JPH08266318A - Bleaching method for pearl - Google Patents

Abstract

PURPOSE: To provide an improved method for bleaching a pearl quickly and economically under a mild condition. CONSTITUTION: Regarding the method for bleaching a pearl, light is applied in the presence of a peroxide, and a transition metal compound or an aluminum compound as a catalyst. As a result, a bleaching time can be surprisingly shortened, and a high pearl bleaching effect can be provided.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to improvements in pearl bleaching methods.

[0002]

2. Description of the Related Art Conventionally, the bleaching method for pearls is pH 7-
A bleaching method is used in which pearls are added to the hydrogen peroxide solution of 9 and left at room temperature for about 7 to 100 days. However, this method takes a long time for bleaching, and the pH of the bleaching solution is lowered during that time by a side reaction. Therefore, the bleaching solution must be replaced once every 2 to 5 days or the pH must be maintained. However, there were problems in workability and economy.

Japanese Patent Publication No. 46-333 discloses a method of bleaching pearls with a combination of hydrogen peroxide, a lower aliphatic saturated ketone and an ether. However, this method uses a volatile organic substance and therefore preserves the working environment. And wastewater treatment is not easy.
In addition, Japanese Patent Publication No. 48-43551 discloses a method of bleaching pearls by combining hydrogen peroxide and heavy water or adding polyvinylinpyrrolidone to this, but this method uses heavy water and therefore costs less. It is costly and not practical.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide a method for bleaching pearls under mild conditions in a short time, efficiently and economically. It is a thing.

[0005]

[Means for Solving the Problems] As a result of intensive studies to develop the pearl bleaching method, the present inventors have added a peroxide and a transition metal catalyst to the treatment liquid and irradiated it with light. As a result, they have found that the bleaching of pearls is significantly promoted, and have completed the present invention. That is, the present invention relates to a method for bleaching pearls, which is characterized in that a peroxide is allowed to act while irradiating light in the presence of a transition metal compound.

The method of the present invention will be specifically described. As the peroxide used in the method of the present invention, hydrogen peroxide, peracetic acid, persulfate, sodium percarbonate, sodium perborate, other inorganic, organic peroxides can be used, but preferably Hydrogen peroxide is used. The amount of peroxide used is
Generally 0.01 to hydrogen peroxide conversion for bleaching solution
The amount is a concentration of 10% by weight, preferably 0.1 to 5% by weight, more preferably 1 to 3% by weight. An aqueous solution of hydrogen peroxide having a concentration of 35% by weight or 60% by weight is commercially available, but this may be diluted before use.

In the method of the present invention, it is preferable that a transition metal compound or an aluminum compound coexists with a peroxide as a catalyst. As the transition metal compound used,
Examples thereof include sulfates, nitrates, hydrochlorides, perchlorates, oxides and hydroxides of iron, manganese, copper, chromium, cobalt, nickel, zinc and the like. Of these, iron, manganese, copper, chromium, cobalt, nickel, zinc sulfate,
Water-soluble salts such as nitrates, hydrochlorides and perchlorates are preferred. In particular, iron sulfate, nitrate or hydrochloride is most preferably used because it is inexpensive and has an excellent bleaching effect.

As the aluminum compound, compounds exemplified by aluminum sulfate, nitrate, hydrochloride, perchlorate, oxide and hydroxide can be used. Of these, water-soluble salts such as sulfates, nitrates, hydrochlorides and perchlorates are preferred. The transition metal compound and the aluminum compound may be anhydrous or hydrated.

The amount of the catalyst used is 0.01 ppm to 20 as the weight of metal atom (or ion) based on the bleaching solution.
It is selected from the amount that gives a concentration of 0 ppm, preferably 0.1 ppm to 100 ppm, and more preferably 1 ppm to 50 ppm.

In the present invention, since the amount of the catalyst used may be a minute amount as described above, the waste liquid is easily treated by a usual treatment method for an aqueous solution containing metal ions, for example, coagulation treatment or ion exchange resin treatment. It

The pH of the treatment liquid during bleaching according to the present invention is generally 4 to 10, and preferably 7 to 9 from the viewpoint of ease of waste liquid treatment.
Is.

Ultraviolet rays are effective as the light used in the method of the present invention. The light source of ultraviolet rays is sunlight,
There are fluorescent lamps, xenon lamps, halogen lamps, low-pressure mercury lamps, high-pressure mercury lamps and the like, preferably xenon lamps, halogen lamps, low-pressure mercury lamps and high-pressure mercury lamps, and more preferably low-pressure mercury lamps.

In order to efficiently carry out the method of the present invention, it is preferable to stir the bleaching solution. The stirring method used at that time is a method capable of stirring the solution, such as a magnetic stirrer, stirring blades, gas bubbling and the like. Any of them will do.
In the method of the present invention, it is also preferable to add a penetrant such as a surfactant to the bleaching solution.

[0014]

EXAMPLES Next, the method of the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples.

Example 1 Water, an aqueous solution of hydrogen peroxide, ferric chloride and an aqueous solution of caustic soda were added to a beaker to prepare an aqueous solution having a hydrogen peroxide concentration of 3% by weight, an iron concentration of 3 ppm and a pH of 7. . As a pearl to be bleached, a round hole pearl with a diameter of about 8 mm was placed in it, and the liquid was stirred at 25 ° C, and a low-pressure UV lamp (10 W) was used.
Was irradiated for 20 hours. The treated pearls were highly white and shining. Further, the processing solution was not exchanged and the pH was not adjusted through the bleaching operation.

Comparative Example 1 The same treatment as in Example 1 was carried out for 20 hours, except that ferric chloride was not added and the ultraviolet lamp was not irradiated.
The treated pearls were not bleached at all.

Comparative Example 2 The same treatment as in Example 1 was carried out for 20 hours except that ferric chloride was not added. The treated pearls were not bleached at all.

Comparative Example 3 The same treatment as in Example 1 was carried out for 20 hours except that the ultraviolet lamp was not irradiated. The treated pearls were not bleached at all.

Comparative Example 4 Water, an aqueous solution of hydrogen peroxide and an aqueous solution of caustic soda were added to a beaker to prepare an aqueous solution having a hydrogen peroxide concentration of 3% by weight and a pH of 7. As the bleached pearls, round hole-shaped pearls having a diameter of about 8 mm were put therein, and the liquid was stirred at 25 ° C. and treated without being irradiated with an ultraviolet lamp. The treatment liquid was replaced with a newly prepared treatment liquid once every three days, and bleaching treatment was performed for 30 days. The treated pearls were bleached white, but Example 1
It was inferior to the pearls bleached in.

Example 2 The same treatment as in Example 1 was carried out for 20 hours, except that manganese chloride was used as the catalyst instead of ferric chloride in the same amount. The treated pearls were well bleached.

Example 3 The same treatment as in Example 1 was carried out for 20 hours, except that copper (II) chloride was used as the catalyst in the same amount as copper (II) chloride instead of ferric chloride. The treated pearls were well bleached.

Example 4 As a catalyst, cobalt (II) chloride was used instead of ferric chloride.
The same treatment as in Example 1 was performed except that the same amount of metal was used.
I went on time. The treated pearls were well bleached.

Example 5 As a catalyst, nickel (II) chloride was used instead of ferric chloride.
The same treatment as in Example 1 was performed except that the same amount of metal was used.
I went on time. The treated pearls were well bleached.

Example 6 As a catalyst, chromium (III) chloride was used instead of ferric chloride.
The same treatment as in Example 1 was performed except that the same amount of metal was used.
I went on time. The treated pearls were well bleached.

Example 7 The same treatment as in Example 1 was carried out for 20 hours except that zinc chloride was used as the catalyst instead of ferric chloride in the same amount. The treated pearls were well bleached.

Example 8 The same procedure as in Example 1 was repeated except that aluminum chloride was used as the catalyst in place of ferric chloride in the same amount.
I went on time. The treated pearls were well bleached.

As can be seen from the above, the method of the present invention can dramatically reduce the bleaching time of pearls and is excellent in the bleaching effect of pearls.

[0028]

According to the present invention, the bleaching time for pearls can be dramatically shortened and the bleaching effect for pearls is excellent as compared with the conventional bleaching methods.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaaki Kanda 6-1, 1-1 Shinjuku, Katsushika-ku, Tokyo Mitsubishi Gas Chemical Co., Ltd. Tokyo Laboratory

Claims (5)

[Claims] 1. A method of bleaching pearls, which comprises irradiating light with a peroxide to act on the pearls. 2. The method for bleaching pearls according to claim 1, wherein a transition metal compound or an aluminum compound is made to coexist with a peroxide as a catalyst. 3. The transition metal compound is a sulfate, nitrate of iron, manganese, copper, chromium, cobalt, nickel and zinc,
The pearl bleaching method according to claim 2, wherein the pearl bleaching is at least one selected from the group consisting of a hydrochloride, a perchlorate, an oxide and a hydroxide. 4. As a catalyst, at least one selected from the group consisting of aluminum sulfate, nitrate, hydrochloride, perchlorate, oxide and hydroxide is allowed to coexist with the peroxide. The method for bleaching pearls according to claim 2. 5. The method for bleaching pearls according to claim 1, wherein the irradiation light is ultraviolet light.