Sweat-resistant Au alloy for jewelry and method for manufacturing the same

Abstract

To provide a sweat-resistant Au alloy for jewelry that comprises a specified quantity of Au, along with relatively large quantities of Ag and Cu to enhance its hardness and tensile strength, thereby preventing any discoloration induced by sweat.SOLUTION: A sweat-resistant Au alloy for jewelry comprises Au of 15.0-30.0 mass%, further comprising at least one platinum group element of 0.005-5.0 mass%, with the total content of Ag and Cu being at least 65.0 mass%, and the balance being Zn.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an Au alloy for jewelry.

Background Art

[0002] Generally, as an Au alloy for jewelry containing a certain amount of Au such as K5, an alloy material in which Au is added with Ag, Cu, and further Zn or the like is known for the purpose of improving workability or hardness and tensile strength (or tensile strength). However, when the blending amounts of Ag and Cu increase, for example, when the total of Ag and Cu reaches about 65% by mass or more, discoloration due to oxidation tends to occur. In particular, jewelry and ornaments such as rings, earrings, and necklaces directly touch the human skin, so there is a problem that the Au alloy easily discolors due to an acidic environment such as sweat. In addition, in an Au alloy for jewelry having a relatively high Au content such as 18K, in order to give a new color tone, it has been conventionally reported that Pt, Pd, Ag, and Cu are added little by little (Patent Document 1), but a technique for preventing discoloration due to sweat has not been reported in these Au alloys.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention aims to prevent the occurrence of discoloration (such as blackening or a decrease in gloss) due to sweat or the like that occurs when Ag and Cu are blended in a relatively large amount (the total of Ag and Cu is 65% by mass or more) in an Au alloy containing a certain amount of Au such as K5 in order to improve workability and give hardness and tensile strength.

Means for Solving the Problems

[0005] In research aimed at developing discoloration-resistant alloys for Au alloys containing a certain amount of Au, such as K5, we found that by adding a certain amount of at least one platinum group element, such as Pt, it is possible to obtain an alloy that is resistant to discoloration in acidic environments such as those caused by sweat. In other words, the present invention provides the following: [1] The Au alloy for jewelry containing 15.0 to 30.0 mass% of Au, containing 0.005 to 5.0 mass% of at least one platinum group element, containing at least 65.0 mass% of Ag and Cu in total, with the remainder being Zn. [2] The Au alloy for jewelry according to [1], wherein at least one platinum group element is Pt and / or Pd. [3] The Au alloy for jewelry described in [1] above, containing 19.0 to 23.0% by mass of Au. [4] The Au alloy for jewelry described in [1] above, containing 0.005 to 2.0 mass% of platinum group elements. [5] The Au alloy for jewelry described in [2] above, containing 0.005 to 2.0 mass% of Pt and / or Pd, 10.0 to 30.0 mass% of Ag, and 35.0 to 70.0 mass% of Cu. [6] The Au alloy for jewelry described in [2] above, containing 19.0 to 23.0 mass% of Au, 0.005 to 2.0 mass% of Pt and / or Pd, 15.0 to 25.0 mass% of Ag, and 40.0 to 60.0 mass% of Cu. [7] A method for producing an Au alloy according to any one of the above items [1] to [6], comprising the step of melting and mixing at least Au, Ag, Cu and at least one platinum group element at 1500 to 1850°C. [Effects of the Invention]

[0006] By using the Au alloy for jewelry of the present invention to manufacture jewelry such as rings and earrings, discoloration in acidic environments such as sweat can be prevented, and jewelry with high added value can be manufactured. [Modes for carrying out the invention]

[0007] <Au alloy for accessories> The Au alloy for jewelry of the present invention is an Au alloy for jewelry containing 15.0 to 30.0 mass% of Au, containing 0.005 to 5.0 mass% of platinum group elements, containing at least 65.0 mass% of Ag and Cu in total, with the remainder being Zn. In this specification, "jewelry" refers to ornaments that are generally manufactured using Au alloy, such as rings, earrings, piercings, bracelets, necklaces, anklets, pendants, brooches, and watches. It is sufficient that at least a portion of these jewels uses the Au alloy of the present invention.

[0008] In this specification, an Au alloy refers to an alloy containing 15.0 to 30.0 mass% of Au. Au alloys include those with various Au content, such as K18, K10, K8, and K5, and are selected appropriately depending on the type, use, or design of the jewelry. The present invention focuses on an Au alloy containing 15.0 to 30.0 mass% of Au, and a total of at least 65.0 mass% of Ag and Cu. For example, Au alloys with gold content such as K5 and K7 are preferred. The Au content in the Au alloy of the present invention is 15.0 to 30.0 mass%, preferably 19.0 to 23.0 mass%, and more preferably 20.5 to 21.5 mass%.

[0009] The Au alloy of the present invention mainly contains Cu and Ag in addition to Au, with a total Cu and Ag content of 65% by mass or more. The inclusion of Cu and Ag particularly improves the workability of the Au alloy and allows for adjustment of hardness and tensile strength. It is preferable to contain 10.0 to 30.0% by mass of Ag, and more preferably 15.0 to 25.0% by mass. It is preferable to contain 35.0 to 70.0% by mass of Cu, and more preferably 40.0 to 60.0% by mass. The total mass of Cu and Ag is preferably 68.0% by mass or more, more preferably 70.0% by mass or more, even more preferably 72.0% by mass or more, and also preferably 85.0% by mass or less, more preferably 80.0% by mass or less, and even more preferably 75.0% by mass or less, from the viewpoint of balancing workability and cost.

[0010] The Au alloy of the present invention is characterized by containing 0.005 to 5.0 mass% of platinum group elements in addition to the predetermined content of Au, Cu, and Ag mentioned above. The reason is unknown, but it has been found that this prevents discoloration in acidic environments such as sweat. That is, by adding 0.005 to 5.0 mass% of platinum group elements such as Pt or Pd to the alloy, it is possible to prevent discoloration (blackening) that is observed in conventional Au alloys that do not contain platinum group elements in acidic environments. The content of platinum group elements in the Au alloy is preferably 0.005 to 2.0 mass%, more preferably 0.008 to 1.0 mass%, even more preferably 0.01 to 0.8 mass%, still more preferably 0.02 to 0.5 mass%, and even more preferably 0.05 to 0.2 mass%. Platinum group elements refer to ruthenium, rhodium, palladium, osmium, iridium, and platinum, which belong to groups 8, 9, and 10 of the periodic table, excluding the iron group elements. It is preferable to select from the group consisting of rhodium, palladium, osmium, iridium, and platinum, and it is preferable that the elements be palladium (Pd) and / or platinum (Pt). Furthermore, from the viewpoint of the effect when used in the same amount, Pt is more preferable.

[0011] As described above, the Au alloy of the present invention contains predetermined amounts of Au, Cu, Ag, and platinum group elements, with the remainder being Zn. The Zn content is preferably in the range of 1.0 to 10.0 mass%, and more preferably in the range of 2.0 to 7.0 mass%. Adding a small amount of Zn lowers the melting point, which improves the fluidity during casting and thus the workability. It is also preferable to add Zn because it has an antioxidant effect on the Au alloy.

[0012] One preferred embodiment of the present invention is an Au alloy for jewelry, which contains 15.0 to 30.0 mass% of Au, 10.0 to 30.0 mass% of Ag, 35.0 to 70.0 mass% of Cu (provided that the total amount of Ag and Cu is 65.0 mass% or more), 0.005 to 2.0 mass% of Pt or Pd, with the remainder being Zn. Another preferred embodiment of the present invention is an Au alloy for jewelry containing 19.0 to 23.0% by mass of Au, 15.0 to 25.0% by mass of Ag, 40.0 to 60.0% by mass of Cu (provided that the total amount of Ag and Cu is 65.0% by mass or more), 0.005 to 2.0% by mass of Pt or Pd, with the remainder being Zn.

[0013] <Manufacturing method for Au alloy used in jewelry> Another aspect of the present invention is a method for producing the above-described Au alloy, comprising the step of melting and mixing at least Au, Ag, Cu and at least one platinum group element at 1500 to 1850°C. In the manufacturing method of the present invention, the temperature for melting and mixing predetermined amounts of each raw material metal of Au, Ag, Cu, and platinum group elements is preferably 1550 to 1750 °C. When the platinum group element is Pd, the temperature is preferably 1550 to 1650 °C, and more preferably 1555 to 1620 °C. When the platinum group element is Pt, the temperature is preferably 1650 to 1850 °C, more preferably 1700 to 1820 °C, and even more preferably 1768 to 1800 °C. When the temperature is low, uniform melting and mixing may not occur. Whether these metals are melted can be confirmed visually and by an X-ray inspection machine. As the X-ray inspection machine, for example, XAN 252 manufactured by Fisher Instruments can be used. After that, the remaining amount of Zn is added and melted to obtain an Au alloy. At this stage, whether the metal is melted can be confirmed visually and by an X-ray inspection machine. The molten metal can be cooled and rolled, for example, into a square bar. Then, the alloy can be melted using a casting machine or the like and an ingot can be manufactured using a mold. From the obtained ingot, it is possible to manufacture the target jewelry and its parts, etc. by a normal method.

Examples

[0014] [Examples 1 to 4 and Comparative Example 1] <Manufacture of K5 alloy (ingot)> The conventional product and the K5 alloy of the present invention were manufactured according to the following procedure. (1) Each amount shown in Table 2 (the “%” in Table 2 means “mass %”) of Au, Ag, Cu, Pt (or Pd) was put into a casting machine and melted. The melting temperature was 1768 °C or higher, which is the melting point of Pt. Whether the above quaternary alloy was uniformly melted was confirmed visually by a veteran casting worker and also by an X-ray inspection machine (XAN 252 manufactured by Fisher Instruments). (2) Then, 5.0 mass % of Zn was added to produce a quinary alloy. Whether Zn was dissolved was confirmed visually by a casting worker and also by an X-ray inspection machine (XAN 252). (3) The manufactured five - element alloy was cooled and rolled into a square bar. (4) The five - element alloy was melted in a casting machine and poured into a mold. The entire five - element alloy poured into the mold was placed in water to cool the ingot. (5) The ingot was taken out of the mold to obtain a K5 cast ingot (Comparative Example 1, Examples 1 - 4).

[0015] <Manufacture of Jewelry> A mold was fabricated from the prototype of the jewelry (ring) according to the conventional method, and the mold was set in a vacuum suction pressure casting machine. The ingots of Comparative Example 1, Examples 1 - 4 prepared above were poured into it. The mold was taken out of the casting machine, quenched and slowly cooled with water, the embedding material was removed, and finally pickling was performed to bring out the original color of the ingot and a polishing finish was carried out.

[0016] <Sweat - resistance Test> The rings manufactured from the ingots of Comparative Example 1, Examples 1 - 4 were immersed in artificial sweat with the following composition (using "ATTS artificial sweat (acidic)" of the ATTS Fiber Products Technology Research Association), and left standing in a constant - temperature bath at 47 ± 2 °C for the following standing time. After that, they were taken out from the artificial sweat, washed, dried, and then the appearance was observed. This test was conducted by Nippon Labotech Co., Ltd. which specializes in product quality control. Based on the appearance observation, a description was made about how the rust and color changed compared with the pre - immersion (untreated product), and based on that, the evaluation was carried out as follows. ○: No rust was confirmed. The color became slightly darker. ×: No rust was confirmed. The darkness increased and the color became darker. The results are shown in Table 2.

[0017]

Table 1

[0018]

Table 2

[0019] As is clear from Table 2, the conventional product showed an increase in blackening and a darker color after 96 hours of immersion in human sweat. On the other hand, in the alloys with 0.01% or 0.1% Pt or Pd added in Examples 1 to 4, the color only slightly darkened after 96 hours (Table 2). Just by adding a very small amount of Pt or Pd, 0.01 - 0.1% by mass, the sweat resistance (discoloration suppression) was clearly improved, which is a surprising effect. After 96 hours, the discoloration gradually progressed, and after 240 hours, the discoloration progressed to the same extent as the conventional product.

[0020] [Example 5] <Manufacture of K5 alloy (ingot)> Following the same procedure as in Example 1, K5 alloys of Example 5 and Comparative Examples 1 - 2 were manufactured. The metal composition of Example 5 used the same composition as that of Example 1, except that Ag was 21.37% by mass and Pt was 0.5% by mass. The metal compositions of Comparative Examples 1 - 2 were exactly the same as those of Comparative Example 1. <Manufacture of ornaments> Ornaments (rings) were manufactured from the K5 alloys of Example 5 and Comparative Examples 1 - 2 in the same way as in Example 1. <Sweat resistance test> The manufactured rings were immersed in artificial sweat under the same conditions as in Example 1. After a predetermined standing time, they were washed and dried, and then the appearance was observed. For Example 5, this was repeated for 3 specimens, and for Comparative Examples 1 - 2, it was repeated for 2 specimens. This test was conducted by Nippon Labotech Co., Ltd., which specializes in product quality control. When evaluated at a standing time of 192 hours, for all specimens of Example 5, compared with before immersion (untreated product), "No rust was confirmed. The color slightly darkened." (Evaluation: ○). On the other hand, for all specimens of Comparative Examples 1 - 2, "No rust was confirmed. The blackening increased and the color darkened." (Evaluation: ×). Just by adding 0.5% by mass of Pt, the sweat resistance (discoloration suppression) was clearly improved, which is a surprising effect.

Claims

1. An Au alloy for jewelry containing 15.0 to 30.0 mass% of Au, further containing 0.005 to 2.0 mass% of at least one platinum group element, containing at least 65.0 mass% of Ag and Cu in total, with the remainder being Zn.

2. The Au alloy for jewelry according to claim 1, wherein at least one platinum group element is Pt and / or Pd.

3. The Au alloy for jewelry according to claim 1, containing 19.0 to 23.0% by mass of Au.

4. The Au alloy for jewelry according to claim 1, containing 0.008 to 1.0 mass% of platinum group elements.

5. The Au alloy for jewelry according to claim 2, containing 0.005 to 2.0 mass% of Pt and / or Pd, 10.0 to 30.0 mass% of Ag, and 35.0 to 70.0 mass% of Cu.

6. The Au alloy for jewelry according to claim 2, containing 19.0 to 23.0 mass% of Au, 0.005 to 2.0 mass% of Pt and / or Pd, 15.0 to 25.0 mass% of Ag, and 40.0 to 60.0 mass% of Cu.

7. A method for producing an Au alloy according to any one of claims 1 to 6, comprising the step of melting and mixing at least Au, Ag, Cu and at least one platinum group element at 1500 to 1850°C.

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