JP2020041170A - Production method of aluminum-plated film - Google Patents

Abstract

To provide a production method of an aluminum-plated film, in which an aluminum-plated film of a stable appearance is obtained even at an increased speed of film formation.SOLUTION: A method is for producing an aluminum-plated film 1 by an electroplating treatment. In the electroplating treatment, a cathode 3 and an anode 4 are immersed in a plating bath 2 including an ionic liquid 21. The ionic liquid 21 is composed of a molten mixture of an aluminum halide and an imidazolium halide. In the electroplating treatment, the ionic liquid 21 around the anode 4 and the anode 4 are relatively moved.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing an aluminum plating film by an electroplating process.

  Aluminum has been used in various applications, for example, because it has excellent corrosion resistance and design properties, and is easy to form an oxide film on the surface, and also has excellent slidability and wear resistance. Aluminum is expected to be a plating material that replaces zinc because it has better corrosion resistance than zinc. The aluminum plating film is manufactured by, for example, an electroplating process.

  However, aluminum has a strong affinity for water and oxygen, and also has a deposition potential lower than the hydrogen generation potential, so that it is difficult to deposit aluminum from an aqueous solution. 2. Description of the Related Art In recent years, research on electrodeposition using an electroaluminum plating solution that does not use water and is obtained by mixing and melting an aluminum halide and an imidazolium halide has been actively performed.

  For example, in Patent Literature 1, metal aluminum is immersed in an electroaluminum plating solution obtained by mixing and melting an aluminum halide and an imidazolium halide, and a plating solution is prepared by bubbling an inert dry oxygen-free gas. A method of performing electric aluminum plating using this plating solution is disclosed.

Japanese Patent No. 3221897

  However, when an ionic liquid obtained by mixing and melting an aluminum halide and an imidazolium halide is used as an electroaluminum plating solution, the electrolytic voltage may increase with time. In particular, when the current density of the cathode is increased to improve the film formation rate, the increase in the electrolytic voltage becomes remarkable.

  The increase in electrolysis voltage promotes decomposition of organic imidazolium halide. Decomposition of organic substances may cause appearance defects such as burns and haze on the aluminum plating film, and may adversely affect formation of a stable plating appearance. Further, a sharp rise or a large rise in the electrolytic voltage hinders the progress of the aluminum plating process.

  As described above, in the electric aluminum plating using the ionic liquid, it is difficult to improve the productivity by increasing the film forming rate. Therefore, improvement for practical use is desired.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a method of manufacturing an aluminum plating film capable of obtaining an aluminum plating film having a stable appearance even when a film forming speed is increased.

One aspect of the present invention is a cathode (3) comprising a substrate (31) and a metal (3) in a plating bath (2) containing an ionic liquid (21) obtained by mixing and melting an aluminum halide and an imidazolium halide. In a method of immersing an anode (4) made of aluminum (41) and forming an aluminum plating film (1) on the surface of the substrate by electroplating,
In the above electroplating process, there is provided a method of manufacturing an aluminum plating film, wherein the ionic liquid existing around the anode and the anode are relatively moved.

  In the above manufacturing method, an aluminum plating film is formed on the surface of the base material in a plating bath containing an ionic liquid by an electroplating process. In the electroplating process, the ionic liquid existing around the anode and the anode are relatively moved. This transfer makes it difficult for the substance causing the increase in the electrolytic voltage to deposit on the anode. As a result, even if the deposition rate is increased, the electrolytic voltage is less likely to increase, and an aluminum plating film having a stable appearance can be manufactured.

As described above, according to the above aspect, it is possible to provide a method of manufacturing an aluminum plating film capable of obtaining an aluminum plating film having a stable appearance even when the film formation rate is increased.
Note that reference numerals in parentheses described in the claims and means for solving the problems indicate the correspondence with specific means described in the embodiments described below, and limit the technical scope of the present invention. Not something.

1A is a perspective view schematically showing an electrolytic plating apparatus for oscillating an anode, and FIG. 2B is an enlarged cross-sectional view of a cathode surface in the first embodiment. FIG. 1 is a perspective view schematically showing an electrolytic plating apparatus for stirring a bath in a first embodiment. FIG. 2 is a cross-sectional view schematically illustrating an electrolytic plating apparatus in Experimental Example 1. FIG. 9 is a diagram showing the relationship between the time of the electroplating process and the voltage when the cathode current density is changed in Experimental Example 1. FIG. 4 is an X-ray diffraction spectrum of the anode in which white deposits are observed on the surface in Experimental Example 1. The X-ray-diffraction spectrum figure of the anode in Experimental example 1 in which the white deposit is not observed on the surface. In Experimental Example 1, activity of the simulation view of AlCl ₃ -EMIC bath. (A) Schematic diagram showing the state of ions in the ionic liquid during the electrolytic reaction, (b) Schematic diagram showing the reaction at the cathode interface during the electrolytic reaction, and (c) anode interface during the electrolytic reaction in Experimental Example 1. FIG. FIG. 4 is a schematic diagram showing a mechanism of producing AlCl ₃ at the anode in Experimental Example 1. Explanatory diagram showing the relationship between (a) the voltage when there is no voltage rise, the amount of AlCl ₃ produced, and the dissolution / desorption speed in Experimental Example 1, and (b) the voltage and the amount of AlCl ₃ produced when there is a voltage rise. FIG. 4 is an explanatory diagram showing the relationship between the dissolution and desorption rates. 9 is a graph showing a change in voltage over time during electroplating at each flow rate in Experimental Example 2. FIG. 9 is a schematic diagram showing a state in which AlCl ₃ is desorbed from the anode surface in Experimental Example 2.

[Embodiment 1]
An embodiment according to a method for manufacturing an aluminum plating film will be described with reference to FIGS. 1 (a), 1 (b), and 2. FIG. As illustrated in FIGS. 1A and 1B, an aluminum plating film 1 is formed on a substrate 31 by an electrolytic aluminum plating process using an electrolytic plating apparatus 100. The electrolytic plating apparatus 100 includes a plating bath 2, an anode 4, and a cathode 3.

<Plating bath>
The plating bath 2 contains an ionic liquid 21. The ionic liquid 21 is obtained by mixing and melting an aluminum halide and an imidazolium halide. The ionic liquid 21 is used as a plating solution for an electroplating process.

(Ionic liquid)
The ionic liquid 21 is sometimes called a normal-temperature molten salt, a low-temperature molten salt, or the like. The ionic liquid 21 can be obtained by mixing and melting an aluminum halide and an imidazolium halide in a molar ratio of, for example, 1: 1 to 3: 1 (however, aluminum halide: imidazolium halide). In the plating bath 2, the temperature of the ionic liquid 21 is adjusted to, for example, a range of 20 to 100 ° C.

(Aluminum halide)
As the aluminum halide, aluminum chloride, aluminum bromide (AlBr ₃ ), aluminum iodide (AlI ₃ ), or the like can be used. Among these, one or more aluminum halides can be used. Preferably, the aluminum halide is aluminum chloride (AlCl ₃ ). In this case, the effect of suppressing the increase in the electrolytic voltage by moving the ionic liquid 21 and the anode 4 relatively increases.

(Imidazolium halide)
As the imidazolium halide, for example, a monoalkyl imidazolium halide or a dialkyl imidazolium halide is used. As the imidazolium halide, one or more substances can be used.

(1) Monoalkyl imidazolium halides Monoalkyl imidazolium halides include 1-methyl imidazolinium chloride, 1-ethyl imidazolinium chloride, 1-propyl imidazolinium chloride, 1-octyl imidazolinium chloride, and the like. Can be used. Chloride, that is, chloride is exemplified as the halide, but other halides such as bromide and iodide may be used.

(2) Dialkylimidazolium halide As the dialkylimidazolium halide, 1-ethyl-3-methylimidazolinium chloride, 1,3-dimethylimidazolinium chloride, 1,3-diethylimidazolinium chloride, 1- Methyl-3-propyl imidazolinium chloride, 1-butyl-3-butyl imidazolinium chloride, and the like can be used. Chloride, that is, chloride is exemplified as the halide, but other halides such as bromide and iodide may be used.

As the imidazolium halide, 1-ethyl-3-methylimidazolinium chloride is preferable. In this case, the melting point of the ionic liquid 21 decreases, and the vapor pressure decreases. Therefore, handling of the ionic liquid 21 becomes easy. Hereinafter, 1-ethyl-3-methylimidazolinium chloride will be referred to as “EMIC” as appropriate. For example, the ionic liquid 21 of AlCl ₃ and EMIC (that is, AlCl ₃ -EMIC) has a melting point of −80 ° C. and almost no vapor pressure, and thus has excellent safety. The structural formula of EMIC is shown in the following formula (1).

<Cathode>
For the cathode 3, a base material 31 to be plated is used. In FIG. 1, a plate-shaped base material 31 is illustrated, but the shape of the base material 31 is not limited to a plate shape. Can be changed. The type of the substrate 31 is not particularly limited, but the substrate 31 is preferably made of a conductive material. The substrate 31 is made of, for example, a conductive metal, a conductive ceramic, a conductive carbon, a resin having an electroless plating film on the surface, or the like. Examples of the metal include copper, steel, a magnesium alloy, and a titanium alloy. The above-mentioned steel is a concept including steel and stainless steel. Examples of the ceramic include silicon carbide and conductive zirconia. By appropriately selecting the substrate 31, the substrate 31 on which the aluminum plating film 1 is formed can be used for various products.

<Anode>
Metal aluminum 41 is used for the anode 4. FIG. 1 illustrates a plate-shaped anode 4, but the shape of the anode 4 is not limited to a plate.

<Electroplating treatment>
The anode 4 and the cathode 3 are each connected to a power supply, and a voltage is applied between both electrodes. The electroplating process can be performed at a cathode current density of 0.1 to 20 A / dm ² . From the viewpoint of increasing the deposition rate, cathode current density is preferably at 1A / dm ² or more, and more preferably 4A / dm ² or more. On the other hand, the cathode current density is preferably 10 A / dm ² or less, more preferably 8 A / dm ² or less, from the viewpoint of suppressing the occurrence of burn or the like due to current concentration.

  It is preferable to adjust the temperature of the plating bath 2 during the electroplating process to a range of 20 to 100 ° C. Thereby, the increase in the electrolytic voltage can be further suppressed. From the viewpoint of further enhancing this effect, it is more preferable to adjust the temperature of the plating bath 2 to a range of 50 to 100 ° C.

  The electroplating process is performed by, for example, a rack plating method. As illustrated in FIG. 1, a base material 31 serving as the cathode 3 and a metal aluminum 41 serving as the anode 4 are immersed in the plating bath 2 while being suspended on a rack.

  In the electroplating process, the ionic liquid 21 existing around the anode 4 and the anode 4 are relatively moved. That is, the ionic liquid 21 and the anode 4 are relatively moved around the anode 4. As a result, a relative flow is given to the ionic liquid 21 existing around the anode 4 and a flow velocity is generated, so that liquid friction occurs on the surface of the anode 4. Due to the liquid friction, an insulator generated in the electroplating process and attached to the anode is easily detached from the anode 4 or easily dissolved in the ionic liquid 21 from the anode 4. As a result, the deposition of the insulator on the anode 4 is suppressed, so that an increase in the electrolytic voltage can be suppressed. The range of “around the anode” is not particularly limited as long as liquid friction can be caused on the anode surface, for example. The “ionic liquid existing around the anode” is present at least at the interface with the anode 4. As long as the ionic liquid 21 is contained, the entire ionic liquid 21 in the plating bath 2 may be used.

  In order to move the ionic liquid 21 and the anode 4 relatively, for example, the relative position of the anode 4 with respect to the ionic liquid 21 is changed by moving the anode 4 or the ionic liquid 21 is moved in the plating bath 2. By moving, the relative position of the ionic liquid 21 with respect to the anode 4 is changed with time. The anode 4 and the ionic liquid 21 may be moved respectively.

  For the relative movement between the anode 4 and the ionic liquid 21, for example, a moving device is used. Illustration of the moving device is omitted. Examples of the moving device of the anode 4 include a swing device and a vibration device. These devices are directly or indirectly connected to the anode 4 and impart movements such as rocking and vibration to the anode 4.

  For the rocking device, for example, a commercially available cathode rocker used for rocking the cathode (that is, the cathode 3) can be used. That is, a cathode rocker that swings the cathode 3 can be used for swinging the anode 4. In this case, since the anode 4 (that is, the anode) is swung, the cathode locker can be called an anode locker. Further, other rocking devices other than the cathode rocker may be used. The cathode rocker generally has a conversion mechanism that converts a rotary motion into a rocking motion, such as a motor and a crank, inside the cathode locker. Such an oscillating device is configured to adjust the speed in the oscillating direction by, for example, a rotational speed. Therefore, the flow rate of the ionic liquid existing around the anode 4 can be controlled by adjusting the rotation speed of the rocking device.

  When a cathode locker is used, the rotation speed can be appropriately set from a range of 500 rpm or less. Accordingly, there is an advantage that the deposition of the insulator is sufficiently suppressed, and the insulator is easily dissolved into the plating solution and ionized again. In addition, by setting the rotation speed to 160 rpm or more, the flow rate of the ionic liquid 21 existing around the anode 4 can be set to 16 cm / sec or more.

  The swing direction is not particularly limited, but is preferably a direction parallel to the plate surface when the anode 4 is plate-shaped. In this case, the variation in the thickness of aluminum deposited on the cathode 3 can be further reduced. The arrow in FIG. 1 is an example of the swing direction.

  As the vibration device, for example, an ultrasonic vibration device, a belt-type vibration device, and a pendulum-type vibration device are used. From the viewpoint that dissolution and desorption of the insulator are further promoted, an ultrasonic vibration device is preferable.

  Examples of the moving device of the ionic liquid 21 include a stirring device and a vibration device. As illustrated in FIG. 2, the ionic liquid 21 in the plating bath 2 can be stirred by the stirring device. Also in this case, relative movement can be given between the anode 4 and the ionic liquid 21 around the anode 4. In FIG. 2, the components other than the plating bath 2 such as the anode 4, the cathode 3, and the power supply are omitted, but the configuration other than the plating bath 2 is the same as, for example, FIG. 1A.

  The ionic liquid 21 in the plating bath 2 can be vibrated by the vibration device for the ionic liquid 21. Due to the vibration of the ionic liquid 21, the ionic liquid 21 and the anode 4 can be relatively moved. As a vibrating device for the ionic liquid 21, a device that applies the same vibration as the above-described vibrating device for the anode 4 is exemplified. The vibration of the ionic liquid 21 and the stirring can be combined.

  In the electroplating process, it is preferable that at least the anode 4 be rocked or vibrated. Thereby, the relative motion is sufficiently provided between the ionic liquid 21 existing around the anode 4 and the anode 4, and the liquid friction increases. Thus, dissolution and desorption of the insulator are promoted, so that deposition of the insulator is sufficiently suppressed. As a result, a sufficient increase in the electrolytic voltage is suppressed, and the film forming speed can be further increased. Further, even if the film forming speed is increased, appearance defects such as burns and haze are less likely to occur, and an aluminum film having a good appearance can be more stably manufactured. Further, in this case, the uniformity of the plating can be further increased, and the variation in the thickness of the aluminum film can be further reduced.

  Preferably, the swing or vibration of the anode 4 and the stirring of the plating bath 2 are combined. In this case, the deposition of the insulator is more sufficiently suppressed, and the increase in the electrolytic voltage is further suppressed. This makes it possible to further increase the film formation rate, and even if the film formation rate is increased, it is possible to more stably produce an aluminum film having a good appearance.

  As described above, in the electric aluminum plating using the ionic liquid 21, the anode 4 and the ionic liquid 21 are relatively moved so that the aluminum plating film 1 having a stable appearance can be obtained even when the film forming speed is increased. Obtainable.

[Experimental example 1]
In the present example, the cause of the increase in the electrolytic voltage in the electric aluminum plating using the ionic liquid 21 will be examined. That is, the reason why the provision of the relative movement between the ionic liquid 21 existing around the anode 4 and the anode 4 as in the first embodiment is effective will be examined. Note that, among the reference numerals used in Experimental Example 1 and thereafter, the same reference numerals as those used in the above-described embodiments represent the same components and the like as those in the above-described embodiments unless otherwise specified.

<Experimental system>
An electroplating apparatus 100 having the same configuration as that of the first embodiment was used as illustrated in FIG. 3 except that a moving device was not used. First, as the ionic liquid 21, AlCl ₃ and EMIC were mixed at a molar ratio of AlCl ₃ : EMIC = 2: 1 and melted to prepare an ionic liquid AlCl ₃ -EMIC. A 50 × 30 mm Cu plate was prepared as the base material 31, and a 200 × 100 mm Al plate was prepared as the metal aluminum 41.

  Using a Cu plate as a cathode 3 and an Al plate as an anode 4, an electric aluminum plating treatment was performed in a plating bath 2 containing an ionic liquid 21. In this example, the electroaluminum plating was performed without imparting a relative movement between the anode 4 and the ionic liquid 21 existing around the anode 4. The electroaluminum plating was performed in a glove box filled with nitrogen gas to avoid the influence of moisture. Then, an Al plating film was formed on the surface of the substrate 31 made of a Cu plate.

  In plating, the film formation speed can be controlled by adjusting the amount of electricity per unit time. Thus, in this example, an experiment was performed in which the Al plating film was formed by changing the cathode current density. FIG. 4 shows the results.

As is known from FIG. 4, when the cathode current density is increased, the voltage rises with time. This voltage rise is the electrolytic voltage rise. At a cathode current density of 1 A / dm ² , almost no increase in electrolysis voltage occurred. The large increase in the electrolysis voltage occurs in a shorter time and more rapidly as the cathode current density increases, as shown by the arrows in the graph of FIG. No significant difference was observed in the appearance of the aluminum plating film 1 formed on the cathode 3 due to the voltage rise.

Next, the factors of the voltage rise were examined as follows. In the electrolytic plating apparatus 100 illustrated in FIG. 3, since the current is constant current electrolysis, the Ohm's law of the formula (I) holds. That is, the voltage is proportional to the sum of all the resistors present in the experimental system.
V = R × I (I)
[V: voltage, R: electric resistance, I: current]

  The electrical resistance of the experimental system includes wiring resistance, output resistance, cathode resistance, etc., but since these are constant, focusing on the solution resistance, cathode interface resistance, and anode interface resistance as follows: Considered. First, the solution resistance is considered to be constant. This is because conduction between the electrodes is due to ion conduction by ions present in the ionic liquid 21. In addition to sufficient ions existing in the plating bath 2, there is no change in the current value during plating. That's why. It is considered that the cathode interface resistance is also constant. This is because the deposition efficiency of Al plating calculated from the weight difference between the cathode 3 before and after plating is about 100%, and there is no side reaction at the cathode 3.

  Next, regarding the anode interface resistance, the dissolving efficiency of Al in the plating bath 2 calculated from the weight difference of the anode 4 before and after plating was about 100%. However, immediately after the electrolysis, the anode 4 was pulled up from the plating bath 2 and the surface of the anode 4 was visually observed. There is a possibility that the white deposit 400 acts as a resistor to increase the voltage. Therefore, the white deposit 400 was analyzed by X-ray diffraction (that is, XRD).

<Identification of white deposits by XRD analysis>
The anode 4 immediately after electroplating at a cathode current density of 1 A / dm ² and the anode 4 immediately after electroplating at a cathode current density of 4 A / dm ² were used as the target samples for the XRD analysis. The target sample of the anode 4 treated at the cathode current density of 4 A / dm ² is hereinafter referred to as “sample 1”, and the target sample of the anode 4 treated at the cathode current density of 1 A / dm ² is referred to as “sample 1”. Hereinafter, it is referred to as “sample 2”. Sample 1 is the anode 4 in which a voltage rise occurred and white deposits 400 were confirmed. Sample 2 is the anode 4 in which no voltage rise occurred and no white deposit 400 was observed. The XRD analysis result of Sample 1 is shown in FIG. 5, and the XRD analysis result of Sample 2 is shown in FIG. The XRD analysis was performed under the condition of non-atmospheric exposure from the viewpoint of preventing a change in composition. As an XRD analyzer, SmartLab (registered trademark) manufactured by Rigaku Corporation was used. The target sample was irradiated with X-rays having a wavelength of 1.54 ° generated from a Cu tube, and an X-ray diffraction spectrum was obtained by the 2θ / θ method.

As shown in FIG. 5, in Sample 1, in addition to the peak derived from Al, a peak derived from AlCl ₃ was confirmed. On the other hand, as shown in FIG. 6, in Sample 2, a peak derived from Al is confirmed, but a peak derived from AlCl ₃ is not confirmed. That is, from the result of the XRD analysis, it was identified that the white deposit 400 was AlCl ₃ . Therefore, it can be seen that AlCl ₃ , which is an insulator, is deposited on the anode 4 as a white deposit 400, which becomes the insulator 400, causing an increase in voltage.

<Estimation of AlCl ₃ formation mechanism>
In order to estimate the mechanism of the generation of AlCl ₃ and the deposition of the insulator 400, the reactions inside the solution, at the cathode interface, and at the anode interface during electrolysis are examined. As shown in FIG. 7, from the activity simulation of each ion species in the AlCl ₃ -EMIC bath, the composition AlCl ₃ : EMIC of the plating bath 2 at this time: AlCl ₃ : EMIC = 2: 1 (however, the molar ratio) indicates that Al ₂ Cl ₇ ^- is a dominant ion species, and Al ₂ Cl ₇ ^- becomes an active species to precipitate Al. The horizontal axis in FIG. 7 shows the mole fraction of AlCl ₃ , and the vertical axis shows the logarithm of the number of each ion species.

As illustrated in FIG. 8A, various ions are present inside the ionic liquid 21 of the plating bath 2, and conduction between the cathode 3 and the anode 4 is maintained by ion conduction. Further, as illustrated in FIG. 8B, at the interface between the cathode 3 and the ionic liquid 21, Al ₂ Cl ₇ ⁻ is reduced and Al is deposited. By this deposition, the aluminum plating film 1 is formed on the cathode 3. On the other hand, as illustrated in FIG. 8C, at the interface of the anode 4, Al ³⁺ having a high charge density is generated by dissolving Al from the interface. Al ³⁺ is presumed to undergo an ion reaction with surrounding anions such as AlCl ₄ ⁻ to generate uncharged AlCl ₃ . AlCl ₃ is an insulator and is considered to be a resistor when generated and deposited at the anode interface. As described above, it is considered that the deposition of an insulator made of an aluminum halide such as aluminum chloride (AlCl ₃ ) on the anode 4 causes an increase in the electrolytic voltage.

<Relationship between AlCl ₃ generation and voltage rise>
It is considered that the electrolytic reaction near the anode 4 proceeds by the reaction steps shown in FIG. First, as shown in the first step S1 of FIG. 9, Al ³⁺ having a high charge density is eluted from the Al plate of the anode 4. Next, as shown in the second step S2, Al ³⁺ ion-reacts with Al ₂ Cl ₇ ⁻ in the ionic liquid 21 to generate and deposit AlCl _{3 on} the surface of the anode 4. Next, as shown in the third step S3, in the vicinity of the anode ⁴ , a dissolution reaction in which AlCl _{3 on} the anode surface becomes Al ₂ Cl ₇ ⁻ by a reaction with AlCl ^4- in the ionic liquid 21; Two reactions occur with an elimination reaction which is eliminated into 21.

Next, for each of the reactions in the first to third steps, the reaction rates for the formation reaction of AlCl ₃ and the dissolution / desorption reaction are summarized. In the following description, the dissolution rate V ₀ which Al ³⁺ in the first step, Al ³⁺ and Al ₂ Cl ₇ in the second step ^- the reaction speed is V _1, dissolved and desorption kinetics of AlCl ₃ It is referred to as V _2.

The reaction speed V ₁ is considered to be very fast because it is the speed of the ion reaction. On the other hand, the dissolution rate V ₀ is assumed since it can be controlled by the amount of current, a V ₀ and generates velocity V ₀ which AlCl _3. FIG. 10A shows the relationship between the amount of generated AlCl ₃ over time and the voltage when no voltage rise occurs. FIG. 10B shows the relationship between the generation amount of AlCl ₃ and the voltage over time when the voltage rises.

As shown in FIG. 10 (a), the dissolution of AlCl _3, when the desorption speed V ₂ is greater than the generation speed V ₀ which AlCl _3, that is, when the V ₀ <V ₂ is no voltage rise. On the other hand, as shown in FIG. 10 (b), the production rate V ₀ which AlCl ₃ is dissolved in AlCl _3, when above the desorption rate V _2, i.e., when V _0> V _2, the surface of the anode 4 AlCl ₃ is deposited. Then, when the deposition amount of AlCl ₃ exceeds a certain threshold, the voltage rise is started. That is, the production rate V _0, dissolution and desorption rate V ₂ of the AlCl ₃ of AlCl ₃ is presumed to affect the voltage.

Thus, in the electric aluminum plating using the ionic liquid 21 composed of AlCl ₃ -EMIC, a white insulator is formed on the surface of the anode 4 by depositing and depositing AlCl _{3 on} the anode 4. This insulator causes an increase in the electrolytic voltage. Similarly to the AlCl ₃ -EMIC, for example, in an ionic liquid 21 of an aluminum halide and an imidazolium halide, it is considered that aluminum halide is deposited and deposited on the anode 4 and causes an increase in the electrolytic voltage.

[Experimental example 2]
In this example, a voltage rise suppression technique is examined by a model experiment. From the results of Experimental Example 1, as a voltage rise suppression scheme in the electrolyte, to reduce the production rate V ₀ which AlCl _3, or a method can be considered to increase the dissolution and desorption rate V ₂ of the AlCl _3. As a method of reducing V _{0, there} is a method of increasing the anode area to decrease the anode current density. However, in mass production equipment, there are restrictions on the product shape and the size of the bathtub.

Therefore, in this example, by applying a flow to the anode surface, the desorption speed V ₂ of the deposited AlCl ₃ is increased, and it is verified whether or not the voltage increase can be suppressed in a model experiment. The model experiment of the electroaluminum plating process of this example was performed by the same electrolytic plating apparatus 100 as that of FIG. 1A of the first embodiment.

  In this example, in order to quantify the flow velocity, the plate-shaped anode 4 is swung in a plane direction (that is, in a direction parallel to the plate surface). Thereby, the anode 4 and the ionic liquid 21 are relatively moved to give a flow to the anode surface. The swing speed was set to 0 to 16 cm / sec, and this swing speed was assumed to be the flow speed on the anode surface.

FIG. 11 shows the relationship between the electrolysis time and the voltage for each flow rate. At a flow rate of 0 to 12 cm / sec, a voltage rise occurred with the passage of the electrolysis time, and white deposits 400 (that is, insulators 400) were confirmed on the surface of the anode 4 after electrolysis. However, the times t ₁ and t ₂ until the electrolytic voltage rises when the anode swing is performed are longer than the times t ₀ until the electrolytic voltage rises when the anode swing is not performed. This means that the rise in the electrolytic voltage is suppressed by the swing of the anode. On the other hand, when the flow rate was increased to 16 cm / sec, the electrolysis voltage did not increase, and AlCl ₃ on the anode surface was not confirmed.

  From the above results, it can be said that, for example, by moving the ionic liquid 21 around the anode 4 and the anode 4 relatively, as in the case of the swinging of the anode, an increase in the electrolytic voltage can be suppressed.

As described above, when the flow rate applied to the anode surface is increased, the time required to start increasing the voltage increases. This is because AlCl ₃ deposited on the surface of the anode 4 during electrolysis is desorbed by the flow of the ionic liquid 21 on the surface of the anode caused by swinging, and the time required to reach a certain thickness d leading to a voltage increase becomes longer. (See FIG. 12). This thickness is hereinafter referred to as “AlCl ₃ layer thickness”.

Therefore, if the thickness of the AlCl ₃ layer at which the voltage rise starts can be derived, the flow velocity on the anode surface required to suppress the voltage rise can be obtained. When the flow rates are 0, 8, and 12 cm / sec, it is considered that the thickness of the AlCl ₃ layer exceeds the limit thickness at which the voltage rise starts at the electrolysis times t ₁ , t ₂ , and t ₃ , respectively, and the thickness dt of the AlCl ₃ layer at that time is considered. _It is assumed that ₁ , dt ₂ and dt ₃ are equal. Note that, during the film formation time in this experiment, at a flow rate of 16 cm / sec, no voltage rise occurs, so it is assumed that the thickness does not exceed the AlCl ₃ thickness d. When the Navier-Stokes equation is developed based on such an assumption, the thickness d of the AlCl ₃ layer is expressed by the equation (a) using the flow velocity U on the anode surface. In equation (a), D is the diffusion coefficient, A is a constant, L is the length of the flow, U is the flow velocity, and ν is the viscosity (see FIG. 12). FIG. 12 shows how AlCl ₃ deposited on the anode 4 is desorbed into the ionic liquid 21.

Further, the thickness d of the AlCl ₃ layer is calculated by multiplying the difference between the deposition rate and the dissolution / desorption rate of AlCl ₃ by the electrolysis time, and can be expressed by equation (b). In the formula (b), V ₀ is a deposition rate, t is an electrolysis time, and V ₂ is a dissolution / desorption rate.

Further, by using the equations (a) and (b), the time required for the voltage rise can be expressed by the equation (c) including the anode current density and the flow velocity. It is possible to derive a relational expression using the time t _{voltage rise} and the flow velocity U until such time. I _p anode current density in the formula (c), d _t1 is AlCl ₃ layers threshold thickness. When the denominator is 0 in equation (c), the _{increase in} the t _voltage is ∞. In the equation (c), it is preferable to adjust the _rise of the t _{voltage on} the left side to be equal to or less than the right side.

[Experimental example 3]
In this example, the effect of suppressing the voltage rise due to the oscillation of the anode and the stirring of the bath is actually measured. In this example, the same electroplating apparatus 100 as in Experimental Example 1 was used except that a rocking device and a stirring device were provided. Using this electrolytic plating apparatus 100, a plurality of electric aluminum plating treatments were performed under different treatment conditions. Table 1 shows the processing conditions.

  The electric aluminum plating treatment in Examples 1 to 6 of Table 1 was performed while giving the flow of the ionic liquid 21 to the surface of the anode 4 as illustrated in FIGS. 1 and 2. The application of the flow of the ionic liquid 21 was performed by oscillating the anode and stirring the bath. The anode rocking was performed by attaching a commercially available cathode locker to the anode 4. The bath was stirred using a stirrer. In Comparative Examples 1 and 2, the electroaluminum plating treatment was performed without relatively moving the ionic liquid 21 existing around the anode 4 and the anode 4. Table 1 shows the results of the voltage rise and the evaluation of the appearance at this time.

The appearance was evaluated as follows. First, an aluminum plating film was formed on eight base materials under the conditions of each example and comparative example. Next, the aluminum plating film was visually inspected and evaluated according to the following criteria. A and B pass.
A: A case where no burn or haze was observed on each aluminum plating film and no difference in the surface properties of each aluminum plating film was observed.
B: A case where no burn or haze was observed on each aluminum plating film and a slight difference in the surface properties of each aluminum plating film was observed.
C: A case where no burn or haze is observed on each aluminum plating film, but a difference in surface properties of each aluminum plating film is clearly observed.
D: A case where even one haze was observed on the aluminum plating film.

  As is known from Comparative Example 1 in Table 1, under the condition where the cathode current density is low, the voltage hardly increases even if the anode is not swung and the bath is not stirred. When the cathode current density is increased as in Comparative Example 2, a large increase in the electrolytic voltage occurs, and the formation of the aluminum plating film 1 hardly progresses. "OL" described in Table 1 means an overload of the power supply.

  On the other hand, as in Examples 1 to 6, by performing the swinging of the anode and the stirring of the bath, it is possible to suppress the voltage rise even if the cathode current density is increased. Further, the swinging of the anode can further stabilize the appearance of the aluminum plating film 1 as compared with bath stirring. By combining the anode rocking and the bath stirring, the effect of suppressing the voltage rise is further enhanced.

  The present invention is not limited to the above embodiments, and can be applied to various embodiments without departing from the gist thereof.

DESCRIPTION OF SYMBOLS 1 Aluminum plating film 100 Electroplating apparatus 2 Plating bath 21 Ionic liquid 3 Cathode 31 Base material 4 Anode 41 Metal aluminum

Claims (6)

In a plating bath (2) containing an ionic liquid (21) obtained by mixing and melting an aluminum halide and an imidazolium halide, a cathode (3) composed of a substrate (31) and an anode composed of metallic aluminum (41) In the method of dipping (4) and forming an aluminum plating film (1) on the surface of the substrate by electroplating,
In the electroplating process, a method for manufacturing an aluminum plating film, wherein the ionic liquid existing around the anode and the anode are relatively moved.   Due to the relative movement between the ionic liquid and the anode, the insulator (400) generated in the electroplating process and attached to the anode is detached from the anode or dissolved in the ionic liquid. The method for producing an aluminum plating film according to claim 1.   The method for producing an aluminum plating film according to claim 2, wherein the insulator is an aluminum halide.   In the electroplating process, by swinging or vibrating the anode, the ionic liquid present around the anode and the anode are relatively moved, and according to any one of claims 1 to 3, The method for producing an aluminum plating film according to the above.   The method for producing an aluminum plating film according to any one of claims 1 to 4, wherein the anode has a plate shape, and in the electroplating process, the anode is swung in a direction parallel to a plate surface of the anode. .   The said electroplating process WHEREIN: By stirring the said plating bath, the said ionic liquid and the said anode which exist around the said anode are moved relatively, The Claims any one of Claims 1-5. Manufacturing method of aluminum plating film.