CH717518A2 - Method of manufacturing an ornamental piece of hard material provided with a polymer coating. - Google Patents

Abstract

The invention relates to an ornamental part (10), for example for watchmaking, jewelery or telephony, in particular a watch case middle (17), and its method of manufacture, the part comprising at least in part a hard material having a Vickers hardness greater than 1000 HV, the method comprising the following main steps: a step of producing a precursor from a mixture of at least one powder material with a binder, an injection step of the precursor in a mold in order to form a green body, a step of sintering said green body in order to form a body of the future part (10) in said hard material, and a step of depositing a coating (16) in material polymer on one face of the part (10), the deposition being carried out by molding on the body, in particular by injection into a mould, the coating and the hard material being inseparable.

Description

Technical area

The invention relates to the field of the manufacture of ornamental parts, in particular in watchmaking, jewelery or telephony, the part being made of hard material with a polymer coating. It relates more specifically to a method of manufacturing a watch middle part provided with a coating of the inner face made of polymer.

Technology background

[0002] In the watch industry or in jewelry, various materials are used for the manufacture of boxes or bracelets of various appearance. It is in particular known to manufacture timepieces, in particular watch cases, from a hard material. By hard material, we mean materials having a Vickers hardness greater than 1000 HV. Such hard materials are, for example, ceramic, silicon nitride, zirconium oxide, sapphire, or alumina.

[0003] In watchmaking, they are used for their mechanical properties, in particular because they are difficult to scratch. They are used, for example, to manufacture parts such as watch cases or bracelet links.

The ornamental parts are obtained after an injection step giving the desired shape to the part, then by a sintering step to harden the material.

[0005] However, this type of injection process does not make it possible to obtain sufficiently precise dimensions. For example, for a watch middle, it is necessary to have housing dimensions enabling a crystal, a bezel or a back to be embedded in such a way as to be held firmly. We also need to drill holes for a crown or pushers, which cannot be obtained with the injection process.

To achieve this, it is necessary to machine the caseband to correct the dimensions of the caseband. However, hard materials are difficult to machine because of their hardness. For this purpose, low-life diamond tools are used, which generate high costs.

Summary of the invention

[0007] It would be advantageous to obtain an ornamental part made of hard material, which requires little or no machining on the hard material, in particular for ceramic materials, but which includes functional surfaces.

The present invention provides this type of process. Thanks to the combination of a hard material and a coating of polymer material, the method makes it possible to avoid the direct machining of the hard material on the faces of the part. Polymer is easier to machine than hard material. Thus, the manufacturing cost of the part is reduced by avoiding machining the hard material as much as possible. In addition, the tightness of the part is ensured between the coating and the hard material.

[0009] More specifically, the invention relates to a method of manufacturing an ornamental part, for example watchmaking, jewelery or telephony, in particular a watch middle, the part comprising at least in part a hard material having a Vickers hardness greater than 1000 HV. According to the invention, the method comprises the following main steps: a step of producing a precursor from a mixture of at least one powdered material with a binder, a step of injecting the precursor into a mold in order to form a green body, a step of sintering said green body in order to form a body of the future part in said hard material, and a step of depositing a coating of polymer material on one face of the part, the deposit being carried out by molding on the body, in particular by injection into a mould, the coating and the hard material being inseparable.

[0010] According to a particular embodiment of the invention, the method comprises an additional step of machining the coating of polymer material.

[0011] According to a particular embodiment of the invention, the method comprises an additional step of assembling the part.

[0012] According to a particular embodiment of the invention, the method comprises a step of machining the green body.

According to a particular embodiment of the invention, the body being provided with an inner face, the deposition step consists in depositing the coating on said inner face.

[0014] According to a particular embodiment of the invention, a bottom of the part is formed in the polymer material during the coating deposition step.

According to a particular embodiment of the invention, the polymer is to be chosen from the following list: POM, PA, PUR, PPS, ABS, PC.

According to a particular embodiment of the invention, the hard material is to be chosen from materials such as ceramic, silicon nitride, zirconium oxide, sapphire, or alumina.

[0017] The invention also relates to an ornamental part, for example watchmaking, jewelery or telephony, in particular a watchband, comprising a body made of hard material and at least one face provided with a coating of material polymer, the body defining an interior space.

According to a particular embodiment of the invention, the coating has a functionalized form.

[0019] According to a particular embodiment of the invention, the coating has the shape of steps, in particular to be able to assemble other parts of a watch case by interlocking.

According to a particular embodiment of the invention, the body defines an internal space, the face bordering said space.

According to a particular embodiment of the invention, the face is an inner face of the body.

According to a particular embodiment of the invention, the part comprises a bottom obtained during the coating deposition step.

[0023] The invention also relates to a watch case comprising such an ornamental piece, as well as a crystal and a bezel for holding the crystal on the piece, the bezel being assembled to the piece by the polymer coating.

Brief description of figures:

The invention will be better understood with reference to the attached drawing in which: FIG. 1 is a block diagram representing the method according to the invention, FIGS. 2a to 2f show perspective views of a watch middle after each step of the method according to the invention, Figure 3 is a sectional view of an assembled watch case comprising a part according to a first embodiment of the invention, FIG. 4 is an inverted perspective view of a watch part according to the first embodiment of the invention, FIG. 5 is a sectional view of an assembled watch case comprising a part according to a second embodiment of the invention, and FIG. 6 is a view is a reversed perspective view of a watch part according to the second embodiment of the invention.

Detailed description of the invention

The method of manufacturing 1 of an ornamental part 10, for example watchmaking, jewelery or telephony, is shown in Figure 1. The ornamental part is for example a watch case middle as represented in FIGS. 2a) to 2f), a bezel, a watch case bottom, a stone or a timepiece pusher, a jewelry ring or bracelet, or even a mobile telephone shell. Part 10 comprises at least in part a hard material having a Vickers hardness greater than 1000 HV. The hard material is, for example, a ceramic material such as an aluminum oxide (Al2O3), a zirconium oxide (ZrO2), a carbide, a nitride, a cermet, a hard metal or any other Vickers hardness material. greater than 1000 HV.

The method 1 comprises a first step 2 of producing a precursor from a mixture of at least one powder material with a binder. In this context, the ceramic-based powder can comprise at least one metal oxide, a metal nitride or a metal carbide. By way of example, the ceramic-based powder may comprise aluminum oxide in order to form synthetic sapphire or a mixture of aluminum oxide and chromium oxide in order to form synthetic ruby, or more zirconium oxide. In addition, the binder can be of various natures such as, for example, polymeric types or organic types.

The method 1 comprises a second step 3 of injection of the precursor into a mold in order to form a green body 12. The mold has substantially the shape of the desired part given a coefficient of retraction of the part. The precursor is injected into the mold through a tube, then through precursor distribution circuits throughout the mold. The precursor thus takes the shape of the mould, for example a watch case middle as in the examples described in the application. Alternatively, it is also possible to carry out the injection by circular layer or by channels.

A third step 4 is to machine the green body 12 to eliminate unnecessary parts of the green body 12 produced by the injection. For example, a pipe 38 or channels 19 formed because of the tube and the distribution circuits are eliminated. Thus, a machined green body 13 is obtained.

The fourth step 5 has the function of sintering said machined green body 13 in order to form a body 14 of the future part in said at least one hard material. Sintering consists of heating the precursor so that the powder grains agglomerate. During sintering, the green body 13 hardens by shrinking to end up with a hard body 14. Preferably according to the invention, the sintering step may include pyrolysis.

A possible fifth step 6 is used to prepare certain parts of the body 14 obtained by sintering for the rest of the steps, in particular to prepare the body 10 for the finishes.

The method 1 comprises a sixth step 7 of depositing a coating 16 of polymer material on one face of the part, the deposit 7 being carried out by overmolding the body 14, 15, in particular by injection into a mold. A watch case middle part is for example provided with an inner face 18, which it is desired to cover with a coating 16 made of polymer. The deposition step 7 consists in depositing the coating 16 on the said inner face 18. Thus, a piece of hard material is obtained with one face 18 covered with a polymer material. In this step, the molding of a polymer material makes it possible to form a coating 16 with more precise dimensions than with a hard material after sintering. By virtue of the method, the need to machine the hard material of the part 10 is avoided. The coating 16 can thus be directly formed to the appropriate dimensions. In addition, the two materials, the hard body and the coating, are assembled inseparably.

The polymer is for example chosen from the following list: POM (for polyoxymethylene or polyformaldehyde or polyacetal), PA (for polyamide), PUR (for polyurethane), PPS (for polyphenylene sulphide), ABS (for acrylonitrile butadiene styrene ), PC (for polycarbonate).

In a seventh step 8, the coating 16 of polymer material can optionally be machined in order to modify certain parts, if necessary, in particular to allow the assembly of the other elements of the box.

[0034] An eighth step 9 may also be necessary to carry out satin finishing and/or polishing of the hard material. Thus, the aesthetic appearance of the middle part is improved.

[0035] Finally, in a ninth step 11, the part 10 is assembled with other elements by interlocking thanks to the coating 16. For example, if the part 10 is a middle part of a timepiece watch, a watch case is formed 17 by assembling a bezel 21, a crystal 25 and a case back.

In Figures 2a) to 2f), bodies are shown which lead to part 10 of a watch case 17 after certain steps of method 1. After the second injection step, as shown in FIG. 2a), a green body 12 having the shape of the middle part of a watch is obtained. The green body describes an open cylinder portion extended on either side by two opposite elements 34, 35 each provided with a fastening system for attaching a bracelet thereto. The green body 12 has an inner face delimiting the interior space of the cylinder portion.

When there are several injection points, the green body 12 is provided with channels 19 connecting the inner face 18 of the green body in a central crossing 36 arranged in the center of the interior space. Four perpendicular channels 18 join a tubing 38 orthogonal to the channels 18, the tubing 28 passing through the central crossing 36. The channels 18 and the tubing 38 are produced during the injection step, the precursor being injected into a mold by a tube .

These channels 18 and the tubing 38 are removed during the third step of machining the green body 12 to obtain a machined green body 13 shown in Figure 2b). The green body 12, 13 is not too hard, so machining can be carried out without difficulty.

After the sintering step, the body 14 of Figure 2 c) retains substantially the same shape with a sintering coefficient, but it is much harder than before. The hard body 14 can then be prepared for finishing if necessary, forming a hard body 15 of Figure 2d).

In Figure 2 e), the part 10 obtained has a polymer coating 16 on the inner face 18. The coating 16 has the desired shape with precise dimensions, which are obtained by overmolding. The part 10 represented comprises a covering 16 in the form of a staircase from the top of the caseband to the bottom. The different steps of the staircase have the function of holding elements inside the space or near the openings, such as the crown at the top or a bottom at the bottom.

After assembly, the watch case 17, shown in Figure 2f), comprises a caseband on which is assembled a bezel 21 and a crystal 25. The bezel 21 is held fitted in the first step 27 of the coating 16 .

[0042] Figures 3 and 4 show a watch case 17 comprising a part 10 of hard material, here a middle part, with a coating 16 of polymer on the internal face 18 of the middle part obtained by the method according to the invention, as well as a bezel 21, a crown 22, a stem 23, a back 24 and a crystal 25. The caseband has the same shape as that described previously. The bezel 21 includes a collar 26 fitted into the first step 27 of the covering 16. The bezel 21 rests on the peripheral contour 28 of the glass 25 to hold it on the caseband. The glass 25 has a rim 29 on the periphery, which is arranged under the collar 26 of the bezel 21 in the assembly position. The flange 29 rests on the first step 27 of the covering 16 and its end is in contact with the vertical part 31 of the step 27 of the covering 16.

The bottom 24 of the box 15 is embedded in the coating 16, the coating 16 comprising a shrinkage of material forming a small step 32 to ensure the maintenance and sealing of the bottom 24.

The part 10 includes a lug 33 on the inner face to prevent the coating from moving in translation or in rotation. The lug 33 is arranged halfway up the part 10.

[0045] Crown stem 23 passes through the middle through an orifice to reach crown 22 arranged outside part 10.

[0046] In a variant of the first embodiment, the bottom covers the coating to hide it on the underside of the middle part.

A second embodiment of the method consists in forming the bottom 41 of the box 45 of the same polymer material as the coating 43. The coating 43 and the bottom 41 are in one piece and formed during the same deposition step. Thus, the piece 40 obtained, represented in FIGS. 5 and 6, comprises a bottom 41 when the method is finished. The back 41 is not removable and preferably comprises a housing 42 for a battery 44. Apart from the back 41, the other characteristics are the same as those of the middle part of the first embodiment.

[0048] Other parts can be made using the method described above. Thus, it is possible, for example, to manufacture a bezel, a back, a stone or a timepiece pusher, as well as a ring or a jewelry bracelet, or even a telephone shell. All of these parts comprise a body of hard material provided with a coating of polymer material on at least one side.

Claims (13)

1. A method of manufacturing (1) an ornamental part (10, 40), for example watchmaking, jewelery or telephony, in particular a watch case middle (17, 45), the part comprising at least in part a hard material having a Vickers hardness greater than 1000 HV, characterized in that the method comprises the following main steps: – a production step (2) of a precursor from a mixture of at least one powdered material with a binder, – a step of injecting (3) the precursor into a mold in order to form a green body (12), – a step of sintering (4) said green body in order to form a body (14) of the future part (10, 40) in said hard material, and – a step of depositing (7) a coating (16, 43) of polymer material on one face of the part (10, 40), the deposit being carried out by molding on the body (14, 15), in particular by injection in a mould, the coating and the hard material being inseparable. 2. Method according to claim 1, characterized in that it comprises an additional step of machining (9) of the coating (16, 43) of polymer material. 3. Method according to claim 1 or 2, characterized in that it comprises an additional assembly step (11) of the part (10, 40). 4. Method according to any one of the preceding claims, characterized in that it comprises a machining step (3) of the green body (12). 5. Method according to any one of the preceding claims, characterized in that the body (14, 15) being provided with an inner face (18), the deposition step (7) consists in depositing the coating ( 16, 43) on said inner face (18). 6. Method according to any one of the preceding claims, characterized in that a bottom (44) of the part (10, 40) is formed in the polymer material during the step of depositing (7) the coating ( 16, 43). 7. Method according to any one of the preceding claims, characterized in that the polymer is to be chosen from the following list: POM, PA, PUR, PPS, ABS, PC. 8. Method according to any one of the preceding claims, characterized in that the hard material is to be chosen from materials such as ceramic, silicon nitride, zirconium oxide, sapphire, or alumina . 9. Ornamental part (10, 40), for example watchmaking, jewelery or telephony, in particular a watch case, comprising a body (14, 15) of hard material and at least one face (18) provided a coating (16, 43) of polymeric material. 10. Ornamental piece according to claim 9, characterized in that the coating (16, 43) has a functionalized shape. 11. Ornamental piece according to claim 9 or 10, characterized in that the body (14, 15) defines an internal space, the face (18) bordering said space. 12. Ornamental piece according to any one of claims 9 to 11, characterized in that it comprises a bottom (41) obtained during the step of depositing (7) the coating (16, 43). 13. Watch case (17, 45) characterized in that it comprises an ornamental part (10, 40) according to any one of claims 9 to 12, as well as a crystal (25) and a bezel (21) to hold the glass (25) on the part (10, 40), the bezel (21) being assembled to the part (10, 40) by the polymer coating (16, 43).