IMPROVEMENTS IN AND RELATING TO THE PRODUCTION OF FLAT PRODUCTS IN STRIP, SHEET OR LIKE FORM

Abstract: A process for producing a flat product such as a coin includes the steps of forming a slurry comprising a suspen­ sion of particulate material in a film-forming cellulose derivative, depositing a quantity of this slurry onto a support surface, drying the slurry to form a self-supporting flat product, and removing the dried product from the support surface. The particulate material essentially comprises metallic particles and matter whose chemical composition and physical properties differ from those of the metallic particles such that the added matter is not or only partially taken into solution with the metallic particles on heat treatment of the product whereby the presence of the added matter can readily be detected following such heat treat­ ment.

Description: The invention concerns the production of disc or similarly shaped products from particulate material. Hitherto, immediate authenticity of coins, tokens, medallions and other valuable items has relied upon the presence of features which can be detected either visually or by touch. Alternatively, the weight or dimensions of such items have been used for authentication, particularly in coin operated machinery. Since such features can readily be reproduced, there is always the possibility of forgery or of a coin or token of inferior value being presented in payment for goods or services. The present invention sets out to provide a process for producing such items which include authentication features which cannot readily be reproduced. The invention also sets out to provide a process by which the intrinsic value of items such as coins or medallions or the like can be increased by the presence of high value materials. A process is known from FR-A-1552998 in which a layer of a slurry containing metal powder and a binder composition is deposited or coated onto a support surface, dried, removed from the support surface and subsequently compacted and heat treated to produce a metal strip of the required composition. FR-A-1552998 also proposes the introduction into the slurry of carbon or tungsten fibres to enhance the mechanical properties of the strip product. In order to achieve the required authentification properties, it is necessary not only to mix into the slurry matter having chemical and physical properties different from those of the main metallic content of the product, but also to ensure that such matter is uniformly distributed within the strip product. Uniform distribution is achieved by means of the present invention. According to the present invention in one aspect, there is provided a process for producing disc or similarly shaped products in which a slurry is formed from a film forming cellulose derivative containing, in suspension, a quantity of metallic particles and a quantity of added matter whose chemical composition and physical properties differ from those of the metallic particles, a quantity of this slurry being deposited onto a support surface, dried to form a self-supporting flat product and subsequently removed from the support surface, the process being characterised by the steps of heating the dried flat product to a temperature at which the added matter is, at most, only partially taken in solution with the metallic particles whereby the presence of the evenly distributed added matter can readily be detected following such heat treatment, and stamping or cutting from the flat product either prior to or following heating the required disc or similarly shaped products. The metallic particles may be magnetic or non-magnetic. In one embodiment of the invention, the metallic particles are produced from a non-magnetic material such as copper or copper nickel, and the other particles from a material having magnetic properties, e.g. a ferrite material. Thus, the presence of the ferrite particles within the product following heat treatment can readily be detected by simple magnetic test. Other physical properties and tests can also be used. Such testing may, for example, occur automatically in a coin or token operated machine. Where a layered or stratified product is produced, authentication may be accomplished visually through suitable selection of the materials employed. In a further embodiment, the intrinsic value of a flat product such as a coin may be increased by the addition of high value particulate material, such as micron or greater size particles of natural or synthetic diamonds to the metal powder. The added matter may be in particulate or filamentary form and may have magnetic properties. The introduced matter may, for example, include high value items such as gems to increase the intrinsic value of the product. The flat product from which the disc or similarly shaped products may be produced in strip or sheet form. In one embodiment exemplary of the invention, a layer of the slurry of the particulate metallic and added particles in a film-forming cellulose derivative is deposited by a set of rollers onto a belt for transport through a drying oven. On leaving the oven, the strip is self-supporting and may be compacted by means of a pair of contra-rotating rolls. The dried, compacted strip is then heat treated within a sinter furnace and can, if required, be further rolled and heat treated. If required, disc or similar shaped product may be stamped or cut from the heat treated or further processed strip. On heat treatment, the metallic particles coalesce to form a sintered product about the other particles which are not taken or only partially taken into solution with the principal metal particles. The presence of the other particles can, therefore, readily be detected by a simple test linked to a difference in the physical properties of the particles. Alternatively, disc or similar shaped flat products may be stamped or cut from the dried strip prior to heat treatment, the individual discs then being subjected to the required heat treatment. By suitable selection of the metallic and other particulate matter, authentication may be achieved either visually or by means of a simple test. In an alternative embodiment, the slurry of the particulate metal and added particles in a film-forming cellulose derivative is cast or injected into moulds located on a support surface, the cast products then being dried and subjected to compaction in a press and/or heat treatment in a manner similar to that described above. Alternatively, separate slurries of the metallic and other particles may be formed, the slurries being sequentially cast or injected as superimposed layers or as side-by-side deposits to form a laminated or stratified product. The process described above provides an even dispersion of the added particles within the slurry thereby ensuring an even distribution of the authentication particles within the products. The added matter may take the shape of filaments or fibres produced from magnetic or non-magnetic metallic or non-metallic material. Typical examples of such matter include carbon fibres and stainless steel filaments. Where magnetic filaments or fibres are employed, they may be aligned lengthwise generally parallel to the longitudinal axis of the strip by a magnetic alignment device. Alternatively, where relatively long fibres or filaments are used, alignment may be achieved by suitable selection of the roll gap between the previously described pair of rotating coating rollers. Alignment of fibres or filaments in directions transverse or inclined to the longitudinal axis of the strip can also be achieved by a suitable magnetic device. Furthermore, the fibres or filaments may be indiscriminately disposed by employing shorter fibres or filaments and/or a roll gap for the coating rollers which would not automatically cause the fibres or filaments to be aligned. Whilst the invention has been described with particular reference to the production of items whose authenticity can be magnetically or visually determined, it is to be understood that various other properties can be employed for authentication purposes by suitable selection of the materials employed. Such properties include, but are not limited to, mass, density, weight, porosity and chemical reactivity.

Claims: A process for producing disc or similarly shaped products in which a slurry is formed from a film forming cellulose derivative containing, in suspension, a quantity of metallic particles and a quantity of added matter whose chemical composition and physical properties differ from those of the metallic particles, a quantity of this slurry being deposited onto a support surface, dried to form a self-supporting flat product and subsequently removed from the support surface, the process being characterised by the steps of heating the dried flat product to a temperature at which the added matter is, at most, only partially taken in solution with the metallic particles whereby the presence of the evenly distributed added matter can readily be detected following such heat treatment, and stamping or cutting from the flat product either prior to or following heating the required disc or similarly shaped products. A process as claimed in Claim 1 characterised in that the metallic particles are non-magnetic and the added matter is produced from a material having magnetic properties. A process as claimed in Claim 1 characterised in that the added matter comprises metallic fibres having magnetic properties.

Inventors: DAVIES, IDWAL, FAGE, JOHN LAWTON
Applicants: MIXALLOY LIMITED
Application year: 1985
Main classification: B22F3
IPC codes: A44C21, B22F7, A44C27, B22F5, B22F3, C22C32