METHOD FOR THE SURFACE TREATMENT OF A JEWEL, IN PARTICULAR FOR THE WATCHMAKING INDUSTRY

Abstract

A method for treating a jewel of the monocrystalline or polycrystalline type (20), in particular for the watchmaking industry, the jewel (20) including a body (23) defining the shape thereof. The method includes a step of ion implantation on the surface (24) of at least a part of the body (23) to modify the roughness of the surface (24).

Claims

1. A method (10) for the surface treatment of a jewel of the monocrystalline or polycrystalline type (20, 30), for the watchmaking industry, the jewel (20, 30) comprising a body (23, 25) defining the shape thereof, the method comprising a step of ion implantation (12) on the surface (24, 27) of at least a part of said body (23, 25) to modify the roughness of said surface (24, 27).

2. The method according to claim 1, further comprising a step (13) of depositing an epilame layer (21) on the surface (24) of the jewel (20).

3. The method according to claim 1, wherein the epilame layer (21) comprises chromium nitride, and is preferably made entirely thereof.

4. The method according to claim 2, wherein the step (13) of depositing the epilame layer (21) is carried out by PVD, PECVD.

5. The method according to claim 1, wherein the ions implanted on the surface (24) reduce the contact angle of a drop of liquid (23), the contact angle being less than 40° for a drop of water.

6. The method according to claim 1, wherein the implanted ions are helium or argon.

7. The method according to claim 1, wherein the ions implanted on the surface (27) of the body (25) increase the contact angle of a drop of liquid (26), the contact angle being greater than 50°, or even greater than 70°, for a drop of water.

8. The method according to claim 7, wherein the implanted ions are nitrogen.

9. The method according to claim 1, wherein the ion implantation step (12) is carried out by ECR-type magnetic electron cyclotron resonance.

10. The method according to claim 1, wherein the ion implantation step (12) is carried out using plasma.

11. The method according to claim 1, wherein the body (23, 25) of the jewel (20, 30) is previously formed in a first step (11) by a Verneuil-type method for a monocrystalline jewel or by a sintering method for a polycrystalline jewel.

12. The method according to claim 1, wherein the jewel comprises Al.sub.2O.sub.3 or ZrO.sub.2.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0027] Other specific features and advantages will be clearly observed in the following description, which is given as a rough guide and in no way as a limiting guide, with reference to the accompanying drawings, wherein:

[0028] FIG. 1 is a diagrammatic view of a bearing for a pivot according to one known embodiment from the prior art;

[0029] FIG. 2 is a block diagram of a method for producing a jewel according to the invention;

[0030] FIG. 3 is a diagrammatic view of a jewel obtained using a first embodiment of the method according to the invention;

[0031] FIG. 4 is a diagrammatic view of a jewel obtained using a second embodiment of the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0032] As explained hereinabove, the invention relates to a method 10 for the surface treatment of a jewel capable of forming a guide element of a timepiece, as shown in FIG. 1. The jewel is, for example, intended to come into contact with a pivot, also referred to as a trunnion, for example of a balance staff, in order to make same able to rotate with minimal friction. It is thus understood that the present invention in particular allows a jewel to be treated, which jewel is capable of forming all or part of a bearing of a staff mounted such that it can rotate, such as that shown in FIG. 1.

[0033] According to the method 10 shown in FIG. 2, the body of the jewel is formed in a first step 11.

[0034] For a polycrystalline-type jewel, a precursor is produced from a mixture of at least one powder material with a binder. This material can be, in a non-limiting and non-exhaustive manner, ceramic. In this context, the ceramic-based powder can contain at least a metal oxide, a metal nitride or a metal carbide. For the purposes of illustration, the ceramic-based powder can contain aluminium oxide in order to form synthetic sapphire or a mixture of aluminium oxide and chromium oxide to form poly-ruby of the Al.sub.2O.sub.3 type, or zirconium ceramic of the ZrO.sub.2 type. Moreover, the binder can have various natures such as, for example, of the polymer or organic type.

[0035] A step of pressing the precursor is then carried out with an upper die and a lower die of a pressing device in order to form a green body of the future jewel.

[0036] Sintering is then carried out for said green body in order to form the mineral body of the future jewel in said at least one material. The material can be, as stated hereinabove, ceramic. In other words, this step is intended to sinter the green body to form a ceramic body of the future perforated jewel. Preferably, according to the invention, the sintering step can include pyrolysis, for example by thermal debinding.

[0037] The mineral body can be machined, for example to shape the top face and bottom face in order to obtain a predefined jewel thickness. Machining can also consist of drilling a hole through the jewel if necessary, and of functionalising the surfaces of the body.

[0038] Lapping and/or brushing and/or polishing the mineral body procures a special finish. This finishing step gives the jewel a surface finish that is compatible with the use thereof. Such a finishing step further allows the final dimensions to be adjusted and/or edges to be removed and/or the surface roughness to be modified locally.

[0039] For a monocrystalline jewel, the body is formed using a Verneuil-type method. A Verneuil-type method comprises a step of melting a material that will crystallise upon contact with a single-crystal seed. Corundum (Al.sub.2O.sub.3) is typically used as a starting material. Machining and lapping are similar to the embodiment of the polycrystalline-type jewel.

[0040] According to the invention, a second step 12 of the method 10 consists of treating at least a part of the surface of the body by ion implantation. Ion implantation is a technology that allows ions to be incorporated into a material.

[0041] Thus, it allows for nanostructuring by modifying the relief of the surface of the body. More specifically, the implantation of ions into the surface creates a relief, which modifies the roughness of the surface. Depending on the type of ions implanted, a different roughness is obtained, as the ions have different sizes, which structure the surface differently. Some ions increase the roughness, whereas other ions decrease the roughness of the surface. Increasing the roughness increases the contact angle, whereas decreasing the roughness decreases the contact angle.

[0042] Facilities exist for such a treatment, which comprise an ion source, a particle accelerator using electrostatic properties to create a beam of ions and an enclosure containing the body of the jewel to receive the ions.

[0043] In a preferred alternative embodiment, the implantation is carried out by immersing the body of the jewel in an ionic plasma. The jewel is submerged into an ion plasma, for example by an ECR-type electron cyclotron resonance method.

[0044] A first embodiment of the second step 12 of the method 10 consists of implanting ions on the surface of the jewel, which ions allow the contact angle of a liquid on said surface to be decreased. The contact angle obtained is preferably less than 40° for a drop of water. Thus, such a surface allows the adhesion of a layer deposited on the surface of the body, for example an epilame layer, to be improved. Preferably, the ions implanted on the surface of the jewel are helium or argon ions, as they decrease the contact angle.

[0045] In a second embodiment of the second step 12, ions are implanted into the jewel, which ions allow the contact angle of a drop of liquid on the surface of the jewel to be increased. Preferably, the ions implanted on the surface of the jewel are nitrogen ions. The contact angle is greater than 60°, or even greater than 70° for a drop of water. This avoids the need for an epilame layer.

[0046] Preferably, the ions are implanted into the body at a depth of up to 150 nm.

[0047] A third step 13 of the method 10 is optional depending on the chosen embodiment, and preferably applies to the first embodiment. The third step 13 consists of depositing an epilame layer on the part of the surface treated by ion implantation in the second step. The epilame layer is preferably a chromium nitride layer. An epilame layer is typically deposited in the vapour phase by a PVD- or PECVD-type method. The epilame layer preferably has a thickness of 0.003 to 0.006 μm.

[0048] Optionally, laser nanostructuring of the epilame layer can be carried out in a fourth step 14. Thus, it is possible to select which part of the surface of the jewel has an epilame layer.

[0049] The part of the jewel 20, shown in FIG. 2, corresponds to a jewel treated according to the first embodiment. The jewel 20 comprises a body 23, the surface 24 whereof has been implanted with ions that reduce the contact angle of a liquid. The jewel 20 further includes an epilame layer 21 deposited on this surface 24. As can be seen, a drop of liquid deposited on the epilame layer forms a contact angle greater than 40° for a drop of oil.

[0050] The part of the jewel 30, shown in FIG. 3, corresponds to a jewel treated according to the second embodiment. The jewel 30 comprises a body 25, the surface 27 whereof has been implanted with ions that allow the contact angle of a drop of liquid to be increased. This jewel does not require an epilame layer, which is absent in the figure. A drop of water, for example, forms a contact angle of at least 70° thanks to the ion implantation.