Classifications

• • A—HUMAN NECESSITIES
  • A44—HABERDASHERY; JEWELLERY
  • A44C—PERSONAL ADORNMENTS, e.g. JEWELLERY; COINS
  • A44C27/00—Making jewellery or other personal adornments
  • A44C27/001—Materials for manufacturing jewellery
  • A44C27/002—Metallic materials
  • A44C27/003—Metallic alloys
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/20—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces by extruding
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C32/00—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ
  • C22C32/0094—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with organic materials as the main non-metallic constituent, e.g. resin

Definitions

• the present invention relates to a method for producing an alloy for ornamental articles and to an alloy for ornamental articles which can be obtained in particular by means of this method.
• the method and the alloy according to the present invention may advantageously be used in the manufacturing industry for the production of precious semi-finished articles.
• gold, silver and platinum are precious metals which are widely used in the production of articles of jewellery, among other things because of their malleability and ductility and their aesthetic characteristics.
• precious metals are not used in the pure state, but alloyed with other metals, in order to modify their mechanical properties, their aesthetic characteristics and in particular their colour or also only the “carat value” and therefore the cost of the ornamental articles obtained with these metals.
• the precious metal content of a product is usually indicated by means of an index called the "purity index" which is generally expressed as a fraction of the metal, in thousandths, relative to the total weight of the said product.
• the said index may also be expressed in carats (K), in this case the fraction of metal relative to the overall weight of the product being expressed in twenty-fourths (1/24), instead of thousandths as with the purity index.
• the platinum alloys which are currently used in the precious metals industry have purity indices which are standardized and equal to 850/1000, 900/1000 or 950/1000, while the purity indices for gold typically are equal to 18 carats (75.0%) for southern Europe; 24 carats 'Chuk Kam' (minimum 99,0%) for the Far East (China, Hong Kong, Taiwan); 22 carats (91.6%) for India; 21 carats (87.5%) for the Arab countries; and 8-18 carats (33.3 - 75.0%) for northern Europe and the USA.
• the mechanical properties must be such as to allow the use of the alloys in the standard processes and treatments employed in the gold and silver industry (ease of melting, weldability, diamond-machinability, possibility of recovering and reusing the waste product, etc.). It is in fact evident that the alloys must at least not require complex processing techniques such that their use becomes uneconomical.
• the alloys for gold and silverware must ensure a slow release of allergy-producing agents such as nickel and cobalt.
• the metal elements which are currently most used for gold alloys are: silver (Ag), copper (Cu); zinc (Zn); indium (In); palladium (Pd); nickel (Ni); while those most used for platinum alloys are: cobalt (Co), iridium (Ir), gold (Au), palladium (Pd), rhodium (Rh) and ruthenium (Ru).
• patent US 4,476,090 describes an alloy for articles of jewellery with a low density, which is composed of a noble metal or a noble metal alloy and by glass in a percentage amount of between 1 and 70 %.
• the patent US 5,578,383 describes an alloy for articles of jewellery with a low density, which is composed of a noble metal or a noble metal alloy in a percentage amount of between 33 and 99 % and a percentage amount of between 1 and 67 % of a thermosetting crosslinkable polymer.
• the end product is obtained by mixing two or more mutually reactive liquid precursors which are poured into a mould and which, as a result of their mutual reaction, are converted into a crosslinked solid which cannot be shaped by the action of heat.
• the articles of the type described hitherto all have the drawback that they require a complex production process which is not practical and unsuitable for achieving a high dispersion of the metallic powder within the polymer or vitreous matrix, which is able in particular to ensure the same concentration or the same purity index at all points within the product.
• the patent US 4,282,174 describes a technique for producing articles for the gold and silver industry which envisages producing beforehand plastics powders with very fine dimensions and combining the plastics powders with metal powders having dimensions of between % and 50 micron, resulting in a mixture of powders which are used for pressing at high pressures and at temperatures of between 100 and 250 °C in order to obtain the articles with the desired shape and size.
• a first drawback of the production process described in this patent consists in the use of complex processes in order to obtain the pulverised plastic material.
• thermoplastic polymers such as polyethylene, polystyrene, polymethylmethacrylate and polyamide which have a limited resistance, namely a high hardness factor and poor elasticity.
• the production method for forming the ornamental articles is performed by dry mixing the particles of the polymer component and metal component in the powder state and then by means of subsequent injection in a mould.
• This production method has, in practice, proved to be unsuitable for obtaining jewellery with superior mechanical properties and in particular with a highly uniform dispersion of the precious metal in the polymer matrix.
• the main object of the present invention is to provide a method for producing an alloy for ornamental articles which allows a homogeneous product to be obtained, having mechanical properties which are able to ensure a notable degree of comfort when the product is worn and are distinguished by a high elasticity.
• Another object of the present invention is to provide an alloy for ornamental articles which is extremely homogeneous and able to ensure a highly uniform concentration of the constituents throughout the product.
• a further object of the present invention is to provide a method for producing an alloy for ornamental articles which is simple to produce and operationally entirely reliable.
• a further object of the present invention is to provide an alloy for ornamental articles which has a homogeneous concentration of precious metal and a high elasticity.
• the alloy according to the present invention may be advantageously used as an intermediate product in the jewellery industry in order to produce ornamental articles which contain percentages of precious metal which are equal to those of any precious-metal alloy, improving the mechanical properties such as, in particular, the elasticity.
• this intermediate product may be used, not only for forming an ornamental article of jewellery but also for forming accessories or inserts for products in the clock and watch-making, spectacles, clothing, footwear and/or leatherwear sector, since these alloys - precisely because of their elasticity and resistance - are, at suitable thicknesses, suitable for stitching.
• the method envisages a step for preparation of a powder of one or more precious metals present individually, or in an alloy or in combination.
• This powder is formed with particles having an average size of less than 0.5 micron.
• the precious metals are chosen from the group containing: gold, silver, platinum or alloys thereof.
• thermoplastic polymer composition The components of a thermoplastic polymer composition are then prepared and introduced in granular form or separately by means of a first gravimetric metering device in an overall percentage by weight ranging between 30 and 95 %, inside a plasticization chamber of an extruder.
• the percentages of powders and polymeric composition are chosen depending on the purity index (or the percentage of precious metal) which is ultimately to be obtained in the finished product.
• the chamber of the extruder is heated to a temperature of between 120 - 220 °C in order to melt and mix thoroughly the constituents of the thermoplastic composition.
• the metallic powder is then introduced and dispersed within the liquid thermoplastic polymer composition, in an overall percentage amount by weight ranging between 30 and 95 % chosen so as to obtain the desired purity in the finished product.
• the plasticization chamber has inside it one or more screws (or augers) composed of conveying segments and mixing segments which, at the cylinder temperature of between 120 and 220 °C and at predefined speeds of rotation, perform optimum mixing of the polymer composition in the liquid state and the amount of powder/metallic powder which obviously does not reach the melted state.
• the extruder used will preferably be one of the single-screw or twin-screw high-shear type able to achieve homogeneous dispersion of the precious metal within the liquid polymer matrix.
• the liquefied mix of metallic powders in the polymer matrix undergoes extrusion, producing an intermediate product in the form of a bead (and/or thin strip).
• the intermediate product obtained from the abovementioned extrusion operation is a composite (or "compound” in the technical jargon of the sector) namely a combination of several materials which are thoroughly mixed together.
• the bead may be used as a base material for a step involving forming of the ornamental articles which is to be produced.
• the intermediate product in the form of a bead upon leaving the extruder, will be cut or shaped into granules having the same original purity index in the form of prismatic, spherical or cylindrical elements.
• the intermediate product may be stored for subsequent use in the forming process which may therefore be performed in a location different from that for production of the intermediate product and also at a considerably later time.
• the forming operation which results in the production of the ornamental articles with the desired carat value may envisage, in accordance with a preferred solution of the present invention, supplying the granular intermediate product to an injection moulding press, or an intrusion moulding press or a compression moulding press, operating at temperatures of between 120 and 220 °C.
• the forming step may envisage supplying the intermediate granular product to an extrusion machine operating at temperatures of between 120 and 220 °C, obtaining continuous shaped profiles.
• the forming step may envisage supplying a cylinder calendering machine so as to obtain a continuous flat and/or foil-like strip which may or may not be embossed and which may undergo further processing steps in order to obtain the finished product.
• the intrusion moulding press, the compression moulding press, the extrusion machine for obtaining continuous shaped profiles and the cylinder calendering machine for obtaining a continuous strip are machines which are well-known per se to a person skilled in the art and for this reason are not described in detail; however their use in the forming process, based on the intermediate product described, is entirely novel and original.
• the product may undergo other processing operations in order to produce the finished product, which may also be stitched onto a fabric.
• the present invention also relates to an alloy for ornamental articles which can be obtained as an intermediate product of the method described above.
• the method described above may be further characterized with reference to the characteristics of the alloy indicated in the description which follows.
• the alloy is obtained as explained above by starting with a suitable amount of precious metal powders present in an alloy or individually with an average size of less than 0.5 micron and by an amount of a homogeneous thermoplastic polymer composition, which amounts are mixed in an extruder.
• the polymer composition comprises thermoplastic polymers which are obtained by means of polycondensation of one or more resins which are chosen from the group comprising: thermoplastic polyurethanes, copolysters and copolyamides.
• thermoplastic polymers may be further elastomerized with compatibilized styrene block resins and/or with other known elastomerizing agents such as nitrile and butadiene resins.
• a particular polymer composition which is particularly suitable for the use according to the objects of the present invention is, by way of example, represented by a thermoplastic polyurethane obtained by means of reaction between aromatic and aliphatic isocyanates, ester base polyols, glycol polytetramethylene ester, carbonate ester with a molecular weight of between 1000 and 4000 and diol chain extenders with a molecular weight of 50 to 400; this reaction may be achieved either by means of the two-step process, which envisages supplying the liquid monomers into a reactive extruder in an operating condition such as to favour the formation of a solid intermediate product, which is subsequently re-extruded and granulated in a second non-reactive extruder, or using the prepolymer process, which envisages a first reaction inside a chemical reactor between part of the components of the formulation, resulting in a reactive liquid intermediate product (called "prepolymer”) subsequently supplied together with the remaining components of the formulation into a reactive extruder, or using "
• thermoplastic polyurethanes comprise aliphatic isocyanates, carbonate esters of the medical type with a molecular weight of between 400 and 4000, and chain extenders with a molecular weight of between 50 and 400.
• thermoplastic polyurethane is advantageously due to the particular biostability which makes it suitable for contact with the skin of any person wearing the ornamental product.
• thermoplastic composition must have nontoxic, anti-allergic and anti-microbial properties since it has to come into contact with the human skin.
• the polymer composition or the alloy also comprise an additive with an anti-microbial action incorporated during the production method in a plasticization chamber and preferably consisting of solution of 2-octyl-2H-isothiazol-3-one and Triclosan, which is known by the tradename of "Sanitized", and is present in percentage amount varying from 0.3 to 1% by weight.
• the alloy composition also contains UV and temperature stabilizers in an amount suitable for best determining the properties thereof as regards resistance to ageing and formation of bacterial colonies.
• the alloy has an elongation at break value in the range of 200 - 800 % and a hardness factor of between 50 Shore A and 70 Shore D.
• 170 g of aliphatic TPU with carbonate ester base (hardness Shore A 73) are mixed thoroughly inside the extruder with 300 g of gold having a purity index of 916 (22 carats) in a single-screw extruder at 160 - 180 °C and cut into granules using a knife cutter after cooling in water.
• the granules thus obtained were dried in an oven at 70°C for two hours and then processed at 160 °C in a hot-cylinder calender so as to obtain a sheet of thermoplastic alloy with a gold purity index of 586 (14 carats).
• Precious metals such as gold, silver and platinum are heavy metals with a density much greater than that of the thermoplastic composition in which they are dispersed inside the alloy.
• an ornamental article also with a high carat value (precious metal percentage) will be distinguished by a volume of polymeric composition which is far greater than the volume of metallic component.
• an 18-carat alloy could be formed by 75 parts by weight of gold and 25 parts by weight of elastomer polymer which, in terms of volume, may be represented by 3.88 cm 3 of gold and 20.83 cm 3 of elastomer with a density 1.2 g/cm 3 .
• the alloy obtained according to the method and according to the characteristic features of the invention described above allows a high dispersion of the metallic powders inside the elastomer plastic matrix, guaranteeing the purity and the mechanical performance throughout the finished product and ensuring a surprising and favourable tactile feel.
• the alloy according to the invention it is possible to produce ornamental articles with the desired purity index (i.e. with a guarantee as to the desired percentage of precious metal) such as, for example, in the gold and silverware sector, necklaces, bracelets, rings, earrings, etc., which have a final aesthetic appearance which is distinguished by a highly appreciated tactile feel and by mechanical properties represented in particular by the hardness and the elasticity which allow extremely versatile use of the alloy.
• desired purity index i.e. with a guarantee as to the desired percentage of precious metal
• the use of the alloy according to the present invention is not limited solely to the jewellery sector, but also extends to other sectors, for example the clock and watch-making, gift article, clothing, footwear or leatherwear sector, considering the fact that these elastic and resistant alloys, at suitable thicknesses, can be stitched.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Adornments (AREA)
• Powder Metallurgy (AREA)

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Cited By (4)

Citations (3)

• 2007
  • 2007-04-13 DE DE602007001180T patent/DE602007001180D1/de active Active
  • 2007-04-13 AT AT07425215T patent/ATE432138T1/de not_active IP Right Cessation
  • 2007-04-13 EP EP07425215A patent/EP1918047B1/de not_active Not-in-force

Patent Citations (3)

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