CH718800A2 - Process for the surface treatment of a stone, in particular for watchmaking. - Google Patents

Abstract

The invention relates to a process for treating a stone of the monocrystalline or polycrystalline type (20), in particular for watchmaking, the stone (20) comprising a body (25) defining its shape, characterized in that it comprises a step of ion implantation on the surface (24) of at least part of said body (25) to modify the roughness of said surface (24).

Description

Technical field of the invention

[0001] The invention relates to a process for the surface treatment of a watchmaking stone, in particular for watchmaking.

Technology background

[0002] In the state of the art of watchmaking, rotating mobiles, such as pendulums, generally comprise two pivots whose ends are inserted into stones in order to be able to rotate. Generally, stones of the ruby, ZrO2 or sapphire type are used to form counter-pivots or guide elements called bearings. These counter-pivots and guide elements are intended to come into contact with the pivots in order to make the latter mobile in rotation and this, with minimal friction. Thus, they form, for example, all or part of a bearing of 1 shaft of the mobile mounted in rotation. The stones serving as a rotation guide element of a pivot generally have a through hole in which the pivot is inserted to rest on a counter-pivot.

[0003] Figure 1 is an example of the prior art, of an assembly 1 comprising a stone 2 provided with a hole 3 and a hemispherical hollow 4 forming the entrance to the hole 3. The assembly 1 comprises yet a pivot 7 configured to be inserted into the hole 3 in order to allow the rotation of a movable element, not shown in the figure.

[0004] In principle, synthetic stones are used in watch movements. In particular, the Verneuil-type process is known for manufacturing stones of the monocrystalline type. There are also stones of the polycrystalline type, which are manufactured by pressing a precursor with a view to obtaining a green body of the future stone from a pressing tool.

[0005] Once formed, the stones are generally subjected to a process of depositing an epilame on the stone. The epilame is a thin layer allowing to modify the physical characteristics of the surface of the stone.

[0006] The surface condition is important for contact with liquids, in particular for the lubrication of the stone, for example with a pivot. Indeed, a drop of liquid deposited on the surface of the stone forms a more or less significant contact angle depending on the surface condition. The smaller the angle, the more the drop spreads over the surface, and the larger the angle, the more the drop remains swollen on the surface of the stone. For example, for an epilame stone, the angle of a drop of lubricating oil is approximately 44°, whereas without epilame, the drop forms a lower angle, and is therefore more spread out. Generally, we don't want the drop to spread out, so that the lubrication is better, for example between the stone and the pivot.

[0007] However, the disadvantage of the epilame layer is that its effect remains limited to an angle of less than 50°, even if it actually increases the contact angle. On the other hand, the epilame layer wears out over time, because the adhesion of the epilame layer to the stone is not optimal. Consequently, the wear of the epilame layer decreases the adhesion of the lubricating oil.

Summary of the invention

The invention aims to overcome the aforementioned drawbacks, and aims to provide a stone whose contact angle with the lubricating oil is greater, and which resists longer.

[0009] To this end, the invention relates to a method for treating a stone, in particular for watchmaking, the stone comprising a body defining its shape.

[0010] The method is remarkable in that it comprises an ion implantation step on the surface of the body to modify the roughness of said surface.

[0011] Thanks to ion implantation, the relief of the surface of the stone is increased or reduced, which modifies its roughness. Depending on the size of the implanted ions, a different roughness is obtained, because the ions structure the surface differently. Some ions increase the roughness, while other ions decrease the surface roughness.

[0012] Thus, ion implantation can produce two particularly advantageous contrary effects depending on the ion chosen to be implanted. With some ions, ion implantation decreases the contact angle of a liquid, while with other ions, the contact angle with a liquid increases.

[0013] For example, by decreasing the contact angle of the surface, the adhesion of a layer of epilame deposited on this ion-implanted surface is increased. Thus, the lifetime of the epilame layer is increased, which wears out less quickly than a layer deposited on a stone without ion implantation.

[0014] On the other hand, by increasing the contact angle of the surface of the stone, it is possible to dispense with an epilame layer, and place the lubricating oil directly on the stone. Thus, the method of manufacturing the stone is simplified, since it avoids having to deposit a layer of epilame, and it is even possible to obtain contact angles much greater than those obtained with a layer of epilame.

According to a particular embodiment of the invention, the method comprises a step of depositing a layer of epilame on the surface of the stone.

According to a particular embodiment of the invention, the epilame layer comprises chromium nitride, preferably entirely.

According to a particular embodiment of the invention, the step of depositing the epilame layer is carried out by PVD, PECVD.

According to a particular embodiment of the invention, the ions implanted on the surface reduce the contact angle of a drop of liquid, the contact angle being less than 40° for a drop of water.

According to a particular embodiment of the invention, the implanted ions are helium or argon.

According to a particular embodiment of the invention, the ions implanted on the surface of the body increase the contact angle of a drop of liquid, the contact angle being greater than 50°, or even greater than 70 ° for a drop of water.

According to a particular embodiment of the invention, the implanted ions are nitrogen.

According to a particular embodiment of the invention, the ion implantation step is carried out by electronic cyclotron magnetic resonance of the ECR type.

According to a particular embodiment of the invention, the ion implantation step is performed by plasma.

According to a particular embodiment of the invention, the body of the stone is formed beforehand during a first step by a Verneuil-type process for a monocrystalline stone or by a sintering process for a polycrystalline stone.

[0025] According to a particular embodiment of the invention, the stone comprises Al2O3 or ZrO2, preferably in full.

Brief description of figures

Other features and advantages will emerge clearly from the description given below, by way of indication and in no way limiting, with reference to the appended drawings, in which: Figure 1 is a schematic representation of a pivot bearing according to a known embodiment of the state of the art; FIG. 2 is a block diagram of a method for producing a stone according to the invention; FIG. 3 is a schematic representation of a stone obtained using a first embodiment of the method according to the invention; FIG. 4 is a schematic representation of a stone obtained using a second embodiment of the method according to the invention.

Detailed description of the invention

As explained above, the invention relates to a surface treatment process 10 of a stone capable of forming a guide element of a timepiece, as shown in Figure 1. The stone is for example intended to come into contact with a pivot, also called pin, for example of a balance shaft, in order to make the latter mobile in rotation with minimal friction. It is therefore understood that the present invention makes it possible in particular to treat a stone that can form all or part of a bearing of an axis mounted in rotation, such as that shown in Figure 1.

According to the method 10 shown in Figure 2, the body of the stone is formed in a first step 11.

[0029] For a stone of the polycrystalline type, a precursor is produced from a mixture of at least one powder material with a binder. This material may be, in a non-limiting and non-exhaustive manner, ceramic. 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 can comprise aluminum oxide in order to form synthetic sapphire or a mixture of aluminum oxide and chromium oxide in order to form poly-ruby of al2O3 type or ZrO2 type Zirconia ceramic. In addition, the binder can be of various natures such as, for example, polymeric types or organic types.

[0030] 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 stone.

Then proceeds to the sintering of said green body to form the mineral body of the future stone in said at least one material. The material can be, as we mentioned earlier, ceramic. In other words, this step is intended to sinter the green body in order to form a ceramic body of the future pierced stone. Preferably according to the invention, the sintering step may include pyrolysis, for example by thermal debinding.

[0032] Machining of the mineral body is possible, in order for example to shape the upper face and the lower face to obtain a predefined stone thickness. Machining can also consist of drilling a hole through the stone if necessary, and functionalizing the surfaces of the body.

[0033] Lapping and/or brushing and/or polishing of the mineral body makes it possible to obtain a particular finish. This finish gives the stone a surface condition compatible with its use. Such a finishing step also allows the adjustment of the final dimensions and/or the removal of edges and/or the local modification of the roughness.

[0034] For a monocrystalline stone, the body is formed by a Verneuil-type process. A Verneuil-type process includes a step of melting a material which will crystallize on contact with a single seed crystal. Corundum (Al2O3) is generally used as the fusion material. Machining and lapping are similar to the embodiment of polycrystalline type stone.

According to the invention, a second step 12 of the method 10 consists in treating at least part of the surface of the body by ion implantation. Ion implantation is a technology for incorporating ions into a material.

[0036] Thus, it makes it possible to carry out nanostructuring by modifying the relief of the surface of the body. Indeed, the implantation of ions in the surface creates a relief, which modifies the roughness of the surface. Depending on the type of implanted ions, a different roughness is obtained, because the ions have different tailies, which structure the surface differently. Some ions increase the roughness, while other ions decrease the surface roughness. Increasing the roughness increases the contact angle, while decreasing the roughness decreases the contact angle.

There are facilities for such treatment, which include an ion source, a particle accelerator using the electrostatic properties to create an ion beam and an enclosure comprising the body of the stone to receive the ions.

[0038] In a preferred embodiment variant, the implantation is carried out by immersing the body of the stone in an ion plasma. The stone is immersed in an ion plasma, for example by an electron cyclotron resonance process of the ECR type

A first embodiment of the second step 12 of the method 10 consists in implanting ions on the surface of the stone, which make it possible to reduce the contact angle of a liquid on said surface. The contact angle obtained is preferably less than 40° for a drop of water. Thus, such a surface makes it possible to improve the adhesion of a layer deposited on the surface of the body, for example a layer of epilame. Preferably, the ions implanted on the surface of the stone are helium or argon ions, because they decrease the contact angle.

In a second embodiment of the second step 12, ions are implanted in the stone, which make it possible to increase the contact angle of a drop of liquid on the surface of the stone. Preferably, the ions implanted on the surface of the stone are nitrogen ions. The contact angle is greater than 60°, or even greater than 70° for a drop of water. Thus, one avoids having recourse to a layer of epilame.

[0041] Preferably, the ions are implanted in the body at a depth of up to 150 nm.

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 in depositing a layer of epilame on the part of the surface treated by ion implantation in the second step. The epilame layer is preferably a chromium nitride layer. A layer of epilame is generally deposited in the vapor phase by a process of the PVD or PECVD type. The epilame layer preferably has a thickness of 0.003 to 0.006 μm.

[0043] Optionally, laser nanostructuring of the epilame layer can be performed in a fourth step 14. Thus, it is possible to select which part of the surface of the stone has an epilame layer.

The stone part 20, shown in Figure 2, corresponds to a stone treated according to the first embodiment. The stone 20 comprises a body 23 whose surface 24 has been implanted with ions reducing the contact angle of a liquid. The stone 20 further comprises a layer of epilame 21 deposited on this surface 24. As can be seen, a drop of liquid deposited on the layer of epilame forms a contact angle greater than 40° for a drop of oil.

The stone part 30, shown in Figure 3, corresponds to a stone treated according to the second embodiment. The stone 30 comprises a body 25 whose surface 27 has been implanted with ions making it possible to increase the contact angle of a drop of liquid. This stone does not need 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 ion implantation.

Claims (12)

1. Surface treatment method (10) of a stone of the monocrystalline or polycrystalline type (20, 30), in particular for watchmaking, the stone (20, 30) comprising a body (23, 25) defining its shape, characterized in that it comprises a step of ion implantation (12) on the surface (24, 27) of at least part of said body (23, 25) to modify the roughness of said surface (24, 27). 2. Method according to claim 1, characterized in that it comprises a step (13) of depositing a layer of epilame (21) on the surface (24) of the stone (20). 3. Method according to claim 1 or 2, characterized in that the epilame layer (21) comprises chromium nitride, preferably entirely. 4. Method according to claim 2 or 3, characterized in that the step (13) of depositing the epilame layer (21) is carried out by PVD, PECVD. 5. Method according to any one of the preceding claims, characterized in that the ions implanted on the surface (24) reduce the contact angle of a drop of liquid (23), the contact angle being lower at 40° for a drop of water. 6. Method according to any one of the preceding claims, characterized in that the implanted ions are helium or argon. 7. Method according to claim 1, characterized in that 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 more than 70° for a drop of water. 8. Method according to claim 7, characterized in that the implanted ions are nitrogen. 9. Method according to any one of the preceding claims, characterized in that the ion implantation step (12) is carried out by electron cyclotron magnetic resonance of the ECR type. 10. Method according to any one of the preceding claims, characterized in that the ion implantation step (12) is carried out by plasma. 11. Method according to any one of the preceding claims, characterized in that the body (23, 25) of the stone (20, 30) is formed beforehand, during a first step (11), by a process of the Verneuil type for a monocrystalline stone or by a sintering process for a polycrystalline stone. 12. Method according to any one of the preceding claims, characterized in that the stone comprises Al203 or ZrO2, preferably entirely.