TW201835387A - Plating solution and method for producing plated product - Google Patents

Abstract

Provided is a plating solution that includes chromium sulfate and formic acid, in which Cr<SP>3+</SP> ion concentration is 0.1 mol/L or more and 1 mol/L or less, and formic acid concentration is 0.05 mol/L or more and 0.2 mol/L or less.

Description

Manufacturing method of plating liquid and plating products

[Cross-reference of related applications]

This case claims the priority of Japanese Invention Patent Application No. 2017-21006, and is incorporated into the description of the specification of this case by reference.

The present invention relates to a method for manufacturing a plating solution and a plated product, and more specifically, to a method for manufacturing a plating solution for trivalent chromium plating and a plated product obtained by performing trivalent chromium plating. method.

Previously, plated products obtained by chromium-plating metal or plastic products have been widely used. When manufacturing such a plated product, the use of a plating solution containing environmentally friendly trivalent chromium instead of a plating solution containing hexavalent chromium has increased (see Patent Document 1 below).

[Prior technical literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2000-249340

[Problems to be solved by the invention]

In recent years, due to the improvement of environmental awareness, it is strongly desired to use trivalent chromium plating instead of hexavalent chromium plating. However, trivalent chromium plating is inferior to hexavalent chromium plating in terms of the uniformity of plating to products that are subject to the plating, so the current situation is that the use of trivalent chromium plating is limited. Moreover, in trivalent chromium plating, it is difficult to make the relationship between the current density and the deposited thickness of the plating linear, and it is difficult to exhibit uniform electrodeposition. According to this situation, examples of the use of trivalent chromium plating can be seen in decorative plating with a coating thickness of several μm level, but in the scene of manufacturing complex-shaped plated products such as molds or thick-plated products. In this scenario, trivalent chromium plating is rarely used. Therefore, the present invention provides a plating solution for trivalent chromium plating, but can produce a plating product equivalent to hexavalent chromium plating, and even expand the application range of environmentally friendly plating products. for purpose.

[Technical means to solve the problem]

In order to achieve the above-mentioned object, the present inventors conducted diligent research, and found that by adjusting the concentration of Cr ³⁺ ions to a specific range in a plating solution containing chromium sulfate, the plating solution exhibited and contained The plating solution of hexavalent chromium has the same uniform plating property, thereby completing the present invention.

That is, the present invention provides a plating solution, which is used for trivalent chromium plating, and contains chromium sulfate and formic acid, and the concentration of Cr ³⁺ ions is 0.1 mol / L or more and 1 mol / L or less. The concentration is 0.05 mol / L or more and 0.2 mol / L or less.

In addition, the present invention provides a method for manufacturing a plated product, which is performed by performing a plating step of performing plating in a plating bath containing a plating solution containing chromium sulfate, and producing a trivalent chromium that has been subjected to the plating step. Those who have plated a plating product, and in the above-mentioned plating step, use a plating solution having a concentration of Cr ³⁺ ions of 0.1 mol / L or more and 1 mol / L or less as the above-mentioned plating solution. The bath temperature is set to 20 ° C. or more and less than 40 ° C., and the current density in the above-mentioned plating is set to 2 A / dm ² or more and 20 A / dm ² or less.

Hereinafter, preferred embodiments of the present invention will be described. First, a method for manufacturing a plated product will be described. In the method for manufacturing a plated product according to this embodiment, a pretreatment step is performed to adjust the surface properties of a product (hereinafter, also referred to as "original product") to be subjected to plating; and a plating step, It performs trivalent chromium plating on a pre-processed original product (hereinafter, also referred to as a "pre-processed product"). In the method for manufacturing a plated product in this embodiment, an under-plating step may also be performed between the pre-treatment step and the plating step, which may perform under-plating on the pre-treatment product; or an intermediate plating step, which may The under-plated pretreatment product (hereinafter, also referred to as "under-plated product") is further subjected to intermediate plating. In this case, trivalent chromium plating is performed in the form of fine plating on a product subjected to intermediate plating (hereinafter, also referred to as "intermediate plating product").

In the manufacturing method of the plated product of this embodiment, the product which has been subjected to trivalent chromium plating in the plating step may be further subjected to chemical surface treatment or heat treatment. In addition, if necessary, the plated product may be coated with a coating such as transparent coating.

Examples of the above-mentioned original products to be subjected to the pretreatment process include resin products, ceramic products, metal products, composite products made of a combination of resin parts and metal parts, and composite products made of metal parts coated with ceramics. Examples of the resin forming the original product include general thermoplastic resins and thermosetting resins. The resin can also be fiber reinforced plastic (FRP). As said ceramic which forms an original product, the general one which has silicon oxide, alumina, etc. as a main component is mentioned, for example. The ceramics may be glassy materials such as enamel. Examples of the metal forming the original product include general metals such as iron and copper. These metals may be alloys or the like. Examples of the pretreatment of such an original product include grinding by mechanical grinding, honing processing, spray processing, and the like, and degreasing such as alkali degreasing. In the above-mentioned underlying plating step or the above-mentioned intermediate plating step, the pre-treated product or the under-plated product can be nickel-plated or plated with a thickness of several μm for the purpose of improving the appearance or corrosion resistance of the plated product. Various platings such as copper and iron plating.

In the above-mentioned plating step in which trivalent chromium plating is performed, electroplating using a pretreatment product, a bottom plating product, an intermediate plating product, and the like as workpieces is performed. In this electroplating, the workpiece is subjected to trivalent chromium plating using a plating bath containing a plating solution containing chromium sulfate. Hereinafter, the plating solution used in the plating step will be described in detail.

In the above-mentioned plating step, it is important to use a plating solution having a concentration of Cr ³⁺ ions of 0.1 mol / L or more and 1 mol / L or less in terms of plating with good uniformity on the workpiece. The above plating solution. The plating solution may contain a complexing agent, a pH buffering agent, a conductive agent, a surfactant, and the like in addition to chromium sulfate as a main component. Examples of water used as a solvent of the plating solution include industrial water, tap water, ion-exchanged water, distilled water, and pure water.

The chromium sulfate is contained in the plating solution such that the concentration of Cr ³⁺ ions in the plating bath is 0.1 mol / L or more and 1 mol / L or less as described above. The chromium sulfate is preferably contained in the plating solution such that the concentration of Cr ³⁺ ions in the plating bath is 0.1 mol / L or more and 0.3 mol / L or less. By using such a preferred plating solution, the uniformity of the trivalent chromium plating of the workpiece in the plating step can be made better.

In the plating solution of this embodiment, a part of chromium sulfate contained as a supply source of Cr ³⁺ ions may be replaced with one selected from the group consisting of chromium hydrochloride, alkaline chromium sulfate, chromium alum, and chromium nitrate. One or more types, but if a large amount of chromium hydrochloride is contained, chlorine gas may be generated at the anode during plating, and if a large amount of chromium nitrate is contained, current density may be reduced during plating. Therefore, the ratio of chromium sulfate in the plating solution to the supply source of Cr ³⁺ ions is preferably 90 mol% or more. The ratio of chromium sulfate is more preferably 95 mol% or more, and still more preferably 99 mol% or more. A particularly preferred supply source of Cr ³⁺ ions in the plating solution is substantially only chromium sulfate.

As the said complexing agent contained in the plating liquid of this embodiment, an organic acid or its salt can be used. Examples of the organic acid include oxalic acid, citric acid, formic acid, maleic acid, malonic acid, tartaric acid, malic acid, acetic acid, phthalic acid, propionic acid, and ethylenediaminetetraacetic acid. Examples of such salts include alkali metal salts such as lithium salts, potassium salts, and sodium salts; and alkaline earth metal salts such as magnesium salts and calcium salts. Among them, the aforementioned formic acid is particularly effective as a complexing agent, and it is important that the formic acid is contained in the plating solution in a concentration of 0.05 mol / L or more and 0.2 mol / L or less. The concentration of the formic acid in the plating solution is more preferably 0.08 mol / L or more and 0.12 mol / L or less.

The organic acid or a salt thereof also exerts a certain effect or more as the pH buffering agent. As the complexing agent, an amine carbonyl compound such as urea or urethane can be used. Among them, urea has a function as a pH buffer, and functions as a supply source of nitrogen for the coating film, and is more effective for hardening the film. Furthermore, for urea, the effect of suppressing the generation of precipitates such as chromium hydroxide in the plating solution can be expected. In this respect, the urea is preferably contained in the plating solution so that the concentration becomes 0.1 mol / L or more and 1 mol / L or less. The concentration of the aforementioned urea in the plating solution is more preferably 0.2 mol / L or more and 0.8 mol / L or less, and even more preferably 0.4 mol / L or more and 0.6 mol / L or less.

Examples of those that can be used as the pH buffering agent other than those described above include, for example, boric acid or borate. When the boric acid is contained in the plating solution, although it depends on the amount of organic acid, urea, etc. contained in the above-mentioned pH buffer, it is usually at a concentration of 0.5 mol / L or more and 1 mol / L or less. The method is contained in the plating solution. The plating solution is preferably adjusted to a pH value of 1 or more and 2 or less with a pH buffer or the like, and more preferably adjusted to a pH value of 1.3 or more and 1.7 or less.

Examples of the conductive agent include ammonium chloride, sodium chloride, potassium chloride, ammonium sulfate, sodium sulfate, potassium sulfate, ammonium nitrate, sodium nitrate, and potassium nitrate. Examples of the surfactant include sodium lauryl sulfate, sodium lauryl sulfate, polyethylene glycol, diisohexyl sulfosuccinate, 2-ethylhexyl sulfate, and disulfo succinate. Isobutyl ester, diisoamyl sulfosuccinate, isodecyl sulfosuccinate, and the like.

The plating solution may contain various additives such as a film-forming agent such as polyethylene glycol, polyvinyl alcohol, and gelatin, and an antifoaming agent.

In the plating step using a plating solution containing such a component, it is important to set the bath temperature in the above-mentioned plating bath to 20 ° C or higher and less than 40 ° C. When the bath temperature of the plating bath in the above-mentioned plating step is low temperature, the uniformity of the trivalent chromium plating on the workpiece can be made better. On the other hand, when the bath temperature of the plating bath has a certain temperature or more, the precipitation of components contained in the plating solution can be suppressed, and the occurrence of coarseness in the plating surface can be suppressed. In this respect, the bath temperature of the plating bath in the above-mentioned plating step is more preferably 23 ° C or higher and 29 ° C or lower, and particularly preferably 24 ° C or higher and 28 ° C or lower. By performing the plating step under such a preferable temperature condition, the finely plated product can be provided with a plating film having a uniform thickness and excellent surface gloss.

In the electroplating in the above-mentioned plating step, it is important to set the current density to 2 A / dm ² or more and 20 A / dm ² or less. More preferably that the current density was 2 A / dm ² or more and ² or less 15 A / dm, and particularly preferably set to ² A / dm 2 or more and ² or less 13 A / dm. By performing plating at such a preferable current density, the uniformity of the trivalent chromium plating on the workpiece can be made better.

In the above-mentioned plating step, bubbles caused by hydrogen gas are generated in the plating solution. Therefore, in order to suppress bubbles from adhering to the workpiece, the workpiece during plating can be vibrated, or bubbles caused by inert gas or the like can be removed from the workpiece. Foaming treatment generated underneath.

Regarding the various conditions in the plating steps such as the component concentration of the plating solution, the bath temperature of the plating solution, and the current density imparted to the workpiece, it is not necessary to start from the beginning of the plating step until the completion of the plating step. The effect is always exhibited when the period is kept within the above-mentioned range, but it is preferable that the entire period is under substantially the same conditions as when the plating is started.

In the above-mentioned plating step of this embodiment, chrome plating is performed at a thickness equal to that of the flat portion even in areas where the thickness of the previous plating layer, such as a corner portion or a fine uneven portion of the workpiece, is likely to be different from that of the flat portion. Valence chromium plating, but the same uniformity and uniform electrodeposition as hexavalent chromium plating. The thickness of the plating layer in the plated product produced in this embodiment can be appropriately set depending on the use of the plated product and the like. In terms of more prominently exerting the effects of the present invention, it is preferable to use a layer other than the underlying plated layer. Only the plating thickness of the trivalent chromium plating portion is set to 5 μm or more and 600 μm or less. The thickness of the plating layer is more preferably 50 μm or more, and even more preferably 100 μm or more. When it is necessary to measure the thickness of the plating layer, it may be measured by, for example, a fluorescent X-ray film thickness meter or the like. However, if the thickness of the plating layer is 50 μm or more, it becomes difficult to measure it with a fluorescent X-ray film thickness meter. Therefore, in this case, the cross-sectional observation of the plated product is performed using a scanning electron microscope (SEM) Just fine. In addition, the above-mentioned plating thickness can be obtained by measuring the plating thickness of the plated product at a number of randomly selected points and arithmetically averaging the measurement results other than the abnormal value.

In addition, the detailed description will not be repeated here, but the manufacturing method of the plated product or the plating solution used for the plating in this embodiment may be used in matters not specifically illustrated above. As long as the effect of the present invention is not significantly impaired, previously known technical matters are appropriately adopted. In other words, the present invention is not limited to the above-mentioned examples.

[Example]

Next, the present invention will be described in more detail with examples, but the present invention is not limited to these.

(Summary of the invention: different from the previous trivalent chromium plating)

The relationship between the current density and the plating thickness in the hexavalent chromium plating and trivalent chromium plating disclosed in the general literature and the like is shown in FIG. 1. According to the figure, in the previous trivalent chromium plating, the slope of the straight line representing the relationship between the current density and the thickness of the plating layer suddenly increased when the current density was around 5 A / dm ² , making it difficult to exert uniform electrodeposition. In addition, according to the figure, it was found that in the conventional trivalent chromium plating, it was difficult to perform plating at a current density of 5 A / dm ² or less, and it was difficult to perform plating with excellent uniformity.

In contrast, when the plating solution of the present invention is used, the relationship between the current density and the thickness of the plating layer is as shown in FIG. 2, which can be lower than 5 A / dm ^{2, which is the} same as that of hexavalent chromium plating. Trivalent chromium plating is performed. In the case of using the plating solution of the present invention, the relationship between the current density and the thickness of the plating layer ranges from a region with a lower current density below 5 A / dm ^{2 to a} region with a higher current density near 30 A / dm ² . Those who are linear can perform plating with excellent uniform electrodeposition. Therefore, it can also be seen from this figure that according to the present invention, a plating solution for trivalent chromium plating having excellent uniform plating properties and uniform electrodeposition properties is provided. In this regard, the results of the study are detailed below.

(Evaluation 1: Bath temperature 1)

A plating solution was prepared in such a manner as to be prepared as shown in Table 1. That is, a plating solution containing chromium sulfate and having a Cr ³⁺ ion concentration of 1 mol / L was prepared. Formic acid and urea were added to the plating solution so as to have a concentration of 0.5 mol / L, respectively. The plating solution was prepared so that the pH value became 1.5.

[Table 1]

Using the above plating solution, a Hall groove test was performed at a current value of 5 A. The test was performed at three bath temperatures of 30 ° C, 35 ° C, and 40 ° C, and the test time was 10 minutes. The results are shown in FIG. 3 and Table 1 together.

The thickness of the plated layer of the sample after the test was measured with a fluorescent X-ray film thickness measuring device. The results are shown in FIG. 4. According to the results shown in Table 1 or FIG. 4, it can be known that even if the concentration of Cr ³⁺ ions is 1 mol / L or less, a certain thickness of the plating layer can be ensured even when the current density is low. From the results shown in Tables 1 and 4, it was found that setting the bath temperature to less than 40 ° C is advantageous in terms of performing trivalent chromium plating having excellent uniformity.

(Evaluation 2: Bath temperature 2)

Accept the results of "Evaluation 1" and further subdivide the bath temperature. The Hall bath test was performed at five bath temperatures of 24 ° C, 26 ° C, 28 ° C, 30 ° C, and 32 ° C. Way to evaluate test results. The results are shown in Tables 2 and 5 and 6.

[Table 2]

It can also be known from the table or the graph that the precipitation of the plating film at each current density can be caused to have a substantially constant speed within a range of a bath temperature of 24 ° C to 28 ° C. In addition, it can be seen that the improvement in uniformity is most visible when the bath temperature is 24 ° C, and better results can be obtained by plating at a lower bath temperature. Therefore, the temperature of the bath was also lowered, but it was found that if the bath temperature was excessively lowered, a part of the bath composition crystallized to produce a coarseness on the plating surface, or the bath viscosity became higher and it became difficult to remove hydrogen at the cathode. The optimal bath temperature is in the range of 24 ° C to 28 ° C. In addition, by using a bath temperature of 24 ° C to 28 ° C, good plating can be performed even when the current density is low. The bent cathode test, which tends to be performed separately, is also confirmed. .

(Evaluation 3: Bath concentration)

In order to suppress the decrease of the bath viscosity or the crystallization of the bath liquid to improve the uniform plating property, the concentration of the bath composition itself is reduced to implement a Hall bath test. Specifically, the bath composition is set to 4/5 (the concentration of Cr ³⁺ ions is 0.8 mol / L, formic acid and urea are 0.4 mol / L, respectively), and ^3/5 (the concentration of Cr ³⁺ ions is 0.6 mol / L, Formic acid and urea were 0.3 mol / L respectively, and 1/2 (0.5 mol / L of Cr ³⁺ ion concentration, and 0.25 mol / L for formic acid and urea were respectively). Hall bath tests were performed at a bath temperature of 25 ° C. The results are shown in Table 3 and Fig. 7. It is also clear from Table 3 or FIG. 7 that in the “Evaluation 3”, a good plating film was obtained when the bath concentration was low. Furthermore, it was also confirmed in a curved cathode test conducted separately that the best results were obtained in a plating solution having a composition of 0.5 times.

[table 3]

(Evaluation 4: Addition amount of formic acid and urea 1)

As a result of "Evaluation 3", the bath concentration was further reduced. Specifically, the Hall composition test was performed with the bath composition set to 1/4 and 1/10. As a result, although the uniform plating property was further improved, abnormal precipitation of the plating was visible. Therefore, the chromium ion concentration is set to 1/4 (0.25 mol / L) and 1/10 (0.1 mol / L), and the formic acid or urea is restored to the original concentration (0.5 mol / L). As a result, as shown in Table 4 or FIG. 8, there was no abnormal precipitation, but the uniform plating property was reduced.

[Table 4]

(Evaluation 5: Addition amount of formic acid and urea 2)

Accepting the result of "Evaluation 4", an attempt was made to improve abnormal precipitation by changing the amounts of formic acid and urea. According to the results of the Hall groove test (refer to Tables 5 and 9), it can be seen that the uniformity of plating is reduced by lowering the concentration of formic acid to 0.1 mol / L and setting urea to the initial concentration (0.5 mol / L). Good and abnormal precipitation was suppressed.

[table 5]

Then, the concentration of urea was fixed to 0.5 mol / L, and the concentration of formic acid was changed from 0.1 mol / L to 0.22 mol / L to confirm whether the uniform plating property was improved. The results are shown in Table 6 and Fig. 10.

[TABLE 6]

It can be seen from the table or graph that good results are obtained when the concentration of formic acid is 0.2 mol / L or less.

Further, the formic acid was evaluated for the low concentration of formic acid. The results are shown in Table 7 and Fig. 11.

[TABLE 7]

It can be seen from the table or the graph that good results are obtained when the concentration of formic acid is 0.05 mol / L or more. Using a cathode having a recessed portion in which a short metal plate is bent and turned into a "U-shape" in a side view, a curved cathode test was performed under the same conditions as those shown in Tables 6 and 7, and the results were confirmed. In a range of a concentration of formic acid of 0.05 mol / L or more and 0.1 mol / L or less, plating is performed in a range of 60% or more even in the recessed portion.

Regarding the plating solution for trivalent chromium plating containing chromium sulfate as described above, it was confirmed that the concentration of Cr ³⁺ ions was set to a range of 0.1 mol / L or more and 1 mol / L or less. When the concentration is set to 0.05 mol / L or more and 0.2 mol / L or less, good uniform plating properties are exhibited. In addition, it was confirmed that the plating solution exhibited particularly good uniform plating properties in a range of Cr ³⁺ ion concentration in a range of 0.1 mol / L to 0.3 mol / L. Furthermore, it was confirmed from the above evaluation that it is effective to set the bath temperature in the plating bath to 20 ° C or higher and less than 40 ° C. It can also be known from this situation that according to the present invention, a plating solution for trivalent chromium plating having excellent uniformity can be provided, thereby expanding the application range of environmentally-friendly plating products.

no

FIG. 1 is a graph showing the relationship between the current density and the thickness of a plating layer in hexavalent chromium plating and trivalent chromium plating disclosed in general literature and the like. FIG. 2 is a graph showing the relationship between the current density and the thickness of a plating layer in trivalent chromium plating using the plating solution of the present invention. FIG. 3 is a graph showing the results of a Hall cell test using a plating solution according to an embodiment. FIG. 4 is a graph showing the results obtained by measuring the thickness of a plating layer using a fluorescent X-ray film thickness measuring device. FIG. 5 is a graph showing the results of a Hall cell test using a plating solution according to another embodiment. FIG. 6 is a graph showing the results obtained by measuring the thickness of a plating layer using a fluorescent X-ray film thickness measuring device. FIG. 7 is a graph showing the results of a Hall cell test using a plating solution according to another embodiment. FIG. 8 is a graph showing the results of a Hall cell test using a plating solution according to another embodiment. FIG. 9 is a graph showing the results of a Hall cell test using a plating solution according to another embodiment. FIG. 10 is a graph showing the results of a Hall cell test using a plating solution according to another embodiment. FIG. 11 is a graph showing the results of a Hall cell test using a plating solution according to another embodiment.

Claims (3)

A plating solution for trivalent chromium plating, which contains chromium sulfate and formic acid. The concentration of Cr ³⁺ ions is 0.1 mol / L or more and 1 mol / L or less. The concentration of the formic acid is 0.05 mol / L. L or more and 0.2 mol / L or less. For example, the plating solution of claim 1 is used for trivalent chromium plating with a thickness of 5 μm or more. A method for manufacturing a plated product is a plating step in which plating is performed in a plating bath containing a plating solution containing chromium sulfate, and a plating process in which trivalent chromium plating is performed by the plating step is produced. For the product, in the above-mentioned plating step, a plating solution having a Cr ³⁺ ion concentration of 0.1 mol / L or more and 1 mol / L or less is used as the above-mentioned plating solution, and the bath temperature in the above-mentioned plating bath is set to 20 ° C. or more and less than 40 ° C., and the current density in the above plating is set to 2 A / dm ² or more and 20 A / dm ² or less.