JPH10158867A - Peeling agent for noble metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a peeling agent which allows the recycling of metallic base materials after peeling as they are by adding carboxylic acid and the its alkaline metal salt to a system contg. a nitrobenzene compd., its alkaline metal salt and their deriv., a lead compd. and a cyan radial supplying source compd. SOLUTION: This peeling material contains, for example, 1 to 100g/l alkaline metal slat of the nitrobenzene sulfonic acid, 0.0001 to 3g/l lead carboxylate, 1 to 100g/l cyan radial supplying source compd. and further, the carboxylic acid and the alkaline metal salt of the carboxylic acid and the pH of the aq. soln. is >=7.5. The concn. of the carboxylic acid and the alkaline metal salt of the carboxylic acid is preferably 0.001 to 10g/l. This peeling agent is perfect in peeling, is fast in a peeling rate and hardly corrodes the metallic base materials and therefor, allows the recycling of the substrates as the base bodies for noble plating, etc., as they are, after peeling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noble metal release agent, and more particularly, to selectively remove a noble metal adhered to a surface of a metal substrate by plating or the like without damaging the metal substrate. And that the substrate after peeling can be reused.

[0002]

2. Description of the Related Art Conventionally, as a method of recovering a noble metal from a product coated with a noble metal, a method of once dissolving the entirety including a metal substrate using nitric acid or aqua regia and then separating and recovering the noble metal is used. Alternatively, a complexing method in which a complex salt is formed by dissolving a cyanide radical with an organic oxidizing agent or thiourea and the like is dissolved and then recovered, or an electrolytic method is used.

However, among these methods, in the method of dissolving the entire metal base including the base metal base using a strong acid, it is naturally impossible to reuse the metal base as it is. Further, in the complexing method, it is extremely difficult to completely remove the noble metal, and even if the noble metal is completely peeled off, it is almost the case that the underlying metal substrate is eroded to such an extent that it cannot withstand reuse.

For example, Japanese Patent Application Laid-Open No. 60-92487 discloses that gold, palladium or palladium / nickel is prepared by using an aqueous solution containing a nitrobenzoic acid derivative, a cyanide radical source compound, a thallium compound and optionally a lead compound. A method for dissolving and removing the adhered substance from a metal substrate is described. However, in this method, the metal substrate was severely dissolved, and it was impossible to reuse the substrate.

[0005]

A conventional release agent used for peeling a noble metal plating layer or the like has a slow release rate, and the base metal substrate serving as an underlayer is severely corroded. Almost impossible. Thereafter, the peel rate has improved considerably, but the control of corrosion of the metal substrate is still insufficient. The present invention is a composition that solves these problems and effectively dissolves and removes a noble metal adhered substance adhered to the surface of a metal substrate without damaging the substrate. The metal substrate after peeling can be reused as it is. It is intended to develop and provide a release agent.

[0006]

Means for Solving the Problems When dissolving and separating a noble metal adhered to a base metal substrate by plating or the like, the present inventors have excellent noble metal solubility and do not damage the metal substrate. A method was studied in which the substrate can be reused as it is after dissolution of the noble metal. As a result, when a system containing an alkali metal salt of nitrobenzene sulfonic acid, a cyan radical source compound and lead carboxylate is used as a release agent, the metal substrate is considerably corroded when the noble metal is dissolved. It has been found that when an acid is added, only the noble metal adhered to the surface can be easily dissolved without corroding the metal substrate. Furthermore, as a result of studying a carboxylic acid derivative having the same effect, the present invention has been reached.

That is, the concentration of at least one compound selected from the group consisting of (A) a nitrobenzene compound, a nitrobenzene compound alkali metal salt and a derivative thereof in an aqueous solution is 1 to 100 g / liter,
(B) the concentration of at least one lead compound is 0.0001 to 3;
g / liter, the concentration of (C) the cyanogen radical source compound is 1 to 100 g / liter, and (D) at least one kind selected from the group consisting of carboxylic acids and alkali metal salts of carboxylic acids. A noble metal release agent fixed to the surface of a metal substrate, which contains a compound and has a pH of an aqueous solution of 7.5 or more.

Here, nitrobenzoic acid is preferred as the nitrobenzene compound, and sodium nitrobenzenesulfonate is preferred as the alkali metal salt of the nitrobenzene compound. In addition, as a lead compound, lead acetate or lead borate is used,
Oxalic acid or malonic acid is preferred as the carboxylic acid.

Hereinafter, the present invention will be described in detail.

The noble metal stripping agent of the present invention is used in the form of an aqueous solution. Not only the form of the aqueous solution but also the necessary chemical components are prepared in advance in a dry state, and when dissolved in water, the noble metal stripping agent is used as it is as a noble metal stripping agent. It may also be prepared as a composition that can be used. The present invention includes these two embodiments.

The noble metal stripping agent contains a plurality of components. One of the components is (A) at least one compound selected from the group consisting of nitrobenzene compounds, nitrobenzene compound alkali metal salts and derivatives thereof. 1 to 100 parts by weight in the composition, 1 to 100 parts by weight in the aqueous solution
Should contain 100 g / l.

The lower limit of the concentration of these components is determined from the viewpoint of the action of peeling the noble metal from the underlying metal substrate to which it is fixed.
1 g / l, and this effect rapidly increases 4
0 g / liter or more is more preferable. The upper limit is 100 g / liter from the viewpoint of the solubility of this component, and more preferably 60 g / liter or less from the viewpoint of the releasability.

A wide range of compounds belonging to nitrobenzene compounds, alkali metal salts of nitrobenzene compounds and their derivatives can be used as one component of the present invention. Among these compounds, o-, m- and p-nitrobenzene Sulfonic acid and their alkali metal salts, o- or m- and p-nitrobenzoic acid and their alkali metal salts, or o-, m- and p-nitrobenzenesulfonyl chloride, m- and p-nitrophenyl esters Is more preferred.

The noble metal stripping agent of the present invention contains, as another component, at least one lead compound (B) in an amount of 0.0001 to 3 parts by weight in the composition and 0.001 to 3 parts by weight in the aqueous solution.
g / liter must be included.

The lower limit of the concentration of this component is 0.0001 g / liter from the viewpoint of preventing the protection effect of the metal substrate from being insufficient when peeling the noble metal and preventing the substrate from eroding. g / liter or more is more preferred. In addition, when the concentration of this component increases, the dissolution rate of the noble metal adhered substance is remarkably reduced, and the practicality is lost. Insoluble matter remains on the surface of the base to stain the base and adversely affect its reuse. Therefore the upper limit is 3g / l.

The lead compound is effective as one component of the noble metal release agent, but particularly preferred are lead acetate, lead borate,
Examples include lead chloride, lead nitrate, lead sulfate, and ethylenediaminetetraacetate.

The noble metal stripping agent of the present invention further comprises (C) 1 to 100 parts by weight of a cyan radical source compound in the composition and 1 to 100 g /
Liters need to be included.

The cyan radical source compound that produces cyan radicals in the state of an aqueous solution is not particularly limited, and examples thereof include cyanides of alkali metals such as sodium and potassium. When the concentration of this component is reduced, the dissolution rate of the noble metal is reduced and it cannot be used. Therefore, the lower limit is 1 g / liter, more preferably 5 g / liter or more. If the concentration of the cyanide compound in the aqueous solution is too high, the metal base may be damaged or discolored, and it may be difficult to reuse the metal base.
00 g / liter, and more preferably 20 g / liter or less.

The noble metal stripping agent of the present invention must further contain, as another component, at least one compound selected from the group consisting of (D) carboxylic acids and alkali metal salts of carboxylic acids. The concentration of these compounds in the aqueous release agent solution is preferably 0.001 to 10 g / liter.

The details of the mechanism of action of the carboxylic acid and the alkali metal carboxylate in the release agent of the present invention are not clear, but when dissolving the noble metal layer fixed to the underlying metal substrate by plating or the like, erosion of the metal substrate occurs. And a remarkable effect of alleviating this is observed. From the viewpoint of this effect, the lower limit of the concentration of this component is preferably 0.001 g / liter, and more preferably 0.01 g / liter or more. The upper limit of the concentration is preferably 10 g / liter, more preferably 8 g / liter, in view of the relationship between the increase in this component and the effect of alleviating erosion of the metal substrate.
Less than a liter. In addition, the ratio of each of these components is preferable also when preparing as a composition.

Although a wide range of compounds contained in carboxylic acids and alkali metal salts of carboxylic acids are all effective as components of the present invention, preferred components among them are glycolic acid, propionic acid, stearic acid, lactic acid, oxalic acid and the like. , Malonic acid, maleic acid, citric acid and their alkali metal salts. More preferred are oxalic acid and malonic acid or alkali metal salts thereof.

The lower limit of the pH of the aqueous solution of the stripping agent of the present invention must be 7.5 from the viewpoint of the stripping effect of the noble metal layer and the prevention of corrosion of the metal substrate as the base, and is more preferably from the viewpoint of the same effect. Is 9.0 or higher and the upper limit is 1
3.0.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION The noble metals to be stripped by the stripping agent of the present invention are mainly gold and silver, palladium or alloys based on these metals. Various metal materials can be used for a metal substrate serving as a base for forming a noble metal layer, and a material obtained by plating nickel on brass or the like is most often used. The method of forming the noble metal layer such as gold, silver, and palladium is not particularly limited, but is usually formed by plating.

In order to prepare a noble metal stripping agent having the above-mentioned composition, (A) a nitrobenzene compound, a nitrobenzene compound alkali metal salt such as sodium nitrobenzenesulfonate and (B) a lead compound such as lead acetate, D) A composition is prepared by mixing a carboxylic acid and a carboxylic acid alkali metal salt, for example, oxalic acid, in a predetermined ratio, and when used, the composition is used in (C) an aqueous solution of a cyan radical source compound, for example, potassium cyanide or sodium cyanide. It is poured into an aqueous solution and dissolved to prepare a noble metal release agent.

For example, in order to peel a thin layer of gold formed by plating on a nickel-plated brass metal, the noble metal product is immersed in a stripping agent solution to form the noble metal layer. It is easily exfoliated by dissolving in a solution.

Although the use temperature of the stripping solution is not constant,
The higher the temperature, the faster the peeling rate, so that the temperature is usually used at about 30 to 70 ° C. The peeling gradually proceeds without stirring, but is often stirred to promote the peeling.

The most significant feature of the release agent of the present invention is that when the noble metal layer is peeled off, the erosion of the surface of the metal substrate as the base metal is extremely small. (A) Sodium nitrobenzenesulfonate, (B) which has been conventionally used as a release agent
The biggest disadvantage of the three-component release agent composed of lead acetate and (C) potassium cyanide is that it is difficult to prevent erosion of the metal substrate surface at the time of release, so that the substrate after peeling can hardly be reused as it is. It is a point.

In order to eliminate the disadvantage, the noble metal release agent of the present invention has been studied by the present inventors. As a result, a carboxylic acid or an alkali metal carboxylate is further added as a fourth component to the three-component release agent. In this respect, the erosion on the surface of the metal substrate is slightly suppressed by the four-component release agent, and the metal substrate can be reused as it is after the release. This is the most significant feature of the present invention.

Further, when the peeling ability is reduced during use, the function of recovering the peeling ability and preventing erosion of the surface of the metal substrate can be obtained by replenishing only the components which have been consumed in the liquid and have a reduced concentration. Can be kept unchanged. This point is also remarkably superior to the above-mentioned three-component release agent as shown in Examples described later.

The noble metal stripping agent of the present invention is used in the form of an aqueous solution. However, the necessary chemical components are mixed in advance in a dry state and supplied to the user. It can also be prepared as a composition that can be used as a noble metal release agent.

[0031]

The present invention will be described more specifically with reference to the following examples.

(Example 1) As a noble metal stripping solution, sodium nitrobenzenesulfonate 50 g / liter, lead acetate
0.25 g / l, potassium cyanide 10 g / l,
100 ml of an aqueous solution containing 2 g / l of oxalic acid was prepared.

A test piece prepared by flash plating gold on the surface of a 3 μm-thick nickel-plated brass substrate was immersed in the stripping solution prepared above at 50 ° C. until the gold plating was completely peeled off, and then lifted up. To observe the surface of the substrate. Table 1 shows the results.

[0034]

[Table 1]

Example 2 An aqueous solution having the same composition as in Example 1 was prepared except that in place of sodium nitrobenzenesulfonate, 50 g / liter of nitrobenzenebenzoic acid and a small amount of sodium hydroxide were used.

In the same manner as in Example 1, a test piece prepared by flash-plating gold on the surface of a 3 μm-thick nickel-plated brass substrate was applied to the stripping solution prepared above.
After immersion at ℃ until the gold plating was completely peeled off, it was pulled up and the surface of the substrate was observed. The results are shown in Table 1.

(Example 3) As a noble metal stripping solution, sodium nitrobenzenesulfonate 50 g / l, lead borate
0.25 g / l, potassium cyanide 10 g / l,
100 ml of an aqueous solution containing 2 g / l of oxalic acid was prepared.

A test piece prepared by flash-plating gold on the surface of a 3 μm-thick nickel-plated brass substrate was immersed in the stripping solution prepared above at 50 ° C. until the gold plating was completely stripped. The substrate was pulled out and the surface of the substrate was observed. Table 1 shows the results.

Example 4 An aqueous solution having the same composition was prepared as in Example 3, except that malonic acid was used in place of oxalic acid at 2 g / liter.

In the same manner as in Example 3, a test piece prepared by flash-plating gold on the surface of a 3 μm-thick nickel-plated brass substrate was applied to the stripping solution prepared above.
After immersion at ℃ until the gold plating was completely peeled off, it was pulled up and the surface of the substrate was observed. The results are shown in Table 1.

Example 5 Using a noble metal stripper having the same composition as in Example 1, a test piece was prepared by flash-plating silver on the surface of a 3 μm-thick nickel-plated substrate made of brass. Then, the substrate was immersed in a stripping solution at 50 ° C. until the silver plating was completely stripped, then pulled up, and the surface of the substrate was observed. Table 1 shows the results.

The results of Examples 1 to 5 shown in Table 1 show that the gold or silver plating layer formed on the surface of the metal substrate was completely peeled off in a short time. Moreover, the nickel-plated surface of the substrate has the same metallic luster as before the treatment, indicating that the substrate surface is hardly eroded and can be reused as it is as a new plated substrate.

When the peeling operation in Examples 1 to 5 was repeated and the peeling speed was reduced, the shortage of each component was replenished so that the composition of the initial peeling liquid was obtained, and the peel test of the test piece was repeated. Carried out. As a result, even when the re-prepared stripping solution is used, it has the same releasability as the newly prepared stripping solution, and the nickel-plated surface of the substrate after the stripping has the same metallic luster as before the treatment. It was confirmed that there was.

(Comparative Example 1) In Example 1, sodium nitrobenzenesulfonate was used as the noble metal stripping solution.
Under the same conditions except that 100 ml of an aqueous solution containing 10 g / liter of potassium cyanide and 10 g / liter of potassium cyanide were used, a peeling test was performed using a test piece prepared by flash-plating gold on the surface of the substrate and similarly prepared. Table 1 shows the results.

From the results shown in Table 1, it was confirmed that when this stripping solution was used, it took a long time to strip gold, and the nickel plating surface of the substrate was significantly corroded.

(Comparative Example 2) In Example 1, sodium nitrobenzenesulfonate was used as the noble metal stripping solution.
g / litre, 0.25 g / l lead acetate, and 100 ml of an aqueous solution containing 10 g / litre of potassium cyanide. A peel test was performed.
Table 1 shows the results.

According to the results shown in Table 1, the gold plating is approximately
Peeling was completed completely in 30 seconds. Further, the corrosion of the nickel plating on the substrate surface was relatively small, and the substrate could be reused.
However, after replenishing and re-preparing each component so as to have the original composition in the used stripping solution, the stripping test was repeated using a similar test piece. As a result, the gold plating could be stripped. However, the nickel-plated surface was significantly corroded and it was impossible to reuse the substrate. Therefore, it was found that the noble metal stripper having such a composition cannot be used for industrial applications that need to be used continuously.

[0048]

According to the present invention, the conventional stripping agent used for stripping a noble metal plating layer has a slow stripping rate, and the metal base as the base is significantly corroded. Therefore, it is impossible to reuse the base as it is after stripping. there were. Although the stripping rates have subsequently improved considerably, the control of substrate corrosion was still insufficient.
Since the peeling agent of the present invention is completely peeled, has a high peeling speed, and hardly corrodes a metal substrate, the substrate can be reused as a substrate for precious metal plating or the like after peeling. Further, when the peeling speed is further reduced, the performance can be restored by replenishing the reduced amount of each component.

Claims (6)

[Claims] 1. A method according to claim 1, wherein at least one compound selected from the group consisting of nitrobenzene compounds, nitrobenzene compound alkali metal salts and derivatives thereof is used in an amount of 1 to 100.
Parts by weight and (B) at least one lead compound
To 3 parts by weight and (C) a cyan radical source compound
100 parts by weight of a noble metal release agent fixed to the surface of a metal substrate containing four types of at least one compound selected from the group consisting of carboxylic acids and alkali metal salts of carboxylic acids. . 2. The concentration of at least one compound selected from the group consisting of (A) a nitrobenzene compound, a nitrobenzene compound alkali metal salt and a derivative thereof in an aqueous solution is 1 to 100 g / liter, B) the concentration of at least one lead compound is 0.0001 to 3 g / l; and (C) the concentration of the cyan radical source compound is 1
(D) the concentration of at least one compound selected from the group consisting of carboxylic acids and alkali metal carboxylate is 0.001 to 10 g / liter,
A stripping agent for a noble metal adhered to the surface of a metal substrate, wherein the pH of the aqueous solution is 7.5 or more. 3. The stripping agent for a noble metal adhered to the surface of a metal substrate according to claim 1, wherein the nitrobenzene compound is nitrobenzoic acid. 4. The stripping agent for a noble metal fixed to the surface of a metal substrate according to claim 1, wherein the alkali metal salt of the nitrobenzene compound is sodium nitrobenzenesulfonate. 5. The lead compound is lead acetate or lead borate,
The stripping agent for a noble metal adhered to the surface of the metal substrate according to claim 1. 6. The stripping agent for a noble metal adhered to the surface of a metal substrate according to claim 1, wherein the carboxylic acid is oxalic acid or malonic acid.