EP0854403B1 - Wear resistant transparent watch crystal and watch case provided with the same - Google Patents

Abstract

The transparent watch glass (18) is made from polycrystalline diamond, can be flat or convex - either spherical or cylindrical - and is between 0.5 and 2 mm thick. A watch case can be made from top and bottom convex glasses joined to a surround. The polycrystalline diamond is obtained, for example, by chemical deposition of a vapour phase on a graphite substrate of the required shape, coated with silicon carbide, and polishing it.

Description

The present invention relates to a watch glass transparent and scratch-resistant, and in particular a glass of shows having a low cost regardless of the complexity of its shape, for example flat or spherical, while having a very high hardness, of the order of 98 GPa (10,000 HV).

The present invention also relates to a box of watch provided with such a glass.

Watch glasses for the protection of dials and needles or the like are made the most often made of synthetic material or mineral glass because of their relatively low cost price. The respective hardness of these categories of materials determines of course the scratch resistance of the glasses. For fix ideas, a watch glass made of materials synthetic materials such as Plexiglas have a hardness Vickers of about 0.98 GPa (100) and mineral or natural glass has a Vickers hardness of about 8.8 GPa (900). Gold experience showed that glasses made in these two categories of materials withstand scratches by some agents very hard, such as silica contained in dust, marble or sand constantly present in our environment, even if the mineral glass resists better to these aggressions than the synthetic materials. he This results in a relatively rapid alteration of the aesthetic appearance by stripes of these types of glasses or watch funds.

To avoid these disadvantages we used sapphire or artificial corundum for making glasses of shows. Such glasses are described for example respectively in the patent CH 632 891 and in the patent FR 1 238 069. These glasses are very resistant to attacks by external agents but the major disadvantage of being long, complex and laborious to manufacture and to have a very high cost price, this which greatly limits their use to very large ladder. As an illustration, energy needs account for 80% of the cost of manufacture of sapphire "pears" from which are cut out the plates which after many subsequent machining operations, will form these glasses of watches. In addition, a medium-sized plant manufacture of sapphire "pears" consumes annually as much electricity as a city of about 50,000 inhabitants.

It is therefore easy to understand, given the current growing concerns about of energy saving, the need to find a solution alternative, especially more economical, to the use of artificial sapphire to make glasses of watches having a high scratch resistance and intended for wide range of watches.

Moreover, the realization mainly during the machining of the finished product from these "pears" leads to significant losses of raw material.

The licensee became aware during the study of new solutions that the application of the diamond polycrystalline in the form of thin blades, especially obtained by chemical vapor deposition on a substrate, to the constitution of watch glasses is particularly interesting because the glasses as well fulfilled the requirements for producing scratch-resistant watch glasses both from economic point of view only from the point of view of their properties of implementation, their properties and their transparency.

The object of the present invention is therefore precisely a scratchproof and transparent watch glass, characterized in that it is made of polycrystalline diamond.

Therefore, complicated and expensive manufacturing artificial sapphire, as well as its transformation laborious and also expensive in watch glasses are replaced by a simple chemical deposition operation polycrystalline diamond vapor phase on a substrate having the shape of the glass that one wishes to obtain, said deposit being followed by a polishing operation.

It should also be noted that the hardness of shows according to the invention is of the order of 98 GPa (10,000 HV) which makes them almost scratch-proof. Diamond glasses polycrystalline of the invention also show the advantage of having excellent resistance to chemical aggressions.

Another important advantage of the choice of diamond for the manufacture of watch glasses is that, unlike artificial sapphire, it is polycrystalline which confers isotropic properties. If one considered sintered sapphire powder, the resulting coin would not be not transparent due to anisotropy properties relative optics of sapphire grains. Such a problem does not exist with diamond made by chemical deposition in the vapor phase.

The present invention also relates to a watch case comprising a case and a bottom, characterized in that it further comprises a glass which consists of polycrystalline diamond.

• les figures 1 et 2 représentent une montre munie d'un verre transparent et inrayable selon l'invention respectivement en plan et en coupe selon la ligne II-II, et
• la figure 3 représente en perspective éclatée une montre munie de deux verres transparents et inrayables selon l'invention, en l'occurrence un verre et un fond.

Other characteristics and advantages of the present invention will appear more clearly on reading the following description of exemplary embodiments, said description being given in a nonlimiting manner and in relation to the attached drawings among which:

• FIGS. 1 and 2 show a watch provided with a transparent and scratch-resistant glass according to the invention respectively in plan and in section along line II-II, and
• 3 shows an exploded perspective a watch provided with two transparent and scratch-resistant glasses according to the invention, in this case a glass and a bottom.

The watch shown in FIGS. box 10, a movement 12 and display means 14, comprising in this case needles and a dial. The box 10 includes a middle 16, a first and a second closure element of the box, respectively a glass 18 and a bottom 20, as well as a casing ring 22. The middle 16 is provided with four horns 24 which extend above the body of the middle part and form claws 26 defining with the body of the middle part a slide inside which the glass 18 is housed. The bottom 20 is attached to the middle part 16 by means of screws represented in the drawing. He also relies on the 22. The latter extends over the whole of height of the middle part 16 and it is in support against the 18. Thus, when the bottom 20 is fixed by means of screw, the casing ring 22 exerts pressure on the glass 18 that leans on the claws 26. This construction is well known to those skilled in the art, also is it unnecessary to describe it more explicitly?

According to the invention, the glass 18 is an element virtually scratch-resistant made of polycrystalline diamond. The glass 18 can be obtained as follows. We first prepares a graphite substrate comprising an upper surface having the negative form of glass that one wishes to obtain. This negative form is plane in the case of the glass 18 but may well be heard non planar for example curved cylindrical, convex spherical or a combination of these forms. The face substrate is polished and then coated with thin layer of silicon carbide (SiC). A layer of polycrystalline diamond is then deposited on the layer of SiC by chemical vapor deposition. During this deposit operation a layer of polycrystalline diamond grows on the SiC surface to the desired thickness.

Once the desired thickness is reached, the polycrystalline diamond to form the glass 18 is then polished and, if necessary, put to the dimensions final to form a watch glass such as glass 18. This dimensioning step is for example performed by laser machining. The polycrystalline diamond layer is finally disintegrated from the substrate, for example by elimination chemical substrate.

The glass thus produced is of course completely transparent in the visible spectrum after polishing and thus protects the display means while allowing their reading.

The measurements carried out gave results of hardness of the order of 98 GPa (10,000 HV). This hardness is about four times greater than that of sapphire so the watch provided with the glass 18 according to the invention is particularly well protected against aggression and especially against scratches that do not could be caused only by an object having itself diamond portions.

The thickness of the watch glass according to the invention is depending on the size of the desired glass and the effect obtain, it will generally be between 0.5 and 2 mm.

A method for obtaining a glass according to the invention such as glass 18 is described in more detail in the patent application EP-A-0 693 573. It is understood that any other process for obtaining plates or blades in polycrystalline diamond are conceivable.

Referring now to Figure 3 we see a another embodiment of a watch provided with glasses of shows according to the invention.

In this example, the watch case has a upper shell 28 in the shape of a spherical cap, of which at least one part is transparent and forms a first watch glass according to the invention.

The box still has a lower shell 30, also shaped spherical cap, and a middle 32 disposed in the vicinity of the periphery of the shells 28 and 30, the lower shell 30 forming a second watch glass according to the invention. The glasses 28 and 30 therefore have non-planar shapes.

As seen in Figure 3, the shells 28 and 30 define an interior space in which takes place a movement (not shown) and the middle part 32 is arranged to fit respectively the shape of the faces lower and upper than the shells upper 28 and lower 30 to serve them of support surface. So when the box is assembled, the edges 34 and 36 of the upper and lower shells are joined throughout their periphery with the exception of places 38 and 40 provided for attaching the strands of bracelet 42 and 44, and the middle part no longer appears.

Here the upper shell 28, the glass, and the lower shell 30, the bottom, forming the glasses scratchproof transparencies are made like glass described in conjunction with FIGS. 1 and 2. As the edges shells are joined, the box thus produced is completely scratchproof. Moreover, thanks to the shape in spherical cap of the glasses according to the invention - normally very expensive when done in artificial sapphire - the box thus obtained presents shock absorption characteristics that it can undergo because shocks are transmitted to the seat of shells located on the middle on which they are fixed, thus benefiting from the vault effect.

It is understood that here again the two shells may have on the periphery of their inner face a masking layer such as a metallization for hide some elements of the box like the middle part.

Watch glasses could be used as transparent background for watch box.

Claims (6)

1. Transparent and scratchproof watch crystal, characterised in that it is made of polycrystalline diamond.
2. Watch crystal according to claim 1, characterised in that it has a non flat shape.
3. Watch crystal according to claim 1 or 2, characterised in that it is partially spherical.
4. Watch crystal according to claim 1 or 2, characterised in that it is partially cylindrical.
5. Watch crystal according to any of the preceding claims, characterised in that it has a thickness of between 0.5 and 2 mm.
6. Watch case including a middle part and a back cover, characterised in that it further includes at least one crystal according to one of the preceding claims.

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