Decorative item made of a heavy composite material

This application claims priority from European Patent Application No. 18215840.2 filed Dec. 24, 2018, the contents of all of which are incorporated herein in its entirety.

The present invention relates to a decorative item or article and in particular to an external component for horology made of a heavy, shock resistant composite material. It also relates to the method for manufacturing the item.

Numerous external components, such as case middles and bracelets are made of plastic materials. These components can be made by moulding processes, which have the advantage of enabling various shapes to be obtained without any finishing operations. These plastic components have the characteristic of having a density close to 1 and therefore of being light. This may constitute a drawback for the user who wishes to wear a watch having a certain weight on the wrist.

To overcome this drawback, it was proposed, for example in EP Patent No. 2482142, to make timepiece components, whether for the timepiece movement or exterior, from plastic materials reinforced with a high density metallic powder such as a tungsten powder. These components are made by an injection moulding process, which maintains the advantage of shaping in the mould without any subsequent finishing while also increasing density.

It is an object of the present invention to propose a novel heavy composite material composition that meets the aesthetic and mechanical, and in particular resistance criteria, of horological applications.

To this end, the present invention proposes a decorative item made of a material containing by weight:

60 to 90% of a metallic or ceramic material having a density higher than or equal to 5 g/cm 3 , 10 to 32% of a plastic material including a thermoplastic resin or a mixture of thermoplastic resins and a coupling agent, 0 to 8% of a reinforcement, 0 to 3% of a pigment.

Preferably, the material includes a stainless steel as the metallic material, a MABS (methyl methacrylate acrylonitrile butadiene styrene) as the thermoplastic resin, and an ethylene methacrylic acid as the coupling agent.

Advantageously, the material includes a reinforcement in a weight percentage greater than or equal to 1% in order to increase the tenacity of the material and/or to limit the shrinkage of material during the moulding process. This reinforcement can be present in various forms, for example, in the form of fibres or particles.

Further, the material may contain an organic pigment such as carbon black.

The composite material thus developed has a density comprised between 2 and 7 g/cm 3 and high tenacity.

Further, the present invention relates to the method for making this material, which is optimised to ensure a homogeneous mixture and good compatibility between the various components of the material.

Other features and advantages of the present invention will appear in the following description of a preferred embodiment, given by way of non-limiting example, with reference to the annexed drawing.

FIG. 1 represents a timepiece comprising a case middle made from the heavy composite material according to the invention.

The present invention relates to a decorative item made from a composite material including a plastic material and a metallic or ceramic material. The decorative item may be a constituent element of watches, jewellery, bracelets, etc. In the field of horology, this item can be an external component, such as a case middle, a case back, a bezel, a pusher, a bracelet link, a hand, a dial index, etc. By way of illustration, a case middle 1 made from the composite material according to the invention is represented in FIG. 1 .

The decorative item is made by injection moulding. The manufacturing method includes the steps consisting in:

a) Preparing granules of several millimetres containing by weight:

60 to 90% of a metallic or ceramic material having a density higher than or equal to 5 g/cm 3 ,

9 to 25% of a thermoplastic resin or of a mixture of thermoplastic resins,

1 to 7% of a coupling agent,

0 to 8% of a reinforcement, preferably between 1 and 6%,

0 to 3% of a pigment,

b) Injection moulding said granules to form the decorative item. The injection moulding process is performed in a mould which has a temperature of around 90-100° C., while during the injection process the material has a temperature comprised between 200 and 300° C. and preferably between 220 and 280° C.

In step a), the granules can be produced by slicing an extruded roll of the aforementioned raw materials. Advantageously, the metallic or ceramic material and the coupling agent, both in powder form, are first introduced into a hopper of the extruder in order to coat the metallic or ceramic powder with the coupling agent prior to introducing the thermoplastic resin and the reinforcement. Thus, in a second phase, the thermoplastic resin and the reinforcement are introduced, for example laterally, into another hopper of the extruder. The pigment can be introduced during the extrusion process and advantageously in the second phase. It could also be mixed with the granules just before injection.

The metallic powder may, for example, be a conventional carbon steel powder, stainless steel powder, copper powder, copper alloy powder, or a tungsten powder. A precious metal powder or a precious metal alloy powder—typically gold, silver or platinum—can also be envisaged. Preferably, it is a nickel free stainless steel powder. The steel powder is preferably present in a weight percentage of between 60 and 80%. The tungsten powder is preferably present in a weight percentage of between 65 and 90%. It may also be a ceramic powder such as a ZrO 2 , CeO 2 , ZnO powder etc. Certain ceramic powders may have the advantage of being white, which, in comparison to metallic powders, facilitates pigment dyeing. Advantageously, the metallic or ceramic powder is present in a weight percentage of between 71 and 80%. The powder has a grain size such that d90 is less than or equal to 100 μm, preferably less than or equal to 30 μm, and more preferably to 16 μm.

The thermoplastic resin may be a polyamide, an acrylic, a polyolefin, a polyester, a polycarbonate, an acrylonitrile butadiene styrene, a methyl methacrylate butadiene styrene, a polylactic acid, a phenylene polysulphide, a polyetheretherketone, a polymethyl methacrylate, a polyoxymethylene, terephthalate (PBT), and thermoplastic elastomer resins etc., or a mixture of thereof. Preferably it is a methyl methacrylate acrylonitrile butadiene styrene (MABS) which is a type of transparent ABS. Preferably, the thermoplastic resin is introduced in powder form to facilitate the mixing process during preparation of the granules. In the case of commercially available MABS in the form of granules several millimetres in diameter, a step prior to step a) consists in micronizing the granules to obtain a powder with a d90 of less than or equal to 500 μm and preferably to 315 μm.

The coupling agent is necessary to ensure proper adhesion between the metallic or ceramic powder and the thermoplastic resin. Advantageously, it is an ethylene-methacrylic acid copolymer with a weight percentage of between 5 and 20% of methacrylic acid in the copolymer. Advantageously, this copolymer is used in combination with the MABS as the thermoplastic resin. This coupling agent can be introduced in powder form with a d90 of less than or equal to 500 μm and preferably to 315 μm.

This reinforcement can be present in various forms, for example, in the form of fibres or particles. For example, it could be glass fibres, glass beads, carbon fibres and/or aramid fibres with a fibre length less than or equal to 300 μm and preferably less than or equal to 200 μm. Its objective is to improve the tenacity of the material and/or to limit shrinkage of the material during the injection moulding process.

The pigment is preferably an organic pigment having a greater power to dye the metallic or ceramic powder than inorganic pigments. For example, it could be carbon black for black, diketopyrrolopyrrole for red (e.g. Irgazin Red K3840LW by BASF), copper phthalocyanine for blue (e.g. Heliogen Blue K7096 by BASF), a monoazo pigment for yellow (e.g. Paliotol Yellow K1760 by BASF), etc. According to a variant, the pigment may be fluorescent and/or phosphorescent.

The item thus obtained includes a metallic or ceramic material and a plastic (or synthetic) material containing the thermoplastic resin, the coupling agent and any product produced by the reaction between the resin and the coupling agent during the extrusion or injection moulding process. It also includes the reinforcement and the pigment, when the latter are present.

By way of example, tests were carried out to produce case middles by injection moulding using cylindrical granules having a diameter and a length respectively on the order of 3 mm. The granules include a homogeneous mixture by weight of 72% of Carpenter Ni-free stainless steel powder (Fe17Cr11Mn3Mo) having a d90<16 μm, 18.5% of micronized MABS (Terlux 2802) with a d90<315 μm, 3.5% of ethylene methacrylic acid with 15% acid (Coathylene RP 9065-34), 6% of 200 μm long glass fibres, (Glasfaser-Flocken by Suter-Kunststoffe AG). Another mixture having the same percentages of MABS and of coupling agent but with 71% of stainless steel and 1% of carbon black (Printex 55 black) was prepared.

The aesthetic finish of the case middles is good with a grey colour for the composition without pigment and a black colour for the composition with pigment. The case middles thus obtained have a density of 3.05 g/cm 3 for the grey version and 3 g/cm 3 for the black version. Charpy pendulum impact tests followed by water resistance tests on case middles integrated in cases also demonstrated the high tenacity of the case middles made from the aforementioned composition,