Patent Application
20210087701
The present disclosure relates to an aluminum plating film and a method for producing an aluminum plating film.
The present application claims priority from Japanese Patent Application No. 2017-097138 filed on May 16, 2017, and the entire contents of the Japanese patent application are incorporated herein by reference.
PTL 1 discloses that a porous plate formed of an insulating material is disposed between a substrate and an anode. An opening ratio of the porous plate described in PTL 1 is adjusted along a direction in which the substrate travels to make a current density distribution uniform in the direction in which the substrate travels. As a result, an aluminum plating film having a uniform thickness can be formed.
PTL 2 discloses that an aluminum plating film is formed on a substrate by using a continuous electrical treatment apparatus that includes a plating bath having a cell structure in which an upper tank and a lower tank are connected to each other with two passages therebetween, a sink roll disposed in the lower tank, and a power supply roll disposed outside the plating bath and above the upper tank. According to the continuous electrical treatment apparatus described in PTL 2, an aluminum plating film can be formed on a surface of a substrate a plurality of times by reciprocating the substrate between the power supply roll and the sink roll a plurality of times.
PTL 1: Japanese Unexamined Patent Application Publication No. 10-317195
PTL 2: Japanese Unexamined Patent Application Publication No. 11-117089
An aluminum plating film of the present disclosure is an aluminum plating film containing aluminum as a main component. The aluminum plating film has, between coating surfaces at both ends in a thickness direction, an intervening layer that contains a metal having a lower ionization tendency than aluminum or an intervening layer that contains an alloy of aluminum and a metal having a lower ionization tendency than aluminum.
A method for producing an aluminum plating film of the present disclosure is a method for producing the aluminum plating film of the present disclosure, the method including a first electrolytic treatment step of forming a pre-aluminum plating film by subjecting a substrate, at least a surface of the substrate being conductive, to an electrolytic treatment in a first electrolyte to electrodeposit aluminum on a surface of the substrate; a replacement step of, after the first electrolytic treatment step, forming a replacement plating film by immersing the pre-aluminum plating film in a replacement solution that contains the first electrolyte and a metal having a lower ionization tendency than aluminum to replace a surface of the pre-aluminum plating film with the metal having a lower ionization tendency than aluminum; and a second electrolytic treatment step of, after the replacement step, forming an aluminum plating film by subjecting the replacement plating film to an electrolytic treatment in a second electrolyte to electrodeposit aluminum on a surface of the replacement plating film. The first electrolyte and the second electrolyte are each a molten salt that contains at least aluminum chloride.
Molten salt baths are used for performing electroplating of aluminum. However, since the molten salt baths have low electrical conductivities, an aluminum plating film cannot be formed at high speed. In particular, in the case of an elongated substrate, such as a steel strip, an aluminum plating film having a sufficient thickness cannot be formed in a plating bath unless a transport speed is set to low. According to the method described in PTL 1, the thickness of an aluminum plating film can be made uniform. However, in the case where the thickness of the aluminum plating film is increased, there is no choice but to decrease the transport speed, resulting in a decrease in production efficiency.
When the substrate has a sheet-like shape such as a steel strip, a continuous electrical treatment apparatus as described in PTL 2 cannot be used. In the continuous electrical treatment apparatus described in PTL 2, a substrate can be reciprocated between the power supply roll and the sink roll a plurality of times because the substrate is a wire rod. In the case of a sheet-like substrate, the substrate cannot be reciprocated between the power supply roll and the sink roll a plurality of times. Furthermore, aluminum is not electrodeposited on the surface of a part of the substrate, the part being in contact with the sink roll in the plating bath, and thus the resulting aluminum plating film has an uneven thickness.
In view of this, the inventors of the present invention have examined that, in order to form an aluminum plating film having a large thickness with high efficiency, an aluminum plating film is formed in multiple stages using a plurality of plating devices configured to form an aluminum plating film while transporting a substrate in a horizontal direction, thereby increasing the transport speed. However, the following has been found. Since aluminum is a metal that is very susceptible to oxidation, an oxide film is formed when the substrate is pulled up from a molten salt bath. Accordingly, when aluminum plating is performed in multiple stages, such an oxide film is inserted, like an annual growth ring, between aluminum plating films formed in the respective plating devices. Even when molten salt aluminum plating is performed in a nitrogen atmosphere (N2: 99.99% or more) or in an argon atmosphere (Ar: 99.99% or more), an oxide film is formed on the surface of an aluminum plating film by a very small amount of oxygen contained in the atmosphere.
It has also been found that since the oxide film formed on the surface of the aluminum plating film is very dense and strong and a current cannot be uniformly allowed to flow, the adhesion between the aluminum plating films formed in multiple stages is poor, which may result in defects such as blistering.
Accordingly, an object of the present disclosure is to provide an aluminum plating film having a large thickness and capable of being produced within a short time at a low cost and a method for producing the aluminum plating film.
According to the present disclosure, it is possible to provide an aluminum plating film having a large thickness and capable of being produced within a short time at a low cost and a method for producing the aluminum plating film.
First, embodiments of the present disclosure will be listed and described.
(1) An aluminum plating film according to an embodiment of the present disclosure is an aluminum plating film containing aluminum as a main component. The aluminum plating film has, between coating surfaces at both ends in a thickness direction, an intervening layer that contains a metal having a lower ionization tendency than aluminum or an intervening layer that contains an alloy of aluminum and a metal having a lower ionization tendency than aluminum.
According to the embodiment of the invention according to (1) above, it is possible to provide an aluminum plating film having a large thickness and capable of being produced within a short time at a low cost.
(2) In the aluminum plating film according to (1) above, the aluminum plating film preferably has an elongated sheet-like shape. According to the embodiment of the invention according to (2) above, it is possible to provide an aluminum plating film that has a large thickness and that is capable of being produced on a surface of a substrate having an elongated sheet-like shape within a short time at a low cost.
(3) In the aluminum plating film according to (1) above, the aluminum plating film preferably forms a skeleton of a metal porous body, the skeleton having a three-dimensional network structure.
According to the embodiment of the invention according to (3) above, it is possible to provide an aluminum plating film that forms a skeleton of a metal porous body, the skeleton having a large thickness, and that is capable of being produced within a short time at a low cost.
(4) In the aluminum plating film according to (3) above, the metal porous body preferably has an elongated sheet-like shape.
According to the embodiment of the invention according to (4) above, it is possible to provide an aluminum plating film that forms a skeleton of a metal porous body having an elongated sheet-like shape as a whole, the skeleton having a large thickness, and that is capable of being produced within a short time at a low cost.
(5) In the aluminum plating film according to any one of (1) to (4) above, the aluminum plating film preferably has a plurality of the intervening layers in the thickness direction of the aluminum plating film.
According to the embodiment of the invention according to (5) above, it is possible to provide an aluminum plating film having a larger thickness and capable of being produced within a shorter time at a low cost.
(6) In the aluminum plating film according to any one of (1) to (5) above, the metal having a lower ionization tendency than aluminum is preferably at least one selected from the group consisting of iron (Fe), zinc (Zn), zirconium (Zr), manganese (Mn), nickel (Ni), and copper (Cu).
According to the embodiment of the invention according to (6) above, it is possible to provide an aluminum plating film having a sufficiently high conductivity.
(7) In the aluminum plating film according to any one of (1) to (6) above, the aluminum plating film preferably has a thickness of 10 μm or more and 1,000 μm or less.
According to the embodiment of the invention according to (7) above, it is possible to provide an aluminum plating film having a larger thickness and capable of being produced within a short time at a low cost.
(8) A method for producing an aluminum plating film according to an embodiment of the present disclosure is a method for producing the aluminum plating film according to (1) above, the method including a first electrolytic treatment step of forming a pre-aluminum plating film by subjecting a substrate, at least a surface of the substrate being conductive, to an electrolytic treatment in a first electrolyte to electrodeposit aluminum on a surface of the substrate; a replacement step of, after the first electrolytic treatment step, forming a replacement plating film by immersing the pre-aluminum plating film in a replacement solution that contains the first electrolyte and a metal having a lower ionization tendency than aluminum to replace a surface of the pre-aluminum plating film with the metal having a lower ionization tendency than aluminum; and a second electrolytic treatment step of, after the replacement step, forming an aluminum plating film by subjecting the replacement plating film to an electrolytic treatment in a second electrolyte to electrodeposit aluminum on a surface of the replacement plating film. The first electrolyte and the second electrolyte are each a molten salt that contains at least aluminum chloride.
According to the embodiment of the invention according to (8) above, it is possible to provide a method for producing an aluminum plating film, the method being capable of producing an aluminum plating film having a large thickness within a short time at a low cost.
(9) In the method for producing the aluminum plating film according to (8) above, the substrate is preferably a resin molded body having a skeleton with a three-dimensional network structure.
According to the embodiment of the invention according to (9) above, it is possible to provide an aluminum plating film that has a large thickness and that is capable of being produced on a surface of a substrate having a skeleton with a three-dimensional network structure within a short time at a low cost.
(10) The method for producing the aluminum plating film according to (8) or (9) above preferably includes a removal step of removing the substrate after the second electrolytic treatment step.
According to the embodiment of the invention according to (10) above, it is possible to provide a method for producing an aluminum plating film, the method being capable of producing the aluminum plating film according to (3) above.
Specific examples of an aluminum plating film and a method for producing the aluminum plating film according to embodiments of the present disclosure will be described below. The present disclosure is not limited to these examples, but is defined by the appended claims, and is intended to cover all modifications within the meaning and scope equivalent to those of the claims.
An aluminum plating film according to an embodiment of the present disclosure contains aluminum as a main component and has an intervening layer between coating surfaces at both ends in a thickness direction. The phrase “contains aluminum as a main component” as used herein means that the aluminum content in an aluminum plating film is 50% by mass or more.
The intervening layer 12 is a layer that contains a metal having a lower ionization tendency than aluminum or a layer that contains an alloy of aluminum and a metal having a lower ionization tendency than aluminum. The intervening layer 12 is formed on a surface substantially parallel to the coating surfaces 11 and 11′ of the aluminum plating film. When the aluminum plating film 10 is an aluminum plating film formed on a surface of a flat-plate substrate, the intervening layer 12 is substantially parallel to the coating surfaces 11 and 11′ over the substantial entirety of the aluminum plating film 10. When the aluminum plating film 10 is an aluminum plating film formed on a surface of a substrate having a complex three-dimensional shape, the intervening layer 12 is often partially substantially parallel to the coating surfaces 11 and 11′ of the aluminum plating film 10.
The thickness of the intervening layer 12 is preferably as small as possible, and the intervening layer 12 may be a one-atomic layer. The upper limit of the intervening layer 12 is not particularly limited but is, for example, about 500 nm or less. With a decrease in the thickness of the intervening layer 12, adhesion force between aluminum layers that are formed on both sides of the intervening layer 12 increases, and a decrease in the conductivity of the aluminum plating film can be prevented. The thickness of the intervening layer 12 is more preferably 1 nm or more and 400 nm or less, still more preferably 10 nm or more and 200 nm or less.
The intervening layer included in the aluminum plating film according to an embodiment of the present disclosure can be confirmed by, for example, observing a section of the aluminum plating film with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). In the case where the thickness of the intervening layer is about 50 nm or more, the intervening layer can be confirmed with a SEM. In the case where the thickness of the intervening layer is less than about 50 nm, the intervening layer can be confirmed by elemental mapping with a TEM.
The metal that constitutes the intervening layer and that has a lower ionization tendency than aluminum is preferably at least one selected from the group consisting of iron (Fe), zinc (Zn), zirconium (Zr), manganese (Mn), nickel (Ni), and copper (Cu). Since these metals have sufficiently high conductivity, the metals do not decrease the conductivity of the aluminum plating film even when they are present as an intervening layer in the aluminum plating film.
When the metal having a lower ionization tendency than aluminum is Fe, Zn, Cu, or, Ni, the aluminum plating film can be produced at a relatively low cost.
When the metal having a lower ionization tendency than aluminum is Zr, adhesion between aluminum layers formed on both sides of the intervening layer can be further enhanced.
When the metal having a lower ionization tendency than aluminum is Mn, the aluminum plating film can also be suitably used as a current collector of a nonaqueous electrolyte battery or the like because Mn has high corrosion resistance.
The metal having a lower ionization tendency than aluminum may form an alloy with aluminum in the intervening layer.
When the aluminum plating film is formed on a surface of a substrate, it is preferable that the thickness of the aluminum plating film be as large as possible from the viewpoint of protecting the substrate. The thickness of the aluminum plating film is preferably about 10 μm or more. When the thickness of the aluminum plating film is 10 μm or more, rupture strength of the aluminum plating film can be increased. The thickness of the aluminum plating film is preferably about 1,000 μm or less from the viewpoint of the production cost and the reduction in the weight. From these viewpoints, the thickness of the aluminum plating film is more preferably 15 μm or more and 700 μm or less, still more preferably 20 μm or more and 500 μm or less.
In the related art, it has taken a lot of time to produce an aluminum plating film having a thickness of 10 μm or more. Furthermore, it has been very difficult to form an aluminum plating film that has an elongated sheet-like shape and that has a thickness of 10 μm or more.
In contrast, according to the aluminum plating film according to an embodiment of the present disclosure, an aluminum plating film can be produced within a short time at a low cost even when the aluminum plating film has a thickness of 10 μm or more, and an aluminum plating film that has an elongated sheet-like shape can also be easily produced. Furthermore, the aluminum plating film according to an embodiment of the present disclosure has no gap in the film and is dense. Accordingly, even when the thickness of the aluminum plating film is increased, the conductivity does not decrease, and the aluminum plating film has a conductivity substantially equal to that of a rolled foil.
As illustrated in
Even when the metal porous body has an elongated sheet-like shape as a whole, an aluminum plating film can be produced within a short time at a low cost because the skeleton is formed by the aluminum plating film according to an embodiment of the present disclosure.
The porosity, the average pore diameter, and the thickness of the metal porous body are appropriately selected in accordance with the application of the metal porous body. For example, when the metal porous body is used as an electrode (current collector) of a battery, a metal porous body having a small average pore diameter and a small thickness is preferred. When the metal porous body is used for heat dissipation, a metal porous body having a large average pore diameter and a large thickness is preferred.
The porosity of the metal porous body refers to a ratio of the volume of an internal space (pore) of the metal porous body to the apparent volume.
The average pore diameter of the metal porous body refers to the reciprocal of the number of cells (cells/inch) formed by the skeleton of the metal porous body.
A method for producing an aluminum plating film according to an embodiment of the present disclosure is a method for producing the aluminum plating film according to an embodiment of the present disclosure and includes a first electrolytic treatment step, a replacement step, and a second electrolytic treatment step. In the case where an aluminum plating film having a larger thickness is produced, a set of a replacement step and an electrolytic treatment step may be further repeatedly performed after the second electrolytic treatment step. As a result, an aluminum plating film having a plurality of intervening layers in the aluminum plating film can be produced. Furthermore, in the method for producing an aluminum plating film according to an embodiment of the present disclosure, a removal step of removing a substrate may be performed as required.
The respective steps will now be described in detail.
The first electrolytic treatment step is a step of forming a pre-aluminum plating film by subjecting a substrate to an electrolytic treatment in an electrolyte to electrodeposit aluminum on a surface of the substrate.
The electrolytic treatment (molten salt electrolysis) can be performed by arranging a substrate and aluminum so as to face each other in an electrolyte, connecting the substrate to the cathode side of a rectifier, connecting the aluminum to the anode side, and applying a voltage between both electrodes. The first electrolytic treatment step is performed in an inert atmosphere such as an argon gas atmosphere or a nitrogen gas atmosphere.
The substrate is not particularly limited as long as the substrate needs to have an aluminum plating film thereon. For example, a copper plate, a steel strip, a copper wire, a steel wire, or a resin molded body that has been subjected to an electrical conduction treatment can be used as the substrate. In the related art, it has been very difficult to form an aluminum plating film having a large thickness on an elongated sheet-like substrate, and a lot of time and a high cost have been required. In contrast, according to the method for producing an aluminum plating film according to an embodiment of the present disclosure, an aluminum plating film having a large thickness can be produced within a short time at a low cost even when a substrate has an elongated sheet-like shape.
For example, a polyurethane, melamine resin, polypropylene, polyethylene, or the like having a surface that has been subjected to an electrical conduction treatment can be used as the resin molded body that has been subjected to an electrical conduction treatment. The resin molded body that has been subjected to an electrical conduction treatment may have any shape. However, by using a resin molded body having a skeleton with a three-dimensional network structure, a metal porous body that exhibits good properties for applications to a filter, a catalyst support, a battery electrode, and the like can be finally produced. As the resin molded body having a skeleton with a three-dimensional network structure, a resin foamed body is preferably used. The resin foamed body may be any porous resin foamed body. A known or commercially available resin foamed body can be used. For example, a urethane foam or a styrene foam can be used. Of these, in particular, a urethane foam is preferred from the viewpoint of high porosity.
The method for subjecting the surface of the skeleton of the resin molded body 66 to an electrical conduction treatment is not particularly limited as long as a conductive layer 67 can be formed on the surface of the skeleton of the resin molded body 66. Examples of the material that constitutes the conductive layer 67 include metals such as nickel, titanium, and stainless steel and carbon powders such as graphite and amorphous carbon, e.g., carbon black. Among these, in particular, carbon powders are preferred, and carbon black is more preferred. In the case where the conductive layer 67 is formed by using amorphous carbon or a carbon powder other than a metal, the conductive layer 67 is also removed together when the resin molded body is removed, as needed.
For example, in the case of using nickel, specific preferred examples of the electrical conduction treatment include a non-electrolytic plating treatment and a sputtering treatment. In the case of using a material such as a metal, e.g., titanium or stainless steel, carbon black, or graphite, an example of the preferred method is a treatment of applying, to the surface of the skeleton of the resin molded body 66, a mixture prepared by adding a binder to a fine powder of any of these materials.
In the non-electrolytic plating treatment using nickel, for example, the resin molded body 66 may be immersed in a known non-electrolytic nickel-plating bath such as an aqueous nickel sulfate solution that contains sodium hypophosphite as a reducing agent. Before immersion in the plating bath, the resin molded body 66 may be immersed in, for example, an activating liquid that contains a very small amount of palladium ions (cleaning liquid, produced by Japan Kanigen Co., Ltd.), as needed.
The sputtering treatment using nickel may be performed as follows, for example. After the resin molded body 66 is attached to a substrate holder, a direct-current voltage is applied between the holder and a target (nickel) while introducing an inert gas, thereby causing the resulting ionized inert gas to collide with the nickel. The resulting sputtered nickel particles are deposited on the surface of the skeleton of the resin molded body 66.
The conductive layer 67 is continuously formed so as to cover the surface of the skeleton of the resin molded body 66. The coating weight of the conductive layer 67 is preferably, but is not necessarily, 1.0 g/m2 or more and 30 g/m2 or less, more preferably 5.0 g/m2 or more and 20 g/m2 or less, still more preferably 7.0 g/m2 or more and 15 g/m2 or less.
The coating weight of a conductive layer refers to the mass of the conductive layer per apparent unit area of a resin molded body that includes the conductive layer formed on the surface of the skeleton thereof.
As the electrolyte, a molten salt (ionic liquid) capable of electrodepositing aluminum on the surface of the substrate may be used. Specifically, the electrolyte may be a molten salt that contains an aluminum halide and may optionally contain an additive.
Examples of the aluminum halide include aluminum chloride (AlCl3), aluminum bromide (AlBr3), and aluminum iodide (AlI3). Among these, aluminum chloride is most preferable.
For example, a chloride or fluoride molten salt can be preferably used as the molten salt. Examples of the chloride molten salt that can be used include KCl, NaCl, CaCl2, LiCl, RbCl, CsCl, SrCl2, BaCl2, MgCl2, and eutectic salts thereof. Examples of the fluoride molten salt that can be used include LiF, NaF, KF, RbF, CsF, MgF2, CaF2, SrF2, BaF2, and eutectic salts thereof.
Among the above molten salts, KCl, NaCl, or CaCl2 is preferably used from the viewpoint of a low cost and ease of availability.
From the viewpoint of lowering the melting point, the molten salt preferably contains at least one molten salt-forming compound selected from the group consisting of alkylimidazolium halides, alkylpyridinium halides, and urea compounds. A compound that forms a molten salt at about 110° C. or lower when mixed with an aluminum halide can be suitably used as the molten salt-forming compound.
Examples of the alkylimidazolium halides include imidazolium chlorides having alkyl groups (each having 1 to 5 carbon atoms) at the 1- and 3-positions, imidazolium chlorides having alkyl groups (each having 1 to 5 carbon atoms) at the 1-, 2-, and 3-positions, and imidazolium iodides having alkyl groups (each having 1 to 5 carbon atoms) at the 1- and 3-positions.
Specific examples thereof include 1-ethyl-3-methylimidazolium chloride (EMIC), 1-butyl-3-methylimidazolium chloride (BMIC), and 1-methyl-3-propylimidazolium chloride (MPIC). Among these, 1-ethyl-3-methylimidazolium chloride (EMIC) can be most preferably used.
Examples of the alkylpyridinium halides include 1-butylpyridinium chloride (BPC), 1-ethylpyridinium chloride (EPC), and 1-butyl-3-methylpyridinium chloride (BMPC). Among these, 1-butylpyridinium chloride is most preferred.
The urea compounds refer to urea and derivatives thereof, and, for example, compounds represented by formula (1) below can be preferably used.
In formula (1), R each represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a phenyl group, and R may be the same or different from each other.
Among the above compounds, urea and dimethylurea can be particularly preferably used as the urea compounds.
In the case where the above molten salt-forming compound is used, an electrolyte suitable for electrodepositing aluminum on the surface of the substrate is obtained by adjusting a mixing ratio of the aluminum halide to the molten salt-forming compound in a range of 1:1 to 3:1 in terms of molar ratio.
Examples of the additive include smoothing agents capable of smoothing a pre-aluminum plating film formed by electrodeposition on the surface of the substrate.
For example, at least one compound selected from the group consisting of 1,10-phenanthroline chloride monohydrate, 1,10-phenanthroline monohydrate, and 1,10-phenanthroline can be preferably used as the smoothing agent. When the electrolyte contains any of these smoothing agents, a smooth, mirror-like pre-aluminum plating film is formed.
The replacement step is a step of immersing the pre-aluminum plating film formed on the surface of the substrate in the first electrolytic treatment step in a replacement solution to replace a surface of the pre-aluminum plating film with a metal other than aluminum. The replacement solution is a solution that contains a metal having a lower ionization tendency than aluminum. Therefore, the surface of the pre-aluminum plating film can be replaced with the metal having a lower ionization tendency than aluminum by immersing the pre-aluminum plating film together with the substrate in the replacement solution.
When the pre-aluminum plating film is taken out from a first electrolyte after the first electrolytic treatment step, an oxide film is formed on the surface of the pre-aluminum plating film by oxygen that is present in a very small amount in the atmosphere. In the replacement step, aluminum on the surface of the pre-aluminum plating film is dissolved into the replacement solution together with the oxide film, and instead, the metal contained in the replacement solution is deposited on the surface of the pre-aluminum plating film to form a replacement plating film. Specifically, aluminum (including the oxide film) on the surface of the pre-aluminum plating film is replaced with the metal contained in the replacement solution, and consequently, a layer made of the metal contained in the replacement solution is formed on the surface of the pre-aluminum plating film. The layer made of the metal contained in the replacement solution functions as the intervening layer in the aluminum plating film according to an embodiment of the present disclosure.
The metal contained in the replacement solution does not form a dense oxide film compared with aluminum. Therefore, aluminum electrodeposited in the second electrolytic treatment step, which is performed subsequently to the replacement step, has high adhesion to a layer made of a metal contained in a second electrolyte.
The time during which the replacement step is performed is not particularly limited, and the replacement step is performed so that the oxide film on the surface of the pre-aluminum plating film is sufficiently removed. From the viewpoint of making the thickness of the intervening layer as small as possible, it is preferable not to perform the replacement step for a time longer than necessary. The replacement step is performed in a range of about one second or more and about one hour or less depending on the metal contained in the replacement solution. In the case where it takes a time to replace aluminum with the metal contained in the replacement solution, the time can be reduced by supplying a current. The temperature of the replacement solution during the replacement step is about 20° C. or higher and about 200° C. or lower.
In the replacement step, the surface of the pre-aluminum plating film is uniformly replaced with the metal contained in the replacement solution. Accordingly, the layer made of the metal contained in the replacement solution is formed substantially parallel to the surface of the substrate (coating surface of the pre-aluminum plating film) as long as the pre-aluminum plating film is uniformly formed on the surface of the substrate in the first electrolytic treatment step.
The replacement solution is a solution in which a metal having a lower ionization tendency than aluminum is added to the first electrolyte used in the first electrolytic treatment step. As the metal having a lower ionization tendency than aluminum, at least one metal selected from the group consisting of iron (Fe), zinc (Zn), zirconium (Zr), manganese (Mn), nickel (Ni), and copper (Cu) can be preferably used.
The replacement solution can be easily prepared by dissolving a chloride of a metal having a lower ionization tendency than aluminum in the first electrolyte used in the first electrolytic treatment step. For example, FeCl4, ZnCl2, ZrCl4, MnCl2, NiCl2, or CuCl2 can be used as the chloride of a metal having a lower ionization tendency than aluminum. The concentration of the chloride of a metal having a lower ionization tendency than aluminum in the replacement solution may be about 10 mmol/L or more and about 1 mol/L or less.
The second electrolytic treatment step is a step of forming an aluminum plating film by subjecting the replacement plating film after the replacement step to an electrolytic treatment in a second electrolyte to electrodeposit aluminum on a surface of the replacement plating film.
In the related art, in the formation of an aluminum plating film in multiple stages, adhesion between aluminum plating films formed in the respective stages cannot be increased due to the influence of an oxide film that is formed on the surface of an aluminum plating film when the aluminum plating film is pulled up from an electrolyte. In contrast, in the method for producing an aluminum plating film according to an embodiment of the present disclosure, a dense oxide film of aluminum is not formed on the surface of the replacement plating film used in the second electrolytic treatment step, and thus adhesion between aluminum plating films formed in the respective stages can be increased.
The second electrolytic treatment step can be performed under the same conditions as those in the first electrolytic treatment step. Specifically, the second electrolytic treatment step can be performed as in the first electrolytic treatment step except that, in the first electrolytic treatment step, the replacement plating film after the replacement step is used instead of using the substrate. It is not essential that the second electrolyte used in the second electrolytic treatment step have the same composition as the first electrolyte used in the first electrolytic treatment step. However, from the viewpoint of preventing another component from entering, electrolytes having the same composition are preferably used in the first electrolytic treatment step and the second electrolytic treatment step.
When the first electrolyte and the second electrolyte have the same composition, it is preferable to separately prepare the respective plating baths. However, from the viewpoint of space-saving, a plating bath that has been used in the first electrolytic treatment step can be used again in the second electrolytic treatment step. When aluminum is uniformly electrodeposited on the surface of the replacement plating film in the second electrolytic treatment step, the layer made of the metal contained in the replacement solution and the surface of the aluminum plating film (coating surface) are substantially parallel to each other.
An aluminum plating film according to an embodiment of the present disclosure can be formed on a surface of a substrate through the first electrolytic treatment step, the replacement step, and the second electrolytic treatment step. However, in the case where the substrate is unnecessary, the removal step of removing the substrate may be performed.
The method for removing the substrate is not particularly limited. For example, when the substrate is a flat-plate substrate, the substrate can be removed by detaching the aluminum plating film from the substrate. When the substrate is a resin molded body, the substrate can be removed by, for example, heat treatment. In the case where the resin molded body is removed by heat treatment, for example, the aluminum plating film is heated to about 400° C. or higher and about 680° C. or lower in an air atmosphere. In the case where heat treatment is performed, an aluminum plating film in which the metal in the intervening layer is alloyed with aluminum is produced.
While the present disclosure will be described in more detail below on the basis of Examples, these Examples are illustrative, and an aluminum plating film of the present disclosure and a method for producing the aluminum plating film are not limited thereto. The scope of the present disclosure is defined by the appended claims and covers all modifications within the meaning and scope equivalent to those of the claims.
A flat plate-like copper plate (50 mm×80 mm×1 mm) was prepared as a substrate.
An electrolyte was prepared as follows. Aluminum chloride (AlCl3) and 1-ethyl-3-methylimidazolium chloride (EMIC) were mixed in a mixing ratio of 2:1 in terms of molar ratio to prepare a molten salt, and 1,10-phenanthroline chloride monohydrate serving as a smoothing agent was added to the molten salt to have a concentration of 0.5 g/L.
Molten salt electrolysis was performed in the electrolyte prepared as described above in such a manner that the copper plate was used as a cathode and an aluminum plate having a purity of 99.99% was used as an anode. As a result, aluminum was electrodeposited on the surface of the copper plate to form a pre-aluminum plating film. The temperature of the electrolyte was 45° C. The current density was adjusted to 3.0 A/dm2.
A replacement solution was prepared by adding FeCl4 to the electrolyte prepared in the first electrolytic treatment step to have a concentration of 20 mmol/L.
The copper plate on which the pre-aluminum plating film was formed was immersed in the replacement solution prepared as described above. The immersion time was 10 seconds, and the temperature of the replacement solution was 40° C. As a result, a replacement plating film in which the surface of the pre-aluminum plating film was replaced with Fe was obtained.
A second electrolytic treatment step was performed as in the first electrolytic treatment step except that, in the first electrolytic treatment step, the copper plate on which the replacement plating film was formed was used instead of the copper plate.
As a result, an aluminum plating film No. 1 having an intervening layer made of Fe between coating surfaces at both ends in the thickness direction was produced. The aluminum plating film No. 1 had a thickness of about 15 μm.
An aluminum plating film No. 2 was produced as in Example 1 except that, in Example 1, a step of removing the copper plate serving as a substrate by immersing the resulting aluminum plating film No. 2 in nitric acid was added after the second electrolytic treatment step. The aluminum plating film No. 2 had a thickness of about 17 μm.
A resin molded body that had been subjected to an electrical conduction treatment was prepared as a substrate.
The resin molded body used was a polyurethane sheet (50 mm×80 mm) having a thickness of 1.0 mm and having a skeleton with a three-dimensional network structure. The resin molded body had a porosity of 96% and an average pore diameter of 450 μm.
The electrical conduction treatment was performed by immersing the polyurethane sheet in a carbon suspension and drying the resulting polyurethane sheet to form a conductive layer on the surface of the skeleton of the polyurethane sheet. The carbon suspension contained, as components, graphite and carbon black in an amount of 25%, a resin binder, a penetrant, and an antifoaming agent. The carbon black had a particle diameter of 0.5 μm.
An electrolyte that was the same as the electrolyte used in the first electrolytic treatment step in Example 1 was prepared as an electrolyte.
Molten salt electrolysis was performed in the electrolyte prepared as described above in such a manner that the polyurethane sheet that had been subjected to the electrical conduction treatment was used as a cathode and an aluminum plate having a purity of 99.99% was used as an anode. As a result, aluminum was electrodeposited on the surface of the polyurethane sheet that had been subjected to the electrical conduction treatment to form a pre-aluminum plating film. The temperature of the electrolyte was 45° C. The current density was adjusted to 6.0 A/dm2.
A replacement step was conducted under the same conditions as those in Example 1. As a result, a replacement plating film was formed on the surface of the skeleton of the polyurethane sheet.
A second electrolytic treatment step was performed as in the first electrolytic treatment step except that, in the first electrolytic treatment step, the polyurethane sheet on which the replacement plating film was formed was used instead of the polyurethane sheet that had been subjected to the electrical conduction treatment.
As a result, an aluminum plating film having an intervening layer made of Fe between coating surfaces at both ends in the thickness direction was formed.
The aluminum plating film formed as described above was heated to 600° C. in an air atmosphere to thereby remove the polyurethane sheet by combustion.
As a result, an aluminum plating film No. 3 that formed a skeleton of a metal porous body having a skeleton with a three-dimensional network structure was produced. The aluminum plating film No. 3 had a thickness of about 15 μm.
An aluminum plating film No. 4 was produced as in Example 3 except that, in Example 3, a replacement solution described below was used. The aluminum plating film No. 4 had a thickness of about 18 μm.
The replacement solution was prepared by adding ZnCl2 to the electrolyte used in the first electrolytic treatment step in Example 1 to have a concentration of 40 mmol/L.
An aluminum plating film No. 5 was produced as in Example 3 except that, in Example 3, a replacement solution described below was used. The aluminum plating film No. 5 had a thickness of about 16 μm.
The replacement solution was prepared by adding ZrCl4 to the electrolyte used in the first electrolytic treatment step in Example 1 to have a concentration of 100 mmol/L.
An aluminum plating film No. 6 was produced as in Example 2 except that, in Example 2, the second electrolytic treatment step was performed without performing the replacement step. The aluminum plating film No. 6 had a thickness of about 16 μm.
An aluminum plating film No. 7 was produced as in Example 3 except that, in Example 3, the second electrolytic treatment step was performed without performing the replacement step. The aluminum plating film No. 7 had a thickness of about 18 μm.
The aluminum plating film Nos. 1 to 7 produced as described above were evaluated as described below. Table 1 shows the evaluation results.
The resistivity of each of the aluminum plating film Nos. 2 to 7 was measured with a resistivity meter so that the distance between measuring terminals was 60 mm.
Table 1 shows the results.
As shown in Table 1, comparing the aluminum plating film No. 2 of Example 2 and the aluminum plating film No. 6 of Comparative Example 1, which were produced by the method for forming an aluminum plating film on a surface of a copper plate, the aluminum plating film No. 2 had a lower resistivity. An aluminum film produced by rolling and having a thickness of 18 μm had a resistivity of 0.031 μΩ·m. This showed that the aluminum plating film No. 2 of Example 2 had a low resistivity that is substantially comparable to the resistivity of the film produced by rolling.
Comparing the aluminum plating film Nos. 3 to 5 of Examples 3 to 5 and the aluminum plating film No. 7 of Comparative Example 2, which were produced by the method for forming an aluminum plating film on a surface of the skeleton of a polyurethane sheet, the aluminum plating film Nos. 3 to 5 each had a lower resistivity.
A section of each of the aluminum plating film Nos. 3, 4, and 7 was observed with a scanning electron microscope (SEM).
As shown in
In contrast, as illustrated in
10 aluminum plating film
11 coating surface
11′ coating surface
12 intervening layer
20 aluminum plating film
21 coating surface
21′ coating surface
22 intervening layer
30 aluminum plating film
31 coating surface
31′ coating surface
32 intervening layer
33 skeleton
34 inside of skeleton
35 pore
65 pore
66 resin molded body
67 conductive layer
71 coating surface
71′ coating surface
72 intervening layer
81 coating surface
81′ coating surface
82 intervening layer
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-097138 | May 2017 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2018/001568 | 1/19/2018 | WO | 00 |
