JP2022111432A - Electrolytic silver plating bath and electrolytic silver plating method using the same - Google Patents

Abstract

To provide an electrolytic silver plating bath capable of suppressing consumption of an additive and suppressing performance deterioration of a plating solution even in continuous plating.SOLUTION: An electrolytic silver plating bath and an electrolytic silver plating method are provided. The electrolytic silver plating bath contain, as a sacrificial reducing agent, a nitrogen-containing compound represented by general formula (I) [In the formula, X1 is hydrogen or an alkali metal] and by general formula (II) [In the formula, R1, R2, and R3 each independently represent hydrogen (except when R1, R2, and R3 are hydrogen at the same time), a hydroxyl group, a phenyl group, an alkyl group of C1 to C6, an alkenyl group, or an alkynyl group].SELECTED DRAWING: Figure 1

Description

The present invention relates to an electrolytic silver plating bath and an electrolytic silver plating method using the same.

Silver plating has long been used for purposes such as decoration. Traditionally, silver plating has been deposited in alkaline electrolytic silver plating baths containing cyanide.

However, since cyanide is highly toxic and requires waste water treatment, so-called cyanide-free electrolytic silver plating baths that do not use cyanide have been developed (Patent Documents 1 and 2).

In general, cyanide-free electrolytic silver plating baths contain brighteners and other additives. Continuous plating in the same plating bath using an insoluble anode will consume the brighteners and other additives rapidly and quickly. However, there is a problem in that a glossy silver plating cannot be obtained.

Usually, when an insoluble anode is used, a method of preventing oxidation of the additive by using a diaphragm or the like is taken as a countermeasure (Patent Document 3).

However, for plating using high current densities, such as sparger plating and hoop plating, where the plating solution passes through the insoluble anode, or when the solution flow requires high-speed anodic shear, the diaphragm surrounding the anode is Not suitable.

JP-A-2000-192279 JP-A-2002-121693 JP 2009-149965 A

Accordingly, an object of the present invention is to provide an electrolytic silver plating bath in which the consumption of additives such as brighteners is suppressed, and deterioration in performance of the plating solution can be suppressed even when plating is performed continuously in the same plating bath.

As a result of intensive research to solve the above problems, the present inventors found that the above problems can be solved by combining an electrolytic silver plating bath containing additives such as brighteners with a specific sacrificial reducing agent. I completed the present invention.

［式中、Ｘ_１は水素あるいはアルカリ金属を表す。］
および一般式（II）

［式中、Ｒ_１、Ｒ_２、Ｒ_３はそれぞれ独立に水素（ただし、Ｒ_１、Ｒ_２、Ｒ_３が同時に水素のものを除く）、水酸基、フェニル基、Ｃ_１～Ｃ_６のアルキル基、アルケニル基あるいはアルキニル基を表し、前記アルキル基、アルケニル基あるいはアルキニル基は水酸基あるいはカルボキシル基を持っていてもよく、Ｒ_１とＲ_２は繋がって環状のアルキルあるいは芳香環を形成してもよい。］
で表される含窒素化合物の１種または２種以上を含むことを特徴とする電解銀めっき浴である。 An electrolytic silver plating bath containing silver ions, a complexing agent, a conductive salt, a brightener and a sacrificial reducing agent,
The following general formula (I) as a sacrificial reducing agent

[In the formula, X ₁ represents hydrogen or an alkali metal. ]
and general formula (II)

[wherein R ₁ , R ₂ and R ₃ are each independently hydrogen (except when R ₁ , R ₂ and R ₃ are all hydrogen at the same time), hydroxyl group, phenyl group, C ₁ -C ₆ alkyl group , represents an alkenyl group or an alkynyl group, wherein the alkyl group, alkenyl group or alkynyl group may have a hydroxyl group or a carboxyl group, and R ₁ and R ₂ may be linked to form a cyclic alkyl or aromatic ring. . ]
It is an electrolytic silver plating bath characterized by containing one or more nitrogen-containing compounds represented by.

Further, the present invention is an electrolytic silver plating method, wherein an object to be plated is immersed in the above silver plating bath for electrolytic plating.

In the electrolytic silver plating bath of the present invention, the specific sacrificial reducing agent contained therein is preferentially oxidized with respect to the oxidizing species generated from the anode, so that the consumption of the brightening agent can be suppressed, so that plating can be used continuously. Even with this, deterioration of the performance of the plating solution can be suppressed.

FIG. 2 is a diagram showing the external appearance of an implementation product and a comparative product in Example 1 after a Hull cell test using an electrolytic silver plating bath. 1 is a diagram showing the state of an electrolytic silver plating bath before and after temperature rise for Hull cell test of a comparative product (fructose) in Example 1. FIG.

The electrolytic silver plating bath of the present invention (hereinafter referred to as "the plating bath of the present invention") is an electrolytic silver plating bath containing silver ions, a complexing agent, a conductive salt, a brightening agent and a sacrificial reducing agent,
The sacrificial reducing agent contains one or more nitrogen-containing compounds represented by the following general formulas (I) and (II).

Silver ions used in the plating bath of the present invention are not particularly limited. There is no particular limitation as long as it is silver ions generated from a silver ion source or the like. These silver ion sources may be used singly or in combination of two or more. Although the content of silver ions in the plating bath of the present invention is not particularly limited, it is, for example, 1 g/L to 80 g/L, preferably 20 g/L to 60 g/L.

The complexing agent used in the plating bath of the present invention is not particularly limited, and examples thereof include imide compounds represented by the following general formula (III).

[In the formula, B is nitrogen or carbon, and R ₄ and R ₅ each independently represent hydrogen or a methyl group. ] Among these complexing agents, hydantoin derivatives such as succinimide, hydantoin and 5,5-dimethylhydantoin are preferred, and 5,5-dimethylhydantoin is more preferred. These complexing agents may be used singly or in combination of two or more. The content of the complexing agent in the plating bath of the present invention is not particularly limited, but is, for example, 10 g/L to 400 g/L, preferably 100 g/L to 360 g/L, particularly preferably 120 g/L to 320 g/L.

The conductive salt used in the plating bath of the present invention is a metal salt of an inorganic acid or an organic acid, and is not particularly limited. Examples include metal salts of acids and citric acid. Among these conductive salts, sodium salts and potassium salts of carbonic acid, nitric acid and methanesulfonic acid are preferred, and potassium carbonate is more preferred. These conductive salts may be used singly or in combination of two or more. The content of the conductive salt in the plating bath of the present invention is not particularly limited, but is, for example, 1 g/L to 80 g/L, preferably 10 g/L to 60 g/L.

The brightening agent used in the plating bath of the present invention is not particularly limited. A metal salt etc. are mentioned. Among these brighteners, thiosulfate or a metal salt of thiosulfate, or thiodiglycolic acid or a metal salt thereof is preferable, and thiosulfate or a metal salt of thiosulfate is particularly preferable. These brightening agents may be used singly or in combination of two or more. Although the content of the brightener in the plating bath of the present invention is not particularly limited, it is, for example, 1 mg/L to 1000 mg/L, preferably 10 mg/L to 600 mg/L.

The sacrificial reducing agents used in the plating bath of the present invention are nitrogen-containing compounds represented by the following general formulas (I) and (II).

In the formula, X1 represents hydrogen or _an alkali metal. Among alkali metals, lithium, sodium or potassium is preferred, and sodium or potassium is more preferred. The compound represented by general formula (I) may be an acid or metal salt. Among the compounds represented by this formula, compounds containing trivalent nitrogen and oxidized to pentavalent nitrogen during plating are preferred. Examples of such compounds include nitrous acid, lithium nitrite, sodium nitrite, potassium nitrite, and the like.

In the formula, R ₁ , R ₂ and R ₃ are each independently hydrogen (except when R ₁ , R ₂ and R ₃ are simultaneously hydrogen (ammonia)), hydroxyl group, phenyl group, C ₁ to C ₆ It represents an alkyl group, alkenyl group or alkynyl group, and the alkyl group, alkenyl group or alkynyl group may have a hydroxyl group or a carboxyl group. R ₁ and R ₂ may combine to form a cyclic alkyl or aromatic ring. The number of carbon atoms in the alkyl group and the like shown here is preferably C ₁ to C ₃ , more preferably C ₂ . Among the compounds represented by this formula, compounds containing trivalent nitrogen and oxidized to pentavalent nitrogen during plating are preferred. Examples of such compounds include glycine, iminodiacetic acid, nitrilotriacetic acid, ethanolamine, 2,2'-iminodiethanol, triethanolamine, aniline and the like.

Among the above nitrogen-containing compounds, sodium nitrite, glycine, iminodiacetic acid, nitrilotriacetic acid, ethanolamine, 2,2'-iminodiethanol and triethanolamine are preferred, and nitrous acid is preferred in terms of plating gloss and stability. More preferred are sodium, glycine, iminodiacetic acid and nitrilotriacetic acid, and particularly preferred is sodium nitrite.

One or more of the above nitrogen-containing compounds can be used in the plating bath of the present invention. Also, the content of the sacrificial reducing agent in the plating bath of the present invention is not particularly limited, but is, for example, 1 g/L to 100 g/L, preferably 5 g/L to 60 g/L.

The plating bath of the present invention may further contain a known leveling agent and/or pH adjuster used in electrolytic silver plating.

Examples of leveling agents include polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyethyleneimine, and the like. The content of the leveling agent in the plating bath of the present invention is not particularly limited, but is, for example, 0.1 mg/L to 1000 mg/L, preferably 10 mg/L to 600 mg/L.

Examples of pH adjusters include sulfuric acid, nitric acid, methanesulfonic acid, sodium hydroxide, potassium hydroxide and the like. Although the content of the pH adjuster in the plating bath of the present invention is not particularly limited, it is adjusted to pH 6.0 to pH 12.5, preferably pH 9.0 to pH 11.5, for example.

The plating bath of the present invention may further contain known grain refiners, discoloration inhibitors and the like used in electrolytic silver plating. Examples of crystal refining agents include selenous acid, selenium and antimony compounds such as potassium antimonium tartrate, and sulfur-containing compounds such as thiourea and potassium thiocyanate. Examples of discoloration inhibitors include nitrogen- or sulfur-containing compounds having a heterocyclic ring such as benzotriazole, 2-mercaptobenzothiazole, and 1,2,3-benzothiadiazole.

The plating bath of the present invention described above can be prepared by mixing each component according to a conventional method. Since the plating bath of the present invention can be made up of only the above components, it can be a so-called cyanide-free electrolytic silver plating bath that does not contain cyanide compounds. Needless to say, the same effect can be obtained by

In the plating bath of the present invention, an object to be plated can be electrolytically plated by immersing it in the electrolytic silver plating bath in the same manner as in the conventional electrolytic silver plating bath.

Objects to be plated that can be plated with the plating bath of the present invention are not particularly limited, but examples thereof include metals and plated objects made of copper, nickel, iron, tin, zinc or alloys thereof. Also, the shape of the object to be plated is not particularly limited.

The conditions for electrolytic silver plating are not particularly limited, but are, for example, a bath temperature of 20 to 70° C., a current density of 0.5 to 70 A/dm ² and an electrolysis time of 3 seconds to 1 hour.

Electrolytic silver plating using the plating solution of the present invention can be carried out with a conventional electroplating apparatus, but an apparatus using an insoluble anode as the anode is particularly preferred. Such equipment includes a hoop plating equipment, a sparger plating equipment, and the like.

In the electrolytic silver plating bath of the present invention, the specific sacrificial reducing agent contained in the bath is preferentially oxidized with respect to the oxidizing species generated from the anode, so that consumption of the brightening agent can be suppressed. Even if it is used, deterioration of the performance of the plating solution can be suppressed.

The electrolytic silver plating obtained by using the plating solution of the present invention as described above is a film having excellent electrical properties such as low contact resistance and excellent hardness. Therefore, this electrolytic silver plating is preferable for uses such as connectors.

EXAMPLES The present invention will be described in detail below with reference to Examples, but the present invention is not limited to these Examples.

Example 1
Electrolytic silver plating:
An electrolytic silver plating bath was prepared by mixing the basic composition of the electrolytic silver plating bath shown in Table 1 below with one of the sacrificial reducing agents. A Hull cell test was performed using these electrolytic silver plating baths. Hull cell test conditions were as follows: copper Hull cell cathode and iridium oxide coated titanium anode, current 2 A, plating time 2.5 minutes, air stirring, bath temperature 50°C, repeated up to 5 times. gone. In addition, the silver ion source, which was reduced by plating, was replenished each time plating was performed. Fig. 1 shows the appearance after the Hull cell test.

※１ 銀として４０ｇ／Ｌ
※２ 各組成の溶解およびｐＨの調整のために適当な量の水酸化カリウムを加えた。

*1 40g/L as silver
*2 An appropriate amount of potassium hydroxide was added to dissolve each composition and adjust the pH.

As shown in the Hull cell test shown in FIG. 1, without the sacrificial reducing agent, a semi-glossy, distinctly white appearance is obtained for the first two consecutive runs, but the haze characteristic of low current densities is exhibited by the third successive run. From the beginning, silver plating with a slightly yellowish tint is formed at the fifth time, so it can be confirmed that the amount of the brightener component has decreased. When the plating solution containing the sacrificial reducing agent shown in Table 1 was tested, the appearance was the same as that of the first plating even if plating was performed continuously up to five times, indicating that the brightener component was not damaged. .

In addition, it was found that sodium hypophosphite and formaldehyde changed the appearance by repeating the Hull cell test, and the intended effect could not be obtained. On the other hand, with regard to fructose, although a certain effect is seen in the results of the Hull cell test, as shown in Fig. 2, the plating solution decomposes during the heating stage before the Hull cell test, so that it does not enter the bath. It dances and becomes turbid, or precipitates in the plating bath after plating. If such an unsuitable substance with strong reducing power is used as a sacrificial reducing agent, it is unsuitable for industrial use.

Besides the sacrificial reducing agents mentioned above, reducing agents that have shown decomposition include hydroquinone, L(+)-sodium ascorbate, benzaldehyde, and sugars such as D(+)-glucose and maltose. Phosphorous acid, sodium formate, and methanol are examples of sacrificial reducing agents that did not exhibit the desired effect.

From the above results, it was found that the decomposition of the brightener component could be suppressed by using the sacrificial reducing agent in the electrolytic silver plating bath containing silver ions, complexing agent, conductive salt and brightener. It was also found that sodium nitrite, iminodiacetic acid, and nitrilotriacetic acid are superior as sacrificial reducing agents in terms of plating gloss, accumulation by replenishment, and stability, and sodium nitrite is particularly superior.

Example 2
Sparger electrolytic silver plating:
Sparger electrolytic silver plating was performed using a known sparger plating apparatus using the electrolytic silver plating bath using sodium nitrite as a sacrificial reducing agent of Example 1 above. Sparger plating is performed by using a copper plate as a test piece, and applying a plating solution jetted from a nozzle opening diameter of φ4 mm at a flow rate of 4 L / min to a mask opening of φ5.5 mm, 10 ASD to 30 ASD, 27 seconds to 9 seconds. I went with The resulting silver plating film was able to be tested with an appearance corresponding to the high current density area in the Hull cell test without oxidation of the brightener component.

INDUSTRIAL APPLICABILITY The present invention can be used for silver plating.

Claims (9)

An electrolytic silver plating bath containing silver ions, a complexing agent, a conductive salt, a brightener and a sacrificial reducing agent,
The following general formula (I) as a sacrificial reducing agent

[In the formula, X ₁ represents hydrogen or an alkali metal. ]
and general formula (II)

[wherein R ₁ , R ₂ and R ₃ are each independently hydrogen (except when R ₁ , R ₂ and R ₃ are all hydrogen at the same time), hydroxyl group, phenyl group, C ₁ -C ₆ alkyl group , represents an alkenyl group or an alkynyl group, wherein the alkyl group, alkenyl group or alkynyl group may have a hydroxyl group or a carboxyl group, and R ₁ and R ₂ may be linked to form a cyclic alkyl or aromatic ring. . ]
An electrolytic silver plating bath characterized by containing one or more nitrogen-containing compounds represented by: 2. The electrolytic silver plating bath according to claim 1, wherein the sacrificial reducing agent is a compound containing trivalent nitrogen which is oxidized to pentavalent nitrogen during plating. 3. The electrolytic silver plating bath according to claim 1, wherein the brightener is thiosulfuric acid or a metal salt of thiosulfuric acid, or thiodiglycolic acid or a metal salt thereof. The complexing agent has the following general formula (III)

[In the formula, B is nitrogen or carbon, and R ₄ and R ₅ each independently represent hydrogen or a methyl group. ]
The electrolytic silver plating bath according to any one of claims 1 to 3, which is an imide compound represented by: The electrolytic silver plating bath according to any one of claims 1 to 4, wherein the conductive salt is a metal salt of an inorganic acid or an organic acid. The electrolytic silver plating bath according to any one of claims 1 to 5, further comprising a leveling agent and/or a pH adjuster. The electrolytic silver plating bath according to any one of claims 1 to 6, which is for silver plating using an insoluble anode. An electrolytic silver plating method, comprising immersing an object to be plated in the silver plating bath according to any one of claims 1 to 6 for electrolytic plating. 9. The electrolytic silver plating method according to claim 8, wherein an insoluble anode is used as the anode for electrolytic plating.

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