CH708998A1 - Timepiece and method for reducing the coefficient of friction of a timepiece. - Google Patents

Abstract

The invention relates to a mechanical part (3) made of diamond or coated with diamond or silicon oxide for watch movement, lubricated with a hygroscopic lubricant.

Description

Technical area

The present invention relates to a lubricated timepiece, for example a watch movement or part of a watch movement.

State of the art

[0002] Mechanical parts for mechanical watch movements are most often made of metal. The moving parts, for example the axles, the wheels, the gears, the anchor of escape, the escape wheel, the balance and the spiral are frequently made of steel, or steel elinvar for the spiral.

The coefficient of friction of the steel is, however, relatively large, which causes significant energy losses by friction including the exhaust and cog. The friction thus has the effect of reducing the running time of the watch, and causing rapid wear of the components.

In order to reduce this coefficient of friction, oils and other lubricants are frequently used. Oils and lubricants, however, have the disadvantage of degrading and spreading leaving the lubricated parts. To reduce this spreading, it is known to perform a surface treatment called epilamization and which increases the lipophobicity and thus reduce the spread of fatty watch lubricants on metal or ceramic watch components in particular.

This technology is however difficult to apply on very small or very thin parts; the oil tends to leave those parts that are difficult to depilate.

To mitigate these disadvantages, some parts undergoing a significant friction, for example the bearings or pallets of the anchor, are often made of ruby. Ceramics are sometimes also used for certain bearings. Although relatively expensive, these materials do not have an optimal coefficient of friction either.

[0007] Extensive research has been conducted to replace these conventional materials and to avoid some of their disadvantages. For example, silicon is today used industrially for the manufacture of the bodies of the escapement or spiral in particular. EP 732 635 A1 (CSEM) discloses a micro-mechanical part, for example an anchor for a watch movement, cut in a silicon wafer by etching by means of a plasma gas around a mask formed previously on the face of the plate.

Silicon has the advantage of being easy to machine, reproducibly, with technologies perfectly mastered for the manufacture of integrated circuits or MEMS in particular. However, it has an insufficient tribological surface state and a relatively high coefficient of friction.

In order to improve this surface state of the silicon, and also to compensate for the thermal drift of the Young's modulus, it is known to coat the functional silicon mechanical parts with a silicon oxide (SiO 2) layer. which can be obtained for example by thermal oxidation in an oven.

Furthermore, CH 669 109 A1 (The Swatch Group R & D Ltd) suggests improving this surface by depositing a layer of carbon DLC ("Diamond Like Carbon") on silicon. Similarly, US 2002/114 225 (Damasko) describes in particular a steel exhaust anchor coated with a DLC ("Diamond Like Carbon") layer. US 2012/0263909 (Diamaze Microtechnology SA et al.) Discloses another example of a diamond coated mechanical part or a DLC layer.

DLC coatings have some of the properties of natural diamond, although their crystalline structure is different. In general, these coatings are produced using a method of carbon deposition by plasma, filtered arcs, ion beams, cathode sputtering, and the like. These fast, high energy processes do not allow the carbon atoms to be arranged according to the typical sp3 cubic disposition of the diamond; the arrangement of the atoms is globally amorphous, with an entanglement of crystalline micro-structures oriented differently from each other.

A piece of steel or silicon coated with a DLC layer thus has tribological surface conditions which are improved without being perfect.

Various lubricants specifically for the lubrication of parts coated with DLC have been proposed. For example, JP-A-2008-56735 discloses a low friction mechanism with sliding surfaces using diamond and a lubricating composition including a specific additive.

Clockwise mechanical functional parts are also known with an amorphous carbon coating which has some of the advantages of DLC.

[0015] Silicon nitride (SiN) or silicon carbide (SiC) coated parts are still known in mechanics.

Also known micromechanical parts made of polycrystalline synthetic diamond. Thus, WO 2004/029 733 A2 (Fore Eagle Co Ltd) describes watch components made at least partially in this material. This document lists various advantages of diamond, including its hardness, low coefficient of friction, good impact resistance, high mechanical strength, high modulus of elasticity, low coefficient of thermal expansion, transparency and the ability to not get scratched.

EP 2 107 434 A1 discloses a mechanical part, including an anchor wheel for watchmaking, silicon or diamond.

CH 701 369 discloses a diamond barrel spring.

There are also known different methods of manufacturing synthetic diamond. US8088221B2 (Z. Shapiro) discloses a low temperature and relatively low pressure synthetic diamond manufacturing process. EP 2 189 555 A2 (Appollo Diamond Inc) discloses another method for producing synthetic diamond. CVD or explosive detonation methods have also been suggested.

The mechanical parts coated with silicon oxide, DLC, amorphous carbon and especially the mechanical parts made entirely of diamond, have a tribological state greatly improved over conventional steel or silicon parts; the coefficient of friction is remarkably low.

However, there is a need, particularly in the mid-range and high-end watchmaking, for watch components having a coefficient of friction even lower than that which can be obtained with the diamond or the parts coated with DLC or amorphous carbon.

In particular, there is a need for a lubricant specifically adapted to diamond or coatings based on DLC or amorphous carbon, and which further reduces the coefficient of friction.

Brief summary of the invention

According to the invention, these objects are attained in particular by means of a functional mechanical part, in particular a timepiece, of which at least the surface comprises one of the materials in the following group: diamond; DLC ("Diamond Like Carbon"); amorphous carbon; silicon oxide; silicon nitride; silicon carbide; the part being lubricated with a hygroscopic lubricant.

A hygroscopic lubricant is a lubricant that has the particularity of absorbing water, including moisture in the air, forming OH- ions.

It has been observed that these OH- ions are favorable to lubrication on the surfaces of the indicated materials.

In a preferred embodiment, the lubricant is water-based.

The use of water-based lubricants in a watch is quite unexpected; there is indeed a tenacious prejudice against the presence of water in watches.

[0028] It is also often considered that oil-based lubricants are more effective than water-based lubricants. However, experiments have shown that on the indicated materials, water-based lubricants and hygroscopic components are significantly superior to oil-based components.

In particular, tests have however shown that the lubrication of monocrystalline diamond parts, polycrystalline and / or coated with DLC, amorphous carbon, or nitride, carbide or silicon dioxide with a water-based lubricant and of a hygroscopic component has the effect of considerably reducing the coefficient of friction.

The use of a highly hygroscopic component absorbs the moisture present in the watch by concentrating it in the lubricant; this moisture does not spread throughout the movement, and is therefore not detrimental to the smooth running of the movement.

The lubricant may be composed of more than 50% of a hygroscopic component.

The hygroscopic component of the lubricant may comprise glycerol. The hygroscopic component of the lubricant may consist mainly of glycerol. The lubricant can be composed of more than 95% glycerol and water.

Glycerol is a relatively economical compound of formula HOH2C-CHOH-CH2OH.

An advantage of using glycerol as a lubricant is to obtain almost perfect lubrication on the diamond; the coefficient of friction becomes almost zero on a carefully polished diamond.

Glycerol and water form on the diamond OH- groups that promote lubrication.

Another advantage is that the lubricant "regenerates" naturally with the moisture present in the air of the watch. Its degradation is therefore minimal and reversible.

Glycerol has the further advantage of partially absorbing shocks.

The method and lubricant described are suitable for the manufacture of micromechanical parts, especially for the watch industry.

In one embodiment, the invention relates to a diamond exhaust anchor or coated with DLC or amorphous carbon and lubricated with such a lubricant.

In one embodiment, the invention relates to a pallet for escape anchor diamond or coated with DLC or amorphous carbon or silicon oxide and lubricated with such a lubricant.

In one embodiment, the invention relates to an exhaust anchor wheel coated with one of the indicated materials and lubricated with such a lubricant.

In one embodiment, the invention relates to a wheel or pinion coated with one of the indicated materials and lubricated with such a lubricant.

In one embodiment, the invention relates to a barrel spring coated with one of the indicated materials and lubricated with such a lubricant.

In one embodiment, the invention relates to a bearing coated with one of the indicated materials and lubricated with such a lubricant.

In one embodiment, the invention relates to a shock absorber coated with one of the indicated materials and lubricated with such a lubricant.

The part may be entirely or partially coated with one of the indicated materials.

The part may be integrally in one of the indicated materials.

The part may be integrally polycrystalline diamond or preferably integrally monocrystalline diamond.

Monocrystalline diamond allows the manufacture of parts of extreme finesse, for example exhaust wheels or other parts with a thickness of 60, 40 or even only 20 microns. This feature reduces the thickness of movement and the inertia of moving parts. This also makes it possible to increase the power reserve of the watch, and to increase the frequency of oscillation of the regulating organ.

The lubrication technique described has the advantage of being adapted to the lubrication of such thin parts.

On the other hand, polished monocrystalline diamonds generally have a smoother surface finish than polycrystalline diamonds or DLC coatings, whose grain structure does not provide an optimal tribological surface.

The part is advantageously a functional mechanical part. Functional mechanical part means in the present application a part that performs a mechanical function, so that it is not possible to remove this part without affecting at least one function of the watch movement. A purely decorative piece, or a piece of watchmaking clothing, is therefore not considered a functional mechanical part.

A piece is said to be "made entirely of diamond" if it consists of a single diamond crystal, without a substrate in another material, without surface coating and generally without assembly. Small quantities of impurities, for example less than 3%, can at most be present, in particular in the case of natural diamonds, but also of synthetic diamonds. The impurities may for example be constituted by doping.

A diamond is considered monocrystalline if it consists of a single crystal, or essentially a single crystal except for a limited number of distinct crystals, often smaller than the main crystal, unwanted but which result for example from the manufacturing process or imperfect crystallization around impurities or edges.

The piece can be made of natural or synthetic monocrystalline diamond.

Synthetic diamonds are in the vast majority of polycrystalline cases; it is generally considered difficult to produce monocrystalline synthetic diamonds, especially large diamonds. It has, however, been observed more recently that the evolution of technologies makes it possible to manufacture monocrystalline synthetic diamonds of more than 1 carat at relatively low costs.

For example, monocrystalline synthetic diamonds can be obtained by growing carbon by CVD deposition around a monocrystalline diamond primer. The monocrystalline diamond primer can be reused to successively grow several monocrystalline synthetic diamonds. It is important that the primer is monocrystalline diamond so that the structure that is deposited is itself monocrystalline. Carbon can be obtained from methane in a CVD reactor.

Monocrystalline synthetic diamond can also be obtained by compression of carbon at high pressure and high temperature. This solution, however, results in higher costs, especially for the manufacture of monocrystalline diamonds of large dimensions.

The diamond can be doped. The doping of the synthetic diamond can be obtained during its manufacture by adding impurities in the gas of the CVD reactor. Doping of diamond can also be achieved by ion implantation using a high energy beam. The doping can be homogeneous throughout the volume of the room. Doping can be limited to the surface, or different in surface and depth. Doping may be chosen to control the hardness and / or color and / or elasticity and / or sensitivity of the Young's modulus to temperature. Different diamond pieces of the same movement can be doped differently.

The part may comprise a metal core or ceramic or silicon coated with a DLC or amorphous carbon envelope.

The part may comprise a metal core or ceramic or silicon coated with a silicon oxide envelope. In this case, the hygroscopic lubricant may consist of silicon oxide, or an additional component such as glycerol or other liquid component on the silicon oxide.

The invention also relates to a watch movement comprising one or more functional mechanical parts in monocrystalline diamond.

The invention also relates to a method for reducing the coefficient of friction of a timepiece of which at least part of the surface comprises one of the materials in the following group: diamond; DLC ("Diamond Like Carbon"); amorphous carbon; silicon oxide; silicon nitride; silicon carbide; the process comprising the following steps: polishing at least a portion of the surface of said workpiece; lubricating said surface with a water-based lubricant and composed more than 50% of a hygroscopic component.

The polishing can be performed with a laser beam.

The polishing can be performed with an ion beam.

The polishing can be performed with electrochemical processes.

The state of at least one surface of the part is advantageously treated both by heat treatment, mechanical polishing and laser grinding.

The polishing can be performed solely or differently on the side surfaces of the part subjected to friction against other parts.

Advantageously, at least a portion of these surfaces is corrected to have a tribological state better than before the correction.

At least a portion of the side faces of the workpiece can be ground with a laser so that this portion is substantially perpendicular to the lower and upper faces of the workpiece.

The method may further comprise a heat treatment step of the surface of said part before lubrication by exposing it to a temperature between 600 ° and 750 ° C, preferably between 650 and 680 ° C. This operation makes it possible to burn the carbon in the form of graphite produced by cutting the diamond and which possibly remains on the surface. This heat treatment also makes it possible to polish the diamond, by burning tips on the surface.

The method may further comprise a gasoline cleaning step of the part before lubrication.

The method may comprise a hygroscopic lubricant deposition step, then voluntary introduction of moisture in a watch case. This introduction of moisture can be carried out for example by injection of air with a controlled rate of humidity, by vaporization, etc.

Brief description of the figures

Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which: <tb> Figs. 1A to 1E <SEP> illustrate different successive steps of a method of manufacturing a mechanical part according to the invention.

Example (s) of embodiment of the invention

We will now describe by way of example different aspects of a method of manufacturing a timepiece functional according to the invention.

FIG. 1A illustrates an uncut monocrystalline or polycrystalline diamond 1 used to make one or more pieces according to the invention. The monocrystalline or polycrystalline diamond may be a natural diamond or a synthetic diamond, advantageously greater than 1 carat, preferably greater than 3 carats.

In the case of a natural diamond, it may be a diamond having a shape or other properties rendering it unfit for recovery for use in jewelry.

A synthetic monocrystalline diamond can be produced for example by means of a filtered arc to deposit carbon on a monocrystalline diamond primer, without the addition of hydrogen or other materials. Another possibility is to perform a CVD deposition of carbon produced from a hydrocarbon such as methane or acethylene on a monocrystalline diamond primer. The primer can be reused after cutting plates in the mass deposited above the primer.

A third, less advantageous, possibility is to produce a synthetic monocrystalline diamond by subjecting a carbon source to a high temperature and a high simultaneous pressure. Other methods may be used.

The monocrystalline diamond thus formed can be doped. In one embodiment, the doping product can be introduced during the formation of the synthetic diamond, for example by adding traces of dopant in the filtered arc respectively in the CVD reactor. In another embodiment, the dopant is added after formation of the synthetic diamond, for example by means of a high energy ion beam. The doping can be carried out homogeneously throughout the mass of the diamond, and / or only at the surface. A first doping may be carried out in the mass and a different doping, for example with another doping product and / or with another concentration, may be carried out on the surface.

The doping can be selected in order to modify the hardness of the pieces produced from this diamond; depending on the doping product, it is possible to increase or reduce this hardness. Doping can also be selected to control the color of the diamond. Doping can be chosen to control the Young's modulus of the diamond. The doping can be chosen so as to reduce the sensitivity of the Young's modulus to the temperature, in order to produce parts whose rigidity is as independent as possible from the temperature. The doping can be chosen so as to reduce the coefficient of expansion of the diamond, in order to produce pieces whose dimensions are as independent as possible from the temperature.

In one embodiment, the diamond is doped with boron ions. Different diamonds used for the production of different pieces in the same watch can be doped differently depending on the desired properties.

The boron doping performed during the organic growth of the synthetic diamond has the advantage of producing a non-radioactive black diamond, unlike doping processes by introducing high energy ions.

The monocrystalline diamond 1 is then cut as illustrated in FIG. 1B, for example by means of a diamond saw, or slit by means of a hammer and a blade, an electric arc, an ion beam, or preferably cut by means of a laser to obtain a planar surface. The laser is advantageously a pulsed laser, for example a laser pulsed at a frequency of 5 to 40 GHz.

In the embodiment illustrated in FIGS. 4A to 4C, the diamond is sliced from a first side by means of a first laser beam 20. The laser beam is rotated by means of a movable mirror, so as to emit in a cone with an opening angle less than 5 °. The diamond is then etched from the other side by means of another laser beam 21 rotated in a cone (Fig. 4B). It is also possible to use the same laser beam to attack both sides of the room, by turning it between the two cuts. This cone machining allows the ablation zone to be enlarged and to avoid poor surface conditions and the destruction of the crystalline structure which may occur if the ablation is performed in a narrow channel, causing a rise in excessive temperature. The process is comparable, proportionately, to that of a lumberjack cutting a trunk by means of two notches sloping from each side of the trunk.

The convex surface thus produced by this cutting is then ground or flattened by means of a laser beam oriented parallel to the surface of the plate that is desired to produce. The pulsation frequency of this laser can be for example between 10 and 100 KHz, to obtain a precise cut without the problems of changes in the crystalline structure caused by the high energy lasers pulsed more quickly.

In a first embodiment, the section plane is determined in order to obtain an active surface of the workpiece oriented along the crystalline plane {111} which is generally the hardest. In the case of a plate intended for the manufacture of a clockwork spiral spring, the cutting plane is preferably parallel to the {111} plane of the diamond. In the case of a plate intended for the manufacture of pallets for a watch anchor, the plane of section is preferably distinct from the plane {111} and chosen so as to allow the cutting of pallets whose impulse surface, obtained in the slice of the cut plates, is parallel to the {111} crystalline orientation plane.

However, it has been found in the context of the invention that even if the crystalline plane {111} is the hardest, this hardness decreases very abruptly in case of slight deviation from this ideal plane. For example, a piece cut or polished in a plane that deviates even a few degrees from the plane {111} has a significantly reduced hardness and surface condition. However, it is difficult, especially in the context of industrial manufacture, to manufacture parts with surfaces oriented precisely along the {111} plane, without any deviation.

Therefore, in a preferred embodiment, the section plane is determined in order to obtain an active surface of the workpiece oriented substantially along the {001} crystalline plane or along the {011} plane; although less hard than the ideal plane {111}, these planes are less sensitive to deviations from the ideal surface. In the case of a plate intended for the manufacture of a clockwork spiral spring, the cutting plane is preferably substantially parallel to the {001} or {011} plane of the diamond. In the case of a plate intended for the manufacture of pallets for a watch anchor, the cutting plane is preferably chosen so as to allow the cutting of pallets whose impulse surface, obtained in the edge of the cut plates, is substantially parallel to the {001} crystalline orientation plane where {011}. Substantially parallel means here that the deflection after polishing is at most + 5 °.

The {011} plane has the best tribological properties - the coefficient of friction is the lowest.

It is possible to maintain the diamond 1 during cutting for example by cementing or gluing on a temporary support.

The rough face 10 obtained at the end of this cut is then ground and / or polished so as to obtain a polished flat face 11 as illustrated in FIG. 1 C .

The rectification of the face 11 can be performed, as indicated, by means of a laser, for example a laser pulsed between 10 and 100KHz.

The polishing of the face 11 may be performed on a rotary grinding wheel covered with synthetic diamond powder, for example polycrystalline diamond powder.

The roughness of the face 11 can also be reduced by means of a high energy ion beam parallel to the surface.

The diamond is then cut according to a new section parallel to the first section, so as to obtain a thin plate 2 as shown in FIG. 1D. This delicate cut is advantageously performed by laser to avoid shocks that could break the plate. Like cutting the upper face, this cutting can be performed by means of one or two laser beams deflected by a mirror to produce a conical ablation zone.

Depending on the type of part desired, this process makes it possible to cut extremely thin diamond plates, for example plates with a thickness of less than 400 microns, for example plates with a thickness of between 100 and 400 microns in each case. the case of plates for machining pallets, and plates with a thickness of between 20 and 80 microns, for example 60 microns, in the case of manufacture of anchor wheels or anchors.

This feature allows to manufacture extremely lightweight parts and therefore reduce the energy required to put them in motion.

The lower face 12 of the plate 2 is relatively crude. For many applications, especially in watchmaking, this aspect not perfectly polished is entirely satisfactory since this face is not visible. However, it is conceivable by making a slightly thicker piece to also polish this face 12, for example by mechanical polishing on a grinding wheel and / or laser. In one embodiment, the part is held without glue during polishing, preferably by vacuum. It is thus possible to very precisely control the thickness of the piece after polishing, without this thickness depending on the thickness of the glue.

The plate 2 produced can be visually inspected to remove the plates which have too many impurities or non-monocrystalline structure. In one embodiment, this control is performed by illuminating the plate with a polarized light that highlights the imperfections. The control can be manual or done by means of a camera and an image analysis software.

During the step illustrated in FIG. 1E, the piece 3 is cut in the surface of the plate 2. This cut is for example obtained by means of a laser beam perpendicular to one of the surfaces 11, 12 or the median plane of the plate 2. In the example of figs. 1E and 2, the piece 3 thus cut is an escapement anchor for watch movement. It is also possible to make other micromechanical parts using the method described above, for example an anchor wheel or a spiral spring or another wheel. Several different pieces can be cut into a single plate.

The cutting process in a plate 2 of the workpiece 3 by means of a laser has the disadvantage of producing lateral flanks not perpendicular to the lower and upper faces. The diamond being more or less transparent, the cut is in fact obtained by the attack of the plasma produced by the interaction between the laser light and the air. This results in non-perpendicular flanks and not very smooth. This surface quality is generally not problematic for parts 3 or portions of parts 3 which are not intended to come into contact with other parts. In some cases, however, these irregular surfaces are undesirable either for aesthetic reasons, or because it is necessary to accurately control the shape of the workpiece and the amount of material, for example in the case of a spiral spring. In the case of a part or part portion intended to come into contact with other components of the movement, it is therefore desirable to control the profile and the surface condition of the flanks 13. These requirements are particularly important if the piece 3 is an anchor pallet, a pallet anchor portion, or a tooth of an anchor wheel or other wheel.

In such a case, an optional sidewall rectification operation 13, or at least a portion of these flanks, can be carried out by means of a laser or a grinding wheel in order to obtain lateral flanks. smooth and perpendicular to the lower and upper planes. In the case of a pallet, at least the active surface can be ground by means of a grinding wheel coated with polycrystalline diamond powder. In the case of an anchor wheel, the portion of each tooth intended to be brought into contact with the pallet may be polished or ground by means of a laser beam.

The surfaces of the piece 3 thus obtained are preferably not coated. However, the surfaces may be covered with traces of graphitized carbon resulting from the destruction of the diamond structure during cutting or polishing operations. In order to eliminate these traces, it is possible in the context of the invention to subject the part 3 to a heat treatment, for example by leaving it for a few seconds or a few minutes in a furnace between 600 ° and 750 ° C., preferably between 650 and 680 ° C; this operation makes it possible to burn the residual graphite at the surface without affecting the carbon in the form of a diamond, and thus to improve the surface state of the part. It also polishes the piece by burning points on the surface.

The piece produced can also be polished by means of an ion beam ("ion etching"), for example an ion beam parallel to the surface to be polished. In one embodiment, this ionic polishing is performed after polishing by heat treatment.

The piece produced can also be polished by means of ultrasound. It can be cleaned with gasoline to improve the appearance of the diamond.

In another embodiment, the timepiece is formed of a metal core, for example steel, brass, etc., ceramic or silicon coated with a layer DLC ("Diamond Like Carbon") or amorphous carbon.

The diamond parts thus polished and cleaned, as well as the parts coated with a DLC or amorphous carbon layer, have an excellent tribological state with a very low coefficient of friction. It has, however, been found within the scope of this invention that the use of water-based lubricants, which has never been seen before in watchmaking, makes it possible to reduce this coefficient of friction even more dramatically.

In a preferred embodiment, the part thus produced is coated, preferably after mounting, a lubricant composed of more than 50% of a hygroscopic component, for example glycerol and water.

Conclusive tests were performed with a lubricant composed of more than 90% glycerol and water, and with a lubricant composed exclusively of glycerol and water. These tests demonstrate for example that the amplitude of oscillations of the balance increases thanks to lubrication with glycerol.

Adjuvants or epilamization may however be provided to limit the spread of glycerol.

The process may comprise the deposition of hygroscopic lubricant, for example glycerol and / or silicon oxide, on a part, then the controlled introduction of moisture into a watch case to create OH- ions. on this hygroscopic surface. The moisture content in the air of the box is advantageously greater than 40%, preferably between 30% and 60%, for example between 40% and 50%. This humidity level, which is higher than the one usually sought in a watch case, makes it possible at the same time to guarantee sufficient lubrication thanks to the hygroscopic lubricant, while avoiding condensation that is too rapid if the watch is exposed to the cold.

Claims (26)

1. Timepiece whose at least one surface includes one of the materials of the following group: diamond; DLC ("Diamond Like Carbon"); amorphous carbon; silicon oxide; silicon nitride; silicon carbide; the part being lubricated with a hygroscopic lubricant. 2. Timepiece according to claim 1, characterized in that the lubricant is water-based. 3. Timepiece according to one of claims 1 or 2, said lubricant being composed of more than 50% of a hygroscopic component. 4. Timepiece according to claim 3, said hygroscopic component comprising glycerol. 5. Timepiece according to claim 4, said hygroscopic component being predominantly composed of glycerol. 6. Timepiece according to one of claims 1 to 5, said lubricant being composed of more than 90% glycerol. 7. Timepiece according to one of claims 1 to 5, said lubricant being composed of more than 95% glycerol and water. 8. Timepiece according to one of claims 1 to 7, made entirely of monocrystalline diamond. 9. Timepiece according to one of claims 1 to 7, made entirely of polycrystalline diamond. 10. Timepiece according to one of claims 1 to 7, made entirely of natural diamond. 11. Timepiece according to one of claims 1 to 7, made entirely of synthetic diamond. 12. Timepiece according to one of claims 8 to 11, said diamond being doped. 13. Timepiece according to claim 12, comprising one or more functional mechanical parts monocrystalline diamond doped differently from each other and lubricated with said lubricant. 14. Timepiece according to one of claims 1 to 7, coated with a DLC coating or amorphous carbon. 15. Timepiece according to one of claims 1 to 7, covered with a coating of silicon oxide. 16. Timepiece according to one of claims 1 to 15, constituted by an exhaust anchor pallet, an escape anchor wheel, a wheel, a pinion, a mainspring, a bearing or a shock absorber. 17. A method for reducing the friction coefficient of a timepiece at least part of the surface of which comprises one of the materials in the following group: diamond; DLC ("Diamond Like Carbon"); amorphous carbon; silicon oxide; silicon nitride; silicon carbide; the process comprising the following steps: polishing at least a portion of the surface of said workpiece; lubricating said surface with a hygroscopic lubricant. 18. The method of claim 17, said lubricant being water-based. 19. The method of claim 18, said lubricant being more than 90% composed of a hygroscopic component and water. 20. Method according to one of claims 17 to 19, said hygroscopic component comprising glycerol. 21. The method of claim 17, said lubricant being predominantly composed of glycerol. 22. Method according to one of claims 17 to 21, comprising a step of depositing a hygroscopic lubricant on said workpiece, and a step of intentionally introducing moisture into a watch case comprising said workpiece. 23. The method of claim 22, wherein said voluntary introduction of moisture comprises introducing air with a moisture content of between 30% and 60% in said box, preferably between 40% and 50%. 24. Method according to one of claims 17 to 23, said polishing step being performed with a laser beam, an ion beam and / or electropolishing. 25. Method according to one of claims 17 to 24, comprising a step of heat treatment of the surface of said part before lubrication by exposing it to a temperature between 600 ° and 750 ° C, preferably between 650 and 680 ° C . 26. Method according to one of claims 17 to 25, comprising a step of cleaning the essence of said part before lubrication.