thickness of the copper layer is not particularly limited, but is preferably 0.5 μm or less. The lower limit of the thickness is not particularly limited, but is preferably 0.1 μm or more, more preferably 0.3 μm or more. If the thickness of the copper layer is within this range, a conductive film having sufficient conductivity while maintaining flexibility and excellent formability can be obtained. 【0030】 (2) Tin layer In the present invention, the tin layer is laminated on the side opposite to the resin film side of the copper layer in contact with the copper layer. 【0031】 The amount of tin applied per unit area in the tin layer (g / m 2 ) is not particularly limited, but is preferably 20 g / m 2 or more, more preferably 30 g / m 2 or more. When the applied amount of tin is large, the formability tends to improve. The upper limit of the applied amount is not particularly limited, but is preferably 110 g / m 2 or less, more preferably 80 g / m 2 or less. If the metal applied amount of the tin layer is within this range, a conductive film having excellent formability can be obtained. 【0032】 The thickness of the tin layer is not particularly limited, but is preferably 5 μm or more, and more preferably 7.5 μm or more. The upper limit of the thickness of the tin layer is not particularly limited, but is preferably 20 μm or less, and more preferably 15 μm or less. When the thickness of the tin layer is within this range, metal cracking tends to occur less during molding, and a conductive film with excellent moldability can be obtained. 【0033】 The tin layer may be a single layer or two or more layers may be laminated together. When two or more tin layers are laminated together, they may have the same or different properties and formation methods. If the composition of the constituent materials of the layers is the same, they are considered as a single layer. The preferred number of tin layers is one. When multiple tin layers are laminated, the preferred metal content and thickness range of the tin layer is the total thickness of the laminated tin layers. 【0034】 The method for forming the tin layer is not particularly limited, but examples include wet film formation methods such as electroless plating and electroplating. It may be formed by either electroless plating or electroplating, but it is preferable to form it by electroplating because it allows for easy control of film thickness and continuous processing. 【0035】 In electroplating, if a sufficient tin film thickness cannot be formed in a single electroplating treatment, one method for forming a tin layer of the desired thickness is to perform multiple electroplating treatments using a tin plating solution of the same composition. In other words, the process can be carried out by passing through multiple tanks of tin plating solution of the same composition. 【0036】 For example, a tin layer of the desired thickness can be formed by rinsing with water after the first tin plating treatment, then rinsing with water after a second tin plating treatment using a tin plating solution of the same composition as the first tin plating treatment, and then rinsing with water after a third tin plating treatment using a tin plating solution of the same composition. There is no particular limit to the number of times the tin plating treatment can be performed using a tin plating solution of the same composition, and the number of treatments can be adjusted as appropriate to achieve the desired thickness. The tin layer of the desired thickness formed in this way can be considered as a single layer because the composition of the materials constituting the tank is the same. 【0037】 In the tin layer, the average grain size of the tin crystals constituting the tin layer is 5.0 μm or larger. There is no particular upper limit to the average grain size, but it is preferably 10 μm or smaller. When the grain size is 5 μm or larger, the advantage is that metal cracking is less likely to occur during molding. 【0038】 One method for adjusting the crystal grain size of the tin layer is to appropriately adjust the plating time during electroplating. If the plating time is too short, crystal growth will not be sufficient, and the grain size will tend to be small. On the other hand, if the plating time is too long, crystal growth will be sufficient, and the grain size will tend to be larger. 【0039】 Furthermore, by using a tin plating solution that is not intended for high-gloss finishes, the grain size of the tin crystals can be increased. When a tin layer is created using a high-gloss tin plating solution, the surface is smoothed to produce a glossy finish, so the resulting tin layer tends to have a very small grain size. 【0040】 A tin plating solution that is not intended for a glossy finish is, specifically, a tin plating solution that does not contain a glossing agent. Examples of glossing agents include acrylic acid, methyl acrylate, methyl methacrylate, benzalacetone, benzaldehyde, and acetophenone, and it is desirable to use a tin plating solution that does not contain these substances. 【0041】 The arithmetic surface roughness Ra of the tin layer surface is preferably 0.25 μm or more. Here, the surface of the tin layer is the surface of the tin layer opposite to the surface on which the copper layer is formed, and is the outermost surface on the metal layer side in the conductive film of the present invention. The upper limit of the arithmetic surface roughness Ra is not particularly limited, but is preferably 0.7 μm or less. 【0042】 If the arithmetic surface roughness Ra of the tin layer is too low, crack initiation points are more likely to occur, and large cracks may develop. If the arithmetic surface roughness Ra of the tin layer is within the above range, cracks tend to be less likely to occur in the tin film. The arithmetic surface roughness Ra of the tin layer refers to the surface roughness of the outermost layer of the conductive film after each layer has been laminated, and can be measured after lamination using a method compliant with JIS B 0601:2001. 【0043】 In order to achieve the above range for the arithmetic surface roughness Ra of the tin layer, it is preferable to perform electroplating to form the tin layer, and to use a tin plating solution that is not intended for brightening. This makes it possible to increase the arithmetic surface roughness Ra of the tin layer surface. 【0044】 3.Layer composition The conductive film of the present invention has at least a copper layer and a tin layer laminated on a resin film in this order. In the present invention, "this order" means that the copper layer and the tin layer are laminated in that order from the side closest to the resin film. The copper layer and the tin layer may be laminated on only one side of the resin film, or on both sides. 【0045】 Examples of the layer configurations of the conductive film of the present invention include resin film / copper layer / tin layer, resin film / copper layer (no. 1) / copper layer (no. 2) / tin layer, and tin layer / copper layer / resin film / copper layer / tin layer. The example including copper layer (no. 1) and copper layer (no. 2) refers to a case where multiple copper layers with the same or different properties and formation methods are laminated. More preferably, a layer configuration of resin film / copper layer (vapor-deposited copper) / copper layer (electroplated copper) / tin layer is provided. 【0046】 Figure 1 shows a schematic cross-section of an example of the conductive film of the present invention. Figure 1(A) shows the configuration of resin film / copper layer / tin layer, and Figure 1(B) shows the configuration of resin film / copper layer (1) / copper layer (2) / tin layer. In Figure 1(A), a is the resin film, b is the copper layer, and c is the tin layer. Also, in Figure 1(B), a is the resin film, b is the copper layer (1), b' is the copper layer (2), and c is the tin layer. 【0047】 In the conductive film of the present invention, in addition to the essential layers of the resin film, copper layer, and tin layer, various optional layers can be provided as needed. For example, adhesive layers can be provided between each layer. Specifically, an adhesive layer can be provided between the resin film and the copper layer to improve adhesion. Furthermore, although the tin layer is the outermost layer of the conductive film, its surface can be treated with a discoloration inhibitor to improve resistance to discoloration. 【0048】 In the copper layer and tin layer of the conductive film of the present invention, the amount of copper added per unit area (g / m²) 2 ) and the amount of tin added per unit area (g / m²) 2 The ratio [Cu / Sn] is 0.15 or less. When [Cu / Sn] is within this range, metal cracking is less likely to occur during molding. The lower limit of [Cu / Sn] is not particularly limited, but it is preferably 0.05 or more. 【0049】 4. Manufacturing method The conductive film of the present invention is manufactured by a method that includes the steps of forming a copper layer on a resin film and forming a tin layer on the copper layer formed in the first step by electroplating. 【0050】 (1) Process of forming a copper layer The method for forming the copper layer on the film substrate is not particularly limited, and known methods can be used. Specifically, examples include copper vapor deposition, electroplating, and electroless copper plating. Of these, copper vapor deposition is preferred. By using vapor deposition to form the copper layer, a copper layer with a highly smooth surface can be formed. 【0051】 Regarding the formation of the copper layer, a copper layer may be formed first by vapor deposition, and then another copper layer may be formed on top of it using electroplating. This allows for a more efficient formation of a thicker copper layer. In this case, the second copper layer formed by electroplating is laminated onto the surface of the copper layer formed by vapor deposition. Furthermore, in this invention, commercially available resin films with a pre-formed copper layer can also be used. 【0052】 In the electroplating process for copper, when a sufficient copper film thickness cannot be formed in a single electroplating treatment, one method for forming a copper layer of the desired thickness is to perform multiple electroplating treatments using a copper plating solution of the same composition. In other words, the process can be carried out by passing through multiple tanks of copper plating solution of the same composition. 【0053】 For example, a copper layer of the desired thickness can be formed by rinsing with water after the first copper plating treatment, then rinsing with water after performing a second copper plating treatment using a copper plating solution of the same composition as the first copper plating treatment, and then rinsing with water after performing a third copper plating treatment using a copper plating solution of the same composition. There is no particular limit to the number of times copper plating treatments can be performed using a copper plating solution of the same composition, and the number of treatments can be adjusted as appropriate to achieve the desired thickness. In addition, the copper layer of the desired thickness formed in this way can be considered as a single layer because the composition of the constituent materials of the tank is the same. 【0054】 (2) Process of forming a tin layer The process of forming a tin layer on the copper layer is performed using electroplating, and the tin plating layer can be formed by a general electroplating method. The plating solution used in the electroplating method can be an aqueous solution of, for example, stannous sulfate, as the tin source, but commercially available electroplating solutions may also be used. Furthermore, it is preferable to use a tin plating solution that is not intended for high gloss as the electroplating solution. This makes it possible to increase the average particle size of the tin crystals and increase the arithmetic surface roughness Ra of the tin layer surface. 【0055】 In particular, it is preferable to limit the addition of organic compounds (brighteners) that can be used in bright tin plating solutions, such as aldehyde compounds, amine compounds, and carboxylic acid (ester) compounds. 【0056】 Brighteners whose addition should be restricted include acrylic acid, methyl acrylate, methyl methacrylate, benzalacetone, benzaldehyde, and acetophenone. It is desirable to use a tin plating solution that does not contain these substances. 【0057】 The conditions for the electroplating method are not particularly limited and should be set within a range that allows for the formation of a tin plating layer of the desired thickness. However, it is desirable to select conditions such that the average particle size of the tin crystals in the tin layer is 5.0 μm or larger. Preferred conditions include a plating solution temperature of 20 to 50°C and a current density of 0.5 to 5.0 A / dm². 2 The processing time can be between 200 and 600 seconds, but is not limited to these values. [Examples] 【0058】 The present invention will be described below with reference to examples, but the present invention is not limited in any way by these examples. Furthermore, the evaluation in the examples was carried out according to the following method. 【0059】 [Evaluation of moldability] Samples (20 mm x 30 mm) were cut from the conductive films prepared in each example and comparative example and used for evaluation. The samples were evaluated according to the methods shown in Figures 2 to 5. Figure 2 is a plan view showing the jig and sample schematic used in the moldability evaluation method, Figure 3 is a cross-sectional view and schematic diagram showing the sample fixing jig used in the moldability evaluation method, Figure 4 is a cross-sectional view schematically showing the molding process, and Figure 5 is a schematic diagram showing the conductive film (evaluation sample molded product) after molding. In the figures, the sample is shown as an example of a conductive film having a layer structure of resin film / copper layer / tin layer, but it is not limited to this as long as the layer structure is within the scope of the present invention. Also, the dimensions in the figures are not necessarily exact proportions for the sake of simplification. 【0060】 (1) The sample (1 in Figure 2(A)) was placed in a commercially available jig (stainless steel bent plate with a staggered edge; length 98 mm x width 20 mm x thickness 0.84 mm; 2 in Figure 2(A)) having four holes p with a diameter of 5 mm and four holes q with a diameter of 3.5 mm (a total of 8 holes), so that the center of the sample overlapped with the 3.5 mm holes. At this time, the 20 mm wide side of the sample was placed along the longitudinal direction of the jig, and the 30 mm wide side was placed along the width direction of the jig. The portion of the sample that protruded from both sides of the jig on the 30 mm wide side was folded to the back of the jig and polyimide tape (3 in Figure 2(B)) was wrapped around it in the width direction to secure the sample. 【0061】 At this time, sample 1 was fixed so that the resin film a side was on the surface and the metal layer (tin layer c) side was in contact with jig 2 (see Figure 3(A)). In addition, if jig 2 had both a smooth and an uneven edge to the inner circle of the hole, it was fixed so that the smooth side was facing upwards (the side in contact with the metal layer c of the sample). By placing the smooth side of the inner circle facing upwards, it is possible to avoid the risk of the sample cracking at a location different from the area to be observed for metal cracking due to the force applied to the inner edge of the hole when the copper pin described later is placed on it, resulting in light leakage at a location different from the area to be observed and potentially hindering evaluation. 【0062】 On top of the sample fixing jig obtained in this way, another similar jig (2' in Figure 3(B)) was placed so that the size and position of the holes matched (see Figure 3(B)), and the whole thing was further secured with polyimide tape to create the sample fixing jig for evaluation (Figure 3(C)). 【0063】 (2) The obtained sample fixing fixture for evaluation was placed in a multi-oven (product name "MOV-300SB"; manufactured by AS ONE Corporation) set to 230°C and left to stand for 2 minutes. After 2 minutes, a φ3.0 mm copper pin (mold; a weight placed inside the tray to which the mold is attached to make a total weight of 7.5 kg; 4 in Figure 4(A)) was placed in the φ3.5 mm hole holding the sample and left to stand for 1 minute to form (see Figure 4(B)). Subsequently, the evaluation sample fixing jig was removed from the multi-oven, and the sample was then removed from the jig to obtain an evaluation sample molded product having a cylindrical protruding molded part as shown in Figure 5. 【0064】 (3) In the evaluation sample molded product having a cylindrical projection formed by a copper pin with a weight on it, the presence or absence of metal cracks was observed using a digital microscope (product name "VHX-8000", manufactured by Keyence Corporation) at the area formed on the bottom surface of the copper pin (the circumference of the cylindrical projection). At this time, only the area formed on the bottom surface of the copper pin was evaluated for metal cracks (5 in Figure 4(B)), and the presence or absence of metal cracks in other areas was not considered. 【0065】 (4) The evaluation sample molded product was observed using the aforementioned digital microscope (product name "VHX-8000", manufactured by Keyence Corporation) with light irradiated from the rear (opposite side from the side where the protruding part of the molded part protrudes) to check for any light leakage. 【0066】 (5) Based on the presence or absence of metal cracks and light leakage, the formability was evaluated according to the following criteria. Formability: Good; No cracking in the metal layer; No light leakage. Formability: △; No cracking in the metal layer, light leakage present. Formability: △; metal layer cracking present, light leakage: absent. Formability: Poor; Cracks in the metal layer: Present; Light leakage: Present. 【0067】 [Measurement of the amount of metal impregnation and thickness of metal layers (copper layer and tin layer)] The sample was cut into 3cm x 3cm pieces and immersed in 10ml of 1 / 2 diluted aqua regia to completely dissolve the metal layer, obtaining a solution in which the metal layer had dissolved. Next, the amount of copper (Cu) and tin (Sn) in this solution was measured using an atomic absorption spectrophotometer (unit: mg / L). The obtained amount of metal (mg / L) was converted to basis weight (g / m²). 2 The amount of metal added was determined by performing the following calculation. Furthermore, the thickness of the metal layer (μm) was determined by converting the specific gravity of each metal to a corresponding thickness. 【0068】 [Average grain size of tin crystals] The average grain size of tin crystals in the tin layer was determined by the average line segment length obtained using automatic area measurement: grain size measurement with a digital microscope (product name "VHX-8000"; manufactured by Keyence Corporation). 【0069】 [Measurement of Arithmetic Surface Roughness Ra] The arithmetic surface roughness Ra was measured using a method compliant with "JIS B 0601:2001". 【0070】 <Examples 1-4, 6> A resin film (manufactured by Toray KP Film Co., Ltd.; hereinafter referred to as "copper-deposited resin film") was prepared by depositing copper using a conventionally known method to form a copper layer on one side. The materials of the resin films in Table 1 are as follows. 【0071】 [PEI]: Polyetherimide film (elastic modulus: 3.2 GPa, tensile strength: 110 MPa, glass transition temperature: 215°C, melting point: 340°C) [PPS]: Polyphenylene sulfide film (elastic modulus: 3.5 GPa, tensile strength: 80 MPa, glass transition temperature: 90°C, melting point: 280°C) 【0072】 Next, the copper-deposited resin film was acid-washed with a 50 mL / L sulfuric acid solution (sulfuric acid concentration: 5 vol% (v / v)), and then immersed in tin plating solution A with the following composition, and plated at 40°C with a current density of 2.0 A / dm² using a soluble tin anode. 2 Electrolytic tin plating was performed for the processing time (sec) shown in Table 1 to form a tin layer on the surface of the copper vapor-deposited layer of the copper vapor-deposited resin film. 【0073】 Subsequently, the film was immersed in a 50 mL / L anti-discoloration treatment solution (product name "501SN"; manufactured by Ishihara Chemical Co., Ltd.) at 40°C for 60 seconds to obtain a conductive film having a layered structure of resin film / copper layer / tin layer. The results of the moldability evaluation of this film are shown in Table 1. Figure 6 shows a digital microscope image observing the presence or absence of metal cracking in the conductive film obtained in Example 1. Figure 6 shows that no metal cracking occurred in the molded portion of the conductive film obtained in Example 1. Images observing the presence or absence of light leakage are not shown for the examples because there was no light leakage and the entire image was black. 【0074】 Table 1 shows the results of determining the average grain size of tin crystals in the tin layer of the obtained conductive film. Figure 7 shows the crystal grain size measurement screen of the tin layer in the conductive film obtained in Example 1 using a digital microscope. According to Figure 7, the average line segment length is displayed as 9.17 μm, and this was taken as the average crystal grain size of the tin layer in Example 1. 【0075】 It should be noted that the amount of metal added and the grain size measured in this example and comparative example may show very slight variations even when the manufacturing and measurement conditions during sample preparation are the same, which may result in slight differences in the measured values. 【0076】 [Composition of tin plating solution A] • Tin (main component is tin methanesulfonate) (product name "UTB PF-SN15", manufactured by Ishihara Chemical Co., Ltd.); 400g / L • Conductive salt (main component is methanesulfonic acid) (product name "UTB PF-A", manufactured by Ishihara Chemical Co., Ltd.); 80g / L • Plating additive (methanesulfonic acid-based additive without brightener) (product name "UTB PF-095SA", manufactured by Ishihara Chemical Co., Ltd.); 25 mL / L 【0077】 <Example 5> A conductive film was created by forming a copper layer and a tin layer on the copper-deposited resin film shown in Table 1. First, the copper-deposited resin film was acid-washed with an acid treatment solution in the same manner as in Example 1, and then immersed in copper plating solution a of the following composition, using an insoluble anode at 40°C and a current density of 2.5 A / dm². 2 Copper plating was performed using the processing times (sec) shown in Table 1. Subsequently, the film was immersed in 10 mL / L of rust-preventive treatment solution (product name "Pal C"; manufactured by Tatsuta Electric Wire Co., Ltd.) at 21°C for 10 seconds to obtain a copper laminated film having a layered structure of resin film / copper layer / copper layer. 【0078】 Next, the obtained copper laminated film was immersed in tin plating solution A in the same manner as in Example 1 under the plating conditions shown in Table 1 to perform tin plating, thereby obtaining a conductive film having a layered structure of resin film / copper layer / copper layer / tin layer. The results of the moldability evaluation of this film are shown in Table 1. In Table 1, the thickness of the copper layer is the total thickness of the formed copper layers. 【0079】 Copper plating solution a: Copper sulfate pentahydrate; 200g / L Sulfuric acid (concentration; 5.5 vol% (v / v)); 55 mL / L NaCl; 85 mg / L Soft copper film-forming agent (additive name "CU-SOFT", manufactured by JCU Corporation); 25 mL / L 【0080】 <Comparative Examples 1, 3> A conductive film having a resin film / copper layer / tin layer structure was created by forming a tin layer on the copper vapor-deposited layer of the copper vapor-deposited resin film using the same method as in Example 1, except that the copper vapor-deposited resin film shown in Table 2 was used and the conditions shown in Table 2 were used. The results are shown in Table 2. 【0081】 <Comparative Example 2> Using the copper vapor-deposited resin film shown in Table 2, and using the bright tin plating solution B described below as the tin plating solution, and a soluble tin anode, the process was performed at 21°C with a current density of 2.0 A / dm². 2Plating was performed for the processing time (sec) shown in the table. Afterwards, the material was immersed in a 50 mL / L anti-discoloration treatment solution of 501SN (manufactured by Ishihara Chemical Co., Ltd.) at 40°C for 60 seconds. Except for the tin plating treatment performed under the conditions shown in Table 1, a tin layer was formed on the copper vapor-deposited layer in the same manner as in Example 1, and a conductive film having a layered structure of resin film / copper layer / tin layer was created. The results of the moldability evaluation of this material are shown in Table 2. Because a tin plating solution for bright tin plating was used, the crystal grain size of the tin layer was small. 【0082】 Tin plating solution B: Stannous sulfate (concentration; 5% w / v); 50 g / L Sulfuric acid (concentration; 11% by volume (v / v)); 110 mL / L Additive for bright tin plating (product name "ST-10", manufactured by Ishihara Chemical Co., Ltd.); 50 mL / L (Note that "ST-10" is an additive containing the necessary components for bright tin plating, including polyoxyethylene nonylphenyl ether, pyrocatechol, methanol, etc., as well as methyl acrylate as a brightener.) 【0083】 <Comparative Examples 4-9> The copper-deposited resin film shown in Table 2 was acid-washed with an acid treatment solution in the same manner as in Example 1, then immersed in copper plating solution a of the above composition, and plated at 40°C with a current density of 2.5 A / dm² using an insoluble anode. 2 Copper plating was performed using the processing times (sec) shown in Table 1. Subsequently, the film was immersed in 10 mL / L of rust-preventive treatment solution (product name "Pal C"; manufactured by Tatsuta Electric Wire Co., Ltd.) at 21°C for 10 seconds to obtain a copper laminated film having a layered structure of resin film / copper layer / copper layer. In Table 2, the thickness of the copper layer is the total thickness of the formed copper layers. 【0084】 Next, the obtained copper laminated film was immersed in tin plating solution A in the same manner as in Example 1 under the plating conditions shown in Table 2 to perform tin plating, thereby obtaining a conductive film having a layered structure of resin film / copper layer / copper layer / tin layer. The results of the moldability evaluation of this film are shown in Table 2. 【0085】 Figure 8 shows a digital microscope image of the conductive film obtained in Comparative Example 5, observing the presence or absence of metal cracking. Figure 8 shows that metal cracking has occurred around the circumference of the cylindrical protrusion. Figure 9 shows a digital microscope image of the conductive film obtained in Comparative Example 5, observing the presence or absence of light leakage. Figure 9 shows that light leakage (whitish areas) has occurred. 【0086】 [Table 1] 【0087】 [Table 2] [Industrial applicability] 【0088】 The conductive film of the present invention is lightweight and does not crack in the metal layer even when molded, making it useful not only as an electromagnetic wave shielding material but also as a grounding material for removing noise. [Explanation of Symbols] 【0089】 1. Conductive film (sample for moldability evaluation) 2. Jig for evaluating moldability 2'. Jig for evaluating moldability 3. Polyimide tape 4. Copper pins 5. Areas to be observed for the presence or absence of metal cracks in the molded part (circumference of the cylindrical protrusion) 6. Cylindrical protrusion-forming part of the evaluation sample molded product a. Resin film b. Copper layer or copper layer (part 1) b'. Copper layer (part 2) c. Tin layer p.hole (φ5mm) q. Hole (φ3.5mm)

Claims

[Claim 1] The resin film has a metal layer on at least one side in which a copper layer and a tin layer are laminated in that order, and the amount of copper added per unit area (g / m²) ２ ) and the amount of tin added per unit area (g / m²) ２ A conductive film characterized in that the ratio [Cu / Sn] to ) is 0.15 or less, and the average particle size of the tin crystals constituting the tin layer is 5.0 μm or more. [Claim 2] The amount of copper added per unit area in the aforementioned copper layer is 10 g / m². ２ The conductive film according to claim 1, which is as follows: [Claim 3] The conductive film according to claim 1, characterized in that the arithmetic mean roughness Ra of the surface of the tin layer is 0.25 μm or more. [Claim 4] The conductive film according to claim 1, characterized in that the thickness of the resin film is 100 to 200 μm. [Claim 5] A method for producing a conductive film according to any one of claims 1 to 4, comprising the steps of: forming a copper layer on a resin film; and forming a tin layer on the copper layer formed in the first step by electroplating. [Claim 6] The method for manufacturing a conductive film according to claim 5, characterized in that a tin plating solution that is not for gloss is used as the plating solution in the electro-tin plating method.

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