Resilient return component for timepiece movement

Abstract

A resilient return component for an inertial element for a timepiece movement, in particular a spiral spring, characterised in that it comprises a substrate on which a coating is deposited, comprising: a first oxide or nitride or carbide primer layer; and a second layer of a hydrophobic and / or oleophobic material formed by a self-assembled monolayer (SAM).

Description

[0001] Elastic return component for watch movement

[0002] Introduction

[0003] The invention relates to an elastic return component of an inertial element for a watch movement, in particular a spiral spring. It also relates to a watch movement or a timepiece, in particular a watch, comprising such an elastic return component. Finally, it also relates to a method of manufacturing such an elastic return component, particularly comprising a method of surface treatment of such a component.

[0004] State of the Art

[0005] The existence of drift phenomena over time in the frequency of an inertial element for a watch movement, particularly a balance-spring oscillator, is well known to watchmakers. Thus, an oscillator equipped with a balance spring made of a raw ferromagnetic alloy can see its frequency gradually increase to reach a rate variation of around 10 s / d after one year. In order to reduce this drift, heat treatments, called stoving treatments, are usually carried out, which make it possible to reduce the rate drift during the first few years to below 1 s / d.

[0006] The same drift phenomenon is observed in the case of balance springs made of paramagnetic alloys, in particular Nb-Zr alloy, as reported in document EP1039352. The same type of baking treatment makes it possible to reduce the rate drift by approximately 5 s / day after one year in the case of a balance spring made of paramagnetic alloy. Another solution proposed by document EP1039352 is to grow a layer of alloy oxide on the surface of the balance spring, in particular by an anodizing process. This process has the advantage of forming an oxide layer at low temperature, without modifying the crystalline structure of the balance spring, with a thickness (and therefore color) that is perfectly reproducible. However, the anodizing solution sometimes proves insufficient, or even unsuitable with certain materials. It cannot be carried out on a balance spring with an assembled collet and / or stud.

[0007] The phenomena described above are examples of irreversible drift. There is also reversible drift in walking, due for example to climatic conditions such as variations in temperature and pressure.

[0008] The aim of the invention is to propose a solution making it possible to improve the frequency stability of an elastic return component of an inertial element for a watch movement.

[0009] Brief description of the invention

[0010] To this end, the invention is based on an elastic return component of an inertial element for a watch movement, in particular a spiral spring, characterized in that it comprises a substrate on which is deposited a coating comprising: a first adhesion layer of oxide or nitride or carbide; and a second layer of a hydrophobic and / or oleophobic material formed by a self-assembled monolayer (SAM).

[0011] The first bonding layer may have a thickness of between 1 and 20 nm, or even between 1 and 10 nm, or even between 1 and 6 nm, or even between 1 and 5 nm, or even between 1 and 3 nm. The thickness of said coating may be less than or equal to 20 nm, or even less than or equal to 10 nm, or even less than or equal to 7 nm, or even less than or equal to 6 nm, or even less than or equal to 5 nm.

[0012] The first bonding layer may be mono-material. Alternatively or additionally, the first bonding layer may comprise alumina AI2O3, titanium dioxide TiC, hafnium dioxide HfC, zirconium dioxide ZrO2, niobium pentoxide Nb20s, or zinc oxide ZnO.

[0013] Said hydrophobic and / or oleophobic material of the second layer may comprise a fluorinated, perfluorinated or aliphatic hydrophobic molecule.

[0014] Said fluorinated, perfluorinated hydrophobic and / or oleophobic molecule may be chosen from perfluorodecyltrichlorosilane (FDTS), fluorooctyltrichlorosilane (FOTS), perfluorodecanoic acid (PFDA) and pentafluorobenzenthiol (PFBT). Alternatively, said aliphatic hydrophobic and / or oleophobic molecule may be chosen from octyltrichlorosilane, dodecyltrichlorosilane (DTS), and octadecyltrichlorosilane (OTS). Alternatively, said hydrophobic and / or oleophobic molecule may be chosen from dichlorodimethylsilane (DDMS) and 1,2-bis(trichlorosilyl)ethane (BTSCE).

[0015] Said substrate may be made of a paramagnetic alloy based on niobium or titanium, such as niobium-zirconium Nb-Zr or niobium-titanium Nb-Ti alloys, optionally oxidized, or of a ferromagnetic alloy, optionally oxidized, or of mono- or polycrystalline silicon, optionally coated with a layer of silicon oxide SiC>2, or of glass, or of ceramic, or of a compound comprising carbon, such as carbon nanotubes or diamond. Said substrate may be made of a paramagnetic alloy based on niobium or titanium and is covered with a layer of anodic oxide, with a thickness of between 5 nm and 200 nm, itself covered by said coating.

[0016] The elastic return component may be a spiral spring, including or not including a flange and / or a ferrule.

[0017] Said coating can be deposited on the entire surface of said elastic return component.

[0018] The invention also relates to a watch oscillator or watch movement comprising an elastic return component as described previously.

[0019] The invention also relates to a timepiece, in particular a watch, comprising at least one elastic return component as described previously.

[0020] The invention also relates to a method for treating a surface of a substrate of an elastic return component of an inertial element for a watch movement, in particular a spiral spring, characterized in that it comprises the deposition of a coating on said surface of the substrate by the following steps: a first step of deposition by atomic layer ALD or by physical vapor deposition PVD or by chemical vapor deposition CVD of a first bonding layer of oxide or nitride or carbide; and a second step of deposition by self-assembled monolayer (SAM) of a hydrophobic and / or oleophobic material. The treatment method may comprise a step of oxidation of said elastic return component, in particular anodization, this anodization step being carried out before the first deposition step.

[0021] The treatment method may comprise a step of baking said elastic return component, this baking step being carried out before the first deposition step or after the second deposition step.

[0022] Said first and said second stages, and optionally a steaming stage, can be carried out successively in the same enclosure, in particular at the same temperature.

[0023] Said first and said second steps can be carried out at a temperature below 300°C, or even below 200°C, and / or at a temperature above 80°C.

[0024] The invention is more precisely defined by the claims.

[0025] Brief description of the figures

[0026] These objects, characteristics and advantages of the present invention will be explained in detail in the following description of particular embodiments made without limitation in relation to the attached figures among which:

[0027] Figure 1 represents the variation of the rate M of a hairspring as a function of time T according to an embodiment of the invention (2), in comparison with a reference hairspring (1).

[0028] Figure 2 represents the influence of the thickness E of an AI2O3 layer on the maximum variation VM of the rate of a hairspring. Graph (3) represents the maximum variation VM of the rate of a reference hairspring. Graph (4) represents the maximum variation VM of the rate of a hairspring according to an embodiment of the invention.

[0029] The invention is based on a method for manufacturing an elastic return component of an inertial element for a watch movement, which particularly comprises a method for treating a surface of a substrate of said component, characterized in that it comprises the deposition of a coating on said surface of the substrate by the following steps: a first step of depositing a first bonding layer of oxide or nitride or carbide, for example by atomic layer deposition (ALD) or by physical vapor deposition (PVD) or by chemical vapor deposition (CVD); and a second step of deposition by self-assembled monolayer (SAM) of a hydrophobic and / or oleophobic material.

[0030] The following description will be detailed in the case of an elastic return component of an inertial element for a watch movement which is a spiral spring, more simply called a "hairspring", intended for integration into a balance-spring type oscillator. Naturally, the invention remains generally applicable to any elastic return component of an inertial element for a watch movement. For example, the spiral spring could be replaced by a blade or by elastic blades allowing the elastic return and possibly the guidance of an inertial element.

[0031] As is known, a hairspring can be made of different materials, including a micro-machinable material. By micro-machinable material, we mean a material that allows the manufacture of a watch component using micro-manufacturing techniques, in particular those involving photolithography or those involving the use of a laser. Thus, such a watch movement component, in particular its general shape, can for example be obtained, at least partially, by a deep reactive ion etching (DRIE) step. Alternatively, such a watch movement component, in particular its general shape, can for example be obtained, at least partially, by UV-Liga technology (Lithographie Galvanik Abformung).Alternatively, a hairspring may be made of a metal alloy, for example obtained by melting the constituent elements and solidification, which is brought to the desired shape and dimensions by wire drawing and rolling steps, then shaped by drawing and fixing heat treatment. For example, the hairspring may be made entirely of or be based on a paramagnetic alloy such as a niobium-based alloy, such as niobium-zirconium Nb-Zr or niobium-titanium Nb-Ti alloys, and / or a titanium-based alloy. Alternatively, the material may be a ferromagnetic alloy, such as a Nivarox-type alloy, or mono- or polycrystalline silicon, coated or not with a layer of SiO2 as will be specified later, glass, ceramic, or a compound comprising carbon in various forms such as carbon nanotubes or diamond.

[0032] Finally, the manufacturing process comprises a preliminary step consisting of providing a hairspring based on one of the materials mentioned above, that is to say comprising at least 50% by weight of such a material, or presented entirely in such a material.

[0033] On the other hand, the invention is compatible and even complementary with existing solutions of the state of the art, and such a hairspring can undergo a first known treatment, as described above, for example baking and / or anodizing. The hairspring resulting from this preliminary step forms or comprises a substrate comprising a surface which will be treated by the invention, to further improve its performance. Such a substrate can therefore be based on one of the aforementioned materials, a surface layer of which is optionally oxidized (anodic oxidation and / or thermal oxidation).

[0034] The invention then proposes a treatment of this surface of the substrate, which will optionally have already undergone other treatments beforehand. Note that this treatment is preferably applied to the entire outer surface of the hairspring. Alternatively, only part of this surface could be treated.

[0035] The first step of this surface treatment allows the deposition of a first bonding layer in oxide or nitride or carbide. This first layer being intended for the bonding of the second layer, it is chosen in a material adapted to the bonding of the material of the second layer as well as to the material of the substrate formed by the hairspring. As a note, the first bonding layer preferentially fulfills a second function of improving the stability of the hairspring, which is added to its first bonding function, as will be detailed later.

[0036] Preferably, for a hairspring made of paramagnetic alloy, for example Nb-Zr or Nb-Ti, with or without anodization, said material of the first attachment layer may advantageously be an oxide chosen from the following oxides: AI2O3, TiC, HfC, ZrO2, or Nb2O5.

[0037] On the other hand, this first bonding layer can be deposited by physical or chemical deposition, advantageously by ALD, PVD, or CVD techniques. Alternatively, an electrochemical deposition or a thermal or thermochemical treatment or any other technology known to those skilled in the art could be implemented. The first bonding layer is preferably deposited in an installation making it possible to carry out the first step of deposition of the bonding layer then the second step of SAM deposition sequentially, for example an enclosure allowing CVD or ALD deposition and SAM deposition.

[0038] The thickness of the first bonding layer represents a compromise between the different functions and advantages it provides. Thus, this thickness is preferably chosen between 1 nm and 20 nm, or even between 1 and 10 nm, or even between 1 and 6 nm, or even between 1 and 5 nm, or even between 1 and 3 nm. This compromise makes it possible to meet the following objectives: guarantee the effectiveness of the deposit, in particular the effectiveness of its two functions, respectively bonding and stabilization; not degrade the properties of the component, particularly having a negligible impact on the physical and mechanical properties such as stiffness, the thermoelastic coefficient and the natural oscillation frequency of the component. For this, a minimum thickness is favorable; having a negligible impact on the color.For this, a minimum thickness is favorable; minimize the risk of cracking and delamination of the bonding layer due to residual stresses created at the interface during deposition. This point is important for components such as watch hairsprings, which are mechanically stressed in tension / compression and / or bending;

[0039] Minimize the impact on the aesthetics of the hairspring, besides its color, for example by minimizing the impact on the shape of the flanges and collets, this shape not being affected with a very thin coating.

[0040] The ALD technique is preferred for the deposition of the first primer layer because it allows low-temperature deposition with perfect conformity of the final layer, continuously covering rough surfaces and asperities with a continuous layer of very low thickness. The low temperature respects the structure of the substrate, and does not modify, for example, its crystallographic organization.

[0041] We will detail the implementation of the deposition of the first layer by an ALD deposit. One or more spiral springs to be treated are placed on metal supports (for example stainless steel or aluminum) or on plastic supports resistant to the temperature required for the deposition (maximum 200°C) and suitable for working under vacuum. Such plastic supports are for example made of PEEK (polyetheretherketone) or PPS (Polyphenylenesulfide). The supports that hold the spiral or spirals are then placed inside an ALD reactor.

[0042] Once the deposition temperature has been reached inside the charged reactor, a stabilization step is carried out followed by alternating exposure of the hairspring(s) to chemical precursors. The deposition is preferably carried out under a continuous flow of nitrogen N2, for example approximately 20 sccm (standard cubic centimeter per minute) and / or for example under a pressure of approximately 20 Pa. The hairspring(s) are exposed sequentially or alternately to trimethylaluminium (TMA) and water (H2O) vapors to form (by successive partial layers) a layer of AI2O3 oxide, for example with an average thickness of 0.1 nm per exposure cycle, until the desired thickness is obtained by repeating the exposure cycles.

[0043] The base pressure in the reactor, reached when no precursor or gas flow is present, may depend on the characteristics of the vacuum chamber and the pumps. For example, for a small reactor, this may be less than or equal to 0.1 Torr (<20 Pa), preferably less than 0.01 Torr (<2 Pa). For example, the pressure in the chamber reached under nitrogen flow is typically 20 Pa, with a working window between 5 Pa and 50 Pa. The pressure may depend on the deposition chamber, the nature and the surface of the components to be coated.

[0044] The method for treating the surface of the substrate according to the invention then implements a second step of depositing a second layer, by self-assembled monolayer (SAM), of a hydrophobic and / or oleophobic material. Note that the thickness of such a second layer is very low, of the order of approximately 1 nm, depending on the material chosen.

[0045] This second layer can be deposited at different stages of the manufacture of a hairspring, as long as the hairspring does not undergo a subsequent heat treatment step at a temperature above 300°C. The surface treatment of the invention therefore allows the deposition of a coating comprising two superimposed layers. This coating deposition method has the advantage of being compatible with different configurations of a hairspring. For example, it can be deposited:

[0046] On shaped hairsprings, without flange and without ferrule; or

[0047] On hairsprings after assembly of the flange and / or the collet; and / or

[0048] On hairsprings after formation of a terminal curve; and / or On hairsprings after heat treatment known as baking after formation of a terminal curve.

[0049] It is particularly possible to apply the coating to finished hairsprings ready for assembly, without any risk of coloring or altering the flanges and ferrules, given the very thin thickness of the coating.

[0050] Different hydrophobic and / or oleophobic materials can be used to form the second layer, which may for example comprise a fluorinated, perfluorinated or aliphatic hydrophobic and / or oleophobic molecule. In particular, FDTS (perfluorodecyltrichlorosilane) is well suited. Alternatively, the following other materials are possible: FOTS (fluorooctyltrichlorosilane), DDMS (dichlorodimethylsilane), PFDA (perfluorodecanoic acid), PFBT (Pentafluorobenzenthiol), BTSCE (1,2-bis(trichlorosilyl)ethane), or compounds allowing the grafting of alkyl / alkene / aliphatic chain molecules, such as octyltrichlorosilane, dodecyltrichlorosilane (DTS), and octadecyltrichlorosilane (OTS). Such a step could for example follow the teaching of document EP1927648.

[0051] Furthermore, the test results (contact angle on control samples, chronometric measurements) show that the two ALD and SAM deposition steps can be carried out independently, before or after baking at 200°C, without affecting the performance of the hairspring. According to an advantageous embodiment, it is possible to carry out the baking heat treatment within the ALD reactor, just before the ALD and / or SAM deposits in the same reactor. Ovens are therefore no longer mandatory. The advantages of such an embodiment are to allow very good control of the baking conditions and the sequencing of operations in the same reactor with time savings and simplification of operations, as well as less handling and risk of contamination of the hairsprings.

[0052] Generally, the minimum deposition temperature is limited to 80°C by the SAM process. Below this temperature, the reaction with the bonding surface becomes too slow. Regarding the maximum temperature, it is limited to 300°C by the significant degradation of the SAM layer and / or the substrate. The temperature of the two deposition steps of the ALD and SAM layers was chosen at 100°C, with identical performances according to our tests to those obtained with a temperature of 80°C (contact angle on silicon between 110-115°). A temperature increase would also be relevant, with the advantage of accelerating the deposition time of the first bonding layer. In the case of the deposition of a first AI2O3 layer by ALD, the acceptable temperature range is between 30°C and 300°C, preferably between 80°C and 300°C, more preferably between 80°C and 200°C.

[0053] More generally, it is advantageous to implement said first and / or said second step, and optionally said baking step, at a temperature below 300°C, or even below 200°C, and / or at a temperature above 80°C. Indeed, such a low temperature has no influence on the crystalline structure of the hairspring.

[0054] The beneficial effects of the surface treatment according to the invention will now be illustrated in certain cases chosen as examples, using hairsprings made of Nb-Zr alloy with a proportion of 15% of the element Zr, and prepared according to the process described in document EP0886195. These hairsprings are previously coated with a layer of anodic oxide approximately 70 nm thick, obtained according to the anodization principle described by document EP1039352.

[0055] These hairsprings receive the deposition of a first layer of AI2O3 bonding agent by the ALD technique. For this, they are placed in a vacuum reactor at 100°C for 2 hours, before the deposition of the first ALD layer. They are freely arranged on a grid inside the ALD reactor. As a note, different tests were carried out by depositing the first layer of ALOs at higher temperatures, respectively 80°C, 100°C and 170°C. No difference in performance was observed between the hairsprings obtained by these different temperatures.

[0056] On the other hand, different tests were carried out by depositing the ALD layer in AI2O3 at 200°C with water or ozone as co-reactant. No significant difference in performance was observed between the spirals obtained by these different co-reactants.

[0057] Finally, a second layer is formed by SAM deposition from the chemical reagent perfluorodecyltrichlorosilane or FDTS (CAS 78560-44-8), at a deposition temperature of 100°C and an incubation time of 15 min. The table below summarizes the operating conditions.

[0058] SAM conditions used for testing

[0059] Dose, [Torr] 1.7

[0060] Deposition temperature, [°C] 80°-170°

[0061] Exposure time, [min] 15

[0062] AI2O3 sub-layer, [nm] 1 - 10

[0063] In addition, the influence of the incubation time of the FDTS in the reactor during the deposition of the second layer of the coating was evaluated. Four batches of 20 oscillators were produced.

[0064] Incubation time tests during SAM deposition by FDTS, with and without first AI2O3 bonding layer

[0065] The test results (contact angle on control samples, but also chronometric measurements) indicate that the standard incubation time (15 min) is sufficient, and that a shorter time (5 min) is already satisfactory from the point of view of the effect of the resulting coating. A longer duration (45 min) does not provide any significant improvement. The contact angles (water) measured on control samples of silicon accompanying the deposits are respectively 111°, 114° and 115° for the respective incubation times of 5, 15 and 45 min. Finally, it is noted that the FDTS molecule alone, without an ALO sub-layer, offers poor performance on the stability of the oscillator operation. The first bonding layer therefore also fulfills a second function of stabilizing the oscillators, in combination with the second layer according to the invention.

[0066] Further tests are carried out on hairsprings prepared as mentioned above, from Nb-Zr hairsprings coated with an oxide layer approximately 70 nm thick by anodization, before the deposition of the coating according to the invention, comprising a first AI2O3 layer deposited by ALD and a second layer resulting from a SAM deposition from FDTS.

[0067] It is specified that the conformity of the deposits is controlled using oxidized silicon control tiles, typically 1-2 nm of native oxide layer, placed near the balance springs to be coated, on which thickness measurements (ellipsometer) and contact angles (by DSA - drop shape analyzer) are carried out. The target contact angles (water) are between 100° and 115°.

[0068] Figure 1 represents the combined effect of the two layers of the coating according to the invention. Indeed, the tests relate to measurements of variation of the diurnal rate M in [s / d] under variable climatic conditions as a function of time T [d] of a cycle lasting 12 days, involving in particular a controlled temperature variation, of two types of balance springs. The diurnal rate M is the difference accumulated over 24 hours (1 day) between the time displayed by a movement, determined by taking the state of this movement (taking an image of the position of an indicator organ such as a seconds hand), and an external time reference. The first balance spring, whose variation in rate as a function of time is represented by curve 1, is a balance spring made of anodized Nb-Zr alloy, according to the state of the art. It serves as a reference balance spring.Curve 2 represents the rate variation as a function of time of a second hairspring, which corresponds to the first hairspring on which a coating according to the invention has been added, comprising a first layer of ALOs with a thickness of 10 nm and a second layer of FDTS with a thickness of 1 nm. This figure 1 therefore illustrates that the invention reduces the rate variation by a factor of two by implementing the invention, curve 2 showing variation amplitudes divided by two.

[0069] As a note, each point on curves 1, 2 in Figure 1 is the average of the variation in walking speed of a batch of 20 movements. Each batch undergoes an identical cycle of exposure to different climatic conditions, notably by varying the temperature in a controlled manner.

[0070] Figure 2 represents the maximum variation VM of the rate over a cycle different from that of Figure 1, as a function of the thickness of the first AI2O3 layer. Curve 3 represents more precisely the maximum variation of the rate of a hairspring comprising only a single AI2O3 layer, not covered, and which is therefore not part of the invention. Curve 4 represents the maximum variation of the rate for the same hairspring comprising a second layer of FDTS on the first AI2O3 layer, in accordance with the invention. More precisely, each point in Figure 2 represents the maximum variation of the rate between the different instantaneous rate measurements carried out during a cycle under climatic enclosure, averaged for a batch of 30 movements comprising a hairspring with a given configuration of protective layer(s).Each batch consists of 3 sub-batches of 10 movements using balance springs from 3 different production batches, and the measurements show no significant difference between the sub-batches. Each batch of 30 movements is subjected to a 90-minute cycle of stages under different conditions, notably varying the temperature, with the instantaneous rate measurement being taken at the end of each stage.

[0071] The maximum variation of the walk is calculated as the difference between the maximum value and the minimum value of the different values ​​measured during a climatic cycle.

[0072] Figure 2 thus shows the effect of the invention relative to a balance spring which comprises only a single AI2O3 deposit. The invention provides a very significant improvement for low thicknesses of the ALOs layer, approximately less than 6 nm, or even less than 5 nm. It then provides a slighter advantage in terms of maximum variation in rate for thicknesses up to 10 nm, according to the tests carried out, but naturally also has the advantage of a hydrophobic property provided by the FDTS layer.

[0073] This figure 2 thus illustrates that the invention has the advantage of leading to an improvement in the stability of a hairspring with a very low thickness of the first layer. This in fact has the advantage that the invention induces little disturbance of a hairspring: the modification of the stiffness is for example, as a first approximation, proportional to the thickness of the deposit. A low thickness thus has little influence on this stiffness. Naturally, the deposit of a low thickness is also faster and less expensive.

[0074] The reduction in rate drift observed in Figures 1 and 2, as well as in other tests, shows that the combination of two layers, the layer deposited in the first step and the SAM layer, synergistically forms a new barrier layer that is more effective than expected by the simple combination of the two layers taken in isolation. One hypothesis to explain this surprising effect is that the ALD layer is not perfectly continuous, conformal and dense, contrary to what is commonly accepted, in particular on a rough surface, and in particular for a low layer thickness. This low thickness is advantageous in the context of the present invention because it makes it possible to minimize the influence of the ALD layer on the mechanical properties and performance of the hairspring. Similarly, a SAM layer is probably not perfectly continuous and dense, in particular on a rough surface.Adding a SAM layer on an ALD layer then reinforces its effect, particularly in places where the ALD layer is not continuous, conformal and / or dense.

[0075] Finally, the invention relates more generally to any elastic return component of an inertial element for a watch movement, in particular a spiral spring, characterized in that it comprises a substrate on which is deposited a coating comprising: a first bonding layer of oxide or nitride or carbide deposited by physical or chemical deposition (ALD, PVD, CVD); and a second layer of a hydrophobic and / or oleophobic material deposited by self-assembled monolayer SAM deposition. As mentioned previously, the first bonding layer advantageously has a thickness of between 1 and 20 nm, or even between 1 and 10 nm, or even between 1 and 6 nm, or even between 1 and 5 nm, or even between 1 and 3 nm.Advantageously, the total thickness of said coating of the invention is less than or equal to 21 nm, or even less than or equal to 20 nm, or even less than or equal to 10 nm, or even less than or equal to 7 nm, or even less than or equal to 6 nm, or even less than or equal to 5 nm.

[0076] The first bonding layer is advantageously a single-material, as described. Alternatively, it could combine several materials, and / or be in several superimposed sub-layers of different materials. Similarly, the SAM layer is advantageously formed by a single molecule, as described. Alternatively, it could combine several molecules, and / or be in several superimposed sub-layers of identical and / or different molecules.

[0077] According to exemplary embodiments, the first bonding layer may comprise alumina AI2O3, titanium dioxide TiC, hafnium dioxide HfC, zirconium dioxide ZrO2, niobium pentoxide Nb20s, or zinc oxide ZnO.

[0078] It should also be noted that the spirals advantageously remain under vacuum in the same reactor after the deposition of the first layer, which guarantees optimal cleanliness of their surfaces coated with the first layer, ensuring optimal deposition and coverage by the second layer.

[0079] In addition, according to exemplary embodiments, the hydrophobic and / or oleophobic material of the second layer may comprise a fluorinated, perfluorinated or aliphatic hydrophobic molecule. Said fluorinated or perfluorinated hydrophobic molecule may be chosen from perfluorodecyltrichlorosilane (FDTS), fluorooctyltrichlorosilane (FOTS), perfluorodecanoic acid (PFDA) and pentafluorobenzenthiol (PFBT). The aliphatic molecule may be chosen from octyltrichlorosilane, dodecyltrichlorosilane (DTS) and octadecyltrichlorosilane (OTS). The molecule may also be chosen from dichlorodimethylsilane (DDMS) and 1,2-bis(trichlorosilyl)ethane (BTSCE). The molecule may also be chosen from the aliphatic and / or perfluorinated molecules described in documents EP2084253 and EP2655577, and / or be deposited by means other than ALD, for example by dipping.

[0080] The substrate formed by the component may be made of a paramagnetic alloy based on niobium or titanium, such as niobium-zirconium Nb-Zr or niobium-titanium Nb-Ti alloys, optionally oxidized, or of a ferromagnetic alloy, optionally oxidized, or of mono- or polycrystalline silicon, optionally coated with a layer of silicon oxide SiC>2, or of glass, or of ceramic, or of a compound comprising carbon, such as carbon nanotubes or diamond. In the case of a substrate made of a paramagnetic alloy based on niobium or titanium, this optional anodic oxidation layer may have a thickness between 5 and 200 nm. It forms the surface on which the coating of the invention will be deposited.

[0081] The elastic return component may be a spiral spring, including or not including a flange and / or a ferrule.

[0082] Said coating may be deposited on the entire surface of said elastic return component, or on only a part.

[0083] The invention also relates to a watch oscillator or a watch movement comprising an elastic return component as described above. The invention also relates to a timepiece, in particular a watch, comprising at least one elastic return component as described above.

[0084] Finally, as described, the invention achieves the desired objects, and has many advantages. The following advantages can again be mentioned:

[0085] - It allows to improve many oscillators, almost independently of their basic material, which can therefore be chosen from a wide choice of materials;

[0086] - In addition, the preferred treatment chosen to form the coating (ALD / SAM) allows the process to be adjusted with great simplicity and the coating to be deposited with very good reproducibility, in particular to achieve a desired thickness reliably and homogeneously;

[0087] - The coating is deposited at low temperature without influencing the crystalline structure of the hairspring;

[0088] - This homogeneity of the coating thickness is even achieved on substrates with complex shapes and / or on a surface with scales and / or cracks and / or roughness;

[0089] - The thickness of the coating is very low, and has a negligible impact on the various mechanical properties as well as on the overall aesthetics, does not induce a change in color for example, while achieving the remarkable effect of stabilizing the component over time.

Claims

Claims:

1. Elastic return component of an inertial element for a watch movement, in particular a spiral spring, characterized in that it comprises a substrate on which is deposited a coating comprising: - a first bonding layer of oxide or nitride or carbide, having a thickness of between 1 and 20 nm; and - a second layer of a hydrophobic and / or oleophobic material formed by a self-assembled monolayer (SAM).

2. Elastic return component according to the preceding claim, characterized in that the first adhesion layer has a thickness of between 1 and 10 nm, or even between 1 and 6 nm, or even between 1 and 5 nm, or even between 1 and 3 nm and / or in that the thickness of said coating is less than or equal to 10 nm, or even less than or equal to 7 nm, or even less than or equal to 6 nm, or even less than or equal to 5 nm.

3. Elastic return component according to one of the preceding claims, characterized in that the first adhesion layer is mono-material and / or in that the first adhesion layer comprises alumina AI2O3, titanium dioxide TiO2, hafnium dioxide HfO2, zirconium dioxide ZrO2, niobium pentoxide Nb20s, or zinc oxide ZnO.

4. Elastic return component according to one of the preceding claims, characterized in that said hydrophobic and / or oleophobic material of the second layer comprises a fluorinated, perfluorinated or aliphatic hydrophobic molecule.

5. Elastic return component according to the preceding claim, characterized in that said fluorinated, perfluorinated hydrophobic and / or oleophobic molecule is chosen from perfluorodecyltrichlorosilane (FDTS), fluorooctyltrichlorosilane (FOTS), perfluorodecanoic acid (PFDA) and pentafluorobenzenthiol (PFBT), or in that said aliphatic hydrophobic and / or oleophobic molecule is chosen from octyltrichlorosilane, dodecyltrichlorosilane (DTS), and octadecyltrichlorosilane (OTS), or in that said hydrophobic and / or oleophobic molecule is chosen from dichlorodimethylsilane (DDMS) and 1,2-bis(trichlorosilyl)ethane (BTSCE).

6. Elastic return component according to one of the preceding claims, characterized in that said substrate is made of a paramagnetic alloy based on niobium or titanium, such as niobium-zirconium Nb-Zr or niobium-titanium Nb-Ti alloys, optionally oxidized, or of a ferromagnetic alloy, optionally oxidized, or of mono- or polycrystalline silicon, optionally coated with a layer of silicon oxide SiC>2, or of glass, or of ceramic, or of a compound comprising carbon, such as carbon nanotubes or diamond.

7. Elastic return component according to the preceding claim, characterized in that said substrate is made of a paramagnetic alloy based on niobium or titanium and is covered with a layer of anodic oxide, with a thickness of between 5 nm and 200 nm, itself covered by said coating.

8. Elastic return component according to one of the preceding claims, characterized in that it is a spiral spring, comprising or not a flange and / or a ferrule, and in that said coating is deposited over the entire surface of said elastic return component.

9. Clock oscillator or clock movement comprising an elastic return component according to one of the preceding claims.

10. Timepiece, in particular watch, comprising at least one elastic return component according to one of claims 1 to 8.

11. Method for treating a surface of a substrate of an elastic return component of an inertial element for a watch movement, in particular a spiral spring, characterized in that it comprises the deposition of a coating on said surface of the substrate by the following steps: - a first step of deposition by atomic layer ALD or by physical vapor deposition PVD or by chemical vapor deposition CVD of a first bonding layer made of oxide or nitride or carbide, this first bonding layer having a thickness of between 1 and 20 nm; and - a second step of deposition by self-assembled monolayer (SAM) of a hydrophobic and / or oleophobic material.

12. Treatment method according to the preceding claim, characterized in that it comprises a step of oxidation of said elastic return component, in particular anodization, this anodization step being carried out before the first deposition step and / or in that it comprises a step of baking of said elastic return component, this baking step being carried out before the first deposition step or after the second deposition step.

13. Treatment method according to one of claims 11 or 12, characterized in that said first and said second steps, and optionally a steaming step, are carried out successively in the same enclosure, in particular at the same temperature.

14. Treatment method according to one of claims 11 to 13, characterized in that said first and said second steps are carried out at a temperature below 300°C, or even below 200°C, and / or at a temperature above 80°C.

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