JP2010031329A - Nickel plating bath - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nickel plating bath which is excellent in uniform electrodeposition properties and with which plating cost is reduced. <P>SOLUTION: The nickel plating bath contains nickel chloride hexahydrate in an amount of 4-100 g/L and sodium citrate dihydrate in an amount of 50-300 g/L, and in the nickel plating bath, a pH buffer agent such as boric acid is not contained or contained in a concentration of not higher than the saturated concentration, while nickel sulfate hexahydrate is not contained or contained in an amount of not higher than 30 g/L, and pH is set to be 6.5 to 10. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nickel plating bath excellent in throwing power.

  As a nickel plating bath that has been practically used in the past, Watt bath (nickel plating bath having a composition of nickel sulfate 240 to 300 g / L, nickel chloride 45 to 50 g / L, boric acid 30 to 40 g / L) and There is a sulfamic acid bath (a nickel plating bath composed of nickel sulfamate 300 to 450 g / L, nickel chloride 0 to 15 g / L, boric acid 30 to 40 g / L). The Watt bath is excellent in current efficiency and has been developed for brighteners and stress relieving agents, so that it can be suitably used as decorative plating. In addition, since the sulfamic acid bath has a feature that the stress of the plating film is small, it is suitable for performing thick plating such as electroforming.

  However, nickel plating using these watt baths and sulfamic acid baths has a problem in throwing power. For example, when nickel plating is applied to deep-drawn press products, when using a Watt bath or a sulfamic acid bath, it is difficult to apply plating to the deeply drawn inside, the nickel plating film becomes thin, and corrosion resistance is reduced. It tends to be insufficient. On the other hand, current tends to concentrate on the convex portions of the object to be plated, and plating has become too thick, resulting in problems such as poor dimensional accuracy.

  As a method for improving the uniform electrodeposition of nickel plating, an auxiliary electrode is inserted into a deeply squeezed interior, or a shielding object is installed in the vicinity of a convex portion. However, installation of auxiliary electrodes and shields is time consuming, resulting in a decrease in productivity and an increase in cost for plating.

  In this regard, if an electroless nickel plating bath excellent in uniform electrodeposition is used, a nickel plating layer having a uniform film thickness can be formed. However, the plating speed of electroless nickel plating is slow, and it must be kept in the plating bath for a long time. In addition, since a reducing agent is required to reduce nickel ions to metal, there is a problem that the plating cost increases, and further, a waste liquid treatment for discarding the used plating bath is required. . In particular, when hypophosphorous acid is used as the reducing agent, the waste liquid contains a large amount of phosphorus, which may cause environmental pollution such as eutrophication of rivers and lakes.

  For this reason, there has been a demand for a nickel plating bath that is excellent in uniform electrodeposition so that a nickel plating film having a uniform thickness can be obtained in any part regardless of the shape of the object to be plated. As such a plating bath, a nickel plating bath containing citric acid or a salt thereof has been proposed (Patent Document 1, Patent Document 2).

JP 2001-172790 A JP 2002-212775 A

  The present invention has been made in view of the above-described conventional situation, and it is an object to be solved to provide a nickel plating bath which is excellent in uniform electrodeposition and low in plating cost.

  The inventors of the present invention have intensively studied to improve the throwing power of the nickel plating bath. As a result, nickel chloride and / or nickel sulfate as a nickel ion source contains 1 g / L to 20 g / L in terms of nickel ion concentration, and citric acid contains 50 g / L to 300 g / L in terms of citric acid / monohydrate. The inventors have found that a nickel plating bath whose pH is adjusted to 6.5 to 10 with ammonia exhibits excellent throwing power, and has already filed a patent application (Japanese Patent Application No. 2007-231095). Further, as a result of earnest research on nickel plating baths having even more uniform electrodeposition, excellent uniform electrodeposition in nickel plating baths of pH buffer system such as nickel chloride-sodium citrate-boric acid. The composition range of the plating bath having the properties was found and the present invention was completed.

  That is, the nickel plating bath of the present invention contains 4 g / L to 100 g / L of nickel chloride hexahydrate, 50 g / L to 300 g / L of sodium citrate dihydrate, and contains a pH buffer. Or no saturation concentration or less, nickel sulfate hexahydrate is not contained or 30 g / L or less, and the pH is 6.5 to 10.

  In the nickel plating bath of the present invention, sodium citrate dihydrate is contained in a large amount of 50 g / L to 300 g / L, and a conventional nickel citrate plating bath (the nickel citrate described in Patent Document 1 above) is contained. The citric acid concentration of the plating bath is higher than that of 12 g / L to 21 g / L). The concentration of nickel chloride hexahydrate in the plating bath is 4 g / L to 100 g / L (0.89 to 22.3 g / L in terms of nickel ion concentration), which is described in Patent Document 1 above. It is lower than the nickel ion concentration in the conventional nickel citrate plating bath and the preferred nickel ion concentration range (15 g / L to 80 g / L) in the nickel citrate plating bath of Patent Document 2. Furthermore, nickel sulfate contained in a large amount as a nickel ion source in a conventional watt bath or the like is as low as 30 g / L or less. Moreover, pH is set to 6.5-10, and it is made high compared with the pH of the conventional nickel citrate plating bath described in the said patent document 1 being 3-5.

  Thus, there is a great difference in the bath composition between the nickel plating bath of the present invention and the conventional nickel citrate plating bath. It is considered that the role of sodium citrate contained in the nickel plating bath of the present invention functions as a nickel ion complexing agent rather than as a pH buffering agent. That is, in the conventional nickel citrate plating bath, since the concentration of nickel ions with respect to citric acid is high and the pH is low, it can be said that citric acid is added as a pH buffer rather than as a complexing agent of nickel ions. On the other hand, in the nickel plating bath of the present invention, since the nickel ion concentration is low, the amount of citric acid added is extremely large, and the pH is high, citric acid functions as a complexing agent for nickel ions. It is thought that there is. For this reason, in the nickel plating bath of the present invention, nickel from a state in which nickel ions are complexed is precipitated, which is very excellent in electrodeposition, unlike the conventional nickel citrate plating bath. It is presumed that this is the cause of the formation of a nickel plating film.

Further, the nickel plating bath of the present invention does not contain a pH buffer or has a saturation concentration or less. The reason why nickel plating is possible without including a pH buffer is considered to be due to the role of sodium citrate dihydrate as a pH buffer. Here, the pH buffering agent is added to obtain a normal nickel plating film by preventing the vicinity of the nickel plating surface from shifting to alkali by OH ⁻ ions generated by electrochemical reduction of water. A drug. As such a pH buffering agent, those widely used in the plating industry can be used. Examples thereof include boric acid, malic acid, citric acid, maleic acid, fumaric acid, glycolic acid, glutaric acid, L-glutamic acid, acetic acid, propionic acid, and salts thereof.
The inventors have confirmed that the use of boric acid as a pH buffering agent enables nickel plating having excellent throwing power.

  Further, in the plating bath of the present invention, nickel is deposited by electroplating as in the case of the conventional watt bath and sulfamic acid bath, so that it is not necessary to add a reducing agent unlike the electroless nickel plating bath. Further, a nickel plating film having a uniform thickness can be formed without installing an auxiliary electrode or a shield. For this reason, the plating cost is also low.

  Sodium citrate may be added as an anhydride in addition to dihydrate, or citric acid may be neutralized with sodium hydroxide. In these cases, it may be contained in an amount of 50 g / L to 300 g / L in terms of sodium citrate dihydrate.

  In the nickel plating bath of the present invention, it is also preferable that a brightener and / or a stress relaxation agent is added. If a brightening agent is added, it can be made into nickel plating with a uniform appearance in a wide current density range, and can therefore be used as decorative nickel plating. Moreover, if a stress relaxation agent is added, the stress of a nickel plating film is relieved and it can prevent becoming abnormal plating, such as a crack.

  Since the nickel plating bath of the present invention uses nickel chloride as the nickel source, the solubility of the nickel anode is good. The addition amount of nickel chloride hexahydrate needs to be in the range of 4 g / L to 100 g / L. When the addition amount of nickel chloride hexahydrate is less than 4 g / L, when nickel plating is continuously performed, the fluctuation rate of the nickel ion concentration becomes large, and bath management of the nickel ion concentration becomes difficult. Also, when the addition amount of nickel chloride hexahydrate exceeds 100 g / L, when the anode is made of nickel, the nickel ions are excessively dissolved by the influence of chlorine ions, and the nickel ion concentration is increased. Bath management becomes difficult. A more preferable nickel chloride hexahydrate concentration range is 8 g / L to 80 g / L.

  The sodium citrate dihydrate preferably contains 50 g / L to 300 g / L. When the amount of sodium citrate dihydrate added is less than 50 g / L, the complexation of nickel does not proceed and the throwing power decreases. On the other hand, when sodium citrate dihydrate exceeds 300 g / L, the limit of solubility is approached, and thus citric acid may not be completely dissolved and may precipitate in winter.

  In the nickel plating bath of the present invention, nickel sulfate needs to be 30 g / L or less in terms of hexahydrate. According to the test results of the present inventors, when nickel sulfate exceeds 30 g / L in terms of hexahydrate, the plating film turns black, resulting in abnormal precipitation or precipitation. In particular, when the amount of nickel chloride hexahydrate is 80 g or more, the throwing power is extremely lowered when nickel sulfate exceeds 30 g / L in terms of hexahydrate.

  In addition, boric acid may be added to serve as a pH buffering agent, but in the plating bath of the present invention, citrate ions serve as a pH buffering agent, so no boric acid is added at all. However, a good nickel plating film can be obtained.

  The pH of the nickel plating bath of the present invention is preferably 6.5 to 10. If it is less than 6.5, a portion having a small current density will not be able to form a normal plating film, and the appearance will be burnt. Moreover, when pH exceeds 10, there exists a problem that a deposit arises in a plating solution. In the nickel plating bath of the present invention, the pH tends to be slightly higher when electroplating is performed, but an acid such as hydrochloric acid can be used to adjust the pH.

  Examples of the brightener used in the present invention include acetylene derivatives such as butynediol, saccharin, and hexynediol. Examples of the stress relaxation agent used in the present invention include benzenesulfonic acid and naphthalenedisulfonic acid.

  When nickel plating is performed using the nickel plating bath of the present invention, nickel is preferably used as the anode. If it is like this, the nickel ion in a plating bath will be replenished from a nickel anode, and will not change easily. Moreover, what is necessary is just to select the bath temperature of a plating bath suitably, but 30-50 degreeC is preferable. If the temperature exceeds 50 ° C., the evaporation of the liquid is promoted, the amount of energy consumption increases, and the working environment becomes worse. Moreover, if it is less than 30 degreeC, a cooling device will be needed according to a season.

Hereinafter, the Example which actualized the nickel plating bath of this invention is further explained in full detail.
Example 1
A nickel plating bath was constructed according to the following procedure. That is, sodium citrate dihydrate was added to water at 200 g / L, nickel chloride hexahydrate was added at 80 g / L, and boric acid was added at 40 g / L. Nickel plating bath. The plating bath has a pH of 5.8 and contains 19.77 g / L of nickel ions in terms of nickel ion concentration.

(Example 2)
In Example 2, the concentration of nickel chloride hexahydrate was 40 g / L. This plating bath contains 9.89 g / L of nickel ions in terms of nickel ion concentration. Others are the same as the nickel plating bath of Example 1, and description is abbreviate | omitted.

(Example 3)
In Example 3, sodium citrate dihydrate was 100 g / L, and the concentration of nickel chloride hexahydrate was 40 g / L. This plating bath contains 9.88 g / L of nickel ions in terms of nickel ion concentration. Others are the same as the nickel plating bath of Example 1, and description is abbreviate | omitted.

Example 4
In Example 4, sodium citrate dihydrate was 300 g / L, and the concentration of nickel chloride hexahydrate was 80 g / L. This plating bath contains 19.77 g / L of nickel ions in terms of nickel ion concentration. Others are the same as the nickel plating bath of Example 1, and description is abbreviate | omitted.

(Example 5)
In Example 5, sodium citrate dihydrate was 200 g / L, and the concentration of nickel chloride hexahydrate was 60 g / L. This plating bath contains 14.84 g / L of nickel ions in terms of nickel ion concentration. Others are the same as the nickel plating bath of Example 1, and description is abbreviate | omitted.

(Examples 6 to 10)
In Examples 6 to 10, a nickel plating solution having the following composition was used, and the addition amount of nickel sulfate hexahydrate was 1 g / L in Example 12, 5 g / L in Example 13, and 10 g / L in Example 14. In Example 15, it was 20 g / L, and in Example 16, it was 30 g / L.
Potassium citrate monohydrate 200g / L
Nickel chloride hexahydrate ... 80g / L
Nickel sulfate hexahydrate .... 1-30g / L
Boric acid ... 40g / L

(Examples 11-14)
In Examples 11 to 14, a nickel plating solution having the following composition was used, and the amount of boric acid added was 10 g / L in Example 11, 20 g / L in Example 12, 30 g / L in Example 13, and 40 g in Example 14. did.
Potassium citrate monohydrate 200g / L
Nickel chloride hexahydrate ... 80g / L
Boric acid ... 10-40g / L

(Example 15)
In Example 15, a nickel plating solution having the following composition was used, and boric acid was not added.
Potassium citrate monohydrate 200g / L
Nickel chloride hexahydrate ... 40g / L
pH ... 9.0

(Example 16)
In Example 16, a nickel plating solution having the following composition was prepared using DL-malic acid as a pH buffer.
Potassium citrate monohydrate 200g / L
Nickel chloride hexahydrate ... 80g / L
DL-malic acid ... 40g / L

(Comparative Example 1)
Comparative Example 1 is a Watt bath having the following composition.
Nickel sulfate hexahydrate 240g / L
Nickel chloride hexahydrate ... 45g / L
Boric acid 30g / L
pH ... 3.38 (After adding basic nickel carbonate and filtering, dilute sulfuric acid
To adjust)

(Comparative Example 2)
In Comparative Example 2, potassium citrate was used in place of sodium citrate to obtain a plating solution having the following composition.
Potassium citrate monohydrate 200g / L
Nickel chloride hexahydrate ... 80g / L
Boric acid ... 40g / L
pH 5.5

(Comparative Example 3)
In Comparative Example 3, potassium citrate monohydrate was 100 g / L and nickel chloride hexahydrate was 40 g / L. About others, it is the same as that of the comparative example 2, and abbreviate | omits description.

(Comparative Example 4)
Comparative Example 4 is a nickel plating bath having the following bath composition, and the amount of nickel sulfate hexahydrate added is increased to 40 g / L.
Sodium citrate dihydrate 200g / L
Nickel chloride hexahydrate ... 80g / L
Nickel sulfate hexahydrate ... 40g / L
Boric acid ・ ・ ・ 40g / L
pH: 4.7

(Comparative Example 5)
In Comparative Example 5, the addition amount of nickel sulfate hexahydrate was further increased to 80 g / L, and the pH was 4.4. About others, it is the same as that of the comparative example 4, and abbreviate | omits description

<Evaluation of throwing power>
Evaluation of throwing power was performed by the Hull cell test. That is, as shown in FIG. 1, a plating tank 1 having a trapezoidal square cross section is used. As shown in FIG. The nickel anode plate 4 is inserted so as to be in contact with the metal plate, and the brass plate 5 is inserted so as to be in contact with the long surface 3. The brass plate 5 is 100 mm × 65 mm, and the nickel anode plate 4 is 63.5 mm. Further, the width X on the short side of the surfaces facing each other in parallel in the plating tank 1 is 47.6 mm, the width Y on the long side is 127 mm, and the depth D is 63.5 mm. 267 mL of a plating bath was placed in the plating tank 1. A constant current power source 6 was prepared as a power source for plating, the anode side was connected to the nickel anode plate 4, and the cathode side was connected to the brass plate 5.

In the hull cell test, 267 mL of a nickel plating bath was placed in the plating tank 1, and the electroplating was performed for a predetermined time with a predetermined constant current using an electric heater and a temperature control device (not shown). And the film thickness of the plating film was measured with the fluorescent X-ray film thickness meter. 2 points (points OA = 5 mm, OB = 20 mm, OC = 81 mm from the end) shown in FIG. 2 and (film thickness at point B) / (point C) The throwing power was evaluated by the values of (film thickness) and (film thickness at point A) / (film thickness at point C). In the hull cell test, the shorter the distance between the anode and the cathode, the larger the current density, and (film thickness at point B) / (film thickness at point C) / (film thickness at point A) / (film thickness at point C). The closer the value of) to 1, the better the electrodeposition. In the hull cell test, when the distance from each point of the brass plate 5 on the cathode side to the nickel anode plate 4 is L, the theoretical current density i not considering the overvoltage at that point is I as the total current. If
i = I (5.10-5.24 logL)
Can be calculated with Thus the current density of the computed each point becomes 1.0A / dm ² at 20.0A / dm ^2, B point in 10.5A / dm ^2, C the point at point A in the constant current is 3A.

<Result>
Table 1 shows the results of the hull cell test performed for the nickel plating bath of Example 1 while changing the plating time.

  The results are shown in Table 1. From this table, it can be seen that in Example 1, the B / C and A / C values are close to 1 and the throwing power is extremely excellent as compared with Comparative Example 1 using a Watt bath. In addition, in the nickel plating bath of Example 1, it was found that the thickness was increased by increasing the plating time, and thick plating of 10 μm or more was possible.

Further, using the nickel plating bath of Example 1, the hull cell test (3A, 3 minutes) was continuously performed 10 times. As a result, as shown in Table 2, excellent uniform electrodeposition was stably obtained, and the film thickness was also stable.

In addition, the nickel plating solutions of Examples 1 to 5 and Comparative Example 1 are 3A (2A in Comparative Example 1) and 40 minutes (however, 3 minutes in Example 1, 20 minutes in Example 5, and 3 minutes in Comparative Example 1). ) Was conducted. As a result, as shown in Table 3, the nickel plating baths of Examples 1 to 5 showed much better throwing power as compared with the watt bath of Comparative Example 1. Among them, Examples 1, 2, 5 and 300 g / L of Examples 1, 2, 5 and 300 g / L of sodium citrate dihydrate were less than 100 g / L of sodium citrate dihydrate. The uniform electrodeposition was superior to that of Example 3.

Further, the nickel plating solutions of Comparative Example 2 and Comparative Example 3 were subjected to a 3A, 10 minute hull cell test. As a result, as shown in Table 4, the throwing power was good, but normal plating was not formed at the portion where the current density was large, and the deposits were peeled off. This indicates that potassium citrate cannot be used in place of sodium citrate.

Further, the nickel plating solutions of Comparative Example 4 and Comparative Example 5 were subjected to a 3A, 10 minute hull cell test. As a result, as shown in Table 5, the throwing power was poor, and it was found that the throwing power worsened when the addition amount of nickel sulfate hexahydrate was increased. There also arises a problem that precipitates are formed in the plating solution.

On the other hand, sodium citrate dihydrate 200 g / L, nickel chloride hexahydrate 40 g / L, boric acid 40 g / L, and nickel sulfate hexahydrate varied in the range of 1 to 30 g / L. Table 6 shows the results of Examples 6 to 10 in which the influence was observed. From this table, when the addition amount of nickel chloride hexahydrate is as small as 40 g / L as compared with Comparative Examples 4 and 5, the addition amount of nickel sulfate hexahydrate is 30 g / L. It was found that if it was L or less, good throwing power could be obtained.

Moreover, Example 11-which changed sodium borate dihydrate 200g / L, made nickel chloride hexahydrate 80g / L, changed boric acid in the range of 10-30g / L, and examined the influence. The results of 14 are shown in Table 7. From this table, it was found that good uniform electrodeposition can be obtained when boric acid is in the range of 10 to 30 g / L.

Further, in Example 15 in which boric acid was not added, as shown in Table 8, good uniform electrodeposition was exhibited. This is presumably because the nickel plating solution of the present invention has a large amount of sodium citrate added, so that the buffering action by sodium citrate serves as an alternative to the buffering action of boric acid. .

Moreover, also in Example 16 using DL-malic acid as a pH buffer, as shown in Table 9, good throwing power was obtained.

  The present invention is not limited to the description of the embodiments and examples of the invention described above. Various modifications are also included in the present invention as long as those skilled in the art can easily conceive without departing from the scope of the claims.

  The present invention can be suitably used for nickel plating that requires particularly uniform electrodeposition, such as a deep-drawn press-formed product.

It is a perspective view of a hull cell. It is a top view in the state where a hull cell was connected to a constant current power supply.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Plating tank 4 ... Nickel anode plate 5 ... Brass plate 6 ... Constant current power supply

Claims (3)

  Contains 4 g / L to 100 g / L of nickel chloride hexahydrate, 50 g / L to 300 g / L of sodium citrate dihydrate, does not contain pH buffering agent, or is less than saturated concentration A nickel plating bath characterized by not containing nickel sulfate hexahydrate or 30 g / L or less and having a pH of 6.5 to 10.   The nickel plating bath according to claim 1, wherein the pH buffer is boric acid.   The nickel plating bath according to claim 1 or 2, wherein the concentration of nickel chloride hexahydrate is in the range of 8 g / L to 80 g / L.

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