CH710219A2 - self-lubricating composite coating. - Google Patents

Abstract

The subject of the invention is a self-lubricating composite solid coating intended in particular for an application to clockwork mechanisms, characterized in that it comprises particles (3) of graphene and / or graphene oxide distributed in a matrix (4). ) metallic.

Description

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

[0002] In watchmaking mechanisms, there are many moving parts in frictional contact with each other. This friction must be reduced as much as possible because it can affect the precision and / or the autonomy of the mechanism.

Indeed, friction leads to wear of the parts, an increase in energy consumption to move the parts and a slowing down of the movement.

To reduce friction, it is known to use liquid lubricants (oils) or pastes (greases). 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. On the other hand, the ability to slip between two rooms can also escape from the space where it has been deposited. It is also very sensitive to the environmental conditions of temperature and relative humidity because its viscosity evolves according to these.

So there are two disadvantages: these liquid or viscous lubricants change in the direction of degradation, for example by loading with dust or becoming more viscous or losing their lubricating capacity by oxidation; Since this type of lubricant is fluid or pasty, the movement of the parts tends to move the lubricant from the zone of the contacts towards a zone that is not subject to friction.

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

These lubricants are constituted by a liquid or viscous medium which may contain particles having tribological properties such as carbon. WO 2012/128 714 describes for example a liquid containing graphene. Graphene was isolated by André Geim in 2004. It is a two-dimensional carbon crystal whose stacking leads to graphite. It appears to have interesting tribological properties.

In parallel liquid or viscous lubricants, there are known dry coatings reducing friction. These coatings are integral with the part to be protected and present less risk of loss or chemical degradation. In addition, 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 US-A-2008 1 323 475.

In the document WO 2013/150 028 the coating metal is gold but this coating is derived from a bath that contains a percentage of Cadmium well above the percentage allowed by the European directives which is problematic.

Graphite is also used as an anti-wear agent in electro-deposited composite coatings.

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 because of the small dimensions of the watch components. The desired coatings must therefore be thin and very effective.

For this purpose, the subject of the invention is a metal composite solid coating having self-lubricating properties, characterized in that it comprises particles of graphene and / or graphene oxide distributed in a metal matrix.

The invention will be better understood from the following description given by way of non-limiting example with reference to the drawing which represents: <Tb> Fig. 1: <SEP> schematic section of the substrate coated with the graphene metal composite. <Tb> Fig. 2: <SEP> Variation of the relative amplitude of a clockwork mechanism with a coating according to the invention (a) and without coating (b) with respect to a clockwork mechanism lubricated with oil. <Tb> Fig. 3: <SEP> cut of a coated support with an extra 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.

Preferably, particles 3 of graphene or graphene oxide are used which are in the form of fibers or flakes (aggregates of fibers or particles).

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

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

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

For the electroplating process, using a bath containing metal ions and graphene particles and / or graphene oxide, in which the object to be coated plunges, the latter forming the cathode in a traditional assembly electrochemical deposition in a bath.

In addition to the 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, molybdenum disulfide, PTFE and / or silicon in pure form, encapsulated carbide, nitride or oxide, or even oil droplets (eg fluorinated oil), including a mixture thereof.

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

Where appropriate, the bath may also contain additives well known electrochemical processes such as, for example, leveling agents, brighteners and voltage reducers.

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

To prevent sedimentation of the particles and promote a regular and homogeneous deposition, the bath will be subjected to mechanical agitation and / or ultrasonic type 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 the metal 4 on the object to be coated, with mechanical and / or ultrasonic agitation of the bath.

The deposited metal may 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 the metallic material depends on the desired side result. For example, phosphorus nickel will make it possible to obtain a coating having non-magnetic properties and bronze will make it possible to obtain a decorative coating. Graphene or graphene oxide can also be deposited with gold and / or copper ions for coating with a base matrix of gold or gold-copper. Other metal ions for producing this base matrix can still be used, for example noble metal ions such as palladium or platinum ions.

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

It will be noted that if graphene oxide is used in the bath, it can be co-reduced during the electrochemical deposition process and can be converted into reduced graphene oxide.

If other particles 6 are contained in the bath, they are co-deposited at the same time as the graphene particles or graphene oxide 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 optimize mechanical properties such as, for example, hardness.

Also after the deposition of the coating 2, it is possible to proceed to a smooth polishing of the coating to reduce its roughness.

Also a gold deposit of a thickness of 5 to 100 nm (nanometer) can be done by a galvanic process or other methods (vapor phase deposition or cathodic sputtering) over the deposited electrochemical coating or electroless deposit and after polishing (see Fig. 3).

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

Such a solid coating is not possible with pure graphene especially because of the cost of the material and a too small thickness.

The chosen solution combines 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 hard surface which therefore limits wear by adding to graphene hard particles selected from the group comprising alumina, diamond, boron nitride, tungsten carbide, including a mixture of these.

The interest is therefore to combine in a metal matrix of a particular metal or alloy particles or aggregates of graphene incidentally combined with other inorganic or organic particles to meet each specific need. It is not a chemical combination but 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.

We can limit the deposition of the coating areas that suffer friction, the rest of the room can be masked during the deposit.

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

EXAMPLE 1

The coatings are produced from a bath comprising from 150 to 600 g / l of nickel sulphate, from 4 g / l to 40 g / l of nickel chloride, from 30 g / l to 50 g / l of nickel chloride. L of boric acid and 0.5 g / L to 5 g / L of graphene oxide in powder form. The pH of the bath is between 3 and 4 and the bath temperature maintained between 50 and 70 * 0. The coatings are deposited directly on watch parts by applying a current density of 1 to 20 A / dm <2>.

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 g / L at 50 g / L of boric acid and 0.1 g / L at 5 g / L of graphene oxide in powder form. At a pH of between 1 and 2, composite coatings based on nickel phosphorus and graphene oxide can be obtained by applying a current density between 0.5 and 10 A / dm <2> and more particularly between 1 and 5 A / dm <2>. Coatings thus formed lead to performance as described in FIG. 2 (curve (a)) at thicknesses between 0.5 and 5 microns.

[0043] If we examine FIG. 2, we see the relative oscillation amplitude variations of a pendulum of a watch movement over a period of 24 hours.

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

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

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

Claims (13)

1. Self-lubricating solid composite coating intended in particular for an application to clockwork mechanisms characterized in that it comprises particles (3) of graphene and / or graphene oxide distributed in a matrix (4) metal. 2. solid composite self-lubricating coating according to claim 1 characterized in that the graphene and / or graphene oxide is in the form of fibers, particles or aggregates. 3. Self-lubricating composite solid coating according to claim 1 or 2 characterized in that the graphene oxide is reduced graphene oxide. 4. Self-lubricating composite solid coating according to any one of claims 1 to 3 characterized in that graphene and / or graphene oxide is associated with metal ions from a pure metal or a metal alloy. 5. Self-lubricating solid composite coating according to any one of the preceding claims, characterized in that the solid coating has undergone an annealing heat treatment. 6. Self-lubricating solid composite coating according to any one of claims 1 to 5 characterized in that the coating has a polished or lapped surface. 7. Self-lubricating composite solid coating according to any one of claims 1 to 6 characterized in that the coating is covered with a film of gold 5 to 100 nm. 8. Self-lubricating solid composite coating according to any one of claims 1 to 6 characterized in that the thickness of the coating is in 0.2 micron and 20 microns. 9. Solid self-lubricating composite coating according to claim 8 characterized in that the thickness of the coating is in 0.5 micron and 2 microns. 10. solid composite self-lubricating coating according to any one of claims 1 to 9 characterized in that a layer (5) of attachment is deposited prior to the formation of the coating. 11. Self-lubricating solid composite coating according to any one of claims 1 to 10 characterized in that the coating is deposited electrochemically or chemically (electroless), the constituents of the coating being suspended in the bath. 12. Self-lubricating composite coating according to any one of claims 1 to 11 characterized in that it further comprises particles selected from the group consisting of alumina, diamond, boron nitride, tungsten carbide, silicon in pure form, carbide, nitride or oxide, including a mixture thereof. 13. Self-lubricating composite coating according to any one of claims 1 to 12 characterized in that it further comprises particles selected from the group consisting of titanium, molybdenum bisulfite, and polytetrafluoroethylene (PTFE) including a mixture of these.