WO2021221575A1 - Silver clays suitable for production of tarnish resistant jewelry - Google Patents

Abstract

It is related to obtaining silver clays, suitable for production of tarnish-resistant silver objects and jewelry, when it is molded or formed by hand and then dried and fired at appropriate temperatures.

Description

SILVER CLAYS SUITABLE FOR PRODUCTION OF TARNISH RESISTANT

JEWELRY

SUMMARY

It is related to obtaining silver clays, suitable for production of tarnish-resistant silver objects and jewelry, when it is molded or formed by hand and then dried and fired at appropriate temperatures.

KNOWN STATE OF THE TECHNIQUE

In the current applications, classical jewelry techniques are used in the main model designs and in the production of certain ornaments and objects, especially in the jewelry sector.

It is necessary to use devices such as cylinders, rolling mills, molds, presses, casting machines, special welding machines for production in workshops and factories working on this subject. In addition to these, it is obligatory to supply various consumables such as investment powders, casting waxes as well as expert personnel who can use these devices.

The device, expert personnel and consumable requirements in question need a substantial investment in the said business area. This situation adversely affects the participation of hobbyists, small-scale designers and manufacturers in the sector.

One of the traditional methods used in the production of metal objects is the use of powder metal technologies. In the said technique, the mixture of resin-containing binders and oils with various metal powders or metal alloy powders is molded and shaped in presses. These formed pieces are then fired in a reducing atmosphere consisting of a mixture of approximately 95% Nitrogen and 5% Hydrogen. Thus, while saving energy, raw materials and auxiliary raw materials, a metal mass is obtained as desired, various machine parts such as complex shaped parts and self- lubricating bearings can be produced with the mentioned technique, as well as decorative items, jewelry products, bijouterie products and sculptures. In powder metal technology, metal alloy powders are used as well as the mixture of elemental metal powders. As a result of sintering, the alloy of these metals is formed. However, due to the need for special atmosphere ovens, mixers and presses in the implementation of the mentioned method, it also eliminates the applicability of the method in an economical and practical way in the workshop and home environment.

Another method currently used is metal powders mixed with water and the binders to make them what is called, metal clays. In this application, after the metal clay is molded, shaped by hand and hand tools, to a desired form and dried. Then it is sintered at the temperature and time recommended by the manufacturer and it turnes to metal.

In the market, there are commercial products related to this subject. Some of these products are silver clays made of pure silver, which are not useful due to the softness of pure silver. To eliminate this disadvantage, silver clays were produced from the metal powder produced from the 925-960 sterling silver alloy prepared by adding an amount of copper between 4.0% and 7.5%, or by adding copper powder to the silver powder in this proportion. However, the parts produced from these low carad silver- clays are not durable enough, and they have firestain when heated for welding, and there is tarnish problem in the finished products. The tarnish problem which is important problfor endusers, is tried to be delayed with a protective coating, but it is not a definitive solution. When the coating on the surface is worn off, the object becomes darker again. Our invention provides the production of silver clays, which enables the production of tarnish resistant objects.

Commercial examples for currently available low-earad silver clays are:

Odak Art Hobby and Kraft Industry. Di§ Tic. Ltd. Sti. Prometheus Silver Clay .960 branded product,

Aida Chemicals co. Art Clay 950 branded product,

Mitsubishi Materials Trading co. PMC Sterling brand product,

Metal Adventures Inc.'s EZ960 branded products.

Some patents on this subject are as follows:

Patent U8S376328 refers to a precious metal product obtained by sintering a precious metal powder into a solid phase form. In order to produce said precious metal product, a moldable mixture containing spherical particulate precious metal powder and a binder that disappears when sintered is formed into a predetermined mold and then the molded element is sintered. The most preferred mo!dabie mixture contains 50-90% by weight of metal powder, 0.8% -8.0% water soluble cellulose binder, 0.08%-3,0% surface-acting agent. Precious metal preferably contains gold powder, silver or copper alloys.

Patent US5702501 discusses a metal clay mixture for a precious metal molded product and a method for producing it. To obtain a molded product containing precious metal, the mixture essentially contains a spherical particulate metal powder and water-soluble organic resin and water as an organic binder with starch. The ratio of total organic binder; starch and water-soluble resin and precious metal powder corresponds to the range of 0.02% to 3.0%.

Patent US629Q744, refers to sintering of noble metals and a method related thereto are mentioned. The mixture of the invention; It contains spherical particulate pure metal powders and metal alloy powders, 0.022% to 3.0% by weight of cellulose-type water soluble resin, 0.02% to 3.0% by weight of starch and 0% to 5% by weight, reticular macromo!ecular material.

Patent US6572670 is about, colored metal clay and colored metals. The mixture for shaping metal objects comprising a powder of jewelry metal and a second powder of a refractory material. It is stated that the mixture allows a wide variety of colors in the preparation of metal jewelry.

US8840979 discloses a clay mixture for forming precious metals and a method for sintering thereof. The mixture of the invention is 30% to 70% by weight spherical powder with an average radius of 2.2 - 3.0 pm as the main component, and 70% to 30% by weight of powder and a binder mixture of a starch and water based cellulose derivative.

US7081149 patent mentions silver clay comprising a silver powder. In particular, a silver clay is proposed by sintering at low temperatures in the present invention. The silver powder for the silver clay mentioned herein comprises silver powders of spherical powder with an average particle radius of less than or equal to 2 pm and 15-50% by weight. The rest of the mixture consists of spherical particles with a particle radius above 2 pm and less than or equal to approximately 100 pm. US 8496726B2 and U89399254B2 are spherical Ag powder obtained by Microtrack method, aimed to increase the mechanical properties of the sintered body and comprises CuQ and Cu2G, which are reducted to Cu and 02 when heated,

Objects produced from currently known metal clays can be easily bent , deformed, and broken, Also, the parts produced from these metal clays are oxidized when they are heated for the welding process and there is a tarnish problem for finished products.

0810,323,310, 11829,708,691 , 0839,222,150 and 0846,168,071 , mention a Ag alloy comprising at least 77% Ag, also Cu, Ge, Zn and B; that the parts produced thereof do not oxidized when heated for welding and the finished products are tarnish resistant. Boron provides grain refinement in this alloy. Germanium oxidizes at about 400 degrees and protects the surface from oxidation by covering the surface of the alloy with the transparent Ge02, which acts as Cr in stainless steel. An alloy with these characteristics is the Argentium® Silver registered trademark of the company, Argentium International Limited and “Argentium Silver Clay Powder”, which is produced by another company using the powder of Argentium® silver alloy, sold as 1 packet of powder and a bottle of liquid that, users must mix them and use, Also, it is adviced by the manufacturer that.it should be consumed in the same day because cannot remain even next day and deteriorates. In addition, the firing of this clay is 2 steps; a burning step at 500 degrees and then embedded in activated carbon in a container and heating at 830 degrees for 2-3 hours . This is long and laborious process for the users

THE AIM OF THE PRESENT INVENTION

Based on the state of the art, the aim of the invention is to create a silver clay at perfect plastic consistency that will not stick to the hands and working tools during use. It is to that enables the production of durable objects. Another object of the invention is to produce silver clays, easy to sinter and turn into metal, and when sintered, the artist can adjust the shape by bending if necessary, and also to produce abrasion resistant jewelry. Another object of the invention is to reveal the silver clays that allow the production of jewelry and objects that shine very well in polishing. Detailed Description of the invention

In the present invention, we used powders of metals, metal alloys, metal salts and oxides clays alone or mixtures thereof differently than those used in the manufacture of silver before. We used synthetic or natural binders for example, Cellulose derivatives, Polymers, Acrylic acid derivatives, Starches, Waxes, Sahlep or mixtures of at least 2 of them. The ratio of binders to metal clay can be 0.1% to 10% by weight. Water, methyl alcohol, ethyl alcohol, synthetic thinner, cellulosic thinner, kerosene, liquid paraffin can be used alone or as a solvent of at least 2 of them. In addition, the surface wetting agent is added to increase the wettability of the powders, and the oil is added to the mixture to prevent the sticking to the working surface and hands; and the metal oxides to increase the plasticity of the clay, helping the burnout of the binder asweil. Oils are natural or synthetic oils in liquid or solid form. The ratio of the mentioned wetting agents to the total weight of metal powders and oxides is 0.01% to 5.00% and oils between 0.01% and 5.00%.

We experimented several powder blends to obtain silver clays which will ensure that the metal object that will be formed as a result of the sintering process will have a hardness suitable for working by the artist with hand tools or hammering if necessary, but allows the production of jewelry and objects that won't tarnish during use, at the same time and not be oxidize when heated for the welding process., which allows the production of jewelry and objects that won't tarnish during use.

We used the powders of Ag, Cu, Ge, In, Zn and Cu powder, Ag alloys, CuB, Cu20, CuO, ZnO, Ge02, InO, ln2G3 and AgO powders. A purpose of using oxides beside or instead of Cu, Ge, In and Zn metal powders is to contribute to the combustion of the binders contained in the structure of the metal clay. In this way, the fired piece, while trying to maintain the oxygen to burn the binder required from the surface, also provides the oxygen released from the metal oxides, while the heat is risingwhich aids the burnout of the binder deep inside the piece.

This mechanism works as follows. The oven temperature starts around 180°C and the binder in the structure of the metal clay is carbonized. The formed carbon, after 60G°C, reduces the metal oxides mentioned, with releasing 02 and the binder completely leaves the body as CO and C02, while the metals formed as a result of the reduction fuse with each other and Ag powder to form a silver alloy whose mechanical properties are ideal. Thus, even thick parts can be sintered more homogeneously without containing carbonized binder residues.

Another benefit of adding metal oxides in addition to metal powders to the metal clay is that thanks to the small size of the oxide particles, the plasticity of the metal clay increases and it is easier to form and mold, and the surface of the sintered part becomes smoother.

In our experiments, (A) .999 carat Ag powder, (B) .930 carat Ag/Cu alloy powder (C) Argentium© Silver alloy powder, (D)A powder mixture: 97% Ag powder, 0.5% Ge powder, 0.5% Zn powder, 0.0002% - 5% B - Cu powder, the rest Cu powder, (E) A powder mixture: 95.0% Ag powder, 2.1% Ge02 powder, 0.6% ZnO powder, 0.0005% B - Gu powder and the rest Gu powder was used. The particle size of the powders in every five groups are <20 pm. A, B, C powders and D and E powder mixtures were kneaded separately with the binder and wafer and made into a homogeneous dough We named them A Clay, B Clay, C Clay, D Clay and E Clay, respectively.

The binder used is Cellulose derivatives, Glycol derivatives, Acetate derivatives, Acrylates, Starches, Sahlep, one or at least a mixture of both. On a Teflon surface using 1.5 mm thickness strips, 10 mm. width and 40 - 50 mm. 2 strips of each clay sample were cut and numbered.

The strips were dried with a hair dryer, their length was measured with a micrometer with a precision of 0.01 , and was fired in Odak Sana! Hobi ve Kraft San. Dis Tic Ltd. Prometheus brand Pro-7 PRG type oven at normal atmosphere environment, at various temperatures and times. The strips removed from the oven were cooled, their surfaces were sanded and then cleaned by washing with detergent. One strip from each of the 5 groups was kept in a 700-degree oven on the rack for 15 minutes and was removed and cooled and observed whether there was blackening (oxidation) on their surfaces.

The second strips were immersed in 0.05% Liver of Sulfur solution, kept at room temperature for 24 hours and it was observed whether there was blackening on their surfaces. The results are summarized in Table 1.

As seen in Table 1 , acceptable sintering was provided in all 5 clays. Sintered pieces of clays A, C, D and E did not darken when heated to 700 only the B darkened. Sintered pieces of clays A and B tarnished after Liver of Sulfur bath, while the parts sintered from C, D and E did not.

As can be seen, the main element of our experiments is Silver, but pure Silver is a soft metal. This softness is unfavorable in terms of bending deformation and easy wear, especially for users of jewelry products. For this reason, 925 - 960 Ag alloys are generally used in silver jewelry; 900 - 910 Ag alloys are used in products such as picture frame, fork - spoon, vase and silverware. The alloys used for this purpose are prepared with mainly Ag, Cu and sometimes Zn and A! metals added in small amounts. Although 910 - 960 carat Ag alloys are sufficient in terms of hardness and durability, they are oxidized when heated for welding, which causes an autogenous welding impossib!e(2 parts to be welded without welding material). In addition, jewelry and other objects made of 910 - 960 carat Ag alloys are highly affected and darkened by sulfur in the air, as well as oxidation during use.

Claims

1 A silver clay, comprising one or more powders, natural and / or synthetic binders, wetting agents, surfactants, oils and water.

2 A powder according to claim 1 , is a Ag alloy powder.

3 An Ag alloy powder according to claim 1 and 2, comprises 90-97% by weight,

2.5% Ge, 0.0000001-0.01% B and 0.5% -7.5% Cu and particle size <40 pm.

4 A natural and synthetic binder according to claim 1 to be cellulose derivatives, polymers, acrylic derivatives, vinyl derivatives, starches, waxes or sahlep or a mixture of at least two of these and at 0.1% to 10% of the silver clay of this invention.

5- A wetting agent and oil according to claim 1 , wherein each ratio to binder is 0.1% to 40% by weight.

6- A silver clay according to claim 1 , wherein the powders in its mixture are 90% - 97% Ag powder, 1% -5% Ge02 powder, 0.0001% -0.01% Gu-B powder and 0.5% - 7% 5 Gu powder and their particle sizes are less than 40 microns.

7- A silver clay according to claim 1 , wherein the binder is Cellulose derivatives, Polymers, Acrylic derivatives, Vinyl derivatives, Starches, Waxes, Sahlep or a mixture of two of them, and this binder is from 0.1% to 10% by weight of the silver clay.

8. A wetting agent, surfactant and oil according to claim 1 , wherein each of their ratio to binder is 0.1% to 40% by weight.

9. A powder of claim 1 , wherein 90% to 97% by weight of Ag powder, 1% - 2.5% of Ge powder, 0.0001% - 0.01% of 2% Gu -B powder and 0.5% - 7.5% is Cu powder and particle sizes are <40 pm.

10-A natural and / or synthetic binder of claim 1 , wherein the cellulose derivatives, polymers, acrylic derivatives, vinyl derivatives, starches, waxes, sahlep or a mixture of at least two of these, and 0.1% to 10% of the silver clay of this invention.

11. A wetting agent and oil of claim 1 , wherein each ratio to binder is 0.1% to 40%.