Chromium plating solution, method for replenishing chromium to chromium plating solution, and chromium plating apparatus

Abstract

This plating solution is a chromium plating solution which contains trivalent chromium as a main component. With respect to the chromium plating solution, chromium metal pieces of 4 mm or less are charged into the chromium plating solution at a bath temperature of 40°C to 80°C inclusive, and are immersed therein for 6 hours or longer, whereby 5% or more of the charged chromium metal pieces are dissolved therein and chromium can be replenished from the dissolved chromium metal pieces.

Description

Chromium plating solution, method for replenishing chromium to the chromium plating solution, and chromium plating apparatus

[0001] The present invention relates to a chromium plating solution, a method for replenishing chromium to the chromium plating solution, and a chromium plating apparatus. This application claims priority based on Japanese Patent Application No. 2025-004068 filed in Japan on January 10, 2025, and incorporates its content herein by reference.

[0002] A technique for replenishing ions to a plating bath containing trivalent chromium ions is described in Patent Document 1 below.

[0003] Japanese Patent Application Laid-Open No. 8-120500

[0004] When replenishing chromium to a plating solution containing trivalent chromium ions, anions contained in the compound are simultaneously replenished at the same time as the chromium replenishment. As a result of the accumulation of these anions, there is a problem of causing poor deposition of the plating film.

[0005] The problem to be solved by the present invention is to provide a chromium plating solution, a method for replenishing chromium to the chromium plating solution, and a chromium plating apparatus that prevent the mixing of harmful components other than chromium into the plating solution containing trivalent chromium ions so that plating defects do not occur.

[0006] (1) A chromium plating solution according to one aspect of the present invention is a chromium plating solution mainly composed of trivalent chromium, wherein a metal chromium piece of 4 mm or less is placed in the chromium plating solution at a bath temperature of 40°C to 80°C and immersed for 6 hours or more, thereby dissolving 5% or more of the placed metal chromium piece, and chromium can be replenished from the dissolved metal chromium piece. (2) The pH value of the chromium plating solution in (1) above may be in the range of 0 to 1.1. (3) The chromium plating solution in (2) above may contain chromium, a pH buffer, a conductive salt, and a complexing agent. (4) The chromium plating solution in (1) above may have a dissolution rate of 5% or more of the metal chromium piece after 6 hours in an un-stirred state after the metal chromium piece is placed in it. (5) In the chromium plating solution in (4) above, the dissolution rate of the metal chromium piece may be higher in a stirred state than in an un-stirred state. (6) A method for supplying chromium to a chromium plating solution according to one aspect of the present invention is a method for supplying chromium to a chromium plating solution comprising adding chromium to a chromium plating solution mainly composed of trivalent chromium, comprising: a temperature adjustment step of adjusting the temperature of the chromium plating solution to 40°C or more and 80°C or less; a chromium addition step of adding metal chromium pieces of 4 mm or less to the chromium plating solution; and a chromium dissolution step of adding the metal chromium pieces to the chromium plating solution and dissolving the metal chromium pieces to 5% or more in an unstirred state. (7) The method for supplying chromium to a chromium plating solution according to (6) above may further comprise an adjustment step of adjusting the pH value of the chromium plating solution to a range of 0 to 1.1. (8) In the method for supplying chromium to a chromium plating solution according to (6) above, a chromium plating solution containing chromium, a pH buffer, a conductive salt, and a complexing agent may be used as the chromium plating solution.(9) A chromium plating apparatus according to one aspect of the present invention is a chromium plating apparatus equipped with a chromium plating solution mainly composed of trivalent chromium, comprising: a temperature sensor for detecting the temperature of the chromium plating solution; a concentration sensor for detecting the chromium concentration of the chromium plating solution; an input device for adding metallic chromium pieces to the chromium plating solution; an agitator for stirring the chromium plating solution; and a control device for controlling the temperature of the chromium plating solution to 40°C or more and 80°C or less, and for determining whether or not to agitate the chromium plating solution according to the chromium concentration in the chromium plating solution after the metallic chromium pieces have been added to the chromium plating solution, and controlling the chromium concentration of the chromium plating solution. (10) The chromium plating apparatus according to (9) above may further include a pH value meter for measuring the pH value of the chromium plating solution. (11) The chromium plating apparatus according to (9) above or (10) above may further include a cathode and an anode immersed in the chromium plating solution and connected to a rectifier.

[0007] According to the above embodiment of the present invention, the plating solution contains trivalent chromium ions, and by immersing metal chromium pieces of 4 mm or less in a bath at a bath temperature of 40°C to 80°C for 6 hours or more, 5% or more of the immersed metal chromium pieces dissolve. Because the plating solution has these characteristics, chromium can be supplied to the chromium plating solution without causing deposition defects.

[0008] This figure illustrates one embodiment of the present invention and is a schematic diagram showing an example of a chromium plating apparatus equipped with a chromium plating solution. This is a chromium potential-pH value diagram, where the horizontal axis represents the pH value and the vertical axis represents the potential. This is a table showing the pH value and the size of the metal chromium pieces added to each plating solution in Test Example 1 and Comparative Example 1 for each bath temperature. This is a table showing the components of each plating solution in Test Example 1 and Comparative Example 1. This is a table showing the dissolution rate and pH value for each size of metal chromium pieces for each bath temperature in the chromium plating solution of Test Example 1. This is a table showing the size, dissolution rate, and pH value of metal chromium pieces at a bath temperature of 70°C in the chromium plating solution of Comparative Example 1. This is a graph showing the chromium dissolution rate for each bath temperature when metal chromium pieces of various sizes are dissolved in the chromium plating solutions of Test Example 1 and Comparative Example 1 without stirring. Here, the horizontal axis represents the bath temperature and the vertical axis represents the chromium dissolution rate. This is a graph showing the chromium dissolution rate for each bath temperature when metal chromium pieces of various sizes are dissolved in the chromium plating solutions of Test Example 1 and Comparative Example 1 with stirring. This graph shows the chromium dissolution rate for each pH value when metal chromium pieces of various sizes were dissolved in the chromium plating solutions of Test Example 1 and Comparative Example 1 without stirring.

[0009] The following describes a first embodiment of a chromium plating apparatus equipped with a chromium plating solution according to the present invention. The embodiments described below are provided specifically to better understand the spirit of the present invention and do not limit the present invention unless otherwise specified.

[0010] Figure 1 shows an example of a chromium plating apparatus equipped with a chromium plating solution according to the first embodiment. The chromium plating apparatus 1 has a chromium plating tank 3 containing a chromium plating solution 2. The scale of Figure 1 has been appropriately changed to make each part easier to see. The chromium plating tank 3 is equipped with a stirring blade 5 for stirring the chromium plating solution 2. A motor 6 is connected to the stirring blade 5 for rotational driving. The motor 6 is connected to a control device 7 which has a rotational control function for the motor 6. The stirring blade 5 and the motor 6 constitute a stirring device for the chromium plating solution. Note that the means for stirring the chromium plating solution 2 is not limited to the combination of the stirring blade 5 and the motor 6, but any conventionally known general stirring device (including jet devices, circulation devices, propeller stirring devices, etc.) may be applied.

[0011] The chromium plating tank 3 is equipped with a temperature sensor 8 for detecting the bath temperature of the chromium plating solution 2, and the temperature sensor 8 is connected to the control device 7. The temperature information of the chromium plating solution 2 measured by the temperature sensor 8 is sequentially input to the control device 7 and recorded in a storage means such as a memory provided in the control device 7. The chromium plating tank 3 is equipped with a heater 9 for controlling the temperature of the chromium plating solution 2. The heater 9 is connected to the control device 7. The heater 9 is energized and controlled based on a command from the control device 7 to heat the chromium plating solution 2 to the required set temperature. For example, the control device 7 can control the bath temperature of the chromium plating solution 2 within a temperature range of 40°C to 80°C by controlling the energization of the heater 9. In Figure 1, the heater 9 is located inside the chromium plating tank 3, but it may also be located in an adjustment tank or replenishment tank (not shown).

[0012] The chromium plating tank 3 is equipped with a chromium concentration measuring means (concentration sensor) 10 for measuring the chromium concentration of the chromium plating solution 2. As an example, an ICP (inductively coupled plasma optical emission spectrometer; ICP-OES) can be used as the chromium concentration measuring means 10. In this case, for example, a portion of the chromium plating solution 2 taken from inside the chromium plating tank 3 via piping 11 can be analyzed by the ICP emission spectrometer to measure the chromium concentration. The chromium concentration of the chromium plating solution 2 measured by the ICP emission spectrometer can be sent to the control device 7 and recorded in a storage means such as the memory provided in the control device 7. In Figure 1, the chromium concentration measuring means 10 is provided in the chromium plating tank 3, but it is not limited to this configuration and may also be provided in the adjustment tank or the replenishment tank.

[0013] The chromium plating tank 3 is equipped with a loading device 12 for loading metal chromium pieces into the chromium plating solution 2. The loading device 12 contains multiple metal chromium pieces, each 4 mm or smaller in size. The bottom of the loading device 12 has a loading port with an adjustable opening, allowing a predetermined amount of metal chromium pieces to be loaded into the chromium plating tank 3 as needed. The mechanism for adjusting the opening of the loading port of the loading device 12 is connected to a control device 7 via wiring, and the loading device 12 can load a predetermined amount of metal chromium pieces into the chromium plating solution 2 in response to a command from the control device 7. By loading metal chromium pieces from the loading device 12, chromium can be replenished in the chromium plating solution 2.

[0014] The metallic chromium pieces used in this embodiment are preferably 4 mm or smaller in size, but any particle size may be used as needed, for example, those with an average particle size of 1.7 mm to 4 mm, 0.6 mm to 1.4 mm, 180 μm to 300 μm, or 60 μm or less. The size (particle size) shown here is defined as the size passing through the mesh specified for each size. For example, metallic chromium pieces with an average particle size of 60 μm or less are defined as those passing through a 60 μm square mesh.

[0015] If the particle size of the metallic chromium fragments is made too small, it will contribute to an improved dissolution rate, but if they are directly added to the chromium plating solution 2 in the chromium plating tank 3, some of the added fragments may become airborne at the site of addition, potentially causing contamination (incorporation into the plating film). Also, if they are added in a filter cloth, small metallic chromium fragments will pass through the mesh of the filter cloth and escape, potentially causing contamination. If the metallic chromium fragments are large, the dissolution rate will be lower, but even if they are directly added to the chromium plating solution 2 in the chromium plating tank 3 and become airborne at the site of addition, their large size makes them less likely to cause contamination. Also, if large metallic chromium fragments are placed in a filter cloth, their large size will prevent them from passing through the mesh of the filter cloth. However, if the metallic chromium fragments are too large, the filter cloth may tear, causing them to sink to the bottom of the chromium plating tank 3 and potentially clogging piping or other equipment provided at the bottom of the chromium plating tank 3.

[0016] The chromium plating apparatus 1 is equipped with a pH meter 15 for measuring the pH value of the chromium plating solution 2. The pH meter 15 is connected to a control device 7. The pH value information of the chromium plating solution 2 measured by the pH meter 15 is sent to the control device 7, so that the control device 7 can continuously monitor the pH value of the chromium plating solution 2. A cathode electrode 16 and an anode electrode 17 are immersed in the chromium plating solution 2 in the chromium plating tank 3. The cathode electrode 16 and anode electrode 17 are connected to a rectifier 18 connected to a power supply (not shown). There are no particular restrictions on the installation positions of the cathode electrode 16 and anode electrode 17, but the installation position of the anode electrode 17 is preferably at the edge of the chromium plating tank 3, and the installation position of the cathode electrode 16 is preferably in the center of the chromium plating tank 3. If, for example, a metal rod is used as the cathode electrode 16, chromium plating can be applied to the surface of the metal rod. A cooler 19 connected to the control device 7 is provided inside the chromium plating tank 3. The control device 7 can control the operation of the cooler 19 to cool the chromium plating solution 2 to an appropriate temperature desirable for the plating process.

[0017] The chromium plating solution 2 of this embodiment is, for example, a solution containing chromium, ammonia, boric acid, chlorine, and glycine. Alternatively, as an example, the chromium plating solution 2 consists of a mixed solution containing chromium(III) chloride hexahydrate, ammonium chloride, boric acid, and glycine. This chromium plating solution 2 is a strong acid bath with a pH value in the range of 0 to 1.1. This chromium plating solution 2 is obtained by adding metal chromium pieces of 4 mm or less to the chromium plating solution at a bath temperature of 40°C to 80°C and immersing them for 6 hours or more, resulting in the dissolution of 5% or more of the added metal chromium pieces. This chromium plating solution 2 is a plating solution in which the dissolution rate of the metal chromium pieces of 4 mm or less is 5% or more after 6 hours have elapsed without stirring after adding the metal chromium pieces of 4 mm or less. This chromium plating solution 2 is a chromium plating solution in which the dissolution rate is higher when stirring is performed after adding the metal chromium pieces of 4 mm or less than when stirring is not performed.

[0018] In this embodiment, the chromium plating solution can be one that contains a trivalent chromium salt, and additives such as a complexing agent, a pH buffer, and a conductivity salt. As the trivalent chromium salt, chromium chloride, chromium sulfate, and basic chromium sulfate can be used, but among these, it is preferable to use the aforementioned chromium chloride. As the complexing agent, carboxylate salts such as glycine, formic acid, oxalic acid, and acetic acid can be used, but among these, it is preferable to use the aforementioned glycine. As the pH buffer, boric acid and citric acid containing boron can be used, but among these, it is preferable to use the aforementioned boric acid. As the conductivity salt, ammonia such as ammonium chloride, ammonium sulfate, and ammonium sulfonate can be used, but among these, it is particularly preferable to use the aforementioned ammonium chloride. As an example of such a chromium plating solution, a chromium plating solution can be used that is formulated with chromium chloride: 100 g / L to 500 g / L, ammonium chloride: 50 g / L to 300 g / L, boric acid: 10 g / L to 100 g / L, and glycine: 50 g / L to 200 g / L as the main components. The formulation of the chromium plating solution is not limited to the above-mentioned range, as long as the chromium plating solution has trivalent chromium as the main component.

[0019] When the chromium plating solution is a strongly acidic plating bath mainly composed of trivalent chromium ions, a pH range of 0 to 1.1 is desirable, but it is preferable to select a strongly acidic solution weaker than pH 0.1, for example, a strongly acidic solution in the range of pH 0.1 to 1.1, and more preferably a strongly acidic solution in the range of pH 0.2 to 1.05. If the strongly acidic solution is less than pH 0.1, it becomes difficult to obtain a chromium-based plating film using the trivalent chromium bath targeted in this embodiment, and if the pH value exceeds 1.1, the dissolution rate of the metallic chromium pieces in the chromium plating solution becomes low. The chromium plating bath consisting of chromium plating solution 2 is preferably maintained at a bath temperature of 40°C or higher and 80°C or lower in order to ensure the dissolution rate of the metallic chromium pieces. If the bath temperature of the chromium plating bath is below 40°C, the required dissolution rate of the metallic chromium pieces cannot be obtained. Although the dissolution rate increases when the bath temperature of the chromium plating bath exceeds 80°C, it damages resin components such as pipes, so it is preferable to keep it below 80°C.

[0020] Using the chromium plating apparatus 1 configured as shown in Figure 1, chromium plating can be formed on the surface of a workpiece immersed in the chromium plating solution 2 as the cathode electrode 16. If the workpiece is a rod-shaped metal rod, the metal rod can be used as the cathode electrode 16 to perform the chromium plating treatment. However, the workpiece is not limited to a metal rod; conductive materials of various shapes can be used, and chromium plating can be performed on the surface of a conductive material of the desired shape to be used as the cathode electrode 16. It is preferable to operate the heater 9 using the control device 7 to adjust the bath temperature of the chromium plating solution 2 to a temperature of 40°C or higher and 80°C or lower. The control device 7 receives information on the bath temperature of the chromium plating solution 2 from the temperature sensor 8, and controls the temperature so that the bath temperature of the chromium plating solution 2 is in the range of 40°C to 80°C. The control device 7 can rotate the stirring blade 5 as needed to stir the chromium plating solution 2. However, the chromium plating treatment may be performed with the rotation of the stirring blade 5 stopped. The chromium concentration of the chromium plating solution 2 can be controlled by taking a sample of the chromium plating solution 2, measuring it using the chromium concentration measuring means 10, and having the control device 7 receive this information. For the initial chromium plating process, it is preferable to prepare the required amount of chromium plating solution containing trivalent chromium salt, additives such as complexing agents, pH buffering agents, and conductivity salts, and then place the required amount into the chromium plating tank 3.

[0021] The object to be chromium plated, such as a metal rod, is immersed as the cathode in the chromium plating solution 2, and the metal rod is immersed as the anode in the chromium plating solution 2. Then, the object to be treated and the metal rod are connected to a rectifier 18 connected to a power supply (not shown), and the required current is applied to enable chromium plating of the object to be treated. In this process, a metal rod is given as an example of the object to be treated, but the object to be treated is not limited to a metal rod; for example, a flat plate may also be used. Furthermore, the material of the object to be treated may be platinum (base material is titanium), iridium oxide (base material is titanium), graphite, etc. Plating conditions include, for example, a pH value of the chromium plating solution 2 of pH 0 to pH 1.1 (preferably pH 0.2 to pH 1.05), a bath temperature of 40°C to 80°C, and a cathode current density of 40 A / cm². ２ ~100A / cm ２You can choose from the following degrees. Figure 2 shows the potential-pH value diagram of chromium. As shown in Figure 2, trivalent chromium ions (chromium ３＋ Since it is found that the substance is stable in the pH range of 0 to 1.1, the aforementioned plating process can form a chromium plating layer on the workpiece.

[0022] When chromium plating is performed repeatedly, the amount of chromium ions in the chromium plating solution 2 gradually decreases. Therefore, to prevent plating defects, metal chromium pieces are added to the chromium plating solution 2 to maintain the chromium ion concentration within an appropriate range. For this reason, in the chromium plating apparatus 1 shown in Figure 1, the required amount of metal chromium pieces is added to the chromium plating solution 2 from the metal chromium piece input device 12. What is added here is metal chromium pieces, not chromium chloride, which has been used conventionally. If chromium chloride is added to the chromium plating solution 2 to replenish the chromium, the accumulation of chloride ions will progress inside the chromium plating solution 2. As the accumulation of chloride ions progresses, it will cause chromium plating defects. When adding metal chromium pieces, in order to prevent scattering, the metal chromium pieces may be placed in a dissolution case such as a filter cloth or titanium mesh case before being added to the chromium plating solution 2. Note that the addition of metal chromium pieces may be performed either during plating or when not plating.

[0023] As the chromium metal pieces are introduced, they gradually dissolve in the chromium plating solution 2 over time, allowing the chromium ions in the chromium plating solution 2 to be maintained within an appropriate concentration range. Therefore, the plating process can be continued while maintaining the chromium ions within an appropriate concentration range. In this embodiment, since the chromium plating solution 2 is a chloride bath with the aforementioned composition and a pH of 0 to 1.1 with high reducing activity, chromium can be supplied to the chromium plating solution 2 by introducing chromium metal pieces of 4 mm or less. In this embodiment, by using a chromium plating solution 2 that is a chloride bath with the aforementioned composition and high reducing activity, has a high bath temperature of 40°C to 80°C, and is a strong acid with a pH of 0 to 1.1, efficient and stable chromium supply can be continuously implemented.

[0024] If a highly reducing chloride bath having the aforementioned composition, a high bath temperature of 40°C to 80°C, and a strong acid chromium plating solution 2 with a pH of 0 to 1.1 is used, and chromium is supplied by adding metal chromium pieces of 4 mm or less, then, for example, even in an unstirred state with the rotation of the stirring blade 5 stopped, more than 5% of the added metal chromium pieces can be dissolved after 6 hours. By supplying chromium to the chromium plating solution 2 by adding metal chromium pieces in an unstirred state, chromium can be supplied without considering variations caused by stirring. Of course, as time passes after addition, the metal chromium pieces will continue to dissolve, so the required amount of chromium can be supplied. The bath temperature of the chromium plating solution 2 shows a better dissolution rate at higher temperatures within the temperature range of 40°C to 80°C, so more chromium can be supplied.

[0025] As mentioned above, the chromium replenishment method, which involves adding chromium to a chromium plating solution 2 mainly composed of trivalent chromium, essentially comprises the following steps: A temperature adjustment step to adjust the temperature of the chromium plating solution 2 to between 40°C and 80°C. A chromium addition step in which metal chromium pieces of 4 mm or less are added to the chromium plating solution. A chromium dissolution step in which the metal chromium pieces are added to the chromium plating solution and the dissolution rate of the metal chromium pieces is 5% or more without stirring.

[0026] By supplying the chromium in the chromium plating solution 2 with metallic chromium pieces as a source of chromium, the accumulation of chloride ions in the chromium plating solution can be prevented compared to conventional methods of supplying chromium chloride, etc. Therefore, chromium ions can be supplied without causing plating defects, and the plating process can be continued. In the process described above, the control device 7 controls the temperature of the chromium plating solution 2 to 40°C or higher and 80°C or lower, and after adding the metallic chromium pieces to the chromium plating solution 2, it has the function of determining whether or not to stir the chromium plating solution 2 according to the chromium concentration in the chromium plating solution 2 and controlling the chromium concentration of the chromium plating solution 2. However, when measuring the chromium concentration with an ICP emission spectrometer, it takes about two hours to measure the chromium concentration. Therefore, since the amount of chromium in the Cr plating solution will decrease further during the time required for chromium analysis, it is preferable to add an appropriate amount of metallic chromium pieces so that the decrease can be compensated for, taking into account the dissolution rate after the aforementioned six hours have elapsed.

[0027] In the chromium plating apparatus 1 shown in Figure 1, metallic chromium pieces are directly added to the chromium plating solution 2 contained in the chromium plating tank 3. However, a separate adjustment tank or replenishment tank connected to the chromium plating tank 3 may also be provided. In that case, the adjustment tank or replenishment tank may also be filled with the chromium plating solution 2, and the chromium plating solution 2 may be supplied from the adjustment tank or replenishment tank to the chromium plating tank 3. In this case, metallic chromium pieces can be added to the chromium plating solution 2 in the adjustment tank or replenishment tank to replenish the chromium, and the chromium-replenished chromium plating solution 2 can be supplied to the chromium plating tank 3.

[0028] Furthermore, in the chromium plating apparatus 1 shown in Figure 1, an ICP (inductively coupled plasma) emission spectrometer was used to measure the chromium concentration, but other analytical means may also be used. The chromium concentration measurement means 10 sends the measured chromium concentration information to the control device 7, and the chromium concentration of the chromium plating solution 2 is recorded in a storage means such as a memory provided in the control device 7. The control device 7 can adjust the amount of metallic chromium pieces introduced from the input device 12 according to the measured chromium concentration, thereby continuously managing the chromium concentration in the chromium plating solution 2.

[0029] A plating bath (bath type: chloride bath) containing chromium(III) chloride hexahydrate, ammonium chloride, boric acid, and glycine was prepared in a 100 mL beaker as a trivalent chromium plating bath. A chromium plating solution was used containing chromium chloride: 100 g / L to 500 g / L, ammonium chloride: 50 g / L to 300 g / L, boric acid: 10 g / L to 100 g / L, and glycine: 50 g / L to 200 g / L. Under the conditions shown in Figure 3—bath temperature 40°C to 80°C, pH: 0.23 to 1.05, input amount 10 g / L, dissolution time 6 hours, and either unstirred or stirred—the amount of chromium dissolved in the metal chromium pieces was measured when the bath temperature and the size of the metal chromium pieces added were varied (Test Example 1). The chromium plating solution was heated using a water bath, and stirring was performed using a stirrer. The chromium dissolution rate was determined by measuring the chromium concentration before and after the dissolution test using ICP emission spectrometry. The components of the chromium plating solution in Test Example 1 are shown in Figure 4.

[0030] For comparison, a hard Cr(III) plating solution (bath type: sulfuric acid bath: manufactured by Atotech) was prepared in a beaker (100 mL size). The chromium plating solution was heated using a water bath, and stirring was performed using a stirrer. The components of the chromium plating solution of Comparative Example 1 are shown in Figure 4. The plating solution of Comparative Example 1 contains Blue Chromium A, Blue Chromium B, Blue Chromium C1, and Blue Chromium C2, all of which are trade names of Atotech. The chromium plating solution was heated using a water bath, and stirring was performed using a stirrer.

[0031] As shown in Figure 3, the amount of chromium dissolved from the metal chromium pieces was measured when the size of the metal chromium pieces added was varied under the conditions of a bath temperature of 70°C, pH: 5.4, an additive amount of 10 g / L, a dissolution time of 6 hours, and either in an unagitated or aagitated state (Comparative Example 1). The chromium dissolution rate was determined by measuring the chromium concentration before and after the dissolution test using ICP emission spectrometry.

[0032] As shown in Figure 3, the chromium plating solution in Test Example 1 is a chloride bath, characterized by a low pH value and high reducing power. Therefore, it is thought that the metallic chromium pieces dissolve easily. On the other hand, the chromium plating bath in Comparative Example 1 is a sulfuric acid bath. Compared to the chloride bath, the sulfuric acid bath has a higher pH value (pH: 5.4) and weaker reducing power, so it is thought that the metallic chromium pieces do not dissolve easily.

[0033] Figure 5 shows the dissolution rate of the sample from Test Example 1 after 6 hours of stirring for each metal chromium piece size at bath temperatures of 40°C, 50°C, 60°C, 70°C, and 80°C. Furthermore, Figure 5 shows the dissolution rate of the sample from Test Example 1 after 6 hours of unstirred application for each metal chromium piece size at each bath temperature. Also, Figure 5 shows the pH value of the chromium plating solution used. Note that the pH value of the chromium plating solution is the same at each bath temperature of 40°C, 50°C, 60°C, 70°C, and 80°C because the chromium plating solution was divided into four portions for each metal chromium piece size and measurements were performed. Figure 6 shows the dissolution rate of the sample from Comparative Example 1 after 6 hours of unstirred application for each metal chromium piece size at a bath temperature of 70°C. Note that the pH value of the chromium plating solution is the same at each bath temperature of 70°C because the chromium plating solution was divided into two portions for each metal chromium piece size and measurements were performed.

[0034] As shown in Figure 5, in Test Example 1, when stirred, a high dissolution rate of 90% to 100% was obtained for metal chromium pieces of any size when the bath temperature was 60°C to 80°C. Furthermore, even when the bath temperature was somewhat lower, such as 50°C and 40°C, a dissolution rate close to 100% was obtained when the metal chromium pieces were small, such as 60 μm to 300 μm. When the bath temperature was somewhat lower, such as 50°C and 40°C, a dissolution rate of 16% to 73% was obtained for metal chromium pieces of 0.6 mm to 4 mm. As shown in Figure 5, in Test Example 1, even without stirring, an extremely high dissolution rate was obtained when the bath temperature was 70°C to 80°C, and even at a bath temperature of 40°C, a dissolution rate of 5% or more was obtained for metal chromium pieces of 1.7 mm to 4 mm. Even without stirring, a dissolution rate of 5% after 6 hours indicates that chromium is being supplied to the chromium plating solution, considering that the dissolution rate was 0% in Comparative Example 1 shown in Figure 6.

[0035] Therefore, when using a chromium plating solution with the aforementioned components and a pH of 0 to 1.1 (pH 0.23 to 1.05) as shown in Figure 5, it is considered that chromium can be replenished by adding metal chromium pieces of 4 mm or less, more specifically 60 μm to 4 mm in size. Furthermore, in this example, chromium can be replenished without increasing the chloride ions in the chromium plating solution, thus ensuring that chromium is replenished without causing poor plating deposition. In contrast, the chromium plating solution of Comparative Example 1 could not dissolve the metal chromium pieces, as shown in Figure 6. Therefore, it can be seen that chromium cannot be replenished by adding metal chromium pieces to the chromium plating solution of Comparative Example 1.

[0036] Figure 7 is a graph showing the relationship between the chromium dissolution rate and the bath temperature of the chromium plating solution in the case of no stirring in the test results of Test Example 1 and Comparative Example 1. Figure 8 is a graph showing the relationship between the chromium dissolution rate and the bath temperature of the chromium plating solution in the case of stirring in the test results of Test Example 1 and Comparative Example 1. A comparison of Figure 7 and Figure 8 shows that chromium cannot be replenished by adding metallic chromium pieces in the chromium plating solution of Comparative Example 1, but chromium can be replenished by adding metallic chromium pieces in the chromium plating solution of Test Example 1. Furthermore, as shown in the results of Figure 8, it can be seen that the chromium dissolution rate of the chromium plating solution of Test Example 1 improves when stirred.

[0037] Figure 9 is a graph showing the relationship between the pH value of each chromium plating solution and the chromium dissolution rate in the test results of Test Example 1 and Comparative Example 1. From the results shown in Figure 9, it can be seen that if the chromium plating solution has a pH of 0.1 to 1.1, chromium can be replenished by adding metallic chromium pieces to the chromium plating solution.

[0038] According to the above embodiment of the present invention, a chromium plating solution can be provided that allows for chromium replenishment using metallic chromium pieces. Furthermore, a method for replenishing chromium using this chromium plating solution and a chromium plating apparatus can be provided. Therefore, it has great industrial applicability.

[0039] 1…Chromium plating apparatus 2…Chromium plating solution 3…Chromium plating tank 5…Agitator 7…Control device 8…Temperature sensor 9…Heater 10…Chromium concentration measuring means (concentration sensor) 12…Metal chromium piece feeding device 15…pH value meter 16…Cathode electrode (workpiece) 17…Anode electrode 18…Rectifier

Claims

1. A chromium plating solution mainly composed of trivalent chromium, wherein, by immersing metal chromium pieces of 4 mm or less in the chromium plating solution at a bath temperature of 40°C to 80°C for 6 hours or more, 5% or more of the immersed metal chromium pieces dissolve, and chromium can be replenished from the dissolved metal chromium pieces.

2. The chromium plating solution according to claim 1, wherein the pH value is in the range of 0 to 1.

1.

3. The chromium plating solution according to claim 2, comprising chromium, a pH buffer, a conductive salt, and a complexing agent.

4. The chromium plating solution according to claim 1, wherein the dissolution rate of the chromium metal pieces after 6 hours in an unstirred state following the addition of the chromium metal pieces is 5% or more.

5. The chromium plating solution according to claim 4, wherein the dissolution rate of the metallic chromium pieces is higher when stirred than when not stirred.

6. A method for supplying chromium to a chromium plating solution, comprising adding chromium to a chromium plating solution mainly composed of trivalent chromium, the method comprising: a temperature adjustment step of adjusting the temperature of the chromium plating solution to 40°C or more and 80°C or less; a chromium addition step of adding metal chromium pieces of 4 mm or less to the chromium plating solution; and a chromium dissolution step of adding the metal chromium pieces to the chromium plating solution and dissolving the metal chromium pieces to a dissolution rate of 5% or more without stirring.

7. The method for supplying chromium to a chromium plating solution according to claim 6, further comprising an adjustment step to set the pH value of the chromium plating solution to a range of 0 to 1.

1.

8. A method for supplying chromium to a chromium plating solution according to claim 6, wherein the chromium plating solution used contains chromium, a pH buffer, a conductivity salt, and a complexing agent.

9. A chromium plating apparatus comprising a chromium plating solution mainly composed of trivalent chromium, the apparatus comprising: a temperature sensor for detecting the temperature of the chromium plating solution; a concentration sensor for detecting the chromium concentration of the chromium plating solution; an input device for adding metallic chromium pieces to the chromium plating solution; an agitator for stirring the chromium plating solution; and a control device for controlling the temperature of the chromium plating solution to 40°C or more and 80°C or less, and for determining whether or not to agitate the chromium plating solution after adding the metallic chromium pieces to the chromium plating solution according to the chromium concentration in the chromium plating solution, and controlling the chromium concentration of the chromium plating solution.

10. The chromium plating apparatus according to claim 9, further comprising a pH meter for measuring the pH value of the chromium plating solution.

11. The chromium plating apparatus according to claim 9 or claim 10, further comprising a cathode and an anode immersed in the chromium plating solution and connected to a rectifier.

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