JP6547232B2 - Plating solution and method of producing plated product - Google Patents

Description

  The present invention relates to a plating solution and a method for producing a plated product, and more particularly to a plating solution used for trivalent chromium plating and a method for producing a plated product to which trivalent chromium plating is applied.

  BACKGROUND ART Conventionally, plated products in which chromium plating is performed on metal products and plastic products are widely used. In the production of this type of plating product, the use of plating solutions containing environmentally friendly trivalent chromium in place of plating solutions containing hexavalent chromium is increasing (see Patent Document 1 below).

JP 2000-249340 A

  With the recent increase in environmental awareness, there is a strong demand for replacing trivalent chromium plating with trivalent chromium plating. However, since trivalent chromium plating is inferior to hexavalent chromium plating in coverage of the product to be plated, situations where it is adopted at present are limited. In addition, in the case of trivalent chromium plating, the relationship between the current density and the deposition thickness of the plating is difficult to be linear and it is difficult to exhibit uniform electrodeposition. As such, in the case of decorative plating with a plating thickness of several μm, there are cases where adoption of trivalent chromium plating can be seen, but in the case of producing plating products with complex shapes such as molds The adoption of trivalent chromium plating has hardly advanced in such a situation. Therefore, the present invention provides a plating solution capable of producing a plating product equivalent to hexavalent chromium plating while being a plating solution for trivalent chromium plating, and aims to expand the application range of environmentally friendly plating products. And

The inventors of the present invention conducted intensive studies to achieve the above object. According to the plating solution containing chromium sulfate, the plating solution contains hexavalent chromium by adjusting the concentration of Cr ³⁺ ions within a specific range. It has been found that the plating solution has the same throwing power as the contained plating solution, and the present invention has been completed.

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

Moreover, this invention implements the plating process which electroplates with the plating bath which accommodated the plating solution containing chromium sulfate, The manufacturing method of the plating product which produces the plating product in which trivalent chromium plating was given by this plating process In the plating step, a plating solution having a concentration of 0.1 mol / L or more and 1 mol / L or less of Cr ³⁺ ions is used as the plating solution, and a bath temperature in the plating bath is 20 ° C. or more and 40 ° C. Provided is a method for producing a plated product, wherein the current density in the electroplating is 2A / dm ² or more and 20A / dm ² or less.

  According to the present invention, a plating solution for trivalent chromium plating with excellent coverage is provided, so the opportunity for adopting environmentally friendly plating products can be expanded.

The related figure of the current density and plating thickness in hexavalent chromium plating and trivalent chromium plating currently indicated in general literatures etc. The figure which showed the relationship of the current density and plating thickness in trivalent chromium plating using the plating solution of this invention. The figure which showed the result of the Hull cell test using the plating solution of one embodiment. The figure which showed the result of having measured plating thickness with the fluorescent X ray type film thickness measuring device. The figure which showed the result of the Hull cell test using the plating solution of other embodiment. The figure which showed the result of having measured plating thickness with the fluorescent X ray type film thickness measuring device. The figure which showed the result of the Hull cell test using the plating solution of other embodiment. The figure which showed the result of the Hull cell test using the plating solution of other embodiment. The figure which showed the result of the Hull cell test using the plating solution of other embodiment. The figure which showed the result of the Hull cell test using the plating solution of other embodiment. The figure which showed the result of the Hull cell test using the plating solution of other embodiment.

Hereinafter, preferred embodiments of the present invention will be described.
First, a method of manufacturing a plated product will be described.
In the method of manufacturing a plated product according to the present embodiment, a pretreatment step for adjusting the surface properties of a product to be plated (hereinafter, also referred to as an original product), and a pretreated original product (hereinafter referred to as The plating step is carried out to apply trivalent chromium plating to a "pre-treated product". In the method of manufacturing a plated product according to the present embodiment, a base plating step of subjecting the pre-treated product to base plating between the pre-treatment step and the plating step, and a pre-plated pretreated product (hereinafter referred to as An intermediate plating step may be performed in which intermediate plating is further performed on the “base-plated product”). In this case, trivalent chromium plating is carried out as finish plating on a product subjected to intermediate plating (hereinafter also referred to as "intermediate plated product").

  In the method of manufacturing a plated product according to the present embodiment, the product to which trivalent chromium plating has been applied in the plating step may be further subjected to chemical surface treatment, heat treatment or the like. Moreover, you may apply coating, such as a clear coating, to a plating product as needed.

  Examples of the base product to be subjected to the pretreatment step include resin products, ceramic products, metal products, composite products in which resin parts and metal parts are combined, and composite products in which metal parts are coated with ceramics, etc. It can be mentioned. As a resin which forms an original product, a general thermoplastic resin and a thermosetting resin are mentioned, for example. The resin may be fiber reinforced plastic (FRP) or the like. As said ceramics which form an original product, the general thing which has a silicon oxide, an aluminum oxide, etc. as a main component is mentioned, for example. The ceramic may be a glass such as a crucible. As said metal which forms an original product, general metals, such as iron and copper, are mentioned, for example. The metal may be an alloy or the like. Examples of pretreatment for such an original product include mechanical polishing, honing, polishing by blasting, and degreasing such as alkaline degreasing. In the base plating step and the intermediate plating step, nickel plating, copper plating, iron plating, etc. with a thickness of several μm on a pre-treated product or a base plated product for the purpose of improving the appearance and corrosion resistance of finished plated products. Various plating can be applied.

  In the plating step of applying trivalent chromium plating, electroplating using a pre-treatment product, a base plating product, an intermediate plating product or the like as a work is performed. In the electroplating, the work is plated with trivalent chromium using a plating bath containing a plating solution containing chromium sulfate. The plating solution used in the plating step will be described in detail below.

In the plating step, it is important to use a plating solution having a Cr ³⁺ ion concentration of 0.1 mol / L or more and 1 mol / L or less as the plating solution in order to perform plating with good throwing power on the work. is there. The plating solution can contain, in addition to chromium sulfate as a main component, a complexing agent, a pH buffer, a conductive agent, a surfactant, and the like. In addition, as water used as a solvent of this plating solution, industrial water, tap water, ion exchange water, distilled water, pure water etc. are mentioned, for example.

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 preferable plating solution, coverage of trivalent chromium plating on a work in a plating process can be made better.

In the plating solution of the present embodiment, part of the chromium sulfate contained as a source of Cr ³⁺ ions is replaced with one or more selected from the group consisting of chromium chloride, basic chromium sulfate, chromium alum and chromium nitrate. However, if a large amount of chromium hydrochloride is contained, chlorine gas may be generated at the anode at the time of plating, and if a large amount of chromium nitrate is contained, the current density may be reduced at the time of plating. Therefore, the proportion of chromium sulfate in the source of Cr ³⁺ ions in the plating solution is preferably 90 mol% or more. The proportion of chromium sulfate is more preferably 95 mol% or more, and still more preferably 99 mol% or more. It is particularly preferred that the source of Cr ³⁺ ions in the plating solution is essentially only chromium sulfate.

  An organic acid or a salt thereof can be used as the complexing agent to be contained in the plating solution of the present embodiment. 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, ethylenediaminetetraacetic acid and the like. Examples of these salts include alkali metal salts such as lithium salts, potassium salts, alkali metal salts such as sodium salts, magnesium salts and calcium salts. Above all, formic acid is a particularly effective component as a complexing agent, and it is important that the formic acid is contained in the plating solution so as to have 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 above-mentioned organic acids and salts thereof exhibit a certain effect or more even as the above-mentioned pH buffer. Moreover, as said complexing agent, you may employ | adopt aminocarbonyl compounds, such as urea and carbamic acid. Among these, urea has a function as a pH buffer, functions as a nitrogen source for the plating film, and is effective for hardening the film. Further, urea can be expected to have the effect of suppressing the formation of precipitates such as chromium hydroxide in the plating solution. From such a point, it is preferable that the urea be contained in the plating solution so as to have a concentration of 0.1 mol / L or more and 1 mol / L or less. The concentration of the urea in the plating solution is more preferably 0.2 mol / L or more and 0.8 mol / L or less, and particularly preferably 0.4 mol / L or more and 0.6 mol / L or less.

  Other than those mentioned above, examples of usable ones as the pH buffer include boric acid and borate. When the boric acid is contained in the plating solution, the concentration is usually 0.5 mol / L or more and 1 mol / L or less depending on the amount of the organic acid, urea, etc. contained as the pH buffer. Contained in the plating solution. The pH of the plating solution is preferably adjusted to 1 or more and 2 or less with a pH buffer or the like, and more preferably adjusted to a pH 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, potassium nitrate and the like. Examples of the surfactant include sodium lauryl sulfate, sodium dodecyl sulfate, polyethylene glycol, diisohexyl sulfosuccinate, 2-ethylhexyl sulfate, diisobutyl sulfosuccinate, diisoamyl sulfosuccinate, and isodecyl sulfosuccinate.

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

  In the plating step using a plating solution containing such components, it is important to set the bath temperature in the plating bath to 20 ° C. or more and less than 40 ° C. The lower the temperature of the plating bath in the plating step, the better the coverage of the trivalent chromium plating on the work can be. On the other hand, when the bath temperature of the plating bath has a certain temperature or more, the deposition of the components contained in the plating solution can be suppressed, and generation of roughness on the plating surface can be suppressed. In such a point, the bath temperature of the plating bath in the plating step is more preferably 23 ° C. or more and 29 ° C. or less, and particularly preferably 24 ° C. or more and 28 ° C. or less. By carrying out the plating process under such a preferable temperature condition, it is possible to provide a plated film having uniform thickness and excellent surface gloss to a finished plated product.

In electroplating in the plating step, it is important to set the current density to 2 A / dm ² or more and 20 A / dm ² or less. The current density is more preferably 2A / dm ² or more 15A / dm ² or less, and particularly preferably 2A / dm ² or more 13A / dm ² or less. Conducting plating at such a preferable current density can improve the coverage of trivalent chromium plating on a work.

  In the plating step, bubbles are generated by hydrogen gas in the plating solution, so that vibration is given to the workpiece during plating to suppress adhesion of the bubbles to the workpiece, or bubbles are generated by inert gas from below the workpiece. Alternatively, bubbling may be performed.

  With regard to various conditions in the plating process such as the concentration of the components of the plating solution as described above, the bath temperature of the plating solution, the current density given to the work, etc. Although the effect is not exhibited unless it is kept within such a range, it is preferable to be under almost the same conditions as the start of plating in all periods.

  In the plating step of the present embodiment, chromium plating is applied to the same thickness as the flat portion even in a portion where the plating thickness is easily different from the flat portion in the conventional case, such as a corner portion or a minute uneven portion of a work In addition to trivalent chromium plating, the same throwing power and uniform electrodeposition as hexavalent chromium plating are exhibited. The plating thickness of the plated product manufactured in the present embodiment may be appropriately set according to the application of the plated product, etc., but in order to more effectively exhibit the effects of the present invention, trivalent plating excluding the base plating etc. It is preferable to set the plating thickness of only the chromium plating portion to 5 μm or more and 600 μm or less. The plating thickness is more preferably 50 μm or more, particularly preferably 100 μm or more. When the plating thickness needs to be measured, for example, it may be measured by a fluorescent X-ray film thickness meter or the like. However, if the plating thickness is 50 μm or more, measurement with a fluorescent X-ray film thickness meter becomes difficult, and in such a case, cross-sectional observation of a plated product with a scanning electron microscope (SEM) is carried out Good. And the said plating thickness can be calculated | required by measuring the plating thickness of a metal-plating product in several places selected at random, and carrying out the arithmetic mean of the measurement result except an abnormal value.

Although the detailed description above will not be repeated here, the method for producing a plated product according to the present embodiment and the plating solution used for plating may be conventionally known even if there is no specific illustration thereof. The technical matters in the above can be suitably adopted within the range where the effects of the present invention are not significantly impaired.
That is, the present invention is not limited to the above exemplified range.

  EXAMPLES The present invention will next be described in more detail by way of examples, which should not be construed as limiting the invention thereto.

(Summary of the invention: Difference from conventional trivalent chromium plating)
The relationship between the current density and the plating thickness in hexavalent chromium plating and trivalent chromium plating disclosed in the general literature and the like is shown in FIG.
From this figure, it can be seen that in the conventional trivalent chromium plating, the slope of the straight line indicating the relationship between the current density and the plating thickness is sharply increased near the current density of 5 A / dm ² , making uniform electrodeposition difficult to be exhibited. .
Further, it can be understood from this figure that in conventional trivalent chromium plating, it is difficult to perform plating at a current density of 5 A / dm ² or less, and it is difficult to perform plating with excellent spinnability.

On the other hand, when the plating solution of the present invention is used, the relationship between the current density and the plating thickness is as shown in FIG. 2, and it is 3 at a low current density of 5 A / dm ² or less similar to hexavalent chromium plating. Valence chromium plating is possible.
When the plating solution of the present invention is used, the relationship between the current density and the plating thickness is linear from the area of low current density of 5 A / dm ² or less to the area of high current density near 30 A / dm ^2. It becomes possible to carry out plating that is excellent in uniform electrodeposition.
Therefore, it can be seen from this figure that the present invention also provides a plating solution for trivalent chromium plating which is excellent in throwing power and uniform electrodeposition.
The examination results will be described in detail below on this point.

(Evaluation 1: Bath temperature 1)
The plating solution was prepared to have the contents of the formulation shown in Table 1.
That is, a plating solution containing chromium sulfate and having a concentration of Cr ³⁺ ion of 1 mol / L was prepared.
Formic acid and urea were added to the plating solution to a concentration of 0.5 mol / L, respectively.
The plating solution was prepared to have a pH of 1.5.

A Hull cell test was conducted at a current value of 5 A using the above plating solution.
The tests were conducted 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.

Moreover, the plating thickness of the sample after the test was measured by a fluorescent X-ray type film thickness measuring device.
The results are shown in FIG.
From the results shown in Table 1 and FIG. 4, it was found that when the concentration of Cr ³⁺ ions is 1 mol / L or less, a plating thickness of a certain level or more can be ensured even in a low current density state.
Further, from the results shown in Table 1 and FIG. 4, it was found that setting the bath temperature to less than 40 ° C. is advantageous for performing trivalent chromium plating with excellent roundness.

(Evaluation 2: Bath temperature 2)
Based on the results of "Evaluation 1", the bath temperature is further subdivided, and the Hull cell test is performed at 24 bath temperatures of 24 ° C, 26 ° C, 28 ° C, 30 ° C and 32 ° C. The test results were evaluated.
The results are shown in Table 2, FIGS.

It can also be understood from this table and figures that, in the bath temperature range of 24 ° C. to 28 ° C., the deposition of the plated film at each current density can be made to have a substantially constant speed.
Further, it was found that the improvement of the throwing power was most observed at a bath temperature of 24 ° C., and it was found that it was better to perform plating at a lower bath temperature.
Therefore, it was also considered to lower the temperature of the bath, but if the temperature of the bath is lowered too much, part of the bath composition crystallizes to cause roughness on the plating surface, and the bath viscosity increases to make it difficult to remove hydrogen at the cathode. The bath temperature was judged to be optimum in the range of 24 ° C. to 28 ° C. because it was recognized.
In addition, by adopting a bath temperature of 24 ° C. to 28 ° C., the tendency for good plating to be possible even when the current density is low was confirmed also in the separately conducted bent cathode test.

(Evaluation 3: Bath concentration)
The Hull cell test was conducted by lowering the concentration of the bath composition itself in order to suppress the reduction of the bath viscosity and the crystallization of the bath liquid to improve the throwing power.
Specifically, the bath composition 4/5 (concentration 0.8 mol / L of ^{Cr 3+} ions, formic acid and urea, respectively 0.4mol / L), 3/5 ( concentration of ^{Cr 3+} ion 0.6 mol / L formic acid The Hull cell test was carried out at a bath temperature of 25 ° C. with each of 0.3 mol / L of urea and urea (0.5 mol / L of Cr ³⁺ ion concentration, 0.25 mol / L of formic acid and urea each).
The results are shown in Table 3 and FIG.
As apparent from Table 3 and FIG. 7, it was found that in this “Evaluation 3”, a better plating film can be obtained when the bath concentration is low.
In addition, it has been confirmed also in the separately conducted bent cathode test that the best result is obtained with the plating solution in which the component is 0.5 times.

(Evaluation 4: Addition amount of formic acid and urea 1)
Based on the results of "Evaluation 3", a further reduction of the bath concentration was tried.
Specifically, the Hull cell test was performed with a bath composition of 1/4 and 1/10.
As a result, coverage was further improved, but abnormal deposition of plating was observed.
Therefore, formic acid and urea were returned to the initial concentration (0.5 mol / L) while the chromium ion concentration was set to 1/4 (0.25 mol / L) and 1/10 (0.1 mol / L).
As a result, as shown in Table 4 and FIG. 8, although abnormal deposition was eliminated, the result was a reduction in the throwing power.

(Evaluation 5: Addition amount of formic acid and urea 2)
Based on the results of “Evaluation 4”, we tried to improve the abnormal deposition by using formic acid and urea.
As a result of the Hull cell test (see Table 5 and FIG. 9), the concentration of formic acid is as low as 0.1 mol / L, and the urea has an initial concentration (0.5 mol / L). It turned out that it is suppressed.

Next, the concentration of urea was fixed at 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 throwing power was improved.
The results are shown in Table 6 and FIG.

  From this table and figures, it was found that good results were obtained when the concentration of formic acid was 0.2 mol / L or less.

In addition, formic acid was further reduced to evaluate its throwing power.
The results are shown in Table 7 and FIG.

From these tables and figures, it was found that good results were obtained when the concentration of formic acid was 0.05 mol / L or more.
The bent cathode test was conducted under the same conditions as shown in Tables 6 and 7 using a cathode provided with a recessed portion in which a strip-like metal plate is bent to make a side view “C” shape, and the concentration of formic acid It was confirmed that in the range of 0.05 mol / L or more and 0.1 mol / L or less, plating was applied in the range of 60% or more also in the recessed portion.

As described above, in the plating solution for trivalent chromium plating containing chromium sulfate, the concentration of Cr ³⁺ ions is in the range of 0.1 mol / L to 1 mol / L, and the concentration of formic acid is 0.05 mol / L or more. It has been confirmed that by setting the concentration to 2 mol / L or less, a good throwing power is exhibited.
Moreover, it has been confirmed that the same plating solution exhibits particularly good throwing power when the concentration of Cr ³⁺ ions is in the range of 0.1 mol / L to 0.3 mol / L.
Furthermore, from the above evaluation, it was confirmed that it is effective to set the bath temperature in the plating bath to 20 ° C. or more and less than 40 ° C.
From these facts, it is understood that according to the present invention, a plating solution for trivalent chromium plating having excellent coverage is provided, and the application range of the environment-friendly plating product can be expanded.

Claims (3)

Plating solution used for trivalent chromium plating,
Containing chromium sulfate, formic acid and urea, and having a Cr ³⁺ ion concentration of 0.1 mol / L to 1 mol / L, and a formic acid concentration of 0.05 mol / L to 0.2 mol / L, of the urea The plating solution whose density | concentration is 0.1 mol / L or more and 1 mol / L or less .   The plating solution according to claim 1, which is used for trivalent chromium plating having a plating thickness of 5 μm or more. A method of producing a plated product, comprising performing a plating step of performing electroplating in a plating bath containing a plating solution containing chromium sulfate, and producing a plated product to which trivalent chromium plating has been applied by the plating step,
In the plating step,
The plating solution contains chromium sulfate, formic acid and urea, and the concentration of Cr ³⁺ ions is 0.1 mol / L to 1 mol / L, and the concentration of formic acid is 0.05 mol / L to 0.2 mol / L. In the following, using a plating solution in which the concentration of the urea is 0.1 mol / L or more and 1 mol / L or less
The bath temperature in the plating bath is 20 ° C. or more and less than 40 ° C., and
The manufacturing method of the metal-plating products which make the current density in the said electroplating ² or more ² dm < ² > or more and 20 A / dm < ² > or less.