EP3204535B1 - Self-lubricating composite coating - Google Patents

Description

The invention relates to a self-lubricating composite solid coating in particular for application to clockwork mechanisms.

In clockwork mechanisms, there are many parts in motion and in frictional contact with one another. This friction must be reduced as much as possible because it can affect the precision and / or the autonomy of the mechanism.

In fact, friction causes wear of the parts, an increase in energy consumption to move the parts and a slowing down of the movement.

To reduce this friction, it is therefore known to use liquid (oils) or pasty (grease) lubricants. These lubricants are used sparingly on well-defined areas and in suitable quantities. This type of lubricant must be able to slip between two parts to minimize friction or must be removed during assembly. Unlike the ability to slip between two rooms, it can also escape from the space where it has been placed. It is also very sensitive to environmental conditions of temperature and relative humidity because its viscosity changes as a function of these.

• ces lubrifiants liquides ou visqueux se modifient dans le sens de la dégradation, par exemple en se chargeant de poussières ou en devenant plus visqueux ou en perdant de leurs capacités lubrifiantes par oxydation ;
• ce type de lubrifiant étant fluide ou pâteux, le mouvement des pièces tend à déplacer le lubrifiant de la zone des contacts vers une zone non soumise à frottement.

So there are two drawbacks:

• these liquid or viscous lubricants change in the direction of degradation, for example by becoming charged with dust or by becoming more viscous or by losing their lubricating capacities by oxidation;
• since this type of lubricant is fluid or pasty, the movement of the parts tends to displace the lubricant from the contact zone towards a zone not subjected to friction.

It is therefore necessary to carry out regular maintenance which consists of cleaning the friction parts and replacing the used lubricant with a new lubricant in the appropriate places.

These lubricants consist of a liquid or viscous support which may contain particles having tribological properties such as carbon. The document WO2012 / 128714 describes for example a liquid containing graphene. Graphene was isolated by André Geim in 2004. It is a two-dimensional crystal of carbon whose stacking leads to graphite. It appears to have interesting tribological properties.

In parallel with liquid or viscous lubricants, dry coatings are known which reduce friction. These coatings are integral with the part to be protected and present less risk of loss or chemical degradation. Furthermore, these coatings are less sensitive to environmental conditions. For example, coatings based on carbon nanotubes dispersed in a nickel matrix are known. Such coatings are for example described in the document US-A- 2008 1323475 .

In the document WO2013 / 150028 the coating metal is gold but this coating is obtained from a bath which contains a percentage of Cadmium much higher than the percentage admitted by European directives, which poses a problem.

Graphite is also used as an antiwear agent in electroplated composite coatings.

The documents CN101192045 A and EP1930793 A1 describe a timepiece having a lubricating coating.

The difficulty for timepieces is that the needs are very different from the needs of the field of general mechanics, in particular because the thickness of the coating must be limited due to the small dimensions of the watch components. The desired coatings must therefore be thin and very effective.

To this end, the invention relates to a solid metal composite coating having self-lubricating properties, characterized in that it comprises particles of graphene and / or graphene oxide distributed in a metal matrix.

• FIG 1 : coupe schématique du substrat revêtu du composite métal graphène.
• FIG 2 : Variation de l'amplitude relative d'un mécanisme d'horlogerie avec un revêtement selon l'invention (a) et sans revêtement (b) par rapport à un mécanisme d'horlogerie lubrifié avec de l'huile.
• FIG 3 : coupe d'un support revêtu avec en supplément une couche d'or.

The invention will be clearly understood with the aid of the description below given by way of nonlimiting example with reference to the drawing which represents:

• FIG 1 : schematic section of the substrate coated with the graphene metal composite.
• FIG 2 : Variation of the relative amplitude of a clockwork mechanism with a coating according to the invention (a) and without coating (b) compared to a clockwork mechanism lubricated with oil.
• FIG 3 : cut of a coated support with an additional layer of gold.

Referring to the drawing, we see a section of a support 1 from a clockwork mechanism coated with a solid coating 2 self-lubricating metal composite according to the invention.

This coating 2 comprises particles 3 of graphene and / or graphene oxide distributed in a metal matrix 4.

According to the invention, use is made of graphene or graphene oxide particles 3 which are in the form of fibers or flakes (aggregates of fibers or particles).

The thickness of this coating is generally between 0.2 microns and 20 microns but preferably it is between 0.5 microns and 2 microns.

In certain cases, before proceeding with the deposition of the coating, a bonding layer 5 is deposited on the support 1. This layer is for example formed of nickel or chromium or gold or gold.

The coating is deposited by electrodeposition if the part to be coated is conductive. If it is a non-conductive part, a purely chemical deposition will be carried out, for example by a so-called "electroless" process using an oxidizing agent (the metal cation (s)), a reducing agent and a catalyst.

For the electrodeposition process, a bath is used containing metal ions and particles of graphene and / or graphene oxide, in which the object to be coated is immersed, the latter forming the cathode in a traditional electrochemical deposition assembly. in a bath.

In addition to particles of graphene and / or graphene oxide, this bath may contain other types of particles 6 such as particles of alumina, boron nitride, tungsten carbide, diamond, bisulphide. molybdenum, PTFE and / or silicon in pure form, carbide, nitride or oxide, or even oil droplets (eg fluorinated oil) encapsulated, including a mixture of the latter.

The metal ions can optionally be bound to complexing agents well known in electrochemical processes, such as cyanide in the case of a gold bath. The pH of the bath can be adapted with buffering agents to a value fixed according to the chemistry of the bath, for example with boric acid in a nickel bath buffered at acid pH.

Where appropriate, the bath may also contain additives which are well known from electrochemical processes, such as, for example, leveling, brightening and voltage reducing agents.

For a good distribution of the particles in the bath, the latter may also contain surfactants which bind to the aforementioned particles, surround them and prevent their agglomeration in solution.

To prevent the particles from settling and to promote regular and homogeneous deposition, the bath will be subjected to mechanical and / or ultrasonic stirring in order to distribute the various components as well as possible.

If a chemical deposition process is used (on non-conductive parts), the composite coating is formed according to the same principles: addition of particles 3 and 6 in the bath with surfactant and co-deposition of particles 3 and 6 with metal 4 on the object to be coated, with mechanical and / or ultrasonic agitation of the bath.

The deposited metal can be pure metal such as pure nickel or a metal alloy such as nickel with phosphorus or an alloy of copper, tin and zinc (bronze). The choice of metallic material depends on the desired additional result. For example, phosphorous nickel will make it possible to obtain a coating having non-magnetic properties and bronze will make it possible to obtain a decorative coating. Gold and / or copper ions can also be deposited with graphene or graphene oxide to produce a coating with a base matrix of gold or gold-copper. Other metal ions to produce this base matrix can also be used, for example noble metal ions such as palladium or platinum ions.

For example, particles of graphene or graphene oxide can co-deposit with nickel and phosphorus in a bath containing nickel (II) ions and phosphorous acid. Another example would be the co-deposition of graphene or graphene oxide in the presence of gold and copper ions.

Note that if graphene oxide is used in the bath, it can be co-reduced during the electrochemical deposition process and can turn into reduced graphene oxide.

If other particles 6 are contained in the bath, these are co-deposited at the same time as the graphene or graphene oxide particles 3 in the metal matrix 4.

After the deposition of these various components, it is possible to carry out an annealing heat treatment to improve the homogeneity of the deposited layer and / or to optimize the mechanical properties such as, for example, hardness.

Also after depositing the coating 2, it is possible to proceed with a gentle polishing of the coating in order to reduce its roughness.

Also a deposit 7 of gold with a thickness of 5 to 100 nm (nanometer) can be done by a galvanic process or other methods (vapor deposition or by cathodic sputtering) on top of the coating deposited by electrochemistry or electroless deposition. and after polishing (see FIG. 3 ).

This thin layer 7 of gold is subjected to the frictional forces which generate a surface penetration of the gold into the metal matrix containing the graphene and / or the graphene oxide.

Such a solid coating cannot be envisaged with pure graphene, in particular because of the cost of the material and of too small a thickness.

The chosen solution makes it possible to combine the effects of graphene with the metal and the other components. It is possible to choose a coating having the property of greatly reducing friction by increasing the level of graphene or obtaining a harder surface therefore limiting wear by adding to the graphene hard particles chosen from the group comprising alumina, diamond, boron nitride, tungsten carbide, including a mixture of the latter.

The advantage is therefore to combine, in a metallic matrix of a particular metal or alloy, particles or clusters of graphene incidentally combined with other inorganic or organic particles in order to meet each specific need. It is not a matter of a chemical combination but of the presence of various particles distributed in the metal matrix.

In addition, the coating is integral with the timepiece which is a guarantee of longevity and better resistance to environmental conditions.

The deposition of the coating can be limited to areas which are subject to friction, the rest of the part being able to be masked during deposition.

As an example of the present invention, there can be described composite coatings comprising a nickel metal matrix in which agglomerates of graphene or graphene oxide are dispersed.

EXAMPLE 1

The coatings are produced from a bath comprising from 150 to 600g / L of nickel sulphate, from 4g / L to 40g / L of nickel chloride, from 30 g / L to 50 g / L of boric acid and from 0.5 g / L to 5g / L of graphene oxide in powder form. The pH of the bath is between 3 and 4 and the temperature of the bath is maintained between 50 and 70 ° C. The coatings are deposited directly on watch parts by applying a current density of 1 to 20 A / dm2.

EXAMPLE 2

Another example is that of coatings obtained from a bath comprising from 60 to 150 g / L of nickel in the form of nickel sulphate, from 5 g / L to 30 g / L of phosphorous acid, from 30 g / L to 50 g / L of boric acid and from 0.1 g / L to 5g / L of graphene oxide in powder form. At a pH of between 1 and 2, composite coatings based on phosphorous nickel and graphene oxide can be obtained by applying a current density between 0.5 and 10 A / dm2 and more particularly between 1 and 5 A / dm2. Coatings thus formed result in performance such as described in fig 2 (curve (a)) at thicknesses between 0.5 and 5 microns.

If we look at the figure 2 , we see the variations in the relative amplitude of oscillation of a balance wheel of a clockwork movement over a period of 24 hours.

The curve (a) corresponds to the ratio in percentage between the value of the oscillation amplitude of the balance of a standard movement with an escape wheel provided with a coating according to the invention divided by the amplitude value of oscillation of the balance of the same type of movement provided with an escapement (teeth of the escape wheel and anchor vanes) lubricated according to the prior art.

The curve (b) corresponds to the ratio in percentage between the value of oscillation amplitude of a balance with an escape wheel and uncoated and unlubricated anchor vanes divided by the oscillation amplitude value of the exhaust (teeth of the escape wheel and anchor vanes) lubricated according to the prior art.

It will be understood that the capacity to reduce the friction of the coating according to the invention is equivalent to the liquid lubrication used previously (curve (a)). Curve (b) shows that without lubricant there is a reduction in the amplitude of oscillation of the balance.

Claims (7)

1. Timepiece mechanism including a timepiece forming a support, said support including a solid self-lubricating composite coating characterised in that the solid self-lubricating composite coating consists of a metal matrix (4) and particles (3) of graphene and/or graphene oxide distributed in said metal matrix (4), in that the graphene and/or graphene oxide is in the form of fibres, particles or aggregates, the latter being completely embedded in said metal matrix, in that the thickness of said coating is comprised between 0.2 and 20 micrometres and preferably between 0.5 and 2 micrometres and in that that the size of said particles is less than the thickness of said coating.
2. Timepiece mechanism according to claim 1, characterised in that the graphene and/or graphene oxide is bound to metal ions from a pure metal or a metal alloy.
3. Timepiece mechanism according to any one of claims 1 to 2, characterised in that the coating has a polished or lapped surface.
4. Timepiece mechanism according to any one of claims 1 to 3, characterised in that the coating is covered with a 5 to 100 nm film 7 of gold.
5. Timepiece mechanism according to any one of claims 1 to 4, characterised in that an attachment layer (5) is deposited prior to formation of the coating.
6. Timepiece mechanism according to any one of claims 1 to 4, characterised in that it additionally comprises particles chosen from the group comprising alumina, diamond, boron nitride, tungsten carbide, silicon in pure form, carbide, nitride or oxide, including a mixture of these.
7. Timepiece mechanism according to any one of claims 1 to 6, characterised in that it additionally comprises particles chosen from the group comprising titanium, molybdenum bisulphite and polytetrafluoroethylene (PTFE), including a mixture of these.

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