Electrolytic silver plating bath and electrolytic silver plating method using the same

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

[Technical Field]

[0001] The present invention relates to an electrolytic silver plating bath and an electrolytic silver plating method using the same. [Background technology]

[0002] Silver plating has long been used for decorative purposes. Until now, silver plating has been deposited in alkaline electrolytic silver plating baths containing cyanide.

[0003] However, cyanide is highly toxic and requires wastewater treatment, so so-called cyanide-free electrolytic silver plating baths that do not use cyanide have been developed (Patent Documents 1 and 2).

[0004] Generally, cyanide-free electrolytic silver plating baths contain additives such as brighteners, but if plating is carried out continuously in the same plating bath using an insoluble anode, the additives such as brighteners are rapidly consumed, and the problem arises that bright silver plating cannot be obtained quickly.

[0005] When an insoluble anode is used, a method of preventing oxidation of the additive by using a diaphragm or the like is usually taken as a countermeasure (Patent Document 3).

[0006] However, a diaphragm surrounding the anode is not suitable for plating using high current densities, such as sparger plating and hoop plating, or when the plating solution passes through an insoluble anode or when a high-speed anode shear solution flow is required. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-192279 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-121693 [Patent Document 3] Japanese Patent Application Laid-Open No. 2009-149965 Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, an object of the present invention is to provide an electrolytic silver plating bath in which consumption of additives such as brighteners is suppressed and deterioration in the performance of the plating solution is suppressed even when plating is performed continuously in the same plating bath. [Means for solving the problem]

[0009] As a result of intensive research to solve the above problems, the present inventors have found that the above problems can be solved by combining an electrolytic silver plating bath containing additives such as a brightener with a specific sacrificial reducing agent, and have thus completed the present invention.

[0010] 1. An electrolytic silver plating bath containing silver ions, a complexing agent, a conductive salt, a brightener, and a sacrificial reducing agent, As a sacrificial reducing agent, [ka] [In the formula, X1 represents hydrogen or an alkali metal.] and general formula (II) [ka] [In the formula, R1, R2, and R3 each independently represent hydrogen (excluding cases where R1, R2, and R3 are simultaneously hydrogen), a hydroxyl group, a phenyl group, a C1-C6 alkyl group, an alkenyl group, or an alkynyl group, and the alkyl group, alkenyl group, or alkynyl group may have a hydroxyl group or a carboxyl group, and R1 and R2 may be linked to form a cyclic alkyl or aromatic ring.] The electrolytic silver plating bath is characterized by containing one or more nitrogen-containing compounds represented by the following formula:

[0011] The present invention also provides an electrolytic silver plating method, characterized in that an object to be plated is immersed in the above silver plating bath to perform electrolytic plating. [Effects of the Invention]

[0012] The electrolytic silver plating bath of the present invention can suppress consumption of the brightener by preferentially oxidizing the specific sacrificial reducing agent contained therein relative to the oxidizing species generated from the anode, thereby suppressing deterioration in the performance of the plating solution even when used continuously for plating. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a diagram showing the appearance of the working product and the comparative product in Example 1 after a hull cell test using an electrolytic silver plating bath. [Figure 2] FIG. 2 is a diagram showing the state of the electrolytic silver plating bath before and after temperature rise in a Hull Cell test of a comparative product (fructose) in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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 brightener, and a sacrificial reducing agent, The sacrificial reducing agent contains one or more nitrogen-containing compounds represented by the following general formula (I) and general formula (II).

[0015] The silver ions used in the plating bath of the present invention are not particularly limited, as long as they are generated from a silver ion source such as silver nitrate, silver sulfate, silver acetate, silver lactate, silver citrate, silver oxide, silver phosphate, silver alkanesulfonate, or silver halide. These silver ion sources may be used alone or in combination. The silver ion content in the plating bath of the present invention is not particularly limited, but is, for example, 1 g / L to 80 g / L, preferably 20 g / L to 60 g / L.

[0016] 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).

[0017] [ka]

[0018] [In the formula, B represents nitrogen or carbon, and R4 and R5 each independently represent hydrogen or a methyl group.] Among these complexing agents, succinimide, hydantoin, and hydantoin derivatives such as 5,5-dimethylhydantoin are preferred, with 5,5-dimethylhydantoin being more preferred. These complexing agents may be used alone 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, and particularly preferably 120 g / L to 320 g / L.

[0019] The conductive salts used in the plating bath of the present invention are metal salts of inorganic and organic acids, and are not particularly limited. Examples include metal salts of sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, sulfamic acid, carbonic acid, boric acid, acetic acid, lactic acid, methanesulfonic acid, and citric acid. Among these conductive salts, sodium and potassium salts of carbonate, nitric acid, and methanesulfonic acid are preferred, with potassium carbonate being more preferred. These conductive salts may be used alone 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.

[0020] The brightener used in the plating bath of the present invention is not particularly limited, and examples thereof include thiosulfuric acid, 2-mercaptoethanesulfonic acid, 3-mercaptopropanesulfonic acid, thiodiglycolic acid, dithiodiglycolic acid, thiourea, and metal salts thereof. Among these brighteners, thiosulfuric acid or metal salts of thiosulfuric acid, or thiodiglycolic acid or metal salts thereof are preferred, with thiosulfuric acid or metal salts of thiosulfuric acid being particularly preferred. These brighteners may be used alone or in combination of two or more. The content of the brightener in the plating bath of the present invention is not particularly limited, and is, for example, 1 mg / L to 1000 mg / L, preferably 10 mg / L to 600 mg / L.

[0021] The sacrificial reducing agent used in the plating bath of the present invention is a nitrogen-containing compound represented by the following general formulas (I) and (II).

[0022] [ka]

[0023] 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 in the form of an acid or a metal salt. Among the compounds represented by this formula, compounds containing trivalent nitrogen that are oxidized to pentavalent nitrogen during plating are preferred. Examples of such compounds include nitrous acid, lithium nitrite, sodium nitrite, and potassium nitrite.

[0024] [ka]

[0025] In the formula, R1, R2, and R3 each independently represent hydrogen (excluding cases where R1, R2, and R3 are simultaneously hydrogen (ammonia)), hydroxyl, phenyl, C1-C6 alkyl, alkenyl, or alkynyl groups, and the alkyl, alkenyl, and alkynyl groups may have a hydroxyl or carboxyl group. R1 and R2 may be linked to form a cyclic alkyl or aromatic ring. The number of carbon atoms in the alkyl group or the like shown here is preferably C1-C3, more preferably C2. Among the compounds represented by this formula, compounds containing trivalent nitrogen and that are oxidized to pentavalent nitrogen during plating are preferred. Examples of such compounds include glycine, iminodiacetic acid, nitrilotriacetic acid, ethanolamine, 2,2'-iminodiethanol, triethanolamine, and aniline.

[0026] Of the above nitrogen-containing compounds, sodium nitrite, glycine, iminodiacetic acid, nitrilotriacetic acid, ethanolamine, 2,2'-iminodiethanol, and triethanolamine are preferred, and from the standpoint of plating brightness and stability, sodium nitrite, glycine, iminodiacetic acid, and nitrilotriacetic acid are more preferred, with sodium nitrite being particularly preferred.

[0027] The plating bath of the present invention can contain one or more of the above nitrogen-containing compounds. 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.

[0028] The plating bath of the present invention may further contain a known leveling agent and / or pH adjuster used in electrolytic silver plating.

[0029] Examples of the leveling agent include polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyethyleneimine, etc. 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, and preferably 10 mg / L to 600 mg / L.

[0030] Examples of pH adjusters include sulfuric acid, nitric acid, methanesulfonic acid, sodium hydroxide, potassium hydroxide, etc. The content of the pH adjuster in the plating bath of the present invention is not particularly limited, but the pH is adjusted to, for example, 6.0 to 12.5, preferably 9.0 to 11.5.

[0031] The plating bath of the present invention may further contain known crystal refiners, discoloration inhibitors, and the like used in electrolytic silver plating. Examples of crystal refiners include selenium and antimony compounds such as selenious acid and potassium antimony tartrate, as well as 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.

[0032] The plating bath of the present invention described above can be prepared by mixing the components in a conventional manner. Since the plating bath of the present invention can be prepared using only the components described above, it can be a so-called cyanide-free electrolytic silver plating bath that does not contain any cyanide compounds. However, it goes without saying that the same effect can be obtained by adding a cyanide compound that has been used in conventional silver plating baths.

[0033] The plating bath of the present invention, like conventional electrolytic silver plating baths, can be used to electroplat an object by immersing the object in the plating bath and electroplating it with silver.

[0034] There are no particular limitations on the objects to be plated using the plating bath of the present invention, including, for example, metals and objects to be plated such as copper, nickel, iron, tin, zinc, and alloys thereof. The shape of the object to be plated is also not particularly limited.

[0035] The conditions for electrolytic silver plating are not particularly limited, but for example, a bath temperature of 20 to 70°C, a current of 0.5 to 70 A / dm 2 The current density is 0.01 and the electrolysis time is 3 seconds to 1 hour.

[0036] Electrolytic silver plating using the plating solution of the present invention can be carried out using conventional electrolytic plating equipment, but equipment using an insoluble anode as the anode is particularly preferred, such as a hoop plating equipment or a sparger plating equipment.

[0037] Furthermore, the electrolytic silver plating bath of the present invention can suppress consumption of the brightener by preferentially oxidizing the specific sacrificial reducing agent contained therein over the oxidizing species generated from the anode, and therefore, deterioration in the performance of the plating solution can be suppressed even when plating is continued.

[0038] The electrolytic silver plating obtained using the plating solution of the present invention as described above is a film that has excellent electrical properties such as low contact resistance and excellent hardness, making it suitable for applications such as connectors. [Example]

[0039] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0040] Example 1 Electrolytic silver plating: Electrolytic silver plating baths were prepared by mixing the basic composition of the electrolytic silver plating bath in Table 1 below with one of the sacrificial reducing agents. A Hull Cell test was conducted using these electrolytic silver plating baths. The Hull Cell test was conducted using a copper Hull Cell cathode and an iridium oxide-coated titanium anode, with a current of 2A, a plating time of 2.5 minutes, air agitation, and a bath temperature of 50°C. This test was repeated up to five times. The silver ion source, which was lost during plating, was replenished after each plating run. Figure 1 shows the appearance after the Hull Cell test.

[0041] [Table 1] *1 40g / L as silver *2 An appropriate amount of potassium hydroxide was added to dissolve each component and adjust the pH.

[0042] As shown in the Hull Cell test in Figure 1, when no sacrificial reducing agent is included, a clear semi-bright white appearance is obtained for the first two consecutive platings, but by the third consecutive plating, a cloudiness characteristic of low current density begins to appear, and by the fifth plating, a slightly yellowish silver color is plated, confirming a decrease in the brightener components. When a test was conducted using a plating solution containing the sacrificial reducing agent shown in Table 1, the appearance was the same as the first plating even after five consecutive platings, demonstrating that the brightener components were not impaired.

[0043] Furthermore, it was found that the appearance of sodium hypophosphite and formaldehyde changed with repeated Hull Cell tests, and the desired effect could not be achieved. On the other hand, while fructose showed a certain degree of effectiveness in the Hull Cell test, as shown in Figure 2, the plating solution decomposed during the temperature rise stage before the Hull Cell test, causing the decomposition to float in the bath, making it cloudy, and to precipitate in the plating tank after plating. Using such an inappropriate substance with strong reducing power as a sacrificial reducing agent would be unsuitable for industrial use.

[0044] In addition to the sacrificial reducing agents mentioned above, other reducing agents that have shown decomposition include hydroquinone, sodium L(+)-ascorbate, benzaldehyde, and sugars such as D(+)-glucose and maltose. Sacrificial reducing agents that have not shown the desired effect include phosphorous acid, sodium formate, and methanol.

[0045] These results demonstrate that the use of a sacrificial reducing agent in an electrolytic silver plating bath containing silver ions, complexing agents, conductive salts, and brighteners can suppress the decomposition of brightener components. Furthermore, in terms of plating brightness, accumulation due to replenishment, and stability, sodium nitrite, iminodiacetic acid, and nitrilotriacetic acid are superior sacrificial reducing agents, with sodium nitrite being particularly superior.

[0046] Example 2 Sparger electrolytic silver plating: Sparger electrolytic silver plating was performed using a known sparger plating apparatus and the electrolytic silver plating bath of Example 1, which used sodium nitrite as a sacrificial reducing agent. Sparger plating was performed on a copper plate as a test piece, with the plating solution sprayed from a nozzle opening of φ4 mm at a flow rate of 4 L / min onto a mask opening of φ5.5 mm, under conditions of 10 ASD to 30 ASD and 27 seconds to 9 seconds. The obtained silver plating film had an appearance equivalent to that of a high current density area in a Hull cell test, without oxidation of the brightener components. [Industrial Applicability]

[0047] The present invention can be used for silver plating.

Claims

1. The electrolytic silver plating bath contained silver ions, a complexing agent, a conductive salt, a brightener, and a sacrificial reducing agent. hand, The sacrificial reducing agent is selected from sodium nitrite, iminodiacetic acid, and nitrilotriacetic acid. and one or more nitrogen-containing compounds, The brightener is thiosulfuric acid or a metal salt of thiosulfuric acid, or thiodiglycolic acid or is a metal salt, The complexing agent is represented by the following general formula (III): 【Chemical 1】 [wherein B is nitrogen or carbon, and R 4 and R 5 each independently represent hydrogen or a methyl group] represents.] is an imide compound represented by the formula: Electrolytic silver plating bath characterized by:

2. 2. The electrolytic silver plating bath according to claim 1, wherein the conductive salt is a metal salt of an inorganic acid or an organic acid.

3. The imide compound represented by general formula (III) is a compound obtained by subjecting hydantoin and 5,5-dimethyl hydantoin to polymerization. 1 or 2 of the hydantoin derivatives selected from the group consisting of hydantoin and hydantoin.

3. The electrolytic silver plating bath according to claim 2.

4. Any one of claims 1 to 3 further contains a leveling agent and / or a pH adjuster. Electrolytic silver plating bath according to any one of claims 1 to 4.

5. 5. The electrolytic silver plating method according to claim 1, which is for silver plating using an insoluble anode. bath.

6. The method comprises immersing an object to be plated in the silver plating bath according to any one of claims 1 to 5 to perform electrolytic plating. An electrolytic silver plating method characterized by:

7. 7. The method according to claim 6, wherein an insoluble anode is used as the anode for electrolytic plating. Electrolytic silver plating method.

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