JP2686494B2 - Discoloration removal method of silver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a brown or black discoloration that occurs in various articles such as silverware and silver or silver-plated tableware, not by physical polishing treatment but by electrochemical treatment. According to the method of removal.

[0002]

2. Description of the Related Art It is well known that silver materials and silver products are covered with a brown or black film on the surface when they are exposed to air during storage or use to change their colors and lose the original beautiful luster of silver. is there. This is because sulfur compounds such as hydrogen sulfide and sulfurous acid gas in the air react with silver to form silver sulfide as a film on the silver surface. Conventionally, as a method for removing such discoloration due to silver sulfide, A physical method of polishing with an abrasive containing soft particles. 2. A chemical method that dissolves and removes the discolored film by immersing it in an aqueous solution containing thiourea mixed with hydrochloric acid, sulfuric acid, glycolic acid or tartaric acid. 3. The silver product to be treated is placed in contact with the aluminum foil or zinc pieces in a enamel container containing an alkaline solution of sodium carbonate, and the solution is heated to 65 ° C. or higher, preferably kept at boiling temperature. There was an electrochemical method that applied a spontaneously generated potential difference to reduce the discoloration of silver due to silver sulfide to metallic silver.

[0003]

However, the above 1.
In the method of (3), not only the surface of the silver is scratched by the abrasive, but also labor and labor for polishing are required, and the workability is extremely poor. The above 2. According to the method of, due to the characteristics of the chemicals used,
The solution containing thiourea as a main ingredient is toxic, and it is a problem in terms of safety and hygiene when applied to tableware, and naturally the range of application is limited. In addition, the above 3. In the case of the method of (3), not only is it necessary to use an alkaline chemical that requires careful handling, and it is necessary to heat and maintain at 65 ° C or higher, preferably at the boiling liquid temperature. It acts by reacting by melting,
It reacts instantaneously at the same time as the reaction, but when aluminum dissolves in sodium carbonate, it does not react immediately and the defrosting effect disappears at an early stage, and it is completely unsuitable for removing the defrosting of a large amount of silver products. On the other hand, recently, air pollution has been increasing more and more, and as a result, discoloration of silver products has been seen to occur frequently in each household. Especially, hotels and restaurants handling a large number of silver or silver-plated tableware, At coffee shops and the like, we are in a difficult situation due to the lack of manpower to remove and clean the discoloration. We strongly wait for the advent of a discoloration removal method that can be processed at once.

[0004]

[Means for Solving the Problems] In view of the various problems described above, the following means are proposed as means for solving these problems. That is, the gist is that an aqueous solution containing one or more of sodium, potassium, or ammonium salts of bicarbonate, carbonic acid, citric acid , malic acid, gluconic acid, or glycolic acid is used as an electrolytic solution, and a DC power source is used. The method for removing discoloration of silver is characterized in that electrolytic treatment is carried out under a voltage condition of at least 1.5 V or more between the silver to be treated connected to the cathode and the conductive counter electrode connected to the anode of the same power source.

[0005]

When silver as the material to be treated is used as a cathode in the electrolytic solution of the above composition and electrolysis is carried out with direct current between one of the anodes, oxygen gas is generated from the anode side and silver on the cathode side is generated. Hydrogen gas is generated from the surface of the. At this time, silver sulfide, which is a discoloring component generated on the silver surface, chemically reacts with this hydrogen gas, and as shown by the following equation,

[0006]

Embedded image By the reduction reaction, silver sulfide (Ag ₂ S) is reduced to silver (Ag), and at the same time, sulfur (S) in silver sulfide reacts with hydrogen (H ₂ ) and scatters as hydrogen sulfide (H ₂ S), It is considered that part of silver sulfide loses its adhesiveness due to hydrogen gas, peels off from the silver surface, and falls into the liquid. As described above, the method for removing discoloration of silver by the method of the present invention is to reduce silver sulfide, which is a discoloration component, directly to metallic silver by a reduction reaction by electrolysis. The surface is not worn at all and, of course, no scratches are produced as with the polishing method, and the original beautiful luster of silver can be restored. However, in the method of the present invention, there is no aging of the chemical liquid, and not only long-time construction and large-scale processing are possible,
It has a number of excellent features such as extremely fast reaction time, quick processing, and suitable finishing conditions by changing the voltage conditions. Furthermore, most of the objects to be treated are tableware, but since the chemicals used in the present invention are food additive grade or food grade, they are safe even orally even if provisional cleaning is insufficient. The DC power supply required for the apparatus for carrying out the method of the present invention is not limited to dry batteries, and does not prevent the use of other DC power supplies. Further, the supply voltage and the concentration of the chemical solution (electrolyte solution) are only related to the finishing time and do not necessarily require a range limit, but in reality, the voltage is about 3 V or more, and the concentration of the chemical solution is about 1% or more. Is preferred. The liquid temperature may be room temperature, but heating to about 50 to 60 ° C. is more effective to accelerate the reaction rate. However, no further heating is required. As the anode material, insoluble materials such as stainless steel, graphite and lead can be used.

[0007]

[Embodiment 1] A silver spoon with clouding due to silver sulfide on its surface is used as the negative pole, and the counter electrode of the positive pole is SUS30.
Using 4V and 6V in which four single batteries were connected in series as a DC power source, the material to be treated and the counter electrode were loaded between them.
On the other hand, sodium bicarbonate was used as the electrolyte and its concentration was adjusted to 0.
The liquid temperature can be varied within the range of 05% to 5%, and the liquid temperature is room temperature (18
As a result of a test at 0.degree. C.), an electrolyte solution concentration of 0.05% acted very slightly to remove cloudiness, but it was not practical and the concentration was 0.
At 1%, the action and effect gradually increase, but it is still not practical, and at a concentration of 0.5%, there is a considerable clouding effect, but about 10 minutes are required for the treatment. It is possible to get cloudy by the minute treatment, and it is practical.
The cloudiness was completely removed by the electrolytic treatment for 5 seconds, and the cloudiness was completely removed by the electrolytic treatment for 10 seconds when the concentration was 5%. Embodiment 2. FIG. As is clear from the results of Example 1, even if the temperature of the electrolytic solution is about the provisional room temperature, if the concentration of the electrolytic solution and the electrolytic voltage are properly selected, the purpose of defrosting the silver product is sufficient. Although satisfactory, in this example, the same voltage and electrolytic solution as in Example 1 were used, the solution temperature was treated at 60 ° C., and the results of a test comparison showed that the reaction rate was naturally increased and the concentration was 0.5.
%, The cloudiness was completely removed by the treatment for 1 minute, and the effect of the liquid temperature was also recognized. However, a liquid temperature of 60 ° C. or higher increases the risk of burns in handling, and it is not necessary as an electrolytic treatment condition. Embodiment 3 FIG. As a result of comparison using sodium carbonate instead of sodium bicarbonate in the electrolytic solution under the same electrolysis conditions as in Example 1, as a result of treating for 1 minute at a liquid concentration of 1% even at room temperature (18 ° C.), complete cloudiness was removed. It was found to be slightly stronger than sodium bicarbonate. Embodiment 4. FIG. Under the same electrolysis conditions as in Example 1, the electrolyte concentration was 5
%, And as a result of testing by changing only the DC voltage, a slight defrosting effect is recognized at a voltage of 1.5V, but it is not practical at all and the effect increases from around 3V.
Further, it was confirmed that the processing time was greatly shortened as the voltage was increased to 4.5V and 6V. As another example, by changing the concentration and voltage of an electrolyte solution containing citric acid, tartaric acid, malic acid, gluconic acid, or an aqueous solution containing one or more sodium salts, potassium salts, or ammonium salts of glycolic acid. The cloudiness removing effect was confirmed, and an effect substantially the same as that of the above-described example was confirmed.

[0008]

According to the method of the present invention, a neutral salt aqueous solution of food grade or food additive grade is used as an electrolytic solution, and an electric current of a certain voltage or more is supplied from an external DC power source for electrolytic treatment. Therefore, the following outstanding effects can be expected. 1. It is possible to remove the discoloration of silver by using almost neutral and extremely safe food additive grades such as sodium bicarbonate and food grade organic acids such as citric acid and their neutral salts. Extremely safe and harmless. 2. Discoloration removal reaction speed is extremely fast. 3. By adjusting the electrolytic treatment voltage, the treatment time can be controlled according to the object to be treated. 4. It does not require heating of the treatment liquid (65 ° C or higher, preferably boiling temperature), which is a necessary condition of the conventional electrochemical method utilizing the potential difference of natural generation, and it can be treated extremely quickly even at room temperature, so there is no risk of burns. Safe and easy to handle. 5. Due to the reduction reaction of silver sulfide, the silver surface very naturally regains the original luster of silver, and the finish is better than any other method, and there are no scratches or abrasion of silver itself. 6. There is no limit to the amount of treatment, and it is particularly effective for treating a large amount of silver products at one time and continuous treatment of large silver products. 7. Electrolyte is a food additive grade or food grade neutral salt aqueous solution, so not only is it easy to handle, but in the case of silver tableware etc., it is orally safe even if the liquid remains due to insufficient provisional washing. It is harmless. 8. Since the processing equipment is simple, there are few consumables, and the processing operation is extremely simple and easy, it is particularly suitable for use in hotels and restaurants that handle a large amount of silver tableware.

Claims (1)

(57) [Claims] 1. An aqueous solution containing one or more of sodium, potassium or ammonium salts of bicarbonate, carbonic acid, citric acid , malic acid, gluconic acid or glycolic acid, respectively, is used as an electrolytic solution, and is used as a cathode of a DC power supply. A method for removing discoloration of silver, characterized in that electrolytic treatment is performed under a voltage condition of at least 1.5 V or more between the connected silver to be treated and the conductive counter electrode connected to the anode of the same power source.